JPH08253600A - Polytetrafluoroethylene fine powder and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a polytetrafluoroethylene fine powder improved, for example, in such points that particle diameters are less scattered and the initial loss at the time of extrusion is less, by stirring an aqueous dispersion of a polytetrafluoroethylene under specified conditions to cause coagulation. CONSTITUTION: This polytetrafluoroethylene fine powder is produced by stirring an aqueous dispersion of a polytetrafluoroethylene in the presence of a water- insoluble organic solvent at a temperature equal to or lower than the room temperature transition point of the polytetrafluoroethylene to cause coagulation. Preferably, the aqueous dispersion of a polytetrafluoroethylene is stirred at a temperature in the range from 10 deg.C or more to that equal to or lower than the room temperature transition point of the polytetrafluoroethylene to cause coagulation. More preferably, the aqueous dispersion of a polytetrafluoroethylene is stirred at a temperature in the range of 10 to 25 deg.C to cause coagulation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polytetrafluoroethylene fine powder and a method for producing the same. More specifically, the powder is a polytetrafluoroethylene fine powder having improved particle size variation, powder fluidity, initial loss during extrusion molding, the magnitude of extrusion pressure and its variation, the degree of fiberization, and the like. Regarding the manufacturing method.

[0002]

2. Description of the Related Art Conventionally, as a method of producing polytetrafluoroethylene fine powder, for example, a method of coagulating an aqueous polytetrafluoroethylene (PTFE) dispersion,
A method of adding a filler to a PTFE aqueous dispersion and adding a water-insoluble organic liquid before or after coagulation, and a non-water-soluble organic liquid having a relatively high boiling point of 30 to 150 ° C. from the start to the end of coagulation. A method of adding a water-soluble organic liquid has been proposed.

However, the PT obtained by these methods is
The FE fine powder has a large variation in particle size, a large initial loss during extrusion molding, a high extrusion pressure, and a large variation in extrusion pressure.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a PTFE fine powder having a small variation in particle size, a small initial loss during extrusion molding, a low extrusion pressure and a small variation thereof, and a method for producing the same. To do.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides PT at a temperature below the room temperature transition point of PTFE in the presence of a water-insoluble organic liquid.
The present invention relates to a method for producing PTFE fine powder by stirring and coagulating an FE aqueous dispersion.

The present invention also provides the P obtained by the above-mentioned manufacturing method.
Regarding TFE fine powder.

[0007]

ACTION AND EXAMPLES In the present invention, the mechanism of action of coagulation of the PTFE particles is not clear, but it can be considered as follows, for example.

The PTFE particles in the aqueous PTFE dispersion are:
It is covered by a monolayer of emulsifier added to stabilize the dispersion of the particles.

When the coagulation is carried out by adding a coagulant, if necessary, while stirring at a temperature below the room temperature transition point of PTFE, the emulsifier is separated from the PTFE particles and the charge density in the system becomes nonuniform. This will trigger the particles to aggregate.

When stirring is continued in such a state, a slurry is formed, and the stirring torque of the dispersion shows a clear peak.

In the present invention, the non-water-soluble organic liquid is added between the time point when the torque becomes maximum and the time point when the torque becomes minimum, so that the non-water-soluble organic liquid is separated from the hydrated layer of the PTFE particles due to the difference in affinity with the PTFE particles. As a result of the replacement with the water-soluble organic liquid, coagulation of the particles is likely to occur, and by keeping the temperature of the system at the room temperature transition temperature of PTFE or lower throughout the entire process, the fibrillation of the PTFE particles becomes higher than the room temperature transition point. Compared with coagulation at temperature, it is less likely to occur, and coagulation can be completed by making hydrophobic, and PTFE fine powder with a uniform particle size can be obtained.

