JP2008013654A - Method for producing fluoroplastic sheet containing filler and fluoroplastic sheet containing filler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluoroplastic sheet containing filler which satisfies both high stress relaxation properties and high airtightness properties and to provide a method for producing the same. <P>SOLUTION: The method for producing the fluoroplastic sheet containing filler comprises the step of mixing a fluoroplastic, a powdery filler, and a processing aid to prepare a sheet molding resin composition and the step of rolling the composition at a roll temperature of 40-80°C, wherein the powdery filler has a particle size distribution satisfying the relationships: V<SB>A</SB>=bV<SB>B</SB>+cV<SB>C</SB>(1≤b≤3 and 1/3≤c≤1), (wherein σ is the particle diameter at which the frequency is maximum; V<SB>A</SB>is the volume of particles of particle diameters of 0.9-1.1σ; V<SB>B</SB>is the volume of particles of particle diameters of 0.73σ or smaller, and V<SB>C</SB>is the volume of particles of particle diameters of 1.37σ or larger), and the processing aid contains at least 30 mass% (the weight of the processing aid is 100 mass%) petroleum hydrocarbon solvent of a fractional distillation temperature range ≤120°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  In order to improve the stress relaxation characteristics of the sheet gasket, it is effective to arrange the filler particles in the sheet as densely as possible. However, when only a filler having a uniform particle diameter is used, a certain gap is generated between the filler particles, and therefore there is a limit to the high density arrangement of the filler. Also, generally available inorganic fillers are those obtained by pulverizing and classifying natural minerals, so the particle size is distributed within a certain range, but there are variations and the particle size is extremely small. There is a limit to high-density filling because it is difficult to reduce the size.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a filled fluororesin sheet having both high stress relaxation properties and high airtightness (sealing performance) and a method for producing the same. And

  As a result of intensive research, the present inventors have used a powder filler having a specific particle size distribution when preparing a sheet-forming resin composition, and in the rolling process during the production of the filled fluororesin sheet, processing aids are used. By gradually evaporating the agent, it was found that a filled fluororesin sheet having both high stress relaxation properties and high airtightness could be produced, and the present invention was completed.

The manufacturing method of the filled fluororesin sheet of the present invention,
A step of preparing a sheet-forming resin composition by mixing a fluororesin, a powder filler and a processing aid, and a step of rolling the composition at a roll temperature of 40 to 80 ° C., wherein the particle size of the powder filler In the distribution, when the particle diameter when the number of particles is maximum is expressed as σ, the volume of the particles having a particle diameter of 0.9 to 1.1σ is V _A and the particle diameter is 0.73σ or less. Where V _B is the volume of particles and the volume of the particles having a particle diameter of 1.37σ or more is V _C , the following relational expression (1) is satisfied:
V _A = bV _B + cV _C (1)
(However, 1 ≦ b ≦ 3 and 1/3 ≦ c ≦ 1.)
The processing aid 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 mass ratio of the fluororesin and the filler in the composition is preferably fluororesin: filler = 1: 0.1-2.
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 is manufactured by the above-described method for manufacturing a filled fluororesin sheet of the present invention.

  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.

  The method for producing a filled fluororesin sheet according to the present invention includes a step of rolling a sheet forming resin composition containing a fluororesin, a powder filler and a processing aid at a roll temperature of 40 to 80 ° C. The filler has a predetermined particle size distribution, and the processing aid contains 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). It is characterized by comprising.

[Resin composition for sheet formation]
<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, 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.

<Filler>
As the powder filler, depending on the purpose, carbon-based fillers such as graphite, carbon black, expanded graphite, activated carbon, and carbon nanotube; inorganic fillers such as talc, mica, clay, calcium carbonate, magnesium oxide; or PPS Resin powder such as
Etc. are used.

The average particle diameter of the filler is usually 0.1 to 100 μm, preferably 1 to 30 μm.
The average particle diameter is the particle diameter (median diameter) when the cumulative number becomes 50% in the particle size distribution measured by the laser diffraction scattering method.

  In general, the particle shape includes a spherical shape and a plate shape. However, the filler having a plate shape is easily pulverized and sliced when the sheet-forming resin composition is roll-stretched. The particle shape is preferably spherical.

In the present invention, in the particle size distribution of the powder filler, when the particle diameter when the number of particles is maximum is expressed as σ, the total volume of the particles having a particle diameter of 0.9 to 1.1σ is When V _A is the total volume of particles having a particle diameter of 0.73σ or less and V _{B is} the total volume of particles having a particle diameter of 1.37σ or more is V _C , the following relational expression (1) is satisfied. .

V _A = bV _B + cV _C (1)
(However, 1 ≦ b ≦ 3 and 1/3 ≦ c ≦ 1.)
When there are two or more particle sizes with the maximum number of particles, σ is the maximum particle size.

  Here, in a filling structure formed by spheres having a radius R, an 8-coordinate space, a 6-coordinate space, or a 4-coordinate space is generated between the spheres. In the simple cubic lattice, an 8-coordinate space is generated, in the body-centered cubic lattice, a 6-coordinate space is generated, and in the cubic close-packing (face-centered cubic lattice) and the hexagonal close-packing, the 6-coordinate space and A tetracoordinate space is created.

