JPH07188315A - Method for producing vinyl chloride polymer - Google Patents

Abstract

PURPOSE:To obtain a polymer large in a gelling and melting rate and a bulk density and good in moldability by polymerizing vinyl chloride monomer, etc., while raising the polymerization temperature with time, and subsequently adding a chain transfer agent, when the polymerization reaches a specific polymerizatior conversion. CONSTITUTION:Vinyl chloride monomer or a mixture containing the vinyl chloride monomer as a main monomer and further another copolymerilzable monomer (e.g. ethylene) is polymerized in the presence of the partially saponified product of polyvinyl acetate and a polymerization initiator in an aqueous medium, while the polymerization temperature is raised within a raising change width of 2-35 deg.C with time in a period occupying >=50% of the whole period during when the polymerization reaction proceeds. When the polymerization conversion reaches 40-70% based on the charged vinyl chloride monomer, a chain transfer agent (e.g. 2-mercaptnethanol) is added to the polymerization system to obtain the objective vinyl chloride polymer large in a gelling and melting rate and a bulk density and excellent in moldability.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a vinyl chloride polymer. More specifically, the present invention relates to a method for producing a vinyl chloride polymer having improved moldability, and particularly having a high gelation melting rate during processing.

[0002]

BACKGROUND OF THE INVENTION A vinyl chloride polymer is a vinyl chloride monomer or a mixture of copolymerizable monomers mainly composed of a vinyl chloride monomer (hereinafter, these are collectively referred to as "vinyl chloride-based monomer"). "Polymer", and the polymer obtained by polymerizing these is referred to as "vinyl chloride polymer".) In the presence of a polymerization initiator in an emulsion polymerization or suspension in an aqueous medium containing an emulsifier or a dispersant. It is produced by polymerizing.

Generally, the moldability of a vinyl chloride resin made of a vinyl chloride polymer strongly depends on the particle morphology, the aggregated state and the molecular structure, and the bulk specific gravity, internal void volume and gelation melting of the vinyl chloride resin are Increasing speed is an important factor for improving moldability. As a method of increasing the bulk specific gravity of a vinyl chloride resin, when a vinyl chloride polymer is produced by polymerizing a vinyl chloride monomer in an aqueous medium to produce a vinyl chloride polymer, a specific amount of the entire period during which the polymerization reaction proceeds A method (Japanese Patent Publication No. 3-57121) has been proposed in which polymerization is carried out while raising the polymerization temperature for a certain period.

[0004]

The vinyl chloride resin obtained by the above method has a large bulk specific gravity and porosity, and is excellent in gelling property during processing. However,
Further, vinyl chloride resin products having good surface smoothness and gloss have been demanded, and also vinyl chloride resins having a higher gelation melting rate during processing have been demanded.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, when the vinyl chloride-based monomer is polymerized in an aqueous medium, the polymerization reaction is In a method in which the polymerization reaction is carried out while raising the polymerization temperature over time for a certain proportion of the entire progressing period (hereinafter referred to as the "conventional temperature rising polymerization method"), chain transfer occurs at a specific time of the polymerization reaction. It was found that by adding an agent, the gelling melting rate is further increased as compared with the vinyl chloride resin obtained by the conventional temperature rising polymerization method, and the bulk specific gravity is also large, and a vinyl chloride polymer can be obtained. The present invention has been completed.

That is, the gist of the present invention is to provide a vinyl chloride monomer or a mixture of copolymerizable monomers mainly composed of a vinyl chloride monomer (“vinyl chloride monomer”) in an aqueous medium. In the method for producing a vinyl chloride polymer by carrying out a polymerization reaction, the polymerization reaction is carried out while raising the polymerization temperature with time in a period of 50% or more of the entire period of the progress of the polymerization reaction. To 35 ° C., and a chain transfer agent is added when the polymerization conversion rate becomes 40 to 70% based on the charged vinyl chloride monomer. Manufacturing method.

