JP2001198918A - Method and apparatus for producing double layer pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce double layer pellets having stable core-shell structure of high quality in good productivity. SOLUTION: A method for producing the pellets P in which a core molding material a is coated with a shell molding material b includes a process (a) in which the material a and the material b are supplied to a die device 3 in which extrusion molding parts are arranged along the circumference, a process (b) in which from the respective extrusion molding parts, the shell material b is applied concentrically on the periphery of the core material, and double layer strands S are extruded, and a process (c) in which the extruded strands S are cut to produce the pellets P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multilayer pellet and a die apparatus for producing a multilayer pellet, and more particularly, to a core-sheath structure comprising a plurality of molding materials, which is a raw material for molding various resin products. The present invention is directed to a method for producing a multilayer pellet having the same, a die apparatus used for producing a multilayer pellet by applying an extrusion molding technique, and an apparatus for producing a multilayer pellet including a die apparatus.

[0002]

2. Description of the Related Art Pellets for resin molding are prepared by heating and melting a resin material that has been previously blended and adjusted, extruding it into strands (strings), and cutting the resulting resin strands into small tablet-shaped pellets. It was made. By preparing the above pellets when molding various resin products, it is not necessary to adjust the compounding of raw materials every time the resin product is molded, and stable resin performance work is possible. It has the advantage that the quality is stable and the work of supplying the raw material to the molding device and other handling becomes easy.

[0003] In general, resin pellets are generally formed of the same resin as a whole, but multilayer pellets or multilayer pellets comprising a plurality of material parts and a method for producing the same have also been proposed. The technique disclosed in Japanese Patent Application Laid-Open No. 7-171828 discloses a method of solving the problem that pellets produced from a material having high tackiness are liable to cause blocking. It is a multilayered pellet having a core-sheath structure in which a resin is used as a sheath. Japanese Patent Application Laid-Open No. 59-81121 discloses a technique for producing pellets from an olefin-vinyl alcohol copolymer in which the melt tension is small and a strand for pellet production cannot be formed. Then, a multi-layered strand having a core-in-sheath structure in which the outer periphery is coated with a resin having a high melt tension is formed and then cut to produce a multi-layered pellet having a core-in-sheath structure. As the manufacturing apparatus, an apparatus having a structure in which a sheath material is supplied around a core material to a die head for pellet molding is shown.

[0004]

In the conventional multi-layer pellet manufacturing technology, the molding speed of the multi-layered strand is relatively low in order to ensure that the outer periphery of the core material is covered with the sheath material during the formation of the multi-layered strand. Must be set low. Therefore, there is a problem that productivity of the multilayered strand and the multilayered pellet is deteriorated, and the production cost of the multilayered pellet is high. In order to solve this problem, it is conceivable to simultaneously manufacture a plurality of multi-layered strands by using a strand forming apparatus having a plurality of die heads or extrusion ports.

[0005] However, it is difficult to make adjustments so that the outer periphery of the core material is surely covered with the sheath material having a constant thickness in each of the plurality of extrusion ports. The molten resin material is supplied to multiple extrusion ports in an equal amount and flow rate,
It is difficult to uniformly control the flow of the core material and the sheath material over the entire circumference of the flow. An object of the present invention is to produce a multilayer pellet having a high quality and a stable core-sheath structure with high productivity in the above-described multilayer pellet manufacturing technology.

[0006]

SUMMARY OF THE INVENTION The method for producing a multilayer pellet according to the present invention is a method for producing a multilayer pellet having a core-sheath structure in which a molding material serving as a sheath is coated on the outer periphery of a molding material serving as a core. In addition, the method includes the following steps (a) to (c). Step (a): The core material and the sheath material are supplied to a die device in which a plurality of extruded portions are arranged along the circumference. Step (b): From each of the extruded portions, the outer periphery of the core material is concentrically covered with the sheath material, and the multilayer strand is extruded.

Step (c): A plurality of extruded multilayer strands are cut to produce multilayer pellets. [Molding material] Various resin materials applicable to normal pellet production can be combined. The raw material supplied to the multilayer pellet manufacturing apparatus described below may be in a solid state such as a powder or a liquid state. [Multilayer Pellet Manufacturing Apparatus] Basically, it has the same structure as a molding apparatus used for ordinary strand pellet production and strand molding.

