JP7708693B2 - Metallic film and its manufacturing method - Google Patents

Description

The present invention relates to a metallic film and a method for producing the same.

Metallic films are used in a variety of products because they can impart a high-luminance metallic luster to the surface of the product, giving it a luxurious feel. Metallic films are required to have various properties depending on the product in which they are used, one of which is radio wave transparency. For example, millimeter wave radars mounted on automobiles and other vehicles are devices that measure the distance to an obstacle by irradiating radio waves in the millimeter wave band (radio waves with a wavelength of 1 to 10 mm) and measuring the time it takes for the radio waves to reflect off an obstacle and return. When metallic films are used in this millimeter wave radar, they are required to have high luminance and excellent radio wave transparency.

As a metallic film having radio wave transmission, for example, a film formed by vapor deposition or sputtering of indium (In), tin (Sn) or chromium (Cr) on the surface of a substrate is widely known (Patent Documents 1 to 3). Also, a film using other metals instead of In, Sn or Cr is known. For example, Patent Document 4 discloses a radio wave transmission metallic glossy member comprising a substrate having radio wave transmission and an aluminum layer having discontinuous regions formed directly on the continuous surface of the substrate, and the metallic glossy member is produced by sputtering. Patent Document 5 discloses an electromagnetic wave transmission metallic coating formed on the surface of a substrate through an electroless plating process, the metallic coating being composed of more than 10,000 fine metallic regions per unit area (1 mm ² ), the fine metallic regions being electrically isolated from each other, and the metallic coating is made of palladium or a palladium alloy. Patent Document 6 discloses a metallic film produced by a method other than vapor deposition, sputtering or plating. Furthermore, Patent Document 7 discloses a composition containing palladium-coated anisotropic gold nanoparticles, and discloses the use of this as a black color developer.

Metallic films using In, Sn, or Cr as disclosed in Patent Documents 1 to 3 have limitations in brightness. In addition, sputtering, which is widely used in the manufacture of metallic films using In, Sn, or Cr and is also used in the manufacture of metallic films using aluminum as disclosed in Patent Document 4, is a vacuum batch process, which increases costs. In addition, if the metal coating is made thicker to increase brightness, it becomes a partially continuous film, which reduces radio wave transmittance. In addition, even in metallic films as disclosed in Patent Documents 5 and 6, it may be desirable to further increase the brightness of the metal coating depending on the application of the metallic film.

JP 2007-285093 A JP 2013-144902 A JP 2016-65297 A JP 2019-123238 A JP 2013-95997 A JP 2021-155844 A JP 2019-215176 A

As mentioned above, conventional methods for manufacturing metallic films can be costly. Furthermore, with conventional metallic films, depending on the application of the metallic film, it may be desirable to further increase the brightness of the metal coating. Therefore, the object of the present invention is to provide a metallic film that combines high brightness and excellent radio wave transparency.

After examining various means for solving the above problems, the inventors discovered that the brightness of the metal coating can be significantly improved by adding a minute amount of palladium to the metal particles, and thus completed the present invention.

That is, the gist of the present invention is as follows.
(1) A metallic film having a resin substrate and a metallic particle layer formed on the resin substrate, wherein in the metallic particle layer, there are gaps between the metal particles, the metal particles contain Pd and at least one other metal other than Pd, and the Pd content in the metal particles is 1.6 mol% to 34.4 mol%.
(2) The metallic film according to (1), wherein the other metal is selected from Ag, Al, Au, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Nb, Mo, In, Co and Sn.
(3) The metallic film according to (1) or (2), wherein the other metal is Ag.
(4) The metallic film according to any one of (1) to (3), wherein the resin substrate is polyimide.
(5) A method for producing a metallic film according to any one of (1) to (4),
Step 1 of preparing a resin substrate having a layer on its surface having functional groups capable of ion-exchange with metal ions;
a step 2 of treating a resin substrate having a surface layer having functional groups capable of ion-exchange with the metal ions with a solution containing Pd ions and ions of at least one other metal than Pd, thereby introducing Pd ions and ions of the other metal into the layer by ion exchange;
and step 3 of treating a resin substrate having a layer on its surface into which Pd ions and ions of the other metal are introduced, with a reducing agent to cause metal particles containing Pd and the other metal to precipitate on the surface.
(6) The method for producing a metallic film according to (5) above, further comprising step 4 of heat treatment after step 3.
(7) The method for producing a metallic film according to (5) or (6), wherein in step 1, a layer having a functional group capable of ion-exchange with the metal ion is formed on the surface of the resin substrate by modifying the surface of the resin substrate.

