JP2002146406A - Lubricant for warm compacting and powdery mixture for warm compacting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant by which the problem of the sticking of raw material powder is not generated even in a preheating stage, extraction force in the extraction of a compact from a die can be reduced, and extruction noise can be reduced. SOLUTION: This lubricant for warm compacting is composed of crosslinked polymer grains with the average grain size of 1 to 80 μm, in which (meta) acrylic alkyl ester (A) in which the number of carbon in the alkyl group is 1 to 8 is used as an essential constitution component, and the gel fraction measured by using methyl ethyl ketone is >=5 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lubricant for warm forming for improving lubricity during warm forming performed using a raw material powder for powder metallurgy, and to the addition of such a lubricant. The present invention relates to a mixed powder for warm compaction capable of obtaining a sintered body having various characteristics.

[0002]

2. Description of the Related Art In a powder metallurgy method using a metal powder such as iron powder or steel powder as a main raw material, an alloy component or a powder such as graphite is added to the main raw material powder as a component for improving the physical properties of a sintered body. The raw material powder for powder metallurgy is added and mixed, a lubricant is added to the raw material powder, and the resulting mixture is compression-molded to form a green compact, and the green compact is subsequently sintered to obtain a sintered product. In the powder metallurgy method, the step of compacting the raw material powder into a green compact is an important step from the viewpoint of obtaining a sintered product having good characteristics. And an additive necessary for facilitating compression molding.

[0003] As a temperature range for compression molding of a raw material powder, three types of temperature ranges are generally employed. That is, room temperature molding (molding at room temperature), hot molding (molding at a temperature at which the metal powder exceeds the work hardening temperature during molding), and warm molding (molding at an intermediate temperature between room temperature molding and hot molding). There are three types.

[0004] Of these compression moldings, when the compression molding is performed in a temperature range exceeding room temperature, the yield stress of the metal decreases, so that
There is an advantage that the density and strength of the green compact can be improved even under a low molding pressure. However, in hot compression molding in an extremely high temperature range, even if a lubricant for hot compression molding having relatively excellent heat resistance is used, the lubricant deteriorates and the lubrication function is reduced,
It has been pointed out that there is a problem of promoting mold wear.

[0005] From these facts, exceeding the normal temperature molding temperature,
In addition, warm compression molding (hereinafter, simply referred to as “warm molding”) that performs compression molding in a temperature region (usually about 100 to 150 ° C.) that is not as high as the hot temperature region has attracted attention. . In this warm compacting, usually, a solid lubricant is present between the powders as a roller, and a solid lubricant for ensuring the ease of movement between the powders, and liquefied to form a lubricating liquid film on the powder surface, A liquid lubricant for lowering the frictional resistance between them is added to and mixed with the raw material powder, thereby facilitating the production of a green compact.

By the way, the raw material powder is stored in a hopper until it is compression-molded in a mold. However, if the temperature is raised to the molding temperature after filling the raw material powder into the mold, it takes a long time to raise the temperature. The raw material powder is preheated to the same temperature as the molding temperature in the hopper to shorten the molding cycle. If the liquid lubricant melts during this preheating stage, the raw powder adheres to the wall of the hopper, the raw powder blocks or forms a bridge, and the powders adhere to each other to reduce the fluidity of the powder. There has been a problem that the number of the components is significantly reduced, and the work of introducing the components into the mold becomes difficult. In addition, when the green compact is extracted from the mold after the compression molding, if the performance of the lubricant is poor, the mold wall may be worn or a loud noise (extraction noise).
This causes a problem that the working environment is deteriorated due to occurrence of the problem.

[0007] For example, Japanese Patent Laid-Open No.
No. 317001 discloses a technique in which a powder is coated with an organometallic coupling agent or the like, and a thermoplastic polymer / elastomer powder that can be heated and melted at a molding temperature is used as a lubricant. However, the presence of the organic metal causes a reduction in the strength of the sintered body. From this point of view,
000-160206 discloses a technique using a thermoplastic polymer powder containing no metal component as a lubricant. However, since the thermoplastic polymer / elastomer powder is melted in the preheating stage, the problem of the adhesion of the raw material powder to the inner wall of the hopper still remains.

