Manufacturing method of metal can and metal can

Abstract

To provide a method of manufacturing a metal can that includes shaping a metal plate having a resin film laminated into members of the metal can such as a can body, a lid, a cap, etc., and then seaming the members and heating and welding seamed parts, and that can tightly weld the seamed parts to suppress contents from leaking from the seamed part.SOLUTION: The present invention relates to a method of manufacturing a metal can that includes shaping metal plates 3c, 5c having films 3a, 3b and 5a, 5b of crystalline resin laminated into members of the metal can, then seaming the members, and heating and welding the seamed part 10, wherein the seamed part is cooled by using cooling means after the seamed part is heated and welded so as to increase a low-temperature crystallization rate of the films at the seamed part.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a metal can in which a metal sheet laminated with a crystalline resin film is seamed and the seamed portion is heated and welded, and to the metal can. [Background technology]

[0002] 2. Description of the Related Art Metal cans such as rectangular metal cans have been used as a means for transporting, storing, etc. various liquid and solid contents.

[0003] Metal cans are required to have a sealability that prevents leakage of the contents when the contents are pressurized due to heating during transportation, storage, etc., or when the contents are dropped or subjected to an impact due to an external force, etc.

[0004] A metal can includes, for example, a can body and a top plate and / or a bottom plate as a lid that is wrapped around at least one of the top and bottom of the can body. A cap, which is a plug that seals an outlet for the contained contents, is fixed to the lid.

[0005] Contents leak from metal cans when the seam between the mouthpiece and the lid, or the seam between the lid and the can body is insufficient. Conventionally, metal plates laminated with a resin film have been used for the mouthpiece, lid, and can body, and in order to bond the seam such as double seams and single seams (rivets) more firmly in metal cans using metal plates laminated with a resin film, a sealant such as rubber or compound, which is a sealant mainly made of resin, was applied and the seam was sealed with the sealant.

[0006] Sealing materials are excellent for sealing the seamed part. On the other hand, technologies that do not use sealing materials are being considered from the viewpoints of shortening the manufacturing process, reducing costs, and environmental issues, as well as from the viewpoint of solvent resistance when dangerous substances such as solvents are contained in the package. For example, a technology has been proposed in which the seamed part is heated by high frequency waves or the like, and a resin film laminated to a metal plate is directly welded to the heated part (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-6978 A [Patent Document 2] JP 2015-160351 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional method of seaming a metal plate laminated with a resin film and then heating and welding the seamed portion was unable to sufficiently prevent leakage of the contents and the resin film was also limited, so further improvements were needed.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for manufacturing a metal can in which a metal plate laminated with a resin film is formed into a metal can component, the component is seamed, and the seamed portion is heated and welded, in which the seamed portion can be firmly welded and leakage of contents from the seamed portion can be suppressed, and the method and metal can can be provided. [Means for solving the problem]

[0010] The inventors have conducted extensive research to solve the above problems, and after welding of the seam, they measured the heat release amount ΔHc and the endotherm of fusion ΔHm from the DSC chart (first run measurement chart) of the film at the seam, defined the low-temperature crystallization rate as the ratio ΔHc / ΔHm multiplied by 100, and investigated the relationship between the low-temperature crystallization rate ΔHc / ΔHm and the adhesive strength and sealability. As a result, they found that an increase in the low-temperature crystallization rate in the first run measurement chart of the DSC increases the adhesive strength and improves the sealability of the metal can. In particular, they found that an increase in the low-temperature crystallization rate by forced cooling after welding of the seam increases the adhesive strength and improves the sealability of the metal can, and thus completed the present invention.

[0011] In DSC measurements, when measuring a target sample, the change in heat capacity during the heating process within the temperature range of the target substance is measured. The measurement during the first heating process is called the 1st run. The same sample may be heated and measured a second time, in which case it is called the 2nd run to distinguish it, but it should be noted that in the following descriptions of DSC thermal analysis, this refers to the 1st run.

