JPH07278314A - Production of polytetrafluoroethylene granulated powder - Google Patents

Abstract

PURPOSE:To obtain the subject powder useful for a thin molded article having high bulk density, flexibility, powder fluidity and mechanical properties of molded article without causing environmental pollution, by blending unbaked polytetrafluoroethylene powder having a specific particle diameter with water and a specific hydrofluorocarbon and stirring. CONSTITUTION:Unbaked polytetrafluoroethylene powder having <=200mum average particle diameter is mixed with (A) water and (B) a 4-10C hydrofluorocarbon in 1<= the number of Hs<= the number of Fs, stirred and granulated to give the objective powder. The component B is preferably C4H2F8, C4H4F6, C4H5F5, C5HF11, C5H2F10, C6HF13, C6H5F9, C7HF15, C8HF17, C9HF19, a compound of formula I, a compound of formula II or a compound of formula III.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a granulated powder of polytetrafluoroethylene (hereinafter referred to as PTFE),
More specifically, it relates to a method for producing a granulated powder of PTFE using hydrofluorocarbon that causes less environmental damage.

[0002]

2. Description of the Related Art Since PTFE powder cannot be melt-molded like a thermoplastic resin or a hot-melt resin, it is used for molding in the form of powder. Therefore, PTFE molding requires special powder characteristics. One of its characteristics is that it has good powder flowability, and it is also required that it has a large bulk density and that it is not easily broken and not too brittle.

By the way, since the primary powder obtained by finely pulverizing the granular solid of PTFE obtained by suspension polymerization does not have the above-mentioned powder characteristics, the PTFE powder is agitated and agglomerated in a solvent to be granulated, and the powder is flowed. A material having improved moldability such as properties and bulk density is used for molding. As a granulation method of PTFE,
A method using only an organic solvent as a medium, a method utilizing dispersion in water, and a method using a two-phase liquid medium of water and an organic solvent are known.

As the above organic solvent, it is insoluble in water and
A physical property in which the surface tension at 25 ° C. is 35 dynes / cm or less in order to moisten TFE, and the recovery temperature of the organic solvent, that is, the boiling point of the organic solvent is 30 to 150 ° C. in order to obtain a PTFE granulated powder having an appropriate softness. It is known to use the organic solvent described in JP-B-44-22619 and JP-A-4-13729.

Specifically, CCl ₄ , C ₂ Cl ₄ , CC
l ₃ F, C ₂ Cl ₃ F _3, C ₂ Cl ₄ F _2, Cl (CF ₂ C
FCl) _m Cl [where m is an integer of 2 to 4], C ₃ Cl
₃ F ₅ , C ₂ Cl ₂ F ₃ H, C ₂ Cl ₂ FH _3, C ₃ Cl
_{An example is 2} F ₅ H halogenated hydrocarbon.

By the way, in recent years, ozone layer depletion has been taken up internationally as a problem of destructing the global environment, and chlorofluorocarbon has been pointed out as the causative substance thereof, and it is heading for global abolition. Therefore, it is necessary to stop the use of chlorofluorocarbon when producing a granulated powder of PTFE.

[0007]

Under these circumstances, the present invention has an excellent ozone depletion potential and is an excellent powder without using chlorofluorocarbons or perfluorocarbons that contribute to global warming. It was made for the purpose of providing a method for industrially producing a granulated powder of PTFE having fluidity and high bulk density, which is industrially advantageous.

[0008]

The present invention has an average particle size of 20.
An unsintered PTFE powder having a particle size of 0 μm or less is mixed with water and a carbon number of 4 to 4
The present invention provides a method for producing a PTFE granulated powder, which comprises mixing with 10 hydrofluorocarbons (where 1 ≦ number of hydrogens ≦ number of fluorines) and stirring to granulate.

The PTFE powder used in the present invention includes, for example, a homopolymer of tetrafluoroethylene (hereinafter referred to as TFE) and a polymer of TFE modified with 2% by weight or less of a copolymerizable monomer. . Examples of the modifier include C3-12 perfluoroalkene (eg, hexafluoropropylene), C3-12.
Perfluoro (alkyl vinyl ether) (for example, perfluoro (propyl vinyl ether)), etc., and the copolymer modified with these does not have melt processability like PTFE.

As the PTFE powder, an unsintered powder obtained by finely pulverizing these polymers to an average particle size of 200 μm or less is used. If the particle size is large, the bulk density of the granulated powder is low, the voids are likely to remain in the molded product, and the uniformity thereof is impaired. The unsintered PTFE powder in the present invention is a PTFE powder that has not been heated above its melting point after polymerization and is suitable for granulation.

