JPH0357121B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a vinyl chloride polymer. Specifically, the present invention relates to a method for producing a vinyl chloride polymer having improved productivity in polymerization reactions and improved molding processability, particularly having a high bulk specific gravity. [Prior Art] Vinyl chloride polymers are vinyl chloride monomers or mixtures of copolymerizable monomers mainly composed of vinyl chloride monomers (hereinafter these are collectively referred to as ``vinyl chloride monomers''). The polymer obtained by polymerizing them is called "vinyl chloride polymer.") is emulsion polymerized or suspended in an aqueous medium containing an emulsifier or dispersant in the presence of a polymerization initiator. Obtained by polymerization. Generally, the moldability of vinyl chloride polymers strongly depends on particle morphology, aggregate state, and molecular structure. Increasing the bulk specific gravity of the vinyl chloride polymer powder reduces the volume of the container required for storage, improves the penetration from the hopper into the processing machine, and makes it possible to process the powder once in batches using a blender, etc. This is an important issue for improving processability due to an increase in the amount of processing per unit. Conventionally, as a method for increasing the bulk specific gravity of a vinyl chloride polymer, when a vinyl chloride monomer is polymerized at a constant temperature in an aqueous medium, the type and amount of dispersant, the shape of the stirring blade, and the A method in which vinyl chloride monomers are added (sequential addition) during the polymerization reaction when vinyl chloride monomers are suspended in an aqueous medium at a constant temperature (sequential addition).・Of Macromolecular Science,
A11, pp. 1223-1224, 1977), when a vinyl chloride monomer is polymerized in an aqueous medium, the polymerization reaction is carried out in two stages, and the first stage reaction and second stage reaction are different. Method conducted at reaction temperature (Special Publication No. 49-20627, Special Publication No. 49-28910)
JP-A-57-192411, JP-A-57-195107 and JP-A-59-96152), etc. have been proposed. [Problems to be Solved by the Invention] However, although the above method can increase the bulk specific gravity to a certain extent, the effect is small and requires modification of the ancillary equipment of the polymerization vessel, so it is not necessarily a preferable method. It can not be said. In addition, although the bulk specific gravity can be increased in the above method, the porosity decreases, and the gelling properties and plasticizer absorption properties also deteriorate, so the resulting vinyl chloride polymer has extremely limited uses. It can only be used. Further, in the above method, although the bulk specific gravity of the resulting vinyl chloride polymer increases and the gelling property is maintained well, the porosity is significantly reduced and the plasticizer absorption property is extremely deteriorated. Furthermore, since this method rapidly changes the reaction temperature, a significantly large heating or cooling capacity is required to raise or cool the temperature, which is extremely disadvantageous in terms of productivity of the polymerization reaction. [Means for Solving the Problems] In order to solve the problems of the conventional method, the present inventors have made various studies and found that when a vinyl chloride monomer is polymerized in an aqueous medium, By carrying out the polymerization reaction while increasing the polymerization temperature over time during a specific proportion of the entire period during which the polymerization reaction progresses, the molding processability is improved, that is, the bulk specific gravity and porosity are large, and The present invention was completed by discovering that a vinyl chloride polymer having excellent gelation properties and plasticizer absorption properties can be obtained. That is, the present invention provides a method for producing a vinyl chloride polymer by reacting a vinyl chloride monomer or a mixture of copolymerizable monomers mainly consisting of vinyl chloride monomer in an aqueous medium. vinyl chloride, characterized in that the polymerization reaction is carried out while the polymerization temperature is increased over time for 50% or more of the entire period during which the polymerization reaction proceeds, and the increase range is in the range of 1 to 20°C. The gist of this paper is a method for producing a polymer. The present invention will be explained in more detail below. The amount of the vinyl chloride monomer used in the method of the present invention includes not only the vinyl chloride monomer itself but also a mixture of copolymerizable monomers mainly composed of vinyl chloride monomer. Examples of monomers copolymerizable with vinyl chloride monomers include olefins such as ethylene and propylene, vinyl esters such as vinyl acetate and vinyl stearate, vinyl ethers such as ethyl vinyl ether and cetyl vinyl ether, and acrylic esters. , unsaturated carboxylic acid derivatives such as esters and anhydrides of maleic acid or fumaric acid, aromatic vinyl compounds such as styrene, unsaturated nitriles such as acrylonitrile, and the like. The copolymerizable monomer is generally used in an amount of 20% by weight or less based on the vinyl chloride monomer. For the polymerization of vinyl chloride monomers in the method of the present invention, commonly known polymerization recipes for vinyl chloride monomers in an aqueous medium are widely employed. The dispersant, emulsifier, polymerization initiator, etc. used do not need to be special, and commonly used dispersants, emulsifiers, polymerization initiators can be used. For example, dispersants and emulsifiers include protective colloidal agents such as partially saponified polyvinyl acetate, acrylic acid copolymers, maleic anhydride copolymers, cellulose derivatives, gelatin, starch, etc.
