KR100381929B1 - Process and apparatus for continuously producing polymer latex into granules - Google Patents

Abstract

The present invention relates to a method and apparatus for producing a thermoplastic polymer resin in powder from latex obtained by emulsion polymerization. The present invention relates to a technique for achieving the goal of increasing the yield of powder per hour with the achievement of low powder properties with both high apparent density and both fine and coarse particle contents. The present invention is to provide a process for the production of polymer powder having a high characteristics and operated with a relatively short residence time.

Description

Process and apparatus for producing polymer latex continuously in granular form

The present invention relates to a method and apparatus for producing a thermoplastic polymer resin in powder from latex obtained by emulsion polymerization. The present invention relates in particular to a technique for achieving the goal of increasing production with the achievement of powder properties with a high apparent density and a low content of both fine and coarse particles. In addition, the present invention is to operate a short residence time, to provide a process for producing polymer powder having a high characteristic.

The polymer latex in the present invention can be obtained by grafting a vinyl monomer to rubber particles by generally known emulsion polymerization. Such polymer resins are often produced in the form of powder finally dried through a polymerization step, an aggregation step, a aging step, a washing and dehydration step, and a drying step.

Among these various steps, the step after the polymerization step is generally carried out continuously. Among them, the coagulation step is the first step in which the polymer latex is mixed with the coagulant to prepare a coagulation slurry, and the coagulation slurry is heated and solidified in the next aging step.

In the washing and dehydration step, the slurry of solidified polymer particles is continuously dehydrated as water and at the same time a solid-liquid separation unit process is performed.

This coagulation / maturation step plays an important role in the overall process flow as an important process linking the subsequent washing / dehydration step and drying step with the previous batch polymerization step process.

That is, the coagulation and aging process not only affects the production of the final polymer powder, but also affects the apparent specific gravity and particle size distribution of the powder.

The fine particles in the final powder produced during this process can be lost during transport and extrusion operations, causing environmental problems, and also acts as a factor to reduce the yield by flowing out during the dehydration process. In addition, the packaging loses resin due to the scattering of fine powder, and dust generation may deteriorate the surrounding working environment.

Coarse particles as well as fine particles also cause various problems. That is, the coarse particles make it difficult to remove residual impurities mixed in the particles, and a large amount of air is required to form a fluidized bed during the drying process. Low apparent densities also lead to increased storage and transport costs.

Various prior arts are known to address the problems caused by the generation of such fine powders, unevenness in particle size distribution and low apparent density.

For example, Japanese Laid-Open Patent Publications No. 53-33244, No. 53-187873, No. 56-41227, No. 57-59929, and the like, spray the aqueous solution of the flocculant into the gas phase to release the polymer latex in a flocculating atmosphere. To induce agglomeration through contact with a flocculant, and then recover it to powder through a aging tank. This has the disadvantage of having a problem of particle adhesion on the coagulation tank wall and the use of a facility which occupies a very large space. In addition, European patent application EP0101576 discloses a process for neutralizing agglomerated slurries having a low pH using an aqueous alkali solution. However, during this process, fine powder may increase, which may cause problems in the dehydration process. In addition, European patent application EP0611788 describes a method of inducing agglomeration continuously through a multistage agglomeration process and agglomerating a polymer having a content of 40 to 80 weight in the first step. This approach has the disadvantage of involving excessive installation and operation of the facility.

In order to solve the problems in the prior art, the present invention provides a method for increasing the production of the polymer powder, reducing the content of fine particles and coarse particles, and producing a polymer powder having a high apparent specific gravity.

1 is a schematic diagram of an apparatus and process for recovering a polymer latex according to the present invention into granular powder.

<Explanation of symbols for the main parts of the drawings>

1. Water inlet

2. Polymer latex inlet

3. Coagulant Inlet

4. Heating source inlet

5. Stirrer

6. Slurry overflow tube

The present invention relates to a process for producing a polymer powder finally through a continuous stirring tank of two stages of the polymer latex prepared by emulsion polymerization to improve the coagulation step and the aging step. In more detail, the process used in the method of the present invention consists of a two-stage agitated tank connected in series, the first stirring tank is called agglomeration tank, and the second stirring tank is called a maturing tank. The flocculation tank is operated to induce particle formation by mixing the polymer latex and flocculant introduced through the pump to the top of the flocculation tank in a strong disturbance flow through the stirrer, and the aging tank increases the strength of the particles through high temperature heat treatment. Play a role.

