JP3856117B2 - Manufacturing method of injection molded body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of an injection molding method.
[0002]
[Prior art]
In the ceramics field and metallurgy field, there are the following methods for obtaining a compact having a complicated shape by molding a molding powder such as ceramic powder or metal powder.
[0003]
(1) Injection molding method using wax and resin binder Molding powder and wax or resin binder are heated and softened above the melting temperature of the resin binder, and after uniform kneading, cooled to a temperature below the melting point of the binder, A molding material is produced by solidification. Since the obtained molding material is so hard that it cannot be deformed by hand at room temperature, it is heated again to the softening temperature of the binder, put into an extruder, and the extrudate is cut and pelletized. Alternatively, the hard molding material can be crushed as it is and pelletized. This pellet is put into an injection molding machine, softened by heating, and molded.
[0004]
(2) Water-based injection molding method using agar This method is described in, for example, Japanese Patent No. 2604925 and Japanese Patent No. 3105225.
(Method 2a)
Mix molding powder and solvent (for example, water), add gel-forming substance (for example, agar) powder to the resulting mixture, and heat the sol above the melting temperature of gel-forming substance (usually 90 ° C or higher) Generate. The sol is then gelled by cooling to a temperature below the gel point. The resulting gel is soft enough to be deformed by hand. In this material system, the sol formed by water and agar serves as a binder for the molding powder. Next, the gel is pulverized to obtain a pellet-shaped molding material. The moisture content in this molding material is adjusted by drying or humidification to obtain a molding material in a state where a specified amount of moisture remains. The shrinkage rate of the molded body and the fired body can be controlled by the residual water content. A molding material having a predetermined moisture content is put into an injection molding machine, and heated and softened for molding.
[0005]
(Method 2b)
Also known is a method of heating a mixture of molding powder, water and a gel-forming substance to form a sol, and then charging the sol into an injection molding machine while heating to perform injection molding.
[0006]
For example, agar, which is a substance extracted from seaweed, becomes a sol-like viscous fluid at 95 to 100 ° C. in the presence of water and gels at 35 to 40 ° C. to become an elastic body. Agar powder having such properties is mixed with molding powder, and kneaded until water is added and clay-like plasticity is obtained. When the kneaded material is put into, for example, an injection molding machine and heated at 80 ° C. or higher, the agar becomes sol and the fluidity is increased, so that injection molding can be performed uniformly at a lower pressure than conventional wax binder materials. In this method, since the mold can be injected into the mold at a low pressure and molded, the transferability of the complex-shaped mold is good and the wear in the molding machine is small. Gelled agar is very easy to release water even under normal temperature ventilation, so it can be easily dried and the molded shape can be maintained with considerable strength. After drying the molded body, it is possible to immediately proceed to the sintering process without going through the degreasing process. Here, the agar contained in the molded body is ashed at 400 ° C. or higher and does not generate harmful gases as in the case of conventional binders such as wax and resin.
[0007]
[Problems to be solved by the invention]
However, the injection molding method using such agar has the following problems. That is, a sol consisting of agar and molding powder is injected through a sprue into a molding space inside the injection molding mold, and then the mold is cooled to gel the molded body, and then from the mold. It is necessary to release the mold. However, the strength of the gel-like molded body is relatively low. In particular, after the molded body is released from the mold, it can be easily dried under normal temperature ventilation and the molded shape can be maintained with a considerable strength. However, at the stage of releasing the molded body from the mold, the molded body has not yet been released, and the strength remains low. When the mold is opened in this state, the molded body adheres to the surface of the mold and it is difficult to release the mold.
[0008]
In the case of a molded body using a resin binder, the molded body can be released from the mold by projecting the ejector pins. However, in the case of a molded body using agar gel, since the strength at the time of mold release is low as described above, when the molded body is pressed with an ejector pin, the ejector pin may break through the molded body.
[0009]
Furthermore, since the molded body does not shrink during gelation in the mold, it is undefined whether the molded body adheres to the movable mold or the fixed mold when the mold is opened. A compact may adhere to the mold.
