JP3340275B2 - Method for producing vinyl chloride polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a vinyl chloride polymer by a suspension polymerization method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a vinyl chloride polymer, a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer is suspended in an aqueous medium in the presence of a suspending agent. A method of turbid polymerization is known. As this suspending agent,
For example, partially saponified polyvinyl alcohol having a high degree of saponification and cellulose derivatives such as hydroxypropylmethylcellulose are known. Among them, partially saponified polyvinyl alcohol having a degree of saponification of 70 to 94 mol% having excellent dispersing ability is compared. Many are used.

[0003] However, the vinyl chloride polymer obtained by the suspension polymerization method has a disadvantage of poor porosity. In particular,
Poor porosity vinyl chloride polymer has the disadvantage of poor workability during processing because of poor plasticizer absorption, and also has a low gelation rate, so processed products tend to be non-uniform, There is a disadvantage that fish eyes increase.
The poor plasticizer absorption or the low gelation rate is due to the presence of a shell called a skin layer on the surface of the vinyl chloride polymer obtained by the suspension polymerization method. Therefore, a so-called non-skin type vinyl chloride polymer having good plasticizer absorption and a high gelation rate is desired.

Heretofore, as a method for obtaining a non-skin type vinyl chloride polymer, there has been known a method in which an oil-soluble partially saponified polyvinyl alcohol having a low degree of saponification and a low degree of polymerization is used alone as a suspending agent. I have. In order to obtain a non-skin type vinyl chloride polymer by this method, a large amount of oil-soluble partially saponified polyvinyl alcohol must be used. However, when a large amount of oil-soluble partially saponified polyvinyl alcohol is used, the suspension system becomes uneven, and it becomes difficult to control the particle size of the vinyl chloride polymer. As a result, many particles having a small particle size are generated, and the particle size distribution of the obtained vinyl chloride polymer becomes broad. Further, when the suspension system becomes non-uniform, there is a problem that the polymer scale easily adheres to the inside of the polymerization vessel.

[0005] Therefore, for the purpose of solving such a problem, the above-mentioned oil-soluble partially saponified polyvinyl alcohol, a water-soluble partially saponified polyvinyl alcohol having a saponification degree of 70 to 94 mol%, and the like are used as suspending agents. A method in which a cellulose derivative such as hydroxypropylmethylcellulose is used in combination has been proposed. However, even if the vinyl chloride polymer obtained by such a method is of a non-skin type, the plasticizer absorption and the gelation rate are not sufficiently satisfactory.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prepare a non-skin type vinyl chloride polymer having a good specific range of particle size distribution, a good plasticizer absorption and a good gelation rate in a polymerization vessel. It is an object of the present invention to provide a method for producing a vinyl chloride-based polymer which can be obtained without a scale attached to the polymer.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, as a suspending agent, a partially saponified polyvinyl alcohol belonging to a specific low saponification degree range and having a low polymerization degree, When used in combination with a carboxyl group-containing crosslinked copolymer, and the partially saponified polyvinyl alcohol and the carboxyl group-containing crosslinked copolymer are added to the polymerization system as an aqueous solution having a specific pH range, a good specific range of particle size distribution is obtained. It has been found that a non-skin type vinyl chloride polymer having good plasticizer absorption and gelation rate can be obtained without depositing scale in a polymerization vessel.

That is, according to the present invention, the average degree of polymerization is from 150 to 600.
A partially saponified polyvinyl alcohol having a saponification degree of 20 to 55 mol%; a 1% by weight aqueous solution having a viscosity at 25 ° C. of 40
A carboxyl group-containing cross-linked copolymer having 0 cP or more; a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer; an oil-soluble polymerization initiator; Suspension polymerization of the polymer in an aqueous medium, comprising adding the partially saponified polyvinyl alcohol, the carboxyl group-containing crosslinked copolymer and water to a polymerization system as an aqueous solution having a pH of 6.0 to 8.0. This is a method for producing a characteristic vinyl chloride polymer. Hereinafter, the present invention will be described in detail.

