JP3471647B2 - Method for producing mixed powder containing polytetrafluoroethylene - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polytetrafluoroethylene-containing mixed powder composed of polytetrafluoroethylene particles (A) having a particle diameter of 10 μm or less and organic polymer particles (B).

[0002]

2. Description of the Related Art Polytetrafluoroethylene (PTF)
E) has excellent heat resistance, chemical resistance, electrical insulation, and has unique surface properties such as water / oil repellency, non-adhesiveness, and self-lubricating property, and is therefore widely used as a coating agent. In addition, since it has high crystallinity and low intermolecular force, it has the property of forming fibers with a slight stress. When compounded with a thermoplastic resin, molding processability, mechanical properties, etc. are improved. It is also used as an agent.

For example, Japanese Patent Laid-Open No. 11-29679 discloses a polytetrafluoroethylene particle (A) having a particle size of 10 μm or less and an organic polymer particle (B) which is excellent in dispersibility of polytetrafluoroethylene in a thermoplastic resin. ) Has been proposed as a polytetrafluoroethylene-containing mixed powder.

[0004]

However, when the tetrafluoroethylene-containing mixed powder described in JP-A No. 11-29679 is coagulated and recovered from an aqueous dispersion, it can be recovered by usual acid coagulation or salt coagulation. If the polymer (1) is coagulated at one time, the particle size uniformity of the resulting powder will be poor, and the blocking resistance, which is an important index for handling powder products, will deteriorate.

An object of the present invention is to obtain a tetrafluoroethylene-containing mixed powder having good blocking resistance.

[0006]

The gist of the present invention is to provide polytetrafluoroethylene particles (A) having a particle diameter of 10 μm or less.
In the method for producing a polytetrafluoroethylene-containing mixed powder composed of and an organic polymer particle (B), the particle diameter is 0.
After mixing the polytetrafluoroethylene particle aqueous dispersion having a particle diameter of 05 to 1.0 μm and the organic polymer particle aqueous dispersion, 40 to 80% by weight of the polymer in the aqueous dispersion is used as the first stage coagulation. And a polytetrafluoroethylene particle aqueous dispersion having a particle diameter of 0.05 to 1.0 μm, characterized in that the coagulation is performed, and the coagulation is completely completed in the second stage coagulation. After emulsion-polymerizing a monomer having an ethylenically unsaturated bond in a dispersion liquid obtained by mixing an aqueous dispersion of organic polymer particles and 40 to 80 in the aqueous dispersion as the first stage coagulation. Coagulate the polymer by weight percent,
Further, the second production method is characterized in that the coagulation is completely completed in the second stage coagulation.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Particle size used in the present invention is from 0.05 to
An aqueous dispersion of 1.0 μm polytetrafluoroethylene particles can be obtained by polymerizing a tetrafluoroethylene monomer by emulsion polymerization using a fluorine-containing surfactant.

During the emulsion polymerization of polytetrafluoroethylene particles, hexafluoropropylene, chlorotrifluoroethylene, fluoroalkylethylene, perfluoroalkyl vinyl ether, etc. are included as copolymerization components as long as the characteristics of polytetrafluoroethylene are not impaired. Fluorine olefins and fluorine-containing alkyl (meth) acrylates such as perfluoroalkyl (meth) acrylates can be used. The content of the copolymerization component is preferably 10% by weight or less based on tetrafluoroethylene.

Commercially available raw materials for the polytetrafluoroethylene particle dispersion are Fluon AD-1 and AD-936 manufactured by Asahi ICI Fluoropolymer, Polyflon D-1 and D-2 manufactured by Daikin Industries, and DuPont Mitsui Fluorochemical. Representative examples include Teflon 30J manufactured by the company.

