Abstract:
A carbon heat source ( 10 ) is equipped with: a cylindrical section ( 11 ) provided with a cavity ( 11 A) through which there is ventilation communication in the longitudinal axis direction (L) of the carbon heat source ( 10 ); and an ignition end ( 12 ) which is provided further to the ignition side of the carbon heat source ( 10 ) than the cylindrical section ( 11 ). Therein, a groove ( 12 A) which connects with the cavity ( 11 A) is formed on the end surface (E) of the ignition side of the ignition end ( 12 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation of co-pending U.S. patent application Ser. No. 14/499,862, filed on Sep. 29, 2014, which claims the benefit under 35 U.S.C. § 119(e) to PCT/JP2013/059141, filed on Mar. 27, 2013, which claims the benefit under 35 U.S.C. § 119(b) to Japanese Application No. 2012-083184 filed on Mar. 30, 2012, all of which are expressly incorporated by reference into the present application which relates to a carbon heat source and a flavor inhaler. 
    
    
     BACKGROUND ART 
     Various proposals have been made for a flavor inhaler provided with a carbon heat source and configured to heat a flavor generating source by the heat generated by the carbon heat source. 
     For example, Patent Literature 1 discloses a flavor inhaler having a carbon heat source provided with a ridge groove on an ignition surface (an end face on an ignition side) across the ignition surface for improving ignitability. 
     Patent literature 2 discloses a flavor inhaler having a columnar carbon heat source that is provided with a through-hole with a diameter of 1.5 mm to 3 mm. 
     A carbon heat source used in a flavor inhaler preferably satisfies the following conditions. 
     The first condition is to provide good ignitability and sufficient heat in a period from a start of burning to an initial puff (smoking). 
     The second condition is to supply a stable amount of heat with less fluctuation in calorific value in a period of middle to late of a puff (smoking). 
     The carbon heat source disclosed in the Patent Literature 1 can improve the ignitability in the period from the start of burning to the initial puff by the groove provided on the ignition surface. However, it merely increases a contact area of an ignition source such as a lighter and an ignition end portion, and an air flow path is not configured to transmit heat efficiently to the ignition end portion in the period from the start of burning to the initial puff. Thus, the effect is insufficient. 
     Further, the carbon heat source disclosed in the Patent Literature 1 is assumed to be used in a flavor inhaler configured to transmit the heat generated by a carbon heat source to a flavor generating source via an enclosing member or a holding member of the carbon heat source. Thus, when used in a flavor inhaler configured to transmit the heat generated by a carbon heat source to a flavor generating source mainly by convection heat transfer, there is a problem that the supply of stable amount of heat is difficult in the period of middle to late of the puff (smoking). 
     The carbon heat source disclosed in the Patent Literature 2 has a uniform circular column shape over the entire length, that is, a groove or the like is not provided on an ignition surface. Thus, there is a problem that efficient heat transfer to an ignition surface is difficult in an ignition source such as a commercially available lighter or the like, and good ignitability is difficult in a period from a start of burning to an initial puff. 
     In a conventional integrally molded carbon heat source as disclosed in the Patent Literatures 1 and 2, it is very difficult to achieve both good ignitability in a period from a start of burning to an initial puff and supply of stable amount of heat in a period of middle to late of a puff (smoking). 
     CITATION LIST PATENT LITERATURE 
     Patent Literature 1: Japanese Patent Application Publication No. H5-103836 
     Patent Literature 2: Japanese Patent Application Publication No. 2010-535530 
     SUMMARY OF THE INVENTION 
     A columnar carbon heat source of a first feature comprises: a cylindrical portion provided with a cavity for ventilating and communicating in a longitudinal axis direction of the carbon heat source; and an ignition end portion provided on an ignition side of the carbon heat source than the cylindrical portion. A groove communicating with the cavity is formed on an end face of the ignition end portion on the ignition side. The ignition end portion has a void that communicates with the cavity in an extending direction of the cavity provided in the cylindrical portion. The groove is formed separately from the void. 
     In the first feature, the groove is exposed to a side surface of the ignition end portion. 
