WO2002040192A1 - Long term stability of fillings in a two piece beverage container - Google Patents

Abstract

The aim of the invention is to improve the long term stability of fillings in two piece containers. Said aim is achieved by means of a method for the production of container bodies (1) with at least one coating layer (40, 39) on an essentially internal surface (6) of the body (1). Said body comprises a centre section (9, 19), a base section (10; 11, 12) and an upper boundary section (1v; 7) suitable for the production of a folding section as the fold producing section. The fluid which produces the coating layer (40, 39) is applied in an application process, in an adhesive manner to the surface (6, 6a) essentially facing inwards, by using a pre-determined volume of the fluid. The distribution of said volume on the surfaces of centre section, base section, and upper edge section occurs such that on retaining a minimum thickness (d0) on the surfaces of the centre and base sections, a proportion of the volume of the adhesive fluid arrives at the fold forming region (1a, 1b, 1k, 1v), such that, along a surface section (1b, 1k), a minimum thickness (d) of the coating layer (40; 41, 42, 43) is achieved which is not less than the actual minimum achieved thickness of the coating layer (39) in the centre section (9).

Description

Long-term stability of a filling in a two-part beverage can

The invention relates to metal hulls of two-part cans and their manufacture and their compatibility with long-term filling goods without these filling goods suffering from a deterioration in their quality (their taste).

The invention relates specifically to two-part metal cans consisting of a metal body and a lid, the metal bodies today mostly being produced by the ironing process and then being given their shape and geometry suitable for forming folds on the upper edge.

A solution has been proposed in the prior art to provide the sealing material (compound) in the rebate area with a component of lubricant in order to reduce mutual rubbing of a "body hook" and a "lid hook" during the closing process, so that damage to the surface of the painted sheet can be reduced in the formation of folds, cf. EP-B 794989, paragraph [09] there. These areas of damage were largely attributed to the fact that they are a source of the release of metal ions which pass into the contents, in particular liquid, and thereby impair the taste. Practice and further intensive tests have shown that such a design of the compound is not always sufficient and that there are other sources of changes in taste which have not yet been able to be determined with regard to their origin (cause).

It is assumed that a hollow metal body made of aluminum sheet can usually realize a very compact fold. Examples of a compact fold are explained in the description of the figures. In contrast, a metal body made of sheet steel tends to have an inherently stronger spring effect, so that here training to a looser (not so compact) fold must be feared. In particular, the storage time is added and during this time, under the effect of the internal pressure, a compact fold also forms into a poorer (less compact) fold. This makes it easier for the filling goods to access the folding area and increases the risk of metal being released.

A compact fold is understood to mean the spatial proximity, in particular the close contact of two sections in the vicinity of the actual fold, namely the upper fuselage wall and the vertically oriented top wall, mostly called "chuck wall". A stronger spacing of these two walls ensures easier access of the filling material to the sealing area of the fold.

Despite a compact fold, there are always changes in the quality of the contents in practice.

The invention has set itself the technical task of further improving the long-term stability of goods in two-part cans (especially beverage cans).

A coating layer, in particular made of lacquer, is proposed for this purpose, which is more strongly emphasized in the fold area than was previously realized in the prior art (claims 1, 25, 27 and claims 20, 30). In the prior art, the fold area was mostly excluded from a varnish application or neglected in terms of the thickness of the varnish application after an "overspray" had to be expected at the upper end of the fuselage when the varnish was sprayed onto the inner surface of the fuselage. The easiest way to avoid the "overspray" is to move the center of gravity of the volume or weight portion of the sprayed paint into the lower part or at least not to emphasize the upper edge area of the metal hull or to spray it only parasitically. In the interior, a sufficiently thick coating of paint is formed in the body area (the wall area) and in the floor area for long-term stability of the contents, which represents the lower end of the wall area for the formation of the trunk.

The minimum thickness in the area of fold formation is achieved according to the invention by changing the balance of the volume or weight distribution of the lacquer. A greater proportion of the weight or volume that is used for a given size and height of a beverage can (for example 0.3 I, 0.5 I or 0.2 I) is shifted towards the fold-forming section, from which mechanical deformation ( Fold) the fold is created between the lid edge and the end of the fuselage.

In addition, several variants are proposed with which such a reoriented distribution can also be implemented while avoiding the overspray. Even if an overspray is accepted, measures are proposed to catch this "overspray" by means of extensive filters in order to in any case to obtain an improved thickness of the coating layer in the fold formation section. The term fold formation section is understood to mean the area above the body area of the metal body from which - at least partially - the fold of the beverage can is produced when the metal body is closed with an associated closure lid. Previously, the contents were filled, usually a drink, such as beer, soft drink or other liquids (claims 12, 13).

The coating can be applied by spraying (claim 16). A separate spray nozzle can be used for the fold forming section. Instead of a separate spray nozzle, a spray nozzle with a changed weight distribution in the spray jet can also be used, so that a higher proportion by weight reaches the upper edge of the metallic fuselage, for a stronger, clearer or improved coating in the upper region of the fuselage with regard to the uniformity of the surface which at least partially forms a mechanically clamping fold with an edge area of the cover used.

