JPH1180705A - Gasket material and gasket using the same - Google Patents

Abstract

(57) [Summary] ePTFE having better creep resistance than before
Provided are a gasket made of such and a gasket material from which such a gasket can be obtained. SOLUTION: This is a gasket material comprising a laminated sheet obtained by laminating a biaxially stretched porous polytetrafluoroethylene film comprising a node and fibrils connecting the node, wherein the biaxially stretched porous polytetrafluoroethylene film is , Scanning electron microscope observation area 330 μm
^{2. A} gasket material having substantially no nodes having a diameter or a major axis exceeding 3 μm per ² and a gasket obtained by forming the gasket material into an appropriate shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasket for sealing a flange portion of a pipe, a lubricated portion of a shaft or a pin, and a material thereof. The present invention relates to an expanded porous polytetrafluoroethylene gasket material suitable for a seal and a gasket using the same.

[0002]

2. Description of the Related Art A gasket excellent in corrosion resistance and heat resistance is used in a joint portion of a pipe through which corrosive fluids such as pharmaceuticals and foods flow. In recent years, a gasket made of expanded porous polytetrafluoroethylene (hereinafter abbreviated as “ePTFE”) has attracted attention because of its excellent corrosion resistance and heat resistance, and its excellent adhesion to a tightening surface. For example, Japanese Unexamined Utility Model Publication No. 3-89133 discloses an ePTFE ring-shaped gasket obtained by punching a sheet formed by laminating and integrating an ePTFE film to a predetermined thickness in a ring shape.

[0003] Here, the ePTFE film refers to a porous polytetrafluoroethylene (PTFE) film having a fibrous structure by drawing, and its production method is disclosed in JP-B-51-18991. Usually, after removing the molding aid from the molded body of the paste obtained by mixing fine powder of PTFE (crystallinity of 90% or more) with the molding aid, the melting point of PTFE (about 3%) is obtained.
It is obtained by stretching at a high temperature (approximately 300 ° C.) of less than 27 ° C. and, if necessary, firing. As shown in FIG. 9, ePTFE obtained by biaxial stretching is a fibril 1 (a linear molecular bundle extracted from the folded crystal by stretching) from the node 2 composed of the folded crystal.
Spread radially, and the nodes 2 connecting the fibrils 1 are scattered in an island shape to form a spider web-like fibrous structure in which many spaces defined by the fibrils 1 and the nodes 2 exist.
The space 3 is defined between the fibrils or between the fibrils and the nodes.

[0004]

However, when an ePTFE gasket prepared using the gasket material made of the ePTFE film manufactured as described above is used for a long time in a state where the gasket is tightened at a high pressure, the gasket is deformed (creep). ) Occurs, and as a result, the sealing performance deteriorates, and finally the gasket cannot function. That is, the period until the gasket can no longer function (hereinafter referred to as the "useful life of the gasket") was insufficient.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ePTFE gasket having better creep resistance and a gasket material from which such a gasket can be obtained. Is to provide.

[0006]

Means for Solving the Problems The present inventors have developed ePTF.
The creep of the E gasket is at the node,
In other words, a fibril from which the folded crystal has been sufficiently drawn by stretching does not show any deformation with respect to the compressive force at the time of use, but a node constituted by a insufficiently stretched folded crystal undergoes deformation due to the compressive force at the time of use. Found to cause creep and eventually no longer function as a gasket. Therefore, the ePTF having an extremely small node where almost all of the folded crystal has been unraveled
The present invention has been completed by focusing on the use of an E film.

That is, the gasket material of the present invention is a gasket material comprising a laminated sheet obtained by laminating a biaxially stretched porous polytetrafluoroethylene film comprising a node and fibrils connecting the node, The porous polytetrafluoroethylene film is
It is characterized in that there is substantially no node whose diameter or major axis exceeds 3 μm per 330 μm ^{2 of the} scanning electron microscope observation area. The elongation at break in the test specified in JIS K7113 is preferably 200% or less,
Tensile strength of gasket material matrix is 10kgf
/ Mm ² or more. In addition, thickness 3mm
In the gasket material having a porosity of 75% or less,
It is preferable that the stress relaxation rate by the ATRS test at 3 ° C. for 96 hours is 35% or less.

