JP2006249359A - High specific gravity plastic composition containing iron powder, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high specific gravity plastic composition hardly getting rusty even under a high humid condition using an iron powder. <P>SOLUTION: The iron powder-containing high specific gravity plastic composition, whose specific gravity is 2-4.6, is produced by kneading a silane coupling-treated iron powder whose average grain diameter is ≥40 μm and ≤150 μm, a titanate coupling-treated zinc powder whose surface treatment is made separately from the iron powder and whose average grain diameter is ≥2 μm and <40 μm, and a heat molten thermoplastic resin, and comprises the coupling-treated iron powder of 30-88 mass%, the coupling-treated zinc powder of 2-60 mass%, and the thermoplastic resin of 10-48 mass%, based on the total mass of the composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high specific gravity plastic composition containing iron powder, and more particularly to improvement of rust resistance of a high specific gravity plastic composition containing iron powder.

  Plastic materials are used in a wide variety of applications because they are lightweight, excellent in workability, and relatively inexpensive. However, the lightness and softness of plastics can be an obstacle. For example, it is a disadvantage that it is too light for applications requiring inertial body use, damping properties, and sound damping properties.

  Therefore, as a means for making up for the drawbacks of such plastic materials, a filler having a large specific gravity is blended with the plastic materials. Examples of such fillers include metal powders such as copper powder, tungsten powder, and iron powder, and inorganic mineral powders such as talc, silica, and calcium carbonate.

  Among these fillers, copper powder has a problem that it elutes harmful ions, and tungsten powder has a problem that it is expensive. Moreover, although inorganic mineral powder is excellent in safety, since specific gravity is small compared with a metal, there exists a problem that it cannot fully raise specific gravity. On the other hand, iron powder has a large specific gravity, does not elute harmful ions, and is inexpensive, and thus is suitable as a material for increasing the specific gravity of plastic.

  However, iron has the disadvantage of being easily rusted. For this reason, there is a problem that discoloration and spots caused by iron rust occur when plastic molded products containing iron powder are placed under high humidity. Therefore, the use of high specific gravity plastic materials containing iron powder is limited. ing.

  By the way, as a prior art which prevents metal rust, such as iron powder, there exist the following patent documents 1-3, for example.

JP 47-42503 A (Claims)

Japanese Examined Patent Publication No. 62-53552 (Claims)

JP 2000-160204 A (summary)

  Patent Document 1 discloses that an additive selected from iron powder, a metal or alloy powder having a higher corrosion potential than iron, and a thermosetting or thermoplastic synthetic resin are compression molded at 180 ° C. for 1.5 hours in air. This is a technique for producing mechanical parts by firing (Example 1). According to this technology, iron-based mechanical parts that are less susceptible to rusting can be provided. However, since this technology is a technology that fires compression-molded products to form a fired body, it has improved rust resistance as a raw material for plastic molded products. It is not a technique for providing a high specific gravity plastic composition.

Patent Document 2 is a technique in which zinc powder coated with conductive particles having a specific resistance of 1 × 10 ⁻² Ωcm or less and a particle size smaller than that of zinc powder is blended in an anticorrosive coating composition. In this technique, the surface of zinc dust is coated with manganese, nickel, tungsten, silicon or the like as conductive particles by a mechanochemical mechanism using a ball mill, a mortar or the like (third column). According to this technique, high-temperature oxidation of zinc powder is remarkably suppressed.

  In Patent Document 3, iron powder obtained by coating reduced iron powder having an average particle diameter of 2 to 20 μm with a compound containing amine quinone as a constituent component is compression-molded by using a binder such as a thermosetting resin, thereby producing a dust magnet. The present invention relates to a technique for manufacturing a core. According to this technique, iron powder for a dust core having improved corrosion resistance can be provided. This technique is not a technique for improving the corrosion resistance of high specific gravity plastic compositions.

  An object of the present invention is to provide a high specific gravity plastic composition containing iron powder, and the problem is to provide a high specific gravity plastic composition containing iron powder that can prevent alteration and discoloration due to iron rust. is there.

