JPH09221505A - Production of vinyl chloride polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a vinyl chloride polymer which gives a molding reduced in fish eyes by elevating the polymn. temp. in three steps from a low temp. to the usual polymn. temp. with the increase in conversion in the water-base suspension polymn. of a vinyl chloride monomer. SOLUTION: In producing a vinyl chloride (co)polymer by the suspension polymn. of a vinyl chloride monomer in an aq. medium, the polymn. temp. is kept below 60 deg.C from the begining of polymn. to a conversion of 3%, elevated to 60 deg.C during the conversion increases from 3% to 20%, and then kept at 60-80 deg.C. This method is applied to a polymer having an average degree of polymn. of 500-1,000 and is esp. effective in decreasing fish eyes of a vinyl chloride (co)polymer produced by the suspension polymn. of 100 pts.wt. vinyl chloride monomer in the presence of 0.001-2 pts.wt. dispersant comprising a water-sol. partially saponified polyvinyl acetate.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for producing a vinyl chloride polymer. Specifically, when a molded product is manufactured using the obtained vinyl chloride polymer, unmelted particles remaining on the surface of the molded product (hereinafter referred to as "fish eye")
The present invention relates to a method for producing a vinyl chloride polymer having a low content.

[0002]

2. Description of the Related Art Generally, a vinyl chloride polymer is a vinyl chloride monomer or a mixture of copolymerizable monomers mainly composed of vinyl chloride monomer (hereinafter collectively referred to as "vinyl chloride monomer"). The polymer obtained by polymerizing this is referred to as "vinyl chloride polymer".) In the presence of a polymerization initiator, suspension polymerization or emulsion polymerization in an aqueous medium containing a dispersant and / or an emulsifier. It is manufactured by

This vinyl chloride polymer is used in a wide range of applications such as pipes, films / sheets, toys, and molded products, but unmelted particles called "fish eyes" are present on the surface of these products. Then, it deteriorates the appearance and becomes a defective product. In order to prevent this, improvement of the vinyl chloride polymer itself is required. Especially for vinyl chloride polymers produced by suspension polymerization, it is important to reduce fisheyes in terms of quality, and as one of the measures, improvement of the particle shape of vinyl chloride polymers and generation of non-uniform particles Attempts have been made to prevent contamination.

[0004]

However, in order to produce a vinyl chloride polymer having an average degree of polymerization of about 500 to 1,000, when the polymerization temperature is set to 60 ° C. or higher, the fish eye remarkably deteriorates. . In particular, it facilitates the removal of vinyl chloride monomer from the produced polymer,
When using certain dispersants to improve product quality,
As a result, the deterioration of the fish eye became more remarkable.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above-mentioned circumstances, and as a result, in the aqueous suspension polymerization of vinyl chloride-based monomers, the reaction conversion rate and the temperature under specific conditions. The present invention has been completed by finding that the above problems can be solved by controlling so as to satisfy. That is, the gist of the present invention is a method for producing a vinyl chloride polymer by suspension polymerization of a vinyl chloride monomer in an aqueous medium,
From the start of polymerization to the reaction conversion rate of 3%, the polymerization temperature is 60
The temperature should be maintained below 60 ° C., the polymerization temperature should reach 60 ° C. until the reaction conversion rate exceeds 3% and reaches 20%, and then the polymerization should be performed while maintaining the temperature at 60 ° C. to 80 ° C. And a method for producing a vinyl chloride polymer.

The gist of the present invention also resides in the above-mentioned method for producing a vinyl chloride polymer, wherein the vinyl chloride polymer obtained has an average degree of polymerization of 500 to 1,000. Another aspect of the present invention is to use a water-soluble partially saponified polyvinyl acetate having a saponification degree of 60 to 90 mol%, particularly a saponification degree of 60 to 78 mol% as a dispersant for suspension polymerization. The above manufacturing method uses 0.001 to 2 parts by weight per 100 parts by weight of the system monomer.

