Patent Description:
Certain metal products, such as aluminum beverage cans, may require or otherwise benefit from a protective layer 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 layers on the interior surfaces of metal products. For example, the protective layer must adequately adhere to the metal product. Conventional protective layers have been found to demonstrate undesirable susceptibility to damage, such as by crazing and/or feathering. Thus, conventional protective layers are ineffective.

<CIT> is directed to an improved aluminum can end stock (CES). The CES includes 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 and a lacquered coating on an exterior-facing side. The CES is formed by performing an annealing process on the laminated metal strip, wherein the metal strip is raised to an annealing temperature above the melting point of the polymer for a sufficient duration to render the polymer amorphous. In some cases, the polymer film laminated to the metal strip is a polyethylene terephthalate (PET) film. <CIT> is also directed to improved aluminum can end stock (CES). The CES includes an adhered polymer coating exhibiting low feathering and high performance in various acid tests. The low feathering and resistance to acid tests is accomplished by incorporating a copolymer adhesion promoter film to an aluminum alloy before lamination. In some cases, the metal strip is pretreated with a conversion layer, which can include compounds of trivalent chromium (Cr(III)) and phosphates or titanium and zirconium. <CIT> is directed to a method for coating a substrate made of an aluminum alloy in the AA3000 or AA5000 series comprising the following steps: a) coating by (co-)extrusion of a polypropylene modified by maleic anhydride adhesion layer on each face of said substrate, and a surface layer made of polypropylene comprising at least one slip agent, so as to form a metalloplastic strip, b) calendering said metalloplastic strip, c) heat treatment of said metalloplastic strip, d) cooling of the metalloplastic strip, to obtain an H48 metallurgical temper and a coefficient of friction of <NUM> or less. The method is particularly suitable for the fabrication of food packaging and particularly for beverage can lids. <CIT> is directed to a method for preparing a metal product comprising applying a polymer film to a surface of a metal substrate, then applying a layer of wax to an outer layer of the polymer film at a coating weight of from <NUM>/m <NUM> to less than <NUM>/m<NUM> and at a thickness of from <NUM> to <NUM>, and heating the polymer film and the layer of wax to a temperature above a melting temperature of the polymer film to result in the metal product, wherein the temperature above the melting temperature of the polymer film is greater than <NUM>° C. ; and wherein the metal product resulting from the heating step comprises the polymer film applied to the surface of the metal substrate and the layer of wax adhered to the outer layer of the polymer film. <CIT> is directed to laminates comprising an aluminum sheet and multilayer polyester film, in particular aromatic polyester films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT) or polyethylene naphthalate (PEN), said polyester films having preferably a biaxial orientation, and is directed to the manufacture and the use of the laminates to produce beverage can ends. <CIT> is directed to a can for canning obtained by seaming a body member and an easily openable closure formed from an aluminum material, said easily openable closure being composed of an aluminum substrate having a score formed so as to reach halfway in the thickness direction of the aluminum substrate, an inside surface material of a crystalline thermoplastic resin film having a tensile strength of <NUM> to <NUM>/mm<NUM> provided on that surface of the aluminum substrate which faces the inside surface of the can, a layer of an adhesive and/or an adhesion promoting agent interposed between the substrate and the inside surface material and bonding the substrate and the inside surface material with an adhesion strength of at least <NUM>/<NUM> width, and a layer of an epoxy-type thermosetting resin film containing a lubricant applied to the surface of the inside surface material.

The present disclosure provides a process for preparing a crazing-resistant can end stock as defined in claim <NUM>, comprising: applying a pretreatment coating to a first side of a metal strip, wherein the pretreatment coating has an average thickness of from <NUM> to <NUM> and wherein the metal strip comprises AA3104, AA5006 or AA5182 series aluminum alloys; laminating a polymer film to the first side of the metal strip to form a laminated metal strip, wherein the polymer film is adhered to at least a portion of the pretreatment coating and wherein the polymer film comprises a polyethylene terephthalate film; and annealing the laminated metal strip at an annealing temperature, wherein the annealing temperature is greater than <NUM> and less than <NUM>. In some cases, the can end stock exhibits no visible crazing. In some cases, the first side of the metal strip corresponds to an interior-facing side of a can end formed from the metal strip. In some cases, the pretreatment coating comprises a polymer or co-polymer. In some cases, the annealing temperatures is less than <NUM>.

In some aspects, the present disclosure provides a can end stock product prepared according to any of the process described herein. In some cases, the first side of the metal strip corresponds to an exterior-facing side of the can end stock product. In some cases, the polymer film has a thickness less than <NUM>.

In some aspects, the present disclosure provide a beverage can comprising a body piece and an end cap, wherein the end cap is formed from can end stock prepared according to any of the process described herein.

