JP3263235B2 - Method for producing granulated powder of polytetrafluoroethylene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a granulated powder of polytetrafluoroethylene (hereinafter referred to as PTFE), and more particularly, to a method of producing a granulated powder of PTFE using a hydrofluorocarbon which hardly causes environmental destruction. It relates to a manufacturing method.

[0002]

BACKGROUND ART PTFE powder can not be different melt molding the thermoplastic resin and the heat-fusible resin, it is subjected to molding remain in powder form. Therefore, special powder characteristics are required for the PTFE powder . As the characteristics, the powder flowability rather good, the bulk density is rather large, unbreakable, it is required that not too brittle.

[0003] Since the suspension polymerized primary powder a particulate solid was milled for PTFE obtained does not have the above powder characteristics, and granulated while stirring aggregating the primary powder in a solvent, the powder flowability What improved the moldability, such as bulk density, is used for molding. Known methods for granulating PTFE powder include a method using only an organic solvent as a medium, a method using dispersion in water, and a method using a two-phase liquid medium of water and an organic solvent.

[0004] As the above-mentioned organic solvent, P does not dissolve in water.
The surface tension at 25 ° C is 35 to wet the TFE powder.
Dyne / cm or less, and PT with appropriate softness
To obtain FE granulated powder recovery temperature Sunawa Chi boiling point 3
It is known to use an organic solvent having a physical property of 0 to 150 ° C. (JP-B-44-21919, JP-A-4-137).
29).

Specifically, CCl ₄ , C ₂ Cl ₄ , CCl ₃
F, C ₂ Cl ₃ F _{3 ,} C ₂ Cl ₄ F _{2 ,} Cl (CF ₂ CFCl) _m
Cl (where m is an integer of 2 to 4 ) , C ₃ Cl ₃ F ₅ , C ₂ C
_{l 2 F 3 H, C 2} Cl 2 FH 3, C 3 Cl 2 F 5 H halogenated hydrocarbons are exemplified.

[0006] the near years, destruction of the ozone layer is internationally taken up as destruction problem of the global environment, chlorofluorocarbons has been pointed out as the causative agent, we are heading in the direction of the worldwide abolition. For this reason, it is necessary to stop using chlorofluorocarbon even when producing PTFE granulated powder.
Oh Ru.

[0007]

SUMMARY OF THE INVENTION Under such circumstances, the present invention provides an excellent powder without using chlorofluorocarbon or perfluorocarbon which has a large ozone depletion potential and contributes to global warming. the granulated powder PTFE having flowability and high bulk density, and to provide an industrially method advantageously produced.

[0008]

According to the present invention, an average particle size of 20 is provided.
Unfired PTFE powder of 0 μm or less is mixed with water and carbon
A method for producing a PTFE granulated powder, comprising mixing with 10 hydrofluorocarbons (where 1 ≦ the number of hydrogen atoms ≦ the number of fluorine atoms ), stirring and granulating.
You.

[0009] PTFE powder used in the present invention, such as tetrafluoroethylene (hereinafter referred to as TFE) homopolymers, and the polymer of the modified TFE with 2% by weight of copolymerizable monomers included. Examples of the above monomers include perfluoroalkenes having 3 to 12 carbon atoms (e.g., hexafluoropropylene), and 3 to 12 carbon atoms.
12 perfluoro (alkyl vinyl ether) (eg, perfluoro (propyl vinyl ether)) and the like
Ani Gerare, in these modified with the copolymer having no PTFE similar melt processability.

[0010] As the PTFE powder, unsintered PTFE powder was finely pulverized these polymers to average particle size below 200μm
The end is used. Large particle size and the bulk density of granulated powder is low, voids are liable to remain in the molded article, since the uniformity is impaired, preferably 70μm or less of the PTFE powder is used. The PTFE powder of unsintered in the present invention, after polymerization is that the powder of PTFE which is not heated above its melting point, you suitable for granulation.

