JP7329563B2 - Iron powder for deoxidizer - Google Patents

Description

TECHNICAL FIELD The present invention relates to iron powder for oxygen scavengers.

Oxygen scavengers are known for applications that utilize the oxidation reaction of iron. Iron reacts with oxygen in a sealed package or container to remove free oxygen and dissolved oxygen, thereby suppressing oxidation and the growth of aerobic microorganisms, thereby preventing quality deterioration. Oxygen scavengers are used in a wide range of fields, such as the deterioration of foods and medicines, and the prevention of oxidation of clothing and cultural properties. The form of use of the oxygen absorber includes a package in which an air-permeable sachet is filled with iron powder, and a sheet-like form in which a resin and an oxygen absorber are kneaded.

Patent Document 1 discloses a reduced iron powder for a deoxidizer with a high oxidation rate, which has 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 diameter of 9.0 μm. The following reduced iron powder has been proposed.

Japanese Patent Application Laid-Open No. 2002-292276

In recent years, food products have become smaller in volume and individually packaged, and along with this, there is a demand for smaller packages for oxygen absorbers.

However, if the amount of iron powder to be filled in the package is simply reduced in accordance with the downsizing of the package, the amount of oxygen absorbed by the iron powder will be reduced. Although the iron powder proposed above has a high oxygen absorption capacity, it has a low apparent density and is considered unsuitable for miniaturization of packages.

The present invention has been made in view of such conventional problems, and its object is to provide an iron powder for a deoxidant that allows the package of the deoxidant to be miniaturized without lowering the oxygen absorption capacity. That's what it is.

The iron powder according to the present invention that achieves the above object is an iron powder that is used as a deoxidizer, has an apparent density of 2.21 g/cm ³ or more and 2.80 g/cm ³ or less, and has a BET specific surface area of It is characterized by being 2.0 m ² /g or more and 4.0 m ² /g or less.

In the iron powder for oxygen scavenger having the above configuration, the metallic iron content is preferably in the range of 83% by mass or more and 93% by mass or less.

Further, in the iron powder for oxygen scavenger having the above constitution, the fluidity is preferably in the range of 28 sec/50 g or more and 50 sec/50 g or less.

In the iron powder for oxygen scavenger having the above constitution, the average particle size is preferably in the range of 30 μm or more and 300 μm or less.

The measurement methods of "apparent density", "BET specific surface area", "metallic iron content", "fluidity" and "average particle size" in the present specification are the measurement methods shown in Examples below. do. In addition, unless otherwise specified, "-" shown in this specification includes the numerical values before and after it as lower and upper limits.

According to the iron powder for oxygen scavenger according to the present invention, it is possible to reduce the size of the package of the oxygen scavenger without lowering the oxygen absorption capacity.

One of the major characteristics of the iron powder for deoxidizing agent according to the present invention (hereinafter sometimes simply referred to as "iron powder") is that the apparent density is 2.21 g/cm ³ or more and 2.80 g/cm ^{3 .} It is the following. If the apparent density of the iron powder is less than 2.21 g/cm ³ , it becomes bulky when packed into a package or the like, and the oxygen absorption amount per unit volume becomes small. On the other hand, when the apparent density of the iron powder exceeds 2.80 g/cm ³ , the packing density of the iron powder becomes too high, so that the diffusibility of oxygen to be reacted deteriorates, and the oxygen absorption amount may decrease significantly. be. A more preferable range of apparent density of the iron powder is 2.21 g/cm ³ or more and 2.60 g/cm ³ or less.

Another feature of the iron powder according to the present invention is that the BET specific surface area is 2.0 m ² /g or more and 4.0 m ² /g or less. When the BET specific surface area of the iron powder is less than 2.0 m ² /g, the reactivity of the iron powder is significantly lowered, and the desired oxygen absorption may not be obtained. On the other hand, if the BET specific surface area of the iron powder exceeds 4.0 m ² /g, the irregularities on the surface of the iron powder increase to increase the friction, which is not preferable because the fluidity of the iron powder may decrease. A more preferable range of the BET specific surface area of the iron powder is 2.1 m ² /g or more and 3.7 m ² /g or less.

