JP7665172B2 - Film that exhibits metallic luster and paint that produces said film - Google Patents

Description

The present invention relates to a film that exhibits metallic luster and a paint that produces the film.

Metals are generally hard and are used in parts that require mechanical strength, such as in home appliances and automobiles. They also have a metallic luster that gives them a nice texture, and they are used in all kinds of items in daily life, such as furniture and miscellaneous goods. However, metals are not only expensive as a material, but are also not easy to process, so items made of metal tend to be expensive.

Methods for inexpensively producing articles with metallic luster include metal plating, which coats the surface of an article made from a polymer compound or glass with a thin metal film, and surface treatment techniques such as applying paint containing fine particles or flakes of metal to the surface of the article.

However, metal plating is limited in the materials that can be surface-treated, and paints containing metals have issues such as the difference in specific gravity between the polymer binder and the metal in the paint causing the metal particles to settle, resulting in spots when the paint is applied.

Therefore, efforts have been made to solve the above problems by using non-metallic substances other than metals to produce a metallic luster. For example, Patent Document 1 describes a technology related to non-metallic substances that exhibit a metallic luster.

Japanese Patent No. 6308624 (pages 8 to 10, Figure 11)

The technology described in Patent Document 1 involves, for example, synthesizing a polymer of 3-methoxythiophene using an oxidizing agent, dissolving the polymer in a solvent to form a coating, and applying the coating to a glass substrate, thereby obtaining a film with a metallic luster that is inexpensive and highly versatile. Such metallic luster films are required to have a stronger luster (higher reflectance), and the inventors' research has led them to discover a film that exhibits a strong metallic luster without using metal.

The present invention was made with a focus on these issues, and aims to provide a film that exhibits a strong metallic luster and a paint that produces such a film.

A film exhibiting metallic luster according to one aspect of the present invention for solving the above problems is as follows:
The composition is characterized by including a thiophene copolymer in which thiophene and a thiophene derivative or a plurality of types of thiophene derivatives are copolymerized.
According to this feature, a film exhibiting a strong metallic luster can be obtained. In addition, by combining thiophene and a thiophene derivative or a combination of multiple types of thiophene derivatives, it is easy to adjust the reflectance and color tone of the resulting film.

The thiophene copolymer is characterized in that it is a random copolymer.
This feature makes it possible to easily dissolve the thiophene copolymer in a solvent.

The plurality of types of thiophene derivatives are characterized in that they have the same substituents.
According to this feature, the structure of the thiophene copolymer is planarized, so that a film exhibiting a strong metallic luster can be obtained.

The multiple thiophene derivatives may be 3-methoxythiophene and 3,4-dimethoxythiophene.
This feature makes it possible to achieve high reflectance.

A coating material for forming a film exhibiting metallic luster according to another aspect of the present invention comprises:
The composition is characterized by including the thiophene copolymer and a solvent.
According to this feature, the occurrence of spots in the formed film can be suppressed.

As described above, the present invention can provide a film that exhibits a strong metallic luster and a paint that produces such a film. In addition, by combining thiophene and a thiophene derivative or a combination of multiple types of thiophene derivatives, it is possible to adjust the reflectance and color tone of the produced film, and the produced film has high extensibility.

FIG. 2 is a schematic cross-sectional view of an object on which a metallic luster film containing a thiophene copolymer according to an embodiment is formed. FIG. 1 is a schematic diagram of a polymerization apparatus used in Example 1. FIG. 2 is an image diagram of the layer structure of the powder obtained in Example 1. FIG. 2 is a photograph of the membrane obtained in Example 1. FIG. 2 is a diagram showing the reflectance spectrum of the film obtained in Example 1. FIG. 13 is a diagram showing the reflectance spectrum of the film obtained in Example 2.

Embodiments of the present invention will be described in detail below with reference to Figures 1 to 6. However, the present invention can be implemented in many different forms and is not limited to the embodiments and examples shown below.

Figure 1 is a schematic diagram of a cross section of an article on which a metallic gloss film containing a thiophene copolymer according to this embodiment is formed.

The articles on which the metallic gloss film according to this embodiment is formed are not particularly limited as long as the metallic gloss film can be formed on the surface, and include not only electronic products such as home appliances and automobiles, mechanical products and their parts, but also miscellaneous goods used in daily life such as furniture and toys, clothing, paper products, packaging, and all sorts of other items. However, it is preferable that the material is made of a polymer compound or glass, from the viewpoint of ease of film formation and low manufacturing costs.

