JPS6214564B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an oil-resistant electrical insulating sheet that has excellent oil resistance and further exhibits little change in the viscosity of insulating oil. Polypropylene has excellent dielectric properties and high electrical breakdown strength, so it is used as an insulating material in electrical equipment such as ultra-high voltage cables and capacitors. However, when this polypropylene is used as an insulating material for electrical equipment, film-like polypropylene is used in combination with insulating oils used in electrical equipment, especially mineral oils that are widely used, or carbonized oils such as alkylbenzenes, alkylnaphthalenes, and diallylethanes. Problems still remain, such as swelling caused by hydrogen-based insulating oil, resulting in an increase in thickness, and elution into the insulating oil, increasing the viscosity of the insulating oil. The increase in thickness due to swelling poses important problems as discussed below. For example, in the case of polypropylene laminated paper, which is made by laminating polypropylene on kraft paper, the first reason is that the thickness of the polypropylene increases, which is necessary to compensate for the expansion and contraction of insulating oil due to temperature changes in electrical equipment. A problem arises in that the flowability of the insulating oil within the insulating layer is reduced. In conventional kraft paper insulated electrical equipment, kraft paper is a porous material, so
Insulating oil can flow through kraft paper in the thickness direction, but because polypropylene laminated paper has a film-like polypropylene layer, insulating oil cannot penetrate through the kraft paper surface or inside. The insulating oil has no choice but to flow through the voids, and even without an increase in the thickness of the polypropylene layer, the flowability of the insulating oil is essentially poor. However, if relatively low-density kraft paper is used, it is possible to sufficiently secure the degree of distribution normally required for electrical equipment. However, when the polypropylene layer swells and increases in thickness, the kraft paper is compressed and the voids decrease, eventually making it impossible to ensure the necessary flow of insulating oil. Second, the compression of kraft paper increases the surface pressure between adjacent tapes, making it difficult for the tapes to slide against each other, which causes wrinkles in the tapes when they are bent during installation, such as in cables. A problem arises. These phenomena become more pronounced as the polypropylene layer swells more easily and the rate of increase in thickness is greater, and as the ratio of the thickness of the polypropylene layer to the total thickness of the polypropylene laminated paper increases. In other words, the easier the polypropylene layer swells, the smaller the proportion of the polypropylene layer in the total thickness of the polypropylene laminated paper needs to be. However, from the point of view of electrical characteristics,
It is better to have a larger proportion of the polypropylene layer, which has better dielectric properties, and it is most desirable to consist only of polypropylene film. Therefore, in order to obtain electrical equipment with excellent performance, it is important to minimize the swelling property of the polypropylene layer. In addition, polypropylene having a relatively low molecular weight eluted from the polypropylene layer into the insulating oil increases the viscosity of the insulating oil and deteriorates the flowability of the insulating oil within the insulating layer. Therefore, it is also important to minimize the increase in viscosity of the insulating oil due to the polypropylene layer. For this reason, several attempts have been made to improve the oil resistance of polypropylene. One of these is a method to improve the isotactic index of polypropylene (Isamu Ono, Tokyo Denki University Press, "Capacitor Utilization Manual," p. 133, published in 1975). An isotactic index of 90% can be obtained by keeping the production of atactic parts low or by cleaning and removing the atactic parts with a solvent.
This is considered to be a method using the above polypropylene. However, this method that focuses only on improving the isotactic index has problems such as the effect of improving the degree of swelling being insufficient or the viscosity of the insulating oil increasing significantly. It has not yet been possible to obtain insulating polypropylene that is fully satisfactory in terms of performance. Another method for suppressing the swelling properties of polypropylene is to perform a heat treatment in vacuum at a temperature below the melting point of polypropylene after forming it into a laminated paper, but this method also has the effect of improving swelling properties. This is insufficient, and the viscosity of the insulating oil increases significantly, resulting in insufficient performance. Furthermore, since the process is carried out under special conditions, the cost increases and it cannot be said to be an economically advantageous method. For this reason, it is impossible to avoid a certain degree of swelling and the resulting increase in thickness in electrical equipment that uses industrially produced and commercially available polypropylene, so multiple polypropylene layers are used and this A method has been proposed in which the apparent thickness increase of the entire laminated paper is reduced by providing a new layer between the layers that can absorb the thickness increase (Japanese Patent Laid-Open No. 53-96083). Although this method is quite effective in reducing the increase in thickness due to swelling, it has the disadvantage that the structure of the laminated paper becomes complicated and the manufacturing process becomes complicated. The inventors of the present invention have conducted intensive studies in view of the drawbacks of the conventional methods described above, and have found that polypropylene with a particularly limited structure has good electrical insulating properties in terms of oil resistance such as swelling properties and changes in the viscosity of insulating oil. It was discovered that it has extremely excellent properties for use, and the present invention was achieved. That is, in the present invention, the isotactic pentad fraction of the boiling heptane insoluble part is 0.955 or more, and the content of the boiling heptane soluble part is 2.0 to 9.0.
% by weight, and further includes a polypropylene film having an intrinsic viscosity of a polymer soluble in xylene at 20° C. of 1.0 dl/g or less. By using this oil-resistant electrical insulating sheet, it is possible to obtain an electrical device with less swelling and an accompanying increase in the thickness of the polypropylene layer, and also with less increase in the viscosity of the insulating oil. In addition, the specific polypropylene used in the present invention has good processability when laminating kraft paper, forming polypropylene films, and extruding sheets, and also has excellent stretchability when producing biaxially oriented films. There is. The isotactic pentad fraction of the boiling heptane insoluble portion, the content of the boiling heptane soluble portion and the intrinsic viscosity of the polymer soluble in xylene at 20° C. in the present invention are determined as follows. After completely dissolving 5 g of polypropylene in 500 ml of boiling xylene, the temperature was lowered to 20°C and left for 4 hours. Thereafter, this is filtered to separate the xylene insoluble portion at 20°C. The filtrate is concentrated to dryness to evaporate the xylene, and further dried under reduced pressure at 60°C to obtain a polymer soluble in xylene at 20°C. The intrinsic viscosity measured in tetralin at 135°C is the intrinsic viscosity of a polymer soluble in xylene at 20°C. The xylene insoluble portion at 20° C. is dried and then Soxhlet extracted with boiling n-heptane for 8 hours. This extraction residue is called the boiling heptane insoluble portion, and the value obtained by subtracting this dry weight from the weight of the prepared sample (5 g) divided by the weight of the prepared sample, expressed as a percentage, is the content of the boiling heptane soluble portion. be. What is isotactic pentad fraction?A.
