JP3317593B2 - Flat reduced iron powder for oxygen scavenger and production method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat reduced iron powder for an oxygen scavenger used for the purpose of imparting a deoxidizing function to a sterilized packaging container and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Oxygen absorbers have been applied to various fields such as various foods and agricultural and marine products in order to prevent quality deterioration due to oxygen. As the iron powder used for the oxygen absorber, atomized iron powder manufactured mainly for powder metallurgy or reduced iron powder manufactured for disposable warmers is used. Density 2.0-3.0 g / cm ³
And the particle shape is irregular.

As an oxygen absorbent suitable for a specific application field, Japanese Patent Application Laid-Open No. 4-90847 or Japanese Patent Application Laid-Open No.
-90848. These applications relate to a resin composition having an oxygen-absorbing property, and a film or sheet and a packaging container using the resin composition having an oxygen-absorbing property, and have a specific surface area of 0.5 m ² as iron powder used herein. / G or more, preferably 1.0 m ² /
g or more, more preferably 2.0 m ² / g or more, and an apparent density of 2.2 g / cm ³ or less, preferably 1.9 g / cm ³ or less.
cm ³ or less, particularly preferably, 1.6 g / cm ³ or less of reduced iron powder, atomized iron powder, is composed of a spongy porous granules having a large number of fine pores from the surface to the inside of such搗砕iron powder Have been awarded.

[0004] In recent years, as a packaging form of food, there is an aseptic packaging and filling in which separately sterilized food and a packaging container are filled and packaged in an aseptic environment to produce a product. Apart from preservation of agricultural and marine products, this container for sterilized packaged food is Lamicontre (PP / EVOH / P
A product having a function as a deoxidizer inside P) is commercially available.

As described above, iron powder having a specific surface area of 0.5 m ² / g or more and an apparent density of 2.2 g / cm ³ or less is recommended as the iron powder used as the oxygen absorbent of this container. However, the deoxygenation absorption performance is not always sufficient.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and has a high deoxidizing function and can be filled in a sterilized packaging container or the like. And a method for producing the same.

[0007]

Means for Solving the Problems The present inventors have conducted experiments and studies on various properties of iron powder as an active ingredient of an oxygen agent incorporated in a sterilized packaging container, and as a result, specific particle size distribution conditions and purity conditions Finding iron powder that can provide excellent performance as a sterile packaging tray with deoxygenation function by satisfying all the factors of apparent density and particle shape, and in that case, ordinary reduced iron powder The shape is flattened by pulverization of so-called primary reduced iron powder that has not been subjected to finish reduction heat treatment as seen in, and has a specific particle size and particle size distribution, and a specific apparent density, and furthermore, the iron powder surface at low temperature The present inventors have found that it is possible to produce an iron powder having high activity while leaving oxides with atomic vacancies as much as possible, and have accomplished the present invention.

That is, the flat reduced iron powder for an oxygen scavenger of the present invention has a metal iron content of 85 to 98% by weight, a median particle diameter of 25 μm or less, and an iron powder content of 10 μm or less in the total powder of 40 or less. It is a flat reduced iron powder for an oxygen scavenger having a volume percentage of not more than 1.0 and an apparent density of 1.0 to 1.8 g / cm ³ .

Hereinafter, the flat reduced iron powder for an oxygen scavenger of the present invention will be described in detail. Currently, the iron powders on the market include sprayed powders for powder metallurgy or oxygen scavengers, and reduced iron powders that have been subjected to a finishing heat treatment and have a metallic iron content of 98% by weight.
The main products are super-fine powders and primary reduced iron powder having a metal iron content of 90 to 98% by weight, which is mainly used for chemical reduction or for use in warming.

[0010] The iron powder to be used in the present invention, for example, used for imparting a deoxygenating function to a container for aseptic packaging and the like is most preferably pulverized using the above iron as a starting material. Although simple, high-purity iron powder with a metal iron content of more than 98% by weight takes time to grind. Rather, it is more convenient to use a porous reduced iron powder containing a small amount of iron oxide as a starting material because the pulverization time can be shortened. Since the duration of the oxygen effect is shortened, it is necessary to increase the use amount of iron powder. As a raw material of the flat reduced iron powder for an oxygen scavenger of the present invention, a primary reduced iron powder having a metal iron content of 85 to 98% by weight is used. It is preferably used.

