WO2007063191A1

WO2007063191A1 - Method in extrusion process, extrusion process and apparatus for extrusion process

Info

Publication number: WO2007063191A1
Application number: PCT/FI2006/050533
Authority: WO
Inventors: Hannu Harjuhahto; Jaakko Harjuhahto; Antti-Jussi Rissanen
Original assignee: Maillefer S.A.
Priority date: 2005-12-02
Filing date: 2006-12-01
Publication date: 2007-06-07
Also published as: FI20055641A0; FI20055641A

Abstract

The invention relates to preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice. In the invention at least one release agent or formulation comprising at least one release agent is introduced to at least a portion of one or more streams of extrudable resinous thermoplastic materials before the extrusion orifice.

Description

METHOD IN EXTRUSION PROCESS, EXTRUSION PROCESS AND APPARATUS FOR EXTRUSION PROCESS

FIELD OF THE INVENTION

The present invention relates to a method, a process and an appa- ratus for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice. More particularly, the present invention relates to a method in a process for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice, according to the preamble of claim 1. Furthermore, the present invention relates to an extrusion process for preparing extruded articles in which process one or more heat plastified streams of extrudable resinous thermoplastic materials are arranged to flow through an extrusion orifice, the process comprising the following steps; providing one or more sources of heat plasti- fied extrudable synthetic resinous thermoplastic materials; and advancing the materials toward the extrusion orifice, according to the preamble of claim 10. Additionally the present invention relates to an apparatus for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice, according to the preamble of claim 19.

BACKGROUND OF THE INVENTION

In m u lti layered extruded articles with resilient properties, mechanical friction and adhesion between layers should be minimised. Additionally, the boundary surfaces between the layers should be as tight as possible in order to prevent water from penetrating between the layers. The layers of an extruded article tend to adhere to one another after the extrusion step through an extrusion orifice. Above facts are true for example for electric cables having a conductor wire, an insulation layer surrounding the wire and a sheath layer surrounding the insulation layer. In this case, the mechanical friction and adhesion between the insulation layer and the sheath layer should be minimised to produce a resilient cable. In the prior art, the above-mentioned minimisation of friction and adhesion between layers is accomplished by introducing talcum powder between the layers. When producing cables, talcum is applied on the insulation layer before forming the sheath layer on the insulation layer. The tal- cum separates the insulation layer and sheath layer from each other, thus reducing the friction and adhesion between these layers.

One disadvantage associated with the above arrangement using talcum is that as a powder it endangers the work hygiene as well as compli- cates the manufacturing process. Furthermore, talcum as a material has some unfavourable side effects affecting life cycle and usability of the end product. Talcum also absorbs and releases humidity, which further hardens the extruded article and makes it brittle. Therefore, the lifetime of the article is often reduced.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is thus to provide a method, a process and an apparatus so as to overcome the above disadvantages. The objects of the invention are achieved by a method that comprises the following step carried out before the extrusion step; selectively introducing and mixing at least one release agent or formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materials, according to the characterising part of claim 1. The objects of the invention are further achieved by a process comprising a step carried out before the extrusion step; introducing and mixing at least one release agent or formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materials, according to the characterising part of claim 10. Additionally, the objects of the invention are further achieved by an apparatus comprising upstream of the extrusion orifice an introducing means for selectively introducing at least one release agent or a formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materials in order to reduce or prevent the adhesion between the outer sheath of a cable and the inner insulation of the cable, according to the characterising part of claim 19.

The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea that a release agent and/or a formulation comprising a release agent is introduced to a heat plastified stream of extrudable resinous thermoplastic material before the extrusion head. The release agent is a compound which alters the adhesion properties of the ex- trudable material. When producing multilayered extruded articles, the different layers tend to adhere to each other after the extrusion step, compromising the resiliency of the article. By introducing a release agent or a compound comprising a release agent to the extrudable material or materials before the extrusion step, the adhesion properties of the materials may be altered in order to prevent or hinder the tendency of the materials from adhering to each other after the extrusion step. The release agent may be intruduced to a portion of a stream of an extrudable material or when extruding more than one stream of extrudable material, the release agent may be introduced to one or more of the streams or in one or more portions of one or more streams. Then the layers may be prevented from adhering to each other and simultaneously provide a tight contact or boundary between the layers.

