GENERAL FIELD OF THE INVENTION The present invention pertains to a method to produce a tufted carpet, comprising tufting yarns into a primary backing thereby forming an intermediate product, and mechanically fixing the yarns to the backing by applying a binding constitution to the back of the carpet

BACKGROUND ART

Floor coverings such as rugs or carpets often consists of dyed pile yarns, a primary support material called primary backing, and in many cases a secondary backing that adds strength to the carpet. The yarns are usually contacted with the primary backing material by a process called tufting, which is a type of textile weaving in which a thread is attached to the support material by mere insertion in that material. Such tufting (which thus includes weaving, stitching and other methods wherein the yarns are simply attached to the support by mere insertion therein) does not provide adequate mechanical bonding between the yarns and the support material. A binding constitution (which could be as simple as an adhesive) is used to provide adequate mechanical bonding between the yarns and the primary (and optional) secondary backing.

Ninety-seven percent of pile yarns today are made up of synthetic polymers. Synthetic polymers are for example nylon (which is in 60-70% of all carpet), acrylics (± 15%), polyester (less than 15%), polypropylene (less than 5%) and blends thereof. These pile yarns are dyed using a variety of organic chemical compounds, or occasionally, organometallic complexes. The backing is in most cases made of woven or non woven polypropylene. The binding constitution used to bind the backings together is almost universally synthetic rubber latex. Latex based floor coverings have several disadvantages. Firstly, since the latex is water-based, latex coverings tend to be non-resistant to moisture. They may allow moisture to pass through which on its turn can lead to the formation of mildew and molds. This cannot only degrade the floor covering, but may also lead to environmental hazards such as poor air quality. As a consequence, when latex based floor coverings are placed in an area where moisture is a concern, for example in lobbies, they may need to be frequently replaced. Secondly, latex is an expensive material and has become increasingly more expensive over the years.

In the art, several solutions have been proposed to overcome or at least mitigate the above described disadvantages. One solution is to replace the conventional latex adhesive with synthetic polymer adhesives such as polyolefines and polyurethanes. This is for example known from US 2010/0260966, which discloses a carpet tile that includes a face fabric having a top surface and a base, and a dimensionally stabilized non-woven cushion material having a stabilizing material incorporated therein. The non- woven cushion material is attached to the face fabric by using a synthetic polymer adhesive, in which adhesive the cushion material as well as the fabric are embedded for adequate bonding. Another proposal is to replace the latex by starch based

compositions (see for example W021012/000609) but these compositions are prone to biodegradation during use.

Yet another solution proposed is the use of hot melt adhesives. These adhesives are popular in conventional roll carpets since they are relatively inexpensive, readily available and can be recycled more easily. Hot melt adhesives are also used in carpet tiles, as is known for example from WO 2007/127222. Given the brittle nature of hot melt adhesives, a very high degree of embedding of the yarns in the adhesive is necessary to provide adequate strength. However, to deep embedding may be disadvantageous for the appearance and feel of the carpet. The find the proper balance between embedding to provide adequate mechanical strength and look and feel of the carpet is difficult. The problem of embedding has been solved in WO 2012/076348 which proposes to fuse and straighten the back surface of the intermediate by melting the tufted yarns, such that there is already a durable bonding without applying any additional binder layer. This method however depends on the yarns being made of a fusable material, and in particular, of a material that can fuse below the melt (or degradation) temperature of the primary backing. In EP 2610 292 it is proposed to create a viscous binder constitution wherein crude tall oil pitch is mixed with a calcium salt and reacted to form a cross-linked very thick binder, whereafter, in order to bring the viscosity down, fresh crude tall oil and a polymer are added to obtain a substance that is thin enough to be used as a carpet backing constitution.

OBJECT OF THE INVENTION There is a need to provide another alternative for latex as a binder in tufted carpets, in particular there is a need to provide such alternative using widely available natural resources.

SUMMARY OF THE INVENTION

In order to meet the object of the invention a method as defined here above in the GENERAL FIELD OF THE INVENTION section has been devised, wherein the binding constitution used is a thixotropic constitution comprising a cross linkable plant oil and a curing agent, the method comprising applying the thixotropic constitution as a layer to the back of the intermediate product and activating the curing agent to induce cross- linking of the plant oil.

