JPS6112150B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in fluororesin-coated gaskets.

In general, fluororesins have excellent chemical resistance, heat resistance,
Due to its aging resistance, it is widely used as a gasket material in the chemical industry. but,
A gasket made of a single fluororesin has poor elasticity and conformability to the joint surface, and also tends to creep (flow), which tends to cause a decrease in tightening pressure.

As a solution to the above-mentioned drawbacks, there is a fluororesin-coated gasket which has a fluororesin outer covering and a cushion material interposed therein. The ones shown in FIGS. 1 to 3 are typical ones, and the cross section of the fluororesin sheath 1 is
), molds (Fig. 2) and molds (Fig. 3), which are processed into a ring shape, are generally used.
On the other hand, as the cushion material 2, depending on the purpose of the gasket, asbestos joint sheets, asbestos cloth, asbestos plates, asbestos felt sheets, synthetic rubber sheets, metal corrugated plates, fluororesin felt, rock wool, glass wool, etc. may be used alone. Or a combination is used.

The above-mentioned fluororesin-coated gasket has a structure in which the chemical resistance depends on the fluororesin of the outer covering, and the compression recovery characteristics, conformability, and creep resistance of the gasket mainly depend on the cushion material. It has excellent elasticity and adaptability, and is suitable for glass lined equipment, glass tubes, carbon equipment, rubber and plastic lined equipment, porcelain equipment, etc., where joint surfaces are fragile and distorted, and smooth surfaces are Taking advantage of its cushioning properties, it is widely used as a sealing material for flanges that cannot be obtained, or flanges that are thin and have low rigidity and are therefore prone to distortion when tightened.

However, if the cushion material is made mainly of fibers, its compressive breaking strength is relatively low, so if the tightening pressure is too large, the cushion material will often break due to compression. There are significant limitations to its use in high-pressure seals that require pressurization.

Among the cushion materials used in the past, asbestos joint seals are relatively resistant to compression failure, and are generally used for high tightening pressures, but in this case, the compression ratio is Because of their small size, they lack the ability to conform to the uneven surface of the flange, and conversely, asbestos boards and asbestos felt, which have a high compression ratio, have the disadvantage of being easily destroyed by compression. The only way to obtain a material that is resistant to compression failure is to combine two or more materials, such as a combination of an asbestos joint sheet and an asbestos board, or a combination of a corrugated metal board and an asbestos board. There is a long-awaited desire for a cushion material that is made from a single material and has the above characteristics.

On the other hand, although the fluororesin used for the outer covering itself has excellent chemical resistance, since it is a type of plastic material, it is obvious that there are many fine voids when viewed microscopically. Therefore, in conventional fluororesin-coated gaskets, when the usage conditions are severe, the internal fluid may penetrate the fluororesin outer jacket and reach the cushion material. Cushion materials are often corroded due to the poor acid resistance of chrysotile asbestos, especially when the internal fluid is acid.

In addition, in conventional products, in order to improve the acid resistance of the cushion material, blue asbestos, which has good acid resistance, is sometimes used, but it has become clear that this blue asbestos is highly harmful to human bodies. ,
Recently, it has become almost prohibited to use.
For these reasons, there is a strong desire for a cushion material that has good chemical resistance and is less harmful.

As mentioned above, most of the cushion materials conventionally used are mainly composed of asbestos, and at present they have all the drawbacks of asbestos.

In addition, as asbestos is a natural mineral, it has become difficult to obtain in recent years due to the depletion of resources and the rise in labor costs for mining, and not only blue asbestos but also chrysotile asbestos However, they have many drawbacks, such as their toxicity to the human body, and their use is being regulated worldwide.

From the above, it can be seen that it is desirable that the cushion material be constructed without using asbestos.

This invention was made to solve the above-mentioned problems, and is a single sheet that has a high compressibility, excellent compressive fracture resistance and chemical resistance, and is constructed without using asbestos. The object of the present invention is to provide a high-performance fluororesin-coated gasket equipped with a cushion material comprising:

The fluororesin-coated gasket according to the present invention is characterized by a structure in which a sheet made of scale-like flakes of expanded vermiculite is used as the cushion material interposed between the fluororesin outer sheath. .

The present inventor has developed a vermiculite sheet material obtained by exfoliating expanded vermiculite into scaly flakes, mixing fibers, fine powder filler, binder, etc. thereto, and paper-making the same. We focused on the fact that it has a large compressibility and excellent compression fracture resistance and chemical resistance, and found that by applying this to cushioning materials, we could obtain high-performance and inexpensive fluororesin-coated gaskets. This invention was completed based on this knowledge.

As mentioned earlier, most of the materials conventionally used as cushion materials are mainly composed of fibrous materials, so they are often anisotropic materials with fiber orientation. However, since the strength in the direction perpendicular to the direction of fiber flow is weak, it has the disadvantage of being susceptible to compression failure in this direction.

