JPS63221037A - Oil-immersed electric insulating polypropylene film and manufacture thereof - 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 [Field of Industrial Application] The present invention relates to a propylene film that is immersed in electrical insulating oil and used as an insulating layer for capacitors, power cables, transformers, etc., and a method for producing the same.

[Prior art] Polypropylene film has excellent electrical insulation properties,
Moreover, because it is lightweight, electric cable can be used instead of insulating paper.
It has come to be used in capacitors, transformers, etc.

However, polypropylene film has poor diffusion of electrical insulating oil (hereinafter referred to as oil) on its surface, and when this film is used in place of insulating paper in a capacitor, for example,
There is a problem that the oil impregnation speed is slow and the oil is not impregnated uniformly, and various methods have been proposed to roughen the surface of the film and improve the oil dispersion (for example, Japanese Patent Application Laid-Open No. 1983-1993).
Publication No. 63500, Special Publication No. 61-5733:3 @ Publication,
(Special Publication No. 61-26168, etc.).

[Problems to be Solved by the Invention] However, the conventional roughened polypropylene film has the drawback of extremely large swelling in oil, and when impregnated with oil, it partially deforms in the thickness direction due to swelling. , the film layers come into close contact and cut off the oil supply route,
For this reason, there are problems in that the dielectric breakdown voltage decreases and the element breaks down in a short period of time due to heat generation and the like.

An object of the present invention is to improve such problems and provide an oil-immersed electrically insulating polypropylene film that has excellent oil impregnability and small oil swelling deformation, and a method for producing the same.

"Means for Solving the Problems" The present invention provides a polypropylene layer (I) which contains substantially no pores, has a porosity of 30 to 85% on at least one side, and an average pore diameter of 0.01 to 5 μm. The porous polypropylene layer (H) is laminated, and the thickness fraction of the (1) layer is 50 to 9.
The present invention relates to an oil-immersed polypropylene film for electrical insulation, characterized in that the oil content is 0%, and a method for producing the same.

In the present invention, the polypropylene constituting the polypropylene layer (1) preferably has an isotactic index (II) of 97% or more in order to reduce the swelling ratio. More preferably, it is 99% or more. In addition, when the intrinsic viscosity [η] of the PP is 1.4 to 2.3, not only the elution valve into oil is reduced, but also the film formation is good, and as a result, mechanical properties and dielectric breakdown voltage are good. This is preferable.

Zara, the PPI! When f(I) is oriented, dielectric breakdown voltage, mechanical properties, and swelling properties are all improved, so it is preferable, and when it is -axis oriented, the birefringence is 0°015 to 0.0°.
035 range, in the case of biaxial orientation, the plane orientation is 0.010-
A value in the range of 0.020 is preferable from the above viewpoint.

Furthermore, the PP layer (1) needs to be substantially free of pores. In the present invention, "substantially" means, for example, that the inclusion of slight pores incidentally caused by polypropylene stretching or the like is allowed.

However, in order to improve the dielectric breakdown voltage, it is preferable to contain as few such pores as possible, and from this point of view, it is preferable that the pore content is less than 5%.

Next, the porous polypropylene layer (H) has a porosity of 30
It is necessary that it is ~85%, preferably 40~85%.
It is 80%. If the porosity is too small, not only will the swelling rate increase when immersed in insulating oil, but the fluidity of the insulating oil will decrease, causing partial heat generation and dielectric breakdown. On the other hand, if the porosity is too large, the (H) layer is likely to cleave, and especially when a large force is applied, such as in a cable, the (H) layer will peel off, causing dielectric breakdown.

Moreover, the average pore diameter of the porous PP layer (H) is 0°01~
It is necessary to have a thickness of 5 μm, preferably 0.1 to 5 μm.
It is 3 μm. If the average pore diameter is too small, impregnating properties and fluidity with insulating oil will be poor, and at the same time, the swelling rate due to oil will increase, causing dielectric breakdown.

On the other hand, if the average pore diameter is too large, it causes insulation defects such as a decrease in dielectric breakdown voltage.

In addition, in increasing the mechanical strength of the (H) layer, the [η
] is preferably 1.6 to 3.0 dl/g. Further, it is preferable that II is 96% or more because the solubility in insulating oil decreases.

Polypropylene layer (I) and porous polypropylene layer (H
) is (I)/(H) or (H)/(1
)/(H), and the fraction of (I> in the total thickness of the layer is 50 to 90%, preferably 60 to 80%.

