JPH02145626A - Polypropylene film for electrical appliance - Google Patents

Abstract

PURPOSE:To obtain the subject film, having a rough surface layer satisfying specific conditions, capable of improving impregnating properties of an insulating oil and withstand voltage and useful as a dielectric layer of capacitors by specifying oil absorption in the film and crystal size thereof. CONSTITUTION:The objective film having a rough surface layer satisfying -0.7MMV+20<=sf<=-0.5MMV+26[sf=(MMV-WMV)/WMVX100 (MMV is the thickness of one sheet obtained by measuring 10 superposed films using a micrometer; WMV is the thickness determined in terms of weight of one film] on at least one surface thereof and 8X10<-5> to 20X10<-5>g/cm<2> oil absorption in the film with <=15nm crystal size thereof. Furthermore, in production, e.g. polypropylene and ethylene propylene block copolymer are preferably respectively melt extruded and joined to provide a laminated sheet, which is then biaxially oriented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a roughened polypropylene film for electrical articles that has improved impregnability with insulating oil.

[Conventional technology]

Plastic films, especially biaxially oriented polypropylene films, have excellent electrical properties and are therefore particularly often used as dielectric layers in capacitors. As a roughened polypropylene film for electrical articles, for example, (a) JP-A-51-63500, (b) JP-A-62-712
Publication No. 11 and the like are known.

[Problem to be solved by the invention]

However, these conventional techniques have the following drawbacks.

In other words, the rough surface film having a network structure due to the formation of β-crystalline spherulites produced in the molten sheet cooling process disclosed in (a) has insufficient penetration of insulating oil, and early dielectric breakdown occurs due to unimpregnated areas. This often shortens the life of the capacitor.

Furthermore, the film disclosed in (b) is not necessarily sufficient as a roughened film because the withstand voltage decreases significantly and early dielectric breakdown occurs when the film is thin with a thickness of 12 μm or less.

The present invention eliminates the above-mentioned conventional drawbacks, improves impregnability,
The purpose of the present invention is to provide a roughened polypropylene film for electrical articles that has an excellent capacitor life.

[Means to solve the problem]

゛The roughened polypropylene film for electrical articles of the present invention has the following formula on at least one side: MMV: Thickness of one sheet when 10 stacked films are measured with a micrometer WMV: Weight equivalent of one sheet It has a rough surface layer that satisfies the thickness determined by
0-5 g/cm2, and the crystal size of the film is 15 nm or less.

The polypropylene film according to the present invention is usually a composite film having a polypropylene film as a base layer and a composite layer laminated on at least one side thereof.

The base layer does not necessarily have to be a propylene homopolymer, and other types of olefins may be copolymerized or mixed as long as the object of the present invention is achieved. Furthermore, various known additives such as stabilizers, fillers, antioxidants, etc. can also be added.

The rough surface of the rough surface layer in the present invention is not particularly limited in its shape or formation method as long as it satisfies the above relational expression, but preferably has a network structure due to α crystal transition of β crystal spherulites. It is better that the surface has an uneven surface shape consisting of independent granular protrusions.

Regarding the degree of roughness, the relationship between MMV and sf (space factor) needs to be 0.7 MMV+20≦sf≦-0,5MMV+26. If sf is smaller than -0.7MMV+20, the roughness of the surface will be insufficient, and it will be difficult to secure an oil layer between the layers, resulting in insufficient penetration of the insulating oil, leading to early failure. When sf is larger than -0.5MMV+26, the surface of the film becomes rough enough to induce abnormal local breakage due to a decrease in the actual thickness, leading to early breakage. Next, the oil absorption amount in the film is 8 x 10 g/cm ~ 20 x 10-5 g/cm2,
Preferably 12X10 g/cm ~ 18X10'
g70m, more preferably 14X10-5g/cm2
~16X10 g/cm2.

Here, the oil absorption amount in the film refers to the impregnating ability when the film is wrapped around a glass rod of 8 mmφ and impregnated for 12 hours in an insulating oil of phenylxylylethane heated to 80°C.

