Patent Publication Number: US-2009229594-A1

Title: Heat source and heating device

Description:
TECHNICAL FIELD 
     The present invention relates to a heat source activated by adding water and a heating device to heat a food (cooked food such as a retort-packed food and canned drink) or other supplies such as a hand-towel, using the heat source. 
     BACKGROUND ART 
     As a heat source activated by adding water, a mixture of aluminum powder and calcium oxide powder has been popularly used for a heat-generating composition (referring to Japanese Patent number 3467729, for example). And, a heating device to heat a lunch bag or Japanese sake, or to re-heat a cooked food such as a retort-packed food in emergency situations, which uses the heat source, has been also known. 
     In such the heat-generating composition, the calcium oxide powder is reacted with the water to generate heat and also calcium hydroxide produced by the reaction is reacted with the aluminum powder to generate heat. The group of reactions makes it possible to generate enough amounts of heat to warm the food within a short period. The above Japanese Patent shows that the disclosed heat-generating composition generates heat of about 100° C. after about 30 seconds from the reaction and the temperature is kept for 20 minutes or longer. And, the heat-generating composition has advantages in which it reacts without generating odor and a small amount of the composition is enough for generating sufficient amounts of heat. 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the aforesaid heating device, the heat-generating composition is packed with an inner bag made by nonwoven fabric and further tightly packed with a watertight outer bag. When to be used, the packed heat-generating composition is taken out of the outer bag and comes in contact with water, resulting in that the heat-generating composition in the inner bag contacts the water to be reacted. The water permeates the inner bag made by nonwoven fabric and reacts with the heat-generating composition in the inner bag. In this case, it is considered that the faster the water contacts the heat-generating composition, the faster the heat-generating reaction proceeds. The generated heat diffuses through the heated water and water vapor. And, it is also considered that the higher the water permeability of the inner bag is, the faster the rate of the heat diffusion is. Accordingly, it is possible that an efficiency of the water permeation of the inner bag (water permeability) influences the proceeding of the heat-generating reaction of the heat-generating composition. However, in such the heating devices, development and proposal concerning to the water permeability of the inner bag have not been done. 
     In view of this regard, the present invention focuses attention on the permeability of the inner bag and the object of the present invention is to provide a heat source capable of a rapid and stable heat-generating reaction and a heating device using the heat source. 
     Means of Solving the Problems 
     A heat source according to the present invention comprises a bag and a heat-generating composition containing aluminum powder and calcium oxide powder, packed in said bag, wherein said bag is formed by a packing material made of a base material of nonwoven fabric of which one surface is coated with a watertight layer, said packing material being punctured with a plurality of pinholes and said packing material has a water permeable rate of 45 to 310 milliliter/min/1 cm 2  measured when head of water is 27 cm. 
     A heat-generating composition containing aluminum powder and calcium oxide powder is reacted with water to cause the following heat-generating reaction: 
       CaO+H 2 0→Ca(OH) 2 +15.2 Kcal, 
       2Al+3Ca(OH) 2 →3CaO.Al 2 O 3 +3H 2 +47 Kcal. 
     According to the present invention, by controlling water permeable rate of the bag, the proceeding of the heat-generating reaction is controlled. That is, when a water permeable rate of the inner bag is set to 45 to 310 milliliter/min/1 cm 2 , preferably 45 to 190 milliliter/min/1 cm 2 , and more preferably 60 to 170 milliliter/min/1 cm 2  measured when head of water is 27 cm, preferable temperature conditions including rate of water temperature rise, risen temperature of the water, duration of the risen temperature of water, rate of vapor temperature rise, risen temperature of the vapor and duration of the risen temperature of vapor under conditions in which a heating device is typically used can be obtained. And, leakage of the heat-generating composition from the bag can be prevented. 
     Examples of the heat-generating composition and nonwoven fabric for use in the prevent invention are described below. 
     Examples of the nonwoven fabric include natural fabric such as cotton and wool; regenerated fiber such as viscose (rayon) and cupra; polyamide such as nylon 6, nylon6,6; straight-chain or branched polyesters having 20 or less carbon atoms such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephalate, polylactic acid and polyglycolic acid; polyolefins such as polyethylene and polypropylene; and synthetic fiber such as acrylic. Two or more kinds of those materials may be used together. The nonwoven fabric may be made by a spunlaced method, spunbond method and the like. 
     Exemplary properties of the nonwoven fabric are followed: basis weight (g/m 2 ); 40˜70, thickness (μm); 170˜460, longitudinal tensile strength (N/5 cm); 35˜380, transverse tensile strength (N/5 cm); 13˜165, longitudinal extensibility (%); 80 and below and transverse extensibility (%); 120 and below. 
