US2384541A

US2384541A - Condenser material and method of making same

Info

Publication number: US2384541A
Application number: US441870A
Authority: US
Inventors: Hal F Fruth
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1942-05-05
Filing date: 1942-05-05
Publication date: 1945-09-11
Anticipated expiration: 1962-09-11

Description

Sept. 11, 1945. F FRUTH I 2,384,541

CONDENSER MATERIAL AND METHODS OF MAKING SAME Fild May 5, 1942 FIG.

BY me/w y 'terial O.

Patented Sept. 11,1945

zsusu cormsusaa m'rsmsr. m ium-non or sans MAKING nunrr-mmmtmaanuhwm Beets-lo can N. Y., a corporation of New York New Isrh,

Application as 5, 1942, Serial No. um

Claims. (cl. 117-17) This invention relates to condensers and to a method of and apparatus for making the same,

and more particularly to condenser materials hav- Y ingorientedcrystallinestructureandtoamethod of and apparatus formakingthesame.

Condensers have been made by impr snating or by coating a dielectric material on a base such as D 9 the dielectric material being suspended ordissolvedinabindercontainingasolvent which evaporates after coating or impresnating is com- An'obiect of the present invention is to provide an improved condenser material having a high dielectric constantand a method of and apparatus for making the same.

In accordance with one embodiment of this invention, titanium dioxide crystals suspended in a liquid binder are coated on a strip of paper, and the coated paper is passed through an electrostatic field causing the crystals to orient their major axes perpendicular-to the paper base. The coated paper is then calendered to increase its density.

In accordance with another embodiment of the invention, a quantity oi titanium dioxide crystals suspended in a liquid binder are poured on a tray of volatile material and an electrostatic field ap-' plied to orient the crystals along their major axes and parallel to each other. As the binder solvent evaporates, the binder hardens and the oriented ate, strontium lirconate andvarlous mixtures of two or more of these compounds. The dielectric 7 material is suspended in a liquid binder such as cellulose acetate using acetone as a solvent, or an aqueous solution of sodium silicate. Polyvinyl aloohol may also be employed and since it is itself polar and desirable dielectric characteristics, its use results in even greater dielectric constant. It will be apparent that if aluminum foil is usedasasupportacoatingonlyisobtained, whereas with porous material, such as certain types of paper, impregnation may also take place, However, with the types of paper commonly used in condensers as base material, impregnation by the dielectric material is negligible.

Titanium dioxide crystals have a dielectric consant of 89-para1lel to their smaller axis and 173 parallel to their major axes and about 115 for random orientation and will orient themselves in the presence of an electrostatic iield so that their major axes are substantially parallel. By orienting the random crystals of a dielectric material comprising one or more of these above-mentioned compounds, a condenser material having increased dielectric constant as compared to a condenser material in which the crystals are random oriented, may be obtained. At the same time,

- since the crystals are aligned along the line of crystals becmne permanently fixed in their oriented position. The tray and contents may then be placed in an oven to volatilize and remove the tray and also to fire the titanium dioxide to produce a ceramic body, the crystals of which will have their major axes substantially parallel.

Other obiects and advantages will be apparent from the following detailed description taken in conjunction with the following drawing, wherein-z Fig. 1 shows schematically an apparatus for 440 coa g st ip material with a dielectric;

Pig. 2 shows schematically an apparatus for making sheets of dielectric material; and

Fig. 3 shows an enlarged fragmentary perspective view of an electrostatic plate such as may be usedwiththeapparatusshowninl 'ig. i.

As may beseen in Fig. 1, a base material 5 suchasapaperstriporaluminmn foilisdrawn,

jv fromasupply reel I overasmall roller 1 and into a tank I containing a ,quantity of dielectric ma- This material may be titanium dioxide crystals or other dielectric material similar polar characteristics such as zirconium dioxide, or certain titanates'and' zirconates such as lead titanate, strontium titanate, lead zirconlowest dielectric loss, a reduction in power iactor is also obtained.

The base material to be coated maybe passed around a roller ll positioned beneath the liquid inthe tank. The coated or impregnated strip.is then drawn from the coating bath and passed between two spaced electrical conducting plates I! which are connected to a source of potential such as an alternating current or direct current generator ii. The charged plates preferably extend downwards as close to the liquid in the tank as practical so that the orienting force of the electrostatic field will be exerted while the crystals are most easily movable, that is, while the binder is most fiuent. Since crystals align themselves in the presence of an electrostatic field along the line of lowest dielectric loss, the titanium dioxide crystals will be oriented with their major axes substantially dicular to the supporting strip and substantially parallel to each other. '"It should be noted that the major axis of a titanium dioxide crystal is not necessarily the physically longer axis, but is, as defined, the line of lowest potential energy.

Either alternating current or direct current may be used; however, alternating current or pulsating direct current has the desirable effector iarring or iolting the crystals into position whereas ordinary direct current merely exerts a constant force. This jarring or iolting appears to produce more complete orientation of the crystals.

The evaporation of the solvent and hardenin of the binder may be expedited by applying heat to the strip as it is drawn between the charged plates. Preferably, the heat is applied by an oven ll positioned so that the charged plates extend below an entrance II to the oven a suillcient distance to orient the crystals of dielectric material substantially completely prior to entering the oven. The plates are long enough, however, to extend into the oven a suillcient distance to main-, tain the crystals in oriented position until the binder has hardened enough to prevent loss of orientation. Heat may be supplied by a number of electric coils it inside the oven, or by gas or hot air.

