JPH1053655A - Biaxially polyprolylene film and film capacitor made thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film excellent in voltage endurance, heat resistance and yield obtained when a metal layer is provided on a film and having excellent resistance to dielectric breakdown from a room temperature to a high temperature region of 105 deg.C and suitable for capacitors. SOLUTION: This biaxially polypropylene film has <=99% isotactic index and has the following characteristics (1), (2) and (3). (1): P1>99%, (2): P2 <=0.1% and (3): P3<=0.8% in which P1 represents a ratio of absorption peak derived from mmmmm among a pentad fraction obtained from<13> C-NMR of polypropylene and P2 represents a ratio of absorption peak derived from mmrr + mmrm + rmrr + rmrm and P3 represents a ratio of absorption peak derived from rrrr + mrrr + mrrm [(m) represents meso configuration of adjacent two recurring units in polypropylene molecular chain and (r) represent racemo configuration thereof].

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 excellent in heat resistance and voltage resistance and a film capacitor using the same as a dielectric material and having excellent heat resistance and voltage resistance.

[0002]

2. Description of the Related Art Biaxially oriented polypropylene films are widely used as films for industrial materials and packaging materials, but are also used for capacitors due to their excellent electrical properties (high withstand voltage, low dielectric loss). I have. Generally, a polypropylene film for a capacitor is used by providing a metal layer made of aluminum, zinc or the like after improving the adhesiveness of the film surface by corona discharge or plasma treatment on the film surface.

[0003] By the way, the polypropylene film is one of the typical materials of a film capacitor, but has low heat resistance and its maximum operating temperature is limited to about 85 ° C. Further, as electronic components have become lighter, thinner and smaller recently, the thickness has been reduced year by year, and recently, a film having a thickness of 5 μm or less has been required. Such a thin polypropylene film has a problem in that the temperature becomes high during the formation of the metal layer, which causes thermal expansion or shrinkage, thereby causing wrinkles.
When the film has wrinkles, it may cause deterioration during use, for example, by retaining air mixed with moisture in that portion. In addition, when a capacitor element is prepared, it is generally heat-treated at a constant temperature. At this time, winding is caused by moderate heat shrinkage to maintain the shape and expel air between film layers. However, if the heat shrinkage is too large, the capacity of the capacitor may be reduced due to deformation of the element. Further, when the thickness level is 4 μm or less, the dielectric breakdown voltage of the film may be reduced due to the crystallinity of the film, the influence of foreign substances, and the like, and the film may not be practically usable.

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 of the boiling n-heptane-insoluble component are preferable.

Japanese Patent Application Laid-Open No. 7-25946 discloses that the boiling n-heptane-insoluble content is 80% by weight or more, particularly preferably 96% by weight or more, and the boiling n-heptane-insoluble content is an isotactic pentad. Fraction is 0.970 ~
There is a disclosure of a propylene polymer in the range of 0.995 and a molded article using the same.

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 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 of boiling n-heptane-insoluble component, but has an isotactic pen-soluble component of n-heptane-soluble component. Since the tod fraction was low, the isotactic pentad fraction as a film was low as a result, and the stereoregularity was insufficient. In addition, a biaxially oriented polypropylene film having a very high isotacticity, that is, a so-called highly crystalline biaxially oriented polypropylene film, has insufficient steric regularity, and thus has extremely poor film-forming properties, and has excellent heat resistance and dielectric breakdown resistance. It has not been established as an industrially useful technique for producing an oriented polypropylene film.

As a technique for overcoming this drawback, Japanese Patent Publication No. 4-28727 discloses an isotactic pentad fraction in the range of 0.960 to 0.990, a boiling n-hexane and a boiling n-hexane. There is a disclosure of a crystalline polypropylene film having excellent moldability 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.

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 deformation temperature and Young's modulus, a high degree of crystallinity and a good stereoregularity. There is a disclosure of a vapor-deposited film capacitor using a functionalized film. However, the stereoregularity was at most about 90%, and the dielectric breakdown characteristics at high temperatures were insufficient.

