KR20010038260A - Method for forming a film onto the inside of the 2-piece steel can - Google Patents

Abstract

PURPOSE: A method for forming a film on the inner surface of a two piece steel can is provided to obtain superior corrosion resistance and form a uniform and continuous film on the inner surface of the steel can by controlling operating factors of the film forming process, for example, spraying direction, spraying pressure, nozzle shape, spraying position, spraying amount, and number of rotations and drying conditions of the can. CONSTITUTION: In a method forming a uniform film having superior corrosion resistance by spraying a liquid phase paint together with a high pressure air in the state of fine particles through first and second spraying nozzles during the revolution of a steel can (11), the method for forming a film on the inner surface of a two piece steel can (11) is characterized in that a total spraying amount of the paint through the first and second spraying nozzles is maintained to the range of 260 to 290 mg/can, and an overlapped distance of the spraying position of the first spraying nozzle (13) and that of the second spraying nozzle is maintained within 30 to 40 mm.

Description

Method for forming a film onto the inside of the 2-piece steel can}

The present invention relates to a method of forming a film on the inner surface of a two-piece steel can so as to have an inner surface excellent in corrosion resistance, and in particular, by appropriately adjusting the distribution and the spraying amount of the paint sprayed on the inner surface of the two-piece steel can, The present invention relates to a method of forming a film on the inner surface of a two-piece steel can so as to uniformly spray the paint on the inner surface of the steel can to suppress the generation of pores by forming a continuous film of the paint, thereby preventing contact of the inner surface of the steel can with the contents.

In general, the can used as a container for storing contents such as food and beverages, in addition to the characteristics that can safely store the contents stored for a long time, such as ease of transport, convenience of use and recycling of resources by can recovery Since it has good characteristics in terms of the situation, it is gradually expanding according to the change of living environment. In particular, steel cans made of steel, such as aluminum, compete with glass, paper, and plastics in terms of function and price, but are most widely used because of advantages in terms of recycling resources and stable prices.

Such steel cans are classified into three-piece steel cans by welding and two-piece steel cans which are combined to process drawing and ironing, depending on a processing method.

The processing of these steel cans is appropriately adopted by considering the price of materials, processing technology, types of contents, and safety (corrosion resistance) due to long-term storage. The processing method of satisfying two-piece steel cans is widely used.

First, considering the processing technology aspect, a three-piece steel can consisting of a body cut to a certain size according to the size of the can, a bottom bottom end, and a top end is formed. It is formed by welding them. The two-piece steel can, which is composed of the body and the upper lid members, is manufactured by a drawing and ironing process, which is a mechanical processing method instead of the welding process, unlike the three-piece steel can.

In addition, considering the cost of materials, we are developing a technology to process the thinner cans as light as possible, that is, the thinner cans are economically advantageous. In the case of a three-piece steel can, the body thickness is 0.19- Although 0.21 mm, the two-piece steel can is about 0.070-0.090 mm, which is very economical in terms of weight by about 1 / 2-1 / 3 compared to the three-piece steel can. In addition, the two-piece steel can is widely used because there is no limitation on the type of the contents and the storage method thereof, and its application range is very wide.

On the other hand, in consideration of the safety of the contents to be stored, the steel can is a container for storing food and beverages, it is necessary to suppress the contact between the contents and the container so that it can be safely stored for a long time without changing the contents. In order to achieve this, by coating a safe paint on the inner surface of the steel can to form a coating on the surface, it is possible to suppress the electrochemical or physical contact between the contents and the steel can.

However, the coating material for forming such a coating is usually based on epoxy or phenol and is a liquid phase dissolved in a solvent. Thus, the steel can is dried at a constant temperature to obtain a solvent. When vaporizing, it is easy to form fine pores in the coating of the paint during the release of the solvent.

Therefore, in order to safely store the contents of the steel can, it is important to distribute the paint tightly and uniformly on the inner surface of the steel can in addition to the safety of the applied paint.

