JPH0685306A - Solar cell module - Google Patents

Abstract

PURPOSE:To make unnecessary a rack for installing a solar cell module, reduce the weight and facilitate the installation on metal roofs by using an adhesive double coated tape to attach solar cell panels to roofs. CONSTITUTION:An adhesive double coated tape 301, having a tensile strength of 5kg/m<2> or above, breaking elongation percentage of 200% or above and thickness of 0.5mm or above, is stuck to solar cell panels 201-204. The solar cell panels 201-204 are then placed on a metal roof 101, and pressure is applied thereto using a jig, such as roller; otherwise, an adhesive double coating tape is stuck to the metal roof 101 instead prior to the placement of the solar cell panels 201-204. This makes a rack for installation work unnecessary, and reduces the weight. It also calls for no troublesome work, leading to the cost reduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roof integrated solar cell module.

[0002]

2. Description of the Related Art Recently, it is predicted that the greenhouse effect due to an increase in CO ₂ will cause global warming, and there is an increasing demand for clean energy that does not emit CO ₂ .

Further, in nuclear power generation which does not emit CO ₂ , the problem of radioactive waste has not been solved, and safer and cleaner energy is desired.

Among the clean energies expected in the future, solar cells, in particular, are highly expected because of their cleanliness, safety and ease of handling.

Among the solar cells, the monocrystalline silicon and polycrystalline silicon solar cell modules are vulnerable to impacts, so that they are thick glass plates and EVA, which is also an adhesive and a filler.
(Ethylene-vinyl acetate copolymer) is used to protect the surface, and it is further held by a frame such as an aluminum agent.

The amorphous silicon solar cell module formed on the glass substrate is also protected on the surface by a thick glass plate like the crystalline silicon solar cell module.

Conventionally, such a solar cell module has a weight of 13 to 15 kg per square meter area, and when installed on a roof, it is not easy to handle due to its heavy weight, and not only that, but also heavy equipment. It was necessary to install the solar cell module on top of the roof, which was installed on the roof. Therefore, the installation time, the installation cost, and the pedestal cost are required.

Among the amorphous silicon solar cell modules, a metal substrate such as stainless steel is used as the substrate material because it is excellent in weather resistance, impact resistance and flexibility. A solar cell module using a metal substrate has the advantage that it is resistant to impacts and the weight per unit area and generated power is extremely light, but conventionally, like the crystalline module, the end face is held by an aluminum frame. However, the method of installing on a pedestal has been adopted, and the original lightweight of the module of the metal substrate has not been utilized.

Therefore, there has been a strong demand for the development of a roof-integrated solar cell module which is lightweight, easy to install, inexpensive, and highly reliable.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a roof-integrated solar cell module which is lightweight, easy to install, inexpensive, and excellent in long-term reliability.

[0011]

The present invention solves the above-mentioned problems and achieves the above-mentioned objects.
Achieved by a roof-integrated solar cell module characterized in that the metal roof and the solar cell panel are fixed on both sides in a roof-integrated solar cell module in which the solar cell panel is fixed on the metal roof can do.

Further, the double-sided tape is preferably composed of a polymer resin substrate and an adhesive material, and the double-sided tape has a tensile strength and a breaking elongation of 5 kg / cm, respectively.
It is preferably ² or more and 200% or more, and the thickness of the double-sided tape is preferably 0.5 mm or more. Further, it is more preferable that the polymer resin substrate of the double-sided tape is an acrylic foam having closed cells.

The solar cell element of the solar cell panel is preferably an amorphous silicon semiconductor formed on a stainless substrate.

[0014]

In the solar cell module of the present invention, since the metal roof and the solar cell panel are fixed by the double-sided tape, conventionally, a crystalline solar cell module or a polycrystalline solar cell module having a thick glass plate, or a glass substrate Since the pedestal for installing the solar cell module, which was necessary for the amorphous silicon solar cell module and the like, is unnecessary, the weight of the solar cell panel on the roof is reduced by the amount of the pedestal, and It is possible to eliminate the cumbersome work of installing a gantry.

Further, the ratio of the cost of the frame to the total cost of the solar cell module is large, and in some cases, the cost of the frame is higher than the cost of the solar cell panel. By using the double-sided tape for joining the metal roof and the solar cell panel, it is possible to significantly reduce the cost of the solar cell module.