In the present invention, it is also possible to add a filler to the PTFE aqueous dispersion and stir at a temperature below the room temperature transition point of PTFE for coagulation to obtain PTFE fine powder containing filler (hereinafter referred to as FPG). Also called). In this case, the action mechanism of coagulation when the amount of the filler added is less than 1% by weight based on the weight of the PTFE particles is considered to be the same as that described above. , For example:

When an aqueous dispersion containing fillers and PTFE particles is stirred, it immediately begins to coagulate and slurry, which is due to heteroaggregation (ie, aggregation of different particles or particles of different sizes). Therefore, even if the surface charge of the filler and that of the PTFE particles have the same sign, aggregation occurs due to the potential difference between them, and moreover, a large number of PTFE particles are electrically present on the surface of the filler which is larger than the primary particles of PTFE. Adheres due to attractive force. Although it is not clear, it is conceivable that the emulsifier covering the PTFE particles may be slightly dislodged during the process in which such adhesion occurs, and then the emulsifiers may be released in earnest due to the collision of these particles.

The agglomerated particles produced in this manner are
On the other hand, by stirring, the emulsifier is bonded through the PTFE particles that have come off and grows.

At this time, growing particles and uncoagulated P
The TFE particles are electrically coupled to each other, and there is temporarily no convection in the tank (so-called stationary state). However, as described above, there is no clear peak of the stirring torque as in the case where the filler is not used.

When stirring is further continued, the non-coagulated PTFE particles are coagulated, the concentration of the PTFE particles in the PTFE dispersion is lowered, and the stationary state ends, but at this point the water-insoluble organic liquid As described above, FPG in which the filler is uniformly dispersed by the progress of coagulation and the hydrophobicization is obtained by the addition of.

In the case of producing FPG, the coagulant may be added after mixing the filler and the PTFE particles, for example, in order to control the rate of slurry formation.

In the production method of the present invention, as the temporal change of the stirring torque of the PTFE aqueous dispersion, for example, the temporal change of the stirring torque of the dispersion before and after coagulation described in JP-B-56-48528 is described. This can be explained based on the diagram schematically shown.

FIG. 3 is a diagram schematically showing the above.

In FIG. 3, Q is the point of time when the coagulant is added, [A] is the pre-coagulation zone,
[B] is a mid-coagulation zone and [C] is a post-coagulation zone. PTFE in PTFE aqueous dispersion in each zone
The state of particles is colloidal particles in [A], jelly in [B] and hydrophobic in [C]. The term "hydrophobic" in [C] means that dispersed particles in the liquid are not soaked in water, for example, they are in a state in which they immediately settle or float to separate from water when stirring is stopped. .

In the coagulation of the PTFE aqueous dispersion, there is one torque peak (curve 1) and two torque peaks (curve 2) as shown in FIG. The state of the dispersion liquid can be clearly divided into the three zones [A], [B] and [C] as described above by the stirring torque.

That is, when, for example, a coagulant is added with stirring, coagulation starts immediately, the PTFE aqueous dispersion becomes jelly-like, the viscosity of the dispersion increases steadily, and finally when it reaches a peak, it becomes hydrophobic. Begins and the viscosity drops rapidly.

In the case of the curve 1, the peak P is the branch point of these. In the case of curve 2, peak P ₁ is the viscosity peak and P ₂ is the point where hydrophobization begins. When the stirring torque becomes constant, the coagulation completion point R is reached.

In the present invention, the coagulant may be added at the start point Q of the coagulation, for example. The reason for this is, for example, that it is for controlling the rate of slurry formation and for controlling the total coagulation time.

In the present invention, the time for adding the water-insoluble organic liquid is preferably between the peak P in the case of curve 1 and the completion point R of the coagulation, and the peak P1 in the case of curve 2.
Between the coagulation completion point R is preferable.

Further, in the present invention, when a filler is added to the PTFE aqueous dispersion and coagulation is performed, no clear peak as shown in FIG. 3 appears, but the stationary state as described above is caused by the above [B]. Appears in the zone.

The filler may be added at a time earlier than the time Q at which the coagulant is added, for example. This is because the aqueous dispersion begins to form a slurry in earnest when the coagulant is added, and a uniform mixture cannot be obtained even if the filler is added thereafter.

