Hot-melt adhesive for PP carpets

Field of invention: hot-melt adhesive for floor covering applications
Applicant: Balta Industries NV
Inventor(s): Rudy EGGERMONT, Berend DEGRIECK
Patent number: EP4253461

The problem

Carpet recycling requires preliminary separation and sorting of components to obtain a single polymer stream. A number of solutions minimise the need for pre-sorting and increase recyclability, such as that described in International Patent Publication WO 93/15909 for a fully recyclable carpet whose primary backing, secondary backing and adhesive all belong to the same polymer family and are all isotactic polypropylene polymers. The first layer applied is an extruded film. A disadvantage of this type of bonding is that the individual fibres in the yarns are sometimes insufficiently bonded, requiring a secondary coating step known as pre-coating. Pre-coating can be carried out with an aqueous dispersion, such as a polyolefin dispersion, but also with a polymeric hot melt adhesive of very low viscosity to ensure the necessary penetration.

The known textile production processes and in particular the carpet production processes for obtaining fully recyclable textile (carpet) products still have problems in obtaining sufficient dimensional stability and good pile and fibre anchoring, mainly due to the adhesives or the fixing method used.

The object of the present invention is therefore to provide a method of producing a hot melt adhesive for textile products which no longer has these drawbacks. Preferably, the textile products comprising said hot melt adhesive should be recyclable at the end of their life into granules suitable for the manufacture of high quality products.

The solution

Balta’s invention provides a method for manufacturing a hot-melt adhesive for textile products, including the following steps: comminution of carpets made of polypropylene to polypropylene granules by mechanical recycling, extrusion of the granules in the presence of peroxides in order to lower the viscosity. The hot-melt adhesive obtained by the method is particularly suitable to produce textile products made of polypropylene, which at the end of their lifespan can be recycled to polypropylene granules that are again perfectly suitable for forming high-grade products. The hot-melt adhesive obtained by the method serves in particular as an adhesive in a textile product comprising a primary backing layer with yarns or fibres made of an isotactic polypropylene material and a secondary backing layer made of an isotactic polypropylene material, wherein the primary and secondary backing layers are firmly bonded together by said adhesive.

The present invention further relates to a textile product, preferably a recyclable textile product, in the form of a carpet, a carpet tile, fabric or non-woven material made of isotactic polypropylene (PP) that comprises a hot-melt adhesive that was obtained by the method according to the invention. The textile product according to the present invention preferably comprises a tufted, woven, knitted or needled top layer.

The polypropylene granules obtained may, depending on the composition of the carpet that is to undergo comminution, sometimes comprise some latex or chalk residues and comprise at least between 85 wt% and 99 wt% polypropylene. If the quality of the recycled polypropylene derived from the comminution of polypropylene carpets is inadequate, in a preferred embodiment the method comprises the extra method step of adding new polypropylene to the polypropylene granules derived from the comminution of polypropylene carpets.

In a preferred embodiment the polypropylene granules comprise 80 wt% of recycled polypropylene. Said recycled polypropylene is preferably derived from the comminution of PP carpets. In an alternative embodiment said recycled PP is derived from other textile sources made of PP, such as for example old yarn, non-woven, production waste, cords, etc.

In a preferred embodiment said granules comprise 0% fillers. In an alternative embodiment said granules also comprise a quantity of fillers. The favourite fillers include titanium dioxide, calcium carbonate, barium sulphate, silica, silicon dioxide, carbon black, sand, glass beads, mineral aggregates, talc, clay and the like. The use of said fillers in the granules may vary from about 0.1% to as high as about 70%.

These fillers are desirable when the adhesive is used for heavier coatings, e.g. for carpet tiles or carpet without secondary backing made of woven or non-woven textile. During recycling, these backings are then separated from the fibres by mechanical processing and are reused. For application with recyclable carpets, the aim is to use the least possible amount of fillers, preferably 0% fillers, more particularly at most 1% fillers.

The invention further relates to a textile product comprising a primary backing layer with yarns or fibres made of an isotactic polypropylene material and a secondary backing layer made of an isotactic polypropylene material, wherein the primary and secondary backing layers are firmly bonded together by the hot-melt adhesive of the present invention, and wherein said hot-melt adhesive was applied by roller coating at a temperature between 190°C and 210°C, preferably at a temperature of 200°C.

Advantages

Application of the hot-melt adhesive by roller coating offers a better contact between the hot-melt adhesive and the yarns and individual fibres, yarns of the primary backing layer. This results in good penetration of the two layers – primary and secondary backing layers – which leads to good fibre bonding/pile bonding with sufficient binding force.
Moreover, the lower temperatures (190°-210°C) used in the processing of the hot-melt adhesive assures that there is no negative effect on the stability of the textile product. At higher temperatures, especially temperatures of 230°C-250°C, there may well be negative effects on the stability of the textile product through thermal shrinkage of polypropylene-based yarns in the woven or non-woven primary backing layer or woven carpet.

Thanks to its composition, the textile product according to the invention can be recycled perfectly by direct mechanical recycling, wherein the textile product can be comminuted mechanically by one of the known techniques, without the need for prior processing.
The resultant recycled polypropylene granules (rPP) can be used integrally for the production of new fibres or other high-grade articles for which the colour is less critical.
The recycled PP may also be used for the production of hot-melt adhesive that can be applied in the textile product as described in the present invention.