JP3156860B2 - Hydrophilic fluororesin powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrophilic fluororesin powder.

[0002]

2. Description of the Related Art Fluororesin powder has a number of excellent properties such as water repellency, chemical stability, thermal stability, low friction, and weather resistance. Used in a wide range of fields. Conventionally, various types of fluororesin powder are commercially available, for example, polytetrafluoroethylene ( PTFE ), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-6-fluoropropylene Copolymer (FEP), ethylene-3-fluoroethylene-6-fluoropropylene copolymer (FEP), ethylene-3-fluoroethylene chloride copolymer (ECTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene -Perfluoroalkyl vinyl ether copolymer (PFA)
There is a powder of a fluororesin, etc., which is commercially available in the form of ground powder or a dispersion in which the powder is dispersed in an aqueous solution containing a surfactant. By the way, since such fluororesin powder has very high water repellency, it is very difficult to disperse it in water or an aqueous solution, and it is necessary to use a large amount of a surfactant. Problem. For this purpose, it has been proposed to coat the surface of a fluororesin powder with a thermosetting resin, metal, ceramics or a mixture thereof to make the surface hydrophilic (Japanese Patent Application Laid-Open No. 64-51454). However, in such a method, the powder surface is made hydrophilic and its wettability is improved, but there is a drawback that the excellent properties inherently possessed by the fluororesin cannot be fully utilized, and the method is still satisfactory. Not something to do. For example, when the powder surface is coated with a thermosetting resin, the chemical stability and weather resistance of the fluororesin are sacrificed. When the metal is coated on the powder surface, the chemical stability and low friction property of the fluororesin are impaired. When coating ceramics on the powder surface, it is necessary to lower the curing temperature to 300 ° C or less, so that the properties of the ceramics cannot be fully utilized and the resulting powder surface has extremely poor chemical stability. Become. On the other hand, when the fluororesin powder is dispersed in an aqueous solution, a large amount of a surfactant of several percent or more is required, so that the resulting dispersion itself is contaminated with the surfactant, and its use is significantly limited. In addition, bubbles are very easy to form, and troubles caused by the foaming also occur.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems found in the prior art, and provides excellent properties inherent to the fluororesin such as chemical stability, heat stability and low friction. Another object of the present invention is to make the fluororesin powder hydrophilic and improve the surface wettability without impairing the weather resistance.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, when coating a fluororesin powder with a film of a fluorine-containing compound having a hydrophilic group, the fluororesin Can impart hydrophilicity to the fluororesin powder and improve its surface wetting characteristics without impairing the excellent properties inherent in the powder, and the coating formed on the powder surface adheres to the powder The present inventors have found that the present invention has excellent properties, and have completed the present invention. That is,
According to the present invention, there is provided a hydrophilic fluororesin powder obtained by coating the surface of a fluororesin powder with a fluorine-containing compound having a hydrophilic group.

The fluororesin powder used in the present invention includes:
Conventionally known ones, for example, polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-trifluorochloroethylene copolymer,
Examples thereof include polyvinylidene fluoride and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. The average particle size of the fluororesin powder is usually
It is 0.1 to 100 μm, preferably 0.5 to 10 μm. In the present invention, a fluorine-containing compound having a hydrophilic group is adhered on the surface of the fluororesin powder in a film form. The fluorine-containing compound having a hydrophilic group only needs to be in a liquid or solid state at room temperature, and includes a low molecular compound, an oligomer, a polymer, and the like. Further, these fluorine-containing compounds can exist in a cross-linked state on the surface of the powder particles. The fluorine-containing compound having a hydrophilic group adhered to the powder surface is 1 to 10 with respect to the final product powder.
% By weight, preferably 2 to 6% by weight. As a method for forming a film by adhering and bonding a fluorine-containing compound having a hydrophilic group to the powder surface, a conventionally known method, for example, a chemical method such as an interfacial polymerization method or an interfacial reaction method, or a phase from an aqueous solution system is used. In addition to a separation method and a physicochemical method such as a phase separation method from an organic solvent system, an air suspension coating method, a spray drying method and the like can be mentioned.

As the fluorine-containing compound having a hydrophilic group,
Hydrophobic part containing fluorine in the molecule, and those having a hydrophilic part having a hydrophilic group, those having some solubility in water or aqueous solution, preferably those which show substantially water insolubility Use is preferred. Examples of the hydrophilic group include, for example, a hydroxyl group, a carboxyl group, a sulfone group, a cyano group, a pyrrolidone group, an isocyanate group, an imidazole group, a phosphoric acid group, an N-substituted amide group, and an N-substituted group. And an amino group and a sulfonamide group. Further, an alkylene oxide such as ethylene oxide or propylene oxide may be added to the active hydrogen of the hydrophilic group.

