JPS582962B2 - Manufacturing method of vinyl chloride resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When carrying out suspension polymerization of vinyl chloride monomer alone or a mixture of vinyl monomers mainly consisting of vinyl chloride monomer, the present invention uses modified polyvinyl alcohol with good dispersion stability to The present invention relates to a method for producing a vinyl chloride resin that is highly porous and has a good particle size with few coarse particles.

When carrying out suspension polymerization of vinyl chloride monomer or a mixture of a monomer copolymerizable with vinyl chloride monomer, polyvinyl alcohol, methyl cellulose, vinyl acetate, maleic anhydride copolymer, gelatin, etc. are usually used. It is known that the following dispersion stabilizers are used.

Regarding W in polyvinyl alcohol, there are ranges suitable for use as a dispersion stabilizer in terms of average degree of polymerization, average degree of saponification, etc., and polyvinyl esters obtained by polymerization in the presence of altehydes or ketones are also suitable for use as dispersion stabilizers. It is also disclosed in JP-A-49-19488 and JP-A-49-53270 that modified polyvinyl alcohol having a carbonyl group in the molecule obtained by hydrolysis is suitable as a dispersion stabilizer for suspension polymerization of vinyl chloride. It is known by its number etc.

However, vinyl chloride-based resins produced using such dispersion stabilizers are not satisfactory in terms of porosity and particle size distribution of resin particles, and there is a large amount of vinyl chloride monomer remaining in the vinyl chloride Xm resin. However, there is a problem that the processability of the resin is poor (the absorption rate of plasticizer is slow), and there is a strong demand for solutions to these problems.

In view of these circumstances, the present inventors conducted various studies and found that when vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride is subjected to suspension polymerization, the present inventors may use altehydes or ketones as a dispersion stabilizer in the presence of altehydes or ketones. Polyvinyl acetate is polymerized, the obtained polyhinyl acetate is saponified to obtain polyvinyl alcohol, and the polyvinyl alcohol is further added in an amount of 0.2 to 2.0% by weight based on the polyvinyl alcohol.
1-3 at 100-150°C in the presence of sodium acetate
The product obtained by heat treatment for a period of time has a degree of polymerization of 1500 or less, a degree of saponification of 90 mol% or less, and has 0 carbonyl groups in the molecule.
．． 280 mμ and 320 mμ according to the ultraviolet absorption spectrum of a 0.2% aqueous solution.
28 when the absorbance of is 0.20 and 0.05 or higher, respectively.
Ratio of absorbance of 320 mμ to 0 mμ (320 mμ/
By using partially saponified polyvinyl alcohol with a particle size (280 mμ) of 0.30 to 1.00, it is highly porous, has a uniform particle size distribution with an appropriate average particle size, and has very few coarse particles, and is easy to process. It was found that an excellent vinyl chloride resin with less residual vinyl chloride monomer can be obtained, and that it has advantages that could not be obtained with conventional dispersion stabilizers, leading to the completion of the present invention. Ta.

Polyvinyl acetate, which is the raw material of polyvinyl alcohol used in the present invention, is produced by adding aldehydes or ketones as a chain transfer agent to the polymerization reaction system using a generally known monomer of vinyl acetate. It is obtained by carrying out partial polymerization so that the ratio becomes 40 to 95%.

By polymerizing in this manner, a carbonyl group can be introduced into the molecule.

Examples of aldehydes as chain transfer agents include acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, etc., and examples of ketones include acetone, methyl ethyl ketone, hexanone, cyclohexanone, etc.

The amount of chain transfer agent added varies depending on the chain transfer constant of the chain transfer agent added, and also varies depending on the degree of polymerization of the target polyvinyl alcohol, and the appropriate amount is determined depending on the state of the polymerization system. When used, it is preferably 0.1 to 5% by weight based on vinyl acetate.

The form of polymerization is not particularly restricted as long as it is a conventional method.

Additionally, a solvent such as methanol, ethanol, methyl acetate, or ethyl acetate may be added as appropriate during the polymerization reaction, but in order to increase the amount of carbonyl groups introduced into the molecule, it is desirable that the amount added be small.

The carbonyl group in the polyhinyl acetate at this time is 0.03 mol% or more, preferably 0.10 mol% or more.

Next, after removing unreacted vinyl acetate present in the polymerization system, saponification is performed to obtain polyvinyl alcohol.

The saponification catalyst may be either acid or alkali and is not particularly limited.

As the saponification method, any method such as slurry saponification, belt saponification, screw saponification, suspension saponification, pipe saponification, or drum saponification can be used.

The saponification method may be a continuous method or a batch method.

The polyvinyl alcohol is then washed, dehydrated, and dried to remove the solvent used during the saponification reaction and the reactants produced as by-products during the saponification reaction to obtain a pure product.

