JPH0675855B2 - Injection molding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an injection molding method, and more particularly to a method capable of minimizing entrainment of bubbles during injection molding of a ceramic material kneaded clay under vacuum.

[Prior Art] Various molding methods for ceramics have been proposed and implemented, but an injection molding method with high productivity is adopted particularly for molding a member having a precise and complicated shape.

In particular, molded products of non-oxide ceramics used as high-temperature / structural materials often have precise and complex shapes, and the injection molding method for such materials should not cause defects in the molded products. Various kinds of additives are added to the resin, and the injection molding method itself is improved.

[Problems to be Solved by the Invention] However, although it is possible to improve the properties of the ceramic raw material puddle itself to be used for injection molding by these conventional methods, in the actual injection molding, the inside of the cavity of the mold is Involves any existing air,
It has a defect that it remains as bubbles or cavities in the molded product, and this portion becomes a defect.

On the other hand, when performing injection molding of a thick plastic product, it is known that the method of injection molding under vacuum is an effective method for avoiding the inclusion of air existing in the mold.

[Means for Solving the Problem] The present inventor has conducted various researches and studies for the purpose of finding means for avoiding the inclusion of bubbles at the time of injection molding of a ceramic material kneaded clay, and as a result, provided for injection molding. It has been found that the above object can be almost uniquely achieved by limiting the combination and the viscosity of the binder of the ceramic raw material clay and injecting it under vacuum.

Thus, the injection molding method of the present invention uses a mixture of polyethylene and polystyrene as a binder, and adjusts the viscosity of the raw kneaded material to 10 ² to 10 ⁴ poises at a shear rate of 10 ¹ to 10 ³ sec ^-1 , and a ceramic raw material. It is characterized in that the kneaded material is injected under vacuum.

In the kneaded material using plastics, which contains a large amount of ceramic powder as a binder, a relatively large amount of plasticizer or lubricant is mixed in order to improve the dispersibility of the ceramic powder and reduce the viscosity of the kneaded material. Therefore, in the present invention, when the viscosity of the raw kneaded material is less than the above range, foaming due to volatilization of the plasticizer, lubricant and the like is increased, and when it exceeds the above range, the flow of the kneaded material is poor and the mold is Since the shape and size cannot be faithfully transferred and the required dimensional accuracy cannot be satisfied, both are unsuitable. Injecting under vacuum here means injecting the kneaded material into the mold after the inside (cavity) of the mold is kept in vacuum.

In the injection molding method of the present invention, a mixture of polyethylene and polystyrene is used as a binder.
-114524 is applicable to the method of removing resin by solvent (polystyrene is dissolved in the solvent and removed, leaving only polyethylene), so degreasing (removal of binder) by heating can be completed efficiently in a short time. .

Furthermore, when 10 ³ to 10 ⁴ poise is adopted within these ranges, it is particularly preferable because foaming of the plasticizer or the lubricant can be substantially prevented. In fact, various methods can be adopted as means for adjusting the viscosity of the raw kneaded clay within the above range. For example,
Control the temperature of the raw kneaded material, adjust the mixed amount of ceramic powder to about 50 to 55% by volume, adjust the viscosity of the polymer melt such as polyethylene or polystyrene serving as a binder, The addition amount of a plasticizer such as a fatty acid ester or a lubricant such as stearic acid, stearyl alcohol or stearic acid ester is controlled, and further, the kneaded material is adjusted to have a predetermined viscosity of the present invention by a combination thereof.

Further, the ceramic kneaded clay adjusted to a predetermined viscosity is used for injection molding, and at this time, the temperature of the cylinder nozzle is set to 13
It is preferable to carry out injection molding at 0 to 200 ° C and at a mold temperature of 20 to 90 ° C because the object of the present invention can be achieved regardless of the shape of the molded product.

At this time, the injection speed is 40-50 cm ³ / sec, the injection holding pressure 3
It is suitable to adopt 70 to 1500 kg / cm ² .

The ceramics to which the present invention is applied is not particularly limited, and examples thereof include non-oxide ceramics such as silicon nitride, silicon carbide, and aluminum nitride, alumina, zirconia, etc. Optimal. Appropriate additives such as metal powder and whiskers can be added to the ceramic raw material to which the method of the present invention is applied, unless the object of the present invention is impaired.

[Examples] 80% by weight of silicon carbide powder having a specific surface area of 17 m ² / g, 5% by weight of polyethylene, 10% by weight of polystyrene, 1% by weight of stearic acid and 4% by weight of fatty acid ester were sufficiently kneaded to obtain 10 ¹ to 10 ^{1 At} a shear rate of ³ sec ^-1 , the viscosity is 1
A ceramic body of 0 ² to 10 ⁴ poise was obtained.

This kneaded clay is heated to 150 ° C from a cylinder nozzle (injection nozzle) with a diameter of 6 mm to an outside diameter of 150 mm and a volume of 320 cc at 80 ° C.
Molding was carried out by injecting under vacuum into the disc-shaped mold cavity held by.

In this molded product, neither visible bubbles on the surface nor bubbles on the inside due to X-ray, which were observed when the conventional injection molding method was adopted.

Claims (2)

[Claims] 1. The viscosity of a ceramics material kneaded clay using a mixture of polyethylene and polystyrene as a binder
An injection molding method characterized by adjusting to 10 ² to 10 ⁴ poise at a shear rate of 10 ¹ to 10 ³ sec ^-1 , and injecting under vacuum. 2. The viscosity of a ceramics material kneaded clay using a mixture of polyethylene and polystyrene as a binder
Injection under vacuum while adjusting the temperature of the cylinder nozzle to 130-200 ° C and the mold temperature to 20-90 ° C by adjusting to 10 ² to 10 ⁴ poise at a shear rate of 10 ^-1 to 10 ³ sec ^-1. An injection molding method comprising: