JPH10130063A - Dewaxing method, dewaxed body obtained thereby and sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost dewaxing method by which an injection molded body is dewaxed by vaporization or evaporation by heating or thermal decomposition in a considerably shortened time while ensuring shape retentivity of the molded body at the time of dewaxing. SOLUTION: A molded body contg. a thermoplastic binder is dewaxed through 1st and 2nd process. In the 1st process, the molded body is put in an atmosphere under reduced pressure and part of the binder is vaporized by >=5wt.% of the total amt. of the binder by heating at a temp. below the m.p. of the binder. Part of the binder is further vaporized by >=10wt.% of the total amt. of the binder by heating at a temp. below the m.p. of one of a readily vaporizable org. compd. and a thermoplastic resin component having a higher m.p. than the other and the final temp. is regulated to <=200 deg.C. In the 2nd process, the molded body is heated to the max. m.p. of the binder or above in an atmosphere of gas inert to a selected powdery material under atmospheric pressure or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing method for degreasing the above-mentioned thermoplastic binder from a molded article obtained by mixing a thermoplastic binder and powder and injection molding, a degreased body obtained by the degreasing method, and a degreasing method therefor. The present invention relates to a sintered body obtained by sintering a body.

[0002]

2. Description of the Related Art In general, in injection molding of powder, a thermoplastic resin or a thermoplastic resin is used to impart fluidity and pressure moldability to powder such as metal powder, ceramic powder, and cermet powder to enable injection molding. A thermoplastic binder made of wax is used. The standard of the usage fee of the thermoplastic binder is usually set to about 40 to 55% by volume in consideration of the relationship with the spherical shape of the powder to be used. This thermoplastic binder is removed by degreasing after injection molding and prior to the sintering step. In this degreasing step,
By heating the injection molded body in an inert atmosphere, the binder is dissolved, evaporated or decomposed and vaporized. However, in the degreasing step, first, the binder coating the powder is dissolved, and the weight of the injection molded body is added, so that the injection molded body formed of the powder becomes structurally unstable. Further, when pressure is applied to the binder in this state when the binder is decomposed and vaporized, the powder moves and the influence of its own weight is added to cause collapse of the load, which causes deformation of the molded body. Further, if the temperature at the time of heating is increased in order to promote the removal of the binder, the binder is boiled and vaporized, and swelling and cracks are generated. Therefore, in order to prevent the occurrence of defects in the degreasing step, it is necessary to slowly advance the removal of the binder in this degreasing step,
The degreasing time is taken into consideration in relation to the size or thickness of the injection molded body, but it usually takes 2 to 3 days. As described above, a degreasing method for removing the thermoplastic binder from the injection molded body in a short time while keeping its shape sound without causing deformation, swelling or cracking of the injection molded body due to its own weight is important. It is a technical issue.

To cope with such a technical problem, Japanese Patent Publication No. 61-48563 discloses a method in which an inert gas is blown in a turbulent state with respect to an injection molded body to dissolve it in a porous body. A degreasing method for absorbing a part of the binder component has been proposed, and Japanese Patent Publication No. Sho 62-33282.
In Japanese Patent Application Laid-Open Publication No. H11-264, a degreasing method has been proposed in which the pressure of the atmosphere of an injection-molded article is kept at a pressure higher than the vapor pressure of a thermoplastic binder.

In US Pat. No. 5,122,326, a molded product using a thermoplastic binder composed of a paraffin wax having a low melting point and a polymer binder having a higher melting point is formed by a diffusion pump while heating. After the wax component is vaporized in a solid state without forming a liquid phase of the wax in a vacuum atmosphere of 5 × 10 ⁻⁴ torr or more, the second high pressure is further reduced in a vacuum atmosphere achievable with a mechanical pump. A degreasing method for vaporizing a molecular binder without forming a liquid phase has been proposed.

Further, Japanese Patent Publication No. 4-74769 discloses that
After a part of the thermoplastic binder is vaporized and removed by heating at a temperature lower than or equal to the softening temperature of the injection molded body, a pressurizing step of pressurizing the injection molded body at a pressure capable of holding the shape of the injection molded body by a pressing means is performed. After that, a degreasing method has been proposed in which most of the thermoplastic binder is vaporized and removed again in an atmosphere inert to the powder.

[0006] Further, in Japanese Patent Application Laid-Open No. Hei 8-25802, a step of evaporating a part of the thermoplastic binder by heating the injection molded body to a temperature lower than the melting point of the thermoplastic binder under a reduced pressure atmosphere is used. A step of heating above the melting point of the thermoplastic binder as a pressure exceeding the normal pressure in an active gas atmosphere, and reducing the atmospheric gas pressure to below the normal pressure, and reducing the atmosphere temperature to at least most of the thermoplastic binder by vaporization. And a step of raising the temperature to a certain temperature.

On the other hand, when degreasing an injection-molded article using a metal powder as a powder, the problem of the amount of carbon remaining in the degreased body in connection with the thermal decomposition of the binder, and conversely, in an oxidizing atmosphere in the air, At the time of degreasing, for example, there is a problem such as cracking due to oxidation of the metal powder, and furthermore, control of carbon component of the sintered body after sintering and variation in sintering temperature due to component failure are important problems. . As a solution to this problem,
It has been reported that selection of a binder for injection molding, adjustment of composition, and degreasing are performed in an N ₂ , Ar, H ₂ gas atmosphere, or a method of adjusting an atmosphere gas during sintering. This is described in Japanese Patent Application Laid-Open No. 5-33150.
No. 3, JP-A-6-200303, JP-A-6-200303
No. 73406 and the like.

[0008]

However, the technique disclosed in the above-mentioned Japanese Patent Publication No. 61-48563 prevents swelling or cracking of the injection molded article caused during degreasing due to the turbulent flow of the blown gas. While it is expected to have the effect of accelerating the vaporization of the thermoplastic binder, it is difficult to keep the inside of the degreasing furnace in a uniform turbulent state. Even if the temperature is uniform, the debinding speed is different between the side of the injection molded body facing the air blow and the back side, and the degree of degreasing is not uniform in some parts of one injection molded body. Become.
In particular, when using a degreasing setter used for efficiently arranging the injection molded bodies in the furnace, it is likely to be non-uniform in a place where the setters are in contact with the setter or where turbulent air blowing is obstructed. When housed in a debinding furnace, the non-uniformity becomes severe and deviations occur in the progress of degreasing between injection molded articles. Therefore, there is actually a problem that it is difficult to stably realize sound degreasing without deformation due to its own weight and without swelling or cracks. Further, in the one described in this publication, a thermoplastic binder composed of binder components having different melting points is used, and by heating, it gradually flows out of a molded body in a liquid state gradually and is absorbed by a porous absorber. It is expected to remove the binder from the injection molded body, thereby preventing the occurrence of swelling and cracks, and to expedite the binder removal.However, in actuality, when the binder is removed from the molded body, it becomes liquid, In the degreasing step, there is a problem that the molded body cannot easily withstand its own weight and the shape easily collapses, and when the binder absorber and a part of the molded body are brought into contact with each other, the molded body is in the same manner as described above. Deviation occurs in the progress of degreasing of, and, due to the constraints when setting a plurality of molded bodies in a degreasing furnace, many molded bodies are not deformed by their own weight, One blister, has a problem that it is difficult to achieve a healthy degreasing no occurrence of cracks stably.

Further, in the technique disclosed in Japanese Patent Publication No. 62-332282, since the atmospheric pressure during degreasing is kept in a pressurized state from beginning to end, the thermoplastic binder contained in the injection molded article is And the difference between the melting point and the boiling point of the thermoplastic binder becomes larger than in the case of a normal pressure atmosphere, thereby suppressing the boiling and vaporization of the thermoplastic binder in the injection-molded product, and causing swelling or cracking. Effectiveness is expected for the prevention of defects such as occurrence of defects. However, placing the inside of the debinding furnace in a pressurized atmosphere from beginning to end causes a rise in the boiling point of the thermoplastic binder as described above, thereby slowing the vaporization of the binder. That is, since the progress of the debinding is shifted to the higher temperature side with respect to the normal pressure state, the degreasing hardly proceeds in a temperature region near the melting point of the thermoplastic binder, for example, where deformation due to its own weight is most likely to occur. Therefore, there is a problem that the injection molded body is liable to be easily deformed by its own weight, and further, to end the degreasing, the temperature at which the degreasing is completed by the amount corresponding to the additional pressure of the atmosphere is increased. There is a problem that the necessity of raising the temperature arises, and a prolonged degreasing time is inevitable.

