Multifilament thread and method of forming same

A flexible thread consisting of filaments held together by twisting, which thread is made of a polymer base material wherein all of the individual filaments of the thread are encased in a synthetic resin and embedded therein so that adjacent filaments are intimately bonded to one another, the synthetic resin being in partially cured state, chemically stable at room temperature, the resin being fully curable by heating; the thread can, therefore, be woven into a mesh before final curing to harden the thread.

The invention relates to a multifilament thread consisting of filaments 
held together by twisting, which filaments are made of polymer material 
and which thread is coated with a synthetic resin. 
Meshes, fabrics and felt combinations are used in the drying zone of a 
papermaking machine and must ensure troublefree transportation and an 
optimum drainage effect of a paper web. These meshes are made to measure, 
suited to the particular dimensions of the papermaking machine. Making to 
measure demands extremely high standards from the thread employed, in 
respect of general uniformity, and specifically in respect of the 
length-elongation characteristics. Particular importance attaches to the 
features of stiffness and dimensional stability of the threads running 
transversely to the machine direction, whilst on the other hand the 
lengthwise threads (in the direction of travel of the wire) should be 
distinguished by dimensional stability and flexibility. Resistance to 
hydrolysis on exposure to superheated steam at atmospheric pressure, to 
which the meshes in the drying section of the papermaking machine are 
constantly exposed during operation, and passive, and where necessary also 
active, soil repellancy are amongst the properties which substantially 
influence the operating ability and working life of the drying meshes. 
Apart from the fact that because of being individually made to measure the 
meshes are expensive, the stoppages of high output papermaking machines 
resulting from mesh defects additionally cause substantial costs. The 
demands made of the thread material of the drying meshes have risen to an 
exceptional degree in respect of purpose-oriented chemical-technological 
and physical properties. The threads from which meshes and mesh felt 
combinations for the drying sections of papermaking machines are nowadays 
manufactured are in the main drawn or spun from polymeric substances, and 
the base yarn or thread is either raw or is finished with synthetic 
resins. Mesh fabrics made from raw threads are also treated, in the form 
of sheet-like structures, with synthetic resins. However, it has been 
found that the threads which have already been treated with synthetic 
resins before the manufacture of the wire make it possible to achieve a 
qualitatively better drying mesh which also gives higher productivity. 
The threads manufactured and finished in the conventional manner can be 
classified in three groups in accordance with their schematic 
cross-sectional appearance, namely; 
Group 1: Monofilaments (FIG. 1) 
Group 2; Raw multifilaments (FIG. 2) 
Group 3; Multifilaments with synthetic resin applied by a dipping process 
(FIG. 3). 
Group 4: Multifilaments with a thermoplastic covering applied by extrusion 
(FIG. 4) 
The thread material shown in FIG. 1 is employed with diameters of up to 0.5 
mm. However, the polyester monofilaments, which are known to be 
dimensionally stable, do not yet possess any special protection against 
hydrolysis, in spite of specific improvements in the polymeric substance, 
so that the dreaded fibrillation effect is a shortcoming which must be 
accepted. In contrast, polyamide multifilaments are more resistant to 
hydrolysis but are unsatisfactory in respect of dimensional stability. 
According to FIGS. 2 and 3, multifilaments are also employed as a starting 
material for the manufacture of meshes, because of the crosslinking of the 
applied synthetic resin with the outer filaments of the thread. 
British Registered Design 1,958,017 shows, for example, a mesh fabric of 
polyester yarn encased in synthetic resin. The invention starts from this 
prior art. 
