Application of liquid material to webs

Disclosed is an applicator for the application of liquid to webs and methods of using it. A web-guide path is defined through the applicator and has an intermediate enlargement. One or more inlets and one or more outlets are provided at the exterior of the applicator and at the enlargement respectively, which are part of a closed passageway system for the supply of liquid to the enlargement. A slit-like passageway system affords passage of web to the enlargement. An exit passageway with one outlet affords passage of web, to which liquid has been applied, from the enlargement out of the applicator. Means are provided for changing characteristics of the exit passageway whereby selectively to influence the application of liquid to the web. By using such an applicator in which provision is made for changing the size or shape, or both, of the exit passageway, considerable control may be exercised over both the degree of impregnation of the liquid into the web and the thickness of liquid coating on the web.

This invention concerns the application of liquid material to webs. The 
term "web" is meant to include any length of flexible material capable of 
being impregnated or coated, or both, with liquid material. Thus, for 
example, the web may be formed simply from a large number of warp yarns in 
side-by-side assembly, or may be a textile or other fabric. The term 
"liquid" is not intended to be construed in a narrow sense, but to include 
liquids in general. Thus, for example, it includes solutions, dispersions 
and suspensions. 
There are a number of industrial techniques for applying liquids to webs. 
Some are pressurised and some are not. 
One example of a pressurised system is described in U.K. Pat. No. 
1,388,970, which is concerned with the encapsulation of reinforcing 
filaments within a ribbon of elastomeric material. The elastomeric 
material is generated in an extruder, and a special cross-head die, 
through which the filaments pass for encapsulation is fitted to the 
extruder outlet. 
The die has an intermediate internal enlargement fed from the extruder via 
passageways which are of complicated shape and which are vented preferably 
in an adjustable manner presumably to prevent the high pressure within the 
enlargement rising to an undesirable level. 
Such a die suffers from the disadvantages that high pressures must be 
accommodated in the enlargement, and difficulty of control of the 
application of the elastomeric material, specially of surface coating. 
Another example of a pressurised system is a pad mangle arrangement. 
Whilst with such a system good impregnation may be achieved, simultaneous 
surface coating control is difficult. 
Examples of techniques which are open (i.e. not pressurized) are knife 
coating or spraying techniques. 
Generally speaking, a spraying technique allows reasonable control of 
surface coating, but does not facilitate any control of impregnation. 
Knife coating techniques are capable of affording reasonable control of 
either impregnation or surface coating but not of both. 
The general objective of the present invention is to provide an applicator 
for applying liquid to a web which incorporates an essentially low 
pressure feed system coupled with effective control of the application of 
the liquid to the web, both so far as impregnation and coating are 
concerned. No existing technique provides such a combination of features. 
According to the present invention an applicator for applying liquid to a 
web, through which is defined a web-guide path having an intermediate 
enlargement, to which enlargement liquid may be supplied, is characterised 
by a first, closed, passageway system which connects the enlargement to 
the exterior of the applicator for the supply of liquid to the 
enlargement, a second, slit-like, passageway system affording passage of 
web to the enlargement, and an exit passageway having a single outlet and 
affording passage of web, to which liquid has been applied, from the 
enlargement to the exterior of the applicator, and by means for changing 
characteristics of the exit passageway whereby selectively to influence 
application of the liquid to the web material. 
By "a closed passageway system", we mean a passageway system which has one 
or more inlets for liquid and, at the enlargement, one or more outlets for 
liquid, there being no other inlet or outlet. 
Also according to the present invention a method of applying liquid 
material to a web comprises the steps of passing web through the slit-like 
passageway system of an applicator or applicator system and conducting 
liquid material to the or each intermediate liquid receiving enlargement 
in sufficient quantity to keep same filled.

In co-pending application U.K. Pat. No. 25552/77 is described the 
manufacture of fabrics, in particular, tyre reinforcing fabrics, from webs 
of closely-spaced warp yarns which are held together in a matrix of latex 
and the applicators now to be described are vey suitable for producing 
such webs. There are of course many other cases when it is desired 
continously to coat a web in the form of a fabric in the piece, and use of 
an applicator according to the present invention will often be suitable 
and advantageous. 