Macromolecules 6 , 925 by Zambelli et al.
(1973), i.e. ¹³ C−
It is an isotactic chain of pentad units in a polypropylene molecular chain measured using NMR, in other words, it is the fraction of propylene monomer units at the center of a chain in which five consecutive propylene monomer units are men-bonded. However, regarding the attribution of NMR absorption peaks, the
Macrmolecules 8 , 687 (1975). Specifically, the isotactic pentad fraction is measured as the area fraction of the mmmm peak among the total absorption peaks in the methyl carbon region of the ¹³ C-NMR spectrum. By this method UK NATIONAL
NPL standard material of PHYSICAL LABORATORY
CRMNo.M19−14Poly propylene PP/MWD/2
When the isotactic pentad fraction was measured, it was 0.944. In the present invention, the isotactic pentad fraction of the boiling heptane insoluble portion must be 0.955 or more. Polypropylene with a value less than 0.955 has poor swelling properties, similar to conventionally commercially available polypropylene, and has a heptane soluble area of 2.0 or more.
Even at 9.0% by weight, the effects of the present invention cannot be achieved. Thus, in the present invention, the isotactic pentad fraction of the boiling heptane insoluble portion is an extremely important factor. Therefore, preferably, the isotactic pentad fraction of the boiling heptane insoluble portion is 0.96 or more. Further, in the present invention, the content of the boiling heptane soluble portion must be 2.0 to 9.0% by weight. In other words, the isotactic
Even if the pentad fraction is 0.955 or more, polypropylene in which the content of boiling heptane soluble parts exceeds 9.0% by weight will cause a large increase in both the swelling property and the viscosity of the insulating oil, making it impossible to achieve the objects and effects of the present invention. In addition, the content of boiling heptane soluble part is 2.0
Polypropylene of less than % by weight has poor processability in lamination to kraft paper, film formation, sheet extrusion, etc., or stretchability in biaxially oriented film production, and is difficult to use in commonly used industrial processing methods. Consequently, a polypropylene layer or polypropylene film with a good thickness distribution cannot be obtained. This is an important issue in electrical equipment applications where uniform thickness is particularly required. Therefore, preferably the content of boiling heptane soluble portion is 3.5 to 8.0% by weight. Furthermore, in the present invention, the intrinsic viscosity of the polymer soluble in xylene at 20°C must be 1.0 dl/g or less. If this exceeds 1.0 dl/g, the viscosity of the insulating oil will increase significantly, similar to conventionally commercially available polypropylene, and electrical equipment with good performance cannot be obtained. Therefore, preferably 20
The intrinsic viscosity of a polymer soluble in xylene at °C is 0.5
dl/g or less. Such polypropylene used in the present invention is, for example, JP-A No. 53-1989, which is filed by the same applicant as the present application and is known before the filing date of the present application.
It can be obtained by the method described in No. 33289. The oil-resistant electrical insulation sheet of the present invention can be widely used in various electrical devices, and can be suitably used in cables and capacitors (so-called OF cables, OF capacitors), etc. that use insulating oil. In such oil-filled electrical parts, mineral oil or synthetic oil such as alkylbenzene, alkylnaphthalene, diallylethane, etc. is generally used as an insulating oil, and the polypropylene of the present invention has excellent oil resistance against such insulating oils. ing. In the electrical equipment described above, the polypropylene of the present invention can be used as a polypropylene film or a polypropylene laminated paper in which polypropylene is laminated on a fiber paper such as kraft paper. The polypropylene film may be an unstretched film or a uniaxially or biaxially stretched film, but a stretched film generally has better oil resistance and is preferably used. Each of these films can be formed by a conventional processing method, taking care not to impair the electrical properties. On the other hand, polypropylene laminated paper can be made by laminating polypropylene onto fiber paper such as kraft paper, or by overlapping or laminating a polypropylene film onto fiber paper. By using the polypropylene of the present invention, electrical equipment with good oil resistance can be obtained without making laminated paper with a special structure or heat treatment under special conditions, but of course these special methods are not necessary. can also be applied. Melt flow rate of the polypropylene of the present invention (based on JIS K-7210, test temperature 230°C, test load
(measured at 2.16 Kg) may be any used in the laminate film, unstretched film and stretched film fields, but generally it is preferably in the range of 0.2 to 100, more preferably in the range of 0.5 to 50. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Moreover, the characteristic values in the following examples were measured by the following method. (1) Degree of swelling Determine from the weight of the sample after 40 hours immersion in xylene (W) and the weight of the sample before immersion (Wo) using the following formula. (W/Wo-1)×100 (2) Amount of elution After immersing in xylene for 40 hours, xylene was evaporated from the immersion liquid and dried at 60℃ under reduced pressure.The weight of the product (Ws) and the sample weight ( (Wo) is determined by the following formula. (Ws/Wo)×100 (3) Viscosity of the eluate The intrinsic viscosity of the eluate obtained in (2) in tetralin at 135°C. Example 1 and Comparative Example 1 Melt flow rate is 2.0, isotactic pentad fraction of boiling heptane insoluble part is 0.965,
The content of boiling heptane soluble part is 6.8% by weight, 20℃
After adding 0.1% by weight of a phenolic stabilizer to polypropylene whose xylene-soluble portion has an intrinsic viscosity of 0.30 dl/g, a sheet with a thickness of 0.5 mm was produced using a hot press molding machine. This sheet was subjected to an oil resistance test in xylene at 100°C. Test results first
Shown in the table. For comparison, analysis and oil resistance tests were conducted on the following commercially available products, and the results are shown in Table 1. Comparative Example 1 is the result for commercially available Sumitomo Noblen FS2011A. Examples 2, 3, 4 and Comparative Examples 2, 3, 4 Oil resistance test results when only the raw material resin was changed under the same conditions as Example 1, and the biaxial stretchability or lamination workability of each sample It was as shown in Table 2.

