JP2843212B2 - Binder and composition for sinterable powder injection molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal powder, ceramic powder, cermet powder (hereinafter abbreviated as "sinterable powder") injection molding binder and a compound used therefor, which are excellent in moldability and shape retention during degreasing. .

[0002]

2. Description of the Related Art In a sinterable powder injection molding method, a kneaded product (compound) of a metal powder, a ceramic powder, a cermet powder and a binder is injection-molded in a mold, and the obtained molded body is debindered (degreased). This technology is suitable for mass production of small and complex shaped parts.

[0003] Binders used for metal powder, ceramic powder and cermet powder injection molding can be roughly classified into thermoplastic and thermosetting, but non-renewable thermosetting binders such as sprues and runners are rarely used. . As the thermoplastic binder, thermoplastic resins, waxes, plasticizers, lubricants and the like are used.

However, the surfaces of metal powders, ceramic powders and cermet powders are, in effect, oxide surfaces, which are usually chemically adsorbed and physically adsorbed on water and distributed as high-concentration hydroxyl groups on the surface. Powder is hydrophilic and has very poor wettability with hydrophobic binders (Bul
l. Chem. Soc. Jpn., 41 , 1533 (1968).). for that reason,
For example, when polyethylene (PE) or polypropylene (PP) is used as a binder, since these resins have poor wettability with metal powder, ceramic powder and cermet powder, the powder is not dispersed in the binder, Becomes For this reason, the compound has problems such as extremely poor fluidity, difficulty in injection molding, and low strength of the obtained molded product.

There are two methods for improving the wettability of the metal powder, the ceramic powder, the cermet powder, and the binder, by treating the surfaces of the metal powder, the ceramic powder, and the cermet powder to make them hydrophobic, and by treating the surface of the powder covered with a hydroxyl group. A method of introducing a functional group that forms a hydrogen bond into a binder component is known. As a specific example of the former, surface treatment of a powder with a silane coupling agent, a titanate coupling agent (Japanese Patent Publication No. 59-41949), and an aluminum chelate compound (Japanese Patent Application Laid-Open No. 61-242947) is known. As a specific example of the latter, an example using a surfactant (JP-A-59-182267)
JP-A-59-35058) and the use of a binder component having a functional group that interacts with the powder surface such as a carboxyl group, an ester, an amino group, or a hydroxyl group. Polymer (EV
A) (Japanese Patent Application Laid-Open No. 52-117909,
135173), ethylene-ethylene acrylate copolymer (EEA) (JP-A-59-121150), and acrylic acid-based copolymer (JP-A-2-283660).
JP-A No. 1-261265), ethylene-
Vinyl alcohol copolymer (JP-A-63-25266), stearic acid (JP-B-36-7883), behenic acid (JP-A-2-267156) and the like are known. By using such a method, the wettability between the powder and the binder is improved, and if the powder is dispersed well in the binder, it can be easily injection-molded and a good molded product can be obtained. became.

[0006]

However, the surface treatment of the sinterable powder involves a costly coupling agent, one additional coupling treatment step, and the sintering of titanium or silicon elements in the coupling agent. There is a disadvantage that it is taken in as an impurity at the conclusion. Further, addition of a surfactant or introduction of a hydrogen bonding functional group (for example, EVA, EEA, EMM)
A) lowers the softening point of the binder, and tends to cause deformation and swelling during heating degreasing. Furthermore, in any case, if the degreasing time is shortened, there is a problem that the degreased body is deformed.

[0007]

Means for Solving the Problems The present inventors have developed a binder which has good wettability with metal powder, ceramic powder and cermet powder, has good moldability, and is not easily deformed during degreasing. As a result of exploring a binder having a functional group that has not been obtained and conducting intensive research, it has been found that the object can be achieved by using a binder containing a thermoplastic resin containing an isocyanate group as an essential component, and the present invention has been accomplished.

That is, the present invention provides a binder for sinterable powder injection molding, comprising a thermoplastic resin having a molecular weight exceeding 2,000 and having at least one isocyanate group in a molecule, Provided is a binder for sinterable powder injection molding containing a plastic resin, a resin other than the thermoplastic resin, and an organic compound having a molecular weight of 2000 or less.
Further, (a) a thermoplastic resin having a molecular weight of more than 2,000 and having at least one isocyanate group in a molecule of 3 to 8;
A binder for sinterable powder injection molding containing 0% by weight and (c) 20 to 80% by weight of an organic compound having a molecular weight of 2000 or less. Further, (a) the molecular weight is 2000
3 to 80% by weight of a thermoplastic resin having at least one isocyanate group in the molecule, (b) 70% by weight or less of a resin other than the thermoplastic resin, and (c) a molecular weight of 2,000 or less. A binder for sinterable powder injection molding containing an organic compound in an amount of 20 to 80% by weight. A sinterable powder injection molding composition comprising the above-mentioned binder for sinterable powder injection molding and a metal powder, a ceramic powder or a cermet powder is provided. The present invention also provides a composition for powder injection molding, wherein the metal powder, ceramic powder or cermet powder has an average particle size of 0.1 to 1000 μm.