  The present invention according to a first aspect for solving the above-described problems is a coupling-treated iron powder surface-treated with a coupling agent, and a coupling surface-treated with a coupling agent separately from the iron powder. A high specific gravity plastic composition having a specific gravity of 2 to 4.6 in which a treated zinc powder and a heat-melted thermoplastic resin are kneaded, wherein the coupling treatment has been performed on the total mass of the composition It is an iron powder-containing high specific gravity plastic composition comprising 30 to 86% by mass of iron powder, 2 to 58% by mass of the zinc powder subjected to the coupling treatment, and 12 to 48% by mass of a thermoplastic resin. .

  In this configuration, the coupling ratio of 30 to 86% by mass, 2 to 58% by mass, and 12 to 48% by mass of the coupling-treated iron powder, the coupling-treated zinc powder, and the heat-melted thermoplastic resin, respectively. However, at this blending ratio, the iron powder mainly acts to increase the specific gravity of the plastic composition to 2 to 4.6, and the zinc powder is in the vicinity of the iron powder and the iron is oxidized. It acts to suppress. Moreover, while a thermoplastic resin adheres iron powder and zinc powder, it functions also as a component which prevents that these metals contact external air.

  In particular, in the above configuration, the coupling-treated iron powder and the coupling-treated zinc powder that have been separately surface-treated are used, but if separately surface-treated iron powder and zinc powder are used, In this case, the mutual positional relationship (mixed state) between the iron powder and the zinc powder is in a suitable state, so that the rust prevention action of the zinc powder and the resin against the iron powder is sufficiently exhibited. As a result, an iron powder-containing high-specific gravity plastic composition that is less susceptible to alteration and discoloration (including the appearance of spots) due to rust is realized.

  In addition, the iron powder containing high specific gravity plastic composition using the thing which used the iron powder and zinc powder which are not coupling-processed, and the thing which was coupling-processed with respect to the mixed powder in which iron powder and zinc powder were mixed is The moldability is poor, and the molded product is inferior in strength because the affinity between the resin and the iron powder and zinc powder is not sufficient.

  According to a second aspect of the present invention for solving the above-mentioned problem, in the first aspect, the coupling-treated iron powder has an average particle size of 40 μm or more and 150 μm or less, and the coupling-treated zinc powder The average particle size of the iron powder is 2 μm or more and less than 40 μm, and the above-treated iron powder is surface-treated with a silane coupling agent. The zinc-treated zinc powder is surface-treated with a titanate coupling agent. It has a further feature in that it has been made.

  With this configuration, the effect of the surface treatment of iron powder and zinc powder separately is further increased. As described above, in order to improve the rust resistance and moldability of the iron powder-containing high specific gravity plastic composition, it is necessary to separately treat the iron powder and the zinc powder. The particle size relationship with the powder is preferably iron powder> zinc powder, the iron powder is preferably subjected to silane coupling treatment, and the zinc powder is preferably subjected to titanate coupling treatment. In other words, when iron powder and zinc powder that are separately surface-treated with different coupling agents are used, a high-specific gravity plastic composition that is more excellent in rust resistance, moldability, workability, and economy is realized. be able to. The reason is that iron powder> zinc powder, particularly preferably the average particle diameter of the silane-coupled iron powder is 40 μm or more and 150 μm or less, and the average particle diameter of the titanate-coupled zinc powder is 2 μm. If the thickness is less than 40 μm, it is considered that a plastic composition structure in which more zinc powder is present in the vicinity of the iron powder is formed.

  The third aspect of the present invention for solving the above-described problems is characterized in that, in the first or second aspect, the thermoplastic resin is a polyamide resin. Polyamide resins are particularly preferred because they are inexpensive and excellent in moldability, and are excellent in toughness, wear resistance, impact resistance and chemical resistance.