The following structures can be provided for the production of multilayer pellets. An extruder that separately heats and melts the raw materials to be the core material and the sheath material, a strand forming die device that forms the molten core material and the sheath material supplied from the extruder into a multilayer strand, and is extruded from the die device. Pelletizers for producing multilayer pellets by cutting multilayer strands. A cooling device such as a cooling tank for cooling the multilayered strand can be provided. A hopper for supplying a raw material to the extruder, and a device for collecting multi-layer pellets produced by a pelletizer or conveying the pellets to the next step can be provided.

[Die Apparatus] The basic structure is the same as that of an ordinary strand forming die apparatus, but it has a structure for forming a multi-layered strand. <Supply port> The supply port includes a core material supply port to which the core material is supplied, and a sheath material supply port to which the sheath material is supplied. The core material supply port and the sheath material supply port may be provided at any positions on the outer surface of the main body of the die device, but are preferably arranged so that the flow of the material to the extruded portion becomes smooth. Specifically, in the main body of the die device, it can be provided at a position on the side surface or the rear surface with respect to the surface on which the extruded portion is arranged.

[0010] Separate extruders are connected to the core material supply port and the sheath material supply port, respectively. The arrangement of each supply port is set in consideration of the installation structure of the extruder and the like. <Extruded part> An extruded part for forming a multilayer strand is provided. The core material is extruded linearly at the center from the extrusion port provided in the extruded portion, and is extruded together with the core material in a state where the outer periphery of the core material is concentrically covered with the sheath material. The outer diameter of the extrusion port is set according to the outer diameter of the multilayer strand. However, the outer diameter of the multilayer strand and the outer diameter of the extrusion port may not be completely the same in consideration of deformation during molding. If the outside diameter of the extrusion opening is too small, the molding material cannot be sufficiently extruded, and if the outside diameter of the extrusion opening is too large, the strand cannot be stably extruded.

The extruded parts are arranged at a plurality of places along the same circumference. As a result, a plurality of multi-layered strands extruded from each extrusion port are sent to the downstream side in a parallel state while forming a cylindrical surface. The number of extruded parts is
The number may vary depending on conditions such as the outer shape of the die device, the diameter of the multilayer strand, and the extrusion discharge amount, and can be set to an appropriate number in the range of about three to several tens. As the structure of the extruded portion, it is possible to combine a core nozzle into which a core material is supplied, and a sheath holder provided with an extrusion port, which is disposed at an interval on the outer periphery on the distal end side of the core nozzle. The sheath material is supplied between the sheath holder and the core nozzle.

The outer diameter of the core material can be adjusted by setting the inner diameter of the core nozzle. By setting the outer shape of the core nozzle and the inner shape of the sheath holder, the thickness of the sheath material and the radial ratio between the core material and the sheath material can be adjusted. If the inner periphery of the sheath holder corresponding to the tip of the core nozzle is tapered, the position of the sheath holder and the core nozzle is adjusted in the front-rear direction, so that the thickness of the sheath material coated on the core material is increased. Can be adjusted. Each of the plurality of extruded portions can be provided with a combination structure of the core nozzle and the sheath holder as described above.

An extruded part having a combination structure of a core nozzle and a sheath holder can be provided detachably with respect to the main body of the die device for each extruded part. In this case, the thickness of the core material and the sheath material, the balance in the circumferential direction, and the like can be adjusted for each extruded portion. The alignment of the core nozzle and the sheath holder can be accurately set. As the means for detachably attaching the extruded portion to the main body of the die device, a detachable attachment means in a normal mechanical device such as fitting, bolting or the like can be adopted.

<Supply path> A flow path of a molten material for guiding the core material and the sheath material from the core material supply port and the sheath material supply port to the extruded portion, and the core material supply path and the sheath material supply path are separately provided. Prepare. The core material supply path first extends from the core material supply port to the center axis of the circumference where the plurality of extruded portions are arranged. Then, it is extended radially from the center axis toward each extruded portion. The radial supply path may be arranged in a plane orthogonal to the central axis, or may be arranged in a conical surface inclined forward. In such a conical radial supply path, the flow of the material is smooth, and the flow can be divided equally in a plurality of directions. A portion extending along the central axis can be provided in front of the radial supply path.

