JPH02275748A - Molding method for powder injection-molding component - Google Patents

Abstract

PURPOSE:To shorten removing time of a binder by irradiating light to a molded article consisting of a mixed body for sintering powder of metal and ceramics and an organic binder containing a prescribed light-degradative resin to degrade the resin. CONSTITUTION:Sintering powder consisting of metal powder and/or ceramic powder is prepared. On the other hand, an organic binder containing a light- degradative resin expressed by the general formula (R1 and R2 are atom or group other than H; (n) is integer of >=1) is prepared. A mixture of the binder and the abovementioned sintering powder is molded to provided a molded article having desired shape, which is then irradiated with light and the abovementioned organic binder is removed by degradation due to the light and heat.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for molding powder injection molded parts, and more specifically, the present invention relates to a method for molding powder injection molded parts. A powder injection molded part characterized in that the components are mixed together, injection molded into a desired shape, the organic binder is photolytically modified, the organic binder is efficiently removed from the molded body by thermal decomposition, and the product is fired. This relates to a molding method.

[Conventional technology]

Recently, various sintered parts using metal powder or ceramic powder have been produced from general industrial materials to precision mechanical parts, electronic parts,
It has become widely used in fields such as electrical parts and automobile parts. Along with this, considerably stricter requirements have been placed on the dimensional accuracy, physical properties, shape, etc. of these parts.

The currently widely used method of structuring powder for molding using a spray dryer and then manufacturing molded products for sintering using a rubber press not only has the problem of extremely complicated processes and extremely low yields. However, it has the disadvantage that a molded product having a complicated shape cannot be obtained.

In order to deal with these demands and problems, an appropriate amount of resin is added to metal powder or ceramic powder to give it thermoplasticity, which is then molded by injection molding, and then the resin contained in this molded product is molded. Several methods have been proposed and implemented to obtain desired metal or ceramic powder injection-molded parts by performing main firing after thermal decomposition and removal of
No. 510. JP-A-55-113511) 6 The important points in these methods are that during injection molding,
In addition to ensuring that the molded product does not crack, it is also important to remove the organic binder, which is a resin, from the resulting molded product in a short time without causing cracks, blisters, or deformation.

[Problem to be solved by the invention]

Conventionally, several thermosetting resins and thermoplastic resins have been studied as these organic binders, but good results have not been obtained with thermosetting resins in terms of fluidity and moldability. On the other hand, as thermoplastic resins, polystyrene resins, polyethylene resins, and atactic polypropylene resins are mainstream, and several types of resins have been proposed, and some of them have been put into practice. In order to remove these organic binders from the molded product, in any case, only heating means are used, and the temperature rise rate per unit time is kept small, and the molded product cracks over several tens to hundreds of hours. Great care was taken to avoid any swelling or deformation.

However, in spite of this, cracks and blisters occur in the molded product relatively frequently in this conventional method, and it cannot be said that this method is necessarily industrially satisfactory.

In order to improve these problems, a method has been proposed and implemented in which a part of the organic binder is removed from the molded body by solvent extraction, and the remaining organic binder is decomposed and removed by heating means (Japanese Patent Application Laid-Open No. 57-1991). -26105 and Japanese Patent Publication No. 59-27743).

However, as shown in Japanese Patent Publication No. 62-33282, when this method of removing binder from molded bodies by solvent extraction is used, in addition to the problem of cracks occurring in the molded bodies, it is also said to have an adverse effect on the health of workers. There are working environment problems, which have the drawback of being difficult and expensive to eliminate. Furthermore,
It has the disadvantage that it is expensive to recover and recirculate the solvent used for extracting the organic binder.

In addition, in the conventional method, in order to prevent cracking, blistering, or deformation of the molded product and to shorten the removal time of the organic binder, components with high sublimability, volatility, and solubility are used. Improvements are being made by mixing etc. into an organic binder. However, the use of such components with high sublimability, volatility, and solubility has the disadvantage of causing problems in the storage stability of the mixture consisting of metal powder and/or ceramic powder and organic binder component. had.