The lacquer layer in the fold-forming section, which has a flange region and a substantially cylindrical region, then merging into a neck region, which is inclined radially outwards and merges into the cylindrical region in a gentle curvature, is (on average) with a thickness of at least 8 μm, in particular at least 10 μm and above.

The paint layer in the flange area of the fuselage can also have a thicker percentage than the paint layer in the body area. This average reinforcement of the cover layer in the flange area is at least 30%, preferably 40% stronger than in the body area.

If two necking areas are used at both ends of the fuselage, the corresponding description also applies to this design of the end areas, one area, mostly the ground contact area, with a "rim" and a "thorn" that bulges inwards. as an expression of a two-part beverage can, which has a lid on one side only, forming a fold in the edge area.

The neck molding processes can take place either as spin-necking or die-necking with stamping. Depending on which of the necking processes is used, a lacquer coating can be provided on the inner wall of the fuselage before or after the necking process. With die-necking, the first step is the non-molded state on the cylindrical fuselage. Then it is pulled in by stamping. A laterally projecting flange is formed in the fold-forming section. Another coat of varnish can then be applied. Two varnish pads are provided for beverage cans with soft drink content.

If the spin necking takes place, the first step is mechanical shaping in the upper neck section by means of a roller movement acting from the outside in order to form the cylindrical can in this area. The flange that forms the fold is then formed. The lacquer is applied after the flange formation. Two varnish layers can be applied here one after the other after a mechanical molding.

If only one varnish layer is provided, this can be done in both one-neck processes at the specified point on the first varnish application.

The lacquer overlay in the fold formation area has a minimum width and a minimum height. It has an areal extension with regard to the minimum thickness, even if certain areas would have a hypothetically assumed lower local thickness due to cracks or breaks in the lacquer layer. Such conditions should not affect the claimed "flat minimum thickness" of the paint. The same is to be understood with regard to a minimum thickness that extends over an area.

The minimum thickness of the paint protects against roughness of the metallic surface against penetration by the paint or an excessive reduction in the paint thickness.

The minimum thickness can also protect against adhesion problems which would lead to tearing of the lacquer under mechanical stress - the formation of the fold by mechanical shaping - if the lacquer is provided in a too thin layer in the fold-forming section.

Finally, the minimum thickness of the lacquer also protects against the penetration of cracks through the entire lacquer layer and thus limits the number of places in the fold formation area where metallic substrates are - even if only on Line-shaped cracks appear. These three effects can occur individually or in combination in any combination.

According to the invention, the contents of the can have practically no access to a metallic base in the area of the fold formation, in particular in the flange area, which is subject to the greatest mechanical deformation during the formation of folds.

Such a coating is achieved with a spray arrangement as a machine arrangement, which is to be emphasized here separately, in which the inner wall of the fuselage (the inner wall and the flange area in the tipped state or the upper section of the beverage can body in a state not yet held) is covered. The spray arrangement ensures that a larger proportion of the volume or weight of the lacquer reaches the fold formation area than was previously the case in the prior art. For this purpose, the spray application can be reduced in its angle and emphasized on the fold-forming section, in particular the area of curvature which lies between the flange and the substantially cylindrical section of the fold-forming section. For this purpose, a separate nozzle can be provided which, as a flat jet nozzle, carries out the coating in the fold-forming section in the case of a rotating metal body. The same is possible with or without a flange, ie also with a cylindrical section if the flange is formed afterwards.

The section at the top of the can, which receives a thicker coating, can be coated several times, for example two or three times. The process of additional painting can also be applied to possibly pre-painted metal surfaces. It is possible to carry out the additional painting in the area of the fold formation before or after painting the inner wall of the fuselage. It is preferred to paint after the entire surface has been painted. If there is no upstream paint layer, the entire interior painting of the can can be carried out in one process step, as described above by adjusting the weight distribution on spray heads or using an additional spray head.

Commercially available can lacquers can be used for the coating. This includes paints based on modified epoxy resins or combinations thereof. Tough-elastic paints are preferred (claims 19, 33). These varnishes have a polymer base, which has a partially crystalline structure in its main component. Lacquers with a proportion of PET are preferred. If such varnishes are used, the varnish layers can be up to 8 μm in the fold formation area in one flat section are reduced, while with conventional paints of a commercial nature the thickness in said section is preferably more than 40% stronger than the paint thickness on the inner wall and is above 10 μm, 12 μm or 15 μm, with a paint density on the inner wall of the body area of between 5 , 5μ to 6μ, up to below 10μm.

If a coating is carried out by a roller, a flexible roller on the surface, the can bodies move with their opening facing downward and a trained flange section past the roller, which causes an additional varnish application in the fold-forming section when it rotates, whereby the thickness ( Thickness) of this varnish is enlarged in this area. In terms of function, reference can be made to commercially available rim coaters, which usually use this technique to coat the bottom edge of the bottom at the closed end of a two-part box from the outside. The rubber blanket roller as an example of an elastically flexible roller is coated with fluid by a transfer roller, which in turn engages in a bath of lacquer at least in sections.