However, in the case of the vermiculite sheet used for the cushion material in the present invention, since the flat surface of the scale-like flakes of expanded vermiculite is laminated and molded in parallel to the flat surface of the sheet,
In the plane direction, it is isotropic in all directions, and unlike a fibrous sheet, there is no direction in which it is particularly easy to break.Moreover, when it is composed of scaly flakes, the contact area with adjacent flakes is is larger than the contact area between fibers, and when compressive stress is applied in the thickness direction, a large resistance force is formed against the strain that occurs in the plane direction, which makes it more resistant to compressive fracture than fibrous materials. This is considered to be the reason why it is excellent.

When the cushion material is made of a sheet mainly made of fibrous material, in order to increase the compression ratio, it is necessary to have a structure with many voids in the sheet, and in this case, the compressive fracture strength is: It decreases considerably. On the other hand, in order to obtain a high compressive fracture strength, it is necessary to have a dense structure, which inevitably results in a small compressibility.

However, in the present invention, the vermiculite sheet used as the cushion material has very good compressive fracture resistance, as described above, and therefore has a structure with many voids. Since the compressive fracture strength is ensured at a level that is acceptable for practical use, it is considered that a large compressibility and good compressive fracture resistance are combined.

In the above description, the case where only a vermiculite sheet is used as the cushion material has been exemplified, but there is no problem in using this in combination with a conventional cushion material. Mica, which is a layered clay mineral like vermiculite, does not have interlayer water between its layers, so it cannot expand like vermiculite. Therefore, the surface of mica flakes does not have a large surface activity like the surface of flakes obtained by crushing expanded vermiculite, and even if the flakes come into contact with each other, there is almost no bonding force there. Even if it hardens, a strong sheet-like product cannot be obtained.

In addition, for the outer coating of fluororesin, there are those commonly called fluororesins, such as tetrafluoroethylene resin, tetrafluoroethylene = hexafluoropropylene copolymer resin, and tetrafluoroethylene = perfluoroalkoxyethylene copolymer resin. is applicable.

Next, examples of this invention will be shown below.

Example (1) No. 3 vermiculite raw stone was fired and expanded in a rotary kiln at 900°C, and then sheared and exfoliated using a miracle mill to form flaky flakes with a thickness of 35 μm and a diameter of about 50 mesh. 41kg of E-glass chopped strands with a fiber diameter of 12μ and a length of 10mm, 22Kg of clay with a particle size of 7μ or less, 4Kg of synthetic rubber latex, and 0.3Kg of vulcanizing agent were mixed in 1000ml of water, and this slurry was mixed in a paper making machine. A vermiculite sheet with a thickness of 1.5 mm and a bulk density of 0.87 g/cm ³ obtained by paper making and drying is punched out into a ring shape with an outer diameter of 71 mm and an inner diameter of 43 mm.
70mm, inner diameter 35mm, wall thickness 0.4mm, interposed in a polytetrafluoroethylene resin jacket with a cross-sectional shape, and the overall thickness is 2.3mm.
A 25A JIS 10Kgf/cm ² -mm fluororesin-coated gasket for pipe flanges was obtained.

The compressibility of the above gasket at room temperature is 70kg surface pressure.
f/cm ² , and the compression rate of a conventional product made by combining an asbestos joint sheet and an asbestos plate as cushion materials of the same size and inserting it into the outer cover is 15%.
Compared to this, a very large compression ratio was obtained.

In addition, the compressive fracture strength of the gasket in this example is:
The resistance was 450 kgf/cm ² in an atmosphere of 160° C., whereas that of the conventional product was 300 kgf/cm ² , and very good compressive fracture resistance was obtained.

Furthermore, the gasket of this example and the conventional gasket described above were attached to a steel pipe lined with tetrafluoroethylene resin, 10% hydrochloric acid was sealed inside, and the pipe was left in an atmosphere of 120°C for 1 hour, and then cooled with water for 30 minutes. When a heat cycle test was conducted for 100 cycles under the conditions of 1 cycle, traces of corrosion were observed in the cushion material of the conventional product, but
No abnormality was observed in the gasket cushion material of this example.

As described above, according to the present invention, in the fluororesin-coated gasket, the cushion material interposed in the fluororesin jacket is a vermiculite sheet mainly composed of scale-like flakes of expanded vermiculite. As a result, a high-performance fluororesin-coated gasket can be obtained which has a higher compressibility than conventional products, and has excellent compressive fracture resistance and chemical resistance.

[Brief explanation of the drawing]

The drawings show typical fluororesin-coated gaskets. Figure 1 is a cross-sectional view of the main part of a type gasket, Figure 2 is a cross-sectional view of the main part of a type gasket, and Figure 3 is a cross-sectional view of the main part of a type gasket.
The figure is a sectional view of the main part of the mold gasket. In the drawing, 1 is the fluororesin jacket, and 2 is the cushion material.

Claims (1)

[Scope of Claims] 1. In a fluororesin-coated gasket, the cushion material interposed in the fluororesin jacket is formed of a vermiculite sheet whose main material is scale-like flakes of expanded vermiculite. A fluororesin-coated gasket featuring: 2. The fluororesin-coated gasket according to claim 1, wherein the vermiculite sheet is a sheet made by mixing scale-like flakes of expanded vermiculite with a fiber material, a filler, and a binder.