JPS6250966B2 - - Google Patents

Description

[Detailed description of the invention]

Conventionally, capacitors have been known in which the surface is coated with heat-shrinkable synthetic resin tubes, but such coatings are prone to defects due to the shrinkability of the tubes in the longitudinal direction. For example, if the surface of the aluminum exterior of a capacitor with an aluminum exterior is shrink-coated with a conventional heat-shrinkable vinyl chloride tube, even if the heat-shrink coating (hereinafter referred to as primary shrinkage) is well applied during the coating process, the temperature will be high. When placed in humid conditions, the synthetic resin coating gradually shrinks (hereinafter referred to as secondary shrinkage), and the capacitor's shoulder becomes exposed, making its insulation protection function unstable. Therefore, there are drawbacks such as limited usage conditions of the capacitor. The present invention relates to a capacitor coating method that improves the above-mentioned drawbacks.The present invention relates to a capacitor coating method that improves the above-mentioned drawbacks. The outer surface of the capacitor, including its shoulders, is coated with heat-shrinkable material.The vertical shrinkage rate of the tube is extremely small, which minimizes secondary shrinkage, prevents exposure of the capacitor's shoulders, and maintains the functionality of the capacitor for a long period of time. It can be kept in good condition. As a capacitor coating tube, a seamless tube obtained by extrusion molding through an annular die is required, but such a tube usually exhibits considerable shrinkage in the longitudinal direction due to manufacturing process constraints. This shrinkage rate in the vertical direction decreases because the tube shrinks both horizontally and vertically when the capacitor is shrink coated (during primary shrinkage).
There is a slight shrinkage remaining in the tube after coating,
The remaining shrinkage appears as secondary shrinkage under high temperature and high humidity conditions. Therefore, in the present invention, the heat-shrinkable synthetic resin tube has a longitudinal shrinkage rate of 5 to -2% (a "-" indicates elongation, but generally, a "-" is added to indicate elongation. (included in shrinkage) is used. This tube is made by extruding synthetic resin such as polyvinyl chloride, polyester, polyethylene, etc. into a tube shape, and then expanding and stretching it in the lateral direction by introducing pressure gas inside at a temperature below the melting temperature and above the glass transition temperature. It is obtained by imparting heat shrinkability to the tube, but the tension in the longitudinal direction is kept as low as possible during the stretching, and the tube after stretching is While maintaining the internal pressure between the two nip rolls to suppress contraction in the radial direction, in the longitudinal direction, the peripheral speed of the downstream nip roll (take-up roll) in the tube flow direction is controlled by the upstream nip roll (delivery roll). It is necessary to take a main step, such as a so-called relaxation heat treatment, in which heat treatment is performed while relaxing by slowing down the heat treatment to cause heat shrinkage only in the longitudinal direction. In this case, if the tension in the longitudinal direction during stretching or relaxation heat treatment is loosened too much, it will be difficult to take up and wind the tube, so it is difficult to lower the longitudinal shrinkage rate below -2% in terms of manufacturing. It is. A transverse heat shrinkage ratio of 30 to 50% is preferable because it facilitates heat shrink coating. Within this range of heat shrinkage, the inner diameter of the tube is preferably 5 to 10% larger than the outer diameter of the capacitor to be coated.
Further, the thickness is preferably about 0.05 to 0.3 mm. As the material, a tube made of polyvinyl chloride is particularly preferable because it is inexpensive and has excellent workability. In addition, there is a tube (conventional) with a longitudinal shrinkage of 8 to 12% when immersed in hot water at 100°C for 30 seconds, and a tube with a longitudinal shrinkage of -2 to 2% under similar conditions (conventional). The tubes of the present invention were heat-shrink coated (primary shrinkage) on capacitors, and then the tubes were peeled off from the capacitors and immersed in hot water at 100°C for 30 seconds. It showed a longitudinal shrinkage rate of ~9%, and even those of the present invention still showed a heat shrinkage rate of -3 to 1%.
Therefore, even after primary shrinkage, the tube still has a slight amount of shrinkage remaining, and this remaining shrinkage appears as secondary shrinkage under hot and humid conditions. Hereinafter, the present invention will be specifically explained using a heat-shrinkable polyvinyl chloride tube (hereinafter referred to as tube) as an example. First, among these tubes, the ones shown below (longitudinal shrinkage rate: 10% conventionally, 0% according to the present invention)
Heat shrink coating on the outside of the capacitor (primary shrink)
After that, we looked at the test results when a secondary shrinkage test was performed. The capacitors used in this test are as shown in the figure. 1 is the capacitor, 2 is the aluminum case, 3 and 4 are the lead wires, 5 is the tube sheathing, and A is the length of the sheath that covers the shoulder of the capacitor. B is the length from the shoulder to the bottom, and C is the length of the part that goes around the bottom. Dimensions of condenser: 10φ Longitudinal shrinkage rate (invention) 0% Transverse shrinkage rate of raw tube 46% (both conventional and present invention) Cutting length of raw tube 19 mm The conditions for heat treatment are as follows. The primary shrinkage is carried out by hot air treatment at 280℃ for 10 seconds.The secondary shrinkage is carried out as follows. Heat resistance test 1000 hours at 105℃ Humidity test 1000 hours at 85℃ and 90% humidity Solder bath test Pass the capacitor lead wire through a phenolic resin insulation board, and connect the lead wire to molten solder (350℃). ) for 10 seconds contact test results are as follows.

【table】

[Table] As seen in the table above, in the conventional tube, A,
It can be seen that although the dimension C was reduced by half due to secondary shrinkage (moisture resistance), it hardly changes in the present invention. Next, we will list the results of tests on a product with a longitudinal shrinkage rate of 5% as an example of the present invention and a product with a longitudinal shrinkage rate of 7% as an example of a conventional product. still,
Other conditions are the same as above.

[Table] As is clear from the table, in the conventional example, the dimensions of A and C significantly shrank from 1.70 to 1.00 due to secondary shrinkage (moisture resistance), whereas in the present invention, the dimensions did not change much to 1.40. In other words, a capacitor made of a heat-shrinkable synthetic resin tube with a heat-shrinkable coating (primary shrinkage) has almost no secondary shrinkage in the resin coating even when placed in a high-temperature, humid environment, and therefore the coating does not come off. Since the capacitor shoulder is not exposed, it has the effect of maintaining excellent performance for a long period of time.

[Brief explanation of the drawing]

The figure is a schematic vertical cross-sectional view of a capacitor covered with a heat-shrinkable synthetic resin tube. 1... Capacitor, 2... Aluminum case, 3, 4
...Lead wire, 5...Coating of heat-shrinkable synthetic resin (heat-shrinkable polyvinyl chloride) tube.

Claims (1)

[Claims] 1. A heat-shrinkable synthetic resin tube with a longitudinal shrinkage rate of 5 to -2% when immersed in hot water at 100°C for 30 seconds is coated on the outer surface of the capacitor, including its shoulders. How to cover a capacitor.