JP2002047367A - Method of forming metal film on polyimide surface and conductive belt using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of directly forming a metal film having excellent adhesion on a polyimide surface and also to provide a conductive belt which is prepared by this method and is suitably used as carrying belt that is used as a belt transferring and fixing of an image forming device. SOLUTION: In the method of forming the metal film, the polyimide surface is treated with a strong alkali to open an imide ring, and then the metal film is laminated on the surface by the vapor phase growing method. As the conductive belt, the metal film having conductivity when transferred and becoming as an exothermic core when fixed is laminated on the surface of a base layer made of the polyimide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for forming a metal film on the surface of polyimide, and a conductive belt manufactured by the method.

[0002]

2. Description of the Related Art In recent years, in the field of image forming apparatuses such as laser beam printers and electrostatic copiers, miniaturization for full color, high image quality, and space saving is progressing. C), three or four corresponding to three colors of magenta (M) and yellow (Y), or four colors obtained by adding black (K) to the above three colors
It has been required to reduce the size of a full-color device having two built-in developing units to the same size as a conventional monochrome machine.

In order to respond to this demand, the surface of a transport belt for transporting paper in the apparatus is provided with conductivity, and the transport belt is used to transfer a toner image formed on the surface of a photoreceptor to the paper. It is becoming mainstream to reduce the number of parts of the apparatus by making it function also as a transfer belt. Also, recently, it has been studied to further reduce the number of parts by making the above-mentioned transport belt function as a fixing belt for heating and pressing the toner image transferred onto the sheet to fix the toner image on the sheet.

At the time of fixing, the paper must be pressurized at a high temperature of about 120 ° C. or more, so that the transfer belt and the transfer belt, which also serve as the transfer and fixing belts, are complicatedly bent in the apparatus as described above. In consideration of the circulation while passing through the fixing section, etc., it is necessary to use a special material having high heat resistance, high strength, and excellent bending resistance and flexibility as a material for forming the transport belt. is there. As such a special material, there are only a few kinds of synthetic resins. Among them, polyimide (especially, Kapton film (trade name) manufactured by Du Pont-Toray Co., Ltd.) has the formula (10):

[0005]

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[0006] A wholly aromatic polyimide film composed of a repeating unit represented by the following formula is preferably used. In recent years, in order to use the transport belt also as a transfer and fixing belt as described above, a metal film that secures conductivity at the time of transfer and generates heat at the time of fixing is recently coated on the surface thereof by electroless plating. Stacking and forming by a conventionally known film forming method such as a method have been studied.

[0007]

However, the surface of the polyimide is smooth, so that the so-called anchor (anchor) effect cannot be expected, and the polyimide is in a stable state having a small surface energy, and has a low surface energy. When the metal film is formed directly on the surface, the adhesion of the metal film becomes insufficient. As for the metal film with insufficient adhesion, the conveyor belt is bent intricately in the device as described above, applying mechanical shock, and also heating at high temperature in the fixing unit and cooling in other parts. By circulating inside the device while applying thermal shock by repeating
There is a problem that cracks are easily formed or peeled off in a short period of time.

[0008] In order to enhance the adhesion of the metal film, it has been studied to form a primer layer on the surface of polyimide and then laminate the metal film. However, since the material of the primer layer is inferior to polyimide in heat resistance, there is a problem that the heat resistance of the conveyor belt at the time of fixing becomes insufficient. An object of the present invention is to provide a novel metal film forming method capable of forming a metal film having better adhesiveness directly on the surface of polyimide, and a method for producing the same,
An object of the present invention is to provide a conductive belt suitably used as a transfer belt or the like of an image forming apparatus, which also serves as a transfer and fixing belt as described above.

[0009]

Means for Solving the Problems and Effects of the Invention In order to solve the above-mentioned problems, the present inventors chemically treat the surface of polyimide to introduce an active group which becomes a nucleus of metal adsorption, and then form a metal. Various studies have been made on the technology to be used. For example, JP-A-10-245444 discloses that the surface of a polyimide is sulfonated by treating it with sulfuric acid in hydrogen peroxide or acetic anhydride to introduce a sulfo group as an active group, and then neutralize. It is described that this sulfo group is treated with a metal ion-containing liquid to convert the sulfo group into a metal salt of a sulfo group, and the metal ion is reduced to form a metal film.

