JP7658754B2 - Method and apparatus for cleaning seamless aluminum cans - Google Patents

Description

The present invention relates to a method and apparatus for cleaning seamless aluminum cans.

Conventionally, aluminum seamless cans have been widely used as containers for food and beverages such as beer and carbonated drinks. Such aluminum seamless cans are obtained by subjecting aluminum sheets to severe processing such as drawing and ironing, and are generally formed using a lubricant (coolant). As a result, the lubricant and aluminum powder (smut) adhere to the seamless can after drawing and ironing. In addition, a coating such as aluminum oxide is formed on the surface of the aluminum sheet.
Cans having such a lubricant and aluminum oxide coating formed thereon need to have the adhering lubricant and the like removed before being subjected to the subsequent painting and printing processes. In addition, the cans are subjected to a degreasing process using a degreaser containing a surfactant and an etching agent, and a water-rinsing process in order to form a good chemical conversion coating on the aluminum surface.

After degreasing and water-rinsing, aluminum seamless cans are subjected to acid washing in order to form an oxide layer mainly composed of aluminum oxide or hydroxide, thereby chemically inactivating the aluminum surface and preventing the occurrence of a defect in appearance known as brown spots (Patent Document 1).
Furthermore, the seamless cans that have been acid-washed are subjected to a water-washing process and a drying process and then transferred to a painting/printing process, etc., but it is required to impart slipperiness to the can surface to improve the transportability of the seamless cans, and to impart hydrophilicity to the can surface so that the water film that has adhered to the can surface in the water-washing process can be effectively removed before the drying process. For this reason, a surface conditioner for reducing the static friction coefficient of the can surface is sprayed onto the seamless cans that have been washed in the water-washing process, and then the cans are subjected to a drying process (Patent Document 2).

Patent No. 5007482 Patent No. 3186189

The above-mentioned method for cleaning aluminum seamless cans requires many steps, including a degreasing step, a water rinsing step, a film formation treatment step for forming a film mainly composed of an oxide or hydroxide of aluminum, a water rinsing step, a surface treatment step, a water rinsing step, and a drying step. This necessitates a very long line for cleaning aluminum seamless cans, and the equipment must be large. On the other hand, each step is essential for providing good aluminum seamless cans, and it is difficult to omit them.

The object of the present invention is therefore to provide a cleaning method and cleaning device for aluminum seamless cans that is simpler than conventional cleaning methods without impairing the quality of the aluminum seamless cans after cleaning.

According to the present invention, a method for cleaning aluminum seamless cans formed by drawing and ironing using a coolant comprises a pre-cleaning step for pre-cleaning the aluminum seamless can, a degreasing step for degreasing the aluminum seamless can using a degreaser, a water-rinsing step for rinsing the degreased aluminum seamless can with water, and a surface treatment step for surface-treating the aluminum seamless can that has been subjected to the water-rinsing step in a surface treatment bath comprising a film-forming treatment agent and a surface conditioner, the film-forming treatment agent being a water-soluble phosphoric acid or phosphate salt having a phosphoric acid concentration of 1 to 50 ppm in the surface treatment bath. The method for cleaning aluminum seamless cans is characterized in that the surface conditioner contains a main component (A) that is a polyoxyethylene alkyl ether with an EO addition mole number of 3 to 8, an HLB value of 8 to 12, and a carbon chain number of 10 to 14, and a dispersant (B) that disperses the main component (A) and the polyoxyethylene alkyl ether with an EO addition mole number of 6 to 10, an HLB value of 12 to 14, and a carbon chain number of 8 to 12, and the ratio of A to B is 1:0.2 to 1:1, and the surface conditioner is used in a surface treatment bath at a concentration of 50 to 1000 ppm.

In the cleaning method of the present invention, it is preferable to include a drying step for drying the aluminum seamless can that has been subjected to the surface treatment step after the surface treatment step.

