JP2006290979A - Polypropylene film for capacitor, metallized polypropylene film for capacitor, and capacitor made of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene film for a capacitor which is excellent in handling property when manufacturing a capacitor element, is excellent in withstand voltage characteristics, and is particularly appropriate for use of a small size with a large capacity. <P>SOLUTION: The polypropylene film for a capacitor comprises a single polypropylene resin layer wherein the difference of a surface gloss of one side from that of another side is 3-20%, and Δd (a thickness measured by a micrometer method minus a thickness measured by a mass method) of the film is 0.05-0.25 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polypropylene film used as a dielectric of a capacitor. More specifically, the present invention relates to a polypropylene film, a metallized polypropylene film suitable for a capacitor used for smoothing a switching power supply, a DC-DC converter, an inverter, and the like, and It relates to a capacitor comprising the same.

  Polypropylene film has a high dielectric breakdown voltage and a low dielectric loss among plastic films, and is therefore excellent as a dielectric for capacitors, and is particularly preferably used as a high voltage capacitor and an AC capacitor. In recent years, there has been a high demand for miniaturization and high capacity of capacitors, and there has been an increasing demand for thinner films. However, as the film becomes thinner, the rigidity of the film decreases and wrinkles are likely to occur during processing. As a result, it has become necessary to improve the slip characteristics of the film.

  In order to meet such demands, the film surface needs to be roughened. As a result, when the surface roughness increases, the film film pressure becomes substantially thin at the valley portion of the surface roughness, so that dielectric breakdown occurs. It has the problem of being lowered.

In order to solve these problems, it is considered as a countermeasure to control the surface roughness of the two front and back surfaces of the polypropylene film as one countermeasure. Conventionally, two types of resins having different compositions and characteristics are used. A method of obtaining polypropylene films having different surface roughness by laminating and stretching in the melt extrusion (Patent Document 1), laminating resin layers to which particles or the like are added, and different surface roughness A method for obtaining a polypropylene film having a thickness (Patent Document 2) has also been proposed.
Japanese Patent Laid-Open No. 9-324056 However, when a multilayer structure using different resin compositions is used, the influence of thickness unevenness of each layer appears, and in particular, if a thin film of 5 μm or less is to be obtained, high-precision control is achieved. Is required. Further, in any case, it is difficult to use the collected resin such as the edge portion of the film formed in the manufacturing process or the non-standard product, resulting in a problem that the manufacturing cost increases.

  The present invention provides a polypropylene film for a capacitor which is composed of a single polypropylene resin layer and has different surface roughnesses on the front and back surfaces of the film, and which is excellent in processability and insulation characteristics.

In order to solve the above problems, the present invention
(1) A film made of a single polypropylene resin, wherein the difference between the surface gloss on one side and the surface gloss on the other side is 3 to 20%, and Δd of the film (thickness by micrometer method− A polypropylene film for capacitors having a thickness (by mass method) of 0.05 to 0.25 μm.
(2) The polypropylene film for capacitors as described in (1), wherein the polypropylene resin has a melting point of 164 to 168 ° C.
(3) The polypropylene film for capacitors as described in (1) or (2), wherein the micrometer thickness is 2.0 to 5.0 μm.
(4) A metallized polypropylene film for a capacitor, wherein metal is deposited on one or both sides of the polypropylene film for a capacitor according to any one of (1) to (3).
(5) The metallized polypropylene film for a capacitor according to (4), wherein metal deposition is performed in a pattern, and at least a part of the margin of the deposition pattern is not parallel to the longitudinal direction.
(6) The metallized polypropylene film for capacitors according to (5), wherein a vapor deposition pattern is applied to a surface having a low surface gloss.
(7) A capacitor comprising the metallized polypropylene film according to any one of (4) to (6).
This is a proposal.

  The present invention is made of a single polypropylene resin, and by making the surface shapes of the front and back surfaces of the film different in roughness, the slipperiness between films can be ensured only by the surface roughness of one surface, and the dielectric breakdown voltage is improved. In addition, since the film is composed of a single resin, it is excellent in uniformity as compared with the case where a difference in roughness between the front and back surfaces of the film is provided using a multilayer structure composed of different resins.

