JPH11286071A - Metallized polypropylene film - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A capacitor that further improves dielectric breakdown resistance and suppresses a decrease in capacitance and an increase in dielectric loss tangent due to corona generation during long-term use at high temperatures without using an insulating oil. A metallized polypropylene film. In a metallized polypropylene film provided with a metal layer on at least one side, a thermal dimensional change rate in a longitudinal direction of the film generated in a temperature rising process from 30 ° C. and an isotacticity of a polypropylene constituting the metallized polypropylene film. And the isotactic pentad fraction is a specific value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metallized polypropylene film in which a metal layer is provided on at least one side of a polypropylene film, and more particularly, to a method using a polypropylene film portion of the metallized polypropylene film as a dielectric of a capacitor. In this case, the present invention relates to a metallized polypropylene film which has a small change in capacitance and dielectric loss tangent even when used for a long time at a high temperature and can provide a capacitor excellent in security.

[0002]

2. Description of the Related Art Metallized polypropylene films are widely used in packaging and capacitor applications due to their excellent mechanical properties, water vapor barrier properties and electrical properties.

[0003] Generally, a polypropylene film is one of the typical materials used as a dielectric for a film capacitor. However, the polypropylene film has a small dielectric loss tangent as compared with a polyester film which is another typical material.
Although it is suitably used as a condenser to be loaded in an AC circuit, the maximum operating temperature is limited to about 85 ° C. The reason for this is that when the operating temperature rises, the dielectric breakdown strength, which should be a feature of the polypropylene film, suddenly drops due to the effects of the amorphous portion of the film and foreign substances, and it can withstand long-term use. This is because it sometimes disappeared.

[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] 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, capacitors that have been used in AC circuits have traditionally been impregnated with insulating oil between film layers to suppress corona generated when AC voltage is applied. Because of the necessity of increasing the capacitance per unit, there is a strong demand that the insulating oil be used without impregnation. That is, conventionally, the capacitor was immersed in insulating oil, and the gap between the film layers was filled with the insulating oil.However, if the insulating oil is used, the capacitor is sealed in the case, and the insulating oil does not leak from the capacitor. Therefore, there is a problem that the shape of the condenser is inevitably increased.

[0006] In order to overcome the above problems, (1)
There is a need for a film that has excellent electrical properties at high temperatures and (2) can suppress corona generation without being impregnated with insulating oil at high temperatures.

[0007] Regarding the problem (1), 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. 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
Propylene polymers in the range of 95 and molded articles using the same have been proposed.

However, as proposed in these publications, a biaxially oriented polypropylene film having only a high isotactic pentad fraction of the boiling n-heptane-insoluble portion has a high insulation resistance at a high temperature exceeding 85 ° C., which is the object of the present invention. 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.

As a technique for overcoming this drawback, Japanese Patent Publication No. 4-28727 discloses that the isotactic pentad fraction is in the range of 0.960 to 0.990, and that boiling n-hexane and A crystalline polypropylene film excellent in moldability has been proposed by setting the total amount of the extract to be extracted sequentially with n-heptane to 3.0 to 6.0%. However, the isotactic pentad fraction was not sufficient, and the dielectric breakdown resistance at high temperatures was insufficient.

Regarding the problem (2), studies have been made to reduce the gap between the film layers.
It has been widely adopted to apply heat to a capacitor element formed by winding a film to make use of the heat shrinkage of the film to tighten the film. For example, JP-A-7-502
No. 24 discloses a metallized polypropylene film having a heat shrinkage at 120 ° C. of 4.0% or less in a length direction and 0.8% or less in a width direction. A capacitor wound with such a film can suppress corona generation at room temperature, but as the ambient temperature to which the capacitor is exposed increases, corona is generated and the capacitance decreases during long-term use. When the isotacticity and stereoregularity of the film used are conventional, the dielectric breakdown resistance at a temperature exceeding 85 ° C., which is the aim of the present invention, is particularly high. Was not enough.

