JPH0559065B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an injection molding composition that is used to produce finely shaped precision mechanical parts by injection molding and sintering alumina powder. (Prior art) Sintered products conventionally obtained by powder metallurgy are produced based on a method in which powder as a molding composition is press-molded and then sintered, resulting in a three-dimensionally complex product. It has been difficult to manufacture products with thin shapes or thin parts such as knife edge parts. Therefore, in an attempt to overcome the drawbacks of the above methods, an injection molding composition consisting of a molding powder and a binder is injection molded into a mold of a predetermined shape, and the resulting injection molded body is heated to remove the binder and then sintered. A method of obtaining a sintered product by applying this method has been proposed (JP-A-57-16103, JP-A-57-26105). (Problem to be solved by the invention) However, since the above method uses powder with an average particle size of 10 μm or less, a product with high sintered density can be obtained, but on the other hand, it takes a long time to remove the binder. .
As a result, there has been an economic disadvantage of increased manufacturing costs. If a binder with a high decomposition rate is used in an attempt to shorten the debinding time, the decomposed gas may cause cracks, blisters, etc. in the molded product during the debinding process.
Defects such as deformation are likely to occur.Conversely, attempts have been made to mix and adjust a binder with a slow decomposition rate and a binder with a fast decomposition rate as appropriate, but the debinding property has not been improved even with this. Improvements in debinding properties mean that the time required to complete debinding is short, the processing temperature can be lowered, and defects such as cracks, blisters, and deformation occur in molded products during the debinding process. It means nothing. The present invention aims to provide an injection molding composition that is useful for improving binder removal properties, which has been difficult to achieve with conventional compositions, in the injection molding of precision parts made from alumina powder. It is a purpose. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present inventors have taken various measures to vary the blending ratio (volume ratio) of alumina powder and binder as well as the weight ratio of each binder composition. As a result of stacking, a composition consisting of a sintering powder made of alumina powder and a binder is obtained, and the binder is composed of 10 to 80% low density polyethylene, 10 to 80% paraffin wax, and 5 to 80% by weight. A composition for injection molding containing 35% boric acid ester, characterized in that the mixing ratio of the sintering powder and the binder is 30 to 70% by volume of the former and 70 to 30% by volume of the latter. It was discovered that problems can be solved by using objects. The sintering powder used in the present invention is alumina powder, the low density polyethylene in the binder is a commercially available product, and the paraffin wax is ordinary paraffin wax. The boric acid ester is one or more selected from triglycol diborates, trialkyl borates, glycerol borates, and alkyne diborates. More specifically, the triglycol diborates include, for example, 1, 6-bis(5-ethyl-4-propyl-1,3,2-dioxabora-2
-cyclohexyloxy)hexane, or 1,4-bis(5-ethyl-4-propyl-1,
3,2-Dioxaborate (2-cyclohexyloxy)butane, etc., trialkylborates such as trimethyl borate, triethyl borate, tributyl borate, triamyl borate, etc., and glycerol borates such as glycerol borate stearate, poly Alkyne diborates such as oxyethylene glycerol borate palmitate include, for example, methyl diborate and ethyl diborate, and particularly preferred are triglycol diborates. These boric acid esters can be used alone or in combination of two or more, and when mixed with other components, they can be dissolved in a solvent such as benzene, toluene, xylene, etc. to a concentration of 60-80% by weight.
It is desirable to mix the alumina powder and the organic binder as a solution, which further improves the miscibility of the alumina powder and the organic binder. Therefore, in this case, the binder composition will also contain a certain amount of solvent as a component. Next, the equipment and equipment used when injection molding the composition of the present invention can be the equipment and equipment conventionally used for injection molding of plastics, and the heating temperature is 80 to 200°C and the injection pressure is 500°C. ~2000
Processed at Kg/ ^cm2 . In addition, when processing precision molded products using the composition of the present invention using the above equipment, when processing powders that are easily oxidized, the powders that are difficult to oxidize should be processed in an atmosphere of an inert gas or reducing gas. In some cases, it is possible to complete the debinding process by heating to 250 to 300°C at a temperature increase rate of about 12 to 30°C/hr in the air or under an inert gas atmosphere. 1 to 1, which had to be processed when trying to obtain a product using a conventional composition.
Since it is no longer necessary to perform high-temperature treatment at a temperature of 400 to 550°C at a slow temperature increase rate of 10°C/hr, it has become possible to significantly improve the efficiency of binder removal processing. (Function) As already mentioned, the composition for injection molding of the present invention is subjected to a binder removal treatment by heating after injection molding.
Subsequently, a sintering process is carried out, and the composition range in terms of weight percentage and volume percentage is as follows.
As long as the compounding ratio is adhered to, it can be heated at a heating rate of about 12 to 30℃/hr in either the reducing gas atmosphere, air, or inert gas atmosphere.
It is possible to advantageously finish the debinding treatment by heating to 250 to 300°C, which is the debinding treatment condition of 1 to 300°C when using conventional compositions.
When compared with high temperature heating of 400-500°C at a heating rate of 10°C/hr, the advantages of the present invention can be significantly appreciated. The reasons for limiting the above component composition range and blending ratio are as follows. The volume percentage of alumina powder as a sintering powder was set at 30 to 70%, but this is because if the volume percentage of alumina powder is less than 30%, it is difficult to maintain fluidity of the composition when injection molding the composition. This is because the injection molding operation becomes impossible, and the packing density of the sintering powder in the injection molded body becomes low, making it difficult to improve the density of the final sintered part. On the other hand, if the volume percentage of the sintering powder exceeds 70%,
This is because the injection molding strength decreases or a defect called surface sinking tends to occur on the surface of the injection molded product, which significantly reduces the injection moldability of the composition. In addition, the composition range of the binder was to contain 10 to 80% by weight of low-density polyethylene, but if the content of low-density polyethylene is less than 10% by weight, the strength and shape retention of the injection molded product will decrease, and the binder removal treatment will be necessary. This is because although the time required for debinding is shortened, cracks are likely to occur on the surface of the molded product, and when it exceeds 80% by weight, the time required for debinding treatment becomes extremely long. Furthermore, 10 to 80% by weight of paraffin wax is contained, but this is because if the amount of paraffin wax is less than 10% by weight, the injection moldability of the composition will be insufficient, and the debinding treatment time will be too long. This is because as the length increases, the binder removal treatment temperature also increases. On the other hand, if the content exceeds 80% by weight, the strength and shape retention of the injection molded product will be insufficient and the molded product will likely become impossible to handle. Finally, the boric acid ester was limited to 5 to 35% by weight because the boric acid ester improves the miscibility of the sintering powder and the binder, ensuring uniform distribution of the powder, and stabilizing processability during binder removal. It serves to improve the density and dimensional accuracy of the final sintered product, and contains 5% by weight.
If it is less than 35% by weight, the compatibility will not be improved and the molded product after binder removal will tend to have porous defects, and if it exceeds 35% by weight, the strength of the molded product will decrease. Furthermore, when mixing the composition, adding stearic acid to the composition in an amount of less than 20% by weight will not reduce the effectiveness of the composition in order to improve the mold release properties between the mold and the molded object during injection molding. This has been confirmed. (Example) Using alumina powder with an average particle size of 0.5 μm, Table 2
Sintered products with sharp edges were produced by combining various binders with the compositions shown below. That is, a binder was added to alumina powder in an amount shown in Table 1, mixed and kneaded, and injection molded into a gear shape. Table 1 shows the results of examining the injection moldability at this time. Next, the injection molded product is heated in an air gas atmosphere, the weight of the molded product is measured before and after the heat treatment, and the binder is removed until the remaining amount of binder is 1% by weight or less of the molded product. After the treatment, the material was heated for temporary sintering, and then cooled to room temperature in a furnace.
Thereafter, the appearance of the molded product was observed. The results are shown in Table 1 along with the heating temperature and time for debinding. The molded product with good appearance is then heated to 1250℃.
After sintering for 1 hour, a good sintered product was obtained. Table 2 shows the results of measuring the strength of the sintered product using a standard plate test piece from the Powder Metallurgy Technology Association.
Shown below. The numerical value indicates the average value of 5 test values. In Conventional Examples 1 to 3, good molded bodies were obtained, but the binder removal properties were poor. Experimental Examples 1 to 8 are examples in which the component composition range or blending ratio is outside the scope of the present invention.
2 shows the composition range within the invention but the blending ratio is outside the invention, and Experimental Examples 3 to 8 show the composition range outside the invention and the blending ratio within the invention. The disadvantage of Experimental Example 1 is that it cannot be molded, the disadvantage of Experimental Example 2 is that surface shrinkage occurs in the molded product, that of Experimental Example 3 is that it cannot be molded, and Experimental Example 4 has good moldability and appearance but has problems with heating at high temperatures and for long periods of time. There is. The disadvantage of Experimental Example 5 is that the strength of the molded product is low; Experimental Example 6, like Experimental Example 4, has problems with high temperature and long-term heating; Experimental Example 7 has the disadvantage of being unable to be molded; and Experimental Example 8 has the defect of binder separation. . On the contrary, those of Examples 1 to 5 were used for 16 to 26 hours.
By heating at a lower temperature than the conventional method of 250°C to 300°C in such a short period of time, good results are achieved in both formability and appearance.

【table】

[Table] Binder composition is weight%, blending amount is volume%

[Table] (Effects of the invention) According to the implementation of the present invention, the processing time of the binder removal process during injection molding of precision ceramic parts obtained using alumina powder has no effect on the properties of the final product. Since it is easy to reduce the size of the product to a large extent, it will contribute to the precision industry by making it possible to supply powder metallurgy products made by injection molding at low prices and in a stable condition, especially for thin-walled parts with complex shapes. There is something big.

Claims (1)

[Scope of Claims] 1 A composition comprising sintering powder made of alumina powder and a binder, the binder being 10 to 80% low density polyethylene, 10 to 80% by weight
% of paraffin wax and 5 to 35% of boric acid ester, and the volume ratio of the sintering powder to the binder is 30 to 70% for the former and 70 to 30% for the latter. An injection molding composition characterized by: 2 The boric acid ester is selected from triglycol diborates, trialkyl borates, glycerol borates and alkyne diborates 1
The injection molding composition according to claim 1, which comprises one or more types. 3. The injection molding composition according to claim 1 or 2, wherein the binder removal treatment is carried out at a temperature of 250 to 300°C at a temperature increase rate of 12 to 30°C/hr.