JPH0212962B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved continuous suspension polymerization process that yields uniformly sized polymer particles. A general method for granular polymerization of an unsaturated compound having a vinyl group is to add a monomer to an aqueous dispersion medium containing a dispersant, and heat polymerize while dispersing it into granules using a mechanical means such as a stirrer. Batch operation is used. According to this method, the particle size of the obtained polymer particles is easily affected by the stirring effect, and it is extremely difficult to provide a uniform stirring effect anywhere in the reactor. The particle size distribution becomes wide. As a method to improve the shortcomings of such general methods, monomers are not dispersed in an aqueous dispersion medium by mechanical stirring or mixing using a stirrer as in the general method, but are dispersed in an aqueous medium through a nozzle or the like. Research has been conducted on methods for producing polymer particles with uniform particle sizes by dispersing monomer droplets with uniform particle sizes in a medium and then heating and polymerizing them without destroying the shape of the droplets. Ta. The present invention relates to the above-mentioned improved manufacturing method, and as a result of the inventor's extensive research,
The specific gravity of the polymerizable droplets increases as the polymerization progresses, and the difference in specific gravity with the aqueous dispersion medium changes. It is divided into three reaction sections that involve operations, and the transfer of polymerization droplets to each reaction section is controlled using the circulation flow of an aqueous dispersion medium and the buoyancy and settling forces of the polymerization droplets, thereby achieving uniform particle size. We have developed a new method for continuously producing polymer particles. In the present invention, a polymerizable liquid made of a monomer in which at least a polymerization initiator is dissolved is introduced into a droplet generation device that generates a group of droplets with substantially uniform particle size, and the generated polymerizable droplets are polymerized. An aqueous dispersion medium having a temperature at which the dispersion medium starts to flow downward is introduced into the first reaction section using the buoyancy force of the droplets, and the droplets are Polymerization proceeds while forming a fluidized bed of particles, and as the specific gravity of the droplets increases as the polymerization progresses, the droplets whose polymerization has progressed to a specific gravity close to that of the aqueous dispersion medium move with the flow of the aqueous dispersion medium. Taking advantage of this fact, it is placed on the downward flow of the aqueous dispersion medium.
The droplet slurry is transferred from the lower part of the first reaction section via a conduit to the second reaction section equipped with a filter that allows only the aqueous dispersion medium to pass through to proceed with polymerization, and then the liquid whose specific gravity is larger than that of the aqueous dispersion medium is Utilizing the sedimentation force of the droplets, the aqueous dispersion medium flows upward to the third reaction section, forming a fluidized bed of droplets, while further polymerizing the liquid until it reaches a specific gravity corresponding to the desired polymerization conversion rate. The aqueous dispersion medium that has passed through the filter of the second reaction section is transferred to the downward flow of the first reaction section and the droplets of the aqueous dispersion medium that have passed through the filter of the second reaction section, so that only the droplets settle and are collected at the bottom of the third reaction section against the upward flow of the aqueous dispersion medium. This is a method for continuously producing polymer particles of substantially uniform particle size, characterized by recycling the polymer particles in the upward flow of three reaction sections. The polymerizable liquid used in the present invention is one in which at least a polymerization initiator is dissolved in a vinyl unsaturated compound monomer. It is also possible to use a solution obtained by dissolving a polymer of a soluble vinyl unsaturated compound in the above, but the viscosity must be within a range that allows the polymerizable liquid to be formed into a group of droplets with uniform particle size. Therefore, subject to limitations, polymerizable liquids in which less than 20% of the polymer is dissolved in the monomer are preferred. The aqueous dispersion medium used in the present invention may be a dispersion stabilizer commonly used in suspension polymerization dissolved or dispersed in water. That is, for example
Organic polymer dispersants such as PVA, PVP, and CMC, inorganic fine powders such as calcium phosphate and calcium carbonate, and combinations thereof can be used. The droplet generation device used in the present invention needs to generate a group of droplets with uniform particle size, and the polymerizable liquid is discharged into an aqueous dispersion medium from an orifice with one or more holes, so that the generated liquid column has a regular pattern. A method is used in which a group of droplets having a uniform diameter is generated by applying mechanical vibration. The particle size of the obtained polymer particles in the present invention is determined predominantly by the particle size of the droplets generated by the droplet generation device, and the conditions for obtaining the desired particle size are the passage of the polymerizable liquid through the orifice. The speed, the viscosity of the polymerizable liquid, and the frequency and amplitude of the vibrations imparted to the liquid column generated after the polymerizable liquid passes through the orifice can be selected as the dominant factors. Hereinafter, the present invention will be explained with reference to the drawings. A polymerizable liquid made of a vinyl unsaturated compound in which a polymerization initiator is dissolved is introduced into a droplet generation device 2 via a conduit 1, forming a group of droplets with a desired particle size, and filled with an aqueous dispersion medium. The liquid droplet is introduced into the cylinder 4, which is the first reaction part, through the introduced tube 3 due to the buoyancy force of the droplet. An aqueous dispersion medium set at a predetermined polymerization temperature is supplied from the upper part of the cylinder 4 through a conduit 6 and a disperser 5 to the cylinder 4.