[0012] That is, the method for producing a metal can of the present invention is a method for producing a metal can by forming a metal plate laminated with a crystalline resin film into a metal can member, seaming the member, and heating and fusing the seamed portion, The method is characterized in that the low-temperature crystallization rate of the film in the seamed portion, which is obtained by DSC thermal analysis (1st run chart), is increased by heating and welding the seamed portion and then cooling the seamed portion using a cooling means.

[0013] The method for producing a metal can of the present invention includes forming a metal plate laminated with a crystalline PET resin film into a metal can member, seaming the member, and heating and fusing the seamed portion, The method is characterized in that the seam portion is heated and welded, and then cooled using a cooling means as necessary, thereby forming the seam portion in which the low-temperature crystallization rate of the film obtained by DSC thermal analysis (1st run chart) is 4% or more.

[0014] The metal can of the present invention is a metal can obtained by forming a metal plate laminated with a crystalline PET resin film into a metal can member, seaming the member, and heating and welding the seamed portion, The low-temperature crystallization rate of the film at the seamed portion is 4% or more as determined by DSC thermal analysis (first run chart). Effect of the Invention

[0015] According to the present invention, in a method for manufacturing metal cans in which a metal plate laminated with a resin film is formed into a metal can component, the component is then seamed, and the seamed portion is heated and welded, the seamed portion can be firmly welded, thereby preventing leakage of contents from the seamed portion. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view of a rectangular metal can, showing an example to which the method of the present invention can be applied. [Diagram 2] FIG. 1 is a vertical cross-sectional view partially showing a cap and a lid of a metal can, illustrating an example to which the method of the present invention is applied. [Diagram 3] FIG. 2 is a vertical cross-sectional view showing a fitting state of a mouthpiece and a cap in a metal can. [Figure 4] 1 is a vertical cross-sectional view partially illustrating a lid and a can body of a metal can, showing an example to which the method of the present invention is applied. [Diagram 5] 13 is a cross-sectional photograph showing another example of a seaming portion. [Figure 6] 1 is a photograph for explaining a pressure resistance test in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described. (Embodiment 1) In the method for manufacturing a metal can in this embodiment, a metal plate laminated with a crystalline resin film is formed into a metal can component, and then the component is seamed and the seamed portion is heated and welded.

[0018] The metal can is not particularly limited, but examples thereof include rectangular metal cans and round metal cans.

[0019] The components of the metal can are not particularly limited, but examples thereof include a can body, a lid, a mouthpiece, etc. The seaming portion is not particularly limited, but examples thereof include a seaming portion between the mouthpiece and the lid, a seaming portion between the lid and the can body, etc.

[0020] The manner of seaming is not particularly limited, but examples thereof include double seam and single seam (rivet), and at the seam between the mouthpiece and the lid, examples thereof include top rivet and bottom rivet.

[0021] In this embodiment, the pair of metal plates to be seamed may be metal plates on both sides of which a crystalline resin film is laminated, or only one of which may be a metal plate on which a crystalline resin film is laminated. The crystalline resin film may be laminated on one side of the metal plate, or on both sides of the metal plate.

[0022] In this embodiment, the crystalline resin refers to a resin having a high ratio of crystalline regions (high degree of crystallinity) in which molecular chains are regularly arranged. In contrast, the amorphous resin is a polymer that has an extremely low degree of crystallinity or cannot be crystallized, and includes amorphous polymers and amorphous polymers. The film of the crystalline resin is not particularly limited, but examples thereof include polyethylene terephthalate (PET) resin, polyethylene resin, polypropylene resin, and the like.

[0023] In this embodiment, the metal plate may be a laminate of a crystalline resin film alone, or may be a film in which a crystalline resin film is used as the outermost layer and one or more layers of crystalline resin and / or amorphous resin are laminated between the outermost layer and the metal plate surface.