Further, it is preferable that at least one reinforcing layer made of a material having higher rigidity than that of the stretched porous polytetrafluoroethylene film is interposed in the laminated sheet, and the reinforcing layer comprises: It is preferable that the pores of the stretched porous polytetrafluoroethylene film are crushed. The gasket of the present invention is obtained by forming the gasket material of the present invention into an appropriate shape.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a biaxially stretched porous polytetrafluoroethylene (hereinafter abbreviated as "biaxial ePTFE") film constituting a gasket material of the present invention will be described.

The biaxial ePTFE film used in the present invention has a scanning electron microscope (SEM) observation area of 330 μm ^2.
EPTFE film in which there are substantially no nodes with a diameter or major axis exceeding 3 μm, in other words, 98% or more of the nodes have ePTFE with a diameter or major axis of 3 μm or less.
Film. The diameter or major axis of a node of ePTFE film conventionally used for gasket material is about 5 μm.
As described above, since nodes having a size of 400 μm or more also exist, it is understood that the nodes of the ePTFE film used in the present invention are considerably small. Hereinafter, in the present specification, an ePTFE film having substantially no nodes whose diameter or major axis exceeds 3 μm is referred to as “small node ePTFE”.
"E-film".

This small-node ePTFE film is an infinitely small node, and most of the folded crystal has already been melted and extended. However, the node is a fibril node (a mass of multiple fibrils connected)
Can be distinguished from fibrils by SEM observation. The basic structure of the small node ePTFE film is the same as that of the conventional ePTFE film. That is,
In the case of a biaxial ePTFE film, the fibrils are spread radially, the nodes connecting the fibrils are scattered in islands, and a spider web in which a large number of spaces defined by the fibrils and the nodes are present. (See FIG. 9).

[0012] Such a small-node ePTFE film, for example, when a sheet obtained by extruding a PTFE paste is stretched unfired, the stretching direction is biaxial, and the stretching speed is lower than that of the conventional one. At a rate of 100% / sec or less, preferably 50% / sec or less, more preferably 20% / sec or less, and a biaxial stretching area magnification of 50 times or more. The details are described in JP-A-7-196831. Further, a semi-sintered body may be used in place of the unsintered body (Japanese Patent Application Laid-Open No. 5-202217).

The term "stretching speed (% / sec)" used herein
Refers to the ratio of the separation speed of the frame to the distance between the frames before stretching when the pin frames are stretched by separating the opposing pin frames.
In the case of stretching between a pair of rolls, it refers to the ratio of the rotation speed difference between the rolls to the distance between the rolls. In addition, the “elongation area magnification” is the stretching magnification (λM) in the longitudinal direction (MD).
And the product of the draw ratio (λT) in the width direction (TD) (λM × λ
It refers to the magnification expressed as T). "Stretching ratio" refers to the ratio (times) of the final inter-frame distance after stretching to the inter-frame distance before stretching, or the initial inter-frame distance before stretching, when stretching is performed by separating opposing pin frames. Is defined as a ratio (%) of the distance (a value obtained by subtracting the initial inter-frame distance before the stretching from the final inter-frame distance after the stretching) with respect to
In the case of stretching between a pair of opposing rolls having different speeds, the ratio of the rotation speed of the pair of rolls (times), or the stretched distance of the formed body with respect to the rotation speed of the first roll (the pair of rolls) Rotation speed difference). Therefore, for example, a stretching magnification of 5 times corresponds to 400%.

