JP2016216691A - Transparent dielectric film, capacitance type touch panel and flexible display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent dielectric film having a high dielectric constant and excellent transparency.SOLUTION: The transparent dielectric film of the present invention contains high dielectric fine particles having polymer graft chains formed therein, which are two-dimensionally or three-dimensionally arranged via the polymer graft chains. The high dielectric fine particles used for the transparent dielectric film of the present invention are preferably at least one type selected from a group consisting of BaTiOfine particles, TiOfine particles and ZrOfine particles.SELECTED DRAWING: None

Description

  The present invention relates to a transparent dielectric film, a capacitive touch panel, and a flexible display.

Touch panels are widely used in various displays used for televisions, mobile phones, portable information terminals, and the like. As a touch panel system, a resistive film type, a capacitive type, and the like are known, and in particular, a capacitive type touch panel that can easily perform multi-input is attracting attention.
Conventionally, a display equipped with a capacitive touch panel has a high transparency, a high dielectric constant, and excellent sensitivity as a cover material disposed on the upper surface (touch surface side) of the capacitive touch panel. For this reason, chemically strengthened glass has generally been used. However, since chemically strengthened glass is expensive, there is a problem that the manufacturing cost of the display increases. On the other hand, chemically tempered glass does not have sufficient flexibility and cannot be used as a cover material for a flexible display provided with a capacitive touch panel. Moreover, since the dielectric constant of the member arrange | positioned from the electrode of a touch panel to a touch surface affects touch sensitivity, if the resin film which has a general dielectric constant is used as a cover material, the sensitivity of a touch panel will fall. The problem arises. Furthermore, for the same reason, when using a resin film having a general dielectric constant as a substrate positioned between the touch panel electrode and the touch surface among the touch panel substrates, the sensitivity of the touch panel is also reduced. Problems arise. Therefore, it has been proposed to use a transparent dielectric film in which high dielectric fine particles such as barium titanate are contained in a resin film as a touch panel substrate or a flexible display cover material (for example, Patent Document 1).

JP 2014-203151 A

  However, it is difficult to disperse the high dielectric fine particles uniformly in the resin film. For example, a resin film containing high dielectric fine particles is produced by molding a resin material containing high dielectric fine particles into a film, and the high dielectric fine particles aggregate and / or precipitate in the resin material. Therefore, it is difficult to obtain a resin film in which high dielectric fine particles are uniformly dispersed. And since aggregation of the high dielectric fine particles in the resin film causes the resin film to become clouded, the transparency of the resin film is not sufficiently ensured.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a transparent dielectric film having a high dielectric constant and excellent transparency. Moreover, an object of this invention is to provide a capacitive touch panel and a flexible display provided with the transparent dielectric film which has the said characteristic.

The present inventors have found that the above problem can be solved by arranging the high dielectric fine particles formed with polymer graft chains in two or three dimensions through the polymer graft chains. The invention has been completed.
That is, the present invention is a transparent dielectric film characterized in that high dielectric fine particles in which polymer graft chains are formed are arranged two-dimensionally or three-dimensionally via the polymer graft chains.
Moreover, this invention is a capacitive touch panel and flexible display characterized by having the said transparent dielectric film.

  According to the present invention, a transparent dielectric film having a high dielectric constant and excellent transparency can be provided. Moreover, according to this invention, a capacitive touch panel and a flexible display provided with the transparent dielectric film which has the said characteristic can be provided.

It is a measurement result of the light transmittance in the visible region of the self-supporting film obtained in Examples 1 and 2 and Comparative Example 1. It is a measurement result of the dielectric constant of the self-supporting film obtained in Examples 1 and 2 and Comparative Example 1.

The transparent dielectric film of the present invention is characterized in that high dielectric fine particles formed with polymer graft chains are arranged two-dimensionally or three-dimensionally via polymer graft chains.
Here, in the present specification, the “polymer graft chain” means a polymer chain having a chain length of 2 or more formed by extending from the surface of the high dielectric fine particles by a polymerization reaction, and is also referred to as a polymer brush. .

