JPH0160487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fine particle aqueous suspension of an organic azo polymerization initiator compound and a method for producing the same.

More specifically, it contains an organic azo polymerization initiator compound, is essentially free of organic solvents, and has long-term dispersion stability and does not contain any bubbles, which are the main cause of inhibiting the polymerization system and dispersion stability. This invention relates to a suspension and a method for producing the same.

Fine particles of organic azo polymerization initiator compounds (hereinafter simply referred to as azo compounds) are used in the field of uniformly and stably dispersing them in an aqueous reaction medium, such as suspension polymerization using an azo compound as a polymerization initiator. , extremely useful.

Conventionally, azo compounds, which are excellent as polymerization initiators, have been introduced into the polymerization reaction system as crystals in the form of small solids or ordinary powder, or as a solution. It has drawbacks such as difficulty in rapidly and uniformly dispersing it into the system.

In this regard, azo compounds with a particle size of approximately 10μ
If the following fine particles are dispersed in water by mechanical means, the dispersion into the polymerization system will be extremely rapid and smooth, and the contribution to the polymerization reaction will be more efficient. , which was previously published (Japanese Patent Application Laid-open No. 151544/1983).

That is, as for the method of obtaining an aqueous dispersion of fine particles of an azo compound, the method is usually a jet mill method for a dry method, and a ball mill (including a vibration mill and a tower type mill) for a wet method at a temperature below the melting point of the azo compound.
A method for obtaining an aqueous dispersion of fine particles of an azo compound by an ultrasonic method is described therein.

According to the invention method 1 of JP-A-55-151544, for example, an azo compound that has been dry-pulverized using a diet mill is dispersed in water in the presence of the dispersing agent of the same invention, or the azo compound is pulverized in a vibrating mill. The process can be carried out in an aqueous medium by supplying a mixture of water, dispersing agent, wet pulverization and dispersion at the same time, etc., to obtain the desired dispersion and supplying this to the industry. In the polymerization reaction of vinyl compounds, all disadvantages, including problems in the working process, were completely eliminated, and productivity on an industrial scale was dramatically improved.

However, when the obtained dispersion is used as it is for polymerization, it interferes with the polymerization reaction, so it could not be used as it is for polymerization.

This drawback was completely eliminated by carrying out the dispersion step in an inert gas atmosphere, preferably nitrogen (Tokukai No. 56-45906).

According to the description in JP-A-56-45906, although it is not necessarily clear why the above drawbacks are resolved, it is said that the obtained dispersion was mechanically stirred in the presence of a dispersing and suspending agent. Because the azo compound that foams due to history and forms a solid phase is a fine particle, it has a thick milky appearance and is difficult to defoam even by vacuum defoaming, making it difficult to perform the dispersion process in normal air. When this process is carried out, the bubbles taken in each contain air or oxygen, so if these bubbles are used as they are in the polymerization, it is thought that this will result in a hindrance to the polymerization reaction.

In addition, these bubbles cause azo compounds, which are hydrophobic substances, to adhere to them, impairing the uniformity and quantitative properties of the aqueous suspension, and as the bubbles float over time, dispersion stability for a long period of one month or more may be affected. inhibit.

The present inventors have developed an aqueous suspension containing an azo compound that is essentially free of organic solvents and has long-term dispersion stability and does not contain any bubbles, which are considered to be the main cause of inhibiting the polymerization system and dispersion stability. As a result of intensive research into liquid suspensions and methods for producing the same, the inventors succeeded in discovering such aqueous suspensions and methods for producing the same, leading to the completion of the present invention.

That is, the present invention provides a long-term stable dispersion that is essentially free of organic solvents and is obtained by evaporating the non-aqueous solvent from an emulsion consisting of a non-aqueous solvent, water, and a dispersing agent in which an azo compound is dissolved. An aqueous suspension having properties and a method for producing the same.

According to the present invention, an aqueous suspension containing no bubbles can be obtained despite the coexistence of a dispersing and suspending agent. There's no need to do it.

The present invention can be easily implemented, for example, as follows.

