JPH07267741A - Composition for slip casting - Google Patents

Abstract

PURPOSE:To obtain a compsn. for slip casting less liable to a change of viscosity or the inclusion of bubbles at the time of molding by mixing ceramic powder with an aq. polyurethane emulsion as a binder. CONSTITUTION:Ceramic powder such as silicon nitride powder is mixed with an aq. polyurethane emulsion as a binder to produce the objective compsn. for slip casting. The proper amt. of the emulsion used is 0.1-2 pts.wt. per 100 pts.wt. of the ceramic powder. The compsn. may further the blended with a sintering aid such as Y2O3, a dispersant, if necessary. The compsn. is molded by slip casting to produce a molding. Since the viscosity of the compsn. is not dependent on the amt. of the binder added, slip is easily produced and maintained, bubbles are not included at the time of molding and a high quality molding is obtd. High dimensional precision is attained because of a low green shrinkage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention produces a molded product having a high strength and a low shrinkage ratio, in which the viscosity of the composition is not affected by the amount of the binder to be added or the kind of the dispersant, and the binder content is small. The present invention relates to a slip casting composition.

[0002]

2. Description of the Related Art A slip cast molding method is one of the typical methods for producing a ceramic molded body. This slip cast molding method usually uses a mold made of an absorbent material such as gypsum and absorbs water from the slip (ceramic powder suspension) injected into the cavity of this mold to form a slip. It is done by solidifying. The obtained molded body is degreased and then fired to obtain a final ceramic member. This method is generally suitable for producing a large-sized and relatively thin-walled molded product or a molded product having a complicated shape.

When a molded body is produced by such a casting method or an extrusion method, the ceramic powder is bound in a dry state in order to improve the dry strength of the green, that is, until the molded body is sintered. As a matrix for this purpose, it has been proposed to add an organic substance (binder) to a slurry or slip as a raw material.

For example, in the case of extrusion tape molding, a slip having a remarkably high viscosity of 2.3 to 13 Pa · s is generally used, and an aqueous polyurethane (Japanese Patent Laid-Open Nos. 55-113665 and 58-58) is used as an organic binder. -190867), hydrophobically modified polyurethane (JP-A-2-307861) and the like have been proposed. In the case of the casting method, castor oil and gelatin are used as organic binders (JP-A-4-7734).
9), pyroxylline (JP-A-4-77350), drying oil or boil oil (JP-A-4-77351), paraffin wax and stearic acid (JP-A-4-77352), acrylic polymer or its emulsion (JP-A-4-27016).
5, JP-A-5-69424) and the like have been proposed.

However, such a binder (binder)
When a composition for slip casting is prepared by using, (a) the viscosity of the slip greatly depends on the amount of the binder contained, which makes it difficult to control the process. (B) When the binder is changed, the viscosity of the slip is a dispersant. It is necessary to change the dispersant according to the type of binder, as it depends on the type of (c) it is easy to entrap air bubbles during molding,
(d) It is difficult to control the green strength, (e) the molded article shrinks greatly when dried, (f) a large amount of binder must be added to obtain good green strength,
There was a problem that it took time to degrease.

Therefore, the object of the present invention is that the viscosity does not depend on the amount of the binder and the kind of the dispersant, and it is difficult to foam.
It is an object of the present invention to provide a composition for slip casting in which a molded article has high strength and a low binder content.

[0007]

As a result of earnest research in view of the above object, the present inventors have found that in a composition for slip casting using an aqueous polyurethane emulsion as a binder, (a) the viscosity of the composition is the binder. (B) a high-strength molded product can be obtained with a small amount of binder, (c) no entrapment of bubbles during molding, and (d) the amount of binder and the strength of the molded product. The inventors have found that they are proportional to each other and (e) that the green shrinkage of the molded body is small, and completed the present invention.

That is, the composition for slip casting of the present invention is a composition for slip casting comprising ceramic powder and a binder, wherein the binder is an aqueous polyurethane emulsion.

The present invention will be described in detail below. The composition for slip casting of the present invention comprises (a) ceramic powder (consisting of (1) silicon nitride powder and (2) sintering aid).
It is prepared by mixing (b) a binder, (c) a dispersant, and (d) water. The method for producing these compositions and molded articles will be described below. Unless otherwise specified, the compounding amount of each composition is a value when the ceramic powder is 100 parts by weight.

