Abstract:
Provided is a footwear last, being of a structure where its interior is hollow. The method includes steps of installing a parison for manufacturing a plastic vessel between left/right molds for manufacturing the footwear last, with the left/right molds opened; injecting a last manufacturing material into a tube of the parison; blowing air while closing the left/right molds; molding the material in a temperature of about 400 C to 70° C. and under an injection pressure of about 600 kg/cm 2  to 1400 kg/cm 2 ; and completing the last whose interior is hollow.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for manufacturing a footwear last, and more particularly, to a method for manufacturing a footwear last using an injection blow molding method, and a footwear last manufactured by the method. 
       BACKGROUND 
       [0002]    In general, a footwear last used for manufacturing a shoe should endure a high pressure and a high heat. Thus, the footwear last is manufactured using an aluminum mold. Highly priced, the footwear last is highly burdened in economy. Metallic, it causes an impact and a noise and in addition, has a difficulty in its manufacture. Heavy in weight, it has a difficulty in treatment. 
         [0003]    A conventional plastic last is formed of polyester to solve such a drawback. However, the convention plastic last is not only deformed during a longtime use because of a heat generated in a heating process, but also it causes an inconvenience in that it should be molded in about a double size of a real thing and then, be cut and processed in its manufacture. Further, its recycle is insignificant for the reason of economy and thus, environmental pollution occurs. 
         [0004]    A conventional method for manufacturing the plastic last will be briefly described with reference to  FIGS. 1A to 1I  below. 
         [0005]    Referring to  FIGS. 1A to 1I , the conventional method includes molding a polyester raw material, cutting (roughing and finishing), finishing both toe and heel ends, painting, a color maker pin process, a stainless pipe process, and checking. 
         [0006]    After the injection molding of the polyester raw material, as shown in  FIG. 1A , the polyester raw material is roughed such that it has a length and a body-around size larger than a finished last by 10 mm to 15 mm and 30 mm to 35 mm, respectively. After that, as shown in  FIG. 1B , the roughed polyester raw material is finished. The finishing is based on” last dimension chart”, and is performed according to bottom, toe, and heel gauges and a stick length. 
         [0007]    After that, as shown in FIGS. IC and  1 D, toe cutting is performed according to the toe gauge and then, heel cutting is performed according to the heel gauge. Next, the heel pin and stainless pipe processes are performed. As shown in  FIG. 1E , the heel pin process is a process of driving five heel pins of Ø2.5 at an interval of 5 mm in a straight line, using a drilling machine of Ø2.5. As shown in  FIG. 1F , the stainless pipe process is a process of driving a stainless pipe of 12.7Ø to a top surface of the last. 
         [0008]    As shown in  FIG. 1G , it is checked whether or not the bottom gauge is matched with a toe bottom line. As shown in  FIG. 1H , a toe and a heel are checked. As shown in  FIG. 1F , the toe and heel of the last are adapted to a front and a rear of a caliper diameter for callipering the length of the last and then, the last is measured in length. 
         [0009]    The conventional method has the above many problems. In addition, the conventional method has disadvantages, in particular, that it has a difficulty, needs a long time, and highly costs in manufacture. In addition, because of a grinding work for the processed heel and toe, a worker should check a gauge by manual one by one. Because of a non-uniform work, an accurate and delicate curved surface of the heel cannot be kept. 
       SUMMARY 
       [0010]    Accordingly, the present invention is directed to a method for manufacturing a footwear last, and a footwear last manufactured by the method that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. 
         [0011]    An object of the present invention is to provide a method for manufacturing a footwear last using an injection blow molding method. 
         [0012]    Another object of the present invention is to provide a method for manufacturing a footwear last in simplicity. 
         [0013]    A further another object of the present invention is to provide a footwear last, which is light in weight and whose interior is hollow. 
         [0014]    A yet another object of the present invention is to provide a footwear last, in which its recycle is possible, thereby preventing environmental pollution. 
         [0015]    A still another object of the present invention is to provide a footwear last and a method for manufacturing the same, for, when a shoe is manufactured, shortening a heat drying time and reducing a chamber staying time owing to a cavity of the footwear last, thereby shortening a work time as well as improving a quality of an adhesive force and the like. 
         [0016]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a footwear last, being of a structure where its interior is hollow. The method includes steps of installing a parison for manufacturing a plastic vessel between left/right molds for manufacturing the footwear last, with the left/right molds opened; injecting a last manufacturing material into a tube of the parison; blowing air while closing the left/right molds; molding the material in a temperature of about 40° C. to 70° C. and under an injection pressure of about 600 kg/cm 2  to 1400 kg/cm 2 ; and completing the last whose interior is hollow. 
