JPH10156940A - Polypropylene film and capacitor using the same as dielectric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance long-term dielectric breakdown characteristics at high temp. and workability by specifying the isotacticity and isotactic pendant ratio of a biaxially oriented polypropylene film and the sum of the moduluses in the longitudinal and laterial directions of the film. SOLUTION: The isotacticity of a biaxially oriented polypropylene film is 98.5-99.5% and the isotactic pendant ratio mmmm displaying the stereoregularity of the film evaluated on the basis of a pendant ratio by the absorption peak of a methyl group measured by<13> C-NMR exceeds 99%. Further, the sum of the moduluses of elasticity in the longitudinal and lateral directions of the biaxially oriented polypropylene film is 7-10GPa. When the sum of the moduluses of elasticity is below 7GPa, heat resistance and high dielectric breakdown characteristics are not obtained and the tension control in a membrane film vapor deposition process becomes difficult. When the sum of the moduluses of elasticity exceeds 10GPa, film forming stability at a time of the production of the film is not obtained and yield lowers.

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, and more particularly to a biaxially oriented polypropylene film having excellent heat resistance and dielectric breakdown resistance, and heat resistance using the same as a dielectric. The present invention relates to a capacitor having excellent dielectric breakdown resistance and current resistance.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene films are excellent in optical properties such as transparency and glossiness, mechanical properties such as rupture strength and elongation at break, as well as water vapor barrier properties and excellent electrical properties. Widely used for applications, tapes, capacitors, etc.

[0003] As described above, the biaxially oriented polypropylene film is one of the typical materials used as a dielectric for a film capacitor, but has a lower heat resistance than a polyester film which is another typical material. The maximum operating temperature of the condenser was limited to about 85 ° C. The reason for this is that when the operating temperature rises,
This is because the dielectric breakdown strength, which should be a feature of the polypropylene film, suddenly decreases due to the influence of the amorphous portion of the film, foreign matter, and the like.

[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) 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.

[0007] Further, with the miniaturization of electric devices, there has been a demand for improvement of the above-mentioned characteristics, while a demand for further miniaturization of the film capacitor itself has been increasing. For this purpose, it is necessary to increase the capacitance per unit volume of the capacitor, and it is necessary to reduce the thickness of the dielectric film.

However, as the film becomes thinner, various problems have arisen with respect to workability and electrical characteristics when handling the film. In particular, in the case of manufacturing a metallized film capacitor using a metal layer provided on at least one side of the film and using it as an internal electrode, there is a serious obstacle to the thinning of the film, and the metal deposition that provides the metal layer on the film In such processes, it becomes difficult to control the winding tension of the film. That is, if the tension is too low, a gap is formed between the film and the cooling roll during vapor deposition. As a result, thermal deformation of the film due to insufficient cooling causes vapor deposition unevenness, or a problem that causes poor winding due to poor flatness. Increase rapidly. On the other hand, if the tension is too high, the number of wrinkles in the form of a record is increased due to the stretching of the film, and the trouble of cracks in the metal layer is rapidly increased.

Furthermore, in one of the manufacturing and processing steps of the capacitor, in the step of forming an end electrode for connecting a metal layer called an internal electrode formed on the film surface to a lead terminal from the capacitor element, the capacitor element is connected to the element. After winding, both sides of the element are sprayed with metal called metallikon, but as the film becomes thinner, the film at the side end of the element drips because the film loses its rigidity, and the sprayed metal contacts the internal electrode Troubles that cause poor contact and poor insulation without entering the inside of the device frequently occur. Further, from the above, there is a case where the quality of the electrical characteristics such as the dielectric breakdown strength varies.

[0010] In addition, even if the initial characteristics of the completed capacitor are normal, repeated charging / discharging may result in insufficient contact, resulting in deterioration of dielectric loss and heat generation inside the capacitor, which may cause dielectric breakdown. .

To solve such a problem, Japanese Patent Laid-Open No. 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. 7-25946 also 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
A propylene polymer in the range of 95 and a molded article using the same are disclosed.

