WO2004039574A2

WO2004039574A2 - Tubular body having isolation layer of foamed plastic and method for producing same

Info

Publication number: WO2004039574A2
Application number: PCT/BE2003/000185
Authority: WO
Inventors: Neil Kaye; Michel Peruch
Original assignee: Plastiflex Belgium
Priority date: 2002-10-31
Filing date: 2003-10-31
Publication date: 2004-05-13
Also published as: AU2003280235A8; WO2004039574A3; AU2003280235A1

Abstract

A tubular body (10; 20) comprising a single-piece first layer (11; 21) of a foamed plastic material for isolating the interior of the body from the exterior of the body, the tubular body having an inner surface (17; 27) and an outer surface (14; 24), at least a part the outer surface (14; 24) of the tubular body (10; 20) having a corrugated shape comprising annular protrusions (15; 25) alternating with annular recesses (16; 26).

Description

Tubular body having isolation layer of foamed plastic and method for producing same

The present invention relates to a tubular body according to the preamble of claim 1. The invention further relates to a method for producing a tubular body according to the preamble of claim 7.

EP-A-1 072 389 discloses a cylindrical body of which the side wall comprises two layers. The inner layer is of a foamed plastic material, more particularly a blow-moulded foam with a cylindrical shape.

EP-A-1 072 389 further discloses a method for producing a multi-layered tubular body of which one layer is a foamed plastic material. The tubular body is formed by co-extrusion of molten resins, one of which is mixed with a foaming agent. This results in a cylindrical parison which comprises a foamed layer. In a subsequent step, the parison is placed into a cylindrical mould in which it is expanded by blow-moulding.

The tubular body known from EP-A-1 072 389 however has the disadvantage that it has insufficient flexibility. It is therefore firstly an aim of the present invention to provide a tubular body comprising a layer of a foamed plastic material having an enhanced flexibility.

This aim is achieved according to the invention with a tubular body showing the technical characteristics of the characterising part of claim 1. It is secondly an aim of the invention to provide a method for producing a tubular body comprising a first layer of foamed plastic material, with which the production speed may be enhanced.

This aim is achieved by the method showing the steps of the characterising part of claim 7.

The tubular body of the invention comprises a single-piece first layer of a foamed plastic material. This first layer is provided for isolating the interior of the body from the exterior of the body. The layer is a single-piece layer in the sense that it is constructed as a single piece, for example by blow-moulding or injection moulding the foamed plastic material. The tubular body of the invention can have multiple layers or a single layer, but it has at least the isolation layer of foamed plastic material.

Over at least a part of its length and preferably over its entire length, the outer surface of the tubular body of the invention has a corrugated shape comprising annular protrusions alternating with annular recesses. The alternation of protrusions and recesses provides an annular space between each pair of adjacent annular protrusions on the outside of the body. Due to the presence of these annular spaces, the annular protrusions can be pressed towards each other, allowing the tubular body to be bent to a larger extent than the prior art cylindrical body. As a result, the flexibility of the tubular body of the invention may be enhanced.

Furthermore, the annular protrusions of the tubular body of the invention form ribs on the outside of the body where the material is concentrated. These ribs act as a reinforcement of the tubular body of the invention which can prevent kinking of the tubular body when it is bent or radially compressed to a large extent. As a result, the corrugated outer surface can also enhance the hub strength of the tubular body of the invention. Furthermore, the need for providing additional reinforcement ribs can be avoided, which can in turn lead to a reduction in the production cost of the tubular body of the invention.

The inner surface of the tubular body of the invention is preferably substantially smooth. This means that the inner surface is preferably approximately cylindrical, i.e. substantially without corrugations. In this way, the tubular body comprises thin-walled portions alternating with thick-walled portions, of which the thin-walled portions have a reduced resistance to compression or expansion in axial direction of the tubular body. This may further enhance the flexibility of the tubular body of the invention. Furthermore, the smooth inner surface of the tubular body makes the body suitable for transporting fluids, since the smooth inner surface forms little or no obstruction to the fluid flow.

