JPH0421965B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an improvement in a polypropylene film that is used as an electrical insulating layer while being immersed in electrical insulating oil. [Prior Art] Conventional electrical insulating paper has been used as the oil-immersed insulation layer (or dielectric layer) of oil-immersed electrical equipment (condensers, transformers, cables, motors, generators, etc.), but recently polypropylene There are cases where film is used. This film not only has a much higher withstand voltage than electrically insulating paper, but also has several advantages, such as a small dielectric loss tangent and a dielectric constant close to that of insulating oil. However, conventional polypropylene films have the disadvantage of extremely high swelling and slippage due to insulating oil, and therefore, when used for oil-immersed insulation applications,
There were various restrictions. For example, when a capacitor element is made by winding a polypropylene film and immersed in insulating oil, the film swells with the oil, the element becomes tightly wound and hard, and the flow of insulating oil between the layers becomes poor. This causes the problem of putting it away. As an emergency measure to avoid this, there is a method of winding the element loosely when first winding it, but if you wind it too loosely, it is likely that the winding will be misaligned, and
Wrinkles are also likely to occur. Therefore, the present inventors found that it is sufficient to use a polypropylene film with a high melting point in order to reduce swelling caused by insulating oil. However, it has been found that even such a specific polypropylene film cannot provide an insulating layer that does not swell, has a sufficiently high withstand voltage, and is stable for a long period of time. [Object of the Invention] The object of the present invention is to not only further improve the above-mentioned disadvantage, that is, the property of being easily swollen when immersed in oil, but also to provide an insulating layer that has a high withstand voltage and is stable even after long-term use. The purpose is to provide a polypropylene film. [Structure of the Invention] In order to achieve the above object, the present invention has the following structure, that is, a film mainly made of polypropylene, which has a small angle X from the edge direction.
The present invention is characterized by an oil-immersed polypropylene film for electrical insulation, which exhibits a layered linear four-point scattering image and is characterized by substantially no voids in the film. Polypropylene (hereinafter abbreviated as PP) herein refers to polypropylene having an isotactic degree of 90% or more, preferably 95% or more, more preferably 97% or more, and a melt index of 0.1 to 100 g/10
minutes, preferably in the range of 1 to 40 g/10 minutes, as swelling by the insulating oil is reduced. Further, when the melt index is within the above range, the amount eluted into the insulating oil is reduced and the viscosity of the insulating oil does not increase, which is preferable. Among the above-mentioned PPs, those having a melt crystallization temperature (T _nc ) in the range of 95 to 130°C, more preferably
The temperature is in the range of 105 to 124°C. If T _nc is within the above range, oil swelling due to insulating oil will be small and film forming properties will be good, making it possible to make a homogeneous film, and as a result, insulation defects will be reduced. preferable. Of course, PP also contains an appropriate amount, preferably 30 mol % or less, of copolymerized components such as olefins such as ethylene, butene, pentene, and hexene. When copolymerized components are included in this way, the number of poids in the PP film decreases, but
On the other hand, since swelling during oil immersion increases, the copolymerization component is desirably 10 mol% or less. Note that the PP may contain any known additives, such as antioxidants, slip agents, antiblocking agents, crystal cutting agents, thickening (lowering) agents, etc., as necessary. Further, other polyolefin resins may be mixed in the PP in an amount of 30% by weight or less, preferably 10% by weight or less, as long as the object of the present invention is not impaired. The film of the present invention is a PP film made of a composition mainly composed of PP as described above. The small-angle X-ray scattering image from the edge direction of the PP film of the present invention must show a layered linear four-point scattering image. This is because the higher-order structure takes a checkerboard-like ordered structure consisting of crystals and amorphous elements.
This is because swelling of the polypropylene film during oil immersion can be prevented or reduced. For the definition of a layered linear four-point scattering image, see "Polymer X-ray Diffraction" by Masao Kakudo and Nobutami Kasai, published by Maruzen Co., Ltd., pp. 298-299.
As described in detail in et al., four scattering peaks appear with mirror symmetry. The repeating unit of the checkered pattern, that is, the size of the long period determined from Bragg's formula, is preferably 260 Å or less in both the longitudinal direction and the thickness direction, preferably in the range of 250 to 180 Å, and is within this range. This makes it possible to prevent the polypropylene film from swelling when immersed in oil. Further, in the case of the PP film of the present invention, substantially no voids should be present in the film. void,
In other words, there are spaces or voids in which another medium with very low density, such as air, is present in the medium made of PP, and the absence of these voids is essential for long-distance materials with sufficiently high withstand voltage. This is a necessary condition for the insulator layer to be stable over a period of time. The presence or absence of voids can also be determined by the presence or absence of scattered small-angle X-ray scattering, but more precisely, the film can be observed using an optical microscope by mounting both surfaces of the film in a liquid with a refractive index close to PP, such as liquid paraffin. Judging by the presence or absence of parts that glow strongly when The number of voids observed under the oblique light of an optical microscope was 1/void in the case of the film of the present invention.