This invention was based on several recognitions. First of all, it was found that be using a thixotropic binder, one creates a great amount of freedom in the process of applying the binder. The thixotropic properties may provide for a low viscosity during processing of the binder, but may also provide for an almost instant thickening once the binder is applied to the backing. With any art known binder materials, one had to find the right viscosity to provide for adequate processing while at the same time prevent that the binder penetrates too deep into the intermediate and ruins negatively influences the ultimate carpet pile properties. This made the processing of the binder very difficult. With a thixotropic binder, a low viscosity during processing may be provided while at the same time, as soon as the binder is applied to the back of the intermediate, the binder turns into a very viscous paste that does only penetrate the first tens of micrometers up to typically a millimeter, just enough the bind the yarns, but not too deep to negatively interfere with the piles. Needed to actually achieve good binding however is a curing agent that is premixed with the plant oil. If not, the curing agent is typically not able to diffuse fast enough through the highly viscous binder layer and therefor, curing will be too slow to maintain good pile properties. This on its turn led to the recognition that the binder has to be applied as a layer (i.e. a continuous covering forming an overlaying part of the back of the intermediate), and not as a pattern of dots of binder.

An advantage of the present invention is that the binder is based on the presence of a cross-linkable plant oil. This is not only a natural resource that is widely available and therefore relatively inexpensive, it also provides the option to produce 100% natural type of carpet. Normally, these plant oil such as soy bean oil, sun flower oil, linseed oil, rapeseed oil, calendula oil, euphorbia oil etc. are too thin to be applied as a cross- linkable binder constitution to the back of the intermediate of a tufted carpet, even in the presence of a fast curing agent. They simply penetrate too fast into the intermediate product and negatively interfere with the properties of the pile of the carpet. Only when having thixotropic properties and being applied as a layer, they appear to be usable as a binder without interfering too much with the properties of the pile of the carpet.

The present invention also pertains to a thixotropic paste comprising a cross linkable plant oil and a curing agent, in particular for use in the method according to the invention.

DEFINITIONS Carpet is a textile floor covering consisting of an upper layer of pile attached to a backing. The pile is generally made from wool, an artificial fibre or mixtures thereof such as wool and TENCEL™. Types of carpets are for example woven, needle felt, knotted or tufted. A thixotropic constitution is a constitution that is a highly viscous fluid under static conditions (like tooth-paste, ketchup etc.), but which becomes thin under stress (when shaken, agitated etc,), a property which is called shear thinning. This means that the very thick fluid will flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed. They are non-Newtonian pseudoplastic fluids Typical examples are gels and colloids, exhibiting a stable (nearly solid) form at rest but become fluid when agitated. A Nucleophilic group is an atom or group that contains an electron or electron pair available for bonding; in chemical reactions a nucleophilic group seeks a positive centre such as the nucleus of an atom or the positive end of a polar molecule or group.

Examples of nucleophilic groups are amines (-NH2), thiols (-SH) and hydroxyl (-OH) groups.

A cross-linkable material is a material comprising molecules that have two or more reactive groups such that each of those molecules can form a cross-link (a molecular bridge) between at least two other molecules. Cross-linking is often initiated by heat, pressure, change in pH, or radiation.

A curing agent is an agent able to induce covalent reactions between molecules.

EMBODIMENTS OF THE INVENTION

In a first embodiment a thixotropic agent is added to the constitution to provide the thixotropic properties. Although it is not excluded that a cross-linkable plant oil containing constitution has thixotropic properties without adding a thixotropic agent, for example when a part of the cross-linkable groups of the oil have already been cross linked to form large gelator molecules, it is preferred that such an agent is added in addition to the plant oil. This way, more freedom is created in providing the thixotropic properties (e.g. the viscosity under static condition, the viscosity under agitation, the time needed for the constitution to reach equilibrium viscosity etc.).

In an embodiment the cross linkable plant oil is an epoxy modified plant oil (also known as epoxidized plant oil), in particular an epoxy modified plant oil with an oxirane content higher than 6%, for example an epoxy modified linseed oil. Epoxy modified plant oils as such are known in the art, e.g. as described in WO 2009/1 14935. It has now been found that these oils are in particular suitable for use as a binder constitution for providing a tufted carpet with good properties with regard to the bonding of the piles and look and feel of the carpet.

In an embodiment the curing agent is a bifunctional agent (which does not exclude that the agent has more than two functional groups) that reacts with the cross linkable plant oil. Such a bifunctional agent is therewith build in the cross-linked network which provides for good durability of mechanical and (physico) chemical properties. Typical examples of such agents are multivalent carboxylic compound such as polyfunctional acids (which term includes the anhydrides of these acids).