Among the binder components of the present invention, a thermoplastic resin having at least one isocyanate group in a molecule is an essential component. Thermoplastic resins having one or more isocyanate groups in the molecule include, for example, amino groups, hydroxyl groups,
Obtained by reacting a thermoplastic resin having a functional group, such as a carboxyl group or an acid anhydride, which reacts with an isocyanate group to form a bond with one of the di- or tri-isocyanate compound isocyanate groups. Can be. Examples of the thermoplastic resin containing a functional group that reacts with an isocyanate group include ethylene-vinyl alcohol copolymer, partially saponified EVA, ethylene- (meth) acrylic acid copolymer, ethylene-maleic anhydride copolymer, Propylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, styrene-paraaminostyrene copolymer, styrene-paravinylphenol copolymer, styrene- (meth) acrylic acid copolymer, styrene-2- Examples thereof include a hydroxyethyl methacrylate copolymer, a methyl methacrylate-2-hydroxyethyl methacrylate copolymer, and a butyl methacrylate-2-hydroxyethyl methacrylate copolymer.

Illustrative isocyanate compounds to be reacted with these are as specific examples of diisocyanate compounds: tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, paraphenylene diisocyanate, tetramethylene diisocyanate. Hexamethylene diisocyanate, dodecamethylene diisocyanate, ortho-xylylene diisocyanate, meta-xylylene diisocyanate, dianisidine diisocyanate, dimeryl diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-
1,3-diisocyanate, transvinylene diisocyanate, N, N ′-(4,4′-dimethyl-3,3 ′
-Diphenyldiisocyanato) uresion, N, N'-
Di (3-isocyanato-4-methylphenyl) urethion, cyclohexane-1,4-diisocyanate, N,
N'-di (p-isocyanatophenyl) carbodiimide, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-bis (isocyanatomethyl) cyclohexane, 1,3-bis (2-isocyanato-2-propyl) )
Benzene, 1,4-bis (2-isocyanato-2-propyl) benzene, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, dicyclohexylmethane diisocyanate, 2,6-diisocyanate Methylbicyclo [2,2,1] heptane is used as a triisocyanate compound. Examples of the triisocyanate compound include triphenylmethane triisocyanate, tris (isocyanatophenyl) thiophosphate, and OCN- (CH ₂ ) ₆ -N [C
NH (CH ₂ ) ₆ NCO] ₂ ,

Embedded image 4,4 ', 4 "-trimethyl-3,3', 3" -triisocyanato-2,4,6-triphenylcyanurate. Examples of the polyisocyanate compound include polymethylene polyphenyl polyisocyanate.

The isocyanate group is one in the polymer molecule.
Must be more than The isocyanate group in the polymer molecular chain is firmly bonded to the surface of the sinterable powder, improving the wettability of the powder and the binder. Prevent deformation.

At least one isocyanate group is required in the polymer molecular chain, but if the isocyanate group is too large, a gelation reaction is likely to occur during kneading of the metal powder, ceramic powder, cermet powder and binder. In addition, there are disadvantages in that the viscosity of the composition (compound) increases and the moldability deteriorates. Although the preferred content of the isocyanate group in the thermoplastic resin cannot be unconditionally determined depending on the molecular weight of the resin, for example, when tolylene diisocyanate is used for isocyanate group introduction, the content of the isocyanate group in the thermoplastic resin is reduced. The content of the compound is 0.05 to 10% by weight.

Thermoplastic resin having at least one isocyanate group in the molecule (thermoplastic resin containing isocyanate group)
Has a preferred molecular weight of 2,000 to 500,000. Molecular weight 2,
If it is less than 000, the strength of the molded body is insufficient, so that cracks are likely to occur during molding, and deformation occurs during degreasing. Molecular weight
If it exceeds 500,000, the melt viscosity becomes high and the moldability deteriorates. Further preferred molecular weight is 50,000-300,000
It is.

