BE1027400A1 - CO-EXTRUSION HEAD FOR THE MANUFACTURE OF COMPOSITE PROFILE PARTS MADE OF LOW DENSITY POLYSTYRENE FOAM - Google Patents

Abstract

The invention provides a coextrusion head, which comprises a first feed channel, which is designed to be fed by a first extruder, so that a first material flow is created, which forms the core of a coextruded composite profile part, and a second feed channel, which is designed for this to be fed by a second extruder, so that a second stream of material is created which forms the shell of the coextruded composite profile part, the second feed channel being connected to an annular region which surrounds the first channel in such a way that a confluence with a flow channel is formed, which unites the core and the shell, the flow channel opening into an extrusion nozzle in which the second feed channel, which is a line of order n = 0, splits at least n times into two sub-areas, where n ≥ 2 before it opens into the annular region, in each case in a pair of Lines of the order n + 1, according to a plane of symmetry which runs at the n-th splitting through the center of the line at the n-th splitting, wherein the angle which the direction of the material flow of the core of a coextruded composite profile part and the direction of the plane of symmetry as it passes through the center of the conduit at the nth split, the center of the first feed channel and parallel to the first stream of the core of a coextruded composite profile part, is equal to 180 ° / (2n), with each pair of conduits being identical in length , the route and the cross-section. The invention further relates to a coextrusion process in which the coextrusion head is used, as well as a coextruded composite profile part which was produced by means of this process, the profile part having a core made of polystyrene foam with a density between 30 and 200 kg / m3, preferably from 60 to 180 kg / m3, and a shell made of plastic with a density of 600 to 1050 kg / m3, preferably from 700 to 900 kg / m3.

Description

CO-EXTRUSION HEAD FOR THE PRODUCTION OF COMPOSITE PROFILE PARTS MADE OF LOWER POLYSTYRENE FOAM

DENSITY Technical Field The present invention relates to a coextrusion head for the production of composite profile parts, in particular for the production of composites comprising a core of low density polystyrene, by coextrusion, and a method for producing such composite profile parts. State of the art Profile pieces made of extruded polystyrene (XPS) of low density (from about 30 to about 150 kg / m 2) have very low manufacturing costs and find numerous applications in fields such as insulation, decoration, packaging. Unfortunately, their very low mechanical parameters, in particular the surface hardness (Shore D -6 for a foam with 60 kg / m 2, whereas the Shore D hardness value for a foam with 400 kg / m 2 is in the order of 50) prove to be inadequate and lead to superficial damage in the event of impacts during transport, handling or use of the same. By co-extruding a thin layer, of a dense or foamed nature, of a mass-produced plastic or technopolymer, which completely envelops the core of the XPS profile, the mechanical surface properties and the general rigidity of the profile are considerably improved. Thanks to the increased density of the coextruded layer, the profile parts produced can in fact withstand impacts, so that they can be used in places where people and movable objects pass, which could collide with them.

The above-mentioned method of coextrusion is unfortunately difficult to implement, since the coextruded layer, which represents the shell of the profile part, must not destroy the cell structure of the foam in the core, in particular because of the associated heat supply.

The coextrusion of a layer of extruded foam of very low density is in fact very difficult because the temperatures and pressures naturally used in the two extrusion processes (main and auxiliary) are quite different.

The density of the extruded foam in the core should be at least 150 kg / m? otherwise it would collapse under the action of the coextruded layer.

In general, coextrusion is accompanied by numerous specifications with regard to temperature, viscosities and possible density values, so that it is generally difficult or even impossible to obtain composites with a foamed core of (very) low density.

In addition, even if certain composites can be made with a core of low density foam, they tend to be unsatisfactory in appearance.

This is of course particularly disadvantageous in applications that require small manufacturing-related tolerances in terms of dimensions, such as in the case of composite profile parts as they are used in many areas, in particular in window or facade elements, in the automotive sector, etc.

The solutions already proposed include, for example, covering the extruded foams with hardening coatings, with layers that have mineral fillers, or compression by means of calibration following foaming.

However, there are numerous disadvantages: these solutions are difficult to implement because the low density foam is delicate.

Since these processes follow the extrusion process, the time required to start up is high, as is the amount of waste.

Furthermore, the lower the density of the core, the more difficult it is to compress the edge area.

In general, the known methods for composite profile parts are difficult to master and require numerous handling steps, so that they are economically unattractive.

Since coextrusion is fast and does not require any intermediate handling steps, it is nonetheless an advantageous process.

It is therefore necessary to provide a new method of manufacturing low density composite profile parts by means of coextrusion.