Next, regarding the particle size and the particle size distribution,
The content of iron powder having a median particle diameter of 25 μm or less and a particle diameter of 10 μm or less in the total powder is preferably 40% by volume or less. For larger particle sizes,
For example, JP-A-4-90847 and JP-A-4-90847
In the case of a film or sheet and a packaging container using a resin composition having an oxygen absorbing property proposed in Japanese Patent No. 90848, miscibility with a resin and uniform dispersibility deteriorate. When the particle size is too small, the miscibility with the resin and the uniform dispersibility are improved. However, when the particle size is too small, spontaneous ignition may occur at the time of production. If the content is not more than 30% by volume, preferably not more than 30% by volume, the dispersibility in the resin and the uniformity of the material of the film or sheet containing the oxygen scavenger and the packaging container using these films or sheets can be achieved. At the same time, the production of iron powder suitable for such uses is made without difficulty and safely.

Further, the shape of the iron powder used for such an application is a very important factor, and the fine powder having a surface area of 45 μm or less, which is usually called superfine, has the smallest surface area, in other words, the surface energy. Since it is stable to take the shape of a sphere or a shape close to it, the fine powder having a size of -45 μm or less is often irregular in shape near a sphere, except for special powders. However, the iron powder having such a shape is not suitable for the above-mentioned use. The present inventors have found that the optimum shape for such an application is a flat shape, and succeeded in devising the shape so that even fine powder has a flat shape. Iron powder having the above-mentioned particle size and particle size distribution and having a flat shape has an apparent density of 1.0 to 1.8 g / cm ³ , but if it is too light, the volume per unit weight is reduced. When it is made into a film or a sheet, it becomes impossible to incorporate a fixed weight of iron powder. On the other hand, if the apparent density is too large, the film, sheet, or packaging container is disadvantageous in that the material becomes non-uniform and the strength is weakened.
0 to 1.8 g / cm ³ .

Next, a method for producing the above-described iron powder will be described. The method for producing a flat reduced iron powder for an oxygen scavenger of the present invention comprises adding 0.05 to 1.0% by weight of fat or oil as a flattening accelerator to reduced iron powder containing 85 to 98% by weight of metallic iron, The content of iron powder having a median particle diameter of 25 μm or less and a particle diameter of 10 μm or less occupying the entire powder is 4
Flat reduction for deoxidation, characterized by obtaining iron powder having a volume density of 0% by volume or less and an apparent density of 1.0 to 1.8 g / cm ³ , and then performing a finish reduction heat treatment at a temperature of 250 to 600 ° C. It is in the manufacturing method of iron powder.

First, as a starting material, it is optimal to use iron ore such as a tunnel kiln or a rotary kiln, or primary reduced iron powder obtained by reducing mill scale generated in a rolling process in an ironworks with a reducing agent such as coal or coke. Usually, the metallic iron content of these primary reduced iron powders is 85
~ 98% by weight. Generally, iron powder for powder metallurgy and welding rods on the market is further subjected to finish reduction heat treatment at a high temperature of 900 to 950 ° C., so that the metallic iron content is 98%.
%, And it is possible to use these iron powders as a raw material of the iron powder of the present invention, but it takes time to pulverize. Further, not only reduced iron powder but also sprayed iron powder has a disadvantage that the metal content exceeds 98% by weight and it is difficult to grind.

As described above, the starting material of the iron powder of the present invention has a metal iron content of 90 to 9 coarsely pulverized to 250 μm or less.
The primary reduced iron powder of 8% by weight is optimal, but these are further finely pulverized by a mechanical pulverization method such as a ball mill, a vibrating mill or a high-speed mill, and the particle size is reduced to 25 μm or less in median particle diameter and the particle size distribution. In order to make the content of iron powder having a particle size of 10 μm or less in all powders to be 40% by volume or less, and to have a flat iron powder shape and an apparent density of 1.0 to 1.8 g / cm ³ , Special devices are required.

As a result of extensive studies, the present inventors have found that 0.05 to 1.0% by weight, preferably 0.1% by weight of fat or oil is used as a flattening accelerator in order to flatten the shape in mechanical pulverization. It has been found that the iron powder of the present invention can be manufactured by mechanically pulverizing to a predetermined particle size by adding about 0.5% by weight. That is, the amorphous iron powder having a metal iron content of 90 to 98% by weight pulverized to about 250 μm or less firstly flattens in the presence of fats and oils, and the flat iron powder gradually disintegrates and becomes finer as the pulverization progresses. I found that. When there is no oil or fat, the iron powder is finely divided, but the shape is irregular and it is difficult to obtain flat iron powder. The pulverizer is a ball mill, a vibration mill, a high speed mill or the like, and is not particularly limited, but a vibration mill or the like is most preferable.

The fats and oils are not particularly limited, but lubricating oils and the like are preferable in addition to fatty acids such as stearic acid and palmitic acid and salts thereof or beef tallow. Addition amount is 0.05 ~
Flattening can be controlled by adding 1.0% by weight, preferably 0.1 to 0.5% by weight. 0.05% by weight has a sufficient effect, but the flattening progresses as the amount of addition increases. However, a remarkable effect cannot be expected even if it is added in excess of 1.0%. On the other hand, if it is less than 0.05% by weight, flattening does not proceed. Therefore, the range of the addition amount is 0.0
The amount is suitably from 5 to 1.0% by weight, and a particularly preferred addition amount is from 0.
1 to 0.5% by weight.

The pulverized and pulverized flat iron powder is further 25
By performing a reduction heat treatment at a low temperature of 0 to 600 ° C., preferably 400 to 500 ° C. so as not to cause sintering and solidification,
Fats and oils are decomposed and removed, and the amount of metallic iron is increased by carbon monoxide gas or hydrocarbons generated when these organic substances are decomposed. Hydrogen as protective atmosphere,
Although a reducing gas such as an ammonia decomposition gas or an endothermic gas is preferably used, a neutral gas atmosphere such as a nitrogen gas may be used. If the temperature is higher than 600 ° C., solidification may occur. If the temperature is lower than 250 ° C., oils and fats may remain.

[0019]

The iron powder of the present invention has a metal iron content of 85 to 98% by weight, a median particle diameter of 25 μm or less, and an iron powder content of 10 μm or less in the total powder of 40% by volume or less. Further, it is a flat reduced iron powder for an oxygen scavenger having an apparent density of 1.0 to 1.8 g / cm ³ and is used for the purpose of imparting a deoxidizing function to a sterilized packaging container or the like. That is, by satisfying all of the specific particle size distribution conditions, purity conditions, apparent density, and particle shape factors, excellent characteristics can be imparted as a sterile packaging tray having a deoxidizing function.

Further, in producing iron powder having such properties, it is necessary to produce iron powder while maintaining a balance between particle size and particle size distribution, apparent density and particle shape. A method for keeping this balance in harmony As a starting material, a primary reduced powder having a metal iron content of 85 to 98% by weight, preferably 90 to 96% by weight is used, and at the time of grinding, 0.05 to 1.0% by weight of a fat or oil as a flattening accelerator is used. Preferably 0.
By adding 1 to 0.5% by weight, it is possible to produce iron powder having a deoxidizing function in a sterilized packaging film or sheet or a packaging container capable of satisfying all the above factors.

[0021]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 As shown in Table 1, primary reduced powder of a tunnel kiln (CSI 150 manufactured by Höganäs, Sweden)-250 μm
32 g of stearic acid (4 kg of iron powder)
%) And 16 kg of steel balls in a small vibration mill and pulverized for 40 hours.
Heat treatment was performed for 1 minute to obtain iron powder. In Table 1, M · Fe indicates the amount of metallic iron in the metallic iron powder in the raw iron powder in terms of% by weight.

The properties (particle size, particle size distribution, apparent density, powder shape, etc.) and properties (oxygen absorption amount) of the obtained iron powder are shown in Table 2.

