Oxygen absorbent

An oxygen absorbent comprising (a) metal halide-coated metal powder having at least one metal halide coated on the surface of at least one metal powder, the amount of metal halide coated being in the range of from about 0.001 part to about 10 parts by weight per 100 parts by weight of the metal powder, and the water content of the metal halide-coated metal powder being less than 1% by weight on the basis of total weight of the metal halide-coated metal powder an (b) a water-containing material and a process for producing the same are disclosed.

This invention relates to an oxygen absorbent comprising a metal 
halide-coated metal powder and a water-containing material and also 
relates to a process for producing the same. 
In order to preserve foodstuffs, such as vegetables, fish, shellfish, 
meats, processed foodstuffs, such as potato chips, cakes, peanuts, etc., 
and so on, it is necessary to prevent the foodstuffs from getting moldy 
and from putrefying. Prior art methods have used freezer storage, cold 
strage, vacuum packaging and replacing the gas present in the inner part 
of packaging by an inert gas for preventing foodstuffs from getting moldy 
and putrefying. Additives, such as antioxidant, have been used for 
preserving foodstuffs. Recently, governments have started to regulate the 
use of additives for food, since it is realized that some additives are 
injurious to humans. The freezer storage method requires large-scale 
apparatus and complicated operation, so the freezer storage method is 
costly. 
Molds or eumycetes, bacterias and higher organisms such as insects tend to 
disturb preservation of foodstuffs. These mold eumycetes, bacterias and 
insects live and grow in the presence of oxygen and cause putrefaction and 
change in quality of foodstuffs. 
Therefore, if oxygen can be selectively removed from the atmosphere in 
which the foodstuffs are packed, the problem of putrefaction and change in 
quality of foodstuff can be overcome, and it will become possible to 
preserve foodstuffs for a long time. 
Attempts have been made for producing such an oxygen absorbent. 
Japanese Pat. No. 19729/1972 discloses the use of an oxygen absorbent 
comprising hydrosulfite, calcium hydroxide, sodium bicarbonate, activated 
carbon and optionally water to preserve vegetables by removing oxygen from 
atmosphere. 
U.S. Pat. No. 2,825,651 proposes a process for preparing an oxygen 
absorbent comprising mixing a finely divided sulfite and a finely divided 
metal salt, at least one of the two compounds having water of 
crystallization and compression-pelletizing the mixture in order to 
increase the rate of the oxidation of sulfite. 
British Pat. No. 553,991 discloses the step of forming pellets comprising 
carbon and highly activated iron powder obtained by hydrogen treatment, 
followed by absorbing oxygen in a container using the resulting pellets. 
Since iron powder contained in the pellets is highly active, the iron 
intensely reacts with oxygen in the container to remove oxygen therein. 
There is the possibility of fire in case of using such highly active iron 
powder. The process of BP No. 553,991 is dangerous. 
Five of the present inventors have carried out wide research to find an 
oxygen absorbent having no such danger while is safe to handle and 
effective. As a result, they found a highly flowable oxygen absorbent 
comprising a metal powder coated with a definite amount of a metal halide 
and having a minor amount of water and proposed the absorbent (refer to 
U.S. Ser. No. 816,134). When the oxygen absorbent is placed in a closed 
container with foodstuffs, it absorbs oxygen in the presence of water 
vapour evaporated from the foodstuffs. However, the absorbing ability of 
the oxygen absorbent depends upon the amount of water vapour evaporated 
from the foodstuffs. So, when the absorbent is used with foodstuffs from 
which little water vapor is generated, the oxygen-absorbing rate of the 
absorbent is slow. 
SUMMARY OF THE INVENTION 
The present inventors have carried out research to find oxygen absorbent to 
overcome such shortcoming. 
Therefore, an object of this invention is to provide an oxygen absorbent 
overcoming the prior art disadvantages, namely, danger and low oxygen 
absorbing rate in the absence of water. 
This invention relates to an oxygen absorbent comprising (a) a metal 
halide-coated metal powder having at least one metal halide coated on the 
surface of at least one metal powder, the amount of metal halide coated 
being in the range of from about 0.001 part to about 10 parts by weight 
per 100 parts by weight of the metal powder, and the water content of the 
metal halide-coated metal powder being less than 1% by weight on the basis 
of total weight of the metal halide-coated metal powder (sometimes 
hereinafter referred to as component (A)) and (b) a water-containing 
material (sometimes hereinafter component (B)). The absorbing ability of 
the present oxygen absorbent is independent of the amount of water vapour 
generated from the foodstuff. So, the oxygen-absorbing rate of the present 
oxygen absorbent is always rapid. 
