JP2005320577A - Aluminum alloy sheet for wide mouthed bottle can cap - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg based aluminum alloy sheet for a wide mouthed bottle cap whose pressure withstanding strength can be improved in such a manner that the improvement in the rigidity of a screw part and the prevention in the doming of a top face in a cap are made possible by increasing its strength in the range where its formability and earing ratio are not damaged. <P>SOLUTION: The aluminum alloy sheet for a wide mouthed bottle can cap has a chemical composition comprising, by weight, >2.1 to 3.5% Mg, and the balance aluminum with inevitable impurities. The original sheet of the aluminum alloy sheet has a tensile strength of 210 to 320 MPa and a proof stress of 160 to 290 MPa. The baked sheet obtained by subjecting the original sheet to heat treatment at 200°C for 10 min has a tensile strength of 210 to 320 MPa, a proof stress of 150 to 280 MPa, and an elongation of ≥5%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an Al—Mg (aluminum-magnesium) based alloy plate suitably used for a PP (pilfer proof) cap for a wide-mouth bottle can.

  PP caps are generally coated and printed on a material aluminum alloy plate, then formed into a plurality of cylindrical cups at the same time, trimmed at the ears of each cup, and then processed into perforations at the hem. It is manufactured by the process. The cap thus formed is filled in the beverage container, and then wound around the threaded portion of the container and put on the market.

  Until now, Al-Mn 3105 alloy (see Patent Document 1) or Al-Fe 8011 alloy has been mainly used for PP caps with a diameter of 28 mm or less (see Non-Patent Document 1). . On the other hand, a wide mouth cap having a diameter of 38 mm or the like uses Al-Mg 5151 alloy because it needs to have higher strength. However, it is considered that the strength of 5151 alloy is insufficient for the contents with higher internal pressure or for gauge down (reduction in plate thickness).

Japanese Patent No. 3153541 Sumitomo Light Metal Technical Report, vol. 23 (1982), p. 36.

  The present invention has been made in view of such conventional problems, and in particular, by improving the strength within a range that does not impair the moldability and the ear rate, the rigidity of the screw portion in the manufactured cap is improved and the top surface is prevented from doming. Therefore, the present invention is to provide an Al—Mg-based aluminum alloy plate for a wide-mouth bottle can cap, which can improve the pressure strength so as to be possible.

The present invention relates to an aluminum alloy plate for a wide-mouth bottle can cap having a chemical composition comprising Mg: exceeding 2.1% (weight%, the same shall apply hereinafter) and not more than 3.5%, the balance being inevitable impurities and aluminum. There,
The tensile strength of the base plate of the aluminum alloy plate is 210 to 320 MPa, the proof stress is 160 to 290 MPa,
And the tensile strength of the baked board which gave the heat processing hold | maintained for 10 minutes at the temperature of 200 degreeC with respect to the said base plate is 210-320 MPa, yield strength is 150-280 MPa, elongation is 5% or more, It is characterized by the above-mentioned. It is in the aluminum alloy plate for wide-mouth bottle can caps (claim 1).

First, the reason for limiting the chemical composition in the present invention will be described.
Mg is an essential component of the present invention. By limiting its content to more than 2.1% and not more than 3.5%, strength and formability can be kept good.
When the Mg content is 2.1% or less, the strength is insufficient for handling high internal pressure contents or handling gauge down, so that a predetermined pressure resistance is obtained as a wide-mouth bottle can cap (hereinafter simply referred to as a cap). I can't. In addition, there is a problem that the rigidity of the threaded portion of the molded cap and the effect of preventing doming on the top surface cannot be sufficiently obtained. In addition, four ears in the 0 °, 90 °, 180 °, and 270 ° directions with respect to the rolling direction are easily developed, so it is difficult to stably obtain a material with a low ear rate, and it is difficult to bend characters. It is not easy to mass-produce. Therefore, as described later, the Mg content is preferably 2.5% or more.

As the Mg content increases, the crystal grains become finer. Therefore, rough skin at the time of cup molding can be suppressed by increasing the Mg content and enhancing the effect of crystal grain refinement.
Further, when the Mg content exceeds 3.5%, the strength is too high, and a great deal of force is required at the time of opening, so that it is difficult to open the plug. Therefore, as described later, the Mg content is preferably 3.0% or less.