[0024] In this embodiment, the thickness of the crystalline resin film that is the outermost layer is not particularly limited, but is preferably 50 μm or less, and more preferably 30 μm or less in terms of material costs.

[0025] An example of a rectangular metal can among metal cans will be described with reference to Figs. 1 to 4. As shown in Fig. 1, a rectangular metal can 1 includes a rectangular parallelepiped can body 2 formed by processing a metal plate and having a cavity therein for accommodating contents, and rectangular metal can lids for covering the top and bottom opening edges of the can body 2. In the figure, the top lid is indicated by reference symbol 3. By seaming two rectangular metal can lids, one at the top and one at the bottom, to the top and bottom opening edges of the can body 2, a rectangular metal can 1 is obtained in which the rectangular metal can lids are double-seamed on the top and bottom of the can body 2. A cap 4 for sealing a discharge port for the accommodated contents may be fixed to a mouthpiece of the top lid 3 for the rectangular metal can.

[0026] FIG. 2 shows the state of the cap 5 being fastened (in the case of top crimping), and FIG. 3 shows the state of fitting the cap 5 and the cap 4. As shown in FIG. 2, the cap 5 and the lid 3 form a fastening portion 10 with the crystalline resin films 5a and 3a as the inner surfaces. The cap 5 has a crystalline resin film 5a laminated on the inner surface of a metal plate 5c such as TFS (tin-free steel) or tinplate, and a crystalline resin film 5b laminated on the outer surface. The lid 3 has a crystalline resin film 3a laminated on the inner surface of a metal plate 3c such as TFS or tinplate, and a crystalline resin film 3b laminated on the outer surface. The inner and outer surfaces of the metal plates 5c and 3c may be plain or may be coated with paint, as long as a crystalline resin film laminated on either the cap 5 or the lid 3 is interposed between the cap 5 and the lid 3. In addition, the seam portion 10 shown within the dotted line in FIG. 2 may have a rounded tip as shown in the photograph of FIG.

[0027] 4 shows a seamed state of the lid 3 and the can body 2. In this manner, the lid 3 and the can body 2 can form a seamed portion 10 with a laminated crystalline resin film (not shown) interposed therebetween.

[0028] Representative examples of rectangular metal cans include 18-liter cans, half cans (half-cut cans), and 5-liter cans, but cans with a capacity of, for example, 4 to 22 liters can also be mentioned. The rectangular metal cans of this embodiment include cans conforming to JIS standards such as JIS Z 1602, as well as general cans (various size cans) that are not standardized by JIS standards. The material is not particularly limited, but examples include tinplate and black tinplate, tin-free steel, new materials (various special surface-treated steel sheets), laminate materials, etc. that conform to JIS standards. There is no particular limit to the thickness of the lid and can body of the rectangular metal can.

[0029] In this embodiment, the contents of the metal can are not particularly limited to food applications, industrial applications, etc., but examples of hazardous materials for industrial applications include first petroleum products such as toluene, hexane, MEK, ethyl acetate, acetone, etc., alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, etc., second petroleum products such as styrene, xylene, diesel, etc., third petroleum products such as ethylene glycol, cresol, nitrobenzene, etc., and fourth petroleum products such as gear oil, cylinder oil, lubricating oil, machine oil, motor oil, etc., the handling of which is regulated by law from the standpoint of safety, such as firefighting and ship safety.

[0030] The means for heating and fusing the seamed portion is not particularly limited, but examples thereof include methods for heating the seamed portion by high-frequency heating, infrared rays, hot air, direct flame, etc., and contact heating with a heater.

