JP2002020676A - Fluoroplastic coating agent and method for preparing same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluoroplastic coating agent which can form a uniform film without pinholes at relatively low temperatures and is excellent in dispersion stability, and a method for preparing the same. SOLUTION: The coating agent is prepared by dispersing a fluoroplastic having an average molecular weight of 10,000-1,500,000 in the form of fine particles having an average particle size of 10 μm or less in a solvent composed primarily of dichloropentafluoropropane by means of a high-pressure homogenizer treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel fluororesin coating agent and a method for producing the same.

[0002]

2. Description of the Related Art Fluororesin coating agents for coating surfaces of metals, glass, ceramics and the like have been known. For example, (1) a dispersion obtained by adding a surfactant to an aqueous dispersion obtained by emulsion polymerization of tetrafluoroethylene (JP-B 32-1844);
(2) An average molecular weight of 600 to 4, synthesized by a gas phase method.
000 fluororesin telomer dispersed in a chlorine-free organic solvent (JP-A-11-43641), (3)
Tetrafluoroethylene is 1,1,2-trichloro-
(1) Telomerization in 1,2,2-trifluoroethane (US Pat. No. 3,067,262); (4) Dispersion of a low molecular weight fluororesin powder having an average particle diameter of 2 μm or less in an organic solvent containing a thickener ( JP-A-11-4364
1) and the like are known.

[0003] However, the above prior art (1),
In order to stabilize an aqueous dispersion of polytetrafluoroethylene (hereinafter also referred to as PTFE), it is necessary to add a surfactant (emulsifier), and the molecular weight of PTFE is as high as several million to 10 million. For this reason, heat treatment at 350 ° C. or higher was required for forming the coating film, and thus the coating workability was not always satisfactory.
(2) has a problem in that PTFE has too low a molecular weight, so that the amount of scattering in the baking step is large. (3)
(4) has a problem that 1,1,2-trichloro-1,2,2-trifluoroethane cannot be used due to regulation.
However, there is a problem that it takes time to disperse the thickener during baking.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fluororesin coating agent which has excellent dispersion stability of particles and can form a uniform film at a relatively low heat treatment temperature, and a method for producing the same. is there.

[0005]

Means for Solving the Problems As a result of intensive studies in view of the state of the prior art, the present inventors have found that a fluororesin having a specific average molecular weight is treated with a high-pressure homogenizer in a specific solvent to obtain a specific resin. The inventors have found that the above problem can be solved by dispersing as fine particles, and have completed the present invention based on the findings. That is, the present invention is characterized in that a fluororesin having an average molecular weight of 10,000 to 1,500,000 is dispersed as fine particles having an average particle diameter of 10 μm or less in a solvent containing dichloropentafluoropropane as a main component. To provide a fluororesin coating agent. Further, the present invention relates to a method for producing a fluororesin,
The present invention provides the above fluororesin coating agent, which is polytetrafluoroethylene at 20 to 338 ° C. Further, a mixture of a fluororesin particle having an average molecular weight of 10,000 to 1,500,000 and an average primary particle diameter of 10 μm or less and a solvent containing dichloropentafluoropropane as a main component is subjected to a high-pressure homogenizer. A method for producing the above fluororesin coating agent, characterized by performing a treatment.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the average molecular weight of a fluororesin is 10,000 to 1,500,000,
100,000 to 1,000,000 is more preferred. If the average molecular weight is too small, the resin component will sublime during the heat treatment or the properties of solid PTFE cannot be exhibited. On the other hand, if the average molecular weight is too large, the melt viscosity at the time of heat treatment is high, and it is difficult to form a film. In the present invention, PTFE can be preferably used as the fluororesin. In the present invention, PTFE includes not only homopolymers of tetrafluoroethylene (hereinafter also referred to as TFE), but also trace amounts of halogenated ethylene such as chlorotrifluoroethylene, halogenated propylene such as hexafluoropropylene, and perfluoropolymer. Modified P containing polymerized units based on a component copolymerizable with TFE such as fluorovinyl ether such as (alkyl vinyl ether), and which cannot be substantially melt-processed.
TFE is also included. In the present invention, PTFE having a melting point of 320 to 338 ° C. is particularly preferred as the fluororesin.

