ARTIFICIAL TURF

Abstract: An artificial turf according to the invention is constructed such that tufts of turf-shaped filaments are planted in a ground structure in a manner to form piles and tufts of subsidiary filaments which are shorter than the turf-shaped filaments are planted between the tufts of turf-shaped filaments. With such arrangement, the turf-shaped filaments are supported by the subsidiary filaments to be prevented from being laid flat over a long period of time, thus providing a good elasticity and a soft feeling of touch similar to natural turf. In addition, when long turf-shaped filaments are used, the artificial turf provides an appearance close to that of natural turf, and a sliding performance is improved on the surface of the artificial turf to facilitate play involving sliding in a game such as soccer and the like. In addition, in the case where a sand layer is provided on a base cloth with tip ends of the turf-shaped piles projecting above the surface of the sand layer, the elasticity of the subsidiary piles prevents the sand layer from being packed when trod, so that the artificial turf can preserve softness which is desired for a court or playground in a long-time use.

Description: Technical Field The invention relates to an artificial turf. Background Art Recently, artificial turfs are often used to cover courts or playgrounds on which sports activities such as tennis, baseball, football, rugby and the like are played. These turfs have the tendency to have their filaments folded by compressive load applied by players' walking, running, jumping or the like. To prevent this problem, short lengths of filaments of about 10 to 15 mm have been tufted at a high density. Alternatively, long lengths of filaments have been used with their lower parts buried in an amount of sand which forms a support layer. However, the former product differs in appearance from natural turf, and the latter has the tendency that the sand layer formed is solidified by being repeatedly stepped during long continued use, resulting in loss of softness suitable for use on courts and playgrounds. The DE-U-8807142 discloses an artificial turf wherein tufts of grass-like filaments are implanted on a backing structure to form a pile surface, and wherein rings are formed between the tufts of grass-like filaments. Further a granular layer (especially EPDM granule) is provided on the backing structure. In addition, assist filaments, which are shorter than the grass-like filaments, are implanted respectively at a bottom part of the artificial turf, which assist filaments are tufted loop-shaped and buried in the granule. The loop-shaped assist filaments of the artificial turf are used to form deep zones for accommodating the granules. A main disadvantage of the artificial turf of the DE-U-8807142 is that the assist filaments do not or not sufficiently support the grass-like filaments together with the granule layer so that the grass-like filaments are not properly prevented from being folded for a long time. A further disadvantage is that the assist filaments do not or not sufficiently prevent the reduction of permeability of the turf. The DE-A-3409361 discloses an artificial turf having a sand layer. This sand layer of a conventional artificial turf is provided to make the characteristic and appearance of an artificial turf closer to a natural turf. A main disadvantage of the artificial turf of the DE-A-3409361 is that there are no assist filaments, which could support the grass-like filaments together with the sand layer so that the grass-like filaments are not properly prevented from being folded for a long time. A further disadvantage is that the filaments of the artificial turf do not or not sufficiently prevent solidification of the sand layer by the resiliency of the filaments. Therefore, desirable softness for use of courts, playground or the like cannot be maintained for a long time. A further disadvantage is that the filaments do not or not sufficiently prevent the reduction of permeability of the turf which permeability is caused by the solidification of the sand layer. The JP-Y-58-22625 discloses an artificial turf having thick filaments and thin filaments between the thick filaments. The thin filaments are curled filaments. The thick filaments are flat filaments. The artificial turf of the JP-Y-58-22625 is not provided with a sand layer. A main disadvantage of the artificial turf of the JP-Y-58-22625 is that the curled thin filaments do not or not sufficiently support the flat thick filaments so that the flat thick filaments are not properly prevented from being folded for a long time. The JP-Y-61-11284 discloses an artificial turf having straight filaments and curled filaments between the thick filaments. The straight filaments and the curled filaments have the same thickness. The artificial turf of the JP-Y-61-11284 is not provided with a sand layer. A main disadvantage of the artificial turf of the JP-Y-61-11284 is that the curled filaments do not or not sufficiently support the straight filaments so that the straight filaments are not properly prevented from being folded for a long time. Disclosure of the Invention It is, therefore, an object of the invention to provide an artificial turf which overcomes the problems associated with the prior art and comprises filaments difficult to fold. It is another object of the invention to provide an artificial turf provided with a sand layer which can maintain desirable softness for a long period of time. The above objects of the invention can be accomplished by an artificial turf comprising tufts of grass-like filaments, implanted on a backing