JP2008007607A - Filler-filled fluororesin sheet and process for producing filler-filled fluororesin sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filler-filled fluororesin sheet that is high in both stress relaxation characteristics and airtight characteristics (sealing capability) even in the case where the filling factor of a fluororesin is low and the filling factor of a filler is high and to provide a process for producing the filler-filled fluororesin sheet. <P>SOLUTION: The filler-filled fluororesin sheet comprises a fluororesin and a filler containing 20 wt.% or more silica. The process for producing the filler-filled fluororesin sheet comprises a step of calendering a resin composition for forming a sheet comprising a fluororesin and a filler containing 20 wt.% or more silica. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a filled fluororesin sheet and a method for producing a filled fluororesin sheet, and more particularly to a filled fluororesin sheet used as a sealing material and the like and a method for producing a filled fluororesin sheet.

  Filled fluororesin sheet is a sheet made by filling fluororesin with a filler. In addition to the chemical resistance, heat resistance, non-adhesiveness, and low friction properties of fluororesin, It is often used for sealing materials by adding the unique functions and characteristics of, or improving the wear resistance and creep resistance, which are disadvantages of fluororesins.

  Sealing materials include fluorine resin filled with metal, graphite, inorganic filler, etc. to improve thermal conductivity, wear resistance, creep properties, etc. in use.

  In U.S. Pat. No. 3,315,020 (Patent Document 1), a long sheet is formed by extruding a mixture of PTFE, a filler, and a processing aid and then passing a pair of rolling rolls once or multiple times. A technique for obtaining the above is disclosed. However, when creating a sheet-like gasket made of a fluororesin sheet with a filler using this technology, if the filling rate of the filler is increased, the stress relaxation property tends to be excellent, but the airtightness is low, and as a sealing material I can't get a satisfactory one.

  On the other hand, in Japanese Patent Application Laid-Open No. 2004-323717 (Patent Document 2), a composition containing a fluororesin, a swellable mineral, a filler and a processing aid is extruded and then passed through a rolling roll and stretched into a sheet shape. A filled fluororesin sheet is disclosed. This filled fluororesin sheet is excellent in stress relaxation rate, tensile strength and the like even when the filling rate of the fluororesin is low and the filling rate of the filler is high.

Conventionally, clay, especially kaolin (aluminum silicate), has been often used as an inorganic filler because it is inexpensive.
US Pat. No. 3,331,020 JP 2004-323717 A

  However, in the fluororesin sheet with a filler described in Patent Document 2, there is a tendency for the fluororesin as a binder to fill the space between hard and particulate inorganic fillers, so that in terms of sealing performance It turns out that there is room for further improvement.

  Furthermore, kaolin, which is often used as an inorganic filler, is a layered silicate mineral and has a relatively low hardness and is vulnerable to crushing. Therefore, in a fluororesin sheet using kaolin as a filler, kaolin collapses when a large load is applied or when the fluororesin softens at high temperatures, and the required performance is not fully exhibited. There was a case.

The present invention has been made in view of the above problems. Even when the filling rate of the fluororesin is low and the filling rate of the filler is high, high stress relaxation property and high airtightness (seal performance). It is an object of the present invention to provide a filled fluororesin sheet and a method for producing the same.

  As a result of intensive studies, the present inventors have found that a filled fluororesin sheet containing a certain amount or more of silica achieves both high stress relaxation properties and high airtightness, and completed the present invention.

The filled fluororesin sheet of the present invention contains a fluororesin and a filler containing 20% by weight or more of silica.
The mass ratio between the fluororesin and the filler in the fluororesin sheet with filler is preferably fluororesin: filler = 1: 0.1-2.

  The method for producing a fluororesin sheet with a filler according to the present invention includes a step of rolling a sheet-forming resin composition containing a fluororesin and a filler containing 20% by weight or more of silica.

The mass ratio of the fluororesin and the filler in the composition is preferably fluororesin: filler = 1: 0.1-2.
The manufacturing method includes:
Including a step of rolling a sheet-forming resin composition containing a fluororesin, a filler containing 20% by weight or more of silica, and a processing aid at a roll temperature of 40 to 80 ° C.,
The processing aid preferably comprises 30% by mass or more of a petroleum hydrocarbon solvent having a fractional distillation temperature of 120 ° C. or less (however, the weight of the processing aid is 100% by mass).

In the composition, the processing aid is preferably contained in an amount of 5 to 50 parts by weight with respect to a total of 100 parts by weight of the fluororesin and the filler.
The production method of the present invention preferably includes a step of further rolling the rolled sheet prepared by the rolling step.

