DE2305341C2 - Ceramic slip concentrate for the production of ceramic capacitors - Google Patents

Description

the mixture to a grinding fineness of 0 to 20, am, measured with a grinding fineness knife, has been ground, characterized in that it is used as a dielectric material Titanate and, as dispersants, polyethylene glycols, lecithin, polyoxyethylene isooctylphenyl ether or Polyoxyäthy'en-Nonylphenyläther contains and a Brookfield Y / viscosity from 6,000 to 15,000 mPas (measured in a Brookfield Viscometer, Model LV, with a No. 4 spindle at 30 rpm) having.

2. slip concentrate according to claim 1, characterized in that it also contains 0.2 to 5 wt .-% Polystyrene, hydrogenated rosin, polymethacrylates, especially polymethyl, or polyethylene Polybutyl methacrylates, their mixtures or copolymers as organic binders and others Contains amounts of the non-aqueous vehicle and as a dilute concentrate having a Brookfield viscosity from 300 to 1500 mP s v. ,lies.

3. Schlickerkonzeiurat according to one of the claims 1 or 2. marked thereby · <net. that it is a mixture of 70% xylene as the non-aqueous carrier and contains 30% amyl acetate.

4. slip concentrate according to any one of claims 1 to 3, characterized in that it is as Contains dispersant lecithin and butyl methacrylate as a binder.

The invention relates to the ceramic slip concentrate for the manufacture of ceramic capacitors.

DE-AS 12 80 515 already has a casting slip known for the production of structures made of difficult-to-melt metals, in which the metal is finely divided Form of about 1 μm and less in larger proportions with an organic carrier such as o-xylene, a suspending aid, d. H. Ethyl cellulose, and optionally a wetting agent and a deflocculating agent is mixed. This well-known casting slip was suitable However, even the composition did not lend for the production of dielectrics in electrical Capacitors.

DE-AS 12 83 728 discloses a casting slip for casting objects from refractory materials known that from a suspension it is finely divided Nitrides, CÜarbids, Silicids and / or bonds of titanium or other metals in a liquid dispersant, e.g. xylene, which is a polymer of cyclopentadiene in contains dissolved form. This known casting slip was also unsuitable for the production of

Dielectrics in electrical capacitors.

The ceramic capacitors made from previous slip concentrates had the disadvantage that they had an uneven grain size and many air holes. These properties led to a low dielectric constant, large differences in dielectric constant within one ceramic capacitor and faster destruction in the endurance test Another disadvantage of the known Slurry concentrates consisted of their comparative high viscosity. For example, if a doctor blade was used to remove an upper part of a known ceramic slip to apply to a base, this technique led to the high Viscosity results in a rather slow process, with uneven topcoats obtained became. Prior art coatings applied by sputtering were also very porous and irregular. In the manufacture of the known ceramic slip concentrates, there was always a pretty good arbitrary technique applied, paying little attention to the final particle size, ratio the components and the viscosity of the slip were used.

The invention is based on the object of a new ceramic slip concentrate for production to provide ceramic capacitors, in particular for the production of capacitors according to The curtain coating process is suitable and dense, regular ceramic layers for capacitors which are free of air holes and have improved dielectric properties.

This object is achieved according to the invention with a ceramic .Schlickerkonzentrat, consisting essentially from a mixture of

70 to 95% by weight of a powdered inorganic dielectric material;

b) 10 to 30% by weight of xylene. Amyl acetate or mixtures thereof as a nonaqueous carrier: and

c) 0.2 to 3% by weight of a dispersant.

wherein the mixture on a fineness of 0 to 20 μπι. measured with a fineness knife.

^{4: 1 has been} ground. solved in that it contains a titanate as the dielectric material and polyethylene glycols, lecithin, polyoxyethylene isooctylphenyl ether or polyoxyethylene nonylphenyl ether as the dispersant and a Brookfield viscosity of 100 to 15,000 mPa s (measured in a Brookfield viscometer. Model LV, with a spindle No. 4 at 30 rpm).

In the slip concentrate according to the invention, the inorganic dielectric material in In the form of a titanate, barium titanate is preferred. d. H. Barium titanate and known modified barium titanates. used. Xylene is used as a non-aqueous carrier. Amyl acetate or mixtures thereof used a the preferred carrier consists of a mixture of 0 to 10 parts of xylene and 0 to 10 parts of amyl acetate.

As dispersing or deflocculating agents in the slip concentrate according to the invention, polyethy lenglycols, lecithin (e.g., soybean lecithin), polyoxy ^ ethylene isooclyl phenyl ether or polyoxyethylene <nonyl phenyl ether used. These materials cause a uniform distribution of the ceramic material in the non-aqueous carrier, with virtually no agglomerates or particle clusters forming.