[0031] In this embodiment, the low-temperature crystallization rate of the film in the seam is increased by heating and welding the seam, and then cooling the seam using a cooling means. If the low-temperature crystallization rate measured by DSC thermal analysis is small, the residual strain increases due to crystallization, the welded resin itself becomes brittle, and the adhesive strength of the welded portion decreases, so it does not contribute to improving the seam strength of the metal can, and when pressure such as internal pressure or impact is applied, the adhesive strength decreases and the sealing property decreases. By increasing the low-temperature crystallization rate, the number of amorphous parts increases in the temperature reduction history from heating for welding, so that the toughness is improved and the residual strain of the welded portion is reduced, thereby improving the seam strength of the metal can. In addition, even when pressure such as internal pressure or impact is applied, the sealing function can be ensured, and the contents can be sealed so as not to leak.

[0032] In this embodiment, the low-temperature crystallization rate is measured with reference to the following conditions. It is also considered that each condition, such as the type of differential scanning calorimeter, may be appropriately changed within a range in which no significant difference occurs in the measurement results. <Measurement of low-temperature crystallization rate> A 5 mg sample is taken from the welded part of the seam after melting, and measured using a differential scanning calorimeter (DSC-7200 manufactured by Hitachi Technos) at a heating rate of 10°C / min to obtain a DSC chart (low-temperature crystallization and melting endothermic curves). Specifically, the exothermic peak of low-temperature crystallization near 130°C and the endothermic peak of melting near 250°C are measured, tangents are drawn to the bottom of the peaks at the low-temperature crystallization peak and the melting peak, and the area (peak area) defined by the two points of contact between the curve and the tangent and the peak is measured, and the ratio ΔHc / ΔHm of the heat of crystallization (ΔHc (J / g)) and the heat of fusion (ΔHm (J / g)) is multiplied by 100 to obtain the low-temperature crystallization rate (%).

[0033] In general, in crystalline polymers, crystalline parts are generated in addition to amorphous parts during the cooling process after heating and melting. For example, when PET is melted and then quenched by immersing it in water, a glass transition occurs around 70°C, an exothermic peak due to crystallization occurs around 130°C, and an endothermic peak due to melting occurs around 250°C. However, when PET is melted and then slowly cooled (gradually cooled) by cooling in air, a DSC measurement is performed. Because it was cooled slowly (gradually cooled), no low-temperature crystallization peak is observed around 130°C, and only an endothermic peak due to melting is observed around 250°C (see Industrial Chemistry Journal, Vol. 73, No. 11 (1970), pp. 217-222, etc.). This indicates that the crystallization progresses when the PET melted by heating is slowly cooled, so no low-temperature crystallization peak occurs around 130°C on the DSC chart.

[0034] In other words, compared with slow cooling, rapid cooling can increase the amount of amorphous regions, and these amorphous regions undergo low-temperature crystallization when the temperature is raised during DSC measurement. Measuring the proportion of the heat of heat of fusion of the entire resin caused by this low-temperature crystallization can be used as an index of the cooling history.

[0035] In other words, when the can is cooled slowly (naturally), the crystallization proceeds and low-temperature crystallization is not observed, but the more rapidly the can is cooled, the more prominent the low-temperature crystallization peak becomes and the amount of heat generated by low-temperature crystallization also increases. In this embodiment, the low-temperature crystallization rate increases by heating and welding the seam portion, and then cooling the seam portion using a cooling means. This increases the amount of amorphous parts in the temperature drop history from the heating for welding, improves toughness, and reduces residual distortion in the welded portion. This improves the seam strength of the metal can and prevents leakage of the contents from the seam portion.

[0036] In this embodiment, the cooling means is not particularly limited, but considering application to a production line, examples include a method of directly cooling the seamed portion with cold air or cold water, a method of cooling by contacting the seamed portion with a cooling jig through which cooling water has passed, etc. The use of the cooling means mainly promotes the cooling rate after the seamed portion is heated and welded, compared to cooling in the air. (Embodiment 2) The method for manufacturing metal cans in this embodiment involves forming a metal plate laminated with a film of crystalline PET resin into a metal can component, then seaming the component, and heating and welding the seamed portion.The seamed portion is heated and welded, and then, if necessary, cooled using a cooling means, to form a seamed portion in which the low-temperature crystallization rate of the film as determined by DSC thermal analysis is 4% or more, preferably 5% or more.

