JP4420870B2 - Oxygen absorbing composition - Google Patents

Description

  The present invention relates to an oxygen-absorbing composition or the like that is packaged when packaging food or the like and can prevent oxidative deterioration of contents. In particular, the present invention relates to an oxygen-absorbing composition containing aluminum as a main component of oxygen absorption.

  By using it in the form of a sachet packaged in food packaging, etc., the inside of the packaging is kept in an oxygen-free state, causing discoloration, fading, taste changes and other performance changes due to oxidative deterioration of the contents during storage. In recent years, oxygen absorbers that can be prevented have been frequently used. Many of these oxygen absorbents are, for example, those based on inorganic oxygen absorbing compositions such as iron powder and silicon fine powder, and those based on organic oxygen absorbing compositions such as ascorbic acid and unsaturated fatty acids. .

  By the way, since aluminum is not detected by a magnetic metal detector unlike iron, an oxygen absorbent mainly composed of aluminum has an advantage that it can be inspected for contamination of food after being sealed together with food. Moreover, since aluminum is relatively inexpensive and is the same material as an aluminum foil or aluminum vapor deposition film that is generally used as a packaging material, it has an advantage that it is easy to separate and dispose of garbage (easy disposal). Furthermore, the reaction activity with oxygen is also high. For these reasons, proposals have been made to use aluminum as a main component of an oxygen absorbent.

  However, it is well known that aluminum forms a dense oxide film on the surface by oxidation, and this oxide film has low permeability to oxygen and water. That is, oxygen absorption is limited to the surface only. Therefore, by adding a salt such as sodium chloride to aluminum (for example, see Patent Document 1) or by making a mixture of aluminum and an alkali metal oxide and / or alkaline earth metal (for example, see Patent Document 2). Attempts have been made to increase the oxygen absorption of aluminum even slightly. However, in any case, the amount of oxygen absorbed is very small compared to the equivalent iron, and the shape and properties of the aluminum particles are almost unchanged before and after oxygen absorption. Therefore, the situation is far from practical use of an oxygen absorbent mainly composed of aluminum.

In addition, since oxidation of aluminum occurs mainly in the presence of water, in an oxygen absorbent mainly composed of aluminum, aluminum is also consumed in side reactions that generate hydrogen in an aerobic state. There was a problem that efficiency decreased.
JP-A-3-137935 JP-A-9-117660

  An object of the present invention is to propose an oxygen-absorbing composition that can greatly improve the oxygen-absorbing capacity per unit mass of aluminum and that hardly generates hydrogen during use.

  A first aspect of the present invention is an oxygen-absorbing composition characterized by containing a metallic aluminum unit, an aluminum compound unit, and a silver or silver compound unit. Here, the aluminum compound is preferably an aluminum oxide. The aluminum oxide is preferably γ-alumina. The aluminum oxide is preferably boehmite. The silver compound is preferably silver oxide or silver nitrate.

  A second aspect of the invention is an oxygen absorbent comprising any one of the above oxygen-absorbing compositions so as to allow oxygen permeation.

  The oxygen-absorbing composition or the like of the present invention has a high oxygen-absorbing ability. Depending on the conditions, it is possible to obtain a value approaching the upper limit of the theoretical absorption amount of aluminum. Therefore, the required oxygen absorption capacity can be obtained with a small amount of metal. On the other hand, the amount of hydrogen generated by side reactions during oxygen absorption is reduced, and the utilization rate of metal aluminum for oxygen absorption is high.

  Hereinafter, the present invention will be specifically described. The oxygen-absorbing composition is a mixture containing a metal aluminum unit, an aluminum compound unit, and a silver or silver compound unit. Here, the unit means that each of these three kinds of substances has an independent form. That is, the oxygen absorbing composition is composed of a mixture of at least three types of these units.

  The metal aluminum unit contained in the oxygen-absorbing composition is a main component of oxygen absorption, and is oxidized by coming into contact with oxygen molecules and consequently has a role of absorbing oxygen gas. The metal aluminum may be one in which an oxide film is not formed on the surface, but one in which a thin oxide film naturally occurs on the surface by touching oxygen in the air during production may be used as it is. Moreover, since impurities such as other metals contained in the metal aluminum tend to hinder oxygen absorption, it is preferable that the aluminum purity is high. Desirably, it is 95 mass% or more, More desirably, it is 99 mass% or more.

