NL1040263C2

NL1040263C2 - Cool artificial turf.

Info

Publication number: NL1040263C2
Application number: NL1040263A
Authority: NL
Inventors: Cornelis Johannes Maria Rijn
Original assignee: Micronext B V
Priority date: 2013-06-19
Filing date: 2013-06-19
Publication date: 2014-12-22
Also published as: US20160201273A1; WO2014204309A1; EP3011084A1

Abstract

The present invention relates to an artificial turf comprising fibers having advantageous properties such as a tuned hydrophilicity and the ability to transport water, enabling self-cooling through water evaporation. For this the artificial turf comprises at least one fiber having a core and a shell, characterized in that an outer surface of the shell has a contact angle with water of less than 90°, and that the shell comprises at least one axially oriented groove with a width of less than 500 micrometers.

Description

COOL ARTIFICIAL TURF TECHNICAL FIELD

The present invention relates to an artificial turf with improved playing properties. The aim is to provide a more multifunctional fiber, saving on production and material costs on the one hand, and resembling advantageous properties of natural turf on the other hand. According to the invention manufacturing steps are disclosed that provide in a synthetic fiber having amongst others, a tuned hydrophilicity, water transport ability, self-cooling, better bending properties, good resilience, longer life-time, reduced friction, anti-electrostatic, controlled biodegradability, anti-bacterial and/or having self-cleaning capability.

BACKGROUND

Artificial turf research is focused on the development of fibers for use in artificial lawns for user friendly sports fields. It is known in the art to make a fiber with a core and a shell from different materials, herewith enabling a separation of the inner core and the outer material surface properties. In US 2010/0173102 an artificial turf fiber is disclosed comprising a core and a cladding, wherein the material for the cladding is tuned for hydrophilicity and where the material for the core is optimized for good bending recovery properties. The fiber is here obtained with a co-extrusion step. The use of co-extrusion for producing artificial turf fibers is however economically unattractive, in particular if only one beneficial property is being addressed. In literature more user friendly functionalities for artificial turf are taught on properties like better sliding and longer life time.

SUMMARY

It is an object of the invention to enable and combine more beneficial properties, such as a tuned hydrophilicity, water transport ability, self-cooling, anti-electrostatic, reduced friction, longer life time, improved bending recovery, good resilience, better sliding, UV-stable, flame retardant, biodegradable, anti-bacterial and self-cleaning capability by introducing pre, post and/or co-extrusion steps to obtain a cost efficient and more user friendly artificial turf.

According to the invention the artificial turf comprises at least one fiber having a core and a shell, characterized in that an outer surface of the shell has a contact angle with water of less than 90°, and that the shell comprises at least one axially oriented groove with a width of less than 500 micrometers, so that the groove is able to transport water over a height of at least a few cm.

It is an insight of the invention and surprisingly it has been found that even open grooves are able to transport water by some reduced form of capillary action. Both rectangular and round shaped open grooves have been found to work. With preference a groove comprises one or more concave regions having a radius of curvature of at least 5 micrometers and not more than 250 micrometers. U or V- shaped grooves having at its bottom sharp rounded comers have proven to be more beneficial for the transport of water against gravity, especially a groove that is at least for a part triangularly shaped, having at its bottom a sharp comer much less than 90°, typically between 5° and 60° and at its vertex a radius of curvature of at least 5 micrometers and not more than 250 micrometers. Grooves with a smaller mean width have a substantially larger capillary action than wider grooves. However the flow resistance of grooves with a smaller width rapidly increases. Grooves with a mean width between 20 and 200 micrometer have proven to be able to transport enough water to have a sufficient cooling effect on the artificial turf by evaporation. The capillary action has been found to be inversely proportional with the value of the water contact angle (cf. wetting) of the shell material. Grooves with higher water contact angles can still transport water when grooves with a smaller width are present in the fiber.

