JPH08290975A - Ceramic composition, core material and production of ceramic product - Google Patents

Abstract

PURPOSE: To stabilize qualities and to prevent occurrence of defects such as sink mark, crack, weld line, etc., by blending a ceramic powder material with an organic binder comprising a lactic acid polymer as an active ingredient. CONSTITUTION: This ceramic composition is obtained by uniformly blending 70-90 pts.wt. of one or a mixture of two or more of materials comprising Al2 O3 , BN, ZrO2 and BeO as an oxide base, SiC, TiC and WC as a carbide base and Si3 N4 , BN, AlN, etc., as a nitride base, having 0.2-1μm particle diameter with 10-30 pts.wt. of a D,L-lactic acid polymer having 10,000-200,000 weight-average molecular weight. Then the composition is molded into a green molding of a fixed shape by a molding means such as injection molding, etc. The green molding is heated at 25-50 deg.C/hour heating rate up to 400-450 deg.C to decompose and remove the lactic acid polymer of a binder and baked at a baking temperature suitable for a ceramic powder material to be constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic composition and a method for producing a ceramic product using the same.
The present invention relates to a ceramic composition using an organic binder that does not generate defects such as formation of cracks and weld lines; a core material that improves the production efficiency of a ceramic product having a hollow structure; and a method for manufacturing a ceramic product using this ceramic composition. .

[0002]

2. Description of the Related Art Conventionally, a ceramic composition obtained by blending a ceramic powder material with an organic binder to give fluidity is made into a molded body (green molded body) by a molding method such as injection molding, and this is degreased and fired. It is well known to manufacture ceramic products.

Examples of the organic binder include polyethylene, polystyrene, polypropylene and ethylene.
Thermoplastic resins such as propylene copolymers, ethylene / butene copolymers, polymethacrylic acid esters, ethylene / acrylic acid ester copolymers, polystyrene and cellulose acetate can be mentioned. These are paraffin wax, microcrystalline wax, diethyl phthalate. , A mixture of a plasticizer such as dibutyl phthalate, dioctyl phthalate, a fatty acid ester, a vegetable oil and an animal oil, and a lubricant such as stearic acid, a metal salt of stearic acid and mineral oil, as appropriate (JP-A-3-29037).
4 publication).

In recent years, ceramic products having a hollow structure or a complicated inner surface structure such as an optical fiber connector have been required, and in the production of such ceramic products, a ceramic powder material is usually blended with an organic binder to improve fluidity. A method is used in which the ceramic composition and the core material are integrally molded, the resulting molded body is heated to remove the core material, and the core material is degreased and fired.

Typical examples of the core material used at this time are sand (sand core), low melting point alloy, wax and the like. As a specific example, a mixture material with a salt is used for the sand core material, and Sn-Bi, Sn-Pd for the low melting point alloy.
Are widely used materials. As the wax, petroleum wax such as paraffin wax and microcrystalline wax, synthetic hydrocarbon wax such as polyethylene wax and polypropylene wax, modified wax such as montan wax derivative, paraffin wax derivative and microcrystalline wax derivative are generally used. It is used.

In addition to the above, as a method of producing a ceramic product having a hollow structure, divided green molded bodies are molded in advance, and then these are chemically or mechanically used by using an adhesive or the like. There is a method of obtaining a ceramic product by mechanically bonding and degreasing and firing the obtained green compact.

[0007]

However, the following problems have been pointed out regarding the organic binder and various additives.

(1) When a thermoplastic resin is used as an organic binder, a ceramic powder material, a lubricant and a plasticizer to which a sintering aid is added, if necessary, are batched at a temperature near the melting point of the thermoplastic resin. It is necessary to knead for several tens of minutes to 1 to 2 hours by the formula treatment. However, in a series of kneading operations, it is difficult to strictly control the amount and timing of addition of the organic binder and the plurality of additives to the ceramic powder material, and the treatment time thereof. Many variables have made the quality of the resulting ceramic composition unstable.