[1] Composition (a) Ceramic Powder (1) Silicon Nitride Powder When a ceramic is produced from a ceramic powder mainly composed of silicon nitride, the silicon nitride powder used is either α type or β type. be able to. Further, as the manufacturing method thereof, a direct nitriding method of Si, a reduction / nitridation method of silica,
There are a thermal decomposition method of silicon diimide and a vapor phase reaction method of SiH ₄ + NH ₃ + N ₂ . The silicon nitride powder has an average particle size of 0.01 to 3
μm is preferable, and more preferably 0.1 to 1.3 μm.
Is.

(2) Sintering aid Since silicon nitride is difficult to sinter by itself, it is usually sintered by adding a sintering aid. In the present invention, Al
₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , HfO ₂ , AlN, M
A simple substance or a compound of gO and a group IIIa element of the periodic table is added as a sintering aid component. The powder of these sintering aids preferably has an average particle size of 0.1 to 8 μm, more preferably 0.3 to 5 μm.

The blending amount of the above-mentioned sintering aid varies depending on the sintering aid used, but is preferably 0.5 to 15% by weight, with the total amount of the ceramic powder including the auxiliary being 100% by weight, It is more preferably 1 to 5% by weight. 0.5
If it is less than 15% by weight, densification of the sintered body does not proceed, and
If it exceeds the weight%, the strength at high temperature cannot be obtained.

(B) Binder In the present invention, a molecular weight of 5 to 200,000 and a carboxylic acid group (-
COOH), an aqueous polyurethane emulsion having a hydrophilic group such as a sulfonic acid group (—SO ₃ Na) is used. The aqueous polyurethane is preferably blended in an amount of 0.1 to 2 parts by weight (weight of resin solid content in emulsion), and more preferably 0.5 to 1.0 part by weight. If it is less than 0.1 part by weight, the green strength is not sufficient, and if it exceeds 2 parts by weight,
The inking rate and the degreasing property decrease, the shrinkage during sintering becomes large, and sticking to the mold occurs during firing.

(C) Dispersant In order to uniformly disperse the ceramic powder, for example, a quaternary ammonium salt (SN No., SN, manufactured by San Nopco Ltd.) is used as a surfactant.
Dispersant 7347C), polycarboxylic acid type surfactant (Chukyo Yushi and Serna D-735), maleic anhydride type surfactant (Daiichi Kogyo Seiyaku Co., Ceramo D-11), ammonia or the like is used. It is preferable to add 0.08 to 0.28 parts by weight (weight of solid content), and more preferably 0.16 to
0.2 parts by weight. If it is less than 0.08 parts by weight, the dispersion of the ceramic powder is incomplete, and if it exceeds 0.28 parts by weight, the viscosity of the slurry is too high.

(D) Water is preferably added in an amount of 38 to 45 parts by weight, more preferably 41 to 43 parts by weight. If it is less than 38 parts by weight, the viscosity of the slurry is high, and if it exceeds 45 parts by weight, the viscosity of the obtained composition is low and the drying becomes difficult.

[2] Method for producing molded body The above silicon nitride powder, sintering aid, dispersant, and water are kneaded in a ball mill or the like for about 20 hours to uniformly mix them. Add a binder to the resulting mixture to obtain 10
Stir for about a minute to prepare a slurry.

The viscosity of the obtained slurry is 0.3 to 0.
7 Pa · s is preferable, and 0.4 to 0.6 Pa is more preferable.
・ S. If the viscosity is less than 0.3 Pa · s, the inking rate will be slow, the molded body will be too clogged and cracks will occur, and burrs will occur. If it exceeds 0.7 Pa · s, the fluidity will be poor. It becomes easy to contain pores and the defoaming property deteriorates,
The shrinkage of the fired body increases.

Next, the obtained composition is cast into a mold made of a material having water absorbability and water permeability such as gypsum. The composition is dehydrated as the dispersion medium is dispersed through the mold. Then, it is removed from the mold and dried sufficiently. Although there is a risk of breakage and cracks in the molded body in this dehydration and drying step, since it is reinforced by the uniformly dispersed binder, breakage and cracks can be sufficiently prevented. A ceramic compact is obtained by the above steps.