In the technique disclosed in US Pat. No. 5,122,326, a low-melting paraffin wax added to a thermoplastic binder contained in a molded article is decomposed instead of camphor as a sublimable substance. It is expected that debinding can be carried out without deformation by preferentially evaporating in a high-vacuum atmosphere using a diffusion pump in a solid state without any deformation. However, generally, paraffin wax, which is a low-melting wax, is mainly composed of a straight-chain saturated hydrocarbon having 20 to 30 carbon atoms, more specifically, a straight-chain saturated hydrocarbon having 24, 25 carbon atoms, and has a molecular weight of 24 to 25. 300-500, the melting point extends from 32 to 65 ° C., and the average melting point is about 5
The boiling point is about 400 to 500 ° C. (1 ° C.).
(Atmospheric pressure) and a boiling point higher than the melting point by an average of about 400 ° C., and a vapor pressure at the melting point of a hydrocarbon component having up to 24 carbon atoms containing about 50% by weight in a paraffin wax as a thermoplastic binder, 5 × At a vacuum of 10 ^-4 torr or more, and at least about 5
Since it is expected that about 0% will need to be removed by heating to an average melting point of 50 ° C., the lowest limit is 5 × 1
An advanced apparatus for constantly achieving a high degree of vacuum of 0 ^-4 torr or more is required, and the amount of evaporation when paraffin wax having a low vapor pressure evaporates as described above depends on the degree of vacuum of the atmosphere and the paraffin. Since it is proportional to the difference between the wax pressure and the wax pressure, there is a natural limit to shortening the debinding time, and the capacity of the vacuum equipment must be increased.As a result, the equipment cost of the debinding furnace becomes expensive. There is a problem that becomes.

Furthermore, a high-performance heat exchange cooler is required to recover a high vaporization of paraffin wax having a low freezing point in a high vacuum, and the freezing point of paraffin wax is close to room temperature. Therefore, it is easy to precipitate and solidify inside the mechanical pump without being collected by the cooler.Therefore, there are many problems in production technology such as the occurrence of troubles in the mechanical pump. When performing, in order to stably achieve a high degree of vacuum, not only in-furnace residues of paraffin wax, but also due to in-furnace deposition of pyrolytic low-molecular residues of polymer binder contained in thermoplastic binder It is necessary to give due consideration to various maintenances such as cleaning and further management of the diffusion pump oil. It becomes a problem. In addition, vacuum was applied by a mechanical pump that is easy to maintain (~ 0.1 torr).
It has been reported that when degreasing is carried out, the debinding time is required to be about three times or more (Yokoze, Shincho:
Industrial materials, Vol. 39, no. 12, September 1991, p. 31), which has a problem that it hardly exerts any substantial effect on shortening the degreasing time.

Also, a polypropylene resin comprising a long straight-chain saturated hydrocarbon, such as the paraffin wax described in the US patent specification, is expected to have good compatibility since it has a chemical structure similar to that of paraffin wax. However, when paraffin wax is added to about 40% by weight or more of the thermoplastic binder, separation of paraffin wax becomes remarkable at the time of adjusting the kneading of the injection material, and separation due to bleeding to the mold during injection molding. There are problems such as defective molds, generation of burrs from the mold split surface, and an increase in mold cleaning frequency. In addition, since paraffin wax itself is a soft material, if the internal cooling time of the mold after molding is not set to be very long, the molded body is likely to be damaged when the molded body is taken out from the mold, and is particularly applicable to large parts. Difficulties, many restrictions on the shape of molded products, and difficulties in automation of injection molding, etc. also have problems in terms of high automation of production and molding of complex shaped parts that are inherent features of powder injection molding technology. Is big. From this point of view, the mechanical pump that has sufficient strength to cope with the mold release resistance from the mold, uses a high-strength binder with few shape restrictions on the molded product, and is easier to maintain and maintain A degreasing method that can quickly perform degreasing at a low vacuum at a low cost is expected.

Further, Japanese Patent Publication No. 4-74769 discloses that after a part of a thermoplastic binder is vaporized at a temperature lower than the softening temperature of an injection molded article, the pressure is maintained at a pressure which can maintain the shape of the injection molded article. By applying a pressurizing step to pressurize, the previously degreased void volume is compressed, and the powder is brought into contact with each other to remove most of the remaining thermoplastic binder. And a method for shortening the binder removal time. However, including a pressurizing step in the debinding step not only increases the number of degreasing steps and increases the technical complexity, but also causes problems such as an increase in the cost of pressurizing equipment. Therefore, development of a degreasing method by heating more quickly is desired.

In the above-mentioned JP-A-8-25802,
By heating under reduced pressure at a temperature lower than the melting point of the thermoplastic binder, a part of the thermoplastic binder is removed, and the thermoplastic binder is maintained in a state where the pressure of the atmosphere gas exceeds normal pressure while securing shape retention. By heating above the melting point of the gas, a gas escape path to prevent swelling and cracking due to the generation of a large amount of gas in the next step is formed, and furthermore, most of the thermoplastic binder under atmospheric gas pressure below normal pressure This method discloses a method for preventing a degreasing defect of a molded article, shortening the degreasing time, and consequently, applicability to a large molded article, and degreasing. There is no disclosure of a technique for reducing the cost of the degreasing, and it is desired to develop a degreasing method for obtaining a degreasing body in a shorter time and sounder.

In the examples in JP-A-7-305101, the carbon content of the iron-based sintered body that has been degreased in N ₂ gas that is inert to the metal powder is determined by the maximum temperature at which degreasing is completed and the binder composition. However, it is difficult to control the amount of residual carbon in an inert N ₂ gas or Ar gas atmosphere in any case, and this point has been reported elsewhere. I have.

On the other hand, when the binder is removed in the air, the thermal decomposition of the thermoplastic binder is accelerated more rapidly from, for example, 200 ° C. or higher than in the thermal decomposition and degreasing in the N ₂ gas atmosphere. From the temperature range of 250 ° C. or higher, a reduction in the degreasing rate, which is considered to be due to the formation of residual carbon content, has been reported, and the formation of internal stress due to the formation of residual carbon content tends to cause cracks in molded products. It has been reported. In addition, when a metal powder that is easily oxidized is used, a new oxide is formed on the metal surface, and as a result, a molded article that is being degreased expands, and it is reported that cracks are likely to occur. I have.

Further, when degreasing is performed in the atmosphere, the residual carbon content is almost 0 or oxygen remains as an oxide, or the carbon content previously contained in the metal powder may decrease. Therefore, there is a complicated problem that the carbon component of the sintered body must be adjusted while finely controlling the powder to be used, the kind of the binder to be used, the compounding amount, and the degreasing conditions in advance.

As a countermeasure technique for the above-mentioned method for adjusting the amount of residual carbon, Miura et al. Report that it can be controlled by degreasing in a mixture of N ₂ gas and a high concentration of H ₂ gas. Also, from the difference in the amount of residual carbon due to degreasing in the N ₂ gas and in the atmosphere, it is easy to imagine adjusting the amount of carbon by mixing air or oxygen into the flow of an inert gas such as N _2. Is done.

As an example of the above-mentioned technique, an example of a method of controlling the amount of carbon by adding hydrogen to N ₂ gas is reported in detail in “Powder and Powder Metallurgy”, Vol. 40, No. 4, p. ing. Under the degreasing condition of 400 ° C., which is commonly practiced, it is necessary to mix a large amount of hydrogen into the N ₂ gas to control the amount of carbon, and the handling of the hydrogen-rich gas led out of the furnace becomes more dangerous. There are problems such as the necessity of management of the removed binder and management of safety equipment against explosive properties, and the small effect of H ₂ gas on controlling the amount of carbon. Note that Japanese Patent Application Laid-Open No. 6-2003
There is a similar problem in the technology disclosed in Japanese Patent Application Publication No. 03-2003.

