twin-screw extruder

Abstract

To provide a twin-screw extruder, especially a conical twin-screw extruder and a parallel twin-screw extruder, which can prevent material from clogging in a drain port while maintaining or improving the efficiency of water squeeze discharge from water-containing material.SOLUTION: The present invention relates to a conical twin-screw extruder and a parallel twin-screw extruder characterized in that: a feed port 3 is provided at the rear side of a casing 2, and a discharge port 4 is provided at the tip; two screws 7 are arranged in the casing 2 so that the distance between the shafts becomes progressively narrower from the feed port 3 side to the discharge port 4 side; a drain port 10 is provided in a rear end wall 11 for discharging water produced by pressing raw material out of the casing 2; and the drain port 10 is located above the lowest end of the rear end wall 11.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a twin-screw extruder for squeezing a water-containing raw material, and more particularly to a conical twin-screw extruder and a parallel twin-screw extruder.

Background Art

[0002] Conical twin-screw extruders for squeezing and dehydrating water-containing raw materials are described in Patent Documents 1 and 2. Also, parallel twin-screw extruders for squeezing and dehydrating water-containing raw materials are described in Patent Documents 3 and 4.

[0003] The raw materials of twin-screw extruders are often in the form of powder, pellets, spheres, etc., and the raw materials often have viscosity. Therefore, in conventional conical twin-screw extruders, parallel twin-screw extruders, etc., the drain openings were clogged with raw materials, and it was necessary to frequently stop the operation and perform cleaning. Also, raw materials may be discharged from the drain openings, which may lead to a decrease in yield and deterioration of quality stability.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a twin-screw extruder, particularly a conical twin-screw extruder and a parallel twin-screw extruder, which can prevent clogging of the drain opening while maintaining or improving the efficiency of squeezing and discharging water from a water-containing raw material. Means for solving the problem

[0006] As a result of diligent research, the inventors of the present invention have completed the present invention based on the finding that the above-mentioned problems can be solved by taking the following measures for a twin-screw extruder.

[0007] The following first and second inventions relate to twin-screw extruders, and in preferred embodiments, inventions have been made for conical twin-screw extruders; however, the present invention is not limited to conical twin-screw extruders.

[0008] The first invention is a conical twin-screw extruder for compressing water-containing raw materials, comprising a casing having a discharge port for kneaded material at its front and a raw material inlet at its rear, and two conical screws installed inside the casing, with a drain port provided in the casing, characterized in that the lowest end of the drain port is located above the lowest end inside the casing. Preferably, the drain port is located on the rear end wall of the casing or at the rear of the casing.

[0009] In one aspect of the first invention, the drain outlet is not provided with a solid-liquid separation means.

[0010] In one aspect of the first invention, the input port is spaced apart from the rear end wall of the casing toward the front end of the casing.

[0011] In one aspect of the first invention, a seal ring is provided on the screw at a position rearward of the rear end of the inlet.

[0012] The second invention is a conical twin-screw extruder for compressing water-containing raw materials, comprising a casing having a discharge port for kneaded material at its front and a raw material inlet at its rear, and two conical screws installed inside the casing, characterized in that a portion of the flight of the screws is missing from a part of the flight that is closer to the front end than the front end of the inlet.

[0013] In one aspect of the second invention, the missing portion has a shape that extends from the outer edge of the flight toward the screw axis.

[0014] In one aspect of the second invention, the gap between the casing and the screw flight narrows as it moves from the inlet to the discharge port.

[0015] The parallel twin-screw extruder of the third invention is a parallel twin-screw extruder for compressing water-containing raw materials, comprising a casing having a discharge port for kneaded material at its front end and a raw material inlet at its rear end, and two parallel screws installed inside the casing, characterized in that no water discharge opening is provided between the inlet and the discharge port.

[0016] In one aspect of the third invention, the casing has a rear end wall or a drain port between the rear end wall and the inlet. [Effects of the Invention]

[0017] According to the twin-screw extruder of the present invention, the efficiency of water discharge from the water-containing raw material is maintained or improved, while preventing (including suppressing) clogging of the drain port with raw material.

[0018] In other words, according to the conical twin-screw extruder of the first invention, the lowest point of the drain port is located above the lowest point of the casing, and water accumulated at the rear of the casing is discharged by overflowing from the drain port. Since the lowest point of the drain port is located above the lowest point inside the casing, it is difficult for the raw material near the bottom of the rearmost part of the casing to reach the drain port, thus preventing the drain port from becoming blocked by the raw material.

[0019] According to the conical twin-screw extruder of the second invention, since the flight is provided with a defect, the water generated by the compression moves backward through the defect, and the compressed water is smoothly discharged from the drain port.

[0020] In the casing of the parallel twin-screw extruder of the third invention, since there is no opening for water discharge in the range from the inlet to the outlet, blockage of the opening in this range does not occur.

