JPH10119127A - Biaxially oriented polypropylene film and condenser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance heat resistance and vapor deposition processability by specifying the isotacticity and isotactic pentad ratio of a biaxially oriented polypropylene film and also specifying the dielectric breakdown voltage per the sum of the heat shrinkage factors of the film in the machine and width directions thereof and the thickness thereof at specific temp. and the thickness of the film. SOLUTION: The isotacticity of a biaxially oriented polypropylene film is 98.5-99.5%. Herein, the isotacticity is defined by the ratio of the wt. of an insoluble component to the wt. of the film before extraction when the film is extracted with boiling n-heptane. The stereoregularity of the biaxially oriented polypropylene film is evaluated by the pentad ratio due to the absorption peak of a methyl group measured by 13C-NMR and the isotactic pentad ratio of the biaxially oriented polypropylene film exceeds 99%. Further, the sum of the heat shrinkage factors in the machine and width directions of the film at a time of heating at 120 deg.C for 15min is 1.5-3.5% and the DC dielectric breakdown strength of the film at 105 deg.C is 580-(200/d<0.5> ) (V/μm) and the thickness of the film is 2-20μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polypropylene film and a capacitor using the same, and more particularly to a biaxially oriented polypropylene film having excellent heat resistance and dielectric breakdown resistance, and a heat resistant film using the same as a dielectric. The present invention relates to a capacitor having excellent properties and dielectric breakdown resistance.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene films are widely used in packaging and capacitor applications due to their excellent optical properties such as transparency and gloss, as well as water vapor barrier properties and excellent electrical properties. .

[0003] This biaxially oriented polypropylene film is
Although it is one of the representative materials for the dielectric of film capacitors, its heat resistance is lower than that of polyester film, which is another typical material, so the maximum use temperature of the capacitor is limited to about 85 ° C. I was The reason is that, when the operating temperature becomes high, the dielectric strength, which should be a feature of the polypropylene film, suddenly decreases due to the amorphous part of the film, the influence of foreign matter, etc.,
This is because, in particular, there is a case where it cannot endure long-term use.

[0004] On the other hand, with the miniaturization of electric devices, the density and temperature of elements have been increased, and there has been an increasing demand for further increasing the maximum operating temperature of conventional polypropylene film capacitors. For this purpose, it is necessary to maintain the performance at a temperature higher than 85 ° C., which is the maximum operating temperature of the conventional polypropylene film capacitor, and for a long time.

[0005] To this end, (1) mechanical deformation due to rapid heating for a short time, that is, a heat shrinkage rate is appropriately small;
It has been required that (2) the film has excellent electrical properties at high temperatures, and (3) that the electrical properties have a small decrease with time at high temperatures.

The reason for the above (1) is that when a capacitor element is produced, a heat treatment is applied at a certain temperature at a stage when the polypropylene film is wound on the electrode so that a proper heat shrinkage is caused to cause tightness. It is common practice to maintain the shape and expel air between the film layers, but if the heat shrinkage is too large, the deformation of the element may cause a reduction in the capacity of the capacitor or the destruction of the element. On the other hand, if the heat shrinkage is too small, the tightness of the winding is insufficient, and the element may be broken due to an increase in the dielectric loss tangent during long-term high-temperature use.

To solve such a problem, Japanese Patent Laid-Open No. Hei 6-236
Japanese Patent Application Publication No. 709 discloses a polymer insulating material having low ash content, having a boiling n-heptane soluble content of 1 to 10% by weight, and having excellent workability, and having excellent electrical insulation from room temperature to 80 ° C. It is suggested that those having an isotactic pentad fraction of 90% or more in the boiling n-heptane-insoluble portion are preferable.

Japanese Patent Application Laid-Open No. Hei 7-25946 discloses that the boiling heptane-insoluble component is 80% by weight or more, particularly preferably 96% by weight or more, and the isotactic pentad fraction of the boiling heptane-insoluble component is 0%. .970-0.9
There are disclosures of propylene polymers in the range of 95 and molded articles using the same.

However, as disclosed in these publications, a biaxially oriented polypropylene film having only a high isotactic pentad fraction of a boiling n-heptane-insoluble component has a high insulation resistance at a high temperature exceeding 85 ° C. The breaking characteristics and the long-term heat resistance of the capacitor element using this film as a dielectric were insufficient. That is, the biaxially oriented polypropylene film having a high stereoregularity according to the conventional technique described above has a high isotactic pentad fraction in the boiling n-heptane-insoluble portion, but has an n-heptane-soluble isotactic pen. Since the tod fraction was low, the isotactic pentad fraction as a film was low as a result, and the stereoregularity was insufficient. The so-called highly crystalline biaxially oriented polypropylene film, which has an extremely high isotacticity, has an extremely poor film-forming property due to insufficient stereoregularity, and has excellent heat resistance and dielectric breakdown resistance. It has not been established as an industrially useful technique for producing a polypropylene film.