The thermoplastic resin (b) other than the isocyanate group-containing thermoplastic resin used in the present invention is preferably added to facilitate degreasing, and any resin may be used as long as it can be degreased by heat or a solvent. As such preferable thermoplastic resin, at the time of solvent degreasing, to be soluble in a solvent that does not dissolve the isocyanate group-containing thermoplastic resin, or to prevent blistering and cracking due to rapid decomposition during thermal degreasing, Those having a different thermal decomposition temperature from the isocyanate group-containing thermoplastic resin can be used. As such a resin, for example, PE, PP, polyisobutylene,
Ethylene-propylene copolymer, polymethylpentene,
Ethylene-butene copolymer, styrene-ethylene-butylene-styrene copolymer, EVA, EEA, EMA, E
Polyolefins such as MMA and chlorinated PE, styrene resins such as polystyrene, poly-α-methylstyrene, styrene-acrylonitrile copolymer, styrene- (meth) acrylate copolymer, and polymethyl (meth) acrylate , Poly (ethyl meth) acrylate, poly (butyl meth) acrylate, poly (meth) acrylic acid
2-ethylhexyl, methyl (meth) acrylate-butyl (meth) acrylate copolymer, butyl methacrylate-
Acrylic resin such as methacrylic acid-2-ethylhexyl copolymer, polyvinyl acetal such as polyvinyl formal, polyvinyl butyral, polyvinyl acetoacetal and polyvinyl propional, polyvinyl ether such as polyvinyl ether and polyvinyl butyl ether, polyethylene oxide, polyoxy Examples include polyethers such as methylene, polypropylene oxide, polytetramethylene glycol, and ethylene oxide-propylene oxide copolymers, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene sebacate, polyamides, polycarbonates, and polyurethanes. Preferred examples of these resins depend on the type of the isocyanate group-containing thermoplastic resin and cannot be said unconditionally, but specific examples show that when an ethylene-based resin is used as the isocyanate group-containing resin, a styrene-based resin is used. It is preferable to combine a resin or an acrylic resin as a binder component. With this combination, styrene-based and acrylic-based resins can be easily degreased from the molded body with a solvent such as toluene, chloroform, or methylene chloride. Since the ethylene resin is decomposed in a short time, generation of a rapid decomposition gas can be suppressed, and blistering and cracking during degreasing can be prevented.

The molecular weight of these thermoplastic resins is 2,000
~ 500,000, more preferably 50,000
~ 300,000. If the molecular weight is less than 2,000, the strength of the molded body is insufficient, so that cracks are likely to occur during molding,
If it exceeds 000, the melt viscosity increases, and the moldability deteriorates.

In the present invention, (c) the organic compound having a molecular weight of 2,000 or less is called a wax, a plasticizer, a lubricant, or the like. It also has the function of being easily degreased.

Examples of organic compounds having a molecular weight of 2,000 or less include waxes, higher fatty acids, higher alcohols, higher fatty acid amides, fatty acid esters, phthalic esters, adipic esters, and sebacic esters. More specifically, as the wax, synthetic waxes such as paraffin wax, microcrystalline wax, oxide wax, petrolatum, petrolatum oxide, polyethylene wax, polypropylene wax, montan wax derivative, whale wax, china wax, dense wax, wool Natural waxes such as wax, candelilla wax, carnauba wax, wood wax, naricure wax, sugarcane wax, montan wax, ozokerite wax, ceresin, and ligrite wax.

Examples of higher fatty acids include stearic acid, lauric acid, balmotinic acid, isostearic acid, behenic acid, myristic acid, oleic acid, linoleic acid, palmitic acid, linolenic acid, arachidonic acid, and arachiic acid. As higher fatty acid amides, oleic acid amide, stearic acid amide, lauric acid amide, ricinoleic acid amide, erucic acid amide, behenic acid amide,
Palmitic acid amide, erucylamide, hardened tallowamide, coconut fatty acid amide, methylenebisstearylamide, ethylenebisstearylamide, methylenebisamide, ethylenebisamide.