Latex and flocculant are added to the flocculation tank, and water is added to control the amount of solids in the flocculation tank. The slurry in the coagulation tank flows into the second aging tank by overflow, and the slurry solidifies through heat treatment in the stirring tank. The slurry in the aging tank flows into the next reservoir by overflow. It is transferred to the dehydrator by a pump to obtain particles from which water has been removed. The powder passed through the dehydrator is obtained as a final granular powder through drying.

As a heating source of each stirring tank, saturated steam or unsaturated steam having a temperature of 80 to 250 ° C. and a pressure of 1 to 10 kgf / cm 2 is used, and is directly introduced into the stirring tank. The higher the temperature of the heating source, the smaller the amount of steam for maintaining each stirring vessel at a constant temperature.

This heating source is effectively dispersed to increase the effective surface area of the vapor (Vapor) should be a smooth heat transfer in the stirring tank.

The above-described goal is to stir the aggregated slurry mixed with the polymer latex and the flocculant at a constant temperature for a certain time, and during the solidification step while the slurry is stirred at a constant temperature higher than the flocculation temperature again in the next stage of aging. This can be achieved through various factors and device improvements.

As the type of flocculant, sulfuric acid, hydrochloric acid, phosphoric acid, and the like are used, and as salts, calcium chloride and magnesium sulfate are used. The heating source was added directly so as to be sufficiently dispersed. In addition, latex was introduced from the top of the coagulation tank so as to aggregate while sufficiently circulating for a predetermined time in the coagulation tank.

The stirring characteristic of the present invention is made under a disturbing flow, and has a great feature of vertical stirring. The circulating flow rate of the fluid in the agitation tank through such agitation is a very important factor. And the general aspect of circulation is downward in the vicinity of the stirrer shaft, and upward in the vicinity of the wall of the stirring vessel. This circulation flow rate is 0.01 to 2 m 3 / sec in the flocculation tank, and preferably should be operated in the range of 0.01 to 1.5 m 3 / sec.

When the agitation force is high, the shear force of the outside is increased rather than the bonding force between particles, thereby causing particle crushing to increase the content of the fine particles. However, when the stirring force is weak, the particles stagnate at the top, making continuous operation impossible.

And, when the operating temperature of each stirring tank is low, the content of fine particles is large, the apparent specific gravity is low. In addition, when the slurry content in the coagulation tank is high, the viscosity in the coagulation tank increases, making it difficult to maintain a uniform shear force as a whole. In this case, continuous operation for a long time is impossible.

In addition, when the residence time decreases, that is, when the flow rate of the input material is increased, the upper stagnation portion is formed, and it is difficult to maintain a uniform shear force as a whole.

Increasing the amount of production decreases the residence time in the coagulation bath continuously operated as the flow rate of the input latex increases, and this residence time should be made more uniform. In addition, the contact between the inlet flocculant and the latex was improved, and the agitation in the flocculation tank was improved, and the shape of the agitator in the flocculation tank and the aging tank was changed.

There is a balance between agglomeration between particles in the flocculation tank and dispersion by agitation forces, whereby the particle diameter is determined. The cohesive force is affected by the amount and temperature of the coagulant, and in the case of the dispersion force, the stirring properties and the residence time are affected.

Hereinafter, the present invention will be described in detail through Examples and Comparative Examples. The conditions and results of the examples are shown in Tables 1 and 2, and the conditions and results of the comparative examples are shown in Table 3.

The polymer latex used in the present invention is prepared by emulsion polymerization, the solid content is 30 to 45 parts by weight, the rubber content of the butadiene component is 25 to 60 parts by weight of styrene 15 to 55 parts by weight, and acrylonitrile 10 to 40 parts by weight The parts are grafted to prepare by emulsion polymerization. In the polymerization, rosin-based surfactants are used. The average particle diameter is 0.1-0.42 micrometers, and pH shows 9-11. Glass transition temperature is 80-110 degreeC.

Particle size was measured by a sieve method. 100 g of powder is weighed and placed at the top of 20, 40, 50, 100, 140, 200, mesh and vibrated for 15 minutes, and then the particle size distribution is determined as the difference between the weight of each mesh and the weight of the powder filtered through the mesh. Measure The apparent specific gravity was measured according to JIS-K-6721.

Example 1

The polymer latex recovery apparatus according to the present invention was used.

The polymer latex, flocculant and water are all transferred to the flocculation tank via a pump. 10% dilute sulfuric acid was used as the flocculant, and the slurry content was maintained at 20-30%. The residence time was 10 minutes, and the sulfuric acid flow rate was set under the condition of 1.0 to 2.5 parts by weight.

