GB2598270A

GB2598270A - Even temperature profile of polymer flow from extruder to spin blocks

Info

Publication number: GB2598270A
Application number: GB1919249.1A
Authority: GB
Inventors: Zampollo Fabio
Original assignee: Teknoweb Materials SRL
Current assignee: Teknoweb Materials SRL
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2022-03-02
Also published as: WO2021130108A1; GB201919249D0

Abstract

Equipment for manufacture of fibres or filaments from polymeric material which is preferably non-synthetic polyester, most preferably PLA and/or PHA. The equipment comprising an extruder and a spin block, the piping connecting the two components characterised by existing at least a section of non-circular cross section, preferably rectangular, oval or elliptical. Exhibiting width W and height H with a ratio of W/H or at least 3, preferably more than 5, most preferably between 15 and 20. Also included is equipment for forming a web using such a system, and a process for forming fibres and webs as such.

Description

EVEN TEMPERATURE PROFILE OF POLYMER FLOW FROM EXTRUDER TO SPIN BLOCKS

Field of the invention

The present invention relates to an equipment adapted to create filaments comprising heat sensitive polymers or being intended to be combined with heat sensitive materials, such as in a coforming process.

Background

The manufacturing of fibers from polymeric materials is well known in the art in processes like mcltblowing, spunbonding or -as a hybrid form thereof-spunblowing.

Often, it is desired to operate such processes at low temperatures e.g. relative to the melt temperature of the polymer.

JP2002-227026 describes a system, wherein a polymer supply pipe from the discharge port of the extruder splits into separate transport pipes each connected to a gear pump integral with the spin beam. These transport pipes comprise heating such that the temperatures of the polymer flow can be adapted to the residence time of the polymer in the pipes and temperature peaks can be reduced.

When combining such polymeric materials with temperature sensitive materials, such as cellulose based materials, such as pulp fibers, certain critical temperatures should not be exceeded so as to minimize degradation or even risks, such as autoignition.

Henceforth, it is desired to supply and the polymeric material to the spinnerettc at a temperature as low as possible. However, for preparing the polymer melt in an extruder, often comprising a blend of polymers, higher temperatures are required than for the spinning of the polymers. This polymer melt is typically transferred to the spin block in circular tubes of often between 2.5 cm and 5.0 cm in diameter. Typically, these pipes are heated at their outer surface in order to maintain the required temperatures during transport.

Due to the flow properties of the polymer melt, its radial mixing is limited, and the temperature close to the heated surface of the pipe is higher than the one in the center of the pipe. However, the latter still needs to be above the required minimum temperature for the spinnerette, such that the other exhibits a higher than required temperature.

Thus it is a first object of the present invention to provide an equipment comprising a transfer piping connecting the extruder and the spin block exhibiting a rectangular cross- -2 -section. It is another object to implement such an equipment in an apparatus for manufacturing composite material, such as coformed webs. It is a further object of the present invention to operate an equipment and apparatus so as to provide a polymer melt to a spin block with minimum temperature variance therein, and even further to allow to minimize the overall temperature.

Summary

Thus, the in a first aspect, the present invention is an equipment for the manufacture of fibers or filaments from polymeric material, wherein the polymeric material is preferably non-synthetic polyester, more preferably selected from the group consisting of PLA and PHA. The equipment comprises an extruder, a spin block, and piping connecting the ex/ruder with the spin block. The piping system exhibits at least a section exhibiting a non-circular cross-section, preferably rectangular, oval, or elliptic, most preferably rectangular, exhibiting characteristic cross-sectional dimensions width W and height H. wherein the ratio of W/H is at least 3.0, preferably more than about 5, even more preferably more than about 5, even more preferably more than about 10, most preferably more than about 15, or less than about 30, more preferably less than about 20. In another aspect, the present invention is an equipment for the manufacture of a web comprising polymeric material, preferably non-synthetic polyester, more preferably selected from the group consisting of PLA and PHA and short fibers, preferably cellulosic, more preferably cellulosic pulp fibers. The equipment comprises the elements -polymeric material supply - extruder -spin block -short fiber supply -combining chamber -laydown system - further comprising piping system connecting the extruder and the spin block. The piping system exhibits at least a section exhibiting a non-circular cross-section, preferably rectangular, oval, or elliptic most preferably rectangular, exhibiting characteristic cross-sectional dimensions width W and height H, wherein the ratio of W/H is at least 3.0, preferably more than about 5, even more preferably more than about 5, even more preferably more than about 10, most preferably more than about 15, or less than about 30, more preferably less than about 20.

