JP2904852B2 - Manufacturing method of sealing material - Google Patents

Description

Description TECHNICAL FIELD [0001] The present invention relates to a method for producing a sealing material containing a fluororesin, which has a small amount of impurities eluted into water or the like and can be suitably used in the field of handling foods or pharmaceuticals.

TECHNICAL BACKGROUND OF THE INVENTION A sealing material obtained by impregnating a fibrous base material such as carbon fiber, glass fiber and aramid fiber with a fluorinated resin such as a woven fabric, a nonwoven fabric and a string or rock wool has excellent heat resistance and chemical resistance. Therefore, they are widely used as gaskets and packings for the chemical industry.

Conventionally, this sealing material is formed by impregnating a fiber base material with an aqueous dispersion obtained by dispersing fluororesin fine particles in water, and then laminating the obtained resin-impregnated base material as necessary to form a predetermined shape. It is manufactured by mounting it in a mold, and then heating and pressurizing it to form the fluororesin while firing it. Unless the fluororesin impregnated in the fibrous base material is uniform, such a sealing material cannot obtain sufficient sealing properties. Therefore, a surfactant is generally added to the aqueous dispersion in order to uniformly disperse the fluororesin in the aqueous dispersion in water.

By the way, a sealing material used in the fields of production and storage of pharmaceuticals, for example, must be formed of a material that is in direct contact with the pharmaceuticals and does not elute impurities or toxic substances into the pharmaceuticals. Therefore, the Japanese Pharmacopoeia defines potassium permanganate consumption as one of the indexes. Potassium permanganate consumption is determined by immersing a sample in purified water for a predetermined period of time and then optimizing the impurities contained in this purified water with an aqueous potassium permanganate solution. Potassium acid consumption is less than 6.3ppm / 100ml.

However, although the sealing material manufactured using the aqueous dispersion of the fluororesin is a material suitable for use in the field of handling pharmaceuticals in particular in terms of excellent chemical resistance, the surfactant used in the aqueous dispersion is used. In addition, impurities and the like mixed in during the manufacturing process are included, and are easily eluted in water or the like, so that the consumption amount of potassium permanganate exceeds the above value. Therefore, this sealing material has a problem that it cannot be used in the field of handling pharmaceuticals, and is not preferable in the field of handling foodstuffs.

One way to solve this problem is to add less or no surfactant to the aqueous dispersion. However, in such a method,
If the amount of the surfactant used is reduced until the potassium permanganate consumption becomes the above value or less, the water dispersibility of the fluororesin decreases, and the fluororesin impregnated into the base fiber becomes heterogeneous, There is a problem that a sealing material having sufficient sealing properties cannot be obtained.

An object of the present invention is to solve such problems associated with the prior art, and is suitable for the field of treating pharmaceuticals and foodstuffs with little elution of impurities or toxic substances into water, and has a sufficient effect. An object of the present invention is to provide a method for producing a fluororesin-containing sealing material having a sealing property.

SUMMARY OF THE INVENTION A method for producing a fluororesin-containing sealing material according to the present invention comprises:
An aqueous dispersion containing a surfactant and fluororesin fine particles, a resin impregnation step of impregnating the fiber substrate surface, and the resin impregnated substrate obtained in the resin impregnation step is heated to a temperature of 350 ° C. or higher of the fluororesin. And a molding step of molding while heating and pressing under a pressure condition of ~ 600 kgf / cm ² , and at least one of the resin-impregnated base material obtained in the resin impregnation step and the molded article obtained in the molding step. Is heated to a temperature of 190 to 210 ° C. under non-pressurization to decompose the contained surfactant and residual impurities.

According to the method for producing a fluororesin-containing sealing material of the present invention, an aqueous dispersion containing a surfactant is used in the resin impregnation step, and the aqueous dispersion is contained in the resin-impregnated base material and / or the molded article in the heat treatment step. Since the surfactant and impurities are decomposed, it is possible to manufacture a sealing material in which the fluororesin impregnated into the fiber base material is uniform and has excellent sealing properties, and the impurities are hardly eluted in water to be brought into contact.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, a method for producing a sealing material according to the present invention will be specifically described.

