Patent Publication Number: US-6907668-B2

Title: Utility knife

Description:
FIELD OF THE INVENTION 
   The present invention relates to a utility knife. More particularly this invention concerns a utility knife that holds a normally trapezoidal flat blade. 
   BACKGROUND OF THE INVENTION 
   Utility knives are known from EP 0,543,781 (U.S. Pat. No. 5,283,954), German Utility Model 1,711,881, German Utility Model 7,207,013, German Utility Model 94 17 085, and U.S. Pat. Nos. 2,679,100, 3,316,635, 4,139,939, 6,163,963, 6,449,850, and 6,546,632 that have an elongated body formed as a grip or handle and from which can project a replaceable steel blade, typically of right-trapezoidal shape. Such a knife is used for opening packages, numerous construction applications, and in the food industry. 
   In most such utility knives the blade is mounted on a slide that can shift it between a retracted position with the blade wholly contained in the housing or handle, so that the knife can be pocketed safely, and an extended position with the blade projecting from a front end of the handle, so that the knife can be used. As a rule a button that actuates the slide and that normally is formed as part of the slide is exposed on the back edge or one side of the housing. The provision on the back edge has the advantage that it allows the knife to be used with equal facility by right- and left-handers, but this construction has the disadvantage that the resultant grip, with the thumb on the back of the knife, is frequently not strong enough. Provision of the button on the left side makes the knife difficult to use for left-handers. 
   The housing is often formed of two separate parts that can be separated to replace the blades, and often also to expose a compartment holding a supply of spare blades. In a standard model, a screw that can be operated by a coin is provided at one end of the housing extending between the housing halves. Thus the screw can be pulled to separate the two housing halves, making blade replacement possible. Such an arrangement has the disadvantage that the screw can easily get lost, making the knife unusable. 
   When used in the food-services industry, it is essential that the knife by constructed such that it does not have crannies that can hold food particles, leading to cross-contamination of product. In such an application it is desirable to make the knife disposable so that it can be replaced frequently, making the transmission of bacteria impossible. 
   OBJECTS OF THE INVENTION 
   It is therefore an object of the present invention to provide an improved utility knife. 
   Another object is the provision of such an improved utility knife which overcomes the above-given disadvantages, that is which is easy to operate, whose blade is easy to change, and which is of simple and inexpensive construction. 
   SUMMARY OF THE INVENTION 
   A utility knife according to the invention has a main elongated housing half formed with a transversely throughgoing aperture, having a flat face, and formed on the flat face with a peripheral annular array of transversely projecting hooks each having an outer end with a face directed back toward the flat face and a secondary elongated housing half geometrically similar to the main housing half, having a flat face, and formed with a peripheral annular array like the array of the main half of transversely throughgoing holes opening at the respective face and each having a ledge directed transversely away from the respective face. The halves are engageable together at their faces with the hooks projecting into the holes and are relatively shiftable parallel to the faces when thus engaged to hook the hook edges in an assembled position over the respective ledges. The secondary half is formed with an aperture like the aperture of the first half and directly transversely aligned therewith in the assembled position. A retaining member snugly engaged in and through the aligned apertures holds the halves in the assembled position. A blade between the halves projects longitudinally from the housing halves. 
   Such a construction is extremely simple. The knife is easily assembled by pressing the two halves together to opposite sides of the blade, shifting them so the hooks lock in the holes, and then installing the retaining member. The provision of an annular array of hooks around the periphery of the two parts ensures that they will be pressed against each other all around their edges, so that foreign matter cannot readily get caught between the two housing halves. 
   In accordance with the invention the two halves are made of plastic. Thus the main half is unitarily formed with the hooks so that at a minimum the knife comprises four simple parts. 
   The hook edges and ledges according to the invention are flat and complementarily angled to the respective flat faces. Thus on shifting into the assembled positions the edges and ledges press the flat faces together. When assembled the two halves are thus very solidly locked together and in fact prestressed together by elastic deformations of the hooks and hole ledges. 
   The blade in accordance with the invention projects longitudinally from a front end of the housing halves and the apertures are provided at an opposite rear end. In addition the retaining member is a sleeve and forms a transversely throughgoing hole at the rear housing end. This makes it possible to hang the knife by the retaining element which is solidly connected to both housing halves. The retaining sleeve has one end formed with radially outwardly projecting lips bearing transversely on one of the halves. It is permanently mounted in the apertures in a disposable knife. The outer ends of the apertures are formed as counterbores so that the entire sleeve can be recessed below the outer surface of the knife. 
   According to another feature of this invention the housing halves together form an internal longitudinally extending guide and at least one of the halves is formed with a longitudinally elongated and transversely throughgoing slot at the guide. A slide holding the blade is longitudinally displaceable in the guide between a retracted position with the blade wholly contained in the housing halves and an extended position with the blade projecting longitudinally from the housing halves. This slide has an actuation button exposed at the slot. More particularly the slide has a pair of similar halves sandwiching the blade, and both of the housing halves are formed with one such longitudinally elongated slide. Each slide half is formed with one such button exposed at the respective slot. Thus the knife is usable as easily in the right hand as in the left hand, but costs no more to manufacture than a standard utility knife. 
   For safety&#39;s sake, a tension spring is provided having a front end connected to the slide and a rear end connected to the housing. This spring urges the slide and blade into the retracted position. Thus when the slide is released, the blade automatically retracts. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: 
       FIG. 1  is a side view of a utility knife according to the invention; 
       FIG. 2  is a top view taken in the direction of arrow II of  FIG. 1 ; 
       FIGS. 3 and 4  are sections taken along respective lines III—III and IV—IV of  FIG. 1 ; 
       FIG. 5  is an end view taken in the direction of arrow V of  FIG. 1 ; 
       FIGS. 6 and 7  are rear and front perspective views of the knife; and 
       FIGS. 8 and 9  are rear and front perspective exploded views of the knife. 
   