structure to form a pile surface, further comprising tufts of assist filaments, implanted between the tufts of the grass-like filaments, and further comprising a sand layer, provided on the backing structure, whereby the assist filaments are shorter than the grass-like filaments and the assist filaments are tufted loop-shaped and implanted on the backing structure and whereby the tips of the grass-like filaments projects from the surface of the sand layer, and whereby the tufts of the assist filaments are buried in the sand layer, whereby the assist filaments are bundled at the surface of the backing structure. The term "filament" as used herein includes yarns called as tape-yam supplied as a continuous ribbon, slit yam, split yam, film yarn and the like. Brief description of the Drawings Fig. 1 is a side elevation in vertical section illustrating an artificial turf which does not form a part of the present invention, but only represents background information, which is useful for understanding the invention. Fig. 2 is an enlarged view of grass-like filaments used for the artificial turf of Fig. 1; and Figs. 3 to 5 are side elevations in vertical section illustrating examples in which a sand layer is provided respectively in different artificial turfs embodying the invention. Best Modes of Carrying Out the Invention Now, embodiments of the present invention will be described with reference to the accompanying drawings. An artificial turf 1 shown in Fig. 1 is constructed such that longer lengths of grass-like filaments 3 and shorter lengths of assist filaments 4 are respectively implanted on a backing material, i.e., a backing cloth 2 so as to form respective tufts. A plurality of the synthetic resin grass-like filaments 3 and assist filaments 4 are respectively bundled and then tufted to form alternate rows of the tufts of the respective filaments. On the underside of the backing cloth is provided a backing resin layer 5 for preventing the filaments from slipping off. To closely resemble the appearance of natural turf, the grass-like tuft 6 is usually cut. However, it may be of a loop type depending on applications. It should be noted that a cut pile construction has advantages of enhancing sliding characteristics of a turf and therefore reducing the generation of frictional heat. In the case of using specially long lengths of grass-like filaments 3 to eliminate unnatural directionality in a pile surface caused by tufting, these filaments are preferably subjected to a crimping process. The assist filaments 4 are preferably loop-shaped to increase their supporting force, but the loops of the filaments may be cut depending on applications. Furthermore, the assist filaments 4 are preferably subjected to a crimping process in order to prevent compressive load from focusing on the base portions of the filaments and to therefore maintain their resiliency for a long period of time. This embodiment uses the grass-like filaments 3 constituted by crimping a wide tape-shaped film and then plying it to have a spiral cross section as seen in Fig. 2 . Inside the spiral cross section, there is a void space formed which can hold water penetrated into the space by surface tension, whereby water retentivity is improved. As the method of crimping filaments, the knitting and deknitting method or other various methods can be used. The thickness and denier number of the grass-like filament used may be appropriately selected within the range that conventional artificial turfs adopt. However, when the grass-like filament 3 is too thin, it lacks durability, and when too thick, it differs from natural grass in appearance and feel. Therefore, the grass-like filament is preferably in the range of 300 to 1,500 denier. When the assist filament 4 is too thin, it can not sufficiently support the tufts of grass-like filaments, and when too thick, it imparts hard feel to the resultant artificial turf. Therefore, the assist filament 4 is preferably in the range of 30 to 300 denier. From the same viewpoint, a bundle of grass-like filaments of the respective tufts 6 preferably have a denier of 3,000 to 12,000, and a bundle of assist filaments of the respective tufts 7 preferably have a denier of 1,500 to 12,000. The length of the grass-like filament may be selected to be an appropriate value, e.g., 15 mm, 20 mm 25 mm, 30 mm or the like, depending on applications. In accordance with the selected length, the height of the assist filament may be correspondingly selected. However, the tips of the assist filaments are formed lower than those of the grass-like filaments whichever height they may have. The height of the assist filaments is so determined that they may be beneath the grass-like filaments so as not to be seen directly and can support the grass-like filaments. More specifically, the height of the assist filaments is preferably 20 to 80 % of that of the grass-like filaments, more preferably 25 to 45 %. The height ratio of the assist filament relative to the grass-like filament is calculated based on the height of -filaments measured by vertically aligning the top ends of the filaments with the bottom ends. In the case of crimped filaments, this ratio is calculated under the same condition, but with crimps in the filaments retained. The artificial turf of the present embodiment is fabricated as follows. In a tufting machine, there is provided a needle row consisting of two types of tufting needles, one of which is used for tufting grass-like filaments and the other is for assist filaments. The descending amount of the needles for assist filaments to penetrate into the backing cloth is set to be less than that of the needles