         [0017]    According to the present invention, a footwear last has an advantage in that it is manufactured using an injection blow molding method, thereby not only increasing a simplicity and a productivity but also making the footwear last light and strong, making its manufacture inexpensive, improving a quality, and making its recycle possible and preventing environmental pollution. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIGS. 1A to 1I  are photographs sequentially illustrating a conventional method for manufacturing a footwear last; 
           [0019]      FIG. 2  is a perspective view illustrating a construction of a mold, which is used for manufacturing a footwear last using an injection blow molding method, according to an exemplary embodiment of the present invention; 
           [0020]      FIGS. 3A and 3B  are diagrams sequentially illustrating a method for manufacturing a footwear last by the mold of  FIG. 2 ; 
           [0021]      FIG. 4  is a cross-sectional view illustrating a structure of a footwear last manufactured using an injection blow molding method according to an exemplary embodiment of the present invention; and 
           [0022]      FIG. 5  is a cross-sectional view illustrating a structure of a footwear last manufactured using an injection blow molding method according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings. 
         [0024]    The present invention is to provide a method for manufacturing a footwear last, for promoting the improvements of same product, cost, time, and quality by employing an injection blow molding method, and realizing a competitive product production. For this, a construction of a mold for applying the blow molding method, and the method for manufacturing the footwear last will be described in detail. 
         [0025]    In the present invention, a term of “bottom” means a bottom surface of the footwear last. A term of “toe” means a front part of the footwear last. A term of “heel” means a rear part of the footwear last. A term of “stick length” means a total length of the footwear last. A term of “gauge” means a reference line. A term of “heel pin” collectively means a plurality of color maker pins for arbitrarily controlling a height of a rear part of a shoe when the shoe is manufactured using the footwear last. 
         [0026]    Hereinafter, an exemplary embodiment of the present invention will be in detail described with reference to the attached drawings. 
         [0027]      FIG. 2  is a perspective view illustrating the construction of the mold, which is used for manufacturing the footwear last using the injection blow molding method according to an exemplary embodiment of the present invention. The mold is comprised of a left mold  10  and a right mold  22 . After the footwear last is previously diagrammed in shape by a three-dimensional (3D) data work, the left/right molds  10  and  22  are manufactured. In other words, the left/right molds  10  and  22  keep a curved surface based on 3D data as it is. Therefore, the footwear last  200  molded by the left/right molds  10  and  22  can also always keep the curved surface uniform. 
         [0028]    Referring to  FIG. 2 , a cavity  12  having the same shape as the footwear last  200  is provided at one side of the left mold  10 . Insertion holes  14  for fitting to the plurality of heel pins  18  are provided at a rear part of the cavity  12 . An insertion hole  16  for fitting to a pipe core pin  20  is provided at one upper side of the cavity  12 . The pipe core pin  20  fixes the footwear last  200  to a shoe manufacturing jig. 
         [0029]    The right mold  22  coupled with the left mold  10  to form one mold also has the same shape as the left mold  10 . As shown in  FIG. 4 , the cavity  12  has the same shape as the footwear last  200 . The insertion holes  14  and  16  provide one hole for inserting the heel pin  18  and the pipe core pin  20 , respectively. As shown in  FIG. 3A , the above constructed left/right molds  10  and  22  are applied to the injection blow molding method. This will be easily understood by the following description. 
         [0030]      FIGS. 3A and 3B  are diagrams sequentially illustrating the method, preferably, the injection blow molding method, for manufacturing the footwear last according to the present invention. 
         [0031]    As shown in  FIG. 3A , in state where the left/right molds  10  and  22  are opened, a parison  100  for manufacturing a plastic vessel is installed between the opened left/right molds  10  and  22 . After that, a gel-state plastic material, for example, high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), and polyethylene (PE), is injected into a parison tube  102  through an injection tube  106  of the parison  100 . 
         [0032]    Next, as shown in  FIG. 3B , air is blown through a nozzle  104  provided at a center of the parison tube  102  while the left/right molds  10  and  22  are closed. Next, the injected gel-state plastic material is molded at a predetermined temperature and pressure and then, air blowing stops. Thus, as shown in  FIG. 4 , the footwear last  200  whose interior is hollow (that is, having a cavity part  202 ) is manufactured. 
         [0033]    The air blowing can be performed even when the left/right molds  10  and  22  are closed. In the above description, blowing position is set to a toe side of the footwear last. However, it is obvious that the blowing position can be set to a heel side of the footwear last. 
         [0034]    A concrete condition, for example, general injection pressure or molding temperature, is shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 HDT 
                 Cylinder 
                 Injection 
                 Mold 
               