Further, by using an elastic polymer substrate as the substrate of the double-sided tape, it is possible to absorb the stress generated between the solar cell panel and the metal roof due to the temperature change, and further to prevent the impact from the outside. On the other hand, it becomes possible to play the role of a cushion.

Further, since the polymer resin substrate of the double-sided tape is an acrylic foam having closed cells, the elasticity is increased and the weather resistance is also excellent. Further, since the bubbles are not communicated with each other, moisture such as rain is double-sided tape. The durability of the double-sided tape itself can be increased without invading the inside of the.

Furthermore, by using an amorphous silicon semiconductor formed on a stainless substrate for a solar cell element of a solar cell panel, a surface coating material such as a fluorine resin film can be used instead of a glass plate. Next to
As a result, the weight of the solar cell panel can be significantly reduced, the double-sided tape can be further reduced, and it is possible to provide a further inexpensive roof-integrated solar cell module.

(Embodiment Example) Hereinafter, an embodiment example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example in which a solar cell panel is fixed on a metal roof by using a double-sided tape. 1A is a perspective view, FIG. 1B is a top view of FIG. 1A, and FIG. 1C is a sectional view taken along the line AA ′ of FIG.

In FIG. 1, (101) is a metal roof, and (2)
Reference numerals 01) to (204) are solar cell panels, and (301) is a double-sided tape for fixing the solar cell panel to the metal roof. (401) is a junction box for taking out terminals, (501) is a connecting cord, and (502) is a connector for connecting adjacent solar cell panels. (60
1) is a support plate for a metal roof. In FIG. 1, the method of fixing the solar cell panel to the metal roof with the double-sided tape is to apply the double-sided tape to the solar cell panel in advance and then apply pressure to each solar cell panel on the metal roof with a jig such as a roller. You can It is also possible to first attach the double-sided tape on the metal roof and then attach the solar cell panel.

The double-sided tape (301) used in the solar cell module of the present invention is preferably composed of a polymer resin base and an acrylic adhesive material, and the base of the double-sided tape is a polymer resin base such as polyester, acrylic or rubber. Or cloth,
Although there are papers and the like, a polymer resin substrate is preferable in consideration of elasticity and durability.

Next, the adhesive material of the double-sided tape is mainly made of rubber,
It can be classified into acrylic type, silicone type, polyvinyl ether type, epoxy type, etc. However, considering adhesive strength, weather resistance, cost, and long-term reliability, acrylic and silicone type, polyvinyl ether type, epoxy type adhesive materials Are preferred, and acrylic and silicone adhesives are more preferred.

Among the adhesive materials, there are general-purpose adhesive materials and permanent adhesive (strong adhesive) adhesive materials, but permanent adhesive adhesive materials are preferred for the purpose of fixing the solar cell panel outdoors.

The double-sided tape used in the present invention has a tensile strength and elongation at break of 5 kg / cm ^2, respectively.
It is preferably at least 200%. When fixing a solar cell panel to a metal roof, the double-sided tape itself needs to absorb the strain because the heat shrinkage rate of the metal roof is different from that of the solar cell panel. When the tensile strength and elongation at break of the double-sided tape are less than 5 kg / cm ^{2 and} less than 200%, the double-sided tape cannot absorb the strain due to the difference in thermal expansion and contraction rates of the metal roof and the solar cell panel, resulting in the outdoor use With the passage of time, the adhesive strength weakens and finally the metal roof and the solar cell panel come off. Here, the tensile strength and the elongation at break are obtained from the strength and elongation at break when the double-sided tape is punched in the length direction with a dumbbell cutter (JIS No. 3), the release paper is peeled off, and the double-sided tape is pulled at 500 mm / min. .

The tensile strength of the double-sided tape is shown in FIGS. 6 and 7.
Degree and elongation at break and maintenance of T-type peeling force after 1 year of outdoor exposure
The relationship with the special rate (%) is shown. Tensile strength is 5 kg /
cm ²Is less than 100% and the elongation at break is less than 200%
You can see that is decreasing.