Small node ePTF obtained in this way
The thickness of the E film is usually about 5 to 200 μm, and the porosity is 40 to 98% similarly to the conventional ePTFE film.
Can be appropriately selected depending on the stretching ratio. The space defined between the fibrils or between the fibrils and the nodes, that is, the average pore diameter of the pores can be appropriately set depending on the stretching ratio, but is preferably 0.5 to 5.0 μm, and particularly preferably 0.5 to 1.
0 μm is preferred. If the pores are too large, the contact area between the films will be small, and the adhesion between the films will tend to decrease. If not used with a high tightening pressure, leakage will occur and the sealing performance will decrease on the contrary. Because.
On the other hand, if the average pore diameter is less than 0.5 μm, stable fiber orientation cannot be obtained due to insufficient stretching.

In such a small node ePTFE film, since the folded crystal portion hardly remains, it can be said that the node is not unraveled and pulled out even when tightened at a high pressure. In other words, it means that creep hardly occurs.

The gasket material of the present invention is a sheet obtained by laminating a plurality of such small node ePTFE films (hereinafter, referred to as “ePTFE laminated sheet”). Since the thickness of the small node ePTFE film is usually about 5 to 200 μm, the number of layers is preferably about 10 to 500, and usually about 100 to 200, although it depends on the thickness of the gasket to be obtained. The lamination and integration of the small node ePTFE film may be performed using an adhesive,
After laminating unfired small-node ePTFE films, it is preferable to integrate them by firing. Firing is PT
The temperature (specifically, 350 ° C.) or more of the melting point of FE (327 ° C.)
(About 380 ° C.).

The thus-obtained small-node ePTFE laminated sheet serving as the gasket material of the present invention has a thickness of about 0.1 to 10 mm, preferably 1.5 to 5 mm.

Further, after lamination (after sintering when sintering is performed), it can be pressed in the laminating direction (the thickness direction of the gasket) at a pressure of 10 to 300 kgf / cm ² .
Generally, when used under conditions of high pressure tightening, ePTF
In the gasket formed of the E laminated sheet, the holes are crushed by the tightening pressure in the early stage of use, and contract in the thickness direction. The shrinkage of the gasket in the thickness direction means that the tightening pressure is lower than at the beginning. Therefore, in the case of the high-pressure tightening specification, the initial tightening force can be reduced by forming the gasket using the gasket material that has been compressed in advance. Further, since the pores of the ePTFE laminated sheet are crushed by the pressing, the leakage of permeation can be reduced even when the gasket is used for a low tightening pressure specification.

The porosity of the gasket material of the present invention is generally equal to or smaller than the porosity of the small node ePTFE film constituting the gasket material. In the case of firing, the porosity is further reduced by about 20%. Accordingly, the porosity of the gasket material of the present invention is preferably 40% or more, particularly preferably 70% or more in relation to the small-node ePTFE film. The porosity is lower than the initial value and may be less than 40% in some cases.

The small node ePTFE laminated sheet as the gasket material of the present invention is harder than the conventional ePTFE laminated sheet and has excellent mechanical properties such as elongation at break, tensile strength, and stress relaxation rate. And MD direction, TD
By selecting the stretching ratio in the direction, mechanical properties close to isotropic are exhibited. This means that even if a gasket having an arbitrary shape is produced from the gasket material of the present invention, desired mechanical properties can be obtained and the characteristics as a gasket can be satisfied.

Specifically, a small node ePTFE laminated sheet used as a gasket has a breaking elongation of 200% in a tensile test based on JIS K7113 (pulling at a constant speed and measuring an elongation (%) when the sample breaks).
The following is preferred. The difference between the elongation at break in the MD direction and the elongation at break in the TD direction is preferably within 20%.

The tensile strength of the gasket material matrix is preferably 10 kgf / mm ² or more. Here, the matrix of the gasket material is a biaxial e
Nodes and fibrils (eP
The tensile strength of the matrix is measured using a sample of a small node ePTFE laminated sheet according to JIS K7113 (pulling at a constant speed and measuring the strength when the sample yields) ) Is obtained by normalizing the result obtained in the following equation.

