JP2002518290A - Barium titanate dispersion - Google Patents

Abstract

  (57) [Summary] The present invention provides a barium titanate-based particle slurry, dispersion, or slip in a non-aqueous medium. The particles have a coating comprising a metal oxide, metal hydrate, metal hydroxide, or organic acid salt of a metal other than barium or titanium. When these coated particles are dispersed by high shear mixing, at least 90% of the particles have a particle size of less than 0.9 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION The present invention relates to barium titanate dispersions, particularly barium titanate dispersions in non-aqueous media.

[0002] Barium titanate-based materials are suitable for multilayer ceramic capacitors commonly referred to as "MLC" because of their high dielectric constant. MLC has alternating layers of dielectric and conductive materials. Examples of MLCs are described in US Pat. No. 3,612,96.
No. 3 and No. 4,435,738. Palladium, silver, palladium-silver alloy, copper, and nickel are common conductive materials used in MLC. MLC dielectrics are usually made from high solids dispersions, which are known in the art as "slips". Such slips typically include a powdered barium titanate-based material and a polymeric binder in an aqueous or non-aqueous solvent. The powdered film, stabilized by a binder and made by slip casting or coating, is dried to provide a "green" layer of ceramic dielectric.
The unfired layer is coated with a specific pattern of conductive material, stacked,
A laminate of alternating layers of green ceramic dielectric and conductor is provided. Cutting the laminate into MLC-sized cubes, heating it to burn off organic materials such as binders and dispersants, and firing to sinter particles of barium titanate-based material; A capacitor structure having a stacked dense ceramic dielectric and conductive layers is created. The sintering temperature is typically between about 1000C and 1500C. During sintering, the ceramic dielectric densities increase due to the melting, bonding and granulation of the particles. Even when a particle growth inhibitor is used, the ceramic particle size of the MLC dielectric is typically relatively large, for example, three times the size of the original primary particles.
Up to 5 times the size. Further, not all porosity is removed during the sintering process. Typically about 2% to 10% of the porosity remains in the MLC dielectric layer. These pores or hole defects in the dielectric layer tend to be relatively large in ceramics having relatively large particle sizes. Certain important properties of capacitors, such as breakdown voltage and DC leakage, are affected by dielectric thickness, grain size, and pore defects. For example, an effective dielectric layer would require a plurality of grain thicknesses, for example, at least 3-5 grain thicknesses. Since defects in any one of the layers of the MLC can be fatal to its performance, the thickness of the dielectric layer should be large enough to effectively eliminate the effects of ceramic defects. Produce MLC. Here, this ceramic defect is caused by random large particles or pores and can have an unfavorable effect on the properties of the MLC.

[0003] The marketplace requires smaller electronic device designs, and the MLC industry is demanding relatively thin dielectric layers without the undesired effects of large particles and pore size on dielectric thickness. Need a ceramic material to make it possible.

[0004] Barium titanate powders made by known methods, such as calcination or hydrothermal processes, have strongly bound fine particles and / or large particles substantially larger than 1 μm. Such particles and agglomerates are not easily adapted to the production of MLCs having very thin dielectric layers of fine particles, for example a dielectric layer of 4-5 μm thickness. Thus, electrical properties such as DC leakage and breakdown voltage are acceptable without the need for extended ball milling, which is suitable for the manufacture of MLCs having relatively thin dielectric ceramic layers, for example, dielectric ceramic layers less than 4 μm. Providing possible and superior barium titanate-based materials and dispersions offers benefits over the prior art.

SUMMARY OF THE INVENTION In one aspect, the present invention provides a slurry, dispersion, or slip comprising particles based on barium titanate dispersed in a non-aqueous medium. The particles have a coating that includes a metal oxide, metal hydrate, metal hydroxide, or organic acid salt of a metal other than barium or titanium, where the high shear is used.
When dispersed by mixing, at least 90% of the particles have a particle size of less than 0.9 μm.

As used herein, the term “based on barium titanate” refers to barium titanate, barium titanate having an oxide coating of another metal, and barium and titanate in the form of the general formula ABO ₃ (A represents one or more divalent metals, such as barium, calcium, lead, strontium, magnesium, and zinc, and B represents one or more trivalent metals, such as titanium, tin, (Representing zirconium and hafnium).

[0007] In another aspect, the invention provides a method of making a slurry, dispersion, or slip. The method involves dispersing the barium titanate-based particles in a non-aqueous medium by high shear mixing until 90% of the particles have a particle size of less than 0.9 μm. The particles have a coating comprising a metal oxide, metal hydrate, metal hydroxide, or organic acid salt of a metal other than barium or titanium.

[0008] In a further aspect, the present invention provides another method of making a slurry, dispersion, or slip. The method comprises producing a slurry of particles based on barium titanate in an aqueous medium by a hydrothermal process. The method further includes making a coating of particles comprising a metal oxide, metal hydrate, metal hydroxide, or organic acid salt of a metal other than barium or titanium. The method further includes replacing the aqueous medium with a non-aqueous medium and dispersing the barium titanate-based particles in the non-aqueous medium by high shear mixing.

[0009] Other novel features and aspects of the present invention will become apparent from the following detailed description and the appended claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION The present invention contemplates a slurry, dispersion, or slip of particles based on barium titanate dispersed in a non-aqueous medium. The particles have a coating on at least a portion of their surface. The coating comprises a metal oxide, metal hydrate, metal hydroxide or organic acid salt of a metal other than barium or titanium, or mixtures thereof. The particle size of the coated particles is less than 0.9 μm when dispersed by high shear mixing.

[0011] These barium titanate-based particles can be dispersed in a sub-micron dispersion in a non-aqueous medium without the need for a ball mill. This is advantageous in the fabrication of MLCs with sub-micron grain size and high breakdown voltage thin dielectric layers. High shear mixing is effective in reducing the size of the agglomerates of barium titanate-based particles, and without ball milling, deagglomerates or separates the agglomerates into relatively small coated particles . Here, in the ball milling, a hard ball mill medium, such as a rod, a ball, or zirconia particles, is used to impact particles. Ball milling breaks the particles into smaller than primary particles and produces non-equiaxes with exposed uncoated surfaces.
In a preferred embodiment, the particles of the present invention are not ball-milled, so that a majority of the particle surface is covered by the coating, as it results in quiaxed particles. In another aspect of the invention, the unmilled particles are equiaxed or spherical.

Particles based on barium titanate are beneficial in providing a monolithic capacitor having a ceramic body with a particle size of less than 0.3 μm. Preferred M
LC indicates X7R or Y5V capacitance temperature coefficient, and the dielectric thickness is 5 μm.
And a dielectric strength of at least 50 V / μm.

[0013] The primary particle size of the particles based on barium titanate can be determined by methods known to those skilled in the art. Examples of such methods use a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Although particles based on barium titanate include primary particles of various sizes, the average primary particle size of the particles based on coated barium titanate is less than 0.6 μm. Preferably the primary particle size of the particles is less than 0.5 μm, more preferably less than 0.4 μm, and more preferably less than 0.3 μm, most preferably less than 0.2 μm.

