JP2909918B2 - Method for producing polytetrafluoroethylene granulated powder - Google Patents

Description

The present invention relates to a method for producing a granulated powder of polytetrafluoroethylene (PTEE, hereinafter the same).

[Prior Art] PTFE molding powder is obtained by finely pulverizing a coarse powder obtained by suspension polymerization, and is used for compression molding or molding by a ram extrusion method. The particle size (primary particle size) after pulverization is at most 5 μm or more, and is as large as about 1000 μm.
0 μm or less.

As described above, since PTFE powder cannot be melt-molded like thermoplastic resin or hot-melt resin, it is provided for molding in powder form. Therefore, special powder characteristics are required for the PTFE molding powder. One of its properties is that the powder flowability is good, and it is also required that the bulk specific gravity is large and that it is not easily broken and not too brittle.

By the way, since the primary powder of PTFE does not have the above-mentioned powder characteristics, usually, PTFE powder is stirred and agglomerated in a solvent, granulated and used for molding. The granulation method includes a dry method using only a water-insoluble organic liquid as a solvent and a dry method using water and an organic liquid.
There is a wet method performed in a phase liquid medium.

The present invention relates to the latter wet method, and as the organic liquid used in this wet method, those having a surface tension at 25 ° C of 35 dynes / cm or less and a boiling point of about 30 to 150 ° C are suitable. (JP-B-44-22719, JP-B-54-40099, JP-A-57-18730, etc.).
Specific examples of such organic liquids include fluorinated hydrocarbons in addition to aliphatic hydrocarbons and aromatic hydrocarbons. Such fluorinated hydrocarbons include trichlorotrifluoroethane, monofluorotrichloromethane, difluorotetrachloroethane, Cl (CF ₂ CFCl) nCl, Cl (CF
₂ CFCl) NCL, is exemplified perhalogenated hydrocarbons, such as trichloro-pentafluoropropane, actual perhalogenated hydrocarbons granulation is used mainly.

[Problems to be Solved by the Invention] Perhalogenated hydrocarbons are preferred as organic liquids used in wet granulation in view of nonflammability, solvent recovery efficiency, etc., but generally have a high boiling point (80 to 130 ° C.) When collecting the liquid, the temperature becomes high, and the granulated powder is heated too much, so that the particles become hard.As a result, the surface of the molded product becomes rough, and the tensile strength and elongation, gas permeability, electrical insulation, etc. descend. Further, energy cost is required for recovery, which is disadvantageous also in this point. In addition, perhalogenated hydrocarbons are said to contribute to the ozone depletion, and their use is considered undesirable.

[Means for Solving the Problems] The present inventors have conducted repeated studies to find an organic liquid that can solve the above-mentioned problems instead of perhalogenated hydrocarbons. As an organic liquid which gives a molded article having excellent and improved physical properties and has little effect on the ozone layer, it is a specific one of halogenated hydrocarbons having 2 or 3 carbon atoms each having at least one fluorine atom and one hydrogen atom. Have been found to give particularly good results, and have completed the present invention.

That is, the present invention provides PTFE powder having an average particle size of 200 μm or less by using 2,2-dichloro-1,1,1-trifluoroethane, 1,1
-Dichloro-1-fluoroethane, 1,1-dichloro-2,
At least one halogenated hydrocarbon selected from the group consisting of 2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (hereinafter, referred to as
A PTFE granulated powder characterized by stirring in a two-phase liquid medium of a specific halogenated hydrocarbon) and water.