OBJECT OF THE INVENTION Accordingly, it is an object of the invention to provide a solution which enables composite profile parts to be produced by coextrusion which have a core of extruded polystyrene of very low density which is encased in a thin layer, or shell, of increased density.

General Description of the Invention In order to achieve the above object, the present invention provides, according to a first aspect, a coextrusion head which, when used in a process with useful polymers, makes it possible to produce coextruded composite profile parts in which the Density of the core made of expanded polystyrene foam not more than 200 kg / m? preferably 30 to 180 kg / m?, particularly preferably 60 to 150 kg / m? and at which the density of the shell is at least 600 kg / m °, preferably 650 to 1050 kg / m?, in particular 700 to 900 kg / m?, and very particularly 750 to 850 kg / m? and the thickness is between 10 and 500 µm.

The coextrusion head comprises a first feed channel, which is designed to be fed by a first extruder, so that a first material flow is created, which forms the core of a coextruded composite profile part, and a second feed channel, which is designed to be fed by a second extruder to become so that a second material flow is created, which forms the shell of the coextruded composite profile part, wherein the second feed channel is connected to an annular region which surrounds the first channel in such a way that a confluence with a flow channel is formed, which the core and the shell combined, wherein the flow channel opens into an extrusion nozzle in which the second feed channel, which represents a line of the order n = O, splits at least n times into two sub-areas, where n 2 is 2, before it opens into the annular region, namely in a pair of lines of order n + 1, according to a r plane of symmetry that runs through the center of the conduit at the nth split, where the angle enclosed by the direction of the material flow of the core of a coextruded composite profile part and the direction of the plane of symmetry as passed through the center of the Line at the nth split, the middle of the first feed channel and parallel to the first material flow of the core of a coextruded composite profile part, is equal to 180 ° / (2 "), each pair of lines being identical in terms of length, route and cross section .

Thanks to the special geometry of the second feed channel, which originates from a second extruder, the material flow, which forms the shell of a coextruded profile part, is characterized by a high degree of homogeneity in kinetic and thermal terms.

The material flow which forms the shell of the coextruded composite profile part is thus similar in every respect and is distributed homogeneously around the main material flow, which originates at a first extruder and forms the core of the coextruded composite profile part.

According to a preferred variant, the new coextrusion head is also optimized with liquid lubrication of the walls of the metal.

Indeed, in an additional way, it comprises a channel for introducing a lubricant into the flow channel, which is located downstream of the confluence, preferably at a distance from the confluence which is at most twice the diameter of the flow channel.

The coextrusion head according to the invention is generally part of a coextrusion device.

This facility includes:

(a) a coextrusion head according to the invention, (b) a first extruder, the outlet opening of which is connected to the first feed channel, which is designed to form the core of a coextruded composite profile part.

5 (c) a second extruder, the outlet opening of which is connected to the second feed channel, which is designed to form the shell of a coextruded composite profile part.

According to a second aspect, the invention provides a method for the production of coextruded composite profile parts which comprises the following steps: (a) metering the components of the core made of foam, in premix or metered in individually, into the feed device of a first extruder; Plasticizing and mixing the components of the foam core at high temperatures in order to melt and homogenize these components; Introducing a propellant gas and homogenizing the constituents of the foam core and the gas; Cooling the stream obtained; (b) metering the components of the casing, in premix or metered in individually, into the feed device of a second extruder; Plasticizing and mixing the components of the shell at high temperatures in order to melt and homogenize these components; Cooling the stream obtained; (C) combining the material flow of the core and the material flow of the sheath to obtain a composite product at the level of the confluence of the coextrusion head according to any one of claims 1 or 2, wherein the material flow of the sheath, which envelops the material flow of the core, in each Is homogeneous in terms of kinetic and thermal properties; (d) directing the composite product into the flow channel to reach the coextrusion die;

(e) foaming the core and, optionally, the shell to form a coextrudate; (f) optionally, calibrating the coextrudate; (g) cooling the product obtained; and (h) optionally, cutting the coextruded composite product.

According to a particularly advantageous variant, the production method according to the invention also includes a step (d ') of introducing a lubricant into the flow channel downstream of the confluence, preferably at a distance from the confluence that is at most twice the diameter of the flow channel.

Within the process for the production of a coextruded composite profile according to the above definition, the sequence of arrival of the starting materials is in principle as follows: The material flow, which forms the material of the core of a coextruded composite profile part, which is loaded with gas, comes in from the first extruder a first feed channel of the coextrusion head, whereupon it meets and is encapsulated by the second material flow, which forms the material of the shell of a coextruded composite profile part and is supplied from the second extruder via a second feed channel, in order to produce a composite product.

