JPH0521956B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a sheet gasket material. [Prior Art] Conventionally, asbestos joint sheet gaskets containing asbestos as a main component are generally known as gasket materials used for valves, pumps, piping joints, various types of equipment, and the like. However, in recent years, asbestos has been considered to be a problem of environmental pollution.
Its use is becoming restricted. Known gasket materials that do not use asbestos include rubber sheets, vermiculite sheets with rubber as a binding material, expanded graphite sheets, glass cloth impregnated with polytetrafluoroethylene resin dispersion, and carbon cloth. . [Problems to be Solved by the Invention] Conventional gaskets have had the following problems. Rubber sheets have low heat resistance, so it is difficult to use them at high temperatures. Vermiculite sheets that use rubber as a binding material cause seizure due to thermal deterioration of the rubber, and have poor sealing properties. Expanded graphite sheets have low strength, are difficult to handle, and are expensive. Glass cloth and carbon cloth impregnated with polytetrafluoroethylene resin dispersion have large stress relaxation and poor sealing properties.
It's expensive. [Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. In other words, we aim to provide a gasket material that can replace asbestos joint sheets, has excellent heat resistance and sealing properties, is free from environmental pollution, is inexpensive, and has excellent oil and water resistance. It contains 5% by weight or more of polytetrafluoroethylene resin and 50% by weight or more of inorganic filler, the polytetrafluoroethylene resin is fibrillated, the inorganic filler is present between the fibrils, and the inorganic filler is The present invention provides a sheet-like gasket material characterized in that the filler is a filler mainly composed of hydrated silicate minerals, and has a porosity of 20% or less and a pore diameter of 0.15μ or less. In this specification, porosity refers to CARLO
Using ERBA Porosimeter 2000, 23℃,
The average pore volume (cm ³ /g) measured when the pressure is changed from normal pressure to 2000 atm at 25RH% and the amount of substance (volume per unit mass of the substance) (cm ³ /g) measured by ASTM D-792. /g) using the following formula: Porosity (%) = pore volume/material volume x 100. Also, the pore diameter is
Using CARLO ERBA porosimeter 2000,
When the pressure is changed from normal pressure to 2000 atm at 23℃ and 25RH%, the formula Pr = 2σcosθ (P is the applied absolute pressure: Kg/cm ² , r is the small diameter radius: nm, and σ is the surface of mercury. Tension: 480 mN/m ² θ is the average value of the pore radius determined from the contact angle (wetting angle): 141.3°. In the present invention, the polytetrafluoroethylene resin (hereinafter referred to as PTFE) is not limited to a homopolymer of tetrafluoroethylene; ) modified by copolymerization with other comonomers are also included. Such copolymers include hexafluoropropylene, perfluoro(alkyl vinyl ether), perfluoro(alkoxyalkyl vinyl ether),
Examples include trifluoroethylene and perfluoroalkylethylene. Moreover, if the molecular weight is too low, it becomes liquid or gel-like, which is undesirable, and preferably contains 50% or more of solids having a molecular weight of 10 ³ or more calculated from standard specific gravity.
Further, PTFE obtained by emulsion polymerization is preferred because it is easily fibrillated. In the present invention, as the inorganic filler, inorganic powder, powdered inorganic fiber, or carbon powder having excellent heat resistance and chemical resistance is preferably employed.
It is particularly preferred that the inorganic filler has a hydrous silicate mineral as its main component. The hydrated silicate mineral, which will be described later, is used as the above-mentioned inorganic powder. As the inorganic powder, one having an average particle size of about 100 μm or less is preferably employed. If the average particle size is too large,
This is not preferable because the surface smoothness is impaired when it is made into a sheet gasket material. In addition, inorganic powder having a large average particle size does not provide the denseness of the sheet-like gasket material, and the porosity and pore size become large, resulting in insufficient sealing performance, which is not preferable. Furthermore, if a hard inorganic powder with a large particle size is used, the molding device may be damaged during molding, which is not preferable. More preferably, the average particle size is 0.1 to 70μ
It is an inorganic powder. Further, it is preferable to use a mixture of two or more types of inorganic powders having different particle sizes, since this improves the filling efficiency. Such inorganic powders include powders of hydrated silicate minerals that are mainly composed of silicon and aluminum and also contain magnesium, iron, alkaline earth metals, alkali metals, etc., generally called clay, and natural mineral powders such as wollastonite. Preferably adopted. Particularly preferred are kaolin-type clays represented by kaolinite, halloysite, sewage halloysite, and the like. In addition, the powdered inorganic fiber has a diameter of about 0.1 to 30μ, particularly preferably about 0.5 to 15μ, and a length of 50 to 30μ.
A thickness of about 300μ, particularly preferably about 70 to 200μ, is preferably adopted. Such powdered inorganic fibers include:
Examples include powdered carbon fiber, powdered glass fiber powder, powdered alumina fiber, and various powdered natural mineral fibers. Further, as the carbon powder, a particle size of about 0.01 to 0.1 μm is preferably employed. Further, in the present invention, as the inorganic filler, an inorganic powder alone or a mixture of an inorganic powder and a small amount of powdered inorganic fiber and/or carbon powder is preferably employed. When inorganic powder is used alone or a mixture of inorganic powder and carbon powder is used, the porosity of the sheet gasket material can be lowered,
This is preferred because it facilitates making the pores smaller. In addition, when powdered inorganic fibers are mixed and used, it is slightly more difficult to lower the porosity and make the pores smaller than when powdered inorganic fibers are not mixed, but the result is a sheet-like gasket material with a high compressibility. . The sealing surface has excellent conformability. In addition, if powdered inorganic fiber or carbon powder is used alone or as a mixture of powdered inorganic fiber and carbon powder as an inorganic filler, it may become difficult to form a sheet, or it may become difficult to form a sheet with a small porosity or pore size. Such a mode of use is not preferable because it may become difficult to obtain gasket material. When using a mixture of inorganic powder and powdered inorganic fiber and/or carbon powder as the inorganic filler, the mixing ratio should be approximately 10 parts by weight or less of powdered inorganic fiber and/or carbon powder per 100 parts by weight of inorganic powder. preferable. If the proportion of powdered inorganic fibers and/or carbon powder is too large, the formability of the sheet gasket material will deteriorate, and the porosity and average pore diameter will increase, resulting in poor sealing properties and shortening the life of the sheet gasket material. It becomes small and undesirable. The sheet-like gasket material of the present invention contains 5 PTFE.
