GB2466067A

GB2466067A - Coating a fabric with a foam

Info

Publication number: GB2466067A
Application number: GB0822704A
Authority: GB
Inventors: Dong Zhenli; Jeffrey Peter Greenwood
Original assignee: AUTOFOAM SYSTEMS Ltd
Current assignee: AUTOFOAM SYSTEMS Ltd
Priority date: 2008-12-12
Filing date: 2008-12-12
Publication date: 2010-06-16
Also published as: GB0822704D0; CN201406570Y

Abstract

An endless web of fabric 1 is passed under an opening in a reservoir 10. The passing fibrous web effectively forms the lower part of the reservoir. Some of the foamed composition is absorbed on one side of the web. The apparatus also includes a foam generator and transport mechanism 2. The un-foamed composition has a viscosity = 100-300 cPs, and the foam has a bulk density = 50-150 g/l. The aqueous composition contains a foaming agent (e.g. lauroylamidopropyl betaine), and preferably a cellulosic viscosity modifier. The hydrophobic or hydrophilic composition preferably comprises a fluorine terpolymer, silicone, or zirconium or paraffin wax. The coatings could be applied to denim, corduroy, velvet, velour, carpets or felts.

Description

TEXTILE COATING METHOD AND APPARATUS

This invention relates to apparatus for application of coating compositions to absorbent webs or sheet materials, particularly but not exclusively for application of coating or impregnating compositions or treatments to absorbent textile webs, polymer films, sheets and laminar products. The compositions may comprise coatings or treatments which are removed from the products after use. Such coatings or treatments may be applied to a single side or to both sides of a textile web or other product.

GB-A-2 120959 discloses apparatus for applying foamed treating solutions to textiles.

A mass of foam is formed over a moving web of textile fabric and the fabric is displaced under a blade which presents a serrated profile to the fabric. The blade may comprise a screw threaded bar. The threaded profile allows spent foam to pass beyond the blade in the direction of fabric movement.

US-A-2004/0037963 discloses a process for manufacturing a textile with hydrophobic properties on one side and hydrophobic properties on the other involving application of a viscous paste to one side of the textile, the paste comprising an emulsion or dispersion of paraffin, polyiloxane andlor fluorine compounds, followed by application of a second paste comprising hydrophilic polymers to the other side.

* h251 * .*.

The present invention particularly relates to application of water repellent coatings to * fabrics and to coating of fabrics provided with a hydrophilic coating on one side and a *: hydrophobic coating on the reverse side.

:.:. According to a first aspect of the present invention, there is provided a method of coating of fabric comprising the steps of: passing an endless web of the fabric through an applicator, the applicator comprising a foam generator adapted to generate a foamed composition, a reservoir for the foamed composition, a lower part of the reservoir being defined by the fabric web; and a profiled member; passing the web under a profiled member to cause the web to absorb a predetermined amount of the foamed composition on a first side of the web to form a treated side of the web;

I

wherein the composition comprises an aqueous solution of a hydrophobic or hydrophilic coating composition and a foaming agent; the composition prior to foaming having a viscosity in the range of 100 -300cPs; and wherein the composition when foamed has a foam density in the range of 50-150 gl; and optionally drying the web.

A coating in accordance with this invention has the advantage that the foamed composition may be only absorbed on a single side of the textile web so that the reverse side can be subsequently coated with a second composition, for example a hydrophilic or hydrophobic coating. In this way a fabric can be produced with a hydrophobic coating on one face and a hydrophilic coating on the reverse face. Use of viscous pastes is avoided.

This invention relates especially but not exclusively to fabrics for manufacture of apparel.

Such fabrics preferably exhibit good breathability and soft handle properties. Use of viscous pastes has been found to adversely affect their properties. The amount of coating applied to the fabric may be accurately controlled by selection of an appropriate blow ratio of the foam and profile of the profiled member for the spreader bar.

In a preferred embodiment the method may further comprise the step of applying a hydrophilic coating composition to the reverse face of a fabric to which a hydrophobic coating composition has been applied or vice versa. S.'.

The two coating steps may be carried out in any convenient order. Preferably a hydrophobic *:*. coating is applied before a hydrophilic coating especially if an intermediate drying step is

S * *

According to a third aspect of the present invention, an apparatus for coating a fabric *.*S.* * . comprises: an applicator, the applicator comprising a foam generator adapted to generate a foamed composition having a density of 50-lSOgr'; wherein the unfoamed composition has a viscosity in the range of I 00-300cPs, a reservoir for the foamed composition, and a profiled member; the reservoir having a downwardly opening window, a transport mechanism adapted to transport a web adjacent said window so that the web forms a lower part of the reservoir, and so that a predetermined amount of foamed composition is absorbed on a first side of the web; the transport mechanism being further adapted to transport the web under the profiled member to form a coated side of the web.

