JP2011098323A - Dispersant for alumina particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersant which, in a dispersant of alumina particles, can keep the viscosity of a dispersion of alumina particles low and suppress a change in the viscosity of the dispersion even when the amount of the dispersant to be added is changed and a dispersant which can produce a stable product especially in the production of a ceramic by using an alumina dispersion whose viscosity is not changed. <P>SOLUTION: In a dispersant for alumina particles containing a (meth)acrylic acid copolymer or its salt (A) in which (meth)acrylic acid or/and its salt (A-1) and a 4-8C alkyl ester (meth)acrylate (A-2) are indispensable structural monomer units and a 4-8C alcohol (B), the ratio of the component (B) to 100 pts.wt. of the component (A) is 1,000-30,000 wt.ppm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dispersing agent for alumina particles and a dispersion for producing a ceramic containing the dispersing agent, and belongs to the technical fields of the dispersing agent and the ceramic production.

Conventionally, polycarboxylic acid compounds are known as dispersants for alumina particles. This polymer is adsorbed on the alumina particles and gives a repulsive action between the particles due to steric hindrance, whereby a stable dispersion can be obtained.
The resulting alumina dispersion is used in papermaking, metal processing, textile, paint, optical material and ceramic applications.

Conventionally, polycarboxylic acid compounds are known as dispersants for the production of ceramics. This dispersant is used together with a ceramic raw material powder and a solvent to prepare a slurry. The obtained slurry is formed into a sheet or the like, dried and fired to produce a ceramic molded product.
Various dispersants have been proposed as dispersants for producing alumina particles and ceramics. Among them, the use of polycarboxylic acid compounds is effective, and the following proposals have been made.
A dispersant comprising a copolymer of a maleic acid monomer and a polyoxyalkylene monomer (Patent Document 1).
A dispersant composed of ammonium polyacrylate having a specific weight average molecular weight (Patent Document 2).
-Dispersant which consists of polycarboxylate (patent document 3).
-Dispersant which consists of acrylic acid-acrylic acid ester copolymer ammonium (patent document 4).

Japanese Patent Laying-Open No. 2007-261911 (Claims) JP 2005-060208 A (Claims) JP 2007-136912 A (Example) JP 2003-238255 A (Example)

In recent years, ultrafine particles such as alumina having a smaller particle diameter have become available.
When this is used, for example, as a ceramic raw material powder, a ceramic product with higher performance than before can be obtained. For this reason, the dispersing agent corresponding to an ultrafine particle came to be calculated | required.
However, the conventional polycarboxylic acid-based dispersant as described above has a problem that the slurry viscosity becomes high when attempting to disperse such ultrafine particles. In addition, the polycarboxylic acid-based dispersant has a tendency that the slurry viscosity greatly changes when the addition amount varies, and the product viscosity varies because the slurry viscosity changes. Furthermore, since ultrafine particles tend to be difficult to disperse, there is a problem that it is difficult to recycle the slurry by adding water to the dried ceramic slurry and redispersing it.
Thus, even when a conventional dispersant is used, a dispersant that sufficiently satisfies the viscosity and redispersibility of the dispersion of ultrafine particles has not been obtained.

  In the dispersant for alumina particles, the present inventors can keep the viscosity of the dispersion of alumina particles low, and find a dispersant having a small change in viscosity of the dispersion even when the amount of the dispersant added varies. In addition, by using an alumina dispersion liquid that does not have such a change in viscosity, intensive studies have been conducted to find a dispersant that can produce a stable product particularly in the production of ceramics.

In order to solve the above problems, the present inventors have effectively used a dispersing agent in which a copolymer of (meth) acrylic acid or a salt thereof and a specific alcohol is used together, and the alumina particles are dispersed using this dispersing agent. The present invention has been completed by finding that the produced dispersion for producing ceramics is effective.
Hereinafter, the present invention will be described in detail.
In the present specification, acrylic acid or methacrylic acid is represented as (meth) acrylic acid.

