Patent Publication Number: US-2021187763-A1

Title: Safety Utility Knife

Description:
TECHNICAL FIELD 
     The present invention relates to a safety utility knife capable of safely cutting cardboard, string material, etc. 
     BACKGROUND ART 
     Various safety utility knives capable of safely cutting cardboard, string material, etc. have hitherto been proposed (e.g. Patent Documents 1 to 4). A safety utility knife of Patent Document 1 is shown in  FIG. 1 . 
     Blades  12   a  and  12   b  protrude from a grip part  11  held by the user to both sides, with head parts  13   a  and  13   b  being disposed at the tip of each blade for the purpose of guide and guard. The user holds the grip part  11  and draws it toward the user to cut cardboard, etc. by the blade  12   a  or  12   b  on one hand. 
     Typically, the blades  12   a  and  12   b  are made of metal, and the grip part  11  and the head parts  13   a  and  13   b  are each made of resin. In the case of manufacturing this, the blades are disposed on a mold and then resin making up the grip part  11  and the head parts  13   a  and  13   b  is poured into the mold. Since the grip part  11  and the head parts  13   a  and  13   b  are mutually separated (disjoined) resin molded pieces, a 3-gate type mold is required as schematically shown in  FIG. 3A . 
     Namely,  FIG. 3A  shows, in a simplified manner, a safety utility knife immediately after molding using the 3-gate type mold. A runner (resin that remained in a flow path of the mold) protrudes from each of the three resin portions ( 11 ,  13   a , and  13   b ), from which it can be understood that the 3-gate type mold was used. This runner is thereafter removed by a proper method. 
     Generally speaking, when using the 3-gate type mold, manufacturing labor and cost including deburring, etc. rise as compared with the case of using a 1-gate type mold that will be described later. 
     Patent Document 4 discloses a safety utility knife used for similar purposes, which can be manufactured using the 1-gate type mold, instead of the 3-gate type mold. That is, the safety utility knife of Patent Document 4 is an integral piece in which the grip part  11  and the head part  13   a  are coupled together, as shown in  FIG. 2 . In this utility knife, a resin part  14  coupling the grip part  11  and the head part  13   a  covers a blade such that only an edge  15  of the blade is exposed. According to such a configuration, the portions molded with resin are integrated, so that the 1-gate type mold can be used to consequently reduce the manufacturing labor and cost. 
     However, due to the resin part  14  covering and extending on the blade, another problem occurs that the cutting resistance at the time of cutting work increases. This results in problems e.g. that hand&#39;s fatigue increases because of unsmooth cutting and that a rough cut end appears. 
     PATENT DOCUMENT 
     
