JP2001059002A - Production of vinyl chloride-based resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a vinyl chloride-based resin having a high bulk density, hardly causing fisheye, increasing the through put of a batch by using a polymerizer with a reflux condenser and exhibiting high productivity in a polymerization process. SOLUTION: When conducting suspension polymerization in an aqueous medium by using a polymerizer with a reflux condenser, vinyl chloride-based monomer is charged in a weight ratio of (aqueous medium/vinyl chloride-based monomer) of (0.5/1.0) to (1.2/1.0), and a partially saponified polyvinyl alcohol having a saponification degree of 65-85 mol% and hydroxypropyl methylcellulose as dispersants are added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a suspension polymerization method for a vinyl chloride monomer (hereinafter referred to as "VC") or a monomer mixture containing VC as a main component and copolymerizable therewith.
The present invention relates to a method for producing a vinyl chloride resin (hereinafter, referred to as “PVC”) having high productivity in a polymerization step, high bulk specific gravity, and low fish eyes.

[0002]

2. Description of the Related Art Conventionally, polymerization of VC is generally carried out in a polymerization vessel equipped with a jacket and a stirrer for heating and cooling.
A batch type aqueous suspension polymerization method has been performed. That is, first, an aqueous medium and a dispersant are charged into a polymerization vessel, then a polymerization initiator is charged, then the inside of the polymerization vessel is evacuated to vacuum, VC is charged, and the temperature is raised to initiate a polymerization reaction. From the time when the temperature comes out, maintain the polymerization temperature by passing cooling water through the polymerization reactor jacket, then recover VC and discharge PVC from the polymerization reactor.
A series of polymerization operations are performed. In such a series of polymerization steps, in order to increase the productivity, there is a method of shortening the time of each step or increasing the yield per batch.

In such a method, one problem is how to efficiently remove the heat of reaction. In general, heat is removed by a reflux condenser (hereinafter referred to as "RC"). However, when RC is used, fisheye is generated and polymerization becomes unstable, which hinders stable production. Therefore, various measures have been disclosed.

Among them, there is a method of increasing the batch yield in order to increase the productivity. For example, the water / VC ratio is set to 0.8 to 1.0 at the time of charging, and the volume is not exceeded during the polymerization. Water was added, and the water / VC ratio after the completion of the polymerization was adjusted to 1.0.
To 1.4 (Japanese Patent Publication No. 3-4561) or a water / VC ratio of 0.8 to 1.5 at the time of charging and a predetermined temperature in the polymerization vessel. A method of performing polymerization by charging and operating a reflux condenser (Japanese Unexamined Patent Publication No.
No. 136,096). However, these methods are insufficient as a measure to prevent fish eyes from occurring in the obtained PVC resin, and furthermore, water / V
Since the C ratio is lower than usual and the amount of PVC generated is large, the viscosity of the suspension becomes high, and the heat removal ability of the polymerization vessel jacket and RC is reduced, making it difficult to control the polymerization. A part of the liquid becomes clumpy and normal particles cannot be obtained.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to increase the volume of a batch by using a polymerization vessel having a high bulk specific gravity, low generation of fish eyes, and an RC. An object of the present invention is to provide a method for producing PVC having high process productivity.

[0006]

The method for producing a vinyl chloride resin according to the invention described in claim 1 (hereinafter referred to as "invention 1") uses a polymerization vessel equipped with a reflux condenser to suspend in a water medium. In the suspension polymerization, the aqueous medium / vinyl chloride monomer weight ratio was 0.5 / 1.0 to 1.2 / 1.0, and a partial saponifier having a saponification degree of 65 to 85 mol% was used as a dispersant. It is characterized by adding polyvinyl alcohol and hydroxypropyl methylcellulose.

[0007] The vinyl chloride resin according to the invention of claim 2 (hereinafter referred to as "invention 2") is a vinyl chloride resin obtained by the method of invention 1, and has a bulk specific gravity of 0.54.
０．５0.58 g / cc. Hereinafter, the present invention will be described in more detail.

In the present invention, a polymerization vessel equipped with RC is used. The RC is for cooling and condensing the gas vaporized from the liquid layer to return to a liquid state and to remove the heat of polymerization, so that the RC is provided so as to communicate with the gas phase in the polymerization vessel. The RC has a known structure as a cooler, and a refrigerant is passed through the RC to cool the gas.