In this case, if the PTFE aqueous dispersion is first added to the coagulation tank and then the filler is added, the filler may be dispersed poorly. Therefore, the aqueous dispersion of the filler may be added to the coagulation tank. Add and then PT with stirring
It is preferable to add the FE aqueous dispersion.

In the present invention, the time for adding the water-insoluble organic liquid when the filler is added as described above may be, for example, from the time when the stationary state is reached to the completion point R of the coagulation. Good.

If a non-water-soluble organic liquid is added in the zone [A], the PTFE particles in the PTFE aqueous dispersion will be stabilized first, leading to granulation of the filler particles, and as a result, in the PTFE aqueous dispersion. The PTFE particles remain in the powder, and the mixing of the PTFE particles and the filler becomes uneven.

The remaining PTFE particles can be coagulated under strong coagulation conditions (for example, strong mechanical force, heating, excess coagulant, etc.), but in this case the uniformity of mixing is further impaired. .

Further, even if the water-insoluble organic liquid is added in the zone [C], the effect of uniform mixing cannot be obtained, and the filler tends to be separated from the PTFE fine powder at the time of hydrophobization.

Examples of the aqueous PTFE dispersion used in the present invention include those usually obtained by emulsion polymerization of tetrafluoroethylene (TFE).

In the above polymerization, for example, chlorotrifluoroethylene, hexafluoropropylene,
TFE such as perfluoro (alkyl vinyl ether)
A small amount of a monomer capable of being copolymerized with may be added.

The average particle diameter of the PTFE particles in the PTFE aqueous dispersion is, for example, 0.05 to 0.6 μm,
It is more preferable that the fine particles are present as fine particles of 0.1 to 0.5 μm, and further preferably 0.2 to 0.4 μm, and the concentration of the fine particles is, for example, 5 to 70% (wt%, the same applies hereinafter), It is more preferably 10 to 40%, further preferably 10 to 20%.

In the present invention, the room temperature transition of PTFE includes a thermodynamic phase change such as a change in the crystal structure of PTFE occurring near room temperature, and the temperature at which such a phase change occurs is called the room temperature transition point. , In the present invention P
The room temperature transition point of TFE refers to a transition that usually exists in the vicinity of 10 ° C. to 30 ° C., and can be measured by differential thermal measurement, viscoelasticity measurement, or the like.

The present inventors have found that at temperatures below the room temperature transition point, the PTFE in the PTFE aqueous dispersion is cooled.
By performing a series of steps in the present invention such as coagulating particles, fibrillation is less likely to occur as compared with coagulation at a temperature higher than the room temperature transition point, resulting in uniform particle size and stable extrusion. It was found that FP particles having good properties can be obtained. Moreover, it was surprisingly found that the initial loss during extrusion is significantly reduced.

The temperature may be 30 ° C. or lower, which is the transition point on the high temperature side, but is preferably 10 to 25 ° C., more preferably 17 to 20 ° C.
If the temperature is lower than 10 ° C, the slurry tends to be mild and the peak tends to be difficult to identify. If the temperature exceeds 25 ° C, the particle size tends to vary between batches, and the improvement tends to be insufficient.

The water-insoluble organic liquid used in the present invention may be any liquid which is insoluble in water or can dissolve a small amount in water to form micelles when stirred in water, for example, hydrofluorocarbon. , Hydrochlorocarbons, hydrochlorofluorocarbons and halogen-free hydrocarbons, chlorocarbons,
Examples include perfluorocarbons, which may be used alone or in combination.

As the hydrofluorocarbon,
For example, 1,1,1,2-tetrafluoroethane, 1,
1-difluoroethane, 1,1,1,3,3-pentafluoropropane, 1,1,1,2,3,3-hexafluoropropane and the like can be mentioned, but coagulate under normal pressure or slight pressure. 1,1,1,3 from the point that
3-pentafluoropropane, 1,1,1,2,3,3
-Hexafluoropropane is preferred.

