Abstract:
The lawn edging ( 10 ) is formed by extruding a thermoplastic resin, preferably a thermoplastic resin such as polyethylene containing a dispersion of prevulcanized elastomer granules through a die ( 62 ) having a vertical die orifice ( 64 ) for forming the wall ( 12 ) of the channel ( 16 ). The vertical die orifice ( 64 ) also contains an element for forming protrusions ( 20 ) on a surface of the wall ( 12 ). The element preferably forms a horizontal edge on the protrusion ( 20 ). The feed rate of the element can be higher than the adjacent sections of the wall ( 12 ) such that the extruded material backs up in the die ( 62 ) and intermittently feeds through the outlet orifice ( 64 ). The channel ( 16 ) can contain a lower bead ( 34 ) and an upper hollow head member ( 14 ) which can be coated with a liquid impervious film ( 100 ) and perforated by a laser ( 120 ) to form spray apertures ( 122 ).

Description:
This application claims benefit to U.S. provisional application Ser. No. 60/023,775 filed Aug. 9, 1996. 
    
    
     TECHNICAL FIELD 
     This invention relates to a lawn barrier and more particularly this invention relates to an improved synthetic composite lawn edging which acts as a divider between lawn areas containing different types of plants or ground cover. 
     1. Background of the Invention 
     Many lawns are landscaped to contain discrete areas or beds of ground cover such as grass, plants or non-growing materials such as stone or bark. In order to prevent growth across the common border; it is quite common to install a physical barrier at the border such as strips of wood, metal, brick or cement walls, or lawn edging formed of synthetic resin. 
     2. Description of the Prior Art 
     A popular form of synthetic resin lawn edging is in the form of a flange having an enlarged tube and a pair of anchoring means such as upwardly facing lips are provided between the lips and bottom of the flange as disclosed in U.S. Pat. No. 4,281,473. 
     This lawn edging is formed from polyethylene. It is very rigid and inflexible. The edging is marketed in twenty foot sections wound into a coil. The edging retains the memory of the bends in the coil. It is hard to install in a straight line and the edging also contains vertical ribs intended to aid in securing the edging in the ground. The edging kinks when bent into a narrow radius. The memory combined with a very smooth surface causes the edging to work its way out of the ground even though it contains the upwardly facing lips on the flange which are backfilled with dirt or stone and the alternating vertical rib structure. 
     Polyethylene is an expensive material and is manufactured by polymerizing ethylene, a material formed from petroleum, a dwindling resource. 
     STATEMENT OF THE INVENTION 
     The lawn edging of the invention is formed from a dispersion of ground-up, recycled rubber particles in a matrix resin. Millions of used tires are generated every year. They are fairly inert and do not decay when buried in land fills. They are a fire hazard when stored in sites above the ground. It is difficult to separate the steel and fabric cord from the rubber. Since the rubber is revulcanized to a cross-linked form, the rubber cannot be recovered by solution in solvent. It is not economical to degrade the long chain rubber molecules to smaller hydrocarbons by thermal or catalytic methods. 
     The rubber particles utilized in the lawn edging invention can be recovered from used tire carcasses by mechanical comminution of tires and separation of the fiber or metal cord from the rubber. Ground rubber particles can be sized between screens generally to particles retained by 10 mesh screens, preferably 30-40 mesh screens. The amount of rubber used in the composite lawn edging of the invention is generally from 20 to 80 percent by weight. The continuous phase binder resin is a thermoplastic polymer capable of melting to disperse the rubber particles into an extrudable mixture. The thermoplastic polymers can be a polymer of an alkylene containing 2 to 8 carbon atoms such as ethylene, propylene, butylene, hexylene and ethyl hexylene or mixtures thereof. Other suitable thermo-plastics polymers are vinyl polymers. 
     The mixture is extruded to form a lawn edging having a rough surface. The rough surface intensifies the frictional resistance of the buried edging reducing the tendency of the edging to creep out of the ground. The composite rubber-polymer lawn edging is much more flexible, pliable and bendable than an equivalent polyethylene edging. It can be bent into tighter radii to follow contours of garden beds without cracking or kinking. It can also be wound into tighter spirals to make smaller packages requiring less shelf space. 
