WO2016110548A1

WO2016110548A1 - Method to produce a laminated carpet tile, and tile obtainable with this method

Info

Publication number: WO2016110548A1
Application number: PCT/EP2016/050225
Authority: WO
Inventors: Chris Reutelingsperger
Original assignee: Dsm Ip Assets B.V.
Priority date: 2015-01-09
Filing date: 2016-01-07
Publication date: 2016-07-14

Abstract

The invention pertains to a method to produce a laminated carpet tile comprising providing a first polymer sheet having yarns fastened thereto, the first sheet having a first surface and a second surface, the yarns extending from the first surface, providing a second polymer sheet,laminating the second polymer sheet to the second surface of the first sheet at a temperature above the glass transition temperature of the first and/or second polymer sheet, cooling the laminated product to room temperature, and optionally cutting the laminated product into multiple sub-products,wherein the step of cooling the laminated product to room temperature includes cooling the laminated product to a temperature below the glass transition temperature of the first and/or second sheet while the laminated product is forced to take a curved constitution wherein the second sheet is positioned at the inner side of the curve.

Description

METHOD TO PRODUCE A LAMINATED CARPET TILE, AND TILE OBTAINABLE

WITH THIS METHOD

GENERAL FIELD OF THE INVENTION

The present invention pertains to a method to produce a laminated carpet tile comprising providing a first polymer sheet having yarns fastened thereto, the first sheet having a first surface and a second surface, the yarns extending from the first surface, providing a second polymer sheet, laminating the second polymer sheet to the second surface of the first sheet at a temperature above the glass transition temperature (Tg) of the first and/or second polymer sheet, and cooling the laminated product to room temperature to form the carpet tile. Optionally the laminated product, if the dimensions are not suitable for use as a carpet tile, is cut into multiple sub-products of the desired dimensions to form multiple corresponding tiles. The invention also pertains to a carpet tile obtainable with this method.

BACKGROUND ART

With laminated carpet tiles a particular problem to be addressed is curling of edges or corners. Curling of edges or corners is a problem since the edges in general to not coincide with an edge of the surface to be covered, and thus, the curled up edges or corners may lead to irregularities in center areas of the covered surface. An important reason for the occurrence of curling is the existence of internal strain in the laminate, even when laminating takes place above the glass transition temperature of the first or second sheet. This can be understood as follows: the laminate comprises different layers (note: the term "layer" or "sheet" does not exclude that the layer or sheet is actually constituted out different sub-layers) that need to provide very different properties to the carpet tile. The first sheet, also called primary backing, needs to stably bear the pile yarns. The second sheet, also called secondary backing, in general provides dimensional stability to the carpet tile. An intermediate layer may be provided to improve the (walking) comfort of the tile or the wear resistance. For this reason, the structure of the different layers is inherently different. And thus, even when for example the first and second sheet are made of the same material, and the laminating is performed above the glass transition temperature to try and prevent any lamination induced internal strain, the occurrence of internal strain due to different deformations by the action of moist and temperature, is inherently present. The problem is even increased when different materials are being used for constituting the sheets, in particular when these materials per se expand and contract differently due to moist and or temperature. For example, typical polymers used for making carpet are polyamide, polyester and polyalkylene. These polymers have totally different deformation characteristics due to moist and temperature.

Various solutions are provided in the art to mitigate the problem of curl. Gluing the carpet tiles firmly to the surface to be covered may be an appropriate solution for those applications where it is no problem that the carpet is durably anchored to the surface, such as for some domestic applications. However, for other applications gluing is not found convenient. For example, gluing is not an option in public areas where part of the surface covering is regularly exchanged due to high wear (shops, airplanes, cruise ships). Other examples are entrance mats and car mats (which are also carpet tiles in the sense of the present invention) that must be easy to remove from the surface for cleaning. Carpet tiles are often used when easy removing from the surface to provide cleaning and/or replacement is needed.

Another solution is to simply provide a thick enough second or intermediate sheet that is dimensionally stable per se, to counteract any internal strain. Typically, thick bituminous layers are provided for this purpose. Disadvantage is that the total weight of the carpet then often exceeds 4.0 kg/m², which makes the carpet not only expensive to make (increased weight inherently adds costs), but also more difficult to process and handle. Such solutions are for example described in DE 2850102, NL 8203180, EP 29761 1 and US 5,030,497.