[0009]

However, ordinary high rigidity or high isotactic index polypropylene films do not have sufficient withstand voltage, especially when dielectric breakdown voltage failure occurs at a film thickness of 4 μm or less. There is. On the other hand, simply with a low ash polypropylene film,
The heat shrinkage rate is large, and the above-mentioned problems may occur when processing into a capacitor element, or it may not be able to withstand use at high temperatures.

The present invention has been made to solve the above-mentioned conventional disadvantages, and has as its object to provide a biaxially oriented polypropylene film having excellent withstand voltage and heat resistance and a capacitor using the same as a dielectric. Things.

[0011]

As a result of intensive studies to solve the above problems, the present inventors have found that the stereoregularity of polypropylene greatly affects the heat resistance of the film, and reached the present invention.

That is, an object of the present invention is to provide a biaxially oriented polypropylene having an isotactic index of 99% or less and having the following formulas (1), (2) and (3). This can be achieved by a film and a film capacitor using the film as a dielectric.

P1> 99% (1) P2 ≦ 0.1% (2) P3 ≦ 0.8% (3) (where P1 is derived from mmmm of the pentad fraction obtained from ¹³ C-NMR of polypropylene) Shows the ratio of the absorption peak, and P2 is also the same mmrr + mmrm.
+ Rmrr + rmrm is shown, and P3 is also the same due to rrrr + mrrr + mrrm. In addition, m represents the conformation of two adjacent repeating units in the polypropylene molecular chain, and r represents racemo. )

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The biaxially oriented polypropylene film in the present invention is a biaxially stretched film mainly composed of polypropylene, and basically does not contain other copolymerized components.

The isotactic index (II) of the biaxially oriented polypropylene film of the present invention needs to be 99% or less from the viewpoint of film forming properties. If it exceeds 99%,
When producing a biaxially stretched film, the stretchability is poor and the film formation becomes extremely difficult. More preferably, those having a range of 97 to 99% are used, and if less than 97%, heat resistance and withstand voltage may be poor.

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 (pentad) of the repeating units 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 is determined by Report of Hayashi et al. [Polymer, 29, 138-143 (198)
8)] and the like, the ratio of the segment having each of the above conformations was determined from ¹³ C-NMR.

The polypropylene film of the present invention is characterized by its stereoregularity, ie, isotacticity.
needs to be higher. That is, it is necessary that P1 which is the meso pentad fraction mmmm exceeds 99%. Furthermore, the ratio of other conformations greatly affects the physical properties of the film. Mmrr, mmrm, rmrr, rm where the conformation before and after the methyl group of interest is m and r
It is necessary that the total P2 of the ratio of rm (the second and third conformations are mr) is 0.1% or less. In addition, two, three
Rrrr, mrrr, mrrm where the th conformation is rr
Is required to be 0.8% or less. Such a polypropylene film is composed of molecules having longer isotactic segments, and can be a film having high crystallinity, high withstand voltage, and high heat resistance. In the stereoregularity of polypropylene of the polypropylene film of the present invention, P1 is more preferably 99.1% or more. Further, P2 is more preferably 0.05% or less. P3 is more preferably 0.5% or less. P1 is 99 or less, or P2 exceeds 0.1%, or P3 is 0.8%
If it exceeds 2,000, the heat resistance and the withstand voltage of the polypropylene film will be reduced.

In the present invention, of the above P2, mmrr
Is less than 0.08%, and the rmrm is less than 0.01%, more preferably for heat resistance and voltage resistance.

In the present invention, the intrinsic viscosity of polypropylene used for the biaxially oriented polypropylene film is not particularly limited, but is preferably 1 to 10 dl from the viewpoint of film forming property.
/ G range is used.

In the present invention, the ash content of the biaxially oriented polypropylene film is preferably at most 30 ppm, more preferably at most 25 ppm, even more preferably at most 20 ppm. If the ash content exceeds 30 ppm, the withstand voltage of the film may be reduced, and the film may not be practically usable as a biaxially oriented polypropylene film for capacitors.

