JPH074899B2 - Oil-immersed polypropylene film for electrical insulation and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a propylene film used as an insulating layer for capacitors, power cables, transformers, etc. by immersing it in an electrically insulating oil, and a method for producing the same.

[Prior Art] Polypropylene film has excellent electric insulation,
Moreover, because it is lightweight, it replaces the insulating paper with the power cable,
It has come to be used for capacitors and transformers.
However, the polypropylene film has a poor diffusivity of electric insulating oil (hereinafter referred to as oil) on the surface, and when the film is used instead of insulating paper of a capacitor, for example,
There is a problem that the oil impregnation rate is slow and the oil is not uniformly impregnated, and various methods for roughening the surface of the film to improve the diffusibility of oil have been proposed (for example, JP-A-51-63).
Japanese Patent Publication No. 500, Japanese Patent Publication No. 61-57333, Japanese Patent Publication No. 61-26168
Issue Bulletin).

[Problems to be Solved by the Invention] However, the conventional roughened polypropylene film has a drawback that the swelling with respect to oil is extremely large, and when impregnated with oil, the swelling causes partial deformation in the thickness direction. , The film layers are in close contact and shut off the oil supply path,
For this reason, there have been problems that the breakdown voltage is lowered and the element is destroyed in a short time due to heat generation or the like.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polypropylene film for oil-immersed electrical insulation, which is excellent in oil impregnation property and has small oil swelling deformation, and a method for producing the same, by solving the above problems.

[Means for Solving Problems] In the present invention, the polypropylene layer (I) having substantially no pores has a porosity of 30 to 85% and an average pore diameter of 0.01 to 5 μm on at least one surface thereof. The present invention relates to a polypropylene film for oil-immersed electrical insulation, characterized in that a polypropylene layer (H) is laminated, and the thickness fraction of the (I) layer is 50 to 90%, and a method for producing the same.

In the present invention, the polypropylene constituting the polypropylene layer (I) is preferably one having an isotactic index (II) of 97% or more in order to reduce the swelling rate. It is more preferably 99% or more. Also, the
When the intrinsic viscosity [η] of PP is 1.4 to 2.3, not only the amount eluted into oil is reduced, but also film production is favorable, and as a result, mechanical properties and dielectric breakdown voltage are favorable, which is preferable.

Furthermore, when the PP layer (I) is oriented, the dielectric breakdown voltage, mechanical properties, and swelling properties are all favorable, and in the case of uniaxial orientation, the birefringence is in the range of 0.015 to 0.035 and biaxial orientation. In this case, those having a plane orientation in the range of 0.010 to 0.020 are preferable from the above viewpoint.

Furthermore, it is necessary that the PP layer (I) contains substantially no pores. In the present invention, “substantially” means that the inclusion of a small amount of pores incidentally generated by, for example, polypropylene stretching is allowed. However, in order to improve the dielectric breakdown voltage, it is preferable that such voids are not contained as much as possible, and from this viewpoint, the void content is 5%.
It is preferably less than.

Next, the porous polypropylene layer (H) has a porosity of 30-
It is necessary to be 85%, preferably 40 to 80%. If the porosity is too small, not only the swelling ratio when immersed in insulating oil increases but also the fluidity of the insulating oil decreases, causing partial heat generation and dielectric breakdown. On the other hand, if the porosity is too large, the (H) layer is likely to be cleaved, and particularly when a large force is applied like a cable, the (H) layer peels off and causes dielectric breakdown.

The average pore diameter of the porous PP layer (H) is 0.01 to 5 μm.
It is necessary to be, and preferably 0.1 to 3 μm. If the average pore size is too small, the impregnation property and fluidity of the insulating oil will be poor, and at the same time, the swelling ratio due to the oil will increase and cause dielectric breakdown. On the other hand, if the average pore size is too large, it causes insulation defects such as a decrease in dielectric breakdown voltage.

In addition, in order to increase the mechanical strength of the (H) layer, [η] of the PP
Is preferably 1.6 to 3.0 dl / g. Also, II is 96%
It is preferable that the solubility is higher in the insulating oil.

The composition of the polypropylene layer (I) and the porous polypropylene layer (H) is (I) / (H) or (H) /
(I) / (H), and the percentage of the total thickness of the (I) layer is 50 to 90%, preferably 60 to 80%.

