HEAT-BONDABLE FIBRE

Abstract: The present invention concerns synthetic fibres for use in fabric production and a process for manufacturing such fibres. The fibres are heat-bondable and are capable of bonding to one another on the application of heat. The fibres also have the advantage of a low shrink force despite a high degree of shrinkage rendering them particularly useful for incorporation in non-woven products.

Description: Heat-bondable fibre The present invention relates to synthetic fibres for use in fabric production and related applications. More specifically, the present invention relates to a heat-bondable fibre which is able to bond to itself following the application of heat. The fibres have a low shrink force despite a high degree of shrinkage. This is particularly useful in the field of non-woven fibres to stabilise a non-woven product. For some years technologists have sought to produce fibrous structures which are stable without the need to use chemical binders or polymer melts . In the case of polyolefin fabrics there has also been particular attention given to the production of structures which are monopolymeric in the sense that they are derived from a single type of polymeric material (for example, 100% polyolefin). The reason for this is so that the whole fabric material can be later recycled or reformed into a secondary product at a later stage in its cycle of use. This could not be done with materials made form polymer mixtures such as, for example, polyolefin and polyester blends. Some current methods of stabilising woven products use liquid binders to bind the individual fibres together in a woven product. This improves the stability of the structure as a whole. For example, latex in solution may be applied to the fibre structure and the treated non-woven product is then heated to set the fibres. There are several disadvantages with this approach. The fibres are dulled and there is an energy and environmental cost ( and risk ) associated with the liquids and volatiles extracted during setting and drying. The resulting fabrics also have some of their desirable textile characteristics reduced, or even lost, by stiff binders. Such binders can also affect the appearance of the structure as well as its handling and feel . Two component fibres of the "core-shell" type can be used to introduce bonding into a non-woven product on heating. However, these have the disadvantage that melted polymeric material can substantially reduce the textile handling properties and aesthetic properties of the material. Two-component fibres nevertheless have been used for essentially flat or two dimensional structures. Fibres of this type have a surface sheath ( shell ) of polymeric material formed from one component having a lower melting point than the one-component material which forms the core. In some thin, flat fabrics made from the "core-shell" fibres, bonding between the contact surfaces (i.e. the outer lower melting point material) of the fibres is achieved by applying both heat and pressure (e.g., by calendering). The outer layers of adjacent fibres melt and fuse together. Such core-shell fibres dominate the fabric structure and properties which they are used. This has the disadvantage that in three dimensional fabric structures such fibres are too much in evidence throughout the structure, even when present in low concentration. The fibres therefore play too great a part in the appearance and properties of the fabric. This is particularly true in coloured products where design and appearance of the material is a key selling feature. Furthermore, the nature of these two-component fibres means that they are expensive to produce and are not readily or cost-effectively produced in a variety of colours, types or shape so as to complement the colours and fibres they are blended with in finished fabric products. Polyolefin shrink fibres which shrink and develop contraction forces within the blend of fibres of which they formed a small part are also known. The contraction (tension) forces developed are often quite large and may be O.lg/denier or more. These properties can be very useful for example if manufacturing high bulk spun yarns, where say 20% of the blend is a higher shrink fibre. On subsequent heating of the spun blend, shrinkage of the whole yarn is made possible by these high shrinkage fibres. When this happens the cross- section of the yarn increases as the majority lower shrink fibres concertina outwards as the high shrinkage contraction forces dominate during the heat setting process . However, a high shrinkage fibre having such high contraction forces is not helpful in setting fabrics when the objective is to find a means of stabilising the fabric which already has the desired shape and appearance. Thus, the use of such shrink fibres can distort and change the shape and appearance of the fabric and this is a significant disadvantage. In addition, shrink fibres do not undergo any useful or controllable bonding to themselves either because the heat setting temperature is too low or because they may suddenly melt if the temperature is taken above their melting point. This is especially true in thicker fabrics where no mechanical pressure can be applied so as to avoid distorting or flattening the fabric. It is an object of the present invention to provide a fibre which can heat-bond to itself without the need for applying any additional setting agents e.g. chemical binders, or which at least significantly reduces the quantity of any such heat setting agent required. It is also an object to provide a fibre which can undergo heat setting at temperatures which are similar to or lower than the temperatures