The preferred fluorine-containing compound having a hydrophilic group used in the present invention is a fluorine-containing hydrophilic polymer. This can be obtained by copolymerizing a fluorine-containing ethylenically unsaturated monomer and a fluorine-containing hydrophilic group-containing vinyl monomer. Examples of the fluorine-containing monomer include tetrafluoroethylene, vinyl fluoride, vinylidene fluoride, monochlorotrifluoroethylene, dichlorodifluoroethylene, and hexafluoropropylene.

[0008] Preferred fluorine-containing monomers can be represented by the following general formula: CXY = CFZ (1) In the above formula, Z represents fluorine or hydrogen, and X and Y represent hydrogen, fluorine, chlorine and trifluoromethyl (—CF ₃ )
Selected from

Another preferred fluorine-containing monomer can be represented by the following general formula. In the above formula, R is hydrogen, fluorine, a methyl group, an ethyl group, a trifluoromethyl group (CF ₃ ) or pentafluoroethyl (C ₂ F ₅ ). Rf represents a perfluoroalkyl group having 4 to 21 carbon atoms.

On the other hand, as the hydrophilic group-containing monomer, the above-mentioned vinyl monomers having various hydrophilic groups and monomers obtained by adding an alkylene oxide, for example, ethylene oxide or propylene oxide, to the active hydrogen of the hydrophilic group are also preferable. is there. As in the case of vinyl acetate, those which give a hydrophilic group-containing copolymer by copolymerization followed by hydrolysis are also used. Specific examples of the hydrophilic monomer include vinyl alcohol, acrylic acid, methacrylic acid,
In addition to unsaturated carboxylic acids such as fumaric acid, maleic acid and itaconic acid, the following alkylene oxide adducts of acrylic acid and methacrylic acid can be mentioned.

[0011] In the above formula, R is hydrogen or a methyl group, and n and m are 1
Is an integer greater than or equal to. Each of the fluorinated monomer and the hydrophilic group-containing monomer may be one type or two or more types. Further, the fluorine-containing monomer and the hydrophilic group-containing monomer,
If necessary, another vinyl monomer, for example, an alkyl ester of acrylic acid or methacrylic acid, or an ester of acrylic acid or methacrylic acid with a polyhydric alcohol such as trimethylolpropane can be used in combination.

A copolymer of vinyl alcohol and a fluorine-containing monomer which is preferably used as a fluorine-containing hydrophilic polymer is obtained by saponifying a copolymer of vinyl acetate and a fluorine-containing monomer, and converting an acetate group contained in the copolymer into a hydroxyl group. Can be obtained by In this case, it is not always necessary to convert all of the acetate groups contained in the copolymer to hydroxyl groups, and the conversion of the acetate groups to hydroxyl groups may be performed to such an extent that the copolymer has hydrophilicity. The fluorine content of the fluorine-containing hydrophilic copolymer is based on weight,
Usually, it is 2% to 60%, preferably 10% to 60%, and more preferably 20% to 60%. If the fluorine content of the fluorine-containing hydrophilic copolymer is too high, the heat resistance is improved, but the hydrophilicity of the polymer is reduced. On the other hand, if the fluorine content is too low, the adhesiveness to the powder of the fluorine-containing hydrophilic copolymer decreases, and the heat resistance also decreases. In the fluorine-containing hydrophilic copolymer preferably used for making the powder hydrophilic, the hydrophilic group equivalent is generally 45 to 70.
0, preferably 60 to 500. When the hydrophilic group equivalent is less than 45, the solubility of the fluorinated hydrophilic copolymer becomes very large, and the copolymer is easily eluted from the powder with water, while when the hydrophilic group equivalent is larger than 700, the hydrophilicity becomes small. It becomes too much, and the hydrophilicity of the powder becomes insufficient.

Tables 1 and 2 show, for some copolymers, mol% of fluorine-containing monomer units, fluorine weight% (F-wt%) and hydrophilic group equivalent (Eq
-W). VOH is vinyl alcohol.

In the present specification, the hydrophilic group equivalent (Eq
-W) is the value obtained by dividing the molecular weight of the copolymer by the number of hydrophilic groups. The hydrophilic group equivalent shown below is calculated by the following equation. In the formula, A · x is a value obtained by multiplying the molecular weight of the fluorine-containing monomer by the number of moles x, while By · y is a value obtained by multiplying the molecular weight of the hydrophilic group-containing monomer by the number of moles y.