[0012]

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 isotactic pentad fraction of the polypropylene film to a high degree. In addition, by adopting appropriate film forming conditions to set the thermal dimensional change rate in a specific range, the dielectric breakdown resistance characteristic of the polypropylene film, which could not be achieved by the conventional technology, is further improved. The present inventors have found that a capacitor capable of suppressing a decrease in capacitance and an increase in dielectric loss tangent due to corona generation during long-term use at a high temperature without using an insulating oil can be obtained, which has led to the present invention.

An object of the present invention is to suppress corona generated when used for a long time at a high temperature in an AC circuit without being impregnated with insulating oil due to a demand for miniaturization of a capacitor because of a demand for miniaturization of a capacitor. It is an object of the present invention to provide a metallized polypropylene film which can be used as a capacitor with less decrease in dielectric loss and increase in dielectric dissipation factor.

[0014]

SUMMARY OF THE INVENTION The present invention achieves the above object and has a thermal dimensional change rate in the longitudinal direction of a film which is increased from 30 ° C to 120 ° C.
A metal layer is provided on at least one surface, characterized in that the polypropylene constituting the film has an isotacticity of 98 to 99.5% and an isotactic pentad fraction of more than 99%. Metallized polypropylene film.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The polypropylene used for the metallized polypropylene film of the present invention is mainly composed of a propylene homopolymer, but other copolymerized components such as unsaturated hydrocarbons may be used as long as the object of the present invention is not impaired. And a polymer other than propylene alone may be blended. Examples of such a copolymer component or a monomer component constituting the blend include ethylene, propylene (in the case of a copolymerized blend), 1-butene, 1-pentene, 3-methylpentene-1, and 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 or the blend amount is preferably less than 1 mol% from the viewpoint of dielectric breakdown resistance and heat resistance, and the blend amount is preferably less than 10% by weight.

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
In producing a biaxially oriented film as disclosed in Japanese Patent Publication No. 236709, 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. More preferable isotacticity is 98.5 to 99.5% for good film forming property, heat resistance and dielectric breakdown resistance, and more preferably 9 to 99.5%.
8.7 to 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, T.D. 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% or more in terms of high heat resistance and high dielectric breakdown resistance. It is.

In order to impart such stereoregularity, it is effective to control the stereoregularity of the polypropylene resin as a raw material 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 polymerization process of the polypropylene used in 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 after the polymerization, if necessary. Competition can be evaluated by determining the amount of metal oxide remaining 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 at most 30 ppm, more preferably at most 25 ppm, even more preferably at most 20 ppm.

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 such a 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, reducing the bleed time to 1 hour A method such as the above-mentioned method can be adopted.

Known additives such as a nucleating agent, an antioxidant, a heat stabilizer, a slipping 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 a coloring inhibitor.

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 preferably in the range of 0.03 to 1% by weight (300 to 10000 ppm) based on the total amount of polypropylene. 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, but is preferably 1 to 10 from the viewpoint of film forming property.
Those in the range of dl / g are preferred. 230 ° C,
The melt flow rate under a load of 2.16 kg is preferably from 1 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 used in the present invention is obtained by using a raw material capable of giving the above-mentioned properties and performing biaxial orientation. An unoriented film cannot provide a film having high crystallinity, high heat resistance, and high dielectric breakdown resistance, which is the object of the present invention. The biaxial orientation method 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, the film forming stability and thickness uniformity are controlled. In this respect, a film formed by a stenter sequential biaxial stretching method is preferably used.

