CA2064939C

CA2064939C - Ultra-high molecular weight polyethylene thin-wall pipe, and method of and apparatus for manufacturing the same

Info

Publication number: CA2064939C
Application number: CA002064939A
Authority: CA
Inventors: Takeshi Shiraki; Iwatosi Suzuki; Kunie Hiroshige
Original assignee: Mitsui Petrochemical Industries Ltd
Current assignee: Mitsui Chemicals Inc
Priority date: 1991-04-03
Filing date: 1992-04-02
Publication date: 1995-08-01
Anticipated expiration: 2012-04-02
Also published as: TW254883B; EP0507613A2; KR920019520A; DE69216133T2; US5417561A; EP0507613A3; DE69216133D1; EP0507613B1; KR950005729B1; US5290498A; US5683767A

Abstract

An ultra-high molecular weight polyethylene thin-wall pipe which is uniform in thickness and free from a folded mark as well as a method of and an apparatus for manufacturing the same. The ultra-high molecular weight polyethylene thin-wall pipe is manufactured by supplying ultra-high molecular weight polyethylene into and melting and kneading, continuously extruding the molten substance of the ultra-high molecular weight polyethylene from a die connected to a screw of the screw extruder to form a cylindrical roughly shaped article, and diametrically expanding the cylindrical roughly extruded article by means of a tapered core and taking up.

Description

~ 2064939 TITLE OF THE INVENTION
Ultra-high molecular weight Polyethylene Thin-wall Pipe, and Method of and Apparatus for Manufacturing the Same FIELD OF THE INVENTION
This invention relates to an ultra-high molecular weight polyethylene thin-wall pipe and a method of and an apparatus for manufacturing the same. More particularly, the present invention relates to a thin-wall pipe such as a shrinkage pipe, a pipe or a film made of ultra-high molecular weight polyethylene and a method of and an apparatus for manufacturing the same.
Specifically, the present invention relates to an ultra-high molecular weight polyethylene shrink pipe which can be employed suitably as a shrink pipe for covering various roles, pipes and steel tubes for its advantages that, since, comparing with a shrink pipe obtained by a conventional blown film extrusion method, it is so thick that it can be finished by a lathe or the like and besides it is low in coefficient ., of shrinkage in a longitudinal direction, it is superior in covering efficiency and is effective to obtain an effective covering and also superior in durability, and also to a method of and an apparatus for manufacturing such ultra-high molecular weight polyethylene shrink pipe efficiently.
In addition, the present invention relates to a method and an apparatus by which an ultra-high molecular weight ~ 2064939 polyethylene film suitable for an application which needs dimensional stability because, comparing with a film obtained by a conventional blown film extrusion method, it is uniform in thickness and has no folded mark at both ear edges thereof can be obtained.
Further, the present invention relates to an ultra-high molecular weight polyethylene thin-wall pipe wherein the ratio of an outer diameter to a thickness is higher than 10 and the coefficient of thermal shrinkage is low and to a method by which an ultra-high molecular weight polyethylene thin-wall pipe of a required thickness can be manufactured readily in accordance with an application of the same as well as to a manufacturing apparatus which can be used suitably for the method.

BAXGROUND OF THE INVENTION
Ultra-high molecular weight polyethylene is superior in abrasion resistance, self-lubrication, chemical resistance and SQ forth, and is applied to various applications making use of the characteristics.
By the way, it is a conventional practice, in order to cover an outer peripheral face of a roll, a pipe, a steel tube or the like to provide weathering resistance, a chemical resistance, a durabllity and so forth, to cover the outer peripheral face of such roll, pipe, steel tube or the like with a pipe, a film or the like. In this instance, it is a - ~J 206493~

conventional practice to insert such ro]l, pipe, steel tube or the like into a shrink pipe or film and then make the shrink pipe or film to shrink and cover them over the roll, pipe, steel tubo or the~like. In such a case, shrink pipes or films made of Teflon~ are conventionally used. However, Teflon~ is inferior in abrasion resistance. For example, Teflon~ has a sand abrasion loss as high as five times that of ultra-high molecular weight polyethylene.
Thus, a shrink pipe or film made of ultra-high molecular weight polyethylene has been proposed, and a method of manufacturing a shrink tube or film made of ultra-high molecular weight polyethylene, for examp~e, by a metho~ which has been proposed and disclosed in Japanese Patent Laid-Open Application No . 62 ~1987 ) -122736 .
However, according to the method disclosed in Japanese Patent ~aid-Open Application No. 62~1987)-122736, a shrink tube or film during manufacture must necessarily be sealed to exclude internal air, therefor it is folded into a flattened - outer profi1e by means of pinch rolls. Consequently, an ul~ra-high molecular weigh~ polyethylene shrink pipe or ~i1m obtained has folded marks at both ear edges chereof, and if the shrink tube or film is caused to shrink ~o cover a roll or the like, then such folded marks will remain on ~he shrink tube or film. Therefore, the method cannot be adopted readily for an application for which a high degree of accuracy is required. Further, since a shrink tube ob~ained ~' by the method has a thickness equal to or less than 1 mm, it is difficult to finish it by lathe machining. Besides, since such product is biaxially oriented, it is also disadvantageous in that shrinkage in a longitudinal direction is great.
It is another conventional practice that, in order to cover an outer peripheral face of a roll, a pipe, a steel tube or the like to provide a weathering resistance, a chemical resistance, a durability and so forth, an ultra-high molecular weight polyethylene thin-wall pipe is heated to 100 to 130 C to expand the diameter thereof by thermal expansion and then the roll, pipe, steel tube or the like is inserted into the ultra-high molecular weight polyethylene thin pipe of the expanded diameter, whereafter the thin pipe is cooled to shrink to cover the roll, pipe, steel tube or the like.
Manufacture of the ultra-high molecular weight polyethylene thin-wall pipe is conventionally made by a method of compression molding or another method of mechanically machining a rod of ultra-high molecular weight polyethylene. However, a thin-wall pipe of an indefinite length cannot be obtained by those methods, and besides a high cost is required and it is dlfficult to manufacture such thin-wall pipe economically.
Thus, a method of manufacturing a flexible tube made of ultra-high molecular weight polyethylene has been proposed and is disclosed in Japanese Patent Publication Application ~_ 2064939 No. 2(1990)-31270 wherein ultra-high molecular weight polyethylene is melted by a screw extruder and extrusion molded from a tube die by an L/D:5 wherein a mandrel is rotated by rotation of a screw.
According to the method disclosed in Japanese Patent Publication Application No. 2(1990~-31270, flexible tubes of comparatively small diameter equal to or less then 20 mm and of comparatively thickness with a ratio of the outer diameter to the thickness equal to or less than 15 can be obtained.
But the method involves draw forming, so it has drawbacks that a pipe with an inner diameter greater than an outer diameter of a mandrel used cannot be obtained and that a pipe obtained gets to expand in diameter when it is heated.
Further, with the method, since an outer diameter is restricted by a sizer, it is difficult to obtain an inner surface with excellent smoothness. Consequently, it is difficult to efficiently manufacture a thin-wall pipe having a low coefficient of thermal shrinkage and having an inner surface with excellent smoothness.

SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an ultra-high molecular weight polyethylene thin-wall pipe which, comparing with an ultra-high molecular weight polyethylene shaped article obtained by a conventional blown film extrusion method, is uniform in thickness and free from :; ~

~ 2064q39 ' ~-a folded mark and can achieve, when it is used to cover a roll, a pipe, a steel tube or the like, a covering with a high degree of accuracy in dimension.
It is a second object of the present invention to provide a method by which such ultra-high molecular weight polyethylene shaped article can be manufactured at a high eff iciency .
It is a third object of the present invention to provide an apparatus which can be used suitably for such manufacturing method for an ultra-high molecular weight polyethylene shaped article.
It is a fourth object of the present invention to provide an ultra-high molecular weight polyethylene shrink pipe which can be employed suitably as a covering shrink pipe for various roles, pipes and steel tubes for its advantages that, since, comparing with a shrink pipe obtained by a conventional blown film extrusion method, it is so thick that it can be finished by a lathe or the like and besides it is low in coefficient of shrinkage in a longitudinal direction, it is superior in covering efficiency and is effective to obtain an effective covering and also superior in durability.
It is a fifth object of the present invention to provide a method by which such ultra-high molecular weight polyethylene shrink pipe can be manufactured at a high efficiency.

~, 2064939 It is a sixth object of the present invention to provide an apparatus which can be used suitably for such manufacturing method for an ultra-high molecular weight polyethylene shrink pipe.
It is a seventh object of the present invention to provide a method by which an ultra-high molecular weight polyethylene film which can be applied suitably for an application for which a high degree of accuracy ln dimension is required since it is uniform in thickness and has no folded mark at both ear edges thereof, comparing with a film obtained by a conventional blown film extrusion method can be obtained.
It is an eighth object of the present invention to manufacture an apparatus which can be used suitably for such manufacturing method for an ultra-high molecular weight polyethylene film.
It is a ninth object of the present invention to provide an ultra-high molecular weight polyethylene thin-wall pipe wherein the ratio of an outer diameter to a ~hickness is equal to or higher than 10 and the coefficient of thermal shrink is low and besides the average roughness of an inner surface is low.
It is a tenth object of the present invention to provide a method by which such ultra-high molecular weight polyethylene thin-wall pipe of a required thickness can be 2064q3q manufactured readily in accordance with an application thereof.
It is an eleventh object of the present invention to provide a manufacturing apparatus which can be used suitably for the manufacturing method for an ultra-high molecular weight polyethylene thin-wall pipe.
In order to attain the first object, according to the present invention, there is provided an ultra-high molecular weight polyethylene pipe-shaped article made of ultra-high molecular weight polyethylene having an intrinsic viscosity [~]
of 5.0 dl/g or more r the pipe-shaped article being uniform in thickness and free from a folded mark.
In order to attain the second object, according to the present invention~ there is provided a method of manufacturing an ultra-high molecular weight polyethylene pipe-shaped article, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic vi.scosity [~] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene in the screw extruder;
continuously extruding the molten ultra-high molecular weight polyethylene from a die having an L/D ratio of at least 10, which includes arl inner die connected to and rotated together with a screw of the extruder, disposed therein, and to form a roughly cylindrical shape; and diametrically expanding the cylindrical rough extruded article by means of a tapered core connected to the inner die, which tapered core includes a tapered portion and a cylindrical portion continuously connected after the tapered portion r and ~ 72736-68 causing the ultra-high molecular weight polyethylene to start to ~ cool to solidify at the tapered core.
In order to attain the third object, according to the present inventionr there is provided an apparatus for manufacturing an ultra-high molecular weight polyethylene thin-wall pipe! comprising:
an extruder including a grooved cylinder and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;
a die having an L/D ratio of at least 10, including an inner die connect~d to an end of the screw of the screw extruder and rotatable tc~gether with the screw and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, a tapered portion not rotata~le together with the shaft and having an increasing diameter in a downstream direction such that a maximum outer diameter therec)f is larger than the diameter of the inner die, and a c~lindrical portion provided continuously to the tapered portion.
In order to attain the fourth o~ject, according to the present invention, there i,s provided a shrink pipe made of ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 ~l~g or more, having an outer diameter (D1) of 10 mm or more and a thickness ~tl) of 0.2 mm or more with a ratio of the outer diameter t.o the thickness (D1/tl) 10 or higher~ and having a coefficient of shrinkage of 20 % or more in a diametrical direction at 140 C.