The present invention makes it possible to provide a metallic film that combines high brightness and excellent radio wave transparency.

1 is a schematic cross-sectional view of one embodiment of a metallic film of the present invention. FIG. 2 is a schematic cross-sectional view of another embodiment of the metallic film of the present invention. 1 shows a graph illustrating the relationship between the Pd content of metal particles and the L value of a metallic film in an example.

A preferred embodiment of the present invention is described in detail below.

The present invention relates to a metallic film having a resin substrate and a metal particle layer formed on the resin substrate. In the metal particle layer, there are gaps between the metal particles, i.e., the metal particle layer is a discontinuous film of metal particles.

Figure 1 shows a schematic cross-sectional view of one embodiment of the metallic film of the present invention. The metallic film 10 has a resin substrate 11 and a metallic particle layer 12 formed on the surface of the resin substrate 11. In the metallic particle layer 12, there are gaps between the metallic particles. The metallic film may also have metallic particle layers on both sides of the resin substrate.

The resin substrate is preferably made of an insulating material. For example, a resin having a group that can be converted to a carboxyl group and/or a sulfo group can be used as the resin substrate. The resin substrate is not particularly limited, and for example, polycarbonate, acrylic, polystyrene, polyimide, polyethylene terephthalate, polymethyl methacrylate, ABS, etc. can be used, with polycarbonate, acrylic, and polyimide being preferred, and polyimide being more preferred.

The resin substrate is not particularly limited and may be a resin film. The thickness of the resin substrate is usually 10 μm to 5 mm, and preferably 20 μm to 800 μm.

The resin substrate may have a film layer on its surface. A metallic film having a film layer can be obtained, for example, by the second embodiment of the manufacturing method of the present invention described below.

Figure 2 shows a schematic cross-sectional view of one embodiment of a metallic film having a film layer. As shown in Figure 2, the metallic film 20 has a resin substrate 21 having a film layer 22 on its surface, and a metallic particle layer 23 formed thereon. The metallic film 20 is formed by laminating the resin substrate 21, the film layer 22, and the metallic particle layer 23 in this order from the bottom up. In the metallic particle layer 23, there are gaps between the metallic particles. The film layer and the metallic particle layer may be formed on both sides of the resin substrate.

The film layer is preferably a resin film layer. The resin constituting the resin film layer may have a functional group capable of ion-exchange with a metal ion, and is preferably a resin having a carboxyl group and/or a sulfo group, more preferably a polyamic acid or a styrene-divinylbenzene copolymer, and particularly preferably a polyamic acid. In one embodiment, when the resin constituting the film layer is a polyamic acid, the film layer may be in a form in which the polyamic acid is dehydrated and cyclized to be converted into a polyimide.

In one embodiment, it is preferred that the resin substrate is polycarbonate or acrylic, and the film layer is polyamic acid or polyimide.

The thickness of the film layer is usually smaller than the thickness of the resin substrate, for example, 0.5 μm to 10 μm, preferably 0.5 μm to 9.0 μm, and more preferably 0.7 μm to 1.5 μm.

The metal particle layer is formed on a resin substrate. In the metal particle layer, the metal particles are formed, for example, in an island shape, i.e., each metal particle is independent of the other, and there are gaps between each metal particle. The gaps between the metal particles allow the film to exhibit radio wave transparency. The metal particles are preferably partially embedded in the surface of the resin substrate or the film layer on the surface thereof, so that the metal particles do not easily peel off, are highly stable, and the metallic film has high corrosion resistance and weather resistance.

The metal particles contain Pd and at least one other metal than Pd, that is, they are alloy particles of Pd and at least one other metal than Pd. The other metal is not particularly limited and may be, for example, Ag, Al, Au, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Nb, Mo, In, Co, or Sn. From the viewpoint of having high brightness, Ag, Al, and Cr are preferable, and Ag is more preferable.

