JPH11193016A - Low positive pressure canned goods and can body thereof having internal pressure inspection bearability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a can body which has an excellent internal pressure inspection bearability and improved deterioration delectability and in which the bottom of the can body has a pressure strength which can withstand a rise in the internal pressure at a retort treatment and a two-piece can with thin wall can be applied to the contents of a can needing retort sterilization. SOLUTION: In the can body, an annular ground-contact part 3 is formed near the outer periphery of a can bottom and a substantially flat part is provided within the part 3. And contents are charged into the can body and sealed under such a low positive pressure that the internal pressure of the can body at room temperatures is 0.2-0.8 kgf/cm<2> , preferably 0.2-0.6 kgf/cm<2> , and variation is ±0.2 kgf/cm<2> , preferably ±0.1 kgf/cm<2> , and hammer test bearability can be provided at the flat part of the bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low positive pressure can having an internal pressure test aptitude and a can body thereof, and more particularly, to an internal pressure capable of performing an internal pressure test with the same accuracy as a tapping test conventionally applied to a negative pressure canned internal pressure test. The present invention relates to a low positive pressure can having inspection suitability and a can body thereof.

[0002]

2. Description of the Related Art Conventionally, for canning of low-acid beverages such as milk-containing beverages, which are very easily deteriorated and putrefactive, it is required to inspect the sealing property after filling and the putrefaction of the contents. In general, the inspection of the sealing property of the can and the decay of the contents are performed by hitting the can lid or the bottom of the can to generate vibration and inspecting the internal pressure based on the correlation between the generated sound and the internal pressure of the can. An inspection method is adopted to detect the hermeticity due to excessive or insufficient internal pressure and to detect the presence or absence of expansion due to putrefactive bacteria. Since low-acid beverages are generally hot-filled (hot-packed) and retorted, when the content of a low-acid beverage can cools to room temperature, negative pressure is generated due to shrinkage of the contents and gas in the headspace. Negative pressure canned. Negative pressure cans have a vacuum of approximately 20-60 cmHg
In the range, the pressure variation is small and the natural frequency changes greatly with respect to the internal pressure fluctuation, so that the detection resolution by percussion inspection is high, and the advantage that leakage and deterioration of contents can be accurately detected by percussion inspection. is there.

[0003] However, in the case of negative pressure cans, there is a problem that a can body having high rigidity to withstand negative pressure is required and the side wall is thicker than a positive pressure can, so that the cost of cans is increased.

On the other hand, by filling an inert (liquefied / solidified) gas such as liquid nitrogen at the time of sealing, a positive pressure is generated in the can by vaporization and expansion of liquid nitrogen or the like, and rigidity is given by the pressure in the can. There are positive pressure cans. Positive pressure cans are usually 1.0 ± 0.3 kgf / cm ² at normal internal pressure (gauge pressure, hereinafter the same)
Since it reaches about 6.0 kgf / cm ² at the time of retort, the bottom of the can is formed in a dome shape bulging inward to withstand the internal pressure. Positive pressure cans have a positive pressure inside the can compared to negative pressure cans, so they can hardly be dented against external pressure and can be made thinner, and can material can be reduced and can cost reduced. There are advantages that can be done.

[0005]