According to the dispersant of the present invention, the viscosity of the dispersion of alumina particles can be kept low. Further, even if the amount of the dispersant added varies, the viscosity change of the dispersion is small. For this reason, it can contribute to the quality stability of the product using an alumina dispersion liquid.
Furthermore, it is possible to add water to a dried sheet of ceramic slurry using alumina or the like and redisperse it, which is useful because of its excellent recyclability.
Although the details of the reason why the dispersant of the present invention exhibits the above-mentioned effects are unclear, the dispersant of the present invention adsorbs to the particles in the dispersion and has a moderate amount of particles between the particles compared to the conventional dispersant. It is presumed that it is for imparting slipperiness.

The present invention comprises (meth) acrylic acid or / and its salt (A-1) and (meth) acrylic acid alkyl ester (A-2) having 4 to 8 carbon atoms as an essential constituent monomer. (Meth) acrylic acid copolymer or / and its salt (A) as a unit, and alcohol (B) having 4 to 8 carbon atoms, and (B) component (B) relative to 100 parts by weight of component (A) The present invention relates to a dispersant for alumina particles having a ratio of 1,000 to 30,000 wtppm.
Hereinafter, (A) component and (B) component which comprise a dispersing agent are demonstrated.

1. Component (A) The component (A) is a (meth) acrylic acid copolymer or / and a salt thereof having monomers (A-1) and (A-2) as essential constituent monomer units.

The monomer (A-1) is (meth) acrylic acid or / and a salt thereof.
Examples of the monomer (A-1) include (meth) acrylic acid alone, a salt in which a part of (meth) acrylic acid is neutralized, and a salt in which all of (meth) acrylic acid is neutralized.
Among these, it is excellent in the polymerizability at the time of manufacturing (A) component, and the water solubility of the obtained (A) component is excellent that it is a salt from which acrylic acid or / and a part of acrylic acid was neutralized. This is preferable.

Examples of (meth) acrylic acid salts include ammonium salts of (meth) acrylic acid, organic amine salts, and alkali metal salts.
Examples of the organic amine in the organic amine salt include triethylamine. Examples of the alkali metal in the alkali metal salt include sodium hydroxide and potassium hydroxide.
Among these, an ammonium salt is preferable from the viewpoint of ceramic performance when the component (A) is excellent in dispersibility and the dispersant is used as a dispersion for producing ceramics.

The monomer (A-2) is an alkyl (meth) acrylate having 4 to 8 carbon atoms in the alkyl group, and an alkyl (meth) acrylate having 4 to 6 carbon atoms in the alkyl group. Esters are preferred.
Specific examples of the monomer (A-2) include n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, and (meth) acrylic. Examples include hexyl acid, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate.
Among these, n-butyl (meth) acrylate, isobutyl (meth) acrylate and t-butyl (meth) acrylate are preferable, and (meth) acrylate n-butyl is particularly preferable. .
By using a (meth) acrylic acid alkyl ester having 4 or more carbon atoms in the alkyl group, the dispersion can be prevented from thickening and aggregating over time, and the ceramic slurry was dried. It can be excellent in redispersion when water is added to the product. This is presumed to be because the (meth) acrylic acid alkyl ester having 3 or less carbon atoms has little slipping between particles. On the other hand, by using a (meth) acrylic acid alkyl ester having an alkyl group having 8 or less carbon atoms, the dispersion can be prevented from being separated and stabilized.

As a copolymerization ratio of the monomers (A-1) and (A-2), the monomer (A-1): monomer (A-2) has a weight ratio of 95: 5 to 60:40. It is preferably 90:10 to 70:30.
By setting the copolymerization ratio of the monomer (A-1) to 60% by weight or more, the component (A) can have excellent water solubility and excellent dispersion stability, while 95% by weight. By making the ratio no more than%, it is possible to suppress an increase in viscosity of the dispersion.

As the component (A), all of the carboxyl groups in the component (A) may remain unneutralized carboxyl groups, but 50 to 100 mol%, particularly 70 to 100 mol% of the carboxyl groups are contained by the base. It is preferable that the salt is in the form of a salt because the water solubility of the component (A) increases and the effect of stabilizing the dispersion increases.
Since it is sometimes difficult to measure the neutralization degree of the carboxyl group in the actual component (A), it is preferable to control the pH of the aqueous solution (A) as a simple method. Specifically, the water solubility of the component (A) is that the carboxyl group is neutralized with a base in such a ratio that the pH of the aqueous solution of the component (A) is 5 to 10, particularly 6 to 9. Is preferable, since the dispersion stabilization effect is enhanced.