An advantage of the present invention is that it provides a hygienic way to alter the adhesion properties of an extrudable material. In this case, no powder material or the like has to be used during the manufacture of the arti- cle. Additionally, the present invention provides a simple solution for preventing, or hindering the adhesion between extruded layers and thereby minimising the mechanical friction between the layers.

In the context of this application, the term "release" means "removal of a force or its effect". This may be related to a material in a flowing form, for example melt or in a solid state. In the case of liquid form, the release properties are usually balanced by the use of external and internal lubricants, which alone or in combination give proper balance of release and adhesion to suit for efficient processing. In the solid state, release properties are usually required to separate the product from a mold in which the product was manufactured or from another product or part of a product. In this context, the release comprises also antiblocking and slip properties. Antiblocking is an action, usually carried out by reformulation (addition of antiblocking agents(s)), which aims at reduction of forces of adhesion between materials in contact. Slip on the other hand means movement by sliding motion, which implies that the slip agent must address a deficiency in the material related to too high a friction between two surfaces in contact. The surfaces in contact may be composed of the same or different materials. The release agent in this application is meant to have above defined release, antiblocking and/or slip properties separately or in any possible combination. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which Figure 1 is schematic view of a electric cable manufactured accor- ing to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows an electric cable having a metallic conductor 2, an insulation layer 4 surrounding the conductor 2 and an outer sheath 6 surround- ing the insulation layer 4. In manufacture of this kind of electric cables, the insulation layer 4 and the outer sheath 6 are provided over the conductor 2 in an extrusion process. In order to produce a resilient cable, the insulation layer 4 and the outer sheath 6 should be prevented from adhering to each other. Therefore, in the extrusion process the extrudable materials are provided with a release agent or a formulation comprising a release agent, which reduces or prevents the insulation layer 4 and the sheath 6 from adhering to each other.

This may be achieved by flowing a heat plastified stream of extrudable resinous thermoplastic material through an extrusion orifice such that the stream is physically separated into a central core stream corresponding to the insulation layer 4 and a boundary stream corresponding to the sheath 6 on the outside of the core stream before the extrusion step. The physical separation of the core and boundary streams is maintained and at least one release agent or formulation comprising at least one release agent is selectively introduced in the boundary stream and/or in the central core stream. After that, the streams are recombined prior to expelling the material out of the extrusion orifice. Recombining of the streams takes place preferably near the extrusion orifice. The release agent prevents the thus formed insulation layer 4 and sheath 6 from adhering to each other, providing a resilient electric cable, as shown in Figure 1. The stream of extrudable material may be separated into one core stream and one or more boundary streams. In that case, the release agent may be introduced in the core stream and/or one or more of the boundary streams before the extrusion orifice. Thus the predetermined layers in the extruded article may be prevented from adhering to each other by the introduc- tion of the release agent. An electric cable according to Figure 1 having an insulation layer 4 and a sheath layer 6 may also be produced by flowing a core stream of ex- trudable thermoplastic material corresponding to the insulation layer 4 and a boundary streams of extrudable thermoplastic material corresponding to the sheath layer 6 through an extrusion orifice and selectively introducing a release agent or a formulation comprising a release agent in the core stream and/or in the boundary stream before the extrusion step. The core stream and the boundary stream may be combined upstream of the extrusion orifice, preferably near the extrusion orifice. In the above case, the material of the core stream and the material of the boundary stream may be of the same material or they may be of different materials or different compounds. Additionally there may be provided more than one boundary stream, which may be of the same or of different material or compounds. The release agent may be introduced only in one or more of these boundary streams and/or in the core stream.

The two above-mentioned methods for producing a multilayered extruded article may also be combined such that two or more streams of extrudable material are flowed towards an extrusion orifice and one or more of these streams are physically separated and recombined in the above identified manner. The release agent may be introduced in at least one portion of these physically separated streams and/or in one or more non-separated streams, upstream of the extrusion orifice. All the non-separated and separated streams may be further combined upstream of the extrusion orifice.

The release agent may also be introduced in only a portion of a stream of an extrudable material, for example in the outer surface portion or an inner surface portion of a stream of an extrudable material. Alternatively, the release agent or a formulation comprising a release agent may be introduced and mixed to a stream of an extrudable material. In this context, the introduction of the release agent comprises also the mixing of the release agent to the extrudable material, when the mixing is desirable.

