JP4575203B2 - Iron powder for oxygen scavenger and method for producing the same - Google Patents

Description

  The present invention relates to an oxygen scavenger iron powder having excellent reactivity with oxygen, which is used for maintaining the quality of foods and drugs, and a method for producing the same.

  Known uses for utilizing the reaction of iron powder with oxygen include oxygen scavengers for preventing quality deterioration due to oxidation of foods, etc., or heat generating agents such as disposable warmers. Iron powder for oxygen scavengers creates oxygen-free conditions (non-oxidizing atmosphere) by iron reacting with oxygen and depriving the atmosphere of oxygen, thereby suppressing activities such as bacteria and mold or preventing oxidation. This suppresses the deterioration of quality of foods and drugs. Since iron powder is relatively inexpensive and has no harm to the human body, it is often used as an oxygen scavenger. Other uses as oxygen scavengers include sterilized packaging containers with a deoxygenation function, in which iron powder is mixed with resin, and materials used to remove trace amounts of oxygen in inert gases. ing.

Conventionally, spray iron powder produced for powder metallurgy or reduced iron powder produced for disposable body warmers is mainly used as iron powder for such applications, and the average particle size is 45 to 150 μm, apparent. The density was about 2.0 to 3.0 g / cm ³ . However, these iron powders have a problem of low reactivity with oxygen. If iron powder with low reactivity is used as an oxygen scavenger, the oxygen absorption rate at the initial stage of oxygen absorption is not sufficient, so it takes time to become oxygen-free. Or there is a problem that it is necessary to limit the products to be applied according to the oxygen absorption rate of the oxygen scavenger.

  Therefore, it can be applied to products in more fields, and can maintain a fresh state by suppressing deterioration of products more than before, with a high initial oxygen absorption rate and more reactive iron Powder was sought. In addition, the conventional iron powder has a problem that only the surface is oxidized and the inside of the particle is not effectively used, and an iron powder that can be effectively used to the inside of the particle has been demanded.

In order to meet this demand, Patent Document 1 describes deoxygenation comprising reduced iron powder having a specific surface area of 1.0 m ² / g or more, an apparent density of 1.0 g / cm ³ or less, and an average particle size of 9.0 μm or less. Agents have been proposed. Patent Document 2 discloses a surface having an oxygen content of 0.7 to 7% by mass and a specific surface area of 200 to 2000 m ² / kg (corresponding to a specific surface area of 0.2 to ² m ² / g). Partially oxidized iron powder has been proposed. However, there is a problem that none of these iron powders have sufficient reactivity.

  Further, Patent Document 3 proposes an iron powder having a coating layer made of iron chloride containing 0.1 to 2% by mass of Cl (chlorine) on the surface of the iron powder. However, although having a coating layer containing Cl slightly improves the reactivity with oxygen, there is a problem that the reactivity of the original iron powder itself is not sufficient.

In addition, there is a method in which iron powder is pulverized to be atomized, but there is a problem that the cost required for pulverization increases, which is not preferable. There are also fine iron powders with a particle size of about 1 μm, but they are excellent in reactivity with oxygen, but the bulk density is small and bulky, the handling property is poor, or the powder itself is food because of the fine powders. There was a problem such as contaminating.
JP 2002-292276 A Japanese Patent Laid-Open No. 11-47585 Japanese Patent Laid-Open No. 11-302706

  Despite the demand for iron powder that has excellent reactivity with oxygen, high initial oxygen absorption rate, high bulk density, excellent oxygen absorption per unit volume, and can be used effectively for the reaction inside the particles. As described above, there is no conventional effective means, and the actual situation is that sprayed iron powder produced for powder metallurgy as usual or reduced iron powder produced for disposable body warmers is mainly used. .

  The present invention has been made in view of the above circumstances, and the object thereof is excellent in reactivity with oxygen, the initial oxygen absorption rate is extremely higher than before, and the bulk density is high. It is an object to provide iron powder for oxygen scavengers that is excellent in oxygen absorption and that can be effectively used for reaction even inside the particles, and a method for producing the same.

The iron powder for oxygen scavenger according to the first invention for solving the above-mentioned problem is obtained by reducing iron oxide particles produced by a fluid roasting method using a reducing gas in a temperature range of 300 ° C. or more and 900 ° C. or less. The iron powder for oxygen scavengers and having a spongy structure with pores connected to the outside inside the spherical particles , and the diameter of the pores measured by mercury porosimetry is 2 μm The specific surface area of the particles is 100 times or more the external specific surface area calculated from the average particle diameter of the particles.

The oxygen scavenger iron powder according to the second invention is characterized in that, in the first invention, the bulk density of the particles is 3 g / cm ³ or more.