The particles based on barium titanate may be present in forms other than the primary particles, for example as conjugates of the primary particles and / or aggregates of the conjugates of the primary particles. SEM
And TEM are not effective in distinguishing the particle size distribution between primary particles, aggregates of primary particles, and aggregates of aggregates of primary particles. Processing that results in a change in the distribution of bound or agglomerated particles, such as sonication, high shear mixing, or deagglomeration by milling, where preparation for analysis is not included, for example, particle size analysis by light scattering techniques , A preferred method for characterizing the particle size of particles based on barium titanate. One such automated light scattering technique is HORIBA LA-910.
Use a (trademark) laser light scattering particle size analyzer or similar device. Such analyzes typically show frequency-normalized volume fractions of each size of particles, including primary particles, conjugates, and aggregates, in groups of ten or decile. Thus, as used herein, the term "particle size" refers to individual particles in a powder, and refers to primary particles, aggregates of primary particles, aggregates of aggregates, and mixtures thereof. Can be included. In one aspect of the invention, the dispersion of the barium titanate-based particles has a particle size of at least 90% of the metal oxide-coated barium titanate-based particles of less than 0.8 μm, preferably 0.7 μm.
m, more preferably less than 0.6 μm. In a relatively preferred aspect of the present invention, at least 90% of the particles in the barium titanate dispersion have a particle size of less than 0.5 μm, preferably less than 0.4, more preferably less than 0.3 μm.

As a feature of the particle size distribution, D₉₀(Smallest decile size of largest particle
), D₅₀(Median diameter), D_Ten(Largest particle size of decile of smallest particle
). Ratio D₉₀/ D_TenValue is used to indicate the width of the particle size distribution curve.
This is a useful feature. In various aspects of the invention, the particle size distribution is narrow, preferably the ratio D₉₀/
D_TenIs less than 4, more preferably D₉₀/ D_TenIs less than 3, more preferably D ₉₀ / D_TenIs less than 2.5.

As used herein, the term “dispersion” refers to a two-phase system of solid particles suspended in a non-aqueous medium. In a preferred embodiment, the stability of the dispersion or the resistance to settling of the suspended solid particles can be promoted by the use of a dispersant.

As used herein, the term “metal oxide” refers to metal oxides, metal hydroxides, hydrates, unless the context clearly indicates only metal oxides. Used to describe coatings of metal oxides and organic acid salts of metals. Such organic acid salts can be converted to oxides or hydroxides, for example, by pyrolysis that occurs during burning of the ceramic binder and / or during heating for ceramic sintering.

As used in the description of the present invention, the term “high shear mixing” refers to imparting sufficient energy to the agglomerates of coated particles, such as rods, cylinders, or hard spherical media, such as zirconia spheres. Means mixing in a liquid medium into relatively small particles without impact of a solid material. In some high shear mixing devices,
Use hard media. Here, a small size medium is used to provide shear without impact. High shear mixing can be performed in a variety of equipment, such as the following, but it is difficult to accurately determine the force applied to separate agglomerates in high shear mixing.

As mentioned above, “based on barium titanate” refers to barium titanate,
Barium titanate having an oxide coating of another metal, as well as general formula A
Other oxides based on barium and titanates of BO ₃ (A represents one or more divalent metals, such as barium, calcium, lead, strontium, magnesium, and zinc, and B represents one or more trivalent metals For example, titanium, tin, zirconium, and hafnium). The structure of a preferred barium titanate-based material, typically used in Y5V applications, is
_{a (1-x) A x} O · Ti (1-y) B y O 2 (x and y may be a 0 to 1, A is one or more divalent metal excluding barium, such as lead, calcium, Or strontium, and B represents one or more trivalent metals except titanium, eg, tin, zirconium, and hafnium). If other metals are present as impurities, the values of x and y are small, for example less than 0.1. In other cases, one or more other metals can be introduced to provide significantly distinguishable compounds, such as barium calcium titanate, barium strontium titanate, barium titanate zirconate, and the like. In still other cases where x or y is 1, barium or titanium can be replaced with other metals of appropriate valency to provide compounds such as lead titanate or barium zirconate. In still other cases, the compound may have multiple partial substitutions of barium or titanium. An example of such a plurality of partially substituted compounds can be represented by the following structural formula: Ba _{(1-x-x'-x ")} Pb _x Ca _{x '} Sr _x" O.Ti _{(1-y-y'-y ")} Sn _y Zr _{y '} Hf _y" O ₂ where x, x', x ", y, y 'and y" are each 0 or more, and (x + x' + x
") Is less than 1 and (y + y '+ y") is less than 1. In many cases, the barium titanate-based material will have a perovskite crystal structure, preferably the barium titanate material will have a perovskite structure.

[0020] The hydrothermally produced barium titanate particles are generally dried to form particles, and the particles form relatively strongly agglomerated particles. It is not effectively deagglomerated by simple high shear mixing. Dispersions made from such dried agglomerated barium titanate-based particles having a submicron primary particle size require substantially long periods of impact milling to provide particles in the micrometer range, Longer and more intense milling is required to obtain submicron sized particles. Conversely, agglomerated particles having a primary particle size of submicron size, which are based on barium titanate coated with a metal oxide, can be a slurry, dispersion, or dispersion of such particles in a non-aqueous medium. The gentle action of the high shear mixing of the slip can cause it to deagglomerate into coated particles in the submicron size range.

The non-aqueous slurry, dispersion, or slip of the barium titanate-based particles of the present invention, which can be prepared from the hydrothermally produced barium titanate-based particles, is an aqueous environment, at least until the particles have a coating. The aqueous phase is replaced by a non-aqueous phase, for example, as maintained in an aqueous slurry, as described further below.

Slurries of particles based on submicron barium titanate can be prepared using hydrothermal processes such as US Pat. Nos. 4,832,939, 4,829,033, and 4,863,833. Can be prepared by the process disclosed in In such a hydrothermal process, an excess of barium hydroxide solution, typically up to about 20 mol%, is added to the hydrous titanium oxide slurry, typically from about 100 ° C to 200 ° C.
Heat to a temperature of ° C. to produce submicron particles with a perovskite crystal structure. Particle size and particle size distribution depend on various variables of the process, such as the temperature of the slurry and solution,
It can be changed by controlling the addition rate, the heating rate to the perovskite formation temperature, and the cooling rate from the perovskite formation temperature. The choice of process variables for the production of the desired particles can be readily made by those skilled in the art according to the following general principles of crystallization. For example, by adding barium hydroxide relatively slowly to a slurry maintained at a relatively low temperature, such as about 35 ° C,
Relatively large particles can be prepared, and relatively small particles can be prepared by adding barium hydroxide relatively quickly to a slurry maintained at a relatively high temperature, for example, about 95 ° C. In order to prepare uniform particles,
Good stirring is important.

After the barium titanate particles are given a perovskite structure by heat treatment of the slurry, the particles are preferably washed to remove unreacted metal species such as barium ions. Washing is performed with deionized water to which ammonia having a pH of 10 has been added so as not to dissolve barium from the particles. This wash water can be removed from the settled particles by filtration or decantation. The number of washing cycles is determined by the purity required in the aqueous phase to provide a low ionic strength slurry with a conductivity of less than 5 millisiemens, preferably less than 1 millisiemens. Four to five wash cycles have been found to be adequate to reduce the ionic content of the aqueous phase to low levels characterized by a conductivity of less than about 100 microsiemens.

