Patent Description:
Certain metal products, such as aluminum beverage cans, may require a protective layer, such as a polymer coating, between the metal and its contents. For example, beverage cans often must provide sufficient protection between the metal of the beverage can and the beverage contained therein to avoid damage to the metal from harsh beverages, such as sodas and colas, as well as to avoid undesirable effects to the beverage, such as discoloration or change in taste.

There are often requirements placed on the protective layer with regard to its fundamental properties. It can be desirable to produce a laminated metal product that meets various requirements. In some cases, it can be desirable to laminate a metal product rather than lacquer a metal product.

For example, certain can end stock (CES) used in beverage cans must have a protective layer that has less than a maximum amount of feathering and less than a maximum amount of blushing. Feathering can refer to the elongation and delamination of the protective layer, especially at breaks in the metal, such as the orifice created when opening a beverage can. Blushing can refer to the discoloration of the protective layer, such discoloration may occur when the coated metal is subjected to elevated temperature in a particular media, for example during a pasteurization or sterilization process. It can be desirable to have no discoloration during the pasteurization process. In some cases, the protective layer must withstand acid tests, such as an acetic acid test. The coated metal strip may need to conform to one or more of these and other requirements.

To ensure metal sheets laminated with polymers meet the desired requirements, it has been asserted that certain limitations must be placed on the choice of material and treatment processes pre-forming. These limitations can include restriction on polymer choice, tight temperature regulation with small windows for error, and other such restrictions.

<CIT> describes a process for producing polymer film coated metal sheet, stating that the use of amorphous polymer is undesirable because it is too elastic and would create too much feathering upon can opening and because it is too prone to blushing due to a crystallization mechanism of the polymer during pasteurization for example. The described process involves maintaining the annealing process temperature below the melting point of the main polymer layer to achieve compliance with CES requirements such as feathering and blushing after pasteurization. Additionally, the Aluminum alloy disclosed in the319 patent has a low range of Mg content, falling outside of the standard industry alloy for AA5182, which in turn has an influence on the product properties. From document <CIT> a method for preparing can end stock is known which comprises a pre-heating of a metal strip to a first temperature, a laminating of a polymer film to the first side of the metal strip and an annealing of the laminated metal strip. For the sake of completeness, reference shall further be made to documents <CIT> and <CIT>.

It can be desirable to provide a laminated metal product capable of meeting or exceeding desired requirements. It can be desirable to create this laminated metal product using amorphous polymer.

The term embodiment and like terms are intended to refer broadly to all of the subject matter of this disclosure and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the claims below. Embodiments of the present disclosure covered herein are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the disclosure and introduces some of the concepts that are further described in the Detailed Description section below. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings and each claim.

Embodiments of the present disclosure include methods for preparing can end stock, comprising: pre-heating a metal strip to a first temperature below <NUM>; laminating a polymer film to a first side of the metal strip to produce a laminated metal strip, wherein a main component of the polymer film has a melting temperature above the first temperature; and annealing the laminated metal strip at an annealing temperature, wherein the annealing temperature is higher than the melting temperature of the polymer film.

In some cases, the metal strip is an aluminum strip, such as AA5182 aluminum alloy. In some cases, the method can include applying a conversion coating to the metal strip, wherein laminating the polymer film to the first side of the metal strip includes laminating the polymer film to the conversion coating. In some cases, laminating the polymer film includes laminating a polyethylene terephthalate film to the metal strip. In some cases, the method includes applying a layer of lacquer or another polymer film to a second side of the metal strip, wherein the first side of the metal strip corresponds to an interior-facing side of a can end formed from the metal strip, and wherein the second side of the metal strip corresponds an exterior-facing side of a can end formed from the metal strip. In some cases, annealing the laminated metal strip includes raising the temperature of the polymer film for a duration sufficient to melt the polymer film into a surface texture of the metal strip. In some cases, annealing the laminated metal strip includes raising the temperature of the polymer film to at least <NUM>. In some cases, annealing the laminated metal strip includes raising the temperature of the polymer film to at least <NUM>. In some cases, annealing the laminated metal strip includes raising the temperature of the polymer film to at least <NUM>. In some cases, the method can include cooling the laminated metal strip after annealing the laminated metal strip to ensure that the polymer film remains amorphous. In some cases, the method can include applying a lubricant to the laminated metal strip after annealing the laminated metal strip. In some cases, the method can include selecting a conversion layer parameter from a plurality of conversion layer parameter candidates based on tested performance and applying a conversion layer to the metal strip, according to the conversion layer parameter, prior to laminating the polymer film to the first side of the metal strip. In some cases, the tested performance is blushing performance.

Embodiments of the present disclosure include methods for determining a conversion layer parameter comprising: determining a plurality of conversion layer parameter candidates; preparing, for each of the plurality of conversion layer parameter candidates, a can end stock sample according to the aforementioned methods; evaluating blushing performance for each of the can end stock samples; and selecting a conversion layer parameter from the plurality of conversion layer parameter candidates based on the evaluated blushing performance.

The methods according to the present invention include adjusting a surface roughness of the metal strip prior to laminating the polymer film to the first side of the metal strip. In some cases, adjusting the surface roughness includes decreasing a height of the surface roughness to a value lower than a thickness of a contact layer of the polymer film. In some cases, laminating the polymer film to the first side of the metal strip includes: compressing the polymer film against the first side of the metal strip using an applicator roller having a compressible layer surrounding a hollow metal core; and passing a fluid through the hollow metal core to control a temperature of the compressible layer. In some cases, the methods can include preheating the compressible layer prior to laminating the polymer film to the first side of the metal strip. In some cases, passing the fluid through the hollow metal core includes cooling the fluid to extract heat from an interior surface of the compressible layer to induce a thermal gradient between the interior surface of the compressible layer and an exterior surface of the compressible layer. In some cases, cooling the fluid includes reducing a temperature of the fluid sufficiently to maintain an interior temperature at the interior surface of the compressible layer below a maximum setpoint and an exterior temperature at the exterior surface of the compressible layer above a minimum setpoint. In some cases, the methods can include determining a temperature of the compressible layer; and adjusting a temperature or volumetric flow rate of the fluid based on the temperature of the compressible layer.

Embodiments of the present disclosure include can end stock products prepared according to the aforementioned methods. Embodiments of the present disclosure include a beverage can comprising a body piece and an end cap, wherein the end cap is formed from can end stock prepared according to the aforementioned methods.

Embodiments of the present disclosure include a system, comprising: a pre-heating furnace for accepting a metal strip and pre-heating the metal strip to a pre-heating temperature; a lamination system positioned downstream of the pre-heating furnace for accepting the metal strip at the pre-heating temperature and applying a polymer film to a first side of the metal strip, wherein the pre-heating temperature is below a melting temperature of a main component of the polymer film; and an annealing furnace positioned downstream of the lamination system for accepting a laminated metal strip and heating the laminated metal strip to an annealing temperature, wherein the annealing temperature is greater than the melting temperature of the main component of the polymer film.