(2) When the ceramic composition is injection-molded, it is necessary to impart heat fluidity, moldability, and mold releasability to the ceramic composition according to the shape of the final product. It depends greatly on the choice of additives. However, it is difficult to select the optimum combination from various types, and depending on the selection of the organic binder, the resulting ceramic product
Defects such as sink marks, cracks, and formation of weld lines are often generated.

(3) Generally, a thermoplastic resin used as a binder has a high melt viscosity, and therefore has a low affinity with a ceramic powder material having a small particle size, and it is difficult to reduce the addition rate as a binder. Is.
In particular, in order to improve the physical properties of ceramic products obtained by degreasing and firing green compacts, considering that the particle size of the powder is submicron and the bulk density is increasing, compounding of organic binders is becoming more and more common. Is becoming difficult, and as a result, it is necessary to increase the amount of binder.

(4) The degreasing step is usually carried out by heating the green compact to thermally decompose and vaporize the organic binder. In that case, if the green molded body is heated rapidly, it will be in a locally heated state, and the organic binder in the green molded body will partially soften and melt and cannot maintain a certain shape, or gas generated by decomposition will be generated. It may be trapped inside and cause defects such as blisters, cracks, or deformation. Therefore, the degreasing process needs to be performed carefully at a very low temperature rising rate of about 0.5 to 10 ° C./hour and for a long time of several tens to several hundreds of hours. for that reason,
The complexity of the degreasing process is a major impediment factor in attempting industrial mass production of sintered ceramic products.

(5) In the degreasing step, when degreasing the green molded body, it is necessary to collect the toxic thermal decomposition gas generated from the organic binder, and a treatment step and a treatment facility therefor are required.

(6) The organic binder made of petroleum-based synthetic resin is decomposed and removed in the degreasing step to become a gaseous monomer, which is not reused as a monomer for a resin raw material but is exhausted in the atmosphere as a waste gas. Has been released to.

On the other hand, in the conventional molding method using the core material,
Each of them has the following drawbacks, and it is difficult to say that the purpose can be sufficiently satisfied.

(1) When a sand core is used as the core material, in order to make the inner surface of the green compact smooth, the particle size of the sand must be fairly small and the particle size must be uniform, which makes it difficult to prepare powder. It is necessary to go through a treatment process.
Further, since the sand particles have poor adhesiveness to each other, the core material may fall off during coating injection molding of the ceramic composition.

(2) If a low melting point alloy is used for the core material, various shapes of core material can be manufactured and it is possible to produce a green molded body having a complicated inner surface structure. The workability is extremely poor because the weight of the core material itself is heavy when it is mounted on or when the green molded body is taken out.
Further, the core material is generally melted by induction heating, but since it is a special heating method and requires a considerable amount of time, it is not an economically advantageous process. In addition, many of these alloys use metals that may adversely affect the human body due to inhalation and accumulation in the body, and it is difficult to say that these are preferable materials for safety and hygiene.

(3) In the case of a wax-based core material, it is necessary to maintain a constant shape as the core material during injection coating molding of the ceramic composition, but since the melting temperature of this material is as low as about 90 ° C., If the holding time in the mold and the set temperature are not strictly controlled, the surface of the core material may be in a molten state and a complicated surface shape may not be reproduced. Moreover, since the absolute strength is low, if the injection pressure or the holding pressure is increased, the core material may be deformed or broken in the mold.

(4) When a low melting point alloy or a wax-based material is used as the core material, when the core material is removed from the green molded body, first, the core material is melted by heating or dissolved in a solvent and then removed. Furthermore, it is necessary to go through two steps of debinding the green molded body.

(5) In the method for producing a ceramic product having a hollow structure without using a core material, the green compacts are divided and molded, and the green compacts are chemically or physically bonded to each other to form a single green compact. Although a green molded body having a hollow structure is used, this joining process is very time-consuming, uneven joining is likely to occur, and various defects such as cracks in the joined portion during degreasing and firing are likely to occur.