2064~3q In order to attain the fifth object, according to the present invention, there is provided a method of manufacturing an ultra-high molecular weight polyethylene -shrink pipe, com-prising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity ~] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;
continuously extruding the molten substance of the ultra-high molecular weiyht polyethylene from a die having an L/~ratio of at least 10, wherein an inner die connected to and rotated together with the screw of the screw extruder, is disposed to form an extruded article of a roughly cylindrical shape; and diametrically expanding the roughly cylindrical extruded article by means of a tapered core connected to the inner die such that the outer diameter of a maximum diametrically expanding portion may be 1.2 to 3.0 times of the outer diameter of the inner die r and taking up the extruded article at a ta~ing up rate five times or lower the extruding rate at the screw extruder, and causing the ultra-high molecular weight poly-ethylene to start to cool to solidify at a tapered or cylindrical portion of the tapered core.
In order to attain the sixth object, according to the present invention, there is provided an apparatus for manufacturing an ultra-high molecular weight polyethylene shrink pipe, comprising:
an extruder including a grooved cylinder, and a screw 206493q inserted in the grooved cylinder and having a compression ratio ~ of 1 to 2.5;
a die having an L/~ ratio of at least 10, including an inner die connected to an end of the screw and rotatable together with the screwp and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, and a tapered forming member not rotatable with the shaft and having an increasing diameter in a downstream direction such that the maximum outer diameter thereof is 1.2 to 3.0 times the diameter of the inner die.
In order-to attain the seventh object, according to the present invention, there is provided a method of manu-facturing an ultra-high molecular weight polyethylene film, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular 0 weight polyethylene;
continuously extrudiny the molten ultra-high molecular weight polyethylene from a die having an L/D ratio of at least 10, wherein an inner die connected to and rotated together with the screw of the .screw extruder is disposed in an inside of an outer die, to form an extruded article of a roughly cylindrical shape; and diametrically expanding the roughly cylindrical extruded article by means of a tapered core connected to the inner die such that the inner diameter of a maximum diametrically expanded portion of the article may be 3 or more times of the outer diameter of the inner die, and taking up the extruded article at a taking up rate three times or higher the extruding rate of the molten ultra-high molecular weight polyethylene at the screw extruder.
In order to attain the eighth object, according to the present invention~ there is provided an apparatus for manu-facturing an ultra-high molecular weight polyethylene film, 0 comprising:
an extruder including a grooved cylinder, and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;
a die having an L/D ratio of at least 10, including an inner die connected to an end of the screw of the screw extruder and rotatable with the screw and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotat~able with the inner die, ~nd a tapered forming member not rotatable with the shaft and having an increasing diameter at an angle of 5 to 50 degrees in a down-stream direction such that a maximum outer diameter thereof is equal to or more t.han 3 times the diameter of the inner die; and a take-up unit including rolls each having a length in the roll axial direction of 50 to 80 % of the width of an ultra-high molecular weight polyethylene film formed by the tapered core and folded by the rolls.
In order to attain the ninth object, according to the 13 2064~39 72736-68 present invention, there is provided a thin-wall pipe made of - ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 dl/g or more and having an outer diameter ~D2) 10 mm or more and a thickness (t2) 0.5 mm or more with a ratio of the outer diameter to the thickness tD2/t2) 1~ or higher, and having a coefficient of shrinkage of 5 % or less in a diametrical direction at 1.n~C.
In order to attain the tenth object, according to the present invention, there is a provided a method of manufacturing an ultra-high molecular weight polyethylene thin-wall pipe, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;
continuously extruding the molten ultra-high molecular weight polyethylene from a die having an L/D ratio of at least 10, including an inner die connected to and rotated together with a screw of the screw extruder, disposed in an outer die, to 0 form a roughly cylindrical extruded article; and diametrically ~xpanding the roughly cylindrical extruded articles by means of a tapere~ core connected to the inner die~
the tapered core including a tapered portion and a cylindrical portion provided continuously to the tapered portion, such that the outer diameter of a maximum diametrically expanded portion may be 1.2 to 3.0 times of the outer diameter of the inner die, taking up the roughly cylindrical extruded article at a taking up rate three times or lower than the extruding rate of the ~ 206493~

ultra-high molecular weight polyethylene at the screw extruder, ~ and causirlg the ultra-high molecular weight polyethylene to start to cool to solidify at the cylindrical portion of the tapered core.
In order to attain the eleventh object, according to the present invention, there is provided an apparatus for -~ 2064939 manufacturing an ultra-high molecular weight polyethylene thin-wall pipe, comprising:
an extruder including a grooved cylinder, and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;
a die having an L/D ratio at least 10 including an inner die connected to an end of the screw of the screw extruder and rotated together with rotation of the screw and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotated together with rotation of the inner die, a tapered forming member not rotating together with the shaft and having an increasing diameter at an angle of 5 to 50 degrees in a downstream direction such that a maximum outer diameter thereof is at least 1.2 to 3.0 times of the diameter of the inner die, and a cylindrical portion provided continuously to the tapered portion with a heat insulating material interposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description, serve to explain the principle of the invention.
Fig. 1 is a schematic view illustrating an ultra-high molecular weight polyethylene shrink pipe which is an ~ 2064939 embodiment of an ultra-high molecular weight polyethylene thin-wall pipe of the present invention;
Fig. 2 is a schematic view illustrating principal steps of a method of manufacturing the ultra-high molecular weight polyethylene thin-wall pipe;
Fig. 3 is a schematic sectional view showing principal part of a manufacturing apparatus for the ultra-high molecular weight polyethylene shrink pipe;
Fig. 4 is a schematic view illustrating a tapered core of the manufacturing apparatus for an ultra-high molecular weight polyethylene shrink pipe of the present invention;
Fig. 5 is a schematic view illustrating principal steps of a method of manufacturing an ultra-high molecular weight polyethylene film of the present invention;
Fig. 6 is a schematic sectional view showing principal part of a manufacturing apparatus for an ultra-high molecular weight polyethylene film of the present invention;
Fig. 7 is a schematic view illustrating a tapered core of the manufacturing apparatus for an ultra-high molecular weight polyethylene film of the present invention;
Fig. 8 is a schematic view showing an ultra-high molecular weight polyethylene thin-wall pipe of the present invention;
Fig. 9 is a schematic sectional view showing principal part of a manufacturing apparatus for an ultra-high molecular _ 2064939 weight polyethylene thin-wall pipe of the present invention;
~ and Fig. 10 is a schematic view showing a tapered core of the manufacturing apparatus for an ultra-high molecular weight polyethylene thin pipe of the present invention.
DETAILED DESCRIPTION OF THE DISCLOSURE
The "L/D ratio" means the ratio of the effective length to the outer diameter of a built-in screw of an injection molding machine or an extruder. The larger this ratio, the larger the heat transfer area becomes. Therefore, an extruder with a larger L/D ratio provides a better kneading effect.
The preferred embodiments of the present invention will be described in detail below.
Ultra-high molecular weight polyethylene which is a raw material for an ultra-high molecular weight polyethylene thin-wall pipe of the present invention consists mainly of ethylene and may ber for exampler homopolymer of ethylene or copolymer which consists of et.hylene as a main component and monomer copolymerizable with ethylene. The monomer co-polymerizable with ethylene may be, for example, a-olefin having a carbon number of 3 or more~ especially 3 to 20.
Such a-olefin having a carbon number of 3 or more may be, for example, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene or 1-eicocene.

- 2064~3~

Such ultra-high molecular weight polyethylene .should have an intrinsic viscosity ~] 5.0 dl/g or higher and preferably have an intrinsic viscosity [~] of 8 to 30 dl/g .so that molten substance thereof may not cause, upon molding, difference in wall thickness by twist of molten substance thereof ~y turnir,g motion thereof together with an inner die which will be hereinafter de.scribed or by distortion of the inner die, and consequently, a thin-wall pipe having a uniform thickness can be obtained.
If necessary, various sta~ilizing agents may be mixed into the ultra-high molecular weight polyethylene. The sta-bilizing agents may bet for example, heat stabilizer such as tetrakis[methylene (3,5-di-t-butyl-4-hydroxy~ hydrocinnamate]
methane, distearylthiodipropionate and so forth/ weathering agents such as bis( 2, 2 ' Ç, 6 ' -tetramethyl-4-piperidine)-sebacate, 2-(2-hydroxy-t-butyl-5-methylphenyl)-5-chlorobenzotriazole and so forth, and so forth. Further, an inorganic or organic dry color may be added as a coloring agent.
An ultra-high molecular weight polyethylene thin-wall pipe of the present invention is uniform in thickness and free from a folded mark.
The ultra-high molecular weight polyethylene thin-wall pipe may assume various forms such as a shrink pipe, a film and so forth.
A method of and an apparatus for manufacturing such ultra-high molecular weight polyethylene thin-wall pipe are generally constituted such that ultra-high molecular weight polyethylene having an intrinsic viscosity of 5.0 dl/g or more 206493~