[0019]

EXAMPLES The present invention will now be described in more detail with reference to specific examples, but the present invention is not limited thereto. Examples 1 to 6 100 parts by weight of a ceramic mixed powder having a composition shown in Table 1, 40 parts of a dispersant and water shown in Table 2 were mixed in a ball mill for 40 hours, and a binder (aqueous polyurethane emulsion) was added to the mixture. The mixture was stirred for 1 minute to prepare a composition for slip casting. Next, the viscosity of the obtained composition was measured. Polyurethanes of 0.3, 1, 1.
The measurement result when 5 parts by weight (weight of solid content) was added is shown in FIG. 1 together with the comparative example.

Next, slip casting was carried out using the composition obtained, solidified in the mold for 1 hour, and dried at room temperature for 48 hours to obtain a high quality molded product having no pores. The green strength and green shrinkage of the obtained molded body were measured. Green shrinkage rate is 100 mm x
It is a linear shrinkage obtained by averaging the shrinkage in each direction of width and depth after drying 100 mm × 10 mm ^t ).
The measurement result of the green strength is shown in FIG. 3 (Examples 1 to 5, 5 and 6) and FIG. 4 (Example 2), and the measurement result of the green shrinkage ratio is shown in FIG. 5 (Example 2). Shown with an example.

Table 1 Average particle size of component (μm) Blending amount (wt%) Si ₃ N ₄ 0.4 96.5 Y ₂ O ₃ 5.0 2.5 Al ₂ O ₃ 0.4 1

Table 2 Binder dispersant compounding amount Compounding amount Water compounding amount Example NO. Type (weight part) ⁽¹⁾ type (weight part) ⁽¹⁾ (weight part) ⁽²⁾ Example 1 SF700 ⁽³⁾ 0.3 7347C ⁽⁴⁾ 0.18 42 Example 2 SF700 1.0 7347C 0.18 42 Example 3 SF700 1.1 7347C 0.18 42 Example 4 SF700 1.5 7347C 0.18 42 Example 5 SF700 1.8 7347C 0.18 42 Example 6 SF700 2.0 7347C 0.18 42 Note (1): The resin solid content is shown with respect to 100 parts by weight of the ceramic powder. (2): parts by weight based on 100 parts by weight of ceramic powder. (3): Superflex 700 (Daiichi Kogyo Seiyaku Co., aromatic isocyanate + ester polyol, hydrophilic group: (-SO ₃ Na)) (4): SN Dispersant 7347C (San Nopco quaternary ammonium salt) )

Examples 7 to 18 100 parts by weight of the same ceramic powder as in Example 1 are shown in Table 3.
The binder (aqueous polyurethane emulsion) shown in Table 3 was added to a mixture of the dispersant shown in 1 above and water with a ball mill for 40 hours, and the mixture was stirred for 10 minutes to prepare a slip casting composition. Next, the viscosity of the obtained composition was measured. The measurement results are shown in FIG.

Table 3 Binder dispersant compounding amount Compounding amount Water compounding amount Example NO. Type (weight part) ⁽¹⁾ type (weight part) ⁽¹⁾ (weight part) ⁽²⁾ Example 7 SF700 ⁽³⁾ 0.3 D735 ⁽⁴⁾ 0.14 42 Example 8 SF700 1.0 D735 0.14 42 Example 9 SF700 1.7 D735 0.14 42 Example 10 SF700 0.3 D114 ⁽⁵⁾ 0.18 42 Example 11 SF700 1.0 D114 0.18 42 Example 12 SF700 1.7 D114 0.18 42 Example 13 SF700 0.3 7347C ⁽⁶⁾ 0.18 42 Example 14 SF700 1.0 7347C 0.18 42 Example 15 SF700 1.7 7347C 0.18 42 Example 16 SF700 0.3 NH ₃ 0.2 42 Example 17 SF700 1.0 NH ₃ 0.2 42 Example 18 SF700 1.7 NH ₃ 0.2 42 Note (1): Shown as the weight of solid content relative to 100 parts by weight of ceramic powder. (2): parts by weight based on 100 parts by weight of ceramic powder. (3): Superflex 700 (Daiichi Kogyo Seiyaku Co., aromatic isocyanate + ester polyol, hydrophilic group: (-SO ₃ Na)) (4): Serna D-735 (Chukyo Yushi, polycarboxylic acid) (5): Ceramo D-114 (Daiichi Kogyo Seiyaku, maleic anhydride) (6): SN Dispersant 7347C (San Nopco quaternary ammonium salt)

Examples 19 to 20 100 parts by weight of the same ceramic mixed powder as in Example 1,
The binder (aqueous polyurethane emulsion) shown in Table 4 was added to a mixture of the dispersant shown in Table 4 and water in a ball mill for 40 hours, and the mixture was stirred for 10 minutes to prepare a slip casting composition.

