Patent Publication Number: US-6989179-B2

Title: Synthetic grass sport surfaces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a Continuation of application Ser. No. 09/818,857, filed on Mar. 28, 2001, now U.S. Pat. No. 6,767,595 and for which priority is claimed under 35 U.S.C. § 120; and this application claims priority of Provisional Application No. 60/256,961 filed in the United States on Dec. 21, 2000 and International Application No. PCT/CA01/00372 filed on Mar. 21, 2001 under 35 U.S.C. § 119; the entire contents of all are hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to synthetic grass surfaces and, more particularly, to a synthetic grass sport surface suited for ball games, such as baseball, cricket, golf and any sport that has a ball landing or rolling on the surface. 
   2. Description of the Prior Art 
   Synthetic grass sport surfaces are well known. They are used to replace natural grass surfaces which do not stand up well to wear and which require a great deal of maintenance. 
   In ball games, such as baseball, cricket, soccer, tennis and golf, one concern has always been to provide a synthetic grass surface which would virtually not affect the travelling direction of a ball rolling thereon, but which would still closely emulate the appearance of natural grass. A ball must roll true in any direction. The means employed to provide the appearance of natural grass must not affect the preferred non-directional properties of the synthetic grass. 
   Another concern is the provision of a synthetic grass sport surface having a layer of infill particulate material which will not create streaks on a ball when the same comes in contact therewith after having been hit or thrown by a player. The provision of a non-marking playing surface is particularly essential to the upper level of play in the college and professional baseball ranks so that the white leather balls used be not constantly rejected by an umpire because of streaks thereon created from the contact of the ball with the infill of the playing surface. 
   It has also been found that there is a need for a new synthetic grass baseball playing surface having a synthetic grass outfield surface and a synthetic grass warning track of different tangible properties to alert an outfielder focusing on a ball in flight that he is approaching an obstacle, such as an outfield fence. 
   SUMMARY OF THE INVENTION 
   It is therefore an aim of the present invention to provide a new synthetic playing surface which is less subject to creating streaks on a sport ball rolling thereon. 
   It is also an aim of the present invention to provide a new synthetic grass sport surface which more closely emulate the appearance of a natural grass sport surface. 
   It is a further aim of the present invention to provide a new synthetic grass warning track to alert a player that he is approaching an obstacle. 
   Therefore, in accordance with the present invention, there is provided a synthetic grass playing surface which is provided with an improved infill layer of particulate material. The infill layer preferably comprises a non-marking particulate material which is distributed so as to prevent a ball from being marked when the same hits the synthetic grass playing surface. 
   Also in accordance with the present invention, there is provided a synthetic grass playing surface having a lawn mowing pattern imitation formed thereon by a checkered pattern of alternating synthetic grass sections of different color tones so as to simulate different grass mowing directions and, thus, improve the resemblance to a natural grass surface. 
   In accordance with a further general aspect of the present invention, there is provided a synthetic grass baseball playing surface having a synthetic grass outfield surface and a synthetic grass warning track, said synthetic grass warning track having tangible properties different from that of said synthetic grass outfield surface so as to alert an outfielder stepping thereon that he is approaching an obstacle. 
   In accordance with a further general aspect of the present invention, there is provided a method of forming a baseball warning track comprising the steps of installing a synthetic grass outfield surface having a backing and a plurality of synthetic ribbons extending upwardly therefrom, delimiting a warning track area and an outfield grass area on the synthetic grass outfield surface, and interspersing first and second layers of infill material among the ribbons of said warning track and outfield grass areas, respectively, the first and second layers having different overall tangible properties so that an outfielder stepping on the warning track area is alerted that he is approaching an obstacle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which: 
       FIG. 1  is a schematic cross-section view of a synthetic grass baseball playing surface in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a schematic cross-section view of a synthetic grass baseball playing surface having a synthetic grass warning track formed therewith; 
       FIG. 3  is a schematic top plan view of a section of a synthetic grass surface having a checkered pattern formed thereon; 
       FIG. 4  is a schematic top plan view of a section of a synthetic grass surface having a checkered pattern formed thereon in accordance with a further embodiment of the present invention; and 
       FIGS. 5   a  and  5   b  are top plan views of a baseball field. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now referring to the drawings, and in particular to  FIG. 1 , a synthetic grass baseball playing surface  10  embodying the characterizing elements of the present invention will be described. 