[0010]
An object of the present invention is to provide a first mold and a second mold, which are filled with a molding material and form a molding space for molding, and the first mold, and the molding material is placed in the molding space. In an injection molding apparatus having a sprue for injection, it is possible to easily release from a mold while preventing the molded body from being destroyed without applying a strong mechanical external force to the molded body. .
[0011]
[Means for Solving the Problems]
The present invention provides a first mold, a second mold, and a first mold that form a molding space for molding a molding material composed of a mixture containing a molding powder, an agar gel forming substance, and a solvent. A sprue for injecting a molding material into the molding space, a porous body provided in each of the first mold and the second mold and facing the molding space, and a gas to the porous body The open porosity of the porous body is 5% or more and 40% or less, and the pore diameter of the porous body is 1 μm or more and 50 μm or less, using an injection molding apparatus including a gas supply mechanism for supplying
The first mold is separated from the second mold, and the molded body is separated from the first mold by ejecting gas from the porous body of the first mold at a pressure of 0.2 MPa or more and 2 MPa or less. Then, the molded body is released from the second mold by ejecting the gas from the porous body of the second mold at a pressure of 0.2 MPa or more and 2 MPa or less. The present invention relates to a method for producing an injection-molded article, which is a reducing atmosphere or an inert atmosphere .
[0012]
The present invention also provides a first mold, a second mold, and a first mold for forming a molding space for molding a molding material comprising a molding powder, a mixture containing an agar gel-forming substance and a solvent. provided, sprue for injecting a molding material into the molding space, a porous body which faces the first mold and the second mold, respectively provided by and and molding space, and to a porous body The porous body has an open porosity of 5% or more and 40% or less, and the porous body has a pore diameter of 1 μm or more and 50 μm or less. ,
The first mold and the second mold are separated , and the molded body is separated from the second mold by ejecting gas from the porous body of the second mold at a pressure of 0.2 MPa or more and 2 MPa or less . Then, the molded body is released from the first mold by ejecting the gas from the porous body of the first mold at a pressure of 0.2 MPa or more and 2 MPa or less. those according to wherein the sexual atmosphere or an inert atmosphere der Rukoto.
[0013]
The inventor installs a porous body at least in a part of the mold that is in contact with the molded body, and blows gas from the porous body at the time of mold release, so that the molded body is floated and separated from the mold without damage. I came up with a mold. As a result, the mold can be easily released without applying excessive mechanical stress.
[0014]
In Japanese Patent Application Laid-Open No. 07-32426, in a method for manufacturing a molded product for a push button switch, at least a part of a mold cavity is a porous metal member. Further, defects such as short shots are prevented by discharging the gas generated from the air in the mold or the molding material to the outside through the porous material. However, unlike the present invention, the application is not mold release, and in the present invention, gas is supplied from the outside.
[0015]
In JP-A-7-164495, before the molten layer of the plastic molded body filled in the mold is solidified, gas is sent from the outside through a porous metal provided in the mold, Prevents warping. However, gas is not sent from the outside for mold release as in the present invention.
[0016]
In the injection mold described in JP-A-10-151647, a part of the mold is formed of a porous body. Then, a raw material such as natural starch is mixed with water and a binder to form a gel, and this gel is heated and supplied to the cavity of the injection mold and foamed inside the cavity. Then, when the mold is cooled and the foam is released, air is blown from the porous body into the cavity, and the formed body is released from the mold. Thereby, a molded article having a good surface condition is obtained.
[0017]
However, in the present invention, a molded body is obtained by injection molding a sol obtained by heating a mixture containing a molding powder, a gel-forming substance and a solvent. Such a molded body is in such a state that a large amount of molding powder is joined together by a relatively small amount of gel molding substance. For this reason, it has been found that when air is blown from the porous body by the above-described injection device, the molded body is deformed and further destroyed by the air pressure sent between the molded body and the mold surface. In the case of an ordinary foamed molded body, when air is sent from the porous body, the molded body is first elastically deformed, then blown off from the mold surface, and then restored. However, it has been found that the molding material of the present invention does not undergo such elastic deformation and is immediately destroyed by air pressure. In order to prevent such a situation, it is necessary to set the air pressure at the time of mold release to 0.2 MPa or more and 2 MPa or less.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The pressure of the gas ejected from the porous body at the time of mold release is preferably 0.2 MPa or more, and more preferably 0.5 MPa or more from the viewpoint of promoting the mold release. Further, from the viewpoint of suppressing breakage of the molded body at the time of mold release, the pressure is preferably 2 MPa or less, and more preferably 1 MPa or less.
