JPS5865711A - Production of polyvinylidene fluoride powder - Google Patents

Abstract

PURPOSE:To produce a polyvinylidene fluoride powder excellent in heat stability, solubility and organosol formability without detriment to the polymerization rate, by using a specified chain transfer agent in polymerizing vinylidene fluoride with the aid of a persulfate initiator. CONSTITUTION:Use is made of, as a chain transfer agent, 0.1-5mol%, based on vinylidene fluoride, methyl acetate and/or ethyl acetate. Namely, water is charged with vinylidene fluoride, 0.001-1wt%, based on water, persulfate (e.g., potassium persulfate, ammonium persulfate), 0.01-0.5wt%, based on water, emulsifier (e.g., ammonium perfluorooctanoate), and a predetermined amount of methyl acetate and/or ethyl acetate, and the mixture is emulsion-polymerized at about 70-100 deg.C and about 5-45kg/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyvinylidene fluoride powder, and more specifically, when polymerizing vinylidene fluoride using persulfuric acid as a polymerization initiator, thermal stabilization is achieved using a specific chain transfer agent. The present invention relates to a method for producing polyvinylidene fluoride powder having excellent properties, solubility, and organosol-forming properties.

Vinylidene fluoride polymers have excellent weather resistance and other physical properties such as elasticity, scratch strength, and toughness, so they are used as coating materials for metal plates, etc. , its applications have expanded significantly in recent years. Organosol-type paints are especially advantageous for outdoor painting, and these organosols contain fine powder of vinylidene fluoride polymer in a latent organic solvent.
It has the advantage that a wide range of processing methods such as spray coating or dip coil coating can be applied when dispersed at a high concentration of 40%. It must be vinyl fluoride fine powder used in organosol. Regarding thermal stability in particular, polyvinylidene fluoride has a tendency to develop a yellowish coloration when heated to the high temperatures applied during baking of organosol paints, and if this coloration is significant, it will not work as a paint film. To avoid this, it is necessary to have good thermal stability at high temperatures, and solubility in solvents is necessary in order to obtain a coating film with no microvoids and good mechanical properties. Furthermore, in order to keep the viscosity of the organosol paint low, the polymer particles are spherical and have a size in the range of 0.2 to 1.0μ, particularly 0.3 to 0.0μ.
A particle size of 5 microns is useful, and fine polyvinylidene fluoride powder useful for such organosols can be obtained by emulsion polymerization.

By the way, regarding the emulsion polymerization method of vinylidene fluoride,
Many studies have been carried out so far, particularly on various compounds used as radical initiators and on chain transfer agents. Radical initiators can be broadly classified into oil-soluble organic peroxides (for example, Japanese Patent Publication No. 88-5489, Japanese Patent Publication No. 46-9476, and Japanese Patent Publication No. 46-2082).
0) and water-soluble peroxides (see U.S. Pat. No. 2)
, 485.587, Japanese Patent Publication No. 45-41596, and Japanese Patent Publication No. 48-555).

In the case of hydrogen peroxide among the former oil-soluble organic peroxides and water-soluble peroxides, it is easy to obtain polymers with excellent thermal stability, but in many cases, the polymerization rate is low, so that economically useful polymerization is difficult. To get the speed 40h/1-
It is necessary to polymerize at a high monomer pressure of rn or higher. On the other hand, when persulfate is used as a polymerization initiator, 40 kg
Even at a monomer pressure of /crn2 or less, the polymerization rate is high and only one high molecular weight polymer can be obtained, which is industrially advantageous. However, the polymers obtained using persulfate initiators are colored when heated to high temperatures, have poor thermal stability, and are partially crosslinked with N,N'-dimethyl There is a problem in that it does not completely dissolve in a solvent such as acetamide and forms a gel or colloid, resulting in poor solubility in the solvent.

Many studies have been made on chain transfer agents used to control molecular weight in vinylidene fluoride emulsion polymerization. For example, Special Publication No. 45-41596.

