GB2143087A - Apparatus for making capacitors by winding - Google Patents

Abstract

Apparatus for making capacitors, comprising: first and second supply rolls 2, 4 of webs A, B; a rotatable drum 20 spaced from said supply rolls; first and second laminator rollers 16a, 16b; a tension-sensing roller 14a, 14b associated with each laminator roller, one web A, B being strained and tensioned over each roller pair; and means 21a for slitting the webs into ribbons prior to winding said ribbons onto said drum; said laminating rollers 16a, 16b being sufficiently close to said drum 20, and said sitting means 21 being sufficiently close to said laminating rollers, such that the ribbons are supported over substantially their full lengths prior to winding onto said drum. <IMAGE>

Description

1 GB 2 143 087 A 1

SPECIFICATION Apparatus for Making Capacitors

This invention relates to an apparatus for making layer or stack wound capacitors.

One such apparatus is shown and described in 70 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 resulstant 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. Thus, there are provided two electrodes or sets of capacitor "piates" which are dielectrically isolated from one another but which are 95 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 an apparatus which applies the layers forming the capacitor to a drum or transfer wheel directly from laminating or lay-on rollers. Such an arrangement prevents the supply material from travelling unsupported in space, thereby reducing weave and consequent misalignment of the capacitor layers.

In accordance with this invention, first and second supply rolls of webs, each web having a dielectric substrate with a metallic film coating; a rotatable drum spaced from said supply rolls; first and second laminator rollers, said rollers being circurnferentially spaced with respect to the periphery of said drum; a tension-sensing roller associated with each laminator roller and in spaced parallel relation thereto to constitute with its associated laminator roller a roller pair, one web being strained and tensioned over each roller pair; and means for slitting the webs into ribbons prior to winding said ribbons onto said drum to provide alternate layers of metallic and dielectric material; said laminating rollers being sufficiently close to said drum, and said slitting means being sufficiently close to said laminating rollers, such that the ribbons are supported over substantially their full lengths prior to winding onto said drum.

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 demetalized zones. These demetalized zones may be made much narrower by laser beam burn-off than would be obtainable by material commercially available with conventional demetalized zones, which are much wider than is necessary for capacitors with low voltage ratings.

The accompanying drawings show examples of apparatus 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, 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 of a modification including a laser burnoff station which forms the demetalized 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 1, 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 J 10 may be of a suitable plastics material such as the resin sold under the trademark "Mylar". The film 8 may be of vapour-deposited 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 metalized film 8 may be of the order of 500 angstrom units (50 mm). Each web A, B has a plurality of parallel demetalized or metal-free 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 demetalized zones are provided on the web A. The webs A, B may have the demetalized 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 2 GB 2 143 087 A 2 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 70 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 1 6a. Between the rollers 14a, 16a 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 12b 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 21 b which cooperate with a polished web support bar 22b over which the web B passes.

Likewise, for the web A the slitting station 105 comprises spaced parallel razor blades 21 a (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 1 6b, as the case may be, and then onto the drum 20. The result is that the ribbons are supported substantially throughout theirfull lengths prior to winding onto the drum 20. Because the ribbons do not travel unsupported in space, weave is eliminated and 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 I 6a, 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 1 6a, 16b may be located either 90' apart as shown in Figure 1, or 1801 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 demetalized zones 10 so as to form marginal metal film bands 24 at one edge of each ribbon 1 8b. A like slitting takes place for the web A except, however, that the slit line for each blade 2 1 a is laterally reversed in position from that in Figure 3 to form marginal film bands 24 on the ribbons 18a. Thus, if each blade 2 1 b is located to the left of the adjacent demetalized zone 10 in cutting the web B (reference to Figure 3) then for the web A each blade 21 a will be to the right of the adjacent demetalized zone, as indicated by arrows 21 aa 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, 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 designated 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 demetalized zone is near the right-hand edge 37, while in the B layers the demetalized zone is near the lefthand 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 may then be cut perpendicular to the edges 32, 34 to form a length of capacitor structure. That length can then be cut again transversely 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 3 GB 2 143 087 A 3 1 8a comprising the metalized film 8a and of the substrate 6a project laterally outwardly of the adjacent edges 36 of the layers from portions of the ribbon 1 8b. The metalized spray coating 40a electrically connects the metalized films 8a to form a set of capacitor electrodes or plates, this being made possible by the spaces between the layers from ribbon 18a. The space between the left-hand metallic coating 40a of the top portion of Figure 6 and the metalized film 8b of the layers from ribbon 1 8b is at least the width of the demetalized 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 prodiving for the floating electrode formed by the band 24, the full width of the demetalized zone 10 is utilized for dielectric separation along the surfaces of the layers, thereby reducing the possibility of shortcircuiting 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 demetalized 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 18b project outwards from the margin 37 of the layers from the ribbon 1 8a 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 18a, and likewise serves as a "floating" electrode or as a barrier, so that full advantage is taken of the demetalized 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 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 demetalized zones.

However, these demetalized zones are usually somewhat wider than is necessary for low voltage capacitors. Accordingly, as shown in Figure 8, it is possible to form the demetalized 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 demetalized 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 (8)

1. Apparatus for making capacitors, comprising: first and second supply rolls or webs, each web having a dielectric substrate with a metallic film coating; a rotatable drum spaced from said supply rolls; first and second laminator rollers, said rollers being circumferentially spaced with respect to the periphery of said drum; a tension-sensing roller associated with each laminator roller and in spaced parallel relation thereto to constitute with its associated laminator roller a roller pair, one web being strained and tensioned over each roller pair; and means for slitting the webs into ribbons prior to winding said ribbons onto said drum to provide alternate layers of metallic and dielectric material; said laminating rollers being sufficiently close to said drum, and said slitting means being sufficiently close to said laminating rollers, such that the ribbons are supported over substantially their full lengths prior to winding onto said drum. 95

2. Apparatus according to claim 1, in which said laminator rollers are approximately 901 apart at the periphery of the drum.

3. Apparatus according to claim 1, in which said laminator rollers are approximately 1801 apart at the periphery of the drum.

4. Apparatus according to any of claims 1 to 3, including means between the rollers of each pair for applying adhesive to the surface of the respective web.

5. Apparatus according to claim 4, in which each adhesive-applying means is between the respective tension-sensing roller and slitting means.

6. Apparatus according to any of the preceding claims, including laser means for forming a plurality of longitudinal parallel metal-free zones on each web prior to slitting of the web.

7. Apparatus substantially as described with reference to Figures 1 to 4 of the accompanying drawings, or modified as described with reference to Figure 7 or Figure

8.

Printed in the United Kingdom for Her Majesty's Stationery Office, Demand No. 8818935, 111985. Contractor's Code No. 6378. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.