The organic solvent used in the present invention has 4 to 4 carbon atoms.
10 hydrofluorocarbons (where 1 ≦ number of hydrogens ≦ number of fluorines). If the carbon number is 3 or less, the boiling point will be too low, and if it is 11 or more, the boiling point will be too high to efficiently obtain a granulated product having an appropriate softness.
The boiling point of the hydrofluorocarbon is preferably 40 to 130 ° C. In addition, in the case of no hydrogen, that is, in the case of perfluorocarbon, the global warming potential is large, and conversely, when the number of hydrogen is larger than the number of fluorine, the surface tension is high and the wetness of the PTFE powder is poor, and preferable particles are obtained. Absent.

Particularly preferred organic solvents are C ₄ H ₂ F ₈ (eg H (CF ₂ ) ₄ H), C ₄ H ₄ F ₆ (eg F).
(CHF) ₄ F), C ₄ H ₅ F ₅ (eg CF ₃ CH
₂ CF ₂ CH ₃ ), C ₅ HF ₁₁ (for example (CF ₃ ) ₂
CFCF ₂ CF ₂ H), C ₅ H ₂ F ₁₀ (eg CF ₃
CF (CHF ₂ ) CF ₂ CHF ₂ ), C ₆ HF ₁₃ (eg H (CF ₂ ) ₆ F), C ₆ H ₅ F ₉ (eg F
(CF ₂ ) ₄ CH ₂ CH ₃ ), C ₇ HF ₁₅ , C ₈ HF ₁₇
(Eg, H (CF ₂ ) ₈ F), C ₉ HF ₁₉ and
It is at least one kind of hydrofluorocarbon selected from the group consisting of:

[0013]

[Chemical 2]

These hydrofluorocarbons may be used in combination of two or more kinds. Especially, the surface tension 15
Dyne / cm or less is preferable.

These hydrofluorocarbons are more advantageous than C ₃ Cl ₂ F ₅ H and the like because they do not cause ozone layer depletion. Moreover, the above hydrofluorocarbons have a surface tension of, for example, C ₆ HF ₁₃ of 13.4 dyne /
cm and C ₆ H ₅ F ₉ are 13.6 dyne / cm, which is smaller than 16 dyne / cm or more of halogenated hydrocarbons. Therefore, by using the hydrofluorocarbon, the PTFE powder becomes wet in the medium and easily aggregates during stirring, and the granules have a uniform interior, a high bulk density with few voids, and a smooth surface and improved fluidity. A powder is obtained. The hydrofluorocarbon was selected because it is chemically stable and its boiling point is suitable for the granulation conditions.

When only the hydrofluorocarbon is used as the medium, the inside of the PTFE granulated product becomes hard, but the hydrofluorocarbon of the present invention is mixed with water.
Although the reason is not clear, the PTFE powder is appropriately moistened by using it as a phase liquid medium, an agglomerate does not proceed excessively and an appropriately soft granulated product is obtained, and the physical properties of the molded product are improved.

The ratio of water / hydrofluorocarbon / PTFE powder used in the present invention is usually 2 to 10 / 0.2.
3.0 / 1 (weight ratio) is preferably used. The order of mixing these is not particularly limited, but preferably P
First, contact the TFE powder with the hydrofluorocarbon,
Wetting the PTFE powder is preferred to avoid particle size variation of the PTFE granulated powder.

In the present invention, the temperature at the time of contact treatment with water is important, and it is preferably the boiling point of the hydrofluorocarbon or less, specifically 40 to 120 ° C. The treatment time is usually about 15 minutes to 10 hours within the above temperature range.

The contact treatment with water in the present invention is usually
It is carried out by stirring a mixture of PTFE and water moistened with the granulation medium under the above-mentioned conditions in a processing apparatus equipped with a stirring blade. Further, in order to obtain a granulated powder having a uniform particle size distribution, strong stirring to some extent is preferable. As a specific stirring condition, the peripheral speed of the stirring blade is usually 1 to 50 m / sec.

The above PTFE powder is mixed with a filler of powder such as glass fiber, carbon fiber, bronze, graphite, molybdenum disulfide, and other melt-moldable fluororesin or heat-resistant resin to prepare a PTFE composition. Granular powder can also be produced. When compounding a filler,
Especially when the blending ratio of the filler is large, the average particle diameter is 0.1 to 0.5 μm, which is effective in preventing the dispersion of the filler.
The PTFE colloidal dispersion of can be used. The amount of the colloidal dispersion used is 1 to 5 with respect to the PTFE powder.
Weight percent is preferred. The PTFE powder, the other filler, the fluororesin and the like are uniformly mixed in a dry manner, and the powder is mixed by stirring in a two-phase liquid medium of water and hydrofluorocarbon.

