GB2333263A

GB2333263A - Co-extrusion methods and apparatus

Info

Publication number: GB2333263A
Application number: GB9900439A
Authority: GB
Inventors: Hugh Aloysius Perera
Original assignee: Epwin Group PLC
Current assignee: Epwin Group PLC
Priority date: 1998-01-14
Filing date: 1999-01-08
Publication date: 1999-07-21
Also published as: CA2258441A1; GB9900439D0; GB9800781D0

Abstract

A primary extrudate material from a first extruder barrel 21 is co-extruded with at least one secondary extrudate material from a second extruder barrel 29 to produce a multi-component product, by feeding them together through an extrusion die 23 via a co-extrusion adaptor 28 positioned upstream of the die 23. The apparatus is arranged so that the secondary material(s) flow(s) in a direction substantially perpendicular to the direction of flow of the primary material at the point where the materials meet within the co-extrusion adaptor 28. The co-extrusion adaptor 28 is designed such that it can be inserted into a conventional extrusion apparatus used to produce a single-component product, so that a multi-component product can be produced instead. The temperatures of the extrudate materials are preferably controlled to be the same, and the extrudate materials temperatures and pressures are also preferably controlled to remain constant between the upstream and downstream ends of the co-extrusion adaptor 28. The rate at which the secondary material(s) enters the co-extrusion adaptor 28 is preferably controlled to control the thickness and area of coverage of the secondary material(s) applied to the substrate produced from the primary material. The product produced is preferably a PVC panel component for use as part of a door, window, roof or conservatory. The primary material may comprise recycled plastics, and the secondary material(s) is preferably a coating for the primary material.

Description

CO-EXTRUSION METHODS AND APPARATUS Field of the invention This invention relates to methods and apparatus for use in the co-extrusion of two or more materials. It also provides products made using the methods, and an adapter for use as part of the apparatus.

Background to the invention The use of extrusion to produce for instance metal or plastics components is known. A material is melted and sheared in an extruder to form a high viscosity "extrudate", which is forced through an appropriately shaped die to produce a continuous length of the material having the desired, uniform, cross sectional profile.

A wide variety of articles may be manufactured in this way, including in particular the components of doors, windows, roofs, conservatories and other building structures. Such components, often known simply as "profiles", tend to have complex cross sectional geometry.

The extrusion of such a component typically runs as follows. A base material (eg, in the case of a plastics component a powder containing the desired plastics material(s) together with any necessary additives such as stabilisers and pigments) is fed into an extruder barrel. There, it is subjected to high temperatures and high mechanical forces, the latter by the action of a rotating screw or (in a "twin-screw" extruder) two inter-meshing, counter-rotating screws. This produces an extrudate with the required viscosity and other physical characteristics. Often the temperature and mechanical force vary between different zones within the extruder barrel.

The extrudate passes from the barrel to an "adapter", which modifies it to produce a linear, uniform flow of a size and shape suitable for entering the die. In particular, the adapter helps to smooth pulses in the extrudate flow.

From the adapter, the extrudate is forced through the die to give it the desired shape. It then passes through a "calibrater" in which it is cooled, often under vacuum.

It is then ready for use.

The process is carried out continuously, with a constant throughput of extrudate.

The die typically comprises a series of die plates, secured adjacent one another to define a specially shaped internal space through which the extrudate must pass.

Where the extruded product is to have a complex cross sectional profile, including for instance internal cavities, and internal as well as external walls, the die geometry is also complex. The plates must provide appropriately positioned baffles in the intemal space, supported in such a way as to allow the extrudate to flow around them into all regions of the die.

Extruded products sometimes require a layer of a secondary material on top of the basic extruded substrate. For instance, a coating may be needed to give a particular surface colour or finish, or a surface layer of "virgin" plastics material may be required to improve the appearance of a recycled plastics substrate. Alternatively, the secondary material may form a sealing means, such as an elastomeric or thermoplastic gasket, applied to the substrate.

Ideally, such secondary materials are co-extruded with the substrate to produce a finished product in a single operation. This is typically achieved (see, eg, GB-23 13088) by extruding the secondary material in a secondary extruder barrel and feeding it, via a secondary adapter, into the downstream end of the die. The secondary material joins the main extrudate just before both leave the die. At least one, more usually two, of the die plates thus need to be modified to allow for the introduction of the secondary material, or alternatively a completely new die is needed. Such die modification can be highly complex and costly, and needs to be carried out separately on each die which the operator uses.