The ceramic slip concentrate according to the invention can be prepared by mixing the powdered inorganic dielectric material, the non-aqueous Carrier and the de-flocculating amount of the dispersant mixed together, the viscosity of the concentrate adjusts so that it is after completion of the Grinding a viscosity of 6,000 to 15,000 m Pas, determined with a Brookfield viscometer, model LV, with a spindle no. 4 at 30 rpm, and the concentrate to a grinding fineness between 0 to 20 μηι, ίο measured with a fineness knife, grinds. The reading on this meter varies between 0 and 20 μΐη depending on the nature of the pulverized Material

To manufacture ceramic capacitors, the slip concentrate can first be mixed with an organic Binder (which is not absolutely necessary) are added, whereupon the concentrate with further non-aqueous carrier is diluted to a mixture with a viscosity of 300 to 1500 m Pa s, determined on a Brookfield Viscometer, Model LV, with a # 2 spindle.

The binder can be any known binder. /. B. Polystyrene, hydrogenated rosin. Polymethacrylates, such as polymethyl, polyethylene or polybutyl methacrylates. Mixtures thereof or copolymers thereof, alone or as a mixture, can be used. For the Most of the mixtures, the binder is in an amount of 0 "? to 5.0 parts by weight, based on the Solids, used.

Then a flat surface is covered by a falling veil or curtain of the mixture passed through, the base receiving a thin even coating of the mixture. Afterward the coated substrate is either (a)} 5 once or several times again through the falling Veil escort. to the desired strength / ti and then to evaporate the solvent dried (after each pass or after several passes), by cutting or block cut into individual pieces and burned to / around the ceramic mass, or (b) the The coating is dried, and electrode and ceramic layers are alternately applied and the body obtained is divided into individual capacitors divided.

When the slip concentrate according to the invention is used to manufacture multilayer capacitors, the flat base must be a porous base. On the other hand, the substrate need not be V) porous if the subsequent coatings are applied to undried or only partially dried previously applied layers. The reason a porous pad is required to form a multilayer capacitor is because it is necessary. each ceramic layer / u dry so that several electrodes with the help of a die, a grid or other devices for embossing «the deposits of the electrodes on the ceramic surface; can be applied.

When dry, the unfired one exists ceramic layer of 50 to 75% by volume of the ceramic material, 0 to 25% by volume of the resinous material Binder and the remainder air in the form of homogeneously distributed micropores. A subsequent damp Support layer that is applied to the surface of this porous Layer is straightened, seals the surface of the dried layer. If solvent seeps out from the top layer, the solvent replaces with tel the air out of the micropores of the dried layer. The air in the micropores must be free Have way to hike down. If it encounters a barrier that is preventing this free movement, d. H. on a non-porous surface, the air is trapped at this barrier and flows in larger holes or gaps together. If this at the time where the whole structure about it a liquid with Low viscosity is large enough, some air rises to the surface, or part of the way up, to the Surface. When it reaches the surface, a superficially visible hole is created, which extends downwards either to the point where the original air hole was formed or to one Point between the original air hole and the surface. As the dried layers are considerable Contain quantities of free air, the important thing is that the air replaced by solvents allows the possibility must have to migrate down into a porous pad. The strength of this porous base must be sufficient to include the amount of air replaced Record normal pressure. It can be seen that this porous base made of paper of various types, woven or non-woven cloth or a thick base made of the unfired ceramic used Mass can exist.

If subsequent layers on undried or partially dried previously applied layers there is no need for a porous base. In this way many can Layers are applied. This is similar to the case in the manufacture of dielectric compacts Discs and plates, as they are usually produced by dry pressing. Any technique (with porous or non-porous base) can be applied to simple ceramic compact bodies to manufacture. However, if electrodes in capacitor design by sputtering using a die or Masking or screen printing is applied, a dry, comparatively solid Preferred structure that requires a porous support.

If the pad is kept at a temperature that is 10 to 50 C below the boiling point of the Tragers lies, can in this way from the slip concentrate according to the invention in a given Time a far greater number of ceramic Coatings are obtained as from a previous slip with scraper blades or dusting. About that In addition, the burnt ceramic coatings, which are obtained in this way from the slip according to the invention, such a uniform grain size o'-fit grain agglomerates. as it was with previous ones Slipperiness was never achieved. At the realization ceramic capacitors from the erfindiingsgemd Ben .Schlickerkonzentrat no air holes or superficially visible holes.

