JPH09111306A - Composition for producing sintered molded body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance production efficiency by regulating the amt. of polyolefin polymer modified polyacetal resin to a specified percentage of all binders. SOLUTION: This compsn. contains a resin binder made of polyolefin polymer modified polyacetal resin by 10-95vol.% of all binders. The ratio between polyacetal and polyolefin polymer skeletons in the polyolefin polymer modified polyacetal resin is (10-95wt.%): (90-50wt.%) (the total amt. of the skeletons is 100wt.%). In the case of <10vol.% of the modified polyacetal resin, a molded body is liable to deformation in a dewaxing process by heating. In the case of >95vol.%, the flowability of this compsn. deteriorates and injection molding for forming a green molded body is not smoothly carried out. Since the resin binder is used, a homogeneous sintered molded body free from the separation of a layer can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding raw material used for producing a sintered compact.

[0002]

2. Description of the Related Art A particularly precise sintered compact or a sintered compact having a complicated shape, which uses a sinterable powder such as ceramics, metal or cermet, is used to produce a sintered compact containing a sinterable powder and a binder. A green molded body is molded by injection molding a molding raw material obtained by heating and kneading the composition for molding, followed by subjecting the green molded body to a degreasing step, and subsequently molding the green molded body by a method of sintering.

In the molding of a sintered compact by the above method, the degreasing step is the most important step for obtaining a good quality compact free from defects such as cracks, swelling and deformation.
This degreasing step is a step of removing the binder from the green molded body made of an injection molded body, by heating the green molded body to thermally decompose the binder to gasify it, or to treat the green molded body with a solvent. A method is used in which the soluble binder component in the green compact is eluted and removed by doing so, and the remaining binder is thermally decomposed and gasified. By the way, in the heat degreasing method of heating and degreasing the green molded body, when thermal decomposition and gasification of the binder in the green molded body occur in a short time, cracks and swelling of the molded body during the degreasing process occur. There is something that occurs, so you have to degrease by heating for a long time. In particular, when using a sintering powder having a small particle size of the powder to be sintered, that is, having a large specific surface area, a binder is mixed so that the heating fluidity of the molding raw material when molding the green molded body is stable. It is necessary to increase the amount, and it is necessary to devise a heating process for degreasing in multiple stages. In addition, even if there is no risk of cracking or swelling during the degreasing process due to heating, in the case of a green compact made of metal powder or spherical powder with a high specific gravity, molding during the degreasing process due to heating Deformation often occurs in the body, which also requires slowing the heating rate during heating during degreasing. Therefore, a method of adding a sublimable substance to the binder has been considered,
When the sublimable substance is added, the sublimable substance evaporates during the kneading of the molding raw material for the green molded body and during the injection molding of the green molded body, so the sprue / runner part during molding of the green molded body Becomes difficult to reproduce.

On the other hand, in a degreasing method comprising a method in which the binder in the green molded body is eluted and removed by subjecting the green molded body to a solvent treatment, and the remaining binder is thermally decomposed and gasified, the solvent treatment is used to remove the green. The solvent-soluble binder in the molded body is removed, and the voids generated by the removal serve as a passage, and the thermal decomposition and gasification of the remaining binder due to heating are smoothly performed. Therefore, it is possible to avoid cracking, swelling, deformation and the like in the degreasing process of the green molded body. However, the binders currently used contain a large amount of liquid raw materials such as mineral oil, fatty acid oil, and natural oil, and these oil components often exude from the green molded body, and also for a long period of time. In the preserved green molded body, this oil component exudes more severely, and the oil component that has exuded on the surface of the green molded body causes cracks and swelling during degreasing by solvent treatment.