The particle size, apparent density, etc.
The measurement was performed with a Microtrac manufactured by Northrup Co., and the powder shape was determined by a scanning electron microscope. The amount of oxygen absorption was measured by the following method.

(Measurement method of oxygen absorption amount) As a deoxidizer packaging material, "Luxer" manufactured by Asahi Kasei Kogyo Co., Ltd., and a vinylon film (polyethylene laminated) on which aluminum is vapor-deposited, are thermocompression-bonded on three sides to a size of 40 × 40 mm I made a bag.

On the other hand, the iron powder 1
g was mixed with commercially available salt (0.012 g), and sealed in the above-mentioned bag to prepare a sample of an oxygen scavenger.

Separately, 350 × made of stretched nylon (polyethylene laminate) coated with polyvinylidene chloride
Into a 250 mm bag, put absorbent cotton (1.5 g) impregnated with 6 g of water, the oxygen absorber sample made by the above method, and 1150 ml of air (equivalent to 230 ml of oxygen) for 1 day.
After 2 days, 4 days, 7 days, 15 days and 30 days, 4 to 7 ml of air is extracted from the bag and "LC-750F" manufactured by Toray
The residual oxygen was analyzed with an oxygen analyzer, and the amount of oxygen absorbed per 1 g of iron powder was calculated.

As a result, as shown in Table 2, 50%
The diameter (median diameter) is 18.70 μm (specific surface area 0.4
78 m ² / ml) and an apparent density of 1.08 g / cm ³ . In addition, the amount of oxygen absorbed was 230 ml / 1 g · Fe after 2 days.
And good results were obtained.

Example 2 As shown in Table 1, the amount of stearic acid as a flattening accelerator in Example 1 was set to 20 g (0.5% by weight based on iron powder) and the pulverization time was set to 42 hours. Except having performed, it manufactured under the same conditions as Example 1, and obtained iron powder.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption) of the obtained iron powder are shown in Table 2.

Example 3 As shown in Table 1, the amount of stearic acid as a flattening accelerator in pulverization in Example 1 was 8 g (0.
2% by weight) and the milling time was changed to 60 hours under the same conditions as in Example 1 to obtain iron powder.

Table 2 shows the properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption amount) of the obtained iron powder.

Example 4 As shown in Table 1, the amount of stearic acid as a flattening accelerator in pulverization in Example 1 was 4 g (0.
1% by weight), the pulverizing time was 48 hours, and the heat treatment temperature after pulverization was 400 ° C. for 30 minutes, and iron powder was obtained under the same conditions as in Example 1.

Table 2 shows properties (particle size, particle size distribution, apparent density, shape, etc.) and characteristics (oxygen absorption amount) of the obtained iron powder.

Example 5 As shown in Table 1, the amount of stearic acid as a flattening accelerator in Example 1 was 2 g (0.
05% by weight), and the heat treatment temperature after pulverization is 250 ° C., 6
Except for 0 minute, it manufactured under the same conditions as Example 1, and obtained iron powder.

Table 2 shows the properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption amount) of the obtained iron powder.

Example 6 As shown in Table 1, a primary reduced powder of a tunnel kiln similar to that used in Example 1 as a starting material was further pulverized to −45 μm with a Sicomant mill (Heganes, Sweden). X-M300), palmitic acid was 12 g (0.3% by weight based on iron powder) as a flattening accelerator in Example 1, and the heat treatment temperature after grinding was 4%.
An iron powder was obtained under the same conditions as in Example 1 except that the temperature was changed to 00 ° C. for 30 minutes.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption) of the obtained iron powder are shown in Table 2.

Example 7 As shown in Table 1, an organic ester-based lubricating oil (commercially available from Swift, USA) was added as a flattening accelerator to 10 kg of the same primary reduced powder of a tunnel kiln as used in Example 1. 10 g (0.1% by weight based on iron powder) was added to a small ball mill containing 10 kg of 50 mmφ steel balls and 20 kg of 25 mmφ steel balls, and ground for 100 hours.
Heat treatment was performed at 0 ° C. for 30 minutes in a hydrogen atmosphere to obtain iron powder.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption) of the obtained iron powder are shown in Table 2.

