JP2000103865A - Production of fluoropolymer powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a fluoropolymer powder which has a good moldability and is suitable for a powder coating material, etc., by granulating, under stirring, fine fluoropolymer particles in a granulation medium, grinding the granulation product, and thermally treating the product in an atmosphere with a temp. equal to or higher than the m.p. of the product to partially melt it. SOLUTION: The fluoropolymer is prepd. by polymerizing a fluoroolefin monomer or a combination of two or more fluoroolefin monomers or by copolymerizing a fluorolefin monomer or monomers with other monomers copolymerizable therewith. The fine fluoropolymer particles are prepd. by the suppension polymn., etc., of above-mentioned monomer or monomers under stirring by using a polymn. initiator and a chain transfer agent. The granulation medium is a mixture of an affinitive medium (e.g. a hydrogen-contg. fluorinated hydrocarbon) and water. The granulation operation is carried out usually in the range of from normal temp. to 150 deg.C, and the treating time is usually 10 min to 15 hr. The average particle size of the granulation product is 0.5-5.0 mm. The heat treatment is carried out by supplying ground particles into a melting zone from a spray nozzle. Hot air at a temp. 30-150 deg.C higher than the m.p. is sent into the melting zone. The dwelling time is 0.1-5 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a novel fluoropolymer powder, and more particularly, to a method for producing a fluoropolymer powder having good moldability.

[0002]

2. Description of the Related Art Fluoropolymer powders are suitably used as powder coatings, and are used for applications such as non-stick coatings and corrosion-resistant linings.

As a method for producing a fluoropolymer powder, a powder obtained by aggregating fine particles of a tetrafluoroethylene copolymer obtained by polymerization to a size of about 0.18 to 2.6 mm is melted together with a gas flow to obtain a melting point of the copolymer. A method of spraying into a firing chamber having an atmosphere maintained at the above temperature is disclosed in JP-B-53-1.
No. 1296.

However, the agglomerated tetrafluoroethylene copolymer powder is easily broken into fine particles of the tetrafluoroethylene copolymer by spraying with a spray nozzle. These fine particles have a small particle size, and are easily fused to each other when melted in a firing chamber. When such a powder is used in a powder coating, the smoothness of the coating film surface is poor and a pinhole is formed in the coating film. Therefore, it is necessary to remove aggregates in which the particles are fused. As a result, there are disadvantages that the product yield is low and the product cost is high.

On the other hand, Japanese Patent Publication No. 7-5743 discloses that a polymer bulk powder, which is a dried product of a tetrafluoroethylene copolymer obtained by suspension polymerization, is formed into a sheet by a roll press to increase the apparent density. A method of grinding is described.

However, the powder of the above tetrafluoroethylene copolymer after polymerization and drying contains many fine particles,
Handling is poor, and it is difficult to form a sheet uniformly with a roll press. Insufficiently compressed parts are re-crushed into fine particles by pulverization in a subsequent step, and parts that are excessively compressed become large particles or whiskers by pulverization. Further, the particle surface of the powder obtained by pulverizing the sheet is cracked in some places, and voids exist inside the particles. When such a powder is used for a powder coating, the coating film tends to entrap air bubbles and easily cause pinholes.

[0007] WO 97/40089 discloses that a fluoropolymer raw material is densified by compression molding with a roll under the condition that a specific gravity of 90% or more of the true specific gravity of the polymer is obtained.
After pulverizing the molded product, fine particles of 3 to 40% by weight of the whole particle size distribution are removed, and 1 to 20% by weight of the whole particle size distribution is further removed.
A method for removing coarse particles is described.

When a high pressure is applied to make the true specific gravity of the fluoropolymer 90% or more, excess energy is converted into heat and the temperature of the polymer rises. In a semi-molten state, and the brittleness tends to be impaired. When such a sheet is pulverized, whisker-like particles are likely to be generated, and as a result, the moldability of the fluoropolymer tends to be deteriorated, which is not preferable.

