JPH0225401B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to iron powder used in applications such as disposable hand warmers that generate heat slowly due to the heat of oxidation reaction in the atmosphere, and a method for producing the same. Recently, disposable hand warmers using iron powder have become widely used. This type of hand warmer utilizes the reaction heat generated by the reaction between iron powder and oxygen in the presence of moisture in the atmosphere. It is required to generate heat stably for a long period of time (that is, the duration of heat generation is long). However, since the heat generation temperature is not sufficient with just iron powder and water, in this type of hand warmer, various catalysts such as salt and activated carbon are generally added to increase the heat generation temperature and sustainability. However, as for the characteristics of the iron powder itself, it is necessary that the heat generation temperature (especially the initial rise temperature) is high and the durability is high. By the way, regarding the properties of the iron powder used in this type of hand warmer, it is said that the larger the specific surface area of the particles, and the higher the purity or activity, the more active the reaction will be, and the higher the exothermic temperature will be. . Therefore, iron powder used in this type of hand warmer has been proposed, for example, those described in Japanese Patent Laid-Open No. 163201/1982 and those described in Japanese Patent Laid-open No. 166155/1983. Here, in the proposal of JP-A-56-163201,
In a hydrogen-containing atmosphere, atomized iron powder with a total iron powder amount of 98 wt% or more and 80 mesh or less is 98 wt% or more, which has been subjected to low-temperature reduction treatment at 600 to 750 °C, is processed by adding mill scale powder, etc. Hand warmer iron mixed with reduced iron powder of high purity iron powder with a total iron powder amount of 95wt% or more and 80wt% or more of 250 mesh or less, which has been subjected to high temperature finishing reduction treatment at 850℃ in a hydrogen atmosphere after rough reduction. Powder is disclosed. In the case of the proposal of Japanese Patent Application Laid-Open No. 6-163201 mentioned above,
The aim is to ensure the initial rise temperature of heat generation using reduced iron powder, and to ensure the temperature and duration of heat generation using atomized iron powder. However, the reduced iron powder used in this proposal, which has been reduced through high-temperature finishing, has a high purity with a total iron powder content of 95 wt% or more.
Although the amount of fine powder below mesh is often 80wt% or more, there are problems in that the specific surface area is small and the activity is reduced. Furthermore, atomized iron powder that has been reduced through low-temperature finishing has a high purity with a total iron powder amount of 98wt% or more, and has high activity, but less than 80 mesh
There is a problem that each particle of 98wt% or less is dense. Therefore, due to these problems, the iron powder for hand warmers used in the above proposal, which is a mixture of atomized iron powder that has been reduced to a low temperature finish and reduced iron powder that has been reduced to a high temperature finish, has a high rise temperature, maximum temperature, average temperature, and When comprehensively evaluated based on duration, the reality is that sufficient rise temperature and duration cannot be obtained. Furthermore, in the proposal of JP-A No. 57-166155, reduced pellets are coarsely reduced at a high temperature of 1200℃ using solid carbonaceous material (coke powder), dried to a moisture content of 0.1 wt% or less, and pulverized to produce 100 meshes or less. Disclosed is a low-purity reduced iron powder for hand warmers in which the activity of the powder particles is increased, the total amount of iron powder is 65 to 95 wt%, and the amount of metallic iron powder is 60 to 90 wt%. Such high-temperature rough reduction and low-purity reduced pellet pulverized iron powder of 100 mesh or less proposed in JP-A No. 57-166155, due to high-temperature reduction and excessive grinding,
Since the specific surface area becomes small, there is a problem that a sufficient duration cannot be obtained when comprehensively evaluated based on the rise temperature, maximum temperature, average temperature, and duration. As mentioned above, various types of reduced iron powder and pulverized dull iron powder are used as iron powder for conventional disposable hand warmers, but hand warmers using these conventional iron powders generally generate less heat. The reality is that things that have a high temperature tend to last for a short time, while things that last a long time tend to generate heat at a low temperature.
