JPH0657307A - Sinterable powder injection molding binder and composition - Google Patents

Abstract

(57) [Abstract] [Purpose] Sinterable powder injection excellent in moldability and strength using a powder injection molding binder containing a resin or compound having one or more isocyanate groups in the molecule having a molecular weight of more than 2000. Providing a molding composition. A binder for sinterable powder injection molding containing a thermoplastic resin having a molecular weight of more than 2000 and having one or more isocyanate groups in the molecule, particularly the thermoplastic resin, a resin other than the resin, and a molecular weight. A binder for sinterable powder injection molding containing 2000 or less organic compounds. (A)
3-80% by weight of a thermoplastic resin having a molecular weight of more than 2000 and having one or more isocyanate groups in the molecule, (b)
70% by weight or less of resin other than (a), and (c)
Provided is a powder injection molding composition of metal powder, ceramic powder or cermet powder using a powder injection molding binder containing an organic compound having a molecular weight of 2000 or less in an amount of 20 to 80% by weight. Furthermore, it is preferable that the various sinterable powders have an average particle diameter of 0.1 to 1000 μm.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

Binders used in metal powder, ceramic powder and cermet powder injection molding methods can be roughly classified into thermoplasticity and thermosetting property, but non-renewable thermosetting binders such as sprue and runner are rarely used. . As the thermoplastic binder, thermoplastic resin, wax, plasticizer, lubricant, etc. are used.

However, the surfaces of the metal powder, the ceramic powder and the cermet powder are, in fact, oxide surfaces, and are usually chemically adsorbed and physically adsorbed on water to be distributed as high-concentration hydroxyl groups on the surface. Therefore, the powder is hydrophilic and has very poor wettability with the hydrophobic binder (Bul
l. Chem. Soc. Jpn., 41 , 1533 (1968).). for that reason,
For example, when polyethylene (PE) or polypropylene (PP) is used as the binder, these resins do not wet the metal powder, the ceramic powder and the cermet powder, and therefore the powder does not disperse in the binder, resulting in agglomerated powder. Becomes Therefore, the compound has problems that the fluidity is extremely poor, injection molding is difficult, and the strength of the obtained molded product is low.

As a method for improving the wettability of the metal powder, the ceramic powder or the cermet powder and the binder, a method of treating the surface of the metal powder, the ceramic powder or the cermet powder to make it hydrophobic, and a surface of the powder covered with a hydroxyl group. A method of introducing a functional group capable of hydrogen bonding into a binder component is known. As a specific example of the former, surface treatment of powder with a silane coupling agent, a titanate coupling agent (Japanese Patent Publication No. 59-41949) and an aluminum chelate compound (Japanese Patent Publication 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) or a binder component having a functional group such as a carboxyl group, an ester, an amino group or a hydroxyl group that interacts with the powder surface, for example, ethylene-vinyl acetate copolymer. Polymer (EV
A) (JP-A-52-117909, JP-A-58-
135173), ethylene-ethylene acrylate copolymer (EEA) (JP-A-59-121150), acrylic acid-based copolymer (JP-A-2-283660).
JP-A No. 1-261265), ethylene-
Vinyl alcohol copolymers (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, the powder is well dispersed in the binder, and it becomes possible to easily perform injection molding and also to obtain a good molded product. became.

[0006]

However, in the method of surface-treating the sinterable powder, the coupling agent is expensive, the number of steps of the coupling treatment is increased by one, and titanium or silicon element of the coupling agent is burnt. There is a defect that it is taken in as an impurity at the time of binding. Further, addition of a surfactant or introduction of a hydrogen-bonding functional group (for example, EVA, EEA, EMM
In the case of A), the softening point of the binder is lowered, and deformation or swelling is likely to occur during degreasing by heating. Furthermore, whichever method is used, there is a problem that the degreased body is deformed when the degreasing time is shortened.

[0007]

The present inventors have developed a binder which has good wettability with metal powder, ceramic powder and cermet powder, good moldability, and is resistant to deformation during degreasing. As a result of searching for a binder having an unfunctionalized functional group and conducting diligent research, the inventors have found that the object can be achieved by using a binder containing a thermoplastic resin containing an isocyanate group as an essential component, and have reached the present invention.

