Tools – Handle for tool
Reexamination Certificate
2000-03-22
2001-10-02
Eley, Timothy V. (Department: 3723)
Tools
Handle for tool
C081S177100, C264S177100, C016S114100
Reexamination Certificate
active
06295903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to torque applying hand tools having handles made with plastic materials and more particularly to a torque applying hand tool having a multi-layer plastic handle and a method for making such a handle.
BACKGROUND OF THE INVENTION
Conventional torque applying tool handles must meet certain basic needs. The handle must bond well to a steel component, such as the shank of a screwdriver. It must be strong enough to withstand the forces and torque applied to the tool. At the same time, the handle must also provide appropriate ergonomics so that a user of the tool may comfortably and securely hold the tool. To achieve a balance between the strength, bonding and comfort of use, tool handles made from two or three shots of plastic are available on the market. Each shot represents a single step in the molding process and is a complete or partial layer forming part of the handle. For example, several varieties of tool handles with two or three shots of material are commercially available. One such type of two shot tool handle has an inner layer of polypropylene and an outer layer of thermoplastic rubber to provide a gripping surface. Another type has a polypropylene layer of one color and a second polypropylene layer of another color. The two layers provide a color pattern and are used, for example, to provide information such as manufacturer brand name.
A commercial three shot handle has an inner polypropylene layer, a second polypropylene layer which covers over the inner layer and an outer thermoplastic rubber layer which covers most of the second layer and provides a gripping surface. For use in a chisel, a three shot handle has been made with two shots of cellulose acetate butyrate and a shot of urethane to provide a gripping surface. The urethane covers a portion of the cellulose acetate butyrate shots, but a portion of those layers remains visible.
Additionally, a three shot handle with two polypropylene layers and a thermoplastic rubber shot is available. The second polypropylene shot is partially visible and the thermoplastic rubber shot provides a gripping surface over a portion of the outside of the handle. In producing the molded plastic handles of the prior art, a determining factor in the cycle time is related to the amount of cooling time necessary before the cycle can be completed by removing the molded structure from the mold.
Based upon the prior art described above, it appears that a saturation point as to the maximum number of layers that is cost-effective has been reached. Nevertheless, there is always a need for cost-effectiveness in the production of commercial products such as the torque applying tools to which the present invention is directed.
SUMMARY OF THE INVENTION
It is an object of the present invention to fulfill the need described above. In accordance with the principles of the present invention, this objective is obtained by providing a method of making a torque applying hand tool which includes molding an inner handle layer of relatively hard thermoplastic material within a die cavity to form a first molded part, molding an intermediate inner handle layer of thermoplastic material on the first molded part within a die cavity to form a second molded part, molding an intermediate outer handle layer of thermoplastic material on the second molded part within a die cavity to form a third molded part, and molding an outer handle layer of elastomeric material on the third molded part within a die cavity to form a handle having an exterior elastomeric gripping surface capable of transmitting torque applied thereto through the third, second and first molded parts to a tool shank fixed within the inner handle layer.
The object of the present invention is also achieved by providing a torque applying hand tool comprising a shank having a tool end constructed and arranged to apply a torque to a member engaged thereby and a handle engaging end portion opposite the tool end. An innermost handle layer of a relatively hard and tenaciously adhering thermoplastic material is molded to form a first molded part. The handle end portion of the shank is fixed within the first molded part. An intermediate inner handle layer of a relatively hard thermoplastic material is molded on the first molded part in fixed torque applying relation thereto to form a second molded part. An intermediate outer handle layer of a relatively hard thermoplastic material is molded on the second molded part in fixed torque applying relation thereto to form a third molded part. An outermost handle layer of elastomeric material is molded on the third molded part in fixed torque applying relation thereto to form a handle on the shank having an exterior elastomeric gripping surface capable of transmitting torque to the shank through the third, second and first molded parts.
Contrary to the prior art maximum number of layers, the inventors of the present invention have found that four layers can be cost-effective. By using a four shot handle, each shot contains less material than would be necessary in a two or three shot handle. Surprisingly, this allows a reduction in total cycle time, even though with one or two additional process steps existing when compared with the prior art. This time savings results in a significant cost savings, as well as an increase in the number of tools which may be produced in a given time period.
The present invention provides the further advantage that the use of four layers gives an opportunity to use a greater variety of materials. This, in turn, provides more versatility in exterior surface variation, both in terms of function and appearance. Because each layer constitutes a lesser percentage of the whole, it becomes possible to use more expensive materials in lesser amounts than was heretofore possible.
Materials such as nylon can be used to provide an increased strength over conventional polypropylene handles. However, the use of nylon can be prohibitively expensive as it costs significantly more than polypropylene. Similarly, thermoplastic elastomers provide improved gripping performance, but they are not suited to provide the bulk of the handle as they are too soft. By using four layers, these needs may be met while selecting other materials for the interior layers. Thus, according to one aspect of the present invention, nylon is used as the first layer, providing high strength at the center of the tool handle. Nylon also provides a bond with the steel shank of the tool which is superior to the bond between polypropylene and steel. However, since the amount of nylon in the tool is only on the order of 25% of the total plastic content, with much of the rest being polypropylene, the handle remains cost effective.
Multiple layers provide an additional advantage in that they allow for greater flexibility in design. According to another aspect of the present invention, each layer may have a different appearance, allowing the manufacturer to provide multiple colors or contrasting designs. This has the advantage of allowing for manufacturer's logos, or information about the tool itself, such as the type of head on a screwdriver, to be conveyed.
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Scott Gary
Tipper J. David
Berry Jr. Willie
Eley Timothy V.
Pillsbury & Winthrop LLP
The Stanley Works
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