If one assumes known volume distributions, there is a quantity of lacquer over the specific weight for commercially available lacquers. The weights are 150 mg for cans with a volume of 150 ml for the first and second spraying, a weight of essentially 145 mg for a volume of 200 ml and for a volume of 250 ml with a weight of 165 mg, in each case for two successive sprayings Application processes by spraying with flat jet nozzles.

If cans of greater height or size are used, for example 330 ml or 500 ml, weights of 160 mg or 240 mg per spraying process are used for two sprayings. These volumes can continue to be used if a greater proportion of the weight (or volume) is shifted to the area from which the fold is formed when closing. Examples illustrate and supplement the invention.

Figure 1 illustrates a finished fold in which an edge portion of a

Lid 2 and an upper end portion of the can body 1 have been mechanically deformed together to form a firm connection.

The lid and body are only shown in sections after the remaining part of the metallic container is known.

Figure 2 illustrates a fold formation before mechanical closing, with a flange 1a, a curvature area 1 k and an essentially cylindrical section 1 b, 1c on the can body and a lid hook 2b with a curved outer end section 2a. If a neck area is provided, this is indicated at 1d by radially molding an upper wall section which is essentially cylindrical. Here too the cover 2 is shown, which has a core wall above the inner one

Radius r and the beginning of a cover mirror from 2a.

Figure 3 illustrates a large enlargement of the flange 1a with curvature 1 k, and cylindrical section 1 b, which define the fold-forming section. The flange as such has an outer one

End 1e 'projecting laterally upwards before the fold is closed. A paint layer 40 with different sections 45, 44, 41, 42 and 43 is shown, which will be explained in more detail later.

Figure 4 illustrates in axial section a beverage can with a

Can body, which is formed in one piece. A body region 9 is provided, a circumferential rim 12 on which the can stands and an inner dome 11. The essentially cylindrical wall, which is shown here in a very shortened form, has a cylindrical wall 1w which leads to the neck region 8 , This neck area leads to the flange via a cylindrical section, the entire area above the neck 8 being referred to as the fold forming section 7. In the left half of FIG. 4, an adhered can body is shown, while in the right section, relative to the central plane of the central axis 100, a cylindrical wall section 19, which has not yet been formed, is shown, the upper one

Section 1 v is molded or changed later or remains unchanged. Drawn in are nozzles 30, 31 which carry out a coating which will be explained in more detail later. FIG. 4a is an enlarged detail of a wall piece 1 w with an inner coating 39 made of lacquer, the thickness of which can be seen.

FIG. 5 shows an example of a conveyor belt 59, on which a can body 1 is moved with its opening pointing downward in the longitudinal direction. It is coated by a roller 50, which applies lacquer from a bath 55. This varnish is applied in the flange region 1a to its essentially inward-facing wall. The cans are with their dome-shaped bottom 11 either by magnetic force or vacuum on the

Conveyor belt 59 held.

Figure 6 illustrates a large enlargement of a metal sheet, the surface of which is very roughened. The roughening shows that the applied lacquer layer 40 appears considerably thinner in several places, but is still so thick in its total thickness d that it does not experience any obvious penetration of larger areas by the unevenness of the sheet metal surface. A hypothetically drawn lacquer thickness 40 ', which is significantly smaller in the thickness dx, would be penetrated by uneven metallic spots that are exposed in the process. The sheet thickness between 180 and 220 μm shown corresponds to the usual sheet thicknesses of stretched can bodies, whereby it should be noted that the paint thickness shown here has been greatly increased and the unevenness 1 * of the surface has been greatly enlarged to reflect the principle of paint penetration

To explain the flange area (fold formation section).

Figure 6a

FIG. 6b illustrates two fold geometries in the cut state, one with a very compact fold, in which the core wall and a cylindrical section of the fold-forming section of the fuselage lie closely together. FIG. 6b illustrates a loose fold geometry in which the walls described are spaced apart from one another and accommodate a wedge-shaped space between them. Figure 1 illustrates a cross section of a finished fold, in which an edge portion 2 * of a lid 2 and an upper end portion (above 1c) of the can body 1 are mechanically connected to one another, deforming a lid hook and a body hook from the illustration of Figure 2 for training of a finished fold according to FIG. 1. The cover 2 and the fuselage 1 are only shown in sections after the remaining part of the metallic container is known and is not to be explained in more detail here, but rather reference can be made to the state of the art. For the design of the cover profile, this also includes the possibility of providing a circumferential groove, as shown in FIG. 2a, or of having the cover edge transferred into a cover mirror without such a groove. The edge section 2 * of the cover with a cover hook 2b, 2a is located radially outside of this mirror design, possibly with a circumferential groove of radius r. Above the still cylindrical section 1c on the fuselage, which leads axially below it into a neck region 1d and above the cylindrical section 1c into a fuselage hook 1b, 1k and 1a (and 1e). The

Curvature section 1 k lies between the two sections 1 a and 1 b, of which section 1 b is approximately cylindrical and section 1a runs approximately radially. The radially outer end of the radially extending section 1e is 1e '.