The present invention will be described in more detail below. The vinyl chloride-based monomer used in the method of the present invention includes the vinyl chloride monomer itself and a mixture of copolymerizable monomers mainly composed of the vinyl chloride monomer. Examples of monomers copolymerizable with the vinyl chloride monomer include ethylene, olefins such as propylene, vinyl acetate,
Vinyl esters such as vinyl stearate, vinyl ethers such as ethyl vinyl ether and cetyl vinyl ether, acrylic acid esters, esters of maleic acid or fumaric acid and unsaturated carboxylic acid derivatives such as anhydrides, unsaturated nitriles such as acrylonitrile. Etc. The copolymerizable monomer is usually used in a proportion of 20% by weight or less based on the vinyl chloride monomer.

For the polymerization of the vinyl chloride monomer in the method of the present invention, a generally known polymerization recipe of the vinyl chloride monomer in an aqueous medium is widely adopted. The dispersant, emulsifier, polymerization initiator, etc. used do not have to be special, and widely used dispersants, emulsifiers, polymerization initiators can be used. For example, as a dispersant and an emulsifier,
Partially saponified polyvinyl acetate, acrylic acid copolymer,
Protective colloidal agents such as maleic anhydride copolymers, cellulose derivatives, gelatin and starch, or natural polymer compounds, esters of higher fatty acids and polyhydric alcohols, nonionic surfactants such as polyoxyethylene derivatives Anionic surfactants such as agents, metal salts of higher fatty acids, and alkali salts of higher alcohol sulfates are used. The amount of these dispersants and emulsifiers used is not particularly limited, and its type, stirring efficiency, polymerization temperature, type and composition of other monomers copolymerizable with vinyl chloride monomer, vinyl chloride polymer Depending on the particle size, etc., it is generally 0.0 with respect to the total amount of vinyl chloride monomer.
It is used in the range of 1 to 2.0% by weight, preferably 0.03 to 1% by weight.

Further, as the polymerization initiator, benzoyl peroxide, lauroyl peroxide, t-butyl peroxypivalate, t-butyl peroxy neodecanoate, α-cumyl peroxy neodecanoate, dioctyl peroxydicarbonate, diisopropyl peroxy dioxide. Organic carbonates such as dicarbonate and acetylcyclohexyl sulfonyl peroxide, azo compounds such as azobisisobutyronitrile and azobis (dimethylvaleronitrile), and persulfates such as potassium persulfate and ammonium persulfate are used. The amount of these polymerization initiators used is generally 0. 1 with respect to the total amount of vinyl chloride-based monomers.
It is in the range of 01 to 1.0% by weight.

In carrying out the method of the present invention, a vinyl chloride monomer alone or a mixture of copolymerizable monomers mainly containing vinyl chloride monomer may be charged all at once before the initiation of polymerization. Alternatively, a part of the vinyl chloride-based monomer may be charged before starting the polymerization, and the rest may be continuously charged after starting the polymerization. Now, in the method of the present invention, the polymerization reaction of the vinyl chloride-based monomer is carried out while raising the polymerization temperature with time in a period of 50% or more of the entire period of the progress of the polymerization reaction. A chain transfer agent is added when the content of the vinyl chloride-based monomer reaches 40 to 70%.

The above "entire period of time during which the polymerization reaction proceeds" means that the vinyl chloride monomer is polymerized in the presence of a polymerization initiator and other additives according to a usual vinyl chloride monomer polymerization recipe. In this case, the period from the time when the polymerization initiator starts to decompose due to the temperature rise of the polymerization reaction system and the polymerization of the vinyl chloride-based monomer starts to the time when the target polymerization rate is reached and the polymerization reaction ends. Means the whole.

Therefore, conventionally, after charging the raw materials into the polymerization reactor, until the polymerization reaction starts, that is, until the polymerization initiator starts to decompose and the exothermic reaction starts, for example, the polymerization reactor is Heat by a normal heating method such as circulating hot water in the jacket attached to, and raise the temperature rapidly,
During the period from the start of the polymerization reaction to the end of the polymerization reaction, that is, during the progress of the polymerization reaction, a large increase in temperature due to heat generation is suppressed by a method such as circulating cooling water in the jacket. While the polymer having the desired degree of polymerization was obtained by maintaining the polymerization temperature at a constant temperature, in the method of the present invention, the polymerization temperature was set to 50% or more in the entire period in which the polymerization reaction proceeds. At the same time, the polymerization reaction is carried out while controlling the degree of cooling so as to increase at an appropriate rate.

