AU2002301682B2

AU2002301682B2 - Die apparatus for use in resin extrusion machine, and extrusion molding method

Info

Publication number: AU2002301682B2
Application number: AU2002301682A
Authority: AU
Inventors: Satoshi Katoh; Yoshimitsu Shirai; Sakae Sone; Tsugio Tenda
Original assignee: Polyplastics Co Ltd
Current assignee: Polyplastics Co Ltd
Priority date: 2001-11-01
Filing date: 2002-10-29
Publication date: 2004-09-30
Anticipated expiration: 2022-10-29
Also published as: JP2003136579A; CN100430195C; MY132561A; CN1417016A; TW565498B; JP3908504B2; HK1054893A1

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Polyplastics Co., Ltd.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Die apparatus for use in resin extrusion machine, and extrusion molding method The following statement is a full description of this invention, including the best method of performing it known to me/us:-

DESCRIPTION

TECHNICAL FIELD The present invention relates to a die apparatus for use in a resin extrusion machine for extrusion molding of resin, in particular, pellet molding, as well as to an extrusion molding method. More particularly, the invention relates to a die apparatus in which a protruding nozzle is provided on a die, and air is jetted from an end potion of the protruding nozzle to an extruded resin material to thereby prevent generation of "adhering resin" at the die exit and prevent cutting of resin such as breakage of a strand, as well as to an extrusion molding method.

BACKGROUND ART Conventionally, resin pellets have generally been manufactured by a method in which molten resin is discharged from a die of an extrusion machine in the shape of a strand, which is then cooled for solidification and cut for pelletization. However, when molten resin is continuously discharged from a die nozzle portion, solidified and adhering mater of resin (called eye mucus; hereinafter referred to as "adhering resin") is generated and accumulated in the vicinity of the nozzle portion, and breakage of the strand or other problems occur, preventing stable operation. Further, when the operation is continued without removal of adhering resin, the adhering resin itself discolors, and falls under its own weight and is included in the product as tramp material. In such a case, the tramp material must be removed after pelletization.

The mechanism of generation of adhering resin is complicated and has not yet been completely elucidated.

However, presumably, generation of adhering resin is mainly caused by friction between the inner surface of a nozzle and molten resin and viscoelastic characteristics of molten resin such as melt fracture. Proposed measures against include adding a lubricant to resin and regulating the surface roughness of the inner surface of the nozzle. However, the former requires modification of the composition of the product, and the latter does not provide any clear effect of mitigating the problem. Measures against include methods for coping with die swell of resin at the exit of the nozzle; a method in which the interior of the nozzle is formed in the shape of a horn opened toward the flow direction of resin to thereby smooth the flow of molten resin, and a method in which the exit is formed to have a rounded circumferential edge. Although these methods can suppress the amount of generated adhering resin, generation of adhering resin cannot be prevented completely. No universal technique for preventing generation of adhering resin has yet been established.

Meanwhile, in place of methods of preventing generation of adhering resin, there has been attempted use of a method in which generated adhering resin is removed-before it grows to a size at which the adhering resin deteriorates product quality or hinders operation. For example, Japanese Patent Application Laid-Open (kokai) Hll-254430 discloses a method in which steam is jetted from a die toward the same direction as the moving direction of a discharged strand and in parallel thereto.

However, the above-mentioned technique has the following drawbacks. Since the structure of a steam jetting opening prevents its disposal near a strand, adhering resin generated between the steam jetting opening and the nozzle cannot be removed until it grows and accumulates to a certain size. Therefore, inclusion of small adhering resin into products cannot be avoided. Moreover, the disclosed technique employs hot steam of 150 to 450 0 C, which is dangerous for workers and may cause alteration of properties of resin or absorption of moisture.

DISCLOSURE OF THE INVENTION In view of the foregoing, an object of the present invention is to provide a die apparatus and an extrusion molding method which are safe, prevent generation of adhering resin for a long period of time, and prevent breakage of a strand, which would otherwise occur due to the presence of adhering resin.

