Patent Publication Number: US-2002011419-A1

Title: Electrodeposition tank, electrodeposition apparatus, and electrodeposition method

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an electrodeposition tank, an electrodeposition apparatus, and an electrodeposition method for forming an oxide film on a substrate such as a long substrate or the like comprised of a stainless steel belt sheet or the like by electrodeposition (having the same meaning as electroplating or electrolytic deposition) and, more particularly, to an electrodeposition tank and an electrodeposition apparatus for forming a zinc oxide film uniformly on a long substrate by use of an electrodeposition bath with high electric conduction.  
       [0003] 2. Related Background Art  
       [0004] The technology for forming an oxide film on a substrate by making use of electrochemical reaction of aqueous solution (hereinafter referred to as “electrodeposition method”) is recently drawing attention, in place of vacuum processes, in production of photovoltaic elements.  
       [0005] Use of this electrodeposition method presents the following advantages.  
       [0006] First, formation of film is extremely simple, different from that by vacuum apparatus such as sputtering apparatus and the like. An expensive vacuum pump does not have to be used and no special care is necessary for design of components around power supplies and electrodes for use of a plasma.  
       [0007] The second advantage is low running cost in most cases. The sputtering apparatus necessitates labor and apparatus for production of a target to raise the cost and the efficiency of utilization of the target is approximately 20% or less. Therefore, if the throughput of apparatus is high or if the thickness of film is large, a percentage of work for target exchange will be considerably high.  
       [0008] The electrodeposition method is also advantageous in the apparatus and running cost, as compared with CVD and vacuum evaporation except for sputtering.  
       [0009] Films made by electrodeposition are of polycrystalline particles in many cases and demonstrate electroconductivity and optical characteristics that are by no means inferior to those by the vacuum processes. Therefore, the electrodeposition method is superior to the sol-gel process, coating methods using organic substances, spray pyrolysis, and so on.  
       [0010] Further, these are also the case with formation of oxide. In addition, waste liquid can be disposed of readily, so that the impact is small on environments. Therefore, the cost is also low for prevention of environmental pollution.  
       [0011] Meanwhile, we found out the following issues when carrying out formation of film by the electrodeposition method.  
       [0012] Specifically, after completion of deposition for a long period, we found the following adverse effects; an oxide film was deposited on a piping system (i.e., pipes and joints) connected to the electrodeposition bath and on a piping system installed in the electrodeposition tank and film peel-off therefrom occurred to produce powder, film chips, etc. in the bath, thereby causing clogging of a circulation system.  
       [0013] Anodes placed under the substrate in the electrodeposition tank exhibited greatly different forming rates, depending upon their locations, whereby hazy irregularities became apt to appear on the film-forming surface. The hazy irregularities remained, for example, even after formation of a semiconductor photovoltaic layer comprising amorphous silicon as a major component by CVD and formation of a transparent electroconductive layer of ITO or the like in order to form a solar cell, posing a problem that they resulted in remaining as nonuniformity of characteristics.  
       [0014] This phenomenon was more prominent with increasing concentration of the electrodeposition bath and became more prominent as the current was increased to raise the deposition rates. These hindered fully enjoying the advantage of the low running cost described above. An object of the present invention is, therefore, to provide an inexpensive electrodeposition tank, electrodeposition apparatus, and electrodeposition method that can prevent the oxide film from being deposited on the piping system connected to the electrodeposition tank and on the piping system installed in the electrodeposition tank during formation of the oxide film on the substrate, thereby inhibiting generation of powder, film chips, etc. in the bath and that can produce a uniform oxide film evenly without occurrence of the hazy irregularities on the substrate.  
       SUMMARY OF THE INVENTION  
       [0015] The present invention provides an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, the electrodeposition tank being formed of a dielectric material.  
       [0016] The present invention also provides an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, comprising an outside wall formed of a metal material and an inside surface thereof covered with a lining formed of a dielectric material.  
       [0017] Further, the present; invention provides an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, comprising an outside tank formed of a metal material and an inside tank formed of a dielectric material for housing the electrode inside thereof.  
       [0018] The present invention also provides an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank is formed of a dielectric material.  
       [0019] Further, the present invention provides an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank is formed of a metal material and an inside surface thereof is covered with a lining formed of a dielectric material.  
       [0020] The present invention also provides an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank comprises an outside tank formed of a metal material and an inside tank formed of a dielectric material for housing the electrode inside thereof.  
       [0021] Further, the present invention provides an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, wherein all or part of a piping system connected to the tank and a piping system disposed in the tank is formed of a dielectric.  
       [0022] The present invention also provides an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, wherein the inside and outside surfaces of all or part of a piping system connected to the tank and a piping system disposed in the tank are coated with a dielectric.  
       [0023] Further, the present invention provides an electrodeposition apparatus for continuously forming a film of an oxide on a substrate by electrodeposition, comprising an electrodeposition tank for retaining an electrodeposition bath, wherein the electrodeposition tank is formed of a metal, and wherein the inside of the electrodeposition tank is kept electrically floating.  
       [0024] In addition, the present invention provides electrodeposition methods comprising forming a film of an oxide on a substrate by the use of each electrodeposition apparatus stated above. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0025]FIG. 1 is a schematic sectional view showing an example of the electrodeposition tank according to the present invention;  
     [0026]FIG. 2 is a schematic sectional view showing an example of the electrodeposition apparatus according to the present invention;  
     [0027]FIG. 3 is a schematic sectional view showing another example of the electrodeposition tank according to the present invention;  
     [0028]FIG. 4 is a schematic sectional view showing another example of the electrodeposition tank according to the present invention;  
     [0029]FIG. 5 is a schematic sectional view showing an example of the inside tank of the electrodeposition tank according to the present invention;  
     [0030]FIG. 6 is a schematic sectional view showing another example of the inside tank of the electrodeposition tank according to the present invention;  
     [0031]FIG. 7 is a schematic sectional view showing another example of the electrodeposition tank according to the present invention;  
     [0032]FIG. 8 is a schematic sectional view showing another example of the electrodeposition tank according to the present invention; and  
     [0033]FIG. 9 is a schematic sectional view showing another example of the electrodeposition tank according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0034] The present invention has been accomplished based on the following experiments conducted by the inventors.  
     [0035] First, as illustrated in FIG. 7, electrodeposition was carried out with keeping the inside of SUS electrodeposition tank  7009  electrically floating by interposing a dielectric spacer  7067  between the electrodeposition tank  7009  and a frame  7066  thereof. This proved that there appeared little difference among the deposition rates depending upon the locations of anodes  7017  and a uniform film was able to be deposited at high deposition rates. At this time, long substrate  7001  was grounded.  
     [0036] Next, as illustrated in FIG. 8, electrodeposition was carried out while a lining  7068  of a 10 mm-thick polytetrafluoroethylene (Teflon) sheet was provided inside the SUS electrodeposition tank  7009 . This proved that there appeared little difference among the deposition rates depending upon the locations of anodes  7017  and a uniform film was able to be deposited at high deposition rates. Further, electrodeposition was carried out with keeping the long substrate  7001  electrically floating and it was proved that deposition was able to be achieved with still higher uniformity.  
     [0037] Moreover, as illustrated in FIG. 9, the electrodeposition apparatus was arranged in such structure that the inside of the electrodeposition tank  7009  was kept electrically floating, six open-box-like inside tanks  7069  of PFA were placed inside the electrodeposition tank  7009 , three anodes  7017  were set in each inside tank  7069 , and the long substrate  7001  covered openings of the inside tanks  7069 . Electrodeposition was carried out in this structure and it was proved that in the case of deposition at a standstill, the shape of the anodes  7017  was projected slightly but there appeared little difference among the deposition rates depending upon the locations of the anodes  7017  and that in the case of the long substrate  7001  being conveyed continuously, a uniform film was able to be deposited at high deposition rates. Further, electrodeposition was carried out with keeping the long substrate  7001  electrically floating and it was proved that deposition was able to be achieved with still higher uniformity.  
     [0038] The present invention has been accomplished based on the results of the above experiments and provides the electrodeposition apparatus for forming a film of an oxide on the long substrate  7001  by electrodeposition, wherein the electrodeposition tank  7009  for retaining the electrodeposition bath  7016  is formed of a metal and the inside of the electrodeposition tank  7009  is kept electrically floating.  
     [0039] An electrodeposition tank of the present invention is an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, the electrodeposition tank being formed of a dielectric material.  
     [0040] This dielectric is preferably reinforced with a metal material.  
     [0041] The dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0042] Further, the substrate is preferably a long substrate and more preferably, the tank is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0043] Another electrodeposition tank of the present invention is an electrodeposition tank for forming a film of an oxide on a long substrate with energizing the long substrate and an electrode in an electrodeposition bath, wherein an outside wall is formed of a metal material and an inside surface thereof is covered with a lining formed of a dielectric material.  
     [0044] This dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0045] It is also preferable that a clearance at a seam of the lining be so set that an electric resistance of the bath from the anode to the metal part of the outside wall is greater than an electric resistance of the bath from the anode to the substrate.  
     [0046] Further, the metal part of the outside wall and the substrate are preferably set at an equal potential.  
     [0047] The substrate is preferably a long substrate and the tank is preferably mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0048] Another electrodeposition tank of the present invention is an electrodeposition tank for forming a film of an oxide on a long substrate with energizing the long substrate and an electrode in an electrodeposition bath, comprising an outside tank formed of a metal material and an inside tank formed of a dielectric material for housing an anode electrode inside thereof.  
     [0049] This inside tank of the dielectric is preferably reinforced with a metal material.  
     [0050] The inside tank is preferably provided with an opening adapted to permit inflow and outflow of the bath inside thereof and the bath outside thereof.  
     [0051] Further, the size of the opening is preferably so set that an electric resistance of the bath from the anode inside the inside tank to the metal outside tank is greater than an electric resistance of the bath from the anode to the substrate.  
     [0052] The inside tank is preferably provided with bath exchanging/moving means for effecting exchange of the bath inside thereof and the bath outside thereof.  
     [0053] This bath exchanging means is preferably provided with a bath outlet system for leading the inside bath solution out of the inside tank, a bath inlet system for leading the outside bath solution into the inside tank, and a pump for circulating the bath solution from the outlet system to the inlet system.  
     [0054] Further, an electric resistance of the bath from the anode through the bath exchanging means to the substrate is preferably greater than an electric resistance of the bath from the anode to the substrate inside the inside tank.  
     [0055] The dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0056] Further, the metal outside tank and the substrate are preferably set at an equal potential.  
     [0057] The substrate is preferably a long substrate and more preferably, the tank is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0058] Further, an electrodeposition apparatus of the present invention is an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank is formed of a dielectric material.  
     [0059] This electrodeposition tank of the dielectric is preferably reinforced with a metal material.  
     [0060] The dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0061] Further, the substrate is preferably a long substrate and more preferably, the tank is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0062] Another electrodeposition apparatus of the present invention is an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a long substrate with energizing the long substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank is formed of a metal material and an inside surface thereof is covered with a lining formed of a dielectric material.  