The partially saponified polyvinyl alcohol obtained as described above has a degree of polymerization of 1500 or less, preferably 500 to 1000.
, the average degree of saponification is 90 mol% or less, preferably 69-7
It is necessary that the content be 5 mol%.

However, if partially saponified polyvinyl alcohol is used as it is as a dispersion stabilizer for suspension polymerization of vinyl chloride monomers, vinyl chloride resins with high porosity, few coarse particles, and a good average particle size cannot be used. cannot be manufactured.

This is clear from Comparative Example B described below.

Therefore, in the present invention, sodium acetate is added to the partially saponified polyvinyl alcohol at a ratio of 0% to the polyvinyl alcohol.
．． By adding 2 to 2.0% by weight and heat-treating at 100 to 150°C, preferably 120 to 130°C for 1 to 3 hours, the molecular chains adjacent to the carbonyl groups introduced into polyvinyl alcohol during the polymerization reaction are An essential condition is to cause acetic acid removal or dehydration reaction to generate a chain of vinylene groups.

Normally, when polyvinyl acetate having a carbonyl group in its molecular chain is saponified, it is conjugated to the carbonyl group to form two vinylene groups (1c-(CH=CH)2-), with an ultraviolet absorption spectrum of 280 mμ. absorption appears, but three vinylene groups are not generated.

However, when sodium acetate is added as described above and heat treatment is performed under the above specific conditions, three vinylene groups {-
C-(CH=CH)3-) is generated and absorption appears at 320 mμ.

If partially saponified polyvinyl alcohol, which shows no absorption at 320 mμ, is used without adding sodium acetate or undergoing heat treatment under the above-mentioned specific conditions, the resulting vinyl chloride resin will be highly porous. , there are many coarse particles, and the particle size distribution is non-uniform, which is not sufficient.

In addition, due to excessive heat treatment, 320 mμ
When the mμ absorbance ratio is 1.00 or more, only a vinyl chloride resin with non-uniform particle shape can be obtained, as in the case of insufficient heat treatment.

This is clear from Comparative Example C described below.

The reason why heat treatment is effective is that hydrophilic hydroxyl groups,
HLB (hy
dropophile-1ipophile balanc
e) It is presumed that this is to provide conditions to change the dispersion of vinyl chloride monomers and polymers in water to a desired state, but it is not clear.

Suspension polymerization of vinyl chloride monomers using such a dispersion stabilizer for suspension polymerization may be carried out in the same manner as conventionally known polymerization methods.

That is, in a stirring reactor, the above dispersion stabilizer, vinyl chloride monomer, water, penzoyl peroxide, α・α
A monomer-soluble polymerization initiator such as '-ambisisobutyronitrile, lauroyl peroxide, diisofuroyl peroxydicarbonate, etc. is charged and reacted with stirring at a temperature of 40 to 70°C.

The dispersion stabilizer for suspension polymerization of the present invention is not necessarily limited to suspension polymerization of a vinyl chloride monomer alone, but is mainly composed of vinyl chloride, and can also be used to copolymerize with styrene and methyl methacrylate. It can also be used for suspension polymerization of vinyl monomer mixtures such as esters.

Examples will be described below.

Example: 30% vinyl acetate and acetaldehyde each in 1 hour.
At the same time, 0.3 kg/kg of a methanol solution containing 0.2% by weight of α・α′-azobisisobutyronitrile was charged into the polymerization reaction tank at a ratio of 0.15 kg/kg.
The mixture was added at a rate of 70%, and unreacted vinyl acetate was separated to obtain a 50% by weight methanol solution of polyvinyl acetate at a rate of 42 kg/hour.

To 100 kg of this polyvinyl acetate solution, 0.5 kg of a methanol aqueous solution in which 4% by weight of sodium hydroxide was dissolved as sodium hydroxide was continuously added, and saponification was carried out using a commonly used continuous saponification device. After crushing, washing, deliquifying, and drying, the degree of polymerization was 760 and the degree of saponification was 7.
Partially saponified polyvinyl alcohol with a content of 1.3 mol% and an ultraviolet absorption spectrum having an absorbance of 0.29 at 280 mμ and 0.03 at 320 mμ was obtained.

The results of suspension polymerization of vinyl chloride using this are shown in the first
Shown in column B of the table.

Sodium acetate was added to the above partially saponified polyvinyl alcohol in an amount of 10% by weight based on the polyvinyl alcohol, and heat treatment was performed at 127°C for 2 hours by a conventional method, resulting in a polymerization degree of 760 and a saponification degree of 71.5 mol. %, absorbance at 280 mμ of ultraviolet absorption spectrum 0.27, 320 m
Partially saponified polyvinyl alcohol was obtained which had an absorbance at μ of 0.15 and a ratio of absorbance at 320 mμ to 280 mμ of 0.55.

