JP7595072B2 - Sealing materials - Google Patents

Description

One embodiment of the present invention relates to a sealing material.

Filled fluororesin sheets are made by mixing fluororesin with a filler and processing it into a sheet. In addition to the chemical resistance, heat resistance, and other properties of fluororesin, they also have the specific functions and properties of the filler, and improve on the creep resistance, a drawback of fluororesin, and are often used as sealing materials, etc.

As an example of such a filled fluororesin sheet, Patent Document 1 describes a filled fluororesin sheet that contains a fluororesin and an inorganic filler with a modified Mohs hardness of 8 or more.

JP 2010-235755 A

In the case of conventional filled fluororesin sheets as described above, when an attempt is made to improve the sealing property, the creep resistance decreases (stress relaxation becomes more likely), and when an attempt is made to improve the creep resistance (stress relaxation is suppressed), the sealing property decreases. Thus, there is a trade-off between sealing property and creep resistance; when one of the properties, sealing property or creep resistance, is improved, the other is sacrificed.
For example, in the conventional filled fluororesin sheets described in Patent Document 1 and the like, when the amount of fluororesin is increased to improve sealing performance, creep resistance decreases, and there is a limit to how much sealing performance can be improved while maintaining the creep resistance required of a sealing material.

One embodiment of the present invention provides a sealing material with improved sealing properties while maintaining the creep resistance required of a sealing material.

As a result of intensive research by the present inventors to solve the above problems, they found that the above problems can be solved by the following configuration examples, and completed the present invention.
A configuration example of the present invention is as follows.

[1] A composition comprising a fluororesin and an inorganic filler,
The sealing material, wherein the crystallinity of the fluororesin is 50% or more.

[2] A sealing material described in [1], in which the ratio of the total volume of the fluororesin to the total volume of the inorganic filler (volume of fluororesin/volume of inorganic filler) is 40/60 to 70/30.

[3] A sealing material described in [1] or [2], wherein the average particle size of the inorganic filler is 1 to 30 μm.

[4] A sealing material described in any one of [1] to [3], wherein the inorganic filler contains two or more types of particles having different average particle sizes.

[5] A sealing material according to any one of [1] to [4], wherein the sealing material is a gasket.

According to one embodiment of the present invention, it is possible to provide a sealing material that has improved sealing properties compared to conventional filler-containing fluororesin sheets, while maintaining the creep resistance required for a sealing material at the same level as that of conventional filler-containing fluororesin sheets.
Moreover, according to one embodiment of the present invention, a sealing material that is resistant to distortion and has high tensile strength can be easily obtained.

<Sealing material>
A sealing material according to one embodiment of the present invention (hereinafter also referred to as "the sealing material") contains an inorganic filler and a fluororesin having a crystallinity of 50% or more.
Because the present sealing material exerts the above-mentioned effects, it can be suitably used as a gasket, in particular a gasket for piping (e.g., piping flanges) and valves, a sealing material for valve opening and closing members, a gasket used for the lids of containers, tanks, etc., and a gasket used for instruments and sight glasses installed in containers, tanks, etc.
The shape and size of the sealing material are not particularly limited, and may be selected according to the desired application.

<Fluoropolymer>
The fluororesin is not particularly limited as long as it has a crystallinity of 50% or more (hereinafter, also referred to as "fluororesin a").
The fluororesin a contained in the present sealing material may be one type or two or more types. The present sealing material may contain one or two or more types of fluororesin a, and may further contain fluororesin b having a crystallinity of less than 50%. The content of fluororesin a relative to the total amount of fluororesins contained in the present sealing material is preferably 30 to 100 mass%.

The crystallinity of the fluororesin a is 50% or more, preferably 55% or more, and more preferably 60% or more, from the viewpoint that a sealing material having improved sealing properties while maintaining creep resistance can be easily obtained, and the upper limit thereof is preferably 80% or less, from the viewpoint that a sealing material having high tensile strength and low crush resistance can be easily obtained.
The degree of crystallinity of the fluororesin contained in a conventional filled fluororesin sheet is usually about 45%, and the degree of crystallinity of the fluororesin a is significantly higher than the degree of crystallinity of the fluororesin contained in a conventional filled fluororesin sheet.