In general, it is preferred that an oxygen absorbent have the following 
properties: 
(a) creating no danger from hydrogen-evolution, 
(b) being high fluidity to being capable of being packed by automatic 
packaging machine, 
(c) not losing the effectiveness of the oxygen absorbent during the 
preparation of the absorbent. 
Component (A) alone does not exhibit oxygen absorbing ability. The present 
oxygen absorbent exhibits oxygen absorbing ability, only after component 
(A) contacts component (B). Therefore, component (A) must not contact 
component (B), before packing components (A) and (B) in a bag made of an 
air-permeable material. 
As soon as components (A) and (B) are packed in the air-permeable bag, the 
bag must be packed in a gas-non-permeable bag. In general, many bags 
containing components (A) and (B) are packed in a gas-non-permeable bag. 
The gas-non-permeable bag is stored, shipped and sold. Alternatively, as 
soon as components (A) and (B) are packed in an air-permeable bag, the bag 
may be packed with foodstuffs to be stored for a long time. 
This invention also relates to a process for producing an oxygen absorbent 
comprising component (A) and component (B), characterized packing 
component (A) and component (B) in an air-permeable bag so that component 
(A) does not contact component (B) before packing them. 
DETAILED DESCRIPTION OF THE INVENTION 
The term "oxygen absorbent" in the specification and the claim means an 
agent for removing or absorbing oxygen. 
The metal powders which can be employed in the present invention may 
include copper powder, iron powder, zinc powder, and mixtures thereof; 
iron powder is preferred. Suitably the metal powder has size of less than 
10 mesh, preferably 50 mesh. The metal powders may be electrolytic metal 
powders, reduced metal powders, atomized metal powders and stamped metal 
powders. Reduced iron powder, electrolytic iron powder and atomized iron 
powder are preferred. The metal does not need to have high purity. The 
metal may contain impurities, as long as the object of this invention can 
be achieved. The mesh screen employed was Tyler Standard Sieve mesh. 
The metals constituting the metal halides may be metal selected from the 
group consisting of alkali metals, alkali earth metals, copper, zinc, 
aluminum, tin, manganese, iron, cobalt and nickel. In order to avoid the 
generation of hydrogen, alkali metals, such as lithium, sodium potassium 
and alkali earth metals, such as calcium, magnesium and barium are 
preferred. The halogen constituting the metal halide may be chlorine, 
bromine or iodine. Chlorine is preferred. 
The amount of the metal halide to be coated on the surface of the metal 
powder is in the range of from about 0.001 part to about 10 parts by 
weight per 100 parts by weight of metal powder, and about 0.01 part to 
about 5 parts of the metal halide is preferred. When the amount of the 
metal halide coated is less than 0.001 part by weight, the absorbing 
ability of oxygen is lowered. When the amount of the metal halide coated 
is more than 10 parts by weight, much water is likely to migrate into the 
oxygen absorbent due to deliquescence of the metal halide. Therefore, the 
metal halide penetrates through the packaging material into foodstuffs and 
the evolution of hydrogen increases. 
The metal powder coated with a metal halide and a binder and/or an alkaline 
material may be used as component (A) in order to improve its 
oxygen-absorbing ability and to prevent the evolution of hydrogen. 
Suitably, the binders may include water soluble polymeric compounds, such 
as sodium alginate, carboxymethyl cellulose (CMC), hydroxymethyl 
cellulose, methyl cellulose, ethyl cellulose, propyl cellulose, sodium 
carboxymethyl cellulose, starch, polyhydric alcohols, polyvinyl alcohol 
(PVA), saccharides, tragacanth gum. The amount of the binder employed may 
be in the range of from about 0.01 part to 10 parts by weight per 100 
parts by weight of the metal powder, and about 0.1 to about 2 parts by 
weight of the binder is preferably employed. 
The alkaline materials may include hydroxides, carbonates, sulfites, 
thiosulfates, dibasic phosphates, tribasic phosphates, polyphosphates, or 
organic acid salts of alkali metals or alkaline earth metals. Sodium 
hydroxide, sodium carbonate, sodium sulfite, sodium thiosulfate, tribasic 
sodium phosphate, dibasic sodium phosphate, potassium hydroxide, potassium 
carbonate, potassium sulfite, tribasic potassium phosphate, dibasic 
potassium phosphate, calcium hydroxide, magnesium hydroxide, calcium 
carbonate, sodium citrate, sodium succinate, sodium propionate and sodium 
fumarate are preferred; and magnesium hydroxide and sodium thiosulfate are 
most preferred. The amount of the alkaline material employed may be in the 
range of from about 0.01 part to about 10 parts by weight, preferably from 
about 0.1 part to about 2 parts per 100 parts of the metal powder. 