  The filled fluororesin sheet of the present invention can be produced by the above-described method for producing a filled fluororesin sheet of the present invention.

The filled fluororesin sheet of the present invention has both high stress relaxation characteristics and high airtight characteristics even when the filling ratio of the fluororesin is low and the filling ratio of the filler is high.
According to the production method of the present invention, it is possible to produce a filled fluororesin sheet that achieves both high stress relaxation characteristics and high airtightness characteristics even though the filling ratio of the fluororesin is low and the filling ratio of the filler is high. Can do.

Hereinafter, the filled fluororesin sheet of the present invention and the method for producing the filled fluororesin sheet will be described in more detail.
[Filled fluororesin sheet]
The filled fluororesin sheet of the present invention contains a fluororesin and a filler containing 20% by weight or more of silica.

<Fluorine resin>
As fluororesin, in addition to tetrafluoroethylene resin (PTFE), modified PTFE, vinylidene fluoride resin (PVDF), tetrafluoroethylene-ethylene copolymer resin (ETFE), trifluorochloroethylene resin (PCTFE), Conventionally known fluororesins such as tetrafluoroethylene-hexafluoropropylene-ethylene copolymer resin (FEP) and tetrafluoroethylene-perfluoroalkyl copolymer resin (PFA) can be preferably used. Among these, use of PTFE obtained by emulsion polymerization is preferable in terms of workability when performing extrusion molding, rolling, or the like.

<Filler>
The filler used in the present invention contains 20% by weight or more, preferably 50% by weight or more, more preferably 100% by weight of silica (provided that the total weight of the filler is 100% by weight).

  Silica has a higher hardness than clays such as kaolin conventionally used as a filler (for example, the Mohs hardness of quartz is 7.0). In this invention, since the filler containing 20 weight% or more of silica is used, the stress relaxation of the fluororesin sheet | seat by crushing of filler itself can be suppressed.

Specific examples of the silica include quartz, cristobalite, tridymite, quartz glass, wet silica, dry silica, and the like, and commercially available products are Toxeal (wet silica, manufactured by Tokuyama Corporation), Leoroseal (dry silica). , Manufactured by Tokuyama Corporation), dry silica HDK (dry silica, manufactured by Asahi Kasei Wacker Silicone Co., Ltd.), and the like. Note that silica in the present invention is an inorganic substance consisting essentially of SiO ₂ , and kaolin (Al ₂ O _3).
The SiO ₂ component constituting (2SiO ₂ .2H ₂ O) and the like is not included in the silica in the present invention. Among these, wet silica and dry silica are preferable in that many grades are marketed, relatively inexpensive and easily available, and excellent in mechanical strength.

As a component other than silica constituting the filler, clay such as kaolin is used.
The mass ratio of the fluororesin and the filler is preferably 1: 0.1 to 2, particularly preferably 1: 1 to 1.8.

The filled fluororesin sheet of the present invention achieves both high stress relaxation and high airtightness even when the filling rate of the fluororesin is low and the filling rate of the filling material is high, and conforms to, for example, JIS R3453 The tensile strength is 10 MPa or more, the stress relaxation rate at 200 ° C. in accordance with JIS R3453 is 45% or less, and the surface of a φ48 mm × φ67 mm × thickness 1.5 mm gasket test piece made from the sheet The leak rate is 1.2 × 10 ⁻⁴ Pa · m ³ / s or less when an airtight test is performed under a pressure of 19.6 MPa (200 kgf / cm ² G) and a nitrogen gas internal pressure of 0.98 MPa (1.0 kgf / cm ² G).

[Method for producing filled fluororesin sheet]
The manufacturing method of the fluororesin sheet with a filler according to the present invention includes a step of rolling a resin composition for forming a sheet containing a fluororesin and a filler containing 20% by weight or more of silica.

[Resin composition for sheet formation]
As the fluororesin, any of the above fluororesins can be preferably used. Among these, it is particularly preferable to use PTFE obtained by emulsion polymerization in terms of workability when performing extrusion molding, rolling, or the like.

As the fluororesin, a powdery one may be used as it is, or a dispersion in which fluororesin fine particles are dispersed in water may be used. In the case of using a dispersion, a composition for forming a fluororesin sheet with a filler can be obtained simply by adding an appropriate amount of water, filler, processing aid, etc. to the fluororesin dispersion and stirring the composition. By using a thing, a filler-containing fluororesin sheet can be obtained more efficiently.

The details of the filler are as described above.
The mass ratio of the fluororesin and the filler contained in the sheet forming resin composition is preferably 1: 0.1 to 2, more preferably 1: 1 to 1.8.

<Processing aid>
The manufacturing method of the fluororesin sheet with a filler according to the present invention comprises a resin composition for sheet formation containing a fluororesin, a filler containing 20% by weight or more of silica, and a processing aid. Including the step of rolling at ~ 80 ° C,
The processing aid preferably comprises 30% by mass or more of a petroleum hydrocarbon solvent having a fractional distillation temperature of 120 ° C. or less (however, the weight of the processing aid is 100% by mass).

  The processing aid is preferably 30% by mass or more, more preferably 50% by mass or more of a petroleum hydrocarbon solvent having a fractional distillation temperature of 120 ° C. or less (provided that the weight of the processing aid is 100% by mass). In particular, it preferably consists essentially of a petroleum hydrocarbon solvent having a fractionation temperature of 120 ° C. or lower.

  As a petroleum-type hydrocarbon solvent whose fractionation temperature is 120 degrees C or less, a paraffin-type solvent etc. are mentioned as a typical example, If it is a commercial item, for example, Isopar C (hydrocarbon-type organic solvent, fractionation temperature: 97- 104 ° C., Exxon Mobil (existing)).

  In the conventional method for producing a fluororesin sheet with a filler, it is common to use a petroleum hydrocarbon solvent having a high fractionation temperature (for example, 180 to 250 ° C.) as a processing aid. Such a processing aid is general-purpose in that the solvent does not volatilize during the rolling operation and a stable rolling operation can be performed, but it is difficult to volatilize even if the roll temperature is increased in the rolling process described later.

  Examples of components other than petroleum hydrocarbon solvents having a fractionation temperature of 120 ° C. or lower that may be included in the processing aid include petroleum hydrocarbon solvents having a fractionation temperature exceeding 120 ° C. Examples of petroleum hydrocarbon solvents having a fractional distillation temperature exceeding 120 ° C. include Isopar G (hydrocarbon organic solvent, fractional distillation temperature: 158 to 175 ° C., Exxon Mobil (existing)).

  The processing aid is contained in the sheet forming resin composition in an amount of 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the total of the fluororesin and the filler. When the processing aid is contained in such an amount, the fluororesin can be sufficiently swollen at the initial stage of the rolling process described later.

The resin composition for forming a sheet essentially consists of the above-described fluororesin, filler, and processing aid.
In order to prepare a resin composition for forming a fluororesin sheet containing these components, the above-mentioned components are added to the container at a time in an arbitrary order, or divided into a plurality of portions, and stirred, mixed, etc. do it.

[Method for producing fluororesin sheet]
A general method for producing a filled fluororesin sheet includes a stirring step, a preforming step, a rolling step, a drying step, and a firing step in this order.

<Stirring step>
In the stirring step, as described above, the fluororesin, the filler, and the processing aid are stirred and mixed in an arbitrary order. If the stirring efficiency is poor, a large amount of processing aid may be added and excess processing aid may be removed by filtration after stirring.

<Preliminary molding process>
In the preforming step, the fluororesin sheet forming resin composition is extruded to produce a preform (extruded product).

The shape of the extruded product (preform) is not particularly limited, but a rod shape or a ribbon shape is desirable in consideration of efficiency of subsequent sheet formation, uniformity of sheet properties, and the like.
In the production method of the present invention, since the processing aid is gradually volatilized in the rolling step described later, the mixing step and the preforming step are performed at a temperature lower than the roll temperature in the rolling step so that the processing aid does not volatilize. It is preferable to carry out with.

<Rolling process>
In the rolling process following the pre-forming process, the preform is rolled and formed into a sheet shape by passing between rolling rolls represented by a biaxial roll. In the prior art, the rolling process is performed without heating, specifically at a temperature of about 10 to 30 ° C. near room temperature, and the processing aid has a high fractional distillation temperature (for example, 180 to 250). C) Petroleum hydrocarbon solvent was generally used, so that the processing aid hardly volatilized in this rolling process.

  This processing aid is used to swell the fluororesin and facilitate fiber formation. A part of the fluororesin is fiberized by the compressive force and shearing force applied to the sheet-forming resin composition in the stirring process, preforming process, and rolling process. Strength and stress relaxation properties are imparted. However, if the fluororesin is swollen inside the rolled fluororesin sheet, this sheet is soft and easily deformed, and therefore deformation in the plane direction takes precedence even when subjected to compression by a biaxial roll or the like. Therefore, it is considered that densification inside the sheet hardly occurs. The densification inside the sheet means that pores inside the composition caused by volatilization of the solvent are filled by rolling.

