JPH08323743A - Extrusion mold for thermoplastic resin of pellet - Google Patents

Abstract

PURPOSE: To obtain a non-defective product without clogging of a nozzle, to easily disassemble and clean by removing a head from a mold and to improve the drawing efficiency of resin strand by providing two or more heads having two or more nozzles of a predetermined diameter at the outlet of the mold. CONSTITUTION: Two or more heads 3 each having two or more nozzles 30 each having a diameter of 0.25 to 3mm are provided at the outlet surface 30 of a mold 2 mounted at the end side of an extruder. The heads 3 are generally formed of metal, coated to suppress the heating in the nozzle 30, thereby increasing the range of the condition for molding a non-defective product. When a pellet containing foaming agent is, for example, manufactured, first, thermoplastic resin is supplied to an extruder, foaming agent is added to be mixed with it, and then the mixture is cooled. Then, the resin is passed through the mold 2 mounted at the end of the extruder and extruded in a strand-like state from the two or more heads 3 provided at the mold 2. Thereafter, it is cooled, cut in a pellet-like state, and formed as thermoplastic resin particles.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a die for extruding a thermoplastic resin for pellets.

[0002]

2. Description of the Related Art A conventional method for producing thermoplastic resin pellets, which are thermoplastic resin particles, is a conventional method for producing a thermoplastic resin pellet. At the same time as the resin is discharged from the nozzle, it is cut in water to make pellets, and a method such as underwater cut pelletizing (hot cutting method) is used, and strands extruded from water through water are extruded into strands and pelletized from water. [Strand method (Japanese Patent Publication No. 48-40053 and JP-A-4-3633)
No. 42, etc.)]), but the extrusion die according to the present invention relates to the latter strand type die.

[0003] Conventionally, a strand type mold has been used in which the mold outlet surface has a rectangular or circular shape and has a plurality of nozzles on those surfaces. . However, when these molds are operated for a long time, the nozzles are clogged, and disassembly and cleaning are required, which requires much time for disassembly. Also, when changing the flow characteristics of the resin (for example, MI (melt index) for the same resin
When changing. Also, when changing to a different resin, changing the amount or type of foaming agent, etc.), it is necessary to adjust the flow within the mold, it is necessary to disassemble the mold and reassemble the parts, and it takes a lot of time. It was necessary and had problems such as low work efficiency.

An object of the present invention is to provide a die for extruding a thermoplastic resin for pellets, which can solve the above-mentioned problems through intensive studies.

[0005]

As a die for extruding a thermoplastic resin for pellets according to the present invention to achieve the above object, a diameter of 0.25 to 3 mm is set forth in claim 1.
It is characterized in that two or more die having two or more nozzles are provided at the die outlet. Further, in order to more easily achieve the above object, in the present invention, as in claim 2, a die outlet provided with a die is provided with two or more die in one row.
It is characterized in that it is arranged in rows or a plurality of rows.

According to the second aspect, the die exit surface is suitable for both a square shape and a circular shape. Further, regarding the embodiment of the mouthpiece array in a plurality of rows, the mouthpiece array position may be different for each row as in claim 3. Further, as a concrete embodiment of each base, claim 4
As described above, it is preferable that at least a part or all of the nozzle serving as the resin passage of the die is made of ceramics containing zirconia.

[0007]

The present invention is configured as described above, and as in claim 1, two or more die having two or more nozzles having a diameter of 0.25 to 3 mm are provided at the die outlet. By making it possible to improve the resin outflow from the nozzle, it is possible to provide pellets efficiently and stably, in the case of a resin containing a foaming agent, good foamed pellets required even when formed as pellets after outflow. It will be easier to provide.

That is, when the diameter of the nozzle is less than 0.25 mm, the extrusion pressure by the nozzle becomes high, heat is generated, the flow of the resin in the nozzle is disturbed depending on the extrusion amount, and the resin strand is cut. In the case of using a foaming agent or when the resin flows out from the nozzle in the case of containing a foaming agent, foaming occurs more than necessary and a good pellet cannot be obtained. Therefore, if the number of nozzles is increased, nozzle clogging will increase partially, and production efficiency will fall.

On the other hand, if the nozzle diameter exceeds 3 mm, when the foaming agent is contained, the pressure in the nozzle is insufficient, and when the resin exits the nozzle, excessive foaming occurs. Therefore, when the number of nozzles is reduced, the diameter of the strand that flows out becomes large, the pellet size becomes too large, and the workability also deteriorates. Therefore, it is necessary to configure the nozzle diameter as specified in claim 1 above.