               
                   
                 Tg 
                 Tm 
                 (18.6 kgf) 
                 Temp. 
                 Pressure 
                 Temp. 
               
               
                 Material 
                 (° C.) 
                 (° C.) 
                 (° C.) 
                 (° C.) 
                 (km/cm 2 ) 
                 (° C.) 
               
               
                   
               
             
             
               
                 HDPE 
                   
                 135 
                   
                 160-310 
                 700-1400 
                 40-70 
               
               
                 LDPE 
                   
                 110 
                   
                 150-310 
                 600-1400 
                 40-70 
               
               
                 PP 
                 −10 
                 167 
                 60 
                 200-280 
                 700-1400 
                 40-70 
               
               
                   
               
             
          
         
       
     
         [0035]    The inventive manufacturing method is compared with a conventional manufacturing method in detail in Table 2 below. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Conventional Method 
                 Inventive Method 
               
               
                   
                 (PE processing method) 
                 (Injection blow method) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Price 
                 Expected comparative price: 
                 4 cavity 2 size general &amp; 
               
               
                   
                 General: 16,000 × 500 
                 special molds 
               
               
                   
                 pairs = 8,000,000 Won 
                 Molding cost: 3,000,000 Won 
               
               
                   
                 Special: 23,000 × 
                 Product cost: 600 to 800 Won 
               
               
                   
                 500 pairs = 
                 3,000,000/500 pairs = 
               
               
                   
                 11,150,000 Won 
                 6,000/2 = 3,000 (2 pairs per 
               
               
                   
                   
                 once injection) 
               
               
                   
                   
                 Expected Comparative Price : 
               
               
                   
                   
                 (1,600 per 1 pair + mold 
               
               
                   
                   
                 depreciation cost 3,000) × 
               
               
                   
                   
                 500 pairs = 2,300,000 Won 
               
               
                 Method 
                 PE Stock machine 
                 Mold blow method 
               
               
                   
                 processing method 
               
               
                 Material 
                 Polyester 
                 Polypropylene, Polyethylene 
               
               
                 Quality 
                 Accurate heel curved 
                 Clean finishing &amp; clean 
               
               
                   
                 surface is difficult 
                 curved surface are kept 
               
               
                   
                 to be kept because of 
                 using gate trimming after 
               
               
                   
                 non-uniform work, such 
                 injection. 
               
               
                   
                 as gauge check for all 
                 Particularly, a smooth 
               
               
                   
                 products, caused by 
                 surface of a heel part is 
               
               
                   
                 grinding work of 
                 kept. 
               
               
                   
                 processed heel &amp; toe. 
               
               
                 Production 
                 Poor workability 
                 Excellent workability 
               
               
                 Site 
                 because of heavy last 
                 because of light past 
               
               
                 Manufac- 
                 Manufacture time per 
                 Mold manufacture time: 10 
               
               
                 turing 
                 one pair: Machining 
                 days, once injection time 
               
               
                   
                 10 min., finishing 30 
                 per 2 pairs: 2 min. (4 
               
               
                   
                 min. (in total, 40 
                 cavity) 
               
               
                   
                 min.) 
                 500 pairs × 2 min./2 = 8.4 
               
               
                   
                 500 pairs × 40 min = 83 
                 hr. = about 2 days 
               
               
                   
                 hr. = about 42 days 
               
               
                 Environ- 
                 Impossible recycle 
                 Possible recycle 
               
               
                 mental 
               
               
                   
               
             
          
         
       
     
         [0036]      FIG. 4  is a cross-sectional view illustrating a structure of the footwear last manufactured using the injection blow molding method according to the present invention. Referring to  FIG. 4 , the inventive footwear last  200  is of a structure whose interior is hollow, and is integrally provided in entirety. 
         [0037]    In other words, the footwear last  200  has the cavity part  202  inside, not being of a conventional structure whose interior is jammed, and keeps a shoe shape (a general last shape) in appearance as it is. Having the structure, the footwear last  200  can be not only greatly light in weight but also can cost a less deal in manufacture and particularly, can improve a workability in comparison with a conventional art. 
         [0038]    The plurality of heel pins  18  is inserted into the rear part of the footwear last  200 . The pipe core pin  20  is inserted at the one upper side. 
         [0039]      FIG. 5  is a cross-sectional view illustrating a structure of a footwear last manufactured using an injection blow molding method according to another exemplary embodiment of the present invention. The footwear last  200   a  is the same as the footwear last  200  of  FIG. 4  in that a heel pin  18  and a pipe core pin are inserted, and a cavity part  202   a  is provided for the footwear last  200   a . However, the footwear last  200   a  has through-holes  300  around by a predetermined interval. The through-holes  300  are to increase a dissipation of a heat when a shoe is manufactured. 
         [0040]    As described above, the present invention has an advantage in that a footwear last is manufactured using an injection blow molding method, thereby not only increasing a simplicity and a productivity but also making the footwear last light and strong, making its manufacture inexpensive, improving a quality, and making its recycle possible and preventing environmental pollution. 
         [0041]    While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.