[0019]
The molding powder targeted in the present invention is not particularly limited as long as it is a molding powder that is sintered by heating to form a sintered body. The molding powder is preferably a powder that does not cause dissolution in a solvent or reaction with the solvent. The molding powder is preferably an inorganic powder, particularly preferably an inorganic powder for sintering.
[0020]
The inorganic powder is typically a ceramic powder, a metal powder, a ceramic-metal composite material powder, or a mixed powder thereof. Examples of ceramics include oxide ceramics such as oxides of rare earth elements such as alumina, zirconia, titania, silica, magnesia, ferrite, cordierite, yttria; barium titanate, strontium titanate, lead zirconate titanate, rare earth Examples include complex oxides such as elemental manganite and rare earth element chromite; nitride ceramics such as aluminum nitride, silicon nitride, and sialon; and carbide ceramics such as silicon carbide, boron carbide, and tungsten carbide. Examples of the metal include iron-based metals such as iron, stainless steel, and carbonyl iron, non-ferrous metals such as titanium, copper, and aluminum, and alloys of non-ferrous metals. Examples of the inorganic powder include graphite, glass, and carbon. Furthermore, resin powder can be illustrated as molding powders other than inorganic powder.
[0021]
The gel-forming substance used in the present invention is an agar gel-forming substance. The agar gel-forming substance includes all gel-forming substances of agar quality, and includes not only high-purity agarose but also low-purity agar containing a lot of agaropectin components, and also includes modified agar. Pure agar is called agarose and is neutral with repeating units of β-D-galactopyranose bonded at the 1,3-position and 3,6-anhydro-L-galactopyranose bonded at the 1,4-position. It is a polysaccharide. The agar gel-forming substance may also contain an agarose derivative. When agarose partially contains sulfate ester, methoxyl, pyruvate, etc., it is called agaropectin. Common agar is a mixture of agarose and agaropectin.
[0022]
When agarose and an agarose derivative (typically agaropectin) are contained in the agar gel forming substance, the ratio of the agarose and the agarose derivative varies depending on the intended use. The agarose derivative contains ash such as sodium, potassium, calcium and sulfuric acid. For this reason, it is preferable that the amount of the agarose derivative is small in applications where impurities are hated, such as fine ceramics. Specifically, an ash content of 2% by weight or less is preferable, and a high-purity agarose having an ash content of 1% by weight or less is particularly preferable.
[0023]
The solvent is a solvent for a gel generating material that dissolves the gel generating material powder, generates a sol when heated, and generates a gel when the temperature drops. The solvent is particularly preferably water, but may be a hydrophilic organic compound solvent such as alcohols, or may be a mixture of water and a hydrophilic organic compound solvent. As the hydrophilic organic compound, alcohols such as methanol, ethanol and propanol, and alcohols substituted with chlorine or bromine atoms are preferable.
[0024]
In the mixing stage, for example, a mixer, in particular a planetary mixer, can be used. At this time, a shear stress can be applied to the mixture by providing a chopper in the mixer.
[0025]
In the step of molding the mixture to obtain a molding material, the molding material can be pelletized to obtain pellets. Moreover, the molded object of a mixture can be obtained using another shaping | molding method, for example, a casting molding method and an extrusion molding method, and this molded object can also be cut | disconnected and granulated. However, the term “cutting” as used herein refers to a process for making a compact of the mixture fine, and is a concept including crushing, pulverization, and granulation.
[0026]
In the injection molding process, the molding material is put into an injection molding machine, and the molding material is heated to a temperature equal to or higher than the melting temperature at the same time as kneading to obtain a fluid sol. The heating temperature is preferably 75 ° C. or higher, more preferably 80 ° C. or higher. Further, from the viewpoint of preventing the molded body from becoming inhomogeneous due to evaporation of the solvent, 120 ° C. or lower is preferable, and 100 ° C. or lower is more preferable. When the heating temperature is 100 ° C. or higher, it is preferable to apply pressure in order to avoid boiling of water.
