JPH0976216A - Composite for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition, reduced in the change in concentration of a compound upon deaeration, long in pot life, and capable of manufacturing a molded form, reduced in deformation due to the change in volume and prominent in strength. SOLUTION: A compositor for injection molding is constituted of inorganic powder and organic binder while the organic binder is liquid at a temperature upon solidifying the compound for injection molding in a shaping mold and contains 10-70vol% of organic constituent having a vapor pressure of 1mmHg or less at a normal temperature to 150 deg.C. Especially, butyl stearate is employed as the organic constituent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composition comprising an inorganic powder and an organic binder, which is used in a method for molding an inorganic powder by injection molding.

[0002]

2. Description of the Related Art When an inorganic powder is molded by an injection molding method, a mixture of the inorganic powder and a large amount of an organic binder is used as a molding material. At this time, the molding material is plasticized by being heated, passes through each part of the injection molding machine, is then injected and filled in the mold, and is cooled to near room temperature in the mold and solidified. Conventionally, solid organic binders such as waxes are often used at room temperature, but there is a problem that density variation occurs due to a large volume change at the time of solidification of a molded body, resulting in cracks. . Therefore, a method has been proposed in which a part of the organic binder is replaced with a solid one at room temperature and an organic solvent is used, for example, a method in which an organic solvent is contained and solidified by a solidifying agent (JP-A-4-224165). Gazette, Japanese Patent Publication 5-4
8724).

However, since the kneaded product of the inorganic powder and the organic binder needs to be degassed in advance, the organic solvent is likely to be volatilized by this process. Therefore, the organic binder concentration of the entire kneaded product is less than the required amount and concentration adjustment is necessary, or a partial density change of the kneaded product occurs, so that the formed molded product has variations in the density of the molded product. However, there is a problem that the strength of the molded product is adversely affected. Furthermore, since highly volatile organic solvents and sublimable substances easily volatilize even at room temperature, the kneaded product cannot be stored for a long period of time, resulting in a short pot life.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a composition which does not change the concentration of the compound during deaeration and has a long pot life. To obtain a moldable composition.

[0005]

The present invention is an injection molding composition comprising an inorganic powder and an organic binder, wherein the organic binder has a temperature (temperature) at which the injection molding composition is solidified in a molding die. Hereinafter, 10 to 70 v of an organic component that is a liquid at a "solidification temperature") and has a vapor pressure of 1 mmHg or less at room temperature to 150 ° C is used.
The present invention provides an injection molding composition characterized by containing ol%.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The inorganic powder used in the composition of the present invention may be either ceramic powder or metal powder. Examples of the ceramic powder include MgO, Al ₂ O ₃ ,
SiO ₂ , TiO ₂ , ZrO ₂ , ZnO, Fe ₂ O ₃ ,
Powders of Si ₃ N ₄ , SiC, BN, TiC, WC and the like, and metal powders include, for example, metal silicon, Fe, A
1, powders of Mg, Ti, etc. may be mentioned.

The preferable average particle size of the ceramic powder and the metal powder is 0.1 to 50 μm, particularly preferably 0.3 to 3
0 μm. An apparatus used for pulverization to obtain a preferable particle size is a ball mill, a stirring mill, a jet mill or the like, and may be either wet pulverization or dry pulverization. As a liquid medium for carrying out the wet pulverization, ethyl alcohol, methyl alcohol and other organic solvents are used.

[0008] These inorganic powders are kneaded with an organic binder to form an injection molding composition. The organic binder used here can be appropriately selected, and examples thereof include organic components such as paraffin wax, microcrystalline wax, oxidized wax, maleated wax, stearic acid, and oleic acid. The other organic components of the organic binder may be used alone or in combination of two or more.

The organic binder used in the present invention, together with the above-mentioned organic components, is a liquid at the temperature at which the composition for injection molding is solidified in the molding die, and is at room temperature to 15 ° C.
It contains an organic component having a vapor pressure at 0 ° C. of less than 1 mmHg (hereinafter referred to as “containing organic component”).

As described above, one of the features of the present invention is that the organic component which is liquid at the temperature at which the composition for injection molding is solidified is used as a part of the organic binder constituting the composition. It is in.

The temperature at which the injection molding composition is solidified in the molding die is nothing but the mold temperature at which the injection molding composition is solidified. At this time, whether the contained organic component is a liquid or a solid in the molding die depends on the temperature and the molding pressure of the mold at the time of molding, but in the injection molding method, the influence of the molding pressure is almost the same. I do not receive it. In particular, in the case of the low pressure injection molding method in which the molding pressure is 10 kg / cm ² or less, the influence of the molding pressure can be ignored.