The three-piece steel can is coated with a paint on the surface of the steel sheet, which is a raw material, to protect the inner surface thereof, and the two-piece steel can is coated with the inner surface after the processing of the can is completed.

However, since the three-piece steel can is manufactured by welding after processing the three components as described above, in consideration of corrosion resistance on the inner surface of the steel can, the three-piece steel can is coated on the weld portion to suppress corrosion in the weld portion. It will require an additional process to deal with. In addition, if the welded portion is not sufficiently protected by the paint, there is a problem that the safety of the stored contents is deteriorated by the local contact of the stored contents with the paint.

In addition, in the case of the two-piece steel can, there is no welding process in the body processing, so there is no additional process of paint on the welded portion or corrosion resistance due to corrosion of the welded portion, so there is an advantage that it can be stably used for various contents.

On the other hand, there is a difference in the method of coating the paint. In the manufacturing process of the three-piece steel can, a roll coating method is used in which the paint is transferred to the steel sheet between the rolls in which the liquid paint is applied. In steel cans, the spraying method of spraying the inside of the can into fine particles under high pressure conditions after processing is mainly used.

Therefore, in the case of the three-piece steel can, the flatness of the roll, the gap between the rolls, and the pressing pressure between the roll and the steel sheet are important for uniformly spraying the paint. Since the coating is applied to the inside of the can, a technique for controlling the spraying amount, the spraying position and state of the paint, and the number of revolutions of the can for smooth movement and distribution of the paint in the steel can is very important to obtain a uniform and dense distribution.

Manufacturing process of two-piece steel can The paint applied inside the can may be uniformly distributed depending on the spraying conditions of the paint, but in some cases, it may be difficult to obtain a uniform distribution by concentrating on a part of the can. It is required to make the injection quantity small.

As described above, the paint on the inner surface of the steel can has a function of suppressing contact with the contents, and therefore, should be uniform and dense, and a continuous film should be formed.

However, the paint sprayed into the liquid phase should be free of pores during drying, but fine pores may be formed when the coating state is not appropriate due to vaporization of the solvent. In addition, when the injection amount of the paint is so small that the inner surface of the steel can cannot be completely covered, a continuous coating cannot be formed. And even when the injection amount of the paint is excessive, the paint is concentrated on a part of the inner surface of the steel can, the amount of gas generated from the excess solvent during drying increases, and the pressure of the gas increases so as to form fine pores in the film, so that the released gas This makes it impossible to form a continuous and uniform film on the inner surface of the steel can.

That is, the corrosion resistance of the inner surface of the steel can is greatly influenced by the amount of the spray of the paint. Therefore, when the amount of the spray of the paint is excessive or too small to form a complete film on the inner surface of the steel can, By direct contact, stored contents are deteriorated or oxygen in the air penetrates into the steel can, thereby causing hole corrosion due to oxidation of the steel can, thus making it difficult to secure a storage function.

Therefore, in the case of steel cans, both the three-piece steel can and the two-piece steel can are coated with two paints, and the coating and drying processes are performed, respectively, but in either case, a uniform and continuous film is formed while the coating amount is minimized and dried. The condition that pore does not occur is required.

In addition, according to the conventional embodiment, since the paint is applied to the inner surface of the three-piece steel can by pressing the roll, the difference in coating amount in the length or width direction of the steel sheet is large depending on the pressure distribution between the roll and the raw steel sheet and the shape of the roll. appear.

In addition, since the paint is dried in a state where it is applied to the steel sheet, when the paint is applied unevenly, there is a non-uniform application state even after drying, and by forming a portion discontinuous coating due to the difference in adhesion amount for each part of the steel sheet, There is a problem that indicates a difference.

In addition, since the steel sheet is continuously moved in order to repeatedly perform the coating and drying processes of the paint, some paint coating surfaces are damaged by friction between the steel sheets surface during the movement of the steel sheet, and also mechanical damage of the steel sheet itself. This can lead to loss of material as well as corrosion resistance inside the steel can.