  The form of the metal aluminum unit is not particularly limited, but a form having a wide surface area for the mass is desirable, and for example, a foil form, a fiber form, a particulate form, a fine particle form, a powder form, and the like are desirable. Moreover, the aggregated thing which particle | grains, powder, etc. gathered may be used. In order to increase the oxygen absorption rate, a form with a large surface area per gram of metallic aluminum is desirable, but from the viewpoint of stably maintaining oxygen absorption over a certain period, a volume portion that does not appear directly on the surface should be secured. Is desirable. Taking into consideration the ease of production, it is desirable to form fine particles. Specifically, the average particle diameter of the aluminum particles is preferably 0.1 μm or more and 1000 μm or less, and more preferably 1 μm or more and 300 μm or less. Particularly preferably, it is 3 μm or more and 100 μm or less.

  When the metallic aluminum unit is in the form of particles, fine particles, powders, etc., the shape of each metallic aluminum particle may be spherical, teardrop-shaped, flake-shaped, needle-shaped, or indefinite. What is necessary is just to select suitably in consideration of speed, duration, the amount of aluminum used, ease of manufacture, etc.

  Such a metal aluminum unit can be obtained by various conventional methods such as a normal atomizing method and a crushing method. In addition, for the purpose of further improving the reaction activity, the metal aluminum unit may be pretreated with an acid, an alkali, a surface treatment agent, or the like, but may not be performed.

  The metal aluminum unit can be almost completely oxidized not only on the surface but also inside the metal aluminum by oxygen absorption in the presence of an aluminum compound (and moisture) described later. Therefore, even if the initial metallic aluminum unit is a spherical particle having a certain average particle diameter, after sufficient oxygen absorption, almost the whole changes to an aggregate of aluminum oxide powders similar to iron red rust. This aggregate is easy to collapse and it is difficult to keep the original shape. Therefore, it is possible to cause oxidation to a point close to the theoretical value (upper limit value) of oxygen absorption calculated from the aluminum equivalent, and the oxygen absorption ability is greatly improved.

  The cause of such an unexpected phenomenon is unknown, but the surface oxide film of the metal aluminum unit is destroyed by the action of the coexisting aluminum compound unit and the formation of a new film is not inhibited. I guess.

  Next, the aluminum compound unit of the oxygen absorbing composition will be described. As described above, the aluminum compound unit is an oxidation accelerator for the metal aluminum unit, and has an action of oxidizing the metal aluminum unit not only to the surface but also to the inside in the presence of moisture. The term “aluminum compound” as used herein means that the mass ratio of the aluminum element to other elements bonded to the aluminum element or the like is in the range of 1: 9 to 8: 2. Within this range, the oxygen absorbing ability when the oxygen absorbing composition is obtained is increased. More preferably, it is 2: 8-7: 3. More preferably, it is 3: 7-6: 4, Most preferably, it is 3: 7-5.5: 4.5. The oxidation number of aluminum in the aluminum compound may be 1, 2, or 3, but an oxidation number of 3 is preferable.

  Suitable aluminum compounds include aluminum oxides, hydroxides, aluminates, aluminosilicates, sulfates, nitrates, phosphates, halides, acetates, among others, oxides or hydroxides. Things are preferred.

Examples of aluminum oxides or hydroxides include anhydrous aluminum compounds such as α-alumina, γ-alumina, η-alumina, δ-alumina, k-alumina, ρ-alumina, Al (OH) ₃ or Al ₂ O. Trihydrates of aluminum compounds such as gibbsite, pyalite, norstrandite represented by ₃ · 3H ₂ O, boehmite, diasbore, etc. represented by AlO (OH) or Al ₂ O ₃ · H ₂ O Monohydrates of aluminum compounds, and simple substances such as todite (5Al ₂ O _a · H ₂ O), alumina gel (Al ₂ O ₃ · nH ₂ O), and mixtures containing one or more of these are fisted. .

  In order to increase the oxygen absorption rate, γ-alumina is preferable among anhydrous oxides, and monohydrate is preferable among hydrates. The aluminum oxide is more preferably a hydrate, and most preferably boehmite.