More precisely, the material flow of the second feed channel, which arrives in a direction which is at right angles to the material flow of the first feed channel, splits for the first time at the level of the coextrusion head into a pair of first-order lines, these having the same cross-section, their route symmetrical to the splitting plane and they are of equal length in opposite directions so that they enclose an angle of 180 ° with the axis of the second feed channel (20), which is perpendicular to the material flow of the first feed channel (10).

Every first-order line, and thus every material flow, splits again into a pair of

Second order lines, from opposite directions, so that they form an angle of 90 ° to each other. The two channels also have the same cross-section, a symmetrical route and the same length.

Similarly, the various channels resulting from the above-mentioned split split at least a third time into a pair of third-order conduits which are of opposite direction, of the same cross-section, of symmetrical route and of the same length, whereby they are form an angle of 45 ° to each other.

The pairs of conduits resulting from the last split connect an annular region 35 which surrounds the first feed channel in such a way that a confluence is formed. The material flow of the core and the material flow of the shell meet at the level of the confluence.

The two material flows of the core and the shell are then assisted in their movement by introducing a lubricant into the flow channel, which is located downstream of the confluence, preferably at a distance from the confluence which is at most twice the diameter of the flow channel. The introduction of the lubricant takes place by means of an introduction channel. The addition of a lubricant to the junction makes it possible to reduce friction on the wall and in this way makes it possible to limit the rise in the temperature of the core and in particular of the casing.

The lubricant is introduced "into the confluence". For the purposes of the present invention, this means between the wall and the outer material flow, that is, the material flow of the shell, so that only the flow channel is lined, namely in a uniform manner, so that a film with a very low coefficient of friction is formed.

Finally, the composite product arrives in the flow channel to the nozzle, where the core and possibly the shell is / are foamed.

If necessary, the extrudate can be calibrated, if necessary stretched, in order to then cut it to size, if necessary, in a subsequent step.

Surprisingly, the method which was developed within the scope of the present invention makes it possible, through the use of a special coextrusion head, to obtain coextruded composite profile parts whose core has a very low density, i.e. less than 200 kg / m 2. or even less than 60 kg / m®.

The foam of the core does not collapse when it comes into contact with the layer which forms the shell of the coextruded composite profile parts.

The selection of the time at which the lubricant is introduced makes it possible, in conjunction with the homogeneous nature of the material flow, as well as the optimal selection of the MFI of the material from which the casing is formed and the lubricant, to produce composite profile parts of low density.

The material from which the shell is formed can be cooled in this way, typically to 115 ° C, without drastically increasing the pressure of the coextruder.

Indeed, the appropriate temperature control, optionally in combination with external lubrication, has enabled the foam in the core to maintain excellent cell structure.

In this way, the new coextrusion head according to the invention makes it possible to overcome all the problems associated with conventional coextrusion, making it possible, in a very surprising way, not to destroy the cellular structure of the foam in the core of the coextruded composite profile part.

Another very important advantage of the invention is that the coextrusion of denser shell materials on the very low density polystyrene foam makes it possible to use in the core as much as possible of materials derived from recycling or biological sources.

"Substances from biological sources" are to be understood as substances that come from renewable resources such as plants, animals, residues or algae.

The coextruded composite profile part owes its performance characteristics of appearance and mechanical strength to the layer which forms the shell of the coextruded composite profile part.

According to a first advantageous embodiment, the material flow of the core of the coextruded composite profile part is composed of polystyrene foam, which can be a homopolymer or a copolymer of styrene.

It is preferably a copolymer of styrene and one or more comonomers, such as styrene-butadiene-styrene, acrylonitrile-butadiene, ethylene-propylene-diene (EPDM), ... According to a first advantageous embodiment, the styrene-based polymer used is or polystyrene selected from the group consisting of (crystalline) polystyrene, impact-resistant polystyrene based on butadiene (HIPS), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene (SBS), styrene-ethylene-butadiene-styrene (SEBS) , solid polystyrene based on ethylene-propylene-diene or mixtures thereof.

It is also possible to use several types of polystyrenes which differ in terms of their viscosity and thus their molecular weight, alone or in a mixture with other copolymers of styrene and a diene monomer.

The appropriate copolymers are, for example, stole-resistant polystyrene based on butadiene (HIPS), shock-resistant polystyrene based on ethylene-propylene-diene (EPDM), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene (SBS) , Styrene-ethylene-butadiene-styrene (SEBS) or their mixtures.

The blowing agent can be a physical blowing agent, a chemical blowing agent or a combination of two or more physical and / or chemical blowing agents.

These are generally those that are commonly used in the manufacture of polystyrene foams.