To avoid cutting injuries during use of the artificial turf field it has been found to prefer grooves having at its top rounded comers or convex areas. Grooves having at least a convex area with a radius of curvature of at least 50 micrometer up to 1500 micrometer have proven to be very functional. It has also been found that the top comer of the grooves has little influence on the water transport capability.

Whereas for the core of the fiber materials can be selected for e.g. a longer life time, improved bending recovery and a good resilience, it will be clear that for the shell other material selection criteria hold, such as preserving for a long time an optimum water contact angle (e.g. between 10° and 30°) to enable water transport. It is known that most polymers become more hydrophobic in time with water contact angles above 60°, also grooves may easily get clogged with organic contaminations both issues limiting sufficient water transport. According to the invention measures have been taken to auto-regenerate the water contact angle and to prevent organic contamination. The artificial turf comprising at least one fiber, having a core and a shell, which core and shell are made of similar base materials, is characterized in that the shell base material comprises particles, which may differ in amount or type with respect to particles in the core material. With preference a hydrocarbon, such as polyethylene and/or polypropylene is chosen as a cost effective base material. Of course other thermo plastic hydrophilic materials such as polycarbonate, polyolefins, polyamides, polyethyleneglycol, polyvinylalcohol and polyesters are equally possible to use as a shell material. By providing the fiber with a core and a shell, it becomes possible to provide each part of the fiber with a location specific functional property, which property does not need to be present elsewhere in the fiber, or needs to be present only to a distinctly reduced degree. With preference the required properties are obtained by adding functional particles, or mixtures of particles with different functionalities. The base materials can however also be completely equal and may contain functional particles, which makes it possible to use a single die extrusion process. With preference an additional hydrophilic coating is then provided over the shell in the grooves in a post extrusion step, e.g. by applying a vapor, spray or solution coating of polyethylene glycol, polyvinyl alcohol, or a low temperature sol/gel metal-oxide coating. The coating can be applied very thin and will not suffer from wear inside the grooves. With preference the shell material is first hydrophilized to promote adhesion of the coating to the shell by grafting one or more reactive groups on the shell material, for example maleic acid anhydride is able to react with polyethylene (as the shell/core material) rendering it more hydrophilic.

With preference the base materials of the core and shell are not identical but similar, such as hydrocarbon mixtures with a similar glass transition temperature. This makes it possible to obtain co-extruded fibers in an easy cost effective way. The melt extrusion of medium and high molecular weight polymers, such as hydrocarbon polymers into the desired flat fiber shape structures is accomplished by well-known procedures wherein a single or a double rotating screw pushes a viscous polymer melt through an extrusion die. The required particles have then to be added to the outer shell after passage through the die, e.g. when the shell base material is still hot and with preference before stretching the fiber to increase e.g. the strength and bending recovery. The particles can be deposited to the shell in powder form or by passing through one or more baths with the required powder in suspension form. Particles with a size between 2 and 200 nanometer have proven to perform very well, and do not have a negative impact on the required (sharp) geometries of the grooves and vertices with curvatures of 5 micrometer or more.

An insight according to the invention is that the water contact angle can be lowered by the addition of hydrophilic particles to the shell material. With preference the surface of the particles should contain a sufficient number of polar groups, such as hydroxyl groups, that are able to bind water molecules and lower the surface energy. These particles can be molecules of organic origin, such as described in (W02005111281A1), ionomers, or with preference they belong to the class of metal and semi-metal oxides. Many metal oxide particles are known to have hydrophilic properties, but some of them have also good flame retardant, anti-electrostatic and/or self-cleaning properties.

A specific demand for artificial turf is the ability to have 1) a low wettability, when the playfield is not used, such as overnight to inhibit evaporation, 2) a moderate wettability on cloudy days to lower friction, and 3) a high wettability when the sun shines to cool the turf by evaporation and to have increased sliding and reduced skin burning properties. With preference according to the invention zinc oxide and/or titanium oxide particles are being applied. Zinc oxide has a band gap of 3.5 eV and UV light with a wavelength beneath 350 nm is able to alter the ZnO particles to a super-hydrophilic state. Also upon UV irradiation mild chemical radicals are being created that have mild antibiotic and self-cleaning properties.