  Further, the aluminum compound may contain one or more metal elements having a high ionization tendency as elements other than aluminum in order to increase the oxygen absorption rate. Examples of the metal element having a high ionization tendency include potassium, calcium, sodium, magnesium, zinc, chromium, manganese, iron (II) and the like.

  The form of the aluminum compound unit is not particularly limited, but it is preferable that the aluminum compound unit has a large surface area and high dispersibility so that a contact point with the surface of the metal aluminum unit is likely to occur. For example, a fiber shape, a particle shape, a fine particle shape, a powder shape, and the like can be mentioned. Further, as a particle shape, a spherical shape, a needle shape, a flake shape, an indefinite shape, and the like can be cited. The average particle size in the case of the particle shape is preferably 0.01 μm or more and 1000 μm or less, and more preferably 0.05 μm or more and 100 μm or less. Especially preferably, they are 0.1 micrometer or more and 10 micrometers or less.

The aluminum compound unit has a specific surface area of 1 m ² / g or more, more preferably 10 m ² / g or more, in order to ensure contact with the metal aluminum unit. Most preferably, it is 50 m < ² > / g or more.

  The aluminum compound unit preferably has a pH of 3 to 11 when 1 g of the aluminum compound unit is dispersed in 100 cc of water. By selecting the aluminum compound unit whose composition is adjusted so as to exhibit such pH, the hydrogen generation reaction that is a side reaction of the reaction between aluminum and oxygen is suppressed to some extent. More preferably, it is 4-9.

  The aluminum compound unit may be produced according to a conventional method. For example, the aluminum compound unit may be produced by performing a dry or wet chemical reaction and, if necessary, a drying treatment, a firing treatment, a purification treatment, a pulverization treatment, and the like.

  The mass ratio of mixing the metal aluminum unit and the aluminum compound unit can be determined in the range of 1:99 to 99: 1. When the ratio of the metal aluminum unit is large, the amount of oxygen that can be absorbed is large, but on the other hand, the oxygen absorption rate is small, and particularly the absorption rate at the initial stage of absorption is small. The reverse is true when the proportion of aluminum compound units is large. The mass ratio to be mixed may be appropriately determined according to specifications required for the oxygen absorbent while taking into consideration the surface area of the metal aluminum unit and the like. Usually, the mass ratio of the metal aluminum unit to the aluminum compound unit is 30:70. It is preferable to be about ~ 70: 30.

  In addition, the oxidation action to the inside of the metal aluminum unit in the presence of the aluminum compound unit and water occurs even if the metal aluminum unit and the aluminum compound unit are lightly mixed with a spoon. Therefore, it is considered that the destruction of the surface oxide film of the metallic aluminum unit is not due to the mechanical action during mixing.

  Next, the unit of silver or silver compound of the oxygen absorbing composition will be described. Although the mechanism of silver or a silver compound unit is unknown, it acts as a suitable inhibitor of hydrogen generation, and effectively suppresses hydrogen generation due to side reactions during the oxidation reaction of the metal aluminum unit. In particular, since the reactivity of the metal aluminum unit is enhanced by the aluminum compound unit, the hydrogen generation suppressing action of the silver or silver compound unit becomes more important.

  Silver means normal metallic silver, but metals other than silver may be mixed as an alloy. In order to sufficiently act as a hydrogen generation inhibitor, the silver content is preferably 50% by mass or more. The silver content is more preferably 80% by mass or more, and further preferably 95% by mass or more.

  The silver compound may be a substance in which a silver element and another element are bonded by a covalent bond or an ionic bond. For example, nitrate, fluoride, chlorate, chlorate, acetate, sulfate, oxide , Sulfides, phosphates, fluoro complexes, silver porphyrin complexes, and the like. The oxidation number of silver in the silver compound may be any of 1 to 3. A preferred silver compound is silver oxide or silver nitrate, and a more preferred silver compound is silver oxide. The content of silver element in the silver compound is preferably 30% by mass or more, more preferably 50% by mass or more, and further preferably 80% by mass or more.