     [0063] The dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0064] A clearance at a seam of the lining is preferably so set that an electric resistance of the bath from the anode to the metal part of the electrodeposition tank is greater than an electric resistance of the bath from the anode to the substrate.  
     [0065] Further, the metal part of the electrodeposition tank, and the substrate are preferably set at an equal potential.  
     [0066] The substrate is preferably a long substrate and more preferably, the apparatus is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0067] Another electrodeposition apparatus of the present invention is an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a long substrate with energizing the long substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for forcedly drying the substrate after passage through the washing means, wherein the electrodeposition tank comprises an outside tank formed of a metal material and an inside tank formed of a dielectric material for housing an anode electrode inside thereof.  
     [0068] The inside tank of the dielectric is preferably reinforced with a metal material.  
     [0069] The inside tank is preferably provided with an opening adapted to permit inflow and outflow of the bath inside thereof and the bath outside.  
     [0070] Further, the size of the opening is preferably so set that an electric resistance of the bath from the anode in the inside tank to the metal outside tank is greater than an electric resistance of the bath from the anode to the substrate.  
     [0071] The inside tank is preferably provided with bath exchanging/moving means for effecting exchange of the bath inside thereof and the bath outside.  
     [0072] This bath exchanging means is preferably provided with a bath outlet system for leading the inside bath solution out of the inside tank, a bath inlet system for leading the outside bath solution into the inside tank, and a pump for circulating the bath solution from the outlet system to the inlet system.  
     [0073] Further, an electric resistance of the bath from the anode through the bath exchanging means to the substrate is preferably greater than an electric resistance of the bath from the anode to the substrate inside the inside tank.  
     [0074] The dielectric is preferably a fluororesin or a fiber-reinforced plastic.  
     [0075] Further, the metal outside tank and the substrate are preferably set at an equal potential.  
     [0076] The substrate is preferably a long substrate and more preferably, the apparatus is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0077] Next described are the constitution and operation of the present invention, together with the details of how we have accomplished the present invention. The inventors conducted studies on the hazy irregularities appearing on the long substrate by the following experiments.  
     [0078] The electrodeposition tank  2009  illustrated in FIG. 2 is normally formed of stainless steel (SUS), whereas we employed FRP as a material replacing it. This verified that there appeared little difference among the deposition rates depending upon the locations of the anodes  2017  and a uniform film was able to be formed at high deposition rates.  
     [0079] Next, a lining of 10 mm-thick polytetrafluoroethylene (Teflon) sheets was provided inside the electrodeposition tank  2009  of stainless steel. There was some clearance at seams between the sheets and part of electrodeposition bath  2016  stayed in this clearance, whereby the substrate  2001  was electrically connected via the electrodeposition bath  2016  to the stainless steel electrodeposition tank  2009 .  
     [0080] The clearance at the seams of the Teflon sheets was not so large, however, so that this electrical connection had a large resistance of several ten Ω or more. The electric resistance between the anode  2017  and the substrate  2001  was 0.3 Ω.  
     [0081] When electrodeposition was carried out using the electrodeposition tank  2009  lined with the Teflon sheets as described above, there appeared little difference among the deposition rates depending upon the locations of the anodes  2017  and a uniform film was able to be formed at high deposition rates, as in the case of the FRP electrodeposition tank being used. When electrodeposition was carried out in such a configuration that the stainless steel electrodeposition tank  2009  and the substrate  2001  were connected by a copper wire having the sectional area of 22 mM 2  so as to be kept at an equal potential, the uniformity of deposition was further improved.  
     [0082] Further, instead of the Teflon sheets, ETFE films 50 μm thick were placed as a lining inside the stainless steel electrodeposition tank  2009 . In this case, part of the electrodeposition bath  2016  also leaked, whereby the anodes  2017  and the electrodeposition tank  2009  were electrically connected via the resistance of the bath. This resistance, however, was greater than 50 Ω. On the other hand, the electric resistance between the anodes  2017  and the substrate  2001  was 0.2 Ω.  
     [0083] When electrodeposition was carried out using the electrodeposition tank  2009  lined with the ETFE films as described above, there appeared little difference among the deposition rates depending upon the locations of the anodes  2017  and a uniform film was able to be formed at high deposition rates, as in the case the FRP electrodeposition tank being used.  
     [0084] Six dish vats of PFA were placed in the stainless steel electrodeposition tank  2009 , three anodes  2017  were set in each vat, and the substrate  2001  was arranged to cover the openings of the vats. When electrodeposition was carried out using the electrodeposition tank provided with the vats as described above, it was verified that in the case of deposition at a standstill, there appeared little difference among the deposition rates depending upon the locations of the anodes  2017 , though the shape of the anodes was projected slightly, and in the case of the substrate being conveyed, a uniform film was able to be produced at high deposition rates.  
     [0085] Subsequently, eight openings having the diameter of 5 mm were bored in the lower part of each of the dish vats so as to let bubbling air go into the vats, whereby agitation of the bath was also effected in the vats. When electrodeposition was carried out with the substrate  2001  being conveyed, using the electrodeposition tank capable of bubbling in the stated arrangement of the vats, further improvement in uniformity was verified at high deposition rates.  
     [0086] Further, an opening of 8 mm was bored in the lower part of the dish vat, a Teflon tube was put into this opening, it was connected to an exhaust port of a circulation pump, and another Teflon tube was also drawn similarly from the lower part of the electrodeposition tank  2009  to be connected to an inlet port of the circulation pump. When electrodeposition was carried out with the substrate  2001  being conveyed in this configuration to form a bath circulation system of 400 ml/min while agitating the bath below the substrate, improvement in uniformity was verified at high deposition rates, as in the case of the bubbling air being introduced into the vats. The resistance of the circulation system between the anodes  2017  and the substrate  2001  was over 1 kΩ.  
     [0087] The dish vats were replaced by stainless steel vats and the inside of the vats was lined with Teflon sheets. When electrodeposition was carried out with the substrate  2001  being conveyed in this configuration, a uniform film was able to be formed.  
     [0088] For accomplishing the above object, an electrodeposition tank of the present invention is an electrodeposition tank for forming an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, wherein all or part of a piping system connected to this tank and a piping system placed in the tank is formed of a dielectric.  
     [0089] In the above configuration of the electrodeposition tank, the piping system placed in this tank is preferably electrically insulated from the tank.  
     [0090] The above dielectric is preferably a fluororesin.  
     [0091] The dielectric is also preferably a fiber-reinforced plastic.  
     [0092] Further, the substrate is preferably a long substrate and more preferably, the tank is mounted in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0093] Another electrodeposition tank of the present invention is an electrodeposition tank for forming an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, wherein the inside and outside surfaces of all or part of a piping system connected to this tank and a piping system placed in the tank are coated with a dielectric.  
     [0094] In the above configuration of another electrodeposition tank, the piping system placed in this tank is preferably electrically insulated from the tank.  
     [0095] The above coating dielectric is preferably a fluororesin.  
     [0096] The coating dielectric is also preferably a fiber-reinforced plastic.  
     [0097] Further, the substrate is preferably a long substrate and more preferably, the tank is set in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0098] On the other hand, an electrodeposition apparatus of the present invention is an electrodeposition apparatus comprising an electrodeposition tank for forming an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for drying the substrate after passage through the washing means, wherein all or part of a piping system connected to the electrodeposition tank and a piping system placed in the electrodeposition tank is formed of a dielectric.  
     [0099] In the above configuration of the electrodeposition apparatus, the piping system placed in the electrodeposition tank is preferably electrically insulated from the electrodeposition tank.  
     [0100] The above dielectric is preferably a fluororesin.  
     [0101] The dielectric is also preferably a fiber-reinforced plastic.  
     [0102] Further, the substrate is preferably a long substrate and more preferably, the apparatus is set in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0103] Another electrodeposition apparatus of the present invention is an electrodeposition apparatus comprising an electrodeposition tank for forming a film of an oxide on a substrate with energizing the substrate and an electrode in an electrodeposition bath, a washing means for washing the substrate after passage through the electrodeposition tank, and a drying means for drying the substrate after passage through the washing means, wherein the inside and outside surfaces of all or part of a piping system connected to the electrodeposition tank and a piping system placed in the electrodeposition tank are coated with a dielectric.  
     [0104] In the above configuration of another electrodeposition apparatus, the piping system placed in the electrodeposition tank is preferably electrically insulated from the electrodeposition tank.  
     [0105] The above coating dielectric is preferably a fluororesin.  
     [0106] The coating dielectric is also preferably a fiber-reinforced plastic.  
     [0107] Further, the substrate is preferably a long substrate and more preferably, the apparatus is set in a roll-to-roll apparatus for conveying the long substrate as stretched between rolls.  
     [0108] The operation of the present invention will be described below, together with the details of how the inventors have accomplished the present invention. Specifically, the inventors conducted studies on the powder and film chips appearing in the bath and on the hazy irregularities by the following experiments.  
     [0109] In the electrodeposition apparatus illustrated in FIG. 2, the whole piping system connected to the electrodeposition tank  2009  and the whole piping system placed in the electrodeposition tank  2009  are normally formed of stainless steel (SUS). The inventors employed FRP as a material replacing it and found out that a uniform film was able to be formed at high deposition rates with little clogging of the circulation system due to the powder and film chips and with little difference among the deposition rates depending upon the locations of the anodes  2017 .  
     [0110] Next, the whole piping system connected to the electrodeposition tank  2009  and the whole piping system placed in the electrodeposition tank were replaced by those obtained by laying a Teflon coating on inside and outside surfaces of stainless steel pipes. Electrodeposition was carried out using the pipes with this coating and it was verified that a uniform film was able to be formed at high deposition rates with little clogging of the circulation system due to the powder and film chips and with little difference among the deposition rates depending upon the locations of the anodes  2017 , as in the case of the FRP piping systems being used.  
     [0111] Heat-resistant vinyl chloride was used as a material for the piping system  3011 ,  3012 ,  3013  disposed in the electrodeposition tank  3000  and for the piping system  3014 ,  3015 ,  3016 ,  3017  connected to the electrodeposition tank  3 , 000 , as illustrated in FIG. 3. Electrodeposition was carried out using the piping systems of heat-resistant vinyl chloride in part and it was verified that a uniform film was able to be formed at high deposition rates with little clogging of the circulation system due to the powder and film chips and with little difference among the deposition rates depending upon the locations of the anodes, as in the case of the FRP piping systems being used.  
     [0112] Preferred embodiments of the electrodeposition apparatus according to the present invention will be described below, but it should be noted that the present invention is by no means intended to be limited to the following embodiments.  
     [0113]FIG. 2 is a schematic diagram showing an example of the apparatus for producing the oxide film by electrodeposition, which is simplified to only the function to form a zinc oxide film by electrodeposition.  
     [0114] In FIG. 2, reference numeral  2001  designates a long substrate such as a stainless steel belt sheet or the like wound in a roll form, which is generally called a roll substrate, a web, a hoop, a coil, a tape, a reel, or the like. Namely, the long substrate is a thin sheet having a belt-like shape of an elongate rectangle, which can be rolled up in the longitudinal direction to be held in the roll shape. Since deposition can be carried out continuously, the long substrate is extremely advantageous from the industrial aspect, for example, in capability of decreasing the availability and running cost. The long substrate  2001  is carried in the form of the cylindrical substrate rolled in a coil shape around a bobbin, to this apparatus.  
