Metal coated with functional polypropylene film

Abstract

This invention relates to an article comprising a metal coated with an aqueous dispersion of polyolefin particles and a metal coated with a polyolefin film formed from the dispersion. More particularly, the polyolefin particles of this invention are primarily polypropylene particles.

Description

[0001] This invention relates to an article comprising a metal coated with an aqueous dispersion of polyolefin particles and a metal coated with a polyolefin film formed from the dispersion. More particularly, the polyolefin particles in the aqueous dispersion of this invention are primarily polypropylene particles.

[0002] It is well-established to apply various treatment and pretreatment solutions to metals to delay or inhibit corrosion. This is particularly true in the field of metal food and beverage cans, buckets and drums, and non-food metal containers. Coatings are used on the interior of such containers to prevent the contents (e.g., food or beverages) from contacting the metal. Contact between metal and food or beverages, as well as non-food substances, can lead to corrosion of the metal container, which subsequently contaminates the food, beverage, or non-food contents. Corrosion is especially problematic when food and beverage products are highly acidic and / or have a high salt content. Additionally, the highly alkaline contents of non-food substances (such as hair dyes) can react with metals (such as aluminum). For example, coatings applied to the interior of food and beverage cans also help prevent corrosion in the headspace of the can, which is the area between the filler line and the lid. Coatings can also be applied to the exterior of metal containers to provide protection against the external environment and / or to provide a decorative layer containing fillers and / or pigments. In addition to corrosion protection, coatings used for food and beverage cans should be non-toxic, inert, and, if applied to the inner surface, should not adversely affect the taste, appearance (e.g., the color of the food or beverage inside), or cause contamination of the can's contents. Resistance to "bursting," "whitening," and / or "bubbling" is also required, especially during high-temperature processing conditions (e.g., retorting). Retorting is a process in which packaged food or beverages are sterilized and, if necessary, cooked to ensure safety and quality. During retorting, sealed food or beverage cans containing their contents are sterilized at approximately 121°C or higher. Many coatings cannot withstand such temperatures and therefore cannot provide the performance required for subsequent coating. Coatings are still required on the metal substrate to achieve excellent retorting performance.

[0003] US Patent Publication 2020 / 0123393A1 discloses an aqueous dispersion and its use in coating metal substrates, particularly in coating metal cans for food and beverage packaging, wherein the aqueous dispersion comprises a solid content of 15 wt.% to 60 wt.% based on the total weight of the aqueous dispersion. This solid content includes a melt blend product having the following components: 15 wt.% to 60 wt.% of an acid-functionalized polypropylene base polymer having a melting point of 155°C to 170°C; and 16 wt.% to 50 wt.% of a polymer having a melting point of less than 0.88 g / cm³. 3The product comprises a polypropylene copolymer of a density of 100 wt.%; 5 wt.% to 20 wt.% acid-functionalized polypropylene wax; and 15 wt.% to 30 wt.% acid-functionalized polyolefin, wherein the wt.% is based on the total weight of the melt blend and the components of the melt blend add up to 100 wt.%. U.S. Patent Publication 2020 / 0123393A1 fails to disclose the use of fatty acid dispersants and the effect of such dispersants on the formulation of coatings on metal substrates.

[0004] US Patent 6,166,118 discloses an emulsion of a functionalized polyolefin for use in coatings comprising temporary metal coatings and paper coatings; wherein the functionalized polyolefin has a weight-average molecular weight greater than 10,000, a fatty acid, and a base sufficient to neutralize the amounts of the functionalized polyolefin and the fatty acid. US 6,166,118 fails to disclose (a) the use of a combination of high-melting-point and functionalized base resins, (b) the use of blends of functionalized and non-functionalized base resins, and (c) the formation of a retort-resistant coated metal article.

[0005] US Patent 9701824 discloses polyolefin dispersion blends for paper coating applications, wherein the polyolefin comprises polyethylene resin or polypropylene resin, and may include up to about 20 wt.% of any modified polyolefin with a melting point of 105°C or higher. US9701824 fails to disclose metal coatings and how to meet the standards required for metal coatings.

[0006] This invention provides a method for preparing a coated metal substrate, the method comprising the following steps:

[0007] a) Applying a coating formulation derived from an aqueous dispersion composition to a metal substrate, the aqueous dispersion composition comprising:

[0008] i) Based on the weight of the polymer solids in the dispersion, 1% to 15% by weight of a fatty acid dispersant having 14 to 60 carbon atoms and an acid value in the range of 60 to 250.

[0009] ii) Based on the weight of polymer solids in the dispersion, greater than 25% by weight and less than 70% by weight of an acid-functionalized propylene-based copolymer, wherein the acid value of the acid-functionalized propylene-based copolymer is in the range of 0.5 to 20 and the melting point is at or above 130°C as determined by DSC.

