JPH0255738A - Method for further enhancing conductivity of conductive plastics - Google Patents

Abstract

PURPOSE:To make it possible to decrease the surface resistance of a conductive plastics to thereby further enhance its conductivity with a simple treatment without increasing the amount of dispersed carbon black by irradiating the plastics with UV rays of a specified wavelength or by heating it. CONSTITUTION:A conductive plastics obtd. by molding a mixture of a thermoplastics with carbon black is irradiated with UV rays of a wavelength of 300-400 nm or is heated. Since the product has been thus heat treated, the molding strain of the surface layer is removed and the surface resistance can be decreased. Since the amt. of the carbon black added in order to decrease the surface resistance can be decreased and the tackiness is also decreased, molding can be easily performed. In addition, the production cost can be reduced and the surface resistance of the molded item can be readily made uniform, because the amt. of loading of an expensive carbon black is decreased and molding can be easily performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for increasing the surface conductivity of conductive plastics.

(Conventional technology) Conventionally, plastics such as PVC and EVA
Conductive plastics obtained by dispersing carbon black of 0 to 30% by weight can be used for high-voltage power transmission cables,
In addition to conductive mats, IC trays, etc., it is also used in capacitive video discs.

FIG. 5 shows a cross-sectional view of an example of a high-voltage power transmission cable.

This high-voltage power transmission cable 7 includes a conductor 8 that transmits electricity, and an insulator 9 covering the periphery of the conductor 8 .

In order to prevent damage to the high-voltage power transmission cable 7 due to corona discharge that occurs due to high-voltage power transmission, a conductive plastic 1 made of a thermoplastic such as EVA with 5 to 30% by weight of carbon black dispersed is placed around the insulator 9. The conductive plastic 1 has a low resistance and carbon black is uniformly dispersed, so that less power is lost due to distortion of the electric field.

In addition, even with capacitive video discs, Tokko Sho Go-
No. 51166, it is manufactured by dispersing a large amount of carbon black in a thermoplastic.

In this capacitive video disc, the more carbon black peaks are dispersed, the lower the volume resistivity value is, and the more the detection output during playback increases.

Therefore, considering only the detection output during reproduction, it is better to have a large amount of carbon black, but if it is too large, the stickiness increases and it becomes difficult to mold the disk.

Further, even if carbon black is improved, the carbon black becomes more expensive, resulting in an increase in cost.

Therefore, JP-A-59-19257@ and JP-A-59-19
As disclosed in No. 258, there are attempts to obtain the necessary hardness by polymerizing a low molecular weight resin during disk molding, but the process of polymerizing this low molecular weight resin during disk molding is It takes 5 to 10 minutes to mold one disk, resulting in poor productivity and, in this case, an increase in costs.

(Problems to be Solved by the Invention) Conventionally, conductive plastics used for high-voltage power transmission cables, conductive mats, IC trays, etc., desirably have a low and uniform surface resistance value.

In the manufacturing process of conductive plastics, carbon black must be uniformly dispersed in order to prevent variations in surface resistance. It is better to reduce the number of suspensions, and when press molding, the less suspension of carbon black, the less viscosity and easier molding.

However, when the amount of carbon black is reduced, the surface resistance value increases and the conductivity deteriorates.

Particularly in the case of a capacitive video disc, the higher the surface resistance value, the lower the re-biopsy wave output and the lower the playback ability.

Therefore, attempts have been made to reduce the variation in the surface resistance of conductive plastics by improving the dispersion machine's ability or by improving the carbon black used, but none of these attempts have yielded good results compared to the cost. It wasn't.

Therefore, an object of the present invention is to reduce the surface resistance value without increasing the amount of carbon black dispersed by simply performing a simple treatment.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an L-m plastic that is obtained by mixing carbon black with a thermoplastic plastic and molding the mixture.
The present invention aims to provide a method for increasing the conductivity of conductive plastics, which is characterized by reducing the surface resistance value by irradiating ultraviolet rays or heat at 00ni.

(Function) As a result of repeated research aimed at lowering the surface resistance value of conductive plastics, it was found that when heat is applied to this conductive plastic, the carbon black in the extreme surface layer rearranges.
It was found that the surface resistance of the surface layer was uniformly reduced.

The stronger the heat energy, the better, and it is better to apply it only for a very short time so that the conductive plastic does not deform.

Moreover, when using light, ultraviolet rays with strong optical energy are preferable, and ultraviolet rays with a wavelength of 300 to 400 nm are particularly effective.

This is because if the wavelength is 300 nm or less, the ultraviolet rays will be absorbed by the [9] of the air, and the plastic plus deck portion will absorb the ultraviolet rays, making it impossible to obtain good results.

Furthermore, visible light with a wavelength of 400 nm or more does not reduce the surface resistance value, while infrared light generates heat from inside the molded conductive plastic, causing the conductive plastic to deform! When the light is moved away, the surface resistance value does not decrease in the same way as with visible light.