The VC used in the present invention may be VC alone or a mixture containing VC as a main component (generally, VC of 50% by weight or more). Further, another vinyl monomer copolymerizable with VC may be contained as long as the production method of the present invention exerts its effects. The other vinyl monomer copolymerizable with the VC is not particularly limited, and examples thereof include vinyl esters such as vinyl acetate and vinyl propionate; and methyl (meth) acrylate and ethyl (meth) acrylate. (Meth) acrylic acid esters; olefins such as ethylene and propylene, (meth) acrylic acid, maleic anhydride, acrylonitrile, styrene, vinylidene chloride and the like. These may be used alone or in combination of two or more.

As the dispersant used in the present invention, partially saponified polyvinyl alcohol (A) having a saponification degree of 65 to 85 mol% and hydroxypropylmethyl cellulose (B) are used. The ratio of A / B to be added is preferably in the range of 1/5 to 5/1 depending on the load of RC heat removal and the polymerization time. The amount of these additives is preferably 0.04 to 0.2 parts by weight in total of A and B with respect to 100 parts by weight of VC. Although dispersants other than A and B can be used in combination, the amount of the dispersant is preferably 30% by weight or less based on the amount of A and B added. Furthermore, since the bulk specific gravity of the produced PVC is easily controlled, 68 to 76 mol% of partially saponified polyvinyl alcohol is preferably used. A and B
If a dispersant other than the above is used, the bulk specific gravity of the produced PVC will be low, many fish eyes will be generated, and in extreme cases, a part of the suspension will be clumpy and normal particles cannot be obtained.

The bulk specific gravity of the vinyl chloride resin of the present invention is:
A range of 0.54 to 0.58 g / cc is preferred. If the bulk specific gravity is less than 0.54 g / cc, the viscosity of the suspension becomes high, and PVC may not be obtained, and the suspension may have a viscosity of 0.58 g / cc.
If it exceeds, a large number of fish eyes may occur.

As the polymerization initiator used in the suspension polymerization of the present invention, a polymerization initiator generally used in the suspension polymerization of VC is suitably used. For example, diisopropyl peroxydicarbonate, di-2-ethylhexyl parper Peroxycarbonate compounds such as oxydicarbonate and diethoxyethylperoxydicarbonate; α-cumylperoxyneodecanate, t-butylperoxyneodecanate, t-butylperoxypivalate, t
-Peroxyester compounds such as hexylperoxyneodecanate; acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-
Peroxides such as peroxyphenoxy acetate; azobis-2,4-dimethylvaleronitrile, azobis (4-
Azo compounds such as methoxy-2,4-dimethylvaleronitrile); potassium persulfate, ammonium persulfate, hydrogen peroxide and the like, which may be used alone;
Two or more kinds may be used in combination.

Further, a polymerization regulator, a chain transfer agent, a pH regulator, a gelling improver, an antistatic agent, a polymerization scale adhesion inhibitor and the like which are appropriately used in general polymerization may be added.

In the present invention, the weight ratio of aqueous medium / VC at the time of preparation is 0.5 / 1.0 to 1.2 / 1.0, which exceeds the volume shrinkage of the suspension due to the progress of the reaction during the polymerization. It is preferable to add water in a range that does not exist continuously or intermittently.
If the aqueous medium / VC weight ratio is less than 0.5, no matter how much the bulk specific gravity is increased, the viscosity of the suspension increases and normal particles cannot be obtained, and the aqueous medium / VC weight ratio exceeds 1.2. Then, the productivity is reduced.

In the suspension polymerization of the present invention, an aqueous medium, V
As a method for charging C, a dispersant, a polymerization initiator, and other additives, a method used in ordinary suspension polymerization is suitably used. For example, an aqueous medium, a dispersant, a polymerization initiator,
A method of sequentially adding VC to a polymerization vessel, a method of continuously charging these at the same time, a method of sequentially or simultaneously charging VC in which a dispersant aqueous solution and a polymerization initiator are dissolved, and the like are included. Further, the reaction heat generated during the polymerization is removed by the polymerization reactor jacket and RC, and the polymerization can be continued and completed while controlling the temperature of the suspension in the polymerization reactor at a predetermined polymerization temperature.

In the suspension polymerization of the present invention, the polymerization temperature is not particularly limited, but is generally preferably from 40 to 80 ° C.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1) A saponification degree of 72 mol% was placed in a 600 liter polymerization vessel equipped with an RC having a heat transfer area of 0.5 m2.
80 parts by weight of water in which 0.03 parts by weight of partially saponified polyvinyl alcohol and 0.03 parts by weight of hydroxypropylmethylcellulose are dissolved and stirred to form a uniform solution, and di-2-ethylhexyl peroxydioxygen is used as a polymerization initiator. 0.08 parts by weight of carbonate was added, and then 100 parts by weight of VC were charged except for the air in the polymerization vessel (water / V
C, the weight ratio was 0.8), and the temperature was raised to 58 ° C. to initiate polymerization. Immediately after that, RC was operated, and when the pressure of the polymerization reactor became 0.75 MPa after 4 hours, unreacted VC
Was recovered to obtain PVC. Here, the heat removal by RC during the polymerization was carried out under the condition that water at 20 ° C. was circulated to remove 60% of the heat of the polymerization reaction. In addition, water was continuously added into the polymerization vessel using a metering pump immediately after the start of the polymerization and throughout the polymerization.