In this embodiment, the thickness of the metallic gloss film is not limited as long as it can exhibit metallic gloss, but if it is 0.1 μm or more, it can be a metallic gloss film, and if it is 1 μm or more, it will be a more sufficient metallic gloss film.

The metallic gloss film according to this embodiment also contains a thiophene copolymer whose weight-average molecular weight distribution peak is in the range of 100 or more and 100,000 or less.

In this embodiment, the "thiophene copolymer" is a copolymer in which a total of two or more thiophenes and thiophene derivatives are bonded to each other and copolymerized, or a copolymer in which two or more types of thiophene derivatives are bonded to each other and copolymerized (for example, a compound represented by the following general formula). In this embodiment, the thiophene copolymer is a so-called oligomer, which is a random copolymer in which the combination of thiophene derivatives, i.e., monomers, is randomly arranged.

In the above formula, R is a substituent, and is not limited as long as it can impart metallic luster to the film. However, it is preferably any one of an alkyl group, an alkoxy group, an amino group, a hydroxy group, a hydroxyalkyl group, an aryl group, a cyano group, or a halogen, and in order to more reliably obtain metallic luster, it is preferably an alkyl group, an alkoxy group, or a halogen. In addition, R may be one or two in one thiophene ring. In addition, in the thiophene copolymer according to this embodiment, R in the above formula of each thiophene derivative may be the same or different.

Note that "thiophene" is a heterocyclic compound containing sulfur, and "thiophene derivatives", as is clear from the above description, are heterocyclic compounds containing sulfur and are compounds represented by the following general formula. The definition of R in the formula is the same as above.

In addition, when R in the above formula is an alkoxy group, the carbon number is preferably 1 or 2. Specific examples include 3-methoxythiophene, 3,4-dimethoxythiophene, 3-ethoxythiophene, 3,4-diethoxythiophene, and 3,4-ethylenedioxythiophene. By making the carbon number 1 or 2, a layered orientation structure can be effectively expressed.

In addition, when R in the above formula is an alkyl group, it is preferable that the carbon number is 1 or 2. Specific examples include 3-methylthiophene, 3,4-dimethylthiophene, 3-ethylthiophene, and 3,4-diethylthiophene. By making the carbon number 1 or 2, a layered orientation structure can be effectively expressed.

When R in the above formula is an amino group, examples include 3-aminothiophene, 3,4-diaminothiophene, 3-methylaminothiophene, and 3-dimethylaminothiophene. In this case, when the amino group contains carbon, the number of carbon atoms is preferably 1 or 2.

In addition, in this embodiment, the molecular weight of the "thiophene copolymer" is not limited as long as it has a metallic luster and can be formed into a film, but it is preferably a so-called oligomer.

In the present embodiment, the thiophene copolymer is not limited as long as it can be made into a metallic gloss film, but it is preferable that the thiophene copolymer is polymerized by a chemical polymerization method. Here, "chemical polymerization method" refers to polymerization carried out in at least one of a liquid phase and a solid phase using an oxidizing agent.

In this embodiment, the reason why the thiophene copolymer obtained by chemical polymerization exhibits metallic luster is thought to be because the molecules constituting the thiophene copolymer are regularly oriented and reflect a specific wavelength, although this is only speculation. This is also supported by the fact that the produced film exhibits a sharp peak in X-ray diffraction. This detail means that in X-ray diffraction measurement of the thiophene copolymer, there is no halo pattern due to the amorphous phase, and peaks thought to be due to the regular structure of the thiophene copolymer can be clearly observed within a specified range of diffraction angles (2θ).

The metallic luster film in this embodiment exhibits metallic luster for a long period of time without deterioration even when left in air for a long period of time because the thiophene copolymer is very stable in air.

Here, we will explain the method for producing a metallic gloss film in this embodiment (hereinafter simply referred to as "this method").

This method includes the steps of (1) polymerizing thiophene and a thiophene derivative or multiple types of thiophene derivatives using an oxidizing agent to obtain a solution containing a thiophene copolymer, and (2) applying the solution containing the thiophene copolymer to an article and drying it. That is, in this embodiment, chemical polymerization is performed to produce a thiophene copolymer.

