JP2001079831A - Twin-screw extruder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw extruder wherein a polymer solution containing high concentration volatile content can be efficiently devolatized and there exists no uselessness in terms of mechanical design and simplification of separation process can be performed by a rational design and cost reduction and energy saving can be performed. SOLUTION: In a flash devolatization region I, two relatively short auxiliary screws 2a and 2b are arranged in a V-shape above base biaxial screws 1a and 1b which are intermeshed and rotated in the same direction to make them intermesh to the twin screws 1a and 1b and a foamed body flow relaxation room 10, a shunt 15 and a flash room 14 are arranged in this order from the top below a feeding pipe 12 for a polymer provided on the upper part of an upper half divided barrel of the flash devolatization region I and gas flow rate of the volatile content separated is relaxed by the flash tank 6 provided on the upstream side of the feeding pipe 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-screw extruder used in a devolatilization step for removing volatile components such as unreacted monomers and solvents from a polymer solution in a polymer production process.

[0002]

2. Description of the Related Art Conventionally, a devolatilizing screw extruder having a flash devolatilizing area includes a meshing type co-rotating twin-screw extruder, a meshing type counter-rotating twin-screw extruder, and a pair of meshing type screw extruders. Non-meshing rotary four-screw extruder with different rotating directions composed of directional rotating twin-screw and non-meshing with different rotating directions composed of two pairs of partially meshing co-rotating twin-screw There is a four screw extruder.

[0003]

A conventional screw extruder for devolatilization including a flash devolatilization operation has a small screw flow path cross-sectional area of a polymer solution supply section, and when performing a flash devolatilization operation, has a high gas velocity. The amount of supply of the polymer solution is limited so as to suppress the generation of entrainment due to the above, and it is considered that the polymer processing capacity of the entire extruder on a dry weight basis is low.

When the flash tank is installed above the feed section of the extruder, the polymer solution is flashed from above the feed section in the flash tank, and the separated volatile components are applied to the side surface above the flash tank. The melt that is exhausted from the provided flow path and is supplied to the extruder. Such flash devolatilization is efficient, but droplets of the molten polymer tend to adhere to the inner wall of the flash tank. Therefore, the flash devolatilization performance of the flash tank is guaranteed,
Periodically stop the extruder and clean the flash tank to prevent degradation of the polymer product processed by the molten polymer that has adhered to the flash tank and degraded flowing into the screw flow path in the supply section. There is a need.

In the case of a four-screw screw extruder, when the polymer solution is fed directly to the supply section, the cross-sectional area of the screw flow path is relatively large, so that the generation of entrainment is suppressed and Although flash devolatilization ability is relatively good, it is difficult to apply and disperse additives and apply water injection devolatilization technology downstream, and for polymer melts whose volume after flashing is small,
Due to the excessive number of screws, the manufacturing cost of screws and barrels is likely to be high.

[0006] Further, since the twin screw extruder and the four screw extruder of the partially meshing type, which rotate in different directions, do not have self-cleaning properties, they accumulate in unscrewed areas in the screw flow path. The quality of the polymer product may be caused by the fact that the deteriorated polymer is easily mixed into the main stream of the molten polymer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and can efficiently devolatilize a polymer solution containing a high-concentration volatile component, and can efficiently and rationally design a mechanical design. It is an object of the present invention to provide a low-cost and energy-saving screw extruder that can simplify a separation process by using a screw extruder.

[0008]

The present invention solves the above-mentioned problems as follows.

In the twin screw extruder according to the present invention, in the flash devolatilization area, two relatively short auxiliary screws are arranged in a V-shape above the twin screw of the meshing type co-rotating base. It is characterized by being engaged with the twin screw.

It is preferable that a foam flow relaxation chamber, a flow divider and a flash chamber are arranged in this order from the top below a polymer solution supply section provided on the upper half barrel of the flash devolatilization area.

In the flash devolatilization area, the polymer solution supplied from the polymer solution supply section and brought into a foamed state by decompression is reduced in flow velocity in the foam flow relaxation chamber, and is diverted by the flow divider. The gas flow rate of the volatile components flashed and separated in the flash chamber is reduced by a flash tank provided on the upstream side of the polymer solution supply section, thereby preventing the occurrence of entrainment.

[0012]

Embodiments of the present invention will be described.

The separation or removal of volatiles from the polymer solution is performed according to a flash devolatilization mechanism when the volatile content is high and a surface renewal devolatilization or water injection devolatilization when the volatile content is relatively low. The number, arrangement and barrel shape or structure of the screws in the flash devolatilization region and the low concentration devolatilization region of the screw extruder are designed based on the polymer processing capacity in the low concentration devolatilization region.