  In the production method of the present invention, this rolling step is preferably performed at a roll temperature of 40 to 80 ° C. using a processing aid containing a large amount of petroleum hydrocarbon solvent having a low fractionation temperature (120 ° C. or less), When rolling is performed in this manner, the processing aid (in the preform) in the sheet-forming resin composition is gradually volatilized and removed during rolling with a biaxial roll or the like. Therefore, since there are many processing aids in the initial stage of the rolling process, the fluororesin can be swollen and fiberized, and in the later stage of the rolling process, the remaining amount of processing aids is small, Since the formation of new pores inside the sheet based on the volatilization of the auxiliary agent is small, it is considered that the densification inside the sheet can be advanced in preference to the deformation in the plane direction of the sheet.

In addition, since the rolling is performed at a relatively high temperature, the hardness of the fluororesin is slightly lowered, and the fluororesin sheet is easily densified.
On the other hand, when the rolling process is performed at a temperature lower than 40 ° C., the processing aid tends to be less volatile. In addition, if rolling is performed at a temperature exceeding 80 ° C., the processing aid is excessively volatilized, and the processing aid remaining at the initial stage of the rolling process is reduced. The strength of the obtained fluororesin sheet with a filler tends to be inferior. Further, the processing aid in the composition is rapidly vaporized to cause a swelling phenomenon, and the hermeticity of the filled fluororesin sheet tends to be lowered.

Moreover, in the manufacturing method of this invention, it is preferable to include the process of further rolling the rolling sheet prepared by the said rolling process, ie, to repeat a rolling process in multiple times. By repeating rolling, the inside of the fluororesin sheet can be further densified. In addition, when repeating a rolling process, a roll space | interval is narrowed every time rolling is repeated.

  When forming the sheet by rolling the preform with a biaxial roll, for example, the distance between the rolls is set to 0.5 to 20 mm, and the roll surface moving speed (sheet extrusion speed) is set to 5 to 50 mm / second. Can be rolled.

<Drying process>
In the drying step, the processing aid is removed by leaving the rolled sheet at room temperature or heating it at a temperature below the boiling point of the fluororesin.

<Baking process>
In the firing step, the dried sheet is heated and sintered at a temperature equal to or higher than the melting point of the fluororesin. The heating temperature varies slightly depending on the type of the fluororesin, for example, 340 to 370 ° C., considering that the entire sheet needs to be uniformly fired and that a fluorine-based harmful gas is generated at an excessively high temperature. Is appropriate.

[Example]
EXAMPLES Hereinafter, although the manufacturing method of this invention is demonstrated in detail by an Example, this invention is not limited at all by these Examples.

<Test method>
Test pieces were prepared from a sheet having a thickness of 1.5 mm, and hermeticity and tensile strength were measured as follows.

Leakage (airtightness);
A gasket test piece punched into a size of φ48mm × φ67mm is mounted between steel flanges of φ100mm × height 50mm, surface roughness Rmax = 12μm, and the surface pressure is 19.6MPa (200kgf / cm ² G) by a compression tester A load was applied. After applying a nitrogen gas internal pressure of 0.98 MPa (1.0 kgf / cm ² G) to the inner diameter of the gasket from the pressure introduction through hole provided in the flange, the pressure introduction pipe was sealed and held for 1 hour. The pressure change before and after holding was read with a pressure sensor, and the amount of leakage was determined from the pressure drop.

Tensile strength;
Test pieces were prepared in accordance with JIS R3453, and the tensile strength was measured.
Stress relaxation rate;
Test pieces were prepared according to JIS R3453, and the stress relaxation rate at 200 ° C. was measured.

[Example 1]
400 g PTFE fine powder (CD-1, manufactured by Asahi Glass Co., Ltd.)
600 g of Toxeal GU (silica, manufactured by Tokuyama Co., Ltd.) and 250 g of Isopar C (hydrocarbon organic solvent, fractional distillation temperature: 97 to 104 ° C., Exxon Mobil (existing))
After mixing with a kneader for 5 minutes, the mixture was aged by standing at room temperature (25 ° C.) for 16 hours to prepare a sheet-forming composition.

This composition was extruded at room temperature (25 ° C.) with a 300 mm × 20 mm die extruder to prepare a preform.
This preform was rolled with a biaxial roll under the conditions of a roll diameter of 700 mm, a roll interval of 20 mm, a roll speed of 6 m / min, and a roll temperature of 80 ° C. Immediately after this rolling, the obtained sheet was rolled again with a roll interval of 10 mm. Furthermore, immediately after this rolling, the obtained sheet was rolled again with a roll interval of 5 mm. Finally, immediately after this rolling, the obtained sheet was rolled again with a roll interval of 1.5 mm, and a sheet having a thickness of 1.5 mm was obtained.

