JP2008087183A - Welding method of modified polytetrafluoroethylene molded object, modified polytetrafluoroethylene molded object and gasket using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding method of a modified polytetrafluoroethylene molded object capable of smoothly forming a joining part, the modified polytetrafluoroethylene molded object and a gasket using it. <P>SOLUTION: The joining surfaces 12 formed to sheetlike modified PTFE molded objects 10 are arranged in mutually facing relationship and brought into contact with each other to form a sheetlike joined body 14. In this case, the joining line 16 formed to the surface of the joined body 14 and the vicinity thereof are covered with a heat-resistant release film 18 and the joined body 14 is heated while pressed from both surface and back sides thereof by hot molds 20 and 22 through the heat-resistant release film 18. The shapes of the hot molds 20 and 22 are set so that one hot mold 20 is formed so that the length in the direction crossing the joining line 16 at a right angle is made larger (wider) than that of the other hot mold 22. A metallic plate member 24 is interposed between the narrow hot mold 22 and the sheetlike joined body 14. After the completion of heat treatment, the joined body 14 is cooled to room temperature while pressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for welding a modified polytetrafluoroethylene molded article, a modified polytetrafluoroethylene molded article, and a gasket using the same.

Conventionally, techniques for joining tetrafluoroethylene molded bodies have been proposed. For example, in Patent Document 1 below, a molded body made of a mixture of a tetrafluoroethylene resin and a perfluoroalkoxy resin is disposed and heated at an overlap joint or a butt joint between the tetrafluoroethylene resin molded bodies. A bonding method is disclosed.
JP-A-52-80369

  However, in the above-described conventional technique, there is a problem that a large step is generated at the joint when the tetrafluoroethylene resin molded bodies are overlapped and joined. In addition, even in the case where the tetrafluoroethylene resin molded bodies are brought into contact with each other, since a mixture of the tetrafluoroethylene resin and the perfluoroalkoxy resin is interposed therebetween, the tetrafluoroethylene resin and the mixture There is a problem in that sinking or the like occurs in the joint due to a difference in shrinkage rate, and it is difficult to reduce the level difference of the joint. Furthermore, by disposing a composition different from the base material in the welded portion, there is a problem that physical properties such as heat resistance and chemical resistance of the welded portion are locally deteriorated.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a method for welding a modified polytetrafluoroethylene molded body and a modified polytetrafluoroethylene molded body that can smoothly form a joint. And providing a gasket using the same.

  In order to achieve the above object, the present invention is a method for welding a modified polytetrafluoroethylene molded article, wherein the joint surfaces formed on the sheet-like modified polytetrafluoroethylene molded article are arranged to face each other, The bonded line formed on the surface of the bonded body by contacting the bonded surface with the bonded surface and the vicinity thereof by a heat-resistant release film having heat resistance equal to or higher than the melting temperature of the modified polytetrafluoroethylene Covering and pressurizing the joining line and the vicinity thereof while heating to a temperature equal to or higher than the melting temperature of the modified polytetrafluoroethylene.

  Further, in the method for welding the modified polytetrafluoroethylene molded body, the joining line and the vicinity thereof are heated while being pressed from both the front and back sides of the joined body by a thermal mold, and one of the thermal molds is wider than the other. It is characterized by being formed.

  In the method for welding the modified polytetrafluoroethylene molded body, a metallic plate member is interposed between the narrow thermal mold and the sheet-like modified polytetrafluoroethylene molded body. It is characterized by that.

  In the method for welding the modified polytetrafluoroethylene molded body, after the heating of the bonding line and the vicinity thereof is completed, cooling is performed while applying pressure from both the front and back surfaces of the bonded body with a cooling mold.

  The present invention also relates to a modified polytetrafluoroethylene molded body, which is a sheet-shaped modified polycrystal obtained by bringing a joint surface into contact with each other to form a joined body, and joining and forming a joining line formed on the surface of the joined body and its vicinity. It is a tetrafluoroethylene molded product, and the step in the joint line and its peripheral part is 120 μm or less as a maximum roughness (Rmax).

  The present invention also provides a gasket, which is characterized by being coated with the modified polytetrafluoroethylene molded body.