A number of particles of 10 mm ² or less, preferably 0.3 pieces/10 mm ² or less is a necessary condition for an insulating layer having a sufficiently high withstand voltage and being stable for a long period of time. Furthermore, the density of the film of the present invention after oil immersion is 0.885.
~0.915g/ ^cm2 , particularly preferably 0.895~0.912g/cm2
Fabrics in the cm ² range are preferred. When the density is within the above range, swelling due to insulating oil is reduced and the mechanical strength of the insulating layer can be maintained. In addition, the birefringence of the film of the present invention after oil immersion is
It is preferably in the range of 0.020 to 0.035, preferably 0.025 to 0.032. If the birefringence is within this range, the swelling caused by the insulating oil will be small, and the film will be less likely to crack, making dielectric breakdown less likely. Further, the crystal melting point of the PP film of the present invention after oil immersion is preferably 166°C or higher, preferably 168°C or higher. Crystal melting point (T _n ) of the film after oil immersion
is less than 166℃, preferably less than 168℃,
When PP film is used as an oil-immersed gas barrier for oil-immersed electrical equipment such as capacitors and cables, PP film undergoes significant swelling due to oil during immersion.
This is because the swelling of the film impairs the flow of insulating oil between the insulating layers, causing dielectric breakdown. Furthermore, in the case of the film of the present invention, the longitudinal heat shrinkage rate before oil immersion is 0.1 to 5%, preferably 0.5 to 3%.
% range, the film can be made more suitable for oil-immersed electrical insulation. If the heat shrinkage rate is within this range, the insulating layer will be tightly wound and wrinkles will not occur, and since it will not stretch in the longitudinal direction in the insulating oil, the wound insulating layer will not loosen. . An example of a method for keeping the longitudinal heat shrinkage within this range is to apply it during the film forming process, but it is also possible to apply it during the film forming process, but it is also possible to keep the PP film in a roll for a long time while relaxing it in the longitudinal direction. (1 to 50 hours) A method of aging treatment at 80 to 140°C is preferred. Next, when using PP film alone, determine the surface roughness (Rmax) of one or both sides of the film of the present invention.
It is preferable to keep it in the range of 1 to 50 μm, preferably 2 to 40 μm. If it is within this range,
The interlayer flowability of the insulating oil is improved, making it difficult to cause dielectric breakdown, and further improving the pressure resistance characteristics. Of course, it is obvious that electrical insulating paper may be laminated and integrated with the PP film to improve interlayer flowability, and the surface roughness described above may be provided as necessary. When electrically insulating paper (hereinafter referred to as paper) is laminated and integrated on one or both sides of this PP film, the paper is a natural paper whose main component is cellulose (JIS C2301, 2302, 2303, 2304, 2306). , 2307 and 2308) and synthetic paper. Note that particularly preferred paper has a density of 0.6 to 0.9 g/cm ³ and a thickness of 10 to 50 mμ. Next, an example of a method for manufacturing the PP film of the present invention will be described. The PP resin is melt-extruded and extruded into a sheet from a die, which is then wrapped around a cooling drum kept at a high temperature of 80 to 120°C, kept at around the melt crystallization temperature of the polymer T _nc , and then cooled and solidified. . This PP sheet is inserted between a set of rolling rolls, and the rolling magnification (value obtained by dividing the sheet thickness before rolling by the sheet thickness after rolling) is 5 to 12 times, preferably 7 to 10 times. Rolling under high wire pressure. The rolling pressure is preferably in the range of 1000 to 3000 Kg/cm, more preferably 1100 to 2000 Kg/cm, and the temperature of the rolling roll is 105 to 160°C, preferably 125 to 150°C.
A range of is suitable. Liquids (water, surfactant aqueous solution, alkylene glycol, polyalkylene glycol, glycerin,
Wetting the material with electrical insulating oil, etc.) before rolling facilitates uniform high-magnification rolling. Film obtained by rolling (usually thickness ranges from 10 to 300 μm)
Reheat to 100-150℃ and cut to original size in the longitudinal direction.
Heat treat for 1 to 20 seconds while giving 0.5 to 10% relaxation. If necessary, 600~
Corona discharge treatment may be performed with an amount of electrical energy of about 6000 J/m ² . If this treatment is performed in an atmosphere such as air, nitrogen, or carbon dioxide, the surface tension will be improved and adhesive properties will be excellent. Then heat this film to 90-140℃ as needed.