An alternative solution is provided in EP 382349. Here it is proposed to use a dimensionally stable (glass-fibre) intermediate layer in combination with a second sheet (the tile backing), which second sheet exactly counteracts the tension induced by the first sheet (the primary backing). This solution however restricts the type of second sheet that can be used to produce the carpet tremendously.

Another solution is described in JPH 01247654 (assigned to Nitto Boseki). It is described to produce a carpet tile as a laminate of multiple layers, a first (top) sheet and a second sheet comprised of three different layers: two polymer sheets with a glass fibre layer in between these sheets. By calendering the laminated product the glass-fibre layer is bent, such that the tile inherently curves downwardly at its edges. An alternative solution using a glass-fibre layer is described in JPH 02142514

(assigned to Senshiyuu Shikimono): here the glass fibre layer serves to prevent curling by specified deformation of the laminated layers.

Yet another solution is known from JPH 0852834 (assigned to Toa Wool Spinning & Weaving). The proposed carpet tile comprises three laminated layers, of which the bottom layer is forced to shrink more than the intermediate and top layer, such that the tile inherently curls down. Disadvantage is that this tile has an inherent built-in strain which is even increased when a tile is forced to remain flat on a surface. The risk of delamination and strain induced wear therefore is high.

W094/16138 discloses a method to produce a laminated carpet comprising a first polymer sheet having yarns fastened thereto, and laminated thereto a second polymer sheet using heat, and cooling the laminated product to room temperature to form the carpet. It is not clear from W094/16138 which temperatures the product should attain at the various heating and cooling stations. Also, since

W094/16138 does not pertain to carpet tiles, the problem of curling of the edges and corners does not exist.

WO2014/198731 and GB2076336 disclose laminated carpet tiles. No specific measures are taken to prevent curling up of the corners or edges.

OBJECT OF THE INVENTION

It is an object of the invention to provide an alternative solution to prevent or at least mitigate the problem of curling of a carpet tile. SUMMARY OF THE INVENTION

In order to meet the object of the invention a laminated textile product as defined in the GENERAL FIELD OF THE INVENTION is devised, wherein the step of cooling the laminated product (i.e. the product as a whole) to room temperature includes cooling the laminated product to a temperature below the glass transition temperature of the first and/or second sheet, while the laminated product is forced to take a curved constitution, wherein the second sheet is positioned at the inner side of the curve.

It was found that by forcing the product to take a curved constitution which corresponds to two parallel edges being curled down, and at the same time cooling the product to a temperature below the glass transition temperature of at least one of the sheets, the corresponding edges of the resulting product, and thus the corners corresponding therewith, have the inherent tendency to curl down. This can be understood as follows: by cooling the product (i.e. the product as a whole) to below the glass transition temperature of this layer while being in a curved ("corners down") constitution, this constitution will to some extent be "frozen" into the end product. Indeed, the freezing in of the curved constitution by cooling the product to below the glass transition temperature of at least one of the sheets, depends on the fact that this sheet as a whole (i.e. the volume or bulk of this sheet) right before the cooling down has a temperature above its glass transition temperature. This means that this particular sheet, due to its rubbery state above the Tg, can easily adapt the curved constitution, whereafter, due to the cooling process, this curved constitution is frozen in by turning at least this sheet of the product into a glassy state. This leads to a product wherein by the frozen-in curved constitution of at least this one sheet, there is an inherent tendency for the edges and corners of the product, i.e. the carpet tile, to curl down. Although counteracted by the weight of the tile itself, in practice it means that the tile remains flat (i.e. on its surface) and the corners do not, or to a very low extend, have the tendency to curl up.