Such a process may suitably included in a a process for the manufacture of a web -3 -material, comprising the steps of -providing - polymeric material adapted to be formed into polymeric fibers or filaments; short fibers, preferably pulp fibers; extruder for melting the polymeric material and optionally combining and mixing it with additives; spin block for forming polymeric fibers or filaments; - piping system connecting the extruder and the spin block; - combining chamber; laydown system; -melting the polymeric material in the extruder, -transporting the molten polymeric material through the piping system, -forming polymeric fibers or filaments in the spin block; -forming a mixture of the polymeric fibers or filament and the short fibers; -forming a web of the mixture in the laydown system.

The piping system is exhibiting a varying cross-sectional shape from essentially circular towards the extruder to rectangular towards the spin block. The molten polymeric material exiting from the extruder exhibits an essentially even extruder discharge temperature. The molten material exiting from the piping system exhibiting a piping exit temperature T2 exhibiting a radial temperature profile exhibiting a difference of less than 40°C, preferably less than 30°C, more preferably less than 15°C or even more preferably less than 5°C, most preferably less than about 1°C between it maximum Th., and its minimum TThih, temperature.

Preferably, the polymeric fibers or filaments exit the spin block at a temperature T3 corresponding in its average temperature T3avg and temperature differential (T3.-T3inin) to the piping exit, and wherein the T3max is below a maximum treatment temperature To of the short fibers.

Brief description of the Figures

Fig. 1 depicts schematically a known set up for a fiber or filament forming process.

Fig. 2A and 2B show schematically a known modification thereof Fig. 3A and 3B depict features of a transfer piping according to the present invention.

Fig. 4A to E depict schematically temperatures and temperature profiles across various steps in the process.

Same numerals refer to same or equivalent features. The figures are schematic and not to -4 -scale.

Detailed description

In a first aspect, the present invention is an equipment for the manufacture of fibers or filaments from polymeric material.

A conventional design is depicted in Fig. 1, wherein polymer is fed from polymer supply 20, optionally with additives, to extruder 22, where the polymer is heated mid melted, further, pushed through filter 23 and metering pump 24 to spin beam 25, where it is then extruded through a spinneret 26 having a plurality of multi-rowed orifices, together forming fibers or filaments, as may be drawn in the drawing unit 31.

An approach for adjusting the temperature of the polymer flow to the spin block is depicted in Fig. 2. so as to reduce degradation of the polymer by high temperatures Therein, the polymer transport pipe 2 from the extruder discharge port 4 is split into smaller pipe branches 2' connected to metering gear pumps 31 through 34. The transport pipes are heated preferably by fluid heating, e.g. double walls 21, respectively 21' after the split, or optionally electric heating (not shown).

As depicted, these conventional approaches employ polymer transport pipes with a circular cross-section, typically of between 1 and 3 inches (about 2.5 to 7.5 cm). Such pipes arc relatively easy to manufacture and implement into the production units.

However, when employing the heating to thc outer surface of these pipes, a radial temperature profile is created, wherein the outer portions of the polymer melt are at a higher temperature than in the core of the flow. In order to ensure sufficiently high temperatures in the spin block also for the material in the core, the temperature of the polymer transport pipe, hence the average temperature of the melt arriving at the spin block must be set high enough and well above the minimum temperature that is required to maintain good fiber forming in the spin block. Hence, also the formed fibers arc at a temperature higher than required.

This is of particular relevance, when materials are employed that exhibit relatively high melting temperatures, and when fibers formed from such materials are to be combined with temperature sensitive other materials, as will be discussed in more detail herein below.

Thus, in order to improve the temperature profile in the transfer pipes, the present invention employs particular shape of the transfer pipes that changes from a circular cross-section at the discharge port of the extruder to a rectangular shape at the connection to the spin block, whilst maintaining essentially the same cross-sectional area.

Without implying any limitation, the principle is explained by referring to Fig. 3. Fig. 3A -5 -depicts schematically the piping at the discharge port 4 of the extruder -whereby the geometry applies to the rest of the piping in conventional circular piping. If exemplarily the inner diameter D of a circular pipe is 1,5" or about 38.4 mm, it exhibits -a cross-sectional area of 1(tr * 112) / 4] or 1140 mm2, -and a circumference C of (n * D) or 120.6 mm.

In order to keep the comparable polymer flow conditions in a rectangular pipe with an inner width W and a inner height H, see Fig. 3B, representing the rectangular section 5 of the piping between the extmder and the spin pack, the cross-sectional area shall be equivalent to the area of the circle, resulting in an increase of the circumference, as is a measure for the area available for the heat transfer, which increases significantly with increasing "flatness", i.e. ratio of the width W to the height H of the rectangular piping, as shown in Table I. It also can be seen, that a similar effect by splitting the pipe into smaller ones, as indicated in the above discussed JP2002-227026, would require 7 pipes of 14.5 mm diameter to provide comparable total cross-section and circumference.