Brief Description of the Drawings

[0021] [Figure 1] It is a longitudinal sectional view of a conical twin-screw extruder according to an embodiment of the first invention. [Figure 2a] It is a horizontal sectional view of the conical twin-screw extruder of FIG. 1. [Figure 2b] It is a longitudinal sectional view of a conical twin-screw extruder according to another embodiment of the first invention. [Figure 2c] It is a horizontal sectional view of the conical twin-screw extruder of FIG. 2b. [Figure 3] It is a longitudinal sectional view of a conical twin-screw extruder according to another embodiment of the first invention. [Figure 4] It is a longitudinal sectional view of a conical twin-screw extruder according to an embodiment of the second invention. [Figure 5] It is a schematic cross-sectional view in a direction perpendicular to the axial center line of the screw of the conical twin-screw extruder of FIG. 4. [Figure 6] It is a schematic cross-sectional view in a direction perpendicular to the axial center line of the screw of the conical twin-screw extruder of FIG. 4. [Figure 7] It is a longitudinal sectional view of a conical twin-screw extruder according to another embodiment of the second invention. [Figure 8] It is a longitudinal sectional view of a parallel twin-screw extruder according to an embodiment of the third invention.

Modes for Carrying Out the Invention

[0022] [Embodiment of the First Invention] FIG. 1 is a longitudinal sectional view of a conical (conical) twin-screw extruder 1 for squeezing and dehydrating a water-containing raw material such as a water-containing thermoplastic elastomer, rubber, resin, etc., and FIG. 2 is a horizontal sectional view thereof.

[0023] This conical twin-screw extruder 1 has a casing 2. A rear end wall 11 is provided at the rear end of the casing 2. A raw material inlet 3 for supplying water-containing raw material is provided on the upper surface of the rear side of the casing 2, and a discharge port 4 for extruding the dewatered raw material is provided at the front end.

[0024] Inside the casing 2 are two screws 7, which transport and compress the water-containing raw material introduced from the inlet 3, arranged horizontally adjacent to each other. Each screw 7 has a rotor shaft 5 and helical flights 6 that rise from the outer circumference of the rotor shaft 5.

[0025] The two rotor shafts 5 are arranged such that the distance between them gradually decreases from the inlet 3 side to the discharge port 4 side. The outer diameter of the rotor shafts 5 and the outer diameter of the flights 6 are formed to decrease from the inlet 3 side to the discharge port 4 side.

[0026] The rotor shafts 5 of the two screws 7 are positioned such that the angle between their axes is in the range of 10 to 40 degrees. The two screws 7 are positioned so that the flights 6 are meshed together.

[0027] The rotor shaft 5 of each screw 7 is cantilevered to the rear end wall 11 of the casing 2 on its larger diameter side, and the drive unit 8 is connected to it.

[0028] The drive unit 8 rotates the two rotor shafts 5 in opposite directions. The direction of rotation of the rotor shafts 5 is such that the raw material fed in from the input port 3 is fed between the two screws 7, 7.

[0029] In this embodiment, one rotor shaft 5 is directly driven by the drive unit 8, and the other rotor shaft 5 is connected by a bevel gear 9 and rotated in the opposite direction. However, the drive system is not limited to this configuration.

[0030] A drain port 10 is provided in the rear end wall 11 for discharging water produced by pressing the raw material to the outside of the casing 2. The lowest end of the drain port 10 is located above the lowest end of the rear end wall 11.

[0031] The drain port 10 has an opening of a size that allows some of the raw material to pass through. In this embodiment, it is not necessary to provide solid-liquid separation means such as a screen in the drain port 10. It is preferable that the gap between the outer circumference of the flight 6 and the inner surface of the casing 2 be narrower than the diameter of most of the raw material. This ensures that most of the raw material is transported from the inlet 3 side to the discharge port 4 side. Even if the raw material passes through the gaps between the flights 6 and accumulates on the bottom surface of the casing 2 near the drain port 10, the rotating flights 6 will scoop up the raw material and move it towards the discharge port. Therefore, by maintaining an appropriate rotation speed of the screw 7 in relation to the amount of raw material supplied from the inlet 3, leakage of raw material from the drain port 10 is suppressed. This is because the specific gravity of the raw material is greater than that of water.

[0032] The distance between the outer circumference of flight 6 and the inner surface of casing 2 is preferably 5 mm or less, more preferably 1 mm or less, and even more preferably 0.5 mm or less. This prevents the raw material from moving from the inlet 3 to the drain outlet 10 and transports it to the discharge outlet 4 by the screw 7.

[0033] In conventional conical twin-screw extruders, the drain port is provided with, for example, a wedge wire screen, a perforated plate, a mesh, or a cloth; however, in this embodiment, it is preferable not to install such a solid-liquid separation means.

[0034] The lower part of the inner surface of the casing 2 has an upward slope from the rear end wall 11 towards the discharge port 4.

[0035] In this conical twin-screw extruder, water-containing raw material is fed in through the inlet 3 and transported toward the discharge port 4 while being compressed by the screw 7. The raw material accumulated on the lower rear surface of the casing 2 is scraped up by the flight 6 of the rotating conical screw 7 and transported to the front of the casing 2 where it is compressed. The compressed water flows backward along the slope of the lower surface of the casing 2 and is discharged from the drain port 10 on the rear end wall 11. In this way, the water generated by compression and the raw material can be efficiently dewatered by reversing their flow directions.