In the present specification, the “high dielectric fine particles” mean dielectric particles having a relative dielectric constant of 10 or more, preferably 20 or more, more preferably 30 or more. Examples of the high dielectric fine particles include BaTiO ₃ (barium titanate) fine particles (relative dielectric constant 1200), TiO ₂ (titanium dioxide) fine particles (relative dielectric constant 100), ZrO ₂ (zirconium oxide) fine particles (relative dielectric constant 30). ) And the like. These can be used alone or in combination of two or more. Among these, BaTiO ₃ fine particles are preferable from the viewpoint of the dielectric constant of the transparent dielectric film.

In the present specification, “fine particles” mean particles having an average particle diameter of 1 μm or less, and “average particle diameter” of fine particles means a 50% cumulative particle diameter measured by a laser diffraction particle size distribution analyzer. Means that.
High dielectric fine particles can improve the transparency of the transparent dielectric film as the average particle size decreases, while the dielectric constant of the particles themselves decreases. Therefore, the average particle size of the high dielectric fine particles is preferably 1 nm to 500 nm, more preferably 2 nm to 100 nm, still more preferably 3 nm to 50 nm, and most preferably 4 nm to 30 nm.

High dielectric fine particles in which polymer graft chains are formed can be formed by a surface graft polymerization method using living radical polymerization. By using this method, a polymer graft chain in which the chain length and the chain length distribution are regulated can be formed at a high density on the surface of the high dielectric fine particles. In the vicinity of the surface of the high dielectric particle, the polymer graft chain is stretched in a direction perpendicular to the surface of the high dielectric particle (dense polymer brush state) due to steric repulsion between adjacent polymer graft chains. Become. Since the steric repulsion between the polymer graft chains is relaxed at some distance from the surface of the high dielectric fine particles, the polymer graft chains have a lower degree of extension than the dense polymer brush state (quasi-dilute polymer brush state) It becomes. In the dense polymer brush state, the graft density of the polymer graft chain is 0.1 chain / nm ² or more, preferably 0.1 to 1.2 chain / nm ² , and in the semi-dilute polymer brush state, the polymer graft chain The chain graft density is less than 0.1 strand / nm ² , preferably 0.01 strand / nm ² or more and less than 0.1 strand / nm ² .

  The graft density of the polymer graft chain can be calculated according to a method known in the technical field. Specifically, the amount (graft amount) of polymer graft chains grafted onto the high dielectric fine particles is determined by elemental analysis, the graft amount, the specific gravity and surface area of the high dielectric fine particles, and the number of polymer graft chains. By using the average molecular weight, the graft density of the polymer graft chain can be calculated.

The polymer graft chain formed on the high dielectric fine particles preferably has only a concentrated brush state, that is, the graft density of the polymer graft chain is preferably 0.1 chain / nm ² or more. By using fine particles having a polymer graft chain only in a dense brush state, characteristics such as heat resistance of the formed transparent dielectric film can be improved. A polymer graft chain only in a concentrated brush state can be obtained by adjusting the degree of polymerization.

  Here, in this specification, “living radical polymerization” means that the chain transfer reaction and termination reaction are not substantially caused in the radical polymerization reaction, and the chain growth terminal is active even after the radical polymerizable monomer is completely reacted. It means a polymerization reaction to be retained. In this polymerization reaction, the polymerization activity is retained at the end of the produced polymer even after the completion of the polymerization reaction, and when the radical polymerizable monomer is added, the polymerization reaction can be started again. In living radical polymerization, a polymer having an arbitrary average molecular weight can be synthesized by adjusting the concentration ratio between the radical polymerizable monomer and the polymerization initiator, and the molecular weight distribution of the resulting polymer is extremely narrow. There are features such as.

  A typical example of the living radical polymerization used in the present invention is atom transfer radical polymerization (ATRP). For example, in the case of performing atom transfer radical polymerization, after fixing the polymerization initiator on the surface of the high dielectric fine particles, by performing atom transfer radical polymerization of a radical polymerizable monomer using a copper halide / ligand complex, a polymer is obtained. High dielectric fine particles in which graft chains are formed can be obtained.

The method for fixing the polymerization initiator to the surface of the high dielectric fine particles is not particularly limited, and for example, the high dielectric fine particles and the polymerization initiator may be brought into contact with each other.
The polymerization initiator used in the present invention is not particularly limited as long as it can be fixed to the surface of the high dielectric fine particles, and those known in the technical field can be used. As a preferable polymerization initiator for use in the present invention, a compound having a halogen at the terminal, for example, a compound represented by the following general formula (1) or (2) can be used.

