Method of Producing a Flexible Carrier Substrate

This application claims the priority of Federal Republic of Germany application Ser. No. P 38 27 433.7 filed Aug. 12th, 1988, which is incorporated herein by reference.

The present invention relates to a method of producing a flexible carrier substrate for a photovoltaic solar generator wherein a polyimide film, for example such a film sold under the trademark KAPTON, which is disposed on a heatable lamination table, is coated with an adhesive and hardened whereupon, after the application of an adhesion promoting layer, a glass filament fabric is placed onto the polyimide film and is subsequently saturated with a silicone adhesive.

A flexible solar generator is known in which a plurality of photoelectric solar cells are arranged on a substrate that can be wound into a roll. The solar cells are electrically conductively connected with one another in parallel and series connections by means of connectors punched out of a rolled material (see German Patent No. 2,160,345). The direction of winding of the substrate is the direction of the parallel connections, with separate connectors being provided for the parallel connections and for the series connections. The connectors are configured in such a manner that the direction in which their material was rolled is the direction in which the respective connections are made.

The required strength of this flexible solar generator system is realized with respect to the carrier material in that the windable substrate serving as the carrier is composed of a polyimide film to which glass filaments are glued. Several adhesives suitable for space travel conditions, for example thin-flowing adhesives which are stable up to 10 to 12 Torr and in a temperature range from -180.degree. to 100.degree. C. are selected, for example polyester adhesives containing a large amount of solvents so as to produce good wetting of the glass filament fabric and good adhesion of the fabric to the polyimide film. A layer of glass filament fabric is glued to the polyimide film in such a manner that initially the layer of glass filaments is placed onto the polyimide film and then the adhesive is applied in a very thin layer. After hardening of the adhesive, there results a substrate which is still sufficiently flexible but whose strength characteristics have been improved considerably. Instead of the above-mentioned adhesives, solvent-containing silicones can be employed for temperature ranges from -60.degree. to +260.degree. C. with which good bonds are realized between the glass filament fabric and the polyimide film. The solar cell modules and strings are glued to the resulting substrate by means of appropriate adhesives.

It is an object of the present invention to provide a method of producing a flexible carrier substrate for a photovoltaic solar generator which is resistant to atomic oxygen, in such a way that, it may preferably travel in an orbit about the Earth containing atomic oxygen percentages, without degradation.

This is accomplished according to the invention in a method in which a polyimide film (for example such a film sold by Dupont under the trademark KAPTON) disposed on a heatable lamination table, is coated with an adhesive and hardened, whereupon, after application of an adhesion promoting layer, i.e. primer, a woven glass filament fabric is placed onto the polyimide film to subsequently be saturated with a silicone adhesive, whereupon the following additional method steps are performed:

(a) after the glass filament fabric is saturated with silicone adhesive, but prior to the silicone adhesive being hardened, a woven tear-away fabric is introduced into the not yet hardened silicone adhesive;

(b) the laminate of polyimide film, silicone adhesive saturated-glass filament fabric and tear-away fabric is hardened under vacuum; and

(c) before solar cells are glued onto the flexible carrier substrate, the tear-away fabric is removed in such a manner that a torn-open, structured silicone surface remains for attachment of the solar cells.

These and other aspects of the invention will be more fully understood from the following detailed description of the preferred embodiments with reference to the accompanying drawing figures wherein:

FIG. 1 is a cross-sectional view of a flexible carrier substrate produced according to the present invention prior to removal of a tear-away fabric; and

FIG. 2 is a cross-sectional view of the flexible carrier substrate produced according to the method of the invention after the tear-away fabric has been removed and solar cells have been applied with an adhesive.

Referring to FIG. 1, in accordance with the method of producing a flexible, windable, carrier substrate for photoelectric solar cells, according to the invention, a polyimide film 11, such as KAPTON (KAPTON is a registered trademark of Dupont), is disposed on a heatable lamination table. An adhesive 12 such as the Dayton Chemical Division of Whittaker Corporation adhesive Type 46970 a polyester adhesive is applied to the polyimide film, and hardened. Then a layer of woven glass filament fabric 14 is placed on the adhesive-coated polyimide film and is saturated with a silicone adhesive 15, such as RTVS 691 manufactured by Wacker Chemie of Munchen, Germany or DC 93500 manufactured by Dow Corning. Prior to placement of the glass filament fabric 14, a primer of Type G790 manufactured by Waker Chemic an adhesion promoter between silicone and substrates or DC 1200 manufactured by Dow Corning, which is a dilute solution of moisture reactive materials in VM and P Naptha, also an adhesion promotor between silicone and substrates, may be applied on the hardened adhesive 12.

Before the silicone adhesive 15 on the glass filament fabric 14 is hardened, a woven tear-away fabric 16 such as nylon 6.6 is applied into the silicone adhesive 15. Then, the laminate of polyimide film 11, hardened adhesive 12, adhesion promoting layer 13, glass filament fabric 14, silicone adhesive 15 and tear-away fabric 16 is subjected to a process under vacuum which hardens the silicone adhesive 15. For example, the silicone adhesive 15 in the laminate may be hardened for four hours under a pressure of 1 bar and at a temperature of 140.degree. C.

The tear-away fabric 16 is then removed from the laminate in such a manner that a torn-open structured silicone surface 15' remains for attachment of the solar cells 18, as shown in FIG. 2. The solar cells 18 are then glued to torn-open structured silicone surface 15' with an adhesive 17 such as the above-mentioned RTVS 691 of Dow Corning. According to a further feature or the invention, application of the solar cells may be delayed for up to 24 hours after the tear-away fabric is removed from the laminate, but not more than 24 hours to avoid an uncleaned and unadhesive surface.

An advantage of the flexible carrier substrate manufactured in accordance with the method of the invention, in addition to providing a-simple and cost-effective manufacturing process, resides in that solar cells can be attached to the hardened silicone surface by means of a silicone adhesive which is resistant to atomic hydrogen. Use of the invention for a photovoltaic solar generator to be used in an orbit about the Earth containing atomic oxygen percentages is thereby facilitated.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

The woven tear-away fabric 16 can be nylon 6.6 of the firm Interglas Textil GmbH with a thickness of 60.+-.5 um, with a typical strength of 75.+-.5 Newtons, with a breaking strength of 13, 5 Newtons per cm, and a threadcount of 68 per cm in warp-direction and a threadcount of 44 per cm in the weft-direction.

In the following list the manufacturer of the applied materials are named.