Advantageous aspects of such a multifilament threads are the good stability 
of shape or dimensional stability of the polyester coupled with the 
synthetic resin stiffening, which at the same time acts as protection 
against hydrolysis, but causes the thread core (see FIG. 3) to remain raw, 
so that it suffers more rapid hydrolytic degradation with increasing 
mechanical wear of the synthetic resin covering. Synthetic resin-covered 
multifilament threads, which compared with monofilament threads are 
thicker and have a higher tensile strength, as a rule give a dimensionally 
stable mesh with a smaller number of threads, so that the weaving process 
becomes more economical. Furthermore, the necessarily more open mesh also 
favours the rate of evaporation. On the other hand, the stiffness of these 
conventional threads presents processing problems during bobbin-winding 
and weaving. Accordingly, even polyamide multifilament threads which are 
more resistant to hydrolysis by virtue of the nature of the polymeric 
substance, and the Dralon multifilaments which are distinguished by even 
better hydrolysis resistance, can only be employed with certain 
limitations, to which of course the poor stability of shape or dimensional 
stability, which is specific to the material, also contributes, very 
particularly in the case of Dralon multifilament threads. 
As shown in FIG. 4, a thread is known in which raw multifilament polyester 
thread is surrounded by a plastics covering in the manner of a sleeve, 
without the covering being intimately bonded to the multifilament core. 
The covering can be pulled off mechanically. The stiffening is low in 
spite of a quantitatively high proportion of thermoplastic covering for 
which reason a dimensionally stable mesh cannot be expected from this 
thread material alone. Furthermore, should the cover become damaged, the 
core, which comprises polyester multifilaments and is prone to hydrolysis, 
is directly exposed to the moist heat in the drying section, for which 
reason local hydrolytic degradation takes place relatively rapidly. 
Amongst the previously described known threads for drying meshes there are 
none which do not exhibit at least one important negative characteristic 
in respect of their use properties in a drying wire. 
It is an object of the present invention to provide an improved 
multifilament thread which does not exhibit the disadvantages of the prior 
art threads. 
In accordance with the present invention, there is provided a flexible 
thread consisting of filaments held together by twisting, which thread is 
made of a polymer base material wherein all of the individual filaments of 
the thread are encased in a synthetic resin and embedded therein so that 
adjacent filaments are intimately bonded to one another, the synthetic 
resin being in partially cured state, chemically stable at room 
temperature, the resin being fully curable by heating. 
Accordingly, the invention departs from the known surface treatment of the 
thread and provides a thread in which the resin reaches the core of the 
thread. As a result, the core region of the thread can be made relatively 
hard or flexible depending on the resin used. If a polyester filament is 
employed, the resin may serve to protect the polyester from hydrolysis at 
the core. 
The synthetic resin, preferably, is curable on heating (by incorporation of 
a catalyst or curing agent) at 160.degree. to 210.degree. C. This makes it 
possible initially to produce the thread in a flexible form suitable for 
processing, so that it can be wound on bobbins even with a small radius 
and so that it can be handled during weaving without resulting in breaks 
and kinks or other permanent deformations of the thread. Only on treatment 
at a temperature substantially above room temperatures, say in the region 
from 160.degree. to 210.degree. C., can the thread be cured so that it 
acquires substantial stiffness and dimensional stability so as to perform 
its functions in a manner which take into account the conditions to which 
it is exposed, for example as a mesh fabric. The final curing temperature 
is also separated by a distinct interval from the evaporation temperature 
of the solvent for the resin. No hardening of the thread takes place at 
room temperature. 
It is particularly advantageous if the resin consists of an unmodified 
epoxy resin mixed with a plasticised epoxy resin and a hot-curing 
catalyst. The two epoxy resins have the advantage that they can be 
employed together in any mixing ratio, which can be chosen at will in 
accordance with the desired further processing properties of the thread. 
In the case of a particularly flexible thread, a higher proportion of 
plasticized resin is employed than in the case of a thread which is 
required to exhibit a certain hardness already in the state in which it is 
processed further. The catalyst can be modified dicyandiamide or a boron 
trifluoride/monoethylamine complex. 