The film is passed through heated embossing rolls to roughen one or both sides of the film so that the surface roughness (Rmax) is in the range of 1 to 50 μm, preferably 2 to 40 μm. As described above, the most preferable method for manufacturing the film of the present invention is to use rolling alone, but stretching may also be combined after rolling. Furthermore, it is clear that the surface may be roughened by sandblasting, etching, or the like instead of embossing. When laminating and integrating PP film and paper, the method of laminating and integrating them is not particularly limited, but may be lamination using an adhesive, and when using an adhesive, it is preferable to This is lamination using thermosetting adhesive. By using a thermosetting adhesive, it is possible to suppress the swelling of the laminated film due to oil, particularly the drawback that the laminated film stretches in the longitudinal direction and width direction due to swelling with oil.
As thermosetting adhesives, amino-based, phenolic-based, resorcinol/formaldehyde-based, xylene-based, furan-based, epoxy-based, polyisocyanate-based, unsaturated polyester-based, and thermosetting acrylic resins can be used. Among these, particularly preferred are polyisocyanate adhesives and epoxy adhesives, and most preferred are polyester to polyisocyanate adhesives. Both of them are particularly excellent in that the extent to which they dissolve into the oil and deteriorate the electrical properties of the oil is extremely small. The amount of adhesive used for laminating and integrating is preferably in the range of 0.5 to 5 g/m ² (weight of adhesive in dry state), particularly preferably in the range of 1 to 5 g/m 2 (weight of adhesive in dry state).
It is in the range of 4g/ ^m2 . Within this range, the electrical properties (especially dielectric loss tangent) of the laminated and integrated film will not deteriorate, and the film and paper will not separate in oil. Describing a typical method of laminating and integrating, the surface of corona discharge treated PP film is
Apply an organic solvent solution of thermosetting adhesive, and
It is pre-dried with hot air at 50 to 100°C, and paper is placed on this surface and pressed with a heated press roll to form a laminated integrated film. This is aged for 10 to 50 hours at 50℃, or for 1 to 7 days at room temperature. [Effects of the Invention] In the present invention, a polypropylene film having a specific higher-order structure and having substantially no voids is used for oil-immersed electrical insulation, so that the following excellent effects are produced. (1) Less swelling due to insulating oil. (2) The insulating layer is less likely to tighten or loosen. (3) The dielectric loss tangent from 0 to 100°C is small, so the dielectric loss is also small, and there is little heat loss. (4) Excellent long-term electrical breakdown characteristics at low and high voltages. (5) It also has excellent electrical insulation properties at high temperatures of 80 to 120°C. (6) The insulating oil easily impregnates the PP film of the present invention,
Becomes a highly accurate and reliable electrical insulator. (7) It has low swelling, easy impregnation, and excellent electrical insulation properties, so it can be used as an electrical insulation material only with plastic materials. Therefore, it can be used as an insulating material for higher voltages than before. Therefore, the film of the present invention can be used in various oil-immersed electrical equipment such as capacitors, transformers, cables,
It is suitable as an oil-immersed insulation layer for motors, generators, etc. Note that the terms and measurement methods used in the present invention will be summarized and explained below. (1) Degree of isotacticity Extract PP with boiling n-heptane, divide the weight of the extracted residue by the original weight, multiply by 100, and display as a percentage. (2) Melt index: ASTM D-1238-73
Measured under condition L. (3) Melt crystallization temperature (T _nc ): 5 mg of the sample was placed in a PerkinElmer DSC-type, and the atmosphere was replaced with nitrogen. Next, at a heating rate of 20℃/min,
Raise the temperature to ℃ and hold at this 200℃ for 5 minutes. Next, the temperature is lowered at a rate of 20°C/min to draw an exothermic peak associated with crystallization of the sample. Let the temperature at the top of this peak be T _nc . (4) Crystal melting point (T _n ): PerkinElmer DSC
- Put 5 mg of the sample into a mold and raise the temperature at a rate of 10° C./min under a nitrogen stream, and let T _n be the temperature at the top of the endothermic peak associated with crystal melting of PP. If the peak is hidden behind another peak and becomes a shoulder, divide the area and create the peak separately. (5) Density: According to ASTM D 1505. (6) 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 calculate the birefringence by subtracting Nx from Ny. Note that a sodium D line is used as a light source during measurement, and methyl salicylate is used as a mounting liquid. (7) Surface roughness (Rmax): Ramx is measured by the method described in JIS B 0601-1976. The cutoff value is 0.8mm. (8) Heat shrinkage rate: from film, length 200mm, width 10