Examples of the fatty acid esters include esters of C ₁₂ -C ₂₂ fatty acids and C ₁ -C ₂₂ monohydric alcohols, mono-, di-esters with glycols, and mono-, di-, and triesters with glycerin. Specifically, butyl stearate, butyl laurate, octyl palmitate, isopropyl palmitate, cetyl palmitate, myristyl palmitate, myristyl cellodate, stearic acid monoglyceride, diethylene glycol dibenzoate, triethylene Glycol di-2-ethyl butyrate, sorbitan triolate, peanut oil, soybean oil, coconut oil, palm oil, linseed oil,
Fish oil, animal oil, hydrogenated oil and the like can be mentioned. Examples of phthalic acid esters include dimethyl phthalate, diethyl phthalate, dibutyl phthalate (DBP), diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate (DOP), dinonyl phthalate, and phthalic acid Diisononyl, didecyl phthalate, diisodecyl phthalate, diundecyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, octyl benzyl phthalate, butyl octyl phthalate; dibasic acid esters such as dibutyl adipate, adipine Di-n-hexyl acid, di-2-ethylhexyl adipate, didecyl adipate, diisodecyl adipate,
Octyldecyl adipate, dibutyldiglycol adipate, di-2-ethylbutyl azelate, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl sebacate, dibutyl maleate, dibutyl maleate -2-ethylhexyl and dibutyl fumarate. Examples of the higher alcohol include cetyl alcohol, ceryl alcohol, melisyl alcohol, stearyl alcohol, myristyl alcohol, and lauryl alcohol. Further, phosphate esters such as triethyl phosphate, tributyl phosphate, trioctyl phosphate, and triphenyl phosphate, borate esters such as triethyl borate, tributyl borate, and trioctyl borate, calcium stearate, magnesium stearate, and stearin Higher fatty acid salts such as aluminum acid can also be used.

The molecular weight of the compound (c) is 2,000 or less, preferably 300 to 1,000. If the molecular weight is less than 300, it becomes difficult to impart appropriate strength to the molded body, and if the molecular weight exceeds 1,000, the moldability and degreasing property deteriorate, and if the molecular weight exceeds 2,000, the formation of a precision molded product becomes difficult. This is because it is impossible, and the degreasing time becomes extremely long, so that it is impossible to efficiently produce a precision component having a complicated shape, which is the object of the present invention, with high precision.

When degreasing is performed using a solvent,
The compound (c) is preferably soluble in a solvent that does not dissolve the resin component (a). When the degreasing treatment is performed by heating, it is preferable to mix two or more components having different boiling points as the component (c) in order to avoid defects such as sagging and swelling during the degreasing step. This is because defects in the degreasing step tend to occur when the low-molecular components are removed at a temperature lower than the resin decomposition temperature. This is because it is better to widen the temperature range to be removed by mixing as described above.

The thermoplastic resin having an isocyanate group in the present invention is contained in the binder in an amount of 3 to 80% by weight.
If the content is less than 3% by weight, the thermoplastic resin cannot sufficiently cover the surface of the sinterable powder, and the wettability between the sinterable powder and the binder is not improved. As a result, the molded article has low strength, is easily cracked, and has disadvantages such as deformation during degreasing, blistering and cracking. If it exceeds 80% by weight,
Compound viscosity increases, moldability deteriorates, and
Cracks and blistering defects are likely to occur during degreasing.

The thermoplastic resin other than the isocyanate group-containing thermoplastic resin in the present invention is not an essential component,
As described above, in order to shorten the degreasing time, it is better that the binder is contained, and the content is 70% by weight or less. If it exceeds 70% by weight, the compound viscosity increases, the moldability deteriorates, and cracks and blistering defects easily occur during degreasing.

The respective resin components of (a) and (b)
The preferred compounding ratio in the binder is preferably such that one does not become extremely large, and the amount of the isocyanate group-containing thermoplastic resin is required to sufficiently cover the surface of the sinterable powder. That is, the amount of the other thermoplastic resin is preferably 10 to 60% by weight with respect to 10 to 70% by weight of the isocyanate group-containing thermoplastic resin, and the sum of the former and the latter resin components is 20 to 70% by weight. And the rest is (c)
Is an organic compound having a molecular weight of 2,000 or less.