Moreover, the generation | occurrence | production state and intensity | strength characteristic of an ear | edge ratio can be adjusted with other manufacturing conditions etc. not only as content of Mg but as mentioned later.
In addition, the above-mentioned character bending is a phenomenon in which a printed pattern or characters are bent and displayed depending on how the material is deformed due to the characteristics of the method of manufacturing a cap formed into a cup shape after printing in a flat state. That means.

  The base plate refers to the aluminum alloy plate of the present invention itself, that is, the plate in the state as manufactured and before being supplied to the cap manufacturing process. The blank plate is a plate in which the base plate is subjected to the heat treatment as described above, and the state after printing in the cap manufacturing process is reflected to some extent for convenience.

The strength of the base plate is limited to a tensile strength of 210 to 320 MPa and a proof stress of 160 to 290 MPa. And the intensity | strength of the said baked board is limited to the range whose tensile strength is 210-320 MPa, proof stress is 150-280 MPa, and elongation is 5% or more.
If the tensile strength and proof stress of the base plate are not within the above ranges, it will be difficult to obtain the desired strength after baking.
When the tensile strength of the blank plate is less than 210 MPa and the proof stress is less than 150 MPa, a predetermined pressure resistance cannot be obtained in the molded cap. On the other hand, when the tensile strength of the blank plate exceeds 320 MPa and when the proof stress exceeds 280 MPa, there is a problem that it is difficult to open the molded cap.
When the elongation of the blank plate is less than 5%, there is a problem that molding defects such as cracks are likely to occur during cap molding.

In the present invention, according to the specifications of the cap to be obtained, the Mg content can be limited to a narrower range and adjusted to a more optimal strength characteristic.
That is, when emphasizing the ease of opening the cap, the Mg content is 3.0% or less, the tensile strength of the base plate is 210 to 280 MPa, and the proof stress is 160 to 250 MPa. The empty fired plate preferably has a tensile strength of 210 to 280 MPa, a proof stress of 150 to 240 MPa, and an elongation of 5% or more.

  In the case where importance is attached to the pressure resistance of the cap, the Mg content is 2.5% or more, the tensile strength of the base plate is 250 to 320 MPa, the proof stress is 200 to 290 MPa, and the air baking is performed. The plate preferably has a tensile strength of 250 to 320 MPa, a proof stress of 190 to 280 MPa, and an elongation of 5% or more.

  In addition, the aluminum alloy plate is replaced with a part of the aluminum in the chemical composition, Cu: 0.01 to 0.20%, Mn: 0.01 to 0.30%, Cr: 0.01 to 0.05%, Zn: 0.01 to 0.25%, Si: 0.01 to 0.20%, Fe: 0.01 to 0.30%, Ti: 0.005 to 0.05% It is preferable that 1 type or 2 types or more are included (Claim 4).

Cu: 0.01 to 0.20%;
Cu is an element that affects the material strength. If it is less than 0.01%, not only the effect cannot be obtained, but it is necessary to use a high purity metal, resulting in an increase in cost. Addition in excess of 0.20% makes rolling difficult in the present Al-Mg alloy.

Mn: 0.01 to 0.30%, Cr: 0.01 to 0.05%, Zn: 0.01 to 0.25%, Fe: 0.01 to 0.30%;
Mn, Cr, Zn, and Fe are elements that affect the formability by crystal grain refinement. If each of these is less than the above lower limit, not only the effect cannot be obtained, but it is necessary to use a high purity metal, which increases the cost. On the other hand, when the above upper limit is exceeded, the crystal grain refining effect is saturated, and therefore the above upper limit is preferably taken into consideration in view of the cost increase required for addition.

Si: 0.01-0.20%;
Si is an element that forms a compound with Mn and Fe and forms a crystallized product such as an Al-Mn-Fe-Si-based or Al-Fe-Si-based compound during casting. If it is less than 0.01%, it is necessary to use high purity metal, which increases costs. When it exceeds 0.20%, the crystallized matter increases and the cap moldability is deteriorated.

Ti: 0.005 to 0.05%;
Ti is an element that affects the improvement of formability by refining the ingot structure. If it is less than 0.005%, the effect cannot be obtained. If it exceeds 0.05%, an insoluble Al—Ti compound tends to appear as a surface defect in the final product.
In addition, when adding an Al-Ti-B intermediate alloy as an ingot structure | tissue refiner, B contains, but it is preferable to add B in 0.02% or less of range.