The barium titanate particles can be maintained in an aqueous state until after the coating process. As mentioned above, the barium titanate-based particles can have a coating comprising an oxide, hydrated oxide, hydroxide, or organic acid salt of at least one metal other than barium and titanium. The coating can be provided by adding to a stirred slurry of particles based on barium titanate an aqueous solution of a salt of a metal corresponding to the desired coating, for example an aqueous solution of nitrate, borate, oxalate, etc. . Precipitation into the coating should be carried out with the appropriate p
Promoted by H. The salt solution may be added as one mixture of salts to create a single layer uniform coating, or separately and sequentially added to individual oxides, hydrated oxides,
A layer of hydroxide or organic acid salt can be made. For relatively soluble metals such as cobalt and nickel, oxide coatings are relatively difficult to apply and maintain without re-dissolution. Therefore, it is often preferred that these relatively soluble metal oxide coatings be applied as an overcoat on the relatively easily deposited metal oxide layer. An alkaline environment also minimizes barium dissolution and readily provides particles with a barium and titanium free coating. The coating thickness of the particles intended for use in ceramic capacitors is typically less than 10% of the diameter of the particles, often 20 nm in thickness, and preferably 5 nm to 10 nm or less. Is preferred.

[0025] Useful organic acid salt coatings can include organic salts of metals with low solubility. Examples of such organic acid salt coatings include metal salts of oxalic acid (eg, niobium oxalate), citric acid, tartaric acid, and palmitic acid. It is believed that the organic acid salt is converted to a metal oxide during burn off of the binder. The choice of metal is based on the promoting effect on the processing or properties of the MLC. The coating metal is typically bismuth, lithium, magnesium, calcium, strontium, scandium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten, manganese, cobalt, nickel, zinc, boron, silicon, antimony, tin, yttrium, It is selected from lanthanum, lead and lanthanide elements. Preferably, the barium titanate particles have a barium and titanium free metal oxide coating. If a ceramic capacitor having X7R dielectric properties is desired, it would be beneficial to provide barium titanate particles containing a dopant such as niobium oxide, tantalum oxide, or neodymium oxide in combination with nickel oxide or cobalt oxide. About 1300 ° C-1600 ° C
If it is desired to provide a ceramic capacitor that sinters at a relatively low temperature relative to the temperature of, for example, about 1000 ° C. to 1200 ° C., provide barium titanate particles with dopants that promote sintering at low temperatures. It is beneficial.
Such low temperature sintering aids can include bismuth oxide, zinc oxide, zinc borate, zinc vanadate, lithium borate, and combinations thereof. The dielectric modification and sintering temperature reduction metal oxide can be effectively added to the particles after washing the particles based on barium titanate and before forming the dispersible wet cake.

After applying the coating to the particles based on the hydrothermally produced barium titanate, the slurry can be washed and the water content of the slurry reduced to provide a concentrated slurry, wet cake, or powder. Further, the slurry, wet cake, or powder can be treated with a dispersant to provide a dispersion, and further treated with a binder and other additives to provide a slip. It is preferred to remove the water by means to prevent or minimize the formation of strongly agglomerated particles, such as calcination. Because they have not been calcined or dried, certain metal oxide coatings also tend to maintain the hydrated metal oxide form and have a pH that minimizes the solubility of this metal oxide.
Unless a pH close to is maintained, they may dissolve. For example, nickel oxide or cobalt oxide tends to dissolve somewhat if the pH is not maintained at a value close to 10. Therefore, to maintain properly coated particles, the pH of the aqueous component is preferably maintained at 9-11. Slurries of particles based on barium titanate coated with metal oxides are conveniently produced with a relatively low solids content, e.g., 30 wt% particles based on barium titanate. Relatively high solids contents are typically preferred for MLC production. Thus, when the slurry of the present invention is used directly in the production of MLC, it is beneficial to concentrate the slurry to a solids content of at least 40 wt%, for example by removing water by means such as filtration. , Preferably at least 50 wt%, more preferably at least 55 wt%, even more preferably at least about 60 or 75 wt%.
wt% range. Dispersants and binders can be added to the concentrated slurry to provide a stable dispersion or slip of barium titanate-based particles.

As mentioned above, after coating the particles based on barium titanate,
The aqueous phase can be replaced by a non-aqueous phase. By solvent exchange or distillation,
The aqueous phase can be replaced with an organic liquid phase. In the solvent exchange process, a filtration device can be used. In a preferred embodiment, the filtration device is a Funda ™ filter, which has a flat tray lined with ultrafiltration membranes. It is attached to a central standpipe. The liquid stream passes through a FUNDA ™ filter and is withdrawn through this central upright tube. After the filtration operation, the filter cake is separated from the tray using centrifugal force. The solid is dropped through the valve and sent to the next processing step. An ultrafiltration membrane material is used for sub-micron particle size hot water barium titanate.

In operation, the solvent exchange process initially involves pumping an aqueous slurry of barium titanate particles into a filtration device. Water is removed through an ultrafiltration membrane. After most of the water has been removed, an anhydrous water-miscible organic solvent such as methyl ethyl ketone (MEK) or toluene (shown below) is introduced into the filtration device. This water-miscible solvent is added and removed from the filter through the ultrafiltration membrane material until the water content of the barium titanate filter cake has been reduced to the desired value. After removing water from the filter cake using a solvent that can dissolve water, add a solvent that cannot dissolve water. A sufficient amount of a solvent that cannot dissolve water is added and removed through an ultrafiltration material to reduce the concentration of the solvent that can dissolve water to a desired value. Thereafter, the barium titanate is separated from the ultrafiltration material and placed in a mixing tank located below the filtration device.

After putting the barium titanate into a mixing tank located below the filtration device,
Add the dispersant and mix the vessel contents until a uniform slurry is obtained. If a low water content is desired, a desiccant, such as activated alumina, can be added. The dispersed slurry is pumped out for pulverization and packing.

Another way to achieve solvent exchange is by a distillation process. The process includes a mixed batch distillation vessel, a condensing heat exchanger, and a phase separation tank. In operation, the aqueous barium titanate slurry is pumped into a distillation tank and the desired organic solvent is added. If the desired organic solvent is not miscible with water, a small amount of a water miscible solvent such as a high molecular weight alcohol can be added. After this,
Mix the ingredients into an emulsion and heat. Preferably, a distillation process is used with a high molecular weight solvent having a higher boiling point than water. Heating the mixture selectively removes water, leaving barium titanate dispersed in the organic medium. A phase separation tank located downstream of the condensing facility separates water from any solvent that was removed during the distillation. The solvent is pumped back to the distillation vessel and the water is pumped to waste. It is also possible to carry out distillation at relatively low temperatures using vacuum with a phase separation tank. A dispersant may be added during the distillation process to prevent the slurry from solidifying in the distillation vessel. Once the desired water content has been achieved, the solvent is no longer circulated and the mixture is concentrated by distillation to achieve the desired solids fraction.

As with the ultrafiltration process described above, if a relatively low water content is desired, the mixture in the distillation tank may be fed through a layer holding a desiccant, such as activated silica or activated alumina. Can be. The thermodynamic efficiency of the distillation process can be improved by adding an ultrafiltration module upstream and adding an aqueous barium titanate slurry to the distillation vessel. These ultrafiltration modules remove most of the water from the aqueous barium titanate slurry before introduction into the upstream process.

The non-aqueous slurry can also be concentrated, for example by filtration, to provide a solid wet cake, which comprises particles based on barium titanate coated with metal oxides and non-flowable solids including liquids. It is. The non-aqueous wet cake may be in the solid state with about 60 wt% solids mixed with the non-aqueous solution. More preferably, the wet cake contains at least 65 wt% solids, more preferably at least 70 wt% solids. The wet cake can include up to about 85 wt% solids. In non-aqueous wet cakes, the pH of the non-aqueous solution should be greater than 8, and dissolution of metals should be suppressed. A preferred pH range is about 8-12, more preferably about 9-11. Wet cakes of particles based on barium titanate are precursors to colloidal dispersions. Accordingly, the wet cake can be dispersed, for example, by mixing with a dispersant. Only a small amount of additional liquid solvent is required, if necessary, to bring the wet cake from a solid state to a fluid dispersion.