The Pd content in the metal particles is 1.6 mol% to 34.4 mol% relative to the metal particles. When the Pd content in the metal particles is within this range, the L value of the metallic film is larger and the brightness is higher than when the metal particles do not contain Pd. From the viewpoint of obtaining a metallic film with higher brightness, the Pd content in the metal particles is preferably 1.6 mol% to 22.0 mol%, and more preferably 1.6 mol% to 9.6 mol%. The Pd content in the metal particles can be determined, for example, by dissolving the metal particle layer in a solvent, subjecting the solution in which the metal constituting the metal particles is dissolved to mass spectrometry, quantifying the amount of metal ions, and calculating it as mol%. It is considered that in the metallic film of the present invention, Pd is contained almost uniformly in each metal particle.

The shape of the metal particles is not particularly limited and may be, for example, spherical, ellipsoidal, plate-like, flake-like, scale-like, dendritic, rod-like, wire-like, or irregular.

The metal particles usually have an average particle size of 5 nm to 200 nm, preferably 10 nm to 200 nm, and more preferably 10 nm to 150 nm. When the average particle size of the metal particles is 5 nm to 200 nm, the metal particles can reflect visible light and transmit millimeter waves, and have excellent radio wave transmittance. In the present invention, the average particle size of the metal particles refers to the number average particle size of the major axis (maximum diameter) of the particles measured from an FE-SEM (50,000x) observation image of the film surface. Note that when the metal particles are spherical, the average particle size refers to the number average particle size of the diameter of the metal particles.

The thickness of the metal particle layer is usually 5 nm to 200 nm, preferably 10 nm to 150 nm.

The L value of the metallic film is usually more than 75, preferably more than 80, and more preferably more than 85. The L value of the metallic film can be determined, for example, by measuring using a spectrophotometer with the SCI method (including specular reflection), determining the spectral reflectance R(λ) as the ratio of the spectral radiant flux of wavelength λ reflected from an object to the spectral radiant flux of wavelength λ reflected from a perfect diffuse reflecting surface (JIS Z 8722), and using the spectral reflectance R(λ) to calculate the index value L* of the CIE1976 (L*, a*, b*) color system defined by the International Commission on Illumination (CIE).

The present invention also relates to a method for producing the metallic film. The method for producing the metallic film of the present invention includes the steps of preparing a resin substrate having a layer on its surface that has functional groups that can be ion-exchanged with metal ions (step 1), treating the resin substrate having a layer on its surface that has functional groups that can be ion-exchanged with metal ions with a solution containing Pd ions and ions of at least one other metal other than Pd to introduce Pd ions and ions of the other metal into the layer by ion exchange (step 2), and treating the resin substrate having a layer on its surface into which Pd ions and ions of the other metal have been introduced with a reducing agent to precipitate metal particles containing Pd and other metals on the surface (step 3). The method for producing the metallic film of the present invention may further include step 4, after step 3, of heat-treating the resin substrate on which metal particles containing Pd and other metals have been precipitated on the surface.

In step 1, a resin substrate is prepared, the surface of which is provided with a layer having functional groups capable of ion-exchange with metal ions. The resin substrate can be any of those described above for the metallic film.

In step 1, a resin substrate having a layer on its surface that has functional groups that can be ion-exchanged with metal ions can be prepared by forming this layer on the surface of the resin substrate. The layer having functional groups that can be ion-exchanged with metal ions can be formed, for example, by modifying the surface of the resin substrate (first embodiment), or by forming a film layer having functional groups that can be ion-exchanged with metal ions on the surface of the resin substrate (second embodiment). That is, the layer having functional groups that can be ion-exchanged with metal ions can be a layer derived from the resin substrate, or a new layer that is not derived from the resin substrate. Hereinafter, the first and second embodiments of the method for producing a metallic film of the present invention will be described.

First Embodiment
The method of the first embodiment includes the steps of modifying the surface of a resin substrate to form a layer (modified layer) having functional groups capable of ion-exchange with metal ions on the surface of the resin substrate (step 1), treating the resin substrate having the modified layer on its surface with a solution containing Pd ions and ions of at least one other metal other than Pd (hereinafter also referred to as a metal ion solution) to introduce Pd ions and ions of the other metal into the modified layer by ion exchange (step 2), and treating the resin substrate having the modified layer on its surface into which Pd ions and ions of the other metal have been introduced with a reducing agent to precipitate metal particles containing Pd and the other metal on the surface, thereby forming a metal particle layer (step 3).

In step 1, the surface of the resin substrate is modified to form a modified layer on the surface of the resin substrate that has functional groups that can be ion-exchanged with metal ions.