The disclosure is described in detail below with reference to the appended drawings, wherein like numerals designate similar parts.

Described herein is a process for producing can end stock from a metal strip, wherein the metal strip is an aluminum strip. In the process described herein, a polymer film, wherein the polymer film is a polyethylene terephthalate film, is laminated to an interior side of the metal strip. The resultant can end stock can be used, for example, in beverage cans.

The can end stock produced according the methods described herein advantageously exhibit improved properties. In particular, the can end stock exhibits resistance to crazing (as defined below). In some cases, the can end stock described herein also exhibits low feathering. The methods described herein also provide a more efficient means of applying protective film(s) to a metal strip.

As explained further in the present disclosure, it has been found that conventional polymer films (such as polyethylene terephthalate) may be highly susceptible to crazing. Conventional polymer films are particularly prone to crazing during a seaming process, whereby can end stock and can body stock are joined. It has been found that seaming processes initiate, encourage, or otherwise exacerbate crazing of the polymer films.

Furthermore, it has been found that process conditions impact the susceptibility of polymer films to crazing. In particular, annealing laminated metal strips at lower temperatures beneficially reduces the susceptibility of the produced can end stock to crazing. Whereas conventional processes encourage high annealing temperatures to produce a polymer film with higher adhesion and resistance to feathering, the novel process described herein anneal at relatively lower temperatures and produce a can end stock with good adhesion as well as resistance to crazing. Said another way, the present disclosure provides a process for producing crazing-resistant can end stock.

As used herein, the terms "invention," "the invention," "this invention" and "the present invention" are intended to refer broadly to all of the subject matter of this patent application and the claims below.

In this description, reference is made to alloys identified by aluminum industry designations, such as "series" or "7xxx. " For an understanding of the number designation system most commonly used in naming and identifying aluminum and its alloys, see "International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys" or "Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot," both published by The Aluminum Association.

Aluminum alloys are described herein in terms of their elemental composition in weight percentage (wt. %) based on the total weight of the alloy. The remainder is aluminum, with a maximum wt. % of <NUM> % for the sum of the impurities.

As used herein, "crazing" refers to the formation and/or propagation of small cracks on or close to the surface of and/or on the opposite face of a protective layer (e.g., polymer film) on the metal strip, especially during a process for seaming, e.g., of a can end stock to a can body stock. In some cases, the cracks extend through the protective layer (e.g., polymer film). i.e., from the surface of the protect layer to the surface facing the metal strip.

As used herein, "feathering" refers to the elongation and delamination of in a protective layer (e.g., polymer film) on the metal strip, especially at breaks in the metal, such as the orifice created when opening a beverage can.

Reference is made in this application to alloy condition or temper. For an understanding of the alloy temper descriptions most commonly used, see "American National Standards (ANSI) H35 on Alloy and Temper Designation Systems. " An F condition or temper refers to an aluminum alloy as fabricated. An O condition or temper refers to an aluminum alloy after annealing. A T1 condition or temper refers to an aluminum alloy cooled from hot working and naturally aged (e.g., at room temperature). A T2 condition or temper refers to an aluminum alloy cooled from hot working, cold worked, and naturally aged. A T3 condition or temper refers to an aluminum alloy solution heat treated, cold worked, and naturally aged. A T4 condition or temper refers to an aluminum alloy solution heat treated and naturally aged. A T5 condition or temper refers to an aluminum alloy cooled from hot working and artificially aged (at elevated temperatures). A T6 condition or temper refers to an aluminum alloy solution heat treated and artificially aged. A T7 condition or temper refers to an aluminum alloy solution heat treated and artificially overaged. A T8x condition or temper refers to an aluminum alloy solution heat treated, cold worked, and artificially aged. A T9 condition or temper refers to an aluminum alloy solution heat treated, artificially aged, and cold worked.

As used herein, the meaning of "a," "an," or "the" includes singular and plural references unless the context clearly dictates otherwise.

As used herein, the meaning of "room temperature" can include a temperature of from about <NUM> to about <NUM>, for example about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM>, or about <NUM>.

All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of "<NUM> to <NUM>" should be considered to include any and all subranges between (and inclusive of) the minimum value of <NUM> and the maximum value of <NUM>; that is, all subranges beginning with a minimum value of <NUM> or more, e.g. <NUM> to <NUM>, and ending with a maximum value of <NUM> or less, e.g., <NUM> to <NUM>.

The present disclosure provides a process for producing can end stock from a metal strip. More specifically, the method described herein includes applying a pretreatment coating to a first side of a metal strip and laminating a polymer film to the first side of the metal strip. The polymer film is applied to an aluminum alloy, such as a continuous coil of an aluminum alloy.