The lid hook protrudes with its edge flange 2b and an inwardly curved end portion 2a over the fuselage hook 1b, 1k and 1a in order to form a fold with a forming roller, be it in a one-step or in a two-step fold-forming process. In the two-stage process, a first roller with a first circumferential groove is used to achieve the first molding movement (the tilting). The molded fold is pressed on with a second roller with a different geometry and shaped in the finished shape, as shown in FIG.

Figure 2 shows the preliminary stage to the shape of Figure 1, showing a slight difference in the transition to the fuselage. A neck region 1d is provided in FIG. 2, while an essentially cylindrical transition to the torso is provided in FIG. 1 with 1d ′, that is to say no transition between the torso section (see reference number 9 in FIG. 4) and the fold region (as shown in FIGS. 1 and 2) has sloping section. The embodiments of the invention are applicable to both hull shapes. In the case of a neck with a radially inwardly shaped oblique neck region 1d, spin-necking can be used, as can die-necking, for the radial tapering of the essentially cylindrical edge section 9 (wall 1 w) of FIG. 4. Also in this figure is a Neck 8 provided at his axially upper end section opens into a section 7, which has the elements of a fold-forming section illustrated in FIGS. 1 and 2.

The axial section of FIG. 4 illustrates in the right field a cylindrical wall 1v which has not been necked in, as corresponds to the illustration in FIG. In the left field, a necked-in (or neck area) 8 is shown above the cylindrical wall 1w between the fold-forming section 7 and the upper end of this wall, as it corresponds to that section 1d of FIG. 2. 1v in the right field is the upper section of the cylindrical wall 19, as it corresponds to 1 d 'of Figure 1.

The cover 2 is also not shown in FIG. 4, but the edge region 2 * of the cover 2 (from FIG. 2) or the corresponding region in the section already provided with a fold above the point 1c of the wall (in FIG. 1) is easily imaginable.

From Figure 1, all dimensions are otherwise designated with parameters that describe the fold. You should have moved in here.

The beverage can shown in FIG. 4 with a can body is made in one piece, i.e. only with a fold area at one end section, while at the other end of the body area 9 (left picture) and 19 (right picture) a bottom section 10 is formed in one piece, which consists of a circumferential rim 12, on which the can stands, and an inner dome 11 is formed. This bottom geometry results from the stretching of a bowl to form the fuselage blank, which can then be necked in section 8. The blank is made of thin sheet metal that is less than 250μm thick. The can has a given size, a height H1 and a diameter D1 being drawn in and defining the maximum size of the can with its edge dimensions.

A coating layer is applied to an inward-facing surface 6, 6a. The inner surface of the fuselage section 9, 19 and the bottom section 10 is designated by 6. A likewise essentially inwardly facing surface 6a in the fold-forming section 7 consists of the surface on the cylindrical section which corresponds to section 1b of FIG. 2 and a flange section which corresponds to section 1k, 1a of FIG. The surfaces described are coated with a fluid, in particular a lacquer or another coating, which adheres to the inward-facing surface 6, 6a. 4a explains how the coating layer 39 is applied to the inwardly facing surface 6, with a wall 1 w in the fuselage section 9. The thickness of the layer 39 is dO. A coating is also applied to the remaining surface 6a in the fold-forming section 7, which coating can be explained in more detail with reference to an enlarged section in FIG. 3. However, it can already be seen in FIG. 2, in which this coating 40 is arranged as a flatly extending layer on the essentially inward-facing surface which lies above point 1c.

FIG. 3 illustrates an enlarged detail of the flange 1a with the curvature region 1 k and the cylindrical section 1 b, which define the fold-forming section, as identified in FIG. 4 by the reference number 7. The flange as such has an outer end 1e 'which projects laterally upwards before the fold is closed, as shown in FIG. A paint layer 40 is shown, which lies on the surface 6a. This coating has 40 different sections as a coating layer or coating layer. The coating layer 40 continues the previously described coating layer 39, the coating layer 39 from FIG. 4a being applied by the spray nozzle 31 when the fuselage rotates. A second spray nozzle 30 which is axially higher and has a different direction has a smaller spray angle α than that

Spray nozzle 31, the spray angle γ of which is larger and is aligned with the wall area 9, 19 or the neck area 8 for the case of the inhaled can. Subsequently, the spray section continues, which reaches an occupancy 40 according to FIG. 3 with a flat jet nozzle of extension angle α in the spray jet.

