JPH0225362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polymerization method for polymerizing vinyl monomers, and in particular to a method using an inorganic salt in place of a conventional emulsifier used in the polymerization procedure. Polymerization of vinyl monomers is carried out in the presence of a water-soluble initiator. In order to suitably adjust the PH value of the reaction mixture, electrolyte and buffer solutions of inorganic salts are introduced into the polymerization mixture at certain points during the reaction period. Furthermore, during the polymerization it is essential to vary the stirring speed by a two-stage operation. The polymer resins produced in this way do not contain emulsifier residues in the polymer particles, and therefore the properties of plastisols from these resins, such as viscosity stability, thermal stability, and clarity, are similar to those of normal emulsion polymers. superior to that of polymer resins produced by legal or microsuspension polymerization methods. The monomer/water ratio in this polymerization procedure is also improved, thus increasing the batch or run productivity of the polymerization. In conventional emulsion polymerization methods for producing vinyl resins, water-soluble polymerization initiators are generally used to obtain latexes or pastes with desired properties. In contrast, oil-soluble polymerization initiators are used to produce vinyl polymers or copolymers in microsuspension polymerization methods. Even if these methods are adopted, a large amount of emulsifier will be included in the polymerization process. Examples of emulsifiers of this type include anionic surfactants such as high fatty acid soaps, sulfates of long-chain alcohols, metal salts of alkylbenzenesulfonates, and nonionic surfactants such as glycerin esters of fatty acids and sorbitan esters. , polyol esters of fatty acids,
Examples include polyoxyethylene compounds. It is known that resins obtained by the emulsifier-containing polymerization method have emulsifier residues contained in the polymer particles. This has a detrimental effect on the properties of the resin. Therefore, when this resin is used in plastisols or organosols in the subsequent process, the viscosity changes during storage and becomes unusable, the thermal stability is also unfavorable, and the clarity of the products manufactured from it is also affected. Not desirable. In view of the negative effect emulsifiers have on the properties of resins, it is clear that significant benefits would be obtained if emulsifiers were removed from the polymerization process.
However, if an emulsifier is not included in the polymerization process, the stability of the colloidal particles during the polymerization period is incomplete. Therefore, an object of the present invention is to provide a polymerization method that does not contain an emulsifier during the polymerization process and can maintain the stability of colloidal particles during the polymerization period. According to the present invention, the process for polymerizing vinyl monomers is carried out in one charged mixture through a two-stage stirring operation. The components having a monomer/water ratio of about 0.1 to about 0.8 are charged into a polymerization reactor. monomer,
The reaction mixture containing demineralized water and water-soluble initiator is thoroughly stirred. The polymerization system is then heated to a reaction temperature ranging from about 30°C to about 75°C. but,
It is desirable to use polymerization temperatures in the range of 35°C to 70°C. It should be noted that if the reaction temperature is higher than the permissible temperature range, a large amount of polymerized colloid will coagulate, resulting in increased polymer agglomeration. The present invention further requires a period of high-speed stirring after initiation of polymerization. In other words, high-speed stirring is performed during the first stage of the reaction. This is because the polymerization reaction is a heterogeneous reaction, and sufficient stirring is required to increase the frequency of collisions between the substantially water-insoluble monomer and the free radicals generated by the polymerization initiator. It's for a reason.
Efficient collisions initiate a reaction between the monomer and the free radicals, thus inducing nucleation of the reaction. The free radicals decomposed from the polymerization initiator become electrically charged. This charge is then transferred to the reaction nucleating particles such that the growing nucleated polymeric particles become electrically charged at the interface between the growing polymer and the aqueous phase. When polymerization reaches about 5% to about 30%, an electrolytic solution with a pH value adjusted to a range of about 7.5 to 11.5 is introduced into the constantly stirred polymerization mixture. This introduction increases the pH of the polymerization mixture.