A 3xxx series aluminum alloy for use as the metal strip includes AA3104.

5xxx series aluminum alloys for use as the metal strip include AA5006 or AA5182.

The metal strip comprises AA3104, AA5006, AA5182, or combinations thereof.

Aluminum alloy products are described throughout the disclosure. The product may include monolithic materials, as well as non-monolithic materials such as roll-bonded materials, clad materials, composite materials, or various other materials. In some examples, the metal article is a metal coil, a metal strip, a metal plate, a metal sheet, a metal billet, a metal ingot, or the like.

The metal strip can be prepared from an alloy of any suitable temper. In certain examples, the alloys can be used in F, O, T3, T4, T6, or T8x tempers. The alloys can be produced by direct chill casting (including direct chill co-casting) or semi-continuous casting, continuous casting (including, for example, by use of a twin belt caster, a twin roll caster, a block caster, or any other continuous caster), electromagnetic casting, hot top casting, or any other casting method.

The process described herein, and the can end stock produced therefrom, comprise applying a pretreatment coating to the metal strip. In particular, the processes of the present disclosure include applying the pretreatment coating on a side (e.g., the first side) of the metal strip and laminating a polymer film thereon. Said another way, the polymer film may be adhered to at least a portion of the pretreatment coating. In some cases, the pretreatment coating is applied to a side of the metal strip that corresponds to an interior-facing side of a can end formed from the metal strip. Thus, the pretreatment coating forms a portion of the product side of the can end stock.

As illustrated in the below examples, the pretreatment coating can provide improved feathering performance. In particular, the adhesion of the polymer film to the metal strip can be controlled (e.g., improved) by the selection of an appropriate pretreatment coating and by controlling process parameters (such as the annealing temperature, described below).

In some embodiments, the pretreatment coating is a pretreatment applied to the metal strip, e.g., a pretreatment suited to the metal strip. In some cases, the pretreatment coating may comprise a polymer or co-polymer, e.g., a poly(vinylphosphonic acid-co-acrylic acid) co-polymer. In some embodiments, commercial examples of suitable pretreatments that can be employed as the pretreatment coating include Addibond <NUM> - CP <NUM> from Solvay (Brussels, Belgium).

The pretreatment coating has an average thickness of from <NUM> to <NUM>, e.g., from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

In terms of lower limits, the pretreatment coating may have an average thickness greater than <NUM>, e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In terms of upper limits, the pretreatment coating may have an average thickness less than <NUM>, e.g., less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>.

The process described herein, and the can end stock produced therefrom, comprise laminating a polymer film to the metal strip. In particular, the processes of the present disclosure include laminating the polymer film on a side (e.g., the first side) of the metal strip that corresponds to an interior-facing side of a can end formed from the metal strip. Thus, the polymer film forms a portion of the product side of the can end stock. As further detailed in the examples below, the use of a polymer film on an interior-facing side of a can end (e.g., as opposed to a lacquer) beneficially improves the quality of the can end product. Furthermore, the polymer films described herein (e.g., produced according to the described process conditions) exhibit reduced feathering. Additionally, lamination of a polymer film on the metal strip is more reproducible and cleaner because impurities are typically rare in polymer films.

The polymer film includes polyethylene terephthalate (PET). In some cases, the polymer film laminated to the metal strip is a biaxially oriented polymer, such as a biaxially-oriented polyethylene terephthalate (BoPET) film. Commercial suppliers of polymer films suitable for use herein include, for example, Toray Plastics (Front Royal, VA), Mitsubishi Polyester Film (Greer, SC), and DuPont Performance Polymers (Wilmington, DE).

In some embodiments, the polymer film further comprises a colorant, such as a dye or a pigment. Said another way, the polymer film may be a colored polymer film (e.g., a colored PET film). The colorant used in the colored polymer film is not particularly limited. Suitable colorants include, for example, titanium dioxide (e.g., to produce a white polymer film).

In some embodiments, the polymer film has an average thickness of from <NUM> to <NUM>, e.g., from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

In terms of lower limits, the polymer film may have an average thickness greater than <NUM>, e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In terms of upper limits, the polymer film may have an average thickness less than <NUM>, e.g., less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>.

Examples of suitable average thicknesses of the polymer film include <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and any thickness there between.

In some embodiments, the process of the present disclosure includes laminating multiple layers of polymer film on the metallic strip. In these embodiments, each layer of polymer film may independently be a polymer film as described above. In some cases, multiple layers of polymer film are laminated on the metallic strip, and one or more of the layers are identical (e.g., in terms of composition and/or thickness). In some cases, multiple layers of polymer film are laminated on the metallic strip, and the layers are not identical (e.g., in terms of composition and/or thickness).