  (A) Polymerization is carried out so that at least 40 mol% (40 to 100 mol%) of the carboxyl group of (meth) acrylic acid is in an unneutralized state before and at the polymerization stage for producing the component (A). The polymerization reaction for producing the component (A) is facilitated by using a basic compound after the polymerization to form 50 mol% or more, more preferably 70 mol% or more of the carboxyl group of the component (A) in the form of a salt. From the point of proceeding to

Component (A) has monomers (A-1) and (A-2) as essential constituent monomers. Depending on the purpose, monomer (A-) Monomers other than 1) and (A-2) [hereinafter referred to as “other monomers”] may be copolymerized.
Other monomers include unsaturated acids such as maleic acid and itaconic acid or salts thereof, unsaturated acid anhydrides such as maleic anhydride and itaconic anhydride, 2-acrylamido-2-methylpropanesulfonic acid and styrenesulfonic acid. And unsaturated sulfonic acids or salts thereof, (meth) acrylic acid hydroxyalkyl ester, acrylamide, (meth) acrylic acid ester having a polyalkylene oxide skeleton in the ester, and the like.
Other monomers can be used alone or in combination of two or more.
The copolymerization ratio of other monomers is preferably 0 to 10 parts by weight, and 0 to 5 parts by weight with respect to 100 parts by weight of the total amount of monomers (A-1) and (A-2). More preferably. By setting the copolymerization ratio of other monomers to 10 parts by weight or less, the viscosity of the dispersion can be prevented.

The method for producing the component (A) is not particularly limited, but among these, the aqueous solution polymerization method is preferable. According to the aqueous solution polymerization, the dispersant can be obtained as a uniform solution.
It is preferable to use a mixed solution of water and an organic solvent as the solvent for the aqueous solution polymerization. As a result, the problem that the monomer (A-2) becomes difficult to dissolve when only water is used as the solvent can be improved. On the other hand, when only the organic solvent is used, it can be used as a dispersant. In addition, since it is necessary to replace the organic solvent with water, the problem of cost and labor can be solved.
Preferred organic solvents include alcohols such as isopropyl alcohol and ketones such as acetone, with isopropyl alcohol being particularly preferred.

In the polymerization reaction, known polymerization initiators can be used, and radical polymerization initiators are particularly preferably used.
Examples of radical polymerization initiators include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, hydroperoxides such as t-butyl hydroperoxide, water-soluble peroxides such as hydrogen peroxide, and methyl ethyl ketone peroxide. Oil-soluble peroxides such as oxides, ketone peroxides such as cyclohexanone peroxide, dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide, 2,2′-azobis (2-methyl) And azo compounds such as propionamidine) dihydrochloride.
The above peroxide-based radical polymerization initiators may be used alone or in combination of two or more.
Among the above peroxide-based radical polymerization initiators, persulfates and azo compounds are preferred, and ammonium persulfate is particularly preferred from the viewpoint that the molecular weight can be easily controlled.
The proportion of the radical polymerization initiator used is not particularly limited, but is used in a proportion of 0.1 to 15% by weight, particularly 0.5 to 10% by weight, based on the total weight of all monomers of component (A). It is preferable. By making this proportion 0.1% by weight or more, the copolymerization rate can be improved, and by making it 15% by weight or less, the stability of the component (A) is improved and the performance as a dispersant is excellent. It will be.
In some cases, the component (A) may be produced using a water-soluble redox polymerization initiator. As a redox polymerization initiator, a combination of an oxidizing agent (for example, the above-described peroxide) and a reducing agent such as sodium bisulfite, ammonium bisulfite, sodium sulfite, sodium hydrosulfite, iron alum, potassium alum, etc. Can be mentioned.

  In the production of the component (A), a chain transfer agent may be appropriately added to the polymerization system in order to adjust the molecular weight. Examples of the chain transfer agent include sodium phosphite, sodium hypophosphite, sodium bisulfite, mercaptoacetic acid, mercaptopropionic acid, 2-propanethiol, 2-mercaptoethanol and thiophenol.