Referring first to FIGS. 1 to 3 the applicator A consists basically of a 
lower block 10 and an upper block 12 secured together but with intervening 
spacers 14, 16, 18, 20 and fitted with side plates 22, adjustable selected 
control plates 24 and curtain plates 26, which are also, preferably, 
adjustable. Each block has formed therein a transverse runnel 28 and in 
the upper block 12 are a number of supply passageways 30 leading from the 
top of the block to the runnel therein. A pad 32 of foam rubber or 
plastics material is provided on the under surface of the rear part of the 
upper block 12 or on the upper surface of the lower block 10. When 
assembled (FIGS. 1 and 2) there is defined, through the applicator, a 
slit-like web-guide path, bounded top and bottom by the blocks 10, 12, pad 
32, and control plates 24, and, at the sides by spacers 14, 16, 18, 20 and 
curtain plates 26, which if adjustable, enable the path width to be 
varied. The runnels 28 run right across the passageway, together forming a 
generally cylindrical enlargement the ends of which are closed by the side 
plates 22. The path of a web W through the applicator is shown in dot-dash 
line. 
FIG. 3 illustrates the treatment of a web W of warp yarns by a method 
according to the invention. The warps Y of the web W are gathered from a 
creel (not shown) and pass through a reed R disposed immediately in front 
of the applicator A (shown in more detail in FIGS. 1 and 2). The 
passageways 30 in the applicator A are supplied with latex L from one or 
more supply vessels S and thereby the enlargement formed by the runnels 28 
is kept filled with latex to coat both sides of the web W. On emerging 
from the applicator A, the web W passes around a four-roll heated calendar 
C1, then through a drying oven O, around traction rollers C2, passing 
finally to a wind-up U. 
It may be found necessary, when coating a web of warp yarns, to design the 
means for handling the web on emergence from the applicator through to 
wind up very carefully. For example, there is a tendency, on emergence 
from the applicator, for the applied latex to be disturbed, and especially 
for "splitting"--i.e. separation of groups of warp yarns one from the 
other--to occur. The use of a high quality reed before the applicator 
reduces splitting, but it has been found desirable also to pass the 
emergent web through a roll system since this helps to re-establish the 
coherence of the web if splitting has occurred. However, unless care is 
taken, calendar systems can themselves cause different kinds of 
disturbances of the latex such as "stringing"--i.e. adherence of latex to 
a roll surface as the coated web leaves it--and displacement of the web 
relative to the latex giving uneven coatings on the two sides. To avoid or 
minimise these disturbances it has been found desirable to ensure that the 
web moves at a different linear speed from the linear speed of the roller 
surfaces with the coated web passing round them in convolutions such as 
shown in FIG. 3. Actually, in practice, provided the calendering rollers 
are maintained at a sufficiently high temperature, and provided that the 
latex is so formulated as to have a high gelling ability, few, if any, 
problems are experienced due to splitting and stringing. 
The oven may be for example a micro-wave or infra-red oven, but air drying 
in a hot enclosure is not precluded. 
It has been found possible to exercise considerable control over the 
coating operation, most importantly by varying the shape and configuration 
of the passageway which affords passage to web leaving the enlargement 28. 
In the embodiment being described these may be varied by suitably 
selecting and adjusting the control plates 24. 
Some control may also be exercised by varying the head of the supply of 
coating liquid, the tension applied to the web passing through the 
applicator, and the take-off angle of the web. 
It will often be that plates 24 shaped to form a convergent nozzle as shown 
in FIG. 1 are very suitable. The thickness of the plates 24 may be 
selected according to the desired effect of the liquid head, since the 
longer the nozzle the less will be the effect of the latter. 
As to the head, increasing it, will, in general, tend to increase the 
coating weight and vice-versa. Thus it may be possible for the system to 
be self-controlling, so far as applied amount of liquid for unit length of 
web is concerned, by feeding supply vessels with coating material metered 
at the desired rate of take-up. If the web is taking up too much or too 
little material the head will drop or rise as the case may be and so 
therefore will the rate of take-up of material by the web decrease or 
increase. Alternatively change in level could be detected and used to 
control some characteristic of the liquid material to correct the rate of 
application--e.g. viscosity of dilution (though dilution would not be a 
desirable characteristic to alter in the case of latex). 
As to the web tension, if this is properly selected the viscous forces at 
the passageway outlet tend to centralise the web in the gap between the 
control plates to give equal coatings on both sides. 
As to the web take-off angle, a controlled doctoring effect can be 
achieved. 
The invention is by no means limited to the details of the embodiment just 
described with reference to FIGS. 1 to 3 of the accompanying drawings. In 
that embodiment like runnels 28 are provided in each block 10, 12. 
