JPH08222477A - Polyethylene naphthalate film for capacitor - Google Patents

Abstract

PURPOSE: To enable a polyethylene naphthalate film used for a capacitor to be enhanced in dielectric breakdown strength and set stable in dielectric characteristics by a method wherein the film is set higher than a prescribed value in fracture strength in both a longitudinal and a lateral direction and to be in a prescribed range of thermal shrinkage rate at a prescribed temperature for a prescribed time along its lengthwise direction. CONSTITUTION: A film is above 25kg/mm<2> in fracture strength in both a longitudinal and a lateral direction and set 3 to 15% in lengthwise thermal shrinkage rate at a temperature of 200 deg.C for 10 minutes. The polyethylene naphthalate film is mainly composed of two units of ethylene and six units of naphthalate. If the film is below 25kg/mm<2> in fracture strength in both a longitudinal and a lateral direction, it deteriorates in dielectric breakdown strength. If the film is less than 3% in lengthwise thermal shrinkage rate at a temperature of 200 deg.C for 10 minutes, it deteriorates in dielectric breakdown strength when it is rolled up or laminated into a capacitor. If the film is more than 15% in lengthwise thermal shrinkage rate at a temperature of 200 deg.C for 10 minutes, it deteriorates also in dielectric breakdown strength the same as above. It is preferable that the film is set 4 to 10% in thermal shrinkage rate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyethylene naphthalate film for capacitors. For more details,
The present invention relates to a polyethylene naphthalate film for capacitors, which can be mounted on a chip and has excellent heat resistance and electrical characteristics.

[0002]

2. Description of the Related Art A film capacitor is generally manufactured by stacking a film such as a biaxially oriented polyethylene terephthalate film or a biaxially oriented polypropylene film on a metal foil film such as an aluminum foil and winding the film, or by winding the film on the surface of the film. It is manufactured by a method of forming a vapor-deposited film of aluminum, zinc or the like and then winding or laminating it.

Recently, with the demand for miniaturization of electric or electronic circuits, miniaturization and mounting of capacitors have been promoted, and improvement of heat resistance and thinning have been promoted. Further, in order to cope with thinning, it is necessary to improve the Young's modulus of the film in order to improve the processability, and a thin film having heat resistance and a high Young's modulus is required.

Films for capacitors which meet this purpose include, for example, Japanese Patent Laid-Open Nos. 62-60214, 62-136013, and 63-1405.
A biaxially oriented polyethylene naphthalate film is proposed in Japanese Patent Application Laid-open No. 12 and Japanese Patent Application Laid-Open No. 4-255208.

[0005]

The polyethylene naphthalate film has a relatively high glass transition temperature while having electrical characteristics close to those of a commonly used polyethylene terephthalate film. Is expected to expand. Further, since the Young's modulus is also high, studies have been made from this viewpoint as a film suitable for thinning. However, in order to use it as a film for capacitors, it is necessary to improve the dielectric breakdown voltage and stabilize the dielectric properties such as permittivity and dielectric loss, and especially for ultra-thin films such as chip capacitors to improve these properties. There is a strong demand for that. It has been proposed to control the film surface roughness for the purpose of solving these, or to specify particles to be added to form protrusions,
The current situation is that it is not always sufficient.

The present invention is intended to improve the dielectric breakdown voltage and stabilize the dielectric characteristics when the above polyethylene naphthalate film is used as a film for capacitors.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the inventors of the present invention have conducted extensive studies on improving the electrical characteristics of a polyethylene naphthalate film for capacitors, and as a result, have found that the film has a specific breaking strength and a specific heat shrinkage rate. Have been found to satisfy these characteristics to a high degree, and have completed the present invention.

That is, the gist of the present invention is that the breaking strength of the film is 25 kg / mm ² or more in both length and width.
The polyethylene naphthalate film for capacitors is characterized in that the heat shrinkage rate in the longitudinal direction of the film at 10 ° C. is 3 to 15%.

The polyethylene naphthalate film referred to in the present invention is a film whose main constituent unit is ethylene-2,6 naphthalate unit.
It may be modified with 0 mol% or less of a copolymerization component. Examples of the copolymerization component include dicarboxylic acids such as adipic acid, sebacic acid, terephthalic acid, isophthalic acid, 2,7 naphthalenedicarboxylic acid, 1,5 naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenylethanedicarboxylic acid and phenylindanedicarboxylic acid. Acid component,
Examples thereof include glycol components such as diethylene glycol, propylene glycol, tetraethylene glycol, cyclohexanedimethanol, xylylene glycol and polyethylene glycol.