The thickness of the double-sided tape used in the present invention is preferably 0.5 mm or more. The solar cell panel and the metal roof are flat, but they are partially wavy or have a slightly different thickness, so if the thickness of the double-sided tape is less than 0.5 mm, the double-sided tape will not be partially attached or pressure will be applied. May not be transmitted evenly.

Further, it is particularly preferable that the polymer resin substrate of the double-sided tape used in the present invention is an acrylic foam having closed cells. Acrylic foam has more elasticity and weather resistance than other polymer resin substrates such as polyester and polypropylene. In addition, since the closed cells can prevent moisture and humidity from entering the inside of the double-sided tape, it is possible to achieve a roof-integrated solar cell module having excellent moisture resistance and long-term reliability. it can.

Before the metal roof and the solar cell panel are bonded with the double-sided tape, the solar cell panel and the metal roof surface may be pretreated in advance. For example, an organic solvent such as IPA (isopropyl alcohol) or acetone can be used to remove dust, dirt, water and the like. In addition, the surface energy of the adherend is increased, and the surface is roughened with a weak acid to improve the adhesiveness, corona discharge treatment method, mechanically roughened the surface by polishing, silane-based or acrylic-based. The method of applying a primer (undercoating liquid) can be selected as necessary.

The solar cell element of the solar cell panel of the present invention is preferably an amorphous silicon semiconductor formed on a stainless steel substrate. An amorphous silicon semiconductor formed on a stainless steel substrate can be thinned to a thickness of about 0.1 mm, and it is not necessary to use glass as a surface coating material, and a surface coating material such as a fluorine resin film can be used. Therefore, the weight of the solar cell panel itself can be significantly reduced to 1/2 to 1/4 as compared with the solar cell panel using glass. By using such a lightweight solar cell panel, the effect of the double-sided tape for joining the metal roof and the solar cell panel can be further enhanced, and a lightweight, inexpensive, and long-term reliable solar cell module is provided. be able to.

(Roof) The metal of the metal roof used in the present invention is not particularly limited as long as it is a metal having weather resistance. For example, a plated steel plate such as a zinc iron plate or a galvalume steel plate, or a fluorine resin or There are steel plates, titanium plates, stainless steel plates, etc. that have weather resistant materials such as vinyl chloride. Further, there is no particular limitation as to the type of construction method of the metal roof of the present invention, for example, a folded plate, a roof tile, a sidewalk, corrugated sheet,
Stands include standing seams.

(Solar Cell Panel) Since the solar cell panel used in the present invention is fixed to the metal roof with double-sided tape,
Light weight is preferable. Therefore, in the solar cell panel used in the present invention, it is preferable to use a solar cell element having an amorphous silicon semiconductor layer formed as a photoelectric conversion member on a conductive substrate having excellent mechanical strength. The surface layer on the incident side is covered with a weather-resistant transparent material.
For example, one having a two-layer structure of a fluorine resin film / EVA (ethylene-vinyl acetate copolymer) (a fluorine resin film on the light incident side), a silicone resin, a fluorine resin and the like can be mentioned.

The back surface material of the solar cell panel bonded with the double-sided tape is not particularly limited, but a material having a large surface energy (dyne / cm) is preferable. Specifically, the surface energy of the surface to which the double-sided tape adheres is 30d.
It is preferably yne / cm or more. If the surface energy of the surface to be adhered is less than 30 dyne / cm, it is generally difficult to adhere.

(Photovoltaic Element) The solar cell panel used in the solar cell module of the present invention comprises at least one photovoltaic element, and as an example, the structure shown in the schematic sectional view of FIG. 5 (b). It has become. In FIG. 5B, (513) is a conductive substrate, (514) is a back reflection layer,
(515) is a semiconductor layer as a photoelectric conversion member, and (51)
6) is a transparent conductive layer, and (517) is a collecting electrode. (5
The back surface reflection layer of 14) can also serve as the conductive substrate of (513).

As the conductive substrate (513), stainless steel, aluminum, copper, titanium, carbon sheet,
Examples thereof include galvanized steel sheets, polyimide, polyester, polyethylene naphthalide, epoxy, and other resin films on which a conductive layer is formed, and ceramics.