However, the runnels need not be of the same shape and size. Indeed in 
some cases there need be a runnel only in the upper block, as for example 
if the coating of one side only of an impervious web is required, or, 
indeed, for applying material to many types of warp sheet, if the nature 
of the sheet is such that the latex or other coating material can pass 
readily therethrough. Furthermore there may be embodiments in which more 
than one intermediate enlargement is provided, perhaps for more than one 
liquid material to be applied to the web or for certain types of 
"wet-on-wet38 processes as will later be described. The form rubber pad 
32 is not essential because the web as it moves into the applicator 
continuously urges back into the cavity 28 any liquid tending to leak out 
contrary to the motion of the web. The form pad is however useful in 
preventing any contact between air and the liquid where it is necessary to 
prevent evaporation or oxidation. As an alternative to the rubber pad, air 
saturated with solvent vapour may be introduced into the passageway, 
thereby preventing evaporation. In the case of liquids which react with 
air, an unreactive gas, such as nitrogen, may be similarly introduced. The 
control plates 24 may be profiled solid bars as shown in the drawings, but 
in some embodiments at least one may be in the form of a blade of a 
compliant nature capable of giving way to allow passage of any lumps or 
the like which might be inadvertently present in the liquid material or in 
the web. Another alternative would be to provide adjustable members in the 
form of inflatable tubes, with or without rigid internal support bars. 
Control plates could take the form of a U-section lower piece and a 
corresponding T-section upper piece with the web passing straight between 
so that they touch both the tops of the U-section and the base of the 
T-section. The tension and close proximity of warp ends of a web may 
prevent any unacceptable leakage of fluid, but the space in the U-section 
would permit knots and the like to pass through. It may, however, be 
desirable to insert within the U-section, or bridge it by, a flexible 
member which contacts the warp ends to make certain of no leakage of 
fluid. In some embodiments, the outer leg of the U-section may become 
superfluous. 
The supply vessel may be connected to applicator by flexible conduits to 
allow the applicator to gimballed if required. In some processes it may be 
necessary or desirable to heat or to cool the applicator, for example to 
control the viscosity of the applied liquid, and in this event suitable 
heating elements or cooling tubs and suitable control means will be 
incorporated in the applicator. 
In some processes (as will later be described) it may be desirable to coat 
a web in two stages by passing it through one applicator according to the 
invention, and then through another, and the latex first applied may not 
be very viscous. In order to prevent leakage it may be desirable to 
contour the opposed edges of the control plates 24 (or one of those edges) 
so as individually to control the passage of each warp end. Although 
reference has been made to coating a single sheet of warp end, other 
assemblies of warp ends may be involved. For example an assembly of rather 
more three-dimensional form may be processed. Again such an assembly may 
be of a generally random, or of a non-random nature. In the latter case 
more than one entry passageway leading to the enlargement may be provided 
for the introduction of several warp sheets. 
When the coated material is to be stentered it is desirable that its edges 
be left free or be starved of coating material so that the stenter pins or 
clips do not become fouled. 
This can be achieved by blocking off the runnels 28, or by specially 
contouring the control plates, or both. 
Turning now to FIGS. 4, 5 and 6 of the drawings, parts corresponding to 
parts of the applicator of FIGS. 1 to 3 have been given the same reference 
numerals. In each case the general construction is similar, and therefore 
only a sectional end view is provided. 
FIG. 4 illustrates an applicator having runnels 28 in both blocks 10, 12, 
like the applicator of FIGS. 1 to 3. The runnels however are of a slightly 
different shape, and extend towards the control plates 24 to provide a 
parallel commencement to the convergent nozzle formed by the latter. 
The lower control plate 24 is normally fixed, once set. The upper control 
plate 24 however is readily adjustable, being slidably mounted in a 
housing 34 on a lead screw 36 which is externally adjustable against the 
action of a compression spring 38. The spring 38 prevents back-lash on 
adjustment, and also enables the top plate 24 to yield if say a lump of 
coating material occurs, or a thick material joint is present. A seal 35 
is accommodated in the top block 12. 
The applicator blocks 10, 12 also have channels 40 (their dimensions are 
smaller than those of the runnels 28). Where latex is the coating material 
these channels 40 will be supplied with and saturated with water vapour in 
order to discourage the formation of a skin on the latex. Where a 
solvent-based coating is being applied then the appropriate solvent vapour 
could be fed to the channels 40. 
The applicator of FIG. 5 is suitable for coating one side only of the web 
W, or both sides of the web W if it is a warp sheet of suitable 
characteristics. There is a runnel 28 in the upper block 12 only. In this 
embodiment a sealing flap/42 prevents contact between air in the entry 
passage and the coating material in the runnel 28; and the lower control 
plate 24 is provided with a resilient insert 44 further to accomodate the 
passage of lumps, knots, joints and the like between the two control 
plates 24. 
