Abstract:
This invention is directed to a cutting filament for a plant-cutting device such as a scrub cutter or edge trimmer. According to the invention, at least one portion of the filament is made on the basis of a mixture of polyamide 6-6 and of a softening agent. A filament with improved mechanical properties is thereby achieved.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to devices for cutting vegetation such as scrub cutters, edge trimmers and the like, and is more particularly directed to new cutting filaments for such devices.  
       BACKGROUND OF THE INVENTION  
       [0002]     A cutting filament is generally made by extruding/drawing polyamide, and significant developments of these filaments have been known for a few years: suitable shapes for reducing noise, improving cutting efficiency, etc., strands in several materials in order to improve cutting efficiency, improve biodegradability, to reduce manufacturing costs, etc.  
         [0003]     Cutting filaments made from two or more components generally by a co-extrusion method from two sources of different materials are thus known.  
         [0004]     More specifically, filaments including a main body or polyamide core and a secondary portion, such as a skin totally or partially surrounding the core, in a material different from that of the core, are known. “Different material” means here a material with at least one physical or chemical property different from that of the material of the core; this may in particular be a polyamide or co-polyamide, different from that of the core, or other natural or synthetic materials or mixtures thereof.  
         [0005]     But, as a general rule, a satisfactory cutting filament results from a compromise between certain flexibility, in particular allowing the filament not to be broken when it encounters obstacles during work, and certain hardness which in particular allows it to attack the plants with the required energy and not to wear out prematurely.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0006]     The present invention is directed to proposing a cutting filament with improved properties regarding this compromise.  
         [0007]     It thus proposes a cutting filament for a plant cutting device such as a scrub cutter or edge trimmer, wherein at least one portion of the filament is made on the basis of polyamide 6-6 enriched with a softening agent.  
         [0008]     Certain preferred but non-limiting aspects of the filament are the following: 
        The softening agent comprises caprolactam.     The softening agent essentially comprises caprolactam.     The filament comprises a first portion forming a body of the filament and a second portion forming at least one area for attacking plants, said first portion being made on the basis of a mixture of polyamide 6-6 and a softening agent.     Said second portion of the filament is also made on the basis of polyamide 6-6.     The second portion of the filament also contains a softening agent, and the first portion contains a larger proportion of softening agent than the second portion.     The first portion of the filament contains from 6 to 15% of caprolactam, and preferably from 11 to 14% of caprolactam.     The second portion of the filament contains from 0 to 4% of caprolactam.     The second portion of the filament contains at least one filler product.     The second portion of the filament includes arrangements capable of promoting the cutting of plants.     The second portion of the filament is essentially distributed in two areas laid out sideways opposite to each other in the working position of the filament.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Other aspects, objects and advantages of the present invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given as a non-limiting example and made with reference to the appended drawings, wherein  FIGS. 1-3  are three sectional perspective views of cutting filaments according to the first, second and third embodiments of the invention, respectively. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     With reference to  FIG. 1 , a cutting filament has been illustrated for a motorized plant-cutting device, such as an edge cutter, a scrub cutter, etc., which comprises a core  10  and a skin  20 .  
         [0021]     In the present example, the skin totally surrounds the core.  
         [0022]     The core has a cross-section with a simple or complex shape. In the case in point, the core has a general rhombic section with beveled edges.  
         [0023]     Also, the skin  20  may have any desired cross-section. In the present example, the skin has a contour with an upper convexity and a lower convexity and defines two serrated areas Da and Db for attacking the plants, which protrude sideways on either side of the core  10 .  
         [0024]     According to the invention, the core is made in polyamide 6-6 added with a certain amount of softening agent. The applicant has discovered that a particularly suitable softening agent is co-monomeric ε-caprolactam (simply designated by caprolactam hereafter), which will be noticed here as being the raw material which polymerizes into polyamide 6.  
         [0025]     A proportion of caprolactam between about 6 and 15%, preferably between 11 and 14% is used to attain a suitable softening effect for use as a cutting filament.  
         [0026]     The skin  20  is also made in polyamide 6-6 here, with this time a much smaller or even zero amount of softening agent (again typically caprolactam here). A proportion from 2 to 3% of caprolactam is typically provided.  
         [0027]     A cutting filament with improved properties is thereby obtained, in the sense that one benefits from the intrinsic strength of polyamide 6-6 without it having the brittle aspect. In particular, by resorting to a core enriched with softening agent, the filament has satisfactory flexibility while being mechanically stronger than a filament based on polyamide 6.  
         [0028]     Additionally, resorting to unsoftened polyamide 6-6, or in any case substantially less softened than the core, for the skin  20 , provides it with suitable hardness for the cutting work on plants, and in particular with better resistance to wear.  
         [0029]      FIG. 2  illustrates another embodiment of the invention, with a central core  10  and two wings  20   a ,  20   b  independent of each other, further forming here serrated cutting areas Da and Db.  
         [0030]     Here, the core  10  has a circular cross-section and both cutting areas are isolated from each other here.  
         [0031]     Polyamide 6-6 enriched with a softening agent such as caprolactam, is further used here, and an unsoftened or substantially less softened polyamide 6-6 is used for both cutting areas.  
         [0032]     Finally,  FIG. 3  illustrates another embodiment of a cutting filament according to the invention, consisting of a single material. The cross-section of the filament is a symmetrical rhombus here, it is made with the same material as that for the core of the filaments of  FIGS. 1 and 2 , i.e., softened polyamide 6-6 for example with between 11 and 14% of caprolactam.  
         [0033]     Advantageously, the filaments according to the invention are made by a conventional extrusion/drawing method (co-extrusion in the case of filaments comprising two or more materials). The softened agent is then carefully mixed with the molten polyamide 6-6 upstream from the drawing process.  
         [0034]     When the filament includes serrations or other reliefs or recesses intended to improve some of its properties (cutting efficiency, operating noise level, etc.), these are made either during the extrusion/drawing process or downstream from this process, for example by means of knives, etc., by removing material.  
         [0035]     Moreover, a filament according to the invention may include, in addition to a main body in softener-enriched polyamide 6-6 providing the filament with the desired flexibility, any other portion in a material which may either belong or not to the polyamide family, which may either contain or not filler products such as mineral fibers, etc.  
         [0036]     In this respect, the invention may be combined by one skilled in the art with many other enhancements generally known in the field of cutting filaments (filaments with a particular shape and/or polymaterials for improving the cutting efficiency, reducing the operating noise, enhancing biodegradability, preventing sticking phenomena, etc.).  
         [0037]     Of course, the present invention is by no means limited to the embodiments described hereinbefore and illustrated in the drawings, but one skilled in the art will know how to provide it with many embodiments and changes.