If the area is less than 8 x 10270 m2, there will be parts in the film that are not impregnated with insulating oil, which will accelerate destruction due to corona deterioration.
Shorten capacitor life. If the oil absorption exceeds 20 x 10270 m2, the inherent properties of the crystalline polypropylene film will be impaired, and the dielectric strength will drop, impairing its reliability as a capacitor. The crystal size of this film is 15 nm or less, particularly preferably 13 nm or less. If it exceeds 15 nm, the proportion of amorphous parts in the film will increase, and the amorphous parts will become longer, leading to a decrease in dielectric strength and shortening the life span.

There are various methods for producing polypropylene films, but a typical example is coextrusion. That is, using two extruders, polypropylene is supplied to one and a block copolymer of ethylene and propylene is supplied to the other, which are melt-extruded, then merged in one die to form a laminated sheet. It is axially stretched.

Alternatively, an ethylene and propylene block copolymer may be melt-extruded and laminated on an unstretched polypropylene sheet, and this may be biaxially stretched.

Next, a more specific example of the method for producing the roughened polypropylene film of the present invention will be described.

However, it is not limited to this.

First, polypropylene having an isotactic degree of 96.5 to 99.5% is supplied to an extruder heated to 240 to 280°C and melted, while the ethylene content is 0.8 to 2.8%.
Weight% ethylene propylene copolymer 72-84% by weight
An ethylene propylene block copolymer with an isotactic degree of 87 to 92% obtained by polymerizing 16 to 28% by weight of ethylene is melted at 240 to 280°C, and these two melts are mixed through one T-die. It was extruded into a two-layer sheet having a thickness of 320 to 900 μm, wound around a chill roll with a surface temperature of 20 to 90° C., and solidified by cooling. The degree of rough surface formation is determined by the polypropylene and ethylene polypropylene block copolymer layer (
The composite (thickness) ratio with the laminate layer (hereinafter also referred to as laminate layer) has a large influence. The partial thickness of the laminate layer in the sheet thickness is
When the film thickness after biaxial stretching is 8 to 12 μm in MMV, it is 30 to 50 μm, preferably 36 to 44 μm.

When the MMV is 13 to 22 μm, the thickness of the laminate layer film is 40 to 72 μm, preferably 48 to 60 μm.

There is no problem with cooling and solidifying at the above temperature, but if the crystal size is reduced to 1
In order to make it 5 nm or less, the temperature is preferably 40°C or less. This laminated sheet was heated at a temperature of 130 to 150°C for 4.
Stretching is performed from 0 to 5.5 times.

Stretching in the length direction has no effect on the formation of a rough film, but in order to maintain the oil absorption in the film, it is recommended to stretch it 4.5 to 5.0 times in the length direction at a high temperature of 145 to 150°C. This is a more preferable range.

Then, after stretching in the length direction, the
Stretching is performed by 7.0 to 11.0 times at a temperature of 75°C.

This stretching in the perpendicular direction has a great effect on the formation of a rough surface, and the preferred temperature is 162 to 168°C, and the preferred magnification is 9.
．． It is 5 to 10.5 times.

After stretching, the film is further heat-treated while relaxing at a temperature of 100 to 160°C, and then wound up. The heat treatment temperature has a great effect on reducing the crystal size, and is preferably 100 to 120°C.

Next, the measurement method and evaluation method used in the present invention will be described.

(1) MMVSWMV, s f (a) A film measuring 300 mm in the length direction x 100 mm in the right angle direction is sampled at 5 locations in the product width direction.

(b) Stack 10 sheets of the above samples.

(c) M
As MV, the average value of the number of measurement points n=5 is used.

(d) Using the same film as used for MMV measurement, measure the weight to the last four decimal places using a precision chemical balance, and set the specific gravity as 0°91 to determine the weight equivalent thickness (WMV).

(e) sf was determined from M'MV and WMV using the following formula.

s f = (MMV-WMV) /WMV x 10
0 (2) Oil absorption in the film (a) Preparation of standard sample A. Cut the film to a size of 10 cm x 30 am.

After sufficiently removing static electricity from the film using an ion gun (manufactured by Zecostat), the weight was precisely weighed to an accuracy of 10 g.