(I> If the thickness fraction of the layer is too small, not only the mechanical strength will decrease, but also the dielectric breakdown voltage will decrease.

On the other hand, if the thickness fraction is too large, the oil impregnating property and swelling properties will be poor, and in particular, the corona discharge voltage will decrease, making it easy to break.

The polypropylene film of the present invention may be embossed on only one layer or the (I) layer in order to roughly reduce the swelling ratio, but from the viewpoint of not reducing the dielectric breakdown voltage, the embossment ratio should be 50% or less. It is preferable that

Next, a method for manufacturing the polypropylene film of the present invention will be explained.

In the present invention, the extractable organic solid other than polypropylene added to polypropylene as a raw material for the (H) layer has a softening point of 35 to 100°C and a molecular weight of 200 to 10°C.
00 is preferred, and specific examples include dicyclohexyl phthalate (D CHP), triphenylene phosphate (TPP), cetyl palmate, stearyl suarate, vantaerythritol stearate, etc.
Especially DCHP containing polarizable and polar groups in its molecular structure.
, TPP is preferred in terms of obtaining the desired porosity and average pore diameter.

In the present invention, the above-mentioned organic solid is polypropylene 1
00 parts by weight, it is necessary to be 70 to 180 parts by weight, preferably 90 to 160 parts by weight. If the amount added is too small, the porosity and diameter of the pores formed will be small, and the impregnating properties and swelling properties of the insulating oil will be poor, resulting in easy dielectric breakdown. On the other hand, if the amount added is too large, not only will the viscosity of the composition significantly decrease and extrusion become difficult when extruding the (H) layer, but also the amount of organic solid transferred to the (1) layer will increase. As a result, problems such as a decrease in dielectric breakdown voltage of the produced polypropylene film arise.

In the present invention, a composition consisting of a polypropylene resin forming the layer (I) and a polypropylene and an organic solid forming the layer (H) are melt-extruded from separate extruders, and laminated in one die. 1)/(H) or (H)
/ (I) / (H) Formed into a sheet or tube shape and extruded. Here, the term "laminated in the die" means that the polymer is already formed as a laminate when it is extruded from the die. Specifically, the lamination method is such that the polymer is laminated in a short tube that leads from the extruder to the die. Examples include a method of laminating layers and a method of laminating layers in a manifold section within the metal, but a method of layering layers in a manifold section is particularly preferable in consideration of the transition from the layer (1-1) of the organic solid to the layer (I). In addition, as a lamination method, a technique is applicable in which only the (I) layer is formed, and after unstretched or at least uniaxially stretched, a separate extruder and die are used to form the (T1) layer. I want to do it. However, it contained a large amount of organic solids (
The former method is superior for strongly adhering and solidly integrating layers H) and (I).

The sheet or tube-shaped product extruded as described above is
After cooling with a cooling drum, cooling mandrel, water tank, etc., the organic solid is introduced into an extraction layer and extracted. In the case of the organic solid, effective extraction solvents that do not elute polypropylene include trichlorethylene, trichloromethane, methyl ethyl ketone, toluene, Examples include xylene, methanol, and ethyl acetate.

Furthermore, in the present invention, stretching may be performed before, after, or during extraction, and furthermore, organic solids may be partially extracted, and after stretching, organic solids may be completely extracted. However, in the stretching process, the added substances tend to migrate between layers, and from this point of view, at least a part, preferably 30% or more, of the added organic solids is extracted before stretching. It is preferable to keep it.

In addition, the stretching ratio during stretching is 2 to 15 in the uniaxial direction.
In the case of double or biaxial stretching, it is preferable that the areal magnification is in the range of 5 to 48 times because the flatness, mechanical properties, and dielectric breakdown voltage of the film are all good.

In the above step, with the organic solids completely extracted, 1
The film of the present invention is obtained by heat treatment at a temperature of 20 to 170°C.

The present invention is characterized by having the properties described above, and the heat shrinkage rate of this film in the longitudinal direction is in the range of 0.5 to 6%, preferably 1 to 4%. and,
This is preferable because the dimensional change during oil immersion is reduced, the winding tightening of the element and the occurrence of wrinkles are eliminated, and long-term reliability is improved.

[Function] The present invention has a porous polypropylene layer (H>) having an average pore diameter of 0.01 to 5 μm and a porosity of 20 to 80% on at least one side of the polypropylene layer (I), thereby improving oil impregnability. In addition, it was possible to suppress swelling due to oil.

[Method of Measuring Characteristics and Method of Evaluating Effects 1] Next, the measuring methods and evaluation methods of the present invention will be summarized.