In preferred embodiments, the tubular body comprises two or more layers, namely the first, isolation layer of foamed plastic material and one or more further layers in a different or the same plastic material, joined to the inside and/or the outside of the first layer. The material of each further layer may also be a foamed plastic material.

In a specifically preferred embodiment, the tubular body comprises a substantially cylindrical foamed layer with a corrugated layer joined to the outside. This means that the first layer, which is the foamed layer, has a substantially cylindrical or smooth inner and outer surface. The corrugated layer on the outside has a corrugated wall, i.e. a corrugated shape on the inside as well as on the outside, with gaps between the annular protrusions and the foamed layer. This structure has the advantage that the annular protrusions are not filled with the material of the foamed layer, so that they can be compressed upon bending of the tubular body. As a result, with this embodiment of the tubular body of the invention, a very high flexibility may be achieved.

The tubular body of the invention is preferably constructed by means of the method described below. It may however also be constructed by means of any other method known to the person skilled in the art.

The method for producing a tubular body comprising a first layer of foamed plastic material according to the invention comprises the following steps. A plastic material is melted and a foaming agent is admixed. The mixture is then extruded to form a first layer of a cylindrical parison. The extrusion is performed at the entrance of a mould for blow/vacuum moulding the parison into the desired tubular body. Upon extrusion a temperature is applied for activating the foaming agent. Simultaneously, a pressure is applied on the inside of the parison and/or a vacuum is applied on the outside of the parison for pulling/blowing the parison against the mould. The process parameters, which comprise the temperature and pressure and/or vacuum, are controlled in such a way that the material of the parison is simultaneously deformed by foaming and blow/vacuum moulding. In other words, the process parameters are controlled such that the foaming agent is active during the blow/vacuum moulding of the parison in the mould.

In the method of the invention, the process parameters, which comprise the extrusion temperature and the pressure/vacuum on the inside/outside of the extruded parison, are carefully selected for activating the foaming agent upon extrusion and simultaneously moving the parison against the side wall of the mould. In this way, the expansion which occurs by foaming and that which occurs by blow/vacuum moulding are brought together to a single process step, i.e. they occur simultaneously. As a result, the number of steps for manufacturing the tubular body according to the invention can be reduced, which can result in a higher production speed and a lower production cost.

Furthermore, by controlling the temperature and pressure in such a way that the foaming and blow/vacuum moulding occur simultaneously, the use of a.o. a corrugated mould is made possible, since the double expansion can ensure that the corrugations of such a mould will be substantially completely filled with the material of the parison. As a result, the method of the invention makes it possible to use moulds of various shapes, for example cylindrical moulds with a smooth side wall as well as corrugated moulds with a corrugated side wall or other, so that a wider variety of shapes of tubular bodies can be produced with the method of the invention.

In a preferred embodiment of the method of the invention, a second layer of the parison is co-extruded with the first layer on the outside of the first layer, so that a multi-layered parison is extruded and a multi-layered tubular body is produced. In case a corrugated mould is used, the process parameters are preferably controlled such that gaps are formed by the foaming agent between the first and second layers at the corrugations of the mould. In this way, a tubular body can be produced which comprises a substantially cylindrical layer of foamed material and a corrugated layer joined to the outside of the foamed layer. More particularly, the corrugated layer has annular protrusions alternating with annular recesses, the recesses being connected to the foamed layer and the protrusions being disconnected from the foamed layer and filled with the foaming agent. This results in a tubular body with a very high flexibility as has been described above.

The temperature and pressure are preferably furthermore controlled such that the expansion of the material of the first layer leads to a smooth inner surface of the tubular body. This produces a tubular body which is for example suitable for transporting fluids. The method of the invention preferably further comprises the step(s) of co-extruding one or more further layers on the inside and/or outside of the first layer.

The invention will be further elucidated by means of the following description and the appended figures. Figure 1 shows a first embodiment of the tubular body according to the invention. Figure 2 shows a second embodiment of the tubular body according to the invention.