The crystallinity of the fluororesin in the present invention refers to the crystallinity of the fluororesin contained in the sealing material, and is not the crystallinity of the fluororesin used as a raw material when producing the sealing material. In other words, it is sufficient that the sealing material contains a fluororesin having a crystallinity in the above range, and the crystallinity of the fluororesin used as a raw material when producing the sealing material may be within the above range or outside the above range.
The crystallinity of the fluororesin in this specification can be specifically measured by the method described in the examples below.

Examples of fluororesins include polytetrafluoroethylene (PTFE), modified PTFE, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE), fluoroethylene-vinyl ether copolymer (FEVE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).
Among these, PTFE or modified PTFE is preferred from the standpoint of moldability, processability, etc., since the present sealing material containing a fluororesin having a crystallinity within the above range can be more easily obtained.

The fluororesin used as a raw material in producing this sealant may be in powder form or may be a dispersion of fluororesin powder. Using a dispersion of fluororesin powder as a raw material in producing this sealant has the advantage that the inorganic filler can be easily and uniformly dispersed.

The content of fluororesin a in this sealing material is preferably 8 to 82% by mass, and more preferably 15 to 82% by mass, since this allows the properties of the fluororesin to be fully exhibited and makes it easy to obtain a sealing material with improved sealing properties while maintaining creep resistance.

<Inorganic filler>
The inorganic filler is not particularly limited, and any conventionally known inorganic filler can be used.
The sealing material may contain one type of inorganic filler or two or more types. When the sealing material contains two or more types of inorganic fillers, two or more types of inorganic fillers different in type (material) may be used, or two or more types of inorganic fillers different in average particle size or shape may be used.

Examples of inorganic fillers include carbon-based fillers such as graphite, carbon black, expanded graphite, activated carbon, carbon nanotubes, diamond, and carbon fibers; oxide-based fillers such as magnesia, silica, alumina, and (fused) zirconia; nitride-based fillers such as boron nitride and silicon nitride; carbide-based fillers such as boron carbide, silicon carbide, tungsten carbide, and tantalum carbide; carbonate-based fillers such as calcium carbonate; sulfate-based fillers such as barium sulfate and calcium sulfate; and mineral-based fillers such as talc, mica, clay, garnet, topaz, and rock wool.
Among these, carbon black, silica, alumina, silicon carbide, barium sulfate, and clay are preferred, and silica, alumina, silicon carbide, barium sulfate, and clay are more preferred, from the viewpoint of easily obtaining a sealing material that is resistant to distortion (deformation) even at high temperatures.

The shape of the inorganic filler is not particularly limited and may be any of particles (including flakes) and fibers, but is preferably particles.
When the inorganic filler is particulate, the average particle size is preferably 1 to 30 μm, more preferably 1 to 20 μm, and even more preferably 1 to 15 μm, from the viewpoint that a sealing material having a low compression ratio even at high temperatures can be easily obtained.

In this specification, "average particle size" refers to the particle size (median diameter) when the cumulative number is 50% in the particle size distribution measured by a laser diffraction scattering method. The particle size distribution can be measured, for example, using a dynamic light scattering particle size distribution measuring device (manufactured by Horiba, Ltd., product number: LB-550).

It is preferable that the present sealing material contains two or more types of inorganic fillers (particles) with different average particle sizes, since this improves sealing properties while maintaining creep resistance, and makes it easy to obtain a sealing material with low compression rate even at high temperatures.

