This invention concerns the manufacture of carpet. It has particular application to the production of a new product comprising a high twist yarn adhesively bonded to a thermoplastic backing but is not limited thereto. The invention also concerns a new method for the manufacture of bonded carpets.

In the manufacture of carpet, there are two principle commercial processes. The first is a tufting process. In this process yarn is threaded through a series of needles and the needles then sew the yarn onto a backing. The yarn so attached forms the carpet pile. The second process is a fusion bonding process where yarn is pressed, usually by a series of blades, into an adhesive plastisol which is then cured. The cured adhesive and yarn is thereafter laminated with a backing. Carpet made by the tufting process is more expensive to make as about 30% of the yarn is inoperative as a pile as it is lost in the back of the carpet. Bonded carpets are more efficient in this respect as almost all of the yarn is operative in the pile. Bonded carpet also has better dimensional stability than tufted carpet as it doesn't have the same tendency to curl at the edges. This makes it more suitable for products such as carpet tiles.

In prior arrangements there has been found to be very significant variation in yarn tension across a run. For example it is not uncommon in conventional apparatus to find the tension of the yarns at the centre of the run to be more than twice the tension of those on the edge. Surprisingly, the applicants have ascertained that if the tensions of each of the respective yarns being introduced into the bonding apparatus are maintained at a substantially uniform level they do not tend to entangle. Thus, in accordance with a first aspect of this invention there is provided a process for making a bonded carpet substrate comprising a thermoplastic material into which there is bonded a plurality of textile yarns, said process comprising:-

(a) forming two adhesive layers and positioning said layers in spaced face to face relation;

(b) feeding a plurality of separated textile yarns between the said adhesive layers in zig-zag manner such that each of the yarns are bonded at intermediate points along the length of each respective yarn successively to both of the adhesive layers;

(c) thereafter curing the adhesive layers to form a composite structure of cured adhesive layers on either side of a sandwiched layer of yarns; and

(d) separating the composite structure into two separate carpet layers by cutting through the sandwiched layer of yarn; wherein the tension of each respective yarn is controlled so that the tension of each such yarn is substantially the same at the point of introduction between the said adhesive layers.

The applicants have found that the method of this invention works best at low yarn tension. Conventionally yarn tensions at the point at which the yarns are introduced into the bonding apparatus are between 25 to 50 grams force. In the present invention it is preferred that the yarn tension be significantly lower than this.

Preferably, the tension of each respective yarn is in the range of between 3 to 10 grams force at the point of introduction between the said adhesive layers. Most preferably, it is about 7 grams force. Preferably, the yarns are fed through tension reducing means (such as a series of rollers and tensioners) adapted to reduce the tension of the yarns such that the yarns may be easily folded in the required zig zag manner.

With low twist yarns the invention enables one to produce carpets of more uniform yarn distribution and this is particularly important when carpet is dyed. If the density of yarns in different areas of the carpet substrate varies then these areas will present different colour shades on the application of the same amount of dye. This can cause matching problems especially when the substrate is cut into carpet tiles. In addition, when the

tensions of the respective yarns being embedded into the adhesive layers are significantly different this generally results in different tuft lengths as the yarns are not embedded into the adhesive by the same amount by the apparatus moving the yarn into the alternate layers of adhesive material.

With high twist yarns, the advantage of the invention is more manifest. It is the ability to use such yarns at all as this has not previously been possible in methods for the production of bonded carpets.

Bonded carpet offers significant advantages over tufted carpet, but it has not previously been possible to manufacture a bonded carpet using a high twist yarn on conventional fusion bonding apparatus. High twist yarn is popular for both aesthetic and functional reasons. Such yarn does not hang or stand as a straight thread but rather is kinked. Accordingly, carpet made from high twist yarn gives an uneven surface which has proved to be a popular appearance commercially. Further because of the uneven surface, areas of use are less visible when a high twist yarn is used.