According to the present invention, a cleaning device for cleaning aluminum seamless cans formed using a coolant includes a pre-cleaning means for pre-cleaning the aluminum seamless cans supplied from a forming means, a degreasing means for degreasing the aluminum seamless cans supplied from the pre-cleaning means with a degreaser, a water washing means for washing the aluminum seamless cans supplied from the degreasing means with water, a surface treatment means for surface-treating the aluminum seamless cans supplied from the water washing means with a surface treatment bath containing a film-forming treatment agent and a surface conditioner, and a drying means for drying the aluminum seamless cans supplied from the surface treatment means, and the aluminum seamless cans are passed through a cleaning device from the forming means to the drying means. The present invention provides an aluminum seamless can cleaning device comprising: a conveying means for continuously conveying cans; the film-forming treatment agent is an aqueous solution of phosphoric acid or a phosphate having a phosphoric acid concentration of 1 to 50 ppm in the surface treatment bath; the surface conditioner contains a main component (A) which is a polyoxyethylene alkyl ether having an EO addition mole number of 3 to 8, an HLB value of 8 to 12 and a carbon chain number of 10 to 14, and a dispersing agent (B) which disperses the main component (A) and is a polyoxyethylene alkyl ether having an EO addition mole number of 6 to 10, an HLB value of 12 to 14 and a carbon chain number of 8 to 12, the ratio of A to B being 1:0.2 to 1:1; and the surface conditioner is used in a concentration of 50 to 1,000 ppm in the surface treatment bath .

In the method for cleaning aluminum seamless cans of the present invention, the film formation process of forming an inactive treatment film on the aluminum surface, which has conventionally been carried out after the degreasing and water-rinsing processes, is carried out simultaneously with the surface treatment process using a surface conditioner. This makes it possible to shorten the line for cleaning aluminum seamless cans and reduce the size of the equipment. Moreover, even with the simplified process, the lubricant that has adhered to the aluminum seamless cans during the drawing and ironing process can be efficiently cleaned.
Furthermore, by simultaneously carrying out acid washing in a surface treatment step using a surface conditioner, the occurrence of brown spots caused by the reaction of water with aluminum can also be effectively prevented.

FIG. 1 is a flow chart showing a general flow of a conventional aluminum can washing process. FIG. 1 is a flow chart showing a preferred flow of the aluminum can washing process of the present invention. FIG. 1 is a side view diagrammatically illustrating an example of a cleaning device of the present invention.

(Cleaning method)
As described above, a method for cleaning aluminum seamless cans (hereinafter, sometimes referred to as "aluminum cans") requires many steps, such as a degreasing step, a water-rinsing step, an acid treatment step, a water-rinsing step, a surface treatment step, and a drying step. If a water-rinsing step is performed before and after each step, as shown in FIG. 1, in addition to the above essential steps, a preliminary cleaning step is provided before the degreasing step, a first water-rinsing step is provided between the degreasing step and the film-forming treatment step, a second water-rinsing step and a rinsing step with pure water are provided between the film-forming treatment step and the surface treatment step using a surface conditioner, and a drying step is provided after the surface treatment step. This increases the number of steps, resulting in a problem of a long cleaning line.
In the cleaning method of the present invention, as shown in FIG. 2, a film-forming treatment step for forming an inactive treatment film on the aluminum surface is carried out simultaneously with a surface treatment step, making it possible to omit the film-forming treatment step and the water rinsing step following the film-forming treatment step, and thus shortening the cleaning line.
Furthermore, in the surface treatment step, a film for inactivating the aluminum surface can be formed simultaneously with the surface treatment with the surface conditioner, so that the occurrence of brown spots can also be effectively suppressed.

[Seamless aluminum cans]
In the cleaning method of the present invention, the aluminum can to be cleaned is an aluminum seamless can formed using a lubricant as a coolant during forming. Specifically, it is a seamless can formed by subjecting an aluminum plate made of known aluminum or aluminum alloy such as 3004 material or 3104 material to severe processing such as drawing, drawing/deep drawing, drawing/ironing, drawing/bending/stretching/ironing, using a conventionally known lubricant such as mineral oil or synthetic oil. Furthermore, seamless cans formed by such a forming method are adhered with not only the lubricant but also smut generated during the processing. Furthermore, as described above, an aluminum oxide coating is formed on the surface of the aluminum plate.