  Hereinafter, the present invention will be described in detail together with preferred embodiments.

  The film of the present invention needs to consist of a single resin of polypropylene resin. Being made of a single resin means that the film is formed without laminating a plurality of different resins, and it is possible to laminate the same resin. However, it is more preferable to consist of a single layer of a single resin.

  If the film has a multi-layer structure made of different resins, the thickness variation of each layer may cause non-uniformity in film characteristics and the dielectric breakdown voltage may be reduced. In particular, when the film thickness is 5 μm or less, it is required to control the thickness of each layer with high accuracy, and as a result, the cost may increase. Furthermore, it is difficult to recycle the edge portions of the film formation and nonstandard resin, which leads to an increase in cost, and the burden on the global environment increases.

  Whether or not the film configuration is a multilayer configuration is exemplified by a method of confirming the boundary line in the film from stained spots when the film is dyed with a staining agent such as osmic acid using an ultrathin section.

  Next, the difference between the surface gloss on one side and the surface gloss on the other side of the film of the present invention means the absolute value of the difference between the surface gloss values, and the difference is 3 to 20%. Is required, preferably 3 to 15%, more preferably 5 to 15%. Furthermore, in the case of a thin film of 4 μm or less, 3 to 10% is preferable. When the surface gloss difference is too small, it becomes difficult to achieve both slipperiness, that is, wrinkle suppression during processing and withstand voltage. On the other hand, if the gloss difference is too large, the curling of the film increases and problems such as film conveyance wrinkles occur.

  In addition, Δd (micrometer method thickness−mass method thickness) of the film of the present invention needs to be 0.05 to 0.25 μm. Preferably it is 0.05-0.20 micrometers. If it does in this way, the slip property between films will become favorable and the handling property of a film will improve, and what was excellent in the safety | security as a capacitor | condenser element and long-term reliability will be obtained.

  Although it does not restrict | limit especially as a polypropylene resin which comprises the film of this invention, In order to exhibit the characteristic outstanding as a dielectric film for capacitors, it is preferable not to contain an impurity as much as possible. That is, it is preferable not to add organic and / or inorganic antiblocking agents, slipping agents and the like. Further, it is preferable that the amount of the organic acid metal salt such as calcium stearate is small, and in the case of calcium stearate, the amount is preferably 100 ppm or less. From the same viewpoint, the total ash content is preferably 100 ppm or less, more preferably 10 to 50 ppm.

  Moreover, the heat resistance of the film is often required, and the melting point is preferably 164 to 168 ° C. from this viewpoint. If the melting point is too low, the thermal dimensional change in a high temperature region of 120 ° C. or higher becomes large, and the withstand voltage characteristic at high temperature is lowered. On the other hand, if the melting point is too high, the stretching tends to become unstable, and the thickness unevenness may increase, or the breakdown voltage may decrease due to an increase in internal voids.

  Moreover, in this invention, it is preferable to add stabilizers, such as antioxidant, in order to improve the oxidation-resistant deterioration property of a film, and as content, it is 500-10000 ppm, More preferably, it is 1000-6000 ppm. Examples of such antioxidants include hindered phenols, phosphites, and lactone compounds, which can be appropriately selected according to the purpose.

  The absolute value of the surface gloss of the film of the present invention is preferably in the range of 110 to 150% on any surface from the viewpoint of withstand voltage.

  The thickness of the film of the present invention is preferably 2.0 to 5.0 μm in terms of the micrometer thickness because the effect of different surface roughness becomes effective, more preferably 2.5 to 4.0 μm, still more preferably. 2.5 to 3.5 μm.

  The electrode in the case of using the film of the present invention for a capacitor is not particularly limited. For example, even if it is a metal foil or a paper or plastic film metallized on both sides, one side of the polypropylene film of the present invention or Although both sides may be directly metallized, it is particularly preferable to directly metallize the film for a capacitor application where a reduction in size and weight is desired. At this time, the type of metal used includes, but is not particularly limited to, simple substances such as zinc, tin, silver, chromium, aluminum, copper, nickel, and a mixture or alloy of plural kinds.

