JPS5848627B2 - Metal plating method for linear objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of metal plating a linear body by vacuum deposition.

Promising methods for applying metal plating to optical fibers include 1) electroplating (electroless plating, electrolytic plating), i1) dipping, and iii) vacuum plating, but each has the following drawbacks. .

That is, in case 1), the optical fiber is exposed to moisture, which increases transmission loss, in case 11), the coating film becomes uneven in thickness and cracks occur, and finally in case 111),
The film thickness is not sufficient, so the plating rate cannot be increased, and the yield of evaporated metal is poor.

The above drawbacks:) and 11) are essential problems, and it seems difficult to solve them technically at this stage.

In this point, the drawback in 111) is not essential and can be solved technically, and therefore, the present invention is directed to the last of the above three means (iii).

By the way, vacuum plating generally evaporates the metal in a crucible and attaches this evaporated metal to a linear object, etc., but the drawback of 111) above is rooted in the fact that the metal in the crucible is evaporated. There is.

That is, in such a method, it is difficult to squeeze the evaporated metal from the crucible onto the object to be plated, in other words, it is difficult to concentrate the evaporated metal on the object to be plated, and for this reason, much of the evaporated metal is wasted. , the yield was poor.

In particular, when the object to be plated is a thin optical fiber with a diameter of 125 μm, the above-mentioned drawbacks are further exacerbated.

The present invention involves melting a metal at a temperature slightly higher than its melting point in a double crucible placed in a vacuum container, and heating a heating tube at a temperature considerably higher than the melting point of the metal for a considerable portion of the metal. The idea is to solve the above problem by providing a heating tube in such a way that it protrudes from the surface of the metal liquid, and by running a linear body inside the heating tube. To explain with reference, the first
As shown in the figure, a double crucible 2 is installed in a vacuum container 1, a metal 3 such as aluminum is placed in the crucible 2, and the crucible 2 is heated by resistance heating of a heating element 4. Melt metal 3.

The tip of a cylindrical heating tube 4' was inserted into the molten metal 3 so that the remaining part protruded upward from the liquid level of the metal 3, and the heating tube 4' was placed around the outer periphery of the molten metal 3. Heating is performed by a resistance heating element 5.

In this state, the temperature of metal 3, that is, aluminum, is set at 680'C, which is slightly higher than its melting point.

Since the vapor pressure of aluminum is low at this temperature, almost no aluminum evaporates even if the pressure inside the vacuum container 1 is set to a high vacuum state of about 10-'Torr.

Next, the temperature of the heating tube 4' is set to above soo'c, which is considerably higher than the melting point of the aluminum.

When the temperatures of the metal 3 and the heating tube 4' are set as described above, the temperature of the heating tube 4' is considerably higher than that of the metal 3, so the metal 3 is heated as shown in FIG. It will climb up the inner circumferential wall of the tube 4'.

The metal 3' that has climbed up in this way is heated to a high temperature by the heating tube 4', and evaporates according to the vapor pressure at that temperature.

On the other hand, if the optical fiber 7 is run from above to the inner tube 6 of the double crucible 2 inside the heating tube 4' from above to the bottom, the evaporated metal 8 can be
It will adhere to the optical fiber 7.

It is preferable to provide a high frequency coil 9 above the heating tube 4' so as to surround the optical fiber 7. If discharge is carried out in such a state, some of the evaporated metal 8 reaching the upper part of the heating tube 4' will be removed. , will be excited and coated on the optical fiber 7.

That is, the optical fiber 7 is first subjected to ion plating and then vacuum plating.
Therefore, as the adhesion strength of the evaporated metal 8 increases, the plating efficiency increases.

Note that 10 and 11 are heat insulating materials provided on the outer peripheries of the heating element 4 and the resistance heating element 5, respectively, to improve thermal efficiency.

Further, 12 is a cooling pipe arranged around the outer periphery of the vacuum container 1, and is used to prevent the container 1 from becoming high temperature.

Here we will discuss a more specific example: 1) The volume of the double crucible 2 is approximately 8 mm, and the inner diameter of the C41 heating tube 4' is 16 mm.
, the length was set to 30 to 40 cIrL, BN (boronite) was used for the double crucible 2, ceramic was used for the heating tube 4', and nickel was added until it reached 80% of the volume of the double crucible 2. Filled.

The optical fiber 7 has an outer diameter of 125μ, an MIO heater is used as the heating element 4, and the high frequency coil 9 has a frequency of 1.3. Passed 1 kW of power at 5 6 MHz.

1i) A PVC-coated cable with an outer diameter of 20 mm was used as the filament to be plated, and was run at a linear speed of 200 m/min to coat aluminum to a thickness of several hundred angstroms.

The coating thickness was uniform.

Note that as the metal to be filled in the double crucible 2, other than aluminum and nickel, lead, copper, chromium, titanium, indium, etc. are used.

In order to further reduce the film thickness, the above structure according to the present invention is
Just make it heavier.

As described above, the present invention does not evaporate the metal in the crucible, but evaporates the metal climbing up the heating tube, so it is possible to narrow down the evaporated metal, and therefore, the yield of evaporated metal is improved. .

Furthermore, since the plating thickness can be reduced, the traveling speed of the object to be plated can be increased.

Furthermore, since the metal evaporates from the periphery of the object to be plated, a uniform thickness of plating can be obtained over the circumference.

[Brief explanation of drawings]

FIG. 1 is a schematic partial sectional view showing an apparatus used in the method according to the present invention, and FIG. 2 is a schematic sectional view showing essential parts of the apparatus. 1... Vacuum container, 2... Double crucible,
3...Metal, 4'...Heating tube, I...
...Optical fiber.

Claims (1)

[Claims] 1. A double crucible for melting metal is provided in a vacuum container, and a heating tube is placed above the liquid level of the metal melted in the crucible, and the metal in the double crucible is The linear body is melted at a temperature slightly higher than the melting point of the metal, the heating tube is set at a temperature considerably higher than the melting point of the metal, and a linear body is run inside the heating tube. Body metal plating method. 2 Metals include aluminum, copper, chromium, nickel, lead,
A method for metal plating a linear body according to claim 1, wherein metal plating is selected from titanium and indium.