DE2305341A1 - Ceramic slip - for curtain coating comprising fine milled mixture of dielectric, vehicle and dispersant - Google Patents

Abstract

Slip produces a uniform product free from pinholes and suitable for electrical components, esp. by fast curtain-coating methods. It comprises (a) 70-95 wt.% powdered titanate, zirconate, niobate, alumina, porcelain or a ferrite, (b) 10-30 wt.% xylene and/or amyl acetate and (c) 0.2-3 wt.% oolyethylene glycol, lecithin, polyoxyethylene isooctylphenyl ether or polyoxyethylene nonylphenyl ether. The mixt. is milled to a fineness of 0-20 mu, and has a Brookfield viscosity of 6000-15000 cPs before addn. of a binder.

Description

Ceramic slip concentrate and its uses for manufacture of a ceramic body The invention relates to a new ceramic slip concentrate and a method of making ceramic coatings and ceramic capacitors by passing a flat surface through a falling veil of the new ceramic slip, whereby the base has a thin, even coating of the ceramic slip. The pad is either once or several times again passed through the falling veil to achieve the desired strength and then dried and baked to the doneness or the coating is dried and there are alternately electrode and in the type known for capacitors ceramic layers applied.

The previous ceramic covers and ceramic capacitors had the disadvantage that they had an uneven grain size and many air holes exhibited. These properties lead to a low dielectric constant, large differences in dielectric constant within a given ceramic Body and faster destruction in the endurance test. Another disadvantage of the known Procedure was that they were slow. So used for example one known method uses a doctor blade to apply a coating of ceramic slip to apply to a pad. This technology and the comparatively high viscosity of the slip resulted in a rather slow process flow, being uneven coatings have been obtained.

Known sputter applied coatings were also very good porous and irregular. In the known methods, it has always been a fairly arbitrary one Technique of the formation of the ceramic slip concentrate applied, with little Pay attention to the final particle size - the ratio of the components and the viscosity of the slip was used.

The invention relates to a new ceramic slip concentrate, that consists essentially of a mixture of a powdered inorganic dielectric Material, a non-aqueous carrier and a deflocculating amount of a dispersant consists, the mixture to a grinding fineness of 0-20 tlm, measured with a Grinds gauges that have been ground.

The invention also relates to an improved method of manufacture ceramic coatings and ceramic Capacitors, which consists in that by mixing or combining the powdered inorganic dielectric Material, the non-aqueous vehicle and the deflocculating amount of the dispersant produces the slip concentrate, adjusts the viscosity of the concentrate in such a way that that it has a viscosity of 1000 to 20,000, preferably after the end of the grinding 6000 to 15,000 cps as determined with a Brookfield Viscometer, Model LV, with a Spindle No. 4 at 0-30 rpm> has the concentrate to a fineness between 0 to 20 nm, measured with a fineness knife, grinds. Reading this Meter varies between 0 to 20 µm depending on the nature of the pulverized Materials. Then an organic binder (which is preferred, but is not absolutely necessary) and the concentrate with further non-aqueous Carrier diluted to a mixture with a viscosity of 300 to 1500 cps, determined with a Brookfield Viscometer Model LVt with a # 2 spindle. Then a flat surface is covered by a falling veil or curtain of the Mixture passed through, with the base a thin even coating of the mixture. Then the coated pad is either (1) once or passed through the falling veil several times again to the desired strength and then dried to evaporate the solvent (after each Pass or after several passes), by cutting or block cutting in divided individual pieces and fired until the ceramic mass is completely burned, or (2) the coating is dried and there are alternating electrode and ceramic Layers are applied and the body obtained is divided into individual capacitors.

When applied to the process of manufacturing multilayer capacitors the flat surface must be a porous surface. On the other hand, she must Underlay will not be porous if the subsequent coatings are on undried or only partially dried previously applied layers are applied. Of the Reason why a porous pad is used to form a multilayer capacitor is required is that it is necessary to cover every ceramic layer dry several electrodes with the help of a die, a grid or other Devices for imprinting (printing) or depositing the electrodes on the ceramic Surface can be applied.

The unfired ceramic layer exists in the dried state from 50 to 75% by volume of the ceramic material, 0 to 25% by volume of the resinous Binder and the remainder air in the form of homogeneously distributed micropores. A subsequent moist carrier layer applied to the surface of this porous layer closes the surface of the dried layer. When solvent out the top layer seeps out, the solvent replaces the air from the micropores the dried layer.

The air in the micropores must have a free way to go down to hike. If it encounters a barrier that is preventing this free movement, i.e. on a non-porous surface, the air is trapped at this barrier and flows together in larger holes or gaps.

