Peelable and sealable cover material for containers

Abstract

A peelable and sealable lidstock comprised of a metal base and a sealing layer, the sealing layer containing (A) 70 wt% to 89 wt% of a copolymer having one or more polymerized olefin monomers and one or more polymerized ethylenically unsaturated (poly)carboxylic acid monomers, (B) 10 wt% to 29 wt% of a copolymer comprising one or more polymerized (meth)acrylate monomers, and (C) 1 wt% to 10 wt% of one or more inorganic particles, the inorganic particles characterized by a mass median diameter (D 50 ) comprised between 1 micrometer and 5 micrometers.

Description

Technical Field

[0001] This invention relates to a peelable and sealable lid for containers and a container sealed with the peelable and sealable lid. Background Technology

[0002] Containers with a metal sealing surface and a flexible peel-off cap are used in food products such as instant coffee, infant formula, and soup powder. The container has a metal body or a metal ring surrounding the open end portion of the container, and the cap is heat-sealed directly to the metal surface or a coating thereon. The cap can be peeled off the container, allowing easy access to the contents.

[0003] A capping material sealing to the container sealing surface typically has at least a metal foil layer and a sealing layer. The sealing layer can be a composite film (extruded polymer) or a heat-sealing varnish. Composite film sealing layers typically offer more robust performance, such as a wider sealing window and more consistent peel force values.

[0004] US 5,958,531 discloses a peelable and heat-sealable capping material for steel end containers. The capping material comprises a membrane containing: (a) 35 to 70 wt% of an ethylene-carboxylic acid copolymer, (b) 10 to 40 wt% of polybutene, and (c) at least 18 wt% of a particulate inorganic filler.

[0005] US 5,626,929 discloses a peelable and heat-sealable cover material comprising a metal or polymer substrate laminated with a monolayer film, the monolayer film comprising (a) 30% to 70% by weight of a butene-1 and ethylene copolymer, wherein ethylene comprises 1 to 15 mole percent of the copolymer, (b) 10% to 40% by weight of an ethylene homopolymer or an ethylene-vinyl acetate copolymer or an ethylene-methyl acrylate copolymer, and (c) at least 18% by weight of a particulate inorganic filler.

[0006] US2005276940 discloses a peelable and heat-sealable material suitable for bonding to a variety of substrates, the material comprising a solid substrate bonded to a membrane comprising (a) an aliphatic-aromatic copolyester, (b) particulate inorganic filler, (c) a butene-1 polymer, and (d) an ethylene-vinyl acetate copolymer, wherein the membrane comprises about 20% to 30% by weight of the inorganic filler.

[0007] US2004180160 discloses a cover material comprising a solid substrate laminated with a film comprising: (a) 15% to 25% by weight of butene-1 polymer, (b) 35% to 55% by weight of high-density polyethylene, (c) 5% to 15% by weight of polypropylene, and (d) at least 18% by weight of particulate inorganic filler.

[0008] US 4,414,053 discloses polymer blends and easy-peel films for the preparation of heat-sealable packaging made of polymer films, wherein the polymer compositions of these easy-peel films consist primarily of: (a) 100 parts by weight of an ethylene copolymer wherein about 70% to 98% by weight of ethylene and the balance being an alkyl ester of acrylic acid or methacrylic acid; and (b) 1 to 5 parts by weight of a polymer of a higher alkyl ester of acrylic acid or methacrylic acid, wherein the polymer is a homopolymer of the ester or a copolymer of the ester and ethylene, wherein the copolymer contains at least 25% by weight of the ester; and the alkyl group of the ester contains about 8 to about 24 carbon atoms.

[0009] Without questioning the relevant advantages of existing technology systems, there is still a need to provide containers with a peelable and sealable cap that has an improved combination of properties in terms of peel force, burst strength, and the footprint of residual seal layer on the edge of the metal container after peeling. Summary of the Invention

[0010] The present invention aims to provide a sealing layer on a peelable and sealable cover material that does not have the disadvantages of the prior art.

[0011] The object of the present invention is to provide a peelable sealing layer for sealing a cap to a container, the sealing layer providing a combination of: (a) a peel force that is approximately constant over a wide heat-sealing temperature range; (b) uniform and consistent cohesive failure in the sealing layer upon peeling; (c) high burst strength of the sealing cap; and (d) a distinct and uniform mark (footprint) on the sealing surface of the container after the cap has been peeled off.

[0012] This invention discloses a peelable and sealable cover material comprising a metal substrate and a sealing layer comprising a) 70% to 89% by weight of a copolymer (A) comprising one or more polymerized olefin monomers and one or more polymerized olefinically unsaturated (poly)carboxylic acid monomers, b) 10% to 29% by weight of a copolymer (B) comprising one or more polymerized (meth)acrylate monomers, and c) 1% to 10% by weight of one or more inorganic particles (C), characterized by a median diameter (D) of the inorganic particles (C). 50 (Including between 1 micrometer and 5 micrometers)

[0013] Some embodiments of the peelable and sealable cover material include inorganic particles (C), which are characterized by a particle size distribution comprising D particles smaller than 10 micrometers. 98 And D10 smaller than 1 micrometer.

[0014] The copolymer (A) may comprise 55% to 90% by weight of one or more polymerizable olefin monomers and 10% to 35% by weight of one or more polymerizable olefinically unsaturated (poly)carboxylic acid monomers selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, and itaconic acid, and the copolymer (B) may comprise one or more polymerizable (meth)acrylic acid C1-C8 ester monomers. The copolymer (A) may have 70% to 85% by weight of polymerized ethylene and 15% to 30% by weight of (meth)acrylic acid.