The structure of the synthetic resin, viewed radially from the centre of 
the core to the periphery of the thread, can also be predetermined. Thus 
it is possible to have a proportion of synthetic resin which 
quantitatively increases from the thread core outwards, or a proportion of 
synthetic resin which is specifically qualitatively oriented from the 
thread core outwards, which in conjunction with the polymeric synthetic 
multifilaments results in a soft flexible thread having particularly 
advantageous processing characteristics, which thread does not change its 
condition on ambient storage and only cures on exposure to elevated 
temperatures, the resulting degree of stiffness depending on the 
particular predetermined characteristics. In order to increase the 
flexibility and permanent elasticity of the thread, the synthetic resin 
can contain a high proportion of internally plasticised epoxy resin. It is 
also possible additionally to cover the compact entire thread with a layer 
of synthetic resin. The covering can determine the strength of the thread, 
which is required for further processing, whilst the thread core is 
relatively soft and flexible and is only fully cured after further 
processing. 
The synthetic resin and the filament material are matched to one another. 
The filament material of the thread may consist of polyester, polyamide, 
polyacrylonitrile, aramide, glass or the like, alone or in a mixture e.g., 
of polyester with polyacrylonitrile or polyester with nylon and 
polyacrylonitrile. 
As a result of the construction, according to the invention, of the new 
thread, the processability during the bobbin-winding and weaving process 
is better compared to that of conventional thread material, and this has 
an effect on the mesh quality as a result of optimised precision, and also 
reduces waste. This is associated with substantial cost savings. 
Furthermore, certain structural effects in the mesh fabric can be achieved 
if, for example the lengthwise thread is woven in an already fully cured 
or substantially cured state, whilst the weft is introduced as a soft 
thread which is only subsequently cured in the mesh. the converse use of 
the threads is also possible. The flexible thread has a further 
substantial advantage. It does not eliminate any volatile substances 
during the heat aftertreatment and thus does not pollute the environment 
in the subsequent processing stages, in contrast to known threads finished 
with phenolic resin. It is clear that the adhesion of the resin to the 
filaments is excellent because the combination is present throughout the 
thread. This is the basis of optimum protection of the thread when exposed 
to mechanical stress, as well as of dimensional heat stability and of 
resistance to chemicals, solvents and water. Of course, the embedding of 
the individual filaments in the thread results in the case of polyester 
multifilaments, in excellent protection against hydrolytic degradation in 
moist heat, for example in the medium resulting from evaporation on a 
papermaking machine. Polyester filaments possess stability of shape, and 
dimensional stability, which are specific to the material and which are 
further optimised by the thread treated according to the invention. 
A process according to the invention for the manufacture of such a thread 
from polymer filaments, which thread is dipped in a synthetic resin is 
characterised in that in order to impregnate the thread with synthetic 
resin solution as far as possible into the thread core, the thread is 
dipped, with little tension, and then with alternate pushing and pulling, 
and that after evaporation (full or partial) of the solvent, the synthetic 
resin is partially cured and is thereby bonded to the filaments. In this 
context it is important, firstly, that the thread should be passed through 
the dipping bath under little tension, so that the individual filaments 
located on the surface leave appropriate gaps between them, through which 
the synthetic resin solution can penetrate into the thread core. This 
treatment is followed by alternate pushing and pulling of the thread in 
the dipping bath, somewhat comparable to the accelerated impregnation of a 
sponge with water by compressing the sponge material and then allowing it 
to spring back automatically. During the pushing, the synthetic resin 
solution is uniformly sucked into the thread core. After evaporation of 
the solvent, the synthetic resin is partially cured. The degree of curing 
depends on the desired further processing characteristics of the thread. 
Before dipping, the filaments are loosened. This can be effected by 
repeatedly bending the thread in a bending unit. This process step is 
particularly important if the raw thread has been brought, by a prior 
thermal treatment, to a reproducible starting condition with corresponding 
starting properties. In order to orient the force-elongation properties 
and decide the heat-shrinkage properties, it is thus possible to carry 
out, prior to dipping, a heat treatment of the raw thread at temperatures 
of about 180.degree. to 250.degree. C., during which the raw thread is 
also stretched, shrunk or kept at the initial length, depending on the 
different properties of the raw thread material as supplied. Furthermore, 
it is important that the raw thread treated in this way should be cooled 
approximately to room temperature before dipping, so that polymerisation 
should not occur immediately in the dipping bath. After such a heat 
treatment and before dipping, the raw thread is subjected to several 
changes in direction, that is to say it is bent and opened up, especially 
in the surface region. This prepares the raw thread for impregnation in 
the dipping bath. 