[0007] The method for producing a fluororesin in the present invention is not particularly limited. Typical PTFE production methods include (1) a method of irradiating PTFE with ionizing radiation in the presence of a mixed gas of an oxygen component and a halogenated methane (Japanese Patent Publication No. 52-25419), (2) TFE and others. (Japanese Patent Publication No. 38-20970), and (3) a method of thermally decomposing a copolymer of TFE and another perfluoroolefin under reduced pressure (Japanese Patent Publication No. Sho 50-970). 15506), (4) T using a chain transfer agent
Method of telomerizing FE (Japanese Patent Publication No. 51-25 / 1972)
275) and the like. In the present invention, it is important that the fluororesin having the above average molecular weight is dispersed in a specific solvent as fine particles having an average particle diameter of 10 μm or less. By setting the average particle diameter of the fluororesin fine particles to 10 μm or less, dispersion in a specific solvent becomes easy, and a uniform film without pinholes can be formed. Preferably, the average primary particle diameter of the fine particles is preferably 10 μm or less, and particularly preferably 0.1 to 9 μm. Here, the primary particle size is the size of a true particle. If the average particle diameter exceeds 10 μm, the dispersibility is reduced, and the coating thickness tends to be uneven.

In the present invention, the concentration of the fluororesin fine particles in the coating agent is preferably 0.5 to 25% by mass, particularly preferably 2 to 20% by mass. If the concentration is too low, it may be difficult to form a uniform film without pinholes. If the concentration is too high, the coating agent may become grease-like and lose fluidity. The solvent in the present invention is mainly composed of dichloropentafluoropropane (hereinafter, also referred to as R225). In the present invention, a solvent consisting of only R225 is preferable. R225 may be a mixture of isomers. For example, as the isomer, CF ₃ CF ₂ CHCl ₂ (hereinafter, R22
Also referred to as 5ca. ) And CClF ₂ CF ₂ CHClF
(Hereinafter also referred to as R225cb). In the present invention, such R225ca and R225cb
Can be used alone or as a mixture. As a commercially available product, AK-225 manufactured by Asahi Glass Co. is suitable.

The solvent in the present invention may contain a small amount of alcohol, ketone or the like in addition to R225.
Preferred examples of the alcohol include methanol, ethanol, and isopropanol, and examples of the ketone include acetone. The content of these alcohols and ketones is preferably 10% by mass or less. R225 has a low surface tension, so that even fluorine resin particles having low wettability can be satisfactorily dispersed, and because of the hydrogen atoms contained, it is easily decomposed and has a small ozone destruction coefficient. Although the fluororesin coating agent of the present invention has good dispersion stability without adding a surfactant, a solvent-soluble surfactant can be added to further assist the dispersion stability. Examples of such a surfactant include a fluorine-based surfactant such as a perfluoroalkyl polyoxyethylene adduct and a silicone-based surfactant. Specific examples thereof include Surflon S-393 manufactured by Seimi Chemical Co., Ltd. Florad FC-430, FC-431 manufactured by 3M, such as S-381, S-383, S-385
Megaface F-177, F-17 manufactured by Dainippon Ink and the like, such as Unidyne DS-451 manufactured by Daikin
8, F-171 and the like.

[0010] If necessary, one or more components such as a pigment, a resin powder other than the fluororesin, and a heat-resistant filler may be added to the fluororesin coating agent of the present invention as needed. In the present invention, the average molecular weight is 10,000 ~
1,500,000 and an average primary particle size of 10
The fluororesin coating agent of the present invention can be produced smoothly and advantageously by subjecting a mixture of a fluororesin particle having a particle size of not more than μm and a solvent containing dichloropentafluoropropane as a main component to a high-pressure homogenizer treatment.
The conditions of the high-pressure homogenizer treatment are not particularly limited, but the temperature is about 10 ° C. to 50 ° C., and the pressure is 10 to 200 MPa.
a is preferable, and particularly preferably 20 to 50 MPa. Even if the average primary particle diameter is small, a fluororesin having an excessively large average molecular weight is usually subjected to secondary agglomeration, so that it cannot be formed into a dispersion of primary particles by a high shear mixer or an ultrasonic emulsifier. . Such a fluororesin cannot be dispersed as fine particles having an average particle diameter of 10 μm even by the high-pressure homogenizer treatment in the present invention.