[Means to solve the problem]

In view of this, the present inventor avoided the use of solvent extraction and the use of sublimable components, volatile components, soluble components, etc.
The organic binder can be efficiently removed from the molded product without causing any deterioration of the working environment, without causing cracks, blisters, or deformation in the molded product, and the organic binder can be removed from the molded product with metal powder and/or ceramic powder. With the aim of finding a molding method for powder injection molded parts that does not have any problems with the storage stability of a homogeneous mixture consisting of an organic binder component, as a result of intensive research and consideration, we have found that metal powder and/or ceramic powder, After uniformly mixing an organic binder component containing at least one type of photodegradable resin and injection molding it into a desired shape, photolytic modification of the organic binder is combined with conventional thermal decomposition removal. It has been found that the above object can be achieved by efficiently removing the organic binder from the molded body and firing it.

Examples of the metal powder used in the present invention include metal silicon powder, iron or iron alloy powder such as high-speed steel powder, superalloy powder such as titanium-based, tungsten-based, and boron-based powder, and various metal powders such as magnetic material powder. There are also ceramic powders such as silicon nitride powder, silicon carbide powder, alumina powder,
There are various ceramic powders such as zirconia powder and sialon powder (silicon nitride-alumina type). Further, it can be used as a cermet powder that is a mixture of metal powder and ceramic powder, and if necessary, one type or two or more types of these various metal powders and ceramic powder can also be mixed and used as appropriate.

Further, among metal fibers and ceramic fibers, short fibers that can be injection molded by mixing with an organic binder are also included within the scope of the present invention.

In addition to the raw material powder, sintering aids, molding aids, other aids for improving physical properties, etc. can be added to these powders in advance as appropriate.

The photodegradable resin used in the present invention is one represented by the general formula (wherein R1 and R2 are atoms other than H (. represents a group, and n represents an integer of 1 or more). Preferred and more preferred are methacrylate resins in which either R or R2 is a methyl group.Specifically, polymethyl methacrylate, polyethyl methacrylate, poly n-propyl methacrylate, polypropylene Methacrylate, poly n-butyl methacrylate, polybutyl methacrylate, poly t-butyl methacrylate, poly 5ec-butyl methacrylate, polycyclohexyl methacrylate, polybenzyl methacrylate, polyethylhexyl methacrylate,
There are various methacrylate resins such as polyphenyl methacrylate, poly neo-pentyl methacrylate, and poly t-pentyl methacrylate. In addition, methyl methacrylate-methacrylic acid copolymer, methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-
Inbutylene copolymer, methyl methacrylate-1-propyl methacrylate copolymer, methyl methacrylate-methyl-a-chloroacrylate copolymer, n-butyl methacrylate-cyclohexyl methacrylate copolymer, n-hexyl methacrylate-methyl -a-chloroacrylate copolymer, methyl methacrylate)-n-
Copolymers such as hexyl methacrylate-methyl-a-chloroacrylate copolymer are also included in the invention. These photodegradable resins can be used alone as an organic binder, but in order to improve their affinity with metal powders and ceramic powders and improve their fluidity during molding, it is necessary to use other known organic binders or It can also be combined with melting point substances. At this time, the content of the photodegradable resin in the organic binder component is preferably 10% by weight or more, more preferably 30% by weight or more.

In general, organic polymer compounds are roughly divided into decomposition types and crosslinked types upon irradiation with light (radiation). Whether an organic polymer compound becomes a decomposed type or a crosslinked type upon irradiation with light (radiation) is determined by the activation energy of the chemical reaction in the excited state induced by irradiation with light (radiation). This has been confirmed both theoretically and experimentally. Also, as a rule of thumb, although there are some exceptions, Millar-W
According to the all-Charlsby rule, the general formula % formula % (in the formula, R, R, are side chains, H is not considered as a side chain, but CI and F are considered as side chains. Also, n is (indicates an integer of 1 or more) is known to be a crosslinked type.