In order to solve these disadvantages, Japanese Patent Publication No.
No. 28727 discloses that the isotactic pentad fraction is in the range of 0.960 to 0.990 and the boiling n-
A crystalline polypropylene film having excellent moldability has been proposed in which the total amount of the extract to be extracted sequentially with hexane and boiling n-heptane is 3.0 to 6.0%. However, this polypropylene film did not have a sufficient isotactic pentad fraction and had insufficient dielectric breakdown resistance at high temperatures.

Further, Japanese Patent Application Laid-Open No. Hei 5-217799 discloses a high-rigidity vapor-deposited metal obtained by vapor-depositing a metal on a high-rigidity polypropylene film having a specific heat deformation temperature and Young's modulus, a high degree of crystallinity, and a good stereoregularity. A vapor-deposited film capacitor using a functionalized film has been proposed. However, the stereoregularity here was at most about 90%, and the dielectric breakdown characteristics at high temperatures were insufficient.

Further, JP-A-7-50224 discloses that
The heat shrinkage at 120 ° C. is 4.0% or less in the length direction,
Disclosed are metallized polypropylene films that are 0.8% or less in the width direction. However, the isotacticity and stereoregularity of this film are at a conventional level, and the dielectric breakdown resistance at high temperatures, which is the object of the present invention, to meet future high demands, is not necessarily sufficient. I couldn't say it.

[0013]

DISCLOSURE OF THE INVENTION The present inventors have made it possible to form a polypropylene film having extremely high isotacticity by controlling the isotacticity and stereoregularity of the polypropylene film to a high degree. By adopting appropriate film forming conditions, the heat shrinkage of the biaxially oriented polypropylene film is optimized, and the dielectric breakdown resistance at high temperatures, which could not be achieved with the conventional technology, has been improved.
Furthermore, they have found that a capacitor in which long-term deterioration at high temperatures is suppressed can be obtained, and the present invention has been accomplished.

An object of the present invention is to provide a biaxially oriented polypropylene film having excellent heat resistance and long-term dielectric breakdown resistance at high temperatures, and another object of the present invention is to provide such a biaxially oriented polypropylene film. It is an object of the present invention to provide a capacitor which uses as a dielectric and has excellent heat resistance and long-term dielectric breakdown resistance at high temperatures.

[0015]

The biaxially oriented polypropylene film of the present invention, which achieves the above object, has an isotacticity of 98.5 to 99.5% and an isotactic pentad fraction of 99%. And the sum of the heat shrinkage in the machine direction and the width direction at 120 ° C. is 1.5 to 3.5%, the thickness d of the film is 2 to 20 μm, and the temperature is 105 ° C.
Breakdown voltage per thickness at 580- (200 / d
^0.5 ) (V / μm) or more, and preferably at least one phenolic antioxidant having a molecular weight of 500 or more is added to the biaxially oriented polypropylene film of the present invention. The preferred content is 0.03 to 1% by weight.

The biaxially oriented polypropylene film of the present invention is particularly suitable for a capacitor. The capacitor of the present invention is obtained by winding or laminating a metallized biaxially oriented polypropylene film obtained by metallizing such a biaxially oriented polypropylene film as a dielectric.

Further, in the capacitor of the present invention,
The following preferred embodiments are included.

(1) The AC breakdown strength at 105 ° C. is 200 V / μm or more per the thickness of the biaxially oriented polypropylene film used as the dielectric.

(2) The biaxially oriented polypropylene film used as a dielectric should have a life of at least 500 hours, more preferably at least 1000 hours at 105 ° C. under the application of an AC voltage of 60 V / μm per thickness.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The biaxially oriented polypropylene film of the present invention is a biaxially oriented film mainly composed of a homopolymer of polypropylene. It may contain a copolymer component or the like, or may be blended with another polymer. As the copolymer component, for example, ethylene,
1-butene, 1-pentene, 3-methylpentene-1,
3-methylbutene-1, 1-hexene, 4-methylpentene-1, 5-ethylhexene-1, 1-octene, 1
-Decene, 1-dodecene, vinylcyclohexene, styrene, allylbenzene, cyclopentene, norbornene, 5-methyl-2-norbornene and the like.
The copolymerization amount is 1 mol from the viewpoint of dielectric breakdown resistance and heat resistance.
% And the blend is preferably less than 1 wt%.