Figure 3 shows a production line for implementing the method of the invention. The tubular body 10 of figure 1 comprises a first layer 11 of a foamed plastic material, a second layer 12 on the outside of the first layer 11 and a third layer 13 on the inside of the first layer 11. The first layer 11 of foamed plastic material is provided for thermally and/or acoustically isolating the interior from the exterior of the tubular body 10.

The tubular body 10 has a corrugated outer surface 14 with annular protrusions 15 alternating with annular recesses 16, which are formed by the corrugated wall of the second layer 12. The annular protrusions 15 are substantially completely filled with the foamed plastic material of the first layer 11. The corrugated wall of the second layer 12 can enhance both the flexibility and the hubstrength of the tubular body 10.

The tubular body 10 of figure 1 has both an outer and an inner layer 12, 13, covering the foamed layer 11 on the outside and inside. These layers 12, 13 are in fact mainly provided as protective cover for the foamed layer 11. If such protection is unnecessary, the outer and/or inner layer 12, 13 may be absent. In other words, the tubular body may comprise one layer of foamed material only, it may comprise two layers, foam on the outside or foam on the inside, or three layers with the foam on the outside, inside or in between the outer layer and inner layer. The body may further comprise more than three layers, with different positions for the foamed layer.

The tubular body 20 of figure 2 comprises a first layer 21 of a foamed plastic material, a second layer 22 on the outside of the first layer 21 and a third layer 23 on the inside of the first layer 21. The first layer 21 of foamed plastic material is provided for thermally and/or acoustically isolating the interior from the exterior of the tubular body 20.

The tubular body 20 has a corrugated outer surface 24 with annular protrusions 25 alternating with annular recesses 26, which are formed by the corrugated wall of the second layer 22. The annular recesses 26 are connected to the first layer 21 , but the annular protrusions 25 are disconnected from the first layer 21. In other words, gaps 28 are located between the protrusions 25 and the first layer 21. These gaps 28 provide space for compressing the protrusions 25 upon bending the tubular body 20, so that its flexibility can be further enhanced with respect to the tubular body 10 of figure 1.

In the embodiment of figure 2, the tubular body 20 comprises at least the first and second layers 21 , 22 and preferably the third layer 23 on the inside for protecting the first, foamed layer 21. In case protection of the first layer 21 is unnecessary, the third layer 23 may also be absent. The tubular body 20 may further comprise further layers on the inside and/or on the outside.

The tubular bodies 10 and 20 of figures 1 and 2 have a substantially smooth inner surface 17, 27, which is formed by the substantially cylindrical third layer 13, 23. The third or inner layer 13, 23 is preferably made of a flexible material and as thin as possible to keep the flexibility of the body. The smooth inner surface 17, 27 makes the tubular bodies 10 and 20 suitable for transporting fluids, since the inner surface 17, 27 has little or no obstructions which can obstruct the fluid flow. For other applications, the inner surface 17, 27 may also be a rough or corrugated or other surface.

The first layer 11 , 21 , which is provided as isolation, is preferably constructed in one of the following preferred materials: thermoplastic elastomers (Santoprene, Forprene, Vyram,...) polyolefins, polyethylene, metallocene polyolefins, polypropylene, PVC, rubbers or any combination of these materials, or any other material deemed suitable by the person skilled in the art. The first layer 11 , 21 is constructed as a single piece, for example by blow/vacuum moulding or injection moulding or by other processes known to the person skilled in the art. The outside and inside layers 12, 22 and 13, 23 are preferably constructed in one of the following materials: thermoplastic elastomers (Santoprene, Forprene, Vyram,...) polyolefins, polyethylene, metallocene polyolefins, polypropylene, PVC, rubbers or any combination of these materials, or any other material deemed suitable by the person skilled in the art. The outside and inside layers 12, 22 and 13, 23 are preferably constructed by means of a continuous moulding process, simultaneously with the first, isolation layer 11 , 21. They may however also be constructed separately and joined to the isolation layer 11 , 21 in a subsequent process step. In this case, for example a straight, i.e. substantially cylindrical outer layer may be joined on the outside of a corrugated isolation body.