Further, as disclosed in Japanese Patent Application Laid-Open No. 5-331503, when air or oxygen is directly added, it is different from the hydrogenation method in principle, and the degreased body by oxygen is removed. Direct reaction with carbon starting to remain C (S) + (１ ／) O ₂ (G) = CO (G) [(S): solid, (G): gas] to control the amount of carbon It is expected that the residual carbon content can be controlled to a greater extent than in the hydrogenation method.

However, in reality, the above direct oxidation reaction of carbon is a large exothermic reaction. Further, when a small amount is added to an inert gas such as N ₂ , this oxidation reaction is Because it is much more extreme according to the principle of Chatelier, it is difficult to control the amount of carbon evenly for many molded products, especially when degreasing many molded products, and the introduced gas is directly The risk of cracking due to excessive oxidation is always involved in the molded product at the point where it is hit. Also, Japanese Patent Application Laid-Open No. 6-19270
The degreasing technique in an oxygen-enriched air atmosphere disclosed in Japanese Patent Publication No. 6 has the same problem as described above.

In view of the above problems, the main object of the present invention is to significantly reduce the time required for the degreasing step by heating, vaporizing, evaporating, and thermally decomposing while ensuring the shape retention of the injection molded body during degreasing. It is an object of the present invention to provide a degreasing method which can be performed at low cost.

Another object of the present invention is to provide a degreasing method using a binder for powder injection molding which has excellent strength and toughness for improving product defects during injection molding and degreasing and is suitable for shortening the degreasing time. Is to provide.

Still another object of the present invention is to provide a degreased body, particularly by injection molding using metal powder, and a degreasing method for controlling the carbon content of a sintered body obtained by sintering after degreased. .

[0025]

In order to achieve the above-mentioned object, a degreasing method according to the present invention comprises the steps of mixing a thermoplastic binder and a powder and molding the mixture by injection molding. In the degreasing method for degreasing, the thermoplastic binder is composed of at least one or more easily vaporizable organic compounds and at least one or more thermoplastic resin components, and the degreasing step comprises the steps of: (a) depressurizing the molded body under a normal pressure or lower. By placing in an atmosphere and heating at a temperature lower than the melting point of the thermoplastic binder, a part of the thermoplastic binder is vaporized by 5% by weight or more of the total thermoplastic binder amount, and an organic compound or thermoplastic which is more easily vaporized By heating at a temperature lower than the melting point of the component having the higher melting point of the resin component, a part of the thermoplastic binder is completely thermoplastically heated. A first step of evaporating 10% by weight or more of the amount of the inder and a final temperature of 200 ° C. or less, and (b) the thermoplastic binder component in a gas atmosphere at an atmospheric pressure or more inert to the selected powder material. The method includes a second step of heating to a temperature equal to or higher than the highest melting point.

Here, the above-mentioned thermoplastic binder is usually composed of two or more components of an organic material, and when its melting point is measured by a thermal analysis method or the like, a temperature lower than the melting point or vitrification temperature of each component alone is measured. Alternatively, the melting point of the low melting point substance is observed. Therefore, this thermoplastic binder means any of these melting points. However, as a basic interpretation, it is appropriate to set the softening point (softening temperature) at which the molded body cannot withstand its own weight deformation. The idea is also appropriate when considering safety against

When the above-mentioned thermoplastic binder is mixed with the powder, in order to ensure fluidity during injection molding, the powder is uniformly coated and voids formed between the powders are completely removed. It is necessary to mix a binder amount larger than the filling amount, and a thermoplastic binder which usually reaches about 40 to 55% by weight of the injection-molded article is used with a target of 1.1 times the void space. Therefore, as described above, at the softening temperature of the molded body, that is, at a temperature equal to or lower than the melting point of the thermoplastic binder, not only the above-mentioned volatile organic compound is removed under reduced pressure, but also about 1% of the total binder amount.
By rapidly vaporizing and evaporating 0% or more, in the quantitative relationship between the powder constituting the molded body and the thermoplastic binder, the opportunity for direct contact between the powders is remarkably increased, The softening resistance of the molded article itself is remarkably increased, in other words, the fluidity is significantly impaired and the shape retention at the time of degreasing is secured, and at this point the thermoplastic binder at this point is released due to the easy-to-evaporate component. Because the component composition approaches the melting point or vitrification temperature of the thermoplastic resin that is difficult to vaporize and becomes higher, the softening resistance of the molded body is further increased, and the shape retention during degreasing is ensured. While continuously degreasing under reduced pressure to a temperature lower than the melting point of the thermoplastic resin which is a strength component of the thermoplastic binder, the organic compound which is easily vaporized is reduced to a total binder amount. 0% by weight or more to vaporize evaporated, and made more reliably complete shape retention ensured during degreasing in relation to the powder and thermoplastic binder amounts described above, and,
By ensuring this shape retention, the shape retention is ensured even at a temperature equal to or higher than the melting point of any of the binder components, and many gas escape paths are formed by preferentially removing the easily vaporizable compound components under reduced pressure. The combination of + and ++, which not only does not require pressurization of the atmosphere in the second step to form the above-mentioned many escape paths, but can further reduce the degreasing time in the second step It is characterized by the first step.

Even when the easily vaporizable component has a higher melting point than the thermoplastic resin component, the same can be considered for a temperature lower than the melting point of the thermoplastic binder and lower than the melting point of the easily vaporizable compound.

The final temperature in the first step is 200 ° C.
The reason is that when many organic materials are heated above 200 ° C., they tend to decompose into lower molecular compounds or polymers, and this tendency to decompose under reduced pressure according to Le Chatelier's law. In order to avoid the risk of cracking of the molded body due to decomposition and gasification from the molded body due to being accelerated by the heating of the above, when these gases are cooled outside the heating furnace, they are collected as solidified products, In many cases, large amounts of these solids are discharged and it is difficult to completely recover them, so troubles are likely to occur in vacuum pump equipment, etc., and the equipment required to avoid these troubles becomes expensive. To avoid.

Further, in the next second step, 20
In many cases, rapid decomposition of the binder at 0 ° C. is unavoidable, and at the final temperature of the first step, 20% by weight or more of the total binder amount is degreased at the final temperature of the first step. In addition, even when the above-mentioned sudden decomposition gas is generated, the degreasing is accelerated without generating a degreasing defect such as cracking or swelling in the molded body. Furthermore, the second
In the step, a gas atmosphere inert to the powder is pressurized to a pressure equal to or higher than normal pressure to suppress a sudden gas generation due to decomposition of the thermoplastic binder. By increasing the degreasing rate of the binder to 20% by weight or more of the total binder weight and sufficiently securing the passage of the decomposed gas, the above-described degreasing defect caused by the generation of the decomposed gas that occurs rapidly under an inert gas atmosphere at normal pressure. In addition, it is possible to shorten the degreasing time by increasing the decomposition rate thereafter.

In the present invention, further, in the third step, it is preferable that the degreasing by heating is accelerated in an atmosphere gas pressure state at normal pressure or lower to shorten the degreasing. Since the third step has a small effect of shortening the degreasing time, the third step can be omitted by raising the temperature to a temperature at which most of the thermoplastic binder is vaporized, decomposed and removed. .

In the present invention, N ₂ ,
In the second and third steps of the above-described degreasing method in which the remaining amount of the binder is vaporized, decomposed and removed by heating in an atmosphere of an inert gas such as Ar, the second and third steps are usually performed. When the heating temperature in the process is about 230 ° C. or higher, high molecular materials such as a lubricant and a polyamide resin material, which are the main components of the remaining binder, are often decomposed and reduced in molecular weight. However, at the same time, the residual carbon due to the carbonization reaction also increases, so the generation of new residual stress is also a risk factor for degreasing defects, and the risk of causing sintering density and sintering trouble during and after sintering As described above, in the present invention, the oxidizing property is controlled by mixing CO ₂ gas with the inert atmosphere gas in the second and third steps, thereby suppressing the above-described carbonization reaction. By It is preferred to control the residual carbon content of the sintered body after the carbon content and sintered brown body after fat.

The decomposition of a lubricant or a polyamide resin by heating in an inert N ₂ or Ar gas atmosphere is much slower than the decomposition in the presence of oxygen, and the decomposition molecular weight unit of the organic material is reduced. Since the gas is vaporized in a large state, the expansion during vaporization is reduced, and it is expected that the occurrence of degreasing defects can be reduced. Therefore, the atmosphere gas in the second step is mainly composed of an inert gas, and the CO ₂ gas is mixed. I decided that.

Furthermore, as a solution for suppressing the above-mentioned technical problems and the above-mentioned dehydrogenation reaction with respect to the above-mentioned direct oxygen addition method and for adjusting and controlling the amount of residual carbon due to the carbonization reaction, there are usually provided: Carbon dioxide gas [C (S) + CO ₂ (G) = 2CO () wherein the oxidation reaction with the residual carbon formed during the debinding of the molded article becomes an endothermic reaction even at a final heating temperature of about 600 ° C. G)], using Le Chatelier's principle to increase the oxidizing property by mixing it with an inert gas such as N ₂ gas to create a mild oxidizing atmosphere, thereby ensuring controllability of the amount of residual carbon. Further, cracks due to excessive oxidation and excessive carbonization of the binder are prevented. In addition, since the above-mentioned action of CO ₂ gas can be easily produced not only by adding a trace amount to an inert gas such as N ₂ but also by simply putting CO ₂ under reduced pressure, the third step is performed under reduced pressure. It is also applicable when implementing.

C (S) + CO ₂ (G) = 2CO (G); ΔG1 = 40800−41.7T C (S) + (１ ／) O ₂ (G) = CO (G); ΔG2 = −26700 −20.95T 350 ° C. (623K) ΔG1 = 14820, ΔG2 = −
39752

In order to solve this problem, in the present invention, as the above-mentioned means, an amide-based and / or amine-based water-soluble compound having a molecular weight of about 1000 or less and having no thermoplasticity and a polymerization degree of almost negligible is dissolved in a binder. In order to secure thermoplasticity as a binder and thermoplasticity, a polyamide resin having high strength and excellent heat resistance compatible with the water-soluble compound is used as a water-insoluble component of the binder. Furthermore, since the use of the water-soluble compound having a substantially negligible degree of polymerization eliminates low molecular weight due to thermal decomposition during heating and kneading with the powder, stable flowability of the kneaded material enables stable injection molding, In addition, it has made it possible to eliminate problems in the reusability of raw materials such as runners and spools.

In the degreasing method of the present invention, the organic compound which is easily vaporized is preferably an amide compound and / or an amine compound. Further, the thermoplastic resin is preferably a polyamide resin.

The first step in the above-described degreasing is performed at a high degree of vacuum (≦ 5 × 10 ^{−4 ton)} such as a diffusion pump.
By heating under reduced pressure of not more than vacuum degree (> 0.05 torr) normally achievable with a mechanical pump which does not require rr), 40 to 70% by weight of the binder contained as the main component of the binder for injection molding is contained. Evaporation and evaporation of part or all of the amide-based and / or amine-based compound components that are easy to vaporize, thereby preventing deformation in the degreasing step and quickly removing the remaining binder by heating in the second step of degreasing. The above-mentioned amide-based thermoplastic binder, which makes it possible to substantially shorten the effective degreasing time, which is substantially safer to degreasing defects, can be used. Utilization of powder injection molding technology for large and thick injection molded products by shortening the degreasing time by eliminating shape restrictions of compacts by utilizing the toughness of It can be expanded to.

In selecting a substance which is easily vaporized, first, a mechanical pump cannot stably achieve a high vacuum side of 0.05 torr or more, especially when a large number of injection molded articles are simultaneously degreased. When the degree of vacuum that can be guaranteed is approximately 0.1 torr, when the melting point exceeds 190 ° C., the fluidity of the binder tends to be impaired, and the injection moldability tends to be impaired. When the boiling point is lower than 175 ° C., the powder During the kneading with the binder or during the injection molding, it is selectively vaporized and evaporated from the binder, which tends to hinder the stability of the injection molding and the reuse of the return material, and the boiling point is higher than the melting point by 250 ° C. or more. For example, the rate of vaporization and evaporation in the first step of degreasing is slowed down, and the substance cannot sufficiently contribute to shortening of the debinding time. In consideration of the following conditions, the vapor pressure at the melting point should be 0.1 torr or more achieved by a mechanical pump, the melting point should be 50 ° C or more and 190 ° C or less, and the boiling point should be 175 ° C or more. so,
(Melting point + 250) ° C. or less, and the vapor pressure at the melting point is preferably 100 torr or less.

As described above, the substance which is easily vaporized in the present invention has a seemingly contradictory problem that its melting point is high while its boiling point is relatively low. The difference between the melting point and the boiling point of paraffin wax, which is listed as a substance that is easily vaporized, is about 400 ° C., which does not satisfy the conditions of the present invention. Therefore, in the present invention, the compound having an amide group or an amine group has a strong bond between the amide group and the amine group in the solid state, and as a result, the structural stability of the amide and the amine compound in the solid state. Although the melting point is increased by increasing the properties, the melt cannot maintain such structural stability.Focusing on the fact that a substance having a smaller molecular weight has a higher vapor pressure and a lower boiling point. 350 gr / mo
The above-mentioned problem has been solved by using amide and amine-based substances of 1 or less as components that are easily vaporized. Further, when selecting a substance that is easily vaporized, the boiling point is set at 20 in the degreasing operation.
0 ° C or higher and 350 ° C or lower, with a vapor pressure of 1.0 at the melting point.
More preferably, it is not less than torr and not more than 50 torr.

In addition, the addition of the amide-based or amine-based substance which is easily vaporized is performed by removing all the amide-based or amine-based substance which is easily vaporized contained in the binder in the first step of degreasing while heating under reduced pressure. Therefore, the minimum amount contained in the thermoplastic binder of the above-mentioned easily vaporizable compound is 2 because the purpose is to secure the shape retention during degreasing and to secure the passage of the decomposition gas generated in the second step.
0% by weight. Further, in order to achieve a remarkable improvement in the degreasing time, which is the gist of the present invention, it is considered preferable to use amide-based and amine-based substances which are easily vaporized in a range in which the binder is a main component. More specifically, from the viewpoint of the binder strength, it is preferable to use it in the range of 40 to 70% by weight.

When the amide-based substance and / or the amine-based substance are added as a substance which is easily vaporized in the thermoplastic binder in an amount of 40 to 70% by weight of the thermoplastic binder and used as a main component of the binder, These amide-based substances and / or amine-based substances are used in the amount of 40-7
It is necessary to ensure sufficient strength of the molded body even if it is contained at 0% by weight and to have sufficient releasability from the mold. By using a thermoplastic binder containing 25-60% by weight of a polyamide resin having excellent compatibility with an amide-based substance and / or an amine-based substance as a strength component as described in the official gazette, a mold after injection molding is used. Sufficient molded body strength is imparted to the mold release and take-out handling.

Further, when the components vaporized and evaporated in the above-mentioned vacuum or reduced-pressure atmosphere in the first step are cooled and solidified and recovered, the melting point of the amide-based and / or amine-based compounds which are easily vaporized is increased. The higher the temperature, the more reliably it can be recovered outside the degreasing furnace, and the more troublesome the vacuum pump system can be prevented. Specifically, the melting point is desirably 50 ° C. or higher. However, the melting point is 70 ° C. or more in consideration of the above-mentioned effects on the binder strength and the economics of the cooling ability of the cooler for cooling and solidifying the vaporized material outside the degreasing furnace, which can be implemented by simple means. Is preferred.

