JP2001127323A - Insulating metallic foil band for solar cell board coated with polyimide-based paint thin film, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an insulating metallic foil band for a solar cell board coated with a very small amount of paint a thickness of which can be accurately controlled and which has a high insulating performance without any defects such as pin holes. SOLUTION: A paint-coated metallic foil band is made by coating a polyimide-based paint on a metallic foil band with use of a plate cylinder roll having a uniform plate groove density in a roll longitudinal direction by means of a roll coater of a gravure or offset type and drying it. Upon its manufacturing, it is desirable that the plate cylinder roll have a diameter of less than 100 mm and that 20 or more sheet grooves per inch are applied to a roll surface. Prior to coating of the polyimide-based paint, it is preferable to degrease the metallic foil band with an organic solvent or an alkaline solution and to perform pickling and coating type chromate treatment over it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell substrate coated with a polyimide paint capable of controlling a film thickness with high precision with a small amount of paint and forming a coating film having high insulation without defects such as pinholes. It relates to an insulating metal foil strip.

[0002]

2. Description of the Related Art Glass and the like have been used for insulating substrates used for solar cells. However, flexible insulating substrates are required so that a place where a solar cell is formed can be bent. A film such as polyimide is used.
However, since the film is accompanied by a small amount of elongation due to heating during the formation of the solar cell, shrinkage during cooling causes cracks or the like in the cell, lowering the power generation efficiency, and causing a reduction in yield. In addition, since rigidity is required to maintain a constant shape, an insulating substrate in which a metal plate is coated with an insulating film has attracted attention. Heating temperature during cell formation is 200
Since the temperature is up to 350 ° C., a polyimide coating is applied to the insulating coating as a coating that can withstand this.

[0003] In the case of applying a polyimide-based paint to a metal foil strip by a roll coating method, the metal foil is wound around a backing roll, the polyimide-based paint put in a pan is picked up by a pickup roll, and transferred to an application roll. A method of transferring to a metal foil strip by a natural method or a reverse method is used.

[0004] In this case, the amount of application is determined by adjusting the pressing force between the pickup roll and the application roll according to the roll hardness, shape, and the like, and by adjusting the drawing. However, since a rubber roll having a smooth surface is generally used as the application roll, it is difficult to make the pressing force uniform by adjusting the application amount.
Since the squeezing of the paint is also uneven, the coating thickness in the width direction of the metal foil is also uneven.

Further, in order to reduce the thickness of the coating film, it is necessary to increase the pressing force of both the pickup roll and the application roll. When both pressures are large, there is a limit in that the application roll is damaged or a rotational load is applied.

[0006]

Although solar cells are used for roofs and watches, there is a demand for weight reduction, miniaturization and cost reduction of products, especially expensive paints such as polyimide-based paints. In this case, the thickness of the insulating film is designed to be as thin as about several μm. Therefore, the control range of the film thickness needs to be on the order of submicrons. As described above, in the conventional roll coating method, the ability to control the coating thickness in the roll longitudinal direction and the width direction is limited, and has a variation of about several μm. There is a demand for a coating method in which the ability to control the coating thickness in the roll longitudinal direction and width direction is on the order of submicrons.

Further, in the roll coating method, if the pressure of the roll is increased in order to reduce the amount of coating, there is a problem that the roll surface is dried and coating unevenness is likely to occur. As a coating method in which the paint is sufficiently squeezed and coating unevenness does not occur, mainly the material of the roll was examined, but none of them was solved.

On the other hand, the insulation required for a solar cell substrate is
Since it is on the order of MΩ / cm ² , even a pinhole having a diameter on the order of submicron may cause a loss in required sheet resistance. In the case of applying by a roll coating method, it is necessary to modify the surface of the metal foil strip so that pinholes on the order of submicron do not occur.

[0009]

According to the present invention, a polyimide coating material is applied to a metal foil strip by a gravure method or an offset method using a roll coater using a plate cylinder roll having a uniform plate groove density in the roll longitudinal direction, It is a coated metal foil strip obtained by drying, which satisfies both thinning and good insulating properties.

In the production, it is desirable to use a plate cylinder roll having a diameter of less than 100 mm and a roll surface spirally formed with at least 20 rolls per inch on the roll surface. In addition, it is preferable that the metal foil strip is degreased with an organic solvent or an alkali solution before the application of the polyimide-based paint, and is subjected to pickling or a coating type chromate treatment.