[0027]
The injection molding apparatus includes a first mold and a second mold that form a molding space. The first mold is provided with a sprue for injecting a molding material into the molding space. The injection molding apparatus of the present invention may include one or a plurality of molds other than the first mold and the second mold.
[0028]
The porous body is provided in the first mold and the second mold, and faces the molding space. The material of such a porous body is not limited, but the following materials are particularly suitable.
(1) Porous sintered body of metal powder: Examples of this material include alloy tool steel, high speed steel, stainless steel, and chromium molybdenum steel.
(2) Porous sintered body of ceramic powder: Examples of this material include alumina, zirconia, cordierite, silicon nitride, and silicon carbide.
[0029]
Porosity of the porous structure improves the ejection efficiency of the gas, from the viewpoint of facilitating the release, and 5% or more, further preferably 15% or more.
[0030]
Open porosity of the porous body from the viewpoint of suppressing the adhesion of the porous body of the molded body was 40% or less, more preferably it is 25% or less.
[0031]
Pore diameter of the porous body, and 1μm or more from the viewpoint of improving the ejection efficiency of the gas, and from the viewpoint of preventing clogging of the porous body the pores by the molding material, and 50μm or less.
[0032]
Although the entire first mold can be made a porous body, it is particularly preferable to integrate the porous body into a main body made of a dense member. Moreover, although the whole 2nd type | mold can be made into a porous body, it is especially preferable to integrate a porous body with the main body which consists of a dense member. In these cases, the entire surface of the mold that faces the molding space can be made porous, or both the main body and the porous body can face the molding space. It can also be.
[0033]
Particularly preferably, the first mold or the second mold is constituted by a main body made of a dense member and a core integrated with the main body, and the core is formed by a porous body.
[0034]
The kind of gas supply mechanism for supplying gas to the porous body is not particularly limited. Typically, the gas supply mechanism includes a compressor for sending pressurized gas and a pipe for sending the pressurized gas to the porous body.
[0035]
Gas, air, a reducing atmosphere, Ru inert atmosphere der.
[0036]
The porous body is provided in the second mold (mold without sprue). After the molding material is injected from the sprue into the molding space and molded, when the mold is opened, the molded body is attached to the second mold without sprue, and then the gas is blown out from the second mold and molded. Release the body.
[0037]
FIG. 1 is a schematic view schematically showing an injection molding apparatus according to a reference example , and FIG. 2 is a schematic view showing a state where the first mold 14A and the second mold 15A are separated.
[0038]
In this example, the first mold 14A is a fixed mold, and the second mold 15A is a movable mold. The first mold 14 </ b> A includes a fixed mold main body 2, and the main body 2 is attached to the attachment plate 1. The main body 2 is provided with a spru 9. The second mold 15A includes a plate-shaped movable mold main body 3 and a core 6 protruding from the center of the main body. The core 6 is made of a porous body. A molding space 20 is formed by the fixed mold body 2, the movable mold body 3 and the core 6. The movable body 3 is attached to the attachment plate 5 by a spacer block 4.
[0039]
The apparatus of this example includes a gas supply mechanism 16 that supplies gas to the core 6. The gas supply mechanism 16 includes a compressor 10 that sends out pressurized gas, a valve 12, and a pipe 11, and the tip of the pipe 11 is connected to the porous body 6.
[0040]
The molding material in a fluid state as described above is injected from the sprue 9 into the molding space 20, molded, and then cooled and solidified. A well-known drive mechanism (not shown) is driven to drive the movable main body 3 and away from the fixed main body 2 as shown in FIG. In this state, the surface 8 a of the molded body 8 is separated from the surface 2 a of the fixed mold body 2, and the surface 8 b of the molded body 8 adheres to the surface 6 a of the core 6.
[0041]
In this state, the valve 12 is opened, and the gas from the compressor is supplied to the porous body 6 as shown by the arrow A through the pipe 11. This gas is ejected from the surface 6 a of the porous body 6 to release the molded body 8.