In the first step of the present invention, 0.1
When heating above 170 ° C. when heating and removing substances that are easily vaporized under a reduced pressure state of a vacuum degree of torr or less, a part of the lubricant used is also removed from the molded body in relation to the vapor pressure and the heating temperature. 230 ° C., which can be removed by evaporation
When heating is carried out beyond the temperature, the vaporized gas such as the amide-based, amine-based substances and lubricants decomposes into a gas of a low-molecular compound having a lower melting point from the principle of gas reaction under vacuum (Le Chatelier's principle). When the evaporative gas is cooled and solidified outside the furnace, it cannot be recovered with a simple cooling device, and the decomposed substances are deposited and recovered in the oil of a mechanical vacuum pump, which may cause troubles in vacuum equipment. There is. To avoid this problem, the first
It is considered necessary to keep the maximum temperature of the process at 230 ° C or less. However, when processing a large amount of compacts, when considering safety such as temperature distribution variation at each furnace position, lubricant etc. It is considered necessary to select a safe temperature at which the evaporative gas does not decompose. Normally, the maximum temperature in the first step is kept at 200 ° C. or lower, and the inert gas flow at normal pressure in the second step is carried out. It is preferable to switch to binder removal by heating.

At the same time, even when the melting point of the lubricant is 50 ° C. or less, even if the molecular weight is not reduced by decomposition, when the evaporative gas is cooled and recovered outside the furnace, it cannot be recovered by a simple cooling device. As described above, it is preferable that the melting point of a substance that is easily vaporized is higher than the minimum temperature of 70 ° C., as there is a risk of causing troubles in vacuum equipment due to precipitation and recovery in oil of a mechanical vacuum pump. It is.

Regarding amide substances and / or amine compounds, from the viewpoint of water-soluble compounds, JP-A-Hei 7
As disclosed in JP-A-305101, these compounds have almost the above-mentioned properties which are easily water-soluble and easily vaporize.
Almost applicable as an amine compound,
For these compounds, it is preferable to consider avoiding the risk of causing the above-described troubles in vacuum equipment.

Further, in the heat degreasing method of the present invention, since there is no restriction on water solubility, even a compound having low water solubility, or conversely, water solubility is remarkable,
It is preferable that the amide-based and amine-based compounds are optimally selected in accordance with the gist of the present invention, since the compound may have little effect on the vaporization of the present invention.

The amide compound is a substance having an amide group and can be classified into those having a benzene ring in the chemical structure and those not having the benzene ring. In particular, the specific examples described in JP-A-7-305101 as water-soluble amide compounds are within the scope of application from the viewpoint of the vapor pressure of the above-mentioned purpose of the present invention. Amide compounds in accordance with the gist of the invention include those having a benzene ring and those having no benzene ring, such as acetamide (water), propynamide (water), alloxanic acid (water), ethyl urethane, ethylene urea, and glycol amide. , Heptanoic acid amide, methylacetamide, methylacetylurea, trimethylurea, ethyl carbamate,
Nitrobenzamide (o), nitrobenzhydrazide (o), phenylsemicarbazide (1) (C ₆ H ₅ NH
CO ₂ C ₆ H ₅ ), phenylcarbamate (C
_{7 H 7 C 6 H 4 O} 2 CNH 2), Toruiruamido (o), Toruiruamido (p), acetaminophenol, Asetonafutarido, besides such aminobenzamide (o), for example, acrylamide (water), 3-acetylindole, 1-acetylsemicarbazide (water), N-
Acetyl-N'-phenylhydrazine, acetanilide (water), acetoloid (o), acetoloid (p), aminoacetophenone (p), diacetamide (water), isovaleramide (water), isobutylamide (water), imidazole ( Water), methyl carbamate, carbonohydrazide, salicylamide (water), diacetamide (water), N, N'-diethyl urea, 3,4-dihydro-2-quinolone, N, N'-dimethyl urea, N , N '
-Diethyl urea, dimethyl parabanic acid, camphor oxime, succinamic acid (water), succinimide (insoluble), (semicarbazyl (water)), (triacetamide), N- (1-naphthyl) acetamide, N- (2-
Naphthyl) acetamide, 2-pyridone, phthalimidine, benzamide, N-benzoyl-p-toluidine,
Benzamide oxime, 1-methylhydantoin, p-
Examples include methoxyacetanilide, octaneamide, butylamide (water), hexaneamide (water), valeramide (water), and stearamide (insoluble).
One type or a mixture of two or more types including those not having a benzene ring and those having a benzene ring is used as an amide-based compound which is easily vaporized.

The amine compound is a substance having an amino group. For example, N, a secondary amine compound obtained by dehydration copolymerization of about 1 mol of hexahydropiperazine and about 2 mol of acetic acid by a conventional method. N'-diacetylpiperazine. Further, from the specific examples described in JP-A-7-305101 as other water-soluble amine-based compounds, primary amine-based and secondary amine-based compounds according to the above-described vapor pressure viewpoint of the present invention are described. Are selected, 2-aminoquinoline, 3-aminoquinoline, diaminohydrazobenzene (p), hexamethylenediamine, naphthylamine (β), nitro-p-aminophenol (3), nitrophenylhydrazine (p ),
Nitrosoaniline (p), toluylenediamine, toluylenediamine (1; 2, 4), acetyl-p-phenylenediamine, aminopyridine (2) (α), diformylhydrazine, dipyridyl (4,4 ′), formyl Phenylhydrazine (β), glucose phenylhydrazone,
Examples include hydroxypyridine, methylamino-p-hydroxybenzoic acid (3), methylbenzimidazole (2), methylglyoxyallidine, nitrophenylhydrazine (p), phenylglycine (N), and triazole. Further, in consideration of the vaporization of the present invention,
For example, 4-aminoquinoline, 4-pyridylamine, nitroaniline (m), phenylenediamine (o), phenylenediamine (p), 2-acetylpyrrole, p-aminoacetophenone, m-aminophenol, indazole, indolizine, 3 , 4-xylidine, 1,4-cyclohexanediamine, 2,5-dimethylpiperazine (c
is, trans), 3,5-dimethylpiperazole,
Tyramine, triacetamine, 2,4,5-trimethylaniline, N-nitrodimethylamine, 2-phenylindole, benzo (h) quinoline, 3-methylindole, 2-methyl-1-phenyl-5-pyrazolone and the like No. These are used as an amine-based compound which is easy to vaporize by mixing one or more kinds including a primary amine-based and a secondary amine-based. Further, an amide compound and an amine compound may be used in combination.

As the raw materials used for the polyamide resin, those described in Japanese Patent Application Laid-Open No. 7-305101, which is a prior application, can be basically employed.

As the lubricant used in the binder for injection molding according to the present invention, all commonly used lubricants are effective, and this information is also disclosed in the prior application (JP-A-7-305101). It is as it is. Further, in consideration of the compatibility between the amide-based and / or amine-based compound used as a substance that is easily vaporized and the polyamide resin used as the strength component, the amide-based compound has an amide-based structure, and mainly has a linear structure. Aliphatic amide,
As disclosed in JP-A-7-305101, N-substituted fatty acid amides are preferred, and substituted ureas are also preferred as lubricants.

In the first step of the present invention, 0.1 to
The technical points to be considered only when heating and removing a substance which is easily vaporized under a reduced pressure state of a vacuum degree of rr or less are as described above, but the amount of the lubricant used in the binder in the range of 0 to 15% by weight is used. Some of them can be evaporated, decomposed and vaporized and removed from the compact in relation to the vapor pressure and the heating temperature.
If the heating is performed at a temperature higher than ° C., there is a risk of causing troubles in vacuum equipment due to the evaporation gas of the lubricant. For this reason, consideration must be given to the boiling point of the lubricant and its decomposability, but there is no problem particularly for the lubricant targeted in the present invention. Further, as described above, the melting point of the lubricant is 50
When the temperature is below ℃, even if the molecular weight is not reduced due to thermal decomposition, when evaporating gas is cooled and recovered outside the furnace, it cannot be recovered with a simple cooling device, but is deposited and recovered in the oil of a mechanical vacuum pump. Obviously, it is preferable that the melting point of the lubricant be higher than the preferable minimum temperature of 70 ° C. of the melting point of the substance which is easily vaporized, since there is the same danger of causing troubles in vacuum equipment.