The resin substrate may be any substrate capable of modifying the surface, and is preferably one having a hydrolyzable functional group and capable of introducing a functional group capable of ion-exchange with metal ions by hydrolysis. For example, a resin having a group capable of being converted to a carboxyl group and/or a sulfo group by hydrolysis can be used as the resin substrate. Examples of such a resin substrate include polycarbonate, acrylic, polyimide, etc., and polyimide having a high functional group density is preferable. When polyimide is used as the resin substrate, a polyamic acid layer is formed on the substrate surface by hydrolysis, and a carboxyl group is generated as a functional group capable of ion-exchange with metal ions. In addition, a resin capable of introducing a sulfo group by modifying the surface can be used as the resin substrate. An example of such a resin is polystyrene, and for example, a sulfo group can be introduced by sulfonating the surface with concentrated sulfuric acid.

In step 1, for example, the surface of the resin substrate can be treated with an alkaline solution to form a modified layer having functional groups that can be ion-exchanged with metal ions through hydrolysis.

The alkaline solution is not particularly limited, and examples thereof include NaOH, KOH, LiOH, CaO, and Ca(OH) ₂ , with KOH being preferred.

The concentration of the alkaline solution is usually 1M (mol/l) to 100M, preferably 1M to 10M.

The conditions for treatment with an alkaline solution are as follows: treatment temperature is usually 15°C to 60°C, preferably 25°C to 50°C, and treatment time is usually 10 seconds to 10 minutes, preferably 30 seconds to 5 minutes.

In step 1, the density of the metal ions and ion-exchangeable functional groups in the formed modified layer is preferably 1 mol/l to 10 mol/l, and more preferably 5 mol/l to 8 mol/l.

In step 1, the thickness of the modified layer is preferably 0.5 μm to 10 μm, more preferably 0.7 μm to 1.5 μm.

In step 2, the resin substrate having the modified layer on its surface is treated with a solution containing Pd ions and ions of at least one other metal than Pd. This treatment replaces the functional groups in the modified layer with Pd ions and ions of the other metal through ion exchange, and these metal ions are introduced into the modified layer.

The ions of other metals are the ions of other metals mentioned above for the metallic film, and are not particularly limited, but are, for example, ions of Ag, Al, Au, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Nb, Mo, In, Co and Sn, and from the viewpoint of having high brightness, ions of Ag, Al and Cr are preferable, and Ag ions are more preferable.

A solution containing Pd ions and ions of other metals can be prepared, for example, by mixing a solution of a compound containing Pd ions with a solution of a compound containing ions of other metals, by adding a compound (solid) containing ions of other metals to a solution of a compound containing Pd ions, or by adding a compound (solid) containing Pd ions to a solution of a compound containing ions of other metals.

Examples of compounds containing Pd ions include salts and complexes of Pd ions, and are not particularly limited to these. Examples include nitrates, sulfates, chlorides, carbonates, acetates, and phosphates of Pd ions, as well as bis(triphenylphosphine)palladium(II) diacetate, bis(benzonitrile)dichloropalladium(II), bis(acetonitrile)dichloropalladium(II), dichloro(ethylenediamine)palladium(II), dichloro(1,10-phenanthroline)palladium(II), dichlorobis(triphenylphosphine)palladium(II), and tetraamminepalladium nitrate(II). Tetraamminepalladium nitrate is preferred.

The concentration of Pd ions in the solution is usually 0.002 mM to 50 mM, preferably 0.02 mM to 20 mM.

As the compound containing the ion of the other metal, for example, a salt or complex of the ion of the other metal can be used, and examples of the salt include nitrates, sulfates, chlorides, carbonates, acetates, and phosphates. When the ion of the other metal is Ag ion, silver nitrate is preferably used.

The concentration of other metal ions in the solution is usually 1 mM to 500 mM, preferably 50 mM to 150 mM.

The molar ratio of Pd ions to other metal ions in the solution (Pd ions: other metal ions) can be selected so as to achieve the desired Pd content in the resulting metallic film, and is usually 1:5 to 1:500, preferably 1:15 to 1:500, and more preferably 1:90 to 1:500.