The sinterable powder that can be used in the binder of the present invention may be any one including a metal powder, a ceramic powder or a cermet powder. Specifically, as the metal powder, iron, nickel, aluminum,
Copper, titanium, zirconium, zinc, chromium, molybdenum, tungsten, beryllium, germanium, cobalt, scandium, yttrium, lanthanide, actinide, hafnium, thorium, vanadium, tantalum,
Manganese, technetium, rhenium, silicon, ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, silver, cadmium, thallium, tin, lead,
Arsenic, antimony, bismuth, tellurium, polonium and alloys or mixed powders thereof, for example, iron-nickel,
Stainless steel, iron-silicon, iron-boron, iron-cobalt, iron-cobalt-vanadium can be mentioned, as ceramics, aluminum oxide, silicon oxide,
Zirconium oxide, titanium oxide, beryllium oxide,
Magnesium oxide, niobium oxide, tantalum oxide, molybdenum oxide, manganese oxide, tungsten oxide, vanadium oxide, technetium oxide, rhenium oxide, cobalt oxide, nickel oxide, ruthenium oxide, rhodium oxide, cadmium oxide, thallium oxide, germanium oxide, tin oxide , Lead oxide, antimony oxide, bismuth oxide, tellurium oxide, beryllium oxide, indium oxide, barium oxide, gallium oxide, yttrium oxide, calcium oxide, strontium oxide, lanthanum oxide, selenium oxide,
Scandium oxide, actinium oxide, thorium oxide,
Hafnium oxide, chromium oxide, palladium oxide, osmium oxide, zinc oxide, iron oxide, lead titanate, barium titanate, lead zirconate, strontium zirconate, lead zirconate titanate, magnesium titanate, manganese titanate, titanate Iron, cobalt titanate, nickel titanate, silicon carbide, boron carbide, aluminum carbide,
Tungsten carbide, titanium carbide, zirconium carbide, hafnium carbide, molybdenum carbide, tantalum carbide, chromium carbide, vanadium carbide, silicon nitride, aluminum nitride, boron nitride, titanium nitride, titanium boride, zirconium boride, lanthanum boride, silicate Molybdenum bromide, cadmium sulfide, zinc sulfide and mixtures of two or more of these can be mentioned. Examples of the cermet include dangsten carbide powder / cobalt powder, aluminum oxide powder / aluminum powder, iron powder / silicon powder, iron powder / boron. Powders, metal powders such as silicon nitride powder / yttrium oxide powder / aluminum oxide powder, alloy powders of the above-mentioned ceramics and metals such as ceramic powders or metal powders / non-metallic powders, or mixed powders or cermet powders. it can.

The method for producing the sinterable powder may be any method, for example, using carbonyl powder, water atomized powder, gas atomized powder, pulverized powder, rotating disk powder, reducing powder, electrolysis powder, rotating consumable electrode powder and the like. it can.

The average particle size of the sinterable powder is 0.1 to 1,000 μm
Range. The smaller the particle size of the sinterable powder, the better the fluidity during injection molding and the better the sinterability, which is advantageous. However, it requires a huge amount of energy to make it into a fine powder, which is disadvantageous in practical use. On the other hand, if it exceeds 1,000 μm, the fluidity of the compound is extremely deteriorated, and injection molding becomes substantially impossible. A practically preferable range of the average particle size is 1 to 50.
μm. Further, the sinterable powder injection molding composition of the present invention may optionally contain additives such as an antioxidant, a flow agent, and a surfactant.

The compound for powder injection molding of the present invention comprises:
Binders 3 to 3 of the present invention based on 100 parts by weight of sinterable powder
It is preferable to manufacture by kneading with 20 parts by weight. If the amount is less than 3 parts by weight, the binder cannot fill the gap between the sinterable powders, so that the fluidity of the compound is poor and injection molding becomes difficult. If the amount exceeds 20 parts by weight, the fluidity is improved and injection molding can be easily performed, but the shape cannot be maintained during degreasing, which is not preferable.

The method of kneading the binder and the sinterable powder of the present invention is not limited, and may be a Henschel mixer, a Banbury mixer, a kneader, a roll mill, a single screw extruder,
Any material such as an axial screw extruder that can knead the binder and the sinterable powder can be used.

The kneaded compound is pulverized or granulated to form a molding material. As the injection molding machine, a general injection molding machine for thermoplastics can be used. Injection molding is carried out at an injection temperature of 100 ° C. to 250 ° C. However, if the injection temperature is too high, the quality of the binder component becomes remarkable, and the moldability of the recycled material and the degreasing property change. The range of 100 ° C to 180 ° C is good.

For degreasing, any of a heating degreasing method and a solvent extraction method can be used. In the case of the heat degreasing method, it is preferable to carry out the method in a stream of nitrogen, argon, hydrogen or the like, or to remove the binder under reduced pressure. The rate of temperature rise depends on the thickness of the molded body, but the temperature is raised in the range of 10 ° C / h to 100 ° C / h. The maximum temperature for degreasing is preferably about 450 ° C to 600 ° C. If the maximum temperature of the degreasing is less than 450 ° C., the resin component is not efficiently decomposed and removed, which is not preferable. Also, even if the temperature is raised to 600 ° C. or more, the rate of decomposing and removing the resin component does not change so much. It is only an extension.

In the case of the solvent extraction method, a binder component other than the isocyanate group-containing thermoplastic resin or a resin component other than the resin component is extracted and removed from the molded product with a solvent, and thereafter, the remaining binder component is removed by heat degreasing.

The sintering step may be performed in the same furnace after the degreasing step, or may be performed in a different furnace after removing the degreased body from the degreasing furnace. Sintering is 800 ° C ~ 200
The sintering is carried out at a temperature of 0 ° C. for 10 minutes to 6 hours. These sintering conditions and sintering atmosphere are appropriately selected and determined according to the material and powder characteristics of the sinterable powder to be used.