Next, slip casting was carried out using the obtained composition, which was solidified in a mold and dried in the same manner as in Example 1 to obtain a high quality molded product having no pores. The green strength and green shrinkage of the obtained molded body were measured. The green strengths of Examples 19 to 20 are shown in FIG. 4 together with those of Example 2 and Comparative Example 5. The green shrinkage of Example 20 is shown in FIG. 5 together with those of Example 2 and Comparative Example 5.

Table 4 Binder Dispersant Blending Amount Blending Amount Water Blending Example NO. Kind (weight part) ⁽¹⁾ Kind (weight part) ⁽¹⁾ (weight part) ⁽²⁾ Example 19 SF410 ⁽³⁾ 1.0 7347C ⁽⁴⁾ 0.18 42 Example 20 SF126 ⁽⁵⁾ 1.0 7347C 0.18 42 Note (1): Shown as the resin solid content weight relative to 100 parts by weight of ceramic powder. (2): parts by weight based on 100 parts by weight of ceramic powder. (3): Superflex 410 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., aliphatic isocyanate + carbonate polyol, hydrophilic group: (-SO ₃ Na)) (4): SN Dispersant 7347C (manufactured by San Nopco, quaternary ammonium salt) ) (5): Superflex 126 (Daiichi Kogyo Seiyaku Co., Ltd., aliphatic isocyanate + ester / ether polyol, hydrophilic group: (-COOH))

Examples 21 to 23 100 parts by weight of Al ₂ O ₃ powder having an average particle size of 0.4 μm, a dispersant shown in Table 5 and water were mixed in a ball mill for 40 hours, and the binder shown in Table 5 was used. (Aqueous polyurethane emulsion) was added and stirred for 10 minutes to prepare a composition for slip casting.

Next, slip casting was carried out using the obtained composition, which was solidified in a mold in the same manner as in Example 1 and dried to obtain a high quality molded product having no pores. The green strength of the obtained molded body was measured. The measurement results are shown in FIG. 3 together with other examples and comparative examples.

Table 5 Binder dispersant compounding amount Compounding amount Water compounding amount Example NO. Type (weight part) ⁽¹⁾ type (weight part) ⁽¹⁾ (weight part) ⁽²⁾ Example 21 SF700 ⁽³⁾ 0.3 D305 ⁽⁴⁾ 0.16 29 Example 22 SF700 1.0 D305 0.16 29 Example 23 SF700 1.7 D305 0.16 29 Note (1): Shown by the resin solid content weight relative to 100 parts by weight of ceramic powder. (2): parts by weight based on 100 parts by weight of ceramic powder. (3): Superflex 700 (manufactured by Dai-ichi Kogyo Seiyaku Co., aromatic isocyanate + ester polyol, hydrophilic group: (-SO ₃ Na)) (4): Serna D305 (Chukyo Yushi Co., Ltd., polycarboxylic acid type) )

[0031]Comparative Examples 1-3  100 parts by weight of the same ceramic mixed powder as in Example 1,
Mix the dispersant shown in Table 6 and water with a ball mill for 40 hours.
The binder (PVA) shown in Table 6 was added to
And stir for 10 minutes to add the composition for slip casting.
It was made. Next, the viscosity of the composition was measured. Example results
It is shown in FIG. 1 together with 1, 2, and 4.

Table 6 Binder dispersant compounding amount Compounding amount Water compounding amount Example NO. Type (part by weight) ⁽¹⁾ type (part by weight) ⁽¹⁾ (part by weight) ⁽²⁾ Comparative Example 1 PVA 0.3 7347C ⁽³⁾ 0.18 42 Comparative Example 2 PVA 1.0 7347C 0.18 42 Comparative Example 3 PVA 1.5 7347C 0.18 42 Note (1): Shown by the resin solid content weight relative to 100 parts by weight of the ceramic powder. (2): parts by weight based on 100 parts by weight of ceramic powder. (3): SN Dispersant 7347C (made by San Nopco, quaternary ammonium salt)

Comparative Examples 4 to 7 100 parts by weight of the same ceramic mixed powder as in Example 1,
The binder (aqueous acrylic emulsion) shown in Table 7 was added to a mixture of the dispersant shown in Table 7 and water in a ball mill for 40 hours, and the mixture was stirred for 10 minutes to prepare a composition for slip casting. Next, a molded body was produced using the obtained composition, solidified and dried in the same manner as in Example 1, and the green strength of the obtained molded body was measured. The measurement results are shown in FIG. 3 together with Examples 1 to 3, 5, 6 and 21 to 23.