  Moreover, examples of the method for directly metallizing the film include a vacuum deposition method and a sputtering method, and are not particularly limited, but the vacuum deposition method is more preferable from the viewpoint of productivity and economy. In general, the crucible method, the boat method, and the like are exemplified as the vacuum deposition method, but the method is not particularly limited and may be appropriately selected. The margin pattern in the case of metallization by vapor deposition is not particularly limited, but the length direction as illustrated in FIGS. 1 and 2 is applied for the purpose of improving the security of the capacitor as compared with the normal pattern. A pattern including a margin that is not parallel to is preferable. Further, when a pattern including a margin that is not parallel to the longitudinal direction as illustrated in FIGS. 1 and 2 is applied to a low-gloss surface, the safety is improved, and when applied to a high-gloss surface, Since the maintenance of the capacitance over time is increased, the surface to be vapor-deposited can be selected as appropriate according to the purpose, and it is possible to prevent capacitors from being destroyed or short-circuited. It is preferable to apply.

  Further, the configuration method of those margins is not particularly limited, and for example, a tape method or an oil method may be used.

  Further, the structure and form of the capacitor made of the film of the present invention are not particularly limited. For example, a dry type, a liquid impregnation type, a round type or a flat press type may be used. It is particularly suitable for a flat capacitor that undergoes a pressing process.

  The film of the present invention is suitable for a small and high-capacity capacitor, and is suitable for a capacitor constituted by a capacitor element having a capacitance of 5 μF or more, more preferably 10 μF or more, and particularly preferably 50 μF or more. is there.

  Next, the method for producing the film of the present invention will be described, but it is not particularly limited.

  A polypropylene resin is melt-extruded from an extruder, formed into a sheet form from a T-die, and cooled and solidified on a cooling roll.

  At this time, the degree of adhesion of the sheet to the cooling roll is increased, or a plurality of cooling rolls are arranged in the longitudinal direction, and the temperature of each cooling roll is adjusted to provide a temperature difference between the front and back sides to be cooled and solidified. When this temperature difference becomes small, the target gloss difference cannot be obtained. As a method of increasing the degree of adhesion of the sheet to the cooling roll, the sheet is brought into close contact by sucking and removing the accompanying airflow from the surface direction where the sheet and the cooling roll contact, or from the opposite direction of the surface where the sheet and the cooling roll contact This can be achieved by using a plurality of nozzles and blowing out air from the nozzles to crimp the sheets, or by combining them. In general, the higher the cooling roll temperature is, the higher the surface roughness is. Therefore, in order to obtain a desired Δd, the cooling roll temperature may be appropriately selected, but 70 to 95 ° C. is preferable.

  Next, the film is stretched 3 to 7 times in the length direction with a stretching roll at 135 to 155 ° C., subsequently stretched 7 to 12 times in the width direction at 155 to 170 ° C., and further subjected to heat treatment at 145 to 165 ° C. . The polypropylene film thus obtained is subjected to a corona discharge treatment on at least one side and then wound up with a winder.