     [0115] In this apparatus, the long substrate of the coil shape is set on a substrate feed roller  2002 , and the substrate fed therefrom in the direction of the arrow  2004  is conveyed to a substrate winding roller  2062  to be wound thereon while an interleaf (e.g., interleaving paper) for protection of the surface is unwound by an interleaf winding roller  2003 .  
     [0116] In more detail, the substrate  2001  is guided via a tension detecting roller  2005  and a power-supply roller  2006  in its conveyance path to enter the electrodeposition tank  2009 . Inside the electrodeposition tank  2009 , the substrate  2001  is positioned by support rollers  2013 ,  2014  and an oxide film is formed thereon by electrodeposition.  
     [0117] Next, the substrate  2001  having passed the electrodeposition tank  2009  is guided into a washing tank  2030  to be washed with water. Positioning inside the washing tank  2030  is effected by support rollers  2031 ,  2066 . The substrate  2001  having passed the washing tank  2030  is guided into a hot air drying furnace  2051  to be dried.  
     [0118] The substrate  2001  having passed the hot air drying furnace  2051  is guided via a support roller  2057  and lateral deviation thereof is corrected by a skew correcting roller  2059 . While a new interleaf fed from an interleaf feeding roller  2060  is interleaved for protection of the surface of deposited film, the substrate is wound up on the substrate winding roller  2062  and then is carried to the next step if necessary.  
     [0119] The tension detecting roller  2005  is arranged to detect dynamic winding tension of the substrate  2001  and feed the detection result back to an unrepresented brake means, such as a powder clutch, linked to a shaft of the substrate feeding roller  2002 , thereby maintaining the tension constant. Based on this, the conveyance path of the substrate  2001  is designed to be a predetermined value between the support rollers.  
     [0120] Particularly, since this apparatus is constructed so that the rollers do not touch the film-forming surface, weak tension will pose issues; for example, the substrate  2001  slips off the support rollers, the substrate  2001  is suspended down at the exit or entrance of the electrodeposition tank  2009  or the washing tank  2030  so as to scratch the film-forming surface, and so on.  
     [0121] The structure of the apparatus that prevents the contact of the film-forming surface has such advantages as capability of protecting the film-forming surface from damage and pollution etc. and is preferably employed for use where asperities of the micron size have to be formed on a thin film, particularly, such as a reflecting film of a solar cell or the like.  
     [0122] The power-supply roller  2006  is provided for applying a cathode-side potential to the long substrate, is set as close to the electrodeposition bath as possible, and is connected to the negative electrode of power supply  2008 .  
     [0123] The electrodeposition tank  2009  retains the electrodeposition bath  2016  and defines the path of the substrate  2001 . The anodes  2017  are set with respect to the path and an anode potential is applied from the power supply  2008  via a supply bar  2015  to the anodes  2017 . This permits an electrochemical, electrolytic deposition process to proceed with the substrate  2001  being negative and the anodes  2017  being positive in the electrodeposition bath.  
     [0124] If the electrodeposition bath  2016  is maintained at high temperature, a considerable amount of water vapor will evolve. Thus, the water vapor is discharged through vapor exhaust ducts  2010 ,  2011 ,  2012 .  
     [0125] For agitating the electrodeposition bath  2016 , air is introduced through an agitating air inlet pipe  2019  and the air is subject to bubbling from an air blow pipe  2018  in the electrodeposition tank  2009 .  
     [0126] For replenishing the high-temperature bath to the electrodeposition tank  2009 , an electrodeposition circulation tank  2025  is provided, a heater  2024  is set therein to heat the bath, and the bath is supplied from a bath circulation pump  2023  through an electrodeposition bath supply pipe  2020  to the electrodeposition tank. The bath overflowing out of the electrodeposition tank  2009  and the bath positively fed back in part is guided through an unrepresented feedback path back to the electrodeposition circulation tank  2025  to be heated again.  
     [0127] When the discharge of the pump is constant, the bath supply amount from the electrodeposition circulation tank  2025  to the electrodeposition tank  2009  can be controlled by valve  2021  and valve  2022 . Specifically, for increasing the supply amount, the valve  2021  is opened more while the valve  2022  is closed more; for decreasing the supply amount, the reverse operation is carried out. The level of the electrodeposition bath  2016  is retained by adjusting the supply amount and the feedback amount not illustrated.  
     [0128] The electrodeposition circulation tank  2025  is provided with a filter circulation system comprised of a circulation pump  2027  and a filter, so as to remove particles from the electrodeposition circulation tank  2025 . If the supply and feedback of the bath are sufficiently large between the electrodeposition circulation tank  2025  and the electrodeposition tank  2009 , the adequate particle removing effect can be achieved by this configuration in which only the electrodeposition circulation tank  2025  is provided with the filter, as described above.  
     [0129] In this apparatus, the electrodeposition circulation tank  2025  is also provided with a vapor exhaust duct  2026  to exhaust water vapor. Particularly, since the electrodeposition circulation tank  2025  is provided with the heater  2024  as a heating source, the exhaust system is extremely effective where evolution of water vapor is considerable and unintentional discharge or dew condensation of the water vapor evolved is not preferred.  
     [0130] An electrodeposition reserve tank  2029  is provided for preventing the heated bath from being discharged into an existing waste liquid system at once to damage a disposal system and is; thus adapted to retain the electrodeposition bath  2016  of the electrodeposition tank  2009  once and increase efficiency of work by making the electrodeposition tank  2009  vacant. Reference numeral  2028  designates a valve.  
     [0131] After completion of electrodeposition in the electrodeposition tank  2009 , the substrate  2001  is then guided to the washing tank  2030  to be washed with water. In the washing tank  2030  the substrate  2001  is positioned by the support rollers  2031  and  2066  and passes a first washing tank  2032 , a second washing tank  2033 , and a third washing tank  2034  in the stated order.  
     [0132] In a washing circulation tank portion  2050 , each of the washing tanks is provided with a washing circulation tank  2047  to  2049  and a water circulating pump  2044  to  2046  and a water supply amount to the washing tank  2030  is determined by two valves, i.e., by valve  2038  and valve  2041 , or by valve  2039  and valve  2042 , or by valve  2040  and valve  2043 . Cleaning water is supplied through a supply pipe  2035 , or through a supply pipe  2036 , or through a supply pipe  2037  to the washing tank  2032  to  2034 .  
     [0133] The control method of supply amount by the two valves is the same as the control in the electrodeposition tank  2009 . Just as in the electrodeposition tank  2009 , overflowing water and unrepresented feedback water positively fed back in part can also be led back to each washing circulation tank  2047  to  2049 .  
     [0134] In the three-stage washing system as illustrated in FIG. 2, the purity of the cleaning water normally increases from the upstream washing tank to the downstream washing tank in the substrate conveying direction, i.e., from the first washing tank  2032  toward the third washing tank  2034 . This means that cleanliness of the substrate  2001  increases toward the end of the process as the substrate  2001  is conveyed.  
     [0135] This allows the use amount of water to be decreased greatly, by first replenishing the third washing circulation tank  2049  with the cleaning water, then replenishing the second washing circulation tank  2048  with the cleaning water overflowing out of the third washing circulation tank  2049 , and further replenishing the first washing circulation tank  2047  with the cleaning water overflowing from the second washing circulation tank  2048 .  
     [0136] After completion of washing, the substrate  2001  is subjected to a draining step with air knife  2065  provided in part of the washing tank  2030  and then is conveyed to the hot air drying furnace  2051 . In this furnace, the substrate is dried by convective air at a temperature enough to evaporate water fully. The convective air is supplied by leading hot air generated by a hot air generator  2055  through a filter  2054  to remove dust and blowing the hot air from hot air blow pipe  2052 .  
     [0137] Overflowing air is collected again by hot air collecting pipe  2053  and is mixed with external air from external air inlet pipe  2056  to be sent to the hot air generator.  
     [0138] The conveyance path of the substrate  2001  in the hot air drier is positioned by support roller  2066  and support roller  2057 .  
     [0139] The skew correcting roller  2059  is adapted to correct widthwise deviation of the substrate  2001  and wind the substrate onto the substrate winding roller  2062  in the direction of the arrow  2061 . An unrepresented sensor detects a deviation amount and the deviation is controlled by rotating the skew correcting roller  2059  about a fulcrum at an unrepresented arm. Normally, deviation amounts detected by the sensor and operating amounts of the skew correcting roller  2059  both are very small and they are designed within 1 mm.  
     [0140] On the occasion of winding the substrate  2001 , a new interleaf is supplied from the interleaf feeding roller  2060  in order to protect the surface of the substrate.  
     [0141] Stopper  2007  and stopper  2058  are members adapted to be actuated simultaneously to keep the substrate  2001  at a standstill with the conveying tension thereon. This improves operability during exchange of substrate  2001  and during maintenance of the apparatus.  
     [0142] Use of the electrodeposition apparatus as illustrated in FIG. 2 presents the following advantages.  
     [0143] First, formation of film is extremely simple, different from the vacuum apparatus such as the sputtering apparatus or the like. An expensive vacuum pump does not have to be used and no care is necessary for the design of components around the power supply and electrode for use of the plasma.  
     [0144] Next, the running cost is low in most cases. This is for the following reason; the sputtering apparatus necessitates the labor and apparatus for production of the target to raise the cost and the utilization efficiency of the target is approximately 20% or less. Therefore, if the throughput of the apparatus is high or if the thickness of film is large, the percentage of the work for target exchange will be considerably high.  
     [0145] The electrodeposition method of the present invention is also superior in the apparatus and running cost to CVD and vacuum evaporation except for sputtering.  
     [0146] In many cases, the films are of polycrystalline particles and demonstrate the electroconductive and optical characteristics comparable to those of films made by the vacuum methods. Therefore, the electrodeposition method of the present invention is superior to the sol-gel process, the coating method using the organic substance, the spray pyrolysis method, and so on.  
     [0147] Further, these also hold in formation of oxide and the waste liquid can be disposed of easily. Therefore, the impact is small on environments, so that the cost is low for prevention of environmental pollution.  
     [0148] Namely, an example of the electrodeposition apparatus of the present invention is an apparatus for continuously forming a uniform oxide film on the long substrate  2001 , the apparatus comprising the electrodeposition tank  2009  for forming the oxide film on the substrate  2001 , the washing means such as the washing tank  2030  or the like for washing the substrate  2001  having passed the electrodeposition tank  2009 , and the drying means such as the hot air drying furnace  2051  or the like for forcedly drying the substrate  2001  having passed the washing means, the apparatus being improved, particularly, in the structure of the piping system (pipes and joints) connected to the electrodeposition tank and the piping system placed in the electrodeposition tank.  