This invention concerning the manufacturing method of the 4th mode for solving the above-mentioned subject is an iron powder with an average particle size of 40 μm or more and 150 μm or less, and a silane coupling agent with a concentration of 0.005 to 0.1 mol / kg of iron powder. , The iron powder coupling treatment step in which the surface of the iron powder is subjected to silane coupling treatment, the zinc powder having an average particle size of 2 μm or more and less than 40 μm, and 0.005 to 0.1 mol / kg of zinc powder. A zinc powder coupling treatment step in which the surface of the zinc powder is subjected to a titanate coupling treatment by stirring and mixing a titanate coupling agent having a concentration, 30 to 86% by mass of the iron powder after the coupling treatment, and the coupling A plastic mixture in which 2 to 58 mass% of the treated zinc powder and 12 to 48 mass% of the polyamide resin are stirred and mixed at a temperature equal to or higher than the melting temperature of the polyamide resin. Characterized in that goods and manufacturing process, a manufacturing method of the plastic kneaded mixture of iron powder-containing high density plastic composition having a specific gravity of 2 to 4.6 comprising, an injection step of curing the plastic kneaded product emits.
According to this production method, the iron powder-containing high specific gravity plastic composition according to the present invention can be produced with high productivity.

According to the present invention, an iron powder-containing high specific gravity plastic composition excellent in rust resistance, moldability, workability, and economy can be realized by a simple means, and such an iron powder-containing high specific gravity plastic of the present invention can be realized. When the composition is used, it is possible to provide a high-quality, high-specific gravity plastic molded product that hardly changes color at a low cost. Specific applications of the iron powder-containing high specific gravity plastic composition of the present invention are derived from a high specific gravity in addition to a rotating inertial body (such as a flywheel) and a non-rotating inertial body (such as a seat belt lock mechanism). Examples of the use of a damping material (such as an electromagnetic relay case) using damping properties can be given.

The best mode for carrying out the present invention will be described based on examples.
[Example 1]
An iron powder having an average particle size of 95 μm (JIP300A manufactured by Kawasaki Steel Co., Ltd.) is placed in a high-speed rotary mixer (super mixer manufactured by Kawata Co., Ltd.), and the silane coupling agent solution is added while stirring, and the rotational speed is about 800 rpm. The mixture was stirred and mixed to volatilize the solution, thereby producing silane-coupled iron powder. As a silane coupling agent solution, a solution obtained by diluting Chisso Co., Ltd. Silaace to a 10-fold concentration in an alcohol solution composed of 90 parts by mass of denatured alcohol and 10 parts by mass of water was used.

  On the other hand, zinc powder having an average particle size of 7.5 μm (F500 manufactured by Honjo Chemical Co., Ltd.) is put into the same high-speed rotating mixer, and the titanate coupling agent solution is added while stirring, and further stirred and mixed at a rotational speed of about 800 rpm. The fraction was volatilized to produce a titanate-coupled zinc powder. As the titanate coupling agent solution, a solution obtained by diluting KR44 plate act manufactured by Ajinomoto Co., Inc. to a 10-fold concentration in an alcohol solution composed of 90 parts by mass of denatured alcohol and 10 parts by mass of water was used.

  Next, the silane coupling-treated iron powder produced above, the titanate-coupled zinc powder, and the powdered nylon 6 (1007FP, manufactured by Ube Industries, Ltd.) have a mass ratio of 86/2/12. Then, the mixture was put into the same high-speed rotating mixer and stirred and mixed at a rotation speed of about 800 rpm. This mixture is put into an injection molding machine equipped with a kneading mechanism shown in FIG. 1, heated to a temperature at which powdered nylon 6 melts (280 ° C.), kneaded and injected to produce a high specific gravity plastic composition containing iron powder. did. In this injection molding, in order to evaluate the physical properties of the injection molded product which is a high specific gravity plastic composition containing iron powder, the shape is ASTM D638 4 type tensile test piece (thickness 3.2 mm) and ASTM D790 bending test piece. The standard shape.

  The injection molding machine will be described. As shown in FIG. 1, this injection molding machine is an injection molding machine capable of melt-kneading a thermoplastic resin and iron powder by a heating cylinder 20 and a rotary screw 30 and injection molding the screw 30. By gradually changing the shaft diameter, the raw material supply zone 301 having a small shaft diameter, the compression zone 302 in which the shaft diameter gradually increases, and the shaft diameter is made larger than other zones to suppress the passage of the raw material. It consists of a measuring zone 303. By using this apparatus, iron powder and zinc powder can be sufficiently kneaded with the thermoplastic resin.