A downward flow of the aqueous dispersion medium is formed in the cylinder 4 by introducing the aqueous dispersion medium into the cylinder 4 and circulating it from the bottom of the cylinder 4 via the conduit 8 to the tank 9 which is the second reaction part. An amount of aqueous dispersion medium corresponding to the aqueous dispersion medium that is extracted from the pipe 7 together with the polymer particles from the cylinder 14, which is the third reaction part, passes through the disperser 5 and enters the cylinder 4. will be introduced in In the cylinder 4, a fluidized bed of polymerizable droplets is formed in the upper layer due to the buoyancy force of the introduced polymerizable droplets and the downward flow of the aqueous dispersion medium, and polymerization of the droplet group proceeds there. As the polymerization conversion rate progresses and the specific gravity of the polymerized droplets increases to near the specific gravity of the aqueous dispersion medium, the droplets lose their buoyancy force to resist the downward flow of the aqueous dispersion medium and move to the lower part of the tube 4, where they move to the bottom of the tube 4 and move toward the bottom of the tube 4. It is transferred to the tank 10 along with the circulating flow. Therefore, in the lower part of the cylinder 4, a separation zone is formed in which the injected droplets before the start of polymerization rise and the droplets that have reached a predetermined conversion rate in polymerization simultaneously descend. As described above, a stable fluidized bed of polymerizable droplets is formed in the upper part of the tube 4, and polymerization proceeds without coalescence or splitting of the polymerizable droplets generated by the droplet generation device. In order to transfer only the polymerizable droplets that have reached a predetermined polymerization conversion rate in the lower layer of tube 4 to the second reaction section, the following conditions for introducing the aqueous dispersion medium into tube 4 and the conditions in tube 4 must be met. This can be achieved by satisfying the downward flow velocity of the aqueous dispersion medium. The method for introducing the aqueous dispersion medium into the tube 4 is to prevent the generation of a strong local shearing field that would apply strong shearing force to the polymerizable droplets and cause the droplets to break up. This can be achieved by passing through the disperser 5 which has the function of diffusing the flow rate from 1 to 5 to a low flow rate. The disperser 5 may be one filled with a foam layer of an aqueous dispersion medium, or a dispersion tube consisting of one or more tapered tubes with an enlarged lower part. The downward flow rate of the aqueous dispersion medium in the cylinder 4 is preferably 0.2 to 1.0 cm/sec in the upper layer, and 0.2 cm/sec in the lower layer in order to increase the polymerization conversion rate of the polymerization droplets transferred to the second reaction section. Preferably it is less than a second. The design of the cylinder 4 to obtain the above downward flow velocity can be easily determined. The specific gravity of the polymerizable droplets transferred to the tank 9, which is the second reaction section equipped with the filter 10, is slightly lower than the specific gravity of the aqueous dispersion medium, but the specific gravity quickly becomes larger than that of the aqueous dispersion medium while staying in the second reaction section. It settles and moves to the third reaction section. The polymerization conversion rate of the polymerizable droplets transferred to the second reaction section can be easily increased to 50% or more by appropriately controlling the downward flow rate of the aqueous dispersion medium in the first reaction section. The polymerizable droplets change into stable beads rather than droplets, and even if the aqueous dispersion medium is removed for circulation through the filter 10 while remaining in the second reaction section, the shape of the polymerized droplets will not change. It can be held in the tank 9 without any problems. It is also possible to install a stirring blade to provide gentle stirring in the second reaction section, or to install a vibration mechanism to prevent clogging of the filter. In the third reaction section 14, a part of the aqueous dispersion medium extracted in the second reaction section is introduced through the conduit 13 to create an upward circulating flow, and the polymerized droplets (beads) that have settled from the second reaction section are The polymer particles that have reached the desired polymerization conversion rate form a fluidized bed in the upper part of the third reaction section until they reach a polymerization conversion rate corresponding to the specific gravity that allows them to settle against the upward flow of the aqueous dispersion medium. , selectively settles at the bottom of the third reaction section and is taken out of the reaction system as a concentrated slurry. A desired polymerization conversion rate of the obtained polymer particles can be obtained by selecting the upward flow rate in the third reaction section. In this method, the desired polymerization temperature can be controlled by installing a heat exchanger in the conduit connecting each reaction section and by insulating each reaction section. Since this is a method that makes the most of the differences, it can be easily inferred that it not only has the advantage of being able to obtain polymer particles with uniform particle sizes, but also has other advantages compared to conventional methods. be. Examples will be explained below. Example: A polymerizable liquid containing 0.32 PHR of benzoyl peroxide dissolved in styrene is passed through conduit 1 to droplet generator 2.
supplied. The droplet generator 2 is made of a stainless steel plate with one orifice hole of 0.4 mm in diameter.
250Hz mechanical vibration is applied in the vertical direction at 10 times per minute.
Polymerizable droplets were generated in ml. The generated polymerizable droplets rose through an introduction tube with an inner diameter of 25 mm filled with an aqueous dispersion medium and were introduced into the cylinder 4. The tube 4 is a stainless steel hollow tube with an inner diameter of 70 mm at the top and a height of 1000 mm at the bottom, an inner diameter of 140 mm at the bottom, and a height of 400 mm at the bottom. 0.35cm/sec at bottom, 0.09 at bottom
It created a downward flow at cm/sec. The aqueous dispersion medium is pure water and fine calcium phosphate powder.
2000 ppm, polyvinyl alcohol 50 ppm, and anionic surfactant (sodium alkyl olefin sulfonate) 50 ppm were mixed and used. The polymerization temperature in the cylinder 4 was controlled to 88-90° C. by installing a heat exchanger in the conduit 6 for circulating the aqueous dispersion medium. Polymerization proceeded in the tube 4 of the first reaction section, and the polymerization conversion rate of the polymerized droplets introduced into the tank 9 of the second reaction section through the conduit 8 was 60 to 65%. The tank 9 in the second reaction section has an inner diameter of 140 mm and a straight body height of 200 mm.
A stainless steel tank with a diameter of 1 mm was used, a filter 10 made of a 100 mesh stainless steel net was installed, and an amount of the aqueous dispersion medium used for circulation was extracted through the filter. The polymerization conversion rate of the polymerization droplets that settle and transfer from the second reaction section to the third reaction section connected to the lower part is
It was 65-70%. The third reaction section is connected to the bottom of the second reaction section and has an inner diameter of 140 mm, a straight body height of 50 mm, and an inner diameter of 55 mm.
A stainless steel cylinder 14 having a straight body part height of 400 mm connected by a tapered part was used, and an aqueous dispersion medium was introduced through the conduit 13 from the middle of the cylinder with an inner diameter of 55 mm to generate an upward flow in the cylinder 14. The polymerization conversion rate of the polymer particles that settled against the upward flow rate and was collected at the bottom of the tube 14 is shown in Table 1, and the results of drying the collected polymer particles and measuring the particle size are shown in Table 2. The grain size was almost uniform.