The organic polymer particles (B) used in the present invention are not particularly limited, but have an affinity for the thermoplastic resin from the viewpoint of dispersibility of polytetrafluoroethylene when blended with the thermoplastic resin. It is preferable to have

Specific examples of the monomer for forming the organic polymer particles include styrene, p-methylstyrene and o.
-Styrene-based monomers such as methylstyrene, p-chlorostyrene, o-chlorostyrene, p-methoxystyrene, o-methoxystyrene, 2,4-dimethylstyrene and α-methylstyrene; methyl acrylate, methyl methacrylate , Ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylic acid-2-
Ethylhexyl, 2-ethylhexyl methacrylate,
(Meth) acrylic ester monomers such as dodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, cyclohexyl methacrylate, cyclohexyl methacrylate; acrylonitrile,
Vinyl cyanide monomers such as methacrylonitrile; vinyl ether monomers such as vinyl methyl ether and vinyl ethyl ether; vinyl carboxylate monomers such as vinyl acetate and vinyl butyrate; ethylene, propylene, isobutylene, etc. Olefin-based monomer; butadiene, isoprene,
Examples thereof include diene-based monomers such as dimethylbutadiene. These monomers can be used alone or in combination of two or more.

When the thermoplastic resin containing the polytetrafluoroethylene-containing mixed powder obtained by the method of the present invention is a polyolefin, the styrene-based monomer is preferable among these monomers from the viewpoint of compatibility. Body, (meta)
Acrylic ester-based monomers and olefin-based monomers can be mentioned. 20% by weight or more of one or more kinds of monomers selected from the group consisting of alkyl (meth) acrylic acid ester-based monomers having an alkyl group having 5 or more carbon atoms, styrene, and olefin-based monomers are particularly preferred. The monomer contained can be mentioned.

When the thermoplastic resin to which the polytetrafluoroethylene-containing mixed powder obtained by the method of the present invention is blended is polymethylmethacrylate, it is preferable among these monomers from the viewpoint of compatibility (meta). It can be mentioned that the acrylic acid ester-based monomer is contained in an amount of 20% by weight or more.

When the thermoplastic resin containing the polytetrafluoroethylene-containing mixed powder obtained by the method of the present invention is polyester, the styrene-based monomer is preferable among these monomers from the viewpoint of compatibility. And a (meth) acrylic acid ester-based monomer. Particularly preferred is a monomer containing 1% by weight or more of a (meth) acrylic acid ester-based monomer having an epoxy group. The method for producing an aqueous dispersion of organic polymer particles used in the present invention is not particularly limited, but for example, an emulsion polymerization method using an ionic emulsifier, a soap-free emulsion polymerization method using an ionic polymerization initiator. Etc. can be mentioned.

As the ionic emulsifier, any of an anionic emulsifier, a cationic emulsifier and a zwitterionic emulsifier may be used. If desired, a nonionic emulsifier may be used in combination with these ionic emulsifiers.

Specific examples of the anionic emulsifier include fatty acid salts, higher alcohol sulfate ester salts, liquid fatty oil sulfate ester salts, sulfate salts of aliphatic amines and aliphatic amides, aliphatic alcohol phosphate ester salts, and dibasic salts. Examples thereof include sulfonates of fatty acid esters, fatty acid amide sulfonates, alkylallyl sulfonates, and naphthalene sulfonates of formalin condensates.

Specific examples of the cationic emulsifier include aliphatic amine salts, quaternary ammonium salts, alkylpyridinium salts and the like.

Specific examples of the amphoteric emulsifier include alkyl betaine.

As the ionic polymerization initiator, persulfates (for example, potassium persulfate and ammonium persulfate), azobis (isobutyronitrile sulfonate), 4,4'-
Anionic polymerization initiators such as azobis (4-cyanovaleric acid), 2,2′-azobis (amidinopropane) dihydrochloride, 2,2′-azobis [2- (5-methyl-2-imidazoline-2- Il) propane] dihydrochloride, 2,2'-
Examples thereof include cationic polymerization initiators such as azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and 2,2′-azobisisobutyramide dihydrate.

The particle diameter d of the organic polymer particles (B) used in the present invention is not particularly limited, but from the viewpoint of the stability of the aggregated state with the polytetrafluoroethylene particles, polytetrafluoroethylene. The range of the following equation is preferable with respect to the particle diameter D of the particles.