A method of eluting the plasticizer or lubricant in the binder with boiling water is also conceivable, but the stability of the molding raw material of the green molded body is maintained, and the heating fluidity of the molding raw material during injection molding is improved. In terms of maintaining the strength and maintaining the strength of the green molded body, it is not possible to increase the blending amount of the plasticizer and the lubricant. Further, a method of extracting a water-soluble resin in a green molded body by water treatment using a binder made of a water-soluble resin has been proposed (Japanese Patent Publication No. 2-10110).
However, this method cannot be applied to those using ceramic powder and metal powder having a property of reacting or corroding with water.

Furthermore, by using a polyacetal resin, which is a depolymerizable polymer, alone or together with another polymer as a binder, the shape retention of the green molded body based on the rigidity of the polyacetal resin and the degreasing step by heating are carried out. It is already known that there is an effect such that the shape retention of the molded body is excellent, the residue does not remain after degreasing by heating, and the degreasing step by heating can enhance the production efficiency, and the like. (For example, JP-A-4-247802 and JP-A-5-98306). On the other hand, on the other hand, when the polyacetal resin is used as a binder, the polyacetal resin is chemically stable and has poor compatibility with many other organic components. However, there is a problem that a homogeneous sintered molded product cannot be obtained because the affinity with wax, lubricant, etc. is poor and layers are easily separated in the components. In particular, in order to improve the above-mentioned effects of using a polyacetal resin as a binder, that is, the shape retention of the green molded body, and the shape retention of the molded body in the degreasing step by heating, and to enhance the heat degreasing efficiency, It is necessary to increase the blending ratio of the polyacetal resin in the binder, and the above-mentioned drawbacks are further exacerbated by the lack of affinity of the polyacetal resin for other resins, wax, lubricants and the like.

Further, a method of degreasing the polyacetal resin as a binder and decomposing the polyacetal resin in the green molded body with an acidic catalyst can be considered, which is a method of significantly reducing the degreasing time.
This method uses a strong acid such as nitric acid as a degreasing catalyst,
The sinterable powder may be altered by oxidation or the like, which has a drawback that the type of the sinterable powder that can be used is greatly limited.

[0008]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to complete the degreasing process of a green molded body by heating for a short time, and further, to the molded body during the degreasing process such defects as cracks, swelling and deformation. It is an object of the present invention to provide a composition for producing a sintered molded product, which does not cause the above-mentioned phenomenon, has a high dimensional accuracy, and can obtain a homogeneous sintered molded product without layer separation.

[0009]

The above object can be achieved by the composition for producing a sintered molded product of the present invention having the following constitution. That is, according to the present invention, in a composition for producing a sintered molded product containing a sinterable powder and a binder, the polyolefin-based polymer-modified polyacetal resin is blended in a proportion of 10 to 95% by volume in all binders. A composition for producing a sintered molded article is provided.
According to the invention, the proportion of the polyacetal skeleton and the polyolefin polymer skeleton in the polyolefin polymer modified polyacetal resin is 10 to 95% by weight: 90.
The composition for producing a sintered compact is provided in the range of 5 wt% (total of 100 wt% of both). Hereinafter, the present invention will be described in detail.

A binder made of a sinterable powder, a polyolefin-based polymer-modified polyacetal resin (hereinafter also simply referred to as "modified polyacetal resin") and a binder other than the modified polyacetal resin (hereinafter referred to as "other binder"). .) And a modified polyacetal resin content of less than 10% by volume in the binder, the molded article in the degreasing step due to heating is easily deformed, and also 95% by volume.
If it exceeds the above range, the fluidity of the composition is lowered, and it becomes impossible to smoothly perform the injection molding when molding the green molded body.