[0042]
In the present invention , the porous body is provided in each of the first mold and the second mold. In this case, the mold can be easily released by the method of the present invention even when the molded body adheres to either the first mold or the second mold. For example, when the molding material is a sol, as described above, since the molded body does not shrink during gelation in the mold, the molded body adheres to the first mold when the mold is opened. It is unstable whether it adheres to the second mold. Therefore, by providing a porous body and a gas supply mechanism in both molds, it is possible to cope with cases where they adhere to either mold.
[0043]
A porous body is provided in each of the first mold and the second mold. And when separating the first mold and the second mold, the molded body is formed into a porous body of a mold that does not eject gas by ejecting gas from the porous body of the first mold or the second mold. To attach. Next, the molded body is released from the mold by ejecting gas from the porous body of the mold to which the porous body is adhered. In this case, when the first mold and the second mold are separated, the molded body can be reliably attached to one mold.
[0044]
FIG. 3 is a schematic diagram schematically showing the injection molding apparatus according to this embodiment, and FIG. 4 is a schematic diagram showing a state where the first mold 14B and the second mold 15B are separated. 3 and 4, the same reference numerals are given to the components shown in FIG. 1 and the description thereof may be omitted.
[0045]
In this example, the first mold 14B is a fixed mold, and the second mold 15B is a movable mold. The first mold 14 </ b> B includes a fixed mold body 2 and a ring-shaped core 7. A sprue 9 is provided at the center of the fixed die 14B, and the periphery of the outlet of the sprue 9 is surrounded by a ring-shaped core 7. The core 7 is made of a porous body.
[0046]
The second mold 15B includes a plate-shaped movable mold main body 3 and a core 6 protruding from the center of the main body. The core 6 is made of a porous body. A molding space 20 is formed by the fixed mold body 2, the movable mold body 3, and the cores 6 and 7.
[0047]
The apparatus of this example includes a gas supply mechanism 16B that supplies gas to the core 6 and a gas supply mechanism 16A that supplies gas to the core 7. Each gas supply mechanism 16 </ b> A, 16 </ b> B includes a compressor 10 for sending pressurized gas, valves 12, 13 and a pipe 11, and the tip of the pipe 11 is connected to the porous bodies 6, 7.
[0048]
The molding material in a fluid state is poured from the sprue 9 into the molding space 20, molded, and then cooled and solidified. The movable mold body 3 is driven and separated from the fixed mold body 2 as shown in FIG. At this time, the valve 13 is opened, and the gas from the compressor is supplied to the core 7 as shown by an arrow B through the pipe 11. This gas is ejected from the surface 7a of the core 7, and the surface 8a of the molded body 8 is levitated from the first mold. As a result, the molded body 8 is reliably attached to the movable mold 15B side.
[0049]
Next, the valve 12 is opened, and the gas from the compressor is supplied to the core 6 as shown by the arrow A through the pipe 11. This gas is ejected from the surface 6 a of the core 6 to release the molded body 8.
[0050]
【Example】
As the alumina powder, 6000 g of an easily sinterable low soda alumina powder was used. As a dispersant, 1 part by weight of an ammonium polyacrylate copolymer was added to 100 parts by weight of alumina powder, and ion-exchanged water was added so that the water content was 21.5 parts by weight, followed by thorough mixing. The mixture was then ground for 5 hours in a pot mill using nylon balls as grinding media. The obtained slurry was passed through a screen having a wire diameter of 390 μm and an aperture of 600 μm (JIS Z8801), and then placed in a mixing tank.
[0051]
The powder agar was weighed at a ratio of 3 parts by weight with respect to 100 parts by weight of the alumina powder. While stirring the mixture, the agar powder was put into the mixing tank and mixed. Next, the mixing tank was heated to dissolve the agar powder and knead. The temperature was raised from room temperature to 95 ° C. in 30 minutes. The slurry was kneaded by rotating the planetary blade at a rotation speed of 30 rpm while maintaining the temperature of the material at 95 ° C. Kneading was performed at 95 ° C. for 30 minutes, and the obtained kneaded product was cooled to room temperature to obtain a molding material. The molding material was taken out from the mixing tank. The molding material was pelletized, and a humidity control operation was performed at this time to adjust the moisture content of the pellets to 17.5%.