  In the general formulas (1) and (2), R1 is each independently a C1-C3 alkyl group, preferably a methyl group or an ethyl group; R2 is each independently a methyl group or an ethyl group; A halogen atom, preferably Br; m is an integer of 2-10, preferably 3-8; n is an integer of 3-10, preferably 4-8. Specific examples of the compound of the general formula (1) include 2-bromo-2-methyl-N- (3-triethoxysilyl) propyl) propanamide (BPA) and the like. Specific examples include (2-bromo-2-methyl) propionyloxyhexyl triethoxysilane (BHE).

  The radical polymerizable monomer used for living radical polymerization has an unsaturated bond capable of radical polymerization in the presence of an organic radical, such as acrylic acid derivative, methacrylic acid derivative, styrene derivative, vinyl acetate and acrylonitrile. Is mentioned. Specifically, methyl methacrylate (MMA), ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, n-octyl Methacrylate, 2-methoxyethyl methacrylate, butoxyethyl methacrylate, methoxytetraethylene glycol methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, tetrahydrofurfuryl methacrylate, 2-hydroxy-3 -Phenoxypropyl methacrylate, diethylene Methacrylate monomers such as recall methacrylate, polyethylene glycol methacrylate, 2- (dimethylamino) ethyl methacrylate; methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, t-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate , Benzyl acrylate, cyclohexyl acrylate, lauryl acrylate, n-octyl acrylate, 2-methoxyethyl acrylate, butoxyethyl acrylate, methoxytetraethylene glycol acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-chloro-2-hydroxy Propyl acrylate, tetrahydrofurfuryl Acrylate monomers such as acrylate, 2-hydroxy-3-phenoxypropyl acrylate, diethylene glycol acrylate, polyethylene glycol acrylate, 2- (dimethylamino) ethyl acrylate, N, N-dimethylacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide Styrene, o-, m-, p-methoxystyrene, o-, m-, pt-butoxystyrene, o-, m-, p-chloromethylstyrene, vinyl propionate, vinyl methyl ketone, vinyl hexyl ketone , Methyl isopropenyl ketone, N-vinyl pyrrolidone, N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, acrylonitrile, methacrylonitrile, acrylamide, isopropyl alcohol Kurylamide, methacrylamide, vinyl chloride, vinylidene chloride, tetrachloroethylene, hexachloroprene, vinyl fluoride and the like can be used. These can be used alone or in combination of two or more.

The copper halide that gives the copper halide / ligand complex is not particularly limited, and those generally known in living radical polymerization can be used. Examples of the copper halide include CuBr, CuCl, and CuI.
The ligand compound that gives the copper halide / ligand complex is not particularly limited, and those generally known in living radical polymerization can be used. Examples of ligand compounds include triphenylphosphane, 4,4′-dinonyl-2,2′-dipyridine (dNbipy), N, N, N ′, N′N ″ -pentamethyldiethylenetriamine (PMDETA), 1, Examples include 1,4,7,10,10-hexamethyltriethylenetetraamine.

  In the production of high dielectric fine particles with polymer graft chains formed, the amount of high dielectric fine particles, polymerization initiator, radical polymerizable monomer, copper halide, and ligand compound used is appropriately determined depending on the type of the high dielectric fine particles. The adjustment is not particularly limited. Further, the production conditions may be appropriately adjusted according to the type of raw material used, and are not particularly limited.

  In addition, although living radical polymerization may be performed without a solvent, you may use the solvent generally used by living radical polymerization. Usable solvents include, for example, benzene, toluene, anisole, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, chloroform, carbon tetrachloride, tetrahydrofuran (THF), ethyl acetate, trifluoromethyl. Examples thereof include organic solvents such as benzene, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 2-methoxyethanol and 1-methoxy-2-propanol, and water. The amount of the solvent may be appropriately adjusted according to the type of raw material to be used, and is not particularly limited.

  The molecular weight of the polymer graft chain formed by living radical polymerization can be adjusted depending on the reaction temperature, reaction time, and the type and amount of raw materials used, but generally the number average molecular weight is 500 to 1,000,000, Preferably it is 1,000-500,000 and a weight average molecular weight is 1,000-2,000,000, Preferably it is 2,000-1,000,000. The molecular weight distribution (Mw / Mn) of the polymer graft chain is not particularly limited, but is 1.05 to 2.80, preferably 1.20 to 2.50.