[0015]

[Table 1] Copolymer In the copolymer The molar ratio of in the copolymer Fluorine-containing monomer F-wt% Eq-W mol% of unit (CF ² = CF ² ) x / (VOH) y X = 1, Y = 40 2.4 4.2 45.5 1, 30 3.2 5.5 46.4 1, 20 4.8 7.9 48.0 1, 10 9.1 14.3 53 1, 4 20 27.5 68 1, 1 50 53.1 143 10, 1 91 72.8 1043 (CF ² = CFH) x / (VOH) y X = 1, Y = 40 2.4 2.1 44.6 1, 30 3.2 2.8 45.2 1, 20 4.8 4.1 46.2 1, 10 9.1 7.5 49 1, 4 20 − − 1, 1 50 33.6 107 10, 191 55.6 683 (CFH = CH ² ) x / (VOH) y X = 1, Y = 40 2.4 1.1 44.2 1, 30 3.2 1.4 45.6 1, 20 4.8 2.1 45.3 1, 10 9.1 4.0 47.6 1, 4 20 − − 1, 1 50 21.3 89 10, 191 37.8 503

[0016]

[Table 2] Copolymer In the copolymer The molar ratio of in the copolymer Fluorinated monomer F-wt% Eq-W Molar% of unit (CF ² = CFCl) x / (VOH) y X = 1, Y = 40 2.4 3.1 46.0 1 , 30 3.2 4.0 46.9 1, 20 4.8 5.8 48.9 1, 10 9.1 10.4 54.6 1, 4 20 − − 1, 1 50 35.8 159 10, 191 47.2 1208 (CF ² = CCl ² ) x / (VOH) y X = 1, Y = 40 2.4 2.0 46.6 1, 30 3.2 2.7 47.7 1, 20 4.8 3.8 50.0 1, 10 9.1 6.7 57 1, 4 20 − − 1, 1 50 20.8 183 10, 1 91 26.3 1442 (CF ² = CFCF ³ ) x / (VOH) y X = 1, Y = 40 2.4 6.1 46.8 1, 30 3.2 7.9 48.0 1, 20 4.8 11.3 50.5 1, 10 9.1 19.6 58 1, 4 20 − − 1, 1 50 59.0 193 10, 1 91 73.9 1543

In order to adhere the fluorinated hydrophilic polymer to the powder surface, for example, a fluorinated hydrophilic copolymer is dissolved in an organic solvent such as alcohol, ketone, ester, amide or hydrocarbon, and The powder is immersed in the solution or the solution is sprayed on the powder surface and then dried. Alternatively, the solution of the fluoropolymer and the powder may be mixed, and the mixture may be freeze-dried by spray drying or ice-drying. Further, a monomer having a hydrophilic group and a fluorine-containing monomer may be polymerized on the powder surface. Thus, the fluorinated hydrophilic polymer adheres to the powder surface, and a powder that has been hydrophilized can be obtained. The amount of the fluorinated hydrophilic polymer adhered to the powder may be an amount sufficient to make the powder surface hydrophilic, and varies depending on the type of powder used, but usually the weight of the final product powder. 1 to 10% by weight, preferably 2 to 6% by weight.

The hydrophilicized fluororesin powder is impregnated with an organic solvent solution of a copolymer of a fluorine-containing monomer and a hydrophobic monomer such as vinyl acetate which can be converted into a hydrophilic group, and the powder is dried. Then, it can be produced by converting at least a part of the acetate group into a hydrophilic group.

The hydrophilic fluororesin powder obtained as described above has a structure in which a hydrophilic fluoropolymer is bonded to the surface in a film-like manner. This makes the surface of the powder hydrophilic. Elution of the polymer itself from the powder can be prevented by regulating the hydrophilic group equivalent of the hydrophilic fluoropolymer within an appropriate range and controlling the solubility of the polymer in water. The adhesive bonding force of the fluorine-containing hydrophilic copolymer to the fluororesin powder becomes strong by the action of fluorine atoms in the copolymer, and is maintained in a stable state for a long period of time.

The other fluorine-containing compound having a hydrophilic group preferably used in the present invention is a fluorine-containing surfactant.
Specific examples of this are shown below. ^{RfCONHC 2 H 4 OC (C 2} H 4 O) nH (11) RfSO 2 NH 2 H 4 O (C 2 H 4 O) nH (12) RfC 2 H 4 OH (13) RfCOOH (14) RfC 2 H 4 N (CH ³ ) ² (15) In the above general formula, Rf is a perfluoro higher alkyl group, and has 8 or more carbon atoms, preferably 12 to 30 carbon atoms.
It is. N is an integer of 1 or more, preferably an integer of 2 to 5. These fluorinated surfactants, at room temperature,
It is liquid or solid. To attach the fluorinated surfactant to the powder surface, the fluorinated surfactant is dissolved in an organic solvent such as a halogenated hydrocarbon, ethyl acetate or acetone, and the powder is immersed in this solution. The solvent may be removed. The concentration of the fluorinated surfactant in the solution is 1 to 10% by weight, preferably 2 to 5% by weight.