In the present invention, the isotacticity of the biaxially oriented polypropylene film is 99.5% or less, particularly in the stretchability in the width direction during biaxial stretching. Here, the isotacticity is defined by the ratio of the weight of the insoluble matter to the weight of the film before extraction when the film is extracted with boiling n-heptane. If the isotacticity is too high, as described in JP-A-6-236709, when producing a biaxially stretched film, the stretchability is poor, and the film formation becomes extremely difficult. The isotacticity is 98.5% or more for heat resistance and dielectric breakdown resistance, especially for long-term heat resistance and dielectric breakdown resistance, which is the most important characteristic as a dielectric for a capacitor element. By setting the isotacticity to 98.5% or more and 99.5% or less as described above, it is possible to form a polypropylene film having a high stereoregularity described below, and to use this as a dielectric of a capacitor element. In this case, a long-term heat resistance and dielectric breakdown resistance, which have never existed before, can be exhibited. In the present invention, more preferable isotacticity is 98.7 to 99.5% for good film-forming property, heat resistance and dielectric breakdown resistance, and 98.
7 to 99.3% is preferred. In order to obtain a biaxially oriented polypropylene film having such isotacticity, a low-molecular-weight component that is easily soluble in boiling n-heptane of a polypropylene resin as a raw material, and a low stereoregularity, a proportion of a so-called atactic portion is appropriate. For example, a method such as selecting a lower one can be adopted.

In the present invention, the stereoregularity of the biaxially oriented polypropylene film can be evaluated by a pentad fraction based on an absorption peak of a methyl group measured by 13 C-NMR. Generally, the conformation of five repeating units (pentads) in a polypropylene molecular chain includes mmmm, mmmr, rmmr,.
r, mrrr, mrrm and the like. Here, m indicates the conformation of meso and r indicates the conformation of racemo.

The pentad fraction of the biaxially oriented polypropylene film is determined, for example, by T.V. Report of Hayashi et al. [Po
lymer, 29, 138-143 (1988)] and the like, the ratio of the segment having each of the above conformations can be determined from 13 C-NMR. Among these, the ratio of the conformation of mmmm to the absorption intensity of all methyl groups, that is, the isotactic pentad fraction (hereinafter sometimes abbreviated as mmmm) is m (mmmm)
It is defined as the sum of three heptad fractions, m, m (mmmm) r and r (mmmm) r. The isotactic pentad fraction mmmm of the biaxially oriented polypropylene film of the present invention exceeds 99%. Since such a film is made of polypropylene composed of molecules having extremely long isotactic segments, it can provide a film having high crystallinity, high heat resistance, and high dielectric breakdown resistance.

The mmmm of the biaxially oriented polypropylene film of the present invention is preferably 99.1% or more, more preferably 99.2%, in view of high heat resistance and high dielectric breakdown resistance.
%, More preferably 99.3% or more.

In order to impart such stereoregularity, it is effective to control the stereoregularity of the raw material polypropylene resin to a high degree. A method for producing such a raw material is achieved by using a catalyst system (solid catalyst, externally added electron-donating compound) and their purity when polymerizing polypropylene. Mmmm of raw polypropylene resin
Is higher, the biaxially oriented polypropylene film mm
mm tends to be high, but extreme thermal degradation of the raw material in the extrusion system also reduces mmmm, so structural measures such as avoiding long-term stagnation of the raw material in the high-temperature extrusion system, extrusion conditions are appropriately Selected.

In the present invention, the heat resistance of the biaxially oriented polypropylene film can be evaluated by the heat shrinkage when heated at 120 ° C. for 15 minutes. In the biaxially oriented polypropylene film of the present invention, the sum of the heat shrinkage in the machine direction and the width direction when heated at 120 ° C. for 15 minutes is in the range of 1.5 to 3.5%. If the heat shrinkage is too large, dimensional changes occur when the metal layer as an electrode is formed, wrinkles are formed in the film roll, and mechanical deformation due to heat during the production of the capacitor element is too large, so that the film roll and / or the external electrode In this case, stress is generated at the contact portion with the capacitor, and the capacity of the capacitor may be greatly reduced or the element may be destroyed. If the heat shrinkage is too low, the tightness due to the heat treatment during the production of the capacitor element becomes insufficient, which adversely affects the shape retention and the capacity change rate. The preferable heat shrinkage is the sum of the above values of 1.6 to 3.3%, further 1.7 to 3%, further 1.8 to 2.8%, particularly 1.8 to 2.5%. Is preferable. To keep the heat shrinkage in such a range,
Conditions during film formation are extremely important.

A conventional biaxially oriented polypropylene film having isotacticity and mmmm is disclosed in JP-A-7-5.
While the casting was performed at a casting drum temperature of 85 ° C. or higher as described in Japanese Patent No. 0224, the biaxially oriented polypropylene film of the present invention was 40 to 40 ° C.
It is preferred that the casting be performed at a lower casting drum temperature, such as 85 ° C. If the temperature of the casting drum is too high, the crystallization of the film proceeds too much, making it difficult to stretch in a subsequent step, or the heat shrinkage becomes too large. The conventional biaxially oriented polypropylene film is 14
In general, a stretching temperature in the machine direction of 0 ° C. or less and a stretching temperature in the width direction of 160 ° C. or less are employed. At a stretching temperature exceeding these temperatures, the orientation decreases, so that the elastic modulus of the biaxially oriented polypropylene film is reduced. It was difficult to keep.