QA:OPER\GCP2002301682c.doc-30i08/04 4 In order to solve the above-described problems, the present inventors have carried out earnest studies and as a result have found that when a protruding nozzle is employed at a molten resin exit, the area of contact between generated adhering resin and the nozzle portion is minimized; that when, in combination of use of such a protruding nozzle, air is jetted at the nozzle end portion in such a manner that the jetted air forming an annular layer along the circumference of the nozzle end portion is jetted toward a resin strand, adhering resin is not generated at all; and that since the annular layer of jetted air maintains the shape of the resin strand, breakage of the strand can be suppressed. The present invention has been completed on the basis of these findings.

More particularly the invention provides a die apparatus used in a resin extrusion machine, comprising a die, a protruding nozzle, and an air jetting unit, wherein the die has at least one resin extrusion hole; the protruding nozzle is provided at a resin exit portion of the resin extrusion hole, and has a hole communicating with the resin extrusion hole and a nozzle end provided at an end of the hole; the air jetting unit has an air supply port and a hole for receiving the nozzle end with a gap provided between the nozzle end and a wall surface of the hole, the air jetting unit being provided on the die to form an air chamber around the protruding nozzle, wherein when resin is extruded from the nozzle end, air supplied to the air chamber from the air supply port is jetted from the gap toward a surface of an extruded portion of the resin.

Q:\OPER\GCP\2002301682c.dc-30/08/04 Preferably, the nozzle end has an outer circumference tapered toward a tip thereof at an inclination angle a of not greater than 750.

Preferably, the wall thickness (PD-Pd)/2 of the nozzle end as measured at a nozzle end surface (14) is not greater than 2 mm, where OD is an outer diameter of the nozzle end as measured at the nozzle end surface (14) and Od is an inner diameter of the nozzle end as measured at the nozzle end surface (14) Preferably, the nozzle end surface (14) projects from an outer surface (16) of the air jetting unit by an amount of 0 to 5 mm.

The invention also provides a die apparatus used in a resin extrusion machine, comprising a die and a protruding nozzle, wherein the die has at least one resin extrusion hole; the protruding nozzle is provided at a resin exit portion of the resin extrusion hole, and has a hole communicating with the resin extrusion hole and a nozzle end provided at an end of the hole; an end surface of the nozzle end has an opening of an annular passage, which is formed in the nozzle end concentrically with the hole so as to have an end surface gap; and the annular passage communicates with an air supply port, wherein air supplied from the air supply port is passed through the annular passage and is jetted from the end surface gap toward a surface of an extruded portion of resin.

Q:\OPER\GCP 002301682cd.-30i08i04 6 Preferably, the annular passage (17) inclines toward a tip end; a flow direction of resin, at an inclination angle of not greater than 750 with respect to the flow direction of resin.

Preferably, a minimum nozzle wall thickness between the annular passage (17) and the nozzle hole is not greater than 2 mm.

Preferably, air is jetted from the gap or the end surface gap (18) at a linear speed of 2 to 80 m/s.

The invention also provides an extrusion molding method wherein air is jetted to a surface of resin extruded from a die of a resin extrusion machine so as to substantially prevent generation of adhering resin.

Preferably, extrusion is performed by use of a die apparatus according to any one of first through eighth inventions.

Q:\OPER\GCP\2002301682c.doc-30/08/04 7 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross sectional view of an example of the protruding nozzle used in a die apparatus of a resin extrusion machine according to the present invention.

FIG. 2(a) is a cross sectional view of an example of the die apparatus of the resin extrusion machine according to the present invention taken along the flow direction of resin.

FIG. 2(b) is an enlarged view of the protruding nozzle and a hole of an air jetting unit into which the protruding nozzle is fitted.

FIG. 3(a) is a plan view of the air jetting unit as viewed from the outer side thereof.

FIG. 3(b) is a plan view of the air jetting unit as viewed from the inner side thereof.