  According to the present invention, the joint portion of the modified polytetrafluoroethylene molded product and its peripheral portion can be formed smoothly.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  FIGS. 1A to 1C are explanatory views of an embodiment of a method for welding a modified polytetrafluoroethylene molded body (hereinafter referred to as a modified PTFE molded body) according to the present invention. In FIG. 1A, a joint surface 12 is formed on a sheet-like modified PTFE molded body 10 shown in a sectional view, and the joint surfaces 12 are arranged to face each other.

  The modified PTFE used here is, for example, polytetrafluoroethylene in which a part of the polymer chain is substituted with perfluoroalkoxy vinyl ether based on JIS K6935-1. The content of the perfluoroalkoxy vinyl ether is 1% by mass or less.

  Although the molded object welded by the welding method of this invention will not be specifically limited if it is a sheet form, For example, it is suitable for welding a thin sheet, for example, 1 mm or less, especially a sheet-like thing of 0.6 mm or less.

  Next, in FIG. 1B, the joint surfaces 12 of the respective modified PTFE molded bodies 10 are brought into contact with each other to form a sheet-like joined body 14. Further, the bonding line 16 formed on the surface of the bonded body 14 with the bonded surfaces 12 in contact with each other and the vicinity thereof are covered with a heat-resistant release film 18 having heat resistance equal to or higher than the melting temperature of the modified PTFE molded body 10. The heat-resistant release film 18 is not limited as long as it is a polyimide resin or other film having heat resistance exceeding 300 ° C.

  Next, in FIG.1 (c), the said joining line 16 and its vicinity are heated, pressing with the heat type | molds 20 and 22 through the said heat-resistant peeling film 18 from the front and back both surfaces of the said conjugate | zygote 14. FIG. The thermal molds 20, 22 are formed such that one thermal mold 20 is longer (wider) in the orthogonal direction than the other thermal mold 22 in the orthogonal direction with respect to the bonding line 16. The ratio of the lengths may be one (long): the other (short) = 2: 1 or more, for example, 3: 1 or 4: 1. Other points are not particularly limited. A metallic plate member 24 is interposed between the thermal mold 22 having a narrow width and the sheet-like joined body 14. The plate member 24 is preferably formed of, for example, stainless steel.

The heating temperature by the thermal molds 20 and 22 may be equal to or higher than the melting point temperature of the modified PTFE, but is preferably 380 ° C. to 420 ° C. The pressure applied during heating is preferably 4 to 16 × 10 ³ N / m ² . If the lower limit of this range is not reached, welding becomes insufficient, and if the upper limit is exceeded, the thickness of the welded portion may be thinner than that of the base material. The heating and pressing time is preferably 10 to 15 minutes.

After completion of the heat treatment, the bonded body 14 is cooled to room temperature while being pressurized with a pressure of 5 to 16 × 10 ³ N / m ² . This pressurization and cooling is performed by a cooling mold. The cooling mold may be a mold wider than the width of the heated and melted portion. The cooling time may be arbitrary. After cooling, the heat-resistant release film 18 is removed.

  With the above procedure, the welding of the modified PTFE molded body according to the present embodiment is completed. According to the present embodiment, the step in the welded line 16 and its peripheral part after welding can be 120 μm or less as the maximum roughness (Rmax), and preferably 50 μm or less as Rmax. Since the modified PTFE molded body thus welded is excellent in surface smoothness, it can be used for a covering material such as a PTFE-coated gasket that requires a sealing property. Furthermore, since it is molded from essentially the same material, the physical properties (mechanical properties and chemical resistance) of the welded molded product and other parts of the welded molded product are uniform, making it ideal for use in coated gaskets in particular. is there.

  Molded bodies welded by conventional welding methods require post-treatment such as cutting the surface after welding to ensure surface smoothness, which is a factor that degrades the strength and chemical resistance of the welded part. Moreover, it is a factor of the cost increase by an increase in a manufacturing process.

  Hereinafter, specific examples of the present invention will be described as examples. The present invention is not limited to the following examples.

  A modified PTFE tape (manufactured by Nichias Co., Ltd.) having a width of 15 mm, a thickness of 0.4 mm, and a length of 2 m is used as the modified PTFE molded body 10, and the end surface in the width direction is used as the joint surface 12 described above by the method of this embodiment. A welding process was performed. As a result, a modified PTFE molded body having a loop shape having a width of 15 mm, a thickness of 0.4 mm, and a peripheral length of 2 m was obtained. Then, the welding location was evaluated by the following method. In addition, as comparative examples, the width of the two heat molds 20 and 22 is equal to those in which the metal plate member 24 is not used during welding (Comparative Example 1), the heat-resistant release film 18 is not used (Comparative Example 2), and The same evaluation was performed on the test piece (Comparative Example 3).

