[0001] A cloth of high tensile and tearing strength is often used for technical purposes,
such as tarpaulins, canopies, air-inflated structures and the like but also for many
other products. Such a cloth comprises a ground fabric of multi-fibre, approximately
equally coarse threads of polyamide, polyester or other synthetic material of high
tensile strength, which are interwoven with approximately the same set of warp and
weft, the finished ground fabric being coated with a plastics or elastomer material,
such as polyvinylchloride, polyurethane or a polymer of 2-chlorobutadiene. It is desired,
with a given fabric weight per surface area, to obtain optimum strength properties
of the coated fabric. To attain optimum strength properties it is essential to reach
a balance of the tensile strengths in the warp and weft directions and at the same
time a balance of the tearing strengths over warp and weft.
[0002] Generally, there is no problem in balancing the tensile strengths in the warp and
weft directions. With the same yarn thickness for warp and weft said tensile strengths
in fact are largely equally high, using the same set of warp and weft. Certainly,
the weft mostly is slightly weaker but this difference is principally marginal and,
if desired, can readily be balanced by a slight increase of the set of weft. It is
considered that the somewhat lower tensile strength of the weft is due to the weft
threads not lying quite as straight as the warp threads in the fabric. When being
tested as well as in practical use the thread systems will therefore be placed under
non-uniform load, resulting in a lower tensile strength in the weft direction.
[0003] A more complex problem is encountered with regard to the balancing of the tearing
strengths over warp and weft. Starting from a plain cloth with 2 ends and fully symmetrical
setting, the tearing strength over the weft will usually be only about 60% of the
value of the tearing strength over the warp. The explanation is that in the coating
operation the coating material is urged in between the individual fibres in the weft
yarn to a much greater extent than in the warp yarn. As a result, the weft yarn becomes
stiffer and the tearing strength drastically decreases.
[0004] To compensate for this, one has in many cases turned to using a simple double-faced
warp rib. It has thus been possible largely to triple the tearing strength over the
weft, but at the same time the tearing strength over the warp decreased by about 20%,
making the cloth still unbalanced.
[0005] Going the whole way and reinforcing the warp in the same manner, one will obtain
a 2/2 dice weave. It has, however, been found that one must at the same time increase
the set of both warp and weft by about 33% in order that the fabric shall permit being
handled without any thread displacements. Now, the same thing happens again, i.e.
the tearing strength over the warp triples whereas the tearing strength over the weft
decreases by about 20%.
[0006] The object of the present invention is to eliminate the above-described problems
encountered in providing balanced optimum strength properties in a cloth intended
for technical purposes, such as tarpaulins, canopies, and the like, of the type indicated
in the preamble of the appendant claim. This object has been realized in that the
threads are interwoven in a weave pattern the repeat of which comprises six warp threads
and six weft threads, the first and fourth weft threads passing over the first, second,
fourth and fifth warp threads, the second weft thread passing over the first, third
and sixth warp threads, the third weft thread passing over the second, third and sixth
warp threads, the fifth weft thread passing .over the third, fourth and sixth warp
threads, and the sixth weft thread passing over the,third, fifth and sixth warp threads.
[0007] The invention is based on the observation that it is possible, in connection with
the plastics coating of ground fabrics, to attain balanced strength properties in
the finished cloth by using for the manufacture of the ground fabric of the cloth
a weave pattern that has been especially designed for the purpose. Said weave pattern
is illustrated in the accompanying drawing. Each small square of the drawing corresponds
to a point of cross-over of a warp thread and a weft thread, every horizontal row
of squares thus corresponding to a weft thread and every vertical row of squares corresponding
to a warp thread. The crossed squares indicate that the warp thread at the respective
cross-over point passes over the weft thread, while every empty square implies that
the weft thread at the respective cross-over point passes over the warp thread. At
the upper left of the drawing figure, thicker lines define a square comprising six
warp threads and six weft threads. This is the pattern repeat for the weave pattern
in question. The portion of the fabric pattern illustrated in the drawing comprises
four pattern repeats for a clear showing of the nature of the pattern.
[0008] The repeat of the weave pattern illustrated in the drawing comprises, as mentioned
above, six warp threads and six weft threads. The first and fourth weft threads pass
over the first, second, fourth and fifth warp threads, the second weft thread passes
over the first, third and sixth warp threads, the third weft thread passes over the
second, third and sixth warp threads, the fifth weft thread passes over the third,
fourth and sixth warp threads, and the sixth weft thread passes over the third, fifth
and sixth warp threads.
[0009] Cloths having a ground fabric of the 2-end type, warp-rib type, 2/2 dice type and
a ground fabric with a weave pattern according to the present invention were manufactured
for illustration of the effect of the invention. The same yarn was employed for all
ground fabrics, and the yarn was used for both the warp and the weft of the fabrics.
The different ground fabrics were then coated with a plastics coat of the same kind
and in the same manner, after which the finished cloths were subjected to tensile
strength tests (5 cm wide strips) in both the warp and the weft direction as well
as to tearing tests over both the warp and the weft. The results will appear from
the following Table.
[0010] The Table shows that the cloth according to the invention had equally good and balanced
tensile strengths in the warp and weft directions as the cloths having a weave with
2 ends and warp rib, but the tearing strengths over warp and weft were practically
the same and substantially higher (approximately 100% or more) than the tearing strength
in the poorest direction for the said two other cloths, simultaneously as the grammage
and thickness of uncoated fabric and the set were practically the same in the three
cases. With regard to the cloth having a ground fabric of 2/2 dice weave it should
be observed that the tensile strengths and the tearing strength over the warp certainly
were higher than for the cloth according to the invention, but the tearing strength
over the weft was somewhat lower. Besides, it should be taken into consideration that
the cloth of 2/2 dice weave, for the reasons earlier indicated, had to be woven with
a substantially higher set and, consequently, substantially higher grammage and thickness
for untreated fabric. Thus the cloth having a 2/2 dice weave was much more expensive
to manufacture and had a substantially unbalanced tearing strength over warp and weft.
Cloth of high tensile and tearing strength comprising a plastics- or elastomer-coated
ground fabric of multi-fibre, approximately equally coarse threads which are interwoven
with approximately the same set of warp and weft, characterised in that the threads
are interwoven in a weave pattern the repeat of which comprises six warp threads and
six weft threads, the first and fourth weft threads passing over the first, second,
fourth and fifth warp threads, the second weft thread passing over the first, third
and sixth warp threads, the third weft thread passing over the second, third and sixth
warp threads, the fifth weft thread passing over the third, fourth and sixth warp
threads, and the sixth weft thread passing over the third, fifth and sixth warp threads.
