JP2022147841A - Method for producing polyvinyl chloride polymer - Google Patents

Abstract

To provide a method for producing a polyvinyl chloride polymer that can stably make a resin of a desired apparent density.SOLUTION: A vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer are polymerized in a reaction tank with an oxygen level of 120 to 220 mol ppm per 1 mol of all the monomers used in the polymerization.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for producing a vinyl chloride polymer, and more particularly to a method for producing a copolymer of a vinyl chloride monomer, a vinyl chloride monomer and a copolymerizable monomer.

Vinyl chloride-based polymers have excellent properties and are used in various fields, and various methods have been proposed for their production up to now.

An example of a method for producing a vinyl chloride polymer includes a polymerization process in which water, a monomer, a polymerization initiator, etc. are charged into a reaction tank to polymerize the monomer, and a reactant in the reaction tank is charged into a demonomer tank. A removal step of removing unreacted monomer from the reactant, a dehydration step of putting the reactant in the demonomerization tank into a dehydration tank and removing water from the reactant, and a drying step of removing water from the reactant in the demonomerization tank. and a drying step in which the reaction product is dried by putting it in the. In the polymerization step, oxygen is also removed from the reaction vessel for the purpose of preventing a decrease in the polymerization rate of the monomer and/or for the purpose of preventing coloring of the produced vinyl chloride polymer. there is In order to achieve these purposes, the oxygen concentration in the reaction tank is controlled to an extremely low concentration.

For example, in Patent Document 1, a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable with vinyl chloride is prepared in the presence of an oil-soluble polymerization initiator and a dispersion stabilizer. In the method of producing a vinyl chloride polymer by performing suspension polymerization in an aqueous medium, the oxygen concentration dissolved in the vinyl chloride monomer is 5 to 40 mol ppm with respect to the vinyl chloride monomer. A method for producing a vinyl chloride polymer is disclosed.

In Patent Document 2, a polymerization vessel with an internal volume of 100 m ³ or more equipped with a stirrer, an external jacket, and a reflux condenser is used to initiate oil-soluble polymerization of a vinyl chloride monomer under specific conditions. In a method of producing a vinyl chloride polymer by carrying out suspension polymerization in an aqueous medium in the presence of an agent and a dispersion stabilizer, the amount of oxygen in the polymerization system is 2.0 x 10 per vinyl chloride monomer. ^-5 to 1.0×10 ^-2 mol%, a method for producing a vinyl chloride polymer is disclosed.

JP-A-9-169804 JP-A-2000-103803

However, as a result of investigations by the present inventors, it is difficult to produce a polymer having a desired apparent density with the above-described prior art, because the apparent density of the resulting polymer does not exceed the target value. It turns out that there is a problem.

An object of one aspect of the present invention is to realize a method for producing a vinyl chloride polymer that can stably obtain a resin having a desired apparent density.

As a result of extensive studies to solve the above problems, the present inventors found that the reason why the apparent density of the polymer obtained by the conventional technology does not exceed the target value is (i) that the oxygen concentration in the reaction vessel is and (ii) that the apparent density of the resulting polymer can be controlled by controlling the oxygen concentration in the reaction vessel within a specific range. I came to complete it. That is, the present invention relates to the following inventions.

[1] A polymerization step of polymerizing a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer in a reaction vessel having an oxygen concentration of 120 mol ppm to 220 mol ppm per 1 mol of all monomers used for polymerization. A method for producing a vinyl chloride polymer.

[2] The monomer copolymerizable with the vinyl chloride monomer is selected from the group consisting of vinyl esters, vinyl ethers, unsaturated carboxylic acid esters, unsaturated carboxylic acids and salts thereof, and crosslinkable monomers. The manufacturing method according to [1], which is at least one.

[3] The production method according to [1] or [2], wherein the vinyl chloride polymer has an apparent density of 0.710 g/mL or more.