  The oxygen scavenger iron powder according to the third invention is characterized in that, in the first or second invention, the average particle diameter of the particles is 2 mm or less.

A method for producing iron powder for oxygen scavengers according to a fourth aspect of the present invention is a sponge-like structure having pores connected to the outside inside spherical particles, wherein the pores measured by mercury porosimetry are used. A method for producing iron powder for oxygen scavengers having a diameter of 2 μm or less and the specific surface area of the particles being 100 times or more the external specific surface area calculated from the average particle diameter of the particles, by a fluid roasting method The manufactured iron oxide particles are reduced using a reducing gas in a temperature range of 300 ° C. or more and 900 ° C. or less.
According to a fifth aspect of the present invention, there is provided a method for producing an oxygen scavenger iron powder according to the fourth aspect, wherein the particle has a bulk density of 3 g / cm ³ or more.
According to a sixth aspect of the present invention, there is provided the method for producing an oxygen scavenger iron powder according to the fourth or fifth aspect, wherein the average particle diameter of the particles is 2 mm or less.

  According to the iron powder for oxygen scavenger of the present invention, since the structure is a sponge structure with a large specific surface area, the reactivity with oxygen is excellent, and the initial oxygen absorption rate is extremely large as compared with the conventional one, It can be effectively used as a site that reacts with oxygen up to the inside of the particle. Furthermore, since the shape of the iron particles is spherical, the bulk density is high, and an extremely large oxygen absorption capacity per unit volume can be obtained. Therefore, when the oxygen powder for oxygen absorber of the present invention is used as an oxygen absorber, it is possible to stably prevent quality deterioration due to oxidation of foods and drugs over a long period of time, which is industrially beneficial. The effect is brought about.

  Hereinafter, the present invention will be specifically described. The oxygen powder for oxygen scavenger according to the present invention is composed of iron particles, and the iron particles have a spherical shape. Since it is spherical, it has excellent handling properties and can be densely packed, so that it has a large bulk density and excellent oxygen absorption per unit volume.

  In addition, the iron powder for oxygen scavenger according to the present invention has one of the other features that a pore connected to the outside exists inside the spherical particle and has a sponge-like structure by the pore. . Since it has such a sponge-like structure, it exhibits the same effect as a collection of many fine iron particles, and has a large specific surface area with respect to the particle size and high reactivity. For this reason, the initial oxygen absorption rate is large, and the inside of the particles is also used for the reaction with oxygen, making it suitable as iron powder for an oxygen scavenger.

  In the iron powder for oxygen scavenger according to the present invention, it is essential that the diameter of the pores forming the sponge structure inside the iron particles is 2 μm or less. This is because the smaller the pore, the larger the specific surface area provided by the sponge structure inside the particle, the better the reactivity with oxygen, and the more effective the inside of the particle is used for the reaction with oxygen. When the pores are large, the ratio of the specific surface area of the particles with respect to the external specific surface area calculated from the average particle diameter of the particles decreases, and the reactivity decreases. Therefore, it is essential that the diameter of the pore is 2 μm or less, preferably 1 μm or less, and more preferably 0.7 μm or less.

  In the oxygen powder for oxygen scavenger according to the present invention, it is essential that the specific surface area of the iron particles is at least 100 times the external specific surface area calculated from the average diameter of the particles. The specific surface area is larger than the external specific surface area due to the sponge-like structure inside the particle. The more the sponge-like structure is developed, the larger the magnification becomes, and the more active iron particles are obtained. From this viewpoint, the specific surface area of the iron particles must be 100 times or more with respect to the external specific surface area calculated from the average particle diameter of the particles, preferably 300 times or more, more preferably 500 times or more, more More preferably, it is desirable that it is 1000 times or more.

  The BET method is generally known as a method for measuring the specific surface area, and the BET method can also be used for measuring the iron powder for oxygen scavenger of the present invention. Of course, there is no problem even with a measurement method other than the BET method. The average particle size is measured by measuring the particle size of 100 or more particles using an electron microscope, as shown in FIG. 1, which is a scanning electron micrograph of the iron powder for oxygen scavenger of the present invention. It is preferable to use a value obtained by averaging these.

The external specific surface area calculated from the average particle diameter of the particles, that is, the total surface area S (m ² / g) per 1 g of the sample can be obtained from the following equation (1).

However, in the formula (1), N is the number (particles / g) of particles in 1 g of the sample, and s is the outer surface area (m ² / particle) per particle. N can be obtained from the following equation (2), and s can be obtained from the following equation (3). W in the formula (2) is a mass (g / piece) per particle, and W can be obtained by the following formula (4). In the formulas (3) and (4), d is the average diameter (μm) of the particles. Here, the true density of pure iron is 7.85 g / cm ³ .

