JP2005329991A - Can body and inner surface coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a can body having a closed-end cylindrical shape, and to provide an inner surface coating method for uniformly coating the entire area of an inner surface of the can body with a paint. <P>SOLUTION: The can body 10 includes a bottom 11 formed of a dome portion 13 concaved to the inside of a can trunk 12, and an annular protrusion 14 extending from the dome portion 13 along its outer peripheral edge and protruding to the outside of the can trunk 12. The annular protrusion 14 has a nose 14a at the tip thereof, an inner peripheral wall 14b extending to the radial inside of the nose 14a, and an outer peripheral wall 14c extending to the radial outside of the nose 14a. Further the inner peripheral wall 14b extends via an annular concave portion 15 to the dome portion 13, and the outer peripheral wall 14c extends via an annular convex portion 16 to the can trunk 12. Herein an angle θ which the inner peripheral wall 14b and a can axis form with each other is set to the range of not less than 8° to not more than 25°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a can body and an inner surface coating method suitable for uniformly applying a paint to the inner surface of a bottomed cylindrical can body.

  As is well known, a can body having a bottomed cylindrical shape made of, for example, an aluminum alloy has been conventionally used as a container filled with a beverage or the like. As this type of can body, the opening is subjected to various processing such as neck-in processing, so that the large-diameter can body and the can shaft direction upper end of the can body can be connected to the can shaft direction. A bottle can provided with a shoulder portion gradually reduced in diameter as it goes upward, and a base portion extending upward in the can axis direction along with the upper end in the can axis direction of the shoulder portion, and a large-diameter can body And a shoulder portion that is provided continuously with the upper end in the can axis direction of the can body and that gradually decreases in diameter toward the upper side in the can axis direction, and is provided continuously with the upper end in the can axis direction of the shoulder portion and radially outward. A can base having a flange portion extending toward the top is known. In the former bottle can, after the contents are filled, a cap is screwed into the cap portion to form a bottle can with a cap. In the latter can base, the flange portion is filled after the contents are filled. The can lid is rolled up into a can.

  And although the structure of the bottom part of these can main bodies changes with the manufacturing methods, it is connected to the dome part dented to the inner side of a can body, and the outer periphery of this dome part as one structure, The exterior of a can body An annular convex portion protruding to the side, and the annular convex portion is continuously provided on a tip nose portion, an inner peripheral wall continuously provided on a radially inner side of the nose portion, and a radially outer side of the nose portion. It is known that the outer peripheral wall is connected to the dome portion via an annular concave curved surface portion, and the outer peripheral wall is connected to the can body via an annular convex curved surface portion. In this configuration, generally, the radius of curvature of the dome portion is about 55 mm, the radius of curvature of the concave curved surface portion is 3 mm to 4 mm, and the angle formed by the inner peripheral wall and the can shaft is 3 ° to 4 °. Yes.

  By the way, on the inner surface of the can body as described above, a synthetic resin such as epoxy acrylic is used to protect the background (metal surface) of the can body against its contents and prevent the can body from corroding. A coating film made of a coating composition containing a copolymer and an aqueous solvent is formed. As a method for forming this coating film, for example, the following method is known as shown in Patent Document 1 below. That is, by rotating the can body around the axis of the can while spraying the paint on the inner surface of the can body before the various processes are applied to the opening by a plurality of paint spraying means, A method for forming a coating film by applying a paint and then drying and curing the paint is known.

By applying the paint as described above, it becomes possible to spray the paint toward the entire circumference of the inner surface of the can body, and by applying a centrifugal force to the paint sprayed on the inner surface, this paint Can be slid and moved on the inner surface of the can body, and the paint can be uniformly applied over the entire inner surface including the bottom. Particularly, the inner peripheral wall of the bottom portion is a portion where the paint is difficult to be directly sprayed by the paint spraying means due to its size, shape, etc. It is also intended to move the paint onto the inner surface of such an inner peripheral wall by applying the centrifugal force to the paint on the surface.
In addition, after the coating material applied as described above is dried and cured to form a coating film, the can body is subjected to the above-described various processing, thereby forming the above-described configuration of the bottle can and the can base. .
JP 2003-226337 A

  However, in the prior art, each part of the bottom is formed in the size as described above, and in particular, since the inner peripheral wall is inclined only 3 ° to 4 ° with respect to the can shaft, the inner surface of the inner peripheral wall is , And extends in a direction substantially perpendicular to the direction in which the centrifugal force acts. Therefore, even if the centrifugal force acts on the paint applied to the inner surface of the dome part and the paint reaches the outer peripheral edge in the radial direction of the dome part, it reaches the inner surface of the inner peripheral wall. Since it is difficult, there is a possibility that a portion where the paint is not applied on the inner surface, that is, a portion where the background of the can body is exposed is generated. Especially in bottle cans, the opening of the can body is subjected to severe processing such as neck-in processing and screw forming processing, so it has the characteristics that can follow the deformation of the can body by such processing without peeling. Since the coating material is employed, and the coating material having such characteristics is generally made to have a high viscosity, the above-mentioned problem is particularly remarkable.