Examples of the hydrochlorocarbon include methylene chloride, chloroform, trichloroethylene and the like, but methylene chloride is preferable from the viewpoint that it can be coagulated under normal pressure.

Examples of the hydrochlorofluorocarbon include 1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,3,3,3-pentafluoropropane, 1,3-dichloro-1, 1, 2, 2,
3-pentafluoropropane, 1,1-dichloro-3,
Examples thereof include 3,3-trifluoroethane, but 1,1-trifluoroethane and the like have a relatively low boiling point and can be coagulated under normal pressure.
Dichloro-1-fluoroethane, 1,1-dichloro-
2,2,3,3,3-pentafluoropropane is preferred.

Examples of the halogen-free hydrocarbon include aliphatic hydrocarbons and aromatic hydrocarbons.

Examples of the aliphatic hydrocarbon include pentane, hexane, heptane, cyclohexane and cyclopentane, but pentane and cyclopentane are preferable from the viewpoint of coagulation under normal pressure.

Examples of the aromatic hydrocarbon include benzene and toluene.

Examples of the chlorocarbon include tetrachloroethylene.

These non-water-soluble organic liquids are used under normal pressure or under pressure (for example, pressure up to about 10 kg / cm ² G).
Therefore, any liquid may be used at a temperature below the room temperature transition point. Among these water-insoluble organic liquids, 1,1-dichloro-1-fluoroethane, methylene chloride, and 1,1-dichloro-can be used because the coagulation is generally carried out under normal pressure. 2,2,2-trifluoroethane, pentane,
Cyclopentane is preferred, and 1,1-dichloro-1-fluoroethane is more preferred.

The present inventors have found that by using these non-water-soluble organic liquids, PTFE particles are easily coagulated and particles having good powder fluidity can be obtained from the granulation effect.

In the present invention, the aqueous PTFE dispersion may contain a filler.

As the filler, for example, carbonaceous powder, carbonaceous fiber, inorganic powder, inorganic fiber, metal or alloy powder, organic powder or organic fiber, etc. are used.

More specifically, carbonaceous powder or carbonaceous fiber such as carbon black, carbon fiber and graphite, oxidic powder such as feldspar, silica, alumina, titanium oxide and iron oxide, silicon nitride, carbon nitride and nitriding. Aluminum,
Boron Nitride, Zirconium Carbide, Silicon Carbide, Tungsten Carbide, Nickel Carbide, Zirconium Sulfate, Barium Sulfate, Kaolin, Clay, Glass Beads, Glass Balloons and Other Inorganic Powders, Complex Oxide Pigments, Glass Fibers, Alumina Fibers, Potassium Titanate Fiber, inorganic fiber such as silica fiber, copper alloy, zinc flower, molybdenum disulfide, aluminum, metal powder such as aluminum alloy, perfluoroalkoxy resin, perfluoroethylene propene resin, polychlorotrifluoroethylene resin, polyamideimide Resin, polyethersulfone resin, polyetherimide resin, polysulfone resin, polyphenylene sulfide resin, polycarbonate resin, polyimide resin,
Examples of the organic powder or fiber include polyphenylene oxide resin, oxybenzoyl polyester resin, liquid crystal polymer, and the like, but these may be used as a mixture.

These fillers are added to improve the mechanical properties (wear resistance, compressive strength, cold flow resistance) and electrical properties (electrostatic removal) of the molded product.

The addition amount of these fillers is PT
PT because the shape of the molded product is maintained by FE
It may be 60% or less, preferably 45% or less, based on the total weight of FE and filler.

The average particle diameter or the average fiber length of the filler may be, for example, 0.001 to 200 μm.

Examples of the coagulant used in the present invention include water-soluble inorganic salts such as aluminum nitrate, aluminum chloride and magnesium chloride, inorganic acids such as nitric acid, hydrochloric acid and sulfuric acid, organic solvents such as alcohol and acetone, and cations. Examples thereof include surfactants. These coagulants may be used alone or in combination, or may be used as an aqueous solution.