According to the present invention, the amide-based and / or amine-based substances that are easily vaporized are vaporized and removed while heating ioite under vacuum or reduced pressure which can be easily achieved by a mechanical pump in the first step of debinding. As a result, the shape retention of the molded body at the time of binder removal is ensured, and the remaining binder component to be removed in the subsequent second step is rapidly removed from the molded body through the escape path created in the first step. As a result, sound degreasing such as swelling and crack generation is reliably performed, and the time required for debinding is significantly shortened as compared with the debinding time in an inert gas at normal pressure. Further, in the case where a thermoplastic binder capable of adding up to 40 to 70% by weight of an amide-based or amine-based substance which is easy to vaporize is used as a main component of the thermoplastic binder, is used in combination in a vacuum in the first step of debinding. The degreasing of the amide-based and amine-based substances under reduced pressure is mainly undertaken, and the number of escape paths when the remaining binder component is removed by heating in the second step is significantly increased. It is possible to further improve, and shortening of the degreasing time can also remarkably improve the shape retention and the occurrence of defects during the above-described degreasing, and is also revolutionary with respect to the degreasing time. It was possible to show a significant shortening effect.

The lubricant is mainly composed of fatty acid amide, N-
Substituted fatty acid amides and substituted ureas are used in the range of 0 to 15% by weight. However, in the present invention, it is basically described that they are treated in a different composition range from amide-based and amine-based substances which are easily vaporized. Many of these lubricants such as fatty acid amide lubricants are substantially vaporized and removed in the first step of degreasing in the same manner as the easily vaporizable amide-based substance of the present invention, so that more effective reduction of the degreasing time can be achieved. It is conceivable that this can be achieved.

The effect of the present invention can be expected from a low vacuum of 0.05 torr or less, which can be achieved by a mechanical pump, to a reduced pressure close to normal pressure in the first step of degreasing, but is more remarkable. In order to obtain the effect of the present invention, it is preferable to carry out in the range of 0.05 torr and the degree of vacuum at the melting point of the amide-based or amine-based substance which is easily vaporized, and specifically 0.1 to 100 torr.
It is preferable to carry out within the range.

The maximum heating temperature in the first step of degreasing can be up to the final temperature of degreasing in principle.
Since the decomposition of the thermoplastic binder starts by heating to a temperature range of 0 ° C or more, it is reduced in molecular weight in the vaporized decomposition gas and is discharged as a compound vapor having a low melting point outside the furnace to be cooled, solidified, or not liquefied and collected. Since it is conceivable that trouble is likely to occur due to being collected in the mechanical pump as it is, the maximum heating temperature in the first step of degreasing is preferably 200 ° C. or lower.

Further, it was found that the amide-based and amine-based substances which were easily vaporized and recovered in the first step of degreasing had a purity that could be reused as a binder component.

Further, by performing degreasing with a flow of inert gas such as N ₂ or Ar gas at normal pressure following the above-mentioned first step, troubles of the vacuum equipment caused by the above-mentioned binder decomposition gas can be prevented. In addition, cracking due to carbonization of the binder was prevented, and cracking was prevented due to the formation of oxides due to oxidation during degreasing when metal powder was used as the powder. In the second step of degreasing, a small amount of CO ₂ gas is mixed in a flow of inert gas such as N ₂ or Ar gas at normal pressure, so that a sintered metal powder is used. The carbon content in the sintered body can be adjusted and controlled in the degreasing step without occurrence of the cracks described above.

It is considered that the technique of the present invention can be applied not only to metal powder having a large specific gravity but also to ceramic powder such as alumina and SiC.

[0060]

EXAMPLES Next, examples and comparative examples of the degreasing method according to the present invention, the degreased body obtained by the method, and the sintered body will be described in detail.

[0061] (A) The polyamide resin as a binder composition binder intensity component, the polyamide resin component described in Japanese Patent Laid-Open No. 7-305101 (4) (; C ₃₆ diacid (Uniqema Corp. Pripol 101
3), azelaic acid, ethylenediamine, and xylidiamine are mixed in equimolar amounts, and the resulting mixture is dehydrated and copolymerized to obtain a polyamide resin having an average molecular weight of about 40,000), a polyamide resin component (1) ( _C44 diacid ( The average molecular weight obtained by mixing, dehydrating and copolycondensing 7 mol of azelain (C ₇ diacid), 7 mol of ethylenediamine, and 13 mol of xylylenediamine with Uniquema's Pripol 1004) is about 5%.
0000, a polyamide resin), a nylon 12 / ether elastomer copolymer (E40S3 manufactured by Daicel Corporation), and N, N'-ethylenebislauric amide (Slipax L, manufactured by Nippon Kasei Co., Ltd., melting point 151 ° C., boiling point) as a lubricant About 400 ° C., molecular weight 424), N, N′-ethylenebisstearic acid amide (manufactured by Nippon Kasei Co., Ltd .: Slipax E,
The melting point is 142 ° C., the boiling point is about 380 ° C., the molecular weight is 592). As the compatibilizer, N, N′-xylylenebisstearic acid amide (manufactured by Nippon Kasei Co., Ltd .: Slipax PXS, melting point 12)
3 ° C., boiling point about 390 ° C., molecular weight 668), amide-based and amine-based substances that are easily vaporized include 3-acetylindole (melting point: 188 ° C., boiling point: about 280 ° C., molecular weight: 159);
1-acetylsemicarbazide (melting point 165 ° C, boiling point about 3
00 ° C, molecular weight 117), N- (1-naphthyl) acetamide (melting point 160 ° C, boiling point 300-350 ° C, molecular weight 185), N, N'-diacetylpiperazine (melting point 14)
1 ° C, boiling point about 290 ° C, molecular weight 170), N- (2-naphthyl) acetamide (melting point 135 ° C, boiling point 300 to 3)
50 ° C., molecular weight 185), butyramide (melting point 117)
° C, boiling point 216 ° C, molecular weight 87), N-N'-diethyl urea (melting point 113 ° C, boiling point 263 ° C, molecular weight 116),
Stearamide (melting point 109 ° C, boiling point about 250 ° C,
Molecular weight 283), toluylenediamine (melting point 89 ° C., boiling point 265 ° C., molecular weight 122), acetamide (melting point 82)
Table 1, Table 2 using diacetamide (melting point 79 ° C, boiling point 216 ° C, molecular weight 101) and ethyl carbamate (melting point 48 ° C, boiling point 184 ° C, molecular weight 89). Were melt-mixed at the weight ratios shown in Table 1, and cooled and pulverized to obtain binders A to Q. The binder A is a conventionally known amide-based binder for comparison. Further, for comparison, conventionally known binders R, S, and T shown in Table 3 were prepared.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

(B) Production of Sintered Body by Thermal Decomposition Fine stainless steel powder (SU
(S430, average particle size: 10 microns) 100 parts of binder A was heated and kneaded at 150 ° C using 10.5 parts of binder A, cooled, and pulverized to obtain a raw material for injection molding.
The injection molding conditions were as follows: the injection temperature was 140 ° C. and the pressure was approximately 70.
The pressure was set to 0 kg / cm ² to obtain a molded body a as shown in FIG. This compact a has a thickness of about 3 mm and a weight of about 45 g.
r / pieces. FIG. 2 shows the form of the compact a when it is degreased. Under this condition, the weight of the small-diameter portion is applied to the base of the small-diameter portion and the large-diameter portion, and this portion is used for determining the degreasing deformation. In addition, this binder A by thermal decomposition
Has a melting point of 125 to 130 ° C.,
The relationship between the length of the compact a and the degreasing rate of the compact at that time was examined while changing the heating rate to 0 ° C. The result of this investigation is shown in FIG. In FIG. 3, circles indicate ±
It was determined that no deformation was found within the dimensional change range of 0.05 mm. The symbol Δ indicates elongation within 0.2 mm, and the symbol X indicates deformation of 0.2 mm or more and generation of microcracks. This is shown. From this result, 13
The boundary of the non-deformable degreasing rate at 0 ° C. is about 10% by weight, and the melting point of the polyamide resin alone is about 165 ° C. and about 15% by weight.
It is understood that it does not deform at more than 15% by weight.
From the above, it is not exactly known that no deformation occurs at a temperature of 200 ° C. or lower.
It was found that no deformation was observed even at 0 ° C.