Suitable physical blowing agents include agents that are gaseous at ambient temperature and pressure, such as CO 2, nitrogen, lower alkanes such as butane or isobutane, etc., and agents that are liquid at ambient temperature and pressure, such as Pentane, (n-pentane or isopentane), hexane (all isomers), ethanol, dimethyl ether, etc.

Chemical foaming agents include azodicarbonamide, a combination of citric acid and sodium hydrogen carbonate, OBSH, etc.

The chemical agents can also be used as so-called active nucleating agents in combination with one or more physical agents.

The propellant content to be provided naturally depends on the nature of the propellant itself, but also on the desired density of the foam.

For example, the percentage by weight of CO, in the case of direct gas introduction, can be in the range from 0.01% to 5%, preferably from 0.015 to 3%.

In the above process, the material of the shell of the coextruded composite profile part generally has a melt flow index (MFI) of at least 20, preferably of at least 25.

In addition, the melt flow index is generally at most 30, preferably at most 28 g / 10 min., 200 ° C .; 5 kg.

The Melt Flow Index (MFI) or Melt Flow Index (SFI), which is also known under the names Melt Flow Rate (MFR) or Melt Index (MI), is a method that is commonly used in the plastics industry to convert thermoplastic materials to characterize.

It makes it possible to estimate their extrusibility.

This conventional and relatively simple method, which is described in the ASTM D1238 standard, can be used in a simple manner to subject production or delivery batches to quality control.

The composition of the material of the shell of the coextruded composite profile part can be identical to or different from the composition of the material of the core.

The material of the shell of the coextruded composite profile part can be of a dense or foamed nature. If it is foamed, it can be the blowing agent and the same as that used in the material of the core of the coextruded composite profile part, or different.

The thickness of the shell of the coextruded composite profile part is advantageously between 10 µm and 500 µm, advantageously between 150 µm and 450 µm, and preferably about 250 µm to 400 µm.

A lubricant is introduced into the flow channel in a very advantageous manner. It is generally a low molecular weight molecule. Of the known products, the esters of C4-C20 monoalcohols, the fatty acid amides, the polyethylene waxes, the oxidized polyethylene waxes, the styrenic waxes, the C1-C4 alcohols, the silicone compounds, etc. should be mentioned. In a preferred manner, the lubricant is thus selected from the group consisting of mineral oils, silicone oils and polymers with a lubricating effect.

A third aspect of the invention relates to coextruded composite profile parts which have been produced by means of the method detailed above, wherein they have a core made of polystyrene foam with a density of up to 200 kg / m? and an envelope with a density of at least 600 kg / m? and a thickness between 10 and 500 µm.

According to a fourth aspect, the invention provides the use of a coextruded composite profile part for insulation, decoration or packaging applications.

Brief description of the drawings Further particularities and characteristics of the invention emerge from the detailed description of some advantageous embodiments,

as set forth below for purposes of explanation, reference being made to the accompanying drawings.

1: a schematic representation of a coextrusion device. A first extruder 20, which is intended to form the core of a coextruded composite profile part, and a second extruder 40, which is intended to form the shell of a coextruded composite profile part connected to a coextrusion head 30.

The first extruder comprises components of the foam core 21 and a propellant gas 22. The second extruder comprises components of the shell 41 and a propellant gas 42. The device furthermore comprises a station for calibrating / drawing / cutting 50. FIG. 2: a schematic representation of FIG three successive splits of the second feed channel, which forms the line of the first order O (100) from the entry into the coextrusion head, into pairs of lines of the order 1 (110), 2 (120) and 3 (130), the lines of the last order (here of order 3) are connected to an annular region 35 which surrounds the first feed channel within the coextrusion head 30 according to the invention.

Legend: first extruder 21 components of the foam core 22 propellant gas coextrusion head annular region 40 second extruder 41 components of the casing 42 propellant 50 station for calibrating / drawing / cutting 100 line of order O, which originates in the second feed channel of the second extruder 40 110 Management of 1st order 120 Management of 2nd order 130 Management of 3rd order

Claims (14)