  Note that reference numeral 12 in FIG. 3 denotes a hopper for charging raw materials, 32 is a flight, 35 is a backflow prevention valve, and 45 is a tip nozzle. Further, reference numeral 31 denotes a blister ring whose outer periphery is flat and has a diameter larger than the axis of a portion where there is a nearby flight. Further, since the blister ring 31 is provided, the molten resin and iron powder or the like are rapidly compressed when passing through a narrow gap formed between the blister ring and the inner periphery of the heating cylinder. Therefore, mixing and dispersion of each component are further promoted.

  Next, the average particle diameter of the iron powder and zinc powder described above will be described. The average particle diameter referred to in the present specification refers to a value (Lean nurse method) calculated based on the specific surface area measured using an air permeation specific surface area measuring device. Specifically, the specific surface area is measured using an air permeable type powder specific surface area measuring device manufactured by Tsutsui Rika Instruments Co., Ltd. At this time, the weight of the sample is adjusted so that the filling height (height after compression) is about 5 mm to 10 mm. The average particle diameter is a value calculated from the specific surface area and the density of the granular material, assuming that the constituent particles of the granular material are all spherical. In addition, the particle size of iron powder and zinc powder does not change substantially by silane coupling treatment or titanate coupling treatment. Therefore, in this specification, the average particle diameter of iron powder and zinc powder and the average particle diameter of iron powder and the like after the coupling treatment are handled as the same.

  In the above embodiment, iron powder and zinc powder having a known average particle diameter are used, but there is no particular limitation on a method for obtaining iron powder and zinc powder having a desired average particle diameter. For example, a plurality of JIS standard sieves with different openings are stacked in the order of increasing openings, iron or zinc pulverized powder is placed in the top sieve, and the pulverized powder is classified by vibrating the sieve to obtain the desired average particle size. A diameter iron powder or the like can be obtained.

[Example 2]
Similar to Example 1 except that the silane coupling-treated iron powder, titanate-coupled zinc powder, and powdered nylon 6 were made to have a mass ratio of 30/58/12. Test specimens were injection molded.

Example 3
Similar to Example 1 except that the silane coupling-treated iron powder, titanate-coupled zinc powder, and powdered nylon 6 were made to have a mass ratio of 42/10/48. Test specimens were injection molded.

Example 4
The above implementation except that the silane coupling-treated iron powder, titanate-coupled zinc powder, and powdered nylon 6 were made to have a mass ratio of 67.4 / 16.8 / 15.8. Test pieces were injection molded in the same manner as in Example 1.

Example 5
A test piece was injection-molded in the same manner as in Example 4 except that both iron powder and zinc powder were subjected to silane coupling treatment.

Example 6
A test piece was injection molded in the same manner as in Example 4 except that zinc powder having an average particle size of 40 μm was used.

Example 7
The mass ratio of iron powder having an average particle size of 40 μm surface-treated with a titanate coupling agent, zinc powder having an average particle size of 40 μm surface-treated with a silane coupling agent, and powdered nylon 6 is 67. A test piece was injection molded in the same manner as in Example 4 except that 4 / 16.8 / 15.8 was obtained.

[Comparative Example 1]
Except for using zinc powder and adding silane coupling-treated iron powder and powdered nylon 6 so that the mass ratio is 84.2 / 15.8, Similarly, a test piece was injection molded. In Comparative Example 1, no zinc powder was added.

[Comparative Example 2]
A test piece was injection molded in the same manner as in Example 4 except that iron powder and zinc powder that were not subjected to any coupling treatment were used. However, the test piece could not be molded.

[Comparative Example 3]
In advance, 67.4 parts by mass of iron powder and 16.8 parts by mass of zinc powder were mixed, and a silane coupling agent was added to the mixed powder to obtain a metal powder subjected to silane coupling treatment. Except for kneading this silane coupling-treated metal powder (iron powder / zinc powder = 67.4 / 16.8 mixed powder) and powdered nylon 6 at a mass ratio of 84.2 / 15.8, An injection molding of a test piece was attempted in the same manner as in Example 4 above. However, the test piece could not be molded.

[Comparative Example 4]
Example 1 above, except that the silane coupling-treated iron powder, titanate-coupled zinc powder, and powdered nylon 6 were made to have a mass ratio of 73.2 / 16.8 / 10. In the same manner as described above, an injection molding of a test piece was attempted. However, the test piece could not be molded.

