JPH04336204A - Injection-molded component for ceramics - Google Patents

Abstract

PURPOSE:To improve injection moldability, mold separating property, and debinding property by constituting from a binder consisting at least of a kind of lubricant selected from baking powder consisting of oxide ceramics and saturated alcohol, multi-unsaturated fatty acid, fatty acid amide or the like, polyethylene and parafiin wax. CONSTITUTION:Baking powder consists of oxide ceramics, and a binder consists at least of a kind of lubricant selected from saturated alcohol, polyunsaturated fatty acid, saturated normal chain fatty acid and monounsaturated fatty acid, low density polyethylene and paraffin wax. Herein, a blend of the baking powder and binder is preferable to be in the range of from 30:70 to 70:30 in its volumetric ratio. Furthremore, it is preferable that the binder consists of a low density polyethylene of 15-70wt.%, paraffin wax of 10-80wt.%, and a lubricant of 0.5-40wt.%.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an injection molding composition, and specifically, it is used to produce precision mechanical parts with complex shapes by injection molding ceramic powder and then sintering it. The present invention relates to an injection molding composition.

0002

BACKGROUND OF THE INVENTION Conventionally, sintered products obtained by powder metallurgy have been produced based on a manufacturing method in which metal powder or ceramic powder as a molding composition is press-molded and sintered. Press molding using only metal powder or ceramic powder makes it difficult to manufacture products with three-dimensionally complex shapes or thin parts such as knife edge parts.

[0003] In an attempt to overcome the drawbacks of the above-mentioned method, an injection molding composition comprising metal powder and a binder is injection molded into a mold of a predetermined shape, and the resulting molded body is heated to remove the binder. A method of obtaining a sintered metal product by performing a sintering treatment has been proposed (for example, JP-A-57-16103, JP-A-57-26105, etc.).

[0004] When obtaining a sintered product from an injection molding composition prepared by mixing ceramic powder and a binder, (1) the final product must have a high sintered density; (3) Good debinding properties of injection molded products; (4) In injection molding of injection molding compositions, unnecessary parts such as sprue and runner parts other than the product must be It is essential to reuse and recycle several times or more, and (5) good recyclability is required, and (5) good releasability between the injection molded article and the mold is required.

[0005] In the method disclosed in Japanese Patent Application Laid-Open No. 57-16103, metal powder having an average particle size of 10 microns or less is used, so that a product with a high sintered density can be obtained.

[0006]

[Problems to be Solved by the Invention] However, injection molding compositions such as those disclosed in JP-A-57-16103 have problems such as variations in weight and dimensions of the final product, organic properties, recyclability, and mold releasability. is not sufficient.

In other words, injection moldability, in other words, variations in weight and dimensions of the final product, are caused by poor fluidity of the injection molding composition, insufficient filling of the mold, cracks in the molded product, etc. There is a problem in that it is difficult to perform stable molding due to breakage when taking it out from the mold.

[0008] Furthermore, with regard to debinding properties, there are problems in that it takes a long time to complete debinding, a high treatment temperature is required, and defects such as cracks, blisters, and deformation are likely to occur in the molded product.

Regarding recyclability, recycling can cause decomposition of the binder in the injection molding composition,
Evaporation or deterioration occurs and the injection moldability of the injection molding composition changes, resulting in a problem in that the dimensional accuracy of the final product is likely to decrease.

[0010] Furthermore, there is a problem that if the recyclability or debinding property is improved, other properties deteriorate.

For example, after injection molding, the molded product is separated into a sprue part and a runner part near the gate, but if the gate method is a side gate, ring gate, etc., part of the runner remains on the product side. Then, it is necessary to perform gate cutting as post-processing. This gate cut increases costs both in terms of product and recycling. Therefore, recently, a pinpoint gate method, as shown in FIG. 1, has been adopted, which allows gate cutting to be performed smoothly and requires no post-processing. In the pinpoint gate method, for example, when molding the gear 10, injection is performed as shown by the arrows through the pinpoint gate part 12, runner part 14, and sprue part 16, and the injection molding composition is also applied to these parts. Things solidify.