     The invention also relates to a unique process for extruding the lawn edging. The lawn edging preferably contains an anchoring means provided at the mid section of the vertical flange of the edging. Prior devices used inverted V-shaped lips for this purpose. In the invention, wave-like protrusions are formed on the flange protruding normal to the axis of the flange. By controlling the pressure of the extrudate entering the central section of the die, pressure on the extruded material in this section is found to periodically build up and release to form wave-like structure corresponding to the die opening and which forms alternating protrusions and dimples in the wall of the flange. The other side has a horizontal edge and may run across the top edge of the wave structure. 
     The lawn edging of the invention contributes to the environment by using a recycled product that otherwise would accumulate and degrade the environment. The lawn edging of the invention is more flexible than prior products, can be installed with less force, can be bent into tighter radii and has less tendency to come out of the ground after installation. 
     These and many other features and attendant advantages of the invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of the lawn edging of the invention installed as a barrier around a flower bed; 
     FIG. 2 is a view in section taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a perspective view of a length of lawn edging of the invention; 
     FIG. 4 is a schematic view partly in section, of an extruder system for use in forming the lawn edging of the invention; 
     FIG. 5 is a view in section taken along line  5 — 5  of FIG. 4; 
     FIG. 6 is a view in section taken along line  6 — 6  of FIG. 5; and 
     FIG. 7 is a schematic view of post extrusion operations to modify the lawn edging of the invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1-3, the lawn edging  10  of the invention is formed of a vertical flange  12  having an enlarged head portion  14 , a bottom edge  16  and an intermediate anchoring section  18 . A series of spaced arcuate like protrusions  20  can be formed on a first side  22  of the flange  12 . The protrusions  20  are separated by indented dimples  24 . The second side  26  of the flange  12  can contain a wavy line  30  having a triangular section with a horizontal ledge  32 . The ledge  32  when loaded with backfilled dirt will prevent lifting of the edging  10  out of the ground. The arcuate protrusions  20  and dimples  24  also contribute to anchoring the edging in the ground. 
     The bottom edge  16  of the edging  10  can contain a sharpened form, a flat form, or a cylindrical bead  34 . The enlarged head portion  14  is preferably hollow containing a cavity  36  which can receive a joining rod, not shown, for joining ends  44  of the sections  40  to form elongated barriers or enclosed rings  42  as shown in FIG.  1 . 
     The lawn edging  10  is manufactured as a unitary, single article by extrusion. Referring now to FIGS. 4-6, a mixture  50  of particles of prevulcanized rubber and matrix resin such as polyethylene pellets are fed from hopper  52  into the inlet  54  of an extruder  55 , preferably, a twin screw, vented extruder. The extruder can be heated by an external heating jacket  56  to a temperature at which the matrix resin melts, usually from 360° F. to 400° F. for polyethylene matrix resin. The rubber particles disperse in the molten matrix resin as the mixture advances as the screw  58  is rotated by the motor  60 . 
     The mixture enters die  62 . The die  62  has elongated vertical channels  64  for forming the flange  12 , a large annular cylindrical channel  66  for forming the hollow pipe-like structure  68 , a small circular channel  70  for forming the lower cylindrical head  34 , and an intermediate channel  74  for forming the means for anchoring the lawn edging in the ground. 
     The channels  66 ,  70 ,  74  each have a front section  61  joined to a narrowed section  63  which terminate in the extrusion orifice  80  of the die  62 . The ratio of the diameter of the first section  61  to the second section  63  in the intermediate channel  74  is larger than the ratio of the diameter of the first section  61  to the second section  63  in the channels  66  and  70 , such that at a given extruder speed and pull rate, the extrudate  82  accumulates in the first  61  section of the intermediate channel, builds up pressure and intermittently extrudes through second section  63  past the triangular structure  88  in the orifice  80  of the die  62 . The triangular band  30  is formed on one side of the flange  12  which undulates across the alternating protrusions  20  and dimples  24  as shown in FIG.  3 . 
     The die  62  is separately heated to a temperature from 360° F. to 380° F. After the hot extrudate  82  leaves the orifice of the die  62 , it is cooled in a bath of cold water before being wound up on a take-up reel, not shown. 