If Schlickerkonzentrat the invention / ur preparation is used multi-layer capacitors, is carried out preferably such that the combination after the first ceramic layer is applied and coated, the solvent is removed by drying and the first Elektrodenübe ^r train and dried, is maintained at a temperature which is high enough to solvent the next ceramic

Drive off layer fast enough that the solvent does not destroy the integrity of the electrode coating. If the temperature is not high enough, the solvent will destroy or disrupt the electrode coating, resulting in discontinuous electrodes in the final product. This temperature range must be adhered to for each subsequent build-up of ceramic layer and electrode. A temperature range between 50 ^° C. below and just below the boiling point of the solvent is suitable for the preferred solvent system. For ceramic layers with a thickness (in the fired state) of 25.4 μm, a temperature range of 55 to 65 ° C. is sufficient, while a temperature range of 60 to 80 ° C. is suitable for layers of 50.8 μm.

The invention is explained in more detail with reference to the drawings.

Figs. I and 2 of the drawing show a section through part of the capacitor, which consists of a known ceramic slip was formed which was not ground to a fineness of 0 to 20 µm became.

3 and 4 of the drawing show a section through part of a capacitor, such as that for example is prepared according to the procedure of Example 3 below. The ceramic layers are completely free of air holes or surface holes and the ceramic grains are in optimal Way packed. The electrodes are thin, continuous, and regular. As electrode materials are prefers silver. Platinum group metals and their alloys are used.

Fig. 1 of the drawing shows an unfired ceramic capacitor 10 according to the previous Method was produced and layers of agglomerates of ceramic grains 11 comprises. Of the Ceramic slip was not ground to a fineness of 0 to 20 μm, as in the present case Invention is required. Located within the agglomerate and between many grains of the agglomerate micropores 12 with air. There are larger air holes 13 between the agglomerates. Between the layers The unfired electrode particles 14 are located in the agglomerates.

FIG. 2 shows the same item as FIG. 1. after it has been burned to the point of fire. The electrode particles under-condense during sintering Formation of extremely irregular but continuous electrodes 15. During sintering, the Micropores of individual ceramic agglomerates are even smaller and are not shown here. The bigger ones Air holes 13 between the agglomerates still remain, albeit with a somewhat reduced size. Indeed, at 16 there is shown a point between two electrodes, which previously was one with electrode material filled hole and remained as a short circuit between the electrodes after sintering.

Fig. 3 shows an unfired capacitor 17 from a slip concentrate according to the invention which has been ground to a fineness of 0 to 20 μm was. The unfired ceramic layers consist of well-packed particles 18, homogeneously distributed there are micropores 19 with air between the particles. The electrode particles 20 form thin, regular ones Layers between the unfired ceramic

1 C ^- -I-; L * T_ J. * _ «.« -. C · - .I. «..— UaH - * ^ .. _i_ 1_

3CiIdI ot ~ tiii ~ iltdl- ItI UCt gcoaiiti & ii on untui Ltt ~ tiiiucii aiujt no large air holes.

F i g. 4 shows the subject matter of FIG. 3 after he has been burned until it is completely burned. The electrode strips condense during sintering with the formation of thin, continuous, regular electrodes 21. During the sintering, the micropores in the ceramic dielectric layer practically and disappear cannot be seen here. The ceramic layers are dense, regular and free from air holes.

Fig. 5 shows a flow diagram for manufacture of the slip concentration according to the invention and

ίο its use for the production of ceramic Capacitors. In stage A, the slip concentrate is reduced to a grinding fineness of 0 to 20μπι ground. In stage B a binder is added and the mixture is diluted to a viscosity of 300 to 150OmPa s. In In step Ci a porous substrate is curtained with the slip to form a capacitor. In Stage Cj, a porous or non-porous substrate is passed through a falling veil of slurry, to form a dielectric compact. In stage D the organic material becomes thermal removed.

Evaporation of the non-aqueous vehicle from the various layers is facilitated by the fact that a heated pad, e.g. B. a glass pad with a thickness of 3.18 mm, which is heated to 110 ° C. used. This mode of operation enables a very fast circulation and a more rapid construction of the Layers. The capacitor assembly can be cut either partially or completely through with a cutting edge torn through the unfired body. The body can either be before or after Burning apart along the scribing lines.