However, this method has the problem of being sensitive to mold releasability. In other words, if this method is adopted, the runner portion 14 becomes very long, and when the molded product is removed from the mold, the releasability between the molded product and the mold is poor.
The molded body cannot be taken out and molding becomes impossible.

Furthermore, in order to improve the binder removal property, for example, in JP-A-59-121150, a processing aid and pore forming agent is added. However, this processing aid and pore forming agent decomposes and evaporates in the range of 100 to 200°C, so under the operating conditions of kneading temperature of 150°C and injection temperature of 150°C, the processing aid and pore forming agent is removed during the process. Deterioration will occur. As a result, repeated recycling changes the fluidity of the composition during injection molding, and the weight and dimensions of the molded product filled into the mold also change with each repeated recycling. There is a problem in that the dimensional accuracy of a certain sintered body also changes, and therefore the dimensional variation of the entire group of sintered bodies becomes large.

[0014] Furthermore, when a processing aid and pore forming agent is added, the releasability from the mold is poor, and as mentioned above, it cannot be used for molds with pinpoint gates that are sensitive to mold releasability. There's a problem.

Therefore, in injection molding of precision parts made from ceramic powder as a raw material, the present invention significantly reduces the weight and dimensional fluctuations of the injection molded body produced by recycling, and improves the dimensions of the final product (sintered body). An object of the present invention is to provide an injection molding composition with significantly improved precision.

[0016] Furthermore, the present invention improves binder removal properties and mold release properties, which have been difficult to achieve with conventional injection molding compositions, in injection molding of precision parts made from ceramic powder. The purpose of the present invention is to provide an excellent injection molding composition.

[0017]

[Means for Solving the Problems] As a result of intensive research, the present inventors have developed a method for solving the above-mentioned problems by using low-density polyethylene, paraffin wax, and a lubricant for ceramic sintering powder. use a binder,
It has been found that the above problems can be solved by selecting the lubricant from the group consisting of saturated alcohol, polyunsaturated fatty acids, fatty acid amides, saturated straight chain fatty acids, and monounsaturated fatty acids.

That is, the injection molding composition of the present invention has the following properties:
An injection molding composition basically consisting of a sintering powder and a binder, wherein the sintering powder is made of an oxide ceramic, and the binder is a saturated alcohol, a polyunsaturated fatty acid, a fatty acid amide, a saturated It consists of at least one lubricant selected from the group consisting of straight chain fatty acids and monounsaturated fatty acids, low density polyethylene, and paraffin wax.

Furthermore, in the present invention, by varying the blending ratio of the sintering powder and the binder, and by varying the blending ratio of the lubricant, low-density polyethylene, and paraffin wax, a suitable material for injection molding can be obtained. It has been found that a composition can be obtained.

[0020] That is, the injection molding composition of the present invention:
The volume ratio of the sintering powder and binder is 30:7.
Preferably, the ratio is within the range of 0 to 70:30.

[0021] The injection molding composition of the present invention also includes a binder containing 15 to 70% by weight of low density polyethylene, 1
0-80% by weight paraffin wax and 0.5-4%
It is preferable that the amount of lubricant is 0% by weight.

[0022]

[Operation] In the present invention, the moldability is controlled by finding factors that improve the binder removal properties and mold release properties in injection molding in the composition and blending ratio of the injection molding composition.

[0023] The sintering powder used in the present invention is as follows:
Oxide ceramics such as zirconia and alumina
It is possible to list things that are made up of more than just seeds.

[0024] Any known low-density polyethylene can be used, but low-density polyethylene with a fluidity of 100 to 300 g/10 minutes as measured by the method specified in JIS K7210 has good injection moldability and binder removal. This is preferred because the strength and shape retention of the molded product at the initial stage of processing are excellent.

[0025] The fluidity of low density polyethylene is 100g/
If the time is less than 10 minutes, injection moldability becomes relatively low. Furthermore, even if the fluidity exceeds 300 g/10 minutes, the strength and shape retention of the injection molded product will be relatively low.

[0026] The paraffin wax may be of any known type, but one preferably has a softening point of 50 to 90°C as measured according to JIS K7206.

If the softening point of the paraffin wax is less than 50° C., the cycle time during injection molding becomes long and the wax tends to soften, resulting in disadvantages such as difficulty in handling during molding. On the other hand, if the softening point exceeds 90°C, the thermal decomposition point will increase and the binder removal property will decrease.

[0028] The lubricant reduces the adhesive strength between the mold and the injection molding composition and improves the mold releasability, and also acts as a bonding agent between the sintering powder and the binder (paraffin wax and polyethylene). It acts as a lubricant, significantly reducing interfacial friction, reducing torque during kneading and improving fluidity of the injection molding composition, resulting in stable injection molding operations. The proportion of lubricant used varies depending on each injection molding composition.

[0029] It is desirable that the lubricant has a melting point of 50°C or lower and a boiling point of 200°C or higher. The melting point of the lubricant is 50
If the temperature is higher than 0.degree. C., the adhesive strength and friction coefficient with the mold cannot be reduced, and there is a risk that the releasability from the mold will be deteriorated when taken out from the mold after injection molding. In addition, if the boiling point of the lubricant is less than 200°C, the lubricant will evaporate during the kneading and injection molding processes, and the viscosity coefficient of the composition will fluctuate, resulting in a large change in the weight of the molded product and the dimensional accuracy of the product. becomes worse.

Among the lubricants, saturated alcohols include Cn H2
It has a chemical structure of n+1OH, and commercially available products can be used as is. Representative examples of saturated alcohols that can be used in the present invention include caprylic alcohol and caprylyl alcohol.

[0031] Furthermore, polyunsaturated fatty acids are Cn H2n+1
It has a chemical structure of O2H, and commercially available products can be used as is. Typical examples of polyunsaturated fatty acids include linoleic acid and linolenic acid.

Furthermore, commercially available fatty acid amides can be used as they are. Representative examples of fatty acid amides include caprylic alcohol and caprylyl alcohol.

[0033] In addition, saturated straight chain fatty acids are Cn H2n+1
It has a chemical structure of CO2H, and commercially available products can be used as is. As a representative example of saturated straight chain fatty acids,
Capric acid, caprylic acid, enanthic acid, caproic acid, pelargonic acid, tridecanoic acid and the like can be mentioned.

[0034] Furthermore, monounsaturated fatty acids include Cn H2n
It has a chemical structure of -1CO2H, and commercially available products can be used as is. Typical examples of monounsaturated fatty acids include lindelic acid, tuzunic acid, myristoleic acid, zomarin, oleic acid, gondolic acid, and the like.

[0035] When injection molding the composition of the present invention, commonly used equipment and devices can be used as they are, and the molded product is heated at a heating temperature of 80 to 200°C and an injection pressure of 50°C.
Molded at 0-2000kg/cm2.

The binder contained in the molded article is removed in various atmospheres. The product rate of injection molded products is usually in the range of 25 to 85% by volume, so the remaining 75 to 15% (mainly sprue and runner parts)
is again used for injection molding, resulting in a product with the same proportions,
The rest is recycled again. Such recycling will normally be repeated several times.

[0037] When removing the binder from a precision molded product using the powder of the injection molding composition of the present invention, when processing powder that is easily oxidized, it is necessary to remove the binder from the powder in an inert gas or reducing atmosphere. When processing difficult powders, the binder can be removed by heating to 250 to 300°C in the air or in an inert gas atmosphere at a temperature increase rate of about 12 to 30°C/h.

[0038] When manufacturing products using conventional injection molding compositions, it was necessary to perform high temperature treatment at a temperature of 400 to 550°C at a slow temperature increase rate of 1 to 10°C/h. In the invention, 250℃ at a heating rate of about 12-30℃/h
It is possible to advantageously finish the debinding treatment by heating at a relatively low temperature of ~300°C.

The reasons for limiting various component composition ranges and blending ratios in each aspect of the present invention will be explained below.

The reason why the volume of the ceramic powder as the sintering powder is set to 30 to 70% is as follows.

