Woven hollow fiber double weft tape with knitted selvedge

A woven hollow tape, for use in exchange devices such as blood oxygenators and heat exchangers, having weft threads and hollow fibers as warp threads, formed as a double weft tape, in which one tape edge is formed as a knitted edge and the weft density is much less than that found in normal woven textile tapes, each weft being spaced apart from the adjacent wefts. The tape is produced by a weft insertion that takes place in a manner similar to that of a shuttleless ribbon loom, especially a needle ribbon loom, preferably using freshly spun hollow fibers. The resultant tape may have hollow fibers along both edges and may be used to form the appropriate products either with or without the weft threads which are easily removed as a result of the tape structure.

BACKGROUND OF THE INVENTION 
The invention relates to a woven hollow fiber tape with weft threads and 
hollow threads as the warp threads. The invention also relates to a method 
and a device for manufacturing the woven hollow fiber tape as well as 
hollow fiber bundles composed of woven hollow fiber tapes. 
A woven hollow fiber tape with weft threads and hollow threads as the warp 
threads and a blood oxygenator manufactured therefrom are known from 
EP-A2-0 089 122. This known woven hollow fiber tape is the type 
manufactured on a so-called shuttle loom. The manufacture of such woven 
hollow fiber tapes is very cumbersome and hence expensive. A further 
disadvantage of hollow fiber tapes woven in this manner is that the weft 
threads cannot be pulled out again as is frequently desired. In addition, 
this hollow fiber tape necessarily has a monofilament (solid fiber) on 
each side edge to protect the hollow fibers at the edge against transverse 
forces and abrasion by the shuttle and to absorb tensile stresses. Such 
threads, however, make the manufacture of the hollow fiber tape more 
difficult and frequently cause problems in the finished device. Processing 
this known woven hollow fiber tape into a blood oxygenator and the blood 
oxygenator itself likewise involve disadvantages. One disadvantage of this 
known processing method to turn a woven hollow fiber tape into a blood 
oxygenator is its considerable engineering cost. Thus, a special device is 
required for reversal when the woven hollow fiber tape is reversed at the 
ends of the winder to form the next hollow fiber layer, said device making 
the reversal possible. In addition, the area of deflection of the hollow 
fibers which thus results and cannot be used is considerable, resulting in 
a large percentage of waste. This method also has the additional 
disadvantage that the winding angle to the axis of the winder is only 
between 30.degree. and 90.degree.. The length of the hollow fibers is then 
a multiple of the axial length of the winder. This results in an increased 
pressure loss in the interior (lumen) of the hollow fibers. In addition, 
if the winding angle between the axis of the winder and the woven hollow 
fiber tape is not modified accordingly as a function of the number of 
layers, the length of the hollow fibers will increase with an increasing 
number of layers. This produces a nonuniform flow through the hollow 
fibers, something which is generally undesirable. 
SUMMARY OF THE INVENTION 
Hence, the goal of the present invention is to provide a woven hollow fiber 
tape which is less expensive to manufacture and can be employed much more 
diversely, the tape also permitting a design in which the weft threads 
perform only a temporary auxiliary function when processing a plurality of 
hollow fibers (hollow fiber sheet), in other words, a processing aid. 
Another goal is to provide a simpler and more economical method of 
manufacture to make a woven hollow fiber tape of this kind as well as a 
device suitable for the purpose. Finally, another goal consists of 
providing hollow fiber bundles which can be produced economically from 
woven hollow fiber tapes with a high material and/or heat exchange 
ability. 
These goals are achieved by a woven hollow fiber tape with weft threads and 
hollow threads as warp threads, designed according to the invention as a 
double weft tape, by the method described below, by the device described 
below, and by the hollow fiber bundles described below. 
Hollow fibers whose walls are completely or partially permeable to 
materials, in other words, are permeable or semi-permeable, and which 
consequently are suitable for material exchange, material separation, 
and/or material transfer, are frequently also referred to as capillary 
membranes. Capillary membranes can be used in medical or technical 
applications. Typical applications for capillary membranes include, for 
example, blood plasmapheresis, hemofiltration, electrodialysis, dialysis, 
oxygenation, reverse osmosis, ultrafiltration, microfiltration, 
pervaporation, etc. 
The outside diameters of hollow fibers (capillary membranes) lie in the 
following ranges, for example: 
for dialysis, from 150 .mu.m to 280 .mu.m; 
for oxygenation, from 150 .mu.m to 500 .mu.m; 
for plasmapheresis, from 150 .mu.m to 650 .mu.m. 