However, as disclosed in these publications, a biaxially oriented polypropylene film having a high isotactic pentad fraction of a boiling n-heptane-insoluble component simply has an 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 drawbacks, 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, the isotactic pentad fraction was not sufficient, and the dielectric breakdown resistance at high temperatures was insufficient.

Further, Japanese Patent Application Laid-Open No. 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 distortion 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
A metallized polypropylene film having a heat shrinkage at 20 ° C. of 4.0% or less in the length direction and 0.8% or less in the width direction has been proposed. However, the isotacticity and stereoregularity of this film are conventional, and the dielectric breakdown resistance at high temperatures, which is the object of the present invention, for responding to future high demands, was not always sufficient. .

[0017]

SUMMARY OF THE INVENTION The present inventors have made it possible to form a polypropylene film having an extremely high isotacticity by controlling the isotacticity and stereoregularity of the polypropylene film to a high degree, and to further improve the appropriateness. By adopting film forming conditions, the dielectric breakdown resistance characteristic of polypropylene film, which could not be achieved with the conventional technology, is further improved, and furthermore, the characteristic deterioration at high temperature and the suppression of long-term deterioration at high temperature are suppressed. It has been found that a capacitor having a small variation in quality can be obtained, which has led to the present invention.

An object of the present invention is to provide a polypropylene film which is excellent in heat resistance, long-term dielectric breakdown resistance at high temperatures, and workability.

Another object of the present invention is to provide a capacitor excellent in heat resistance, long-term dielectric breakdown resistance at high temperatures, and current resistance.

[0020]

That is, the present invention achieves the above-mentioned object, and is a biaxially oriented polypropylene film, wherein the isotacticity of the film is 98 to 99.5%, A polypropylene film having a tactic pentad fraction of more than 99% and a sum of elastic moduli in a longitudinal direction and a width direction of 7 to 10 GPa.

The capacitor of the present invention uses the above polypropylene film as a dielectric.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene used in the polypropylene film of the present invention mainly comprises a homopolymer of propylene, but contains other unsaturated hydrocarbon copolymer components and the like within a range not to impair the object of the present invention. Or a polymer other than propylene alone may be blended. Examples of such copolymer components and monomer components constituting the blend include ethylene, propylene (in the case of a copolymerized blend), 1-butene, and 1-butene.
-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 amount of the copolymer or the amount of the blend is preferably less than 1 mol% from the viewpoint of dielectric breakdown resistance and heat resistance, and the blend is preferably less than 10% by weight, though depending on the copolymerization ratio.

In the present invention, the isotacticity of the polypropylene film needs to be 99.5% or less from the viewpoint of film forming properties. Here, the isotacticity is defined by the ratio of the weight of the insoluble content to the weight of the film before extraction when the film is extracted with boiling n-heptane. If the isotacticity is too high, the
When a biaxially oriented film is produced as disclosed in Japanese Patent No. 6709, stretchability is poor and film formation becomes extremely difficult. Further, the isotacticity needs to be 98% or more in terms of heat resistance and dielectric breakdown resistance. Good film forming properties and heat resistance,
A more preferred isotacticity for dielectric breakdown resistance is 98.5 to 99.5%, and more preferably 98.7 to 98.7%.
99.3% is preferred.

In order to obtain a polypropylene film having such isotacticity, the proportion of a low molecular weight component which is easily soluble in the boiling n-heptane of the polypropylene resin as a raw material or a so-called atactic portion having low stereoregularity is appropriate. For example, a method such as selecting a lower one can be adopted.

In the present invention, the stereoregularity of the polypropylene film can be evaluated by a pentad fraction based on an absorption peak of a methyl group measured by ¹³ C-NMR. Generally, 5 in the polypropylene molecular chain
The conformation of the repeating units (pentads) is mmm
m, mmmr, rmmr, ..., rrrr, mrrr,
mrrm. Here, m is a meso (me
so) and r show the conformation of racemo.