In the biaxially oriented polypropylene film of the present invention, the stretching temperature in the machine direction of 140 to 150 ° C. and the temperature of 160 to 1
A stretching temperature in the width direction of 65 ° C. is preferably employed in order to obtain the desired heat shrinkage while maintaining the elastic modulus of the biaxially oriented polypropylene film. If these stretching temperatures are too low, the heat shrinkage will be too large. It is also effective to set the heat treatment temperature at 150 to 160 ° C. while relaxing in the width direction. If the heat treatment temperature is too low, the heat shrinkage becomes too large, and if it is too high, the heat shrinkage becomes too small.

In the present invention, the thickness of the biaxially oriented polypropylene film is from 2 to 20 μm in view of film forming properties, mechanical properties and electrical properties. If the thickness of the film is too small, the dielectric strength and mechanical strength may be poor, and the film may be damaged due to heat loss during metallization. If the thickness of the film is too large, it is difficult to form a film having a uniform thickness, and if it is used as a dielectric for a capacitor, the capacity per volume is undesirably small.

In the present invention, the dielectric breakdown resistance of the biaxially oriented polypropylene film can be evaluated by the DC dielectric breakdown strength at 105 ° C. In general, as for the dielectric breakdown strength of a biaxially oriented polypropylene film, as the film thickness decreases, the dielectric breakdown strength per unit thickness (V / μm) decreases. The dielectric breakdown strength at 105 ° C. of the biaxially oriented polypropylene film of the present invention is 580-
(200 / d ^0.5 ) (V / μm) or more. More preferably, it is 600- (200 / d ^0.5 ) (V / μm) or more. If the dielectric strength at 105 ° C. is too low, dielectric breakdown at a high temperature is easily generated, which may not be suitable for practical use as a capacitor. To achieve such a range,
This can be achieved by further reducing the ash content and internal haze of the film or by increasing the crystallinity as much as possible within the scope of the present invention.

In the present invention, the intrinsic viscosity of the polypropylene having excellent stereoregularity used for the biaxially oriented polypropylene film is not particularly limited, but is preferably in the range of 1 to 10 dl / g from the viewpoint of film forming properties. . Also, 23
The melt flow rate at 0 ° C. and a load of 2.16 kg is preferably 2 to 5 g / 10 min from the viewpoint of film forming properties. In order to set the intrinsic viscosity and the melt flow rate to the above values, a method of controlling the average molecular weight and the molecular weight distribution and the like are adopted.

In the polymerization process of polypropylene, it is common to use a compound containing a metal as a catalyst and, if necessary, remove this residue after the polymerization, but this residue is a residue obtained by completely burning the resin. Can be evaluated by determining the amount of the metal oxide, which is referred to as ash in the present invention. Ash content of the biaxially oriented polypropylene film of the present invention is 30 ppm
Or less, more preferably 25 ppm
Or less, more preferably 20 ppm or less.
If the ash content is too large, the dielectric breakdown resistance of the film is reduced, and the dielectric strength of a capacitor using the film may be reduced. In order to keep the ash content within this range, it is important to use a raw material that has little residual catalyst, but a method such as minimizing contamination from the extrusion system during film formation, for example, applying a bleed time of 1 hour or more, etc. Method can be adopted.

The surface roughness of the biaxially oriented polypropylene film of the present invention is appropriately selected according to the purpose.
The range of from 02 to 0.2 μm is preferred. If the center line average roughness is too large, air may enter between the layers when the films are laminated, leading to deterioration of the capacitor element. On the other hand, if it is too small, the film slides poorly and may be inferior in handleability. For oil impregnation applications, the center line average roughness is preferably in the range of 0.1 to 0.8 μm.

The biaxially oriented polypropylene film of the present invention contains known additives such as a crystal nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, an antistatic agent, an antiblocking agent,
A filler, a viscosity modifier, a coloring inhibitor and the like may be contained.

Of these, the selection of the type and amount of the antioxidant is important for long-term heat resistance. Preferred antioxidants to be added to the biaxially oriented polypropylene film of the present invention are phenolic ones having steric hindrance, and at least one of them is a high molecular weight type having a molecular weight of 500 or more to prevent scattering during melt extrusion. Preferred for. Various specific examples are given. For example, 2,6-di-t-butyl-p-cresol (BH
T: molecular weight 220.4) together with 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4).
-Hydroxybenzyl) benzene (for example, Irganox1330 manufactured by Ciba-Geigy: molecular weight 775.2) or tetrakis [methylene-3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (for example, Irganox1010 manufactured by Ciba-Geigy: molecular weight) 1177.7) and the like are preferably used in combination. The total content of these antioxidants is 0.03 to 1% by weight based on the total amount of polypropylene.
(300 to 10000 ppm) is preferable. If the total content is small, the long-term heat resistance may be poor. If the total content is too large, blocking at a high temperature due to bleed-out of these antioxidants may adversely affect the capacitor element. A more preferable content is 0.1 to 0.9% by weight, and further preferably 0.2 to 0.8% by weight.