It is preferable that the supply path from the center axis to each of the extruded sections has the same structure in all the extruded sections in order to uniformly supply the material to the extruded sections. The sheath material supply path also first extends from the sheath material supply port to the center axis of the circumference where the plurality of extruded portions are arranged. Then, it is extended radially from the center axis toward each extruded portion.
Since a more specific structure is common to the core material supply path, a detailed description is omitted. When there are portions extending along the central axis in the core material supply path and the sheath material supply path, they are provided in an arrangement that overlaps front and rear on the central axis but does not interfere with each other. The radial portion of the sheath supply channel can be located in front of the radial portion of the core material channel, ie, closer to the extrusion.

[Multi-Layer Strand Forming] The core material and the sheath material supplied from the extruder to the die device in a molten state flow through the respective supply paths and are divided into a plurality of extruded portions. In each supply path, the core material and the sheath material flowing from the central axis direction to the radial direction are equally divided and flow under the same conditions. As a result, the multilayered strand is formed from the core material and the sheath material under the same conditions in a plurality of extruded portions. By adjusting the supply amounts of the core material and the sheath material to the die device, the ratio of the thickness of the core material to the thickness of the sheath material in the multilayer strand can be adjusted.

The layer structure of the multi-layered strand also changes depending on the shape and structure of the extruded portion. For example, the settings of the inner and outer diameters of the core nozzle, the inner diameter of the sheath holder disposed outside the core nozzle, and the inner diameter of the extrusion port at the tip determine the layer structure of the multilayer strand. The outer diameter of the multi-layered strand and the ratio of the thickness of the core material to the thickness of the sheath material can be appropriately set according to the purpose of use of the multi-layered pellet, required performance, and the like.
For example, the outer diameter of the multilayer strand is usually set to 1 to 10 mm, preferably 3 to 7 mm. [Manufacture of Multilayer Pellet] The extruded multilayer strand is cooled if necessary and then cut with a pelletizer to form a multilayer pellet.

For cooling, ordinary cooling means can be employed, for example, a method of immersing the multilayered strand in cooling water in a water tank is employed. The water-cooled multi-layered strand is preferably sent to a pelletizer after removing water adhering to the surface by a drainer. The pelletizer drives a rotary blade or the like to cut the multilayered strand at predetermined lengths. In a state where the multilayer strand is cut, a double columnar multilayer pellet composed of a core material and a sheath material can be obtained. By rounding the cut end face, it is possible to obtain a spherical, elliptical spherical, or disc-shaped multilayer pellet in which the entire periphery including the end face of the core material is covered with the sheath material. Such a form in which the sheath material covers the entire periphery of the core material is also included in the technical concept of the core-sheath structure in the present invention.

The pellets having an outer diameter of about 2 to 8 mm are usually produced. (Underwater cut pelletizer) As an apparatus for cutting multilayer strands to obtain multilayer pellets, an underwater cut pelletizer is disposed adjacent to the exit of the multilayer strand in the extrusion section of the die apparatus, that is, the extrusion port. Can be kept. The underwater cut pelletizer includes a rotary blade driven to rotate by a motor or the like, and a water holding space in which the rotary blade is housed and through which water flows. If an underwater cut pelletizer is arranged so that the rotary blade passes through the extrusion port just outside the die port so as to cross the extrusion port and water is always present outside the extrusion port, the The extruded multilayer strand is immediately cut by a rotary blade to form a multilayer pellet.
The cut multi-layer pellets are released into water, are immediately cooled, and can be transported by a water stream.