required in conventional heat-setting processes (which are typically about 120°C to 130°C at the fibre surface). It is an aim to provide a low-shrinkage fibre which exerts a relatively low force on surrounding material in a web of fibre so that the non-woven fibre web may be stabilised without disturbing the structure of the web. It is also desirable that the fibre should have a pleasing appearance and be easy and cost effective to manufacture. It is therefore a further aim to provide a fibre which can be coloured so as to match other materials with which it may be blended. It is also desirable that the fibre does not lose its appearance on heating and setting. We have discovered that it is possible to produce heat sensitive fibres satisfying some or all of these objects. These fibres become sticky at temperatures below conventional heat setting temperatures and yet do not melt and lose their identity at temperatures much higher than conventional heat setting temperatures. These fibres therefore make possible the desired stabilisation of fabrics, without adversely affecting the shape, appearance and other essential properties of the fabric. Indeed there is usually an improvement in the appearance and handling properties of the fabric when compared with fabrics containing conventional chemical binders and surface treatment agents. According to one aspect of the present invention, there is provided a heat-bondable polyolefin fibre, the fibre comprising a blend of an amount of 70 to 90 % inclusive by weight of polyethylene, and an amount of 10 to 30 % inclusive by weight of polypropylene, the fibre optionally further including one or more polyolefin copolymers in an amount of not more than 10% by weight, the fibre having a degree of shrinkage of between 20 and 50%, inclusive, when measured at 120°C and a shrink tension of not more than 0.015g per denier when measured in the range 90 to 120°C. Preferably, the polyethylene is a low density polyethylene ( LDPE ) or linear low density polyethylene ( LLDPE ) . Low density means a polyethylene having a density of not more than 0.925g/cm 3 . It is important to have sufficient of the high melting point polymer present to ensure adequate mechanical properties of the fibre hence the requirement for an amount of polypropylene of 30 to 10% by weight inclusive. Preferably, there is 15 to 10% by weight of polypropylene in the fibre, and most preferably 10%. This also helps to ensure there is retention of a fibre shape and an interconnected fibrous structure in place in the fabric after heat- setting and subsequent cooling of these heat-sensitive fibres. The polyethylene contributes to the stickiness of the fibre over a broad range of temperature. Preferably, there is 85 to 90% by weight of polyethylene in the fibre, and most preferably 90%. The nature of the polymeric components in the extruded fibre is not certain. It is believed that the fibre contains a dispersion of discrete strands or regions of one component surrounded by regions or strands of another component. The important feature is that there is sufficient of the low melting point component present in the region of the surface of the fibre to assist bonding. Also, there must be sufficient of the higher melting point component present in the body of the fibre to provide adequate strength during heat setting. The fibre when placed in the chosen position in the fabric construction or cross-section shrinks when heated at the conventional (or even below) heat setting temperatures, but the forces of contraction developed are sufficiently low (i.e. less than 0.015g/denier ) so that when these shrinking fibres meet a restriction or resistance to further shrinkage they stop moving. Such resistance might be caused by the presence of a majority of other fibre elements in the bulk of a fabric construction. The fibres bond together at their points of surface contact when at the heat setting temperature. When the fabric is subsequently cooled, a fibrous bonded and interconnected structure within the cross-section of the fabric is produced thereby providing the necessary binding and stabilisation of the fabric structure. The fibres take up the shape of the fabric construction without distorting it and create an intimate network of heat-bonded fibres. At the same time, the handling and appearance of the fabric remain more or less unaffected because the fibres readily shrink into the body of the fabric without disturbing the bulk of the fabric significantly. The heat sensitive fibres have a high potential shrinkage (typically in the range of 20 - 50% inclusive depending on the temperature and heat applied) even though the shrink force is low. In addition, the design and method of manufacture of the fibres lends itself easily to melt colouration of the fibre by adding colour to one or more of the major polymer elements in its composition before extrusion. Heat- sensitive fibres in a variety of colours can therefore be readily produced. This may be useful in fabrics and designs where colour is critical or when the chosen concentration of the heat-sensitive fibres is relatively high and/or they are placed near to the surface of the fabric. The fibres of the present invention can play a useful role in locking, bonding and setting the final fabric construction and shape, for example, in the production of non-woven or needle punch fabrics. In this case, fibres of one or more type and of various colours and deniers can be blended together. This blend of fibres is then carded into a web, which can be useful in its own right. The web is usually folded and cross layered to provide an assembled uniform web of fibres, having strength in machine