[4] In the polymerization step, among the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer, the monomer having the slowest polymerization rate is initially charged into the reaction vessel, and the polymerization rate is The production method according to any one of [1] to [3], which includes a step of dividing and charging the fastest monomer into the reaction vessel.

According to one aspect of the present invention, it is possible to stably obtain a vinyl chloride polymer having a desired apparent density.

4 is a graph showing the relationship between oxygen concentration and apparent density in examples and comparative examples according to one embodiment of the present invention.

One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and can be modified in various ways within the scope of the claims, and the technical means disclosed in different embodiments and examples. Embodiments and examples obtained by appropriate combinations are also included in the technical scope of the present invention. All documents mentioned herein are incorporated herein by reference. In this specification, when "A to B" is described with respect to a numerical range, the description intends "A or more (including A and greater than A) and B or less (including B and less than B)".

In one embodiment of the method for producing a vinyl chloride polymer of the present invention, all monomers used for polymerization (more specifically, It has a polymerization step of polymerizing in a reaction tank having an oxygen concentration of 120 mol ppm to 220 mol ppm per 1 mol of vinyl chloride monomers and all monomers copolymerizable with vinyl chloride monomers. As the monomer copolymerizable with the vinyl chloride monomer, one type of monomer may be used, or two or more types (for example, two types, three types, four types, five types) of monomers may be used. . The method for producing a vinyl chloride polymer according to one embodiment of the present invention can also be considered as a method for controlling the apparent density of the vinyl chloride polymer.

The polymerization method in the polymerization step is not limited, and examples thereof include suspension polymerization, fine suspension polymerization, seed fine suspension polymerization, emulsion polymerization, and seed emulsion polymerization. Among the above polymerization methods, suspension polymerization is preferred from the viewpoint of more stably producing a vinyl chloride polymer having a desired apparent density.

The polymerization temperature in the polymerization step is not limited, and can be appropriately set in order to adjust the polymerization degree or K value of the resulting resin. The polymerization temperature in the polymerization step must be set so as to obtain the desired K value, preferably 50° C. to 90° C., more preferably 60 to 80° C., more preferably 65 to 75° C. °C, most preferably between 69°C and 70°C. With this configuration, a vinyl chloride polymer having a desired apparent density can be more stably produced.

The polymerization time in the polymerization step (specifically, the time from the time the polymerization temperature is reached to the time the polymerization is completed) is not limited, and is set according to the type of monomer used to produce the copolymer. can do. The polymerization time in the above polymerization step is preferably 200 to 500 minutes, more preferably 300 to 400 minutes, and most preferably 350 to 370 minutes.

In the polymerization step, the oxygen concentration per mol of all the monomers used in the polymerization is 120 mol ppm to 220 mol ppm in the reaction tank, but from the viewpoint of further increasing the apparent density of the copolymer, it is preferably 125 mol ppm to 210 mol ppm, more preferably 130 mol ppm to 205 mol ppm, more preferably 130 mol ppm to 200 mol ppm, more preferably 140 mol ppm to 195 mol ppm, more preferably is from 150 molar ppm to 195 molar ppm, more preferably from 160 molar ppm to 180 molar ppm, most preferably from 160 molar ppm to 170 molar ppm. In addition, with this configuration, the oxygen concentration per 1 mol of all the monomers used in the polymerization is not too low, so it is possible to prevent the shape of the produced copolymer from becoming coarse (coarsening of particles). The oxygen concentration per 1 mol of all the monomers used in the polymerization can be measured according to the method described in Examples below.

The reaction tank used in the polymerization step is not limited, and a synthesis can used for resin synthesis may be used. The lower limit of the volume of the reaction tank is not limited, for example, 1 L or more, 10 L or more, 100 L or more. , or 1000 L or more. The upper limit of the volume of the reaction tank is not limited, and can be, for example, 1.0×10 ⁵ L.