Further, according to the above-mentioned method, after crushing, fine particles and coarse particles of 4 to 60% by weight of the whole particle size distribution must be removed as a whole, resulting in poor production efficiency.

In this publication, there is no description as to how the bulk of the fluoropolymer was obtained.

[0011]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention solves the above-mentioned problems and provides a method for producing a fluoropolymer powder having good moldability and a method for producing the same. The purpose of the present invention is to provide a fluoropolymer powder as described above.

[0012]

According to the present invention, there is provided a process for producing a fluoropolymer powder having good moldability, comprising the steps of: (1) producing a fluoropolymer fine particle obtained by polymerization; A process of forming a granulated product by stirring and granulating in a granulating medium,
(2) a step of pulverizing the granulated material; and (3) a step of heat-treating the pulverized fluoropolymer particles in an atmosphere having a temperature equal to or higher than the melting point thereof to melt at least a part of the powder particles. And a method for producing a fluoropolymer powder, characterized in that:

Further, according to the present invention, there is provided a process for producing a fluoropolymer powder having good moldability, comprising:
A step of agitating and granulating the fluoropolymer fine particles obtained by the polymerization in a granulating medium to form a granulated product; (2) a step of compression-molding the granulated substance; (4) further comprising a step of heat-treating the pulverized fluorine-containing polymer particles in an atmosphere at a temperature equal to or higher than its melting point to melt at least a part of the powdery particles. A method for producing a powder is provided.

[0014]

Embodiments of the present invention will be described below in detail.

The fluoropolymer of the present invention is obtained by polymerizing a fluoroolefin monomer alone or in combination of two or more, or a copolymerizable monomer other than a fluoroolefin monomer and a fluoroolefin monomer. Is produced by copolymerizing Specifically, a tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as PFA), a tetrafluoroethylene / hexafluoropropylene copolymer (hereinafter FE)
P), ethylene / tetrafluoroethylene copolymer (hereinafter referred to as ETFE), polyvinylidene fluoride (hereinafter referred to as PVdF), ethylene / chlorotrifluoroethylene copolymer (hereinafter referred to as ECTFE), and the like. .

The fluoropolymer fine particles used in the present invention are prepared by solution polymerization of the above polymer or copolymer by using a polymerization initiator such as di (perfluoroacyl) peroxide and a chain transfer agent such as methanol or hexane. Alternatively, it is obtained by production by a suspension polymerization method.

As a polymerization medium for carrying out the polymerization reaction, a medium having an affinity for a fluoropolymer (hereinafter referred to as an affinity medium) such as a hydrogen-containing fluorinated hydrocarbon or a hydrogen-containing chlorinated fluorinated hydrocarbon in solution polymerization. In suspension polymerization, a mixed medium of these affinity media and water is used. Thus, since it is preferable to use an affinity medium as a granulation medium used in the step of forming granules described below, it is most preferable to use such a granulation medium as a polymerization medium during the polymerization reaction. desirable.

Preferred granulation media for use in the present invention are media having an affinity for the fluoropolymer as described above (affinity media), water, and mixtures thereof. A particularly preferred granulation medium is a mixed medium of an affinity medium and water. As the affinity medium, hydrogen-containing fluorinated hydrocarbons and hydrogen-containing chlorinated fluorinated hydrocarbons as described above are preferable. Among them, compounds having 3 to 10 carbon atoms are most preferred. If the number of carbons is 2 or less, the boiling point is too low, and if it is 11 or more, the boiling point is too high, so that desirable particles cannot be obtained efficiently.

Examples of such compounds that can be used as an affinity medium are as follows.