In the past it has not been possible to use high twist yarn in conventional fusion bonding apparatus because of its difficulty to control. Control difficulties create problems in a number of respects on conventional apparatus. In such apparatus, it is necessary to introduce the yarn intended to form the carpet pile between folding blades and holding blades which co-operatively feed the yarn in zig zag manner between two layers of supported adhesive. Each return corner of the zig zag configuration makes contact with the adhesive so to form a number of respective bonds along the length of the adhesive layers.

Low and medium twist yarn can be introduced between the folding blades in conventional apparatus in a uniform manner. By contrast, high twist yarns when delivered at varying tensions have been found in the past to respond erratically and less uniformly. Twists and kinks in some of the fibres can cause bunching and tangling. In

addition, conventional equipment includes a series of combs located between the yarn supply means and the bonding apparatus. Generally the combs are located immediately prior to the point at which the yarns enter into the bonding apparatus.

The applicants have unexpectedly found that such comb separators can be dispensed with if the tensions of the respective yarns are controlled so that the tensions of the respective yarns as they enter into the bonding apparatus are substantially uniform. This means that this area of entanglement is removed if the process of the present invention is used. High twist yarns become entangled in comb separators making the process unworkable on conventional apparatus. Furthermore, because high twist yarns will not uniformly hang straight down, it is difficult to commence any run with new yarn as the ends of the high twist yarns will not all properly hang down between the folding blades of the bonding apparatus.

It is thus a further advantage of the present invention that one can produce a bonded carpet using a high twist yarn. In this specification, it should be understood that the term "high twist yarn" is intended to encompass any yarn, the length of which will not hang straight down in an unkinked fashion. Without limiting the generality of the above definition, such yarn is deemed to include any yarn having a twist constant of over 5500. A twist constant of any yarn may be measured in accordance with the following formula:-

Twist constant = / ^" linear density of yarn (tex) x twists per metre

For example, a yarn having a linear density of 750 tex and having 250 twists per metre has a twist constant of:-

y 750 x 250 = 6,846

A medium twist yarn conventionally used in fusion

bonding apparatus has a twist constant of about 5,000.

Thus, in accordance with a further aspect of the present invention there is provided a process for making a bonded carpet substrate comprising a thermoplastic material into which there is bonded a plurality of high twist textile yarns, said process comprising:-

(a) forming two adhesive layers and positioning said layers in spaced face to face relation;

(b) feeding a plurality of separated high twist textile yarns between the said adhesive layers in zig-zag manner such that each of the yarns are bonded at intermediate points along the length of each respective yarn successively to both of the adhesive layers;

(c) thereafter curing the adhesive layers to form a composite structure of cured adhesive layers on either side of a sandwiched layer of yarns; and

(d) separating the composite structure into two separate carpet layers by cutting through the sandwiched layer of yarns; wherein the tension of each respective high twist yarn is controlled so that the tension of each such yarn is substantially the same at the point of introduction between the said adhesive layers.

Preferably each of the yarns have a twist constant above 5,500. Most preferably each respective yarn has a twist constant between 6,000 and 7,500.

High twist yarns tend to respond to tensional variations to a greater extent than medium or low twist yarns. In particular, if the yarns are fed to the tension reducing means at a substantially higher tension than that to which they are to be reduced, at the point of tension reduction, high twist yarns have a greater propensity to kink, bend and hence entangle. Therefore, it is preferred that the yarns be fed to the tension reducing means at a tension which is not substantially greater than the tension to which the yarns are to be reduced prior to introduction between the said adhesive layers. Most preferably, the tensional variation of the yarn prior to and after being fed through the tension reducing means is

no greater than 20%. Most preferably, it is less than 10%. The applicants have discovered that the propensity of the all yarns (but particularly high twist yarns) to kink (and therefore to entangle) may be further reduced by increasing the moisture content of the yarn so that when introduced between the respective adhesive layers it is 10% (by weight) or greater. If the moisture content of the yarn is modified in this way, it is preferred that the tension in the yarns be controlled so that they are uniform and at the desired level after the moisture content has been varied and prior to any further tension reduction. In conventional bonding processes, the moisture content of the yarn is often no more than about 5%. It has been found by the applicant that by increasing the moisture content of the yarn, it swells and bulks and that by increasing the moisture content to 10% or greater, a yarn becomes easier to control and thus easier to fold in a uniform manner between the adhesive layers.