[0008]

Therefore, in the present invention,
The problem is to find a lubricant that does not cause the problem of sticking of the raw material powder even in the preheating stage, reduces the ejection force when extracting the green compact from the mold after compression molding, and reduces the ejection noise. Raised.

[0009]

SUMMARY OF THE INVENTION The lubricant of the present invention is measured using methyl ethyl ketone, which contains an alkyl (meth) acrylate having an alkyl group of 1 to 8 carbon atoms (A) as an essential component. The gel fraction is 5% by mass or more,
The lubricant for warm forming has a gist in that it is a crosslinked polymer particle having an average particle diameter of 1 to 80 µm. By using the crosslinked polymer particles as a lubricant, both functions of a solid lubricant and a liquid lubricant could be exhibited in a preheating / forming temperature range in warm forming. In addition, since the polymer is crosslinked, it does not melt at the preheating temperature, so that inconvenience such as adhesion to the inner wall of the hopper does not occur. The gel fraction which is a measure of the degree of crosslinking is more preferably 20% by mass or more.

The above-mentioned crosslinked polymer particles comprise a polyfunctional monomer (B) having two or more radically polymerizable unsaturated groups together with an alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms (A). Is an essential component. This is a means of pre-crosslinking molecular chains by copolymerization. Further, together with the alkyl (meth) acrylate (A), a functional group capable of reacting with a crosslinking agent
It can also be obtained when the functional group-containing monomer (C) having at least one monomer is used as an essential component and is crosslinked by the above crosslinking agent during or after polymerization. of course,
It is also possible to obtain crosslinked polymer particles by using the polyfunctional monomer (B) and the functional group-containing monomer (C) in combination.
It is preferable that the crosslinked polymer particles contain 50% by mass or more of the alkyl (meth) acrylate (A). This is because they exhibit good lubricating properties and have excellent heat decomposition properties.

The present invention also includes a mixed powder for warm compaction which essentially contains a lubricant for warm compaction and a raw powder for powder metallurgy. If necessary, a fatty acid-based and / or polyolefin-based lubricant may be used in combination. In the following description, “mixed powder” refers to a powder that essentially contains a powder metallurgy raw material powder and a lubricant, and “raw powder” refers to a metallurgical raw material powder that does not contain a lubricant.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The lubricant for warm forming according to the present invention is a crosslinked polymer particle,
Alkyl (meth) acrylate is an essential component. This is because the (meth) acrylic polymer has an appropriate plastic deformability even when crosslinked, and is excellent in lubricating performance. In addition, the heat decomposition property during sintering after green compact formation is good, and no toxic gas is generated.

In particular, it is preferable to use an alkyl (meth) acrylate (A) having an alkyl group having 1 to 8 carbon atoms. In the alkyl (meth) acrylate having an alkyl group having 9 or more carbon atoms, the tackiness of the resulting polymer increases, and after adding a lubricant to the raw material powder,
It is not preferable because the powder adheres to the inside of the hopper or the like and the powder fluidity cannot be secured.

As the alkyl (meth) acrylate (A), methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, Isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth)
Acrylate and the like;
A mixture of more than one species can be used. It is preferable to select appropriately so as to satisfy the requirement of Tg described later. Most preferred is methyl methacrylate (MMA) in terms of lubricity. The Tg of the uncrosslinked homopolymer of MMA is 105 ° C. (however, it may vary from 105 to 130 ° C. depending on the polymerization method and the measuring instrument), the softening temperature (Vicat) is 110 to 140 ° C., and the melting point is 160.
It is around ° C.

The crosslinked polymer which is the lubricant of the present invention must be crosslinked. The degree of crosslinkage should be at least 5% by mass based on the gel fraction. If the gel fraction is lower than 5% by mass, the lubricant loses its particle shape due to preheating and melts and flows, which is not preferable because it becomes a factor of fixing the mixed powder. If the crosslinked polymer particles have a gel fraction of 5% by mass or more, the shape of the particles can be maintained even if the particles are preheated, so that there is no problem such as sticking of the mixed powder. In addition, even though it is cross-linked, the polymer molecular chains are easy to move by heating, so during the compression molding of the mixed powder, the lubricant particles are appropriately plastically deformed. In this case, it is possible to reduce the output power and the output sound when the mold is removed. Moreover, it is preferable because the gap between the metal powders is reduced by appropriate plastic deformation, the density of the green compact is improved, and the strength of the sintered body is improved. A more preferred gel fraction is 20% by mass or more.