The amount of the water-insoluble organic liquid added is
For example, 10 to 150 per 100 kg of PTFE particles
It is preferably 30 to 120 liters, and if the water-insoluble organic liquid is less than 10 liters, the granulation effect cannot be obtained, and particles having good powder fluidity tend to be difficult to obtain, and 150 liters If it exceeds, the apparent density tends to increase, and it tends to be difficult for the auxiliary agent to penetrate during extrusion molding.

The amount of the coagulant added is, for example, P
For 100 parts of TFE particles (parts by weight, the same applies hereinafter), 0.
5 parts or less, preferably 0.3 parts or less,
The purpose is to control the speed at which the slurry is formed, and if the coagulant exceeds 0.5 parts, it tends to cause poor dispersion.

Examples of the method for producing the PTFE fine powder of the present invention include the following methods.

An aqueous PTFE dispersion (PTFE particle concentration 10 to 20%) is placed in a coagulation tank having an internal volume of 7 liters, and stirring is started by a stirrer at a speed within a range of 250 to 400 rpm.

The temperature of the dispersion liquid is adjusted to a temperature in the range of 10 ° C. or higher and the room temperature transition temperature or lower throughout the entire process.

One minute after the start of stirring, 50 g of an aqueous solution of aluminum nitrate (3%) as a coagulant is added.

The stirring torque of the dispersion liquid in the tank is constantly measured using a torque meter.

The non-water-soluble organic liquid is added all at once or at a rate of 150 cc / 30 seconds from the time when the stirring torque reaches its maximum to the time when it decreases and becomes constant.

When the stirring torque decreases and becomes constant, stirring is stopped and the PTFE fine powder of the present invention can be obtained by a usual method such as filtration, washing with water or drying.

The obtained PTFE fine powder has an average particle diameter of about 400 to 600 μm.

The FPG production method of the present invention includes the following methods.

A coagulation tank having an internal volume of 7 liters was filled with 5 to 5 fillers.
Add an aqueous dispersion containing 45 parts by a stirrer to 250-4
Start stirring at a speed in the range of 00 rpm.

The temperature of the dispersion liquid is adjusted to a temperature in the range of 10 ° C. or higher and the room temperature transition temperature or lower throughout the entire process.

After the stirring is started, an aqueous PTFE dispersion (particle concentration 10 to 20%) is added.

Further, an aqueous solution of a coagulant is added after 1 to 3 minutes.

The stirring torque of the dispersion liquid in the tank is constantly measured using a torque meter.

The non-water-soluble organic liquid is added all at once or at a rate of 150 cc / 30 seconds from the time when the dispersion liquid is in a stationary state until it becomes hydrophobic.

When the granules are formed, the stirring is stopped,
The FP of the present invention can be prepared by a conventional method such as filtration, washing with water or drying.
Get G.

The average particle size of the obtained FPG is about 4
It is from 00 to 800 μm.

The PTFE fine powder and FPG of the present invention have good powder fluidity and excellent extrusion stability, etc., as compared with, for example, conventional PTFE fine powder and FPG.

Next, the present invention will be described more specifically based on examples, but the present invention is not limited to these.

Example 1 333 g of an aqueous filler dispersion (30% aqueous dispersion of Econol E101 (average particle size of about 10 μm, wholly aromatic polyester) manufactured by Sumitomo Chemical Co., Ltd.) was added to a glass cylindrical coagulation tank (contents). Anchor-type stirring blade with a volume of 7,000 ml and a baffle plate with a width of 17 mm vertically attached to the inner wall at opposite positions) and maintaining the temperature of the dispersion liquid at 19 ± 0.5 ° C. using a temperature control jacket. Continue stirring at a speed of 350 rpm using a stirrer with.

Next, 3000 g of an aqueous PTFE dispersion (PTFE having a room temperature transition temperature of 25 ° C.) produced by emulsion polymerization based on the method described in JP-B-56-26242 is added.