Next, the features of the present invention will be described. As described later in the embodiment, P which has been conventionally used as a binder
E, PP, PS, EVA, EEA, EMMA, and acrylic resin are almost washed off from the surface of the sinterable powder by the hot toluene extraction of the compound, but the isocyanate group-containing thermoplastic resin of the present invention is used as a binder component. In the compound used, about 0.1 to 0.15% of an organic substance which cannot be washed away with hot toluene remains on the surface of the sinterable powder in terms of carbon amount.

The fixation between the sinterable powder covered with the hydroxyl group and the resin component in the binder is achieved by using PE, P having no functional group.
In the case of P and PS, EVA, EEA, EMMA and an acrylic resin having an ester group are considered to be hydrogen bonds, and these bonds are weak bonds which are washed away by hot toluene. However, in the binder composition of the present invention, an organic substance is fixed to the surface of the sinterable powder with a strong bond that cannot be cut with hot toluene. Possibly, the isocyanate group reacts with the hydroxyl group on the surface of the sinterable powder to form a strong bond such as a covalent bond, resulting in a polymer grafted on the surface of the sinterable powder. . The features of the present invention are considered to be due to the polymer firmly grafted on the surface of the sinterable powder. Hereinafter, features of the present invention will be described.

When the binder of the present invention is used, the dispersion of the sinterable powder during kneading is very good, a uniform compound can be obtained, and the fluidity does not deteriorate due to the remaining of the agglomerated powder, and the moldability is excellent. Further, since the fluidity is excellent, a small amount of binder is sufficient. As a result, degreasing becomes easier,
It is possible to reduce the time required for degreasing and prevent the occurrence of defects such as deformation, blistering and cracks during degreasing. Since the interface between the sinterable powder and the binder is firmly bonded, the strength of the molded body is high, and cracks during molding and transportation of molded products,
Less deformation. Deformation hardly occurs during heating degreasing of the molded body, and defects such as blisters and cracks hardly occur.

[0037]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples. First, raw materials and evaluation methods used in the examples will be described.

1. Raw materials 1) Metal powder: average particle size 9.5 μm, tap density 3.8
g / cc water atomized stainless steel powder 2) Ceramic powder: silicon nitride powder with an average particle size of 1.0 μm 3) PE: LDPE (Sumikacene G807, manufactured by Sumitomo Chemical Co., Ltd.) 4) EVA: vinyl acetate content 20% by weight (NUC31
50, manufactured by Nippon Unicar Co., Ltd.) 5) EEA: Ethyl acrylate content 28% by weight (M
B910, manufactured by Nippon Unicar Co., Ltd.) 6) EMMA: methyl methacrylate content 20% by weight
(Aclift WH501, manufactured by Sumitomo Chemical Co., Ltd.) 7) Acrylic acid-modified PE: acrylic acid content 6% by weight
(PB-1008, manufactured by BP Performance Polymers Inc.) 8) PS: weight average molecular weight of 60,000 (Hymer SB-12
5, manufactured by Sanyo Kasei Kogyo Co., Ltd.) 9) Polybutyl methacrylate (PBMA): n-butyl methacrylate was polymerized in toluene at 95 ° C. for 4 hours under nitrogen using AIBN as an initiator. The polymerization solution was reprecipitated in methanol, and the obtained PBMA was heated at 50 ° C.
Dry for 4 hours. The number average molecular weight is about 125,000. 10) Isocyanate-modified PBMA: Mixed monomer of 2-hydroxyethyl methacrylate (HEMA) and n-butyl methacrylate (BMA) (HEMA / BMA = 0.
05 / 99.95, 0.1 / 99.9, 0.5 / 99.5, 1/99, 5/95
(Weight ratio) was polymerized and purified in the same manner as in PBMA.
In a toluene solution of the obtained HEMA-BMA copolymer,
Excess tolylene diisocyanate (2.4 / 2.6 = 80/20
The mixture was reacted at 30 ° C. under nitrogen overnight. The reaction solution was reprecipitated in hexane, separated and washed, and dried under reduced pressure to obtain an isocyanate-modified PBMA shown in Table 1. The content of tolylene disocyanate was determined from the infrared absorption peak of the isocyanate group at 2250 cm ^-1 .

[0039] 11) Isocyanate-modified PS: as a chain transfer agent, 2-
A styrene monomer to which 1.0% by weight of mercaptoethanol was added was thermally polymerized in benzene under nitrogen to synthesize polystyrene having a hydroxyl group at one end. After polymerization,
Diphenylmethane diisocyanate was added at a molar ratio of 1.2 times that of 2-mercaptoethanol, and the mixture was allowed to stand at room temperature for 24 hours. The reaction solution was poured into n-hexane, and the resulting polymer precipitate was separated, washed and dried. Number average molecular weight and GPC determined from the quantitative value of isocyanate group of the obtained polymer
Is relatively close to 12,000 for the former and 11,000 for the latter, indicating that the obtained polystyrene has almost one isocyanate group at one end. Was.