         
         Patent Document 1: U.S. Design Pat. USD 784,107S 
         Patent Document 2: U.S. Design Pat. USD 660,675S 
         Patent Document 3: U.S. Design Pat. USD 802,394S 
         Patent Document 4: U.S. Design Pat. USD 527,604S 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The present invention was devised in view of the above problems of the prior art and its object is to provide a safety utility knife capable of simplifying the manufacturing process without increasing the cutting resistance, by integral configuration of a grip part and a head part using resin, etc. 
     Means for Solving Problem and Effect of the Invention 
     A safety utility knife of the present invention comprises “a grip part”, “a blade projecting from the grip part”, and “a head part arranged at a tip of the projecting blade”. A through-hole is formed in the blade, and a coupling part lying within the through-hole couples the grip part and the head parts together. 
     It is preferred that the coupling part be made of resin widely usable for molding, but aluminum, zinc, magnesium, or other metals usable for diecast molding may also be available. 
     In the safety utility knife of the present invention having the above configuration, the coupling part lying within the through-hole formed in the blade couples the grip part and the head parts together. Accordingly, manufacture using the 1-gate type mold becomes possible so that the mold configuration can be simplified to suppress cost, as compared with the case of using the 3-gate type mold. In addition, manufacturing time and labor including deburring immediately after molding can be saved, and cost can be reduced from this point as well. 
     Moreover, since the coupling part coupling the grip part and the head parts together lies within the through-hole formed in the blade, the total thickness of the blade is prevented from increasing. This results in no increase in cutting resistance when cutting cardboard and other objects, and therefore cutting work becomes smoother (as compared with the case of increased thickness caused by the coupling part covering the blade), leading to effects of less hand fatigue and of prevention of rough cut end. 
     Additionally, due to lying within the through-hole, that coupling part has a higher durability as compared with the case of extending along the back of the blade. That is, breakage of the coupling part arising from repeated use of the safety utility knife is hard to occur and hence it can effectively be prevented that the broken coupling part mixes in somewhere as foreign fragments. 
     In the safety utility knife of the present invention, both ends of a single blade (embedded in the grip part) may protrude from the grip part to both sides in opposite directions away from each other, with the head parts being disposed at the both ends, respectively. It is preferred in this case that the above through-hole be formed in the single blade and extend from the head part on one hand to the head part on the other. 
     By adopting such a configuration, the single blade may only be arranged within the mold in order to configure the safety utility knife having two cutting parts. Accordingly, the blade arrangement within the mold becomes simple, resulting in reduced manufacturing labor and cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view explaining an example of a conventional safety utility knife. 
         FIG. 2  is a view explaining another example of the conventional safety utility knife. 
         FIG. 3A  is a schematic perspective view explaining a case of manufacturing the safety utility knife by use of a 3-gate type mold. 
         FIG. 3B  is a schematic perspective view explaining a case of manufacturing the safety utility knife by use of a 1-gate type mold. 
         FIG. 4A  is a view showing a tip-near region of a safety utility knife according to a first embodiment of the present invention. 
         FIG. 4B  is an opened-up view showing a blade arranged within the safety utility knife of  FIG. 4A . 
         FIG. 5  shows perspective views of back and front shapes of the safety utility knife of the present invention. 
         FIG. 6  shows six different views of the safety utility knife of  FIG. 5 . 
     
    
    