[Degreasing and cleaning processes]
Aluminum cans with lubricating oil on them are continuously conveyed at high speed to the degreasing process of the washing equipment with the bottoms facing up. Before the degreasing process, a preliminary washing process is provided as necessary to remove smut and other impurities.
In the degreasing step, a conventionally known degreaser made of an alkali or acid can be used. Specifically, a degreaser containing a surfactant and an etching agent is used and sprayed onto the aluminum can from above and below. The physical impact of the surfactant removes the lubricant adhering to the surface of the aluminum can, and the etching agent dissolves the aluminum, removing the aluminum oxide film that has formed on the surface of the aluminum can.
The aluminum cans subjected to the degreasing step are washed with water in a washing step, and then transported to a surface treatment step. In the preferred embodiment shown in Fig. 2, the washing step is performed in two steps, a first water washing step and a pure water rinsing step, but the washing step is not limited to this and can be changed as appropriate.

[Surface treatment process]
In the surface treatment process, a surface treatment bath containing a film-forming treatment agent and a surface conditioner is applied to the surface of the aluminum can. By applying the surface conditioner to the surface of the aluminum can, hydrophilicity is imparted to the outer surface of the aluminum can and the lubricity of the aluminum can is improved. That is, when a surfactant is used as the surface conditioner, the hydrophilic group of the surfactant is adsorbed to the aluminum substrate surface, and the hydrophilic group and hydrophobic group are arranged on the surface layer side, thereby imparting hydrophilicity to the aluminum can. As a result, it is possible to remove and reduce the moisture attached to the can by washing with water after the surface treatment before the drying process, and the drying temperature in the drying process can be reduced. In addition, after drying, the lubricity of the hydrophobic group improves the lubricity, improving the transportability of the aluminum can.
Furthermore, in the present invention, by carrying out surface treatment in this surface treatment step using a surface treatment bath containing a film-forming treatment agent together with a surface conditioner, it becomes possible to effectively suppress the occurrence of brown spots on aluminum cans, which was previously suppressed by the film-forming treatment step for inactivating the aluminum surface that was conventionally carried out after the degreasing step.
That is, when aluminum reacts with the pure water used in the washing process, an oxide film called a boehmite film grows significantly, causing brown spots. When these brown spots occur, printing unevenness occurs in the subsequent printing and painting processes, resulting in poor appearance characteristics. However, in the present invention, by treating the surface of an aluminum can with a film-forming treatment agent in the surface treatment process, a film mainly composed of an oxide or hydroxide of aluminum is formed, which makes it possible to chemically inactivate the aluminum surface, and it becomes possible to effectively prevent the occurrence of brown spots without providing a separate acid treatment process.

In the present invention, as the surface conditioner, it is preferable to use a surfactant as described above, and in particular, a nonionic surfactant such as polyoxyethylene alkyl ether can be suitably used, and by using a main component (A) which is a polyoxyethylene alkyl ether having 3 to 8 moles of EO added, an HLB value of 8 to 12, and 10 to 14 carbon chains, and a polyoxyethylene alkyl ether dispersant (B) which disperses the main component (A) and has 6 to 10 moles of EO added, an HLB value of 12 to 14, and 8 to 12 carbon chains, the stock solution to be replenished to the surface treatment bath is stabilized, enabling production with stable quality. The ratio of B to A is 1:0.2 to 1:1, and if it is 1:1 or more, foaming occurs and treatment becomes impossible, and if it is 1:0.2 or less, the stock solution stability decreases.
The film-forming treatment agent to be contained in the surface treatment bath together with the surface conditioner preferably contains an inorganic acid such as sulfuric acid, nitric acid or phosphoric acid or an inorganic acid salt thereof, and is particularly preferably an aqueous solution containing phosphoric acid or a phosphate salt.

The surface treatment bath used in the surface treatment step contains the above-mentioned surface conditioner and film-forming treatment agent, and it is preferable that the surface treatment bath contains the above-mentioned surfactant as a surface conditioner in an amount of 50 to 1000 ppm, particularly 100 to 400 ppm. If the amount of the surfactant is less than the above range, there is a risk that sufficient slipperiness cannot be imparted to the aluminum can, whereas if the amount of the surfactant is more than the above range, there is a risk that the appearance characteristics of the outer surface of the can after drying will be impaired.
On the other hand, when phosphoric acid or an aqueous solution containing phosphoric acid is used, the film-forming treatment agent is preferably contained so that the phosphoric acid concentration in the surface treatment bath is 1 to 50 ppm, particularly 5 to 10 ppm. If the phosphoric acid concentration is lower than the above range, there is a risk that the generation of an oxide film on the surface of an aluminum can cannot be sufficiently suppressed, while if the phosphoric acid concentration is higher than the above range, further improvement in the effect of suppressing the generation of brown spots cannot be expected, and the cost efficiency will be poor.

