Pesticide and process for its production

The present invention relates to a pesticide comprising a molded body made of a water-insoluble organic solid substance in which at least one finely divided metal phosphide is embedded, the molded body being coated on at least one side with a fibrous substance which is permeable to water vapor and the fibers of which at least partially extend as far as the embedded phosphide particles, and to a process for producing such a pesticide.

BACKGROUND OF THE INVENTION 
The present invention relates to pesticides. 
More particularly, the present invention relates to a pesticide comprising 
a molded body made of a water-insoluble organic solid substance in which 
one or more finely divided metal phosphides, preferably aluminum phosphide 
and/or magnesium phosphide, are embedded, and to a process for producing 
such a pesticide. 
PRIOR ART 
French Patent Specification No. 1,531,677 describes molded bodies, e.g. 
tablets or pellets, which are used as insecticides. These comprise finely 
divided metal phosphides, preferably the phosphides of aluminum and 
magnesium, especially with particle diameters of 10 1,000 microns, which 
are embedded in a polyester resin, polyurethane resin, polyvinyl resin or 
polystyrene resin. These molded bodies may contain 30 to 60 percent by 
weight of the mtal phosphide/phosphides. 
The disadvantage of these insecticides is that they give off gas slowly. 
When brought into an atmosphere having 60 percent relative humidity at 
room temperature, compositions having 60 or 50 percent by weight of 
aluminum phosphide and magnesium phosphide and having 40 or 50 percent by 
weight of polyester resin, frequently release the full amount of gas only 
after approximately twenty days. It is obvious, therefore, that a long 
time is needed before the residues do not contain any considerable 
quantities of phosphides and can therefore be removed and eliminated 
safely, and that the concentration of hydrogen phosphide in the gas-filled 
room is only very low because of the slow release of gas with a given 
quantity of the composition. 
The present invention seeks to provide pesticides of the type mentioned 
such that they release gas more quickly and can be removed easily and 
completely from the gas-filled room after the release of gas. 
DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, this aim may be achieved in that the 
molded body is coated on one or more sides with a fibrous substance which 
is permeable to water vapor and the fibers of which at least partially 
extend as far as the embedded phosphide particles. 
These fibers which extend to the inside of the molded bodies act as 
"wicks", by means of which the atmospheric moisture reaches at least some 
of the phosphide particles. The particles of the metal phosphides thus 
decompose with the development of gaseous hydrogen phosphide and with an 
increase in volume. Consequently, the water-insoluble organic solid 
substance around the remaining phosphide particles is shattered and a 
regulated and quick release of gas takes place. 
The pesticides of the present invention preferably contain as the 
water-insoluble organic solid substance a thermoplastic substance, such as 
polyethylene, polypropylene, hard paraffin, polyvinyl chloride, polyvinyl 
acetate, polystyrene, copolymerisates of vinyl acetate and vinyl chloride, 
copolymerisates of polyethylene, polystyrene, polypropylene, polyvinyl 
chloride and other polyvinyl compounds, or similar compounds with other 
copolymerizable material. Any other thermoplastic substance is suitable. 
The substance must be thermoplastic, since otherwise it is not possible to 
achieve a penetration of the fibrous substance employed. 
Finely divided aluminum phosphide and/or magnesium phosphide having 
particle diameters up to 300.mu. have proved to be particularly suitable. 
Good results are obtained with pesticides which contain 60 to 120 parts by 
weight of the water-insoluble organic solid substance per 100 parts by 
weight of the metal phosphide. The release of gas is usually slower than 
desirable when the content of water-insoluble organic solid substance is 
increased, and it frequently occurs too quickly and even during the time 
needed for positioning, placing, or exposing the pesticide for application 
when a smaller content is present. 
The fibrous substance which coats the molded body on one or more sides may, 
for example, be a fabric, a felt, or a non-woven fabric. Fibrous 
substances made of cellulose, such as cotton fibers, wood pulp, 
regenerated cellulose, or the like, are particularly suitable. These 
substances conduct the atmospheric moisture into the interior of the 
molded bodies particularly well. 
The pesticide according to the present invention is preferably in the shape 
of a plate, a band, or a strip. It is therefore easily possible to bring 
the respective desirable quantities of the composition into the room which 
is to be filled with gas, e.g., by cutting off the desired lengths from a 
band. 
The plate, the band, or the strip is preferably 3 to 9 mm. thick. 
A particular embodiment of the present invention relates to a process for 
the production of such a pesticide. The process is characterized in that a 
layer comprising a mixture of the at least one finely divided metal 
phosphide and the water-insoluble organic solid substance is applied to a 
layer of the fibrous substance, the composite then being heated to such a 
high temperature and for so long that a molded body is produced from the 
thermoplastic water-insoluble organic substance and the at least one 
phosphide and this molded body becomes joined to the layer of the fibrous 
substance, the thermoplastic organic substance hardening upon being 
allowed to cool to room temperature. 
Thus, the whole may, for example, be heated at a temperature of from 
approximately 140.degree. to 160.degree. C. and for a time of from 
approximately 3 to 8 minutes, and then allowed to cool. 
If it is desirable to produce a layered body which is coated with a fibrous 
substance on two sides, then a second layer of a fibrous substance is 
rolled onto the molded body while it is warm and plastic. 
The process may be carried out continuously or discontinuously. 
The pesticides of the present invention may be used to fill, with gas, 
rooms where there may even be, for example, cereals, tobacco, foodstuffs, 
or luxury foodstuffs. The hydrogen phosphide which is thus developed 
destroys all pests such as insects or rodents.

