JP2019151887A - Method for producing molding of magneto-caloric effect material - Google Patents

Abstract

To provide a method for producing a molding of a magneto-caloric effect material in which a change in its properties can be suppressed.SOLUTION: A method for producing a molding of a magneto-caloric effect material has a molding step S4, and defatting steps S5, S6. The molding step is the step for preparing a molding 1 by molding a mixture in which La(Fe, Si)powder raw material is mixed with polyacetal. The defatting steps are the steps for removing polyacetal from the molding prepared in the molding step.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method for manufacturing a molded body of a magnetocaloric effect material.

  Conventionally, in order to form a fine flow path in a magnetocaloric effect material, for example, machining for forming a groove in a plate-like magnetocaloric effect material has been performed. However, the formation of the fine flow path by machining has a problem that the yield tends to be low depending on the shape of the fine flow path. Therefore, it has been studied to manufacture a molded body in which the magnetocaloric effect material is previously molded into a desired shape.

  One of the means for forming the molded body is micro metal injection molding (MIM) for forming a fine flow path. In the micro metal injection molding, if the particle size of the raw material powder of the magnetocaloric effect material is too large, the fluidity at the time of injection molding is deteriorated and the moldability may be lowered. However, if the particle size is reduced in order to improve fluidity, the performance of the magnetocaloric effect material may be degraded.

  Patent Document 1 below proposes a technique for improving moldability by mixing a raw material of a magnetocaloric effect material and a polyalkylene carbonate as a binder.

JP 2017-14617 A

  However, as a result of detailed studies by the inventors, when polyalkylene carbonate is used as a binder, a relatively large amount of carbon remains in the magnetocaloric effect material, and the phase transition temperature changes when carbon is incorporated into the magnetocaloric effect material. At the same time, a problem has been found that the magnetocaloric effect decreases.

  One aspect of the present disclosure is to provide a method for producing a molded body of a magnetocaloric effect material having a high magnetocaloric effect.

One aspect of the present disclosure is a method for manufacturing a molded body of a magnetocaloric effect material, and includes a molding step (S4) and a degreasing step (S5, S6). The forming step is a step of forming a molded body (1) by forming a mixture of a powder raw material of La (Fe, Si) ₁₃ and polyacetal. The degreasing step is a step of removing polyacetal from the molded body produced in the molding step.

  According to such a configuration, it is possible to manufacture a magnetocaloric effect material molded body having a high magnetocaloric effect by reducing the residual amount of carbon. Further, the moldability can be improved by the polyacetal functioning as a binder, whereby the complex shape molding of the magnetocaloric effect material, the fine molding, and the decrease in the yield of the molded body can be suppressed.

  Note that the reference numerals in parentheses described in this column and in the claims indicate the correspondence with the specific means described in the embodiment described later as one aspect, and the technical scope of the present disclosure It is not limited.

It is a flowchart explaining the manufacturing process of a magnetocaloric effect material. It is a front view which shows typically the shape of the magnetocaloric effect material after an injection molding process.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
[1. Raw material and binder of magnetocaloric effect material]
A desirable magnetocaloric effect material is a magnetocaloric effect material having a NaZn ₁₃ type crystal structure. Therefore, the raw material powder which consists of the element which can comprise La (Fe, Si) ₁₃ , and a suitable quantity can mainly be used. The raw material powder described above may be prepared by, for example, a melting and quenching method and having a peritectic shape of LaFeSi + αFe. The raw material powder may contain a metal other than La, Fe, and Si.

As the binder, polyacetal (hereinafter referred to as POM) can be used. As the POM, a homopolymer may be used. Since the homopolymer POM has a simple structure, when it is used as a binder, decomposition begins at a relatively low temperature range, and there is an advantage that residual carbon can be greatly reduced after degreasing.
The resin used as the binder is not limited to one type, and two or more types of resins may be used. In that case, it is conceivable to select resins having different decomposition temperatures, melt flow rates, and solubility in solvents. In particular, it may be selected in consideration of injection moldability, that is, appropriate fluidity when performing injection molding, shape maintenance performance of a molded body molded by injection molding, and shape maintenance performance after temporary degreasing. Good.