Therefore, the contained organic component which is liquid at the temperature at which the injection molding composition is solidified in the molding die is also solidified when the injection molding composition is injected and apparently solidified in the molding die. It remains liquid. For this reason, the volume of the molded body is unlikely to change during solidification, and even if the molded body is a thick product, the molded body is less likely to be deformed such as warp or twist. On the other hand, if the contained organic component is a solid at the solidification temperature, the volume change at the time of solidification of the molded body is large, while if the contained organic component is a gas at the solidification temperature, the contained organic component is in the mold. It may vaporize and cause non-uniformity of the density of the compact.

Here, it should be noted that even when a liquid-containing organic component is used at the solidification temperature,
When it is a solid at room temperature, the temperature at which the contained organic component does not solidify when the molded body after solidification is stored, that is,
It may be necessary to heat to a temperature equal to or higher than the melting point of the contained organic component.

The temperature at which the composition for injection molding is solidified is selected in the range of the temperature at which the organic components other than the contained organic components in the organic binder are solidified, the molding efficiency, the quality of the molded product to be obtained, and the like. Is taken into consideration. At this time, when two or more kinds of organic components other than the contained organic component are used, they can be selected within a temperature range in which at least one of them is solidified. A solidification temperature of 25 to 50 ° C. is suitable when injection molding is performed at a low pressure. If the temperature of the mold is lower than 25 ° C, the volume change becomes large and the density of the molded body becomes non-uniform, while if it exceeds 50 ° C,
The strength of the molded body becomes low, which may cause deformation and cracks at the time of release.

Next, the contained organic component also has a vapor pressure of 1 mmHg or less at room temperature to 150 ° C. Here, the normal temperature is a temperature at which neither heating nor cooling is performed,
Specifically, it refers to 20 to 25 ° C. Usually, the degassing process is
Since it is carried out at a temperature of room temperature to 150 ° C. under a pressure of more than 1 mmHg, another feature of the present invention is that the contained organic component which is not vaporized and removed during the degassing treatment is used as a part of the organic binder. I used it. Therefore, even if the composition of the present invention is degassed, the contained organic components do not evaporate and the density of the organic binder does not vary.

In the present invention, butyl stearate is preferable as the contained organic component. Butyl stearate has a melting point of 27 ° C., which is considerably lower than other organic components commonly used as organic binders. Moreover,
Since the vapor pressure at 150 ° C. or higher is high, it is difficult to be removed during the degassing process, and there is an advantage that the degreasing rate is fast. However, butyl stearate is applied only when the solidification temperature is 27 ° C. or higher. FIG. 1 shows the results of measuring the body expansion coefficient of butyl stearate by the duraometer method, and FIG. 2 shows the results of measuring the vapor pressure by using the isoteniscope method / boiling point method in combination.

The proportion of the contained organic component in the organic binder must be 10 to 70 vol%.
It is particularly preferably 20 to 60 vol%. The ratio of contained organic components is 10 vol% with respect to the organic binder.
If it is less than 70%, the volume change during solidification of the molded product becomes large, density unevenness may occur, and thus cracks may occur in the molded product. On the other hand, if it exceeds 70 vol%, it will be sufficient in the mold. It does not solidify, and cracks may occur during release from the mold.

Here, the mixing ratio of the organic binder to the inorganic powder can be appropriately selected, but usually,
25-55 vol% is preferable, and especially 30-50 vol
% Is preferred. If the mixing ratio is less than 25, the inorganic powder and the organic binder are difficult to be sufficiently kneaded, while 55
If it exceeds vol%, the viscosity is too low, so that many burrs are generated and degreasing takes a long time. The kneading of the above-mentioned inorganic powder and organic binder is carried out by a usual method using a commonly used apparatus such as a double-arm type pressure kneader or a Banbury mixer.

The composition of the present invention is used in a method of molding by injection molding. At this time, the injection pressure is 0.5 to 10 kg / cm ² , low pressure injection molding, 200 to
It can be used for any method of high pressure injection molding of 2,000 kg / cm ² . The molded body molded in this way is
It can be of any shape, including thick products and complex shapes.

As described above, the composition of the present invention comprises, as one component of the organic binder constituting the composition, a certain amount of a liquid component at the temperature at which the composition for injection molding is solidified in the molding die. Since it contains, even if the molded body is apparently solidified, the contained organic component remains liquid. For this reason, the volume of the molded body is unlikely to change during solidification, and even if the molded body is a thick product, the molded body is less likely to be deformed such as warp or twist. Furthermore, if the contained organic components that are liquid even at room temperature are used, there is no need to heat the molded body after solidification to prevent the contained organic components from solidifying, and since it can be stored at room temperature, handling after injection molding Is easy.

Further, since the contained organic component has a vapor pressure of 1 mmHg or less at room temperature to 150 ° C., it is not vaporized and removed even if it is heated to a negative pressure and negative pressure is applied. For this reason, the contained organic components do not volatilize during degreasing, the composition has a long pot life, and uneven density is unlikely to occur in the molded body.