is supplied into, and molten and kneaded in a screw extruder, ~ and then the molten substance is continuously extruded from a die having an L/D ratio of at least 10, wherein an inner die connected to and rotated with a screw of the screw extruder is disposed in the inside thereof, to form a roughly cylindrical extruded article. The roughly cylindrical extruded article is diametrically expanded by a tapered core connected to the inner die, which includes a tapered portion and a cylindrical portion provided continuously to the tapered portion. Where required, the diametrically expanded article is taken up by a take-up unit, and then the ultra-high molecular weight polyethylene starts to cool to solidify at the tapered core and then may fur~her be cooled sufficiently by a cooling apparatus to obtain a desired thin-wall pipe.
In the follQwing, the present invention will be described first by way of an example of an ultra-high molecular weight polyethylene shrink pipe as a specific form of the thin-wall pipe.
An ultra-high molecular weight polyethylene shrink pipe of the present invention has an outer diameter (D1) of 10 mm or more as shown in Fig. 1. When the outer diameter (D1) is small, a shaft for a tapered core is so thin accordingly that it cannot be connected readily to an inner dier but on the contrary when the outer di~meter IDl) is large, there is the possibility that the cost of equipment is very high, which is economically disadvantageous. Accordingly, a preferable outer diameter rar,ges from 10 to 150 mm. Furthér, the thickness (tl) should be 0.2 mm or more, and particularly the ultra-high molecular weight ~064~9 _ polyethylene shrink pipe is used for the covering of a roll, the thickness (tl) should preferably be 0.5 to 3 mm since machining a surface of the ultra-high molecular weight polyethylene shrink pipe can be performed by a lathe at a following step. In addi-tion, the ratio of the outer diameter to the thickness ~D1/tl~
should be 10 or higher and preferably from 15 to 150 in view of economy.
An ultra-high molecular weight polyethylene shrink pipe of the present invention has a coefficient of shrinkage of 20 % or more at 140 C in a diametrical direction, and when the shrink pipe is to be used as a covering member, the coefficient of shrinkage in a diametrical direction at 140 C is preferably from 40 to 150 % in order to assure a high covering strength against a core member to be coated with the shrink pipe.
Such ultra-high molecular weight polyethylene shrink pipe can be manufactured by a method comprisin0 the steps that ultra-high molecular weight polyethylene having an intrinsic viscosity of 5. n dl/g or more is supplied into~ and molten and kneaded r and then the molten substanc.e of the ultra-high molecular weight polyethylene is continllously extruded from a die having an L/D
ratio of at least 10, wherein an inner die connected to and rotated with a screw of the screw extruder is disposed in the inside thereof, to form a roughly cylindrical shape, and after that, the roughly cylind.rical extruded article is taken up at a taking up rate equal to or less than five times of the extruding rate of the ultra-high molecular weight polyethylene by the 21 7273~-68 screw extruder, while the diameter thereof is expanded by a tapered core connected to the inner die such that the inner diameter of a maximum diamet,rically expanded portion t,hereof may be 1.2 to 3.0 times of the outer diameter of the inner die and the ultra-high molecular weight polyethylene starts to cool to solidify at a tapered portion of the tapered core.
Subsequently, the manufacturing method will be described in detail in connection with an embodiment of a manufacturing apparatus for an ultra-high molecular weight polyethylene shrink pipe of the present invention shown in Figs.
2 to 4.
The manufacturing apparatus for an ultra-high molecular weight polyethylene shrink pipe shown in Fig. 2 includes as essential components a screw extruder 1, a die 2 mounted on the screw extruder 1, and a tapered core 3 provided continuously to the die 2.

The screw extruder 1 includes, as shown in Fig. 3, a grooved cylinder 4, a screw 5 inserted in the groove cylinder 4 and a hopper 6 for supplying ultra-high molecular weight polyethylene of raw material.
The inner diameter of the grooved cylinder 4 is selected suitably so that a shrink pipe of a desired outer diameter may be obtained. Meanwhile, the grooves of the grooved cylinder 4 are formed to extend linearly in a downstream direction and disposed by a number of 8 to 12 in an equidistantly spaced relationship in a circumferential direction such that the length (L/D) thereof ranges from 3 to 10 and preferably from 5 to 8. The shape of the grooves is preferably an angular shape or a semicircular shape so that they can reinforce a driving force for ultra-high molecular weight polyethylene in the extruder. Further, the screw 5 should have a compression ratio of 1 to 2, and preferably a compression ratio of 1.3 to 2Ø The effective length (L/D) of the screw 5 normally ranges from 20 to 28 or so. The length of a~compressing portion of the screw 5 ranges from 25 to 80 ~ or so of the effective length (L/D). Meanwhile, the screw flight pitch normally ranges from 0.4 to 0.8 or so.
The speed of rotation of the screw 5 is normally 10 to 30 rpm or so. Further, the hopper 6 is preferably a two-stage hopper since it facilitates, when the raw material is powder, back flows of air in the cylinder 4 and can prevent _ 2064939 occurrence of a failure in dropping of raw material which arises from a hopper bridge.
A heating barrel 7 is disposed on a circumferential wall of the screw extruder 1 in order to melt ultra-high molecular weight polyethylene supplied into the screw extruder 1, and a water cooling barrel 8 is disposed in order to regulate the heating temperature by the heating barrel 7. The heating temperature at the screw extruder 1 is normally adjusted to a temperature higher than a melting point of ultra-high molecular weight polyethylene but equal to or lower than 340 C and preferably to a temperature from 160 to 330 C.
The die 2 mounted on the screw extruder 1 is constituted from an inner die 9 and an outer die 10 in which the inner die 9 is inserted. The inner die 9 is connected to an end 11 of the screw 5 of the screw extruder 1 and is rotated by rotation of the screw 5. Meanwhile, the outer die 10 is mounted at an end 12 of the heating barrel 7 of the screw extruder 1. The die 2 has an L/D ratio at least 10 and preferably from 20 to 50. Further, the inner die 9 is preferably constituted such that, since it is rotated by rotation of the screw 5, the outer diameter of the inner die is reduced in a tapering condition from the connecting portion thereof, and then has a fixed outer diameter at the other end portion from a mid portion thereof, and besides it is coated at a surface thereof with fluorocarbon resin in order to assure high smoothness thereof with ultra-high ` ` ~, 206493q molecular weight polyethylene which circulates in the inner die 9. A heating barrel 13 is disposed on an outer circumferential wall of the die 2 for regulating the temperature of ultra-high molecular weight polyethylene which moves in the die 2. The heating temperature of the die 2 is normally adjusted to 160 to 250 C.
In the manufacturing apparatus, the tapered core 3 shown in an enlarged view of Fig. 4 is provided continuously to the inner die 9. The tapered core 3 includes a shaft 16 connected to an end 15 of the inner die 9, and a tapered forming member 17 loosely fitted on the shaft 16.
The shaft 16 connected to the end 15 of the inner die 9 is rotated together with the inner die 9 connected to the screw 5. The outer diameter of the shaft 16 ls normally smaller than the outer diameter of the inner die 9, and the length of the shaft 16 is normally equal to 10 to 50 cm or so.
Meanwhile, the tapered forming member 17 is loosely fitted on the shaft 16 by means of a bearing 14 and is mounted on the shaft 16 such that it may not rotate together with the shaft 16. The tapered forming member 17 has a tapered portion 18 which is formed in an inclined relationship at an angle normally of 5 to 50 degrees and preferably of 10 to 30 degrees with respect to an axial direction of the shaft 16 so that frictional resistance upon diametrical expansion may be reduced to perform shaping readily. The tapered forming member 17 further has a 2064~39 cylindrical portion 19 provi~ed continuously to the tapered portion 18 A coating of fluorocarbon resin such as ~eflon (registered trade mark) is preferably applied to surfaces of ~he tapered portion 18 and the cylindrical portion 19 of ~t-e tapered forming member 17 so that the coefficient of friction with an ultra-high molecular weight polyethylene molded article may be reduced to perform molding smoothly The ratio in length of the tapered portion 18 to the cylindrical portion 19 of the tapered forming member 17 in its axial direc~ion is normally set to 0 2 to 1 or so and preferal~ly to 0 3 to 0 7 or so Further the outer diame~er of the cylindrical portion 19 should be set at least to 1 2 to 3 0 times the diameter of the inner die 9 and preferably to 1 5 to 3 0 times and further preferably to 1 7 to 2 5 times ~he dlame~:er of the inner die ~
The method of the ~resent invention proceeds on the manufacturing apparatus described above such that ultra-1ligh Inolecular weight polyethylene having an in~rirlsic viscosity ~ o~ 5 0 dl/g or more ls firs~ su~pli~d into molten ~n~

kneaded in the screw extruder 1 and then the molten substance of the ultra-high molecular weiqh~ polyet~ylene is continuously extruded from t~le die 2 to form a roughly cylindrical shape whereafter the diameter of the roughly cylindrical extruded article is expanded by the tapered core 3 such that the inner diameter of a maximum diametrically ~., .

expanded portion of the cylindrical roughly molded form may be 1.2 to 3.0 times of the outer diameter of the inner die 9 of the die 2 and preferably l.2 to 3.0 times and further preferably 1.7 to 2.5 times of the diameter c,f the inner die 9 so that a good shrink pipe of an appropriate thickness can be obtained. The thus diametrically expanded shrink pipe is cooled in a cooling tank 20 and t.hen taken up by a take-up unit 21. The taking up rate of the take-up unit 21 is set equal to or lower then 5 times the extruding rate of the ultra-high molecular poly-ethylene by the screw extruder 1 and preferably lower than 3 times or less.
The take-up unit 21 may be, for example, of the roll type, caterpillar type or belt type.
Further, in the present method, it is preferable to adjust such that ultra-high molecular weight polyethylene begins to cool to solidify at the tapered portion 18 of the tapered core 3, and preferably at a portion of the tapered portion 18 at which the diameter is smaller than that at a mid portion of the tapered portion 18 so that an ultra-high molecular weight poly-ethylene shrink pipe having a high coefficient of shrinkage canbe obtained. Such adjustment of beginning of the solidification of the ultra-high molecular weight polyethylene shrink pipe can be performed by adiusting the extruding rate of the screw extruder 1, the position of the tapered core 3, the position of a blowing ring for cooling air or the like.
The ultra-high molecular weight polyethylene shrink pipe taken up by and formed on the take-up unit 21 is suitably cut by a cutting machine. The cutting machine may be an 206493q automatic cutting machine such as, for example, a shearing cutter of the round saw type or of the type using a blade.
While mainly the method of and the apparatus for manu-facturing an ultra-hiyh molecular weight polyethylene shrink pipe having a circular inner profile has been described so far, the ultra-high molecular weight polyethylene shrink pipe is not limited to that which has a circular inner profile, but may be made a pipe of an outer profile conforming to an application thereof by suitably selecting an outer profile of a tapered core to be used. For examplel if the outer profile of the tapered core is an angular shape or an elliptic shape, then an ultra-high molecular weight polyethylene shrink pipe as a pipe of an outer shape having an inner profile corresponding to such angular or elliptic shape can be obtained.
The ultra-high molecular weight polyethylene shrink pipe of the present invention can be used to cover an outer profile of a tubular member by inserting the tubular member into the inside of the same and heating to cause the same to shrink with making use of the shrinking property of the same. For example, a tubular member such as a roll or a steel tube is inserted into the ultra-high molecular weight polyethylene shrink pipe, and then the ultra-high molecular weight poly-ethylene shrink pipe is heated to lOo to 160C to cause the same to shrink to cover the tubular member. The heating can be performed by immersing the ultra-high molecular weight polyethylene shrink pipe into a heating fluid such as air or liquid, or by blowing hot air or flame to the ultra-high molecular weight polyethylene shrink pipe.