It is particularly advantageous to lead the raw thread, which has been 
impregnated as far as the thread core, vertically out of the dipping bath, 
so that irregularities in impregnation with the synthetic resin solution 
can still level out as a result of running-together. This effect manifests 
itself particularly in the gravitational direction. 
After leaving the dipping bath, the impregnated raw thread is dried until 
the solvent has completely evaporated, this drying of course being carried 
out at a lower temperature than that corresponding to curing. For drying, 
temperatures of about 80.degree. to 150.degree. C. can be used. The object 
of this process step is to ensure that the thread is dressed with a 
proportion of resin which, both quantitatively and qualitatively, is very 
uniform from the inside to the outside of the thread. 
However, it is also possible to use a method wherein the impregnated raw 
thread, after leaving the dipping bath, is only partially dried, with 
partial evaporation of the solvent, and is subsequently passed through a 
further dipping bath containing a resin solution of thicker consistency or 
containing a different resin/catalyst combination, after which the thread 
is dried until the solvent has completely evaporated. In this case, the 
partial evaporation of the solvent first takes place at about 120.degree. 
to 140.degree. C. This is followed by the second dipping process. The 
total evaporation of the solvent can then be carried out at 80.degree. to 
150.degree. C. The object of this process step is to dress the thread with 
a proportion of resin which quantitatively increases from the inside to 
the outside, and/or to dress it with a qualitatively oriented resin 
component. 
It is particularly advantageous to carry out any subsequent partial curing 
of the synthetic resin under increased thread tension. This achieves 
intimate bonding to the filaments during the partial curing of the resin, 
so that a soft supple thread is produced, which is easy to process and 
which can be cured in a subsequent heat-treatment process, so as to 
acquire its final properties. 
A further variant consists of a method wherein between the first and second 
dipping process of the raw thread a partial curing of the synthetic resin 
takes place and that after the second dipping process a complete curing of 
the resin coating applied in the second dipping bath, and possessing a 
plasticised permanently elastic character, takes place. This achieves a 
dressing of the core of the thread, which is only fully cured, during a 
subsequent heat treatment, whilst the thread material is easily processed 
further because of the soft thread core and, as a result of the already 
cured but flexible, permanently elastic coating acquires surface 
protection against mechanical stress during processing, which protection 
of course also still manifests itself advantageously in the case of the 
finished product. The converse of this variant is also possible; in this 
case, the plasticised flexible permanently elastic epoxy resin is 
introduced into the thread core and the outer film is made hard but 
flexible. This, in conjunction with the filaments of the thread, improves 
the damping properties and hence the compressibility of the mesh felt 
combination which travels under pressure in a papermaking machine.

FIG. 1 shows a monofilament 1, that is to say a single thread of relatively 
large diameter, which as such is prior art. FIG. 2 shows a multifilament 
thread 2 consisting of a plurality of filaments 3 at the surface of the 
thread 2 and further similar filaments 4 in the core region of the thread. 
FIG. 2 shows the multifilament thread 2 in a completely untreated 
condition, that is to say the raw thread. 
The multifilament thread 2 according to FIG. 2 can, according to FIG. 3, be 
provided, by a dipping process with an application of synthetic resin, 5, 
which however at best extends to the region of the filaments 3 on the 
outer surface of the thread 2, whilst the core region, that is to say the 
filaments 4, remain free from synthetic resin. 
A further thread 2 of the prior art is shown in FIG. 4. In this case, an 
extruded thermoplastic synthetic resin covering 6 is applied to the 
filaments 3 and 4; this covering does not even form an intimate bond with 
the filaments 3 on the surface, and instead can be pulled off 
mechanically. 
FIG. 5 shows the thread according to the invention, consisting of the 
multifilament thread 2 comprising the filaments 3 and 4. Between all of 
the filaments 3 and 4 there is synthetic resin 7, in which the individual 
filaments 3,4 are completely embedded and enclosed. The synthetic resin 7 
is intimately bonded to the individual filaments 3 and 4. 