On the other hand, in the case of a two-piece steel can, since the paint is applied after the body of the can is processed, there is almost no loss of film due to mechanical damage or friction. However, as described above, since the paint on the inner surface of the two-piece steel can is applied by spraying, the film on the inner surface of the steel can is influenced by the spraying position, the spray amount and the number of revolutions of the steel can, so it is important to select appropriate conditions. .

That is, the position where the paint is sprayed is directed to the inner surface of the steel can, but when the spraying position is not appropriate, the paint is sprayed to the outside of the can or the atmosphere, so that sufficient paint continuity cannot be obtained and the pollution or environment of the equipment can be obtained. It is also important to distribute a sufficient amount of paint on the inner surface of the can with a minimum amount of paint, as this may cause a problem.

However, according to the conventional embodiment, when forming a coating on the inner surface of the two-piece steel can, the bottom portion or the body of the steel can in order to increase the amount of paint on the inner surface of the steel can or to obtain a thick coating to improve the corrosion resistance of the inner surface of the steel can. Applying an excessive amount of paint over the site causes economic losses, such as the flow of a portion of the paint on the inner surface of the steel can, the uneven distribution of the paint, and increased the formation of bubbles in the coating.

Therefore, in order to solve the conventional problems as described above, in order to form a uniform and continuous coating on the inner surface of the two-piece steel can, the liquid paint is sprayed on the inner surface of the steel can in a fine particle state at high pressure and then dried. In this case, since the state of the paint remaining on the inner surface of the steel can varies depending on the method of spraying the paint, work factors of the film forming process mainly affecting the corrosion resistance of the paint, for example, spray pressure, nozzle type, spray position, spray amount, An object of the present invention is to provide a method of forming a film on an inner surface of a steel can by adjusting the rotational speed and drying conditions of the can.

In addition, the present invention relates to a method for forming a film on the inner surface of the steel can can be formed so that the inner surface of the two-piece steel can has a uniform and continuous coating on the inner surface of the two-piece steel can to have an inner surface with improved corrosion resistance. And to provide good corrosion resistance to the inner surface of the steel can by appropriately adjusting the state, the injection amount and the rotation speed of the can for smooth movement of the inner paint.

In addition, an object of the present invention is to form a coating on the inner surface of the steel can for storing the contents, such as food, when spraying the paint on the inner surface of the steel can, in order to suppress direct contact of the inner surface of the steel can and the contents stored therein, It is to provide a method for forming a uniform and continuous coating on the inner surface of the two-piece steel can by adjusting the spraying position and state of the paint, the spraying direction and the number of revolutions of the steel can on the inner surface of the steel can.

Therefore, according to an embodiment of the present invention for achieving the above object, the method for forming a film on the inner surface of the steel can, through the first spray nozzle and the second spray nozzle, while the steel can is rotated, on the inner surface of the steel can, The liquid paint, which is a fine particle, is sprayed together with the high pressure air, and the total spraying amount of the paint through the first spray nozzle and the second spray nozzle is maintained in the range of 260-290 mg per can, and the spray of the first spray nozzle The overlapping distance between the position and the injection position of the second spray nozzle is maintained within 30 to 40 mm.

1 is an explanatory view showing a state in which paint is sprayed through a first spray nozzle on an inner surface of a steel can according to an embodiment of the present invention.

2 is an explanatory view showing a state in which paint is sprayed on the inner surface of the steel can through the second spray nozzle according to an embodiment of the present invention.

3 is an enlarged cross-sectional view illustrating that a film is formed on an inner surface of a steel can by enlarging a portion indicated by a solid line in FIG. 2;

Figure 4 is a table showing embodiments according to the distribution conditions of the paint sprayed on the inner surface of the steel can.

5 is a table showing the corrosion resistance of the inner surface of the steel can according to the distribution conditions of the paint shown in FIG.