Further, as another aspect, when the value of {BET specific surface area (m ² /g)/apparent density (g/cm ³ )} of the iron powder is in the range of 0.7 or more and 1.9 or less, the unit volume It is preferable because the amount of oxygen absorbed per unit increases. The reason for this is not clear at the moment, but depending on the ratio of the contact area between the powders, which correlates with the BET specific surface area, and the bulkiness, which correlates with the apparent density, the volume change accompanying oxidation aggregation becomes appropriate, and ventilation accordingly. It is presumed that this is because the diffusibility of oxygen to the iron powder becomes appropriate. A more preferable range of {BET specific surface area (m ² /g)/apparent density (g/cm ³ )} of the iron powder is 0.8 or more and 1.6 or less.

The metallic iron content of the iron powder according to the present invention is preferably in the range of 83% by mass or more and 93% by mass or less. If the metal iron content of the iron powder is less than 83% by mass, there is a risk that the apparent density of the iron powder will not reach the range specified in the present invention, or that the BET specific surface area of the iron powder will exceed the range specified in the present invention. There is In addition, there is a possibility that the desired oxygen absorption amount cannot be obtained. On the other hand, if the metal iron content of the iron powder exceeds 93% by mass, the apparent density of the iron powder may exceed the range specified in the present invention, or the BET specific surface area of the iron powder does not reach the range specified in the present invention. There is a risk. A more preferable range of metallic iron content is 85% by mass or more and 92% by mass or less.

The fluidity of the iron powder according to the present invention is preferably in the range of 28 sec/50 g or more and 50 sec/50 g or less. When the fluidity of the iron powder is within the above range, a high oxygen absorption amount per unit volume is achieved. A more preferable range of the fluidity of the iron powder is 32 sec/50 g or more and 40 sec/50 g or less.

The average particle size of the iron powder according to the present invention is preferably in the range of 30 µm or more and 300 µm or less. A more preferable average particle size of the iron powder is in the range of 50 µm or more and 200 µm or less. When the average particle size of the iron powder is within the above range, a high oxygen absorption amount per unit volume is achieved.

(Manufacturing method of iron powder)
The method for producing the iron powder according to the present invention is not particularly limited, but the production method described below is preferable.

The iron powder according to the present invention is obtained by reducing an iron raw material such as iron ore and a reducing agent in a rotary kiln at 740° C. to 1000° C., preferably 760° C. to 980° C. while rolling. is preferred. If the reduction temperature is increased, the reduction reaction is accelerated, but the iron particles are also sintered, and there is a possibility that the BET specific surface area specified in the present invention cannot be obtained. On the other hand, if the reduction temperature is too low, a significantly long reduction time is required to obtain the desired metallic iron content, which may reduce productivity. The time for reducing the iron raw material while rolling in the rotary kiln (or the residence time in the furnace) is 1 hour or longer, preferably 2 hours or longer, and more preferably 3 hours or longer. However, this is not the case when iron raw materials such as iron ore to be reduced are physically scarce.

Iron ore containing trivalent iron oxide as a main component is preferably used as the iron raw material. Since trivalent iron oxide becomes spongy in the portion where oxygen has been removed by the reduction reaction, iron powder with a higher specific surface area can be easily obtained. The particle size of the iron ore is preferably 50 mm or less, preferably 30 mm or less, for ease of handling.

The reducing agent used in the present invention includes coal, coal char, coke, anthracite, semi-anthracite, bituminous coal, sub-bituminous coal, lignite and the like. Among these, coal, coal char, coke, bituminous coal, sub-bituminous coal, lignite and the like are preferably used.