In some cases, the metal strip is an aluminum strip, such as AA5182 aluminum alloy. In some cases, the system includes a conversion coating application system for applying a conversion coating to the metal strip, wherein the lamination system is configured to apply the polymer film to the conversion coating. In some cases, the lamination system is coupled to a supply of polyethylene terephthalate film. In some cases, the system includes a lacquer application system for applying a layer of lacquer to a second side of the metal strip. In some cases, the lamination system is configured to apply an additional polymer film to a second side of the metal strip opposite the first side. In some cases, the annealing furnace has a length sufficient to raise the temperature of the polymer film for a duration sufficient to melt the polymer film into a surface texture of the metal strip. In some cases, the annealing furnace is configured to provide heat sufficient to raise the temperature of the polymer film to at least <NUM>. In some cases, the annealing furnace is configured to provide heat sufficient to raise the temperature of the polymer film to at least <NUM>. In some cases, the annealing furnace is configured to provide heat sufficient to raise the temperature of the polymer film to at least <NUM>. In some cases, the system includes a conversion layer applicator for applying a conversion layer to the metal strip according to a conversion layer parameter selected from a plurality of conversion layer parameter candidates based on tested performance. According to the present invention, the system includes a surface roughness adjustor for adjusting a surface roughness of the metal strip, wherein the surface roughness adjustor is located upstream of the lamination system. The surface roughness adjustor is configured to decrease a height of the surface roughness to a value lower than a thickness of a contact layer of the polymer film. In some cases, the lamination system comprises: an applicator roller comprising a compressible layer surrounding a hollow metal core; and a coolant source for providing coolant to a passage of the hollow metal core to control a temperature of the compressible layer. In some cases, the system includes an external heater positioned adjacent the compressible layer to preheat the compressible layer. In some cases, the lamination system further comprises a controller coupled to the coolant source for adjusting a volumetric flow rate or temperature of the coolant provided by the coolant source to maintain a temperature gradient across an interior surface of the compressible layer and an exterior surface of the compressible layer. In some cases, the lamination system further comprises a temperature sensor coupled to the controller for providing a temperature signal associated with a temperature of the compressible layer. In some cases, the lamination system further comprises a data store containing a model, and wherein the controller is coupled to the data store to control the coolant source based on the model. In some cases, the lamination system further comprises a controller coupled to the coolant source for adjusting a volumetric flow rate or temperature of the coolant provided by the coolant source to maintain an interior temperature of an interior surface of the compressible layer below a maximum setpoint and an exterior temperature of an exterior surface of the compressible layer above a minimum setpoint.

Embodiments of the present disclosure include methods for laminating metal, comprising: compressing a polymer film against a first side of a preheated metal strip using an applicator roller having a compressible layer surrounding a hollow metal core; and passing a fluid through the hollow metal core to control a temperature of the compressible layer. In some cases, the methods include preheating the compressible layer prior to laminating the polymer film to the first side of the metal strip. In some cases, preheating the compressible layer includes passing heated fluid through the hollow metal core. In some cases, preheating the compressible layer includes externally heating the compressible layer. In some cases, passing the fluid through the hollow metal core includes cooling the fluid to extract heat from an interior surface of the compressible layer to induce a thermal gradient between the interior surface of the compressible layer and an exterior surface of the compressible layer. In some cases, cooling the fluid includes reducing a temperature of the fluid sufficiently to maintain an interior temperature at the interior surface of the compressible layer below a maximum setpoint and an exterior temperature at the exterior surface of the compressible layer above a minimum setpoint. In some cases, the methods include determining a temperature of the compressible layer; and adjusting a temperature or volumetric flow rate of the fluid based on the temperature of the compressible layer. In some cases, wherein determining the temperature of the compressible layer comprises receiving a temperature measurement of the compressible layer from a temperature sensor. In some cases, determining the temperature of the compressible layer comprises receiving a temperature measurement of an element near the compressible layer from a temperature sensor. In some cases, determining the temperature of the compressible layer comprises accessing a model. In some cases, the methods include sensing a change in line speed of the preheated metal strip; and adjusting a temperature or volumetric flow rate of the fluid based on the change in line speed.

Certain aspects and features of the present disclosure relate to aluminum can end stock (CES) with a laminated, amorphous polymer coating exhibiting low feathering, low blushing and high performance in an acetic acid test. The laminated metal strip can include the laminated polymer coating on an interior-facing side (e.g., product side) and a lacquered coating on an exterior-facing side (e.g., consumer side). The process can include heating the bare metal strip to a temperature below the melting point of the main polymer component of the polymer film, applying the crystalline polymer to an interior-facing side of the strip, and heating the combined strip and polymer to an annealing temperature above the melting point of the polymer. In some cases, the polymer film laminated to the metal strip can be a biaxially oriented polymer, such as an amorphous Polyethylene terephthalate (PET) film from a continuous production line. The polymer film may be rendered amorphous during an annealing process. The polymer film can comprise only a main component (e.g., PET layer), or can comprise a main component and one or more supplemental components(e.g., adhesive layers). As used herein, the melting temperature of the polymer or polymer film refers to the melting temperature of the main component, unless otherwise specified.

Through significant trial and experimentation, techniques have been found to produce laminated can end stock having low feathering (e.g., <NUM> or less overhanging coating around a scoreline on open ends as defined by the specific customer specification), low blushing, and high performance in an acetic acid test. These techniques can include applying a polymer to a metal strip heated to a first temperature (T<NUM>) before heating the combined strip and polymer to an annealing temperature (T<NUM>), wherein T<NUM> is below the melting temperature (Tm) of the polymer and T<NUM> is above Tm. In some cases, T<NUM> is at or above <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. In some cases, the annealing that occurs at a temperature higher than the melting temperature of the polymer can improve the adhesion sufficiently to provide increased performance in an acid resistance test. During annealing at temperatures above the melting point of the film, the film is allowed to flow into the topography of the metal strip, thus improving adhesion between the metal strip and the film through mechanical bonding.

In some cases where the film possess a given color or greyness, blushing performance after pasteurization is not impaired by the amorphous state of the polymer after processing at a temperature T<NUM>.

In some cases, a metal strip can be laminated on two sides. In some cases, a metal strip can be laminated on one side and lacquered on an opposite side. For example, a metal strip can be laminated on an interior-facing side and lacquered on an exterior-facing side, although other configurations can be used. This hybrid laminated/lacquered metal strip can provide improved functional performance on the interior of the can end stock through use of the PET laminate while maintaining high cosmetic performance on the exterior of the can end stock through use of a lacquer, which may not be prone to blushing, such as during pasteurization. In some cases, the PET film can include additives that provide a slight coloration to the film which does not change during pasteurization.

In some cases, the laminated metal stock is passed directly from a lamination process into an annealing process (e.g., into an annealing furnace). In some cases, the laminated metal stock is passed directly from a lamination process into a lacquer application system and then into an annealing process (e.g., into an annealing furnace).

Through trial and experimentation, it has been found that amorphous film can provide improved feathering performance when adhesion between the film and metal strip can be controlled. Trial and experimentation has shown that adhesion can be controlled by controlling the annealing temperature (e.g., higher annealing temperatures can lead to improved adhesion, to a point), controlling substrate properties (e.g., textures and chemistry), and film chemistry.

Traditional laminated metal strip often scored poorly on a <NUM>% acetic acid test. However, through trial and experimentation, it was found that laminates annealed at a temperature above the melting point of the polymer would perform better on a <NUM>% acetic acid test. As used herein, a <NUM>% acetic acid test can include assessing the resistance of a coating against diluted acidic media at approximately <NUM> for <NUM> minutes. The test can include cutting crosshatched markings into samples and placing the samples into a <NUM>% acetic acid solution at approximately <NUM> for <NUM> minutes, after which the samples are removed and cooled down, after which an additional set of cross cuts are performed on each sample and adhesive tape is placed over the pre- and post- acid bath crosshatched regions and removing the tape steadily in <NUM> to <NUM> second at an angle of approximately <NUM>°. The results of the test (e.g., based on the presence of and intensity of delamination) can be used to determine if the metal strip is acceptable or unacceptable given the desired specifications. In some cases, the annealed, laminated can end stock disclosed herein passes <NUM>% acetic acid tests without delamination. In some cases, the annealed, laminated can end stock disclosed herein obtain more favorable results in the <NUM>% acetic acid tests (e.g., no or low delamination) than a standard, lacquered can end stock.

