Murata Manufacturing Co., Ltd.

Ichiro Nakaso

Shinichi Kobayashi

Tomomichi Ichikawa

Norihiro Yoshikawa

Yasunori Hioki

Tomoki Inakura

Ichiro Nakamura

A dielectric resin composition for a film capacitor is a mixture containing an organic material A and an organic material B. The organic material A includes at least two kinds of organic material components A, A, . . . having reactive groups (for example, OH, NCO) that cross-link each other. The organic material B does not have a reactive site capable of reacting with the organic material A and has a dielectric loss tan &#x3b4; of 0.3% or less at a temperature of 125&#xb0; C. The mixture has a glass transition temperature of 130&#xb0; C. or higher and preferably 280&#xb0; C. or lower.

Dielectric resin composition for film capacitor and film capacitor

To increase the heat resistance of a film capacitor, a dielectric resin composition is used as a material for a dielectric resin film used in a film capacitor, the dielectric resin composition being cured by mixing and crosslinking two or more organic materials having functional groups that react with each other to provide a cured article. At least one pair highly cohesive atomic groups which has a molecular cohesive energy equal to or higher than that of a methyl group and capable of cohering with each other due to the molecular cohesive energy is linked to the organic material. The highly cohesive atomic groups form a cohesive portion serving as pseudo-crosslinking.

To increase the heat resistance of a film capacitor, a cured article obtained by curing a mixed solution of a polyvinyl acetal having a hydroxyl group content of 10% to 38% by weight, the number of backbone carbon atoms of the polyvinyl acetal being 100 or more, and a polyisocyanate having an isocyanate content of 1% to 50% by weight is used as a dielectric resin films material arranged between first and second counter electrodes facing each other. At least the polyvinyl acetal is subjected to high-pressure homogenization in which a shearing force is applied such that a pressure applied to the polyvinyl acetal is 50 MPa or more when the material is passed through a path having a diameter of 0.125 mm and a length of 5 mm, so that the solubility is increased to allow a curing reaction to proceed uniformly. The cured article has a glass transition temperature of 130&#xb0; C. or higher and a breakdown voltage of 350 V/&#x3bc;m or more.

A resin composition constituting dielectric resin films of a film capacitor includes a first atom group including at least one functional group selected from among a methylene group, an aromatic ring and an ether group and having a relatively small molar polarizability, and a second atom group including at least one functional group selected from among a hydroxyl group, an amino group and a carbonyl group and having a relatively large molar polarizability. The resin composition satisfies the condition that a value calculated from the formula (sum of absorption band intensities of first atom group)/(sum of absorption band intensities of second atom group) is 1.0 or more. Herein, as absorption band intensities of the functional groups, peak intensities detected in specific wavenumber ranges are employed.

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Ichiro Nakaso