The present invention is intended to overcome the above-mentioned drawbacks in the production of conventional ceramic compositions and ceramic products, provides an excellent organic binder and core material, and obtains the quality of the obtained ceramic molded product. Is stable, does not cause defects such as sink marks, cracks, and formation of weld lines, and has an excellent mass productivity, and a method for producing a ceramic product having a hollow structure using the same It is what A further object of the present invention is to provide a method for producing a ceramic product in which the core removal and binder removal steps can be performed at the same time.

[0021]

Based on these findings, the present inventor has found that the organic binder and the core material of the ceramic composition have fluidity imparting properties to the ceramic powder material and their affinity, and the ceramic composition. We investigated from various points of view such as moldability of products, ease of removal of core material, lightness, influence of organic binder and core material on environment. As a result, the lactic acid polymer has polar groups such as carboxyl groups and hydroxyl groups, has a better affinity with ceramic powder materials than general thermoplastic resins, and has high thermal fluidity when heated and small amounts. It is possible to impart appropriate fluidity to the ceramic powder material with the composition of, and in the degreasing process, as the temperature rises, it is a depolymerizable polymer that undergoes thermal decomposition and vaporization at a relatively low temperature. It has been found that it is a very useful material as an organic binder. In addition, lactic acid polymer is easily reduced to monomers, water, carbon dioxide, etc. by thermal decomposition during the decoreing operation, and these decomposition products are also non-toxic, so they can be removed without adversely affecting the environment. It has been found that a core process can be performed and it is also useful as a core material.

Further, if a ceramic composition using a lactic acid polymer as an organic binder is integrally molded with a core material using a lactic acid polymer and a heating operation is performed for the purpose of removing the core material from the obtained green molded body, At the same time, it was found that the binder can be removed at the same time, and the shape of the green molded body does not collapse during the process, and the strength (green strength) is sufficient, and the present invention has been completed.

That is, the present invention provides a ceramic composition comprising a ceramic powder material and an organic binder containing a lactic acid polymer as an active ingredient.

The present invention also has a weight average molecular weight (Mw) of 5
It is intended to provide a core material for producing a ceramic product having a hollow structure, which comprises a D- or L-lactic acid polymer of 20,000 to 200,000 as an active ingredient.

Further, the present invention provides a method for producing a ceramic product, which comprises molding the above-mentioned ceramic composition, heating the obtained green molded body to remove the lactic acid polymer, and then firing. Is.

Furthermore, the present invention has a hollow structure characterized in that the above-mentioned ceramic composition containing the above-mentioned core material is molded, and the obtained green molded body is baked after removing the heated lactic acid polymer. A method of manufacturing a ceramic product is provided.

The lactic acid polymer used in the present invention is represented by the following general formula (1).

[0028]

Embedded image

As the lactic acid polymer used as the organic binder in the present invention, D, which has no optical activity,
The L-form is preferred. On the other hand, as the lactic acid polymer used for the core material of the present invention, the optically active D- or L-form is preferable. This is because the D, L-lactic acid polymer mixed with the ceramic powder material as the binder material is amorphous and does not have a melting point, so that D- or L- of the core material is used.
If the molding is carried out below the melting point of the lactic acid polymer, only the binder will be in the molten state while the core material retains the desired shape, and it is possible to mold the ceramic powder material while imparting appropriate fluidity. is there.

When the green compact obtained as described above is decoreed and debindered, if the temperature of the green compact is raised in a heating furnace, a binder material having no melting point can be obtained. The D, L-lactic acid polymer first becomes a fluid, and then gradually thermally decomposes and vaporizes. At this time D-
Alternatively, if the melting point of the L-lactic acid polymer is lower than the melting point of the L-lactic acid polymer, the core material retains the solid shape and plays a role of preventing rapid collapse of the green molded body. Further, if the melting point is higher than the melting point, it is gradually pyrolyzed like the D, L-lactic acid polymer and finally vaporized. These are ceramics produced when the binder which is the D, L-lactic acid polymer is thermally decomposed and vaporized. Through the flow path between particles, it is completely removed to the outside of the molded body.