The invention is also embodied in a carpet tile obtainable by using the method according to the invention. This tile is advantageous over prior art tiles in that it does not need a thick rigid layer to prevent curl, or an internal glass-fibre layer. Also, as opposed to the tile as known from JPH 0852834, the new tile does not need to rely on the existence of internal strain that is even increased during normal use, to have the tendency for the corners to curl down. DEFINITIONS

A carpet tile is a textile product having a pile of yarns extending from a dimensionally stable carrier, which product is used to cover surfaces of any kind (e.g. floors, walls, interiors of vehicles), as a primary covering of this surface or as secondary covering (i.e. to overlay a primary covering; examples are entrance mats and runners), but has limited dimensions, below a width of 1 to 2 meters, typically below a width and length of 1x1 meters, as opposed to broadloom carpet which has a typical width of about 4-6 meters and a length of about 10-50 meters. Carpet tiles can be of various different constructions such as woven, needle felted, knotted, tufted and/or embroidered, though tufted products are the most common type. The pile may for example be cut (as in a plush carpet) or form loops (as in a Berber carpet).

The glass transition temperature (abbreviated "Tg") of a sheet is the temperature at which the solid amorphous material of which the sheet is made becomes soft upon heating or brittle upon cooling. The Tg is the temperature region where the polymeric material (when heated) transitions from a hard, glassy material to a soft, rubbery material. The Tg of the sheet is thus the temperature at which the sheet as a whole undergoes this transition. The glass transition temperature is always lower than the melting temperature (Tm) of the crystalline state of the material. The Tg can be established by using Differential Scanning Calorimetry (DSC) at speed of 20K/min as commonly known in the art, typically by defining the midpoint of the said

temperature region as Tg.

Tensile stress in a sheet-like product is a common situation wherein the sheet is subjected to tension by opposite forces in its horizontal plane.

A radius of curvature of an arbitrary curve, is the radius of the circle that best fits the curve over its full length.

Calendering is a finishing process used to make a product more smooth and optionally glossy by applying pressure, heat or a combination of pressure and heat to the product.

A sheet is a substantially two dimensional mass or material, i.e. a broad and thin, typically, but not necessarily, rectangular in form.

The horizontal direction in relation to a laminated textile product is the two-dimensional plane in which the laminated textile product extends.

A laminate is a structure comprising multiple stacked layers mechanically connected to each other, for example by (partly) melting the layers and fusing them together or by using an adhesive.

Resilient means to be able and deform and automatically return to the original configuration.

A hot melt adhesive is a thermoplastic adhesive that is designed to be melted, i.e. heated to transform from a solid state into a liquid state to adhere materials after solidification. Hot melt adhesives are typically non-reactive, crystalline and comprise low or no amount of solvents so curing and drying are typically not necessary in order to provide adequate adhesion.

EMBODIMENTS OF THE INVENTION

In a first embodiment of the method according to the invention, in which method the step of laminating the second polymer sheet to the first sheet takes place at a temperature above the glass transition temperature of the first and second polymer sheet, in the step of cooling the laminated product while this product is forced to take a curved constitution, leads to a temperature below the glass transition temperature of the first and second sheet. This means that the product as a whole reaches this indicated temperature below the glass transition temperature of the first and second sheet. In this embodiment, the curved constitution is "frozen" for the first and second sheet, which further decreases the risk of curling.

In another embodiment the cooling of the product while being in the curved constitution takes place without applying tensile stress to the product. Applying tensile stress during cooling, for example by pulling the product through the process (which is the typical way of transporting a product through a lamination set up), introduces all kinds of unwanted internal strain which is disadvantageous for the stability of the resulting carpet tile. In this embodiment, such internal strain will not be introduced in the carpet tile.

In yet another embodiment the product is forced to take a curved constitution by guiding the product along at least part of an outer circumferential surface of a drum, wherein the said surface of the drum is cooled in order to cool the product. This embodiment has shown to be a relatively simple way to introduce the tendency of the edges and corners to curl down. It makes use of a simple cooling drum, along the surface of which the product in transported in thermal contact. By keeping the temperature of the surface of the drum sufficiently low, the product can be cooled down to a temperature below the glass transition temperature as required.

In still another embodiment the radius of curvature of the curved constitution is between 10 and 300 cm. Depending on the specific materials used to make the carpet tile, the tile will have a lower or higher tendency of curling. If this tendency is very high, the product needs to be cooled down while being formed into a curve with a relatively small radius of curvature. If this tendency is very low, a relatively high radius of curvature will be sufficient to introduce forces to counteract this tendency. It was found that with a radius of curvature between 10 and 300 cm, for the vast majority of materials used, tiles can be made that have no, or only a very low tendency to curl.