That is, the present invention comprises a binder for sinterable powder injection molding, characterized by containing a thermoplastic resin having a molecular weight of more than 2000 and having one or more isocyanate groups in the molecule, or the above-mentioned thermoplastic resin. Provided is a sinterable powder injection molding binder 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 2000 and having at least one isocyanate group in the molecule is 3 to 8
Provided is a binder for sinterable powder injection molding containing 0% by weight and (c) an organic compound having a molecular weight of 2000 or less in an amount of 20 to 80% by weight. Furthermore, (a) the molecular weight is 2000
Of 3 to 80% by weight, and (b) 70% by weight or less of a resin other than the thermoplastic resin, and (c) a molecular weight of 2000 or less. Provided is a sinterable powder injection molding binder containing 20 to 80% by weight of an organic compound. There is provided a sinterable powder injection molding composition comprising the above-mentioned sinterable powder injection molding binder and a metal powder, a ceramic powder or a cermet powder. Further, the present invention 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, the thermoplastic resin having at least one isocyanate group in the molecule is an essential component. Thermoplastic resins having one or more such isocyanate groups in the molecule include amino groups, hydroxyl groups,
Obtained by reacting one of the di- or triisocyanate compounds with a thermoplastic resin having a functional group such as a carboxyl group or an acid anhydride that reacts with an isocyanate group to form a bond. You can 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, a butyl methacrylate-2-hydroxyethyl methacrylate copolymer and the like.

Illustrative examples of the isocyanate compound to be reacted therewith include, as specific examples of the diisocyanate compound, tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, paraphenylene diisocyanate and tetramethylene diisocyanate. , Hexamethylene diisocyanate, dodecamethylene diisocyanate, orthoxylylene diisocyanate, metaxylylene diisocyanate, dianisidine diisocyanate, dimeryl diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-
1,3-diisocyanate, transvinylene diisocyanate, N, N ′-(4,4′-dimethyl-3,3 ′
-Diphenyldiisocyanato) urezion, N, N'-
Di (3-isocyanato-4-methylphenyl) urezion, 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-diisocyanato Methylbicyclo [2,2,1] heptane is used as an example of a triisocyanate compound, triphenylmethane triisocyanate, tris (isocyanatophenyl) thiophosphate, OCN- (CH ₂ ) ₆ -N [C
NH (CH ₂ ) ₆ NCO] ₂ ,

[Chemical 1] Mention may be made of 4,4 ', 4 "-trimethyl-3,3', 3" -triisocyanato-2,4,6-triphenylcyanurate. Examples of the polyisocyanate compound include polymethylene polyphenyl polyisocyanate.

The isocyanate group has 1 in the polymer molecule.
There must be more than one. 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, and also by strongly adhering the sinterable powder-binder interface during heating and degreasing. Prevent deformation.

At least one isocyanate group is required in the polymer molecular chain, but if there are too many isocyanate groups, a gelling reaction is likely to occur during the kneading of the metal powder, ceramic powder or cermet powder and the binder. However, the viscosity of the composition (compound) increases and the moldability deteriorates. The preferred content of the isocyanate group in the thermoplastic resin, depending on the molecular weight of the resin, can not be said unequivocally, for example, when using tolylene diisocyanate for the introduction of the isocyanate group, in the thermoplastic resin The content of the compound is 0.05 to 10% by weight.

