JPH10120858A - Aqueous fluoro copolymer dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous fluoro copolymer dispersion markedly improved in mechanical stability by using a copolymer comprising vinylidene fluoride, hexafluoropropene and chlorotrifluoroethylene in a specified ratio. SOLUTION: This dispersion is prepared by dispersing a copolymer having a composition of about 70 to 90mol% vinylidene fluoride, about 2 to 30mol% hexafluoropropene and about 1 to 10mol% chlorotrifluoroethylene in an aqueous medium. To satisfy requirements for the chemical resistance and solvent resistance of a coating film, it is also possible that tetrafluoroethylene is used in an amount of at most 20mol%, and the hexafluoropropene is used in an amount of about 2 to 10ml%. In the production of the copolymer, it is desirable that the monomers are emulsion-polymerized in the presence of an emulsifier being ammonium perfluorooctanoate. It is desirable from a commercial viewpoint that the obtained aqueous dispersion has a solid concentration of about 30-50wt.%. A mechanical stability index determined by passing the latex through a 325 mesh screen ten times shows that the latex of this formulation has a reduced tendency toward the agglomeration and deposition of particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous dispersion of a fluorine-containing copolymer. More specifically, the present invention relates to a fluorocopolymer aqueous dispersion which is stable against mechanical treatment.

[0002]

2. Description of the Related Art An aqueous dispersion of a fluorinated (co) polymer is used for water-repellent, oil-repellent, antifouling, and mold release to various substrates such as resin, rubber, fiber, metal, glass, wood, and building materials. It is useful as a coating agent for imparting properties and chemical resistance. Thus, in order for the fluorine-containing (co) polymer aqueous dispersion to exhibit practicality as a coating agent, not only the aqueous dispersion has excellent sedimentation stability, but also stirring of the aqueous dispersion,
It is important to have sufficient stability against mechanical processing such as transfer, metering, pigment mixing, spraying and the like.

[0003] JP-A-7-258,499 discloses that vinylidene fluoride is 50 to 80% by weight and hexafluoropropene is 20 to 5%.
A monomer consisting of 0% by weight was copolymerized, and the average particle diameter was 30.
An aqueous dispersion of a fluorinated copolymer in which a fluorinated copolymer particle of ~ 200 nm is dispersed in an aqueous medium is described, and this fluorinated copolymer aqueous dispersion is excellent in sedimentation stability, It is described that a coating film having excellent weather resistance and stain resistance is easily formed. However, this aqueous dispersion cannot be said to be satisfactory in terms of mechanical stability, as shown in the results of Comparative Example 1 described later.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous dispersion of a fluorocopolymer used as a coating agent or the like, which has improved mechanical stability.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
About 70-90 mol% of vinylidene fluoride, about 2-30 mol% of hexafluoropropene and about chlorotrifluoroethylene
This is achieved by a fluorocopolymer aqueous dispersion in which a copolymer having a composition of 1 to 10 mol% is dispersed in an aqueous medium. This copolymer may further be obtained by copolymerizing about 20 mol% or less of tetrafluoroethylene.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the fluorinated copolymer, vinylidene fluoride [VdF] is about 70 to 90 mol%, preferably 72 to 88 mol%.
Is copolymerized at a ratio of At a copolymerization ratio of less than this, the adhesion to various substrates will be reduced, while when copolymerized at a higher ratio, the alkali resistance of the aqueous dispersion and the coating film formed therefrom will be reduced. Become.

[0007] Hexafluoropropene [HFP] is copolymerized at a ratio of about 2 to 30 mol%, preferably 4 to 22 mol% in the fluorinated copolymer. At a copolymerization ratio below this,
The hardness of the formed coating film becomes unnecessarily hard, which is not preferable. On the other hand, the copolymerization at a higher ratio not only makes the copolymerization reaction difficult, but also makes it possible to reduce the flexibility at low temperature of a coating film formed therefrom even if the copolymerization can be performed. Become. In addition, hexafluoropropene is relatively expensive, so using it more often leads to an increase in cost.