[0010] iii) 15% to 60% by weight of nonfunctionalized propylene-co-olefin-based copolymer, based on the weight of polymer solids in the dispersion;

[0011] iv) Based on the weight of the polymer solids in the dispersion, 2% to 15% by weight of a functionalized polyolefin wax, wherein the acid value of the functionalized polyolefin wax is in the range of 25 to less than 60; and

[0012] v) A neutralizing agent, wherein the neutralizing agent is an organic base or volatile base having a boiling point of less than 250°C; and

[0013] b) The composition is cured by heating or solidifying it to produce a cured film with a thickness in the range of 1 μm to 20 μm.

[0014] The present invention also provides a metal-coated article prepared according to the method of the present invention.

[0015] Compositions comprising an aqueous dispersion of a dispersant, a base polymer, a functionalized polyolefin wax, and a neutralizing agent can be prepared by continuous or batch methods. A preferred example of a continuous method is twin-screw extrusion, as described in Comparative Example E of US 8,722,787. Batch methods can be performed, for example, using a 2CV Helicone agitator, which is a conical batch agitator that uses two interlocking conical blades to mix high-viscosity materials. Based on the weight of the combined water and polymer, the concentration of the polymer in the aqueous dispersion is preferably in the range of 20% by weight, more preferably 25% by weight, and most preferably 30% by weight to preferably 60% by weight, and more preferably to 55% by weight.

[0016] dispersant

[0017] Dispersants comprise fatty acids having 14 to 60 carbon atoms and an acid value ranging from 60 to 250. The term "acid value" (or acid number) refers to the mass of potassium hydroxide (KOH) in milligrams required to neutralize one gram of copolymer, determined by ASTM (D974). All individual values ​​and subranges of 60 to 250 are included herein and disclosed herein. For example, acid values ​​may be from the lower limit of 60, 75, 80, 100, 120, or 150 to the upper limit of 250, 225, 200, or 175. For example, acid values ​​may be from 75 to 250, or alternatively, from 80 to 250, or alternatively, from 75 to 200, or alternatively, from 100 to 250. The term "fatty acid" refers to a carboxylic acid containing a long, saturated or unsaturated fatty acid chain. Fatty acid dispersants may contain linear, branched, cyclic, or aromatic segments or combinations thereof. Suitable fatty acids include, but are not limited to, acids, anhydrides, and esters, such as myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, tall oil, tall oil fatty acids, alkenyl succinic anhydride, monoesterified alkenyl succinic anhydride, and combinations thereof. Based on the weight of the polymer solids in the dispersion, the concentration of the fatty acid dispersant is preferably in the range of 1% to 15% by weight, and preferably 2% to 10% by weight, based on the weight of the polymer solids in the dispersion.

[0018] Dispersants may also include high molecular weight acid-functionalized polyolefin copolymers, where "high molecular weight" refers to a weight-average molecular weight of at least 10,000 as determined by GPC. Acid-functionalized polyolefin copolymer dispersants typically contain structural units of ethylene and carboxylic acid monomers (such as acrylic acid, methacrylic acid, or itaconic acid), such that the dispersant is a copolymer containing structural units of ethylene and acrylic acid (EAA) or ethylene and methacrylic acid (EMAA). The term "structural unit" specifying a monomer refers to the monomer residue after polymerization. For example, the structural unit of methacrylic acid is shown below:

[0019]

[0020] The dashed lines represent the connection points between the structural units and the polymer backbone.

[0021] The acid-functionalized polyolefin copolymer dispersant has a melt flow index (according to ASTM D1238) in the range of 50 g / 10 min to 2000 g / 10 min at 190 °C / 2.16 kg, and the weight-to-weight ratio of the structural units of ethylene to carboxylic acid monomers, based on the weight of the copolymer, is in the range of 95 wt%:5 wt%, preferably 90 wt%:10 wt%, and more preferably 85 wt%:15 wt% to 70 wt%:30 wt%, and preferably 75 wt%:25 wt%. The acid value of the polymer dispersant is between 60 and 250. It is preferable not to use additional acid-functionalized polyolefin copolymer dispersants to prepare aqueous dispersions of polyolefin particles. However, if added, the concentration of the acid-functionalized polyolefin copolymer dispersant is in the range of 5% to 30% by weight, more preferably up to 15% by weight, based on the weight of the polymer solids in the dispersion; provided that the concentration of the dispersant in the composition is sufficient to produce a cured film with a retort adhesion of 4B, more preferably 5B (measured at 135°C / 60 min, 2% lactic acid) on a metal substrate. Suitable commercially available acid-functionalized polyolefin copolymer dispersants include NUCREL. TM 960 (EMAA copolymer with an acid value of approximately 98) or Primacor 5980i (EAA copolymer with an acid value of approximately 155).

