JP6489094B2 - Mixed powder for powder metallurgy - Google Patents

Description

  The present invention relates to a mixed powder for powder metallurgy.

  Powder metallurgy is a technique for producing a sintered part such as a machine part by pressing a mixed powder containing an iron-based powder and the like to obtain a green compact and then sintering the green compact.

In recent years, with the progress of powder metallurgy technology, it has become possible to manufacture sintered parts having high dimensional accuracy and complex shapes in a near net shape, and powder metallurgy technology is used in products in various fields.
However, if sintered parts require extremely strict dimensional accuracy, or if a side hole shape, undercut shape, or other highly complex shape is required, post-sintering ( Cutting etc.) may be required.
However, sintered parts are high in strength for post-processing and have a high void content ratio, so that cutting resistance and frictional heat increase, and the surface temperature of the cutting tool tends to increase. Therefore, the cutting tool is easily worn out and has a short life, resulting in a problem that the cutting cost is increased and the manufacturing cost of the sintered part is increased.

Therefore, as a solution to the above problem, so-called green processing, in which a green compact before sintering is cut and then sintered, is attracting attention.
However, generally, the green compact before sintering is brittle and the workability is often insufficient. That is, the green compact before sintering cannot withstand the stress applied to the jig during green processing or during cutting, and is easily damaged. For this reason, it is desired to increase the strength of the green compact so that it can withstand green processing.
From the viewpoint of increasing the strength of the green compact, for example, Patent Document 1 discloses a mixed powder for powder metallurgy containing “thermosetting resin powder”. Is "Because of having an appropriate density and strength even before sintering, cutting is possible" (paragraph [0015] of Patent Document 1).

JP 2006-124777 A

  As described above, from the viewpoint of green processing, the green compact obtained by pressure forming the mixed powder for powder metallurgy has excellent workability before sintering (processing such as cutting while suppressing damage). Is possible).

By the way, in the mixed powder for powder metallurgy, for example, the fluidity of the mixed powder for powder metallurgy at the time of transfer such as discharging from the storage hopper or filling into the mold is important to affect the production speed and fillability. One of the characteristics. For this reason, in order to improve product quality, reduce manufacturing costs, etc., it is required that the mixed powder for powder metallurgy has good fluidity.
Then, when the present inventors examined the mixed powder for powder metallurgy described in Patent Document 1, it was found that fluidity may be insufficient.

  The present invention has been made in view of the above points, and provides a mixed powder for powder metallurgy that has good flowability and excellent workability before sintering when formed into a green compact. Objective.

As a result of intensive studies, the present inventors have found that the above object can be achieved by the following constitution, and have completed the present invention.
That is, the present invention provides the following [1] to [3].
[1] An iron-based powder and a microcapsule are contained, and the microcapsule includes at least a liquid curable compound, and the content of the liquid curable compound not included in the microcapsule is 100 masses of the iron-based powder. Mixed powder for powder metallurgy, which is 0.10 parts by mass or less with respect to parts.
[2] For powder metallurgy according to the above [1], further containing at least one selected from the group consisting of a curing agent, a curing accelerator, a plasticizer, and a coupling agent not encapsulated in a microcapsule Mixed powder.
[3] The content of the microcapsule encapsulating the liquid curable compound is 0.05 to 2 parts by mass with respect to 100 parts by mass of the iron-based powder, as described in [1] or [2] above. Mixed powder for powder metallurgy.

  ADVANTAGE OF THE INVENTION According to this invention, the fluidity | liquidity is favorable and can provide the mixed powder for powder metallurgy which is excellent in the workability before sintering when it is set as a green compact.

[Mixed powder for powder metallurgy]
The mixed powder for powder metallurgy of the present invention (hereinafter also simply referred to as “mixed powder of the present invention”) contains an iron-based powder and microcapsules, and the microcapsules include at least a liquid curable compound, The mixed powder for powder metallurgy, wherein the content of the liquid curable compound not encapsulated in the capsule is 0.10 parts by mass or less with respect to 100 parts by mass of the iron-based powder.