Still another subject matter of the present invention is that the oxygen concentration in the polymerization system is 10 weight p with respect to the charged vinyl chloride monomer.
It also exists in the above-mentioned production method in which the reaction is started by controlling the pressure to pm or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. <Monomer> The vinyl chloride-based monomer used in the method of the present invention includes a vinyl chloride monomer alone and a mixture of copolymerizable monomers mainly composed of a vinyl chloride monomer. As the other monomer copolymerizable with the vinyl chloride monomer, those conventionally used in suspension polymerization of the vinyl chloride monomer can be used and are not particularly limited. Examples of the other monomers include vinyl esters such as vinyl acetate, alkyl vinyl ethers such as cetyl vinyl ether, α-olefins such as ethylene and propylene, and (meth) acrylic such as methyl acrylate and methyl methacrylate. Acid alkyl esters, vinylidene compounds such as vinylidene chloride, and the like. These other monomers are usually 20% by weight based on the vinyl chloride monomer.
Used in the following proportions.

<Dispersant> As the dispersant used in the method of the present invention, those generally used in the suspension polymerization method of vinyl chloride monomers can be used. Examples of the dispersant include partially saponified polyvinyl acetate (so-called polyvinyl alcohol), cellulose derivatives such as hydroxypropylmethylcellulose, and water-soluble polymers such as gelatin.

Particularly in the method of the present invention, when a partially saponified polyvinyl acetate is used, the effect of improving the fish eye is high. Among them, the saponification degree is 60 to 90 mol%, and more preferably the saponification degree is 60 to 78 mol%. The effect is most remarkable when the water-soluble partially saponified polyvinyl acetate is used.
When the water-soluble partially saponified polyvinyl acetate having the above specific saponification degree is used, the reason why the effect of the present invention is particularly remarkable is that the dispersion form of these partially saponified polyvinyl acetate changes depending on the temperature, water and This is probably because the properties of the dispersion containing the vinyl chloride-based monomer have changed significantly.

Further, anionic surfactants such as sodium lauryl sulfate and nonionic surfactants such as sorbitan fatty acid esters and glycerin fatty acid esters may be used as a dispersion aid. These dispersants can be used alone or in combination of two or more. The same applies to the dispersion aid. There is no particular limitation on the amount of the dispersant used, its type, stirring strength, polymerization temperature, type and composition of other monomers to be copolymerized with the vinyl chloride monomer, particle size of the vinyl chloride polymer produced. It may be adjusted according to the like, but generally 0.001 to 2 parts by weight, preferably 0.0 to 100 parts by weight of the vinyl chloride monomer.
It is used in the range of 3 to 1 part by weight.

<Polymerization Initiator and Other Auxiliary Agents> The polymerization initiator used in the method of the present invention may be one generally used in the suspension polymerization method of vinyl chloride type monomers,
There is no particular limitation. For example, perester compounds such as t-butyl peroxypivalate, t-butyl peroxy neodecanoate, t-hexyl peroxy pivalate, t-hexyl peroxy neodecanoate, α-cumyl peroxy neodecanoate, dilauroyl Peroxide compounds such as peroxides, percarbonate compounds such as diisopropylperoxydicarbonate and di-2-ethylhexylperoxydicarbonate, azo compounds such as azobis (2,4-dimethylvaleronitrile) and azobisisobutyronitrile. . These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator used varies depending on the type of the initiator, the polymerization temperature, the desired reaction time, etc.,
Generally 0.0 per 100 parts by weight of vinyl chloride monomer
It is in the range of 1 to 1 part by weight.

Further, in the method of the present invention, various polymerizations such as a cross-linking agent, a chain transfer agent, an antioxidant, a pH adjusting agent, and a scale anti-adhesion agent, which are used for the polymerization of vinyl chloride-based monomers, are optionally used. Auxiliary agents can be used as appropriate, and the amount and method of charging these auxiliary agents can be the general conditions used for the polymerization of vinyl chloride-based monomers.

<Control of Oxygen Concentration> When the method of the present invention is used, if the oxygen concentration at the start of the reaction in the polymerization system is controlled to 10 ppm by weight or less based on the charged vinyl chloride monomer, the fish eye improving effect is obtained. It gets even bigger. As a method for controlling the oxygen concentration, for example, a method in which nitrogen is replaced in the polymerization vessel prior to the start of the polymerization reaction, a method in which vacuum degassing is performed, or a method in which both are performed, and deoxidation is performed before charging raw materials used for polymerization. You can use the method. You may perform combining these methods. The specific conditions for setting the oxygen concentration at the start of the polymerization reaction to 10 ppm by weight or less can be selected by trial and error.