[0036] In this embodiment, the drain port 10 is provided above the lowest end of the rear end wall 11 (the point where the inner surface of the rear end wall 11 and the rearmost and lowest part of the inner surface of the casing 2 intersect). The lowest end of the drain port 10 is located above the lowest end of the rear end wall 11. Preferably, the drain port 10 is provided so that its lowest end is located 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more above the lowest end of the rear end wall 11, and is not particularly limited, but preferably within a range of 200 mm or less, more preferably 100 mm or less. As a result, since the raw material has a higher specific gravity than water (pressed water), it sinks in the pressed water, and only the pressed water is selectively discharged from the drain port. Note that if the drain port is provided at the lowest end of the rear end wall 11 of the casing, the drain port is more likely to be blocked by the raw material, making it difficult to discharge the pressed water.

[0037] If the height of the drain port 10 is too high, the water level of the compressed water accumulated in the casing 2 will reach the lower edge of the discharge port 4, and water will be discharged from the discharge port 4 along with the raw material. Therefore, it is preferable that the level of the lower edge of the opening of the drain port 10 be lower than the level of the lower edge of the discharge port 4.

[0038] The preferred positioning height of the drain outlet 10 depends on the size of the casing 2; a higher position is preferred when the casing 2 is large, and a lower position is preferred when the casing 2 is small or the raw material diameter is small.

[0039] The conical twin-screw extruder of this embodiment can be suitably used with screw diameters (rear end diameters) ranging from 100 mm to 500 mm.

[0040] In this embodiment, by not providing a solid-liquid separation means at the drain port 10, blockage of the drain port 10 is prevented even when the raw material reaches the drain port 10.

[0041] In this embodiment, it is preferable that the raw material inlet 3 is located at a predetermined distance forward from the rear end wall 11. By having the inlet 3 located forward of the rear end wall 11 and the drain outlet 10 located on the rear end wall 11, the flow of water produced by compression and the flow of raw materials can be separated.

[0042] Furthermore, because the input port 3 is separated from the rear end wall 11, the raw material introduced into the casing 2 from the input port 3 is prevented from directly reaching the drain port 10, allowing for efficient dewatering of the raw material.

[0043] The distance between the rear end of the inlet 3 and the rear end wall 11 is preferably 10 mm or more, more preferably 15 mm or more, and especially preferably 20 mm or more. There is no particular upper limit to this length, but since it is necessary to secure an area in which the raw material is compressed between the screw 7 and the casing 2, it is preferably 1000 mm or less for a conical twin-screw extruder with a screw diameter of 200 mm.

[0044] The preferred distance between the rear end of the input port 3 and the rear end wall 11 depends on the size of the casing 2; a longer distance is preferable when the casing 2 is large, and a shorter distance is preferable when the casing 2 is small, etc.

[0045] In one aspect of the first invention, the distance between the rear end of the inlet 3 and the rear end wall 11 is such that, for a flight 6 having N strands, a screw flight with a radius of 360 / N° can exist between the rear end of the inlet 3 and the rear end wall 11. This ensures that the raw material comes into contact with the screw flight and is transported to the discharge port 3 before reaching the drain port. The number of strands in N refers to the number of helices constituting the screw flight being N sets.

[0046] In the embodiments shown in Figures 1 and 2, the drain port 10 is provided on the rear end wall 11, but it may also be provided on the casing 2. An example of such a conical twin-screw extruder 1' is shown in Figures 2b and 2c.

[0047] In this conical twin-screw extruder 1', drain ports 10', 10' are provided on the lower rear surface of the casing 2, slightly above the lowest point of the casing 2. The distance between the rear edge of the drain port 10' and the inner surface of the rear end wall 11 on the inner surface of the casing 2 is preferably 1 mm or more, particularly 3 mm or more, and the front edge of the drain port 10' is preferably behind the rear edge of the inlet 3. By not having a drain port below the inlet 3, it is possible to prevent the problem of raw material flowing directly into the drain port and blocking it when raw material is fed in. Since the raw material collects on the lower surface of the casing 2 and moves to the rear, in this invention, no drain port is provided on the lower surface of the casing 2, even if not at the very bottom of the casing 2.

[0048] In this embodiment as well, the drain port 10 is provided such that its lowest point (the lowest point of the drain port 10' on the inner surface of the casing 2) is located above the lowest point of the rear end wall 11 (the part where the inner surface of the rear end wall 11 and the last and lowest part of the inner surface of the casing 2 intersect), more preferably 5 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more, and although not particularly limited, preferably 200 mm or less, more preferably 100 mm or less. As a result, since the raw material has a higher specific gravity than water (pressed water), it sinks in the pressed water, and only the pressed water is selectively discharged from the drain port.

[0049] The other components of this conical twin-screw extruder 1' are the same as those of the conical twin-screw extruder 1, and other reference numerals in Figures 2b and 2c indicate the same parts as in Figures 1 and 2a.