When the proportion of the polyacetal skeleton in the modified polyacetal resin blended as the binder is less than 10% by weight, the heat deformation temperature of the green molded body is greatly lowered, and the molded body is deformed in the degreasing step by heating. It tends to occur. Further, the amount of residual carbon after degreasing of the green molded body increases, and it becomes impossible to obtain a sintered molded body of good quality. Furthermore, when the proportion of the polyacetal skeleton is more than 95% by weight, the amount of decomposed gas of the polyacetal resin generated in the degreasing process by heating the green molded body increases, and cracks and swelling of the molded body occur in the degreasing process. It will be easier. Furthermore, since the compatibility with other binders is greatly reduced, the strength of the green molded body is reduced and the green molded body becomes brittle.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the composition for producing a sintered molded product of the present invention, the polyacetal resin constituting the substrate of the polyolefin polymer-modified polyacetal resin which is an essential binder component is an oxymethylene group (--CH ₂
Any polymer compound having O-) as a main constituent unit may be used, and any of a polyoxymethylene homopolymer, a copolymer containing another constituent unit other than oxymethylene, a terpolymer, and a block copolymer may be used. The molecule may have not only a linear shape but also a branched or crosslinked structure. Examples of the comonomer serving as the other structural unit include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane, and dioxepane. To be done.

The polyolefin-based polymer used for modifying the polyacetal resin is a homopolymer of α-olefin such as ethylene, propylene, butene, hexene, octene, nonene, decene, dodecene, or a combination of two or more of these. Random, block or graft copolymers, or non-conjugated dienes such as 1,4-hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene and 2,5-norbonadiene, and conjugation such as butadiene, isoprene and piperylene Diene components, α, β-unsaturated acids such as acrylic acid and methacrylic acid, or derivatives thereof such as esters, acrylonitrile, styrene,
A random or block containing one or more of an aromatic vinyl compound such as α-methylstyrene, a vinyl ester such as vinyl acetate, a vinyl ether such as vinyl methyl ether and a comonomer component such as a derivative of these vinyl compounds. Or a graft copolymer. Depending on the modification method of the polyacetal resin, these polyolefin-based polymers can be modified with an acid anhydride in advance or modified with a polyfunctional compound such as a polyfunctional isocyanate compound or a polyfunctional epoxy compound before use. It is also possible to use the above-mentioned monomer component in the state of a monomer or an oligomer thereof and to carry out polymerization and modification of the polyacetal resin in the modified polyacetal resin production process. The method for producing the polyolefin-based polymer-modified polyacetal resin used in the present invention is not particularly limited, and examples thereof include the following methods.

(1) Formaldehyde or trioxane is homopolymerized in the presence of a polyolefin polymer having a functional group such as a hydroxyl group, a carboxyl group, an acid anhydride group, an amino group or an epoxy group, or a cyclic formaldehyde or trioxane is used. A method of copolymerizing an ether or a cyclic formal, (2) a polyacetal resin and a polyolefin-based polymer, a polyfunctional compound, for example, a polyisocyanate compound, etc., and a method of melt heating in the presence or absence of a catalyst, (3 ) A method in which a polyacetal resin or a polyolefin-based polymer is previously reacted with a polyfunctional compound, and this and the other resin component are melt-heated in the presence or absence of a catalyst can be mentioned. the above
In the methods (2) and (3), it is preferable to use a polyacetal resin rich in hydroxyl groups as the polyacetal resin. As the polyolefin-based polymer, it is preferable to use a polyolefin-based polymer modified with an acid anhydride, or a polyolefin-based polymer having an active hydrogen species such as a hydroxyl group, a carboxyl group and an amino group. Depending on the production method of these polyolefin-based polymer-modified polyacetal resins, the unreacted polyacetal resin and / or the unreacted polyolefin-based polymer coexist with the modified polyacetal resin which is a reaction product, and are substantially compatible or uniformly dispersed. It may take the form of the composition described above. In such a case, the entire composition can be treated as the modified polyacetal resin used in the present invention.

In the composition for producing a sintered molded product of the present invention, the proportion of the polyacetal skeleton in the modified polyacetal resin is preferably 10 to 95% by weight, particularly preferably 20 to 80% by weight. All binder 100
The ratio of the modified polyacetal resin in the volume% is 10 to 95.
% By volume, preferably 15 to 80% by volume, particularly preferably 20 to 70% by volume, the remainder being other binders.

