Flammable barrier wrap for solid fuel/firestarter composition

A novel package for a solid or gelled heating fuel comprises a flammable plastic film wrapped around the shaped fuel. Preferably, the plastic film is nonporous to prevent sublimation of the fuel.

BACKGROUND OF THE INVENTION 
This invention relates to a novel means of packaging solid or gelled 
heating fuels. 
Solid or gelled heating fuels have wide potential application as 
convenient, easily handled and comparatively safe heat sources. Gelled 
heating fuels in portable form can be employed in civilian uses such as 
camping, outdoor cooking of all sorts, fire-starting, emergency heat and 
light supplies, and the like. Gelled heating fuels are also essential for 
military use, including the heating of field rations, etc. 
The most widely accepted forms of gelled heating fuels at present are ethyl 
alcohol gelled with a metallic soap and trioxane formed from compaction of 
powdered trioxane with or without compaction aids such as magnesium 
stearate and an organic binder, or a trioxane melt. Compacted or melted, 
and then molded or otherwise shaped, gelled heating fuel such as trioxane 
in the shape of pellets is advantageous in view of the lack of toxicity 
and ease of ignition of this fuel. The low luminosity of trioxane fuel is 
especially useful for military applications. However, gelled heating fuels 
have not proven to be fully satisfactory. Trioxane fuel pellets and the 
like have a rather low caloric value on the order of 4,000 kcal/kg. 
Moreover, although the low luminosity of trioxane and other oxygenated 
hydrocarbon gelled fuels may be advantageous in military field 
applications, the rather non-luminous flame is not easily detected and may 
lead to accidental burns and fires. 
In accordance with the invention described in copending, commonly assigned 
U.S. patent application Ser. No. 836,792, filed Mar. 6, 1986, it is 
possible to increase the luminosity of the flame obtained from solid 
trioxane fuel by adding thereto certain non-toxic sodium salts. 
Additionally, copending, commonly assigned U.S. patent application Ser. 
No. 836,889, filed Mar. 6, 1986, describes increasing the caloric content 
of trioxane fuels by adding thereto dialkyl ethers of alkanediols. By such 
improvements to trioxane heating fuels it is believed that these fuels 
will be more readily accepted as a convenient and safe portable energy 
source. 
While the heat content of gelled fuels can be increased and the luminosity 
of the flame increased for improved safety such as just described for 
trioxane fuel, many gelled fuels are still particularly disadvantageous 
because such fuels readily evaporate, i.e, sublime, from the containers 
under normal atmospheric conditions. Accordingly, gelled fuels which are 
highly volatile must be kept in tightly sealed containers to prevent 
excessive loss by sublimation. A typical container or package for a solid 
or gelled fuel pellet comprises a metal film, such as aluminum foil 
wrapped tightly around the fuel pellet. Thus, to use the fuel, the metal 
foil must be unwrapped and the unwrapped fuel subsequently ignited. 
Unwrapping the tightly wrapped package prior to using the gelled heating 
fuel is an inconvenience. This lack of convenience is more readily 
apparent in military field applications where time, safety, and ease of 
comfort are important considerations. 
A known method of packaging solid or gelled fuels, in particular, starter 
or decorative logs for fireplace use, comprises wrapping the log-shaped 
fuel in a combustible paper wrapper. To use such fuels, the paper wrapper 
is ignited, such as along an edge of the wrapper, and the solid log-shaped 
fuel is subsequently ignited by the flame from the packaging. The paper 
packaging is not removed prior to use. As discussed above, many gelled 
fuels and, in particular, gelled oxygenated hydrocarbon fuels evaporate 
from the containers even under normal atmospheric conditions. Accordingly, 
a paper covering or package for highly volatile fuels would be wholly 
unsatisfactory because such porous coverings would not prevent sublimation 
of the fuel. Moreover, it is unlikely that a paper package could be 
tightly wrapped around a gelled fuel pellet and the like to hermetically 
seal the fuel pellet to prevent sublimation. 
It would be an obvious advantage if readily sublimable solid or gelled 
fuels could be hermetically packaged in a flammable wrapper. Accordingly, 
it is an object of the present invention to provide a combustible wrapper 
for solid or gelled fuels to eliminate the need for unwrapping the package 
to ignite the solid fuel. Another object is to package highly volatile 
solid or gelled fuels in a combustible wrapper which is capable of 
hermetically sealing the fuel to prevent sublimation. 