     The binder resin is a thermoplastic material capable of softening at a temperature below about 300° F. during extrusion. The resin must be stable to long term exposure to soil environment and to fertilizers, herbicides, or pesticides seeping into the adjacent soil or to fertilizers, growth regulators herbicides or pesticides. The resin must be inert to the other components of the edging such as the crumb rubber under extrusion conditions. Polyvinyl acetate is excluded from use since it will react with the crumb rubber. Styrene polymers including impact polystyrene copolymers are useful as are linear polyamides such as various Nylons, polyvinylchloride, polypheneylene oxide and polypheneylene sulfide polymers. 
     The most preferred group of polymers are the linear polymers of alkenes of 2 to 4 carbon atoms such as polyethylene, polypropylene, or polybutene. These polymers are unreactive in soil and in the extrusion barrel and have long segments of linearity providing crystal-line behavior. Polyethylene have lower melting temperatures, are tougher and hold shape better. High density polyethylene have densities from about 0.94 to about 0.97 gm/cc. Lawn edging prepared with all high density polyethylene binder are somewhat stiff, brittle and difficult to extrude. Lawn edgings prepared using low density polyethylene have densities from about 0.90 to 0.93 gm/cc, and lawn edging prepared with all low density polyethylene binder are very flexible and can readily be bent to follow a desired path and are readily extruded. The polyethylene can be used in any commercial form such as powder, flake or pellets. Reclaimed poly-ethylene materials can also be used. The form and color of such materials have little effect upon the product. Particles of ground rubber from tires or other sources are commercially available. 
     EXAMPLE 
     A lawn edging was prepared from a mixture of 50 percent by weight of 30 mesh vulcanized rubber particles from tires and 50 percent linear, low density polyethylene pellets. The particles and pellets were mixed. The mixture was fed to a vented twin screw extrude heated to a temperature of 380° F. The die was heated to a temperature from 360° F. to 380° F. As the mixture was extruded through a die orifice as shown in FIG. 5, lawn edging as depicted in FIGS. 2 and 3 was extruded. 
     The lawn edging was tested for bending and was substantially more flexible than commercial polyethylene lawn edging. The composite lawn edging was easily planted into a curved trench and showed no tendency to creep up out of the ground. 
     Further aspects of the invention are illustrated in FIG.  7 . The lawn edging  10  formed from a rubber-thermoplastic resin is usually porous. Since the enlarged head  14  can be in hollow pipe form, it can be used as a drip emitter. When fitting  67  is connected to the orifice  36  and to high pressure water from a source  65 , the head  14  will expand slightly and water drops  69  drip from the outside surface  71  of the head. 
     The hollow head can also be modified to form a hose impervious to water or one containing apertures for spray irrigation. Referring again to FIG. 7, the extrudate  82  is coated with a continuous film  100  of thermoplastic resin such as polyethylene in sufficient thickness to seal the surface  71  of the head  14  by feeding the extrudate through a second die  110  containing an annular orifice  112  for applying the film  110  coating of resin to the surface  71  of the lawn edging  10 . The film  110  could also be applied by spraying resin onto the surface  71  or by dipping the extrudate in a bath of resin. An orifice could also be added to the die  62  to apply the coating  110 . The capability to apply a separate film to the head permits inclusion of dyes and pigments in the coating. Two-colored lawn edgings have been enthusiastically accepted by the consuming public. The color of the head of the edging can be matched and coordinated with the color of buildings in the vicinity of the lawn edging. 
     The head  14  with liquid impervious coating  100  can also be readily converted into a spray hose. As shown in FIG. 7, at least one laser  120  mounted downstream from the die  110  can be used to form perforations  122  through the wall  44  of the hollow head  14 . The laser is pulsed by a power-controller  124  to form a narrow, collimated beam  126 . When the perforated hose is connected to a high pressure water source sprays of water will emit from the perforations on one and/or more sides of the head  14  depending on the location of the perforations. 
     The cavity  36  in the sealed head can be used to transmit water. A hollow connector, not shown, should be used to connect lengths of edging  10 . 
     The thickness and uniformity of the wall  44  of the hollow head  14  can be improved by injecting air from air source  104  through injector  106  into the hollow section  36  while the extrudate  82  is in the die  62 . 
     It is to be realized that only preferred embodiments of the invention have been described and that numerous substitutions, modifications and alterations are permissible without departing from the spirit and scope of the invention as defined in the following claims.