[0050] Figure 2b is a longitudinal cross-sectional view of the same section as in Figure 1, and Figure 2c is a horizontal cross-sectional view of the same section as in Figure 2a. In Figures 2b and 2c, screws 6 and 7 are shown with a portion of their base end cut out to clearly indicate the drain port 10', but the actual screws 6 and 7 do not have such cutouts. The actual shape of screws 6 and 7 is the same as that of screws 6 and 7 in Figures 1 and 2a.

[0051] Figure 3 is a longitudinal cross-sectional view of a conical twin-screw extruder 1A according to another embodiment of the first invention.

[0052] In this embodiment, a seal ring 12 is provided on the screw 7 located in the section from the rear end of the inlet 3 to the rear end wall 11. The other components of the conical twin-screw extruder 1A in Figure 3 are the same as those of the conical twin-screw extruder 1 described above, and the same reference numerals indicate the same parts.

[0053] In this conical twin-screw extruder 1A, the raw material fed in is transported to the discharge port 3 by the screw 7 without reaching the drain port 10, and the raw material can be efficiently dewatered.

[0054] The seal ring 12 seals the surfaces that would be created if the internal space of the casing 2 were virtually cut at a cross-section angled between 45° and 135° with respect to the axis of the screw 7 or the bottom surface of the casing 2. Preferably, the seal ring 12 seals the surfaces that would be created if the internal space were virtually cut at a cross-section perpendicular to the axis of the screw 7.

[0055] The distance between the outer circumference of the seal ring 12 and the inner surface of the casing 2 is preferably 10 mm or less, more preferably 5 mm or less, even more preferably 1 mm or less, and particularly preferably 0.5 mm or less. This prevents the raw material from moving behind the seal ring 12 and transports it to the discharge port 4 by the screw 7.

[0056] The preferred range of the gap between the outer circumference of the seal ring 12 and the inner surface of the casing 2 depends on the size of the conical twin-screw extruder 1A. A wider gap is preferable when the conical twin-screw extruder 1A is large or the raw material diameter is large, and a narrower gap is preferable when the conical twin-screw extruder 1A is small or the raw material diameter is small. In this embodiment, the screw diameter of the conical twin-screw extruder 1A is preferably between 100 mm and 500 mm.

[0057] <Reference example 1> The test was conducted using EM Giken's CF-1V conical twin-screw extruder. The screw diameter of the CF-1V is 160 mm.

[0058] A 9mm wide gap was created at the bottom of the rear end wall of this conical twin-screw extruder, and a dewatering test was conducted using this as a drain outlet. The test was performed under conditions of discharge rates from 25 kg / h to 90 kg / h and rotation speeds from 15 rpm to 45 rpm. The raw material used was a rubber composition with a moisture content of 30%. This rubber composition mainly consists of emulsion polymerized SBR (styrene-butadiene rubber) and carbon black. This raw material is spherical with a diameter ranging from 1 mm to 50 mm, and its specific gravity is approximately 1.1.

[0059] The results of this test showed that under the conditions with the lowest moisture content, the moisture content reached approximately 4%. However, during the test, the raw material frequently clogged the drain, requiring manual removal of the clogged material to resolve the blockage.

[0060] Furthermore, tests were conducted using the same equipment under the same conditions with different raw materials. The raw material used was a rubber composition with a moisture content of 50% or more. This rubber composition mainly consists of natural rubber and carbon black, and also contains one or more of the following as other components: silica, carbon nanotubes, carbon nanofibers, graphene, cellulose, cellulose nanofibers, etc. This raw material is spherical with a diameter of 0.5 mm or less. Generally, rubber compositions with small particle sizes have a high moisture content and are difficult to compress, making dewatering difficult. As a result of this test, the rubber composition used as the raw material clogged the drain port and was not compressed or dewatered.

[0061] [Embodiment of the second invention] In the second invention, as shown in the conical twin-screw extruder 1B in Figure 4, the flight 6 of the screw 7 has a missing portion 13. A missing portion is a screw flight that has a hole, a notch, or a combination thereof. The other components of the conical twin-screw extruder 1B in Figure 4 are the same as those of the conical twin-screw extruder 1 in Figures 1 and 2, and the same reference numerals indicate the same parts.

[0062] In this conical twin-screw extruder 1B, the raw material can be dewatered more uniformly compared to a screw flight extruder which has no missing parts. Specifically, as the raw material moves from the inlet 3 to the discharge port 4, some of the material passes close to the rotor shaft 5, while other material passes farther away from the rotor shaft 5 and closer to the inner surface of the casing 2. The water produced when the raw material passes close to the rotor shaft 5 has nowhere to go and is difficult to drain. On the other hand, the water produced when the raw material passes close to the inner surface of the casing 2 can easily pass through the gap between the bottom surface of the casing 2 and the flight 6, and the water is guided to the drain port 10 and easily drained. By providing missing parts such as holes or notches in the flight 6, the water dewatered from the raw material passing close to the rotor shaft 5 can be effectively guided to the drain port.

[0063] Although the raw material itself can pass through holes, notches, or other defects 12, in such cases the residence time of the raw material from the inlet 3 to the outlet 4 increases, which increases the time the raw material is compressed, thus improving the efficiency of water discharge from the raw material.