C ₃ Cl ₂ F ₅ H (eg, CHCl FCF ₂
CF ₂ Cl), C ₄ H ₂ F ₈ (for example, H (CF ₂ ) ₄ H
), C ₄ H ₄ F ₆ (eg, F (CHF) ₄ F) , C ₄ H
₅ F ₅ (e.g. _{CF 3 CH 2 CF 2 CH 3} ), C 5 HF
₁₁ (eg, (CF ₃ ) ₂ CFCF ₂ CF ₂ H), C ₅ H ₂
F ₁₀ (for example, CF ₃ CF (CHF ₂ ) CF ₂ CH
F ₂ ), C ₆ HF ₁₃ (for example, H (CF ₂ ) ₆ F), C
₆ H ₂ F ₁₂ (e.g., _{(CF 3) 2 CF (CFH} ) 2 CF 3)
, C ₆ H ₅ F ₉ (eg, C ₄ F ₉ CH ₂ CH ₃ ), C
₇ HF ₁₅ , C ₈ HF ₁₇ (for example, H (CF ₂ ) ₈ F)
, C ₉ HF _{19 After the} polymerization reaction is completed, the fluoropolymer fine particles are in a slurry state by the affinity medium or the mixed medium of the affinity medium and water. An appropriate amount of the affinity medium and / or water is added to the slurry to obtain a granulation medium in which the granulation action is effectively performed.

The amount of the granulating medium coexisting with the fluoropolymer is not particularly limited. However, if the amount is too small, the effect of the present invention cannot be sufficiently achieved. If the amount is too large, the amount of the affinity medium is simply reduced. It only increases, which is not preferable from the viewpoint of economy, processing equipment, work and the like. Usually, the amount of the granulating medium is at least 150 parts by weight, preferably about 300 to 9000 parts by weight, particularly preferably about 2000 to 7000 parts by weight, based on 100 parts by weight of the fluoropolymer.

When a mixed medium of an affinity medium and water is used as the granulation medium, the amount of the affinity medium in the mixed medium is desirably 10 to 40% by weight. Further, the amount of the affinity medium in the mixed medium is desirably 500 to 2,000 parts by weight based on 100 parts by weight of the fluoropolymer. In the following description, a case where an affinity medium is used as a polymerization medium will be described unless otherwise specified.

The apparatus for forming the granules is not particularly limited, but a stirring tank provided with a stirring means, a heating means and a cooling and reflux means can be suitably used. The stirring means is preferably a tank-type apparatus having a propeller blade, a turbine blade, a paddle blade, a paddle blade, a horseshoe blade, a spiral blade, and the like, and further having an appropriate number of baffle plates.

It is preferable to form a granulated product by using such a stirring tank type apparatus and raising the temperature of the fluoropolymer particles in a granulating medium under stirring. The preferred temperature range for the granulation operation is from room temperature to 150 ° C, particularly preferably from 40 to 100 ° C.
It is about ° C. The granulation time varies depending on the temperature, but is usually about 10 minutes to 15 hours, preferably about 15 minutes to 10 hours. Incidentally, the average particle size of the obtained granulated material also varies depending on the stirring strength. Generally speaking, in order to obtain a granulated product having a uniform particle size distribution, it is preferable that the stirring speed is somewhat high, When the stirring intensity is high, the particle size tends to be small, and when the intensity is low, the particle size tends to be large.

The affinity medium in the granulation medium is azeotroped with water and is distilled out of the stirring tank. This is cooled by cooling and reflux means to separate it into two layers, and the water is refluxed into the tank. Is preferred.

The granulated fluoropolymer obtained as described above is spherical particles having an average particle diameter of 0.5 to 5.0 mm, preferably 0.5 to 3.0 mm.

An important feature of the present invention is that the fluoropolymer fine particles are once granulated in a granulating medium. In general, the dry powder of the fluoropolymer obtained by polymerization has a small particle size, also contains a lot of voids, and has an apparent specific gravity as small as 0.3 to 0.4. Various problems occur. However, by agitating and granulating the fluoropolymer obtained by polymerization in a granulating medium, a granulated product in which primary particles are densely aggregated is obtained, and fine powder can be significantly reduced. In addition, there are few voids, and the apparent specific gravity is as high as 0.6 to 0.8.