<Description of the code | symbol about the principal part of drawing>

11: steel can

13: first spray nozzle

15: second injection nozzle

17a: first film

17b: second film

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

First, in order to provide sufficient corrosion resistance on the inner surface of the two-piece steel can to safely store the contents to be stored, the liquid paint is applied as fine particles by high pressure air and then dried to form a film.

According to the present invention, in order to obtain a uniform and dense coating film, the spraying conditions such as the spraying position and the spraying amount of the paint and the number of revolutions of the can after spraying are controlled, and these spraying conditions will be described below.

According to an embodiment of the present invention, the spraying position of the paint applied to the inner surface of the steel can is an important item for obtaining a uniform coating. For example, as illustrated in FIGS. 1 and 2, two spray nozzles, a first spray nozzle 13 and a second spray nozzle 15 are used to spray paint on the inner surface of the steel can.

First, while the steel can 11 is rotated, the first coating nozzle 17 is formed by spraying (A) a paint on the bottom 11a of the inner surface of the steel can 11 and its surroundings through the first spray nozzle 13. Subsequently, a coating is sprayed on the body portion 11b of the inner surface of the steel can 11 through the second spray nozzle 15 to form a second film 17b.

In this case, as shown in FIG. 3, a portion of the tip portion of the first film 17a formed by the paint sprayed from the first spray nozzle 13 and a paint sprayed from the second spray nozzle 15 are formed. The paint is sprayed on the inner surface of the steel can 11 so that a part of the tip portion of the second film 17b may overlap (C).

As described above, by spraying the paint on the inner surface of the steel can 11 while the steel can 11 is rotated, the sprayed paint is uniformly distributed on the inner surface of the steel can 11, the liquid paint in the subsequent drying process By vaporizing the solvent present in the gaseous state, a uniform coating can be formed on the inner surface of the steel can 11.

On the other hand, the supplied steel can is continuously rotated by a mechanical method, the injection nozzles are placed in a predetermined position, it is possible to adjust the injection position of the injection nozzle and the distance to the steel can. In addition, the steel can continues to rotate even after spraying the paint, in order to make the distribution of some uneven paint uniform. At this time, since there is no rotation in the drying process of the paint, the distribution state of the paint on the inner surface of the steel can is determined by the spraying conditions of the paint and the rotation of the steel can.

However, the paint sprayed at a high pressure is not distributed in a predetermined portion, and as shown in FIGS. 1 and 2, the paint is distributed and distributed on the inner surface of the steel can 11, and thus, through these two spray nozzles 13 and 15. The sprayed paints overlap each other, and in particular, some paints are overlapped. Therefore, it is necessary to prevent the coating from being excessively formed at a specific site, thereby preventing the formation of a continuous coating due to the flow of the paint applied to the inner surface of the steel can 11 during the transportation of the steel can 11.

According to an embodiment of the present invention, the paint is sprayed on the inner surface of the steel can 11 in order to prevent the formation of bubbles due to the increase in the amount of gas discharged from the solvent during drying to concentrate the paint on the bottom end of the steel can 11, in particular. In order to minimize the spraying amount of the paint and to control the spraying position and the rotational speed of the steel can through the two spray nozzles 13 and 15 during the spraying of the paint, a uniform and continuous film is formed on the inner surface of the steel can 11. Let's do it.

Next, the present invention and the comparative example will be described in detail through examples.

In FIG. 4, according to the Example of this invention, a conventional example, and a comparative example, the injection conditions for spraying paint on the inner surface of a steel can are compared and shown.

The spraying conditions shown in FIG. 4 were carried out under the condition of continuously processing the entire process from the processing of steel cans to the spraying and drying of steel cans using a pilot plant having the same function as a general commercial equipment. It is the same condition as facilities.