  The present invention has been made in consideration of such circumstances, and a can body and an inner surface coating method capable of uniformly applying a paint over the entire inner surface of a bottomed cylindrical can body The purpose is to provide.

  In order to solve such problems and achieve the above-mentioned object, the can body of the present invention includes a dome portion recessed toward the inside of the can body at the bottom portion, and an outer peripheral edge of the dome portion. An annular convex portion that protrudes to the outside of the trunk, and the annular convex portion includes a nose portion at the tip, an inner peripheral wall that is continuously provided radially inward of the nose portion, and a radially outer side of the nose portion. And the outer peripheral wall is connected to the dome portion via an annular concave curved surface portion, and the outer peripheral wall is connected to the can body via an annular convex curved surface portion. A can body, wherein an angle formed between the inner peripheral wall and the can shaft is 8 ° or more and 25 ° or less.

  According to the present invention, the angle formed by the inner peripheral wall and the can shaft is 8 ° or more, and therefore, the paint sprayed on the inner surface of the dome portion is generated by rotating the can body around the can shaft. When the centrifugal force acts, the paint is moved while sliding the inner surface of the dome part radially outward by this centrifugal force, and after reaching the outer peripheral edge, the inner wall of the inner peripheral wall is continuously moved. It is moved while sliding on the surface outward in the radial direction. Accordingly, the paint can be uniformly applied over the entire inner surface of the can body including the bottom. In particular, even when a paint having a relatively high viscosity is applied, the paint can be applied uniformly. Further, since the angle is set to 25 ° or less, it is possible to minimize a decrease in the pressure resistance strength and buckling strength of the can body.

  Here, it is desirable that the radius of curvature of the concave curved surface portion is 2 mm or more and 5 mm or less. In this case, by applying the centrifugal force to the paint applied to the inner surface of the dome, it is possible to reliably move the paint while sliding on the inner surface of the inner peripheral wall as described above. In addition, it is possible to reliably suppress a decrease in the pressure strength and buckling strength.

  The can body is preferably formed by subjecting a plate made of an aluminum alloy having a thickness of 0.35 mm or more and 0.41 mm or less to drawing and ironing. In this case, the can body having the above-described effects can be easily and reliably formed. That is, if the thickness is smaller than 0.35 mm, when drawing and ironing are performed, the can body may be broken, so that the pressure resistance and buckling strength may be reduced. On the other hand, if the thickness is larger than 0.41 mm, it is necessary to increase the ironing rate in particular, which may reduce the production efficiency of the can body.

  Furthermore, an epoxy acrylic copolymer in which the acrylic resin (A) and the epoxy resin (B) are bonded to the inner surface of the can body in a mass ratio (A) / (B) = 12/88 to 35/65 and aqueous Contains a solvent, the acrylic resin (A) is 20 to 60% by mass of the methacrylic acid unit (a), 35 to 70% by mass of the styrene unit (b), and the glass transition temperature (Tg) of the polymer is −40 ° C. A coating film made of a coating composition containing 1 to 10% by mass of the low Tg polymer-forming monomer unit (c), wherein the epoxy resin (B) contains 5 to 45% by mass of the phenoxy resin (ii), It is desirable to be formed. In this case, since the coating composition has a high viscosity, the effect of being able to uniformly apply the coating to the inner surface of the can body described above is particularly remarkable. Furthermore, since this paint composition is subjected to severe processing on the can body, even if the can body is deformed, it has excellent workability such that it can follow the deformation well without peeling from the can body. Such a coating film having excellent processability can be uniformly formed on the inner surface of the can body.

  Further, the inner surface coating method of the present invention rotates the can body around the can axis while spraying the paint by a plurality of paint spraying means toward the inner surface of the can body according to any one of claims 1 to 4. And coating the inner surface with a paint. In this case, the above-described operational effects are surely achieved.

  According to the can body and the inner surface coating method of the present invention, the paint can be uniformly applied over the entire area of the inner surface of the bottomed cylindrical can body.