The mixed powder of the present invention has good fluidity and excellent workability before sintering when formed into a green compact. The reason is presumed as follows.
First, when the mixed powder of the present invention is pressure-molded to obtain a green compact, the liquid curable compound exudes from the microcapsule, spreads between the iron-based powder particles, and the iron-based powder particles adhere to each other. Is done. For this reason, the green compact obtained by pressure-molding the mixed powder of the present invention has high strength even before sintering, and can perform processing such as cutting while suppressing damage (processing) It is considered that the property is excellent.
Further, in the mixed powder of the present invention, the liquid curable compound is encapsulated in the microcapsule and substantially contains the liquid curable compound not encapsulated in the microcapsule before being pressure-molded. Therefore, it is considered that the particles of the iron-based powder are not adhered to each other and have excellent fluidity.
On the other hand, mixed powder for powder metallurgy containing a curable resin powder (see, for example, Patent Document 1) is considered to have relatively good workability before sintering when it is formed into a green compact. However, it is considered that the fluidity is inferior because adhesion performance can be exhibited even before pressure molding.

  Next, each component contained in the mixed powder of the present invention will be described.

[Iron-based powder]
Examples of the iron-based powder include pure iron powder and alloy steel powder.
Specific examples of the pure iron powder include atomized iron powder and reduced iron powder.
Specific examples of alloy steel powder include partially diffused alloyed steel powder, fully alloyed steel powder (in which alloy components are included from the time of melting), and hybrids in which alloy components are partially diffused into fully alloyed steel powder. Examples include steel powder. Examples of the alloy component in the alloy steel powder include Cr, Mn, Ni, Mo, V, Ti, Cu, and Nb. In particular, Ti, Ni, Mo, Cu, and the like can be added by diffusion bonding. Content of an alloy component will not be specifically limited if the premise (Fe: 50 mass% or more) which is an iron-based powder is satisfy | filled.
The iron-based powder may contain, for example, impurities of about 3% by mass or less in total. Typical impurity content is mass%, C: 0.05% or less, Si: 0.10% or less, Mn (when not added as an alloying element): 0.50% or less, P: 0.03 %: S: 0.03% or less, O: 0.30% or less, N: 0.1% or less.
The average particle size of the iron-based powder is preferably 70 to 100 μm as a normal range used for powder metallurgy. The particle size of the iron-based powder is a measured value by dry sieving based on JIS Z 2510: 2004 unless otherwise specified.

[Microcapsule]
The microcapsules in the present invention include at least a liquid curable compound as an encapsulating agent (core substance) inside a capsule wall made of a film substance. That is, the liquid curable compound is microencapsulated. For this reason, in the state before press-molding the mixed powder of the present invention, the particles of the iron-based powder are not adhered to each other, and the fluidity is excellent.

  In this specification, “liquid” means liquid at normal temperature (25 ° C.). Similarly, “powdered” means solid at room temperature.

The method for microencapsulating the liquid curable compound is not particularly limited, and a conventionally known method can be used, for example, S / O microcapsule method, phase separation method, interfacial polymerization method, in-situ polymerization method, spray Examples thereof include, but are not limited to, a dry method.
The in-situ polymerization method is a method of preparing a microcapsule by dissolving a membrane substance that becomes a capsule wall in a dispersion solution of a core substance that becomes an encapsulating agent and causing a polymerization reaction at the interface. Specifically, for example, the method described in paragraph [0144] of JP 2010-128317 A can be mentioned, but the method is not limited thereto.

The material of the capsule wall of the microcapsule (capsule wall material) is not particularly limited, and conventionally known resins can be used, and examples thereof include urea resin, melamine-formaldehyde resin, polyester resin, styrene acrylic resin, and the like. However, it is not limited to these resins.
In the microcapsule, the mass ratio between the encapsulating agent and the capsule wall (encapsulating agent / capsule wall) is not particularly limited, and is, for example, 99/1 to 50/50, and preferably 95/5 to 70/30.

  The mixed powder for powder metallurgy is usually often mixed with a lubricant (release agent) in order to improve the pullability after pressure molding. However, in the mixed powder of the present invention, microcapsules are used. By including the extractability can be improved. However, blending a lubricant with the mixed powder of the present invention is not excluded.