The mass ratio of the compound containing Pd ions to the compound containing ions of other metals in the solution may be selected so as to satisfy a predetermined Pd content in the resulting metallic film. For example, in one embodiment, when tetraaminepalladium nitrate is used as the compound containing Pd ions and silver nitrate is used as the compound containing ions of other metals, the mass ratio of tetraaminepalladium nitrate to silver nitrate in the solution is typically 1:5 to 1:300, preferably 1:8 to 1:300, and more preferably 1:50 to 1:300.

Treatment with a metal ion solution can be carried out, for example, by immersing the resin substrate in the metal ion solution. The treatment conditions with the metal ion solution are as follows: the treatment temperature is preferably 10°C to 50°C, more preferably 20°C to 30°C, and the treatment time is preferably 10 seconds to 30 minutes, more preferably 1 minute to 10 minutes.

In step 3, the resin substrate having a surface modified layer into which Pd ions and ions of other metals have been introduced is treated with a reducing agent. This treatment causes metal particles containing Pd and other metals to precipitate on the surface, resulting in a metallic film with a metallic particle layer. The metal ions diffuse to the surface where the reducing agent is present and are reduced to metallic particles, so the resulting metallic film has a resin substrate, a modified layer formed thereon, and a metallic particle layer formed thereon. In the present invention, the precipitated metallic particles are not easily peeled off because part of each metallic particle is embedded in the modified layer (surface of the resin substrate).

The reducing agent is not particularly limited, and examples thereof include phosphoric acid compounds, boron hydride compounds, and hydrazine derivatives. Examples of phosphoric acid compounds include hypophosphorous acid, phosphorous acid, pyrophosphoric acid, and polyphosphoric acid. Examples of boron hydride compounds include methylhexaborane, dimethylamine borane, diethylamine borane, morpholine borane, pyridineamine borane, piperidine borane, ethylenediamine borane, ethylenediamine bisborane, t-butylamine borane, imidazole borane, methoxyethylamine borane, and sodium borohydride. Examples of hydrazine derivatives include hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride, and hydrazine derivatives such as pyrazoles, triazoles, and hydrazides. Among these, examples of pyrazoles that can be used include pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone in addition to pyrazole. As the triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, etc. can be used. As the hydrazides, adipic acid hydrazide, maleic acid hydrazide, carbohydrazide, etc. can be used. The reducing agent is preferably dimethylamine borane (DMAB).

Treatment with a reducing agent can be carried out, for example, by immersing the resin substrate in a reducing agent solution. The concentration of the reducing agent solution is usually 0.01 mM to 100 mM, preferably 0.01 mM to 10 mM, more preferably 0.01 mM to 1 mM, and particularly preferably 0.01 mM to 0.5 mM. The conditions for treatment with a reducing agent are a treatment temperature of preferably 10°C to 60°C, more preferably 20°C to 50°C, and a treatment time of preferably 10 seconds to 60 minutes, more preferably 30 seconds to 30 minutes. By applying such reducing conditions, it is possible to improve the adhesion, durability, and abrasion resistance of the metal particles while reducing the amount of reducing agent used.

The method of the first embodiment may further include, after step 3, step 4 of heat treating the resin substrate on whose surface metal particles containing Pd and other metals are precipitated to convert the modified layer. In one embodiment, when the modified layer contains carboxyl groups and/or sulfo groups, these groups are dehydrated by the heat treatment. In this embodiment, the heat treatment temperature is typically 100°C to 300°C.

The metallic film obtained by the method of the first embodiment includes a resin substrate, a modified layer formed thereon, and a metal particle layer formed thereon. When step 4 is performed, the modified layer is converted into a resin substrate, so that the obtained metallic film includes a resin substrate and a metal particle layer formed thereon. The metallic film shown in FIG. 1 is obtained by performing steps 1 to 4 in the method of the first embodiment. As described above, the metallic film 10 shown in FIG. 1 has a resin substrate 11 and a metal particle layer 12 formed on the surface of the resin substrate 11.

In a preferred embodiment of the method of the first embodiment, the resin substrate is polyimide, and the other metal is Ag. In this embodiment, the manufacturing method of the present invention includes the steps of modifying the surface of a polyimide resin substrate with an alkaline solution (e.g., KOH) to hydrolyze the polyimide and form a polyamic acid layer having carboxyl groups on the surface of the resin substrate (step 1), treating the polyimide resin substrate having the polyamic acid layer on the surface with a solution containing Pd ions and Ag ions to replace H of the carboxyl groups with Pd ions and Ag ions by ion exchange, and introducing Pd ions and Ag ions into the polyamic acid layer (step 2), and treating the polyimide resin substrate having the polyamic acid layer on the surface with a reducing agent (e.g., dimethylamine borane) to precipitate alloy particles of Pd and Ag on the surface of the polyamic acid layer (step 3). In this embodiment, step 4 may be performed after step 3 to convert the polyamic acid layer to polyimide by heat treatment.