The value is adjusted to a range of about 7.5 to about 11.5. This PH
When the value is 4 or less, the amount of scum-like precipitates increases and the heat resistance of the product deteriorates. (See Comparative Example 3 and Table 1 below). Also, if the pH value is 13 or higher, there will be more slag.
(See Comparative Example 4, Table 1). And the PH value is 7.5~
These experiments showed that the best effect can be achieved when the ratio is 11.5. Therefore, the aforementioned PH
The value is between 4 and 13, preferably between 7.5 and 11.5. Further, the reason why the electrolytic solution or buffer solution is introduced when the polymerization rate of the reaction reaches about 5% to about 30% is as follows. That is, when the polymerization rate (conversion rate) is 5% or less, there is little polymerization of monomers into polymers and the polymerization is stable, so there is no point in introducing a buffer solution or the like. However, when this reaches 5% to 30%, a good electronic double layer cannot be maintained and stability can be maintained unless the reaction mixture is adjusted to an appropriate pH, so a buffer solution etc. must be introduced at this time. The need arises. Furthermore, if the concentration exceeds 30% and a buffer solution or the like is not introduced, the polymer (PVC) particles will become unstable and clumps will increase. (See Comparative Example 2 below). The charged polymeric particles are surrounded by counterions and form an electronic double layer around each particle, allowing the polymer to remain in a colloidal state. When polymerization reaches a range of about 50% to about 70%, the polymer has grown and propagated to a certain extent and the monomer concentration is relatively reduced. In this case, maintaining the high speed stirring of the first stage destroys the stability of the polymer. If the polymer is produced in this manner, it will solidify the precipitate or otherwise form undesirable polymer clumps. Furthermore, if high-speed agitation is unduly prolonged, free radical termination reactions occur, preventing polymer growth or propagation, and the nucleation of the reaction shifts toward the diluted monomer in the water, leading to the termination of the reaction. Undesired new particles are formed. To avoid these undesirable phenomena, the stirring speed should be reduced at this point. (Hereinafter, this will be referred to as second stage agitation.) It has been found that the preferred second stage agitation speed is about 1/3 to 1/6 of the first stage speed. In the present invention, "vinyl monomer" refers to vinyl halides, such as vinyl chloride, ethylene halides, such as ethylene bromide, vinylidene halides, such as vinylidene chloride, vinyl esters, such as vinyl acetate, nitriles, such as Acrylonitrile, etc., and other known oil-soluble olefin monomers. The present invention applies to the production of monopolymers of one of the above olefin monomers, and also to the production of copolymers of at least two of the above olefin monomers. However, it is preferred to use slightly water-soluble polar monomers. Since the water solubility of oil-soluble monomers is 0.2% or more,
It was found that the probability of nucleation of the reaction increases. The preferred monomer/water ratio in the present invention is about
It ranges from 0.1 to about 0.8. Unless the polymerization conditions are maintained strictly, i.e., a buffer solution is not used during the process to adjust the PH value of the reaction mixture to a range of about 7.5 to about 11.5, or the agitation speed is not maintained at the correct initial speed. If not maintained and then changed to the preferred second stage velocity at a suitable time, or alternatively if the electrolyte solution is not introduced at the correct moment, the colloidal state of the reaction mixture will become unstable and the reaction mixture will thus The monomer/water ratio was adjusted to approx.
A reduction in the range of 0.05 to about 0.1 is required. On the other hand, if the polymerization conditions are maintained strictly according to the method of the present invention, the monomer/water ratio can be increased to the range of the present invention, ie, from about 0.1 to about 0.8. Note that this ratio is 0.1
When it is smaller than 0.8, it is economically disadvantageous, and when it is larger than 0.8, the PVC emulsion becomes unstable. In the present invention, the initiator is a water-soluble compound, such as hydrogen peroxide, an alkali metal persulfate, or a water-soluble reducing agent with or without ammonium ions in its structural formula, such as an alkali metal sulfite. or bisulfites. The amount of initiator used is about 0.05% to monomer weight.