The fabric preferably has a weight of about 80 to 800gm2, more preferably about 80 to 400gm2, more preferably about 100 to 200gm2, especially about 120 to 150gn12.

In preferred embodiments the amount of liquid contained in the foam applied to the fabric does not exceed the imbibation value.

The imbibation value of the fabric is the amount of water as a percentage of the weight of the fabric which can be applied to the fabric before the water is transmitted away from the surface of the fabric. The imbibation value is important in the present application because only a single side of the fabric is to be treated. Accordingly the amount of solution applied should not exceed the imbibation value. The imbibation value of a cellulosic fabric such as cotton is about 22%. If a cotton fabric has a weight of 200gm2 then water or an aqueous solution applied in an amount up to 44gm2 will not penetrate to the reverse side of the fabric. At higher loadings the water or solutions may not move unless the fluid is calendarised or squeezed. In preferred embodiments the aqueous solution is applied at an amount below the imbibation value. * **

* ** S 0*5* Imbibation values can be obtained from commonly available texts. S. * * * * S.

The foam may have a preferred density of about 100-l50g12. This may be expressed as a blow ratio of about 10-6. * S *

In a preferred embodiment the aqueous foamed composition may be absorbed onto a single side of the fabric in an amount of 20-40% for example 22% by weight of the fabric.

The composition may comprise aqueous fluorine terpolymers, zirconium or paraffin waxes or silicones or a mixture thereof in an amount of said 100 to 500 g1', preferably about 120 to 200gF', more preferably about 150 to l8Ogr'.

An amount of 20 gl of a foaming agent may be employed. Preferred foaming agents include cationic surfactants eg alkyl betaines, for example (chain length) in a 28-30% solution. A preferred foaming agent is lauroylamidopropyl betaine (LAB).

A viscosity modifier is preferably used, for example modified or substituted cellulose, preferably hydroxyethyl cellulose more preferably with a molecular weight of 550.

Carboxymethyl cellulose may be used. Polyacrylic and poiy methacrylic acids may be used, for example as the ammonium salts. An especially preferred viscosity modifier is dimethyl propane sulphonate cellulose.

The foam generator preferably comprises a double rotor dynamic foam mixer.

Preferred foam generators comprise a plurality of notched or toothed rotors interdigitated with notched or toothed stators in order to provide a high shear labyrinthine passageway for a liquid-air foamable composition supplied to the generator from a mixing pump. Each rotor may have a diameter of about 200mm and may rotate at about 240 rpm. The rotor may comprise a circular disc carrying upstream and downstream facing cylindrical arrays of teeth or cylindrical coaxial arrays of notched or toothed cylindrical rotors interdigitated between stator teeth or cylindrical arrays of notched or toothed stator projections.

An axial inlet or outlet may be arranged to deliver the liquid-air composition from the pump to successive rotor-stator assemblies and then via a manifold to the reservoir for application to the fabric. * * . *

In this embodiment the rotor provides a plurality of circular arrays of rotating teeth to ***.

cause shear to fluid flow passing from the axial inlet to the circumference of the rotor on the I: ., upstream side of the rotor and subsequently from the circumference to the axial outlet on the downstream side of the rotor. I. * * S **..

The distance between the rotor and stationary teeth may be about 0.5mm so that the **.* liquid-air mixture is forced radially outwardly or inwardly between the notches or teeth between the two sets of teeth.

In preferred embodiments, two or more preferably two rotor assemblies are employed.

In preferred embodiments, the foamed mixture produced by the foam generator is extruded from a manifold into the reservoir through a slot or die extending laterally of the reservoir parallel to the width of the web. The extrusion slot may be rectangular to deliver a constant flow across the width of the web. Alternatively shaped slots may be employed.

The slot or die may be located on an upper part of a downstream wall of the reservoir extending above the spreader. This facilitates cleaning and drainage of the apparatus and also causes the foam to circulate within the reservoir from the inlet slot to the outlet between the spreader and the web as the web moves through the apparatus.

In a preferred embodiment, the liquid is pumped into the foam generator at a rate of about 0.5-20 1 mm1 dependent on the capacity of the apparatus and the absorbent of the fabric to be coated. The rate of pumping of foam into the reservoir may be controlled to equal the rate of uptake by the fabric surface.

