JPS58102404A - Oil-immersed electrically insulating polypropylene film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in polypropylene films used as electrical insulating layers when immersed in electrical insulating oil. Traditionally, electrical insulating paper has been used as the oil-immersed insulation layer (or dielectric layer) of oil-immersed electrical equipment (capacitors, transformers, cables, motors, generators, etc.), but recently polypropylene film has been used as the oil-immersed insulation layer (or dielectric layer). It came out. This film not only has a much higher voltage resistance than electrically insulating paper, but also has several advantages, including a low dielectric loss tangent and a dielectric constant close to that of insulating oil.

However, conventional polypropylene films have the drawback of extremely large swelling due to insulating oil, and as a result, there are various limitations when using them for oil-immersed insulation applications.

For example, when a capacitor element is made by wrapping polypropylene film and immersed in insulating oil, the film swells with the oil.

The element becomes tightly wound and hard, causing problems such as poor circulation of insulating oil between the nine layers. As a temporary measure to avoid this, there is a method of winding the element loosely when first winding it.

If you wind it too loosely, the 9th turn is likely to be misaligned, and the 1st turn is also likely to wrinkle.

Another disadvantage of conventional polypropylene film is 1.
Because the surface roughness is insufficient, when these are wrapped in layers, the circulation of insulating oil tends to be insufficient between the eyebrows, which tends to cause dielectric breakdown.

The object of the present invention is to provide a polypropylene film that has improved the two drawbacks mentioned above, namely, both swelling properties and poor oil circulation.

The present invention has a ninth-order configuration to achieve the above object.

That is, the density is 0.905 to 0.915 g/an3.
Birefringence 0.020-0.035. The strength ratio in both axial directions (longitudinal tensile strength/width direction tensile strength) is in the range of 5 to 15.

And the surface roughness Rmax) of one or both sides is 1
It is characterized by an oil-immersed polypropylene film for electrical insulation having a thickness in the range of ~50 μm. What does polypropylene (hereinafter abbreviated as PP) refer to here?

It has an isotactic degree of 90 degrees or more, preferably 95 degrees or more, more preferably 97% or more, and a melt index of 0.5 to 40 g710 minutes.

Preferably it is in the range of 1 to 20 g/l 0 min.

If the isotactic degree is lower than the above, swelling due to insulating oil will increase, which is preferable. Also.

If the melt index is smaller than the above range, the swelling due to the insulating oil will increase, and conversely, if it is larger than the above range, the amount eluted into the insulating oil will increase, causing an increase in the viscosity of the insulating oil. Undesirable. Among the above-mentioned ppOs, those having a melt crystallization temperature (Tmc) of 105 to 120°C, more preferably 108 to 118°C are particularly preferred for the film of the present invention. If the Tmc is lower than the above range, the oil swelling due to the insulating oil will be severe, and conversely, if the Tmc is higher than the above range, the film forming property will deteriorate and it will be difficult to form a homogeneous film. As a result, insulation defects and the like increase, which is not preferable.

Next, the density of the film of the present invention is 0905 to 0.915 g/
(To) 3. Particularly preferably 0.907 to 0.912g/
It is necessary to be within the range of mouth 3. If the density is smaller than the above range, the swelling due to the insulating oil will be large; if the density is larger than the above range, the film will become brittle and the mechanical strength of the insulating layer will be insufficient. Next, what is the birefringence of the film of the present invention?

0020-0.055. Preferably 0.025-0.
It needs to be in the range of 0.032.

If the birefringence is smaller than this range, the swelling caused by the insulating oil will increase, and conversely, if the birefringence is larger than this range, the film will be more likely to crack, causing dielectric breakdown. Not fit for purpose. Next, 1) the strength ratio in both axial directions of the film of the present invention, that is, the value obtained by dividing the tensile strength in the longitudinal direction of the film by the tensile strength in the width direction, is in the range of 5 to 15, preferably 7 to 12. is necessary. When this intensity ratio becomes smaller than this range,
The swelling caused by the insulating oil will increase.

Conversely, if it exceeds this range, the difference in characteristics depending on the direction within the film plane becomes too large.

The workability when winding the insulating layer becomes extremely poor (for example, when winding the insulating layer, it tends to stretch, wrinkle, or tear easily). Next, the surface roughness Rm of one or both sides of the film of the present invention
ax) is required to be in the range of 1 to 50 μm, preferably 2 to 40 μm. If it is smaller than this range, the flowability of the insulating oil between the eyebrows will be poor, causing dielectric breakdown. Conversely, if it is larger than this range, the pressure resistance will deteriorate (1').