[2. Production process of magnetocaloric effect material]
Based on FIG. 1, the manufacturing process of a magnetocaloric effect material is demonstrated.
(S1) Crushing / dispersing step In the crushing / dispersing step of S1, metal powder aggregates containing La, Fe, and Si, which are magnetocaloric effect materials, are pulverized to produce raw material powder. The metal may have a particle size of 0.1 μm to 200 μm. As described above, the raw material powder may contain a metal other than La, Fe, and Si.

  In addition, the particle diameter can be set to 1 μm to 50 μm so as to ensure a high degree of fine channel forming, uniform diffusion, and tissue uniformity. The effect becomes more remarkable when the particle diameter is set to 1 μm to 10 μm. In addition, the particle size mentioned above is a value of D50 (median diameter). The calculation method can use a light scattering method by laser diffraction / scattering, but is not limited thereto.

(S2) Kneading Step In the kneading step of S2, a mixture obtained by mixing and kneading La, Fe, Si metal powder powdered in S1 and POM as a binder is generated. The particle size of the POM may be the same as that of the raw material powder of the magnetocaloric effect material. The binder may contain a resin other than POM as long as it contains at least POM. A binder can be mix | blended in the ratio of 20 vol%-80 vol% with respect to raw material powder, for example. By mix | blending in the ratio of 30 vol%-50 vol%, the shape maintenance performance after injection moldability and temporary degreasing can be improved.

(S3) Granulation step In the granulation step of S3, the mixture kneaded in S2 is granulated by extrusion to form MIM raw material pellets. This MIM raw material pellet includes not only a raw material powder containing an appropriate amount of each element for constituting the final magnetocaloric effect material and a resin used as a binder, but also a lubricant such as a solvent and a surfactant. You may use what mixed these.

(S4) Molding step In the molding step of S4, a molded body is molded by injection molding using the MIM raw material pellets molded in S3. This molded body is formed by molding at least a powder raw material of a magnetocaloric effect material and polyacetal.

  An example of a molded article molded by injection molding is shown in FIG. A molded body 1 shown in FIG. 2 has a plurality of minute slit-shaped flow paths 2. The width of the slit can be 50 to 100 μm. Thus, by making the flow path 2 into a fine flow path, it can promote that the solvent which flows through a flow path becomes a laminar flow. In addition, although the deformation | transformation by expansion | swelling and shrinkage | contraction may arise even after passing through the process of S5 and S6, the basic shape is the same.

(S5) Temporary degreasing process In this embodiment, it has a temporary degreasing process and this degreasing process mentioned later as a process for degreasing the molded object after injection molding. The degreasing here means removing polyacetal, but when other resin or carbon component is included as a binder, it means removing the resin and carbon component. The polyacetal may be removed in at least one of S5 and S6.

  In the temporary degreasing step of S5, degreasing is performed using a solvent. The solvent may be any solvent that can remove the binder resin. As the solvent, for example, phenols, ketones, esters, aromatic compounds and the like can be used, but not limited thereto. This temporary degreasing step is not necessarily performed, and may be omitted when sufficient degreasing can be performed in the main degreasing step of S6.

(S6) Main degreasing step In the main degreasing step of S6, the molded body temporarily degreased in S5 is further degreased by heat treatment. Specifically, heating may be performed at 600 ° C. or lower in a controlled atmosphere selected from hydrogen, vacuum, inert gas, and the like. In addition, by setting the atmospheric temperature for degreasing to 300 ° C. or less, it is possible to suppress the reaction between the powder raw material of the magnetocaloric effect material and the carbon as much as possible, and it is possible to suppress the performance deterioration due to the composition shift due to the heterogeneous mixture. .
The temporary degreasing step of S5 corresponds to the first step, and the main degreasing step of S6 corresponds to the second step.

(S7) Sintering step In the sintering step of S7, the green body degreased in S6 is sintered to produce a sintered body. The sintering temperature may be in the range of 900 ° C to 1300 ° C. By setting the sintering temperature in the range of 1050 ° C. to 1150 ° C., single-phase La (Fe, Si) ₁₃ can be obtained satisfactorily, and the magnetocaloric effect in which mixing of different phases such as α-Fe is suppressed. Can obtain a sintered body with high.