If this at the time where the whole structure about a Low viscosity liquid is large enough, some air will rise the surface or part of the way to the surface. When they surface reached, a superficially visible hole is created that extends downwards, and either up to that Point where the original air hole was formed, or to a point between the original vent and the surface. Because the dried layers contain considerable amounts of free air it is important that the air replaced by solvent must be able to to migrate down into a porous pad. The strength of this porous base must be sufficient to absorb the amount of replaced air at normal pressure. It it can be seen that this porous base is made of paper of various types, woven or non-woven cloth, a thick base made of the unfired ceramic mass, which is used in the process, and the like. Can exist.

If subsequent layers on undried or partially dried There is no need for previously applied layers to be applied a porous pad. That way you can have many layers, actually one indefinite number. This is the case in the manufacture of dielectric Compact bodies (compacts) similar to disks and plates, as they are usually made by Dry pressing are manufactured.

Any technique (with a porous or non-porous base) can be used to produce simple ceramic compact bodies, but if electrodes in condenser design with the help of dusting through a die or cover panel or silk lattice are applied, a dry, comparatively solid one Preferred structure that requires a porous base when the base is used a temperature is maintained which is 10 to 500C below the boiling point of the support with this method, a far greater number can be found in a given time ceramic coatings obtained are considered in a proceeding with Doctor blade or dusting. In addition, the fired ceramic coatings, which are obtained by the process according to the invention, a uniform grain size and are so without grain agglomerates (grain clusters), as is the case with previous processes was never achieved. The method according to the invention completely avoids air holes and holes visible on the surface in the unfired ceramic compact.

When the process is used to manufacture multilayer capacitors It is preferred to work in such a way that this combination after the first ceramic Layer applied and the solvent removed by drying and the first Electrode coating is applied and dried, is kept at a temperature which is high enough to solvent the next ceramic layer quickly enough to drive off the solvent so that the integrity of the electrode coating not destroyed. If the temperature is not high enough, it will destroy or break the solvent removes the electrode coating, resulting in discontinuous electrodes in the End product leads. This temperature range must be used for any subsequent build-up of ceramic layer and electrode are respected for the preferred solvent system of the present invention is a temperature range between 500C below the Boiling point of the solvent and just below this boiling point suitable. For ceramic layers a thickness (fired thickness) of 25.4 µm is a temperature range 55 to 65 ° C is sufficient, while a temperature range of 50.8 μm is sufficient for layers from 60 to 800C is suitable.

The present invention is based on the object of a new ceramic Slurry concentrate and a method for producing a comparatively dense one provide ceramic body with the help of this slip concentrate. The procedure according to which ceramic capacitors in particular can also be manufactured are more economical and can be carried out more quickly than previous methods for the production of ceramic coatings by means of dusting or doctor blades, and the ceramic pieces produced should have dielectric properties, which could not be reached by previous methods and should not have any holes.

The invention is explained in more detail with reference to the drawings, FIG. 1 the drawing shows an unfired ceramic capacitor 10, according to previous Process was made and layers of agglomerates of ceramic grains 11 having. The ceramic slip was not reduced to a fineness of 0 to 20 to be ground, as required by the present invention. Within each agglomerate and between many grains of the agglomerate there are micropores 12 with air. Between the agglomerates there are larger air holes 13. Between the layers of the The unfired electrode particles 14 are agglomerates.

Fig. 2 shows the same item as Fig. 1 after it has been up to Garbrand was fired. The electrode particles under-condense during sintering Formation of extremely irregular but continuous electrodes 15.

During sintering, the micropores of individual ceramics become more ceramic Agglomerates are even smaller and are not shown here. The larger air holes 13 between the agglomerates still remain, albeit at a somewhat reduced rate Grffr3e.

In fact, at 16 a point is shown between two electrodes, which was previously a hole filled with electrode material and after sintering remained as a short circuit between the electrodes.

3 shows an unfired capacitor 17 according to the present invention Invention. The ceramic slip used had a grind fineness of 0 to 20 µm has been ground. The unfired ceramic layers consist of well-packed Particles 18. Micropores 19 are homogeneously distributed between the particles with air. The electrode particles 20 form thin, regular layers between them the unfired ceramic layers.

There are no large air holes in the entire structure.

FIG. II shows the object of FIG. 3> after it has been cooked has been burned. The electrode particles condense with formation during sintering thinner, continuous, regular electrodes 21. Disappear during sintering the micropores in the ceramic dielectric layer come in handy and are here not to see. The ceramic layers are dense, regular and free of air holes.

