JPH0413729A - Production of polytetrafluoroethylene granulated powder - Google Patents

Abstract

PURPOSE:To obtain the soft title powder being excellent in powder characteristics such as powder fluidity and apparent density by stirring polytetrafluoroethylene powder in two-phase liquid medium consisting of water and hydrocarbon halide. CONSTITUTION:Polytetrafluoroethylene powder having <=200mum average grain size is stirred in a two-phase liquid medium consisting of water and at least one kind of hydrocarbon halide selected from a group consisting of 2,2- dichloro-1,1,1-trifluroethane, 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3- pentafluoro-propane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane to provide the aimed powder.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses polytetrafluoroethylene (PTEE).

The present invention relates to a method for producing a granulated powder (the same applies hereinafter).

[Prior Art] PTFE molding powder is obtained by finely pulverizing coarse powder obtained by suspension polymerization, and is used for molding by compression molding or ram extrusion. The particle size after crushing (-charcoal particle size) is at most 5J1
As mentioned above, the maximum diameter is about 1000 ρ, but it is usually 200 am or less.

As described above, since PTFE powder cannot be melt-molded unlike thermoplastic resins or thermoplastic resins, it is subjected to molding in its powder form. Therefore, special powder properties are required for PTFE molding powder.

One of its characteristics is good powder flowability, and it is also required to have a high bulk specific gravity, and to be hard to break and not too brittle.

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

The present invention relates to the latter wet method, and the organic liquid used in this wet method has a surface tension of 85 dynes/country or less at 25°C and a sludge point of about 30 to 150°C.
It is said that the appropriate
Publication No. 19, Japanese Patent Publication No. 54-40099, Japanese Patent Application Publication No. 1977
7-18730). Specific examples of such organic liquids include aliphatic hydrocarbons, aromatic hydrocarbons, and fluorinated chlorinated hydrocarbons. Such fluorinated chlorinated hydrocarbons include trichlorotrifluoroethane, monofluorotrichloromethane, difluorotetrachloroethane, CI (CF2 CPCI)n C1=CI
Perhalogenated hydrocarbons such as (CF2 CPCI )n C1 and trichloropentafluoropropane are exemplified, and perhalogenated hydrocarbons are mainly used in actual granulation.

[Problems to be Solved by the Invention] Perhalogenated hydrocarbons are preferable as organic liquids used in wet granulation methods from the viewpoint of nonflammability and solvent recovery efficiency, but generally have a boiling point of high <(80 to 130°C), When collecting organic liquid, the temperature becomes high and the granulated powder is exposed to too much heat, which makes the particles hard.As a result, the surface of the molded product becomes rough, and the tensile strength, elongation, gas permeability, electrical insulation, etc. descend. In addition, energy cost is required for recovery, which is also disadvantageous. Additionally, Par/X rhodanized hydrocarbons are said to contribute to the depletion of the ozone layer, making their use undesirable.

[Means to solve the problem]

The present inventors conducted repeated research to find an organic liquid that could solve the above problems in place of perhalogenated hydrocarbons, and found that a molded product that is economically advantageous, has excellent powder properties, and has improved various physical properties. As an organic liquid that gives a low impact on the ozone layer, certain halogenated hydrocarbons having 2 to 3 carbon atoms and having at least one fluorine atom and at least one hydrogen atom give particularly good results. This discovery led to the completion of the present invention.

That is, in the present invention, PTFE powder having an average particle size of 200 or less is mixed with 2,2-dichloro-1,1,1-)lifluoroethane, 1. ■-dichloro-1-fluoroethane, 1.1
- At least one halogenated carbonized member selected from the group consisting of dichloro-2,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane The present invention relates to a method for producing PTFE granulated powder, which is characterized by stirring in a two-phase liquid medium of hydrogen (hereinafter referred to as a specific halogenated hydrocarbon) and water.