The above stainless steel fine powder (100 parts) was heated and kneaded at 120 to 150 ° C. using 10.5 parts of each of binders A to Q and R to T, cooled and pulverized. Raw material. The injection molding conditions were such that the injection temperature was adjusted in the range of 120 to 175 ° C.
00 kg / cm ^2, and a molded body b as shown in FIG.
I got The weight of the molded body b is about 130 gr / piece and the maximum thickness is 11 mm, which is very large as a part to which the injection molding technique is applied.

Next, the maximum temperature in the first step of degreasing is set at 90 to 200 ° C. in accordance with the easily vaporized components in each binder, and the temperature is gradually lowered for 24 hours under a vacuum of about 0.2 torr and 2.0 torr. Then, in a heat circulating furnace in an N ₂ gas atmosphere, the wind speed was increased to 1.0 m / sec, and the temperature was increased to a final temperature of 350 ° C. in 8 hours, and the remaining binder was heated. The removed two levels of degreasing were performed. The entire degreasing treatment time is unified to be 32 hours, and the heating pattern is kept at a predetermined temperature at 155 ° C. as a temperature lower than the melting point of the polyamide resin by 10 ° C. lower than the melting point of the easily vaporized compound. Unified thinking. After observing deformation, cracks, and the like caused by the degreasing treatment, vacuum sintering was performed on the defatted good product at 1240 ° C. for 4 hours.

The experimental results of the thus obtained compact, degreased body and sintered body are as shown in Table 4. In the table, the mark x indicates large degreasing deformation and / or the occurrence of large cracks, and the mark Δ indicates that little deformation is observed but small cracks are observed.印 indicates a state in which the above-described degreasing defect is not recognized. Further, the-mark indicates that sintering was not performed because no good degreased product was obtained. In addition, although a sufficiently good injection molded article using the binders R, S, and T was not obtained, a degreasing treatment was performed to confirm the degreasing property. Was done.

[0069]

[Table 4]

Next, in order to confirm the component effect on shortening of the degreasing time, molding using binders A to F was carried out.
Change the time of the first step of degreasing in the range of 7 to 100 hours,
Further, a degreasing test was performed by selecting the second step of degreasing performed in the N ₂ gas atmosphere at 8 hours and 33 hours. The degree of vacuum in the first step of degreasing is about 0.2 torr, and the heating pattern in the middle is set to a pattern of 7 to 100 hours by proportionally reducing and enlarging the example of 22 hours shown in FIG. The maximum temperature was 170 ° C. The final temperature of the degreasing was set to 350 ° C., and the condition was set such that the temperature was increased 8 hours after the completion of the first step.

Table 5 shows the defect status of the degreased body after degreasing. Note that the crosses, triangles, and circles in the table are as described above.

[0072]

[Table 5]

Next, using binders A, D, S and T and carbonyl iron powder material (CS iron powder manufactured by BASF, average particle size: 5 μm), kneading and heating at 140 ° C. A molded product c having a shape as shown in FIG. 6 was molded by an injection molding machine under conditions of an injection pressure of 660 kg / cm ² . The following degreasing conditions are (1) 10 Nl / mi
In the heat circulating oven atmosphere of N ₂ gas is mixed with CO ₂ in the range of 0 to 0.5% by volume of n, up to a final temperature 350 ° C. The molded body c under the conditions of wind speed 1.0 m / sec 50
Level 1 degreasing over time, (2) The first step of degreasing shown in Table 4 was 24 hours, and the second step was performed under the same N ₂ -CO ₂ mixed gas atmosphere as in Level 1 above. It was set to the level 2 which was degreased over 8 hours. After degreasing, 1200 ° C
For 5 hours under vacuum sintering. The reason why the degreasing time is set long is to prevent the molded body using the binder A from being deformed during degreasing. Further, the molded body using the binder A was subjected to stress relieving heating at 110 ° C. × 4 hours in an N ₂ gas atmosphere in order to prevent the occurrence of internal cracks.

Since the binders S and T containing a large amount of paraffin wax and / or butyl phthalate are weak in strength, when the molded article c of FIG. 6 was manufactured by injection molding, all of the parts were partially broken. Since no good product was obtained, the subsequent degreasing treatment and sintering for controlling the residual carbon amount were stopped, and an experiment of controlling the residual carbon amount was performed using a molded body of the binders A and D having strong strength. .

No defects were found in the compacts A and D after degreasing in the above-mentioned CO ₂ gas mixed atmosphere. The results of carbon analysis after sintering are as shown in Table 6.

[0076]

[Table 6]

(C) Results of Test (1) Results of Degreasing Deformation Confirmation (See FIG. 3) The results of investigating the relationship between the amount of degreasing deformation, the degreasing temperature, and the degreasing rate using binder A were determined. At a melting point of 130 ° C. and a melting point of 155 ° C. of the polyamide resin, if the degreasing rate of each easily vaporizable component is approximately 10% by weight or 15% by weight or more, even in a severe package as shown in FIG. It can be seen that the degreasing deformation can be prevented, and as a condition for effectively utilizing the principle of vaporization and evaporation under reduced pressure in the first step of the degreasing method of the present invention, the compound component which is easily vaporized is 15% by weight or more, preferably 20% by weight. %. In addition, the heating temperature in the first step can be set to be higher than the melting point of the polyamide resin if a degreasing rate of 15% by weight or more is realized at the melting point of the polyamide resin, thereby further preventing degreasing deformation and shortening the degreasing time. It turned out to be more effective.

(2) Result of degreasing for 32 hours (see Table 4) Since binder Q among binders A to Q mainly contains low-melting point ethyl carbamate, the strength of the binder is reduced and the product of the injection molded article is reduced. Although a defect occurred, there was no molding defect in the molded body using another polyamide-based binder. In addition, since the conventionally known binders R, S, and T used for comparison were expected to have a remarkable lack of strength, the mold temperature was set to 20 ° C., and the cooling time in the mold was set to 2 minutes or more. Although it was set, almost no good molded product was obtained. However, in the degreasing test, in order to confirm the degreasing property of the binder, a defective molding was provided as a reference.

The degreasing property of each binder was examined from the shape retaining property of the molded article after degreasing and the degree of crack generation.
According to the results of orr, remarkable degreasing deformation, foaming, and generation of large cracks were observed in the molded products of the binders A, E, and F containing 30% by weight or less of the amide-based compound or the amine-based compound which is easily vaporized. Significant deformation was also observed in the molded products of the binders R, S and T, but good results were obtained in other molded products containing the above compound at 50% by weight. When the first step of degreasing was performed at 2 torr, a sound degreased body was obtained in a binder having a high vapor pressure at a melting point, and deformation and cracks were observed in a binder having a low vapor pressure. A remarkable effect was also observed in the degree of vacuum by the rotary pump.

In the first step of degreasing, the solidified cooling and recovery of the removed binder was carried out in a pipe outside the furnace at a thickness of 2 mm.
Stainless steel inner diameter is about 12cm, length is about 3
A simple operation was carried out by placing a 0 cm bellows in front of the roots pump.
0% recovery was obtained, and no trouble was observed in the vacuum pump system. However, when the binder Q was degreased, cloudiness was generated in the vacuum oil in the roots pump and the rotary pump, and it was found that a recovery device with higher cooling performance was required. Furthermore, when the maximum temperature of the first step of degreasing was raised to 250 ° C. for the molded products of the binders A to F, a large amount of white solidified material was precipitated in the roots pump, causing the roots pump to lock. However, it was found that a recovery device with higher cooling performance was required in this case as well. In addition, the deposit in the pump in this case is determined to be mainly a thermally decomposed product of N, N'-diacetylpiperazine and other lubricants and compatibilizers described in Table 1 based on the vapor pressure and the result of the thermal decomposition investigation. Therefore, in order to avoid the above-described trouble, the maximum temperature in the first step of degreasing is set to 230 ° C. or less, preferably 200 ° C.
I think it is better to keep the temperature below ℃. In addition, even when selecting amide-based or amine-based compounds that are easy to be vaporized, the temperature of 70 ° C.
It is preferable to select a compound having the above melting point. The sound degreased body was a sound sintered body in the next sintering step, and a sufficient sintered density was obtained.