C. The film is immersed in heated phenylxylylethane and impregnated with different amounts of oil for different times.

2. Completely wipe off the phenylxylylethane on the film surface with "Kimwipe" manufactured by Jujo Kimberly Co., Ltd. (
It is OK if no oil is visible on the surface. ) Weigh accurately in the same manner as in section E5 and B.

(b) Creating a calibration curve The standard sample created in section (a) is 4cm wide x 7cm long.
m, and for that sample, using an infrared spectrophotometer (EP-1-G3 manufactured by Hitachi, Ltd.), the chart speed was set to FAST-2, and the temperature was 750-650 am-
1, draw a peak that appears near 700 cm-1, calculate the area of the peak using the half-width method, plot the unit oil amount (g/cm2) against the peak area, and create a calibration curve. do. An example of creating a calibration curve is shown in the table below.

(c) Quantification of the sample The sample film was immersed in phenylxylylethane heated to 80°C, the oil on the surface of the impregnated film was wiped off with "Kimwipe", and the infrared spectrophotometer was used to measure 750 cm'. The area of the peak appearing near 700 cm-1 is measured by scanning between ~650 am1, and the unit oil i (g/cm2) is determined from the calibration curve, which is taken as the oil absorption amount in the film.

(3) Crystal size Using a wide-angle X-ray diffraction device (reflection method) manufactured by Rigaku Denki ■, applied voltage: 35KV-15MA, 5can 5
speed: 1°/min, TimeConst 2s
ec, FS: 8000cps.

5lit system DS, SSI°R3, filter is Q, 3
After measurement under the conditions of nickel and nickel, the crystal size (nm) was determined from the measured value of the (110) plane using the following formula.

Crystal size - (Kλ/β・CO6θ) A constant number of K. niziella, here set to ~1.

λ: 0.15418 β: Half width θ: Peak angle (4) Three layers of capacitor life film are stacked to form a dielectric layer, and the electrode is 6 μm thick.
A 0.2 μF capacitor was manufactured using a thick aluminum foil, and after drying under vacuum at 70°C for 24 hours, 8.
It was impregnated with phenylxylylethane insulating oil for 24 hours at 0'C to form an oil-impregnated capacitor. Here, MMV was used for the film thickness.

(a) Short-term withstand voltage life: 4.5K for 18μm products at room temperature using the above capacitors
For the V-AC, 10 μm product, 2.8 KV-AC was applied and the breakdown time was expressed as the time required to break down.

02900 seconds or more 02600 seconds or more less than 900 seconds △: 300 seconds or more and less than 600 seconds The lifespan of the capacitors until breakdown was compared by applying 2° OKV AC and was expressed by the breakdown time.

◎: 1000 hours or more ○: 600 hours or more 1 question 00 The isotactic degree 92 obtained by block copolymerizing 83% by weight of an ethylene propylene random copolymer with an ethylene content of 1.8% by weight and 17% by weight of ethylene was melted and placed in the other extruder. .7% ethylene propylene block copolymer was melted at a temperature of 260°C, and both melts were formed into two layers using a T-die with a width of 660 mm and a gap of 1.5 mm, with a base layer of 410 μm and a laminate layer of 40 μm in thickness. Composite extrusion, after being cooled and solidified with a chill roll cooled to 35°C, stretched 4.5 times in the longitudinal direction at a temperature of 145°C, and then stretched 10.0 times in the perpendicular direction at a temperature of 162°C. , a relaxation heat treatment was performed at 120° C., and the product was wound up.

The MMVIO μm film obtained as above was
The dielectric layers are stacked one on top of the other, and aluminum foil with a thickness of 6 μm is used as an electrode. A 2 μF capacitor was manufactured, and the capacitor element was impregnated with an insulating oil of phenylxylylethane at 80° C. for 24 hours under vacuum with the clamping rate set at 115% to form an oil-impregnated capacitor. Using this capacitor, the short-term lifespan is 2.
8KV-AC charging, long-term life test is 2°0K at 80℃
The withstand voltage life of the capacitor under V-AC voltage application was measured. The results are shown in Table 1.

Example 2 The pressure life of a capacitor was measured in the same manner as in Example 1, except that the sheet thickness was changed: base layer: 420 μm, laminate layer: 30 μm. The results are shown in Table 1.

