KR100547256B1 - Crack Inhibition Method for Alumina Ceramics Molded by Wet Molding - Google Patents

Abstract

The present invention relates to a method for suppressing cracking of alumina ceramic molded bodies manufactured by a wet molding method, and more particularly, to mixing a ceramic slurry and a polysaccharide-based polymer aqueous solution, which is a room temperature solidified polymer, as a gel-forming polymer. By injecting alumina ceramics into the mold by adding polyvinyl alcohol as a polymer for strength reinforcement during wet molding, alumina ceramics molded products are produced without cracking even if dried in a shorter time than the conventional molded product manufacturing method. As the strength thereof is effectively increased, it is possible to suppress the occurrence of fine cracks, which may occur during drying, handling or processing. About All.

Polysaccharides, polyvinyl alcohol, alumina ceramics

Description

Inhibition method for dry crack of alumina green body prepared by wet forming technique}             

1 is a flow chart showing the overall process of the present invention.

Figure 2 is a photograph of the alumina ceramic moldings produced in the present invention.

3 is a graph showing the change in the dry shrinkage of the alumina ceramics molded product prepared by adding only the gel-forming polymer according to the comparative example and the alumina ceramics molded product prepared by adding the polymer for strength reinforcement according to Examples 2, 3 and 4.

4 is a graph showing the change in strength of the molded body according to the amount of the polymer for strength reinforcement.

The present invention relates to a method for suppressing cracking of alumina ceramic molded bodies manufactured by a wet molding method, and more particularly, to mixing a ceramic slurry and a polysaccharide-based polymer aqueous solution, which is a room temperature solidified polymer, as a gel-forming polymer, to a desired shape. By injecting alumina ceramics into the mold by adding a polyvinyl alcohol as a polymer for strength reinforcement during the wet molding process, the alumina ceramics molded body is dried within a shorter time than the conventional molding method, and its strength is effectively increased. The present invention relates to a method of manufacturing alumina ceramics molded body having improved reliability in terms of mechanical strength and thus, in a simpler form, as it becomes possible to suppress occurrence of fine cracks, which may occur during drying, handling or processing.

Ceramic materials are widely used in the semiconductor, display, and steel industries because of their excellent heat resistance, abrasion resistance, and corrosion resistance. Parts using ceramic materials require formulation in various shapes ranging from simple shapes to complex shapes. do. As such, the importance of ceramics is increasing as an industrial material. However, due to the large-scale product characteristics and excessive initial investments related to the actual shape of ceramics in complex shapes, domestic research has focused on the ceramic material itself rather than the improvement of the manufacturing method. I'm staying in the study.

Therefore, the development of a method that can easily and inexpensively form a low-cost real-shaped ceramics is indispensable in order to provide a breakthrough for the practical use of ceramic materials that are applied in various fields as described above.

Conventional ceramic molding methods include slip casting, injection molding, cold isostatic pressing, and the like.

Here, the slip casting technique is a method of separating and solidifying the water in the slurry in the mold, so that the composition and density of the molded body are non-uniform, so that cracking and warping occurs during drying and sintering, and that the strength of the molded body is low and thick (about 10 mm or more). ) There was a problem in manufacturing the molded article. Injection molding technology is a method of molding by applying pressure to a slurry to which a large amount of organic material (20 to 25% by weight) is added. The problem of completely removing organic materials without cracking after injection molding and the environmental pollution problem of harmful gas treatment generated at this time There is a problem such as the rise. In addition, since the cold isostatic pressing is difficult to manufacture in a real shape, and the amount of processing after the molding is increased, the parts price is high, and therefore, problems in industrialization, such as lack of economics, have been pointed out.