The weight average molecular weight Mw of the lactic acid polymer suitable in the present invention is appropriately in the range of 10,000 to 200,000 in the case of the D, L-lactic acid polymer used as the binder. Further, in the case of D- or L-lactic acid polymer used as the core material, 50,000 to 200,0
The range is 00. Therefore, the degree of polymerization n shown in the above formula
Is 10,000 to 200,000 when the weight average molecular weight is D, L-lactic acid polymer, and D- or L
-50,000 to 200,000 in the case of lactic acid polymers
It is desirable to show a value such that it becomes zero. Further, if the molecular weight is within this range, the polymer can be synthesized in a relatively short time by the ring-opening polymerization method of lactide which is a cyclic dimer of lactic acid.

The weight average molecular weight Mw of the lactic acid polymer is 20.
There is no particular problem even if it exceeds 50,000, but when trying to obtain one having a molecular weight exceeding this, it is necessary to use lactide having a considerably high purity and for a long time under an atmosphere in which water and oxygen are completely removed. It is necessary to synthesize the polymer over time.
At this time, if the reaction conditions are not rigorously set, the ring-opening polymerization reaction of lactide does not proceed sufficiently, and the Mw is 200,0.
It becomes impossible to obtain a high molecular weight polymer exceeding 00.

D and L used as organic binders
-If the weight average molecular weight Mw of the lactic acid polymer is less than 10,000, the melt viscosity of the heat fluid is remarkably reduced, so that the viscosity of the ceramic composition is reduced, and the composition is molded into a complex shape or a shape having a hollow structure. It is difficult to do so, which is not preferable. Furthermore, in the case of core material, D-
Alternatively, the weight average molecular weight Mw of the L-lactic acid polymer is 50,
If it is less than 000, the melting point of the polymer becomes low,
In addition to being capable of being molded only at a temperature below a limited temperature, the mechanical strength becomes poor, which may cause deformation or destruction during molding of the ceramic composition, which is not preferable.

When the D, L-lactic acid polymer having the above-mentioned molecular weight range is used as an organic binder, the melt viscosity is lower than that of other thermoplastic resins, and therefore the amount of the binder is smaller than that of the conventional method. It is possible to form a thin film on the surface of and to provide an ideal fluidized state as a filled state of a mixed system of powder and an organic binder. Such a ceramic composition is easily plastically deformed,
In addition, since the thermal fluidity is also improved, it becomes possible to obtain a green molded body without causing defects such as sink marks and cracks during molding. Further, in the conventional method, a lubricant such as wax was added to improve the surface wettability of the ceramic powder material, but the lactic acid polymer has a polar group and has a good affinity with the surface of the ceramic powder material. Therefore, a single binder can sufficiently achieve the purpose.

In the present invention, the weight average molecular weight Mw
Indicates a value measured by gel filtration permeation chromatography (GPC), and more specifically, a value measured under the following measurement conditions. Measuring device: HLC-8020 (manufactured by Tosoh Corporation) Column: TSK gel GMH-H _HR X 2 TSK gel G1000H-H _HR X 1 TSK gel G5000H-H _HR X 1 Separation solvent: Chloroform Sample concentration: 0.3 % (W / v) Sample injection volume: 100 μl

The method for synthesizing the lactic acid polymer as described above is as follows:
It can be produced by a ring-opening polymerization method which has been widely used from the past. This method uses, for example, 1 lactide
When heated to 00 to 120 ° C and in a molten state,
180 ° C while adding 0.05 to 1 part by weight of a catalyst such as tin octylate, stannous chloride and antimony trioxide.
The ring-opening polymerization is carried out while the temperature is raised to 1, and the degree of vacuum in the reaction vessel is raised to 1 to 100 mmHg.