  Next, the aluminum alloy plate has four locations (45 °, 45 ° in the rolling direction) with respect to the rolling direction among the ears generated in the opening portion of the drawn cup used for the ear rate test of the base plate or the blank plate. 135 degrees, 225 degrees, 415 degrees directions), or the ear ratio of the ears occurring at 4 positions of 0 degrees, 90 degrees, 180 degrees, 270 degrees direction is 2.0% or less and in the rolling direction. On the other hand, it is preferable that the ear ratio of the ears generated at two locations in the 0 ° and 180 ° directions is 2.0% or less.

  When the ear rate of the four ears in the 45 ° direction exceeds 2.0%, the bending of printed characters or the like at the bottom of the molded cap becomes noticeable in the 45 ° direction and is difficult to prevent. The smaller the ear ratio, that is, the lower limit is preferably 0%, but it is difficult due to the nature of the metal plate. Actually, an ear rate of 0.5% to 2.0% is more preferable.

  Further, even when the ear rate of the ears occurring at the four locations in the 0 °, 90 °, 180 °, and 270 ° directions exceeds 2.0%, the ear rate at the four locations in the 45 ° direction is 2.0%. As in the case of exceeding, bending of printed characters or the like becomes remarkable.

  Furthermore, even when the ear-ear ratio occurring at two locations in the 0 ° and 180 ° directions with respect to the rolling direction exceeds 2.0%, it is possible to prevent bending of printed characters and the like on the molded cap hem portion. It becomes difficult. In the case of drawing of an Al-low Mg alloy, ears in the directions of 0 ° and 180 ° tend to occur particularly with respect to the rolling direction, and it is important to control the ears in this direction. In order to more reliably suppress the bending of printed characters and the like, it is preferable that the ear ratio of the ears generated at 0 ° and 180 ° with respect to the rolling direction is 1.5% or less.

  Here, the drawn cup is a cup-shaped test material obtained by drawing a blank cut out from the cap Al—Mg alloy plate under predetermined conditions. At the opening end of the throttle cup, the portion protruding in the axial direction is called an ear, and the most depressed portion between the ears is called a valley. The distance from the bottom of the squeeze cup to the tip of the ear is defined as the ear height, and the distance from the bottom of the squeeze cup to the tip of the valley is defined as the valley height. The ear rate can be calculated as follows.

<Ear rate of ears at 45 points in 45 ° direction>
45 ° ear height = A, 135 ° ear height = B, 225 ° ear height = C, 315 ° ear height = D,
Minimum valley height between 45 ° and 135 ° = E,
Minimum valley height between 135 ° and 225 ° = F,
Minimum valley height between 225 ° and 315 ° = G,
Minimum valley height between 315 ° and 45 ° = H,
Ear average: M45 = (A + B + C + D) / 4,
Average valley: V45 = (E + F + G + H) / 4
Ear rate = [(M45−V45) / {(M45 + V45) / 2}] × 100 (%)

<Ear rate of ears at 4 locations in 0 °, 90 °, 180 °, 270 ° direction>
0 ° ear height = A ′, 90 ° ear height = B ′, 180 ° ear height = C ′, 270 ° ear height = D ′, minimum valley height between 0 ° and 90 ° = E ',
Minimum valley height between 90 ° and 180 ° = F ′,
Minimum valley height between 180 ° and 270 ° = G ′,
Minimum valley height between 270 ° and 0 ° = H ′,
Ear average: M ′ = (A ′ + B ′ + C ′ + D ′) / 4
Average valley: V ′ = (E ′ + F ′ + G ′ + H ′) / 4
Ear rate = [(M′−V ′) / {(M ′ + V ′) / 2}] × 100 (%)

<Ear ratio of ears at two locations at 0 ° and 180 °>
Average height of cup = P (average height obtained by measuring the height of the open end at 1000 points),
0 ° ear height = Q, 180 ° ear height = R,
Ear average: S = (Q + R) / 2,
Ear rate = {(SP) / P} × 100 (%)

<Cup drawing molding conditions>
Using a die with a die diameter of 33.6 mm, a punch diameter of 33 mm, and a punch shoulder R of 1.5 mm, a cup blank was carried out with a drawing material blank diameter of 55 mm and a drawing ratio of 1.67.