   The synthetic grass baseball playing surface  10  generally includes a thin flexible backing mat  12  with parallel rows  13  of synthetic ribbons  14  projecting upwardly from the backing mat  12 , and representing grass blades. A relatively thick infill layer  16  of particulate material is provided on the baking mat  12  to support the ribbons  14  in a relatively upright position on the backing mat  12  and to provide resiliency to the surface  10 . The backing mat  12  and the ribbons  14  are preferably of the type disclosed in U.S. Pat. No. 5,958,527, issued to Prevost on Sep. 28, 1999 and assigned to the Assignee of the present application, and the contents of which are incorporated herein by reference. 
   The ribbons  14  are made from suitable synthetic plastic material which is extruded in a strip that is relatively wide. The strips are mechanically fibrillated or split to approximately one-eight of an inch or more. The fibrillation, which is done during the manufacturing of the strip, provides a ribbon which resembles a hair net, that is, the resulting fibers are interconnected. 
   The rows  13  of ribbons  14  are spaced-apart by a distance that ranges between ⅝″ and 2¼″. Furthermore, it has been found that the thickness of the infill layer  16  should be about two-thirds the length of the ribbons  14  and that the free terminal ends  18  of the ribbons  14  should extend anywhere from ¼″ to 1⅛″ above the top surface of the infill layer  16  to form a top void  20 . The infill layer can be about 1¼″ to 2″ thick. The top void  20  and, thus, the length of the ribbons  14  should be greater within about 15 feet of the home plate H (see  FIG. 5 ) of the baseball field to contribute to prevent the particulate material of the infill layer  16  from being dislodged by a hard hit ball. 
   The infill layer  16  preferably comprises a base sub-layer  22  of sand, a main intermediate sub-layer  24  of a mixture of hard sand, such as silica, and cryogenically ground crumb rubber, and a top covering sub-layer  26  of non-marking ground rubber particles. The base layer  22  may include 1 lb. of sand per square foot of playing surface, whereas the top covering layer  26  may include 0.3 lb. to 1.5 lbs. of non-marking ground rubber particles. The amount of mixture of hard sand and cryogenically ground crumb rubber is calculated so as to obtain an infill layer having a desired thickness (for instance about 1⅛″ or more depending on the friction the ball creates with the sport surface). According to a preferred embodiment of the present invention, the ratio sand/rubber is approximately equal to 3 or close to that number, but could be less if we use more sand in the bottom of the infill. However, it is noted that a greater proportion of rubber can be provided if the surface requires additional resiliency. The sand particles and the ground crumb rubber particles range in size between 10 mesh and 40 mesh. The non-marking rubber particles range in size between 4 mesh to 20 mesh. The non-marking rubber particles must be larger than the underlying ground crumb rubber and sand particles to prevent the non-marking particles from falling therein. 
   The non-marking ground rubber particles forming the top covering layer  26  preferably consist of particulate material made from recycled soles of running shoes that have non-marking rubber. Alternatively, the non-marking material could be made of other non-marking rubber e.p.d.m, plastics with relatively high specific gravity ratio, round stone or sand. The non-marking material must be of such quality and composition such that it does not oxidize too much under UV rays. If the non-marking material oxidizes, it may mark up the balls. By evenly spreading a topcoat of non-marking material on the underlying infill material, streaks on the ball resulting from the ball entering in collision with the synthetic grass surface  10  and infill layer  16  are virtually prevented, thereby prolonging the service life of the ball. It is pointed out that the top void  20  also adds to the non-marking features of the present system. 
   Instead of solely forming a top covering layer  26  of non-marking material, the entire infill layer  16  could be of a non-marking kind. 