For the measurement of the gel fraction, methyl ethyl ketone is used as a solvent. More specifically, a precisely weighed predetermined amount W ₁
Put the crosslinked polymer particles of
The mixture was allowed to stand at 5 ° C. for 20 hours, filtered through a glass filter in which particles of 7 μm or more were retained, and then heated and dried (not the residue on the filter), and then dried to dryness (dissolved crosslinked polymer). Min) and the mass W ₂ of
0 × (W ₁ −W ₂ ) / W ₁ was defined as a gel fraction (% by mass).

In order to obtain crosslinked polymer particles having a gel fraction of 5% by mass or more, the polyfunctional monomer (B) having two or more radically polymerizable unsaturated groups in the alkyl (meth) acrylate (A) and It is necessary to copolymerize a functional group-containing monomer (C) having at least one functional group capable of reacting with a crosslinking agent.

Examples of the polyfunctional monomer (B) include ethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and hexane diol Polyfunctional (meth) acrylates having two or more (meth) acryloyl groups, such as (meth) acrylate, polyoxyethylene di (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate; Monomers having (meth) acryloyl group and vinyl / allyl group such as vinyl (meth) acrylate and allyl (meth) acrylate; two allyl groups such as triallyl trimellitate and triallyl isocyanurate Aromatic monomers such as divinylbenzene; butenes such as butadiene, isoprene, 1,3-pentadiene and cyclopentadiene; and non-conjugated dienes such as ethylidene norbornene and vinylcyclohexene. 1
Species or a mixture of two or more can be used.

When a polyfunctional monomer (B) is used, a crosslinked polymer can be obtained only by polymerization. However, it is sometimes difficult to react both double bonds during polymerization with dienes and non-conjugated dienes, so organic peroxides such as benzoyl peroxide, hydrogen peroxide, azobisisobutyronitrile, etc. Preferably, a radical generator is added to the polymer after polymerization to promote the crosslinking reaction.
The adding method will be described later.

The functional group of the functional group-containing monomer (C) includes an epoxy group, a carboxyl group (or an acid anhydride group), a hydroxyl group, an amino group, an amide group and the like. Specific examples of the functional group-containing monomer (C) include epoxy group-containing monomers such as glycidyl (meth) acrylate and 3,4-epoxydicyclohexylmethyl (meth) acrylate; (meth) acrylic acid, maleic anhydride, fumaric acid And carboxyl group (or acid anhydride group) -containing monomers such as crotonic acid; hydroxyl-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate;
Examples thereof include amino- or amide-group-containing monomers such as 2-aminoethyl (meth) acrylate, 2-aminopropyl (meth) acrylate, N-2-aminoethyl (meth) acrylamide, and (meth) acrylamide.

The functional group monomer (C) is used in combination with a crosslinking agent having two or more functional groups in one molecule. When the polymer has an epoxy group, aliphatic diamines such as ethylenediamine; aromatic diamines such as m-xylenediamine and metaphenylenediamine; and melamine compounds such as hexamethoxymelamine can be used as the crosslinking agent. When the polymer has carboxyl groups (acid anhydride groups), polyisocyanate compounds such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, and isocyanurate-modified toluene diisocyanate; A metal chelate compound or the like coordinated with methyl acetoacetate or the like can be used as a crosslinking agent. When the polymer has a hydroxyl group, the melamine compound, the polyisocyanate compound, the polycarbodiimide compound having a carbodiimide (RN = C = N-) group, or the like can be used as a crosslinking agent. When the polymer has an amino group or an amide group, an epoxy resin such as a bisphenol epoxy resin or a novolak epoxy resin; a polyepoxy compound such as sorbitol polyglycidyl ether; and the above polyisocyanate compound can be used as a crosslinking agent. . The method for adding the crosslinking agent will be described later.

As monomers for obtaining crosslinked polymer particles, other than the above-mentioned alkyl (meth) acrylate (A), polyfunctional monomer (B) and / or functional group monomer (C), other monomers are used. Monomer (D)
As, vinyl acetate, styrene, α-methylstyrene,
Vinyl toluene, acrylonitrile and the like may be used.