The monomer copolymerizable with the vinyl chloride monomer is not limited, and examples include vinyl esters (e.g., vinyl acetate, vinyl propionate, vinyl stearate), vinyl ethers (e.g., methyl vinyl ether, ethyl vinyl ether, octyl vinyl ether, Lauryl vinyl ether, isobutyl vinyl ether), unsaturated carboxylic acid esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, monomethyl maleate, maleic acid dimethyl, butyl benzyl maleate), unsaturated carboxylic acids and their salts (e.g. acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride), and cross-linking monomers (e.g. at least one selected from the group consisting of diallyl phthalate). From the viewpoint of more stably producing a vinyl chloride polymer having a desired apparent density, vinyl acetate, vinyl propionate, and vinyl stearate are among the monomers copolymerizable with vinyl chloride monomers. At least one selected from the group consisting of is preferred.

In the above polymerization step, among vinyl chloride monomers and monomers copolymerizable with vinyl chloride monomers, monomers with the slowest polymerization rate are initially charged in a reaction vessel, and monomers with the fastest polymerization rate are charged in the reaction vessel. (For example, when two or more types of monomers are used as monomers copolymerizable with vinyl chloride monomers). In the above process, of the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer, the monomer with the slower polymerization rate is initially charged into the reactor, and the monomer with the faster polymerization rate is reacted. It is preferable to divide and charge into the tank (for example, when using one type of monomer as the monomer copolymerizable with the vinyl chloride monomer). With this configuration, it is possible to prevent preferential polymerization of the monomer having a high polymerization rate, and thereby the content ratio of the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer is the desired ratio. A copolymer can be produced efficiently. In the present specification, the term "initial charging" means "adding the monomers into the reaction vessel by the time the heating is started in order to adjust the internal temperature of the reaction vessel to the polymerization temperature".

When dividing the monomer and charging it into the reactor, the timing of charging the monomer is not limited. For example, a portion of the monomer may be initially charged into the reaction vessel, and thereafter (preferably after reaching the polymerization temperature), the rest of the monomer may be charged into the reaction vessel all at once or in portions.

The terms "slowest polymerizing monomer", "fastest polymerizing monomer", "slower polymerizing monomer" and "faster polymerizing monomer" refer to the monomers used to make the copolymer. It is not limited because it varies depending on the type. Examples of the "monomer with the fastest polymerization rate" and the "monomer with the faster polymerization rate" include vinyl chloride. In this case, examples of the "monomer with the slowest polymerization rate" and the "monomer with the slowest polymerization rate" include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl stearate.

In the polymerization step, in addition to the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer, a solvent (for example, water), a dispersant, a polymerization initiator, and the like may be added to the reactor. In this case, a copolymer of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer can be obtained, for example, in a slurry state.

Examples of polymerization initiators include oil-soluble polymerization initiators and water-soluble polymerization initiators.

Oil-soluble polymerization initiators include, for example, 3,5,5,trimethylhexanoyl peroxide, diacyl peroxides (eg, dilauroyl peroxide, di-3,5,5,trimethylhexanoyl peroxide), peroxide Oxydicarbonates (e.g. diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate), organic peroxide initiators (e.g. t-butyl peroxypivalate, t-butyl peroxyneodecano ate, peroxyesters), and azo initiators (eg, 2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile)).

Examples of water-soluble polymerization initiators include ammonium persulfate, potassium persulfate, sodium persulfate, and aqueous hydrogen peroxide. When using a water-soluble polymerization initiator, a reducing agent (e.g., sodium sulfite, sodium thiosulfate, formaldehyde sodium sulfoxylate dihydrate, ascorbic acid, sodium ascorbate) may be used in combination if necessary. good.

It is preferable to select an initiator that exhibits an appropriate half-life temperature for the polymerization temperature.

The dispersant is not limited, and examples thereof include methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, partially saponified polyvinyl alcohol, and the like.

From the viewpoint of polymerization stability, hydroxypropylmethylcellulose and partially saponified polyvinyl alcohol are preferred among the above dispersants.