<Reaction Temperature and Degree of Polymerization> In the method of the present invention, a vinyl chloride-based monomer is suspension-polymerized in an aqueous medium to produce a vinyl chloride-based polymer. Until the reaction conversion exceeds 3% and reaches 20%, the polymerization temperature reaches 60 ° C, and thereafter the temperature is from 60 ° C to 8 ° C.
Polymerization is carried out while maintaining at 0 ° C.

The polymerization temperature from the start of polymerization to the reaction conversion rate of 3% is not particularly limited as long as it is less than 60 ° C.
For example, if the temperature is set to 50 ° C. to 59 ° C., the time required to raise the temperature to reach 60 ° C. during the reaction conversion rate exceeding 3% to 20% can be shortened, and the temperature can be shortened. It is preferable because it is possible to suppress the rapid decomposition of the polymerization initiator due to the increase.

If the conditions regarding the polymerization temperature and the reaction conversion rate are not satisfied, the fish eyes are not sufficiently reduced, and the effect of the present invention is not exhibited. In this temperature control, the polymerization temperature may be kept constant up to the reaction conversion rate of 3% or may be changed during this. For example, during this period, the heat of polymerization of the vinyl chloride-based monomer may be used to gradually increase the temperature so that the polymerization temperature exceeds 60 ° C. when the reaction conversion exceeds 3%. . In the present invention, "initiation of polymerization" refers to the time when the polymerization system is heated and heated to reach a predetermined reaction temperature.

Further, in the present invention, the reaction conversion rate is 3%.
The temperature is controlled so that the polymerization temperature reaches 60 ° C. until the temperature exceeds 20% and exceeds 20%. The polymerization temperature after reaching the temperature of 60 ° C. is not particularly limited as long as it is in the range of 60 ° C. to 80 ° C., but considering the operation operability, controllability, etc., it is constant so as to attain the target average degree of polymerization. It can be said that it is preferable to carry out the polymerization at a temperature. The reaction conversion was estimated by performing a test run under predetermined polymerization conditions, sampling the reaction mixture at each time, calculating the conversion by weighing the produced vinyl chloride-based polymer, and calculating the conversion curve versus time. If prepared for each polymerization condition, it can be carried out accurately from the polymerization conditions and the reaction time.

The average degree of polymerization of the produced polymer is generally considered as the weight average of the polymer having a specific degree of polymerization produced at a certain reaction temperature when the polymerization temperature changes with the progress of the reaction as in the present invention. Target. However, when the method of the present invention is used, for example, when the method is such that the temperature is raised to 60 ° C. or more immediately after the reaction conversion rate exceeds 3%, and thereafter the reaction is performed at a constant reaction temperature, the product vinyl chloride-based It may be considered that the degree of polymerization of the coalescence is approximately the degree of polymerization of the polymer produced at the constant reaction temperature. This is because the conversion rate of the polymerization reaction of vinyl chloride type monomer is generally 7
Since it is 0 to 90%, it can be said that the influence of the polymer produced up to the reaction conversion rate of 3% on the product polymerization degree is relatively small. In addition, when it is desired to set the degree of polymerization to exactly the target value, the operating condition can be determined by trial and error several times.

<Polymerization / Drying Method> In carrying out the method of the present invention, the charging ratio and the charging method of the aqueous medium, vinyl chloride monomer, dispersant, polymerization initiator and various polymerization aids to the polymerization vessel are particularly Not limited. Further, the shape of the stirring blades, baffles, etc., which are the auxiliary equipment of the polymerization vessel used in the method of the present invention, is not particularly limited, and conventionally commonly used equipment / equipment can be used.

As a method for stopping the polymerization, a so-called polymerization inhibitor or a polymerization terminator may be added, or a method of recovering unreacted monomer from the polymerization vessel may be used. As the method for dehydrating / drying the vinyl chloride-based polymer slurry thus produced, conventional methods such as centrifugal dehydration / fluid drying may be used. To remove the residual vinyl chloride monomer from the produced vinyl chloride polymer, a method such as heating under reduced pressure may be used.