[0022] Basic polymers

[0023] The basic polymer or basic copolymer includes both nonfunctionalized polypropylene copolymers and high-melting-point acid-functionalized propylene-based polyolefin copolymers. The terms "polypropylene copolymer" and "propylene-based polyolefin copolymer" each refer to a repeating polymer chain comprising at least 60 wt.% (wt.%) of propylene-derived structural units and 0.1 wt.% to 40 wt.% of structural units derived from one or more α-olefin comonomers. Examples of comonomers that can be used to manufacture polypropylene copolymers or propylene-based polyolefin copolymers are C2 and C4 to C10 α-olefins. All individual values ​​and subranges from 0.1 wt.% to 40 wt.% are included herein and disclosed herein. For example, the wt.% of units derived from one or more α-olefin comonomers may be from a lower limit of 0.1 wt.%, 1 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 7 wt.%, or 9 wt.% to an upper limit of 40 wt.%, 35 wt.%, 30 wt.%, 27 wt.%, 20 wt.%, 15 wt.%, 12 wt.%, or 9 wt.%. For example, a polypropylene copolymer may contain 0.ea1 wt.% to 35 wt.% of structural units derived from one or more α-olefin comonomers; or alternatively, a polypropylene copolymer may contain 1 wt.% to 30 wt.% of structural units derived from one or more α-olefin comonomers; or alternatively, a polypropylene copolymer may contain 3 wt.% to 27 wt.% of structural units derived from one or more α-olefin comonomers; or alternatively, a polypropylene copolymer may contain 3 wt.% to 20 wt.% of structural units derived from one or more α-olefin comonomers; or alternatively, a polypropylene copolymer may contain 3 wt.% to 15 wt.% of structural units derived from one or more α-olefin comonomers; embodiments of this disclosure specify that, according to ASTM D792, the nonfunctional polypropylene copolymer has a content of less than 0.900 g / cm³. 3 The density. For example, nonfunctional polypropylene copolymers can have a density of 0.858 g / cm³. 3 Up to 0.891 g / cm 3 The density is within the range of 0.858 g / cm³. 3 Up to 0.891 g / cm 3 All individual values ​​and subranges are included and disclosed herein. For example, a nonfunctional polypropylene copolymer may have a value of 0.858 g / cm³. 3 0.860 g / cm 3 Or 0.862 g / cm 3 The lower limit is 0.891 g / cm³. 3 0.878 g / cm 3 Or 0.876 g / cm 3The upper limit of the density. Embodiments of this disclosure specify that, according to ASTM D792, the high-melting-point acid-functionalized propylene-based polyolefin copolymer has a density of at least 0.900 g / cm³. 3 The density. For example, high-melting-point acid-functionalized propylene-based polyolefin copolymers can have a density of 0.900 g / cm³. 3 Up to 0.910 g / cm 3 The density within the range, all individual values ​​and subranges are included in this document and disclosed herein.

[0024] The nonfunctionalized polypropylene copolymer base polymer includes nonfunctionalized propylene-co-olefin copolymers, wherein the weight-to-weight ratio of propylene to olefin structural units is in the range of 99.8:0.2, preferably 99.7:0.3, and more preferably 99.6:0.4 to 50:50, more preferably to 60:40, and most preferably to 65:35. Preferred nonfunctionalized propylene-co-olefin copolymers include propylene-co-ethylene, propylene-co-octene, propylene-co-butene, propylene-co-hexene, or mixtures thereof. Commercial examples of nonfunctionalized polypropylene copolymer base polymers include: VERSIFY. TM 4200 (propylene-ethylene copolymer, with a melt index of 25 g / 10 min (2.16 kg at 230 °C) according to ASTM D1238 and 0.876 g / cm³ according to ASTM D792). 3 (density and melting point of 84℃) and VERSIFY TM 3000 (propylene-ethylene copolymer, with a melt index of 8 g / 10 min (2.16 kg at 230°C) according to ASTM D1238 and 0.891 g / cm³ according to ASTM D792). 3 The density and melting point of the polymer (108°C); all were purchased from Dow, Inc. or its affiliates. The concentration of the nonfunctionalized polypropylene copolymer base polymer is sufficient to produce a cured film with a retort adhesion of 4B, more preferably 5B (measured at 135°C / 60 min, 2% lactic acid) on a metal substrate; the concentration is preferably up to 60% by weight, more preferably up to 50% by weight, preferably at least 15% by weight, and more preferably at least 30% by weight, based on the weight of the polymer solids in the dispersion. Preferably, the concentration of the nonfunctionalized polypropylene copolymer base polymer is preferably in the range of 15% by weight, more preferably 30% by weight to 60% by weight, more preferably to 50% by weight, based on the weight of the polymer solids in the dispersion.

