JP2663610B2 - High dielectric constant film and capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-dielectric-constant film having excellent heat resistance and mechanical properties, and a capacitor.

[Prior art] Polypropylene, polyethylene terephthalate, etc. are mentioned as materials for films used for capacitors and the like, but the dielectric constant is as low as 3.5 or less, and polyvinylidene fluoride having a dielectric constant of about 10 to obtain high capacity is used. Used. Further, a high dielectric constant film in which an inorganic filler having a high dielectric constant such as barium titanate is added to a polymer such as polyvinylidene fluoride (Makromol, Chem., Rapid Commun. 6, 133 (198)
5), JP-A-58-166609 and JP-A-60-107204).

[Problems to be Solved by the Invention] However, in order to obtain a high capacity, there is a limit in strength even if the thickness of the polyvinylidene fluoride film is reduced, and a method of adding an inorganic filler having a high dielectric constant to a polymer is not known. In general, the affinity between the polymer and the inorganic filler is poor, so that voids are formed and a film having sufficient strength cannot be obtained. Also, the dielectric breakdown strength is poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable high dielectric constant film having improved mechanical properties by suppressing generation of voids and having good dielectric breakdown strength.

[Means for Solving the Problems] The present invention relates to a film-like film containing at least one polymer selected from aromatic polyamides and aromatic polyimides and 5 to 90% by volume of an inorganic filler having a high dielectric constant based on the polymer. A high dielectric constant film, wherein a void area ratio in a cross section of the film is 0.4 or less, and a capacitor characterized by using the high dielectric constant film. Things.

Those consisting of aromatic polyamide and polymer containing a repeating unit represented by the general formula _{HN-Ar 1 -NHOC-Ar 2} -CO 70 mol% or more of the present invention is preferred.

Here, Ar ₁ and Ar ₂ contain at least one aromatic ring and may be the same or different, and representative examples thereof include the following.

Also, part of the hydrogen on these aromatic rings are halogen (especially chlorine), a nitro group, an alkyl group of C ₁ -C ₃ (especially methyl), such as alkoxy groups C ₁ -C ₃ Also includes those substituted with a substituent. X represents —O—, —CH _{2
-, - SO 2 -, -} S -, - CO- , and the like. These are included in the form of homopolymer or copolymer.

A polymer having an alkyl group or —CH ₂ — is preferable because solubility in a polymer solution is improved as compared with one having no substituent, and compatibility with an inorganic filler is improved.

And the like containing 70 mol% or more.

Further, the aromatic polyimide of the present invention is a polymer containing at least one aromatic ring and at least one imide ring in the repeating unit of the polymer, and has the general formula Or Those containing 70 mol% or more of the repeating unit represented by are preferred.

Here, Ar ₃ and Ar ₅ contain at least one aromatic ring, and two carbonyl groups forming an imide ring are bonded to adjacent carbon atoms on the aromatic ring. This Ar ₃ is derived from an aromatic tetracarboxylic acid or its anhydride. Representative examples include the following.

Here, Y _{is, -O -, - CH 2 -} , - SO 2 -, - S-,
—CO— and the like.

Ar ₅ is derived from tricarboxylic acid or its anhydride.

Ar ₄ and Ar ₆ contain at least one aromatic ring and are derived from aromatic diamines and aromatic diisocyanates. Further, it may contain an amide bond, a urethane bond, or the like. Ar ₄ , A
Typical examples of r ₆ include the following.

Here, some of the hydrogens on these aromatic rings are substituted with substituents such as halogen groups, nitro groups, C _{1 to} C ₃ alkyl groups, and C _{1 to} C ₃ alkoxy groups. Including. Z
_{Is, -O -, - CH 2 -} , - SO 2 -, - S -, - CO- , and the like. These are included in the form of homopolymer or copolymer.

Further, the aromatic polyamide and the aromatic polyimide of the present invention may be blended with a lubricant, an antioxidant, other additives, and other polymers to the extent that the physical properties of the film are not impaired.