Kusaka et al., The inventor of the invention described in the above publication, treat the surface of polyimide with a strong alkali to open the imide ring, thereby forming an amide bond and a carboxyl group, both of which function as active groups. It has also been proposed that after forming a metal film, the metal ion is adsorbed by treating with a metal ion-containing liquid in the same manner as described above, and then the metal ion is reduced to form a metal film [Hidemi Nabune, Taro Nishioka, Tsuji Tsuji Haruo, Shozo Mizumoto, Yu Kiyota, Dai Kusaka “Basic Study on Direct Metallization Using Surface Modification of Polyimide and Epoxy Resins” Journal of Japan Institute of Electronics Packaging Vol.2 No.5
(1999)].

However, according to the studies made by the inventors, in both of the above methods, whether the films grown at a plurality of places on the polyimide surface by the reduction treatment are connected to each other by using the metal ion adsorbed on the active group as a nucleus or not. Only a very thin metal film of such a degree as not to be connected can be formed. Therefore, in the above publication, a metal film is further laminated and formed on the metal film by electroplating, and the metal film has a structure discontinuous in the thickness direction.

It is considered that such a discontinuous structure may be used as long as it is an ordinary conductive film. However, this structure is applied to a metal film of a transport belt to which mechanical shock and thermal shock are repeatedly applied as described above. In this case, the adhesion is not yet sufficient, and there is a possibility that cracks or peeling may occur in the metal film. Therefore, the inventors have further studied a method of forming a metal film on the surface of the polyimide into which the active group has been introduced by the above treatment.

As a result, by treating with a strong alkali to open the imide ring, the above-mentioned metal ion is adsorbed and reduced by the above-mentioned metal ion adsorption and reduction on the surface of the polyimide in which an amide bond as an active group and a carboxyl group are formed. It has been found that a metal film having a predetermined film thickness is directly formed by a vapor phase growth method without performing a chemical conversion treatment, and the present invention has been completed. That is, the invention according to claim 1 is to form a metal film on the surface of the polyimide by a vapor phase growth method after treating the surface of the polyimide with a strong alkali to open the imide ring. This is a method for forming a metal film.

In the method for forming a metal film according to the first aspect of the present invention, first, when the surface of the polyimide is treated with a strong alkali, the imide ring of the polyimide located on the outermost surface in contact with the strong alkali is in contact with the strong alkali. The ring is opened by the reaction to generate an amide bond and a carboxyl group, both of which function as active groups that serve as nuclei for metal adsorption. Therefore, in the next step, when a metal film is formed on the surface of the polyimide by vapor phase epitaxy, the film first grows with the metal atom adsorbed on the amide bond and the carboxyl group as a nucleus. In addition, it is possible to form a metal film having a predetermined thickness and a uniform structure which is more excellent in the adhesiveness and continuous in the thickness direction.

[0015] Therefore, at least a surface of the base layer is formed of polyimide, and a metal film is laminated and formed on the surface of the base layer by the method of forming a metal film according to claim 1. The conductive belt according to the third aspect of the present invention is excellent in the adhesion of the metal film, and even if a mechanical shock or a thermal shock is repeatedly applied, in a short time as before. Cracks and peeling of the metal film are prevented.

Therefore, in combination with the fact that the metal film secures conductivity at the time of transfer and serves as a nucleus of heat generation at the time of fixing, the conductive belt serves as a transfer and fixing belt, such as a transfer belt of an image forming apparatus. Can be suitably used.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. << Metal film forming method >> The metal film forming method of the present invention forms a metal film on the surface of a wholly aromatic polyimide composed of the repeating unit represented by the above formula (10), such as the aforementioned Kapton film. It is suitable for.

However, the metal film forming method of the present invention forms a metal film having excellent adhesion on the surface of not only the above-mentioned wholly aromatic polyimide but also various polyimides having an imide ring in the molecule. It is also effective for. In the metal film forming method of the present invention, the surface of the polyimide is first treated with a strong alkali to open the imide ring. Examples of the strong alkali include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

The treatment is performed by immersing the polyimide in an aqueous solution of a strong alkali at a predetermined concentration and temperature for a certain period of time. Among them, the concentration of the strong alkali aqueous solution is preferably about 3 to 7 M in the case of, for example, an aqueous solution of potassium hydroxide in order to perform an efficient and uniform treatment. The temperature of the solution may be around room temperature (23 ± 1 ° C.), but it is preferable to heat the solution to about 40 to 60 ° C. in consideration of performing an efficient and uniform treatment without bias. preferable.

