JPH07238104A - Production of vinyl chloride polymer - Google Patents

Abstract

PURPOSE:To obtain by suspension polymerization a vinyl chloride polymer having a high bulk specific gravity, a high saponification rate, and a satisfactory thermal stability and containing few fisheyes by using a partially saponified poly(vinyl alcohol) as a dispersion stabilizer. CONSTITUTION:This process comprises suspending a monomer ingredient (A), e.g. vinyl chloride alone or a mixture of a major proportion of vinyl chloride and a minor proportion of comonomer, in an aqueous medium (B) in an (A) to (B) ratio of about 0.8-4.0, adding an oil- or water-soluble polymerization initiator optionally together with a modifier and a pH regulator, and using as a stabilizer a partially saponified poly(vinyl alcohol) having an average degree of polymerization of 600-800 and a degree of saponification of 65-75%. The stabilizer is first added before the initiation of the polymerization in an amount of 0.01-0.1wt.% based on the ingredient (A). The stabilizer is thereafter again added continuously or intermittently in an amount of 0.01-0.1wt.% based on the ingredient (A) during the period of from initiation of the polymerization to the time when the degree of polymerization reaches 10-30%. The ratio of the stabilizer added first to that added secondly is 2/1 to 3/5 by weight. Thus, a decrease in bulk specific gravity or gelation rate is prevented.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Prior Art Vinyl chloride polymers are resins having excellent physical properties and are widely used as hard and soft molding materials. As the molding method of this vinyl chloride polymer, methods such as calender molding, extrusion molding, and injection molding are widely applied, but particularly in the case of extrusion molding of a hard polymer, the extrusion amount from the extruder is increased. Therefore, the development of a vinyl chloride polymer having a high bulk specific gravity is desired.

As a method for producing a vinyl chloride-based polymer, a suspension polymerization method in which a vinyl chloride monomer is suspended and dispersed in an aqueous medium to carry out polymerization is widely adopted. A polymer obtained by this method is used. It is known that the bulk specific gravity of is affected by the type of dispersant, stirring conditions, water / monomer charging ratio, and the like. For example, as a method for producing a vinyl chloride polymer having a high bulk specific gravity by a suspension polymerization method, a method of adding a vinyl chloride monomer during the polymerization (JP-A-59-168008), a vinyl chloride monomer A method using a highly saponified vinyl alcohol as a dispersion stabilizer for suspending and dispersing the above in an aqueous medium (JP-A-57-76008) has been proposed.

[0004]

However, in the above-mentioned method, although it is satisfactory in that a vinyl chloride polymer having a high bulk specific gravity is obtained, the resulting polymer becomes poor in porosity, so that a molded article is obtained. There was a problem that the fish eyes of the fish increased. Further, since the obtained polymer has a slow gelation rate, it has a problem in its moldability. Further, there is also a problem that the thermal stability of the obtained vinyl chloride polymer is lowered depending on the dispersion stabilizer used.

Therefore, the object of the present invention is to have a high bulk specific gravity, a high gelation rate and a certain level of thermal stability by the suspension polymerization method, and further, a fish eye when formed into a molded article is effective. Another object of the present invention is to provide a method capable of obtaining a vinyl chloride-based polymer which is suppressed by the above.

[0006]

According to the present invention, vinyl chloride or a vinyl-based monomer mixture containing vinyl chloride is
In a method for producing a vinyl chloride polymer having a step of performing suspension polymerization by suspending and dispersing in an aqueous medium charged in a polymerization vessel, an average degree of polymerization of 600 to 800, a degree of saponification of 65 to 75 mol% The partially saponified polyvinyl alcohol is subjected to the above suspension dispersion using 0.01 to 0.1% by weight of the dispersion stabilizer based on the charged monomers, and then the suspension polymerization is started. Of vinyl chloride polymer, characterized in that the partially saponified polyvinyl alcohol in an amount of 0.01 to 0.1% by weight based on the charged monomer is continuously or intermittently post-added over the time of reaching 30% to 30%. A method is provided.

[0007]

In suspension polymerization, the dispersion stabilizer is generally charged into the polymerization vessel at the stage before the start of polymerization, simultaneously with the aqueous medium or after the aqueous medium is charged. In this case, the amount of the dispersion stabilizer in the aqueous phase decreases as the stirring time elapses, and this tendency is particularly large after the initiation of polymerization. Therefore, in order to maintain the suspension stability of the polymerization system, it is necessary to use an excessive amount of dispersion stabilizer. As a result, although the suspension stability is ensured, a skin layer is thickly formed by the dispersion stabilizer on the surface of the obtained polymer, and the porosity decreases, so that the polymer becomes solid and the fish eye It is considered that this is the cause of the increase and delay of gelation rate.