  By the way, the presence of sponge iron is conventionally known as an iron powder having a sponge-like structure. Sponge iron is also a raw material for reduced iron, which is also used as an oxygen scavenger. This sponge iron has a sponge-like structure because whisker-like particles grow from the surface of the primary particles of iron oxide when iron oxide such as iron ore and mill scale is CO-reduced. is there.

  On the other hand, the iron powder for oxygen scavenger of the present invention has a sponge structure with fine pores of 2 μm or less inside the particles, and these pores are much smaller than the pores of sponge iron. Yes, the generation mechanism is quite different. 2 and 3 show scanning electron micrographs of the cross section of the oxygen scavenger iron powder according to the present invention. FIG. 3 is an enlarged photograph of FIG. As apparent from FIGS. 2 and 3, the sponge structure of the iron powder for oxygen scavenger according to the present invention can be obtained by reducing and removing oxygen in iron oxide when reducing spherically shaped iron oxide. The structure is essentially different from the sponge structure of sponge iron. That is, in sponge iron, columnar particles only grow on the outer peripheral portion of the particles, so the specific surface area of the particles cannot be more than 100 times the external specific surface area calculated from the average diameter of the particles, and according to the present invention. The remarkable activity like iron powder for oxygen scavengers cannot be expected.

Moreover, the oxygen powder for oxygen scavenger according to the present invention preferably has a bulk density of 3 g / cm ³ or more. Since the iron particles that are the iron powder for oxygen scavenger of the present invention have a spherical shape, they can be packed densely and a high bulk density can be obtained. Moreover, having a fine pore compared with the reduced iron powder which has a sponge structure used as a normal oxygen scavenger is also a reason why a high bulk density can be obtained. Since a high bulk density is obtained, the oxygen scavenger itself can be made compact. For this reason, the bulk density of the oxygen scavenger iron powder for the present invention is preferably from 3 g / cm ³ or more, further preferably at 3.5 g / cm ³ or more.

  Moreover, it is preferable that the average particle diameter of the iron powder for oxygen scavengers according to the present invention is 2 mm or less. This is because if the average particle diameter exceeds 2 mm, the gap between the particles increases, the bulk density decreases, and the oxygen absorption capacity per unit volume decreases. Further, it is not preferable because it takes time to completely reduce the inside of the particles, and when the particle size is large, oxygen is less likely to enter the inside as compared with the small particles. On the contrary, if the average particle diameter is too small, problems such as poor handling properties occur, which is not preferable. Therefore, the average particle size of the oxygen powder for oxygen scavenger according to the present invention is preferably 2 mm or less, more preferably 30 μm to 2 mm, further preferably 50 μm to 1.5 mm, and still more preferably 100 μm to 1 mm. Is desirable. Classification may be performed as necessary to adjust the average particle size.

Furthermore, the iron powder for oxygen scavengers of the present invention, that is, the spherical iron oxide used as the raw material for the iron powder for oxygen scavengers of the present invention, preferably contains silica (silicic acid: SiO ₂ ). This is because the presence of silica helps to form a unique sponge structure. The iron powder for oxygen scavenger of the present invention is obtained by reducing spherical iron oxide, and when it does not contain silica, the irons that should form a sponge structure due to the release of oxygen are sintered together. This is because the destruction of the sponge structure proceeds. This is because fine sponge-like iron produced by reduction is very fine and highly reactive. However, when silica is contained, it is possible to prevent the iron particles forming the sponge structure from being sintered, which is very effective in obtaining the iron powder for oxygen scavenger according to the present invention having a sponge structure.

  As for the quantity of the silica contained in the spherical iron oxide used as the raw material of the iron powder for oxygen scavengers of this invention, 30 ppm or more and 5 mass% or less are desirable. If the silica is less than 30 ppm, it is difficult to prevent the sintering of iron that forms a sponge structure. On the other hand, if the silica exceeds 5% by mass, there is an effect of preventing the sintering of iron that forms a sponge structure. This is because the reaction with oxygen is inhibited, that is, the ability as an oxygen scavenger is reduced. Accordingly, the amount of silica in the spherical iron oxide is preferably 30 ppm or more and 5% by mass or less, more preferably 50 ppm or more and 3% by mass or less, still more preferably 100 ppm or more and 1% by mass or less, and still more preferably 200 ppm or more and 5000 ppm or less. Preferably they are 300 ppm or more and 3000 ppm or less. In addition to silica, oxides such as Al, Ti, Cr, and Ni may be included as elements for preventing sintering.