[0025] The high-melting-point acid-functionalized propylene-based polyolefin base polymer is an acid- or anhydride-functionalized propylene homopolymer or copolymer having an acid value in the range of 0.5 to 20 and a melting point at or above 130°C as determined by DSC as described in the Experiments and Examples section. The concentration of the high-melting-point acid-functionalized propylene-based polyolefin base polymer is sufficient to produce a cured film with a retort adhesion of 4B, more preferably 5B (measured at 135°C / 60 min, 2% lactic acid) on a metal substrate; preferably less than 70% by weight, more preferably less than 65% by weight, preferably more than 25% by weight, and more preferably more than 30% by weight, based on the weight of polymer solids in the dispersion. Preferably, the concentration of the high-melting-point acid-functionalized propylene-based polyolefin base polymer is in the range of greater than 25% by weight to less than 70% by weight, based on the weight of polymer solids in the dispersion. Commercial examples of high-melting-point acid-functionalized propylene-based polyolefin base polymers include: Fusabond P613 (an anhydride-modified polypropylene with a melt index of 49 g / 10 min (190 °C / 1.0 kg) according to ASTM D1238 and 0.903 g / cm³ according to ASTM D792). 3 The density and melting point of the polypropylene are 162°C according to ASTM D3418, and Fusabond P353 (an anhydride-modified polypropylene with a melt index of 22 g / 10 min (160°C / 325 g) according to ASTM D1238 and 0.904 g / cm³ according to ASTM D792). 3 (Density and melting point of 135°C according to ASTM D3418); all were purchased from Dow, Inc. or its affiliates.

[0026] wax

[0027] The functionalized polyolefin wax has an acid value in the range of 20 to less than 60, more preferably 25 to less than 60. All individual values ​​and subranges of 20 to less than 60 are included herein and disclosed herein. The functionalized polyolefin wax of this disclosure may include any material having a desired acid value (AN) and a desired melt index (500 g to 5,000,000 g, preferably 1,000 g or more of polymer melt passed through a heated syringe or cylinder at 190°C within 10 minutes via a plunger loaded with 2.16 kg), or alternatively, any material to which the polymer has a viscosity of 75 Pa·s to 10,000 Pa·s, preferably 150 Pa·s or higher as measured by DIN 53019 method (2010) at 170°C, wherein more than 50 wt.% of the polymer comprises propylene in polymeric form, which improves the compatibility between the acid-functionalized polypropylene base polymer of this disclosure and optional acid-functionalized polyolefin copolymer dispersants. The melt index of acid-functionalized polypropylene waxes will be significantly higher than the corresponding measures of both polypropylene copolymers and acid-functionalized polypropylene base polymers, and can be so high that viscosity may be a better practical measure for defining acid-functionalized polyolefin waxes. Suitable acid-functionalized polyolefin waxes may include acid-functionalized modified polypropylene, preferably maleic anhydride polypropylene copolymers, maleic anhydride-grafted polypropylene, or maleic anhydride-modified polypropylene waxes.

[0028] The concentration of the functionalized polyolefin wax is sufficient to produce a cured film with a post-reheat adhesion of 4B, more preferably 5B (measured at 135°C / 60 min, 2% lactic acid) on a metal substrate; preferably at least 2% by weight, and preferably at most 15% by weight, based on the weight of the polymer solids in the dispersion. Preferably, the concentration of the functionalized polyolefin wax is in the range of 2% to 15% by weight, based on the weight of the polymer solids in the dispersion. Commercially available functionalized polyolefin waxes include: LICOCENE TM PP MS 641 (maleic anhydride-grafted polypropylene wax (sometimes referred to as MA-g-PP), with an acid value of 41 according to QM-AA-634, a density of 0.93 g / cm³ according to ISO 1183, and a viscosity of 1100 mPa·s at 170°C according to QM-AA-158), was purchased from Clariant Corporation or its affiliates. For direct comparison, the melt flow index of Licocene PP MS 641 was estimated to be >700 g / 10 min (190°C / 2.16 kg) according to the method described in reference (Dutta A. Onviscosity-melt flow index relationship, Rheol Acta 23:565-569, 1984).

[0029] The dispersion solids may optionally contain 0.1% to 5% by weight of unfunctionalized wax, such as POLYWAX, purchased from Baker Hughes, Inc. or its affiliates. TM 655 polyethylene.

[0030] Neutralizing agent

[0031] The neutralizing agent can be an organic base or a volatile base having a boiling point of less than 250°C. Suitable organic bases or volatile bases include ammonia or amines; examples of suitable amines include N,N-dimethylethanolamine (DMEA), diethylamine, and morpholine. Preferably, the neutralizing agent is ammonia or dimethylethanolamine (DMEA). The concentration of the neutralizing agent is high enough to neutralize at least half of the carboxylic acid groups present in the dispersion composition. For example, if the dispersion composition contains 0.05 mol of carboxylic acid groups by a given mass, at least 0.025 mol of a base such as DMEA will be required. Therefore, the molar ratio of the basic functional group in the neutralizing agent to the carboxylic acid group in the dispersion composition is at least 0.5:1. Preferably, this ratio is in the range of 0.7:1, more preferably 0.9:1 to 2.5:1, to preferably 2:1, and more preferably to 1.7:1.

