Seat gasket

Abstract

To provide a sheet gasket with excellent sealing performance at low clamping pressures while maintaining good rigidity, making it suitable for use in applications requiring chemical resistance.SOLUTION: A method for manufacturing a sheet gasket made of fluororesin, characterized by heating a fluororesin sheet that has been uniaxially or biaxially stretched to a temperature of 250°C to a temperature lower than the melting point of the fluororesin used in the fluororesin sheet, shrinking the fluororesin sheet to a shrinkage rate of 10 to 35%, and then cooling it.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheet gasket. More specifically, the present invention relates to a sheet gasket that can be suitably used in fields where chemical resistance is required and low clamping pressure is desired when clamping the sheet gasket. [Background technology]

[0002] A sheet gasket has been proposed that is composed of multiple segments, and in which a step is formed in advance between one end and the other end of the segments that are to be assembled together, and when these step portions are overlapped, the thickness of the segments is set in the range of 1.05t≦T≦1.5t, where t is the overall thickness of the segments and T is the overall thickness of the joined ends after the one end and the other end are assembled (see, for example, Patent Document 1).

[0003] The sheet gasket is said to be effective in ensuring a reliable seal between the connected ends, particularly when a large-diameter sheet gasket is constructed from multiple divided bodies, and in preventing leakage due to poor adhesion or shrinkage caused by the adhesive when the sheet gasket is manufactured without using adhesive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-16843 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors focused on fluororesin, which has excellent chemical resistance, in order to use sheet gaskets in fields where chemical resistance is required and low tightening pressure is desirable when tightening the sheet gasket, and attempted to use sheet gaskets made of fluororesin as sealing materials. However, it was found that the sheet gaskets in question were poor in mechanical strength and rigidity and therefore not suitable for use as sealing materials.

[0006] Therefore, the present inventors biaxially stretched a sheet gasket made of a fluororesin in order to improve the performance of the sheet gasket, but found that the biaxially stretched sheet gasket not only did not have sufficient rigidity, but also had poor sealing properties.

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a sheet gasket that has good rigidity, excellent sealing properties at low tightening pressure, and can be suitably used in fields where chemical resistance is required. [Means for solving the problem]

[0008] The present invention provides (1) A method for producing a sheet gasket made of a fluororesin, comprising heating a uniaxially or biaxially stretched fluororesin sheet to a temperature of 250°C or higher that is lower than the melting point of the fluororesin used in the fluororesin sheet, shrinking the fluororesin sheet to a shrinkage rate of 10 to 35%, and then cooling the sheet; (2) The method for producing a sheet gasket according to (1) above, wherein the stretching ratio of the uniaxially or biaxially stretched fluororesin sheet is 2 times or more. (3) The density of the sheet gasket is 0.65 to 1.0 g / cm 3 The method for producing a sheet gasket according to (1) or (2), (4) A sheet gasket made of fluororesin, with a density of 0.65 to 1.0 g / cm 3 A sheet gasket having a density of Regarding. [Effects of the Invention]

[0009] According to the present invention, there is provided a sheet gasket that has good rigidity, excellent sealing properties, and can be suitably used in fields where chemical resistance to foods, chemicals, etc. is required and where low tightening pressure is desirable. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a scanning electron microscope photograph of the sheet for sheet gaskets obtained in Example 1. [Figure 2] 1 is a scanning electron microscope photograph of the sheet for sheet gaskets obtained in Example 2. [Figure 3] 1 is a scanning electron microscope photograph of the sheet for sheet gaskets obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] According to the method for producing a sheet gasket of the present invention, as described above, a sheet gasket can be obtained by heating a uniaxially or biaxially oriented fluororesin sheet to a temperature of 250°C or higher that is lower than the melting point of the fluororesin used in the fluororesin sheet, shrinking the fluororesin sheet to a shrinkage rate of 10 to 35%, and then cooling it.Since the sheet gasket of the present invention is produced by the method described above, it has good rigidity and excellent sealing properties and can be suitably used in fields where chemical resistance, such as for food and pharmaceuticals, is required and where low clamping pressure is desirable.