As the thin film semiconductor layer (515), a compound semiconductor such as an amorphous silicon semiconductor, crystalline silicon or copper indium selenide is suitable. In the case of an amorphous silicon semiconductor, it is formed by plasma CVD using silane gas or the like. In the case of a polycrystalline silicon semiconductor,
It is formed by forming a sheet of molten silicon or by heat treatment of an amorphous silicon semiconductor.

In the case of CuInSe ₂ / CdS, it is formed by a method such as electron beam evaporation, sputtering, electrodeposition (deposition by electrolysis of an electrolytic solution) or the like. As a structure of the semiconductor layer, a pin junction, a pn junction, or a Schottky junction is used. The semiconductor layer is at least the back electrode layer (51
4) and the transparent conductive layer (516) are sandwiched. A metal layer, a metal oxide, or a composite layer of a metal layer and a metal oxide layer is used for the back electrode layer (514). The material of the metal layer is Ti, A
1, Ag, Ni, etc. are used, and Z is used as the metal oxide layer.
nO, TiO ₂ , SnO ₂ or the like is adopted. Resistance heating vapor deposition as a method of forming the metal layer and the metal oxide layer,
Electron beam evaporation, sputtering method, spray method, CV
D method, impurity diffusion method and the like. Further, as the material of the collector electrode (517) on the grid for efficiently collecting the current generated by the photovoltaic power on the transparent conductive layer, Ti, Cr, Mo, W, Al is used. , Ag, N
A conductive paste such as i, Cu, Sn and silver paste is used. The grid electrode can be formed by sputtering using a mask pattern, resistance heating, vapor deposition such as CVD, or by depositing a metal layer on the entire surface and then etching and patterning, or directly forming the grid electrode pattern by photo-CVD. Method, a method of forming by plating after forming a negative pattern mask of the grid electrode, a method of forming a conductive paste by printing, and the like. The conductive paste is usually fine powder gold, silver,
A material in which copper, nickel, carbon or the like is dispersed with a binder polymer is used. Examples of the binder polymer include resins such as polyester, epoxy, acrylic, alkyd, polyvinyl acetate, rubber, urethane and phenol.

As the material of the bus bar for further collecting and feeding the current collected by the grid electrode, tin, solder coated copper, nickel or the like is used.
The connection of the bus bar to the grid electrode is made with a conductive adhesive or solder.

(Electrical Connection Between Solar Cell Panels) The method for electrically connecting the solar cell panels is not particularly limited, and can be arbitrarily determined according to the voltage, current and power of the solar cell module used.

FIG. 1 shows solar cell panels (202) and (2).
01), (201) and (203), (203) and (20
This is an example in which 4) is connected in series. Here, (401) is a junction box, (501) is a lead wire, (50)
2) is a waterproof connector. The solar cell panel may be connected without using a junction box or the like.
Further, the solar cell panels can be connected with a connecting cord using the space of the metal roof.

[0041]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 This example is an example in which a solar cell panel is fixed on a roof tile type metal roof with double-sided tape.

FIG. 2 is a view of the roof integrated solar cell module of this embodiment.

The metal roof of this embodiment is a roof tile type roof, and an amorphous silicon semiconductor formed on a stainless steel substrate is used for the solar cell panel, and both are made into an acrylic foam having completely closed cells. This is an example of joining with a double-sided tape containing a permanent adhesive.

In FIG. 2, (240) is a roof tile type metal roof, and a 0.4 mm thick galvalume steel plate (55% aluminum-zinc alloy iron plate) was used as the roof material. Also (2
80) is a heat insulating material, (281) is a purlin, (282)
Is an asphalt roofing. Also, (220)
Is an amorphous silicon semiconductor device formed on a stainless steel substrate, (210) is a solar cell panel in which an amorphous silicon semiconductor device is resin-sealed, and (230) is acrylic permanent bond to acrylic foam having completely closed cells. A double-sided tape with an agent, (250) a junction box for taking out terminals, (260) a lead wire, and (270) a waterproof connector.

A fluorine resin film was used for the light incident side surface of the solar cell panel (210), and a laminated film in which an aluminum foil was sandwiched between the fluorine resin films was used for the back surface. In addition, the surface of the backside fluororesin film and the surface of the frontside fluororesin film opposite to the incident light side is subjected to corona discharge treatment in order to enhance the adhesiveness.