The biaxially oriented polypropylene film of the present invention is preferably subjected to a corona discharge treatment or a plasma treatment on at least one surface on which a metal layer is formed, in order to increase the adhesive strength. A known method can be used for the corona discharge treatment. In the treatment, treatment in an atmosphere gas such as air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof is preferable. For the plasma treatment, a method in which various gases are kept in a plasma state to chemically modify the film surface can be employed.
For example, there is a method described in Japanese Patent No. 40 gazette.

The biaxially oriented polypropylene film used as a dielectric material in the capacitor of the present invention may be wound together with a metal foil used as an electrode, or may be metalized in advance as an electrode. For miniaturization, it is more preferable to use a metalized and wound metal.

The metal for forming a metal layer on the biaxially oriented polypropylene film of the present invention and metallizing it is not particularly limited, but aluminum, zinc, copper, tin, silver, nickel or the like may be used alone or in combination. It is preferable to use the metallized layer in terms of durability and productivity. The method for forming a metal layer on the biaxially oriented polypropylene film of the present invention includes, but is not particularly limited to, a vacuum deposition method, a sputtering method, and an ion beam method.

In the present invention, the film resistance of the metallized film is preferably in the range of 1 to 40 Ω / □. More preferably, it is 1.2 to 30 Ω / □. If the film resistance is too small, the thickness of the deposited film is so large that heat loss occurs during the deposition, and an avatar-shaped surface defect or a hole in a thin film of about 4 μm may occur. If the film resistance is too large, when the deposited film clears during the application of electricity, the film is likely to disappear, and the change in capacitance may be large. In order to keep the film resistance within this range, a method of controlling the film resistance at the time of vapor deposition by monitoring is preferably adopted.

In the present invention, the specification of the margin provided when the metal layer is formed on the biaxially oriented polypropylene film (the portion without the metal layer provided on the surface on which the metal layer is formed for the purpose of electrical insulation) is a normal type. In addition to the above, various types including a fuse mechanism can be adopted according to the purpose, and there is no particular limitation.

The type of the condenser of the present invention may be dry type,
An oil immersion type or the like may be used, but is not particularly limited.

105 ° C. of a film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric
AC breakdown strength at 200V / μ per unit thickness
m or more. This is because the rated voltage of the polypropylene film capacitor is usually 45 to 50 V / μm, and preferably 4 times or more of this value in consideration of safety. More preferably, it is 210 V / μm or more.
In order to keep the dielectric breakdown strength of the film capacitor within this range, it is effective to avoid wrinkles and scratches during processing into the capacitor.

105 ° C. of a film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric
60V / μm per unit thickness at
The life under the application of AC voltage (1.3 times) is preferably 500 hours or more, more preferably 1000 hours or more, in terms of the warranty period of the device loaded with the capacitor. To keep the life within this range, add an appropriate amount of antioxidant, and 100% when processing into a capacitor.
It is effective to perform a heat treatment at about ℃, avoid wrinkles and scratches, block the contact with the outside air by embedding epoxy resin or impregnating resin or oil and sealing it inside a metal can (exterior). It is.

Next, a method for producing the biaxially oriented polypropylene film of the present invention and a capacitor comprising the same will be described below, but the present invention is not limited thereto.

First, a polypropylene raw material was supplied to an extruder, heated and melted, and passed through a filter.
Melt extrusion from a slit die at a temperature of 320 ° C, 40
It is wound around a casting drum maintained at a temperature of 85 ° C. and solidified by cooling to produce an unstretched film.

Next, the unstretched film is biaxially stretched to be biaxially oriented. As the stretching method, a sequential biaxial stretching method is preferable. As a sequential stretching method, first, the unstretched film is preheated by passing through a roll maintained at 120 to 150 ° C, and then the sheet is passed between rolls provided with a peripheral speed difference while maintaining the temperature at 140 ° C to 150 ° C. 2 to 6 in the longitudinal direction
Stretch twice and immediately cool to room temperature. Here, the biaxially oriented polypropylene film having a mmmm of more than 99% of the present invention may have a preheating temperature of 130 ° C. or less, and a stretching temperature of 140 ° C. or less. It is important to employ a stretching temperature above 140 ° C. Subsequently, the stretched film is guided to a tenter, and is heated at a temperature of 160 to 165 ° C. in a width direction.
The film is stretched by a factor of 10 to 10 and then heat-set at a temperature of 150 to 160 ° C. while giving a relaxation of 2 to 20% in the width direction and wound up. In the present invention, the heat setting temperature is important. If the heat setting temperature is too low, the heat shrinkage increases, which may exceed the range of the present invention.