In the present invention, the biaxially oriented polypropylene film preferably has an iron content in the ash content of 2 ppm or less, more preferably 1.5 ppm or less, and even more preferably 1 ppm or less. When the ash content exceeds 2 ppm, the withstand voltage of the film is remarkably reduced, and the film may not be practically usable as a biaxially oriented polypropylene film for capacitors.

In the present invention, the degree of crystallinity determined from the density of the biaxially oriented polypropylene film is preferably at least 70%, more preferably at least 72%,
More preferably, it is at least 74%. 70% crystallinity
If it is less than 1, the withstand voltage, heat resistance, and furthermore, the evaporation processability of the biaxially oriented polypropylene film may be reduced.

In the present invention, the thickness of the biaxially oriented polypropylene film is not particularly limited, but is preferably in the range of 0.5 to 40 μm from the viewpoint of film forming properties and mechanical properties.

In the present invention, the withstand voltage of the biaxially oriented polypropylene film can be evaluated by a dielectric breakdown voltage at direct current. In general, as for the dielectric breakdown voltage of a biaxially oriented polypropylene film, as the film thickness decreases, the dielectric breakdown voltage per unit thickness (V / μm) decreases. The dielectric breakdown voltage of the biaxially oriented polypropylene film of the present invention is expressed as follows:
m) is preferably 700-200 / d ^1/2 (V / μm) or more. If the value is less than this value, dielectric breakdown easily occurs, which may not be suitable for practical use as a capacitor.

In the present invention, the heat resistance of the biaxially oriented polypropylene film can be evaluated by the heat shrinkage at the time of heating at 120 ° C. for 15 minutes. The biaxially oriented polypropylene film of the present invention preferably has a heat shrinkage in the longitudinal direction when heated at 120 ° C. for 15 minutes in a range of 1 to 3%. If the heat shrinkage exceeds 3%, dimensional changes occur when the metal layer is formed, which may cause wrinkles in the film roll or a large decrease in the capacity of the capacitor. When the heat shrinkage ratio is less than 1%, the tightening by heat treatment at the time of producing the capacitor element becomes insufficient, which may adversely affect the shape retention and the capacity change rate. More preferably, 1.5 to 2.
The range is 5%.

In the present invention, the biaxially oriented polypropylene film may contain additives such as a nucleating agent, an antioxidant, a heat stabilizer, a slipping agent, an antistatic agent, an antiblocking agent, a filler, a viscosity modifier, and a coloring inhibitor. And the like.

In the present invention, the surface of the biaxially oriented polypropylene film on which the metal layer is to be formed is preferably subjected to a corona discharge treatment or a plasma treatment in order to increase the adhesive strength. The corona discharge treatment is preferably carried out in air, carbon dioxide gas, nitrogen gas or a mixed gas thereof as an atmosphere gas during the treatment. The plasma treatment includes a method in which various gases are kept in a plasma state to chemically modify the film surface, for example, a method described in JP-A-59-98140.

In the present invention, the metal forming the metal layer on the biaxially oriented polypropylene film may be aluminum, zinc, copper, tin, silver, nickel or the like alone or in combination, but is not particularly limited.

In the present invention, a method for forming a metal layer on a biaxially oriented polypropylene film includes a vacuum deposition method, a sputtering method, and an ion beam method, but is not particularly limited.

In the present invention, the metallized film typically has a film resistance of 2 to 40 Ω / □. Membrane resistance value is 2
If it is smaller than Ω / □, the thickness of the vapor-deposited film is so large that heat loss occurs during vapor-deposition, and there is a high possibility that an avatar-shaped surface defect or a hole in a thin film of about 4 μm or the like will occur. If the film resistance exceeds 40 Ω / □, when the deposited film clears during the application of electricity, the film is likely to disappear and the capacity change is likely to increase.

In the present invention, the specifications 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, etc.) Various types provided with a fuse mechanism have been proposed, are adopted according to the purpose, and are not particularly limited.

The type of the capacitor made of the biaxially oriented polypropylene film of the present invention may be a dry type, an oil immersion type, or the like, but is not particularly limited.