EVA (ethylene-vinyl acetate copolymer) is provided between the fluorine resin film on the front surface of the solar cell panel (210) and the amorphous silicon semiconductor element, and between the laminate film on the back surface and the amorphous silicon semiconductor element. )
Was filled as an adhesive layer, and these were prepared by a vacuum laminating method.

The photovoltaic element was prepared by the following procedure.

0. On a stainless steel substrate with a thickness of 125 mm,
Form Al / ZnO which is the back surface reflection layer by the putter method
After that, an n-type a-Si layer, i
A semiconductor layer of a p-type a-Si layer and a p-type microcrystalline Si layer is formed,
Next, In as a transparent electrode layer ₂O₃To O₂I in the atmosphere
It was formed by vapor deposition of n by a resistance heating method. Furthermore
Screen-print a silver paste as a collector electrode on the
A rufus silicon photovoltaic device was created.

Next, the method of attaching the solar cell panel to the metal roof was performed as follows.

First, a double-sided tape in which an acrylic adhesive having completely closed cells and an acrylic adhesive is attached to the entire back surface of the solar cell panel (double-sided tape manufactured by Sumitomo 3M = “Y-
4950 ") is applied with a roller by applying a pressure of 10 kg / cm ² , and then the roof tile type metal roof (240)
The above-mentioned solar cell panel was adhered to the top by holding a pressure of 10 kg / cm ² with a roller.

The double-sided tape used here has a thickness of 1.1.
mm, tensile strength (kg / cm ² ) and elongation at break (%) are 12 (kg / cm ² ) and 600 (%), respectively.
Is.

Then, the solar cell panels were connected to each other with a waterproof connector. A metal roof with a solar cell panel bonded was installed on the south side at an installation angle of 22 ° and an outdoor exposure test was conducted.

(Embodiment 2) In this embodiment, a tiled bar type folding roof using a 0.8 mm galvalume steel plate on the metal roof as shown in FIG. 3 was used.

FIG. 3 (a) is a sectional view thereof, and FIG. 3 (b) shows the position of the double-sided tape attached to the solar cell panel.
The double-sided tape was attached only to both ends of the back surface material of the solar cell panel.

The photovoltaic element of this example was prepared in the same manner as in Example 1. Next, the terminals of the solar cell panel (310) of the present example are taken out from the back surface of the solar cell panel, connected to the adjacent element using the flat cable (360), and then taken out with a silicone resin (370). Was sealed.

Next, the same double-sided tape as in Example 1 was applied to the connected solar cell panel as shown in FIG. 3 at 10 kg / cm.
The pressure of ² was applied with a roller and it stuck.

The folded metal roof was prepared as follows. First, a tight frame (341) on the purlin (350)
After welding, the roofing material (344) was installed between the tight frames. Next, the adjacent roofing material (344) was fixed with a partial hanging member, and the cap (342) was covered.

A solar cell module was produced by sticking the above-mentioned solar cell panel on the roof material of this folded plate as shown in FIG. 3 (a).

The solar cell module of the present embodiment is the first embodiment.
An outdoor exposure test was conducted in the same manner as in.

(Results of Outdoor Exposure Test) FIG. 4 shows the results of outdoor exposure tests of the solar cell modules of Examples 1 and 2. The adhesive force between the solar cell panel and the metal roof was examined by T-type peeling force.

As is clear from FIG. 4, the solar cell module of the present invention was a good solar cell module with almost no decrease in adhesive strength due to the outdoor exposure test.

(Embodiment 3) In this embodiment, by devising the shape of the double-sided tape for attaching the solar cell panel and the metal roof, the rain flowing between the solar cell panel and the metal roof is allowed to flow only in a certain direction. . FIG. 8 shows the structure of the roof integrated solar cell module of this example.

FIG. 8 (a) is a diagram showing the shape of the double-sided tape when the double-sided tape is previously attached to the back surface of the solar cell panel, and FIG. The panel was mounted on the metal roof in such a direction that the position A was higher.

In FIG. 8, (811) is a solar cell module, (812) is a double-sided tape affixed in a shape that allows rain to flow only in a fixed direction, and (813) is a metal roof.