In the method for producing a sealing material according to the present invention, a fiber base material and an aqueous dispersion containing fine particles of fluororesin are used as raw materials.

As the fiber substrate used in the present invention, specifically,
In addition to rock wool and asbestos, woven fabrics, nonwoven fabrics, and strings made of inorganic fibers such as carbon fibers and glass fibers and organic fibers such as aramid fibers can be used.

Specific examples of the material of the fluororesin fine particles added to the aqueous dispersion include polytetrafluoroethylene (PTFE), a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), and polychlorotrifluoroethylene (CTFE). ), A copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PF
A) can be used.

The primary particle diameter of the fluororesin fine particles is usually 0.5 μm.
m or less, preferably 0.2 to 0.4 μm. By setting the particle diameter of the fluororesin fine particles to such a value, the fluororesin fine particles can be sufficiently dispersed with a small amount of the surfactant used.

Such fluororesin fine particles are generally obtained by an emulsion polymerization method.

Further, in the present invention, a surfactant is added to the aqueous dispersion in order to improve the water dispersibility of the fluororesin fine particles. Such surfactants are usually polyoxyethylene alkylphenol ethers,
Non-ionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide, sorbitan alkyl ester, and polyoxyethylene sorbitan alkyl ester are preferably used. The surfactants may be used alone or in combination.

In the present invention, the surfactant can be used as long as the surfactant can be prevented from being eluted from the sealing material and can be sufficiently improved in the water dispersibility of the fluororesin fine particles in the heat treatment step described in detail below. Not limited.

The aqueous dispersion used in the present invention may contain an inorganic filler, a pigment, and the like, if necessary, in addition to the fluororesin fine particles and the surfactant described above.

In such an aqueous dispersion, the fluororesin fine particles are used in an amount of 50 to 70% by weight, preferably 55 to 65% by weight.

Further, the surfactant is contained in the aqueous dispersion in an amount of 3 to
It is used in an amount of 9% by weight, preferably 5-7% by weight.

In the method for manufacturing a sealing material according to the present invention, a resin impregnating step using the fiber base and the aqueous dispersion as described above, and a resin-impregnated base obtained in the resin impregnating step are formed to produce a molded body. And a heat treatment step of heating at least one of the resin-impregnated base material and the molded body at a predetermined temperature.

In the resin impregnation step, the fiber base material is impregnated with the aqueous dispersion. Specifically, in the resin impregnation step, the aqueous base material is coated with the aqueous dispersion or the fiber base material is subjected to the aqueous dispersion. It is carried out by immersion in the glass.

The fiber substrate impregnated with the fluororesin is dried, but this impregnation and drying may be repeated a plurality of times.

The resin-impregnated substrate thus obtained is usually 50 to 70
It contains the fluororesin in an amount of from about 55% to about 65% by weight.

The resin-impregnated base material is formed into a shape corresponding to the shape of the molded article to be produced, for example, by punching out a fiber base material before impregnation or a resin-impregnated base material obtained after impregnation.

In the molding step, such a resin-impregnated base material is heated and pressurized in a mold having a predetermined shape, whereby the fluororesin is molded while being fired to produce a molded body.

In such a molding step, the heating temperature is equal to or higher than the melting point of the fluororesin, preferably 370 to 390 ° C.
Usually, it is 350 to 600 kgf / cm ² , preferably 450 to 500 kgf / cm ² .

At this time, if a single resin-impregnated base material is mounted on a mold and pressed and compressed, a single-layer molded body can be obtained. If it is compressed, it is possible to obtain a molded body formed into a laminate. Further, the molded body can be formed into various shapes such as a ring shape, a V shape, a J shape, and an L shape by forming the resin-impregnated base material to be used into a predetermined shape.

In the method for producing a sealing material according to the present invention, at least one of the resin-impregnated base material obtained in such a resin impregnation step and the molded product obtained in the molding step are usually 100 to 3
A heat treatment step of heating to a temperature of 00C, preferably 190 to 210C is included. The heat treatment is usually performed for 0.5 to 2 hours, preferably 1 to 1.5 hours.