Therefore, there is a strong demand for the development of iron powder that has a high rise temperature in the initial stage of heat generation and can stably generate heat for a long period of time. This invention was made against the background of the above circumstances, and provides iron powder for slow heat generation in the atmosphere, which has a high initial temperature and can generate heat stably for a long period of time, and is suitable for disposable hand warmers, etc., and a method for producing the same. The purpose is to In order to achieve the above-mentioned purpose, the present inventors carried out experiments and experiments on various properties of iron powder that affect the heat generation properties of iron powder.
As a result of repeated studies, it was discovered that by satisfying specific particle size distribution conditions, specific surface area conditions, and purity conditions, iron powder with excellent heat generation properties suitable for disposable hand warmers can be obtained, and in that case,
In particular, by increasing the activity by pulverizing sponge iron to obtain a specific particle size and particle size distribution, and by achieving a specific purity by magnetic separation without final reduction heat treatment, it is possible to achieve low cost and industrial production. They discovered that it was possible to produce iron powder with excellent heat generation properties, and came up with this invention. Specifically, the reduced iron powder for slow heat generation in the atmosphere of the first invention of the present application contains metallic iron in the range of 75 to 99% by weight, has a particle size of 60 mesh or less, and accounts for 200 mesh in the total powder. The proportion of powder below mesh size is 40~
Within the range of 80% by weight, and the specific surface area is 0.120m ² /
g or more. Further, the method for producing reduced iron powder for slow exotherm in the atmosphere according to the second invention includes pulverizing sponge iron obtained by reducing iron oxide,
The particle size is less than 60 mesh and accounts for the entire powder.
It consists of a stage of obtaining iron powder in which the proportion of powder of 200 mesh or less is within the range of 40 to 80% by weight, and a stage of purifying the metallic iron to a content of 75 to 99% by weight by magnetic separation without final reduction. It is characterized by this. The reduced iron powder for slow exotherm in the atmosphere and the method for producing the same according to the present invention will be explained in detail below. In general, iron powder used in disposable hand warmers is preferable as it has a larger specific surface area, and iron powder with higher purity or activity, as the oxidation reaction proceeds more actively and the heat generation temperature increases. Therefore, active iron powder with a large specific surface area is required, especially in order to increase the rising temperature at the initial stage of heat generation. In general, it is believed that the more irregularly shaped the iron powder particles are, the finer the particles of the same shape, the larger the specific surface area, and the greater the processing strain introduced by grinding etc., the more active the iron powder is. Therefore, it is considered preferable to use iron powder for hand warmers that has been finely ground into irregular shapes. As a result of considering the particle size, particle size distribution, and specific surface area of iron powder from this perspective,
It is iron powder obtained by finely pulverizing sponge iron obtained by reducing iron oxide such as mill scale to 60 mesh or less,
Moreover, the particle size is not constant, and iron powder of irregular shape with a particle size distribution in which 40 to 80% by weight is 200 mesh or less and a specific surface area of 0.120 m ² /g or more is suitable. It turns out that
These particle size, particle size distribution conditions, and specific surface area conditions are defined in this invention. The reason why the particle size of the iron powder was limited to 60 mesh or less as described above is as follows. In other words, when used in a disposable hand warmer, the oxidation reaction of iron powder particles proceeds sequentially from the particle surface toward the inside of the particle, but once the oxidation reaction has progressed to a certain depth, the reaction progresses slowly beyond that point. In particular, it was found that with coarse powders exceeding 60 meshes, unreacted metallic iron remained inside the particles even after using the hand warmer, resulting in poor heat generation efficiency. Therefore, the particle size of iron powder is 60
It is necessary that the value is less than or equal to mesh. In addition, the reason why the particle size distribution of iron powder was specified so that 40 to 80% by weight should be 200 mesh or less, in other words, 60 to 20 weight % should be 60 to 200 mesh was as follows. It is. In other words, it is considered that it is preferable that the fine powder particles be as fine as possible in order to increase the rising temperature at the initial stage of heat generation.