Next, measurement methods and evaluation methods used in the examples of the present invention will be described.
(1) Surface gloss According to JIS Z-8741. However, the angle was 60 degrees.
The measurement was repeated 7 times, and the average of the remaining 5 points excluding the maximum and minimum values was defined as the surface gloss.
(2) Micrometer method thickness, weight method thickness, Δd
A micrometer thickness (hereinafter referred to as MMV) was measured according to 7.4.1.1 of JIS C-2330 (2001 edition).
Subsequently, after measuring the mass method thickness (hereinafter referred to as WMV) according to 7.4.1.2 of JIS C-2330 (2001 edition), it was obtained by the following formula.
Δd (μm) = MMV (μm) −WMV (μm)
(3) Melting point (° C)
The measurement was performed under the following conditions using a DSC-7 differential scanning calorimeter manufactured by PerkinElmer.
Sample preparation:
Weigh 10 mg of sample into an aluminum pan for measurement, and sandwich the aluminum pan with a crimper attached to the device.
Measurement condition:
1st run: The temperature is raised to 280 ° C. at a rate of 10 ° C./min and held for 5 minutes. Thereafter, the temperature is lowered to 125 ° C. at a rate of 50 ° C./min and held for 60 minutes, and then lowered to 25 ° C. at the same rate and held for 10 minutes.
2nd run: Immediately after the first run, the temperature is increased to 280 ° C. at a rate of 10 ° C./min.
The melting peak value at the 2nd run is read as the melting point. When there are a plurality of melting peak values, the melting peak having the largest peak area is adopted.
The above measurement was repeated 5 times, and the average value of the remaining 3 points excluding 2 points of the maximum value and the minimum value was taken as the melting point.
(4) Dielectric breakdown voltage (BDV)
According to JIS C2330 (2001 edition) 7.4.11.2 B method (plate electrode method).
In the measurement, a value obtained by dividing the dielectric breakdown voltage by MMV was taken as the dielectric breakdown voltage. When the MMV thickness is 3.5 μm or less, 450 V / μm or more was regarded as acceptable.
(5) Wrinkle generation rate On the films obtained in Examples and Comparative Examples described later, aluminum was vapor-deposited so as to have a membrane resistance of 10 Ω / sq with a vacuum vapor deposition machine manufactured by ULVAC, and the film longitudinal direction was taken as the length direction. It was slit to a width of 50 mm and a length of 20000 m, and 24 (12 pairs) vapor deposition reels were collected. In order to provide a security function, the margin pattern is a T-shaped margin of the pattern shown in FIG. 2, the width of the margin part in the longitudinal direction is 0.7 mm, and a margin of 0.4 mm is provided in the width direction at intervals of 16 mm. . Next, winding was performed in the same manner as in a normal capacitor forming process, 100 capacitor elements having a capacity of 20 μF (± 1 μF) were formed, and the wrinkle generation rate was examined. The main winding conditions at this time are as follows.
Winder: KAW-4L manufactured by Minato Seisakusho
Winding speed: 2000rpm
Tension: 600g
In the present invention, one having a wrinkle generation rate of 5% or less was regarded as acceptable for 100 capacitor elements produced.
(6) Capacitor evaluation Ten capacitors were extracted from the capacitor element normally obtained in the above (5), heat-treated at 120 ° C. for 16 hours in a vacuum, and then metallized and lead terminals were attached. A capacitor element having a capacitance of 20 μF (± 1 μF) was produced by covering this element with an epoxy resin. Of these, five capacitor elements were used, and a so-called life test was conducted in which a voltage of 700 VDC was continuously applied in an oven at 100 ° C., and the capacity (μF) after 100 hours with respect to the initial capacity (μF) for each capacitor. ) Was calculated by the following equation, and the average value of five capacitor elements was defined as the capacitance change rate (%). The capacity change rate at this time was within ± 3%.
Capacity change rate = ((capacity after 100 hours−initial capacity) / initial capacity) × 100
In addition, using another five capacitor elements, a voltage of 600 VDC is applied for 10 minutes at room temperature, and then the applied voltage is increased to 700 VDC and then applied for 10 minutes, so that the applied voltage is increased by 100 VDC every 10 minutes. The so-called step-up test was performed up to 1200 VDC, and the presence or absence of destruction of the capacitor element was measured.

  Next, description will be made based on an embodiment of the present invention.

Example 1
Polypropylene resin “Borclean” HC300BF (melting point: 165 ° C.) manufactured by Borealis is melted by feeding it to an extruder at 250 ° C., extruded into a sheet form from a slit-shaped T die, and cooled and solidified with a cooling roll at a temperature of 90 ° C. did. At this time, using two slit-like nozzles (nozzle width is equivalent to the sheet width) from the opposite direction of the surface where the sheet and the cooling roll contact, air is blown out from the nozzles at a pressure of 0.02 MPa, The sheet was crimped. Subsequently, the film was stretched 4.7 times in the length direction at a temperature of 135 ° C., then held at both ends with clips and guided into a hot air oven, preheated in an atmosphere of 167 ° C., and then 9 times in the lateral direction at 158 ° C. The film was stretched and then heat treated at a temperature of 150 ° C. Then, after corona discharge treatment was applied to the surface with the lower surface gloss of the film so that the wetting tension was 44 mN / m and the film was wound with a winder, the film was further cut into a width of 630 mm and a length of 40000 m. The obtained film had an MMV of 3.12 μm and a Δd of 0.12 μm, the surface gloss of the surface subjected to the corona discharge treatment was 128%, the other surface gloss was 135%, and the difference in surface gloss was 7 %Met. The BDV of this film was 492 V / μm. In addition, the rate of wrinkle generation is 2% when a capacitor element is produced by performing vapor deposition on the lower surface gloss side of the film, and the capacitance change rate by the life test of the capacitor element is -0.9%. The number of destruction by the step-up test was 0.