Hollow fibers with a wall that is essentially impermeable to materials are 
frequently used for heat transfer, in other words, in heat exchangers. 
Hollow fibers with a (micro-)porous wall are used, for example, for 
(micro-)filtration, membrane distillation, etc. 
To make material and heat exchangers of this type, a plurality of hollow 
fibers is normally combined to form a hollow fiber bundle and thereby, 
preferably placed in a certain arrangement, to shape the flow area between 
the hollow fibers for the medium flowing around the outsides of the hollow 
fibers in such a way that, depending on the application of such a hollow 
fiber bundle, specific requirements regarding momentum, heat, and material 
transport phenomena are met. 
For example, in a capillary membrane oxygenator the blood flows between the 
capillary membranes, that is, the latter have the blood flowing around 
them externally. Capillary membranes are terminated by embedding them in 
such a way that their openings terminate in separate supply and discharge 
chambers for the oxygen flowing through the capillary membranes, their 
lumina. For gas exchange between the blood and the oxygen through the 
walls of the capillary membranes it is therefore advantageous to arrange 
the capillary membranes in such a way that a high oxygen/carbon dioxide 
exchange is achieved and only a small blood/membrane contact area is 
required. 
These and other requirements are met by the invention in an economical and 
technically superior fashion. For an improved understanding of the 
terminology employed here and the technology of the preferred 
manufacturing method and the device suitable for the purpose, the reader 
is referred to the following patents, which also serve for disclosure of 
the invention: U.S. Pat. No. 4,399,841, U.S. Pat. No. 4,761,864, U.S. Pat. 
No. 3,605,225, U.S. Pat. No. 4,006,758. 
The term "double weft tape" will be understood in the context of the 
present invention to be a woven tape in which a double weft insertion has 
taken place, in other words, two weft threads are inserted per weft 
insertion, producing so-called double wefts. Double weft insertion in 
textile fabrics is a type of rib weave and, with the usual high weft 
density, results in double-weft rib (grain); for this reason it is also 
referred to as grain weave. In the manufacture of woven tapes on shuttle 
looms, a so-called true selvage is produced on both sides of the tape. 
Shuttleless weaving methods, on the other hand, make it possible to 
manufacture woven tapes in which at least one edge of the tape is not made 
in the form of a true selvage. One embodiment of a non-true selvage is the 
knitted edge, which is also selected as an especially preferred embodiment 
of the woven hollow fiber tape according to the invention. The knitted 
edge is produced, for example, in the shuttleless weaving method in which 
the weft thread is laid as a thread loop through the shed (inserted) and 
the laterally projecting weft thread loop is knitted into a stitch 
(crocheted or stitched), in other words, the weft thread is tied to 
itself. This process is also referred to as the formation of a knitted 
edge by stitching the weft thread. Such a knitted edge, if desired, can be 
tightened further (rippled), so that the weft thread can easily be pulled 
out again completely and removed. However, it is also possible with this 
technique to tie off the weft thread loops, for example using an auxiliary 
thread, or to fasten them, for example by gluing, so that rippling is not 
possible. Tying off or stitching is usually performed using a knitting 
needle. 
The term "weft density" is the number of weft threads per unit length of a 
woven tape. In the hollow fiber tape woven according to the invention, it 
is preferably much less than in normal woven textile tapes, whereby 
firstly, a loose, woven hollow fiber tape with sufficiently dimensioned 
intermediate spaces for a low-pressure loss flow around the hollow fibers 
is produced, in which the hollow fibers, however, are arranged at definite 
mutual intervals, in other words, in the arrangement described above for 
high material and/or heat transfer ability. The low weft density also 
provides in advantageous fashion a high manufacturing speed for the woven 
hollow fiber tape. The term "low weft density" refers, for example, to one 
that has 3 to 35 mm and especially 10 to 15 mm per weft, but in any case 
one in which the adjacent weft threads do not lie close together or do not 
touch one another. The weft threads, therefore, run meanderwise or form a 
zigzag line, a sawtooth line, or the like, and form an angle with the warp 
threads which is smaller on the average than 90.degree., for example, 
15.degree. or 30.degree. or 45.degree.. 
