JPS5833094B2 - Method for manufacturing tetrafluoroethylene resin moldings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for producing a tetrafluoroethylene resin molded article having excellent compression creep resistance, tensile creep rupture strength, compressive strength, and flexibility.

In general, tetrafluoroethylene resin moldings (hereinafter referred to as 4F resin moldings) have superior heat resistance, chemical resistance, and electrical properties compared to other synthetic resin moldings, and are used in many applications. ing.

In addition to the above-mentioned properties, 4F resin molded bodies have a very small coefficient of friction and can easily slide, so they are used as bearing materials in many fields.

However, while having the above-mentioned excellent properties, conventional 4F resin moldings are manufactured from powder obtained by suspension polymerization, so they are prone to cold flow under compressive loads and have poor compression creep resistance. It has some drawbacks, such as being easily deformed under high loads and lacking in flexibility.

In order to overcome these drawbacks, conventional methods have been to improve the above characteristics by mixing appropriate amounts of various inorganic filler powders such as glass fiber, carbon, graphite, molybdenum disulfide, bronze, etc. alone or in combination with 4F resin powder. However, the heat resistance, chemical resistance, electrical properties, etc. inherent to 4F resin may be impaired depending on the type of filler used in 4F resin molded bodies mixed with fillers. In particular, the compression creep resistance in a high-temperature atmosphere was not as good as the 4F resin molded product containing no filler.

This invention was made in order to solve the above-mentioned drawbacks of the conventional production method, and it is made of 4F resin powder containing tetrafluoroethylene and perfluoroalkyl l-IJ having 3 to 10 carbon atoms in a weight range of 98 or more based on the total amount. Commercially available 4F resin powder for paste extrusion (hereinafter referred to as modified 4F resin powder) made into granules by emulsion polymerization of fluoroethylene or oxyperfluoroalkyl trifluoroethylene having 3 to 10 carbon atoms was subjected to shearing force by stirring. A process of applying a load to form a fine powder, and a normal compression molding method from this fine powder to a density of 1.
60-2.15 g/cri1. A method for producing a 4F resin molded body, comprising: a step of molding a preformed body; and a step of firing this preformed body in air or a gas containing oxygen. By manufacturing in this manner, it is intended to provide a 4F resin molded article having excellent compression creep resistance, tensile creep rupture strength, compressive strength, and flexibility without mixing any inorganic fillers.

The modified 4F resin powder used in this invention is a low-crystalline copolymer with side chains obtained by emulsion polymerization as described above, has a molecular weight of about 5 million, and has a cotton candy-like shape of about 500 μm. Since it is a soft granule, when a shearing force due to stirring is applied to the powder, it undergoes physical transformation and is easily pulverized into a fibrous or granular fine powder.

Pulverization, which is the first step in the manufacturing method of the present invention, involves, for example, placing the modified 4F resin powder in a stirrer with rotating blades and applying shearing force by high-speed stirring (1500 to 250 Orpm) while drying to form an exothermic atmosphere. Under this, the powder is made into a fibrous fine powder, or a shearing force is applied by low-speed stirring (760 rpm) to make a granular fine powder.

The fine powder obtained by any of the above methods is a dense powder with a very large surface area and broken cotton candy-like soft granules.

In particular, since the powder is dense as mentioned above, it has become possible to compression mold the modified 4F resin powder, which was previously very difficult. Therefore, various molded bodies such as cylindrical, cylindrical, and annular shapes can be molded using normal compression molding. The law has made it easier to manufacture.

Next, in the second step, it is important to limit the density of the preform to a relatively porous range of 1.60 to 2.15 g/-. Coupled with the increase in powder surface area in one step, the hot air can flow to every corner inside the preform, and after firing, a final molded product with a density of 2.14 to 2.17 g/H can be obtained.

When the density of the preform is set to 1.60 g/cril or less, even if hot air flows well during firing, the void content is too large and it is not possible to obtain a void-free molded product with the target density. However, this is not preferable because mechanical properties such as compression creep resistance, tensile creep resistance to rupture, compressive strength, and flexibility deteriorate.

If it is 2.15 g/- or more, there will be almost no residual voids inside the preform, and therefore the circulation of hot air will be blocked, and it will not be possible to improve the mechanical properties peculiar to the modified 4F resin, and it will also cause the entire mold to This is undesirable because uniform firing is not possible and abnormalities such as cracks are likely to occur in the molded product.

Since the preform obtained in the above two steps is fired in a gas containing oxygen in the final firing process, the above three factors act together to prevent the preform from being fired in a conventional inert gas such as nitrogen gas. This heat treatment produces a different effect from that of calcination, and can significantly improve mechanical properties such as compression creep resistance, tensile creep rupture strength, compressive strength, and flexibility.

This phenomenon of improved mechanical properties cannot be predicted from the case of conventional 4F resin molded products, but in the case of the present invention, a structure similar to a crosslinked structure is probably formed between the side chain molecules of the modified 4F resin. This is thought to be due to the fact that

As described above, 4 obtained by the production method of the present invention
F resin moldings are conventional 4F resin moldings and 4F resin moldings with fillers.
Even if the flexibility, 1% compressive deformation strength, and compressive elastic modulus are the same compared to the F resin molded product, the flexibility, 0.2% offset strength (compressive yield strength), 25% compressive deformation strength,
It has extremely excellent mechanical properties such as tensile creep rupture strength and compressive creep properties in an atmosphere from room temperature to high temperature, and since no filler is mixed in this molded product, the original properties of 4F resin, i.e. It also has heat resistance, chemical resistance, electrical properties, etc.