The pentad fraction of the polypropylene film is, for example, as described in T.W. Report of Hayashi et al. [Polyme
r, 29, 138 to 143 (1988)], the ratio of the segments having each of the above-mentioned conformations is ¹³ C-
It can be determined from 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) m, m (mmm
m) defined as the sum of three heptad fractions, r and r (mmmm) r. The isotactic pentad fraction mmmm of the 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 polypropylene film of the present invention is preferably 99.1% or more, more preferably 99.2% or more, and still more preferably 99.3% in terms of high heat resistance and high dielectric breakdown resistance.
% 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 can be achieved by selecting a catalyst system (solid catalyst, externally added electron donating compound) and purifying them when polymerizing polypropylene. M of raw material polypropylene resin
The higher the mmm, the mmm of the polypropylene film
m 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 and extrusion conditions are appropriately adjusted. Selected.

In the process of polymerizing the polypropylene used for the polypropylene film of the present invention, it is general to use a compound containing a metal as a catalyst, and to remove this residue if necessary after the polymerization. Can be evaluated by determining the amount of the remaining metal oxide after the resin has been completely burned, and this is referred to as ash in the present invention. The ash content of the polypropylene film of the present invention is preferably 30 ppm or less, more preferably 25 ppm or less,
More preferably, it is 20 ppm or less. If the ash content is too large, the dielectric breakdown resistance of the film may decrease, and the dielectric strength of a capacitor using the film may decrease. In order to keep the ash content within this range, it is important to use a raw material with little residual catalyst, but a method such as minimizing contamination from the extrusion system during film formation, for example, bleeding time of 1 hour or more is required. Such a method can be adopted.

Known additives such as a nucleating agent, an antioxidant, a heat stabilizer, a sliding agent, an antistatic agent, an antiblocking agent, a filler, and a viscosity modifier are added to the polypropylene used in the polypropylene film of the present invention. And an anti-coloring agent may be contained within a range that does not deteriorate the characteristics of the present invention.

Of these, the selection of the type and amount of the antioxidant is important for long-term heat resistance. The antioxidant to be added to the polypropylene film of the present invention is a phenolic compound having steric hindrance, and at least one of them is preferably a high molecular weight type having a molecular weight of 500 or more for preventing scattering during melt extrusion. Although various examples are given as specific examples thereof, for example, 2,6-di-t-
Butyl-p-cresol (BHT: molecular weight 220.4)
Together with 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)
Benzene (for example, Irganox 1330 manufactured by Ciba Geigy: molecular weight 775.2) or tetrakis [methylene-3 (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate] methane (for example, Irganox 1010 manufactured by Ciba Geigy:
It is preferable to use a compound having a molecular weight of 1177.7) or the like.

The total content of these antioxidants is 0.03 to 1% by weight (300 to 100%) based on the total amount of polypropylene.
00 ppm) is preferred. If the content is small, the long-term heat resistance may be poor. If the content is too large, the antioxidant may bleed out and block at a high temperature, which 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.

In the present invention, the intrinsic viscosity of the polypropylene having excellent stereoregularity used for the polypropylene film is not particularly limited.
Those in the range of dl / g are preferred. 230 ° C,
The melt flow rate under 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.

The polypropylene film of the present invention is obtained by using a raw material capable of giving the above-mentioned properties and performing biaxial orientation. An unoriented film has high crystallinity, high heat resistance, and high dielectric breakdown resistance, which are the objects of the present invention, and a film having good workability cannot be obtained. The method of biaxial orientation can be obtained by any of the following methods: inflation simultaneous biaxial stretching method, stenter simultaneous biaxial stretching method, and stenter sequential biaxial stretching method. Among them, film forming stability, thickness uniformity From the viewpoint of controlling the elastic modulus, which will be described later, a film formed by a stenter sequential biaxial stretching method is preferably used.

The sum of the elastic modulus in the longitudinal direction and the width direction of the biaxially oriented polypropylene film of the present invention is 7 to 10 GP.
must be a. When the sum of the elastic modulus in the longitudinal direction and the width direction of the film is less than 7 GPa, the heat resistance and the high dielectric breakdown resistance aimed at by the present invention cannot be obtained, and the tension control becomes difficult not only in the thin film film deposition process. As a result, the yield in the metallikon process deteriorates. On the other hand, when the sum of the elastic modulus in the longitudinal direction and the width direction of the film exceeds 10 GPa, film formation stability during film production cannot be obtained, and the yield decreases.
The more preferable range of the sum of the elastic modulus in the longitudinal direction and the width direction of the film of the present invention is 7.5 to 9.5 GPa, most preferably 8 to 9 GPa.