Therefore, comparing the conventional method of carrying out the polymerization reaction by keeping the polymerization reaction system at a constant temperature (hereinafter referred to as "constant temperature reaction method") and the method of the present invention, the former is the same as the polymerization temperature. There is a difference in that the latter is limited only by the “height”, whereas the latter is limited by both the “height” and the “width of change”. However, the setting of the "highness" and the "variation width" of the polymerization temperature in the method of the present invention is essentially determined experimentally so that a vinyl chloride polymer having a desired degree of polymerization can be obtained. However, specifically, it can be decided according to certain guidelines.

That is, first, it is known that the degree of polymerization of the vinyl chloride polymer produced in the constant temperature reaction method is governed by the "highness" of the polymerization temperature, which is also essential in the method of the present invention. Is similar to. Therefore, for example, considering the "average height" of the polymerization temperature based on the change range of the polymerization temperature in the method of the present invention, the "average height" is defined as the vinyl chloride type having the desired degree of polymerization in the constant temperature reaction method. If set near the "height" of the polymerization temperature for obtaining the polymer,
It is possible to obtain a product having a desired degree of polymerization. Of course, the “constant temperature reaction method” and the so-called “temperature rising reaction method” of the present invention are not the same, and the latter is also affected by the temperature rising pattern. That is, the average degree of polymerization of all the obtained polymers is the weighted average of the degree of polymerization of the polymer formed at each point in the temperature rising process and the amount of the polymer produced at that time, and the amount of production increases. It is also affected by the choice of temperature pattern. Therefore, it is desirable to set the accurate "average height" experimentally after determining the temperature rise pattern.

Next, the "variation width" of the polymerization temperature mainly controls the effect of increasing the temperature in the method of the present invention. If the "variation width" is too small, the above effect is not sufficiently exhibited,
On the other hand, if it is too large, the temperature rises from an extremely low temperature to an extremely high temperature, so it is necessary to select a polymerization initiator system that gives good reactivity in such a wide temperature range.

However, the preferable values of the "average height" and "variation width" of the polymerization temperature are influenced by the specific reaction system, mainly the monomer composition and the performance of the polymerization initiator, and therefore these values are also set. It is desirable to empirically select a specific reaction system including the above, but it is particularly preferable that the change range of the increase in the polymerization temperature is in the range of 2 to 35 ° C. The rise change width is 2 ℃
If it is less than the above range, the increase in the gelling melting rate, which is the effect of the present invention, is not sufficient, and a vinyl chloride resin product having good surface smoothness and gloss cannot be obtained. On the other hand, when the temperature exceeds 35 ° C., an initiator system showing stable activity in this wide temperature range has not been found, so that the reaction becomes unstable such as a decrease in reaction rate at the end of the reaction. Further, there is a problem that equipment cost is required, such as a refrigeration facility is required for temperature control, a polymerization reactor internal pressure is high on a high temperature side, and a can with high pressure is required.

When the range of temperature rise change of the polymerization temperature is 2 to 35 ° C., the specific range of change of the polymerization temperature, that is, the temperature rising start temperature and the temperature rising end temperature in the polymerization temperature range are determined as follows, for example. Can be done That is, as a model, considering the case where the polymerization reaction rate is constant over the entire temperature rise range, and the entire period during which the polymerization reaction proceeds is the temperature rise period,
When the polymerization temperature necessary for obtaining a vinyl chloride polymer having a desired degree of polymerization in the constant temperature reaction method is t ₀ (° C) and the temperature increase width in the temperature rising reaction method is 2x (° C), the temperature rising start temperature is the (t ₀ -x), the heating end temperature (t ₀ + x), thus it to the polymerization temperature range and _{(t 0 -x) ~ (t} 0 + x). As mentioned above, x is usually 1-17.5.
℃.

For example, in the method of the present invention, the degree of polymerization is 1
In order to obtain a vinyl chloride polymer of about 030, since the polymerization temperature in the constant temperature reaction method is around 58 ° C, the polymerization temperature range in the present invention is usually 57 ° C to 59 ° C to 4 ° C.
Select from the range of 0.5 to 75.5 ° C. Further, for example, when a vinyl chloride polymer having a degree of polymerization of about 800 is obtained, the polymerization temperature in the constant temperature reaction method is around 65 ° C., and thus the polymerization temperature range is usually 64 ° C. to 66 ° C.
To 47.5 to 82.5 ° C.