As noted above, conventional can end stock products preferentially include polymer films that have been temperature treated (e.g., a high temperature treatment, such as pretreatment). It was believed that high temperature treatment was necessary to provide certain properties, such as high adhesion and low feathering. Conventionally temperature treated polymer films, however, are highly susceptible to crazing. In particular, crazing is seen close to or on the surface of amorphous polymer films (e.g., PET films) that are laminated on an interior-facing (e.g., product) side of a can end stock. It has been found that temperature treatment (e.g., high temperature treatment) alters the conformation of polymer films. The modified conformation of the polymer films may be more susceptible to crazing. Stress applied to the can end stock (e.g., during a seaming process with the can body stock) exacerbates this crazing. Crazing on the interior-facing side of the can end stock is particularly problematic because the products contained within the can (e.g., a liquid beverage) can further exacerbate the crazing and/or react with the metal strip. This can impact the integrity and quality of both the can and the product by leaching metal from the metal strip.

To address the issue of crazing, in the process described herein, as well as the can end stock produced therefrom, the polymer film does not comprise a high temperature treated polymer. Said another way, the conformation of the polymer film is not substantially modified. In some cases, the polymer film has a similar conformation before and after production of the can end stock. In some cases, the polymer film has the same conformation before and after production. In some embodiments, this is accomplished by preventing or limiting the melting of the polymer film during lamination. This is accomplished by preventing or limiting the exposure of the polymer film to high temperatures, e.g., temperatures greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. Utilizing a non-temperature treated polymer film, as described herein, advantageously produces a can end stock with low susceptibility to crazing. That is, the can end stock produced according to the present disclosure is crazing-resistant. Beneficially, the can end stock may also exhibit low susceptibility to feathering.

In some cases, the suitability of a polymer film for the can end stock may be assessed by a Fourier-transform infrared spectroscopy (FTIR) test developed by the present inventors. FTIR is a technique used in various quantitative analyses to obtain an infrared spectrum of absorbance or emission of a solid, liquid, or gas. In the FTIR test of the present disclosure, an FTIR absorbance spectrum of the polymer film is analyzed to determine the suitability of the polymer film for use in the can end stock. In particular, the FTIR test assesses the ratio (A/B) of the absorbance peak intensity at a first wavenumber (A) to the absorbance peak intensity at a second wavenumber (B).

The FTIR absorbance spectrum may be obtained by commercially available spectrometers, including, for example, the model <NUM> from Varian, Inc. (Palo Alto, CA). In some cases, the FTIR spectrometer may include an attenuated total reflectance (ATR) attachment, such as a diamond ATR. One example of a commercially available ATR attachment is GladiATR from Pike Technologies (Madison, WI). In some embodiments, the FTIR absorbance spectrum is obtained by measuring at one location on the polymer film. In some embodiments, the FTIR absorbance spectrum is obtained by measuring at multiple locations (e.g., at least two, at least three, or at least four locations) on the polymer film and averaging the outputs from the spectra.

The suitability of the polymer film for the can end stock may be determined by evaluating and comparing the relative intensity of two absorbance peaks. That is, the suitability of the polymer film may be determined from the ratio (A/B) of the FTIR absorbance peak intensity at a first wavenumber (A) to the absorbance peak intensity at a second wavenumber (B). In some cases, the suitability of the polymer film (as used herein) refers to the susceptibility of the polymer film to crazing before and/or after annealing.

In some embodiments, the first absorbance peak (A) of the FTIR ratio is a peak at a wavenumber from <NUM>-<NUM> to <NUM>-<NUM>. In terms of lower limits, the first absorbance peak (A) may be a peak at a wavenumber greater than <NUM>-<NUM>, e.g., greater than <NUM>-<NUM>, greater than <NUM>-<NUM>, greater than <NUM>-<NUM>, or greater than <NUM>-<NUM>. In terms of upper limits, the first absorbance peak (A) may be a peak at a wavenumber less than <NUM>-<NUM>, e.g., less than <NUM>-<NUM>, less than <NUM>-<NUM>, less than <NUM>-<NUM>, or less than <NUM>-<NUM>.

In some embodiments, the first absorbance peak (A) may be at wavenumber <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, or <NUM>-<NUM>, or at any wavenumber there between.

In some embodiments, the second absorbance peak (B) of the FTIR ratio is a peak at a wavenumber from <NUM>-<NUM> to <NUM>-<NUM>. In terms of lower limits, the second absorbance peak (B) may be a peak at a wavenumber greater than <NUM>-<NUM>, e.g., greater than <NUM>-<NUM>, greater than <NUM>-<NUM>, greater than <NUM>-<NUM>, or greater than <NUM>-<NUM>. In terms of upper limits, the second absorbance peak (B) may be a peak at a wavenumber less than <NUM>-<NUM>, e.g., less than <NUM>-<NUM>, less than <NUM>-<NUM>, less than <NUM>-<NUM>, or less than <NUM>-<NUM>.