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

The thermoplastic resin (b) other than the isocyanate group-containing thermoplastic resin used in the present invention is preferably added in order to facilitate degreasing, and any resin can be degreased by heat or a solvent. As such a preferable thermoplastic resin, during solvent degreasing, one that is soluble in a solvent that does not dissolve the isocyanate group-containing thermoplastic resin, or to prevent blistering or cracking due to rapid decomposition during thermal degreasing, Examples thereof include those having a thermal decomposition temperature different from that of the thermoplastic resin containing an isocyanate group. Examples of such resins include PE, PP, polyisobutylene,
Ethylene-propylene copolymer, polymethylpentene,
Ethylene-butene copolymer, styrene-ethylene-butylene-styrene copolymer, EVA, EEA, EMA, E
MMA, polyolefin such as chlorinated PE, polystyrene, poly-α-methylstyrene, styrene-acrylonitrile copolymer, styrene-based resin such as styrene- (meth) acrylic acid ester copolymer, poly (meth) acrylic acid methyl ester , Poly (meth) acrylate, poly (meth) acrylate, poly (meth) acrylic acid-
2-ethylhexyl, methyl (meth) acrylate-butyl (meth) acrylate copolymer, butyl methacrylate-
Acrylic resin such as 2-ethylhexyl methacrylate copolymer, polyvinyl formal, polyvinyl butyral, polyvinyl acetoacetal, polyvinyl acetal such as polyvinyl propional, polyvinyl ether, polyvinyl ether such as polyvinyl butyl ether, polyethylene oxide, polyoxy Polyethers such as methylene, polypropylene oxide, polytetramethylene glycol, ethylene oxide-propylene oxide copolymers, etc., polyesters and polyamides such as polyethylene terephthalate, polybutylene terephthalate, polyethylene sebate, polycarbonates, polyurethanes and the like. Preferred examples of these resins cannot be unequivocally described because they depend on the type of the isocyanate group-containing thermoplastic resin, but specific examples show that when an ethylene-based resin is used as the isocyanate group-containing resin, a styrene-based resin is used. Resin or acrylic resin may be combined as a binder component. With this combination, it is possible to easily degrease the styrene-based and acrylic-based resins from the molded product with a solvent such as toluene, chloroform, and methylene chloride. Since the ethylene-based resin is decomposed, it is possible to suppress the generation of a rapid decomposition gas and prevent the generation of blisters and cracks during degreasing.

The molecular weight of these thermoplastic resins is 2,000.
~ 500,000 range is preferred, more preferably 50,000
~ 300,000. If the molecular weight is less than 2,000, the strength of the molded product will be insufficient, so cracking will easily occur during molding, and
If it exceeds 000, the melt viscosity becomes high and the moldability deteriorates.

The (c) organic compound having a molecular weight of 2,000 or less in the present invention is called a wax, a plasticizer, or a lubricant, and has the function of reducing the viscosity of the compound and improving the moldability, and the solvent or heat. It also has the function of being easily degreased with.

Examples of organic compounds having a molecular weight of 2,000 or less include wax, higher fatty acid, higher alcohol, higher fatty acid amide, fatty acid ester, phthalic acid ester, adipic acid ester and sebacic acid ester. More specifically, waxes include paraffin wax, microcrystalline wax, oxidized wax, petrolatum, petrolatum oxide, polyethylene wax, polypropylene wax, montan wax derivatives, synthetic waxes such as whale wax, Chinese wax, beeswax, and wool. Natural waxes such as wax, candelilla wax, carnauba wax, wood wax, nourish wax, sugar cane wax, montan wax, ozokerite wax, ceresin, and ligrite wax can be mentioned.

Examples of higher fatty acids include stearic acid, lauric acid, valmotic acid, isostearic acid, behenic acid, myristic acid, oleic acid, linoleic acid, palmitic acid, linolenic acid, arachidonic acid and arachidic acid. As the higher fatty acid amide, oleic acid amide, stearic acid amide, lauric acid amide, ricinoleic acid amide, erucic acid amide, behenic acid amide,
Examples thereof include palmitic acid amide, erucylamide, hardened beef tallow amide, coconut fatty acid amide, methylenebisstearylamide, ethylenebisstearylamide, methylenebisamide, and ethylenebisamide.