As described above, to reduce the thickness of the can material, a positive pressure can can be used. However, the conventional positive pressure can is lacking in the suitability for internal pressure inspection for the following reasons. And the quality assurance is insufficient, the content of low acid beverages, such as beverages containing milk, has a can bottom thickness of 0.24.
It is applied to negative pressure cans made of steel with a relatively thick plate thickness of about 0.26 mm and a can body of about 0.2 mm. Positive pressure cans are applied to contents that are relatively hard to perish or perish. It was not too much. In the case of positive pressure canning, the internal pressure is generated by the charged gas, and thus the variation in internal pressure is greater than that in negative pressure canning. With conventional gas displacement positive pressure cans, the variation of internal pressure with respect to the set internal pressure is ± 0.3 kgf / cm ² or more, and positive pressure cans with internal pressure variation of ± 0.3 kgf / cm ² or less with respect to the set internal pressure have not yet been provided. . Therefore, even if the can internal pressure can be measured accurately, it cannot be distinguished whether the measured can internal pressure is due to deterioration of the contents or due to the variation of the filling gas amount due to the large variation range. , It is difficult to accurately detect the decaying can. In the case of a positive pressure can with a dome-shaped can bottom to increase pressure resistance, the bottom wall is unlikely to change with internal pressure. The quality assurance is lacking for canned contents that cannot be made and easily perish. Furthermore, in the case of positive pressure canning by the conventional gas replacement method,
Since the internal pressure of the can is generally as high as 1.0 ± 0.3 kgf / cm ² , even if there is a small internal pressure fluctuation due to minute leakage or decay, it is difficult to detect because the internal pressure fluctuation rate relative to the whole is low, When the bottom is subjected to beating inspection, accurate internal pressure detection cannot be performed because the internal pressure region has a small change in vibration characteristics with respect to a change in can internal pressure. Also, when detecting the can internal pressure by the displacement amount of the lid, the bottom or the body, or when detecting the can internal pressure by pressing the body or the like at a predetermined pressure and measuring the reaction force thereof, such a case is also considered. In the case of the internal pressure of the can, the rigidity of the can is increased, and the amount of change in the displacement or the reaction force is small, so that the internal pressure inspection becomes difficult. When retort sterilizing positive pressure cans by the conventional gas replacement method, etc., the internal pressure increases during retort processing and the positive pressure state further increases, so the strength to withstand the internal pressure, especially the bottom and lid that are likely to cause buckling Pressure resistance performance is required. Therefore, it is difficult to endure retort treatment with the conventional bottom shape for negative pressure cans in terms of strength, and in order to make cans necessary for retort treatment, the bottom must be thickened and the plate material is thinned. The advantage of positive pressure canning employed is lost.

Accordingly, the present invention solves the problems of positive pressure cans that lack the suitability for internal pressure inspection as described above at once,
It is intended to enable the use of thin-walled cans for cans of low-acid beverages such as milk-containing beverages. Specifically, it is excellent in internal pressure inspection such as percussion inspection and has the ability to detect leakage and deterioration. high,
It is an object of the present invention to provide a low positive pressure can having an internal pressure inspection suitability and a can body thereof that can withstand an increase in the internal pressure during retort processing and can reduce the cost of the can by reducing the thickness of the can material. is there.

[0007]

Means for Solving the Problems A positive pressure can having an internal pressure test suitability according to the present invention which solves the above-mentioned problems is filled and sealed so that the internal pressure of the can is at least a positive pressure with respect to an external pressure. Wherein the internal pressure of the can is 0.2 to 0.8 kgf / cm ² at room temperature, preferably 0.2 to 0.6 kgf.
/ cm ² so as to have an internal pressure inspection suitability. The can internal pressure, in the range of the set pressure 0.2~0.8kgf / cm ^2, variation ±
0.2 kgf / cm ² or less, preferably If it is ± 0.1 kgf / cm ² or less. If there is variation ± 0.2kgf / cm ² or more,
It is not preferable because the reliability of detecting a minute internal pressure change due to a minute leak or deterioration is lowered. The internal pressure inspection characteristic means that, for example, when an internal pressure inspection is performed by punching, the response of the sound (frequency) generated by the impact is good even for a small change in the internal pressure of the can, and the displacement of the outer peripheral portion of the can is changed. When the internal pressure test is performed by measuring with a gauge, the response of the displacement of the measurement site to a small change in the internal pressure of the can is good. When the internal pressure inspection is performed by measuring the internal pressure, the response of the reaction force is good even for a minute change in the internal pressure of the can, and this means the ability to accurately measure the internal pressure.

In order to reduce the cost of the can with the can, a seamless can having a body and a bottom integrally formed is desirable. Further, the bottom of the can has an annular grounding portion, and the outer annular grounding portion is formed. It is more desirable to have a bottom wall that is a substantially flat portion on the inside, and to have internal pressure test suitability at the bottom. In addition,
When the can is a seamless can and the bottom is a dome-shaped can, the lid or the body of the can is made to have an internal pressure inspection suitability.