When the total monomer for obtaining the crosslinked polymer particles is 100% by mass, the total amount of the alkyl (meth) acrylate (A) is preferably at least 50% by mass. If the amount is less than 50% by mass, lubricating properties may not be sufficiently exhibited. More preferably, 80% by mass
That is all. However, if the amount is too large, the amount of the polyfunctional monomer (B) or the functional group monomer (C) involved in the crosslinking becomes small, and the requirement of the gel fraction of 5% by mass or more cannot be satisfied. It is preferable to suppress.

When the polyfunctional monomer (B) is used,
In order to make the gel fraction 5% by mass or more, the polyfunctional monomer (B) is preferably used in an amount of 1% by mass or more in all the monomers. However, if the amount is too large, gelation may occur during polymerization. It is preferable to suppress the content to 10% by mass or less.
More preferably, it is 3 to 8% by mass. The functional group monomer (C) is preferably used in an amount of 1% by mass or more.
% By mass or more is more preferable. The preferred upper limit of the functional group monomer (C) is not particularly limited. This is because the amount of crosslinking can be adjusted by the amount of the crosslinking agent of the reaction partner. However, if the amount of the functional group monomer (C) is too large, the particles become too hard at the warm molding temperature and the lubricating effect is inferior. Therefore, the content is preferably 30% by mass or less.

The crosslinked polymer has a glass transition temperature (Tg)
Is preferably 70 ° C. or higher. It is recommended that the above various monomers (A) to (D) be appropriately selected so that Tg is 70 ° C. or higher. It is advisable to refer to a known formula that can calculate the Tg of the produced polymer from the Tg and the mass fraction of the homopolymer of various monomers. If the Tg of the polymer is lower than 70 ° C., the shape of the polymer particles cannot be maintained during warm forming, and the polymer particles exhibit stickiness and cause sticking and aggregation of the raw material powder, which is not preferable. Also, the lubrication performance is low. 75 ° C. or higher is more preferable. On the other hand, when the degree of crosslinking of the polymer is considerably advanced, for example, when measured by DSC (differential scanning calorimeter), the baseline of the DSC curve does not show a clear inflection point and substantially does not show Tg. Such crosslinked polymers are also useful as the lubricant of the present invention.

The method of polymerizing the polymer is not particularly limited, but a polymerization method such as emulsion polymerization, seed emulsion polymerization, suspension polymerization, milk suspension polymerization, microsuspension polymerization, etc., which can easily obtain granules, may be used. preferable. In emulsion polymerization or seed emulsion polymerization, a known water-soluble polymerization initiator such as ammonium persulfate and a known emulsifier such as sodium dodecylbenzenesulfonate are used.In suspension polymerization, benzoyl peroxide and azobisisobutyronitrile are used. By polymerizing under known conditions using a known oil-soluble initiator and a dispersant such as polyvinyl alcohol or phosphate, an aqueous dispersion in which polymer particles (primary particles) are dispersed in an aqueous medium can be obtained. By changing the monomer composition of the first and second stages by a known core-shell polymerization method, the core may be made of a polymer having a high degree of crosslinking and the shell may be made of a core-shell particle of a polymer having a low degree of crosslinking. Further, hollow particles may be used.

The size of the particles can be controlled by appropriately selecting the type and amount of the emulsifier or dispersant and the stirring state, but in the case of emulsion polymerization or seed emulsion polymerization, the primary particles are about 0.05 to 1 μm. It is. In the present invention, since the crosslinked polymer particles having an average particle size of 1 to 80 μm are used as the lubricant, the primary particles may be too small in some cases. For this reason, after the polymerization, when the obtained aqueous dispersion is dried by coagulation drying, spray drying, flash drying, fluidized bed drying, freeze drying, or the like, it is preferable to form secondary aggregated particles. In particular, agglomerated particles in which the primary particles are fused to some extent and the shape of the primary particles cannot be clearly observed are preferably used because of their high holding strength in the aggregated state. In order to obtain such agglomerated particles, it is preferable to heat at a temperature equal to or higher than the Tg of the polymer in the drying step. In this regard, it is recommended to employ a spray drying method, a flash drying method, and a fluidized bed drying method. The crosslinked polymer particles obtained in this manner are also affected by the force applied during mechanical mixing when preparing the mixed powder for warm compaction,
It has strength that does not return to primary particles. Secondary particles in a state where the shape of each primary particle can be clearly observed are not preferable because they easily collapse and immediately return to the primary particles.