That is, in the low-concentration devolatilization region, the surface renewal devolatilization technology and the water-injection foaming devolatilization technology can be used alone or in combination, and the kneading is applied to the mixing and dispersion of the additive in the molten polymer. Screw elements with good kneading and sealing properties, such as a ring and a ring, can be used.The advantages such as relatively small torque or specific energy required for kneading and extruding the melt and relatively small interference between screws are provided. A relatively long L / D (screw length / screw long diameter) screw design and the installation of one vent or more multi-stage vents are possible. A directional rotating twin screw and its usual barrel are used.

In the flash devolatilization area, the torque or specific energy required for extruding the melt after flashing is smaller than that required for the entire devolatilization treatment of the polymer solution. Due to the large amount of volatile matter generated in the gas, the gas flow velocity increases,
In consideration of the fact that entrainment is likely to occur, the extension of the mesh type co-rotating twin-screw of the base to the flash devolatilization area of the base takes advantage of the mesh type co-rotating twin-screw, and By adding two relatively short auxiliary screws with a negligible effect of interference between them and arranging them in a co-rotatable and V-shape in engagement with the two-axis screw of the base, the flash area The cross-sectional area of the screw flow path is almost doubled than that of the low-concentration devolatilization region.

Further, regarding flash devolatilization of a polymer solution, it is extremely difficult to reduce the concentration of volatile components therein to an equilibrium concentration, unlike the case of a low-viscosity low-molecular-weight component mixture system. That is, flushing is a very short gas-liquid separation operation. Once exposed to a low pressure atmosphere, the polymer solution heated to a permissible degradation temperature of the polymer under a certain pressure, due to extreme supersaturation, volatiles in the polymer solution take heat from the polymer solution block and rapidly To evaporate. The melt in the foamed state after flashing has a higher viscosity due to a significant drop in temperature, and still contains a high concentration of volatiles therein. In consideration of the characteristics of the flash devolatilization described above, the flash devolatilization is controlled and progresses stepwise.

That is, when a polymer solution having a high volatile concentration is supplied to the flash devolatilization section, first, the polymer solution is put into a relaxation chamber having a flow path cross-sectional area larger than the flow path cross-sectional area of the supply pipe. The vaporized volatiles are separated into both a gas phase and a foamed melt phase. The volatile matter in the gaseous phase is discharged to the flash tank by bypassing through the flow divider, and the foamed molten phase or foam is removed from the bubble cell having a reduced volatile matter concentration and the volatile matter in the bubble. The gas is in a phase separated state. The residence time of the foam in the relaxation chamber is relatively long, the temperature in the block approaches uniform, and the degree of supersaturation is increased by the heating of the inner wall of the hardware, so that the generation and growth of air bubbles proceed constantly.

Next, the foam passes through a flow divider provided with a number of slits or holes, and is diverted to a flash chamber provided below the flow dividing chamber. When passing through the slit or hole of the flow divider, the foam is subjected to a shearing force while being diverted and decompressed, so that bubbles therein are relatively uniformly collapsed from the inside to the periphery of the foam block. As a result, volatile components in the bubbles are released to the outside. In addition, the melt exposed to the low-pressure atmosphere in the flash chamber after passing through the flow divider has a large specific surface area, and the volatile matter remaining therein easily diffuses to the outside of the melt.

In this way, in the flash chamber, the entire melt is relatively uniformly concentrated and the viscosity is increased, and the cross-sectional area of the flow between the separated melt flows is relatively large. Due to the large channel cross-sectional area of the auxiliary twin-screw and the base twin-screw, the gas flow rate of the volatile component in the flash chamber is suppressed, and the generation of splashes is also suppressed.

In the flash chamber, the temperature of the melt after flashing is remarkably reduced due to evaporation of volatiles, and the twin screw of the base and the auxiliary screw rotated while meshing at the bottom of the flash chamber. In the case of the conventional twin-screw, it is quickly transported to the downstream of the flash devolatilization zone, and is heated to the barrel of the flash devolatilization area having an inner wall area of about twice the inner wall area of the barrel for the twin-screw. Since the surface area of the melt is about twice as large, free-foaming devolatilization after flash devolatilization or surface renewal devolatilization can be efficiently continued by rotation of the base twin-screw and the auxiliary twin-screw.

Further, the volatile gas generated in the flash chamber portion and the downstream region has a cross-sectional area approximately twice as large as the cross-sectional area of the conventional twin-screw flow path. When passing through the flow path of the screw and the auxiliary screw, the flow velocity can be reduced by about twice as compared with the case of the twin screw, or the allowable gas flow rate that can suppress the generation of entrainment can be doubled.