In this way, when the present sealing material contains two or more inorganic fillers (particles) having different average particle sizes, it is preferable that the sealing material contains inorganic filler A having an average particle size in the range of 7 to 30 μm and inorganic filler B having an average particle size in the range of 1 to 5 μm, from the viewpoint of easily obtaining a sealing material having a low compression ratio even at high temperatures.
The average particle size of the inorganic filler A is more preferably 7 to 20 μm, and the average particle size of the inorganic filler B is more preferably 2 to 5 μm.

In addition, when the sealing material contains the inorganic fillers A and B, the volume ratio thereof (volume of inorganic filler A/volume of inorganic filler B) is preferably 45/55 to 80/20, and more preferably 50/50 to 75/25, from the viewpoint that a sealing material having a low compression rate even at high temperatures can be easily obtained.

In the present sealing material, the ratio of the total volume of the fluororesin, particularly the fluororesin a, to the total volume of the inorganic filler (volume of fluororesin/volume of inorganic filler) is preferably 40/60 to 70/30, more preferably 40/60 to 60/40, and even more preferably 45/55 to 55/45, from the viewpoints of easily obtaining a sealing material that is excellent in sealing properties and has a low compression ratio even at high temperatures.
If the content of the fluororesin is below the above range, the sealing property tends to be easily degraded, whereas if the content of the fluororesin is above the above range, the creep resistance tends to be easily degraded.

<Other ingredients>
The present sealing material may be a sealing material consisting of the above-mentioned fluororesin and inorganic filler (only), or may contain, in addition to the above-mentioned fluororesin and inorganic filler, other components that have been conventionally used in sealing materials, within the scope of not impeding the object of the present invention.
Examples of the other components include tackifiers such as terpene resins, terpene-phenol resins, coumarone resins, coumarone-indene resins, and rosin, ultraviolet absorbers, antioxidants, polymerization inhibitors, colorants such as pigments, resin powders such as PPS, and organic fibers such as aramid fibers.
These other components may be used alone or in combination of two or more.

<Method of manufacturing the present sealing material>
The present sealing material can be produced, for example, by forming a resin composition containing a fluororesin, an inorganic filler, and, if necessary, a processing aid and the other components described above, into a sheet.

The fluororesin used in the resin composition may be in the form of a powder or a dispersion in which the fluororesin powder is dispersed in a dispersion medium. When a dispersion of the fluororesin powder is used, the inorganic filler can be easily and uniformly dispersed.
The fluororesin and inorganic filler in the resin composition may be used so that the amounts in the resulting sealing material are within the above ranges.

The processing aid is not particularly limited, but examples thereof include petroleum-based hydrocarbon solvents such as paraffin-based hydrocarbon solvents.
The petroleum-based hydrocarbon solvent may be one that is readily commercially available, and examples thereof include Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M (all trade names, manufactured by Exxon Mobil Corporation).
The content of the processing aid in the resin composition can be appropriately selected depending on the type of sealing material, etc., and cannot be generally determined, but is usually preferably about 5 to 35% by mass.

The resin composition can be prepared by mixing the fluororesin, inorganic filler, and, if necessary, the processing aid and the other components in any order, either all at once or in small amounts in multiple batches, so as to have a uniform composition. In order to obtain a resin composition having a uniform composition, the processing aid may be added in an excess amount to the resin composition, thoroughly stirred, and then the excess processing aid may be removed, for example, by filtration, volatilization, or other means.

There are no particular limitations on the method for forming the resin composition into a sheet, but it is preferable to produce the sheet by sequentially carrying out preforming, rolling (drying if necessary) and firing the resin composition.

The preforming can be carried out, for example, by extrusion molding the resin composition. A preform (extrusion molded product) is obtained by this extrusion molding. The shape of the preform is not particularly limited, but considering the efficiency of the subsequent sheet formation and the uniformity of the sheet properties, it is preferable that the preform be rod-shaped or ribbon-shaped.

