JP7673155B2 - Can for carbonated beverages and method for manufacturing same - Google Patents

Description

The present invention relates to a can for carbonated beverages and a method for manufacturing the same.

Sparkling drinks such as beer are often served in containers. One of the important characteristics of sparkling drinks is their effervescence. Various studies have been conducted to ensure that the right amount of foam is obtained when the drink is consumed.

There are also known containers whose structure has been modified to enhance the fizz. However, when fizz is enhanced by changing the container's structure, fizzing also occurs when the sparkling beverage is filled into the container, which can make it difficult to fill the desired amount of beverage.

In relation to the above, Patent Document 1 (JP Patent No. 4758693) discloses a technology aimed at providing a can for carbonated beverages that does not adversely affect filling properties and can improve foaming properties when opened. Patent Document 1 describes that an organic resin coating layer is provided on the inner surface of a can for carbonated beverages, that an organic resin coating material containing a predetermined amount of large diameter particles occupies 20% to 60% of the inner surface area of the can, and that an organic resin coating material containing a predetermined amount of small diameter particles occupies the remainder of the inner surface area of the can, and that the organic resin coating layer is formed with recesses formed by at least a portion of the large diameter particles detaching or protrusions formed by remaining large diameter particles, and recesses formed by the detachment of small diameter particles.

Patent No. 4758693

The inventors of the present invention wish to further improve the foaming property without impairing the filling property. Therefore, the object of the present invention is to provide a can for a sparkling beverage that can further improve the foaming property without impairing the filling property, and a method for manufacturing the same.

The present inventors have found that the above problems can be solved by forming a predetermined structure on the inner surface of the can, and have arrived at the present invention. That is, the present invention is realized by the following means.
[1] A can for a sparkling beverage having an upper surface, a lower surface, and a body, and a plurality of caldera-shaped structures having an average diameter of 10 to 60 μm are provided on at least the inner surface of the body, and the number of the plurality of caldera-shaped structures is 7 to 30 ^per mm2.
[2] The can for a sparkling beverage according to [1], wherein the average depth of the plurality of caldera-shaped structures is 5 to 20 μm.
[3] A can for a sparkling beverage according to [1] or [2], wherein a resin layer is provided on at least the inner surface of the body, and the caldera-shaped structure is formed in the resin layer.
[4] A can for a sparkling beverage according to any one of [1] to [3], wherein the top surface is formed by a can lid configured to be opened in a full-open manner.
[5] A can for a sparkling beverage according to any one of [1] to [4], wherein the caldera-shaped structure is provided over 95% or more of the inner surface of the body.
[6] A method for manufacturing a can for a sparkling beverage having an upper surface, a lower surface, and a body, comprising the steps of: applying a paint containing a resin and a wax to at least the inner surface of the body or an area intended to become the inner surface of the body; and heat-treating the applied paint to form a resin layer and remove the wax, wherein the wax in the paint has an average particle size of 12 to 25 μm and the wax content per 100 parts by mass of non-volatile components (excluding wax) in the paint is 1.5 to 5 parts by mass.
[7] The manufacturing method described in [6], wherein the wax includes a polyethylene wax.
[8] The manufacturing method according to [6] or [7], wherein the coating material contains at least one resin selected from the group consisting of epoxy resins, acrylic resins, polyester resins, and urethane resins.
[9] A sparkling beverage comprising a beverage can according to any one of [1] to [5] and a sparkling drinkable liquid filled in the beverage can.

The present invention provides a can for carbonated beverages and a method for manufacturing the same that can improve the fizziness without compromising filling properties.

FIG. 1 is a micrograph showing the inner surface of the body. FIG. 2 is a partial cross-sectional view of the trunk, showing each caldera-like structure in schematic form. FIG. 3 is a micrograph showing the inner surface of the body of a commercially available metal can. FIG. 4 is a cross-sectional view that illustrates a resin layer.