  Next, an embodiment of a method for producing spherical iron powder suitable for the oxygen scavenger according to the present invention will be described.

  The spherical iron powder for oxygen scavenger according to the present invention is obtained by reducing spherical iron oxide particles. As a method for producing the spherical iron oxide particles as a raw material, a fluid roasting method can be used as an example. When the fluid roasting method is used, spherical iron oxide particles can be easily obtained. Further, by producing iron oxide particles by a fluid roasting method using a raw material solution containing silica, iron oxide particles in which silica is uniformly dispersed inside can be obtained. Since silica is uniformly dispersed inside the particles, a sponge-like structure can be obtained without sintering even when spherical iron oxide particles are reduced.

  As the raw material solution of iron oxide, ferrous chloride solution or ferric chloride solution, a mixed solution of ferrous chloride solution and ferric chloride solution, or the like, which is a pickling solution for steel materials, can be used. Further, the iron chloride solution may contain additives or impurities other than silica.

  As a method for reducing the spherical iron oxide, a general reduction furnace can be used. As the reducing gas, a general reducing gas such as hydrogen or carbon monoxide can be used. The reduction temperature may be reduced at 300 ° C. or higher at which iron oxide can be reduced. However, if the temperature is too high, the particles sinter or the sintering of the sponge structure proceeds and the pores disappear, so it is not preferable that the temperature is too high. From this viewpoint, the reduction temperature needs to be 300 ° C. or higher and 900 ° C. or lower, preferably 300 ° C. or higher and 800 ° C. or lower, more preferably 300 ° C. or higher and 700 ° C. or lower.

  As described above, according to the iron powder for oxygen scavenger of the present invention, since the structure is a sponge structure with a large specific surface area, the reactivity with oxygen is excellent, and the initial oxygen absorption rate is higher than conventional. It becomes extremely large and can be effectively used as a site that reacts with oxygen up to the inside of the particle. Furthermore, since the shape of the iron particles is spherical, the bulk density is high, and an extremely large oxygen absorption capacity per unit volume can be obtained. For this reason, when the iron powder for oxygen scavenger of the present invention is used as the oxygen scavenger, it is possible to stably prevent deterioration of quality due to oxidation of foods and drugs over a long period of time.

  Hereinafter, the present invention will be described in more detail with reference to examples.

18 types of ferrous chloride solutions in which the content of silica (SiO ₂ ) in the solution was changed to 18 types within the range of 20 to 80,000 ppm in terms of iron oxide were roasted in a Lurgi type fluid roasting furnace. Spherical iron oxide particles were prepared. Here, the meaning of “iron oxide conversion” of content means the content in iron oxide produced from a ferrous chloride solution.

The obtained iron oxide particles were classified using a sieve having an aperture of 1 mm and 0.5 mm to obtain iron oxide particles having a particle size in the range of 0.5 mm to 1.0 mm. The obtained iron oxide particles were reduced with hydrogen or carbon monoxide in a box furnace in a reduction temperature range of 290 to 1000 ° C., respectively, to obtain 18 types of iron particles having a spherical shape (the present invention). Examples 1 to 15 and Comparative Examples 1 to 3). In Comparative Example 1, the content of silica (SiO ₂ ) is small, so that the pore size is 2.5 μm and exceeds the upper limit of the range of the present invention. In Comparative Example 2, the reduction temperature is Iron particles reduced at 290 ° C. lower than the lower limit of the range of the invention, in which the unreduced iron oxide component remains, Comparative Example 3 has a reduction temperature of 1000 higher than the upper limit of the range of the present invention. It is iron particles reduced at 0 ° C., and the particles are sintered and the disappearance of pores is observed.

  The produced iron oxide particles were reduced without classification, and the reduced iron particles were classified to produce iron particles in which only the size was changed (Invention Examples 16 to 28). That is, a ferrous chloride solution containing 800 ppm of silica in terms of iron oxide was roasted in a Lurgi-type fluid roasting furnace to produce spherical iron oxide particles. The obtained iron oxide particles were reduced with hydrogen using a box furnace at a reduction temperature of 600 ° C. to obtain iron particles having a spherical shape. The iron particles were classified with a sieve to obtain iron particles having different particle sizes.