The range of the can internal pressure of 0.2 to 0.8 kgf / cm ^2, preferably 0.2 to 0.6 kgf / cm ² , as shown in the graph of FIG. The change rate (slope) of the change in the vibration frequency at the bottom is large, and the vibration frequency changes greatly even with a slight change in the internal pressure, which is confirmed as a range in which the measurement of the can internal pressure can be detected well. This range is a positive pressure state corresponding to the degree of vacuum of the negative pressure can, and means that the tapping can be performed with the same accuracy as the negative pressure can. When the internal pressure of the can is out of the above range, the change of the vibration frequency with respect to the change of the internal pressure of the can is small, resulting in poor judgment. Further, when the can internal pressure is higher than 0.8 kgf / cm ² , in the case of canned to be retorted, the differential pressure between the inside and outside of the can becomes too large during the retort processing (immediately after taking out from the retort pot), and the above substantially flat portion is removed. With the provided can bottom shape, the can material must be made thick to maintain pressure resistance, and the suitability for internal pressure inspection is poor. In addition, the displacement amount of the lid or the bottom or the trunk portion is measured by a change in the internal pressure of the can within the internal pressure range of the can, and when the internal pressure is to be inspected, the internal pressure inspection has good suitability except for a dome-shaped bottom having high rigidity. Is out of the above-mentioned can internal pressure range.
is insufficient determination sealing guaranteed in kgf / cm ² less than the can internal pressure, by the can internal pressure the can rigidity is increased in the range above 0.8 kgf / cm ^2, since the change amount of the displacement is small, accurate pressure Inspection becomes difficult.

The contents of the positive pressure cans are not particularly limited, and the contents of the cans are not particularly limited. However, the contents are low-acid beverages, sealed under a positive pressure by a gas exchange method, filled and sealed, and then subjected to a retort sterilization treatment. It can be suitably applied to any of the above, and has an internal pressure inspection suitability at any of the bottom, the trunk, and the lid. In addition, the gas replacement method referred to in the present invention is not limited to the case where an inert gas such as a nitrogen gas is blown into a head space to perform the replacement, and the inside of the can is filled with a liquefied gas such as liquid nitrogen or a solidified gas such as dry ice. This also includes the case where a positive pressure is generated in the can due to its vaporization and expansion.

[0011] The can body used for low positive pressure canning of the present invention has a body and a bottom formed seamlessly and integrally, the bottom having an annular grounding portion in the vicinity of an outer peripheral portion. Forming an inner rising wall having an inner side rising inside the can, and forming a bottom wall having a substantially flat shape and a height of 0.5 to 6 mm from a ground contact position inside the inner rising wall; The center portion of the bottom wall has applicability for percussion. The shape of the bottom of the can is such that the depth from the bottom wall toward the inside of the can is 0.1 to 4 at the bottom of the inner rising wall of the annular grounding portion.
It is desirable to form an annular bead of mm, the ground diameter of the can bottom is 70-98% of the can body diameter, and the flat part diameter of the can bottom is preferably 60-90% of the ground diameter. .
Further, the inclination angle of the rising wall is desirably 65 to 110 °. The annular bead is not limited to an inverted U-shaped cross section, but may be formed so as to have a gentle slope from the top to the bottom wall so as to continue to the bottom wall. The number of the annular beads is not limited to one, and a plurality of annular beads may be formed.

The height of the bottom wall flat portion from the ground contact position is as follows:
If it is less than 0.5 mm, the deformed bottom after retorting may be convex below the grounding part, and if it is more than 6 mm, the thickness from the grounding to the rising part will be thinner due to molding, Become. In addition, the content with respect to the height of the can is reduced, and the material cost is relatively increased, which is not preferable. If the depth of the annular bead is less than 0.1 mm, the effect on the pressure resistance performance of the central portion of the bottom wall cannot be sufficiently obtained, and if it is more than 4 mm, molding becomes difficult. Furthermore, if the sloped wall of the rising wall is smaller than 65 °, the pressure resistance performance of the grounding portion is reduced, and the area of the bottom wall flat portion is reduced, so that the suitability for internal pressure inspection is deteriorated. It will be difficult.

