IE53253B1 - Capacitors and methods for making them - Google Patents

Abstract

A capacitor comprises a plurality of layers 18a, 18b each layer comprising a dielectric substrate 6a and a metallic film 8a extending from one edge to the other but including a zone 10 free of said metallic film and adjacent to but spaced from one edge to leave a narrow marginal metal film band 24 at said edge. The layers are disposed alternately offset and reversed laterally, such that alternate edges 33 of layers 18a lie beyond the marginal band edged 36 of the layers 18b, and vice versa at the opposite side of the capacitor. The outwardly lying edges 33, of the layers are coated with electrically- conductive material 40a to connect electrically the alternate metal film layers in two groups. The capacitors are made by laser- scribing parallel metal-free zones onto webs A and B. The webs are slit into ribbons by blades 21a prior to winding onto a drum 20 on offset and laterally reversed fashion, to produce a plurality of side-by-side annular layered members. Rollers 16a, 16b and said slitting blades 21a are close to the drum 20, such that the slit ribbons are supported over substantially their full lengths prior to winding onto said drum. The annular members are separated and individually cut transversely to the ribbons, to form stacked capacitors.

Description

PATENT APPLICATION BY (71) ILLINOIS TOOL WORKS INC., A CORPORATION ORGANISED UNDER THE LAWS OF THE STATE OF DELAWARE, UNITED STATES OF AMERICA, OF 8501, WEST HIGGINS ROAD, CHICAGO, ILLINOIS 60631, UNITED STATES OF AMERICA.

Price 90p This invention relates to layer or stack wound capacitors and to methods for making them.

One such method of making layer or stack wound capacitors is shown and described in U.S. Patent No. 3,670,378. In that patent the process for the production of the capacitors comprises first forming capacitor bodies by winding alternate metallic and dielectric films on a drum, contemporaneously winding separating layers between the capacitor bodies to form a parent winding having alternate layers of capacitor bodies and separating layers, then applying a metallic spray coating to the edges of the parent winding to connect metallic films, and thereafter severing the parent winding perpendicular to the separating layers to form the individual capacitor bodies. These resultant capacitor bodies have interwoven metallic layers which are separated by dielectric layers. The layers of one group comprising dielectric substrates and metallic films project outwardly from one side of the capacitor body while another group of substrates and films, alternating with the first group, project from the other side of the capacitor body. The metallic coating is applied such that it connects electrically together the metallic films on the outwardly projected group of layers - 2 Thus, there are provided two electrodes or sets of capacitor plates which are dielectrically isolated from one another but which are interwoven.

In the foregoing arrangement it sometimes happens that during the winding process the being-wound layers will weave or depart from their intended paths, resulting in one or more layers being improperly located with respect to the adjacent layers. If the lateral offset between the groups of layers is not sufficient, the capacitor may be short-circuited or it may have a lower than intended dielectric strength at one or more regions. If the lateral offset is excessive, the resulting capacitance of the capacitor is reduced.

An object of this invention is to provide a high quality commercial capacitor of the general type stated, but which is different in structure and wherein the manufacturing process is considerably lower in cost.

A further object of this invention is to provide an arrangement of the type stated which materially reduces the possibility of short-circuiting the being-wound capacitor as a result of improper disposition of the metallic and dielectric films.

In accordance with one aspect of this invention, a capacitor comprises a plurality of superposed substantially flat layers, each layer having a pair of opposed ends and a pair of opposed sides, and comprising a dielectric substrate and a metallic film, the metallic film extending from one end towards the other end, each layer including a zone free of said metallic film, said zone being adjacent but spaced from said other end to leave a marginal band of metal film at said other end which is spaced by said zone from the remainder of said metallic film, said layers being disposed with layers in a first group of layers alternating with layers of a second group of layers and with the metal film of one layer being separated by dielectric material from the metal film of the adjacent layer, adjacent layers being laterally reversed and also offset, such - 3 S3 that at one end of the capacitor said one ends of the first group of layers lie outwards beyond said other ends of the second group of layers, and at the opposite end of the capacitor said one ends of the second group of layers lie outwards beyond said other ends of the first group of layers; the outwardly lying ends of the layers in each group being coated with electricallyconductive material to connect electrically the metal film of the layers in each group.