(1) Evaluation of tensile strength The micro-dumbbell mold was punched out so as to include the welded portion (bonding surface) of the modified PTFE tape, and the obtained micro-dumbbell was pulled at a speed of 200 mm / min to measure the tensile strength and elongation. In this test, an electronic measurement control type universal material testing machine (Tensilon UTM-10T manufactured by Orion Tech Co., Ltd.) was used.

(2) Measurement of level difference The level difference of the welded portion of the modified PTFE tape was measured with a surface roughness meter (SURFCOM130A manufactured by Tokyo Seimitsu Co., Ltd.) according to JIS B0601-1982. The test result was 30 μm or less as Rmax.

  FIG. 4 shows a measurement range of the joined body 14 in which the above step measurement is performed. In FIG. 4, the joined body 14 formed by contacting the modified PTFE molded body 10 is heated and melted by the heat molds 20 and 22 in the vicinity of the joining line 16 and the vicinity thereof, but the melted portion ( Measurement with the surface roughness meter was performed in a measurement range including a melted part) and a part that was not melted (unmelted part), and a cross-sectional curve of the measurement range was obtained. Next, an average line in the height direction of the cross-sectional curve was obtained, and an interval between the two straight lines when the cross-sectional curve was sandwiched between two straight lines parallel to the average line was defined as Rmax. In addition, the said measurement range is the range of 5-10 mm centering on the joining line 16, and the range of 5-10 mm centering on the boundary of a fusion | melting part and an unmelted part.

(3) Appearance of weld location The appearance of the weld location was observed visually.

(4) Seal test The welded modified PTFE tape was cut out to a total length of about 10 cm centering on the welded portion, and used as a seal test tape sample. The surface of the tape sample for the seal test was subjected to a treatment for extracting fluorine atoms with metallic sodium and generating radicals, and then a molded product obtained by pre-molding a commercially available EPDM rubber (ethylene / propylene rubber) into a ring shape was added. A sample for sealing test was prepared by sulfur bonding.

  The size of the ring-shaped preform of EPDM rubber was 109 mm outer diameter × 97 mm inner diameter × 2.75 mm thickness. Further, the vulcanization adhesion means that the adhesion treatment is performed simultaneously with the vulcanization treatment of the rubber material, and the adhesion can be performed by applying a primer between the modified PTFE tape and the EPDM rubber.

  FIG. 2 shows a sample for the seal test. In FIG. 2, a modified PTFE tape 28 is bonded to an EPDM rubber ring 26. The modified PTFE tape 28 is formed by welding the end surfaces of two modified PTFE tapes at the joint 30. In FIG. 2, the joint portion 30 is indicated by a broken line for convenience of explanation, but this does not represent a crack in the joint portion 30.

  The seal test sample formed as described above was attached to a seal test apparatus, and a seal test was performed.

  FIG. 3 shows a cross-sectional view of the seal test apparatus. In FIG. 3, a sample for a seal test was placed between two flanges 32 and 34, and the sealing performance at the joint 30 of the modified PTFE tape 28 was evaluated as follows.

  Of the two flanges 32 and 34, one flange 34 is formed with a ring-shaped inner spacer 38 and an outer spacer 40 that match the shape of the ring 26 of EPDM rubber. An EPDM rubber ring 26 is disposed between the two. Also, the portion of the EPDM rubber ring 26 to which the modified PTFE tape 28 is bonded is also closely bonded to the EPDM rubber ring 26 and the thickness thereof is thin (0.4 mm). The space formed by the inner spacer 38 and the outer spacer 40 can be repaired.

  From the above state, the distance between the two flanges 32 and 34 was decreased, and the EPDM rubber ring 26 was pressed until the inner spacer 38 and the outer spacer 40 and the flange 32 contacted each other. The distance between the flanges 32 and 34 at this time is 2.4 mm. Thereafter, high pressure water having a pressure of 2 MPa was supplied from the water pressure pump 36 and left for 5 minutes, and then the presence or absence of water leakage from the joint 30 of the modified PTFE tape 28 was confirmed.

The above evaluation results are shown in Table 1.