[0032] Other components

[0033] The composition may optionally be mixed or formulated with one or more additional components or additives, as will be understood by those skilled in the art. Examples of additives include, but are not limited to, crosslinking agents, other water-based dispersions, resin binders (including but not limited to epoxy resins, polyurethanes, polyesters, polyvinyl chloride-containing organosol / vinyl resins, phenolic resins, alkyd resins, oleopolymers, acrylic resins, etc.), pigments, fillers, wetting agents, defoamers, solvents, rheology modifiers, surfactants, antioxidants, catalysts, flow agents, release agents, slip agents, lubricants, anti-caking agents, additives for masking sulfur dyeing, anti-settling agents, UV stabilizers, tackifiers, corrosion inhibitors, preservatives, and other additives that improve the aesthetic and performance properties of the coated metal. Various additives in different amounts can be used for different coating applications.

[0034] As mentioned, the coating compositions disclosed herein can be applied to metallic substrates. Examples of metallic substrates include, but are not limited to, metal sheets or rolls, beverage cans, food cans; aerosol containers, such as those used for non-food products, such as hairspray, hair dye, or color spray paint; drums; small barrels; buckets; decorative cans; open trays; tubes; bottles; integral parts; caps, lids such as foil-based caps or crown stoppers for yogurt and butter containers; closures for glass jars and bottles, such as roll-on closures, vacuum closures, tamper-evident closures, easy-peel caps for can closures, and easy-open or conventional ends for cans. Cans to which the coating compositions disclosed herein can be applied can be two-piece or three-piece cans. Beverage cans include, but are not limited to, beer cans, carbonated soft drink cans, sports drink cans, isotonic beverage cans, water cans, juice cans, tea cans, coffee cans, milk cans, etc. Food cans include, but are not limited to, vegetable cans, fruit cans, meat cans, soup cans, ready-to-eat food cans, fish cans, cooking oil cans, sauce cans, etc. Such containers can have various shapes. For example, they can be cylindrical, cubic, spherical, hemispherical, bottle-shaped, elongated cubic, shallow or tall, circular or rectangular, or other suitable shapes or combinations thereof. Examples of metals include, but are not limited to, aluminum and aluminum alloys, steel, electrolytic tinplate cold-rolled low-carbon mild steel, electrolytic chromium / chromium oxide coated cold-rolled low-carbon mild steel, and other pretreated steels. Pretreatment may include, but is not limited to, treatment with phosphoric acid, zirconium phosphate, chromium phosphate, Cr(III) and Cr(VI) compounds, and silanes, for reasons such as primary corrosion protection and improved adhesion. The metal substrate may include sheets, strips, or rolls. The substrate may be pre-coated with one or more pre-coating compositions. Such pre-coating compositions include, but are not limited to, one or more resin adhesives, one or more resin crosslinking agents, one or more solvents, one or more additives, and one or more pigments. Examples of resin adhesives include, but are not limited to, epoxy resins, polyurethanes, polyesters, polyvinyl chloride-containing organosol / vinyl resins, phenolic resins, alkyd resins, oleopolymers, acrylic resins, coatings derived from polyolefin dispersions, etc. Examples of crosslinking agents include, but are not limited to, hydroxyalkylamides, phenol-formaldehyde resins; aminoformaldehyde resins, including but not limited to urea-formaldehyde, melamine-formaldehyde, and benzoguanamine-formaldehyde; acid anhydride resins, end-capped isocyanate resins, and epoxy-containing resins, including but not limited to epoxy resins, epoxy-containing polyesters, acrylic resins, and vinyl resins. Examples of solvents and diluents include, but are not limited to, ethylene glycol ethers, alcohols, aromatic compounds (such as aromatic hydrocarbons), petroleum solvents, branched ketones, and esters. Examples of additives include, but are not limited to, catalysts, lubricants, wetting agents, defoamers, flow agents, release agents, slip agents, anti-caking agents, additives for masking sulfur dyeing, pigment wetting / dispersing agents, anti-settling agents, UV stabilizers, and tackifiers. Pigments include, but are not limited to, titanium dioxide, carbon black, zinc oxide, aluminum oxide, zinc, and aluminum. The substrate may also be pre-coated with one or more pre-coated laminating compositions.Such compositions may include, for example, polyethylene, polypropylene, or polyester compositions, and may be applied as a film to a metal substrate via a film lamination process or a melt extrusion coating process.