On the other hand, in the case of suspension polymerization or milk suspension polymerization, the primary particles are about 1 to 100 μm. As in the case of the emulsion polymerization, the obtained aqueous dispersion can be dried to form secondary particles from primary particles. In addition, since the particle size of the primary particles is relatively large, it is possible to dry and use the primary particles without producing secondary (aggregated) particles. In any case, it is advisable to classify the dry powder and adjust it to have an average particle size of 1 to 80 μm.

The shape of the crosslinked polymer particles is not limited to a true sphere, but may be uneven or have protrusions such as confetti. The average particle size of the crosslinked polymer particles is 1μ
If it is smaller than m, lubricity and fluidity are not exhibited, and the raw material powder may be fixed. If it exceeds 80 μm, it is not preferable because it is too large and causes the density of the green compact and the strength of the sintered body to decrease. After drying, it may be sieved to remove large particles. The “average particle size” refers to a particle size that results in an integrated value of 50% in a mass distribution when measured using a laser diffraction / scattering type particle size distribution analyzer or the like.

In the case of synthesizing a polymer using the above-mentioned functional group monomer (C), it is necessary to react with a cross-linking agent to crosslink, but it is possible to react with the functional group of the functional group monomer (C) used. It is preferable that the above-mentioned crosslinking agent having two or more functional groups is added to the aqueous dispersion of the polymer at the stage when the polymerization is completed and reacted. Further, after the polymer is dried, a crosslinking reaction can be carried out by mixing the polymer powder with the crosslinking agent as it is or in a state where the crosslinking agent is dissolved or dispersed in water or an organic solvent. Crosslinking reaction conditions are:
What is necessary is just to select suitably according to the kind of crosslinking agent. When a diene or a non-conjugated diene is used as the polyfunctional monomer (B), a means for adding a radical generator for accelerating crosslinking may be performed in the same manner as described above.

The lubricant of the present invention comprises crosslinked polymer particles having a gel fraction of 5% by mass or more, but it is not necessary that all the particles are crosslinked particles having a gel fraction of 5% by mass or more. When the particles are sampled and the gel fraction is measured by the above method, it may be 5 mass% or more. In this sense,
The lubricant of the present invention is also obtained by obtaining crosslinked polymer particles by the method described above, separately producing uncrosslinked polymer particles, mixing the two, and adjusting the mixture so that the gel fraction is 5% by mass or more. Can be used as However, the content of uncrosslinked polymer particles is preferably 50% by mass or less. This is to prevent the raw material powder from sticking during preheating and molding.

The mixed powder for warm compacting of the present invention essentially contains the raw metal powder for metallurgy and the lubricant of the present invention. As metallurgical raw material powders, known metallurgical raw material powders such as various metal powders and various alloy powders such as iron powder, steel powder, and copper powder, graphite powder, and cuprous oxide powder are used according to applications. The amount of the crosslinked polymer particle-based lubricant used is 0.0
5 to 0.6% by mass is preferred. More preferably 0.09
０．５0.5% by mass. If the amount of the lubricant is small, the lubricating effect is not exhibited.

Other lubricants may be blended with the mixed powder. Since the lubricant of the present invention is a crosslinked polymer capable of maintaining the particle shape at the preheating / molding temperature, a lubricant having a lower viscosity than this, that is, a lubricant that becomes a low-viscosity liquid at the temperature of warm molding is used in combination. Is preferred.

Specific examples of the lubricant that can be used in combination include stearic acid (melting point: 52 to 67 ° C.), lauric acid (melting point: 40
-44 ° C), montanic acid (melting point 79-85 ° C), stearic acid amide (melting point 100 ° C or more), palmitic acid amide (melting point 95-100 ° C), methylene bisstearamide (melting point 140 ° C), ethylene bistea Loamide (melting point 137 ° C), zinc stearate (melting point 125
C), calcium stearate (melting point 146 ° C), magnesium stearate (melting point 132 ° C), and other fatty acid-based lubricants, and polyethylene wax (depending on the molecular weight,
Polyolefin-based lubricants such as melting point of about 100 to 140 ° C.) and polypropylene wax (melting point of 140 to 150 ° C.). These low-viscosity type lubricants are excellent in lubricity because they form a low-viscosity liquid film at a warm molding temperature, but may cause sticking of the raw material powder during preheating. Therefore, it is preferable to use one having a melting point as high as possible.
The amount of these lubricants used is preferably 0 to 100 parts by mass with respect to 100 parts by mass of the crosslinked polymer particles of the present invention.

