TWI513673B - Approach for promoting ceramic powders evenly and stably dispersed in slurry - Google Patents

Description

Pulping method for improving stable and uniform dispersion of ceramic powder in slurry

The invention relates to a method for modifying the surface of a ceramic powder in a ceramic slurry, in particular to a pulping method for improving the stable and uniform dispersion of the ceramic powder in the slurry.

The laminated ceramic component in the prior art includes various laminated ceramic components such as a varistor, a piezoelectric element, a heat sensitive element, an inductance element, a capacitance element, and a resistance element, and is characterized by being light, thin, short, and small, with 3C (electronic The rapid growth of the industry, computer and communication industry has been widely used in miniaturized, thin-sized consumer electronics, communication equipment and computer products.

In the process of laminating ceramic components, the preparation of "ceramic slurry" is a very important process. The traditional method is to ball mill the ceramic powder, solvent and dispersant together until the hard agglomeration of the ceramic powder is eliminated. Adhesives and plasticizers, and continue to be ball milled to uniformly disperse the ceramic powder in additives such as solvents, plasticizers and binders (hereinafter referred to as glues), that is, the ceramic powder and the glue are evenly distributed. a ceramic slurry of a mixed degree, and is applied to a subsequent layered ceramic component process to form a sheet of thin green embryo by tape casting or curtain coating, and then made according to a conventional conventional process. Laminated ceramic components.

Therefore, in the process of preparing the ceramic slurry, how to obtain a high-content ceramic powder with good dispersibility and stable properties in the formulation of the ceramic slurry, and satisfying the conditions required for forming the thin green embryo process, in the laminated ceramic component The process is very important.

However, in the formulation of the ceramic slurry, the ceramic powder is a surface-charged polar substance, and the property is usually mixed with a non-polar substance in a liquid phase, and there is a problem of poor compatibility between the two, so the ceramic The powder is essentially difficult to disperse uniformly in the glue. In order to solve this problem, the amount of the glue needs to be greatly increased, and the grinding time of the ball-milled mixed ceramic powder and the glue liquid needs to be longer, and the low-viscosity ceramic powder slurry having the stability to the required degree can be prepared. However, the ceramic slurry has a low solid content (ceramic powder) and a low initial density for forming a thin green embryo, which will limit the performance of the laminated ceramic component.

In view of this, the main object of the present invention is to provide a pulping method for improving the stable and uniform dispersion of ceramic powder in a slurry, which is suitable for preparing a slurry of ceramic powder, and the key technology relates to the ceramic powder in the ceramic slurry. A method of surface modification to modify the surface of a polar ceramic powder to a non-polar surface. According to the thermodynamics point of view, the surface of the modified ceramic powder is consistent with the characteristics of non-polar and non-polar glue, and has excellent compatibility between the two, which helps the ceramic powder to have self-dispersing ability. Stable dispersion in the glue, and with the aid of (ball milling) mechanical force, it is possible to prepare a ceramic powder slurry with good dispersibility, high stability and low viscosity without adding a large amount of glue, because it meets the forming thinness The conditions required for the embryonic process can greatly enhance the performance of the laminated ceramic component.

The pulping method of the invention has the characteristics of improving the stable and uniform dispersion of the ceramic powder in the slurry, and the pulping step comprises:

a. selecting a ceramic powder for use in modulating a ceramic slurry;

b. selecting a glue for modulating the ceramic slurry, including additives such as a solvent, a dispersant, a plasticizer, and a binder;

c. selecting the type and amount of the modifier according to the degree of non-polarity of the glue selected in step b;

d. using the modifier selected in step c, chemically modifying the ceramic powder selected in step a to modify the polar surface of the ceramic powder to a non-polar surface;

e. Using the ceramic powder of step d and the glue of step b to form a ceramic slurry having good dispersibility, high stability and low viscosity.

The pulping method of the present invention has the following unexpected effects:

1. Improve the ceramic powder to achieve stable and uniform dispersion in the slurry;

2. Significantly reduce the amount of glue

3. Increase the solid content of the slurry;

4. Increasing the initial density of the raw embryos made using the slurry;

5. Improve the performance of laminated ceramic components.

In the following text, "multilayer ceramic components" are used to refer to various laminated ceramic components such as varistor, piezoelectric element, heat sensitive element, inductance element, capacitance element and resistance element.

