JP2015101677A - Dielectric film, and film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric film having excellent slidability, and a film capacitor obtained by using the dielectric film.SOLUTION: A dielectric film 1 contains an organic resin as a main component thereof and has concave parts 5, which are formed repeatedly in the planar direction, on the surface 3 thereof. When the cross section of the dielectric film 1 is viewed, a convex part 7 exists between the adjacent concave parts 5 and has a flat top part 7a and a curved plane 11 curved toward the bottom 9 side of the convex part 7. The film capacitor has a metallic film 21 on the surface of the dielectric film 1. The dielectric film 1 of the film capacitor is hardly stuck closely to another dielectric film 1 or another metallic film 21 even when the thickness of the dielectric film 1 is thin. Since the dielectric film 1 has high slidability, the dielectric film is used suitably in the wound type film capacitor.

Description

  The present invention relates to a dielectric film and a film capacitor.

  The film capacitor has, for example, a metal film formed by vapor deposition on the surface of a dielectric film obtained by filming a polypropylene resin as an electrode. In recent years, as with other electronic components, the demand for miniaturization has been increasing, and attempts have been made to make the dielectric film thinner. However, if the dielectric film is made thinner, The unevenness on the surface of the dielectric film is reduced and smoothed.

  In this case, for example, when a metal film is formed on the surface of the smoothed dielectric film and wound to form a so-called wound capacitor, the surface of the dielectric film on which the metal film is not formed, When the dielectric film and the metal film are integrally wound, the surface of the metal film that comes into contact with each other is easily adhered.

  When the dielectric film and the metal film are in close contact with each other, when the dielectric film and the metal film are subjected to thermal shock, cracks or tears occur in either of them due to the difference in the coefficient of thermal expansion between the two. This causes a problem of lowering.

  Fig.3 (a) is a perspective view which shows the conventional dielectric film typically, (b) is the sectional view on the AA line of (a). In the conventional dielectric film 101 shown in FIGS. 3A and 3B, concave portions 105 and convex portions 107 having a shape in which the convex portion 107 side gently curves toward the upper side (the top side) are periodically arranged. It has a configuration. Patent Documents 1 and 2 also disclose the same configuration, which can reduce the surface frictional resistance, so that the slipperiness of the dielectric film 101 can be improved.

  However, even in the conventional dielectric film 101 as disclosed in the above patent document, the dielectric film 101 is thinned, and the height difference (h) between the convex portion 107 and the concave portion 105 is reduced. In this case, since the area near the top of the convex portion 105 becomes large, the surface 103 of the dielectric film 101 is likely to be in close contact with other parts of itself and the metal film, and still difficult to slip. have.

JP 2009-141293 A JP 2013-207158 A

  The present invention has been made in view of the above problems, and an object thereof is to provide a dielectric film having good slipperiness and a film capacitor using the dielectric film.

  The dielectric film of the present invention is a dielectric film having an organic resin as a main component and having concave portions repeatedly provided on the surface in a plane direction. When the dielectric film is viewed in cross section, the concave portions are convex portions. The convex portion has a flat top portion and a curved surface that curves toward the bottom side of the convex portion.

  The film capacitor of the present invention has a metal film on the surface of the dielectric film.

  ADVANTAGE OF THE INVENTION According to this invention, a dielectric film with favorable slip property and a film capacitor using the same can be obtained.

(A) is a perspective view which shows typically one Embodiment of the dielectric film of this invention, (b) is the sectional view on the AA line of (a). (A) is sectional drawing which shows typically the structure which has an electrode layer on both surfaces of a dielectric film, (b) is an external appearance perspective view which shows one Embodiment of the film capacitor of this invention. (A) is a perspective view which shows the conventional dielectric film typically, (b) is the sectional view on the AA line of (a).

  The dielectric film 1 of the present embodiment has a configuration in which an organic resin is a main component and a concave portion 5 is repeatedly provided on the surface 3 in a planar direction. Further, when the dielectric film 1 is viewed in cross section, the convex portions 7 are formed between the concave portions 5, and the top portion 7a of the convex portions 7 is flat and curves toward the bottom portion 9 side of the convex portions 7. It has a curved surface 11.

