A MIXTURE OF COMPONENTS, A PLURAL LAYER PRODUCT, AND A METHOD FOR THE MANUFACTURE THEREOF

Abstract: A component mixture is provided to be extruded in order to produce a product. The component mixture comprises a first component (4), and a second component (5) which has a higher viscosity than the first component. The invention also includes a method for the production of a product constituted by a plurality of layers (1, 2, 3). The method comprises the preparation of a component mixture according to the invention and the extrusion of the mixture in order to produce the product. Further, the invention includes a product which comprises a plurality of layers (1, 2, 3), and which comprises an extruded, inventive component mixture.

Description: A mixture of components, a plural layer product, and a method • for the manufacture thereof THE BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a component mixture provided to be extruded in order to produce a product. The present invention also relates to a product which is constituted by a plurality of layers, and a method for the production thereof. Component mixtures of the above type are often used and well known in prior art, amongst others for the production of elongated tubular products provided to be, for instance, used as cables by electrical applications, conduits in gen- eral, cooling water conduits, etc. For a plurality of applications, the cables or tubes that are used also, a part from their ability of conducting a fluid for instance, need to be fire resistant when being used in environments where fire hazards may occur and where it is important that the risk for igniting the tubes and cables used is minimized. Such are the prerequisites for, amongst others, cooling water tubes that, for instance, are used in different industrial plants. Apart from the fact that there are requirements on the fire resistance of such tubes, it is also required that they show satisfactory mechanical and electrical properties for a relatively extensive period. A typical requirement for such a cooling water tube is that, during a period of thirty years, it should re- liably be able to be percolated by water having a temperature in the range of 60 °C with a pressure in the range of 6- 10 bars. Further, it is required that the tube presents fire resistance. As the product obtained by the manufacturing method and the component mixture suggested by the present invention is particularly well suited for an application of the above type, the invention will hereinafter be explained by way of example, but not in order to delimit it, with reference to such an application. In prior art, it is known that tubes with a generally homogenous composition are produced through extrusion of component mixtures. Amongst others, it is known to flame retard commercial cross linkable polyethylene types, PEX, for elec- trical applications by adding halogenated compounds or high concentrations of minerals thereto. Thereby, there is a disadvantage that the fire resistance is obtained at the expense of the mechanical property of the cables or tubes manufactured in this way. Moreover, halogenated flame retar- dants are not desirable from an environmental point of view. By electrical plants, in the case of minor fires, they may produce strongly corrosive (and toxic) gases that might destroy the whole plant . A material which in itself is fire resistant and has satisfactory mechanical properties is polyvinylidene fluoride, PVDF, which, above all, is characterized by a good chemical resistance and flame resistance at elevated temperatures. If, however, such a fluoride plastic as PVDF would be sub- jected to a powerful outer heat affection or fire from an external fire source, it has the disadvantage of then emitting toxic, strongly corrosive gases. Its high density and high price are further disadvantages . In order to produce a tube, particularly a cooling water tube, it is also known, through prior art, to initially pro- duce a tube of such a material, preferably polyethylene, that the required mechanical and also electrical properties of the tube are obtained and to, subsequently, by means of extrusion onto it, provide the tube with an outer sleeve of a polymer which is in itself flame resistant or has been made flame resistant by means of the above prior art. A disadvantage of this method is, however, that it is relatively complicated and that a bad adhesion is obtained between the outer sleeve and the tube itself. A bad adhesion will, in its turn, result in boundaries that effect the electrical properties in a negative way. There might also be problems if such an extruded profile is postprocessed by means of, for instance, hot bending, whereby the layers might delami- nate . SUMMARY OF THE INVENTION It is an object of the present invention to provide a component mixture which makes it possible, by way of extrusion in one single step, to produce a product which is constituted by a plurality of layers, with different compositions, in order to enable the production of a product with different properties in the different layers, and to obtain a good adhesion between the layers. This object is obtained by way of the initially defined component mixture, which is characterized in that it comprises a first component, and a second component which has a higher viscosity than the first component . Thereby, the different components will, due to their different viscosities, preferably form different layers in the extruded product. As a rule, the component having the lowest viscosity at the processing conditions, will occupy the peripheral positions of the extruded product and will, thereby, form the outer surfaces thereof. The properties of these surfaces can thereby by controlled through a suitable choice of the component having the lowest viscosity, while the properties of the layers that comprise the component with the higher viscosity, in their turn, can be controlled through a suitable choice of this component . According to a preferred embodiment of the component mixture according to the invention, the first component comprises a first polymer which is a thermoplastic, and the second com- ponent comprises a second polymer which also is a thermoplastic . An advantage thereby particularly obtained, is that such polymers may be transformed to a ductile, workable melt well suited for extrusion mainly by means of a slight heating thereof. For example, crystalline thermoplastics are used, among which