First, in this method, (1) thiophene and a thiophene derivative or multiple types of thiophene derivatives are copolymerized using an oxidizing agent to prepare a solution containing this thiophene copolymer. The "thiophene derivative" used here and the resulting "thiophene copolymer" are as described above. As described above, the thiophene copolymer is preferably in the range of a so-called oligomer.

In this process, the oxidizing agent is not limited as long as it can produce a thiophene copolymer, and various oxidizing agents can be used. Examples of the oxidizing agent include ferric salts, cupric salts, cerium salts, dichromates, permanganates, ammonium persulfate, boron trifluoride, bromates, hydrogen peroxide, chlorine, bromine, and iodine. Among these, ferric salts are preferred. Hydrates may also be used. In this case, the counter ions can also be adjusted as appropriate and are not limited. Examples include chloride ions, citrate ions, oxalate ions, paratoluenesulfonate ions, perchlorate ions, hexafluorophosphate ions, and tetrafluoroborate ions. Among these, the use of at least one of perchlorate ions, hexafluorophosphate ions, and tetrafluoroborate ions is preferred because it can obtain a metallic luster close to gold. The reason why a metallic luster close to gold can be obtained is only a matter of speculation, but it is thought that perchlorate ions, hexafluorophosphate ions, and tetrafluoroborate ions are incorporated into the thiophene copolymer as dopants during polymerization, and bond with the cationic sites generated within the thiophene copolymer to stabilize it and contribute to the formation of a regular structure. In fact, analysis of the metallic luster film has confirmed that these exist stably.

In addition, in this process, it is preferable to use a solvent and carry out the copolymerization in this solvent. The solvent to be used is not limited as long as it can sufficiently dissolve the oxidizing agent and thiophene and the thiophene derivative or multiple types of thiophene derivatives and efficiently copolymerize them, but it is preferable to use an organic solvent that has high polarity and a certain degree of volatility. For example, acetonitrile, nitromethane, γ-butyrolactone, propylene carbonate, nitromethane, 1-methyl-2-pyrrolidinone, dimethylsulfoxide, 2-butanone, tetrahydrofuran, acetone, methanol, anisole, chloroform, ethyl acetate, hexane, trichloroethylene, cyclohexanone, dichloromethane, chloroform, dimethylformamide, ethanol, butanol, pyridine, dioxane, and mixtures thereof can be used, but acetonitrile, nitromethane, γ-butyrolactone, and propylene carbonate are preferable because they dissolve the thiophene copolymer and tend to form a film with better metallic luster.

In this process, the amounts of thiophene and thiophene derivatives or multiple types of thiophene derivatives, and oxidizing agent used in the solvent can be adjusted as appropriate and are not limited, but when the weight of the solvent is taken as 1, the total weight of thiophene and thiophene derivatives or multiple types of thiophene derivatives is preferably 0.00007 to 7, more preferably 0.0007 to 0.7, and in the case of iron (III) chloride anhydride, the total weight is preferably 0.0006 to 6, more preferably 0.006 to 0.6.

In addition, in this process, the ratio of thiophene or thiophene derivatives to the oxidizing agent is preferably 0.1 to 1000, and more preferably 1 to 100, when the total weight of the thiophene derivatives is taken as 1.

In addition, in this process, the molar ratio of thiophene and thiophene derivative or multiple types of thiophene derivatives used can be adjusted as appropriate and is not limited, but for example, when two types of thiophene derivatives are used, a thiophene derivative with a small molecular weight and a thiophene derivative with a large molecular weight are preferably copolymerized at a molar ratio of 5:1 to 20:1, more preferably a molar ratio of 9:1. Within this range, the thiophene derivative is easily soluble in water and it is easy to produce a water-soluble paint. In addition, when producing an oil-soluble paint, a thiophene derivative with a small molecular weight and a thiophene derivative with a large molecular weight are preferably copolymerized at a molar ratio of 20:1 to 1:20, more preferably a molar ratio of 1:1.

In addition, in this process, multiple types of thiophene derivatives and an oxidizing agent may be added to a solvent at once, but two types of solutions may be prepared separately: one in which multiple types of thiophene derivatives are added to a solvent, and the other in which an oxidizing agent is added to a solvent, and then these solutions may be added together to carry out the polymerization reaction.