[Function and Examples] The specific halogenated hydrocarbon used in the present invention has a surface tension of 35 dynes/cs or less at 25°C,
Specifically, 2,2-dichloro-1,1,1-trifluoroethane (surface tension (25°C): 17 dynes/cs
s boiling point: 27°C), 1.1-dichloro-2,2,8,3,3-pentafluoropropane (16 dyne/am, 32°C), 1.1-dichloro-2,2,8,3,3-pentafluoropropane (16 dyne/am, 32°C) 101,51°C) and 1,3-dikuo
o −1゜1.2.2. : l-vantafluoropropane (18 dynes/country, 56°C). Among these, dichloropentafluoropropane is particularly preferred because it further improves the economy of solvent recovery, powder properties, and various physical properties of molded products. When the boiling point becomes high, the granulated powder becomes hard as described above, while when the boiling point becomes too low, the aggregation becomes incomplete and tends to be easily broken by a small external force.

A particularly preferred boiling point range is 40 to 60°C. These specific halogenated hydrocarbons may be used alone or in combination of two or more. Further, other conventionally used organic liquids may be used in combination, if necessary.

Certain halogenated hydrocarbons form two-phase liquid media with water. The mixing ratio with water varies depending on the type of specific halogenated hydrocarbon and the target average particle size, but usually the water/specific halogenated hydrocarbon (weight ratio) is 2.
071 to 3/1, preferably 10/1 to 5/1.

This two-phase liquid medium consists of approximately 2 ml of water per 1 kg of PTPE powder.
~1ON and certain halogenated hydrocarbons about 0.2-2
．． Use the amount of OfI.

The PTPE powder used in the present invention includes, for example, a homopolymer of tetrafluoroethylene (TPE, hereinafter the same),
TFE modified with 2% by weight or less of a copolymerizable monomer
Contains copolymers of Examples of the modifier include perfluoroalkenes having 3 to 6 carbon atoms (for example, hexafluoropropylene), perfluoroalkenes having 3 to 6 carbon atoms (for example, hexafluoropropylene),
Copolymers modified with these materials do not have melt processability like PTFE. These copolymers are used as a powder that has been ground to an average particle size of 100 microns or less.

When a filler is blended in addition to the above PTFE powder, it can be used in a PTFE colloidal dispersion with an average particle size of 0.1 to 0.5AIIIl, and its use is recommended in order to prevent separation of the filler. It is particularly effective when the filler content is high. The amount of colloidal PTFE used is preferably 1 to 5% by weight based on the PTFE powder. Also, the appropriate time to add it is before adding the halogenated hydrocarbon.

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

That is, the PTFE powder and filler if necessary are mixed uniformly, and the powder is stirred and mixed in a two-phase liquid medium. The temperature of the medium is usually about 10-50°C, preferably 20-40°C.
It is 0°C. Although the stirring conditions affect the powder properties of the resulting PTFE granulated powder, conventionally known stirring conditions are employed in the present invention. Such a conventional wet granulation method for PTFH is described, for example, in the above-mentioned patent publications, as well as in Japanese Patent Publications No. 1549/1980, Japanese Patent Publication No. 17855/1982, and Japanese Patent Application Laid-open No. 849/1984.

The PTFE granulated powder obtained by the production method of the present invention has an average particle size of 200 to 800 pm and an apparent density of about 0.50 to 1.00.
g/cc, powder flowability (angle of repose) of approximately 30 to 45 degrees, especially 30 to 40 degrees, which has excellent powder properties and is relatively soft, and has good pressure transmission properties during compression molding. It produces delicate molded products with excellent tensile strength and elongation and low vapor permeability.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited to these Examples.