     In the first feature, the cylindrical portion has a circular cylinder shape. A difference between a diameter of the cavity and an outer diameter of the carbon heat source is configured to be 1 mm or more. 
     In the first feature, the cylindrical portion and the ignition end portion are integrally molded. 
     In the first feature, a size of the carbon heat source is configured to be 10 mm to 30 mm in the longitudinal axis direction of the carbon heat source. A size of the carbon heat source is configured to be 4 mm to 8 mm in a direction orthogonal to the longitudinal axis direction. 
     In the first feature, a size of the cavity is configured to be 1 mm to 4 mm in a direction orthogonal to the longitudinal axis direction of the carbon heat source. 
     A flavor inhaler of a second feature comprises the carbon heat source of the first feature. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view of a flavor inhaler having a carbon heat source according to an embodiment of the present invention. 
         FIG. 2  is a view of the carbon heat source according to the embodiment of the present invention. 
         FIG. 3  is a view of the carbon heat source according to the embodiment of the present invention. 
         FIG. 4  is a view showing an example of a groove formed on an ignition surface of the carbon heat source according to the embodiment of the present invention. 
         FIG. 5  is a view showing an example of the groove formed on the ignition surface of the carbon heat source according to the embodiment of the present invention. 
         FIG. 6  is a flowchart for explaining a method of manufacturing a carbon heat source  10  according to the embodiment of the present invention. 
         FIG. 7  is a view for explaining an example 1 of the present invention. 
         FIG. 8  is a table for explaining an example 2 of the present invention. 
         FIG. 9  is a view illustrating a carbon heat source according to a modification 1 of the present invention. 
         FIG. 10  is a view of the carbon heat source according to a modification 1 of the present invention. 
         FIG. 11  is a view of a carbon heat source according to a modification 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment of the Invention 
     A flavor inhaler  1  according to an embodiment of the present invention will be described with reference to  FIG. 1  to  FIG. 6 . 
       FIG. 1  is a view of a flavor inhaler  1  according to the embodiment seen from a lateral direction.  FIG. 2( a )  is a view of a carbon heat source  10  according to the embodiment seen from a lateral direction Z.  FIG. 2( b )  is a view of a carbon heat source  10  according to the embodiment seen from an ignition surface direction X.  FIG. 2( c )  is a view of a carbon heat source  10  according to the embodiment seen from a direction Y on the opposite side (an end face of a puff side) of an ignition surface E. 
     As shown in  FIG. 1 , the flavor inhaler  1  according to the embodiment includes a flavor generating source  2 , a carbon heat source  10 , and a holder  3  for holding the flavor generating source  2  and the carbon heat source  10 . 
     The flavor generating source  2  releases a flavor by transmission of heat generated by the carbon heat source  10 . 
     As a flavor generating source  2 , for example, a tobacco leaf can be used. It is possible to use tobacco material, such as, general cut filter tobacco used for a cigarette, granular tobacco used for snuff, roll tobacco, and molded tobacco. A carrier made of porous or non-porous material may be used as the flavor generating source  2 . 
     The roll tobacco is obtained by forming sheet-like regenerated tobacco into a roll, and has a flow path inside. The molded tobacco is obtained by molding granular tobacco. 
     The tobacco material or the carrier used as the flavor generating source  2  may contain a desired flavor. 
     The holder  3  may be configured by a paper tube that is formed as a hollow cylindrical body by cylindrically curving a rectangular cardboard and combining both side edge portions. 
     The carbon heat source  10  and the flavor generating source  2  may be configured not adjacent by providing a gap or by placing a nonflammable member having air permeability between the carbon heat source  10  and the flavor generating source  2 . 
     Further, as shown  FIG. 1 , it is possible to improve visibility of a burning state of the carbon heat source  10  by protruding at least a part of the carbon heat source  10  from the holder  3 . 
     As shown in  FIG. 2  and  FIG. 3 , the carbon heat source  10  has a circular column shape, and comprises a circular cylinder portion  11  and an ignition side end portion  12 . 