The liquid curable compound (hereinafter also simply referred to as “curable compound”), which is an encapsulating agent for microcapsules, exudes from the microcapsules when the mixed powder of the present invention is pressed to obtain a green compact. Adhere the iron-based powder particles together.
As the liquid curable compound, a conventionally known curable compound can be appropriately used as an adhesive or the like. For example, a resol type phenol resin, a novolac type phenol resin, a urethane prepolymer, an epoxy resin prepolymer, a (meth) acrylate compound (anaerobic) Properties), modified silicone resins, and the like, but are not limited thereto. Here, “(meth) acrylate” means “acrylate and / or methacrylate”.

  In addition, the mixed powder of the present invention may further contain additives such as a curing agent, a curing accelerator, a plasticizer, and a coupling agent, and among others, from the group consisting of a curing agent and a curing accelerator. It is preferable to contain at least one selected. These may be liquid or powdery, may be encapsulated in microcapsules, or may not be encapsulated.

  When the novolak type phenol resin is encapsulated in the microcapsule, for example, hexamethylenetetramine may be added to the mixed powder of the present invention as a powdery curing agent. At this time, the mass ratio of each component (novolak type phenol resin / curing agent) is preferably 50/50 to 99.99 / 0.01.

  When the urethane prepolymer is encapsulated in the microcapsule, a curing accelerator (for example, lead octenoate, phenylmercury propionate, dibutyltin dilaurate, bismuth acetate, etc.) may be encapsulated in the microcapsule. The mass ratio of each component (urethane prepolymer / curing accelerator) is preferably 50/50 to 99.99 / 0.01.

Although it does not specifically limit as an epoxy resin prepolymer, Specifically, the epoxy resin prepolymer (bisphenol A type epoxy resin) which carried out condensation polymerization of bisphenol A and epichlorohydrin is mentioned, for example.
When such an epoxy resin prepolymer is encapsulated in a microcapsule, a powdered curing agent (eg, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetrahydrate) is separately added to the mixed powder of the present invention. Carboxylic acid, ethylene glycol bis trimellitate, glycerol trislimitate, maleic anhydride, tetrahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, methylcyclohexenedicarboxylic anhydride, alkylstyrene- Maleic anhydride copolymer, chlorendic acid anhydride, polyazeline acid anhydride and other acid anhydrides; metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone and other aromatic amines; The value based on the epoxy equivalent is optimal for the addition amount of the curing agent. For example, when an aromatic diamine is used as the curing agent, usually 25 to 35 parts by mass with respect to 100 parts by mass of the epoxy resin prepolymer. Is preferred.
Furthermore, a curing accelerator (for example, N, N-dimethylpiperazine, 2,4,6-tris (dimethylaminomethyl) phenol, benzyldimethylamine, 2- (dimethylaminomethyl) phenol, etc.) is added to the microcapsules. The tertiary amine) may be included in an amount of 0.01 to 20 parts by mass with respect to 100 parts by mass of the epoxy resin prepolymer, for example.

  In the case of a (meth) acrylate compound (anaerobic), as an example, the microcapsule has 3 to 97 mass% of (meth) acrylate monomer such as di (meth) acrylate and 3 to 97 mass of peroxide as a curing agent. In addition, the amine as a curing accelerator can be included in an amount of 0.1 to 30 parts by mass with respect to a total of 100 parts by mass of the (meth) acrylate monomer and the peroxide.

  In the case of a modified silicone resin (including epoxy / modified silicone resin, acrylic / modified silicone resin, etc.), as an example, the microcapsule has a modified silicone resin catalyst of 0.1 to 20 masses per 100 mass parts of the modified silicone resin. Part, 0.1 to 200 parts by weight of a filler having an inorganic agent on the surface of the foam and having a bulk specific gravity of 0.5 or less, 0.5 to 300 parts by weight of epoxy resin, and 0.1 to 0.1 part of epoxy resin curing agent 200 parts by mass or the like can be included.