When the polyimide is immersed in a strong alkaline aqueous solution heated to the above temperature for about 3 to 7 minutes, for example, in the case of a wholly aromatic polyimide composed of a repeating unit represented by the above formula (10), As shown in the formula (11), the imide ring of the repeating unit located on the outermost surface in contact with the strong alkali opens as a result of the reaction with the strong alkali to function as an active group that serves as a core of metal adsorption. An amide bond and a carboxyl group are generated.

[0021]

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Next, the treated polyimide is neutralized by dipping in an aqueous solution of an acid or the like, washed with water, dried sufficiently, and then a metal film is laminated on the surface thereof by vapor phase epitaxy. ,Form. As the metal forming the metal film,
Any of various metals that can be formed by a vapor phase growth method can be used, and may be appropriately selected according to the use of the metal film. For example, copper (Cu), aluminum (Al), titanium (Ti), and the like are examples of the metal that forms the metal film formed on the surface of the transport belt that also serves as the transfer and fixing belts described above. Each of these metals is 1
In addition to being able to form a metal film alone, two or more species can be used in combination,
That is, the metal film can be formed in an alloy state.

The vapor phase growth method for forming a metal film on the surface of polyimide includes, for example, (a) glow discharge by applying an electric field in a vacuum or gas atmosphere, such as a DC bipolar sputtering method or a high frequency sputtering method. Sputtering method that generates metallization and contacts it with the target to sputter the metal of the target and reach the surface of polyimide as the base material to form a metal film. (B) DC excitation method, high frequency excitation method, etc. In the gas atmosphere, an electric field is applied to generate plasma, and the metal evaporated from the evaporation source is brought into contact therewith, and in a state of ionization, reaches the surface of the polyimide as a base material to form a metal film. Either the ion plating method or the like to be formed can be adopted, and particularly, the sputtering method is suitably adopted.

In particular, considering that the amide bond or carboxyl group as an active group formed on the surface of the polyimide by the treatment with the strong alkali is prevented from being crushed by exposure to glow discharge, other factors are considered. The film deposition rate is higher than that of
In addition, a magnetron sputtering method that easily suppresses damage to the base material due to charged particle collisions, particularly a helicon sputtering method, is particularly preferably employed.

The conditions of the sputtering method and the like are appropriately set according to the type of the sputtering method to be used, based on the dimensions and shape of the polyimide as the base material, the type and thickness of the metal film to be formed, and the like. When forming a metal film made of an alloy of two or more kinds of metals, an alloy whose composition is adjusted based on the sputtering rate of each metal is used as a target. Or alternately sputtering.

According to the metal film forming method of the present invention,
As described above, by combining the pretreatment of the polyimide with a strong alkali and the lamination and formation of a metal film by a vapor deposition method such as a sputtering method, directly on the surface of the polyimide, more adhesive than before. In addition, it is possible to form a uniform metal film having a predetermined thickness which is continuous in the thickness direction. << Conductive Belt >> The conductive belt of the present invention has at least a surface of a surface of a base layer formed of polyimide,
That is, a metal film is laminated and formed on the surface of polyimide by the above-described metal film forming method of the present invention.

Of these, the base layer can be formed of a polyimide film alone such as the above-mentioned Kapton film, or, in some cases, has a laminated structure of polyimide and a base layer formed of metal foil, fiber cloth, or the like. You can also.
The thickness of each layer constituting the conductive belt is not particularly limited, for example, a base layer formed of a single polyimide film, in the case of a transfer belt of an image forming apparatus also serving as a transfer and fixing belt, the thickness of the base layer, that is, polyimide Preferably, the thickness of the film is about 10 to 100 μm, and the thickness of the metal film is about 1 to 5 μm.