Furthermore, in the present invention, the biaxially oriented polypropylene film has an elastic modulus in the width direction of 4.5 to 4.5.
When it is in the range of 6.5 GPa, even in the case of a thin film, the stiffness in the width direction is strong, and almost no obstruction path of the sprayed metal at the end on the element side in the metallicon process is obtained.

If the elastic modulus in the width direction of the film is small, even in the case of the film of the present invention, it may not be possible to stabilize the yield of the metallikon process. If the elastic modulus in the width direction of the film is too large, the elastic modulus is too biased in the width direction,
The balance with the elastic modulus in the longitudinal direction may be lost, and the film formation may not be stable, or the tension control in the vapor deposition process may be difficult. The more preferable range of the elastic modulus in the width direction of the biaxially oriented polypropylene film of the present invention is 5.0 to 6.3G.
Pa, and more preferably 5.2 to 6.2 GPa.

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 preferably in the range of 1.5 to 3.5%. . If the heat shrinkage is too large, dimensional changes occur during the formation of the metal layer as an electrode, 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 the external electrode and Stress may occur at the contact portion of 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 heat treatment during the production of the capacitor element becomes insufficient, which may adversely affect the shape retention and the rate of change in capacity. The more preferable heat shrinkage ratio is 1.6 to 3.3% of the above sum, further 1.7 to 3%, further 1.8 to 2.8%, particularly 1.8 to 2.5%. % Is preferred.

In the present invention, the thickness of the biaxially oriented polypropylene film is preferably 2 to 30 μm, more preferably 2.30 μm, from the viewpoint of film forming properties, mechanical properties and electrical properties.
It is 5 to 20 μm, more preferably 2.5 to 10 μm. If the thickness of the film is too small, the dielectric strength or mechanical strength may be poor, and the film may be damaged due to metallization, particularly heat loss. 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 capacitance per volume is undesirably small.

The biaxially oriented polypropylene film used as a dielectric in the capacitor of the present invention may be used by being wound together with a metal foil used as an internal electrode.
The internal electrode may be wound and used as a metallized film in which a metal layer is provided on at least one surface of the film surface in advance. Those wound and used as a metallized film provided with a layer are more preferred. In addition, by providing a metal layer on at least one surface of the film surface as an internal electrode, the capacitor is provided with a self-healing capability of a dielectric breakdown portion, which is called self-healing, to further maintain security.

When a metal layer is formed on the surface of the film of the present invention, it is preferable to perform a corona discharge treatment or a plasma treatment on the surface on which the metal layer is formed in order to increase the adhesive strength. A known method can be used for the corona discharge treatment, but treatment is preferably performed in air, carbon dioxide gas, nitrogen gas, or a mixed gas thereof as an atmosphere gas. For the plasma treatment, a method in which various gases are put into a plasma state and the film surface is chemically denatured can be adopted, for example, a method described in JP-A-59-98140.

The metal for forming the metal layer on the biaxially oriented polypropylene film of the present invention is not particularly limited, but aluminum, zinc, copper, tin, silver, nickel, etc. may be used alone or in combination. Is preferred in terms of the durability and productivity of the metallized layer, and among these, aluminum and zinc are most preferred.

The method of forming a metal layer on the biaxially oriented polypropylene film of the present invention includes a vacuum deposition method, a sputtering method, an ion beam method and the like, and is not particularly limited. From the viewpoint of ease of use and maximizing the features of the film of the present invention, a method using a vacuum deposition method is preferable.

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.

The value of the film resistance was determined by cutting out a vapor-deposited film sample in the longitudinal direction at a width of 2 mm and a length of 50 mm, and measuring the longitudinal resistance value of the cut out sample by a four-point contact method.
Calibrate with width and voltage measurement terminal gap.