Hereinafter, an embodiment of the present invention will be described in detail.
The can for a carbonated beverage according to this embodiment has a top surface, a body portion, and a bottom surface. The body portion and the bottom surface are integrated or joined together to form a cylindrical shape with a bottom, and an upper opening portion is closed by the top surface so as to be retractable.

A number of caldera-shaped structures are provided over almost the entire inner surface (95% or more of the area) of the body. Figure 1 is a micrograph showing the inner surface of the body. Figure 2 is a partial cross-sectional view of the body, showing each caldera-shaped structure in a simplified manner.
As shown in Figures 1 and 2, each caldera-shaped structure has a convex portion 2 having a closed shape (approximately circular) when viewed from the front, and a concave portion 3 provided inside the convex portion 2.
The average diameter of the plurality of caldera-shaped structures is 10 to 60 μm, preferably 15 to 50 μm, and more preferably 20 to 40 μm. The diameter of each caldera-shaped structure means the diameter of the protrusion 2 (see diameter a in FIG. 2). The diameter of each caldera-shaped structure can be determined from a micrograph.

The average depth of the multiple caldera-shaped structures is, for example, 5 to 20 μm, and preferably 7 to 13 μm. The depth of each caldera-shaped structure is the difference between the height of the convex portion 2 and the height of the lowest part of the concave portion 3 (see depth b in Figure 2). Note that, as shown in Figure 2, when there is a difference in the height of the convex portions 2, the distance between the line connecting the apexes of the convex portions 2 and the concave portion 3 can be obtained as depth b. The depth of each caldera-shaped structure can be obtained, for example, using a laser microscope.

The number of the caldera-shaped structures ^per mm2 is, for example, 7 to 30, and preferably 8 to 20. When the number of the caldera-shaped structures ^per mm2 is 7 or more, high foaming performance can be obtained. Also, when the number of the caldera-shaped structures ^{per mm2} is 30 or less, the filling property is not impaired.

Preferably, the sparkling beverage can according to the present embodiment is made of metal, and preferably, a resin layer obtained by painting and drying a paint on a metal layer is provided on the inner surface of the body, and the caldera-shaped structure is formed in the resin layer.
It should be noted that in the present invention, the "resin layer" refers to a layer formed after the applied paint has been dried, and is distinguished from a layer of paint before drying.

Preferably, the carbonated beverage can according to this embodiment is a full-open type. That is, the top surface forms a can lid that is configured to be opened in a full-open type. A full-open type refers to a configuration in which the entire top surface separates from the body when the can is opened.

Figure 3 is a micrograph showing the inner surface of the body of a commercially available metal can. As is clear from a comparison of Figures 1 and 3, no caldera-shaped structure is observed on the inner surface of the commercially available metal can.

Next, an example of a method for manufacturing the above-mentioned sparkling beverage can will be described.
The manufacturing method according to this embodiment includes a step of applying a paint containing resin and wax, and a step of subsequently heating the applied paint to form a resin layer on the inner surface and remove the wax (hereinafter also referred to as the baking step).
Examples of methods for forming a can body having a resin layer on its inner surface include a method in which a cylindrical can body with a bottom is first formed by drawing and ironing, and then the paint of the present invention is spray painted and baked to form a resin layer (the resulting can is called a two-piece can); and a method in which the paint of the present invention is painted on an area of a metal plate that is to become the inner surface, and baked to form a resin layer, and then the metal plate with the resin layer is formed into a cylindrical shape and the can bottom, which becomes the lower surface, is rolled up to obtain a cylindrical can body with a bottom (the resulting can is called a three-piece can).