[0035] Metal substrates can be formed by stamping, drawing, redrawing, hot stamping, bending, beading, embossing, debossing, flanging, necking, stretching, blow stretching, and / or other suitable conventional methods. Such methods are known to those skilled in the art. According to several embodiments, a coating composition can be applied, for example, to a metal substrate, such as a metal sheet or foil, and the coated substrate can then be formed into a coated article, such as a container device like a metal can or a coated closure. According to several embodiments, the substrate can be formed into a container, such as a container device or closure, and the container device or closure can then be coated with a coating composition to form a coated article. The coating composition can be applied by a variety of methods. For example, via roll coating, spraying, powder coating, dip coating, electrodeposition coating, printing, wash coating, flow coating, blade coating, and / or curtain coating. The coating, i.e., the coating composition applied to the metal substrate, can have a thickness ranging from 0.01 micrometers (μm) to 2 millimeters (mm). All individual values ​​and subranges of 0.01 μm to 2 mm are included herein and disclosed herein. For example, the coating can have a thickness from a lower limit of 0.01 μm, 0.05 μm, or 1 μm to an upper limit of 2 mm, 1.5 mm, or 1 mm. For example, the coating can have a thickness of 0.01 μm to 2 mm; 0.05 μm to 1.5 mm; or, alternatively, 0.1 μm to 1 mm. According to various embodiments, the coating can have a thickness in the range of 5 μm to 50 μm, preferably 1 μm to 20 μm, and more preferably 7 μm to 10 μm. The coating can also be stacked on top of each other as a multilayer coating.

[0036] The coating composition applied to a substrate can be cured, for example, to form a cured coating. The curing process may include drying, such as air drying, convection oven drying, hot air drying, and / or infrared oven drying. According to several embodiments, curing may include radiation curing, such as electron beam curing. The coating composition applied to the substrate can be cured at a metal temperature in the range of 140°C to 375°C for less than 60 minutes, for example, less than 40 minutes, less than 30 minutes, less than 20 minutes, less than 10 minutes, less than 5 minutes, less than 2 minutes, less than 1 minute, or less than 20 seconds. All individual values ​​and subranges of 140°C to 375°C are included herein and disclosed herein. For example, the coating composition applied to the substrate can be cured at a metal temperature in the range of 160°C to 260°C for less than 60 minutes, such as less than 40 minutes, less than 20 minutes, less than 10 minutes, less than 5 minutes, less than 2 minutes, or less than 1 minute. Alternatively, the coating composition applied to the substrate can be cured at a metal temperature in the range of 180°C to 235°C for less than 60 minutes, such as less than 40 minutes, less than 10 minutes, less than 5 minutes, less than 2 minutes, or less than 1 minute.

[0037] As mentioned, for some coating applications, it is desirable for the coated article to simultaneously provide performance characteristics, such as specific mechanical and chemical resistance, as well as specific appearance properties. Specific mechanical properties required for some coating applications include a König hardness value, such as a König hardness value greater than 70 seconds. Specific chemical resistance requirements for some coating applications include a methyl ethyl ketone (MEK) dual friction value; for example, a MEK dual friction value of 200 or greater is required for some coating applications; and appearance ratings after cooking, such as in 2% lactic acid solutions, 3% acetic acid solutions, and 3% citric acid solutions.

[0038] Experimental preparation and testing methods

[0039] Dispersion preparation

[0040] The polyolefin aqueous dispersion (POD) was prepared according to the procedure in the examples. The degree of neutralization (DoN), expressed as a percentage of the polyolefin dispersion, was determined according to the following equation:

[0041]

[0042] Where W is the weight (grams) of the added alkali, and E B It is the equivalent weight of the base, A i It is the acid value of the i-th component (in mgKOH / g) and ω i It is the weight fraction of the i-th component in the POD dispersion solid.

[0043] Coating formulations and preparation

[0044] When preparing POD-based can coating formulations, aqueous and / or water-soluble components are added to the POD dispersion before the addition of solvent-based and / or water-insoluble components. The pH of the aqueous components is typically adjusted to a level similar to the pH of the POD dispersion using alkaline water (e.g., 0.3% dimethylethanolamine (DMEA) dissolved in DI water), typically 9 to 10. Primid, purchased from EMS-Chemie AG. TM QM-1260 is a hydroxyalkylamide compound derived from its own diacid and diisopropanolamine, and is used as a crosslinking agent for acidic functional groups in POD resin blends. Primid TM The content of QM-1260 is calculated based on the required equivalent of the acid functional groups using the following equation:

[0045]

[0046] Where W is the amount of Primid per 100g of resin blend. TM The weight of the QM-1260. A i It is the acid value (expressed in mg KOH / g) of the i-th component in the resin blend, ω i It is the weight fraction of the i-th component, and 94 is the Primid. TM The equivalent molecular weight of the hydroxyl group in QM-1260, and E is the Primid in the formulation. TM QM-1260 design equivalent. Typically, Primid... TM QM-1260 is added after being dissolved in alkaline water at a concentration of 30 wt%.