In the present invention, when a metal layer is formed on one surface of a biaxially oriented polypropylene film, and when there is a difference between the front and back surfaces in the center line average surface roughness of the film, the surface roughness is increased. It is preferable to form a metal layer on a surface having a small size. By doing so, surface defects of the metal layer can be minimized, leading to an improvement in dielectric breakdown strength and element life.

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 usually specified. It can be adopted according to the purpose, such as various types provided with a fuse mechanism other than the type, and is not particularly limited.

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.

A film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric is described below.
AC breakdown strength at 05 ° C is 200V per unit thickness
/ Μm or more. The rated voltage of a polypropylene film capacitor is usually 45 to 50 V / μm
This is because a value four times or more of this is preferable 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.

A film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric is described below.
The life under AC voltage application of 60 V / μm per unit thickness (1.2 to 1.3 times the rated voltage) at 05 ° C. is 500 hours or more in terms of the warranty period of the device equipped with the capacitor. Preferably, more preferably 1000
More than an hour. To keep the service life within this range, add an appropriate amount of antioxidant, heat-treat the capacitor at about 100 ° C during processing, avoid wrinkles and scratches, and embed epoxy resin. It is effective to block the contact with the outside air by sealing inside a metal can after impregnation or oil impregnation.

In the film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric, ΔD represented by the following formula is preferably 200% or less from the viewpoint of improving current resistance. In order to make ΔD 200% or less, it is effective to use the polypropylene film of the present invention as a dielectric and to select a sprayed metal used for the metallikon.

D (%) = (D ₁ / D ₀ ) × 100 [where D ₀ and D ₁ are the dielectric loss (tan δ) at 1 kHz of the capacitor before and after the charge / discharge test, respectively.
Is the rate of change of the dielectric loss (tan δ) at 1 kHz.] Next, a method for producing a biaxially oriented polypropylene film of the present invention and a capacitor using the same as a dielectric will be described below, but is not necessarily limited thereto. Not something.

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, 50
It is wound around a casting drum maintained at a temperature of 85 ° C. and solidified by cooling to produce an unstretched film. At this time, if the casting drum temperature is too high, the crystallization of the film proceeds too much, and it may be difficult to stretch in a subsequent step.

Next, the unstretched film is biaxially stretched and biaxially oriented. First, unstretched film is 120-150
The sheet is preheated by passing through a roll maintained at a temperature of 140 ° C. to 155 ° C., and subsequently passed between rolls provided with a peripheral speed difference, stretched 2 to 6 times in the longitudinal direction, and immediately brought to room temperature. Cooling. The polypropylene film having a mmmm of more than 99% of the present invention has a preheating temperature of less than 130 ° C. and a stretching temperature of less than 140 ° C. may cause insufficient stretching due to insufficient heat, and may not be able to form a film due to uneven stretching. It is important to employ a stretching temperature of 145 ° C. or higher.

Subsequently, the obtained stretched film was guided to a stenter and 5-1 to 165.degree.
The film is stretched 5 times, and then heat-set at a temperature of 150 to 160 ° C. while giving a 2 to 20% relaxation in the width direction, and wound.

After stretching in the width direction, stretching in the longitudinal direction again before performing heat setting is effective for obtaining the preferable elastic modulus of the present invention. The stretching temperature for such re-stretching is preferably 155 to 170 ° C. and the stretching ratio is about 1.1 to 2 times, from the viewpoint of film-forming stability.

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

Further, aging the wound film in an oven or room controlled at an atmosphere of 50 to 80 ° C. for at least 5 hours is effective for obtaining a film having a preferable elastic modulus of the present invention. It is. If the ambient temperature is lower than 50 ° C., the aging effect is hardly obtained. If the temperature is higher than 80 ° C., the film shrinks to cause tightness of the film, which may cause wrinkles or poor flatness.

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. Thereafter, the capacitor is wound into an element shape, hot-pressed and formed into a flat shape, and is subjected to metal spraying (metallicon process) at the end, a lead is taken out, and a capacitor is formed through the exterior.