The coating and baking process will be described below.
The paint to be used is preferably made of resin, such as epoxy resin, acrylic resin, polyester resin, or urethane resin.
The thickness of the resin layer after baking is, for example, 1 to 10 μm, and preferably 3 to 8 μm.
The average particle size of the wax is 12 to 25 μm, and preferably 15 to 20 μm. The average particle size here refers to the particle size (D50) at which the cumulative frequency is 50% in volume conversion, and is a value measured by diluting an aqueous dispersion containing about 20% by mass of wax 500 times with water using a dynamic light scattering particle size distribution measuring device (Microtrac S3500 manufactured by Nikkiso Co., Ltd.).
The content of the wax in the coating material is 1.5 to 5 parts by mass, preferably 2.0 to 4.0 parts by mass, per 100 parts by mass of the non-volatile components (excluding wax) in the coating material.
The wax used has a softening point of 90 to 160°C, preferably 110 to 140°C.
As the wax, a polyethylene wax is preferably used.
The wax may be in the form of a powder, a paste, or a dispersion in water or a solvent. From the standpoint of dispersion stability in the coating material, it is preferable to use a dispersion in water or a solvent.

The coating method in the present invention is preferably spray coating such as air spray, airless spray, electrostatic spray, roll coater coating, dip coating, electrodeposition coating, etc., and more preferably spray coating.
In order to dry the paint and form a uniform resin layer, it is preferable to carry out a baking treatment immediately after painting.
The conditions for the baking step can be appropriately selected so that the paint can be dried and a resin layer can be formed, but baking at 150 to 280° C. for about 10 seconds to 30 minutes is preferable. In order to melt the wax during baking and cause it to be detached from the coating film, baking at 180 to 280° C. for about 1 minute to 30 minutes is more preferable.
Fig. 4 is a cross-sectional view showing a schematic diagram of the resin layer 5. As shown in Fig. 4, by applying and drying the paint, water and solvents are first evaporated, and the resin layer 5 is formed. Here, the wax 4 is temporarily placed so as to be embedded in the resin layer 5. The upper part of the wax 4 is exposed on the surface of the resin layer 5. Next, the wax 4 melts and is detached from the recesses of the resin layer 5, forming a caldera-shaped structure as shown in Fig. 2.

Thereafter, beverage cans are manufactured, filled with potable liquid and sealed as is conventional in the industry.
The filling of the drinkable liquid is preferably carried out at low temperature (eg 1-20°C).

As described above, according to this embodiment, a caldera-shaped structure of a specific size is formed on the inner surface of the body with a specific density by using a paint containing a specific amount of wax with a specific average particle size. By using a can for carbonated beverages with such a special structure formed in the body, extremely high foaming properties can be achieved without sacrificing filling properties.

The beverage filled in the sparkling beverage can according to the present embodiment is not particularly limited as long as it is a sparkling liquid. Preferably, the beverage filled is beer. When the sparkling beverage can according to the present embodiment is filled with beer, foam is generated from the inner surface of the can as soon as the can is opened, and the foam and the beer can be consumed together.
Even if a beverage other than beer is filled, the aroma components will evaporate as the beverage foams, allowing the flavor of the content to be strongly felt.
Preferably the sparkling beverage has a gas pressure of between 2 and 4 gas volumes.

To explain the present invention in more detail, examples carried out by the inventors are described below.

(Example 1)
An aluminum container (350 ml) having a bottom and a body was prepared. A water-based epoxy acrylic paint containing 3 parts by mass of polyethylene wax with an average particle size of 17 μm and a softening point of 130° C. per 100 parts by mass of non-volatile components (excluding wax) in the paint was prepared. The prepared paint was spray-painted on the entire inner surface of the body of the container, and then heated at 200° C. for 2 minutes to obtain a beverage can according to Example 1. The thickness of the body resin layer was 5 μm on average.

(Example 2)
A beverage can according to Example 2 was obtained using the same method as in Example 1, except that the content of wax in the paint was changed to 1 part by mass per 100 parts by mass of the non-volatile components (excluding wax) in the paint.

(Example 3)
The wax was changed to a polyethylene wax having an average particle size of 10 μm. The content of the wax in the paint was 3 parts by mass per 100 parts by mass of the non-volatile components (excluding wax) in the paint. In other respects, the same method as in Examples 1 and 2 was used to obtain a beverage can according to Example 3.