It is in the range of 0.4% (by weight). The amount of initiator used is actually determined by the production efficiency of the reaction system equipment, but if it is less than 0.05%, the reaction will be slow and economical, and if it is less than 0.4%, it will be less economical. If there is too much, it will affect the heat dissipation limit of the reactor,
There is a risk of loss of control. Preferred initiators are compounds containing a sulfate group (SO ₄ ^-- ), a carboxyl group (COO ^- ) or a hydroxyl group (OH ^- ) in their structural formula. An example of this type of initiator is:
These include K ₂ S ₂ O ₈ , K ₂ S ₂ O ₅ , K ₂ S ₂ O ₃ , NaHSO ₃ and H ₂ O ₂ . The initiator is decomposed into electrically charged free radicals during the polymerization process, and the propagated polymer thereby produced contains charged groups at its end groups.
The end groups of each polymer in the reaction nucleation cell face outward and, together with the electrolyte ions in the water, form an electronic double layer around each nucleation particle, thus avoiding coagulation or agglomeration. , and a colloid stable in suspension is obtained. A small amount of oxidizing agent can be added during the polymerization process to promote uniform decomposition of the initiator and to stabilize the polymerization mixture at a suitable reaction temperature. Oxidizing agents that can be used include salts of transition elements (metals), e.g.
Nitrates of Fe, Cu, Zn, Ce, Sn, Co and V,
These include hydrochloride, bromate, or sulfate. The preferred amount of the oxidizing agent added is about 0.1 to about 10 times the moles of the initiator added. However, when using the oxidizing agent, consideration must be given to the concentration and type of initiator contained in the polymerization process, and the oxidizing agent must not inhibit the reaction. Otherwise, the stability of the polymerized colloid will be lost. The colloid stabilizer used in the present invention is a water-soluble inorganic salt-based electrolyte substance, such as a member of group A of the periodic table,
A genus A, or a hydroxide, chloride, carbonate, bicarbonate, phosphate, or nitrate of genus A.
The optimum amount of stabilizer depends primarily on the ionic strength of the total reaction mixture and should be kept in good balance with the initiator and oxidizing agent used. Preferred amounts are from about 0.01% to about 0.01% by weight of monomer.
It is in the range of 0.5% (by weight). If it is less than 0.01%, the stability of the PVC emulsion will be poor and it will cause coagulation, and if it is more than 0.5%, it will affect the physical properties of the PVC product. In practicing the present invention, the reaction mixture has a pH of about 7.5 to
A buffer solution, which can be maintained in the preferred range of 11.5, is also introduced during the polymerization process. This is the pH of the reaction system
Any type can be used as long as NH ₃ /
NaOH, NaHCO ₃ /NaOH or Na ₃ PO ₄ /
_NaHPO4 . To maintain the PH value in the range of about 7.5 to about 11.5, it is sufficient to precisely define the amount of buffer solution. By using an appropriate amount of buffer solution, the end groups of the propagating polymer become sufficiently negatively charged throughout the entire polymerization process in the basic atmosphere. In order to explain the method of the present invention in more detail, examples for the vinyl chloride polymerization process are shown below. Of course, this example is for explaining the method of the present invention, and the method of the present invention is not limited thereto. Example 1 1 liter capacity polymerization vessel (or reaction vessel)
was charged with a mixture of 0.5 g K ₂ S ₂ O ₈ and 500 c.c. demineralized water. Then, close the container tightly and -740
Vacuum was applied to mmHg. This contains 100c.c. of vinyl chloride.
was added and the system was stirred at a stirring speed of 600 rpm. The mixture was heated at a reaction temperature of 52° C. for half an hour. Next, the electrolyte solution (0.04g
A premix of CaCO ₃ +0.8 g 25% NH ₃ /NaOH solution) was introduced. After 2.5 hours, reduce the stirring speed to
The speed was reduced to 100 rpm. The reaction continued until the pressure drop reached 2 kg. A stable polymer with a particle size of about 0.4 microns to about 1.5 microns was obtained. The polymer mass was approximately 0.1% of the loaded stock. The electrolyte solution was introduced when the polymerization of the reaction reached 5% to 30% to adjust the PH of the mixture.