and transverse directions, of the required weight and thickness. The resulting web can then be fed into a needling process in which barbed or forked needles penetrate the web providing fibre interlocking and fabric compaction. Additional needling processes can be applied as required to move and place the different fibre deniers in the cross-section of the web's thickness. For example, with the suitable choice of blend and deniers, it is possible to move the thicker fibres (e.g., 65 - 110 deniers) into the pile of the fabric, leaving the finer fibres (e.g., 10 - 20 denier) behind in what effectively becomes the back of the fabric. The layout and type of needles can also be varied to control the pattern of the surface of this type of fabric (e.g., ribbed patterns ) . When blending the fibres of the present invention with a conventional blend used for this type of construction, the fibres of the present invention can be positioned as a result of the process of needling largely in the base or back of the fabric construction, as required. The fibres of the invention are sufficiently fine and easily deflected by these needles, and so do not readily move into the pile (or surface) of the fabric. By using the fibres of the present invention, the need to use such liquid binding systems can be avoided totally in many cases. Alternatively, in certain cases, a conventional binding system can supplement the binding due to heat setting of the fibres of the present invention. The heat-sensitive fibres of the present invention are produced by using at least two polyolefin polymers of notably different melting points. It is desirable the melting point of one of the components is at least similar to the dominant fibre in the fabric composition or at least is above the heat setting temperatures employed when finishing the fabric. For example in the case of fibres to be incorporated in an essentially polypropylene fabric such as carpets, then one polymer would ideally be a polypropylene homopolymer (e.g., melting point 160 - 165°C, inclusive). The other polymer component in the fibre ideally has a melting point in the region of the operating temperatures conventionally used on heat-setting. For example, a low density (i.e. 0.925g/cm 3 or less) polyethylene (LDPE) polymer of melting point 118°C is one suitable choice. Linear low density polyethylene (LLDPE) is also highly suitable for use as the low melting point component in the fibre of the present invention. In certain cases, it may be desirable to include one or more further polyolefin components in the fibre in order to modify the melting point, stickiness of the fibre or the tensile strength. Examples of suitable polyolefins include homopolymers or copolymers of polyolefins including butylene or copolymers of ethylene and propylene. Such optional ingredients when present account for not more than 10% by weight of the fibre content. An amount in excess of this leads to a deterioration in the melting and heat-bonding properties of the fibre. In another aspect of the present invention, there is provided a process for producing a heat-bondable polyolefin fibre, the process comprising the steps: (a) extruding a polymer mixture comprising polyethylene in an amount of from 70 to 90% by weight inclusive, polypropylene in an amount of from 30 to 10% by weight inclusive, and optionally not more than 10% by weight of a further polyolefin component; (b) air cooling and drawing the extruded mixture to produce a fibre; (c) heating the fibre in an oven to soften the fibre and stretching the fibre at a stretching ratio of from 1.5 to 4.0 times inclusive; (d) feeding the stretched fibre to a crimper to produce crimped fibre; and (e) cooling and cutting the crimped fibre. The air cooling serves to quench the extruded material and is preferably effected by an air knife which provides a concentrated blast of cooling air. The air knife thus serves to ensure adequate cooling of the extruded material which is usually in the form of several filaments. The air cooling stiffens the polymer melt at the point it flows from the die into the air cooling zone. Not only does the extrusion process become more stable and easier to operate, but we also unexpectedly found that the bonding and shrinking properties are improved. The cooling air ideally has a temperature of from 5 to 20°C inclusive, and more preferably 8 to 10°C. The drawing of the extruded polymer to produce fibre is effected at a ratio of between 10 and 100 times. The fibre cools naturally during the drawing and it is not necessary to provide any additional cooling, although further cooling may optionally be provided. The fibre is then fed to an oven to heat the fibre to a temperature at which the fibre can be stretched uniformly and in a controlled manner. The fibre is heated by means of warm air in the oven with the oven temperature ideally being in the range of 90 to 120°C inclusive, with a temperature in the range 100 to 110°C inclusive being preferable in view of ease of control and ensuring uniformity during stretching. It is preferable that the stretching, which is performed in the oven during the heating step, is effected at a stretching ratio of 1.5 to 2.5 inclusive since this leads to finished fibres which have both a particularly low shrink tension and a good degree of shrinkage. The stretched fibres are then fed to the crimper under slight tension so that no shrinkage of the fibre occurs before the crimping process. The crimping process is a conventional process and may be effected, for example, using a stiffer box crimper. The crimped fibres are then cooled and cut in a conventional manner. Figure 1 is a schematic diagram of the process of