The surface treatment bath can be applied to the surface of an aluminum can by a conventional method such as an immersion method or a spray method, as long as the surface treatment bath can be brought into contact with the inner and outer surfaces of the aluminum can. From the viewpoint of productivity, however, the spray method is preferable. The surface treatment bath is preferably brought into contact with the aluminum can for 3 to 10 seconds, depending on the concentration of phosphoric acid. If the contact time is shorter than the above range, it may not be possible to form a good coating mainly composed of an oxide or hydroxide mainly composed of aluminum. On the other hand, if the contact time is longer than the above range, the coating formed will not change and the productivity may decrease. In addition, the surface treatment bath is preferably adjusted to a temperature of 20 to 40° C., which allows efficient formation of a good coating capable of suppressing the occurrence of brown spots.
The aluminum cans that have been surface-treated in the surface treatment bath are transported to a drying process.

[Drying process]
The surface-treated aluminum cans that have been transported to the drying process are heated and dried in a dryer such as an oven. As described above, aluminum cans that have been subjected to the surface treatment process have excellent hydrophilicity and therefore reduced adhering moisture, and by drying at a temperature of 160 to 210°C for 70 to 240 seconds, aluminum cans that are free of brown spots and have excellent lubricity are produced.
Since the dried aluminum cans have excellent slipperiness, even when the aluminum cans are placed next to each other with no gaps between them, they do not clog the conveying path and can be smoothly conveyed to the printing process. In addition, since the inner surface of the aluminum cans also has high slipperiness, the mandrels for holding the aluminum cans can be smoothly inserted, significantly improving productivity.

(Cleaning device)
The washing apparatus for washing aluminum cans of the present invention comprises a pre-washing means for pre-washing aluminum cans having a lubricant or the like attached thereto and supplied from a forming apparatus, a degreasing means for degreasing the aluminum cans supplied from the pre-washing means with a degreaser, a water-washing means for rinsing the aluminum cans supplied from the degreasing means, a surface treatment means for surface-treating the aluminum cans supplied from the water-washing means with a surface treatment bath containing a film-forming treatment agent and a surface conditioner, and a drying means for drying the aluminum cans supplied from the surface treatment means, as well as a conveying means for continuously conveying the aluminum cans from the forming apparatus to the drying means.
That is, in the cleaning device of the present invention, the film forming means and the water washing means following the film forming means, which are conventionally provided after the degreasing means, are omitted, so that the cleaning device can be made compact and energy-efficient. Also, the number of steps is reduced, so the workload for maintenance and cleaning of the device is reduced.

3 is a side view that shows a schematic diagram of one example of the cleaning apparatus of the present invention, in which aluminum cans 1 having a lubricant or the like attached thereto, carried in from a molding apparatus (not shown), are continuously transported by a transport means 2 until they reach a drying means 8. As the transport means, a conventionally known transport means such as a mesh conveyor or a belt conveyor can be used, and a plurality of aluminum cans are placed in a line in the width direction of the transport means (perpendicular to the traveling direction) with their openings facing downward, and are continuously transported.
As is clear from FIG. 3, in a preferred embodiment of the cleaning apparatus of the present invention, a preliminary cleaning means 3, a degreasing means 4, cleaning means (a first water-washing means 5 and a pure water rinsing means 6), a surface treatment means 7 and a drying means 8 are provided along the conveying means 2 from the upstream (the left side of FIG. 3) to the downstream (the right side of FIG. 3) of the cleaning apparatus.
Each of the preliminary cleaning means 3, degreasing means 4, cleaning means 5 and 6, and surface treatment means 7 is provided with spray devices 10, 10, 10... each having a plurality of nozzles capable of spraying a degreaser, cleaning water, pure water, and a surface treatment bath from above and below the aluminum can in each process, and blower devices 11, 11, 11... for blowing away the degreaser, cleaning water, and the like that have accumulated at the bottom of the aluminum can. The provision of the blower device 11 makes it possible to prevent cleaning water and the like from accumulating even if the can bottom is a dome-shaped bottom that is concave inward.
In addition, following the surface treatment means 7, a vacuum transfer device 9 is provided which adsorbs the bottoms of the aluminum cans and transports them in a bridging manner in order to remove aluminum cans that are not in an inverted position with their bottoms facing upward.