If the PH value is less than 4, scum-like precipitates will increase and the heat resistance of the product will deteriorate. (See Comparative Example 3 and Table 1 below). Also, if the pH value is 13 or higher, there will be a lot of slag. (See Comparative Example 4 and Table 1 below.) And PH
The best effect can be achieved when the value is between 7.5 and 11.5. Furthermore, if the polymerization of the reaction is 5% or less, the polymerization into the polymer is small and stable, so there is no point in introducing an electrolyte solution. However, this is 5% to 30%
If the PH of the reaction mixture reaches an appropriate value, it will not be possible to maintain a good electronic double layer and achieve a stable state, so an electrolyte solution must be introduced and the PH must be adjusted. Note that even if the polymerization rate exceeds 30%, if the electrolyte solution is not introduced, the polymer particles will become unstable and the number of lumps will increase. (See Comparative Example 2 below). Furthermore, the addition amount of the electrolyte solution mentioned above is 0.01% ~
0.5% (weight). If the amount added is less than 0.01%, the stability of the polymer emulsion deteriorates and it coagulates. Also, if this is more than 0.5,
The physical properties of the polymer product are affected. Further, the optimal monomer/water ratio is 0.1 to 0.8. If this is smaller than 0.1, it will be less economical;
Moreover, when it is larger than 0.8, the polymer emulsion becomes unstable. Comparative Example 1 Until the reaction pressure drop reached 2Kg/ ^cm2 ,
The polymerization reaction was repeated as in Example 1 while maintaining a stirring speed of 600 rpm. The polymer mass was approximately 30% of the loaded stock. The particle size of the polymer was in the range of about 0.2 to 0.7 microns. Comparative Example 2 After 2.5 hours of reaction, electrolyte solution and buffer solution were introduced into the polymerization mixture, other polymerization conditions were as in Example 1. The polymer mass was approximately 12% of the loaded stock. The particle size of the polymer is approximately 0.2 to
It was in the 1.5 micron range. Comparative Example 3 The PH value of the electrolytic solution was regulated within the range of 3.5 to 4.0,
Other polymerization conditions were the same as in Example 1. The polymer mass was approximately 25% of the loaded stock. The particle size of the polymer ranged from about 0.2 to 1.4 microns. Comparative Example 4 The polymerization mixture was controlled to have a pH value of 13, and other polymerization conditions were maintained as in Example 1. The reaction time was long and no pressure drop was observed in this system. When the reaction mixture became basic, the initiator K ₂ S ₂ O ₈ was unable to initiate the reaction and the reaction was incomplete. The particle size of the polymer ranged from about 0.2 to 0.9 microns. The polymer mass was about 8% of the loaded stock. Table 1 shows the results of the above-mentioned Examples and Comparative Examples.

[Table] From Comparative Example 1, it can be seen that unless two-stage stirring is employed, ie, high-speed stirring in the first stage of the reaction and low-speed stirring in the second stage, the propagated polymer becomes unstable in the system. Comparative Example 2 shows that the electrolyte stabilizer solution should be introduced into the polymerization mixture at the correct step of the reaction in order to form a stable reaction mixture. Comparative Examples 3 and 4 clearly show that the PH value of the polymerization mixture should be regulated within the preferred range.