Or natural polymer compounds, esters of higher fatty acids and polyhydric alcohols, nonionic surfactants such as polyoxyethylene derivatives, metal salts of higher fatty acids, anionic surfactants such as alkali salts of higher alcohol sulfates, etc. is used.
There are no particular restrictions on the amount of these dispersants and emulsifiers to be used, and the types, stirring efficiency, polymerization temperature, types and composition of other monomers to be copolymerized with the vinyl chloride monomer, vinyl chloride polymer Although it varies somewhat depending on the particle size, etc., it is generally used within the range of 0.01 to 2.0% by weight, preferably 0.03 to 1% by weight, based on the total amount of vinyl chloride monomers. In addition, as a polymerization initiator, benzoyl peroxide, uraloyl peroxide, t-butyl peroxy pivalate, t-butyl peroxy neodecanoate, α-cumyl peroxy neodecanoate, dioctyl peroxy dicarbonate,
Organic peroxides such as diisopropyl peroxydicarbonate, acetylcyclohexylsulfonyl peroxide, azobisisobutyronitrile,
Azo compounds such as azobis (dimethylvaleronitrile) and persulfates such as potassium persulfate and ammonium persulfate are used. The amount of these polymerization initiators used is generally in the range of 0.01 to 1.0% by weight based on the total amount of vinyl chloride monomers. Further, in the polymerization reaction of the present invention, generally known polymerization aids, such as chain transfer agents such as trichlorethylene, dodecylmercaptan, 2-mercaptoethanol, propionaldehyde, antioxidants, etc. can be optionally used. . In carrying out the method of the present invention, vinyl chloride monomer alone or a mixture of copolymerizable monomers mainly consisting of vinyl chloride monomer may be charged all at once before the start of polymerization, or vinyl chloride monomer It is also possible to charge a part of the system monomers before the start of polymerization, and the rest continuously after the start of polymerization. Now, in the method of the present invention, the polymerization reaction of the vinyl chloride monomer is carried out while the polymerization temperature is increased over time for 50% or more of the entire period during which the polymerization reaction substantially proceeds. That is, when a vinyl chloride monomer is polymerized in the presence of a polymerization initiator and other additives according to the usual polymerization recipe for a vinyl chloride monomer, the polymerization initiator is substantially removed by increasing the temperature of the polymerization reaction system. The entire period from the time when decomposition starts and substantial polymerization of the vinyl chloride monomer starts until the time when a predetermined polymerization rate is reached and the polymerization reaction is terminated, that is, the polymerization reaction is substantially stopped. The polymerization reaction is carried out while the polymerization temperature is increased over time for 50% or more of the entire progress period. Therefore, conventionally, after charging raw materials into a polymerization reactor, until the actual polymerization reaction starts,
That is, until the polymerization initiator begins to substantially decompose and an exothermic reaction begins, the temperature is rapidly raised by heating, for example, by a normal heating method such as circulating hot water through a jacket attached to the polymerization reactor. Then, during the period from the time when the polymerization reaction substantially starts to the time when the polymerization reaction ends, that is, during the period during which the polymerization reaction substantially proceeds, cooling water is poured into the jacket to prevent a significant rise in temperature due to heat generation. Whereas a polymer with a predetermined degree of polymerization was obtained by keeping it at a constant temperature by a method such as circulation, in the method of the present invention, especially during the entire period during which the polymerization reaction substantially proceeds, % or more, the polymerization reaction is carried out while controlling the degree of cooling so that the polymerization temperature is increased at an appropriate rate over time. Therefore, when comparing the conventional method in which the polymerization reaction is carried out by maintaining the polymerization reaction system at a constant temperature (hereinafter referred to as "constant temperature reaction method") and the method of the present invention, it is found that the former has a higher Whereas the latter was governed only by its "height"