W [mm] H [mm] W/H [-] C [mm] 75.5 15,1 5.0 180.2 106.8 10.7 10.0 233.4 130.8 8.7 15.0 279.0 151.0 7.6 20.0 315.2 For Reference Circular 0 38.mm Circular 0 38.4nun 1 120.6 Multiple Circular Cross-section 1155.9 mm2 1 318.9 7 pipes at 0 14.5mm

Table 1

Whilst such increase of heat transfer surface area can also be achieved by other cross-sectional shapes, such as elliptical or oval ones, which are also included herein with their wider extension W and their smaller extension H, it is preferred to use rectangular ones, of course including typical radii in the corners, to ease the transition to the polymer channels within the spin block typically having a rectangular shape, too.

It should be noted that the transition from a circular cross-section to a rectangular one does not need to begin at the extruder discharge port, but a portion of the pipping can be executed as a circular pipe.

Such an arrangement allows to reduce the maximum as well as the mass average temperature of the polymer flowing to the spin block and then also of the resulting fibers -6 -significantly, by at least about 10°C, preferably more than about 20°C, or more than about 30°, or even more, though the difference will typically be less than 50°C.

As indicated in the above, this is of particular interest if the selected polymeric material is a material that exhibits biodegradable properties and/or is derived from natural based materials, which for same applications, such as disposable wipes exhibit higher melting temperatures as conventional material, such as polypropylene, polyethylene, or typical polyester derived from synthetic material. For commonly used synthetic polymers, extruder polymer extruder exit temperatures range typically from about 180°C to about 270°C.

A suitable group of polymers is generally called aliphatic polyesters, exhibiting microbial degradation characteristics. Specifically, such polymers include, for example, poly-alpha-hydroxyalkanoate as represented by microbially degradable polyester, poly-alphahydroxyalkanoate as represented by polycaprolactone, polyalkylene dicarboxylate composed of a polvcondensatc of glycol and dicarboxylic acid, such as polybutylene succinate, or copolymers of these polymers. In such situation, and with recent development of a new polymerization process which can efficiently produce polymers of high polymerization degree, various attempts have been made to produce filaments from polyoxyacid, a polymeric product as represented by poly-L-lactic acid, and nonwoven fabrics comprised of such filaments.

Of particular interest in the present context are materials of the polylactic acid (PLA) type and polyhydroxyalkanoates (PHA). Whilst PLA material may exhibit a range of properties, an exemplary PLA material as INGEO NatureWorksk PLA Polymer 6202D (2005) of Nature Works. Whilst it exhibits a polymer melt temperature of 170°C, typical melt spinning temperatures are 220 -240°C, however, overheating should be avoided as the polymer may release undesirable fumcs. Polyhydroxyalkanoatcs, as have been described e.g. in US6013590A (1995) (lsao Noda, P&G) are known to be susceptible to thermal instability at temperatures near its melt temperature, which led to modified polymers, e.g. poly(3-hydroxybutcaate-co-3-hydroxyvalerate) (PHBV), as being commercially available from Imperial Chemical Industries under the tradename METABOL1X 'um by Metabolix, USA. Still, such polyhydroxyalkanoates as PHB and PHBV are difficult to process into films, fibers, and nonwovcns suitable for hygiene applications. Further, fibers comprising polyhydroxyalkanoate copolymer/polylactic acid polymer or copolymer blends have been described in W02002077335A1 (Isao Noda, P&G) A particular application of the present invention relates to coforming processes, as such well known in the art. Without intending any limitation, express reference is made to copending application GB1916086 (unpublished) as far as the cofonning process is -7 -concerned. The benefits of the present invention become clear, when the short fibers added in the cofonning to the polymeric fibers or filaments are heat sensitive, such as with cellulosic fibers.

It has been found that when using such new materials such as PLA or PHA, the temperature of the filaments when contacting the cellulose fibers in conventional processes, a maximum treatment temperature To for cellulose fibers may be exceeded, and degradation, charring, or even autoignition may occur, the latter being for fluff pulp, such as of the Northern Softwood type, typically about 450°F (about 232°C), see e.g., OSHA HCS 2012, Canada HPR 2015, Referring now to Fig 4, the temperature conditions are explained for operating a system according to the present invention with rectangular pipe cross-section (see Fig. 4E) at the spin pack entry 5 to a conventional circular cross-section (Fig.4D) in the general processing set-up for an exemplary coforming process, as depicted in Fig. 4A with extruder 22, piping 2 with extruder discharge port 4 and piping exit corresponding to the spin pack entry section 5 for connecting to the spin pack 25 (here filter and metering pumps are omitted), where fibers or filaments 31 are formed and combined with the short fibers 41 as supplied from the short fiber supply 40 in the combining chamber 50. The molten material exiting from said extruder into the transfer piping exhibits at its discharge port 4 an essentially even (i.e. homogeneous across its cross-section extruder discharge temperature T1 and a temperature differential (Delta Ti), if any, of less than 1°C. This is both the case for conventional approaches (see Fig. 4B) as for the current invention (see Fig. 4C). , where the transition to the rectangular shape begins. For conventional approaches, the circular shape will be maintained through to the spin block, here shown for the case of non-split piping.