     [0149] The present invention is also characterized in that the inside of the electrodeposition tank  2009  ( 7009 ) is kept electrically floating in the electrodeposition apparatus described above. The electrically floating state of the inside of the electrodeposition tank  7009  can be realized by interposing the dielectric spacer  7067  between the electrodeposition tank  7009  and the frame  7066  thereof, as illustrated in FIG. 7. A more preferable result can be achieved by providing the electrodeposition tank  7009  with the dielectric lining  7068  and electrically floating the long substrate  7001  as well, as illustrated in FIG. 8.  
     [0150] Another preferred configuration is such that the inside of the electrodeposition tank  7009  is kept electrically floating as described above, the inside tanks  7069  of the open-box shape formed of the dielectric, inside of which the anodes  7017  are disposed, are set in the electrodeposition tank  7009 , and the conveyance path of the long substrate  7001  is set so as to cover the openings of the inside tanks  7069 , as illustrated in FIG. 9. In this case, a more preferable result can also be achieved by further electrically floating the long substrate  7001  as well.  
     [0151] Another electrodeposition apparatus of the present invention is an apparatus for continuously forming a uniform oxide on the long substrate  2001 , the apparatus comprising the electrodeposition tank  2009  for forming the oxide on the substrate  2001  with energizing the long substrate  2001  and anodes  2017  in the electrodeposition bath  2016 , the washing means such as the washing tank  2030  or the like for washing the substrate  2001  having passed the electrodeposition tank  2009 , and the drying means such as the hot air drying furnace  2051  or the like for forcedly drying the substrate  2001  having passed the washing means  2030 , in which, particularly, the electrodeposition tank  2009  is improved or the electrodeposition tank  2009  is used as an outside tank while a separate inside tank is provided. Each of the components will be described below in detail.  
     [0152] [Substrate] 
     [0153] A material for the substrate  2001  used in the present invention is any material that permits electrical conduction at the film-forming surface and that is not corroded with the electrodeposition bath  2016 , and is selected from metals such as stainless steel (SUS), Al, Cu, Fe, Cr, and so on, and alloys thereof. The substrate can also be a PET film coated with a metal or the like.  
     [0154] Among these, where an element forming process is carried out in a succeeding step, stainless steel is suitable for the long substrate, because it is relatively inexpensive and excellent in anticorrosion.  
     [0155] The surface of the substrate may be either flat or rough. In the case of rough surfaces not less than 1 μm, even if a film is formed with good wettability, dry irregularities are apt to take place between the electrodeposition tank  2009  and the washing tank  2003  and thus the present invention is effective.  
     [0156] Further, another electroconductive material may also be deposited on the substrate  2001  and it is selected according to the purpose of electrodeposition.  
     [0157] When the long substrate is of stainless steel, it has the electric resistance greater than the other metals; therefore, particularly, if the thickness of the substrate is not more than about 0.1 mm the electric resistance of the substrate will often be greater than the electric resistance between the anodes  2017  and the substrate  2001  through the electrodeposition bath  2016 , described hereinafter.  
     [0158] In such cases, control of the anode potential to the substrate  2001  is not easy and the electric current expected to flow between the substrate  2001  and the anodes  2017  leaks through other members, for example, through the electrodeposition tank itself and the pipes, posing difficulties of the control thereof. The difficulties of the control of the anode potential often result in an issue of the above-stated irregularities and, therefore, the present invention is effective particularly in such cases.  
     [0159] [Oxide Film] 
     [0160] Oxide films that can be formed by the present invention include a polycrystal film of zinc oxide aligned along the c-axis, a polycrystal film of zinc oxide having the c-axis inclined, and so on.  
     [0161] (Electrodeposition Bath)  
     [0162] The electrodeposit:ion bath  2016  retained in the electrodeposition tank  2009  can be selected from wellknown baths for plating of metal and those comprising zinc nitrate for deposition of zinc oxide (available in the form of hexahydrate) as a major ingredient. A saccharide such as sucrose, dextrin, or the like can also be added in order to enhance uniformity of film.  
     [0163] The electric conductivity of the electrodeposition bath  2016  used in the present invention is preferably not less than 1 mS/cm and the effect appears prominent, particularly, if the conductivity is not less than 10 mS/cm. This is for the reason that as the electric conductivity of the electrodeposition bath  2016  increases, other current paths than those from the anodes  2017  to the substrate  2001  are established, including current paths from the anodes  2017  to the electrodeposition tank  2009  and current paths toward the pipes and other members.  
     [0164] In other words, though the increase per se of the current other than the current paths flowing from the anodes  2017  to the substrate  2001  simply means just loss of current (which is not always preferable, because the current sometimes becomes over several times the original current paths), potentials are often instable at flow end sites in the case of the current other than the current paths flowing from the anodes  2017  to the substrate  2001  in almost all practical systems, so that fluctuations of the current flowing from the anodes  2017  to the substrate  2001  become very large.  
     [0165] It was verified in fact by experiments conducted by the inventors that to make the potential of the electrodeposition tank  2009  equal to the potential of the substrate  2001  was able to make steady the current flowing from the anodes  2017  to the substrate  2001 , subject to the fluctuations, i.e., the original current for deposition of oxide.  
     [0166] The essence of deposition of uniform oxide in the electrodeposition bath  2016  with high conductivity according to the present invention is to stabilize or make more efficient the current flowing from the anodes  2017  to the substrate  2001  by making steady or decreasing the current other than the current paths flowing from the anodes  2017  to the substrate  2001 .  
     [0167] Particularly, for forming a film of zinc oxide with surface roughness approximately equal to the wavelengths of light, effective as an optical confinement reflecting layer of a solar cell, the concentration of zinc nitrate is preferably not less than 0.1 mol/l. For obtaining the zinc oxide film aligned along the c-axis, the concentration of zinc nitrate is preferably not more than 0.05 mol/l in general, though depending upon the substrate.  
     [0168] In either case, the saccharide added is preferably 3 g/l or more of sucrose or 0.001 g/l or more of dextrin. In these cases, the temperature of the bath is preferably not less than 60° C., because deposition of metal does not take place. Particularly, the temperature is preferably not less than 80° C. for improvement in uniformity of film. This temperature makes the effect of the present invention more prominent, because the electric conductivity is increased remarkably at; this temperature.  
     [0169] [Electrodeposition Tank] 
     [0170] For the electrodeposition tank  2009 , metals applicable are stainless steel (SUS), Fe, Al, Cu, Cr, brass, and so on because of their excellent heat resistance and workability, among which stainless steel is preferably used in consideration to corrosion resistance. The stainless steel can be either ferritic, martensitic, or austenitic stainless steel.  
     [0171] When the electrodeposition tank is required to have a heat retaining property, the electrodeposition tank can be constructed in dual structure and complemented by a heat insulator between tank walls. Examples of the heat insulator include air, oil, glass wool, urethane, and so on, taking the temperature and simplicity into consideration.  
     [0172] Particularly, the present invention employs the dielectric for the electrodeposition tank itself or for the inside tanks disposed in the electrodeposition tank  2009 . The electrodeposition tank or the inside tanks formed of the dielectric can be molded members of resins described below or members formed of the fiber-reinforced plastics.  
     [0173] (Dielectrics used for the Electrodeposition Tank etc.)  
     [0174] The dielectric materials applicable for formation of the electrodeposition tank or the inside tanks described above include ceramics including alumina, magnesia, calcia, silicon nitride, silicon carbide, and so on, glasses such as lead-potassium glass, lead-potassium-sodium glass, zinc borosilicate, aluminosilicate, borosilicate, barium borosilicate, alkali-barium glass, and so on, and styrene-based resins such as AAS (acrylonitrile acrylate styrene), ABS (acrylonitrile butadiene styrene), ACS (acrylonitrile polyethylene chloride styrene), AES (acrylonitrile ethylene styrene), AS (acrylonitrile styrene), and so on.  
     [0175] Other dielectric materials applicable are vinyl resins such as EVC (ethylene vinyl chloride), EVA (ethylene vinyl acetate), PVC (polyvinyl chloride), VP (vinyl propionate), PVB (polyvinyl butyral), PVF (polyvinyl formal), and so on, fluororesins such as PTFE (polytetrafluoroethylene), FEP (fluoroethylene polypropylene), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether), ETFE (ethylene tetrafluoroethylene), CTFE (polychlorotrifluoroethylene), PVDF (polyvinylidene fluoride), ECTFE (ethylene chlorotrifluoroethylene), PVF (polyvinyl fluoride), and so on, polyacetal resins, polyamide resins including nylon etc., polyamide-imide resins, polyarylate resins, and polyimide resins.  
     [0176] Further dielectric materials applicable are polyethylene resins such as LDPE (low density polyethylene), LLDPE (linear low density polyethylene), HDPE (high density polyethylene), UHMWPE (ultra-high molecular weight polyethylene), and so on, polyester resins such as PET (polyethylene terephthalate), PBT (polybutylene terephthalate), polycarbonate, and so on, styrol resins such as polystyrene, polyparamethylstyrene, and so on, propylene resins such as polypropylene and the like, acrylic resins such as PMMA (polymethyl methacrylate) and the like, epoxy resins such as BPA (bisphenol A) and the like, allyl resins such as DAP (diallyl phthalate) and the like, phenol resins such as bakelite and the like, unsaturated polyester resins, furan resins such as furfuryl alcohol polymer, furfuryl alcohol furfural copolymer, furfural phenol copolymer, furfural ketone copolymer, and so on, urethane resins, and urea resins.  
     [0177] Other dielectric materials can be mixtures of these materials and composite materials with fibers. Among the resins, the fluororesins are preferably used, particularly, where the operating temperature of the electrodeposition bath is high and high corrosion resistance is expected.  
     [0178] The form of the dielectric used for the electrodeposition tank or the inside tanks can be either one selected from molded products of the ceramics, glasses, and resins described above by use of a hollow box die or a cylindrical die, sheets, films, foamed products, fabric of fibers, etc. thereof, and molded products of combinations thereof. When the tank cannot stand alone, it can also be constructed with a framework of metal or other thermosetting resin.  
     [0179] (Inside Tank)  
     [0180] Those described above in the sections of [electrodeposition tank] and [dielectrics used for the electrodeposition tank etc.] can also be applied similarly to the inside tank used in the present invention. Materials inferior in strength can also be applied to the inside tank, however, because the inside tank does not have to support the entire weight of the electrodeposition tank, different from the outside tank. Therefore, a material can be selected with focus on characteristics, price, etc. as a dielectric. An example conceivable is a box formed of PFA sheets 5 mm thick and stainless steel fasteners.  
     [0181] The electrodeposition tank itself cannot be constructed of only PFA, because it is required to prevent the bath from leaking and to be capable of supporting the entire weight of the electrodeposition bath. It needs to be constructed using a metal box of stainless steel or the like as a support.  
     [0182] On the other hand, in the case of the inside tank, the leak of the bath is not problematic and there are little restrictions on the strength. When the inside tank is formed of the dielectric so as to prevent the leak of current, however, electrical insulation has to be maintained at the operating temperatures of the electrodeposition bath and PFA meets that condition. In this case, if the operating temperatures are about 70° C., PV can also be used instead of PFA, whereby the production cost can be decreased.  