The type and particle size of the ceramic powder material in the ceramic composition of the present invention are not particularly limited, but as the type, oxide type Al ₂ O ₃ ,
ZrO ₂ and BeO; carbide-based SiC, TiC and WC; nitride-based Si ₃ N ₄ , BN and AlN. The particle size is preferably 0.2 to 1 μm. Two or more types of ceramic powder materials can be mixed and used.

The mixing ratio of the lactic acid polymer as the organic binder in the ceramic composition of the present invention is preferably 10 to 30 parts by weight, more preferably 70 to 90 parts by weight of the lactic acid polymer, more preferably the ceramic powder material. Lactic acid polymer 1 to 75 to 88 parts by weight
2 to 25 parts by weight.

The ceramic powder material having the above blending ratio and the lactic acid polymer as the organic binder are uniformly mixed by using an appropriate means such as a pressure kneader to obtain the ceramic composition of the present invention. be able to.

The ceramic composition thus obtained is made into a green molded body having a desired shape by a conventional method for manufacturing a ceramic product, for example, a molding means such as injection molding, and the obtained green molded body is heated. Then, the lactic acid polymer is removed (defatted), and then fired to obtain a ceramic product.

Here, the heating temperature necessary for removing the lactic acid polymer as the organic binder may be at least the thermal decomposition temperature of the lactic acid polymer, and for example, 400 to 450 ° C. is sufficient. In addition, the rate of temperature increase at this time can be set to a high rate of 25 to 50 ° C. per hour in view of the thermal characteristics of the lactic acid polymer. Usually, when a thermoplastic resin is used as an organic binder, it is necessary to perform a debinding operation at a slow heating rate in order to prevent defects such as blisters and cracks in the molded body. However, lactic acid polymer gradually undergoes thermal decomposition upon heating, and
Since this completes at a low temperature of 00 to 450 ° C., the degreasing step can be performed efficiently and without causing defects in the green molded body.

The firing temperature in the firing step is usually Al.
_In the case of ₂ O ₃ , it is 1550 to 1750 ° C., in the case of ZrO ₂ , it is 1550 to 1650 ° C., and in the case of Si ₃ N ₄ , it is 1650 to 1650 ° C.
The temperature is 1800 ° C., and in the case of SiC, it is about 2050 to 2200 ° C.

When a ceramic product having a hollow structure is obtained, the above ceramic composition is integrally molded by encapsulating a core material formed by molding a lactic acid polymer, and the obtained green molded body is heated to obtain an organic binder. Alternatively, a method of firing after removing the lactic acid polymer that is the core material may be adopted.

Here, the molding is preferably injection molding, and in particular, a method in which a core material having a desired shape is placed in the mold cavity in advance and the core material and the ceramic composition are injection-molded is preferable.

In order to remove the core material from the obtained green molded body, it is sufficient to heat it to a temperature at which the lactic acid polymer as the organic binder can be removed. That is, when the temperature is gradually raised, the organic binder is first thermally decomposed and vaporized, and then the organic binder is gradually thermally decomposed and vaporized through the space between the ceramic powder materials which is the vaporization flow path of these organic binders. The core material and the organic binder are removed at the same time. The subsequent firing process may be the same as described above.

[0046]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 84 parts by weight of Al ₂ O ₃ powder (center particle size: 0.6 μm),
16 parts by weight of D, L-lactic acid polymer powder having a weight average molecular weight Mw of 28,500 was added to 140 parts by using a batch pressure kneader.
The mixture was kneaded at 40 ° C. for 40 minutes to obtain a lump-like uniform mixture (ceramic composition). This was crushed to obtain an injection molding mixture (ceramic composition). Next, using an in-line screw type injection molding machine with a mold clamping force of 40 tons, the core material which had been molded into a desired shape was mounted in the mold, and while being coated with the ceramic composition, the L-shaped mold was formed. The pipe having a hollow shape of was molded by injection molding. The green molded body thus obtained was heated from room temperature to 450 ° C. at a temperature rising rate of 40 ° C./hour for decoreing and debinding. No defects such as swelling, cracks, and surface peeling were observed in this degreased molded body (degreased body). Then, this degreased body is heated from room temperature to 1600 ° C. for 200 hours per hour.
The mixture was heated at a temperature rising rate of ° C and held at the temperature for 1 hour for firing. Thus, a good ceramics sintered product was obtained.