  The convex portion 7 formed on the surface 3 of the dielectric film 1 has a shape in which the surface 3 of the top portion 7a is flat and has a curved surface 11 that curves toward the bottom portion 9 side. Even when 1 is thinned, the shape of the recess 5 tends to remain on the surface 3 of the dielectric film 1. For this reason, when the dielectric film 1 is wound together with the metal film, the area to be bonded becomes narrow due to the gap formed by the concave portion 5 formed on the surface 3 of the dielectric film 1 even if they are in close contact with each other. . As a result, the metal film in contact with the dielectric film 1 can be made difficult to adhere, and the slipperiness is high.

  That is, like the above-described conventional dielectric film 101 shown in FIGS. 3A and 3B, the convex portion 107 formed on the surface 103 is gently curved toward the upper side (the top side). If the surface 103 is curved, the area at the top of the convex portion 107 is larger than the flat surface because the surface 103 is curved. When the surface 103 of the dielectric film 101 has such a shape, when the dielectric film 101 is thinned, the height difference (h) between the convex portion 107 and the concave portion 105 becomes small, and at the same time, the convexity Since the curvature (radius) at the top of the portion 107 is increased, the area at the top of the convex portion 107 of the dielectric film 101 is further increased. For this reason, the dielectric film 101 becomes easy to adhere, and slipperiness becomes inferior.

  On the other hand, as shown in FIGS. 1A and 1B, the dielectric film 1 of this embodiment has a flat top portion 7a of the convex portion 7, and thus the surface 3 of the convex portion 7 is curved. The area of the convex portion 7 is narrower than that of the structure.

  Moreover, in the dielectric film 1 of this embodiment, since the convex part 7 has the structure which has the curved surface 11 which curves toward the bottom part 9 side, the dielectric film 1 is thinned and the concave part 5 of FIG. Even if the depth becomes shallow, a gap is likely to remain in the recess 5, and the contact area is difficult to expand. For this reason, the dielectric film 1 becomes difficult to adhere and the slipperiness is improved. The dielectric film 1 having such a structure is suitable for a thin dielectric film 1 having a thickness (average thickness) of 0.5 to 3 μm.

  Here, the organic resin as a main component means that the dielectric film 1 contains 70% by volume or more of an organic resin, and includes a high dielectric constant material such as ceramic particles in addition to the organic resin. May be.

  The state in which the concave portion 5 and the convex portion 7 are formed on the surface 3 of the dielectric film 1 is that when the surface roughness of the dielectric film 1 is measured, the convex portion 7 and the concave portion 5 (the top portion 7a of the convex portion 7). And the bottom 5a) of the recess 7 are those having a height difference of 50 nm or more.

  In the case of the dielectric film 1 having such a surface structure, the total area A of the recesses 5 when the dielectric film 1 is viewed in plan is the total area B of the top portion 7a in that the adhesion of the surface 3 can be further reduced. It is desirable that it is wider. Here, the total area A of the recesses 5 is the sum of the areas of the recesses 5 in a predetermined region that is a unit area of the dielectric film 1, while the total area B of the protrusions 7 is the same area. It means a region excluding the portion of the total area A of the recess 5.

  Moreover, in the dielectric film 1 of this embodiment, it is desirable that the surface connecting the top portions 7a of the convex portions 7 is substantially flush. In the case where the height positions of the convex portions 7 formed on the dielectric film 1 are different, the convex portions 7 are flattened after the flattening process performed after the metal film is formed on the surface 3 thereof. At the same time, the depth of the recess 7 becomes shallow, and the area of the surface 3 tends to increase. On the other hand, when the surface connecting the top portions 7a of the convex portions 7 is originally substantially flush, the deformation of the concave portions 5 and the convex portions 7 is small even after the flattening process. The area of the top portion 7a is maintained, and it is possible to suppress the adhesion of the dielectric film 1 from being increased in the processing step.

  Here, being substantially flush means that the height position of the surface 3 when the dielectric film 1 is placed on a flat surface such as a surface plate is 20 nm or less.

  The concave portion 5 and the convex portion 7 of the dielectric film 1 can be detected using, for example, an atomic force microscope (AFM).

  2A is a cross-sectional view schematically showing a structure having metal films on both surfaces of a dielectric film, and FIG. 2B is an external perspective view showing an embodiment of the film capacitor of the present invention. is there.