The multi-layer pellets conveyed together with the water stream from the underwater cut pelletizer are separated from water by a dehydrator or the like, and the dried multi-layer pellets can be collected. When the underwater cut pelletizer is mounted adjacent to the die apparatus, the die apparatus is cooled by water flowing through the underwater cut pelletizer, and the core material and the sheath material may be excessively cooled in an extruded part or the like. In order to solve this problem, it is effective to provide a die device, particularly a temperature control device for heating and maintaining the extruded portion. The temperature control device controls the temperature by heating the die device adjacent to the heating path by arranging a heating path through which the heating oil or the like circulates around the extruded portion or inside the die device. be able to.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment shown in FIG. 1 shows the overall structure of a multilayer pellet manufacturing apparatus and the cross-sectional structure of a manufactured multilayer strand or multilayer pellet. FIG.
As shown in (a), an extruder 1 for a core material and an extruder 2 for a sheath material are connected to a die device 3 from directions orthogonal to each other. In the core extruder 1, a resin raw material serving as a core material is supplied and heated and melted. In the extruder 2 for a sheath material, a resin raw material as a sheath material is supplied and heated and melted.
The heated and melted material is supplied to the die device 3.

A plurality of multilayer strands S are extruded from the die apparatus 3 so as to be parallel to each other and to form a cylindrical surface. As shown in FIG. 1 (b), the cross-sectional shape of the multi-layered strand S is such that a core material a is disposed at the center, and the outer periphery thereof is covered with a sheath material b with a relatively small thickness. The extruded multilayer strand S is sent to the cooling tank 4 to be cooled and solidified. The multi-layered strand S coming out of the cooling tank 4 is sent to a pelletizer 6 via a drainer 5. In the pelletizer 6, the multilayer strand S is finely cut, and the multilayer pellet P is obtained. The cross-sectional structure of the multilayer pellet P is also shown in FIG.
As shown in (b), the core material has a core-sheath structure composed of a core material a and a sheath material b.

[Die Apparatus] As shown in FIGS. 2 and 3, the die apparatus 3 has a substantially cylindrical main body 10. As shown in detail in FIG. 3, a core material supply cylinder 21 and a sheath material supply cylinder 41 are provided at positions orthogonal to each other on the cylindrical peripheral surface of the main body 10. The end surface of the core material supply tube 21 is the core material supply port 20, and the end surface of the sheath material supply tube 41 is the sheath material supply port 40. The core material supply port 20 is connected to the core material extruder 1, and the sheath material supply port 40 is connected to the sheath material extruder 2.

Extrusion ports 12 are arranged at a plurality of locations along the circumference on the distal end surface of the main body 10. In the case of the drawing, there are six extrusion ports 12 at equal intervals. A line extending the center of the circumference formed by the extrusion port 12 in a direction perpendicular to a plane including the circumference represents the central axis C. As shown in FIG.
Material supply paths 22, 24, 26 from
And sheath material supply passages 42, 44, 46 extending from the sheath material supply port 40 (see FIG. 3) to the respective extrusion ports 12. The core material supply path extends from the core material supply port 20 toward the central axis C at the center of the main body 10, and then extends along the central axis C toward the front extrusion port 12 side, and a relatively thick main supply path 22. A plurality of radial supply paths 24, which are thinner than the main supply path 22 and extend slightly obliquely forward in the radial direction along the conical surface, following the main supply path 22; It comprises a parallel supply path 26 extending forward parallel to the axis C and reaching the extrusion port 12.

The parallel supply path 26 passes through the center of the cylindrical core nozzle 14 which is detachably embedded in the main body 10,
It extends toward the extrusion port 12. The tip of the core nozzle 14 is tapered and thin, and is arranged inside the holder hole 52 of the extrusion board 50 arranged on the front surface of the main body 10. The extruder 50 is provided with a holder hole 52 for each extruded portion, and the tip of the holder hole 52 is the extrusion port 12. The sheath material supply path extends from the sheath material supply port 40 toward the central axis C at the center of the main body 10, and then extends along the central axis C to the front extrusion port 12 side, and a relatively thick main supply path 42. A radial supply path 44 which is thinner than the main supply path 42 and extends slightly obliquely forward in the radiation direction, and a radial supply path 44 which is narrower than the main supply path 42 and extends forward in parallel with the central axis C. And a parallel supply path 46 extending to the extrusion port 12.