The present invention will now be further described with reference to the 
following Example. 
EXAMPLE 
A layer, approximately 7 mm. thick, of aluminum phosphide having particle 
diameters of 10 to 300.mu. and granulated polyvinyl acetate in the weight 
ratio of 80 parts of polyvinyl acetate, containing plasticizers, to 100 
parts of aluminum phosphide is applied to a layer, 0.2 mm. thick, of 
non-woven fabric comprising cellulose fibers. The composite is heated to 
160.degree. C. for approximately 5 minutes by means of an infra-red 
radiator. 
A second layer of the non-woven fabric, which serves as the under layer, is 
rolled onto the surface of the molded body thus produced while it is still 
hot, by means of a roller heated to approximately 150.degree. C. and for a 
period of approximately 1 minute. Upon cooling to room temperature, a 
plate which is 4 mm. thick is produced. 
When this molded body is brought into an atmosphere of 65 percent relative 
humidity at a room temperature of 20.degree. C., gas is released from the 
phosphide contained in the composition at the rate of 1.2 percent of the 
total amount of phosphide after two hours, 9.5 percent after five hours 
and 21 percent after ten hours, the greatest possible release of gas being 
achieved after seventy-two hours. At the end of this time, the aluminum 
phosphide contained in the pesticide has been decomposed to the extent of 
approximately 96 percent with consequent evolution of phosphide to the 
same extent. 
In the same manner, similar advantageous products and results are obtained 
when: the phosphide is magnesium phosphide or a mixture of aluminum 
phosphide and magnesium phosphide; the organic solid substance is 
polyethylene, polypropylene, polyvinyl chloride, hard paraffin, polyvinyl 
acetate, polystyrene, copolymerisates of vinyl acetate and vinyl chloride, 
copolymerisates of polyethylene, polystyrene, polypropylene, polyvinyl 
chloride and other polyvinyl compounds, or similar compounds with other 
copolymerizable material; the fibrous substance comprises, partly or 
completely, cellulose fibers such as cotton fibers, wood pulp, or 
regenerated cellulose, a fabric or a felt; the material is in the form of 
a strip or band instead of a plate; the strip, band, or plate varies from 
3 to 9 mm. in thickness; the phosphide particles are up to 300.mu. 
particle diameter; and especially when the water-insoluble organic solid 
substance is present in an amount of 60 to 120 parts per about 100 parts 
by weight of the metal phosphide. 
The present invention will now be further illustrated by way of the 
accompanying drawing which shows, on an enlarged scale, a section through 
a pesticide according to the present invention. 
In the FIGURE, particles 2 of aluminum phosphide are embedded in a plate 1 
comprising polyvinyl acetate. On the surface there is a non-woven fabric 3 
comprising cellulose fibers, the fibers of which extend to a portion of 
the embedded phosphide particles. 
It is to be understood that the invention is not to be limited to the exact 
details of operation or exact compounds, compositions, methods, or 
procedures shown and described, as obvious modifications and equivalents 
will be apparent to one skilled in the art.