Contains at least 50% by weight of inorganic filler. If the amount of PTFE is less than 5% by weight, it is difficult to form the sheet into a sheet-like gasket material, and the formed sheet also has a low recovery rate against compression, making it difficult to form a gasket material with a small porosity. This is not preferable because it becomes difficult to obtain and cannot withstand use as a gasket. It is preferable that the special zone contains 10% by weight or more of PTFE. The upper limit of the amount of PTFE is not particularly limited, but if it is too large, it will become expensive, its characteristics as a general-purpose gasket material will be weakened, and the compressibility of the gasket material will decrease, so it should be 50% by weight or less, especially The content is preferably 40% by weight or less. In addition, the amount of inorganic filler is 50% by weight
If it is smaller than , the stress relaxation rate becomes large, which is not preferable. Furthermore, since it is expensive, it may not be suitable for use as a general-purpose gasket. As the amount of inorganic filler increases, the stress relaxation rate decreases, but it becomes difficult to obtain a dense sheet-like gasket material with small porosity and pore diameter. That is, there is a tendency for the sealing performance to deteriorate easily. The preferred content of inorganic filler is 60 to 90% by weight. The sheet-like gasket material of the present invention has the above-mentioned properties.
In addition to PTFE and inorganic fillers, it may also contain synthetic resins, inorganic fibers, and the like. Such synthetic resins preferably have excellent heat resistance, oil resistance, etc., such as fluororesins such as perfluoroalkoxy resins and perfluoroethylene propylene resins, phenolic resins, polyimide resins, and polyarylsulfone resins. Illustrated. In addition, examples of inorganic fibers include alumina fibers, carbon fibers, and glass fibers, which are crushed during mixing or forming sheet gasket materials, but few are crushed into powder, and most are relatively long. It will be present in the gasket material as fibers. When such fibers are present, the strength of the gasket material is improved, but it is difficult to reduce the porosity and average pore diameter, so it is not preferable to add too much.
The amount of inorganic fiber added is preferably 3% by weight or less. The sheet gasket material of the present invention has a porosity of 20
% or less is important. If the porosity is greater than 20%, stress relaxation will be large, the life of the gasket material will be shortened, and the sealing performance will also be poor, which is not preferable. The lower limit of the porosity is not particularly limited, and the lower the porosity, the better the sealing performance, etc., which is preferable. However, it is extremely difficult to produce a sheet gasket material with a porosity of 0%, and the porosity is usually It will be about 1% or more. Further, the sheet-like gasket material of the present invention has a pore diameter of 0.15 μm or less. Even when the porosity is low, the presence of large-diameter pores is undesirable because the sealing performance deteriorates. Furthermore, when pores with a large diameter are present, the porosity tends to increase. The smaller the lower limit of the pore size, the better, and a pore size of 0 is most preferable from the standpoint of sealing performance.However, it is quite difficult to produce a gasket material with a pore size of essentially 0, that is, no pores at all, and it is usually , there are pores of about 0.009μ. Particularly preferably, the pore diameter is about 0.08μ to 0.01μ. There are various methods for producing sheet-like gasket materials with small porosity and pore diameter, but an easy method is exemplified below. The first method is to impregnate or add synthetic resin or liquid material. In this method, a synthetic resin such as a thermoplastic resin is added before forming the sheet, and the pores are filled with the synthetic resin by heating it above the melting point of the synthetic resin during or after forming the sheet. By this, the porosity and pore diameter can be reduced, and after forming the sheet-like material, the porosity and pore diameter can be reduced by impregnating it with a liquid material such as oil or a synthetic resin melt. However, with this method,
Due to the presence of synthetic resin inside and on the surface of the sheet gasket material, there is a risk of seizure when using the sheet gasket material at high temperatures, so this method is preferred as a manufacturing method for sheet gasket materials to be used at high temperatures. I can't say that. The second method is to pressurize the sheet material again after forming it. This is a method in which pressure is applied after forming or firing the sheet-like material. Examples of this pressurizing method include a press mold or a roll pressurizing method.
Here, pressurization using a roll is more preferable than pressurization using a press die because continuous pressurization work is possible, and therefore it is superior in workability and is preferably employed. Also,
The pressure to be applied is preferably equal to or higher than that used when forming a sheet-like object. This pressure is appropriately selected depending on the condition of the sheet material, the required physical properties of the gasket material, etc.
Even if the pressure is too high, the improvement effect will not be as expected. The surface pressure is preferably about 1000Kg/ ^cm2 or less, and usually 200~200kg/cm2 or less.
Approximately 700Kgf/cm ² is adopted. Moreover, in this pressurizing method, it is preferable to simultaneously heat. Heating improves the plasticity of PTFE, so
Even if the applied pressure becomes that high, the porosity and pore diameter can be easily reduced. As for the pressurizing temperature, if the temperature is too high, the effect will not be sufficiently exhibited, and if the temperature is too high, there is a possibility that PTFE will be thermally decomposed, so it is not preferable. The temperature is preferably about 250 to 400°C, particularly about 300 to 380°C. The third is the mixed use of two or three types of inorganic fine powders with different particle sizes as an inorganic filler, or the use of two or three types of inorganic particles with different particle sizes.