In addition, the mixed powder of this invention can contain a plasticizer and a coupling agent. When the liquid curable compound is a modified silicone resin, it is preferably contained.
Examples of the plasticizer include phthalic acid alkyl esters such as dioctyl phthalate, dibutyl phthalate, and butyl benzyl phthalate; aliphatic carboxylic acid alkyl esters such as dioctyl adipate, diisodecyl succinate, dibutyl sebacate, and butyl oleate. Pentaerythritol esters; phosphate esters such as trioctyl phosphate and tricresyl phosphate; epoxy plasticizers such as epoxidized soybean oil and benzyl epoxy stearate; polypropylene glycol; polyethylene glycol; chlorinated paraffin; For example, it can contain 10-300 mass parts with respect to 100 mass parts of liquid curable compounds.
Examples of the coupling agent include N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and γ-glycidoxypropyltri Examples include silane coupling agents such as methoxysilane and N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane. For example, 1 to 15 parts by mass can be contained with respect to 100 parts by mass of the liquid curable compound.

  The molecular weight (including the weight average molecular weight and number average molecular weight) of the liquid curable compound described above is not particularly limited as long as the curable compound is liquid, and is appropriately set.

<Average particle size of microcapsules>
If the average particle size of the microcapsules is too large, the density of the mixed powder of the present invention may decrease and the target strength may be difficult to obtain, and if it is too small, the fluidity may be insufficient. 5-100 micrometers is preferable, 20-90 micrometers is more preferable, and 30-80 micrometers is still more preferable. When the average particle diameter of the microcapsules is within this range, the mixed powder of the present invention has better fluidity and better workability before sintering when it is formed into a green compact.
In addition, the average particle diameter of a microcapsule can be measured using a laser diffraction / scattering particle size distribution meter, and refers to a volume average particle diameter.

<Content of microcapsules>
If the content of the microcapsules in the mixed powder of the present invention is too small, the encapsulating agent may not sufficiently bleed out during pressure molding, and sufficient strength may be difficult to obtain. Since necking may be inhibited and the strength may decrease, 0.05 to 2 parts by mass is preferable, 0.08 to 1.5 parts by mass is more preferable, and 100 parts by mass of iron-based powder. More preferably, it is 10 to 1.0 parts by mass.

[Other additives]
The mixed powder of the present invention can further optionally contain other additives as required.
For example, the mixed powder of the present invention may contain a lubricant as an additive, and specific examples thereof include metal soap (such as zinc stearate), amide wax, polyamide, polyethylene, polyethylene oxide and the like.

[Liquid curable compound not encapsulated in microcapsules]
In the mixed powder of the present invention, the content of the liquid curable compound not encapsulated in the microcapsule is 0.10 parts by mass or less, preferably 0.01 parts by mass or less with respect to 100 parts by mass of the iron-based powder. Further preferred is an embodiment which does not substantially contain a liquid curable compound not encapsulated in microcapsules.
Thereby, in the state before press-molding the mixed powder of this invention, the particle | grains of iron-based powder are not adhere | attached, but it is excellent in fluidity | liquidity.
Examples of the liquid curable compound that is not encapsulated in the microcapsule include those described as the liquid curable compound that is the encapsulating agent of the microcapsule.
In the present invention, a mode in which a liquid curable compound not encapsulated in microcapsules is not added to the powder mixture for powder metallurgy is referred to as “a mode that substantially does not contain a liquid curable compound not encapsulated in microcapsules”. .

[Production method and usage of mixed powder for powder metallurgy]
The mixed powder of the present invention can be obtained by appropriately mixing the above-described essential components and optional components using, for example, a conventionally known mixer.
The mixed powder of the present invention thus obtained can be used as a raw material for powder metallurgy. That is, the mixed powder of the present invention is pressed into a green compact (a green compact) by a general method, and then the green compact is sintered at 1000 to 1300 ° C., for example. Sintered parts such as machine parts can be manufactured.

At this time, the mixed powder of the present invention is excellent in fluidity at the time of transfer such as discharging from a storage hopper or filling into a mold when being pressure-molded. Expected to improve quality and reduce manufacturing costs.
Further, the green compact obtained by pressure-molding the mixed powder of the present invention has high strength, and even before sintering, processing such as cutting (green processing) while suppressing damage. Can be performed.