Table 7binder Dispersant Mixing amount Mixing amount Water mixing amountExample NO. type (Part by weight) ⁽¹⁾ Kind (Part by weight) ⁽¹⁾ (part by weight) ⁽²⁾  Comparative Example 4 WA311⁽³⁾ 0.4 7347C^(Four) 0.9 42 Comparative Example 5 WA311 1.0 7347C 0.9 42 Comparative Example 6 WA311 1.3 7347C 0.9 42 Comparative Example 7 WA311 2.1 7347C 0.9 42 Note (1): Resin solid based on 100 parts by weight of ceramic powder
The weight is shown. (2): parts by weight based on 100 parts by weight of ceramic powder. (3) ： Bind Serum WA311 (Mitsui Toatsu Chemicals, water-based
Kuril emulsion (4): SN Dispersant 7347C (Made in San Nopco, 4th grade)
Ammonium salt)

As is apparent from FIG. 1, the composition of the comparative example to which the PVA aqueous solution was added showed a large change in viscosity with the addition amount of the binder, whereas the composition according to the present invention showed a change in the viscosity with the addition amount of the binder. It was small and the viscosity of the composition was stable irrespective of the added amount of the binder.

As is apparent from FIG. 2, even if the kind of the dispersant of the composition according to the present invention was changed, the effect that the viscosity did not depend on the added amount of the binder was maintained.

As is apparent from FIG. 3, the molded product of the composition of the present invention exhibits higher green strength than the molded product of the conventional product using the acrylic binder, and the high green strength can be obtained by adding a small amount of the binder. Was obtained. Moreover, the same effect was obtained even if the type of ceramic powder was changed.

As is apparent from FIG. 4, the molded product of the composition of the present invention had higher green strength than the molded product of the conventional product.

As is apparent from FIG. 5, the molded product of the composition of the present invention had a smaller green shrinkage ratio than the molded product of the conventional product.

[0040]

As described in detail above, according to the composition for slip casting of the present invention, the following effects can be obtained. (a) Since the viscosity of the composition does not depend on the amount of the binder added, the slip preparation and maintenance are easy. (b) Since the viscosity of the composition does not depend on the type of dispersant, the degree of freedom in selecting a dispersant increases. (c) A high-quality molded product can be obtained without entrapment of bubbles during molding. (d) Since the additive amount of the binder and the green strength are in a proportional relationship, the green strength can be easily controlled. (e) Since the green shrinkage rate is small, good dimensional accuracy can be obtained. (f) Since the amount of binder can be reduced, degreasing is easy. Therefore, the composition for slip casting of the present invention is suitable for producing a large-sized, relatively thin-walled molded product or a molded product having a complicated shape.

[Brief description of drawings]

FIG. 1 is a schematic diagram of Examples 1, 2 and 4 and Comparative Examples 1 to 3.
3 is a graph showing the relationship between the amount of binder added and the viscosity of the slip casting composition.

FIG. 2 is a graph showing the relationship between the amount of binder added for each dispersant and the viscosity of the slip casting composition in Examples 7 to 18.

FIG. 3 is a graph showing the relationship between the amount of binder added and green strength in Examples 1 to 3, 5, 6, 21 to 23 and Comparative Examples 4, 6 and 7.

FIG. 4 shows the results of Examples 2, 19, 21 and Comparative Example 5,
It is the graph which compared the green strength when changing the kind of binder (the addition amount is 1 weight part).

FIG. 5 is a graph comparing the green shrinkage rates in Examples 2 and 20 and Comparative Example 5 when the type of binder is changed (addition amount is 1 part by weight).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ichikawa 1-4-1, Chuo, Wako-shi, Saitama Honda R & D Co., Ltd.

Claims (2)

[Claims] 1. A slip casting composition comprising ceramic powder and a binder, wherein the binder is an aqueous polyurethane emulsion. 2. The slip casting composition according to claim 1, wherein 0.1 to 2 parts by weight of the aqueous polyurethane emulsion is mixed with 100 parts by weight of the ceramic powder. Composition.