The aluminum alloy plate preferably has a thickness of 0.20 to 0.25 mm.
That is, the thickness of the aluminum alloy plate for the wide-mouth bottle can cap affects the pressure resistance of the cap, which is the subject of the present invention. The thicker the plate, the greater the pressure resistance, but the thinner the plate is preferable from the viewpoint of resource saving. In the present invention, by increasing the strength as described above, it becomes possible to reduce the plate thickness while maintaining a predetermined pressure strength. Conventionally, a plate thickness of less than 0.25 mm has been difficult from the viewpoint of pressure resistance, but in the present invention, sufficient pressure resistance can be obtained even when a plate thickness of 0.20 mm or more and less than 0.25 mm is applied. It is. Further, in the case of 0.25 mm, it is possible to increase the strength with respect to the demand for a high breakdown voltage. When the plate thickness is less than 0.20 mm, the current cap shape does not provide a predetermined pressure strength. However, when the cap shape is improved by technological advancement, the material of the present invention can be put to practical use. Conceivable.

Next, preferable production conditions for obtaining the aluminum alloy plate of the present invention will be described.
The basic manufacturing process is to homogenize and heat the ingot, then hot-roll to form a plate, and then anneal, cold-roll, anneal, and cold-roll sequentially to obtain the product thickness, and finally strength In order to stabilize the heat treatment, stabilization heat treatment is performed. In many cases, surface treatment such as degreasing and chemical conversion treatment is performed before or after the stabilization heat treatment.

  The said homogenization heat processing is the conditions which hold | maintain an ingot at the temperature of 450-580 degreeC for 1 to 24 hours. If the holding temperature is less than 450 ° C. or the holding time is less than 1 hour, the ear formation becomes unstable and control becomes difficult. When the holding temperature exceeds 580 ° C. or the holding time exceeds 24 hours, Mg easily diffuses on the surface, the Mg oxide layer on the surface becomes thick, and the amount of chamfering needs to be excessively increased, which is uneconomical.

Subsequently, for example, hot rolling, annealing, cold rolling, annealing, cold rolling, and stabilizing heat treatment are sequentially performed. In this step, a predetermined strength and ear rate can be obtained.
In the said annealing 1 and 2, it carries out on the conditions hold | maintained at the temperature of 300-550 degreeC. When the holding temperature is less than 300 ° C., a predetermined ear ratio cannot be obtained with the final plate, and the strength becomes too high and the moldability is poor. When the holding temperature exceeds 550 ° C., the surface tends to be oxidized, which is not preferable. The holding time is not particularly limited, but when annealing at a relatively high temperature such as rapid heating / cooling using a continuous annealing line or the like, holding is performed for 0 to 20 seconds, holding when annealing at a relatively low temperature using a batch annealing furnace. 30 minutes to 5 hours is appropriate.

  What is necessary is just to perform the cold rolling 2 after the said annealing 2 in 30 to 70% of range. When the rolling rate is less than 30%, it is difficult to obtain a predetermined strength, and it becomes difficult to obtain a predetermined ear rate. If the rolling rate exceeds 70%, the formability is lowered, the strength is too high and it is difficult to open the plug, and the rolling texture is developed so much that the ears in the 45 ° direction become large.

  The performance as a cap material is almost achieved with cold rolling, but in the case of an Al-Mg alloy, when the cold rolling is left at room temperature, a phenomenon in which the strength gradually decreases occurs. In order to prevent this and stabilize the strength, a heat treatment (stabilized heat treatment) is required which is heated at a temperature of 100 to 300 ° C. for 30 minutes or more. If it is less than 100 ° C., the strength is not stable, and if it exceeds the upper limit of 300 ° C., softening increases and a predetermined strength cannot be obtained.

The content of the present invention will be described with reference to specific examples, but the following shows one embodiment of the present invention and the present invention is not limited thereto.
Example 1
Aluminum alloy ingots containing the chemical components shown in Table 1 are ingoted by semi-continuous casting, and after the surface segregation layer has been cut, homogenized heat treatment is maintained at 500 ° C. for 8 hours, and then removed from the homogenized heat treatment furnace. Hot rolling was started immediately. Hot rolling is finished at a sheet thickness of 3 mm, and after recrystallization is obtained by annealing, cold rolling is performed to a predetermined sheet thickness, and further intermediate annealing is performed to obtain a recrystallized structure. The specimens were cold-rolled to the product thickness at the cold working degree and subjected to stabilization heat treatment.

The following evaluation tests were performed using the obtained five types of test materials E1 to E5. Some specimens were observed for material structure.
<Mechanical properties>
A tensile test was performed using a JIS No. 5 test piece.

<Ear rate>
Using a die with a die diameter of 33.6 mm, a punch diameter of 33 mm, and a punch shoulder R of 1.5 mm, a cup blank was performed with a drawing material blank diameter of 55 mm and a drawing ratio of 1.67.
The ear rate is calculated based on the above-mentioned conditions, and the ear rate of the ears at 45 locations in the 45 ° direction (A direction) or 4 locations at the 0 °, 90 °, 180 °, and 270 ° directions (B The ear rate of the ears in the direction) and the ear rates of the ears at two locations in the 0 ° and 180 ° directions were measured.