[Table] The extrusion properties and biaxial stretchability of these samples were both good.

【table】

[Table] Example 5 and Comparative Example 5 Five sheets each of 50μ thick biaxially stretched polypropylene film obtained from the polypropylene used in Example 1 and Comparative Example 1 and 50μ thick kraft insulating paper as fiber paper The thickness increase after 40 hours of immersion in insulating oil (xylene at 100°C) by stacking them alternately was compared. The thickness increase rate (ratio of the thickness increase after immersion to the thickness before immersion) was 11% for the comparative product, while it was 6% for the inventive product. The thickness increase caused by swelling is reduced. Example 6 and Comparative Example 6 The following tests were conducted using the polypropylene used in Example 4 and Comparative Example 4. Two sheets of kraft insulating paper with a thickness of 50μ as fiber paper were composited and integrated with melt-extruded polypropylene to obtain a polypropylene laminated paper with a thickness of 250μ for each sample. This laminated paper was immersed in insulating oil (hard type alkylbenzene at 100°C) for 40 hours, and then the thickness increase rate was compared. The thickness increase rate was 9% for the product of the present invention, while it was 16% for the comparative product.

Claims (1)

[Claims] 1. The isotactic pentad fraction of the boiling heptane insoluble part is 0.955 or more, and the content of the boiling heptane soluble part is 2.0 to 9.0% by weight, and
The intrinsic viscosity of the polymer soluble in xylene at 20℃ is 1.0.
An oil-resistant electrical insulating sheet comprising a polypropylene film having a dl/g or less.