     As shown in  FIG. 2( a ) , the circular cylinder portion  11  is provided with a cavity  11  for ventilating and communicating in the longitudinal axis direction L of the carbon heat source  10 . 
     Further, as shown in  FIG. 2( c ) , the cavity  11 A may have a coaxial circular column shape, having a central axis that is the same as a central axis of the circular cylinder portion  11  over the entire length of the carbon heat source  10 . In such a case, a process of manufacturing the cavity  11 A can be simplified. 
     It is preferable to reduce a contact area between a burning portion and inlet air during a puff for supplying a stable amount of heat in a period of middle to late of a puff, that is, for suppressing a fluctuation between a calorific value during natural burning (non-smoking) and a calorific value during a puff. 
     Therefore, it is possible to suppress a fluctuation between a calorific value during natural burning and a calorific value during a puff by making a cylindrical shape having only a single cavity  11 A as shown in  FIG. 2( a ) . 
     As for a difference (the wall thickness of the circular cylinder portion  11 ) between a diameter R 1  of the cavity  11 A and an outer diameter R 2  of the carbon heat source (the circular cylinder portion  11 ), a numeric value for obtaining sufficient ignitability is appropriately selected according to a carbon mixing ratio or the like of a carbon heat source. The difference may be 1 mm or more, preferably 1.5 mm or more, more preferably 2.0 mm or more. In such a configuration, the user can inhale flavor by a sufficient number of times. 
     The diameter R 1  of the cavity  11 A may be configured to be 1.5 mm or more, more preferably 2.0 mm or more. In such a configuration, it is possible to reduce a pressure loss to occur during inhalation. 
     Alternately, the cavity  11 A may have a shape with a different diameter along the longitudinal axis direction L, as a conical shape or the like. In such a case, it is possible to precisely control the amount of heat to be supplied in a period of middle to late of a puff. 
     As shown in  FIG. 2( a ) , the ignition end portion  12  is provided on the ignition side (the ignition surface E) than the circular cylinder portion  11 . The ignition end portion  12  has a void that communicates with the cavity  11 A in the extending direction of the cavity  11 A provided in the circular cylinder portion  11 . In the first embodiment, the void of the ignition end portion  12  has a diameter smaller than that of the cavity  11 A. The void in the ignition end portion  12  may have a diameter equal to that of the cavity  11 A. 
     As shown in  FIG. 2( b )  and  FIG. 3 , on the ignition surface E of the ignition end portion  12 , a groove  12 A is formed in communication with the cavity  11 A. It is to be noted that the groove  12 A is formed separately from a cavity in the ignition end portion  12 . In other words, a cavity is formed along the longitudinal axis direction L over the entire length of the carbon heat source, and in the case that the cavity is exposed to the ignition end E, the cavity exposed to the ignition end E does not correspond to the groove  12 A. In such a configuration, as “the area of the ignition surface E (except for the area of the part provided with the groove  12 A)” is reduced and “the area of the groove wall in the groove  12 A” is increased, the heat of an ignition source such as a lighter is efficiently transmitted to the ignition end portion, and good ignitability can be obtained in a period from a start of burning to an initial puff. 
     In other words, to obtain sufficient ignitability, it is desirable to increase the ratio of “the area of the groove wall of the groove  12 A” to “the area of the ignition surface E (except for the area of the part provided with the groove  12 A)”, and “the area of the groove wall of the groove  12 A”/“the area of the ignition surface E (except for the area of the part provided with the groove  12 A)”. 
     For the ratio of “the area of the groove wall of the groove  12 A” to “the area of the ignition surface E (except for the area of the part provided with the groove  12 A)”, a numeric value for obtaining sufficient ignitability is appropriately selected according to a carbon mixing ratio or the like of the carbon heat source. Sufficient ignitability can be obtained at a value of 0.5 or more, preferably 1.25 or more, more preferably 2.5 or more, for example. 
     “The area of the ignition surface E (except for the area of the part provided with the groove  12 A)” mentioned here is an area of the shaded part shown in  FIG. 5 , and “the area of the groove wall of the groove  12 A” is an area to be calculated by “the entire length of the groove  12 A in the ignition surface E (the total of the lengths of eight sides of A to H shown in  FIG. 5 )”×“the depth of the groove  12 A”. 