(Example 2)
A polypropylene film was obtained under the same conditions as in Example 1 except that the sheet extruded from the T-die provided with slits was cooled and solidified with a 92 ° C. cooling roll. The obtained film had an MMV of 3.20 μm and a Δd of 0.20 μm, the surface gloss of the surface subjected to the corona discharge treatment was 124%, the other surface gloss was 131%, and the difference in surface gloss was 7 %Met. The BDV of this film was 463 V / μm. In addition, the rate of wrinkle generation is 0% when a capacitor element is formed by vapor deposition of the surface having the lower surface gloss of this film, and the rate of change in capacitance by the life test of the capacitor element is -2.4%. The number of destruction by the step-up test was 0.

(Example 3)
A polypropylene film was obtained under the same conditions as in Example 1 except that the sheet extruded from the T-die provided with slits was cooled and solidified with a 88 ° C. cooling roll. The obtained film had an MMV of 3.07 μm and Δd of 0.07 μm, the surface gloss of the surface subjected to the corona discharge treatment was 133%, the other surface gloss was 139%, and the difference in surface gloss was 6 %Met. The BDV of this film was 520 V / μm. In addition, the rate of wrinkle generation when a capacitor element is made by performing vapor deposition on the surface with the lower surface gloss of this film is 4%, and the capacitance change rate by the life test of the capacitor element is -0.3%. The number of destruction by the step-up test was 0.

Example 4
Example of the two nozzles shown in FIG. 3 except that the air pressure of the nozzle on the downstream side from the contact point between the sheet extruded from the slit-shaped T-die and the cooling roll is 0.01 MPa. A polypropylene film was obtained under the same conditions as in 1. The obtained film had an MMV of 3.12 μm, Δd of 0.12 μm, a surface gloss of the surface subjected to the corona discharge treatment was 129%, the other surface gloss was 133%, and the difference in surface gloss was 4%. The BDV of this film was 480 V / μm. In addition, the rate of wrinkle generation is 2% when a capacitor element is made by performing vapor deposition on the low gloss surface of the film, and the rate of change in capacitance by a life test of the capacitor element is -1.8%. The number of destruction by the step-up test was 0.

(Example 5)
A polypropylene film was obtained under the same conditions as in Example 1 except that the surface with higher surface gloss was subjected to corona discharge treatment so that the wetting tension was 44 mN / m. The obtained film had an MMV of 3.12 μm and a Δd of 0.12 μm, the surface gloss of the surface subjected to the corona discharge treatment was 135%, the other surface gloss was 128%, and the difference in surface gloss was 7 %Met. The BDV of this film was 492 V / μm. In addition, the rate of wrinkle generation is 2% when a capacitor element is formed by vapor deposition on the surface with the higher surface gloss of the film, and the rate of change in capacitance by the life test of the capacitor element is + 0.1%, step The number of destruction by the up test was two.

(Example 6)
A polypropylene film was obtained under the same conditions as in Example 1 except that “Borclean” HC318BF (melting point: 162 ° C.) manufactured by the polypropylene resin Borealis was used. The obtained film had an MMV of 3.10 μm and Δd of 0.10 μm. The surface gloss of the surface subjected to the corona discharge treatment was 132%, the other surface gloss was 138%, and the surface gloss difference was 6. %Met. The BDV of this film was 475 V / μm. In addition, the rate of wrinkle generation is 3% when a capacitor element is produced by performing vapor deposition on the surface having the lower surface gloss of the film, and the rate of change in capacitance by a life test of the capacitor element is -2.8%. The number of destruction by the step-up test was 0.