The thickness of the biaxially oriented polypropylene film used in the present invention is desirably from 2 to 30 μm, preferably from 2.5 to 30 μm, from the viewpoint of film forming properties, mechanical properties and electrical properties.
２０20 μm. If the thickness of the film is too small, the dielectric breakdown strength and mechanical strength may be poor, and the film may be damaged due to metallization, particularly heat loss.
On the other hand, 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 center line average surface roughness of both surfaces of the biaxially oriented polypropylene film used in the present invention is preferably 0.01 to 0.4 μm.
If the center line average roughness is too large, air will enter between the film layers when the films are laminated, leading to deterioration of the capacitor element. In some cases, the dielectric breakdown strength and element life of the device may be reduced, or charges may be concentrated when a voltage is applied, which may cause insulation defects. On the other hand, if it is too small, the film slides poorly and may be inferior in handleability. A more preferable range of the center line average surface roughness of both surfaces of the film is 0.03 to 0.3 μm, most preferably 0.03 to 0.3 μm.
4 to 0.25 μm.

Further, the maximum roughness of both sides of the biaxially oriented polypropylene film used in the present invention is 0.1
The range is preferably from 4.0 to 4.0 μm, and more preferably from 0.1 to 4.0 μm.
3 to 3.0 μm. When the maximum roughness is less than 0.1 μm, the slipperiness is deteriorated, air escape is poor, and vertical wrinkles and the like enter,
The winding property and the handling property may decrease. On the other hand, if Rt exceeds 4.0 μm, the surface becomes too rough, and when the films are laminated, air enters between the layers and not only leads to deterioration of the capacitor element, but also causes film breakage,
Productivity may decrease.

The metallized polypropylene film of the present invention can be obtained by forming a metal layer on at least one surface of the above-mentioned biaxially oriented polypropylene film. When a film without a metal layer is used as a dielectric of a capacitor, the shape of the capacitor becomes large due to the necessity of using a metal foil as an electrode inside the capacitor, and it is not possible to meet the demand for downsizing. In addition, by providing a metal layer on at least one surface of the film as an internal electrode, the capacitor can be provided with a self-healing ability of a dielectric breakdown portion called self-healing to further maintain security.

If necessary, the metallized polypropylene film of the present invention may be provided with a portion having no metal layer in an area ratio of 5% or less. In the case where the metallized polypropylene film of the present invention is used for a capacitor, a portion without an metal layer (insulating groove) is generally provided in a stripe shape in the longitudinal direction in order to insulate a pair of electrodes from each other. It is a target.

The method of forming a metal layer on at least one side of the biaxially oriented polypropylene film in the metallized polypropylene film of the present invention is not particularly limited, and examples thereof include a vacuum deposition method, a sputtering method, and an ion beam method.

In the present invention, the metal used for the metal layer is preferably aluminum, zinc, copper, tin, silver, nickel, etc., alone or in combination, in view of the durability and productivity of the metallized layer. It is more preferable to use a metal containing zinc as a main component because the capacitor has corona resistance. Here, the metal as the main component indicates that it is 50% by weight or more of the metal forming the metal layer. In order to actually determine the content of each metal constituting the metal layer, first, a certain amount of the metal layer is dissolved using hydrochloric acid, and then the content of each metal is measured by a plasma emission spectrometer (ICP). Is preferably employed. Further, an alloy using zinc as a main component as a metal layer and aluminum as a metal other than the main component is more preferable because both the corona resistance and the self-healing property (self-healing property) when an appropriate capacitor is broken are compatible. . When an alloy of zinc and aluminum is used, the content of zinc is preferably 80% by weight or more and 95% by weight or less, and aluminum is most preferably 5% by weight or more and 20% by weight or less.

Further, it is preferable to perform a corona discharge treatment or a plasma treatment on the surface of the biaxially oriented polypropylene film used in the present invention, on which the metal layer is to be 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 of subjecting various gases to a plasma state and chemically modifying the film surface can be employed.
There is a method described in JP-A-98140.

In the present invention, the film resistance of the metallized polypropylene film is preferably in the range of 1 Ω / □ to 20 Ω / □. More preferably 1.5Ω / □ to 15Ω
/ □. If the film resistance value is too small, the thickness of the deposited film is so large that heat loss occurs during the deposition, resulting in an avatar-shaped surface defect or 4 μm.
In the front and rear thin films, holes may occur, and furthermore. If the film resistance value is too large, the dielectric loss tangent deteriorates, and the long-term breakdown voltage may not be maintained due to heat generated from the inside of the capacitor during AC application. 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.