Matrix tensile strength = tensile strength (measured value) × 2.2 / density The density in the formula is an apparent weight obtained by dividing the measured weight (W) of the laminated sheet sample by the volume (V) of the laminated sheet sample. Density (D = W / V: unit is g / cm ³ ),
2.2 is the density of 0% porosity (PTFE sheet obtained by sintering). The higher the tensile strength of the matrix, the more the stretching is performed, which means that the creep is less likely to occur and the gasket has a longer service life.

The gasket material of the present invention has a small node eP
Due to the properties of the TFE laminated sheet, the stress relaxation rate is smaller than that of the conventional ePTFE laminated sheet. Here, the stress relaxation means that the stress of the gasket decreases with time due to creep, and the tightening pressure decreases due to the stress relaxation. FIG. 1 is a graph showing a relationship between a tightening pressure and a leak amount when an internal pressure is 28 kgf / cm ² using a ring-shaped gasket having an outer diameter of 149 mm, an inner diameter of 124 mm, and a thickness of 3.2 mm. As can be seen from FIG. 1, the leak amount increases as the tightening pressure decreases.
In the gasket material having a thickness of 3 mm or more and a porosity of 75% or less according to the present invention, the ATR for 96 hours at 93 ° C.
The stress relaxation rate by the S test is preferably 35% or less, particularly preferably 25% or less. This is because a gasket material having a stress relaxation rate of 35% or less can maintain a high initial tightening pressure and can provide a gasket that can exhibit excellent sealing characteristics over a long period of time.

The ATRS test is a test performed using a jig as shown in FIG. Specifically, a strip (127 mm x 12.7 mm) made of gasket material
The bolts 9 formed in the sample 5 are clamped by the platens 6 and 6 through the bolts 9, and both ends of the bolts 9 are applied via springs 7 and 7 (the springs 7 reproduce the rigidity of the flange) at an initial tightening force of 350 kg / cm. Tighten with nuts 8, 8 so that it becomes ² . In such a jig, the bolt elongates when a tightening force (bolt axial force) is applied to the sample 5, but when the tightening force decreases, the elongation of the bolt decreases in proportion thereto. Assuming that the elongation of the bolt 9 before the test (at the time of initial tightening) is D ₀ and the elongation of the bolt after the test is D ₁ , (D ₀ −D ₁ ) / D ₀ × 100 is calculated, and this is calculated as the stress relaxation rate ( %).

Further, the gasket material of the present invention can be used in a small node ePTFE laminated sheet.
It is preferable that at least one reinforcing layer made of a material having higher rigidity than the film is provided. FIG.
FIG. 3A shows a ring-shaped gasket formed by using a gasket material in which only one layer of the reinforcing layer 12 is interposed between the ePTFE layers 11, and FIG.
12 shows a ring-shaped gasket made by using a gasket material interposed therebetween, in which an ePTFE layer 11 and a reinforcing layer 12 are alternately stacked. Each ePT
The FE layer 11 is composed of an ePTFE film or a laminate of the films, and the reinforcing layer 12 is composed of a film-like material made of a highly rigid material. By laminating the reinforcing layer 12 between the ePTFE layers 11 in this manner, the bending rigidity and strength of the entire gasket are improved, so that the handleability as a large-diameter ring-shaped gasket is improved. Here, the material constituting the reinforcing layer 12 is a small node e
Any material may be used as long as it has higher rigidity than the PTFE film and has heat resistance equal to or higher than that of the PTFE. Those satisfying such conditions include metal foil and film-like sintered P
TFE and ePTFE films obtained by crushing pores are exemplified. Among these, the expanded non-porous PTFE film in which the pores of the ePTFE film are crushed,
It is preferably used because of its excellent adhesion to the ePTFE layer. The non-porous expanded PTFE film may be a conventional ePTFE film or a small-node ePTFE film. This is because a hard expanded PTFE film can be obtained by crushing the pores. However, it is more preferable that the pores of the small node ePTFE film are crushed in terms of rigidity and strength.