The main supply path 42 for the sheath material is disposed on the front side closer to the extrusion port 12 than the main supply path 22 for the core material. The radial supply path 44 of the sheath material continues to the inner periphery of the core nozzle 14. The parallel supply path 46 of the sheath material extends to a gap between the outer periphery of the core nozzle 14 and the holder hole 52 and reaches the extrusion port 12. The thickness of the sheath material b changes in the gap between the outer diameter of the tip of the core nozzle 14 and the holder hole 52,
The ratio of the thickness of the core material a to the thickness of the sheath material b is determined. By adjusting the position of the core nozzle 14 in the front-rear direction parallel to the central axis C, the thickness of the sheath material b can be adjusted.

[Formation of Multi-Layer Strand] Each extruder 1, 2
The core material a and the sheath material b in the molten state supplied to the die device 3 from the core material supply passages 20 to 26 and the sheath material supply passage 4
Flow through 0-46. In the extrusion port 12, the core material a flows in the center and the sheath material b flows in the outer periphery, so that a multi-layered strand S having a so-called core-sheath structure is formed. Core material supply path 20-2
In 6, the core material a sent from the main supply path 22 to the position of the central axis C is evenly distributed from the central axis C to each radial supply path 24. Even in the sheath material supply paths 40 to 46, the main supply path 4
The sheath material b sent to the position of the central axis C from
From each other to each radial supply path 44.

As shown in FIG. 4, both the core material a and the sheath material b are sent to the parallel supply passages 26 and 46 in a state of being evenly distributed by the radial supply passages 24 and 44. In the extruded portion, it is possible to prevent the supply amounts of the core material a and the sheath material b from being different from each other, and prevent the thickness ratio of the core material a and the sheath material b in the multilayer strand S from being varied. At the extruder 50, the core material a and the sheath material b flowing through the parallel supply passages 26 and 46 on the inner and outer circumferences of the core nozzle 14 join at the tip of the core nozzle 14. The outer diameter is adjusted at 12 and the core material a
A multilayer strand S in which the sheath material b is coated at a constant thickness ratio is formed.

[Manufacture of Multilayer Pellets] The multilayer strands S extruded by the die device 3 are sent out in such a manner that six multilayer strands S form a cylinder in accordance with the arrangement structure of the extrusion ports 12. come. As shown in FIG. 1, the plurality of multilayer strands S enter the cooling tank 4 in a parallel state, and are cooled while traveling while being immersed in water. The multi-layered strand S that has exited the cooling tank 4 is drained by a drainer 5
After removing the water adhering to the surface with the pelletizer 6
To form a multilayer pellet P.

In the pelletizer 6, a plurality of multi-layered strands S arranged circumferentially can be simultaneously cut by a cutting blade driven to rotate. [Use of Sheath Holder] The embodiment shown in FIGS. 5 and 6 differs from the above embodiment in the structure of the die device. However, since the basic structure is common to the above-described embodiment, different structural parts will be mainly described. Main body 10 of die device 3, core material supply path 2
The arrangement structure of 0 to 26 and the sheath material supply passages 40 to 46 is common to the above embodiment.

However, the structure of the extruder 50 is different. In other words, the extruder 50 has a plurality of extruded portions arranged along the circumference and the sheath holder 60 made of a separate component from the main body of the extruder 50. The sheath holder 60 has a holder hole 62 surrounding the outer periphery of the core nozzle 14, and the tip of the holder hole 62 is the extrusion port 12. The sheath holder 60 has a stepped cylindrical shape as a whole, and the rear part of the sheath holder 60 is fitted into a plurality of recesses provided along the circumference on the front surface of the extrusion board 50. The holding members 54 having attachment holes into which the front portions of the sheath holders 60 fit are bolted to the front surface of the extrusion board 50, so that the sheath holders 60 are fixed.