The difference is that it is governed by both the "range of change" and the "range of change." Therefore, the settings of the "height" and "variation range" of the polymerization temperature in the method of the present invention are essentially determined experimentally so that the desired vinyl chloride polymer can be obtained. Specifically, it can be decided according to certain guidelines. That is, first, it is known that the degree of polymerization of vinyl chloride polymers produced in a constant temperature reaction method is controlled by the "height" of the polymerization temperature, and this is essentially the same in the method of the present invention. The same is true. Therefore, for example, if the "average height" of the polymerization temperature is considered based on the variation range of the polymerization temperature in the method of the present invention, the "average height" can be calculated as a product with the desired degree of polymerization in the constant temperature reaction method. By setting the polymerization temperature close to the "height" for obtaining the desired polymerization degree, a product having approximately the desired degree of polymerization can be obtained. Of course, the "constant temperature reaction method" and the so-called "temperature raising reaction method" of the present invention are not the same, and the latter is also influenced by the temperature raising pattern. In other words, the average degree of polymerization of all the polymers obtained is the weighted average of the degree of polymerization produced at each point in the temperature raising process and the amount of polymer produced at that time. It is also affected by the choice of temperature pattern. Therefore, it is desirable to set an accurate "average height" experimentally after determining the temperature increase pattern. Next, the "change width" of the polymerization temperature mainly controls the effect of continuous temperature increase in the method of the present invention. If the "variation width" is too small, the above effect will not be fully realized, and if it is too large, the temperature will rise from an extremely low temperature to an extremely high temperature, which is not only impractical but also Due to history,
There are drawbacks such as poor thermal stability of the resulting polymer. Moreover, a polymerization initiator system that provides good reactivity over such a wide temperature range would be extremely complex and impractical, and a suitable "variation range" naturally exists. However, the suitable values for the "average height" and "variation range" of the polymerization temperature are also influenced by the specific reaction system, mainly the monomer composition and the performance of the polymerization initiator, so these should also be considered. It is desirable that the selection be made empirically based on the specific reaction system. However, for ordinary polymerization reaction systems, standard numerical ranges can be shown more specifically. That is, firstly, the temperature rise width of the polymerization temperature in the method of the present invention is usually 1 to 20°C, preferably 4 to 12°C.
℃ range. When the temperature increase width of the polymerization temperature is less than 1°C, the improvement effect of the present invention is obtained, namely, vinyl chloride with large bulk specific gravity and porosity, excellent gelling properties, plasticizer absorption, etc., and good moldability. The effect of obtaining a system polymer is small, and
If the temperature increase exceeds 20° C., the initiator used in the polymerization reaction will not show isokinetic decomposition, and reaction controllability will deteriorate, which is not preferable. Therefore, the determination of the specific polymerization temperature change range, that is, the temperature increase start temperature and temperature increase end temperature in the polymerization temperature range, can be performed, for example, as follows. That is, considering the case where the polymerization reaction rate is kept constant over the entire temperature increase range and the temperature increase period is substantially the entire period of the polymerization reaction, it is assumed that the desired degree of polymerization is achieved in the constant temperature reaction method. When the polymerization temperature required to obtain a vinyl polymer is t ₀ (°C), and the temperature increase width in the temperature rising reaction method is 2x (°C), the heating start temperature is (t ₀ −x), and the temperature rise is The ending temperature is (t ₀ +
x), therefore, the polymerization temperature range is (t ₀ −x) to (t ₀ +x). As mentioned above, x usually ranges from 0.5 to
The temperature is 10°C, preferably 2-6°C. For example, in order to obtain a vinyl chloride polymer with a polymerization degree of about 1030 in the method of the present invention, the polymerization temperature in the constant temperature reaction method is around 58 °C, so the polymerization temperature range in the present invention is usually 57 °C to 59 °C. From ℃