When the copolymer of the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer obtained in the polymerization step is in a slurry state, the production method includes, after the polymerization step, (i and/or (ii) a drying step to dry the slurry (or the slurry from which the solvent has been removed).

The removal step is not limited to a specific configuration (method) as long as it is a step capable of removing at least part of the solvent from the slurry. The removing step may be performed, for example, by (i) removing the solvent from the slurry by filtration, or (ii) removing the solvent from the slurry by centrifugation.

The drying step is not particularly limited as long as it can dry the copolymer particles after removing the solvent. The drying step includes, for example, (i) a method of drying the slurry by hot air drying (e.g., hot air temperature: 50° C. to 70° C., drying time: 300 minutes to 400 minutes), or (ii) drying the slurry in a reduced pressure state. It may be carried out by a drying method or the like.

The apparent density of the copolymer produced by the production method of one embodiment of the present invention is not limited, but is preferably 0.710 g/mL or more, more preferably 0.715 g/mL or more, and more preferably is 0.720 g/mL or more, more preferably 0.725 g/mL or more, more preferably 0.730 g/mL or more. The upper limit of the apparent density of the copolymer produced by the production method of one embodiment of the present invention is not limited, but can be, for example, 1.000 g/mL. Copolymers having such apparent densities have the advantage that more copolymers can be filled in a fixed volume reservoir. The apparent density of the copolymer can be measured according to the method described in Examples below.

The K value of the copolymer produced by the production method of one embodiment of the present invention is not limited, but is preferably 20 to 80, more preferably 30 to 70, more preferably 40 to 60. , most preferably 45-55. With this configuration, a copolymer having a desired apparent density can be produced more efficiently. The K value of the copolymer can be measured according to a known method (eg JIS K7367-2).

The content of the monomer copolymerizable with the vinyl chloride monomer contained in the copolymer produced by the production method of one embodiment of the present invention is not limited, but is preferably 10 to 20% by weight, more preferably 12-18% by weight, most preferably 15-16% by weight. With this configuration, a copolymer having a desired apparent density can be produced more efficiently. The content of the monomer copolymerizable with the vinyl chloride monomer contained in the copolymer can be measured according to a known method.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples. Measurements and tests in Examples and Comparative Examples were carried out as follows.

[Measurement of oxygen content in reaction tank]
The gas in the reaction tank after charging a part (1 to 2 parts by weight) of the initial amount of vinyl chloride monomer was charged into a Tedlar bag (about 1 L of gas collecting bag by reducing the pressure inside the gas collecting bag). The air inside the air bag was removed). The amount of oxygen in the reaction tank was measured by analyzing the composition of the gas in the Tedlar bag using gas chromatography (manufactured by Shimadzu Corporation). The measurement conditions for gas chromatography and the formula for calculating the amount of oxygen were as follows.

<Measurement conditions for gas chromatography>
・Carrier gas: gas type, helium gas flow rate 30 ml/min,
・Injection volume: 0.1 ml,
・ Column: SHIN CARBON-ST (50-80) (manufactured by Shinwa Kako Co., Ltd.),
・Column length: 4m,
・Column temperature: 40°C,
- Detector temperature: 200°C.

<Formula for calculating oxygen content>
Standard gases containing various (known) concentrations of oxygen were prepared. Each standard gas was subjected to gas chromatography, and the detection peak of oxygen was recorded for each standard gas. Each standard gas is plotted on a plane defined by the X-axis (area of oxygen detection peak [count number]) and Y-axis (oxygen weight [g]), and the oxygen concentration is calculated from the area of the detection peak. A calibration curve was created for The calibration curve created in this test was "Y=4.6393×X".

For gas A containing an unknown concentration of oxygen, gas A was first subjected to gas chromatography, and the detected oxygen peak for gas A was recorded. Then, by substituting the area [number of counts] of the detected peak for X in the calibration curve, the oxygen weight Y _A [g] contained in the gas A was calculated as Y in the calibration curve.

Then, based on the oxygen weight Y _A [g] contained in the gas A, the oxygen concentration Z [mole ppm] per 1 mol of all the monomers used in the polymerization was calculated.