Thereafter, in order to improve the adhesion of the deposited metal to the surface on which the deposition is to be performed, a corona discharge treatment is performed in air, nitrogen, carbon dioxide, or a mixture thereof, and the film is wound by a winder.

The obtained film is set in a vacuum deposition apparatus, and a metal suitable for the purpose is deposited on a predetermined film resistance. This vapor deposition film is slit to form a pair of vapor deposition reels on two reels for producing a capacitor element. Then, it is wound into an element shape, hot-pressed and formed into a flat shape, metal sprayed at the end, a lead is taken out, and a capacitor is formed through a sheath.

The biaxially oriented polypropylene film of the present invention can suppress deformation due to heat during processing such as vapor deposition, printing, laminating, and heat sealing by utilizing a low heat shrinkage rate in addition to the above-mentioned capacitor use. For various packaging applications, for example, it can be used by laminating it with a heat seal layer, and can also be suitably used as an adhesive tape, a polished film (print laminate), and the like.

The method for measuring and evaluating the characteristic values in the present invention are as follows.

(1) Isotacticity (isotactic index: II) A sample is extracted with n-heptane at a temperature of 60 ° C. or less for 2 hours to remove additives to polypropylene. Then 13
Vacuum dry at 0 ° C. for 2 hours. From this, a sample of weight W (mg) is taken, placed in a Soxhlet extractor and extracted with boiling n-heptane for 12 hours. Next, the sample was taken out, washed sufficiently with acetone, vacuum-dried at 130 ° C. for 6 hours, and then cooled to room temperature, and the weight W ′ (mg) was measured and determined by the following equation. II = (W ′ / W) × 100 (%) (2) Isotactic pentad fraction A sample was dissolved in o-dichlorobenzene, and JN made by JEOL was used.
Using an M-GX270 device, a resonance frequency of 67.93 MH
13C-NMR was measured at z. For the assignment of the obtained spectra and the calculation of the pentad fraction, see T.W. Ha
Yashi et al. [Polymer, 29,
138 to 143 (1988)], the peak derived from the methyl group had a mmmmmm peak of 21.8.
Each peak was assigned as 55 ppm, the peak area was determined, and the ratio to the total peak area derived from the methyl group was expressed as a percentage. Detailed measurement conditions are as follows.

Measurement solvent: o-dichlorobenzene (90 wt.
%) / Benzene-D6 (10 wt%) Measurement temperature: 120 to 130 ° C Resonance frequency: 67.93 MHz Pulse width: 10 μsec (45 ° pulse) Pulse repetition time: 7.091 sec Data point: 32K Integration frequency: 8168 Measurement mode: Noise decoupling (3) Heat shrinkage The film is 260 mm long in the machine and width directions, respectively.
Sampling is performed 10 mm in width and a mark is placed at 30 mm from both ends to make the original size (L ₀ : 200 mm).
A weight of 3 g is applied to the lower end of the sample, and the sample is suspended in an oven at 120 ° C. and heat-treated for 15 minutes. Thereafter, the sample was taken out, the marked length (L ₁ ) was measured, the heat shrinkage was calculated by the following equation, and the sum in the machine direction and the width direction was defined as the heat shrinkage. Heat shrinkage = [(L ₀ −L ₁ ) / L ₀ ] × 100 (%) (4) Ash content According to JIS-C-2330. The biaxially oriented polypropylene film of the initial weight W _0, placed in a platinum crucible, after first thoroughly burned by a gas burner, an electric furnace at 750 to 800 ° C., to completely incinerated treated for about 1 hour, the resulting ashes the weight W ₁ and measurement of, was determined from the following equation.

Ash content = (W ₁ / W ₀ ) × 1,000,000 (ppm) W ₀ : initial weight (g) W ₁ : ashed weight (g) (5) Internal haze Measured according to JIS-K-7105, It was determined from the following equation. However, in order to remove light scattering due to unevenness on the film surface, the measurement was performed in a state where the sample was immersed in a quartz cell filled with liquid paraffin.

H = (Td / Tt) × 100 (%) H: internal haze (%) Td: diffuse transmittance Tt: total light transmittance (6) Film thickness Dial gauge thickness gauge (JIS-B-7503) It measured using.