When the amount of the copolymerization component is increased, the heat resistance originally possessed by the polyethylene 2,6 naphthalate film is lowered, so that it is preferably 10 mol% or less, more preferably 5 mol% or less. preferable.

Polyethylene naphthalate is generally a known method in which naphthalene-2,6-dicarboxylic acid or a functional derivative thereof such as dimethyl naphthalene-2,6-dicarboxylic acid and ethylene glycol are polycondensed in the presence of a catalyst under appropriate reaction conditions. Manufactured in.

At this time, for the purpose of imparting slipperiness to the obtained film and improving processability, for example, titanium oxide,
Inert particles such as calcium carbonate, silica, inorganic particles such as alumina and zirconia, silicon particles, organic particles such as crosslinked acrylic particles and crosslinked polystyrene particles are added, and calcium acetate and lithium acetate are used during polymer synthesis. However, a known method such as precipitation of particles in the synthesis process is preferably used. The average diameter and the amount of the particles used are selected from the viewpoint of the surface roughness of the film described later, but the average particle diameter is preferably 0.01 to 3 μm.
And a range of 0.05 to 1% by weight with respect to polyethylene 2,6 naphthalate is preferably used.
Further, coarse particles cause insulation defects and reduce the dielectric breakdown voltage, and therefore it is preferable not to include coarse particles of 5 μm or more. Therefore, inactive particles such as inorganic particles and organic particles are made into a slurry in a solvent such as ethylene glycol and dispersed by a medium agitation type dispersion device such as a sand grinder or an ultrasonic dispersion device, and then classified by a wet classification device or a filter. It is preferable to carry out filtration to remove coarse particles.

If the degree of polymerization of the polyethylene naphthalate used in the present invention is too low, the mechanical properties of the polyethylene naphthalate will deteriorate. Therefore, the intrinsic viscosity thereof is 0.4 or more, preferably 0.5 or more, and most preferably 0.6 or more. .

Further, the polymer may be subjected to heat treatment or solid phase polymerization under reduced pressure or in an inert gas atmosphere at a temperature below its melting point. By performing this treatment, the amount of oligomer can be reduced and the intrinsic viscosity can be increased, which is preferable as a film for capacitors.

The polyethylene naphthalate film for capacitors of the present invention has a breaking strength of 25 in both length and width.
and in kg / mm ² or more, it is necessary that the longitudinal direction of the film heat shrinkage rate of 200 ° C. 10 minutes is 3 to 15%.
If the breaking strength in the vertical and horizontal directions is smaller than 25 kg / mm ² , the dielectric breakdown voltage is lowered, which is not preferable. A preferred breaking strength is 30 kg / mm ² or more, more preferably 35 kg / m
m ² or more.

When the heat shrinkage ratio in the longitudinal direction of the film at 200 ° C. for 10 minutes is less than 3%, aluminum or the like is vapor-deposited and is not wound or laminated with a metallized film to form a capacitor or wound with an aluminum foil. When a foil wound capacitor is created and then pressed and heat treated to create a capacitor product, the breakdown voltage drops,
Not preferred. Also, when the heat shrinkage ratio in the longitudinal direction of the film at 200 ° C. for 10 minutes exceeds 15%, the dielectric breakdown voltage similarly lowers, which is not preferable. The preferred heat shrinkage rate is 4 to
It is 10%.

The polyethylene naphthalate film for capacitors of the present invention has a film surface roughness Ra of 0.0.
It is necessary that the number of protrusions is 1 to 1.0 μm, and the number of protrusions having a height of 0.1 μm or more is 10 ⁴ / mm ² or less.
When Ra is less than 0.01 μm, the film is too flat and the workability tends to deteriorate. On the other hand, when Ra is larger than 1.0 μm, the protrusions on the film are too large, and when a capacitor is formed, air is present between the films, the dielectric properties become unstable, and the dielectric breakdown voltage tends to decrease. Furthermore, the number of protrusions with a height of 0.1 μm or more is 10 ⁴ / mm ²
When it exceeds the above value, a capacitor is created by vapor deposition of aluminum or the like and winding or stacking without a metallized film, or a foil wound capacitor is created by winding with aluminum foil, and then pressed and heat-treated to create a capacitor product. In that case, the dielectric breakdown voltage decreases, which is not preferable.