  The film capacitor of the present embodiment including the dielectric film 1 described above is constituted by a main body portion 23 having a basic structure in which a metal film 21 is provided on both surfaces of the dielectric film 1. The main body 23 is suitable for a wound type film capacitor in which the long dielectric film 1 and the metal film 21 are wound because the dielectric film 1 has high slipperiness.

  The film capacitor may further have a lead wire 25 as a terminal on the external electrode 24, but a structure without the lead wire 25 is desirable in terms of miniaturization of the film capacitor. Further, the main body 23, the external electrode 24, and a part of the lead wire 25 may be covered with the exterior member 26 in terms of insulation and environment resistance.

  Next, the dielectric film and film capacitor of the present embodiment can be obtained, for example, by a manufacturing method as described below. First, an organic resin that serves as a base material for the dielectric film 1 is prepared.

  As the organic resin, polyethylene terephthalate (PET), polypropylene (PP), polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), cycloolefin polymer (COP), and the like are suitable.

  The relative dielectric constant (ε) of these organic resins at room temperature (about 25 ° C.) is, for example, 3.3 for polyethylene terephthalate (PET), 2.3 for polypropylene (PP), and 3.0 for polyphenylene sulfide (PPS). The cycloolefin polymer (COP) is 2.2 to 3.0.

  The breakdown electric field strength (E) of these organic resins at room temperature (about 25 ° C.) is, for example, 310 (V / μm) for polyethylene terephthalate (PET), 380 (V / μm) for polypropylene (PP), polyphenylene The sulfide (PPS) is 210 (V / μm), and the cycloolefin polymer (COP) is 370 to 510 (V / μm).

  The raw material composition to be the metal oxide 5a is selected from tetra-i-propoxy titanium, tetra-n-butoxy titanium, tetra-n-butoxy zirconium, tri-i-propoxy aluminum, and tri-n-butoxy aluminum. At least one metal alkoxide compound can be applied.

  When forming the dielectric film 1, for example, a PET film is applied as a base material, and a molding method such as a solution casting method is applied to the surface to form an organic resin sheet, thereby forming the dielectric film. 1 can be obtained.

  As the slurry for the dielectric film 1, a resin slurry prepared by dissolving an organic resin in a solvent is used. At this time, the slurry is preferably adjusted to a solid content concentration at which Marangoni convection is generated in the drying process after coating. In this case, the solid concentration of the slurry is preferably in the range of 10 to 20% by mass. Thereby, while the top part 7a of the convex part 7 in the dielectric film 1 is flat, the dielectric film 1 which has the curved surface 11 which curves toward the bottom part 9 side of the convex part 7 can be obtained. The convex part 7 of the dielectric film 1 obtained by such a manufacturing method has a structure in which the width of the top part 7a is as thin as 50 nm or less, and the convex part 7 is the outline of the concave part 5. As a result, many concave portions 5 are formed in close contact with the surface 3 of the dielectric film 1, so that the concave portions 5 are likely to remain even when the thickness of the dielectric film 1 is reduced.

  Examples of the solvent used for film formation include methanol, isopropanol, n-butanol, ethylene glycol, ethylene glycol monopropyl ether, methyl ethyl ketone, methyl isobutyl ketone, xylene, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, dimethylacetamide, It is preferable to use an organic solvent containing cyclohexane, ethylcyclohexane, or a mixture of two or more selected from these.

  Next, the metal film 21 is formed by vapor-depositing a metal component such as Al (aluminum) on the surface of the dielectric film 1, and then the dielectric film 1 on which the metal film 21 is formed is wound to form a film capacitor. A main body 23 is obtained.

  Next, the external electrode 24 is formed on the end surface of the main body 23 where the metal film 21 is exposed. For the formation of the external electrode 24, for example, metal spraying, sputtering, plating, or the like is suitable. Here, the lead wire 25 may be formed on the external electrode 24. Next, the film capacitor of the present embodiment can be obtained by forming the exterior resin 26 on the surface of the main body 23 on which the external electrodes 24 (including the lead wires 25) are formed.

  A specific material was selected to produce a dielectric film, and the following evaluation was performed.

