JPS608687B2 - Method for producing vinyl acetate polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a vinyl acetate polymer.

More specifically, this invention involves removing vinyl acetate from a vinyl acetate homopolymer or copolymer,
The present invention relates to a method for producing a vinyl acetate polymer or copolymer with a small amount of residual vinyl acetate monomer. Homopolymers or copolymers of vinyl acetate are used in various fields because they are easily dissolved in organic solvents and have good adhesive properties. These polymers are produced by dispersing vinyl acetate alone or with other monomers that can be copolymerized with vinyl acetate in an aqueous soot, and adding a polymerization initiator to this dispersion. Manufactured by emulsion polymerization or suspension polymerization. The polymer or copolymer thus obtained (hereinafter simply referred to as a polymer) can be used in various fields, either as it is dispersed in aqueous soot, or by separating only the polymer from it. be done. In the polymerization of vinyl acetate, the polymerization reaction becomes extremely slow after the polymerization rate reaches a certain value.

Therefore, in order to produce polymers industrially, the polymerization reaction is terminated when the polymerization rate reaches a certain value, for example, 80% to 95% by weight. The remaining monomers are recovered and used as a product. The remaining unreacted monomer may be recovered in the polymerization vessel itself in which the polymerization reaction was carried out, but may also be carried out by transferring it from the polymerization vessel to a separate container. A polymer obtained by emulsion polymerization or suspension polymerization in aqueous soot is a dispersion in aqueous soot, and is in the form of a slurry. Therefore, unreacted monomers are recovered by heating the slurry, reducing pressure, or using a combination of heating and reduced pressure to dust off unreacted monomers from the slurry. There is. However, it is not easy to remove vinyl acetate from vinyl acetate polymers using these methods. This is because vinyl acetate is a liquid with a high boiling point (boiling point approximately 72°C), so once the content is reduced, it is extremely difficult to further reduce the content by simply heating and reducing pressure. . Vinyl acetate polymers may be used as they are dispersed in aqueous soot, or may be used after being separated.

However, if vinyl acetate monomer remains in the polymer,
When this is used, the vinyl acetate monomer evaporates and gives off a strange odor, making the work environment worse. Not only that, absorbing vinyl acetate has a negative effect on the human body.Therefore, there was a desire for a method to completely remove vinyl acetate from polymers.This invention was created in response to these demands. The inventor discovered that ``unreacted vinyl acetate could be removed by adding magnesium oxide or magnesium hydroxide to a slurry containing unreacted vinyl acetate and allowing it to stand for a while.''

It has also been found that it is not necessary to remove the magnesium oxide or magnesium hydroxide added at that time by any special operation unless the amount is particularly large. That is, it has been found that even if a small amount of magnesium oxide or magnesium hydroxide remains, the physical and chemical properties of the obtained polymer are not significantly changed. This invention was made based on such knowledge.
It is known to use alkali metal hydroxides to remove unreacted vinyl acetate.

It is described, for example, in Japanese Patent Laid-Open No. 141707/1983. However, magnesium oxide or magnesium hydroxide does not belong to alkali metals, and it is quite surprising that magnesium oxide or magnesium hydroxide is convenient for removing unreacted vinyl acetate. This invention involves dispersing vinyl acetate alone or as a monomer mixture with a monomer that can be copolymerized with vinyl acetate in an aqueous medium, and adding a polymerization initiator to this dispersion to form a monomer. The present invention relates to a method for producing a vinyl acetate polymer, which comprises polymerizing or copolymerizing and adding magnesium oxide or magnesium hydroxide to the resulting polymer dispersion.

In the method of this invention, vinyl acetate monomer alone or mixed with a monomer copolymerizable with vinyl acetate monomer is dispersed in aqueous soot, and the monomer is polymerized in this dispersed state.

This polymerization process is generally called suspension polymerization or emulsion polymerization. The polymerization process in the method of this invention is no different from the methods that have been carried out up to now. Specifically, deionized water is used as the aqueous substance, a dispersant or emulsifier is used to help disperse the monomer in the aqueous soot, and a polymerization initiator is used to effect the polymerization. However, in these respects, the method of this invention is no different from the conventional method. The monomer used in the method of this invention is vinyl acetate alone or a mixture of a monomer copolymerizable with vinyl acetate and vinyl acetate.