It is selected from the range from 48°C to 68°C, preferably from 56°C to 60°C to 52°C to 64°C. For example, when obtaining a vinyl chloride polymer with a degree of polymerization of about 800, if a chain transfer agent is not used, the polymerization temperature in the constant temperature reaction method is around 65°C, so the polymerization temperature range is usually set at 65°C. ℃～66℃～55℃～
Range up to 75°C, preferably from 63°C to 67°C to 59°C
Select from the range up to ~71℃. Note that the above explanation is based on the most common linear heating pattern, and in this case almost the expected results can be obtained. The reaction results are also affected by the temperature increase pattern, so if a non-linear temperature increase pattern is used, it may be necessary to make some experimental adjustments depending on the desired product. is desirable. In the method of the present invention, after charging the raw materials, the temperature is rapidly raised by heating, and after reaching the predetermined heating start temperature, the heating temperature is increased for at least 50 minutes during the entire period of the polymerization reaction. The polymerization reaction is carried out over a period of 75%, preferably 75% or more, while increasing the temperature over time. When the heating period is less than 50%, the bulk specific gravity of the vinyl chloride polymer obtained is large and the gelation property is also good, but the porosity is small and the plasticizer absorption property is poor, and the above-mentioned conventional It is only as effective as the law. In the method of the present invention, it is easiest to set the rate of increase in the polymerization temperature to a rate that is uniquely determined from the range of temperature increase in the polymerization temperature and the temperature increase period (i.e., a linear temperature increase pattern). Yes, it gives good results. For example, when the polymerization temperature range is 55 to 60°C, the total polymerization reaction time is 8 hours, and 5 hours of that time is the heating period, the heating rate may be 1°C/hr. Furthermore, changing the temperature increase rate during the temperature increase, that is, providing a bending point in the temperature increase pattern, requires excessive heating or cooling capacity at that point, which is not preferable. Fluctuations within an allowable range for temperature control do not significantly affect the results, and are therefore permissible as one embodiment of the present invention. For example, change the temperature increase rate from 1.5℃/hr to 0.5℃/hr during the reaction.
Methods such as changing the temperature to a constant temperature, or setting a period to maintain a constant temperature before and after the heating period are also effective as part of the present invention, as long as the total temperature raising period is 50% or more of the total weight reaction period. This is an acceptable embodiment. In the method of the present invention, the rate of increase in polymerization temperature is usually 5° C./hr or less, particularly preferably 3° C./hr or less from the viewpoint of reaction controllability. Control of the polymerization reaction in the method of the present invention is not particularly limited as long as it allows smooth temperature rise, but in particular DDC (Direct
Control using the Digital Control method is preferable in terms of productivity, controllability, and safety. TIC (temperature indicating controller) control involves some difficulty in achieving smooth temperature rise, but a control method that is equipped with a program control mechanism is relatively good. Although the method of the present invention can be applied to any method for polymerizing vinyl chloride monomers in an aqueous medium, it is particularly suitable for suspension polymerization using an oil-soluble polymerization initiator. , the most industrially useful and valuable. [Examples] Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. The physical properties of the obtained vinyl chloride polymer were evaluated using the following physical property measuring method. Physical property measurement method Average degree of polymerization and bulk specific gravity Determined according to the method shown in JIS K-6721. Porosity Pore volume per gram of each vinyl chloride polymer (hereinafter abbreviated as PVC) obtained was determined by mercury intrusion method. The equipment used is Carlo Erba model 800. Gel time: 100 parts by weight of PVC, 3 parts by weight of lead-based powder stabilizer,
60 g of a sample blended with 0.5 parts by weight of a barium-based powder stabilizer was kneaded in a Brabender Plasteyucoder (187°C, 45 rpm), and the time required to reach maximum torque was measured. 100 parts by weight of plasticizer-absorbing PVC and 50 parts by weight of the plasticizer dioctyl phthalate (hereinafter abbreviated as DOP) were put into a planetary mixer and mixed (80℃,
70 rpm) and measured the time until the end of dry-up. Fuitsyu Eye (hereinafter abbreviated as FE)
