Coating and calendaring of 2-dimensionally tensioned fabric

A method of coating a fabric material and calendering the material while longitudinally and transversely tensioning the material, the coating being synthetic and being applied to one side of the material, and being heated in a curing oven. Then applying more synthetic material of a similar type to the calendered and heated material and then passing it through another oven and calendering it again before the tensioning is relaxed.

FIELD OF INVENTION 
The present invention relates to improvements in methods of coating a 
fabric with layers of synthetic heat curable plastic material, such as 
polyvinyl chloride, resin, elastomers, etc., to produce a non-shrinking, 
substantially smooth resulting product while at the same time using less 
coating material. 
BACKGROUND AND PRIOR ART 
It is known that in conventional installations, the fabric is unwound from 
a bobbin or other similar supply support, stretched in the longitudinal 
direction, run through a coating machine having a doctor blade which 
deposits a layer of the synthetic material in question on one of its 
sides. The fabric thus coated then passes through a heating oven, at the 
outlet of which it may be subjected to a calendering operation by passing 
between two rotating rollers. Then, it is cooled before being finally 
wound on a support. 
One main drawback encountered in conventional methods resides in transverse 
shrinkage of the fabric, which shrinkage is particularly severe when 
dealing with a fabric produced with synthetic fibres (polyamide or 
polyester). These fibres normally leave the spinning mill in a condition 
in which they are not heat-fixed, so that they undergo an appreciable 
shrinkage effect when they are subjected to an elevated temperature. 
Naturally, shrinkage of this type is a considerable detriment to the value 
of the fabric/synthetic material complex obtained. 
In order to remedy this fault, it has been proposed to produce the basic 
fabric from yarn stabilized by a heat treatment. However, it will be 
understood that this is a relatively difficult operation, it also being 
noted that the cost of the fabric produced from yarn of this type is 
further increased by the fact that the latter has a weight per meter 
greater than that of untreated yarn, without having the better mechanical 
characteristics. Furthermore, fabric made from stabilized yarn has a 
greater coeffeicient of elongation, which is detrimental in many 
applications. Finally, and above all, whatever the quality of the 
stabilization treatment, the shrinkage phenomenon is not completely 
eliminated. 
Now, apart from the above-mentioned drawbacks, the shrinkage of coating 
fabrics opposes the production of complexes in which the basic fabric is 
constituted by a mixture of synthetic yarn and natural, artificial or 
synthetic discontinuous fibres. Coated fabrics of this type would have 
excellent resistance to tearing owing to the presence of continuous yarn, 
whilst having a more agreeable texture due to the discontinuous fibres in 
the case of coating on one side and better adhesion of the coating to the 
fabric with coating on one or two sides. However, a complex of this type 
cannot be envisaged at the present time, owing to the very substantial 
shrinkage differences between the two types of textile fibres, even if the 
synthetics have been previously treated. 
THE INVENTION 
According to the invention there is provided a method for coating fabric or 
similar flexible supports, wherein the support is unwound and placed under 
longitudinal tension, coated with a layer of synthetic material, heated 
for the purpose of gelifying or polymerising the coated material, 
hot-rolled, cooled and wound-up. However, prior to its passage in a coated 
condition through a curing oven and through calendering apparatus, the 
longitudinal edges of the fabric are introduced between retaining members 
of a tenter which accompanies said fabric until the termination of a 
calendering operation and whilst still stretched in the transverse and 
longitudinal directions, it is subjected to at least one second similar 
coating operation on the same side, whilst the first coat is still hot. 
In order to provide as smooth a surface of the finished coated fabric as 
possible while using a minimal amount of coating material to achieve the 
purpose, the present invention teaches the use of two successive coatings 
at two successive stations, rather than merely filling the fabric with a 
single coating in a one-stage operation. Moreover, the fabric must be 
coated as thinly as possible, not only for economy reasons but also to 
preserve flexibility of the fabric. When the fabric to be coated is 
initially unrolled, the plastic threads of the fabric are not all 
uniformly tensioned and have a strong tendency to shrink when heated. When 
one attempts to provide a smooth finish on one side of the fabric using 
only a single coating step followed by calendering and heat treating, the 
grain of the fabric show through to a considerable extent, and thus grain 
is not uniform over the entire fabric surface because some threads tend to 
stick up more than others above the surface of the fabric through the 
coating since they are not all equally tensioned. The applicant has found 
that by applying a first coating and heat curing that coating and 
immediately calendering the coating, he can make the nubs of the fabric 
lie down and be essentially uniform in height. Thereafter, when a second 
coating is applied on top of the first coating which has alreadly been 
cured, a relatively thin coating can be used as the second coating because 
the nubs of the fabric are essentially the same height all over, and 
therefore it is only necessary to fill the surface of the fabric to that 
particular height in order to produce a fabric having a smooth and uniform 
appearance over its entire surface. In other words, the application of the 
first coating not only seals the fabric so that the second coating will 
not pass all the way through it, but it also holds down threads of the 
fabric which might otherwise stick up higher than other threads since the 
threads used in the initial fabric are not entirely stabilized. The 
continuous transverse and longitudinal tensioning applied to the fabric 
during the heat treating and calendering of the first coating and during 
the entire second coating, heating and calendering steps, also pulls the 
threads down and tends to hold them essentially at the same height, 
whereupon the tensioned threads will be set at the crossings of the warp 
and weft by the subsequent calendering operation. Thus, the thickness of 
the second coating can be reduced, and is much less than the thickness 
which would be required if the fabric were released from tension and 
allowed to cool between the two coating steps. 