In general, any combination of the above mentioned materials can be used for the different layers 11-13 and 21-23. The tubular body 10, 20 can be constructed in different diameters and with different thicknesses of the respective layers.

The tubular bodies 10 and 20 shown in figures 1 and 2 are intended for application in airconditioning systems. The tubular bodies of the invention can however also be applied to the following other fields, where requirements of isolation for temperature and noise are determinant for the tubular body: the floorcare market, the pool and spa market, the industrial market, the automotive and aviation market and medical devices.

The tubular bodies 10 and 20 are generally intended for use in applications where a cold medium (e.g. cold fluids) or a hot medium (e.g. steam, hot fluids) is transported through the body and where it is desirable that the medium is isolated from the environment. The foamed layer 11 , 21 forms an isolation layer of a foamed plastic material. A constraint for this isolation layer 11 , 21 can for example be that the outside of the tubular body is to be kept between reasonable temperatures, so that in case of a hot medium a person can safely touch the hose without risking skin-burn and in case of a cold medium the forming of condensation on the outside can be prevented.

The tubular bodies 10 and 20 can further be intended for use in applications where any fluid, gas or liquid is transported, or where cables, electrical wires, optical fibres or other are placed inside the body and need to be insulated from the environment. The isolation 11 , 21 can be for damping outside temperature variations or for damping noise, which may for example arise from fluid turbulences or vibrations of the electrical cables, wires and optical fibres encapsulated within the body 10, 20, or by the conveying of particles (dust, pellets) within the body 10, 20 using suction or pressurised flows.

The tubular bodies 10, 20 are preferably constructed by means of the process implemented by the production line shown in figure 3. They may however also be constructed by means of other processes. The production line of figure 3 is intended for producing a.o. the corrugated tubular bodies 10, 20 of figures 1 and 2. More generally, the production line is intended for producing tubular bodies which have at least the isolating layer, i.e. the layer of foamed plastic material 11 , 21 , and preferably at least one other layer 12, 13, 22, 23. The tubular bodies can be flexible hoses or rigid pipes, depending on the application for which they are intended.

The production line of figure 3 comprises the following devices: an extruder 1 for extruding a single- or multilayered parison, a corrugator 3 for shaping the parison into the desired tubular body 7, a cooling system 6, a cutting unit 8 and a guiding and packaging unit 9. In the extruder 1 , the material of the different layers of the parison is melted, so that it can be fed via different feed lines to a co-extrusion head 2 for extruding the parison. For at least one layer 11 , 21 , but possibly also for more than one layer, a foaming agent is admixed. The co-extrusion head 2 forms the molten materials to the parison, which comprises the different layers of the tubular body to be constructed. The extruded parison may comprise one layer of foaming material only. It may comprise two layers, foam on the outside or foam on the inside, or three layers with the foam on the outside, inside or in between the outer layer and inner layer. The parison may further comprise more than three layers, with different positions for the foamed layer. Finally, the parison may comprise more than one foaming layer.

For constructing the foaming layer(s) 11 , 21 , preferably one of the following materials is used: thermoplastic elastomers (Santoprene, Forprene, Vyram,...) polyolefins, polyethylene, metallocene polyolefins, polypropylene, PVC, rubbers or any combination of these materials, or any other material deemed suitable by the person skilled in the art. The foaming agent for this layer 11 , 21 can be an endothermic or an exothermic chemical foaming agent, for example foaming agents based on Azodicarbonamide, Bicarbonate, or other chemical foaming agents known to the person skilled in the art. An endothermic foaming agent starts foaming at a certain temperature and produces more foam when the temperature is increasing until a maximum foaming is reached. An exothermic foaming agent releases all the foam at once, when above a certain temperature. An alternative for adding these chemical foaming agents, which are initially in solid form, is the gas injection technique with agents in liquid or gaseous form. Optionally, the material of the foaming layer 11 , 21 can be stiffened by crosslinking, i.e. by chemically connecting the chains of the plastic material. This makes it possible to foam the material to a larger extent, so that a lighter foam is achieved. For constructing the other layer(s) 12, 13, 22, 23, preferably one of the following materials is used: thermoplastic elastomers (Santoprene, Forprene, Vyram,...) polyolefins, polyethylene, metallocene polyolefins, polypropylene, PVC, rubbers or any combination of these materials, or any other material deemed suitable by the person skilled in the art.