Second Embodiment
The method of the second embodiment includes the steps of forming a film layer having functional groups capable of ion-exchange with metal ions on the surface of a resin substrate (step 1), treating the resin substrate having the film layer on its surface with a solution containing Pd ions and ions of at least one other metal other than Pd to introduce Pd ions and the ions of the other metal into the film layer by ion exchange (step 2), and treating the resin substrate having the film layer on its surface into which Pd ions and ions of the other metal have been introduced with a reducing agent to precipitate metal particles containing Pd and the other metal on the surface, thereby forming a metal particle layer (step 3).

The resin substrate is not particularly limited, and a resin film can be used. The resin film is preferably a transparent film, and examples thereof include polyethylene terephthalate, polycarbonate, polymethyl methacrylate, and acrylic, with polycarbonate and acrylic being preferred. In the method of the second embodiment, a film layer having functional groups capable of ion-exchange with metal ions is formed on the resin substrate, so the resin substrate does not need to have groups that can be converted into functional groups capable of ion-exchange with metal ions, as in the method of the first embodiment.

The film layer may be any material having a functional group capable of ion-exchange with a metal ion, and may be, for example, a resin having a carboxyl group and/or a sulfo group. As the film layer, polyamic acid and styrene-divinylbenzene copolymer are preferred, and polyamic acid is more preferred.

The film layer can be formed, for example, by applying a solution of the resin to be used to form the film layer onto a resin substrate and then drying to remove the solvent.

The thickness of the film layer is usually 0.5 μm to 10 μm, preferably 0.7 μm to 1.5 μm.

The density of metal ions and ion-exchangeable functional groups in the film layer is preferably 1 mol/l to 10 mol/l, and more preferably 5 mol/l to 8 mol/l.

The metal ions are not particularly limited and may be, for example, Ag, Al, Au, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Nb, Mo, In, Co, and Sn ions. From the viewpoint of having high brightness, Ag, Al, and Cr ions are preferred, and Ag ions are more preferred.

In step 2, the resin substrate having the film layer on its surface is treated with a solution containing Pd ions and ions of at least one other metal than Pd. This treatment replaces the metal ions and ion-exchangeable functional groups with Pd ions and ions of the other metal through ion exchange, and these metal ions are introduced into the film layer.

The metal ion solution and its concentration used in step 2 are as described above for the method of the first embodiment.

Treatment with a metal ion solution can be carried out, for example, by immersing a resin substrate having a film layer on its surface in a solution containing Pd ions and ions of at least one metal other than Pd. The treatment conditions with this solution are a treatment temperature of preferably 10°C to 50°C, more preferably 20°C to 30°C, and a treatment time of preferably 1 minute to 60 minutes, more preferably 15 minutes to 45 minutes.

In step 3, the resin substrate having a film layer on its surface into which Pd ions and ions of other metals have been introduced is treated with a reducing agent. This treatment causes metal particles containing Pd and other metals to precipitate on the surface, resulting in a metallic film with a metallic particle layer. The Pd ions and ions of other metals diffuse to the surface where the reducing agent is present and are reduced to metallic particles, so the resulting metallic film has a resin substrate, a film layer formed thereon, and a metallic particle layer formed thereon. In the present invention, the precipitated metallic particles are not easily peeled off because part of each metallic particle is embedded in the film layer.

The reducing agent used in step 3 is as described above for the method of the first embodiment.

Treatment with a reducing agent can be carried out, for example, by immersing the resin substrate in a reducing agent solution. The concentration of the reducing agent is preferably 0.01 mM to 100 mM, more preferably 0.01 mM to 50 mM. The conditions for treatment with a reducing agent are a treatment temperature of preferably 25°C to 60°C, more preferably 40°C to 60°C, and a treatment time of preferably 1 minute to 60 minutes, more preferably 5 minutes to 30 minutes.