The amount of the reducing agent to be added is preferably equal to or more than the molar ratio of the iron raw material. More preferably 1.5 times or more, still more preferably 2 times or more. According to the studies of the present inventors, if the amount of the reducing agent added to the iron raw material is less than 1:1 in molar ratio, the reduction reaction itself to the iron powder is difficult to proceed, and the desired reduced iron powder can be obtained. may not be possible. On the other hand, if the amount of the reducing agent added is too large, the reduction reaction does not proceed, and separation of the obtained iron powder and residual coal becomes difficult. Therefore, the upper limit of the amount of the reducing agent to be added is preferably 10 times, preferably 7.5 times the molar ratio of the iron raw material. If the reducing agent is coal, the total amount is considered as carbon for conversion, and the total amount of the iron raw material is considered as iron oxide for conversion.

The reduced iron powder (reduced iron) is then cooled. After that, the reducing agent remaining without reacting is separated from the reduced iron to obtain the reduced iron from which the impurity components have been removed. A known method can be used for separation, but separation by magnetic separation is the most efficient.

Next, the obtained reduced iron is pulverized into sponge iron powder. The pulverization treatment can be performed using known devices and methods. Examples of pulverizing devices include vibration mills, ball mills, rod mills, roll crushers and the like.

The sponge iron powder thus obtained is sieved through a sieve with an opening of 180 μm to 350 μm. At this time, the iron powder that does not pass through the sieve is subjected to a pulverization process again, and is repeatedly pulverized until it passes through the sieve. All of the iron powder that has passed through the sieve is mixed to obtain the iron powder of the present invention. The apparent density and BET specific surface area of the produced iron powder can be adjusted by the sieve opening in this treatment.

(Oxygen absorber)
The iron powder thus produced is mixed with an oxidation accelerator such as a metal halide to form the oxygen scavenger according to the present invention. Examples of metal halides include alkali metal or alkaline earth metal halides such as sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, calcium chloride, magnesium chloride, and barium chloride. 1 or 2 or more are preferably used.

The amount of the metal halide compounded with respect to the iron powder is preferably in the range of 0.05 to 50 parts by mass, more preferably in the range of 0.1 to 20 parts by mass, per 100 parts by mass of the iron powder.

The iron powder and the metal halide can be formed by simply mixing the iron powder and the metal halide powder, or by coating the surface of the iron powder with the metal halide powder by various means.

The oxygen scavenger is used by enclosing it in a packaging bag, or by kneading it with a resin and molding it into a sheet or film.

Example 1
Iron ore with a particle size of about 10 mm and coal char with a particle size of about 10 mm were mixed while being transported by a screw conveyor so that the weight ratio was 7:3. This mixture was put into an internal combustion rotary kiln which had been heated and adjusted without adjusting the atmosphere so that the total feed amount of the mixture was 400 kg/h to 450 kg/h. When heating was adjusted so that the temperature in the furnace was 1000°C or less, the minimum temperature in the furnace was 740°C and the maximum temperature was 980°C. While maintaining this furnace temperature, the rotation speed of the rotary kiln was set to about 0.35 rpm, and reduction treatment was performed for 8 hours. The mixture after the reduction treatment was subjected to magnetic separation to separate the remaining unreacted coal char and reduced iron to remove impurities. The obtained reduced iron is pulverized by a vibration mill, and then classified into iron powder of more than 263 μm and iron powder of 263 μm or less by a sieve with an opening of 263 μm. The pulverization process and the classification process were continuously repeated until a passing particle size was achieved. Thus, the iron powder according to Example 1 was obtained. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured by the methods described later. Table 1 shows the measurement results.

Example 2
Iron powder was obtained in the same manner as in Example 1, except that the weight ratio of iron ore and coal char was 6:4, and the total ore supply amount of the mixture was 700 kg/h to 750 kg/h. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

Example 3
An iron powder was obtained in the same manner as in Example 1, except that the reducing furnace was changed from an internal combustion rotary kiln to an external combustion rotary kiln. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

Example 4
An iron powder was obtained in the same manner as in Example 3, except that the total ore supply amount of the mixture was 500 kg/h to 550 kg/h. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

Comparative example 1
In Example 1, the iron powder obtained by passing through a sieve with an opening of 263 μm after the first pulverization treatment by the vibration mill was used as the iron powder according to Comparative Example 1. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

Comparative example 2
The iron powder obtained in Comparative Example 1 was passed through a sieve with an opening of 109 μm, and the iron powder obtained in Comparative Example 3 was obtained. The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

Comparative example 3
Example 1 except that mill scale was used as iron ore and coke was used as coal char, the reduction furnace was changed from an internal combustion rotary kiln to a tunnel kiln, the reduction temperature was adjusted to 1050 ° C. to 1250 ° C., and the reduction time was 38 hours. Iron powder was obtained in the same manner as The composition, powder characteristics and oxygen absorption characteristics of the obtained iron powder were measured in the same manner as in Example 1. Table 1 shows the measurement results.