One or more different substances may be used as a release agent, and different streams may be provided with different release agents according to the material of the particular stream of extrudable material. A release agent is a substance that alters the adhesion properties of the extrudable material in order to reduce adhesion of the extruded material with another material. A formulation comprising a release agent may also include other substances that alter the properties of the extrudable material, such as viscosity and cross linking. The substances used as release agent comprise the following: ceramic spheres, diatomaceous earth, fatty acid amides, fatty acid esters, fatty acid salts, fatty asids, fluorocompounds, graphite, molydenum sulfide, kaolin, ligno- sulfonates, limestone, polytetrafluoroethylene, polyvinylalcohol in solution, resins in solution, secondary amides, silica slilicates, silicones (oils and crosslinked), talcum, waxes zeolithes. Also other compounds and substances and chemical groups having release properties may be used. Formulation comprising release agent(s) may have one or more of the above-mentioned substances. The invention is not limited to certain compounds or substances. These substances and their release properties may be found for example from Handbook of antiblocking, release and slip additives, George Wypych, 1. edition (ISBN 1-895198-31-3).

After the extrusion step the extruded article, for example an electric cable, may be twisted around its longitudinal axis in order to ensure that the layers of the extruded article, of which at least one comprises a release agent, do not adhere to each other during cooling of the materials of the extruded article.

All above tasks may be conducted as a method in a process for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice, or as a process for preparing extruded articles in which process one or more heat plastified streams of extrudable resinous thermoplastic materials are arranged to flow through an extrusion orifice. There may also be only one stream of ex- trudable material, which is flown through an extrusion orifice without separating it physically. Thus according to the present invention, it is possible to produce a single layered extruded article having at least one release agent or a formulation having at least one release agent introduced thereto. With release agent altered adhesion properties, the article may be utilised in subsequent proc- esses or steps carried out to or on the article.

In an extrusion process for preparing extruded articles, one or more sources of heat plastified extrudable synthetic resinous thermoplastic materials are provided and the materials are advanced toward an extrusion orifice. Before the extrusion step, at least one release agent or formulation comprising at least one release agent is introduced into at least a portion of one or more streams of extrudable resinous thermoplastic materials. The process may ad- ditionally comprise diverting a portion of the material from a first flow path to a second flow path and introducing and mixing at least one release agent or formulation comprising at least one release agent to the diverted flow and/or to the material remaining in the first flow path and applying the second flow path as a relatively thin layer to the surface of the resin flowing in the first flow path prior to passing the material through the extrusion orifice. The application of he second flow path as a relatively thin layer to the surface of the resin flowing in the first flow is done preferably near the extrusion orifice.

The present invention also relates to an apparatus for preparing ex- truded articles by flowing heat plastified stream of extrudable resinous thermoplastic material through an extrusion orifice. The apparatus comprises before the extrusion orifice introducing means for selectively introducing at least one release agent or a formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materi- als so as to reduce or prevent the adhesion between the outer sheath of a cable and the inner insulation of the cable. Further the apparatus may comprise a first means for physically separating a stream into a central core stream and at least one boundary stream on the outside to the core stream. The introducing means are preferably arranged to introduce at least one release agent or a formulation comprising at least one release agent into one or more of the boundary streams and/or core stream while maintaining physical separation of the core and boundary streams. Additionally, the apparatus may further comprise a third means for recombining the streams prior to expelling the material from the extrusion orifice. The third means is preferably placed near to the ex- trusion orifice. The apparatus may furthermore comprise twisting means for twisting the article around its axis after the extrusion step.

It is therefore the object of the present invention to introduce a release agent to the extrudable material before expelling it from an extrusion orifice. This is advantageous when the extruded article is provided with two or more layers such that these layers may be prevented from adhering to each other. This is also advantageous when the extruded article is subject to subsequent processes or process steps in which it is preferable that the material has altered adhesion properties. Altered adhesion properties may also be utilized during the actual use of the extruded article, as it does not adhere permanently or too tightly to other materials or articles during use. It should also be noticed that the release agent may be provided in only a portion of the extruded article, such as the surface of the article, or to only one layer of the extruded article. Optionally it also possible to mix the release agent to the extrudable material or materials such that the whole extruded article has altered adhesion properties. For example the sheath 6 of the electric cable or the insulation layer 4 of the electric cable may each be provided with a release agent, but it is also possible provide them both with a release agent.