0.1D <d <10D First in the present invention
Examples of the coagulant used for the second stage coagulation and the second stage coagulation include inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid, formic acid,
Organic acids such as acetic acid, inorganic salts such as aluminum sulfate, magnesium sulfate, sodium chloride, calcium chloride, sodium sulfate, magnesium chloride, sodium acetate,
Organic salts such as calcium acetate can be mentioned, and these can be used alone or in combination. In the present invention, as the first stage coagulation, it is necessary to coagulate 40 to 80% by weight of the polymer in the aqueous dispersion. The amount of polymer coagulated here was obtained by comparing the coagulated slurry with Toyo Filter Paper No. 131 (J
It is obtained by converting it from the amount of uncoagulated polymer obtained by measuring the polymer concentration in the filtrate by filtration with ISP 3801 type 3). When the amount of polymer coagulated by the first stage coagulation is less than 40% by weight, many polymer particles are rapidly coagulated by the second stage coagulation, resulting in poor particle size uniformity. Become. On the other hand, if it is 80% by weight or more, the coagulation of the first step proceeds rapidly, so that the uniformity of the particle diameter becomes poor.

The concentration of the coagulant for coagulating 40 to 80% by weight of the polymer in the first stage coagulation is appropriately selected depending on the kind and amount of the emulsifier contained in the target aqueous dispersion. You have to choose.

The coagulated particles obtained by the method of the present invention have a structure in which fine particles are agglomerated, and it is desirable that the coagulated particles be heat-treated for 30 minutes or more at a temperature range of 90 to 120 ° C. Under such a strong heat treatment condition, fusion between fine particles is promoted, the particle density is improved, and the particle shape retention force is also strengthened. The heat-treated and solidified particles are washed with water, dehydrated and dried to be recovered as a powdery polymer.

A typical apparatus used to carry out the present invention will be described with reference to FIG. The polymer particle aqueous dispersion is sent from the metering pump (1) to the coagulant from the metering pump (2) to the first tank (5). The coagulant added to increase the recovery rate of the polymer is from the metering pump (3) to the second tank (6).
Sent to. When the coagulant is an acid, alkali as a pH adjuster is sent to the third tank (7) from the metering pump (4). After the slurry is heat-treated in the fourth tank (8), it is further washed with water, dehydrated and dried, although not shown, to obtain a powdery polymer.

The present invention will be described below with reference to examples.
The present invention is not limited to these.

[0026]

EXAMPLES In each description, "part" means part by weight and "%" means% by weight.

Reference Example 1 <Production of polytetrafluoroethylene particle-containing aqueous dispersion (L-1)> 0.1 part of 2,2'-azobis (2,4-dimethylvaleronitrile) was dissolved in 100 parts of dodecyl methacrylate. Let To this, a mixed solution of 2.0 parts of sodium dodecylbenzenesulfonate and 300 parts of distilled water was added, and the mixture was stirred with a homomixer at 10000 rpm for 2 minutes, and then passed through a homogenizer twice at a pressure of 30 MPa to obtain a stable dodecyl methacrylate preliminary. A dispersion was obtained. This is a stirring blade,
A separable flask equipped with a condenser, a thermocouple, and a nitrogen inlet was charged, the internal temperature was raised to 80 ° C. under a nitrogen stream, and the mixture was radically polymerized by stirring for 3 hours to obtain a dodecyl methacrylate polymer particle dispersion (hereinafter referred to as P -1) was obtained.

The solid content concentration of P-1 was 25.2%, the particle size distribution showed a single peak, and the weight average particle size was 195.
nm, and the surface potential was -38 mV.

As a polytetrafluoroethylene particle dispersion liquid, Fluon AD936 manufactured by Asahi ICI Fluoropolymers Co., Ltd.
Was used. AD936 has a solid content concentration of 63.0% and contains 5% of polyoxyethylene alkylphenyl ether with respect to polytetrafluoroethylene. The particle size distribution of AD936 showed a single peak, the weight average particle size was 290 nm, and the surface potential was -20 mV.

83.3 parts of AD936 to distilled water 116.
7 parts were added to obtain a polytetrafluoroethylene particle dispersion F-1 having a solid content concentration of 26.2%. F-1 is 25%
Of polytetrafluoroethylene particles and 1.2% of polyoxyethylene nonylphenyl ether.