In order to overcome the shortcomings of the conventional ceramic molding techniques as described above, the gel casting technique (US Pat. No. 5,028,362) was developed at Oak Ridge National Laboratory in 1989. The above-mentioned gel casting technique disperses ceramic powder in a solution in which 10 to 20% by weight of monomer is dissolved in a solvent to make a slurry, adds a gelling initiator and a catalyst, and injects it into a mold to be molded, and at a temperature of 60 to 80 ° C. It is a method of manufacturing a molded object by the method of gelatinizing by superposing | polymerizing. Since this technique uses a slurry having a relatively low viscosity, it has good fluidity during injection, which makes it possible to homogeneously manufacture a complex shaped body, and the strength of the molded body is higher than that of the slip casted by the polymer, and the content of organic matter in the manufactured molded body. Since it is about 2.5 to 5% by weight, there is an advantage that the removal of organic matter is relatively easy as compared with injection molding during firing. However, since the monomers such as acrylamide and methylenebisacrylamide used in the gel casting technique, initiators such as ammonium persulfate or potassium persulfate, and catalysts such as tetradimethylenediamine, there are toxicity and environmental pollution problems. The polymerization temperature is relatively high, such as 60 to 80 ℃, the strength of the molded body is easy to handle, but may have a problem that breaks or breaks during processing, there is a problem that toxic gas is generated by decomposition of organic matter during firing.

Among other molding methods, a molding method using a polysaccharide-based gel-forming polymer (US Pat. No. 4,734,237) is a method of injection molding at 80 to 100 ° C. by adding about 4% by weight of organic material, which uses acrylamide as described above. Compared to the gel casting method, the problem of generation of toxic gas due to decomposition of organic matter is reduced, but due to the characteristics of the polysaccharide gel, the strength of the molded body is low, making it difficult to handle and difficult to process.

Accordingly, in the present invention, as a result of research efforts to solve the above problems, when polyvinyl alcohol is added as a strength-reinforcing polymer when molding alumina ceramics using a polysaccharide-based gel-forming polymer, the amount of the gel-forming polymer can be minimized. While it was confirmed that the occurrence of dry cracking can be suppressed and the strength of the alumina ceramic molded body can be effectively increased, the present invention was completed.

In the present invention, it is confirmed that the formation of cracks during drying can be further suppressed by adjusting the drying rate in three steps according to the moisture content of the molded body when the molded product is added to the above-described strength reinforcing polymer. This invention was completed.

Therefore, in the present invention, when molding alumina ceramics using a polysaccharide-based gel-forming polymer, the strength of the molded product is improved to suppress dry cracking by adding a strength reinforcing polymer and to improve handling and workability by controlling the drying speed during drying. Its purpose is to provide a way to make it work.

According to the present invention, in the wet molding method of an alumina ceramic molded body using a polysaccharide-based gel-forming polymer, after molding the alumina ceramic molded body by a gel casting method using polyvinyl alcohol as a polymer for strength reinforcement, the water content of the molded body is 0.18 or more. In the first step is carried out at a drying rate of 20 × 10 ^-3 g / hr · cm 2, The second step is carried out at a drying rate of 10 × 10 ^-3 g / hr · cm 2, and the water content in the range of 0.17 ~ 0.07 If less than 0.07 is characterized in that the crack suppression method of the alumina ceramics molded body dried in a third step carried out at a drying rate of 1 × 10 ^-3 g / hr · cm 2.

The present invention will be described in detail as follows.

The present invention mixes a polysaccharide-based polymer aqueous solution of a room temperature solidification polymer as a ceramic slurry and a gel-forming polymer and injects it into a mold of a desired shape to form polyvinyl alcohol when the alumina ceramics are formed by a wet method. It is characterized in that it is added as a polymer for strength reinforcement, the detailed process is shown in the accompanying drawings.

First, an aqueous alumina ceramic slurry solution is prepared. A dispersant and an antifoaming agent are mixed with water as a solvent, a ceramic powder is added, and then a stable ceramic slurry is prepared by using a ball mill, wherein the solid content of the ceramic slurry solution is 40 to 55 vol. If the solid content is less than 40% by volume, cracking is liable to occur due to large drying shrinkage during drying after molding, and if the solid content exceeds 55% by volume, the viscosity of the slurry becomes high Injection becomes difficult. As a dispersant, an aqueous dispersant such as an aqueous solution of ammonium polymethacrylate may be used. The amount of the dispersant is preferably 1 to 2% by weight based on the amount of ceramic powder used.