If the thickness fraction of the (I) layer is too small, not only the mechanical strength decreases, but also the dielectric breakdown voltage decreases. On the other hand, if the thickness fraction is too large, the oil impregnation property and the swelling property are poor, and especially the corona discharge voltage is lowered and the breakdown is likely to occur.

The polypropylene film of the present invention may be embossed on all layers or only the (I) layer for the purpose of further reducing the swelling rate, but the embossing rate is 50% or less from the viewpoint of not lowering the dielectric breakdown voltage. Preferably there is.

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

In the present invention, the extractable organic solid other than polypropylene added to polypropylene as the raw material for the (H) layer preferably has a softening point of 35 to 100 ° C. and a molecular weight of 200 to 1000, and specifically, Dicyclohexyl phthalate (DCHP), triphenylene phosphite (TPP), cetyl palmitate, stearyl suareto, panthaerythritol stearate, etc. It is preferable for obtaining the porosity and the average pore size.

In the present invention, the above organic solid is polypropylene 10
It is necessary to be 70 to 180 parts by weight, preferably 90 to 160 parts by weight, relative to 0 parts by weight. If the amount of addition is too small, only the porosity and the pore diameter of the formed pores are small, and the impregnating property of the insulating property and the swelling property are poor and the dielectric breakdown is likely to occur. On the other hand, if the addition amount is too large, (H)
When the layer is extruded, the viscosity of the composition is remarkably reduced to make the extrusion difficult, and the transfer layer of the organic solid to the (I) layer is increased, so that the dielectric breakdown voltage of the produced polypropylene film is increased. It causes problems such as deterioration.

In the present invention, the polypropylene resin forming the (I) layer and the polypropylene forming the (H) layer and the composition comprising the organic solid are melt-extruded from separate extruders, laminated in one die, and ( I) / (H) or (H)
/ (I) / (H) is formed into a sheet or tube and extruded. Laminating in the die here means that it is already formed as a laminate when extruded from the die, and specifically, in the short tube for guiding the polymer to the die from the extruder as the laminating method. A method of laminating and a method of laminating in the manifold portion in the die are mentioned, and in particular, the method of laminating in the manifold portion is preferable in consideration of the transition of the organic solid (H) layer to the (I) layer. As a stacking method, only the (I) layer is formed,
A technique of forming an (H) layer by using another extruder and a die after being unstretched or stretched at least uniaxially is also applicable. However, (H) and (I) containing a large amount of organic solids
The former method is superior for strongly adhering the layers and firmly integrating them.

The sheet or tube extruded as above is
After cooling with a cooling drum or a cooling mandrel, a water tank or the like, an organic solid is extracted and guided to an extraction layer.In the case of the organic solid, an effective extraction solvent that does not elute polypropylene is trichloroethylene, trichloromethane, methyl ethyl ketone, toluene, Examples include xylene, methanol and ethyl acetate.

Further, in the present invention, stretching may be performed before extraction, after extraction, or during extraction, and further, organic solid may be partially extracted, and after stretching, organic solid may be completely extracted. However, in the stretching step, migration of the added substance is likely to occur between the layers, and from this viewpoint, at least a part of the organic solid added, preferably 30% or more, is extracted before stretching. It is preferable to keep.

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

After the above steps, with the organic solids completely extracted, 12
The film of the present invention is obtained by heat treatment at a temperature of 0 to 170 ° C.

The present invention is characterized by having the above-mentioned characteristics, but when the heat shrinkage in the longitudinal direction of this film is in the range of 0.5 to 6%, preferably 1 to 4%, This is preferable because the dimensional change during oil immersion is reduced, the element is not tightened and wrinkles are not generated, and the long-term reliability is improved.

[Operation] The present invention has good oil impregnation by laminating 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 surface of the polypropylene layer (I). In addition, swelling due to oil could be suppressed.

[Characteristic measuring method and effect evaluating method] Next, regarding the measuring method and the evaluating method of the present invention,
Shown together.

(1) Isotactic index (II) A sample is vacuum dried at 130 ° C. for 2 hours. From now on, weight W (m
Take the sample of g), put it in a Soxhlet extractor, and boil it n
-Extract for 12 hours with heptane.

Next, after taking out this sample and thoroughly washing with acetone,
After vacuum drying at 130 ° C. for 6 hours, the weight W ′ (mg) is measured and calculated by the following formula.