Next, an example of a method for manufacturing the film of the present invention will be described. pp
The resin is melt-extruded and extruded into a sheet from one die, which is then wound around a cooling drum and cooled and solidified. This pp
The sheet is inserted between - sets of rolling rolls, and the rolling magnification (the value obtained by dividing the sheet thickness before rolling by the sheet thickness after rolling) is 5 to 12 times.

Preferably, it is rolled to a size of 7 to 10 times.

The rolling pressure is preferably in the range of 10 to 3000 kThan, more preferably 100 to 1000 V'cm,
The temperature of the rolling roll is 60-160°C, preferably 80-160°C.
A range of 150°C is preferred. When rolling, wetting the surface of the PP sheet with a liquid (water, aqueous surfactant solution, alkylene glycol, polyalkylene glycol, glycerin, electrical insulation oil, etc.) before rolling facilitates uniform high-magnification rolling. . Film obtained by rolling (usually
The thickness is in the range of 10 to 300 μm) at 100 to 150°C.
and heat-treated for 1 to 20 seconds while giving a relaxation of 0.5 to 10 inches of the original size in the longitudinal direction. Next, this film.

Pass the film between embossing rolls heated to 90 to 140°C to make one or both sides of the film faceted.

Surface roughness (Rmax) is 1 to 50 μm, preferably 2
The thickness should be within the range of ~40 μm. As described above, the most preferred method for producing the film of the present invention is a combination of rolling and embossing.

It may also be made using other methods. For example, a combination of rolling and stretching or close-spaced roll stretching may be used for rolling, and instead of embossing, the surface may be roughened by sandblasting, etching, or the like.

The present invention is characterized by having the characteristics described above, and the heat shrinkage rate in the longitudinal direction of this film is 0.1 to 5q6. Preferably, by setting it in the range of 0.05 to 3.07, the film can be made more suitable for oil-immersed electrical insulation. If the heat shrinkage rate is greater than this range,
This is undesirable because the insulating layer tends to be tightly wound and wrinkles occur, and conversely, if it is smaller than this range, it tends to stretch in the longitudinal direction in the insulating oil and the insulating layer once wound becomes loose, which is undesirable. . Here is an example of how to keep the heat shrinkage rate in the longitudinal direction within this range.

The film made by the method described above is 80 to 140
C., preferably 90 to 130.degree. C., and held under tension or for 0.5 to 50 hours, preferably 1 to 20 hours, while allowing relaxation of 0.1 to 5% of the original size in the longitudinal direction. By this aging heat treatment, the heat shrinkage rate in the longitudinal direction can be kept in the range of 0.1 to 5 inches, preferably 0.5 to 3%.

The present invention produces an excellent first-order effect by combining the density of the PP film, the birefringent intensity ratio in one and both axes directions, and the specific range values of the surface roughness.

(1) Less swelling due to insulating oil.

(2) Good circulation of insulating oil between the insulating layers.

(3) Excellent mechanical properties as an insulating layer and workability during winding.

(4) Both tightening and loosening of the insulation layer occur.
'□It's hard to do.

(5) Excellent dielectric loss tangent, dielectric constant, and breakdown voltage characteristics.

Therefore, the film of the present invention is suitable as an oil-immersed insulating layer for various oil-immersed electrical devices such as capacitors, transformers, cables, motors, generators, and the like.

Note that the terms and measurement methods used in the present invention will be summarized below.

(1) Extract the isotactic degree pp with boiling n-hebutane, divide the weight of the extracted residue by the original weight, multiply by ioo, and display it as:

(2) /' Root index: ASTM D-12
Measured under the conditions of 38-75.

(3) Melt crystallization temperature (Tmc): 5 mg of the sample was placed in a DSC-II model manufactured by PerkinElmer, and the atmosphere was replaced with nitrogen. Next, the temperature was raised to 200° C. at a temperature increasing rate of 20 r: 7 minutes, and held at this temperature of 200° C. for 5 minutes. Next, the temperature is lowered at a rate of 20r:7 minutes to draw an exothermic peak associated with crystallization of the sample. The temperature at the top of this peak is T
Let it be mc.

(4) Density: ASTM D1505Kj.

(5) Birefringence: Using Atsube's refractometer, measure the refractive index in the longitudinal direction (Ny) and the refractive index in the width direction (Nx) of the film.
The value obtained by subtracting Nx from N7 is determined as birefringence. In addition, sodium D line was used as the light source during measurement.
Methyl salicylate is used as the mounting solution.

(6) Strength ratio in both axial directions: Tensile strength σy (lqx/mm2) in the longitudinal direction of the film and tensile strength ax (?/an2) in the width direction of the film, according to ASTM D-882-6
7, and the value obtained by dividing σy by σX is defined as the intensity ratio.