Preferably, woollen yarns are increased in moisture content to between 12 to 20%. Most preferably, the moisture content is about 15%. When nylon yarns are used, the preferred moisture content is about 10 to 15% and most preferably about 12%. In one embodiment of the invention, the moisture content of the yarn is increased to the required level by passing the yarn through a steaming mechanism prior to the introduction of the yarn between the adhesive layers. Most preferably, the yarns are passed through the steaming mechanism and the tension of the yarns is controlled (by apparatus known in the art) so that the yarns are delivered from the steaming mechanism having the desired moisture content and at substantially uniform tension across the yarn run. The yarns are then fed through tension reducing means following which they are introduced between the respective adhesive layers. The adhesive layers used in any of the embodiments of this invention are preferably formed from a vinyl chloride resin polymer. Desirably, this resin bonding layer is incorporated about an inert structural layer such as a fibreglass matt. The thermoplastic adhesive is

usually in the form of a plastisol which will cure on heating. After the composite structure has been formed and separated into two separate carpet layers, it is preferable that a separate backing layer (again preferably reinforced PVC) be laminated so to form a more rigid and stable carpet structure.

Depending on the number and spacing of the yarns used in any one run, it is also desirable to utilize means which maintain the yarns in separated fashion as they are being fed to the bonding apparatus but which will not unduly interfere with the yarns which might lead to entanglement - such as happens with a comb separator. It is preferred that the respective yarns be passed over a support means which is adapted to do this. It is desirable that the support means be positioned such that the respective yarns are physically supported on at least one portion of the surface of the support means as they are fed to the adhesive layers. The support means may be of any suitable shape. Preferably, it is a bar of circular, square or rectangular cross section and of such length to extend across the full width of the yarn run. In such embodiment, the bar is placed above the level of the travel of the yarn preceding the bar so that the angle of contact between the yarn and the bar is greater than 0°. Preferably, it is between 0 to 10°, most preferably between 2 to 5°. As previously stated, it has been found by the applicants that a high twist yarn could not be effectively separated using a comb as the yarn would become entangled in the comb. The applicants have found that low and high twist yarns can be uniformly separated without a comb if the tensions of the yarns are uniform especially if their bulk has been increased by humidification. The replacement of such a comb with a single support surface was not expected by the applicant to provide and encourage the maintenance of the required yarn separation. However, surprisingly, this simple expedient of passing the yarn over such support means in conjunction with the uniform tensions of the yarns has been found to very effectively maintain yarn separation

without any additional separating apparatus. Preferably, such separating means is located between the steamer and the folding blades of the bonding apparatus.

A further problem that arises especially in the use of high twist yarn in convention fusion bonding apparatus is in the start up phase. As discussed above, high twist yarn does not hang straight down and thus it is not adapted for easy uniform introduction between the adhesive layers. Whilst maintaining substantially uniform tension across the yarns and increasing the moisture content of the yarn ameliorate this problem, it is preferred that new yarn be introduced between the adhesive layers by attachment to yarn which has been previously introduced between the adhesive layers. In conventional processing, carpet substrates are formed in sheets (usually about six foot wide) . Across this width, it is not unusual to have well over 500 individual yarn threads each of which are required to be simultaneously introduced in a uniform manner between the two respective adhesive layers. In accordance with the abovementioned preferred method of introducing new yarns, the start ends of new yarns and the ends of existing yarns which have already been introduced between the respective adhesive layers (and in conventional apparatus hence introduced between the folding blades), are secured together by a joining band which is preferably at least one sheet of adhesive material positioned across the full width of the yarns to be introduced into the bonding apparatus. There is no need to attempt to obtain end to end connection of individual threads. It has been found that this methodology is very effective with conventional fusion bonding apparatus as it enables the yarns within the apparatus to effectively draw the new yarns whether these be high or low twist yarns between the folding blades so to commence the new run. It will be appreciated that this method of yarn connection can only be contemplated when using the method of the present invention when there is no separating comb near the entrance of the bonding apparatus. A joining band could