     The watertight layer may be formed by laminating a synthetic-resin film on the nonwoven fabric. Exemplary synthetic-resin films include polyolefin resin such as polyethylene and polypropylene; polyamide resin; polyester resin; polyvinyl chloride resin; polystyrene resin; copolymer polyamide resin; copolymer polyester resin; ethylene-vinyl acetate resin; elastomer; and mixed resin of two or more of those resins. The synthetic-resin film may be a single layer or laminated layer. The synthetic-resin film has a thickness of 0.01 to 0.3 mm, preferably 0.02 to 0.1 mm 
     When the heat-generating composition containing aluminum powder and calcium oxide powder has a weight of 3 g or more, it makes possible to heat a subject such as hand towel. A weight ratio of the aluminum powder to the calcium oxide powder is set to 10:90˜60:40. Especially, in view of rate of temperature rise and duration of the risen temperature, a weight ratio of the aluminum powder to the calcium oxide powder is preferably set to 35:65˜50:50. 
     The aluminum powder preferably has following grain size distribution: ˜45 μm; 35˜60%, 45˜63 μm; 15˜30%, 63˜75 μm; 5˜25% and +75 μm; 10˜28%. The calcium oxide powder preferably has following grain size distribution: ˜75 μm; 10˜55%, 75˜150 μm; 25˜55% and +150 μm; 0˜65%. 
     A heating device according to the present invention comprises: a heat source described above; a container having an exhaust vent and water for activating a heat-generating reaction, wherein said heat source is put in said container together with a subject to be heated, said water is added to said container to be reacted with said heat source and the subject is heated by the generated heat. 
     Examples to be heated by the heating device include a food such as a retort-packed food, canned drink, boiled egg and lunch bag, and other supplies such as a hand towel. 
     The container may have any forms including a bag, box and pan. The exhaust vent is for discharging H 2  and H 2 O produced by the aforesaid heat-generating reaction. A size and number of the port is selected such that expansion and breakage of the container can be prevented while keeping heat-retaining property. 
     In the present invention, it is possible to attach said subject to the lid mounted at the upper portion of said container and to heat the subject by water vapor produced by evaporating said water. This case is suitable for heating a hand-towel. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     As described above, according to the present invention, a heat source and a heating device using the same, having preferable temperature conditions including rate of water temperature rise, risen temperature of the water, duration of the risen temperature of water, rate of vapor temperature rise, risen temperature of the vapor and duration of the risen temperature of vapor under conditions in which a heating device is typically used, can be provided. And, the present invention shows that heat-generating ability of the heat source can be controlled by water permeability of the inner bag as well as the property of the heat-generating composition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing showing a structure of a heat source according to the present invention;  FIG. 1A  is a plane drawing and  FIG. 1B  is a cross-section drawing; 
         FIG. 2  is a drawing showing a heating device according to the present invention; 
         FIG. 3  is a drawing showing the water permeable rate measuring method in the present invention; 
         FIG. 4  is a graph showing a relation between the air permeable rate and the water permeable rate; 
         FIG. 5  is a drawing showing the method for measuring the temperature; 
         FIG. 6  is a graph showing a relation between the water temperature and measuring time of each sample; 
         FIG. 7  is a graph showing a relation between the environmental temperature and measuring time of each sample; 
         FIG. 8  are drawings showing a structure of a heating device according to the second embodiment of the present invention;  FIG. 8A  is a perspective drawing and  FIG. 8B  is a sectional front drawing; and 
         FIG. 9  is a drawing showing the method for measuring the temperature. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be precisely described, referring to the drawings. 
     First, water permeability of an inner bag and a relation between the water permeability and temperature of a heat source will be described. 
     &lt;Water Permeability&gt; 
     Sample bags made by various base materials which are punctured with pinholes in various densities were prepared. And, water permeability (water permeable rate) of each sample was measured. 
     (1) Base Material 
     As the base material, a non water-shedding nonwoven fabric (made by 100% cotton, CO40s/PP40, manufactured by Unitika Ltd.) was used. The nonwoven fabric has the following properties: basis weight (g/m 2 ); 40, thickness (μm); 330, longitudinal tensile strength (N/5 cm); 35, transverse tensile strength (N/5 cm); 15, longitudinal extensibility (%); 25 and transverse extensibility (%); 75. The nonwoven fabric is made by a spunlaced method in which columnar water flow injects toward fibers at high pressure to entwine the fibers and thus to produce a nonwoven fabric. The spunlaced method allows a production of a highly flexible napless nonwoven fabric having high drape property. A nonwoven fabric produced by the method is used for livelihood materials such as diaper, medical supplies, food supplies and cleaning supplies. On one surface of the nonwoven fabric, a water-resistant layer (made by polypropylene) was laminated. Or, the water-resistant layer may be made by a heating bonding and the like in exchange for the laminating. The water-resistant layer had a thickness of 40 μm. 
     (2) Pinholes 
     Each of the prepared base materials was punctured with pinholes in various densities using a pinhole opening machine, which comprises a roller on which needles were arranged at intervals of 3.3 mm in the transverse direction and at intervals of 3 mm in the longitudinal direction and a base material supporting roller confronting to the former roller. Or, another type of the pinhole opening machine may be used, which is provided with needles capable of being heated and the heated needles are made to contact the laminated film to fuse the film, resulting in opening pinholes. After the base material was supported to the base material supporting roller, each of the rollers rotated in opposite directions. As the result, pinholes having a diameter of 0.1 to 0.4 mm were formed on the base material in substantially the uniform density over the almost full area. And, a number of rows of the needles on the roller, or a number of times in which the roller passed on the base material was adjusted to vary the density of the pinholes of the base material. In this embodiment, ten base materials having various pinhole densities were prepared. The pinhole densities varied over a range of 800 to 8000/100 cm 2 . If the diameter of the pinhole is larger, the small particulate heat-generating composition may be leaked through the pinhole from the bag, causing unfavorable situation. Accordingly, the pinhole density is preferably 2000 to 8000/100 cm 2 , more preferably 3800 to 7100/100 cm 2 . 
     Each of the base materials was cut into a piece having a size of 50 mm by 50 mm to prepare a sample for measuring water permeability. 
     (3) Water Permeability 
     There is no official standard showing water permeability of fabric and the like. According to a method for measuring water permeable rate of perforated film, water permeability of each sample was examined by a water permeable rate measuring method, described later. 
       FIG. 3  is a drawing showing the water permeable rate measuring method in the present invention. 
     A stainless-steel measuring tank  51  (inside dimension of 335×535×178 mm) was prepared and filled with ion-exchange water of 23±3° C. An inflow pipe  53  from which the ion-exchange water flowed in the tank  51  was formed at the under portion of the side wall of the tank  51  and an overflow pipe  55  was formed at the upper portion of the side wall of the tank  51 . The pipes  53  and  55  were openable and closable by cocks  54  and  56 , respectively. The ion-exchange water was poured into the tank  51  from the inflow pipe  53  and overflowed through the overflow pipe  55 . 
     An outflow pipe  57  (diameter of 19.05 mm) extending downward was formed on the bottom of the tank  51 . The outflow pipe  57  was openable and closable by a cock  58 . The sample base materials S was temporarily attached to the opening of the outflow pipe  57  by a rubber band  59  with the watertight surface of the sample S being upside. Then, the periphery of the sample was closely attached to the pipe by a sealing tape to block the opening with the sample S and then further tightly attached by a water impermeable adhesive tape made by polypropylene. A distance H between the opening of the outflow pipe  57  and the overflow port of the overflow pipe  55  was 270±9.5 mm (head of water). Under the opening of the outflow pipe  57 , a collection vessel  61  was disposed. The collection vessel  61  was set on a measurement apparatus (not shown, GF-3000, manufactured by A&amp;D Co., Ltd.). 
     The tank  51  was kept the overflow state with the both cocks  54  and  56  opened. When the cock  58  of the outflow pipe  57  was opened, the water was collected by the vessel  61 . And, the amount (milliliter) of the collected water was weighed. In this case, after an amount of the permeated water per unit time had got constant (after a variation in amount of the permeated water per 10 seconds was within 5% at least consecutive three times), an amount of the permeated water measured in any one minute during the measurement for one minute or more was defined as a water permeable amount (milliliter). And, a water permeable amount per one minuet per 1 cm 2  of the sample was converted to water permeable rate (milliliter/min/cm 2 ). A specific gravity of the ion-exchange water is set to 1.000 (g/cm 3 ). 
     Then, a relation between the measured water permeable rate and air permeability, which had been publicly known, was examined. Because, the measurement of the water permeable rate needs troublesome handling, and, therefore if the water permeable rate is correlated with the air permeability, the measurement of the air permeability can be employed in exchange for the measurement of the water permeable rate. 
     The air permeability was measured using a gurley type densometer (range; 300 ml, timer; s,t&lt;1, a diameter of measuring section; 30 mm, manufactured by Toyo Seiki Seisaku-Sho, Ltd., based on JIS P8117). The measured value (sec/300 ml) was converted to an air permeable rate (milliliter/min/cm 2 ). 
     The prepared ten samples having various pinhole densities were examined for water permeability using the aforesaid measuring apparatus and also for air permeability using the gurley type densometer. 
     Table 1 shows the measured air permeability, air permeable rate converted from the measured air permeability, the measured water permeability and water permeable rate converted from the measured water permeability. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 air permeability 
                 water permeability 
               