In the woven hollow fiber tape according to the invention, the weft threads 
are preferably made of monofil or multifil endless thread which is unwound 
during manufacture, for example, continuously from a bobbin. The weft 
threads can be much finer than the hollow fibers. The weft threads can 
also be made of threads twisted in different ways. In special 
applications, it may be advantageous for the weft threads to be made of 
the same material as the warp threads (hollow fibers). 
It is also possible to use as weft threads those which themselves possess a 
property that performs material exchange, which therefore are able, for 
example, to absorb or adsorb a substance from the medium flowing around 
the hollow fibers, or to give a substance off to it, possibly with a delay 
or slowly. The weft threads can also be arranged or made such that they 
contribute to the formation of turbulence or laminar mixing. The weft 
threads can also be inserted in such a way that they produce an undulation 
of the hollow fibers (warp threads), which can result in an increase in 
the ability to transfer materials and/or heat. 
The woven hollow fiber tape can contain, for example, 3 to 300 hollow 
fibers as the warp threads, with one preferred embodiment containing 15 to 
40 hollow fibers. The width of the woven hollow fiber tape essentially 
reflects the diameter of the hollow fibers. A width of 10 mm, mentioned 
here only as an example, has proven to be highly suitable in the 
subsequent processing of the woven hollow fiber tape onto bobbins and into 
hollow fiber bundles. 
The woven hollow fiber tape can also have hollow fibers with different 
properties for the warp threads. Typical properties of hollow fibers used 
for different purposes include, for example, wettability (hydrophilia, 
hydrophobia), permeability, UF rate, etc. The woven hollow fiber tape can 
also have hydrophobic and hydrophylic hollow fibers in it, or hollow 
fibers with different permeabilities, each of which serves a different 
purpose. It can also include hollow fibers that promote material exchange 
and those which serve for simultaneous heat transfer. Such different 
hollow fibers can be present in any mixing ratios that correspond to the 
specific requirements. 
In addition, the woven hollow fiber tape can also have a number of threads 
as warp threads which, for example, have a supporting function or increase 
the tensile strength of the hollow fiber tape and accept possibly high 
tensile stresses during subsequent processing of the woven tape. Such 
threads can also have adsorptive or desorptive properties and remove 
materials from the medium surrounding them and the hollow fibers, or give 
off materials to this medium, possibly in a controlled manner. 
Threads with precisely adjustable and triggerable shrinking properties can 
be used, for example, to crimp the hollow fibers in a desired fashion at a 
given point in time, for example during a certain processing step. 
The high order of the woven hollow fiber tape, therefore, makes it 
possible, for example, to make a woven hollow fiber tape for an IV filter 
with venting, in which one or more hydrophobic porous hollow fibers for 
venting are arranged along at least one edge. The hollow fibers can then 
be embedded in such a way that, because of the high order within the woven 
hollow fiber tape, the hydrophobic edge fibers which bring about the 
venting are separated from the hydrophylic hollow fibers which promote 
filtration, in the embedding area by a suitable distributor head. 
The warp and/or weft threads can also perform a function as catalyst, 
enzyme storer, heat storer, heat dispenser, and the like and be provided 
for this purpose as hollow fibers or other fibers. If hollow fibers are 
used for this purpose as warp threads, they can be sealed at their ends 
and the resultant encapsulated interior (lumen) can be filled with a 
suitable substance. With such a combination of different functions, the 
woven hollow fiber tape offers the advantage that it favors a uniformly 
repeatable local order. 
The manufacture of the woven hollow fiber tape proceeds similarly to a 
shuttleless ribbon loom, as far as the weft insertion is concerned. It has 
been found especially advantageous in this regard when a device is used 
for this purpose that it is similar to that usually employed in needle 
ribbon looms. In this method, the shuttle is inserted very carefully so 
that no additional special monofilaments need to be provided to protect 
the hollow fibers along the side edges of the hollow fiber tape. It is 
also possible, however, to use a device like that usually employed in 
rapier looms. 
In the method according to the invention for manufacturing woven hollow 
fiber tape, the drive for the transport of the warp threads (hollow 
fibers) and the drive for the device for inserting the weft threads are 
preferably decoupled or decouplable. This has the advantage that the weft 
thread density can be altered independently of the transport speed of the 
warp threads, or the weft insertion can be shut off completely even 
without interrupting the transport of the warp threads, which is highly 
advantageous when starting or changing the shuttle insertion device. 