According to the present invention, therefore, only the amount of the dispersion stabilizer necessary for dispersing the droplets of the monomer or the like is used in the stage before the initiation of the polymerization (hereinafter, the dispersion stabilizer added in this stage). The agent is referred to as "first dispersion stabilizer"), and an amount of the dispersion stabilizer (hereinafter, the dispersant added at this stage is used to compensate for the deficiency in the aqueous phase from the start of polymerization to a certain period). The above-mentioned inconvenience is effectively eliminated by continuously or intermittently adding the "second dispersion stabilizer" afterwards. In addition, in the present specification, the time of starting the polymerization means the time when the polymerization initiator is charged and the temperature rise in the polymerization vessel is started.

In particular, it is extremely important to add the second dispersion stabilizer continuously or intermittently over a period from the initiation dictionary until a certain polymerization conversion rate is reached. For example, this is added all at once. Then, the interfacial tension changes abruptly, resulting in poor reproducibility of the polymer particles,
The particle size becomes finer, the bulk specific gravity decreases, and the fish eyes increase, which causes inconvenience. As described above, it is not clear why the above inconvenience does not occur when added continuously or intermittently over a certain period of time without adding them all at once, but the monomer droplets are almost constant in the aqueous phase. It is considered that the monomer droplets are coalesced and dispersed more uniformly by being covered with the suspending agent of the concentration. When the second dispersant is added intermittently, the interval should be such that the advantages of the present invention with respect to bulk specific gravity, gelation rate, fish eyes, etc. are not impaired, and the interval is too large. If opened, the same inconvenience as when added all at once occurs, so caution is required.

The first and second dispersion stabilizers used in the polymerization method of the present invention have an average degree of polymerization of 600 to 800, especially 700 to 800, and a degree of saponification of 65 to 75 mol%, especially 70 to 70%.
When the partially saponified polyvinyl alcohol in the range of 75 mol% is used and the other partially saponified polyvinyl alcohol is used, the following various problems occur.

For example, when the average degree of polymerization of the partially saponified polyvinyl alcohol is less than 600, the protective action against the droplets of the monomer is lowered, so that the droplets are likely to be aggregated and the polymer produced is formed. There is a risk of coarse particles and further blocking. Further, when the average degree of polymerization exceeds 800 or the degree of saponification becomes higher than 75 mol%, the bulk specific gravity of the polymer produced increases, but the porosity decreases, resulting in deterioration of gelation property and This causes the disadvantage that a lot of fish eyes are generated during the molding of the coalescence. Further, when the saponification degree is less than 65 mol%,
There is a possibility that the amount of the partially saponified polyvinyl alcohol acting on the monomer becomes too large, the dispersion stability in the aqueous medium decreases, and the resulting polymer becomes coarse particles or blocks.

Therefore, a partially saponified polyvinyl alcohol which has been frequently used as a dispersion stabilizer for suspension polymerization of vinyl chloride-based monomers, for example, a partial saponification having an average degree of polymerization of 1500 to 3000 and a degree of saponification of about 80 mol%. Polyvinyl alcohol cannot be used as the first and second dispersion stabilizers in the present invention.

Further, in the present invention, as the first and second dispersion stabilizers, only those having the above-mentioned average degree of polymerization and saponification degree are used, and other dispersion stabilizers such as, for example, Other partially saponified polyvinyl alcohol, water-soluble cellulose ethers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose; water-soluble polyacrylic acid, gelatin, styrene-maleic acid copolymer, polyvinylpyrrolidone, etc. Polymers; sorbitan monolaurate, sorbitan trioleate, sorbitan monostearate, glycerin tristearate, oil-soluble emulsifiers such as ethylene oxide-propylene oxide block copolymers; polyoxyethylene sorbitan Laurate, polyoxyethylene grayed serine oleate, it is used in combination such as water-soluble emulsifiers sodium laurate, etc., can not substantially. The reason is not clear, but the thermal stability of the obtained vinyl chloride polymer is lowered.