It is described in Japanese Patent Publication No. 45-18870, Japanese Patent Publication No. 51-25078, Japanese Patent Application Laid-open No. 10428-1973, etc.
In most cases, water-soluble ketones, alcohols, ethers, and halogenated hydrocarbons are used as chain transfer agents. However, when the above-mentioned transfer agent is used in emulsion polymerization based on persulfate initiators, the polymerization rate decreases significantly, and this tendency is particularly noticeable with halogenated hydrocarbons and alcohols, resulting in unavoidable industrial disadvantages and adding Thermal stability when using the polymer and ether obtained by this method was very poor. When alcohol is used, the stability of the dispersed particles during polymerization is poor, and coagulation occurs at low concentrations, making it impossible to obtain a highly concentrated dispersion, which is not preferred. The best of the chain transfer agents mentioned above are water-soluble ketones, such as acetone, but the reduction in polymerization rate is quite large, and the thermal stability of the polymer is not as good as that obtained with oil-soluble peroxide initiator systems. It is inferior to other polymers, and is not industrially sufficient in terms of production of single polymers and applications such as coating polymers.

In view of these circumstances, the present inventors have developed a system for emulsion polymerization using a persulfate initiator alone, which is an initiator that has the great advantage of easily producing a high molecular weight polymer in a high yield even in low-pressure polymerization. As a result of investigating chain transfer agents in order to develop a method that causes less deterioration and has excellent thermal stability and solvent solubility of the obtained polymer, we found that methyl acetate or ethyl acetate was used as a chain transfer agent. The inventors have discovered that a polymer with excellent thermal stability and solvent solubility can be obtained as a highly concentrated dispersion, and that the polymerization rate does not decrease, thereby completing the present invention.

That is, 1. The gist of the present invention is a polyvinylidene fluoride powder characterized in that methyl acetate and/or ethyl acetate are used as a chain transfer agent when emulsion polymerizing vinylidene fluoride using a persulfate as a polymerization initiator. It consists in the manufacturing method.

According to the method of the invention, using persulfate as an initiator, 70
When emulsion polymerization is carried out at a temperature of ~110°C, there is little decrease in the polymerization rate, and a dispersion with a high concentration of 25% by weight or more can be obtained.
Furthermore, the resulting polymer is completely and uniformly dissolved in dimethylacetamide, does not gel, and is colored similarly to polymers obtained with oil-soluble peroxide initiators even when heated to high temperatures. It has exceptional thermal stability.

The amount of methyl acetate and/or ethyl acetate used as a chain transfer agent varies depending on the intended use of the resulting polymer.

For example, the properties for coating materials are greatly influenced by the molecular weight and melt flowability of the polymer/body, but in this case, the melt flow value is 2X10 by the measurement method defined below.
- to 2 x 10-2 crn3/sec is preferred, and to achieve this desired range, 0.1 to 5 mol% of methyl acetate and/or ethyl acetate is added to the vinylidene fluoride monomer. It can be used in proportion.

Persulfate is used alone as a polymerization initiator.

Potassium or ammonium persulfate is preferred.

The amount of initiator added is selected to obtain an economical polymerization rate, but is generally 0.001 to 1% by weight based on water.

Particularly preferred is 0.01 to 1% by weight. The addition of initiator is
The entire amount may be added at once at the start of polymerization, but in many cases, adding it in several portions during the polymerization time, or adding it continuously using a feed pump will result in a polymer with a uniform degree of polymerization. Good results can be obtained.

The polymerization temperature is 70-100℃ to perform stable emulsion polymerization.
℃, especially preferably 85 to 95℃, and the polymerization pressure is 5
A range of from 15 to 80 ky7cm2 is preferred, particularly from 15 to 80 ky7cm2.