If the heating temperature is set to 100 ° C. or lower, the elution of impurities is so large that the specified value cannot be satisfied. Also, set the heating temperature
If the temperature is set to 300 ° C. or higher, there is a large possibility that the material will flow poorly at the time of molding and delamination will occur.

By performing such a heat treatment, it is possible to decompose the surfactant contained in the resin-impregnated base material or the molded article and the impurities mixed into the dispersion in the resin impregnation step or the like, and therefore, the surfactant is contained in water or the like. In addition, it is possible to manufacture a sealing material from which impurities are hardly eluted.

Effect of the Invention According to the method for producing a fluororesin-containing sealing material according to the present invention, an aqueous dispersion containing a surfactant is used in the resin impregnation step, and the resin-coated fiber base material and / or molding is used in the heat treatment step. Since the surfactant and impurities contained in the body are decomposed, the fluororesin impregnated into the fiber base material is uniform and has excellent sealing properties, and the impurities are hardly eluted in the water that comes in contact with it. A sealing material suitable for packing, gaskets, and the like used in the field can be provided.

EXAMPLES Hereinafter, a method for manufacturing a sealing material according to the present invention will be described based on examples.

The potassium permanganate consumption was measured and calculated as follows.

(1) 100 ml of purified water was added to each sample, heated at a temperature of 95 ° C. for 1 hour, left to reach room temperature, and then the sample was immediately taken out and the obtained liquid was used as a test liquid.

(2) To 100 ml of the test solution, add potassium permanganate and dilute sulfuric acid, boil for 3 minutes, and then add sodium oxalate. A 0.01 N potassium permanganate solution is added dropwise to the obtained solution, and the amount of this solution used is measured.

(3) Using 100 ml of distilled water, the amount of the potassium permanganate solution dropped in the same manner is measured.

(4) From the potassium permanganate solution usage amount a obtained in (2) and the potassium permanganate solution usage amount b obtained in (3), the potassium permanganate consumption M is calculated according to the following equation. Calculated.

Here, f is a factor of a 1N potassium permanganate solution.

Example 1 An aqueous dispersion containing 60% by weight of PTFE fine particles (0.4 μm or less in particle diameter) and 5% by weight of polyoxyethylene alkylphenol ether is applied to a woven cloth made of carbon fiber three times and air-dried. In this way, a resin-impregnated base material containing 60% by weight of a fluororesin was prepared.

The obtained resin-impregnated substrate was heated in an electric furnace at a temperature of 200 ° C. for 1 hour.
Heat treatment was performed for a time.

Next, the resin-impregnated base material is punched into a ring shape, and 5
A plurality of sheets were laminated to form a preform. The preform was mounted in a mold, and heated and pressed at a temperature of 380 ° C. and a pressure of 500 kg / cm ² to obtain a preform.

This molded body was subjected to a heat treatment at a temperature of 200 ° C. for 1 hour in an electric furnace.

The potassium permanganate consumption of the obtained sealing material was determined. Table 1 shows the results.

Example 2 A sealing material was produced in the same manner as in Example 1 except that the resin-impregnated base material was not subjected to a heat treatment.

The potassium permanganate consumption of the obtained sealing material was determined. Table 1 shows the results.

Example 3 A sealing material was manufactured in the same manner as in Example 1, except that the heat treatment was not performed on the molded body.

The potassium permanganate consumption of the obtained sealing material was determined. Table 1 shows the results.

Comparative Example 1 A sealing material was produced in the same manner as in Example 1, except that the resin-impregnated base material and the molded body were not subjected to the heat treatment.

The potassium permanganate consumption of the obtained sealing material was determined. Table 1 shows the results.

Claims (1)

(57) [Claims] 1. A resin impregnating step of impregnating a fiber base with an aqueous dispersion containing a surfactant and fluororesin fine particles; and a resin impregnated base obtained in the resin impregnating step having a melting point of the fluororesin or higher. And a molding step of molding while heating and pressurizing under a temperature of 350 to 600 kgf / cm ² under the pressure condition of the resin-impregnated base material obtained in the resin impregnation step and the molded article obtained in the molding step. At least one of
A method for producing a sealing material, comprising a heat treatment step of heating to a temperature of 190 to 210 ° C. under non-pressure to decompose a surfactant and residual impurities contained therein.