            
           
           
               
               
               
               
               
            
               
                   
                 measured 
                 air permeable 
                 measured 
                 water permeable 
               
               
                 Sample 
                 value 
                 rate 
                 value 
                 rate 
               
               
                 No. 
                 (sec/300 ml) 
                 (ml/min./cm 2 ) 
                 (ml/min.) 
                 (ml/min./cm 2 ) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 40.7 
                 62.57 
                 60.66 
                 21.28 
               
               
                 2 
                 11.0 
                 231.50 
                 39.28 
                 13.78 
               
               
                 3 
                 9.9 
                 257.22 
                 52.87 
                 18.55 
               
               
                 4 
                 7.3 
                 348.83 
                 52.46 
                 18.41 
               
               
                 5 
                 6.8 
                 374.48 
                 63.89 
                 22.42 
               
               
                 6 
                 3.0 
                 848.83 
                 190.83 
                 66.95 
               
               
                 7 
                 1.9 
                 1340.25 
                 301.80 
                 105.89 
               
               
                 8 
                 1.1 
                 2314.98 
                 478.23 
                 167.79 
               
               
                 9 
                 0.7 
                 3637.83 
                 739.90 
                 259.59 
               
               
                 10 
                 0.5 
                 5092.96 
                 1024.70 
                 359.51 
               
               
                   
               
            
           
         
       
     
