Process for preparing polyolefin coating for paper substrate

Abstract

The present invention relates to a process comprising the steps of: a) applying to paper a composition comprising an aqueous dispersion of poly-C2-C3-olefin particles, a dispersant and a C5-C26-alkyl primary fatty amide; and b) drying the composition to form a coating having a coating weight in the range of 1 g / m2 to 20 g / m2. The method of the present invention can be used to prepare coatings on paper having desired moisture conversion and coefficient of friction characteristics.

Description

Background Art

[0001] The present invention relates to a process for preparing a thin polyolefin coating for a paper substrate. The coated paper has been found to have useful moisture vapor transmission rate properties.

[0002] Consumer demand for sustainable paper used in packaging is spurring interest in improving the barrier properties and recyclability of coated paper. It is known to enhance the barrier properties of paper using polyolefin coatings which also provide heat sealing properties; however, <10 g / m2 is achieved by applying an extruded polyolefin layer to a paper substrate. 2 Achieving these ultra-low coating weights is particularly important in flexible packaging applications where paper substrates have a coating area density (coat weight) of <60 g / m 2 of paper area density (basis weight), and where the market requires >85wt% fiber recycling based on the quality of the product.

[0003] As disclosed in US 10,612,193 B2 (column 2, Table 2), ultra-thin coatings can be prepared by applying a water-based polyolefin emulsion to a paper substrate followed by curing; however, meeting targets for moisture vapor transmission rate (MVTR) and coefficient of friction (CoF) remains elusive. Therefore, preparing thin coatings that meet application requirements for MVTR and provide recyclable packaging would be an advance in the art of coating paper substrates. Summary of the invention

[0004] The present invention solves the need in the art by providing a method comprising the steps of: a) applying a composition comprising poly-C2-C3-olefin particles, a dispersant and a C5-C 26 - an aqueous dispersion of an alkyl primary fatty amide; and b) drying the composition to form a dispersion having a 2 Up to 20g / m 2 The method of the present invention can be used to provide ultra-thin coatings on paper substrates having favorable moisture vapor transmission rate and coefficient of friction properties. DETAILED DESCRIPTION

[0005] The present invention is a method comprising the steps of: a) applying a composition comprising poly-C2-C3-olefin particles, a dispersant and C5-C 26 - an aqueous dispersion of an alkyl primary fatty amide; and b) drying the composition to form a dispersion having a 2 Up to 20g / m 2 coatings within a range of coating weights.

[0006] As used herein, "poly-C2-C3-olefin particles" refers to polyethylene particles, polypropylene particles, and poly(ethylene-propylene) copolymer particles. 10 -α-olefin copolymers (i.e., linear low density polyethylene), such as ethylene-1-butene copolymer, ethylene-1-hexene copolymer, and ethylene-1-octene copolymer. A commercially available linear low density polyethylene is AFFINITY PL1280 LLDPE ethylene-octene copolymer (a trademark of Dow Chemical Company or its affiliates). The polyethylene may also be a high density polyethylene, such as DOW TM DMDA-8940 NT 7 HDPE resin is commercially available; or low density polyethylene. An example of a commercially available ethylene-propylene copolymer is VERSIFY TM The polypropylene commercially available is Braskem 4200 propylene-ethylene copolymer (trademark of Dow Chemical Company or its affiliates), and the polypropylene commercially available is Braskem 6D43 random copolymer. It is believed that the particles containing the C2-C3-polyolefin and some amount of dispersant and primary fatty amide associated therewith preferably have a volume average particle size in the range of 200 nm or 300 nm to 5 μm or 3 μm or 1.5 μm as measured by dynamic light scattering.

[0007] The dispersant is a copolymer of ethylene and a carboxylic acid monomer or a salt thereof. Examples of suitable dispersants include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and ethylene-itaconic acid copolymers, and their lithium, sodium, and potassium salts.