  As shown in Table 1, in this example, the tensile strength was 24.0 MPa and the elongation was 250%. In general, if the tensile strength is 22.0 MPa or more and the elongation is 200 to 550%, there is no practical problem. Therefore, the modified PTFE molded body welded according to this example can be said to be a sufficiently practical level. Further, the appearance of the welded portion was good, and water leakage did not occur in the seal test.

  On the other hand, in Comparative Example 1, wrinkles were generated at the welding locations, Comparative Example 2 was partially cracked at the welding locations, and Comparative Example 3 had a large step difference at the welding locations. These problems are all due to inappropriate temperature control of the modified PTFE molded body during welding. That is, if the metallic plate member 24 is not used at the time of welding as in Comparative Example 1, the temperature difference between the portion of the modified PTFE molded body that is in contact with the thermal molds 20 and 22 and the portion that is not in contact is increased. Wrinkles are likely to occur. For this reason, in this embodiment, the plate member 24 is used, and the generation of wrinkles is suppressed by adjusting the heat radiation from the modified PTFE molded body to smooth the temperature gradient.

  Moreover, if the heat-resistant peeling film 18 is not used like the comparative example 2, the heat radiation from the joint surface 12 of the modified PTFE molded body will increase, and it will not be sufficiently welded and cracks will easily occur. For this reason, in this example, by covering the bonding line 16 formed on the surface of the bonded body 14 with the heat-resistant release film 18 and the vicinity thereof, the heat radiation from the bonding surface 12 is reduced and the occurrence of cracks is suppressed. ing.

  Furthermore, when the widths of the two thermal dies 20 and 22 are made equal as in Comparative Example 3, a large step is generated in the joint 30 due to the influence of the temperature gradient during heating in the modified PTFE molded body. For this reason, in this embodiment, the ratio of the widths of the two thermal molds 20 and 22 is 2: 1.

It is explanatory drawing of the welding method of the modification | denaturation PTFE molded object concerning this invention. It is a figure which shows the sample for a seal test. It is sectional drawing of a seal test apparatus. It is a figure which shows the measurement range of the conjugate | zygote which performed the level | step difference measurement.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Modified PTFE molded object, 12 Bonding surface, 14 Bonded body, 16 Bonding line, 18 Heat-resistant peeling film, 20, 22 Thermal type, 24 Plate member, 26 EPDM rubber ring, 28 Modified PTFE tape, 30 Bonded part, 32 , 34 Flange, 36 Hydraulic pump, 38 Inner spacer, 40 Outer spacer.

Claims (6)

The joint surfaces formed on the sheet-like modified polytetrafluoroethylene molded body are placed opposite to each other, and brought into contact with each other to form a joined body.
Covering the bonding line formed on the surface of the bonded body in contact with the bonding surface and the vicinity thereof with a heat-resistant release film having heat resistance equal to or higher than the melting temperature of the modified polytetrafluoroethylene,
Pressurizing the joining line and its vicinity while heating to a temperature equal to or higher than the melting temperature of the modified polytetrafluoroethylene,
A method for welding a modified polytetrafluoroethylene molded product characterized in that:   2. The method for welding a modified polytetrafluoroethylene molded body according to claim 1, wherein the joining line and the vicinity thereof are heated while being pressed from both the front and back surfaces of the joined body by a thermal mold, and one of the thermal molds is the other. A method for welding a modified polytetrafluoroethylene molded product, characterized in that it is formed wider.   The method for welding a modified polytetrafluoroethylene molded body according to claim 1, wherein a metallic plate member is interposed between the narrow thermal mold and the sheet-shaped modified polytetrafluoroethylene molded body. A method for welding a modified polytetrafluoroethylene molded article characterized by comprising:     The method for welding a modified polytetrafluoroethylene molded body according to claim 1, wherein after the heating of the joint line and the vicinity thereof is finished, cooling is performed while applying pressure from both the front and back surfaces of the joined body with a cooling mold. A method for welding a polytetrafluoroethylene molded body.   A sheet-shaped modified polytetrafluoroethylene molded body obtained by bringing a bonding surface into contact to form a bonded body and heat-welding a bonding line formed on the surface of the bonded body and the vicinity thereof, in the bonding line and the periphery thereof A modified polytetrafluoroethylene molded product, wherein the step is 120 μm or less in terms of maximum roughness (Rmax).   A gasket coated with the modified polytetrafluoroethylene molded product according to claim 5.

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