Ordinary ribbon looms, such as needle ribbon looms, do not offer this 
advantage and are also not designed for a high weft density. The transport 
speed for the warp threads is so low that these machines are not suitable 
either for making hollow fiber tapes with much smaller weft densities or 
for integration into the manufacturing process for hollow fibers. Use of 
the known needle ribbon looms results in hollow fiber tapes with the usual 
high weft density and also allows only processing of hollow fiber bobbins. 
However, an advantage is also gained in that, with a suitable design of 
the knitted edge of the hollow fiber tapes, the weft threads can be pulled 
out again at a later point in time, since a double weft hollow fiber tape 
is also produced in this case. 
One important advantage, however, is achieved in looms of this kind, 
especially when, as described above, the drive for the transport of the 
warp threads and the drive for the insertion of the shuttle can be 
decoupled or are decouplable. Hence, the merely optional coupling 
mentioned in the latter case of the two drives can also be performed 
mechanically or electrically. 
When manufacturing the especially preferred embodiment of the hollow fiber 
tape with a low weft density, the otherwise normal reed can be eliminated, 
by which the weft threads are beaten onto the weft threads that have 
already been woven. This in turn results in a simplification of the 
manufacturing method and of the device suitable for the purpose. 
Shedding can be performed in such a way that every second hollow fiber is 
raised as in a plain weave. When using more than two shedding devices 
and/or appropriately designing the shedding devices, other types of weave 
can be produced, for example, those with a float weave and the like, in 
which the shed is formed for example as in satin or body weave. 
For simplified shedding, even in the method according to the invention, it 
is also possible to use ordinary heddles with healds. However, it is much 
more advantageous to use for shedding, reeds that are open at the top (or 
bottom) with thread heddles of different depths. Reeds of this kind or 
similar devices can be provided with a device by which the thread heddles 
can subsequently be closed from above (or from below), for example, 
covered. 
A rotating device or one that can be rotated backward and forward, similar 
to a camshaft, can also be used for shedding, in which the "cams" raise 
the hollow fibers to shed. When using reeds, the latter can be arranged to 
be moved like the heddles of ordinary looms; however, they can also be 
mounted on a common rotatable shaft so that shedding takes place in a 
manner similar to the device resembling a camshaft described above. It is 
also possible to guide more than one thread through one heald or one 
thread heddle (when using reeds). 
Such reeds which are open at the top (or bottom) or similar devices for 
shedding can be inserted advantageously not only into a resting warp 
thread group from below (or from the top or from the side) but into one 
that is moving, considerably facilitating the initiation of the weaving 
process on resting warp threads and making it possible for the first time 
to work with moving warp threads. 
The continuous hollow fiber manufacturing process is not interrupted as a 
result, and if the loom breaks down a spare unit can be inserted without 
interruption. Maintenance and replacement of weaving equipment is also 
possible without interrupting or influencing the manufacture of hollow 
fibers. 
The embodiment of the method for manufacturing a woven hollow fiber tape, 
in which the activity is performed without a reed and with decoupled or 
decouplable drives for the warp and weft threads, as described above, and 
with reeds open at the top (or at the bottom) or similar devices for 
shedding, is therefore especially suited for being integrated into the 
manufacturing process for the hollow fibers. This ability, which did not 
exist in the previously known methods for manufacturing a woven hollow 
fiber tape, constitutes an important advantage and a significant technical 
advance which consists, for example, in reducing the method steps and 
hence the expense in manufacturing woven hollow fiber tapes, since it is 
no longer necessary as formerly to wind the hollow fibers initially onto 
bobbins and only later process them into woven hollow fiber tapes. 
Thus, the method in its preferred embodiment can also be performed on 
hollow fibers which are still wet, damp, or generally unfinished, in other 
words, even before the extraction of solvents, before drying, or at 
another point in the manufacturing process. This is possible because 
hollow fibers generally reach a basic strength immediately after 
coagulation or phase separation, which makes it possible to transport the 
hollow fibers through the weaving device according to the invention in 
which weft insertion takes place in a very careful manner. In this way, 
even at a very early stage in the manufacturing process, a fiber tape, 
namely a woven hollow fiber tape, can be manufactured which behaves much 
more favorably during the process and is much easier to handle. Thus, the 
tangles, sags, or rideovers (undesired threads crossing over one another), 
which are frequently observed, for example, on or between deflecting 
rollers, in thread sheets with hollow fibers running parallel to one 
another are avoided. It is also possible to improve the mutual spacing in 
the hollow fibers in this fashion, making it as small as possible 
initially, which can be utilized for a higher degree of implementation of 
existing facilities or results in much smaller (narrower) machines with 
the same production output, but still large enough for a good flow around 
the hollow fibers in method steps such as extraction, washing, drying, 
etc. A hollow fiber spacing in the range from 0.2 d to 1.5 d (d=hollow 
fiber outside diameter) has proven advantageous for most applications. In 
addition, the risk of threads breaking during the process is reduced and 
hence the processability of hollow fiber sheets is considerably improved. 