Gel-forming polymer aqueous solution is prepared by placing the gel-forming polymer in water and heating it to a temperature of 60 ~ 80 ℃ dissolved. The gel-forming polymer to be used is a polysaccharide-based polymer that melts well in water, which is a solvent at a temperature of 60 to 80 ° C, and solidifies when cooled to 5 to 25 ° C. In this case, as the polysaccharide-based polymer, For example, those selected from agar and derivatives thereof can be used. The amount of the gel-forming polymer is 0.2 to 0.7% by weight relative to the ceramic powder. When the amount of the gel-forming polymer is less than 0.2% by weight, the amount of organic matter that hardens the molded body after wet molding is difficult to maintain the shape of the molded body. When the weight% is exceeded, the viscosity of the wet molding slurry is increased, so that the fluidity is increased, so that it is difficult to inject into the complex mold and it is difficult to remove the organic matter after molding.

The polymer solution for strength reinforcement is prepared by dissolving polyvinyl alcohol in water so as to be 0.2 to 0.7% by weight based on the amount of ceramic powder used. At this time, when the amount of the polymer for strength reinforcement is less than 0.2% by weight, the strength reinforcing effect of the molded body does not appear, and when it exceeds 0.7% by weight, the viscosity of the ceramic slurry becomes too high, making it difficult to inject into the mold, and harmful substances generated during organic matter removal. The amount of gas also increases, which is undesirable.

The aqueous alumina ceramic slurry, the gel-forming polymer aqueous solution and the strength-reinforcing polymer aqueous solution prepared as described above are placed in a high viscosity stirrer and mixed uniformly, and then degassed in a vacuum of 200 to 700 mmHg. At this time, the temperature of the mixing vessel is controlled to maintain the 60 ~ 80 ℃ to prevent the gel-forming polymer to coagulate so that the final solid content of the slurry for wet molding is 40 to 55% by volume.

A uniformly mixed wet molding slurry is injected into a mold maintained at 40 to 60 ° C. to form a desired shape. At this time, the injection pressure is 1 to 5 kgf / cm ² and the isolation pores are not generated in the mold. Design the mold or vacuum the inside of the mold.

After the injection into the mold is completed, the temperature of the mold is sufficiently cooled in the range of 5 to 25 ° C. to solidify the injected slurry, and then the mold is removed and demolded.

Drying the demolded molded body by controlling temperature and humidity to produce a ceramic-shaped ceramic molded body without cracks, and when demolding, the temperature is controlled to be in the range of 20 to 80 ° C., and the relative humidity is 60 to 90%. Do.

In the present invention, there are other characteristics in that the drying conditions are carried out in three steps according to the water content of the molded body.

That is, the optimum drying conditions, the first step to dry relatively quickly at a drying rate of 20 × 10 ^-3 g / hr · cm 2 when the water content of the molded body is 0.18 or more, and 10 × 10 ^-3 g in the water content 0.17 ~ 0.07 range The second step of drying at an intermediate rate of / hr · cm 2 and the third step of drying at a slow rate of 1 × 10 ⁻³ g / hr · cm 2 or less from a water content of less than 0.07 may be used to produce a molded product without cracking. To help.

The molded article dried as described above is sintered at a temperature of 1550 to 1750 ° C. for 1 to 3 hours to prevent cracking desired in the present invention and to produce an alumina ceramic molded article having excellent strength.

The sintered body prepared as described above was measured and compared by the four-point bending strength test of the wavelet coefficient, fracture toughness and strength of the sintered body. The wavelet coefficient of the sintered compact manufactured by this invention showed the value of 8-15, fracture toughness of 4.3-5.4 MPa * m ^1/2 , and fracture strength of 390-420 MPa.

The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited thereto.

Example 1

Alumina powder (AES11, Sumitomo Co. Ltd, Japan) was added to a solution in which 2% by weight of Darvan C (RT Vanderbilt Co. Inc, USA, main ingredient name ammonium polymethacrylate) was dissolved in alumina powder as a dispersant in water. Ball milling for 4 hours using a ball to prepare a water-based alumina ceramic slurry. Agar, which is a polysaccharide-based polymer, was used as a gel-forming polymer, and weighed to 0.7 wt% with respect to alumina powder, and then dissolved in water at 80 ° C. to prepare an aqueous solution. At this time, the concentration of the gel-forming polymer aqueous solution was 10% by weight. Polyvinyl alcohol was used as a polymer for strength reinforcement, and weighed to 0.2% by weight with respect to alumina powder, and dissolved in water to prepare an aqueous polymer solution for strength reinforcement, and its concentration was 10 to 30% by weight.

An aqueous alumina ceramic slurry is placed in a stirring vessel, and 0.7 wt% of an aqueous gelling polymer solution is added while maintaining the temperature of the slurry at 60 to 80 ° C. 0.2 wt% of polyvinyl alcohol aqueous solution, which is a polymer for strength reinforcement, was added thereto to prepare a wet alumina ceramic slurry. At this time, the solid content of the final slurry was adjusted to 47% by volume.

For the homogeneous mixing, the stirring time was 2 hours, and degassed in a vacuum of 600 torr to prepare a uniform casting slurry containing no pores. A mold in the form of a square plate, a tube, a dome, or the like was maintained at a temperature of 50 ° C., and then the slurry was injected by injection at a pressure of 2 kgf / cm 2.

After molding, after cooling sufficiently to the internal molded body at a temperature of 5 ° C. and demolding to prepare a molded product, when the water content of the molded product is 0.18 or more, it is dried at a rate of 20 × 10 ⁻³ g / hr · cm 2. Dry relatively fast at 90% relative humidity and dry at a rate of 10 × 10 ^-3 g / hr · cm2 at a moisture content of 0.17 to 0.07 at medium speed at a temperature of 20 ° C and 90% relative humidity. From the water content of less than 0.07, to dry at a rate of 1 × 10 ^-3 g / hr · cm 2 or less to dry at a slow rate of 100% relative humidity at a temperature of 20 ℃ to prepare alumina molded body.

Examples 2-4

An alumina ceramics molded body was manufactured in the same manner as in Example 1 except that the amount of polyvinyl alcohol added as a polymer for strength reinforcement was 0.3 wt%, 0.4 wt%, and 0.5 wt%.

Comparative Example 1

Alumina ceramics molded body was prepared through the same method as Example 1, except that polyvinyl alcohol, which is a polymer for strength reinforcement, was not used.

Experimental Example: Evaluation of Properties of Alumina Molded Body

Dry shrinkage rate, dry molded body strength, and sintered body of the molded body according to the addition amount of the strength-reinforcing polymer added to the wet-molded alumina molded body using the gel-forming polymer with reference to Examples 1 to 4 and Comparative Example 1 Mechanical properties were measured.

Shrinkage was calculated by observing the length change of the molded body during drying, and the optimum drying condition was selected by calculating the change of moisture content from the following equation 1 by observing the weight change.

In Equation 1, W _d is the moisture content, W _w is the weight of water in the molded body, W _s is the weight of the solid component in the molded body.

Table 1 below shows the presence or absence of cracks in the dried moldings when the polymer for strength reinforcement was used or not. In addition, Figure 2 shows a picture of the alumina ceramic molded body produced in the present invention, it can be seen that the real ceramic molded body can be produced without cracking by adding the polymer for strength reinforcement of the present invention.

Comparative example Example 1 Example 2 Example 3 Example 4 Polymer content for strength reinforcement (wt%) 0 0.2 0.3 0.4 0.5 Dry crack occurrence U U radish radish radish

Dries quickly at a drying rate of 20 × 10 ^-3 g / hr · cm 2 until the water content is 0.18, and then dries at an intermediate rate of 10 × 10 ^-3 g / hr · cm 2 at a water content of 0.17 to 0.07 and less than 0.07. In the case of drying at a slow speed of 1 × 10 ⁻³ g / hr · cm 2, no dry cracking occurred in the molded article to which 0.3 to 0.5% by weight of polyvinyl alcohol as a polymer for strength reinforcement was added.

On the contrary, in the case of the comparative example in which only the gel-forming polymer was added, dry cracks occurred when dried under the same conditions. The reason for this is that the gel-forming polymer alone can not prevent the stress generated during the dry shrinkage of the molded article, but if the strength of the molded article is increased by adding the strength reinforcing polymer, it can withstand the stress generated during the dry shrinkage.

