JPH1158367A - Twin-screw extruder and pressure control method for twin-screw extruder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a twin-screw extruder and a pressure control method for the twin-screw extruder that can prevent the change in resin properties caused by the decomposition and crosslink of resin when air intrudes into downstream side of a gate portion in a cylinder main body of the twin-screw extruder, restrain the fluctuation of the pressure inside the cylinder main body so as to maintain the feed volume of resin constant and provide pellets in a uniform size. SOLUTION: Nitrogen gas is controlled such that it is supplied into a cylinder main body 4 from a nitrogen gas source 31 so as to increase the pressure inside the cylinder main body of a transfer section 15 to a predetermined pressure when the pressure inside the cylinder main body decreases below the predetermined pressure, while when the pressure exceeds the predetermined pressure, nitrogen gas is controlled such that it is discharged from the cylinder main body 4.

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 for melting and kneading synthetic resin powder such as polyolefin, and molding the same into pellets, and a pressure control method for the twin-screw extruder.

[0002]

2. Description of the Related Art Conventionally, for example, when a synthetic resin powder such as polyolefin is melted and kneaded to form a pellet, and the pellet is used as a plastic material for producing various molded products, a twin-screw extruder is used. Machines are often used.

[0003] As shown in FIG.
1 is an extruder 1 for feeding resin powder from a resin supply port 102.
01, and the resin powder enters between two screws 104, 104 called full flights, which are arranged in the cylinder body 103 so as to be rotatable with respect to each other in the axial direction. In the portion 105, feeding of the resin powder and residual heat are performed. And
The resin powder sent from the supply unit 105 is mixed with the kneading unit 10.
At 6, the resin is compressed and generates heat by its shear heat, and is melted and kneaded. At this time, on the downstream side of the kneading unit 106,
In order to adjust the degree of kneading of the resin in the kneading section, a gate section 107 whose opening degree can be adjusted to adjust the degree of filling in the kneading section is provided. The molten resin melted and kneaded in the kneading section 106 passes through the gate section 107, is conveyed forward by the conveying section 108, and sent to the discharge port 109 provided on the side of the cylinder main body 103. Further, the toner is pressure-fed to the downstream side by a gear pump 111 through a transport unit 110 connected to the discharge port 109. The molten resin pumped by the gear pump 111 is of a so-called underwater cut type in which a die 116 is placed in water after a foreign substance or the like is removed by a screen 112 and cut by a rotary blade 113 provided on the die surface. The pellets are formed into pellets by the pelletizer 114, and then are discharged to the outside by a pellet separation and discharge device (not shown).

[0004]

By the way, in such a twin-screw extruder 101, due to the molecular weight of the resin powder material, the number of rotations of the screw, the feed amount of the resin powder, etc.
The pressure in the vicinity of the kneading unit 106 in the cylinder body 103 may increase or decrease. In this case, in particular, when the pressure in the cylinder body 103 of the transport unit 108 becomes lower than the external pressure, external air, particularly oxygen, is supplied to the cylinder body 103 through the sealing portion of the gate unit 107.
May invade.

As described above, when oxygen enters from the outside, for example, in the case of polypropylene, resin decomposition occurs, and in the case of polyethylene, resin decomposition or cross-linking occurs, resulting in a change in physical properties. That is, when resin decomposition occurs, the generated low molecular weight substance causes odor and discoloration, while when cross-linking occurs, a high molecular weight gel-like substance is generated, so-called “fish eye” When formed into a film, foreign matters which are observed as small irregularities are generated, and the commercial value is reduced.

For this reason, although not shown, a certain amount of nitrogen gas is conventionally purged into the seal portion and the labyrinth seal portion of the gate portion 107 to prevent intrusion of oxygen. However, according to such a method, when the pressure in the cylinder body 103 is largely changed and decreased,
In addition to the purged nitrogen gas, oxygen may also enter from the outside and cause the same problem as described above. Further, the pressure fluctuation in the cylinder body 103 cannot be suppressed only by purging a certain amount of nitrogen gas in this manner, so that the resin feed amount changes, and the pelletizer 1
As a result, the supply amount of the molten resin to 14 varied, and the dimensions of the pellets were not uniform.