[0064] If the missing portion 12 consists of a hole, the diameter of the hole is preferably greater than 0.5 mm and less than 30 mm, and the position of the hole is preferably close to the rotor shaft 5.

[0065] When the missing portion 12 consists of a notch 13a or 13b as shown in Figures 5 and 6, the depth of the notch is preferably greater than 0.1 mm, and the width of the notch is preferably greater than 0.1 mm and less than 30 mm. There is no upper limit to the depth of the notch, and the notch 13a may be deep enough to reach the rotor shaft 5, as shown in Figure 5.

[0066] In one embodiment of the second invention, as shown in the conical twin-screw extruder 1C of Figure 7, the gap between the casing 2 and the flights 6 is narrower near the discharge port 4 than near the inlet port 3. In this embodiment, this gap narrows as it moves from the inlet port 3 towards the discharge port 4. The other components of Figure 7 are the same as those in Figure 4, and the same reference numerals indicate the same parts.

[0067] This embodiment is particularly effective when the screw flight has defects 12 such as holes or notches, and it is especially effective in dewatering raw materials located in the region close to the screw shaft. In particular, the dewatering effect is remarkable in large conical twin-screw extruders with high processing capacity, and the combination with partially defective screw flights is very effective for efficient dewatering. That is, the raw material is gripped well by the flight 6, and the raw material can be compressed and dewatered at high pressure.

[0068] In this conical twin-screw extruder 1C, if A is the distance from the inner surface of the casing 2 to the tip (outer edge) of the flight 6 on a plane perpendicular to the screw axis at the front end position of the inlet 3, and B is the distance from the inner surface of the casing 2 to the tip of the flight 6 on a plane perpendicular to the screw axis at the tip position of the screw 7, then it is preferable that A / B be 1.01 or more, and more preferably 1.05 or more. If the gap between the casing 2 and the flight 6 is too wide, the compression of the raw material will be weaker and the dewatering efficiency will decrease, so it is preferable that A / B be 1.5 or less.

[0069] <Reference example 2> The test was conducted using EM Giken's CF-1V conical twin-screw extruder. The screw diameter of the CF-1V is 160 mm. This screw has no defects, and the gap between the screw and the casing is constant from the inlet to the outlet.

[0070] A 9mm wide gap was created at the bottom of the rear end wall of this conical twin-screw extruder, and a dewatering test was conducted using this as a drain outlet. The test was performed under conditions of discharge rates from 25 kg / h to 90 kg / h and rotation speeds from 15 rpm to 45 rpm. The raw material used was a rubber composition with a moisture content of 30%. This rubber composition mainly consists of emulsion polymerized SBR (styrene-butadiene rubber) and carbon black. This raw material is spherical with a diameter ranging from 1 mm to 50 mm, and its specific gravity is approximately 1.1.

[0071] After this test, the moisture content of the raw materials remaining on the screw was compared between those closer to the screw shaft and those further away. The results showed that the raw materials closer to the screw had a higher moisture content.

[0072] Furthermore, tests were conducted using the same equipment under the same conditions with different raw materials. The raw material used was a rubber composition with a moisture content of 50% or more. This rubber composition mainly consists of natural rubber and carbon black, and also contains one or more of the following as other components: silica, carbon nanotubes, carbon nanofibers, graphene, cellulose, cellulose nanofibers, etc. This raw material is spherical with a diameter of 0.5 mm or less. Generally, rubber compositions with small particle sizes have a high moisture content and are difficult to compress, making dewatering difficult. As a result of this test, the rubber composition used as the raw material clogged the drain port and was not compressed or dewatered.

[0073] [Embodiment of the Third Invention] Figure 8 is a longitudinal cross-sectional view of a parallel twin-screw extruder 1D according to an embodiment of the third invention.

[0074] In this embodiment, two parallel screws 7D are housed within a casing 2D. The height and width inside the casing 2D are the same along its entire length. The rotor shaft 5D is of equal diameter along the entire longitudinal direction of the screws 7D, and the diameter of the flights 6D is also uniform. However, the diameter of the flights 6D may be larger towards the discharge port 4 side, as will be described later. The other components of this conical twin-screw extruder 1D are the same as those of the conical twin-screw extruder 1 in Figures 1 and 2, and the same reference numerals indicate the same parts.

[0075] In this parallel twin-screw extruder 1D, there is no water discharge opening between the inlet 3 and the discharge port 4. Note that there are two types of water discharge openings: a dewatering port and a drain port. Both the dewatering port and the drain port discharge water from inside the casing 2, but water is discharged from the dewatering port almost simultaneously with the compression of the water-containing raw material. Therefore, the water produced by the compression and the compressed or uncompressed raw material pass through a position that comes into contact with the dewatering port. Contact of the raw material with the dewatering port can cause the raw material to leak out and block the dewatering port. The drain port is an opening for discharging water outside the casing 2, but the raw material does not pass through a position that comes into contact with the drain port.