the present invention and is described in detail in conjunction with Example 1. The conditions extrusion and drawing of the polymer are such as to produce the desired properties in the fibre. Stretching of the drawn fibre results in stresses being set into the fibre which is then cooled and packaged. The advantageous properties of the fibres of the present invention are believed to result from the thermal history of the fibre as a result of its processing. The fibre begins to melt and deform (if there is any contact pressure) over a broad temperature range which is dictated by the proportion of the components in the polymer. This is typically in the range of 105 to 155°C. Whilst the exact mode of operation of the heat-setting process is not understood, it is believed that the stresses which are subsequently released in these fibres on heating in the heat-setting process ( and which cause shrinkage ) appear to depend on the degree of stretching and annealing applied in the fibre extrusion and stretching process, and on the relative proportion of the polymers in the fibre composition. We have found that draw ratios following extrusion through the die (this is known as melt spinning) in the range of 10 to 100 and subsequent stretching in the range of 1.5 to 4.0 times are necessary to ensure the desired properties. The polymeric components are metered as a blend in proportion into the extruder and are melted and mixed in a conventional extruder. Blending in the extruder is carried out in the temperature range of 220 to 280°C, inclusive, with a temperature in the range 230 to 250°C, inclusive, being preferred. The exact temperature will, of course, depend on the nature of the components to be blended. Alternatively, the separate components may be fed directly to the extruder throat and co-extruded. The fibres of the present invention will be illustrated by the following examples. Examples 1 A 15 denier fibre was made by feeding the following component polymers directly into the throat of a 115mm extruder and coextruded: a) 90% Linear low density polyethylene - LLDPE (e.g. grade 18QFA from Elenac; density 0.919g/cm 3 and MFR 2.8 for 190°C 2.16kg; melting point 126°C) b) 10% polypropylene homopolymer - PP (e.g. grade 1101M from Targor with MFR 9.0 for 230°C 2.16kg; melting point 163°C) Referring to Figure 1 of the drawings, the molten flow of extrudate was fed into a spinning beam and filtration system via metering pumps to the die plates in the die block ( 1 ) . In this extrusion process there were 8 stainless steel die plates in the die block ( 1 ) , each with 11,232 holes with each hole having a diameter of 0.5mm. The resulting extruded polymer was discharged from the die holes through a concentrated air cooling zone with input air temperature measured at 8°C. The draw down from these die holes was achieved by first haul- off rollers (2) operating at a surface speed of lOm/min to produce a bundle of fibres. The bundle of fibres (89,856 in total) then passed to second haul-off rollers (3) at a surface speed of 11 m/mins (3) (i.e. a higher speed than the first haul-off rollers ( 2 ) to maintain sufficient tension in the fibres to stop shrinkage taking place ) . No additional heating was applied to the fibres after leaving the die holes and before the second haul- off roller ( 3 ) and the fibres travelled a distance of about 8m. During this time the fibres cooled but were not allowed to shrink. These cooled fibres were pulled through an oven (4) which was 3.5m long at an air temperature of 100°C by a third set of haul-off rollers ( 5 ) running at a speed of 22m/min. The higher speed of the rollers (5) ensured the fibres were drawn at a draw ratio of 22 ÷ 11 = 2.0. The fibres were then passed to the nip rollers ( 6 ) of a stuffer box crimping machine ( 7 ) . These rollers were operated at 22m/min to ensure the filaments did not shrink as they cooled and travelled from the third haul-off rollers (5). The crimped cooled fibres were then taken through a guiding system into a cutter before being conveyed by air into a bale press. The extrusion process had the following temperature profile: Barrel zones profile 235, 235, 245, 245, 250, 250°C Adapter, filters etc. 240°C Feed/pump/beam centre 235°C Die head 240°C The outputs of extruder and metering pumps were set to give individual fibres at the end of the process of 15 denier (50 micron diameter). The shrinkage of the fibres was measured as follows: 30cm length bundles of the fibres (approx. 1000 denier in total ) were exposed in an hot air oven for 10 minutes at 120°C. The bundles were laid loose and flat on smooth cardboard without any touching of the bundles or any applied tension and were allowed to cool for 5 minutes. The change in length was measured and the % shrinkage was calculated as follows: % shrinkage = original length - shrunk length x 100 original length Typical results of 45%, 46%, 47% shrinkage were measured for the fibres. In a repeat of this same test method but with a heating temperature of 100°C, for fibres produced by the same process, typical results were 33, 32, 34% shrinkage. It was noted that in the test at 100°C the filaments hardly stuck together, but at the 120°C test there was notable sticking of the filaments together in each bundle. This was believed to be caused by the softening and partial melting of the LLDPE component at the fibre surface of each fibre. On cooling an effective bond between fibres which had been heated to 120°C was therefore created. Example 2 The extrusion and process conditions of Example 1 were used in this Example. However, the proportion of the two same polymers fed into the extruder was varied as follows: LLDPE 90 80 70 