Patent Application
20080014412
Referring now to the figures of the drawing in detail and first, particularly, to
The core 3 may be formed of any material that is suitably moldable and also provides for the proper rigidity. Preferred materials are saturated or unsaturated poly-propylene. Other materials are polyethylene (PE), ethylene vinyl acetate (EVA), acrylonitrile butadiene styrene (ABS), styrene acrylonitrile (SAN), TPK, polystyrene (PS), acrylonitrile-styrene-acrylate terpolymer (ASA), or co-polymers such as PPE (phenylene ether co-polymer), to name a few. In the preferred implementation, the materials should be suitable in particular for injection molding. The handle 2 is formed with a core opening 5, in which an attachment stem of the trowel 1 is inserted.
The soft grip cover 4 is intimately integrated in the handle 2. That is, the transition boundaries between the visible exterior surfaces of the core 3 and of the grip cover 4 are quite smooth. Any leftover flashings from the molding process (first and second shot) are carefully avoided and removed. The grip cover 4 contains biological material from a renewable resource. In a preferred embodiment, the natural material is wood, bark, cork, cotton, flax, and/or leather. Particles 6 or strands of the natural material are integrated in a matrix of synthetic material. The hardness of the synthetic, or plastic, material matrix, and thus of the grip cover, may be adjusted depending on the intended use and designed withstand strength of the handle. The plastic material matrix may include any elastomeric and thermoplastic materials such as, for example, styrene ethylbutylene styrene (SEBS), styrene-butadiene-styrene (sBS), thermoplastic (poly)olefin (TPO), ethylene vinyl acetate (EVA), polypropylene (PP), polyethylene (PE), PS, TPK, plasticizers, and stabilizers.
The natural component is embedded in the matrix of the synthetic material. Cork is integrated as grains having a mean diameter of 4-7 mm. Cotton would typically be provided in rods with a maximum length of 10 mm. Leather is best provided in grains or leather flakes of 3-5 mm diameter. Flax would be provided in rods having a length of approx. 10 mm and a diameter of 2-3 mm.
The hardness and the relative malleability of the grip cover are adjusted by a suitable addition of plasticizers and by selecting polymers of specific hardness. These selections depend on the intended use of the handle. A hammer or hatchet handle, for example, may be configured with a Shore A hardness of approximately 70 to 80, while a chisel handle or a trowel handle may be configured with a softer grip of, say, Shore A hardness of approximately 45-60. Similarly, the “feel” of the grip during an extended working session must be assured to remain pleasing to the hand of the user. The relative slip or non-slip characteristics of the grip may also be adjusted by a proper selection of the material composition.
In addition, a high degree of UV resistance has been achieved, as well as an advantageous soiling behavior and easy washability. Finally, we have been able to avoid using a number of toxicologically and environmentally questionable additives, such as plasticizers, accelerators, cadmium, heavy metals, color additives, and the like. The resulting handle (bio handle) can thus be recycled.
The intimate connection between the core and the grip cover lies at the heart of this invention. In tool, in particular, where extended use and a demanding work environment places considerable stress on the materials, it is paramount for a good tool that the integrity of the handle remain properly intact. We refer to the connection as a 100% connection in this context, where the boundary or transitional layer material is as structurally resistant as the substrate and/or as the grip cover material itself. We have found that our finely tuned molding process leads to just such a 100% connection.
We use a fully automatic process in manufacturing the novel handles. The processing of the hard component (i.e., the core) following the first shot injection is timed with a relatively tight cycle time, so that it retains a carefully adjusted elevated temperature. This temperature then assures that the softer material (i.e., the grip cover) applied in the second shot injection is properly bound to hard component and that the result is the above-noted 100% connection between the components.
It is further important to intimately integrate the natural component within the plastic matrix of the synthetic grip cover material. The natural component mixtures are produced in a heavy-duty compounder. The natural components are also carefully selected so as to allow for a processing temperature of approximately 200° C. or even 220° (without charring of the natural component), which has been found to be ideal for the proper connection of the grip cover material to the hard component of the core.
The mixture for the grip cover material is prepared in a high-energy mixing system, in which the natural component and the synthetic component are formed into a mass of granules.
The process according to the invention may be best understood with reference to a specific embodiment of the molding process. Here, we form a handle for a bricklayer trowel with a cork grip. Reference is had to
The hard component is polypropylene (PP). It may or may not contain a filler (e.g., glass fibers, carbon fibers, etc.—for improving the working characteristics and the rigidity). The polypropylene component is obtained in granule form with a mean particle diameter of approx. 3 mm. First, the granules are added into a hopper of an injection molding machine at step 101. At this time, any type of pigment or other coloring agent may be added to adjust the color of the handle core. Then the granules are melted at 220° and delivered via a screw feeder and injected into a first mold, at step 102. The injection pressure is approximately 100 bar.
In step 103, the polypropylene component is subsequently removed from the first mold and delivered for the second injection shot. The transfer from the first mold to the second mold may either be effected by index or rotary table process, or the component may be completely removed and delivered for the second injection shot. Either way, the second mold contains additional cavities as compared to the first mold, for the natural component, here the cork grip cover. First, the component is either cooled down to 55°-70° C. (index table) or reheated to that temperature.
The second component, i.e. the natural component is also provided in granule form. The cork mass, as here, is provided as grains having a mean diameter of 4-7 mm. Such cork granules are commercially available. By way of example, a suitable material is “Kork UV 75410-7-D beige A104” of Wind Thermoplast-handel of Traiskirchen, Austria. The grains of the natural component are dried in a dry air dryer with a dew point set to −35° C. at step 104. This removes any residual moisture and prepares the cork component for the molding process. Then the grain bulk is delivered to the injection machine, where it is heated in the material hopper to about 130°-1750. The heated material is then delivered through a screw feeder with a one way check valve for injection into the second mold at step 105. There, the polypropylene handle core is already present with a temperature of 55°-70° C. The injection is carefully timed with a proper injection profile and with an injection pressure of approx. 80 bar. The mold temperature is set to between 40° and 60° C. The mold surfaces of the second mold are provided with a suitable non-stick coating, such as a PTFE (polytetrafluoroethylene, Teflon®) coating.
The selection of the materials, which are chemically compatible, and the temperature characteristics during the molding process cause the first component to be melted at the boundary surfaces and the second component to be fused into the first component. This leads to the above-defined 100% connection between the components.
Then the finished two-component handle is removed from the second mold at step 106. After any flashings that may be present are removed, the handle is ready for delivery and for assembly on the tool. It should be understood, however, that the handle may also be molded directly onto the tool.
One example of such a directly molded handle set is illustrated in
This application claims the benefit, under 35 U.S.C. §§ 119 and 172, of European Community (OHIM—Office for the Harmonization of the Internal Market) design application No. 000509815 of Apr. 7, 2006, and of Austrian design patent application MU 629-635/2006 of May 26, 2006; the prior applications are herewith incorporated by reference in their entirety.