The aluminum cans 1 carried out from the forming device are first sprayed with cleaning water from a spray device 10 in the preliminary cleaning means 3 from above and below by the conveying means 2, and then the cleaning water accumulated at the bottom of the can is blown away by a blower device 11, thereby removing in advance any dirt other than the lubricant and the like that adhered during forming. The cans are then carried into the degreasing means 4, where a degreaser containing a surfactant and an etching agent is sprayed from above and below the aluminum cans 1 from the spray device 10, and the degreaser that has accumulated at the bottom of the can is removed by the blower device 11, thereby removing the lubricant and smut that have adhered to the aluminum cans, and also removing the aluminum oxide film that has formed on the surface by etching the aluminum surface.
The aluminum cans 1 conveyed from the degreasing means 4 are washed by spraying and blowing off cleaning water using the spray device 10 and blower device 11 of the first water washing means 5, and then the pure water rinsing means 6 has the pure water sprayed by the spray device 10 and the pure water accumulated at the bottom of the can removed by the blower device 11, and the cans are conveyed to the surface treatment means 7.

In the surface treatment means 7, a surface treatment liquid containing a surface conditioner and a film-forming treatment agent is sprayed from above and below the aluminum cans by a spray device 10, thereby treating the surface of the aluminum cans. After the excess surface treatment liquid that has accumulated at the bottom of the cans is blown away by a blower device 11, only the aluminum cans in an inverted state with their bottoms facing up are carried into the drying means 8 by a vacuum transfer device 9. As described above, since the surfaces of the surface-treated aluminum cans have excellent hydrophilicity, the washing water from the washing means 5 and 6 is easily removed by the blown air from the blower device 11, and therefore the drying time in the drying means 8, which is then carried in, can be shortened.
The drying means 8 can be a conventional heating and drying device such as an oven. As described above, the aluminum cans dried by the drying means 8 have their surfaces coated with a surface conditioner to improve slipperiness, so that the aluminum cans do not stick to each other and cause clogging of the conveyance path when conveyed to the printing process, and can be conveyed smoothly to the printing process. In addition, the occurrence of brown spots is suppressed by the film-forming treatment agent, so that the cans have excellent printability.

The cleaning device of the present invention is not limited to the specific example shown in FIG. 3. It is sufficient to install the required number or length (line length) of cleaning means before and after the degreasing means and surface treatment means. Similarly, the number of nozzles of the spray device and the number of blower devices can be changed appropriately. In addition, the installation position of the vacuum transfer device 9 can also be changed appropriately as long as the aluminum cans conveyed from the cleaning device of the present invention do not cause clogging of the conveying path.

The following examples of the method for cleaning seamless aluminum cans are given below, but the present invention is not limited to these examples.
<Examples 1 to 6 and Comparative Examples 1 to 8>
The surface treatment baths according to the examples and comparative examples were prepared at the concentrations shown in Table 1. For the preparation, an aqueous solution containing 5% by mass of polyoxyethylene alkyl ether (A), an aqueous solution containing 5% by mass of polyoxyethylene alkyl ether (B), and an aqueous solution containing 2% by mass of sodium dihydrogen phosphate in terms of phosphate ions were used, and the surface treatment baths were prepared by diluting with water to the concentrations shown in Table 1. An aluminum seamless can was used as the object to be treated, and after a preliminary water washing step, the can was spray washed with water for 10 seconds, and after a degreasing step, the can was spray degreased for 60 seconds using a degreaser Surf Cleaner NHC310 manufactured by Nippon Paint Surf Chemicals Co., Ltd., and then sprayed with water for 10 seconds as a water washing step. After a pure water rinsing step by spraying for 10 seconds, the can was sprayed with the above-prepared surface treatment bath for 10 seconds as a surface treatment step, and then dried at 170°C for 3 minutes as a drying step. After drying, the aluminum seamless cans were evaluated for brown spots, appearance, and lubricity under the following conditions, and the stock solutions for preparing the surface treatment baths and the stability and foaming properties of the stock solutions of the surface treatment baths were evaluated under the following conditions.