The gasket of the present invention is manufactured by punching or cutting the gasket material (small node ePTFE laminated sheet) of the present invention into an arbitrary shape such as a ring-shaped or bolted hole. The gasket of the present invention exhibits excellent mechanical properties (especially creep resistance) and, consequently, sealing properties (service life of gasket) due to the characteristics of the gasket material (small node ePTFE laminated sheet) of the present invention. Further, by using a substantially isotropic gasket material, a gasket having desired physical properties can be obtained even if a gasket having an arbitrary shape is obtained from an arbitrary portion of the laminated sheet.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. [Evaluation Method] First, the measurement method and the evaluation method used in the examples will be described.

[1] Node Size (μm) The maximum node size (indicated by “long axis × short axis”) was determined in an SEM photograph (5000 ×). Gasket material of Example 1 and Comparative Examples 1 and 2 (ePTFE laminated sheet)
SEM photographs of the surface are shown in FIGS.

[2] Porosity (%) Density (D = W / V: unit is g / cm ³ ) and porosity 0 obtained by dividing the weight (W) of the laminated sheet by the volume (V) % (2.2) and was calculated by the following equation. Porosity = {1- (D / 2.2)} × 100

[3] Stress relaxation rate (%) An ATRS test was performed at 93 ° C., 204 ° C., and 315 ° C. The initial tightening pressure is 350 kgf / cm ² ,
The tightening time was 96 hours.

[4] Elongation at break (%) A tensile test was conducted at normal temperature (23 ° C.) according to JIS K7113. That is, each gasket material (ePTF
No. 2 test piece (dumbbell-shaped test piece) was prepared from the E-laminated sheet), and both ends of the test piece were gripped, and the speed was 200 mm / m.
elongation (%) when the test piece breaks when pulled in
Was measured.

[5] Matrix tensile strength (kgf / mm
² ) According to JIS K7113, a tensile test was performed at normal temperature (23 ° C.). That is, each gasket material (ePTF
No. 2 test piece (dumbbell-shaped test piece) was prepared from the E-laminated sheet), and both ends of the test piece were gripped, and the speed was 200 mm / m.
in, and the strength (kgf /
mm ² ) was measured. Measured tensile strength (kgf / mm
² ) was calculated by standardizing with the following formula. still,
The density in the equation is the density (D) used for the porosity. Matrix tensile strength = tensile strength x (2.2 / density)

[6] Q _p is a value that is an index of the service life of the gasket. The stress relaxation rate obtained above and the tensile strength according to the ATRS test after standing at 93 ° C., 204 ° C., and 315 ° C. for 96 hours, It was measured. That is, a strip-shaped (127 mm × 12.7 mm) sample is prepared from each gasket material (ePTFE laminated sheet), and is pulled at 23 ° C. at a pulling speed of 51 mm / min to obtain a tensile strength at break (kgf / mm ² ). It is calculated based on the following equation based on the above equation. (A) When the tensile strength is less than 1.75 kgf / mm ² : Q _p = (tensile strength / 0.7) × {(100−stress relaxation rate) / 75} ² (b) The tensile strength is 1.75 kgf / mm ² or more: Q _p = 2.5 × {(100−stress relaxation rate) / 75} ²

[7] Maximum operating temperature (° C.) Since Q _p is a function of temperature, Q _p at each temperature may be obtained, and a temperature at which Q _p = 1 may be obtained. Where Q _p
= 1 is a value corresponding to an asbestos joint sheet. The reason why the asbestos joint sheet is used as a standard is that it has been used for several decades at actual sites and is known to exhibit sufficiently reliable sealing characteristics.

[8] Area increase rate (%) A ring-shaped gasket sample having an outer diameter × inner diameter × thickness of 55 mm × 28 mm × 3 mm was tightened at a pressure of 300 kgf / cm ^2.
And left at 200 ° C. for 1 hour. Before tightening, the ring shape is close to a perfect circle as shown in FIG. 7A, but creep occurs due to the tightening and deforms as shown in FIG. , The area increases). The area before fastening (S ₀ ) and the area after fastening and leaving (S
₁ ) is calculated, and the rate of increase in the area ((S ₁ −S ₀ ) ÷)
S ₀ ) was calculated.