2. Physical property evaluation method 1) Amount of organic substance bound to sinterable powder: A binder was extracted and removed from the pulverized compound by a Soxhlet extractor using a toluene solvent. The sinterable powder from which the binder was removed was subjected to carbon quantitative analysis after drying. In addition,
The extraction was performed sufficiently until the amount of carbon became a constant value. The difference between this carbon content and the carbon content of the raw material powder before kneading is
This is due to a polymer that cannot be extracted even with hot toluene and is firmly fixed to the powder surface, and the strength of the interaction between the binder and the sinterable powder can be evaluated based on the degree of the polymer. 2) Degreasing test: A plate having a thickness of 4 mm shown in FIG. 1 was molded into a trapezoid having a flat portion 1 and support portions 2 and 2 to obtain an injection molded test piece (molded product). The shape of the other parts is as shown in FIG. The test piece was heated from normal temperature to 250 ° C. for 12 hours under reduced pressure, and kept at 250 ° C. for 1 hour. Thereafter, nitrogen was introduced, the temperature was raised to 500 ° C. in a nitrogen stream for 1 hour, and the temperature was further maintained for 1 hour and then cooled. FIG. 2 is a cross-sectional view showing a molded body (a) before degreasing and a molded body (b) after degreasing. Degreasing deformation is measured by measuring the amount of deformation at the center of the flat portion 1 of the molded body before and after the degreasing step. did. This amount of deformation is due to its own weight during degreasing.

(Examples 1 to 10, Comparative Examples 1 to 6) A binder composed of 25% by weight of each of the two resins shown in Table 2, 30% by weight of paraffin wax (melting point 60 ° C.), and 20% by weight of DBP was used. First, after heating the pressure kneader to 140 ° C., 9.8 parts by weight of the binder component is charged and melted,
Next, 100 parts by weight of stainless steel powder was gradually charged. After the whole amount of the powder was charged and kneaded for 1 hour, the kneaded material was taken out, cooled and pulverized. The pulverized compound measured the amount of powdered carbon after removing the binder. Further, using the same pulverizing compound, the test piece shown in FIG. 1 was injection molded and subjected to a degreasing test. Table 2 shows the results. In the case of Comparative Examples 1 and 6, the powder and the binder component were separated during molding, and molding was impossible. In the case of using EVA, EEA, EMMA, and modified acrylic acid PE (Comparative Examples 2 to 5), although a good molded body was obtained, blistering occurred during degreasing,
Or caused significant deformation. However, Examples 1 to 10
As shown in Table 2, when the isocyanate-modified resin was used, the moldability was good in each case, the molded article and the degreased article had no defects such as blisters and cracks, and the degreased deformation was small.

(Examples 11 to 20) Table 3 shows the binder composition.
, Kneading, grinding, injection molding and degreasing were performed in the same manner as in Example 1. Table 3 shows the results. In Examples 11 to 14, the isocyanate-modified PBMA was used, and the compounding ratio was in the range of 3 to 80%, and the compounding ratio and molecular weight of other components were appropriate, so that both the moldability and the degreasing property were good. In Examples 15 and 16, although the isocyanate-modified PBMA was used, the degreasing property was slightly inferior because the compounding ratio was as small as 1% or as large as 85%. In Examples 17 and 18, isocyanate-modified PBMA was used, but microcrystalline wax, which is a low molecular component,
Since the total blending ratio of DOP and DBP was as small as 15% or as large as 85%, the degreasing property was slightly poor. Example 1
In No. 9, since the mixing ratio of the resin (PE) other than the isocyanate-modified resin was as large as 75%, the deformation at the time of degreasing was slightly large. In Example 20, the molecular weight of the low-molecular-weight component PE wax was 3,
000 and over 2,000, so the amount of degreasing deformation was somewhat large. However, Examples 15 to 20 were excellent binders as compared with Comparative Examples 1 to 6 not using the isocyanate-modified resin (see Table 2).

Example 21 1.0% Tolylene diisocyanate-modified PBMA / soybean oil / DBP = 50/30 /
Kneading, pulverization and injection molding were carried out in the same manner as in Example 1 except that a binder having a composition ratio of 20 (weight ratio) was used. The injection molded body was immersed in methanol for 12 hours, and after extracting most of the plasticizer, the molded body was vacuum dried for 30 minutes. The molded body was heated from room temperature to 500 ° C. for 4 hours in a nitrogen stream, kept at 500 ° C. for 1 hour, and then cooled. Molded product appearance,
Both the appearance of the solvent degreased body and the appearance of the thermally degreased body were satisfactory without any defects, and the deformation was as small as 20 μm.

