JPS6117648B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a sealing material made of polytetrafluoroethylene resin (hereinafter referred to as PTFE) that is wound around a joint part such as a flange part of a fluid transport pipe to provide a sealing effect to the hand part. The present invention relates to a manufacturing method.

Conventionally, synthetic rubber packing such as butyl rubber or fluorocarbon rubber, or metal packing such as copper has been used as a sealing material for joints such as flanges, but these O-ring-shaped or disc-shaped packings are pre-coated with transport pipes. It was difficult to join and seal the packing at the construction site because it had to be molded according to the diameter of the pipe. For this reason, it was necessary to prepare packings of many different shapes, and there were also problems such as a decrease in sealing effectiveness due to slight deviations in diameter.

In recent years, porous sealing materials that have improved the above-mentioned drawbacks have begun to be used, but due to their porous nature, they tend to shrink, especially when they have a circular cross section, shrinkage progresses depending on the degree of compression, causing flange It was found that the diameter of the part tends to decrease.

The present invention has been made as a result of various studies aimed at providing a product that improves the above-mentioned drawbacks, and has completed a sealing material that has excellent workability at construction sites. That is, in the present invention, an unfired PTFE rod or tube is stretched to provide a large number of fine pores to give it flexibility, and then passed through a furnace at 327°C or higher, which is the melting point of PTFE, to form a PTFE rod. Alternatively, the outer peripheral surface of the tube is fired, but the inside is left unfired, and after heating and before cooling to room temperature, a PTFE rod or a drawing die having a diameter smaller than the outside diameter of the tube is used. It is characterized in that the cross-sectional area of the rod or tube is reduced by passing the rod or tube through it, and at this time, the hole shape of the drawing die may be circular, but it is preferably a flat oval shape. This reduces shrinkage during tightening of the flange portion, improving ease of handling and reliability. Furthermore, by applying adhesive to only one surface of the surface that has passed through the drawing die, rather than the entire circumference, it is easy to apply the adhesive to the flange surface, further improving workability at the construction site.

In the present invention, a mixture consisting of an unfired PTFE fine pounder and a liquid lubricant is formed into a rod or tube using a ram extruder, and then the liquid lubricant is removed. This is stretched in the length direction by at least 300% or more, preferably in the range of 800% to 1500%. At this time, room temperature may be used, but it is preferably carried out at a temperature range of 200° C. or higher and 327° C. or lower before firing, thereby creating a large number of fine pores and, as a result, a highly flexible structure. Next, the rod or tube is passed through a furnace heated to at least 327°C or higher, preferably 400°C or higher, thereby firing the outer peripheral surface of the rod or tube while leaving the inside unfired. Furthermore, before it cools down to room temperature, it passes through a drawing die to reduce its cross-sectional area.

Here, the effects of using the drawing die will be explained in detail. Unfired stretched PTFE exhibits excellent flexibility by increasing its stretching ratio, but by rubbing the surface with a slight force, fine fiber pieces are peeled off.
The so-called "fluff" becomes noticeable. On the other hand, when a stretched material is completely fired, its flexibility is greatly reduced, and it must be said that it becomes hard, although it varies somewhat depending on the stretching ratio. Therefore, the above-mentioned "fluff" can be prevented by compressing only the outermost surface of the PTFE rod or tube, in which fine pores have been uniformly generated by stretching, using a drawing die. At this time, as described above, by setting the outer circumferential surface to a temperature higher than the firing temperature, "fluffing" can be further reduced.
The degree of fluffing can be easily determined by whether or not fiber pieces are generated when the adhesive tape is peeled off after being applied.

The second effect is that it is possible to arbitrarily produce products with diameters different from those produced using an extruder.
In particular, rods or tubes with circular cross sections can still be adjusted relatively easily using an extruder, but rods or tubes with cross sections other than circular, such as square, elliptical, oblate elliptical, etc., can be stably produced using an extruder. This would require a large amount of money to manufacture the die, making a drawn die much more advantageous. Furthermore, since the dimensional accuracy of the final product depends solely on the accuracy of the drawing die, it has the third effect of being able to obtain a product with better reproducibility than when it is simply set using an extruder. This tends to become more pronounced as the shape becomes more complex. Although the shape of the drawing die can be selected arbitrarily, a flat oval shape is preferable from the viewpoint of its properties as a material for sealing the flange portion and the like. The oblate ellipse here refers to a shape surrounded by two circles and tangents to the two circles, and in most cases, the diameters of these circles are equal, so the tangents are parallel lines. If the two circles are in contact, that is, the ratio of the short axis to the long axis of the oblate ellipse is 1:
It has been found that a particularly preferable shape is one in which the ratio of the short axis to the long axis of the oblate ellipse is within a range of 1:4 with two to four circles in contact with each other. If the ratio of the short axis to the long axis is less than 1:2, contraction in the length direction occurs when tightening to the flange portion, and for example, when the ratio is 1:1, a shortening of up to 30% may occur.

On the other hand, when the ratio exceeds 1:4, the flange becomes too flat, resulting in decreased flexibility and flexibility, and the flange surface with a small diameter becomes difficult to handle due to insufficient flexibility. To make it easier to attach to the flange, apply adhesive to a part of the surface whose cross-sectional area has been reduced using a drawing die, especially if the shape is an oblate oval, apply adhesive to the flat part. Preferably attached. This adhesive can be of any type, such as a solution type or a hot melt type, but it is easiest to use it in the form of a double-sided adhesive tape integrated with a release paper.

