Patent Publication Number: US-4653644-A

Title: Package for toxic fumigant material in pellet or tablet form and method of making same

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to application packages for fumigant material such as aluminum phosphide and magnesium phosphide both of which are available in tablet or pellet form and which decompose upon contact with moisture in the atmosphere to form a toxic gas. 
     As is well known, the handling of pesticides, particularly those that result in the production of a toxic gas, are dangerous and require extreme care in handling and applying the pesticide to an area where one desires to eliminate rodent and insect parasites. Specifically, with the use of aluminum phosphide or magnesium phosphide such as that disclosed in U.S. Pat. No. 3,888,347 and which is assigned to the same assignee as the present application, it is important to avoid physical contact with the fumigant material itself. To this end, various types of mechanical applicators have been employed in the past to disperse the fumigants in pellet or tablet form throughout a locality or area. These specific fumigants decompose upon exposure to moisture in the atmosphere and generate a toxic gas which, if properly confined in an area, will effectively eliminate any pests and then dissipate to the atmosphere or break down into non-toxic products without leaving any harmful residue. 
     Due to the foregoing properties, it is obviously important that the pellets or tablets, once distributed, uniformly decompose to provide the required concentration of gas in an area and, that the decomposition period be relatively short to permit use of the product under various time, temperature and humidity conditions. 
     Previous application packages for these fumigants have required extensive periods for sufficient decomposition of the pellets or tablets to take place and therefore have resulted in undesirable delays in workers gaining access to the area that has been fumigated. 
     According to the present invention, it has now been found that a spun-bonded synthetic filament sheet can be used as the packaging material. More specifically, where the synthetic filament is a polyester and where the sheets, constructed according to a known process, are made with an average weight per unit of area of approximately 100 grams per square meter (g/m 2 ), the best results are obtained in terms of decomposition time and package strength, tear resistance and handling and storage characteristics. The characteristic of polyester fibers, that they can be heat set in a specific configuration, makes this fiber very suitable for this type of packaging. 
    
    
     In addition to the foregoing advantages, other advantages will become apparent as consideration is given to the following detailed description taken in conjunction with the accompanying drawings, in which: 
     BRIEF SUMMARY OF THE DRAWINGS 
     FIG. 1 is a perspective view of one end of a package of the present invention; 
     FIG. 2 is a view along lines 2--2 of FIG. 1; 
     FIG. 3 is a magnified view of the fibers of one of the sheet of the package of the present invention; and 
     FIG. 4 is a view similar to FIG. 3 but showing another orientation of the fibers used in the sheet material of the package of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As is well known, pesticides that leave harmful residues such as ethylene dibromide, can no longer be safely used due to the toxic materials that appear in the food chain. It is, therefore, highly desirable that other fumigants such as magnesium phosphide and aluminum phosphide be used so long as these materials can be safely applied to an area it is desired to fumigate. 
     Referring now to the drawings, wherein like numerals designate corresponding parts, there is shown a package 10 of the present invention which will greatly facilitate the application of these fumigants in pellet or tablet form to a locality while avoiding hazardous contact by workers (and the commodity to be fumigated) with the toxic material. To this end, the present invention utilizes spun-bonded synthetic filament sheets and, more specifically, spun-bonded polyester filament sheets to form the package 10. 
     In constructing the package, a first sheet 12 which has previously been formed with a plurality of hemispherical indentations or recesses 14, may be passed beneath an automatic dispensing machine so that a tablet 16 will be deposited in each of the recesses 14 of the sheet 12. Subsequently, a second sheet 18 of spun-bonded polyester filament, which has previoulsy been coated with a polyethylene powder as an adhesive is placed over the flat surface of the sheet 12 and bonded thereto by the application of heat and pressure. This may be accomplished by passing the package 10 with the two sheets in juxtaposition and with the lower sheet located in a perforated screen whereby the recesses 14 may protrude through the recesses, beneath a heated pressure plate to effect the adhesive bonding of the sheet 18 to the flat surface area of sheet 12. 
     The materials for the sheets 12 and 18 are available from the Dupont Company and sold under the trademark &#34;REEMAY&#34;. As shown in Dupont Technical Bulletin S-13 of August 1974, which is incorporated herein by reference, the &#34;REEMAY&#34; sheets are made from a continuous-filament polyester fiber that are randomly arranged and highly dispersed and bonded at the filament junctions. The sheets may be made with crimped fibers which, with a 50X magnification will appear as shown in FIG. 3 while the sheets made with the straight fibers, with a similar degree of magnification will appear as shown in FIG. 4. 
     Preferably, sheet 12 should be that sold under the style number 2295 and which has a unit weight of 100 g/m 2  while the sheet 18 is preferably that sold under the style number 2414 which has a unit weight of 34 g/m 2 . 
     