At this time, the material used was about 0.245mm in thickness, and was made into the material generally applied commercially, the tin plating amount on the surface of the material was 2.8 / 2.9gr / m 3, and the surface roughness was 0.9 μm. And, the size of the steel can is 350ml and the ironing speed for processing the body was 350 cans per minute, which can be seen that it was performed slightly faster than the commercial speed (250-270 cans / min). In addition, the processed steel cans were washed to remove the processing oil adhering to the surface, dried, and continuously passed through the paint spraying machine.

At this time, the speed of the paint sprayer was to process 350 cans per minute in the same way as the processing speed of the body, and the type of paint used was epoxy paint applied commercially to beverage cans. The spraying of the paint was supplied by maintaining a pressure of 70Opsi, and was sprayed according to the advancing speed of the can while maintaining a high pressure by a pump in accordance with the processing speed of the steel can 11.

For the practice of the present invention, the spraying angle of the nozzle was adjusted to change the distribution condition of the paint on the inner surface of the steel can, and the spraying amount of the paint was finely adjusted by adjusting the spraying pressure of the paint.

For example, the first spray nozzle 13 is positioned so that the paint can be applied (A) to the lower part of the body 11b around the bottom portion 11a of the steel can 11, and the second spray nozzle 13 is positioned. The nozzle 15 is positioned so that the trunk 11b of the steel can 11, that is, the wall portion of the steel can can be coated (D).

On the other hand, unlike the above, since the position of the injection nozzles may be different by adjusting according to the height difference of the steel can 11, the continuity and distribution of the paint according to a certain position was investigated.

Then, the steel cans, which have been sprayed with paint, passed through the drying process with the upper part of the steel cans up, similar to the commercial equipment conditions. At this time, the drying conditions were continuously performed at 190 ° C, 200 ° C, and 200 ° C for 1 minute each. To dry. The spraying amount of the paint was calculated by subtracting the weight of the steel can after drying by the weight of the steel can before spraying. In order to evaluate the corrosion resistance of the steel can 11, whether or not bubbles were observed at the bottom of the steel can was visually observed, while fine pores in the body were observed. Since visual observation is difficult to observe, it was measured by an Enamel Rating Value (ERV) instrument that evaluates the continuity of the film.

ERV is a method for evaluating the continuity of the film on the inner surface of the steel can by measuring the amount of current passing through the film, which means that the lower the ERV value, the more the film is formed continuously and the better the corrosion resistance.

FIG. 4 compares the conditions for spraying paint on the inner surface of the steel can according to the conventional example, the comparative example and the embodiment of the present invention, and FIG. 5 shows the distribution of the paint distributed on the inner surface of the steel can according to the spraying conditions of FIG. 4. The distribution state is shown by the ERV value which is corrosion resistance property, the bubble generation in the bottom of a steel can which shows workability, and the pinhole occurrence in the wall part.

First, in order to ensure corrosion resistance, the steel can is sprayed with paint twice, dried after the first spray, and then dried after the second spray. In this process, the effect of corrosion on the pilot location was investigated by varying the position of injection, injection quantity, distance of overlap and rotation speed of can.

Referring to Fig. 4, the conventional example shows the conditions for the conventional two-piece steel can, and the injection amount of the first spray nozzle and the second spray nozzle is 160 mg and 170 mg, respectively, and the overlap distance is It was kept at about 15 mm and the rotation speed of the can was maintained three times during the injection.

That is, the conventional example is an example of improving the corrosion resistance of the inner surface of the steel can by increasing the injection amount, unlike the conditions of the overlap distance, the rotation speed of the can, and the total injection amount range, which will be described later in the present invention. The amount of injection was 330 mg, and the film was formed in the bottom and the trunk of the can.

However, in the conventional example, despite the relatively large amount of paint sprayed, uncoated surfaces are formed on the wall of the steel can, resulting in an ERV value higher than 0. Also, excessive spraying results in equipment contamination and paint loss. I have a problem.