[0033] At least in the case of non-aqueous wet cakes, the particles in the cake are compared as long as the liquid content of the cake is maintained at least 15 wt%, more preferably at least 20 wt%, more preferably at least 25 wt%. Maintain a weakly agglomerated state for an extended period of time.

[0034] Preferably, the wet cake is placed in a moisture barrier to suppress loss of water content. Such loss of water content may promote the formation of strongly agglomerated particles that are not easily deagglomerated. Such moisture barriers, such as polyethylene bags or polyethylene coated fiber drums, have an extended shelf life of at least 1 day or more, preferably at least 3 days, more preferably at least 30 days, most preferably at least 90 days. Can be provided.
Such features facilitate storage and transport of the wet cake aspect of the present invention.

By adding the dispersant to the wet cake without adding a significant amount of fluid, the wet cake easily becomes a fluid dispersion. Although fluid can be added to the cake, the amount of dispersant required to make the solid cake into a fluid dispersion is fairly small, for example, typically less than 2 wt% based on barium titanate-based material. is there. In some cases, no additional fluid other than the fluid volume of the dispersant is required to make the wet cake a fluid dispersion. Considered dispersants are polyelectrolytes, which include organic polymers with anionic or cationic functional groups. Anionic functionalized polymers may include carboxylic acid polymers such as polystyrene sulfonic acid and polyacrylic acid, and cationic functionalized polymers may include polyimides such as polyetherimide and polyethylene imine. Polyacrylic acid is preferred for many applications. The acid groups of the polymer can be protonated, such acid groups having a counter cation, and the pH of the dispersion can be reduced to barium or other metal species, such as other metal species that may be present in the dopant coating. Is preferably prevented from lowering to a level that promotes dissolution. For capacitor applications, the preferred cation is an ammonium ion. In some cases, it may be possible to use a dopant metal as a counter cation for the polymeric acid dispersant. Regardless of the dispersant selected, the appropriate amount of dispersant can be readily determined by one skilled in the art using a titration process. When the amount of the dispersant selected is the amount that minimizes the viscosity of the dispersion, the concentration of the dispersant decreases in the use of the dispersion due to dilution or interaction with additives, and the viscosity is desired. First, it can be high. Thus, for many applications, it is desirable to use a "viscosity minimizing amount" of the dispersant.

A preferred dispersant for use in capacitor applications and colloidal dispersions intended for such testing has been found to be ammoniated polyacrylic acid having a number average molecular weight of about 8,000. For example, 0.75 wt% of such an ammoniated polyacrylic acid (as a 40 wt% aqueous solution) has been found to be beneficial in making the wet cake a liquid dispersion. The dispersant can be introduced by any convenient means, such as mechanically incorporating the dispersant into the wet cake. When using high shear mixing, excess dispersant is consumed by the new particle surface area exposed in the deagglomeration. Thus, in high shear mixing, it may be convenient to gradually add the dispersant.

[0037] Wet cakes are different from slurries, dispersions, slips, and dry powders. That is, wet cake is a non-flowable solid, while slurries, dispersions, and slips are flowable liquids, and dry powders are flowable solids. A wet powder may or may not be flowable, depending on the amount of liquid present. As the liquid is removed, the wet powder gradually dries. However, it is understood that the dry powder need not be completely dehydrated. Spray-drying, freeze-drying, and low-temperature vacuum accelerated drying are dry powders of particles based on coated barium titanate, which are still dispersible by simply mixing into a dispersant-containing solution, for example by high shear mixing. This is the preferred method of providing the powder. Thus, a dry powder of particles based on coated barium titanate can be unexpectedly dispersed in a dispersion of submicron particles without the need for prolonged impact milling. Unlike known materials, the dispersion or slip of coated barium titanate-based particles is used to reduce the particle size until it can be used to make finer particles, thinner dielectric layers, and capacitors with high breakdown voltages. No need for high energy milling over several hours.

Another aspect of the present invention provides a method of making a dispersion of submicron coated barium titanate-based particles in a solution. The method relies on deagglomeration of a dispersion of particles based on barium titanate coated with large (> 1 μm) weakly agglomerated metal oxides until substantially all particles are below 1 μm. In a preferred method of the invention, a high solids dispersion containing about 30 wt% to 75 wt% particles is deagglomerated by high shear mixing with a dispersant. The optimal time for high shear mixing is readily determined by routine experimentation. High shear mixing can be performed in a centrifugal pump deagglomeration pulverizer, such as, for example, Sil
version Machine Inc. (East L, Mass.)
engmeadow). Other devices useful for providing deagglomerated dispersions include super-pulverizers (super
mill), a colloid mill, and a device known as a cavitation attritor. The super milling device has a milling vessel filled with media, which has a high speed rotating disc on the central axis. This is, for example, Pre
commercially available from mir Mill (Reading, PA). The colloid mill has a grinding gap between the extended surface of the high speed rotor and the stator, which is also commercially available, for example, from Premier Mill. For example, Arde Barinco Inc. A cavitation comminuting device, commercially available from Norwood, NJ, pumps fluid through a series of containers that open and close quickly, which rapidly compresses and decompresses the fluid to break up particles. Provides a high frequency shear effect that results in agglomeration. Concentrated slurries, dispersions, wet cakes, wet powders, or dry powders may perform equally well in providing slips for the manufacture of high performance capacitors, depending on the respective capacitor manufacturing facility or method. Conceivable.

[0039] Tests to determine the effective amount of dispersant for weakly agglomerated coated barium titanate particles are based on high shear mixing equipment such as Silverson.
Model L4R high shear laboratory mixing equipment, equipped with a square hole high shear screen to effect high shear mixing of a 500 g dispersion sample. This sample contains 70 wt% of the coated particles in an alkaline non-aqueous solution at a temperature of 25 ° C. to 30 ° C. at a pH at which the coating does not dissolve, and dissolves the coated particles in an effective time. It contains an effective amount of dispersant to effect flocculation. An effective amount of dispersant is sufficient to maintain relatively small particle sizes without reaggregating the separated agglomerates and agglomerates. The effective amount of dispersant will vary depending on such factors as the size of the particles, the nature of the coating, and the strength of the dispersant. The effective amount and effective time of the dispersant can be determined by performing some routine experimentation to determine the effect of variables such as the concentration of the dispersant and high shear mixing time on the reduction in the degree of particle size distribution. It can be easily determined by observation by a trader. An effective number of these variables allows for particle size analysis, which reflects the actual impact of high shear mixing on deagglomeration. In many cases, an effective amount of an ammoniated polyacrylic acid dispersant (number average molecular weight about 8,000) is 1 wt% based on the total weight of the particles and dispersant, resulting in an effective high shear mixing The time is about one minute.

Particles based on coated barium titanate prepared by a hydrothermal process are substantially spherical and equiaxed in appearance. Such particles remain substantially spherical, even after being reduced in size by high shear mixing. In some cases, substantially spherical particles may be paired. The generation of paired particles is desirably rare. The use of spherical particles, especially when compared to the use of non-spherical finely divided particles, results in a particularly high surface area, a BET surface area of at least about 4 m ² / g, preferably at least about 8 m ² / g, more preferably at least about 12 m ² / g. A powder is provided.

[0041] Submicron coated barium titanate particles can be prepared using a variety of binders, dispersants, and release agents using non-aqueous solvents.
) To provide a ceramic casting slip.