Further, in the present invention, the film resistance of the metal layer continuously changes in the film width direction, and the contact portion with the external electrode has the lowest film resistance and is close to the insulating groove, ie, substantially the film dielectric. It is preferable that a portion that actually functions as an internal electrode across the body has a relatively high film resistance value. Specifically, a minimum of 2Ω / □ to a maximum of 10
It is preferable to provide a configuration in which a metal layer whose resistance continuously changes in the range of Ω / □ is provided. Such a configuration reduces the strength of the metal flux in the film width direction by installing a comb-shaped anti-blocking plate extending in the running direction of the base film between the base film and the metal when forming the metal layer. It can be achieved by providing.

Further, in the present invention, the specifications of the insulating grooves (portions without the metal layer provided on the surface where the metal layer is formed for the purpose of electrical insulation) provided when the metal layer is formed on the biaxially oriented polypropylene film are as follows. In addition to the normal type, it can be adopted according to the purpose such as various types provided with a fuse mechanism, and particularly, a metal layer serving as an internal electrode is provided at one end in the width direction of the film with an insulating groove portion continuously in the longitudinal direction of the film. An internal electrode that is formed and formed and has a security function of electrically insulating an internal electrode around the discharge breakdown from other internal electrode portions where no discharge occurs by a current when a discharge breakdown occurs in the film. Is preferable because the change in capacitance after continuous use of the capacitor can be minimized.

The inventors of the present invention have conducted intensive studies on a technique for suppressing the generation of corona in the capacitor without impregnating the insulating oil. As a result, the gap (air layer) between the film layers of the capacitor element is closely related to the generation of corona. Focusing on the relationship, the inventors have found that a film in which the gap between the film layers of the capacitor element does not greatly expand within the operating temperature range of the capacitor can suppress corona, and arrived at the present invention.

Conventionally, as a method of reducing the gap between the film layers, it has been widely adopted that the film is wound and heated by applying heat to the element of the capacitor to utilize the heat shrinkage of the film to tighten the film. The condensed condenser was able to suppress corona generation at room temperature. However, it has been found that as the ambient temperature to which the condenser is exposed increases, corona starts to be generated, and in particular, a phenomenon occurs in which the use at a temperature exceeding 85 ° C., which is the aim of the present invention, cannot be tolerated. This has been found to be due to the reversible thermal expansion inherent in the film as the ambient temperature of the condenser increases. In other words, at room temperature, at first glance, the film is tightly wound, and even with a capacitor that does not generate corona, as the temperature rises, the film undergoes thermal expansion, and as a result, the film starts to loosen tightly. It has been found that corona is generated due to a gap between the layers. Therefore, as described above, when adopting a method of applying heat to the element and tightening by utilizing irreversible heat shrinkage of the film, even if a capacitor is used at a high temperature, only a gap is not generated between the film layers. It is necessary to perform sufficient shrinkage.

As a material for judging how much film shrinkage is necessary, a method of tracking a thermal dimensional change rate when a constant load is applied to the film and the ambient temperature is increased is preferably adopted. Is done. The advantage of this measurement method is that, as in the measurement method described in JIS-C2318 and the like, the film sample is exposed to an oven at a constant temperature for a certain period of time, then the film sample is taken out, and the dimensions of the film sample returned to room temperature and before being put in the oven Unlike the thermal shrinkage rate, which is determined as the difference from the size of the film, the temperature dependence of the dimensional change of the film sample can be measured by taking into account the reversible and irreversible thermal expansion of the film at each temperature. It is in. By adopting such a measuring method, for example, when it is desired to use a capacitor even under a temperature condition of about 120 ° C., the thermal dimensional change taking into account the reversible thermal expansion and irreversible thermal shrinkage of the film at 120 ° C. It is sufficient that the rate is 0% or the contraction side.