These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative embodiments but, like the illustrative embodiments, should not be used to limit the present disclosure. The elements included in the illustrations herein may not be drawn to scale.

In some cases, the aspects and features of the present disclosure are especially useful with aluminum AA5182, although other types of aluminum can be used.

<FIG> is a schematic diagram of a system <NUM> for preparing can end stock (CES) according to certain aspects of the present disclosure. A metal strip <NUM> is passed into a pre-heating furnace <NUM> that heats the metal strip <NUM> to a pre-heating temperature (T<NUM>). The pre-heating temperature T<NUM> is well below the melting temperature of the polymer film <NUM> that will be laminated to the metal strip <NUM>. In some cases, the pre-heating temperature T<NUM> is at or below <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In some cases, the pre-heating temperature T<NUM> is within a range of <NUM> and <NUM>, within a range of <NUM> and <NUM>, or <NUM> and <NUM>. The pre-heated metal strip <NUM> can pass into a lamination system <NUM>. The metal strip <NUM>, as a pre-licatcd metal strip <NUM>, is passed through a lamination system <NUM> that applies a polymer film <NUM> to one side of the metal strip <NUM>. In some cases, polymer film can be applied to both sides of the metal strip <NUM>. The lamination system <NUM> can be any suitable system for laminating a polymer film <NUM> to the metal strip <NUM>. A laminated metal strip <NUM> exits the lamination system <NUM>, combining the metal strip <NUM> with a polymer film <NUM>.

In some cases, the laminated metal strip <NUM> can pass into a lacquer application system <NUM>. Lacquer <NUM> is applied to the metal strip <NUM> by the lacquer application system <NUM>. The lacquer application system <NUM> can be any suitable system for applying lacquer <NUM> to the metal strip <NUM>. A lacquer application system <NUM> can include an oven for heating or curing the lacquer <NUM> onto the metal strip <NUM>. In some cases, the lacquer application system <NUM> is downstream of (e.g., after) the lamination system <NUM>. In some cases, the lacquer application system <NUM> is upstream of (e.g., before) the annealing furnace <NUM>. In some cases, the lacquer application system <NUM> is upstream of the lamination system <NUM> or the pre-heating furnace <NUM><NUM>. In some cases, the lacquer application system <NUM> is downstream of both the lamination system <NUM> and the annealing furnace <NUM>. As shown in <FIG>, the lacquer application system <NUM> is located between the lamination system <NUM> and the annealing furnace <NUM>. A laminated, lacquered metal strip <NUM> can exit the lacquer application system <NUM>.

When an upstream lacquer application system <NUM> is used, laminated, lacquered metal strip <NUM> can pass into an annealing furnace <NUM>. In some cases, where no lacquer application system <NUM> is used between the lamination system <NUM> and the annealing furnace <NUM>, laminated metal strip <NUM> can pass into the annealing furnace.

The annealing furnace <NUM> can be positioned downstream of (e.g., after) the lamination system <NUM> and optionally the lacquer application system <NUM>. In some cases, the annealing furnace <NUM> is positioned immediately downstream of the lacquer application system <NUM>, such that the lacquered, laminated metal strip <NUM> exiting the lacquer application system <NUM> passes into the annealing furnace <NUM> before passing or coming into contact with other machinery or systems.

The annealing furnace <NUM> raises the temperature of the lacquered, laminated metal strip <NUM> to an annealing temperature (T<NUM>). The annealing temperature T<NUM> is higher than the melting temperature (Tm) of the polymer film <NUM>. In some cases, T<NUM> is at or above <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. Therefore, during the annealing process, the polymer film <NUM> is able to flow into the mechanical features (e.g., surface textures) of the metal strip <NUM> and becomes amorphous. The lacquered, laminated metal strip <NUM> spends a duration in the annealing furnace <NUM> of sufficient length to impart the desired properties on the lacquered, laminated metal strip <NUM>, including annealing of the metal strip <NUM> and desired adhesion of the polymer film <NUM>. The duration within the annealing furnace <NUM> can be based on furnace length and the speed of the metal strip. In some cases, the duration can be within the range of approximately <NUM> seconds to approximately <NUM> seconds, approximately <NUM> seconds to approximately <NUM> seconds, approximately <NUM> seconds to approximately <NUM> seconds, or approximately <NUM> seconds. In some cases, the duration can be adjusted (e.g., by adjusting the metal strip speed) as necessary to compensate for changes in the temperature within the annealing furnace <NUM>.

After exiting the annealing furnace <NUM>, the can end stock <NUM> (e.g., annealed, lacquered and laminated metal strip) can optionally be quenched, such as in a volume of quenching liquid or through application of coolant to the can end stock <NUM>. The can end stock <NUM> can be cooled immediately after exiting the annealing furnace <NUM>, through quenching or otherwise, at a rate sufficient to avoid substantial recrystallization of the amorphous polymer. In some cases, the can end stock <NUM> is cooled to below approximately <NUM> within a desired duration of approximately <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, or <NUM> seconds or less. In some cases, the can end stock <NUM> is cooled to below approximately <NUM> within a duration of approximately <NUM> to <NUM> seconds. Avoiding substantial recrystallization can avoid blushing of the polymer. It can be desirable to have a weight fraction at or below <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the recrystallizable part of the polymer being recrystallized. It can further be desirable for crystals formed to be at or below approximately <NUM>.

In some cases, the can end stock <NUM> produced by system <NUM> can include a metal strip <NUM> to which a layer of lacquer <NUM> has been applied to a first side and to which a layer of laminated polymer film <NUM> has been applied to a second side, as shown in <FIG>. The metal strip <NUM> of the can end stock <NUM> can be annealed and can include an crystalline polymer film <NUM> laminated thereto prior to being heated to a temperature above the melting temperature of the polymer film <NUM> for a sufficient duration to allow the polymer film <NUM> to melt into the surface texture of the metal strip <NUM> and become amorphous. As used herein, the duration sufficient to allow the polymer film <NUM> to melt into the surface texture of the metal strip <NUM> can be assessed by the polymer film <NUM> sufficiently adhering to the metal strip <NUM> to result after pasteurization in overhanging coating around a scoreline on open ends of <NUM> or less, <NUM> or less, <NUM> or less, or <NUM> or less.

As described herein, a standard feathering test for a can end may include immersing a can end in a bath of deionized water at approximately <NUM> for thirty minutes, rinsing the can end in cool deionized water to return the can end to room temperature, and then immediately opening the end tab of the can end. Feathering can be observed and measured on the scored panel or pour hole opening. In some cases, a feathering test can be conducted on a flat sheet of metal, such as a flat sheet of can end stock. In such cases, the feathering test can include immersing the sample in demineralized water at <NUM> for forty minutes, after which the sample is allowed to cool down to room temperature and the sample can be cut and a strip of metal can be separated by pulling the strip in a direction away from the cut. Other feathering tests can be used.