                       TABLE NO. 1                                                 
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Hydrogen Phosphide Gas Evolution Rates                                    
           Exposure  Times to 10, 50 and 90%                              
           Conditions                                                     
                     Decomposition                                        
             Temp.   R.H.    T.sub.10                                     
                                   T.sub.50                               
                                         T.sub.90                         
Products     (°C.)                                                 
                     (%)     (hrs) (hrs) (hrs)                            
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Aluminum Phosphide                                                        
             20-22   85-95   4.8   13.9  24.6                             
Tablets                                                                   
Aluminum Phosphide                                                        
             20-22   85-95   4.1   10.9  19.2                             
Pellets                                                                   
Aluminum Phosphide                                                        
             20-22   85-95   4.5   16.6  34.9                             
Prior Art Pack.                                                           
Mag. Phosphide                                                            
             20-22   85-95   1.5   7.5   18.0                             
Tablets                                                                   
Mag. Phosphide                                                            
             20-22   85-95   1.5   6.2   12.2                             
Pellets                                                                   
Mag. Phosphide                                                            
             20-22   85-95   0.4   2.5   6.0                              
Magtoxin Pellets                                                          
Package of Spun-                                                          
Bonded Polyester                                                          
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     With reference now to Table 1, it will be seen that aluminum phosphide tablets when simply exposed to the atmosphere at the stated exposure conditions take just over 24 hours to decompose by 90% whereas under the same stated exposure condition when enclosed in a prior art package, the aluminum phosphide pellets required almost 35 hours to decompose by 90%. The magnesium phosphide pellets under the stated exposure conditions normally require 12 hours to decompose 90% without any package. However, with the package of the spun-bonded polyester of the present invention, the pellets only required only 6 hours to decompose by 90%. With, of course, lower relative humidity, decomposition times would be longer for both aluminum phosphide as well as magnesium phosphide, as is expected. 
     
                       TABLE NO. 2                                                 
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Residual Metal Phosphide Levels in Partially                              
Spent Fumigants Exposed at High Humidity                                  
Residual Metal Phosphide                                                  
Conc (% Metal Phosphide)                                                  
       Mag.                                                               
       Phosphide Modified Mag.                                            
Exposure                                                                  
       Tablet    Phosphide   Mag.    Mag.                                 
Period Prior     Pellet      Phosphide                                    
                                     Phosphide                            
(hrs)  Package   Package     Tablets Pellets                              
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0      66.0      66.0        66.0    66.0                                 
19     10.4      1.0         3.7     0.6                                  
27.5   0.9       0.7         1.2     0.7                                  
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     The residual metal phosphide levels in partially spent fumigants is shown in Table 2. The modified magnesium phosphide pellet package is the package of the present invention. 
     
                       TABLE NO. 3                                                 
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Residual Metal Phosphide Levels in Partially                              
Spent Fumigants Exposed at Low Humidity                                   
Residual Metal Phosphide                                                  
Conc (% Metal Phosphide)                                                  
       Mag.                                                               
       Phosphide Modified Mag.                                            
Exposure                                                                  
       Tablet    Phosphide   Mag.    Mag.                                 
Period Prior     Pellet      Phosphide                                    
                                     Phosphide                            
(hrs)  Package   Package     Tablets Pellets                              
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 0     66.0      66.0        66.0    66.0                                 
14     --        28.4        --      28.3                                 
19     47.5      9.6         47.5    24.3                                 
22     --        0.8         36.6    24.4, 23.1                           
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     Table 3 shows the residual metal phosphide levels at low humidity conditions. The data clearly establishes that the packaging of the pellets in the spun-bonded polyester aids in the degassing of the magnesium phosphide. This will greatly facilitate the use of this fumigant without regard to temperature or relative humidity. 
     Having described the invention, it will be apparent that modifications may be made thereto without departing from the spirit and scope of this invention as defined in the appended claims.