   Non-marking material could also be used for other sports, such as soccer, golf and in all sports in which a ball is rolled or the ball impacts on a playing field. In a golf application, the non-marking rubber material would advantageously contribute to reduce abrasion on the golf balls as well as not marking them. 
   The synthetic grass baseball playing surface  10  could be provided in a modular form including a number of individual synthetic grass units adapted to be laid flat on a field and fit side by side to provide a flat and continuous synthetic grass surface. The synthetic grass units are preferably installed from the home plate H through the second base B 2  as with the rolls of artificial grass. The grain (i.e. the direction and pattern in which the ribbons  14  extend from their original packaging condition) must preferably be lying towards the outfield. The foul lines F 1 , F 2  ( FIGS. 5   a  and  5   b ) can be installed from synthetic grass units having white lines formed thereon. The synthetic grass units with the white lines thereon are installed parallel to the foul lines F 1  and F 2 . 
   Alternatively, the infield and the outfield could be formed from rolls R of synthetic grass laid side by side on the field ground so that the original grain of the synthetic grass generally extends towards the outfield fence (not shown). As seen in  FIG. 5   b , the rolls of synthetic grass are preferably installed from the home plate H through the second base B 2 . However, as seen in  FIG. 5   a , the rolls R of synthetic grass could also be installed parallel to either one of the first or the third base line F 1  and F 2  to reduce the waste. Once installed, the synthetic grass is fibrillated and brushed to remove the grain therefrom and, thus, ensure a uniform ball roll. 
   Once the synthetic grass surface  10  has been laid on the field ground, the infill layer  16  of particulate material is distributed between the ribbons  14 . More particularly, the infilling procedure comprises the steps of first installing successive thin layers of sand in view of forming the base layer  22  and then additional layers of sand are installed to complete the base layer  22  and the sand is brushed in. After having installed the base layer  22 , the main intermediate layer  24  of pre-mixed sand and rubber is installed gradually. This layer can also be layered in special cases where there is not enough room to mix the infill. This step is repeated until the level of the infill layer  16  reaches the desired height. Prior to adding the top covering layer  26  of non-marking particulate material, the synthetic grass surface  10  needs to be seriously further fibrillated so that the surface takes on a general non-directional result and, thus, allows a ball to roll straight in any direction on the playing surface  10 . Next, combing the grass in a generally radial direction, as depicted by arrows  35  (see  FIG. 1 ) from the home plate towards the outfield is essential until the synthetic grass becomes very uniform. Combing is effected by rotating a stiff nylon or plastic bristled brush into the synthetic grass surface  10  by applying pressure to get all the ribbons  14  laying in a same direction or by using a rake type of unit with metal prongs that adequately agitate the blades of grass (ribbons  14 ) in the desired direction. The individual ribbons  14  need to be additionally fibrillated and combed so the ribbons  14  that are split are really individual fibers. This will cause the fibers to lay over more easily and interlock, thereby trapping the infill particulate material in the synthetic grass surface  10 . The combing and brushing action are also designed to perfectly level the infill in the surface so the final layer(s) of non-marking material is/are installed evenly. Thereafter, the final layer(s) of non-marking material is/are added in a very precise manner. 
   The on site fibrillating operation is done using a nylon brush (not shown) that is preferably rotating or by a steel brush or a combination of both. The playing surface  10  must be brushed several times during the infilling process. It has been found that the surface  10  should be brushed primarily only radially from the home plate H towards the outfield, as illustrated by arrows  35  in  FIGS. 5   a  and  5   b . This should be done late in the process. Brushing in any other direction will create grain that the operator will have to subsequently undo. Once the intermediate layer  24  has nearly reached the desired level, a final infill leveling pass has to be made to properly level the intermediate layer  24  in a uniform manner to accept the top covering layer  26 . When doing this final leveling pass, the combination steel and/or nylon brush or a brush with all metal bristles should be used. This final pass must be done only in a generally radial direction (see  FIGS. 5   a  and  5   b ) from the home plate H to the end of the outfield. This will prevent creating grain in a wrong direction. To properly assess the amount of fibrillation required, the operator will need to closely inspect the ribbons  14  to be sure they are split individually. 