As described above, in the metallized polypropylene film of the present invention, the rate of change in thermal dimensional in the longitudinal direction of the film in the process of raising the temperature from 30 ° C. must be 0 to 2% at 120 ° C. In addition, the thermal dimensional change rate at 120 ° C. in the longitudinal direction of the film generated in the process of raising the temperature from 30 ° C. is defined as follows. That is, Vacuum Engineering Co., Ltd.
A film sample is sampled into a strip having a width of 5 mm in a longitudinal direction of a film having a width of 5 mm, and a sample holder is self-weighted in a longitudinal direction by using a measurement module TM-9400 made by the company and a thermal analysis system MTS-9000 made by the company as a data analyzer. And the temperature is raised from 25 ° C. at a rate of 10 ° C./min under a constant load of 0.8 MPa. The initial length of the sample is 15 mm. At this time, the film sample length L ₃₀ (mm) at 30 ° C. and 12
0 obtains a film sample length L _{12 0} (mm) at ° C., is defined to calculate the heat dimensional change by the following equation (1).

Thermal dimensional change rate = (L ₃₀ −L ₁₂₀ ) / 15 × 100 (%) (1)

If the thermal dimensional change rate in the longitudinal direction is less than 0% at 120 ° C., corona is generated when the capacitor is used in a high temperature region around 120 ° C., so that the capacitance decreases due to the deterioration of the metal layer. An increase in the dielectric loss tangent occurs. On the other hand, if it exceeds 2%, it can withstand use in a high-temperature region, but when used near room temperature, excessive stress is applied to the dielectric film, so that the dielectric breakdown resistance becomes poor. The thermal dimensional change rate in the longitudinal direction of the metallized polypropylene film of the present invention in the longitudinal direction which occurs during the temperature rise process from 30 ° C. is more preferably 0.5 to 1.5% at 120 ° C.

Further, in the metallized polypropylene film of the present invention, the rate of change in thermal dimension in the width direction of the film in the process of raising the temperature from 30 ° C. is preferably in the range of −1 to 1% at 120 ° C. Thermal dimensional change rate in the width direction is 120 ° C
If it is less than -1% or more than 1%, the contact with the external electrode becomes poor, which may be one factor of the deterioration of the dielectric loss tangent. From this viewpoint, the thermal dimensional change rate in the width direction of the film is 1
More preferably, it is in the range of -0.5 to 0.5% at 20C.

Next, the method for producing the metallized polypropylene film of the present invention will be described below, but is not necessarily 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. At this time, if the temperature of the casting drum is too high, the crystallization of the film proceeds too much, and it may be difficult to perform stretching in the subsequent step.

Next, this unstretched film is biaxially stretched,
Make it biaxially oriented. First, the unstretched film is
The sheet is preheated by passing through a roll maintained at 0 ° C., and subsequently, the sheet is passed through a roll provided with a peripheral speed difference maintained at a temperature of 140 ° C. to 150 ° C., stretched 2 to 6 times in the longitudinal direction, and immediately at room temperature. Cool. When the mmmm exceeds 99% of the polypropylene film of the present invention, if the preheating temperature is 130 ° C. or lower and the stretching temperature is 140 ° C. or lower, the calorific value may be insufficient to cause uneven stretching or tearing, and the film may not be formed. It is important to adopt

Subsequently, the stretched film was guided to a stenter, stretched 5 to 15 times in the width direction at a temperature of 155 to 165 ° C., and then given 2 to 20% relaxation in the width direction.
Winding with heat setting at a temperature of 130 to 150 ° C.

[0050] As the polypropylene film biaxially oriented can be applied to metallized polypropylene film of the present invention, or employing a low melt flow rate polypropylene material, the birefringence as optimized stretching conditions -2X10 ^{- It} is effective to control the temperature within the range of ² to ^-1 × 10 ⁻² or to lower the heat setting temperature within a range where the thickness unevenness of the film does not deteriorate.