  In each of the above Examples and Comparative Examples, the production status of the iron powder-containing high specific gravity plastic composition (test piece) was observed. Moreover, while measuring the specific gravity of each test piece, each test piece was immersed in 23 degreeC tap water and 10 mass% salt solution, and the presence or absence of discoloration or the generation | occurrence | production of a spot was investigated over time. A list of production conditions in the above Examples and Comparative Examples is shown in Table 1, and the test results are shown in Table 2.

  From Tables 1 and 2, the following becomes clear. Although the silane coupling-treated iron powder and zinc powder were used, the molding of Comparative Example 4 in which the blending ratio of the plastic resin (nylon 6) was 10% by mass was poor. The reason for this is considered that the amount of resin was insufficient. From this result and the result of Example 1, the amount of resin for the iron powder-containing high specific gravity plastic composition needs to be 12% by mass or more from the viewpoint of moldability.

  Moreover, from the result of Example 3, in order to set the specific gravity of the iron powder-containing high specific gravity plastic composition to 2 or more, the blending amount of the resin is 48% by mass or less with respect to the iron powder-containing high specific gravity plastic composition. There is a need. From the results of Example 1 and Comparative Example 1, it can be seen that if the zinc powder is contained at least 2% by mass with respect to the iron powder-containing high specific gravity plastic composition, there is an antirust effect. On the other hand, the upper limit of the zinc powder is 58% by mass. The reason for this is that zinc powder is added to increase rust resistance, and is more expensive than iron powder, and the tendency that mixed moldability tends to deteriorate as the amount of zinc powder increases (Example 2). This is because it is desired that the upper limit is 58 mass% and the iron powder content is at least 30 mass%.

  In addition, from comparison between Example 4 using the titanate-coupled zinc powder and Example 5 using the silane-coupled zinc powder, the use of the titanate-coupled zinc powder increases the mixing moldability. I understand.

  In addition, from comparison between Example 4 using zinc powder having an average particle diameter of 7.5 μm and Example 6 using zinc powder having an average particle diameter of 40 μm, when the average particle diameter of the zinc powder increases, iron powder containing high specific gravity It can be seen that the rust resistance of the plastic composition is reduced. In addition, from comparison between Example 5 and Example 5 using both the titanate-coupled iron powder having an average particle diameter of 40 μm and the silane-coupled zinc powder, the resistance of the zinc powder increases as the particle diameter of the zinc powder increases. It can be seen that the rust is reduced. From these results, the average particle size of the zinc powder is preferably less than 40 μm. However, zinc powder having an average particle size of less than 2 μm is not preferable because it is difficult to produce and the handleability is deteriorated. Therefore, zinc powder having an average particle size of 2 μm or more and less than 40 μm is preferably used.

  On the other hand, the zinc powder in the iron powder-containing high specific gravity plastic composition must always be present in the vicinity of the iron powder. This is because zinc powder plays a role of suppressing oxidation of iron powder. This means that it is desirable that the particle size of the zinc powder is smaller than that of the iron powder. That is, it is desirable that the particle size of the iron powder> the particle size of the zinc powder, but as described above, the upper limit of the zinc powder (average particle size) is preferably less than 40 μm, so the lower limit of the iron powder is preferably 40 μm. That's it. However, if the average particle size of the iron powder exceeds 150 μm, the mixing property with respect to the plastic composition is deteriorated, and the surface of the molded product is rough when molded, which is not preferable. Therefore, the average particle size of the iron powder is preferably 40 μm or more and 150 μm or less.

  Moreover, it turns out that the shaping | molding as a composition will become difficult from the result of the comparative example 2 if a coupling process is not performed. Furthermore, from the results of Examples 4 to 7 and Comparative Example 3, it is understood that iron powder and zinc powder need to be individually coupled in terms of formability.

〔extra content〕
In the above examples, nylon 6 (polyamide 6) is used as the thermoplastic resin, but in the present invention, various thermoplastic resins such as low density polyethylene, high density polyethylene, polypropylene, high impact polystyrene, ABS resin are used. it can. Specifically, for example, instead of nylon 6, resins such as nylon 66, nylon 12, aromatic nylon, polypropylene, polycarbonate, and ABS can be used.