[Heat curing]
For example, when a thermosetting compound such as a (meth) acrylate compound, a phenol resin, and an epoxy resin prepolymer is used as the liquid curable compound, the green compact obtained by pressure molding is used. Before the sintering, a heat curing treatment for curing the liquid curable compound may be performed. The strength of the green compact can be further improved by curing the liquid curable compound.
What is necessary is just to determine the conditions of a heat-hardening process according to the kind of liquid curable compound (thermosetting compound) to be used. For example, the heating temperature in the heat curing process is generally 80 to 200 ° C. The heating time in the heat curing treatment is, for example, 10 minutes to 1 hour, and preferably 15 to 30 minutes.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.

<Examples 1-3>
An iron-based powder prepared by adding copper powder: 2% by mass and graphite powder: 0.8% by mass to pure iron powder (atomized iron powder 301A manufactured by JFE Steel) was prepared. 0.5 mass of microcapsules (details will be described later) encapsulating a liquid epoxy resin prepolymer and aromatic amine (metaphenylenediamine) as a powdery curing agent in a ratio (mass ratio) of 4: 1. Partly added and mixed for 15 minutes with a V-type blender to obtain a mixed powder for powder metallurgy.
In addition, the difference of Examples 1-3 is the difference of the presence or absence of the heat-hardening process with respect to the green compact obtained using the mixed powder for powder metallurgy, or the difference of heat-hardening process conditions so that it may mention later.

  -Microcapsules: average particle diameter: 60 μm, capsule wall: urea resin, liquid epoxy resin prepolymer: bisphenol A type epoxy resin, mass ratio (encapsulant / capsule wall): 80/20

  In addition, the said microcapsule was produced based on the method described in Paragraph [0144] of Unexamined-Japanese-Patent No. 2010-128317.

<Examples 4 to 6>
Powder metallurgy mixing in the same manner as in Examples 1 to 3 except that 1 part by mass of microcapsules and a curing agent was added at a ratio (mass ratio) of 4: 1 to 100 parts by mass of iron-based powder. A powder was obtained. The difference between Examples 4 to 6 is the difference in the presence or absence of heat-curing treatment on the green compact obtained using the powder mixture for powder metallurgy, or the difference in heat-curing treatment conditions, as will be described later.

<Standard example 1>
For 100 parts by mass of iron-based powder prepared in Example 1 (iron-based powder obtained by adding 2% by mass of copper powder and 0.8% by mass of graphite powder to atomized iron powder 301A manufactured by JFE Steel), stearin 1 part by mass of zinc acid was added and mixed to obtain a mixed powder for powder metallurgy.

<Standard example 2>
Only the iron-based powder prepared in Example 1 (iron-based powder obtained by adding 2% by mass of copper powder and 0.8% by mass of graphite powder to atomized iron powder 301A manufactured by JFE Steel Co., Ltd.) A mixed powder for metallurgy was obtained.

<Comparative Example 1>
Instead of microcapsules and powdered curing agents, clear powder paint (trade name: Konak No. 3700, manufactured by NOF BASF Co., Ltd., uncured epoxy resin cured with amine curing agent), iron-based Powder metallurgy mixing in the same manner as in Example 1 except that 0.5 part by mass is added to 100 parts by mass of powder and 1 part by mass of zinc stearate is added to 100 parts by mass of iron-based powder. A powder was obtained.

<Comparative example 2>
What mixed 0.20 mass parts of liquid epoxy resins (brand name: Epicoat 828, the product made from Yuka Shell Epoxy Co., Ltd.) with respect to 100 mass parts of iron-base powder to the mixed powder for powder metallurgy of Example 1, and mixed. The mixed powder for powder metallurgy of Comparative Example 2 was obtained.

<Evaluation>
The following evaluation was performed using the obtained mixed powder for powder metallurgy. The results are shown in Table 1 below. In addition, when evaluation was not performed, "-" was described in Table 1 below.

(Fluidity)
The fluidity is an index indicating the fluidity of the powder when filling the mold.
The obtained powder mixture for powder metallurgy: 50 g was filled in a container having an orifice diameter: 2.5 mm, and the time from filling to discharging was measured to determine the fluidity (unit: sec / 50 g). . Other measurement conditions were based on JISZ2502: 2012. The smaller the fluidity value, the better the fluidity.