Partially saponified polyvinyl alcohol The partially saponified polyvinyl alcohol used in the present invention has an average degree of polymerization of 150 to 600, preferably 200 to 500, more preferably 200 to 400. This average degree of polymerization is 1
If it is less than 50, the bulk specific gravity of the obtained vinyl chloride polymer becomes low, and if it exceeds 600, the porosity of the polymer becomes poor. The partially saponified polyvinyl alcohol used in the present invention has a degree of saponification of 20 to 55 mol%, preferably 30 to 50 mol%, more preferably 30 to 50 mol%. If the degree of saponification is less than 20 mol%, the bulk specific gravity of the polymer becomes low, and if it exceeds 55 mol%, the porosity of the polymer becomes poor.

Carboxyl group-containing crosslinked copolymer The carboxyl group-containing crosslinked copolymer used in the present invention comprises 25
The viscosity of a 1% by weight aqueous solution of the carboxyl group-containing crosslinked copolymer at 400 ° C is 400 cP or more, preferably 1000 cP or more,
More preferably, it is 1000 to 4000 cP. This viscosity is 400
If it is less than cP, the suspension polymerization system becomes unstable, such as the inner wall of the polymerization vessel, where the polymer scale adheres to the place where the monomer comes into contact, or the obtained vinyl chloride polymer tends to coarsen, Not preferred. The carboxyl group-containing crosslinked copolymer has a property of thickening by neutralizing an aqueous solution thereof with an appropriate base, and this is effective for improving the plasticizer absorption of the obtained vinyl chloride polymer. It is believed that there is. The carboxyl group-containing crosslinked copolymer used in the present invention is obtained by crosslinking a carboxylic acid compound having a polymerizable unsaturated bond and a crosslinking agent using a polymerization initiator.
ion with crosslinking).

As the carboxylic acid compound having a polymerizable unsaturated bond, for example, acrylic acid, methacrylic acid,
Itaconic acid, chloroacrylic acid, cyanoacrylic acid, α
-Phenylacrylic acid, α-benzylacrylic acid, crotonic acid, maleic acid, fumaric acid, sorbic acid and the like. These can be used alone or in combination of two or more. As the crosslinking agent, for example,
Two or more polymerizable molecules in one molecule

[0012]

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[0013] Specific examples thereof include compounds having a terminal at the terminal. Specific examples thereof include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; polybutadiene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, methylene bisacrylamide, divinyl ether; Soluble polymerizable dienes such as diallyl ether;
Polyvinyl; the following general formula (1):

[0014]

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(In the formula, R independently represents a hydrogen atom or a methyl group, and p, m and n are each a number greater than or equal to 0 and satisfy the following condition: 0 <p + m + n ≦ 500. Is a hydrogen atom and only when n = 0, p + m =
A compound satisfying 1), for example, diethylene glycol bisallyl ether, diethylene glycol bismethallyl ether, or the following formula:

[0016]

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And the like. These can be used alone or in combination of two or more. Examples of the polymerization initiator used for the cross-linking polymerization include azo-based, peroxide-based, and redox-based polymerization initiators, for example, azobisisobutyronitrile, 2,2
2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), benzoyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide,
Examples include persulfate, a combination of persulfate and percarbonate, and a combination of persulfate and sulfite. These polymerization initiators, for example, benzene,
It is preferable to use it after dissolving it in a solvent such as toluene, n-hexane or ethyl acetate.

The mixing ratio of the carboxylic acid compound having a polymerizable unsaturated bond and the crosslinking agent is usually
The crosslinking agent is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, per 100 parts by weight. If the blending amount of the crosslinking agent is too small, crosslinking is not sufficient, and if it is too large, crosslinking is excessive, and the resulting carboxyl group-containing crosslinked copolymer has a dispersing effect of vinyl chloride monomer and the like. May disappear.

Suitable as the carboxyl group-containing crosslinked copolymer thus obtained are the carboxylic acid compound having a polymerizable unsaturated bond and the compound represented by the general formula (I)
And more preferably a crosslinked polymer of acrylic acid and diethylene glycol bisallyl ether or diethylene glycol bismethallyl ether, particularly preferably acrylic acid
100 parts by weight and diethylene glycol bisallyl ether or diethylene glycol bismethallyl ether 0.05 to
It is a crosslinked polymer with 10 parts by weight.