Example 8 As shown in Table 1, RD-3 manufactured by Powdertech Co., Ltd. was used as a starting material, and 8 g of zinc stearate (0.2% by weight based on iron powder) was used as a flattening accelerator. Pulverization and heat treatment were performed under the same conditions as in Example 1 except that the pulverization time was changed to 48 hours, to obtain iron powder.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption) of the obtained iron powder are shown in Table 2.

Comparative Example 1 As shown in Table 1, iron powder was pulverized under the same conditions as in Example 4 except that no flattening accelerator was added and no heat treatment was performed after pulverization. Then, iron powder was obtained.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption) of the obtained iron powder are shown in Table 2.

Comparative Example 2 As shown in Table 1, primary reduced iron powder CMS manufactured by Sweden Höganäs Co., Ltd. was used as a starting material, no flattening accelerator was added, and no heat treatment after pulverization was performed. Except that iron powder was crushed under the same conditions as in Example 1,
Iron powder was obtained.

The properties (particle size, particle size distribution, apparent density, shape, etc.) and characteristics (oxygen absorption) of the obtained iron powder are shown in Table 2.

Comparative Example 3 As shown in Table 1, iron powder N.C100-24 for powder metallurgy manufactured by Höganäs, Sweden was used as a starting material.
Iron powder was pulverized under the same conditions as in Comparative Example 1 except that the pulverization time was changed to 52 hours to obtain an iron powder.

Table 2 shows the properties (particle size, particle size distribution, apparent density, shape, etc.) and properties (oxygen absorption amount) of the obtained iron powder.

[0049]

[Table 1]

[0050]

[Table 2]

As can be seen from these results, Example 1
It can be seen that the iron powder for oxygen scavengers of No. 8 to No. 8 has excellent initial rising properties and absorbs oxygen in the air that enters from the outer bag for a long time. On the other hand, since the iron powder of Comparative Example 1 did not contain the flattening accelerator, the apparent density was high and the deoxidizing ability was poor. In addition, the iron powder of Comparative Example 2 had a low M.Fe and thus had a poor deoxygenation rise, and when used for a long period of time, tended to be unable to absorb oxygen in the air that entered through the outer bag. The iron powder of Comparative Example 3 was M ·
Pulverization takes a long time because iron powder having a high purity of more than 98% by weight of Fe is used. In addition, since no flattening accelerator is added, the apparent density is high and the rising characteristics of deoxygenation are poor.

[0052]

As is apparent from the above description, the flat reduced iron powder of the present invention is used for an oxygen scavenger, particularly for imparting a deoxygenating function to a container such as sterilized packaged rice which has recently grown remarkably. It has extremely excellent properties as an active ingredient for deoxidation.

Further, according to the method for producing a flat reduced iron powder of the present invention, an excellent iron powder as an effective deoxidizing component can be produced safely and at low cost.

Continuation of front page (56) References JP-A-6-142502 (JP, A) JP-A-2-290902 (JP, A) JP-A-3-223401 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B01J 20/00-20/34 A23L 3/3436 501

Claims (3)

(57) [Claims] 1. A metal iron content of 85 to 98% by weight, a median particle diameter of 25 μm or less, and 10 μm in the total powder
A flat reduced iron powder for an oxygen scavenger, wherein the content of iron powder having the following particle diameter is 40% by volume or less, and the apparent density is 1.0 to 1.8 g / cm ³ . 2. A reduced iron powder containing 85 to 98% by weight of metallic iron is added with 0.05 to 1.0% by weight of a fat or oil as a flattening accelerator, and a median particle diameter of 25 μm is obtained by mechanical pulverization.
The content of iron powder having a particle size of 10 μm or less in the whole powder is 40% by volume or less, and the apparent density is 1.0 to 1.8 g / c.
A method for producing a flat reduced iron powder for deoxidation, comprising obtaining an iron powder having a m ^{3 value} and then performing a finish reduction heat treatment at a temperature of 250 to 600 ° C. 3. The flattening accelerator is stearic acid, palmitic acid or a salt thereof.
3. The method for producing a flat reduced iron powder for an oxygen scavenger according to item 1.