The gas of the volatile matter generated in this manner is provided upstream of the flash chamber, and the cross-sectional area of the flow passage is much larger than the total cross-sectional area of the biaxial screw and the auxiliary screw flow passage of the base. When entering the flash tank, the flow rate is significantly reduced, and even if melt droplets are generated, the gas flow rate is reduced, so that the rotating twin-screw of the base and the auxiliary screw in the flow path at the bottom of the flash tank. It is returned and sent to the downstream of the flash tank.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A twin screw extruder according to one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view of a twin-screw extruder with an auxiliary screw for enhancing flash devolatilization according to the present invention.
As shown in the figure, the entire devolatilization area of the screw extruder includes the flash devolatilization area I and other operations, such as addition and dispersion of additives, and the surface renewal devolatilization technique and the water injection foaming devolatilization technique are independent. Alternatively, it is divided into a low-concentration devolatilization region II that can be used in combination.

The flash devolatilization area I basically includes a lower half barrel 5b of the base, an upper half barrel 5a which is easy to mount and remove, a flash tank 6 mounted above the upper half barrel 5a, and a polymer solution. It is composed of hardware 9 connected below the supply pipe 12. In the devolatilization areas I and II-1, the reason why the two-part barrel is used is to make it easier to mount / detach the two-shaft screws 1a and 1b and the two auxiliary screws 2a and 2b.

The low-concentration devolatilization region II is provided with a two-shaft screw barrel II-1 adjacent to the flash devolatilization region I downstream of the flash devolatilization region for assisting screw mounting / removal, and a normal barrel connected next thereto. It consists of a twin screw barrel II-2. Further, the two-part barrel I-1 for the twin screw is provided.
Is composed of a lower half barrel 11b of the base and an upper half 11a which is easy to be attached and detached.

FIGS. 2 and 3 are views showing the configuration of a flash devolatilization area according to the present invention. FIG.
3B is a sectional side view of a main part of FIG. 3A, and FIG.
2A is a plan view of FIG. 2A, and FIG. 2B is an enlarged view of a portion A of FIG. 2A. 4 is a sectional view taken along line AA of FIG. 2, and FIG.
FIG. 7 is a sectional view taken along line BB of FIG.

As shown in FIGS. 2 to 5, in the flash devolatilization area I, the upstream portions of the base twin-screw screws 1a and 1b assembled to the shafts 3a and 3b, and the shafts 4a and 4b
4b, insertable nut 13 (see FIG. 3 (b))
The two auxiliary screws 2a and 2b fixed in the above manner are mounted in a V-shape.

The flash tank 6 has a flange 6a.
Is fixed to the upper half barrel 5a with a bolt 6b. The hardware 9 and the shunt 15 installed under the hardware 9
It is fixed to the upper half barrel 5a by a bolt 9c through a flange 9b which is easily detachable. The supply pipe 12 is fixed to the upper part of the hardware 9 by bolts 12b through a flange 12a.

The metal member 9 has a foam flow relaxation chamber 10 extending downward, and a flow divider 15 disposed below the foam flow relaxation chamber 10 is a plate-like body having many slits or holes. A flash chamber 14 is provided between the vessel 15 and the V-shaped screw. The width of the inner wall of the flash chamber 14 in the direction perpendicular to the screw axis is equal to or larger than the center distance of the biaxial screws 1a and 1b of the base.

In order to observe the operation state in the flash tank 6, an obliquely upward observing port 7 on which a sight glass 8 is installed on the side surface of the flash tank 6.
Is provided. The inner wall width of the flash tank 6 in a direction perpendicular to the screw axis is equal to or greater than the entire width of the base biaxial screws 1a and 1b.

In the flash devolatilization region I, the upper half barrel 5a is fixed to the lower half barrel 5b of the base with bolts 5c. Further, the adjacent two-part barrel II-1 for a twin screw is formed by connecting the upper half part 11a with a bolt 1
At 1c, it is fixed to the lower half barrel 11b of the base, and is fixed to the barrels 5a, 5b of the flash devolatilization area I by bolts 5d.

In order to promote the separation of volatile components from the melted and foamed polymer block whose temperature has been reduced by vaporizing the volatile components, the flash devolatilization zone I and the low concentration devolatilization zone II barrel are used. Heating medium flow paths 5e, 1
1d, the hardware 9 and the auxiliary screws 2a, 2
b split barrel for twin screw adjacent to the end of b
A structure capable of heating, for example, flow paths 9a and 11e for a heating medium are provided in the flange portion of the upper half barrel 11a of -1.