The solution containing the thiophene copolymer obtained by this process may be stored as it is, but the solvent in this solution may be removed, washed with a solvent, and then dried to obtain a thiophene copolymer powder, and when forming a film, a solvent may be added again to prepare a solution containing the thiophene copolymer. In this case, the solvent used is the same as the solvent exemplified above, and may be the same as or different from the solvent used in the polymerization. This is preferable because it allows the removal of residual monomers and oxidizing agents that were added in excess during the polymerization reaction. However, when an oxidizing agent containing the above-mentioned perchlorate ions, hexafluorophosphate ions, and tetrafluoroborate ions is used as the oxidizing agent, these ions remain because they are stably bonded to the copolymer, and the metallic luster state can be stably maintained.

The method also includes a step (2) of applying a solution containing a thiophene copolymer to an article and drying it. In this embodiment, the article on which the film is formed is one of the above-mentioned examples.

In this process, the method of applying the solution containing the thiophene copolymer to the article is not limited as long as it is possible to apply the solution. For example, spin coating, bar coating, dip coating, drop casting, etc. can be used, but the drop casting or dip coating methods are suitable for forming a thick layer thick enough to provide a metallic luster.

In this method, the metallic luster may be more pronounced by polishing the film after drying in the above process, although this will vary depending on the solvent used. By polishing the film, the degree of orientation of the copolymer can be increased, and a better metallic luster can be obtained. For example, when nitromethane is used as the solvent, a film with metallic luster can be obtained without polishing, but when acetonitrile is used, it is highly desirable to polish the film. The method for polishing the film is not particularly limited, but it is preferable to use a cloth or paper rag, for example.

As described above, the present invention can provide a film that exhibits a strong metallic luster and a paint that produces such a film. In addition, by combining thiophene and a thiophene derivative that constitute the thiophene copolymer, or a combination of multiple types of thiophene derivatives, it is possible to adjust the reflectance and color tone of the resulting metallic luster film, and the resulting film has high extensibility.

The metallic gloss film according to the present invention is also electrically conductive, and by forming the film according to this embodiment on an insulating article, it is possible to ensure electrical conductivity, which is an advantage.

Here, the film of Example 1 according to the above embodiment was actually produced, and its effects were confirmed. The details are explained below.

(1) Synthesis of 3-methoxythiophene, 3,4-dimethoxythiophene copolymer First, 20 ml of an acetonitrile solution (concentration: 0.2 M) of anhydrous iron (III) chloride as an oxidizing agent was prepared and magnetically stirred.

Next, 3-methoxythiophene as a thiophene derivative with a low molecular weight and 3,4-dimethoxythiophene as a thiophene derivative with a high molecular weight were weighed out to a molar ratio of 9:1, and 20 ml of acetonitrile solution (concentration 0.1 M) was prepared by adding these, which was then placed in a glass flask and subjected to magnetic stirring while bubbling with N2 for approximately 30 minutes. A schematic diagram of the apparatus used in this case is shown in Figure 2.

Then, the acetonitrile solution of the iron(III) chloride anhydride was added to the acetonitrile solution of the 3-methoxythiophene and 3,4-dimethoxythiophene, mixed, and stirred for 2 hours to allow copolymerization to proceed.

Then, the solution was distilled under reduced pressure using an evaporator, and a small amount of ethanol was added to it.

Then, the solution and precipitate in the flask were aspirated and filtered using a membrane filter (pore diameter 0.1 μm). The residue on the filter was thoroughly washed with ethanol to remove the oxidizing agent.

The residue was then dried under vacuum at 50°C to obtain a powder of 3-methoxythiophene, 3,4-dimethoxythiophene copolymer. 3-Methoxythiophene, 3,4-dimethoxythiophene copolymer is a compound represented by the following general formula. Note that the dopant contained in the copolymer is omitted. The powder was black, with scattered metallic luster like gold or copper.

In addition, a schematic diagram of the thiophene copolymer structure is shown in FIG. 3. As shown in this figure, it is presumed that the thiophene copolymer structure is planarized due to the interaction between S in the five-membered ring structure and the substituent (specifically, O in the methoxy group), which is one of the causes of the strong metallic luster. In particular, in this embodiment, since the substituents of the two types of thiophene derivatives constituting the 3-methoxythiophene and 3,4-dimethoxythiophene copolymers are the same methoxy group, it is presumed that the structure of the thiophene copolymer is more easily planarized. The substituents of the multiple types of thiophene derivatives constituting the thiophene copolymer may be different. For example, a combination of a methoxy group and a butoxy group is preferable because the electron donating properties of both substituents are close and the structure of the thiophene copolymer is easily planarized. It is also presumed that the planarized thiophene copolymer is regularly stacked in layers, which is also one of the causes of the metallic luster.