Moreover, a modified die may not then be usable to extrude a simple singlecomponent product; cutting off the secondary extrudate could risk leakage of the substrate material out of the die through the secondary material inlet. Thus, when a manufacturer wishes to change between producing, say, a coated and an uncoated product, he must swap the modified and unmodified die plates accordingly. This involves shutting down and re-starting production, a lengthy, costly and inconvenient process.

Where the secondary material is a sealing gasket or the like, it is more conventionally introduced after the substrate has exited the main die. The substrate is locally re-heated to bond the two materials as they come into contact. EP-0455670 describes such a process, in which a sealing or damping element or a protective coating is extruded onto a heated region of an extruded profile, post-calibration. EP0290536 also describes a process for mounting an extruded seal onto a ready-formed extrusion.

In the process disclosed in NL-72 1 1692, a seal is extruded onto a plastics substrate either towards the downstream end of the substrate die or between the die and the calibrater.

In the co-extrusion of multi-component products of relatively simple cross sectional profile, such as films, sheets or tubes, two materials may be fed together into a die and co-extruded through it. However, for products of a more complex cross section, passing through a correspondingly complex die, the introduction of a secondary material pre-die would be expected to compromise the resultant product.

Any change in the flow characteristics of the extrudate passing through the die, in particular its cross sectional temperature or viscosity distribution, could affect its pattern of flow through the die, resulting in significant dimensional changes in the extruded product. Since the die and the substrate extruder (or rather, the die and the properties of the extrudate entering it) have to be "tuned" to run together to create a desired product, the tuning involving for instance alterations to the conditions in the extruder or to the internal die geometry, any change in the extrudate properties predie can affect that tuning and hence the end product. This is why, in the manufacture of more complex multi-component extrusions, such as coated building components, the secondary material is conventionally introduced at the last possible moment, ie, at the downstream end of, or beyond, the die. In contrast, in the extrusion of simple sheets and films, the tuning between die and extruder is less significant.

Some existing systems do allow for the co-extrusion of multi-component products, including sheets, sidings and other relatively simple profiles, through unmodified dies, but in these cases extra equipment parts are needed pre-die, and those parts tend to be relatively complex, cumbersome and costly as well as being difficult to instal in and remove from an existing extrusion line. Moreover, the additional parts tend to alter the flow properties of the extrudates passing through them, again necessitating the re-tuning of the die and extruders each time the additional parts are installed or removed.

Examples of such equipment are disclosed in, for instance, EP-0050476 (in which each extrudate is passed through a manifold, a feedblock and an adapter prior to entering the die, and is reduced in cross sectional area within the feedblock), US4911628 (which requires a pre-die co-extrusion adapter having a special internal channel arrangement) and US-5076777 (which again shows the use of a relatively complex co-extrusion adapter/secondary extruder arrangement).

The present invention aims to provide an alternative system for co-extruding two or more materials, which can be used to make products of relatively complex cross section.

Statements of the invention According to a first aspect of the present invention there is provided a method for co-extruding a primary, substrate material and at least one secondary material to produce a multi-component product, the method comprising preparing a primary extrudate of the substrate material; preparing a secondary extrudate of the secondary material; and feeding the extrudates together through an extrusion die via a coextrusion adapter positioned upstream of the die, wherein the secondary extrudate flows in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet within the co-extrusion adapter.

The primary extrudate is thus fed through the co-extrusion adapter from a point upstream of it, and the secondary extrudate is introduced via the co-extrusion adapter so as to flow with the primary extrudate into the die. The secondary extrudate need not be fed directly into the die and the die needs no modification to allow the coextrusion to take place. Because the secondary extrudate is introduced perpendicular to the primary extrudate flow (or substantially so - ideally at an angle of between about 80 and 100 , more preferably between about 85 and 95 , to the primary extrudate flow), the co-extrusion adapter can be of relatively simple and compact construction, compared for instance to prior art assemblies which introduce two extrudates tangentially to one another. It can be inserted into, or removed from, a production line with relative ease, and can be generally more flexible in operation.

For instance, it can be used with several different dies, and in each case be mounted in conventional fashion onto the outlet flange of an extruder, adjacent a similarly mounted die, without external support.

Preferably, the internal geometry of the co-extrusion adapter is such as to cause substantially no change in the flow characteristics of the primary extrudate passing through it, or rather, such that at least one, preferably more, of the flow characteristics of the combined primary and secondary extrudates entering the die from the co-extrusion adapter is the same, or substantially the same, as that of the primary extrudate entering the adapter. By "flow characteristics" is meant properties such as the cross sectional shape and dimensions of the extrudate, its absolute temperature, its cross sectional temperature and viscosity distributions and its pressure, in particular its temperature distribution and its shape and dimensions.