-For covering an outer surface of the tubular member ~ with the ultra-high molecular weight polyethylene shrink pipe, the outer surface is preferably formed in advance as a rough surface so that slide resistance between contacting faces of the shrink pipe and the tubular member may be improved.
Further, preferably an adhesive resin may be applied to an outer surface of the tubular member such as a roll or a steel tube before the shrink pipe is coated on the tubular member so that the adhesive stren~th at an interface between them may be imprQved remarkably. Such method can be performed by thermally fusion applying powder or a film of an adhesive resin in advance to an outer surface of the tubular memher. The adhesive resin used may be, for example, Addmer NE060 (Mitsui Petrochemical Industries, Ltd.~ trade-mark) or the like or a modified product of the sarne.
Hereinunder, a method of and an apparatus for manufacturing an ultra-high molecular weight polyethylene film as another particular form of the ultra-high ~ 2064939 molecular weight polyethylene polyethylene thln-wall pipe of the present invention will be described with reference to Figs. 5 to 7.
The manufacturing apparatus for an ultra-high molecular weight polyethylene film shown in Fig. 5 includes as essentlal components a screw extruder 31, a die 32 mounted on the screw extruder 31, a tapered core member 33 provided continuously to the die 32, and a take-up unit 34.
The screw extruder 31 includes, as shown in Fig. 6, a grooved cylinder 35, a screw 36 inserted in the grooved cylinder 35 and a hopper 37 for supplying ultra-high molecular weight polyethylene of raw material.
The inner diameter of the grooved cylinder 35 is selected suitably so that a film of a desired outer diameter may be obtained. The screw 36 should have a compression ratio of 1 to 2.5 and preferably a compression ratio of 1.3 to 2Ø The effective length (L/D) of the screw 36 normally ranges from 20 to 28 or so. The length of a compressing portion of the screw 36 ranges from 25 to 80 % or so of the effective length (L/D). Meanwhile, the screw flight pitch normally ranges from 0.4 to 0.8 or so. The speed of rotation of the screw 36 is normally 10 to 50 rpm or so. Further, the hopper 37 is preferably a two-stage hopper since it facilitates, when raw material in the form of powder is to be handled, back flows of air in the cylinder 35 and can prevent ~_ 2064939 occurrence of a failure in dropping of raw material which arises from a hopper bridge.
A heating barrel 38 is disposed on a circumferential wall of the screw extruder 31 in order to melt ultra-high molecular weight polyethylene supplied into the screw extruder 31, and a water cooling barrel 39 is disposed ln order to regulate the heating temperature by the heating barrel 38. The heating temperature at the screw extruder 31 is adjusted normally to a temperature higher than a melting point of ultra-high molecular weight polyethylene but equal to or lower than 340 C and preferably to a temperature from 160 to 330 C.
The die 32 mounted on the screw extruder 31 is constituted from an inner die 40 and an outer die 41 in which the inner die 40 is inserted. The inner die 40 is connected to an end 42 of the screw 36 of the screw extruder 31 and is rotated by rotation of the screw 36. Meanwhile, the outer die 41 is mounted at an end 43 of the heating barrel 38 of the s~crew extruder 31. The die 32 has an L/D ratio at least 10 and preferably 20 to 50. Further, the inner die 40 is preferably constituted such that, since it is rotated by rotation of the screw 36, a diameter decreases in a tapering condition from the connecting portion thereof and then has a fixed outer diameter at the other end portion from a mid portion thereof, and besides it is coated at a surface thereof with fluorocarbon resin in order to assure a high ` ` ~ 2064939 slipping property thereof with resin. An electric heater 44 is disposed on an outer circumferential wall of the die 32 for regulating the temperature of molten substance of ultra-high molecular weight polyethylene which moves in the die 32.
The heating temperature of the die 32 is normally adjusted to 160 to 250 C or so.
In the manufacturing apparatus, the tapered core member 33 shown in an enlarged view of Fig. 7 is provided continuously to the inner die 40 of the die 32. The tapered core member 33 is loosely fitted on a shaft 47 connected to an end 46 of the inner die 40. The shaft 47 connected to the end 46 of the inner die 40 is rotated together with the inner die 40 connected to the screw 36. The outer diameter of the shaft 47 is normally smaller than the outer diameter of the inner die 40, and the length of the shaft 47 is normally 10 to 50 cm or so.
Meanwhile, the tapered core member 33 is loosely fitted on the shaft 47 by means of a bearing 49 and is mounted on the shaft 47 such that it may not rotate together with the shaft 47.
The tapered core membér 33 has a tapered portion 45 which is formed in an inclined relationship at an angle normally of 5 to 50 degrees and preferably of 10 to 30 degrees with respect to an axial direction of the shaft 47 so that frictional resistance between the tapered core member 33 and an ultra-high molecular weight polyethylene film upon 2064q39 diametrical expansion may be reduced to perform a shaping ~ operation readily. The tapered core member 33 further has a cylindrical portion 50 provided continuously to the tapered portion 45.
A coating of fluorocarbon resin such as Teflo ~ is preferably applied to surfaces of the tapered portion 45 and the cylindrical portion 50 of the tapered core member 33 so that the coefficient of friction with an ultra-high molecular weight polyethylene molded article may be reduced to perform molding smoothly.
The ratio in length of the tapered portion 45 to the cylindrical portion 50 of the tapered core member 33 in its axial direction is normally set to 0.2 to 2 or so and preferably to 0.5 to 1.0 or so. Further, the maximum outer diameter of the tapered portion 45, that is, the outer diameter of the cylindrical portion 50, should be set at least to 3.0 times or more than the diameter of the inner die 40 and preferably to 4 times or more and further preferably to 5 to 7 times of the diameter of the inner die 40.
The manufacturing apparatus includes the take-up unit 34 as shown in Fig. 5. The take-up unit 34 includes 2 to 4 pairs, preferably 4 pairs, of rolls 51 disposed serially in a taking off direction of an ultra-high molecular weight poly-ethylene film. The rolls 51 preferably have a length in the roll axial direction of 50 to 80 %, preferably of 70 to 80 %f of the width of the ultra-high molecular weight polyethylene film shaped by the tapered c.ore member 33 and folded by the rolls so that a sufficient taking up force may be obtained and a film which is uniform without having a wrinkle and has no folded mark ~ at both ear edges thereof may be obtained.
In t,he manufacturing apparatus described above, ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 dl/g or more is first supplied into, molten and kneaded in the screw extruder 31 r and then the molten substance of the ultra-high molecular weight polyethylene is continuously extruded from the die 32 to form a roughly cylindrical shape, whereafter the diamet,er of t,he roughly cylindrical extruded artic.les is expanded by the ta~ered core member 33 such that the inner diameter of a maximum diametrically expanded portion of the roughly cylindrical extruded articles may be 3 times or more than the outer diameter of t,he inner die 40 of the die 32 and preferably 4 times or more and further preferably 5 times or more than the diameter of the inner die 40 so that a good film of an appropriate thickness can be obtained. In this instance, in case the maximum outer diameter of the tapered portion 45, that is, the outer diameter of the cylindrical portion 50, is set to 5 times or more than the diameter of the inner die 40, a small hole may be formed at a location of the connecting portion at which the shaft 47 is connected to the end 46 of t,he inner die 40 so that compressed air may be 206493q blown in through the small hole to promote the diameter expanding operation.
The thus diametrlcally expanded film is cooled in a cooling tank 52 and then taken up by the take-up unit 34.
The taking off rate of the take-up unit 34 is adjusted equal to or higher than 3 times and preferably to 3 to 20 times the extruding rate of the molten substance of the ultra-high molecular weight polyethylene by the screw extruder 31.
The ultra-high molecular weight polyethylene film of the present invention taken up by and formed on the take-up unit 34 is obtained in the form of a tube. The ultra-high molecular weight polyethylene film in the form of a tube may be used as a film in the form of a tube as it is or may be cut at a portion thereof by a cutting machine and developed so that it may be used as a biaxially oriented film which has a great width and is free from a folded mark. The cutting machine may be a popular cutting machine such as, for example, a cutter blade. Or else, a biaxially oriented film obtained may be divided into belts or tapes elongated in a direction of a flow so that they may be used as base paper for stretchable tapes.
Subsequently, a method of and an apparatus for manufacturing an ultra-high molecular weight polyethylene thin-wall pipe as a further concrete embodiment of an ultra-high molecular weight polyethylene thin-wall pipe of the present invention will be described with reference to Figs. 8 to 10.
An ultra-high molecular weight polyethylene thin-wall pipe of the present invention has an outer diameter (D2) of 10 mm or more as shown in Fig. 8, and has a thickness (t2) of 0.5 mm or more, and in a range within which it can be shaped economically at a high productivity, preferably the outer diameter (D2) ranges from 25 to 100 mm and the thickness (t2) ranges from 1 to 5 mm. Further, the ratio of the outer diameter to the thickness (D2/t2) should be 10 or higher and preferably 15 to 50 so that a pipe having a high rigidity may be obtained. Further, the surface roughness of an inner face of the plpe in an extruding direction is equal to or less than 1.0 ln average roughness and equal to or less than 5 in maximum roughness (Rmax). Preferably, the average roughness (Ra) is equal to or less than 0.5 and the maximum roughness (Rmax) is equal to or less than 5 so that the flowing resistance thereof when it is used as a conveying hose for powder or fluid may be suppressed to a low level.
The ultra-high molecular weight polyethylene thin-wall pipe has a coefficient of shrinkage in a diametrical direction which is 5 % or lower at 100 C, and when it is used in an environment of a high temperature, or when the dimension of the inner diameter is very significant on an application and a function of the pipe, the coefficient of ~ - ~ 2064939 shrinkage of the pipe in a diametrical direction at 100 C is preferably from O to 3 %.
The ultra-high molecular weight polyethylene thin-wall pipe can be manufactured in accordance with such a process that the ultra-high molecular weight polyethylene is supplied into, molten and kneaded in a screw extruder and then the molten substance of the ultra-high molecular weight polyethylene is continuously extruded from a die connected to a screw of the extruder to form a roughly cylindrical shape, whereafter the roughly cylindrical extruded articles is taken up while diametrically expanding the same by means of a tapered core.
An apparatus for manufacturing the ultra-high molecular weight polyethylene thin-wall pipe basically has the same construction as that of the apparatus shown in Figs. 2 and 3.
In particular, the manufacturing apparatus basically includes a screw extruder, a die mounted on the screw extruder,a tapered core member provided continuously to the die, and a take-up unit. The screw extruder is similar to those for an -ultra-high molecular weight polyethylene shrink pipe and an ultra-high molecular weight polyethylene film described hereinabove in that it includes, as shown in Fig. 9, a grooved cylinder 65, a screw 66 inserted in the grooved cylinder 65, and a hopper 67 for supplying ultra-high molecular weight polyethylene of raw material.