The profiled member may serve as a spreader. This member preferably comprises a threaded member or a member having axially spaced rings. These are preferably triangular and domed in cross section. Threaded members are preferred for ease of manufacture the member may be C-shaped in cross section. Alternatively a comb may be used. Use of a Whitworth thread having 15-25 threads per inch or more, preferably about 20 threads per inch, is preferred. A Whitworth or other widely used thread is convenient, to enable a user to easily check the conformity and correct selection of the profile during use. Selection of an appropriate pitch of thread is important to control the amount of foam passing beyond the s. spreader so that the amount of liquid absorbed by the fabric is sufficient only to penetrate a * single side of the fabric. **..

The foam preferably has a bubble size with a median diameter of 0.2 to 0.3 preferably about 0.3mm � 20%. The foam preferably has a half life of about 15 minutes. The half life is defined as the time for half of the liquid to drain from the foam. * . *SS.

*....: In preferred embodiments the volume of foam applied to the fabric substrate is controlled, The fabric substrate may be a fabric, carpet, felt or other non-woven material.

The amount of foam which is deposited onto the substrate depends on various factors including the amount metered onto the substrate by the profiled member preferably across the substrate, the absorbency of the substrate and the rate of movement of the substrate through the apparatus.

The substrate may be maintained in contact with the spreader profile bar by use of a substrate presentation table and a support bar. These are arranged so that the substrate is mounted in contact with the profile bar to a maximum extent during use.

Foam generated by the foam generator may be delivered to the applicator and onto the surface of the substrate by means of a slot in a manifold or using an oscillating pipe or pipes which traverse reciprocally across the substrate surface.

Following application of the foam to the moving substrate surface in the reservoir, the foam forms a pool or bank on the substrate surface. Movement of the substrate through the applicator causes the pool or bank of foam to form into a cylindrical body of foam rolling on the substrate of the surface upstream of the profile member. Foam is transferred to the substrate surface from the body of foam as the substrate passes underneath the profile member.

The volume of foam that is transferred to the substrate comprises the sum of three components: I. the volume applied by passage between the teeth as rings of the profiled member (volume X); 2. the volume applied by virtue of any spaces in the substrate structure (volume Y); and 3. the volume that is adsorbed by the substrate as it passes underneath the rolling foam * * bank (absorbency A). * *.S*

The volume passing between the teeth, volume X, depends on the area of the spaces . between the grooves, rings or teeth of the profile member. The geometry of these grooves, rings or teeth is predetermined and consequently provides a predetermined area for passage of foam supported on the surface of the substrate. Passage of a completely flat, non-* * ***.

absorbent substrate under the profile member would allow the volume of foam to be calculated from the area of the spaces between the teeth, or rings of the profiled member.

Profile of member bars may be constructed with differently shaped or sized teeth or rings for different levels of foam application. For example carpet backing requires a high chemical application rate so a profiled member with larger teeth may be used. Lightweight fabrics require application of less chemicals so that a profiled member with smaller teeth may be used.

The applications for various sizes of teeth are shown in Table 1.

Foam is also applied to the substrate by virtue of the spaces in the substrate structure.

Usually this volume Y which can pass through the spaces of the substrate structure is quite small compared to volume X for example no more than about 10%. For example spaces in a non-woven structure of a felt or in the weave of a denim fabric are very small compared to the spaces in the teeth of the profile bar. However an amount of foam carried by the spaces in the substrate structure should be taken into account for accurate metering of the foam.

In certain circumstances the volume Y is large. The reverse side of woven and tufted carpet substrates has a very defined ribbed structure that provides a larger volume. These type of substrates can be processed using a profiled member having small teeth or a smooth, toothless surface.

Absorbency A is the amount of the foam which is absorbed by the substrate at the point of application due to contact between the substrate and the rolling foam body. The degree of absorbency is affected by several factors including foam stability. The more stable a foam the less likely it is to be absorbed by the substrate. For adequate processing a foam should have a half-life of 15 to 20 minutes. That is it should take 15 or 20 minutes for the foam to degrade to a volume of liquid that is half the total volume of liquid contained within the foam. * *

S *S*.

Foam stability is influenced by the foam structure. Preferably a stable foam with a large Se amount of small bubbles, or cells are provided by use of a foam mixer which imparts a high dynamic shearing energy into the mixing process. * *0 * * ***.

Drainage of the foam may be controlled by use of a viscosity modifier to improve foam I.....

stability. In most applications it is necessary that the foam degrades to a liquid over a convenient period of time. Care should be taken to ensure that the foam is not sufficiently stable to retain the foam structure during or after the drying process.

Substrate absorbency is an important factor. Dependent on the fibre or polymer type and structure and any previous chemical treatments, the substrate can absorb more or less foam directly during contact with the foam bank. For example a fabric which has been bleached is more absorbent than fabric which has not been bleached.