Likewise titanium dioxide particles can be used or blended with zinc oxide. UV treatment of Ti02 particles, especially from the anatase form are known to create strong electron-hole radicals that are able to create hydroxyl groups. Adding these Ti02 particles can thus induce an enhanced tunable hydrophilicity. According to the invention also the life time of the fiber itself can be tuned with these particles. The strong radicals can also cut the C-C organic bonds of the fiber molecules itself, which is a great advantage in biodegradable artificial turf applications. With preference a

Ti02 partiele powder with a mean particle size smaller than 50 nanometer is being employed. It has been found that this very fine powder becomes more transparent and the normally white pigment effect of titanium dioxide is strongly diminished. Likewise the white pigment effect of Ti02 can be tempered by adding carbon black powder. An advantage of this combined black/white dispersion is that the UV light can herewith be tuned to have a certain penetration depth, herewith controlling the life time of the fiber. The man skilled in the art has now tools to choose the further right pigments to control the demanded color of the fiber for the intended application. Titanium dioxide incorporating a small amount (< 1%) of manganese in the crystal lattice can also be employed in the shell material. This allows absorbed UV energy to be dissipated, virtually eliminating the generation of free radicals. Manganese at the surface of the particle can scavenge free radicals that have been generated. This may significantly extends polymer lifetime under solar exposure. On the other hand titanium dioxide, when spiked with nitrogen ions or doped with metal oxide like tungsten trioxide will have increased photocatalyst properties under either visible or UV light and can be used to promote self-cleaning properties of the fiber, especially preventing the build-up of organic contamination in the grooves.

It is also an insight according to the invention that relative many injuries result from a high friction between the artificial turf fibers and the player, because the conventional fibers are smooth and dry and have thus a large friction contact area with the injured parts of the player. The injuring energy transfer is directly proportional with the contact area. Reducing this contact area with low friction particles of a specific size and surface density will be disclosed. The invention teaches the use of PTFE (polytetrafluoroethylene) nanoparticles with a mean particle size between 20 and 2000 nanometer and with a mean surface coverage between 0.1 and 10%. Particles having fluorinated molecules have been tested to have extremely low adhesion forces with respect to natural and synthetic materials or attributes of the players. Especially friction forces between skin, cloths or shoes have been tested advantageously. The coefficient of friction of PTFE varies within the range 0.02 - 0.1, and does not depend on the environment. It is as low in oxidizing, as in non-oxidizing moist and dry atmospheres encountered at the artificial turf play field. Also due to non-stick properties of polytetrafluoroethylene there is very small difference between the static and dynamic coefficients of friction. Likewise, of course in some cases also non- or partly fluorinated particles can be employed in the shell material.

A specific demand for artificial turf is the ability to tune the resilience properties. According to the invention for this silicondioxide particles are known to be hydrophilic but also to improve the bending recovery of many plastics. These particles can thus be added both to the shell and the core material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: FIG. 1-4 shows schematic embodiments of a cross section of the shell of an artificial turf fiber and FIG. 5 shows attained heights (against gravity) for transport of water along a groove with a given width.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Fig. 1 schematically depicts a cross section part of the shell of an artificial turf fiber 1 according to the invention with four different grooves 2 with a mean width 3 and a mean depth 4. Semi-circular, rectangular and triangular grooves are depicted, the latter also with a vertex having a concave (less sharp) shape 5. The concave comer 5 avoids the formation of micro shear forming in the shell material.

In Fig. 2 the grooves are filled with water 6 showing a hollow meniscus 7. All grooves with a mean width less than 500 micrometer are capable in transporting water against gravity against a height of at least a few cm. Triangular shapes having at its bottom a sharp comer much less than 90°, typically between 30° and 80° and at its vertex a radius of curvature of at least 5 micrometers and not more than 50 micrometers have proven to function better that semi-circular and square shaped grooves.