  FIG. 1 shows a can body 10 according to an embodiment of the present invention, and a bottom portion 11 thereof is connected to a dome portion 13 recessed toward the inside of a can body 12 and an outer peripheral edge of the dome portion 13. And an annular convex portion 14 projecting to the outside of the can body 12. The annular convex portion 14 includes a tip nose portion 14a, an inner peripheral wall 14b continuously provided on the radially inner side of the nose portion 14a, and an outer peripheral wall 14c continuously provided on the radially outer side of the nose portion 14a. The peripheral wall 14 b is connected to the dome portion 13 via an annular concave curved surface portion 15, and the outer peripheral wall 14 c is connected to the can body 12 via an annular convex curved surface portion 16. Note that the inner surface of the inner peripheral wall 14b is a substantially flat surface having almost no curvature. Moreover, each part 12-16 of the above-mentioned bottom part 11 is smoothly connected without a level | step difference without having a bending part etc. between these 12-16.

  In this embodiment, the curvature radius R1 on the inner surface of the dome portion 13 is about 55 mm, the curvature radius R2 on the inner surface of the concave curved surface portion 15 is 2 mm or more and 5 mm or less, and the inner surface of the inner peripheral wall 14b and the can The angle θ formed by the axis is 8 ° to 25 °, preferably 10 ° to 20 °. Moreover, the epoxy acrylic copolymer which acrylic resin (A) and epoxy resin (B) couple | bonded with the inner surface of the can main body 10 in the range of mass ratio (A) / (B) = 12 / 88-35 / 65. And an aqueous solvent, the acrylic resin (A) is 20 to 60% by mass of the methacrylic acid unit (a), 35 to 70% by mass of the styrene unit (b), and the glass transition temperature (Tg) of the polymer is − The illustration which consists of a coating composition which contains 1-10 mass% of low Tg polymer formation monomer units (c) which are 40 degrees C or less, and an epoxy resin (B) contains 5-45 mass% of phenoxy resin (ii). The coating film which does not do is formed. Here, the low Tg polymer-forming monomer unit (c) is, for example, 2-ethylhexyl acrylate.

  Next, a manufacturing method of the can body 10 configured as described above will be described. First, the can body 10 is formed into a bottomed cylindrical shape by drawing and ironing a plate material made of an aluminum alloy having a thickness of 0.35 mm or more and 0.41 mm or less. Then, the coating material which consists of the said coating composition is sprayed on the inner surface of the can main body 10 so that it may mention later by the inner surface coating apparatus 20 as shown in FIG.

  The inner surface coating apparatus 20 includes a plurality of paint spraying means 21 configured to spray the paint toward the inner surface of the can body 10, and a paint supply means (not shown) that supplies the paint to the paint spraying means 21. And holding means (not shown) for holding the bottom 11 of the can body 10 and rotating the can body 10 about the can axis. The plurality of paint spraying means 21 includes a first spraying means 22 for spraying paint on the bottom portion 11 of the inner surface of the can body 10, and a second spraying means 23 for spraying paint on the lower portion 12 a in the can axis direction of the can body 12. And a third spraying means 24 for spraying the paint onto the can axis direction upper part 12 b of the can body 12. The paint spraying means 21 sprays the paint toward the entire area of the inner surface of the bottom 11 of the can body 10 and the entire area of the inner surface of the can body 12 in the can axis direction.

  A method of spraying paint on the inner surface of the can body 10 by the inner surface coating apparatus 20 configured as described above will be described. First, the can body 10 is held by the holding means in a state where the bottom portion 11 is in contact with the holding means and the can shaft and the rotating shaft of the holding means are substantially matched. The holding means is rotated to rotate the can body 10 around the can axis, and the paint is sprayed toward the inner surface of the can body 10 simultaneously from all of the plurality of paint spraying means 22 to 24. As a result, when the can body 10 is rotated by one rotation around the can axis, the paint is sprayed toward the entire inner surface of the can body 10 and is sprayed on the inner surface of the can body 10 by this rotation. Further, a centrifugal force directed radially outward acts on the paint. Therefore, in particular, the paint sprayed on the inner surface of the dome portion 13 is moved while sliding on the inner surface toward the radially outer side by the centrifugal force, and reaches the outer circumferential edge of the dome portion 13. After that, it is continuously moved through the inner surface of the concave curved surface portion 15 while sliding on the inner surface of the inner peripheral wall 14b outward in the radial direction. As described above, the paint is uniformly applied over the entire inner surface of the can body 10 including the inner peripheral wall 14b where the paint is difficult to spray directly by the paint spraying means 21. Thereafter, the paint is dried and cured to form a coating film.