In modifications, the spray angle of the first spray nozzle 31 can also be supplemented by the angle β in FIG. 4, so that a larger area of the inwardly facing surface 6 is reached, and not just the wall section 9 with the neck section 8 for the inhaled can or the wall section of the fuselage 19 for the can not be inhaled, rather also the fuselage section 10 with the base ring 12 and the upwardly curved base 11. The extension and orientation of the second spray nozzle 30, which is directed onto the flange area 7 or its inner area, is independent of this Surface 6a targets.

The distribution of the volume of the fluid to be applied is designed in such a way that the minimum thickness d0 of the coating layer 39 is achieved in the body section 9, 19 and in the bottom section 10, specifically via the spray nozzle 31. The spray nozzle 30 receives such a volume proportion that for the total coating of the inner Surface of the can provided fluid that the upper edge portion, so the fold-forming portion 7 on the inner surface 6a receives a thicker coating than the body and bottom portion. A technically predetermined minimum thickness of the coating should not be undercut in the body section, but usually a larger amount of fluid is applied in the prior art in order to achieve this minimum thickness at all points of the trunk. A portion of the fluid used for this purpose, in particular lacquer, is fed to the nozzle 30 so that it can cover a surface section with a coating layer 40 in a narrow area above the neck section 8, which does not fall below the actually achieved minimum thickness of the coating layer 39 in the body section 9 or 19 lies. In other words, the coating thickness 40 lies above the layer thickness 39.

The flat area according to FIG. 3 is composed of a transition section n, an essentially axial section m, a curved section k and an essentially radially outwardly projecting end section g. The greater coating thickness has a section h from section g, with an unoccupied section remaining at the end of section g up to the outer edge of the fuselage sheet 1a, 1 k, 1 b, until the end 1e ", so that an overspray (i.e. spraying of the coating material from the nozzle 30 past the free end 1 e ') can be avoided. The layer thickness of the coating 40 is greater than that

Layer thickness dO. The layer thickness of the layer sections 42, 41 and 44 is particularly relevant because this is the area according to FIG. 2 and FIG. 1 in which the greatest curvature of the fuselage flange occurs when the fold is formed. This area is marked with an angle φ ₁ in FIG. 2, starting from a hypothetically assumed point u _{1 (} which can be traced in its determination on the basis of the illustration), with an assumed fold height H (in the non-formed state) and an assumed horizontal plane the low point of the circumferential groove 2a or approximately the height of the cover mirror for those covers which have no circumferential groove.

Starting from the sketched orientation point u., The angle φ _{1 is} between 50 ° and 70 ° and extends to the coating sections 42, 41 and 44 of FIG. 3, which can be attributed to the surface of the flange sections 1b, 1k and 1a of the fuselage flank. The thickness d of the coating 40 obtained here on the surface 6a (cf. FIG. 4) is preferably above 10 μm to 15 μm, if it is assumed that the coating thickness dO in the fuselage area is between 5 μm and below 10 μm. In its absolute dimensions, this depends on whether single or double-coated cans are used. It can of it it can be assumed that double-coated cans receive about 5μm applied per layer of paint. For both single and multi-coated cans, the thickness d in the areas h, k and m is greater than the thickness dO.

Regarding the geometries of a fold common today, reference is made to FIG. 3 and the dimensions of the lengths g, h, k and m given there, which are not to be repeated here but only to be included. The thicker layer thickness 40 can also extend over section n, n corresponds in length to approximately m.

Outside of section h and below section m, a

Coating layer of the same thickness d can be provided, but it can also be reduced because there are no particularly critical requirements for improving the fold. Thus, the described distance of the end of the coating layer 45 with the extending length g (with a circumferentially oriented design) can ensure that no increased overspray is generated by the coating nozzle 30. 1e ^* is the free edge of the end section 1e, starting from the flange section 1a.

Below section m, the thicker coating continues in section 43 along the height n, as shown in FIG. 2 for section 1b. The thicker coating layer 40 is thus arranged in the fold formation section 7, it can also extend beyond it, but the described area is sufficient for the function of the better fold formation and the avoidance of surface defects (roughness, adhesion problems or penetration of sheet metal surfaces).

The job process shown in Figure 4 can be replaced by alternative job processes which are described below. Depending on the type of necking (left section of FIG. 4, left of the axis 100 of the beverage can), the application of the coating layer 40 described and the shaping of the neck and the formation of the flange are placed in time. Will the

The metal body is first mechanically deformed to form the neck region 8, the diameter of which is smaller than a diameter of the body section 9, the fluid for forming the layer 40 is then applied, which occurs during spin-necking. The mechanical reshaping of the neck also includes shaping the fold-forming section with the flange described on the fuselage. After the mechanical shaping, several varnish layers can be applied one after the other. For example, two lacquer pads are provided for beverage cans with soft drink contents. If die-necking (forming with axially movable stamps) is achieved, neck formation can be assumed, for example, from the right field in FIG. Here, the fluid adhering to the inner surface is first applied before the mechanical shaping takes place in the stamp shaping, based on the upper section 1v of the body section 19, to form a neck, corresponding to the neck 8 of the left representation of FIG. 4. After the shaping of the The flange is formed at the neck. A further lacquer application can then be provided, for example as shown in FIG. 4 with the spray nozzle 30.