Example: In a stainless steel cylindrical granulation tank with a capacity of 3 g and equipped with two baffle plates and a stirrer with two flat blades in the center, 1 liter of water was poured.
500 ml and 300 ml of halogenated hydrocarbon shown in Table 1
Add ml of the mixture. Furthermore, the average particle size is 35Affl
600g of granular type PTFE powder (+) was placed in a granulation tank and stirred at a rotation speed of 120 rpm for 5 minutes, then the rotation speed was reduced to 600 rpm and stirred for an additional 30 minutes to agglomerate and granulate the PTPE powder. do.

After stirring, the granulated product is filtered through a 60-mesh wire mesh, and the filtered solid is directly dried 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 resulting granulated powder were examined. In addition, the vapor permeability, dielectric breakdown voltage, tensile strength, and elongation of the molded products produced using each granulated powder were examined.

These results are shown in Table 1. Moreover, the above test was measured in the following manner.

Average particle size: Layer 1O120, 32, 48, BO and 80 mesh standard sieves in order from the top, place the powder on the IO mesh sieve and sieve, calculate the weight of the powder remaining on each sieve, and based on this weight. Log probability 50 on paper
The % particle size is defined as the average particle size (-).

Apparent density: According to JIS K-8891 (inner volume 1
The weight (g) of a sample dropped from a damper into a 00cc stainless steel cylindrical container and scraped off with a flat plate is calculated as the internal volume (CC
) is defined as the apparent density (g/cc)).

Angle of repose: A stainless steel funnel with an inner diameter of 4 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 days at the outlet, 20 m from the floor.
This is done by gently flowing the powder to be measured through the funnel. The powder builds up on the bed until the tip of the pile touches the funnel outlet. Since the powder is deposited in an almost conical shape, the radius γ (am
) and find the angle of respiration according to the following formula.

Angle of repose θ-tan-1(-) γ To measure this "angle of repose", the sample powder must be thoroughly dehumidified and static electricity must be removed in advance. Moreover, the measurement shall be performed at 23°C.

Vapor permeability: 300 g of sample powder was preformed in a cylindrical mold with an inner diameter of 7 hn under a pressure of 300 kg/c-, and then the temperature was increased to 370° C. at a rate of 150° C. per hour in an electric furnace with a stirrer. A block of about 701 mm in diameter and 80 ml in height was obtained by firing at 370°C for 8 hours, and then cooling to room temperature at a rate of 40°C per hour. This tape was then subjected to a vapor permeability test at 40°C in accordance with JIS Z-0208, and the values are expressed in units of g/rrr 24hr.

Tensile strength and elongation: A sheet with a thickness of 1.5 am obtained by preforming under a pressure of 500 kg/c-, firing at 380°C for 3 hours, and cooling outside the furnace. The tensile strength (kg/cj) and elongation (%) are the measured values of the strength and elongation at break of a sample punched with a dumbbell type No. 3 specified in -8031.
It is determined that

Dielectric breakdown voltage: Tape-shaped test piece specified in JIS K 8891 (width 30 m + s, thickness 0.10 ± 0.01
ams about 1 m long is sandwiched between electrodes (a pair of well-polished brass spheres with a diameter of 12.5 fins), and a load of 500 gf' is applied. The voltage is uniformly increased from zero at a rate of I KV/s in air, and the breakdown voltage (KV) is measured.

The test is conducted 10 times with measurement points separated by at least 50 mm, and the average value is determined as the dielectric breakdown voltage (KV).

[Effects of the Invention] According to the production method of the present invention, it is possible to produce a relatively soft PTFP granulated powder that has excellent powder properties such as powder fluidity and apparent density, and it is possible to easily recover the solvent. It can be done efficiently. Furthermore, the obtained PTFE granulated powder provides a molded article that is dense and has excellent mechanical properties.

Procedural amendment

Claims (1)

[Claims] 1 Polytetrafluoroethylene powder with 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, 1,1-dichloro-2 ,2,3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,
A method for producing polytetrafluoroethylene granulated powder, which comprises stirring in a two-phase liquid medium with at least one halogenated hydrocarbon selected from the group consisting of 2,3-pentafluoropropane.