If the powder is pulverized to more than 80%, the irregularity of the particles will be lost due to repeated pulverization for pulverization, and the particles will become spheroidal, and the pores inside the particles will also be closed, so that the rise temperature will actually be almost the same. The amount will not rise, and the cost required for crushing will also increase. while 200
If the content of the mesh or less is less than 40%, the effect of increasing the rise temperature due to refinement is insufficient, and a sufficient rise temperature cannot be obtained. In addition, in order to increase the sustainability of heat generation, that is, to lengthen the duration of the oxidation reaction, it is necessary to increase the purity of the iron powder and at the same time increase the particle size to a certain extent. exceeds 80% by weight
If the content of 60 to 200 meshes is less than 20% by weight, the sustainability of heat generation will not be sufficient. Therefore, in order to sufficiently increase the rising temperature at the initial stage of heat generation and ensure the sustainability of heat generation, it is necessary to use powders with a particle size of 200 mesh or less among powders with a particle size of 60 mesh or less.
It is necessary to have a particle size distribution that accounts for 40 to 80% by weight. Next, the reason why the specific surface area of the iron powder was limited to 0.120 g/m ² or more is as follows. Normally, disposable hand warmers that use iron powder are often used after opening the outer bag and then kneading them by hand, but this brings the surface of the iron powder particles into sufficient contact with the atmosphere to accelerate the oxidation reaction, which increases the initial rise temperature. The purpose is to increase the iron powder, and for this purpose, it is preferable that the iron powder has a large reaction area, that is, a specific surface area.According to the experiments conducted by the present inventors, the specific surface area of the iron powder is less than 0.120 m ² /g. It was found that a sufficient rise temperature could not be obtained due to insufficient reaction area. Therefore, in this invention, the specific surface area of the iron powder must be 0.120 m ² /g or more. Furthermore, in the iron powder of the present invention, in addition to the particle size, particle size distribution conditions, and specific surface area conditions as described above, as purity conditions, the metallic iron content is 75 to 99% by weight.
Must be within the range. The reason is as follows. In other words, the conventional idea was that in hand warmers that utilized the heat of oxidation reaction of iron powder, if the purity of the iron powder was low (i.e., the amount of metallic iron was low), the amount of heat generated would be low, making it impossible to obtain sufficient heat generation temperature. It was said that it was preferable to use iron powder with the highest possible purity, but in order to increase the metallic iron content to 99% or more, it was necessary to perform high-temperature reduction treatment at a temperature of about 800 to 1000 degrees Celsius in an atmosphere containing hydrogen. This high-temperature reduction treatment stabilizes the iron powder particles and reduces their activity, and the sintering and crushing impairs the irregularity of the iron powder particles, resulting in a sufficient rise in the initial stage of heat generation. It is not preferable to increase the purity of the iron powder, that is, the amount of metallic iron above 99%, because the temperature cannot be obtained and the production cost increases due to the high-temperature reduction treatment. On the other hand, if the metallic iron content is less than 75%, a sufficient exothermic temperature and sufficient exothermic duration cannot be obtained, and in particular, the exothermic duration is insufficient. Therefore, in this invention, the amount of metallic iron contained in the iron powder must be 75% or more and 99% or less. Next, a method for producing iron powder as described above will be explained. First, as the starting material iron oxide, various materials can be used, such as iron ore, mill scale generated in the rolling process of steel mills, and converter dust. A raw material containing few impurity components that sometimes generate foul-smelling gases such as H ₂ S or NH ₃ is preferable, and from this point of view, mill scale is optimal. Iron oxide such as mill scale is reduced to sponge iron using coke or the like. A conventionally known method may be applied to this method for producing sponge iron. For example, iron oxide such as mill scale crushed to 16 mesh or less and coke powder are packed in concentric layers in a refractory container (sagger) and held at a temperature of 900 to 1050°C for 1 to 20 hours to achieve rough reduction. Then, the amount of metal iron powder is
Sponge iron may be obtained by applying a known method to reduce the content to less than 75 wt%. The obtained sponge iron is ground into irregularly shaped iron powder particles of 60 mesh or less, and the particle size of the powder as a whole is
The proportion of particles of 60 mesh or less and 200 mesh or less is 40 to 80% by weight, and the specific surface area is 0.120.
The iron powder should be m ² /g or more. In this case, the sponge iron is first roughly pulverized to a size of several centimeters using a coarse pulverizer, then medium pulverized to a size of several mm using a medium pulverizer, and finally finely pulverized to a size of 60 mesh or less using a pulverizer. It is desirable to carry out the grinding stepwise in this way, so that particles having a relatively irregular shape can be obtained. Of course, this pulverization step may also include a step of classifying so that the particle size distribution falls within the above-mentioned range, that is, 40 to 80% by weight of the particles are 200 mesh or less. The iron powder pulverized as described above is purified by magnetic separation without undergoing final reduction treatment in an atmosphere containing hydrogen, and has a metallic iron content of 75 to 99% by weight.
The purity of iron powder must be within the range of . Here, a known method may be applied as a specific method of magnetic selection. Furthermore, it goes without saying that magnetic separation may be performed multiple times as appropriate in combination with the above-mentioned pulverization step, and therefore, the magnetic separation step is not limited to being performed only after the pulverization step. In this way, by increasing the purity through magnetic separation without performing a final reduction heat treatment in an atmosphere containing hydrogen, the activity of the iron powder particles can be improved as in the case of a final reduction heat treatment in an atmosphere containing hydrogen. Moreover, the irregularity of the particles is not impaired by sintering and crushing, and furthermore, the processing cost is significantly reduced. Examples and comparative examples of the present invention will be described below. Table 1 shows the raw materials and manufacturing methods for the iron powder for slow heat generation in the atmosphere (present invention material) A to D of the present invention and the iron powder for slow heat generation in the atmosphere (comparative material) E to I of the comparative examples. The conditions and chemical composition at each step in the manufacturing process are shown. In addition, in Table 1, T.Fe
is the total iron content including iron oxides in the powder, or
M.Fe indicates the amount of metallic iron in the powder. Table 2 shows the chemical composition (T.Fe and
M.Fe), powder properties and particle size distribution. The specific manufacturing method of each iron powder A to I is as follows. Iron powder A to G are made from mill scale generated at a steelworks, and are filled in concentric layers together with coke powder into a refractory container (sagger).
It was maintained at 1000°C and 1100°C for 5 hours and crudely reduced to obtain sponge iron. Next, these sponge irons were pulverized into 60 mesh or less through a three-step pulverization process: coarsely pulverized with a single toggle crusher, medium pulverized with an impeller breaker, and finely pulverized with a novolo rotor mill. Subsequently, magnetic separation was repeated 2 to 7 times using a dry drum type magnetic separator to increase purity, and the particle size was adjusted by sieving to produce the product. In addition, iron powder G is obtained by crushing and magnetically separating sponge iron in the same manner as above, and then adding 75 vol% H ₂ −
After being held at 900° C. for 1 hour in a 25 vol% N ₂ atmosphere, the sintered cake was crushed in a hammer mill and sieved to a size of 60 mesh or less to produce a product. Iron powder H uses water atomized iron powder as raw material,
After reducing by holding at 700℃ for 1 hour in a 75vol% _H2 -25vol% _N2 atmosphere, the sintered cake was crushed in a hammer mill and sieved to 60 mesh or less without magnetic separation. . Iron powder I is made by pelletizing iron ore powder using a pelletizing sig, sifting the pellets to 5 to 16 mm, filling them together with coke powder in concentric layers in a sagger, and holding the pellets at 1100°C for 5 hours for rough reduction. It was made of sponge iron made of pellets stuck together. This sponge iron was pulverized in the same three-step pulverization process as described above, and sieved to 60 mesh or less without magnetic separation to produce a product. Here, iron powders A to D are materials of the present invention, among which iron powder A is one in which the proportion of powder with a particle size of 200 mesh or less is near the upper limit of the range of the present invention;
For iron powder C, the ratio of powder with a particle size of 200 mesh or less is near the lower limit of the range of the present invention, and for iron powder B, the ratio of powder with a particle size of 200 mesh or less is between iron powders A and C. It is something. Further, the iron powder D has a relatively low purity (M.Fe) within the scope of the present invention. In addition, iron powder A to D
The specific surface area of each is 0.13 m ² /g or more, which is within the scope of the present invention. On the other hand, iron powders E to I are comparative materials, of which iron powder E has a particle size of 200 mesh or less, which weighs 26.9wt.
%, and the specific surface area is as low as 0.11 m ² /g, which is outside the scope of this invention. Iron powder F has a purity (M.Fe) as low as 52.6 wt%, which is outside the scope of this invention. There is. In addition, iron powder G has a low ratio of particle size of 200 mesh or less at 36.7wt%, and a specific surface area of 0.11.
m ² /g, which is outside the scope of this invention, and iron powder H has a high (M.Fe) content of 99.2wt% and a specific surface area of
Iron powder I has a low purity (M.Fe) of 67.7wt%, which is outside the scope of this invention as low as 0.09m ² /g.
It is outside the scope of this invention. Table 3 shows the heat generation characteristics when each of these iron powders A to I is used as a hand warmer. Generally, in hand warmers that utilize the heat of the oxidation reaction of iron powder, various catalysts such as salt and activated carbon are added in addition to the iron powder and water in order to accelerate the oxidation reaction and improve the sustainability of heat generation. However, in this example as well, a hand warmer was manufactured using the most common method and a heat generation test was conducted. That is, the composition of the hand warmer and the test method for conducting the heat generation test as a hand warmer are as follows. Iron powder 35g, water 15.4g, salt 4.2g, activated carbon powder 10.5g
After thoroughly mixing g and 4.9 g of perlite powder,
It was sealed in a thick synthetic resin film bag with ventilation permeability. After leaving it as it is for a day and night, open it again, attach a thermocouple to the center of the bottom of the bag, cover the entire pocket warmer with a cloth, and measure the temperature for 24 hours while it is standing still to determine the rise temperature, maximum temperature, average temperature, and duration of heat generation. I asked for time.
The rising temperature is the temperature 30 minutes after the start of heat generation, and the maximum temperature is the highest value of the heat generation temperature.
The average temperature is the average value of the values measured at 15-minute intervals for 24 hours, and the duration of fever is shown as the elapsed time from the start of fever until the fever temperature drops to 40°C or less. As is clear from Table 3, iron powder A of the present invention material
～D shows higher values in rise temperature, average temperature, and duration of heat generation than the comparative iron powders E～I, and is excellent as an iron powder used for slow heat generation in the atmosphere such as disposable hand warmers. It is clear that the material has excellent exothermic properties. In other words, in general, it is considered preferable for a pocket warmer using iron powder to have a high start-up temperature at the initial stage of heat generation and a long duration of heat generation in order to provide a pleasant feeling of use, and the iron powder of the present invention satisfies both of these conditions. It is clear that Furthermore, when examining each iron powder in the Examples in detail, it is found that the iron powder A of the present invention has a relatively high purity with a metallic iron content of 97.1%, and a purity of 200 mesh or less is 79.3%.
% and a large specific surface area of 0.16 m ² /g, the rise temperature shows the highest value. On the other hand, iron powder C has a metallic iron content of 96.9, similar to iron powder A.