The transparent dielectric film of the present invention has a structure in which high dielectric fine particles on which polymer graft chains having the above-described characteristics are formed are arranged two-dimensionally or three-dimensionally via polymer graft chains.
The transparent dielectric film of the present invention can be formed as a self-supporting film. Here, in the present specification, the “self-supporting film” means a film that can sufficiently retain its shape independently without using a support.

  The transparent dielectric film of the present invention can be produced using a method known in the art. For example, when the solvent casting method is used, a transparent dielectric film is formed by dispersing high dielectric fine particles in which polymer graft chains are formed in a solvent, applying the dispersion onto a substrate, and evaporating the solvent. Thereafter, it can be produced by peeling the formed transparent dielectric film from the substrate.

  The substrate on which the dispersion liquid in which high-dielectric fine particles are dispersed in a solvent is applied is not particularly limited, and those known in the technical field can be used. Examples of the substrate include a glass plate, a stainless plate, a stainless belt, a polyethylene terephthalate (PET) film, and the like. In order to improve the peelability of the transparent dielectric film, these substrates may be subjected to mirror finishing or surface release agent treatment as necessary.

  The solvent for dispersing the high dielectric fine particles in which the polymer graft chains are formed is not particularly limited, and those known in the technical field can be used. Examples of solvents include aprotic polar solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide; dichloromethane, chloroform, 1,2-dichloroethane Chlorine solvents such as chlorobenzene and dichlorobenzene; alcohols such as methanol, ethanol and propanol; alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether; Toluene; anisole; water and the like. These can be used alone or in combination of two or more.

  The concentration of the high dielectric fine particles in which the polymer graft chains are formed in the dispersion is not particularly limited, but is generally 0.1 to 30% by mass, preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass.

  The amount of the dispersion applied to the substrate is not particularly limited as long as it is appropriately adjusted according to the use for which the transparent dielectric film is used. Moreover, in order to obtain a transparent dielectric film having a desired thickness, the dispersion may be applied and the solvent may be evaporated a plurality of times. The thickness of the transparent dielectric film suitable for the cover material of the flexible display is generally 0.1 μm to 500 μm, preferably 0.5 μm to 300 μm, more preferably 1 μm to 250 μm. If the thickness of the transparent dielectric film is thinner than 0.1 μm, mechanical strength that can be used as a cover material may not be obtained. On the other hand, when the thickness of the transparent dielectric film exceeds 500 μm, the flexibility and transparency of the transparent dielectric film may be impaired. The thickness of the transparent dielectric film can also be adjusted by laminating a transparent dielectric film obtained by a casting method, and integrating by heating and pressing.

  Moreover, the conditions for evaporating the dispersion are not particularly limited, and may be appropriately adjusted according to the type of the solvent used in the dispersion. In general, it may be heated to a temperature higher than the boiling point of the solvent.

  Since the transparent dielectric film of the present invention produced as described above uses high dielectric fine particles in which a polymer graft chain is formed, the high dielectric fine particles aggregate in the transparent dielectric film. In addition to being uniformly dispersed, the dielectric constant is not only high, but also excellent in transparency.

  The volume content of the high dielectric fine particles in the transparent dielectric film of the present invention is not particularly limited, but is preferably 2% by volume to 30% by volume, more preferably 3% by volume to 20% by volume, and even more preferably 4% by volume. -15% by volume, most preferably 5% to 12% by volume. Here, in this specification, the “volume content of high dielectric fine particles” means the volume fraction of high dielectric fine particles calculated by TGA (thermogravimetry). Specifically, the transparent dielectric film is heated to 450 ° C. at 10 ° C./min, and the volume fraction of the high dielectric fine particles can be determined from the amount of residue at 450 ° C.

  In the transparent dielectric film of the present invention, chemical bonds may be formed between the polymer graft chains of the high dielectric fine particles adjacent to each other. For example, as a radically polymerizable monomer used in living radical polymerization, a monomer having a functional group that is cross-linked or polymerized by an external stimulus such as light or heat is introduced into a side chain, and an external stimulus such as light or heat is applied to a self-supporting film. Thus, a chemical bond can be formed between the polymer graft chains of fine particles adjacent to each other. Thereby, the mechanical characteristic of a transparent dielectric film can be improved.