  Incidentally, Example 16 of the present invention collects iron particles in this particle size range using sieves having a mesh size of 2 mm and 3 mm, and Example 17 of the present invention collects iron particles of this particle size range using a sieve having a mesh size of 1.5 mm and 2 mm. In Example 18 of the present invention, iron particles of this particle size range were collected using a sieve having a mesh size of 1 mm and 1,5 mm, and Example 19 of this invention was collected using a sieve having a mesh size of 500 μm and 1000 μm. The present invention example 20 collects iron particles of this particle size range using sieves with openings of 300 μm and 500 μm, and the inventive example 21 collects iron particles of this particle size range using sieves with openings of 100 μm and 300 μm. In Example 22 of the present invention, iron particles in this particle size range were collected using sieves with openings of 100 μm and 200 μm, and in Example 23 of this invention, this particle size range was collected using sieves with openings of 75 μm and 125 μm. Iron particles Thus, Example 24 of the present invention collects iron particles in this particle size range using sieves with openings of 75 μm and 106 μm, and Example 25 of the present invention collects iron particles of this particle size range using sieves with openings of 45 μm and 75 μm. In the present invention example 26, iron particles in this particle size range were collected using a sieve having an opening of 25 μm and 45 μm, and in the invention example 27, iron particles smaller than 25 μm were collected using a sieve having an opening of 25 μm. Invention Example 28 uses iron powder obtained by reduction without classification as it is.

  Further, as conventional iron particles for comparison, atomized iron powder (conventional example 1), iron particles obtained by pulverizing sponge iron obtained by reducing the mill scale (conventional example 2), and conventional example Iron particles obtained by further pulverizing the iron particles of No. 2 with an atomizer (Conventional Example 3) were also prepared.

  For these iron powders, the average particle size, specific surface area, external specific surface area, silica content, pore size, bulk density, and oxygen absorption ability were investigated. The average particle size was determined by measuring the particle size of 100 or more particles with a scanning electron microscope, and obtaining the average value as the average particle size. The specific surface area was measured by the BET method. The external specific surface area was calculated using formulas (1) to (4) based on the obtained average particle diameter. The content of silica was determined by ICP analysis. The size of the pores in the iron particles was determined by a mercury intrusion method. The bulk density was measured using a powder tester. Oxygen absorption capacity is obtained by mixing 5 g of each iron powder and 1 g of sodium chloride, putting absorbent cotton containing this mixture and 5 g of distilled water into a glass petri dish, and further adding this glass petri dish and 1500 ml of air to a KON bag. The oxygen concentration in the bag was measured while keeping at 25 ° C., and the oxygen absorption capacity was evaluated from the change in oxygen concentration. The oxygen concentration was measured 3 hours, 5 hours, and 7 hours after the start of measurement. Table 1 shows the measurement results.

  In the iron powders of Invention Examples 1 to 28, it was found that the initial oxygen absorption rate was larger than that of the iron powders of Conventional Examples 1 to 3 and Comparative Examples 1 to 3, and was suitable as an oxygen scavenger. In addition, it was found that the iron powders of Invention Examples 1 to 28 had a larger bulk density than that of Conventional Examples 1 to 3, and were excellent in oxygen absorption per unit volume.

It is a scanning electron micrograph of iron powder for oxygen scavengers of the present invention. It is a scanning electron micrograph of the cross section of the iron powder for oxygen scavengers of this invention. It is a scanning electron micrograph of the cross section of the iron powder for oxygen scavengers of this invention.

Claims (6)

An iron powder for oxygen scavenger formed by reducing iron oxide particles produced by a fluid roasting method using a reducing gas in a temperature range of 300 ° C. or more and 900 ° C. or less, and inside the spherical particles, Sponge-like structure with connecting pores, the pore diameter measured by mercury porosimetry is 2 μm or less, and the specific surface area of the particles is calculated from the average particle diameter of the particles. Iron powder for oxygen scavengers, characterized by having a specific surface area of 100 times or more. 2. The iron powder for oxygen scavenger according to claim 1, wherein a bulk density of the particles is 3 g / cm ³ or more.   The iron powder for oxygen scavenger according to claim 1 or 2, wherein an average particle diameter of the particles is 2 mm or less. Sponge-like structure having pores connected to the outside inside the spherical particles, the diameter of the pores measured by mercury intrusion method is 2 μm or less, and the specific surface area of the particles is A method for producing oxygen powder for oxygen scavengers that is 100 times or more of the external specific surface area calculated from the average particle diameter , wherein the iron oxide particles produced by fluid roasting method are in a temperature range of 300 ° C. or higher and 900 ° C. or lower. A method for producing iron powder for oxygen scavengers, characterized by performing reduction using a reducing gas. The bulk density of the particles is 3 g / cm ^Three  It is the above, The manufacturing method of the iron powder for oxygen absorbers of Claim 4 characterized by the above-mentioned. 6. The method for producing iron powder for oxygen scavenger according to claim 4 or 5, wherein the average particle diameter of the particles is 2 mm or less.