Specifically, the oxygen concentration Z [moles ppm] per 1 mol of all the monomers used in the polymerization was calculated based on the oxygen weight YA [g] contained in the gas _A as follows.

When all monomers used for polymerization are vinyl chloride X _VCM [g] and vinyl acetate X _VAc [g], the total number of moles of all monomers used for polymerization is X _VCM /62.5+X _VAc /86.1 becomes [mole]. When the weight of oxygen is Y _A [g], the number of moles of oxygen is Y _A /16 [mol]. Therefore, the oxygen concentration Z [mole ppm] per 1 mol of all monomers used for polymerization is "moles of oxygen / total mols of all monomers = (YA / 16) / (X _VCM / 62.5 _{+ X VAc /} 86 .1)”.

[Apparent density]
Apparent density was calculated by a method based on JIS K7365 using a bulk density measuring instrument.

More specifically, by sliding the bottom plate provided at the bottom of the upper hopper, the copolymer powder filled in the upper hopper of the bulk density measuring device (manufactured by Kuramochi Scientific Machinery Co., Ltd.) is placed in the upper hopper. It was allowed to fall freely into the measurement container through the opening of the measurement container (container volume: 100 [mL], container shape: cylindrical) arranged on the lower side.

Excess powder deposited above the opening of the measuring container was removed by moving the glass rod along the opening of the measuring container.

The mass of the powder (m [g]) was measured by subtracting the mass of the measurement container without the powder from the mass of the measurement container with the powder. The apparent density [g/mL] was calculated according to the formula "m/100". The apparent density was calculated twice for the same sample, and the average value of the measured values was taken as the apparent density.

(Example 1)
120 parts by weight of ion ^- exchanged water, 0.84 parts by weight of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd.) as a dispersant, and partially saponified poly( 0.22 parts by weight of vinyl alcohol (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and 0.115 parts by weight of (3,5,5-trimethylhexanoyl) peroxide (manufactured by NOF Corporation) as a polymerization initiator are charged, and further , 1 to 2 parts by weight (1600 to 3200 mol) of 37 parts by weight of the vinyl chloride monomer initially charged was charged, and the pressure in the reactor was adjusted to 0.05 MPa. The weight of oxygen in the reactor at this point was 710 g (22.1875 mol). On the other hand, since all the monomers used in the polymerization are vinyl chloride monomer (134073 mol) and vinyl acetate monomer (18676 mol), the oxygen concentration per 1 mol of all monomers is 145 mol ppm (=22.1875/ 152749×10 ⁻⁶ ).

Next, 35 to 36 parts by weight (56,000 to 58,000 mols) of vinyl chloride monomer are charged into the reaction vessel to bring the total amount of initially charged vinyl chloride monomers to 37 parts by weight (59,126 mols), and vinyl acetate monomer is added. 16.1 parts by weight (18676 mol) were charged.

After that, the temperature in the reactor was raised from 20° C. to 69.5° C. (polymerization temperature) in 80 minutes to initiate the polymerization reaction between the vinyl chloride monomer and the vinyl acetate monomer. Further, 46.9 parts by weight (74,947 mol) of vinyl chloride monomer was introduced into the reactor within 320 minutes after reaching the polymerization temperature. After 360 minutes from reaching the polymerization temperature, the unpolymerized monomer was recovered and the polymerization reaction was completed (polymerization conversion rate of vinyl chloride monomer was 85%).

After dehydrating the obtained slurry, it was dried in a hot air dryer at 60° C. for 360 minutes to obtain a vinyl chloride-vinyl acetate copolymer (1). The apparent density of the resulting vinyl chloride-vinyl acetate copolymer (1) was 0.726 g/mL. Moreover, the apparent density of the resulting copolymer was at least the target value (for example, 0.710 g/mL).