     The groove  12 A may be arbitrarily arranged as long as it has a shape communicating with the cavity  11 A. 
     For example, as shown in  FIG. 2( a )  and  FIG. 3 , the groove  12 A may be exposed to a side surface  12 B of the ignition end portion  12 . In such a configuration, the sidewall of the groove  12 A can be burnt more efficiently in a period from a start of burning to an initial puff, and the ignitability is further improved. 
     Further, as shown in  FIG. 2( b ) , two grooves  12 A may be arranged to be orthogonal to each other on the ignition surface E. As shown in  FIG. 4 , three grooves  12 A may be arranged to be orthogonal to each other on the ignition surface E. 
     By arranging two or more grooves  12 A so as to divide equally the ignition surface E, it is possible to transmit heat evenly and efficiently to the entire ignition surface E during a period from a start of burning to an initial puff. 
     The groove  12 A may be arranged as a curved shape. As long as each groove communicates with the cavity  11 A, two or more grooves  12 A may be arranged so as to intersect at a position other than the center of the cavity  11 A. 
     Further, the groove  12 A may be inclined to become deeper toward the cavity  11 A. 
     By intersecting two or more curved grooves  12 A or linear grooves  12 A at various positions within the ignition surface E, a plurality of projected shapes may be provided on the ignition surface E. 
     By making the depth of the groove  12 A deeper, the area of the airflow path in the ignition end portion is increased, and the ignitability can be improved. 
     For improving the ignitability, although the effect is less than the groove  12 A, from the viewpoint of design or the like, the present invention includes, of course, making a groove or the like not communicating with the cavity  11 A as well as the groove  12 A. 
     Further, it is possible to prevent a lack in the ignition surface E by chamfering the ignition surface E. 
     The carbon heat source  10  (the circular cylinder portion  11  and the ignition side end portion  12 ) may be integrally molded by a method of extrusion, tableting, press casting or the like as described later. 
     Further, the length L 1  in the longitudinal axis direction L of the carbon heat source  10  may be configured to be 8 to 30 mm, preferably 10 to 30 mm, more preferably 10 to 15 mm. The carbon heat source  10  having such a configuration can be suitably employed as a heat source of a flavor inhaler. 
     The outer diameter R 2  of the carbon heat source  10  may be configured to be 4 to 8 mm, more preferably 5 to 7 mm. The carbon heat source  10  having such a configuration can be suitably employed as a heat source of a flavor inhaler. 
     The outer diameters of the circular cylinder portion  11  and the ignition end portion  12  are configured to be the same as the outer diameter R 2  of the carbon heat source  10 . 
     The length of the circular cylinder portion  11  in the longitudinal axis direction L can be arbitrarily set within a range not to impair the function (ignitability) of the ignition end portion  12 . For example, the length of the circular cylinder portion  11  in the longitudinal axis direction L may be a length obtained by subtracting the depth of the above groove  12 A from the entire length of the carbon heat source  10  in the longitudinal axis direction L. 
     Hereinafter, an example of a method of manufacturing the carbon heat source  10  according to the embodiment will be explained by referring to  FIG. 6 . 
     As shown in  FIG. 6 , in step S 101 , primary molding of the carbon heat source  10  is performed. 
     In the primary molding, the carbon heat source  10  may have a circular column shape without the cavity  11 A or a circular column shape with the cavity  11 A for ventilating and communicating in the longitudinal axis direction. 
     The carbon heat source  10  can be obtained by integrally molding a mixture containing water, carbon material derived from plants, nonflammable additive or binder (organic binder or inorganic binder) or the like by a method of extrusion, tableting, press casting or the like. 
     As such a carbon material, it is desirable to use one obtained by removing volatile impurities by heat treatment or the like. 
     The carbon heat source  10  can contain a carbon material in a range of 10 wt % to 99 wt %. From the standpoint of supplying a sufficient amount of heat and burning characteristics such as tight ash, the carbon heat source  10  preferably contains a carbon material of 30 wt % to 70 wt %, more preferably a carbon material of 40 wt % to 50 wt %. 
     As an organic binder, it is possible to use a mixture containing at least one of the CMC (carboxymethyl cellulose), CMC-Na (carboxymethyl cellulose sodium), alginates, EVA, PVA, PVAC and sugars. 