If several application processes are provided, the volume of the fluid for coating can be divided so that the first volume part produces the first layer thickness and the second volume part generates the second layer thickness, in order to sum up a total thickness dO as the technically required minimum thickness in the fuselage and a total thickness d in the fold area, which is greater in strength than that of the trunk.

After coating, there is a drying process to stabilize the surface. The can body can then be filled and then closed with a lid to form a fold with at least a portion of the fold forming portion.

A lacquer which contains portions of PET can be used as the adhesive fluid, and the lacquer can also contain polybotyl terephthalate.

The drying process for curing the coating takes place at a temperature above 200 ° C. A shortening can be achieved if the temperature is increased to essentially 270 ° C.

With the lacquer overlay 40 according to the preceding description, the effect of the thickness of the lacquer overlay in the fold-forming section 7 can be seen in a further enlargement of the detail according to FIG. The minimum thickness d of the fluid layer (hereinafter referred to simply as lacquer, but not necessarily limited to it) ensures that the roughness is covered, for example, in section 1a. This section h of FIG. 1e is drawn out enlarged in FIG. 6, with a sheet thickness of between 180 μm to 220 μm in the flange area. The lower layer of lacquer 40 'compensates for the roughness, while a remainder of the lacquer thickness ensures reliable compensation for even strong roughness 1 *. The lacquer layer 40 is thinner in several places due to the roughness, but is still so thick in its total thickness d that it does not experience any obvious penetration of larger surface sections by the unevenness of the sheet metal surface. A hypothetically assumed lacquer thickness d _x , corresponding to a layer 40 'as the lower section of the layer 40 shown, would not achieve that all the roughness is covered, rather some spots can still be recognized as penetrating through the lacquer layer. They are exposed to the surface and can have an influence on the quality and long-term stability of the fold in the case of a strong curvature in the area 1k, as described above.

The drawn bumps on the surface are shown greatly enlarged to explain the principle. A further illustration is possible on the basis of FIGS. 6a and 6b.

FIG. 6 a shows a very compact fold in the cut state, in which the core wall and a cylindrical section of the fuselage, corresponding to section 1 b of one of FIGS. 1 to 3, lie closely together. A fold geometry which is also possible is illustrated in FIG. 6b in such a way that it can be described as loose. The described walls are clearly distant from the ideal shape, they are spaced far apart, and a wedge-shaped space is formed, which leads directly to the highly endangered curvature section 1 k. The contents of the can can easily penetrate this area and dissolve metal surfaces that may protrude from the paint layer. This can be avoided if the thicker coating layer as described above in

Folding section is provided, in particular in the radius of curvature and also radially inside and radially outside of it, in order to achieve long-term stability of the filling material without transfer of metal ions, regardless of a possibly not optimally designed folding geometry. The dimensions shown in FIGS. 6a and 6b are in mm and can easily be referred to FIGS. 1 and 2 and the dimensions specified there and the variables specified there. For example, the rebate height fh is given as 2.55 mm (in FIG. 6a), which is reduced in the case of a more widely diverging rebate in accordance with FIG. 6b. It should be mentioned that the thicker varnish layer 40 extending into the fold is not shown in FIGS. 6a, 6b, but has to be added mentally.

An alternative covering or application of a layer on the inner wall takes place according to the example of FIG. 5. Here, a conveyor belt 59 is shown on which there is a can body 1 with its opening pointing downwards moved in the longitudinal direction. It is coated by a roller 50, which applies lacquer from a bath 55. The varnish is applied in the flange region 1a and on its essentially inwardly facing surface 6a. The lacquer thus reaches the fold-forming section 7 according to FIG. 4 to an increased extent, the can already being formed in a section provided with a flange, but still without necking. An intermediate roller 51 can even out the application of the lacquer from the bath 55 to the transfer roller 50. The cans conveyed on the conveyor belt 59, of which only a portion 59 of the belt 59 is shown near the deflection roller, are held either by magnetic force (in the case of steel cans) or by vacuum. In the same way, FIG. 5 can also be used for beverage cans that already have a necked-in section 8, as shown with reference to FIG. 4. A geometry which is still provided without a flange (FIG. 4, right section) is not suitable for coating the fold section; here, for the application variant of FIG. 5, a deformation in the region 1v must first take place.