After 3 minutes, when 20 g of a coagulant (5% aluminum nitrate aqueous solution) was added, the viscosity rapidly increased and a slurry was formed.

After 4 minutes, it will be in a detention state, so at this time,
150 ml of a water-insoluble organic liquid (1,1-dichloro-1-fluoroethane (referred to as Freon 141b)) is injected at one time.

After 5 minutes, stirring is stopped and coagulation is completed.

Next, the content in the coagulation tank is filtered through a net (# 60) to obtain a hydrous coagulate, which is further dried at 150 ° C. for 12 hours and then the PTFE powder 50 containing the filler of the present invention is added.
After obtaining 0 g, the following test was conducted. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent.

The test was conducted as follows. Average particle size: The average particle size was measured according to JIS K6891-77 5.4. Apparent density: It was performed according to JIS K6892-76 5.4. Extrusion pressure: Mold RR100, auxiliary agent Isopar E and petroleum hydrocarbon synthetic oil (manufactured by Esso Co.) The results are shown in Table 1.

Example 2 In Example 1, a PTFE aqueous dispersion was prepared as in JP-B-5.
Same as Example 1 except that 3125.0 g of the dispersion obtained by the production method described in JP-A-6-26242, 7.7 g of carbon paste (DR600 manufactured by Mikuni pigment) and 37.7 g of zirconium silicate were used as the filler. The PTFE powder containing the filler of the present invention is obtained by the method of
The same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 3 In Example 1, a PTFE aqueous dispersion was prepared as in JP-B-5.
The filler-containing PTFE of the present invention was used in the same manner as in Example 1 except that 3125.0 g of the dispersion obtained by the method described in 6-26242 and 2.5 g of a red pigment (made by Hoechst) were used as the filler. The powder was obtained and the same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 4 In Example 1, as a PTFE aqueous dispersion, a Japanese Patent Publication No.
Dispersion liquid 3125.0 g obtained by the production method described in JP-A-6-26242, carbon paste 1 as a filler
A PTFE powder containing a filler of the present invention was obtained in the same manner as in Example 1 except that 4.3 g was used, and the same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 5 In Example 1, as a PTFE aqueous dispersion, a Japanese Patent Publication No.
The filler-containing PTFE powder of the present invention was obtained in the same manner as in Example 1 except that 3125.0 g of the dispersion obtained by the production method described in 6-26242 and 167.0 g of carbon graphite were used as the filler. The same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 6 In Example 1, 3125.0 g of the dispersion obtained by the method described in Japanese Examined Patent Publication No. 56-26242, 500 g of the aqueous econol dispersion of Example 1 as a filler and 1 as the water-insoluble organic liquid were used. , 1,2,2-Tetrachloro-1,2-difluoroethane (referred to as CFC 112) 1
The PTFE powder containing the filler of the present invention was obtained by the same method as in Example 1 except that 50 cc and a coagulation temperature of 17 ° C. were used, and the same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 7 In Example 1, 3125.0 g of the dispersion obtained by the method described in Japanese Patent Publication No. 56-26242, 500 g of the aqueous econol dispersion of Example 1 as a filler and Freon as a water-insoluble organic liquid. 112 and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC 1
13) and a 1: 1 mixed solution of 150 cc and a coagulation temperature of 19.5 ° C. were used to obtain the PTFE powder containing the filler of the present invention in the same manner as in Example 1, and the same test as in Example 1 was performed. I went. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 8 In Example 1, 3125.0 g of the dispersion obtained by the method described in JP-B-56-26242, 500 g of the enochol aqueous dispersion of Example 1 as a filler and 1 as the water-insoluble organic liquid , 1-Dichloro-2,2
A mixture of 3,3,3-pentafluoropropane and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (called chlorofluorocarbon 225) of 150 cc and a coagulation temperature of 17.1 ° C. were used. Other than the above, the PTFE powder containing the filler of the present invention was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 9 In Example 1, 3125.0 g of the dispersion obtained by the method described in Japanese Examined Patent Publication No. 56-26242, 500 g of the enochol aqueous dispersion of Example 1 as a filler and Freon as a water-insoluble organic liquid. PTFE containing a filler of the present invention was prepared in the same manner as in Example 1 except that 113 150 cc and a coagulation temperature of 19.7 ° C. were used.
The powder was obtained and the same test as in Example 1 was performed. In addition,
There was almost no filler in the drainage when filtered, and the drainage was transparent. The results are shown in Table 1.

