WO2025118093A1

WO2025118093A1 - Article coated with high-density polyethylene and a dispersant

Info

Publication number: WO2025118093A1
Application number: PCT/CN2023/136053
Authority: WO
Inventors: Yifan Xu; Qiangqiang YAN; Zheng Zhang; Xiaomei Song; Hanze YING; David L. Malotky; Wenwen MEI; Ray E. Drumright
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2023-12-04
Filing date: 2023-12-04
Publication date: 2025-06-12
Anticipated expiration: 2026-06-04

Abstract

An article comprising a substrate superposed with a cured coating comprising a high-density polyethylene and a dispersant having a degree of neutralization in the range of from 5 to 60 percent, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt; wherein the coating has a coat weight in the range of from 1 g/m2 to 20 g/m2. The coated article exhibits an exceptional moisture vapor transmission rate even at low areal density of the cured coating.

Description

Article Coated with High-Density Polyethylene and a Dispersant

Summary of the Invention

The present invention relates to an article coated with a high-density polyethylene and a poly (ethylene- (meth) acrylic acid) dispersant. The article is useful in packaging applications, especially paper packaging applications.

Paper products used in the packaging industry require a low coat weight superposing film that exhibits low moisture vapor transmission rate (MVTR) properties. This combination of low coat weight with concomitant low MVTR is essential for attaining the dual goals of protecting food from spoilage and recycling the coated paper.

The art discloses delivering low MVTR for paper package using extruded films of polyvinylidene chloride (PVDC) or high-density polyolefin (HDPE) . PVDC provides excellent MVTR as compared with HDPE, but environmental concerns regarding chlorinated hydrocarbons renders this approach commercially unacceptable. Moreover, in each instance, acceptable MVTRs are achievable using film areal densities (coat weights) that are prohibitively high (＞ 15 g/m²) for recyclability.

Waterborne dispersions have been used to deliver acceptable coat weight of ＜ 10 g/m², yet low MVTRs remain a challenge. While different approaches such as adding wax have been reported, (WO 2022/243445 A1) the demonstrated MVTR is too high (60 g/m²/day even under nontropical conditions of 23 ℃ and 50%relative humidity) at a coat weight of 10 g/m². Moreover, the presence of wax in coatings can render the fibers unsuitable for reuse. In the absence of wax, many waterborne coatings demonstrate subpar MVTR performance compared with the extruded polyolefin/PVDC films, which is the bottleneck for further adoption for real packages. Consequently, alternative solutions based on waterborne coatings are needed to deliver MVTR of ≤ 40 g/m²/day at coat weights ＜ 15 g/m².

Summary of the Invention

The present invention addresses a need in the art by providing, in one aspect, an article comprising a substrate superposed with a cured coating comprising, based on the weight of cured coating, a) from 45 to 75 weight percent of a high-density polyethylene having a density in the range of from 0.93 g/cm³ to 0.97 g/cm³; and b) from 25 to 55 weight percent of a dispersant having a degree of neutralization in the range of from 5 to 60 percent, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt; wherein the mole-to-mole ratio of units of ethylene to units of (meth) acrylic acid and the (meth) acrylic acid salt is in the range of from 95: 5 to 90: 10; wherein the coating has a coat weight in the range of from 1 g/m² to 20 g/m². The article of the present invention is useful in packaging applications, particularly paper packaging applications that require a coating with a low MVTR and a low coat weight.

Detailed Description of the Invention

In one aspect, the present invention is an article comprising a substrate superposed with a cured coating comprising, based on the weight of the cured coating, a) from 45 to 75 weight percent of a high-density polyethylene having a density in the range of from 0.93 g/cm³ to 0.97 g/cm³; and b) from 25 to 55 weight percent of a dispersant having a degree of neutralization in the range of from 5 to 60 percent, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt; wherein the mole-to-mole ratio of units of ethylene to units of (meth) acrylic acid and the (meth) acrylic acid salt is in the range of from 95: 5 to 90: 10; wherein the coating has a coat weight in the range of from 1 g/m² to 20 g/m².

The term “ (meth) acrylic acid” refers to acrylic acid or methacrylic acid. Similarly, (meth) acrylic acid salt” refers to a salt of acrylic acid or methacrylic acid, preferably a lithium, sodium, or potassium salt.

The term “units” of the recited monomer refers to the remnant of the monomer after polymerization. For example, a structural unit of methacrylic acid is as illustrated:

where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.

The term “cured coating” refers to a coalesced coating arising from applying an aqueous dispersion of high-density polyethylene particles and the dispersant to the surface of the substrate, which may be pretreated with one or more pre-coats, and drying the coating. Examples of substrates are paper, metal, glass, and plastic substrates.

The concentration of the high-density polyethylene, based on the weight of the cured coating, is in the range of from 45 or from 50 or from 55 weight percent, to 75 or to 70 weight percent, based on the weight of the cured coating; the concentration of the dispersant, based on the weight of the cured coating, is in the range of from 20 or from 25 or from 30 weight percent, to 55 or to 50 or to 45 weight percent, based on the weight of the cured coating.