Mixture of Fine Powders This method uses a mixture of fine carbon powders to improve filling efficiency. This method can reduce the porosity and pore size because the spaces between large particles of inorganic fine powder are filled with medium and small particle size fine powder. In addition, carbon powder fills the gaps between large, medium, and small inorganic fine powders, and at the same time, its low friction property promotes the sliding of inorganic fine powders during sheet forming, which has the effect of increasing the filling properties of fillers. . Furthermore, this method makes it easier to manufacture gaskets than the above-mentioned methods, so it is possible to obtain gaskets with excellent versatility. In the sheet gasket material of the present invention,
PTFE is fibrillated and mineral fillers are present between the fibrils. PTFE is not fibrillated or has an inorganic filler.
Without the presence of PTFE between the fibrils, the sheet gasket material would be extremely brittle and unfit for practical use. In the sheet gasket material of the present invention, PTFE is fibrillated, that is, it forms a micro three-dimensional network structure, and the inorganic filler exists uniformly dispersed between the three-dimensional network structure. There is, that is,
Since the inorganic filler is firmly held by the PTFE fibrils, it has sufficient strength as a gasket material. Furthermore, the sheet gasket material of the present invention having such a structure is made of PTFE.
exists uniformly throughout the gasket material, so the excellent water and oil repellency of PTFE is exhibited throughout the gasket material, despite the small amount of PTFE content. In other words, the gasket material has excellent oil resistance and water resistance. PTFE, which can be easily fibrillated by applying high shear forces. In addition, as a method for uniformly dispersing inorganic filler between PTFE fibrils,
After adding non-fibrillated PTFE and inorganic filler, simultaneously with mixing or after homogeneous mixing
This can be easily achieved by fibrillating PTFE. For example, this can be achieved by stirring and mixing a predetermined ratio of PTFE powder and an inorganic filler under high shear force, such as by stirring at high speed with a mixer, in the presence or absence of a processing aid such as naphtha. In addition, by applying higher shear force, such as by extruding this mixture using an extruder with a large ratio of the cross-sectional area of the cylinder to the cross-sectional area of the nozzle,
PTFE can also be fibrillated to a higher degree. The sheet-like gasket material of the present invention is as described above.
A composition in which an inorganic filler is dispersed between PTFE fibrils can be produced by a known sheet forming method such as pressure forming or rolling using a press mold or roll. Particularly from the viewpoint of manufacturing operations, a roll forming method that allows continuous forming is preferably employed. In the sheet gasket material of the present invention,
PTFE may be fired or unformed. When PTFE is unfired, the sheet-like gasket material has a relatively high compressibility, so it conforms well to the sealing surface even at low tightening pressures and exhibits excellent sealing performance. That is, it is particularly useful in applications such as glass piping where strong clamping pressure cannot be applied. Furthermore, when PTFE is fired, the sheet-like gasket material has excellent strength and is therefore particularly useful in applications where relatively high clamping pressure is applied. When PTFE is fired, it is preferable to perform the firing after forming the sheet. If PTFE is fired before sheet forming, sheet forming becomes difficult. Furthermore, there is a problem in that fibrillation becomes difficult if PTFE is fired before fibrillation. The sheet gasket material of the present invention may be used alone as a sheet gasket, or may be laminated with a metal plate or the like to form a composite gasket. When making a composite gasket, use a metal plate with irregularities such as a claw steel plate or an embossed aluminum plate,
This can be accomplished by integrally molding the sheet-like gasket material of the present invention onto a carrier such as a metal plate or wire gauze having a mesh-like opening by a method such as bonding or pressure bonding. For example, a composite gasket with a metal core can be made by crimping sheet gasket material on both sides of a wire mesh using iron biaxial rolls, and similarly, a steel plate for claws can be crimped on both sides of the sheet gasket material. By doing so, it is also possible to obtain a metal-coated composite gasket. [Example] Examples 1 to 3, Comparative Examples 1 to 3 40 parts by weight of polytetrafluoroethylene resin powder (CD-1 manufactured by Asahi Fluoropolymer), inorganic filler (kaolinite clay: Katalupo manufactured by Tsuchiya Kaolin Industries, average particle size) diameter 10μ) 60 parts by weight and 1,1,1
- 250 parts by weight of trichloroethane in a mixer
After stirring for 20 minutes and filtering, the filtrate was dried at room temperature. 17 parts by weight of a high viscosity organic solvent (Isopar M manufactured by Exxon) was added to the dried product, stirred for 10 minutes in a kneader, and then aged for about 15 hours.
The aged product is injected into a mold with a conical part of 105 mm and an angle of 40°, and a ratio of the cross-sectional area of the cylinder to the cross-sectional area of the nozzle part is 15.
It was extruded at room temperature, under a pressure of 40 Kgf/cm ² , and at a pressure rate of 120 mm/hr to form a rod-shaped product. This rod-shaped object has an outer diameter of 200 mm,
Compression ratio 18, speed on 400mm long steel twin rollers
It was inserted at a rate of 1800 mm/hr to obtain a long sheet with a width of 300 mm and a thickness of 1 mm. After drying the long sheet with hot air at 300°C, it was fired at 350°C for 3 hours. The fired sheet was flattened using two iron rollers at a surface pressure of 300 Kgf/cm ² to obtain a sheet gasket material having a porosity of 5% and a pore diameter of 0.02 μm. Table 1 shows the results of tests on compressibility, recovery rate, stress relaxation rate, water resistance, oil resistance, and sealability of this sheet gasket material. By changing the flattening conditions, sheet gasket materials having the pore diameters and porosity shown in Table 1 were obtained. Similar tests were conducted on this sheet gasket material, and the results are shown in Table 1.