   Once the grass has been properly fibrillated and the intermediate layer  24  properly leveled, the top covering layer  26  of non-marking rubber particles is ready to install. The top covering layer  26  must be installed very evenly and at the right rate in order to not have to seriously agitate the synthetic grass to make all of the non-marking rubber particles fall into the underlying sub-layers of the infill layer  16 . As mentioned hereinbefore, the size of the non-marking particles must be larger than that of the underlying particles. Once the top covering layer  26  is down, the synthetic grass baseball playing surface  10  can be brushed by not rotating the brush but by placing the same at an angle and lowering it to the depth of the infill layer  16  or by using a soft drag brush. The brush must then be driven back and forth a few times to lightly agitate the ribbons  14  just enough to make the top infill material, i.e. the non-marking rubber particles drop onto the underlying infill material but not mixing the non-marking rubber particles and the underlying infill material. The infill material can then be compacted using a vibrating 2000 to 3000 lbs. roller. The final step of the fibrillating process consists of pulling a 15 foot drag brush or smaller attached to a three point hitch in one direction only, towards the outfield in a very uniform pattern always being sure that there is no mixing of the non-marking material and the underlying infill material. 
   The clay C surrounding the bases and the home plate needs to be leveled at the same level as the top covering level  26  of infill material. Stepping on the transition of the two surfaces must result in a perfectly flat area at all points. The ribbons  14  will protrude above the clay C and will look like real grass. The leveling of the clay zones is accomplished only after the infilling procedure of the synthetic grass surface  10  is completed. The amount of infill material in the synthetic grass needs to stay constant so a small border (not shown) of plastic or ⅛″ fiberboard can be temporarily placed in an upright position to keep the infill material in the synthetic grass while the clay C is installed at the proper level. The clay C next to the synthetic grass surface  10  needs to be compacted properly. Once the clay C is installed, the border can be removed and fine-tuning can proceed. To obtain a real grass look, the synthetic grass surface  10  needs to be raked up at its juncture with the clay C. This is accomplished by hand raking the grass in a straight line and tucking in dry clay C next to the synthetic grass surface  10  in order to prevent the infill material from falling out. The wide blades of fiber in the synthetic grass keep the clay from falling in between these blades of grass. However, if there was too much fibrillation of the fibers, the edge would not look so real. 
   Another method of obtaining a non-directional surface, i.e. a surface in which the fibers forming the surface extend in no specific visual pattern or direction but are rather randomly oriented, consists of twisting individual strips of slit ribbons together to form a fibrous tuft. The number of twisted slit ribbons twisted together can modify the playing characteristics of the field surface to achieve the anticipated results. These slit ribbons would not need to be fibrillated on site since they would be already individual ribbons. Another reason to use slit ribbons is to have stronger individual strands of ribbons if necessary. When fibrillating pre-fibrillated fibers on site, the result is that some of the fibrillated or split fibers become smaller that what may be more desirable. These smaller ribbons are the ones that wear first. They are by their physical nature more fragile than the larger fibers and therefore are not really desirable. Therefore, by using the slit ribbon fiber, a more predictable life span duration is possible as well as a more predictable ball roll and or field result. However, infilling slit ribbons is much harder since they tend to fall with the weight of the sand or rubber. 
   By having the same sized fiber blades, a more uniform surface could be attained since rolling the fibers will mat them down evenly because they are of uniform size. 
   As shown in  FIG. 2 , the synthetic grass baseball playing surface  10  includes a synthetic grass warning track  34  having tangible properties (firmness, resiliency, coefficient of friction etc . . . ) different from that of the synthetic grass surface laid on the outfield ground so as to alert an outfielder focusing on a ball flight that he is approaching the outfield fence (not shown). The difference in tangible properties between the warning track  34  and the synthetic grass outfield surface  10  can be achieved by varying the spacing between the rows  13 ′ of ribbons  14 ′, the stiffness of ribbons  14 ′, the length of the ribbons, the thickness of the infill layer  16 ′, the type of infill material, etc . . . 