   SPECIFIC DESCRIPTION 
   As seen in  FIGS. 1  to  5 , a utility knife  10  according to the invention has an elongated housing  13  having a front end  13   a  from which can project a standard steel utility-knife blade  14  and a rear end  13   b . The housing  13  is formed by a pair of injection-molded plastic main and secondary housing halves  11  and  12  having faces  11   a  and  12   a  that abut flatly on a plane  33  extending along a longitudinal axis  18 . 
   The housing halves  11  and  12  are each formed near the front end  13   a  with a transversely throughgoing and longitudinally elongated slot  15  in each of which is slidable a bump  16  of a slide  17  having a pair of slide halves  21  and  22  sandwiching the blade  14  and meeting on the plane  33 . As shown in  FIGS. 8 and 9 , the halves  11  and  12  have longitudinally extending edge surfaces  42  and  43  that guide the slide  17 . The bumps  16  of the halves  21  and  22  of the slide  17  each have a transversely directed grooved surface  16   a  exposed at the respective slot  15 . Thus a right- or left-handed user holding the knife  10  can press his or her thumb through one of the slots  15  against the respective surface  16   a  to shift the slide  17  and blade  14  parallel to a longitudinal axis  18  of the housing  13  between the illustrated use position with the blade  14  projecting from the end  13   a  and an unillustrated rear position with the blade  14  retracted wholly inside the housing  13 . 
   As shown in  FIG. 9 , the slide half  22  is formed with pins or bumps  19  that project across the plane  33 , that fit into complementary seats or bores  20  on the other slide half  21 , and that pass through the blade  14  to lock it in place in the slide  17 . The slide half  22  is formed with a transversely projecting pin  23  to which is hooked a front end  24   a  of a tension spring  24  having a rear end  24   b , hooked to another pin  25  formed on the secondary housing half  12  near the rear end  13   b  of the housing  13 . Thus this spring  24  pulls the blade  14  and slide  17  back into the retracted position unless the user&#39;s thumb is pressed against one of the surfaces  16   a  to forcibly lock the slide  17  in place. 
   According to the invention as better shown in  FIGS. 6  to  9 , the main housing half  11  is formed along a peripheral line  40  with six hooks  26  projecting transversely across the plane  33  and engaged in respective seats or holes  27  formed along an identical peripheral line  41  of the secondary housing half  12  and each having an undercut  28  so that the holes  27  are generally complementary to the hooks  26 . As best shown in  FIG. 1 , the hooks  26  have angled inner faces  32  that fit with complementary angled faces  31  of the seats  27 . Thus the two halves  11  and  12  can be fitted transversely together with the hooks  26  engaging into the holes  27 , and then the secondary housing half  12  is shifted in a longitudinal direction  29  relative to the main housing half  11  or the main housing half  11  is shifted in a longitudinal direction  30  relative to the secondary housing half  12  to engage the faces  31  and  32  together, thereby locking the two halves  11  and  12  together with a camming action that presses their faces  11   a  and  12   a  tightly and, indeed, hermetically together. 
   To prevent the two halves  11  and  12  from shifting relatively longitudinally, as this could cause them to separate from each other, the halves  11  and  12  are formed with holes  35   a  and  35   b  that together form at the rear end a transversely throughgoing cylindrical hole  35  having at each outer end a setback  36 . A retaining element, here a sleeve  34 , has a head  37  engaged flush in one of the setbacks  36  and at the opposite setback  36  it has lips  39  bent back from split regions  38  of this sleeve  35 . The lips  39  are flush with the outer face of the part  12  so that there are no projecting parts of the sleeve  34  and it is extremely difficult or impossible to remove. This sleeve  34  forms a transversely throughgoing hole  44  that is handy for hanging up the knife  10 .