[Actions and Examples] The specific halogenated hydrocarbon used in the present invention has a surface tension of not more than 35 dynes / cm at 25 ° C. Specifically, 2,2-dichloro-1,1,1 -Trifluoroethane (surface tension (25 ° C): 17 dynes / cm, boiling point: 27 ° C), 1,1-
Dichloro-1-fluoroethane (20 dynes / cm, 32
° C), 1,1-dichloro-2,2,3,3,3-pentafluoropropane (16 dynes / cm, 51 ° C) and 1,3-dichloro-1,1,
2,2,3-Pantafluoropropane (18 dynes / cm, 56 ° C)
It is. Among these, dichloropentafluoropropane is particularly preferred because it further improves the economics of solvent recovery, powder properties, and various physical properties of molded articles. When the boiling point is high, the granulated powder is shaped as described above. On the other hand, when the boiling point is too low, agglomeration becomes incomplete and tends to be broken by a small external force. A particularly preferred boiling point range is 40 to
60 ° C. These specific halogenated hydrocarbons are used alone or in combination of two or more. Further, if necessary, other conventionally used organic liquids may be used in combination.

Certain halogenated hydrocarbons combine with water to form a two-phase liquid medium. The mixing ratio with water varies depending on the type of the specific halogenated hydrocarbon and the desired average particle size. Usually, water / specific halogenated hydrocarbon (weight ratio) is
It is 20 / 1-30 / 1, preferably 10 / 1-5 / 1. This two-phase liquid medium uses about 2 to 10 water and about 0.2 to 2.0 specific halogenated hydrocarbons per kg of PTFE powder.

The PTFE powder used in the present invention includes, for example, a homopolymer of tetrafluoroethylene (TFE, hereinafter the same), and a copolymer of TFE modified with 2% by weight or less of a copolymerizable monomer. Examples of the modifying agent include a carbon number of 3 to
Examples thereof include six perfluoroalkenes (eg, hexafluoropropylene) and perfluoro (alkyl vinyl ethers) having 3 to 6 carbon atoms (eg, perfluoro (propyl vinyl ether)). Copolymers modified with these are PTFE. Similarly, it does not have melt processability. These copolymers are used as powder ground to an average particle size of 100 μm or less. When a filler is added in addition to the above PTFE powder, a small proportion of PTFE colloidal dispersion having an average particle size of 0.1 to 0.5 μm can be used, and its use is effective in preventing the separation of the filler. It is useful especially when the mixing ratio of the filler is large. Colloidal PTFE
Is preferably 1 to 5% by weight based on the PTFE powder. It is appropriate to add it before the halogenated hydrocarbon is added.

In the production method of the present invention, except that a specific halogenated hydrocarbon is used as the organic liquid, the procedure is substantially the same as that of the conventional wet granulation method of PTFE powder.

That is, the PTFE powder and, if necessary, the filler are uniformly mixed, and this powder is stirred and mixed in a two-phase liquid medium. The temperature of the medium is usually about 10 to 50 ° C, preferably 20 to 40 ° C. Although the stirring conditions affect the powder characteristics of the obtained PTFE granulated powder, conventionally known stirring conditions are employed in the present invention. Such a conventional wet granulation method of PTFE is disclosed in, for example, Japanese Patent Publication No. 47-1549,
It is described in JP-B-49-17855 and JP-A-47-34936.

The PTFE granulated powder obtained by the production method of the present invention has an average particle size.
200-800μm, apparent density about 0.50-1.00g / cc, powder fluidity (angle of repose) about 30-45 degrees, especially 30-40 degrees with excellent powder properties and relatively soft It provides a dense molded product having good pressure transmission during compression molding, excellent tensile strength and elongation, and low vapor permeability.

Next, the production method of the present invention will be described based on examples, but the present invention is not limited to only these examples.

Example Water was placed in a stainless steel cylindrical granulation tank having a capacity of 3 and having two agitating plates having two flat blades in the center and having a stirrer having two blades.
A mixture of 1500 ml and 300 ml of the halogenated hydrocarbon shown in Table 1 is charged. Further, a granular type PTFE powder 600 having an average particle diameter of 35 μm is put into a granulation tank, and the rotational speed is set to 1200 rpm.
After stirring for minutes, the number of revolutions is reduced to 600 rpm, and the mixture is further stirred for 30 minutes to aggregate and granulate the PTFE powder.

After completion of the stirring, the granulated material is filtered through a 60-mesh wire net, and the filtered solid is dried as it is in a drying oven at 150 ° C. for 16 hours to obtain a granulated powder.