In some embodiments, the second absorbance peak (B) may be at wavenumber <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, or <NUM>-<NUM>, or at any wavenumber therebetween.

Polymer films that exhibit a high FTIR ratio (A/B) are particularly suitable for can end stock described herein. In particular, utilizing a polymer film having a high FTIR ratio produces a can end stock with low susceptibility to crazing. In some embodiments, the polymer film exhibits an absorbance peak intensity ratio (A/B) greater than <NUM>, e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In terms of upper limits, the absorbance peak intensity ratio (A/B) of the polymer film may be less than <NUM>, e.g., less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>.

In some embodiments, the can end stock produced according the present disclosure comprises a layer of lacquer. In some cases, for example, a layer of lacquer may be applied to a surface of the metal strip, e.g., the external-facing surface. In these embodiments, the lacquer forms a protective layer between the metal strip and the contents of the can end stock (e.g., the contents of a beverage can formed from can end stock).

The composition of the lacquer suitable for use in the processes described herein is not particularly limited. In some cases, the lacquer comprises a water-based and/or solvent-based composition, which preferably may be sprayed, poured, or otherwise applied to a surface of the metal strip. In some embodiments, the lacquer applied to a surface of the metal strip comprises an epoxy-based solution. A commercial example of a composition suitable for use as a lacquer for the present disclosure includes packaging coatings from AkzoNobel (Amsterdam, Netherlands).

In some embodiments, the layer of lacquer has an average thickness of from <NUM> to <NUM>, e.g., from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

In terms of lower limits, the layer of lacquer may have an average thickness greater than <NUM>, e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In terms of upper limits, the layer of lacquer may have an average thickness less than <NUM>, e.g., less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>.

Examples of suitable average thicknesses of the layer of lacquer include <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and any thickness therebetween.

In some cases, the thickness of the layer of lacquer may be expressed in terms of basis weight. In some embodiments, the layer of lacquer has a basis weight of from <NUM>/m<NUM> to <NUM>/m<NUM>, e.g., from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, from <NUM>/m<NUM> to <NUM>/m<NUM>, or from <NUM>/m<NUM> to <NUM>/m<NUM>.

In terms of lower limits, the layer of lacquer may have a basis weight greater than <NUM>/m<NUM>, e.g., greater than <NUM>/m<NUM>, greater than <NUM>/m<NUM>, greater than <NUM>/m<NUM>, or greater than <NUM>/m<NUM>. In terms of upper limits, the layer of lacquer may have a basis weight less than <NUM>/m<NUM>, e.g., less than <NUM>/m<NUM>, less than <NUM>/m<NUM>, less than <NUM>/m<NUM>, less than <NUM>/m<NUM>, or less than <NUM>/m<NUM>.

Examples of suitable basis weight of the layer of lacquer include <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, and any thickness therebetween.

In some embodiments, the can end stock produced according the present disclosure comprises an adhesion coating between the metal strip and the layer of lacquer. In particular, an adhesion coating may be applied to the metal strip, and the lacquer may be applied thereon. The adhesion coating beneficially fixes the lacquer to the metal strip. In some embodiments, the adhesion coating is a pretreatment applied to the metal strip, e.g., a pretreatment suited to the metal strip. The adhesion coating between the metal strip and layer of lacquer may be the same as or different from the adhesion coating between the polymer film and the metal strip. Commercial examples of suitable pretreatments that can be employed as the adhesion coating between the metal strip and the lacquer include titanium zirconium (Ti-Zr) based pretreatments or chromium (Cr3) based pretreatments, such as Bonderite from Henkel Adhesive Technologies (Düsseldorf, Germany).

The present disclosure provides a process for preparing can end stock. The process described herein produces crazing-resistant can end stock. In some embodiments, the processes described herein produce a laminated can end stock that also exhibits high performance in other testing parameters, such as in an acetic acid test which can assess the corrosion resistance of the laminate against acidic conditions that can result in delamination. These processes can include applying a pretreatment coating to a metal strip, laminating a polymer film to the metal strip, and annealing the laminated metal strip at an annealing temperature (TA). According to the processes of the present disclosure, annealing the laminated metal strip comprises heating to a temperature TA that is greater than <NUM> and less than <NUM>. Annealing at this temperature prevents the polymer film from becoming amorphous (e.g., by melting) and thereby greatly improves the performance characteristics of the produced can end stock.