The polymerization temperature for producing the component (A) is not particularly limited, but the polymerization temperature is preferably 60 to 100 ° C.
By setting the polymerization temperature to 60 ° C. or higher, the polymerization reaction is quick and excellent in productivity, and by setting the polymerization temperature to 100 ° C. or lower, the coloring of the product can be reduced.
The reaction can be carried out under pressure or reduced pressure, but it is preferable to carry out the reaction at normal pressure because it requires a cost for making equipment for pressure or reduced pressure reaction. The polymerization time is preferably 2 to 20 hours, particularly about 3 to 10 hours.

(A) As an average molecular weight of a component, it is preferable that it is 2,000-10,000 by weight average molecular weight, More preferably, it is 3,000-8,000.
When the weight average molecular weight is 2,000 or more, it is possible to prevent the dispersant from desorbing from the particles in the dispersion to increase the viscosity of the dispersion. On the other hand, by setting the weight average molecular weight to 10,000 or less. The dispersant itself can be prevented from increasing the viscosity of the dispersion, and the viscosity of the dispersion can be reduced.
In the present invention, the weight average molecular weight means a value obtained by converting an average molecular weight measured by GPC (gel permeation chromatography) based on a standard sample of polyacrylic acid.

After removing the organic solvent from the solution containing the component (A) obtained above, the solution is neutralized with a basic compound as necessary.
As described above, the degree of neutralization is preferably 50 to 100 mol%, particularly 70 to 100 mol%, neutralized with a base and in the form of a salt. Examples of basic compounds used for neutralization include aqueous ammonia, organic amines (eg, triethylamine), alkali metal hydroxides, and the like. Among them, aqueous ammonia is preferable from the viewpoint of dispersibility and ceramic performance.
As described above, since the neutralization degree of the carboxyl group in the actual component (A) may be difficult to measure, it is preferable to control the pH of the component (A) aqueous solution. Specifically, the pH of the aqueous solution of component (A) is preferably 5 to 10, and more preferably 6 to 9.

2. Component (B) The component (B) is an alcohol having 4 to 8 carbon atoms, preferably an alcohol having 4 to 6 carbon atoms.
Examples of the component (B) include n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, pentyl alcohol, n-hexyl alcohol, heptyl alcohol, octyl alcohol, and 2-ethylhexyl alcohol. Among these, n-butyl alcohol, isobutyl alcohol and t-butyl alcohol are preferable from the viewpoint of performance as a dispersant, and n-butyl alcohol is particularly preferable.
By using an alcohol having 4 carbon atoms, an increase in the viscosity of the dispersion can be suppressed. On the other hand, by using an alcohol having 8 or less carbon atoms, the separation of the dispersant can be suppressed. it can.

3. Dispersant for Alumina Particles The dispersant of the present invention comprises the components (A) and (B) as essential components.
Examples of the method for producing the dispersant include a method of adding and mixing the component (B) to the component (A).
The dispersant of the present invention contains the component (B) at a ratio of 1,000 to 30,000 wtppm with respect to 100 parts by weight of the component (A), preferably 1,500 to 20,000 wtppm, particularly preferably. 2,000 to 15,000 wtppm.
By setting the ratio of the component (B) to 1,000 wtppm or more, it becomes excellent in re-dispersion when water is added to the dried ceramic slurry, and by setting it to 30,000 wtppm or less, the particles are aggregated. Can be suppressed.

  When (A) component is manufactured, alcohol [(B) component] derived from a raw material monomer (A-2) may be included in the obtained copolymer aqueous solution. In this case, there is a method in which the component (B) is quantified by a method such as gas chromatography and the component (B) is added so as to satisfy the ratio of the component (B) in the present invention.

The dispersant of the present invention is preferably in the form of an aqueous solution of components (A) and (B).
In this case, it is preferable that the total amount of the components (A) and (B) is 30 to 50% by weight in water, more preferably 35 to 45% by weight.
By setting it to 30% by weight or more, the problem of transportation cost can be reduced, and by setting it to 50% by weight or less, it can be made low in viscosity and easy to handle.

  The dispersant of the present invention is suitably used for dispersing alumina particles. Hereinafter, the alumina particles will be described.

  In the case of producing a dispersion of alumina particles, it is preferable to use 0.01 to 5.0 parts by weight of a dispersant in solid content with respect to 100 parts by weight of alumina particles.