[0011]

[Function] In the gravure method or offset method, a doctor knife is brought into contact with a metal plate cylinder roll to scrape off excess paint, so that only polyimide-based paint adheres to the plate cylinder roll in the plate groove. . If a plate cylinder roll having a uniform plate groove density in the longitudinal direction is used, the coating amount in the width direction of the metal foil strip to be coated becomes uniform.

In the gravure method, as shown in FIG. 1, the plate cylinder roll draws up the paint and becomes the application roll as it is, so that there is no drying on the roll surface and application unevenness can be prevented. In the offset method, as shown in FIG. 2, the paint adhered to a metal plate cylinder roll is transferred to a rubber cylinder roll, and then transferred to a metal foil strip, so that the coating thickness of the polyimide-based paint becomes uniform. . The diameter of the plate cylinder roll is 100m
When the thickness is less than m, the coating film does not dry on the roll surface and coating unevenness can be prevented.

The plate groove of the plate cylinder roll is, as shown in FIG.
To make it easier to draw up the polyimide paint and to reduce the contact resistance with the metal foil strip, if the density is set to 20 or more per inch, the coating thickness will be 4-6.
μm or less, and the accuracy can be applied in the submicron range. If the number is less than 20, the thickness of the coating film becomes too thick, exceeding the design value of the insulating film required for the solar cell substrate.

At the time of coating, the metal foil strip is stretched with two separated impression cylinder rolls and applied by a method in which the metal foil plate cylinder roll is brought into contact between the impression cylinder rolls. Since it does not contact the roll, the life of the plate cylinder roll is prolonged.
In addition, no scratch is generated on the metal foil strip due to rubbing of the roll.
In addition, bubbles generated when the paint is stirred cause pinholes in the coating film, but it is necessary to prevent pinholes that cause short circuits in the insulating film for a solar cell substrate as much as possible.
Conventionally, a roll with a large diameter was used, so a lot of air bubbles were generated when the paint pumped up by the roll rotation dropped into the paint pan, and the paint containing the air bubbles pumped by the roll entrained the air bubbles in the object to be coated It is transferred in shape and affects the coated surface. In the present invention, since the roll diameter is as small as less than 100 mm, the distance over which the drawn paint falls into the paint pan is short, and bubbles are hardly mixed into the paint. Therefore, a good coated surface can be obtained.

[0015] The metal foil strip coated with the polyimide-based paint is
A heat-drying treatment is performed to form a polyimide coating film.
The heat drying treatment is preferably performed at 300 to 400 ° C. If the temperature is lower than 300 ° C., the reaction speed of imidization is slow, so that the line speed needs to be extremely low in order to sufficiently sinter in the continuous coating line of the metal foil strip, which is not practical in terms of productivity. 400 ℃
Above, a decomposition reaction of the polyimide-based coating film occurs, so that the heat resistance of the coating film decreases.

In order to prevent pinholes from being generated on both the plate cylinder roll and the impression cylinder roll, it is preferable to rotate the metal foil strip in a direction opposite to the moving direction.

As means for preventing the occurrence of pinholes,
It is desirable to degrease the metal foil strip with an organic solvent or an alkaline solution before applying the polyimide paint. Although ordinary metal foil strips have a thin gauge thickness by rolling, rolling oil is used as a lubricant during rolling, and most of the surface oil has been removed by degreasing afterwards, Depending on the surface finish, oil may remain in fine gaps on the surface. Also, if the coil after degreasing is left for a long period of time, organic matter in the air will adhere and repel the paint during painting, causing pinholes. Even if the adhesion of organic matter is at a level that does not cause a problem in a normal coated steel sheet, pinholes on the order of submicron that can cause a short circuit in the insulating film of the solar cell substrate can occur. As the degreasing liquid, an organic solvent such as trichlene or methacrene or an alkaline solution such as an aqueous sodium hydroxide solution is suitable, and the degreasing effect is enhanced when it is heated to 30 to 70 ° C. and used.

Further, if the metal foil strip is pickled before the application of the polyimide-based paint, it is effective in preventing the occurrence of pinholes.
Even when the surface cleaning by degreasing is insufficient, the remaining organic components can be removed by performing surface etching by pickling.
As the pickling liquid, there are phosphoric acid-based, hydrochloric acid-based, sulfuric acid-based, and hydrofluoric-acid-based liquids, which are selected and used depending on the etching effect on the underlying metal.