The mixed powder for warm forming according to the present invention is 100 to 100%.
It is formed into a green compact at about 150 ° C., and after that, it becomes a product through a dewaxing step and a sintering step.

[0036]

EXAMPLES The present invention will be described in more detail with reference to the following examples. However, the following examples do not limit the present invention, and all modifications and alterations may be made without departing from the spirit of the present invention. Is included. In addition, "part", "%"
Is based on mass unless otherwise specified, and each physical property value was measured by the following method.

[Tg (° C.)] DSC (differential scanning calorimeter)
Was measured at a heating rate of 10 ° C./min. In addition, since the inflection point of the baseline of a DSC chart was not clearly recognized, the polymer having a high degree of crosslinking was “not shown”.
It was written.

[Weight average molecular weight] The polymer was dissolved in tetrahydrofuran (THF) and measured by gel permeation chromatography (GPC), and the peak value was determined from a calibration curve using a polystyrene standard sample. The crosslinked polymer could not be measured because it did not dissolve in THF.

[Gel fraction (mass%)] Predetermined amount W
Polymer ₁ was placed in methyl ethyl ketone (MEK), allowed to stand at 25 ° C. for 20 hours, filtered through a glass filter retaining 7 μm particles, and the filtrate was dried by heating.
After completely volatilizing the EK, the mass W ₂ of the residual dried product (the dissolved polymer component) was measured, and 100 × (W ₁ −W ₂ ) /
The W ₁ was gel fraction (% by weight).

[Average Particle Size (μm)] Using a laser diffraction / scattering particle size distribution analyzer (COULTER MULTISIZER), the particle size when the integrated mass became 50% was defined as the average particle size (μm).

[Mixed powder flow (sec / 50 g)] JI
According to SZ2502 (Test method for metal powder flowability),
The time required for 50 g of the powder to flow through the orifice having a diameter of 2.63 mm was defined as the mixed powder fluidity (sec / 50 g).

[Green Compact Density (g / cm ³ )] The mass of the obtained green compact was measured, and the value obtained by dividing by the volume (g / cm ³ ) was shown.

[Extraction Output] A value (MPa) obtained by dividing the force required for extracting the green compact from the mold after the heat compression molding by the contact area between the mold and the molded body was shown.

[Ejection Sound] When the mold was opened after the molding at 130 ° C. and 150 ° C., the presence or absence of a sound generated was discriminated and judged. When a sound was generated at one or both temperatures, the sound was determined to be "loud".

[Powder fixation] The mixed powder was held at 150 ° C for 12 hours, and it was visually observed whether or not the powder solidified.

Example 1 (Suspension polymerization) In a flask equipped with a dropping funnel, a stirrer, a thermometer, a nitrogen gas inlet tube and a reflux condenser, polyvinyl alcohol (hydrolysis rate: 80 mol%, polymerization degree: 150
0) 200 parts of deionized and exchanged water in which 0.2 part was dissolved was charged and the atmosphere was replaced with nitrogen. A monomer mixture having the composition shown in Table 1 was charged into a flask, and the temperature was adjusted to 60 ° C. with good stirring under a nitrogen atmosphere. Then, 0.15 part of benzoyl peroxide was added, and suspension polymerization was performed for 10 hours. . In the table, MMA is methyl methacrylate, BA is butyl acrylate, EDMA is ethylene glycol dimethacrylate, MAA is methacrylic acid, and St is styrene.

After completion of the polymerization, most of the water was separated and removed from the obtained aqueous dispersion by a centrifuge, and the water content was 15 to 30%.
And a water content of about 5% under reduced pressure
After evaporating the water up to 110 ° C
While flowing the polymer particles with nitrogen gas, the solution was dried until the water content became 0.2% or less. The obtained polymer particles were pulverized by a ball mill until the particle size became a predetermined size, and separated by a sieve. Tg of the obtained crosslinked polymer
(° C.), weight average molecular weight (Mw), gel fraction, and average particle size are shown in Table 1.