On the other hand, Comparative Example 2 shows a case similar to the injection amount in Comparative Example 1, there is no overlap between the nozzles and the number of rotations of the can is four times, although the number of rotations of the steel can for uniformly distributing the paint is sufficient. Bubbles were formed at the bottom after drying by excessive paint spraying in the first spray nozzle, and because there was no overlap between nozzles, an uncoated surface was formed inside the can. As a result, as shown in Fig. 5, the ERV values show 5.3 and 3.2 after one injection and two injections, respectively, indicating that it is difficult to obtain sufficient corrosion resistance.

In addition, in Comparative Example 3, the condition of the overlapping distance between the nozzles and the number of revolutions of the steel can is within the condition range of the present invention, but since the amount of paint is sprayed, bubbles are easily formed at the bottom, and the ERV value is 1.2 after two injections. It can be seen that it did not satisfy.

In addition, Comparative Example 4 is a case where the spraying amount of the paint is relatively smaller than that of Comparative Examples 1 to 3, and even if the spraying position of the nozzle or the number of rotations of the can is appropriate, the spraying amount is absolutely small and the inner surface of the can cannot be sufficiently coated. Some uncoated surfaces are formed. In other words, uncoated surfaces were identified on some walls, and as a result, the ERV value was about 0.8 after 2 coatings.

Therefore, referring to Comparative Examples 1 to 4, the injection amount of the paint applied to the inner surface of the steel can is very important in terms of corrosion resistance, but the excessive injection is caused by the release of the solvent during drying since the paint accumulates at the bottom of the can inner surface. It can be seen that there is a problem that it is difficult to form a uniform film due to an increase in pressure and bubbles are formed, and when it is relatively small, it is difficult to form a continuous film on the inner surface of the can.

Therefore, in order to form a film having excellent corrosion resistance, it is necessary to have a uniform distribution by adjusting the first spray nozzle and the second spray nozzle during the spraying of the paint, and by appropriately rotating the steel can, the paint on the inner surface of the steel can is evenly distributed. It can be seen that it is important to distribute the entire inner surface.

On the other hand, Comparative Examples 5 and 6 show the effect of corrosion resistance according to the number of revolutions of the steel can, in the case of Comparative Example 5, the total injection amount, the overlapping distance between the nozzles and the number of revolutions of the can satisfy the scope of the present invention, In this case, the paint was accumulated at the bottom of the can, and in this case, the paint was collected locally at the can wall, so that a uniform distribution could not be obtained and the ERV value was 4.5 to satisfy the corrosion resistance.

In Comparative Example 6, the coating is formed without increasing rotation during the spraying of the paint, and the coating is sufficient. At this time, the paint is sufficient but the paint on the inner surface is not uniformly distributed because there is no rotation of the can during the spraying. It was difficult to secure corrosion resistance because the ERV value was 1.8 even after two injections.

In addition, referring to Comparative Examples 5 to 8, it can be seen that the number of revolutions of the steel can has a function of uniformly distributing the paint on the inner surface. Concentrating on the wall, it can be seen that bubbles or pinholes are easily formed.

In this way, it is also shown in Comparative Example 7 that the number of revolutions of the steel can during injection is important.

In other words, the injection amount and the injection position satisfy the scope of the present invention, but when the rotation is three times, the paint sprayed on the inner surface cannot be uniformly distributed, so pinholes are generated at some walls, and the ERV value is very high as 4.5.

On the other hand, in Comparative Example 8, when the injection amount is appropriate and the rotation of the steel can is sufficient, the overlapping distance of the nozzle is excessively long. Since the injection position of the nozzle is set too far inside the steel can, a nozzle having a constant width is used for the steel can. Could not spray enough to the upper end.

Therefore, since the uncoated surface is formed at the upper end of most steel cans, the ERV value was very high due to the internal surface exposure. Therefore, it is preferable that the injection position of the nozzle is as close to the inside of the can as possible, but if it is too far, it is important to form an exposed surface at the upper end so that an appropriate overlap is formed.