Upon extrusion, the foaming agent of the foaming layer 11 , 21 is activated, mainly due to a pressure drop on the outside of the parison, but also due to a well-chosen temperature in the extruder 1. In the production line of figure 3, the co-extrusion head 2 is placed directly at the entrance of the corrugator 3, which makes it possible to start with deforming the parison to the desired tubular body 7 at the same time as the activating of the foaming agent.

The tubular body 7 is produced from the parison with the technology of blow moulding and/or vacuum moulding. In the corrugator 3, the parison is expanded into mould blocks, which are mounted on rotating chains. When using the technology of the blow moulding, air is blown on the inside (through the male pin of the co- extrusion die) of the parison to expand the parison into the mould blocks. The pressure of the blown air is for example 0.1-1.5 bar. With the vacuum moulding technology a vacuum is created in the mould blocks through small circular openings in the moulds on the outside of the parison. The vacuum suction, which is applied via a vacuum supply 4, pulls the parison into the mould blocks. The blow and vacuum technologies may also be combined.

In the production line of figure 3, the expansion into the mould blocks of the corrugator 3 by applying pressure and/or vacuum is activated simultaneously with the foaming of the layer(s) 11 , 21 to which a foaming agent is admixed. The temperature and pressure at the co-extrusion die 2 are controlled to this end, i.e. for achieving the simultaneous expansion. In this way, the foaming agent helps to push the material into the profile of the mould blocks, so that a wide variety of shapes of tubular bodies can be produced.

In case an outside layer 12, 22 is provided around the isolation layer 11 , 21 , the process parameters can furthermore be controlled such that the foaming agent partially separates the outside layer 12, 22 from the isolation layer 11 , 21 , as is for example the case in the tubular body 20 of figure 2. This can for example be achieved by applying a vacuum on the outside of the parison to such an extent that the cells of the foaming layer 21 at the outside explode, so that the foaming agent is released from the cells and creates gaps between the layers. The space under the corrugations of the outer layer 22 of the finished tubular body 20 is then partially filled with the foaming agent.

Furthermore, an inside layer 13, 23 can be applied on the inside of the foaming layer 11 , 21 , for example for achieving a smooth inner surface 17, 27 when the cells of the isolation layer 11 , 21 of the finished product. In any case, the process parameters are preferably controlled such that the inner surface 17, 27 of the finished product is substantially cylindrical, i.e. substantially without corrugations or irregularities. For constructing a flexible tubular body, a flexible material is chosen for the inside layer 13, 23. However, for some applications also a more rigid body can be preferred, in which case a stiffer material is chosen.

The mould blocks of the corrugator 3 are cooled by means of a cooled liquid or gas to cool down the heated plastic of the tubular body 7. The cooled liquid or gas is supplied from a chiller 5 and passes through the mould blocks of the corrugator 3. After leaving the corrugator 3 the tubular body 7 is further cooled in a cooling system 6, for example a spray cooler, it is cut in the desired length in the cutting unit 8 and it is packaged in the guiding and packaging unit 9. Using the blow moulding or vacuum moulding process has the advantage that cuffs or connections for connecting the tubular body to further bodies or devices can be integrated in the moulding chain of the corrugator 3. As a result, the need for an additional step for applying the cuffs or connections can be avoided. The shape of the cuff is then determined by the shape of the mould block. As a result, a complete finished product can be made by means of the production line of figure 3.

Finally, examples of process settings are given for producing the tubular body 10 of figure 1 and the tubular body 20 of figure 2.

In both cases, the inside layer 13, 23 is PE or TPE extruded according to standard process settings (supplied by the manufacturer). The outside layer 12, 22 is PE, also extruded according to standard process settings (supplied by the manufacturer). The foamed layer 11 , 21 is produced by means of an endothermic foaming agent.