  The form of the silver or silver compound unit is not particularly limited, but it is preferable to have a large surface area and high dispersibility so that a contact point with the surface of the metal aluminum unit is likely to occur. Examples of the form of silver unit include silver wire, fiber, particle, fine particle, powder, etc., and the particle shape is fisted in the form of a sphere, needle, flake, indefinite shape, etc. It is done. The average particle size of the silver unit particle shape is preferably 1 μm or more and 1000 μm or less, and more preferably 5 μm or more and 300 μm or less. Especially preferably, they are 10 micrometers or more and 100 micrometers or less.

  As the form of the silver compound unit, a powdery or indefinite shape, or a spherical or indefinite shape in which a large number of powders or fine particles are aggregated, or a liquid or the like can be used. The average particle diameter of the silver compound unit is preferably 0.1 μm or more and 1000 μm or less, and more preferably 0.5 μm or more and 300 μm or less. Especially preferably, they are 1 micrometer or more and 100 micrometers or less.

  The silver unit can be produced by an atomizing method or a crushing method according to a conventional method. The silver compound unit can be produced by a method of subjecting it to a chemical reaction in an aqueous system or an organic system according to a conventional method, followed by a drying treatment while granulating as necessary.

  Moreover, it is preferable that the mass ratio of a metal aluminum unit and the unit of silver or a silver compound at the time of mixing as an oxygen absorption composition shall be 10000: 1-10: 1, More preferably, it is 5000: 1-50: 1, more preferably 1000: 1 to 100: 1.

  A stoichiometrically necessary amount of water for the oxygen absorption reaction of the metal aluminum unit may be added to the oxygen absorbing composition in advance in accordance with the use of the oxygen absorbing composition. As an addition method, water may be added directly as it is, or it may be added while being supported on a water retention agent or a carrier. Further, it may be added as an aqueous solution in which a silver compound is dissolved.

  When adding water directly, in order to avoid non-uniformity such as aggregation of specific components, first, after dispersing any component, for example, aluminum compound unit in water, the dispersion is thoroughly stirred. However, a method such as adding a metal aluminum unit may be taken.

  A water retention agent is a known thickening agent or gelling agent that is hydrophilic and can hold hydration more than its own weight to form a sol or gel. For example, a synthetic polymer such as polyacrylate or carrageenan A polysaccharide etc. can be mentioned and it does not restrict | limit in particular.

  Carriers include fiber products with water retention properties such as absorbent cotton and nonwoven fabric, and inorganic powders such as activated carbon, zeolite, diatomaceous earth, activated clay, silica, talc, gypsum, calcium silicate, calcium chloride, graphite, carbon black, and carbon nanotubes Or an inorganic granular material is mentioned, It does not restrict | limit in particular. One type of water retention agent or carrier may be used, or two or more types may be used in combination.

  It should be noted that moisture is not necessarily added to the oxygen-absorbing composition, moisture separated from a packaged product such as a food packaged together with the oxygen-absorbing composition, or air remaining in the bag when packaging the packaging bag Oxygen absorption reaction may be performed using water vapor or water vapor that permeates the packaging bag after packaging and enters the bag.

  As long as the effects of the present invention are not impaired, an oxygen-sparking agent and other additives may be added to the oxygen-absorbing composition.

  The oxygen-absorbing composition can be obtained by mixing the above-mentioned components at a predetermined ratio, and stirring and homogenizing. For homogenization, the metal aluminum unit, the aluminum compound unit, and the like may be stirred while being simultaneously pulverized. The mixing and homogenizing treatment is desirably performed in an oxygen-free atmosphere using an inert gas such as nitrogen gas or argon gas, carbon dioxide gas, or the like. Carbon dioxide is particularly preferable from the viewpoint of oxygen absorption performance.