FIG. 6 shows a further embodiment of the thread 2 according to the 
invention, which has an internal structure like that of FIG. 5 and, in 
addition to the synthetic resin 7 in the core, a synthetic resin covering 
8 is applied externally, which covering may impart to the thread, in the 
region of the surface, a different property to that aimed at in the core 
region by using the synthetic resin 7. 
The process for the production of the thread according to the invention is 
explained in detail, in relation to FIGS. 7 to 10, of which FIGS. 7a, b, c 
show sketches, in sequence summarising the principle of the entire process 
and the installation employed for the process, whilst FIGS. 8, 9 and 10 
are each to be regarded as successively adjoining one another and show 
three parts of the installation according to FIG. 7. 
The raw polyester filaments which run off the creel 9 are formed, by means 
of a guide rod 10 and a guide rail 11 into a bundle of aligned filaments. 
This filaments bundle passes a tensioning beam 12, guide rollers 13 and 
14, a group of rollers forming a stretching unit 15, and a guide roller 
16, and is fed via a guide roller 17 into a heating tunnel 18, through 
which the filament bundle travels back and forth over guide rollers 19, 20 
and 21; thereafter the bundle is taken up, via a guide roller 22, by a 
further group of rollers forming a stretching unit 23. The speeds of the 
groups of rollers of the stretching units 15 and 23 are infinitely and 
independently variable, so that the length of thread between these groups 
of rollers can be longitudinally stretched, shrunk or kept at the initial 
length. Heating in the heating tunnel 18 is carried out at a high 
temperature, viz 180.degree. to 250.degree. C., (preferably 236.degree. 
C., in the case of a polyester) to heat-set the filaments in the bundle, 
so that the bundle acquires stable force-elongation properties after 
cooling to room temperature. The resulting thread is `after cooling` 
mechanically stressed, via guide rollers 24, 25, 26 in a thread-bending 
unit 27, which may consist of rotating and/or stationary shafts of about 
30 mm diameter, so that any stiffening or mechanical sealing of the thread 
surface, resulting from the heating step, tensioning step or by spin-dip 
and possible other surface treatments is reduced; the thread is then taken 
up, via a guide roller 28, by a group of rollers forming another 
stretching unit 29. The thread 2, reproducibly prepared to this stage, is 
delivered via a guide roller 30. The raw thread pretreatment, in the 
section from the stretching unit 15 up to and including the stretching 
unit 29, which is integrated in the process of manufacture according to 
the invention, prepares the thread to an optimum starting condition for a 
synthetic resin finishing process. The thread passes, via guide rollers 31 
and 32, under little tension, into a dipping bath 33 (FIGS. 7 and 9) 
contacting the resin. In the section of the dipping bath 33 into which the 
raw multifil thread 2 is introduced under little tension, the resin 50 
penetrates, by capillary action, into the thread 2 between dipping rollers 
34 and 35 in the bath, which is provided with automatic level regulation. 