The particles based on barium titanate contain dissolved polymer binders and optionally other dissolved substances such as plasticizers, release agents, dispersants, release agents, antifouling agents (ant
Ifoling agent) and a wetting agent are dispersed in an organic solvent. Useful organic solvents are of low boiling point, for example benzene, methyl ethyl ketone, acetone, xylene, methanol, ethanol, propanol, 1,1,1-
Trichloroethane, tetrachloroethylene, amyl acetate, 2,2,4-triethylpentanediol-1,3-monoisobutyrate, toluene, methylene chloride, turpentine, ethyl alcohol, bromochloromethane, butanol, diacetone, methyl isobutyl ketone, cyclohexanone, Methyl alcohol, n
-Propyl alcohol, isopropyl alcohol, n-butyl alcohol, n-
Octyl alcohol, benzyl alcohol, glycerol, ethylene glycol, benzaldehyde, propionic acid, n-octanoic acid, ethyl acetate, butyl butyrate, n-hexane and the like, and mixtures thereof, and mixtures with water, such as methanol / water mixtures Can be mentioned. Further, a plurality of azeotropic organic solvent mixtures have a low boiling point and can be used as a carrier vehicle. Examples of the solvent mixture include 72% trichloroethylene / 28% ethyl alcohol, 66%
% Methyl ethyl ketone / 34% ethyl alcohol, 70% methyl ethyl ketone /
30% ethyl alcohol, 59% methyl ethyl ketone / 41% ethyl alcohol, 50% methyl ethyl ketone / 50% ethyl alcohol, 80% toluene / 20
% Ethanol, 80% toluene / 20% ethyl alcohol, 70% toluene / 3
0% ethyl alcohol, 60% toluene / 40% ethyl alcohol, 70% isopropyl alcohol / 30% methyl ethyl ketone, 40% methyl ethyl ketone /
60% ethyl alcohol, and mixtures thereof.

In addition to those described above, useful dispersants (defoamers / wetting agents) in sub-micron, non-aqueous dispersions of barium titanate particles coated with metal oxides include, for example, phosphate esters, Glycol trioleate, ethoxylate, 2-amino-2-methyl-1-propanol, tall oil hydroxyethyl imidazoline,
Hydroxyethylimidazoline oleate, fatty acids such as glycerol trioleate, lanolin fatty acid, poly (vinyl butyral), sodium bis (tridecyl) sulfosuccinate, diisobutylsodium sulfosuccinate, sodium dioctylsulfosuccinate, ethoxylated alkylguanidine Amine, sodium dihexyl sulfosuccinate, sodium diisobutyl sulfosuccinate, benzenesulfonic acid, oil-soluble sulfonate, alkyl ether of poly (ethylene glycol), ethylene oxide oleate adduct, sorbitan trioleate, steric amide ethylene oxide Adducts, alkyl allyl polyether alcohols, poly (ethylene glycol) ethyl ether, ethyl phenyl Glycol, polyoxyethylene acetate, and polyoxyethylene esters. Preferred dispersants for organic solvent suspensions and slips include menhaden oil, corn oil, polyethylene imine, and ammoniated polyacrylic acid.

Polymer binder materials useful in non-aqueous slips include poly (vinyl butyral), poly (vinyl acetate), poly (vinyl alcohol), cellulose polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, methylhydroxyethylcellulose, cellulose Acetate butyrate, nitrocellulose, polypropylene, polyethylene, silicone polymers such as poly (methylsiloxane) and poly (methylphenylsiloxane), polystyrene, butadiene / styrene copolymer, poly (vinylpyrrolidone), polyamide, polyether, poly (ethylene oxide- Propylene oxide), polyacrylamide, and acrylic acid polymers such as sodium polyacrylate, poly (methyl Acrylate), poly (methyl methacrylate), polyacrylate esters and copolymers, such as copolymers of ethyl methacrylate and methyl acrylate, poly (vinyl alcohol), poly (vinyl chloride), vinyl chloride acetate, poly (tetrafluoroethylene), poly (A-methylstyrene) and the like. The polymer binder typically has about 5-20 watts.
It is beneficial in the range of t%. A preferred commercially available polymer is ACRYL
OID ™ B-7 acrylate polymer (Rohm & Haas Co.
Philadelphia, PA).

The organic medium also contains a small amount of a plasticizer, so that the glass transition temperature of the binder polymer (
Tg) is often lowered. The choice of plasticizer mainly depends on the polymer that must be modified, including phthalates (and mixed phthalates) such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, Butylbenzyl phthalate, alkyl phosphate, poly (alkylene glycol), polyethylene glycol, glycerol,
Examples include poly (ethylene oxide), hydroxyethylenated alkylphenol, dialkyldithiophosphonate, poly (isobutylene), butyl stearate, methyl aviate, tricresyl phosphate, dipropyl glycol dibenzoate, and the like.

In one embodiment, the organic solvent based slip of the present invention comprises 25-40 parts of organic solvent, 2-5 parts of dispersant, 5-20 parts of polymer per 100 parts by weight of barium titanate based particles A binder, and 0 to 15 parts of a plasticizer.

The dispersion of the barium titanate-based particles in various non-aqueous solvents can be facilitated by applying various coatings, such as coupling agents, to the surface of the particles. Various silane coupling agents that can be utilized in particular provide a means for adjusting the surface of the particles to the selected carrier vehicle.
Coating of particles based on hydrothermally produced barium titanate with silane coupling agents is beneficial not only for dry powders, but also for particles in solution. The silane coupling agent can be applied to the surface of the dried or undried particles, but preferably the coupling agent is applied after drying of the particles to disperse these particles in the carrier vehicle. To assist. In addition, drying the powder provides an easy mechanism to determine if the particles are finished by trying to disperse the treated particles in water. Uncoated or partially coated particles are partially or completely dispersed in the water, and fully coated particles float on the water surface even with stirring.

The particles can be coated in one carrier vehicle and transferred to the other carrier vehicle by a solvent exchange process (as described above) or a distillation process. The silane coupling agent can be applied to the surface of the powder before or after the solvent exchange, but it is preferred to apply the coating after the solvent exchange process. A silane coupling agent can be attached to the particle surface to aid in dispersion in the desired carrier vehicle and to promote passivation of the particle surface.

The general formula of the organosilane R _n SiX _(4-n) shows two classes of functionality. The X group reacts with the inorganic substrate. The bond between X and the silicon atom in the coupling agent is replaced by the bond between the inorganic substrate and the silicon atom. X is a hydrolysable group, typically an alkoxy, acyloxy, amine, or chlorine. The most common alkoxy groups are methoxy and ethoxy, which give methanol and ethanol as by-products during the coupling reaction. Chlorosilanes are generally used less than alkoxysilanes because they provide hydrogen chloride as a by-product during the coupling reaction. R is an unhydrolyzed organic radical that has a functional group that can couple the coupling agent to organic resins and polymers. Most commonly used organosilanes have one organic substituent. In most cases, the silane is hydrolyzed prior to surface treatment.
After hydrolysis, reactive silanol groups are formed and condense with other silanol groups, for example on siliceous fillers, resulting in siloxane bonds. Stable condensation products are also made with other oxides, such as oxides of aluminum, zirconium, tin, titanium, and nickel. Relatively unstable bonds are created with oxides of boron, iron, and carbon. Alkali metal oxides and carbonates do not form stable bonds with Si-O-.