5 shows a flow diagram of the method according to the invention. Included the slip concentrate is ground to a fineness of 0 to 20 μm in stage A. In stage B a binder is added and a viscosity of 300 to 1500 cps diluted. In stage C a porous pad becomes through a falling veil of the slip to form a condenser. In step C2 becomes a porous or non-porous base through a falling veil of the Schlickers passed to form a dielectric compact. In stage D the organic material is removed thermally, the ceramic according to the invention Slurry concentrate preferably has the following composition and properties: It is a mixture consisting essentially of: a) 7-9.5 parts by weight of one inorganic dielectric material; b) 1-3 parts by weight of a non-aqueous Carrier; and c) a dispersing amount of a dispersant; being the mixture ground to a fineness of 0 to 20 µm, measured with a fineness knife has been.

The final ceramic slip is formed by making a binding amount of an organic binder to the concentrate and so much non-aqueous vehicle adds that a mixture having a viscosity of 300 to 1500 cps is formed. As the inorganic material, any known ceramic Material such as the titanates, zirconates> Nio! Ave, alumina, porcelain, ferrites and the like., can be used.

Preferred materials for capacitors are barium titanates, i. Barium titanate and known modified barium titanates.

Preferred materials for underlays designed for hybrid thick and thin-coated electrical conductors used are alumina and titanate tea As non-aqueous Carrier can be a variety of organic carriers, such as turpentine, xylene, amyl acetate, paint thinner, benzene, toluene, ester, ether, Alcohols, pine oil and the like, as well as mixtures thereof, can be used. A preferred one Trager consists of a mixture of 0 to 10 parts of xylene and 0 to 10 parts of amyl acetate, The dispersing or deflocculating agents employed herein '-c-nnen, are those materials that have a uniform distribution of the ceramic Effect material in the non-aqueous carrier, practically none Form agglomerates or collections of particles. To the intended dispersants include the polyethylene glycols, lecithin (e.g. soybean lecithin), polyoxyethylene isooctylphenyl ether, Polyoxyethylene nonylphenyl ether. For most mixtures, the dispersant should be can be used in an amount of from 02 to 3.0 parts by weight of the mixture.

Any known binder, for example polystyrene, hydrogenated Rosin, polymethacrylates, such as polymethyl, polyethylene or polybutyl methacrylates, Mixtures thereof or mixed polymers thereof, used alone or as a mixture will. For most mixtures, the binder will be used in an amount from 0.2 to 5.0 parts by weight, based on the solids, used.

Figures 1 and 2 of the drawing show a section through part of a Capacitor, which was formed from a ceramic slip that does not a fineness of 0 to 20 microns was milled, as according to the present invention is required. In addition, this condenser unit was made using previous deposition methods by dusting and not as in accordance with the invention?> by passing flux through obtained by a falling veil of the ceramic slip.

Figures 7 and 4 of the drawings show a section through part of a Capacitor, as it is, for example, according to the procedure of the following example 4 is produced. The ceramic layers are completely free of air holes or Surface holes and the ceramic grains are packed in an optimal way. the vlektroden are thin, continuous and regular. The electrode materials, preferred EPJ for the present invention are silver, platinum group metals, and their alloys.

Fig. 5 describes a flow dingram for the essential stages of the Process in which the ceramic slip is deposited. The slip concentrate must first be prepared in the composition according to the invention and then on the a certain fineness of grind can be ground. A binder is then added and dilute the concentrate to the specified viscosity range.

The slip then has the right properties for the use in a facility where it is applied as a falling veil. For education Dielectric compact body can pass through the obtained bad after every pass the falling veil or only dried once after several passes will. To form a capacitor, it is when covering devices with a ceramic layer should come into contact, required, before application to dry the ceramic layers of each electrode layer. The electrodes of the unfired units must be very porous and must not have any obstacles for the Provide passage of the replaced air.

The evaporation of the non-aqueous vehicle from the various Layering is facilitated by having a heated surface such as a glass surface 3.18 mm thick, heated to 11,000, is used. This way of working enables very rapid circulation and a more rapid build-up of the layers. The ceramic structure or the capacitor structure can be either with a cutting edge be partially or completely torn through the unfired body.

The body can either be before or after the burn along the. Scribing lines are broken apart.

The following examples illustrate the invention.

Example 1 A mixture of 89% by weight of a commercially available BaTiO3 (with an average grain size of 1.8 llms determined with the lower sieve tester according to Fisher (Fisher sub sieve sizer)), 9.5% by weight of a mixture of xylene and Amyl acetate in a weight ratio of 7: 3 and 1.5% by weight soybean lecithin was premixed and then in a ball mill to a fineness of grinding of 7.5 µm, determined with a fineness knife from Precision Gage and Tool Company, Dayton, Ohio, Catalog No. 625 1/2-MU, ground. This meter is from 0 to 12.5 tlm divided into finities of 0.5 µm each. After adding a binding amount Butyl methacrylate was added to the mixture with additional amounts of the 7: 3 mixture of xylene and amyl acetate diluted to a viscosity of 600 cps.