In the case where tetrafluoroethylene [TFE] is further copolymerized in the fluorinated copolymer, it is used in an amount of about 20 mol% or less, preferably 4 to 17 mol%. The copolymerization ratio of tetrafluoroethylene is increased or decreased according to the chemical resistance required for the coating film, especially the polar organic solvent resistance. At that time, the copolymerization amount of vinylidene fluoride is adjusted according to the copolymerization amount of tetrafluoroethylene, and the copolymerization ratio of hexafluoropropene is set in a range of about 2 to 10 mol%.

[0009] Chlorotrifluoroethylene [CTFE] copolymerized with each of these monomer components significantly improves the mechanical stability of the aqueous fluorocopolymer dispersion. The copolymerization ratio is about 1 to 10 mol%, preferably 3 to 7 mol% .Even if the copolymerization is carried out at a higher ratio, the effect of improving mechanical stability does not improve significantly. This is not preferable because it only increases the cost of the product.

[0010] The above-mentioned patent publication discloses that 0 to 30% by weight
It is described that other copolymerizable monomers can be copolymerized, and tetrafluoroethylene, chlorotrifluoroethylene and the like are mentioned as one example of such a monomer exemplified in a large number. It is pointed out that there is no specific description about them, and no mention is made of any specific effect of copolymerizing chlorotrifluoroethylene.

At the time of the copolymerization reaction, other fluorinated olefins, various olefin compounds or vinyl compounds can be copolymerized to such an extent that the copolymerization reaction is not inhibited (about 20 mol% or less). As other fluorinated olefins, for example, monofluoroethylene, trifluoroethylene, trifluoropropylene, pentafluoropropylene, hexafluoroisobutylene, dichlorodifluoroethylene and the like are used, and as the olefin compound or vinyl compound, for example, ethylene, propylene ,
1-butene, isobutylene, methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, trifluorostyrene and the like are used. Of these, at least one of trifluoroethylene, chlorotrifluoroethylene, methyl vinyl ether and the like is preferably used. In addition, perfluorovinyl ether compounds such as perfluoro (methyl vinyl ether), perfluoro (ethyl vinyl ether), and perfluoro (propyl vinyl ether) can also be used.

The copolymerization reaction can be carried out by any polymerization method such as emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization and the like, but the emulsion polymerization method is preferred from the viewpoint of increasing the degree of polymerization and economy. The emulsion polymerization reaction uses a water-soluble inorganic peroxide such as ammonium persulfate or a redox system thereof and a reducing agent as a catalyst to form ammonium perfluorooctanoate, ammonium perfluoroheptanoate, ammonium perfluorononanoate, perfluorooxyalkyl carboxylate. Ammonium or the like or a mixture thereof, preferably using ammonium perfluorooctanoate as an emulsifier, generally at a pressure of about 10 MPa or less, preferably about 0 to 5 MPa
a, the reaction is carried out at a temperature of about 0 to 100 ° C, preferably about 20 to 90 ° C. At that time, in order to adjust the pH in the polymerization system, Na
₂ HPO ₄ , NaH ₂ PO ₄ , KH ₂ PO ₄ or the like may be used by adding an electrolyte substance having a buffering ability.

The obtained fluorinated copolymer generally has a solution viscosity ηsp / c of about 0.5 to 1.5 dl / g, preferably 0.8 to 1.2 dl / g.
Has the value of

The aqueous dispersion is prepared by using the aqueous dispersion obtained by the emulsion polymerization method as it is, or by dispersing the copolymer obtained by another polymerization method using an emulsifying / dispersing machine. However, from the viewpoints of production cost, fineness of the particle size of the obtained aqueous dispersion, etc., it is preferable that the aqueous dispersion is prepared by a method using the emulsion polymerization aqueous dispersion as it is or a method of further adding a dispersion operation thereto. On this occasion,
In the aqueous dispersion, an emulsifier, an emulsifier, an antifoaming agent, a thickener,
Various additives such as a freeze stabilizer, a bulking agent, and a coloring agent are added as necessary.