[0052]
A mold as shown in FIGS. 3 and 4 was attached to an electric injection molding machine with 30 tons of mold clamping, and was molded by the method described above. The main bodies 2 and 3 were made of stainless steel. The cores 6 and 7 were made of stainless steel having an open porosity of 25% and a pore diameter of 7 μm. Air was used as the pressurized gas, and the ejection pressure was 0.5 MPa. In the obtained molded product, defects such as cracks, cracks, and surface peeling were not observed.
[0053]
The obtained molded body was dried at room temperature all day and night, after which residual moisture was removed in a dryer at 130 ° C., and the temperature rising rate was 300 ° C./hour, the maximum temperature was 1620 ° C., and the holding time was 2 hours at 1620 ° C. Baked in. Cooling was performed by natural cooling. In the obtained sintered body, density unevenness and defects were not observed.
[0054]
【The invention's effect】
As described above, according to the present invention, the first mold and the second mold that form the molding space for filling and molding the molding material, and the first mold, the molding mold is provided. In an injection molding apparatus equipped with a sprue for injecting molding material into the space, it can be easily released from the mold while preventing the molded body from being destroyed without applying a strong mechanical external force to the molded body. .
[Brief description of the drawings]
FIG. 1 is a schematic view schematically showing an injection molding apparatus according to a reference example , and a movable die 15A is provided with a core 6 made of a porous body.
2 is a schematic view showing a state in which a movable mold and a fixed mold are separated from each other in the injection molding apparatus of FIG. 1;
FIG. 3 is a schematic diagram schematically showing an injection molding apparatus according to an embodiment of the present invention, in which a fixed core 14B is provided with a core 7 made of a porous body, and a movable die 15B has a porous A core 6 made of a material is provided.
4 is a schematic view showing a state in which a movable mold and a fixed mold are separated from each other in the injection molding apparatus of FIG. 3;
[Explanation of symbols]
2 Main body of the first mold 2a Surface of the main body 3 Main body of the second mold 6 Core made of the porous body on the second mold side 6a Surface of the core 6 7 Made of the porous body on the first mold side Core 7a Surface of core 7 8 Molded body 8a, 8b Surface of molded body 8 Sprue 10 Compressor 11 Piping 12, 13 Valves 14A, 14B First mold 15A, 15B Second mold 16, 16A, 16B Gas supply Mechanism 20 Molding space

Claims (2)

A first mold and a second mold forming a molding space for molding a molding material comprising a molding powder, a mixture containing an agar gel-forming substance and a solvent, provided in the first mold, sprue for injecting the molding material into the molding space, the porous body facing the first mold and the second mold is provided respectively and said molding space, and the porous body On the other hand, using an injection molding apparatus equipped with a gas supply mechanism for supplying gas, the open porosity of the porous body is 5% or more and 40% or less, and the pore diameter of the porous body is 1 μm or more and 50 μm. And
The first mold and the second mold are separated from each other , and the gas is ejected from the porous body of the first mold at a pressure of 0.2 MPa or more and 2 MPa or less . The mold is attached to the second mold away from the mold, and then the gas is ejected from the porous body of the second mold at a pressure of 0.2 MPa to 2 MPa. A method for producing an injection-molded article , wherein the gas is an atmosphere, a reducing atmosphere or an inert atmosphere . A first mold and a second mold forming a molding space for molding a molding material comprising a molding powder, a mixture containing an agar gel-forming substance and a solvent, provided in the first mold, sprue for injecting the molding material into the molding space, the porous body facing the first mold and the second mold is provided respectively and said molding space, and the porous body On the other hand, using an injection molding apparatus equipped with a gas supply mechanism for supplying gas, the open porosity of the porous body is 5% or more and 40% or less, and the pore diameter of the porous body is 1 μm or more and 50 μm. And
Apart and said second mold and said first mold, said second mold from said porous material gas the green body the second by ejecting above and 2MPa pressure below 0.2MPa of The molded body is attached to the first mold away from the mold, and then the gas is ejected from the porous body of the first mold at a pressure of 0.2 MPa or more and 2 MPa or less. was released from the mold, the gas, air, a reducing atmosphere or an inert atmosphere der wherein Rukoto method of injection molding.

Images