As is known, the oxygen-absorbing composition can be enclosed in an oxygen-permeable paper sachet as it is, and can be enclosed in a package as an oxygen absorbent. Since the oxygen-absorbing composition has a relatively high oxygen-absorbing capacity, it can perform a necessary oxygen-absorbing function in a small amount. Therefore, it is suitable for processing and using other forms of oxygen absorbents. For example, it may be mixed with a binder at the time of paper production, or may be kneaded at the time of production of resin pellets or resin sheets using an oxygen permeable resin. In addition, a layer of an oxygen absorbing composition processed with a binder may be sandwiched between paper and a resin sheet to form a multilayer structure sheet or film, and may further be processed into a tray or lid of a package. . In this case, an oxygen-permeable sheet or film is used for at least the inner surface portion of the package. It is desirable to use a sheet or film on the outer surface of the package that is less permeable to oxygen. It is optional to make the sheet or film moisture permeable or moisture impermeable as required.
[Example]

Hereinafter, although an example etc. are given and the present invention is explained still in detail, the present invention is not limited to the concrete mode of the following example. In addition, the measuring method and evaluation method of various physical properties in Examples etc. are as follows.
(1) Oxygen absorption (V _OS ) and hydrogen generation (V _HG )

  Under a room temperature (20 ° C.) environment, a storage sealed container having an initial capacity of 1000 cc (the material of the main body and the lid is PMMA (acrylic), the lid packing is silicon, and the volume is variable so that the inner pressure of the container is constant) was prepared. . A predetermined amount of the oxygen-absorbing composition was sealed in the container under atmospheric pressure, and then left in a 20 ° C. atmosphere for 4 hours. The oxygen gas concentration and the hydrogen gas concentration in the container were measured before the oxygen absorbing composition was charged and after 4 hours had elapsed from the charging.

  The oxygen concentration was measured with a compact oxygen analyzer (manufactured by Aichi Sangyo Co., Ltd., trade name: Model 1100BE, sensor: MAX250E). The hydrogen concentration was measured with an air / dissolved hydrogen measuring device (Able Co., Ltd., trade name: DM-10B2). Subsequently, the oxygen absorption amount at the time when 4 hours elapsed was calculated by the following formula (a).

V _OS = {(C _O2,0 / 100) × V ₀ − (C _{O2, t} / 100) × V _t } / x (a)
(In the formula (a), V _OS is the amount of oxygen absorbed per gram of metallic aluminum (cc / g) from the start of measurement until 4 hours have passed, and C _{O2, t} is the oxygen concentration in the container (vol. %), _{CO 2} , ₀ is the oxygen concentration (vol.%) In the container before _charging the oxygen absorbing composition, V ₀ is the initial volume of the container (= 1000 cc), V _t is the volume of the storage container after 4 hours ( cc) and x mean the weight (g) of metallic aluminum contained per gram of the oxygen-absorbing composition.

The obtained oxygen absorption (V _OS ) was evaluated according to the following criteria.
-Compared with the case where the unit of silver or a silver compound is not included (Comparative Example 1), the oxygen absorption amount is 110% or more, which is excellent (indicated by the symbol “◎”).
-Compared to the case where the unit of silver or silver compound is not included (Comparative Example 1), the oxygen absorption amount is in the range of 70% or more and less than 110%, which is good (indicated by the symbol “◯”). .
-Compared with the case where the unit of silver or a silver compound is not included (Comparative Example 1), the oxygen absorption amount is less than 70%, which is inferior (indicated by symbol "x").
Further, the hydrogen generation amount (V _HG ) after 4 hours from the start of measurement was calculated by the following formula (b).
V _HG = (C _{H2, t} / 100) × V _t (b)
(In formula (b), V _HG is the amount of hydrogen generated per gram of metallic aluminum (cc / g) from the start of measurement until 4 hours have passed (measurement time), and C _{H2, t} is the hydrogen in the container when 4 hours have passed. concentration (vol.%), V _t denotes the volume at the time of four hours of storage container (cc), respectively.)
The obtained hydrogen generation amount (V _HG ) was evaluated according to the following criteria.
-Compared with the case where the unit of silver or silver compound is not included (Reference Example 1 below), the hydrogen generation amount is less than 25%, which is excellent (indicated by symbol “記号”).
-Compared with the case where the unit of silver or a silver compound is not included (Reference Example 1), the hydrogen generation amount is 25% or more and less than 40%, which is good (indicated by a symbol “◯”).
-Compared to the case where the unit of silver or silver compound is not included (Reference Example 1), the hydrogen generation amount is 40% or more of the decrease, but is insufficient (indicated by symbol “△”). .
(2) Dispersion pH