[0076] Conventional parallel twin-screw extruders typically have a dewatering port between the raw material inlet and discharge port, as dewatering is one of the purposes of the process. Furthermore, to prevent leakage of the raw material from the dewatering port, solid-liquid separation means such as slits, meshes, or perforated metal are installed at the port. However, even with solid-liquid separation means, when the raw material fills the parallel twin-screw extruder and the pressure increases, the raw material leaks out of the dewatering port. Even with improvements to the structure of the slits, meshes, and perforated metal, and the screw shape, it is extremely difficult to prevent the flowing raw material from moving from areas of high pressure to areas of low pressure.

[0077] In the parallel twin-screw extruder of the third invention, leakage of the raw material is prevented by not providing a water discharge opening in the area where the raw material is present, that is, between the inlet 3 and the discharge port 4. The raw material is transported from the inlet 3 to the discharge port 4 by the screw 7D, and is compressed as the pressure increases during this process. Since the compressed water has a much lower viscosity than the raw material, it easily moves in the direction of lower pressure, that is, from the discharge port 4 towards the inlet 3.

[0078] In the third invention, preferably, a drain port 10 is provided on the rear end wall 11 of the parallel twin-screw extruder 1D or on the lower surface of the casing 2D between the rear end wall 11 and the inlet 3. This allows water to be efficiently discharged from the drain port 10 without leakage of raw material.

[0079] In the third invention, the drain opening 10 is preferably provided at the lowest vertical part of the rear end wall 11 or above the lowest part, more preferably above the lowest part and within 30 mm from the lowest part.

[0080] The drain port of the parallel twin-screw extruder of the third invention does not have a solid-liquid separation means such as a wedge wire screen, a punching plate, a mesh, or a cloth, which are provided in the dewatering port of a conventional parallel twin-screw extruder.

[0081] In the third invention, the diameter of the flight 6D may be increased towards the discharge port 4 side of the parallel twin-screw extruder 1D, thereby reducing the distance between the tip of the flight 6D and the inner surface of the casing 2D from the inlet 3 to the discharge port 4 side. This allows the water produced by the compression of the raw material to flow efficiently to the rear, and thus the water produced by the compression is efficiently discharged from the drain port 10.

[0082] In the third invention, a vacuum vent may be installed between the inlet 3 and discharge port 4 of the parallel twin-screw extruder 1D, and on the lowest surface of the casing 2. By vacuuming from this vacuum vent, the moisture content in the extruded material can be further reduced.

[0083] The water extracted from the raw materials moves to the bottom of the casing 2 due to gravity, so the mixture inside the casing 2 contains more water at the bottom. Therefore, water is more efficiently removed by vacuuming from the bottom of the casing 2 than by vacuuming from the top.

[0084] Furthermore, the well-mixed mixture is transported from the inlet 3 to the discharge port 4 as a single unit. Impurities that do not easily integrate with the mixture, such as burnt and altered resin or foreign matter, move downwards due to gravity and are easily discharged from the vacuum vent at the bottom.

[0085] If solid-liquid separation means such as slits, mesh, or perforated metal are provided in the vacuum vent, there is a risk of raw material accumulating and causing blockage, so it is preferable not to provide such solid-liquid separation means. Generally, if the vacuum vent at the uppermost vertical end of a parallel twin-screw extruder is operated under conditions where venting does not occur, raw material will not leak from the vacuum vent on the lowest side.

[0086] Parallel twin-screw extruders are often installed with the screw axis direction horizontal, but they may also be installed with the screw axis direction inclined. When the screw axis direction is inclined, it is preferable to install the extruder so that the rear end wall is lower than the discharge port side. This makes it easier for the water produced by pressing the raw material to flow to the drain port according to the inclination of the casing.

[0087] The moisture content in the extruded product is preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0.1% by weight or less, depending on the required performance.

[0088] When attempting to dewater a rubber composition using a conventional parallel twin-screw extruder, dewatering was extremely difficult when the moisture content of the rubber composition exceeded 50%. In contrast, by using the parallel twin-screw extruder of the third invention, even when the moisture content of the rubber composition exceeds 50%, sufficient dewatering can be achieved, reducing the moisture content to 1% or less. (Is this possible with just parallel twin-screws?)

[0089] Furthermore, when attempting to dewater a rubber composition using a conventional parallel twin-screw extruder, if the moisture content of the rubber composition is 10-50%, dewatering occurs, but the moisture content does not decrease to 1%. Therefore, for rubber compositions that need to be dewatered to a moisture content of 1% or less, drying using a dryer is necessary, but drying with a dryer requires a great deal of energy and time, making it costly. By using the parallel twin-screw extruder of the third invention, even when the moisture content of the rubber composition is 10-50%, sufficient dewatering can be performed, reducing the moisture content to 1% or less.