Becoming too acidic or too basic creates a polymerization atmosphere that is unacceptable outside these conditions, and these effects result in the formation of unstable polymers and increased agglomeration. . In addition to the polymerization method described above, another advantage of the present invention is that the resulting resin has excellent properties. A comparison is made between the polymeric resins produced according to the present invention and those obtained by conventional emulsion polymerization methods and microsuspension polymerization methods. Example 2 In a 20 liter capacity polymerization vessel, 1.2 gr of K ₂ S ₂ O ₈
and 8 liters of demineralized water mixture.
The vessel was then tightly closed and vacuum was applied to -740 mmHg. Two liters of vinyl chloride was added to this. Turn on the stirrer and run the system at a speed of 650 rpm.
Stir for 15 minutes. The mixture was then heated at a reaction temperature of 52° C. for half an hour. Then _16grNH3 /
A premix of electrolyte solution containing 25% NaOH solution + 0.01 gr CaCl ₂ + 4 gr CaCO ₃ was introduced into the reaction vessel. After 2.5 hours, the stirring speed was reduced to 200 rpm and the reaction continued until a pressure drop of 2 Kg/cm ² was reached. The particle size of PVC resin from the process is about 0.4 to 1.5
It was micron. Comparative Example 5 Microsuspension Polymerization 8 liters of demineralized water, 2.5 gr of 2-4-dimethyl-2-2'-azobis-valeronitrile,
A charge containing 24gr sodium dodecyl sulfate, 36gr hexadecanol, and 12gr stearic acid.
It was introduced into a 20 liter capacity polymerization vessel. Then,
The container was tightly closed and vacuum was applied to -740 mmHg. Add 4.5 liters of vinyl chloride to this,
The system was stirred for 15 minutes. The mixture was then completely homogenized using a homogenizer and heated to a reaction temperature of 52°C. The reaction was carried out until the pressure drop reached 2 Kg/cm ² . This process resulted in a latex with particle sizes ranging from about 0.2 to 2.0 microns. Comparative Example 6 Emulsion Polymerization A charge containing 6 liters of demineralized water, 2.5 gr of K ₂ S ₂ O ₈ , 10 gr of sodium dodecylhenzenesulfonate, 18 gr of stearic acid, and 20 gr of hexadecanol was added to a 20 liter volume. It was introduced into a polymerization vessel.
The vessel was then tightly closed and vacuum was applied to -740 mmHg. 4.5 liters of vinyl chloride was added to this and the system was stirred for 15 minutes. The mixture was heated to a reaction temperature of 52°C. Add 2 liters of 0.6% sodium dodecylhenzenesulfonate to the reaction mixture.
Addition was made continuously at a flow rate of 0.4 liters/hour.
The reaction was continued until the pressure drop reached 2 Kg/cm ² . This process resulted in a latex with particle sizes ranging from about 0.2 to 1.4 microns. The polymer latex or slurry in each of the three steps is taken out of the reactor, spray dried,
The dried PVC or resin was collected. The properties of the resins from each of the experiments were compared for evaluation purposes. Appropriate data regarding properties are shown in Table 2.

【table】

[Table] The data in Table 2 was obtained from the following test steps. (1) Test process for thermal stability: In order to measure thermal stability, plastisol was produced in the following manner using resins or polyvinyl chloride (PVC) from each process. PVC resin 100PHR (a) Dioctyl phthalate 80PHR CaCO ₃ 10PHR Ba-Zn liquid stabilizer 2PHR (a) PHR: parts per 100 parts of resin A film with a thickness of 0.2 mm was produced from the above plastisol, and the rate was 190 per minute. Heated at gel point of °C. The films of each process were cut into small pieces and placed in an open ripening oven at a temperature of 220°C. One of the specimens was removed from the oven every 30 seconds.