[0050] Water for hydrolysis can come from several sources. This can be due to the addition, the presence on the substrate surface, or the atmosphere. The reaction of these silanes with a trimethoxy hydrolyzable X group involves the following four steps. 1. Initially, hydrolysis of the three silicon-bonded releasable X groups occurs:

Embedded image 2. Condensation to the following oligomers:

Embedded image 3. The oligomer forms a hydrogen bond with the OH group of the substrate:

Embedded image 4. Finally, during drying or curing, a covalent bond with the substrate is formed with the loss of water:

Embedded image

At the interface, there is usually only one bond from each silicon of the organosilane to the substrate surface. The remaining two silanol groups are bound to the other coupling agent silicon atom or are free.

With slips based on organic solvents, unfired tapes can be made on a carrier substrate by methods known to those skilled in the art. For example, J. C. Williams C
eramic Fabrication Processes, Treatis
e on Materials Science and Technology
Volume 9 of y (Academic Press (1976)), pp. 173-197
And U.S. Patent Nos. 3,717,487 and 4,640,905. The descriptions of these documents are hereby incorporated herein by reference.

In addition, various techniques exist for making slips into thin films, green layers, and fired ceramics. The dispersions of the present invention have applications with minor modifications, such as selection of a preferred suspension medium or binder, dilution to the desired fluid viscosity, etc., in various ceramic processes for the production of dielectric phases for MLC. It is thought that. The slip can be formed on the film by spraying, layering from a waterfall or die (eg a doctor blade) into a moving sheet, and other methods used in the MLC industry. Removal of sufficient non-aqueous liquid from the film provides an attached solid "green" film, which is a conductive material or a precursor of a conductive material, such as palladium, silver, nickel, or an alloy of palladium and silver Can be coated with the indicated pattern on one or both sides. Such conductive inks can contain metal and ceramic particulates. The sheets of green film are typically laminated, e.g., 250 or more layers, which are cut into MLC sized cubes and fired to remove the polymer binder and dispersant. It is burned off and sintered to form a dense multilayer capacitor structure having a fine grain structured dielectric layer. A conductive metal applied to the ends can connect the conductive layers making up the MLC.

It is believed that the unique particle size characteristics of the barium titanate-based particles of the present invention allow for the production of new MLCs with very thin dielectric ceramic layers containing sub-micron sized particles. Such a dielectric material should promote a significant increase in volume capacitance. Furthermore, MLC is expected to have an unexpectedly high breakdown voltage. The absence of large, eg, greater than 1 μm, particles may be multiple, eg, 4
It will allow MLCs with more than zero dielectric layers to be commercially manufactured with high yields, for example, higher than 98%. The particles of the present invention preferably have a dielectric ceramic layer with a maximum particle size of 0.9 μm or less, more preferably a maximum particle size of less than 0.8, and most preferably a particle size of 0.7 μm or less. It is expected to be used in the manufacture of MLC. Another aspect of the invention provides an X7R or Y5V capacitor having more than 20 dielectric layers of barium titanate-based material sintered into a ceramic structure, wherein the thickness of these layers is 5 μm. Less than, for example, in the range of 2 to 4 μm. Relatively large,
For example, 250 or 500 dielectric layers may be preferred depending on the design of the MLC. The thin dielectric layer is a standard sized MLC or MLCs, which allows the MLC to use multiple dielectric layers and, for a fixed number of layers, in a relatively small package. Can be adapted. Therefore, the capacitance of a standard size MLC package can be easily increased by a factor of 5 to 10 or more.

To provide a monolithic X7R MLC, the particles used to make the dielectric are preferably coated with niobium, cobalt, nickel, and manganese oxides. For low sintering capacity, for example, sintering below 1200 ° C., preferred metal oxide coatings can also include bismuth oxide. To achieve a very thin dielectric layer with a thickness of less than 4 μm, the primary particle size of the particles is preferably less than 0.3 μm, most preferably in the range of 0.1 to 0.2 μm.
The uniform and fine particle size of a very thin dielectric multilayer, for example less than 0.3 μm,
It provides excellent dielectric strength and a low dissipation factor above 0 V / μm. These properties are
Increase the reliability of high capacitance high voltage ceramic capacitors.
The ability to provide a thin dielectric layer makes it possible to manufacture capacitors with 5 to 10 times the capacitance in standard sizes. Such an MLC is preferably a monolithic ceramic body of, for example, barium titanate doped with a metal oxide, two sets of interdigital electrodes embedded in the ceramic body and each extending to the opposite end of the ceramic body, and At the end there are two conductive terminations in contact with the two sets respectively. In the MLC having the X7R characteristic, the change in the temperature coefficient of the capacitance at a temperature of −55 ° C. to 125 ° C. is within ± 15% of the capacitance at 25 ° C. In a preferred aspect of the invention, the ceramic of X7R MLC has a particle size of less than 0.3 μm;
93-98 wt% barium titanate based ceramic, and 2-7 wt%
Other metal oxides.

The following examples do not limit the scope of the invention.

Example 1 To determine the dispersion efficiency of barium titanate-based particles in a non-aqueous solvent, the hydrothermally provided low calcined X7R particles after drying were mixed with 80 toluene / 20 with a phosphate ester dispersant. Dispersed in ethanol solution.

X7R hot water produced barium titanate wet cake, 72w
The one containing t% solids and 28 wt% water was dried at 200 ° C. in a vacuum rotary drying unit.

Twenty pounds (9071.8 g) of dry X7R hot water produced barium titanate particles were mixed with 6.7 pounds (3041.8 g) of a 80 toluene / 20 ethanol solvent mixture to form a slurry. The slurry was mixed in a DISPERSATOR ™ high shear mixer (Premier Mill) for 45 minutes,
During this time, 0.8 pounds (363.2 g) of RHODAFAC RS-410 ™ phosphate ester dispersant (Rhone-Poulenc) was added. The particle size distribution (sample 1) of the obtained slurry was measured, and the results are shown below and are shown in FIG. 1A.

[0060] The slurry was then subjected to a PREMIER ™ horizontal media mill (Premier M) for 30 minutes.
ill). The particle size distribution (sample 2) of the obtained slurry was measured, and the results are shown below and are shown in FIG. 1B.

The slurry was then added to the PREMIE for an additional 15 minutes (45 minutes total).
The mixture was mixed with a R (trademark) horizontal medium fine grinding device. The particle size distribution (sample 3) of the obtained slurry was measured, and the results are shown below and are shown in FIG. 1C. Final solids content is 78
%Met.

[Table 1]

The above experimental results show that dried hot water produced X7R powder can be dispersed in an 80 toluene / 20 ethanol solution mixture using a phosphate ester dispersant. This demonstrates the ability to make a slurry of particles with a ratio (D ₉₀ / D ₁₀ ) of less than 3 from the hydrothermally produced X7R powder in a non-aqueous solvent by selecting an appropriate dispersant. It is contemplated that other solvents with suitable dispersants (eg, as described above) can be used to make slurries of particles having a ratio (D ₉₀ / D ₁₀ ) of less than 3.

The results show that the barium titanate wet cake produced by the hot water of X7R can be dried and redispersed in a non-aqueous solvent to make a slurry of particles with a ratio (D ₉₀ / D ₁₀ ) less than 3. As shown, dry particles that have been relatively agglomerated into particles cannot be effectively deagglomerated by high shear mixing. Dispersions made from such dry, agglomerated barium titanate-based particles, where the primary particle size is submicron sized, require substantially long media milling to provide particles in the submicron range. I do. Also, the heating used to dry the wet cake, especially when the heating is performed at a high temperature and / or for a long time,
It is believed that barium titanate may have potential effects on the coating of the particles. Such potential negative effects include, for example, the bonding of the hydrated coating between the particles, which may cause separation of the coating layer from the particles based on some barium titanate without causing detachment or spalling of the coating layer. It can be difficult to do.