[0015] The copolymer (B) may contain up to 30% by weight of one or more olefinically unsaturated (poly)carboxylic acid monomers selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, and itaconic acid. The copolymer (B) may include a polymeric mixture of methyl methacrylate and butyl methacrylate. The copolymer (B) may also include a polymeric mixture of methyl methacrylate, butyl methacrylate, and methacrylic acid.

[0016] Inorganic particles (C) can be selected from the group consisting of halloysite, kaolinite, illite, montmorillonite, vermiculite, talc, sepiolite, palygorskite, pyrophyllite, and mixtures thereof. Inorganic particles (C) can have a density of 8 micrometers or smaller. 98 The particle size distribution. Inorganic particles (C) can have a D size of 6 micrometers or smaller. 98 Particle size distribution. The sealing layer may contain inorganic particles (C) between 1 wt% and 5 wt%.

[0017] The metal substrate for the peelable and sealable cover can be aluminum foil with a thickness between 20 and 200 micrometers. The thickness of the sealing layer can be between 2 and 13 micrometers. The thickness of the sealing layer can be between 4 and 10 micrometers. The thickness of the sealing layer can be between 6 and 9 micrometers.

[0018] This document also discloses a method for producing a peelable and sealable cover. The method includes the following steps: a) unwinding a roll of material with a metal substrate; b) applying a water-based paint comprising copolymer (A), copolymer (B), and inorganic particles (C) to the unwound metal substrate using a coating system; and c) drying the water-based paint to form a sealing layer. These steps produce a peelable and sealable cover comprising a metal substrate and a sealing layer, the thickness of which is between 2 micrometers and 13 micrometers. The water-based paint may have a solids content between 35% and 55% by weight.

[0019] This document also discloses a sealing container comprising a peelable cap sealed to a container sealing surface, the cap comprising a peelable and sealable cap material. The container sealing surface is a rigid ring. The average peel force between the peelable cap and the container sealing surface ranges from 8 N to 15 N according to ASTM F2824-10 (45° peel angle). The burst strength of the sealing container is at least 2 bar according to ASTM F1140 / F1140M-13 Test Method A. The container sealing surface exhibits a continuous, well-defined footprint of the sealing layer remaining after the peelable cap is peeled off. The initial maximum peel force between the peelable cap and the container sealing surface can be between 15 N and 40 N according to ASTM F2824-10 (45° peel angle). The container sealing surface can be selected from the group consisting of bare tinplate, tin-free steel, and aluminum. The container sealing surface can be coated or otherwise treated.

[0020] The invention disclosed herein may include other features as outlined below. Attached Figure Description

[0021] Figure 1A This is a perspective view of an embodiment of a sealed container including a peel-off cap;

[0022] Figure 1B This is a perspective view of an embodiment of a sealed container including a peel-off cap, wherein the cap is partially peeled off from the sealing surface of the container;

[0023] Figure 2 This is a top view showing an embodiment of the container without the peel-off lid;

[0024] Figure 3 This is a top view of an embodiment of a container including an embodiment of a peel-off cap;

[0025] Figure 4 This is a cross-sectional view of an embodiment of a peelable and sealable cover material;

[0026] Figure 5 This is a top view of an embodiment of the container after the peel-off cap has been removed;

[0027] Figures 6A to 6E An exemplary diagram showing the appearance of the footprint obtained after removing the peel cap from the container sealing surface; and

[0028] Figure 7 This is an exemplary chart of peel force obtained using ASTM F2824-10 (45° peel angle). Detailed Implementation

[0029] This invention provides a peelable and sealable cap material for containers. The container may have a sealing surface comprising a metallic material. The cap material refers to a metallic substrate coated with a sealing layer. The cap material may be in the form of a material web (i.e., a sheet or film), or the web may be cut into a desired shape, such as a disc or rectangle (i.e., a die-cut cap). In some cases, the cap material is a die-cut cap. Die-cut caps may be embossed. The coated sealing layer comprises a blend of materials that enables a previously unattainable balance of performance in terms of peel force, burst strength, and footprint appearance.

[0030] Figure 1A and Figure 1B A specific embodiment of a sealed container 10 is depicted, comprising a peelable cap 105 made of a peelable and sealable cap material 100. The peelable cap 105 is sealed to a container sealing surface 200. As depicted in the figure, the container sealing surface 200 is part of a rigid cylindrical container body 210. The container body 210 may be wholly or partially made of metal.

[0031] According to some embodiments disclosed herein, at least the sealing surface (i.e., container sealing surface 200) to which the peel-off cap 105 of the container body is sealed comprises metal. The container sealing surface may be in the form of a rigid ring constructed of metal.

[0032] According to some embodiments disclosed herein, the sealing surface to which the peel-off cap of the container body is sealed comprises a polymer material, such as a coating.

[0033] In some embodiments of the sealed container, the sealing surface of the container body comprises bare tinplate, tin-free steel, or aluminum. The release cap is directly sealed to the metal material of the container sealing surface. The release cap may also be directly heat-sealed to the metal material of the container sealing surface.

[0034] In some embodiments of the sealed container, the sealing surface of the container comprises a metal having a coating applied to its surface by painting, extrusion coating, lamination, or any other means. In some cases, the coating on the sealing surface of the container may be similar to or the same as the sealing layer of the peel-off cap, as will be discussed later. The sealing layer of the peel-off cap is sealed to the coating on the metal material. The sealing layer of the peel-off cap may be heat-sealed to the coating on the metal material.

[0035] like Figure 1A and Figure 1B As shown, the container body 210 includes a bottom wall and side walls extending upward from the bottom wall. The container body 210 may be constructed of metal, polymer, glass, or fiber-based materials, or combinations thereof. According to the invention, the top of the sealed container 10 is a peel-off cap 105.

[0036] Sealed containers can be produced by heat-sealing a peel-off cap 105 to the container sealing surface 200 in a separate process. The finished end, or "peel-off end" (the peel-off cap 105 heat-sealed to the container sealing surface 200), is then attached to the side wall of the container body 210. The side wall can be made of metal, polymer, glass, or spiral-wound cardboard.

[0037] In different embodiments of the sealed container, the lid material may be directly sealed to the upper edge portion, upper lip, or sealing flange of the metal sidewall. The container body 210 and the container sealing surface 200 may be constructed from a single piece of metal selected from the group consisting of tinplate, tin-free steel, and aluminum.

[0038] like Figure 1B As shown, in use, the sealed container 10 can be opened to access the contents. The peel-off cap 105 can be manually peeled off from the container sealing surface 200, thereby effectively breaking the seal created to construct the sealed container 10.

[0039] Figure 2 and Figure 3 Top views of an embodiment of the sealed container 10 are shown before and after the peel-off cap 105 is attached. Figure 2 A container sealing surface 200 is shown. The container sealing surface 200 has an outer edge and an inner edge, and is shown herein as having an annular shape. The container sealing surface 200 can have any other shape, such as a rectangle. In some cases, the inner edge of the sealing surface has a different shape than the outer edge of the sealing surface.

[0040] The interior of container 10 can be accessed through the hole in the center of the ring. Figure 3 In this embodiment, a peelable cap 105, comprising a peelable and sealable cap material 100, is attached to a container sealing surface 200 via a seal 300. The boundary of the seal 300 is shown by a dashed line, and in this embodiment, the seal is annular. The peelable cap 105 overlaps with the container sealing surface 200, and the two components are heat-sealed together in the overlapping area. The peelable cap 105 also includes a peel tab 130, which can be gripped and pulled to initiate removal of the peelable cap 105 from the container sealing surface 200.

[0041] In some embodiments, seal 300 may be heat-sealed. As used herein, “seal” or “sealable” means bonding two or more components together. In some cases, a seal bonds cap material to a container, thereby creating an airtight environment inside the container. A seal can be formed by any known means, such as using heat generated by conduction, induction, or radiation (e.g., by infrared), typically while simultaneously applying a certain pressure. A seal can also be achieved by any other suitable means, such as ultrasonic sealing. As used herein, “peelable” or “removable” means a seal that can be manually separated at the original interface or at another location within one of the components. Peeling may include causing a portion of one of the components to break off, followed by cohesive failure within that component. In contrast, an adhesive may be a fusion seal (non-peelable), and manual force may result in the complete breakage of one of the components, or the container may be unable to be opened manually.

[0042] Figure 4 A cross-section of an embodiment of the peelable and sealable cover material of the present invention is provided. It can be used... Figure 4 The embodiments shown, or any other embodiments of the peelable and sealable cap, are used to form a peelable cap for a sealed container. The peelable and sealable cap 100 has two layers: a metal substrate 120 and a sealing layer 110. The sealing layer 110 may be directly or indirectly adhered to the metal substrate 120. The sealing layer 110 and the metal substrate 120 may be continuous with each other.

[0043] Embodiments of the peelable and sealable cap 100 may include other layers. For example, a continuous or discontinuous ink layer may be applied to the side of the metal substrate 120 opposite to the sealing layer 110 to provide a pattern for the cap. Regardless of the other layers, the sealing layer 110 must be on the surface of the peelable and sealable cap 100 and, when used to close the sealed container 10, this surface contacts the sealing surface 200.

[0044] The metal substrate for the peelable and sealable cover is preferably aluminum foil with a thickness between 20 micrometers and 200 micrometers.

[0045] The sealing layer of the present invention comprises polymeric materials including copolymers (A) comprising one or more polymerized olefin monomers and one or more polymerized olefinically unsaturated (poly)carboxylic acid monomers, copolymers (B) comprising one or more polymerized (meth)acrylate monomers, and one or more types of inorganic particles (C). Blends of these materials form the sealing layer, which, as will be further detailed below, possesses advantageous sealing and peel properties. Using the sealing layer as described herein, superior peel strength and burst strength previously unattainable with thin, paint-type sealing layers can be achieved. The performance of the capping material is demonstrated not only by measurable peel strength and burst strength but also by the visual appearance of the footprint remaining after peeling.

[0046] The sealing layer comprises 70% to 89% by weight of copolymer (A), 10% to 29% by weight of copolymer (B), and 1% to 15% by weight of one or more inorganic particles (C).

[0047] The copolymer (A) of the sealing layer described herein comprises one or more polymerized olefin monomers and one or more polymerized olefinically unsaturated (poly)carboxylic acid monomers. In some embodiments, copolymer (A) comprises 60% to 90% by weight of one or more polymerized olefin monomers and 10% to 40% by weight of one or more polymerized olefinically unsaturated (poly)carboxylic acid monomers. In some embodiments, the polymerized olefinically unsaturated (poly)carboxylic acid monomers of copolymer (A) are selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, and itaconic acid.

[0048] In some embodiments of the peelable and sealable cover material, the olefin monomer of copolymer (A) is ethylene, and the olefinic unsaturated (poly)carboxylic acid of copolymer (A) is acrylic acid and / or methacrylic acid.

[0049] In some embodiments of the peelable and sealable cover, the copolymer (A) comprises 15% to 30% by weight of polymeric (meth)acrylic acid and 85% to 70% by weight of polymeric ethylene.