FIG. 4 is a cross sectional view of another example protruding nozzle used in the die apparatus of the resin extrusion machine according to the present invention.

FIG. 5 is a cross sectional view of still another example protruding nozzle used in the die apparatus of the resin extrusion machine according to the present invention.

FIG. 6 shows an outside plan view, an elevational view, and a side view (as viewed from the right-hand side in the outside plan view), in this sequence from the upper side, of a die apparatus of an extrusion machine used in Example 2.

DESCRIPTION OF REFERENCE NUMERALS 1: die, 2: protruding nozzle, 2-1: molten resin inlet, 2-2: molten resin outlet, 3: hole, 4: nozzle end, 5: resin extrusion hole, 6: air jetting unit, air jetting unit, 7: hole, hole, 8: gap, 9: air supply port, 10: air chamber, air chamber, 14: nozzle end surface, 16: outer surface, 17: annular passage, 18: end surface gap, 19: air supply port, 21: packing BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will next be described.

FIG. 1 is a cross sectional view of an example of a protruding nozzle 2 used in a die apparatus of a resin extrusion machine according to the present invention, taken along a flow direction of resin.

FIG. 2(a) is a cross sectional view of the die apparatus of the resin extrusion machine according to the present invention, taken along the flow direction of resin.

A protruding nozzle 2 is attached to a die i, on which an air jetting unit 6 is provided in order to form an air chamber around the protruding nozzle 2. A nozzle end 4 of the protruding nozzle 2 is fitted into a hole 7 formed in the air jetting unit 6, whereby, as shown in FIG. a gap 8 is formed between the nozzle end 4 and the wall surface of the hole 7.

As shown in FIG. i, the protruding nozzle 2 has a projecting exit end from which molten resin is extruded. In FIG. i, reference numeral 2-1 denotes a molten resin inlet located within the extrusion machine; reference numeral 2-2 denotes a molten resin exit located on the strand side; and reference numeral 3 denotes a hole formed in the protruding nozzle 2 to extend between the molten resin inlet 2-1 and the molten resin exit 2-2. The nozzle end 4, which is an end portion of the protruding nozzle 2 located on the resin exit side, has a tapered outer circumference such that the diameter decreases toward the tip thereof. In the present embodiment, the protruding nozzle 2 is attached to the die i.

However, the protruding nozzle 2 may be formed integrally with the die i.

As shown in FIG. the air jetting unit 6, which is attached to the die i, has the above-described hole 7 for receiving the nozzle end 4 and forming the gap 8, and, in cooperation with the die i, forms the air chamber 10 around the protruding nozzle 2. An air supply port 9 (see, for example, FIG. 6) is provided in the air jetting unit 6. Air supplied from the air supply port 9 fills the chamber 10 and is caused to jet from the exit; the gap 8 between the nozzle end 4 and the wall surface of the hole 7, to the surface of a resin strand extruded from the nozzle end 4. As a result, nuclei of adhering resin, which would otherwise adhere to the nozzle end portion and grow there, are pressed against the resin strand to thereby suppress adhesion of the nuclei to the nozzle end portion. Further, even when nuclei of adhering resin adhere to the nozzle end portion, the nuclei are blown away before growing to adhering resin.

The hole 3 shown in FIG. 1 may have any shape. For example, a portion of the hole 3 on the resin inlet 2-1 side may be increased in diameter toward the inlet to form a hornlike shape, and/or a portion of the hole 3 on the resin exit 2-2 side may be increased in diameter toward the exit to form a horn-like shape. Alternatively, the exit portion of the hole 3 may be formed to have a rounded circumferential edge.