The inorganic filler having a high dielectric constant used in the present invention expresses a dielectric constant higher than the dielectric constant of the polymer itself when added to the polymer, and a metal oxide is preferable in consideration of affinity with the polymer. Specifically, barium titanate, zinc titanate, strontium titanate, calcium titanate, lead titanate, magnesium titanate,
Titanium oxide, barium antimonate, magnesium antimonate, strontium antimonate, calcium antimonate, magnesium antimonate, lead antimonate, barium stannate, strontium stannate, and the like can be mentioned. You may. The shape of the inorganic filler may be any of a spherical shape, a scale shape, a needle shape, an amorphous shape, and the like, and there are also synthetic methods such as a hydrothermal synthesis method and a solid-phase reaction synthesis method, but are not limited thereto. is not. The crystal structure includes a rutile type, an anatase type, a perovskite type, and the like, but is not limited thereto. This filler has high dielectric properties, and has an average particle size of 10 μm or less and a particle size of 30 μm.
It is preferable that the average particle diameter is 30% or less, and more preferably the average particle diameter is 1 μm or less and the particle diameter is 30 μm or more is 10% or less. If the average particle size is larger than 10 μm, the effects of the present invention cannot be fully utilized, and particularly in the case of a thin film, the mechanical properties deteriorate.

Further, the content of the inorganic filler with respect to the polymer of the obtained film-like material needs to be 5 to 90% by volume. When the content is less than 5% by volume, the effect of containing an inorganic filler on the dielectric constant is hardly exerted, and when it exceeds 90% by volume, the mechanical properties of the film-like material deteriorate.

The film-like material of the present invention has a unit area of Am in its cross section.
m ² , and the void area ratio (B / A) needs to be 0.4 or less, where B mm ² is the sum of the areas of all the voids.

At this time, the voids are voids formed at the interface between the polymer and the inorganic filler, and the formation of the voids greatly affects the mechanical properties and electrical properties (for example, dielectric strength) of the film. That is, if the above B / A is larger than 0.4, the mechanical properties are deteriorated, the dielectric breakdown voltage is lowered, and the material is not suitable for practical use. Further preferred B / A is 0.2 or less.

The film-like material of the present invention varies depending on the application, but has a thickness of 0.1.
~ 30μ, more preferably 0.5-10μ.

The film-like material of the present invention may be a simple substance (film) or a substance obtained by coating on a support.
In this case, the heat shrinkage at 250 ° C. in at least one direction is preferably 5% or less, more preferably 2% or less, and the strength and elongation are preferably 5 kg / mm ² or more and 5% or more in at least one direction. , More preferably 8 kg / mm ² or more, and 10% or more. Further, the moisture absorption of the film is preferably 5% or less,
It is more preferably at most 4%. If it is more than 5%, the fluctuation of the dielectric constant due to the humidity increases, which may cause a practical problem.

Further, it is desirable that the dielectric constant of the film of the present invention is 4 or more, preferably 8 or more. The breakdown voltage (BD
V) is desirably 0.1 kV or more at a film thickness of 10 μm.

Next, a method for producing the high dielectric constant film material of the present invention will be described.

In order to achieve the present invention, the above inorganic filler, a coupling agent, a dispersant, a surfactant, or the like is present in a solution of aromatic polyamide, aromatic polyimide, or polyamic acid (polyimide precursor). This solution is formed by forming a film.

First, in the case of an aromatic polyamide, from an acid chloride and a diamine, in an aprotic organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide, a solution polymerization or an aqueous medium is used. It is synthesized by interfacial polymerization or the like. When acid chloride and diamine are used as monomers in a polymer solution, hydrogen chloride is produced as a by-product.To neutralize this, an inorganic neutralizer such as calcium hydroxide or an organic neutralizer such as ethylene oxide is used. Add the agent.