* * *

Claims

Expectations: 1. A method for producing or treating can bodies (1) of a given size or height (D1, H1) consisting of (thin) sheet metal, with at least one coating layer (39) on an essentially inwardly facing surface (6) of the fuselage ( 1), wherein the fuselage has a body section (9, 19), a bottom section (10; 11, 12), an upper edge section (1v; 7; 1a, 1b, 1 k; fold formation section) suitable for folding, and wherein in an application process the fluid forming the coating layer (39) is adhered to the essentially inward-facing surface (6), using a predetermined volume of the adhering fluid, which is adapted to the hull size, to obtain a minimum thickness (dO ) the Coating layer (39) in the body section (9, 19) and bottom section (10); wherein the distribution of the volume on the inwardly facing surface (6) of the body portion and bottom portion and a surface (6a) of the upper edge portion (fold-forming portion) is such that while maintaining the minimum thickness (dO) on the surface (6) of the Such a volume fraction of the adhesive fluid reaches the surface of the fold-forming section (1a, 1b, 1k; 1v) in the body and bottom section in order to have a minimum thickness (d) of a coating layer (40; 41, 42,44) there along at least one surface section of the surface ) which is not below an actually achieved minimum thickness of the coating layer (39) in the body section (9). 2. The method according to claim 1, wherein the minimum thickness (d) achieved in the fold-forming section occupies at least one flat area. 3. The method according to claim 1, wherein the application process is divided into two, a first application and a second application later in time, and the volume of the fluid is divided into a first volume fraction and a second volume fraction, corresponding to the two application processes. 4. The method according to claim 1 or 3, wherein the metal body is first mechanically formed to form a neck region (1d, 8), the diameter of which is smaller than a diameter of the body section (9), in order to subsequently apply the fluid, in particular during spin necking. 5. The method according to claim 1 or 3, wherein the fluid is first applied before mechanical reshaping of an upper portion of the body portion to form a neck area, in particular in stamping (die-necking). 6. The method according to claim 1 or 3, wherein in at least one of the application processes, the fold-forming section (1a, 1b, 1k) receives the predetermined areally extending minimum thickness of coating (40), based on the actual minimum thickness (dO) in the body section (9 ) after the first or after the second application. 7. The method according to claim 1, wherein the surface section of the coating layer (41, 42, 44; 40) on the flange section (1 b, 1k) extends in the circumferential and at least axial direction. 8. The method according to claim 7, wherein the surface section also extends in the radial direction in the section (44) in which it is also formed in the axial direction to form an inclined surface with respect to an axis (100) of the can body. 9. The method according to claim 1, wherein the surface section of the coating layer occupies an axially distinct area of the fold-forming section, in particular continuously extending into at least one curvature area (1 k) of the fold-forming section. 10. The method according to claim 9, wherein the surface section extends beyond the curvature region (1k) to form a section of the coating layer (44), which has a corresponding extension, into a fuselage hook (1a) of the can body. 11. The method according to claim 1, wherein the can body is a mechanically formed body, in particular an elongated body, consisting of a thin sheet material less than 0.25 mm thick. 12. The method of claim 1, wherein the metal body is a beverage can body. 13. The method according to claim 12, wherein the body (1) is filled with a beverage after the coating has dried and is then closed with a lid (2) to form a fold (FIG. 1) with at least a portion of the fold-forming section. 14. The method according to claim 1, wherein the fluid contains a proportion of PET as the lacquer or the lacquer contains polybutyl terephthalate. 15. The method according to claim 1 or 13, wherein the lacquer is baked after application, at a temperature above 200 ° C, in particular 270 ° C. 16. The method of claim 1, wherein the fluid to form the coating layer (39,40) is applied to the can body by spraying (30,31). 17. The method according to claim 1, wherein the minimum thickness of the coating layer (40) in the fold-forming section is greater than 8 μm, in particular above substantially 10 μm, 12 μm, 15 μm or above. 18. The method according to the preceding claim, wherein an axial or radial extension (h, k, m) of the coating layer in the fold-forming section (7; 1a, 1 k, 1 b) does not fall below 2 mm, in particular between 2.2 mm and 2.8 mm or above 3 mm. 19. The method according to claim 1, wherein the adhesive fluid is a lacquer, in particular a viscous lacquer. 20. Can body of a given size or height (D1, H1) for a container made of fuselage and a lid (2), which are connected to one another via a fold (FIG. 1), with at least one coating layer (40, 39) on an inner one Surface (6,6a) of the fuselage (1) is applied, the one consisting of sheet metal Can body a body section (9, 19), a bottom section (10; 11, 12), 'an upper edge section (1v; 7) suitable for fold formation on the body section for at least partial participation in the fold (Fold-forming section), and wherein an areally extending minimum thickness (dO) of the coating layer (39) on the surface (6) of the body and bottom section as well as an areal minimum thickness (d) of a coating layer (40; 41, 42,43,44 ) is provided along a surface section in the fold forming section (1a, 1 b, 1 k; 1v), the latter minimum thickness (d) being more than essentially 8 μm, in particular more than 10 μm. 21. Can body (1) according to claim 20, wherein the coating layer consists of lacquer and the lacquer layer in the fold-forming section (7) has a thickness which is at least 8 μm on average and the thickness of the lacquer layer in the fold-forming section on average at least 30%, in particular 40 % is stronger than an average thickness of the coating layer (40.39) in the body section (9.19). 