Comparative Example 1.2 A capacitor similar to Example 1 except that the sheet thickness was changed to 435 μm for the base layer and 15 μm for the laminate layer (Comparative Example 1), and the sheet thickness was changed to 390 μm for the base layer and 60 μm for the laminate layer (Comparative Example 2). Manufactured and life tested. The results are shown in Table 1.

From Table 1, if sf is (-0,7MMV+20) or more, (
-0.5MMV+26) or less, and the oil absorption amount in the film is 8X10 270m2 or more, 20X
It can be seen that the capacitors with a size of 10270 m2 or less and a crystal size of 15 nm or less, that is, Example 1 and Example 2, have improved breakdown voltage and clearly have superior capacitor life compared to Comparative Example 1 and Comparative Example 2. .

Example 3 A sheet with a base layer thickness of 810 μm and a laminate layer thickness of 60 μm was stretched 4° and 5 times in the length direction at a temperature of 150°C.
Stretched 10.0 times in the perpendicular direction at a temperature of 165°C.
Relaxation heat treatment was performed at 25°C, and other conditions were the same as in Example 1, and a capacitor was fabricated by stacking three films with an MMV of 18 μm. The clamping rate and insulating oil impregnation are exactly the same as in Example 1, and the voltage applied to the capacitor is 4.5 KV-AC at room temperature for short-term life and 8 KV-AC for long-term life.
The withstand voltage life of the capacitor was measured under 3.6 KV-AC voltage application at 0°C. The results are shown in Table 1.

Example 4 The pressure life of a capacitor was measured in the same manner as in Example 3 except that the sheet thickness was changed to 825 μm in base layer thickness and 45 μm in laminate layer thickness. The results are shown in Table 1.

Comparative Examples 3 to 7 The base layer thickness was 840 μm, the lamination layer thickness was 30 μm, and the sheet thickness was changed (Comparative Example 3).The sheet thickness was the same as in Example 3, and the sheet was cooled and solidified at a chill roll temperature of 92°C.
The relaxation heat treatment after biaxial stretching was changed to 1°55°C (
Comparative example 4), base layer thickness 775 μm 1 laminate layer thickness 95
one in which the μm and sheet thickness were changed (Comparative Example 5), one in which polypropylene with an isotactic degree of 94.2% was used as the base layer and the magnification in the longitudinal direction was increased to 4.0 times (Comparative Example 6), Polypropylene with an isotactic degree of 94.2% is used for the base layer, and the base layer thickness is 840 μm.
The film and capacitor were manufactured in the same manner as in Example 3 except that the thickness of one laminate layer was changed to 30 μm, the sheet thickness was changed, and the magnification in the length direction was increased to 4.0 times (Comparative Example 7). , measured their capacitor life. The results are shown in Table 1.

From Table 1, sf is (-0.7MMV+20) or more, (
-0.5MMV+26) or less, the oil absorption amount within the film is 8 x 10270 m2 or more, 2 = 50 x lO270 m2 or less, and the crystal size of the film is 1
5 nm or less, that is, Example 3 and Example 4,
Compared to Comparative Examples 3 to 7, an improvement in breakdown voltage was observed, and it was clearly seen that the life of the capacitor was excellent.

〔Effect of the invention〕

As mentioned above, the roughened polypropylene film of the present invention has a relationship between MMV and sf of −0.7MMV+20≦
sf≦-0.5MMV+26, oil absorption inside the film is 8×
Since it is a film with an area of 10270 m2 or more and 20 x 10270 m2 or less, and a crystal size of 15 nm or less,
When used as a dielectric layer in an oil-impregnated capacitor, it has excellent oil impregnation properties, improves voltage resistance, and extends the life of the capacitor.

Claims (1)

[Claims] (1) At least on one side, the relational expression −0.7MMV+20≦sf≦−0.5MMV+26(
However, sf=(MMV-WMW)/WMV×100MMV
: Thickness of one sheet when 10 layers of film are measured with a micrometer WMV: Thickness calculated from the weight of one sheet) It has a rough surface layer that satisfies the following, and the oil absorption inside the film is 8
A polypropylene film for electrical articles, characterized in that the crystal size of the film is 0^-^5 to 20 x 10^-^5 g/cm^2 and 15 nm or less.