  Next, various processes are given to the opening part of the can main body 10 according to the structure of the can main body 10 to form. For example, when the can body 10 to be formed is a bottle can 30 as shown in FIG. 2, a neck-in process is performed on the can axis direction upper part 12 b of the can body 12, and the can axis direction lower part 12 a is placed at the upper end in the can axis direction. The shoulder 31 is gradually reduced in diameter as it goes upward in the can axis direction, and the base 32 extending upward in the can axis direction is formed at the upper end of the shoulder 31 in the can axis direction. Thereafter, the base portion 32 is threaded to form a male screw portion, and the opening end is turned back outward in the radial direction to form the bottle can 30.

  As described above, according to the can body and the inner surface coating method according to the present embodiment, the angle θ formed between the inner peripheral wall 14b and the can shaft is 8 ° or more, so that it is sprayed on the inner surface of the dome portion 13. After the coating material reaches the outer peripheral edge of the dome portion 13 by the centrifugal force, the inner surface of the inner peripheral wall 14b is continuously directed radially outward through the inner surface of the concave curved surface portion 15. It is possible to reliably realize the sliding movement. Accordingly, the paint can be uniformly applied over the entire inner surface of the can body 10 including the bottom 11. In particular, even when a paint having a relatively high viscosity is applied, the paint can be applied uniformly. Moreover, since the angle θ is set to 25 ° or less, it is possible to minimize a decrease in the pressure resistance strength and buckling strength of the can body 10.

  Further, since the radius of curvature R2 on the inner surface of the concave curved surface portion 15 is set to 2 mm or more and 5 mm or less, the centrifugal force is applied to the coating material applied to the inner surface of the dome portion 13 to thereby apply the coating material to the coating material. As described above, it is possible to more surely realize the movement while sliding on the inner surface of the inner peripheral wall 14b satisfactorily, and it is possible to similarly suppress the decrease in the pressure resistance strength and the buckling strength.

  Furthermore, since the can body 10 is formed by drawing and ironing a plate material made of an aluminum alloy having a thickness of 0.35 mm or more and 0.41 mm or less, the can body 10 having the above-described effects. Can be formed easily and reliably. That is, if the thickness is smaller than 0.35 mm, when drawing and ironing are performed, the can body may be broken, so that the pressure resistance and buckling strength may be reduced. On the other hand, if the thickness is larger than 0.41 mm, it is necessary to particularly increase the ironing rate, which may reduce the production efficiency of the can body 10.

  Moreover, the epoxy acrylic copolymer which acrylic resin (A) and epoxy resin (B) couple | bonded with the inner surface of the can main body 10 in the range of mass ratio (A) / (B) = 12 / 88-35 / 65, and It contains an aqueous solvent, the acrylic resin (A) is 20 to 60% by mass of the methacrylic acid unit (a), 35 to 70% by mass of the styrene unit (b), and the glass transition temperature (Tg) of the polymer is −40. A coating film comprising a coating composition containing 1 to 10% by mass of a low Tg polymer-forming monomer unit (c) having a temperature of not higher than ° C., and wherein the epoxy resin (B) comprises 5 to 45% by mass of a phenoxy resin (ii). Therefore, even when various processes such as a neck-in process are performed on the can body 10, the can body can be formed without cracking or peeling the coating film from the inner surface of the can body 10. Can follow 10 deformationsHowever, since the coating composition has a relatively high viscosity, when the coating is applied to the inner surface of the can body 10 by the centrifugal force, the coating is applied to the concave curved surface portion 15 and the inner surface of the inner peripheral wall 14b. It is difficult to slip and it may be difficult to achieve uniform application. However, in the present embodiment, the bottom portion 11 is configured as described above, and in particular, the angle θ is set in the above-described range. Therefore, even with a paint having such a high viscosity, the concave curved surface portion 15 and It becomes possible to slide the inner peripheral wall 14b on the inner surface of the inner peripheral wall 14b sequentially and reliably in the radial direction. As described above, while having excellent processability as described above, even a paint having a high viscosity can be uniformly applied over the entire area of the inner surface of the can body.

  A verification test was conducted on the effects of the can body and the inner surface coating method of the present embodiment described above. As can bodies used for this verification test, as shown in FIG. 3, eleven types of can bodies having different angles θ and curvature radii R2 were formed. All of these eleven types of can bodies were formed by drawing and ironing a plate made of an aluminum alloy having a thickness of 0.36 mm, and the radius of curvature R1 on the inner surface of the dome was about 55 mm. 2 is applied to the inner surface of the can body by the above-described apparatus 20 and the method described above with reference to FIG. Formed.