Here, as a method of manufacturing a capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric, a metal (including an alloy) such as aluminum, copper, zinc, tin, solder, etc. Any of these may be used, but taking advantage of the features of heat resistance and high elastic modulus of the film of the present invention, in particular, a melting temperature of 100 to 20.
The use of a metal (including an alloy) at 0 ° C. is preferably employed in order to reduce thermal spray spots and improve the current resistance of the capacitor. Also, a method in which a metal having good electrical adhesion to the metal layer on the film surface is thermally sprayed on the first layer, which is referred to as a two-layer metallikon process, and a metal on which a lead wire is easily bonded is sprayed thereon. good.

In the case where the biaxially oriented polypropylene film of the present invention is used as a dielectric and a thermosetting resin is used in the exterior step of the production of a capacitor, the heat resistance and high elastic modulus of the film of the present invention can be improved. Taking advantage of the features, the curing temperature can be set higher than before to shorten the curing time and improve the productivity.

The biaxially oriented polypropylene film of the present invention can be used in various packaging applications, for example, by laminating it with a heat seal layer, by utilizing its heat resistance and high elastic modulus in addition to the above-mentioned capacitor applications. Further, it can be suitably used as an adhesive tape, a polishing film (print laminate), or 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, sufficiently washed 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 (1). II = (W ′ / W) × 100 (%) (1)

(2) Isotactic Pentad Fraction A sample was dissolved in o-dichlorobenzene, and JN
Using an M-GX270 device, a resonance frequency of 67.93 MH
The ¹³ C-NMR was measured at z. For the assignment of the obtained spectra and the calculation of the pentad fraction, see T.W. Hay
, et al. [Polymer, 29, 13]
8 to 143 (1988)], the peak derived from the mmmmmm was 21.855 for the spectrum derived from the methyl group.
Each peak was assigned as 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%) Sample concentration: 15 to 20 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 times: 8168 Measurement mode: Noise decoupling

(3) Modulus of elasticity According to the method specified in ASTM-D882, 23
The film was measured 10 times in the longitudinal direction and the width direction of the film under the conditions of ° C. and 50% RH, respectively, and the average value was used as the measured value.

(4) Film thickness The film thickness was measured using a dial gauge thickness gauge (JIS-B-7503).

(5) Heat Shrinkage The film was machined 260 mm long in the machine direction and in the width direction.
Sampling is performed 10 mm in width, a mark is placed at 30 mm from both ends, and the original size (L ₀ : 200 mm) is obtained. A weight of 3 g was applied to the lower end of this sample,
And heat-treat 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 (2), 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 (%) (2)

(6) 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 measured in, was determined from the following equation (3).

Ash content = (W ₁ / W ₀ ) × 1,000,000 (ppm) (3) W ₀ : initial weight (g) W ₁ : ashing weight (g)

(7) Evaluation of vapor deposition processability The following judgment was made based on the yield in the vapor deposition process.

：: yield is 95% or more Δ: yield is 90 to 95% X: yield is less than 90%

(8) Evaluation of yield in metallurgical process The end of the capacitor element manufactured up to the pressing process was sprayed with a metal mainly composed of aluminum (melting temperature: 150 ° C.), and a DC high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd. Connect to 2
A voltage was applied while increasing the voltage at a rate of 50 V / sec at 5 ° C. and 65% RH, and the voltage when the element was destroyed was determined. At this time, 1000 elements were measured, and the breakdown voltage was 100
The number of defective elements less than V / μm was determined as follows.
Divided into ranks.

A: The number of defects is 3 or less, and the yield is good. B: The number of defects is 4 to 10, but there is no problem. C: The number of defects exceeds 10 and there is a problem in practical use.

(9) Element Dielectric Breakdown Strength A capacitor element maintained at 105 ° C. in a hot air oven was connected to an AC high-voltage stabilized power supply (frequency 60
Hz), and a voltage was applied while increasing the voltage at a rate of 200 V / sec. The voltage when the element was broken was determined, and the average value of 10 measured elements was defined as the element breakdown strength.

(10) Element Life Test An AC voltage of 60 V / μm per film thickness (frequency 6
0 Hz) is continuously applied to the capacitor element, and 105
The time until the device was destroyed in an atmosphere of ° C. was measured.