[0012] Fluororesin sheets are used as raw materials for fluororesin gaskets. Examples of fluororesins used for fluororesin sheets include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE), but the present invention is not limited to these examples. These fluororesins may be used alone or in combination of two or more. Among these fluororesins, polytetrafluoroethylene (PTFE) is preferred from the viewpoints of moldability and processability. Polytetrafluoroethylene (PTFE) usually has a density of 2.14 to 2.20 g / cm. 3 It has a density of

[0013] The fluororesin may contain fillers, tackifiers, ultraviolet absorbers, antioxidants, polymerization inhibitors, fillers, colorants such as pigments, and the like, within the scope of not impairing the object of the present invention.

[0014] Examples of methods for producing a fluororesin sheet include a method for producing a fluororesin sheet by extrusion molding a fluororesin, and a method for producing a fluororesin sheet by compression molding a fluororesin, but the present invention is not limited to these examples.

[0015] The thickness of the fluororesin sheet varies depending on the application of the sheet gasket of the present invention and cannot be determined in general, so it is preferable to adjust it appropriately depending on the application of the sheet gasket. The thickness of the fluororesin sheet is usually 0.5 to 200 mm, but for example, when the sheet gasket of the present invention is used in fields where chemical resistance such as food and chemicals is required and low tightening pressure is desirable, the thickness is preferably about 0.5 to 3 mm.

[0016] Next, the fluororesin sheet is uniaxially or biaxially stretched. In the present invention, since a uniaxially or biaxially stretched fluororesin sheet is used, a sheet gasket having good rigidity and excellent sealing properties can be obtained.

[0017] The fluororesin sheet may be uniaxially or biaxially stretched, but in the present invention, a biaxially stretched fluororesin sheet is preferred from the viewpoint of obtaining a sheet gasket having good rigidity and excellent sealing properties.

[0018] The lower limit of the stretching ratio of the fluororesin sheet is preferably 2 times or more, more preferably 2.5 times or more, and even more preferably 3 times or more, from the viewpoint of obtaining a sheet gasket having good rigidity and excellent sealing properties. The upper limit of the stretching ratio of the fluororesin sheet is not particularly limited, but from the viewpoint of obtaining a sheet gasket having good rigidity and excellent sealing properties, it is preferably 10 times or less, more preferably 8 times or less, and even more preferably 6 times or less. The stretching ratio of the fluororesin sheet means the value obtained by dividing the length of the fluororesin sheet after stretching by the length of the fluororesin sheet before stretching. Furthermore, in the case of biaxial stretching, the stretching ratio of the fluororesin sheet means the stretching ratio in each axis.

[0019] In the present invention, a fluororesin sheet that has been stretched to a predetermined stretch ratio may be used as the fluororesin sheet.

[0020] The fluororesin sheet stretched as described above (hereinafter referred to as "stretched fluororesin sheet" for convenience) usually has a density of 0.5 to 0.6 g / cm 3 It has a density of about

[0021] Next, the expanded fluororesin sheet is heated to a temperature of 250°C or higher that is lower than the melting point of the fluororesin used in the expanded fluororesin sheet, and shrunk to a shrinkage rate of 10 to 35%. In the present invention, the expanded fluororesin sheet is heated to a temperature of 250°C or higher that is lower than the melting point of the fluororesin used in the expanded fluororesin sheet, and shrunk to a shrinkage rate of 10 to 35%, and therefore, by using the expanded fluororesin sheet, a sheet gasket having good rigidity and excellent sealing ability can be obtained.

[0022] The temperature to which the stretched fluororesin sheet is heated is 250°C or higher from the viewpoint of rapidly shrinking the stretched fluororesin sheet. Furthermore, the temperature to which the stretched fluororesin sheet is heated is lower than the melting point of the fluororesin used in the stretched fluororesin sheet, and preferably is 5°C or higher lower than the melting point of the fluororesin used in the stretched fluororesin sheet, from the viewpoint of preventing deformation of the stretched fluororesin sheet. For example, when polytetrafluoroethylene (PTFE) is used as the fluororesin, the melting point of polytetrafluoroethylene is 327°C, so the temperature to which the stretched fluororesin sheet is heated is lower than 327°C, preferably 325°C or lower, and more preferably 320°C or lower.