[0050] The copolymer (B) of the sealing layer described herein comprises one or more polymerized (meth)acrylate monomers. In some embodiments of the peelable and sealable cover material, the copolymer (B) comprises one or more polymerized (meth)acrylate monomers selected from methyl-, ethyl-, and linear and branched propyl-, butyl-, pentyl-, hexyl-, heptyl-, and octyl- esters of (meth)acrylate. The copolymer (B) may comprise polymerized methyl methacrylate and butyl methacrylate; more preferably, the copolymer (B) comprises polymerized methyl methacrylate and butyl methacrylate; most preferably, the copolymer (B) comprises polymerized methyl methacrylate and butyl methacrylate.

[0051] The copolymer (B) may comprise polymerized (meth)acrylate C1-C8 ester monomers comprising between 5% and 75% by weight of methyl methacrylate and between 25% and 95% by weight of butyl methacrylate based on the total amount of methyl methacrylate and butyl methacrylate, and up to 30% by weight of one or more (meth)acrylate alkyl esters selected from the group consisting of (meth)acrylate C2-alkyl esters, (meth)acrylate C3-alkyl esters, (meth)acrylate C4-alkyl esters, (meth)acrylate C5-alkyl esters, (meth)acrylate C6-alkyl esters, (meth)acrylate C7-alkyl esters, (meth)acrylate C8-alkyl esters, and mixtures thereof based on the total amount of (meth)acrylate C1-C8 alkyl esters.

[0052] In some embodiments of the peelable and sealable cover, the copolymer (B) of the sealing layer comprises polymerized (meth)acrylate C1-C8 ester monomers, comprising between 40% and 90% by weight of methyl methacrylate and between 10% and 60% by weight of butyl methacrylate based on the total amount of methyl methacrylate and butyl methacrylate, and up to 20% by weight of one or more (meth)acrylate alkyl esters selected from the group consisting of (meth)acrylate C2-alkyl esters, (meth)acrylate C3-alkyl esters, (meth)acrylate C4-alkyl esters, (meth)acrylate C5-alkyl esters, (meth)acrylate C6-alkyl esters, (meth)acrylate C7-alkyl esters, (meth)acrylate C8-alkyl esters, and mixtures thereof based on the total amount of (meth)acrylate C1-C8 alkyl esters.

[0053] The copolymer (B) may further comprise up to 30% by weight of one or more olefinically unsaturated (poly)carboxylic acid monomers selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, and itaconic acid, based on the total amount of (meth)acrylic acid C1-C8 alkyl esters and olefinically unsaturated (poly)carboxylic acid monomers. Preferred olefinically unsaturated (poly)carboxylic acid monomers are acrylic acid and methacrylic acid.

[0054] The copolymer (B) may be further characterized in that its glass transition temperature, as measured by differential scanning calorimetry according to ASTM D3418-03, is greater than 15°C, preferably greater than 20°C, and more preferably greater than 30°C. The copolymer (B) may also be characterized in that its glass transition temperature, as measured by differential scanning calorimetry according to ASTM D 3418-03, is between 55°C and 75°C, or between 60°C and 70°C.

[0055] The composition of the blend of copolymer (A) and copolymer (B), as well as qualitative and quantitative data on the individual copolymers (A) and (B), can be obtained by methods known in the art from a dried film (i.e., a sealing layer) comprising the blend of copolymer (A) and copolymer (B) and / or from a dried film of copolymer (A) and a dried film of copolymer (B).

[0056] The inorganic particles (C) can be selected from metals, oxides, hydroxides, carbonates, sulfates, phosphates, silicates, and mixtures thereof. Preferably, the inorganic particles (C) are selected from the group consisting of halloysite, kaolinite, illite, montmorillonite, vermiculite, talc, sepiolite, palygorskite, pyrophyllite, and mixtures thereof. In embodiments of peelable and sealable capping materials, the inorganic particles of the sealing layer are talc particles (Mg3Si4O3). 10 (OH)2 hydrated magnesium silicate).

[0057] The sealing layer of the present invention may contain up to 15 wt%, 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, or 5 wt% inorganic particles. The polymer sealing layer of the present invention may contain more than 0.5 wt%, 1 wt%, 2 wt%, or 3 wt% inorganic particles. For example, the sealing layer may contain inorganic particles (C) between 1 wt% and 10 wt%, or between 0.5 wt% and 5 wt%. The inorganic particles are characterized by a median diameter (D). 50 The diameter of inorganic particles is between 1 and 5 micrometers. The characteristic of inorganic particles can be identified by their median diameter (D). 50 (less than 5 micrometers, between 0.5 and 4 micrometers, or between 0.5 and 3 micrometers.) As used herein, “median mass diameter” (or median mass particle size) is the particle size at which 50% of the particles by mass are larger and 50% of the particles by mass are smaller when the particle size distribution is being examined.

[0058] Inorganic particles can be characterized by a particle size distribution of less than 10 micrometers, or between 4 and 9 micrometers, or between 4 and 8 micrometers. 98 Inorganic particles can be characterized by a particle distribution with a density (D) of less than 1 micrometer, or between 0.1 and 0.9 micrometers, or between 0.1 and 0.8 micrometers. 10 As used in this paper, the particle size distribution D x The value represents the diameter of X% of the particles by mass that are smaller than this value. For example, if the particle size distribution D... 10 If the diameter is 5 micrometers, then 10% of the particles by mass have a diameter less than 5 micrometers. (D) x The value can be determined via SediGraph according to ISO 13317.