Examples of the fatty acid ester include esters of C ₁₂ -C ₂₂ fatty acids and C ₁ -C ₂₂ monohydric alcohols, mono- or diesters of glycols, or mono-, di-, or triesters of glycerin. Specifically, butyl stearate, butyl laurate, octyl palmitate, isopropyl palmitate, cetyl palmitate, myricyl palmitate, myricyl serotinate, stearic acid monoglyceride, diethylene glycol dibenzoate, triethylene. Glycol di-2-ethylbutyrate, sorbitan trioleate, peanut oil, soybean oil, coconut oil, palm oil, linseed oil,
Examples thereof include fish oil, animal oil, hydrogenated oil and the like. Examples of phthalates 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, butylbenzyl phthalate, octylbenzyl phthalate, butyloctyl phthalate, dibasic acid dibutyl adipate, adipine Acid di-n-hexyl, di-2-ethylhexyl adipate, didecyl adipate, diisodecyl adipate,
Octyldecyl adipate, dibutyl diglycol adipate, di-2-ethylbutyl azelate, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl sebacate, dibutyl maleate, dimaleate. Examples include 2-ethylhexyl and dibutyl fumarate. Examples of higher alcohols include cetyl alcohol, ceryl alcohol, melysyl alcohol, stearyl alcohol, myristyl alcohol, and lauryl alcohol. Furthermore, phosphates such as triethyl phosphate, tributyl phosphate, trioctyl phosphate, triphenyl phosphate and the like, borate esters such as triethyl borate, tributyl borate, trioctyl borate, calcium stearate, magnesium stearate, stearin Higher fatty acid salts such as aluminum acid salts 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 will be difficult to impart appropriate strength to the molded product. If the molecular weight exceeds 1,000, the moldability and degreasing property will deteriorate, and if it exceeds 2,000, precision molded products will not be formed. This is because it is impossible, and the degreasing time becomes extremely long, so that it is not possible to efficiently manufacture the precision parts having a complicated shape, which is the object of the present invention, with high accuracy.

When the degreasing treatment is carried out 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 kinds of the components (c) having different boiling points in order to avoid defects such as sagging and swelling during the degreasing process. This tends to occur when the low-molecular component is removed at a temperature lower than the resin decomposition temperature during the degreasing process, so two types of the low-molecular component (c) are used in order to avoid the defect. This is because it is better to widen the temperature range for removal by blending the above.

The thermoplastic resin containing an isocyanate group in the present invention is contained in the binder in an amount of 3 to 80% by weight.
When it is less than 3% by weight, the surface of the sinterable powder cannot be sufficiently covered with the thermoplastic resin, and the wettability between the sinterable powder and the binder is not improved. As a result, the strength of the molded body is low and the molded body is easily cracked, which causes a defect such as deformation during degreasing, swelling or cracking. If it exceeds 80% by weight,
The compound viscosity becomes high, the moldability deteriorates, and
During degreasing, cracks and blister defects are likely to occur.

Thermoplastic resins other than the isocyanate group-containing thermoplastic resin in the present invention are not essential components,
As described above, in order to shorten the degreasing time, it is better to be contained in the binder, and the content is 70% by weight or less. If it exceeds 70% by weight, the compound viscosity becomes high, the moldability is deteriorated, and cracks and swelling defects are likely to occur during degreasing.

Of the resin components of (a) and (b),
The preferable blending ratio in the binder is such that one does not become extremely large, and the thermoplastic resin containing an isocyanate group is required in an amount sufficient to cover the surface of the sinterable powder. That is, it is preferable that the thermoplastic resin other than this is 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 with 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 powder containing metal powder, ceramic powder or 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 their alloys or mixed powders such as iron-nickel,
Stainless steel, iron-silicon, iron-boron, iron-cobalt, iron-cobalt-vanadium can be mentioned, and 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, 2 silica Examples of the cermet include molybdenum oxide, cadmium sulfide, zinc sulfide, and a mixture of two or more thereof. Examples of cermets include tungsten carbide powder / cobalt powder, aluminum oxide powder / aluminum powder, iron powder / silicon powder, iron powder / boron. Powder, metal powder / ceramic powder such as silicon nitride powder / yttrium oxide powder / aluminum oxide powder, alloy powder of the above ceramics and metal such as metal powder / non-metal powder, mixed powder or cermet powder. it can.

The sinterable powder may be produced by any method, for example, carbonyl powder, water atomized powder, gas atomized powder, crushed powder, rotating disk powder, reducing powder, electrolysis powder, rotating consumable electrode powder, etc. it can.

The average particle size of the sinterable powder is 0.1 to 1,000 μm.
Is the range. The smaller the particle size of the sinterable powder, the better the flowability during injection molding and the better the sinterability, which is advantageous, but a huge amount of energy is required to make the powder fine, which is disadvantageous in practice. On the other hand, if it exceeds 1,000 μm, the fluidity of the compound is extremely deteriorated, making injection molding practically impossible. Practically preferable average particle size range is 1 to 50.
μm. Further, additives such as an antioxidant, a flow agent, and a surfactant may be added to the sinterable powder injection molding composition of the present invention as appropriate.