[0037] In addition, the metal can in this embodiment is a metal can in which a metal plate laminated with a crystalline PET resin film is formed into a metal can component, the component is then seamed, and the seamed portion is heated and welded, and the low-temperature crystallization rate of the film in the seamed portion, as determined by DSC thermal analysis, is 4% or more, preferably 5% or more.

[0038] Detailed explanations of the same parts as those in the first embodiment will be omitted.

[0039] This embodiment is characterized by using a metal plate laminated with a crystalline PET resin film, and forming a seam portion in which the low-temperature crystallization rate of the film obtained by DSC thermal analysis is 4% or more. As a result, the amount of amorphous parts increases in the temperature reduction history from heating for welding, so that the toughness is improved and the residual strain of the welded portion is reduced, and therefore the seam strength of the metal can is improved and leakage of the contents from the seam portion can be suppressed. For this purpose, as in the above-mentioned embodiment 1, after the seam portion is heated and welded, the seam portion can be cooled using a cooling means. On the other hand, in the case of a crystalline homo-PET resin that has been conventionally used in a resin-laminated metal plate of a metal can, the low-temperature crystallization rate of the film obtained by DSC thermal analysis is 0% under slow cooling conditions in which PET is melted and then cooled in air. However, for example, in the case of a copolymerized PET resin with lower crystallinity than a homo-PET resin, if the low-temperature crystallization rate of the film obtained by DSC thermal analysis is 4% or more, it is not necessary to cool the seam portion using a cooling means.

[0040] When the low-temperature crystallization rate measured by DSC thermal analysis becomes small, the residual distortion increases due to crystallization, and the adhesive strength of the welded part decreases, so the welded resin itself becomes brittle and does not contribute to improving the seaming strength of the metal can. When pressure such as internal pressure or impact is applied, the adhesive strength decreases and the sealing performance decreases. When the low-temperature crystallization rate is 4% or more, the amorphous part increases due to crystallization, so the toughness improves and the residual distortion of the welded part decreases, improving the seaming strength of the metal can. Therefore, the sealing function can be secured even when pressure such as internal pressure or impact is applied.

[0041] The crystalline PET resin is not particularly limited. The PET resin used for laminated steel sheets for can manufacturing and the like is generally PET with terephthalic acid and ethylene glycol as monomer components, particularly crystalline homo-PET resin. In this embodiment, in addition to the crystalline homo-PET resin, a copolymerized PET resin with lower crystallinity than the homo-PET resin can be used. The copolymerized PET resin with lower crystallinity than the homo-PET resin is obtained by copolymerizing another monomer component as a third component in addition to terephthalic acid and ethylene glycol, and examples of such copolymerized PET resins include PET resins that are copolymerized by adding an acid (isophthalic acid, etc.) or an alcohol (CHDM, etc.) to impart processability. In the copolymerized PET resin with lower crystallinity than the homo-PET resin, when the low-temperature crystallization rate of the film obtained by DSC thermal analysis is 4% or more under slow cooling conditions of melting and cooling in air, it is not necessary to cool the seamed portion using a cooling means.

[0042] Although the present invention has been described above based on the embodiments, the present invention is not limited to these embodiments, and various modifications are possible without departing from the spirit and scope of the present invention. EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0044] Regarding the crimping part of the base of a square metal can (18-liter can) made of TFS (tin-free steel), using a lid of a square metal can with a crystalline homo-PET resin with a film thickness of 12 μm laminated on the welding surface (the thickness of the metal plate is 0.32 mm) and a base with a crystalline homo-PET resin with a film thickness of 12 μm laminated on the welding surface (the thickness of the metal plate is 0.30 mm), after crimping (seaming) both laminated plates, they were melted at 270 °C for 20 seconds and immediately cooled by the cooling method described in Table 1.