0.35 parts of the crosslinked polymer particles and a highly compressible iron powder (manufactured by Kobe Steel; trade name “Atmel 300NH”; particle size of 180 μm or less) as a raw material powder for metallurgy 100
And 0.8 parts of graphite powder were mixed to prepare a mixed powder for warm compaction.

This mixed powder was formed into a green compact having a width of 32 mm, a length of 13 mm and a height of 6 mm using a powder compression molding machine. The molding pressure was 686 MPa, the molding temperature was 130 ° C. and 150 ° C., and the green compact density (130 ° C. and 150 ° C.), the ejection force (same as above), and the ejection sound were examined. In addition, the fluidity of the mixed powder and the presence / absence of powder fixation were also examined, and the results are shown in Table 2.

Examples 2 to 5 and Comparative Examples 1 to 4 Suspension polymerization was carried out in the same manner as in Example 1 except that the monomer composition was changed as shown in Table 1, to prepare polymer particles. The evaluation results are shown in Tables 1 and 2.

Example 6 (Seed polymerization) Deionization exchange in which 0.3 part of sodium dodecylbenzenesulfonate as an emulsifier was dissolved in a flask equipped with a dropping funnel, a stirrer, a thermometer, a nitrogen gas inlet tube and a reflux condenser. 200 parts of water was charged and the atmosphere was replaced with nitrogen. Then M
10 parts of MA and 3 parts of BA were charged into a flask, adjusted to 60 ° C. while sufficiently stirring under a nitrogen atmosphere, and then 0.1 part of ammonium persulfate was added and polymerized for 1 hour to synthesize a seed polymer latex. Then, MMA7
87 parts of a monomer mixture of 5 parts, 2 parts of BA, 5 parts of EDMA, and 5 parts of MAA were charged, the temperature was adjusted to 70 ° C. with good stirring under a nitrogen atmosphere, and 0.1 part of ammonium persulfate was added, followed by polymerization for 10 hours. After completion of the polymerization, drying was performed in the same manner as in Example 1 to obtain polymer particles.

Comparative Examples 5 to 6 (Emulsion Polymerization) In a flask equipped with a dropping funnel, a stirrer, a thermometer, a nitrogen gas inlet tube and a reflux condenser, 0.3 part of sodium dodecylbenzenesulfonate as an emulsifier was dissolved. 200 parts of ion-exchanged water was charged and the atmosphere was replaced with nitrogen. Thereafter, 100 parts of the monomer mixture having the composition shown in Table 1 was charged, and the mixture was stirred well under a nitrogen atmosphere to emulsify the monomer.
Was adjusted. Next, 0.3 part of ammonium persulfate was charged and emulsion polymerization was performed for 10 hours. After completion of the polymerization, drying was performed in the same manner as in Example 1 to obtain polymer particles.

[0053]

[Table 1]

[0054]

[Table 2]

In the examples of the present invention, the green compact density was high, the ejection force and ejection noise were small, and no powder sticking occurred. However, in Comparative Examples 1, 2, 5 and 6, powder sticking was observed because of the thermoplastic polymer powder. Comparative Example 3
The particle size is 0.8 μm, which is too small and the lubricating property is insufficient, so that the extraction force is high and the extraction sound is large. On the contrary, in Comparative Example 4 having a large particle size, although the extraction sound is small, It is expected that the density of the green compact will be low and the strength of the product will be low.

Examples 7 to 10 In the same manner as in Example 1, suspension polymerization of polymers having the compositions shown in Table 3 was carried out. Hexamethylene diisocyanate (HDI) as a crosslinking agent was added to the obtained aqueous dispersion in an amount shown in Table 3 (based on 100 parts of polymer), and the mixture was allowed to stand for 1 hour. Thereafter, in the same manner as in Example 1, water was separated by a centrifugal separator, and drying by drying under reduced pressure was performed. Next, while flowing the polymer particles at 80 ° C. in a fluidized drier, the polymer particles were dried until the water content became 0.2% or less. Thereafter, pulverization, classification and the like were performed in the same manner as in Example 1, and various evaluation results are shown in Tables 3 and 4.

Comparative Example 7 Various evaluations were carried out in the same manner as in Example 7 except that HDI as a crosslinking agent was not reacted. The results are shown in Tables 3 and 4.