  First, when a voltage was applied to each can body configured as described above, a current value flowing on the surface of the coating film, that is, an enamel value (ERV value) was measured. When this ERV value is large, it can be seen that the coating film is not formed on the inner surface of the can body, and there is a portion where the ground (metal surface) is exposed. In general, when the ERV value is 25 mA or less, it is determined that the coating film is applied almost uniformly on the inner surface of the can body over the entire area. The results are shown in FIG. In this figure, it can be confirmed that the ERV value is smaller than 25 mA when the angle θ is 8 ° or more.

  Next, the internal pressure of each can body is raised, the inner peripheral wall 14b is deformed radially inward, and the internal pressure value when the concave curved surface portion 15 begins to deform downward in the can axis direction, that is, pressure resistance The strength was measured. Generally, it is determined that the pressure strength is 686 kPa or more. The results are shown in FIG. In this figure, it can be confirmed that the pressure resistance strength is greater than 686 kPa when the angle θ is 25 ° or less.

  As described above, if the angle θ is 8 ° or more and 25 ° or less, preferably 10 ° or more and 20 ° C. or less, even if the paint has a high viscosity, the paint is applied to the inner surface of the can body over the entire area. As a result, it was confirmed that the can body 10 can be uniformly coated and the can body 10 can be provided with necessary and sufficient pressure-resistant strength.

The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the said embodiment, although the can main body 10 (what is called DI can) before shape | molding into the bottle can 30 and the bottle can 30 was shown as an example of a can main body, the part located in the can axial direction upper part from the bottom part 11 The shape of is not particularly limited, for example, a large-diameter can barrel, a shoulder portion that is connected to the upper end of the can barrel in the can axis direction and gradually decreases in diameter toward the upper direction of the can axis, The can base may be provided with a flange portion that is provided continuously with the upper end of the shoulder in the can axis direction and extends radially outward.

  The paint can be uniformly applied over the entire area of the inner surface of the bottomed can body.

It is a partially expanded sectional view which shows the bottom part of the can main body of one Embodiment which concerns on this invention. It is a schematic block diagram of the inner surface coating apparatus for enforcing the inner surface coating method of one Embodiment which concerns on this invention. It is a figure which shows the verification result which verified the effect which the can main body and inner surface coating method of one Embodiment concerning this invention show | play.

Explanation of symbols

10, 30 Can body 11 Bottom portion 12 Can body 13 Dome portion 14 Annular convex portion 14a Nose portion 14b Inner peripheral wall 14c Outer peripheral wall 15 Concave surface portion 16 Convex surface portion θ angle R2 Radius of curvature of concave surface portion

Claims (5)

The bottom is provided with a dome that is recessed toward the inner side of the can body, and an annular protrusion that is connected to the outer peripheral edge of the dome and protrudes toward the outer side of the can body. Part, an inner peripheral wall continuously provided on the radially inner side of the nose part, and an outer peripheral wall continuously provided on the radially outer side of the nose part, the inner peripheral wall passing through the annular concave curved surface part A can body that is connected to the dome portion and the outer peripheral wall is connected to the can body via an annular convex curved surface portion,
The can main body characterized in that an angle formed between the inner peripheral wall and the can shaft is 8 ° or more and 25 ° or less. The can body according to claim 1,
A can body having a radius of curvature of the concave curved surface portion of not less than 2 mm and not more than 5 mm. The can body according to claim 1 or 2,
A can body formed by drawing and ironing a plate material made of an aluminum alloy having a thickness of 0.35 mm or more and 0.41 mm or less. The can body according to any one of claims 1 to 3,
The inner surface contains an epoxy acrylic copolymer in which an acrylic resin (A) and an epoxy resin (B) are bonded in a mass ratio (A) / (B) = 12/88 to 35/65 and an aqueous solvent. The acrylic resin (A) has a methacrylic acid unit (a) of 20 to 60% by mass, a styrene unit (b) of 35 to 70% by mass, and the glass transition temperature (Tg) of the polymer is -40 ° C. or lower. A coating film comprising a coating composition containing 1 to 10% by mass of the Tg polymer-forming monomer unit (c) and the epoxy resin (B) containing 5 to 45% by mass of the phenoxy resin (ii) is formed. A can body characterized by that. While spraying paint with a plurality of paint spraying means toward the inner surface of the can body according to any one of claims 1 to 4, the can body is rotated around the can axis and the paint is applied to the inner surface. An internal coating method characterized by

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