Cut a mm sample (the direction in which the heat shrinkage rate is measured is the length direction). The sample is kept in a hot air circulation oven at 120°C for 15 minutes, then taken out to room temperature and its length is measured. Its length is L
(mm), the thermal contraction rate can be calculated using the following formula. Heat shrinkage rate (%) = 100 x (200-L) / 200 (9) Degree of swelling due to insulating oil: 100mm from the film
Cut a sample of ×100 mm and calculate the weight of this
(mg). This sample is immersed in alkylbenzene oil at 80°C and left for 24 hours. Next, take out this sample, wipe off the oil on the surface with filter paper, wash it by immersing it in acetone, and completely remove the oil on the surface with gauze soaked in acetone. Measure the weight of this sample and let it be W' (mg), then the degree of swelling (%) can be calculated using the following formula. Swelling degree (%) = 100 x (W'-W)/W (10) Flowability of insulating oil: A capacitor element is made by alternately winding a 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: Oil-free areas exist across the surface 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. (11) Electrical insulating oil: A general term for various known electrical insulating oils, such as mineral oil, castor oil, cottonseed oil, alkylbenzene (eg, dodecylbenzene), diallylalkane, and polybutene oil. In addition, JIS C
Electrical insulating oils having the properties specified in 2320 are preferred. (12) Long period L Calculated using the Bragg equation from the small-angle X-ray scattering image in the edge direction. Long period L=λ/2 sin (1/2 tan ⁻¹ L ₀ /R) where R is the camera radius, and L ₀ is the distance from the equator (meridian) in the longitudinal direction (thickness direction) to the center of scattering. (13) Small-angle X-ray scattering image Refers to the image captured in a small-angle X-ray scattering photograph obtained by irradiating a sample with X-rays.The measurement conditions for that photograph are as follows. Output 50kV-200mA, CuKα ray Ni filter used, 0.3mmφ collimator, camera radius 400
mm, exposure time 1 hour. The presence or absence of a layered linear four-point scattering image is determined from the above photograph. (14) Mount liquid paraffin on both sides of the void sample and observe it under oblique light using an optical microscope. At that time, change the focus from the front side of the film to the back side, and what appears to be a foreign object is a void.
Convert that number to 10 mm ² and count. It is necessary to see at least 10 fields of view, and the number of voids is expressed as the arithmetic mean value. If the number of voids is 1/10mm2 ^or less, it is considered that there are virtually no voids. [Example] Next, embodiments of the present invention will be described based on Examples. Example 1 PP resin pellets with an isotactic structure content of 98.5%, a melt index of 6 g/10 min, and a T _nc of 110.5°C were fed into an extruder, melted and extruded at 240°C, and discharged into a sheet from a T-shaped nozzle. I forced it. This molten sheet was wound around a cooling drum at 98°C, held on a roll kept at 115°C for about 3 seconds, and then cooled to produce a sheet with a thickness of about 2 mm. This sheet is rolled through a set of rolling rolls (roll diameter
250mm) and rolled 10 times. Rolling pressure is 1200Kg/cm, rolling roll temperature 146
℃, and rolling was carried out while the sheet surface was wetted with ethylene glycol. The resulting 200 μm thick film was placed in an atmosphere at 140°C, and the film was heated by 1% in the longitudinal direction.
Heat treatment was performed for 10 seconds while providing relaxation. Next, this film is passed between embossing rolls heated to 130℃, and approximately
100 mesh sandplast processing pattern was transferred. Next, this film was kept under tension in an atmosphere at 120° C. for 10 hours for aging heat treatment, and then slowly cooled to room temperature. The properties of the film thus obtained are summarized in Table 1. The film of the present invention exhibits a layered linear four-point scattering image, and the repetition period is 200 Å.
As there are no voids in the film, the swelling caused by insulating oil is as low as 1.2%, and it has excellent flowability for insulating oil (dodecylbenzene), making it an extremely excellent film for oil-immersed electrical insulation. It turns out that it is something.

【table】

[Comparative example]

Using the cast sheet used in Example 1, the rolling pressure was 500 kg/cm and the rolling roll temperature was 90°C.
A film with a thickness of 200 μm was obtained in the same manner as in Example 1, except that the rolling was carried out in stages for a total of 10 times. Various properties of the film thus obtained are summarized in Table 2.

[Table] As shown above, when the rolling conditions, i.e., line pressure and rolling temperature, are changed, the higher-order structure and the state of voids change drastically. It turns out that this is a condition.

Claims (1)

[Claims] 1. A film mainly composed of polypropylene, which is characterized in that a small-angle X-ray scattering image from the edge direction shows a layered linear four-point scattering image, and there are substantially no voids in the film. Oil-immersed polypropylene film for electrical insulation.