JPS6224886B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to polypropylene laminated paper for electrical insulation with improved resistance to insulating oil. Polypropylene laminate paper for electrical insulation, which is made by laminating fiber paper to fiber paper or fiber paper and stretched or unstretched polypropylene film, has a high isopulse withstand voltage when immersed in oil and has excellent dielectric properties, so it is used in high-voltage power cables, etc. Its practical use as an insulating material for electrical equipment is being actively promoted. However, the biggest problem in the practical application of this polypropylene laminated paper is the polypropylene film layer, which is a component of this polypropylene laminated paper. )
Alternatively, a pre-prepared stretched or unstretched polypropylene film layer or a composite layer thereof may be swollen by a hydrocarbon insulating oil such as mineral oil, alkylbenzene, argylnaphthalene, or diallylethane commonly used in electrical equipment. This results in an increase in thickness, which causes the following serious problems. One of them is that due to the increase in the thickness of the polypropylene film layer, the flowability of the insulating oil within the electrical equipment insulation layer, which is necessary to compensate for the expansion and contraction of the insulating oil due to temperature changes in the electrical equipment, decreases. That's true.
In traditional kraft paper insulated electrical equipment, since kraft paper is a porous material, the insulating oil can penetrate through the kraft paper in the thickness direction, but in polypropylene laminated paper, there is a polypropylene film layer. Therefore, the insulating oil cannot penetrate through the thickness direction, and has no choice but to flow through the voids caused by the unevenness of the kraft paper surface or the voids between the fibers inside the kraft paper. Even when there is no increase, the flowability of 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 thickness of the polypropylene film layer increases, the kraft paper layer is compressed, the voids are reduced, and the flow of insulating oil further decreases, eventually making it impossible to secure the required flow of insulating oil. be. A second problem is also caused by the kraft paper layer being compressed. In other words, compression of kraft paper inevitably increases the surface pressure between adjacent tapes, but this makes it difficult for the tapes to slide against each other, and when bent during installation, such as in cables, etc. This causes wrinkles in the tape. These phenomena become more pronounced as the rate of increase in the thickness of the polypropylene film layer increases and as the proportion of the thickness of the polypropylene film layer to the total thickness of the polypropylene laminated paper increases. In other words, the greater the rate of increase in the thickness of the polypropylene film layer, the smaller the proportion of the polypropylene film layer in the total thickness of the polypropylene laminated paper needs to be. However, from the point of view of the electrical properties of polypropylene laminated paper, the proportion of the polypropylene film layer should be large, and therefore, in order to obtain electrical equipment with excellent performance, it is important to minimize the swelling of the polypropylene film layer. It is. Furthermore, in addition to swelling, the polypropylene film layer contains relatively low molecular weight polypropylene that dissolves into the insulating oil, which increases the viscosity of the insulating oil and deteriorates the flowability of the insulating oil within the insulating layer. let Therefore, suppressing the increase in viscosity of the insulating oil is also an important issue. For this reason, several proposals have been made to improve the insulating oil resistance of polypropylene laminated paper for electrical insulation.For example, in the case of power cables, heat treatment is performed at a temperature below the melting point of polypropylene after winding the tape. For example, the apparent thickness increase of the entire laminated paper can be reduced by forming a polypropylene film layer and inserting a new layer between the layers to absorb the increase in thickness. However, all of these methods are based on the premise that swelling of the polypropylene film layer and the resulting increase in thickness are inevitable, and although they have some effect in suppressing swelling, an increase in the viscosity of the insulating oil is unavoidable. Moreover, it is not necessarily preferable from a process and economic point of view. The inventors of the present invention have conducted intensive studies in view of the problems of the conventional method described above, and have found that by using polypropylene with a particularly limited structure, it is possible to obtain polypropylene laminated paper with little swelling property and viscosity change in insulating oil. They discovered this and arrived at the present invention. That is, the present invention provides a polypropylene laminated paper for electrical insulation consisting of a fiber paper layer and a polypropylene film layer, characterized in that the polypropylene film layer is made of a polypropylene resin that meets the following requirements (1) to (3). Polypropylene laminated paper for use. (1) The isotactic pentad fraction of the boiling heptane insoluble part is 0.955 or more. (2) The content of the boiling heptane soluble part is 2.0 to 9.0% by weight. (3) The intrinsic viscosity of the polymer soluble in xylene at 20°C is
1.0dl/g or less. By using this polypropylene laminated paper, it is possible to obtain an electrical device in which the swelling of polypropylene caused by insulating oil and the resulting increase in the thickness of the polypropylene layer is small, and furthermore, the viscosity of the insulating oil is less increased. Further, this polypropylene laminated paper has good processability when laminating fiber paper, forming a polypropylene film, and extruding a sheet, and also has excellent stretchability when producing a biaxially stretched film. 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 oil residue is referred to as boiling heptane insoluble portion, and the value obtained by subtracting this dry weight from 5 g divided by 5 g is the content of the boiling heptane soluble portion expressed as a percentage. What is isotactic pentad fraction?A.