[0033] The ratio of the breakdown voltage V ₂₅ in the twin screw breakdown voltage V ₁₀₅ at 105 ° C. and 25 ° C. of oriented polypropylene film of the present invention (V ₁₀₅ / V ₂₅₎ is preferably 0.75 or more . More preferably, it is 0.8 or more.
When this value is small, the dielectric breakdown voltage at a high temperature becomes small, and it may not be practically used at a high temperature.

105 ° C. of a film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric
AC breakdown voltage at 200V / μm per unit thickness
It is preferable that it is above. More preferably 210V
/ Μm or more. The AC breakdown voltage at 85 ° C. is preferably 220 V / μm or more.

Further, the DC breakdown voltage of the film capacitor using the biaxially oriented polypropylene film of the present invention as a dielectric is preferably 300 V / μm or more per unit thickness, more preferably 320 V / μm.
That is all.

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

A raw material composed of polypropylene was supplied to an extruder, heated and melted, and passed through a filter.
Melt extrusion from slit die at a temperature of ~ 320 ° C, 4
The film is wound around a casting drum maintained at a temperature of 0 to 100 ° C. and solidified by cooling to produce an unstretched film. If the temperature of the casting drum is lower than 40 ° C., the crystallinity of the film may decrease.

Next, the unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method,
Alternatively, a simultaneous biaxial stretching method can be used. As the sequential stretching method, first, the unstretched film is subjected to 120 to 150
The sheet is preheated by passing through a roll maintained at 100 ° C., and then is passed through a roll provided with a peripheral speed difference while maintaining the temperature at 100 ° C. to 150 ° C., stretched 2 to 6 times in the longitudinal direction, and immediately brought to room temperature. Cooling. Here, the raw material having a P1 of 98 and 5% or more of the present invention may have a preheat temperature of 130 ° C. or less and a stretching temperature of 135 ° C. or less, and may have insufficient heat quantity to cause stretching unevenness or tear, making it impossible to form a film. Subsequently, the stretched film is guided to a tenter, and is heated at a temperature of 150 to 170 ° C. in a width direction of 5 to 1 °.
The film is stretched to 0 times and then heat-set at a temperature of 160 to 170 ° C. while giving a relaxation of 2 to 20% in the width direction, and wound. Thereafter, in order to improve the adhesiveness of the metal to be vapor-deposited on the surface to be vapor-deposited, a corona discharge treatment is performed in air, nitrogen, carbon dioxide, or a mixed gas thereof, and the film is wound by a winder.

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

[0040]

[Method for measuring characteristics and method for evaluating effects] The method for measuring characteristic values and the method for evaluating effects according to the present invention are as follows.

(1) Isotactic index (I
I) Extract the sample with n-heptane at a temperature below 60 ° C for 2 hours to remove additives to the 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 (%)

(2) 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 methyl group was 21.855 pp in the mmmm peak.
Each peak was assigned as m, 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 w
t%) / benzene-D6 (10 wt%) Measurement temperature: 120 to 130 ° C. Resonance frequency: 67.93 MHz Pulse width: 10 μsec (45 ° pulse) Pulse repetition time: 7.091 sec Data point: 32K Integration frequency: 8168 Measurement mode : Noise decoupling

(3) 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 : ashing weight (g)

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

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

(6) Element breakdown voltage (element BDV) A capacitor element maintained at 105 ° C. in a hot air oven was connected to a DC (or AC) high-voltage stabilized power supply manufactured by Kasuga Electric Co., Ltd. A voltage was applied while increasing the voltage at a speed, and a voltage when the element was destroyed was determined. The average value of 10 measured elements was defined as the element BDV.