The present invention will be specifically explained below based on examples thereof.

Example 1 The modified 4F resin powder (Teflon 62-J manufactured by Mitsui Fluorochemical Co., Ltd.) was placed in a stirrer with ordinary rotary blades and subjected to drying speed rotation (1500 to 2500 rpm) to apply high-speed shearing force to the powder. temperature is 40-70'C
Stir for 4 minutes so that the average particle size is 25-100μ
A fibrous fine powder with an average length of about 500 to 1000 μm was obtained.

Next, this fibrous fine powder was filled into a mold and compression molded at a molding pressure of 100 kg/d to achieve a density of 1.60 g/cI!
A preformed body of , was obtained.

Finally, this preform is placed in air at 360°010
After baking for an hour, it is cooled at 50QC/h and the density is 2.15-4.
An F resin molded body was obtained.

Example 2 Similar to Example 1, fibrous modified 4F resin fine powder Teflon 62J was filled into a molding die and the molding pressure was increased to 400 to 9/-
A preformed body having a density of 2.14 g/ffl was obtained by compression molding.

This preform was fired and cooled in the same manner as in Example 1, and the density was 2.1.
A 4F resin molded article of No. 6 was obtained.

Comparative Example 1 4F resin powder for general compression molding (Teflon 7AJ manufactured by Mitsui Shiro Chemical Co., Ltd.) was directly filled into a mold for molding, and the molding pressure was 300 kg/c11! A preform with a density of 2.20 g/cyj was obtained by compression molding using L.

Next, the obtained preform was placed in air at 360'CI.
After baking for O hours, it was cooled at 50°C/h to give a density of 2.17.
An F resin molded body was obtained.

Comparative Example 2 As the 4F resin powder, 4F resin powder for general compression molding (Afron G-700 manufactured by Asahi Glass Co., Ltd.) was used at a molding pressure of 250 kg/c11 as in Comparative Example 1! Compression molded with L and density 2.
After obtaining a preformed body of 25 g/criL, this was fired and cooled in the same manner as in Comparative Example 1 to obtain a 4F resin molded body having a density of 2.21.

Comparative Example 3 A mixture of the Teflon 7AJ 80 weight φ and glass fiber 20 weight φ was compression molded as a 4F resin powder at a molding pressure of 500 kg/i in the same manner as in Comparative Example 1 to obtain a density of 2.
．． After obtaining a 30 g/- preform, this was fired and cooled in the same manner as in Comparative Example 1 to obtain a 4F resin molded product having a density of 2.29 g/cffl.

Comparative Example 4 A mixture of the above-mentioned Teflon 7AJ80 weight ratio, glass fiber 15 weight weight, and molybdenum disulfide 5 weight φ was used as a 4F resin powder in the same manner as in Comparative Example 1 under a molding pressure of 500 kg.
/- to obtain a preformed body with a density of 2.26 g/-, which was then fired and cooled in the same manner as in Comparative Example 1 to a density of 2.2 g/-.
A 4F resin molded article weighing 6 g/- was obtained.

Typical characteristic values of the 4F resin molded bodies produced according to the above Examples and Comparative Examples are listed in Tables 1 to 4 in comparison.

Among the compressive properties, compressive strength and compressive elastic modulus are determined according to ASTM D6.
Table 1 shows the results of the test based on ASTM D.95, and Table 2 shows the results of the compression creep resistance test based on ASTM D 621.

In addition, the results of the tensile IJ-pull fracture strength test in Table 3 are A
The test method is based on STMD 1708, that is, a test film with a thickness of 1 mvt is subjected to a tensile stress of 110 ky/i, and the ambient temperature is adjusted to 1°C/min.
The temperature at which the sample undergoes tensile creep failure was measured by increasing the temperature from room temperature to 200°C at a heating rate of .

It is now possible to produce a compression molded body using a conventional compression molding method using modified 4F resin powder, which has been extremely difficult in the past.
It has extremely superior compression creep resistance, tensile creep rupture strength, compressive strength, and flexibility, especially at high temperatures, compared to F resin shaped bodies and filled 4F resin molded bodies, and has the inherent heat resistance of 4F resin. , chemical resistance, and electrical properties, it is possible to provide a 4F resin molded product with extremely high utility value.

Claims (1)

[Claims] 1 As tetrafluoroethylene resin powder, 98% by weight or more of tetrafluoroethylene and perfluoroalkyltrifluoroethylene having 3 to 10 carbon atoms or 3 carbon atoms
A step of applying shear force by stirring to a commercially available tetrafluoride ethylene resin powder for paste extrusion, which is made into granules by emulsion polymerization of ~10 oxyperfluoroalkyl l-IJ fluoroethylenes, to form a fine powder. , from this fine powder to a density of 1.60 to 2.15 g by normal compression molding method.
1. A method for producing a tetrafluoroethylene resin molded article, comprising the steps of: molding a preformed body of /criL, and further firing the preformed body in air or a gas containing oxygen.