After passing over the dipping rollers 35, the thread passes through a 
slalom zone, over which the rollers 36 to 40 are driven at infinitely 
variable speeds, the speeds differing, in accordance with the desired 
effect, both between one another and, as a group, from the speeds of the 
dipping rollers 34 and 35, so that the rollers exert a push-pull effect on 
the thread bundle. This construction of the dipping station 33 to 40 
ensures optimum penetration of the resin 50 into the multifilament thread 
2 as far as the thread core (compare FIG. 5). The thread leaves the 
dipping station 33 to 40 vertically upwardly via a roller 40, if necessary 
also with subsequent flanking contact with doctoring rollers 41 and 42 
which can be pivoted onto, and away from, the thread. This arrangement 
results in even distribution of the resin in the thread. A guide roller 43 
guides the thread into an evaporation tunnel 44, through which it passes, 
via guide rollers 45 and 46, to a guide roller 47, after which it passes 
through a dipping bath 48 possessing dipping rollers 51 and 52. In this 
bath the thread which is already impregnated with synthetic resin receives 
an additional surface application a resin, which may be the same as that 
in the dipping bath 33 to 40, or may be a different resin 50'. This resin 
50', may be a modified thermally self-curing liquid epoxy resin; the 
thread is then passed, via a guide roller 49, into an evaporation tunnel 
44 (or alternatively is passed, without a by-pass 47,48,49 from the guide 
roller 46 directly further through the evaporation tunnel 44) over 
subsequent guide rollers 53, 54 and 55 and as far as a guide roller 56, 
from where it continues via a guide roller 57 into a group of rollers 
forming a stretching unit 58. The last treatment zone, which now follows, 
incorporates guide rollers 59 and 60, and a heating tunnel 61 possessing 
guide rollers 62, 63, 64 65. Instead of being lead directly into the 
heating tunnel 61, the thread can be led from the guide roller 59 via a 
guide roller 66 into a further dipping bath 67, filled with a resin 50", 
via dipping rollers 68, 69 and 70, then to the guide roller 60 and from 
there into the heating tunnel 61. Any combination between the dipping 
baths 33, 48 and 67 is possible. 
The thread then passes via guide rollers 68, 69 (FIGS. 7 and 10) to a 
further group of rollers (stretching unit 70). The group of rollers 71 
ensures that the individual threads of the thread bundle are transferred, 
without slippage, to a bobbin-winding machine 72 for winding up the 
thread. 
The speeds of the groups of rollers of the stretching units 29, 58, 70 and 
of the stretching units 15 and 23 are infinitely variable, independently 
of one another, within predetermined programmes, so that the thread bundle 
can forcibly be influenced in the longitudinal direction between any two 
groups of rollers, which can also, in general terms, be described as 
stretching units. As a result, the thread can, as in the dipping stations, 
be run under little tension in the solvent evaporation zone, so that the 
solvent can more readily escape from the thread core. The hot air flowing 
in metered amount into the evaporation tunnel 44 can be at a temperature 
of 80.degree. to 160.degree. C. For practical purposes, this air takes up 
the medium resulting from evaporation, and is fed, as a defined solvent 
vapour/air mixture, to a solvent recovery installation, which at the same 
time serves as a waste air installation, via the tunnel 73. In the heating 
stage, the resin/curing agent material present as a dressing on all 
individual filaments 3,4 forms a homogeneous bonding material in the 
multifilament thread 2, which in the subsequent stage, in the heating 
tunnel 61, at temperatures of 90.degree. to 180.degree. C. preferably 
140.degree. C., only partly polymerises to the stage that the final 
condition of the thread is still soft and flexible. A subsequent heat 
treatment of a mesh produced from these new threads, is required to 
complete polymerisation, this treatment being carried out at 170.degree. 
to 210.degree. C. depending on the construction and weight per unit area 
and depending on the heat-setting installation, including the temperature, 
residence time and nature of the heating medium (contact heat, convection 
heat or radiant heat). As a result of this curing, the final 
characteristics of the thread 2 develop and as a direct consequence 
determine the improved characteristics of the mesh. 
In summary, of the continuous five-stage finishing process; 
In the first stage, a longitudinal change of the raw thread bundle by 
exposure to a high temperature (180.degree. to 250.degree. C.) occurs. 
This has the purpose of bringing the force-elongation characteristics and 
the heat shrinkage characteristics to the technological requirements in 
the end product, for example the mesh. The second stage is cooling of the 
thread to room temperature and breaking-up of the stiffening effect 
produced in the heat-treated raw threads, as well as a loosening of the 
filaments in the thread and the introduction of the thread, under little 
tension, into the dipping station. This second stage serves the purpose of 
optimising the absorbency of the heat-pretreated threads. The third stage 
embraces the impregnation of the thread bundle with a synthetic resin 
solution by means of a two-stage dipping process with a capillary action 
stage and a push-pull stage, to bring about optimum impregnation of the 
thread with the resin. In the fourth stage, one alternative is that a 
partial evaporation of the solvent takes places in hot air at 120.degree. 
to 150.degree. C.; thereafter, a second dipping process in a solution of 
thicker consistency or with a different resin is carried out and 
thereafter the solvent is evaporated virtually completely in hot air, 
preferably at 80.degree. to 160.degree. C. This serves the purpose of 
producing the thread dressing with a proportion of resin which increases 
quantitatively from the inside outwards, and/or with a resin component 
which is qualitatively oriented. In the other alternative, the solvent can 
be fully evaporated in hot air at 80.degree. to 160.degree. C. on the 
direct path through the evaporation tunnel without an interposed second 
dipping process, in order to obtain a thread dressing with a resin content 
which, from the inside outwards, is homogeneous. 