The sheet was left at room temperature (25 ° C.) for 24 hours to remove the solvent, and then baked in an electric furnace at 350 ° C. for 3 hours to obtain a sheet gasket.
The sheet gasket had a leakage amount (airtightness) of 9.0 × 10 ⁻⁵ Pa · m ³ / s, a tensile strength of 11 MPa, and a stress relaxation rate at 200 ° C. of 40%.

[Example 2]
In place of 600 g of Toxeal GU, 300 g of Toxeal GU and A. A sheet gasket was produced in the same manner as in Example 1 except that 300 g of A kaolin (Kaolin clay, manufactured by Sanyo Clay Industry Co., Ltd.) was used.

This sheet gasket had a leakage amount (air tightness) of 9.3 × 10 ⁻⁵ Pa · m ³ / s, a tensile strength of 10 MPa, and a stress relaxation rate of 42% at 200 ° C.
[Example 3]
In place of 600 g of Toxeal GU, 120 g of Toxeal GU and A. A sheet gasket was produced in the same manner as in Example 1 except that 480 g of A kaolin (Kaolin clay, manufactured by Sanyo Clay Industry Co., Ltd.) was used.

The sheet gasket had a leakage amount (air tightness) of 1.0 × 10 ⁻⁴ Pa · m ³ / s, a tensile strength of 10 MPa, and a stress relaxation rate at 200 ° C. of 43%.
[Comparative Example 1]
Tokushir GU 600g A sheet gasket was produced in the same manner as in Example 1 except that 600 g of A kaolin was used.

This sheet gasket had a leakage amount (air tightness) of 4.0 × 10 ⁻⁴ Pa · m ³ / s, a tensile strength of 9 MPa, and a stress relaxation rate at 200 ° C. of 58%.
[Comparative Example 2]
A sheet gasket was produced in the same manner as in Example 1 except that 250 g of Isopar G (hydrocarbon organic solvent, fractional distillation temperature: 158 to 175 ° C., Exxon Mobil Corporation) was used instead of 250 g of Isopar C.

This sheet gasket had a leakage amount (air tightness) of 1.5 × 10 ⁻⁴ Pa · m ³ / s, a tensile strength of 10 MPa, and a stress relaxation rate of 45% at 200 ° C.
[Comparative Example 3]
A sheet gasket was produced in the same manner as in Example 1 except that the rolling roll temperature was 25 ° C.

This sheet gasket had a leakage amount (air tightness) of 2.9 × 10 ⁻⁴ Pa · m ³ / s, a tensile strength of 9 MPa, and a stress relaxation rate of 49% at 200 ° C.
[Comparative Example 4]
A sheet gasket was produced in the same manner as in Example 1 except that the rolling roll temperature was 100 ° C.

This sheet gasket had a leakage amount (air tightness) of 5.0 × 10 ⁻⁴ Pa · m ³ / s, a tensile strength of 8 MPa, and a stress relaxation rate at 200 ° C. of 60%.

Claims (8)

  A filled fluororesin sheet containing a fluororesin and a filler containing 20% by weight or more of silica.   2. The filled fluororesin sheet according to claim 1, wherein a mass ratio of the fluororesin to the filler is fluororesin: filler = 1: 0.1-2.   The manufacturing method of the fluororesin sheet | seat with a filler characterized by including the process of rolling the resin composition for sheet formation containing a fluororesin and the filler which contains a silica 20weight% or more.   4. The filled fluororesin sheet according to claim 3, wherein a mass ratio of the fluororesin and the filler in the composition is fluororesin: filler = 1: 0.1-2. Manufacturing method. Including a step of rolling a sheet-forming resin composition containing a fluororesin, a filler containing 20% by weight or more of silica, and a processing aid at a roll temperature of 40 to 80 ° C.,
The processing aid comprises 30% by mass or more of a petroleum hydrocarbon solvent having a fractional distillation temperature of 120 ° C. or less (provided that the weight of the processing aid is 100% by mass). A method for producing a filled fluororesin sheet according to 3 or 4.   6. The filled fluororesin sheet according to claim 5, wherein the processing aid is contained in the composition in an amount of 5 to 50 parts by weight with respect to 100 parts by weight of the total of the fluororesin and the filler. Production method.   The method for producing a filled fluororesin sheet according to any one of claims 3 to 6, further comprising a step of rolling the rolled sheet prepared by the rolling step.   A filled fluororesin sheet produced by the production method according to claim 3.