Example 2 To determine the dispersion efficiency of barium titanate-based particles in a non-aqueous solvent, a hydrothermally produced low calcined X7R particle was subjected to a solvent exchange process, followed by a phosphate ester dispersant. And dispersed. The hydrothermally produced low calcined X7R particles were initially in the water. Water was replaced with an 80 toluene / 20 ethanol solvent mixture.

X7R hot water produced barium titanate wet cake, 72 watts
One kilogram, containing t% solids and 28 wt% water, was slurried with 1 kg ethanol. The slurry was placed in a Buchner funnel with an ultrafiltration membrane. This ultrafiltration membrane was subsequently used as filter media. The ethanol was filtered through the resulting wet cake and the cracks formed were removed mechanically. When the initial filtration was almost complete, 1 kg of ethanol was poured and filtered through the wet cake. This step was repeated when the second filtration was almost complete.

After the ethanol filtration was completed, 1 kg of toluene was added, and the mixture was filtered through a wet cake. The wet cake is then dried to reduce the solids fraction to 75 wt%.
I made it.

The resulting wet cake (859.3 g) was weighed in a DISPERSATOR ™ high shear mixer (Premier Mill) with 26.81 g of RHODAF.
AC RS-410 ™ phosphate ester dispersant (Phone-Pou)
line). The high shear mixer mixed the wet cake for 10 minutes (Sample 4) and 30 minutes (Sample 5). The particle size distribution was measured and the results are shown below and are shown in FIGS. 2A and 2B.

[Table 2]

The experimental results described above show that the solvent exchange can be used to replace the aqueous solvent with a non-aqueous solvent, and then, if desired, with the addition of a suitable dispersant and the appropriate ratio (D ₉₀ / D ₁₀ ) Can be achieved. The solvent exchange process is significantly less (without horizontal media milling) by only a relatively short period of high shear mixing compared to dispersions obtained from dry powders (as shown in Example 1, Sample 1). Provide a dispersion having a small particle size distribution. Furthermore, in non-aqueous media (due to solvent exchange) with the appropriate dispersant selected, a ratio of less than 3 (D ₉₀ / D ₁₀ ) due to the hot water-provided X7R powder results in a horizontal media milling. It is believed that this can be achieved with a small amount of subsequent processing in the equipment (depending on other factors such as batch size). Using other solvent with a suitable dispersing agent, it is believed to be able to make a slurry of the appropriate ratio (D ₉₀ / D _10).

[0069] In addition to the above, the solvent exchange process avoids the potential undesired effect of drying the wet cake on the coating layer on the barium titanate-based particles. This is especially true for high temperatures and / or prolonged drying.

Example 3 To determine the effect of using a silane coupling agent to promote the dispersion of barium titanate-based particles in a non-aqueous medium, a hydrothermally brought X7R powder was used to couple the coupling agent With methyltrimethoxysilane as the coating.

Methyltrimethoxysilane provided a hydrophobic coating and was placed as follows on the surface of BaTiO ₃ particles exposed to X7R hot water: 95 ml of ethanol was mixed with 5 ml of deionized water. The pH of the solution is 0
. Adjusted to 4 using 1M HNO ₃ . Methyltrimethoxysilane (5g)
Was added to the acidified ethanol / water solution and stirred for 5 minutes to effect hydrolysis of the three methoxy groups of interest. 2. 250 ml of X7R BaTiO ₃ wet cake (solids 70 wt%)
And emulsified at 7000 rpm for 1 minute. 3. Ethanol / water solution containing the hydrolyzed silane coupling agent,
In addition to the slurry containing the hydrolyzed particles of X7R,
Emulsified at 00 rpm. 4. The resulting slurry was air dried for 24 hours to remove excess carrier. The resulting material was then placed in a vacuum oven at 80 ° C. for 12 hours to completely dry the powder.

Dilution of the X7R wet cake with ethanol resulted in a very viscous suspension by emulsification. The resulting dried powder was tested using the water sink / float test to determine if the hydrophobic surface was well adhered to the powder surface. The powder was gently ground with a mortar and pestle, then sprinkled over water in a beaker. The particles initially floated on the surface of the water, but with stirring some particles went into solution. Therefore, when the X7R wet cake was first diluted with ethanol, only a partial coating of the surface was achieved. It is believed that this partial coating approximates the high viscosity of the X7R wet cake when first diluted with ethanol. High viscosity results in a coating of aggregates,
This agglomerate tends to be broken by mixing in the sink / float test.

Example 4 To determine the effect of using a silane coupling agent to promote the dispersion of barium titanate-based particles in a non-aqueous medium, a hydrothermally derived X7R powder was used to couple the coupling agent With methyltrimethoxysilane as the coating.

Methyltrimethoxysilane provided a hydrophobic coating, and the coating was applied to BaTiO ₃ particles brought with hot water of X7R as follows: 95 ml of methanol was mixed with 5 ml of deionized water. The pH of the solution is 0
. Adjusted to 4 using 1M HNO ₃ . Methyltrimethoxysilane (5g)
Was added to the acidified methanol / water solution and stirred for 5 minutes to effect hydrolysis of the three methoxy groups of interest. 2. 250 ml of X7R BaTiO ₃ wet cake (solids 70 wt%)
Of methanol and emulsified at 7000 rpm for 1 minute. 3. Methanol / water solution containing the hydrolyzed silane coupling agent,
In addition to the slurry containing the particles of X7R hot water,
Emulsified at 0 rpm. 4. The resulting slurry was air dried for 24 hours to remove excess carrier. The resulting material was then placed in a vacuum oven at 80 ° C. for 12 hours to completely dry the powder.

The resulting dried powder was tested using a sink / float test in water to determine if the hydrophobic surface was successfully adhered to the powder surface. The powder was gently ground with a mortar and pestle, then sprinkled over water in a beaker. The particles floated on the water surface and remained on the surface even with stirring. Therefore, complete dilution of the surface was achieved when the X7R wet cake was first diluted with methanol.
Dilution of the X7R wet cake with methanol results in a low viscosity, well dispersed slurry. Upon addition of the hydrolyzed silane coupling agent solution, this achieves complete coating of the particles.

Those skilled in the art will readily recognize that all parameters listed here are exemplary and that the actual parameters will depend on the particular application for which the method and apparatus of the present invention is used. It is therefore to be understood that the above-described embodiments are merely exemplary, and that other embodiments than the specific ones described above can be practiced within the scope of the following claims and equivalents thereof.

[Brief description of the drawings]

FIG. 1A is a particle size distribution graph of one embodiment of the barium titanate particles of the present invention after high shear mixing for 45 minutes.

FIG. 1B is a particle size distribution graph of one embodiment of the barium titanate particles of the present invention after 30 minutes of further mixing in a horizontal media mill.

FIG. 1C is a particle size distribution graph of one embodiment of the barium titanate particles of the present invention after 45 minutes of further mixing in a horizontal media mill.

FIG. 2A is a particle size distribution graph of another embodiment of the barium titanate particles of the present invention after high shear mixing for 10 minutes.