(11) Evaluation of Current Resistance Under an atmosphere of 23 ° C. and 65% RH, 7 per film thickness
A DC voltage of 0 V / μm is applied to a capacitor element (a sample that was not defective in the yield evaluation of the metallicon process).
The cycle of charging for 30 seconds at a cycle of 1 minute and discharging for 5 minutes and 30 seconds is defined as 1 cycle, and 1000 cycles are performed.
△ D of 100 capacitor elements per test is 2
Evaluation was made with the number of capacitor elements exceeding 00%. The smaller the number, the better the current resistance and the ΔD
When mounted on a charging / discharging circuit such as a strobe light, a capacitor element having 200% or less has a very small dielectric breakdown, and a capacitor excellent in security can be obtained.

ΔD (%) = (D ₁ / D ₀ ) × 100 (4) (where D ₀ and D ₁ are 1 kHz dielectric loss (tan δ) of the capacitor before and after the charge / discharge test, respectively, and Δ D
Is the rate of change of the dielectric loss (tan δ) at 1 kHz)

[0079]

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

(Example 1) II: 99.0%, mmmm
Is 99.6%, the ash content is 14 ppm, the melt flow rate is 3.7 g / 10 min, and the polypropylene raw material is 2,6-di-t-butyl-p-cresol (BHT) 3000 pp.
m, to which 4,000 ppm of telorakis [methylene-3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane (Irganox1010) was added and fed to an extruder and melted at a temperature of 280 ° C. The sheet was extruded into a sheet from a die and wound around a casting drum at a temperature of 83 ° C. to be cooled and solidified. Then, the sheet is
It was preheated at 43 ° C., and then passed between rolls provided with a peripheral speed difference while maintaining the temperature at 148 ° C., and stretched 4.8 times in the longitudinal direction. Subsequently, the film was guided to a tenter, stretched 11 times in the width direction at a temperature of 158 ° C., and then subjected to a heat treatment at 150 ° C. while giving 10% relaxation in the width direction to 3.3 μm.
To obtain a biaxially oriented polypropylene film having a thickness of Further, a corona discharge treatment was performed in the atmosphere at a treatment intensity of 30 W · min / m 2.

Then, the obtained film was aged in an atmosphere of 60 ° C. for 24 hours while being wound on a roll, and was again rewound. II of the obtained film was 98.9% and mmmm was 99.5%. 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 / □. This film is slit, the total width is 38 mm,
A metallized film with a margin width of 1 mm was obtained. An element was wound using a pair of two reels of the obtained film, and the end face of the element was thermally sprayed with a metal containing aluminum as a main component (melting temperature: 150 ° C.), and a lead wire was taken out therefrom to prepare a capacitor element having a capacity of 5 μF. . Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

(Comparative Example 1) II was 97.7%, mmmm
Is 99.3%, the ash content is 18 ppm, the melt flow rate is 4.2 g / 10 min, and a polypropylene film (II is 97.6) is prepared in the same manner as in Example 1 except that the aging treatment is not performed. %, Mmm
m is 99.1%) to obtain a capacitor element. In addition, it was difficult to set the film tension at the time of vapor deposition, and film tearing and vapor deposition spots occurred frequently. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Comparative Example 2 A polypropylene film (II: 97.6%, mmmm: 9 mm) was prepared in the same manner as in Example 1 except that the same polypropylene raw material as in Comparative Example 1 was used.
9.1%) and a capacitor element were obtained. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

(Comparative Example 3) II was 99.8%, mmmm
Was manufactured in the same manner as in Example 1 except that a polypropylene raw material was used, which was 99.9%, an ash content was 11 ppm, and a melt flow rate was 2.2 g / 10 min. As a result, the film was frequently broken, and the film could not be collected stably.
The II of the film collected without breaking was 99.7%, mm
mm was 99.9%.