The tapered outer circumference of the nozzle end 4 of the protruding nozzle 2 preferably has an inclination angle a of not greater than 750, more preferably, 20 to 600. When the angle x exceeds 750, an annular layer of air jetted toward the circumference of the strand may undesirably cut the strand. Further, when the angle a becomes excessively small, the tip portion becomes excessively sharp, which is undesirable from the viewpoint of strength. Moreover, the wall thickness of the nozzle end portion D-d)/2 is preferably not greater than 2 mm, where D is the outer diameter of the nozzle end portion and 4d is the inner diameter of the nozzle end portion. More preferably, the wall thickness of the nozzle end portion is decreased to a possible limit above which the nozzle end portion does not break mechanically. When the wall thickness of the nozzle end portion exceeds 2 mm, the contact area between the nozzle and generated adhering resin increases, which makes it impossible to remove the adhering resin until it grows to a certain size. In addition, jetted air disperses before reaching the resin strand, thereby greatly lowering the effects of the present invention.

FIG. 3(a) is an outside plan view of the air jetting unit 6, and FIG. 3(b) is an inside plan view of the air jetting unit 6 as viewed from the side of the die 1.

The air jetting unit 6 shown in FIGS. 3 and 3(b) operates properly so long as the inner diameter of the hole 7 is slightly greater than the outer diameter of a portion of the protruding nozzle to be fitted into the hole 7. The main body of the air jetting unit 6 may assume any shape. Further, no particular limitation is imposed on the position of the air supply port 9, and the air supply port 9 may be provided at an arbitrary position on the air jetting unit 6 (see FIG.

6).

FIG. 2(b) is an enlarged view of the protruding nozzle 2 and the corresponding hole 7 of the air jetting unit 6 into which the protruding nozzle 2 is fitted. The gap 8 between the protruding nozzle 2 and the wall surface of the hole 7 has a size Z as shown in FIG. which is determined in such a manner that the linear velocity of jetted air falls within a range of 2 to 80 m/s; the size Z is preferably set to about 0.2 to 1.5 mm depending on the flow rate and pressure of air that can be supplied. Note that although the arrows indicating the size Z in FIG. 2(b) are depicted not perpendicular to the gap 8, the size Z is a value as measured perpendicular to the gap 8. When a plurality of resin extrusion holes 5 are provided, the gaps 8 of the respective holes 5 are not necessarily identical in size, and the gaps may vary in size so long as the linear velocity of air jetted from each gap 8 falls within the range of 2 to 80 m/s.

The end surface 14 of the protruding nozzle 2 must project from the outer surface 16 of the air jetting unit 6 by an amount of 0 to 5 mm, preferably 0 to 3 mm. When the projection length is less than 0 mm; when the end surface 14 of the protruding nozzle 2 is retreated from the outer surface 16 of the air jetting unit 6, resin may undesirably block the gap 8. When the projection length is in excess of 5 mm, jetted air disperses before reaching the resin strand, thereby greatly lowering the effects of the present invention.

FIG. 4 is a cross sectional view of another example protruding nozzle 2 used in the die apparatus of the resin extrusion machine according to the present invention, taken along the flow direction of resin.

An end surface 14 of a nozzle end 4 has an opening of an annular passage 17, which is formed in the nozzle end 4 concentrically with the hole 3, so as to have an end surface gap 18. The annular passage 17 communicates with an air supply port 19. Air supplied from the air supply port 19 flows through the annular passage 17 and jets from the end surface gap 18 toward the surface of an extruded resin strand.

No limitation is imposed on the manner of attaching the nozzle end 4 to the main body portion of the protruding nozzle 2. The nozzle end 4 may be attached to the main body portion of the protruding nozzle 2 by means of a screw engagement having a cutaway portion, partial welding or bonding, or any other suitable joining means. Air is supplied through the cutaway portion of the thread, unwelded portions, or unbonded portions.

In the structure of FIG. 4, no limitation is imposed on the manner of supplying air to the air supply port 19. For example, an air jetting unit 6' having a structure similar to that shown in FIG. 1 may be used. The air jetting unit 6' has a tapered hole into which the nozzle end 4 formed into a tapered shape is closely fitted, and forms an air chamber 10' around the protruding nozzle 2 in cooperation with the die 1. Alternatively, instead of providing the air jetting unit the air supply port 19 may be connected to an air source by use of an air supply pipe.