The thickness of the film of the present invention is preferably 50 μm, more preferably 25 μm or less, and preferably 5 μm or less and more preferably 3 μm or less for chip capacitors.

Next, the method for obtaining the film of the present invention will be specifically described below, but the method is not limited thereto.

After the polyethylene naphthalate containing fine particles obtained by melt polymerization or solid phase polymerization is dried, 280 to 32
Extruded into a sheet from an extruder at a temperature in the range of 0 ° C.,
It is cooled to a temperature of ℃ or below to obtain a substantially amorphous sheet. In addition, it is preferable to filter with a filter at the time of melt extrusion, and it is preferable to use a multistage filter as needed. Further, it is preferable to apply the electrostatically applied casting method because it is brought into close contact with the casting drum when it is cooled and solidified.

First, the unstretched sheet material is formed in the longitudinal direction by 120
It is stretched at a temperature of ˜170 ° C. from 2.5 times to 6 times, preferably from 3 times to 5 times. The uniaxially stretched film is once cooled to a glass transition temperature or lower, or preheated to 120 to 170 ° C. without cooling, and then at a temperature of about the same in the width direction at a magnification of 2.5 times or more and 6 times or less. Stretch to obtain biaxial stretching. In this case, the film can be further stretched in the longitudinal direction and the width direction at a ratio of 1.1 times or more and 3 times or less. The temperature during stretching in the longitudinal direction is preferably 130 to 180 ° C, and the subsequent stretching in the width direction is preferably performed at 150 to 240 ° C. Then, the obtained biaxially oriented film is heat-set in the temperature range of 120 to 250 ° C., preferably 180 to 240 ° C. for 1 second to 1 hour. When the heat setting temperature is higher than 250 ° C, the breaking strength decreases and
If the temperature is lower than 20 ° C, the heat shrinkage in the longitudinal direction increases, which is not preferable.

Further, the obtained film is 20 in a roll state.
It is preferable to perform heat treatment in the temperature range of 120 to 120 ° C, preferably 40 to 100 ° C for 1 hour to 7 days.

In this manner, a polyethylene naphthalate film having a stable dielectric breakdown property and dielectric property can be obtained as compared with the hitherto known films, and a chip-like film having particularly excellent heat resistance can be obtained. It can be suitably used as a film for capacitors.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. The measured values of the physical properties of the films obtained in the examples are as follows.

(1) Breaking strength According to JIS-K-7127. Using an Instron type tensile tester, a sample having a sample length of 50 mm and a sample width of 10 mm was pulled at 20 ° C. and 65% RH until the film broke, and the stress at break was measured.

(2) Heat shrinkage rate Marked lines were put on the measurement sample at intervals of about 30 cm, and heat treatment was performed for 10 minutes in a heating oven controlled at 200 ° C. without tension to measure the sample length after the heat treatment. It was calculated by the following formula.

Thermal shrinkage = 100 × (length before heat treatment−length after heat treatment) / length before heat treatment (3) Center line average surface roughness (Ra: μm) Surface roughness manufactured by Kosaka Laboratory Ltd. It measured according to JIS-B-0601 using the measuring device (SE-3FK).

(4) The flat part of the film surface was measured by a scanning electron microscope "EMS-3200, manufactured by Elionix Co., Ltd." and a cross-section measuring device "PMS-1, manufactured by Elionix Co., Ltd." in which the number of surface protrusions was two. The height measurement value of the protrusion when scanned as 0 is sent to an image analyzer [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] to reconstruct the film surface protrusion image. Next, the projection portion is binarized in this surface image, the highest value in the distribution of individual projections is taken as the height of the projection, and this is calculated for each projection. This measurement was repeated 50 times in different places. The number of protrusions having a height of 0.1 μm or more measured here was measured. Scanning electron microscope magnification is usually 3000
The optimum magnification can be selected in the range of 2000 to 5000 times according to the size of the projections.

(4) Dielectric property It was measured by the measuring method of JIS-C-5102.