Examples of copolymerizable monomers include methyl methacrylate,
Methacrylate esters such as propyl methacrylate. Acrylic acid esters such as ethyl acrylate and n-butyl acrylate, unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, unsaturated dicarboxylic acids such as maleic acid and fumaric acid, vinyl stearate, vinyl Vinyl esters such as palmitate, vinyl chloride, halogenated vinyl compounds such as vinyl furomide, and ethylene, acrylonitrile,
Vinylpyrrolidone, etc., and mixtures thereof can also be used. In addition, other polymers or copolymers may be present during polymerization of this monomer. That is, it may be a case where graft polymerization is performed. In the case of graft polymerization, the main polymer is ethylene. Vinyl acetate copolymers, chlorinated polyethylene, ethylene-propylene copolymers, polyvinyl chloride, and copolymers containing vinyl chloride as a main component with other monomers can be used. Dispersants or emulsifiers are used to disperse the monomers in the aqueous soot.

Among them, dispersants or emulsifiers used for carrying out suspension polymerization include partially saponified polyvinyl alcohol, cellulose derivatives such as methylcellulose or hydroxymethylcellulose, a copolymer of vinyl acetate and maleic anhydride "polyacrylic dispersants or emulsifiers used for emulsion polymerization include sodium alkylsulfonate, sodium benzenesulfonate, polyoxyethylene lauryl ether,
Polyoxyethylene nonyl phenyl ether and the like.
In the method of this invention, a polymerization initiator is used, but as is well known, the type of polymerization initiator used differs depending on whether emulsion polymerization or suspension polymerization is performed.

In the case of suspension polymerization, oil-soluble materials are used, such as organic peroxides such as penzoyl peroxide, lauroyl peroxide, and dialkyl peroxydicarbonates, and azolic peroxides such as azobisisobutyronitrile. A compound is used. In the case of emulsion polymerization, water-soluble materials are used, such as persulfate, hydrogen peroxide, ammonium persulfate, and the like. Although it is necessary to add the polymerization initiator after the inside of the polymerization reactor is degassed under reduced pressure, it may be added after the aqueous dispersion is heated and raised to a certain temperature. These points are the same as the conventional method. The polymerization reaction is discontinued when the polymerization progresses to a certain extent and the speed of progress of the polymerization reaction becomes slow.

The termination point is appropriately determined by estimation based on the relationship between various conditions regarding polymerization and the polymerization rate obtained in advance through experiments. For example, in the case of copolymerization of vinyl chloride or ethylene with vinyl acetate, the point at which the polymerization is terminated is determined by estimating the relationship between the internal pressure of the polymerization vessel and the polymerization rate, which has been previously obtained through experiments. In the method of this invention, magnesium oxide, magnesium hydroxide, or a compound that easily produces these (hereinafter collectively referred to as a magnesium compound) is added to the aqueous suspension after the polymerization reaction.

The magnesium compound must be added after the polymerization reaction has been terminated. Moreover, it is desirable that the timing is before the collection of unreacted monomers. This is because the dispersion is in a uniformly dispersed state before monomer recovery, and it is easy to disperse the magnesium compound in the aqueous dispersion. It is desirable to use the magnesium compound as a fine powder if possible. The degree of powder is JI
It is desirable that the S standard ring passes 200 meshes. This powder may be used as it is, but in order to improve dispersion in an aqueous dispersion, it is desirable to moisten the surface of the powder with a small amount of water or a hydrophilic organic solvent before adding it. The amount of magnesium compound added is
It is determined based on the amount of unreacted vinyl acetate monomer present in the polymer. Specifically, when using magnesium oxide, it is 0.24 to 1 part by weight per 1 part by weight of unreacted vinyl acetate, and when using magnesium hydroxide, it is 0.3 part by weight.
4 None, 1 part by weight is used. Among these, when the obtained polymer is particularly required to be transparent, 0.24 parts by weight or 2 parts by weight is used when magnesium oxide is used, and 0.34 parts by weight is used when magnesium hydroxide is used. The amount is preferably 2 parts by weight. After adding the magnesium compound, it is desirable to continue viewing the aqueous dispersion for a while. It is desirable that the test time is 0.2 to 2 hours. Further, the temperature at that time is desirably 3000 or 9000. Thereafter, if the dispersion also contains monomers other than vinyl acetate, the gas above the dispersion is removed in order to remove the monomers. When the vinyl acetate polymer is used in the form of an aqueous dispersion, it is used directly as a product.

However, when the polymer is used separated from the aqueous medium, the dispersion is then passed through a knot to separate the aqueous medium and the polymer particles. At this time, most of the magnesium compound remaining in the dispersion migrates with the aqueous soot, and a small amount of the magnesium compound adheres to the polymer particles. However, this deposited magnesium does not cause any harm. In fact, the polymer particles thus obtained are such that the presence of magnesium compounds is hardly recognized. The polymer thus obtained has a significantly reduced content of vinyl acetate monomer.