~ 2064939 The inner dlameter of the grooved cylinder 65 is selected suitably so that a thin-wall pipe of a desired outer diameter may be obtained. The screw 66 should have a compression ratio of 1 to 2.5, and preferably a compresslon ratio of 1.3 to 2Ø The effective length (L/D) of the screw 66 normally ranges from 20 to 28 or so. The length of a compresslng portion of the screw 66 ranges from 25 to 80 % or so of the effective length ~L/D). Meanwhile, the screw flight pitch normally ranges from 0.4 to 0.8 or so. The speed of rotation of the screw 66 is normally 10 to 50 rpm or so. Further, the hopper 67 is preferably a two-stage hopper since it facilitates, when raw material in the form of powder is to be handled, back flows of air in the cylinder 65 and can prevent occurrence of a failure in dropping of raw material which arises from a hopper bridge.
A heating barrel 68 is disposed on a circumferential wall of the screw extruder in order to melt ultra-high molecular weight polyethylene supplied into the screw extruder, and a water cooling barrel 69 is disposed in order to regulate the heating temperature by the heating barrel 68.
The heating temperature at the screw extruder is adjusted normally to a temperature higher than a melting point of ultra-high molecular weight polyethylene but equal to or lower than 340 C and preferably to a temperature from 160 to The die 62 mounted on the screw extruder is constituted from an inner die 70 and an outer die 71 in which the inner die 70 is inserted. The inner die 70 is connected to an end 72 of the screw 66 of the screw extruder and is rotated by rotation of the screw 66. Meanwhile, the outer die 71 is mounted at an end 73 of the heating barrel 68 of the screw extruder. The die 62 has an L/D ratio at least 10 and preferably 20 to 50. Further, the inner die 70 is preferably constituted such that, since it is rotated by rotation of the screw 66, lt decreases in thickness in a tapering condition from the connecting portion thereof and then has a fixed outer diameter at the other end portion from a mid portion thereof and besides it is coated at a surface thereof with fluorocarbon resin in order to assure a high slipping property thereof with ultra-high molecular weight polyethylene which passed through in the inside thereof. A
heating barrel 74 is disposed on an outer circumferential wall of the die 62 for regulating the temperature of molten substance of ultra-high molecular weight polyethylene which moves in the die 62. The heating temperature of the die 62 is normally adjusted to 160 to 250 C or so.
In the manufacturing apparatus, the tapered core member 63 shown in an enlarged view of Fig. 10 is provided continuously to the inner die 70 of the die 62. The tapered core member 63 includes a shaft 77 connected to an end 76 of the inner die 70, and a tapered forming member 78 loosely 39 2064~39 72736-68 fit,ted on the shaft 77. The shaft 77 connected to the end 76 of the inner die 70 is rotated together with the inner 70 connected to the screw 66. The outer diameter of the shaft 77 is normally smaller than the outer diameter of the inner die 70, and the length of the shaft, 77 is normally 10 to 50 cm or so.
Meanwhile, the tapered forming member 78 is loosely fitted on the shaft 77 by means of a bearing 79 and is mounted on the shaft 77 such that it may not rotate together with the shaft 77. The tapered forming member 78 has a tapered portion 80 which is formed in an inclined relationship at an angle normally of 5 to 50 degrees and preferably of 10 to 30 degrees with respect to an axial direction of the shaft 77 so that frictional resistance between the tapered shaping member 78 and an ultra-high molecular weight polyethylene thin-wall pipe upon diametrical expansion may be adjusted to a range within which a shaping operation can be performed readily. The tapered forming member 77 further has a cylindrical portion 81 provided continu-ously to the tapered portion 80.
The t,apered portion 80 of the tapered forming member 78 preferably has cQnvex and concave portions on a surface thereof so that the contact area thereof with a roughly molded form may be reduced to delay the solidification of the roughly shaped article such that the pipe made of the ultra-high molecular weight polyethylene may be cooled at the cylindrical portion 81 so as to obtain a thin-wall pipe having a low co-efficient of thermal shrinkage. Such convex and concave portions formed on the surface of the tapered portion 80 of the tapered forming member 78 may be provided, for example, by forming convex and concave portions in the form of a satin crape finish Qn the ~urface or by cutting several grooves in a direction perpendicular to t.he axis of the tapered portion 80 like annular rings Meanwhile, the cylindrical portion 81 of the tapered forming member 78 has a smooth surface.
Further, in order to prevent that the tapered portion 80 of the tapered forming member 78 is deprived of heat by the cylindrical portion 81 immersed in and cooled by a cooling water tank to drop the temperature thereof so that a roughly molded form begins to solidify at the tapered portion 80, but to delay the solidification of the roughly molded form so that it may begin at the cylindrical portion 81, the tapered portion 80 and the cylindrical portion 81 are connected to each other with a heat insulating material 82 interposed therebetween in order to thermally isolate the tapered portion 80 and the cylindrical portion 81 from each other. The heat insulating material 82 may be~ for example, a Teflo~ sheet.
A coatiny of fluorocarbon resin such as Teflo ~ is preferably applied to surfaces of the tapered portion 80 and the cylindrical portion 81 of the tapered forming member 78 41 ~
~ 2064939 so that the coefficient of friction with an ultra-high molecular weight polyethylene molded form may be reduced to perform molding smoothly.
The ratio in length of the tapered portion 80 to the cylindrical portion 81 of the tapered shaping member 78 ln its axial direction is normally set to 0.2 to 1 or so and preferably to 0.3 to 0.7 or so. Further, the maximum outer diameter of the tapered portion 80, that is, the outer diameter of the cylindrical portion 81, should be set at least to 1.2 to 3 times the diameter of the inner die 70 and preferably to 1.5 to 3.0 times and further preferably to 1.7 to 2.5 times the diameter of the inner die 70.
The present manufacturing apparatus includes the take-up unit. The take-up unit includes 2 to 4 pairs, preferably 4 pairs, of rolls disposed serially in a taking up direction of an ultra-high molecular weight polyethylene thin pipe.
In the manufacturing apparatus described above, ultra-high molecular weight polyethylene having an intrinsic viscosity [~] of 5.0 dl/g or more is first supplied into, molten and kneaded in the screw extruder, and then the molten substance of the ultra-high molecular weight polyethylene is continuously extruded from the die 62 to form a roughly cylindrical shape, whereafter the diameter of the roughly cylindrical extruded article is expanded by the tapered core 63 such that the inner diameter of a maximum diametrically expanded portion of the roughly cylindrical extruded articles may be 1.2 to 3 times and preferably 1.5 to 3 times and further preferably 1.7 to 2.5 times as the diameter of the inner die 70 so that a good film of an appropriate thickness can be obtained.
In this instance, the manufacturing apparatus is adjusted such that a thin-wall pipe to be shaped by the tapered core member 63 may begin tQ be cooled to solidify at the cylin-drical portion 81 of the tapered core member 63 so that a pipe having a low coefficierlt of thermal shrinkage may be obtained.
Such adjustment of the start,ing point of the solidification to the location of the cylindrical portion 81 can be performed by .suitably selecting the extruding rate of the die 62, the distance hetween the tapered portion 80 of the tapered core member 63 and the inner die 70, or the position at which cooling by air or water takes place, The thus diametrically expanded thin-wall pipe is cooled in the cooling tank and then taken up by the take-up unit. The taking up rate Qf the take-up unit is adjusted 3 times or lower the extruding rat,e of the molten substance of the ultra-high molecular weight polyethylene by the screw extruder 2n and preferably 1.1 to 2 times so that a slack does not occur at the roughly extruded article and shaping operation is easy and besides an ult,ra-high molecular weight polyethylene thin pipe having a low coefficient of thermal shrinkage in its lon~itudi-nal direction may be obtained.

~., 2064939 The ultra-hlgh molecular weight polyethylene thin pipe taken up by and formed on the take-up unit can be cut with a required length by a cutter. The cutter may be a popular apparatus such as a shearing cutter employing a round saw or a blade.
Further, the ultra-high molecular weight polyethylene thin pipe of the present invention can be partially cut away and developed into a sheet, which is then cut into belts or tapes elongated in a direction of a flow so that they may be used as base threads for stretchable yarns.

EXAMPLES
In the following, the present invention will be described in detail in connection with examples of the present invention and comparative examples. However, the present invention shall not be restricted by the examples at all unless the spirit and scope of the present invention are exceeded.