In some examples, a laminated metal strip annealed at a temperature of <NUM> provided a mean amount of feathering of <NUM> with a standard deviation of <NUM>, whereas a laminated metal strip annealed at a temperature of <NUM> provided a mean amount of feathering of <NUM> with a standard deviation of <NUM>. Through experimentation, it has been shown that improvement in feathering and delamination can be substantial at temperatures at or above the metaling temperature of the polymer film, such as at or above <NUM>. This amount of feathering may be located at certain indicative positions along the orifice of the opened can end. Through experimentation, it has been shown that the amount of feathering of the film also depends on the cutting, forming and stamping tool design of the product.

In some cases, the metal strip <NUM> can include one or more conversion layers, as described in further detail below, pre-applied prior to entering the pre-heating furnace <NUM> or the lamination system <NUM>.

In some cases, a lubricant can be further applied to the can end stock <NUM> after exiting the annealing furnace <NUM>.

<FIG> is a close-up side view of the can end stock <NUM> of <FIG>. The can end stock <NUM> includes metal strip <NUM> sandwiched between a layer of lacquer <NUM> and a laminated polymer film <NUM>.

In some cases, to prepare the aluminum to provide enhanced adhesion and blushing performance, one or more conversion layers <NUM> may be applied on bare aluminum. In some cases, this layer <NUM> can include components of chromium(III) and phosphates. This layer <NUM> can provide enhanced adhesion, low blushing after pasteurization, and good corrosion performance in the acetic acid test. In some cases, the metal strip <NUM> can include one or more conversion layers <NUM> located between one or both of the layer of lacquer <NUM> and laminated polymer film <NUM>. Characteristics of the conversion layers <NUM> can be selected to provide optimal blushing after pasteurization, as described in further detail with respect to <FIG>.

<FIG> are axonometric depictions of can end stock <NUM> in various stages of production. In some cases, the can end stock <NUM> is the can end stock as described herein, including laminated amorphous polymer and lacquer as described herein.

<FIG> is a sheet of can end stock <NUM> according to certain aspects of the present disclosure. The sheet of can end stock <NUM> can be can end stock <NUM> depicted in <FIG>, or a similar can end stock. <FIG> depicts the sheet of can end stock <NUM> of <FIG> after it is cut. The sheet of can end stock <NUM> can be die cut, punched, or otherwise cut to produce can end blanks <NUM> as seen in <FIG> depicts a set of can end blanks <NUM> produced from the sheet of can end stock of <FIG> depicts a beverage can <NUM> including a can end <NUM> formed from a can end blank <NUM> from <FIG>.

The can end <NUM> includes an exterior-facing side (e.g., visible in <FIG>) and an interior-facing side (e.g., facing the interior of the beverage can <NUM>). As described herein, the can end <NUM> can be formed such that a layer of lacquer is present on the exterior-facing side while a laminated polymer film is present on the interior-facing side, although it need not be.

<FIG> is an isometric cutaway diagram depicting the multiple layers of a section of can end stock <NUM> according to certain aspects of the present disclosure. The can end stock <NUM> can include a layer of metal <NUM>, such as aluminum surrounded by a layer of lacquer <NUM>, and a layer of polymer film <NUM>. The can end stock <NUM> can be the can end stock <NUM> of <FIG>.

<FIG> is a flowchart depicting a process <NUM> for manufacturing can end stock according to certain aspects of the present disclosure. At block <NUM>, the metal strip is provided. At optional block at block <NUM>, the surface roughness of the metal strip can be increased, such as described below with reference to <FIG>. The metal strip can be an aluminum strip suitable for forming can end stock. At block <NUM>, the metal strip is preheated to a pre-heat temperature T<NUM>. At block <NUM>, the metal strip is laminated with a PET polymer film. At block <NUM>, the laminated metal strip is annealed at an annealing temperature T<NUM>, where the annealing temperature T<NUM> is higher than the melting temperature of the PET polymer film. At block <NUM>, the annealed metal strip is optionally quenched. At block <NUM>, a lubricant can be optionally applied to one or both sides of the metal strip.

<FIG> is a partial top view depicting a piece of can end stock <NUM>. The can end stock <NUM> includes a layer of polymer film <NUM> that has not been annealed according to certain aspects of the present disclosure. The can end stock <NUM> has been separated along a score line <NUM>. The polymer film <NUM> can be seen feathering out past the score line <NUM>. The can end stock <NUM> of <FIG> can be considered to have poor feathering.

<FIG> is a partial top view depicting a piece of can end stock <NUM> according to certain aspects of the present disclosure. The can end stock <NUM> includes a layer of polymer film that has been annealed according to certain aspects of the present disclosure, such as the can end stock <NUM> of <FIG>. The can end stock <NUM> has been separated along a score line <NUM>. The polymer film has not feathered out past the score line <NUM>. The can end stock <NUM> of <FIG> can be considered to have good feathering (e.g., feathering of less than <NUM>) or no feathering.

<FIG> is a schematic diagram of a lamination system <NUM> according to certain aspects of the present disclosure. The lamination system <NUM> can be the lamination system <NUM> of <FIG>, or another lamination system. Certain elements depicted in <FIG> are shown at an exaggerated scale for demonstrative purposes only.

The lamination system <NUM> can include a pair of rollers <NUM> through which a pre-heated metal strip <NUM> may pass. The pre-heated metal strip <NUM> can include a metal strip <NUM> that has been pre-heated, such as by a pre-heating furnace <NUM> of <FIG>. In some cases, the pre-heated metal strip <NUM> includes one or more conversion layers <NUM>.

When passing through the rollers <NUM>, a polymer film <NUM> can be pressed against the pre-heated metal strip <NUM> to produce a laminated metal strip <NUM>. In some cases, a single lamination system <NUM> can include additional sets of rollers to apply a second polymer film to an opposite side of the pre-heated metal strip <NUM> from the polymer film <NUM>. In some cases, rollers <NUM> can additionally apply a second polymer film to an opposite side of the pre-heated metal strip <NUM> from the polymer film <NUM>.

<FIG> is a flowchart depicting a process <NUM> for determining desirable conversion layer characteristics for a laminated metal strip according to certain aspects of the present disclosure. Blushing of certain products, such as CES material, is traditionally associated with underperformance of or a defect in a lacquer layer of the material. Characteristics of the conversion layer have not been considered with regard to blushing performance. Conversion layers generally have a thickness on the nanometer scale, which is generally one or more orders of magnitude thinner than a lacquer layer or thin film layer. However, it has been discovered that, unexpectedly, characteristics of a conversion layer can provide a noticeable and controllable impact on the blushing properties of a metal product (e.g., aluminum CES material) having a laminated film layer (e.g., laminated PET film). The metal product can be any suitable metal product, such as the laminated metal strips disclosed above. The characteristics of the conversion layer (e.g., chemical nature, thickness, or texture) have a noticeable impact on blushing performance of a film layer applied to the conversion layer. The blushing performance of a metal product with a laminated film layer is the result of a different mechanism from the standard blushing associated with lacquered metal products. Further, annealing a metal product having a laminated film layer can further affect blushing performance through a different mechanism than standard blushing associated with lacquered metal products. It has been discovered that the blushing performance of metal products with laminated film layers, with or without subsequent annealing, can be controlled through manipulation of conversion layer characteristics. Process <NUM> can be used to test the blushing performance of different conversion layer parameter candidates against a given combination of substrates (e.g., aluminum metal strips), films (e.g., PET film), and process steps (e.g., post-lamination annealing) so that the optimal conversion layer parameter(s) for a particular use case (e.g., combination of substrates, films, and process steps) can be selected prior to mass production.