(Example 4)
The wax was changed to a polyethylene wax having an average particle size of 10 μm. The content of the wax in the paint was 10 parts by mass per 100 parts by mass of the non-volatile components (excluding wax) in the paint. In other respects, the same method as in Examples 1 to 3 was used to obtain a beverage can according to Example 3.

(Foaming performance)
Each beverage can of Examples 1 to 4 was filled with 350 ml of beer at a liquid temperature of 2°C, and the opening was closed with a full-open can lid. The can lid was then opened, and the time until foam rose from the opening (hereinafter referred to as "hat time") was measured. The measurement was carried out five times for each of Examples 1 to 4. The results are shown in Table 1.

As shown in Table 1, Example 1, in which the average wax particle size was 17 μm and the wax content was 3 parts by mass per 100 parts by mass of the non-volatile components (excluding wax) in the paint, tended to have a shorter hat time than Examples 2 to 4. In other words, Example 1 had higher foaming properties than Examples 2 to 4.

(Filling ability)
One hundred beverage cans of each of Examples 1 and 2 were filled with beer at a liquid temperature of 2° C. with the amount of beer filled per can set to 367 g, and the can lids were then tightened. Seventy-two beverage cans of each type were extracted, and the mass (g) of each was measured. The results are shown in Table 2.

The results in Table 2 show that the beverage cans of Examples 1 and 2 both have no problems with filling.

(Counting caldera-like structures)
The inner surface of the body of each of the beverage cans according to Examples 1 and 2 was observed under a microscope, and the number of caldera-shaped structures within an area of 1 mm x 1 mm was counted. The photograph shown in Figure 1 is of the beverage can according to Example 1.
In each example, the number of caldera-like structures was counted in five regions. The results are shown in Table 3.

As shown in Table 3, an average of about 12 caldera-shaped structures were observed per ^mm2 in the beverage can of Example 1. On the other hand, in the beverage can of Example 2, the number of caldera-shaped structures per ^mm2 was about 6.

(Profile of caldera-like structure)
The inner surface of the body of the beverage can of Example 1 was observed with a laser microscope, and the profile of the caldera-shaped structure was measured. Specifically, the diameter (diameter of the convex portion) and depth (difference in height between the convex portion and the concave portion) of the caldera-shaped structure were measured. The measurement was performed on five caldera-shaped structures. The results are shown in Table 4.

From the results in Table 4, the diameter of the caldera-shaped structure formed in the beverage can of Example 1 was approximately 31 μm on average. Also, the depth was approximately 11 μm on average.

Considering the results of Tables 1 to 4, the following can be understood.
It was found that the beverage can of Example 1 had improved foaming properties without impairing filling properties, as compared with the beverage cans of Examples 2 to 4. The beverage can of Example 1 was a can whose inside surface was coated with a paint containing 3 parts by mass of wax with an average particle size of 17 μm per 100 parts by mass of non-volatile components (excluding wax) in the paint, and as shown in Table 3, about 12 caldera-shaped structures were formed per ^mm2 . Furthermore, the average diameter of the caldera-shaped structures was about 31 μm, and the average depth was about 11 μm.

1 Caldera-shaped structure 2 Convex portion 3 Concave portion 4 Wax 5 Resin layer

Claims (3)

A method for manufacturing a can for a sparkling beverage having a top surface, a bottom surface, and a body portion, comprising the steps of:
A step of applying paint containing resin and wax to at least the inner surface of the body portion or an area to become the inner surface of the body portion;
The method includes a step of heat-treating the applied paint at 180 to 280° C. for 1 to 30 minutes to form a resin layer and remove the wax,
The wax in the coating material has an average particle size of 12 to 25 μm, a softening point of the wax in the coating material is 90 to 160° C., and a content of the wax in the coating material is 1.5 to 5 parts by mass per 100 parts by mass of non-volatile components (excluding wax) in the coating material. The method of claim 1, wherein the wax comprises polyethylene wax. The manufacturing method according to claim 1 or 2, wherein the coating material contains at least one resin selected from the group consisting of epoxy resin, acrylic resin, polyester resin, and urethane resin.

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