Although the purity is high at %, 42.2% is less than 200 mesh.
%, the particle size is small, and the specific surface area is 0.13m ² /g.
Because it is small, the start-up temperature is slightly lower, but the duration of heat generation is the longest. Furthermore, although iron powder D has a large specific surface area, it has low purity and therefore exhibits the lowest heat generation properties among the materials of the present invention, but all properties are higher than those of the comparative materials, indicating that the present material is superior to the conventional iron for hand warmers. It can be seen that it is superior to powder. Note that iron powder B exhibits intermediate characteristics between iron powder A and iron powder C. On the other hand, iron powder E, which is a comparative material, has a high purity with a metallic iron content of 96.7%, but it has a fine powder of less than 200 mesh.
Since it has a small specific surface area of 26.9% and a small specific surface area of 0.11 m ² /g, its heat generation properties including the rise temperature are inferior to the materials of the present invention. Also, iron powder F is 200
Although it contains a large amount of fine powder (54.2%), and has an extremely high specific surface area of 6.13 m ² /g, it has a low purity metal iron content of 52.6%, so sufficient exothermic properties cannot be obtained, and the exothermic temperature and the duration of fever is the poorest. In addition, although iron powder G has a high metallic iron content of 98.7%, the activity of the iron powder decreases due to high-temperature reduction heat treatment to increase purity, and fine powder of 200 mesh or less is 36.7%. Since the specific surface area is as low as 0.11 m ² /g, the rise temperature does not rise much. Furthermore, iron powders H and I, which are comparison materials, are iron powders for hand warmers that have been proposed in the past, and iron powder H is a high-purity iron powder that is made by subjecting atomized iron powder to low-temperature reduction heat treatment to increase its activity as described above. In this case, although the metallic iron content is high at 99.2%, the specific surface area is 0.09%.
Since it is as small as m ² /g, the rise temperature does not rise much. In addition, Iron Powder I is made by finely pulverizing reduced iron particles to increase the activity of the iron powder, with 78.6% of the iron powder being 200 mesh or less in size, and a specific surface area of 3.86 m ² /g.
Although it is large, the amount of metallic iron powder is 67.7%, which is a low purity, so sufficient heat generation characteristics cannot be obtained, and it is inferior in both heat generation temperature and heat generation duration. As is clear from the above examples, the iron powder for slow heat generation in the atmosphere of the present invention has a high rising temperature at the initial stage of heat generation, and also generates heat stably for a long time to obtain a long heat generation duration. It has excellent heat generation properties suitable for uses such as disposable hand warmers. Further, according to the method for producing iron powder of the present invention, in order to improve the purity and activity of iron powder, these can be improved by crushing and magnetic separation treatment without performing final reduction heat treatment at low or high temperatures. Therefore, the manufacturing cost of iron powder is significantly reduced compared to the conventional method, and it is possible to industrially supply a large amount of iron powder for slow heat generation in the atmosphere, which is inexpensive and has excellent properties.

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Claims (1)

[Scope of Claims] 1. Contains metallic iron in the range of 75 to 99% by weight, and the particle size of the entire powder is 60 mesh or less, and the proportion of the powder in the total powder is 200 mesh or less.
Within the range of 40-80% by weight, with a specific surface area of 0.120
Reduced iron powder for slow exotherm in the atmosphere, characterized by having a particle size of m ² /g or more. 2. Pulverize the sponge iron obtained by reducing iron oxide to obtain particles with a particle size of 60 mesh or less and which account for a large proportion of the total powder.
A step of obtaining iron powder in which the proportion of powder of 200 mesh or less is within the range of 40 to 80% by weight, and a step in which the metallic iron content is within the range of 75 to 99% by weight by magnetic separation without final reduction heat treatment. 1. A method for producing reduced iron powder for slow exotherm in the atmosphere, comprising the steps of purification as follows.