II (%) = (W '/ W) x 100 (2) Intrinsic viscosity ([η]) In accordance with ASTM D 1601, 0.1 g of material is used for tetralin 10 at 135 ° C.
It was completely dissolved in 0 ml, measured, and expressed in dl / g.

(3) Average Pore Size Obtained from the results of surface and cross-section observation by a scanning electron microscope (SEM).

(4) Porosity (Pr) A sample (10 cm x 10 cm) was immersed in flowing paraffin for 24 hours,
The weight (W ₂ ) of the surface layer after the fluid paraffin was sufficiently wiped off was measured, and the void volume (V ₀ ) was calculated from the weight (W ₁ ) of the sample before immersion and the density (ρ) of the fluid paraffin as follows. Ask in.

V ₀ = (W ₂ −W ₁ ) / ρ Porosity (Pr) is the apparent volume of all layers (value calculated from thickness and dimensions) V, pore volume V ₀ and volume of polypropylene layer (I) It is calculated by the following equation using (V ₁ ).

Pr = V ₀ / (V-V ₁ ) × 100 (%) (5) Birefringence The refractive index (Ny) in the longitudinal direction and the refractive index (Nx) in the width direction of the film are measured using Abbe's refractometer. The absolute value of the difference between Ny and Nx is defined as birefringence. In addition, sodium D ray is used as a light source at the time of measurement, and methyl salicylate is used as a mount solution.

(6) Plane orientation Using the Abbe refractometer, the refractive index, Ny, Nx, Nz in the longitudinal direction, width direction and thickness direction of the film are measured,
Calculate with the following formula.

Plane orientation = (Ny + Nx) / 2−Nz The measurement conditions are the same as those for birefringence.

(7) Heat shrinkage rate A sample with a length of 200 mm and a width of 10 mm is cut out from the film (the direction in which the heat shrinkage rate is measured is the length direction). 20 this sample
After being kept in a hot air circulation oven at ℃ for 15 minutes, it is taken out at room temperature, and its length L (mm) is measured and calculated by the following formula.

Thermal shrinkage (%) = 100 x (200-L) / 200 (8) Swelling degree with insulating oil A 30 mm x 30 mm sample was cut from the film, and the thickness (D ₁ )
To measure. Then, this sample is immersed in an alkylbenzene oil at 100 ° C., immersed in a load of 1 kg / mm ₂ for 24 hours, cooled to room temperature, and immediately taken out to measure the thickness (D ₂ ). The degree of swelling is calculated by the following formula.

Swelling degree (%) = 100 × (D ₂ −D ₁ ) / D ₁ (9) Flowability of insulating oil A film and an aluminum foil are alternately wound to form a capacitor element. This is dipped in insulating oil to vacuum impregnate the oil. After that, the element is disassembled, and it is visually judged whether or not the insulating oil has spread between all layers of the element.

Rank A: Evenly spread over the entire surface.

Rank B: There is a slight oilless point.

Rank C: There is a flat surface with no oil.

(10) Electric insulating oil A general term for various known electric insulating oils such as mineral oil, castor oil, alkylbenzene, diallyl alkane, polybutene oil, and silicone oil.

EXAMPLES Next, the present invention will be described based on examples.

Examples 1 and 2 As PP layer (I), II is 97%, [η] is 1.8 dl / g PP resin, and II is 97%, [η] is the raw material of porous PP layer (H).
A composition of 100 parts by weight of PP resin of 2.8 dl / g and 150 parts by weight of dicyclohexyl phthalate (DCHP, melting point 63 ° C) is prepared, melt-extruded by using different extruders, and laminated at the manifold part in the T-die. , (I) layer / (H) layer was extruded. The sheet was cooled and solidified on a cooling drum at 60 ° C., immediately introduced into a trichlene bath,
DCHP was extracted by 99.7% or more.

The sheet thus obtained has a total thickness of 700 μm,
The (I) layer was 600 μm and the (H) layer was 100 μm. Next, the sheet was preheated at 140 ° C., stretched 7.5 times in the longitudinal direction (hereinafter abbreviated as MD), and then heat-treated at 150 ° C. while allowing MD to relax by 5% and wound (Example 1). .

In addition, after stretching the sheet 4.5 times in MD at 140 ° C., it is guided to a stenter and stretched in transverse direction (hereinafter abbreviated as TD) 9 times at 155 ° C. while allowing 7% relaxation at 160 ° C. The edge of the film was heat-treated and wound after slitting (Example 2). The properties of the film obtained as described above were evaluated. The results are shown in Table 1. All of them were excellent in oil impregnation property and swelling property. It can be seen that it is extremely excellent as an immersion insulating material.