The powder injection molding compound of the present invention comprises:
The binder of the present invention 3 to 100 parts by weight of the sinterable powder is used.
It is preferably kneaded with 20 parts by weight to produce. If the amount is less than 3 parts by weight, the binder cannot fill the gaps between the sinterable powders, resulting in poor fluidity of the compound and making injection molding difficult. On the other hand, if the amount exceeds 20 parts by weight, the fluidity is improved and the injection molding can be easily performed, but it is not preferable because the shape cannot be maintained during degreasing.

The method of kneading the binder and the sinterable powder of the present invention is not limited, and a Henschel mixer, a Banbury mixer, a kneader, a roll mill, a single screw extruder, 2
Any material can be used as long as it can knead the binder and the sinterable powder, such as an axial screw extruder.

The kneaded compound is crushed or granulated to obtain a molding material. As the injection molding machine, a general injection molding machine for thermoplastics can be used. The injection molding is carried out at an injection temperature in the range of 100 ° C to 250 ° C. However, if the injection temperature is too high, the deterioration of the binder component becomes remarkable and the recyclability of the reclaimed material is changed. The range of 100 ° C to 180 ° C is preferable.

Degreasing can be performed by either a heat degreasing method or a solvent extraction method. In the case of the heat degreasing method, it is preferable to remove the binder in a stream of nitrogen, argon, hydrogen or the like or under reduced pressure. The temperature rising rate depends on the thickness of the molded product, but the temperature is raised in the range of 10 ° C / h to 100 ° C / h. The maximum temperature for degreasing is preferably 450 ° C to 600 ° C. If the maximum degreasing temperature is less than 450 ° C, the resin component is not efficiently decomposed and removed, which is not preferable, and even if the temperature is raised to 600 ° C or higher, the decomposition and removal rate of the resin component does not change so much, and conversely the degreasing time It's just an extension.

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

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

Next, the features of the present invention will be described. As will be described later in Examples, P that 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 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, organic substances that cannot be washed away with hot toluene remain on the surface of the sinterable powder in an amount of about 0.1 to 0.15% in terms of carbon.

The sinterable powder covered with hydroxyl groups and the resin component in the binder are fixed to each other by PE, P having no functional group.
In the case of P and PS, it is considered to be Van der Waals force, and EVA, EEA, EMMA, and acrylic resin having an ester group are considered to be hydrogen bonds, but these bonds are weak fixation washed out by hot toluene. However, in the binder composition of the present invention, the organic substance is fixed to the surface of the sinterable powder by a strong bond that cannot be cut with hot toluene. Probably, 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, and as a result, a polymer is grafted on the surface of the sinterable powder. . The characteristic of the present invention is considered to be due to the polymer strongly grafted on the surface of the sinterable powder. The features of the present invention will be described below.

When the binder of the present invention is used, the sinterable powder is very well dispersed at the time of kneading, a uniform compound is obtained, and the fluidity is not deteriorated due to the remaining aggregated powder, and the moldability is excellent. Moreover, since it has excellent fluidity, a small amount of binder is sufficient. As a result, degreasing becomes easier,
Degreasing time can be shortened, and deformation such as degreasing, blistering, and cracking can be prevented. 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 during transportation of molded products,
Little deformation. When heated and degreased, the molded body is unlikely to deform and defects such as blisters and cracks are less likely to occur.

[0037]

EXAMPLES The present invention will be specifically described below 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 diameter 9.5 μm, tap density 3.8
g / cc water atomized stainless iron powder 2) Ceramic powder: Silicon nitride powder with an average particle size of 1.0 μm 3) PE: LDPE (Sumikasen G807, 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
(Aklift WH501, manufactured by Sumitomo Chemical Co., Ltd.) 7) Acrylic acid-modified PE: Acrylic acid content 6% by weight
(PB-1008, manufactured by BPPerformance Polymers Inc.) 8) PS: weight average molecular weight 60,000 (Himmer SB-12
5. Sanyo Chemical Industry Co., Ltd. 9) Polybutylmethacrylate (PBMA): n-butylmethacrylate was polymerized at 95 ° C. for 4 hours in toluene under nitrogen using AIBN as an initiator. The polymerization solution was reprecipitated in methanol, and the obtained PBMA was heated at 50 ° C.
It was dried for 4 hours. Number average molecular weight of about 125,000. 10) Isocyanate-modified PBMA: Mixed monomer (HEMA / BMA = 0.0.2) of 2-hydroxyethyl methacrylate (HEMA) and n-butyl methacrylate (BMA).
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.
To a toluene solution of the obtained HEMA-BMA copolymer,
Excessive tolylene diisocyanate (2.4 / 2.6 = 80/20
(Mixture) was added, and the mixture was reacted under nitrogen at 30 ° C. overnight. The reaction solution was reprecipitated in hexane, separated and washed, and then dried under reduced pressure to obtain an isocyanate-modified PBMA shown in Table 1. The tolylene diisocyanate content was determined from the infrared absorption peak of the isocyanate group at 2250 cm ^-1 .