In the present invention, the amount of the first dispersion stabilizer added before the start of polymerization is 0.01 to 0.1 per the charged monomer.
It is set in the range of 0.03 to 0.05% by weight, especially 0.03 to 0.05% by weight. If the amount is less than this range, the suspension system becomes unstable and coarse-grained or block-like polymer is produced, and if used in a larger amount than the range, it is difficult to obtain a polymer having a high bulk specific gravity. Therefore, it becomes difficult to improve the gelation rate.

The total amount of the second dispersion stabilizer added continuously or intermittently from the start of the polymerization to the time when the polymerization rate becomes 10 to 30% is 0.01 to 0.
It is set to 1% by weight, particularly 0.02 to 0.05% by weight.
If it is less than this range, it cannot be supplemented with the insufficient amount of the suspending agent in the aqueous phase, so that the number of coarse particles in the polymer increases, and the disadvantages such as increase in fish eyes occur. When it is used in a large amount, fine particles in the polymer increase and porosity decreases, which causes a disadvantage such as a slow gelation rate.

Further, if the addition of the second dispersion stabilizer is started from the stage before the start of polymerization, it becomes difficult to obtain a polymer having a high bulk specific gravity, and the addition is carried out even when the polymerization rate exceeds 30%. Continuing with, although the increase in the bulk specific gravity of the obtained polymer is observed, but the porosity decreases,
It results in increased fish eyes and slowed gelation rate.
The polymerization rate can be estimated from the elapsed time by measuring the conversion rate in advance with respect to a predetermined polymerization system at each elapsed time from the start of the polymerization. The first dispersion stabilizer / second dispersion stabilizer (weight ratio) is 2/1 to 3/5.
It is desirable to set the range to. If the first dispersion stabilizer is used in a larger amount than this range, the bulk specific gravity of the resulting polymer will be lowered and the gelation rate will be slow, while the second dispersion stabilizer will be used in a larger amount than this range. Then, the gelation rate also tends to decrease.

Polymerization component In the production method of the present invention, as the monomer, vinyl chloride can be used alone, or a monomer mainly containing vinyl chloride and containing a comonomer copolymerizable with vinyl chloride. Mixture (usually containing 50% by weight or more of vinyl chloride)
Can also be used. Such comonomers include:
Vinyl esters such as vinyl acetate and vinyl propionate,
Examples thereof include (meth) acrylic acid esters such as methyl acrylate and ethyl acrylate, olefins such as ethylene and propylene, maleic anhydride, acrylonitrile, styrene and vinylidene chloride.

A polymerization initiator is used as the other polymerization component suspended and dispersed in the aqueous medium together with the above-mentioned monomer. As this polymerization initiator, those conventionally used for the polymerization of vinyl chloride can be used,
For example, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-hexyl peroxypivalate, α-cumylperoxy neodecanoate, t-hexyl neohexanoate, 2,4 Perester compounds such as 4,4-trimethylpentyl-2-peroxy-2-neodecanoate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxyisopropyl peroxy Percarbonate compounds such as dicarbonate, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, p-menthane hydroxide Peroxides, peroxide compounds such as 3,5,5-trimethylhexanoyl peroxide, isobutyryl peroxide, acetylcyclohexylsulfonyl peroxide, α, α′-azobisisobutyronitrile, α, α′-azobis (2, 4-dimethylvaleronitrile), α, α′-azobis (4-methoxy-2,4
Azo compounds such as dimethylvaleronitrile) can be used alone or in combination of two or more. Further, although these are oil-soluble polymerization initiators, water-soluble polymerization initiators such as potassium persulfate, ammonium persulfate and hydrogen peroxide may be used alone or in combination. The polymerization initiator may be added during the charging of water or the monomer, or after the completion of the charging, may be uniformly mixed with the monomer in advance and charged with the monomer, or may be charged with the aqueous medium as an aqueous emulsion. Good.

Polymerization Conditions In the production method of the present invention, the above-mentioned first dispersion stabilizer is used to suspend and disperse the above-mentioned monomers in an aqueous medium.
Moreover, suspension polymerization can be carried out under conditions known per se, except that the second dispersion stabilizer is added to the polymerization system at a constant timing from the start of polymerization. For example, the amount of the aqueous medium used to suspend and disperse the polymer component such as the monomer is similar to that in the conventional method, and the charging ratio with the monomer (water / monomer) is 0.8 to 4.0. The degree is sufficient, and if necessary, water or a monomer can be added during the polymerization.

The amount of the polymerization initiator used, the polymerization temperature, etc. are
It may be in the range conventionally used, and if necessary, a polymerization degree adjusting agent, a pH adjusting agent, etc. may be added to the polymerization system.