for grass-like filaments. A cut knife synchronous with a looper may work on the rows implanted by one or both of the needles when necessary. In the illustrated example, the looper works on only the tufts of grass-like filaments so as to form rows of loop tufts of shorter length (assist tufts) and rows of cut tufts of longer length (grass-like tufts). Further, grass-like tufts of longer length and crimped assist tufts of shorter length can be formed utilizing the heat applied in the backing process. In one method, non-heat shrinkable fibers are used as the grass-like filaments, and heat shrinkable fibers are used as the assist filaments. Both of the filaments are tufted at the same level. When the backing process is conducted thereto, only the assist filaments are heat-shrunk, whereby the grass-like tufts of longer length and the crimped assist tufts of shorter length are formed. The heat shrinkable fibers may be general synthetic fibers such as nylon and polyethylene. The non-heat shrinkable fibers can be obtained by an elongation process of a higher temperature than the backing process and therefore are not heat-shrunk during the backing process. In a second method, both of the grass-like filaments and assist filaments are heat-shrinkable fibers, wherein the heat shrinkage of the former is small, and the same of the latter is large. During the backing process, the assist filaments shrink much more than the grass-like filaments so that the grass-like tufts of longer length and the assist tufts of shorter length are formed. The heat-shrinkage of the respective filaments can be controlled by adjusting the stretched amount before a spinning process. When the stretched amount is set to be large, the heat-shrinkage of the filaments becomes large, and when the stretched amount is set to be small, the heat-shrinkage becomes small. In a third method, both of the grass-like filaments and the assist filaments are heat-shrinkable fibers. The former is thick and the latter is thin. During the backing process, the assist filaments shrink much more than the grass-like filaments so that the grass-like tufts of longer length and the crimped assist filaments of shorter length are formed. In the artificial turf of the invention, the tufts of grass-like filaments are implanted on the backing structure so as to form a pile surface, and the tufts of assist filaments of shorter length are implanted between the tufts of grass-like filaments. Therefore, the grass-like filaments are supported by the assist filaments and are prevented from folding for a long period of time. Furthermore, it is possible to use long lengths of filaments to thereby obtain the appearance closely resembling natural turf. The use of long lengths of filaments improves sliding characteristics on the turf surface, whereby sliding actions in a soccer game or the like can be performed without difficulty. The friction on the long lengths of filaments is small so that skin burns or frictional injuries can be prevented. Further, due to the resilient support by the assist filaments, the surface of the artificial turf is provided with resiliency so that the turf of the invention can rapidly respond to applied load and the release thereof compared with the case where an underlay is placed under an artificial turf to provide resiliency, whereby prompt actions as in sports activities or the like can be made without difficulty. When using assist filaments thinner than grass-like filaments, water retentivity in a turf can be improved. Figs. 3 to 5 illustrate embodiments in which a sand layer is provided in the artificial turf of the invention. In the cross section shown in Fig. 3 , the artificial turf 10 comprises a plurality of synthetic resin grass-like filaments 3' bundled together and implanted on the backing cloth 2 of a backing structure by tufting to form a number of rows of grass-like tufts 6 (the drawing shows a lateral cross section of a row formed by tufting). A plurality of assist tufts, consisting of a plurality of bundled synthetic resin assist filaments 4 , are implanted along the rows of grass-like tufts 6 of the artificial turf 10 , thereby forming their own rows 70 . In this embodiment, the assist tufts 70 is of a loop type in which case the loop shape imparts resiliency to the assist tufts 7 Fig. 4 is a cross section illustrating still another embodiment, i.e., an artificial turf 10' . This artificial turf comprises a plurality of synthetic resin grass-like filaments 3' bundled together and implanted on the surface of the backing cloth 2 as in the case of Fig. 3 to form a number of rows of grass-like tufts 6 and further a plurality of synthetic resin assist filaments 4 bundled together and implanted along the rows of the grass-like tufts 6 to thereby form rows of assist tufts 70' . In this embodiment, the assist tuft 70' is of a cut pile type in which case the assist filaments 4' constituting the cut pile are preferably plied or crimped by a crimping process. The artificial turfs 10 or 10' are placed and appropriately fixed on a ground surface such as a playground or a court. For using the turf as a sand-filled artificial turf, sand is filled to a level (i.e., to the level indicated by an arrow A in the drawing) on the backing cloth 2 so as to form a sand layer 8 with the top ends of the grass-like tufts projected from the surface of the sand. The assist tufts 70 or 70' are formed lower than the grass-like tufts 6 as described above so that the assist tufts are buried in the sand layer 8 formed on the backing cloth as shown in Figs. 3 and 4 . As the material for the grass-like tuft, it is possible to use such synthetic resins as