It has been found that it is possible to reduce the thickness of the coated base material by calenderi'ng without materially affecting the orientation of the dielectric crystals. If the thickness of the dielectric material and base is reduced, the capacitance of the condenser is increased proportionately. This result obtains regardless of the original thickness of the dielectric material and support. At the same time the density of the dielectric material is increased, which also results in increased capacity, since more dielectric material is thereby compacted into a given space. A further advantage of calendering lies in the fact that the surface of the dielectric is rendered smoother and more resistant to abrasion. The coated, r impregnated, strip is therefore passed over apair of rollers I l and I 8 and between a pair of steel calenderlng rolls I! and 20. The strip is finally wound on a take-up reel 2|.

By calendering it is possible to reduce the thickness of sheets of coated base material by approximately 30 to 45%, thus increasing the density of the dielectric material approximately 43 to 82%. This increase in density produces, as stated above, a corresponding increase in capacitance of the condenser with which the dielectric material is used. A coated sheet of .001" thickness is de-' sirable as an ultimate size. By calendering, it is possible to obtain a sheet of this size vfrom a coated sheet originally .0016". However, coated sheets as thick asxOOZO" have been successfully calendered and used as condenser materials, and calendered sheets as thin as .0008" have been successiully used as condenser materials. The amount of widening of the sheet during calendering is negligible.

In Fig. 2 another embodiment of this invention is shown. Here, instead of coating dielectric material on a strip, a quantity of dielectric material 25, which may be titanium dioxide suspended in an aqueous solution oi sodium silicate, or any other suitable liquid dielectric binder as previously described, is poured onto a tray 25 or platter of easily volatile, combustible or soluble material, such as polystyrene, or of non-porous material such as glass. An electrostatic field is applied to the material by positioning an electrical conducting plate 21 above, or in contact with, the liquid and a similar plate II below the tray. The plates are connected to a source of potential 29, which, as previously described, may be alternating current or direct current, or pulsating direct current. The crystals are thereby oriented with their major axes substantially parallel and as the binder dries and hardens, they become fixed in position. If a polystyrene tray is used, the tray may then be placed in an oven and heated sumciently to volatilize the polystyrene and to tire the titanium dioxide, thus leaving a sheet oi ceramic dielectric material, the crystals of which are oriented along their major axes and fused. together. I! a glass tray is used, the dielectric material may be removed from the tray and then fired. This method is feasible only when the dielectric material has considerable flexibility and may be handled without breaking. By dispensing with a base material, a dielectric body of minimum dimensions is obtained. This economy of dimensicns makespossible increased capacitance per given volume 0! condenser.

Some increase in the effectiveness of the potential applied to the platw used in the first oi the above described embodiments of this invention may be obtained by providing each plate with a number of relatively small cone shaped points 30,. as shown in Fig. 3, of conducting material, such as used for the plates, attached to one side of each plate in rows spaced about 1 to 1" of an inch apart. The points on one plate face the points on the other and the rows of points are staggered so that all portions or a strip passing between the plates are subjected substantially equally to the concentrated charge at the points. By concentrating the potential in this way, a higher eil'ective potential is obtained between the plates without increasing the voltage supplied to the plates or the net potential between the plates. High potential is desirable because the degree of orienting force exerted on the crystals is directly proportional to the potential gradient.

While but two embodiments of this invention have been shown and disclosed, it will be understood that many changes and alterations may be 'made therein without departing from the spirit and scope of the present invention.

What is claimed is:

l. A dielectric body having high dielectric constant comprising a base having a coating of titanium dioxide particles, said particles having a higher dielectric constant along one axis than along another axis and said particles being oriented so that the major electrical axes oi said particles are substantially perpendicular to the base so as to increase the eiiectlve dielectric constant of said body, and a binder of a solidifiable illm forming type to bond said particles in oriented position.

2. A dielectric body having high dielectric constant comprising a base having a coating of particles selected from the group consisting of titanates and zirconates, said particles having a higher dielectric constant along one axis than along another axis and said particles being oriented so that the major electrical axes of said particles are substantially perpendicular to the base so as to increase the effective dielectric constant of said body, and a binder of a solidiilable film forming type to bond said particles in oriented position.

3. A method oi making a dielectric body comprising coating a base of metal fail with particles of dielectric material selected from the group consisting of titanates, zirconates, titanium dioxide, and zirconium dioxide, and suspended in a solidiflable liquid binder of film forming material containing a voiatilesolvent, said particles havin a higher dielectric constant along their maJor electrical axis than along their minor electrical axis, orienting said particles by applying an electrostatic field thereto so that their major electrical axes are substantially perpendicular to said 4. A method of making a dielectric body comprising coating a base of metal foil with particles of dielectric material suspended in a solidiflable liquid binder oi sodium silicate containing a volatile solvent, said particles being selected from the group consisting of titanates, zirconates, titanium dioxide and zirconium dioxide and being orientable along one axis to increase the eilective dielectric constant of the body, orienting said particles by applying an electrostatic field thereto so that the major electrical axes of said particles are substantially perpendicular to the base, and

binder.

5. a dielectric body having a high dielectric constant comprising a base having a coating of particles selected. (mm a group consisting or titanates, zirconates, titanium dioxide and zirconium dioxide. said particles havinga higher dielectric constant along one axis tha'n along another axis and being oriented so that their major electrical axes are substantially perpendicular to the base so as to increase the eflective dielectric constant of the body, and a binder of a solidifiable fllm forming type to bond said particles in oriented position.

HAL' F. FRUTH.