The following examples illustrate the invention.

example 1

A mixture of 89% by weight of a commercially available BaTiO (with an average grain size of 1.8 μm. determined with the under sieve tester according to Fisher). 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 ground in a ball mill to a fineness of 7.5 μm. After adding a binding amount Butyl methacrylate was mixed with additional amounts of the 7: 3 mixture of xylene and amyl acetal diluted to a viscosity of 600 mPa s

The mixture was pumped in one continuous cycle into a sprue, from there as a

5ό continuous, uniform, falling veil shed and pumped back into the casting spigot. A flat pad was several times through the curtain passed through to form a top coat of about 50.8 to 1270 μm thickness. The upper pull was then

-v> dried and burned until it is burnedL

The cooked ceramic piece is completely free of air holes. The complete lack of holes leads to a more stable design when the ceramic body is in electrical components and

w> micro lines is used. The missing of Air holes and the effectively packed ceramic grains mean greater dielectric density.

Example 2
* · - ■ 89% by weight of a chemically pure BaTiOj with a

VnmrrrÄRo im u / £ * contllation linfAr f um nntr / lpn mit

about 9.5% by weight 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 BaTiOj is below

I μΐϋ lies, the particles agglomerate easily Agglomerates with a size of 50 to 500 μm. These Agglomerates must be broken up and the particles effectively dispersed throughout the liquid medium will. This is achieved after premixing by placing the mixture in a ball mill rhahi ;. to a fineness of less than 2 μm is reached. After adding a binding amount of a commercially available hydrogenated binder The ground concentrate was mixed with additional amounts of the 7: 3 mixture of xylene and rosin Amyl acetate diluted to a viscosity of about 600 mPa s.

The mixture was pumped in one continuous cycle into a sprue, poured therefrom as a continuous, uniform, falling veil, and pumped back into the sprue. A flat pad with a porous decking paper was passed 2S through the curtain to coat the uniform mixture. The substrate was passed through the curtain several times, each new layer being dried in order to form a coating with a thickness of about 50.8 to 1270 μm. The coating was then removed from the paper and baked to the bake. The cooked ceramic piece of this example was very dense and completely free of air holes.

Example 3

The mixture of Example 2 was used to prepare several electrical block capacitors are used. A flat surface with a porous cover paper was passed through a continuous curtain of the mixture of Example 2. the The substrate was again passed through the curtain until a structure of 25.4 to 50.8 μm was reached. The assembly was then dried to remove the organic carrier. Multiple palladium electrodes were applied to the surface of the unfired ceramic layer by screen printing. These The procedure was repeated until the construction

II contained ceramic layers and 12 palladium samples in a capacitor arrangement. During the application of each subsequent layer of the ceramic structure at a temperature of about 55 was kept to 8O ⁰ C, to facilitate the removal of the solvent from each layer applied. The finished structure was divided into individual capacitor units. These units were then burned until they were burned. A silver electrode tap was attached to the exposed electrodes and leads were soldered to it. Electrical measurements showed a 5 to 25% increase in capacitance per unit volume over typical known capacitor units of the same pattern obtained by sputtering.

When trying to do the same procedure without using a porous pad, this gives capacitors with many cavities and holes.

According to another embodiment, the electrodes can be applied by curtain-coating the already deposited, preferably dry, ceramic layer, which is covered with a suitable cover panel or matrix, with a dispersion of a metal powder. Open areas in the die allow the liquid dispersion of the electrode metal to come into contact with the ceramic layer in these specific areas. According to Enlfer- »>*>» ** » ζίζν Cover BicriuC ^ ci ^ r ^ j ^ ii ·! '» »Ν ,,, ίΐ α *** · 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) binding agent (ethyl cellulose,

Polystyrene, etc.) 1-10

3) solvents (turpentine,
Pine oil, terpineoI, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, etc.

or mixed solvents) 40 - 90

Even if in the examples the base several times through the curtain of the mixture of ceramic Material and solvent was passed to build up a ceramic layer, so it is easy to see that this can also be achieved in a single pass if you keep the speed of the The passage of the substrate through the curtain and the flow rate of the curtain of the ceramic Adjust dispersion accordingly.

It goes without saying that the number and size of the individual layers are not limited, apart from of practical conditions. The thickness of the capacitor pieces that are cut out of the build is not limited either. Writes the physical size and capacity desired in each unit the dimensions of the layers and the thickness of the capacitor pieces.

1 sheet of drawings

Claims (1)

Patent claims: Ceramic slip concentrate for the production of ceramic capacitors, consisting of essentially from a mixture of a) 70 to 95% by weight of a powdered inorganic dielectric material; b) 10 to 30% by weight of xylene, amyl acetate or mixtures thereof as a non-aqueous carrier; and c) 0.2 to 3% by weight of a dispersant,