On the other hand, conventionally, in order to control the resin pressure in the cylinder body 103, a pressure sensor 115 is disposed near the upstream side of the gear pump 111 as shown in FIG. The suction pressure is measured, and when the suction pressure decreases, the rotation speed of the gear pump 111 is increased to increase the feed amount, and the pressure in the cylinder body 103 is reduced. A method is adopted in which the number of rotations of the gear pump 111 is reduced to reduce the feed amount, the pressure in the cylinder body 103 is increased, and a constant amount of molten resin is always fed.

However, in such a method, since the pressure of the resin is controlled, the pressure fluctuation is very large,
Further, since there is a pressure difference between the vicinity of the kneading section 106 and the vicinity of the gear pump 111, it is not possible to control the pressure independently, and it is difficult to precisely control the pressure fluctuation in the cylinder body 103.

Therefore, also in this case, the cylinder body 1
Since the pressure fluctuation in the inside of the pellet 03 could not be suppressed, the feed amount of the resin changed, and the supply amount of the molten resin to the pelletizer 114 changed, resulting in uneven dimensions of the pellets.

In view of the above-mentioned circumstances, the present invention takes into consideration the fact that air enters from a seal portion or the like downstream of a gate portion in a cylinder body of a twin-screw extruder and causes resin decomposition and cross-linking to cause physical properties of the resin. Does not change, and the pressure fluctuation in the cylinder body can be suppressed, and the resin feed amount is constant. As a result, the molten resin can be stably supplied to the pelletizer at a constant supply amount. It is an object of the present invention to provide a twin-screw extruder and a method of controlling the pressure of the twin-screw extruder that can be performed without causing variation in the dimensions of the pellets.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in order to achieve the above-mentioned objects and objects of the prior art, and a twin-screw extruder according to the present invention comprises a resin powder extruder. A resin supply port for supplying the resin into the cylinder body, and a resin powder supplied from the resin supply port are arranged so as to be axially rotatable in the cylinder body of the extruder in order to melt and knead the resin powder. Biaxial screw, melted by the screw, in order to form a molten resin kneaded into pellets, comprising a pelletizer disposed downstream of the screw, the cylinder body, the resin powder A supply unit that performs feeding and residual heat, a kneading unit that melts and kneads the resin powder sent from the supply unit, and is disposed downstream of the kneading unit, and adjusts a kneading degree of the resin in the kneading unit. In order to adjust the feed amount from the kneading unit to the pelletizer, and a throttling means, disposed between the kneading unit of the screw and the pelletizer, melted in the kneading unit, the molten resin kneaded to the pelletizer. In a twin-screw extruder equipped with a pumping means for pumping, on the downstream side of the throttle means of the cylinder body, supply nitrogen gas into the cylinder body or discharge excess gas from inside the cylinder body, Gas supply / discharge control means for controlling the pressure in the cylinder body to a constant pressure is connected.

Further, in the twin-screw extruder of the present invention, the gas supply / discharge control means includes a pressure detection means for detecting a pressure in the cylinder body, and the pressure detected by the pressure detection means is: When the pressure is lower than a predetermined pressure, nitrogen gas is supplied from the nitrogen gas supply source into the cylinder main body, and when the pressure detected by the pressure detection means exceeds a predetermined pressure, extra nitrogen is supplied from the cylinder main body. The gas is configured to be discharged to the outside.

Further, according to the pressure control method for a twin-screw extruder of the present invention, in the twin-screw extruder having the above-described structure, nitrogen gas is supplied into the cylinder main body downstream of the throttle means of the cylinder main body. An extra gas is discharged from the cylinder body to control the pressure in the cylinder body to a constant pressure.

The pressure control method for a twin-screw extruder according to the present invention detects the pressure in the cylinder main body, and when the detected pressure falls below a predetermined pressure, the nitrogen gas is supplied from a nitrogen gas supply source. While supplying gas into the cylinder body, when the detected pressure exceeds a predetermined pressure,
An extra gas is discharged from the cylinder body to the outside.