The core material a and the sheath material b are used for the core nozzle 1
4 is supplied from the parallel supply paths 26 and 46 arranged on the inner and outer circumferences of the core material a to the extrusion port 12 through the holder holes 52 of the extrusion board 50 and the holder holes 62 of the sheath holder 60. Is formed with a sheath strand b. In the above embodiment, the mounting state of the sheath holder 60, the dimensional shape of the holder hole 62 or the extrusion port 12, and the mounting state and the dimensional shape of the core nozzle 14 are adjusted for each of the extruded portions, so that a plurality of positions are obtained. The extrusion shape of the multi-layered strand S in the extruded portion of can be set or adjusted accurately.

For example, if the alignment between the core nozzle 14 and the extrusion port 12 is misaligned, the thickness of the sheath material b in the multilayer strand S may be thinner and thicker in the circumferential direction. If the core position of the sheath holder 60 is adjusted according to the core position of the nozzle 14, a multilayer strand S in which the thickness of the sheath material b is constant over the entire circumference can be obtained. As a result, even when a plurality of multi-layered strands S are simultaneously formed in a plurality of extruded portions, it is easy to obtain a multi-layered strand S having no variation in quality performance. [Manufacturing apparatus provided with underwater cut pelletizer] FIGS. 7 to 9
The embodiment shown in Fig. 1 shows an apparatus for manufacturing a multilayer pellet incorporating an underwater cut pelletizer.

<Overall Arrangement> As shown in FIG. 7, as an arrangement structure of the manufacturing apparatus, an extruder 1 for a core material a and an extruder 2 for a sheath material b are connected to a die device 3. . The extruder 2 for the sheath material b includes a gear pump 28 driven by a motor or the like between the extruder 2 and the die device 3. A temperature control pipe 80 extending from the temperature control device 8 is connected to the die device 3. The oil heated by the temperature control device 8 is supplied from the temperature control device 8 to the die device 3 and returns to the temperature control device 8 again. Die device 2
Of the core a, a motor 7
The underwater cut pelletizer 7 driven by 5 is mounted. A water supply pipe 90 and a water discharge pipe 91 are connected to the underwater cut pelletizer 7, and the pipes 90 and 91 are connected to the dehydrator 9. The dewatering machine 9 is provided with a water circulating device 92 having a pump and the like. Water circulates between the dewatering machine 9 and the underwater cut pelletizer 7, and the multilayer pellet P obtained by the underwater cut pelletizer 7 is provided. Is taken out together with water, separated from water by the dehydrator 9, and the multi-layer pellets P are collected.

<Structure of Principal Parts> As shown in FIG. 8, the basic structure of the die device 1 is common to that of the above-described embodiment. Will be mainly described. The die device 1 includes a main body 10 and an extruder 50, and is provided with core material supply paths 20 to 26 and sheath material supply paths 40 to 46. Core material supply path 20-26
Among them, the core material supply port 20 is provided at the position of the central axis C on the rear end surface of the main body 10 and is connected to the main supply path 22 extending the central axis C.

As shown in FIG. 9, the extrusion ports 12 are provided at seven of the eight positions in the circumferential direction.
In one place, the extrusion port 12 is not provided to arrange the supply port 40 and the main supply path 42 of the sheath material b.
As described above, even if the extrusion ports 12 are not equally arranged on the circumference, the sheath material b and the core material a to be supplied to each extrusion port 12 are provided.
If the flow is appropriately designed, a uniform multi-layered strand S can be formed at the plurality of extrusion ports 12. Extruder 50
Is provided with an oil passage 84. Oil flow path 84
The oil supply port 81 and oil discharge port 82
And is connected to the temperature control pipe 80. The oil flow path 84 is disposed so as to surround the outer periphery of a portion near the extrusion port 12 on the distal end side of the parallel supply path 46. The heating oil supplied from the temperature control device 8 to the oil flow path 84 heats the extrusion board 50 around the extrusion port 12 and the core material a and the sheath material b flowing near the extrusion port 12.

The underwater cut pelletizer 7 has a water holding space 70 in which water w is stored. A water supply port 71 provided in the water holding space 70 is connected to the water supply pipe 90 and a water discharge port 72. Is connected to a water discharge pipe 91. One surface of the water holding space 70 is open to the front of the extrusion board 50. A cutting blade 74 is pivotally mounted on the opening surface of the water holding space 70. The cutting blade 74 is supported by a rotating shaft 73 that extends through the water holding space 70 and extends to the outside. Rotating shaft 7
3 is connected to a motor 75 provided outside the underwater cut pelletizer 7 and is driven to rotate. The cutting blade 74 operates so as to cross the extrusion port 12 opened in the front of the extrusion board 50.