[0021]

The fluororesin powder coated with the fluorine-containing compound having a hydrophilic group according to the present invention has a hydrophilic surface and a remarkably improved wettability. Excellent properties are not impaired at all. The fluorine-containing resin powder of the present invention can be easily dispersed in water or an aqueous solution, and can be handled in the same manner as a conventional general hydrophilic powder. The fluororesin powder of the present invention can be used for applications such as pigments, plating bath additives, and lubricants.

[0022]

Next, the present invention will be described in more detail with reference to examples. Example 1 Polytetrafluoroethylene fine powder for lubrication (A) (low molecular weight tetrafluoroethylene resin powder, manufactured by Daikin Industries, Lubron L-2, particle diameter: 5 μm, bulk specific gravity: about 0.35 g)
/ Cc) and a 0.1% methyl alcohol solution of a tetrafluoroethylene / vinyl alcohol copolymer (fluorine content 27% by weight) in a resin solid content weight ratio of 100: 0.
The solution mixed at a ratio of 5 was spray-dried in an atmosphere at 80 ° C. to obtain a fine powder whose particle surface was coated with a tetrafluoroethylene / vinyl alcohol copolymer.

Example 2 Fine powder of polytetrafluoroethylene (A) for lubrication and a fluorine-based surfactant (Fluorad RC, manufactured by Sumitomo 3M Limited)
-170C, perfluoroalkyl polyoxyethylene ethanol) and a 0.2% isopropyl alcohol solution were mixed at a resin solid content weight ratio of 100: 1, and spray-dried in a 100 ° C atmosphere to obtain a particle surface. It was a fine powder coated with a fluorine-based surfactant.

Comparative Example 1 A solution obtained by mixing a polytetrafluoroethylene fine powder for lubrication (A) treated with an ammonia solution of metallic sodium and a polyamideimide resin paint at a resin solid content weight ratio of 100: 40 was used. It was spray-dried in an atmosphere at 150 ° C. to obtain a fine powder whose particle surface was coated with a polyamideimide resin. Comparative Example 2 Fine lubricating polytetrafluoroethylene powder (A) treated with an aqueous ammonia solution of metallic sodium was sequentially immersed in an aqueous solution of tin chloride, an acidic aqueous solution of palladium chloride, and an electroless nickel plating bath, and the particle surface was plated with nickel. Powder. Comparative Example 3 Lubricating polytetrafluoroethylene fine powder (A) which had been treated with an ammonia solution of metallic sodium was immersed in an isopropyl alcohol solution of silicon isopropoxide Si [OCH (CH ³ ) ² ] ⁴ and then hydrolyzed in water. The powder was decomposed to obtain a fine powder whose particle surface was coated with SiO ² . Reference Example A lubricating polytetrafluoroethylene fine powder (A) which had not been subjected to any surface treatment was used.

Next, the following evaluation was performed using the above samples. Table 1 shows the results. (Wettability) 5 parts by weight of the obtained powder was added to 100 parts by weight of water, the mixture was stirred with a homogenizer, the state of dispersion of the powder in water was observed, and evaluated according to the following criteria. A: Powder is uniformly dispersed in water B: Powder agglomerates in water C: Powder separates into wet and non-wet parts D: Powder does not get wet and floats on water surface or adheres to vessel wall (Adhesion of Film) After the obtained powder was ground in a mortar, the above-mentioned wettability test was performed. (Acid resistance) After the obtained powder was immersed in 3N hydrochloric acid at room temperature for 24 hours, the above-mentioned wettability test was performed. (Alkali Resistance) The obtained powder was immersed in a 1N aqueous solution of sodium hydroxide at room temperature for 24 hours, and then the above wettability test was performed.

(Appearance of coating film) To 100 parts by weight of a commercially available alkaline paint, 20 parts by weight of the obtained powder was added.
A weight part (weight ratio of solid content with the fluororesin: 100: 10) was added, and the mixture was stirred with a homogenizer to obtain a test paint. Next, a coating film is formed on SUS304 with these test paints,
The appearance of the coating film was observed. (Weather resistance) Test pieces similar to those in the section of the appearance of the coating film were prepared, and after performing an outdoor exposure test for 60 days, the state of the coating film was observed. (Coefficient of dynamic friction) Create a test piece similar to that of the appearance of the coating film,
The dynamic friction coefficient was measured using a Suzuki friction wear tester. Test conditions: Counterpart material SUS304 Load 10kg Speed 1m / s

[0027]

[Table 1]

Claims (3)

(57) [Claims] 1. A hydrophilic fluororesin powder obtained by coating the surface of a fluororesin powder with a fluorine-containing compound having a hydrophilic group. 2. The powder according to claim 1, wherein said fluorine-containing compound is a fluorine-containing polymer. 3. The powder according to claim 1, wherein said fluorine-containing compound is a fluorine-containing surfactant.