The fluororesin coating agent of the present invention can be used for coating various substrates. Examples of the substrate include various metals, glass, and ceramics having heat resistance. As the coating treatment method using the fluororesin coating agent of the present invention, any method can be adopted according to the form of the substrate. For example, preferable examples include spin coating, spray coating, bar coating, roll coating, dipping, and brush coating. After the substrate is coated with the fluororesin coating agent of the present invention, the substrate is dried and then heated to a high temperature to obtain a uniform film without pinholes. Heating temperature is 320 ° C ~ 34
5 ° C. is preferred. If the temperature is too low, a film will not be formed. The thickness of the film to be formed can be appropriately selected according to the application characteristics.
The thickness may be set to μm, and it is possible to increase the thickness to an arbitrary film thickness by further coating.

[0012]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, which should not be construed as limiting the present invention.

Example 1 100 g of PTFE particles (average molecular weight: 1,000,000, melting point: 330 ° C., average primary particle size: 0.2 μm) were placed in a beaker having an internal volume of 1000 mL.
Dichloropentafluoropropane (AK-2 manufactured by Asahi Glass Co., Ltd.)
25 g) was added and stirred at room temperature. Then, 8000 mi using a high shear stirrer (biomixer).
The mixture was stirred at n- ¹ for 3 minutes, and further passed once through a high-pressure homogenizer (manufactured by Goulin Co.) at a pressure of 40 MPa.
A transparent milky white dispersion was obtained. This dispersion produced a supernatant over time, but was uniformly redispersed only by gentle shaking. The average particle size measured by an electron microscope is 0.1.
2 μm, and was dispersed to primary particles. The composition was applied on an iron plate by a spray coating method so as to have a dry film thickness of 15 μm, and heated at 335 ° C. for 15 minutes. As a result, formation of a uniform continuous film without pinholes was observed.

Example 2 PTFE particles (average molecular weight 8
00,000, melting point 325 ° C, average primary particle diameter 9 µm)
A milky white dispersion was obtained in the same manner as in Example 1 except that This dispersion produced a supernatant over time, but was uniformly redispersed only by gentle shaking. The average particle size measured by an electron microscope was 9 μm. It was applied to an iron plate by a spray coating method so as to have a dry film thickness of 15 μm, and heated at 330 ° C. for 15 minutes. As a result, formation of a uniform continuous film without pinholes was observed.

Example 3 PTFE particles (average molecular weight 9
00,000, melting point 327 ° C, average primary particle size 0.2μ
Except for using m), a milky white dispersion having a transparent feeling was obtained in the same manner as in Example 1. This dispersion produced a supernatant over time, but was uniformly redispersed only by gentle shaking. The average particle diameter measured by an electron microscope was 0.2 μm, and the particles were dispersed up to the primary particles. The composition was applied on an iron plate by a spray coating method so as to have a dry film thickness of 15 μm, and heated at 335 ° C. for 15 minutes. As a result, formation of a uniform continuous film without pinholes was observed.

Comparative Example 1 PTFE Obtained by Emulsion Polymerization
Dispersion (average molecular weight 3,000,000, melting point 3
(40 ° C., average primary particle diameter 0.25 μm) was applied on an iron plate by a spray coating method so as to have a dry film thickness of 15 μm, and heated at 335 ° C. for 15 minutes. As a result, a continuous film was not formed. To form a continuous film, 3
Baking at 50 ° C. for 1 hour was required.

Comparative Example 2 PTFE particles (average molecular weight 8
00,000, melting point 325 ° C, average primary particle size 25μ
A dispersion was obtained in the same manner as in Example 1 except that m) was used. The average particle size measured by an electron microscope remained at 25 μm. This dispersion sedimented quickly, and the sedimentation was so rapid that a uniform coating could not be obtained.

[0018]

The fluororesin coating agent of the present invention comprises:
A uniform continuous film without pinholes can be formed at a relatively low heating temperature, and the dispersion stability is excellent without adding an emulsifier or a surfactant.

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Claims (3)

[Claims] (1) An average molecular weight of 10,000 to 1,500,00
A fluororesin coating agent, wherein the fluororesin is dispersed as fine particles having an average particle diameter of 10 μm or less in a solvent containing dichloropentafluoropropane as a main component. 2. The fluororesin coating agent according to claim 1, wherein the fluororesin is polytetrafluoroethylene having a melting point of 320 to 338 ° C. 3. An average molecular weight of 10,000 to 1,500,0.
The mixture of a fluororesin particle having an average primary particle diameter of 10 μm or less and a solvent containing dichloropentafluoropropane as a main component is subjected to a high-pressure homogenizer treatment. A method for producing the fluororesin coating agent according to the above.