[0058]

[Table 3]

[0059]

[Table 4]

In Comparative Example 7 in which the thermoplastic polymer powder having a gel fraction of 0% was used, sticking of the powder was observed and the output was large.

Examples 11 to 12 and Reference Examples 1 to 2 The same procedure as in Example 1 was carried out except that the amount of the crosslinked polymer particles obtained in Example 1 in the mixed powder was changed as shown in Table 5. A mixed powder was prepared and the physical properties were evaluated.

[0062]

[Table 5]

From Table 5, it can be seen that in Reference Example 1 in which the lubricant of the present invention is less than the preferred range, the lubricity is insufficient and the output and output noise are large. Conversely, in Reference Example 2 with a large amount, although the output power and the extraction sound are small, it is considered that the product strength is insufficient because the compact density is low.

Examples 13 to 16 Low-viscosity fatty acid-based lubricants (stearic acid amide: S
A, methylene bisstearamide: MS, ethylenebisstearamide: ES) and a polyolefin-based lubricant (polyethylene wax: PE) are used in combination with the crosslinked polymer particle-type lubricant of the present invention obtained in Example 6. Table 6 shows the results of compression molding. Comparative Example 8 is an example not including the crosslinked polymer particle type lubricant of the present invention.

[0065]

[Table 6]

In Comparative Example 8 using only a low-viscosity lubricant, it can be seen that the fluidity is low because no crosslinked polymer particles are contained. Also, although the extraction output is small, the extraction sound is loud. This is considered to be because a liquid film of a low-viscosity lubricant is formed on the interface between the mold wall surface and the molded body, and this liquid film is broken, resulting in a loud ejection noise. Further, powder adhesion was also observed due to the low viscosity type.

On the other hand, in the examples of the present invention, a low extraction noise was observed, no powder sticking was observed, and a high-density green compact was obtained. Also, as compared with the example of Table 2, the temperature was 150 ° C.
In Examples 13 to 16 in which a low-viscosity type lubricant is contained, the extraction force at 130 ° C. is lower than that in Examples 1 to 6 and Examples 13 to 16 at 130 ° C. No. 16, there was no significant difference, and it was confirmed that the crosslinked polymer particle type lubricant exhibited good lubricity.

[0068]

According to the present invention, since the crosslinked polymer particles having viscoelasticity are used as a lubricant during warm forming in powder metallurgy, a solid lubricant and a liquid are used in a preheating stage and a warm forming stage using a hopper or the like. Good lubricating performance having both actions of the lubricant could be exhibited. In addition, even in the preheating stage, since the crosslinked polymer particles do not thermally melt, it is possible to prevent inconveniences such as sticking of the metal powder,
High density compacts can be manufactured with good productivity.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // C10N 20:00 C10N 20:00 Z 20:06 20:06 Z 40:24 40:24 Z (72 ) Inventor Hironori Suzuki 2-3-1 Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside Kobe Steel, Ltd.Takasago Works (72) Inventor Kinichi Okumura 244-1 Kobayashi, Bessho-cho, Miki City, Hyogo Prefecture F Term (reference) 4H104 CB08A CB09A CE01A CE03A CE05A CE11A CE13A EA01A EA08A PA27 4K018 BC12 CA08

Claims (5)

[Claims] 1. An alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms (A) as an essential component, a gel fraction measured using methyl ethyl ketone of 5% by mass or more, and an average A lubricant for warm forming, which is a crosslinked polymer particle having a particle size of 1 to 80 µm. 2. The warm forming lubricant according to claim 1, wherein the gel fraction is 20% by mass or more. 3. The method according to claim 1, wherein a polyfunctional monomer (B) having two or more radically polymerizable unsaturated groups is an essential component together with the alkyl (meth) acrylate (A). Lubricant for warm forming. 4. A functional group-containing monomer (C) having at least one functional group capable of reacting with a crosslinking agent together with the alkyl (meth) acrylate (A), as an essential component,
The lubricant for warm forming according to any one of claims 1 to 3, wherein the lubricant is crosslinked by the crosslinking agent during or after the polymerization. 5. A mixed powder for warm compacting, which essentially comprises the lubricant for warm compacting according to claim 1 and a raw powder for powder metallurgy.