(5) Dielectric breakdown voltage It was measured using a DC voltage according to the measuring method of JIS-C-2318. The dielectric breakdown voltage was calculated as an average value of 50 measurement results.

Example 1 100 parts of dimethyl-2,6-naphthalate (parts by weight, unless otherwise specified, parts are parts by weight), 60 parts of ethylene glycol and 0.06 part of manganese acetate tetrahydrate were placed in a reactor, The temperature was gradually raised to 230 ° C. over about 4 hours. The methanol generated at this time was distilled off to complete the transesterification reaction. To this reaction product was added 0.04 part of trimethyl phosphate, 0.03 part of antimony trioxide and 0.2 part of spherical silica having an average particle size of 0.3 μm dispersed in 10 parts of ethylene glycol, and polymerization was carried out according to a conventional method. A chip having an intrinsic viscosity of 0.68 was obtained. The chips were vacuum-dried at 160 ° C. for 10 hours, melted at 300 ° C., extruded from a T die, and rapidly cooled by an electrostatic impression casting method to obtain an amorphous sheet. The obtained amorphous sheet is 135
The film was stretched 5.0 times in the longitudinal direction at 50 ° C., then 5.0 times in the width direction at 135 ° C., heat-set at 240 ° C. for 2 seconds, and then wound into a roll. The thickness of this film is 2.0 μm,
Film surface roughness (Ra) is 0.030μm, 0.1μ
The number of surface protrusions having a height of m or more was 3 × 10 ³ pieces / mm ² , the breaking strength in the longitudinal direction was 35 kg / mm ² , and the breaking strength in the width direction was 34 kg / mm ² . The shrinkage rate after heat treatment at 200 ° C. for 10 minutes was 8%.

Next, aluminum was vacuum-deposited in a strip shape with a width of 20 mm on one surface of the film (margin width: 3 mm), and cut and wound between the vapor deposition portion and the margin portion. The cut films are overlapped and wound so that the margin parts are on opposite sides, and pressed, heat treated,
The end face was sealed and the leads of each electrode were attached to produce a capacitor having a capacity of 0.1 μF. The dielectric loss tangent was 0.4%, the dielectric breakdown voltage was 590 V, and the minimum value of the 50 measurements was 400 V, indicating a good breakdown voltage.

Examples 2-5 A biaxially stretched film having a thickness of 1.5 μm was obtained in the same manner as in Example 1 except that the amount of particles added and the stretching conditions were changed. I made a condenser. The characteristics of the film, the dielectric constant of the capacitor and the dielectric breakdown voltage are shown in Table 1.

[0034]

[Table 1] Comparative Examples 1 to 4 In Example 1, the addition amount of particles, the stretching conditions, and the heat setting conditions were changed to prepare a 2.0 μm-thick film in which the breaking strength and surface characteristics of the film and the heat shrinkage ratio were changed,
The dielectric breakdown voltage and dielectric loss tangent of the capacitor were measured in the same manner as in Example 1. The results are shown in Table 2.

[0035]

[Table 2] As a result, when the breaking strength, the heat shrinkage ratio, and the surface characteristics were beyond the ranges of the present invention, the dielectric breakdown voltage and the dielectric characteristics were unstable, and the dispersion was large, and the capacitor was not good.

[0036]

INDUSTRIAL APPLICABILITY The polyethylene naphthalate film for capacitors of the present invention is excellent in heat resistance, and has stable dielectric breakdown voltage and dielectric properties, and thus a capacitor excellent in heat resistance, dielectric properties and electric properties can be obtained. In particular, it is suitable as a film for a chip capacitor which requires miniaturization and heat resistance.

Claims (3)

[Claims] 1. The breaking strength of the film is 25 kg in both length and width.
/ Mm ² or more, and a heat shrinkage ratio in the longitudinal direction of the film at 200 ° C. for 10 minutes is 3 to 15%, which is a polyethylene naphthalate film for capacitors. 2. The surface roughness of the film is 0.01 to 1.0 μm.
m, and the number of protrusions with a height of 0.1 μm or more is 10 <sup>4
2. The</sup> polyethylene naphthalate film for capacitors according to claim 1, wherein the number is not more than 1 piece / mm ² . 3. The polyethylene naphthalate film for capacitors according to claim 1, which is used in a chip-shaped film capacitor.