On the other hand, Inventive Example 1 according to an embodiment of the present invention, when the paint is sprayed on the inner surface of the steel can under the condition that the amount of paint sprayed 288 mg per can, the overlap distance between the nozzles is 35 mm and the number of rotation of the can during spraying is 4 to be.

Such paint spray conditions fall within the condition range of the present invention, and as shown in FIG. 5, there was no bubble generation or pinhole generation at the trunk portion during drying. And ERV in the completion can after 2 injections showed 0. This means that the paint on the inner surface of the can is uniform, dense, and continuous coating is formed, and also the spraying position of the spray nozzle and the can during the spraying, despite being smaller than the spraying amount of the conventional (prior example, Comparative Examples 1, 3, 6). By appropriately adjusting the number of revolutions, it is possible to secure economically excellent corrosion resistance on the inner surface of the steel can.

In addition, the invention examples 2 and 3 of FIG. 5 are the conditions of the invention examples 2 and 3 of FIG. 4 contained within the injection conditions of this invention, that is, the injection amount of 260-290 mg, the overlap distance of a nozzle 30-40 mm, and rotation speed 4 When the paint was sprayed on the inner surface of the steel can under the condition of more than twice, the ERV value, which is the corrosion resistance evaluation index, was 0. Thus, it can be seen that the method of the present invention can produce a two-piece steel can excellent in corrosion resistance.

The following describes the reasons for limiting the spraying conditions of the paint in the claims of the present invention.

The present invention relates to a method for producing a two-piece steel can having an inner surface excellent in corrosion resistance, and when spraying the paint on the inner surface of the two-piece steel can, the spraying amount of the total paint after two sprays is in the range of 260-290 mg per can, The overlapping distance between the first spray nozzle and the second spray nozzle is in the range of 30-40 mm, and the can is rotated at least four times during spraying to obtain a uniform paint distribution on the inner surface of the steel can.

At this time, the reason why the total injection amount of paint was limited to 260-290 mg is as follows. That is, the injection amount of the paint is a basic requirement for completely applying the inner surface of the steel can. When the liquid paint is excessively sprayed to 290 mg or more, the paint is accumulated at the bottom of the steel can during drying, and As the amount increases, the pressure inside increases, which damages the coating. That is, as shown in Comparative Examples 1, 3, 5, and 6 of FIG. 5, since bubbles are formed, it is difficult to form a continuous film, so the spray amount of the paint is limited to a maximum of 290 mg.

In addition, when the total spray amount of the paint is less than 260 mg, it is difficult to form a uniform coating due to the lack of an absolute amount in which the paint can be evenly distributed on the inner surface of the steel can, thereby forming fine pores (compare FIG. 5). Example 4).

Therefore, in the present invention, the total spray amount of the paint is limited to the range of 260 mg to 290 mg so as to suppress bubble formation at the bottom of the steel can or pores at the body portion. This is less than the total injection amount of the coating material (Fig. 4, conventional example, Comparative Example 1) in the conventional embodiment, it has an economic effect of about 10% and showed excellent characteristics in terms of corrosion resistance.

On the other hand, the injection position of the first injection nozzle and the second injection nozzle is also an important process factor for forming a uniform coating as a factor influencing the distribution of the paint. That is, when there is no overlap in the position where the paint is sprayed, since there is a gap between the spray positions of the two spray nozzles, an uncoated surface is formed in this space, and the corrosion resistance is deteriorated, so that the spray positions are preferably partially overlapped. That is, the overlapping position during the spraying is a overlapping position between the bottom of the steel can and the paint sprayed on the body from the spraying nozzles, and has a function of mutually complementing a space that is not easily applied.

On the other hand, since the spraying of the paint is sprayed at a high pressure as described above, the paint sprayed into the steel can is dispersed into very small particles, so that some uncoated surfaces may be formed when the overlapping portion is not appropriate. Therefore, formation of an uncoated surface can be suppressed by adjusting the overlap distance suitably.