With this configuration, when the pressure in the cylinder main body is lower than the external pressure, nitrogen gas can be introduced to maintain the pressure in the cylinder main body at a constant pressure. If the cylinder pressure is increased beyond a certain pressure due to a gas such as nitrogen gas accompanying the resin powder material supplied to the
By discharging nitrogen gas from the cylinder body, the pressure inside the cylinder body can be maintained at a constant pressure.

Therefore, the pressure fluctuation in the cylinder main body can be suppressed and the pressure can be maintained at a constant pressure, so that the pressure in the cylinder main body is reduced, and a portion near the downstream of the gate portion in the cylinder main body of the twin-screw extruder is provided from a seal portion or the like. Air does not enter, causing resin decomposition or cross-linking, which does not change the physical properties of the resin.Furthermore, since the pressure in the cylinder body can be suppressed, the feed amount of the resin becomes constant, and as a result, The molten resin can be stably supplied to the pelletizer at a constant supply amount, and there is no variation in the dimensions of the pellet.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments (examples) of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a first embodiment of an extruder body of a twin-screw extruder according to the present invention, and FIG. 2 is a longitudinal section of a pellet manufacturing machine body of a first embodiment of a twin-screw extruder of the present invention. FIG. 3 is a schematic plan view of the entire twin-screw extruder according to the first embodiment of the present invention.

In FIGS. 1 and 2, reference numeral 1 indicates the twin screw extruder of the present invention as a whole. The twin-screw extruder 1 has an extruder main body 2 as shown in FIG. 1 and a downstream side of the extruder main body 2 as shown in FIG. And a pellet making machine main body 3 connected in a letter shape.

The extruder main body 2 includes a cylinder main body 4, and as shown in FIG.
Two substantially cylindrical cylinder chambers 5 and 6 are formed. In these cylinder chambers 5 and 6, biaxial screws 7 and 8 called full flight are rotatably arranged in the cylinder body 4 via bearings 9 respectively. These screws 7 and 8 are driven by a motor (not shown), are provided on the screws 7 and 8, and are driven to rotate in opposite directions by gears 10 meshing with each other as shown by arrows. I have.

The cylinder body 4 is made of, for example, a synthetic resin powder such as polyolefin such as polyethylene or polypropylene produced by a polymerization apparatus, and a hopper 1.
1, and thereafter, a resin supply port 12 for supplying the resin into the cylinder body 4 of the extruder 1 is provided.

A resin supply port 12 is provided in the cylinder body 4.
A supply unit 12 is provided in which the supplied resin powder is sent to the downstream side by the rotation of the screws 7 and 8, and the residual heat is generated by a heater provided in a cylinder body (not shown).

On the downstream side of the supply section 12, the groove depth of the screws 7, 8 is reduced so that the two screws 7, 8
Between them, there is provided a kneading unit 13 for compressing the resin sent from the supply unit 12 to generate heat by the shearing heat, and melting and kneading the resin. Further, on the downstream side of the kneading section 13, a gate section 14 whose opening degree can be adjusted to adjust the filling degree in the kneading section 13 is provided in order to adjust the kneading degree of the resin in the kneading section 13.

Further, on the downstream side of the kneading section 13, there is formed a conveying section 15 for conveying the molten resin melted and kneaded in the kneading section 13 and having passed through the gate section 14 to the downstream side. A discharge port 16 is provided below the cylinder body 4 of the transfer section 15, and a transfer pipe 17 is connected to the discharge port 16, and the molten resin discharged through the discharge port 16 is supplied to the discharge port 16.
It is sent to a gear pump 18 connected to the transport pipe 17.

The gear pump 18 is configured to feed the molten resin conveyed by the conveying pipe 17 to the downstream side of the gear pump 18 by gear members 19 and 20 rotating in opposite directions. The molten resin pressure-fed by the gear pump 18 is supplied to a pelletizer 22 after foreign substances and the like are removed by a screen 21 formed of a mesh or the like.

This pelletizer is a so-called underwater cut type pelletizer in which a die 23 is placed in water and a resin is cut on the die surface in water by a rotary blade 24 driven by a motor 25. It is formed into a pellet. The synthetic resin formed into a pellet shape by the pelletizer 22 is carried out to the outside by a separating and carrying out device (not shown).