In the present invention, the organic polymer compounds represented by the general formulas (1) and (2), specifically polypropylene and polyethylene, cannot achieve the object of the present invention and, on the contrary, have an adverse effect. In other words, Tokuko Sho 59-27743
The object of the present invention cannot be achieved with an organic polymer compound that simply has a methyl group in a side chain in the molecule, as shown in the above publication. That is, in order to achieve the object of the present invention, a compound represented by the general formula % (wherein R1 and R2 represent atoms or groups other than H, and n represents an integer of 1 or more) This can only be achieved by using an organic polymer compound that becomes decomposable upon irradiation with light as a photodegradable resin.

Mixing of the metal powder and/or ceramic powder and the organic binder in the present invention is performed by a known method. Specifically, metal powder and/or ceramic powder, photodegradable resin and/or other known organic binder are melt-mixed in a pressure kneader to efficiently form a homogeneous mixture. can,
Mixtures and molded bodies having constant moldability, constant weight, and density can be obtained.

The homogeneous mixture in the present invention is molded by a known method using an injection molding machine to obtain a molded product in a desired shape. At this time, by using a homogeneous mixture, stable molding can be performed.

The most important feature of the present invention is that ultraviolet rays, electron beams, or
The purpose of this method is to photodecompose and modify an organic binder having a certain molecular weight on the surface of a molded article by irradiating it with radiation. What is important in the step of removing the organic binder is to gradually remove the organic binder component from the surface of the molded article as a decomposition gas, and to allow the decomposition to progress sequentially into the interior.

It is very difficult to control the progress of such decomposition using a method that only uses heating means.

In order to solve this problem, various types and combinations of organic binders have been investigated, but nothing effective has yet been found. According to the method of the present invention, it is possible to easily control the decomposition and removal of the organic binder component from the surface of the molded body to the inside of the molded body. In other words, when the surface of the molded object after molding is irradiated with ultraviolet rays, electron beams, or X-rays, these doses are absorbed or scattered on the irradiated surface.
It decreases as it progresses inside the molded body.

That is, photodecomposition modification inevitably occurs from the photodegradable resin on the surface of the molded article, and the photodecomposition modification progresses sequentially into the interior of the molded article. Depending on the type of photodegradable resin used, the progress of this photodegradable modification may be caused by external light energy or by external light energy.
There are things that occur in a chain due to radical depolymerization,
There are cases where both occur simultaneously. The organic binder that has been photodecomposed and modified in this way is gasified or reduced in molecular weight, and is removed by volatilization from the surface of the molded product, or remains as a residue on the surface layer of the molded product. At this time, the generated decomposition gas is sequentially volatilized and removed from the surface of the molded article, so that no cracks or blisters occur in the molded article.

In the present invention, at least one type of photodegradation accelerator may be added to the organic binder mixture in order to more efficiently perform photodegradable modification of the photodegradable resin. Specific examples of the photodegradation accelerator include α-methylstyrene, 2-mercaptoethanol, ethylbenzene, methyl p-hydroxybenzony), p-methoxybenzoic acid, and the like.

The organic binder removal step in the present invention is carried out using heating means, and by irradiating the surface of the molded object with ultraviolet rays, electron beams, or By photolytically modifying the organic binder having the following properties, it becomes possible to remove the organic binder more efficiently by thermal decomposition.

This is because, through this photolytic modification, the organic binder is volatilized and removed from the surface of the molded product, and micropores are formed in the surface layer of the molded product, which then become micropassages for gasified components generated by thermal decomposition. . Further, since the low molecular weight components of the organic binder are present as a residue in the surface layer of the molded body, these low molecular weight components having a low thermal decomposition temperature can be thermally decomposed in order. In other words, since the microbaths formed and produced by photodecomposition modification and the low molecular weight component of the organic binder are present from the inside of the molded product to the surface, the remaining organic binder can be efficiently removed by thermal decomposition in a short time. However, cracks and blisters caused by the generated decomposed gas,
No deformation occurs in the molded body. In the present invention, by performing these photodecomposition modification and thermal decomposition removal at the same time, it becomes possible to remove the organic binder more efficiently. In addition, before performing these photolytic modification and thermal decomposition removal at the same time,
By heating and melting and removing the low melting point substances in the organic binder component in advance, micropores are actively formed in the surface layer of the molded product, thereby efficiently photodegrading the photodegradable resin inside the molded product. be able to. The simultaneous use of photolytic modification and thermal decomposition removal in the present invention, and the heating and melting removal of low melting point substances before photolytic modification and thermal decomposition removal, are particularly effective for thick powder injection molded parts. In the present invention, the removal rate in the organic binder removal step is 7
0% to 90% is preferable, more preferably 80% to
It is 90%.