(composition analysis)
(Metallic iron (M.Fe))
The amount of metallic iron (M.Fe) in the sample is measured according to JIS M8713-1977 "Reduction test method for iron ores". to extract and dissolve metallic iron, and titrate with a chelate using a potentiometric automatic titrator.

(oxygen (O))
The oxygen content (O) in the sample was calculated using an oxygen/nitrogen analyzer (TCH600 manufactured by LECO).

(Carbon (C))
The carbon content (C) in the sample was calculated using a carbon/sulfur analyzer (LECO CS-744).

(apparent density)
The apparent density of the sample was measured according to the procedure of JIS Z 2504, Method for Measuring Apparent Density of Metal Powder.

(BET specific surface area)
The BET specific surface area of the sample was measured using a BET one-point specific surface area measuring device (manufactured by Mountec Co., Ltd., model: Macsorb HM model-1208).

(Average particle size)
The particle size distribution of the sample was measured using a laser diffraction particle size distribution analyzer MT (manufactured by Nikkiso Co., Ltd., Microtrac Model 9320-X100), and the cumulative 50% particle size on a volume basis was taken as the average particle size.

(flow rate)
The fluidity of the sample was measured according to the procedure of JIS Z 2502, Metal Powder Fluidity Test Method.

(oxygen absorption)
1 g of a composition obtained by mixing 0.5% by mass of salt with respect to 100% by mass of a sample is placed in a breathable packaging material, sealed in a gas barrier bag together with absorbent cotton impregnated with 10 mL of water, and the inside of the bag is evacuated once with a pump. did. Next, 1500 mL of air was put into the gas barrier bag and stored at 20° C. After 96 hours, the oxygen concentration in the bag was measured and the oxygen absorption was calculated by the following equation.
Oxygen absorption (mL/cm ³ ) = {(20.9-X)/(100-X)} x 1500 x apparent density X: oxygen concentration after 96 hours (%)

As is clear from Table 1, the apparent density is 2.21 g/cm ³ to 2.47 g/cm ³ and the BET specific surface area is 2.14 m ^{2 /g} to 3.20 m ² /g, which are within the specified ranges of the present invention. The iron powders of Examples 1 to 4 are the iron powders of Comparative Examples 1 and 2, which have apparent densities of 2.00 g/cm ³ and 1.98 g/cm ³ , which are smaller than the specified range of the present invention, and Compared to the iron powder of Comparative Example 3, which has a BET specific surface area of 0.25 m ² /g, which is smaller than the specified range of the present invention, the oxygen absorption amount per unit volume was large. That is, the iron powders of Examples 1-4 could reduce the volume of the iron powder used while maintaining the desired oxygen absorption amount compared to the iron powders of Comparative Examples 1-3.

According to the iron powder according to the present invention, it is possible to reduce the size of the package of the oxygen scavenger without lowering the oxygen absorption capacity.

Claims (2)

An iron powder used as an oxygen absorber,
An apparent density of 2.21 g/cm ³ or more and 2.80 g/cm ³ or less,
BET specific surface area is 2.0 m ² /g or more and 4.0 m ² /g or less ,
The metallic iron content is in the range of 83% by mass or more and 93% by mass or less,
The fluidity is in the range of 28 sec/50 g or more and 50 sec/50 g or less,
An iron powder for a deoxidizer, characterized by having an average particle size in the range of 30 µm to 300 µm . The iron powder for oxygen scavenger according to claim 1;
a metal halide;
An oxygen scavenger comprising: