JPH02111654A - Composition for injection molding - Google Patents

Abstract

PURPOSE:To improve the binder-removing efficiency in sintering operation after injection molding by adding a specific binder to alumina powder. CONSTITUTION:A composition composed of (A) 30-70vol.% of sintered alumina powder and (B) 70-30vol.% of a binder (composed of 10-80wt.% of a low-density polyethylene, 10-80wt.% of paraffin wax and 5-35wt.% of a boric acid ester) is injection molded at 80-200 deg.C under a pressure of 500-2,000kg/cm<2>. The molded article is subjected to a binder-removal treatment by heating to 250-300 deg.C at a rate of 12-30 deg.C/hr. The boric acid ester is one or more substances selected from triglycol diborate, trialkyl borate, glycerol borate and alkyne borate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an injection molding composition used in producing 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, thin parts such as knife parts, etc.

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 sintered crystals by subjecting the
-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 fast decomposition rate is used in an attempt to shorten the debinding time, defects such as cracks, blisters, and deformation will easily occur in the molded product due to decomposition gas during the debinding process. Attempts have also been made to mix and adjust the
Even with this, the binder removal property has not been improved.

In this 1, improvements in debinding properties mean that the time required to complete debinding is short, the processing temperature can be lowered, and defects such as cranks, blisters, deformation, etc. are avoided in the molded product during the debinding process. It means that it will not occur.

An object of the present invention is to provide an injection molding composition useful for improving binder removal properties, which has been difficult to achieve with conventional compositions, in injection molding of precision parts made from alumina powder. It is something.

(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. The result is a composition consisting of sintering powder made of alumina powder and a binder, the binder consisting of 10-80% low-density polyethylene, 10-80% paraffin wax, and 5-80% by weight. Contains 35% 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.
It has been discovered that the problems can be solved by using an injection molding composition characterized by the following.

The sintering powder used in the present invention is alumina powder.

Commercial products are available as low-density polyethylene in the binder.
As the paraffin wax, normal paraffin wax is used. The boric acid ester is one or more selected from triglycol diborates, trialkyl borates, glycerol borates, and alkyne borates; more specifically, 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-dioxabora-2
-cyclohexyloxy)butane, etc., trialkylborates such as trimethylborate, triethylborate, tributylborate, triamylborate, etc., and glycerolborates such as glycerolborate stearate, polyoxyethyleneglycerolborate palmate, etc. Tate etc.

Examples of the alkyne chevrobates include methyl chevrobates and ethyl chevrobates, and particularly preferred ones include 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, equipment used when injection molding the composition of the present invention,
The equipment can use the same equipment and devices conventionally used for plastic injection molding, and has a heating temperature of 80~80℃.
It is processed at 200°C and an injection pressure of 500 to 2000 kg/cJ.

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 12-00°C in the air or under an inert gas atmosphere, and products cannot be obtained using conventional compositions. Since it is no longer necessary to perform high-temperature treatment at 1~550°C, which was required in the case of 1~b~550°C, it has become possible to significantly improve the efficiency of binder removal treatment.

(Function) As mentioned above, after injection molding, the injection molding composition of the present invention is subjected to a binder removal treatment by heating, and then a sintering treatment, but the composition range in terms of weight percentage as explained by the following. The binder can be removed by heating to 250 to 300"C at 12 to 30 degrees in either the reducing gas atmosphere, air, or inert gas atmosphere, as long as the mixing ratio in terms of volume and volume % is set. The process can be finished advantageously, and when compared with the high temperature heating of 1 to b °C, which is the debinding treatment condition when using conventional compositions, the advantage of the present invention is significantly evaluated. However, the reason for limiting the above component composition range and blending ratio is as follows.The volume percent of alumina powder as a sintering powder was set at 30 to 70%, but this is because the volume percent of alumina powder is less than 30%. If this happens, it becomes difficult to maintain fluidity of the composition when injection molding the composition, which makes injection molding impossible, and the packing density of the sintering powder in the injection molded body becomes low. This is because it becomes difficult to improve the density of the final sintered part.

On the other hand, if the volume percentage of the sintering powder exceeds 70%, the injection molding strength will decrease or a defect called surface sinking will easily occur on the surface of the injection molded product, which will significantly reduce the injection moldability of the composition. It is for this purpose.

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, it contains 10 to 80% by weight of paraffin wax, which means that the amount of paraffin wax is 10% by weight.
If it is less than % by weight, the injection moldability of the composition will be insufficient, and as the binder removal treatment time becomes longer, the binder removal treatment temperature will also become higher.

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. This has the effect of ultimately improving the density and dimensional accuracy of the fired crystals, and if it is less than 5% by weight, the miscibility will not be improved and porous defects will occur in the molded product after binder removal. This is because it becomes easy to bend, and if it exceeds 35% by weight, the strength of the molded product decreases.

Furthermore, when mixing the composition, adding stearic acid to the composition in an amount of less than 20% by weight will not reduce the effect of the composition in order to improve the releasability of the molded product from the mold during injection molding. This has been confirmed.

(Example) Alumina powder having an average particle size of 0.5 μm was used in combination with various binders having the compositions shown in Table 2 to fabricate sintered products having a shape with sharp edges.

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 body is heated in an air gas atmosphere, the weight of the molded body 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 body. After treatment, it is heated and temporarily sintered.
The mixture was cooled in the oven to room temperature.

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 a good appearance was then heated at 1250°C for 1
After time sintering treatment, a good sintered product was obtained. In addition, Table 2 shows the results of determining the strength of the fired crystal using a standard plate test piece from the "Powder Metallurgy Technology Association." 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 range of the present invention, and among these, Experimental Examples 1 and 2 show cases where the composition range is within the present invention but the blending ratio is outside the invention. Examples 3 to 8 show compositions outside the invention and blending ratios within the invention. The disadvantage of Experimental Example 1 is that it cannot be molded, Experimental Example 2
The drawbacks are that the molded product is troublesome, that of Experimental Example 3 cannot be molded, and that of Experimental Example 4 has good moldability and appearance but has problems with heating at high temperatures and for long periods of time. 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, Example 1
- 5 is 250℃ in a short time of 16 to 26 hours.
Even when heated at a lower temperature than the conventional temperature of 300°C, good results are achieved in terms of moldability and appearance.

(The following is a blank space) Table 2 (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 significantly without giving any damage, it is possible to supply powder metallurgy products made by injection molding method at low cost and in a stable condition, especially for thin-walled parts with complex shapes, making it possible for the precision industry to supply them in a stable condition. There is a lot to contribute.

-And more-

Claims (3)

[Claims] 1. A composition consisting of a sintering powder made of alumina powder and a binder, the binder having a weight ratio of 10
Contains ~80% low-density polyethylene, 10-80% paraffin wax, and 5-35% boric acid ester, and the volume ratio of the sintering powder to the binder is 30-70% of the former. %, the latter being 70 to 30%. 2. 2. The injection molding composition according to claim 1, wherein the boric acid ester is one or more selected from triglycol diborates, trialkyl borates, glycerol borates, and alkyne borates. 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.