Thereafter, in order to improve the adhesion of the deposited metal to the surface on which the biaxially oriented polypropylene film is to be deposited, a corona discharge treatment is performed in air, nitrogen, carbon dioxide, or a mixed gas thereof to winder. And take up.

The obtained film is set in a vacuum deposition apparatus, and a metal suitable for the purpose is deposited on a predetermined film resistance. Further, if necessary, oil may be applied by gravure coating or the like before vapor deposition to form an insulating groove, and a method in which a portion to which the oil is applied is not deposited can be adopted.

[0053]

EXAMPLES Examples of the present invention will be shown below and will be described in more detail. In addition, about the measuring method of physical property and evaluation,
This was performed by the method described below.

(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.

II = (W '/ W) × 100 (%)

[0056] (2) was dissolved isotactic pentad fraction samples o- dichlorobenzene / benzene -D _6, using a JEOL Ltd. JNM-GX270 apparatus was measured ¹³ C-NMR at the resonant frequency 67.93MHz . For the assignment of the obtained spectra and the calculation of the pentad fraction, see T.W. The method performed by Hayashi et al. [Poly
mer, 29, 138-143 (1988)].
The peak was assigned to 21.855 ppm, each peak was assigned, 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 -D ₆ (10 wt%) Sample concentration: 15~20wt% Measurement temperature: 120 to 130 ° C. resonance frequency: 67.93MHz Pulse width: 10 .mu.sec (45 ° pulse) Pulse repetition time: 7.091Sec data points ： 32K Total number of times ： 8168 Measurement mode ： Noise decoupling

(3) Thermal dimensional change rate Measuring module TM-9400 manufactured by Vacuum Riko Co., Ltd. and a thermal analysis system MTS- manufactured by the company as a data analyzer.
Using a 9000 type, a film sample is sampled in a long strip shape in the direction of measurement of a film having a width of 5 mm from a film having a width of 5 mm. The temperature was raised at a rate of 10 ° C./min. The initial length of the sample was 15 mm. At this time, the film sample length L ₃₀ (mm) at ₃₀ ° C. and the film sample length L ₁₂₀ (mm) at 120 ° C. were determined, and the thermal dimensional change was calculated by the following equation (1).

Thermal dimensional change rate = (L ₃₀ −L ₁₂₀ ) / 15 × 100 (%) (1)

(4) Measurement of birefringence In accordance with the method specified in JIS-K7105, the refractive index in the longitudinal direction and the width direction was measured using an Abbe refractometer with sodium D line as a light source (nMD and nT, respectively).
D). Here, the mounting liquid was measured using methyl salicylate at 25 ° C. and 65% RH. Next, birefringence was calculated by the following equation (2). In addition, the measurement of the vapor deposition film was performed after immersing the vapor deposition film in 1N sodium hydroxide aqueous solution once, dissolving a vapor deposition metal, and washing with purified water.

Birefringence = nMD−nTD (2)

(5) 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 : Ash weight (g)

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

(7) Element Dielectric Breakdown Strength A capacitor element maintained at 25 ° C. and 115 ° C. was connected to an AC high-voltage stabilized power supply (frequency 60
Hz), 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 at each temperature.

(8) Element Life Test The capacitance C ₀ and the dielectric loss tangent D ₀ at 25 ° C. of each of the ten capacitor elements were measured before the life test was started. Next, each capacitor element was placed in an oven at 115 ° C., and an AC voltage (60 Hz) was continuously applied for 6 hours, and a continuous application for 2 hours was repeated for 200 cycles. The AC voltage value is 65 to the film thickness of the polypropylene film used as the dielectric.
V / μm. Next, for each capacitor element that has been subjected to the 200-cycle high-temperature load test, 25
The capacitance C ₁ and the dielectric loss tangent D ₁ at ℃ are measured, and the capacitance change rate ΔC and the dielectric loss tangent change ΔD before and after the life test are obtained for each of the capacitor elements from the following formula. (If there is a capacitor element broken during the life test,
The average value was calculated excluding the broken capacitor element). It can be said that the smaller the rate of change, the better the capacitor.