[9] Blowout temperature Outer diameter x inner diameter x thickness of 127 mm x 89 mm x 3 mm
Ring-shaped gasket sample, tightening pressure 350kgf / c
m^Two Set on the flange with 70kgf / cm ^Two Internal pressure
Was loaded. Then, the flange temperature is raised,
Sket sample blows out (opens when ring is broken
Ring) was measured.

[10] Leakage (initial) Measured by a ROTT test. That is, as shown in FIG. 8, a ring-shaped gasket 23 (outer diameter × inner diameter × thickness of 149 m
mx 124 mm x 3 mm) with a tightening pressure of 200 kgf / cm
² and a closed system with an O-ring 22. In this state, helium gas is injected from the injection port 24 so that the pressure inside the ring of the ring-shaped gasket becomes 70 kgf / cm ^2, and the amount of helium leaked out from the leak port 25 to the outside is measured by a helium leak detector. did.

[Preparation of Gasket Material and Gasket] Example 1: PTFE fine powder (manufactured by Daikin)
A paste-like material obtained by adding 17% by weight of a solvent naphtha as a lubricant was extruded into a sheet and then roll-rolled, and the lubricant was dried and removed to a thickness of 0.6.
An unfired tape having a width of 6 mm and a width of 153 mm was obtained. This tape was stretched in the MD direction at a stretching speed of 90% / sec and a stretching ratio of 7.0 while maintaining at 300 ° C. Then 2
While maintaining the temperature at 75 ° C., the stretching speed is 85% / sec, and the stretching ratio is 1
The film was stretched in the TD direction under the condition of 8.5 times. The stretched area ratio of the obtained stretched film with respect to the unbaked tape is defined as a draw ratio in the MD direction (7.0 times) and a draw ratio in the TD direction (1 times).
8.5 times) (129.5 times). This film has a porosity of 86.6% at a thickness of 39 μm,
A small node e having a maximum node size of 2 μm × 2 μm
It was a PTFE film. 244 of these small node ePTFE films were stacked and baked at 366 ° C. for 60 minutes to tightly integrate the films to obtain a laminated sheet having a thickness of 3.66 mm and a porosity of 74.6%.

Example 2: A paste obtained by adding 16% by weight of solvent naphtha as a lubricant to PTFE fine powder (manufactured by DuPont) was extruded into a sheet, and then roll-rolled, and the lubricant was dried and removed. hand,
An unfired tape having a thickness of 1.3 mm and a width of 302 mm was obtained.
While maintaining the tape at 300 ° C., a stretching speed of 80%
The film was stretched in the MD direction at a rate of 9.5 times / sec and a stretching ratio of 9.5.
Next, the film was stretched in the TD direction at a stretching speed of 95% / sec and a stretching ratio of 13.5 times while maintaining the temperature at 280 ° C. The stretch area magnification of the obtained film with respect to the green tape was M
This corresponds to the product (128.3 times) of the stretching ratio in the D direction (9.5 times) and the stretching ratio in the TD direction (13.5 times). This film was a small node ePTFE film having a thickness of 52 μm, a porosity of 80.0%, and a maximum node size of 1 μm × 1 μm. This small node ePTF
72 E films were stacked and baked at 365 ° C. for 60 minutes to tightly integrate the films to obtain a laminated sheet having a thickness of 2.88 mm and a porosity of 74.6%. This laminated sheet (gasket material) was punched into a ring shape having an outer diameter of 55 mm and an inner diameter of 28 mm to form a ring-shaped gasket.