The method of the second embodiment may further include, after step 3, step 4 of heat treating the resin substrate on which metal particles containing Pd and other metals have precipitated on the surface of the film layer to convert the film layer. In one embodiment, if the film layer contains carboxyl groups and/or sulfo groups, these groups are dehydrated by heat treatment. In this embodiment, the heat treatment temperature is typically 100°C to 300°C.

The metallic film obtained by the method of the second embodiment includes a resin substrate, a film layer formed thereon, and a metal particle layer formed thereon. The metallic film shown in FIG. 2 is obtained by the method of the second embodiment. As described above, the metallic film 20 shown in FIG. 2 has a resin substrate 21 having a film layer 22 on its surface, and a metal particle layer 23 formed thereon.

In a preferred aspect of the method of the second embodiment, the resin substrate is polycarbonate or acrylic, the film layer is polyamic acid, and the other metal is Ag. In this aspect, the manufacturing method of the present invention includes forming a film layer made of polyamic acid on the surface of a polycarbonate or acrylic resin substrate (step 1), treating the resin substrate having the film layer on its surface with a solution containing Pd ions and Ag ions to replace H of the carboxyl group with Pd ions and Ag ions by ion exchange to introduce Pd ions and Ag ions into the film layer (step 2), and treating the resin substrate having the film layer on its surface with a reducing agent (e.g., dimethylamine borane) to precipitate alloy particles containing Pd and Ag on the surface of the film layer (step 3). In this aspect, step 4 may be performed after step 3, in which the polyamic acid of the film layer is converted into polyimide by heat treatment.

The metallic film of the present invention is capable of achieving both high brightness and radio wave transparency, and therefore can be suitably used as a metallic film for products that require radio wave transparency.

The present invention will be described in more detail below using examples. However, the technical scope of the present invention is not limited to these examples.

Example 1
A polyimide film (Kapton 200H, manufactured by Toray DuPont) having a thickness of 50 μm was used as the resin substrate. The size of the polyimide film was 5 cm×5 cm.

The polyimide film was immersed in a 5M KOH solution at 40°C for 1 minute to hydrolyze the surface of the polyimide film and form a polyamic acid layer.

Silver nitrate (AgNO ₃ ) (Nacalai Tesque, Inc., 31018-14) was dissolved in pure water to prepare a 100 mM silver nitrate solution. An aqueous solution of tetraaminepalladium nitrate was added to the prepared silver nitrate solution so that the molar ratio of Pd to Ag (Pd:Ag) was 1:10, producing a mixed solution of tetraaminepalladium nitrate and silver nitrate. After washing the film with water, the film was immersed in the prepared mixed solution at room temperature for 5 minutes to introduce Ag ions and Pd ions into the polyamic acid layer by ion exchange.

Dimethylamine borane (DMAB) (028-08401, manufactured by Wako) was dissolved in pure water to prepare a 0.1 mM DMAB solution. After washing the film with water, it was immersed in the DMAB solution at 30°C for 10 minutes to reduce the Ag ions and Pd ions, and Ag and Pd alloy particles were precipitated on the surface of the polyimide film. The film was washed with water and heat-treated at 200°C to convert the polyamic acid to polyimide, and a metallic film was obtained. The surface of this metallic film was observed with a SEM (scanning electron microscope), and the cross section of the metallic film was observed with a TEM (transmission electron microscope). It was found that Ag and Pd alloy particles were precipitated in islands on the surface of the polyimide film, with gaps between each particle.

Examples 2 to 5
The metallic films of Examples 2 to 5 were obtained in the same manner as in Example 1, except that a mixed solution of tetraamminepalladium nitrate and silver nitrate having the molar ratio of Pd to Ag shown in Table 1 was used.

Comparative Example 1
A metallic film of Comparative Example 1 was obtained in the same manner as in Example 1, except that the mixed solution of tetraamminepalladium nitrate and silver nitrate was changed to a 100 mM silver nitrate solution. In Comparative Example 1, a metallic film having a layer of Ag particles on the surface of a polyimide film was obtained.

The following measurements were performed on the metallic films of Examples 1 to 5 and Comparative Example 1.

Pd Content The Pd content in the metal particles was measured as follows. First, the metallic film was immersed in nitric acid to dissolve Ag and Pd in the nitric acid. The nitric acid solution in which Ag and Pd were dissolved was analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) to quantify the amounts of Ag ⁺ and Pd ²⁺ , and the Pd content (mol%) in the metal particles was calculated from these results.