The dry shrinkage rate varies slightly depending on the shape of the molded article, but the dry export rate of the alumina molded article produced according to the method of the present invention was about 1.3 to 7.0%. Figure 3 shows the change in the dry shrinkage of the molded article added only the gel-forming polymer and the molded article added the strength reinforcing polymer. When the polymer for strength reinforcement was added, there was no significant change in the shrinkage regardless of the added amount, and the dry shrinkage rate of the molded product was about 3% in the longitudinal direction and about 5% in the thickness direction for the square plate of 450 × 400 × 30mm. Indicated. The strength of the dried molded body was obtained from Equation 2 by performing a compressive strength test on a specimen having a diameter of 10 mm and a thickness of 5 mm. The cross head speed was 0.5 mm / min.

In Equation 2, σ _f is the strength, P is the load at break, D is the diameter of the specimen, t is the thickness of the specimen.

In general, the molded article containing only the gel-forming polymer shows the strength of 1 to 5 MPa, but the molded article prepared by the method of the present invention has an increased strength of about 4 to 7 times that of the existing molded article. It was found through the change in strength of the molded body according to the amount of the polymer for strength reinforcement. That is, the shrinkage did not show a significant change according to the amount of strength reinforcing polymer added, while the strength of the molded article increased significantly as the amount of the polymer for reinforcing reinforcement increased. The strength of 8 to 14 MPa increased by 4 to 7 times compared to 2 MPa of.

The results of measuring the mechanical properties of the specimens sintered under the same conditions of the examples of the present invention and the comparative examples are summarized in Table 2 below.

Comparative example Example 1 Example 2 Example 3 Example 4 Polymer content for strength reinforcement (wt%) 0 0.2 0.3 0.4 0.5 4-point bending strength (MPa) Average 420.3 413.5 420.6 415.3 410.7 Standard Deviation 62.0 37.2 71.0 37.5 37.3 Fracture Toughness (MPa · m ^1/2 ) IF law Average 5.0 5.1 4.9 5.4 4.8 Standard Deviation 0.5 0.5 0.3 1.2 0.5 IS law Average 4.9 4.8 4.6 4.3 4.3 Standard Deviation 0.2 0.3 0.4 0.1 0.2 Wavelet coefficient 8.22 7.82 10.29 12.23 14.63

As shown in Table 2, the four-point bending strength results did not show a significant difference as compared with the case where the strength-reinforcing polymer of the comparative example was not added at about 410 to 420 MPa. Fracture toughness also had a value of 4.3 to 5.4 MPa · m ^1/2 , and there was no significant difference between the comparative examples and the examples.

On the other hand, the wavelet coefficient, which is a measure of reliability of material destruction, was higher when 0.3 wt% or more of the polymer for strength reinforcement was added as in the case of the example. A large wavelet coefficient means that the fracture strength of the material has a narrow dispersion, which indicates that the strength of the material is distributed in a reliable section, which is one of the most important properties in the engineering application of ceramics. The reason for this is that by adding a strength reinforcing polymer to improve the strength of the molded body, it effectively suppresses the occurrence of defects such as microcracks that may occur during handling or drying.

Therefore, according to the present invention, in the case of wet molding using a polysaccharide-based gel-forming polymer, the addition of polyvinyl alcohol as a strength-reinforcing polymer increases the strength of the molded body, thereby inhibiting the occurrence of cracks during drying. The drying time can be made relatively short compared to the case where only the bay is added. In addition, the effect of suppressing dry cracking by the addition of a polymer for strength reinforcement has the effect of improving reliability in terms of mechanical strength of the sintered body.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (4)

In the wet molding method of an alumina ceramic molded body using a polysaccharide gel-forming polymer, After molding the alumina ceramic molded body by gel casting method using polyvinyl alcohol as a polymer for strength reinforcement, When the water content of the molded body is 0.18 or more, the first step is carried out at a drying rate of 20 × 10 ^-3 g / hr · cm 2, If the water content is 0.17 ~ 0.07 range is carried out at a drying rate of 10 × 10 ^-3 g / hr · cm 2 And a second step, and a moisture content of less than 0.07, drying in a third step performed at a drying rate of 1 × 10 ⁻³ g / hr · cm 2. The method of claim 1, wherein the alumina ceramic contains alumina powder in a solid content of 40 to 55% by volume in water. The method of claim 1, wherein the polyvinyl alcohol is used in an amount of 0.2 to 0.7% by weight based on the amount of alumina used. delete

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