It is the object of the improvements to which the present invention 
relates, to remedy the aforementioned drawbacks and to achieve the 
production of a smooth-surface coated fabric which is not subject to any 
shrinkage during its manufacture.

Referring to the drawings, the installation illustrated in FIG. 1 comprises 
an unwinding station able to receive a bobbin or reel 1 supporting the 
fabric 2 to be coated in the wound state. This fabric 2 passes through a 
longitudinal tensioning mechanism 3 before being supplied to a coating 
station 4 arranged in the customary manner. This station 4, appropriately 
supplied with synthetic material, deposits a film or layer of synthetic 
material on the fabric 2 by means of a doctor blade. 
According to the invention, on leaving the coating station 4, the fabric 2 
passes to a station 5, in wich its longitudinal edges are introduced in 
lateral retaining means (grippers, hooks etc.) of a tenter of the type 
used in the textile-finishing industry or the like. The reference numeral 
5' designates one of the grippers of a tenter of this type, supported by 
lateral chains longitudinally displaced in exact synchronism with the 
fabric 2. Naturally, these chains are guided in order to keep the coated 
fabric 2 in a stretched condition in the transverse direction, without any 
possibility of shrinkage. 
The coated fabric 2 retained in this way by the tenter then passes through 
a curing oven 6 in which the synthetic material deposited forms a gel or 
polymerises in the usual manner, being at least partially cured at this 
stage. In this oven, the coated fabric 2 is supported from a place to 
place by transverse drums 6' able to oppose any sagging of said fabric in 
the transverse or longitudinal direction, these drums being cooled and 
driven in rotation. On leaving the oven 6, the fabric 2, still retained by 
the tenter, travels in hot condition to a calender 7, comprising two 
superimposed rollers, one of which may have projecting parts able to make 
an impression in the layer of synthetic material. 
On leaving the calender and whilst it is still in a hot state, the coated 
fabric 2, still retained by the tenter, is subject to a new coating with 
similar heat curable plastic applied on the same side of the fabric at a 
second station 8 similar to the first station 4. It will be understood 
that this coating is carried out on a complex which has already been 
heat-treated and subjected to calendering, such that the smoothness 
characteristics of the second layer thus deposited are considerably 
improved. 
After this coating operation, the fabric 2 passes successively through a 
second curing oven 9 provided with support rollers 9' and a calendering 
station 10 identical to the first. Then the tenter which was tensioning 
the fabric widthwise is removed at station 11, and the fabric is passed 
through tensioning rollers, is further cooled, and wound-up at a station 
12. 
Tests have shown that a coated fabric is obtained having no shrinkage 
effect, in the sense that its width when coated and wound-up at the 
station 12 is absolutely identical to the width of fabric 2 wound on the 
initial support 1, whatever the nature (natural, artificial, synthetic, 
etc.) and constitution of this fabric. Consequently, it is possible to use 
untreated yarn or fibres, which are clearly lighter. In addition and above 
all, it is possible, particularly in the weft, to alternate various types 
of material without any risk of differential shrinking, which makes it 
possible to create new articles from the coated fabric obtained. 
It is interesting to note that if the widthwise stretching produced by the 
tenter 5', and the longitudinal tensioning ensured between the 
longitudinal tensioning station 3 and the second calender 10 oppose any 
shrinkage nevertheless the warp and weft threads themselves do undergo 
shrinkage, which has the result of flattening the fabric and smoothing out 
the nubs from the surface of the latter. It has been possible to verify 
that the decrease in thickness was of the order of 25%, so that ultimately 
the fabric 2 was in the form of a virtually smooth support similar to a 
strong sheet of paper. Under these conditions it will be understood that 
perfectly regular coating is achieved. With an equal weight of synthetic 
material per square meter, the covering is clearly improved and the 
adhesion of this material to the fabric is considerably facilitated. In 
addition, depending on the textures, the synthetic material may penetrate 
the fabric, through which is passes at least partially, such that the 
reverse side is finally covered as well as the front side. 