The octacoordinate space can be filled with a sphere having a radius of 0.732R ((√3-1) R) or less, and the hexacoordinate space has a radius of 0.414R ((√2- 1) R) or less spheres can be filled, and this 4-coordinate space can be filled with spheres having a radius of 0.225R (((√6-2) / 2) R) or less.
(See http://www.nda.ac.jp/cc/users/asanoa/lectures/ch1/ch1-06crystal.pdf etc.)
Therefore, the space in the filling structure (unit cell) formed by the spheres having the radius R can be further filled with spheres having a radius of 0.732R or less, while the sphere having the radius R has a radius of 1.37R ( = (1 / 0.732) R) It is possible to fill a space in a filling structure (unit cell) formed by spheres of more than one.

The filling rate of the spheres in the unit cell (that is, the proportion of the volume of the sphere in the unit cell) and the proportion of the space excluding the spheres are as follows. (Http://www.nda.ac.jp/cc/users/asanoa
See /lectures/ch1/ch1-06crystal.pdf etc. )

Thus, in the unit cell filled with spheres, the volume ratio between the sphere and the remaining space is in the range of 1.1 to 2.8 depending on the unit cell.
Therefore, when the particle shape of the filler is considered to be a sphere, the particle diameter when the number of particles is maximum is represented by σ, and the volume of the particle having a particle diameter of 0.9 to 1.1σ (that is, particle diameter) the volume of the filler particles but the total) V _a volume of the filler particles is 0.9～1.1Shiguma, volume (i.e. diameter of the particles having a particle diameter of less 0.73σ or less 0.73σ V _B , and the volume of particles having a particle diameter of 1.37σ or more ((1 / 0.73) σ or more) (that is, the total volume of filler particles having a particle diameter of 1.37σ or more). When V _C , the following relational expression (1):
V _A = bV _B + cV _C (1)
If b is in the range of 1 to 3 which is substantially the same as 1.1 to 2.8, and c is in the range of 1 to 3 to 1 which is substantially the same as 1 / 2.8 to 1 / 1.1, The space in the packed structure formed by the particles having a diameter of 1.37σ or more is efficiently filled with filler particles having a particle diameter of 0.9 to 1.1σ, which is substantially the same as σ, and the particle diameter is set to 0.1. It is possible to efficiently fill the filler particles having a particle diameter of 0.73σ or less into the space in the filling structure formed by the remainder of the filler particles having 9 to 1.1σ.

  In an actual filler, the filler particle shape is not a true sphere, and the particle diameter also varies, but by using a filler having a specific particle size distribution as described above, the filler particles are primary aggregated. It is considered that a fluororesin sheet filled with a higher density than in the past can be produced in the aggregate, and as a result, the stress relaxation property and airtightness of the fluororesin sheet are improved.

  According to the present invention, even when the filling rate of the fluororesin is low and the filling rate of the filling material is high, it is possible to produce a filled fluororesin sheet having both high stress relaxation properties and high airtightness. The mass ratio of the fluororesin and the filler can be 1: 0.1 to 2, preferably 1: 1 to 1.8.

<Processing aid>
The composition for forming a fluororesin sheet contains a processing aid.
The processing aid used in the present invention contains 30% by mass or more, preferably 50% 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). Particularly preferably consists essentially of petroleum hydrocarbon solvents having a fractional distillation 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 fluororesin, the filler A, and the filler B in total. Is desirable. 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 sheet-forming resin composition essentially consists of the above-described fluororesin, filler A and filler B, 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 A and the filler B, 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 is unlikely to occur. In addition, the densification inside a sheet | seat means that the void | hole inside the composition produced by volatilization of the solvent is filled up by rolling.

  In the production method of the present invention, this rolling step is performed at a roll temperature of 40 to 80 ° C., and a processing aid containing a large amount of a petroleum hydrocarbon solvent having a low fractional distillation temperature (120 ° C. or less) is used. Therefore, 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.

[Filled fluororesin sheet]
By such a production method of the present invention, a filled fluororesin sheet is produced. This filled fluororesin sheet has both high stress relaxation and airtightness.

Claims (5)

A step of preparing a sheet-forming resin composition by mixing a fluororesin, a powder filler and a processing aid, and a step of rolling the composition at a roll temperature of 40 to 80 ° C.,
In the particle size distribution of the powder filler, when the particle diameter when the number of particles is maximum is expressed as σ, the volume of the particles having a particle diameter of 0.9 to 1.1σ is V _A and the particle diameter is 0. When the volume of a particle having a particle diameter of .73σ or less is V _B and the volume of a particle having a particle diameter of 1.37σ or more is V _C , the following relational expression (1) is satisfied,
V _A = bV _B + cV _C (1)
(However, 1 ≦ b ≦ 3 and 1/3 ≦ c ≦ 1.)
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). Manufacturing method of fluororesin sheet containing material.   The filled fluororesin sheet according to claim 1, wherein a mass ratio of the fluororesin and the filler in the composition is fluororesin: filler = 1: 0.1-2. Manufacturing method.   The filled fluororesin according to claim 1 or 2, wherein the processing aid is contained in the composition in an amount of 5 to 50 parts by weight based on 100 parts by weight of the total of the fluororesin and the filler. Sheet manufacturing method.   The method for producing a filled fluororesin sheet according to any one of claims 1 to 3, further comprising a step of rolling the rolled sheet prepared by the rolling step. The fluororesin sheet | seat with a filler manufactured by the manufacturing method in any one of Claims 1-4.