     As an inorganic binder, it is possible to use, for example, a mineral binder such as mineral purified bentonite, or a silica-based binder such as colloidal silica, water glass and calcium silicate. 
     For example, from the viewpoint of flavor, the above binder preferably contains CMC or CMC-Na of 1 wt % to 10 wt %, more preferably CMC or CMC-Na of 1 wt % to 8 wt %. 
     As a nonflammable additive, it is possible to use oxides or carbonates composed of sodium, potassium, calcium, magnesium, silicon, or the like. The carbon heat source  10  can contain a nonflammable additive of 40 wt % to 89 wt %. 
     It is preferable to use calcium carbonate as a nonflammable additive, and the carbon heat source  10  preferably contains a nonflammable additive of 40 wt % to 55 wt %. 
     The carbon heat source  10  may contain alkali metal salts such as sodium chloride at a ratio of 1 wt % or less for the purpose of improving the burning characteristics. 
     In step S 102 , processing of forming the circular cylinder portion  11  is performed. For example, the circular cylinder portion  11  having the cavity  11 A is formed by making a hole up to a predetermined position with a drill in one end face (the puff side end face) of the primarily molded carbon heat source  10 . 
     In step S 103 , processing of forming the ignition end portion  12  is performed. For example, a groove  12 A is formed by performing predetermined processing on the surface (ignition surface) opposite to the surface (puff side end face) where a drill is inserted in step S 102 , by means of a diamond cutting disc. 
     Good ignitability can be obtained by appropriately adjusting the number, depth or width of the groove  12 A in accordance with the composition (carbon blended rate, or the like) and outer diameter R 2  of the carbon heat source  10 . 
     The order of steps S 102  and S 103  may be reversed. When the cavity  11 A has been formed in the primary molding, step S 102  may be omitted. 
     In the flavor inhaler  1  and the carbon heat source  10  according to the embodiment, it is possible to satisfy good ignitability on the ignition surface E and stable heat supply in the circular cylinder portion  11  at the same time by forming the groove  12 A on the ignition surface E and forming the cavity  11 A for ventilating and communicating in the longitudinal axis direction L of the carbon heat source  10  in the circular cylinder portion  11 . 
     EXAMPLE 1 
     A test performed for evaluating the relationship between the ignitability and the shape of the groove  12 A in the ignition surface E will be explained with reference to  FIG. 7 . 
     In the test, a plurality of test samples A-1 to E-3 has been prepared. Table 1 shows the number, width and depth of the groove  12 A in the test samples A-1 to E-3. 
     First, activated carbon of 100 g, calcium carbonate of 90 g, and CMC of 10 g (degree of etherification 0.6) have been mixed, then water of 270 g containing sodium chloride of 1 g has been added and mixed further. 
     Second, the mixture has been kneaded, and then extrusion molding has been performed to make a circular column shape with an inner diameter of 0.7 mm and an outer diameter of 6 mm. 
     Third, the molded product obtained by the extrusion molding has been dried, and then cut to a length of 13 mm, and a primarily molded body (the carbon heat source  10  of the primary molding) has been obtained. 
     Fourth, the circular cylinder portion  11  having the cavity  11 A has been formed by making a hole up to a predetermined position in one end face (puff side end face) of the primarily molded body, by using a drill with a diameter of 2 mm. 
     Fifth, the groove  12 A has been formed by performing predetermined processing on the surface (ignition surface) opposite to the surface (puff side end face) where a drill has been inserted in step S 102 , by means of a diamond cutting disc. 
     Then, an ignitability evaluation test has been performed for each test sample A-1 to E-3 (the carbon heat source  10 ) by the following method. 
     First, as shown in  FIG. 7 , the circular cylinder portion  11  of each test sample A-1 to E-3 (the carbon heat source  10 ) has been connected to the holder  3  made of a paper tube. 
     Second, each test sample (the carbon heat source  10 ) has been heated for three seconds by bringing into contact with the flame of a commercially available gas lighter  100 , then a puffed of 55 ml/2 seconds have been performed. The puff has been repeated at 15 second intervals. 
     Table 1 shows the result of the ignitability evaluation test for each test sample A-1 to E-3. 
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Burning continuation after 
               