     [0183] (Glass Fiber-reinforced Plastics)  
     [0184] Fiber-reinforced plastics (FRP) that can be used for the electrodeposition tank of the present invention include those using glass fibers as reinforcing fibers (GRP), those using carbor fibers (CRP), those using boron fibers (BRP), and so on.  
     [0185] Resins suitably applicable for the FRPs are unsaturated polyester resins, epoxy resins, urethane resins, vinyl ester resirs, phenol resins, and diallyl phthalate resins.  
     [0186] When only the fiber-reinforced plastic is used for the dielectric electrodeposition tank in the present invention, it is not preferable to increase the electrical conductivity by a metal coating on the reinforcing fibers. Preferred FRPs are those having the resistivity of not less than 100 Ωcm.  
     [0187] Since there are possibilities that the FRPs are deformed after long-term use in the high-temperature bath, they are preferably reinforced by a support of metal angles or the like.  
     [0188] (Bath Exchanging Means)  
     [0189] In the present invention, where the inside tank is disposed in the electrodeposition tank  2009 , this inside tank is provided with the bath exchanging means. The bath exchanging means used in the present invention can be either one selected from a single opening or plural openings bored in the bottom or a side wall of the inside tank, a circulation system for circulating part of the bath, comprised of a pump and a tube or pipe, and so on.  
     [0190] The openings have advantages of basically simple structure and capability of being made at low cost. Preferred openings are those permitting free replacement of the bath and having a large electric resistance due to the bath. For achieving this, the openings can be formed in a large diameter and the openings can be provided with a cover or be formed in a maze shape so as to prevent a linear current path from the anode  2017  from being created to the electrodeposition tank  2009 . The opening may also be provided with a fan for the bath so as to promote the replacement of the bath positively.  
     [0191] The circulation system of the bath is superior to the simple openings in that the current path from the anode  2017  can be made electrically narrow. Further, the circulation system has an advantage of easiness to control the degree of replacement of the bath.  
     [0192] In cases where a plurality of anodes  2017  and a corresponding number of inside tanks are disposed in the electrodeposition tank  2009 , there is also freedom of arrangement; for example, a configuration in which there are one suction pipe of the bath and a plurality of return pipes to the inside tanks.  
     [0193] If there are possibilities that the operating temperatures of the bath are decreased greatly in the above circulation system, temperature retaining means or heating means can also be provided midway of the circulation system. It is also possible to perform management of the bath by measuring the concentration of the bath or particles therein in the circulation system.  
     [0194] [Piping Systems (Pipes and Joints)] 
     [0195] For the piping systems applicable to the present invention, metals applicable are stainless steel (SUS), Fe, Cu, Cr, brass, and so on because of their excellent heat resistance and workability, among which stainless steel is preferably used in consideration to corrosion resistance. The stainless steel can be either ferritic, martensitic, or austenitic stainless steel.  
     [0196] When the piping systems are formed of a dielectric, they can be molded of the resins described below, they can be metal pipes with a coating on inside and outside surfaces, and they can be formed of the fiber-reinforced plastics described below.  
     [0197] The structure of the piping systems can be selected from dielectric piping systems, metal piping systems coated with the dielectric, or combinations of these with metal piping systems.  
     [0198] (Dielectrics used for the Piping Systems (Pipes and Joints))  
     [0199] The dielectric materials that can be used for the above piping systems are styrene-based resins such as AAS (acrylonitrile acrylate styrene), ABS (acrylonitrile butadiene styrene), ACS (acrylonitrile polyethylene chloride styrene), AES (acrylonitrile ethylene styrene), AS (acrylonitrile styrene), and so on.  
     [0200] Other dielectric materials applicable are vinyl resins such as EVC (ethylene vinyl chloride), EVA (ethylene vinyl acetate), PVC (polyvinyl chloride), VP (vinyl propionate), PVB (polyvinyl butyral), PVF (polyvinyl formal), and so on, fluororesins such as PTFE (polytetrafluoroethylene), FEP (fluoroethylene polypropylene), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether), ETFE (ethylene tetrafluoroethylene), CTFE (polychlorotrifluoroethylene), PVDF (polyvinylidene fluoride), ECTFE (ethylene chlorotrifluoroethylene), PVF (polyvinyl fluoride), and so on, polyacetal resins, polyamide resins including nylon etc., polyamide-imide resins, polyarylate resins, and polyimide resins.  
     [0201] Further dielectric materials applicable are polyethylene resins such as LDPE (low density polyethylene), LLDPE (linear low density polyethylene), HDPE (high density polyethylene), UHMWPE (ultra-high molecular weight polyethylene), and so on, polyester resins such as PET (polyethylene terephthalate), PBT (polybutylene terephthalate), polycarbonate, and so on, styrol resins such as polystyrene, polyparamethylstyrene, and so on, propylene resins such as polypropylene and the like, acrylic resins such as PMMA (polymethyl methacrylate) and the like, epoxy resins such as BPA (bisphLenol A) and the like, allyl resins such as DAP (diallyl phthalate) and the like, phenol resins such as bakelite and the like, unsaturated polyester resins, furan resins such as furfuryl alcohol polymer, furfuryl alcohol furfural copolymer, furfural phenol copolymer, furfural ketone copolymer, and so on, urethane resins, urea resins, and ketone resins.  
     [0202] Other dielectric materials can be mixtures of these materials and composite materials with fibers. Among the resins, the fluororesins are preferably used, particularly, where the operating temperature of the bath is high and high corrosion resistance is expected.  
     [0203] The form of the dielectric used for the piping systems applicable to the present invention can be selected from a molded form of the above resins by a cylindrical die, fabric of fibers of the resins, or a combination thereof.  
     [0204] (Glass Fiber-reinforced Plastics)  
     [0205] Fiber-reinforced plastics (FRP) that can be applicable to the piping systems in the present invention include those using glass fibers as reinforcing fibers (GRP), those using carbon fibers (CRP), those using boron fibers (BRP), and so on.  
     [0206] Resins suitably applicable for the FRPs are unsaturated polyester resins, epoxy resins, urethane resins, vinyl ester resins, phenol resins, and diallyl phthalate resins.  
     [0207] When only the fiber-reinforced plastic is used for the dielectric piping systems in the present invention, it is not preferable to increase the electrical conductivity by a metal coating on the reinforcing fibers. Preferred FRPs are those having the resistivity of not less than 100 Ωcm.  
     [0208] [Washing Means] 
     [0209] The washing means used in the present invention can be a shower for washing, in addition to the method of letting the substrate  2001  pass through water reserved in the washing tank  2030  as illustrated in FIG. 2.  
     [0210] [Drying Means] 
     [0211] Very effective drying means used in the present invention is one for first removing water-soluble solutes sufficiently and thereafter draining water by the air knife as illustrated in FIG. 2. In that case, hot air suffices for subsequent heat drying. If a vacuum device is used in the succeeding step, an infrared heater or the like can also be utilized for removing adsorbed water.  
     [0212] [Conveying Means] 
     [0213] The conveying means of the substrate used in the present invention is preferably arranged to exert the tension of not less than 0.5 kg per cm of the width of the substrate thereon so as to prevent vertical vibration of the substrate and in turn prevent occurrence of stepped irregularities between the tanks.  
     [0214]FIG. 2 shows horizontal conveyance of the substrate by the roll-to-roll method, but oblique conveyance of the substrate using a folding roller between the tanks can also be applied.  
     [0215] [Spacer  7067 , Lining  7068 , and Inside Tanks  7069 ] 
     [0216] The dielectrics used for the spacer  7067 , lining  7068 , and inside tanks  7069  in the present invention are ceramics including alumina, magnesia, calcia, silicon nitride, silicon carbide, and so on, glasses such as lead-potassium glass, lead-potassium-sodium glass, zinc borosilicate, aluminosilicate, borosilicate, barium borosilicate, alkali-barium glass, and so on, styrene-based resins such as AAS (acrylonitrile acrylate styrene), ABS (acrylonitrile butadiene styrene), ACS (acrylonitrile polyethylene chloride styrene), AES (acrylonitrile ethylene styrene), AS (acrylonitrile styrene), and so on, vinyl resins such as EVC (ethylene vinyl chloride), EVA (ethylene vinyl acetate), PVC (polyvinyl chloride), VP (vinyl propionate), PVB (polyvinyl butyral), PVF (polyvinyl formal), and so on, fluororesins such as PTFE (polytetrafluoroethylene), FEP (fluoroethylene polypropylene), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether), ETFE (ethylene tetrafluoroethylene), CTFE (polychlorotrifluoroethylene), PVDF (polyvinylidene fluoride), ECTFE (ethylene chlorotrifluoroethylene), PVF (polyvinyl fluoride), and so on, polyacetal resins, polyamide resins including nylon etc., polyamide-imide resins, polyarylate resins, polyimide resins, polyethylene resins such as LDPE (low density polyethylene), LLDPE (linear low density polyethylene), HDPE (high density polyethylene), UHMWPE (ultra-high molecular weight polyethylene), and so on, polyester resins such as PET (polyethylene terephthalate), PBT (polybutylene terephthalate), polycarbonate, and so on, styrol resins such as polystyrene, polyparamethylstyrene, arid so on, propylene resins such as polypropylene and the like, acrylic resins such as PMMA (polymethyl methacrylate) and the like, epoxy resins such as BPA (bisphenol A) and the like, allyl resins such as DAP (diallyl phthalate) and the like, phenol resins such as bakelite and the like, unsaturated polyester resins, furan resins such as furfuryl alcohol polymer, furfuryl alcohol furfural copolymer, furfural phenol copolymer, furfural ketone copolymer, and so on, urethane resins, and urea resins. Further, the dielectrics can also be mixtures of these materials and composite materials with fibers. In the case of the resins being used, the fluororesins are preferably used, particularly, where the operating temperature of the electrodeposition bath  7016  is high and high corrosion resistance is expected.  
     [0217] The spacer  7067  and the lining  7068  in the present invention can be made in the form of sheets, films, foamed products, fabric of fibers, etc. of the above-stated ceramics, glasses, and resins. Further, the inside tanks  7069  can be made as molded products of the above-stated ceramics, glasses, and resins, for example, by use of a box-shape or cylindrical die.  
     [0218] [Electrical Floating] 
     [0219] The electrical floating of the inside of the electrodeposition tank  7009  or the long substrate  7001  means that the inside surface of the electrodeposition tank  7009  or the long substrate  7001  is electrically floating with respect to the main body of the apparatus. Since the main body of the apparatus is grounded in general, it indicates electrical floating with respect to the ground.  