Comparative Example 7 Isocyanate-Modified PBMA
Was performed in the same manner as in Example 21 except that PBMA was used instead of Cracks occurred in some of the compacts during injection molding, and cracks also occurred in the thermally degreased body, resulting in deformation of 2,800.
It was as large as μm.

[0045]

[Table 1]

[0046]

[Table 2]

(Example 22, Comparative Examples 8 to 11) 25% by weight of each of the two resins shown in Table 4, 30% by weight of paraffin wax (melting point 60 ° C.), dibutyl phthalate (DBP) 2
A binder consisting of 0% by weight was used. First, after heating the pressure kneader to 140 ° C., 12 parts by weight of a binder are charged and melted, and then, 94% by weight of silicon nitride powder having an average particle diameter of 1.0 μm and yttrium oxide powder having an average particle diameter of 0.4 μm 100 parts by weight of a mixed powder of 3% by weight and 3% by weight of aluminum oxide powder having an average particle diameter of 0.3 μm were gradually added. After the whole amount of the powder was charged, the mixture was kneaded for 1 hour, then the kneaded material was taken out, cooled, and pulverized. In the pulverized compound, the binder was removed with a Soxhlet extractor, and the amount of powdered carbon was measured. Further, using the same pulverizing compound, a test piece shown in FIG. 1 was injection-molded and subjected to a degreasing test. Table 4 shows the results.

In Comparative Example 8, the powder and the binder were poor in wettability, and the powder and the binder were separated during injection molding, and molding was impossible. In the case where EVA, EEA or acrylic acid-modified PE was used (Comparative Examples 9 to 11), although good molded articles were obtained, blistering occurred during degreasing and significant deformation occurred. However, as shown in Example 22,
When the isocyanate-modified resin was used, the moldability was good, the molded body and the degreased body had no defects such as blisters and cracks, and the degreased deformation was small.

[0049]

[Table 3]

[0050]

According to the present invention, a thermoplastic resin having at least one isocyanate group in a molecule, which is firmly bonded to a powder, is used as a binder component, so that a metal powder, a ceramic powder or a cermet powder and a binder resin are used. A powder injection molding compound having a strongly bonded interface was obtained. For this reason, the compound for powder injection molding of the present invention has good moldability, in addition to manufacturing advantages such as short degreasing time, and because of its high strength, cracking during molding, deformation and deformation during degreasing, It has the advantage that blisters and cracks are drastically reduced, and precision parts with complicated shapes can be efficiently produced with high precision dimensions.

[Brief description of the drawings]

FIG. 1 is a perspective view showing dimensions of a test piece manufactured in an example.

FIG. 2 is a cross-sectional view illustrating measurement of a deformation amount of a test piece.

[Explanation of symbols]

 1 flat part 2 support part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B22F 3/00-3/26 B28B 1/24 C04B 35/632 C08K 5/00 C08L 101/02

Claims (6)

(57) [Claims] 1. A binder for sinterable powder injection molding, comprising a thermoplastic resin having a molecular weight of more than 2,000 and having at least one isocyanate group in the molecule. 2. The binder for sinterable powder injection molding according to claim 1, wherein the binder contains the thermoplastic resin, a resin other than the thermoplastic resin, and an organic compound having a molecular weight of 2000 or less. 3. A thermoplastic resin having a molecular weight of more than 2,000 and having at least one isocyanate group in the molecule in an amount of 3 to 80% by weight, and (c) an organic compound having a molecular weight of 2,000 or less in an amount of 20 to 20%. The binder for sinterable powder injection molding according to claim 1, which contains 80% by weight. (A) 3 to 80% by weight of a thermoplastic resin having a molecular weight exceeding 2,000 and having at least one isocyanate group in the molecule; and (b) 7% of a resin other than the thermoplastic resin.
An organic compound having a molecular weight of not more than 0% by weight and (c) a molecular weight of not more than 2000 is contained in an amount of 20 to 80% by weight.
4. The binder for sinterable powder injection molding according to 1.). 5. A composition for sinterable powder injection molding comprising the binder for powder injection molding according to claim 1, and a metal powder, ceramic powder or cermet powder. 6. The composition for injection-molding sinterable powder according to claim 5, wherein the metal powder, ceramic powder or cermet powder has an average particle size of 0.1 to 1000 μm.