These and other objects, aspects, and advantages of the invention will be 
readily apparent to those of ordinary skill in the art on consideration of 
the following description of the invention. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, solid fuels in the form of 
tablets, pills, or the like are packaged in flammable, nonporous plastic 
films. The use of a flammable plastic film to package the solid fuel 
eliminates the necessity of unwrapping the package prior to igniting the 
fuel. Ignition of the solid fuel is simply initiated by igniting the novel 
package. The flame from the burning package subsequently ignites the solid 
fuel and both the package and fuel burn completely. It is important that 
the plastic film be flammable or capable of supporting a flame and does 
not merely melt away from a source of flame. 
Besides being flammable, the use of plastic films as packaging for solid 
fuels is advantageous because such films can be produced as nonporous 
materials and are sufficiently flexible to tightly cover the shaped fuel. 
Moreover, plastic films, in particular, thermoplastic films can be sealed 
by heat such as by heat fusion or ultrasonic welding. Plastic films can 
thus form a hermetic barrier around the solid fuel and prevent losses by 
sublimation from highly volatile fuels.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is applicable to any of the solid or gelled heating fuels 
which are available. Such fuels can be formed from pure melts of the fuel 
which is then shaped and cooled, by gelling normally liquid fuels with the 
use of gelling agents such as metallic soaps and compacting normally solid 
powdered fuel. Additionally gelled fuels may be formed from liquid 
hydrocarbons and oxygenated hydrocarbons which are gelled in a polymeric 
matrix such as disclosed in U.S. Pat. No. 3,355,269, which patent is 
herein incorporated by reference. Thus, among the oxygenated hydrocarbons 
which can be gelled include ethyl acetate; 1,4-dioxane; 1,3-dioxolane; 
diethyl carbonate; diethyl ether of ethylene glycol; dimethyl ether of 
diethylene glycol; trioxane; propyl acetate; butyl acetate; amyl acetate; 
hexyl acetate; methyl propionate; methyl butyrate; ethyl formate; diethyl 
ether of diethylene glycol; diethyl formyl; dimethyl acetal; and the like. 
Liquid hydrocarbons which may be gelled include saturated hydrocarbons 
preferably not having more than 10 carbon atoms and which have a boiling 
point of at least about 35.degree. C. to avoid excessive losses by 
evaporation. Such examples of preferred liquid hydrocarbons include 
heptane, octane, cyclohexane, methyl cyclohexane, dimethyl cyclohexane, 
and gasoline fractions of saturated aliphatic and fully hydrogenated 
cycloaromatic compounds. Preferred heating fuels include normally liquid 
hydrocarbons which are gelled in some manner and meltable fuels such as 
trioxane which can be formed from a pure melt or from compacting the dry 
solid with compaction aids such as metal stearates and organic binders. 
The particular shape of the gelled fuel is not critical. Thus, gelled fuel 
in the shape of bars, pellets, candles, etc. are useful examples. As can 
readily be determined, the gelled fuel can be shaped to fill various 
domestic needs. For example, for outdoor use such as in camping, the 
gelled fuel can be shaped in pellet form for use in cooking such as 
heating water or other prepared foods. Additionally the gelled fuel can be 
in the shape of cylinders or candle-like form to provide heat and/or 
light. Similarly, the fuel can be shaped for use in the household such as 
in candle form to provide light as well as in the larger log form as a 
starting log for fireplace use or for providing a decorative fire for 
light and heat. A preferred form of gelled heating fuels is as a portable 
heat source in which the gelled fuel is in the shape of 10 to 30 gram 
pellets which can be used such as in the outdoors for camping as well as 
for the heating of field rations in military applications. 
The particular chemical composition of the plastic film which forms the 
barrier wrap packaging of the present invention can be any of many 
synthetic resins which are flammable. By flammable is meant that the 
plastic should support a flame and not merely melt away from a source of 
flame and that it ignites easily and burns rapidly. Additionally, the 
plastic film is preferably substantially nonporous so as to be capable of 
preventing excessive evaporation of those gelled fuels which readily 
sublime under normal atmospheric conditions, i.e., temperatures of about 
25.degree. C. Among examples of useful plastic films include polyacetal 
resins, cellosics, including cellulose nitrate, cellulose butyrate, 
cellulose acetate and cellulose proprionate. 