Maintaining these characteristics as nearly constant as possible enables the mixture of primary and secondary extrudates to pass through an unmodified die as though the primary extrudate had not been altered at all, thus minimising disturbance in the die and any consequent effects on the final product. In other words, the co-extrusion adapter can be "transparent" to the die. It can be inserted between a pre-tuned die/extruder pair without substantially affecting the tuning, because at the die entrance the primary/secondary extrudate combination is functionally (in particular in terms of its flow characteristics) almost identical to the primary extrudate entering the co-extrusion adapter.

The temperature distribution is particularly important. Generally an extrudate of circular cross section has a radial temperature gradient. The absolute temperature at each level, and the gradient, can be controlled using techniques such as screw cooling and barrel zone heating within the extruder. The temperature distribution results in a similar viscosity distribution within the extrudate, and that in turn helps to determine its flow pattern through the die.

The internal geometry of the co-extrusion adapter is to this end preferably as simple as possible, a cylindrical tube of the same or substantially the same cross section as that of the primary extrudate being the preferred choice, with a cylindrical inlet into that tube for introduction of the secondary extrudate. The tube is preferably of uniform, or substantially uniform, cross section along its length. Such a design carries the added advantages of low fabrication and maintenance costs, and reduced size and weight, compared to conventional co-extrusion apparatus (including modified dies).

It has been found that, using a co-extrusion adapter according to the invention, the primary and secondary extrudates can retain their positional relationship throughout their passage through the die. Surprisingly, this can occur even when relatively complex profiles are being extruded, with little or no significant disruption at the interface between the two extrudates.

The multi-component product made using the method of the invention is typically a component for use, for example, as part of a door, window, roof, conservatory or other building structure. It may be a structural component or a nonstructural one such as a length of cladding or trim, and it will usually be rigid or semirigid. Its substrate is preferably made of a plastics material, although it may be of a metal such as aluminium. Typical plastics substrates include PVC, ABS (acrylonitrile butadiene styrene), foamed PVC, polyolefins or other engineering thermoplastics.

The product may have a relatively complex cross sectional profile. Indeed, the method of the invention can be ideally suited to the production of more complex components than simple sheets, films, plates, tubes and the like. Thus, it may be used to produce non-planar, non-circular products typically having little if any rotational symmetry about their central longitudinal axis, preferably non-symmetrical about any plane containing that central axis, and usually having two or more discrete internal cavities in their cross sectional profile and/or one or more internal walls (which walls may be joined at both ends to other parts of the profile, or may, in the case of projections such as fins and flanges, have a free end).

The secondary material is typically a plastics material. It may be a coating material, for instance to provide a colour, protective skin or other finish to the substrate, or an acrylic or foamed acrylic coating. In a preferred embodiment of the invention, the substrate comprises a recycled plastics material (such as PVC), and the secondary material comprises a non-recycled plastics material (again, such as virgin PVC) for use in improving the substrate appearance. Where the secondary material is applied to the substrate in the form of a coating, typical coating thicknesses achievable using the present invention can be anything from about 0.1 mm upwards, preferably between about 0.1 and 5 mm, more preferably between about 0.1 and 0.8 mm, most preferably between about 0.2 and 0.5 mm.

The secondary material may alternatively comprise a sealing material such as an elastomeric or thermoplastic material.

The substrate and secondary materials should of course be mutually compatible under the extrusion conditions used.

The method of the invention usually results in the deposit of a relatively small amount of the secondary material onto the primary extrudate. The volume ratio of the secondary material deposited, to the substrate material it is deposited on, is ideally about 1:50 or lower, more preferably between about 1:50 and 1:200 and most preferably between about 1:90 and 1:150, for example about 1:100.

The method may be used to apply more than one secondary material to the same substrate, by feeding more than one secondary extrudate into the die via the coextrusion adapter.

The manner in which the primary and secondary extrudates are prepared may be entirely conventional. Ideally, both extrudates enter the die at the same or substantially the same temperature and the same or substantially the same speed.

However, the primary will generally determine the speed of both extrudates because of its greater volume, ie, the secondary extrudate will be "carried along by" the primary.

Preferably, primary and secondary adapters are used to ensure that the primary and secondary extrudates respectively are smooth-flowing when they enter the coextrusion adapter. The primary and secondary adapters may also be conventional in construction. Both extrudates conveniently have circular cross sections, at least on exiting their respective adapters.