(Example 2)
Vinyl chloride-acetic acid was prepared in the same manner as in Example 1, except that the weight of oxygen after the initial charging of the vinyl chloride monomer was changed to 820 g (that is, the oxygen concentration per 1 mol of all monomers used in the polymerization was 168 mol ppm). A vinyl copolymer (2) was obtained. The apparent density of vinyl chloride-vinyl acetate copolymer (2) was 0.735 g/mL. Moreover, the apparent density of the resulting copolymer was at least the target value (for example, 0.710 g/mL).

(Example 3)
Vinyl chloride-acetic acid was prepared in the same manner as in Example 1, except that the weight of oxygen after the initial charging of the vinyl chloride monomer was changed to 930 g (that is, the oxygen concentration per 1 mol of all the monomers used in the polymerization was 190 mol ppm). A vinyl copolymer (3) was obtained. The vinyl chloride-vinyl acetate copolymer (3) had an apparent density of 0.728 g/mL. Moreover, the apparent density of the resulting copolymer was at least the target value (for example, 0.710 g/mL).

(Example 4)
Vinyl chloride-acetic acid was prepared in the same manner as in Example 1, except that the weight of oxygen after the initial charging of the vinyl chloride monomer was changed to 1050 g (that is, the oxygen concentration per 1 mol of all monomers used in the polymerization was 215 mol ppm). A vinyl copolymer (4) was obtained. The vinyl chloride-vinyl acetate copolymer (4) had an apparent density of 0.718 g/ml. Moreover, the apparent density of the resulting copolymer was at least the target value (for example, 0.710 g/mL).

(Comparative example 1)
Vinyl chloride-acetic acid was prepared in the same manner as in Example 1, except that the weight of oxygen after the initial charging of the vinyl chloride monomer was changed to 1270 g (that is, the oxygen concentration per 1 mol of all monomers used in the polymerization was 260 mol ppm). A vinyl copolymer (4) was obtained. The vinyl chloride-vinyl acetate copolymer (4) had an apparent density of 0.665 g/ml. Also, the apparent density of the resulting copolymer was less than the target value (eg, 0.710 g/mL).

(Test results)
Table 1 shows the numerical data of the test results. Further, FIG. 1 shows the relationship between oxygen concentration and apparent density in Examples and Comparative Examples. In FIG. 1, the curve indicated by the dotted line is obtained by analyzing the data of Examples 1 to 4 and Comparative Example 1 by the least squares method, modeling the relationship between the oxygen concentration and the apparent density. is a function. In this function, when the apparent density is 0.710 g/mL, the oxygen concentration is 220 molar ppm.

From Table 1 and FIG. 1, it is clear that the apparent density of the copolymer can be controlled to a desired value by using a reactor with an oxygen concentration of 120 mol ppm to 220 mol ppm with respect to charged monomers.

Further, when the copolymers of Examples 1 to 4 were visually observed, no coarsening of the shape of the copolymers (coarsening of particles) and no coloration of the copolymers were observed.

INDUSTRIAL APPLICABILITY The present invention can be widely used in the field of producing vinyl chloride polymers.

Claims (4)

a polymerization step in which a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer are polymerized in a reaction vessel having an oxygen concentration of 120 mol ppm to 220 mol ppm per 1 mol of all monomers used for polymerization; A method for producing a vinyl polymer. The monomer copolymerizable with the vinyl chloride monomer is at least one selected from the group consisting of vinyl esters, vinyl ethers, unsaturated carboxylic acid esters, unsaturated carboxylic acids and salts thereof, and crosslinkable monomers. The manufacturing method according to claim 1, wherein The production method according to claim 1 or 2, wherein the vinyl chloride polymer has an apparent density of 0.710 g/mL or more. In the polymerization step, among the vinyl chloride monomer and the monomer copolymerizable with the vinyl chloride monomer, the monomer with the slowest polymerization rate is initially charged in the reaction vessel, and the monomer with the fastest polymerization rate is charged. The production method according to any one of claims 1 to 3, comprising a step of dividing and charging into the reaction vessel.

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