In the case where the fluoropolymer fine particles are subjected to stirring granulation, as described above, it is most preferable to carry out granulation while raising the temperature in the granulating medium with stirring to drive out the affinity medium. In some cases, a granulated product may be formed by stirring and aggregating in a granulating medium without driving out the affinity medium.

In the present invention, the densely agglomerated granules obtained as described above are then pulverized to obtain a pulverized powder adjusted to a desired particle size. The apparatus used for pulverization is not particularly limited, and may be a known apparatus. For example,
Pin mill, impeller mill, jet mill, hammer mill, ball mill, tube mill, conical mill, rod mill, micronizer, jetmizer, marjack mill, micron mill, colloid mill. What is called a fine pulverizer such as a micro atomizer or a Raymond vertical mill or an ultra fine pulverizer is preferable.

Further, in order to further increase the specific gravity of the powder, the granulated material is once compression-molded into a molded product such as a sheet or flake.
Next, the molded product can be pulverized into a pulverized powder as described above. In the compression molding of the granulated product, it is easy to obtain a uniformly compacted product, and it can be formed at a relatively low pressure. The pulverized powder obtained by pulverizing the molded product has few re-crushed fine particles and hardly generates large particle diameter and whisker-like particles.

The pulverized powder thus obtained has a very small amount of fine powder. For example, the ratio of fine powder of 10 μm or less is 10%.
The following are easily and preferably obtained. Here, the amount of the fine powder of the pulverized powder is measured using a laser diffraction type particle size distribution analyzer (for example, Sympatec, HELOS & RODOS).
) Is obtained by measuring the particle size distribution by the dry method.

Further, in the present invention, the pulverized fluorine-containing polymer particles are subjected to a heat treatment in an atmosphere having a temperature equal to or higher than the melting point, and at least a part of the particles is melted. This is one of the important features of the present invention, at least a part of the particles,
Normally, by melting the outer surface, the surface of the molten particles approaches a sphere due to surface tension in an attempt to minimize the surface area. That is, the surface area can be significantly reduced. Such spherical particles, when used as a powder coating, can be molded favorably without remaining bubbles and pinholes in the coating film.

As a specific heat treatment method, a known method can be arbitrarily employed, but a method in which the particles are sprayed and melted in an atmosphere at or above the melting point of the particles is particularly desirable. Although a rotary kiln or a flash dryer can be used to heat the material to a temperature higher than the melting point, the former method is disadvantageous in that a large amount of heat is required because the molten powder adheres to the wall of the apparatus, and the latter generates a high-temperature airflow.

The structure of the heat treatment apparatus is as follows. In order to prevent the particles from fusing together or fusing inside the apparatus, the particles are supplied while being sufficiently dispersed, and a melting zone and a cooling zone are provided. A structure that allows the molten particles to be cooled immediately in the cooling zone is preferred.

For example, a heat treatment device is a container whose upper portion is cylindrical and whose lower portion is tapered to form a heat treatment device. Hot air is supplied from the upper side surface to form this region as a melting zone, and processing is performed from the upper portion of the cylindrical container. The pulverized fluoropolymer particles are supplied to the melting zone by a spray nozzle or the like.
During the short time when the polymer particles fall through this melting zone,
The polymer particles are brought into contact with hot air, and the outer surface of the particles is brought into contact with the hot air so that at least a portion thereof is melted.
The temperature of the melting zone, that is, the temperature of the hot air in the melting zone is 30 to 150 ° C. higher than the melting point of the fluoropolymer.
It is maintained at a temperature as high as possible, preferably about 50 to 100 ° C. At a temperature higher than the melting point and about 30 ° C. higher than the melting point, the particles are not sufficiently melted. Conversely, when the temperature is higher than the melting point and higher than 150 ° C., the thermal decomposition of the fluoropolymer proceeds and the working environment deteriorates.