       FIG. 4  is a graph showing a relation between the air permeable rate and the water permeable rate. The vertical axis indicates the water permeable rate converted from the measured water permeability, and the horizontal axis indicates the air permeable rate converted from the air permeability measured by the gurley type densometer. 
     As shown in the graph, although the values varies when the both rates are small (when the air permeable rate is less than 400 ml/min/cm 2 ), the water permeable rate can be expressed by a direct function of the air permeable rate when the both rate are larger. Accordingly, the graph shows that the water permeable rate is correlated with the air permeable rate. From the graph, a ratio of the water permeable rate to the air permeable rate is substantially equal to 1/13 in a case of the packing material of the present invention. 
     The following examinations were carried out using the air permeable rate capable of converting to the water permeable rate because the measurement of the water permeable rate is a time-consuming process as described above. Suppose that the water permeable rate was expressed by the air permeable rate/13. 
     &lt;Relation Between the Water Permeability of the Bag and the Temperature of Heat Source&gt; 
     A heat source was produced using each of the prepared bags. And, a relation between the temperature of the heat source and the air permeability of the bags was examined. 
     (1) Heat-Generating Composition 
     As the heat-generating composition, a mixed powder of calcium oxide powder (manufactured by Tagen lime industry) of 30 g and aluminum powder (manufactured by YAMAISHI METALS Co., Ltd.) of 20 g was used. 
     The calcium oxide powder has the following grain size distribution: ˜75 μm; 11.69%, 75˜150 μm; 29.27% and +150 μm; 59.04%. The aluminum powder has the following grain size distribution: ˜45 μm; 43.52%, 45˜63 μm; 19.85%, 63˜75 μm; 18.90% and +75 μm; 17.73%. 
     The calcium oxide powder consists of the following elements: calcium oxide (measured by an EDTA titration method (NN indicator)); 93% or more, carbon dioxide (measured by a Sutorelain method); 2.0% and below and impurities (measured by an EDTA titration method, perchloric acid method, absorption spectroscopy); 3.2% and below. The impurities include silicon dioxide, aluminum oxide, ferric oxide and magnesium oxide. 
     (2) Samples of the Bag 
     The same nonwoven fabric as that used for the measurement of the water permeability was used. By varying a number of times in which the roller of the pinhole opening machine passed on the base material, the samples of nonwoven fabrics in various air permeable rates, described below, were prepared. 
     Sample 1; 170˜250 (milliliter/min/cm 2 ), 
     Sample 2; 250˜400 (milliliter/min/cm 2 ), 
     Sample 3; 400˜600 (milliliter/min/cm 2 ), 
     Sample 4; 600˜1300 (milliliter/min/cm 2 ), 
     Sample 5; 1300˜2000 (milliliter/min/cm 2 ), 
     Sample 6; 2000˜3600 (milliliter/min/cm 2 ), 
     Sample 7; 3600˜4000 (milliliter/min/cm 2 ) and 
     Sample 8; 4000˜5000 (milliliter/min/cm 2 ). 
     By using the samples, the bag having a receptacle for containing the heat-generating composition was produced. The receptacle had a size of 90 mm×150 mm. 
     (3) Method for Measuring Temperature of the Heat-Generating Composition 
       FIG. 5  is a drawing showing the method for measuring the temperature. 
     The heat source  1 , a food F (retort-packed cooked rice) and water of 130 g were put in a heating bag  31  having exhaust vents  32 . In this example, the heating bag  31  was openable and closable and had two exhaust vents  32 . In a temperature-controlled room of which room temperature was kept at 20° C., the heating bag  31  was supported in a stainless-steel container  73  set on a heat insulating material  71 . And, for 20 minutes after the heat-generating reaction, a temperature in the heating bag  31  (steam temperature) T 1 , a temperature T 2  of the heated water and an environmental temperature T 3  were measured by the measuring apparatus D. 
       FIG. 6  is a graph showing a relation between the water temperature and measuring time of each sample. 
       FIG. 7  is a graph showing a relation between the environmental temperature and measuring time of each sample. 
     The horizontal axes indicate a measuring time (minute), and the vertical axes indicate the water temperature T 2  ( FIG. 6 ) and environmental temperature T 1  ( FIG. 7 ). 
     As shown in  FIG. 6 , the water temperature T 2  of the sample 1 having slow air permeable rate rises rapidly just after the heat-generating reaction; begins to fall down shortly thereafter and falls down to about 40° C. after 20 minutes. And, the water temperature T 2  of the sample 2 having slow air permeable rate, as well sample 1, rises to about 50° C. at a maximum. On the contrary, the water temperature T 2  of each of the samples 3, 4 and 5 having middle air permeable rate rises just after the heat-generating reaction, to 70° C. or higher after 5 minutes and the risen temperatures is maintained for 20 minutes. The water temperature T 2  of each of the samples 6, 7 and 8 having faster air permeable rate rises to 90° C. or higher just after the heat-generating reaction, the risen temperatures is maintained for 10 minutes after 5 minutes and then 80° C. or higher is maintained after 20 minutes. 
     As shown in  FIG. 7 , the steam temperature (environmental temperature) T 1  of each of the samples 1, 2, 3 and 4 having slow air permeable rate does not rise to 50° C. or higher. On the contrary, the steam temperature of each of the samples 5, 6, 7 and 8 having fast air permeable rate rapidly rises to 70° C. or higher after 2 minutes and the risen temperature of 70° C. or higher is maintained for about 10 minutes. 
     Next, whether the samples satisfied the following temperature conditions required for the food heating device was considered. 
     1) To keep the water temperature of 80° C. or higher for 13 minutes or more. 
     2) To keep the steam temperature of 70° C. or higher for 10 minutes or more. 
     3) To rise the steam temperature to 70° C. or higher after 2 minutes from the heat-generating reaction. 
     Table 2 shows a result whether or not the samples satisfied the temperature conditions. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                   
                 1) water 
                 2) steam 
                   