(S8) Hydrogen Treatment Step In the hydrogen treatment step of S8, the sintered body sintered in S7 is subjected to hydrogen treatment. By this hydrogen treatment, the Tc temperature of the magnetocaloric effect material can be adjusted.

The sintered body produced through the above steps has a fine flow path, and the medium flowing through the fine flow path becomes a laminar flow.
[3. Example]
(3-1) Example 1
The raw material powder is composed of (La ₁ Fe ₁ Si ₁ + α-Fe). The particle size of the raw material powder was set to 1-100 μm and D50 = 60 μm by the crushing / dispersing step of S1. This raw material powder was mixed with POM as a binder resin, and MIM raw material pellets were produced through the steps S2 and S3. In the produced MIM raw material pellet, POM was 40 vol%. Using the produced MIM raw material pellets, in the molding step of S4 described above, injection molding was performed at 200 ° C. in an inert gas atmosphere to form a desired shape.

In this example, the temporary degreasing step was omitted. In the main degreasing step of S6, the molded body molded in the molding step was degreased at 550 ° C. in a vacuum atmosphere (10 ⁻³ Pa). In the sintering step of S7, a magnetocaloric material molded body having a desired shape was obtained by sintering at 1150 ° C. It shows in Table 1 regarding the characteristic of the obtained molded object. Moreover, the hydrogen treatment process of S8 was performed after the sintering process. The hydrogen treatment was performed in a hydrogen atmosphere at 400 ° C. for 2 hours. In Table 1, it describes also about Tc of the molded object after a hydrogen treatment.

(3-2) Example 2
Step S1 was performed in the same manner as in Example 1, and a mixture of the La, Fe, Si metal powder powdered in S1 in the kneading step of S2, and POM and ABS as binders was mixed to produce a mixture. . Steps S3 to S4 were performed in the same manner as in Example 1 to produce a molded body having a desired shape.
In this example, unlike Example 1, temporary degreasing was performed using acetone in the temporary degreasing step of S5. Subsequent steps S6 to S8 were performed under the same conditions as in Example 1. Table 1 shows the characteristics of the molded body after step S7 and the characteristics of the molded body after step S8.

(3-3) Comparative Example 1
As in Example 1, a raw material powder composed of (La ₁ Fe ₁ Si ₁ + α-Fe) and having a particle size of 1-100 μm and D50 = 60 μm was prepared. Polypropylene (PP) as a binder resin was mixed with this raw material powder, and MIM raw material pellets were produced by the same steps as steps S2 and S3 of Example 1. The produced MIM raw material pellets were injection molded at 180 ° C. in an inert gas atmosphere and molded into a desired shape.

Then, the temporary degreasing process was abbreviate | omitted and the process S6-S8 similar to Example 1 was performed, and the magnetocaloric effect material molded object which has a desired shape was obtained.
(3-4) Comparative Example 2
In the same manner as in Comparative Example 1, MIM raw material pellets in which PP was mixed as a binder resin were prepared, and injection molding was performed at 180 ° C. in an inert gas atmosphere to prepare a molded body having a desired shape.

  Unlike the comparative example 1, in this comparative example, temporary degreasing was performed using the organic solvent in the temporary degreasing process. Thereafter, the same steps S6 to S8 as in Example 1 were performed to obtain a magnetocaloric effect material molded body having a desired shape.

(3-5) Evaluation Table 1 shows the performance evaluation of the magnetocaloric effect materials produced in Examples 1 and 2 and Comparative Examples 1 and 2.

In Table 1 above, Tc represents the Curie temperature, and ΔS represents the entropy change amount. Tc and ΔS were determined by measuring magnetic properties such as VSM. The crystal structure was confirmed by XRD. The amount of residual coal was determined by carbon analysis (combustion-infrared absorption method described in JIS G-1211-3).