The high-density polyethylene has a density in the range of from 0.930 g/cm³, preferably from 0.945 g/cm³, to 0.970 g/cm³ preferably to 0.960 g/cm³more preferably to 0.955 g/cm³. DOW^TM DMDA-8940 NT 7 and DOW^TM DMDA-8965 NT 7 High Density Polyethylene Resins (density = 0.951 g/cm³) are examples of commercially available high-density polyethylene resins.

The degree of neutralization of the dispersant in the cured coating (calculated as described in the example section) is in the range of from 5 or from 15 or from 30 or from 45 or from 50 percent to 60 or to 58 or to 55 percent. The dispersant is neutralized with a hard base, which is an alkali metal hydroxide, carbonate, or bicarbonate such as LiOH, NaOH, KOH, LiHCO₃, NaHCO₃, KHCO₃, and Na₂CO₃.

The cured coating comprises high-density polyethylene, the dispersant, and optionally ancillary solids such as extenders, waxes, and compatibilizers. In one aspect, the high-density polyethylene and the dispersant comprise more than 90 or at least 92 or at least 95 or at least 97 weight percent of the cured coating.

The cured coating is conveniently prepared by applying to the substrate an aqueous dispersion of high-density polyethylene and the dispersant, then removing the water, preferably at an advanced temperature, to form a cured (dried) coating with a coat weight in the range of from 1 g/m², preferably from 3 g/m², more preferably from 5 g/m², and most preferably from 7 g/m² to 20 g/m², preferably to 15 g/m², more preferably to 12 g/m², and most preferably to 10 g/m².

The aqueous dispersion comprises high-density polyethylene and the dispersant, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt at a solids content preferably in the range of from 30 to 60 percent; wherein the mole-to-mole ratio of units of ethylene to units of (meth) acrylic acid and the (meth) acrylic acid salt is in the range of from 95: 5 to 90: 10, and wherein the dispersant has a degree of neutralization, wherein from 5 to 60 percent the degree of neutralization of the dispersant is attributable to a hard base. Accordingly, the dispersant may be neutralized in part with a fugitive base that boils off or evaporates when the composition is applied to a substrate and cured. Examples of fugitive bases are ammonium hydroxide, amines, and amino alcohols, examples of which include ethylene diamine, N-ethylmonoethanol amine, N-ethyldiethanolamine, N, N′-dimethylmonoethanolamine, and N, N′-diethylmonoethanolamine. Accordingly, while a fugitive base (if present in the composition) contributes to the degree of neutralization of the composition or coating in the wet state, the degree of neutralization of the cured coating arises from the presence of the hard base.

It has been surprisingly discovered that a coated article can be prepared with a coat weight of ＜ 12 g/m² and a moisture vapor transition rate at 38 ℃ and 90%relative humidity of 60 g/m²/d, preferably less than 50 g/m²/d, and more preferably less than 40 g/m²/d, especially where the article is a paper article.

Examples

Method for Preparing Coated Substrates and Measuring Coat Weights

UPM Brilliant 62 Glassine Paper (basis wt. 62 g/m²) was coated with the polyolefin dispersion using a drawdown bar and dried in a forced air oven for 2 min at 100 ℃ to a final coating areal density (coat weight) of 8 g/m² (～ 8 to 9 μm coating thickness) . Coat weights were measured by punching holes in coated and uncoated UPM paper with a circular die to form discs having a specified diameter (D cm) . The coated discs (W1) were weighed against the uncoated disc (W2) and the coat weights were calculated by the formula:

Moisture Vapor Transmission Rate Measurements

Moisture Vapor Transmission Rates (MVTRs) were determined in accordance with ASTM E96/E96M. A coated paper sample was sealed to the open end of a permeability cup followed by exposure of the sample to a controlled temperature and humidity environment (typically, a humidity chamber) . MVTR was determined based by measuring mass uptake for the cup as a function of time.

Calculation of Degree of Neutralization

The degree of neutralization of the polyolefin dispersions was determined by the following equation:

where A is the total number of acid units and B is the total number acid salt units.

General Procedure for Preparation of Aqueous Dispersions of Polyolefin Dispersions

DOW^TM DMDA-8940 NT 7 High Density Polyethylene Resin (HDPE resin) and poly (ethylene-methacrylic acid) dispersant pre-neutralized with 17 mole percent NaOH (pEMAA, with an ethylene: COOH: COO^-mole: mole: mole ratio of 93.5: 5.4: 1.1) were fed into a 25-mm diameter twin screw extruder using separate controlled rate feeders. The HDPE resin and dispersant were then forwarded through the extruder and melted to form an intermediate polymer melt blend.