In order to improve the mechanical stability of the dispersion, a fluorine-containing emulsifier that is substantially telogen-inactive can also be used as the emulsifier. As a fluorine-containing emulsifier, for example, a carbon number of 7
Examples include the above-mentioned perfluorocarboxylic acids, perchlorofluorocarboxylic acids, ω-hydrofluorocarboxylic acids, and their sodium salts or ammonium salts. Among these, perfluorocarboxylic acid salts, particularly ammonium perfluorooctanoate, are preferred. The amount of emulsifier added is 0.01 to 0.5% by weight, especially 0.05 to 0.0% by weight based on water.
．． 2% by weight is preferred. When using these emulsifiers,
If the entire amount is added at the start of polymerization, it is not preferable because the emulsifier wrinkles so much that many particles are generated and the particle size tends to become small. Therefore, it is preferable to add a small amount of emulsifier at the beginning of polymerization, and then add the emulsifier in several portions as the polymerization progresses, or add additionally continuously using a pump.

Further, as an emulsion stabilizer, a saturated hydrocarbon which is liquid at the polymerization temperature, such as paraffin wax, may be used.

In addition, the method of the present invention is not limited to the polymerization of vinylidene fluoride alone, but can also be used to polymerize vinylidene fluoride and other comonomers, as long as a copolymer containing as little as 80 mol% of vinylidene fluoride can be obtained. can equally be applied to the copolymerization of

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. Parts and percentages in each example are by weight unless otherwise specified.

In each Example and Comparative Example, 1 polymerization was generally carried out as follows: A stainless steel autoclave with an internal volume of 8.2 tons equipped with a stirrer was charged with 1.2 tons of ion-exchanged water and specified additives, and the autoclave was sealed. , the internal air was removed under vacuum with vinylidene fluoride monomer, replaced with nitrogen under pressure, then the specified chain transfer agent was added, and the pressure was increased to 1 snout/crn2G with vinylidene fluoride monomer, followed by stirring. Start and heat and hold at 90°C. Next, a 0.5% aqueous solution of ammonium persulfate (25-) was charged, and vinylidene fluoride monomer was immediately introduced under pressure to raise the pressure to 201 q/cm G.

As the internal pressure decreases as the polymerization reaction progresses, the weight decreases to 19 kg/
When the pressure drops to mG'E, vinylidene fluoride monomer is again forced in and the pressure is increased to 20/crn2G. In this manner, the seven-mer feeding operation is repeated during the reaction. In addition to adding the ammonium persulfate aqueous solution at the start of polymerization, additional charges of 7,5- are added every 30 minutes to prevent low F in the polymerization reaction rate. After supplying 7-mers 25 times, stop stirring,
The monomer in the autoclave is discharged and cooled to obtain a white dispersion in which polyvinylidene fluoride particles are emulsified. The polyvinylidene fluoride particle size in the obtained dispersion was measured using a Union particle size analyzer model PA-101 (Union Giken Co., Ltd.).
The 50% value of the distribution curve obtained by measurement at a rotational speed of 280 Orpm is determined as the particle diameter.

Examples 1-2 and Comparative Examples 1-3 Following the general procedure above, 1.2 ft. of ammonium perfluorooctanoate was used as the emulsifier.

Polymerization was carried out by adding the chain transfer agents shown in Table 1.

The polymer concentration of the polyvinylidene fluoride dispersion was 11%. A portion of the dispersion was taken, coagulated with an aqueous potassium chloride solution, washed with water, and dried to obtain white polyvinylidene fluoride powder. The obtained polymer was tested using a Koka type flow tester (manufactured by Takafusa Seisakusho) at 220°C from a nozzle for 1 day at 220°C. The degree of coloring was evaluated after heat treatment for 1 hour. The evaluation was divided into five levels, with 1 indicating no change and 5 indicating dark brown. Other polymerization conditions and results are shown in Table 1.

These results show that the methyl acetate and ethyl acetate of the present invention cause less decrease in the polymerization rate than the conventionally used methanol, acetone, and dioxane, and furthermore, the stability of the obtained polymer is good. be understood.