The average particle diameter of the alumina particles may be appropriately set according to the purpose, but is preferably 0.01 to 5.0 μm.
In the present invention, the average particle diameter means an average value of individual particle diameters measured with a scanning electron microscope.
By making the average particle diameter 0.01 μm or more, it becomes advantageous in terms of cost. On the other hand, by making it 5.0 μm or less, the ceramic becomes excellent in toughness when producing ceramic from alumina particles. .
The blending amount of the alumina particles is preferably 40 to 85% by weight with respect to the dispersion. By setting the content to 40% by weight or more, the ceramic can be excellent in dimensional accuracy when the ceramic is produced from the alumina particles. On the other hand, when the content is 85% by weight or less, the dispersion liquid has a low viscosity and is easy to handle.
The pH of the alumina dispersion is preferably 5-10. By setting this pH range, aggregation of alumina particles can be suppressed.
The pH can be adjusted by adding nitric acid, acetic acid, oxalic acid, citric acid, malic acid, lactic acid, and aqueous ammonia.

  The method for dispersing alumina particles is not particularly limited as long as alumina is dispersed using the dispersant of the present invention. For example, a slurry can be prepared by dissolving a dispersant in a dispersion medium, blending alumina, and stirring at high speed.

The alumina dispersion obtained by using the dispersant of the present invention can be used for various applications. Examples include papermaking applications, metal processing applications, textile applications, paint applications, optical material applications, and ceramic applications.
Among these, the alumina dispersion can be suitably used as a ceramic application, more specifically as a ceramic production dispersion.
Hereinafter, the dispersion for producing ceramics will be described in detail.

4). Dispersion liquid for producing ceramics The dispersion liquid containing the alumina particles of the present invention can be used for various applications, and particularly preferably used as a dispersion liquid for producing ceramics.
In this case, it can be used together with ceramic raw material powder other than alumina.
As the ceramic raw material powder, inorganic powder can be used, metal oxides such as titania, magnesia and zirconia, metal carbides such as silicon carbide, nitrides such as aluminum nitride and silicon nitride, carbonates such as calcium carbonate and barium carbonate. Examples thereof include salts and barium titanate.

A binder, a lubricant, and a plasticizer can be used in the dispersion for producing a ceramic in the present invention, if necessary.
Examples of the binder include polyvinyl alcohol, partially acetalized polyvinyl alcohol, polyethylene oxide, methyl cellulose, hydroxyethyl cellulose, acrylic polymer, starch, and agar. These binders have a weight average molecular weight of 10,000 or more. When using a binder, it is preferable to use 0.1-20 weight part with respect to 100 weight part of ceramic raw material powders.
Examples of the lubricant include magnesium stearate and paraffin emulsion. When using a lubricant, it is preferable to use 0.1 to 1 part by weight per 100 parts by weight of the ceramic raw material powder.
Examples of the plasticizer include polyethylene glycol and dibutyl phthalate. When using a plasticizer, it is preferable to use 0.1-5 weight part with respect to 100 weight part of ceramic raw material powders.

  As a method for producing a dispersion for producing a ceramic, a conventional method may be followed. For example, a slurry-like dispersion for producing a ceramic can be produced by dissolving a dispersant or a binder in a dispersion medium, blending ceramic raw material powder, and mixing and dispersing with a ball mill or the like.

As a method for producing a ceramic molded product using the ceramic production dispersion, a conventional method may be followed.
For example, a dispersion for ceramic production is formed, dried, and fired to produce a ceramic molded product.
Examples of the molding method include sheet molding, cast molding, injection molding, press molding, and extrusion molding.
More specifically, taking sheet formation as an example, if a dispersion for ceramic production is applied onto a film with a doctor blade, dried, the ceramic sheets are peeled off, and a plurality of sheets are laminated, a thin sheet called a green sheet is obtained. A sheet is obtained. When this is cut into a desired size and fired, a ceramic molded product is obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following examples, “%” means% by weight, “part” means part by weight, and “ppm” means wtppm.