[0047] The Primid with a total acid functionality of 0.25 equivalents was used. TM QM-1260 was added to the exemplary POD coating formulations included in this application. Acrysol TM ASE 75 thickener (acid-containing acrylic emulsion copolymer purchased from Dow, Inc.) is added at 1% by weight of the total formulation to adjust the viscosity. All formulations also contain a 1 / 1 mixture of butanol and butyl ether (CELLOSOLVE). TM (Fast-evaporating glycol ether purchased from Dow, Inc.) with a POD solids ratio of 0.4. All exemplary formulations have a formulation solids content of 26 wt%.

[0048] Metal-coated sample preparation

[0049] Before preparing the coated substrate, the coating formulation is typically aged at room temperature for at least overnight. A doctor blade coating is prepared on the substrate using a wire-wound doctor blade (typically #16) on a tinplate substrate (0.25# Bright T-1 measurement .009" × 4" × 12") supplied by Lakeside Metal. Unless otherwise specified, the coating is cured in a Despatch oven (serial number 183952) at 205°C for 4 minutes. The dry coating thickness is typically in the range of 7 μm to 10 μm (0.3 mils to 0.4 mils).

[0050] DSC Standard Methodology

[0051] Differential scanning calorimetry (DSC) results were determined using a TA Instruments Q1000DSC equipped with an RCS cooling accessory and an autosampler. A nitrogen purge flow of 50 ml / min was used. The sample was pressed into a thin film and melted in a press at approximately 175 °C, then air-cooled to room temperature (25 °C). 3 mg to 10 mg of material was then cut into 6 mm diameter discs, accurately weighed, placed in a lightweight aluminum disc (approximately 50 mg), and then rolled up. The thermal behavior of the sample was investigated using the following temperature profiles. The sample was rapidly heated to 180 °C and held isothermally for 3 minutes to remove any prior thermal history. The sample was then cooled to -90 °C at a cooling rate of 10 °C / min and held at -90 °C for 3 minutes. The sample was then heated to 180 °C at a heating rate of 10 °C / min. The cooling and heating profiles were recorded.

[0052] The DSC melting peak temperature is measured as the maximum heat flux (W / g) relative to a linear baseline plotted between -30°C and the end of melting. The heat of fusion is measured as the area under the melt curve using a linear baseline between -30°C and the end of melting. For vinyl materials, the total percentage crystallinity is equal to 100 * sample enthalpy / enthalpy of PE crystals, where the enthalpy of perfect polyethylene crystals is equal to 292 J / g, as reported in Macromolelcular Physics, Vol. 1, Academic Press, New York, 1973, p. 154. For propylene-based materials, the total percentage crystallinity is equal to 100 * sample enthalpy / enthalpy of PP crystals, where the enthalpy of perfect polypropylene crystals is equal to 165 J / g, as reported by P. Edward, J.R. Moore, Polypropylene Handbook, Hanser Publisher, Cincinnati, 1996.

[0053] Boiling test

[0054] Tuttnauer TMAn EZ10 autoclave or similar autoclave is used for the cooking test. A 2"×3" (2 inch × 3 inch) strip cut from the coated sample is placed in a glass beaker half-filled with food simulant. The beaker is covered with aluminum foil and then treated in the autoclave at 135°C for 60 minutes. The autoclave is allowed to cool to 60°C, then opened and the test sample is removed. The test sample is rinsed and patted dry, and then a cross-cut adhesion test is performed on the area immersed in the simulant 30 minutes after removal from the autoclave. A 2% lactic acid solution in deionized water is used as the simulant in the example disclosed in this invention.

[0055] Cross-cut adhesion test

[0056] Adhesion was measured using the cross-cut adhesion test according to ASTM D 3359-09. Method "B" was used because the coating thickness was less than 5 mils. In this test, a square grid pattern was created with 10 cuts in each direction, with a distance of 1 mm between two adjacent cuts. Pressure-sensitive adhesive tape was applied to the grid and then removed. Adhesion was evaluated according to the following ratings:

[0057] 5B: The edges of the cut are perfectly smooth; no squares are detached from the grid.

[0058] 4B: Thin flakes of coating detach at the intersection; less than 5% of the area is affected.

[0059] 3B: Small flakes of coating detach along the edges and at the intersections of the cuts. The affected area is 5% to 15% of the grid.

[0060] 2B: The coating peels off along the edges and on a portion of the square. The affected area is 15% to 35% of the grid.

[0061] 1B: The coating has peeled off along the cut edges in the large strip and the entire square has detached. The affected area is 35% to 65% of the grid.

[0062] 0B: Peeling and detachment are worse than grade 1.

[0063] Materials used

[0064] Table 1 shows the materials used to prepare polyolefin dispersions.

[0065] Table 1: POD Materials

[0066] Example:

[0067] Example 1—Preparation of an aqueous dispersion of polypropylene—P613 base polymer, V4200 base polymer, wax, and dispersant in a ratio of 32:51:10:7 (w / w / w / w).