60 50 40 20 PP 10 20 30 40 50 60 80 Using the same test at 120°C and 100°C for determining the shrinkage of the fibres ( see Example 1), on relaxed bundles of filaments (1000 denier), it was found that the measured shrinkage reduced as the percentage of LLDPE was reduced (see below). Results of shrinkage measurements for variation of LLDPE in fibre polymer composition are as follows: LLDPE % 90 80 70 PP % 10 20 30 Shrinkage (%) at 120°C 45 32 27 Shrinkage (%) at 100°C 33 28 26 At the same time, the stickiness of the fibres in the 120°C test was not evident for concentrations below 70% LLDPE. The optimum stickiness was for the 90% concentration. Other experiments showed that fibres with 95% or more LLDPE were stickier but difficult to process and thus unsuitable. Example 3 First and second comparative fibres comprising 100% polypropylene and 100% linear low density polyethylene, respectively, and fibres according to the present invention (containing 70 to 90% LLDPE and 30 to 10% polypropylene) were tested on a calibrated hot- plate. The hot-plate was set with a temperature gradient of 100 - 180°C. All these tests on the hotplate were performed without applying any overall pressure or tension to the fibres. Samples were placed at intervals along the plate to study how the fibres behaved as the temperature increased. In particular, the melting and softening properties were examined. The results are as follows: a) The first comparative fibre comprising 100% polypropylene fibres remained fibrous up to the melting point of 165°C. At this temperature the fibres became a viscous liquid. At above 155°C they began to become slightly sticky. b) The 100% linear low density polyethylene fibres remained fibrous but become sticky and softened as the temperature reached 110°C. The fibres melted at 125°C and became a molten mobile liquid, and remained so as the temperature increased (e.g. to 135, 145, 155°C etc... ) c) The fibres according to the present invention behaved in totally differently manner from their separate constituents. Even in the case of a fibre containing as little as 10% polypropylene the fibres became sticky below the expected melting point of 125°C of the LLDPE component ( typically they became sticky at temperatures of 105 to 110°C) and remained fibrous and kept their identity at temperatures as high as 155°C. Even at temperatures above 155°C the fibres still formed a sticky network. Only at 165°C did final melting of the whole fibrous network take place. As the proportion of polypropylene in the fibre was increased, the degree of softening of the fibres reduced and the degree of stickiness of the fibres also reduced. Accordingly, an LLDPE content of 85 to 90% inclusive is preferred in view of the intended end use because the stickiness ( as a measure of the efficacy of the bond) is important. At the same time, it is important that the fibrous nature of the material remains . Example 4 In another experiment, a fibre comprising a blend of 90% LLDPE and 10% polypropylene was used to make fibres of lower deniers, namely 6 and 10 denier. We established that the properties of heat shrinkage and bonding are also possible at these lower diameters of fibre and it is envisaged that fibres as low as 1 denier can be suitably employed in the present invention. We have also established that the above methods and compositions also work for 25 or higher denier fibre. On this basis it is expected that even higher denier fibres i.e. greater than 25 denier and up to 100 denier will also be possible. For practical reasons connected with the intended end uses of the fibres, fibres in the range of 5 to 25 denier are preferred. More particularly, fibres in the range 10 to 20 denier are more preferred with 13 to 17 denier being most preferable. Example 5 By way of comparison, bundles (600 denier) of commercially available high shrink fibres were taken and heated at known temperatures in an oven with and without a known tension (of 0.015 g.p. denier). This fibre was the Charisma fibre ( a registered trade mark of Plasticisers Limited). This fibre contains polypropylene as the dominant component and typically contain 40% or less by weight of polyethylene. The shrinkage (%) was measured as described previously: In¬ Temperature ( °C ) Without tension With tension 0. .015 o.p. denier 90 9 10 100 12 14 110 16 15 120 20 16 130 24 19 The measured results show that the applied tension only has a small effect in reducing the resultant shrinkage of the bundle of filaments. When such high shrink fibres are blended (e.g. 15 - 25%) with low shrink fibres in a yarn or fabric, they can generate sufficient forces on heating to change the size of the yarn or fabric (e.g. 16 - 19% shrinkage depending on temperature applied to this fibre in the construction) . The 15 denier fibres produced in Example 1 were also tested at the same temperatures with and without the applied tension. The results were as follows: Temperature ( °C ) Shrinkage ( % ) With tension without tension 0.015 g.p. denier 90 15 14 100 20 18 110 28 14 120 30 - 13 (stretching occurred) The shrinkage without applied tension of the fibres of Example 1 is notably higher than the shrinkage when even only a small tension is applied. As the test temperature was increased above 120°C the shrinkage increased dramatically (e.g. 35 - 40% at 122°C) but it became increasingly difficult to measure consistently because at 122°C and upwards the filaments stretched exponentially beyond their limits. This example illustrates how fibres of the present invention could be blended into a fabric and heat-set to form a stabilised structure without significant distortion or movement in the fabric construction.

