GB2120959A - Applying foamed treating solutions to textiles - Google Patents

Abstract

Treating solutions are applied to textiles wherein a mass of foam (26) is formed over a moving web (18) of textile fabric and the fabric is displaced under a blade-over-air coating device (24). The coating device (24) is in the form of a blade (25) which presents a serrated profile (30) to the fabric (18). <IMAGE>

Description

SPECIFICATION Apparatus and method for applying foamed treating solutions to textiles The present invention is concerned with the application of foamed treating solutions to textiles.

There are presently known a number of machines and techniques for the controlled application of foamed chemical treating solutions to textile fabrics, and each of these has its own advantages and disadvantages. One of the objects of such techniques is the ability to apply treating agents to a textile fabric in a uniform and controlled manner, but with a much reduced liquor add-on compared with conventional impregnation and mangling techniques. For example, typical liquid add-on using foam techniques might be in the range 15-30% by weight, based on the dry weight of the textile.

The ability to apply treating agents with such a low liquor pick-up provides a number of advantages over the aforementioned conventional techniques, for example significant energy and cost saving during subsequent drying, reduced migration of treating agents during drying, and a reduction in the quantity of treating agent necessary.

A problem in practice with the known foam applying machines is that they are normally relative ly expensive, highly specialised machines, designed to operate only with a specific grade of textile fabric.

Furthermore, such known machines do not readily fit into existing production lines and are not easily adapted to meet special requirements such as, for example, to apply foam to both sides of a fabric web in a single pass through the machine, should the latter operation be desirable in a particular instance.

It is an object of the present invention to provide an apparatus for applying foamed treating solutions which is of increased versatility and enables more accurate control of the foam application compared with the known machines.

Pending UK Patent Application No. 8136765 de scribes an embodiment of a foam application system, involving automatic control of the foam quality and quantity, in relation to fabric throughput speed, fabric weight and desired liquor pick-up. The design of this system is based on the well-known principle of blade-over-air coating, using a blade with a bevelled or radiused profile. This system relies on the foam collapsing into the fabric during its contact with the mass of foam rotating in front of the blade, and also by the action of the profiled blade.

The mechanism of liquor transfer from the foam to the fabric is rather complicated, but clearly a signifi cant proportion of this transfer takes place as a result of the foam "de-watering" into the fabric as it passes beneath the foam roll in the applicator. Any such de-watering taking place inevitably removes some of the liquid phase without destroying the foam, thus leaving behind a "spent" foam of higher blow ratio.

This spent foam can not pass beyond the blade in the direction of travel of the fabric, because the fabric is in permanent contact with it, and so the spent foam becomes re-incorporated into the foam roll within the applicator, where it is mixed with incoming "new" foam of a lower blow ratio. This can produce an out-of-balance situation yielding a foam roll with blow ratios varying throughout its mass.

This, in turn, upsets the smooth rotation of the foam roll within the applicator, which can then result in uneven application of processing chemicals to the fabric.

It has been observed that certain types of fabric are more prone than others to this phenomenon of de-watering, with polyester/cotton and polyester/ viscose blends being particularly bad in this respect.

With such blended fabrics, extensive de-watering has been shown to occur when running with foam blow ratios as high as 12 or more.

It is a feature of the present invention to provide a modification to the applicator described in UK 8136765 so as to minimise or even eliminate the serious adverse effects caused by the de-watering phenomenon, whilst still retaining the many advantages of the blade-over-air principle.

In accordance with the present invention, the blade profile is arranged to present a serrated profile to the fabric which allows "spent foam" (as hereinb- efore defined) to pass beyond the blade where it is absorbed into the fabric downstream of the applicator.

Thus, in accordance with one aspect of the invention, there is provided a method of applying foamed treating solutions to textiles, comprising forming a mass of foam over a moving web of textile fabric and displacing the fabric under a blade-overair coating device disposed downstream of said mass of foam, the blade of said coating device presenting a serrated profile to the fabric such as to provide an escape route for "spent foam" (as herenbefore defined), which is then absorbed into the fabric downstream of the applicator.

The action of this serrated edge is not, as thought at first, to meter on to the fabric a quantity of stable foam. On the contrary, it has been clearly shown that such a blade profile unexpectedly functions mainly by providing an "escape" route for the spent foam, produced during the de-watering occurring when the fabric passes underneath the foam roll within the applicator. Indeed, the use of such a device permits the use of less-stable foams which previously have been unusable because of the excessive de-watering occurring with such foams.

Afurther benefit accruing from the use of such a serrated profile is that it facilitates an accurate prediction of blow ratio to be made, in relation to fabric weight and desired wet pick-up. This, in turn, guarantees a satisfactory start-up to a foam production run, without having to wait for equilibrium running conditions to be attained, which otherwise would put the first 50-100 metres of fabric at risk.

The way in which this prediction of blow ratio is made is by taking advantage of the fact that such a profile applies a relatively constant volume of foam per unit area of fabric, irrespective of fabric weight and type. This "volume factor" will be virtually constant for a particular profile and, in conjunction with the fabric weight per unit area and the desired wet pick-up, can be used to derive the foam blow ratio required. If the calculated blow ratio is then considered to be either too high or too low, a different profile would then be selected to yield a blow ratio within an acceptable range.

During continuous running with the above applicator system, the quantity of spent foam produced by de-watering is leaked past the profile, to be absorbed by the fabric downstream of the applicator. This means that the blow ratio of the foam roll within the applicator, at equilibrium, will be substantially the same as that of the new foam being delivered.

If, for any reason, the quantity of spent foam was small, then some new foam would pass through the serrated profile, to make up the volume deficiency.