Examples 3-5 and Comparative Example 4 According to the general procedure above, 1.2y of ammonium perfluorooctanoate and 0.81y of ammonium carbonate were used as additives, and methyl acetate was used as a chain transfer agent as described in Table 2. Polymerization was carried out by supplying 7-mers 101 times under the conditions that the amount of ammonium persulfate aqueous solution added at the start of one polymerization was 15-, and the additional amount was 5- for each addition.

The resulting dispersion was a white, stable polyvinylidene fluoride dispersion with a polymer concentration of 80.1% by weight without precipitation or creaming. A potassium chloride aqueous solution was added to a portion of this dispersion to cause coagulation, washing with water, and drying to obtain a white polyvinylidene fluoride powder.

The melt flow value and thermal stability of the obtained polymer were determined in Example 1.
was obtained in the same manner as above, and dimethylacetamide (DM
The solubility in A) was adjusted to 15% polymer concentration and 60°
It was evaluated by heating at C for 1 hour.

Note that Comparative Example 4 shows a case in which no chain transfer agent was used at all. The results are shown in Table 2.

Example 5 A polymerization reaction was carried out by repeating the same procedure as in Example 4 except that methanol of methyl acetate was used as the chain transfer agent.
Stirring became abnormal during monomer supply 8, and as soon as the polymerization reaction stopped, we stopped supplying the monomer and stirring, and after releasing the monomer, when we opened the tank, we found that there was no monomer at all, and it was all coagulated cake-like powder. This means that when methanol is used, unlike in the case of chill, one dispersion is extremely rare and a highly concentrated dispersion cannot be obtained.

Example 6 The white polyvinylidene fluoride powder obtained in Example 4 was mixed with the tylphthalate/carpitol acetate mixed solvent using a paint mill to prepare an organosol having a body concentration of 33.3%.

When the viscosity of the organosol was measured using a B-type rotational viscometer, it was 1.
The viscosity was as low as 10 cpoise. After applying this organosol to an aluminum plate, it was heat-treated at 270'C for 6 minutes to form a glossy, uncolored film.

Similarly, when the polymer powder obtained in Comparative Example 5 was mixed with a mixed solvent, a paste-like fluid organosol was not formed but only absorbed the solvent.

Patent applicant Daikin Industries, Ltd. Agent Patent attorney Aoyama Aoyama (and 2 others) Procedural amendment (voluntary) March 8, 1980 Commissioner of the Japan Patent Office Mr. ■ Case indication 1982 Patent Application No. 146649 2. Name of the invention: Process for manufacturing polyvinylidene fluoride powder 3. Relationship with the person making the amendment Patent applicant address: 1-12t139 Kouda, Kita-ku, Osaka-shi, Osaka Prefecture New Hankyu Building Name (285) Daikin Industries, Ltd. Representative: Mt. 1) Minoru 4, Agent A5, Sode 6, Sode 7 amended self-answer memorandum #l, the width of the detailed explanation of the invention, the following one point has been amended.

(1) In lines 10 and 11 of 1ON, the phrase [vacuum......replaced] was corrected to "replace the internal air with vacuum pressure."

(2) In the last line of page 11, insert "Inner diameter x length" after "By,".

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Claims (1)

[Scope of Claims] 1. Polyvinylithia fluoride powder (characterized in that methyl acetate and/or ethyl acetate is used as a chain transfer agent when emulsion polymerizing vinylidene fluoride using persulfate as a polymerization initiator) 7) Manufacturing method. 2. The manufacturing method according to claim 1, in which methyl acetate and/or ethyl acetate is used in an amount of 0.1 to 5 mol % based on vinylidene fluoride. 3. The manufacturing method according to claim 1, wherein the persulfate is potassium persulfate or ammonium persulfate. 4. The manufacturing method according to claim 1 or 8, in which the persulfate is used in an amount of o, oot to 1% by weight based on the amount of water. 5. The manufacturing method according to claim 1, wherein the polymerization temperature is 70 to 100°C. 6. The manufacturing method according to claim 1, wherein the polymerization pressure is 5 to 45 m/1-1 n.