The residence time of the particles in the melting zone may be about 0.1 to 5 seconds, particularly preferably 0.5 to 3 seconds. If the time is less than 0.1 second, the particles do not melt sufficiently, and if the time exceeds 5 seconds, the melting process proceeds too far into the interior, and the molten particles often collide with each other before being cooled. It will be easier to wear.

By introducing a cooling gas (cold air) along the inner wall of the apparatus, the outside of the melting zone is used as a cooling zone, and this region is maintained at least below the melting point of the polymer. The particles melted in the melting zone are immediately cooled in the cooling zone. Insufficient cooling may cause the fused particles to fuse together or adhere to the device wall, causing problems.

The powder particles cooled as described above are:
It is taken out from the lower part of the heat treatment equipment and collected by a cyclone or bag filter.

The particles obtained by the method of the present invention are not necessarily true spheres, but belong to a broad sphere having roundness and no chipped or whisker-like portions.
The spherical particles according to the present invention have such a meaning.

[0040]

The present invention will be described below with reference to examples. However, these are examples of the present invention, and the present invention is not limited to these.

In the following examples, the physical properties and properties of the fluoropolymer, its powder and the coating film were measured by the following methods.

(1) Average particle size: Measured by a dry method using a laser diffraction type particle size distribution analyzer (HELOS & RODOS, Sympatec).

(2) Apparent specific gravity: Measured according to JIS K 6891.

(3) Film thickness: The magnetic substrate was measured using an electromagnetic film thickness meter, and the non-magnetic substrate was measured using an eddy current film thickness meter.

(4) Pinhole: Measured at an applied voltage of 5 KV using a low-frequency high-voltage pulse discharge type pinhole detector.

Example 1 (1) Tetrafluoroethylene, ethylene and (perfluorobutyl) ethylene were copolymerized in C ₄ F ₉ CH ₂ CH _{3 to} obtain 8% by weight of ETFE [copolymer composition: A slurry containing fine particles of (polymerized units based on tetrafluoroethylene / polymerized units based on ethylene / polymerized units based on (perfluorobutyl) ethylene = 53/46/1 (mol%)] was obtained.

Granules were formed using C ₄ F ₉ CH ₂ CH ₃ in this slurry as an affinity medium. That is, 500 ml of this ETFE slurry was added to 1000 m of water.
together with 6 turbine blades and 2 baffles, the mixture was charged into a stirrer, heated to 90 ° C. and treated at a rotation speed of 400 rpm for 1 hour to perform an operation of granulating ETFE fine particles. . In addition, stirring was performed while driving out an azeotrope of the affinity medium and water, and water of the distillate was returned to the system.

After the granulated material is separated by filtration and separated from the medium and water, it is further dried by heating to 120 ° C.
6 mm spherical granules were obtained.

(2) The granulated product was pulverized by an impact mill LS-1 (Dalton). The average particle size of the pulverized powder is 32 μm, and 8.2% is fine powder of 10 μm or less.
Met.

(3) As a heat treatment apparatus for pulverized particles, a tapered portion is provided by squeezing the lower portion, a hot air inlet is provided on an upper side surface of a cylindrical container having an upper portion, and a powder supply nozzle is provided on an upper portion, and cool air is introduced along the inner wall of the container. An apparatus equipped with a port and a port for taking out powder from the lower part of the taper was used. 32 crushed powder
It was sprayed and melted in a hot air atmosphere in a melting zone maintained at 0 ° C. The residence time in the melting zone is about 1 second. Immediately cool the molten powder particles by contact with cold air,
The particles were collected by a cyclone to obtain powder particles having an average particle diameter of 43 μm and an apparent specific gravity of 0.81 g / cc. When the particles were observed under a microscope, it was confirmed that the particles were spherical particles without whiskers or corners.

(4) An electrostatic coating machine (G from Onoda)
X3300S), applied to a 150 × 150 × 2 mmt aluminum plate, and fired in an electric furnace at 300 ° C. for 10 minutes. After that, when cooled and solidified at room temperature,
A coating film having a thickness of μm and having no pinhole was formed.