Further, if a coating type chromate treatment is applied to the metal foil strip before applying the polyimide-based paint, the occurrence of pinholes can be prevented with high precision. The coating type chromate treatment film covers the remaining organic components on the surface of the metal foil strip, not only prevents the occurrence of pinholes due to the repelling of the polyimide paint, but also improves the adhesion between the polyimide paint and the metal foil strip,
Further, the corrosion resistance of the metal foil strip can be improved.

The production of the coated metal strip using the polyimide-based paint of the present invention can be applied to any metal foil without limiting the kind of metal used as the base material of the metal foil strip. For example, there are iron foil, aluminum foil, copper foil, stainless steel foil, titanium foil, zinc plating foil, copper plating foil, aluminum plating foil, nickel plating foil, and foil obtained by cladding different metals.

[0021]

EXAMPLE 1 An example of the production of a metal foil strip coated with a polyimide-based paint by the gravure method will be described with reference to FIG. The metal foil strip 1 is adjusted by two spaced-apart parallel impression cylinder rolls 2 and 2a, and a gravure printing machine 3 is arranged between the impression cylinder rolls 2 and 2a. The gravure printing machine 3
The plate cylinder roll 4 is arranged so as to be on the opposite side to the metal impression cylinder rolls 2 and 2a with the metal foil strip 1 as a boundary, and the plate cylinder roll 4 is brought into contact with the metal foil strip 1. In this state, the metal foil strip 1 is moved from right to left as viewed in FIG. The gravure printing machine 3
The polyimide paint 6 is put into the paint pan 5 and the plate cylinder roll 4
Is to immerse the lower part in the paint 6 and the doctor knife 7
And rotate counterclockwise. Plate cylinder roll 4
A spiral plate groove 8 as shown in FIG. 3 was used.

The polyimide paint 6 is obtained by dissolving a polyimide resin in an organic solvent. Drying after painting,
The firing was performed under the condition that the temperature of the metal foil strip reached 350 ° C. The plate cylinder roll 4 used had a diameter of 25 mm and a spiral plate groove at a density of 70 per inch. The metal foil strip used was a SUS304 2B finish having a thickness of 0.05 mm and a width of 300 mm.

Example 2 An example of a method for producing a metal foil strip coated with a polyimide-based paint by an offset method is shown in FIG.
It is explained according to. An offset printing press 9 was arranged in place of the gravure printing press 3 used in Example 1. The offset printing press 9 puts the polyimide-based paint 6 in the paint pan 5 and immerses the lower part of the metal plate cylinder roll 4 in the paint 6.
The doctor knife 7 was arranged on the right side. Above the plate cylinder roll 4, a rubber drum roll 10 is arranged adjacent to the plate cylinder roll 4, and paint 6 is pumped up from the paint pan 5 by the plate cylinder roll 4.
The paint is transferred from the plate cylinder roll 4 to the cylinder roll 10 and further to the metal foil strip 1. The metal foil strip 1 is extruded in the direction of the impression cylinder rolls 2 and 2a. In this state, the metal foil strip 1 is moved from right to left as viewed in FIG. 10 rotates counterclockwise.

The polyimide coating used, the drying conditions after coating, and the metal foil strip used are the same as in Example 1. The plate cylinder roll 4 had a diameter of 50 mm and a spiral plate groove at a density of 90 per inch. The body roll 10 has a diameter of 50
mm.

[Embodiment 3] The spiral plate groove of the plate cylinder roll is set to 1
The procedure was performed in the same manner as in Example 1 except that the number of wires per inch was 30.

Example 4 The same procedure as in Example 1 was carried out except that the diameter of the plate cylinder roll was 90 mm.

Example 5 The same procedure as in Example 1 was carried out except that the metal foil strip was degreased with an aqueous sodium hydroxide solution before the application of the polyimide-based paint.

Example 6 The procedure of Example 1 was repeated, except that the metal foil strip was pickled with a phosphoric acid aqueous solution before the application of the polyimide-based paint.

Example 7 The same procedure as in Example 1 was carried out, except that the metal foil strip was subjected to a coating type chromate treatment before the application of the polyimide paint.

Example 8 The same procedure as in Example 1 was carried out except that the diameter of the plate cylinder roll was changed to 150 mm.

[Embodiment 9] The spiral plate groove of the plate cylinder roll is set to 1
The procedure was performed in the same manner as in Example 1 except that the number of wires per inch was 10.

Comparative Example 1 A conventional roll (diameter 200 mm, roll surface smooth) was used instead of the plate cylinder roll.
The procedure was performed in the same manner as in Example 1.