The other binder is specifically one or more kinds of organic substances such as thermoplastic resins, waxes, plasticizers, and lubricants.

Examples of the thermoplastic resin include acrylic resin, polyethylene, polypropylene, polystyrene,
Examples thereof include ethylene-vinyl acetate copolymer and polyvinyl butyral. Examples of waxes include paraffin wax, polyethylene wax, carnauba wax, polyethylene glycol, beeswax, wood wax, and synthetic wax. Furthermore, examples of the plasticizer include phthalic acid compounds such as dioctyl phthalate, dibutyl phthalate, and diethyl phthalate. Furthermore, examples of the lubricant include fatty acid esters such as stearic acid esters and derivatives thereof.

The composition for producing a sintered compact of the present invention containing a sinterable powder, a modified polyacetal resin binder and other binders can be used in various types of sinterable powders such as ceramics, metals and cermets. , The total amount of binders is usually 20 to 60% by volume, preferably 25 to 55% by volume in 100% by volume of the composition for producing a sintered molded product, although it varies depending on other kinds of binders.
It is particularly preferably 30 to 50% by volume. The compounding method and the compounding order are not particularly limited, but these are usually compounded together.

The above-described composition for producing a sintered molded product of the present invention is a raw material for molding when a green molded product, which is a preformed product of the sintered molded product, is molded by injection molding. After molding a green molded body by injection molding a molding raw material obtained by heating and kneading the material, the green molded body is subjected to a degreasing step by heating, and the molded body after degreasing is sintered to obtain the purpose. A sintered molded body of is obtained.

[0020]

EXAMPLES Hereinafter, more specific component compositions of the composition for producing a sintered molded product of the present invention having the above-mentioned constitution will be explained based on examples, but the present invention is not limited to these.

(Example 1) <Preparation of modified polyacetal resin> 99 parts by weight of a polyacetal resin and 1 part by weight of isophorone diisocyanate were added,
After melt kneading at 190 ° C. in the presence of zinc stearate to obtain an isocyanate-modified polyacetal resin,
20 parts by weight of maleic anhydride-modified polyethylene was added thereto, and the mixture was melt-kneaded at 190 ° C. to obtain a polyethylene-modified polyacetal resin.

<Production and Evaluation of Sintered Molded Product> A powder of SUS316L (average particle size 10 μm) as a powder capable of being sintered, and the above-mentioned modified polyacetal resin / low density polyethylene / paraffin wax = 40 / as a binder.
Using a mixture of 10/50 (volume%), SUS316L
A composition for producing a sintered compact by mixing 60% by volume of powder with 40% by volume of the binder, kneading the mixture with a pressure kneader at 160 ° C. for 40 minutes, and cooling and crushing the kneaded product ( A raw material for injection molding) was prepared. Next, using this raw material for injection molding, a molding temperature of 140
Injection molding was performed at ˜180 ° C. to obtain a dumbbell test piece-shaped green molded body shown in FIG. The moldability was extremely good. This green compact is held as shown in FIG. 2, heated to 120 ° C. over 2 hours, heated to 320 ° C. at a heating rate of 30 ° C./hour, and further heated to 320 ° C. for 2 hours. Degreasing was performed depending on the heating conditions to be maintained. When the amount of deformation of the central part of the dumbbell test piece after degreasing was measured, the deformation was only 0.2.
mm. After degreasing, it was further sintered in air at 1320 ° C. for 2 hours to obtain a sintered compact. The sintered compact obtained here had a good appearance without cracking or swelling, and the amount of carbon remaining in the sintered compact was 80 p.
It was as small as pm, and there was no problem at all.