The firing in the present invention is carried out by 10% to 3% during firing of the powder raw material.
To completely remove 0% residual organic binder,
The desired shape and dimensions can be obtained by heating the organic binder to be heated to a predetermined decomposition temperature or higher, or by holding the organic binder at a predetermined decomposition temperature or higher for a predetermined period of time, and then performing sintering at a predetermined temperature in a predetermined atmosphere depending on the powder raw material. It is possible to obtain defect-free powder injection molded parts with , and density.

〔Example〕

The effects of the present invention will be shown below with reference to Examples, but the present invention is not limited thereto.

(Example 1) To 92.6% by weight of carbonyl iron powder, 2.8% by weight of methyl methacrylate-imbutylene copolymer, which is a photodegradable resin, 2.4% by weight of ethylene-vinyl acetate copolymer, 2.2% by weight of paraffin wax was thoroughly melted and mixed at 130° C. and 4 Kgf/C111 using a pressurized Niegu, and then the mixture was pelletized. The pellets are molded into a heating cylinder at a temperature of 150°C using an injection molding machine.
1 injection pressure 1t/Cr? I, 3mm at mold temperature 40℃
A plate-shaped molded body measuring 12 mm x 60 mm was obtained. This molded body was irradiated with deep ultraviolet rays of 190 nm to 240 nm for 10 minutes to perform photodecomposition modification of the organic binder. The far ultraviolet light intensity was set at 50 mW/cnt. Thereafter, this molded body was heated from room temperature to 200°C for 2 hours, and then heated for 2 hours.
Heated from 00℃ to 350℃ in 3 hours, and further heated to 350℃.
The remaining organic binder was thermally decomposed and removed by heating from 0° C. to 420° C. over 2 hours. The removal rate of this organic binder was 88%. When the surface of the molded article subjected to the organic binder removal treatment was observed, no cracks, blisters, or deformations were observed. Next, this molded body was fired in a hydrogen atmosphere from room temperature to 450°C over 1 hour, held at that temperature for 1 hour, and after completely removing 12% of the remaining organic binder, the temperature was increased to 450°C. After heating from 1,450° C. to 1,450° C. for 3 hours, the temperature was maintained for 2 hours to obtain a sintered body. In the obtained sintered body, no cranks, bulges, or deformations were observed.

(Example 2) Based on 92.6% by weight of carbonyl iron powder, 2.8% by weight of methyl methacrylate-imbutylene copolymer, which is a photodegradable resin, 2.1% by weight of ethylene-vinyl acetate copolymer, Using 2.2% by weight of paraffin wax and 0.3% by weight of α-methylstyrene as a photodegradation accelerator, far ultraviolet rays were irradiated for 4 minutes to perform photodecomposition modification. Others are
Everything was carried out in the same manner as in Example 1. The removal rate of the organic binder at this time was 88%, and no cranks, bulges, or deformations were observed in the obtained molded body. No swelling or deformation was observed.

(Example 3) Based on 76.4% by weight of silicon nitride powder, 10.6% by weight of methyl methacrylate-isobutylene copolymer, 5.1% by weight of ethylene-vinyl acetate copolymer, and 6.9% by weight of paraffin wax. was used. The melt mixing, molding, photodecomposition modification, and organic binder removal method were performed in the same manner as in Example 1. The removal rate of this organic binder is 85%
Met. This molded body was fired in the air at a heating rate of 200°C/hour from room temperature to 1750°C to remove the remaining organic binder and sinter the molded body. No cracks, bulges, or deformations were observed in the obtained sintered body.