Ceramic powders are polar materials that are surface charged and include alkaline oxides, acidic oxides, and amphoteric oxides.

Common alkaline oxides are capable of reacting with acids, mostly metal oxides such as magnesium oxide (MgO), sodium oxide (NaO), copper oxide (CuO) or barium oxide (BaO).

Common acidic oxides can react with bases such as boron oxide (B ₂ O ₃ ), cerium oxide (SiO ₂ ), sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ) or nitrogen oxides (NO _x ).

Common amphoteric oxides can react with acids or with bases such as alumina (Al ₂ O ₃ ), lead oxide (PbO), zinc oxide (ZnO) or antimony trioxide (Sb ₂ O ₃ ).

The glue used to prepare the ceramic slurry is usually a non-polar substance, including additives such as a solvent, a dispersant, a plasticizer, and a binder.

In the prior art, the method of modifying the surface of the ceramic powder is roughly divided into two major categories: physical surface modification and chemical surface modification.

Physical method Surface modification is the physical adsorption or coating of the modified component on the outer surface of the ceramic powder. Common methods are surfactant method and surface deposition coating method. However, this method of using physical methods to achieve surface modification, the modified component of the surface of the ceramic powder is only weakly coated by physical adsorption, and under the action of external force, such as stirring, shearing or grinding, it is possible Fall off.

The method for modifying the surface of the ceramic powder of the present invention is to chemically modify the surface of the ceramic powder to modify the polar surface of the ceramic powder to a non-polar surface.

The surface modification of the chemical method is based on the chemical reaction characteristics between the modifier and the surface of the ceramic powder, and the ceramic is changed between the modifier and the surface of the ceramic powder by the selection of the modifier. The structure of the surface of the powder further achieves the purpose of surface modification of the ceramic powder.

A method for chemically modifying a ceramic powder by a surface method includes a coupling agent method, an esterification reaction method, and a surface graft modification method.

Suitable for chemical modification of ceramic powders, including anionic, cationic, amphoteric and nonionic surfactants, selected from decane coupling agents, titanate coupling agents, zirconium aluminates One or more of a group consisting of a coupling agent, an organic chromium coupling agent, a higher fatty acid, a higher fatty acid salt, a phosphate ester, an unsaturated organic acid, and an organic amine salt are mixed.

Among them, the higher fatty acids include:

1. Saturated fatty acids: Lauric Acid, Myristic Acid, Palmitic Acid, Stearic Acid, Behenic Acid;

2. Unsaturated fatty acids: Oleic Acid, Linoleic Acid;

3. Other fatty acids: Hydroxyoleic Acid, Hydroxystearic Acid, Lanolin Fatty Acid.

The unsaturated organic acid refers to an organic compound having an acidic and unsaturated hydrocarbon, and common ones are acrylic acid, crotonic acid, methacrylic acid, cinnamic acid, vinyl acetate, propylene acetate, sorbic acid, A modifier such as maleic acid.

The method for modifying the surface of the ceramic powder of the present invention is to select the type, amount and use method of the modifier according to the following conditions:

1. The type of functional group on the surface of the ceramic powder;

2. The acidity and alkalinity, moisture content and specific surface area of the ceramic powder surface;

3. The physical properties of the ceramic powder; physical properties such as solubility, melting point, etc., are related to the polarity of the ceramic powder molecules;

4. The degree of non-polarity of the glue;

5. Process equipment and modification process for manufacturing ceramic slurry.

Among them, the acidity and alkalinity of the surface of the ceramic powder has a great influence on the type of the modifier selected. The type of functional groups on the surface of the ceramic powder will affect whether the force between the modifier and the surface of the ceramic powder is strong or weak.

The acid-base of the surface of the ceramic powder, the order of interaction with various functional groups is shown in Table 1: When the surface of the ceramic powder is acidic, such as acidic oxide SiO ₂ , the interaction between the functional group and the amine type is the strongest. When the surface of the ceramic powder is neutral, for example, amphoteric oxide alumina (Al ₂ O ₃ ), the interaction with the carboxylic acid type functional group is the strongest; when the surface of the ceramic powder is alkaline, such as alkaline oxidation Magnesium oxide (MgO) also has the strongest interaction with carboxylic acid type functional groups.