               
               
                   
                 air permeability 
                 temperature 
                 temperature 
                 3) rate of steam 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 measured 
                 air permeable 
                 80° C. or higher 
                 70° C. or higher 
                 temperature rise 
               
               
                 Sample 
                 value 
                 rate 
                 for 13 min. or 
                 for 10 min. or 
                 70° C. or higher 
               
               
                 No. 
                 (sec/300 ml) 
                 (ml/min./cm 2 ) 
                 more 
                 more 
                 in 2 min. 
               
               
                   
               
               
                 1 
                 ab. 10.0~15.0 
                 170~250 
                 x 
                 x 
                 x 
               
               
                 2 
                  ab. 6.0~10.0 
                 250~400 
                 x 
                 x 
                 x 
               
               
                 3 
                 ab. 4.0~6.0 
                 400~600 
                 x 
                 x 
                 x 
               
               
                 4 
                 ab. 2.0~4.0 
                  600~1300 
                 ∘ 
                 x 
                 x 
               
               
                 5 
                 ab. 1.3~2.0 
                 1300~2000 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                 6 
                 ab. 0.7~1.3 
                 2000~3600 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                 7 
                 ab. 0.6~0.7 
                 3600~4000 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                 8 
                  ab. 0.5~0.67 
                 4000~5000 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                   
               
            
           
         
       