Example 2 (1) As an affinity medium in a polymerization medium and a granulation medium, C ₄
CF ₃ C (CF ₃ ) FCF instead of F ₉ CH ₂ CH ₃
Polymerization and granulation were carried out in the same manner as in Example 1 except that HCFHCF ₃ was used. As a result, the average diameter was 2.1 m.
m was obtained.

(2) The granulated product is subjected to Impact Mill LS-1
(Manufactured by Dalton Co.), average particle size 88 μm, 1
A pulverized powder of 4.9% of a fine powder of 0 μm or less was obtained.

(3) Further, the pulverized particles were sprayed and melted in the atmosphere of a melting zone maintained at 335 ° C. using the heat treatment apparatus of Example 1. The residence time of the particles in the melting zone is about 0.8 seconds. The melted powder particles were contacted with the blown cold air, immediately cooled, and collected by a cyclone. As a result, powder particles having an average particle size of 95 μm and an apparent specific gravity of 0.84 g / cc were obtained. When the particles were observed under a microscope, it was confirmed that the particles were spherical particles without whiskers or corners.

(4) An electrostatic coating machine (G from Onoda)
X3300S), applied to a 150 × 150 × 2 mmt aluminum plate, and fired in an electric furnace at 300 ° C. for 10 minutes. After that, when cooled and solidified at room temperature,
A coating film having a thickness of 5 μm and having no pinhole was formed.

Example 3 (1) Tetrafluoroethylene and perfluoro (propyl vinyl ether) were copolymerized in CHClFCF ₂ CF ₂ Cl, and 6% by weight of PFA [copolymer composition: polymerization based on tetrafluoroethylene] Unit / perfluoro (
Polymerized units based on propyl vinyl ether) = 98.7
/1.3 (mol%)].

500 ml of this PFA slurry was added to 100 parts of water.
The mixture was charged together with 0 ml into a stirrer equipped with six turbine blades and two baffles, heated to 95 ° C., and treated at a rotation speed of 400 rpm for 1.5 hours. In addition, stirring was performed while driving out an azeotrope of the affinity medium and water, and water of the distillate was returned to the system.

Further, the product was heated to 120 ° C. and dried to obtain a spherical granulated product having an average diameter of 1.1 mm.

(2) The obtained granulated product is compressed into a sheet having a thickness of 3 mm by a compression molding machine (Pharmabactor L200 / 50P, manufactured by Hosokawa Micron), and the sheet is crushed to have an apparent specific gravity of 0.75. A flaky molded product was obtained.

(3) The molded product was pulverized with a flake crusher FC-200 (manufactured by Hosokawa Micron). The average particle size of the pulverized powder is 33 μm, of which 10 μm
The following fine powder was 3.2%.

(4) The pulverized particles were sprayed and melted in the melting zone maintained at 370 ° C. using the heat treatment apparatus used in Example 1. The residence time in the melting zone is about 1.5 seconds. The melted powder particles were immediately cooled and collected by a cyclone to obtain powder powder having an average particle size of 40 μm and an apparent specific gravity of 0.82 g / cc. When the particles were observed under a microscope, it was confirmed that the particles were spherical particles without whiskers or corners.

(5) This powder was applied to an electrostatic coating machine (G
X3300S), painted on a 150 × 150 × 2 mmt aluminum plate, and fired in an electric furnace at 380 ° C. for 15 minutes. After that, when cooled and solidified at room temperature,
A micron, pinhole-free coating was formed.

Comparative Example 1 (1) Copolymerization of tetrafluoroethylene, ethylene and (perfluorobutyl) ethylene in C ₄ F ₉ CH ₂ CH ₃ , followed by drying to remove the polymerization medium and ETFE
Fine particles of [copolymer composition: polymerized units based on tetrafluoroethylene / polymerized units based on ethylene / polymerized units based on (perfluorobutyl) ethylene = 53/46/1 (mol%)] were obtained.