In accordance with another aspect of this invention, a method of making a capacitor comprises; providing first and second webs of material each having a dielectric substrate, a metallic film coating, and narrow parallel longitudinal metal-free zones; slitting said webs along parallel lines that are offset from said metal-free zones to form ribbons each of which has a narrow marginal metal film band extending inwards from one longitudinal edge of the ribbon to said metal-free zone; winding said ribbons from said first and second webs alternately on a drum with the narrow marginal metal film band and the metal free zones of the first and second webs being laterally reversed, and in said winding offsetting the ribbons of one web from the ribbons of the other web to form a plurality of adjacent side-by-side rings of capacitance structure each having alternately disposed metal and dielectric layers, with there being in each capacitance structure the layers from the ribbons of each web respectively projecting laterally outwards from said marginal metal film bands of the ribbons from the other web; removing the capacitance structures from the drum and separating the structures from each other; coating the laterally projecting parts of each structure with a metal substance to connect electrically the metal films of the respective webs of the structure; and severing the structure transversely of the ribbons to form individual substantially flat capacitors. - 4 53253 Preferably in a capacitor said metal-free zone and said narrow marginal metal film band have a combined width which is a minor fractional part of the corresponding dimension of the associated layer.

The method may also include the application to both of the webs of a thin film of adhesive in at least a portion of the electric field regions of a capacitor, but the adhesive is not applied in the region of slitting of the web nor in the laterally projected parts of the structure where a spray contact is made with the metallic coating. The purpose of the adhesive is, to the extent needed, to lock the lamination so that the wound capacitor structure can be handled without delamination.

Preferably each of the webs is passed through a station where a number of laser beams can burn off the metal to form precisely spaced demetallized zones. These demetallized zones may be made much narrower by laser beam burn-off than would be obtainable by material commercially available with conventional demetallized zones, which are much wider than is necessary for capacitors with low voltage ratings.

The accompanying drawings show examples of capacitors embodying the invention.

In these drawings:Figure 1 is a diagrammatic view of the apparatus; Figure 2 is a fragmentary enlarged section view taken along the line 2-2 of Figure 1; Figure 3 is a fragmentary top-plan view of the structure of Figure 2; Figure 4 is a further enlarged fragmentary sectional view taken along the line 4-4 of Figure 3; Figure 5 is an enlarged diagrammatic view, partially in section taken along the line 5-5 of Figure 1; - 5 253 Figure 6 is a much enlarged fragmentary sectional view, on the same scale as Figure 4, of parts of a capacitor; Figure 7 is an enlarged fragmentary portion of Figure 2 and showing a modification for applying adhesive to the web; and, Figure 8 is a diagrammatic perspective view showing a modification including a laser burn-off station which forms the demetallized zones as a web is withdrawn from its supply roll.

Referring now in more detail to the drawings, in Figure 1 there is shown a pair of supply rolls 2, 4 from which webs A and B are withdrawn. Each of the webs A, B comprises a dielectric substrate 6 and a metallic film 8 (Figure 4). The substrate 6 may be of a suitable plastics material such as the resin sold under the trade mark Mylar. The film 8 may be of vapourdeposited aluminium, and both the substrate 6 and the metallic film 8 are exceedingly thin. By way of example but not of limitation, the substrate 6 may be of the order of 0.001 inches (0.025 mm) or less in thickness while the thickness of the metallized film 8 may be of the order of 500 angstrom units (50 nm). Each web A, B has a plurality of parallel demetallized or metalfree zones 10. These are best seen in Figures 3 and 4 with respect to the web B, but it is understood that a like series of demtallized zones are provided on the web A. The webs A, B may have the demetallized zones 10 preformed thereon, or these zones may be formed by a laser burn-off method as will later be described. In any case the webs pass over a series of rollers respectively, for slitting into ribbons and for interleaved or alternate winding onto a large diameter drum or transfer wheel 20.

In particular, the web A passes over an idler roller 12a, the axis of rotation of which is shiftable to control weave of the web A. The idler roller 12a moves parallel to its axis as a unit with the supply roll 2 under the control of a conventional edge guide sensor (not shown) to control the weave. From the idler roller 12a, the web passes by the aforementioned edge guide sensor to a tension-sensing roller 14a. The tension-sensing roller sends a signal to a variable-drag clutch (not shown) on which the supply roll 2 is mounted.

This closed loop control maintains the tension at any preset value. The apparatus also includes a laminating or lay-on roller 16a. Between the rollers 14a, 16^ is a web-slitting station at which the web A is slit into a plurality of ribbons prior to passage around the lay-on roller 16a and wrapping onto the drum or transfer wheel 20. Similarly, the web B passes over a shifting idler roller 12b and from there to a tension-sensing roller 14b, past the slitting station and onto a laminating or lay-on roller 16b, and the idler roller 12jo responds to a second edge guide sensor (not shown) to control the weave of web B while the tension-sensing roller 14b again sends a signal to a variable-drag clutch (not shown) on which the supply roll 4 is mounted, to maintain the tension at a preset value.

The tension sensing and edge guide control systems employed are available from Advanced Web Systems, Inc., 4793 Colt Road, P.O. Box 6025, Rockford, Illinois 61125, United States of America.