[0041] When the volume of the sintering powder is less than 30%,
When injection molding the composition, it becomes difficult to ensure fluidity of the composition, making injection molding impossible, and the degree of filling of the sintering powder in the injection molded body becomes low, resulting in poor quality of the final sintered part. It becomes difficult to improve density. On the other hand, if the volume of the sintering powder exceeds 70%, the strength of the injection molded article will decrease or the fluidity of the composition will decrease, making injection molding difficult.

The reason why the composition range of the binder is to contain 15 to 70% by weight of low density polyethylene is as follows.

If the content of low density polyethylene is less than 15% by weight, the strength and shape retention of the injection molded article will decrease, and although the time required for binder removal treatment will be shortened, cracks will easily occur on the surface of the molded article. On the other hand, if the content of low density polyethylene exceeds 70% by weight, the time required for the binder removal process becomes unnecessarily long.

10 to 80% by weight of paraffin wax
The reason for including it is as follows.

[0045] The weight of paraffin wax is 10% by weight.
If it is less than this, the fluidity of the composition will decrease, injection moldability will be insufficient, the debinding treatment time will become long, and the debinding treatment temperature will also increase. Conversely, 80% by weight
If it exceeds this, the strength and shape retention of the injection molded product will be insufficient, and the molded product will likely become impossible to handle.

The reason why the amount of lubricant is limited to 0.5 to 40% by weight is as follows.

If the lubricant content is less than 0.5% by weight, the mold releasability from the mold will be poor, and it cannot be used in a pinpoint gate type mold. Furthermore, the torque during kneading will be large, and the ceramic powder It is very difficult to mix the paraffin wax and polyethylene binder uniformly. On the other hand, if it exceeds 40% by weight, the strength of the molded product decreases and the molded product becomes easily broken when taken out from the mold after injection molding, making injection molding very difficult.

[0048]

【Example】

[Examples 1 to 6] Binders having the compositions shown in Table 1 were prepared from paraffin wax, low density polyethylene, and a lubricant (oleic acid). The low-density polyethylene used had a fluidity of 200 g/10 minutes, and the paraffin wax had a softening point of 70°C.

Example 1 having the composition shown in Table 1 was added to high purity zirconia powder with an average particle size of about 0.5 μm.
~ 6 binders are combined and mixed and kneaded to create a pitch circle diameter of 20 mm, thickness of 5 mm, and number of teeth of 18.
A sintered product with a gear shape and a bending test piece for measuring mechanical strength were manufactured.

The mold is a pinpoint gate type mold as shown in FIG. That is, the gear 10, the pinpoint gate section 12, the runner section 14, and the sprue section 16.
A mold with a shape corresponding to that is used.

[0051] Injection molding in this mold was carried out at an injection speed of 10
The speed was 0 mm/sec.

Injection moldability was evaluated based on the presence or absence of incomplete filling into the mold due to poor fluidity of the injection molding composition, cracks in the molded product, and damage when taken out from the mold. Moreover, the mold releasability was evaluated by the mold releasability of the sprue portion 16 from the mold. Table 4 shows the results of injection moldability and mold releasability.

[0053] Further, the injection molded body is heated in an air stream to remove the binder from the molded body, and the binder is removed until the remaining amount of binder becomes 1% by weight or less of the molded body. I observed the appearance. The results are shown in Table 5 along with the heating temperature and time required for debinding. All of the binder-free bodies had good surface roughness.

[0054] Furthermore, these binder-removed bodies were
Sintering treatment was performed at 0° C. in an oxygen stream for 4 hours. The dimensions of the obtained sintered body were measured. Furthermore, the sprue part, runner part, etc. were reused and recycled three times for each of Examples 1 to 6, and the dimensions of the obtained sintered bodies were measured. Table 6 shows the variation in dimensions of these sintered bodies.

Table 7 shows the results of measuring the three-point bending strength of the sintered body. The numerical value indicates the average value of 5 test values.

From the above, it can be seen that in Examples 1 to 6, the appearance of the molded bodies is good and the variation in the dimensions of the sintered bodies is extremely small.