The reaction between the isocyanate and the carboxylic acid is performed in an aprotic organic polar solvent in the presence of a catalyst. These polymer solutions may be directly used as a stock solution for forming a film, or the polymer may be isolated once and then redissolved in the above solvent to prepare a stock solution. In some cases, an inorganic salt such as calcium chloride or magnesium chloride is added as a dissolution aid to the film forming stock solution. The polymer concentration in the film forming stock solution is preferably about 2 to 40% by weight.

On the other hand, a solution of aromatic polyimide or polyamic acid is obtained as follows. That is, polyamic acid is N-
It can be prepared by reacting tetracarboxylic dianhydride with an aromatic diamine in an aprotic organic polar solvent such as methylpyrrolidone, dimethylacetamide and dimethylformamide. The aromatic polyimide can be prepared by heating a solution containing the above-mentioned polyamic acid or adding an imidizing agent such as pyridine to obtain a polyimide powder, which is dissolved in a solvent again. The polymer concentration in the film forming solution is preferably about 5 to 40% by weight.

The kneading of the inorganic filler and the polymer includes, but is not limited to, the following methods.

(1) The inorganic filler is dispersed in a solvent in which the polymer is soluble and added to the polymer solution, or a previously isolated polymer is added to the filler dispersion.

(2) The polymerization is performed after the filler is dispersed in the polymerization solvent before the polymerization.

(3) Add the inorganic filler to the polymer solution as a powder.

At this time, trace additives such as a surfactant, a coupling agent, and a dispersant are added in order to improve the affinity between the inorganic filler and the polymer and suppress generation of voids. Here, the surfactant and dispersant include, for example, anionic surfactants such as carboxylate and sulfonate, cationic surfactants such as secondary amine salt, and amphoteric surfactants such as amino acid type and betaine type. And nonionic surfactants such as polyethylene glycol type, copolymerization type of ethylene glycol and propylene, and polyhydric alcohol type. Examples of the coupling agent include titanate, aluminum, silane, and zirconia.

These addition methods include, but are not limited to, the following methods.

(1) A method of directly treating an inorganic filler with a sprayer or the like.

(2) A method in which the inorganic filler is dispersed in a solvent in which the polymer is soluble in advance.

(3) A method of adding to a mixed solution of an inorganic filler and a polymer.

The addition amount depends on the type and specific surface area of the selected inorganic filler or the type of the additive, but is preferably 0.5 to 20% by weight based on the inorganic filler. If the amount is less than 0.5% by weight, the effect is not exhibited. If the amount is more than 20% by weight, mechanical and electrical properties are poor.

In order to obtain the film-like material of the present invention, there are a general film-forming method for obtaining a film-like material alone (hereinafter referred to as a film) and a method of applying a mixture of a polymer and an inorganic filler on a support.

The ordinary film forming method referred to herein is a so-called solution film forming method, which includes a dry-wet method, a dry method, a wet method, and the like, and the dry-wet method and the dry method are preferable for obtaining a film having a good surface property.

It is preferable to adjust the polymer concentration and temperature of the stock solution so that the viscosity at the time of casting is 100 to 10,000 poise. Here, the viscosity refers to a value measured with a rotary B-type viscometer under the same conditions (concentration and temperature) as at the time of casting.

Casting is performed on a support such as a metal drum or an endless metal belt, where the drying or imidization reaction is promoted until the film is self-supporting. At this time, it is necessary to adjust so that the solvent does not suddenly scatter and cause surface roughness, and is generally room temperature to 300 ° C, preferably 50 to 250 ° C.
It takes place within 60 minutes.

The film which has become self-holding is peeled from the support and introduced into a wet bath when a dry-wet process is employed. This bath is generally composed of an aqueous medium, and may contain an organic solvent, an inorganic salt or the like in addition to water. In the bath, the remaining solvent, inorganic salt and imidizing agent in the film are extracted.

Further, stretching or relaxation is performed in the longitudinal direction of the film. The film exiting the bath is then dried, stretched, relaxed and heat treated. These treatments are generally performed at 100 to 500 ° C.