a plurality that are well suited for the use in loaded details, such as, for example, cooling water tubes, are found. Such plastics, such as for example, polyethylene, often also have the advantage of being cheep. Also amorphous thermoplastics as PVC and semi or partially crystalline thermoplastics such as polyamide are possible to use. Preferably, the first and the second components are not molecularly mixable with each other. According to another preferred embodiment of the component mixture according to the invention, the first component comprises a flame retarding agent . Thereby, layers that to a high degree or to a minor degree are comprised by the first component will present flame security. As the first component preferably will be present in the peripheral region of the extruded product, the manufacture of a tube for instance, the outer surface of which is formed by a layer which to a major part or totally is comprised by the first component and thereby being flame secure, is made possible. Through a suitable choice of the second component, a tube product may thereby be obtained, said product being well suited to be used as cooling water tubes by which the requirements regarding mechanical and electrical properties and flame security are satisfied. According to another preferred embodiment of the component mixture according to the invention, the flame retarding agent comprises a non-halogenated compound such as a compound containing phosphor or silicone, or minerals, said compound being provided to bring to the first polymer its flame retarding properties. The character of the flame retarding agent should be such that it is, preferably, present only in small amounts in the first component and does not spread also in the second com- ponent . Thereby, for instance, the first component is prevented from being depleted from its flame retarding agent, which could lead to the need of adding unnecessary large amounts thereof to the mixture at the same time as, for example, deteriorated mechanical properties would be obtained in the second component. Through the use of a non-halogenated compound it is possible to avoid the creation of toxic, corrosive, halogen-containing gases in the case where a layer formed by the first component after all would be subjected to intensive heat or fire. According to another preferred embodiment of the component mixture according to the invention, this mixture comprises a means for maintaining a distribution of one component in another component . Thereby, in a layer which, for instance, comprises a matrix of the second component and a plurality of particles or the like of the first component, a coalescence of the particles of the first component is prevented. In that way, uneven distributions and properties, for example locally deteriorated mechanical properties, of a product obtained from the inventive component mixture is avoided. It is another object of the invention to provide a method for producing a product which is constituted by a plurality of layers, wherein said method is to be simple and is to permit the produced product to present different compositions and properties in different such layers. This object is obtained by means of the initially defined method, which is characterized in that it comprises preparation of a component mixture according to the invention and extrusion of the mixture in order to produce the product . As described above, a differentiated localization of the first and second component is obtained, such that these substantially will be present in different layers. Thereby, it is not excluded that mixed structures may occur in one layer, for example that the first component is present as more or less continuous particles in a layer in which the second component forms a matrix, or vice versa. The method results in the possibility of obtaining a good adhesion or binding between different layers. According to a preferred embodiment of the method according to the invention, the mixture of the first and second components is extruded to a tubular product, the inner and outer surfaces of which are defined through layers which substan- tially comprise the first component and by which a layer located between said surfaces comprises the second component. The boundary between the layers may be more or less diffuse or pronounced. In the case where the first component presents a good flame resistance and the second component particularly presents good mechanical properties, for example the ability of taking important strains during a long period and at relatively high temperature, this makes it possible to produce, for instance, a cooling water tube which presents the required me- chanical properties as well as flame security at its outer surface. The principle of the method is of course also applicable when other specific features are required for the extruded product than flame security and mechanical strength. According to another preferred embodiment of the method according to the invention, the first and the second components are chosen such that the viscosity ratio ^/^ thereof is at least 1/2 during such extrusion, that is under the given extrusion conditions. By choosing the respective components in such a way that there is a certain viscosity ratio therebetween, the thickness of the respective layers is controlled. The higher the viscosity ratio is, that is the greater the difference in viscosity between the compo- nents is by the extrusion conditions, the more will these be concentrated to different respective layers. By the manufacture of extruded profiles, for example cooling water tubes, it has been proven that the viscosity ratio between the first and the second component preferably is at least 1/2. According to another preferred embodiment of the method according to the invention, the first and the second components are chosen in such a way that the viscosity ratio η x /η 2 thereof is at least 1/3 by said extrusion. Thereby, a con- centration of the respective component to respective layers is obtained, as is particularly advantageous in the case of flame proof, mechanically resistant cooling water tubes. It is another object of the invention to provide a product which comprises a plurality of layers and by which the respective layers present individually different properties, for example regarding flame resistance, mechanical strength and electrical properties. This object is obtained by means of the initially defined