As the metal material of the can applied to the present invention, a metal plate such as tinplate, TFS, surface-treated steel plate, or a laminated plate obtained by laminating a synthetic resin such as a polyester film on the metal plate is used. , Seamless cans by a combination of normal drawing and ironing or stretching, or 3-piece cans with a lid wrapped around the bottom,
The material and the production method and form of the can are not particularly limited, but according to the present invention, the thickness of the bottom of the can is 0.15 to 0.25 mm for steel and 0.1 mm for aluminum.
The thickness can be reduced to a range of 25 to 0.35 mm.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a sectional view of a main part of a can according to an embodiment of the present invention. The can body 1 of the present embodiment is a two-piece can (seamless can) in which a body and a bottom are integrally formed, and is made of a steel plate or an aluminum plate, or a PET plate.
Squeezing and ironing of laminated composite boards such as films,
Alternatively, they were formed by processing them in combination with stretching or the like. The bottom of the can 1 has a mountain-shaped annular grounding portion 3 and a valley-shaped annular bead 5 between the body wall 2 and the bottom wall 6. The bottom of the inner rising wall 4 of the annular ground contact portion 3 projects from the bottom wall surface into the can and is folded to form an annular bead 5 having an inverted U-shaped cross section that projects into the can. In this embodiment, the bottom wall 6 inside the annular bead is formed entirely flat.

The inclination angle α of the outer rising wall 7 of the annular contact part 3
Is 5 ° to 30 °, and the inclination angle β of the inner rising wall 4 is 65 °.
It forms in the range of -110 degrees. In addition, the height h of the center of the bottom wall from the grounding surface is such that the can bottom expands with an increase in internal pressure during retort processing, and the bulge remaining on the bottom wall does not protrude outward from the annular grounding portion when the temperature returns to room temperature. It is necessary that 0.1
10 mm, preferably 0.5 mm to 6 mm.
Furthermore, it was confirmed that the annular bead 5 plays a role of increasing the pressure resistance of the bottom against the internal pressure, and the internal pressure resistance improves when the depth is increased to some extent. The presence of the annular bead 5 functions to increase the pressure resistance of the bottom part because the annular bead shape increases the peripheral rigidity against the swelling to the outside of the flat bottom wall with the increase of the internal pressure, and the bottom center In order to obtain this effect, the depth m of the annular bead 5 is 0.1 to 5 mm, preferably 0.1 to 3 mm. The ground diameter of the annular ground part 3 is in the range of 70 to 98% of the can body diameter from the standpoint of independence and strength, and the diameter of the flat part of the bottom wall is 60 to 90% of the ground diameter of the annular ground part. It was confirmed that the formation in the range described above was a range in which suitability for the internal pressure test at the bottom was good.

By forming the bottom portion in the above-mentioned shape, the pressure resistance of the bottom wall is improved.
A pressure resistance that can withstand kgf / cm ² can be obtained. As described later, the pressure resistance is a strength that can withstand a pressure increase during retort processing required for sterilization of contents during retort processing. The plate thickness at the bottom of the can is 0.15 to 0.25 mm for steel and aluminum for the range of keeping the pressure resistance and making the plate as thin as possible.
0.25-0.35mm due to lower pressure resistance than steel
Is appropriate.

The bottom of the can body of the present embodiment has the above-described shape, and an embodiment of a low positive pressure can with the suitability for percussion of the present invention using the can body will be described. Hot-pack milk-containing low-acid beverages in cans, and use liquid nitrogen or dry ice or other inert gas (hereinafter simply referred to as nitrogen, etc.).
And sealed at that time, the internal pressure of the can at room temperature after filling with nitrogen or the like is 0.2 to 0.8 kgf / cm ^2, preferably 0.2
The internal pressure is set to 0.6 kgf / cm ² , which is lower than that of the normal canned positive pressure, and the set pressure is ± 0.2 k.
Filling and sealing are performed by controlling the filling amount of nitrogen or the like so as to maintain the accuracy of gf / cm ^2, preferably ± 0.1 kgf / cm ² . In the present invention, it is important to set the internal pressure to a low value and to reduce the variation in the set pressure, whereby the detected internal pressure of the can is caused by deterioration, or the mere internal pressure of the can is reduced. It is possible to determine whether or not the variation is caused, and if the bottom pressure inspection or the like used in a conventional negative pressure can is performed for the inspection of the internal pressure of the can, the deterioration can be accurately detected.