PATENT CLAIMS 1. Coextrusion head, comprising a first feed channel, which is designed to be fed from a first extruder, so that a first material flow is created, which forms the core of a coextruded composite profile part, and a second feed channel, which is designed to be fed by a second extruder to be fed, so that a second stream of material arises which forms the shell of the coextruded composite profile part, the second feed channel being connected to an annular region which surrounds the first channel in such a way that a confluence with a flow channel is formed, which the core and the Sheath combined, the flow channel opening into an extrusion nozzle, in which the second feed channel, which is a line of the order n = O, splits at least n times into two subregions, where n 2 is 2, before opening into the annular region , in each case in a pair of lines of order n + 1, according to a Sy mmetry plane which runs through the center of the line at the nth split at the nth split, the angle enclosed by the direction of the material flow of the core of a coextruded composite profile part and the direction of the plane of symmetry as they pass through the center of the line at the nth split, the center of the first feed channel and parallel to the first material flow of the core of a coextruded composite profile part, is equal to 180 ° / (2 "), each pair of lines being identical in terms of length, route and cross section. 2. Coextrusion head according to claim 1, which further comprises a channel for introducing a lubricant into the flow channel, which is located downstream of the confluence, preferably at a distance from the confluence that is at most twice the diameter of the flow channel. 3. Coextrusion device, comprising: (a) a coextrusion head according to one of the preceding claims, (b) a first extruder, the outlet of which is connected to the first feed channel, which is designed to form the core of a coextruded composite profile part, (c) a second extruder, the outlet of which is connected to the second feed channel, which is designed to to form the shell of a coextruded composite profile part. 4. Coextrusion device according to claim 3, which further comprises (d) a unit for calibrating, a unit for drawing and / or a unit for cutting the coextruded profile part, downstream of the coextrusion head. 5. A method for producing a coextruded composite profile part by means of a coextrusion head according to one of claims 1 or 2, or by means of a coextrusion device according to one of claims 3 or 4, the method comprising the following steps: (a) adding the components of the foam core, in premix or individually metered into the feed device of a first extruder; Plasticizing and mixing the components of the foam core at high temperatures in order to melt and homogenize these components; Introducing a propellant gas and homogenizing the constituents of the foam core and the gas; Cooling the stream obtained; (b) metering the components of the casing, in premix or metered in individually, into the feed device of a second extruder; Plasticizing and mixing the components of the shell at high temperatures in order to melt and homogenize these components; Cooling the stream obtained; (c) combining the material flow of the core and the material flow of the sheath to obtain a composite product at the level of the confluence of the coextrusion head according to any one of claims 1 or 2, wherein the material flow of the sheath, which envelops the material flow of the core, in each Is homogeneous in terms of kinetic and thermal properties; (d) directing the composite product into the flow channel toward the coextrusion die; (e) foaming the core and, optionally, the shell to form a coextrudate; (f) optionally, calibrating the coextrudate; (g) cooling the product obtained; and (h) optionally, cutting the coextruded composite product. 6. The method according to claim 5, wherein it further comprises the step (d ') of introducing a lubricant into the flow channel downstream of the confluence, preferably at a distance from the confluence which is at most twice the diameter of the flow channel. 7. The method according to claim 6, wherein the lubricant is selected from the group consisting of the mineral oils, the silicone oils and the polymers having a lubricating effect. 8. The method according to any one of claims 5 to 7, wherein the material flow of the core of the coextruded composite is composed of coextruded polystyrene foam, which can be a styrene homopolymer or copolymer, the polystyrene preferably being a copolymer of styrene and one or more comonomers. 9. The method according to claim 8, wherein the polystyrene is selected from the group consisting of (crystalline) polystyrene, impact-resistant polystyrene based on butadiene (HIPS), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene (SBS) , Styrene-ethylene-butadiene-styrene (SEBS), impact-resistant polystyrene based on ethylene-propylene-diene or mixtures thereof. 10. The method according to any one of claims 5 to 9, wherein the material flow of the shell of the coextruded composite profile part is composed of a plastic whose MFI is at least 20 g / 10 min., 200 ° C, 5 kg and preferably between 22 and 30 g / 10 min., 200 ° C., 5 kg, particularly preferably between 23 and 28 g / 10 min., 200 ° C., 5 kg. 11. Coextruded composite profile part obtained by means of the method according to one of claims 5 to 10, wherein the profile part has a core made of polystyrene foam with a density between 30 and 200 kg / m? preferably from 60 to 180 kg / m 2, and an envelope made of plastic with a density of 600 to 1050 kg / m 2, preferably from 700 to 900 kg / m 2. 12. Coextruded composite profile part according to claim 11, wherein the core made of polystyrene foam of the coextruded composite profile part comprises polystyrene, which may be a styrene homopolymer or copolymer, the polystyrene preferably being a copolymer of styrene and one or more comonomers . 13. Coextruded composite profile part according to one of claims 11 or 12, wherein the plastic casing has a thickness which is between 10 and 500 μm, preferably between 150 and 450 μm, particularly preferably between 250 and 450 μm. 14. Use of a coextruded composite profile part according to one of claims 11 to 13, for applications in insulation, decoration or packaging.