The slitting station for the web B comprises a plurality of spaced parallel cutters such as razor blades 21b which cooperate with a polished web support bar 22b over which the web B passes. Likewise, for the web A the slitting station comprises spaced parallel razor blades 21a (Figure 7) which cooperate with a web support bar. For each web the slitting station forms a plurality of ribbons which immediately pass onto the roller 16a or 16b, as the case may be, and then onto the drum 20. The result is that the ribbons are supported substantially throughout their full lengths prior to winding onto the drum 20. Because the ribbons do not travel unsupported in space, weave is eliminated and - 7 the ribbons can be accurately deposited onto the drum 20. This is in contrast to prior art arrangements which rely upon edge guides, sometimes unsatisfactorily, to prevent weave of the web.

The laminating or lay-on rollers press against the drum or transfer wheel 20, and the razor blades may operate directly in narrow slits on the rollers 16a, 16b. In any event, the arrangement for slitting the webs provides smooth cuts by the razor blades without causing the web material to wrinkle. This is particularly important as it is difficult to obtain smooth cuts without wrinkling in web material as thin as that utilized in the present invention.

In the present apparatus, the rollers 16a^, 16b may be located either 90° apart as shown in Figure 1, or 180° apart.

The web B is slit into the plurality of ribbons 18b, as seen in Figures 2 to 4.

The web A is also slit to provide ribbons 18a which, like the ribbons 18b ultimately will become capacitor layers, as seen in Figure 6. The slit lines for the web B are offset from the demetallized zones 10 so as to form marginal metal film bands 24 at one edge of each ribbon 18ΪΛ A like slitting takes place for the web A except, however, that the slit line for each blade 2 k is laterally reversed in position from that in Figure 3 to form marginal film bands 24 on the ribbons 18^. Thus, if each blade 21b is located to the left of the adjacent demetallized zone 10 in cutting the web B (reference to Figure 3) then for the web A each blade 2k will be to the right of the adjacent demetallized zone, as indicated by arrows 21aa in Figure 3.

The ribbons are disposed simultaneously upon the drum 20 to produce the layered pattern shown in Figure 5. There are formed a plurality of hoops or rings 30 of capacitor structure from which individual capacitors may be formed. In Figure 5 only one of the rings 30 is shown in cross section for purposes of clarity of illustration. Moreover, the sources of the various ribbons, - 8 53253 namely from the supply web A or B, is indicated on one of the rings 30 in Figure 5. It will also be apparent that the ribbons are not illustrated to scale, but rather the thickness is greatly exaggerated. In any case, there is an initial winding of layers of web A adjacent to the drum 20, as shown by the lower five such layers designed in Figure 5. Thereafter, the ribbons are interleaved and offset from each other as they are simultaneously wound onto the drum 20 to form the pattern indicated by the A and B alternate layers in Figure 5. In the A layers, the demetallized zone is near the right-hand edge 37, while in the B layers the demetallized zone is near the left-hand edge 36. That is to say the layers are identical but relatively reversed laterally. Thereafter, another group of A layers are wound over the group of A and B alternate layers. The inner and outer A layers serve as reinforcement on the faces of the capacitors, while the interweaved A and B layers or ribbons provide the active portion of the capacitor structure.

Each of the separate rings 30 is removed from the drum 20, and the sides 32, 34 thereof then coated in a conventional manner with a metallic spray coating 40 (Figure 6). That is to say, one coating 40a is applied to the outwardly lying left-hand edges 33 of the A layers 8a, 6a, and the other coating 40b is applied to the outwardly lying right-hand edges 35 of the B layers 8b, 6b.

The ring 30 is cut perpendicular to its edges 32, 34 to form individual capacitor units.

Figure 6 shows an enlarged sectional view through several interleaved layers of the capacitor. It will be seen that, at the left side of the capacitor, layers from portions of the ribbon 18a comprising the metallized film 8a and of the substrate 6a project laterally outwardly of the adjacent ends 36 of the layers from portions of the ribbon 18_b. The metallized spray coating 4(ta electrically connects the metallized films 8a to form a set of capacitor electrodes or plates, this being made possible by the spaces between the layers from ribbon 18 - 9 53253 space between the left-hand metallic coating 40a of the top portion of Figure 6 and the metallized film 8b of the layers from ribbon 18b is at least the width of the demetallized zone 10 plus the width of the marginal metal film band 24. In general, the coating 40a does not penetrate to the edges 36, and so does not make any electrical connection with the bands 24.

Thus, in effect, each band 24 is a floating electrode. By providing for the floating electrode formed by the band 24, the full width of the demetallized zone 10 is utilized for dielectric separation along the surfaces of the layers, thereby reducing the possibility of short-circuiting or changing the capacitance of the capacitor from its prescribed value. If by chance the coating 40a does penetrate to any of the edges 36, the relevant band 24 acts as a barrier, so that the full width of the demetallized zone 10 is preserved as insulation between the band 24 and the respective film 8b.