As a method for accurately setting the set internal pressure by gas replacement, for example, a liquefied gas such as mist-like liquid nitrogen or dry ice, a low-temperature nitrogen A method of simultaneously filling an inert gas such as a gas can be adopted. By spraying a mist-like liquefied gas having a predetermined particle size or a mixture of dry ice and an inert gas onto the head space, air in the head space is expelled and replaced by gas. Then, by making the liquefied gas or dry ice that evaporates into an inert gas into fine particles in the form of a mist, the effect of viscosity becomes more dominant than the effect of inertia at the time of tightening with a seamer. Liquefied gas or dry ice stays in the can without being scattered to the outside without being affected by centrifugal force due to rotation, and after sealing, generates internal pressure in the can due to their vaporization expansion and temperature expansion of the low-temperature gas. Irrespective of the variation in the pressure, a constant internal pressure can always be obtained. By controlling the ratio between the vaporization expansion and the temperature expansion, the filling internal pressure can be controlled, and a desired internal pressure can be accurately and stably obtained.

Next, in the retort sterilization process performed after sealing and filling, the retort sterilization process is performed such that the pressure difference between the inside and the outside of the can at the time of the retort treatment is within 5 kgf / cm ² . Differential pressure between can and outside 5
In the present invention, the internal pressure of the can before the retort sterilization is set at 0. kgf / cm ² .
Since it is set to ² to 0.8 kgf / cm ^2, preferably 0.2 to 0.6 kgf / cm ^2, it means that the pressure rise during the retort sterilization treatment can be tolerated up to 4.2 to 4.8 kgf / cm ^2. However, this pressure increase is within a range in which a sufficient retort treatment can be ensured for sterilizing the low-acid beverage as the content.

[0020] The canned product manufactured through the above-described process is capable of backing up against the internal pressure increase during the retort sterilization process, even though the can material is a thin-walled can mainly made of steel or aluminum. Deformation such as ringing can be suppressed, and the bottom of the can has sufficient pressure resistance. In addition, the internal pressure of the can at room temperature is ± 0.2 kgf / cm ^2, preferably ± 0.1 kgf / cm ^2.
Since it has an accuracy of / cm ² , deterioration of contents can be detected. In addition, since at least the central portion of the bottom wall of the can is a flat surface, it is excellent in percussion suitability. Therefore, according to the present invention, a low-acid beverage requiring retort sterilization can be filled in a thin two-piece can to have pressure-resistant strength and to ensure sufficient deterioration detection ability of contents. ,
Compared to conventional low-acid beverage cans, it can be made thinner and lighter, and can be used with aluminum cans, and can cost can be reduced.

Although one embodiment of the present invention has been described above, the present invention can be variously modified within the scope of the technical idea, and is not limited to the above embodiment. Further, in the above-described embodiment, the case where the internal pressure test is performed by punching is described, but the positive pressure can of the present invention is not necessarily limited to punching. For example, by measuring the displacement of the outer peripheral portion of the can, such as the lid portion, the bottom portion, or the body portion of the can with a displacement meter, to perform an internal pressure test by converting the internal pressure state of the can, or pushing the outer peripheral portion of the can at a predetermined pressure, The present invention can also be suitably applied to a device in which an internal pressure test is performed by measuring the reaction force and converting it into a can internal pressure state. Regardless of which internal pressure inspection method is adopted, the measurement site on the outer peripheral portion of the can is in a state where it is easy to accurately measure the change in the frequency, displacement, or reaction force in response to the change in the internal pressure. It is necessary to set an internal pressure range in which a lost can can be detected. Therefore, in the present invention, the internal pressure of the can is 0.2 to 0.8 at room temperature.
kgf / cm ² preferably set in a range of 0.2~0.6kgf / cm ^2, and preferably ± 0.2 kgf / cm ² with respect to the set pressure to maintain accuracy of ± 0.1 kgf / cm ² Was confirmed to be a low positive pressure can having the most preferable internal pressure test suitability. The contents are not necessarily limited to low-acid beverages.