【table】

[Table] *Reference Example 1 shows the results of a similar test using an asbestos joint sheet.
Examples 4 to 7 20 parts by weight of polytetrafluoroethylene resin powder (CD-1 manufactured by Asahi Fluoropolymer), 80 parts by weight of inorganic filler (kaolinite clay: Catalpo manufactured by Tsuchiya Kaolin Industries, average particle size 10μ) and 1,1 ,1
- 250 parts by weight of trichloroethane in a mixer
After stirring and mixing for 20 minutes, the mixture was dried at room temperature. 17 parts by weight of a high viscosity organic solvent was added to this dried product, stirred in a kneader for 10 minutes, aged for about 15 hours, and then the extruded part had a cross-sectional dimension of 105 mm, a conical part with an angle of 40°, a cylinder cross-sectional area, and a nozzle cross-sectional area. The aged product was injected into a mold with a ratio of 15 and heated at room temperature, pressure 40Kgf/cm ² , and pressurization speed.
It was extruded at 120 mm/hr to form a rod. This rod-shaped material was inserted into a two-roll iron roller having an outer diameter of 200 mm and a length of 400 mm at a compression ratio of 18 and a speed of 1800 mm/hr to obtain a long sheet with a width of 300 mm and a thickness of 0.65 mm. 300 long sheets
After drying with hot air at 350°C for 3 hours.
SPCC material, thickness 0.25mm, with two iron rollers.
A fired sheet was crimped on both sides of a steel plate with a round hole hook with a hole diameter of 1.2 mm at a surface pressure of 1000 kg/ ^cm2 , and the thickness was
A 1.2mm composite gasket was obtained. The porosity of the fired body part of this composite gasket is 8%;
It was 0.04μ. About this composite gasket,
Table 2 shows the results of tests on compression ratio, recovery ratio, stress relaxation ratio, oil resistance, water resistance, and sealability. Table 2 shows the results of similar tests conducted on composite gaskets using sheet gasket materials having different porosity and pore diameter.