Example 3: A paste obtained by adding 13% by weight of a solvent naphtha as a lubricant to PTFE fine powder (manufactured by DuPont) was extruded into a sheet, and then roll-rolled, and the lubricant was dried and removed. hand,
An unfired tape having a thickness of 1.3 mm and a width of 302 mm was obtained.
The tape was stretched at 95% /
The film was stretched in the MD direction under the conditions of 9.1 times the stretching ratio for Sec. Next, the film was stretched in the TD direction at a stretching speed of 90% / sec and a stretching ratio of 15.5 while maintaining the temperature at 280 ° C. The elongation area ratio of the obtained film to the unfired tape is MD
Stretching ratio in the TD direction (9.1 times) and the stretching ratio in the TD direction (1 times).
5.5 times) (141.1 times). This film has a porosity of 78.3% at a thickness of 65 μm,
A small node e having a maximum node size of 1 μm × 1 μm
It was a PTFE film. Fifty-three small node ePTFE films were stacked and baked at 365 ° C. for 60 minutes to tightly integrate the films to obtain a laminated sheet having a thickness of 3.41 mm and a porosity of 72.3%. This laminated sheet (gasket material) was punched into a ring shape having an outer diameter of 55 mm and an inner diameter of 28 mm to form a ring-shaped gasket.

Comparative Example 1: A paste obtained by adding 17% by weight of solvent naphtha as a lubricant to PTFE fine powder (manufactured by Asahi Glass Co., Ltd.) was extruded into a sheet, and then roll-rolled, and the lubricant was dried and removed. Thus, an unsintered tape having a thickness of 0.24 mm and a width of 152 mm was obtained.
This tape is stretched at a stretching speed of 150% while being kept at 300 ° C.
The film was stretched in the MD direction at a stretch ratio of 2.0 times / sec.
Next, while maintaining the temperature at 275 ° C., the stretching speed was 150% /
The film was stretched in the TD direction under the conditions of a draw ratio of 7.0 times for 7.0 seconds. The elongation area magnification of the obtained film with respect to the unfired tape corresponds to the product (14 times) of the MD-direction stretching ratio (2.0) and the TD-direction stretching ratio (7.0). This film was an ePTFE film having a thickness of 45 μm, a porosity of 79.5%, and a maximum node size of 5 μm × 1 μm. 90 layers of this ePTFE film,
The film was baked at 365 ° C. for 60 minutes to tightly integrate the films to obtain a laminated sheet having a thickness of 3.2 mm and a porosity of 72.7%. This laminated sheet (gasket material) has
A ring-shaped gasket was prepared by punching into a ring having an inner diameter of 28 mm and an inner diameter of 28 mm.

Comparative Example 2: A commercially available (PTFE SEALON (registered trademark) manufactured by YEU MING TAI) ePTFE laminated sheet (thickness: 3 mm, porosity: 67.0%) was used as a gasket material. This laminated sheet (gasket material) was punched into a ring shape having an outer diameter of 55 mm and an inner diameter of 28 mm to form a ring-shaped gasket.

With respect to the gaskets (or gasket materials) of Examples 1 to 3 and Comparative Examples 1 and 2, matrix tensile strength, elongation at break, stress relaxation rate, area increase rate, blowout temperature, and leak amount were evaluated according to the following evaluation methods. It was evaluated based on: Table 1 shows the results.

[0045]

[Table 1]

[Evaluation] As can be seen from Table 1, the gasket material having the long axis of the node of 3 μm or less and the gasket prepared using the same (Examples 1 to 3) correspond to the conventional ePTF.
Compared with the E-sheet and the gasket prepared using the same (Comparative Examples 1 and 2), the elongation at break, the stress relaxation rate were small, the matrix tensile strength was large, and the maximum use temperature and blowout temperature were high. As for the initial leak amount, Example 1 was superior to Comparative Example 2, but slightly inferior to Comparative Example 1. However, since other physical properties such as a stress relaxation rate and a maximum operating temperature are superior to those of Comparative Example 1, when used for a long period of time at a high temperature or at a high tightening pressure, the sealing property decreases (the amount of leak increases). Is larger in Comparative Example 1, and it can be predicted that Example 1 is more excellent in sealing properties in the long term.