Further, the die itself can be of conventional design. In particular, it can be the same die as would be used to produce a single-component product of the same geometry as the multi-component product to be produced using the method of the invention. It is preferred that the die contain few, if any, channels which serve to move extrudate from the outside to the centre of the die; ideally it is of the type which allows the outer surface of the incoming extrudate to remain the outer surface in the finished product, ie, it is designed to avoid, as far as possible, turbulence in the material passing through it and to maintain the flow pattern of the material throughout. As for the finished product, the geometry of the die may be such that its internal cavity has little if any rotational symmetry about its central longitudinal axis, preferably no symmetry about any plane containing that central axis.

The co-extrusion adapter is ideally positioned immediately upstream of the die, more preferably directly adjacent it. It is conveniently a separate piece of apparatus which can be added to an existing extrusion line between the die and the conventional primary and secondary adapters. It ideally directs the secondary material to flow adjacent that region or regions of the primary extrudate which correspond to the substrate surface or surfaces to which the secondary material is intended to be applied.

A preferred form of co-extrusion adapter comprises a primary cavity, typically in the form of a cylindrical tube as described above, through which the primary extrudate can flow; one or more inlets (again, preferably cylindrical) into which the secondary extrudate(s) can be fed; and a secondary cavity with which the inlet or inlets communicate, the secondary cavity communicating with the primary cavity at or downstream of the inlet(s), and defining the region or regions into which the secondary extrudate is to flow, the secondary cavity being adjacent the region or regions of the primary cavity which correspond, in use, to the surface or surfaces of the primary extrudate to which the secondary material is intended to be applied. For instance, the secondary cavity might lie adjacent the upper part of the primary cavity, to allow a secondary coating material to be applied to the upper surface of the substrate material.

The secondary cavity preferably communicates with the primary cavity via a weir, which presents a higher resistance to flow of the secondary extrudate than does the secondary cavity.

The method of the invention may be used to apply a secondary material to just one surface of a substrate (for instance, a window profile made from recycled plastics need only be coated with virgin plastics at the surface which, once the profile is installed as part of a window, will be visible to the user), or to apply one or more secondary materials to more than one surface of a substrate, either simultaneously or sequentially, on introduction of the necessary secondary extrudate(s) to appropriate regions in the co-extrusion adapter. Thus, the co-extrusion adapter may comprise more than one secondary cavity, each adjacent a different region of the primary cavity. It may even be designed to achieve full coverage of the substrate surface, by allowing the secondary extrudate to flow around the entire perimeter of the primary extrudate.

The co-extrusion adapter may be comprised in another apparatus part such as a modified conventional adapter. For instance, the primary adapter may serve both to "adapt" the primary extrudate and then to introduce the secondary extrudate. The coextrusion adapter may also function as a secondary adapter, ensuring the secondary extrudate is smooth-flowing on introduction to the primary.

Like an extrusion die, the co-extrusion adapter may be constructed from two or more plates positioned adjacent one another and defining between them the cavities through which the extrudates are to flow. Its preferred simple construction, together with its position upstream of the die, can also allow sealing off of the secondary extrudate inlet(s), when producing a single-component product, with minimal adverse effects. Thus, the operator may be able to switch for instance between making coated and uncoated products, without needing to interrupt production. Similarly, he can switch relatively easily between different secondary materials (for instance, different coloured coatings).

In the method of the invention, the secondary extrudate is typically applied to a primary extrudate of simple circular cross-section. This makes possible a number of enhancements which would be difficult if the secondary extrudate were to be applied, within the die, to an irregularly shaped substrate.

Firstly, the co-extrusion adapter can be rotated (using appropriate means) about the longitudinal axis of the primary extrudate, to allow targeting of the secondary extrudate to a particular region of the substrate surface. Again, the introduction of the secondary extrudate perpendicular to the direction of flow of the substrate, and the preferred simple construction of the co-extrusion adapter, help to make this achievable.

Secondly, the co-extrusion adapter may include means for adjusting the size and/or position of the region(s) over which the secondary extrudate is applied, for instance by altering the size and/or position of its secondary cavity(ies). Such means may be mechanical in operation, allowing adjustment of the co-extrusion adapter plates.

The method of the invention preferably involves controlling the operating conditions (in particular, the extrudate temperatures and pressures) to ensure that they remain constant or substantially so between the upstream and downstream ends of the co-extrusion adapter. It also ideally involves controlling the rate at which the secondary extrudate enters the co-extrusion adapter, for instance by varying the relative rotational speeds of the primary and secondary extruder screws, to control the thickness and area of coverage of the secondary material applied to the substrate.