Mention has been made earlier of applicators according to the present 
invention suitable for certain types of "wet-on-wet" processes and for 
coating a web in two stages. The applicator illustrated in FIG. 6 is an 
example. It is intended for coating heavy fabrics as in the production of 
polyvinyl chloride coated conveyor belts where the carcass is a heavy, 
closely woven fabric which must be well penetrated and have a substantial 
coating built upon each side. In such demanding processes it is desirable 
to use two applicators according to the invention in tandem and such an 
arrangement is illustrated in FIG. 6. 
The first applicator is of the same general construction as before, having 
runnels 28a and elongated control plates 24a defining a long convergent 
passageway which leads to the second applicator which has runnels 28b and 
control plates 24b which close the otherwise parallel-walled exit 
passageway quite abruptly with knife edges. 
In operation, the first applicator exerts, in the passageway, defined by 
the control plates 24a, increasingly high pressure in the PVC in liquid 
form which has been taken up by the web W in passing through the 
enlargement formed by the runnels 28a thus forcing that liquid well into 
the web interstices. The thus impregnated web then passes through the 
second applicator where it picks up further PVC in liquid form. However 
the control plates 24b, according to the spacing of their opposed edges, 
now control the add-on of PVC at both sides of the already impregnated 
web. 
In this manner a well-impregnated heavily coated and product results. 
Finally FIG. 7 illustrates diagrammatically an annular applicator according 
to the invention for coating an tubular web W1. It consists of a annular 
body 46 and an internal former 48. The body has an annular runnel 50 with 
feed passages 52 for coating material. The former would need to be 
magnetically supported if the coating of say a woven or knitted fabric 
were involved, but wire supports 54 could be employed if a tubular arrry 
of warps was being coated. 
In all the embodiments described the coating or impregnating of the web 
could be encouraged by the provision of a steam box just prior to the 
entry side of the applicator so that the web would be steam purged just as 
it moves into the applicator. The steam condenses during the passage of 
the web towards the runnel or runnels which tends to give rise to a vacuum 
in the interstitial spaces of the web so encouraging the impregnation and 
coating action. In some cases steam would be unsuitable and a different 
vapour would be used. 
The invention has numerous applications apart from the impregnating and 
coating on both sides of a sheet or web of warp yarns with latex. For 
example it is frequently necessary in manufacturing to coat textile 
fabrics with various liquids which are later dried and solidifed, as in 
the manufacture of conveyor belting and waterproof materials. Paper also 
sometimes needs to be coated. As coating materials may be mentioned by way 
of example not only latex but polyvinyl chloride, polyurethane, and 
acrylic and epoxy resins. 
When coating with polyvinyl chloride a standard PVC plastisol formulation 
could be used, incorporating at least a base polymer, plasticiser, filler, 
stabilisers, antistatic agent and pigment, either with or without an 
isocyanate or other bonding agent. 
Another important anticipated use of the invention is to make structural 
material which can replace structural material which is presently made 
from asbestos, regarded in many forms as a health hazard. The web to be 
coated consists of a fibrillated polypropylene film and the coating or 
encapsulating material is a cement sherry. Preferably several such webs 
will be coated with the sherry and laid one on the other before the cement 
hardens. In a particular example of this use of the invention may be 
envisaged continuous production and utilisation of such a coated web for 
lining culverts and the like. Also embodiments in which the applicator, 
rather than the web, moves can be foreseen. 
According to one specific example a tarpaulin is made from a fabric woven 
from 940 d/tex continuous filament nylon yarn type 126 manufactured by 
I.C.I. Limited, and having no twist, 22 ends per inch and 22 picks per 
inch, of weight 5.1 ozs. per square yard which is passed through an 
applicator similar to that shown in FIG. 4 but without the runnels 40. A 
PVC plastisol is supplied to the runnels 28. The plastisol comprises a PVC 
polymer, plasticiser, filler, stabilisers, antistatic agent and pigment, 
together with an ISO cyanate bonding agent. 
By suitably adjusting the member 24 an applied weight of 7 oz. per square 
yard with good penetration and a coating of slightly greater thickness on 
one side than the other was achieved. 
Among the advantages of the invention are the total enclosure of the 
coating region which prevents the undue release of noxious fumes when 
present, and facilitates a clean process; the controllability of the 
application of the liquid material; the fact that both sides of a web may 
be simultaneously coated; and that, provided the coating substance is 
sufficiently viscous, the applicator can be used in any orientation as its 
operation would be largely uninfluenced by gravity (though an applicator 
according to the invention can be arranged to operate by gravity feed). 
However, perhaps the main advantage of the invention is that it 
facilitates, in a particularly efficacious manner, the application of 
relatively thick coatings, or deep and thorough penetration, or both.