[0068] Using a rate-controlled feeder, P613 was added to a 25mm diameter twin-screw extruder at rates of 24.2 g / min, V4200 at 38.6 g / min, Lico641 at 7.6 g / min, and U350 at 5.3 g / min to propel and melt-blend these components. The extruder temperature profile was raised to approximately 170°C. Water and alkali (dimethylethanolamine / DMEA) as a neutralizing agent were fed into the extruder at rates of 5.9 g / min and 3 g / min, respectively. Diluent water was pumped into the dilution zone of the extruder at a rate of 90 g / min. The extruder temperature profile was cooled back to below 100°C at the extruder end. The extruder speed was approximately 450 rpm. At the extruder outlet, a back pressure regulator was used to adjust the appropriate pressure inside the extruder barrel to reduce steam formation. The resulting aqueous dispersion was filtered through a 100-micron filter. The remaining dispersion examples and comparative dispersion examples shown in Table 2 were prepared according to the procedure of Dispersion Example 1, but using the components listed in Table 2. The solids content of the aqueous dispersion examples and comparative examples listed in Table 2 was measured using an infrared solids analyzer; and the particle size of the solid particles in the aqueous dispersion examples and comparative examples in Table 2 was measured using a COULTER analyzer. TM Measurements were taken using an LS-230 particle size analyzer (Beckman Coulter Corporation, Fullerton, CA). Solid content ranged from 30 wt.% to 50 wt.%, and the average particle size (PS) of the solid particles in the dispersion was 10 nm to 10 μm. Table 2 also shows the post-cooking adhesion test results for each metal-coated sample as described in the experimental preparation and testing methods. PP represents polypropylene, PE represents polyethylene, and HDPE represents high-density polyethylene.

[0069] Table 2: Post-reboil adhesion of formulated polyolefin dispersion-derived coatings applied to tin plates

[0070]

[0071]

Claims

1. A method for preparing a coated metal substrate, the method comprising the following steps: a) Applying a coating formulation derived from an aqueous dispersion composition to a metal substrate, said aqueous dispersion composition comprising: i) Based on the weight of the polymer solids in the aqueous dispersion composition, 1% to 15% by weight of a fatty acid dispersant having 14 to 60 carbon atoms and an acid value in the range of 60 to 250. ii) Based on the weight of polymer solids in the aqueous dispersion composition, greater than 25% by weight and less than 70% by weight of an acid-functionalized propylene-based copolymer, wherein the acid-functionalized propylene-based copolymer has an acid value in the range of 0.5 to 20 and a melting point at or above 130°C as determined by DSC. iii) 15% to 60% by weight of nonfunctionalized propylene-co-olefin-based copolymer, based on the weight of polymer solids in the aqueous dispersion composition; iv) Based on the weight of the polymer solids in the aqueous dispersion composition, 2% to 15% by weight of a functionalized polyolefin wax, wherein the acid value of the functionalized polyolefin wax is in the range of 25 to less than 60; and v) A neutralizing agent, wherein the neutralizing agent is an organic base or volatile base having a boiling point of less than 250°C; and b) The aqueous dispersion composition is cured by heating or solidifying it to produce a cured film with a thickness in the range of 1 µm to 20 µm.

2. The method of claim 1, wherein the aqueous dispersion composition further comprises, based on the weight of the polymer solids in the aqueous dispersion composition, 5% to 30% by weight of an acid-functionalized polyolefin dispersant copolymer, the acid-functionalized polyolefin dispersant copolymer having a molecular weight of at least 10,000 as determined by GPC and an acid value between 60 and 250.

3. The method according to claim 1, wherein the cured film has a thickness in the range of 2µm to 10µm.

4. The method of claim 1, further comprising the step of mixing the aqueous dispersion composition with one or more additives prior to curing the aqueous dispersion composition, wherein the one or more additives are selected from crosslinking agents, other water-based dispersions, pigments, resin binders, wetting agents, defoamers, solvents, rheology modifiers, surfactants, antioxidants, fillers, catalysts, flow agents, release agents, slip agents, lubricants, antiblocking agents, additives for masking sulfur dyeing, UV stabilizers, thickeners, corrosion inhibitors, preservatives, and combinations thereof.

5. The method of claim 1, further comprising the step of mixing the aqueous dispersion composition with one or more additives prior to curing the aqueous dispersion composition, wherein the one or more additives are selected from crosslinking agents, other water-based dispersions, pigments, resin binders, wetting agents, defoamers, solvents, surfactants, antioxidants, fillers, catalysts, flow agents, release agents, slip agents, lubricants, anti-blocking agents, additives for masking sulfur dyeing, anti-settling agents, UV stabilizers, thickeners, corrosion inhibitors, preservatives, and combinations thereof.

6. A metal-coated article, said metal-coated article being prepared by the method according to any one of claims 1 to 5.

7. The article of claim 6, wherein the metal-coated article is part of a beverage can or a food can.

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