In yet another embodiment the thixotropic agents is chosen from the group consisting of particulate material, synthetic polymer, natural polymer, protein, and small molecule gelator. A small molecule gelator is a type of gelator that consist of small (often soluble) molecules, but which molecules upon cooling of the constitution crystallize to form large molecules that provides for the gelling properties. Such small molecule gelator molecules are for example described in US patent US 6,471 ,758 B1 .

In a further embodiment the thixotropic agent is particulate material, chosen from the group of silica and clay. Although commonly known as thixotropic agents, these compounds have been to be particularly suitable for use in binding constitution for providing a tufted carpet.

In another embodiment the thixotropic constitution comprises lignin. Lignin is a quinone precursor of natural origin, which quinones on their turn have two reactive carbonyl nuclei which are highly reactive to nucleophilic groups such as amines (-NH2), thiols (- SH) and hydroxyl (-OH) groups. Reaction may lead to Schiff-base formation and 1 ,4 Michaels additions leading to polymer formation. It is known that quinones may react to form large polymers, and at the same time, in the presence of a compound that has multiple (i.e. at least two) nucleophilic groups, such as the cross-linkable plant oils, may provide cross-links with these compounds. As such, the addition of lignin may provide for a better bonding of the tufted yarns to the primary backing. In an embodiment an enzyme is used to convert the lignin. Applicant recognised that lignin is known to be very stable and indigestible by animal enzymes, but is susceptible to enzymatic conversion by a variety of enzymes to form reactive nuclei. Such enzymes are for example enzymes produced by some bacteria or fungi such as lignin peroxidase (from the white-rot fungus Phanerochaete chrysosporium) manganese peroxidase, laccase or cellobiose dehydrogenase. Applicant recognised that enzymatic conversion inherently goes together with the formation of reactive nuclei at some stage. The use of enzymes may contribute to easy conversion of the precursor into an actual (reactive) quinone. Also it is recognised that no synthetic reactants are needed in this embodiment .In particular in combination with yarns and a support material that both consist of biodegradable materials, such as biodegradable polymers, this embodiment may lead to a 100% recyclable textile product, e.g. through natural decomposition. In a preferred embodiment the yarns are made of a material comprising nucleophilic groups. This may lead to covalent bonds between the components of the binder constitution and the yarns, and thus to an even more durable bonding of the yarns to the backing. In a further embodiment the yarns comprise keratin fibres, preferably wool fibres. These natural fibres comprise nucleophilic amine groups.

In yet another embodiment the primary backing is a fabric comprising fibres of natural origin, preferably cellulosic fibres such as cotton, jute, rayon, lyocell (such as

TENCEL™), hemp and ramie. In still another embodiment the thixotropic paste is applied to the back of the

intermediate product through the nip of a pair of opposing rollers. This appears to be a convenient way of providing a layer of the binding constitution to the back of

intermediate product. The present invention can e.g. be advantageously used in connection with yarns and or a support material comprising biodegradable materials, such as biodegradable polymers. Such polymers will decompose in natural aerobic (e.g. composting) and/or anaerobic (e.g. landfill) environments. They may be composed of either biopolymers, which may be naturally produced polymers or polymers whose components are derived from renewable raw materials, but may also be petroleum-based, or a blend of one or more of these types of polymers. Most aliphatic polyesters are biodegradable due to their potentially hydrolysable ester bonds. Typical examples of naturally produced biodegradable polymers are polyhydroxyalkanoates (PHA's) like poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate (PHH), and starch, cellulose, keratin and derivatives thereof. A biodegradable polymer from a renewable resource is for example polylactic acid (PLA). Examples of other synthetic

biodegradable polymers are polybutylene succinate (PBS), polycaprolactone (PCL), polyvinylacetate (PVA) and cellulose esters like cellulose acetate, nitrocellulose and their derivates such as celluloid. The invention will now be further illustrated based on the following non limiting examples.

EXAMPLES In general, the binding constitution used in the examples pertains to a mixture of a) epoxidized plant oil, b) a multivalent carboxylic compound as curing agent, and c) a thixotropic agent.