The above description is based on the most general linear temperature rising pattern, and in this case, almost the expected result can be obtained. Since the reaction results of the "warm reaction method" are also affected by the temperature rise pattern, some modifications should be made experimentally according to the desired product, especially when a non-linear temperature rise pattern is adopted. Is desirable.

In the method of the present invention, the rate of temperature rise of the polymerization temperature may be a rate of temperature uniquely obtained from the temperature rise range of the polymerization temperature and the temperature raising period (that is, a linear temperature rising pattern). It is the simplest and gives good results. For example, when the polymerization temperature range is 55 to 60 ° C., the total polymerization reaction time is 8 hours, and the heating period is 5 hours, the heating rate may be 1 ° C./hr. Further, changing the heating rate during heating, that is, providing a bending point in the heating pattern is not preferable because it requires excessive heating or cooling capacity at that point. Variations that are tolerable for temperature control do not significantly affect the results, and are therefore acceptable as an embodiment of the present invention. For example, a method of changing the temperature raising rate from 1.5 ° C./hr to 0.5 ° C./hr during the reaction, or providing a period for maintaining a constant temperature before and after that is also a method of increasing the temperature raising period. It is acceptable as one embodiment of the present invention if the total is 50% or more of the total polymerization reaction period. The rate of temperature increase of the polymerization temperature in the method of the present invention is usually 10 ° C./hr or less, which is desirable from the viewpoint of reaction controllability.

The control of the polymerization reaction in the method of the present invention is not particularly limited as long as it is a control method which enables a smooth temperature rise, but for example, feedback control incorporating a computer, feedforward control, etc. It is suitable in terms of productivity, controllability, and stability. Further, in the polymerization reaction of the present invention, the chain transfer agent used may be any one generally known as a chain transfer agent, for example, trichloroethylene, 2-mercaptoethanol, 2-pentene, dodecylmercaptan and the like. Is mentioned. These chain transfer agents are added in an amount usually used with respect to the vinyl chloride monomer, for example, 0.005
1.0 wt%, preferably 0.01 to 0.1 wt% may be added, and the polymerization conversion ratio is 40 to 70%, preferably 40 to 60%, based on the charged vinyl chloride-based monomer. It may be added all at once or continuously in the polymerization tank. If the addition timing of the chain transfer agent deviates from the above range, the gelling melting rate becomes low, and the object of the present invention cannot be achieved.

The method of the present invention can be applied to any method as long as it is a method of polymerizing a vinyl chloride-based monomer in an aqueous medium, but is particularly applied to a suspension polymerization method using an oil-soluble polymerization initiator. Is industrially most useful and valuable.

[0023]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. The physical properties of the obtained vinyl chloride polymer were evaluated by the following physical property measuring methods. Since the gelling time is greatly affected by the average degree of polymerization, the reaction conditions were set so that the average degree of polymerization was about 1030.

Physical Property Measurement Method Average degree of polymerization and bulk specific gravity: Determined according to the method specified in JIS K 6721. Gelation time 60 g of a sample prepared by blending 100 parts by weight of vinyl chloride resin, 3 parts by weight of lead powder stabilizer, and 0.5 parts by weight of barium powder stabilizer was used as a Brabender Plasticorder (18).
Kneading was performed at 7 ° C. and 45 rpm), and the time until the maximum torque was exhibited was measured.

Examples 1 to 3 100 kg of vinyl chloride monomer, 150 kg of deionized water, and 60 g of partially saponified polyvinyl acetate were placed in a stainless steel polymerization container equipped with a stirrer and a jacket having an internal volume of 400 liters.
Then, the reaction raw materials excluding the chain transfer agent shown in Table 1 were charged. After the completion of the charging, warm water was circulated in the jacket and rapidly heated to the temperature rising start temperature shown in Table 1 to start the polymerization reaction. Thereafter, the temperature is continuously raised at a rate of 0.5 ° C./hr in Example 1, about 2.0 ° C./hr in Example 2, and about 3.4 ° C./hr in Example 3 to carry out polymerization conversion. 10 g of 2-mercaptoethanol was added at a rate of 55%. The temperature increase was completed at the temperature shown in Table 1, and thereafter this temperature was maintained until the desired polymerization rate was reached. The vinyl chloride polymer thus obtained (hereinafter referred to as "PV
The results of the physical property evaluation of "C" are shown in Table-2.