Example 1: -Ultra-high molecular weight polyethylene shrink pipes were manufactured using an apparatus which has the same construction as that of the manufacturing apparatus for a shrink pipe shown in Fig. 2 and wherein specifications of the components are such as follows:
Extruder:

outer dlameter of screw 30 mm~
effectlve length (L/D) of screw 22 fllght pltch 18 mm compresslon ratio of screw 1.8 Dle:
length of dle 750 mm lnner dlameter of outer dle at exlt 20 mm~
of dle effectlve length ~L/D) of dle 37.5 outer dlameter of lnner dle 15 mm~
Tapered core connected to end of lnner dle: havlng tapered portlon and cyllndrlcal portlon lntegrally shaped from alumlnum metal and coated wlth Teflon~ at surface thereof.
tapered portlon maxlmum dlameter 26 mm~
length 50 mm cyllndrlcal portlon outer dlameter 26 mm~
length 80 mm The apparatus further lncludes an alr rlng for coollng a roughly molded form of resln, a coollng water tank, a take-up 0 unlt of the roll type and a plpe cuttlng machlne.
Powder resln of ultra-hlgh molecular welght poly-ethylene ([~]: 15.1 dl/g, meltlng polnt: 136~C, bulk speclflc gravlty; 0.43 g~cc) (Mltsul Petrochemlcal Industrles, Ltd., HIZEX MILLION 240M~ was supplled lnto the apparatus, and the temperatures at the water coollng barrel (Cl) and the heatlng Trade-mark 2V~Iy3~

barrel which was divided into three zones (C2, C3 and C4) were adjusted to 20 C, 290 C, 330 C and 330 C, respectively.
Further, the temperatures of the die which was divided into three zones (Dl, D2 and D3) were adjusted to 230 C, 180 C
and 170 C, respectively. In this condition, the ultra-high molecular weight polyethylene was extrusion molded into a roughly molded form at the number of revolution of the screw of 12 rpm and at the extruding rate of 18 cm/min. At the exit of the die, the roughly cylindrical extruded article was cut in the extruding direction by a knife and passed through the cooling water tank. Then, the extruded article was introduced into the take-up unit of the roll type including rolls rotating at the speed of 30 cm/min. After then, the cutting operation by means of the knife was stopped, and the diameter of the extruded article was expanded by the tapered portion of the tapered core, and cooling air was blown from the air ring to the extruded article. The amount of the cooling air was adjusted so that cooling cure of the extruded article might start at an intermediate portion of the tapered portion. Thus, shrink pipes made of the ultra-high molecular weight polyethylene wherein the outer diameter is 27.0 mm0 while the inner diameter is 25.5 mm0 and the expansion ratio (inner diameter ratio) is 1.7 were manufactured.
Coefficients of thermal shrinkage of the ultra-high molecular weight polyethylene shrinkage pipes were measured by the following method. Results are shown in Table 1.

i Measurement of Coeff;cient of Thermal Shrink~ge Every specimen was heated for one hour at 140 C in an air oven, and after lapse of 24 hours at 23 C a coefficient of shrinkage of an inner diameter in a diametrical direction was measured and decided as an index to a coefficient of thermal contraction.
coefficient of thermal shrinkage (%) =
{(dimension before heating - dimension after heating)/dimension before heating} x lOO

Example 2 Ultra-high molecular weight shrink contraction pipes having an outer diameter of 44.9 mm0 and an inner diameter of 44 mm0 were manufactured in the same conditions as those in the Example 1 except that another tapered core having an outer diameter of 45 mm0 (expansion ratio of 3) was used, and coefficients of thermal shrinkage of them were measured.
Results are shown in Table 1.

Comparative Example 1 Pipes made of ultra-high molecular weight polyethylene having an outer diameter of 17.7 mm0 and an inner diameter of 14.0 mm0 (expansion ratio: 0.93) were manufactured in the same conditions as those in the Example 1 except that no tapered core was used and the taking up rate was set differently to 20 cm/min, and coefficients of thermal shrlnkage of them were measured. Results are llsted ln Table 1.

Comparatlve Example 2 Moldlng of shrlnk plpes was attempted ln the same condltlons as those in the Example 1 except that polyethylene powder resln havlng an lntrlnslc vlscoslty [r,] of 3.5 dl/g, a denslty of 0.950 g/cc and a bulk speclflc gravlty of 0.38 g/cc (Mltsul Petrochemlcal Industrles, Ltd., HIZEX 8000FP) was used and the heatlng temperatures at the zones Cl, C2, C3 and C4 of the extruder were ad~usted to 20 C, 210 C, 230 C and 230 C, respectlvely. However, slnce the resln was turned together wlth rotatlon of the lnner dle, lt was dlfflcult to manufacture roughly shaped artlcles, and consequently, no shrlnk plpes were manufactured.

Trade-mark Table 1 Example 1 Example 2 Comparative Comparative Example 1 Example 2 Outer Diameter27.0 44.9 17.7 (D) (mm) Inner Diameter25.5 44.0 14.0 Shaping (D) (mm) Impossible Thickness 0 75 0 95 1.85 (t) (mm) (D)/(t) 36.0 99.8 9.6 Expansion 1.7 2.9 0.93 Ratio (Inner Dia.) (times) Coefficient 30 91 3.6 of Thermal Shrinka~e (~) Example 3:
Ultra-high molecular weight polyethylene films were manufactured using a manufacturing apparatus for an ultra-high molecular weight polyethylene film which has such structure as shown in Fig. 5 and includes a screw extruder wherein various portions have the following specifications:
outer diameter of screw 30 mm0 effective length (L/D) of screw 22 flight pitch 18 mm (fixed) compression ratio of screw 1.8 a dle wherein various portions have the following specifications:

2~64939 length of pipe die 750 mm inner diameter of outer die 20 mm0 at exit of die effective length (L/D) of die 37.5 outer diameter of inner die 15 mm0 a tapered core including a tapered portion connected to an end of the inner die and having an increasing diameter at an angle of 15/100 (11.7 degrees3 with respect to a shaft and further having a maximum outer diameter of 60 mm0 and a length of 110 mm, and a cylindrical portion having an outer diameter of 60 mm0 and a length of 200 mm and having a fluorocarbon resin coating applied to a surface thereof, a cooling water tank, a take-up unit of the roll type including four pairs of rubber rolls having an outer diameter of 150 mm0 and a width of 65 mm, and a take-up unit.
Ultra-high molecular weight polyethylene in the form of powder having an intrinsic viscosity [~] of 15.4 dl/g, a melting point of 136 C and a bulk specific gravity of 0.43 g/cc was supplied into the manufacturing apparatus, and the preset temperatures at a water cooling barrel (C1) and the heating barrel which was divided into three zones (C2, C3 and C4) were adjusted to 20 C, 290 C, 335 C and 335 C, respectively. Further, the preset temperatures at three zones (D1, D2 and D3) of the die were adjusted to 230 C, 180 C and 168 C, respectively. In this condition, the ultra-high molecular weight polyethylene was extrusion molded, ~ 2064939 `

while being molten and kneaded, into a roughly cylindrlcal extruded article at the number of revolution of the screw of 10 rpm and at the extruding rate of 15 cm/min. The roughly cylindrical extruded article was cut by a knife located at the exit of the die and passed through the cooling water tank. Then, the roughly extruded article was introduced into the take-up unit in which the 4 pairs of rubber rolls were rotating at the speed of 20 cm/min. After then, the cutting operation of the extruded article was stopped, and the diameter of the extruded article was expanded into the profile of a pipe by the tapered portion of the tapered core.
Subsequently, the thus diametrically expanded extruded article was advanced, at a portion thereof of a length of 200 mm from an end of the cylindrical portion thereof, into the cooling water tank so that the extruded article in the profile of a pipe may be cooled to cure at the cylindrical portion of the tapered core. The taking up rate of the take-up unit was adjusted to 2 m/min. Consequently, ultra-high molecular weight polyethylene films having a thickness of 55 ~m and free from a folded mark at both ear edges thereof were obtained.
The ultra-high molecular weight polyethylene films were applied to a tensile test and coefficients of thermal shrinkage were measured in accordance with the following method. Results are listed in Table 2.
Tensile Test ` 2064939 A tensile strength at breaking point (TS: kg/cm2) and an elongation (EL: %) of specimen were measured for both of a longitudinal direction (MD) and a transverse direction (TD) in the following testing conditions:
shape of specimen JIS K6781 chucking distance 86 mm stretching speed 200 mm/min temperature 23 C
Coefficient of Thermal Shrinkage Specimen was heated for one hour at 130 C in an air oven, and after lapse of 24 hours at 23 C, coefficients of thermal shrinkage both in a longitudinal direction (MD) and a transverse direction (TD) were measured in accordance with the following expression:
coefficient of thermal shrinkage (%) =
l(dimension before heating - dimension after heating)/dimension before heating~ x 100 Example 4 Ultra-high molecular weight polyethylene films having a thickness of 58 ~m and free from a folded mark at both ear edges thereof were manufactured in the same conditions as those in the Example 3 except that a further tapered core having a tapered portion having a maximum outer diameter of 75 mm0 and a take-up unit including rolls having a width of 90 mm were used and the taking up rate of the take-up unit was set to 1.5 mm/min, and a tensile test was conducted for them and coefficients of thermal shrinkage of them were measured. Results are shown in Table 2.

Comparative Example 3 Ultra-high molecular weight polyethylene films having a thickness of 40 ~m and free from a folded mark at both ear edges thereof were manufactured in the same conditions as those in the Example 3 except that a different tapered core having a tapered portion having a maximum outer diameter of 40 mm0 and a different take-up unit including rolls having a width of 50 mm were used and the taking up rate of the take-up unit was set to 4 m/min, and a tensile test was conducted for them and coefficients of thermal shrinkage of them were measured. Results are shown in Table 2.

Comparative Example 4 Manufacture of polyethylene films was attempted in the same conditions as those in the Example 3 except that, in place of ultra-high molecular weight polyethylene, powder of general purpose polyethylene resin having an intrinsic viscosity [~] of 3.5 dl/g, a density of 0.950 g/cc and a bulk specific gravity of 0.38 g/cc (Mitsui Petrochemical Industries, Ltd., HIZEX 8000FP) was used and the heating temperatures at the water cooling barrel ~C1) and three zones (C2, C3 and C4) of the heating barrel of the extruder were adjusted to 20 C, 210 C, 230 C and 230 C, respectively.
However, since a roughly molded form in the form of a pipe was turned together with rotation of the inner die due to a low melt viscosity of the resin, no films were manufactured.
Results are shown in Table 2.