not pass through the comb. Thus this simplified method of starting a new yarn run is a further consequent advantage brought about by the present invention. Preferably, a single sheet of heat sensitive tape is positioned between the respective layers of the new and old yarns. Alternatively, heat sensitive adhesive tape can be used both above and below the joined yarns. Once the tape is correctly positioned, heating means may be applied to the tape so to effect the securement to both ends of the respective yarns. The applicants have found that this process works well for all yarns. In the case of high twist yarns it is of particular value as no practical atlernative exists.

This process may be utilized when an existing roll of high twist yarn is about to be exhausted and a new roll of high twist yarn is to be introduced into the bonding apparatus or alternatively, on initial start up, a length of low twist yarn may be introduced into the bonding apparatus in the normal fashion, this yarn cut, and new high twist yarn attached thereto in accordance with the methodology described above.

In accordance with another aspect of this invention there is provided an apparatus for making a bonded carpet substrate which includes:- (a) yarn supply means;

(b) yarn tension adjustment means adapted to simultaneously receive a plurality of textile yarns at different tensions and adjust the tensions of the yarns so that they are substantially uniform; (c) yarn bonding means adapted to simultaneously receive a plurality of textile yarns and bond each of said yarns in zig-zag manner between two respective adhesive layers so to form a carpet composite comprising two adhesive layers sandwiching a layer of yarn; and (d) separating means for separating the carpet composite into two bonded carpet substrates; the said apparatus being configured so that a plurality of yarns can pass from the yarn supply means to the yarn tension adjustment means and thereafter to the

yarn bonding means for the formation of a carpet composite which is then fed to the separating means for the formation of carpet substrates.

Preferably the yarn tension adjustment means is adapted to reduce the tensions of the respective yarns to tensions of between 3 to 10 grams force.

The apparatus also desirably includes humidifying means adapted to raise the moisture content of the yarns to between 10 to 20%. The apparatus does not include a comb yarn separator. However, if further yarn separation is required, it has been found that a shallow coil spring can be used to separate yarns. Usually it is preferred to provide a coil spring separator at a location prior to the position of the humidifying means. The separator is preferably a coil spring over which the yarns can lie. In one embodiment a support is positioned within the coil spring and located so to hold the yarns passing through the spring at the desired height. In such an embodiment it is preferred that the support include a plurality of spaced pegs oriented so to pass between various coils of the spring. This enables an operator to adjust the tension of the coil spring in different locations along its length and thus the number of coils per unit length. This is useful in quickly and easily adjusting the yarns passing over the separator to a substantially uniform density across the run.

When such a coil separator is used it is preferred to join new yarns with the joining band at a point somewhere between the humidifying means and the coil separator. This avoids the need to run the tape through the separator. Whilst this is possible with the coil separator of this invention (and would not be possible with a comb) it is not preferred as it can upset the distribution of the yarns running through the coil spring separator.

The present invention also relates to a new carpet structure comprising a cured thermoplastic adhesive layer into which there is bonded a plurality of high twist

yarns. Preferably, the high twist yarns have a twist constant of 5,500 or greater. Most preferably, it is between 6,000 and 7,500. Preferably, the thermoplastic adhesive layer includes an inert structural layer such as a fibreglass mat. The thermoplastic may be selected from a range of suitable materials but is preferably a vinyl chloride polymer, a latex rubber or polypropylene. The carpet structure may optionally include further support layers laminated to the adhesive layer. The high twist yarn is preferably wool yarn between 650 and 900 tex which has 240 or more twists per metre or nylon yarn between 680 and 920 tex which has 225 or more twists per metre.