The method according to the invention can also be integrated into the 
manufacturing process, with the hollow fibers being produced by melt 
spinning. 
The shuttleless weaving method according to the invention allows 
(especially when the weft insertion is performed in a manner similar to 
that in a ribbon loom) high processing speeds for hollow fibers, i.e. 
hollow fiber sheets, into woven hollow fiber tapes according to the 
invention, with the processing speed being limited by the technically 
feasible weft frequency. The ratio of the weft frequency to the warp 
thread speed produces the weft density, in other words, the distance 
between the individual weft threads. When the speed at which the hollow 
fibers are brought to and carried away from the weft insertion device 
decreases, while keeping the weft frequency constant, a resultant increase 
in weft density is produced and vice versa. Weft density should be kept as 
low as possible for cost reasons but so that the technical requirements 
are met in every case. Here again, an optimum can be determined by simple 
tests. The method according to the invention is consequently employed 
preferably at processing speeds of the hollow fibers in the range from 10 
to 80 m/min, with a weft frequency in the range from 30 to 200 Hz. 
The woven hollow fiber tape according to the invention can be processed, 
for example, into bobbins, hollow fiber bundles, or other hollow fiber 
arrangements. 
Frequently, multifil bobbins are desired for manufacturing certain hollow 
fiber structures, in other words bobbins onto which a predetermined number 
of hollow fibers has been wound. This is frequently desirable when the 
number of hollow fibers in the finished structure (e.g. IV filter) is 
relatively low and so small a number of hollow fibers can be wound onto a 
bobbin. When a woven hollow fiber tape with a corresponding number of 
hollow fibers is used, it is no longer necessary to fit together a 
plurality of hollow fibers unwound from different bobbins to form multifil 
bobbins. 
When unwinding the multifil bobbins previously in normal use, pinched 
threads or sags were frequently encountered, which led to discontinuities 
or broken threads. These problems can be avoided with multifil bobbins in 
which the hollow fibers are wound as woven hollow fiber tape. Frequently, 
however, the weft thread is undesirable in the finished product, and there 
may be many different reasons for this. The woven hollow fiber tape 
according to the invention also offers another important advantage, namely 
the possibility that the weft thread, with a corresponding tie 
(stitching), after unwinding the hollow fiber tape from the bobbin, can be 
pulled out immediately before further processing of the hollow fibers. 
This provision opens up a much broader range of applications for the woven 
hollow fiber tapes according to the invention, especially when the warp 
thread has only a temporary auxiliary function. 
The woven hollow fiber tape according to the invention can also be wound 
into hollow fiber hanks, from which hollow fiber bundles of the desired 
length can then be cut. For this purpose a method or device can be used, 
for example like those described in U.S. Pat. No. 4,681,720. 
The processing of the woven hollow fiber tape according to the invention 
into hollow fiber bundles, however, can be performed in a different way, 
whereby especially preferred manufacturing methods for hollow fiber 
bundles and the hollow fiber bundles manufactured by this method will be 
described below and explained in greater detail with the aid of the 
figures. The so-called packing density, in other words the ratio of the 
volume filled with hollow fibers to the total volume, can be set to the 
range from 30 to 60% in a device made from hollow fiber tapes according to 
the invention (dialyzer, oxygenator, heat exchanger, etc.).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a section through a woven hollow fiber tape, consisting of hollow 
fibers 1 as the warp threads and weft threads 2. The weft threads 2 in 
this embodiment of the woven hollow fiber tape run essentially parallel to 
one another and perpendicularly to the hollow fibers (warp fibers) 1, 
whereby the double wefts are clearly evident. The left-hand edge of the 
woven hollow fiber tape in the drawing is designed as a true selvage. The 
right-hand tape edge, on the other hand, is designed as a knitted edge, 
with the laterally projecting weft thread loops being knitted together 
(stitched) or, in other words, tied to themselves. A knitted edge of this 
kind can be tightened further if desired. The low weft density is also 
clearly apparent, which results from the fact that the adjacent weft 
threads 2 do not contact one another but are arranged at a distance from 
one another, which is a multiple of the thickness of the weft threads. 