After 1 g of aluminum compound unit is immersed in 100 cc of water and dispersed by stirring well with a glass rod, the pH of this dispersion is measured with a pH meter (manufactured by Shindengen Industrial Co., Ltd., trade name: Shindengen ISFET pH meter KS723). Measured using.
[Reference Example 1]

Aluminum powder 0.5g (made by Eka Granular Japan Co., Ltd., grade name 8F02A, particle size 8μm, purity 99.7%) as metal aluminum unit and boehmite powder 1.0g (made by Daimei Chemical Co., Ltd.) as aluminum compound unit , Grade name AE-001, particle size 0.2 μm, purity 99.9%, dispersion pH 8.7) and 1.5 g of pure water are mixed and stirred with a spoon to prepare a uniform reference sample. Created. Using this, the amount of oxygen absorbed (V _OS ) and the amount of hydrogen generated (V _HG ) were measured. As a result, the amount of oxygen absorbed (V _OS ) was 208.0 cc as good as 4 hours later. The amount generated (V _HG ) was also as large as 592.4 cc.

Except for adding 0.01 g of AgO powder (made by Wako Pure Chemical Industries, Ltd., particle size 2.6 μm, purity 98%) as a silver compound unit to the composition of the reference sample prepared in Reference Example 1, A sample of a uniform oxygen absorbing composition was prepared in the same manner as in Reference Example 1. Using this, the amount of oxygen absorbed (V _OS ) and the amount of hydrogen generation (V _HG ) were measured.

  The amount of oxygen absorbed was 272 cc / g, which was higher than that of the reference example after 4 hours. Considering that the theoretical oxygen absorption amount (upper limit value) obtained from the total number of equivalents of metal aluminum is about 620 cc / g, it can be seen that the oxidation does not stay on the aluminum surface but clearly proceeds to the inside of the particles. . In addition, it was found that the oxygen absorption reaction still continued even after 4 hours when the change with time was followed. On the other hand, the amount of hydrogen generated was only 85 cc / g after 4 hours, indicating that most of the aluminum was used for oxygen absorption. In addition, following the time course of hydrogen generation, hydrogen increases at the beginning of the reaction, but the hydrogen concentration reaches an equilibrium state in about 1 to 2 hours. In other words, hydrogen generation almost stops in a short time, which is effective. It was found to be suppressed. Moreover, when the metal aluminum powder particles after 4 hours were visually observed with a microscope, the original smooth metal surface was lost and changed into an irregular shape very similar to the state of iron red rust. The evaluation results of the measured values are shown in Table 1.

Instead of AgO powder, 0.1 g of Ag ₂ O powder (made by Wako Pure Chemical Industries, Ltd., particle size 5.3 μm, purity 99%) is used as the silver compound unit, and the amount of pure water is from 1.5 g. A sample of the oxygen-absorbing composition was prepared in the same manner as in Example 1 except that the amount was increased to 1.6 g. Using this, the oxygen absorption amount and the hydrogen generation amount were evaluated in the same manner as in Example 1. The results are shown in Table 1. Both oxygen absorption capacity and hydrogen generation yielded excellent results.

  Oxygen absorption was carried out in the same manner as in Example 1 except that 0.1 g of Ag powder (made by Wako Pure Chemical Industries, Ltd., particle size 23.3 μm, purity 99%) was used instead of AgO powder. A sample of the material composition was prepared, and using this, the oxygen absorption amount and the hydrogen generation amount were evaluated in the same manner as in Example 1. The results are shown in Table 1.

  Instead of AgO powder, a 1 mol / l silver nitrate solution was used as a silver compound unit, and silver nitrate as a solid content was added to 0.02 g. In addition to 0.1 g of water from the silver nitrate solution, pure water 1 A sample of the oxygen absorbent material composition was prepared in the same manner as in Example 1 except that .4 g was added, and the oxygen absorption amount and the hydrogen generation amount were evaluated in the same manner as in Example 1 using this sample. The results are shown in Table 1.

Claims (3)

And metallic aluminum unit, an oxygen absorbent composition, wherein the boehmite units that each contain a unit of silver or silver compounds. Silver compounds of the found oxygen absorbent composition according to claim 1, characterized in that the silver oxide or silver nitrate. The oxygen absorbent composition according to claim 1 or 2, the oxygen permeability so that it may encompass oxygen absorbent composition include body.