[Table] *As Reference Example 2, the results of a similar test using an asbestos header gasket.
showed that.
Examples 8 to 10 Polytetrafluoroethylene resin powder (Asahi Fluoropolymer CD-1) in the weight parts shown in Table 3, an inorganic filler (kaolinite clay: Catalpo manufactured by Tsuchiya Kaolin Industries, average particle size 10μ), and 1 ,1,
250 parts by weight of 1-trichloroethane was stirred and mixed using a mixer for 20 minutes, filtered, and then dried at room temperature. Add 17 parts by weight of a high viscosity organic solvent (Isopar M manufactured by Exxon) to this dried material, and use a kneader to
After stirring for several minutes, the mixture was aged for about 15 hours. This aged product was injected into a mold with an extrusion section having a cross-sectional dimension of 105 mm, a conical section at an angle of 40 ^degrees , and a ratio of the cross-sectional area of the cylinder to the cross-sectional area of the nozzle section of 15.
It was extruded into rods using hr. This rod-shaped object has an outer diameter
Compression ratio for 200mm and 400mm long iron rollers
18, Insert at a speed of 1800mm/hr, width 300mm, thickness 1
A long sheet of mm was obtained. This long sheet is heated to 300℃
After drying with hot air, apply surface pressure using two iron rollers.
A sheet gasket material was obtained by flattening at 600 kg/cm ² . Table 3 shows the results of tests on compressibility, recovery rate, stress relaxation rate, oil resistance, water resistance, and sealability of this sheet gasket material.

[Table] Examples 11 to 15 Sheet-like gaskets were obtained in the same manner as in Example 1, except that the composition ratios in Table 4 were used instead of the composition ratios in Example 1. Table 4 shows the results of tests conducted using this sheet gasket. Examples 16 to 19 Sheet-like gaskets were obtained in the same manner as in Example 1, except that the composition ratios in Table 5 were used instead of the composition ratios in Example 1. Table 5 shows the results of tests conducted using this sheet gasket.

【table】

【table】

[Table] [Effects of the Invention] Since the sheet-like gasket material of the present invention has a specific porosity and pore diameter, the stress relaxation rate is small and the sealing performance is good. That is, it has excellent sealing properties, has a long life as a gasket material, and can be used for a long period of time. Also, since it does not contain asbestos, there is no problem of environmental pollution. Furthermore, it has excellent heat resistance and does not deteriorate, harden, or seize due to heating, so it can be used continuously for a long period of time, significantly reducing repair costs and eliminating the need for anti-seizure materials. It has the following effects.
Furthermore, since it has extremely excellent oil resistance and water resistance, it can exhibit excellent effects as a sealing material for various liquids.
Further, since the sheet gasket material of the present invention can be formed into a long sheet, it has excellent productivity and can be manufactured at low cost. In addition, inorganic fillers
Strongly held between PTFE fibrils, it has great strength and is easy to handle.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the gasket material of Example 1, FIG. 2 is a cross-sectional view of the composite gasket of Example 2, and FIG. 3 is a plan view of the composite gasket of Example 2. . In the figure, 1 is a sheet gasket material, 2 is an inorganic filler, 3 is a PTFE fibril, 4 is a nail stand steel plate, and 5 is a sheet gasket material.

Claims (1)

[Claims] 1 Contains 5% by weight or more of polytetrafluoroethylene resin and 50% by weight or more of inorganic filler,
The polytetrafluoroethylene resin is fibrillated, an inorganic filler exists between the fibrils, the inorganic filler is a filler whose main component is a hydrous silicate mineral, and the porosity is 20% or less.
A sheet-like gasket material characterized by a pore diameter of 0.15μ or less.