  The transparent dielectric film of the present invention has a relative dielectric constant (25 ° C.) at a frequency of 1 kHz of 3.5 or more, preferably 4.0 or more. The relative dielectric constant can be measured by a commercially available relative dielectric constant measuring apparatus.

  The transparent dielectric film of the present invention has an average value of light transmittance of 80% or more in the visible region (wavelength 400 nm to 800 nm). In particular, the transparent dielectric film of the present invention has a light transmittance at 550 nm of 80% or more, preferably 85% or more. Here, “light transmittance” in this specification means a ratio of light passing through a transparent dielectric film having a thickness of 100 μm, and the larger the value, the higher the transparency. The light transmittance can be measured by a commercially available light transmittance measuring device.

  Since the transparent dielectric film of the present invention has a high dielectric constant and excellent transparency, it can be used as a cover material for various displays equipped with a capacitive touch panel. In particular, since the transparent dielectric film of the present invention is excellent in flexibility, it can also be applied as a cover material for a flexible display provided with a capacitive touch panel. Moreover, the transparent dielectric film of this invention can also be applied as a base material of a capacitive touch panel. Furthermore, as described in Japanese Patent Application No. 2014-212174 filed on October 17, 2014 by the present applicants, the transparent dielectric film of the present invention also has heat resistance and surface hardness. Since it is excellent and has a small retardation value, it can also be used as a substrate used in a flexible display.

EXAMPLES Hereinafter, although an Example demonstrates the detail of this invention, this invention is not limited by these.
Example 1
Add 1.5 mL of ammonia water to 15.5 g of 2-methoxyethanol dispersion (manufactured by JGC Catalysts & Chemicals, Inc., BaTiO ₃ fine particle content 8% by mass) of barium titanate (BaTiO ₃ ) fine particles having an average particle diameter of 7 nm. And stirred at 40 ° C. for 15 minutes. Next, 1.00 g of a polymerization initiator (BPA) dissolved in 2.0 g of 2-methoxyethanol was slowly dropped into this mixed solution, and the mixture was stirred at 40 ° C. for 18 hours. Next, after removing the solvent from the mixed solution using an evaporator, a small amount of water was added, and centrifugation was performed at 4500 rpm for 10 minutes, whereby BaTiO ₃ fine particles (hereinafter referred to as “BPA- Abbreviated as “BaTiO ₃ fine particles”).

Next, MMA 500 mg, DMF 6.00 g, and PMDETA 33.7 mg were added to 204.9 mg of BPA-BaTiO ₃ fine particles, and the mixture was stirred in an ice bath using a homogenizer. Next, this mixed solution was put into a two-necked flask and degassed three times by a freeze-thaw method. Then, 24.6 mg of CuBr was added to perform nitrogen substitution, and a polymerization reaction was performed at 70 ° C. for 1 hour. After completion of the reaction, the mixed solution was bubbled to deactivate Cu. Next, the mixed solution was dissolved in THF, reprecipitated with a mixed solution of methanol / 0.1 M EDTA aqueous solution (volume ratio 20/1), and centrifuged at 4500 rpm for 10 minutes. After reprecipitation and centrifugation were repeated three times, vacuum drying was performed at 80 ° C. overnight to obtain BaTiO ₃ fine particles in which PMMA chains were formed (hereinafter abbreviated as “PMMA-BaTiO ₃ fine particles”). .

The PMMA-BaTiO ₃ fine particles obtained above are immersed in hydrofluoric acid, and the molecular weight of the PMMA (polymer graft chain) separated by dissolving the BaTiO ₃ fine particles is measured using a GPC measuring device (LC-2000plus manufactured by JASCO Corporation). ). Polystyrene was used as the standard sample, and a UV detector was used as the detector. As a result, the number average molecular weight was 39,500, and the weight average molecular weight (Mw) was 92,000.
In addition, the graft density of the PMMA-BaTiO ₃ fine particles was calculated according to a method known in the art, and was found to be 0.18 strands / nm ² .