(Production of metallic gloss film)
The 3-methoxythiophene, 3,4-dimethoxythiophene copolymer powder obtained by the above procedure was dissolved in distilled water to prepare two types of water-soluble paints with concentrations of 0.2 wt % and 0.3 wt %. The paints were deep blue in color.

Then, the paint was applied onto the glass substrate using a dropper. In this case, the paint was applied thickly so that the other side of the substrate was not visible through the paint.

Then, the substrate coated with the paint was allowed to dry naturally. The surface changed from the deep blue color of the paint to a copper color with a metallic luster. A photograph of this metallic luster film is shown in Figure 4, and its reflection spectrum is shown in Figure 5.

As shown in Figure 5, the reflectance spectra of four types of films were measured: (1) a metallic luster film prepared from 3-methoxythiophene polymer (polymer A) to a concentration of 0.3 wt %, (2) a metallic luster film prepared from a mixture of 3-methoxythiophene polymer (polymer A) and 3,4-dimethoxythiophene polymer (polymer B) to a concentration of 0.3 wt %, (3) a metallic luster film prepared from 3-methoxythiophene, 3,4-dimethoxythiophene copolymer (copolymer A) to a concentration of 0.2 wt %, and (4) a metallic luster film prepared from 3-methoxythiophene, 3,4-dimethoxythiophene copolymer (copolymer B) to a concentration of 0.3 wt %. The results showed that a strong metallic luster was observed with reflectances of 33% and 35% around 700 nm. In addition, the reflectance of the metallic luster films (3) and (4) prepared from a 3-methoxythiophene and 3,4-dimethoxythiophene copolymer was approximately 5% higher than that of the metallic luster film (1) prepared from a polymer obtained by polymerizing one type of 3-methoxythiophene. In addition, the reflectance was significantly higher than that of the metallic luster film (2) prepared from a mixture of a 3-methoxythiophene polymer and a 3,4-dimethoxythiophene polymer, demonstrating that a strong metallic luster can be obtained by using a 3-methoxythiophene and 3,4-dimethoxythiophene copolymer.

As shown in Figure 5, the reflection spectrum of the metallic gloss films (3) and (4) prepared from 3-methoxythiophene and 3,4-dimethoxythiophene copolymers has a peak value around 700 nm, which indicates a copper color, but the color tone can be adjusted appropriately by changing the type and molar ratio of the monomers that make up the thiophene copolymer.

Because the thiophene copolymer is a random copolymer, the monomer arrangement in copolymer A forming the metallic gloss film (3) is different from that in copolymer B forming the metallic gloss film (4). In addition, because the thiophene copolymer is a random copolymer, it is more soluble in a solvent than when it is formed from a single monomer, such as polymer A forming the metallic gloss film (1), and the occurrence of spots in the metallic gloss film formed on the glass substrate can be suppressed.

Next, a film according to Example 2 of the above embodiment was produced, and its effects were confirmed. Note that a description of the configuration that is the same as that of Example 1 will be omitted.

(1) Synthesis of 3-methoxythiophene, 3,4-dimethoxythiophene copolymer First, 10 ml of an acetonitrile solution (concentration: 0.2 M) of iron (III) perchlorate n-hydrate as an oxidizing agent was prepared and magnetically stirred.

Next, 3-methoxythiophene as a thiophene derivative with a low molecular weight and 3,4-dimethoxythiophene as a thiophene derivative with a high molecular weight were weighed out in two amounts, with a molar ratio of 1:1 and 9:1, and these were added separately to prepare 10 ml of acetonitrile solution (concentration 0.1 M). The solution was placed in a glass flask and subjected to magnetic stirring while bubbling with N2 for approximately 30 minutes.

Then, the acetonitrile solution of the iron(III) chloride anhydride was added to the acetonitrile solution of the two types of 3-methoxythiophene and 3,4-dimethoxythiophene, mixed, and stirred for 1 hour to allow copolymerization to proceed.