Comparative Example S
Ultra-high molecular weight polyethylene films were manufactured in the same conditions as those in the Example 3 except that a take-up unit including rolls having a width of 100 mm was used, and a tensile test was conducted for them and coefficients of thermal shrinkage of them were measured.
Results are shown in Table 2.

Comparative Example 6 Manufacture of ultra-high molecular weight polyethylene films was attempted in the same conditions as those in the Example 3 except that a take-up unit including rolls having a width of ~5 mm was used. However, the taking up force was not able to stand frictional resistance upon diametrical expansion of a roughly molded form by the tapered core, and consequently, no films were manufactured.

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Example 5:
Ultra-hlgh molecular welght polyethylene thin-wall plpes were manufactured uslng an apparatus whlch has the same constructlon as that of the manufacturlng apparatus for a thln plpe shown ln Flgs. 2 and 9 and whereln speclflcatlons of the components are such as follows:
Extruder:
outer dlameter of screw 30 mm~
effectlve length (L/D) of screw 22 fllght pltch 18 mm compresslon ratlo of screw 1.8 Dle:
length of dle 750 mm lnner dlameter of outer dle at exlt 20 mm~
of die effectlve length (L/D) of dle 37.5 outer dlameter of lnner dle 15 mm~
Tapered core shown ln FIG. 10, connected to end of lnner dle: havlng tapered portlon dlametrlcally expandlng at angle of 14/100 (8 degrees) wlth respect to shaft and coated wlth Teflon~
at surface thereof. Teflon~ sheet of 1 mm thlck ls held between tapered portlon and cyllndrlcal portlon as heat lnsulatlng materlal.
tapered portlon maxlmum dlameter 26 mm length 50 mm 206493g cylindrical portion outer diameter 26 mm0 length 150 mm The apparatus further include a cooling water tank, a take-up unit of the roll type and a pipe cutting machine.
Powder resin of ultra-high molecular weight polyethylene ([~]: 15.4 dl/g, melting point: 136 C, bulk specific gravity: 0.43 g/cc) (Mitsui Petrochemical Industries, Ltd., HIZEX MILLION 240M) was supplied into the apparatus, and the -temperatures at the water cooling barrel (C1) and the heating barrel which was divided into three zones (C2, C3 and C4) were adjusted to 20 C, 290 C, 330 C and 330 C, respectively.
Further, the temperatures of the die which was divided into three zones (D1, D2 and D3) were adjusted to 230 C, 180 C
and 170 C, respectively.
In this condition, the ultra-high molecular weight polyethylene was extrusion molded into a extruded article at the number of revolution of the screw of 20 rpm and at the extruding rate of 30 cm/min. At the exit of the die, the cylindrical extruded article was cut in the extruding direction by a knife and passed through the cooling water tank. Then, the roughly molded form was introduced into the take-up unit of the roll type including rolls rotating at the speed of 40 cm/min. After then, the cutting operation by means of the knife was stopped, and the diameter of the extruded article was expanded by the tapered portion of the tapered core. Subsequently, the thus diametrically expanded extruded article was advanced, at a portion thereof of a length of lOO mm from an end of the cylindrical portion thereof, into the cooling water tank. Thus, ultra-high molecular weight polyethylene thin-wall pipes having an outer diameter of 27.8 mm0 and an inner diameter of 25.6 mm0 were obtained.
Coefficients of thermal shrinkage and surface roughnesses of the ultra-high molecular weight polyethylene thin-wall pipes were measured in accordance with the following method. Results are shown in Table 3.

Measurement of Coefficient of Thermal Shrinkaae Every specimen was heated for one hour at lOO C in an air oven, and a coefficient of shrinkage of an inner diameter in a diametrical direction after lapse of 24 hours at 23 C
was measured and decided as an index to a coefficient of thermal shrinkage.
coefficient of thermal shrinkage (%) =
{(dimension before heating - dimension after heating)/dimension before heating} x lOO
Surface Roughness Surface roughnesses of inner and outer diameters of every thin-wall pipe were measured in conformity to JIS
BO601.
Ra: center line average roughness (~m) Rmax: maximum roughness (~m) Example 6 Ultra-high molecular weight polyethylene thin-wall pipes having an outer diameter of 45.7 mm0 and an inner diameter of 44.5 mm0 were manufactured in the same conditions as those in the Example S except that a tapered core having an outer diameter of 45 mm0 was used, and coefficients of thermal shrinkage and surface roughnesses of them were measured.
Results are shown in Table 3.

Example 7 Thin-wall pipes made of ultra-high molecular weight polyethylene and having an outer diameter of 45.5 mm0 and an inner diameter of 44.2 mm0 were manufactured in the same conditions as those in the Example 5 except that a tapered core having an outer diameter of 45 mm0 was used and a extruded article was advanced, at a portion thereof of a length of 120 mm from an end of the cylindrical portion of the tapered core, into the cooling water tank so that the cooling cure point of the roughly shaped article might be at the tapered portion, and coefficients of thermal shrinkage and surface roughnesses of them were measured. Results are shown in Table 3.

Comparative Example 7 Pipes made of ultra-high molecular weight polyethylene and having an outer diameter of 18.1 mm0 and an inner diameter of 14.3 mm0 were manufactured in the same conditions as those in the Example 5 except that no tapered core was used and the taking up rate was set differently to 35 cm/min, and coefficients of thermal shrinkage and surface roughnesses of them were measured. Results are shown in Table 3.

Comparative Example 8 Molding of thin-wall pipes was attempted in the same conditions as those in the Example 5 except that polyethylene powder resin having an intrinsic viscosity [~] of 3.5 dl/g, a density of 0.950 g/cc and a bulk specific gravity of 0.38 g/cc (Mitsui Petrochemical Industries, Ltd., HIZEX 8000FP) was used as raw material and the heating temperatures at the zones C1, C2, C3 and C4 of the extruder were adjusted to 20 C, 210 C, 230 C and 230 C, respectively. However, since the molten resin was turned together with rotation of the inner die, it was difficult to manufacture roughly shaped articles, and consequently, no shrink pipes were manufactured. Results are shown in Table 3.

`-- 2064939 Table 3 Evaluation Items Examples Comparative [~ of Raw Material 15 4 15.4 15.4 15.4 3.5 Ultra-high molecular weight Polyethylene(dl/q) Outer Diameter (D) (mm) 27.8 45.7 45.5 18.1 Inner Diameter(mm) 25.6 44.5 44.2 14.3 Shaping Thickness (t)(mm) 1.1 0.6 0.65 1.9 Impossible D/t 25 76 70 10 Expansion Ratio 1.7 3.0 2.9 0.95 (Inner Dia.)(times) Coefficient of Thermal (~) 0.2 2.8 8.2 -0.1 Shrinkaqe (Inner Dia.) Surface Average Surface 0-26 0-23 0.41 1.33 Roughness(Ra) Roughness Surface 1. 47 1.72 2.55 1.58 (~m) Maximun Inner 2.0 1.6 2.4 8.3 Surface Roughness(Rmax) Surface 9 3 10.8 15.2 9.1 Since an ultra-high molecular weight polyethylene thin-wall pipe of the present invention is uniform in thickness and free from a folded mark, when a roll, a pipe, a steel tube or the like is coated with this thin-wall pipe, a coating with a high degree of accuracy can be obtained.
Further, a method of and an apparatus for manufacturing can manufacture the thin-wall pipe as described above at a high efficien~y and have a large merit in industrial practicle.
An ultra-high molecular weight polyethylene shrink pipe of the present invention is thick and allows finish working thereof by means of a lathe or the like and besides is low in coefficient of shrinkage in a longitudinal direction, comparing with a shrink pipe obtained by a conventional blown film extrusion method. Accordingly, the coating efficiency is high and an coating can be obtained economically.
Further, since ultra-high molecular weight polyethylene is superior in abrasion resistance, self-lubrication and chemical resistance, and particularly superior in abrasion resistance to fluorocarbon resins, the ultra-high molecular weight polyethylene shrink pipe of the present invention is superior in durability. Consequently, the ultra-high molecular weight polyethylene shrink pipe of the present invention can be applied suitably as a shrink pipe for covering for various rolls, pipes, steel tubes and so forth.
Further, a manufacturing method for an ultra-high molecular weight polyethylene shrink pipe of the present invention can manufacture the ultra-high molecular weight polyethylene shrink pipe described above efficiently.
Further, a manufacturing apparatus for an ultra-high molecular weight polyethylene shrink pipe of the present invention can be used suitably for the manufacturing method 62 206~939 ~, for an ultra-high molecular weight polyethylene shrink pipe described above.
According to a manufacturing method for an ultra-high molecular weight polyethylene film of the present invention, an ultra-high molecular weight polyethylene film can be obtained which is suitable for an application for which a high degree of accuracy in dimension is required, because it is uniform in thickness and free from a folded mark at both ear edges thereof comparing with a film obtained by a conventional blown film extrusion method. Particularly, since ultra-high molecular weight polyethylene is superior in abrasion resistance, self-lubrication and chemical resistance and particularly superior in abrasion resistance to fluorocarbon resins, the ultra-high molecular weight polyethylene film of the present invention is superior in durability. Consequently, the ultra-high molecular weight polyethylene film of the present invention can be applied suitably as a film for covering for various rolls, pipes, steel tubes and so forth.
Further, a manufacturing apparatus for an ultra-high molecular weight polyethylene film of the present invention can be used suitably for the manufacturing method for an ultra-high molecular weight polyethylene film described above.
An ultra-high molecular weight polyethylene thin-wall pipe of the present invention has a ratio of an outer '- 2064939 diameter to a thickness of 10 or more and is low in thermal shrinkage comparing with a conventional thin-wall pipe. The ultra-high molecular weight polyethylene thin pipe is useful for a conveying pipe for powder making use of the abrasion resistance, self-lubrication and chemical resistance ultra-high molecular weight polyethylene has, and can also be used suitably as a tubular cover for a roll, a pipe or a steel tube, or as a guide rail cover for a transport line or the like.
Further, a manufacturing method for an ultra-high molecular weight polyethylene thin pipe of the present invention can manufacture the ultra-high molecular weight polyethylene thin pipe at a high efficiency.
Further, a manufacturing apparatus for an ultra-high molecular weight polyethylene thin pipe of the present invention can be used suitably for the manufacturing method for an ultra-high molecular weight polyethylene thin pipe described above.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of manufacturing a thin-wall pipe of ultra-high molecular weight polyethylene, comprising:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;
continuously extruding the molten ultra-high molecular weight polyethylene from a die which has an L/D ratio of at least 10 and includes an inner die connected to and rotated together with a screw of the screw extruder and disposed therein, to form a cylindrical extruded article; and diametrically expanding the cylindrical extruded article by means of a tapered core connected to the inner die through a shaft and not rotatable with a shaft rotating together with the inner die, which tapered core includes a tapered portion and a cylindrical portion provided continuously to the tapered portion, and causing the ultra-high molecular weight poly-ethylene to start to cool to solidify at the tapered portion or the cylindrical portion of the tapered core.