<Manufacture of Multilayer Pellets> In FIG. 8, the core material a is supplied to the core material supply passages 20 to 26 and the sheath material supply passage 40 is supplied.
When the sheath material b is supplied to ４６46, the multilayer strand S in which the outer periphery of the core material a is covered with the sheath material b is extruded from the extrusion port 12 into the water holding space 70 of the underwater cut pelletizer 7.
The multi-layered strand S in contact with the water w is cooled. The tip of the multilayer strand S protruding into the water holding space 70 is immediately cut by the rotating cutting blade 74 to become a small multilayer pellet P. By setting the rotation speed of the cutting blade 7 and the extrusion speed of the multilayer strand S, the size and shape of the multilayer pellet P to be manufactured can be adjusted. The cut multilayer pellet P moves with the water flow while being cooled in water.

The water w in the water holding space 70 is sent from the water discharge port 72 to the dehydrator 9 via the water discharge pipe 91, where the multi-layer pellets P separated from the water w are taken out. By using the underwater cut pelletizer 7, the multilayer strand S extruded from the die device 1 can be immediately converted into the multilayer pellet P, and the productivity of the multilayer pellet P is improved, and the entire apparatus is improved. Space is also reduced. When the underwater cut pelletizer 7 is mounted on the die device 3, the extrusion port 1
Although the extruder 50 and the core material a and the sheath material b around 2 may be excessively cooled, extrusion may not be performed properly.
If the temperature control device 8 is provided, the extruder 50 and the core material a and the sheath material b around the extrusion port 12 can be heated and maintained at a temperature suitable for extrusion molding.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example in which a multilayer pellet is manufactured using the multilayer pellet manufacturing apparatus shown in FIG. 1 will be described. Die device 3: device with sheath holder 60 shown in FIGS. 6 outlets. Core material a: Low density polyethylene resin (MI = 2g / 10min)
, D = 0.92 g / cc) Colored blue. Sheath material b: low density polyethylene resin (MI = 2 g / 10 min)
, D = 0.92 g / cc) White color.

Core material extruder 1: a 46 mmφ twin-screw extruder.
L / D = 35. Sheath extruder 2: 50 mmφ single screw extruder. L / D = 25). Example 1 A core material a and a sheath material b were supplied to a die device 3 at a temperature of 180 ° C. from each of the extruders 1 and 2. Core material a
The ratio of the supply amount of the sheath material b and the core / sheath ratio is as follows:
It was 50/50% by weight. Six multilayer strands S extruded from the die device 3 were cooled in the cooling bath 4 and then cut by the pelletizer 6 to obtain multilayer pellets P.

The obtained multilayer pellet P has an outer diameter of 3.0 mm.
φ, length was 3.0 mm. Example 2 A multilayer pellet P was prepared under the same conditions as in Example 1 except that the core / sheath ratio was changed to core / sheath = 70/30% by weight.
Was manufactured. Example 3 A multilayer pellet P was prepared under the same conditions as in Example 1 except that the core-sheath ratio was changed to core / sheath = 90/10% by weight.
Was manufactured. The sheath thickness of the multilayer pellet P obtained in each example was measured. The measurement was performed by observing with an optical microscope.
The results are shown in Table 1 below.

<Table 1: Dimensions of Multilayer Pellet> ──────────────────────────── Core-sheath ratio Sheath thickness (mm) ( % By weight) Theoretical value Measured value Example 1 50/50 0.44 0.43-0. 45 Example 2 70/30 0.25 0.24 to 0.26 Example 3 90/10 0.08 0.07 to 0.09結果 As a result of the above measurement, the multilayer pellet P obtained in the example of the present invention has a sheath thickness as the theoretical value, and has a high precision and high quality performance. It was proved to be a layer pellet P.