(Comparative Example 1) In place of the modified polyacetal resin in Example 1, an unmodified polyacetal resin was used, and an attempt was made to manufacture a sintered compact by the same method as in Example 1, but the moldability was extremely poor. However, it was not possible to obtain a green molded body that can withstand the subsequent thermal degreasing and sintering.

(Comparative Example 2) The modified polyacetal resin in Example 1 was reduced to 5% by volume (in the total binder), the amount of low density polyethylene was increased by an amount equivalent to this, and baking was carried out in the same manner as in Example 1. A molded body was manufactured and evaluated. In this case, the moldability was good, but the amount of deformation after degreasing was as large as 3.8 mm, and the amount of carbon remaining in the sintered compact was as great as 1100 ppm.

(Example 2) <Preparation of modified polyacetal resin> 20 parts by weight of trioxane and 50 parts by weight of ethylene-vinyl acetate copolymer were dissolved in benzene, and then 2 parts by weight of dioxolane was added to the mixture, and boron trifluoride ethyl ether was added. Is used as a catalyst to carry out a graft copolymerization reaction at 60 ° C. for 15 hours, and after the polymerization termination treatment, washing,
It was dried to obtain a prepolymer for producing a modified polyacetal resin. 6.5 parts by weight of this prepolymer, 92 parts by weight of trioxane and 1.5 parts by weight of dioxolane are subjected to a graft copolymerization reaction at 60 ° C. for 15 minutes using boron trifluoride ethyl ether as a catalyst, followed by a polymerization termination treatment, followed by washing and drying. Then, the unstable portion was removed by heating to obtain a modified polyacetal resin having an ethylene-vinyl acetate copolymer content of 12% by weight.

<Manufacture and Evaluation of Sintered Molded Product> Using this modified polyacetal resin, a sintered molded product was manufactured in the same manner as in Example 1, and the same favorable results as in Example 1 were shown. The amount of deformation after degreasing was 0.3 mm, and the amount of carbon remaining in the sintered compact was 90 ppm, which were all good.

[0027]

The composition for producing a sintered molded product according to the present invention contains a resin binder comprising a polyolefin-based polymer-modified polyacetal resin in an amount of 10 to 95% by volume based on all binders.
It is mixed in the ratio of.

Therefore, according to the composition for producing a sintered molded product of the present invention having the above constitution, the effect obtained by using the modified polyacetal resin having a polyacetal skeleton which is a depolymerizable polymer as a binder, that is, the polyacetal resin It has excellent shape retention of the green molded body based on its rigidity and shape retention of the molded body in the degreasing process by heating, and because the residue does not remain after degreasing by heating, the molded body is cracked during the degreasing process. Further, defects such as swelling and deformation do not occur, and the degreasing process by heating is quick, so that the production efficiency can be improved. Further, according to the composition for producing a sintered molded product of the present invention, the polyolefin-based polymer skeleton constituting the modified polyacetal resin in the composition for producing a sintered molded product is good for many other organic components. Since it has compatibility, it has a good affinity between the polyolefin polymer skeleton and other thermoplastic resins, waxes, lubricants, etc. that constitute the binder, so that a homogeneous sintered structure without layer separation is formed. A feature is obtained.

[Brief description of the drawings]

FIG. 1 shows a dumbbell test piece shape obtained by molding a green molded body.

FIG. 2 shows a measurement position of a deformation amount after degreasing of a green molded body having a dumbbell test piece shape.

Claims (2)

[Claims] 1. A composition for producing a sintered molded product, comprising a sinterable powder and a binder, wherein a polyolefin-based polymer-modified polyacetal resin is contained in 10 parts of all binders.
A composition for producing a sintered molded product, characterized in that the composition is blended at a ratio of ˜95% by volume. 2. The proportion of the polyacetal skeleton and the polyolefin polymer skeleton in the polyolefin polymer modified polyacetal resin is in the range of 10 to 95% by weight: 90 to 5% by weight (total of 100% by weight of both). The composition for producing a sintered molded body according to claim 1.