It is assumed that this is because the residual vinyl acetate monomer is decomposed by the magnesium compound and removed as something like acetaldehyde, but the details are not clear. In fact, this polymer does not emit the unpleasant odor of vinyl acetate even when it is heated and melted for use. In addition, there is almost no evidence of deterioration due to the addition of the magnesium compound. Furthermore, the method of the present invention is extremely easy to operate, since it is sufficient to add a magnesium compound after polymerization. The method of this invention is superior in these respects. Next, the method of the present invention will be explained with reference to examples.

In the following, parts simply mean parts by weight.
Example 1 In an autoclave with a loss speculator, 200 parts of water from which ions were removed by ion exchange≠sword resin, 0.2 part of partially saponified polyvinyl alcohol with a degree of saponification of 80%, 0.05 part of lauroyl peroxide, After adding 7.5 parts of vinyl acetate monomer and degassing in vacuum, 10 parts of vinyl chloride monomer were charged.

Thereafter, the temperature was raised to 65°C, suspension polymerization was carried out for 6 hours, a vinyl chloride/vinyl acetate copolymer was produced, and the polymerization reaction was completed. At this time, 2.7 parts of vinyl acetate monomer remained for every 10 parts of the copolymer.
2 parts of finely powdered magnesium oxide (JIS standard section 250 mesh pass product) is suspended in a small amount of methanol,
This suspension was added to the suspension immediately after the polymerization reaction was completed. After that, I continued playing Azusa for an hour. Thereafter, the mixture was degassed under reduced pressure to remove unreacted vinyl chloride monomers, centrifuged to remove polymer particles, and dried to obtain a copolymer.

When this copolymer was analyzed to measure the amount of vinyl acetate monomer remaining, it was found that the amount of vinyl acetate monomer was less than 1 part by weight. Comparative Example 1 A vinyl chloride/vinyl acetate copolymer was obtained in the same manner as in Example 1 except that magnesium oxide was not used.

When the amount of residual vinyl acetate monomer in this copolymer was examined, the residual amount was 700% by weight.

Example 2 In this example, a pinyl chloride/vinyl acetate copolymer was obtained in the same manner as in Example 1, except that 2.5 parts of magnesium hydroxide, a substitute for magnesium oxide, was used.

In this copolymer, only 1 part by weight of vinyl acetate monomer remained in the copolymer. Example 3 In this example, it was confirmed that by adding magnesium oxide to an emulsion of vinyl acetate/ethylene copolymer, the amount of vinyl acetate monomer contained in the emulsion was reduced.

The material used was a vinyl acetate/ethylene copolymer emulsion copolymerized with 6% by weight of vinyl acetate and 4% by weight of ethylene, had a Mooney viscosity of 15, and had a resin content of 5% by weight.

This emulsion 10 parts also contain magnesium oxide 0.5
After adding 100% of the pseudo-azusa at room temperature for 10 minutes, leave it for 24 hours.
The concentration of residual vinyl acetate monomer was measured. As a result, before adding magnesium oxide, 250%
The residual vinyl acetate monomer, which was contained in ppm by weight, was reduced to 30 ppm by weight after the addition of magnesium oxide. Example 4 This example was processed much like Example 3 using magnesium hydroxide.

That is, 8% by weight of vinyl acetate, 2% by weight of ethylene.
1 part of magnesium hydroxide was added to 100 parts of an emulsion with a resin content of 55% by weight, and after being heated at room temperature for 1 hour, it was left to stand for 2 hours to remove the residual vinyl acetate monomer. I confirmed that it decreased. The emulsion contained 100 ppm by weight of residual vinyl acetate monomer before the addition of magnesium hydroxide, but after addition the residual vinyl acetate monomer was reduced to 2 parts by weight. Example 5 In this example, magnesium oxide was added to an ethylene-vinyl acetate copolymer emulsion to reduce residual vinyl acetate.

Specifically, it was carried out as follows.

Claims (1)

[Claims] 1. A vinyl acetate monomer alone or as a monomer mixture with a monomer copolymerizable with the vinyl acetate monomer is dispersed in an aqueous medium, and a polymerization initiator is added to this dispersion. A method for producing a vinyl acetate polymer, which comprises polymerizing or copolymerizing monomers and adding magnesium oxide or magnesium hydroxide to the resulting polymer dispersion. 2. The method according to claim 1, wherein the copolymerizable monomer is vinyl chloride. 3. The method according to claim 1, wherein the copolymerizable monomer is ethylene. 4. The method according to claim 1, wherein the copolymerizable monomers are vinyl chloride and ethylene.