In again another embodiment the cooling of the laminated product while the laminated product is forced to take a curved constitution, takes between 0.1 and 5 seconds. It was found this this time slot is suitable to apply the present method.

In an embodiment the second surface of the first sheet is subjected to a calendering process before the step of laminating the sheets. Calendering appears to lead to surface that is better suited for laminating since it is more smooth than the original surface. During lamination therefore, less stress is induced.

In an embodiment, during the calendering process the second surface is treated by applying heat such that the yarns adjacent the second surface at least partly melt during the calendering process. Due to the fact that the yarns are at least partly molten, the calendering process may lead to an even more smooth and glossy surface. Although it was expected that this would lead to even more internal strain (due to the fact that the previous discontinuous assembly of yarns is transformed into a more or less continuous layer), it appeared that this embodiment may lead to very stable carpet tiles.

In yet another embodiment wherein the yarns extend through the second surface of the first sheet, the molten part of the yarns is spread in a direction parallel to the first surface of the first sheet by imparting a mechanical force on the molten fraction of the yarns in the said direction. This mechanical force may lead to yet again an improved calendering process, virtually uniting the yarn elements at the back into one continuous layer of material. In a further embodiment the calendering process takes place by pressing the second surface of the first sheet against a heated body that has a relative speed with respect to the second surface, for example, by keeping the heated body stationary while transporting the product along this body.

In still another embodiment the first sheet and second sheet are laminated by applying a hot melt adhesive between these sheets (which does not exclude that the hot melt adhesive is combined with another type of adhesive). It was expected that the hot melt adhesive might not withstand the imposed curvature. A hot melt adhesive, due to its crystalline properties, is relatively brittle when cold. As such, it was expected that the local deformation of the adhesive layer would lead to breakage of this layer and hence delamination. Surprisingly, this does not appear to be the case. The reason for this is unclear. In a further embodiment the hot melt adhesive comprises at least 50% by weight of a polymer chosen from the group consisting of polyurethane(s), polycarbonate(s), polyester(s), polyamide(s), poly(ester-amide(s)), polyolefine(s), mixtures thereof and/or copolymers thereof. This provides for example the option to choose an adhesive of the same type of polymer as used for constituting the sheets. This may help when recycling the textile product.

In an embodiment of the method according to the invention, in which embodiment an intermediate layer is positioned between the first sheet and second sheet, which intermediate layer together with the first and second sheet is laminated into the laminated product, the intermediate layer is resilient to allow local deformation of the layer along the second surface of the first sheet and along the surface of the second sheet adjacent to the intermediate layer. It was found that the resilient property of the intermediate layer is able to further mitigate the problem of curl arising from internal strain. Without being bound to theory, it is believed that due to the resilient properties as defined here above, it is provided that each of the sheets may expand or contract ("deform") in the horizontal direction independently of an expansion or contraction of the second sheet, and thus, that no (or only low) internal strain may arise. This can be understood as follows: due to the resiliency of the intermediate layer which allows local deformation of the material in this layer along the surface of at least one sheet, the horizontal deformation of (one of) the sheet(s) may now be locally absorbed by the intermediate layer, without mechanical forces being transferred directly from the first sheet to the second sheet or vice versa. Although there are many ways in which a resilient layer according to the invention can be constituted, the common properties are that such a layer has a relatively open (not massive) structure, is resilient and does not have horizontal rigid layers along both surfaces that cannot deform substantially independently. This provides that the intermediate layer can deform locally along the surface of at least one of the sheets without substantially transferring deformation forces to the surface of the other sheet.

In another embodiment the intermediate layer is mechanically discontinuous in two perpendicular horizontal directions. Mechanical discontinuity allows for bigger local deformations without transferring forces to the neighbouring areas. For example, using an open foam that has in a horizontal plane considerably more "air" than polymer, is able to resist transfer of forces better than a mechanically continuous but very elastic material.

In yet another embodiment the intermediate layer is a fibrous layer. Fibres can be easily assembled to form a stable layer, and still provide for the option of local deformation. For example when fibres are entangled but not mechanically connected at the sites were fibres cross, deformation may stay locally, while the layer as a whole has significant mechanical stability.