(Comparative Example 1)
A polypropylene film was obtained under the same conditions as in Example 1 except that the sheet extruded from the T-die provided with slits was cooled and solidified with a 96 ° C. cooling roll. The obtained film had an MMV of 3.28 μm, Δd of 0.28 μm, a surface gloss on the surface subjected to corona discharge treatment was 120%, the other surface gloss was 124%, and the difference in surface gloss was 4 %Met. The BDV of this film was 427 V / μm. In addition, the rate of wrinkle generation is 0% when a capacitor element is produced by performing vapor deposition on the lower surface gloss side of the film, and the capacitance change rate by the life test of the capacitor element is -4.3%. The number of destruction by the step-up test was 0.

(Comparative Example 2)
A polypropylene film was obtained under the same conditions as in Example 1 except that the sheet extruded from the T-die provided with slits was cooled and solidified with a 86 ° C. cooling roll. The obtained film had an MMV of 3.03 μm and Δd of 0.03 μm, the surface gloss of the surface subjected to corona discharge treatment was 138%, the other surface gloss was 143%, and the difference in surface gloss was 5 %Met. The BDV of this film was 543 V / μm. In addition, when the capacitor element is made by vapor deposition of the surface with the lower surface gloss of this film, the wrinkle generation rate is 8%, and the capacitance change rate by the life test of the capacitor element is + 0.4%, step. The number of destruction by the up test was four.

(Comparative Example 3)
Among the two nozzles shown in FIG. 3, the use of the nozzle on the downstream side is stopped from the contact point between the sheet and the cooling roll extruded from the T-die because of the slit, and the nozzle on the upstream side is set to 1 A polypropylene film was obtained under the same conditions as in Example 1 except that only one was used. The obtained film had an MMV of 3.14 μm, Δd of 0.14 μm, a surface gloss on the surface subjected to corona discharge treatment was 128%, the other surface gloss was 129%, and the difference in surface gloss was 1%. The BDV of this film was 440 V / μm. In addition, the rate of wrinkle generation is 1% when a capacitor element is produced by performing vapor deposition on the surface with the lower surface gloss of the film, and the rate of change in capacitance by the life test of the capacitor element is -3.9%. The number of destruction by the step-up test was 0.

  The results of Examples and Comparative Examples are shown in Table 1.

Capacitor polypropylene film with excellent workability and withstand voltage characteristics can be obtained, and a capacitor can be obtained. Particularly, it is effective for a thin film and is suitable for a capacitor requiring a small size and a large capacity.

The example of the vapor deposition pattern containing the margin which is not parallel to the length direction of a metallization film. Another example of a deposition pattern that includes a margin that is not parallel to the length direction of the metallized film. The relationship with the cooling roll of an Example and a comparative example, a slit-shaped nozzle, and a sheet | seat.

Explanation of symbols

1. 1. Metal deposition part Margin (non-deposited part)
3. T-die 4. 4. Cooling roll Slit nozzle (upstream side)
6). Slit nozzle (downstream)
7). Sheet

Claims (7)

A film made of a single polypropylene resin, the difference between the surface gloss on one side and the surface gloss on the other side is 3 to 20%, and Δd (micrometer method thickness-mass method thickness of the film) A) polypropylene film for capacitors, characterized in that it is 0.05 to 0.25 μm. The polypropylene film for a capacitor according to claim 1, wherein the melting point of the polypropylene resin is 164 to 168 ° C. The polypropylene film for capacitors according to claim 1 or 2, wherein the micrometer thickness is 2.0 to 5.0 µm. A metallized polypropylene film for a capacitor, wherein metal is deposited on one or both sides of the polypropylene film for a capacitor according to any one of claims 1 to 3. 5. The metallized polypropylene film for a capacitor according to claim 4, wherein metal deposition is performed in a pattern, and at least a part of the margin of the deposition pattern is not parallel to the longitudinal direction. 6. The metallized polypropylene film for capacitors according to claim 5, wherein a vapor deposition pattern is applied to a surface having a low surface gloss. A capacitor comprising the metallized polypropylene film according to claim 4.

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