[Comparative Examples 1-2] Processing and measurement were carried out in the same manner as in Examples 1-6, except that the weight ratio of the lubricant was not within the range of the present invention. Table 2 shows the formulation of the injection molding composition.
Table 4 shows the results of injection moldability and mold releasability, Table 5 shows the heating temperature and time required for removing the binder, and surface roughness. Table 6 shows the variation in the dimensions of the sintered body. Table 7 shows the point bending strength.

[Conventional Examples 1 to 3] Examples 1 to 6 except that an additive not within the scope of the present invention was included instead of the lubricant.
It was treated and measured in the same manner as above. The formulation of the injection molding composition is shown in Table 3, the results of injection moldability and mold releasability are shown in Table 4, the heating temperature and time required for debinding and the surface roughness are shown in Table 5, and the variation in dimensions of the sintered body is shown in Table 5. Table 6 shows the three-point bending strength of the sintered body, and Table 7 shows the three-point bending strength of the sintered body.

[Examples 7-8] The sintering powder shown in Table 8 was used instead of the zirconia powder used in Examples 1-6, and the powder was injected in the same manner as in Examples 1-6. A molded body was obtained, subjected to binder removal treatment, and further sintered under the conditions shown in Table 8, and the three-point bending strength was measured in the same manner as in Examples 1 to 6. The results are shown in Table 8.

[Conventional Examples 4 to 5] In order to compare with Examples 7 to 8, the same sintering powders as in Table 8 were used, and after compression molding by the usual powder metallurgy method, these molded bodies were It was sintered under the same conditions as in Example 8, and the three-point bending strength was measured in the same manner as in Examples 7-8. The results are shown in Table 9.

From the above results, it can be seen that the composition of this example is particularly effective for injection molding.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5] <Note> If the maximum height (width, R max ) measured according to JIS B 0601 is 6.3 μm or less ▽▽▽
In the case of 6.3 to 25 μm, ▽▽.

[0067]

[Table 6]

[0068]

[Table 7]

[0069]

[Table 8]

[0070]

[Table 9]

[0071]

[Effects of the Invention] Since the present invention is constructed as described above, the binder removal process can be advantageously performed by heating at a relatively low temperature of 250 to 300°C, and furthermore, the molded product and the mold can be released smoothly. This improves the stability of injection molding.

Further, according to the present invention, a good injection molded body can be obtained using ceramic sintering powder,
Furthermore, it can be used for pinpoint gate type molds that do not require gate cutting, and the weight of the molded product can be reduced by recycling.
It is possible to obtain a sintered body with no dimensional variations and extremely small dimensional variations, and as a result, it is possible to satisfy the dimensional accuracy required for electronic parts and precision mechanical parts, especially for thin parts with complex shapes. The present invention makes it possible to supply powder metallurgy products produced by injection molding at low cost and in a stable state, making a great contribution to the precision industry.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a gear immediately after being molded from an injection molding composition using a mold.

[Explanation of symbols]

10 Gear 12 Pinpoint gate section 14 Runner part 16 Sprue part

Claims (4)

[Claims] 1. An injection molding composition comprising a sintering powder basically made of ceramics and a binder, wherein the sintering powder is made of an oxide ceramic, and the binder is made of saturated alcohol. , at least one lubricant selected from the group consisting of polyunsaturated fatty acids, fatty acid amides, saturated straight chain fatty acids, and monounsaturated fatty acids, low density polyethylene, and paraffin wax. thing. 2. The injection molding composition according to claim 1, wherein the mixing ratio of the sintering powder and the binder is in the range of 30:70 to 70:30 by volume. 3. The binder contains 15 to 70% by weight.
2. The injection molding composition according to claim 1, comprising: low density polyethylene, 10 to 80% by weight of paraffin wax, and 0.5 to 40% by weight of a lubricant. 4. The binder contains 15 to 70% by weight.
3. The injection molding composition according to claim 2, comprising: low density polyethylene, 10 to 80% by weight of paraffin wax, and 0.5 to 40% by weight of a lubricant.