A second aspect of the present invention provides a method for adapting an existing apparatus, designed for the extrusion of a single-component product, to allow its use in the co-extrusion of a multi-component product from a primary, substrate material and a secondary material, the existing apparatus comprising a primary extruder for producing a primary extrudate of the substrate material and an extrusion die downstream of the primary extruder, the method comprising inserting into the existing apparatus (a) a secondary extruder for producing a secondary extrudate of the secondary material and (b) between the die and the two extruders, preferably directly adjacent the upstream end of the die, a co-extrusion adapter of the type described in connection with the first aspect of the invention. The co-extrusion adapter is for introducing the secondary extrudate to the primary extrudate, in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet, and for feeding both extrudates together into the die.

According to a third aspect, the present invention provides a multi-component product made using the method of the first aspect.

According to a fourth aspect of the invention, there is provided apparatus for producing a multi-component product having an extruded substrate with at least one co-extruded secondary material applied to it, the apparatus comprising: (a) a source of a primary extrudate of the substrate material; (b)a source of a secondary extrudate of the secondary material; (c) an extrusion die; and (d) a co-extrusion adapter, positioned between the die and the two sources (a) and (b), for introducing the primary and secondary extrudates into the die together, the co-extrusion adapter serving to introduce the secondary extrudate to the primary extrudate in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet.

The co-extrusion adapter is preferably of the type described in connection with the first aspect of the invention. The die, and the two extrudate sources, may be entirely conventional.

The apparatus may include one or more of: (i) means for rotating the co-extrusion adapter about the longitudinal axis of the primary extrudate (in use); (ii) source(s) of one or more additional secondary materials and means for switching between them to allow a desired secondary material or combination of secondary materials to be introduced via the co-extrusion adapter; and (iii) means for adjusting the size and/or position of one or more cavities within the co-extrusion adapter so as to control the size and/or position of the region(s) of the substrate over which the secondary material may be applied using the apparatus.

The apparatus may of course be used to carry out a method according to the first aspect of the invention.

Finally, a fifth aspect of the invention provides a co-extrusion adapter for use as part of the apparatus of the fourth aspect, or for use in the method of the first or the second aspect of the invention.

The present invention will now be described by way of example only and with reference to the accompanying illustrative drawings, in which: Fig 1 shows the essential parts of a conventional extrusion line for manufacturing a single-component extruded product; Fig 2 shows the essential parts of a conventional extrusion line for manufacturing a product with a co-extruded coating; Fig 3 shows the main parts of apparatus in accordance with the fourth aspect of the present invention, for manufacturing a product with a co-extruded coating; Fig 4 is a transverse vertical cross section through a co-extrusion adapter for use in the apparatus of Fig 3; Fig 5 is a longitudinal vertical cross section through the co-extrusion adapter shown in Fig 4; Fig 6 is a perspective view of a cut-away part of the co-extrusion adapter of Figs 4 and 5; Fig 7 is a transverse vertical cross section through a two-component extrudate as it leaves the co-extrusion adapter of Figs 4-6; Figs 8A-8C are transverse vertical cross sections through co-extruded products which can typically be made using the apparatus of Figs 3-6; Figs 9A-9C illustrate, with transverse and longitudinal vertical cross sections, an alternative form of co-extrusion adapter, also for use in the apparatus of Fig 3; Figs 1 0A- 1 0C illustrate apparatus used to carry out an experimental example detailed below; and Fig 11 is a cross section through the product made in that example.

Detailed description The conventional extrusion line shown in Fig 1 may be used to manufacture an extruded plastics product such as a door or window component. It includes an extruder barrel 1 into which a powdered or granulated plastics mixture is fed via a hopper (not shown). The plastics material emerges from the extruder barrel in the form of a high viscosity melt, which is then fed into the adapter 2 and from there to the die 3. The adapter ensures that the flow of extrudate entering the die is linear and uniform. Inside the die, which is made up of a series of die plates 4, the extrudate flows around a number of appropriately shaped and positioned baffles and slots, and is thereby shaped into the desired profile. The profile emerges from the die at 5, and passes through a calibrater (shown schematically as 6) where it is cooled using water and an applied vacuum.

The extrusion line shown in Fig 2 is also known, and is used to produce a twocomponent plastics product, such as a PVC profile with a protective or coloured coating. Here, the substrate material is extruded in the extruder barrel 11 and fed through an adapter 12 and a die 13 made up of die plates 14. The die has been specially modified at its downstream end 17 (ie, the last two die plates), to include an inlet 18 for introduction of the coating material, which is in the form of a secondary extrudate made in the secondary extruder barrel 19 and passing through secondary adapter 20 (both shown schematically). The coating material flows into specially shaped cavities within the die 13, adjacent the cavities through which the substrate material is already flowing. The product emerging from the die consists of the extruded substrate with the co-extruded coating applied to it. This passes through a calibrater 16 for cooling, in the usual way.

The extrusion line illustrated in Fig 3 comprises apparatus in accordance with the fourth aspect of the present invention. Again there is a primary extruder barrel (21) and adapter (22) producing a flow of a primary extrudate to be fed into a die 23.

There is also a secondary extruder (29) and a secondary adapter (30), which produce a flow of a secondary extrudate, typically of a coating material. However, in this case the die 23 is more like the die 3 shown in Fig 1, as would be used to produce a simple uncoated extrusion. It has not been modified to allow introduction of the secondary extrudate.

Instead, the primary and secondary extrudate meet at the co-extrusion adapter 28 and are fed together through the die 23. What emerges from the die is a twocomponent extrusion comprising a substrate and a co-extruded coating. This passes through a conventional calibrater 26 to produce the final product.

The secondary extrud cavity 42. The arrows in Figs 4 and 6 indicate the directions of flow of the coating material.

The weir arrangement serves to smooth the flow of the secondary extrudate, and helps to ensure uniform coverage of the desired region of the substrate surface.

Upon entering the co-extrusion adapter, the coating material flows outwards around the concave secondary cavity. Once it has filled that cavity, the pressure inside the adapter rises and the coating material is forced through a narrow gap defined partly by the flat surface of the weir 45, which presents a greater resistance to flow than the cavity 43. The material flows radially over the weir towards the perimeter of the primary cavity 42.

The radial depth L of the weir region can be used to influence the coating material flow; as L increases the resistance to flow also increases, so for instance L is made greatest in the entrance region E (nearest the inlet 44), to reduce the greater tendency of the coating material to flow straight through into the primary cavity at that point.

The weir is in this case provided in the upstream adapter plate 41. However, it could alternatively be provided in the downstream of the two plates.

By the time the primary extrudate 51 leaves the co-extrusion adapter to enter the die, the coating material 52 covers its upper surface in the manner shown in Fig 7.

In the case illustrated, the final product has a coating on the upper surfaces only of the substrate, as in the example window components of Figs 8A-8C. Here, Fig 8A shows a heavy duty 1 1/2" "brick mould" component, Fig 8B a 3 3/16" "extension jamb" and Fig 8C a 21/z" exteriorjamb. In each case, the PVC substrate is labelled 61 and the coating layer 62. Such components can be produced using the method and apparatus described above.

If a different surface region is to be coated, the co-extrusion adapter (in particular, the shape and position of its secondary cavity) needs to be modified accordingly. The co-extrusion adapter may have more than one secondary cavity, to allow coating of several discrete surfaces of the substrate, and/or may have more than one inlet for the or another coating material. Alternatively, the co-extrusion adapter may simply be rotated, about the direction of flow of the primary extrudate, to achieve coating of different substrate regions.

The alternative co-extrusion adapter illustrated in Figs 9A-9C can also be used as part of the apparatus of Fig 3, to carry out a method in accordance with the present invention. It comprises three plates 69, 70, 71, seen in the longitudinal cross sections Figs 9A and 9B. These plates are secured adjacent one another to define three sealed internal cavities, as best seen in Fig 9C. The primary cavity 72 is a tube through which the primary extrudate can flow. The secondary cavities 73 and 74 surround the upper and lower surfaces respectively of the primary cavity. A main inlet 75 is used to introduce a secondary extrudate into the co-extrusion adapter and direct it, via a bifurcated inlet passage 76, into both secondary cavities 73 and 74. Weirs 77 and 78 help to control the secondary extrudate flow from the secondary to the primary cavities. In this way, the secondary extrudate can be made to flow around the upper and lower surfaces of the primary extrudate, so as to coat both the upper and the lower surfaces of the final co-extruded product. Again, the arrows indicate the directions of flow of the secondary extrudate, which are analogous to those described in connection with Figs 4 and 6.

Experimental example The following experiment was carried out using a method and apparatus in accordance with the present invention, to produce acoated PVC window component.

The substrate material was PVC powder (Oxvl 1301 lot # 7032) and the coating

material was Oxy,ssbeige powder used to create a coloured surface. The finished product is shown in Fig 11, in which 91 indicates the PVC substrate and 92 the coating layer.

The apparatus used corresponded to that shown in Fig 3 but included the coextrusion adapter illustrated in Figs 1 OA-1OC. Fig 10A is a side view of the adapter, showing its main constituent plates 80, 81 and a locating pin 89 used to secure them together.