As shown in Table 1, the crystal structure was NaZn ₁₃ type in any magnetocaloric effect material. In Example 1 and Example 2, the amount of residual coal was 0.3 wt% or less. Thus, a characteristic change can be suppressed by reducing the amount of remaining charcoal. Further, by reducing the amount of residual coal, ΔS in Example 1 and Example 2 was larger than those in Comparative Examples 1 and 2. In particular, in Example 2, the amount of remaining coal was less than 0.01 wt%, and ΔS was also a larger value. In Examples 1 and 2, there was no decrease in ΔS due to the hydrogen treatment.
The residual carbon amount refers to the carbon content obtained when the obtained magnetocaloric effect material shaped body is subjected to carbon analysis.

[4. Other Embodiments]
As mentioned above, although embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and can carry out various modifications.

(4A) Additives A, B, and C to be described later may be added to the magnetocaloric effect material La (Fe, Si) ₁₃ . Here, the additive A, B, C has the general formula _{La 1-x A x (Fe} 1-y-z B y Si z) 13: In _{C n, A = Ce, Sm} , Nd , etc., B = Mn , Co, Ni, Al, etc., such as C = H, B, N, etc.

  (4B) The case where only POM is used as the binder resin and the case where POM and ABS are used are exemplified. However, resins that can be used as the binder are not limited to these, and two or more kinds of resins including POM can be used. A specific example will be described below.

  After the mixture containing the magnetocaloric effect material, the resin 1 (POM) and the resin 2 (PS) is molded in the molding process, the resin 2 is eluted and degreased by washing with an organic solvent such as toluene. Thereafter, the remaining resin 1 can be degreased by heating at about 550 ° C. By using the resin 2 in this way, it is possible to improve the injection property and moldability at the time of injection molding. In addition, since the resin 1 is insoluble in an organic solvent containing aromatics and the resin 2 is soluble in an organic solvent containing aromatics, the molded state can be maintained even by degreasing with an organic solvent.

  As described in Example 2, when resin 1 (POM) and resin 2 (ABS) are used as the binder, the resin 2 may be eluted and degreased by washing with an organic solvent such as acetone. Good. After the degreasing, the remaining resin 1 can be degreased by heating at about 550 ° C. By using the resin 2 in this way, it is possible to improve the injection property and moldability at the time of injection molding. Further, since the resin 1 is insoluble in an organic solvent of ketones such as acetone and the resin 2 is soluble in an organic solvent of ketones, the molded state can be maintained even by degreasing with an organic solvent.

  In the example described above, two types of resins are used, but three or more types may be used. Moreover, the kind of resin to be used is not limited to the above, and various resins selected in consideration of characteristics can be used. The resin here includes general-purpose plastic, engineering plastic, and super engineering plastic.

  Furthermore, in order to improve injection property and moldability, a solvent and a surfactant can be added in the kneading step and the granulating step. As a solvent, the organic solvent which can melt | dissolve resin 2 and can raise fluidity | liquidity can be used. Examples of such an organic solvent include acetone when the binder contains ABS, and toluene when the binder contains PS. As the surfactant, one having high compatibility with the resin (in other words, having a close SP value) can be used. For example, a polyethylene glycol type nonionic surfactant can be used. Examples of such surfactants include polyethylene glycol monoester derivatives and polyethylene glycol diester derivatives. Of course, the solvent and surfactant that can be used are not limited to those described above. In addition, you may add a solvent and surfactant also when using only POM as a binder.

(4C) In the molding step, molding other than injection molding may be performed. For example, the molding may be performed by press molding, extrusion molding, or molding by a 3D printer.
(4D) An important point in the production method of the present disclosure is that a mixture in which raw material powder and POM are mixed is molded and then degreased. Therefore, if it has the point, the process of S1-S8 may not necessarily be as FIG. 1, and the manufacturing method different from the detail of the process mentioned above may be sufficient. For example, MIM raw material pellets may not be manufactured or hydrogen treatment may not be performed.

  (4E) In the said Example, the temporary degreasing process is a process of degreasing with an organic solvent, and the example in which this degreasing process is a process of degreasing by heat processing was shown. However, when degreasing is performed in a plurality of steps as described above, degreasing may be performed by combining degreasing steps other than the two steps described above. When combining a plurality of degreasing processes, each process may be a process having different degreasing characteristics. The degreasing characteristic here means the classification or type of resin that can be satisfactorily degreased in the process. High degreasing can be achieved by combining degreasing steps having different degreasing properties.