[0045] As the cooling method after melting to 270 °C, for the case of using immersion cooling, a cooler (a simple spot cooler manufactured by Sunwa Enterprise Co., Ltd.), and the case of using a spot cooler (a spot air conditioner manufactured by Sweden Co., Ltd.), samples with different low-temperature crystallization rates were prepared by changing the distance from the cold air outlet nozzle. <Measurement of low-temperature crystallization rate> A 5 mg sample was taken from the welded part in the crimping part after melting, and using a differential scanning calorimeter (DSC-7200 manufactured by Hitachi High-Tech Corporation), it was measured under the condition of a heating rate of 10 °C / min to obtain a DSC chart (low-temperature crystallization and melting endothermic curve). Specifically, the exothermic peak of low-temperature crystallization near 130 °C and the endothermic peak of melting near 250 °C were measured. At the low-temperature crystallization peak and the melting peak, a tangent was drawn at the lower end of the peak, and the two contact points between the curve and the tangent and the area (peak area) defined by the peak were measured. The ratio ΔHc / ΔHm of the crystallization heat (ΔHc (J / g)) and the melting heat (ΔHm (J / g)) was multiplied by 100 to obtain the low-temperature crystallization rate (%). <T peel adhesion strength> The PET laminated plate was cut into a width of 10 mm × a square of 40 mm. After stacking two PET films and heating an area of 10 mm × 10 mm at 290 °C for 20 seconds, a predetermined cooling treatment was performed, and after 1 day, the T peel strength was measured with a tensile tester. <Pressure resistance test> A cap was fitted to the mouthpiece to close the can, and a pressure test tool was attached to the flat part of the square metal can, and the internal pressure of the can was pressurized with water to 100 Kpa for 5 minutes to check for leakage from the mouthpiece seam. The photograph in Figure 6 shows the state of this pressure test (internal pressure test). Any leakage, even if slight, from the mouthpiece seam was judged to indicate leakage, and the number of cans that passed the test out of 10 cans tested is recorded in the examples and comparative examples in Table 1.

[0046] The results of the above measurements and evaluations are shown in Table 1.

[0047] [Table 1] [Explanation of symbols]

[0048] 1. Square metal can 2 Can body 3 Lid 3a Crystalline resin film 3b Crystalline resin film 3c metal plate 4 Cap 5. Base 5a Crystalline resin film 5b Crystalline resin film 5c metal plate 10. Sealing section

Claims

1. A method for manufacturing a metal can, comprising forming a metal plate having a crystalline PET resin film laminated on one or both sides thereof into a metal can component, seaming the components together, and heating and fusing the seamed portion, The method for manufacturing a metal can includes heating the seamed portion where the metal plates are seamed together to melt and weld the crystalline PET resin film of the metal plate, and then cooling the seamed portion using a cooling means to form the seamed portion in which a low-temperature crystallization rate of the film is 4% or more, which is obtained by multiplying 100 by the ratio ΔHc / ΔHm of the heat of crystallization (ΔHc (J / g)) and the heat of fusion (ΔHm (J / g)) obtained by DSC thermal analysis.

2. The metal can includes a metal can lid having a cap, The method for producing a metal can according to claim 1 , wherein the cap and the metal can lid form the seamed portion having the film as an inner surface.

3. A metal can comprising a metal plate having a crystalline PET film laminated on one or both sides thereof formed into a metal can member, the members being seamed together, the seamed portion being heated to melt and weld the crystalline PET resin film, and then the seamed portion being cooled using a cooling means, The metal can has a low-temperature crystallization rate of the film in the seamed portion, which is obtained by multiplying the ratio ΔHc / ΔHm of the heat of crystallization (ΔHc (J / g)) to the heat of fusion (ΔHm (J / g)) obtained by DSC thermal analysis by 100, of 4% or more.

4. The metal can includes a metal can lid having a cap, 4. The metal can according to claim 3, wherein the cap and the metal can lid form the seamed portion with the film as an inner surface.

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