The specific surface area of the ceramic powder surface is directly related to the amount of modifier. When the specific surface area of the ceramic powder surface is larger, the amount of modifier required is larger.

When the ceramic powder is chemically surface-modified, the modifier is selected according to the non-polarity (or characteristic) of the glue of the ceramic slurry, and the polar surface of the ceramic powder can be modified to a non-polar surface, and It has the same characteristics as non-polar glue, so it has excellent compatibility between the two, which helps the ceramic powder to disperse itself and stably disperse in the glue. With the aid of a large amount of glue, it is possible to prepare a ceramic powder slurry with good dispersibility, high stability and low viscosity.

The method of using the modifier is closely related to the modification equipment and process, including the type and dispersion method of the solvent selected, and the composite use of the surface modifier. In order to achieve a good modification effect on the surface of the ceramic powder, a certain reaction temperature and reaction time must be satisfied when the ceramic powder is chemically surface-modified. When setting the reaction temperature range, the sensitivity of the modifier to temperature should be considered to prevent the modifier from volatilizing or decomposing due to excessive temperature. Moreover, the temperature is too low, not only the reaction time is long, but also the surface modification of the ceramic powder. The effect is not good.

In summary, the pulping method of the present invention has the effect of improving the stable and uniform dispersion of the ceramic powder in the slurry, and the pulping step comprises:

a. selecting a ceramic powder for use in modulating a ceramic slurry;

b. selecting a glue for modulating the ceramic slurry, including additives such as a solvent, a dispersant, a plasticizer, and a binder;

c. selecting the type and amount of the modifier according to the degree of non-polarity of the glue selected in step b;

d. using the modifier selected in step c, chemically modifying the ceramic powder selected in step a to modify the polar surface of the ceramic powder to a non-polar surface;

e. Using the ceramic powder of step d and the glue of step b to form a ceramic slurry having good dispersibility, high stability and low viscosity.

In order to improve the performance of "multilayer ceramic components", the selection or partial selection of nanomaterials has become an important measure. However, the nanomaterial has a large specific surface area and a high surface energy, and is easy to form agglomerated particles. When the surface characteristics of the nanomaterial are incompatible with the properties of the glue, it is more difficult to disperse.

The pulping method of the invention is suitable for the nano ceramic powder, and the effect of achieving stable and uniform dispersion of the nano ceramic powder in the glue liquid is more remarkable, in particular, the dispersion property is good without adding a large amount of glue liquid. The high-stability and low-viscosity nano-ceramic slurry can greatly improve the performance of the laminated ceramic component because it meets the requirements of the forming process.

Hereinafter, the effects of the present invention will be further specifically described by way of examples, but the scope of the invention patent is not limited to the examples.

Example :

The pressure-sensitive ceramic powder (hereinafter referred to as zinc oxide varistor ceramic powder) for manufacturing a laminated wafer type zinc oxide varistor is selected, and the main component is zinc oxide, which accounts for about 90% of the total weight, and the rest is cerium oxide and cobalt oxide. , cerium oxide, manganese oxide or a small amount of rare earth oxide. The surface of the zinc oxide varistor ceramic powder is alkaline; the average particle diameter is 1 micrometer.

The selected ester is a solvent. According to the non-polarity of the ester solvent, stearic acid and a hydrazine coupling agent KH-550 (γ-aminopropyltriethoxydecane) are used as a composite modifier.

The modifier uses pure water as the solvent, and the preparation steps of the composite modification liquid are as follows:

1. Add 25 kg (Kg) of purified water to 0.25 kg of acetic acid to make a mixture;

2. For the mixture of the previous step, adding 0.325 kg of hydrazine coupling agent KH-550, stirring and hydrolyzing for 20 minutes to prepare a solution A;

3. Using 2 kg of absolute ethanol to add 0.375 kg of stearic acid to make solution B;

4. The solution B of the step 3 was gradually added to the solution A of the step 2 under stirring, and sufficiently dispersed to prepare a composite modification liquid in a white suspension.

For equipment for chemically modifying the surface of zinc oxide varistor ceramic powder, a mixing drum and a ball mill are selected. Pour the prepared composite modified liquid into the mixing drum, slowly add 25 kg of the zinc oxide varistor ceramic powder under stirring, stir evenly, then pour the slurry into the ball mill, ball mill Take it out after 1~2 hours, and dry it at 160 °C for use.