In still another embodiment the intermediate layer is a non woven layer. Non woven layers are easy to assemble, even when using very short fibres and are therefore economically attractive. While short fibres may prevent deformation to be easy transferred over distances considerably longer than the fibres themselves, long fibres, due to the non-woven arrangement (for example meandering like a river) may also be perfectly capable of allowing local deformation and not transferring forces to the neighbouring areas.

In again another embodiment the intermediate layer is a knitted layer. A knitted layer (for example available as Caliweb® from TWE, Emsdetten, Germany), although the fibres are in essence endless, appears to be perfectly suitable to allow only local deformation. Like a tubular knitted sock that fits every curve of a foot, a knitted layer can easily deform locally without transferring forces to neighboring areas. EXAMPLES

Figure 1 schematically shows a cross section of a carpet tile according to the invention Figure 2 schematically shows various types of resilient layers

Figure 3 schematically shows a configuration for applying a calendering process Figure 4 schematically represents a laminating and cooling down configuration

Figure 1

Figure 1 is a schematic representation of the respective layers of a carpet tile 1 according to the invention. The tile comprises a first sheet 2, the so called primary backing, which is a tufted nonwoven sealed nylon obtained from Shaw

Industries, Dalton USA. The nylon yarns 5 extend from the first surface 3 of the sheet and are sealed to the second surface 4 of the sheet using the fibre binding method as known from WO2012/076348 (see also the RD591084 disclosure with reference i.a. to figures 3 and 5 of that disclosure). The weight of this first sheet is 670 g per m². In order to provide mechanical stability, the tile 1 comprises a second sheet 6, in this case a backing of a polyester needle felt backing fleece obtained as Qualitex Nadelvlies from TWE, Emsdetten, Germany. The weight of this second sheet is about 800 g/m ². In this particular embodiment, in between the first and second sheet is a resilient layer 10, in this case a polyester expansion fleece having a weight of 330 g/m², which is obtained from TWE as Abstandsvliesstof, a non-woven fabric which has not been needle-punched. Both sides of this layer 10 are constructed of a mesh of 100% PET which has been only mechanically solidified. The thickness of this intermediate layer is about 4 mm. The three layers (first and second sheet and intermediate layer) are glued together using a polyester hot melt glue obtainable as Uralac from DSM, Geleen, the Netherlands, applied as layers 1 1 and 12 at a weight of about 300 g/m². The total weight of the carpet tile is thus about 2.4 kg/m².

The resilient layer 10 may be sufficient to prevent curl under normal interior circumstances. The intermediate layer has adequate resilient properties, i.e. it is able to locally deform along the second surface 4 of the first sheet and along the surface of the second sheet 6 to prevent mechanical forces from being transferred directly between the first sheet and the second sheet, even when expanding or contracting at different magnitudes. This way curl due to the different deformation of the first sheet 2 and the second sheet 6 can typically be prevented when the temperature varies between 20° and 28°C and relatively humidity varies between 30% and 60%. These variations define recommended office conditions. In order to even further improve the anti curl properties of the tile, the tile is laminated using the method according to the current invention, i.e. wherein the freshly laminated hot constitution of different layers is cooled down while being curved. This is further elaborated upon in connection with figure 4.

It is noted that in this example the different layers are interconnected using the same hot melt adhesive (HMA) applied in the form of a layer having a weight of about 300 g/m² (about 0.3 mm thick). However, different HMA's could be used for the two layers 1 1 and 12. Also, for connecting the second sheet (6) another type of adhesive (or other connection means) could be used, for example when de-coupling of the second sheet 6 from the intermediate layer 10 is not necessary when recycling the end product (for example when the two layers are in essence made of the same polymer).

Figure 2

Figure 2, composed of sub-figures A through E, schematically represents a number of examples of resilient layers 10 for possible use in the present invention. In figure 2A, the resilient layer 10 consists of an open foam structure 15. The foam is made of an elastic polymer and comprises a high content of air bubbles 16. These bubbles cross the upper and lower surfaces 20 and 21 of the structure 15 (in other words: there are no continuous closure layers provided at these surfaces 20 and 21 ). This way, the foam 15 can easily deform locally along any of the two surfaces 20 and 21 without forces being transferred substantially through the layer.

In figure 2B a resilient layer 10 is shown that comprises one continuous layer 25 at the bottom. This layer is provided with multiple individual fibres that are packed so dense that a next layer can be glued against the distal ends of the fibres. Each fibre can move individually at its top without passing any (significant) forces to neighbouring fibres.