  The silane coupling agent used in the present invention means a compound represented by X to Si (OR) 3, and the titanate coupling agent means a compound represented by X to Ti (OR) 3. To do. X has a functional group that reacts with an organic group (eg, amino group, vinyl group, epoxy group, mercapto group, chloro group, etc.), and OR is an alkoxy group (R is methoxy, ethoxy group, etc.).

  Examples of the silane coupling agent include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, aminosilane, γ-methacryloxypropyltrimethoxysilane, N- β- (N-vinylbenzylaminoethyl) -γ-aminopropylmethyldimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, aminosilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxy Silane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethyldisilazane, γ-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl {3-trimethoxysilyl), propi Chloride}, .gamma.-chloropropyl methyl dimethoxy silane, .gamma.-mercapto pre pills methyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, such as trimethylchlorosilane can be exemplified.

  Moreover, as a titanate coupling agent, what replaced the silane in each said compound with titanium etc. can be illustrated.

  These coupling agents are usually used at a concentration of 0.005 to 0.1 mol / iron powder or 1 kg of zinc powder, preferably 0.01 to 0.04 mol / iron powder or 1 kg of zinc powder. If the concentration is 0.005 mol or less, the coupling effect is insufficient, and even if the concentration exceeds 0.1 mol, further increase in the effect is reduced, which is uneconomical.

  In addition, the iron powder-containing high specific gravity composition according to the present invention can of course contain additives other than iron powder and zinc powder. For example, if necessary, an affinity agent, a pigment, a color tone stabilizer, It is preferable to add a release agent, reinforcing fiber, and the like.

  Further, the iron powder-containing high specific gravity plastic composition according to the present invention is a concept including an iron powder-containing high specific gravity plastic molded product, but in a narrow sense, means a composition as a raw material of the high specific gravity plastic molded product. .

  As described above, according to the present invention, it is possible to provide a high specific gravity plastic composition capable of preventing alteration due to iron rust by using cheap iron powder compared to other metals. The composition is excellent in economy, moldability and the like as compared with conventional products. Therefore, the industrial applicability is high.

FIG. 1 is an explanatory view of an injection molding machine used in the embodiment of the present invention.

Claims (4)

  Coupling-treated iron powder surface-treated with a coupling agent, coupling-treated zinc powder surface-treated with a coupling agent separately from the iron powder, and a heat-melted thermoplastic resin are kneaded A high specific gravity plastic composition having a specific gravity of 2 to 4.6, wherein the coupling-treated iron powder is 30 to 86% by mass relative to the total mass of the composition, and the coupling-treated zinc powder is 2 An iron powder-containing high specific gravity plastic composition comprising ˜58% by mass and 12 to 48% by mass of a thermoplastic resin. The coupling-treated iron powder has an average particle size of 40 μm or more and 150 μm or less, and the coupling-treated zinc powder has an average particle size of 2 μm or more and less than 40 μm,
The coupling-treated iron powder is surface-treated with a silane coupling agent, and the coupling-treated zinc powder is surface-treated with a titanate coupling agent. The high specific gravity plastic composition containing iron powder according to 1.   The iron powder-containing high specific gravity plastic composition according to claim 1 or 2, wherein the thermoplastic resin is a polyamide resin. Iron powder for silane coupling treatment of the surface of the iron powder by stirring and mixing an iron powder having an average particle size of 40 μm or more and 150 μm or less and a silane coupling agent having a concentration of 0.005 to 0.1 mol / kg of iron powder. A coupling process;
Zinc powder whose surface is coated with titanate by stirring and mixing a zinc powder having an average particle size of 2 μm or more and less than 40 μm and a titanate coupling agent having a concentration of 0.005 to 0.1 mol / kg of zinc powder. A coupling process;
The coupling-treated iron powder is 30 to 86% by mass, the coupling-treated zinc powder is 2 to 58% by mass, and the polyamide resin is 12 to 48% by mass or higher than the melting temperature of the polyamide resin. A plastic kneaded preparation process for stirring and mixing at a temperature of
An injection step of injecting the plastic kneaded product and curing the plastic kneaded product;
A method for producing an iron powder-containing high specific gravity plastic composition having a specific gravity of 2 to 4.6.

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