In some embodiments, the metal strip is coated on both sides. In embodiments according to the present disclosure, 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 polymer film while maintaining high cosmetic and functional performance on the exterior of the can end stock through use of a lacquer.

In some cases, the laminated metal stock is passed directly from a lamination process into an annealing process (e.g., into an annealing oven). 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 oven). In some cases, the laminated metal stock is quenched (e.g., air quenched or water quenched) before entering into the lacquer application system.

The process described herein, and various additional features and examples thereof, are described herein 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.

<FIG> is a schematic diagram of a system <NUM> for preparing can end stock according to certain aspects of the present disclosure. A metal strip <NUM> is passed into a pretreatment coating application system <NUM> that applies a pretreatment coating to the metal strip <NUM>. The pretreatment coating application system <NUM> can be any suitable system for applying a pretreatment coating to the metal strip <NUM>.

In some cases, the metal strip <NUM> may be processed before entering the pretreatment coating application system. In some embodiments, the surface of the metal strip <NUM> may be degreased (e.g., using an acid solution) to clean the surface. In some embodiments, the metal strip <NUM> may be preheated before entering the pretreatment coating application system.

The pretreated metal strip <NUM> passes into a lamination system <NUM>. The metal strip <NUM>, as a pretreated 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>. In some cases, the lamination system <NUM> is a hot melt lamination system. A laminated metal strip <NUM> exits the lamination system <NUM>, combining the metal strip <NUM> with a polymer film <NUM>.

In some embodiments, the laminated metal strip <NUM> can pass into an optional 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 oven <NUM>. In some cases, the lacquer application system <NUM> is upstream of the lamination system <NUM> or the pre-heating oven <NUM>. In some cases, the lacquer application system <NUM> is downstream of both the lamination system <NUM> and the annealing oven <NUM>. In the embodiment shown in <FIG>, the lacquer application system <NUM> is located between the lamination system <NUM> and the annealing oven <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 oven <NUM>. In some cases, where no lacquer application system <NUM> is used between the lamination system <NUM> and the annealing oven <NUM>, laminated metal strip <NUM> can pass into the annealing oven.

The annealing oven <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 oven <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 oven <NUM> before passing or coming into contact with other machinery or systems.

The annealing oven <NUM> raises the temperature of the lacquered, laminated metal strip <NUM> to an annealing temperature (TA). The annealing temperature TA may be lower than the melting temperature (Tm) of the polymer film <NUM>. In some embodiments, the annealing temperature TA is a temperature e.g., from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. In terms of lower limits, T<NUM> may be greater than <NUM>, e.g., greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, or greater than <NUM>. In terms of upper limits, TA is less than <NUM>, and may be less than <NUM>, or less than <NUM>.

The lacquered, laminated metal strip <NUM> spends a duration in the annealing oven <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 oven <NUM> can be based on oven 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 oven <NUM>.

After exiting the annealing oven <NUM>, the can end stock <NUM> (e.g., annealed, lacquered and laminated metal strip) may optionally be quenched, such as in air or a volume of quenching liquid (e.g., water) or by application of coolant to the can end stock <NUM>. The can end stock <NUM> can be cooled immediately after exiting the annealing oven <NUM>, through quenching or otherwise.

In some cases, the can end stock <NUM> produced by system <NUM> can include a metal strip <NUM> to which a layer of laminated polymer film <NUM> has been applied to a first side and to which an optional layer of lacquer <NUM> has been applied to a second side, as shown in <FIG>.

<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 laminated polymer film <NUM> and an optional layer of lacquer <NUM>. Sandwiched between the laminated polymer film <NUM> and the metal strip <NUM> and between the optional layer of lacquer <NUM> and the metal strip <NUM> is the pretreatment coating <NUM>.

<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 polymer film and lacquer.

<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 shown 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 by the can end blank <NUM> from <FIG> to a can body.

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 laminated polymer film is present on the interior-facing side.

A conventional seaming process may be used to form the beverage can of <FIG> from the can end blank <NUM> of <FIG> and a can body. Described herein are methods for preparing a beverage can comprising seaming a can end blank, formed from the can end stock described herein, to a can body. The seaming process may include the steps of placing the can end blank over the can body, and applying a seaming chuck to the can end. The method may also include a step of seaming the can end and the can body, optionally with a seaming roll. The seaming roll may form and/or engage a curl in the can end, which may be compressed the peripheral curl against the chuck to form a seal between the can end and the can body.

As noted above, conventional can end stock (e.g., those including a polymer film in an amorphous state) exhibit crazing following a seaming process. The can end stock of the present disclosure, on the contrary, is crazing resistant. In some embodiments, for example, the can end stock exhibits no visible crazing before and/or after a seaming process.