If the quantity of spent foam exceeded the capacity of the profile, then the equilibrium blow ratio would rise appreciably beyond that of the new foam, and in these circumstances a coarser profile would be used.

In any event, provided the foam roll is maintained at a constant size, by automatic adjustments to the air supply, and provided the liquor pump is delivering liquor in proportion to fabric requirements then clearly the correct quantities of processing chemicals are being applied to the fabric.

The manner in which the serrated edge is formed is not critical. However, the edge presented to the fabric should preferably not be too sharp so as to avoid problems of damage to the fabric. One convenient way of deriving the serrated edge is by forming a screw-thread, e.g. a Whitworth thread, on the periphery of a cylindrical bar. It has been found that such a thread can operate without imparting to the fabric any tendency for lateral displacement, even with a single continuous thread over the whole width of the fabric. Another technique would be to form on the bar a plurality of closely spaced parallel grooves but this is rather more expensive to achieve.

Another profiled bar, known per se, is formed by winding a continuous iength of thin wire around a plain bar, the interstices between the adjacent turns of the wire providing the serrations.

When a bar is used having a profiled periphery as described above, this can be simply fitted to the existing blade in a readily releasable manner by forming the bar with a longitudinal peripheral slot dimensioned to fit over the existing blade with, for example, tight interference fit therebetween to hold the bar in place. A different bar having an alternative serrated profile can then be substituted in a matter of minutes.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic side view of a foam applicator having a profiled blade edge in accordance with the present invention; and Figure 2 is a front view of part of the profiled blade of Figure 1.

The foam applicator 10 shown in simplified form in Figure 1 has two side plates 12 and a front plate 14 which together define an open container for receiving treatment foam via a supply pipe 16. Fabric 18 to be treated is guided underneath the applicator assembly 10 by means of a guide plate 20 and roller 22 so that the fabric 18 passes over and under a depending coating device 24 in accordance with the conventional "blade-over-air" technique. The arrangement is such that the foam entering via the pipe 16 forms a foam roll 26 within the applicator and over the moving fabric, the prevailing size of the foam roll being monitored by one or more proximity detectors 28. The apparatus as thus far described is already known.For further information as to the details of this type of apparatus, being an example of an apparatus to which the present invention is applicable, attention is hereby directed to our U.K.

Patent Application No.8136765.

The principal difference introduced by the present invention is that, for example as shown in Figure 2 instead of its normal smooth profile the blade 25 of the coating device 24 presents a serrated profile to the fabric 18 such as to allow "spent foam" to pass beyond the blade in the direction of fabric movement. The example of Figure 2 shows the blade having the profile of a Whitworth thread, as indicated at 30.

As shown in Figure 2, the blade 24 can be attached to the applicator by means of a longitudinal slot 32 which receives a fixed member 34 with an interference fit therebetween. Alternatively, the blade can; for example, be fitted directly to the applicator front plate 14 by means of screws or bolts.

The number of threads per inch in the case of a Whitworth thread is selected in dependence on the fabric weight per square metre and the desired wet pick-up. Typical figures might, however, be over the range 7 T.P.I. to 40 T.P.I. for fabric weights from 1000gm/m2 (carpets) down to 80 gm/m2 (voiles).

The thread can be turned on a tube or rod which can be either a durable plastics material or stainless steel.

In use, a tachometer signal is received from the machine drive mechanism (not shown) and processed through two gain controls. The first gain control allows the fabric weight per linear metre to be pre-set, and the second allows the desired wet pick-up to be present. The processed signal then operates, via a thyristor, to control the speed of a pump delivering liquor to the foam generator.

Hence, the liquor delivery is maintained in proportion to fabric throughput requirements.

A further signal is taken from the pump motor and is processed through a further gain control to allow the air/liquor ratio (blow ratio) to be pre-set. This processed signal then acts upon a stepping motor operating a needle valve in the air supply to the foam generator. In this way, the air/liquor ratio remains constant over the whole range of fabric throughput speed.

Superimposed on this control system is a proxistor capacitance probe (or probes), shown at 28 in Figure 1,which detects the diameter of the foam roll, without actually touching it.

If the foam roll diameter varies for any reason, such as fabric absorbency, temperature, surface characteristics etc., then a signal from the proxistor(s) 28 makes small adjustments to the air supply, in order to maintain the foam roll diameter within pre-set limits.

Claims (7)

1. A method of applying foamed treating solutions to textiles, comprising forming a mass of foam over a moving web of textile fabric and displacing the fabric under a blade-over-air coating device disposed downstream of said mass of foam, the blade of said coating device presenting a serrated profile to the fabric such as to provide an escape route for "spent foam" (as hereinbefore defined), which is then absorbed into the fabric downstream of the applicator.

2. An apparatus for applying foamed treating solutions to textiles, comprising a means for establishing a mass of foam over a moving web of textile fabric upstream of a blade-over-air foam coating device, said means including a foam generator having a foam delivery system controlled in accordance with the fabric requirements and throughput speed, and an electronic sensing arrangement which is adapted to detect the size of the mass of foam present over the web during running and to maintain the size of the mass of foam within predetermined limits, the blade of said coating device presenting a serrated profile to the fabric.

3. An apparatus as claimed in claim 2 wherein the serrated profile of the blade is achieved by forming the blade from a tube or bar having a peripheral screw-thread.

4. An apparatus as claimed in claim 3 wherein the tube or bar is made of a durable plastics material orfo stainless steel.

5. An apparatus as claimed in claim 2 wherein the serrated profile of the blade is achieved by forming the blade from a tube or bar having a plurality of closely spaced parallel grooves in its peripheral surface.

6. An apparatus for applying foamed treating solutions to textiles, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

7. A method of applying foamed treating solutions to textiles, substantially as hereinbefore described with reference to the accompanying drawings.