In the subsequent fifth stage, partial polymerisation by means of a short 
residence time in hot air at 80.degree. to 160.degree. C. under increased 
thread tension is effected. This process step serves the purpose of 
achieving incipient curing of the resin and bonding of the resin to the 
filaments which provides the strength, so that a soft supple thread, which 
is easily processable, is produced, which thread can be fully cured in a 
subsequent heat-treatment process, so as to acquire its final properties. 
A catalyst (or curing agent) is used which is effective only at high 
temperatures. Variants are also possible: a partial polymerisation of the 
resin which has penetrated into the thread in the first dipping process 
and encloses the individual fimaments, and which possesses the character 
of a thermosetting resin, is carried out, and at the same time complete 
polymerisation of a thermoplastic resin coating which is applied in the 
second dipping process, is effected. This is done with the object of 
providing a core which only undergoes complete polymerisation during a 
subsequent heat treatment of the mesh but which is surface-protected 
against mechanical stress, during processing until the final mesh is 
produced. 
An inversion of this variant, in which the thermoplastic resin is 
introduced into the thread core and the outer film is thermosetting but 
flexible, improves the damping properties of the thread and hence the 
compressibility of a mesh/felt structure which travels under pressure in a 
papermaking machine. 
In the process described above for the manufacture of a thread. A synthetic 
resin mixture of two liquid epoxy resins, of which one is unmodified and 
the other incorporates a plasticiser, has been found to be especially 
suitable. Both resins are 100% reactive and are miscible with one another 
in all ratios. In the lengthwise warp threads of the mesh, for example, 
the resin with the plasticiser should predominate, whilst in the weft 
threads the unmodified resin should predominate. As a result of this the 
mesh, in the cured state, remains suitably flexible in the machine 
direction, and has good dimensional stability, whilst in the transverse 
direction it becomes stiffer and markedly of stable shape. The liquid 
resins should be diluted with a suitable solvent so as to give a solids 
content of, preferably 30 to 40%. However, solutions with a solids content 
of 5 to 60% can also be used. Admittedly, numerous conventional solvents 
were found to dissolve the synthetic resins, but failed to dissolve the 
hot-curing agent present as a crystalline powder. Only one solvent was 
found which satisfactorily dissolved both all the suitable epoxy resins 
and the hot-curing agent, which agent is for example, a modified 
dicyandiamide or boron trifluoride/monoethylamine complex, (the hot-curing 
agent should be present in a proportion of 3.5 to 6.0% by weight of the 
resin). The solvent which was found to be particularly suitable, was 
dimethylformamide (DMF). This ensures an unusually long container life at 
room temperature and prevents the formation of agglomerates on the rollers 
over the entire zone of contact with the resin/curing agent solution. 
Presumably, the markedly low volatility of DMF contributes to this fact. 
It is probable that the complete coating of the filaments is favoured by 
this low volatility. 
In practice, the time for the coating resin solution to flow between the 
individual filaments in the thread is extended because, analogously to the 
relatively difficult evaporation of the solvent, the viscosity only rises 
slowly. The quantitative proportion of the resin in the thread for example 
reached a total of 19% as a result of dipping in a solution of 35% solids 
content in dipping stations 33 to 40 and 48, whilst without dipping in 
dipping station 48 it reached a value of about 15%. The preferred object, 
depending on the starting material for the mesh is a resin uptake of 12 to 
20%, but this figure can be reduced to 8% by mechanically increasing the 
tension during dipping.