<FIG> is an isometric cutaway diagram depicting the multiple layers of a section of can end stock <NUM> prepared according to the present disclosure. The can end stock <NUM> can include a layer of metal <NUM>, such as aluminum (e.g., an aluminum alloy) surrounded by a laminated polymer film <NUM>, and an optional layer of lacquer <NUM>. The can end stock <NUM> can be the can end stock <NUM> of <FIG>.

<FIG> is a flowchart depicting a process <NUM> for preparing can end stock according to embodiments of the present disclosure. At block <NUM>, the metal strip is provided. The metal strip can be an aluminum strip suitable for forming can end stock. At block <NUM>, the surface of the metal strip is optionally degreased (e.g., using an acid solution). At block <NUM>, the pretreatment coating is applied to the metal strip. At block <NUM>, the metal strip is laminated with a polymer film, i.e., a PET film. At block <NUM>, the laminated metal strip is annealed at an annealing temperature TA. At block <NUM>, the annealed metal strip is optionally quenched (e.g., in air). At block <NUM>, a wax coating can be optionally applied to one or both sides of the metal strip.

<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 pretreated metal strip <NUM> may pass. The pretreated metal strip <NUM> can include a metal strip <NUM> that has been pretreated, such as by a pre-heating oven <NUM> of <FIG>. In some cases, the pretreated 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 pretreated 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 pretreated metal strip <NUM> from the polymer film <NUM>.

As noted above, the can end stock of the present disclosure, e.g., the can end stock produced according to the described processes, advantageously exhibits a number of improved properties.

In some embodiments, the can end stock of the present disclosure exhibits low susceptibility to crazing. Said another way, the present disclosure described crazing-resistant can end stock. As defined above, crazing refers to the formation and/or propagation of small cracks on or close to the surface of a protective layer (e.g., polymer film) on the metal strip, especially during a process for seaming, e.g., of a can end stock to a can body stock. In some embodiments, the can end stock exhibits no visible crazing. For example, the can end stock may exhibit no visible crazing before and/or after a seaming process.

In some cases, the can end stock of the present disclosure exhibits improved results on a <NUM>% strain test. As used herein, a <NUM>% strain test can include assessing the susceptibility of the can end stock to crazing in response to tensile stress. In particular, the strain test may simulate a seaming process, where crazing is particularly problematic. The test can include stamping a sample of the can end stock (e.g., using an automatic press). The sample may be stamped into any shape suitable for a tensile strength test. The stamped samples are then stressed by applying a <NUM>% strain with <NUM> N/mm<NUM>·s. Afterwards, the stressed samples are left, e.g., at room temperature, for <NUM> hours, during which time any crazing becomes visible.

In some cases, the <NUM>% strain test may be carried out on an aged sample to maximize the susceptibility of the sample to crazing. For example, the sample can end stock may be heated in an oven for several days (e.g., two days, three days, or four days) at a temperature <NUM> below the glass transition temperature of the polymer film.

In some cases, crazing may be visible on the can end stock, e.g., to the naked eye. In some cases, crazing may be visible with the help of a light source. For example, light may be shone on the sample from the direction of the camera and in a flat angle to the sample (e.g., parallel to the sample). In some embodiments, the light source may shine visible light on the sample. In some embodiments, the light source may shine UV light on the sample. To facilitate observation using a UV light source, the samples may be coated with a fluorescent marker. For example, the samples may be covered with a fluorescent marker (e.g., FBP-<NUM> from MET-L-CHEK (Santa Monica, CA)) for <NUM> minutes and rinsed with water. The fluorescence can greatly increase the visibility of crazing under a UV light.

In some embodiments, the can end stock exhibits no visible crazing after the strain test. In some embodiments, the can end stock exhibits no visible crazing under light after the strain test. In some embodiments, the can end stock exhibits no visible crazing under UV light after the strain test.

In some embodiments, the can end stock of the present disclosure exhibits improved adhesion. In some cases, for example, the can end stock of the present disclosure exhibits improved results 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 cooling, 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. The degree of delamination is observed and, to the extent delamination occurs, valued on a scale from <NUM> (minimal delamination) to <NUM>. As used herein, a sample passes the <NUM>% acetic acid test if the sample demonstrates no or low delamination.

Conventional metal strips (e.g., metal strip having a layer of lacquer applied to an external surface) often score poorly on a <NUM>% acetic acid test. 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. In some embodiments, the can end stock disclosed herein passes the <NUM>% acetic acid test with low delamination. In some cases, the annealed, laminated can end stock disclosed herein passes <NUM>% acetic acid tests without delamination.

In some embodiments, the can end stock of the present disclosure exhibits reduced feathering. In some cases, for example, the can end stock of the present disclosure exhibits improved results on a standard feathering test. As used herein, a standard feathering test can be conducted on a can end and 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. In either feathering test, the amount of feathering can be measured, and the can end stock exhibiting a maximum amount of feathering less than <NUM> is said to pass the test.