     
     The samples 1, 2, 3 and 4 having the air permeable rate of 1300 and below does not satisfy all of the temperature conditions. And, the food (retort-packed cooked rice) of each sample was not warmed. On the contrary, the samples 5, 6, 7 and 8 having the air permeable rate of 1300 to 5000 satisfy all of the temperature conditions. And, the foods were warmed. But, in the sample 8 having the air permeable rate of 4000 or more, the heat-generating composition was leaked through the pinholes of the bag. Because, the sample, having fast air permeable rate, had any large diameter pinholes formed by lapping the pinholes owing to many times of pass of the needles of the pinhole opening machine. 
     From these results, the following were obtained: 
     (1) Temperature of the heat source can be controlled by the air permeable rate of the bag. 
     (2) The air permeable rate of the bag required for heating a food (retort-packed cooked rice) is 1300 to 4000 milliliter/min/cm 2  (water permeable rate is about 100 to 310 milliliter/min/cm 2 ). 
     Note that the sample 4 having the air permeable rate of 600 to 1300 milliliter/min/cm 2  (water permeable rate is about 46 to 100 milliliter/min/cm 2 ) satisfies the aforesaid temperature condition (1) (to keep the water temperature at 80° C. or higher for 13 minutes or more). Accordingly, if the subject to be heated is so small as to be soaked with the water, the sample 4 can heat such subject. Therefore, the water permeable rate of the bag preferable for heating a subject is 45 to 310 milliliter/min/cm 2 . 
     Next, an effect of an amount of the heat-generating composition consisting of the calcium oxide powder and the aluminum powder on the temperature of the heat source will be described. 
     &lt;An Amount and Amount Ratio of the Heat-Generating Composition and the Temperature&gt; 
     (1) Heat-Generating Composition 
     By using the aforesaid aluminum powder and calcium oxide powder, the following samples were prepared. 
     (1) Sample 1; aluminum powder:calcium oxide powder=50:50, a total weight: 10 g, 
     (2) Sample 2; aluminum powder:calcium oxide powder=50:50, a total weight: 5 g, 
     (3) Sample 3; aluminum powder:calcium oxide powder=50:50, a total weight: 3 g and 
     (4) Sample 4; aluminum powder:calcium oxide powder=10:90, a total weight: 20 g. 
     (2) Method for Measuring the Temperature 
       FIG. 9  is a drawing showing the method for measuring the temperature. 
     A disposable paper towel T was attached to an inside surface of a lid  42  of a paper box  41  of which the inside surface was water-resistant processed. The heat source  1  produced by using each of the prepared four samples was put in the paper box  41 . And, after applying water W in the box, the lid  41  was closed. A weight of the water was 2.6 times of a weight of the heat-generating composition. Then, a temperature T 1  of the paper towel T, a temperature T 2  of the heated water and an environmental temperature T 3  were measured with the measuring apparatus for 3 minutes after the heat-generating reaction. The vapor and hydrogen gas produced by the heat-generating reaction were leaked from the clearance between the body of the box  41  and the lid  42 . 
     Then, whether the samples satisfied the following temperature condition required for a heating device was discussed. 
     1) To Rise the Temperature T 1  of the Paper Towel to about 50° C. in 3 Minutes. 
     Table 3 shows results whether the samples satisfied the temperature conditions. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 paper towel 
                   
               
               
                   
                   
                   
                 temperature (T1) 
               
               
                 Sample 
                 amount ratio 
                 weight 
                 ab. 50° C. 
               
               
                 No. 
                 (aluminum:calcium oxide) 
                 (g) 
                 in 3 min. 
                 result 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 50:50 
                 10 
                 ⊚ 
                 ◯ 
               
               
                 2 
                 50:50 
                 5 
                 ◯ 
                 ◯ 
               
               
                 3 
                 50:50 
                 3 
                 ◯ 
                 ◯ 
               
               
                 4 
                 10:90 
                 20 
                 ◯ 
                 ◯ 
               
               
                   
               
            
           
         
       
     