[0021]

EXAMPLE A mixer (Toshiba MX-393GN) having an internal volume of 2 liters was used for mixing and stirring. Put 300 g of PTFE powder having an average particle size of 40 μm by suspension polymerization in a mixer,
Hydrofluorocarbon 135c of Examples 1 to 8 shown in Table 1
After adding c, 1000 cc of water was added and stirred at room temperature for 5 minutes to granulate the PTFE powder. The peripheral speed of the stirring blade is 20
It was m / sec. In addition, Example 9 is a comparative example.

After granulation, the PTFE granulated powder was separated by filtration and dried in an oven at 120 ° C. for 3 hours. The average particle size, bulk density and powder fluidity (slit flow) of the obtained granulated powder were measured. Further, the tensile strength, the elongation, and the dielectric breakdown voltage of the molded product prepared by molding the granulated powder were measured. The method of each test is shown below. The test results are also shown in Table 1.

[Average particle size] 16, 20, 2 from the top
Using standard sieves of 4, 28, 35, 60, and 150 meshes, the weight percentage of the powder remaining on each sieve was obtained, and the 50% particle size on the logarithmic establishment paper was calculated as the average particle size (unit: μm).
And

[Bulk Density] According to JIS K 6891 (the apparent density (unit: g / cc) is the value obtained by dividing the weight of a sample dropped in a cylindrical container having an internal volume of 100 cc from a damper and scraped off with a flat plate by 100 cc). Establish).

[Slit flow] Using the slit flow tester shown in FIG. 1, 100 g of a sample passed through a 9-mesh screen at 25 ° C. was placed in the first hopper 1 (length 80 mm,
Cross section 57mm x 27mm), put into the lower door 2 of the hopper
To open the second hopper 3 (bottom angle 60 °, depth 6
4 mm side plate). The connecting rod 7 of the inclined side plate 4 of the second hopper is opened at a constant speed to expand the opening when the polymer 50g in the hopper flows out (the width of the gap, that is, the scale 6 indicating the opening of the slit).
The flowability (unit: mm) is indicated by. H ₁ is 68 mm,
H ₂ is 88 mm.

[Molding conditions] PTFE granulated powder 1700 g
Was placed in a cylindrical mold of 108 mmφ × 36 mmφ × 100 mmH, pressed at a pressure of 320 kg / cm ² , and operated in an oven at a temperature raising / lowering rate of 70 ° C./h to 380
Baking was performed at 4 ° C. for 4 hours. 0.5m from this molded product
m and 0.1 mm thick sheets were cut.

[Tensile Strength and Tensile Elongation] Thickness 0.5 m
Tensile strength (unit: kg / cm ² ) and tensile elongation (unit:%) were measured using a sheet of m according to JIS K 6891.

[Dielectric Breakdown Voltage] Using a sheet having a thickness of 0.1 mm, a dielectric breakdown voltage test was conducted according to JIS K 6891. Dielectric breakdown voltage (unit: kV / 0.1mm)
Is inversely proportional to the amount of voids left in the molded product.

[0029]

[Table 1]

[0030]

EFFECT OF THE INVENTION By the production method of the present invention, a relatively soft PTFE granulated powder having excellent powder fluidity and high bulk density can be obtained, which is particularly useful as a raw material for a thin molded product. Also,
The PTFE granulated powder gives molded articles with excellent mechanical properties.

[Brief description of drawings]

FIG. 1 is a sectional view showing the function and main dimensions of a slit flow tester for examining powder fluidity.

[Explanation of Codes] 1: First hopper 2: First hopper lower door 3: Second hopper 4: Movable rectangular side plate of second hopper 5: Slit 6: Scale indicating the opening of the slit (slit flow is m
(opening degree indicated by m) 7: connecting rod of the moving side plate of the second hopper 8: dish for receiving falling PTFE granulated powder

Claims (2)

[Claims] 1. An unsintered polytetrafluoroethylene powder having an average particle size of 200 μm or less is mixed with water and a hydrofluorocarbon having 4 to 10 carbon atoms (where 1 ≦ number of hydrogen ≦ number of fluorine) and stirred. A method for producing a polytetrafluoroethylene granulated powder, comprising: 2. A hydrofluorocarbon is C ₄ H ₂ F.
₈ , C ₄ H ₄ F ₆ , C ₄ H ₅ F ₅ , C ₅ HF ₁₁ , C ₅ H
₂ F ₁₀ , C ₆ HF ₁₃ , C ₆ H ₅ F ₉ , C ₇ HF ₁₅ , C ₈
The method for producing a polytetrafluoroethylene granulated powder according to claim 1, which is at least one selected from HF ₁₇ , C ₉ HF ₁₉ and Chemical formula 1. [Chemical 1]