[0023] The heating time of the stretched fluororesin sheet cannot be determined in general because it varies depending on the heating temperature of the stretched fluororesin sheet. The heating time of the stretched fluororesin sheet is the time required for the stretched fluororesin sheet to shrink to a shrinkage rate of 10 to 35%.

[0024] The shrinkage rate of the stretched fluororesin sheet is calculated using the formula: [Shrinkage rate of stretched fluororesin sheet (%)] = {[Area of ​​the expanded fluororesin sheet before shrinkage (mm 2 )-Area of ​​the expanded fluororesin sheet after shrinkage (mm 2 )] / [Area of ​​the expanded fluororesin sheet before shrinkage (mm 2 )]}×100 This is the value calculated based on the above.

[0025] The shrinkage rate of the stretched fluororesin sheet is 10% or more, and preferably 15% or more, from the viewpoint of increasing the rigidity of the sheet gasket and improving sealing properties, and is preferably 30% by mass or less, and more preferably 25% by mass or less, from the viewpoint of preventing the rigidity of the sheet gasket from becoming too high.

[0026] The atmosphere in which the expanded fluororesin sheet is heated may be air or an inert gas such as nitrogen gas, argon gas, etc. The pressure of the atmosphere in which the expanded fluororesin sheet is heated is not particularly limited and is usually atmospheric pressure, but the atmosphere may be pressurized or depressurized.

[0027] Next, the heated stretched fluororesin sheet is cooled. When the heated stretched fluororesin sheet is cooled, the heated stretched fluororesin sheet is usually left to cool, but may also be cooled slowly or, if necessary, may be cooled rapidly. The heated stretched fluororesin sheet is usually cooled to room temperature.

[0028] After the heating and cooling of the expanded fluororesin sheet is completed, a sheet gasket of a predetermined size and shape can be cut out from the expanded fluororesin sheet to obtain a sheet gasket. The size and shape of the sheet gasket vary depending on the application of the sheet gasket and cannot be determined in general, so it is preferable to adjust them appropriately depending on the application.

[0029] The density of the sheet gasket of the present invention obtained as described above is 0.65 to 1.0 g / cm 3 The density of the sheet gasket can be determined by dividing the mass of the sheet gasket by the volume of the sheet gasket.

[0030] The sheet gasket of the present invention has a resistance of 0.65 to 1.0 g / cm 3Since it has a density of 1000 ppm or less, it has good rigidity and excellent sealing properties, and can be suitably used in various fields, including those that require chemical resistance for food, medicines, etc., and where low clamping pressure is desired. [Example]

[0031] The present invention will now be described in more detail based on examples, but the present invention is not limited to these examples.

[0032] Examples 1 to 4 The fluororesin sheets used were square sheets (length of one side: 300 mm) made of polytetrafluoroethylene (PTFE) and biaxially stretched with a stretch ratio of 3 on each axis. The thickness of the biaxially stretched sheets was 1.0 mm in Examples 1 and 2 and Comparative Example 1, and 1.5 mm in Examples 3 and 4 and Comparative Example 2.

[0033] Next, the biaxially stretched sheet was heated at the heating temperature shown in Table 1 until the shrinkage ratio shown in Table 1 was reached, and then allowed to cool to room temperature to obtain a sheet for sheet gaskets.

[0034] The sheet gasket sheets obtained above were used to examine the sealing properties and rigidity of sheet gaskets according to the following methods. The results are shown in Table 1.