The release agent is usually provided to the surface of a stream of extrudable material prior to the extrusion head. The portion may be a separate boundary stream, segment, section, sector or the like of a stream of an ex- trudable resinous thermoplastic material. When producing flexible or rigid cables or the like, it is advantageous that the outer layer sheath layer may be skimmed or peeled away as easily as possible when desired. Therefore the release agent is provided to the outer sheath layer, to the inner insulation layer or to both of them. This may be done as described earlier. This may be done by extruding an insulation layer over an electric conductor and providing this insulation layer with a release agent prior to expelling it out from the extrusion head. The release agent may be provided only to the outer surface layer of the extrudable insulation layer or to a portion of the extrudable insulation layer, as described above. Alternatively, the release agent may be provided to an outer sheath layer being extruded over an insulation layer surrounding an electrical conductor. In this case, the release agent may be provided to the whole sheath material or only to an inner surface portion of the extrudable sheath material prior to the extrusion head. Yet in another case, the release agent may be provided to both the insulation layer and the sheath layer. The same may also be applied to other extrudable articles which come into contact with plastic material. It is essential that at least the portion of the extruded article that comes into contact with another extruded article or with another layer of extruded material or with another plastic article, is provided with the release agent. This may be controlled by dividing a stream of extrudable material into two or more sub streams. It is also essential that the introduction or the mixing of the release agent is accomplished in situ in the extruder.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method in a process for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice, c h a ra cte ri z e d in that the method comprises the following step carried out before the extrusion step,

- selectively introducing at least one release agent or formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materials.

2. The method according to claim 1, characterized by selec- tively introducing at least one release agent or formulation comprising at least one release agent to the surface portion and/or inner portion of one or more streams of extrudable resinous thermoplastic materials.

3. The method according to claim 1 or 2, cha racte rized in that the method further comprising the following steps carried out before the extrusion step:

- physically separating a stream into a main stream and at least one sub stream;

- while maintaining physical separation of the main and sub streams, selectively introducing at least one release agent or formu- lation comprising at least one release agent to at least one sub stream and/or to the main stream; and thereafter

- recombining the streams prior to expelling the material out of the extrusion orifice.

4. The method according to claim 3, characterized in that the streams are recombined near the extrusion orifice.

5. The method according to claim 3 or 4, ch a racte rized in that the main stream is the core stream and the substream is a boundary stream surrounding the core stream.

6. The method according to claim 3 or 4, ch a racte rized in that the sub stream is a segment, section, portion, sector or the like of the stream of an extrudable resinous thermoplastic material.

7. The method according to claim 1, characterized by flowing a core or a main stream of extrudable thermoplastic material and one or more boundary or sub streams of extrudable thermoplastic material through an extrusion orifice and selectively introducing at least one release agent or formulation comprising at least one release agent to the core or main stream and/or to one or more boundary or substreams before the extrusion step.

8. The method according to claim 7, characterized in that the core or main stream and the boundary or substreams are merged near the extrusion orifice.

9. The method according to any one of the previous claims 1 - 8, c h aracterized in that the release agent introduced comprises at least one of the following: ceramic spheres, diatomaceous earth, fatty acid amides, fatty acid esters, fatty acid salts, fatty acids, fluorocompounds, graphite, molybdenum sulfide, kaolin, lignosulfonates, limestone, polytetrafluoroethylene, polyvi- nylalcohol in solution, resins in solution, secondary amides, silica slilicates, silicones (oils and crosslinked), talcum, waxes zeolithes.

10. The method according to any one of the previous claims 1 - 9, c haracterized in that the method is performed in the field of manufacturing electric cables in order to reduce or prevent adhesion between the outer sheath (6) of a cable and the inner insulation (4) of the cable.

11. The method according to claim 10, characterized in that it further comprises twisting the cable around its longitudinal axis after the extrusion step.