[0021]

EXAMPLES In the following examples, the bulk specific gravity, particle size distribution, plasticizer absorption, fish eye, gelling time and thermal stability of the obtained vinyl chloride polymer were measured by the following methods. Bulk specific gravity: Measured according to JIS K 6721. Particle size distribution: Sieving was performed using each of # 60, # 100, and # 200 sieves according to JIS Z 8801, and the passing amount (% by weight) was measured. Fish eye: 100 parts by weight of vinyl chloride polymer, 1 part by weight of tribasic lead sulfate, and 1.5 parts of lead stearate.
Parts by weight, titanium oxide 0.2 parts by weight, carbon black
A mixture prepared by mixing 0.1 part by weight and 50 parts by weight of DOP with a roll was kneaded at 145 ° C. for 3 minutes, and then the thickness
The sheet was molded into a 0.2 mm sheet, and the number of fish eyes contained in 100 cm ^{2 of} the sheet was counted. Gelation time: 100 parts by weight of vinyl chloride polymer, 0.5 parts by weight of tribasic lead sulfate, 2.5 parts by weight of lead stearate and 0.7 parts by weight of barium stearate were mixed, and 68.5 g of this mixture was Brabender. Kneading was carried out under the conditions of 205 ° C. and 50 rpm by a Plastograph manufactured by the company, and the time until the maximum torque was exhibited was taken as the gelation time. It can be said that the shorter the gelling time is, the more excellent the gelling property is. Thermal stability test: 100 parts by weight of sample vinyl chloride polymer,
1.0 parts by weight of tribasic lead sulfate and 3.0 parts of lead stearate
After mixing by weight, the mixture was kneaded with a roll at 175 ° C. for 5 minutes to prepare a sheet having a thickness of 1 mm. This sheet was placed in an oven at 190 ° C. and the time (minutes) until blackening was measured.

Example 1 A stainless steel autoclave having an internal volume of 2 m ³ (with a stirrer and a jacket) was charged with 900 kg of deionized water and a saponification degree of 72.9.
Mol%, average degree of polymerization 780, viscosity of 4% aqueous solution at 20 ° C. of 7.3 cP and ultraviolet absorption of 1% aqueous solution at 280 nm.
An aqueous solution of partially saponified polyvinyl alcohol of 3.0
(A) (Concentration: 4.0% by weight) 8750 g was charged. Next, after degassing until the internal pressure of the autoclave reached about 50 mmHg, 700 kg of vinyl chloride monomer was charged, hot water was passed through the jacket while stirring to start the temperature increase, and at the same time, as a polymerization initiator, An aqueous emulsion solution of 2-ethylhexyl peroxydicarbonate (concentration: 20% by weight) (1200 g) was charged. At the same time, 8750 g of the partially saponified polyvinyl alcohol aqueous solution (A),
It was continuously charged uniformly until the polymerization rate reached 20% (charge rate 60 g / min). Polymerization is continued at a temperature of 57 ℃, and when the internal pressure of the autoclave reaches 6.0 kg / cm ² G, the reaction is stopped, unreacted monomers are recovered, dehydrated and dried to remove vinyl chloride polymer. Obtained. The bulk density, particle size distribution, fish eye, gelling time and thermal stability of the obtained polymer were measured, and the results are shown in Table 1.

Example 2 In Example 1, instead of the partially saponified polyvinyl alcohol aqueous solution (A) used before the initiation of polymerization, the saponification degree was 72.4.
An aqueous solution (B) of partially saponified polyvinyl alcohol (mol.%, Average degree of polymerization: 770, viscosity of a 4% aqueous solution at 20 ° C .: 6.5 cP, and UV absorption of a 1% aqueous solution at 280 nm: 6.5) (concentration: 4. 0 wt%) 5250 g, and instead of the partially saponified polyvinyl alcohol aqueous solution (A) added from the start of the polymerization, the partially saponified polyvinyl alcohol (B) 3500 g was added at a feeding rate of 24 g / min. A polymer was produced in the same manner as in Example 1 except that
Various characteristics were measured. The results are shown in Table 1.

Example 3 In Example 1, the partially saponified polyvinyl alcohol aqueous solution (A) added from the start of the polymerization had a polymerization rate of 20%.
Polymer was produced in the same manner as in Example 1 except that the charge was divided into 12 times (charge interval: 12 minutes, charge amount per time: 60.3 g), and various properties were measured. The results are shown in Table 1.