At block <NUM>, one or more conversion layer parameter candidates can be determined. A conversion layer parameter can be any suitable parameter of a conversion layer or its application process, such as type of conversion layer, depth of conversion layer, parameters of the application process of the conversion layer (e.g., type of conversion solutions, application time, treatment temperature, drying time, or application thickness), or other such parameters. Varying one or more parameters of the conversion layer can result in conversion layers having different characteristics. In some cases, determining one or more conversion layer parameter candidates can include determining a set of conversion solutions having different properties that result in a set of conversion layers with differing characteristics (e.g., thickness, texture, chemical makeup, or other characteristics). For example, the set of conversion materials can include chromium phosphate conversion solutions using different concentrations of chromic acid, phosphoric acid, and hydrofluoric acid. In some cases, determining one or more conversion layer parameter candidates can include determining a set of parameters that result in a set of conversion layers with differing thicknesses. In some cases, a single parameter candidate will be determined at block <NUM> and the process <NUM> can still test multiple parameters by determining a new conversion layer parameter candidate at optional block <NUM>, as described in further detail below. In some cases, determining conversion layer parameter candidates at block <NUM> can include accessing a set of pre-determined parameters that are likely to produce desired results.

At block <NUM>, one or more conversion layers are applied to the surface(s) of one or more metal strips according to the desired conversion layer parameter candidates. In some cases, conversion layers can be applied to continuous metal strips or individual metal blanks. In some cases, all conversion layers can be applied to different locations of a single metal strip or metal blank, however in other cases each metal strip or metal blank is treated with a single conversion layer.

Applying a conversion layer to a surface of a metal strip or blank can include degreasing the surface (e.g., through application of hydrofluoric acid), drying the surface, applying a wet film (e.g., by roll coating or other suitable mechanisms) of the conversion material (e.g., a chromium based conversion material in a water-bome solution), and drying the surface to allow a conversion layer to form. In some cases, when multiple conversion layers are being tested on a single metal strip or metal blank, parameters of the conversion layer application process can be manipulated across one or multiple dimensions of the surface of the single metal strip or metal blank. For example, the thickness of the wet film can be adjusted with respect to horizontal distance across a surface of a metal strip or metal blank so that various sections of the metal strip or metal blank at different horizontal locations will have different conversion layer characteristics. In another example, different conversion solutions can be applied at different locations of single metal strip or metal blank.

At block <NUM>, a polymer film can be applied to the surface of the metal strip or metal blank having the conversion layer. The polymer film can be applied in any suitable manner, such as described above, including with reference to <FIG>, <FIG>, and <FIG>.

At optional block <NUM>, the one or more laminated metal strips or metal blanks can be annealed, such as described above, including with reference to <FIG> and <FIG>.

At block <NUM>, a pasteurization process can be performed on the one or more laminated metal strips or metal blanks. In some cases, a pasteurization analog can be performed, which can include performing a process that is different from pasteurization, but designed to produce similar blushing effects as standard pasteurization processes. In some cases, a sterilization process can occur instead of a pasteurization process. In some cases, another process that may potentially elicit blushing of the one or more laminated metal strips or metal blanks can be performed instead of a pasteurization process. In an example, the one or more laminated metal strips or metal blanks can be placed in water heated to a desired temperature (e.g., a temperature suitable for pasteurization) for a desired duration (e.g., for a duration suitable for pasteurization).

At block <NUM>, each of the one or more laminated metal strips or metal blanks can be tested for blushing performance. Blushing testing can be performed by using subjective or objective characterizations of the blushing properties of a surface of a metal strip or metal blank. For example, objective characterizations can include taking measurements of blushing using a camera, a light sensor, or other suitable sensor. As an example, subjective characterizations can include having an individual perform a visual inspection of a surface of a metal strip or metal blank and rank the apparent blushing performance. In some cases, a sample that has been processed at block <NUM> (e.g., pasteurized) can be compared with a sample that has been immersed in water at room temperature for the same duration as the sample immersed in heated water at block <NUM> to determine the amount of blushing attributable to the process at block <NUM>.

When multiple conversion layer parameter candidates have been selected at block <NUM>, the testing at block <NUM> can include testing the blushing properties of multiple samples. At block <NUM>, one or more desired conversion layer parameters can be selected based on the blushing properties tested at block <NUM>. For example, out of all conversion layer parameter candidates tested, the conversion layer parameters of the best performing sample (e.g., the sample showing the least amount of blushing) can be selected as the desired conversion layer parameters.

In some cases, after testing blushing properties at block <NUM>, one or more new conversion layer parameter candidates can be determined at block <NUM>. The one or more new conversion layer parameter candidates can be used to prepare and test one or more new sample with new conversion layer(s) at blocks <NUM>, <NUM>, <NUM>, and <NUM>. When multiple iterations of blocks <NUM>, <NUM>, <NUM>, and <NUM> are performed (e.g., when block <NUM> is performed), selecting one or more desired conversion layer parameters at block <NUM> can include comparing the results of a current iteration of block <NUM> with the results from a previous iteration of block <NUM>.

The conversion layer parameter(s) selected at block <NUM> can be used in mass production. For example, when the different conversion layer parameter candidates include using chromium-phosphate conversion solutions with differing concentrations of its components, the particular conversion solution selected at block <NUM> can be provided to a process line for mass producing the final laminated product (e.g., laminated can end stock).

Process <NUM> is described in further detail with respect to <FIG>.

<FIG> is a highly-magnified partial cross sectional view of a portion of a metal strip <NUM> having a film <NUM> laminated thereon according to certain aspects of the present disclosure. Certain elements depicted in <FIG> are shown at an exaggerated scale for demonstrative purposes only. The metal strip or metal blank can have a surface with a surface roughness. The ability for a film, such as a PET film, to adhere to the surface of the metal strip or metal blank may be affected by the surface roughness of the metal. Surface roughness can affect not only the adhesion of the film to the metal during lamination, but also the ongoing adhesion of the film to the metal during the lifespan of an end product. Adherence can be determined in various manners, such as disclosed above. The roughness of PET films is much lower than standard surface roughness of metal strips used for CES, so it may have been assumed that a lower roughness increasing immediate contact area in the lamination process would be beneficial. However, it has been determined that, unexpectedly, low roughness of the metal's surface is detrimental to some of the adhesion related properties of laminated metal products. Therefore, metal surfaces having a roughness at or above a minimum threshold roughness may be desirable for film lamination applications. In some cases, it can also be desirable for the metal surfaces to have a roughness at or below a maximum threshold roughness.

The metal strip <NUM> can have a surface roughness <NUM> defined by the presence of hills and valleys in the surface of the metal. A lower surface roughness <NUM> can be defined by fewer or less intense hills and valleys in the surface of the metal, and thus a smoother surface of the metal. Additionally, surface roughness <NUM> can be defined by a height <NUM> between the lowest valleys and the highest hills of the surface of the metal (e.g., within a localized region of the surface of the metal). The metal strip <NUM> can have a conversion layer <NUM> on a surface. The conversion layer <NUM> may generally be small enough to not have a noticeable or significant impact on the surface roughness <NUM> of the metal strip <NUM>.