In some examples, the can end stock described herein passes a standard feathering test. In some embodiments, the can end stock exhibits a maximum amount of feathering of less than <NUM>, e.g., less than <NUM>, less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>. This amount of feathering may be located at certain indicative positions along the orifice of the opened can end. The amount of feathering of the film also depends on the cutting, forming and stamping tool design of the product.

The following examples will serve to further describe the present invention without, however, constituting any limitation thereof.

Several samples of can end stock were prepared according to the disclosed methods. The samples were prepared using <NUM> thick AA <NUM> aluminum alloy as the metal strip. Each of the samples tested is shown in Table <NUM>. Each sample was pretreated, as indicated in Table <NUM>, and can end stock was prepared by laminating a <NUM> polymer film to a first side (internal) and annealing at an annealing temperature.

To evaluate the performance of the above sample can end stock, various tests were performed. To assess the susceptibility of the can end stock to crazing, several tests were carried out. Each sample was tested according to the FTIR test, described above, with the test for each sample being performed from the middle position of the sheet. The FTIR ratio (A/B) was calculated by comparing the absorbance peak intensity at about <NUM>-<NUM> (A) to the absorbance peak intensity at about <NUM>-<NUM> (B). To observe crazing, the <NUM>% strain test, described above, was carried out. Strain tests of Samples <NUM>-<NUM> were run on aged examples. For Samples <NUM>-<NUM>, after the <NUM>% strain test was carried out, the samples were coated in the fluorescent marker FBP-<NUM> from MET-L-CHEK (Santa Monica, CA) for <NUM> minutes and rinsed with water. A UV light was shone on the samples to better indicate crazing. The results of these tests are shown in Table <NUM>.

As the above samples demonstrate, aged can end stock becomes susceptible to crazing as the annealing temperature increased. This demonstrates that a low annealing temperature beneficially imparts crazing resistance.

To further assess susceptibility of the can end stock to aging, several samples (Samples <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) were selected for additional crazing testing. In this testing, the can end stock was subjected to a seaming process. Ends prepared from the sample can end stock were placed on empty can bodies (AA3104, <NUM>) and seamed with a laboratory seamer (Stiller DV10 PS-SD). To seam the can end to the body, the edge of the can end is curled and compressed around a rim of the body. After seaming, the can was stored for <NUM> hours. Afterward, the can end at the seam was covered in a fluorescence marker for <NUM> minutes, washed, and illuminated under UV light to observe any crazing. The results of this test are shown in Table <NUM>.

To further assess susceptibility of the can end stock to corrosion, several samples (Samples <NUM>, <NUM>, and <NUM>) were subjected to a pack-test corrosion evaluation. Ends prepared from the sample can end stock were placed on can bodies (AA3104, <NUM>) and seamed with a laboratory seamer (Stiller DV10 PS-SD). The cans were filled with different beverages. Afterward, the cans were stored for <NUM> months upside down, such that the seam between the can end and body was covered by the beverage. The cans were evaluated for corrosion at <NUM> months and <NUM> months. No corrosion was found, as reported in Table <NUM>.

The above samples again demonstrate that aged can end stock becomes susceptible to crazing as the annealing temperature increased. This further demonstrates that a low annealing temperature beneficially imparts crazing resistance and is beneficial for downstream commercial processes.

To assess adhesion, each sample was tested according to the <NUM>% acetic acid test, described above, with the test for each sample being performed from the middle position of the sheet. To the extent delamination was observed, it was valued on a scale from <NUM> (minimal delamination) to <NUM>. To assess feathering, the above-described test was carried out by immersing the sample in demineralized water at <NUM> for forty minutes. Feathering was assessed at a middle position of the sheet, and each sample was assessed twice. The results of these tests are shown in Table <NUM>.

Claim 1:
A process for preparing a crazing-resistant can end stock (<NUM>), comprising:
applying a pretreatment coating (<NUM>) to a first side of a metal strip (<NUM>), wherein the pretreatment coating (<NUM>) has an average thickness of from <NUM> to <NUM> and wherein the metal strip (<NUM>) comprises AA3104, AA5006 or AA5182 series aluminum alloys;
laminating a polymer film (<NUM>) to the first side of the metal strip (<NUM>) to form a laminated metal strip, wherein the polymer film (<NUM>) is adhered to at least a portion of the pretreatment coating (<NUM>) and wherein the polymer film (<NUM>) comprises a polyethylene terephthalate film; and
annealing the laminated metal strip at an annealing temperature, wherein the annealing temperature is greater than <NUM> and less than <NUM>.