[0059] The sealing layer can be formed by applying a water-based heat sealant, as described herein, containing copolymer (A), copolymer (B), and inorganic particles (C), to a metal substrate. The water-based heat sealant can be an aqueous dispersion having a solids content between 10% and 60% by weight, or between 20% and 50% by weight. The water-based heat sealant can be a blend of a first aqueous dispersion containing copolymer (A), a second aqueous dispersion containing copolymer (B), and inorganic particles (C).

[0060] Suitable aqueous dispersions containing copolymer (A) are commercially available for heat-sealing applications, for example from Michelman. The Prime product line may be sourced from Paramelt. The product line is commercially available. It is well known to those skilled in the art that aqueous dispersions of copolymers of polymerized olefin monomers and olefinically unsaturated (poly)carboxylic acid monomers contain neutralizing agents that convert the carboxylic acid groups into tertiary ammonium carboxylic acid or alkali metal carboxylate groups. Suitable aqueous dispersions containing copolymer (B) are commercially available for heat-sealing or primer applications, for example from Evonik. The series or from Synthomer The series is commercially available. The water-based paint containing copolymer (A), copolymer (B) and inorganic particles (C) can be obtained by stirring a water-based dispersion containing copolymer (A) and a water-based dispersion containing copolymer (B) (with inorganic particles (C) added to the stirred mixture while stirring).

[0061] The water-based paint is applied to one side of the metal substrate by spraying, curtain coating, roller coating, or any other suitable coating method. Preferably, the coating is applied by roller coating. The paint is then dried, removing most of the liquid and leaving the resulting sealing layer. After application, the water-based paint can be dried in a ventilated air oven using convective heat or infrared heat or a combination of convective heat and infrared heat, in a manner that allows for adjustment to achieve a metal temperature of at least 190°C or at least 195°C, which is maintained for less than 15 seconds, or a time period between 1 and 10 seconds, or between 2 and 8 seconds, or between 2 and 5 seconds.

[0062] Water-based paint is applied at a certain thickness (i.e., coating weight) to ensure a final sealant thickness between 2 and 13 micrometers, or between 4 and 10 micrometers, or between 5 and 9 micrometers, or between 6 and 8 micrometers after drying.

[0063] The metal substrate may also be provided with a protective varnish on the side opposite to the sealing layer. The protective varnish helps prevent adhesion of the sealing side during both the processing of the roll-to-roll substrate and during the application and unfolding process before further processing. Furthermore, the protective varnish protects the bare aluminum from corrosion during the use of the cover material in packaging applications. Preferred coating thicknesses for the protective varnish include between 0.5 micrometers and 2.5 micrometers, or between 1.0 micrometers and 2.0 micrometers, or between 1.2 micrometers and 1.8 micrometers.

[0064] In some embodiments, the cover material is further provided with a printable primer on the side opposite to the sealable coating. The printable primer facilitates the application of printed labels onto the substrate. Preferably, the printable primer has a coating thickness of less than 2.5 micrometers, or less than 2 micrometers, or less than 1.8 micrometers.

[0065] In an embodiment of the method for producing a peelable and sealable cap, a roll of metal substrate (i.e., a roll of web-based material) is unrolled and coated with a water-based paint comprising copolymer (A), copolymer (B), and inorganic particles (C). The coated metal substrate is then heated to dry the paint, leaving a sealing layer and forming a peelable and sealable cap. Finally, the cap is rewound into a roll. The roll of coated metal foil (i.e., the cap) can then be unrolled for further processing. Further processing may include slitting into narrower rolls, cutting into sheets, or stamping to produce die-cut caps of any desired shape.

[0066] Footprint description

[0067] As previously mentioned, the performance of a peelable and sealable cap material's sealing layer can be demonstrated by the footprint left on the container's sealing surface after the peelable cap has been removed. As used herein, a seal's "footprint" is a visually perceptible remnant of the seal, consisting of a small amount of the sealing layer remaining on the container's sealing surface, with the residual material having a slightly opaque or whitish appearance. This visible material is the footprint.

[0068] As described herein, the blend of materials used in the sealing layer unexpectedly and advantageously provides consistent cohesive failure of the sealing layer when force is applied to peel the cap material from the container sealing surface. This consistent cohesive failure can be visually detected in the seal footprint. Because the method of seal failure is consistent, an excellent footprint indicating good cohesive failure is quite uniform and clean. Furthermore, the footprint is desirable because it is regarded by brand owners, consumers, and others as an indicator of a perfect or tight seal. It can even be expected as a feature of tamper-proof evidence. Figure 6A The footprint as a result of the present invention is shown. Figures 6B to 6E This illustrates the shortcomings of the previously used sealing layer.

[0069] Figure 6AAn embodiment of the container according to the invention is shown, exhibiting a continuous, well-defined footprint on the sealing surface after the peel-off cap has been removed. The sealing container is characterized by a continuous, well-defined footprint on the container sealing surface, showing the seal layer remaining after the peel-off cap has been removed. As indicated by a uniform texture and continuous edges, the footprint mimics the sealing area (i.e., the area affected by pressure and heat or other sealing mechanisms). The footprint has very few gaps or no gaps in its visual appearance. This is evidence of very consistent cohesive failure within the sealing layer of the peelable and sealable cap material.

[0070] Figure 6B An example of an undesirable footprint on the sealing surface of a container after the peel cap has been removed is shown. Dashed lines indicate locations where the seal has been affected. As shown, there is no visual indication of a seal. Upon peeling, the seal layer has separated from the container sealing surface in an adhesive manner. This is undesirable because adhesive breakage provides less consistent sealing properties compared to cohesive breakage within the seal layer.