A film <NUM> (e.g., PET film) can be applied to a metal strip <NUM>, such as described herein, such as with reference to <FIG>, <FIG>, and <FIG>. The film <NUM> can be a multilayer film and can include at least a primary layer <NUM> and a contact layer <NUM> (e.g., a hot mate layer), however the film <NUM> may include additional layers. The contact layer <NUM> can be a layer that comes into direct contact with the surface of the metal strip <NUM>. The contact layer <NUM> can have a melting point that is lower than a melting point of the primary layer <NUM>. During the lamination process, heat and/or pressure from the lamination process can cause the contact layer <NUM> to melt before the primary layer <NUM>, if the primary layer <NUM> melts at all, and the contact layer <NUM> can melt into the surface topology of the metal strip <NUM>. The contact layer <NUM> can have a thickness <NUM>. The thickness <NUM> of the contact layer <NUM> may be at or greater than the height <NUM> of the surface roughness <NUM>. If the contact layer <NUM> has a thickness <NUM> that is too thin, voids may form from the contact layer <NUM> melting into a valley and separating from the primary layer <NUM> that is supported above the contact layer <NUM> by a tall hill. The contact layer <NUM> may have a thickness <NUM> that is at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% greater than the height <NUM>. The contact layer <NUM> can have a thickness that is <NUM> micron or within <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of <NUM> micron. The height <NUM> of the surface roughness <NUM> can be less than <NUM> micron, less than <NUM> micron, less than <NUM> micron, or less than <NUM> micron. In some cases, the height <NUM> of the surface roughness <NUM> can be at least <NUM> micron, <NUM> micron, or <NUM> micron.

In some cases, a metal strip can be treated to increase its surface roughness prior to being laminated. For example, the system <NUM> of <FIG> can include an additional roughening apparatus upstream of the laminating system <NUM> for measuring and/or increasing the surface roughness of the metal prior to lamination. In some cases, the metal strip to be laminated can be rolled using rolls designed to impart a desired surface roughness.

<FIG> is a partial side cutaway view of a lamination system <NUM> according to certain aspects of the present disclosure. The lamination system <NUM> can be the lamination system <NUM> of <FIG>, or another lamination system. Certain elements depicted in <FIG> are shown at an exaggerated scale for demonstrative purposes only.

The lamination system <NUM> can include an application roller <NUM> opposite a metal strip <NUM> from a backing roller <NUM>. The pre-heated metal strip <NUM> may pass through a gap formed between the application roller <NUM> and the backing roller <NUM>. The pre-heated metal strip <NUM> can include a metal strip <NUM> that has been pre-heated, such as by a pre-heating furnace <NUM> of <FIG>. In some cases, the pre-heated metal strip <NUM> includes one or more conversion layers <NUM>.

When passing the application roller <NUM>, a polymer film <NUM> can be pressed against the pre-heated metal strip <NUM> to produce a laminated metal strip <NUM>. In some cases, a single lamination system <NUM> can include additional sets of rollers to apply a second polymer film to an opposite side of the pre-heated metal strip <NUM> from the polymer film <NUM>. In some cases, backing roller <NUM> can be replaced with an additional application roller to simultaneously apply a second polymer film to an opposite side of the pre-heated metal strip <NUM> from the polymer film <NUM>.

The application roller <NUM> can include a compressible layer <NUM> (e.g., a rubber coating) surrounding a metal core <NUM>. The compressible layer <NUM> can be adhered to (e.g., via glue) or mechanically fixed to the core <NUM>. The metal core <NUM> can be made of any suitable metal, such as steel. The compressible layer <NUM> can be made of any suitable compressible material, such as foam or rubber. In some cases, the compressible layer <NUM> has a thickness of <NUM> or within <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of <NUM>, although other thicknesses can be used. The degree of compressibility of the compressible layer <NUM> can be selected to achieve desired lamination results. For example the type of rubber selected for the compressible layer <NUM> can include a hard rubber, a soft rubber, or any rubber therebetween.

The compressible layer <NUM> can aid in applying the polymer film <NUM> to the surface of the metal strip <NUM> without the presence of entrapped air. Even small amounts of entrapped air can cause blisters during later processes, such as post-lamination annealing. For example, during post-lamination annealing, entrapped air can blow out of and rupture the film. Entrapped air and blisters can affect adhesion and blushing, among other characteristics of the laminated product. Therefore, the presence of entrapped air and/or blisters may result in an undesirable product.

In some cases, the application roller <NUM> can include a mechanism for controlling the temperature of the compressible layer <NUM>. For example, heat can be extracted from the compressible layer <NUM> to ensure the compressible layer <NUM> does not become so hot as to tinderperform, such as through losing its ability to rebound when compressive forces are released or losing its adherence to the metal core <NUM>, thus causing slipping. For example, a rubber compressible layer <NUM> may delaminate from the metal core <NUM> if the temperature of the compressible layer <NUM> at the metal core <NUM> (e.g., where adhesive may be located) reaches sufficiently high temperatures, such as temperatures at or in excess of <NUM>. In some cases, the compressible layer <NUM> can be externally cooled, such as through application of coolant fluid (e.g., cool air) to an exterior surface of the compressible layer <NUM> or through direct conduction with a cooled roll in contact with the exterior surface of the compressible layer <NUM>.

However, it has been found that internally cooling the compressible layer <NUM> can have unexpected benefits. The compressible layer <NUM> can be internally cooled by passing coolant through a passage <NUM> within a hollow metal core <NUM> of the application roller <NUM>. Any suitable coolant can be used, including fluids such as air and water. Coolants can be pumped using any suitable pumping source. Coolants can temperature controlled by passing through heat exchangers. Coolants can be designed to pass through the passage <NUM> at desired temperatures, which may be higher or lower than ambient room temperature, higher or lower than the temperature of the compressible layer <NUM>, and higher or lower than the temperature of the pre-heated metal strip <NUM>. Therefore, coolants can act to increase or decrease the temperature of the compressible layer <NUM>. When a hollow metal core <NUM> is used to provide temperature control of the compressible layer <NUM>, the core <NUM> can be made of a material having high thermal conductivity. The compressible layer <NUM> can be selected to have high or low thermal conductivity, however improved results can be obtained when using compressible layers <NUM> without high thermal conductivity.

In some cases, heated coolant can be passed through the passage <NUM> to heat the compressible layer <NUM> prior to a lamination process so that the compressible layer <NUM> is sufficiently hot ensure the contact layer of the polymer film <NUM> is molten or semi-molten when it is compressed against the pre-heated metal strip <NUM>, thus allowing the contact layer to melt into the hills and valleys of the metal strip <NUM>. In some cases, cooled coolant (e.g., below the temperature of the pre-heated metal strip <NUM>) can be passed through the passage <NUM> during a lamination process to remove heat from the compressible layer <NUM>. Because the compressible layer <NUM> is continuously heated by the environment of the lamination process (e.g., the heat from the pre-heated metal strip <NUM>) and any other heated elements in proximity to the lamination nip (e.g., space between the application roller <NUM> and backup roller <NUM>), the outside surface of the compressible layer <NUM> is drawn towards a high temperature. However, the inner surface of the compressible layer <NUM> is cooled through conduction with the hollow metal core <NUM> and the coolant passing therethrough. Therefore, the use of a hollow metal core <NUM> can ensure the inner surface of the compressible layer <NUM> is maintained at a suitable temperature (e.g., for avoiding delamination of the compressible layer <NUM>) despite having a higher temperature at its outer surface. Thus, a radial temperature gradient is induced in the compressible layer <NUM>.