In the example of FIG. 4, the size Z of the end surface gap 18 can be readily set to a predetermined desired value, and establishment of close contact between the nozzle end 4 and the wall surface of the hole 7' of the air jetting unit 6' can be readily established through fitting of the nozzle end 4 to the hole When the nozzle end 4 is attached through screw engagement, the gap size Z and the projection amount can be changed. Therefore, screw engagement can be employed in a case in which the die 1 has a large number of resin extrusion holes 5 arranged on its circular surface and the gap size Z of each nozzle must be maintained constant to a possible extent, or in a case in which articles having a complicated cross-sectional shape are to be produced through extrusion.

FIG. 5 is a cross sectional view of still another example protruding nozzle 2 used in the die apparatus of the resin extrusion machine according to the present invention, taken along the flow direction of resin.

FIG. 5 shows a modification of the die apparatus shown in FIG. 4. The nozzle end 4 has a shape of a box nut. One or more, preferably four or more, air supply ports 19 are formed on the side surfaces of the box-nut-shaped nozzle end 4. Air supplied through the annular passage 17 and jetted from the end surface gap 18 is directed to the surface of an extruded resin strand.

In the example shown in FIG. 5, the size Z of the end surface gap 18 and the projection length can be readily adjusted and fixed to respective predetermined desired values.

Further, close contact between the nozzle end 4 and the wall surface of the hole 7' of the air jetting unit 6' can be readily established through fitting of the nozzle end 4 to the hole 7' via a packing 21.

In the structure of FIG. 5, no limitation is imposed on the manner of supplying air to the air supply port 19. For example, an air jetting unit 6' having a structure similar to that shown in FIG. 1 may be used. The air jetting unit 6' has a hole into which a smaller diameter portion (stepped portion) of the nozzle end 4 is closely fitted, and, in cooperation with the die 1, forms an air chamber 10' around the protruding nozzle 2. Alternatively, instead of fitting the nozzle end into the hole, the nozzle end surface 14 may be brought into contact with the air jetting unit 6' in which a hole 7' is formed in such a manner that the annular passage 17 is not blocked by the air jetting unit 6'.

Alternatively, instead of providing the air jetting unit the air supply port 19 may be connected to an air source by use of an air supply pipe.

Although the term "air" used herein has a broad meaning to encompass not only atmospheric air but also inert gas and other suitable gases, atmospheric air is preferably used.

Air may be dried air or air having a regulated temperature and humidity. No particular limitation is imposed on the temperature of air to be jetted to resin. Although air may be used without temperature regulation, use of air having undergone temperature regulation, such as air properly heated, mitigates temperature drop at the die nozzle portion, to thereby suppress solidification of resin which would otherwise occur due to excessive cooling.

No particular limitation is imposed on resin to be used in the present invention. General purpose resin, engineering resin, or biodegradable resin may be used. Resin to be used may contain a reinforcing material such as fibers or fillers.

The present invention is particularly effective for resin which easily generates adhering resin, such as polyphenylene sulfide.

EXAMPLES

Next, the present invention will be described specifically by way of examples; however, the present invention is not limited thereto.

Example 1 A protruding nozzle as shown in FIG. 1 (4D 3.6 mm, 4d mm, a 280) was manufactured by use of a base material obtained through quenching of an alloy tool steel SKD 11.

The protruding nozzle and a ring-shaped air jetting unit (Z 0.4 mm) were used, and the projection length of the nozzle end surface from the outer surface of the air jetting unit was set to 0.5 mm. A resin strand was extruded, while air was jetted to the surface of the resin at a speed of 20 m/s.

The thus-obtained strand was cut to yield pellets. An extruder of Ikegai Corporation, model PCM 45 was used, and extrusion was performed under conditions of an extrusion rate of 20 kg/h and a screw rotation speed of 150 rpm.