[0090] [Raw materials] The raw materials used in the present invention are not particularly limited as long as they are water-containing raw materials that should be dehydrated by pressing, but examples include thermoplastic elastomers, rubber components such as rubber, and water-containing raw materials such as resins. Rubber components are preferably used. The rubber components are not particularly limited, but examples include solution-polymerized SBR (styrene-butadiene rubber), emulsion-polymerized SBR, and natural rubber. As water-containing raw materials, compositions of rubber components, carbon black, antioxidants, oils and fats, and other components are preferably used, as well as rubber components. Other components are not particularly limited, but examples include silica, carbon nanotubes, carbon nanofibers, graphene, cellulose, and cellulose nanofibers. The specific gravity of the raw material is preferably greater than 1.0, more preferably 1.05 or higher, and even more preferably 1.1 or higher, because it facilitates separation from water (pressed water). The size of the water-containing raw material is not particularly limited, but is usually spherical with a diameter of 1 to 50 mm.

[0091] For equipment that continuously molds dewatered raw materials, it is preferable to provide a tubular die at the discharge port of a parallel twin-screw extruder and attach a cutter blade to a part of the die. This allows the raw material coming out of the discharge port to be molded into a sheet.

[0092] <Combination of Inventions 1-3> Furthermore, the first, second, and third inventions can be combined in any way. By combining them, a series of dehydration, kneading, and molding processes can be obtained.

[0093] By using this series of dewatering, kneading, and molding processes, it is possible to continuously dewater raw materials with different characteristics such as shape, viscosity, and fluidity. Furthermore, because there is no dewatering port and drain port blockage is virtually eliminated, advantages such as improved yield, reduced operation stoppages, and reduced cleaning frequency can be obtained.

[0094] For example, by combining the conical twin-screw dewatering machine and the parallel twin-screw dewatering machine of the present invention in series, raw materials with a moisture content of 60-70% can be reduced to 20-30% using the conical twin-screw dewatering machine, and then further reduced to 5% or less using the parallel twin-screw dewatering machine. Furthermore, with the same combination, raw materials with a moisture content of 30-50% can be reduced to 5-10% using the conical twin-screw dewatering machine, and then further reduced to 1% or less using the parallel twin-screw dewatering machine. [Examples]

[0095] <Example 1> The tests were conducted using the TEX44α parallel twin-screw extruder manufactured by Japan Steel Works. This parallel twin-screw extruder has a drain port on the rear end wall and does not have a dewatering port between the raw material inlet and discharge port. Tests were conducted under conditions of discharge rate from 15 kg / h to 70 kg / h and rotation speed from 30 rpm to 80 rpm. The raw material used was a rubber composition with a moisture content of 30%. This rubber composition mainly consists of emulsion polymerized SBR (styrene-butadiene rubber) and carbon black. This raw material is spherical with a diameter of 1 mm to 50 mm and has a specific gravity of approximately 1.1.

[0096] The results of this test showed that, under all conditions, the rubber composition, which is the raw material, was not detected in the drain. Furthermore, the moisture content reached a minimum of 0.57% under the condition with the lowest moisture content.

[0097] Furthermore, tests were conducted using the same equipment under the same conditions with different raw materials. The raw materials used were rubber compositions with a moisture content of 50% or more. These rubber compositions mainly consist of natural rubber and carbon black, and also contain one or more of the following as other components: silica, carbon nanotubes, carbon nanofibers, graphene, cellulose, cellulose nanofibers, etc. These raw materials are spherical with a diameter of 0.5 mm or less. Generally, rubber compositions with small particle sizes have a high moisture content and are difficult to compress, making dewatering difficult.

[0098] However, the results of this test showed that the raw material, the rubber composition, could be dewatered and was not detected at the drain outlet; instead, minute rubber composition particles were discharged from the drain outlet along with the compressed water. The discharged minute rubber composition particles could be easily separated from the water and recovered. Since there is no solid-liquid separation mechanism at the drain outlet, it does not cause blockage in the equipment. Furthermore, since raw material recovery is easy, it is clear that when using this equipment for continuous operation, the maintenance frequency can be kept low and the continuous operation time can be ensured. Although there is no solid-liquid separation mechanism at the drain outlet, the amount of raw material discharged from the drain outlet is minute and can be recovered and put back into the equipment as raw material.

[0099] <Example 2> We modified EM Giken's CF-2V conical feeder and used it as a conical twin-shaft dewatering machine for testing. The CF-2V is a larger version of the previously mentioned CF-1V, with the same basic structure and a screw diameter of 200 mm. Before modification, the CF-2V, like typical conical feeders, had no openings for discharging raw materials or moisture other than the discharge port, and the inlet was not separated from the rear end wall towards the casing front. Furthermore, this conical feeder did not have a sealing ring. We modified the CF-2V to add a drain port so that the lowest point of the drain port was above the lowest point inside the casing. In addition, the inlet was separated from the rear end wall towards the casing front. We also added a sealing ring.

[0100] Tests were conducted under conditions ranging from a discharge rate of 3 kg / h to 100 kg / h and a rotation speed of 5 rpm to 30 rpm. The raw material used was a rubber composition with a moisture content of 30%. This rubber composition mainly consists of emulsion-polymerized SBR (styrene-butadiene rubber) and carbon black. The raw material was spherical, with a diameter of 1 mm to 50 mm, and its specific gravity was approximately 1.1. As a result of these tests, the rubber composition was not detected at the drain outlet under any conditions, and the drain outlet did not become blocked during the 6-hour test. Furthermore, the moisture content reached a minimum of 4.1% under the condition with the lowest moisture content.