The surface-modified zinc oxide varistor ceramic powder is mixed with a solvent such as an ester solvent and a binder to form a ceramic slurry according to a weight ratio of 1:0.50, and is prepared into a sterling silver according to a conventional conventional process. 2220 gauge laminated wafer type zinc oxide varistor for internal electrodes. The pressure sensitive properties were measured, and the results are shown in Table 2.

Comparative example:

The zinc oxide varistor ceramic powder of the embodiment is selected as a pulping material, but has not been surface-modified. The weight ratio of the zinc oxide varistor ceramic powder to the glue was changed to 1:0.75, and it was used to make a 2220-size laminated wafer type zinc oxide varistor using pure silver as an internal electrode. The pressure sensitive properties were measured and the results are shown in Table 3.

Result :

Comparing the results of Table 2 and Table 3, the laminated wafer type zinc oxide varistor made of surface-modified zinc oxide varistor ceramic powder has excellent effects in various aspects:

1. In the surge current processing capacity (Surge), from 2558A to 4558A, the performance of the 2220 specification laminated wafer type zinc oxide varistor increased by 78%;

2. In terms of leakage current (I _L ), from 8μA to 3.6μA, the performance of the 2220 specification laminated wafer type zinc oxide varistor is also improved;

3. The amount of glue used to prepare the ceramic slurry is reduced from 75% to 50%, saving one-third of the amount of glue.

The above proves that the pulping method of the present invention can first select the binder and solvent to be used, and can indeed greatly reduce the amount of solvent and binder, effectively increase the solid content in the slurry, and improve the initial of the embryo. Density, which greatly enhances the performance of laminated ceramic component products.

Claims (4)

A pulping method for improving stable and uniform dispersion of ceramic powder in a slurry, characterized in that it comprises the following pulping step: a. selecting a ceramic powder for use in modulating a ceramic slurry used for forming a blade; wherein the ceramic The powder is magnesium oxide (MgO), sodium oxide (NaO), copper oxide (CuO), barium oxide (BaO), boron oxide (B ₂ O ₃ ), cerium oxide (SiO ₂ ), sulfur dioxide (SO ₂ ), Sulfur trioxide (SO ₃ ), nitrogen oxides (NO _x ), alumina (Al ₂ O ₃ ), lead oxide (PbO), zinc oxide (ZnO) or antimony trioxide (Sb ₂ O ₃ ); b. Selecting a glue solution for modulating the ceramic slurry used for forming the blade; wherein the composition of the glue includes a solvent, a dispersant, a plasticizer, and a binder; c. selecting the modifier according to the following conditions c1 to c4 Type and amount; c1) the type of functional group on the surface of the ceramic powder selected according to step a; c2) the acidity and alkalinity, moisture content and specific surface area of the surface of the ceramic powder selected according to step a; c3) the ceramic powder selected according to step a The solubility and melting point of the body; and c4) the characteristics of the solvent, dispersant, plasticizer and binder selected according to step b; d. Using the modifier selected in step c, the ceramic powder selected in step a is chemically surface-modified, and a chemical reaction between the modifier and the surface of the ceramic powder is performed to change the polar surface of the ceramic powder to a non-polar surface. a polar surface; e. using the ceramic powder of step d and the glue of step b to form a ceramic slurry. A ceramic powder as described in claim 1 of the patent application is stable in the slurry. The uniformly dispersed pulping method, wherein the method for chemically modifying the ceramic powder in the step d comprises a coupling agent method, an esterification reaction method and a surface graft modification method. A pulping method for enhancing stable and uniform dispersion of a ceramic powder in a slurry according to the first aspect of the invention, wherein the modifier selected in the step c includes an anion, a cation, an amphoteric type and a nonionic surface active agent. Agent. A pulping method for improving stable and uniform dispersion of a ceramic powder in a slurry according to the first aspect of the invention, wherein the modifier selected in the step c is selected from the group consisting of a decane coupling agent and a titanate coupling. Agent, zirconium aluminate coupling agent, organic chromium coupling agent, phosphate ester, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, hydroxyoleic acid, hydroxyl One or more of a group consisting of stearic acid, lanolin fatty acid, acrylic acid, crotonic acid, methacrylic acid, cinnamic acid, vinyl acetate, propylene acetate, sorbic acid, maleic acid, and an organic amine salt.