[0071] Figure 6C An example of an undesirable footprint on the sealing surface of a container after the peel-off cap has been removed is shown. As illustrated, the footprint visually presents a significant gap. Dashed lines indicate locations where the seal is affected. Figure 6D Another embodiment of undesirable footprint on the sealing surface of a container after the peel-off cap has been removed is shown. As illustrated, only a small area of ​​footprint is present. Dashed lines indicate locations where the seal is affected. Figure 6C and Figure 6D The footprints shown are undesirable because they exhibit inconsistent cohesive failure within the seal layer of the peelable and sealable capping material.

[0072] Figure 6E An example of an undesirable footprint on the sealing surface of a container after the peel-off cap has been removed is shown. As illustrated, the footprint has uneven edges, indicating that cohesive failure of the sealing layer has extended beyond the edges of the affected seal.

[0073] Peeling force and burst strength

[0074] As previously described, a sealed container can be formed by heat-sealing a peelable cap, made of a peelable and sealable cap material, to the sealing surface of the container body. This seal forms an airtight seal that protects the product inside.

[0075] A sealed container is characterized by an average peel force between 8 N and 15 N between the cap and the container sealing surface when tested at a 45° angle, according to ASTM F2824-10. A sealed container is also characterized by an initial maximum peel force between 15 N and 40 N according to ASTM F2824-10 (45° angle).

[0076] Figure 7 An example of a peel strength profile 500 is shown, which can be obtained by testing a sealed container according to ASTM F2824-10 as described herein. For Figure 7 The peel test shown depicts the lid being pulled open approximately halfway, but not completely removed from the container. Peel strength curve 500 illustrates the variation of the measured seal strength (i.e., peel strength or peel force) with the distance traveled by the test fixture (i.e., the test arm). As used herein, the initial maximum peel force 510 is the peak peel force measured at the start of the test and is the result of seal breakage. As used herein, the average peel force is the calculated average of the relatively “flat” data peel force measurements 520 obtained during the test. The average peel force is the force required to propagate the peel throughout the entire container.

[0077] A sealed container may be characterized by a burst strength of at least 2 bar according to Test Method A of ASTM F1140 / F1140M-13. The burst strength test may be performed on a fully sealed container or on a peel-off end unit (metal ring plus a peelable and sealable cap), as is known in the art. According to Test Method A, the metal ring (200) of the peel-off end, along with the peelable cap (105), can be fixed in a manner that allows for unrestrained deformation by applied pneumatic pressure. The burst strength is given by the maximum pressure measured before the packaging breaks. Ideally, the breakage should not occur at the sealed area of ​​the sealed container, but rather by the tensile strength of the cap material.

[0078] Example

[0079] The following illustrative examples are intended to illustrate the invention only and are not intended to limit or otherwise restrict the scope of the invention.

[0080] The sealant is made from the following components: an aqueous dispersion (DA) of copolymer (A), an aqueous dispersion (DB1) of copolymer (B1), an aqueous dispersion (DB2) of copolymer (B2), and inorganic particles (C1), (C2), and (C3). The materials and blends are described below.

[0081] The copolymer (A) was obtained by polymerization of methacrylic acid at 5 mol% to 10 mol% and ethylene at 93.5 mol%. The dispersion (DA) had a pH of 8.5 ± 0.5, a solids content of 40 ± 1%, and a viscosity of 50 ± 2 s. The dried film of the dispersion (DA), i.e., the solid film of the copolymer (A), had a melting peak at 90 °C, a crystallinity of 11% (by comparing the melting enthalpy from DSC with the melting enthalpy of pure polyethylene of 295 J / g), and a time-dependent second endothermic peak at 50 °C (sometimes referred to in the literature as the room temperature annealing peak).

[0082] Copolymers (B1) and (B2) were obtained by polymerization of methyl methacrylate (between 65 mol% and 70 mol%), butyl methacrylate (between about 25 mol%), and methacrylic acid (between 5 mol% and 10 mol%). Dispersions (DB1) and (DB2) were adjusted to a pH of 8.6 ± 0.5, a solids content of 50 ± 1%, and a viscosity of 150 ± 15 mPa·s. The glass transition temperature of the dried film of copolymer (B1) was 70 °C. The glass transition temperature of the dried film of copolymer (B2) was 69 °C.

[0083] For pH measurements, an MColorpHast indicator strip purchased from Merck was used. Solid content was determined using a Mettler Toledo HR83 halogen moisture analyzer. In the case of the dispersion of copolymer (A), viscosity was measured using a 4mm DIN flow cup according to DIN 53211. For the dispersion of copolymer (B), viscosity was measured using a No. 2 rotor at 100 rpm at 20°C according to DIN EN ISO 2555. All DSC measurements were performed according to ASTM D3418-03.

[0084] The sealant is prepared by blending an aqueous dispersion containing copolymer (A) and copolymer (B1) or copolymer (A) and copolymer (B2). The blend of dispersions is mixed for 15 minutes at room temperature using a laboratory stirrer.

[0085] Inorganic particles (C1), (C2), or (C3) are added to the thus obtained aqueous dispersion, and the aqueous dispersion containing these particles is stirred for another 15 minutes. The inorganic particles used are as follows: (C1) is talc, specifically from Elementis. M05SL, characterized by D 50 It is 2.2 micrometers, and D 98 It is 7.5 micrometers (ISO 13317); (C2) is talc, specifically from Imerys. 1A, characterized by D 50 It is 1.1 micrometers, and D 98 It is 4.8 micrometers (ISO 13317); (C3) is kaolinite, which comes from Engelware. Its characteristic is D 50 It is 0.7 micrometers, and D 98 It is 5.9 micrometers (ISO 13317).