Then, the solution and precipitate in the flask were aspirated and filtered using a membrane filter (pore diameter 0.1 μm). The residue on the filter was thoroughly washed with methanol to remove the oxidizing agent.

The residue was then dried under vacuum at 50°C to obtain two types of 3-methoxythiophene and 3,4-dimethoxythiophene copolymer powders.

(Production of metallic gloss film)
The two types of 3-methoxythiophene and 3,4-dimethoxythiophene copolymer powders obtained by the above procedure were dissolved in nitromethane solution to prepare two types of oil-soluble paints with a concentration of 1 wt %. The paints were deep blue in color.

The above paints were then applied to the glass substrates using a dropper. In this case, the paint was applied thickly so that the other side of the substrate was not visible through the paint.

Next, the substrate coated with the paint was allowed to dry naturally. The surface changed from the deep blue color of the paint to a gold color with a metallic luster. The reflectance spectrum of this metallic luster film is shown in Figure 6.

As shown in Figure 6, the reflectance spectra of three types of films, (1) a metallic luster film prepared from 3-methoxythiophene polymer (polymer C) at a concentration of 1 wt%, (2) a metallic luster film prepared from 3-methoxythiophene and 3,4-dimethoxythiophene copolymer (molar ratio 1:1, copolymer C) at a concentration of 1 wt%, and (3) a metallic luster film prepared from 3-methoxythiophene and 3,4-dimethoxythiophene copolymer (molar ratio 9:1, copolymer D) at a concentration of 1 wt%, were measured, and a strong metallic luster was observed with reflectances of 20% and 21% at around 600 nm. In addition, compared to the metallic luster film (1) prepared from a polymer polymerized with one type of 3-methoxythiophene, the reflectances of (2) and (3) prepared from 3-methoxythiophene and 3,4-dimethoxythiophene copolymers were about 5% higher. In addition, the metallic luster film (2) prepared from a 3-methoxythiophene polymer with a molar ratio of 1:1 has a higher reflectance than the metallic luster film (3) prepared from a 3,4-dimethoxythiophene polymer with a molar ratio of 9:1. This shows that in the case of oil-soluble paints, a strong metallic luster can be obtained by preparing 3-methoxythiophene as a thiophene derivative with a low molecular weight and 3,4-dimethoxythiophene as a thiophene derivative with a high molecular weight in a molar ratio of 1:1.

As shown in Figure 6, the reflection spectrum of the metallic gloss films (2) and (3) prepared from 3-methoxythiophene and 3,4-dimethoxythiophene copolymers has a peak value around 600 nm, which indicates a golden color, but the color tone can be adjusted appropriately by changing the type and molar ratio of the monomers that make up the thiophene copolymer.

As described above, by using Examples 1 and 2, it was possible to produce a film that exhibits a strong metallic luster and a paint that produces such a film. In addition, by combining thiophene and a thiophene derivative that constitute the thiophene copolymer, or a combination of multiple types of thiophene derivatives, it is possible to adjust the reflectance and color tone of the resulting metallic luster film, and the resulting film has high extensibility.

As described above, these embodiments and examples can provide a film that exhibits a strong metallic luster and a paint that produces such a film.

The present invention has industrial applicability as a copolymer that exhibits strong metallic luster. The present invention can be used as a substitute for metal films, and has a wide range of applications, including inks for writing instruments with metallic luster, oil-based paints, water-based paints, and cosmetics.

Claims (5)

The thiophene copolymer includes thiophene and a thiophene derivative or a thiophene copolymer including a plurality of thiophene derivatives.
The thiophene derivative has the same alkoxy group as the substituent,
The thiophene copolymer is formed by chemical polymerization, has a layered orientation structure in which the molecules of the thiophene and the thiophene derivative or the multiple types of thiophene derivatives are regularly oriented , and is a film that exhibits a metallic luster, characterized in that no halo pattern is present in X-ray diffraction measurement . The film exhibiting metallic luster according to claim 1, characterized in that the thiophene copolymer is a random copolymer. The film exhibiting metallic luster according to claim 1 or 2, characterized in that the thiophene copolymer contains a dopant. The film exhibiting metallic luster according to any one of claims 1 to 3, characterized in that the thiophene derivative has a substituent that is an alkoxy group having 1 or 2 carbon atoms. A coating material for producing a film exhibiting metallic luster, comprising the thiophene copolymer according to any one of claims 1 to 4 and a solvent.

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