A vinyl chloride monomer or a vinyl chloride monomer
Monomer mixture as a main monomer The monomer to be subjected to suspension polymerization in the production method of the present invention is a vinyl chloride monomer alone or another monomer which is mainly composed of a vinyl chloride monomer and can be copolymerized therewith. (Usually at least 50% by weight of vinyl chloride). Examples of monomers to be copolymerized with the vinyl chloride monomer include vinyl esters such as vinyl acetate and vinyl propionate; acrylates or methacrylates such as methyl acrylate and ethyl acrylate; ethylene, propylene and the like. Olefins; maleic anhydride; acrylonitrile; styrene; and monomers such as vinylidene chloride.

Oil-soluble polymerization initiator As the oil-soluble polymerization initiator used in the present invention, those which are conventionally used for polymerization of a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer are used. Specific examples thereof include t-butyl peroxy neodecanoate, t-butyl peroxy pivalate, t-hexyl peroxy neodecanoate, t-hexyl neohexanoate, and t-hexyl par. Perester compounds such as oxypivalate, α-cumylperoxyneodecanate, 2,4,4-trimethylpentyl-2-peroxy-2-neodecanate; diisopropylperoxydicarbonate, di-2-ethoxyethylperoxy Dicarbonate, di-2-ethylhexylperoxydicarbonate, dimethoxyisopropylperoxydica Boneto, percarbonate compounds such as diethoxyethyl peroxydicarbonate; decanoyl peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, p- methane hydroperoxide,
Isobutyryl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, 3,5,5
Peroxides such as trimethylhexanoyl peroxide and lauroyl peroxide; α, α′-azobisisobutyronitrile, α, α′-azobis (2,4-dimethylvaleronitrile), α, α′-azobis (4-methoxy-
Azo compounds such as 2,4-dimethylvaleronitrile) and the like, and these can be used alone or in combination of two or more. These oil-soluble polymerization initiators can be used in combination with a water-soluble polymerization initiator such as potassium persulfate, ammonium persulfate, and hydrogen peroxide, if necessary.

[0022] In the manufacturing method of the charge present invention to the polymerization vessel, wherein partially saponified polyvinyl alcohol, carboxyl group-containing crosslinked copolymer and water, pH
The solution is charged into a polymerization vessel as an aqueous solution having a pH of 6.0 to 8.0, preferably pH 6.5 to 7.5. If the pH is too small, the viscosities of the aqueous solution of the carboxyl group-containing cross-linked copolymer become insufficient, so that the porosity of the obtained vinyl chloride polymer does not improve. Becomes unstable, which is not preferable. PH of the aqueous solution of the partially saponified polyvinyl alcohol and the carboxyl group-containing crosslinked copolymer
Is adjusted to 6.0 to 8.0 by adding a known inorganic or organic base, for example, amines such as sodium hydroxide, potassium hydroxide, ammonia, and triethylamine. Among these, preferred are sodium hydroxide,
Potassium hydroxide.

The order of charging the partially saponified polyvinyl alcohol, the carboxyl group-containing crosslinked copolymer, water, an oil-soluble polymerization initiator, and a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer is as follows. For example, the partially saponified polyvinyl alcohol, the carboxyl group-containing cross-linked copolymer and water are charged into a polymerization vessel as an aqueous solution having a pH of 6.0 to 8.0, and the polymerization vessel is evacuated. After charging the monomer or the monomer mixture into a polymerization vessel, stirring the contents in the polymerization vessel and adding a polymerization initiator, the contents in the polymerization vessel are heated to a preset polymerization temperature. The procedure for performing polymerization may be sufficient.

The amount of the suspending agent comprising the partially saponified polyvinyl alcohol and the carboxyl group-containing crosslinked copolymer is determined based on the amount of the vinyl chloride monomer or the monomer mixture mainly composed of the vinyl chloride monomer. 0.01 to 1.0% by weight, preferably 0.05 to 1.0% by weight. If the charged amount is too small, the polymerization system may be unstable, and if it is too large, the particle size of the obtained polymer may be too small, which is not preferable in handling resin powder.