Comparative Examples 1 and 2 Commercially available biaxially oriented polypropylene films for oil-immersion capacitors, smooth type (Comparative Example 1) and single-sided roughened type (Comparative Example 2) were obtained and evaluated. The results are summarized in Table 1 in comparison with the examples, but in Comparative Example 2,
Although they have oil impregnation properties, Comparative Examples 1 and 2 both have a large degree of swelling, showing that there is a problem as an oil-immersed insulating material.

Example 3 As the PP layer (I), PP having II of 99.2% and [η] of 2.1 dl / g
Resin, porous PP layer (H), II is 99%, [η] is 2.
A composition of 100 parts by weight of 5 dl / g PP resin and 140 parts by weight of triphenylene phosphite (TPP, melting point 49 ° C.) was melt extruded by using different extruders, and (H) / (I) / ( H) 3
Layered sheets are stacked in a die and extruded, cooled and solidified on a cooling drum at 70 ° C., extracted in the same manner as in Example 2, and then 4.2 × 9 times (MD × TD) biaxially stretched and heat set. Then, a film having a thickness of 50 μm was obtained. The characteristics of the film are summarized in Table 1, and it can be seen that the oil impregnability and the swelling characteristics are good as in Examples 1 and 2.

Comparative Example 3 As a raw material for the (H) layer, P with II of 97% and [η] of 1.8 dl / g
P resin and calcium carbonate (made by Kinpei charcoal, average particle size 3μ
m) Melt extrusion was performed in the same manner as in Example 3 except that the composition was used in an amount of 25 parts by weight, the molten sheet was cooled, and biaxially stretched to obtain a film. The results of evaluating the properties of the film are summarized in Table 1. The average pore diameter of the (H) layer is as large as 30 μm, so that the wettability with 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 material as in Example 1 was prepared as the PP layer (I) and the porous PP layer (H), and this time, only the raw material of the (I) layer was fed from the extruder.
It was extruded as a single layer from a T-die, cooled on a cooling drum at 50 ° C., and subsequently stretched to MD at 4.2 times at 140 ° C. Before introducing such a uniaxially stretched film into a stenter, the porous PP layer raw material was extruded from another extruder and laminated on one side of the uniaxially stretched film, and stretched 9 times at TD at 150 ° C. and wound after slitting the edge portion. .

Then, the biaxially stretched film was introduced into a trichlene bath in the same manner as in Example 1 to extract 99.7% or more of DCHP in the (H) layer, dried at 120 ° C, and subjected to tension heat treatment at 155 ° C. I wound it up.

The constitution and characteristics of such a film are summarized in Table 1, and it can be seen that the film has excellent swelling degree and insulating oil flowability.

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

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

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

(3) The corona breakdown voltage is particularly high because the uniformity of the porous layer formed on the surface layer is extremely high.

Therefore, capacitors, cables, transformers, motors,
It is suitable as an insulating layer for oil-immersed electrical equipment such as generators, and particularly in oil-immersed capacitors, in the type in which electrodes are formed by vapor deposition of metal such as aluminum or zinc, the porous polypropylene layer side of the film of the present invention When the vapor-deposited layer is formed on, the dimensional change during oil immersion of the layer is extremely small.
This is preferable because problems such as an increase in δ can be avoided.

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Claims (3)

[Claims] 1. A porous polypropylene layer (H) having a porosity of 30 to 85% and an average pore diameter of 0.01 to 5 μm on at least one side of a polypropylene layer (I) having substantially no pores.
Is laminated, and the thickness fraction of the layer (I) is 50 to 90%, and a polypropylene film for oil-immersed electrical insulation. 2. A composition (a) consisting of 100 parts by weight of polypropylene, 70 to 180 parts by weight of an extractable organic solid other than polypropylene, and a polypropylene resin (b) are melt-extruded in a die using separate extruders. 2. The method for producing a polypropylene film for oil-insulated electrical insulation according to claim 1, wherein the organic solid is extracted after being laminated and melt-formed. 3. The polypropylene film for oil-immersed electrical insulation according to claim 2, wherein the extractable organic solid is at least one selected from dicyclohexyl phthalate and triphenylene phosphite. Manufacturing method.