ΔC = (C ₁ −C ₀ ) / C ₀ × 100 (%) ΔD = (D ₁ −D ₀ ) / D ₀ × 100 (%)

(9) Center line average surface roughness, maximum roughness (hereinafter referred to as Ra and Rt, respectively) Measured using a stylus type surface roughness meter according to JIS-B0601. In addition, using a high-precision thin film step measuring device (model: ET-10) manufactured by Kosaka Laboratory Co., Ltd., a stylus diameter cone type 0.5 μmR, load 5 mg, cut-off is 0.08 mm.
And

(Comparative Example 1) II was 99.0%, mmmm
99.3%, ash content 15ppm, intrinsic viscosity 1.8d
l / g, polypropylene having a melt flow rate of 2.8 g / 10 min, 3000 ppm of 2,6-di-t-butyl-p-cresol (BHT), 1,3,5-trimethyl-
2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene (for example, Iriba manufactured by Ciba-Geigy)
ganox1330) A polypropylene raw material added with 4000 ppm is supplied to an extruder, melted at a temperature of 280 ° C., extruded into a sheet form from a T-type die, wound around a casting drum at a temperature of 85 ° C., cooled and solidified, and the sheet is cooled. Was peeled off from the casting drum, and then gradually cooled with a roll at 60 ° C. to return to room temperature.

Next, the obtained sheet was preheated at 143 ° C., continuously passed between rolls having a peripheral speed difference maintained at a temperature of 148 ° C., and stretched 5 times in the longitudinal direction. Subsequently, the film was guided to a tenter, stretched 8 times in the width direction at a temperature of 163 ° C., and then subjected to a heat treatment at 145 ° C. while giving a 10% relaxation in the width direction to obtain a biaxially oriented polypropylene film having a thickness of 4.5 μm. Obtained. 30W · min
The corona discharge treatment was performed in the atmosphere at a treatment intensity of / m ² .
II of the obtained film is 98.9%, mmmm is 9
9.2% and birefringence was -0.5 × 10 ^-2 .

This film was set in a vacuum vapor deposition machine, and zinc (containing 8% by weight of aluminum) was vapor-deposited on the corona-treated surface so that the film resistance was 4.0 Ω / □. At this time, as shown in FIG. 1, an insulating groove portion 2 (margin portion: 1 mm in width direction length) in which the metal layer 1 is continuous in the longitudinal direction of the film as shown in FIG. As it is formed,
The metal layer 1 is provided at intervals of 30 mm in the longitudinal direction so that the metal layer 1 is separated into a plurality of islands in the longitudinal direction of the film by the insulating grooves 3 (width of 1 mm in the longitudinal direction). Vapor deposition was performed so as to be connected by a continuous metal layer (width 1 mm) at the end and a bottleneck 4 (length 1 mm in both the longitudinal and width directions). Slit this film,
A metallized polypropylene film having a total width of 30 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

Example 1 A polypropylene film (I) was prepared in the same manner as in Comparative Example 1 except that the polypropylene raw material of Comparative Example 1 was used and the stretching in the width direction was increased 11 times at 163 ° C.
I is 98.9%, mmmm is 99.2%, and birefringence is-
1.3 × 10 ⁻² ), and then a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

(Comparative Example 2) II was 98.6%, mmmm
98.9%, ash content 15 ppm, intrinsic viscosity 1.8d
l / g, a melt flow rate of 2.8 g / 10 min. A polypropylene raw material obtained by adding the same amount of an antioxidant as in Comparative Example 1 to polypropylene, except that the stretching in the width direction was increased 11 times at 163 ° C. In the same manner as in Example 1, a polypropylene film (II: 98.5%, mmmm: 98.8%)
% And birefringence of -2.1 × 10 ^-2 ), and then Comparative Example 1
A metallized polypropylene film was obtained by the same vapor deposition method as described above. An element is wound using the obtained film pair of two reels,
Metal spraying was performed on the end face of the element, and a lead wire was taken out from the metal to form a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements. In the capacitor using the metallized polypropylene film, dielectric breakdown occurred in 5 out of 10 capacitors in the element life test.