In figure 2C an alternative arrangement of the fibre bearing sheet 25 as depicted in figure 2B is shown in order to create a resilient layer for use in the present invention. In this case, the sheet 25' is provided with fibres 26'and 26" on both sides. This way, the resilient layer can deform locally along both sides of the layer 10. In figure 2D a resilient layer 10 is depicted which consists of long entangled (braided) yarns 36, in this case according to an irregular pattern. By creating a package with a certain thickness (thicker than the yarn 36 itself), the layer may deform locally along both its surfaces.

In figure 2E yet another alternative resilient layer 10 is schematically shown. In this case the layer consists of needle-felted short fibres 46. Since the fibres 46 are not durably three dimensionally arranged (i.e. there is no durable mechanical interconnection to fix the position of the fibres), the layer may deform locally along both its surfaces.

Figure 3

Figure 3 schematically represents a configuration for applying a yarn melting process (also called a fibre-binding process) for use in the present invention. In the configuration shown in Figure 3 a first heating block 500 and a second heating block 501 are present, in order to heat the heating elements, also denoted as heating blades or heating bodies, 505 and 506 respectively. These heating elements have a working surface 515 and 516 respectively, which surfaces are brought in contact with a product to be processed, typically a primary carrier to which yarns are applied via a stitching process such as tufting. The working surfaces both have a working width of 18 mm, and the intermediate distance is 26 mm. The back surface of the product is brought in contact with the working surfaces of the heating elements such that the surface is calendered. In order to be able and apply adequate pressure for the product to be processed, a Teflon support 520 is present which is used to counteract a pushing force applied to the heating elements. In operation, the heating elements are moved relatively to the product in the indicated direction X. Typically, the heating elements are stationary and the product is forced to travel between the working surfaces and the Teflon support in a direction opposite to the direction indicated with X.

The (intermediate) textile product to be processed with the above described configuration (the product itself is not shown in Figure 3) consists of a primary sheet provided with a cut pile of yarns, tufted into the sheet. The yarns typically have a melting temperature of about 250-280°C depending on the type of polymer used. This product is processed using a temperature of the first heating element of typically 200-220°C, in order to pre-heat the product. The second heating element is kept at a temperature about 15°C above the melting temperature of the yarns. To keep the temperatures at the required level, the heating blocks and heating elements are provided with layers of insulating material 510, 51 1 , 512 and 513 respectively. The product is supplied at a typical speed of 1 -20 meters/min, and the pressure applied with the heating elements is about 1.35 Newton per square centimetre. Figure 4

Figure 4 schematically represents a laminating configuration for applying a second sheet, in this case a dimensionally stable secondary backing sheet (cf. sheet 6 of Figure 1 ), to the back of the first sheet (cf. sheet 2 of Figure 1 , with yarns 5 applied thereto) that is produced with a method as described in conjunction with Figure 3, and cooling the laminated product down in accordance with the present invention. In this figure a first roller 600 is depicted on to which roller is wound a 2 metre wide web of the said (pre-fabricated) product made according to the method described in conjunction with Figure 3 (cf. sheet 2). The product is unwound from the roller 600 to have its back-side 217 to come into contact with a second roller 601 . This roller is provided to apply a layer of hot melt adhesive (HMA) 219 to the back side 217. For this, a bulk amount of HMA 219 is present and heated between the rollers 601 and 602. The thickness of this layer can be adjusted by adjusting the gap between these two rollers. Downstream of the site of HMA application is the second sheet 215 (cf. sheet 6), which sheet is unwound from roller 603. This sheet is pressed against the hot and tacky adhesive and the lamination process takes place in the unit 700. This unit consists of two heated belts 701 and 702 which press the sheets together. When the laminated product 201 leaves unit 700 it still has a temperature above the glass transition temperatures of the sheets 2 and 6 respectively (typically above 150 °C). This intermediate product is thereafter cooled down to a temperature below the glass transition temperature of both sheets while this laminated product is forced to take a curved constitution. For this, cooling drum 604, having a radius of 200 cm, is used. The laminated intermediate product 201 is fed along drum 604, wherein the second sheet (6, not shown) is positioned against the surface of the drum (thus, at the inner side of the curve). To keep the product 201 free from tensile stress during contact with the drum 604, this product is transported merely by a pushing force that results from the transport of the product in unit 700, leading a process speed of X meters/minute, while at the same time the drum 604 rotates at exactly the same (circumferential) speed of X meters/min. By cooling the intermediate product rapidly while being in the curved configuration corresponding to the outer circumference of the drum, the curved constitution is to some extent "frozen" into the end product 1. When a tile is cut from this end product, this tile has some (very light) tendency to curve such that its corners are curling down. During use however, gravity working on the tile keeps the tile perfectly flat.