The partially saponified polyvinyl alcohol,
The mixing ratio with the carboxyl group-containing crosslinked copolymer is usually from 2 to 5, preferably from 2 to 4, by weight ratio of the partially saponified polyvinyl alcohol to the carboxyl group-containing crosslinked copolymer. If the ratio is too small, a skin layer may be formed on the surface of the obtained polymer particles and a non-skin type polymer may not be obtained.If the ratio is too large, the polymerization system becomes unstable and is obtained. It is not preferable because the polymer particles are liable to be coarsened, and the polymer scale is easily attached to a portion where the monomer contacts, such as the inner wall of the polymerization vessel. The amount of the oil-soluble polymerization initiator used is usually from 0.001 to 100 parts by weight of the vinyl chloride monomer to be charged.
It is 3 parts by weight, preferably 0.01 to 0.1 part by weight.

Polymerization Conditions The production method of the present invention uses a suspending agent comprising the partially saponified polyvinyl alcohol and the carboxyl group-containing crosslinked copolymer, and further comprises the partially saponified polyvinyl alcohol, the carboxyl group-containing crosslinked copolymer and Water is added at pH 6.
Suspension polymerization can be carried out under known conditions except that an aqueous solution of 0 to 8.0 is added to the polymerization system. For example, the amount of the aqueous medium required for suspending and dispersing a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer is the same as in the conventional method. The charge ratio (water / monomer ratio) to a monomer mixture mainly composed of a vinyl monomer may be about 1.0 to 2.5, and water can be added during the polymerization as needed. Further, in the present invention, the polymerization temperature, pressure, etc. may be those conventionally used, and may be used for the polymerization of a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer, if necessary. It is also optional to add a polymerization regulator appropriately used to the polymerization system.

[0027]

EXAMPLES The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to the following. Example 1 60 g of partially saponified polyvinyl alcohol having an average degree of polymerization of 230 and a saponification degree of 48 mol%, and a 1% by weight aqueous solution were used as suspending agents in a stainless steel polymerization vessel equipped with a stirrer and a jacket having a capacity of 100 liters. Has a viscosity of 25 at 25 ° C.
A crosslinked acrylic acid copolymer which is 00 cP (acrylic acid 100
30 g of a crosslinked acrylic acid copolymer of 1 part by weight of diethylene glycol bisallyl ether and 1 part by weight of diethylene glycol bisallyl ether were dissolved in 60 kg of warm water (pH = 11.0) to which 3 g of sodium hydroxide was added. At this time, the pH of the aqueous medium as the content in the polymerization vessel was 7.5. Next, exhaust the inside of the vessel,
Next, 30 kg of vinyl chloride monomer was charged, and the mixture was stirred for 3 minutes. Then, 21 g of t-butylperoxyneodecanate was charged as a polymerization initiator, and the temperature was raised to 57 ° C. to initiate polymerization.
Then, the polymerization was carried out while maintaining the temperature at 57 ° C. When the internal pressure of the polymerization vessel dropped to 6 kg / cm ² G, the polymerization was terminated, and then the unreacted monomer was recovered, and the obtained polymer was converted into a slurry. , And dehydrated and dried to obtain a polymer.

[Example 2] In Example 1, 60 kg of warmed water was prepared by changing the addition amount of sodium hydroxide from 3 g to 0.3 g.
Polymerization was carried out in the same manner as in Example 1 except that (pH = 10.0) was used to obtain a polymer. The pH of the aqueous medium before charging the vinyl chloride monomer was 7.0.

Example 3 Polymerization was carried out in the same manner as in Example 1 except that the amount of the crosslinked acrylic acid copolymer was changed from 30 g to 15 g to obtain a polymer. The pH of the aqueous medium before the vinyl chloride monomer was charged was 7.2.

Comparative Example 1 The procedure of Example 1 was repeated except that the partially saponified polyvinyl alcohol and the crosslinked acrylic acid copolymer were dissolved in 60 kg of warm water (pH = 6.3) to which no sodium hydroxide was added. A polymer was obtained in the same manner as in Example 1. The pH of the aqueous medium before charging the vinyl chloride monomer
Was 4.5.

Comparative Example 2 In Example 1, 60 g of partially saponified polyvinyl alcohol and a crosslinked acrylic acid copolymer were added to 60 kg of heated water (pH = 6.3) without adding sodium hydroxide.
A polymer was obtained in the same manner as in Example 1, except that 15 g of the polymer was dissolved and charged. The pH of the aqueous medium before charging the vinyl chloride monomer was 5.0.