(Example 4) 3.4% by weight of poly n-butyl methacrylate, which is a photodegradable resin, based on 92.6% by weight of carbonyl iron powder,
Using a pressure kneader, 1.8% by weight of ethylene-vinyl acetate copolymer and 2.2% by weight of paraffin wax were mixed for 12% by weight.
0℃, 4Kg f should be thoroughly melted and mixed, and then,
The mixture was pelletized.

The pellets are molded into a heating cylinder at a temperature of 140℃ using an injection molding machine.
, injection pressure 1, mold temperature 28℃, 3mm x 12
A plate-shaped molded product measuring 60 mm x 60 mm was obtained. This molded body was irradiated with an electron beam for 10 seconds to photodecompose the organic binder. This electron beam irradiation was performed at an accelerating voltage of 20 KV and
A dose of μC/cf was given.

Removal of the organic binder and firing were performed in the same manner as in Example 1. The removal rate of organic binder is 90%.
Met. No cracks, blisters, or deformations were observed in the obtained organic binder-removed body and sintered body.

(Example 5) To 92.6% by weight of carbonyl iron powder, 3.3% by weight of methyl methacrylate-1-propyl methacrylate copolymer, which is a photodegradable resin, and 1.9% by weight of ethylene-vinyl acetate copolymer. %, paraffin wax 2.2% by weight
Using a pressure kneader, 150℃, 4Kgf/cr?
I was thoroughly melt mixed and the mixture was then pelletized. The pellets were molded using an injection molding machine at a heating cylinder temperature of 180°C, an injection pressure of 1t/cnl, and a mold temperature of 45°C.
A plate-shaped molded product measuring 3 mm x 12 mm x 60 mm was obtained at ℃. This molded body has a strength of 5 at 190 nm to 240 nm.
The organic binder was removed by thermal decomposition while being irradiated with deep ultraviolet rays of 0 mW/cml to perform photodecomposition modification of the organic binder. Thermal decomposition removal of the organic binder from this molded body was carried out by heating from room temperature to 200°C for 2 hours, then heating at 200°C.
Heated from °C to 350 °C in 3 hours, then further heated to 350 °C.
This was carried out by increasing the temperature from °C to 420 °C in 2 hours. The removal rate of this organic binder was 88%. The surface of the molded body from which the organic binder had been removed was observed, and no cracks, blisters, or deformations were observed.Next, this molded body was fired in the same manner as in Example 1. The obtained organic binder-removed body and sintered body showed no cranks, bulges, or deformations at all.

(Example 6) In Example 5, the thermal decomposition removal of the organic inder from the molded body was carried out by heating from room temperature to 200°C in 2 hours, and then from 200°C to 350°C in 1.5 hours. This was carried out by heating to a high temperature, and then increasing the temperature from 350°C to 420°C in 1 hour, and otherwise carried out in the same manner as in Example 5.The removal rate of this organic binder was 86%. No cracks, blisters, or deformations were observed in the obtained organic binder-removed body and sintered body.

(Example 7) In Example 6, paraffin wax with a low melting point was used as the paraffin wax, and heat extraction removal was performed at a predetermined temperature for 1 hour before photolysis modification and heat decomposition removal. In this example, 8mmX 12n+n+X
A 60 mm plate-shaped molded body was molded.

Everything else was carried out in the same manner as in Example 6. Note that the removal rate of the organic binder was 87%. No cracks, blisters, or deformations were observed in the obtained organic binder-removed body and sintered body.

(Comparative Example 1) In Example 3, the organic binder was not photolytically modified, but otherwise everything was carried out in the same manner as in Example 3. Cracks and blisters were observed in the obtained organic binder-removed body.

(Comparative Example 2) In Example 5, the organic binder was not photolytically modified, but otherwise everything was carried out in the same manner as in Example 5. Cracks and blisters were observed in the obtained organic binder-removed body.

(Comparative Example 3) In Example 3, the organic binder was not photolytically modified, and the organic binder was removed by thermal decomposition from room temperature to 100%
℃ for 1 hour, then heated from 100℃ to 42000℃ for 15 hours, kept at 420℃ for 1 hour,
It took a long time.

