EP-4741545-A1 - HELICAL ARTIFICIAL TURF FIBER WITH DIFFERENT POLYMERS IN CORE AND PERIPHERY

EP4741545A1EP 4741545 A1EP4741545 A1EP 4741545A1EP-4741545-A1

Abstract

Disclosed is an artificial turf fiber (204, 502-510, 804, 902-906, 1500, 1602-1618) comprising a longitudinal cross-sectional profile, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape, wherein the core of the fiber consists of or predominantly comprises a core polymer, and wherein the periphery of the fiber consists of or predominantly comprises a cladding polymer, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment.

Inventors

Dr. SICK, Stephan
Dr. GROCHLA, Dario

Assignees

Polytex Sportbeläge Produktions-GmbH

Dates

Publication Date: 20260513
Application Date: 20241107

Claims (20)

An artificial turf fiber (204, 502-510, 804, 902-906, 1500, 1602-1618) comprising a longitudinal cross-sectional profile, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape, wherein the core of the fiber consists of or predominantly comprises a core polymer, and wherein the periphery of the fiber consists of or predominantly comprises a cladding polymer, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment.
A helical artificial turf fiber (204, 502-510, 804, 902-906, 1500, 1602-1618) comprising a longitudinal cross-sectional profile, wherein the core of the fiber consists of or predominantly comprises a core polymer, and wherein the periphery of the fiber consists of or predominantly comprises a cladding polymer, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment.
The artificial turf fiber according to claim 1 or 2, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0,
The artificial turf fiber according to any one of the previous claims, wherein the cross-sectional fiber profile has a central bulb and two wings extending from the central bulb in different directions.
The artificial turf fiber according to claim 4, wherein the core polymer is comprised in the core of the central bulb and wherein the cladding polymer is comprised in the wings and optionally also in peripheral regions of the central bulb.
The artificial turf fiber of any one of the previous claims, wherein the helical artificial turf fiber has a 3D-helical shape characterized in that the fiber winds around a central cylinder, wherein the fiber maintains a distance from the cylinder axis as it rotates, and advances along the axis, resulting in a three-dimensional spiral curve.
The artificial turf fiber of any one of the preceding claims, wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis.
The artificial turf fiber according to any one of the claims 1-7, wherein the cross-sectional profile has a maximum length to maximum thickness ratio of at least 3.0, in particular at least 4.0, in particular at least 5.0, and wherein the helical artificial turf fiber is a twisted fiber that is rotated around its own axis.
The artificial turf fiber according to any one of the preceding claims, wherein the artificial turf has a core-cladding structure as the result of a co-extrusion step of a stream of the core polymer concentrically surrounded by a stream of the cladding-polymer.
The artificial turf fiber according to any one of the preceding claims, wherein the core polymer is or predominantly comprises polyethylene and the cladding polymer is or predominantly comprises polyamide.
The artificial turf fiber according to any one of claims, wherein the core polymer is a blend of aged polymer and a first virgin polymer, wherein the cladding polymer is made of a second virgin polymer, and wherein in particular the first and the second virgin polymers are both polyethylene polymers.
The artificial turf fiber according to any one of the previous claims, wherein the cladding polymer comprises a higher amount of HDPE than the core polymer.
The artificial turf fiber according to any one of the preceding claims, wherein the artificial turf comprises an anti-splicing agent, wherein the anti-splicing agent is in particular a compatibilizer, and/or a low-density polyethylene - LDPE.
The artificial turf fiber according to any one of the preceding claims, wherein the fiber comprises a hydrophilization agent, in particular hydrophilic fumed silica, and/or a nucleating agent.
An artificial turf, comprising: - a carrier - a plurality of helical artificial turf fibers according to any one of the previous claims 2-14, wherein the fibers are integrated into the carrier and extend to one side of the carrier.
The artificial turf according to claim 15, further comprising: - an infill layer, - wherein the number of twists per fiber and the height of the infill is chosen such that in at least 80% of the helical fibers, the part of the helical fibers that protrudes above the infill layer makes at least 1.0 turns.
A method for manufacturing an artificial turf fiber that is under internal stress, the method comprising: - extruding (104) a combination of at least a core polymer and a cladding polymer into a monofilament via an extrusion nozzle into a monofilament, the monofilament having a longitudinal cross-sectional profile, in particular a cross-sectional profile with a central bulb and two wings extending from the central bulb in different directions, wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment, wherein the extrusion is performed such that the core polymer is exclusively or predominantly located in the core of the cross-sectional fiber profile and such that the cladding polymer is exclusively or predominantly located in peripheral regions of the cross-sectional profile; - quenching (106) the monofilament; - controlling (108) equipment for processing the monofilament such that a temperature gradient is formed reproducibly in the cross-section of the monofilament; - stretching (110) the monofilament while the temperature gradient is present to form the monofilament into the artificial turf fiber, thereby introducing the internal stress into the fiber, wherein the internal stress is adapted to cause the artificial turf fiber, upon receiving heat treatment, to assume a helical shape.
A method for manufacturing a helical artificial turf fiber, comprising: - Executing the method of claim 17; and - heating (112) the monofilament, thereby causing the artificial turf fiber to assume a helical shape and become a helical artificial turf fiber.
The method according to claims 17 or 18, the method further comprising: creating (102) a polymer mixture comprising the core polymer and the cladding polymer, wherein the polymer mixture is extruded into the monofilament, wherein in particular the extruding is performed via an extrusion channel having a capillary length of less than 2.5 mm, in particular a capillary length of less than 2.0 mm, in particular of 1.4 to 1.6 mm.
The method according to claims 17 or 18, wherein the extrusion nozzle is a coextrusion nozzle for co-extruding the core polymer and the cladding polymer such that the core of the fiber is made of the core polymer and that the periphery of the fiber is made of the cladding polymer.