Further, it is preferable that two or more dies are arranged in one row or in a plurality of rows at the die outlet for providing the die (claim 2) in order to improve the extraction efficiency of the resin strands. Particularly in the case of an array of a plurality of rows, it is preferable to shift the die array position for each row so as to be different from each other in order to prevent the resin strands from contacting each other (claim 3). It is preferable to use ceramics containing zirconia in at least a part or all of the nozzles that serve as resin passages in the die (claim 4) because the heat resistance and durability of the die are increased and the life of the die is extended.

[0011]

EXAMPLES Next, examples of a mold for extruding a thermoplastic resin pellet of the present invention will be sequentially described with reference to the drawings. In FIG. 1, 1 is an extruder, 2 is an extrusion die at the end of the extruder, 3 is a die with a nozzle provided in the extrusion die, 4 is a cooling device for extruded resin strands, and 5 is a pellet. A cutting device, 6 is a foaming agent press-fitting device.
The nozzle base 3 with a nozzle is illustrated in FIGS. 2 and 3, and assuming that the area of the inlet 31 of the nozzle 30 of the base 3 is S ₁ and the area of the outlet 32 is S ₀ , there is no change in shape on the way. Regardless of this, it is preferable that the range of 2> S ₁ / S ₀ ≧ 1 is satisfied from the viewpoint of preventing foaming more than necessary in practice.

The diameter D at the outlet of the nozzle 30 having two or more nozzles in each of the mouthpieces 3 is 0.25 m.
It needs to be specified in the range of m to 3 mm. Because, if it is less than 0.25 mm, the pressure by the nozzle 30 becomes high, heat is generated, and depending on the extrusion amount, the nozzle 3
The flow of resin in 0 is disturbed, and cutting occurs. Also,
In the case of containing a foaming agent, when the resin comes out of the nozzle 30, foaming occurs more than necessary, and a good product cannot be obtained. Therefore, if the number of nozzles 30 is increased, the nozzle clogging will increase partially and the production efficiency will decrease. On the other hand, when it exceeds 3 mm, the pressure in the nozzle 30 becomes insufficient when the foaming agent is contained, and when the resin exits the nozzle 30, excessive foaming occurs. If the number of nozzles 30 is reduced, the size of the pellet becomes too large and the workability deteriorates.

The base 3 has a plurality of nozzles 30. The nozzle 30 is generally provided in the die 3 of the tip exit surface 20 of the die 2 of the extruder 1 that extrudes molten resin, and does not increase the area S ₀ near the exit 32 from the area S _{1 of the} entrance 31. In addition, it is a hollow one that is continuous from the inlet 31 to the outlet 32. This is shown in FIGS. 2 and 3. In FIG. 2, the die 2 is screwed 7 to the tip of the extruder 1. For the sake of explanation, FIG. 2 and FIG. 3 show a state in which only one nozzle 30 is cut. The die 2 is provided with a die 3 having a hollow nozzle 30 formed on the outlet surface 20. The length of the nozzle portion is L and the diameter of the outlet 32 is D. It may be chamfered by cutting the edge E at the nozzle exit. In addition, the edge E may be chamfered or the area may be enlarged to some extent near the exit. However,
The diameter S ₀ of the chamfered outlet 32 is the diameter just inside the chamfered portion. Arrow A indicates the flow direction of the resin.

In the extruder 1 shown in FIG. 1, the shape of the exit surface 20 of the mold 2 attached to the tip side of the extruder 1 is rectangular as shown in FIG. 4 and that as shown in FIG. The circular shape shown in FIG. 6 is a square shape, and these are the most commonly used shapes, but the shapes are not necessarily limited to these shapes, and other shapes can be used. Then, a mouthpiece 3 having a plurality of nozzles 30 formed on the outlet surface 20.
2 or more, for example, screwed 7
It is attached at.