polypropyrene, polyethylene, nylon, polyester and vinylidene chloride, which have been used for conventional artificial turfs and have excellent weather-resistant properties and durability. As the material for the assist tuft, natural fibers can be used besides the above-raised synthetic resins. The natural fibers are preferably those having stiffness and excellent resiliency such as hemp and jute. As monofilaments constituting the grass-like tufts and the assist tufts, i.e., the grass-like and assist filaments, it is possible to use usual flat filaments, filaments having a circular cross section or film yarn having nick portions to be divided into a grass-like shape. As these filaments, especially as the assist filaments, it is also possible to use filaments having an excellent water absorbing capability, such as hollow filaments or natural fibers. Still further, another embodiment shown in Fig. 5, i.e., an artificial turf 10" comprises assist tufts 70" constituted by bundling and cutting thin filaments 40 of natural fibers or synthetic fibers, those tufts extending and spreading upward from the backing cloth 2 . In the case of using thin synthetic filaments as the assist tufts 70" , the filaments may be subjected to a crimping process beforehand so as to impart preferable resiliency to the filaments. Analogously to the previous embodiment (Figs. 3 and 4 ), the artificial turf comprises the assist turfs 70" with their tips formed lower than the grass-like tufts 6 , wherein each row of the assist tufts 70" is formed lower between the rows of the grass-like tufts 6 . As in the previous embodiment, this artificial turf 10" is filled with sand up to the level indicated by an arrow A in the drawing in such a manner that only the tip portions of the grass-like tufts 6 be projected from the sand layer 8 . Accordingly, the assist tufts 70" are buried in the sand layer. In the artificial turf with the sand layer thus formed, compressive load applied by a foot is transmitted to the assist tufts 70 , 70' and 70" buried in the sand layer 8 , as well as to the sand layer 8 . At this time, the density of sand particles in the sand layer 8 is increased by the applied compressive load, and the assist tufts 70 , 70' and 70" deform and absorb the compressive load transmitted from surrounding sand particles. After the compressive load is released, the assist tufts restore their original forms and push back the sand layer 8 because of their resiliency. In order for the assist tufts to easily push back the sand layer, the heights ( A ) of the sand layer respectively indicated in the drawings are determined so that the resiliency of the assist tufts 70 , 70' and 70" can be fully utilized, and that not so much weight of sand is applied on the assist tufts. That is, the sand layer is formed about 3 to 10 mm higher than the tips of the assist tufts, more preferably about 5 mm higher. In the artificial turf of this embodiment, the rows of assist tufts are formed between the rows of grass-like tufts on the backing structure with the tips of the assist tufts lower than those of the grass-like tufts, and the assist tufts are buried in the sand layer formed on the backing cloth with the tip portions of the grass-like filaments projected from the surface of the sand layer. Therefore, the sand layer in the artificial turf is prevented from solidifying because of the resiliency of the assist tufts so as to maintain desirable softness for long use on courts, playgrounds or the like. Further, the artificial turf is advantageous in that it prevents the reduction of permeability which is caused by the solidification of the sand layer. Depending on applications, a plurality of rows of assist tufts may be implanted between the adjacent rows of the grass-like tufts implanted on the backing structure. Alternatively, each row of assist tufts may be formed per a plurality of rows of grass-like tufts so as to adjust the softness of the artificial turf. In this case, the production of the artificial turf is conducted by a tufting machine which comprises needles, loopers and knives suitable for tufting the grass-like tufts and assist tufts to be provided.

Claims: An artificial turf (10) comprising tufts (6) of grass-like filaments (3'), implanted on a backing structure (2.5) to form a pile surface, further comprising tufts (70) of assist filaments (4), implanted between the tufts (6) of the grass-like filaments (3'), and further comprising a granular layer (8), provided on the backing structure (2.5), whereby the assist filaments (4) are shorter than the grass-like filaments (3') and the assist filaments (4) are tufted loop-shaped and implanted on the backing structure (2.5) and whereby the tips of the grass-like filaments (3') project from the surface of the granular layer (8), and whereby the tufts (70) of the assist filaments (4) are buried in the granular layer (8), characterized in that the assist filaments (4) are bundled at the surface of the backing structure (2.5) and the granular layer (8) is a sand layer. An artificial turf (10) according to claim 1, characterized in that the tufts (6) of grass-like filaments (3') and the tufts (70) of the assist filaments (4) are implanted to form respective rows, and wherein the tufts (70) of the assist filaments (4) are formed between the rows of the tufts (6) of the grass-like filaments (3).

Inventors: FUKUMOTO HIROAKI, ISHIKAWA YOSHIO, FUKUMOTO, HIROAKI, ISHIKAWA, YOSHIO, FUKUMOTO, HIROAKI, 1-22-16,TAKATSUKADAI, ISHIKAWA, YOSHIO, 249-13,HIGASHIOJICHO
Applicants: OTSUKA KAGAKU KK, OTSUKA KAGAKU KABUSHIKI KAISHA
Application year: 1993
Main classification: E01C13
IPC codes: D02G3, E01C13, D05C17