     [0220] The electrical floating of the inside of the electrodeposition tank  7009  can be achieved by interposing the spacer  7067  of the dielectric, for example, such as Teflon, Delrin, or the like, between the frame  7066  supporting the electrodeposition tank  7009 , and the electrodeposition tank  7009 , as illustrated in FIG. 7. If the electrodeposition tank  7009  is fixed to the frame  7066  by bolts or the like, a necessary measure will be taken to prevent the electrodeposition tank  7009  from becoming electrically conductive to the frame  7066  through the bolts. The electrical floating can also be implemented by interposing the spacer  7067  of the dielectric, for example, such as Teflon, Delrin, or the like, between the frame  7066  and the ground surface, but the way of interposing the spacer  7067  between the electrodeposition tank  7009  and the frame  7066  as illustrated in FIG. 8 is simpler. Where the spacer  7067  is interposed between the frame  7066  and the ground surface and if anchor bolts are screwed into the ground surface, a necessary measure will be taken to prevent the frame  7066  from becoming electrical conductive to the ground surface through the anchor bolts. When the pipes to the electrodeposition tank  7009  are SUS pipes or the like, it is preferable to interpose a pipe, a joint, or the like of heat-resistant polyvinyl chloride midway. Namely, it is preferable to maintain the electrodeposition tank  7009  at the same potential as that of the pipes inside the electrodeposition tank  7009 .  
     [0221] The electrical floating of the long substrate  7001  ( 2001 ) can be achieved by covering bearing surfaces of rotational shafts of all the rollers in contact with the long substrate  7001  ( 2001 ) (for example, the support rollers  2005 ,  2013 ,  2014 ,  2031 ,  2057 ,  2066 , the skew correcting roller  2059 , etc.) except for the power-supply roller  2006  with the dielectric, for example, such as Teflon, Delrin, or the like, or by making the bearings of the rotational shafts of all the rollers in contact with the long substrate  2001  except for the power-supply roller, of the dielectric. The electrical floating of the long substrate can also be realized by covering the surfaces of all the rollers in contact with the long substrate  2001  except for the power-supply roller with the dielectric or by making all the rollers in contact with the long substrate  2001  except for the power-supply roller, of the dielectric. The covering can be achieved, for example, by attaching a dielectric film such as a polyimide film or the like to the surfaces with two sided adhesive tape, by impregnating them with the dielectric of the resin such as Teflon or the like, and so on, and may also be achieved by a combination of some of these methods.  
     [0222] The electrical floating can be checked by measuring the electric resistance between the inside surface of the electrodeposition tank  7009  and the ground surface, the electric resistance between the long substrate  7001  and the ground surface, and the electric resistance between the electrodeposition tank  7009  and the long substrate  7001  by a tester with nothing inside the electrodeposition tank  7009  and confirming that the result is of the MΩ order.  
     EXAMPLES  
     [0223] Examples based on the present invention will be described below, but it should be noted that the present invention is by no means intended to be limited to these examples.  
     Example 1  
     [0224] The electrodeposition tank  7009  as illustrated in FIG. 7 was incorporated as the electrodeposition tank  2009  into the electrodeposition apparatus as illustrated in FIG. 2, and deposition was carried out therein.  
     [0225] In FIG. 7, the electrodeposition tank  7009  is formed of SUS and in the dual structure in which glass wool is put as a heat insulator, thus having good heatinsulating and heat-retaining properties. The long substrate  7001  of SUS430 is conveyed through a slit formed in the both side walls of this electrodeposition tank  7009 . Each of the both side wall portions of the electrodeposition tank  7009  having the slit is double walls. The electrodeposition bath  7016  retained in the electrodeposition tank  7009  is arranged to overflow to drop into between the double walls. The electrodeposition bath  7016  overflowing to drop into between the double walls is guided through the unrepresented circulation system to be used again as the electrodeposition bath  7016  herein. The circulation amount was controlled so that the height from the overflowing point to the bath surface became 35 mm.  
     [0226] The electrodepositicn bath  7016  was zinc nitrate of 0.2 mol/l and was kept at 80° C. Zinc nitrate is for electrochemically depositing zinc oxide on the surface of the long substrate  7001  by cooperation of existing zinc ions or complex ions and nitric ions. The electrodeposition bath  7016  contained dextrin 0.7 g/l in order to enhance uniformity of the zinc oxide film. The electric conductivity of the electrodeposition bath  7016  was 65 mS/cm.  
     [0227] Four anodes  7017  were disposed inside the electrodeposition bath  7016 . These anodes  7017  are provided for advancing the electrochemical reaction when the voltage is placed between the anodes  7017  and the long substrate  7001 . For formation of zinc oxide, the potential of the anodes  7017  is maintained higher than the potential of the long substrate  7001 .  
     [0228] The electrodeposition tank  7009  is installed through the spacer  7067  of an acrylic sheet on the frame  7066 . This keeps the inside of the electrodeposition tank  7009  electrically floating with respect to the ground, whereby electric lines are prevented from directly running from the anodes  7017  to the SUS electrodeposition tank  7009 . The anodes  7017  are connected to respective separate power supplies  7008 , so as to be powered independently of each other. The return of the current is implemented as a common return from the power-supply roller  7006  driven in contact with the long substrate  7001 . Each power supply  7008  was controlled as a constant current source and the electrodeposition current density toward the long substrate  7001  was arranged to be able to be set in the range of 0.2 mA/cm 2  to 30 mA/cm 2  at each of the anodes  7017 .  
     [0229] While the conveyance of the long substrate  7001  was stopped, deposition was investigated at a standstill. The deposition rates approximately proportional to the current, 1 to 200 Å/s, were obtained by the current densities in this range. The present example employed the current density of about 13 mA/cm 2 . The deposition rate obtained at a standstill was about 100 Å/s. The size of each anode  7017  was 110×500 mm in a surface opposed normally to the long substrate  7001  and the thickness thereof was 20 mm. The anodes were of zinc having the purity of 4 N. A current set value of each power supply  7008  was about 7 A and the power-supply voltages indicated 2.5 to 4.0 V.  
     [0230] The distance between the anodes  7017  and the long substrate  7001  was either of 10 mm and 25 mm and in either case an electrodeposited zinc oxide film was extremely uniform. Further, the uniform zinc oxide film 1 μm thick was able to be continuously formed on the long substrate  7001  at the conveyance speed of 1200 mm/min of the long substrate  7001 .  
     Comparative Example 1  
     [0231] The electrodeposition tank  7009  similar to that in Example 1 was electrically grounded and incorporated as the electrodeposition tank  2009  in the electrodeposition apparatus as illustrated in FIG. 2, and then formation of film was carried out therein.  
     [0232] The current density of about 180 mA/cm 2  was needed for obtaining the deposition rate of about 100 Å/S. Namely, the electric current that had to be supplied from the power supplies was about 100 A, which was close to the capacity limit of the power supplies. Besides, deposition was very apt to be affected by the magnitude of the distance between the anodes  7017  and the long substrate  7001 . When the distance between the anodes  7017  and the long substrate  7001  was set to 15 mm, heavily uneven patterns appeared in the film, and great variations of characteristics took place when solar cells were made. When the distance between the anodes  7017  and the long substrate  7001  was increased to 50 mm in order to reduce the relative distance differences, the deposition rates of film were decreased by an order of magnitude or more and were values not satisfying the demanded specifications of the present apparatus at all.  
     [0233] On the other hand, when the electrodeposition tank  7009  was made floating with respect to the ground as in Example 1, the current to be supplied from the power supply  7008  was 7 A, as described above, and there was little change of the current with change in the distance between the anodes  7017  and the long substrate  7001  to either of 10 mm and 25 mm. In addition, the electrodeposited zinc oxide film was uniform and the uniform zinc oxide film 1 μm thick was able to be continuously formed on the substrate at the conveyance speed of 1200 mm/min of the long substrate  7001 .  
     Example 2  
     [0234] As illustrated in FIG. 8, the lining  7068  of the Teflon sheets 5 mm thick was provided inside the electrodeposition tank  7009  of Example 1, this electrodeposition tank  7009  was incorporated as the electrodeposition tank  2009  in the electrodeposition apparatus as illustrated in FIG. 2, and electrodeposition was carried out therein.  
     [0235] The deposition rates of about 70 Å/s were achieved with supply of the current of about 5 A from each of the power supplies  7008 . The distance between the anodes  7017  and the long substrate  7001  was either of 10 mm and 25 mm and the electrodeposited zinc oxide film was extremely uniform in either case. Further, the uniform zinc oxide film 1 μm thick was able to be continuously formed on the long substrate  7001  at the conveyance speed of 850 mm/min of the long substrate  7001 .  
     Example 3  
     [0236] Electrodeposition was carried out in similar fashion to that in Example 2 except that the long substrate  7001  was made electrically floating with respect to the ground. The electrical floating of the long substrate  7001  was effected by using Delrin bearings for the respective rollers.  
     [0237] The deposition rates of about 70 Å/s were obtained with supply of the current of about 5 A from each of the power supplies  7008 . The distance between the anodes and the substrate was either of 10 mm and 25 mm and the electrodeposited zinc oxide film was extremely uniform in either case. Further, the extremely uniform zinc oxide film 1 μm thick was able to be continuously formed on the long substrate  7001  at the conveyance speed of 850 mm/min of the long substrate  7001 .  
     Example 4  
     [0238] The electrodeposition tank  7009  as illustrated in FIG. 9 was incorporated as the electrodeposition tank  2009  in the electrodeposition apparatus as illustrated in FIG. 2 and deposition was carried out therein.  
     [0239] In FIG. 9, the electrodeposition tank  7009  is formed of SUS and in the dual structure in which glass wool is put as a heat insulator, thus having good heat-insulating and heat-retaining properties. The long substrate  7001  of SUS430 is conveyed through a slit formed in the both side walls of this electrodeposition tank  7009 . Each of the both side wall portions of the electrodeposition tank  7009  having the slit is double walls. The electrodeposition bath  7016  retained in the electrodeposition tank  7009  is arranged to overflow to drop into between the double walls. The electrodeposition bath  7016  overflowing to drop into between the double walls is guided through the unrepresented circulation system to be used again as the electrodeposition bath  7016  herein. The circulation amount was controlled so that the height from the overflowing point to the bath surface became 35 mm.  
     [0240] The electrodeposition tank  7009  and the long substrate  7001  were made each electrically floating with respect to the ground, independently of each other.  
     [0241] The electrodeposition bath  7016  was zinc nitrate of 0.2 mol/l and was kept at 80° C. Zinc nitrate is for electrochemically depositing zinc oxide on the surface of the long substrate  7001  by cooperation of existing zinc ions or complex ions and nitric ions. The electrodeposition bath  7016  contained dextrin 0.7 g/l in order to enhance uniformity of the zinc oxide film. The electric conductivity of the electrodeposition bath  7016  was 65 mS/cm.  
     [0242] Four anodes  7017  were disposed inside the electrodeposition bath  7016 . These anodes  7017  are provided for advancing the electrochemical reaction when the voltage is placed between the anodes  7017  and the long substrate  7001 . For formation of zinc oxide, the potential of the anodes  7017  is maintained higher than the potential of the long substrate  7001 .  
     [0243] Each anode  7017  is disposed in the inside tank  7069  of PFA having the thickness of 2 mm and the inside dimensions of 210 mm×120 mm. This structure prevents electric lines from directly running from the anodes  7017  to the SUS electrodeposition tank  7009 . The anodes  7017  are connected to the respective separate power supplies  7008 , so as to be powered independently of each other. The return of the current is implemented as a common return from the power supply roller  7006  driven in contact with the long substrate  7001 . Each power supply  7008  was controlled as a constant current source and the electrodeposition current density toward the long substrate  7001  was arranged to be able to be set in the range of 0.2 mA/cm 2  to 30 mA/cm 2  at each of the anodes  7017 .  