   The warning track  34  can be made with more or less the same composition of grass than that of the outfield, with a different density of grass, or of a different contrasting color to easily catch the eye of the player. However, it is preferable to use a radically different texture underfoot so that the baseball player will recognize the warning track  34  as he steps thereon. This can be done by modifying the infill to change the actual feel underfoot. Using an all sand infill could achieve that result, or using entirely rubber infill could also achieve that result. Various other types of infill material, such as coal slag, granular rock, granulated brick particles, or granulated lava rock that will create a supporting surface having a different texture underfoot and that will produce a sound when stepped thereon could be used as well. These granulated particles are brushed in between the fibers of the field surface to a height that would cover the grass fibers. 
   Alternatively, the warning track  34  could be formed by providing a synthetic grass surface having a sand filled infill layer on which warning track clay is dispersed in a thickness adequate enough to completely cover the green synthetic grass underneath. This results in having a warning track surface that can be very easily converted to a playing surface for other sports applications. 
   By evenly infilling the synthetic grass surface with sand to a uniform level, a certain upper portion of the ribbons  14 ′ can be void of infill  16 ′. This allows room in the synthetic grass matrix to accept the granulated infill mixture used to color the warning track  34 ′ on a baseball field as well as a texture difference with the outfield surface. 
   The warning track infill material will be held in place by the fibers  14 ′. The friction created by the fibers  14 ′ will make the warning track infill material stable. 
   For conversion to other sports not requiring a clay warning track, the warning track top infill material, for instance, clay granules, only need to be brushed off and removed from the area so as to expose the underlying synthetic grass which is infilled with sand or other suitable resilient particulate materials. A certain portion of the infill material could be removed from the synthetic grass and replaced, for instance, by adding a resilient infill of ground rubber if a resilient surface is required. This would advantageously eliminates the need to remove grass sections of a different color or texture that would be used to identify the warning track  34 . 
   This would eliminate seams at the junction of the warning track and the outfield synthetic grass surface, reduce conversion time, possibly painting of lines in a specific areas by having them permanently installed if necessary, and would be far more efficient than having a different color of another material laid on the area to be converted. 
   The visual aspects of a baseball field are important. Uniformity and the appearance (of grass) is critical. It has been found that the overall natural appearance of a synthetic grass surface can be improved by creating a checkered pattern of light and dark green colored grass sections in order to emulate the strips left in a natural grass by a lawn mower machine due to the different grass trimming angles when the machine is driven in different directions. 
     FIG. 3  illustrates a checkered pattern  36  including grass sections  38   a  and  38   b  of alternating color tones. It has been found that by creating a checkered pattern on a synthetic grass surface, the natural appearance thereof can be improved. The variation in color from one section to the other can be obtained by having grass sections of different ribbon densities, the denser grass section being darker. Alternatively, the grass sections  38   a  and  38   b  could be provided with ribbons of different color tones. Also, the grass sections could be provided with ribbons oriented in different directions to provide the desired grass trimming pattern if the fiber grain does not affect play in a particular sport. The grass sections can be subsequently fibrillated to not affect the direction of travel of a ball rolling thereon for such applications that require a specific ball roll characteristic. 
   The synthetic grass surface is preferably manufactured in the form of synthetic grass panels  40   a  and  40   b  adapted to be placed side by side to form a continuous support surface. Each panel  40   a / 40   b  is formed of a number of square or rectangular grass sections  42   a  and  42   b  cut from different color tone grass panels and sewn, glued, or attached together by a hook and loop attachment in a criss crossed way to create a checkered pattern  36 ′, as shown in  FIG. 4 . For instance, the grass sections  42   a  and  42   b  could be obtained from 15′ wide panels of grass made in long lengths and cut at each 7½′. The sections of grass can be assembled together with respective ribbons or fibers thereof lying in different directions, as depicted by arrows  44  in  FIG. 4 . Once on site, the ribbons of grass panels are fibrillated to remove the grain directions thereof when it is desired to obtain a non-directional playing surface as explained hereinbefore.