In the case of any shape, the outlet face 20 is provided with a plurality of caps 3 in a single row, and as shown in FIGS. It is desirable to attach a plurality of mouthpieces 3 in each row to a plurality of rows or more. For example, a staggered shape (FIG. 4) in which the locations of the mouthpieces 3 in each row are different is a udon shape that is discharged from the nozzle 30 It is also advantageous in that the resin strands can be smoothly drawn out without interfering with each other and sticking together. Further, in the die 2, the inlet side of the die 3 to the nozzle 30 is formed by being conically narrowed, and it is preferable to carry out the treatment so that the resin does not stay near the inlet of the nozzle 30. This point is the same even if the number of nozzles 30 in the base 3 increases, and even if the nozzle inlet 31 serving as the resin inlet of the base 3 is formed into a conical shape, the same effect can be obtained. Good.

Further, FIG. 7 illustrates a cross section when the die 3 is arranged in the mold 1 in only one row, and FIG. 8 illustrates a cross section when a plurality of rows are arranged. In practice, the nozzle 30 opened in the base 3
Is at least 3 apart from the nearest nozzle 30 next to it.
It is necessary to set the length to at least mm, because this is to prevent the resin strands from adhering to each other from sticking to each other and to facilitate the take-up work. 9A to 9E show examples of the shape of the die and the position of the nozzle 30, but the invention is not limited to these.

The diameter D and the length L of the outlet 32 of the nozzle 30 are in the range of L / D of 1 to 20. L / D is 1
When it is less than the above value, the resin flow from the nozzle 30 is not stable when the nozzle diameter is small, and when the nozzle diameter is large, the pressure is insufficient and the resin foams more than necessary. If it exceeds 20, the pressure from the nozzle 30 becomes high and heat is generated, resulting in excessive foaming. When the nozzle diameter is small, heat generation is especially large. If the nozzle diameter is large, if bubbles are created inside the pellets even if control is performed within the required foaming, the bubble size becomes large and the quality of the final product deteriorates.

The base 3 to be used is generally made of metal, and is used in the market such as Teflon coat, Kanigen plating, Nidax Caniflon, Fukudaloy, Clean S treatment, Teflon or silicon plasma treatment,
It is preferable that the plate has been treated with a Protonix system or a treatment such as chrome plating. Sialon treatment is also effective. In addition, Teflon may be processed on zirconia-based ceramics or ceramics. These treatments may be performed on at least a part of or all of the nozzles forming the resin passages, or on the resin passage surface of the mold body.

By these coating treatments, heat generation in the nozzle 30 can be suppressed, and the range of conditions in which a good product can be obtained is expanded. Among these, the die of ceramics containing zirconia has good heat resistance and durability, and also has good slidability and can suppress heat generation. In addition, the nozzle is not clogged, and long-term continuous operation is possible. Next, as an example of using the extrusion die according to the present invention, a method for producing foaming agent-containing pellets will be described.

First, a thermoplastic resin is supplied to the extruder 1,
After adding and mixing a foaming agent to this, it is cooled. After a while
The resin passes through a die 2 shown in FIG. 1 attached to the tip of the extruder 1 and is extruded in a strand form from several die 3 attached to the die 2. Then, it is cooled and cut into pellets by a cutting device to form thermoplastic resin particles. The thermoplastic resin used in the present invention is not particularly limited, and examples thereof include polystyrene resin, polycarbonate resin, nylon resin, polyethylene terephthalate resin, ABS resin, and the like. In the styrene resin, styrene maleic anhydride, styrene. Resin copolymers and blends of acrylic acid, styrene / acrylonitrile, acrylonitrile / butadiene / styrene, etc. can be used. In particular, styrene or a block polymer composed of a styrene component is mainly surrounded by a polymer composed of a butadiene component. A resin having a structure dispersed in a styrene resin, or a resin dispersed in a styrene resin as a styrene-butadiene copolymer is preferable. These resins may be used alone, or may be a mixture of these resins or a mixture of these with another styrene resin.

Examples of the foaming agent contained in the thermoplastic synthetic resin include normal-butane, iso-butane, neo-pentane, normal-pentane, iso-pentane, n-hexane, neo-hexane, propane and CH. ₂ FCF ₃ ,
1,1,1,2-Tetrafluoroethane (HFC-134
a), CH ₃ CHF ₂ (HFC-152a), CH ₃ C
_{F 3 (HFC-143a),} CF 3 CHF 2 (HFC-
125), CH ₂ F ₂ (HFC-32), etc. can be used,
It is also possible to use a mixture of these with air, N ₂ , CO ₂ and an organic-inorganic foaming agent generating N ₂ or CO ₂ .