According to the present invention, this arrangement can also be designed 
a meander-shaped pattern of weft threads. 
FIG. 2 shows the section of a woven hollow fiber tape in which weft threads 
2 form a zigzag line and hence an angle smaller than 90.degree. with the 
hollow fibers (weft threads) 1. The weft density is even less than in the 
woven hollow fiber tape shown in FIG. 1. With regard to the other features 
of this embodiment of the woven hollow fiber tape, the reader is referred 
to the description of the embodiment of the woven hollow fiber tape shown 
in FIG. 1. 
FIG. 3 shows a weft insertion device which resembles the type 
conventionally used in needle ribbon looms, and which is preferably used 
in the method and device for manufacturing the woven hollow fiber tape. 
Hollow fibers 1 run through the loom in the direction indicated by arrow 
3. The device consists of the inserting element (needle) 4, with eye 5 for 
the weft thread (not shown), which is permanently attached to retaining 
arm 6. Retaining arm 6 is permanently attached to the shaft 8 which 
rotates back and forth, consequently executing a movement as indicated by 
arrow 7. The movement of retaining arm 6 causes needle 4 to perform a 
corresponding movement between two end positions as indicated by arrow 10. 
In the drawing, needle 4 is shown in its left-hand (in the plane of the 
drawing) end position. The right-hand (in the plane of the drawing) end 
position is located at the right above deflecting rod 11, as indicated by 
the tip 4a of needle 4 which is shown in dashed lines. Deflecting rod 11 
is mounted perpendicular to the plane of the drawing and hence 
perpendicular to the plane in which the hollow fibers (warp fibers) 1 pass 
through the active area of the loom. Another part of the loom is retaining 
element 9 for the weft thread (not shown), which is mounted essentially 
perpendicular to the plane of the drawing, in other words perpendicular to 
the hollow fiber tape plane, and can be moved up and down. To stitch the 
weft thread loops on the right-hand hollow fiber tape edge at the right 
(in the plane of the drawing), the knitting needle (tongue needle) 12 is 
used which is mounted parallel to the lengthwise direction of the hollow 
fiber tape and can move back and forth, as indicated by arrow 13. The 
operation of the weft insertion device shown in FIG. 3 essentially 
corresponds to that known from needle ribbon looms, and therefore need not 
be described in greater detail here. The reed, as is usually found in 
needle ribbon looms, is missing from the device as shown, however. 
FIG. 4 shows two reeds 14 and 15 open at the top for shedding. Reeds 14 and 
15 have thread heddles 18 and 19 of different depths, with thread heddle 
18 being approximately twice as deep as heddle 19. Reeds 14 and 15 can be 
moved up and down, as indicated by arrows 16 and 17. Thread heddles 18 and 
19 of reed 14 are mounted staggered opposite thread heddles 18 and 19 of 
reed 15, in other words looking in the direction of travel of the warp 
threads, a thread heddle 18 of reed 14 and a thread heddle 19 of reed 15 
occur sequentially. The shed is shown only by the hollow fibers (warp 
threads) drawn on both sides of reeds 14 and 15. In the embodiment of 
reeds 14 and 15 shown here, each deep thread heddle is followed by a 
thread heddle 19 which is a little less deep, so that the shedding takes 
place in the same way as in plain weaving. However, it is also possible to 
provide a different arrangement of the thread heddles, for example such 
that two deep thread heddles 18 follow one or two less deep thread heddles 
19, and so on. Thread heddles 18 and 19 of the reeds 14 and 15 shown, 
after insertion of hollow fibers 1, can also be covered to prevent hollow 
fibers 1 from jumping out during weaving. The open reeds 14 and 15 shown 
can, in the arrangement shown, be brought in and out advantageously from 
below, even with the warp thread sheet in motion, whereby the weaving 
process on a running warp thread sheet can be initiated or discontinued at 
any time, of course before or after a planned covering of thread heddles 
18 and 19. With the reverse arrangement of reeds 14 and 15, the movement 
into and out of the warp thread sheet takes place from above. 