The conductive belt of the present invention is excellent in the adhesion of the metal film as described above, so that even if a mechanical or thermal shock is repeatedly applied, the conductive belt can be used in a short time as before. In addition, cracking and peeling of the metal film are prevented. Therefore, in combination with the fact that the metal film secures conductivity at the time of transfer and serves as a nucleus of heat generation at the time of fixing, the conductive belt of the present invention also serves as the transfer belt of the image forming apparatus, which also serves as the transfer and fixing belts described above. And the like.

[0029]

The present invention will be described below based on examples and comparative examples. Example 1 A polyimide film having a thickness of 25 μm as a base layer [Kapton film manufactured by Toray Dupont Co., Ltd. as a base layer] in order to prepare a model of a conductive belt used as a transfer belt also serving as a transfer and fixing belt of an image forming apparatus. ] Was subjected to the following treatment.

That is, first, the above polyimide film is
It was immersed for 5 minutes in a 5M aqueous solution of potassium hydroxide maintained at a liquid temperature of 50 ° C. to open the polyimide imide ring on the outermost surface. Next, the polyimide film was neutralized with a 6 M hydrochloric acid aqueous solution, sufficiently washed with water, and further sufficiently dried. Then, the inside of a chamber of an ultra-high vacuum helicon sputtering device (MUE series manufactured by Japan Vacuum Engineering Co., Ltd.) was used. , Set in the substrate holder, close the chamber, and reach the inside of the chamber with a vacuum system of 10 ^-6 hPa by the vacuum system.
While evacuating to a vacuum, a copper film having a thickness of 2 μm was formed by sputtering on one surface thereof by a helicon sputtering method.

Comparative Example 1 The same polyimide film was treated with strong alkali, neutralized,
The washing and drying steps were omitted and directly set on the substrate holding part in the chamber of the ultra-high vacuum helicon sputtering apparatus, and under the same conditions as in Example 1, a thickness of 2
A μm copper film was formed by sputtering. Comparative Example 2 After treating the same polyimide film with a strong alkali,
It was immersed in a 05M aqueous solution of copper sulfate for 1 minute to adsorb copper ions on its surface.

Next, this polyimide film was treated with 0.01
M sodium borohydride (NaBH ₄ ) for 5 minutes
After a copper film was deposited on the surface of the polyimide film by immersion and reduction, electrolytic copper plating was performed using the copper film as a cathode to form a copper film having a total thickness of 2 μm. Metal film adhesion test Japanese Industrial Standard JIS K5400 "General paint test method"
Example 1 according to the adhesion test (cross-cut method) described in
In Comparative Examples 1 and 2, the adhesion of the metal film laminated and formed on the surface of the polyimide film was tested. The test was performed on two samples in both Example 1 and Comparative Example 1.

Then, according to the evaluation method of the above test, the adhesion of the metal film was evaluated using the evaluation points specified by the evaluation method. Comparative Example 1 had 0 to 2 evaluation points. It was found that the metal film hardly adhered.
In Comparative Example 2, the evaluation score was 4 to 5 points, and although the adhesion of the metal film was improved as compared with the above, it was found that it was still insufficient. On the other hand, in Example 1, the evaluation score was 8
At 10 to 10, it was confirmed that the metal film was firmly adhered.

Table 1 shows the above results.

[0035]

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // C08L 79:08 C08L 79:08 (72) Inventor Shin Shinitani 3-chome, Wakihama-cho, Chuo-ku, Kobe City, Hyogo Prefecture No. 6-9 Sumitomo Rubber Industries, Ltd. F term (reference) 2H032 BA09 BA18 BA21 BA23 2H033 AA23 AA31 BA11 BA12 BB01 4F006 AA39 AB73 BA07 DA01 5G307 GA06 GC02 5G323 AA01

Claims (3)

[Claims] 1. A method of forming a metal film on a polyimide surface, comprising treating a polyimide surface with a strong alkali to open an imide ring, and then forming a metal film on the polyimide surface by a vapor phase growth method. Method. 2. The method for forming a metal film on a polyimide surface according to claim 1, wherein the vapor phase growth method is a sputtering method. 3. A method according to claim 1, further comprising a base layer formed of polyimide on at least the surface thereof, and a metal film formed on the surface of the base layer by the metal film forming method according to claim 1. Conductive belt.