Specific examples of manufacturing will be shown below. <Specific Example> Example 1 The ingredients shown in Table 1 were blended, charged into a hopper of a 90 mm extruder, heated and melted at a screw rotation speed of 27 rpm, and a foaming agent was injected at about 1.33 mol / kg, followed by cooling and then extruding To 112 nozzles for all caps (14 caps having 8 nozzles on the circumference are used), nozzle diameter 0.7 mm, nozzle type L / D = 7 shown in FIG. Flow into the mold and extrude at a nozzle internal speed of 35.4 cm / sec, take up the resin strand at a take-up speed of 63 cm / sec, pelletize it to a length of 2.58 mm, and a caliber of 2.58 mm.
Pellets having an expansion ratio of 1.10 were obtained in a substantially cylindrical shape. The nozzle is made of zirconia ceramics, the water surface distance from the nozzle outlet to the water tank is 5 mm, the first water tank temperature is 32 ° C, the second water tank is 31 ° C, and the drying time is 48 ° C.
It was seconds. The pellet was sliced parallel to the cylindrical surface, and the bubbles on the inner surface were measured and found to be 10 to 50 μm. The residual gas was 1.18 mol / kg after one day and 0.79 mol / kg after one week. The pre-expansion ratio was 0.1 kg / cm ² after one day and the product was foamed with steam for 3 minutes. 75 times the inner diameter of the bubble is 0.5 mm
It was below. The pre-expanded particles were steam-molded on the next day with a sample having a thickness of 50 mm and a width of 300 mm and a length of 400 mm, and the result was 65 times, and the bending strength was 2.65 kgf / cm.
² , the compressive strength was 0.88 kgf / cm ² (5% compression), and a good molded product was obtained with no problems in fusion property and appearance.

[0023]

[Table 1]

[0024]

As described above, the die for extruding the thermoplastic resin for pellets according to the present invention has a diameter of 0.25-3.
Since two or more die having two or more mm nozzles are provided at the die outlet, it is possible to efficiently draw out the resin strand that becomes the thermoplastic resin for pellets from the die,
In the case of the resin containing the foaming agent, it is possible to prevent the foaming more than necessary and to provide the good product without causing the nozzle clogging.

Further, since the mouthpiece can be removed from the mold, the disassembly and cleaning can be easily performed without replacing the whole mold. After the replacement, the spare cap can be used for operation, and the replaced cap can be maintained during the operation. Furthermore, when two or more ferrules in one row are arranged in one row or a plurality of rows, it is convenient for improving the extraction efficiency of the resin strands, and the arrangement positions are different for each row. In this case, the resin strands can be prevented from sticking to each other and can be smoothly drawn out.
Further, if at least a part of the die that serves as a resin passage or all of the die is made of zirconia-containing ceramics, heat resistance and durability of the die are increased, and the life of the die is extended, which is advantageous.

[Brief description of drawings]

FIG. 1 is a schematic view of an entire extrusion device.

FIG. 2 is a sectional view of a die outlet side.

FIG. 3 is an enlarged cross-sectional view of a die.

FIG. 4 (a) is a front view of the die exit side with the nozzle omitted. (b) It is a side view of the same die exit side.

FIG. 5 is a side view of the die outlet side in another shape with the nozzle omitted.

FIG. 6 is a side view on the die outlet side according to still another shape in which the nozzle is omitted.

FIG. 7 is a cross-sectional view in the case where the mouthpiece has one row.

FIG. 8 is a cross-sectional view in the case of two rows of caps.

9 (a) to 9 (e) are side views of bases having different outer shapes and different nozzle arrangements.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 2 Mold 20 Exit face of mold 3 Base 30 Nozzle 31 Nozzle inlet 32 Nozzle outlet

Claims (4)

[Claims] 1. A die for extruding a thermoplastic resin for pellets, wherein two or more die having two or more nozzles having a diameter of 0.25 to 3 mm are provided at the die outlet. 2. A die for extruding a thermoplastic resin for pellets according to claim 1, wherein two or more die in one row are arranged in one row or a plurality of rows at a die outlet provided with the die. Type. 3. A die according to claim 2, wherein two or more die are arranged in a plurality of rows, wherein the die arrangement position is different for each row. Extrusion die. 4. A thermoplastic resin for pellets according to claim 1, wherein at least a part or all of a nozzle serving as a resin passage of the die uses ceramics containing zirconia. Extrusion die.