  As shown in Example 2, by performing both a degreasing step with an organic solvent and a degreasing step with a heat treatment, a resin that is well degreased with an organic solvent, and a resin that is well degreased with a heat treatment Both can be suitably degreased. In addition, although the example which uses 2 types of resin as a binder was shown in Example 2, even if a binder is substantially only POM, performing a high degreasing | defatting by performing several different degreasing processes repeatedly. Can do.

  The combination of the degreasing process mentioned above is not limited to the combination of the degreasing process by an organic solvent and the degreasing process by heat processing. For example, a combination of a process of heat treatment at a relatively high temperature and a process of heat treatment at a relatively low temperature, or a combination of a degreasing process using a different organic solvent may be used. Moreover, you may combine three or more degreasing processes.

[5. Effects of this disclosure]
According to the manufacturing method of the present disclosure described in detail above, the following effects are obtained.
(5A) By using mainly polyacetal as a binder, the molded body can be highly degreased and the amount of residual coal can be reduced. This is thought to be because polyacetal has a simpler structure than, for example, polyalkylene carbonate. As a result of reducing the amount of residual carbon in the molded body, the magnetocaloric effect of the magnetocaloric effect material molded body can be enhanced, and the change in characteristics over time of the magnetocaloric effect material, particularly the operating temperature, is suppressed, In addition, it is possible to suppress the functional deterioration of the system using the magnetocaloric effect material.

  (5B) By using mainly polyacetal as the binder, the injection property and moldability are improved. If the particle size of the raw material powder is reduced, the fluidity of the raw material powder is improved, so that injection molding may be possible without using a binder. However, it becomes difficult to improve the magnetocaloric effect as the particle size decreases. By using the above-mentioned binder, micro metal injection molding using a powder raw material of a magnetocaloric effect material having a relatively large particle size can be performed. By performing the micro metal injection molding, for example, the fine flow paths in the molded body can be collectively formed, and the productivity of the molded body is improved as compared with the case of forming a plurality of fine flow paths by performing physical processing.

(5C) By removing the binder by degreasing, voids are generated in the molded body. This void acts as a buffer portion, so that hydrogen embrittlement and cracking of the molded body can be suppressed when hydrogen treatment is performed.
(5D) The molded body produced in Example 2 had a residual carbon content of less than 0.01 wt%. Thus, the change of operating temperature can be suppressed highly by reducing the amount of remaining charcoal.

1 ... molded body, 2 ... channel

Claims (6)

A method for producing a molded body of magnetocaloric effect material,
A forming step (S4) of forming a formed body (1) by forming a mixture of La (Fe, Si) ₁₃ raw material powder and polyacetal;
A degreasing step (S5, S6) for removing the polyacetal from the molded body produced in the molding step. A method for producing a molded body of the magnetocaloric effect material according to claim 1,
The molding step is a method for producing a molded body of a magnetocaloric effect material, which is a process of producing the molded body by injection molding. A method for producing a molded body of the magnetocaloric effect material according to claim 1 or 2,
The said powder raw material is a manufacturing method of the magnetocaloric effect material whose particle size is 0.1-200 micrometers. A method for producing a molded body of the magnetocaloric effect material according to any one of claims 1 to 3,
The degreasing step includes a first step (S5) and a second step (S6),
The method for producing a molded body of a magnetocaloric effect material, wherein the first step and the second step are steps having different degreasing characteristics. A method for producing a molded body of a magnetocaloric effect material according to any one of claims 1 to 4,
Sintering the molded body degreased in the degreasing step, and having a sintering step (S7) for producing a sintered body,
The manufacturing method of the molded object of the magnetocaloric effect material whose residual carbon amount of the said sintered compact is less than 0.01 wt%. A method for producing a molded body of a magnetocaloric effect material according to any one of claims 1 to 5,
In the molding step, a method for producing a molded body of magnetocaloric effect material, in which a molded body having one or more flow paths (2) is formed.