Example 10 In Example 1, 3125.0 g of the dispersion obtained by the method described in Japanese Examined Patent Publication No. 56-26242, 500 g of the aqueous econol dispersion of Example 1 as a filler, and chloride as the water-insoluble organic liquid The PTFE containing filler of the present invention was prepared in the same manner as in Example 1 except that 150 cc of methylene and 19.9 ° C. were used as the coagulation temperature.
The powder was obtained and the same test as in Example 1 was performed. In addition,
There was almost no filler in the drainage when filtered, and the drainage was transparent. The results are shown in Table 1.

Example 11 In Example 1, 3125.0 g of the dispersion obtained by the method described in Japanese Examined Patent Publication No. 56-26242, 500 g of the econol aqueous dispersion of Example 1 as a filler and Freon as a water-insoluble organic liquid. The filler-containing PTF of the present invention was prepared in the same manner as in Example 1 except that 141b and 150cc and a coagulation temperature of 19.4 ° C were used.
E powder was obtained and the same test as in Example 1 was performed. In addition, almost no filler was present in the drained liquid after the filtration, and the drained liquid was transparent. The results are shown in Table 1.

Example 12 3000 g of a PTFE aqueous dispersion (F-201 manufactured by Daikin Industries, Ltd.) produced by emulsion polymerization was added to a glass cylindrical coagulation tank (internal volume: 7,000 ml; width of 17 mm at inner wall opposite positions). (A baffle plate is attached vertically) and the temperature of the dispersion is adjusted to 19 ± 0.5 using a temperature control jacket.
While maintaining at 0 ° C., stirring is continued at a speed of 350 rpm using a stirrer having an anchor type stirring blade.

After 3 minutes, when 40 g of a coagulant (5% aluminum nitrate aqueous solution) is added, the viscosity sharply rises and a slurry is formed.

After 4 minutes, the viscosity of the slurry reached its maximum, and at this time, the water-insoluble organic liquid (1,1-dichloro-1
Inject 150 ml of fluoroethane) at a time.

After 5 minutes, stirring is stopped and coagulation is completed.

Next, the content in the coagulation tank was filtered through a net (# 60) to obtain a hydrous coagulate, which was further dried at 150 ° C. for 12 hours to obtain 500 g of the PTFE powder of the present invention. The same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 1 In Example 1, the coagulation temperature was set to 33.2 ° C., the econol aqueous dispersion 333 g of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
In the same manner as in Example 1, was added when the suspension state was reached, PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 2 In Example 1, the coagulation temperature was set to 29.6 ° C., 333 g of the econol aqueous dispersion of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
As a filler, econole aqueous dispersion 33 of Example 1
Using 3 g, a PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 3 In Example 1, the coagulation temperature was set to 30.6 ° C., 333 g of the noecoanol aqueous dispersion of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
In the same manner as in Example 1, was added when the suspension state was reached, PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 4 In Example 1, the coagulation temperature was set to 30.2 ° C., 333 g of the econol aqueous dispersion of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
In the same manner as in Example 1, was added when the suspension state was reached, PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 5 In Example 1, the coagulation temperature was set to 30.1 ° C., 333 g of the econol aqueous dispersion of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
In the same manner as in Example 1, was added when the suspension state was reached, PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

Comparative Example 6 In Example 1, the coagulation temperature was set to 29.5 ° C., 333 g of the econol aqueous dispersion of Example 1 was used as the filler, and Freon 113 150 cc as the water-insoluble organic liquid.
In the same manner as in Example 1, was added when the suspension state was reached, PTFE fine powder containing filler was obtained by the same method as in Example 1, and the same test as in Example 1 was performed. The results are shown in Table 1.