<Crystal grain size>
The plate surface of the test material was electropolished and the crystal grains were observed with a polarizing microscope. The crystal grain size was determined from the comparative method using an ASTM card.

<Character bending>
10 characters are printed on the blank before drawing so that the character comes to a position 3 to 5 mm from the cap opening end, and a 28 mm diameter PP cap cup with a drawing ratio stricter than the diameter 38 mm is drawn and formed. Character bending was visually observed and evaluated.
<Cap formability>
The appearance of the cap cup after molding was visually confirmed for the presence of defects such as cracks, wrinkles, and rough skin.

  Table 2 shows the evaluation results. The test materials E1 to E5 of this example have good results as cap materials for wide-mouth bottle can caps in all the evaluation items of mechanical properties, ear ratio, crystal grain size, letter bending, and cap moldability. Indicated.

(Comparative Example 1)
An aluminum alloy ingot having a component whose Mg content shown in Table 3 is outside the scope of the present invention was manufactured under the same conditions as in Example 1 to obtain specimens C1 and C2.

These evaluation results are shown in Table 4.
As can be seen from Table 4, the sample material C1 has an Mg amount less than the lower limit of the present invention, so that high strength cannot be obtained and it is not suitable for a product with high pressure resistance.
Since the amount of Mg exceeded the upper limit of the present invention, the test material C2 had a strength that was too high, an opening force increased, and a cap that was difficult to open. In addition, the ear rate of the ears occurring at four positions in the 45 ° direction exceeds 2%, and the character is bent, which is not suitable.

Claims (6)

Mg: 2.1% (weight%, the same shall apply hereinafter), including 3.5% or less, the balance being an aluminum alloy plate for a wide-mouth bottle can cap having a chemical composition consisting of inevitable impurities and aluminum,
The tensile strength of the base plate of the aluminum alloy plate is 210 to 320 MPa, the proof stress is 160 to 290 MPa,
And the tensile strength of the baked board which gave the heat processing hold | maintained for 10 minutes at the temperature of 200 degreeC with respect to the said base plate is 210-320 MPa, yield strength is 150-280 MPa, elongation is 5% or more, It is characterized by the above-mentioned. Aluminum alloy plate for wide mouth bottle can cap.   The Mg content is 3.0% or less, the tensile strength of the base plate is 210 to 280 MPa, the proof stress is 160 to 250 MPa, and the tensile strength of the blank plate is 210. An aluminum alloy plate for a wide-mouth bottle can cap, characterized in that it has ˜280 MPa, a proof stress of 150 to 240 MPa, and an elongation of 5% or more.   The Mg content is 2.5% or more, the tensile strength of the base plate is 250 to 320 MPa, the proof stress is 200 to 290 MPa, and the tensile strength of the blank plate is 250. An aluminum alloy plate for a wide-mouth bottle can cap, characterized by having ~ 320 MPa, a proof stress of 190 to 280 MPa, and an elongation of 5% or more.   The aluminum alloy sheet according to any one of claims 1 to 3, further comprising Cu: 0.01 to 0.20%, Mn: 0.01 to 0 instead of a part of the aluminum in the chemical composition. .30%, Cr: 0.01 to 0.05%, Zn: 0.01 to 0.25%, Si: 0.01 to 0.20%, Fe: 0.01 to 0.30%, Ti: An aluminum alloy plate for a wide-mouth bottle can cap, comprising one or more of 0.005 to 0.05%.   In any one of Claims 1-4, among the ear | edge which generate | occur | produces in the opening part of the drawing cup used for the ear | edge rate test of the said base plate or the said unbaked plate, four places of a 45 degree direction with respect to a rolling direction, Or the ear | edge ear rate which generate | occur | produces in four places of 0 degree, 90 degrees, 180 degrees, and 270 degrees directions is 2.0% or less, and the ears which generate | occur | produce in two places of 0 degree and 180 degrees direction with respect to a rolling direction. An aluminum alloy plate for a wide-mouth bottle can cap characterized by having an ear rate of 2.0% or less.   The aluminum alloy plate for a wide-mouth bottle can cap according to any one of claims 1 to 5, wherein the aluminum alloy plate has a thickness of 0.20 to 0.25 mm.