The mixture was poured into a sprue in one continuous cycle pumped, from there shed as a continuous, uniform, falling veil and in the Cast spigot pumped back. A flat surface was made passed several times through the falling veil to create a coating of about 50.8 to 1270 to form strength. The coating was then dried and dried until Burned Garbrand.

The cooked ceramic piece is completely free of air holes. The complete absence of holes results in a more stable design than the ceramic Body used in electrical components and micro lines. The missing of air holes and the effectively packed ceramic grains mean a larger one dielectric density.

Example 2 89% by weight of a chemically pure BaTiO. with a grain 3 size essentially below 1 tlm were with about 9.5 wt. »of a mixture of Xylene and amyl acetate in a weight ratio of 7: 3 and about 1.5% by weight of polyoxyethylene isooctylphenyl ether premixed. Even if the particle size of the BaTiO3 is below 1 µm, it will agglomerate the particles easily form agglomerates with a size of 50 to 500 µm. These Agglomerates must be broken and the particles effective throughout the liquid Medium to be dispersed. This is achieved after premixing by the mixture is ground in the ball mill to a fineness of less than 2 µm is achieved on the test device of Example 1. After adding a binding amount of a commercially available hydrogenated ko uophonium binder was the ground concentrate with additional amounts of the 7: 3 mixture of xylene and amyl acetate diluted to a viscosity of about 600 cps.

The mixture was poured into a sprue in one continuous cycle pumped, poured out of it as a continuous, uniform, falling veil and pumped back into the sprue. A flat surface with a porous cover paper was passed through the falling veil to form a coating of the uniform To obtain a mixture. The pad was several times through the falling veil passed through it, drying each new layer to form a coating with a thickness of about 50.8 to 1270 µm. The coating was then from the Paper removed and burned to the point of fire. The cooked ceramic piece this example was very tight and completely free of air holes.

Example 3 86% by weight alumina with a particle size of about 2 µm were premixed with 13% by weight of xylene and 1% by weight of lecithin as dispersants. This mixture was then ground in the ball mill to a grind fineness of less than 3 im was achieved on the tester of Example 1. After adding hydrogenated rosin as a binder in an amount of 5% by weight of the solids the ground concentrate was diluted with further amounts of xylene until a viscosity of about 1000 cps was reached.

This mixture was pumped into a sprue as in Example 2, shed from it as a continuous, uniform, falling veil and pumped back into the cast spigot. A flat surface with a porous cover paper was passed through the falling veil to form a coating of the uniform To obtain a mixture.

The pad was several times through the falling veil directed, each new layer being dried to form a coating with a thickness of 762 rim to form. The coating was removed from the paper and until it was burned burned. The burnt clay piece was extremely dense, firm and completely free of air holes.

Example L1 The mixture of Example 2 was used to make several electrical block capacitors are used. A flat surface with a porous Cover paper was covered by a continuous falling veil of the mixture of Example 2 passed through. For so long the underlay was again through the veil passed until a build-up of 25.4 to 50.8 µm was reached. The construction was then dried to remove the organic vehicle. Multiple palladium electrodes were applied by a Se-lennet2 to the surface of the unfired ceramic layer upset. This procedure was repeated until the structure 11 was ceramic Layers and 12 palladium patterns in a capacitor arrangement. During the Application of each subsequent ceramic layer was the construction at one temperature Maintained from about 55 to 80 ° C in order to remove the solvent from each applied Layer to make it easier. The finished structure was divided into individual capacitor units divided. These units were then burned until they were burned. On the exposed Electrodes were attached to an electrode tab made of silver, and leads were attached to them soldered on. Electrical measurements showed an increase in capacity per unit volume from 5 to 25% over typical known capacitor units of the same pattern, obtained by sputtering.

Trying to do the same thing without using a To carry out a porous substrate, capacitors with many cavities are obtained and holes.

According to another general guide, the electrodes can be applied be made by making a dispersion of a metal powder continuously as falling Let the veil run around and through this falling veil the already deposited, preferably dry, ceramic layer passes through, which is covered with a suitable Cover panel or die is covered. Enable open areas in the die contact of the liquid dispersion of the electrode metal with the ceramic Layer in these specific areas. After removing the cover or die the electrode coating must be dried before the next ceramic layer is applied.