Claims: CLAIMS : 1. A heat-bondable polyolefin fibre, the fibre comprising a blend of an amount of 70 to 90 % inclusive by weight of polyethylene, and an amount of 10 to 30 % inclusive by weight of polypropylene, the fibre optionally further including one or more polyolefin copolymers in an amount of not more than 10% by weight, the fibre having a degree of shrinkage of between 20 and 50%, inclusive, when measured at 120°C and a shrink tension of not more than 0.015g per denier when measured in the range 90 to 120°C. 2. A fibre as claimed in claim 1, wherein the polyethylene is a low density polyethylene ( LDPE ) or linear low density polyethylene ( LLDPE ) , wherein low density means that the polyethylene has a density of not more than 0.925g/cm 3 . 3. A fibre as claimed in claim 1 or 2, wherein there is 10 to 15% by weight of polypropylene in the fibre. 4. A fibre as claimed in claim 1, 2, or 3, wherein there is 85 to 90% by weight of polyethylene in the fibre. 5. A fibre as claimed in any preceding claim, wherein the fibre includes homopolymers or copolymers of butylene or copolymers of ethylene and propylene in an amount of not more than 10% by weight of the fibre content. 6. A fibre as claimed in any preceding claim, wherein the polypropylene is a polypropylene homopolymer having a melting point of 160 - 165°C, inclusive. 7. A process for producing a heat-bondable polyolefin fibre, the process comprising the steps: (a) extruding a polymer mixture comprising polyethylene in an amount of from 70 to 90% by weight inclusive, polypropylene in an amount of from 30 to 10% by weight inclusive, and optionally not more than 10% by weight of a further polyolefin component; ( b ) air cooling and drawing the extruded mixture to produce a fibre; (c ) heating the fibre in an oven to soften the fibre and stretching the fibre at a stretching ratio of from 1.5 to 4.0 times inclusive; (d) feeding the stretched fibre to a crimper to produce crimped fibre; and (e) cooling and cutting the crimped fibre. 8. A process as claimed in claim 7, wherein cooling is effected by an air knife and wherein the cooling air has a temperature of from 5 to 20°C inclusive. 9. A process as claimed in claim 7 or 8, wherein the drawing of the extruded polymer to produce fibre is effected at a ratio of between 10 and 100 times. 10. A process as claimed in claim 7, 8 or 9, wherein the temperature of the oven is in the range of 90 to 120°C inclusive. 11. A process as claimed in any of claims 7 to 10, wherein the stretching, which is performed in the oven during the heating step, is effected at a stretching ratio of 1.5 to 2.5 inclusive. 12. A process as claimed in any of claims 7 to 11, wherein blending in the extruder is carried out in the temperature range of 220 to 280°C, inclusive. 13. A process as claimed in any of claims 7 to 11, wherein separate polymer components are fed directly to the extruder throat and co-extruded.

Inventors: BAILEY KEITH, ELLIS DAVID GEOFFREY, BAILEY, KEITH, ELLIS, DAVID, GEOFFREY
Applicants: BAILEY KEITH, ELLIS DAVID GEOFFREY, PLASTICISERS LTD, BAILEY, KEITH, ELLIS, DAVID, GEOFFREY, PLASTICISERS LIMITED
Application year: 1999
Main classification: D01F6
IPC codes: C08L23, D01F6