Polyacetal engineering resins, i.e., oxymethylene polymers, are the 
preferred material for forming the flammable barrier wrap in accordance 
with the present invention. The oxymethylene polymer which can be used to 
form the barrier wrap of the present invention is well known in the art. 
The polymers are characterized as having recurring oxymethylene groups or 
units, i.e., --CH.sub.2 O--. The term oxymethylene polymer as used herein 
is intended to include any oxymethylene polymer having --CH.sub.2 O-- 
groups comprising at least about 50 percent of the recurring units, for 
example, homopolymer, copolymers, terpolymers and the like. 
Typically, the homopolymers are prepared by the polymerization of anhydrous 
formaldehyde or by the polymerization of trioxane which is a cyclic trimer 
of formaldehyde. For example, high molecular weight polyoxymethylenes have 
been prepared by polymerizing trioxane in the presence of certain fluoride 
catalysts such as antimony fluoride and may also be prepared in high 
yields and at rapid reaction rates by the use of catalysts comprising 
boron fluoride coordinate complexes with organic compounds, as described 
in application Ser. No. 691,143, filed Oct. 21, 1957, by Hudgin and 
Berardinelli. 
The homopolymers are usually stabilized against thermal degradation by 
end-capping or the incorporation therein of stabilizer compounds such as 
described in U.S. Pat. No. 3,133,896 to Dolce and Berardinelli. 
Oxymethylene polymers that are particularly adapted for use in the barrier 
wrap of the present invention are oxymethylene copolymers, which may be 
prepared as described in U.S. Pat. No. 3,027,352 of Walling et al by 
copolymerizing, for example, trioxane with any of various cyclic ethers 
having at least two adjacent carbon atoms, e.g., ethylene oxide, 
dioxolane, and the like. 
Especially suitable oxymethylene copolymers which may be used in the 
barrier wrap of the present invention usually possess a relatively high 
level of polymer crystallinity, i.e., about 70 to 80 percent. These 
preferred oxymethylene copolymers have repeating units which consist 
essentially of (a) --OCH.sub.2 -- groups interspersed with (b) groups 
represented by the general formula: 
##STR1## 
wherein each R.sub.1 and R.sub.2 is selected from the group consisting of 
hydrogen, lower alkyl and halogen-substituted lower alkyl radicals, each 
R.sub.3 is selected from the group consisting of methylene, oxymethylene, 
lower alkyl and haloalkyl-substituted methylene, and lower alkyl and 
haloalkyl-substituted oxymethylene radicals, and n is an integer from zero 
to three inclusive. 
Each lower alkyl radical preferably has from one to two carbon atoms, 
inclusive. The --OCH.sub.2 -- units of (a) constitute from about 85 to 
about 99.9 percent of the recurring units. The units of (b) may be 
incorporated into the copolymer during the step of copolymerization to 
produce the copolymer by the opening of the ring of a cyclic ether having 
adjacent carbon atoms, i.e., by the breaking of an oxygen-to-carbon 
linkage. 
In general, the cyclic ethers employed in making the preferred oxymethylene 
copolymers are those represented by the general formula: 
##STR2## 
wherein each R.sub.1 and R.sub.2 is selected from the group consisting of 
hydrogen, lower alkyl and halogen-substituted lower alkyl radicals, and 
each R.sub.3 is selected from the group consisting of methylene, 
oxymethylene, lower alkyl and haloalkyl-substituted methylene, and lower 
alkyl and haloalkyl-substituted oxymethylene radicals, and n is an integer 
from zero to three inclusive. Each lower alkyl radical preferably has from 
one to two carbon atoms, inclusive. 
The preferred cyclic ethers used in the preparation of the preferred 
oxymethylene copolymers are ethylene oxide and 1,3-dioxolane, which may be 
represented by the formula: 
##STR3## 
wherein n represents an integer from zero to two, inclusive. Other cyclic 
ethers that may be employed are 1,3-dioxane, trimethylene oxide, 
1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide and 
2,2-di-(chloromethyl)-1,3-propylene oxide. 
The preferred catalyst used in preparing the desired oxymethylene 
copolymers is the aforementioned boron trifluoride as discussed in the 
previously identified Walling et al patent. Reference is made to this 
patent for further information concerning the polymerization conditions, 
amount of catalyst employed, and the like. 