FIG. 2B is a particle size distribution graph of another embodiment of the barium titanate particles of the present invention after high shear mixing for 30 minutes.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY , CA, CH, CN, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE , KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventor Clancy, Donald Jay. United States, Pennsylvania 19464, Pottstown, Vail Circle 1296 F-term (reference) 4G030 AA02 AA07 AA08 AA09 AA10 AA11 AA13 AA16 AA17 AA18 AA19 AA20 AA21 AA24 AA25 AA28 AA29 AA37 AA39 AA43 BA09 GA01 GA03 GA03

Claims (38)

[Claims] 1. A slurry, dispersion or slip containing particles based on barium titanate dispersed in a non-aqueous medium, said particles comprising a metal oxide of a metal other than barium or titanium, a metal hydrated oxide. Having a coating comprising a metal hydroxide, or an organic acid salt, wherein when the particles are dispersed by high shear mixing,
A slurry, dispersion, or slip containing particles based on barium titanate dispersed in a non-aqueous medium, wherein at least 90% of the particles have a particle size of less than 0.9 μm. 2. The particle size distribution decile ratio D ₉₀ / D ₁₀ of the particles is less than 4.
A slurry, dispersion, or slip according to claim 1. 3. The particle size distribution decile ratio D ₉₀ / D ₁₀ of the particles is less than 3.
A slurry, dispersion, or slip according to claim 1. 4. The slurry, dispersion or slip according to claim 1, wherein the particle has a particle size distribution decile ratio D ₉₀ / D ₁₀ of less than 2.5. 5. The slurry, dispersion or slip of claim 1, wherein at least 90% of the particles have a particle size of less than 0.8 μm when the particles are dispersed by high shear mixing. 6. A slurry, dispersion or slip according to claim 1, wherein at least 90% of the particles have a particle size of less than 0.7 μm when the particles are dispersed by high shear mixing. 7. The slurry, dispersion or slip of claim 1, wherein at least 90% of the particles have a particle size of less than 0.6 μm when the particles are dispersed by high shear mixing. 8. The slurry, dispersion, or slip of claim 1, wherein at least 90% of the particles have a particle size of less than 0.5 μm when the particles are dispersed by high shear mixing. 9. The slurry, dispersion, or slip of claim 1, wherein at least 90% of the particles have a particle size of less than 0.4 μm when the particles are dispersed by high shear mixing. 10. The slurry, dispersion or slip of claim 1, wherein at least 90% of the particles have a particle size of less than 0.3 μm when the particles are dispersed by high shear mixing. 11. The slurry, dispersion or slip according to claim 1, comprising at least 50% by weight of said particles. 12. The slurry, dispersion or slip according to claim 1, comprising at least 60% by weight of said particles. 13. The slurry, dispersion or slip according to claim 1, comprising at least 75% by weight of said particles. 14. The slurry, dispersion or slip according to claim 1, further comprising a dispersant. 15. The slurry, dispersion, or slip according to claim 1, wherein the particles have a coupling agent coating on a surface thereof. 16. The method of claim 15, wherein said coupling agent comprises an organosilane.
A slurry, dispersion, or slip according to 1. 17. The slurry, dispersion, according to claim 1, further comprising 3 to 20% by weight of a binder composition comprising a dissolved or suspended film-forming polymer.
Or slip. 18. The method of claim 1, wherein substantially all of the particles are equiaxed or spherical.
A slurry, dispersion, or slip according to 1. 19. The slurry, dispersion, or slip according to claim 1, wherein the particles are hydrothermally produced. 20. The slurry, dispersion, or slip of claim 1, wherein the coating covers a majority of the surface of the particles. 21. The coating according to claim 19, wherein the coating comprises bismuth, lithium, magnesium, calcium, strontium, scandium, zirconium, hafnium, vanadium, niobium, tantalum, tungsten, manganese, cobalt, nickel,
2. The composition according to claim 1, comprising at least one metal selected from the group consisting of zinc, boron, silicon, antimony, tin, yttrium, lanthanum, lead and lanthanide.
A slurry, dispersion, or slip according to 1. 22. The slurry, dispersion, or slip of claim 1, wherein said non-aqueous medium comprises an organic solvent. 23. The slurry, dispersion, or slip of claim 22, wherein said non-aqueous medium comprises a mixture of an organic solvent and water. 24. The organic solvent is benzene, methyl ethyl ketone, acetone, xylene, methanol, ethanol, propanol, 1,1,1-trichloroethane, tetrachloroethylene, amyl acetate, 2,2,4-triethylpentanediol-1,3. -Monoisobutyrate, toluene, methylene chloride, turpentine, ethyl alcohol, bromochloromethane, butanol, diacetone, methyl isobutyl ketone, cyclohexanone, methyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, n-octyl alcohol , Benzyl alcohol, glycerol, ethylene glycol, benzaldehyde, propionic acid, n-octanoic acid, ethyl acetate, butyl butyrate, n-hexane, and 3. The composition of claim 2, wherein the composition is selected from the group consisting of mixtures thereof.
3. The slurry, dispersion, or slip according to 2. 25. The slurry, dispersion, or slip according to claim 24, wherein the organic solvent is ethanol. 26. The slurry, dispersion, or slip of claim 1, wherein the non-aqueous medium comprises a mixture of more than one organic solvent. 27. The mixture comprises 72% trichloroethylene / 28% ethyl alcohol, 66% methyl ethyl ketone / 34% ethyl alcohol, 70% methyl ethyl ketone / 30% ethyl alcohol, 59% methyl ethyl ketone / 41
% Ethyl alcohol, 50% methyl ethyl ketone / 50% ethyl alcohol, 8
0% toluene / 20% ethanol, 80% toluene / 20% ethyl alcohol,
The method according to claim 1, wherein the solvent is selected from the group consisting of 70% toluene / 30% ethyl alcohol, 60% toluene / 40% ethyl alcohol, 70% isopropyl alcohol / 30% methyl ethyl ketone, 40% methyl ethyl ketone / 60% ethyl alcohol, and mixtures thereof. 28. The slurry, dispersion, or slip according to 26. 28. The slurry, dispersion or slip of claim 27, wherein said non-aqueous medium is 80% toluene / 20% ethanol. 29. A slurry of particles based on barium titanate in an aqueous medium by a hydrothermal process to remove a metal oxide, metal hydrate, metal hydroxide, or organic acid salt of a metal other than barium or titanium. Making a coating of the particles comprising: displacing the aqueous medium with a non-aqueous medium; and dispersing the particles in the non-aqueous medium by high shear mixing. Method. 30. The method of claim 29, wherein the particles are dispersed in the non-aqueous medium by high shear mixing until 90% of the particles have a particle size of less than 0.9 μm. 31. The method of claim 29, wherein replacing the aqueous medium with a non-aqueous medium comprises a solvent exchange process. 32. The method of claim 31, wherein the solvent exchange process comprises: filtering a slurry of barium titanate-based particles in the aqueous medium, and introducing the filtered particles into a non-aqueous medium. The described method. 33. The method of claim 29, wherein replacing the aqueous medium with a non-aqueous medium comprises a distillation process. 34. The method of claim 33, wherein said distillation process comprises: adding said non-aqueous medium to a slurry of particles based on barium titanate in said aqueous medium and evaporating said aqueous medium. . 35. The method of claim 29, further comprising providing a coupling agent to the surface of the particles after replacing the aqueous medium with a non-aqueous medium. 36. The method of claim 29, further comprising applying a coupling agent to the surface of the particles after forming a coating on the particles and before replacing the aqueous medium with a non-aqueous medium. The described method. 37. The coupling agent according to claim 35, wherein the coupling agent comprises an organosilane.
Or the method of 36. 38. Dispersing particles based on barium titanate in a non-aqueous medium by high shear mixing until 90% of the particles have a particle size of less than 0.9 μm, wherein said particles are barium or Metal oxides of metals other than titanium,
A method for producing a slurry, dispersion, or slip having a coating comprising a metal hydrate, a metal hydroxide, or an organic acid salt.