The term "water content" in the specification and the claims means content 
of free water, and excludes content of water of crystallization. Component 
(A) of this invention has less than 1% of free water on the basis of the 
total weight of component (A), preferably less than 0.5% by weight of 
water, and more preferably less than 0.2% by weight of water. 
Component (A) of this invention is prepared in the following way: 
The metal powder is mixed with a solution of the metal halide and 
optionally the binder and/or the alkaline material, thereby coating the 
metal halide and optionally the binder and/or the alkaline material on the 
surface of the metal powder; and the resulting coating is dried until the 
water content thereof amounts to less than 1% by weight based on the total 
weight of the absorbent. 
The solution of the metal halide may be a conventional aqueous solution 
thereof. The metal halide may be dissolved in a mixture of water and 
another solvent. The halide concentration may be suitably selected from 
any concentration up to saturated concentration. 
The metal powder is mixed with the solution of the metal halide until the 
halide is coated on the powder particle. 
When the metal powder is coated with the metal halide as well as the binder 
and/or the alkaline material, the order of the coating is not critical. 
The metal powder may be coated with these materials simultaneously or 
successively. The mixing process and the coating process are not critical. 
Conveniently, the mixture of the metal powder and the solution of the 
metal halide and other component may be dried as it is, or after the 
mixture is filtered, the precipitate may be dried. 
Preferably the metal powder is mixed with the solution of the metal halide 
and optionally the binder and/or the alkaline material containing a minor 
amount of water, and the resulting mixture is dried. The coating is dried 
until the water content amounts to less than 1%, preferably less than 
0.5%, more preferably less than 0.2% and most preferably is substantially 
zero. When the water content is more than 1%, the resulting absorbent has 
poor fluidity, it is difficult to pack the absorbent, it penetrates 
through the packaging material and more hydrogen is evoluted. 
The drying process is not critical. For example, the coating may be dried 
at one atmospheric pressure, at a reduced pressure, or in or inert gas 
atmosphere. In order to shorten the drying time, the metal halide, and 
optionally the binder and/or the alkaline material are dissolved in the 
mixture of water and a hydrophilic solvent, such as an alcohol. 
The water-containing material is one from which water vapor is evaporated 
or generated. In general, materials having water content of more than 1% 
by weight and equilibrium humidity of more than 30% are preferred. For 
example, water-containing materials include water-containing particulate 
materials, compounds having water of hydration and natural materials. 
Water-containing particulate is preferred from the view point of 
controlling the amount of water vapor evaporated from the water-containing 
material. 
Water-containing particulate material means particulate material 
impregnated with water or water-containing humidity-controlling agent. The 
particulate materials include diatomaceous earth, perlite, zeolite, 
activated alumina, silicagel, activated carbon, activated clay, sand, 
pebble and mixtures thereof. 
The term "particulate material" generally means material having particle 
size of 0.5 mm to 10 mm. 
The humidity-controlling agents include water and an aqueous solution of 
certain materials having equilibrium humidity of more than 30%. The 
aqueous solution is the one in which a hydrophilic inorganic or organic 
compound is dissolved. Aqueous solutions of an inorganic compounds or 
salts are preferred. Examples of inorganic compounds include NaCl, NaBr, 
CaCl.sub.2, MgCl.sub.2, KHSO.sub.4, (NH.sub.4).sub.2 SO.sub.4, 
Ca(NO.sub.3).sub.2, Mg(NO.sub.3).sub.2, K.sub.2 HPO.sub.4, Na.sub.2 
CO.sub.3, K.sub.2 CO.sub.3 and the like. Chlorides of alkaline earth 
metals and alkali metals, such as NaCl, NaBr, CaCl.sub.2 and MgCl.sub.2, 
and phosphates, such as K.sub.2 HPO.sub.4 are preferred. NaCl and 
MgCl.sub.2 are more preferred. Saturated aqueous solution of NaCl or MgCl 
are preferred. Examples of organic compounds include polyvalent alcohols, 
such as glycerin and ethylene glycol, organic salts, such as sodium 
acetate and magnesium acetate; and oxalic acid. Aqueous solutions if 
different equilibrium humidity can be obtained by adjusting concentration 
of the compound. 