On the right side of the capacitor, as shown by the lower portion of Figure 6, the layers from portions of the ribbon 1813 project outwards from the margin 37 of the layers from the ribbon 18^ for receiving the right-hand metal spray coating 40b, shown in the bottom portion of Figure 6. Each marginal metal film band 24 is, in the lower portion of Figure 6, located on a layer from ribbon 18ji, and likewise serves as a floating electrode or as a barrier, so that full advantage is taken of the demetallized zones 10, as previously described.

In a modified form of the invention shown in Figure 7 any suitable thin adhesive may be deposited on both of the webs A and B by applicators 50 positioned just before the slitting operation occurs. Epoxy resin is one type of adhesive that may be used, but the invention is not limited thereto. The adhesive is not applied in the region of slitting or in the extension area of the web where the metallic spray is to be applied. The purpose of the adhesive, if needed, is to lock the laminations together after being wound onto the drum 20 - 10 53253 so that the rings 30 can be handled without delamination. The adhesive can be deposited and spread in a film thickness substantially less than one micron, and the adhesive may thus be used without materially reducing an efficient capacitance-to-volume ratio.

The web material used in the present invention may be purchased with the demetallized zones. However, these demetallized zones are usually somewhat wider than is necessary for low voltage capacitors. Accordingly, as shown in Figure 8, it is possible to form the demetallized zones 10 as the web A or B is being withdrawn from the supply roll. This may be accomplished by running the web through a laser burn-off station 52 at which laser beams 53 may be utilized to burn off the deposited metal and form extremely narrow demetallized zones 10, much narrower than are provided on commercially available webs. Consequently, material cost is reduced along with the size of the capacitor. For example, the width of the zones 10 may be about 200 microns.

Claims (9)

1. A capacitor comprising a plurality of superposed substantially flat layers, each layer having a pair of opposed ends and a pair of opposed sides, and comprising a dielectric substrate and a metallic film, the metallic film extending from one end towards the other end, each layer including a zone free of said metallic film, said zone being adjacent but spaced from said other end to leave a marginal band of metal film at said other end which is spaced by said zone from the remainder of said metallic film, said layers being disposed with layers in a first group of layers alternating with layers of a second group of layers and with the metal film of one layer being separated by dielectric material from the metal film of the adjacent layer, adjacent layers being laterally reversed and also offset, such that at one end of the capacitor said - 11 53253 one ends of the first group of layers lie outwards beyond said other ends of the second group of layers, and at the opposite end of the capacitor said one ends of the second group of layers lie outwards beyond said other ends of the first group of layers; the outwardly lying ends of the layers 5 in each group being coated with electrically-conductive material to connect electrically the metal film of the layers in each group.

2. A capacitor according to Claim 1, in which said metal-free zone and said narrow marginal metal film band have a combined width which is a minor fractional part of the corresponding dimension of the associated layer. 10

3. A capacitor according to Claim 2, further including reinforcing layers on opposite faces of said assembled first and second groups of layers.

4. A method of making capacitors, comprising: providing first and second webs of material each having a dielectric substrate, a metallic film coating, and narrow parallel longitudinal metal-free zones; slitting said webs along 15 parallel lines that are offset from said metal-free zones to form ribbons each of which has a narrow marginal metal film band extending inwards from one longitudinal edge of the ribbon to said metal-free zone; winding said ribbons from said first and second webs alternately on a drum with the narrow marginal metal film band and the metal free zones of the first and second webs 20 being laterally reversed, and in said winding offsetting the ribbons of one web from the ribbons of the other web to form a plurality of adjacent side-by-side rings of capacitance structure each having alternately disposed metal and dielectric layers, with there being in each capacitance structure the layers from the ribbons of each web respectively projecting laterally outwards from 25 said marginal metal film bands of the ribbons from the other web; removing the capacitance structures from the drum and separating the structures from each other; coating the laterally projecting parts of each structure with a metal substance to connect electrically the metal films of the respective webs - 12 53253 of the structure; and severing the structure transversely of the ribbons to form individual substantially flat capacitors.

5. A method according to Claim 4, comprising placing the webs in tension over a length of each web, and slitting the webs at said tensioned lengths. 5

6. A method according to Claim 5, further comprising interposing adhesive between the ribbons of each structure as they are wound.

7. A capacitor substantially as described with reference to Figure 6 of the accompanying drawings.

8. A method substantially as described with reference to Figures 1 to 6 of 10 the accompanying drawings, or modified as described with reference to Figure 7 or Figure 8.

9. Capacitors whenever made by a method as claimed in any of Claims 4 to 6 or 8.