In the case of the dry method, the self-holding film is generally separated from the support by at least 3 vol.
Drying, stretching relaxation, and heat treatment are performed until the amount becomes less than the weight percent. These treatments are generally performed at 150 ° C to 500 ° C.

As described above, in any of the film forming methods of the dry-wet method and the dry method, stretching or relaxation is performed at an area magnification of preferably 0.8 to 5.0 times, more preferably 1.1 to 3.0 times. The area ratio refers to the product of the stretching ratio in the film longitudinal direction (MD direction) and the stretching ratio in the width direction (TD direction). If the area magnification is smaller than 0.8, deterioration in film physical properties and deterioration in flatness are seen,
On the other hand, when the ratio exceeds 5.0, the inorganic filler is oriented in the plane direction in the film, or the distance between the fillers increases, so that high dielectric property is not exhibited.

Known methods for applying the mixture of the polymer and the inorganic filler on the support include, but are not limited to, a gravure coater or a reverse roll coater, a rod coater or an air doctor coater. As the support, a film of polyester, polycarbonate, polypropylene, polyphenylene sulphite, aromatic polyamide or the like, a metal layer provided on the film, or a single metal foil such as an aluminum foil can be used, but is not limited thereto. Not something.

 Next, a method for manufacturing a capacitor will be described.

In the case where a single film is used as the film without the support, a metal thin film is formed on the film by a method such as vacuum deposition, plating, sputtering, or ion plating to form a capacitor element. Get. Examples of the metal at this time include aluminum, zinc, nickel, and nickel-chromium alloy. Of these, aluminum is preferred in terms of vapor deposition properties and characteristics.

In the case of a film-like material obtained by coating on a support, for example, a method in which the support is metallized in the same manner as described above and then a mixture is applied, or a method in which the mixture is metallized in the same manner as above after coating, or a support. Then, a metallized film to be a capacitor element is obtained by a method using a metal foil.

Next, the film metallized as described above is wound or laminated to obtain the capacitor of the present invention. For example, if one side of the film is metallized, two layers are rolled or laminated, or if both sides are metalized, the layer is rolled or laminated with a non-metallized film to form a capacitor element. To make a capacitor.

[Effects of the Invention] The film-like product obtained in the present invention is one in which the affinity between the polymer and the inorganic filler is improved by adding a surfactant, a dispersant or a coupling agent to suppress the generation of voids. Even if a large amount of an inorganic filler is added to increase the dielectric constant, the material still has excellent heat resistance, mechanical strength such as strength and elongation, and good dielectric breakdown voltage. Therefore, the range of use is wide, including dielectrics for capacitors, dielectrics for variable capacitors, transformer insulators, insulators for various motors, coil insulators, bases for flexible printed circuit boards, and the like.

[Evaluation method of physical properties] (1) Mechanical properties (strength, elongation) Test width 1 in Tensilon type tensile tester according to ASTM-D-882
Set to 0mm, test length 50mm, pulling speed 300
Measure the strength and elongation when the film is broken by pulling at mm / min. The atmosphere is 25 ° C. and 55% RH.

(2) Dielectric constant and dielectric loss tangent (loss) According to ASTM D-150-68.

(3) Dielectric breakdown voltage (BDV) Place electrodes on the top and bottom of the film and apply the voltage while increasing the voltage at a rate of 100 V / sec. The dielectric breakdown voltage (BDV) was used.

(4) Heat resistance (thermal shrinkage ratio) Cut out the film so as to have a test width of 10 mm and a test length of 200 mm, apply a load equivalent to 1 kg / mm ² , heat it in an oven at 250 ° C for 10 minutes, and then test pieces. Was taken out, allowed to cool, and calculated by the following equation. + Means elongation and-means shrinkage.

(Heat shrinkage)% = (length after heating−test length) / test length × 100 (5) Measurement of void area ratio (B / A) Cross section of film-like material taken by electron microscope or optical microscope The image is sent to an image processing apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.], and the void portion is binarized to determine the area of each void.