, Tl5 (7) Surface roughening (Rmax): Self-kicking BO601
- Measure Rmax by the method described in 1976.

The cutoff value is 0.8ll1ml.

(8) Heat shrinkage rate: from film, length 200mm, width 1
Cut out a 0 mm sample (the direction in which the heat shrinkage rate is measured is the length direction). After holding this sample in hot air circulating ozone at 120° C. for 15 minutes.

Take it out to room temperature and measure its length. Its length is L
(mm), the heat shrinkage rate is expressed by the following formula (%) (9) Swelling degree due to insulating oil: From the film, 100 m x
A 100-mm sample is cut out, and its weight is defined as W (mg). This sample is immersed in alkylbenzene oil at 80°C and left for 24 hours.

Next, this sample is taken out, and after wiping off the oil on the surface with filter paper, it is immersed in acetone for washing, and the oil on the surface is further completely removed using gauze soaked in acetone. If the weight of this sample is measured and it is defined as W' (mg), then the degree of swelling (a) is determined by the following formula.

Swelling degree (%) = I Do x (W' - W) /
WOI Distribution of insulating oil: Make a capacitor element by alternately winding film and aluminum foil. This is immersed in insulating oil and vacuum impregnated with oil. Thereafter, the device is disassembled and visually determined whether the insulating oil has spread between all layers of the device.

Rank A: Uniformly distributed over the entire surface Rank B: There are slight oil-free spots Rank C: Oil-free areas exist in a planar manner As an oil-immersed insulating material, it must be rank A. However, in low pressure applications, even rank B may be used. Rank C is unsuitable as an oil-immersed insulating material.

(Ill electrical insulating oil: A general term for various known electrical insulating oils such as mineral oil, castor oil, cottonseed oil, alkylbenzene, diallyl alkane, polybutene oil, silicone oil, etc.)

Next, nine embodiments of the present invention will be described based on Examples.

Example 1 Melt indeno2F6 pellets with an isotactic structure content of 97.6% were prepared. Supply it to the extruder. Melt extrusion at 260℃. It was discharged in a sheet form from a T-shaped nozzle.

This melted sheet. Wrap it around a cooling drum at 60°C to cool and solidify. A sheet with a thickness of about 300 μm was made. This sheet is rolled onto a set of rolling rolls (roll diameter 250 mm).
It was inserted between the sheets and rolled to about 10 times the original size.

The rolling pressure was 5[1[]pu/cIn, the temperature of the rolling roll was 1
The sheet surface was rolled at 40° C. while wetting the sheet surface with polyethylene glycol. The resulting 30 μm thick film was... It was placed in an atmosphere at 130°C and heat treated for 10 seconds while giving 1% relaxation in the longitudinal direction. next.

This film was passed through embossing rolls heated to 130°C. on both sides of the film. Approximately 100 meshes of sandblasted Evaturn were transferred. next. This film was placed under tension in an atmosphere of 120℃ for 10 minutes.
Hold for a long time and perform aging heat treatment. This was slowly cooled to room temperature. The various properties of the film thus obtained are summarized below.

Density (g/rB'): 0.9 1 0 birefringence
: 0.030 Strength ratio in both axial directions: 10.2 Heat shrinkage rate (CH): 1.3 Surface roughness Rmax) (μm): 1 2.5 Swelling degree (%): 5.1 Distribution of insulating oil Characteristic: Rank A From this result, one film of the present invention was found. Swelling caused by the insulating oil is small, and the insulating oil has excellent flowability. It can be seen that it is extremely useful for oil-immersed electrical insulation.

Comparative Example 1 To compare the properties of a commercially available unstretched PP film and a commercially available biaxially stretched PP film for use in oil-immersed capacitors. They are summarized below. Unstretched biaxially stretched PP film PP film density <g/eIn3) 0.899 0.905
: Birefringence 0.003 0.013
Strength ratio in both axial directions 1. 3 1. 9 Heat shrinkage rate (%) 0 28 Surface roughness Rma
x), (am) o. 6 0. 9
Degree of swelling (ch) 11. <5 6.3
Flowability of Insulating Oil Rank C When these values are compared with the films of the present invention in the above examples, the superiority of the present invention becomes clear.

Patent Applicant Toshi Co., Ltd. Sumitomo Electric Industries Co., Ltd. Agent Patent Attorney Itaru Nakamura Continuing from page 1 Inside the office

Claims (1)

[Claims] 3. Density 0.905 to 0.915 g/. Birefringence 0.02
0-0.035. The strength ratio in both axial directions (longitudinal tensile strength/width direction tensile strength) is in the range of 5 to 15, and. The surface roughness (Rmax) of one or both sides is 1~
Polypropylene film for oil layer electrical insulation in the range of 50μm.