  First, a cycloolefin polymer (COP; molecular weight: Mw = 20000) was prepared as a resin.

  Next, this resin (COP) was dissolved in a solvent containing cyclohexane as a main component to prepare a slurry. The solid content concentration of the slurry at this time was in the range of 10 to 20% by mass, and Marangoni convection was observed when heated.

  Then, the dielectric film was produced by apply | coating the said slurry on a polyethylene terephthalate (PET) film with a coater on the conditions which made relative humidity 55% +/- 5%. The top of the convex portion was flat and had a curved surface that curved toward the bottom side of the convex portion (Sample 1).

  The produced dielectric film had an average thickness of 2.5 μm after solvent removal at 180 ° C.

  Next, an Al electrode layer having an average thickness of 75 nm was formed on both surfaces of the dielectric film by vacuum deposition.

  The average thickness of the dielectric film and the metal film was obtained from an average value obtained by measuring a region obtained by cutting out a part of the produced sample (dielectric film with metal film) and dividing it into 10 equal parts.

  The adhesion strength of the dielectric film was evaluated using a cross-cut method (JISK5600-5-6). Using a cutter, 6 cuts were made on the surface of the dielectric film at intervals of 2 mm, and 6 cuts that were changed perpendicularly by changing the 90 ° direction were further made into a lattice shape. A cellophane tape cut out to a length of 75 mm was attached to the cut portion of the metal film lattice and pressed firmly, and then the end of the tape was peeled off at an angle of about 60 °. The peeled state of the dielectric film was evaluated by the 0-5 scale evaluation method of JISK5600-5-6. The number of measurement samples was 10.

  The surface form of the film in the dielectric film of Sample 1 was confirmed by an atomic force microscope (AFM). The difference in height between the concave and convex portions was about 60 nm. Further, this dielectric film had a substantially flat surface connecting the convex portions. Further, the total area of the recesses when the dielectric film was viewed in plan was about 10% larger than the total area of the top. These measurements were performed in an area of 2 mm × 2 mm or less.

  In addition, a dielectric film was produced from a slurry in which the amount of solvent was reduced from the slurry used to produce the dielectric film of Sample 1 and the slurry viscosity was 1.5 times. In the dielectric film of Sample 2, the total area of the recesses when the dielectric film was viewed in plan was about 5% smaller than the total area of the top (Sample 2).

  As a comparative example, a dielectric film was prepared using a slurry having a solid content concentration of 25 to 35% by weight, and the same evaluation as described above was performed. The slurry prepared at this time did not show Marangoni convection even when heated, and the surface roughness of the produced dielectric film was 10 nm or less, and there were almost no concaves and convexes on the surface (Sample 3). ).

  Moreover, the dielectric film which shape | molded the slurry prepared in order to produce the dielectric film of a comparative example was made to contact the roll which has an unevenness | corrugation was also produced (sample 4).

The produced dielectric film was evaluated for adhesion strength. The dielectric film of sample 1 was in stage 5 in a five-step evaluation by the cross-cut method, but the dielectric film of sample 2 was in stage 4, both of which had low adhesion strength and good slipperiness. there were. On the other hand, the dielectric film of Sample 3 as a comparative example was in stage 1. In addition, the dielectric film of Sample 4 formed by contacting with a roll having irregularities was in stage 2, which had higher adhesion strength than Sample 1 and Sample 2, and was inferior in slipperiness.

1, 101... Dielectric film 3, 103 .. Surface 5, 105... Recess 5a. Bottom 7, 107... Convex 7a... (Convex) Top 9... (Convex) Bottom 11 ········ curved surface 23 ··································・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Exterior material

Claims (4)

  A dielectric film comprising organic resin as a main component and having concave portions repeatedly provided in a plane direction on the surface, and when the dielectric film is viewed in cross section, the concave portions are convex portions, and the convex portions Is a dielectric film characterized in that the top part is flat and has a curved surface that curves toward the bottom side of the convex part.   2. The dielectric film according to claim 1, wherein a total area of the recesses in a plan view is wider than a total area of the top part.   The dielectric film according to claim 1, wherein a surface connecting the tops is substantially flush. A film capacitor comprising a metal film on a surface of the dielectric film according to claim 1.