[0011] The organic solvent used in the present invention, 4 carbon atoms
10 hydrofluorocarbon (where, 1 ≦ hydrogen atoms
(Number of children ≦ number of fluorine atoms ). Number boiling point low to skills If it is 3 or less carbon atoms, also the granulated powder having a certain when moderate softness and boiling is too high at 11 or more can not be obtained efficiently. The boiling point of the hydrofluorocarbon is 40 to 1
30 ° C. is preferably employed. Further, there is no hydrogen, i.e. large global warming potential when perfluorocarbon, even if the number of reverse hydrogen atom is larger than the number of fluorine atoms, is poor wettability of the surface tension is high PTFE powder, preferably concrete No granular powder is obtained.

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 (CH
F) ₄ F), C ₄ H ₅ F ₅ (eg CF ₃ CH ₂ CF ₂ C
H ₃ ), C ₅ HF ₁₁ (for example, (CF ₃ ) ₂ CFCF ₂ CF _{2
H), C 5 H 2 F} 10 ( e.g. 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 H
F ₁₅ , C ₈ HF ₁₇ (eg, H (CF ₂ ) ₈ F), C ₉ HF
_19, 1,1,2,2,3,3,4,4,5,6- Dekafu
Fluorocyclohexane, 1,1,2,2,3,3,4
5,5,6-decafluorocyclohexane and 1-to
Trifluoromethyl-1,2,2,3,3,4,4,5
It is at least one kind of hydrofluorocarbon selected from the group consisting of 5,6-decafluorocyclohexane .

[0013]

These hydrofluorocarbons may be used in combination of two or more. In particular, the surface tension 15
Dyne / cm or less is preferred.

These hydrofluorocarbons are more advantageous than C ₃ Cl ₂ F ₅ H and the like because they do not cause the ozone layer destruction. In addition, the above hydrofluorocarbon has a surface tension of, for example, C ₆ HF ₁₃ of 13.4 dynes / c.
m, C ₆ H ₅ F ₉ is 13.6 dynes / cm, smaller than said Ha <br/> of halogenated hydrocarbons 16 dyne / cm or more. Therefore, by using the hydrofluorocarbon, the PTFE powder is moistened in the medium and easily agglomerated during stirring, and has a uniform interior, few voids , a high bulk density, a smooth surface and improved fluidity. A granular powder is obtained. Further, the hydrofluorocarbon is chemically stable, its boiling point you apply to granulation conditions.

When only the hydrofluorocarbon is used as the medium, the inside of the PTFE granulated powder is hardened. However, the reason is obvious by using the hydrofluorocarbon of the present invention as a two-phase liquid medium with water. However, the PTFE powder is appropriately moistened, the agglomeration does not proceed excessively, and a PTFE granulated powder having an appropriate softness 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 from 2 to 10 / 0.2 to
3.0 / 1 (weight ratio) is preferably used. Although the order of mixing is not particularly limited, is first contacted with P TFE powder and hydrofluorocarbon, it is preferable to avoid the particle size variation of PTFE granulated powder to wet the PTFE powder.

In the present invention, the temperature during the contact treatment with water is important, and the temperature is preferably lower than the boiling point of the hydrofluorocarbon, specifically 40 to 120 ° C. The processing time is usually about 15 minutes to 10 hours in the above temperature range.

The contact treatment with water in the present invention is usually carried out by
The treatment is carried out by stirring a mixture of PTFE powder and water wetted with a granulating medium under the above-mentioned conditions in a processing apparatus provided with stirring blades. Further, in order to obtain a granulated powder having a uniform particle size distribution, a certain amount of strong stirring is preferable. Concretely
As for the peripheral speed of the stirring blade, usually 1 to 50 m / sec is adopted.

[0020] Glass fiber P TFE powder, carbon fiber, bronze, graphite, disulfide filler or a powder such as molybdenum, granulation of the molten moldable other fluororesin and heat-resistant resin such as distribution combined PTFE composition Powders can also be produced. PTF having an average particle size of 0.1 to 0.5 μm, which is effective in preventing the dispersion of the filler when the filler is blended, particularly when the blending ratio of the filler is large.
Kill in use E colloidal dispersion. The use amount of the colloidal dispersion is preferably 1 to 5% by weight based on the PTFE powder.
PTFE powder and other fillers and a fluororesin such uniformly mixed dry <br/> formula, stirred mixture is mixed in a 2-phase liquid medium of water and hydrofluorocarbon.