Examples of metal powder electrode dispersions: parts by weight 1) Palladium (or platinum, silver, nickel, gold, etc.) 10 - 60 2) Binder (ethyl cellulose, Polystyrene etc.) 1 - 10 3) Solvents (turpentine, pine oil, terpineol, diethylene glycol monobutyl ether, Ethylene glycol monobutyl ether 40 - 90 acetate, etc. or solvent mixtures) if also in the examples the base several times through the falling veil of the mixture Ceramic material and solvent was passed to form a ceramic layer To build up, it is easy to see that this can also be done in a single pass can be achieved if you consider the speed of passage of the substrate through the veil and the flow velocity of the falling veil of the ceramic Adjust dispersion accordingly.

It goes without saying that the number and size of each Layers are not limited, apart from practical considerations. The strenght the capacitor piece that is cut from the structure is also not limited. Writes the physical size and capacity desired in each unit the dimensions of the layers and the thickness of the capacitor pieces.

Claims (15)

Claims 1. Ceramic slip concentrate, consisting essentially of a mixture of: a) 70 to 95% by weight of a powdered inorganic dielectric Materials; b) 10 to 30% by weight of a non-aqueous carrier; and c) a dispersing one Length of a dispersant; the mixture to a fineness of grind from 0 to 20 µm, measured on a fineness knife, has been ground. 2. slip concentrate according to claim 1, characterized in that it contains xylene, amyl acetate or mixtures thereof as a non-aqueous carrier. 3. slip concentrate according to claim. 2, characterized in that that the non-aqueous carrier is a mixture of 70% xylene and 30% amyl acetate contains. 4. - slip concentrate according to any one of claims 1 to 3, characterized characterized in that it is a titanate, a zirconate, as the dielectric material Contains niobate, alumina, porcelain or a ferrite. 5. slip concentrate according to any one of claims 1 to 4, characterized characterized in that it is used as a dispersant in an amount of 0.2 to 3 wt .-% Polyethylene glycols, lecithin, polyoxyethylene isooctylphenyl ether or Contains polyoxyethylene nonylphenyl ether. 6. slip concentrate according to any one of claims 1 to 5, characterized characterized as having a Brookfield viscosity of 6,000 to 15,000 cps, measured in a Brookfield Viscometer, Model LV, with a # 4 spindle at 30 rpm, having. 7. slip concentrate according to one of claims 1 to 6, characterized Indicates that there is an additional 0.2 to 5 wt .-% of an organic binder and contains additional amounts of the non-aqueous vehicle and a Brookfield viscosity from 300 to 1500 cps. 8. slip concentrate according to claim 7, characterized in that it as an organic binder polystyrene, hydrogenated rosin, polymethacrylate, in particular polymethyl, polyethylene or polyeutyl methacrylates, their mixtures or mixed polymers thereof. 9. slip concentrate according to any one of claims 1 to 8, characterized characterized in that it contains a titanate as dielectric material. 10. slip concentrate according to any one of claims 1 to 8, characterized characterized in that it contains alumina as the dielectric material. 11. slip concentrate according to one of claims 9 or 10, characterized characterized in that it contains lecithin as a dispersant and butyl methacrylate as a binder contains. 12. A method for producing a ceramic body by means of a - Ceramic slip concentrate according to claim 1, characterized in that a) a ceramic slip consisting essentially of the following components Manufactures: 1) 70 to 95% by weight of a powdered inorganic dielectric Materials; 2) 10 to 30% by weight of a non-aqueous carrier; and 3) a dispersing one Amount of a dispersant; b) the concentrate obtained to a fineness of grind grinds from 0 to 20 µm as measured on a fineness knife; c) the concentrate with further amounts of the non-aqueous carrier, which is a binding amount of an organic Contains binder, with the formation of a slip with a viscosity of 300 diluted to 1500 cps; d) a pad at least once through a falling one Passing a veil of the slurry therethrough to obtain a coating of the slurry; e) drying the coating; f) the coating removed from the substrate and until it is cooked burns. 13. The method according to claim 12, characterized in that the dried coating divided into smaller units either before or after firing. 14. The method according to claim 12, characterized in that as Pad used a porous pad and applied to the surface of the dried applying a plurality of metal electrodes to the ceramic coating; the working method repeats, alternating layers of ceramic coatings and electrode patterns in a capacitor arrangement build up; the finished structure is divided into individual capacitor units and these Units burn up to the point of fire. 15. The method according to claim 14, characterized in that according to each application of an electrode layer during the application of the next ceramic Layer keeps the dried coating and electrodes at a temperature that between about 500C below the boiling point of the non-aqueous vehicle and even is below this boiling point. L e r s e i t e