Comparative Example 4 II: 98.4%, mmmm
Using a polypropylene raw material of 98.9%, an ash content of 23 ppm, and a melt flow rate of 4.4 g / 10 min.
8.3%, mmmm is 98.6%) to obtain a capacitor element. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Comparative Example 5 The same polypropylene raw material as in Example 1 was used, and the preheating temperature in the longitudinal stretching was 142 ° C.
A polypropylene film (II: 99.0) was prepared in the same manner as in Example 1 except that the stretching temperature in the longitudinal direction was set to 144 ° C.
%, Mmmm is 99.6%) to obtain a capacitor element. In addition, it is difficult to set the film tension during evaporation,
Frequent film tears and evaporation spots. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

(Example 2) The same method as in Example 1 was used except that the same polypropylene raw material as in Example 1 was used, and after stretching in the width direction, re-stretching was performed 2.5 times in the longitudinal direction at 160 ° C. Polypropylene film (II is 99.0%, mmm
m is 99.6%) to obtain a capacitor element. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Example 3 A polypropylene film (II: 99.0%, mmmm: 99.0%) was produced in the same manner as in Example 2 except that the redrawing ratio in the longitudinal direction was 1.5 times.
6%) and a capacitor element. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Example 4 A polypropylene film (II: 99.0%, mmmm: 99.6) was prepared in the same manner as in Example 3 except that aging was performed at 60 ° C. for 24 hours.
%) And a capacitor element. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Comparative Example 6 A trial production of a polypropylene film was conducted in the same manner as in Example 2 except that the magnification of the re-stretching in the longitudinal direction was changed to 3.0, but the film was frequently broken during the re-stretching. The film could not be stably collected. Table 1 summarizes the evaluation results of the films that could be collected without breaking.

(Example 5) A polypropylene film (II: 99.0%, mmmm: 99.6%) and a capacitor element were obtained in the same manner as in Example 1 except that the aging temperature was 90 ° C. In addition, wrinkles were formed in the longitudinal direction of the film at the time of aging, and the flatness was slightly deteriorated. Table 1 summarizes the evaluation results of the obtained polypropylene films and capacitor elements.

Example 6 A capacitor element was prepared in the same manner as in Example 1 except that the metal used for the metallikon was a metal containing aluminum as a main component (melting temperature: 210 ° C.). Table 2 summarizes the evaluation results of the obtained capacitor elements.

Example 7 A capacitor element was produced in the same manner as in Example 1 except that the metal used for the metallikon was a metal composed of tin and lead (melting temperature: 80 ° C.). Table 2 summarizes the evaluation results of the obtained capacitor elements.

Comparative Example 7 A capacitor element was prepared in the same manner as in Comparative Example 4, except that the metal used for the metallikon was a metal consisting of tin and lead (melting temperature: 80 ° C.). Table 2 summarizes the evaluation results of the obtained capacitor elements.

[0095]

[Table 1]

[0096]

[Table 2]

[0097]

According to the present invention, there is provided a polypropylene film which is excellent in heat resistance and long-term dielectric breakdown resistance at high temperatures, suppresses the deterioration in the yield of the capacitor manufacturing process, and reduces the variation in quality. A capacitor having excellent heat resistance, long-term dielectric breakdown resistance at high temperatures, and current resistance using a polypropylene film as a dielectric can be obtained.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 7:00 31:34 C08L 23:12

Claims (5)

[Claims] A biaxially oriented polypropylene film having an isotacticity of 98-9.
9.5% and an isotactic pentad fraction of 9
Exceeds 9%, and the sum of the elastic modulus in the longitudinal direction and the width direction is 7 to
A polypropylene film having a pressure of 10 GPa. 2. The polypropylene film according to claim 1, wherein the elastic modulus in the width direction is 4.5 to 6.5 GPa. 3. A capacitor comprising the polypropylene film according to claim 1 as a dielectric. 4. A capacitor comprising the polypropylene film according to claim 1 as a dielectric, and a metal layer provided as an internal electrode on at least one surface of the film. 5. The capacitor according to claim 3, wherein ΔD represented by the following formula is 200% or less. ΔD (%) = (D ₁ / D ₀ ) × 100 [where D ₀ and D ₁ are the dielectric loss (tan δ) at 1 kHz of the capacitor before and after the charge / discharge test, respectively.
Is the rate of change of the dielectric loss (tan δ) at 1 kHz]