Examples 2 to 4 Polymerization was carried out in the same manner as in Example 1 except that the weight ratio of water / VC charged and the amount of the dispersant charged were changed as shown in Table 1, to obtain PVC.

(Comparative Example 1) As a dispersant, water in which 0.02 part by weight of partially saponified polyvinyl alcohol having a degree of saponification of 47 mol% and 0.05 part by weight of hydroxypropylmethylcellulose were dissolved (water / VC charged weight ratio) To 0.
8) The polymerization was carried out under the same conditions as in Example 1 except for the above. As a result, the suspension did not move during the polymerization, and normal particles could not be obtained.

(Comparative Examples 2 to 5) Polymerization was carried out in the same manner as in Comparative Example 1 except that the weight ratio of water / VC and the type and amount of the dispersant were changed as shown in Table 1, and normal particles were obtained. PVC was obtained only for the polymerizations performed.

The physical properties of the PVC obtained in the above Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1. (1) Observation of the viscosity of the suspension Because it is difficult to measure the viscosity of the suspension during the reaction, a pressure-resistant transparent glass that allows the inside to be observed is provided at the top of the polymerization vessel, and the state of the suspension entrainment is observed. Then, the level of viscosity was determined based on the following criteria. The observation was performed from the second hour after the start of the polymerization. ；: The suspension was active and involved, and the liquid level at the center was lowered (the viscosity was low). Δ: The suspension was poorly moved and involved, but no drop in the liquid level at the center was observed (high viscosity state). ×: no movement of suspension.

(2) Bulk specific gravity Measured according to JIS K6721.

(3) Fish Eye 50 parts by weight of plasticizer (dioctyl phthalate), 0.5 part by weight of stabilizer (barium stearate), and stabilizer (zinc stearate) based on 100 parts by weight of the obtained PVC. 0.
5 parts by weight, 0.5 parts by weight of a filler (titanium dioxide) and 0.1 parts by weight of a filler (carbon black) are mixed, and this mixture is kneaded at 140 ° C. for 5 minutes on a 6-inch roll to obtain a thick layer. A sheet having a thickness of 0.3 mm was produced. 100 of this sheet
The number of transparent particles in cm 2 was counted to determine the number of fish eyes.

[0025]

[Table 1]

As shown in Table 1, Examples 1 to 3 of the present invention
In PVC of No. 4, the viscosity of the suspension is not high and the generation of fish eyes is small.

On the other hand, as shown in Table 1, the saponification degree was 6
In Comparative Example 1 using less than 5 mol% of partially saponified polyvinyl alcohol, the viscosity of the suspension was too high to obtain PVC, and the degree of saponification was more than 85 mol%. In the PVC of Comparative Example 2 using alcohol, the viscosity of the suspension was increased and many fish eyes were generated.

Further, as shown in Table 1, Comparative Example 3 using only partially saponified polyvinyl alcohol as a dispersant was used.
And the PVC of Comparative Example 4 using only hydroxypropylmethylcellulose, the viscosity of the suspension was increased, and
Many fish eyes occurred.

Further, as shown in Table 1, the aqueous medium / V
In Comparative Example 5 in which the charged weight ratio of C was less than 0.5, PVC was not obtained because the viscosity of the suspension was too high.

[0030]

As described above, according to the present invention, the bulk specific gravity is high, the generation of fish eyes is small, and the production volume of the batch is increased by using a polymerization vessel having an RC to increase the productivity of the polymerization step to reduce the PVC. Can be manufactured.

Claims (2)

[Claims] When a suspension polymerization is carried out in an aqueous medium using a polymerization vessel provided with a reflux condenser, the weight ratio of the aqueous medium / vinyl chloride monomer is 0.5 / 1.0 to 1.2 /. Charge at 1.0,
A method for producing a vinyl chloride resin, comprising adding partially saponified polyvinyl alcohol having a degree of saponification of 65 to 85 mol% and hydroxypropyl methylcellulose as a dispersant. 2. A vinyl chloride resin obtained by the method according to claim 1, having a bulk specific gravity of 0.54 to 0.58 g.
/ Cc, a vinyl chloride resin.