[0022]

EXAMPLES Next, the specific contents of the method of the present invention will be described using examples, but the present invention is not limited to the following examples unless it exceeds the gist. <Physical property measurement method> The physical properties of the produced vinyl chloride polymer were evaluated by the following methods. Average degree of polymerization Measured according to the method shown in JIS K6721. Fisheye (FE) 100 parts by weight of vinyl chloride polymer, 40 parts by weight of plasticizer (di-2-ethylhexyl phthalate (DOP)), 3 parts by weight of lead-based powder stabilizer were premixed in a beaker,
The mixture is kneaded with a mill roll at 155 ° C. for 3, 4, 5, and 7 minutes, respectively. The number of fish eyes in the obtained square of 5 cm on each side of the roll sheet (area: 25 cm ² ) was defined as the number of fish eyes.

<Measurement Method of Dissolved Oxygen Amount> A preliminary experiment was conducted under the same conditions as in each of the examples and comparative examples, and the concentration of the aqueous phase was measured using a Beckman type dissolved oxygen meter and the organic phase was measured using a gas chromatograph. Was carried out and converted into ppm by weight based on the vinyl chloride-based monomer.

Example 1 A stainless steel polymerization can equipped with a stirrer and a jacket having an internal volume of 400 liters was charged with 150 kg of deionized water and 55 g of water-soluble partially saponified polyvinyl acetate having a degree of polymerization of 700 and a degree of polymerization of 70%. Then, reduce the pressure to -0.95 kg / cm ² (gauge pressure) with a vacuum pump,
Degassed. After that, 100 kg of vinyl chloride monomer and 45 g of a polymerization initiator (t-butylperoxypivalate) were charged, the temperature was raised to 58 ° C to start the reaction as shown in the table, and then the reaction conversion rate was 6% and the polymerization temperature was 60 ° C. After the temperature was raised to 65.5 ° C., the temperature was maintained to carry out the polymerization reaction.

The reaction is terminated when the internal pressure of the polymerization vessel drops by ² kg / cm ² below the saturated vapor pressure of the vinyl chloride monomer at 65.5 ° C., and the unreacted vinyl chloride monomer is removed to the atmospheric pressure outside the system. Then, the inside of the polymerization vessel was evacuated. The produced slurry was taken out, dehydrated and dried to obtain a vinyl chloride polymer. The physical properties of this vinyl chloride polymer were evaluated, and the results are also shown in the table.

<Embodiment 2> Vacuum deaeration before charging is performed at -0.
Example 1 except that it was up to 93 kg / cm ² (gauge pressure) and the polymerization initiator was a combination system of t-butylperoxypivalate and di-2-ethylhexylperoxydicarbonate (15 g / 30 g each).
Preparation was carried out in the same manner as.

As shown in the table, after the temperature was raised to 52 ° C. to start the reaction, the temperature was gradually raised to a reaction conversion rate of 10%.
At that time, the polymerization temperature was set to 60 ° C., and after the reaction temperature reached 66 ° C., the temperature was maintained to carry out the polymerization. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1.

<Embodiment 3> The vacuum deaeration before charging is set to −0.
Preparation was performed in the same manner as in Example 1 except that the pressure was set to 90 kg / cm ² (gauge pressure). As shown in the table, after the temperature was raised to 57 ° C. to start the reaction, the temperature was gradually raised to a polymerization temperature of 60 ° C. when the reaction conversion rate was 7%, and after the temperature reached 66 ° C. Maintained its temperature and polymerized. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1.

<Example 4> Saponification degree of 76% as a dispersant
In the same manner as in Example 1 except that a water-soluble partially saponified polyvinyl acetate having a polymerization degree of 2300 was used.
As shown in the table, after the temperature was raised to 57 ° C. to start the reaction, the temperature was gradually raised to a polymerization temperature of 60 ° C. when the reaction conversion rate was 6%, and the reaction temperature was further increased to 65.5 ° C. After the temperature was reached, the temperature was maintained and the polymerization was carried out. Subsequent termination of the reaction, removal of vinyl chloride monomer and dehydration of the resulting slurry
Evaluation of the dried and produced polymer was carried out in the same manner as in Example 1.

<Example 5> Saponification degree of 80% as a dispersant
In the same manner as in Example 4 except that the water-soluble partially saponified polyvinyl acetate having a degree of polymerization of 2300 was used, a vinyl chloride polymer was obtained. The vinyl chloride polymer was evaluated in the same manner as in Example 1.