22. Can body (1) according to claim 20, wherein the fold forming section Has flange area (1a, 1 k, 1e) and a section (1 b) which is substantially cylindrical. 23. Can body (1) according to claim 20, wherein the fuselage is a mechanically formed fuselage, in particular an elongated body, consisting of a sheet metal less than 0.25 mm thick. 24. Can body (1) according to claim 23, wherein the body is a beverage can body. 25. Method for producing or treating can bodies (1) of a given size or height (D1, H1) consisting of (thin) sheet metal, with at least one coating layer (40, 39) on a substantially inwardly facing (inner) surface ( 6, 6a) of the fuselage (1), the fuselage having a body section (9, 19), a bottom section (10; 11, 12) and an upper edge section (1 v; 7; fold forming section) suitable for crimping on the body section , and wherein in one application process the fluid forming the coating layer (40, 39) is adhered to the surface (6, 6 a), below Using a predetermined weight of the adhering fluid, which is adapted to the hull size, to obtain a minimum thickness (dO) of the coating layer (39) in the body section (9, 19) and bottom section (10); wherein the distribution of the weight of the fluid over the inner surface of the body portion, bottom portion and upper edge portion (Folding section) takes place such that, while maintaining the minimum thickness (dO) on the surface (6) of the body and bottom section, such a proportion by weight of the adhesive fluid reaches the folding section (1a, 1 b, 1 k, 1v), in order to along there To achieve a minimum thickness (d) of the coating layer (40; 41, 42, 43) in the surface section, which is not less than an actually achieved minimum thickness of the coating layer (39) in the body portion (9). 26. Can body according to claim 20 or claim 1 with a seam between the body portion (9) and bottom portion (10). 27. Method for producing or treating can bodies (1) of a given size or height (D1, H1) consisting of (thin) sheet metal, with at least one coating layer (40, 39) on a substantially inwardly facing (inner) surface ( 6,6a) of the fuselage (1), the fuselage having a body section (9, 19), a bottom section (10; 11, 12), an upper edge section (1v; 7; fold forming section) suitable for crimping on the body section, and wherein in one application process the fluid forming the coating layer (40, 39) is adhered to the surface (6, 6 a), below Using a predetermined weight of the adhesive fluid which is sufficient to achieve a minimum thickness (dO) of the coating layer (39) in the body section, in particular essentially at half its axial height (100); and wherein a further proportion by weight of the adhesive fluid in the Fold-forming section (7; 1v) is applied (50, 30) in order to apply a coating layer (40) of the fluid with a thickness (d) which is greater (i) than the minimum thickness (dO.) Along a surface section of the surface (6a) ) in the body section or (ii) as essentially 10 μm; and wherein the fluid is dried and cured, in particular baked, in a subsequent temperature treatment. 28. The method according to claim 27, wherein after the temperature treatment, the layer thickness (d) of the coating layer (40) in the fold-forming section is greater than essentially 10 μm. 29. The method according to claim 28, wherein the layer thickness (d) is not greater than 20 μm, in particular below substantially 15 μm, in the fold-forming section. 30. Thin-walled tin made of sheet metal in a given size or height (D1, H1) for receiving a drink, wherein a body (1) and a lid (2) are mechanically clamped together via a fold (Fig. 1), at least a coating layer (40, 39) is applied to an essentially inwardly facing surface (6, 6 a) as the inside of the body (1), the can body has a body section (9, 19), a bottom section (10; 11, 12), has an upper edge section (1v; 7) at least partially involved in the fold formation on the body section, and wherein (i) a flat minimum thickness (dO) of the coating layer (40, 39) on the Inside (6) of the body and bottom portion, and (ii) a flat minimum thickness (d) of a coating layer (40; 41, 42, 43) is provided along a surface piece in the fold (1a, 1b, 1k, 1v), which the latter minimum thickness (d) is above essentially 8 μm, in particular above 10 μm. 31. Thin-walled can according to claim 30, with a can body according to one of claims 20 ff. 32. Thin-walled can according to claim 30, wherein at least one neck region (1d; 8) is provided, at least one axial end of the trunk below the fold-forming section, in which neck region the body region (1w, 9) in a transition section while reducing the diameter to Folding section (7) is tapered. 33. Thin-walled can according to claim 30, wherein the coating layer is a lacquer, in particular a tough elastic lacquer. 34. Thin-walled can according to claim 30, wherein the coating layer (40) along the surface piece is at least 30%, in particular 40% thicker than the flat minimum thickness of the coating layer on the inside of the body section. 35. Can body according to claim 30 or claim 20 with a seam between the body portion (9) and bottom portion (10). 36. The method according to claim 1 or 25, wherein the coating layer (40) in the fold-forming section as a flat coating essentially has a constant thickness (d) or is flat, at least in a curvature section (1 k, 41) of the fold-forming section. 37. The method of claim 36, wherein the substantially equal thickness (d) also extends into a substantially cylindrical section (1b) of the fold forming section. 38. The method of claim 36, wherein the substantially equal thickness (d) of the coating (44) also extends into a section (1a) of the fuselage hook (1a, 1e).