Further, by forming the compressible layer <NUM> from a material with a suitable low thermal conductivity and internally cooling the compressible layer <NUM> through the use of a hollow metal core <NUM>, the temperature of the external surface of the compressible layer <NUM> is able to be maintained at a higher temperature without fear of the inner surface delaminating from the metal core <NUM>.

This ability to keep the compressible layer <NUM> running at a higher temperature (e.g., a temperature that is higher than if internal cooling were not used) has many benefits. The higher temperature of the external surface of the compressible layer <NUM> can allow the metal strip <NUM> to be preheated to a lesser degree, thus saving energy. For example, the higher temperature of the external surface of the compressible layer <NUM> can be used to melt the contact layer of the polymer film <NUM>, thus obviating the need to rely as much on the heat from the pre-heated metal strip <NUM> to melt the contact layer of the polymer film <NUM>. Additionally, the ability to have a larger window of available temperatures for preheating the metal strip <NUM>, which is enabled by being able to support a larger window of temperatures of the external surface of the compressible layer <NUM>, allows additional upstream and downstream processes to be more easily tailored to work with a laminating system, such as laminating system <NUM>.

For example, a downstream process may require a metal strip at approximately <NUM>. Normally, without interior-cooled compressible layers <NUM>, the external temperature of the compressible layer would be maintained no greater than approximately <NUM>, thus requiring the metal strip to be preheated to approximately <NUM>. Thus, that preheated metal strip would need to be cooled prior to entering the downstream process. However, when an interior-cooled compressible layer <NUM> is used, the external temperature of the compressible layer can be set to approximately <NUM>, thus allowing the metal strip <NUM> to be preheated to approximately <NUM>, allowing the metal strip <NUM> to enter the downstream process much faster and with much more overall efficiency.

Additionally, allowing the external surface of the compressible layer <NUM> to reach a higher temperature can allow the lamination system <NUM> to operate at a faster speed, thus potentially allowing the entire processing line to operate at a faster speed.

<FIG> is a schematic diagram depicting a control system <NUM> for an application roller <NUM> of a lamination system according to certain aspects of the present disclosure. The application roller <NUM> can be application roller <NUM> of <FIG>. The control system <NUM> can include a controller <NUM>, which may be any suitable controller or processor. The controller <NUM> can be coupled to a data store <NUM> for storing programming instructions, collected data, models, predicted data, presets, and other information. The controller <NUM> can be coupled to a coolant source <NUM> for providing and/or circulating coolant through the application roller <NUM>. The controller <NUM> can transmit command signals to the coolant source <NUM> to cause the coolant source <NUM> to adjust the amount of cooling or heating to desired levels. The command signals can cause the coolant source <NUM> to adjust the volumetric flow rate of the coolant, the temperature of the coolant, or other characteristics of the coolant or its flow through the application roller <NUM>. Coolant can be routed through conduits <NUM>, <NUM> between the coolant source <NUM> and application roller <NUM>. The coolant source <NUM> can include a pressurization source (e.g., a pump), a heat exchanger, an optional storage tank, and any other suitable elements for providing control of the coolant or its flow through the application roller <NUM>.

The controller <NUM> can be coupled to one or more sensors, including one or more temperature sensors <NUM>. A temperature sensor <NUM> can be positioned within, adjacent, proximate to, or spaced apart from the application roller <NUM> to measure a temperature associated with the application roller <NUM>. For example, temperature sensors can measure the internal coolant temperature, the temperature of the metal core, the temperature of the internal surface of the compressible layer, or the temperature of the external surface of the compressible layer. Any suitable temperature sensor <NUM> can be used, including contact and non-contact temperature sensors. In some cases, temperature sensors <NUM> can measure temperature of elements adjacent the application roller <NUM> (e.g., a polymer film, metal strip, or other elements) to infer a temperature of the application roller <NUM>. Signals from the temperature sensor(s) <NUM> can provide feedback to the controller <NUM> to help the controller <NUM> ensure desired operation of the application roller <NUM> (e.g., to ensure sufficiently low temperature of the internal surface of the compressible layer or sufficiently high temperature of the external surface of the compressible layer).

In some cases, the controller <NUM> can instruct a coolant source <NUM> to pump heated coolant through the application roller <NUM> to increase the temperature of the external surface of the compressible layer of the application roller <NUM> to a minimum desired temperature. The controller <NUM> may then pump cooled coolant to maintain the temperature of the external surface of the compressible layer within a desired range during a lamination process (e.g., when a much hotter preheated metal strip is conducting heat into the application roller <NUM>). The "cooled coolant" may be colder than the preheated metal strip, but may still be warmer than ambient room temperature. In some cases, the controller <NUM> can control an optional external heater <NUM> to preheat the application roller <NUM> instead of or in addition to pumping heated coolant through the application roller <NUM>.

In some cases, the controller <NUM> can operate based on feedback from temperature sensor(s) <NUM> and/or other sensors. In some cases, controller <NUM> can operate based on models stored in the data store <NUM> (e.g., thermal models) instead of or in addition to sensors, such as temperature sensor(s) <NUM> and/or other sensors. For example, controller <NUM> can automatically increase the amount of cooling provided to the application roll <NUM> whenever the line speed increases.

<FIG> is a plot <NUM> depicting temperature as a function of radial distance from the axis of rotation of an application roller of a lamination system according to certain aspects of the present disclosure. The application roller can be application roller <NUM> of <FIG>. The plot depicts a temperature curve <NUM> at various radial distances from the axis of rotation (e.g., center) of the application roller. Plot <NUM> and its elements, including curve <NUM> and the depicted zones, are not drawn to scale and are shown for demonstrative purposes, without units. Along a direction from the center of the application roller outwards, the application roller can include a coolant zone, a metal core zone, and a rubber coating zone. A film can be positioned adjacent the application roller such that, along the same direction, the film includes a primary layer and a contact layer. The film can be compressed against a metal strip.

The preheated metal strip can be provided at a temperature <NUM> (e.g., <NUM>). The coolant, however, can be provided at a temperature <NUM>, which may be substantially cooler than the preheated metal strip. Thus, a temperature gradient exists between the coolant and the metal strip, approximated by curve <NUM>. The coolant <NUM> will absorb heat from the interior surface <NUM> of the compressible layer, trying to pull the temperature of the interior surface <NUM> down towards temperature <NUM>. Simultaneously, the higher temperature <NUM> of the preheated metal strip will be conducted through the film and will try to raise the temperature of the external surface <NUM> of the compressible layer. Thus, a temperature gradient exists within the compressible layer defining a temperature gap <NUM> between the interior surface <NUM> and exterior surface <NUM>. This temperature gap <NUM> can be controlled by selecting, for the compressible layer, materials with desirable thermal conductivities. This temperature gap <NUM> can be further controlled by adjusting the temperature <NUM> of the coolant <NUM> and the temperature <NUM> of the preheated metal strip. The temperature gap <NUM> can be controlled such that the temperature of the interior surface <NUM> is maintained below a maximum setpoint <NUM> (e.g., a maximum temperature before the risk of delamination or other failure is unacceptably high, such as a melting temperature of glue used to adhere the compressible layer to the metal core), and such that the temperature of the exterior surface <NUM> is maintained above a minimum setpoint <NUM> (e.g., a minimum temperature to ensure proper melting of the contact layer of the polymer film during lamination).

<FIG> is a flow chart depicting a process <NUM> for controlling the temperature of an application roll during a lamination process according to certain aspects of the present disclosure. Process <NUM> can use the application roller <NUM> and lamination system <NUM> of <FIG>. At optional block <NUM>, a compressible layer of the application roll can be preheated. As described herein, the compressible layer can be preheated using heated cooling fluid and/or an external heater. Other mechanisms can be used to preheat the compressible layer (e.g., resistive heaters embedded within the metal core).