In the present invention, as described above, as long as it has a circular outer surface of unfired PTFE, it may be rod-shaped or tube-shaped. In any case, it is first stretched to give flexibility, then heated to a state where the outer surface is fired but the inside is unfired, and before cooling, the cross-sectional area is reduced by a drawing die or it is made into an irregular cross-section. This is an essential condition, and an adhesive is additionally applied at the end.

The present invention will be explained in more detail with reference to Examples below.

Example 1 10 kg of Polyflon F-104 manufactured by Daikin Industries, Ltd. was mixed with 2.2 kg of solvent naphtha and extruded into a rod shape of 12 mmφ from a 130 mmφ cylinder. After removing solvent naphtha in a hot air drying oven, 120
The film was stretched into a 300° C. cm long furnace at a feed rate of 50 cm/mm and a winding speed of 550 cm/mm. Then 550℃ for 80cm length
The material was fed into a furnace at a speed of 120 cm/mm to bake the outer surface, and drawn and stretched near the exit of the furnace using a flat oval die with a short diameter of 6 mm and a long diameter of 12 mm.
The mmφ rod was an oblate ellipse with a minor axis of 5.9 mm and a major axis of 11.8 mm.

5mm with release paper on one side of this flattened surface.
The weight of the 1 m length of the product to which the double-sided adhesive tape was attached was 33 g.

After attaching it to a 4-inch flange joint and sealing it with 8 M-20 bolts with a tightening torque of 3 kg-m, water pressure was applied to find the pressure at which it started to leak.
It was found that leakage started at 160Kg/cm ² . Next, when the tightening torque was set to 6Kg-m, it was 250Kg/cm ²
But nothing leaked.

Example 2 Produced in the same manner as in Example 1, except that drawing and stretching was performed using a flat oval die with a minor axis of 4.5 mm and a major axis of 9 mm, and the stretching rate was doubled. The weight at 1 m length was 21 g. Summer. When the same airtightness test as in Example 1 was conducted with a tightening torque of 4 kg-m, there was no leakage up to 200 kg/ ^cm2 , but 220
The first leak occurred at Kg/cm ² .

Example 3 800% at a temperature of 290℃ using a 5.5mmφ rod
Immediately after passing through a furnace at 450°C, the film was drawn and drawn using a flat oval die with a minor axis of 2 mm and a major axis of 4 mm. The weight of a 1m long piece of double-sided tape with a width of 3mm attached to a flat surface on one side is
The weight was 3.1g, and the same airtight test as in Example 1 was carried out at 3kg.
-m tightening torque leaked at 200Kg/ ^cm2 , but when I tightened it to 4Kg-m, it leaked at 250Kg/cm2.
No leakage occurred even at Kg/ ^cm2 .

Comparative Example 1 When conducting an airtightness test using a round rod manufactured in the same manner as in Example 3 except for not carrying out any stretching, the entire rod shrank in the direction of the center of the 4-inch flange, resulting in a weight of 4 kg-m. Even with the tightening torque, it started leaking due to the pressure at 45Kg/cm ² . Although the torque increased to 6 Kg-m, the pressure at the beginning of the leak only increased to 70 Kg/cm ² .

Example 4 A flat sealing material was manufactured in the same manner as in Example 1 except that the short axis of the flat oval die was 3 mm and the long axis was 16 mm, and a watertight test was conducted using a 4-inch flange joint. I was able to attach it by sequentially pressing the flange surface with adhesive tape, but it started leaking at 160 kg/cm ² even with a tightening torque of 6 kg-m.

Example 5 Manufactured in the same manner as in Example 3 except for using a drawing die with a rectangular hole with a short diameter of 3 mm and a long diameter of 4 mm, and a watertight test with a tightening torque of 3 kg-m showed that leakage did not occur even at 200 kg/ ^cm2 . Nakatsuta.

Example 6 A tube was manufactured in the same manner as in Example 3 except that a tube with an outer diameter of 5.5 mmφ and an inner diameter of 4.0 mmφ was used, and the weight of a 1 m length was 2.6 g. Of course, the same drawing and stretching as in Example 3 was performed. In a watertight test with a tightening torque of 3 kg-m, leakage started at 220 kg/cm ² , but no leakage occurred even at 250 kg/cm ² with a tightening torque of 4 kg-m.

Claims (1)

[Claims] 1. Conditions in which an unfired polytetrafluoroethylene resin rod or tube is stretched to provide a large number of fine pores to give it flexibility, and then the outside is fired but the inside is left unfired. 1. A method for producing a sealing material, characterized in that the cross-sectional area of the rod or tube is reduced or the cross-section of the rod or tube is modified by heating the rod or tube at a lower temperature and passing it through a drawing die before cooling to room temperature. 2. The method for producing a sealing material according to claim 1, wherein the drawing die has a hole having an oblate oval shape. 3. The method for manufacturing a sealing material according to claim 2, wherein the ratio of the short axis to the long axis of the oblate ellipse is in the range of 1:2 to 1:4. 4. An unfired polytetrafluoroethylene resin rod or tube is stretched to provide a large number of fine pores to give it flexibility, and then heated under conditions such that the outside is fired but the inside remains unfired, and then heated to room temperature. The cross-sectional area of the rod or tube is reduced by passing it through a drawing die before being cooled, or an adhesive is attached to one surface of the sealing material that has passed through a drawing die without having an irregular cross-section. Method of manufacturing sealing material. 5. The method for producing a sealing material according to claim 4, wherein the adhesive is applied in the form of a double-sided adhesive tape.