[0086] The water-based dispersion (water-based paint) thus obtained is applied to an aluminum substrate with a thickness of 60 or 90 micrometers using a scraper to achieve a final seal layer thickness between 6 and 13 micrometers. A dry seal layer is obtained by directly transferring the coated aluminum substrate into a ventilated air oven for 15 seconds after the coating process (15 seconds corresponds to heating time (10 to 12 seconds) + time at 197°C (3 to 5 seconds)); the oven settings are controlled to achieve a substrate temperature of 197°C as measured by a temperature indicator strip commercially available from Reatec.

[0087] The composition of the produced cover material examples is shown in Table 1. The values ​​shown for A, B1, B2, C1, C2, and C3 are the weight percentages of these components in the dried sealing layer composition.

[0088] Table 1: Composition of the sample cover material (Examples 1-7 of the present invention and comparative examples 8-10)

[0089]

[0090] After cooling to room temperature, a circular blank with a diameter of 96 mm, exhibiting a pull tab shape, was die-cut from the sample cover material. At a temperature of 200°C, with both the upper and lower jaws at 730 N / cm... 2 Under pressure, the circular blank is heat-sealed to the metal surface of a suitable tinplate ring for 0.5 seconds. As is known to those skilled in the art, the tinplate ring uses 2.8 g / m² on the sealing side. 2 The tin coating weight and passivation are 300.

[0091] Peeling tests on tinplate with various types of passivation (e.g., according to codes 300, 311, 314, and 555) have indeed shown comparable results. Similarly, sometimes the aging effects observed on passivated tinplate surfaces have no significant impact on the measured properties of assemblies using the cover material for which protection is sought. The codes for different types of passivation refer to:

[0092] 300: Impregnation passivation; 1 mg / m2-3 mg / m2 chromium

[0093] 311: Electrochemical passivation; 3.5 mg / m²-9 mg / m² chromium

[0094] 314: Electrochemical passivation; >5 mg / m² chromium

[0095] 555: Chromium-free passivation; 0.8 mg / m²-1.2 mg / m² titanium

[0096] After conditioning at 23°C and 50% relative humidity for 24 hours, the prepared sealing assembly (peel end) was tested. The test results of average peel force, initial maximum peel force, and burst pressure are reported in Table 2, where samples 1 to 7 are examples according to the present invention, and samples 8 and 9 are comparative examples.

[0097] Table 2: Test results of sample assemblies (lids) (Examples 1-7 of the present invention and comparative examples 8-10)

[0098]

[0099] 1 The average peel force and initial maximum peel force were measured according to ASTM F2824-10;

[0100] 2 Burst strength is measured according to ASTM F1140 / F1140M-13 Test Method A. The burst failure mode indicates whether the burst was measured as seal failure (peeling) or material failure, i.e., tearing (fracture).

[0101] 3 The footprint indicates a visual assessment of the seal on the metal edge of the container, referring to... Figures 6A to 6E .

[0102] Peel force was measured on a Zwick 1425 tensile testing machine at a pull speed of 100 mm / min; tests were conducted at a pull angle of 45° according to ASTM F2824-10 (2015). Analysis of the initial maximum peel force and average peel force was determined using partial peel distance (i.e., without peeling the entire cap off the container). Peel force tests were performed using a 30 mm test cell arm travel distance (i.e., pull distance), which resulted in approximately 17 mm of peel distance. Peel force data were obtained from the average of three sequential measurements.

[0103] The different test results in Examples 5 and 6 are due to the different aluminum substrate thicknesses.

[0104] Comparative Example 9 has a sealing layer containing a polymer composition similar to that of Example 1. However, Comparative Example 9 does not contain inorganic components. This results in very low burst strength.

[0105] Comparative Example 8 has a sealing layer containing a polymer composition similar to Examples 4, 5, 6, and 7. However, Comparative Example 8 lacks an inorganic component. This results in low burst strength and a poor footprint.

[0106] As expected from a mechanical perspective, comparing capping samples 2 and 3 reveals increased initial and maximum peel forces due to the increased layer thickness. However, given that the layer thickness is almost doubled, this increase remains within the preferred range, as unexpectedly observed with the heat-sealing mixtures described herein. This implies that the capping material is stable with respect to possible variations in the coating film thickness.

[0107] Comparison of cap samples 9 and 10 shows that, within the preferred peel force range, by using only the polymer component, low burst pressure values ​​are typically found when the footprint criteria are met. Conversely, at sufficiently high burst pressure values, the footprint typically exhibits an undesirable appearance. By adding the inorganic component (C), all criteria were found to be met. According to the invention, even within a series of different combinations of (A), (B), and (C), as can be seen, for example, by comparison with Examples 1-7.

[0108] Unlike extrusion coating processes for sealable layers, painting processes allow for very low seal thicknesses; however, the lower limit of the seal thickness is determined by the roughness of the aluminum cap material (e.g., Ra = 0.5 μm and Rmax = 3-4 μm) and the roughness of the container sealing surface substrate (e.g., tinplate) (Ra = 0.2 μm), and by the requirement to achieve a full and saturated footprint on the metal edge substrate. For these reasons, the thickness of sealable layers typically results in a range of 6 to 8 μm.

[0109] Variations of sample assembly 5 were constructed using different sealing conditions. The mean peel force, initial maximum peel force, and burst strength of these variations of the assembly were then tested using the previously described testing methods. The results of these tests, along with burst failure modes and footprint analysis, are shown in Table 3. This testing indicates that the inventive concept disclosed in this application unexpectedly produces robust performance for cap applications. The test results are excellent over a wide range of sealing temperatures, sealing pressures, and sealing times.