[0021]

[Example] in volume 2-liter mixer (Toshiba MX-3
93GN ), 300 g of suspension-polymerized PTFE powder having an average particle size of 40 μm was added, and 135 cc of the hydrofluorocarbons of Examples 1 to 8 shown in Table 1 were added. Then, 1000 cc of water was added, and the mixture was stirred at room temperature for 5 minutes to produce PTFE powder. Granulated. The peripheral speed of the stirring blade was 20 m / sec. Example 9 is a comparative example.

After the granulation, the granulated PTFE 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, elongation, and dielectric breakdown voltage of the molded product obtained 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, 24, 28, 35, 60, 15 in order from the top
It was: a laminate of a 0 mesh standard sieve, average particle size 50% particle diameter on a logarithmic probability paper obtains the ratio of the weight of the powder remaining on each sieve ([mu] m units).

[Bulk density] According to JIS K6891 (The apparent density (unit: g / c) is obtained by dividing the weight of a sample dropped from a damper into a cylindrical container having an inner volume of 100 cc and rubbed with a flat plate by 100 cc.
c)).

[ Powder Fluidity ( Slit Flow ) ] Using a slit flow tester shown in FIG. 1, 100 g of a sample passed through a 9-mesh sieve at 25 ° C. was put into a first hopper 1 (80 mm long, 57 mm × 27 mm cross section). And open the lower door 2 of the hopper at a stretch to open the second hopper 3
(Consisting of a side plate having a base angle of 60 ° and a depth of 64 mm). Open the connecting rod 7 of the inclined plate 4 of the second hopper at a constant speed, the scale indicating the extent (width i.e. the slit gap opening of the opening portion when the polymer 50g was out <br/> flow from the second hopper Table 6) shows the powder fluidity (unit: mm)
I forgot . H ₁ is 68mm, H ₂ is 88mm.

[Molding conditions] 1700 g of the PTFE granulated powder was charged to 108 mmφ × 36 mm
320kg / c in a φ100mmH cylindrical mold
and pressed at a pressure of m ^2, operating at elevating temperature rate of 70 ° C. / time in an oven and subjected to 4 hours firing at 380 ° C.. Sheets having a thickness of 0.5 mm and 0.1 mm were cut from the molded product.

[Tensile Strength and Tensile Elongation] Using a sheet having a thickness of 0.5 mm, a tensile test was conducted in accordance with JIS K6891 and a tensile strength (unit: kg / c) was measured.
m ² ) and tensile elongation (unit:%) were measured.

[Dielectric Breakdown Voltage] Using a sheet having a thickness of 0.1 mm, a dielectric breakdown voltage test was performed according to JIS K6891. The dielectric breakdown voltage (unit: kV / 0.1 mm) is inversely proportional to the amount of void remaining in the molded product.

[0029]

[Table 1]

[0030]

By the production method of the present invention, excellent powder flowability, bulk density is high, Ru relatively soft PTFE granulated powder was obtained. PTFE granulated powder obtained, particularly thin it practical as a molded article of a raw material, gives molded products having excellent mechanical properties.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a slit flow tester for evaluating powder fluidity.

[Explanation of symbols]

1: first hopper 2: the first hopper lower door 3: second hopper 4: second movable plate rectangle of the hopper 5: slit 6: tick marks 7 showing the opening of the slit: variable rotating side plates of the second hopper of the connecting rod 8: receiving dish PTFE granulated powder falling

Claims (2)

(57) [Claims] An unfired polytetrafluoroethylene powder having an average particle diameter of 200 μm or less is mixed with water and a hydrofluorocarbon having 4 to 10 carbon atoms (where 1 ≦ the number of hydrogen atoms ≦ the number of fluorine atoms ), A method for producing a polytetrafluoroethylene granulated powder, which comprises stirring and granulating. 2. The method of claim 1, wherein the 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 H
_{F 13, C 6 H 5 F} 9, C 7 HF 15, C 8 HF 17, C 9 HF 19,
1,1,2,2,3,3,4,4,5,6-decaffluo
Rocyclohexane, 1,1,2,2,3,3,4,5
5,6-decafluorocyclohexane and 1-trif
Fluoromethyl-1,2,2,3,3,4,4,5,5
At least one process for producing a polytetrafluoroethylene granulated powder according to claim 1, wherein selected from the group consisting of 6-decafluoro cyclohexane.