Macromolecules 6 , 925 by Zambelli et al.
(1973), i.e. ¹³ C−
It is the fraction of propylene monomer units in an isotactic chain of pentad units in a polypropylene molecular chain measured using NMR, in other words, a chain in which propylene monomer units are meso-bonded five times in succession. However, regarding the attribution of NMR absorption peaks, the
Macromolecules 8 , 687 (1975). 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 boiling heptane soluble area of 2.0~
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 2.0% 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 increases 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
If the amount of polypropylene is less than % by weight, processing methods such as lamination to fiber paper, film production, sheet extrusion, etc., or stretchability during biaxially stretched film production, etc. will be poor, and it will not be possible to use 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 applications where uniform thickness is sometimes required. Therefore, preferably,
The content of boiling heptane soluble portion is 3.5-8.0% 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. The polypropylene laminated paper for electrical insulation of the present invention can be widely used in various electrical devices, but it can fully demonstrate its performance especially when applied to cables and capacitors impregnated with insulating oil. That is, mineral oil or synthetic oil such as alkylbenzene, alkylnaphthalene, diallylethane, etc. is normally used as insulating oil in these electrical devices, but the polypropylene laminated paper of the present invention has excellent oil resistance against these insulating oils. There is. The polypropylene laminated paper of the present invention can be made by conventional processing methods. For example, a method may be used in which a stretched or unstretched polypropylene film made in advance of fiber paper or fiber paper and the polypropylene is pasted together as an adhesive while the polypropylene is melt-extruded, or the film is directly thermocompressed. However, in the former case of melt extrusion, there is almost no need to consider the adverse effects of heating on the fiber paper stock. Further, as the polypropylene film, the polypropylene (resin) in the present invention is
The melt flow rate (measured based on JIS K-7210 at a test temperature of 230°C and a test load of 2.16 kg) may be any value used in the fields of laminated films, unstretched films, and stretched films, but is generally 0.2 to 100. The range is preferably 0.5 to 50, more preferably 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. In addition, the swelling ratio and dissolution amount in the following examples were measured by the following method. (1) Swelling rate 10 samples are stacked and inserted between two metal plates,
After drying at 100° C. for 4 hours under a load of 1 Kg/cm ² , the thickness is measured and defined as T ₁ . Thereafter, it is impregnated with hard alkylbenzene that has been kept at 100℃ in advance, left at 100℃ for 24 hours, the thickness is measured again, and the thickness is defined as T ₂ . The swelling rate is given by the rate of change in thickness after impregnating with the alkylbenzene, ie, from the following equation. Swelling rate = T ₂ −T ₁ /T ₁ ×100 (%) (2) Dissolution amount The resin is melted and extruded using a T-die to create a film with a thickness of about several tens of μm. Take an appropriate amount of the film, accurately measure its weight, and
Let W ₁ (g). This film sample is placed in a test tube, an excess of hard alkylbenzene is added, and the tube is heated at 100° C. in vacuo and left for 7 days. Thereafter, the film sample is taken out, and the hard alkylbenzene on the surface and inside of the film is washed away with a suitable solvent (acetone) using a Soxhlet extraction device. Thereafter, the film is vacuum dried and its weight is precisely measured, which is defined as W ₂ (g). The amount of dissolution is given by the weight change rate of the film before and after impregnation with the hard type alkylbenzene, that is, from the following equation. Dissolution amount = W ₁ - W ₂ / W ₁ × 100 (%) Example Melt flow rate is 50, isotactic pentad fraction of boiling heptane insoluble part is 0.970,
Using the polypropylene of the present invention, which has a boiling heptane soluble content of 5.0 and a xylene soluble content of 0.25 dl/g at 20°C, it is made into a capacitor insulating paper with a thickness of 43 μm using a T-die. A polypropylene laminated paper having a thickness of 125 μm was produced by extrusion between two sheets. In addition, a 125 μm polypropylene laminate paper having the same structure was prepared using commercially available Sumitomo Noblen Y-101 in the same manner as above, and this was used as a comparative example. These two samples were tested for oil resistance and electrical properties, and the results shown in Table 1 were obtained.

[Table] As shown in Table 1, when polypropylene with the limited characteristics of the present invention is used, the swelling rate and dissolution amount of polypropylene laminated paper due to insulating oil are remarkable compared to the case of conventional polypropylene. There are few. Moreover, this does not have any adverse effect on the electrical characteristics.

Claims (1)

[Scope of Claims] 1. In a polypropylene laminated paper for electrical insulation consisting of a fiber paper layer and a polypropylene film layer, the polypropylene film layer has the following (1) to (3).
A polypropylene laminate paper for electrical insulation, characterized in that it uses polypropylene that meets the following requirements: (1) The isotactic pentad fraction of the boiling heptane insoluble part is 0.955 or more; (2) The content of the boiling heptane soluble part is 2.0 to 9.0. Weight% (3) The intrinsic viscosity of a polymer soluble in xylene at 20℃ is
1.0dl/g or less.