As epoxidized plant (vegetable) oil, any product obtainable by epoxidation of naturally occurring unsaturated triglycerides can be used. Non-limiting examples of such triglycerides are soybean oil, sunflower oil, rape seed oil, safflower oil, linseed oil, castor oil, perilla oil, lallemantia iberica oil, mixtures or derivatives thereof or new cultures of oil containing plants. As multivalent carboxylic compound any product with an anhydride or an acid group can be used (the term acid also includes the corresponding anhydride). A preferred compound is a mixture of a polycarboxylic acid with a reaction product of a

polycarboxylic acid and a polyol. As polycarboxylic acid any compound with an anhydride or an acid group can be used. Non-limiting examples are acyclic

polyfunctional acids or anhydrides of them such as maleic acid, maleic anhydride, malic acid, succinic acid, citric, phosphoric acid, oxalic acid, malonic acid, terahydrophthalic anhydride, norbornendicarboxylic anhydride, citraconic anhydride,

methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride,

methylhexahydrophthalic anhydride, aromatic or heteroaromatic polyfunctional acids or anhydrides of them such as phthalic acid, phthalic anhydride, trimellitic anhydride, pyromellitic dianhydride and any mixtures or derivatives of thereof.

As polyol any compound with two or more hydroxylic groups can be used. Non-limiting examples are ethanediol, propanediol, ethylene glycole, diethylene glycole, triethylene glycole, propylene glycole, dipropylene glycole, tripropylene glycole, glycerol, trimethylolpropane, pentaerythritol and any mixtures or derivatives of thereof. The thixotropic agent, which may be silica, serves to adjust the viscosity of the composition in use: thin viscous while agitated and thick viscous when under static conditions (e.g. after being applied as a thin layer on the back of an intermediate product in the sense of the present invention). The required physical parameters depend on various factors such as the type of yarns, the type of tufting, the type of piles etc. The skilled person can adjust the required viscosity, using one or more thixotropic agents (optional in addition to inherent thixotropy of the plant oil, if any) in various amounts and by adjusting the process parameters such as temperature and process speed (the latter of course determining for a large part the stress in the binding constitution and thus, the viscosity under shear). Other thixotropic agents may be modified Castor oil (hydrogenated castor oil), sulfonates, gums, organosilicones, cellulosics (CMC, HMC, HPMC and others), PVA (poly vinyl alcohol), clays (bentonite, montmorillonite), polyurethane polymers, (meth)acrylic polymers (Carbomers), latex, styrene/butadiene copolymers, polyurea derivatives, polysaccharides (starches, vegetable gums, carrageen, pectin, Alginat), proteins (casein, collagen, gelatin, Agar), and others.

Example 1: Preparation of multifunctional carboxylic acid A

A multifunctional carboxylic acid was prepared by the reaction of one equivalent monoethylene glycol with two equivalents phthalic anhydride. 62 g of monoethylene glycol and 296 g of phthalic anhydride were mixed and heated up to 140 °C. The mixture is stirred at this temperature for further three hours.

Example 2: Preparation of multifunctional carboxylic acid B

A multifunctional carboxylic acid was prepared by the reaction of one equivalent trimethylolpropane with three equivalents phthalic anhydride. 134 g of

trimethylolpropane and 444 g of phthalic anhydride were mixed and heated up to 140 °C. The mixture is stirred at this temperature for further three hours.

Example 3: Preparation of multifunctional carboxylic acid C

A multifunctional carboxylic acid was prepared by the reaction of one equivalent monoethylene glycol with two equivalents trimellitic anhydride. 62 g of monoethylene glycol and 384 g of trimellitic anhydride were mixed and heated up to 170 °C. The mixture is stirred at this temperature for further three hours.

Example 4: Preparation of multifunctional carboxylic acid D

A multifunctional carboxylic acid was prepared by the reaction of one equivalent tnmethylolpropane with three equivalents maleic anhydride. 134 g of tnmethylolpropane and 294 g of maleic anhydride were mixed and heated up to 80 °C. The mixture is stirred at this temperature for further five hours.

Example 5: Preparation of multifunctional carboxylic acid E

A multifunctional carboxylic acid was prepared by the reaction of one equivalent monoethylene glycol with two equivalents phthalic anhydride. 62 g of monoethylene glycol and 296 g of phthalic anhydride were mixed and heated up to 140 °C. The mixture is stirred at this temperature for further three hours. It is then cooled to room temperature. 200 g of methylhexahydrophthalic anhydride are added while stirring.

Example 6: Preparation of epoxidized vegetable oils

200 g of soybean oil (corresponds to approximately 1 .1 mol C=C double bond) and 17 g of 90% formic acid are stirred vigorously. 107 g of 35% hydrogen peroxide are slowly proportioned into the main mixture. The temperature increases and is kept under cooling at maximum of 50 °C. The reaction is stopped when the iodine value is decreased fewer than five. The product is washed at least three times with water that means until the acid value is decreased less than 1 . Then the organic phase is dried at 100 °C under vacuum. The achieved oxirane content is about 6.5%.