(7) Film dielectric strength (film B
DV) It measured according to JIS-C-2110. 1 thickness on cathode
00μm, 10cm square aluminum foil electrode, brass 2 on anode
Using a 5 mmφ electrode, sandwiching the film between them, and using a DC high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd., 200 V
A voltage is applied while increasing the voltage at a speed of
The case where the flow was A or more was regarded as the breakdown. The value obtained by dividing the voltage at that time by the film thickness at the measurement point was defined as the dielectric breakdown strength, and the average value was measured at 20 points. The measurement at 105 ° C. was performed by setting the electrodes and the sample in a hot-air oven, connecting the above-mentioned power source with a heat-resistant cord, and starting pressure increase one minute after the oven was turned on.

(8) Element Dielectric Breakdown Strength (Element BDV) A capacitor element maintained at 105 ° C. in a hot air oven was connected to a DC (or AC) high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd. A voltage was applied while increasing the voltage at a speed, and a current flowed through the device due to discharge breakdown (maximum 18 amps). The voltage at the time of breakdown was determined, and the average value of 10 devices measured was taken as the device BDV.

(9) Element Life Test An AC voltage of 60 V / μm per film thickness was applied to the capacitor element, and the time until the element was destroyed in an atmosphere at 105 ° C. was measured.

[0058]

EXAMPLES The present invention will be described in detail below based on examples and comparative examples.

(Example 1) A polypropylene raw material having an isotactic index II of 98.8%, an isotactic pentad fraction mmmm of 99.5%, and an ash content of 19 ppm was used as a starting material for polypropylene. p-cresol (BHT) 0.3%, telorakis [methylene-3 (3,3)
5-Di-t-butyl-4-hydroxyphenyl) propionate] methane (Irganox1010) 0.5% was added to the extruder, melted at 280 ° C., extruded from a T-type die into a sheet. It was molded, wound around a casting drum at a temperature of 70 ° C., and cooled and solidified. Next, the sheet was preheated at 135 ° C., continuously passed between rolls having a peripheral speed difference maintained at a temperature of 143 ° C., and stretched 5 times in the longitudinal direction. Continue guiding the film to the tenter,
The film is stretched 10 times in the width direction at a temperature of 162 ° C., and then heat-treated at 158 ° C. while giving 8% relaxation in the width direction.
A biaxially oriented polypropylene film having a thickness of μm was obtained.
Further, a corona discharge treatment was performed in the atmosphere at a treatment intensity of 30 W · min / m 2. The ash and pentad fractions of the resulting films did not differ from those of the raw materials.
This film was set in a vacuum evaporation machine, and copper was used as a nucleation metal, and zinc was evaporated on the corona-treated surface so that the film resistance became 4.0 Ω / □. Slit this film and make it 3
A metallized film having a width of 8 mm and a margin width of 1 mm was obtained. The element was wound using a pair of two reels of the obtained film, metal sprayed on an end face of the element, and a lead wire was taken out from the element to form a capacitor element having a capacity of 5 μF.

Example 2 II: 98.9%, mmmm
And a capacitor element was obtained in the same manner as in Example 1 using a polypropylene raw material having a solid content of 99.1% and an ash content of 18 ppm.

(Examples 3 and 4) Using the same raw materials as in Example 1, a biaxially oriented polypropylene film having a film thickness of 2.5 μm and 8 μm and a capacitor element were obtained under the same conditions.

(Examples 5, 6, 7) The same raw materials as in Example 1 were used, and the antioxidant-added formulation was BHT 0.3%, 1, 3, 5
-Trimethyl-2,4,6-tris (3,5-di-t-
Butyl-4-hydroxybenzyl) benzene 0.3% (Example 5), BHT only 0.3% (Example 6), BHT 0.3% and Irganox1010
By using 1.2% (Example 7), a biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1.

[0063]

[Table 1] Table 1 shows the characteristics of the biaxially oriented polypropylene films of Examples 1 to 7 and the characteristics of the capacitor element. All of them had II, mmmm, heat shrinkage, thickness, and dielectric strength within the range of the present invention. As a result, high dielectric strength with a capacitor element and sufficient element life were obtained. In Example 6, the addition amount of the phenolic antioxidant having a molecular weight of 500 or more was 0%, and the device life was slightly inferior. Similarly, Example 7
In Comparative Example 1, the addition amount of the antioxidant exceeded 1%, and the device breakdown voltage and the device life were slightly inferior due to the deterioration of the device winding property.

(Comparative Example 1) 98.3% of II, mmmm
Of a biaxially oriented polypropylene film and a capacitor in the same manner as in Example 1 except that a polypropylene material having an antioxidant formulation of 98%, an ash content of 19 ppm and the same antioxidant formulation as in Example 1 was used, and the casting drum temperature was set at 85 ° C. An element was obtained. The characteristics are also shown in Table 1. Although II and mmmm were out of the range of the present invention, the heat shrinkage rates were both within the range of the present invention. The dielectric strength of the film was insufficient, and the dielectric strength and life of the capacitor element were also insufficient. The characteristics are shown in Table 1.