After blending 100 parts by weight of PVC, 50 parts by weight of plasticizer (DOP), and 3 parts by weight of lead-based powder stabilizer,
Knead with rolls at 155°C for 4 minutes, 5 minutes, and 7 minutes, respectively. The number of FEs observed in 25 cm ² of the obtained roll sheet was counted and determined as the number of FEs. The maximum value (Δt _MAX ) of the difference (Δt) between the reaction temperature and the temperature of the cooling water circulated through the jacket of the polymerization vessel is used as _a guideline for the required level of cooling capacity. The larger △t _MAX , the greater the cooling capacity required, and if the cooling capacity is limited, productivity will be low. Example 1 The reaction materials shown in Table 1 were charged into a stainless steel polymerization vessel having an internal volume of 400 mm and equipped with a stirrer and a jacket. After the charging was completed, hot water was circulated through the jacket and the jacket was rapidly heated to the substantial polymerization initiation temperature (heating initiation temperature) shown in Table 1 to initiate the polymerization reaction. Thereafter, the temperature was raised continuously at a rate of 0.5° C./hr, and the temperature raising was completed at 60.3° C., and thereafter this temperature was maintained for 2 hours and 4 minutes until a predetermined polymerization rate was reached. Table 2 shows the results of evaluating the physical properties of the PVC thus obtained. Examples 2 to 6 Preparation was carried out in the same manner as in Example 1, except that the reaction raw materials were changed as shown in Table 1. Next, the same procedure as in Example 1 was carried out except that the polymerization reaction was carried out under the reaction conditions shown in Table 1. Table 2 shows the results of evaluating the physical properties of the obtained PVC. Example 7 The reaction materials shown in Table 1 were charged in the same manner as in Example 1, and a substantial polymerization reaction was carried out as follows. After preparation is complete, warm water is circulated through the jacket and the surface is heated.
After rapidly heating to the substantial polymerization initiation temperature (55 ° C.) shown in 1, a polymerization reaction is carried out at this temperature for 1 hour,
Thereafter, the temperature was continuously raised to 60.3°C at a rate of 0.5°C/hr, and then maintained at that temperature for 1 hour and 4 minutes to complete the polymerization reaction. Table 2 shows the evaluation of the physical properties of the obtained PVC. Example 8 The reaction raw materials shown in Table 1 were charged in the same manner as in Example 1, and a substantial polymerization reaction was carried out as follows. Maintained at substantial polymerization initiation temperature (55°C) for 2 hours and 4 minutes, then continuously heated at a rate of 0.5°C/hr for 60.3
The temperature was raised to ℃ to complete the polymerization reaction. Table 2 shows the evaluation of the physical properties of the obtained PVC. Comparative Examples 1 to 4 Preparation was carried out in the same manner as in Example 1, except that the reaction raw materials were changed as shown in Table 1. Next, this temperature was maintained until a predetermined polymerization rate was reached in the same manner as in Example 1, except that a constant temperature polymerization reaction was carried out under the reaction conditions shown in Table 1. Table 2 shows the results of evaluating the physical properties of the PVC thus obtained. Comparative Example 5 After the reaction raw materials were charged in the same manner as in Example 1, hot water was circulated through the jacket and the jacket was rapidly heated to the heating start temperature shown in Table 1 to initiate the polymerization reaction. From 3.5 hours after the start of the reaction, the temperature was raised continuously to the final temperature at the temperature increase rate shown in Table 1, and thereafter, as in Example 1, this temperature was maintained until a predetermined polymerization rate was reached. Table 2 shows the results of evaluating the physical properties of the PVC thus obtained. Comparative Examples 6 to 7 The preparation was carried out in the same manner as in Example 1, except that the reaction raw materials were changed as shown in Table 1, and then hot water was circulated through the jacket, and the reaction materials were changed as shown in Table 1. The polymerization reaction was started by rapidly heating to the first-stage polymerization temperature. Five hours after the start of the polymerization reaction, the temperature was raised to the second stage polymerization temperature, and thereafter, as in Example 1, this temperature was maintained until a predetermined polymerization rate was reached. Table 2 shows the results of evaluating the physical properties of the PVC thus obtained.