The stirrer in the coagulation tank was configured in multiple stages. Agitator diameter (d) is 35 to 75% of the total agitator diameter (T), it was operated so that the linear velocity is 2.17 m / sec. In addition, the input position of the heating source was put at 15% of the total length of the stirring vessel, and the polymer latex was put at 80% of the stirring center axis relative to the radius of the stirring vessel.

The stirrer in the aging tank consisted of multiple stages. The stirrer diameter (d) is 30 to 65% of the total stirring tank diameter (T), and this was operated so that the linear velocity is 3.4 m / sec. And the heating source was put into 30% from the bottom compared with the full length of the stirring vessel.

Under these conditions, the coagulation aging process can be stably operated continuously.

Example 2

The injection position of the latex was changed to 40% under the conditions of Example 1. The linear velocity of the stirrer in the coagulation tank is 3.5 m / sec.

Example 3

In the conditions of Example 1, the input position of the heating source was changed to 25%. And the residence time was reduced to 7 minutes.

Example 4

The loading position of the latex was changed to 40% under the conditions of Example 3. The linear velocity of the stirrer in the coagulation tank is 5.83 m / sec.

Example 5

The linear velocity is 1.2 m / sec under the conditions of Example 1. The residence time was reduced to 7 minutes.

The linear velocity of the aging stirrer was operated to be 6.7 m / sec. And, the heating source was added to 15% from the bottom relative to the entire length of the stirring vessel.

Example 6

The loading position of the latex was changed to 40% under the conditions of Example 5. The linear velocity of the stirrer in the coagulation tank is 6.05 m / sec.

Example 7

The linear velocity of the flocculation tank stirrer under the conditions of Example 5 is 2.17 m / sec. The residence time was reduced to 4 minutes.

The linear velocity of the aging stirrer was operated to be 8.3 m / sec.

Example 8

In the conditions of Example 7, the linear velocity of the coagulation tank stirrer is 1.2 m / sec, and the linear velocity of the aging tank stirrer is 13.2 m / sec.

Comparative Example 1

It carried out by changing the linear velocity of the agitator in agglomeration tank to 8.42 m / sec on the conditions of Example 1.

Comparative Example 2

It carried out by changing the input position of a heating source to 5% on the conditions of Example 1.

Comparative Example 3

In the condition of Example 1, the input position of the aging tank heating source was introduced at 5%, and the linear velocity of the aging tank stirrer was operated to be 6.8 m / sec.

Comparative Example 4

Under the conditions of Example 1 the residence time was reduced to 4 minutes.

TABLE 1

TABLE 2

TABLE 3

Claims (9)

The polymer latex obtained by grafting the polymer particles having rubber properties to emulsion polymerization, the polymer latex having a glass transition temperature of 80 ° C. to 110 ° C. is introduced into a plurality of stirring tanks connected in series, and then a coagulant is added to make the latex into a slurry and aggregated. Forming the particles, and then washing, dehydrating, and drying the solidified particles by heat treatment, wherein the polymer latex is placed in a stirring tank at 60 to 90% from the center relative to the radius of the stirring tank. A granular powder production method characterized by the above-mentioned. The method of claim 1 wherein the flocculant is sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, magnesium sulfate, calcium chloride or sodium chloride. The method for producing a polymer powder according to claim 1 or 2, wherein the amount of flocculant used is 0.5 to 5% by weight based on the total resin composition. The method of claim 1, wherein the stirring vessel comprises a multi-stage pitched paddle, and the diameter of the paddle is 30 to 60% of the diameter of the stirring vessel. The method for producing a polymer powder according to claim 4, wherein the stirring linear velocity is 0.5 to 20 m / sec, and the circulation flow rate is 0.05 to 1.4 m 3 / sec. The method for producing a polymer powder according to claim 1, wherein the residence time during formation of the flocculation slurry in the flocculation tank is 3 to 20 minutes. The method for producing a polymer powder according to claim 1, wherein the stirring tank is heated while using saturated steam or unsaturated steam having a pressure of 1 to 10 kgf / cm 2. The method for producing a polymer powder according to claim 7, wherein the position at which the heating source is introduced is introduced at a position of 20 to 40% from the lower portion relative to the entire length of the stirring vessel. a) a plurality of stirring vessels each comprising a polymer latex supply device, a flocculant supply device and a water supply device; b) an agitator installed in the agitation vessel and including a plurality of paddles having a diameter of 30 to 67% of the diameter of the agitating vessel; c) a slurry overflow tube connecting a plurality of stirring vessels; And d) a heating source capable of maintaining the stirring tank at a predetermined temperature Polymer powder production apparatus comprising a.