The rolling is preferably performed by rolling the obtained preform. For example, the method of rolling the preform includes a method of passing the preform between rolling rolls such as biaxial rolls and rolling-molding the preform into a sheet. The rolled sheet obtained by rolling the preform may be further rolled several times. By repeating the rolling, the inside of the rolled sheet can be further densified. When the rolling is repeated using the biaxial roll, it is preferable to narrow the roll gap of the rolling rolls each time the rolling is repeated.
When a rolled sheet is produced by rolling a preform using a biaxial roll, for example, the distance between the rolls is adjusted to 0.5 to 20 mm, and the moving speed of the surface of the roll (sheet extrusion speed) is set to 5 to 50 mm/sec.

If processing aids remain in the rolled sheet obtained as described above, they may be removed, if necessary, by leaving the rolled sheet at room temperature or by heating the rolled sheet at a temperature below the melting point of the fluororesin.

Next, the rolled sheet obtained above is fired. For example, the method of firing the rolled sheet includes a method of heating the rolled sheet at a temperature equal to or higher than the melting point of the fluororesin to sinter it. The heating temperature varies depending on the type of fluororesin, but is preferably about 340 to 370°C from the viewpoints of firing the entire rolled sheet uniformly and suppressing the generation of fluorine-based gases at high temperatures.
The fired sheet is usually cooled to about room temperature before use. In this case, by slowly cooling at a temperature decreasing speed of preferably 1.0° C./min or less, more preferably 0.85° C./min or less, and even more preferably 0.7° C./min or less, a sealing material containing a fluororesin having a crystallinity in the above range can be easily obtained.
The cooling speed is preferably 0.1° C./min or more, since a sealing material with high tensile strength can be easily obtained.

The sheet produced in this manner may be used as a gasket as is, or may be cut to the desired shape and used as a sealing material.

The present invention will now be described in further detail with reference to examples, but the present invention is not limited to these examples.

[Example 1]
A sheet-forming composition was prepared by mixing 1,000 g of fluororesin powder (AGC Corporation, polytetrafluoroethylene powder, product number: CD-1, density: 2,200 kg/ ^m3) , 1,400 g of silicon carbide particles (Shinano Electric Smelting Co., Ltd., product number: #1200, average particle size: 9.5 μm), 125 g of auxiliary A (Exxon Mobil, product name: Isopar C, distillation temperature: 97-104° C.), and 125 g of auxiliary B (Exxon Mobil, product name: Isopar G, distillation temperature: 158-175° C.) in a kneader for 5 minutes and then allowing to stand at room temperature (25° C.) for 16 hours to allow maturation.

The sheet-forming composition obtained above was extruded at room temperature (25°C) using an extruder with a die of 300 mm x 20 mm to produce a preform. The preform obtained above was rolled using a biaxial roll under conditions of a roll diameter of 700 mm, a roll spacing of 20 mm, a roll speed of 6 m/min, and a roll temperature of 40°C. This rolled sheet was rolled again using a biaxial roll with a roll spacing of 10 mm, and this rolled sheet was further rolled again using a biaxial roll with a roll spacing of 5 mm, and finally this rolled sheet was rolled using a biaxial roll with a roll spacing of 1.5 mm to obtain a rolled sheet with a thickness of 1.5 mm.

The rolled sheet obtained above was left at room temperature (25°C) for 24 hours to remove the auxiliary agent, and then baked in an electric furnace at a temperature of 350°C for 3 hours, and then slowly cooled at a temperature drop rate of 0.7°C/min to produce a sealing material. The volume ratio of the fluororesin to the inorganic filler (fluororesin/inorganic filler) in this sealing material was 51/49.

[Example 2]
A rolled sheet was obtained in the same manner as in Example 1, and the obtained rolled sheet was left at room temperature (25°C) for 24 hours to remove the auxiliary agent. Thereafter, the sheet was fired at a temperature of 350°C for 3 hours in an electric furnace, and then slowly cooled at a temperature decreasing rate of 0.5°C/min to produce a sealing material.