By the way, in such a twin-screw extruder 1,
Properties such as molecular weight of resin powder material, screw rotation speed,
The pressure in the vicinity of the kneading portion 13 in the cylinder body 4 may increase or decrease due to the feed amount of the resin powder or the like. In this case, as described above, particularly, the pressure in the cylinder body 4 is reduced by the external force. If the pressure is lower than the pressure, external air, particularly oxygen, enters the cylinder body 4 through the sealing portion of the gate portion 14 to cause resin decomposition or cross-linking, thereby causing a change in physical properties.

Therefore, the extruder 1 of the present invention is provided with a gas supply / discharge control means 40. That is, an opening 26 is provided in the transfer section 15 of the cylinder body 4, and an opening box 27 is formed in the opening 26.
7 is connected to a gas supply / discharge line 28. The gas supply / discharge line 28 is connected to a nitrogen gas supply source 31 by a nitrogen gas introduction control valve 30 via a branch line 29. On the other hand, the other end of the gas supply / discharge line 28 is open to the outside via a gas discharge control valve 32.

A pressure sensor 33 is provided inside the opening box 27 so that the pressure in the cylinder 4 of the transport unit 15 is detected by a pressure gauge 34 connected to the pressure sensor 33. Has become. Then, the pressure value detected by the pressure gauge 34 is supplied to the pressure control unit 35.
To be entered.

On the other hand, from the pressure control unit 35, a line 36,
37, the nitrogen gas introduction control valve 3
0, a signal for controlling the opening and closing of the gas discharge control valve 32 is sent.

More specifically, the pressure controller 35 controls the pressure as shown in FIG. First, in step S1, the type and amount of resin powder to be supplied, the number of rotations of the screws 7 and 8, and the number of rotations of the gear pump 18 are input.

In step S2, based on these input values, the type of resin powder, the supply amount, the number of rotations of the screws 7 and 8, and the gear pump 18 are stored in advance in a database stored in the memory of the pressure control unit 35. The optimal pressure value P in the transport unit 15 stored in advance is read according to the rotation speed. This optimum pressure value is set to a predetermined pressure such that the pressure in the cylinder body 4 of the transport unit 15 is higher than the external pressure.

Then, in step S3, the pressure in the cylinder body 4 of the transport section 15 is measured by the pressure gauge 34 to obtain an actually measured pressure value p. In step S4, it is compared whether the actually measured pressure value p and the optimum pressure value P are the same value, and whether the pressure value is within an allowable range. When the measured pressure value p and the optimum pressure value P are not the same value or deviate from the allowable range, the process proceeds to step S5. On the other hand, if the measured pressure value p and the optimum pressure value P are the same, or if they are within the allowable range, there is no need for pressure control, and the process ends.

In step S5, it is determined whether or not the actually measured pressure value p is larger than the optimum pressure value P. That is, when the actually measured pressure value p is larger than the optimum pressure value P, the process proceeds to step S6, and in step S6, the nitrogen gas introduction control valve 30 is closed, and the nitrogen gas supply source 31 The introduction of the nitrogen gas into the cylinder body 4 is stopped, and the gas discharge control valve 32 is opened.
A gas such as nitrogen gas existing in the cylinder main body is discharged to the outside, and the pressure in the cylinder main body 4 is controlled to be reduced.

Conversely, if the measured pressure value p is smaller than the optimum pressure value P, the process proceeds to step S7, and the process proceeds to step S7.
, The gas discharge control valve 32 is closed and the nitrogen gas introduction control valve 30 is opened to introduce nitrogen gas from the nitrogen gas supply source 31 into the cylinder body 4 of the transport unit 15. The pressure is controlled to increase.

After the steps S6 and S7, the process returns to the step S3 again, and the steps S3 to S3 are repeated.
S6 is repeatedly performed. In this case, step S3 can be performed continuously or at a preset timing.