     The heat source using either sample satisfies the temperature condition. Note that the sample 1 (an amount ratio of 50:50, a total weight of log) shows most preferable temperature rise. 
     From the results, in a case in which the subject to be heated is small, a heat-generating composition having a low ratio of the aluminum powder to the calcium oxide powder of 10:90 (sample 4) can be used. And, a heat-generating composition, having a relatively large amount ratio of the aluminum powder to the calcium oxide powder of 50:50, needs a small total weight (3 g, sample 3). Accordingly, an amount of high-price aluminum powder can be reduced. 
     Example 1 
       FIG. 1  is a drawing showing a structure of a heat source according to the present invention;  FIG. 1A  is a plane drawing and  FIG. 1B  is a cross-section drawing. 
     The heat source  1  comprises a bag  10  and a heat-generating composition  20  packed in the bag  10 . 
     The bag  10  is made of a cotton nonwoven fabric  11  (CO40s/PP40, manufactured by Unitika Ltd.) of which inner surface is coated with a water-resistant layer  13  made of polypropylene. Almost full area of the bag  10  is punctured with pinholes  15  in substantially the uniform density. The pinhole  15  has a diameter of 0.2 to 0.4 mm. The bag  10  has a water permeable rate, measured by the aforesaid method (as shown in  FIG. 3 ), of 100 milliliter/min/cm 2 . The water permeable rate can be converted from the air permeable rate measured by the gurley type densometer. The bag  10  has a size of 90 mm×155 mm. 
     The heat-generating composition  30  is a mixed powder of calcium oxide powder (manufactured by Tagen lime industry) of 30 g and aluminum powder (VA-150, manufactured by YAMAISHI METALS Co., Ltd.) of 20 g. The heat-generating composition  30  is packed in the bag  10  to produce the heat source  1 . 
     Example 2 
       FIG. 2  is a drawing showing a heating device according to the present invention. In this embodiment, the heating device is used for warming a retort-packed cooked rice. 
     The heating device  30  comprises a heating bag (container)  31  having exhaust vents  32 ; the heat source  1  shown in  FIG. 1  and water for activating a heat-generating reaction. In this embodiment, two circular exhaust vents  32  having a diameter of 5 mm are formed. Or, one to two exhaust vents  32  having a diameter of 10 to 15 mm, or eight to ten exhaust vents  32  having a diameter of 1 to 2 mm may be formed. The shape of the exhaust vent is not limited to a circular shape; may be any shape capable of venting water vapor and hydrogen gas. 
     The heat source  1  is packed in an air-tight outer bag during storing in order to prevent the heat-generating composition from contacting moisture in air. 
     The heat source  1 , taken out of the outer bag, and the retort-packed cooked food F were put in the container  31 , water of 130 g was added and then the container  31  was sealed. The heat source  1  caused a heat-generating reaction to heat the retort-packed cooked rice H in the container  31 . Water vapor and hydrogen gas produced by the heat-generating reaction were vent through the exhaust vents  32 . And, after 15 minutes from the activation of the heat-generating reaction, the retort-packed cocked rice H was heated sufficiently. And, leakage of the heat-generating composition did not occur. 
     In exchange for the aforesaid nonwoven fabric, another type of non water repellent nonwoven fabric may be used, for example, Soflon EMR-50 (manufactured by Kokko Paper Mfg. Co., Ltd.), which has the following properties: basis weight (g/m 2 ); 50.0±5.0, thickness (μm); 0.40±0.10, longitudinal tensile strength (N/25 mm); 41.00±10.00, transverse tensile strength (N/25 mm); 9.50±3.00, longitudinal extensibility (%); 27 and below; transverse extensibility (%); 120 and below, longitudinal 5% modulus (n/25 mm); 17.00±7.00 and transverse 50% modulus; 3.10±1.00. The nonwoven fabric was made by a spunlaced method. 
     Example 3 
       FIG. 8  are drawings showing a structure of a heating device according to the second embodiment of the present invention;  FIG. 8A  is a perspective drawing and  FIG. 8B  is a sectional front drawing. 
     The heating device  40  comprises a heating box (container)  41 , the heat source  1  and water for activating a heat-generating reaction. The heat source  1  is packed in an air-tight outer bag during storing in order to prevent the heat-generating composition from contacting moisture in air. 
     The heat source  1  comprises a bag  10  and a heat-generating composition  20  packed in the bag  10 , as well Example 1. In this Example, the bag  10  has a size of 50 mm×110 mm. 
     The heat-generating composition is a mixed powder of calcium oxide powder of 5 g and aluminum powder of 5 g (a total weight of 10 g). 
     The heating box  41  is made of a paper of which inner surface is water-resistant processed. The upper face of the box  41  is openable and closeable by a lid  42 . On the inner surface of the lid  42 , a disposable paper towel T is detachably attached. 
     The heat source  1 , taken out of the outer bag, was put in the container  41 , water of 26 g was added and then the lid  42  was closed. The heat source  1  caused a heat-generating reaction to heat the disposable paper towel attached to the inner surface of the lid  42 . Water vapor and hydrogen gas produced by the heat-generating reaction were vent through a clearance between the container  41  and the lid  42 . And, after 3 minutes from the activation of the heat-generating reaction, the paper towel was heated sufficiently. 
     A weight ratio of the aluminum power and the calcium oxide powder, weight of the heat-generating composition and properties are not limited to the aforesaid values.