In the embodiment of the present invention, the reason why the overlap distance between the nozzles is limited to 30 to 40 mm is as follows.

First, when the overlapping distance is less than 30 mm, the injection zone between the first injection nozzle and the second injection nozzle is narrow, and the complementary roles could not be sufficiently fulfilled, as shown in Comparative Example 2 or the conventional example of FIG. Likewise, some uncoated surfaces are formed on the inner surface of the steel can, and thus there is a problem of deterioration of corrosion resistance. In the case where the overlapping distance is 40 mm or more, the paint is concentrated in a partial region of the inner surface of the steel can, so that the fluidity of the paint is lowered, and in particular, it is difficult to obtain a uniform distribution in the body of the steel can (FIG. 4, Comparative Example 8). ).

In addition, since the nozzle is sprayed only inside the steel can, the spray of paint is relatively reduced at the upper end of the can. In this case, bubbles are generated by local concentration of the paint on the inner surface of the steel can, or an uncoated surface is formed on the upper end of the steel can, and the corrosion resistance of the steel can inner surface is deteriorated. Therefore, in order to ensure the corrosion resistance of the inner surface by the uniform distribution of the coating and the formation of the continuous coating, the overlapping distance between the spray nozzles was limited to 30-40 mm.

In addition, the rotation speed of the steel can plays an important role for mechanically and uniformly distributing the paint sprayed in the liquid state. That is, when some uncoated surfaces are formed during paint spraying or paint is locally accumulated, as the steel can rotates, the paint is uniformly distributed on the inner surface of the steel can, which is maintained even during drying to form a continuous coating. That is, as shown in Comparative Examples 5 and 6 of FIG. 5, when the injection amount of the paint was sufficient but there was no rotation of the steel can, it was difficult to obtain a uniform distribution of the paint and sufficient corrosion resistance could not be obtained.

On the other hand, referring to Comparative Example 7 of FIG. 5 which shows the case where the number of revolutions of the steel can is three times during spraying, the corrosion resistance evaluation result shows that the ERV value is 2.7, making it difficult to ensure sufficient corrosion resistance. In the case (Invention Example 2), since the corrosion resistance range was satisfied by the uniform distribution of the paint, the number of revolutions of the can during spraying was limited to four or more in order to obtain excellent corrosion resistance.

Therefore, the range of paint spraying conditions for producing a two-piece steel can excellent in corrosion resistance was limited as follows.

In the paint spray of two-piece steel can, the total amount of paint sprayed after two sprays is in the range of 260-290mg per can, and the overlap distance between the first spray nozzle and the second spray nozzle is in the range of 30-40mm Rotate at least four times.

Therefore, according to the present invention, by forming a coating in which the paint is uniformly and continuously applied in order to improve the corrosion resistance of the two-piece steel can, there is an advantage in that the can can be manufactured in an economical manner by minimizing the amount of paint used. It is not only possible to manufacture steel cans with excellent corrosion resistance to stably store contents such as food and beverages for a long time, but also is an industrially available technology that can be directly used for current can manufacturing technology.

The foregoing merely illustrates preferred embodiments of the present invention, and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. Can be.

Claims (3)

A method of forming a uniform film having excellent corrosion resistance by spraying a liquid paint with high pressure air in a fine particle state on the inner surface of the steel can through the first spray nozzle and the second spray nozzle while the steel can is rotating. To The total spray amount of the paint through the first spray nozzle and the second spray nozzle is maintained in the range of 260-290 mg per can, The overlapping distance between the spraying position of the first spray nozzle and the spraying position of the second spray nozzle is maintained within 30 to 40 mm. The method of claim 1, wherein during spraying the paint, the steel can is rotated at least four times. The spraying position of the first spray nozzle is located at a distance of 2 mm to 35 mm from the bottom of the steel can, and the spraying position of the second spray nozzle is 125 mm to 110 mm from the top of the steel can. How to form a film on the inner surface of the two-piece steel can, characterized in that located at a distance of.