Next, a dispersion liquid containing 1% by mass of PMMA-BaTiO ₃ fine particles was prepared using anisole as a solvent. Next, this dispersion was applied onto a substrate at room temperature, and then dried at 80 ° C. under vacuum to obtain a self-supporting film having a thickness of 100 μm.
It was confirmed that the obtained self-supporting film could be wound around a rod having a diameter of 6 mm and had sufficient flexibility. Also, the self-supporting film, BaTiO ₃ results of volume content of the fine particles was calculated by TGA (thermogravimetry), the volume content of BaTiO ₃ fine particles was 10.0% by volume. Further, as a result of small-angle X-ray scattering (SAXS) measurement and scanning electron microscope (TEM) observation of the self-supporting film, the PMMA-BaTiO ₃ fine particles are not aggregated and are uniformly dispersed. confirmed.

(Example 2)
The polymerization conditions were the same as in Example 1 except that the mixing ratio (mass ratio) of BPA-BaTiO ₃ fine particles and MMA was adjusted to 1:10 and the polymerization time was changed to 3 hours. BaTiO ₃ fine particles were prepared to obtain a self-supporting film.
About the PMMA-BaTiO ₃ fine particles obtained above, the molecular weight of PMMA (polymer graft chain) was evaluated in the same manner as in Example 1. As a result, the number average molecular weight was 38,700, and the weight average molecular weight (Mw) was 61, 800.
In addition, the graft density of the PMMA-BaTiO ₃ fine particles was calculated according to a method known in the art, and as a result, it was 0.43 strands / nm ² .

Next, a dispersion liquid containing 1% by mass of PMMA-BaTiO ₃ fine particles was prepared using anisole as a solvent. Next, this dispersion was applied onto a substrate at room temperature, and then dried at 80 ° C. under vacuum to obtain a self-supporting film having a thickness of 100 μm.
It was confirmed that the obtained self-supporting film could be wound around a rod having a diameter of 6 mm and had sufficient flexibility. Also, the self-supporting film, BaTiO ₃ results of volume content of the fine particles was calculated by TGA (thermogravimetry), the volume content of BaTiO ₃ fine particles was 4.7% by volume. Further, as a result of small-angle X-ray scattering (SAXS) measurement and scanning electron microscope (TEM) observation of the self-supporting film, the PMMA-BaTiO ₃ fine particles are not aggregated and are uniformly dispersed. confirmed.

Example 3
The polymerization conditions were the same as in Example 1 except that the mixing ratio (mass ratio) of BPA-BaTiO ₃ fine particles and MMA was adjusted to 1: 4, and the polymerization time was changed to 3 hours. BaTiO ₃ fine particles were prepared to obtain a self-supporting film.
The PMMA-BaTiO ₃ fine particles obtained above were evaluated for the molecular weight of PMMA (polymer graft chain) in the same manner as in Example 1. As a result, the number average molecular weight was 125,000 and the weight average molecular weight (Mw) was 159. 100.
In addition, the graft density of the PMMA-BaTiO ₃ fine particles was calculated according to a method known in the art, and was found to be 0.10 strands / nm ² .

Next, a dispersion liquid containing 1% by mass of PMMA-BaTiO ₃ fine particles was prepared using anisole as a solvent. Next, this dispersion was applied onto a substrate at room temperature, and then dried at 80 ° C. under vacuum to obtain a self-supporting film having a thickness of 100 μm.
It was confirmed that the obtained self-supporting film could be wound around a rod having a diameter of 6 mm and had sufficient flexibility. Also, the self-supporting film, BaTiO ₃ results of volume content of the fine particles was calculated by TGA (thermogravimetry), the volume content of BaTiO ₃ fine particles was 6.2% by volume. Further, as a result of small-angle X-ray scattering (SAXS) measurement and scanning electron microscope (TEM) observation of the self-supporting film, the PMMA-BaTiO ₃ fine particles are not aggregated and are uniformly dispersed. confirmed.

Example 4
The polymerization conditions were the same as in Example 1 except that the mixing ratio (mass ratio) of BPA-BaTiO ₃ fine particles and MMA was adjusted to 1: 4 and the polymerization time was changed to 20 hours. BaTiO ₃ fine particles were prepared to obtain a self-supporting film.
The PMMA-BaTiO ₃ fine particles obtained above were evaluated for the molecular weight of PMMA (polymer graft chain) in the same manner as in Example 1. As a result, the number average molecular weight was 64,900, and the weight average molecular weight (Mw) was 100, 700.
Further, the graft density of the PMMA-BaTiO ₃ fine particles was calculated according to a method known in the art, and as a result, it was 0.13 chain / nm ² .