FIG. 3 shows various embodiments in which the shape of the can bottom of the can body of the present invention is modified.
Similar effects can be obtained. In the following embodiment, only portions different from the can body of the embodiment shown in FIG. 1 will be described. The can body 10 shown in FIG.
1 has a slightly increased inclination angle β of the inner rising wall 12, and the annular bead 13 has a gentle inclined portion 13 ′ linearly inclined gradually from the top toward the bottom wall 14 and connected to the bottom wall. I have.

The can body 15 shown in FIG. 2B has a particularly different bottom wall shape. The bottom wall 17 of this embodiment has a flat central portion 17 ′ but an outer peripheral portion 17 ″ having an annular bead 16.
Is formed to be inclined toward the end of the gentle inclined portion 16 '. The can body 20 shown in FIG. 3C is characterized in that the annular ground portion 21 is formed wide as a whole. That is, the annular grounding portion 21 has a gentle inclined surface 21 ″ from the tip end 21 ′, and forms an inner rising wall 22 that continues from the gentle inclined surface to the annular bead 23. As shown in FIG. In the can body 25, the annular grounding portion 26 is wider than that of the embodiment shown in FIG.
The bottom wall 27 is formed higher than the bottom wall 27. The can body 30 shown in FIG. 3E corresponds to a case in which an annular bead is formed in two lines of a concave bead 32 and a convex bead 33 between an annular ground portion 31 and a flat bottom wall 34.

[0024]

EXAMPLE 1 A surface of a surface-treated steel sheet was drawn and ironed and stretched from a 0.18-mm-thick steel sheet blank obtained by laminating a polyester film on both sides to obtain a can body diameter of 53 mm and a ground contact diameter of 4 mm.
6.8 mm, the inclination angle α of the outer rising wall is α = 10 °, the inclination angle β of the inner rising wall is 78 °, the height h of the bottom wall from the ground contact position is 3.3 mm, the flat part diameter of the bottom wall is 35.6 mm, The depth from the flat portion to the annular groove is 1.9 mm, and its inclination angle is 43 °.
A seamless can having a height of 100 mm was formed. The plate thickness at the bottom of the can was 0.18 mm.

The above-mentioned molded seamless can is filled with 190 g of milk coffee, and the internal pressure of the can is 0.5 ± 0.1 kgf /
After filling with liquid nitrogen so as to generate cm ² , it was tightly sealed and then heat sterilized and cooled in a usual retort treatment step to obtain 1000 cans of positive pressure cans. It was confirmed that the obtained can had no abnormal deformation of the can and had a pressure resistance to the retort treatment. Then, a punching inspection was performed on all the obtained cans. As a result, it was confirmed that appropriate punching accuracy with respect to the internal pressure was obtained for all the cans, and that all the cans had suitability for punching.

Comparative Example 1 Using a seamless can molded in the same manner as in Example 1,
Fill 190g of milk coffee and can pressure 1.0 ±
After filling with liquid nitrogen so as to generate 0.1 kgf / cm ² , it was tightly wound and sealed, and then heat sterilized and cooled in a usual retort treatment step to obtain 1000 cans of positive pressure cans.
Among them, it was found that the 250 cans had local buckling deformation on the inner rising wall, and lacked pressure resistance under these internal pressure conditions. Also, for the remaining cans that have not buckled, the deformation of the flat part near the annular bead is relatively large,
As a result of the percussion inspection, there were many different cans from the frequency characteristics of the cans that did not undergo the retort treatment, and percussion aptitude was not obtained.

Comparative Example 2 A 1000-pressure canned can of 190 g of milk coffee was prepared in the same manner as in Example 1 and Comparative Example 1 except that the amount of liquid nitrogen was reduced so that the internal pressure of the can became 0.1 kgf / cm ^2. Obtained. In all of the obtained cans, the strength of the can was insufficient in all the cans, so that the cans could not be transported or handled by a vendor.

Comparative Example 3 In the seamless can of Example 1, the diameter of the flat portion was 44 mm.
To obtain a seamless can under the same processing conditions as in Example 1, but the annular groove was cracked and could not be processed.