At block <NUM>, compressive forces are applied between the preheated metal strip and the application roll. Compressive forces can be applied to securely adhere the polymer film to the metal strip.

At block <NUM>, a temperature associated with a surface of the compressible layer can be determined. The temperature can include a temperature of an internal surface or external surface of the compressible layer. Determining a temperature can include directly measuring the temperature of the compressible layer, measuring a temperature of an adjacent element and inferring the temperature of the compressible layer, or using a model with or without input from other sensors. At block <NUM>, parameters of the coolant source can be adjusted based on the temperature determined at block <NUM>. The parameters of the coolant source can adjust the amount of cooling or heating provided to the compressible layer from the coolant passing through the application roll at block <NUM>. The parameters of the coolant source can include parameters associated with pressure sources, valves, heat exchangers, and other such parameters. Adjusting parameters of the coolant source can result in a change in the volumetric flow rate or temperature of the coolant, among other characteristics.

At block <NUM>, the coolant is passed through the application roll. The coolant can be passed according to the parameters set at block <NUM> or according to previously set parameters. Passing coolant through the application roll can including inducing a temperature gradient in the application roll. The temperature gradient can be induced such that the temperature of the internal surface of the compressible layer is maintained below a maximum setpoint and the temperature of the external surface of the compressible layer is maintained above a minimum setpoint.

During continuous lamination, coolant can be continuously flowing through the application roll at block <NUM> while the compressive forces are being applied between the application roll and the preheated metal strip at block <NUM>. During continuous lamination, the temperature of a surface of the compressible layer can be continuously or repeatedly determined at block <NUM> to provide continuous or repeated adjustment of the parameters of the coolant source at block <NUM>.

In some cases, process <NUM> can be performed without block <NUM> if inferences or models are used to determine appropriate parameters for the coolant source.

In some cases, the systems and methods described with reference to <FIG> can enable lamination of film to metal strips at high speeds and with greatly reduced risk of air entrapment or blistering. In some cases, these systems and methods can be used to control the amount of air entrapment or blistering to produce certain desirable results. For example, increased air entrapment or blistering may be preferable for certain use cases where lower thermal conductivity or rougher surfaces are desirable. In some cases, these systems and methods can be advantageously used when the laminated metal strip is to be annealed, however these systems and methods can also be used to provide laminated metal strip that is not thereafter annealed.

<FIG> is a graphical matrix depicting a set <NUM> of samples of laminated aluminum metal processed and tested according to certain aspects of the present disclosure. Set <NUM> is arranged vertically according to the pretreatment method used (e.g., conversion layer applied, such as according to process <NUM>) and horizontally according to the annealing temperature used (e.g., T<NUM> at block <NUM> of process <NUM>). Testing and comparing samples, as seen in <FIG>, can inform a determination of what combination(s) of pretreatment nietliod(s) and annealing temperature(s) would produce desirable results. Separate from differing pretreatment and annealing, each of the samples of the set <NUM> includes an aluminum sheet that has been laminated with the same type of film.

Each sample of the set <NUM> displays the results of similar testing procedures, including an acid bath test and a delamination test. For the acid bath test, approximately the lower two-thirds of each sample was submerged into a <NUM>% acetic acid bath at <NUM> for <NUM> minutes. Some degree of blushing can be seen in each sample, with some samples having more or less blushing than others. The level of blushing was scored on a scale of <NUM>-<NUM> according to visual inspection, with a score of <NUM> being borderline desirable and a score of <NUM> being the best performance (e.g., minimal blushing). For the delamination test, each sample was scratched with a material having a hardness greater than the aluminum metal strip (e.g., greater than the aluminum itself and/or greater than the conversion layer of the metal strip) in various directions. Generally, the delamination test includes a diagonal scratching pattern and a vertical-horizontal scratching pattern. The presence of delamination and a determination of the amount of delamination was recorded for each sample. The presence of delamination can be easily seen, especially in the vertical-horizontal scratching pattern. The amount of delamination can be determined based on visual inspection.

The first row of samples, including samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM> were all pre-treated using a silane-based (e.g., silicon tetrahydride-based) pretreatment. The second row of samples, including samples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> were all pre-treated using a chromium-III-based (e.g., chromium sesquioxide-based) pretreatment. The third row of samples, including samples <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> were all pre-treated using a Titanium/Zirconium-based pretreatment.

The first column of samples, including samples <NUM>, <NUM>, <NUM> were all prepared without post-lamination annealing (e.g., without performing block <NUM> of process <NUM>). The second column of samples, including samples <NUM>, <NUM>, <NUM> were all annealed at <NUM> after lamination (e.g., T<NUM> = <NUM> during block <NUM> of process <NUM>). The third column of samples, including samples <NUM>, <NUM>, <NUM> were all annealed at <NUM> after lamination (e.g., T<NUM> = <NUM> during block <NUM> of process <NUM>). The fourth column of samples, including samples <NUM>, <NUM>, <NUM> were all annealed at <NUM> after lamination (e.g., T<NUM> = <NUM> during block <NUM> of process <NUM>). The fifth column of samples, including samples <NUM>, <NUM>, <NUM> were all annealed at <NUM> after lamination (e.g., T<NUM> = <NUM> during block <NUM> of process <NUM>).

As seen in <FIG>, samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, which were annealed at temperatures at or above <NUM>, such as above <NUM>, after lamination performed well in the delamination tests, with little or no delamination of the film apparent after the tests. The amount of delamination was substantially worse with no annealing or annealing temperatures at or below <NUM>.

The blushing performance of the samples of set <NUM> can be seen in <FIG> and/or quantified as follows on a scale of <NUM>-<NUM> with <NUM> being the best. Samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can have blushing values of <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively. Samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can have blushing values of <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively. Samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM> can have blushing values of <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, respectively. Of note, the blushing performance can be characterized by comparing the approximately lower two-thirds of each sample to a sample or portion of aluminum metal that either has not been exposed to any acid test or similar conditions, or has been exposed to a neutral bath (e.g., deionized water bath) under similar conditions (e.g., time and temperature) as the acid-tested samples. For example, while the difference in color between the top one-third and lower two-thirds of sample <NUM> may be only slight, the blushing performance of sample <NUM> may be characterized as a <NUM> when compared against an untreated piece of aluminum metal.

Claim 1:
A method for preparing can end stock (<NUM>), comprising:
pre-heating a metal strip (<NUM>) to a first temperature below <NUM>;
laminating a polymer film (<NUM>) to a first side of the metal strip (<NUM>) to produce a laminated metal strip (<NUM>), wherein a main component of the polymer film (<NUM>) has a melting temperature above the first temperature (T<NUM>); and
annealing the laminated metal strip (<NUM>) at an annealing temperature (T<NUM>), wherein the annealing temperature (T<NUM>) is higher than the melting temperature of the polymer film (<NUM>), characterized in that annealing the laminated metal strip (<NUM>) includes raising the temperature of the polymer film (<NUM>) for a duration sufficient to melt the polymer film into a surface texture of the metal strip, and
in that the method further comprises decreasing a height of the surface roughness of the metal strip (<NUM>) to a value lower than a thickness of a contact layer of the polymer film (<NUM>) prior to laminating the polymer film (<NUM>) to the first side of the metal strip (<NUM>).