The extruder temperature profile was ramped up to 150 ℃ for Dispersions 1, 2, 3, 4, and 120 ℃ for Dispersions 5, 6, and 7. Water and an aqueous solution of KOH (25%or 30%KOH) were mixed together from separate sources at predetermined flow rates and fed to the extruder at an initial water (H₂O_o) introduction site after a uniform polymer melt blend was formed; then, dilution water (H₂O_d) was fed into the extruder. The extruder speed was 450 rpm for all samples. At the extruder outlet, a backpressure regulator was used to adjust the pressure inside the extruder barrel to a pressure adapted to reduce steam formation, generally in the range of 2 MPa to 4 MPa.

Each aqueous dispersion exited from the extruder and was filtered first through a 200-μm filter. The solids content of dispersions was measured using an infrared solids analyzer, and the volume mean particle size of the polymer particles was measured using a COULTER^TM LS-230 particle size analyzer (Beckman Coulter Corporation, Fullerton, CA) .

Table 1 illustrates the flow rates for the various components used to make the dispersions. HDPE refers to the flow rate of the HDPE resin in g/min; pEMAA refers to the flow rate of the pEMAA in g/min; KOH refers to the flow rate of KOH in water in mL/min; NH₃refers to the flow rate of ammonia, 28%aq. in mL/min; H₂O_o refers to the flow rate of the water at the introduction site in mL/min; H₂O_d refers to the flow rate of the dilution water in mL/min; and PS refers to the volume mean particle size of the dispersed particles. The concentration of KOH was 25%KOH based on the weight of KOH and water, except dispersion 12, which was 30%KOH based on the weight of KOH and water.

Table 1 -Components and Flow Rates used to Prepare Dispersions

The dispersions were used alone or in combination to prepare the example and comparative example compositions. When used in combination, the dispersions were blended using an overhead mixer.

Table 2 illustrates the Example and comparative example formulations.

Table 2 -Example and Comparative Example Formulations

Coated substrates were prepared and MVTRs were measured. Table 3 illustrates the MVTR for the examples and comparative examples.

Table 3 -MVTR Data

The data show the criticality of degree of neutralization. The best MVTRs are observed at a DoN at or below 60%.

Claims

An article comprising a substrate superposed with a cured coating comprising, based on the weight of cured coating, a) from 45 to 75 weight percent of a high-density polyethylene having a density in the range of from 0.93 g/cm³ to 0.97 g/cm³; and b) from 25 to 55 weight percent of a dispersant having a degree of neutralization in the range of from 5 to 60 percent, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt; wherein the mole-to-mole ratio of units of ethylene to units of (meth) acrylic acid and the (meth) acrylic acid salt is in the range of from 95: 5 to 90: 10; wherein the coating has a coat weight in the range of from 1 g/m² to 20 g/m².
The article of Claim 1 wherein the substrate is a paper, glass, metal, or plastic substrate.
The article of Claim 2 wherein the high-density polyethylene has a density in the range of from 0.945 g/cm³ to 0.960 g/cm³ and the substrate is paper, wherein the coating has a coat weight in the range of from 3 g/m² to 15 g/m².
The article of Claim 3 wherein the dispersant has a degree of neutralization in the range of from 15 to 60 percent, wherein the coating has a coat weight in the range of from 5 g/m² to 12 g/m².
The article of Claim 3 wherein the dispersant has a degree of neutralization in the range of from 45 to 60 percent.
The article of Claim wherein the dispersant has a degree of neutralization in the range of from 50 to 60 percent, wherein the (meth) acrylic acid units are methacrylic acid units; the (meth) acrylic acid salt units are sodium methacrylate units or potassium methacrylate units or a combination thereof, wherein the coating has a coat weight in the range of from 7 g/m² to 10 g/m².
The article of Claim 6 wherein, based on the weight of the cured coating, the concentration of the high-density polyethylene particles is in the range of from 50 to 70 weight percent, and the concentration of the dispersant is in the range of from 30 to 45 weight percent.
The article of any of Claims 1 to 7 wherein the high-density polyethylene and the dispersant comprise more than 90 weight percent of the cured coating.
The article of Claim 8 wherein the high-density polyethylene and the dispersant comprise at least 95 weight percent of the cured coating.
A process comprising the steps of:

1) applying to a paper substrate a coating of an aqueous dispersion comprising, based on the weight of composition solids, a) from 45 to 75 weight percent of high-density polyethylene having a density in the range of from 0.93 g/cm³ to 0.97 g/cm³; and b) from 25 to 55 weight percent of a dispersant having a degree of neutralization, wherein the dispersant is a copolymer containing ethylene units, (meth) acrylic acid units, and units of a (meth) acrylic acid salt; wherein the mole-to-mole ratio of units of ethylene to units of (meth) acrylic acid and the (meth) acrylic acid salt is in the range of from 95: 5 to 90: 10, and wherein from 5 to 60 percent the degree of neutralization of the dispersant is attributable to a hard base; then

2) curing the coating to a coat weight in the range of from 5 g/m² to 12 g/m².