As described above, in the extruder 1 of the present invention, when the pressure in the cylinder main body falls below the predetermined pressure so that the pressure in the cylinder main body 4 of the conveying section 15 becomes the predetermined pressure, the nitrogen gas supply is performed. Nitrogen gas is supplied from a source into the cylinder body, and when the pressure exceeds a predetermined pressure, control is performed such that a gas such as nitrogen gas is discharged from the cylinder body to the outside.

Accordingly, since the pressure fluctuation in the cylinder body can be suppressed and maintained at a constant pressure, the pressure in the cylinder body decreases, and a portion near the downstream of the gate portion in the cylinder body of the twin-screw extruder is provided from a seal portion or the like. It is possible to prevent the invasion of air and the change in the physical properties of the resin due to the decomposition or crosslinking of the resin.

Furthermore, since the fluctuation of the pressure in the cylinder body can be suppressed, the feed amount of the resin is constant, and as a result, the molten resin can be stably supplied to the pelletizer at a constant supply amount. Variations in pellet dimensions and production volume can be prevented.

In this case, in addition to such control, a method of purging a fixed amount of nitrogen gas into the seal portion and the labyrinth seal portion of the gate portion 14 to prevent oxygen from entering as in the related art is also used. Of course, it is possible. Further, a pressure sensor is disposed near the upstream side of the gear pump 18 to measure the suction pressure of the molten resin. When the suction pressure decreases, the rotation speed of the gear pump 18 is increased to increase the feed amount. When the suction pressure increases while the pressure in the cylinder body 4 is decreased, the rotation speed of the gear pump 18 is reduced to reduce the feed amount, and the pressure in the cylinder body 4 is increased to a certain amount. Of course, it is also possible to use together the method of controlling so that the molten resin is fed.

In this embodiment, the gate section 14
Although the filling degree in the kneading section 13 is adjusted, an orifice may be used instead of the gate section 14. Further, the opening 2 is provided in the cylinder body of the transport section 15.
6, the opening box 27 is formed in the opening 26, but if a gas supply / discharge line 28 is connected using a vent box provided in a conventional extruder,
Since there is no need to separately form the opening box 27, manufacturing costs and the like can be reduced.

In the first embodiment, as shown in FIG. 3, the extruder main body 2 and the pellet manufacturing machine main body 3 connected in a flat L-shape on the downstream side of the extruder main body 2 are provided. However, as shown in FIG. 5, it is of course possible to apply the present invention to the extruder 1 in which the extruder main body 2 and the pellet maker main body 3 are connected linearly.

Further, as shown in FIG. 6, the present invention can be applied to an extruder of a type in which molten resin is supplied to a pelletizer 22 by an extruder 18 'instead of a gear pump on the downstream side of the extruder main body 2. It is possible.

[0043]

As described above, according to the present invention,
When the pressure in the cylinder main body falls below the predetermined pressure so that the pressure in the cylinder main body of the transfer section becomes the predetermined pressure, nitrogen gas is supplied from the nitrogen gas supply source into the cylinder main body and the predetermined pressure is reduced. If it exceeds, control is performed such that a gas such as nitrogen gas is discharged from the cylinder body to the outside.

Therefore, since the pressure fluctuation in the cylinder body can be suppressed and maintained at a constant pressure, the pressure in the cylinder body decreases, and the air from the seal portion near the gate in the cylinder body of the twin-screw extruder decreases. To prevent the resin from decomposing or cross-linking to change the physical properties of the resin.

In addition, since the fluctuation of the pressure in the cylinder body can be suppressed, the feed amount of the resin becomes constant, and the molten resin can be stably supplied to the pelletizer at a constant supply amount, and the size and the size of the pellet can be reduced. There is no variation in production volume.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a first embodiment of an extruder main body of a twin-screw extruder according to the present invention.

FIG. 2 is a longitudinal sectional view of a pellet making machine main body of a first embodiment of a twin-screw extruder of the present invention.

FIG. 3 is a schematic plan view of the entire twin-screw extruder according to the first embodiment of the present invention.

FIG. 4 is a flowchart illustrating a control method of a gas supply / discharge control unit according to the present invention.

FIG. 5 is a schematic view showing another embodiment of the twin-screw extruder of the present invention.

FIG. 6 is a schematic view showing another embodiment of the twin-screw extruder of the present invention.