Example 2 A polypropylene film (I) was prepared in the same manner as in Comparative Example 1 except that the polypropylene raw material of Comparative Example 1 was used and the stretching in the width direction was increased 11 times at 160 ° C.
I is 98.9%, mmmm is 99.2%, and birefringence is-
1.6 × 10 ^-2 ), and then a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

Example 3 The same procedure as in Comparative Example 1 was carried out except that the polypropylene raw material of Comparative Example 1 was stretched 11 times at 160 ° C. in the width direction and then 12% relaxation was provided in the width direction. Polypropylene film (II is 98.9%,
mmmm was 99.2% and birefringence was -1.5 × 10 ^-2 ). Then, a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

Example 4 A polypropylene film (I) was prepared in the same manner as in Comparative Example 1 except that the polypropylene raw material of Comparative Example 1 was used and the stretching in the width direction was increased by 12 times at 160 ° C.
I is 98.9%, mmmm is 99.2%, and birefringence is-
1.8 × 10 ⁻² ), and then a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

(Example 5) A polypropylene film (I) was produced in the same manner as in Comparative Example 1 except that the longitudinal direction stretching was made 5 times at 145 ° C using the polypropylene raw material of Comparative Example 1.
I is 98.9%, mmmm is 99.2%, and birefringence is-
2.2 × 10 ^-2 ), and then a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

(Comparative Example 3) A polypropylene film (I) was produced in the same manner as in Comparative Example 1 except that the polypropylene raw material of Comparative Example 1 was used and the stretching in the width direction was 12 times at 158 ° C.
I is 98.9%, mmmm is 99.2%, and birefringence is-
2.8 × 10 ^-2 ), and then a metallized polypropylene film was obtained by the same vapor deposition method as in Comparative Example 1. 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 therefrom to prepare a capacitor element having a capacity of 6 μF. Table 1 summarizes the evaluation results of the obtained metallized polypropylene films and capacitor elements.

(Comparative Example 4) II was 99.8%, mmmm
Is 99.5%, ash content is 15 ppm, intrinsic viscosity is 1.8 d
1 / g, using a polypropylene raw material having a melt flow rate of 2.8 g / 10 min. to produce a polypropylene film in the same manner as in Comparative Example 1, but the film was frequently torn after stretching in the width direction and was stable. And no film could be collected.

[0080]

[Table 1]

[0081]

As described above, the metallized polypropylene film of the present invention further improves the dielectric breakdown resistance characteristic of the polypropylene film, and further reduces the capacitance and increases the dielectric loss tangent due to corona generation during long-term use at high temperatures. Can be obtained without using an insulating oil.

[Brief description of the drawings]

FIG. 1 shows a metal layer provided on one side according to an embodiment of the present invention;
FIG. 3 is a plan view of a polypropylene film in which electrodes are separated in an island shape.

[Explanation of symbols]

 1. 1. Metal layer (internal electrode) 2. Insulation groove (margin) 3. Insulating grooves (separate electrodes into islands) bottleneck

Claims (3)

[Claims] The film has a thermal dimensional change in a longitudinal direction of from 0 ° C. to 2% at 120 ° C., and the isotacticity of polypropylene constituting the film is 98 to 99.5%. And a metallized polypropylene film provided with a metal layer on at least one surface, wherein the isotactic pentad fraction exceeds 99%. 2. The metallized polypropylene film according to claim 1, wherein the metal constituting the metal layer mainly comprises zinc. 3. The metallized polypropylene according to claim 1, wherein the rate of change in thermal dimension in the width direction of the film in the process of raising the temperature from 30 ° C. is -1 to 1% at 120 ° C. the film.