product, which is characterized in that it comprises an extruded component mixture according to the invention. According to a preferred embodiment of the product according to the invention, it comprises at least one first layer, which mainly comprises the first component, and a second layer which comprises the second component. Thereby, the second layer comprises a larger amount of the second component and a smaller amount of the first component. Thereby, the product will have layers which differ from each other as to their composition and, thereby, properties. The thicknesses and properties of the respective layers may, in their turn, be varied through a suitable choice of the included components with regard to, for example, viscosity and composition, and through a suitable choice of such process pa- rameters as the temperature, and the shearing velocity during the extrusion. Further advantages and features of the present invention will appear from the following, detailed description and from the other dependent patent claims. BRIEF DESCRIPTION OF THE DRAWING Hereinafter, the present invention will be described in detail, by way of example but not in order to delimit it, with reference to the annexed drawing, in which: Fig 1 is a cross-section of an embodiment of a product according to the invention. DETAILED DESCRIPTION OF AN EMBODIMENT In Fig 1, an embodiment of the inventive product is shown, said product comprising a plurality of layers, 1, 2, 3 among which at least one layer 3 presents a composition and a structure that differs from the ones of the rest of the layers 1, 2. First layers, 1, 2 which form the peripheral surfaces of the product, here the inner periphery and the outer periphery respectively of a tube, mainly comprise a first component 4 which, due to its viscosity, is concentrated to these layers during a preceding extrusion of an inventive component mixture. Here, the second, intermediate layer 3 comprises a larger portion of a second component 5 and a smaller portion of the first component 4. By the extrusion, the second component 5 has a higher viscosity than the first component 4, and will, because of this reason, not be concentrated to peripheral surfaces of the product . Depending on the choice of process parameters such as shearing velocity and temperature, and mutual viscosity ratio between the first and the second components, a larger or smaller amount of the first component will be present in the second layer 3. A large difference in viscosity between the first and the second component is taken advantage of by the extrusion in order to accomplish a thicker and more homogenous first layer 1, but results in a less good dispersion of the first component 4 in the second component 5 being obtained in the second layer 3. In order to obtain and maintain a good distribution of one component in another one, here the first component 4 in the second component 5, the component mixture that is extruded in order to produce the product comprises a particular agent, a so called compatibilizer, the main task of which is to accomplish a morphology stabilization and to prevent coa- lescence of the components of the product. Accordingly, in this case, this agent counteracts the first component 4 dispersed in the second layer 3 from coalizing and forming larger continuous portions, such that the latter continues to be present in a well distributed state in a matrix com- prised by the second component 5. This agent is also of a type which promotes an interaction between the respective components and, thereby, a better adhesion between the layers, promoting the mechanical properties of the product. The agent for maintaining the distribution comprises a co-poly- mer or a polymer grafted with reactive groups, preferably the second polymer with reactive groups, in this case func- tionalized or modified PE. The component mixture used for the manufacture of the prod- uct is, in this case, a melted mixture of polymers, the first component 4 and the second component 5 being included in said mixture . The product is a cooling water tube . The first component comprises a partially crystalline or, alternatively, liquid crystalline thermoplastic, in this case for instance polyamide 12 or polyester (LCP) , and a flame retarding agent in order to accomplish flame resistance of the surfaces formed by the first layer or layers 1, 2. Thereby, particularly, the outer periphery of the tube requires such a flame resistant layer. The second layer 3 has a substan- tially larger thickness than the first layer 1, 2 and has as its main task to provide the product with good mechanical properties. For this purpose, the second layer 3 mainly comprises the second component 5 which, in its turn, comprises a second polymer which, in its turn, suitably comprises a polyolefin, in this case polyethylene. The second layer 3 also comprises a smaller amount of the first component 4 dispersed into it . The flame retarding ability of the first component may be obtained through the use of a first polymer which in itself is flame resistant. Alternatively, the first component comprises a flame retarding agent, the flame retarding agent comprising a smaller amount of a non-halogenated compound provided to bring the flame retarding properties to the first polymer, for example polyamide 12. The manufacturing method is performed in the following way: Initially, the inventive component mixture is prepared by mixing the first and the second component. Thereby, each component respectively may be present as granulates which are subsequently melted, or as already existing melts. The agent for maintaining a distribution of one component in another one is also added to the very component mixture or, alternatively, to any of the components. The component mixture is then placed in an extruder, preferably a double extruder, and is then extruded therein in order to obtain a product with the requested profile. Thereby, the embodiment shown refers to a tubular product, suited to be used as a cooling water conduit, but could as well refer to a product with another shape, for example a flat product to be used as such or to be bent and then welded to a tubular product . Of course, a number of varieties and alternative embodiments will be obvious for a man skilled in the art without thereby departing from the very invention. Thereby, the invention is to be defined only through what is stated in the annexed claims, the drawing and the rest of the description.