When exposed to ultraviolet light with a wavelength of 300 to 400 nm, only the carbon black in the surface layer absorbs the ultraviolet light and rearranges it.
Plastic parts do not absorb UV light.

Therefore, use the ultraviolet part of a xenon lamp, high-pressure mercury lamp, or use a well-heated electric oven (approximately 2
It is best to heat it by heating it for a short time in a container that can be heated to 00°C.

(Example) [Example 1] To 100 parts by weight of vinyl chloride resin, a hanging portion of 31 tin-based stabilizers was added as a stabilizer.

And Cabot's [Black Pearl 1]
18 parts by weight or 20,451 parts by weight of carbon black called 300J were added, thoroughly kneaded, and sheet pressed at 180° C. to form a flat plate with a thickness of 111 IIll.

Next, this plate was cut into a 1.5 cm x 4 cm rectangle, and Genkasei's conductive paint [Dotite D550J was applied to the surface at 1.5 cm intervals to form electrodes 2. This rectangular conductive plastic was used as sample 1. did.

Then, as shown in Fig. 1, this sample 1 was
H xenon lamp 4 with a transmission wavelength of 300nIll to 3
Irradiation was performed using a device equipped with an 80ni ultraviolet transmission filter 3.

Then, the irradiation time was changed and the change in surface resistance value between the electrodes 2 before and after irradiation rjA was measured.

[Example 2] The same sample 1 as in [Example 1] was heated in the electric oven 5, and the heating temperature and heating time were changed to measure the change in surface resistance value between the electrodes 2 before and after heating. (Figure 2) [Example 3] A high-pressure mercury lamp (25(E)) was irradiated from a distance of 30ca+ onto the surface of a capacitance type video disk that was normally commercially available, and the irradiation time and detection output during playback were measured. It was measured.

[Example 4] Two commonly available capacitive video discs were
The sample was left in an electric oven kept at 00°C, and the heating time and detection output during playback were measured.

[Results] The results of [Example 1] are shown in Table 1, the results of [Example 2] are shown in Table 2, and the results of [Example 3] and [Example 4] are shown in Figures 3 and 4, respectively. Draw on the graph.

In Tables 1 and 2, those marked with an asterisk (*) used 18 parts by weight of carbon black, and those without marks used 20 parts by weight.

Table 1 Table 2 When irradiated with ultraviolet rays from xenon lamp 4 in [Example 1], as can be seen from Table 1, the surface resistance value of all samples 1 decreased, and the longer the irradiation time, the better the results. It is being

Moreover, when the electric oven 5 of [Example 2] was used, it can be seen from Table 2 that the surface resistance value decreased.

In particular, better results were obtained by increasing the heating temperature and shortening the heating time by that much rather than increasing the heating time.

When the electrostatic volume type video disc of [Example 3] is irradiated with a high-pressure mercury lamp, the graph shown in Figure 3 shows that the detection output increases until the irradiation time reaches 20 minutes, and It more than doubles, but after that it becomes saturated and there is almost no change.

In addition, when using the electric oven of [Example 4],
From the graph shown in FIG. 3, the detection output increases until about 15 seconds, more than doubling, but after 20 seconds, warping occurs and it becomes impossible to measure the detection output.

(Effects of the Invention) Since the method for making conductive plastic highly conductive according to the present invention applies heat to the conductive plastic, molding distortion of the surface layer can be removed and the surface resistance value can be lowered.

Therefore, the amount of carbon black used for lowering the surface resistance value can be reduced, the tackiness is reduced, and molding is facilitated.

In addition, the amount of expensive carbon black used is reduced and molding becomes easier, resulting in cost reduction.

When the amount of carbon black used is reduced, the surface resistance value of the molded product can be easily made uniform.

Furthermore, in the case of a capacitive volume type video disk, the detection output is increased due to a decrease in the surface resistance value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the method for making conductive plastic highly conductive according to the present invention, FIG. 2 is a block diagram showing a second embodiment, and FIG. FIG. 4 is a graph showing the results of the fourth embodiment of the present invention, and FIG. 5 is a top view showing the conventional example. 1... Conductive plastic, 2... Electrode, 3...
Ultraviolet I2 transmission filter, 4...Xenon lamp, 5.
...Electric oven, 6...Resistance measuring device, 7...High voltage power transmission cable, 8...Conductor, 9...Insulator.口===ko～3 Patent Applicant: Japan Victor Co., Ltd. Representative: Kakiki
Japanese Figure 1 Figure 2

Claims (1)

[Claims] A conductive plastic obtained by mixing carbon black with a thermoplastic plastic and molding the mixture is irradiated with ultraviolet rays with a wavelength of 300 to 400 nm or heat to lower the surface resistance value. Method for making conductive plastic highly conductive.