Next, a dispersion liquid containing 1% by mass of PMMA-BaTiO ₃ fine particles was prepared using anisole as a solvent. Next, this dispersion was applied onto a substrate at room temperature, and then dried at 80 ° C. under vacuum to obtain a self-supporting film having a thickness of 100 μm.
It was confirmed that the obtained self-supporting film could be wound around a rod having a diameter of 6 mm and had sufficient flexibility. Also, the self-supporting film, BaTiO ₃ results of volume content of the fine particles was calculated by TGA (thermogravimetry), the volume content of BaTiO ₃ fine particles was 9.1% by volume. Further, as a result of small-angle X-ray scattering (SAXS) measurement and scanning electron microscope (TEM) observation of the self-supporting film, the PMMA-BaTiO ₃ fine particles are not aggregated and are uniformly dispersed. confirmed.

(Comparative Example 1)
In Comparative Example 1, a self-supporting film having a thickness of 100 μm made of only PMMA containing no BaTiO ₃ fine particles was produced.
It was confirmed that the obtained self-supporting film could be wound around a rod having a diameter of 6 mm and had sufficient flexibility.

Next, for the self-supporting films obtained in Examples 1 and 2 and Comparative Example 1, the light transmittance in the visible region was measured using V-570 manufactured by Shimadzu Corporation. The result is shown in FIG.
Moreover, about the self-supporting film obtained in Examples 1 and 2 and Comparative Example 1, the relative dielectric constant was measured at 25 ° C. using a Solatron 1255B impedance analyzer connected to a SH2-Z sample holder manufactured by Toyo Corporation. did. The result is shown in FIG.

As shown in FIG. 1, the self-supporting films of Examples 1 and 2 had an average value of light transmittance of 80% or more in the visible region, and were confirmed to have sufficient transparency. Among them, the self-supporting film of Example 1 has a light transmittance at 550 nm of 85% or more, and it was confirmed that the transparency is particularly excellent.
Further, as shown in FIG. 2, it was confirmed that the self-supporting films of Examples 1 and 2 had a higher dielectric constant than the self-supporting film of Comparative Example 1. Among them, it was confirmed that the self-supporting film of Example 1 had a high relative dielectric constant of 4.0 or more at a frequency of 1 kHz and a particularly high dielectric constant.

  As can be seen from the above results, according to the present invention, a transparent dielectric film having a high dielectric constant and excellent transparency can be provided. Moreover, according to this invention, a capacitive touch panel and a flexible display provided with the transparent dielectric film which has the said characteristic can be provided.

Claims (11)

  A transparent dielectric film, wherein high dielectric fine particles in which polymer graft chains are formed are arranged two-dimensionally or three-dimensionally through the polymer graft chains. The transparent dielectric film according to claim 1, wherein the high dielectric fine particles are at least one selected from the group consisting of BaTiO ₃ fine particles, TiO ₂ fine particles, and ZrO ₂ fine particles.   The transparent dielectric film according to claim 1, wherein a relative dielectric constant at a frequency of 1 kHz is 4 or more.   The transparent dielectric film according to any one of claims 1 to 3, wherein the light transmittance at 550 nm is 80% or more.   5. The transparent dielectric film according to claim 1, wherein a volume content of the high dielectric fine particles is 2% by volume to 30% by volume.   The transparent dielectric film according to claim 1, wherein the high dielectric fine particles have an average particle diameter of 100 nm or less. The transparent dielectric film according to claim 1, wherein a graft density of the polymer graft chain is 0.1 chain / nm ² or more.   8. The polymer graft chain is formed by living radical polymerization of one or more compounds selected from acrylic acid derivatives, methacrylic acid derivatives, styrene derivatives, vinyl acetate and acrylonitrile. The transparent dielectric film as described in any one of the above.   The transparent dielectric film according to claim 1, wherein a chemical bond is formed between the polymer graft chains of the high dielectric fine particles adjacent to each other.   A capacitive touch panel comprising the transparent dielectric film according to claim 1.   A flexible display comprising the transparent dielectric film according to claim 1.

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