[Example 3]
A rolled sheet was obtained in the same manner as in Example 1, and the obtained rolled sheet was left at room temperature (25°C) for 24 hours to remove the auxiliary agent. Thereafter, the sheet was fired at a temperature of 350°C for 3 hours in an electric furnace, and then slowly cooled at a temperature decreasing rate of 0.25°C/min to produce a sealing material.

[Example 4]
A rolled sheet was obtained in the same manner as in Example 1, and the obtained rolled sheet was left at room temperature (25°C) for 24 hours to remove the auxiliary agent. Thereafter, the sheet was fired in an electric furnace at a temperature of 350°C for 3 hours, and then slowly cooled at a temperature decreasing rate of 0.1°C/min to produce a sealing material.

[Example 5]
A sealing material was prepared in the same manner as in Example 2, except that CD-1 and silicon carbide particles were used so that the volume ratio of the fluororesin to the inorganic filler (fluororesin/inorganic filler) was 40/60.

[Example 6]
A sealing material was produced in the same manner as in Example 2, except that CD-1 and silicon carbide particles were used so that the volume ratio of the fluororesin to the inorganic filler (fluororesin/inorganic filler) was 60/40.

[Example 7]
A sealing material was prepared in the same manner as in Example 2, except that silicon carbide particles (manufactured by Shinano Electric Refining Co., Ltd., product number: #4000, average particle size: 3 μm) were used as the inorganic filler.

[Example 8]
A sealing material was prepared in the same manner as in Example 2, except that silicon carbide particles (manufactured by Shinano Electric Refining Co., Ltd., product number: #8000, average particle size: 14 μm) were used as the inorganic filler.

[Example 9]
A sealing material was prepared in the same manner as in Example 2, except that silicon carbide particles (manufactured by Shinano Electric Refining Co., Ltd., product number: #7000, average particle size: 17 μm) were used as the inorganic filler.

[Example 10]
A sealing material was prepared in the same manner as in Example 2, except that silicon carbide particles (manufactured by Shinano Electric Refining Co., Ltd., product number: #5000, average particle size: 25 μm) were used as the inorganic filler.

[Example 11]
A sealing material was prepared in the same manner as in Example 2, except that silica (Tokuyama Corp., Excelica, average particle size: 10 μm) was used as the inorganic filler.

[Example 12]
A sealing material was prepared in the same manner as in Example 2, except that α-alumina (A-420, manufactured by Showa Denko KK, average particle size: 3.9 μm) was used as the inorganic filler.

[Example 13]
A sealing material was prepared in the same manner as in Example 2, except that clay (manufactured by Showa KDE Co., Ltd., NK300, average particle size: 9.5 μm) was used as the inorganic filler.

[Example 14]
A sealing material was prepared in the same manner as in Example 2, except that barium sulfate (manufactured by Takehara Chemical Industry Co., Ltd., W-10, average particle size: 10 μm) was used as the inorganic filler.

[Example 15]
A sealing material was prepared in the same manner as in Example 2, except that 350 g of silicon carbide particles (manufactured by Shinano Electric Smelting Co., Ltd., product number: #4000, average particle size: 3 μm) and 1050 g of silicon carbide particles (manufactured by Shinano Electric Smelting Co., Ltd., product number: #1200, average particle size: 9.5 μm) were used as the inorganic filler.

[Example 16]
A sealing material was prepared in the same manner as in Example 2, except that 700 g of silicon carbide particles (manufactured by Shinano Electric Smelting Co., Ltd., product number: #4000, average particle size: 3 μm) and 700 g of silicon carbide particles (manufactured by Shinano Electric Smelting Co., Ltd., product number: #1200, average particle size: 9.5 μm) were used as the inorganic filler.

[Comparative Example 1]
A rolled sheet was obtained in the same manner as in Example 1, and the obtained rolled sheet was left at room temperature (25°C) for 24 hours to remove the auxiliary agent. Thereafter, the sheet was fired in an electric furnace at a temperature of 350°C for 3 hours, and then air-cooled to obtain a sealing material.