In the solar cell module of this embodiment, even if it rains, the inner side surface of the double-sided tape attached to the solar cell panel is not directly exposed to rain, so that the decrease in adhesive strength due to moisture is suppressed. As a result, it has been possible to provide a roof-integrated solar cell module having excellent long-term reliability even with a small amount of double-sided tape. Further, since rainwater does not stay between the back surface of the solar cell panel and the surface of the metal roof, deterioration of the performance of the solar cell due to temperature can be reduced.

[0067]

In the solar cell module of the present invention, since the metal roof and the solar cell panel are fixed by the double-sided tape, the frame for installing the solar cell panel is unnecessary, and the intestinal cell panel on the roof is unnecessary. The weight of the unit was reduced by the amount of the gantry, and the complicated work of installing the gantry could be eliminated.

Further, since the mount for installing the solar cell panel is unnecessary, it is possible to significantly reduce the cost of the solar cell module.

Since an acrylic adhesive was used as the adhesive for the double-sided tape, long-term reliability outdoors could be ensured.

Further, by using an elastic polymer substrate as the substrate of the double-sided tape, it is possible to absorb the stress generated between the solar cell panel and the metal roof due to the temperature change, and further to prevent the impact from the outside. On the other hand, it became possible to play the role of a cushion.

Furthermore, since the polymer resin substrate of the double-sided tape is an acrylic foam having closed cells, the elasticity is increased and the weather resistance is also excellent. Further, since the bubbles are not communicated with each other, moisture such as rain can get on the double-sided tape. It was possible to increase the durability of the double-sided tape itself without penetrating inside.

Furthermore, by using an amorphous silicon semiconductor formed on a stainless steel substrate for the solar cell element of the solar cell panel, the weight of the solar cell panel can be greatly reduced, and the amount of double-sided tape is further reduced. In addition, it is possible to provide an inexpensive roof-integrated solar cell module.

[Brief description of drawings]

FIG. 1 is a diagram of a solar cell module according to an embodiment of the present invention.

FIG. 2 is a solar cell module according to an embodiment of the present invention.

FIG. 3 is a solar cell module according to another embodiment of the present invention.

FIG. 4 shows the results of an outdoor exposure test.

FIG. 5 is a photovoltaic device of the present invention.

FIG. 6 is a diagram showing a relationship between tensile strength and T-type peeling force retention rate.

FIG. 7 is a diagram showing a relationship between elongation at break and retention rate of T-type peeling force.

FIG. 8 is a solar cell module according to another embodiment of the present invention.

[Explanation of symbols]

 101: Metal roof, 201: Solar cell panel, 202: Solar cell panel, 203: Solar cell panel, 204: Solar cell panel, 301: Double-sided tape, 401: Junction box, 501: Lead wire, 502: Waterproof connector, 601 : Purlin, 210: Solar cell panel, 220: Solar cell element, 230: Double-sided tape, 240: Metal roof 250: Junction box, 260: Lead wire, 270: Waterproof connector, 280: Heat insulating material, 281: Purlin, 282: Asphalt roofing, 310: Solar cell panel, 330: Double-sided tape, 340: Metal roof, 341: Tight frame, 342: Cap, 343: Partial suspension member, 344: Roofing material, 350: Purlin, 370: Silicon resin, 360: Flat cable, 5 13: conductive substrate, 514: back surface reflection layer, 515: semiconductor layer 516: transparent conductive layer, 517: collector electrode 811: solar cell panel, 812: double-sided tape, 813: metal roof.

Claims (6)

[Claims] 1. A roof-integrated solar cell module in which a solar cell panel is fixed on a metal roof, wherein the metal roof and the solar cell panel are fixed by a double-sided tape. 2. The roof-integrated solar cell module according to claim 1, wherein the double-sided tape comprises a polymer resin substrate and an adhesive material. 3. The roof-integrated solar cell module according to claim 1, wherein the double-sided tape has a tensile strength and a breaking elongation of 5 kg / cm ² or more and 200% or more, respectively. 4. The roof integrated solar cell module according to claim 1, wherein the double-sided tape has a thickness of 0.5 mm or more. 5. The roof integrated solar cell module according to claim 2, wherein the polymer resin substrate of the double-sided tape is an acrylic foam having closed cells. 6. The roof-integrated solar cell module according to claim 1, wherein the solar cell element of the solar cell panel is an amorphous silicon semiconductor formed on a stainless steel substrate.