The oxymethylene copolymers produced from the preferred cyclic ethers have 
a structure composed substantially of oxymethylene and oxyethylene groups 
in a ratio of from about 6 to 1 to about 1000 to 1. 
With respect to the oxymethylene terpolymer, it may be prepared, for 
example, by reacting trioxane and a cyclic ether and/or cyclic acetal such 
as in the preparation of the oxymethylene copolymer, with a third monomer 
which is a bifunctional compound such as a diglycide of the formula: 
##STR4## 
wherein Z represents a carbon-to-carbon bond, an oxygen atom, an 
oxy-alkoxy of 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms, and 
which may be an oxycycloalkoxy of 4 to 8 carbon atoms, or an 
oxy-poly(lower alkoxy), preferably of 2 to 4 recurring groups each with 1 
to 2 carbon atoms, for example, ethylene diglycide, diglycidyl ether and 
diethers of 2 mols of glycide and 1 mol of formaldehyde, dioxane or 
trioxane, or diethers of 2 mols of glycide and 1 mol of an aliphatic diol 
with 2 to 8 carbon atoms, advantageously 2 to 4 carbon atoms, or a 
cycloaliphatic diol with 4 to 8 carbon atoms. 
Examples of suitable bifunctional compounds include the diglycidyl ethers 
of ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-diol, 
1,2-propane-diol, cyclohexane-1,4-diol and 
2-dimethyl-4-dimethyl-cyclobutane-1,3-diol, with butanediol diglycidyl 
ethers being most preferred. 
Generally, in preparing the terpolymer of trioxane, cyclic ether and/or 
cyclic acetal and at least one bifunctional diglycide compound, a ratio of 
from 99.89 to 89.0 weight percent trioxane, 0.1 to 10 weight percent of 
the cyclic ether and/or cyclic acetal, and 0.01 to 1 weight percent of the 
bifunctional compound is preferred, with the percentage figures being 
based on the total weight of monomers used in forming the terpolymer. The 
terpolymers thus obtained are characterized as being essentially white and 
having a particularly good extrudability. 
It is within the ambit of the present invention to use oxymethylene 
polymers that include, if desired, plasticizers, formaldehyde scavengers, 
lubricants, antioxidants, fillers, colorants reinforcing agents, light 
stabilizers, pigments, other stabilizers, and the like. 
The synthetic resin is converted into a film or sheet by conventional 
molding techniques such as by extrusion. The film or sheet which is formed 
into the barrier wrap of the present invention will have a thickness of 
from about 0.5 micron to about 200 microns. The package is formed by 
simply wrapping the film around the gelled fuel and sealing the film 
around the fuel composition by heat fusing or ultrasonic welding of the 
film surfaces. 
The flammable, nonporous wrap for the solid or gelled fuel composition can 
be structured so as to improve the ease of use of the package. For 
example, FIG. 1 illustrates an embodiment of the novel packaging of the 
present invention wherein one or more edges of the flammable film extend 
past the plane of the fuel and serve as a point or points of ignition of 
the packaged fuel. Thus, in FIG. 1, the solid or gelled fuel is indicated 
by reference numeral 1 and the flammable plastic packaging material 
indicated by reference numeral 2. The plastic film 2 is sealed around fuel 
1 at fusion points 3 such as by heat fusion, ultrasonic welding, and the 
like. At least one edge 4 of plastic wrap 2 freely extends beyond the mass 
of fuel 1 so as to serve as an ignition point on the packaged fuel. Once 
edge 4 is ignited, the full film ignites which subsequently ignites the 
solid fuel and both solid fuel 1 and plastic film 2 burn. 
An alternative package is shown in FIG. 2 in which the solid or gelled fuel 
10 is sealed between a bottom container 11 such as formed from a metal 
foil including aluminum foil and a top covering 12 which is formed from 
the flammable plastic film as previously described. The plastic film can 
be sealed to the metallic foil at points 13 such as by heat fusion or 
ultrasonic welding as described for the embodiment in FIG. 1. Again, at 
least one edge 14 of film 12 should freely extend beyond the mass of mass 
of fuel 10 for ease of igniting the packaged fuel. In this embodiment, the 
metal foil 11 serves as a support for the burning fuel. The support can 
further act as a heat reflector if folded around the pellet of fuel in a 
cup shape to cover the bottom and a plurality of the sides of the fuel as 
shown in FIG. 2 to concentrate the flame and heat from the burning fuel.