Comparative Example 1 A polymer was produced in the same manner as in Example 1 except that the entire amount of the partially saponified polyvinyl alcohol aqueous solution (A) used in Example 1 was charged in a stage before the initiation of polymerization, and various properties were obtained. Was measured. The results are shown in Table 2.

Comparative Example 2 A polymer was prepared in the same manner as in Example 1 except that the partially saponified polyvinyl alcohol aqueous solution (A) was not charged from the beginning of the polymerization, and various properties were measured. I went. The results are shown in Table 2.

Comparative Example 3 In Example 1, the polymerization rate was 30% when the partial saponified polyvinyl alcohol aqueous solution (A) was charged from the start of the polymerization.
A polymer was produced and various properties were measured in the same manner as in Example 1 except that the polymerization rate was continuously increased to 50% (charge rate: 65 g / min) from the time when the temperature reached the above. The results are shown in Table 2.

Comparative Example 4 In Example 1, the polymerization rate was 20% when the partial saponified polyvinyl alcohol aqueous solution (A) was charged from the start of the polymerization.
A polymer was produced and various properties were measured in the same manner as in Example 1 except that the process was carried out all at once when the temperature reached the above. The results are shown in Table 2.

Comparative Example 5 Instead of the partially saponified polyvinyl alcohol aqueous solution (A) used before the initiation of polymerization in Example 1, an average degree of polymerization of 26
00, partially saponified polyvinyl alcohol aqueous solution (C) with a saponification degree of 80.2 mol% (concentration: 4.0% by weight) 3675 g, methoxy substitution degree 29.2% by weight, hydroxyporopoxy substitution degree
Viscosities (20 ° C) in 8.9 wt% and 2 wt% aqueous solutions
49.5 cP Hydroxypropyl Methyl Cellulose Aqueous Solution
(D) (concentration: 3.5% by weight) 1800 g was used, and the partially saponified polyvinyl alcohol aqueous solution (C) 2450 was used instead of the partially saponified polyvinyl alcohol aqueous solution (A) added from the start of polymerization. g and the above-mentioned aqueous solution of hydroxypropylmethyl cellulose (D) 1200 g, 3650 g of a mixture aqueous solution was continuously charged at a charging rate of 25.2 g / min to prepare a polymer in the same manner as in Example 1 and to obtain various characteristics. Was measured. The results are shown in Table 2.

Comparative Example 6 Instead of the partially saponified polyvinyl alcohol aqueous solution (A) used before the initiation of polymerization in Example 1, 5250 g of the partially saponified polyvinyl alcohol aqueous solution (C), the hydroxypropylmethylcellulose aqueous solution (D) were used. ) 4000 g,
, And from the start of the polymerization, the partial saponified polyvinyl alcohol aqueous solution (C) 7500 g,
A polymer was produced and various properties were measured in the same manner as in Example 1 except that continuous feeding was performed at 51.7 g / min. The results are shown in Table 2.

Comparative Example 7 In Example 1, 8750 g of the partially saponified polyvinyl alcohol aqueous solution (C) was used in place of the partially saponified polyvinyl alcohol aqueous solution (A) used before the initiation of the polymerization, and the polymerization was performed. From the start point, 8750 g of the partially saponified polyvinyl alcohol aqueous solution (C) was introduced at a feed rate of 60.0 g.
A polymer was produced and various properties were measured in the same manner as in Example 1 except that continuous feeding was performed at / min. The results are shown in Table 2.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

INDUSTRIAL APPLICABILITY According to the present invention, suspension polymerization has a high bulk specific gravity, a high gelation rate, a certain level of thermal stability, and a fish eye when formed into a molded product is also effective. It is possible to obtain a vinyl chloride-based polymer which is suppressed by the above.

Claims (1)

[Claims] 1. A vinyl chloride polymer having a step of carrying out suspension polymerization by suspending and dispersing a vinyl chloride or a vinyl monomer mixture containing vinyl chloride in an aqueous medium charged in a polymerization vessel. In the production method, a partially saponified polyvinyl alcohol having an average degree of polymerization of 600 to 800 and a degree of saponification of 65 to 75 mol% is used in an amount of 0.
The suspension dispersion is carried out using 01 to 0.1% by weight of a dispersion stabilizer, and then suspension polymerization is started. From the start of suspension polymerization, the polymerization rate reaches 10 to 30%. A method for producing a vinyl chloride polymer, characterized in that the partially saponified polyvinyl alcohol in an amount of 0.01 to 0.1% by weight per body is post-added continuously or intermittently.