     [0244] While the conveyance of the long substrate  7001  was stopped, deposition was investigated at a standstill. The deposition rates approximately proportional to the current, 1 to 200 Å/s, were obtained by the current densities in the above range. The present example employed the current density of about 10 mA/cm 2 . The deposition rate achieved at a standstill was 80 Å/s. The size of each anode  7017  was 110×200 mm in a surface opposed normally to the long substrate  7001  and the thickness thereof was 20 mm. The anodes were of zinc having the purity of 4 N. A current set value of each, power supply  7008  was about 2 A and the power-supply voltages indicated 1.5 to 2.5 V.  
     [0245] The distance between the anodes  7017  and the long substrate  7001  was either of 10 mm and 25 mm and in either case the electrodeposited zinc oxide film was extremely uniform. Further, the uniform zinc oxide film 1 μm thick was able to be continuously formed on the long substrate  7001  at the conveyance speed of 400 mm/min of the long substrate  7001 .  
     Example 5  
     [0246]FIG. 4 is a schematic diagram showing an example of the electrodeposition tank of the present invention. In FIG. 4, the outside tank  4000  of the electrodeposition tank is formed of stainless steel (SUS) and in the dual structure in which a heat insulator of glass wool is interposed, thereby having good heat-insulating and heat-retaining properties.  
     [0247] The long substrate  4002  is formed of a stainless steel belt sheet (SUS430) and this substrate  4002  is conveyed through a slit formed in each of the both side walls of the outside tank  4000  of the electrodeposition tank.  
     [0248] Each of the side walls of the outside tank  4000  having the slit is double walls and overflows  4007  and  4008  of the electrodeposition bath  4001  retained in the tank are arranged to drop into the space between the double walls. The overflowing bath is returned to the unrepresented circulation system to be used again as the electrodeposition bath  4001 . With consideration to the circulation amount, the height from the overflowing point to the bath surface was set to 35 mm.  
     [0249] The electrodeposition bath  4001  is zinc nitrate of 0.2 mol/l and is kept at 80° C. Zinc nitrate makes zinc ions or complex ions present in the bath and also makes nitric ions present in the bath to electrochemically deposit zinc oxide on the surface of the substrate by interaction of the ions. The electrodeposition bath  4001  contains dextrin 0.7 g/l in order to enhance the uniformity of zinc oxide film. The electric conductivity of the electrodeposition bath  4001  was 65 mS/cm.  
     [0250] There are anode A  4003 , anode B  4004 , anode C  4005 , and anode D  4006  disposed in the electrodeposition bath  4001 . The voltage is placed between these anodes and the long substrate  4002 , whereupon the electrochemical reaction proceeds. For forming a film of zinc oxide, the potential of the anodes has to be maintained higher than the potential of the long substrate.  
     [0251] Each anode is covered by the inside tank of PFA  4011  to  4014  having the thickness of 2 mm and the inside dimensions of 210 mm×120 mm. This structure prevents electric lines from directly running from the anodes to the stainless steel electrodeposition outside tank  4000 .  
     [0252] The anodes are connected to the respective separate power supplies  4021  to  4024 , so as to permit independent current to flow. The return of the current is implemented as a common return from the power-supply roller  4010  driven in contact with the long substrate.  
     [0253] Each power supply is controlled as a constant current source and the electrodeposition current density to the substrate  4002  is arranged to be able to be set in the range of 0.2 mA/cm 2  to 30 mA/cm 2  at each anode.  
     [0254] While the conveyance of the long substrate  4002  was stopped, deposition was investigated at a standstill. The deposition rates approximately proportional to the current, 1 to 200 Å/sec, were obtained by the current densities in the above range and the present example employed the current density of about 10 mA/cm 2 . The deposition rate obtained in the deposition at a standstill was 80 Å/sec.  
     [0255] The size of each anode was 100×200 mm in a surface opposed to the long substrate  4002  and the thickness thereof was 20 mm. Each anode was formed of zinc having the purity of 4 N. At this time, the current set value of each power supply was 2 A and the power-supply voltages indicated 1.5 to 2.5 V.  
     [0256] In the present example, the electrodeposition outside tank  4000 , together with the return path to the power supplies, was connected to the common ground  4025 . This configuration was employed because the apparatus would have become expensive if the apparatus should have been constructed by electrically insulating all the rollers supporting the long substrate  4002 . Insulation of the large electrodeposition outside tank  4000  would also result in increasing the cost similarly. If insulated, the tank has to be constructed so as to be adapted for short-circuits due to water drops or other contact objects.  
     Comparative Example 2  
     [0257] Prior to the investigation of Example 5, deposition was carried out without the inside tanks  4011  to  4014  in the electrodeposition bath  4001 . As a result, the current density of 350 mA/cm 2  was necessary for obtaining the deposition rate of 200 Å/sec. Namely, the current to be supplied from the power supplies was 40 A, which was close to the capacity limit of the power supplies.  
     [0258] Besides, deposition was very sensitive to the magnitude of the distance between the anodes and the substrate. When the distance between the anodes and the substrate was set to 10 mm, heavily uneven patterns appeared in the film and large variations of characteristics occurred when solar cells were made. When the distance between the anodes and the substrate was increased to 50 mm in order to decrease the relative distance differences, the deposition rates of film were decreased by an order of magnitude or more, and were values not satisfying the required specifications of the present apparatus at all.  
     [0259] On the other hand, where the inside tanks were disposed as in Example 5, the current to be supplied from the power supplies was 2 A, as described above, and there was little influence appeared when the distance between the anodes and the substrate was changed to either of 10 mm and 25 mm. As a result, the zinc oxide film was uniform with only one interference ring in the deposition area.  
     [0260] Further, in this case, the uniform zinc oxide film 1 μm thick was able to be formed on the substrate at the conveyance speed 350 mm/sec of the long substrate  4002  and asperities of about 1 μm were formed in this film.  
     Example 6  
     [0261] The inside tanks of Example 5 were replaced by the inside tanks  5011  as illustrated in FIG. 5. In FIG. 5, a plurality of openings  5038  to  5041  are bored in the bottom of the inside tank  5011 . An intermediate control plate  5042  having a plurality of openings  5035  to  5037  is disposed inside the inside tank  5011  and a control plate  5043  having a plurality of openings  5031  to  5034  is spaced above it. The spacing between the intermediate control plate  5042  and the control plate  5043  is set to be so small that the electric resistance from the unrepresented anode disposed above the upper control plate  5043  to the electrodeposition outside tank  4000  of such metal as stainless steel or the like is smaller than that in the case without the inside tank  5011 . On the other hand, this spacing is set to be so large as to permit sufficient inflow and outflow of the bath as indicated by an arrow in the figure.  
     [0262] Normally, the openings have the cross-sectional area not less than the diameter of 2 mm and the spacing between the control plates is 1 mm to 50 mm. In the present example each control plate was perforated to have eleven openings of the diameter of 10 mm and the PFA control plates 2 mm thick were spaced 2 mm apart from each other.  
     [0263] Deposition was carried out in the electrodeposition apparatus of the long substrate illustrated in FIG. 2, the electrodeposition apparatus incorporating the inside tanks  5011  of the present example instead of those in Example 5. The deposition rate of 80 Å/sec was obtained with supply of the current of 3 A from each power supply and the zinc oxide film was extremely uniform even with change in the distance between the anodes and the substrate to either of 10 mm and 25 mm.  
     [0264] Further, in this case, the extremely uniform zinc oxide film 1 μm thick was able to be continuously formed on the substrate at the conveyance speed 350 mm/sec of the long substrate  2001 , and asperities of about 1 μm were formed in this film. When observed in detail, the present example did not show fine stains, considered to be traces of bubbles as seen in Example 1, and the air by air bubbling was introduced into the inside tanks  5011  to effect agitation of the bath, thereby implementing further excellent uniformity of deposition.  
     Example 7  
     [0265] The inside tanks of Example 5 were replaced by the inside tanks  6011  as illustrated in FIG. 6. In FIG. 6, the inside tank  6011  is formed of stainless steel (SUS304) 3 mm thick and in a box shape opening up and the inside of the inside tank is lined with sheets of polyvinylidene fluoride which is a fluororesin. The lining was constructed so that the seams of this lining  6045  became not more than 0.2 mm.  
     [0266] Opening  6043  and opening  6044  are formed in the upper part of the side walls of this inside tank  6011  so as to permit inflow and outflow of the bath. There is a fan  6046  in the bath outside the opening  6043 , so that the bath outside the inside tank  6011  can be led into the inside tank  6011 .  
     [0267] The resistance from the anode  6003  placed in the inside tank  6011  to the electrodeposition outside tank of stainless steel  4000  was 20 times greater than that in the case without this inside tank  6011 . The flow rate of the bath by the fan  6046  was set to about 100 ml/min.  
     [0268] Deposition was carried out in the electrodeposition apparatus of the long substrate illustrated in FIG. 2, the electrodeposition apparatus incorporating the inside tanks of the present example instead of those in Example 5. The deposition rate of 80 Å/sec was obtained with supply of the current of 2.1 A from each power supply and the extremely uniform zinc oxide film 1 μm thick was able to be continuously formed on the substrate at the conveyance speed 350 mm/sec of the long substrate  2001 , as in Example 6. Asperities of about 1 μm were formed in this film.  
     [0269] Since the electrodeposition tank  2009  of FIG. 2 is provided with the active bath exchanging means, use of this electrodeposition tank  2009  permits temperature irregularities and concentration irregularities of the electrodeposition bath to be decreased remarkably and permits replenishment of new bath and removal of byproducts to take place effectively on the film-forming interface, thereby greatly enhancing microscopic uniformity of deposition.  
     Example 8  
     [0270] The electrodeposition tank formed of FRP was used in place of the outside tank of the electrodeposition tank of Example 5. The electrodeposition tank of FRP was formed of SMC (sheet molding compound) containing glass fibers and unsaturated polyester. The inside tanks all were removed.  
     [0271] This electrodeposition tank was incorporated into the electrodeposition apparatus of the long substrate illustrated in FIG. 2 and deposition was carried out in the electrodeposition apparatus. The deposition rate of 70 Å/sec was obtained with supply of the current of 2.3 A from each power supply and the extremely uniform zinc oxide film 1 μm thick was able to be continuously formed on the substrate at the conveyance speed 300 mm/sec of the long substrate  2001 , as in Example 6. Asperities of about 1 μm were formed in this film.  
     [0272] Use of the electrodeposition tank of the present example permits us to employ the configuration without the inside tanks. Particularly, in cases where the deposition rates are slow and some film thickness is required, the total length of the electrodeposition tank has to be set long; but many inside tanks do not have to be installed in such cases and thus the total cost of the electrodeposition apparatus can be decreased. Further, this electrodeposition tank also has the industrial merits of easier maintenance and easier action to an unforeseen accident by the degree of simplicity of the structure.  