[0022]

EXAMPLES The present invention will be described below with reference to examples. Example 1 and Comparative Example 1 Silicon nitride powder was used as the inorganic powder, and 50 vol% paraffin (melting point: 57 as an organic binder.
° C), butyl stearate 40 vol% (melting point; 27
℃), stearic acid 10 vol% (melting point; 70.5 ℃)
Using the organic binder consisting of, the inorganic powder and the organic binder were blended so as to have a volume ratio of 56:44 and kneaded to prepare an injection molding composition.

The composition for injection molding was contained in a tank, the temperature in the tank was 90 ° C., the degree of vacuum was 1 mmHg, and the composition for injection molding was heated and deaerated for 2 hours, and then the temperature was kept at 30 ° C. The mold was injection-molded under a pressure of 4 kg / cm ² to obtain 70 × 70 × 20 mm and 70 × 70 × 30 mm injection-molded articles. This injection-molded body was heated at 1,800 ° C for 4
The sintered body obtained was fired for a period of time, and the presence or absence of cracks and the degree of deformation were examined (Example 1). The degree of deformation was the difference between the maximum value and the minimum value of the wall thickness at each position (AK) of the sintered body shown in FIG. Further, as an organic binder, 90 vol% paraffin, 1 stearic acid
Using an organic binder of 0 vol%, a sintered body was prepared through ordinary steps such as degreasing, and the presence or absence of cracks and the degree of deformation were examined (Comparative Example 1). The results are shown in Table 1.

[0024]

[Table 1]

The sintered body of the composition of Example 1 had a thickness of 3
Even if the product had a wall thickness of 0 mm, no crack was generated, and a good sintered body was obtained. On the other hand, in the case of a thick product having a thickness of 30 mm, cracks were generated in the sintered body of the composition of Comparative Example 1. In addition, the sintered body of the composition of Example 1 is the same as Comparative Example 1
The degree of deformation is considerably smaller than that of the sintered body obtained by using the composition.

Examples 2-5, Comparative Examples 2-4 Except that the organic binders had the compositions shown in Tables 2-3.
An injection molding composition was prepared in the same manner as in Example 1 and
The obtained injection-molded body was sintered by injection molding in a mold of 0 × 70 × 30 mm. When the shape of the sintered body was examined, the results shown in Table 2 were obtained.

[0027]

[Table 2]

In Comparative Example 2, the volume change during solidification of paraffin was large, and cracks were formed in the sintered body, which are thought to be due to uneven density. Further, in Comparative Examples 3 to 4, cracks that are considered to be due to a decrease in the strength of the molded body were generated at the time of releasing from the mold. On the other hand, in Examples 2 to 5, cracks did not occur and good sintered bodies were obtained. Thus, when butyl stearate is used, the compounding ratio needs to be 10 to 70 vol% in the organic binder.

Examples 6 to 7 and Comparative Examples 5 to 6 Using the compositions prepared in the same manner as in Example 1, after heating and degassing in the same manner, the temperature of the mold was adjusted to the temperature shown in Table 3. Then, injection molding was performed, and this was sintered at 1,800 ° C. for 4 hours, and the presence or absence of cracks and the degree of deformation were examined.

[0030]

[Table 3]

In Comparative Examples 5 to 6 in which the mold was adjusted to a temperature lower than the melting point of butyl stearate, the volume change was large when the molded body was solidified by the mold, which is considered to be due to the volume change in the molded body. A crack has occurred. On the other hand, in Examples 6 to 7 in which the mold was adjusted to a temperature higher than the melting point of butyl stearate and lower than the boiling point, the deformation of the molded body was small and no crack was generated.

[0032]

EFFECTS OF THE INVENTION According to the composition of the present invention, it is difficult for a molded body to undergo a volume change during solidification, deformation of the molded body such as warpage and twist is unlikely to occur, and strength and dimensions of a thick product can be obtained. It is possible to obtain a molded product having excellent accuracy. Further, since the organic binder used in the composition of the present invention is less likely to volatilize, it has a long pot life and keeps a good state in which the components do not change for a long time.

[Brief description of drawings]

FIG. 1 is a chart showing the measurement results of the body expansion coefficient of butyl stearate.

FIG. 2 is a chart showing measurement results of vapor pressure of butyl stearate.

3 is a front view of the molded body of Example 1. FIG.

Claims (2)

[Claims] 1. An injection molding composition comprising an inorganic powder and an organic binder, wherein the organic binder is a liquid at a temperature at which the injection molding composition is solidified in a molding die and at room temperature to 150. Vapor pressure at 1 ℃ is 1mmH
An injection molding composition, characterized by containing 10 to 70 vol% of an organic component of g or less. 2. The composition for injection molding according to claim 1, wherein the organic component is butyl stearate.