Comparative Example 4 A seamless can was obtained under the same processing conditions as in Example 1, except that the diameter of the flat portion was changed to 26 mm in the seamless can of Example 1. Through the same process as in Example 1, 1000 cans of positive pressure canned milk coffee of 190 g were obtained. The obtained cans had a low pressure resistance at the bottom of the can at the time of retort treatment, and all the cans were deformed at the bottom of the can by the retort treatment and could not be inspected.

Example 2 The following test was conducted to examine the pressure resistance of the can bottom having the can bottom shape shown in FIG. 2 and the can bottom having the can bottom shape shown in FIG. 3A. In the can body shape shown in FIGS. 1 and 2,
Plate thickness t = 0.185 mm, β = 74 °, h = 3.3 mm, m
= 1.8 mm and a can inner diameter d = 52.5 mm were obtained by drawing and ironing a seamless steel can. The internal pressure of the can body, gradually increased until the pressure difference between the inside the outside and the can from 0 kgf / cm ² at room temperature to 5 kgf / cm ^2, in the case of returning to the original 0 kgf / cm ² by lowering thereafter the internal pressure gradually A test was performed to measure the displacement of the center of the bottom wall. In addition,
In FIG. 1, a broken line indicates a state where the bottom of the can is displaced to the maximum.

FIG. 4A shows the result. In the graph, the upper right corner is the origin, the vertical axis is the displacement (mm) at the center, and the horizontal axis is the can internal pressure (kgf / cm ² ). As a result, the amount of displacement from the initial shape at the center of the bottom wall when the pressure difference between the can and the outside became 5 kgf / cm ² was about 1.5 mm.
Although there was a, but remain slightly deformed can bottom is in a state of returning the pressure to its original ranges absolutely no problem, the can is up to pressure difference 5 kgf / cm ² to poor deformation such buckling that It was confirmed that it had sufficient pressure resistance.

Example 3 A similar experiment was carried out on a steel seamless can having a bottom shape shown in FIG. 3 (a) as described above. The dimensional relationship of the can body is as follows. Body thickness t = 0.185 mm, β = 88 °, h = 2.4 mm, m
= 1.8 mm, d = 52.5 mm. The result is shown in FIG.
(B). It was confirmed that the can body showed substantially the same results.

EXPERIMENTAL EXAMPLE In order to determine the appropriate range of the internal pressure of the can for obtaining the suitability for the internal pressure test, a positive pressure test can was prepared by changing the internal pressure of the can from 0 to 1 kgf / cm ² for each can. Then, a punching test was performed on the test cans, and a punching test was performed on positive pressure cans. Similar experiments to create a negative pressure supply trial canned changing the set pressure of the can internal pressure in the range of 0~-1kgf / cm ^2, was negative圧打test tested in the can bottom. The can body used was a 250 g 2-piece can of a steel can laminated with a PET film. The results are shown in the can pressure-frequency distribution curve of FIG.
In FIG. 5, triangles indicate canned positive pressure, and x indicates canned negative pressure. Horizontal axis for negative pressure can (pressure inside the can)
Represents the absolute value without the minus sign. The vertical axis is the detected vibration frequency.

From the graph, in the case of canned positive pressure, approximately 0.2 to
It can be seen that in the range of 0.8 kgf / cm ^2, preferably 0.2 to 0.6 kgf / cm ² , the slope of the increase in the vibration frequency with respect to the increase in the pressure in the can is large, and the detection ability is high. Further, this range substantially coincides with the slope of the negative pressure canned beating inspection curve, and it can be understood that the internal pressure inspection aptitude has substantially the same discrimination ability as that of the negative pressure canned.

[0035]

As described above, according to the present invention, the internal pressure of the can is set to 0.2 to 0.8 kgf / cm ^2, preferably 0.2 to 0.6 kgf / cm ^2.
With a very low positive pressure of / cm ² , seamless thin-walled cans can withstand pressure at the bottom that can withstand an increase in internal pressure during retort processing, and can be filled and sealed with little variation in can internal pressure. Therefore, canned foods have suitability for internal pressure inspection such as percussion inspection, and it is possible to reliably detect deteriorated cans by internal pressure inspection.