Fig lOB is a section along line A in Fig 1 or. It shows the following components of the adapter: plate 81; primary cavity 82 with a tapered end shown at 86; shaped secondary cavity 83; inlet 84; weir 85; and bolt holes 87 and locating pin holes 88 used in securing plate 81 to plate 80.

Fig l OC, a section along line B in Fig 1 or, shows the construction of plate 80, with bolt holes 87 and locating pins 89.

The other apparatus and operating conditions employed in producing the coated product were as follows: 1. Primary extruder: 52 mm, conical twin-screw extruder by American Maplan.

Extruder Parameters Measured Value Die zone 1 195(C) Die zone 2 195(C) Co-extrusion Adapter zone 175(C) Adapter zone 173(C) Extruder barrel zone 1 150(C) Extruder barrel zone 2 160(C) Extruder barrel zone 3 170(C) Screw cooling 155(C) Screw motor load 64(A) Screw motor speed 270(RPM) Melt Temperature 186(C) Melt pressure 3200(PSI) Doser motor speed 160(RPM) Degree of fill 75% Extruder vacuum -25 in.Hg 2. Secondary extruder: single screw 22 mm (Actual of America) with 3 barrel zones eat only).

Extruder Parameters Measured Value Barrel zone 1 175(C) Barrel zone 2 180(C) Barrel zone 3 185(C)

Extruder Parameters Measured Value Adapter 175(C) Screw motor speed 275(RPM) Screw motor load 6(A) The line speed was 1.0 metre/minute and the water temperature for the calibrators was 14"C. The coverage ofthe beige coating was complete (ie no voids or uncoated areas). The coating thickness was very small, approximately 0. I mm.

Thus, the method and apparatus of the present invention had successfully been used to co-extrude a two-component product, having a thin and uniform coating layer.