FIG. 5 shows a hollow fiber sheet made of woven hollow fiber tapes in which 
the ends of hollow fibers 1 are embedded in head plates 3. Usually the 
hollow fiber ends are embedded by spinning them into a curable potting 
compound. After curing of the potting compound, as much material is 
removed endwise as is necessary to expose the open ends of hollow fibers 
1, so that a throughflow in the chamber (lumen) of hollow fiber 1 is 
possible. This can be done at one end, for example, in so-called dead end 
filters, or at both ends, as for example in dialyzers, oxygenators, heat 
exchangers, etc. For legibility, only three hollow fiber tapes are shown, 
arranged in layers around a core 4 (e.g., a core tube) in such a way that 
hollow fibers 1 of adjacent layers form layers with an angle .alpha. which 
is preferably .ltoreq.30.degree. and in special cases can also be only 
about 1.degree.. The fact that weft threads 2 are present means that even 
at such small angles of intersection the overlap is maintained and the 
hollow fibers of one layer do not, as is unavoidable in hollow fiber tapes 
without weft threads, slip into the spaces of an adjacent layer, whereby a 
disorderly hollow fiber bundle would result, with hollow fibers 
essentially arranged parallel to one another and touching one another as 
well, which would result in an extremely inadequate surrounding flow 
distribution. The angle which hollow fibers 1 form with the lengthwise 
axis of the bundle (not shown) is about .alpha./2. 
A hollow fiber bundle made of woven hollow fiber tapes can also be formed 
without a core. Thus, for example, two layers of woven hollow fiber tape 
can be formed, with the woven hollow fiber tapes being arranged parallel 
to one another inside a layer, but forming an angle .alpha. with the 
hollow fiber tapes of the other layer. The two layers can then be wound up 
in a spiral even without a core to form a hollow fiber bundle. It is 
understood, of course, that initially more than two layers can be formed 
when the hollow fibers of adjacent layers form an angle of intersection 
.alpha. and that this multilayer structure can then be wound up spirally, 
for example around a core, to form a hollow fiber bundle. 
FIG. 6 shows in perspective view a hollow fiber structure of woven hollow 
fiber tapes 1, 2 formed by the simultaneous meanderwise laying down of two 
woven hollow fiber tapes 1 and 2, whereby the hollow fibers 1a and 2a 
extending in a lengthwise direction of such a woven hollow fiber tape 
intersect at right angles in the finished hollow fiber structure. This 
type of construction is termed plaiting for textile webs and the like. It 
can be done manually or by machine. Further processing of the hollow fiber 
structure to a hollow fiber module can be accomplished as follows: the 
deflecting points (bends) of the woven hollow fiber tapes 1 and 2 can be 
embedded along the four long sides of the hollow fiber structure in a 
suitably dimensioned potting compound plait and the hollow fiber spaces 
(lumina) are then exposed. A hollow fiber module of this kind makes it 
possible to enable three fluids to participate in a material and/or heat 
exchange, with the first fluid being guided through hollow fibers 1a, the 
second fluid through hollow fibers 2a, and the third fluid externally 
around hollow fibers 1a and 2a. It is also possible, however, to punch 
e.g. round segments out of the multilayered structure and process these 
further individually or in the punched-out multilayer structure, in other 
words the hollow fiber ends can be mixed into a curable potting compound. 
FIG. 7 shows a portion of the cross section of a hollow fiber bundle made 
of woven hollow fiber tapes in which hollow fibers 1 are arranged 
essentially parallel to the lengthwise axis of the bundle, with the woven 
hollow fiber tapes being formed into partial bundles with any cross 
section, essentially irregular, in such a way that hollow fibers 1 are 
distributed essentially without gaps uniformly over the cross section of 
the hollow fiber bundle. The hollow fiber bundle, therefore, consists of a 
plurality of woven, essentially parallel woven hollow fiber tapes. The 
limit lines 20 shown of a shaped woven hollow fiber tape serve only for 
clarification; for example, there is only an imaginary and not a real 
limit between the individual partial bundles. Despite this arrangement, 
the presence of the weft threads (not shown) means that hollow fibers 1 
will not slide into the spaces between adjacent hollow fibers 1, but that 
a relatively loose bundle of hollow fibers through which flow can occur 
smoothly is formed. In this arrangement of woven hollow fiber tapes as 
well, it is possible to provide a core (core tube) and to arrange the 
woven hollow fiber tapes essentially without gaps uniformly over the 
remaining annular cross section and to distribute them there.