The molten material exiting the transfer piping exhibits a mass average pipe exit melt temperature T2avg with a maximum pipe exit melt temperature T./max close to the outer wall and surface of the pipe, and a minimum pipe exit melt temperature too..

As Tm,in has to be higher than the minimum temperature to allow good fiber or filament forming T3, the heating of the pipe needs to ensure that 1.2mill does not drop too low, such that due to the pronounced temperature profile T2max is increased and hence as the temperature differential is not eliminated during the passing through the spin pack, the maximum temperature T3o,,, correspond essentially to tr..

Comparing to conventional piping systems with circular cross-section, the present invention allows to operate the system with minimum temperature differential at the pipe exit (T2ma, -'Loth), resulting in a reduced maximum fiber or filament temperature floa, -down to temperature ranges below the maximum treatment temperature To of heat sensitive -8 -short fibers such as the mentioned cellulose fibers. -9 -

Claims

CLAIMSI. An equipment for the manufacture of fibers or filaments from polymenc material, wherein said polymeric material is preferably non-synthetic polyester, more preferably selected from the group consisting of PLA and PHA, said equipment comprising an extnider, a spin block, and piping connecting said extruder with said spin block, characterized in that said piping system exhibits at least a section exhibiting a non-circular cross-section, preferably rectangular, oval, or elliptic, most preferably rectangular, exhibiting characteristic cross-sectional dimensions width W and height H, wherein the ratio of W/H is at least 3.0, preferably more than about 5, even more preferably more than about 5, even more preferably more than about 10, most preferably more than about 15, or less than about 30, more preferably less than about 20.
2 An equipment for the manufacture of a web comprising polymeric material, preferably non-synthetic polyester, more preferably selected from the group consisting of PLA and PHA and short fibers, preferably cellulosic, more preferably cellulosic pulp fibers, said equipment comprising -polymeric material supply -extruder - spin block - short fiber supply -combining chamber -laydown system - further comprising piping system connecting said extruder and said spin block, said equipment being characterized in that said piping system exhibits at least a section exhibiting a non-circular cross-section, preferably rectangular, oval, or elliptic -1 0 -most preferably rectangular exhibiting characteristic cross-sectional dimensions width W and height wherein the ratio of V'//H is at least 3.0, preferably more than about 5, even more preferably more than about 5, even more preferably more than about 1ft most preferably more than about 15, or less than about 30, more preferably less than about 20.
3. A process for the forming of polymeric fibers or filaments comprising the steps of -providing polymeric material adapted to be formed into polymeric fibers or filaments - extruder for melting said polymeric material and optionally combining and mixing it with additives; spin block for forming polymeric fibers or filaments; -piping system connecting said extruder and said spin block; - melting said polymeric material in said extruder, -transporting the molten polymeric material through said piping system, -forming polymeric fibers or filaments in said spin block; characterised in that said piping system is exhibiting a varying cross-sectional shape from essentially circular towards said extruder to rectangular towards said spin block, and in that said molten polymeric material exiting from said extruder exhibits an essentially even extruder discharge temperature, and in that said molten material exiting from said piping system exhibiting a piping exit temperature T, exhibiting a radial temperature profile exhibiting a difference of less than 40°C, preferably less than 30°C, more preferably less than 15°C or even more preferably less than 5°C, most preferably less than about 1°C between it maximum T2 and its minimum Luna temperature.
4. A process for the forming of a cofonned web comprising the steps according to claim 3 further comprising the steps of - providing -short fibers, preferably pulp fibers; a combining chamber for combining said polymeric fibers or filaments with said -11 -short fibers; -laydown system; -forming a mixture of said polymeric fibers or filament and said short fibers in said combining chamber; -forming a web of said mixture in said laydown system,
5. A process for the manufacture of a web material according to claim 4, wherein said polymeric fibers or filaments exit said spin block at a temperature T3 corresponding in its average temperature T3ayg and temperature differential (T3 T3min) to the piping exit; -and wherein said T3max is below a maximum treatment temperature To of said short fibers.