<Comparative Example 1> Charge and degassing were carried out in the same manner as in Example 1, the reaction was started by raising the temperature to 65 ° C as shown in the table, and thereafter the polymerization was continued at a constant temperature of 65 ° C. It was The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1. The results are shown in the table.

<Comparative Example 2> Vacuum deaeration before charging was carried out at −0.
The charging / reaction and the polymer produced were evaluated in the same manner as in Comparative Example 1 except that the pressure was set to 90 kg / cm ² (gauge pressure).

<Comparative Example 3> Charge and deaeration were carried out in the same manner as in Example 1, the temperature was raised to 63 ° C. to initiate the polymerization as shown in the table, and then the temperature was gradually raised to the reaction conversion rate. Is 6%
At that time, the polymerization temperature was set to 65.5 ° C., and the temperature was continuously maintained to carry out the polymerization. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1. The results are shown in the table.

Comparative Example 4 A combination system of t-butylperoxypivalate and di-2-ethylhexylperoxydicarbonate as a polymerization initiator (15 g / 3 each).
Preparation was performed in the same manner as in Example 1 except that the amount was 0 g).

As shown in the table, after the temperature was raised to 58 ° C. to start the reaction, the temperature was raised to a polymerization temperature of 60 ° C. at a reaction conversion rate of 2%, and after the temperature reached 65 ° C., the temperature was raised. The polymerization reaction was carried out while maintaining. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1. The results are shown in the table.

Comparative Example 5 Charge was carried out in the same manner as in Example 1 except that di-2-ethylhexyl peroxydicarbonate (50 g) was used as the polymerization initiator. As shown in the table, the temperature was raised to 58 ° C. to start the reaction, and then the temperature was maintained at 58 ° C. to carry out the polymerization reaction. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1. The results are shown in the table.

<Comparative Example 6> Charge was carried out in the same manner as in Comparative Example 5, and the temperature was raised to 52 ° C. to start the reaction as shown in the table.
After that, the temperature was gradually raised, and the polymerization temperature was 58.5 ° C when the reaction conversion rate was 6%, and the temperature was 6% when the reaction conversion rate was 40%.
The temperature was set to 0 ° C., and then the temperature was raised until the temperature reached 65 ° C., and thereafter the temperature was maintained to carry out polymerization. The subsequent termination of the reaction, removal of the vinyl chloride monomer, dehydration / drying of the produced slurry, and evaluation of the produced polymer were carried out in the same manner as in Example 1. The results are shown in the table.

[0038]

EFFECT OF THE INVENTION By using the method of the present invention, a vinyl chloride polymer can be obtained which has a small number of fish eyes during processing and can give a molded product of excellent quality.

[0039]

[Table 1] Oxygen concentration at the start of polymerization: Oxygen concentration at the start of polymerization with respect to vinyl chloride monomer (wt ppm)

Claims (5)

[Claims] 1. A vinyl chloride monomer or a mixture of vinyl chloride monomer-based copolymerizable monomers (hereinafter collectively referred to as “vinyl chloride-based monomer”) is suspended in an aqueous medium. In the method for producing a vinyl chloride polymer by turbid polymerization, the polymerization temperature is maintained below 60 ° C. from the initiation of polymerization to the reaction conversion rate of 3%, and the reaction conversion rate exceeds 3% to 20%.
The method for producing a vinyl chloride polymer, characterized in that the polymerization temperature is reached to 60 ° C. until the temperature reaches, and then the polymerization is carried out while maintaining the temperature at 60 ° C. to 80 ° C. 2. The method for producing a vinyl chloride polymer according to claim 1, wherein the vinyl chloride polymer obtained has an average degree of polymerization of 500 to 1,000. 3. A saponification degree of 60 as a dispersant for suspension polymerization.
The method for producing a vinyl chloride-based polymer according to claim 1 or 2, wherein 0.0090 to 2 parts by weight of water-soluble partially saponified polyvinyl acetate is used per 100 parts by weight of the vinyl chloride-based monomer. 4. The method for producing a vinyl chloride polymer according to claim 1, wherein the saponification degree of the water-soluble partially saponified polyvinyl acetate is 60 to 78 mol%. 5. The vinyl chloride according to claim 1, wherein the reaction is started by controlling the oxygen concentration in the polymerization system to 10 ppm by weight or less based on the charged vinyl chloride-based monomer. Of producing a base polymer.