This tile can be distinguished from prior art tiles in that its corners have the inherent tendency to curl down (which can be checked by keeping the tile in an upright position) without any of the prior art layers to force the corners down {viz. glass-fibre layers), or build in strain in the bottom layer (which can be checked using polarized light), being present.

Claims

Method to produce a laminated carpet tile comprising:

providing a first polymer sheet having yarns fastened thereto, the first sheet having a first surface and a second surface, the yarns extending from the first surface,

providing a second polymer sheet,

laminating the second polymer sheet to the second surface of the first sheet at a temperature above the glass transition temperature of the first and/or second polymer sheet,

cooling the laminated product to room temperature,

optionally cutting the laminated product into multiple sub-products, characterised in that the step of cooling the laminated product to room temperature includes cooling the laminated product to a temperature below the glass transition temperature of the first and/or second sheet while the laminated product is forced to take a curved constitution wherein the second sheet is positioned at the inner side of the curve.

Method according to claim 1 , wherein the laminated carpet tile has a width below 2 meters.

Method according to claim 2, wherein the laminated carpet tile has a length below 1 meter.

Method according to any of the preceding claims, wherein the step of laminating the second polymer sheet to the first sheet takes place at a temperature above the glass transition temperature of the first and second polymer sheet, characterised in that in the step of cooling the laminated product while the this product is forced to take a curved constitution, leads to a temperature below the glass transition temperature of the first and second sheet.

Method according to any of the preceding claims, characterised in that the cooling of the product while being in the curved constitution takes place without applying tensile stress to the product.

Method according to any of the preceding claims, characterised in that the product is forced to take a curved constitution by guiding the product along at least part of an outer circumferential surface of a drum, wherein the said surface of the drum is cooled in order to cool the product.

Method according to any of the preceding claims, characterised in that the radius of curvature of the curved constitution is between 10 and 300 cm.

Method according to any of the preceding claims, characterised in that the cooling of the laminated product while the laminated product is forced to take a curved constitution, takes between 0.1 and 5 seconds.

Method according to any of the preceding claims, characterised in that the second surface of the first sheet is subjected to a calendering process before the step of laminating the sheets.

Method according to claim 9, characterised in that in the calendering process, the second surface is treated by applying heat such that the yarns adjacent the second surface at least partly melt during the calendering process.

Method according to claim 10, wherein the yarns extend through the second surface of the first sheet, characterised in that the molten part of the yarns is spread in a direction parallel to the first surface of the first sheet by imparting a mechanical force on the molten part of the yarns in the said direction.

Method according to claim 1 1 , characterised in that the calendering process takes place by pressing the second surface of the first sheet against a heated body that has a relative speed with respect to the second surface.

Method according to any of the preceding claims, characterised in that the first sheet and second sheet are laminated by applying a hot melt adhesive between these sheets.

Method according to claim 13, characterised in that the hot melt adhesive comprises at least 50% by weight of a polymer chosen from the group consisting of polyurethane(s), polycarbonate(s), polyester(s), polyamide(s), poly(ester-amide(s)), polyolefine(s), mixtures thereof and/or copolymers thereof.

Method according to any of the preceding claims, wherein an intermediate layer is positioned between the first sheet and second sheet, which intermediate layer together with the first and second sheet is laminated into the laminated product, characterised in that the intermediate layer is resilient to allow local deformation of the layer along the second surface of the first sheet and/or along the surface of the second sheet adjacent to the

intermediate layer.

Method according to any of the preceding claims, characterised in that the intermediate layer is a knitted layer.

17. A carpet tile obtainable according to a method as defined in any of the preceding claims.