(Density and extraction force)
When the obtained powder mixture for powder metallurgy was molded as described below, its density (unit: g / cm ³ ) and extraction force (unit: MPa) were measured. The lower the extraction force value, the better the extraction performance.

(Folding strength)
The bending strength of the green compact is a numerical index for cracks that occur during drilling.
With respect to the obtained mixed powder for powder metallurgy, the bending strength (unit: MPa) of the green compact molded at a molding pressure of 690 MPa was determined in accordance with Japan Powder Metallurgy Industry Association Standard JPMA P10-1992. The larger the value of the bending strength, the higher the strength of the green compact, and it can be evaluated that it is excellent in the workability of the green compact before sintering.

Before determining the bending strength of the green compact, the green compact was heat-cured at 80 ° C. for 30 minutes in Examples 2 and 5, and 120 ° C. for 30 minutes in Examples 3 and 6. Heat curing treatment was performed for each.
When heat-curing treatment was performed on the green compact before determining the bending strength, “-” was entered in the column of heat-curing treatment conditions in Table 1 below.

  As is clear from the results shown in Table 1 above, when Example 1 is compared with Comparative Example 1, first, the mixed powder for powder metallurgy of Example 1 in which microcapsules encapsulating a liquid curable compound are blended is cured. Compared with the mixed powder for powder metallurgy of Comparative Example 1 in which a conductive resin powder was blended, the fluidity value was small and the fluidity was good. In addition, Example 1 has a higher bending strength than Comparative Example 1, indicating that the processability of the green compact before sintering is equal to or better than that of Comparative Example 1.

  Further, in Comparative Example 2 in which a liquid curable compound not encapsulated in microcapsules was blended, the powdered metallurgy mixed powder did not flow (not discharged from the container) and flowed even when the fluidity was obtained under the above-described conditions. It was found that the property was remarkably inferior.

  Further, in Example 1, although the lubricant (stearic acid) was not blended, the value of the extraction force was slightly larger than that of the standard example 1 blended with the lubricant (stearic acid), The drawability was good. This is considered to be because the extractability is improved by containing the microcapsules.

  In addition, Example 1 had a smaller fluidity value and better fluidity than Standard Example 2, which was only an iron-based powder. This is presumably because the fluidity was improved by containing microcapsules.

  Looking at Examples 1 to 6, Examples 2 to 6 are similar to Example 1 in that the fluidity value is small and the fluidity is good, and the bending strength is large and the pressure before sintering. The processability of the powder was good.

In contrast to Examples 1 to 3, Examples 2 to 3 in which the heat-curing treatment was performed on the green compact were more resistant than Examples 1 in which the heat-curing treatment was not performed on the green compact. The value of the folding strength was larger.
Further, in contrast to Examples 2-3, the value of the bending strength is higher in Example 3 where the heating temperature of the heat curing treatment is 120 ° C. than in Example 2 where the temperature is 80 ° C. It was.

In Examples 4 to 6, the same tendency as in Examples 1 to 3 was observed.
That is, the value of the bending strength is larger in Example 5 in which the heat curing process at 80 ° C. was performed than in Example 4 in which the heat curing process was not performed, and the heating at 120 ° C. was higher than in Example 5. The value of the bending strength was larger in Example 6 where the curing treatment was performed.

Claims (3)

Contains iron-base powder and microcapsules, does not contain wax having a dropping point of 50-100 ° C., an acid value of 5-150, a hydrolysis value of 15-160 and a density of 0.95-1.20 g / cm ³ ,
The microcapsules include at least a liquid curable compound;
The content of the liquid curable compound which is not enclosed in the microcapsules, the relative iron-base powder 100 parts by state, and are 0.10 parts by weight, is not enclosed in the microcapsules, the liquid curable compound Mixed powder for powder metallurgy that does not contain any liquid substances other than .   The mixed powder for powder metallurgy according to claim 1, further comprising at least one selected from the group consisting of a curing agent, a curing accelerator, a plasticizer, and a coupling agent that is not encapsulated in microcapsules.   3. The mixed powder for powder metallurgy according to claim 1, wherein the content of the microcapsules enclosing the liquid curable compound is 0.05 to 2 parts by mass with respect to 100 parts by mass of the iron-based powder. .