     EMBODIMENT(S) FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A first embodiment of the present invention will now be described with reference to the accompanying drawings. Although details of the first embodiment are described below, a grip part  31 , head parts  33   a  and  33   b , and a coupling part  35  are made of resin and manufactured using a mold. 
       FIG. 4A  shows a safety utility knife  30  according to a first embodiment of the present invention. Although only near the tip of the safety utility knife  30  is shown in  FIG. 4A , the whole is elongated similar to the conventional ones shown in  FIGS. 1 and 2 , and the user holds the grip part  31  and draws it toward the user to cut cardboard, etc. by a blade  50   a  or  50   b  on one hand. 
       FIGS. 5 and 6  show an example of the overall shape of the safety utility knife of the present invention. 
     The blades  50   a  and  50   b  protrude from (a tip region of) the grip part  31  toward both sides, with the head parts  33   a  and  33   b  being disposed on tips of the blades for the purpose of guide and guard. Such a feature itself is similar to a conventional safety utility knife shown in  FIG. 1 . 
     A principal feature of the present invention lies in that a blade  50  has an elongated hole (through-hole)  55 . As a result, as described hereinbelow, effects can be obtained that a safety utility knife is manufacturable using a 1-gate type mold and, additionally, that there is no increase in the blade total thickness. 
     &lt;Manufacturable Using 1-Gate Type Mold&gt; 
       FIG. 4B  is an opened-up view showing the blade  50  in the safety utility knife  30  of  FIG. 4A . It can be seen that the elongated hole  55  formed in the blade  50  extends from the head part  33   a  on one hand to the head part  33   b  on the other. 
     Although the safety utility knife  30  is made by molding, the blade  50  is set in the mold at that time so that resin is poured thereinto. 
     For example, when allowed to flow from the gate into a cavity portion corresponding to the grip part  31  using the 1-gate type mold, resin flows through the interior of the cavity while advancing in the through-hole  55  of the blade, to finally form the head parts  33   a  and  33   b . After completion of molding, cured resin remaining in the through-hole  55  is the coupling part  35  in  FIG. 4A . 
     Although there exist three resin-made parts (the grip part  31  and the head parts  33   a  and  33   b ) in this manner, these three parts are integrated by the coupling part  35  similarly made of resin, and accordingly the safety utility knife  30  of the present invention can be manufactured using the 1-gate type mold. 
       FIG. 3B  explains this schematically and shows, in a simplified manner, the safety utility knife immediately after molding using the 1-gate type mold. As is apparent from comparison with  FIG. 3A  referred to in the description of the prior art, the runner protrudes only from one point. 
     Generally speaking, as compared with use of the 3-gate type mold, use of the 1-gate type mold can suppress labor and cost for manufacture including deburring. The 1-gate type mold can simplify the mold configuration for suppression of cost. 
     &lt;No Increase in Blade Total Thickness&gt; 
     In addition, according to the configuration shown in  FIGS. 4A and 4B , since the coupling part  35  joining the grip part  31  and the head parts  33   a  and  33   b  is enclosed in the elongated hole (through-hole) formed in the blade  50 , there is no increase in thickness of the blade  50 . 
     If the resin part  14  extends overlapping the blade as in the prior art shown in  FIG. 2 , the total thickness of the blade increases, which induces an increased cutting resistance or a deteriorated cut end. In the safety utility knife of the present invention, the coupling part  35  lies within the elongated hole  55  so that the blade thickness is unchanged from its original thickness (typically of the order of 0.5 to 0.6 mm), thereby preventing the increased cutting resistance or a rough cut end from occurring. 
     Moreover, since the coupling part  35  lies within the elongated hole  55  (in other words, since the entire circumference is surrounded by the blade  50 ), a higher durability is ensured as compared with the case of extending along the back of the blade  50 . If the case is considered where the resin part extends outward along the back of the blade  50 , repeated use of the safety utility knife allows upward forces in  FIG. 4A  to act on the coupling part  35  due to the friction with objects (cardboard, string material, etc.) to be cut, with the result that there is a high possibility that the coupling part  35  will break. In the present invention, since the coupling part  35  is surrounded over its entire circumference by the blade  50 , such a break is hard to occur and hence it can effectively be prevented that the broken coupling part  35  mixes in somewhere as foreign fragments. 
     Second Embodiment 
     In the first embodiment, the “grip part  31 ”, “head parts  33   a  and  33   b ”, and “coupling part  35 ” making up the safety utility knife were made of resin and manufactured using the mold. 
     On the contrary, in a second embodiment, the safety utility knife is manufactured by diecast molding. That is, a molten metal (aluminum, zinc, magnesium, etc.) is injected at a high pressure into a die attached to a diecast machine and is solidified. Therefore, all of the “grip part  31 ”, “head parts  33   a  and  33   b ”, and “coupling part  35 ” are made of metal. 
     Also in the second embodiment, similarly to the case of the first embodiment, the 1-gate type mold can be used for manufacture with no increase in the blade total thickness. Accordingly, effects similar to the case of the first embodiment described above can be obtained. 
     For both of the first embodiment and the second embodiment described above, variants as will be described below can each be adopted. 
     Variants 
     (1) 
     In the embodiment shown in  FIGS. 4A and 4B , the blades  50   a  and  50   b  project from the grip part  31  to both sides so that the safety utility knife  30  has a cutting part at two sites. The present invention is not limited to such a configuration, but, for example, the blade may project only to one side. 
     Also in such a case, the grip part and the head parts can be coupled together via the coupling part by providing a proper through-hole in the blade, thus enabling the 1-gate type mold to be used for manufacture. 
     (2) 
     In the embodiment shown in  FIGS. 4A and 4B , a single blade  50  was embedded inside the grip  31  such that both ends  50   a  and  50   b  of the single blade each projected to the side of the grip part  31 . However, the present invention is not limited to such a configuration, but two separate blades may be used to make up a safety utility knife. 
     Furthermore, three or more separate blades may be used to obtain a safety utility knife having three or more cutting parts. In any case, the blades are each formed with a through-hole so that the coupling part poured thereinto couples the grip part and the head parts together. Thereby, the safety utility knife can be manufactured using the 1-gate type mold. 
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
           11  grip part 
           12   a ,  12   b  blade 
           13   a ,  13   b  head part 
           14  resin part 
           15  edge 
           30  safety utility knife 
           31  grip part 
           33   a ,  33   b  head part 
           35  coupling part 
           50 ,  50   a ,  50   b  blade 
           55  elongated hole