The average particle size, apparent density, and powder fluidity (angle of repose) of the obtained granulated powder were examined. Further, with respect to a molded article produced using each of the granulated powders, the vapor permeability, dielectric breakdown voltage, tensile strength and elongation of the molded article were examined.

Table 1 shows the results. Further, the above test was measured in the following manner.

Average particle size: stack 10,20,32,48,60 and 60 mesh standard sieves in order from top, put the powder on 10 mesh sieve, sieve, determine the weight of powder remaining on each sieve, The 50% particle size on the log probability paper is determined as the average particle size (μm) based on this.

Apparent honey: According to JIS K-6891 (Appearance is obtained by dividing the weight (g) of a sample dropped from a damper into a stainless steel cylindrical container with an inner volume of 100 cc and scraped off with a flat plate by the inner volume (cc)) Determine the density (g / cc).

Angle of breath: a stainless steel funnel with an inner diameter of 40 mm at the top, an inner diameter of 6 mm at the bottom, and a height of 40 mm, and an orifice with an inner diameter of 6 mm and a length of 3 mm at the outlet, placed 20 mm away from the floor,
The measurement is performed by gently flowing the powder to be measured through the funnel. The powder accumulates on the bed until the tip of the accumulation touches the outlet of the funnel. Since the powder is deposited in a substantially conical shape, the radius γ (mm) of the bottom surface is measured, and the angle of repose is determined according to the following equation.

In order to measure the "angle of repose", the sample powder must be sufficiently dehumidified and static electricity must be removed in advance. The measurement is performed at 23 ° C.

Vapor permeability: 300 g of sample powder in a cylindrical mold with an inner diameter of 70 mm
Preforming under a pressure of 300 mkg / cm ² , then raising the temperature to 370 ° C at a rate of 150 ° C per hour in an electric furnace with a stirrer, baking at 370 ° C for 8 hours, Approximately 70m in diameter obtained by cooling to room temperature at a rate of 40 ° C
m, a 0.1 mm tape was cut from a block with a height of 80 mm on a lathe, and then the tape was subjected to a vapor permeability test at 40 ° C. in accordance with JIS Z-0208, and the value was expressed in units of g / m ² 24 hr. .

Tensile strength and elongation: Preformed under a pressure of 500 kg / cm ² , fired at 380 ° C for 3 hours, and allowed to cool outside of the furnace to JIS K-6031 from a 1.5 mm thick sheet. The values obtained by measuring the strength and elongation at break of a sample punched with a specified dumbbell-shaped No. 3 mold are defined as tensile strength (kg / cm ² ) and elongation (%).

Dielectric breakdown voltage: Tape-shaped test piece specified in JIS K 6891 (width 30mm, thickness 0.10 ± 0.01mm, length about 1m
A pair of 12.5 mm polished brass spheres) is sandwiched between them, and a load of 500 gf is applied. Voltage from zero to 1KV in air
The breakdown voltage (KV) is measured at a uniform rate of / s. The test is performed 10 times with the measurement points separated from each other by 50 mm or more,
The average value is defined as the dielectric breakdown voltage (KV).

[Effect of the Invention] According to the production method of the present invention, it is possible to produce a relatively soft PTFE granulated powder having excellent powder properties such as powder fluidity and apparent density, and to easily and efficiently recover a solvent. Can be done Also, the obtained PTFE granulated powder,
Gives molded products that are dense and have excellent mechanical properties.

Continuation of the front page (72) Inventor Hirokazu Yukawa 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works (56) References JP-A-63-159438 (JP, A) JP-A-54- 54156 (JP, A) JP-A-51-124147 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 3/12-3/16 C08L 27/18

Claims (1)

(57) [Claims] 1. A polytetrafluoroethylene powder having an average particle size of 200 μm or less is mixed with water and 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane,
At least one member selected from the group consisting of 1,1-dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane A method for producing a polytetrafluoroethylene granulated powder, comprising stirring in a two-phase liquid medium with a halogenated hydrocarbon.