Everything else was carried out in the same manner as in Example 3. No cracks, blisters, or deformations were observed in the obtained organic binder-removed body and sintered body.

However, the processing time is long and no improvement in productivity can be expected.

(Comparative Example 4) Polypropylene was used in place of the photodegradable resin methyl methacrylate-isobutylene copolymer in all the experiments. All other operations were carried out in the same manner as in Example 1. The molded product obtained by injection molding had severe molding shrinkage, and cracks were observed on the surface of the molded product. Moreover, cracks and blisters were also observed in the obtained organic binder-removed body. Therefore, it was determined that the use of polypropylene as a photodegradable resin is problematic.

[Effects of the Invention] From the results of the Examples and Comparative Examples above, it is possible to uniformly mix the metal powder and/or ceramic powder of the present invention and an organic binder containing a photodegradable resin, and shape the mixture into a desired shape. After injection molding, by simultaneously performing photolytic modification and thermal decomposition removal of the organic binder, the organic binder can be efficiently removed from the molded product without causing cracks, blisters, or deformation of the molded product. Furthermore, by adding a photodisintegration accelerator, it became possible to remove the organic binder from the molded article even more efficiently. In addition, organic binders can be removed from thick molded bodies even more efficiently by photolytic modification of the organic binder from the molded body and heat-melting removal of low-melting-point substances before thermal decomposition removal. It became. In other words,
It is clear that compared to the conventional method, the time required to remove the organic binder from the molded body is significantly shortened and productivity can be improved. In addition, it avoids the use of solvent extraction and the use of sublimable components, volatile components, soluble components, etc., does not cause deterioration of the working environment, and is made of metal powder and/or ceramic powder and an organic binder component. We have found a method for molding powder injection molded parts that does not have any problems with the storage stability of homogeneous mixtures.

Claims (4)

[Claims] (1) In order to manufacture parts as a sintered particle structure, a sintering powder consisting of one or more types of metal powder and/or ceramic powder, and at least one type of photodegradable resin as an organic binder. In a molding method that uses an organic binder mixture comprising: a combination of photodecomposition modification of the organic binder by light irradiation of the molded body and thermal decomposition removal of the organic binder by heating the molded body, the photodegradable resin is It is an organic polymer compound represented by the general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R_1 and R_2 represent atoms or groups other than H, and n represents an integer of 1 or more.) A method for molding powder injection molded parts, characterized by: (2) A method for molding a powder injection molded part, which comprises further adding at least one type of photodegradation accelerator to the organic binder mixture according to claim 1. (3) In order to manufacture parts as a sintered particle structure, a sintering powder consisting of one or more types of metal powder and/or ceramic powder and an organic binder containing at least one type of photodegradable resin. (1) to form a homogeneous mixture; (2) to mold this mixture into a molded body of a desired shape; A process of photolytically modifying an organic binder having a certain molecular weight on the surface of a molded body by irradiating it with ultraviolet rays, electron beams, or X-rays, and a process of thermally decomposing and removing the organic binder by heating the molded body. By the step (3) carried out simultaneously and the step (4) of firing the molded body obtained in the step (3),
A method for molding powder injection molded parts, characterized by obtaining a sintered body. (4) In order to produce a part as a sintered particle structure, a sintering powder made of one or more metal powders and/or ceramic powders, at least one photodegradable resin, and at least one A step (1) of mixing an organic binder containing various types of low melting point substances to form a homogeneous mixture, a step (2) of molding this mixture into a molded body of a desired shape, and a step (2) of forming a molded body from this molded body. The process (3) of heating and melting away the low-melting-point organic binder component, and irradiating the surface of the molded body with ultraviolet rays, electron beams, or X-rays as light having a predetermined energy or higher, will result in a constant molecular weight on the surface of the molded body. A step (4) of simultaneously carrying out photodecomposition modification of the organic binder having the above-mentioned organic binder and a step of thermally decomposing and removing the organic binder by heating the molded body, and sintering the molded body obtained in the step (4). A method for molding a powder injection molded part, characterized in that a sintered body is obtained by step (5).