The invention is hereafter described by reference to a preferred embodiment which is illustrated in the accompanying drawings in which:-

Figure 1 is a schematic representation of apparatus used in the process of the present invention;

Figure 2 is a cross sectional view of a composite substrate formed in accordance with the invention; Figure 3 illustrates the joining of a new set of yarns to existing yarns using a joining tape;

Figure 4 illustrates a preferred bonded carpet substrate as formed in accordance with the invention; and

Figure 5 illustrates a coil spring separator as used in the apparatus of this invention.

Referring first to figure 1, there is generally illustrated a fusion bonding machine 1 adapted to support bonding layers 2 and 3 positioned in face to face relation. An example of such a machine is manufactured by Deering Milliken Research Corporation. The respective layers are generally separated by between 10 mm to 30 mm. Bonding layers 2 and 3 may be made from any suitable thermoplastic resin preferably in the form of a plastisol reinforced with fibreglass material. High twist yarn 4 is delivered from a roll 5 and maintained in generally separate and uniform relation by passing through coil spring 6. In one preferred bonded carpet, the high twist yarn has a twist constant of about 6,850. The coil spring 6 is preferably stretched so that

there is between 3 to 4 mm between each coil of the spring and the yarns are uniformly distributed along the length of the coil spring by adjusting the gaps between the coils by pegs 7 located in a support rod 8 (see Figure 5). With further reference to Figure 5 it can be seen that the yarns 4 can be separated by a wide amount (designated W), a small amount (designated S) or a normal amount (designated N) by adjusting the coil spring in various locations and maintaining it in place by pegs 7. The tensions of the respective yarns at this stage vary significantly across the run from, for example, 45 grams force to 90 grams force. High twist yarns 4 are thereafter introduced and taken through a humidifier 9 in the nature of a steam box. The yarns pass through the steam box 9 at such rate so that the moisture content of the yarn increases to about 15% on a weight basis. A tensioner (not shown) within the steam box 9 is provided so to reduce and moderate the tension of the fibres so that each is substantially the same as the yarn leaves the steam box 9. Preferably, the tension of each respective yarn is reduced to about 7 to 15 grams force. The yarn is thereafter drawn over bar 10 which acts to maintain the uniform separation of the yarns one from the other. These yarns then enter the fusion bonding apparatus 1 through a series of rollers and tensioners (generally shown at 11) which further reduce the tension of the yarns uniformly to about 5 grams force. The yarn is then fed through folding blades 12 which are adapted to fold the yarn and introduce it between the adhesive layers 2 and 3 in a zig zag pattern as generally shown in Figure 2.

In Figure 2, it can be see how the high twist yarn is introduced between the respective adhesive layers 2 and 3. As shown, the yarn is continuous and is intermediately bonded successively to each of the adhesive layers, for example at points 13, 14, 15 and 16.

The composite product generally illustrated in Figure 2 is thereafter conveyed to a heating station (not shown) wherein the resin plastisol is cured. The composite product is then separated in half by cutting

generally down the centre of the yarn (shown by the dashed line if Figure 2) . Separate layers are then laminated with a further reinforced PVC layer to form a carpet product as shown in Figure 4. With reference to Figure 3, there is illustated a preferred method of enabling the initial introduction of a high twist yarn into the fusion bonding machine. Adhesive tape 17 extends between old yarns 18 and new yarns 19. The old yarns effectively draw the new high twist yarns into the folding blades 12 of the fusion bonding apparatus. Once the adhesive tape 17 has passed through the bonding apparatus, this section of carpet is simply cut from the roll and discarded.

The product produced by this methodology is illustrated in Figure 4. Using the process as described, it has been found that high twist yarn can be effectively utilized in bonding apparatus without yarn entanglement. Such product has not hitherto been available in such format. The preferred carpet structure comprises a fibreglass reinforced backing layer 20, a fibreglass reinforced bonding layer 21 (both layers are preferably of a PVC resin) and a pile 22 embedded in the bonding layer comprised of high twist yarn.

Finally, it is to be understood that various modifications and alterations may be made to the methods and products previously described without departing from the spirit and ambit of the invention as hereinbefore described.