(3) Confirmation of degreasing time and shortening effect (Table 5)
FIG. 6 shows the effect of shortening the degreasing time by setting the degree of vacuum in the first step of degreasing to 0.1 to 0.2 torr and the maximum temperature to 170 ° C. using binders A to F and SUS430 steel fine powder. As a result of investigating molded products having a thickness of 11 mm, the total degreasing time for binders B and C was 22 hours,
A sound degreased body can be obtained.
A healthy degreased body was obtained in 2 hours. However, N, N'-
Binder A containing 30% by weight of diacetylpiperazine,
In the case of E, a healthy degreased body can be obtained only after 67 hours, and in the case of the binder F containing 15% by weight, 1% is obtained.
It turns out that a healthy degreased body cannot be obtained even for 33 hours.
From this, it can be seen that in the binder mainly composed of N, N'-diacetylpiperazine, which is easily vaporized, the effect of shortening the degreasing time is embodied more than the effect inversely proportional to the simple addition amount. In order to exhibit the effect of shortening the degreasing time, it is preferable that the addition amount range of the easily vaporizable compound is 40% by weight or more.

(4) Adjustment of Residual Carbon Amount Using CO ₂ Gas (See Table 6) In this experiment, the whole degreasing step was performed in N ₂ gas at normal pressure, and the first step in the initial stage of degreasing was performed. after subjected to heat in a vacuum at a result of investigating the adjustment method of the residual carbon content due to contamination of the CO ₂ gas in the degreasing method of two levels of heating in N ₂ gas at atmospheric pressure, in any of the levels, CO ₂
It was found that remarkable carbon controllability was obtained even at a gas mixing ratio of 0.5% by volume. Furthermore, it was found that the degreased body after the completion of degreasing was sound without degreasing defects such as cracks.

Considering the addition amount of CO ₂ gas, when CO ₂ is used in place of N ₂ gas, considering that the degreasing end temperature is usually about 500 ° C., Since the reaction between CO ₂ and CO ₂ is an endothermic reaction even at this temperature and has a protective atmosphere effect,
The upper limit of the mixing amount of the CO ₂ gas is 100% by volume, that is, the degreasing method in the CO ₂ gas atmosphere is considered to contribute to the solution of the above-described problem in the degreasing in the air and enriched oxygen atmosphere.

The simplest method of adding CO ₂ is to add a single gas. However, for example, the addition of a substance that decomposes by heating and decomposing CO ₂ gas, such as alcohol, or CO, such as RX gas, is used. A method of adding in the state of a mixed gas with H ₂ is considered.

[Brief description of the drawings]

FIG. 1 is a sectional view of a molded body a.

FIG. 2 is a view showing the appearance of a molded article a when degreased.

FIG. 3 is a graph showing a relationship among a degreasing rate, a heating temperature, and a degreasing deformation in a molded body a.

FIG. 4 is a sectional view of a molded body b.

FIG. 5 is a graph showing an example of a heating pattern for a total degreasing time of 22 hours.

FIG. 6 is a view showing a molded body c.

Continued on the front page (72) Inventor Masato Miyake 61-6 Ao Nishi, Arai-nishi, Terai-cho, Nomi-gun, Ishikawa Prefecture (72) Inventor Katsuyoshi Saito 36 Shimogamo-Kifune-cho, Sakyo-ku, Kyoto-shi 140-3 Kubojima, Kumagaya-shi, Saitama Amtech Research Institute

Claims (20)

[Claims] 1. A degreasing method for degreasing the thermoplastic binder from a molded product obtained by mixing a thermoplastic binder and a powder and performing injection molding, wherein the thermoplastic binder comprises at least one or more volatile organic compounds. The degreasing step comprises at least one or more thermoplastic resin components, and the degreasing step comprises: (a) placing the molded body in a reduced-pressure atmosphere at normal pressure or lower and heating the molded body at a temperature lower than the melting point of the thermoplastic binder; 5% by weight of the total amount of thermoplastic binder
By vaporizing above, the organic compound or the thermoplastic resin component which is more easily vaporized is heated at a temperature lower than the melting point of the component having the higher melting point, so that part of the thermoplastic binder is 10% by weight of the total thermoplastic binder amount. % In which the final temperature is 200 ° C. or less, and (b) a temperature not lower than the highest melting point of the thermoplastic binder component in a gas atmosphere not lower than normal pressure which is inert to the selected powder material. A degreasing method comprising a second step of heating to a maximum temperature. 2. In the second step, the amount of residual carbon in the degreased body obtained and the sintered body obtained by sintering after degreasing is adjusted by mixing CO ₂ gas into the inert gas. The degreasing method according to claim 1. 3. The method according to claim 1, further comprising a third step of reducing the atmospheric gas pressure to a value equal to or lower than normal pressure and increasing the ambient temperature to a temperature at which at least most of the thermoplastic binder is removed by vaporization and thermal decomposition. Claim 1
3. The degreasing method according to 1. 4. In the second step and the third step,
CO in inert gas _TwoBy mixing gas,
Degreased body and sintered body obtained by sintering after degreasing
The degreasing method according to claim 3, wherein the amount of residual carbon is adjusted. 5. The degreasing method according to claim 1, wherein the organic compound that easily vaporizes is an amide-based and / or amine-based compound. 6. The amide-based compound is a substance having an amide group, and the amine-based compound is a substance having an amine group, and the amide-based substance and the amine-based substance have a melting point of 50 ° C. or more and 190 ° C. or less, And a boiling point of 17
5 ° C or higher, and the vapor pressure at the melting point is 0.1 to 100 t
6. The degreasing method according to claim 5, wherein one or a mixture of two or more of those within the range of orr is used. 7. The degreasing method according to claim 1, wherein the thermoplastic resin is a polyamide resin. 8. The thermoplastic polyamide resin has a phase in which the number of carbon atoms sandwiched between amide groups is 8 or more, relative to a polyamide resin raw material in which the number of carbon atoms sandwiched between amide groups is 8 or more. 8. The degreasing method according to claim 7, wherein one or two or more kinds of polyamide resins obtained by mixing aromatic bisamides as a solvent to approximately equal weight% are mixed. 9. The thermoplastic polyamide resin according to claim 7, wherein one or two or more kinds of polyamide resin raw materials having an average of 10 or more carbon atoms between amide groups are mixed. Degreasing method. 10. The polyamide resin raw material comprises C ₃₆ diacid, C ₄₄ diacid, or a mixture of C ₃₆ diacid and C ₄₄ diacid, an aliphatic dicarboxylic acid having 6 to 10 carbon atoms, The degreasing method according to claim 8 or 9, which is obtained by copolycondensing a rangeamine with ethylenediamine and / or hexamethylenediamine. 11. The degreasing method according to claim 10, wherein the polyamide resin raw material has an average molecular weight of 20,000 or more. 12. The degreasing method according to claim 8, wherein the polyamide resin raw material mainly comprises nylon 11 and nylon 12. 13. The polyamide resin raw material having an average molecular weight of 13,000 or more.
3. The degreasing method according to 2. 14. The composition according to claim 5, comprising 20 to 80% by weight of the amide-based and / or amine-based compound which is easily vaporized and 20 to 65% by weight of a thermoplastic polyamide resin.
14. The degreasing method according to any one of claims 13 to 13. 15. The thermoplastic binder further comprises:
The degreasing method according to claim 14, wherein a lubricant mainly composed of 15% by weight or less of fatty acid amide is mixed. 16. The method according to claim 1, wherein the organic compound which is easily vaporized is vaporized in a reduced pressure state or a vacuum state lower than normal pressure, and then cooled and solidified outside the furnace to be recovered. Degreasing method. 17. The degreasing method according to claim 1, wherein the thermoplastic binder component vaporized on the low temperature side in the second step is cooled, solidified and liquefied outside the furnace, and collected. 18. The method according to claim 1, wherein vaporized gas and / or decomposed gas generated at the time of degreasing are introduced together with the heated air into another furnace installed outside the furnace and heated to 800 ° C. or higher, and burned and decomposed. A degreasing method according to any of the claims. 19. A degreased body obtained by degreasing according to the degreasing method according to claim 1. Description: 20. A sintered body obtained by sintering after degreasing by the degreasing method according to any one of claims 1 to 18.