Column A shows the results of suspension polymerization of vinyl chloride using this.

Similarly, when heat treatment was performed at 127°C for 5 hours, the degree of polymerization was 750, the degree of saponification was 71.6 mol%, the ultraviolet absorption spectrum was 0.25 at 320 mμ, the absorbance at 280 mμ was 0.2], and the absorbance at 280 mμ was 320 mμ. A partially saponified polyvinyl alcohol having an absorbance ratio of 120 was obtained.

Using this, suspension polymerization of vinyl chloride was carried out and the result was C
Shown in the column.

As a comparative example, vinyl acetate was polymerized in the presence of methanol that does not contain acetolthehyde, and then normal saponification was performed in a methanol system, followed by heat treatment with the same degree of polymerization and saponification with a lower content of carbonyl groups. Because it is not
Partially saponified polyvinyl alcohol with a small ultraviolet absorption spectrum was obtained.

Furthermore, sodium acetate was added to this to give a concentration of 1% based on polyvinyl alcohol, and heat treatment was performed at 127° C. for 2 hours.

Suspension polymerization of vinyl chloride was carried out using these two types of partially saponified polyvinyl alcohols.

The results are shown in columns D and E. The suspension polymerization of vinyl chloride was carried out under the following conditions.

A suspending agent aqueous solution and a catalyst were charged in the following proportions into a stainless steel autoclave with a capacity of 5 liters, and after replacing the air inside the vessel with nitrogen gas, vinyl chloride monomer was charged, and the internal temperature was brought to 57° C. without stirring. The temperature was raised to 0.degree. C. to carry out polymerization, and the polymer solution after polymerization was filtered, washed with water, and dried.

The proportions of the ingredients during polymerization are as follows.

From Table 1, partially saponified polyvinyl alcohol (D, E
), the quality of the vinyl chloride resin obtained is poor and impractical regardless of whether heat treatment is performed, and although aldehyde is used for polymerization, sodium acetate is added to partially saponified polyvinyl alcohol obtained by saponification. In the product (B), which is neither added nor heat-treated, it is also polymerized* using aldehyde, and sodium acetate is added to the partially saponified polyvinyl alcohol obtained by saponification, but the heat treatment is excessive. Therefore, the absorbance ratio (320 mμ
/280 mμ) is too thick (C), the resulting vinyl chloride resin has many coarse particles and is of poor quality.

On the other hand, partially saponified polyvinyl alcohol (A) obtained by polymerizing using the altehyde of the present invention and further saponifying the partially saponified polyvinyl alcohol obtained by adding sodium acetate and performing an appropriate heat treatment has high porosity. It can be seen that a vinyl chloride resin with few coarse particles, a desirable particle size, a fast plasticizer absorption rate, and a small amount of residual vinyl chloride monomer was obtained.

(1) Plasticizer absorption rate: Add 501 parts of dioctyl phthalate (DOP) to 1001 parts of polyvinyl chloride, stir at a constant temperature of 75°C in a Henschel mixer type mixer, and occasionally mix the sample. Pick it up, sandwich it between rice paper and press it with a 500g weight.

If there is DOP contamination, it has not yet been completely absorbed.

This time (time until DOP contamination disappeared) was measured as the plasticizer absorption rate.

Note that the fact that the plasticizer absorption rate is fast indicates that the processability of the obtained polyvinyl chloride is excellent.

(2) Vinyl chloride monomer remaining in polyvinyl chloride: Polyvinyl chloride was dissolved in tetrahydrofuran and measured by gas chromatography.

Claims (1)

[Claims] 1. When vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride is subjected to suspension polymerization, vinyl acetate is polymerized in the presence of aldehydes or ketones as a dispersion stabilizer, and the resulting polyvinyl acetate is quenched. The polyvinyl alcohol was further heated at 100 to 150°C in the presence of 02 to 2.0% by weight of sodium acetate based on the polyvinyl alcohol.
A polymer obtained by heat treatment for ~3 hours, has a degree of polymerization of 1500 or less, a degree of saponification of 90 mol% or less, and contains 0.03 mol% or more of carbonyl groups in the molecule, and two vinylene groups adjacent to it. and 3 vinylene groups, and 280 mμ and 320 m according to the ultraviolet absorption spectrum of a 0.2% aqueous solution.
The absorbance of μ is 0.20 and 0.05 or more, respectively,
The ratio of absorbance at 320 mμ to 280 mμ is 0.30
A method for producing a vinyl chloride resin, characterized by using partially saponified polyvinyl alcohol having a molecular weight of 1.00 to 1.00.