(Coating Film Performance Evaluation Method and Evaluation Results) [Coating Appearance] The coating film surface was visually observed, and the coating appearance was judged based on the presence of roll eyes, coating unevenness, and the like. The normal surface was rated as ○, and the case where there was an abnormal portion was rated as ×.

[Film Thickness Controllability] The film thickness was measured at the center in the width direction of the metal foil strip on which the polyimide-based coating film was formed.
The position of the left edge and the right edge, and for each position in the width direction, the reference point in the longitudinal direction, in the longitudinal direction from the reference point
Point moved by 1000mm and 2000mm in the longitudinal direction from the reference point
A total of nine points were measured as points moved. The evaluation of thinning was evaluated as ○ when the average value of the 9 measurement points was 6 μm or less, Δ when the average value was 10 μm or less, and × when the average value exceeded 10 μm. In addition, the evaluation of the film thickness fluctuation is as follows.
Less than ○, less than 2 μm, Δ, 2 μm or more. , ○
And △ were accepted.

[Insulation] A metal foil strip on which a polyimide coating film was formed was sampled at a length of 300 mm in the longitudinal direction (sample size: 300 × 300 mm), and an Al electrode having a diameter of 50 mm was placed on the painted surface side in both the width direction and the longitudinal direction. A total of 25 electrodes were formed at 60 mm intervals, a voltage of 1 V was applied between the electrode surface and the back surface of the metal foil strip, and the number of electrodes having an area resistance of MΩ · cm ² or more was evaluated. MΩ
A sample in which the number of electrodes having cm ² or more was 25 was evaluated as ◎, 23 or more as 、, 20 or more as △, 19 or less as ×, and ◎, △ and △ were accepted.

The metal foil strips on which the polyimide-based coating films were formed in Examples 1 to 9 and Comparative Example 1 were evaluated as follows. Table 1 shows the results.

[0037]

[Table 1]

[0038]

As described above, according to the present invention, the width of the metal foil strip coated with the polyimide-based paint and the coating thickness in the longitudinal direction can be made uniform and the film thickness can be reduced at the same time. Its accuracy is improved. In addition, the metal foil strip is not damaged due to little wear of the coating roll. By defining the diameter of the coating roll and rotating the coating roll in the direction opposite to the direction of movement of the metal foil strip, pinholes are less generated in the coating film of the polyimide-based paint. further,
By performing degreasing, pickling, and coating-type chromate treatment on the metal foil strip before applying the polyimide-based paint, pinholes can be prevented, and the insulation properties of the polyimide-based paint film can be improved.

[Brief description of the drawings]

FIG. 1 shows an outline of manufacturing by a gravure method of the present invention.

FIG. 2 shows an outline of manufacturing by a gravure method of the present invention.

FIG. 3 shows an outline of manufacturing by a gravure method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal foil strip 2, 2a Impression cylinder roll 3 Gravure printing machine 1 Plate cylinder roll 2 Paint pan 3 Polyimide paint 4 Doctor knife 5 Spiral plate groove 6 Offset printing machine 7 Body roll

Claims (6)

[Claims] 1. A polyimide-based paint obtained by applying a polyimide-based paint to a metal foil strip by a roll coater of a gravure method or an offset method using a plate cylinder roll having a uniform plate groove density in a roll longitudinal direction and drying. An insulating metal foil strip for a solar cell substrate coated with a thin film. 2. The insulating metal foil strip for a solar cell substrate coated with a polyimide-based paint thin film according to claim 1, wherein the metal foil strip is degreased with an organic solvent or an alkaline solution before coating with the polyimide-based paint. 3. The insulating metal foil strip for a solar cell substrate coated with the polyimide-based paint thin film according to claim 1, wherein the metal foil strip is subjected to an acid washing treatment before the application of the polyimide-based paint. 4. The insulated metal foil strip for a solar cell substrate coated with a polyimide-based paint thin film according to claim 1, wherein a coating-type chromate treatment is applied to the metal foil strip before applying the polyimide-based paint. 5. The insulating metal foil strip for a solar cell substrate coated with a polyimide-based paint thin film according to any one of claims 1 to 4, wherein the film thickness after drying is 10 μm or less. 6. When a polyimide coating material is applied to a metal foil strip by a roll coater by a gravure method or an offset method using a plate cylinder roll having a uniform plate groove density in the roll longitudinal direction, the plate cylinder roll has a diameter. Manufacture of an insulated metal foil strip for a solar cell substrate coated with a polyimide-based paint thin film, characterized in that the roll surface is less than 100 mm and a roll groove is spirally formed at a roll surface of 20 or more per inch. Method.