               
                   
                 Outer diameter R2 of 
                 Groove 
                 Groove 
                   
                 Area ratio of groove wall 
                   
                 2nd puff 
               
               
                   
                 carbon heat source 
                 width 
                 depth 
                 Number of 
                 with respect to ignition 
                 Burning area after 1st puff 
                 (◯: Continued, X: Not 
               
               
                 Sample 
                 [mm] 
                 [mm] 
                 [mm] 
                 grooves 
                 surface 
                 (◯: Whole, Δ: Part) 
                 continued) 
               
               
                   
               
             
             
               
                 A-1 
                 5.7 
                 1 
                 1 
                 2 
                 1.22 
                 Δ 
                 X 
               
               
                 A-2 
                 5.7 
                 1 
                 1 
                 2 
                 1.22 
                 Δ 
                 X 
               
               
                 A-3 
                 5.7 
                 1 
                 1 
                 2 
                 1.22 
                 Δ 
                 X 
               
               
                 B-1 
                 5.7 
                 1 
                 2 
                 2 
                 2.43 
                 ◯ 
                 ◯ 
               
               
                 B-2 
                 5.7 
                 1 
                 2 
                 2 
                 2.43 
                 ◯ 
                 ◯ 
               
               
                 B-3 
                 5.7 
                 1 
                 2 
                 2 
                 2.43 
                 ◯ 
                 ◯ 
               
               
                 C-1 
                 5.7 
                 1 
                 3 
                 2 
                 3.65 
                 ◯ 
                 ◯ 
               
               
                 C-2 
                 5.7 
                 1 
                 3 
                 2 
                 3.65 
                 ◯ 
                 ◯ 
               
               
                 C-3 
                 5.7 
                 1 
                 3 
                 2 
                 3.65 
                 ◯ 
                 ◯ 
               
               
                 D-1 
                 5.7 
                 1 
                 1 
                 1 
                 0.57 
                 Δ 
                 X 
               
               
                 D-2 
                 5.7 
                 1 
                 1 
                 1 
                 0.57 
                 Δ 
                 X 
               
               
                 D-3 
                 5.7 
                 1 
                 1 
                 1 
                 0.57 
                 Δ 
                 X 
               
               
                 E-1 
                 5.7 
                 1 
                 1 
                 3 
                 2.69 
                 Δ 
                 ◯ 
               
               
                 E-2 
                 5.7 
                 1 
                 1 
                 3 
                 2.69 
                 Δ 
                 ◯ 
               