A process for impregnating the particulate material with water or the 
aqueous solution is not critical. For example, a process for mixing the 
particulate material with water or the aqueous solution in such an amount 
that the flowability of particulate material does not become worse; and a 
process for immersing the particulate material in the aqueous solution or 
water, followed by removing the liquid from the surface of the material 
through filtration or centrifugal separation may be used. In order to 
improve the flowability of the water impregnated particulate material, the 
wet surface of the material may be dried with air or warm air or may be 
coated with finely divided filler. The finely divided fillers include 
gypsum, baked gypsum, activated carbon, calcium carbonate, magnesium 
hydroxide and the like having particle size of less than 100 mesh. 
When the water-containing material obtained by impregnating particulate 
material with water, followed by coating the surface of the material with 
finely divided filler is used as component (B), an oxygen absorbent having 
good flowability and capable of being packed automatically can be 
obtained. 
Examples of Compounds having water of hydration include inorganic 
compounds, such as oxides, hydroxides, sulfides, halides, sulfates, 
sulfites, thiosulfates, nitrates, borates, phosphates, hydrogenphosphates, 
pyrophosphates, hydrogenpyrophosphates, carbonates, hydrogencarbonates, 
silicate, metasilicate, chromates, iodates, bromates, trimolybdates and 
tungstates, ammonium salts of metals; organic compounds, such as organic 
acids and organic acid salts; complexes; and double salts having water of 
hydration in its crystal structure. Compound(s) having water of hydration 
with a desired equilibrium humidity can be obtained by combinating two or 
more compounds having water of hydration and/or by selecting the amount of 
the compounds. 
Natural materials include rice and beans. 
The ratio of component (A) to compound (B) is not critical. The ratio is 
determined from the view points of the oxygen-absorbing rate, the amount 
of oxygen absorbed and economy. In general, the ratio is preferably 
determined so that the oxygen absorbent contains more than 0.1 part by 
weight of water, more preferably from 1 to 100 parts by weight of water 
per 100 parts by weight of metal powder. It is understood that the oxygen 
absorbent may contain much water. 
Even when the present oxygen absorbent is used with foodstuffs from which 
little water vapor is evaporated, the oxygen-absorbing rate of the 
absorbent is rapid. 
When particulate material impregnated with a humidity-controlling agent in 
which a salt or a polyvalent alcohol is dissolved is used as component 
(B), the oxygen-absorbing rate of the resulting oxygen absorbent can be 
adjusted. When an oxygen absorbent having an equilibrium humidity near 
that of the foodstuffs is used, the amount of water migrated into the 
foodstuffs can be made small. 
The oxygen absorbent made according to the present process loses little of 
its effectiveness without need for purging with nitrogen.

The present invention is further illustrated by the following Examples and 
Comparative Examples. However, this invention should not be limited by 
these examples and comparative examples. The percent and parts in the 
Examples are based on weight unless otherwise specified. 
EXAMPLE 1 
To 100 gr of Fe powder was added 2 ml of a 20% aqueous solution of NaCl. 
The resulting mixture was mixed thoroughly and dried at 40.degree. C. 
under reduced pressure of 40 mm Hg until its water content was 
substantially to zero to obtain component (A). To 100 gr of gypsum powder 
was added 20 ml of water. The resulting mixture was mixed sufficiently to 
obtain component (B). Components (A) and (B) were mixed in a nitrogen 
atmosphere. 6 Gr of the mixture was placed in a perforated polyethylene 
film-laminated paper bag of 5 cm.times.5 cm in a nitrogen atmosphere. The 
bag was placed in a 1 liter sealed container. After 24 hours, the oxygen 
concentration in the container was 0.0%. 
COMATIVE EXAMPLE 1 
3 Gr of component (A) employed in Example 1 was placed in the bag employed 
in Example. The bag was placed in a 1 liter sealed container. After 24 
hours, the oxygen concentration in the container was 20.89%. Component (A) 
did not absorb any oxygen at all. 
EXAMPLE 2 
To 100 gr of Fe powder was added 2 ml of a 20% aqueous solution of NaCl. 
The resulting mixture was mixed thoroughly and dried at 40.degree. C. 
under reduced pressure of 40 mm Hg until its water content was 
substantially zero to obtain component (A). 100 Gr of natural zeolite 
having 1-3 mm particle size was immersed in water. The zeolite was removed 
from water and was treated with centrifugal separator to obtain zeolite 
with 32.3% of water. The water-containing zeolite is called component (B). 
3 Gr of each components (A) and (B) was charged in a perforated 
polyethylene film-laminated paper bag of 5 cm.times.5 so that the two 
components did not contact before charging them. The bag was placed in a 1 
liter sealed container. After 24 hours, the oxygen concentration in the 
container was 0.0%. 