Example 2 86 parts by weight of Si ₃ N ₄ powder (center particle diameter 0.45 μm) and 14 parts by weight of D, L-lactic acid polymer powder having a weight average molecular weight Mw of 37,400 were used in the same manner as in Example 1. The mixture was kneaded and pulverized in the step to obtain a mixture for injection molding. Next, using an in-line screw type injection molding machine with a mold clamping force of 50 tons,
The ceramic material was coated and injection-molded on the core material that had been mounted in advance in the mold to form the auxiliary combustion chamber. The obtained green molded body was heated from room temperature to 45 in a nitrogen atmosphere.
The binder was removed and the cores were removed by heating to 0 ° C. at a temperature rising rate of 30 ° C. per hour. No defects such as blisters, cracks, and surface peeling were observed in this degreased body. continue,
This degreased body was heated from room temperature to 1750 ° C. at a temperature rising rate of 200 ° C./hour, and baked for 1 hour while maintaining the temperature.
The sintered body thus obtained was a good ceramic product without defects such as cracks and deformation.

[0049]

As is apparent from the above description, according to the present invention, in the manufacturing process of a ceramic product having a hollow structure using a core material, a decoreing and debinding process which has been conventionally performed separately. However, by using the same type of polymer for the core material and the binder material, it is possible to do this in parallel at the same time, and it is possible to significantly reduce the number of steps compared to the conventional process. Becomes In addition, even though the binder is mixed at a smaller addition rate than the organic binders that have been conventionally used, good green molded products can be obtained without causing defects such as cracks and weld lines during injection molding. Can be obtained. Further, even when the debinding operation is performed at a rapid temperature rising rate of 25 to 50 ° C./hour, which has been difficult to achieve so far, defects such as swelling and cracks are not generated, and good characteristics are obtained. It is possible to obtain a ceramics sintered product. Therefore, the time required for manufacturing the ceramics sintered product, which has been required up to now, is significantly reduced, and economically, it becomes possible to mass-produce the product inexpensively. Furthermore, in the above degreasing step,
The organic binder of the lactic acid polymer used in the present invention is completely decomposed by heat, and its decomposition products are mainly recyclable monomers, and the gas produced by decomposition is water or carbon dioxide, so to speak, an ecosystem. Since only the substances present inside are contained, it is possible to reduce the load on the environment as much as possible. In other words, it can be said that the manufacturing method has very excellent characteristics from the viewpoint of environmental protection and effective use of resources.

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Claims (5)

[Claims] 1. A ceramic composition comprising a ceramic powder material and an organic binder containing a lactic acid polymer as an active ingredient. 2. The lactic acid polymer has a weight average molecular weight (Mw).
The ceramic composition according to claim 1, which is a D, L-lactic acid polymer of 10,000 to 200,000. 3. A weight average molecular weight (Mw) of 50,000 to 2
A core material for producing a ceramic product having a hollow structure, characterized by comprising an active ingredient of 100,000 D- or L-lactic acid polymer. 4. A method for producing a ceramic product, which comprises molding the ceramic composition according to claim 1 or 2 and heating the molded body thus obtained to remove the lactic acid polymer, followed by firing. 5. The ceramic composition according to claim 1, which contains the core material according to claim 3, is molded, and the molded body obtained is heated to remove the lactic acid polymer and then fired. Of manufacturing a ceramic product having a hollow structure.