               
                 E-3 
                 5.7 
                 1 
                 1 
                 3 
                 2.69 
                 Δ 
                 X 
               
               
                   
               
             
          
         
       
     
     Here, as an ignitability evaluation test, we have confirmed “a burning state of the ignition surface of each test sample after a first puff (whether or not the whole ignition surface burns)” and whether “the burning continues after a second puff (whether the burning continues uniformly)”. 
     According to the results of the evaluation test, it is confirmed that when the number of the grooves  12 A is “two”, sufficient ignitability is obtained even with a commercially available gas lighter  100  by making the depth of the groove  12 A of “2 mm or more”. 
     Further, even when the depth of the groove  12 A is “1 mm”, the ignitability has been improved by making “three or more” numbers of grooves  12 A. 
     Further, according to the results of the evaluation test, it is proved that the ignitability is improved as the ratio of the groove wall in the groove  12 A to the area ratio of the groove wall with respect to the ignition surface (the area of the ignition surface E (except for the area of the part where the groove  12 A is formed)) is greater. 
     The groove depth mentioned here means a distance from the ignition surface E to the bottom of the groove  12 A in the longitudinal axis direction L. The groove width means a size of the groove  12 A in the direction orthogonal to the extension direction of the groove  12 A on the ignition surface E. 
     EXAMPLE 2 
     Hereinafter, an example 2 will be explained. In the example 2, a plurality of samples (samples L-1 to M-2) shown in  FIG. 8  are prepared, and confirmed were a temperature difference between puffs and the puff number that continue burning. 
     Each sample is a carbon heat source composed of activated carbon, calcium carbonate, and CMC. When the total weight of a sample is 100 wt % or more, a sample is composed of activated carbon of 80 wt %, calcium carbonate of 15 wt %, and CMC of 5 wt %. The length of each sample in the longitudinal axis direction L is 15 mm.  FIG. 8  shows the number of cavities of each sample, the size of a cavity, and the number of cavities. 
     Such a sample has been inserted into a paper tube, and a puff of 55 ml/2 seconds has been performed after bringing an ignition end into contact with the flame of commercially available light for three seconds. 
     As shown in  FIG. 8 , compared with the samples M-1 to M-2 having a plurality of cavities, the samples L-1 to L-3 having a single cavity can provide good results in both the temperature difference between puffs and the burning continued puff number. 
     In other words, compared with the case that a plurality of cavities is provided, when a single cavity is provided, “a molded body cross-sectional area/flow path perimeter” is great, and reduction of the temperature difference between pulls has been confirmed. Further, as compared with the case that a plurality of cavities is provided, when a single cavity is provided, “a molded body cross-sectional area/flow path perimeter” is great, and an increase in the puff number has been confirmed. 
     Modification 1 
     Hereinafter, a modification 1 of the embodiment described above will be explained. Differences from the embodiment described above will be explained. 
       FIG. 9  and  FIG. 10  show a carbon heat source  10  according to the modification 1.  FIG. 9  is a view of the carbon source  10  seen from the end face (hereinafter, an ignition surface E) on the ignition side.  FIG. 10  is a view of the cross section S shown in  FIG. 9  seen from the T side. The cross section S is a section passing through the center of the cavity  11 A and the groove  12 A. In  FIG. 10 , for convenience of description, it should be noted that the ridge line seen on the front side is indicated by a dotted line. 
     As shown in  FIG. 9 , the ignition surface E of the carbon heat source  10  is provided with a cross-shaped groove  12 A passing through the center of the cavity  11 A. 
     In the modification 1, the ignition end portion  12  has a void communicating with the cavity  11 A in the extending direction of the cavity  11 A provided in the circular cylinder portion  11 . In the modification 1, the void in the ignition end portion  12  has the same diameter as that of the cavity  11 A. It should be noted that the cross-shaped groove  12 A is formed separately from the void in the ignition end portion  12 . 