That is, the azo compound is dissolved in a non-aqueous solvent in advance,
After forming a homogeneous and stable emulsion with water and a small amount of dispersing and suspending agent, the non-aqueous solvent is concentrated and removed at a low temperature, preferably at a temperature of 20°C or less. Particle azo compound 5-40% by weight, dispersing agent 0.5-10% by weight, water 50-95% by weight
It is possible to produce an aqueous suspension with long-term dispersion stability, which is essentially free of organic solvents and contains no bubbles, which are the main cause of inhibiting the polymerization system and dispersion stability.

More specifically, an azo compound is dissolved in a non-aqueous solvent, preferably a non-aqueous solvent with a boiling point of 100°C or less, and mixed with water,
A uniform and stable emulsion is prepared by adding appropriate amounts of dispersing and suspending agents selected from Groups A and B below, and using conventional stirring, a high shear mixer, or a homogenizer. Next, add this emulsion for 10 to 30 minutes under normal stirring.
When the nonaqueous solvent is removed under reduced pressure at a pressure of 100 mmHg, preferably 10 to 50 mmHg, fine particles of the azo compound, most of which have a particle size of 20 μ or less, are precipitated, and the azo compound 5 to
40% by weight, dispersing agent 0.5-10% by weight, water 50-95
essentially free of organic solvents, containing % by weight;
A pumpable, fluid aqueous suspension is obtained. These operations are usually carried out at a temperature below the melting point of the azo compound, preferably at an appropriate low temperature (usually 5 %) to completely prevent the azo compound from deteriorating due to its activity.
~20°C). Also, when concentrating nonaqueous solvents under reduced pressure, add a few drops of antifoaming agent (Shin-Etsu Silicone KM-68, etc.)
is more effective in obtaining a foam-free aqueous suspension.

Since the aqueous suspension of the azo compound of the present invention does not contain any bubbles, there is no inhibition of polymerization reaction or quantification due to oxygen contamination, and the dispersion stability is maintained for a long period of one month or more. have. Another great advantage is that an aqueous suspension can be produced in a simplified process without the need for an expensive pulverizer. Furthermore, since the azo compound forming the solid phase of this suspension is fine particles with a particle size of approximately 20μ or less, and a suitable amount of a dispersing and suspending agent is present, it can be supplied to the polymerization system as a stable dispersion suspension. This improves the work process, work efficiency, etc., and disperses the polymerizable monomer very finely and rapidly uniformly into the aqueous medium of the polymerization system, effectively dissolving it in the oil droplets of the polymerizable monomer, and reducing the time required for polymerization. As a result, the quality of the polymer obtained is extremely good as the time is significantly shortened, and as a result of not containing any solvent other than water, the effects are enormous, and the contribution to this industry is extremely large.

Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,3,3-trimethyl Valeronitrile), 2,2'-azobis(2,4,4-trimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 1,1'-azobis(cyclomexane-1-carboxylic acid) nitrile),
2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), 2-tertiary butyl-azo-
2,4,4-trimethylvaleronitrile, 2-α
- Naphthylazoisobutyronitrile, 2,2'-azobis(methyl isobutyrate), 2,2'-azobis(N,N'-dimethyleneisobutyramidine), etc., which are usually solid at room temperature or below; There is no problem in widely applying the invention.

Examples of the nonaqueous solvent of the present invention include ethyl ether,
Ethers such as isopropyl ether, aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, alcohols such as n-butyl alcohol, isobutyl alcohol, and isoamyl alcohol, and ethyl acetate, methyl acetate, and butyl acetate. esters, linear or cyclic hydrocarbons such as n-hexane, n-heptane, n-nonane, cyclohexane, methylene chloride, dichloroethane,
Examples include halogenated hydrocarbons such as chloroform, carbon tetrachloride, and trichloroethylene, and those having excellent solubility for azo compounds are preferred, and more preferably those having a boiling point of 100°C or less under normal pressure or an azeotropic point with water. Good solvent. These may be used alone or in combination of two or more, and there is no problem when used in combination with a water-soluble solvent.