Color Difference The initial color L (i.e., L*) of the metallic film was measured as follows. The spectral reflectance R(λ) was determined by the ratio of the spectral radiant flux of wavelength λ reflected from an object to the spectral radiant flux of wavelength λ reflected from a perfect diffuse reflecting surface (JIS Z 8722). Measurements were performed using the Murakami Color Research Laboratory CMS-35SP spectrophotometer by the SCI method (specular reflection included). The calculated spectral reflectance R(λ) was used to calculate the index values L*, a*, and b* of the CIE1976 (L*, a*, b*) color system defined by the International Commission on Illumination (CIE). Here, the L value is an index that describes the lightness of a color, and the larger the L value, the brighter the color.

Millimeter wave attenuation The millimeter wave attenuation of the metallic film was measured to evaluate the millimeter wave transmittance. The millimeter wave attenuation was obtained by measuring the one-way attenuation using a millimeter wave characteristic measuring device having a horn antenna and doubling the measured value. Specifically, the measurement sample was irradiated with millimeter waves from the transmitting horn antenna, and the intensity of the millimeter waves passing through the sample and entering the receiving horn antenna was measured to determine the one-way attenuation. The distance between the transmitting and receiving horn antennas was 95 cm. The sample was installed with an elevation angle of 17° relative to the transmitting horn antenna and a distance of about 40 mm between the sample and the transmitting horn antenna. The measurement was performed at 77 GHz, which is the applicable frequency of the millimeter wave radar for vehicles.

Table 1 shows the measurement results (Pd content, L value, millimeter wave attenuation) of the metallic films of Examples 1 to 5 and Comparative Example 1. Figure 3 also shows the relationship between the Pd content of the metal particles and the L value of the metallic film.

As shown in Table 1, the metallic films of Examples 1 to 5, in which the metal particles contain Pd, had a larger L value and higher brightness while having the same excellent radio wave transmittance as the metallic film of Comparative Example 1, in which the metal particles do not contain Pd. In the metallic films of Examples 1 to 5, the crystallinity of the particles was increased by using alloy particles of Ag and Pd, which made it easier for total reflection of light to occur on the particle surface, resulting in high brightness. In addition, as shown in Table 1 and Figure 3, the L value of the metallic film could be significantly improved by adding a small amount of Pd. Furthermore, as shown in Figure 3, there was a linear correlation between the Pd content in the metal particles and the L value of the metallic film, and the L value of the metallic film tended to decrease as the Pd content increased. As shown in Figure 3, when the Pd content in the metal particles was 34.4 mol% or less, the L value of the metallic film was more than 75, exceeding the L value of Comparative Example 1, which did not contain Pd. Furthermore, when the Pd content in the metal particles was 22 mol% or less, the L value of the metallic film exceeded 80, and when the Pd content in the metal particles was 9.6 mol% or less, the L value of the metallic film exceeded 85, resulting in a metallic film with higher brightness.

10: Metallic film, 11: Resin substrate, 12: Metal particle layer 20: Metallic film, 21: Resin substrate, 22: Film layer, 23: Metallic particle layer

Claims (5)

A metallic film having a resin substrate and a metal particle layer formed on the resin substrate,
In the metal particle layer, there are gaps between the metal particles, the metal particles are made of Pd and Ag , and the Pd content in the metal particles is 1.6 mol% to 34.4 mol%. The metallic film according to claim 1 , wherein the resin substrate is a polyimide. A method for producing the metallic film according to claim 1 or 2 ,
Step 1 of preparing a resin substrate having a layer on its surface having functional groups capable of ion-exchange with metal ions;
a step 2 of treating a resin substrate having a surface layer having functional groups capable of ion-exchange with the metal ions with a solution containing Pd ions and Ag ions to introduce Pd ions and Ag ions into the layer by ion exchange;
and step 3 of treating a resin substrate having a layer on its surface into which Pd ions and Ag ions have been introduced with a reducing agent to cause metal particles consisting of Pd and Ag to precipitate on the surface. The method for producing a metallic film according to claim 3 , further comprising a step 4 of performing a heat treatment after the step 3 . 5. The method for producing a metallic film according to claim 3 or 4 , wherein in step 1, a layer having functional groups capable of ion-exchange with the metal ions is formed on the surface of the resin substrate by modifying the surface of the resin substrate.