Claims: Claims 1. A component mixture to be extruded in order to produce a product, characterized in that it comprises a first compo- nent (4) , and a second component (5) which has a higher viscosity than the first component. 2. A component mixture according to claim 1, characterized in that the first component (4) comprises a first polymer. 3. A component mixture according to claim 2 , characterized in that the first polymer is a thermoplastic. 4. A component mixture according to any one of claim 2 and 3, characterized in that the first polymer is of a flame resistant type. 5. A component mixture according to any one of claims 1-4, characterized in that the first component (4) comprises a flame retarding agent. 6. A component mixture according to claim 5, characterized in that the flame retarding agent comprises a non-halogenated compound, such as a compound containing phosphor or silicon. 7. A component mixture according to any one of the preceding claims, characterized in that the second component (5) comprises a second polymer. 8. A component mixture according to claim 7 , characterized in that the second polymer is a thermoplastic. 9. A component mixture according to claim 7 or 8, charac- terized in that the second polymer is a polyolefine. 10. A component mixture according to any one of claims 1-9, characterized in that it comprises a means for maintaining the distribution of one component in another one. 11. A method for manufacturing a product constituted by a plurality of layers (1, 2, 3), characterized in that it comprises preparation of a component mixture according to any one of claims 1-10, and - extrusion of the mixture in order to produce the product. 12. A method according to claim 11, characterized in that at least one of the components (4, 5) is in a melted state when being mixed with the other component (4, 5) . 13. A method according to any one of claims 11 or 12 , characterized in that the mixture of the first and second components (4, 5) is extruded to a tubular product, the inner and outer surfaces of which are defined by a first layer (1, 2) that mainly comprises the first component (4) and by which a second layer (3) located between said surfaces comprises the second component (5) . 14. A method according to claim 13 , characterized in that the intermediate layer (3) comprises a larger amount of the second component (5) and a smaller amount of the first component (4) . 15. A method according to any one of claims 11-14, charac- terized in that the first and the second component (4, 5) is chosen in such a way that the viscosity ratio η x /η 2 thereof is at least 1/2 during said extrusion. 16. A method according to any one of claims 11-14, charac- terized in that the first and the second component (4, 5) are choosen in such a way that the viscosity ratio η x /η 2 thereof is at least 1/3 during said extrusion. 17. A product comprising a plurality of layers, character- ized in that it comprises an extruded component mixture according to any one of claims 1-10. 18. A product according to claim 17, characterized in that it comprises at least one first layer (1, 2) which mainly comprises the first component (4) , and a second layer (3) which comprises the second component ' (5) . 19. A product according to claim 18, characterized in that the second layer (3) comprises a larger amount of the second component (5) and a smaller amount of the first component (4) . 20. A product according to any one of claims 18 or 19, characterized in that it is tubular and that its inner and outer surfaces are defined by first layers (1, 2) , and that an intermediate layer, located between these surfaces, is formed by the second layer (3) .

Inventors: FELIX JOHAN, FELIX, JOHAN
Applicants: ABB RESEARCH LTD, FELIX JOHAN, ABB RESEARCH LTD., FELIX, JOHAN
Application year: 1998
Main classification: C08L101
IPC codes: B29C47, C08L23, C08L101