[Brown spot evaluation]
The aluminum seamless cans of each Example and Comparative Example were visually inspected for the presence or absence of brown spots (parts discolored to brownish red) in the center of the inner surface and evaluated according to the following criteria. The results are shown in Table 1.
○: No occurrence ×: Occurrence

[Appearance evaluation]
The aluminum seamless cans of each Example and Comparative Example were visually inspected for the presence or absence of whitening in the center of the outer can bottom according to the following criteria. The results are shown in Table 1.
○: No whitening ×: Whitening

[Evaluation of stability of stock solution]
An aqueous solution containing 5% by mass of polyoxyethylene alkyl ether (A) and (B) in total in the ratio (A:B) shown in Table 1 was prepared, and after standing for 24 hours, the presence or absence of separation was visually evaluated. The results are shown in Table 1.
○: No separation ×: Separation

[Evaluation of Slipperiness]
Two seamless aluminum cans from each of the Examples and Comparative Examples were placed horizontally in contact with each other in the same direction, and one can was placed on top of the other in the opposite direction like a bale. The cans were then tilted at a speed of 50°/30 seconds, at which the angle at which the cans began to slide was measured. The results are shown in Table 1.
○: Less than 50° ×: 50° or more

[Foaming evaluation]
30 L of the surface treatment bath was prepared, and the foaming height when the prepared surface treatment bath was sprayed and stirred for 3 minutes was evaluated. The results are shown in Table 1.
○: Less than 5 cm ×: 5 cm or more

1 Aluminum can, 2 Conveying means, 3 Pre-cleaning means, 4 Degreasing means, 5, 6 Cleaning means, 7 Surface treatment means, 8 Drying means, 9 Vacuum transfer device.

Claims (3)

A method for cleaning aluminum seamless cans formed by drawing and ironing using a coolant, comprising the steps of:
the aluminum seamless can is subjected to a pre-cleaning step, a degreasing step, a water-washing step, a surface treatment ...
a surface conditioner that is used in a surface treatment bath at a concentration of 50 to 1000 ppm; and a surface conditioner that is used in a surface treatment bath at a concentration of 50 to 1000 ppm. The method for cleaning aluminum seamless cans is characterized in that the film-forming treatment agent is an aqueous solution of phosphoric acid or a phosphate salt having a phosphoric acid concentration of 1 to 50 ppm in the surface treatment bath; the surface conditioner contains a main component (A) that is a polyoxyethylene alkyl ether having an EO addition mole number of 3 to 8, an HLB value of 8 to 12, and a carbon chain number of 10 to 14, and a dispersant (B) that disperses the main component (A) and the polyoxyethylene alkyl ether having an EO addition mole number of 6 to 10, an HLB value of 12 to 14, and a carbon chain number of 8 to 12, the ratio of A to B being 1:0.2 to 1:1. The cleaning method according to claim 1, further comprising a drying step of drying the aluminum seamless can that has been subjected to the surface treatment step after the surface treatment step. A cleaning device for cleaning aluminum seamless cans formed using a coolant, comprising:
the aluminum seamless can supplying means for supplying the aluminum seamless cans from the forming means to the drying means; a pre-cleaning means for pre-cleaning the aluminum seamless cans supplied from the pre-cleaning means, a degreasing means for degreasing the aluminum seamless cans supplied from the pre-cleaning means with a degreaser; a water-washing means for rinsing the aluminum seamless cans supplied from the degreasing means with water; a surface treatment means for surface-treating the aluminum seamless cans supplied from the water-washing means with a surface treatment bath containing a film-forming treatment agent and a surface conditioner; and a drying means for drying the aluminum seamless cans supplied from the surface treatment means; and a conveying means for continuously conveying the aluminum seamless cans from the forming means to the drying means ,
The cleaning device for aluminum seamless cans is characterized in that the film-forming treatment agent is an aqueous solution of phosphoric acid or a phosphate having a phosphoric acid concentration of 1 to 50 ppm in the surface treatment bath, the surface conditioner contains a main component (A) which is a polyoxyethylene alkyl ether having an EO addition mole number of 3 to 8, an HLB value of 8 to 12, and a carbon chain number of 10 to 14, and a dispersant (B) which disperses the main component (A) and the polyoxyethylene alkyl ether having an EO addition mole number of 6 to 10, an HLB value of 12 to 14, and a carbon chain number of 8 to 12, the ratio of A to B being 1:0.2 to 1:1, and the surface conditioner is used in a surface treatment bath at a concentration of 50 to 1,000 ppm .