[0049]

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

Example 1 II: 98.9%, P1: 99.5%, P2: 0.01
%, P3 0.38%, and ash 13 ppm are supplied to an extruder, melted at a resin temperature of 280 ° C., extruded from a T-type die into a sheet, and cast at a temperature of 70 ° C. The sheet is pre-heated at 135 ° C., and then the sheet is kept at a temperature of 140 ° C., passed between rolls provided with a peripheral speed difference, stretched 5 times in the longitudinal direction, and immediately at room temperature. Cool. Subsequently, the film is guided to a tenter, preheated to a temperature of 170 ° C., and then continuously heated at a temperature of 165 ° C. in the width direction.
Double stretching, then 8% relaxation in the width direction, 30W
Corona discharge treatment was performed in the air at a rate of min / m ² . The ash and pentad fractions of the resulting films did not differ from those of the raw materials. This film was set in a vacuum evaporation machine, and copper was used as a nucleation metal, and zinc was evaporated on the corona-treated surface so that the film resistance became 4.0 Ω / □. This film was slit to obtain a metallized film having a total width of 38 mm and a margin width of 1 mm. The element was wound using a pair of two reels of the obtained film, metal sprayed on an end face of the element, and a lead wire was taken out from the element to form a capacitor element having a capacity of 5 μF. Various properties of the obtained film and capacitor element are as shown in Table 1, and the film was excellent in dielectric breakdown voltage property. Also, 105 of the element
The dielectric breakdown voltage characteristics at ° C. were also good.

Examples 2 and 3 and Comparative Examples 1 to 5 As shown in Table 1, in the same manner as in Example 1, biaxially oriented polypropylene films and capacitors under various conditions were obtained.

The properties of the film and the condenser were as shown in Table 1.

[0053]

[Table 1] The abbreviations in the table indicate the following.

P1: Pentad fraction (mmmm) P2: Pentad fraction (mmrr + mmrm + rmrr + rmrm) P3: Pentad fraction (rrrr + mrrr + mrrm) BDV: Dielectric breakdown voltage AC: AC DC: DC Within this range, the obtained biaxially oriented polypropylene film had good withstand voltage, and the capacitor obtained from the film had good high-temperature withstand voltage.

On the other hand, in Comparative Examples 1 to 5, all or any one of P1, P2, and P3 was out of the range of the present invention, and the obtained biaxially oriented polypropylene film had a low dielectric breakdown voltage and was formed of the film. 105 ℃ of condenser
The dielectric breakdown voltage at the time was also inferior.

Comparative Example 6 P1, P2 and P3 are within the scope of the present invention, and II is 99.
Although 4% of the polypropylene resin was used, the biaxially oriented film could not be produced due to poor stretchability and tearing during stretching in the width direction.

[0057]

As described above, the polypropylene film of the present invention has good heat resistance and voltage resistance by specifying the ratio of each component of the pentad fraction, and a highly reliable film capacitor can be obtained from this. Obtainable.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08F 110/06 MJF 7446-4J C08F 110/06 MJF H01G 4/18 H01G 4/24 331Z // B29K 23:00 B29L 7:00 31:34 C08L 23:12

Claims (5)

[Claims] 1. An isotactic index of 99%
A biaxially oriented polypropylene film, which has the following formulas (1), (2) and (3). P1> 99% (1) P2 ≦ 0.1% (2) P3 ≦ 0.8% (3) (where P1 is the absorption peak derived from mmmm in the pentad fraction determined from ¹³ C-NMR of polypropylene. And P2 is also mmrr + mmrm
+ Rmrr + rmrm is shown, and P3 is also the same due to rrrr + mrrr + mrrm. In addition, m represents the conformation of two adjacent repeating units in the polypropylene molecular chain, and r represents racemo. ) 2. The ratio of the absorption peak derived from mmrr in the pentad fraction determined from ¹³ C-NMR of polypropylene is less than 0.018%, and the ratio due to rmrm is less than 0.01%. Ash content is 30pp
2. The biaxially oriented polypropylene film according to claim 1, wherein m is equal to or less than m. 3. A film capacitor using the biaxially oriented polypropylene film according to claim 1 or 2 as a dielectric. 4. The film capacitor according to claim 3, wherein an AC breakdown voltage per thickness at 105 ° C. is 200 V / μm or more. 5. The film capacitor according to claim 3, wherein a DC breakdown voltage per thickness at 105 ° C. is 300 V / μm or more.