In Fig. 3 triangular shaped grooves 2 are depicted with a convex (rounded) area 8 in between with a radius of curvature of at least 50 micrometer up to 500 micrometer or more, to smoothen the top of the grooves with the outer surface, to avoid cutting injuries.

Fig. 4 depicts cross sections of a preferred embodiment. A pair of triangular shaped grooves 2 is mirrored with respect to each other and together forms a common deepened surface with a width 10 that can vary from 250 micrometer up to a few mm. A rounded vertex 5 to avoid micro-tear/crack formation and a rounded convex area 9 to prevent injuries are depicted. The deepened hydrophilized surface with a width 10 has a number of advantages: - it will not wear or suffer from mechanical abrasion, even when a thin hydrophilic coating has been applied, -it serves as the cooling/ evaporation area of the water that has been transported via the grooves, - it can mechanically lock the coating or shell material inside this area even when this material has been abrased from other exposed parts of the fiber.

Fig. 5 shows a graphic presentation of different experiments of a hydrophilized shell with grooves having a different width and different bottom profiles: • half spherical grooves, U-shaped grooves with a slightly rounded bottom, and ▲ V-shaped triangular grooves with a bottom angle of 30° and a relatively sharp vertex according to the invention (see also fig. 1). All grooves were able to transport water very well when the contact angle for water was less than 60°, although the transport of water in semi-circular grooves was significantly slower. V-shaped grooves were able to transport water against gravity to a height of 10 centimeter in less time (typically » 1 cm/sec seconds) than comparable U-shaped grooves (typically between 0.1 and 1 cm/sec seconds) with the same mean width of 100 micrometer.

Claims

Artificial grass comprising at least one fiber with a core and a shell, characterized in that an outer surface of the shell has a contact angle with water of less than 90 °, and in that the fiber has at least one axially oriented groove with an average width of less than 500 micrometres, whereby the groove is capable of transporting water over a height of at least a few cm.

Artificial grass according to claim 1, characterized in that a cross-section of the groove is V or U-shaped, and comprises one or more concave areas with a radius of curvature of a minimum of 5 microns and a maximum of 250 microns.

3. An artificial grass according to claim 1 or 2, characterized in that at least two V-shaped grooves lie in mirrored relation to each other and together form a joint plateau recessed into the outer surface, the plateau having a contact angle with water of less than 90 °. .

Artificial grass according to claim 1,2 or 3, characterized in that a cross-section of the groove on the top of the shell near the groove comprises at least one convex region with a radius of curvature of at least 50 microns and at most 1500 microns.

Artificial grass according to one of the preceding claims, characterized in that the material of the shell contains hydrophilic particles with a size of 2 - 200 nanometers.

Artificial grass according to claims 1,2,3 and 4, characterized in that the core and shell material is polyethylene.

7. Artificial grass according to claim 1,2,3,4 and 5, characterized in that the peeling material is polyethylene and the core material is polypropylene.

The artificial grass according to any one of the preceding claims, characterized in that the shell material comprises particles selected from the group of organic materials, in particular a hydrophilic material that gives the shell a water contact angle of less than 60 °.

9. An artificial grass according to any one of the preceding claims, characterized in that the peeling material comprises particles selected from the group of inorganic materials, in particular metal oxides or semi-metal oxides.

10. An artificial grass according to any one of the preceding claims, characterized in that the particles present in the peeling material are in an amount of about 0.05 to about 5 volume percent, and preferably about 0.1 to about 1.0 percent at basis of the total volume are of the peel material.

The artificial grass according to claim 9, characterized in that the particles comprise at least about 50% by weight of inorganic materials, such as titanium dioxide or zinc oxide.

12. An artificial grass according to claim 11, characterized in that the titanium dioxide particles have an anatase crystal form in an amount of at least 20%.