[Comparative Example 2]
A sealing material was prepared in the same manner as in Comparative Example 1, except that CD-1 and silicon carbide particles were used so that the volume ratio of the fluororesin to the inorganic filler (fluororesin/inorganic filler) was 39/61.

[Comparative Example 3]
A sealing material was prepared in the same manner as in Comparative Example 1, except that CD-1 and silicon carbide particles were used so that the volume ratio of the fluororesin to the inorganic filler (fluororesin/inorganic filler) was 73/27.

<Degree of crystallinity of fluororesin in sealing material>
The crystallinity of the fluororesin in the sealing material obtained above was measured as follows. The results are shown in Table 1.
A DSC6200 manufactured by Seiko Instruments Inc. was used as the device. The sealing material was heated from 30° C. at a heating rate of 5° C./min. The heat of fusion (ΔH) was measured, calculated from the peak area of the endothermic peak observed in the first heating curve, and the crystallinity was calculated from the following formula.
Crystallinity (%) = ΔH × 100 / (ΔHb × w)
[Here, ΔHb is the heat of fusion of the fluororesin, and w is the content (mass%) of the fluororesin in the sealing material.]

The ΔHb can be measured by measuring the heat of fusion of the raw fluororesin used in the same manner as the heat of fusion of the sealing material, but when the fluororesin contained in the sealing material is PTFE, the present invention adopts a value of 54.8 mJ/mg as ΔHb, and when the fluororesin contained in the sealing material is modified PTFE, the present invention adopts a value of 50.0 mJ/mg as ΔHb.

Specifically, the fluororesin content w in the sealing material can be calculated from the amount of weight loss observed around 420 to 645° C. when measured under the following conditions using a thermogravimetric analyzer (TG).
Equipment used: TG/DTA6200 (Seiko Instruments Inc.)
Test temperature: 30 to 800°C
Heating rate: 10° C./min. Atmosphere: nitrogen gas

<Sealing performance>
A gasket with an outer diameter of 65 mm and an inner diameter of 50 mm was produced from the sealing material obtained above. The produced gasket was sandwiched between metal platens, and nitrogen gas with an internal pressure of 0.98 MPa was sealed in a state where a stress of ^19.8 MPa was applied, and the nitrogen gas leaked from the gasket was collected with a sleeve, and the sealing property (leakage amount) was measured using a soap film flowmeter. In addition, the case where the leakage amount was 1.7 x ^10-4 Pa.m3/s or less was evaluated as ○, and the case where the leakage amount exceeded 1.7 x ^{10-4 Pa.m3} /s was evaluated as ×. The results are shown in Table 1.

<Creep resistance (stress relaxation rate)>
Test pieces were prepared from the sealing material obtained above, and the stress relaxation rate of the test pieces was measured in accordance with JIS R 3453:2001, except that the heating temperature was changed from 100° C. to 200° C. In addition, the stress relaxation rate was evaluated as ◯ when it was 70% or less, and as × when it was more than 70%. The results are shown in Table 1.

<Tensile strength>
Test pieces were prepared from the sealing material obtained above, and the tensile strength was measured in accordance with JIS R 3453: 2001. The tensile strength was evaluated as ◯ when it was 9.8 MPa or more, Δ when it was 5 MPa or more and less than 9.8 MPa, and × when it was less than 5 MPa. The results are shown in Table 1.

Claims (4)

Contains a fluororesin and an inorganic filler,
The crystallinity of the fluororesin is 50% or more,
The ratio of the total volume of the fluororesin to the total volume of the inorganic filler, that is, the volume of the fluororesin/the volume of the inorganic filler, is 40/60 to 70/30;
Sealing material. 2. The sealing material according to claim 1 , wherein the inorganic filler has an average particle size of 1 to 30 μm. The sealing material according to claim 1 , wherein the inorganic filler contains two or more types of particles having different average particle sizes. The sealing material according to any one of claims 1 to 3 , which is a gasket.