[0039] 11) Isocyanate-modified PS: 2-
A styrene monomer containing 1.0% by weight of mercaptoethanol was thermally polymerized in benzene under nitrogen to synthesize polystyrene having a hydroxyl group at one end. After completion of polymerization
Diphenylmethane diisocyanate in an amount 1.2 times the molar amount of 2-mercaptoethanol was added, and the mixture was allowed to stand overnight at room temperature. The reaction solution was poured into n-hexane, and the resulting polymer precipitate was separated, washed and dried. The number average molecular weight and GPC obtained from the quantitative value of the isocyanate group of the obtained polymer.
The number average molecular weights obtained by the method are relatively close to 12,000 for the former and 11,000 for the latter, indicating that the polystyrene obtained has almost one isocyanate group at one end. It was

2. Evaluation method of physical properties 1) Amount of organic substance bound to sinterable powder: The binder was extracted and removed from the crushed compound with a Soxhlet extractor using a toluene solvent. The sinterable powder from which the binder was removed was dried and then subjected to quantitative carbon analysis. In addition,
The extraction time was sufficient until the carbon content reached 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 the 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 depending on the amount 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 surface portion 1 and supporting portions 2 and 2 to obtain an injection molded test piece (molded body). The shapes of the other parts are as shown in FIG. This test piece was heated from normal temperature to 250 ° C. under reduced pressure in 12 hours and kept at 250 ° C. for 1 hour. Then, nitrogen was introduced, the temperature was raised to 500 ° C. in a nitrogen stream in 1 hour, and the temperature was maintained for 1 hour and then cooled. FIG. 2 is a cross-sectional view showing the molded body (a) before degreasing and the molded body (b) after degreasing. The degreasing deformation amount is measured by the deformation amount at the center of the flat surface portion 1 of the molded body before and after the degreasing step. did. This amount of deformation is the amount of deformation due to its own weight during degreasing.

(Examples 1 to 10 and 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 added and melted,
Next, 100 parts by weight of stainless powder was gradually added. The entire amount of the powder was added, and the mixture was kneaded for 1 hour, then the kneaded product was taken out, cooled, and pulverized. In the pulverizing compound, the amount of carbon powder was measured after removing the binder. Furthermore, the same grinding compound was used to injection-mold the test piece shown in FIG. 1 and the test piece was subjected to a degreasing test. The results are shown in Table 2. In Comparative Examples 1 and 6, the powder and the binder component were separated during molding, and molding was impossible. When EVA, EEA, EMMA, and acrylic acid-modified PE were used (Comparative Examples 2 to 5), good moldings were obtained, but blistering occurred during degreasing,
It caused a remarkable deformation. However, Examples 1-10
As shown in Table 1, when the isocyanate-modified resin was used, the moldability was good, the molded body and the degreased body did not have defects such as blister and crack, and the degreased deformation was small.

(Examples 11 to 20) Table 3 shows the binder composition.
Kneading, pulverization, injection molding and degreasing were performed in the same manner as in Example 1 except that the one shown in FIG. The results are shown in Table 3. In Examples 11 to 14, the isocyanate-modified PBMA was used, and the compounding ratio thereof was in the range of 3 to 80%, and the compounding ratio of other components and the molecular weight were also appropriate, so that the moldability and degreasing property were good. In Examples 15 and 16, isocyanate-modified PBMA was used, but 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, the isocyanate-modified PBMA was used, but microcrystalline wax, which is a low-molecular component,
Since the total compounding ratio of DOP and DBP was as small as 15% or as large as 85%, the degreasing property was rather poor. Example 1
In No. 9, since the compounding ratio of the resin (PE) other than the isocyanate-modified resin was as high as 75%, the deformation during degreasing was slightly large. In Example 20, the low molecular weight PE wax has a molecular weight of 3,
Since it was 000 and exceeded 2,000, the amount of deformation of degreasing was also rather large. However, Examples 15 to 20 were excellent binders as compared with Comparative Examples 1 to 6 (see Table 2) in which the isocyanate modified resin was not used.