Example 1 (Manufacture of dispersant)
A tank reactor equipped with a stirrer and a condenser was charged with 170 kg of deionized water and 250 kg of isopropyl alcohol and maintained at 80 ° C.
To this reactor, 255 kg of a monomer mixed with 255 kg of acrylic acid (hereinafter referred to as “AA”), 75 kg of n-butyl acrylate (hereinafter referred to as “nBA”), and 60 kg of a 15% aqueous solution of ammonium persulfate for 5 hours. It was supplied over time. After completion of dropping, the reaction solution was held at 80 ° C. for 1 hour.
Subsequently, isopropyl alcohol was distilled off under reduced pressure while adding deionized water. Thereafter, the reaction solution was kept at 50 ° C. and neutralized by supplying 25% aqueous ammonia.
Here, when the liquid was analyzed by gas chromatography, 300 ppm of n-butanol (hereinafter referred to as “nBL”) was detected. Therefore, nBL was added and adjusted to 1,500 ppm.
Thus, the polymer [(A) component] and nBL [(B) component] are included, the solid content concentration is 40%, the pH is 7, and the (B) component is 1,500 ppm [(A) component] And 3,750 ppm] was obtained.
The weight average molecular weight (hereinafter referred to as “Mw”) of the obtained component (A) was measured by gel permeation chromatography (GPC). The measurement conditions of GPC were HLC8020 system (manufactured by Tosoh Corporation), the columns used were G4000PWxl, G3000PWxl, G2500PWxl (manufactured by Tosoh Corporation), and the eluent was 0.1M NaCl + phosphate buffer (pH 7). The calibration curve was prepared using polyacrylic acid Na (manufactured by Sowa Kagaku). As a result of the measurement, Mw was 6,000.

Examples 2 to 7 (Production of dispersant)
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed as shown in Table 1.
In the analysis after neutralization, the component (B) was detected at the following ratios, so the component (B) was added as necessary.

Example 2
100 ppm of 2-ethylhexanol (hereinafter referred to as “EHL”) was detected, and EHL was added to adjust to 3,000 ppm.
Example 3
Since nBL was detected at 800 ppm, no additional alcohol was added.
Example 4
nBL was detected at 500 ppm, and nBL was further added to adjust to 5,000 ppm.
Example 5
Isobutanol (hereinafter referred to as “iBL”) was detected at 100 ppm, and iBL was added to adjust to 2,000 ppm.
Example 6
Since nBL was detected at 500 ppm, no additional alcohol was added.
-Example 7
nBL was detected at 500 ppm, and nBL was further added to adjust to 11,000 ppm.

  Table 1 shows the results of measuring the solid content, pH, and Mw of the obtained dispersant.

● Comparative Examples 1 to 4
In Example 1, polymerization, vacuum distillation and neutralization were performed in the same manner as in Example 1 except that the monomers used were changed as shown in Table 1.
In the analysis after neutralization, alcohol or component (B) was detected at the following ratios, respectively, and component (B) was added as necessary.

Comparative Example 1: Although 350 ppm of methanol was detected but the component (B) was not detected, nBL was added and adjusted to 1,500 ppm.
Comparative Example 2: Although ethanol was detected at 250 ppm, but component (B) was not detected, nBL was added to adjust to 1500 ppm.
Comparative Example 4: Since 300 ppm of nBL was detected, the component (B) was not added additionally.
Comparative Example 5: nBL was detected at 100 ppm, and nBL was added to adjust to 13,000 ppm.
In Comparative Example 3, polymerization, distillation under reduced pressure, and neutralization were performed in the same manner as in Example 1, but no evaluation was performed because a uniform liquid could not be obtained.

  Table 1 shows the results of measuring the solid content, pH, and Mw of the obtained dispersant.

Abbreviations in Table 1 mean the following, except for those defined above.
-EHA: 2-ethylhexyl acrylate-iBA: isobutyl acrylate-MA: methyl acrylate-EA: ethyl acrylate-LA: lauryl acrylate