160. 0 part of F-1 (40 parts of polytetrafluoroethylene) and 119.0 parts of P-2 (30 parts of polydodecyl methacrylate) were placed in a separable flask equipped with a stirring blade, a condenser, a thermocouple, and a nitrogen inlet. After charging, 82.9 parts of distilled water was added, and the mixture was stirred under a nitrogen stream at room temperature for 1 hour. After that, the temperature of the system was raised to 80 ° C., and a mixed solution of 0.001 part of iron (II) sulfate, 0.003 part of disodium ethylenediaminetetraacetate, 0.24 part of Rongalit salt, and 10 parts of distilled water was added, Methyl methacrylate 30
Mixture of 0.6 parts and tertiary butyl peroxide was added dropwise over 1 hour, and the internal temperature was adjusted to 1 at 80 ° C after the addition was completed.
Hold for time to complete radical polymerization. Separation of solids was not observed through a series of operations, and a uniform polytetrafluoroethylene particle-containing aqueous dispersion (L-1) was obtained. L
The solid content concentration of -1 was 24.9%, the particle size distribution was relatively broad, and the weight average particle size was 242 nm.

Examples 1 and 2, Comparative Examples 1 and 2 L-1 obtained in Reference Example 1 was coagulated by the apparatus shown in FIG.
Aluminum sulfate 0.3% aqueous solution was used as the first stage coagulant, and aluminum sulfate 3.0% aqueous solution was used as the second stage coagulant, and the supply amount was the first stage coagulation amount. Was adjusted to the amount shown in Table 1. The slurry discharged from the fourth tank was washed with water, dehydrated and dried to obtain a polytetrafluoroethylene-containing powder.

Various properties of the obtained powder were measured by the following methods. The results are shown in Table 1.

(1) Particle uniformity: The particle size distribution of the powder was determined by the sieving method, and the particle uniformity (N) was determined by the following formula.

N = D75 / D25 (wherein D75 represents the particle size (μm) at 75% of the integrated weight distribution curve, and D25 represents the particle size (μm) at 25% of the integrated weight distribution curve.) (2 ) Bulk specific gravity: determined by the method of JIS K-6721.

(3) Blocking resistance: A sample was filled in a powder adhesion measuring device (Model ED-2000CH manufactured by Shimadzu Corp.), a constant load (0.02 MPa) was applied, and then a breaking test was conducted. The maximum load was measured and the tensile strength per unit area was calculated. Unit [g / cm ² ]

[0037]

[Table 1]

[0038]

According to the method of the present invention, a powder having a sharp particle size distribution can be obtained by controlling the amount of precipitation during the first stage coagulation in the production of polytetrafluoroethylene-containing mixed powder. Thus, a product powder having excellent blocking resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a typical apparatus for carrying out the present invention.

[Explanation of symbols]

1 to 4 ... Constant pump, 5 ... 1st tank, 6 ... 2nd tank,
7-third tank, 8-third tank

Claims (2)

(57) [Claims] 1. A method for producing a polytetrafluoroethylene-containing mixed powder comprising polytetrafluoroethylene particles (A) having a particle diameter of 10 μm or less and organic polymer particles (B), wherein the particle diameter is 0.05 to 1 After mixing the 0.04 μm polytetrafluoroethylene particle aqueous dispersion and the organic polymer particle aqueous dispersion, 40 to 80% by weight of the polymer in the aqueous dispersion is coagulated as the first stage coagulation. And further complete the coagulation in the second stage coagulation. 2. A method for producing a polytetrafluoroethylene-containing mixed powder comprising polytetrafluoroethylene particles (A) having a particle diameter of 10 μm or less and organic polymer particles (B), wherein the particle diameter is 0.05 to 1 After emulsion-polymerizing a monomer having an ethylenically unsaturated bond in a dispersion obtained by mixing an aqueous dispersion of polytetrafluoroethylene particles of 0.0 μm and an aqueous dispersion of organic polymer particles, the first step As a coagulation, 40 to 80% by weight of a polymer in an aqueous dispersion is coagulated, and the coagulation is completely completed in the second stage coagulation.