[0034]

The twin screw extruder with an auxiliary screw for flash devolatilization according to the present invention is constructed as described above. The following effects can be obtained. (A) The same high content of volatile matter is contained, and the processing capacity for a polymer solution based on the dry weight of the polymer can be significantly improved. (B) The present invention can be applied to the devolatilization treatment of a polymer solution in which the allowable concentration of volatile matter relating to the generation of entrainment is twice or more. (C) Entrainment that is likely to occur during flash devolatilization can be completely suppressed or prevented. (D) The separation step downstream of the polymer solution polymerization process can be simplified, for example, the number of flash tanks can be reduced. (E) Cost reduction of capital investment in the separation step and the post-treatment step can be achieved. (F) Energy can be saved in the separation step and the post-treatment step. (G) Space can be saved in the separation step and the post-treatment step. (H) It is possible to reduce the cost of polymer production relating to the polymer solution polymerization process.

[Brief description of the drawings]

FIG. 1 is a schematic view of a twin-screw extruder with an auxiliary screw for enhancing flash devolatilization according to the present invention.

FIGS. 2A and 2B are configuration diagrams of a flash devolatilization area, where FIG. 2A is a cross-sectional front view of a main part, and FIG.

FIG. 3 is a configuration diagram of a flash devolatilization area, and FIG.
2A is a plan view of FIG. 2A, and FIG. 2B is an enlarged view of a portion A of FIG. 2A.

FIG. 4 is a sectional view taken along line AA of FIG. 2;

FIG. 5 is a sectional view taken along line BB of FIG. 2;

[Explanation of symbols]

 1a, 1b Twin screw 2a, 2b Auxiliary screw 3a, 3b Shaft (for twin screw) 4a, 4b Shaft (for auxiliary screw) 5a Upper half barrel (for flash devolatilization area) 5b Lower half barrel (for flash 5c bolt 5d bolt 5e Heat medium flow path 6 Flash tank 6a Flange (for flash tank) 6b Bolt 7 Observation port 8 Sight glass 9 Hardware 9a Heat medium flow path 9b Flange (for metal) 9c Bolt 10 Foam flow Relaxation chamber 11a Upper half barrel (for twin screw) 11b Lower half barrel (for twin screw) 11c Bolt 11d Heat medium flow path 11e Heat medium flow path 12 Supply pipe (polymer solution supply unit) 12a Flange (supply pipe 12b Bolt 13 Nut 14 Flash chamber 15 Divider

Claims (7)

[Claims] In the flash devolatilization area (I), a meshing type co-rotating base twin-screw (1a, 1a,
Above b), two relatively short auxiliary screws (2a,
2b) are arranged in a V-shape and the twin screw (1a, 1a
b) A twin screw extruder characterized by interlocking with b). 2. The flash devolatilization area (I) is divided into two barrels so that the twin screw (1a, 1b) and the two auxiliary screws (2a, 2b) can be easily attached and detached. (5a, 5b), the barrel of the low concentration devolatilization region (II) on the downstream side adjacent thereto is a partial bisected barrel (11a, 11b), and the partial bisected barrel (11a, 11b) is usually 2. The twin screw extruder according to claim 1, wherein the barrels are connected. 3. A foam flow relaxation chamber (10) and a flow divider (15) below a polymer solution supply section (12) provided above an upper half barrel (5a) of the flash devolatilization area (I). 3. The twin-screw extruder according to claim 2, wherein the flash chamber and the flash chamber are arranged in this order from above. 4. The twin-screw extruder according to claim 3, wherein the foam flow relaxation chamber (10) is formed in a heatable hardware (9). 5. The flash chamber according to claim 3, wherein an inner wall width of the flash chamber in a direction perpendicular to a screw axis is equal to or longer than a center distance of the biaxial screw of the base. Twin screw extruder. 6. An inner wall width of a flash tank (6) provided upstream of the polymer solution supply section (12) in a direction perpendicular to a screw axis is the entire width of the base twin screw (1a, 1b). The twin screw extruder according to claim 3, characterized in that: 7. In the flash devolatilization area (I), the polymer solution supplied from the polymer solution supply section (12) and brought into a foamed state by decompression has a flow rate in the foam flow relaxation chamber (10). After being alleviated and diverted by the diverter (15), the flash chamber (1)
4. The method according to claim 3, wherein the gas flow rate of the volatile matter flashed and separated in the step (4) is reduced by a flash tank (6) provided on the upstream side of the polymer solution supply part (12). Shaft screw extruder.