Comparative Examples 1 and 2 Polymerization was carried out in the same manner as in Example 1 except that the timing of adding the chain transfer agent (polymerization conversion rate) was changed as shown in Table 1. The results of physical property evaluation of the obtained PVC are shown in Table 2. Comparative Example 3 Polymerization was carried out in the same manner as in Example 1 except that the chain transfer agent was not added. The results of physical property evaluation of the obtained PVC are shown in Table 2.

Comparative Example 4 Polymerization was carried out in the same manner as in Example 1 except that the chain transfer agent was not added and the polymerization temperature was kept constant at 58 ° C. from the start to the end of the polymerization. The results of physical property evaluation of the obtained PVC are shown in Table 2. Comparative Example 5 Polymerization was carried out in the same manner as in Example 1 except that the polymerization temperature was constant at 56 ° C. from the start to the end of the polymerization. Obtained P
The results of physical property evaluation of VC are shown in Table 2.

Comparative Example 6 Polymerization was carried out in the same manner as in Example 2 except that the chain transfer agent was not added. The results of physical property evaluation of the obtained PVC are shown in Table 2. Comparative Example 7 Polymerization was performed in the same manner as in Example 3 except that the chain transfer agent was not added. The results of physical property evaluation of the obtained PVC are shown in Table 2.

In Comparative Examples 3, 4, 6 and 7, since the chain transfer agent was not added, the degree of polymerization at the end of the polymerization was large, so that the polymerization reaction time and the temperature rising temperature range were not changed. 1, Comparative Examples 1, 2, 5, In order to obtain PVC having substantially the same degree of polymerization as in Examples 2 and 3, the polymerization initiation temperature and the like were raised,
And the amount of the polymerization initiator was reduced.

[0030]

[Table 1]

[0031]

[Table 2]

The following is clear from Table-2. Comparing Example 1 with Comparative Example 3, Example 2 with Comparative Example 6, Example 3 with Comparative Example 7, and Comparative Examples 4 and 5, gelation and melting by adding a chain transfer agent during the polymerization reaction. It can be seen that PVC having a high speed (short gelation time) can be obtained. Comparing Example 1 with Comparative Examples 1 and 2, the gelling melting rate (gelling time) depends on the time when the chain transfer agent is added.
It can be seen that, by changing the addition timing within the range of the polymerization conversion rate in the present invention (Example 1), PVC having a high gelation melting rate can be obtained. From Example 1 and Comparative Example 5, the chain transfer agent was added, and the chain transfer agent was added as compared to the case where the polymerization was carried out at a constant temperature.
Moreover, it can be seen that by increasing the polymerization temperature for a specific period to carry out the polymerization, a PVC having a higher gelation melting rate can be obtained. From the above, it can be seen that the PVC obtained by the present invention has a remarkably high gelation melting rate as compared with the PVC obtained by the conventional method.

[0033]

The PVC obtained according to the present invention has an extremely high gelling and melting rate, a large bulk specific gravity, and excellent moldability, as compared with the PVC obtained by the conventional method. A product obtained by molding and processing this PVC has excellent surface smoothness and gloss.

Claims (1)

[Claims] 1. An aqueous medium comprising a vinyl chloride monomer or a mixture of copolymerizable monomers mainly composed of vinyl chloride monomer (hereinafter, these are collectively referred to as "vinyl chloride-based monomer"). In the method of producing a vinyl chloride polymer by performing a polymerization reaction in a room temperature, the polymerization reaction is performed while the polymerization temperature is increased with time in a period of 50% or more of the entire period in which the polymerization reaction proceeds, Is 2-35
A method for producing a vinyl chloride-based polymer, characterized in that the chain transfer agent is added when the polymerization conversion is in the range of 40 ° C. and the polymerization conversion rate becomes 40 to 70% with respect to the charged vinyl chloride-based monomer. .