(1) Isotactic index (II) Vacuum dry the sample at 130°C for 2 hours.
A sample of W(m(J)) is taken, placed in a Soxhlet extractor, and extracted with boiling 111j!n-hebutane for 12 hours.

Next, take out this sample, wash it thoroughly with acetone, and then
Vacuum dry at 130°C for 6 hours, then hand ff1W'
(mO) is measured and calculated using the following formula.

II (%) = (W' /W) Expressed as

(3) Average pore diameter Determined from surface and cross-sectional observation results using a scanning electron microscope (SEM).

(4) Porosity (Pr) Sample (10cm x 10cm) was soaked in liquid paraffin for 24 hours.
The weight (W2) after immersing the sample for an hour and thoroughly wiping off the liquid paraffin on the surface layer was measured, and the weight (W2) of the sample before immersion was measured.
l) Pore volume (vO) from density (ρ) of liquid paraffin
is calculated using the following formula.

Vo = (W2-Wl)/ρ The porosity (Pr) is the apparent volume of the entire layer (value calculated from the thickness and dimensions), the pore volume Vo, and the volume of the polypropylene layer (1) ( Vl) using the following formula.

Pr=Vo/(V-Vl)xloo (%) (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, and take the absolute value of the difference between Ny and NX as birefringence. A sodium D line is used as a light source during measurement, and methyl salicylate is used as a mounting liquid.

(6) Using a refractometer for plane orientation, measure the refractive index, Ny, NX, and NZ in the longitudinal direction, width direction, and thickness direction of the film, and calculate them using the following equations.

Planar orientation = (Ny+Nx>/2-Nz Note that the measurement conditions are the same as for birefringence.

(7) Cut a sample with a length of 200 mm and a width of 1101I1 from the heat shrinkage film (the direction in which the heat shrinkage is measured is the length direction).
. After holding this sample in a hot air circulation oven at 120° C. for 15 minutes, it is taken out to room temperature, and its length L (mm>) is measured and determined by the following formula.

Heat shrinkage rate (%) = 100 x (200-L) /
200 (8) Degree of swelling with insulating oil Cut a sample of 30 mm x 30 mm from the film,
Measure the thickness (Dl). Next, this sample is immersed in alkylbenzene oil at 100°C, and after being immersed in the oil for 24 hours under a load of 1 kC1/mm2, the sample is cooled to room temperature, and the sample is immediately taken out and its thickness (D2) is measured.

The degree of swelling is calculated using the following formula.

Swelling degree (%) = 100X (D2-Dl)/D1(9)
A capacitor element is made by alternately wrapping insulating oil circulation 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: Evenly distributed over the entire surface.

Rank B: There are slight oil-free spots.

Rank C: There is a planar portion without oil.

(10) Electrical insulating oil A general term for various known electrical insulating oils such as mineral oil, castor oil, alkylbenzene, diallylalkane, polybutene oil, and silicone oil.

[Example] Next, the present invention will be explained based on examples.

Examples 1 and 2 As the PP layer (1), II was 97% and [η] was 1.8d
l/! :1 PP resin, as raw materials for the porous PP layer (H), 100 parts by weight of PP resin with 97% II and 2.3 dl/g, and cyclohexyl phthalate (DCHP).
, melting point 63°C) and 150 parts by weight (5) were prepared and melt-extruded using separate extruders, and laminated in the manifold part of the T-die to form a sheet consisting of (I) layer/(H) layer. Extruded. Such a sheet was cooled and solidified on a cooling drum at 60°C, immediately introduced into a trichlene bath, and (H)li
More than 99.7% of DCHP in J was extracted.

The total thickness of the thus prepared 1q sheet was 700 μm, the (I) layer was 600 μm, and the (T1) layer was 100 μm. Next, the sheet was preheated at 140°C, stretched 7.5 times in the longitudinal direction (hereinafter abbreviated as MD), heat-treated at 150°C while allowing 5% relaxation in MD, and then rolled up (Example 1).

In addition, after stretching the sheet 4.5 times in the MD at 140°C,
15 in the lateral direction (hereinafter abbreviated as TD) into the stenter.
The film was stretched 9 times at 5°C, heat treated at 160°C while allowing 7% relaxation, and the edges were slit and then rolled up (Example 2) The properties of the film obtained as described above were evaluated. The result is as shown in Table 1, and it can be seen that all of them have excellent oil impregnation properties and swelling properties, and are extremely excellent as oil-immersed insulating materials.