The absorption of foam may take place during a short time, for example about 0.2 seconds. The substrate speed and the size of the rolling foam bank are important factors in the absorption of foam. A higher speed produces a smaller degree of absorption. A smaller foam bank results in less absorption.

The coated web may be treated by conventional techniques. For example the fabric may be washed by rolling through a water wash, for example through two tanks of water maintained at 90°C.

Amounts, percentages and other proportions referred to in this specification are by weight unless indicated otherwise and are selected from any ranges give to total 100%.

The invention is further described by means of example but not in any limitative sense with reference to the accompanying drawings of which: Figure 1 is a diagrammatic side elevation of an apparatus in accordance with this invention; Figure 2 is a cut-away view of a foam generator in accordance with this invention; Figure 3 is a further cut-away view of the foam generator; Figure 4 shows the rotor of the generator shown in Figures 2 and 3; and * ** Figure 5 is a cross-sectional view of the foam generator. ***.

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* * . . . . ..

* *: Figure 1 illustrates a single sided mercerising apparatus in accordance with this invention. An endless web (1) of denim, corduroy, velvet, velour or other cellulosic textile passes over a driven scroll or open roller (2) to a fabric support table (3). The table (3) is arranged generally horizontally or slowing downwardly (as shown) at an angle of between 10-25°. A static roller (4) is adjustable vertically to tension the web against a spreader (5).

The spreader (5) comprises a C-shaped or otherwise circular or part circular member mounted beneath the downstream wall (6) of the reservoir (10) generally vertical beneath the inlet of the foam extruder die or slot.

Fabric edge detectors (8) serve to monitor the positions of independently controllably moveable edge dams located at the edges of the web, to ensure contact with edge seals (9) of the reservoir.

A foam delivery conduit (11) carries foamed aqueous alkali from a mixing pump and foam generator to a manifold (12). The rate of production and consumption of foam is monitored by a flow meter and laser foam level detector in order to ensure a constant head of foam within the reservoir (10).

In use of the apparatus the web (I) is drawn by the roller (2) across the table (3) in contact with the bottom of the reservoir (10) so that a body of foam delivered to the manifold (12) and subsequently through the extrusion die (7) is maintained in the reservoir (10) in contact with the upper surface of the web. As the web is drawn under the spreader (5), the foam is urged into contact with the upper surface of the web causing the foam to break and pass between the threaded serrations of the spreader (5). The foam composition is absorbed into the upper surface of the web. The fabric is then dried.

Figures 2-5 show a foam generator in accordance with this invention. Figures 2 and 3 are cut away views of a double rotor pump for use in accordance with the present invention.

A drive shaft (20) powered by a motor (not shown), two generally cylindrical rotors (21,22) are mounted on the shaft (20). Each rotor, e.g (21), has a series, for example seven, concentric arrays of teeth facing forwardly and backwardly from each rotor and meshing in an interdigitated manner with stators (32). Each rotor (21) comprises a cylindrical disc-* I. * *.. shaped member from which stream facing teething (36) are separated by toothed or notched apertures (25). Cooling jackets (35) connected to inlets (24) and outlets (29) serves to add ** * * circulation of cooling water through a cooling jacket (35) during use. A liquid and air mixture supplied by a mixing pump (not shown) is supplied to a cylindrical chamber (30) : *. surrounding the shaft (20) to supply an axial flow to the upstream surface of the first rotor ***.

* (22). The rotor and stator components have a small clearance (e.g. 0.5 mm) so that the liquid *** air mixture is forced generally radially outwardly across the upstream face of the first rotor, being sheared by the rotating teeth. At the circumference of the rotor, the liquid passes through an outer duct. The liquid air mixture then passes radially inwardly over the downstream face of the first rotor to an axial duct surrounding the rotor communicating with the upstream face of the second rotor, the liquid air flowpath being repeated across the second rotor before foam emerges from the outlet (27).

Figure 4 illustrates a rotor of a foam generator in accordance with the invention.

Concentric arrays of teeth (40,41) define apertures therebetween (e.g. 23) 50 that a radial passageway for liquid air mixture is provided.

Figure 5 is an exploded cross-sectional view showing the components of the foam generator shown in Figures 2 -4.

Example 1

A 20 teeth per inch profiled member was calculated to have a volume X of 406cm1m2.

A typical 50/50 cottonlviscose sateen weave fabric with a weight of 220gm2 had an average volume Y of approximately 70cm 3m2. The fabric did not have a stain repellent finish and accordingly the adsorbents A was approximately 70cm 3m2.

The total volume of foam applied was 546cm 3m2.