For the foamed layer 11 of the body 10 of figure 1 , the basic material is TPE. The body 10 was produced with the following temperature sequence set on the extruder 1 : 175, 205, 200, 190, 180 °C. The typical melt pressure was 280 bar.

For the foamed layer 21 of the body 20 of figure 2, the basic material is PE or a PE/ EVA copolymer. The body 20 was produced with the following temperature sequence set on the extruder 1 : 125, 150, 185, 185, 170°C. The typical melt pressure was 300 bar.

Claims

1. A tubular body (10; 20) comprising a single- piece first layer (11 ; 21) of a foamed plastic material for isolating the interior of the body from the exterior of the body, the tubular body having an inner surface (17; 27) and an outer surface (14; 24), characterised in that at least a part the outer surface (14; 24) of the tubular body (10; 20) has a corrugated shape comprising annular protrusions (15; 25) alternating with annular recesses (16; 26).

2. The tubular body according to claim 1 , characterised in that the inner surface (17; 27) of the tubular body (10; 20) is substantially smooth.

3. The tubular body according to claim 1 or 2, characterised in that the body further comprises a second layer (12; 22) of a second plastic material joined to the outer surface of the first layer (11 ; 21).

4. The tubular body according to claim 3, characterised in that the outer surface of the first layer (21) is substantially smooth and that the second layer (22) has a corrugated wall of annular protrusions (25) alternating with annular recesses (26), the first and second layers being joined to each other at the annular recesses (26) and gaps (28) being located in between the annular protrusions (25) and the first layer (21).

5. The tubular body according to any one of the claims 1-4, characterised in that the body (10; 20) further comprises a third layer (13; 23) of a third plastic material joined to the inner surface of the first layer (11 ; 21).

6. The tubular body according to any one of the previous claims, characterised in that the body (10; 20) further comprises at least one further layer on the inside and/or the outside of the first layer (11 ; 21).

7. A method for producing a tubular body (7; 10; 20) comprising a first layer (11 ; 21) of foamed plastic material, comprising the steps of: a) melting a first plastic material and admixing a foaming agent, b) extruding the mixture of molten first plastic material and foaming agent in the form of a first layer of a cylindrical parison, c) applying a temperature suitable for activating the foaming agent upon extrusion, d) placing the cylindrical parison into a mould (3) for blow and/or vacuum moulding the body, e) applying a pressure on the inside of the parison and/or a vacuum on the outside of the parison for blowing/pulling the cylindrical parison against the mould (3) and forming a tubular body (7; 10; 20) by blow/vacuum moulding, characterised in that the parison is extruded at an entrance of the mould (3) and that the extrusion temperature and/or the pressure and/or the vacuum are controlled such that the parison is simultaneously deformed by foaming and by blow/vacuum moulding.

8. The method according to claim 7, characterised in that the method further comprises the step of co- extruding a second layer (12; 22) of the parison simultaneously with the first layer (11 ; 21), the second layer being located on the outside of the first layer.

9. The method according to claim 7 or 8, characterised in that the mould (3) has a side wall with corrugations and that the extrusion temperature and/or the pressure and/or the vacuum are further controlled such that the material of the parison substantially completely fills the corrugations of the mould (3).

10. The method according to claim 9, characterised in that the extrusion temperature and/or the pressure and/or the vacuum are further controlled such that gaps (28) are formed by the foaming agent between the first (21) and second layers (22) at the corrugations of the mould (3).

11. The method according to any one of the claims 7-10, characterised in that the extrusion temperature and/or the pressure and/or vacuum are further controlled such that the tubular body (7; 10; 20) has a smooth inner surface (17; 27).

12. The method according to any one of the claims 7-11 , characterised in that the method further comprises the step of co-extruding a third layer (13; 23) of the parison simultaneously with the first layer (11 ; 21), the third layer being located on the inside of the first layer.

13. The method according to any one of the claims 7-12, characterised in that the method further comprises the step of co-extruding at least one further layer of the parison simultaneously with the first layer (11 ; 21), the further layer being located on the inside or outside of the first layer.