[0044]

According to the method for producing a multilayer pellet according to the present invention, a die apparatus in which a plurality of extruded portions are arranged along the circumference is used for forming a multilayer strand which is a stage prior to the multilayer pellet. Thereby, a multilayer strand can be efficiently manufactured. As a die device, for the extruded portions arranged at a plurality of locations along the same circumference, the core material and the sheath material are respectively supplied to the extruded portions via supply paths extending radially from the central axis of the circumference. By supplying, the core material and the sheath material can be evenly supplied to the plurality of extruded portions, and the thickness ratio and arrangement of the core material and the sheath material in the multilayer strand formed by each extruded portion. The shape can be made to have stable quality without variation.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, and is a schematic diagram (a) showing the entire structure of a manufacturing apparatus and an enlarged cross-sectional view (b) of a manufactured multilayer strand.

FIG. 2 is a sectional view of a die device.

FIG. 3 is a front view of a die apparatus.

FIG. 4 is a schematic diagram showing a flow of a molding material.

FIG. 5 is a cross-sectional view of a die apparatus representing another embodiment.

FIG. 6 is a front view of a die apparatus.

FIG. 7 is a configuration diagram of an entire manufacturing apparatus showing another embodiment.

FIG. 8 is a sectional view of a die apparatus and an underwater cut pelletizer.

FIG. 9 is a front view of a die apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Extruder 3 Die apparatus 4 Cooling tank 5 Drainer 6 Pelletizer 7 Underwater cut pelletizer 8 Temperature controller 9 Dehydrator 10 Die main body 12 Extrusion port 14 Core nozzle 20 Core material supply port 22 Main supply path 24 Radiation Direction supply path 26 Parallel direction supply path 40 Sheath material supply port 42 Main supply path 44 Radial direction supply path 46 Parallel direction supply path 50 Extruder 52 Holder hole 54 Pressing member 60 Sheath holder

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naohiko Mushiaki 1-35 Morimoto, Itami-shi, Hyogo Sumika Color Co., Ltd., Osaka Plant F-term in Ikegai Tsukuba Plant (reference) 4F201 BA03 BC17 BC19 BC29 BD05 BL13 BL29 BL42 BM06

Claims (5)

[Claims] 1. A method for producing a multilayer pellet having a core-sheath structure in which a molding material serving as a sheath is coated on the outer periphery of a molding material serving as a core, wherein a plurality of extruded portions are arranged along a circumference. (A) supplying the core material and the sheath material to the die device, and (b) extruding the multilayer strand by concentrically covering the outer periphery of the core material with the sheath material from the respective extruded portions.
And (c) producing a multilayer pellet by cutting a plurality of extruded multilayer strands. 2. The method for producing a multilayer pellet according to claim 1, wherein the multilayer strand extruded in the step (b) has an outer diameter of 1 to 10 mm. 3. A die apparatus used for producing a multi-layer pellet having a core-sheath structure in which a molding material serving as a sheath is coated on the outer periphery of a molding material serving as a core, wherein the core material is supplied with the core material. A supply port, a sheath material supply port to which the sheath material is supplied, an extruded portion disposed at a plurality of locations along the same circumference, and covering the outer periphery of the core material concentrically with the sheath material and extruding; After extending from the core material supply port to the center axis of the circumference where each extruded portion is disposed, the core material is supplied in a radial direction from the center axis toward each extruded portion to supply the core material. A core material supply path leading from the mouth to the center of each extruded part, and extending from the sheath material supply port to the central axis of the circumference where each extruded part is arranged, and then extruding each part from the central axis. The sheath material is extended in the radial direction toward the forming part, and the core material of each extruded part is supplied from the sheath material supply port. Die assembly and a Sayazai supply passage leading to the outer circumference of. 4. The die device according to claim 3, wherein the extruded portions are detachable from a main body of the die device for each extruded portion. 5. A die device according to claim 3 or 4, a core material supply device for supplying the core material to the die device, a sheath material supply device for supplying the sheath material to the die device, An apparatus for producing a multilayer pellet, comprising: an underwater cut pelletizer disposed adjacent to an extrusion section of a die apparatus; and a temperature control device for heating at least the extrusion section of the die apparatus.