The concentration of the fluorinated copolymer (solid content) in the aqueous dispersion may vary depending on the characteristics required when applied to the substrate to be treated, the treatment method, and the like. Is desirably a stock solution concentration of about 30 to 50% by weight, and the mechanical stability and storage stability (sedimentation stability) in such a concentration range must be good. At the time of use, it is appropriately diluted with water or the like according to each use.

The average particle size of the fluorocopolymer particles in the aqueous dispersion is about 30 to 200 nm, preferably about 50 to 135 nm.
nm. If the particle size is larger than this, not only is the storage stability of the aqueous dispersion inferior, but also the gloss of the coating film formed therefrom is inferior. On the other hand, if the particle size is to be made smaller than this, it is necessary to increase the amount of a surfactant that adversely affects the water resistance and durability of the coating film, and also requires an expensive emulsifying and dispersing apparatus. Become like

[0017]

The aqueous dispersion comprising a copolymer of vinylidene fluoride, hexafluoropropene (and tetrafluoroethylene) is obtained by further copolymerizing chlorotrifluoroethylene in the copolymer. The mechanical stability can be significantly improved.

[0018]

Next, the effects of the present invention will be described with reference to examples.

Example 1 Into an autoclave having an internal volume of 10 L, 6 L of deionized water, 20 g of ammonium perfluorooctanoate and 2 g of sodium hydroxide (for adjusting pH) were charged, and the internal space was replaced with nitrogen gas. Vinylidene-hexafluoropropene-chlorotrifluoroethylene (molar ratio 42.3: 49.7: 8.
0) The internal pressure is 24 kg / cm ² G using the mixed gas as the initial charge gas.
Until it became Thereafter, 10 g of diethyl malonate was injected, and the internal temperature was raised to 80 ° C. (internal pressure: 37 kg / cm ² G).

Thereafter, 5 g of ammonium persulfate was added to 150 ml of water.
The polymerization initiator aqueous solution dissolved in was poured into an autoclave to start the polymerization reaction. When the internal pressure drops to 29 kg / cm ² G, vinylidene fluoride-hexafluoropropene-chlorotrifluoroethylene (molar ratio 72.5: 20.5: 7.
0) The mixed gas was used as a dispensing gas and was injected until the internal pressure reached 30 kg / cm ² G.

Each time the internal pressure is reduced to 29 kg / cm ² G, the operation of injecting the above-mentioned dispensing gas until the internal pressure becomes 30 kg / cm ² G is performed by increasing the solid content concentration of the aqueous dispersion obtained after polymerization to 40 kg / cm ² G. The procedure was repeated until the weight% was reached. Thereafter, the unreacted gas was immediately purged, and the inside of the autoclave was rapidly cooled to stop the polymerization reaction.

The following items were measured for the obtained aqueous dispersion. Composition of fluorinated copolymer: Determined by ¹⁹ F-NMR for particles obtained by agglomerating and breaking an aqueous dispersion with a homomixer and drying with water, and determined by ¹⁹ F-NMR. Solution viscosity of fluorinated copolymer ηsp / c : Agglomeration and destruction of the aqueous dispersion with a homomixer, particles obtained by washing and drying were measured at 35 ° C. as a methyl ethyl ketone solution having a concentration of 1 (w / v)% Solid component concentration: aqueous dispersion Approximately 10 g is precisely weighed on an aluminum dish, and evaporated to dryness at 120 ° C. for 24 hours, and the evaporation residue is precisely weighed and calculated.
Mechanical stability test by UPA9340: 325 aqueous dispersion of fluorinated copolymer
The average particle diameter and solid component concentration of the aqueous dispersion passing component after passing through the mesh metal sieve 10 times are measured, and the decrease rate of the solid component concentration and the increase rate of the particle diameter are calculated. As an index of strategic stability

Comparative Example 1 A copolymerization reaction was carried out in the same manner as in Example 1 except that the composition of the initially charged gas and the composition of the added gas were changed as shown in the following table, and the same procedure was carried out for the obtained aqueous dispersion of fluorine-containing copolymer. A measurement was taken.