【table】

[Table] A Tyler standard sieve was used as the classification width.

[Brief explanation of drawings]

The figure is an explanatory cross-sectional view of an apparatus used in the method of the present invention. 1... Polymerizable liquid conduit, 2... Droplet generator, 3...
Polymerizable droplet introduction pipe, 4, 14... cylinder, 5... aqueous dispersion medium disperser, 6, 7... aqueous dispersion medium conduit, 8... slurry conduit, 9... tank, 10... filter, 11, 13
... aqueous dispersion medium conduit, 12 ... aqueous dispersion medium circulation pump, 100 ... first reaction section, 200 ... second reaction section,
300...Third reaction section.

Claims (1)

[Claims] 1. Droplets of polymerizable liquid having a uniform droplet diameter by discharging a polymerizable liquid into an aqueous dispersion medium from an orifice with one or more holes and applying regular mechanical vibrations to the resulting liquid column. After forming a group of droplets and introducing this group of droplets into an aqueous dispersion medium, the polymerizable droplets are held without splitting or coalescing within a range where the specific gravity of the polymerizable droplets is smaller than the specific gravity of the aqueous dispersion medium. The first reaction part undergoes polymerization while the polymerizable droplets are polymerized, and then only the aqueous dispersion medium is recovered for circulation from the slurry consisting of the polymerizable droplets and the aqueous dispersion medium within a range where the specific gravity of the polymerizable droplets is approximately equal to the specific gravity of the aqueous dispersion medium. The second reaction section is followed by a third reaction section where only those droplets whose specific gravity has reached a specific gravity corresponding to a desired polymerization conversion rate within a range where the specific gravity of the polymerizable droplets is greater than the specific gravity of the aqueous dispersion medium are sedimented and recovered. The reaction section is guided through a conduit so that the polymerizable droplets pass through it in sequence, and the aqueous dispersion medium extracted in the second reaction section is circulated in a downward flow in the first reaction section and an upward flow in the third reaction section. A continuous suspension polymerization method for obtaining polymer particles of substantially uniform particle size. 2. The continuous suspension polymerization method according to claim 1, wherein the polymerizable liquid has 20% or less of the polymer substance dissolved in the monomer. 3. The continuous suspension polymerization method according to claim 1, wherein the downward flow of the aqueous dispersion medium in the first reaction section is 1 cm/sec or less based on the reactor cavity. 4. The continuous suspension polymerization method according to claim 1, wherein a retention tank is provided to increase the polymerization conversion rate of the polymerizable droplets transferred to the second reaction section after the first reaction section. 5. The continuous suspension polymerization method according to claim 1, wherein the slurry flowing out from the first reaction section is used as an upward flow in the third reaction section, and then circulated to the first reaction section through a filter in the second reaction section. . 6. The continuous suspension polymerization method according to claim 1, wherein the polymerization temperature is controlled by installing a heat exchanger between the conduits.