If the foam was applied with a blow ratio of 4 then the volume of foam applied contained 136.5cm 3m2 of liquid. If the blow ratio was 10 then the volume of foam applied contained 54.6cm 3m2 of liquid. Thus a wide variety of application rates could be achieved for a given profile and substrate. * * S * * 0. a... *a*. *. .

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Table 1

Profile Teeth Volume Common usage Typical Application range per inch factor (approximate) __________ (t.p.i.) (mI/rn2) ________________________________________ _________________________________________ 1 5 1622 mI/rn2. Heavy application of latex to 1000-200 mI/rn2 of _______ _________ ____________ carpets. liquor/latex.

2 7 1158 mI/rn2. Application of latex to carpets 800-150 mI/rn2 of liquor/latex.

_______ _________ ____________ and needle-felt. __________________________ 3 9 901 mI/rn2. Application of latex to carpets 600-1 00 mI/rn2 of liquor/latex.

_______ _________ ____________ and needle-felt. __________________________ 4 12 676 mI/rn2. Application of latex to carpets 450-80 mI/rn2 of liquor/latex.

_______ _________ ____________ and needle-felt. __________________________ 16 507 mI/rn2. Application of coatings to 300-60 mI/rn2 of liquor/latex.

light needle-felts and heavy ________ __________ _____________ fabrics. ____________________________ 6 20 406 mI/rn2. Application of finishes to 225-50 mI/rn2 of liquor/latex.

_______ _________ ____________ heavy to lightweight fabrics. ___________________________ 7 26 312 mI/rn2. Application of finishes to 150-30 mI/rn2 of liquor/latex.

medium to lightweight ________ __________ _____________ fabrics. ____________________________ 8 Plain ZERO Application of finishes to very 70-30 mI/rn2 of latex (fabric), lightweight fabrics, or, to or, 1000-200 mI/rn2 of latex _______ _________ ____________ tufted/woven carpets. (carpet). * * * * * * ** *a*. *. * a * * * a.

I * ** * * S *ISI

1:. * * 1*

Claims

CLAIMS1. A method of coating a fabric comprising the steps of: passing an endless web of the fabric through an applicator, the applicator comprising a foam generator adapted to generate a foamed composition, a reservoir for the foamed composition, a lower part of the reservoir being defined by the fabric web; and a profiled member; passing the web under a profiled member to cause the web to absorb a predetermined amount of the foamed composition on a first side of the web to form a treated side of the web; wherein the composition comprises an aqueous solution of a hydrophobic or hydrophilic coating and a foaming agent; wherein the composition prior to foaming has a viscosity in the range of I 00-300cPs; and wherein the foamed composition has a density in the range of 50-lSOgl'; and optionally drying the web.

2. Apparatus for coating a fabric comprising; * .* **, an applicator, the applicator comprising a foam generator adapted to generate a foamed * *.

*.** composition having a density of 50-150g1'; wherein the unfoamed composition has a * viscosity in the range of 100-300 cPs; a reservoir for the foamed composition, and a profiled * * member; : the reservoir having a downwardly opening window, a transport mechanism adapted to : *. transport a web adjacent said windows so that the web forms a lower part of the reservoir, ***.and so that a predetermined amount of foamed composition is absorbed on a first side of the web; the transport mechanism further transporting the web under the profiled member to form a treated side of the web.

4. A method fabric or apparatus as claimed in any preceding claim wherein the fabric has a weight of about 80 to 800gm2.

5. A method fabric or apparatus as claimed in claim 4 wherein the fabric has a weight of about 80 to 400gm2.

-6. A method fabric or apparatus as claimed in claim 5 wherein the fabric has a weight of about 100 to 200gm2.

7. A method fabric or apparatus as claimed in any preceding claim wherein the fabric has a weight of about 120 to 150gm2.

8. A method or apparatus as claimed in any preceding claim wherein the foamed composition is absorbed onto a single side of the fabric in an amount of about 20 to 25% by weight of the fabric.

9. A method or apparatus as claimed in any preceding claim wherein the composition is selected from the group consisting of: aqueous fluorine terpolymers, silicones or zirconium or paraffin wax and mixtures thereof.

10. A method or apparatus as claimed in any preceding claim wherein the composition includes a foaming agent 11. A method or apparatus as claimed in any preceding claim wherein the amount of solution applied does not exceed the imbibation value of the fabric. * *S** * *12. A method or apparatus as claimed in any preceding claim, wherein the composition *S * * includes a viscosity modifier.S....:S13. A method or apparatus as claimed in Claim 12, wherein the viscosity modifier is * . . * S..selected from the group consisting of: modified or substituted cellulose polymers.