Example 2 and Comparative Example 2 In Example 1, the composition of the initially charged gas and the composition of the added gas were changed as shown in the table below, the amount of ammonium perfluorooctanoate was changed to 30 g, and the addition was further performed. The copolymerization reaction was continued while the gas was charged until the solid component concentration became 45% by weight, and the same measurement was performed on the obtained aqueous dispersion of a fluorinated copolymer.

The results obtained in each of the above Examples and Comparative Examples are as follows, together with the initial gas composition and the divided gas composition.
This is shown in the following table. Table Example 1 Comparative Example 1 Example 2 Comparative Example 2 [Initial charge gas composition] VdF (mol%) 42.3 46.0 81.9 83.1 HFP (mol%) 49.7 54.0 8.7 11.0 TFE (mol%) 5.3 5.9 CTFE (mol%) 8.0 4.1 [Partition gas composition] VdF (mol%) 72.5 78.0 85.0 87.6 HFP (mol%) 20.5 22.0 6.0 6.2 TFE (mol%) 6.0 6.2 CTFE (mol%) 7.0 3.0 [Copolymer composition] VdF (mol%) 72.5 78.0 85.0 87.6 HFP (mol%) 20.5 22.0 6.0 6.2 TFE (mol%) 6.0 6.2 CTFE (mol%) 7.0 3.0 [Copolymer composition] VdF (wt%) 54.4 60.2 75.0 78.3 HFP (wt%) 36.0 39.8 12.0 13.0 TFE (wt%) 8.0 8.7 CTFE (wt%) 9.6 5.0 [Copolymer solution viscosity] ηsp / c (g / dl) 0.90 0.88 0.95 0.94 [Aqueous dispersion properties] Solid concentration (wt%) 40.1 40.0 45.5 45.2 Average particle size (nm) 125 118 60 57 [Mechanical stability of aqueous dispersion] Solid component concentration (% by weight) 39.4 37.9 45.0 43.2 Reduction rate (%) 1.7 5.3 1.1 4.4 Average particle size (nm) 130 140 71 78 Growth rate (%) 4.0 18.6 18.3 36.8

From the above results, the following can be said. (1) While maintaining the VdF / HFP molar ratio of Comparative Example 1, a total of 7
In Example 1 in which an amount of CTFE corresponding to mol% was copolymerized, the solid concentration after mechanical treatment was increased from 5.3% to 1.7%.
Decreased to. In addition, the average particle diameter increase rate is from 18.6% to 4.0%
Decreased to. This indicates that aggregation and precipitation of the particles were reduced even by the mechanical treatment. (2) With respect to Example 2 in which an amount of CTFE corresponding to 3 mol% of the whole was copolymerized while maintaining the VdF / HFP / TFE molar ratio of Comparative Example 2, the same as (1) above was observed. I can say.

Claims (4)

[Claims] 1. A copolymer having a composition of about 70 to 90 mol% of vinylidene fluoride, about 2 to 30 mol% of hexafluoropropene and about 1 to 10 mol% of chlorotrifluoroethylene is dispersed in an aqueous medium. An aqueous dispersion of a fluorinated copolymer. 2. An amount of about 20 mol% or less of tetrafluoroethylene is further copolymerized and hexafluoropropene is added to about 2 mol%.
The aqueous dispersion of a fluorine-containing copolymer according to claim 1, wherein a copolymer copolymerized at a ratio of about 10 mol% is used. 3. The aqueous dispersion of a fluorine-containing copolymer according to claim 1, wherein a copolymer having an average particle size of about 30 to 200 nm is dispersed in an aqueous medium. 4. The aqueous dispersion of a fluorine-containing copolymer according to claim 1, wherein the copolymer having a solid content of about 40 to 50% by weight is dispersed in an aqueous medium.