Example C1
100 parts of alumina particles [Showa Denko Co., Ltd., AL-160SG-4, average particle size: 0.6 μm average value of individual particle sizes measured with a scanning electron microscope], obtained in Example 1 as a dispersant Then, 0.15 part of solid dispersant (hereinafter referred to as Dispersant 1) and 31 parts by weight of pure water were put into a SUS mug and stirred at 4000 rpm for 5 minutes. When the viscosity was immediately measured with a B-type viscometer, it showed 540 mPa · s.
To this slurry, 0.05 part of dispersant 1 was added in solid content (total 0.20 parts by weight) and stirred at 4000 rpm for 5 minutes. Immediately measure the viscosity, add 0.05 part of Dispersant 1 to this slurry, add each amount of Dispersant 1 shown below and stir under the same conditions, and measure the viscosity under the same conditions. did.
0.05 parts added (0.20 parts in total): 220 mPa · s
0.05 part addition (total 0.25 part): 210 mPa · s
0.05 parts added (0.30 parts in total): 220 mPa · s
0.10 parts added (0.40 parts in total): 270 mPa · s
0.10 parts added (0.50 parts in total): 350 mPa · s
The lower the measured viscosity of the slurry, the better the dispersibility. When 0.25 part by weight of Dispersant 1 was added, the slurry viscosity was as low as 210 mPa · s. Thus, Dispersant 1 had good dispersibility.
Further, based on the additive amount of the dispersant in which the slurry showed the lowest viscosity, the dispersion stability was judged to be better as the change in the viscosity of the slurry was smaller even if the added amount was changed. Even if the dispersant 1 is changed from 0.25 parts by weight to minus 0.05 parts by weight (ie 0.20 parts by weight) and plus 0.05 parts by weight (ie 0.30 parts by weight), the slurry viscosity is There was little change with 210-220 mPa * s. From this, the polymer 1 had favorable dispersion stability.
The slurry was applied onto the polyester film using a doctor blade to prepare a sheet having a thickness of 25 μm. It dried at 80 degreeC for 15 minutes, peeled hardened | cured material from the polyester film, and obtained the ceramic sheet. Ten sheets were laminated to form a green sheet.
1 g of a green sheet was taken and stirred in pure water, and it was visually evaluated whether it was uniformly dispersed, and evaluated according to the following level.
○: Uniform dispersion, ×: Non-uniform liquid

As a result, a uniform dispersion was obtained. Thus, the dispersant 1 had good redispersibility.
These results are shown in Table 2.

Example C2 to C7
A ceramic slurry was produced in the same manner as in Example C1, except that the dispersant was changed as shown in Table 2 above in Example C1.
The obtained ceramic slurry was evaluated in the same manner as in Example C1. The results are shown in Table 2.

● Comparative Examples C1 to C4
A ceramic slurry was produced in the same manner as in Example C1, except that the dispersant was changed as shown in Table 2 above in Example C1.
The obtained ceramic slurry was evaluated in the same manner as in Example C1. The results are shown in Table 2.

  The dispersant for alumina particles of the present invention can be used for papermaking applications, metal processing applications, fiber applications, paint applications, optical material applications, ceramic applications, and the like, and can be particularly preferably used as a dispersion for producing ceramics. .

Claims (10)

(Meth) acrylic acid or / and a salt thereof (A-1) and an alkyl group (meth) acrylic acid alkyl ester (A-2) having 4 to 8 carbon atoms are essential constituent monomer units ( The (meth) acrylic acid copolymer or / and salt thereof (A), and alcohol (B) having 4 to 8 carbon atoms, the ratio of component (B) to 100 parts by weight of component (A) is 1, A dispersant for alumina particles having a viscosity of 000 to 30,000 wtppm. The dispersant for alumina particles according to claim 1, wherein the component (A) is a copolymer having a copolymerization ratio of (A-1) :( A-2) = 95: 5 to 60:40 (weight ratio). . The dispersant for alumina particles according to claim 1 or 2, wherein the component (A) is a copolymer having a weight average molecular weight of 2,000 to 10,000. It is an aqueous solution of (A) component and (B) component, The dispersing agent for alumina particles in any one of Claims 1-3. The dispersant for alumina particles according to claim 4, wherein the pH is in the range of 2-9. An aqueous dispersion containing alumina particles and the dispersant according to any one of claims 1 to 5. The aqueous dispersion according to claim 6, comprising 0.01 to 5.0 parts by weight of a dispersant in solid content with respect to 100 parts by weight of the alumina particles. The aqueous dispersion according to claim 6 or 7, comprising alumina particles in a proportion of 40 to 85% by weight. The aqueous dispersion according to any one of claims 6 to 8, wherein the average particle diameter of the alumina particles is 0.01 to 5.0 µm. A dispersion for producing a ceramic comprising the aqueous dispersion according to any one of claims 6 to 9.