In addition, as the dispersing and suspending agent of the present invention, preferably used is a peach used as a suspending agent in suspension polymerization, and one or more of them are selected from the following groups A and B. Use with a suspending agent. Group A includes synthetic polymers such as polyethyleneimine, polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone, cellulose derivatives such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylulose, hydroxypropylmethylcellulose, and cellulose acetate phthalate, and glue gelatin. Examples include animal proteins, plant mucilage substances such as gum arabic, pectin, and saponin, alginic acid, carrageenan, seaweed-derived substances such as farsen orchid, and other starches and processed starches. Group B includes nonionic, cationic, and Anionic surfactants, preferably nonionic surfactants, include sorbitan monolaurate, sorbitan monooleate, sorbitan sesquiolate, glyceryl monostearate, polyoxyethylene sorbitan monolaurate, and the like.

Further, the water used is usually deionized water or distilled water.

Examples are shown below.

Example 1 Sorbitan monolaurate was placed in a flask equipped with a stirrer with half-moon blades, a cold trap connected to an aspirator, and a condenser.
Mix and dissolve 150g of 1% methylcellulose aqueous solution into 2.2g, cool to below 15℃, stir, and add 88g of 2,2'-azobisisobutyronitrile to 150g of methyl acetate.
Add the solution dissolved in the solution dropwise to create a stable emulsion. The methyl acetate was distilled off from this solution under reduced pressure of about 50 mmHg and below 15°C until no fraction was observed.
Contains approximately 37% by weight of azobisisobutyronitrile, has a viscosity of 3800 cps (Burtzkfield viscometer),
A creamy aqueous suspension with a particle size of less than 20 μm (95%) was obtained and exhibited dispersion stability for about 2 months.

This solution was extracted with n-hexane and subjected to GC measurement, but no residual methyl acetate was observed.

Example 2 In a flask similar to that described in Example 1, 2.5 g of glyceryl monostearate, 170 g of 3% hydroxypropyl methylcellulose, and Shin-Etsu Silicone KM-68.1 cc as an antifoaming agent were mixed and dissolved, and the mixture was cooled to 15°C or less and stirred. Below, a solution of 66 g of 2,2'-azobis(2,4-dimethylvaleronitrile) dissolved in 250 g of isopropyl ether was added dropwise to create a stable emulsion. When processed in the same manner as in Example 1, 2,
Contains approximately 28% by weight of 2'-azobis(2,4-dimethylvaleronitrile), viscosity 2200cps, particle size 20μ
A creamy aqueous suspension of (95%) was obtained.

Example 3 In a flask similar to that described in Example 1, 3.2 g of sorbitan sesquiolate and 180 g of 1.5% hydroxyethyl cellulose were mixed and dissolved, and while cooling to below 15°C and stirring, 1,1'-azobis(cyclohexane-
A solution of 52 g of 1-carbonitrile) dissolved in 80 g of methylene chloride was added dropwise to form an emulsion, and then treated in the same manner as in Example 1. A creamy aqueous suspension with a viscosity of 1900 cps and a particle size of less than 20 μm (95%) was obtained.

Claims (1)

[Scope of Claims] 1. Essentially free of organic solvents, obtained by evaporating the non-aqueous solvent from an emulsion consisting of a non-aqueous solvent in which an organic azo polymerization initiator compound is dissolved, water, and a dispersion/suspension agent. , an aqueous suspension with long-term dispersion stability. 2. Claim No. 2 containing 5 to 40% by weight of an organic azo polymerization initiator compound consisting mostly of fine particles with a particle size of about 20μ or less, 0.5 to 10% by weight of a dispersing agent, and 50 to 95% of water. Aqueous suspension according to item 1. 3. The aqueous suspension according to claim 1 or 2, wherein the organic azo polymerization initiator compound is organic azonitrile. 4. Dissolving an organic azo polymerization initiator compound in a non-aqueous solvent, adding water and a small amount of a dispersing/suspending agent to form a uniform emulsion, and then concentrating and removing the non-aqueous solvent at a low temperature. , a method for producing an aqueous suspension essentially free of organic solvents and having long-term dispersion stability. 5. The manufacturing method according to claim 4, wherein the non-aqueous solvent is evaporated by distilling it off under reduced pressure at a temperature of 20° C. or lower. 6. The manufacturing method according to claim 4 or 5, wherein the organic azo polymerization initiator compound is organic azonitrile.