[0035] [Sealing properties (airtightness)] The airtightness (sealing performance) was investigated in accordance with Appendix C of JIS B2490 (2008), "Test Method for Sealing Characteristics of Gaskets for Pipe Flanges." The specimens were sheet gaskets made by punching out a sheet gasket sheet to dimensions of 35 mm inner diameter and 74 mm outer diameter. The sheet gaskets were mounted between steel flanges with a diameter of 100 mm, a height of 50 mm, and a surface roughness Rz of 15 μm. A load of 10 MPa was applied using a compression testing machine. A pressure of 0.5 MPa was applied to the inner diameter side of the sheet gasket through a pressure-introducing through-hole in the flange, and after leaving it for 5 minutes, the amount of nitrogen gas leakage was measured using a soap film flowmeter.

[0036] The sheet gasket is primarily used as a sealing material where chemical resistance to food, chemicals, etc. is required and low tightening pressure is desirable. Therefore, the leakage amount is set to 6.0 x 10 -3 Pa·m 3 The acceptable criterion for sealability (airtightness) was a value of 0.1 / s or less, and the sealability was evaluated based on the following evaluation criteria.

[0037] (Evaluation criteria) ◎: Leakage amount is 5.0 x 10 -3 Pa·m 3 / s. ○: Leakage amount is 5.0 × 10 -3 Pa·m 3 / s or more 6.0×10 -3 Pa·m 3 / s. ×: Leakage amount is 6.0×10 -3 Pa·m 3 / s or more.

[0038] 〔rigidity〕 The sheet gasket produced for evaluating the sealing property was used to apply a load of 40 MPa to the gasket, and the rate of change in the thickness direction of the gasket was calculated using the following formula: [Thickness change rate (%)] = {[Change in thickness of sheet gasket when load is applied (mm)] / [Thickness of sheet gasket before load is applied (mm)]} x 100 The stiffness was evaluated based on the following criteria.

[0039] (Evaluation criteria) ◯: The rate of change in the thickness direction is 70% or more and less than 80% (the sheet gasket has appropriate rigidity). △: The rate of change in the thickness direction is less than 70% (the sheet gasket is rigid). ×: The rate of change in the thickness direction is 90% or more (the sheet gasket is flexible) (failure).

[0040] Comparative Example 1 The sealing properties and rigidity of the sheet gasket were examined in the same manner as above using the sheet gasket sheet that had not been heated in Example 1. The results are shown in Table 1.

[0041] Comparative Example 2 The sealing properties and rigidity of the sheet gasket were examined in the same manner as above using the sheet gasket sheet that had not been heated in Example 3. The results are shown in Table 1.

[0042] For reference, scanning electron microscope photographs of the sheets for sheet gaskets obtained in Example 1, Example 2 and Comparative Example 1 are shown in FIGS. 1 to 3, respectively.

[0043] [Table 1]

[0044] The results shown in Table 1 show that the sheet gaskets obtained in each Example had excellent sealing properties even when fastened at a low surface pressure of 10 MPa, and further had appropriate rigidity, making them easy to handle. Furthermore, the sheet gaskets (Comparative Examples 1 and 2) made using sheet gasket sheets obtained by simply stretching a fluororesin sheet were inferior in sealing properties and rigidity, and did not exhibit the effects of the sheet gaskets obtained in each Example.

[0045] The embodiments and examples shown in this specification should be considered as illustrative and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include various modifications within the meaning and scope of the claims.

Claims

1. A method for producing a sheet gasket made of a fluororesin, comprising heating a uniaxially or biaxially stretched fluororesin sheet to a temperature ranging from 250°C to a temperature lower than the melting point of the fluororesin used in the fluororesin sheet, shrinking the fluororesin sheet to a shrinkage rate of 10 to 35%, and then cooling the sheet.

2. 2. The method for producing a sheet gasket according to claim 1, wherein the uniaxially or biaxially stretched fluororesin sheet is stretched at a stretch ratio of 2 or more.

3. The density of the sheet gasket is 0.65 to 1.0 g / cm 3 3. The method for producing a sheet gasket according to claim 1 or 2, wherein

4. A sheet gasket made of fluororesin, having a density of 0.65 to 1.0 g / cm 3 A sheet gasket having a density of

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