Claims

CLAIMS 1 A method for co-extruding a primary, substrate material and at least one secondary material to produce a multi-component product, the method comprising preparing a primary extrudate of the substrate material; preparing a secondary extrudate of the secondary material; and feeding the extrudates together through an extrusion die via a co-extrusion adapter positioned upstream of the die, wherein the secondary extrudate flows in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet within the co-extrusion adapter.
2 A method according to claim 1, wherein the internal geometry of the coextrusion adapter is such that at least one of the flow characteristics of the combined primary and secondary extrudates entering the die from the co-extrusion adapter is the same, or substantially the same, as that of the primary extrudate entering the adapter.
3 A method according to claim 2, wherein at least the cross sectional temperature distribution of the combined primary and secondary extrudates entering the die from the co-extrusion adapter is the same, or substantially the same, as that of the primary extrudate entering the adapter.
4 A method according to claim 2 or claim 3, wherein the cross sectional shape and dimensions of the combined primary and secondary extrudates entering the die from the co-extrusion adapter are the same, or substantially the same, as those of the primary extrudate entering the adapter.
5 A method according to any one of the preceding claims, wherein the multicomponent product is a non-planar, non-circular product.
6 A method according to claim 5, wherein the product has no rotational symmetry about its central longitudinal axis.
7 A method according to claim 5 or claim 6, wherein the product is nonsymmetrical about all planes containing its central longitudinal axis.
8 A method according to any one of claims 5 to 7, wherein the product has two or more discrete intemal cavities and/or one or more internal walls in its cross sectional profile.
9 A method according to any one of the preceding claims, wherein the multicomponent product is a component for use as part of a door, window, roof conservatory or other building structure.
10 A method according to any one of the preceding claims, wherein the substrate material is a plastics material.
11 A method according to any one of the preceding claims, wherein the secondary material is a plastics material.
12 A method according to any one of the preceding claims, wherein the secondary material is a coating material.
13 A method according to claim 12, wherein the thickness of the coating material in the multicomponent product is between about 0.1 and 5 mm.
14 A method according to claim 13, wherein the thickness of the coating material is between about 0.1 and 0.8 mm.
15 A method according to claims 10, 11 and 12, wherein the substrate material comprises a recycled plastics material and the secondary material comprises a nonrecycled plastics material.
16 A method according to any one of the preceding claims, wherein the volume ratio of the secondary material to the substrate material to which it is applied is between about 1:50 and 1:200.
17 A method according to any one of the preceding claims, wherein more than one secondary material is co-extruded with the substrate, by feeding more than one secondary extrudate into the die via the co-extrusion adapter.
18 A method according to any one of the preceding claims, wherein the primary and secondary extrudates enter the die at the same or substantially the same temperature and the same or substantially the same speed.
19 A method according to any one of the preceding claims, wherein the primary and secondary extrudates have circular cross sections on entering the co-extrusion adapter.
20 A method according to any one of the preceding claims, additionally involving controlling the extrudate temperatures and pressures to remain constant or substantially constant between the upstream and downstream ends of the co-extrusion adapter.
21 A method according to any one of the preceding claims, additionally involving controlling the rate at which the secondary extrudate enters the co-extrusion adapter, to control the thickness and area of coverage of the secondary material applied to the substrate.
22 A method for co-extruding a primary, substrate material and at least one secondary material to produce a multi-component product, the method being substantially as herein described with reference to the accompanying illustrative drawings.
23 A multi-component product made using a method according to any one of the preceding claims.
24 A method for adapting an existing apparatus, designed for the extrusion of a single-component product, to allow its use in the co-extrusion of a multi-component product from a primary, substrate material and a secondary material, the existing apparatus comprising a primary extruder for producing a primary extrudate of the substrate material and an extrusion die downstream of the primary extruder, the method comprising inserting into the existing apparatus: (a) a secondary extruder for producing a secondary extrudate of the secondary material; and (b) between the die and the two extruders, a co-extrusion adapter for introducing the secondary extrudate to the primary extrudate in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet, and for feeding both extrudates together into the die.
25 Apparatus for producing a multi-component product having an extruded substrate with at least one co-extruded secondary material applied to it, the apparatus comprising: (a) a source of a primary extrudate of the substrate material; (b) a source of a secondary extrudate of the secondary material; (c) an extrusion die; and (d) a co-extrusion adapter, positioned between the die and the two sources (a) and (b), for introducing the primary and secondary extrudates into the die together, the co-extrusion adapter serving to introduce the secondary extrudate to the primary extrudate in a direction perpendicular, or substantially perpendicular, to the direction of flow of the primary extrudate at the point where the two extrudates meet.
26 Apparatus according to claim 25, wherein the internal geometry of the coextrusion adapter is such that at least one of the flow characteristics of the combined primary and secondary extrudates entering the die from the co-extrusion adapter is the same, or substantially the same, as that of the primary extrudate entering the adapter.
27 Apparatus according to claim 26, wherein at least the cross sectional temperature distribution of the combined primary and secondary extrudates entering the die from the co-extrusion adapter is the same, or substantially the same, as that of the primary extrudate entering the adapter.
28 Apparatus according to any one of claims 25 to 27, wherein the co-extrusion adapter comprises a primary cavity through which the primary extrudate can flow; one or more inlets into which the secondary extrudate(s) can be fed; and a secondary cavity with which the inlet or inlets communicate, the secondary cavity communicating with the primary cavity at or downstream of the inlet(s), and defining the region or regions into which the secondary extrudate is to flow, the secondary cavity being adjacent the region or regions of the primary cavity which correspond, in use, to the surface or surfaces of the primary extrudate to which the secondary material is intended to be applied.
29 Apparatus according to claim 28, wherein the secondary cavity communicates with the primary cavity via a weir, the weir presenting a higher resistance to flow of the secondary extrudate than does the secondary cavity.
30 Apparatus according to claim 28 or claim 29, wherein the primary cavity comprises an internal cylindrical tube of the same or substantially the same cross section as that of the primary extrudate, and the secondary extrudate inlet(s) are cylindrical in cross section.
31 Apparatus according to claim 30, wherein the internal tube is of uniform, or substantially uniform, cross section along its length.
32 Apparatus according to any one of claims 28 to 31 , wherein the co-extrusion adapter comprises more than one secondary cavity, each adjacent a different region of the primary cavity.
33 Apparatus according to any one of claims 28 to 32, wherein the secondary cavity(ies) allow the secondary extrudate(s) to flow around the entire perimeter of the primary extrudate.
34 Apparatus according to any one of claims 25 to 33, wherein the co-extrusion adapter is positioned directly adjacent the die.
35 Apparatus according to any one of claims 25 to 34, additionally including one or more of: (i) means for rotating the co-extrusion adapter about the longitudinal axis of the primary extrudate (in use); (ii) source(s) of one or more additional secondary materials and means for switching between them to allow a desired secondary material or combination of secondary materials to be introduced via the co-extrusion adapter; and (iii) means for adjusting the size and/or position of one or more cavities within the co-extrusion adapter so as to control the size and/or position of the region(s) of the substrate over which the secondary material may be applied using the apparatus.
36 Apparatus substantially as herein described with reference to the accompanying illustrative drawings.
37 A co-extrusion adapter for use as part of apparatus according to any one of claims 25 to 36, or for use in a method according to any one of claims 1 to 24.