     Example 9  
     [0273] The outside tank  4000  of the electrodeposition tank of Example 5 was equipped with the lining of ETFE film. The ETFE used had the thickness of 50 μm. Although the covering of ETFE was not perfect only in part because of formation of air holes for the air bubbling or the like, the electrical insulation of ETFE itself was sufficient and the electric field from the anode to the stainless steel electrodeposition tank was effectively intercepted in most part. It was verified that 70% or more of the current flowing to the anode without the inside tanks being disposed, flowed toward the substrate. Measurement of current was carried out by measuring the return current at the power supply part, using a clamp ammeter.  
     [0274] On the occasion of incorporation of the tank into the electrodeposition apparatus, all the inside tanks were removed, as in Example 8.  
     [0275] The electrodeposition tank provided with this lining of ETFE film was incorporated into the electrodeposition apparatus of the long substrate illustrated in FIG. 2 and deposition was carried out in the electrodeposition apparatus. The deposition rate of 60 Å/sec was obtained with supply of the current of 3 A from each power supply and the extremely uniform zinc oxide film 2 μm thick was able to be continuously formed on the substrate at the conveyance speed 200 mm/sec of the long substrate  2001 , as in Example 6. Asperities of about 1 μm were formed in this film.  
     [0276] Since the present example permits stainless steel to be used for the outside tank  4000  of the electrodeposition tank, the tank will experience little mechanical and chemical change with a lapse of time and is extremely tough. The ETFE is readily available, strong against high temperatures, and excellent in chemical resistance as well, so that stable characteristics can be expected over a long period. Further, the structure can be simple, because the inside tanks do not have to be set, as in Example 8. Therefore, the production cost can be decreased and the maintenance cost can also be decreased.  
     Example 10  
     [0277]FIG. 1 is a schematic diagram showing an example of the electrodeposition tank of the present invention.  
     [0278] In FIG. 1, the electrodeposition tank  1000  is formed of stainless steel (SUS) and in the dual structure in which a heat insulator of glass wool is interposed, thereby having good heat-insulating and heat-retaining properties.  
     [0279] The long substrate  1002  is formed of a stainless steel belt sheet (SUS430) and this substrate  1002  is conveyed through a slit formed in each of the both side walls of the electrodeposition tank  1000 .  
     [0280] Each of the side walls of the electrodeposition tank  1000  having the slit is double walls and overflows  1007  and  1008  of the electrodeposition bath  1001  retained in the tank are arranged to drop into the space between the double walls. The overflowing bath returns through an unrepresented return path to electrodeposition bath circulation tank  1025  and then is supplied again from bath circulating pump  1024  through bath supply pipe  1023  to the electrodeposition tank  1000 . With consideration to the circulation amount, the height from the overflowing point to the bath surface was set to 35 mm.  
     [0281] For agitating the electrodeposition bath  1001 , air is introduced from agitating air inlet pipe  1022  to effect bubbling of air from air blow pipe  1021  in the electrodeposition tank  1000 .  
     [0282] All the piping systems connected to the electrodeposition tank  1000  and placed in the electrodeposition tank  1000  are formed of heat-resistant vinyl chloride to be electrically insulated from the electrodeposition tank.  
     [0283] The electrodeposition bath  1001  is zinc nitrate of 0.2 mol/l and is kept at 70° C. Zinc nitrate makes zinc ions or complex ions present in the bath and also makes nitric ions present in the bath to electrochemically deposit zinc oxide on the surface of the substrate by the substrate by interaction of the ions. The electrodeposition bath  1001  further contains dextrin 0.7 g/l in order to enhance the uniformity of zinc oxide film. The electric conductivity of the electrodeposition bath  1001  was 65 mS/cm.  
     [0284] There are anode A  1003 , anode B  1004 , anode C  1005 , and anode D  1006  disposed in the electrodeposition tank  1000 . The voltage is placed between these anodes and the long substrate  1002 , whereupon the electrochemical reaction proceeds. For forming a film of zinc oxide, the potential of the anodes has to be maintained higher than the potential of the long substrate.  
     [0285] The anodes are connected to the respective separate power supplies  1011  to  1014 , so as to permit independent current to flow. The return of the current is implemented as a common return from the power-supply roller  1010  driven in contact with the long substrate.  
     [0286] Each power supply is controlled as a constant current source and the electrodeposition current density to the substrate  1002  is arranged to be able to be set in the range of 0.2 mA/cm 2  to 150 mA/cm 2  at each anode.  
     [0287] While the conveyance of the long substrate  1002  was stopped, deposition was investigated at a standstill. There appeared little clogging of the circulation system due to the powder and film chips and little difference among the deposition rates depending upon the locations of the, anodes, and the deposition rates approximately proportional to the current, 1 to 200 Å/sec, were obtained in the above range of the current densities. The present example employed the current density of about 60 mA/cm 2 . The deposition rate obtained in the deposition at a standstill was 80 Å/sec.  
     [0288] The size of each anode was 100×200 mm in the surface opposed to the long substrate  1002  and the thickness thereof was 20 mm. Each anode was made of zinc having the purity of 4 N. At this time, the current set value of each power supply was 12 A and the power-supply voltages indicated 2.5 to 3.5 V.  
     [0289] In the present example, the electrodeposition tank  1000 , together with the return path to the power supplies, is connected to the common ground. This configuration was employed because the apparatus would have become expensive if the apparatus should have been constructed by insulating all the rollers supporting the long substrate  1002 . If insulated, the tank has to be constructed so as to be adapted for short-circuits due to water drops or other contact objects.  
     Comparative Example 3  
     [0290] Prior to the investigation of Example 10, deposition was carried out by employing stainless steel piping systems as all the piping systems connected to the electrodeposition tank  1000  and disposed in the electrodeposition tank  1000 . Since these piping systems were made of stainless steel, they were grounded through the electrodeposition tank. The current density of 300 mA/cm 2  was necessary for obtaining the deposition rate of 200 Å/sec.  
     [0291] Namely, the current to be supplied from the power supplies was 60 A, which was close to the capacity limit of the power supplies. Besides, oxide films were deposited on the piping system connected to the electrodeposition tank  1000  and on the piping system placed inside the electrodeposition tank  1000 , and there appeared the powder, film chips, etc. due to peel-off of film therefrom, thereby adversely affecting the system by clogging of the circulation system or the like.  
     [0292] Deposition was very sensitive to the magnitude of the distance between the anodes and the substrate. When the distance between the anodes and the substrate was set to 10 mm, heavily uneven patterns appeared in the film, and large variations of characteristics occurred when solar cells were made. When the distance between the anodes and the substrate was increased to 50 mm in order to decrease the relative distance differences, the deposition rates of film were decreased by an order of magnitude or more, and were values not satisfying the required specifications of the present apparatus at all.  
     [0293] On the other hand, where the electrodeposition bath supply pipe and air blow pipe were made as in the above example, the current to be supplied from the power supplies was 12 A, as described above, and there was little influence appeared when the distance between the anodes and the substrate was changed to either of 10 mm and 25 mm. As a result, the zinc oxide film was uniform with only one interference ring in the deposition area.  
     [0294] Further, in this case, the uniform zinc oxide film with asperities about 1 μm thick was able to be continuously formed in the thickness of 1 μm on the substrate at the conveyance speed 350 mm/sec of the long substrate  1002 .  
     Example 11  
     [0295] All the piping systems connected to the electrodeposition tank  1000  and disposed in the electrodeposition tank  1000  were FRP piping systems, instead of the piping systems of Example 10.  
     [0296] The piping systems were incorporated into the electrodeposition apparatus illustrated in FIG. 2 and deposition was carried out in the electrodeposition apparatus. There appeared little clogging of the circulation system due to the powder and film chips and little difference among the deposition rates depending upon the locations of the anodes. In addition, the deposition rate of 60 Å/sec was obtained with supply of the current of 10 A from each power supply and the uniform zinc oxide film with asperities about 1 μm thick was able to be continuously formed in the thickness of 1 μm on the substrate at the conveyance speed 300 mm/sec of the long substrate  2001 , as in Example 10.  
     Example 12  
     [0297] The piping systems of Example 10 were replaced by piping systems obtained by coating inside and outside surfaces of stainless steel pipes or the like with Teflon.  
     [0298] The piping systems were incorporated into the electrodeposition apparatus illustrated in FIG. 2 and deposition was carried out in the electrodeposition apparatus. There appeared little clogging of the circulation system due to the powder and film chips and little difference among the deposition rates depending upon the locations of the anodes. In addition, the deposition rate of 70 Å/sec was obtained with supply of the current of 15 A from each power supply and the uniform zinc oxide film with asperities about 1 μm thick was able to be continuously formed in the thickness of 1 μm on the substrate at the conveyance speed 200 mm/sec of the long substrate  2001 , as in Example 11.  
     [0299] Since the present example can employ the metal material such as stainless steel or the like for the piping systems, they can be extremely tough against mechanical and chemical change with a lapse of time.  
     Example 13  
     [0300] The piping systems of Example 10 were modified into the structure as illustrated in FIG. 3, in which air blow pipe  3011 , agitating air inlet pipe B  3015 , and electrodeposition bath supply pipe  3016  in the figure were made of stainless steel whereas air blow pipe joint  3012 , agitating air inlet pipe A  3013 , agitating air inlet pipe joint  3014 , and electrodeposition bath supply pipe  3017  were made of heat-resistant vinyl chloride. In FIG. 3, reference numeral  3000  designates the deposition tank,  3001  the deposition bath,  3021  the bath circulation pump, and  3022  the electrodeposition circulation tank.  
     [0301] The piping systems of this configuration were incorporated into the electrodeposition apparatus illustrated in FIG. 2 and deposition was carried out in the electrodeposition apparatus. There appeared little clogging of the circulation system due to the powder and film chips and little difference among the deposition rates depending upon the locations of the anodes. In addition, the deposition rate of 72 Å/sec was obtained with supply of the current of 17 A from each power supply and the uniform zinc oxide film with asperities about 1 μm thick was able to be continuously formed in the thickness of 1 μm on the substrate at the conveyance speed 200 mm/sec of the long substrate  2001 , as in Example 11.  
     [0302] Since the present example can employ the metal material such as stainless steel or the like for part of the piping systems, they can be extremely touch against mechanical and chemical change with a lapse of time.  
     [0303] As detailed above, the present invention can provide the inexpensive electrodeposition tank and electrodeposition apparatus that can prevent the oxide film to be deposited on the piping system connected to the electrodeposition tank and on the piping system disposed in the electrodeposition tank during formation of the oxide film on the substrate, so as to suppress appearance of the powder, film chips, etc. in the bath and that can evenly form the uniform oxide film without irregularities on the substrate.  
     [0304] The electrodeposition apparatus according to the present invention can be obtained readily by making use of the existing apparatus.  
     [0305] The present invention permits formation of the oxide film suitable for the reflecting layer of the solar cell or the like. Particularly, the invention can provide the inexpensive electrodeposition tank that can remarkably enhance the uniformity of film and the film characteristics in the formation of zinc oxide on the long substrate, and also provide the inexpensive electrodeposition apparatus provided with the tank. Further, it can facilitate the maintenance of the tank and apparatus.