[0101] Furthermore, tests were conducted using the same equipment under the same conditions with different raw materials. The raw material used was a rubber composition with a moisture content of 65% or more. This rubber composition mainly consists of natural rubber and carbon black, and also contains one or more of the following as other components: silica, carbon nanotubes, carbon nanofibers, graphene, cellulose, cellulose nanofibers, etc. This raw material is spherical with a diameter of 0.5 mm or less. Generally, rubber compositions with small particle sizes have a high moisture content and are difficult to compress, making dewatering difficult. However, the results of this test showed that the raw rubber composition was dewatered to 24.5% under the most effective conditions. In addition, the raw rubber composition was not detected at the drain outlet.

[0102] <Comparative Example (Comparative Example corresponding to Example 2)> The drain port and sealing ring described in Example 2 are detachable and can be returned to their original state. Similarly, the separated inlet described in Example 2 can be returned to its original position. Therefore, we also confirmed whether each component functions independently.

[0103] First, a drain port was placed at the very bottom of the casing, and without a sealing ring, the inlet was not separated from the rear end wall. The test was then conducted under the same conditions and using the same raw materials as in Example 2. As a result, within a few minutes of starting the test, the drain port at the very bottom of the casing became blocked by the raw materials, leaving no outlet for the compressed water, and thus no dewatering effect was obtained.

[0104] Furthermore, the drain port was positioned so that its lowest point was above the lowest point inside the casing, without a sealing ring, and with the input port not separated from the rear end wall, and the test was conducted under the same conditions and with the same raw materials as in Example 2. As a result, the drain port became blocked within a few minutes of the test, and no dewatering effect was obtained. This is because, before the input raw materials are sent forward by the screw, there is a time when a large amount of raw materials are present at the rear, and when the raw materials at the rear are scraped up by the screw in that state, the drain port becomes blocked.

[0105] Next, the drain port was positioned so that its lowest point was above the lowest point inside the casing, a sealing ring was attached, and the test was conducted using the same raw materials under the same conditions as in Example 2, with the inlet not separated from the rear end wall. As a result, the drain port became blocked within a few minutes of the test, and no dewatering effect was obtained. Even with a sealing ring, if the inlet is not separated from the rear end wall, not all of the raw materials enter in front of the sealing ring during input; some enter behind the sealing ring, and when this is scraped up by the screw, it blocks the drain port.

[0106] Furthermore, a test was conducted using the same raw materials under the same conditions as in Example 2, with the drain port located at the lowest end of the casing, a sealing ring attached, and the inlet separated from the rear end wall. As a result, the drain port became blocked within a few minutes of the test, and no dewatering effect was obtained. Even with a sealing ring attached and the inlet separated from the rear end wall, if the drain port is located at the lowest end of the casing, a small amount of raw materials sent to the rear will enter the drain port and gradually become blocked.

[0107] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible without departing from the intent and scope of the invention. [Industrial applicability]

[0108] This invention can be used in manufacturing and processing equipment for thermoplastic elastomers, rubber, and resins.

[0109] This application is based on Japanese Patent Application No. 2019-053136, filed on March 20, 2019, which is incorporated herein by reference in its entirety.

Claims

1. A casing having a discharge port for the kneaded material at the front and a raw material input port at the rear, It comprises two screws installed inside the casing, In a twin-screw extruder for compressing water-containing raw materials, the casing is provided with a drain port, The drain outlet is provided on the lower surface of the rear of the casing, such that the lowest end of the drain outlet is higher than the lowest end inside the casing. The front edge of the drain opening is located behind the rear edge of the aforementioned inlet opening. The gap between the casing and the screw flight narrows as it moves from the inlet to the outlet. A conical twin-screw extruder characterized in that a portion of the screw flight is missing from a part of the screw that is closer to the tip than the front end of the inlet.

2. A rear end wall is provided at the rear end of the casing. A conical twin-screw extruder according to claim 1, characterized in that the distance between the trailing edge of the drain port on the inner surface of the casing and the inner surface of the rear end wall is 1 mm or more.

3. A rear end wall is provided at the rear end of the casing. The conical twin-screw extruder according to claim 1, characterized in that the rear edge of the drain port on the inner surface of the casing is located in a range of 5 to 200 mm above the point where the inner surface of the rear end wall and the rearmost and lowest part of the inner surface of the casing intersect.

4. The twin-screw extruder according to any one of claims 1 to 3, characterized in that the drain port is not provided with a solid-liquid separation means.

5. The twin-screw extruder according to claim 2 or 3, characterized in that the input port is spaced apart from the rear end wall of the casing toward the front end of the casing.

6. The twin-screw extruder according to any one of claims 1 to 5, characterized in that the missing portion is a shape that extends from the outer edge of the flight toward the screw axis.

7. A method for dewatering a rubber composition by pressing it using a twin-screw extruder according to any one of claims 1 to 6.

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