Correspondingly, epoxidized plant oils such as epoxidized soybean oil can be provided. These oils are obtainable as Merginate oils from Hobum Oleochemicals, Hamburg, Germany.

Example 7: Preparing tufted carpets

In this example various tufted carpets (5/32 loop pile, 1/2 loop pile and 1/8 cut pile), all of them comprising wool yarns tufted into a primary backing of (single/single) woven from either Tencel™ (available from Lenzing AG, Lenzing, Austria) or polypropylene (PP, available from Propex, Gronau, Germany) are formed, wherein the yarns are mechanically fixed to the backing by applying a binding constitution to the back of the intermediate product. In each case, the binding constitution used is a thixotropic constitution comprising as a cross linkable plant oil Merginate ELO, the curing agent of Example 5, and ACEMATT TS 100 silica (available from Evonik Industries, Essen Germany).

The process setup is given in Figure 1 . In figure 1 the intermediate product 1 is depicted, having a front face 1 1 and a back face 21. The intermediate product 1 is fed over a large roller 2 to a nip 8 formed by rollers 3 and 4. The diameter of roller 3 is 210 mm, the diameter of roller 4 is 1 10 mm. The pressure with which these rollers form the nip 8 is 240 kg per meter. With this nip, the intermediate product is actually forced to proceed, in this case by rotating roller 3 at a (surface) speed of 1.2 meters per minute. Roller 3 on its turn forms nip with static roller 5 which has a diameter of 1 10 mm. In the nip between these rollers is the binding constitution 10. Through rotation of roller 3, a thin layer 1 1 of this constitution forms on the surface of roller 3. This layer is transferred to the back 21 of the intermediate product in nip 8. The nip between the rollers 3 and 5 has a variable width (see Table 1 ) in order to adjust the thickness of the layer 1 1. The binding constitution is applied at room temperature. Thereafter the binding constitution is cured by feeding the carpet through an oven at 130°C for 10 minutes.

The binding constitution 10 is made by mixing the various constituents in a Hobarth model AE 120 mixer (having a capacity of approximately 10 liters). In this mixer 4000 grams of the epoxidized plant oil is mixed with 2000 grams of curing agent and 600 grams of silica during 10 minutes. Thereafter, the binding constitution is ready for application as described here above.

An overview of the different tests is given in the table here beneath in table 1 .

Carpet produced this way can withstand the common hexapod test (CRI Test Method 103, The Carpet and Rug Institute, Dalton, Georgia, USA) at 20.000 rpm. Table 1 Overview of different tests.

Example 8: binding constitutions with lignin

The methods as described in example 7 can be repeated with another binding constitution comprising lignin. The mixture was made using 1000 grams of Merginate oil, 410 grams of curing agent, 140 grams of silica and 140 grams of lignin (available from Borregaard, Sarpsborg, Norway). The rest of the setup is identical. In an alternative setup, a laccase enzyme is added to the binding constitution in order to convert the lignin to a reactive molecule. The curing temperature is then decreased to 100°C, and the time for curing prolonged.

Example 9: determination of tuft bind

Tufted carpet as described in example 7, (5/32 loop pile, wool on Tencel™) was used for further trials wherein a paste of thixotropic cross linkable plant oil comprising a curing agent was used to create sufficient tuft bind. The paste in this case was an epoxy modified linseed oil comprising silica as a thixotropic agent. This paste was hardened at 130°C for about 20-25 minutes. Table 2 gives the amount of paste applied in grams per square meter and the resulting tuft bind in N. A tuft bind above 20 N is adequate for use as a carpet. Table 2 Tuft bind of woollen carpet

From the experiments it seems that there is an optimum in tuft bind strength in relation to the amount of paste applied. For this particular paste, applied under the

circumstances chosen, an amount of about 710-720 g/m ² seems to lead to an optimal tuft bind.

Example 10 use of plant oil with added wool powder

An experiment was conducted wherein in the paste, the same as used for Example 9, powdered recycled wool (used wool fibres cut short, having a length around 1 mm) was added to the paste in an amount of 27 g/m ² . It is believed that due to nucleophilic amine groups present in the wool an inherent additional cross-linking takes place with the added wool fibres. This may provide for an increased inherent strength of the hardened paste layer, but also, provides a possibility to colour the back of the woollen carpet through the use of recycled (coloured) wool. By the fact that the coloured wool fibres are cross-linked into the paste, the colouration is very durable and restricted to the back- side. This cannot be achieved by applying any regular colouration process.