Comparative Examples 1 and 2 Commercially available biaxially oriented polypropylene films for oil-immersed condensers of a smooth type (Comparative Example 1) and a one-sided roughened type (
Comparative Example 2) was obtained and evaluated. The results are compared with Examples and summarized in Table 1. Although Comparative Example 2 has oil-impregnated properties, both Comparative Examples 1 and 2 have a large degree of swelling and can be used as oil-impregnated insulating materials. I can see there is a problem.

Example 3 As the PP layer (I), II was 99.2% and [η] was 2.
1 dl/a PP resin, as a porous PP layer (H), I
PP resin 10 with 99% I and 2.5d110
(H)/(I)/
(H) A sheet consisting of three layers is laminated and extruded in a nozzle,
Cooled and solidified on a cooling drum at 70°C, extracted in the same manner as in Example 2, and then biaxially stretched with 4.2 layers and 9 times (HD x TD).
Heat setting was performed to obtain a film with a thickness of 50 μm. The properties of this film are summarized in Table 1, and it can be seen that, like Examples 1 and 2, both oil impregnation and swelling properties are good.

Comparative Example 3 As a raw material for the (H) layer, II was 97% and [η] was 1.8.
dl/a PP resin and calcium carbonate (manufactured by Kinpei Tancal,
After melt extrusion and cooling of the melt sheet in the same manner as in Example 3 except for using a composition with 25 parts by weight (average particle size 3 μm),
A biaxially stretched film was obtained. The results of evaluating the properties of such a film are summarized in Table 1. (H> Because the average pore diameter of the layer is as large as 30 μm, the wettability to insulating oil is poor, and the flowability of insulating oil is rank C. It turns out that it cannot be used as an oil-immersed insulating material.

Example 4 The same raw materials as in Example 1 were prepared for the PP layer (I) and the porous PP layer (H), and this time only the raw material for the (I) layer was extruded as a single layer from a T-die using an extruder at 50°C. The film was cooled on a cooling drum, and then stretched to 4.2 times in the MD at 140°C. Before introducing the axially stretched film into a stenter, the raw material for the porous PP layer is extruded from a separate extruder, laminated on one side of the axially stretched film, stretched 9 times in the TD at 150°C, and slitted at the edges. I took it.

Next, the biaxially stretched film was introduced into a Triclean bath in the same manner as in Example 1, and the DCHP in the layer was set to 99.
After extracting 7% or more, it was dried at 120'C, subjected to tension heat treatment at 155C, and then rolled up.

The structure and properties of this film are summarized in Table 1, and it can be seen that the film has excellent properties in both swelling degree and insulating oil distribution.

[Effects of the Invention] The oil-immersed polypropylene film for electrical insulation of the present invention thus obtained and the method for producing the same have the following effects.

(1) Excellent insulating oil impregnability and fluidity, and stable initial characteristics when an oil-immersed element is formed.

(2) Since the swelling rate when immersed in insulating oil is extremely small, there are no problems such as increases in internal pressure of the element, and long-term reliability is high.

(3) Since the porous layer formed on the surface layer has extremely high uniformity, the corona breakdown voltage is particularly high.

Therefore, capacitors, cables, transformers, motors,
It is suitable as an insulating layer for oil-immersed electrical equipment such as generators, etc. In particular, in oil-immersed capacitors, the porous polypropylene layer side of the film of the present invention is of a type in which electrodes are formed by vapor deposition of metals such as aluminum and zinc. When the vapor deposited layer is formed, the dimensional change of the layer when immersed in oil is extremely small, so cracks occur in the vapor deposited layer and the tan of the capacitor increases.
This is preferable because problems such as an increase in δ can be avoided.

Claims (3)

[Claims] (1) Polypropylene layer containing substantially no pores (I
) with a porous polypropylene layer (H
) are laminated, and the thickness fraction of the (I) layer is 50 to 90%.
An oil-immersed polypropylene film for electrical insulation. (2) Composition (a) consisting of 100 parts by weight of polypropylene and 70 to 180 parts by weight of extractable organic solids other than polypropylene and polypropylene resin (b) are laminated in a melt extrusion die using separate extruders. The method for producing an oil-immersed polypropylene film for electrical insulation according to claim 1, characterized in that the organic solid is extracted after the melt formation. (3) The method for producing an oil-immersed polypropylene film for electrical insulation according to claim 2, wherein the extractable organic solid is at least one selected from dicyclohexyl phthalate and triphenylene phosphate.