The fading of the test pieces in each step was compared, and the aging time (minutes) until blackening was recorded. (2) Test process for clarity: The following samples were prepared. PVC resin 100 PHR Dioctyl phthalate 80 PHR Organotin stabilizer 1 PHR A film with a thickness of 0.2 mm was produced from the PVC resin of each step above and heated at 190° C. for 3 minutes. Then,
The film was placed on a glass plate and observed for clarity under a standard illuminant. Clarity comparison:
"Excellent" means better clarity than "Good". (3) Test process for viscosity measurement after plastisol preparation: Using the PVC resins from each process, plastisols with the following formulations were made. PVC resin 100PHR Dioctyl phthalate 70PHR Dioctyl adipate 10PHR CaCO ₃ 10PHR The viscosity values are the values measured using a Bruckfield type B viscometer. The viscosity of each plastisol is shown in Table 2.
Measurements were made using centipoise (cps.) units at a temperature of 25°C after several days of preparation. The above results show that the product of the present invention retains excellent properties. Among the many advantages of the present invention, the properties of the resin are greatly improved, in particular:
Due to the improved monomer/water ratio provided by the process of the present invention, productivity for batches or runs of polymerization is increased. Although the present invention has been described with reference to the above embodiments, the scope of the present invention is not limited thereto, and various modifications can be made within the scope of the present invention.

Claims (1)

[Claims] 1. A method for polymerizing vinyl monomers in the presence of a water-soluble polymerization initiator in a reactor, the method comprising: adjusting the monomer/water ratio of the polymerization reaction mixture to 0.1 to 0.8; The vinyl-based monomer is stirred at an initial stirring speed sufficient to promote the collision frequency between the free radicals generated by the monomer and the polymerization initiator, i.e., a high first stage stirring speed of 500 rpm to 800 rpm. When the polymerization rate of the polymerization reaction reaches approximately 5% to 30%, the pH of the polymerization mixture is adjusted to a range of approximately 7.5 to 11.5 to bring the polymerization mixture into a stable colloidal state. About 0.01% of the monomer in the polymerization mixture while maintaining the high initial or first stage stirring speed described above.
% ~ 0.5% (wt%) of a water-soluble inorganic salt-based electrolyte solution that is a colloid stabilizer and a small amount of buffer are mixed and stirred with the polymerization mixture, and the polymerization rate of the polymerization reaction is approximately 50% ~ 70%. When the above stirring speed reaches 1/3 to 1/6 of the initial high speed stirring speed of the first stage.
and switch to a second or later stage slow stirring speed sufficient to maintain the stability of the colloidal state, thereby eliminating the presence of emulsifier residues contained in the polymer particles and improving the stability of the colloidal state. A method for producing a homopolymer or copolymer of vinyl monomers, characterized in that a homopolymer or copolymer resin having physical properties is obtained. 2. In the method according to claim 1, the water-soluble inorganic salt-based electrolyte solution as a colloid stabilizer is a hydroxide, chloride, or carbonate of Group A, Group A, or Group A of the Periodic Table. , bicarbonate, phosphate, or nitrate. 3. In the method according to claim 1, the polymerization initiator is used in an amount of about
0.05% to 0.4% (wt%) is used, and the polymerization initiator is a water-soluble compound that decomposes in the polymerization mixture to produce sulfate, hydroxyl or carboxyl groups, or contains ammonium ions in its structural formula. Or a method that does not contain a water-soluble reducing agent. 4. In the method described in claim 1, the buffer used to maintain the pH value of the reaction mixture in the range of 7.5 to 11.5 together with the electrolyte solution which is a colloid stabilizer is ammonia/sodium hydroxide, phosphoric acid. sodium/sodium hydrogen phosphate,
A method selected from sodium carbonate/sodium bicarbonate and sodium bicarbonate/sodium hydroxide. 5 In the method described in claim 1, the monomer is a vinyl halide such as vinyl chloride, a vinylidene halide such as vinylidene chloride, a vinyl ester such as vinyl acetate, or a halogenated vinyl such as ethylene bromide. The method is ethylene, or other oil-soluble olefin monomers such as acrylonitrile. 6. The method according to claim 5, wherein the monomers are two types or a mixture of two or more types.