[0110] Table 3: Test results of sample assembly 5 under different sealing conditions

[0111]

[0112] 1 . Similar temperatures on the upper and lower claws

[0113] 2 The average peel force and initial maximum peel force were measured according to ASTM F2824-10;

[0114] 3Burst strength is measured according to ASTM F1140 / F1140M-13 Test Method A. The burst failure mode indicates whether the burst was measured as seal failure (peeling) or material failure or tearing (fracture).

[0115] 4 The footprint indicates a visual assessment of the seal on the metal edge of the container, referring to... Figures 6A to 6E .

Claims

1. A peelable and sealable cover material comprising a metal substrate and a sealing layer, the sealing layer comprising: 70% to 89% by weight of copolymer (A), which comprises one or more polymerized olefin monomers and one or more polymerized olefinically unsaturated carboxylic acid monomers or olefinically unsaturated polycarboxylic acid monomers; 10% to 29% by weight of copolymer (B), wherein copolymer (B) comprises one or more polymerized (meth)acrylate monomers; and One or more inorganic particles (C) from 1% to 10% by weight, characterized in that the median diameter (D50) is between 1 micrometer and 5 micrometers.

2. The peelable and sealable cover material according to claim 1, wherein, These inorganic particles (C) are characterized by a particle size distribution including D particles smaller than 10 micrometers. 98 and D smaller than 1 micrometer 10 .

3. The peelable and sealable cover material according to claim 1 or 2, wherein: The copolymer (A) comprises 55% to 90% by weight of one or more polymerizable olefin monomers and 10% to 35% by weight of one or more polymerizable olefinically unsaturated carboxylic acid monomers or olefinically unsaturated polycarboxylic acid monomers selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, and itaconic acid; and The copolymer (B) comprises one or more polymerized (meth)acrylate C1-C8 ester monomers.

4. The peelable and sealable cover material according to claim 1 or 2, wherein, The copolymer (B) comprises up to 30% by weight of one or more olefinically unsaturated carboxylic acid monomers or olefinically unsaturated polycarboxylic acid monomers selected from the group consisting of (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid and itaconic acid.

5. The peelable and sealable cover material according to claim 1 or 2, wherein, These inorganic particles (C) are selected from the group consisting of halloysite, kaolinite, illite, montmorillonite, vermiculite, talc, sepiolite, palygorskite, pyrophyllite, and mixtures thereof.

6. The peelable and sealable cover material according to claim 1 or 2, wherein, The particle size distribution of these inorganic particles (C) includes D particles of 8 micrometers or smaller. 98 .

7. The peelable and sealable cover material according to claim 1 or 2, wherein, The particle size distribution of these inorganic particles (C) includes D particles of 6 micrometers or smaller. 98 .

8. The peelable and sealable cover material according to claim 1 or 2, wherein, The metal substrate is an aluminum foil with a thickness of 20 micrometers to 200 micrometers.

9. The peelable and sealable cover material according to claim 1 or 2, wherein, The copolymer (A) comprises 70% to 85% by weight of polymeric ethylene and 15% to 30% by weight of (meth)acrylic acid.

10. The peelable and sealable cover material according to claim 1 or 2, wherein, The copolymer (B) comprises a polymeric mixture of methyl methacrylate and butyl methacrylate.

11. The peelable and sealable cover material according to claim 1 or 2, wherein, The copolymer (B) includes a polymeric mixture of methyl methacrylate, butyl (meth)acrylate and methacrylic acid.

12. The peelable and sealable cover material according to claim 1 or 2, wherein, The sealing layer contains inorganic particles (C) ranging from 1% to 5% by weight.

13. The peelable and sealable cover material according to claim 1 or 2, wherein, The thickness of the sealing layer is between 2 micrometers and 13 micrometers.

14. The peelable and sealable cover material according to claim 1 or 2, wherein, The thickness of the sealing layer is between 4 micrometers and 10 micrometers.

15. The peelable and sealable cover material according to claim 1 or 2, wherein, The thickness of the sealing layer is between 6 and 9 micrometers.

16. A method for producing a peelable and sealable cover material according to any one of claims 1 to 15, the method comprising the steps of: Unroll the roll of the metal substrate; A water-based paint containing copolymer (A), copolymer (B), and inorganic particles (C) is applied to an unfolded metal substrate using a coating system; and The water-based paint is dried to form a sealing layer, thereby producing a peelable and sealable capping material comprising the metal substrate and the sealing layer; and The thickness of the sealing layer is between 2 micrometers and 13 micrometers.

17. The method of claim 16, wherein, The solids content of this water-based paint is between 35% and 55% by weight.

18. A sealable container comprising a peelable cap that seals to a sealing surface of the container, said cap comprising a peelable and sealable cap material according to any one of claims 1 to 15, wherein The sealing surface of the container is a rigid ring; According to ASTM F2824-10, at a peel angle of 45°, the average peel force between the peel cap and the sealing surface of the container ranges from 8 N to 15 N. According to ASTM F1140 / F1140M-13 Test Method A, the burst strength of this sealed container is at least 2 bar; and The container's sealing surface exhibits a continuous, clearly defined footprint of the sealing layer remaining after the peel-off cap has been removed.

19. The sealed container according to claim 18, wherein, According to ASTM F2824-10, at a peel angle of 45°, the initial maximum peel force between the peel cap and the container sealing surface is between 15 N and 40 N.

20. The sealed container according to claim 18 or 19, wherein, The sealing surface of the container is selected from a group consisting of bare tinplate, tin-free steel, and aluminum.

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