Description

FIELD OF THE INVENTION The invention relates to the field of artificial turf, and methods of manufacturing the same. BACKGROUND Artificial turf is a surface made of synthetic fibers designed to resemble natural grass. It is commonly used in sports fields, residential lawns, and commercial landscaping, offering low maintenance, durability, and the ability to withstand heavy use and varying weather conditions. Helical artificial turf fibers offer several advantages over straight fibers in terms of durability, aesthetics, and performance: The helical structure allows the fibers to spring back more easily after being compressed, making the turf more durable in places where there is frequent foot traffic, such as sports fields or playgrounds. This resilience is critical for maintaining the appearance and functionality of artificial turf over time, as straight fibers are more likely to flatten or break down under constant pressure. Furthermore, the helical design gives artificial turf a more natural look and feel, mimicking the way natural grass blades appear at different angles. Straight fibers tend to reflect more sunlight, creating an unnatural shiny appearance. Helical fibers help diffuse light, reducing glare and providing a more matte finish, which enhances the natural look of the turf. The helical nature of these fibers also provides better grip and traction. This can be particularly important for sports fields, where players need a stable surface to run and play without slipping. The Korean patent KR102535359B1 describes a method of manufacturing spiral or spring-shaped artificial turf yarn. US patent US 10,760,225 B2 1 describes a system for manufacturing helix-shaped artificial turf filaments, wherein the system comprises a first and a second air drawn oven downstream of an extrusion spinneret consecutively heat artificial turf filaments to a first and then a second temperature, wherein the second temperature is higher than the first temperature. SUMMARY OF THE INVENTION It is an objective to provide for an improved helical artificial turf fiber and for a method of manufacturing the same. The objectives underlying the invention are solved by the features of the independent claims. Embodiments of the invention can freely be combined with each other unless they are mutually exclusive. In one aspect, the invention relates to an artificial turf fiber comprising a longitudinal cross-sectional profile, the artificial turf fiber being under internal stress that causes the artificial turf fiber, upon receiving heat treatment, to assume a helical shape, wherein the core of the fiber consists of or predominantly comprises a core polymer, and wherein the periphery of the fiber consists of or predominantly comprises a cladding polymer, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment. In a further aspect, the invention relates to a helical artificial turf fiber comprising a longitudinal cross-sectional profile, wherein the core of the fiber consists of or predominantly comprises a core polymer, and wherein the periphery of the fiber consists of or predominantly comprises a cladding polymer, wherein the core polymer and the cladding polymer are different polymer materials, and wherein the core and cladding polymers are selected such that the core polymer undergoes greater shrinkage than the cladding polymer when subjected to the heat treatment. Hence, the helical structure of the fiber is the result of subjecting the fiber to heat treatment, the heat treatment having caused the core polymer to shrink stronger than the cladding polymer. For example, before the heat treatment, the core polymer and the cladding polymer may have the same length in any length unit of the fiber. However, as a result of the heat treatment, the length of the core of said sub-unit may be at least 2%, e.g., at least 5% or at least 10% shorter than the length of the periphery of said sub-unit. For example, the length of the core of the subunit may be measured as the distance of two points at the center of the fiber profile and the length of the periphery of the sub-unit may be measured as the distance of two points on the surface of the tip of one of the fiber arms. The applicant has identified that the combination of a fiber with a longitudinal cross-sectional profile and the use of a core polymer that exhibits greater shrinkage compared to a cladding polymer at the periphery during heat treatment offers significant advantages in producing fibers with a pronounced and stable helical configuration. By carefully selecting polymers with differing shrinkage properties for the core and cladding materials, it becomes possible to precisely control the degree of helicity, as well as the number of twists per unit length of the fiber. The greater t