     As described in the above embodiment, chamfering may be given to the ignition surface F. For example, as shown in  FIG. 9  and  FIG. 10 , chamfering has been given to the outer end U 1  in the radial direction of the ignition surface E. Chamfering has been given to the inner end U 2  in the radial direction of the ignition surface E. Chamfering has been given to the outer end U 3  in the radial direction of the non-ignition end provided on the opposite side of the ignition surface E. In other words, the outer end U 1 , inner end U 2  and outer end UE have a tilt with respect to a vertical plane relative to the longitudinal axis direction L. By such chamfering, a lack of the carbon heat source  10  is suppressed. P, Q and R show the same portions between  FIGS. 9 and 10 . 
     The diameter of the cavity  11 A is 2.5 mm for example. The groove width of each groove  12 A is smaller than the diameter of the cavity  11 A, for example, 1 mm. The length of the carbon heat source  10  in the longitudinal axis direction L is 17 mm for example. The length of the ignition end portion  12  in the longitudinal axis direction L is 2 mm for example. Of the ignition end portion  12 , the length of the part where chamfering is performed is 0.5 mm for example. In other words, in the longitudinal axis direction, of the ignition end portion  12 , the length of the part where chamfering is not performed is 1.5 mm. 
     In the modification 1, it should be noted that the carbon heat source  10  (the circular cylinder portion  11  and the ignition end portion  12 ) is integrally molded. For example, after molding a lump body that is composed of a carbon material and has a cavity extending along the longitudinal axis direction by a method of extrusion, tableting or press casting, a groove may be formed by cutting the ignition end face. 
     Modification 2 
     Hereinafter, a modification 2 of the embodiment described above will be explained. Differences from the embodiment described above will be explained. 
       FIG. 11  is a view of a carbon heat source  10  according to the modification 2. In  FIG. 11 , for convenience of description, an outer profile of the ignition end portion  12  is virtually shown in dotted lines by extending the outer profile of the circular cylinder portion  11  along the longitudinal axis direction L. 
     As described in the aforementioned, a plurality of projections may be formed on the ignition surface E. As shown in  FIG. 11 , the ignition end portion  12  has a plurality of projections  12 P. The tips of the projections  12 P constitute an ignition surface E. The above mentioned groove  12 B is a pace between the projects  12 P adjacent each other. 
     Although the present invention has been described in detail by using the embodiments described hereinbefore, it is apparent that the invention is not to be limited to the embodiments explained in this specification. The invention may be embodied in various modifications and alterations without departing from the spirit and scope of the invention defined in terms of the claims, and thus, the description of the specification is to be considered as illustrative and not intended to have any restrictive meaning to the present invention. 
     For example, the carbon heat source  10  has a circular column shape in the embodiments, but the embodiments are not limited thereto. The carbon heat source  10  may have a rectangular column shape. In the embodiments, the cavity  11 A has a circular shape in the cross section orthogonal to the longitudinal axis direction L, but the embodiments are not limited thereto. The cavity  11 A may have a rectangular shape or an elliptical shape in a cross section orthogonal to the longitudinal axis direction L. In such a case, the diameter R 1  of the cavity  11 A and the outer diameter R 2  of the carbon heat source  10  may be read as a size in the direction orthogonal to the longitudinal axis direction L. In such a case, the size in the direction orthogonal to the longitudinal axis direction L may be a maximum length, a minimum length, or an average length of a straight line passing through the center of the carbon heat source  10  (the cavity  11 A) in the cross section perpendicular to the longitudinal axis direction L. 
     As a reference, the entire content of Japanese Patent Application No. 2012-083184 (filed on Mar. 30, 2012) is incorporated herein. 
     INDUSTRIAL APPLICABILITY 
     As described hereinbefore, according to the present invention, it is possible to provide a carbon heat source and a flavor inhaler, which have good ignitability in a period from a start of burning to an initial puff, and can realize supply of stable amount of heat in a period of middle to late of a puff.