The gasket materials of Examples 1 to 3
The difference between the breaking elongation in the MD direction and the breaking elongation in the TD direction is 20%
It can be seen that the value is smaller than that of the gasket material of the comparative example, and that the gasket material is isotropic.

[0048]

The gasket material of the present invention is a conventional eP
Since an ePTFE film (small node ePTFE film) having smaller nodes than the TFE film is used,
It has excellent mechanical properties such as elongation at break and tensile strength, and is also excellent in creep resistance. Therefore, a gasket made using the gasket material of the present invention is a conventional gasket.
It can be used at a higher temperature and a higher tightening pressure than a gasket made using a sheet made of a sheet, and the service life of the gasket is longer.

Further, in the gasket material in which the reinforcing layer is interposed, since the bending rigidity of the gasket is high, the handling property is improved as a large-diameter ring-shaped gasket. In addition, a gasket made of 100% PTFE can effectively exhibit the heat resistance and corrosion resistance of PTFE, in which the reinforcing layer is formed by crushing the pores of the ePTFE film.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a tightening pressure and a leak amount.

FIG. 2 is a diagram showing a configuration of a jig used for an ATRS test.

FIG. 3 is a diagram showing a configuration of a gasket on which a reinforcing layer is laminated.

FIG. 4 is a SEM photograph (5000 times) of the biaxial ePTFE of Example 1 of the present invention.

FIG. 5 is an SEM photograph (50) of the biaxial ePTFE of Comparative Example 1.
00 times).

FIG. 6 is an SEM photograph (50) of the biaxial ePTFE of Comparative Example 2.
00 times).

FIG. 7 is a diagram for explaining a method of measuring an area increase rate.

FIG. 8 is a diagram showing a configuration of a jig used for measuring a leak amount.

FIG. 9 is a schematic view showing the structure of a biaxial ePTFE film.

[Explanation of symbols]

 Reference Signs List 1 fibril 2 node 3 hole 5 gasket material sample 11 small node ePTFE layer 12 reinforcing layer 23 ring-shaped gasket

Continued on the front page (72) Inventor Toru Sakamoto 1-42-5 Akatsutsumi, Setagaya-ku, Tokyo Inside Japangore-Tex Co., Ltd. (72) Inventor Fumihiro Sasaki 1-42-5 Akatsutsumi, Setagaya-ku, Tokyo Japangore-Tex stock Inside the company (72) Inventor Kiminobu Yamamuro 1-42-5 Akatsutsumi, Setagaya-ku, Tokyo Inside Japango Tex Co., Ltd.

Claims (7)

[Claims] 1. A gasket material comprising a laminated sheet obtained by laminating a biaxially stretched porous polytetrafluoroethylene film comprising a node and fibrils connecting the node, wherein the biaxially stretched porous polytetrafluoroethylene film is provided. Is, per 330 μm ² of the scanning electron microscope observation area,
A gasket material characterized in that there are substantially no nodes with a diameter or major axis exceeding 3 μm. 2. The gasket material according to claim 1, which has a breaking elongation of 200% or less in a test specified in JIS K7113. 3. The gasket material according to claim 1, wherein the matrix of the gasket material has a tensile strength of 10 kgf / mm ² or more. 4. The gasket material having a thickness of 3 mm or more and a porosity of 75% or less, wherein a stress relaxation rate by ATRS test at 93 ° C. for 96 hours is 35% or less. Gasket material. 5. The laminated sheet according to claim 1, wherein at least one reinforcing layer made of a material having higher rigidity than the stretched porous polytetrafluoroethylene film is provided. Gasket material as described. 6. The gasket material according to claim 5, wherein the reinforcing layer is formed by crushing pores of an expanded porous polytetrafluoroethylene film. 7. A gasket obtained by forming the gasket material according to claim 1 into an appropriate shape.