Comparative Example 3 In Example 1, 30 g of partially saponified polyvinyl alcohol and a crosslinked acrylic acid copolymer were added to 60 kg of warm water (pH = 6.3) without adding sodium hydroxide.
A polymer was obtained in the same manner as in Example 1 except that 60 g was dissolved and charged. The pH of the aqueous medium before the vinyl chloride monomer was charged was 4.2. For the vinyl chloride polymers obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the following methods were used to determine bulk specific gravity, particle size distribution, plasticizer absorption, plasticizer absorption time, scale adhesion, and the presence or absence of a skin layer. Was evaluated. Table 1 shows the results.

<Bulk specific gravity>
It was measured according to S K-6721. <Particle size distribution># 60, # 100, and # 200 according to JIS Z-8801
The obtained polymer powder was sieved using each sieve described above, and the weight% of the powder that passed through the sieve was determined. <Amount of plasticizer absorbed> Glass fiber was packed in the bottom of an aluminum alloy container having an inner diameter of 25 mm and a depth of 85 mm, and 10 g of the obtained vinyl chloride polymer was charged as a sample. Add 15cc of dioctyl phthalate (DOP) to this and leave it for 30 minutes to
P was fully penetrated into the polymer. After that, the excess DOP was centrifuged at 1500 G acceleration, and the DO absorbed by 10 g of polymer was absorbed.
The amount of P was measured and converted to 100 g of the polymer.

<Plasticizer Absorption Time> 400 g of a vinyl chloride polymer powder was placed in a plastograph (planetary mixer), preheated (4 minutes) with stirring at 60 rpm to 80 ° C., and then 200 g of DOP was added thereto. The time from the time of addition to the time when the torque drop was completed was measured and defined as a plasticizer absorption time. <Scale adhesion> After the polymerization was completed, the state of adhesion of the polymer scale in the polymerization vessel was visually observed. <Presence / absence of skin layer> The polymer resin was observed with an electron microscope to determine the presence / absence of a skin layer.

[0035]

[Table 1]

As is clear from the results shown in Table 1, the vinyl chloride polymer powder obtained by the production method of the present invention has no skin layer on its surface, has a sharp particle size distribution, and has a plasticizer absorbency. Excellent.

On the other hand, even when the same partially saponified polyvinyl alcohol and crosslinked copolymer as the suspending agent of the present invention are used, the pH of the aqueous medium before charging the vinyl chloride monomer is 4.
In the case of 5 to 5.0 (Comparative Examples 1 and 2), the plasticizer absorption is poor. The pH of the aqueous medium before charging the vinyl chloride monomer
Was 4.2 and the proportion of partially saponified polyvinyl alcohol was reduced (Comparative Example 3), a skin layer was formed on the surface, the plasticizer absorption was poor, and scale adhered in the polymerization vessel. .

[0038]

According to the present invention, a non-skin type vinyl chloride polymer having a good particle size distribution, a good plasticizer absorption and a good gelation rate can be obtained without causing scale to adhere to the polymerization vessel. Obtainable.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-217804 (JP, A) JP-A-8-109207 (JP, A) JP-A-7-70211 (JP, A) JP-A-2- 305804 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08F 2/00-2/60 C08F 14/06

Claims (1)

(57) [Claims] 1. A partially saponified polyvinyl alcohol having an average degree of polymerization of 150 to 600 and a degree of saponification of 20 to 55 mol%;
A 1% by weight aqueous solution of a carboxyl group-containing crosslinked copolymer having a viscosity of 400 cP or more at 25 ° C .; a vinyl chloride monomer or a monomer mixture mainly composed of a vinyl chloride monomer; an oil-soluble polymerization initiator; A method in which water is charged into a polymerization vessel and the monomer is subjected to suspension polymerization in an aqueous medium, wherein the partially saponified polyvinyl alcohol, the carboxyl group-containing cross-linked copolymer and water have a pH of 6.0 to 8.0. A process for producing a vinyl chloride polymer, which is added to a polymerization system as an aqueous solution of a vinyl chloride polymer.