Therefore, to date, canned contents such as low-acid beverages which easily perish or perish can be applied only to negative pressure cans which are excellent in internal pressure inspection from the viewpoint of quality assurance of the contents. According to the present invention, it is possible to adopt a seamless can for positive pressure canning, which can reduce the thickness of the plate, and it is possible to reduce the thickness and weight of the can material, reduce the cost of cans, and save resources. It is possible to obtain canned low-acid beverages and the like having a high ability to detect lost cans.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a can body for low positive pressure cans according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of the main part.

FIGS. 3 (a) to 3 (e) are schematic diagrams of main parts of can bodies for low positive pressure cans according to other different embodiments of the present invention.

4A and 4B are graphs showing the amount of displacement of the can bottom with respect to the internal pressure of the can. FIG. 4A shows the case of the can of the embodiment shown in FIG. 1, and FIG. 4B shows the case of the can shown in FIG. Is the case.

FIG. 5 is a graph showing a comparison of internal pressure-frequency distribution curves of canning of a positive pressure can and a negative pressure can with a can bottom, and shows an absolute value in the case of a negative pressure can.

[Explanation of symbols]

 1, 10, 15, 20, 25, 30 Can body 2 Body wall 3, 11, 21, 26, 31 Annular ground part 4, 22 Inner rising wall 5, 13, 16, 23, 32, 33 Annular bead

Claims (15)

[Claims] 1. A can which is filled and sealed with contents so that the internal pressure of the can is at least a positive pressure with respect to the external pressure, wherein the internal pressure of the can is 0.2 to 0.8 kgf / cm ² at room temperature.
Characterized by having a suitability for an internal pressure test, characterized by having a suitability for an internal pressure test. 2. The set internal pressure of the can pressure is ± 0.2 kgf /
while maintaining the accuracy of cm ^2, low positive pressure canned according to claim 1, characterized in that the filled sealed canned. 3. The low positive pressure can according to claim 1, wherein the body and the bottom are cans hermetically sealed in a seamless can body formed integrally. 4. The seamless can body according to claim 3, wherein the bottom has an annular grounding portion near an outer peripheral portion, and a substantially flat portion inside the annular grounding portion. Low positive pressure canned. 5. The canned product is a low acid beverage,
The low positive pressure can according to any one of claims 1 to 4, which is subjected to a retort sterilization treatment after filling and sealing. 6. The low positive pressure can according to claim 1, wherein the can is brought into a positive pressure state by a gas replacement method. 7. The low positive pressure can according to any one of claims 1 to 6, wherein the internal pressure inspection suitability is a punching suitability. 8. The low positive pressure can according to any one of claims 1 to 6, wherein the suitability for the internal pressure test is a suitability for an internal pressure test by measuring a displacement amount of an outer peripheral portion of the can with respect to a change in the internal pressure. 9. The low positive pressure can according to any one of claims 1 to 6, wherein the suitability for the internal pressure test is a suitability for an internal pressure test by measuring a reaction force of an outer peripheral portion of the can with respect to a change in the internal pressure. 10. A body and a bottom are seamlessly and integrally formed, and the bottom has an annular grounding portion in the vicinity of an outer peripheral portion, and the inside of the annular grounding portion constitutes an inner rising wall which rises inward of the can. A low positive pressure having an internal pressure inspection suitability, wherein a bottom wall having a substantially flat shape and a height of 0.5 to 6 mm from a ground contact position is formed inside the inner rising wall. Can body for canning. 11. A bottom portion of a rising wall of the annular ground portion,
The can body according to claim 10, wherein an annular bead having a depth of 0.1 to 4 mm from the bottom wall surface toward the inside of the can is formed. 12. The ground diameter of the bottom of the can is 70 to 70 mm of the can body diameter.
98%, the diameter of the flat part at the bottom of the can is 6
The can according to claim 11, which is 0 to 90%. 13. The rising wall has an inclination angle of 65 to 110.
The can according to claim 10, 11 or 12, which is in degrees. 14. The can body according to claim 11, wherein the annular bead has a gentle slope extending from the top to the bottom wall. 15. The plate thickness of the bottom of the can is 0.1% of steel material.
5 to 0.25 mm or 0.25 to 0.25 in aluminum material.
The low positive pressure can according to any one of claims 10 to 14, which is 35 mm.