FIG. 7 is a schematic view of a conventional twin-screw extruder.

[Explanation of symbols]

 1 ··· Twin screw extruder 2 ··· Extruder body 3 ··· Pelletizing machine body 7 and 8 · Screw 12 ··· Supply section 13 ··· Kneading section 14 ··· ··· Gate unit 15 ··· Transport unit 16 ··· Outlet 18 ··· Gear pump 23 ··· Pelletizer 27 ··· Opening box 28 ··· Gas supply / discharge line 30 ··· · Nitrogen gas introduction control valve 31 ··· Nitrogen gas supply source 32 ··· Gas discharge control valve 34 ··· Pressure gauge 35 ··· Pressure control unit 40 ··· Gas supply and discharge control means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshihiro Okano 3 Chigusa Coast, Ichihara City, Chiba Prefecture Inside Mitsui Petrochemical Engineering Co., Ltd. Petrochemical Engineering Co., Ltd. (72) Inventor Norio Hattori No. 3, Chigusa Coast, Ichihara-shi, Chiba Mitsui Petrochemical Engineering Co., Ltd.

Claims (4)

[Claims] A resin supply port for supplying the resin powder into a cylinder body of the extruder; and a shaft provided in the cylinder body of the extruder for melting and kneading the resin powder supplied from the resin supply port. A biaxial screw disposed so as to be rotatable mutually in the direction, and a pelletizer disposed downstream of the screw in order to form a molten resin that has been melted and kneaded with the screw into a pellet shape. A supply unit for feeding and preheating the resin powder; a kneading unit for melting and kneading the resin powder sent from the supply unit; and a kneading unit disposed downstream of the kneading unit. Throttle means for adjusting the feed amount from the kneading section to the pelletizer, in order to adjust the kneading degree of the resin in the section, disposed between the kneading section of the screw and the pelletizer. Wherein the molten resin melted and kneaded in the kneading section is provided with a pumping means for pumping the molten resin to a pelletizer. Nitrogen gas is supplied to the cylinder main body downstream of the throttle means of the cylinder main body. A twin-screw extruder characterized in that a gas supply / discharge control means for supplying gas into the cylinder or discharging extra gas from the cylinder body and controlling the pressure in the cylinder body to a constant pressure is connected. 2. The gas supply / discharge control means includes a pressure detection means for detecting a pressure in the cylinder main body. When the pressure detected by the pressure detection means falls below a predetermined pressure, nitrogen gas Nitrogen gas is supplied from a gas supply source into the cylinder body, and when the pressure detected by the pressure detecting means exceeds a predetermined pressure, an extra gas is discharged from the cylinder body to the outside. The twin-screw extruder according to claim 1, wherein 3. A resin supply port for supplying the resin powder into the cylinder body of the extruder; and a shaft inside the cylinder body of the extruder for melting and kneading the resin powder supplied from the resin supply port. A biaxial screw disposed so as to be rotatable mutually in the direction, and a pelletizer disposed downstream of the screw in order to form a molten resin that has been melted and kneaded with the screw into a pellet shape. A supply unit for feeding and preheating the resin powder; a kneading unit for melting and kneading the resin powder sent from the supply unit; and a kneading unit disposed downstream of the kneading unit. Throttle means for adjusting the feed amount from the kneading section to the pelletizer, in order to adjust the kneading degree of the resin in the section, disposed between the kneading section of the screw and the pelletizer. A molten resin melted and kneaded in the kneading section, a pressure control means of a twin-screw extruder comprising a pressure feeding means for pressure feeding to a pelletizer, wherein the cylinder body is downstream of the squeezing means. Supplying a nitrogen gas into the cylinder body or discharging extra gas from the cylinder body to control the pressure in the cylinder body to a constant pressure. 4. A pressure in the cylinder body is detected, and when the detected pressure is lower than a predetermined pressure, a nitrogen gas is supplied from a nitrogen gas supply source into the cylinder body, and The pressure control method for a twin-screw extruder according to claim 3, wherein when the applied pressure exceeds a predetermined pressure, excess gas is discharged from the cylinder body to the outside.