For the purpose of further improving the uniformity of coating, it is 
possible to adopt the modification illustrated in FIG. 2, in which the 
positioning of the tenter for widthwise stretching (station 5) is carried 
out prior to the first coating step (station 4). In other words, the 
fabric or support 2 receives the film of synthetic material when it is 
already transversely stretched, a heating unit 13 being advantageously 
provided upstream of the coating station 4 for ensuring heat tensioning 
and at least temporary fixing of longitudinal and transverse forces which 
are exerted on the fabric. 
Naturally any number of coating operations in excess of two may be 
provided, depending on the desired thickness of the coating. 
ILLUSTRATIVE EXAMPLES 
The present process is illustrated by the following examples in which a 
coated fabric is made, suitable for covering cargo on trucks, for making 
awnings, tents, clothings, or other similar heavy duty service. The fabric 
is a woven fabric having similar warp and weft yarns comprising synthetic 
continuous filaments, preferably high strength polyamid or polyester of 
210 to 2000 denier, the weight of fabric in this range varying 
approximately from 70 to 350 grams per square meter. As stated above, it 
is a particular feature of this invention that the fabric can be woven 
using un-set filaments. The coating material is preferably polyvinyl 
chloride resin, although where ovens are equipped with accurate heat 
control and safety means preventing firing, it is also satisfactory to use 
elastomeric coating materials, or polyurethane or acrylic resins. The 
coating adds about 150 to 1000 grams per square meter to the weight of the 
fabric itself within the denier range quoted above, so that the weight of 
the coated fabric will be in the range of 220 to 1350 grams per square 
meter. 
The following specific example is typical: 
The support fabric comprises a woven polyester yarn of 1000 denier 
including 200 filaments twisted together 60 turns per meter. The filaments 
are not preset and the weave includes 8 yarns per centimeter. The cloth is 
183 centimeters in width and weights 180 grams per square meter. The 
fabric moves through the machine at a linear rate of 17 meters per minute, 
and is subjected to two successive coating operations. 
The first coating step provides an under-layer which is designed to adhere 
as well as possible to the fabric filaments. The polyester includes 11% 
Di-isodecylphtalate, 30% 7-11 linear phlate, 53% PVC resin, 0.82% pigment, 
2.10% isocyanurate bonding agent, and 3.08% other agents including 
bactericide, fungicide and ultra violet absorber. The temperature in the 
first curing oven is 165.degree. C, and calendering of the fabric 
immediately follows the heat curing stage. 
The second coating step is similar except that the linear speed of the 
fabric through the machine is preferably reduced somewhat to about 13 
meters per minute. The coating material is the same but it is applied in 
somewhat different quantity. A higher oven temperature is used following 
the second coating step, the temperature being about 180.degree. C. This 
higher temperature plasticizes the PVC resin more completely which 
provides a smoother surface for the finished product. The fabric is again 
calendered. 
The tension produced in the filaments is about 0.9 gram per denier. Thus 
each 1000 denier yarn is subjected to a tension of about 900 grams, and 
since the weave includes 8 yarns per centimeter, the tension on the fabric 
as the yarn shrinks is about 7.2 kilograms per centimeter at the elevated 
oven temperatures. 
If the fabric were free to shrink, its dimensions would shrink about 17% at 
the elevated temperatures, but the tensioning means prevent such shrinkage 
in overall dimensions. The shrinkage therefore goes into reduction of 
thickness of the fabric to the extent of about 20%. Therefore the surface 
of the fabric is made very regular at the nubs, and the amount of coating 
material required to make a smooth surface is correspondingly reduced. As 
stated above the initial width of the fabric is 183 centimeters. The 
tenters prevent it from diminishing, but the selvage portions of the 
fabric are not regular. Therefore about 15 millimeters of the edge is 
severed on each side of the fabric, reducing its width to 180 centimeters 
for the finished product. 
The improved weight per meter of this product can be seen by comparing a 
four layer product (coated on both sides) with a similar product made 
according to prior art methods using the same initial fabric. The present 
product weighed 580 grams per square centimeter as compared with a weight 
of 670 grams per square centimeter for the prior art product having a 
poorer surface smoothness, but similar tensile strength and tearing 
strength. 
This invention is not to be limited by the above recited examples and 
drawings, for obviously changes can be made within the scope of the 
following claims.