(2) The fine particles were sprayed and melted in the melting zone atmosphere maintained at 320 ° C. using the heat treatment apparatus used in Example 1. The residence time in the melting zone is about 1 second. The molten particles were immediately cooled and collected by a cyclone to obtain a powder having an average particle diameter of 13 μm and an apparent specific gravity of 0.61 g / cc.

When this powder was observed under a microscope, many aggregates in which the fused particles were fused together were present.

(3) This powder was applied to an electrostatic coating machine (G
X3300S), applied to a 150 × 150 × 2 mmt aluminum plate, and fired in an electric furnace at 300 ° C. for 10 minutes. After that, when cooled and solidified at room temperature, the film thickness 73 was obtained.
At μm, pinholes were detected in the coating.

Comparative Example 2 (1) Tetrafluoroethylene and perfluoro (propyl vinyl ether) were copolymerized in CHClFCF ₂ CF ₂ Cl, and then dried to remove the polymerization medium.
Fine particles of A [copolymer composition: polymerization units based on tetrafluoroethylene / polymerization units based on perfluoro (propyl vinyl ether) = 98.7 / 1.3 (mol%)] were obtained.

(2) The fine particles were sprayed and melted in the atmosphere of a melting zone maintained at 370 ° C. using the heat treatment apparatus used in Example 1. The residence time in the melting zone is about 1.5 seconds. The melted powder particles were immediately cooled and collected by a cyclone to obtain a powder having an average particle size of 14 μm and an apparent specific gravity of 0.42 g / cc.

When this powder was observed under a microscope, many aggregates in which the fused particles were fused together were present.

(3) This powder was applied to an electrostatic coating machine (G
X3300S), painted on a 150 × 150 × 2 mmt aluminum plate, and fired in an electric furnace at 380 ° C. for 15 minutes. Then, when the mixture was cooled and solidified at room temperature, the film thickness 57
At microns, pinholes were detected in the coating.

As described above, the fluoropolymer fine particles are agitated and granulated in a mixed medium comprising an affinity medium and water, and the primary particles are formed into a densely aggregated granule, followed by grinding and heat treatment. Alternatively, the granulated material is further compression-molded and then pulverized and heat-treated to produce a spherical fluorinated copolymer powder having good moldability, which is suitably used for powder coatings and the like. it can. On the other hand, it can be seen that the powder without this granulation operation has poor molding workability, and when formed into a powder coating, defects such as pinholes occur in the coating film.

[0072]

According to the present invention, it is possible to efficiently produce a fluorine-containing copolymer powder having good moldability and suitable for use in powder coatings and the like.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F070 AA23 AA24 AC12 AC34 DA23 DA31 DA44 DA52 DB01 4J100 AA02P AA02Q AC24P AC26P AC27Q AC31Q AE39Q CA01 CA04 EA05 GC19 GC29 GC32 JA01

Claims (4)

[Claims] 1. A method for producing a fluoropolymer powder having good moldability, comprising: (1) granulating a fluoropolymer fine particle obtained by polymerization in a granulation medium with stirring. (2) a step of pulverizing the granulated substance; and (3) a heat treatment of the pulverized fluoropolymer particles in an atmosphere having a temperature equal to or higher than the melting point of the pulverized fluoropolymer particles. A method for producing a fluoropolymer powder, comprising the step of melting 2. A method for producing a fluoropolymer powder having good moldability, comprising: (1) granulating a fluoropolymer fine particle obtained by polymerization in a granulation medium by stirring and granulating. A step of forming granules, (2) a step of compression-molding the granules, (3) a step of pulverizing the compression-molded articles,
(4) A method for producing a fluoropolymer powder, comprising a step of heat-treating the pulverized fluoropolymer particles in an atmosphere having a temperature equal to or higher than the melting point thereof and melting at least a part of the powder particles. 3. The method according to claim 1, wherein the granulating medium is a mixture of a medium having an affinity for the fluoropolymer and water. 4. A fluoropolymer powder having good molding processability, obtained by the method according to claim 1.