(Example 21) 1.0% tolylene diisocyanate-modified PBMA / soybean oil / DBP = 50/30 /
Kneading, pulverization, and injection molding were performed in the same manner as in Example 1 except that the binder having a composition ratio of 20 (weight ratio) was used. The injection molded body was immersed in methanol for 12 hours to extract most of the plasticizer, and then the molded body was vacuum dried for 30 minutes. The molded body was heated from normal temperature to 500 ° C. in 4 hours in a nitrogen stream, kept at 500 ° C. for 1 hour, and then cooled. Appearance of molded body,
The appearance of the solvent-degreased body and the appearance of the heat-degreased body were good with no defects, and the deformation was as small as 20 μm.

(Comparative Example 7) Isocyanate-modified PBMA
Example 21 was repeated except that PBMA was used instead of. Some of the moldings cracked during injection molding, and the thermal degreased body also cracked and deformed 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 a pressure kneader to 140 ° C., 12 parts by weight of a binder is charged and melted, and then 94% by weight of silicon nitride powder having an average particle size of 1.0 μm and yttrium oxide powder having an average particle size 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 size of 0.3 μm were gradually added. After the whole amount of the powder was added and kneading was carried out for 1 hour, the kneaded product was taken out, cooled and pulverized. The crushed compound was prepared by removing the binder with a Soxhlet extractor and measuring the amount of carbon powder. Further, the same grinding compound was used to injection-mold the test piece shown in FIG. 1 and the test piece was subjected to a degreasing test. The results are shown in Table 4.

In Comparative Example 8, the wettability between the powder and the binder was poor, and the powder and the binder separated during injection molding, and molding was impossible. When EVA, EEA, or acrylic acid-modified PE was used (Comparative Examples 9 to 11), good moldings were obtained, but blistering occurred or significant deformation occurred during degreasing. 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]

INDUSTRIAL APPLICABILITY According to the present invention, since a thermoplastic resin having one or more isocyanate groups in the molecule, which firmly binds to the powder, is used as the binder component, the metal powder, the ceramic powder or the cermet powder and the binder are combined. A powder injection molding compound with strongly bonded interfaces was obtained. Therefore, the powder injection molding compound of the present invention has good moldability, in addition to manufacturing advantages such as short degreasing time, and high strength, therefore, cracking during molding, deformation during deformation and deformation during degreasing, It has the advantage that blisters and cracks are greatly reduced, and precision parts with complicated shapes can now be efficiently produced with high-precision dimensions.

[Brief description of 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 the deformation amount of a test piece.

[Explanation of symbols]

 1 plane part 2 support part

Claims (6)

[Claims] 1. A sinterable powder injection molding binder comprising a thermoplastic resin having a molecular weight of more than 2000 and having at least one isocyanate group in the molecule. 2. The binder for sinterable powder injection molding according to claim 1, which 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 2000 and having at least one isocyanate group in the molecule is 3 to 80% by weight, and (c) an organic compound having a molecular weight of 2000 or less is 20 to 20%. The binder for sinterable powder injection molding according to claim 1, containing 80% by weight. 4. A thermoplastic resin having a molecular weight of more than 2000 and having at least one isocyanate group in the molecule is 3 to 80% by weight, and (b) a resin other than the thermoplastic resin is 7% by weight.
0 to 80% by weight and (c) 20 to 80% by weight of an organic compound having a molecular weight of 2000 or less are contained.
The binder for sinterable powder injection molding according to 1. 5. A sinterable powder injection molding composition comprising the powder injection molding binder according to any one of claims 1 to 4 and a metal powder, a ceramic powder or a cermet powder. 6. The sinterable powder injection molding composition according to claim 5, wherein the metal powder, the ceramic powder or the cermet powder has an average particle size of 0.1 to 1000 μm.