[0105]

[Table 1]

As is clear from the results of Example 1 and Comparative Examples 1 to 6 in Table 1, when the FPG of the present invention coagulates at a temperature lower than the room temperature transition point, the conventional high temperature coagulated product (comparative example 1 to
The extrusion pressure is obviously lower than that of 6). Also,
As is clear from the results of Examples 6 to 11, similar results were obtained even when various solvents were used.

Next, the initial loss and extrusion pressure when extrusion molding was performed using the FPG of the present invention and the FPG of the comparative example were examined.

FIG. 1 shows the FPG of the present invention obtained in Example 1.
In the case of FIG. 2, FIG. 2 is a graph showing the relationship between the extrusion pressure and the time in each of the cases of the FPG obtained in Comparative Example 1.

Further, the initial overshoot is small (arrow portion in FIG. 1), the initial loss is small as a result, and the FPG of the present invention, which is a low temperature coagulation, has better extrusion stability, It can also be seen that the extrusion pressure is low.

[0110]

The PTFE fine powder obtained by the production method of the present invention has a small variation in particle size and an improved powder fluidity, has little initial loss during extrusion molding, and has a low extrusion pressure. The fluctuation is also small.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between extrusion pressure and time during extrusion molding of the FPG of the present invention.

FIG. 2 is a graph showing the relationship between extrusion pressure and time during extrusion molding of a conventional FPG.

FIG. 3 is a graph schematically showing the change over time of the stirring torque of the PTFE aqueous dispersion.

[Explanation of symbols]

1 and 2 Curves showing changes in torque over time [A] Zone before coagulation [B] Zone during coagulation [C] Zone after coagulation G Point when coagulant is added P Branch point P ₁ Viscosity peak P ₂ Hydrophobicization start Point R Coagulation completion point

Claims (9)

[Claims] 1. A process for producing a polytetrafluoroethylene fine powder, which comprises stirring and coagulating an aqueous polytetrafluoroethylene dispersion at a temperature below the room temperature transition point of polytetrafluoroethylene in the presence of a water-insoluble organic liquid. 2. The method according to claim 1, wherein the polytetrafluoroethylene aqueous dispersion is stirred and coagulated at a temperature within the range of 10 ° C. or higher and the room temperature transition point of polytetrafluoroethylene or lower. 3. The method according to claim 1 or 2, wherein the polytetrafluoroethylene aqueous dispersion is stirred and coagulated at a temperature in the range of 10 to 25 ° C. 4. The production method according to claim 1, wherein the water-insoluble organic liquid is added between the time point when the stirring torque of the polytetrafluoroethylene aqueous dispersion liquid becomes maximum and the time point when the stirring torque becomes minimum. 5. The production method according to claim 1, wherein the polytetrafluoroethylene aqueous dispersion contains a filler. 6. The method according to claim 5, wherein the polytetrafluoroethylene aqueous dispersion containing the filler is obtained by mixing the aqueous dispersion of the filler and the aqueous dispersion of polytetrafluoroethylene. . 7. An aqueous dispersion of filler is added to the aqueous dispersion of polytetrafluoroethylene while being stirred at a temperature within a range not higher than the room temperature transition point of polytetrafluoroethylene. A method for producing polytetrafluoroethylene fine powder in which a water-soluble organic liquid is added and agitated to coagulate. 8. The water-insoluble organic liquid is selected from the group consisting of 1,1-dichloro-1-fluoroethane, methylene chloride, pentane, cyclopentane and 1,1-dichloro-2,2,2-trifluoroethane. It is at least 1 sort (s) selected, The manufacturing method in any one of Claims 1-7. 9. A polytetrafluoroethylene fine powder obtained by the method according to claim 1.