2. An apparatus for manufacturing a thin-wall pipe of ultra-high molecular weight polyethylene, comprising:
an extruder including a grooved cylinder, and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;

a die having an L/D ratio of at least 10 and including an inner die connected to an end of the screw and rotatable together with the screw and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, a tapered portion not rotatable together with the inner die and the shaft and having an increasing diameter in a downstream direction such that a maximum outer diameter thereof is larger than the diameter of the inner die, and a cylindrical portion provided continuously to the tapered portion.

3. A shrink pipe made of ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more, wherein the shrink pipe has an outer diameter (D1) of 10 mm or more, a thickness (t1) of 0.2 mm or more with a ratio of the outer diameter to the thickness (D1/t1) 10 or higher, and has a coefficient of shrinkage of 20 % or more in a diametrical direction at 140°C.

4. A method of manufacturing a shrink pipe, mode of ultra-high molecular weight polyethylene, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;

continuously extruding the molten ultra-high molecular weight polyethylene from a die which has an L/D ratio of at least 10 and includes an inner die connected to and rotated together with a screw of the screw extruder and disposed therein, to form a cylindrical extruded article; and diametrically expanding the cylindrical extruded article such that the inner diameter of a maximum diametrically expanded portion is 1.2 to 3.0 times the outer diameter of the inner die, by means of a tapered core connected to the inner die through a shaft and not rotated with a shaft rotating together with the inner die, which includes a tapered portion and a cylindrical portion provided continuously to the tapered portion, and taking up the extruded article at a taking up rate five times or lower the extruding rate at the screw extruder, and causing the ultra-high molecular weight polyethylene to start to cool to solidify at the tapered portion or the cylindrical portion of the tapered core.

5. An apparatus for manufacturing a shrink pipe of ultra-high molecular weight polyethylene, comprising:
an extruder including a grooved cylinder, and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;
a die which has an L/D ratio of at least 10 and includes an inner die connected to an end of the screw and rotatable together with the screw, and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, and a tapered portion not rotatable together with the inner die and the shaft and having an increasing diameter in a downstream direction such that a maximum outer diameter thereof is at 1.2 to 3.0 times the diameter of the inner die.

6. A method of manufacturing a film by ultra-high molecular weight polyethylene, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;
continuously extruding the molten ultra-high molecular weight polyethylene from a die having an L/D ratio of at least 10, which includes an outer die and an inner die connected to and rotated together with a screw of the screw extruder and disposed in an inside of the outer die, to form a cylindrical extruded article; and diametrically expanding the cylindrical extruded article such that the inner diameter of a maximum diametrically expanded portion of the article is 3 times or more the outer diameter of the inner die, by means of a tapered core connected to the inner die through a shaft and not rotated with a shaft rotating together with the inner die, which includes a tapered portion and a cylindrical portion provided continuously to the tapered portion, taking up the extruded article at a taking up rate three times or higher the extruding rate of the molten ultra-high molecular weight polyethylene at the screw extruder; and causing the ultra-high molecular weight polyethylene to start to cool to solidify at the tapered portion or the cylindrical portion of the tapered core.

7. An apparatus for manufacturing a film of ultra-high molecular weight polyethylene, comprising:
an extruder including a grooved cylinder and a screw inserted in the grooved cylinder having a compression ratio of 1 to 2.5;
a die which has an L/D ratio of at least 10 and includes an inner die connected to an end of the screw and rotatable together with the screw, and an outer die connected to the grooved cylinder;
a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, and a tapered forming member not rotatable together with the inner die and the shaft and having an increasing diameter at an angle of 5 to 50 degrees in a downstream direction such that a maximum outer diameter thereof is equal to or more than 3 times the diameter of the inner die; and a take-up unit including rolls each having a length in the roll axial direction of 50 to 80 % of the width of the ultra-high molecular weight polyethylene film formed by the tapered core and folded by the rolls.

8. A thin-wall pipe made of ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more, wherein the thin-wall pipe has an outer diameter (D2) of 10 mm or more and thickness of (t2) 0.2 mm or more with a ratio of the outer diameter to the thickness (D2/t2) of at least 10, and has a coefficient of shrinkage of 5 % or less in a diametrical direction at 100°C.

9. A method of manufacturing a thin-wall pipe of ultra-high molecular weight polyethylene, comprising the steps of:
supplying ultra-high molecular weight polyethylene having an intrinsic viscosity [?] of 5.0 dl/g or more into a screw extruder, and melting and kneading the ultra-high molecular weight polyethylene;
continuously extruding the molten ultra-high molecular weight polyethylene from a die which has an L/D ratio of at least 10 and includes an outer die and an inner die connected to and rotated together with a screw of the screw extruder, and disposed inside of the outer die, to form a cylindrical extruded article; and diametrically expanding the cylindrical extruded article such that the outer diameter of a maximum diametrically expanded portion is 1.2 to 3.0 times the outer diameter of the inner die, by means of a tapered core connected to the inner die through a shaft and not rotated with a shaft rotating together with the inner die, which includes a tapered portion and a cylindrical portion provided continuously to the tapered portion, and taking up the extruded article at a taking up rate three times or lower the extruding rate of the ultra-high molecular weight polyethylene at the screw extruder, and causing the ultra-high molecular weight polyethylene to start to cool to solidify at the cylindrical portion of the tapered core.

10. An apparatus for manufacturing a thin-wall pipe of ultra-high molecular weight polyethylene, comprising:
an extruder including a grooved cylinder, and a screw inserted in the grooved cylinder and having a compression ratio of 1 to 2.5;
a die having an L/D ratio of at least 10, including an inner die connected to an end of the screw of the screw extruder and rotatable together with the screw, and an outer die connected to the grooved cylinder; and a tapered core including a shaft connected to an end of the inner die and rotatable together with the inner die, a tapered portion disposed not rotating together with the inner die and the shaft and having an increasing diameter at an angle of 5 to 50 degrees in a downstream direction such that the outer diameter thereof is 1.2 to 3.0 times the diameter of the inner die, and a cylindrical portion provided continuously to the tapered portion with a heat insulating material interposed therebetween.

11. The shrink pipe according to claim 3, wherein:
the ultra-high molecular weight polyethylene is homopolymer of ethylene or copolymer of ethylene as a main component and an .alpha.-olefin of 3 to 20 carbon atoms as a minor component and has an intrinsic viscosity [?] of 5 to 30 dl/g;
the pipe has a uniform thickness (t1) of 0.2 to 3 mm;
the pipe is free from a folded mark;
the pipe has an outer diameter (D1) of from 10 to 150 mm;
the D1/t1 ratio is 10 to 150; and the pipe has a coefficient of shrinkage of 20 to 150% at 140°C in a diametrical direction.

12. The shrink pipe according to claim 11, wherein:
the ultra-high molecular weight polyethylene has an intrinsic viscosity [?] of 8 to 30 dl/g;
the thickness (t1) is 0.5 to 3 mm;
the D1/t1 ratio is 15 to 150; and the coefficient of shrinkage in a diametrical direction is 40 to 150%.

13. The method according to claim 4, wherein:
the ultra-high molecular weight polyethylene is homopolymer of ethylene or copolymer of ethylene as a main component and an .alpha.-olefin of 3 to 20 carbon atoms as a minor component and has an intrinsic viscosity [?] of 5 to 30 dl/g;
the pipe has a uniform thickness (t1) of 0.2 to 3 mm;
the pipe is free from a folded mark;
the pipe has an outer diameter (D1) of from 10 to 150 mm;
the D1/t1 ratio is 10 to 150; and the pipe has a coefficient of shrinkage of 20 to 150% at 140°C in a diametrical direction.

14. The method according to claim 13, wherein the L/D
ratio is 20 to 50.

15. The method according to claim 6, wherein:
the ultra-high molecular weight polyethylene is homopolymer of ethylene or copolymer of ethylene as a main component and an .alpha.-olefin of 3 to 20 carbon atoms as a minor component and has an intrinsic viscosity [?] of 5 to 30 dl/g; and the L/D ratio is 20 to 50.

16. The thin-wall pipe according to claim 8, wherein:
the ultra-high molecular weight polyethylene is homopolymer of ethylene or copolymer of ethylene as a main component and an .alpha.-olefin of 3 to 20 carbon atoms as a minor component and has an intrinsic viscosity [?] of 5 to 30 dl/g;
the pipe has a uniform thickness (t2) of 0.2 to 3 mm;
the pipe is free from a folded mark;
the pipe has an outer diameter (D2) of from 10 to 150 mm;
and the ratio of the outer diameter to the thickness (D2/t2) is more than 10 but no more than 150.

17. The method according to claim 9, wherein:
the ultra-high molecular weight polyethylene is homopolymer of ethylene or copolymer of ethylene as a main component and an .alpha.-olefin of 3 to 20 carbon atoms as a minor component and has an intrinsic viscosity [?] of 5 to 30 dl/g;

the pipe has a uniform thickness (t2) of 0.2 to 3 mm;
the pipe is free from a folded mark;
the pipe has an outer diameter (D2) of from 10 to 150 mm;
a ratio of the outer diameter to the thickness (D2/t2) is more than 10 but no more than 150; and the pipe has a coefficient of shrinkage of 5% or less in a diametrical direction at 100°C.