12. An extrusion process for preparing extruded articles in which process one or more heat plastified streams of extrudable resinous thermoplastic materials are arranged to flow through an extrusion orifice, the process comprising:

- providing one or more sources of heat plastified extrudable synthetic resinous thermoplastic materials; - advancing the materials toward the extrusion orifice, characterized by the step carried out before the extrusion step,

- introducing at least one release agent or formulation comprising at least one release agent to at least a portion of one or more streams of extrudable resinous thermoplastic materials.

13. The process according to claim 12, c h a r a c t e r i z e d by introducing at least one release agent or formulation comprising at least one release agent to the surface portion and/or inner portion of one or more streams of extrudable resinous thermoplastic materials.

14. The extrusion process according to claim 12 or 13, characte r i z e d by further steps in a process in which a heat plastified stream of ex- trudable resinous thermoplastic material is arranged to flow through an extrusion orifice,

- diverting a portion of the material from a first flow path to a second flow path and introducing and mixing at least one release agent or formulation comprising at least one release agent to the diverted flow and/or to the material remaining in the first flow path; and

- applying the second flow path as a relatively thin layer to the surface of the resin flowing in the first flow path prior to passing the material through the extrusion orifice.

15. The process according to claim 14, characterized in that applying the second flow path as a relatively thin layer to the surface of the resin flowing in the first flow path is performed near the extrusion orifice.

16. The process according to claim 12, ch a racte rized by flowing a core stream of extrudable thermoplastic material and one or more boundary streams of extrudable thermoplastic material through an extrusion orifice and selectively introducing at least one release agent or formulation comprising at least one release agent to the core stream and/or to one or more boundary streams before the extrusion step.

17. The process according to claim 16, characterized in that the core stream and the boundary streams are combined near the extrusion orifice.

18. The process according to any of the previous claims 12 - 17, c h aracterizedin that the release agent introduced comprises at least one of the following: ceramic spheres, diatomaceous earth, fatty acid amides, fatty acid esters, fatty acid salts, fatty acids, fluorocompounds, graphite, molybdenum sulfide, kaolin, lignosulfonates, limestone, polytetrafluoroethylene, polyvi- nylalcohol in solution, resins in solution, secondary amides, silica slilicates, silicones (oils and crosslinked), talcum, waxes zeolithes.

19. The process according to any of the previous claims 12 - 18, c h aracterizedin that the process is used in the field of manufacturing electric cables, in order to reduce or prevent the adhesion between the outer sheath of a cable and the inner insulation of the cable.

20. The process according to claim 19, characterized in that it further comprises twisting the cable around its longitudinal axis after the ex- trusion step.

21. An apparatus for preparing extruded articles by flowing one or more heat plastified streams of extrudable resinous thermoplastic materials through an extrusion orifice, c h a r a c t e r i z e d in that the apparatus comprises, before the extrusion orifice introducing means for selectively introduc- ing at least one release agent or a formulation comprising at least one release agent at least to a portion of one or more streams of extrudable resinous thermoplastic materials in order to reduce or prevent adhesion between two or more extruded material layers.

22. The apparatus according to claim 21 , c h a r a c t e r i z e d in that the apparatus further comprises first means for physically separating a stream into a central core stream and at least one boundary stream on the outside of the core stream, that the introducing means are arranged to introduce at least one release agent or a formulation comprising at least one release agent to one or more boundary streams and/or core stream while main- taining physical separation of the core and boundary streams and that the apparatus further comprises third means for recombining the streams prior to expelling the material out of the extrusion orifice.

23. The apparatus according to claim 21 or 22, c h a r a c t e r i z e d in that the apparatus further comprises first means for physically separating a stream into a main core stream and at least one sub stream, that the introducing means are arranged to introduce at least one release agent or a formulation comprising at least one release agent to one or more sub streams and/or main stream while maintaining physical separation of the main and boundary streams and that the apparatus further comprises third means for recombining the streams prior to expelling the material out of the extrusion orifice.

24. The apparatus according to claim 23, c h a r a c t e r i z e d in that the substream is a segment, section, portion, sector or the like of the stream of an extrudable resinous thermoplastic material.

25. The apparatus according to claim 22, 22 or 23, c h a r a c t e r i z e d in that the third means is placed near the extrusion orifice.

26. The apparatus according to claim 21 or 20, c h a r a c t e r i z e d in that it further comprises twisting means for twisting the article around its axis after the extrusion step.