【table】

【table】

【table】

[Table] The following is clear from Table-2. First, when comparing Examples 1 to 3 and Comparative Example 1, Example 4 and Comparative Example 2, and Example 5 and Comparative Example 3, it is found that if a vinyl chloride polymer is produced by the method of the present invention, porosity will be reduced. It is clear that the bulk specific gravity can be increased while keeping properties such as , gelling time, plasticizer absorption, FE, and Δt _MAX almost the same as conventional ones. However, when the range of increase in polymerization temperature is as small as 1°C, as in Example 6, the bulk specific gravity is relatively small, and it can be seen that it is desirable that the range of increase is 2°C or more. Next, comparing Examples 1 to 3 and Comparative Example 6, and Example 5 and Comparative Example 7, it is found that when the temperature was rapidly raised, (Comparative Examples 6 and 7) the present invention method had a lower bulk specific gravity. However, it is clear that the properties required of other vinyl chloride polymers are significantly inferior to those of other vinyl chloride polymers. Furthermore, when comparing Examples 1 and 3 and Comparative Example 5, it is found that when the temperature increase period is short (Comparative Example 5), porosity, plasticizer absorption, etc. tend to deteriorate, and the reaction time is long. It is clear that Δt _MAX is large and the productivity is relatively poor. Furthermore, when comparing Examples 1 to 3 and Comparative Example 4, it is found that in the method of adding a vinyl chloride monomer during the polymerization reaction (Comparative Example 4), the bulk specific gravity increased to the same extent as in the method of the present invention. However, it is clear that it is significantly inferior in terms of the properties required of other vinyl chloride polymers. Example 9 In the same manner as in Example 1, PVC was produced by preparing the reaction raw materials shown in Table 1 and using the reaction conditions as follows.
The evaluation of its physical properties is shown in Table 3. After the preparation was completed, warm water was circulated through the jacket and the temperature was rapidly raised to the actual polymerization initiation temperature of 55°C. 57.5 continuously from this temperature at a rate of 0.5℃/hr
℃ over 5 hours, then this temperature was increased to 2
The temperature was maintained for 4 minutes, and the temperature was further raised continuously to 60.3°C at a rate of 0.5°C/hr to complete the polymerization reaction. The period during which the polymerization reaction actually progresses is 12 hours and 40 minutes, of which the period required for temperature rise is 10 hours.
It was hot in 36 minutes. Example 10 In the same manner as in Example 9, the actual polymerization initiation temperature was
From when it reached 55℃, the temperature was raised continuously at a rate of 0.5℃/hr to 56.5℃ in 3 hours, held at this temperature for 1 hour, and then continuously raised to 58.5℃ at a rate of 0.5℃/hr.
The temperature was raised to ℃ over 4 hours. Furthermore, at the temperature
After holding for 4 minutes, the temperature was continuously raised to 60.3°C at a rate of 0.5°C/hr, at which point the polymerization reaction was terminated.
The physical properties of the obtained PVC were evaluated and are also listed in Table 3. In addition, the period during which the polymerization reaction proceeded in this example was 12
The time was 40 minutes, of which the period required for temperature rise was 10 hours and 36 minutes. Example 11 In the same manner as in Example 9, the actual polymerization initiation temperature was
After reaching 55°C, the temperature was held for 30 minutes, then the temperature was increased continuously at a rate of 0.5°C/hr to 57°C, held at this temperature for 1 hour, and then continuously increased at a rate of 0.5°C/hr.
The temperature was raised to 60.3°C at a rate of hr and then held at this temperature for 34 minutes to complete the polymerization reaction. Of the total reaction time of 12 hours and 40 minutes, the time required to raise the temperature was 10 hours and 36 minutes. The physical properties of the obtained PVC were evaluated and the table below shows
Also listed in 3.

〔Effect of the invention〕

According to the method of the present invention, the polymerization reaction of a vinyl chloride monomer in an aqueous medium is carried out by raising the polymerization temperature for a specific period of time, thereby increasing the bulk of the vinyl chloride monomer compared to that obtained by a conventional constant temperature reaction. A vinyl chloride polymer having a high specific gravity and improved moldability can be obtained. In addition, the method of the present invention requires less cooling capacity for heat removal than the two-stage reaction method (rapidly increasing temperature), so it is possible to improve productivity and improve moldability. can do.

Claims (1)

[Claims] 1. A method for producing a vinyl chloride polymer by polymerizing a vinyl chloride monomer or a mixture of copolymerizable monomers mainly consisting of vinyl chloride monomer in an aqueous medium, in which the polymerization reaction is substantially A vinyl chloride polymer characterized in that the polymerization reaction is carried out while the polymerization temperature is increased over time for 50% or more of the entire period during which the polymerization occurs, and the range of increase in the temperature is in the range of 1 to 20°C. manufacturing method.