EXAMPLE 3 
To 100 gr Fe powder was added 20 ml of a 20% aqueous solution of 
MgCl.sub.2. The resulting mixture was mixed and dried at 80.degree. C. at 
reduced pressure of 20 mm Hg to obtain component (A). 100 Gr of 
particulate activated carbon with 0.5-2 mm size was mixed with 20 ml of 
water to allow the carbon to absorb the water. 10 Gr of gypsum was mixed 
with the water-containing activated carbon to coat the surface of the 
carbon with gypsum. The resulting gypsum-coated carbon is called component 
(B). 3 Gr of each of components (A) and (B) was charged in a perforated 
polyethylene film-laminated paper bag of 5 cm.times.5 cm so that the two 
components did not contact before charging them. The bag was placed in a 1 
liter sealed container. After 24 hours, the oxygen concentration in the 
container was 0.0%. 
EXAMPLE 4 
100 Gr of powdery pulp was impregnated with 20 ml of water. The mixture was 
mixed sufficiently. 1 Gr of finely divided silica was mixed with the 
mixture to obtain water-containing powder with very good flowability. The 
powder is called component (B). 3 Gr of each of the component (B) and the 
component (A) employed in Example 2 was charged in a perforated 
polyethylene film-laminated paper bag of 5 cm.times.5 cm so that the two 
components did not contact before charging them. The bag was placed in a 1 
liter sealed container. After 24 hours, the oxygen concentration in the 
container was 0.0%. 
EXAMPLE 5 
100 Gr of Na.sub.2 SO.sub.4.1OH.sub.2 O in particulate state was mixed with 
20 gr of Mg(OH).sub.2. The mixture was mixed sufficiently to obtain 
particles with high fluidity in which Mg(OH).sub.2 was coated on Na.sub.2 
SO.sub.4.1OH.sub.2 O particles. The powder is called component (B). 3 Gr 
each of the component (B) and the component (A) employed in Example 2 was 
charged in a perforated polyethylene film-laminated paper bag of 5 
cm.times.5 cm so that the two components did not contact before charging 
them. The bag was placed in a 1 liter sealed container. After 24 hours, 
the oxygen concentration in the container was 0.0%. 
EXAMPLE 6 
Unhulled rice particles with moiture content of 14% were employed as 
component (B). 2 Gr each of the component (B) and the component (A) 
employed in Example 3 was charged in a perforated polyethylene 
film-laminated paper bag of 5 cm.times.5 cm so that the two components did 
not contact before charging them. The bag was placed in a 500 ml sealed 
container. After 24 hours, the oxygen concentration in the container was 
1.2%, and after 48 hours, the oxygen concentration in the container was 
0.0%. 
EXAMPLE 7 
100 Gr of natural zeolite having 1-3 mm particle size was mixed with 40 gr 
of a saturated aqueous solution of NaCl,20 gr of Mg(OH).sub.2 to coat the 
magnesium hydroxide on the surface of the mixture. The resulting particles 
were allowed to stand in a sealed container to measure the equilibrium 
humidity thereof. The humidity was 78%. 2 Gr each of the particles and the 
component (A) employed in Example 2 were charged in a perforated 
polyethylene film-laminated paper bag so that the particles and the 
component (A) did not contact before charging them. The bag and sponge 
cake having water content activity of 0.78 were placed in a sealed 
container and allowed to stand therein. After 24 hours, the oxygen 
concentration in the container was 0.0%. After 30 days, the water content 
in the sponge cake did not change, no mold was observed on the cake, and 
quality of the cake was good. When the sponge cake alone was placed in the 
sealed container as a control test, after 10 days, growth of mold on the 
cake was observed. 
EXAMPLE 8 
100 Gr of natural zeolite having 1-3 mm particle size was mixed with 40 gr 
of a 80% glycerin aqueous solution. 20 Gr of gypsum was added to the 
mixture to coat the gypsum on the mixture. The resulting mixture was left 
standing in a sealed container to measure its equilibrium humidity. The 
humidity was 50%. 2 Gr each of the mixture and the component (A) employed 
in Example 3 was charged in a perforated polyethylene film-laminated paper 
bag so that the mixture and the component (A) did not contact before 
charging them. The bag and dried mushroom having water content activity of 
0.50 were placed in a sealed container and were left standing. After 90 
days, the amount of oxygen in the container was 0.0%. The water content of 
the mushroom did not change; and its original color and its quality were 
kept good. When the dried mushroom alone was left to stand under the same 
conditions as a control test, after 90 days, the color of the mushroom was 
changed to yellow.