(Comparative Example 2) II was 99.7%, mmmm
However, it was attempted to form a film under the conditions of Example 1 using a polypropylene raw material having a solid content of 99.2% and an ash content of 22 ppm. However, film formation was impossible due to film breakage. Stretching temperature, 167 ° C
The film was formed at a transverse stretching temperature of A capacitor element was obtained in the same manner as in Example 1. The characteristics are shown in Table 1. I
I exceeded the upper limit of the present invention, and the heat shrinkage ratio was within the range of the present invention. However, since the internal haze increased to 0.6% and voids were generated, the dielectric breakdown strength of the film was insufficient, and The dielectric breakdown strength and element life of the element were also insufficient.

Comparative Example 3 A film was formed under the same conditions as in Example 1 except that the same polypropylene raw material as in Example 1 was used and the temperature of the casting drum was changed to 95 ° C., and a biaxially oriented polypropylene film and a capacitor element were formed. I got The characteristics are shown in Table 1. Since the heat shrinkage was as large as 4.2% and the internal haze was as large as 0.8%, the dielectric strength of the film was insufficient, and the dielectric strength and life of the capacitor element were insufficient. Was. The characteristics are shown in Table 1.

(Comparative Example 4) II: 98.1%, ash content: 1
5 ppm, titanium is 0.3 ppm, and chlorine content is 0.1 ppm.
Using a 4 ppm polypropylene raw material, a biaxially oriented polypropylene film and a capacitor element were obtained in the same manner as in Example 1. The characteristics are shown in Table 1. 23 ° C and 80
605 V / μm, 520
V / μm, but the dielectric breakdown strength at 105 ° C. dropped sharply to 380 V / μm.
The element life was insufficient. When the n-heptane-insoluble content mmmm of the film was measured, it was 99.3%, which was a very high value, but the film mmmm was 98.3%.
Met.

Comparative Example 5 Using the same polypropylene raw material as in Example 1, a biaxially oriented polypropylene film having a thickness of 1.5 μm was prepared in the same manner as in Example 1 to obtain a capacitor element. The characteristics are shown in Table 1. 1.5μ thickness
m was out of the range of the present invention, and the dielectric breakdown strength and the element breakdown strength were inferior.

(Comparative Examples 6 and 7) Using the same raw materials as in Example 1, the heat treatment temperature was set at 145 ° C. (Comparative Example 8) and 167 ° C.
A film was formed under the same conditions as in Example 1 except that (Comparative Example 9) was used to obtain a biaxially oriented polypropylene film and a capacitor element. The characteristics are shown in Table 1. The respective heat shrinkage ratios were 4.6% and 0.9%, and the dielectric breakdown strength of the film was the same as in Example 1. However, the dielectric breakdown strengths of the capacitor elements were 148 V / μm and 161 V / μ.
m, and the element life was unsatisfactory, 46 hours and 17 hours.

[0070]

According to the present invention, the biaxially oriented polypropylene film according to the present invention has excellent heat resistance and long-term dielectric breakdown resistance at high temperatures. The usable temperature of the capacitor can be improved by up to 20 ° C from the maximum operating temperature of 85 ° C of the capacitor using the conventional biaxially oriented polypropylene film, which enables the miniaturization of electric devices and the density of elements. be able to. Also,
By utilizing the small heat shrinkage, deformation due to heat during processing in various packaging applications can be suppressed, and the industrial utility value is extremely large.

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Claims (7)

[Claims] 1. A biaxially oriented polypropylene film having an isotacticity of 98.5 to 99.5%, an isotactic pentad fraction of more than 99%, and a temperature of 120 ° C. Is 1.5 to 3.5%, the thickness d of the film is 2 to 20 μm, and the dielectric breakdown voltage per thickness at 105 ° C. is 580− ( 200 / d ^0.5 )
(V / μm) or more. 2. The method according to claim 1, wherein at least one phenolic antioxidant having a molecular weight of 500 or more is added, and the content of the antioxidant is 0.03 to 1% by weight. Biaxially oriented polypropylene film. 3. A capacitor comprising the biaxially oriented polypropylene film according to claim 1 or 2 as a dielectric. 4. The metallized film capacitor according to claim 3, wherein the metallized biaxially oriented polypropylene film is wound or laminated. 5. The AC dielectric breakdown strength at 105 ° C. per unit thickness of the biaxially oriented polypropylene film used as the dielectric is 200 V / μm or more. condenser. 6. The life at 105 ° C. under the application of an AC voltage of 60 V / μm is 500 hours or more per the thickness of the biaxially oriented polypropylene film used as the dielectric. The capacitor according to claim 5. 7. The life of the biaxially oriented polypropylene film used as the dielectric at 105 ° C. under an AC voltage application of 60 V / μm is 1000 hours or more per thickness. The capacitor according to claim 6.