Polyphenylene sulfide (PPS) containing 25 wt% glass fibers was used as a resin to be extruded. Results of the experiment demonstrate that stable operation can be continued for 6 hours without generation of adhering resin.

Example 2 A protruding nozzle (4D 4.0 mm, d 3.2 mm, a 26.50) was manufactured by use of a superhard base material.

The protruding nozzle and a ring-shaped air jetting unit (Z mm) were used, and the projection length of the nozzle end surface from the outer surface of the air jetting unit was set to 0.5 mm. A resin strand was extruded, while air was jetted to the surface of the resin at a speed of 15 m/s.

The thus-obtained strand was cut to yield pellets (see FIG.

An extruder of Japan Steel Works, Ltd., model TEX 65 was used, and extrusion was performed under conditions of an extrusion rate of 200 kg/h and a screw rotation speed of rpm. The same resin as that in Example 1 was used. Results of the experiment demonstrate that stable operation can be continued for 72 hours without generation of adhering resin.

INDUSTRIAL APPLICABILITY The present invention prevents generation of adhering resin from a die nozzle of an extrusion machine, so that strand breakage by adhering resin and inclusion of small adhering resin into products can be prevented, and thus stable extrusion can be performed continuously.

The present invention is effective for extrusion molding of articles, in particular, for extrusion molding of a strand for pelletization.

The reference numerals in the following claims do not in any way limit the scope of the respective claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

2. A die apparatus used in a resin extrusion machine according to claim i, wherein the nozzle end has an outer circumference tapered toward a tip thereof at an inclination angle a of not greater than 750.
3. A die apparatus used in a resin extrusion machine according to claim 1 or 2, wherein the wall thickness (4D- 4d)/2 of the nozzle end as measured at a nozzle end surface (14) is not greater than 2 mm, where D is an outer diameter of the nozzle end as measured at the nozzle end surface (14) and d is an inner diameter of the nozzle end as measured at the nozzle end surface (14)
4. A die apparatus used in a resin extrusion machine according to any one of claims 1 to 3, wherein the nozzle end surface (14) projects from an outer surface (16) of the air jetting unit by an amount of 0 to 5 mm. A die apparatus used in a resin extrusion machine, comprising a die and a protruding nozzle wherein the die has at least one resin extrusion hole the protruding nozzle is provided at a resin exit portion of the resin extrusion hole and has a hole (3) communicating with the resin extrusion hole and a nozzle end provided at an end of the hole an end surface (14) of the nozzle end has an opening of an annular passage which is formed in the nozzle end (4) concentrically with the hole so as to have an end surface gap and the annular passage (17) communicates with an air supply port wherein air supplied from the air supply port (19) is passed through the annular passage (17) and is jetted from the end surface gap (18) toward a surface of an extruded portion of resin.
6. A die apparatus used in a resin extrusion machine according to claim 5, wherein the annular passage (17) inclines toward a flow direction of resin at an inclination angle of not greater than 750 with respect to the flow direction of resin.
7. A die apparatus used in a resin extrusion machine according to claim 5 or 6, wherein a minimum nozzle wall thickness between the annular passage (17) and the nozzle hole is not greater than 2 mm.
8. A die apparatus used in a resin extrusion machine according to any one of claims 1 to 7, wherein air is jetted from the gap or the end surface gap (18) at a linear speed of 2 to 80 m/s.
9. An extrusion molding method wherein air is jetted to a surface of resin extruded from a die of a resin extrusion machine so as to substantially prevent generation of adhering resin. An extrusion molding method according to claim 9, wherein extrusion is performed by use of a die apparatus according to any one of claims 1 to 8. 1 I Q:\OPER\GCP\2002301682c.doc-30/08J4 22
11. Die apparatus substantially as hereinbefore described with reference to the drawings and/or examples.
12. An extrusion molding method substantially as hereinbefore described with reference to the drawings and/or examples. DATED this 30th day of August 2004 POLYPLASTICS CO., LTD. By its Patent Attorneys DAVIES COLLISON CAVE