This measurement repeated 500 times at different sites and by dividing the sum Bmm ² of area of the measured voids entire measurement area Amm ² calculates an area ratio of voids.

(6) Average particle size of particles Particle images taken with an electron microscope or optical microscope are processed by an image processor [IBAS2000, Carl Zeiss Co., Ltd.]
And a particle equivalent is determined from the area of each particle obtained by binarizing the particle portion, and the average diameter of the particle is determined. This measurement was repeated 500 times at different locations, and the average value of the average diameter of the measured particles was defined as the average particle diameter.

[Examples] Next, examples will be shown in order to explain the present invention more specifically, but the present invention is not limited thereto.

Example 1 Barium titanate having an average particle diameter of 1.0 μm was dispersed in NMP (N-methylpyrrolidone) in which 5% by weight of a surfactant, Solsperse # 20000 manufactured by ICI, was dissolved with respect to barium titanate. Of polymers synthesized from -chloro-p-phenylenediamine and 2-chloroterephthalic chloride
Barium titanate was added to the NMP solution at 30% by volume with respect to the polymer to obtain a 3000 poise solution (Table 1).
reference). This was cast on a glass plate, dried at 150 ° C. for 3 minutes, then peeled from the glass, immersed in running water for 10 minutes, and further subjected to a heat treatment at 300 ° C. for 2 minutes under tension. This is referred to as a film-like material 1. As shown in Table 2, the thickness of the film-like material 1 was 10 μm, the void area ratio was 0.30, and the heat resistance, mechanical properties, and electrical properties were excellent.

Example 2 Barium titanate having an average particle size of 0.1 μm was dispersed in NMP to which 3% by weight of barium titanate of a titanate-based coupling agent Prenact KR-TTS manufactured by Ajinomoto Co., Inc. was added. Of polymers synthesized from 4,4'-diaminodiphenylmethane and 2-chloroterephthalic acid chloride
Barium titanate was added to the NMP solution at 25% by volume with respect to the polymer to obtain a 3000 poise solution (Table 1).
reference). 3 μm thick film 2 in the same manner as in Example 1
Was created. As shown in Table 2, the void area ratio 0.11
And heat resistance, mechanical properties, and electrical properties were excellent.

Example 3 Titanium oxide having an average particle size of 0.5 μm was added to an aluminum-based coupling agent AL manufactured by Ajinomoto Co., Inc. at 3% by weight based on titanium oxide
-M added to DMAc (N, N-dimethylacetamide), and this was dispersed in a DMAc solution of polyamic acid synthesized from 4,4'-diaminophenyl ether and pyromellitic anhydride. To a volume of 40% by volume to give a 3000 poise solution (see Table 1). This solution was cast on a glass plate, dried at 160 ° C. for 3 minutes, then peeled from the glass, and then heat-treated under tension at 400 ° C. for 2 minutes to obtain a polyimide film. This is referred to as a film 3. As shown in Table 2, this film 3 had a void area ratio of 0.20
And heat resistance, mechanical properties, and electrical properties were excellent.

Comparative Example 1 A film-like substance 4 was obtained in the same manner as in Example 1 except that no additive (Solsperse # 20000) was added (see Table 1). The void area ratio of this film was 0.50, which was very poor in mechanical and electrical characteristics.

Comparative Example 2 A film 5 was obtained in the same manner as in Example 3 except that the additive (AL-M) was not added (see Table 1). The void area ratio of this film was 0.45, and the mechanical and electrical characteristics were very poor.

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Claims (2)

(57) [Claims] 1. A film comprising at least one polymer selected from aromatic polyamide and aromatic polyimide and an inorganic filler having a high dielectric constant in an amount of 5 to 90% by volume of the polymer. The void area ratio in the cross section of the object is 0.4
A high dielectric constant film-like material characterized by the following. 2. A capacitor comprising the high dielectric constant film according to (1).