[0008] The weight to weight ratio of the structural units of ethylene to carboxylic acid monomers or their salts is preferably in the range of 95:5, more preferably 90:10 and most preferably 85:15; to 70:30, more preferably 75:25. As used herein, the term "structural unit" of a given monomer refers to the residue of the monomer after polymerization. For example, the structural unit of methacrylic acid is shown below:

[0009]

[0010] The dotted lines represent the connection points between the structural units and the polymer backbone.

[0011] Examples of commercially available dispersants include PRIMACOR TM 5980i Ethylene-acrylic acid copolymer and NUCREL960 TM Ethylene methacrylic acid copolymer (a trademark of The Dow Chemical Company or its affiliates).

[0012] C5-C 26-Alkyl primary fatty amides may be straight chain or branched and may be saturated or partially unsaturated, with one or two or three double bonds. Fatty amides may also be C 10- -C 24 -alkyl primary fatty amide or C 16 -C 22 -alkyl primary fatty amides. Examples of suitable fatty amides include straight chain and branched C 18- -Alkyl monounsaturated fatty amides; linear and branched C 18 -Alkyl saturated fatty amides; straight chain and branched C 22 -Alkyl monounsaturated fatty amides; linear and branched C 22 -Alkyl saturated fatty amide. C5-C 26 The -alkyl primary fatty amide preferably has a melting point in the range of 50°C or 65°C to 115°C or 100°C or 90°C.

[0013] Based on polyolefins, dispersants and C5-C 26 The concentration of the poly-C2-C3-olefin particles minus any associated dispersant or primary fatty amide is preferably in the range of 40 wt % or 60 wt % or 70 wt % to 95 wt % or 90 wt %. 26- The concentration of the dispersant is preferably in the range of 4 wt % or 9 wt % or 15 wt % to 50 wt % or 40 wt % or 30 wt % based on the weight of the polyolefin particles, dispersant and C5-C 26 -The weight of alkyl fatty amide, C5-C 26 The concentration of the -alkyl primary fatty amide is preferably in the range of 0.5 wt% or 1 wt% to 5 wt% or 4 wt% or 3 wt%. The pH of the composition is preferably in the range of 8 to 11. A neutralizing agent such as KOH is advantageously used to adjust the pH to the desired level.

[0014] The composition advantageously also comprises a stabilizing amount of anionic surfactant such as C 10 -C 24 linear or branched alkyl or aralkyl carboxylates, sulfates or phosphates; or nonionic surfactants such as secondary alcohol ethoxylates or ethylene oxide propylene oxide block copolymer surfactants. The composition is advantageously applied to a paper substrate with a doctor bar, followed by removal of water, preferably at elevated temperature as described in the next section.

[0015] It has been found that it is possible to achieve 1g / m 2 or 2g / m 2 or 5g / m 2 Up to 20g / m 2 or 12g / m 2or 10g / m 2 The coating weight within the range of , and the desired moisture vapor transmission rate (MVTR) and coefficient of friction (CoF) properties.

[0016] Methods for preparing coated substrates and measuring coating weights

[0017] UPM Brilliant 62 glass paper (basis weight 62 g / m 2 ), and dried in a forced air oven at 100°C for 2 min to reach 8 g / m 2 The final coating area density (coating weight) of 100 μm (approximately 8 μm to 9 μm coating thickness) was measured by punching holes in coated and uncoated UPM paper with a circular die to form discs with a specified diameter (D cm). The coated disc (W1) was weighed relative to the uncoated disc (W2) and the coating weight was calculated by the following formula:

[0018]

[0019] Moisture Vapor Transmission Rate Measurement

[0020] Moisture Vapor Transmission Rate (MVTR) is determined according to ASTM E96 / E96M. A coated paper sample is sealed to the open end of a permeable cup, after which the sample is exposed to a controlled temperature and humidity environment (typically a humidity chamber). MVTR is determined by measuring the mass absorption of the cup over time.

[0021] Dynamic friction coefficient measurement

[0022] The coefficient of dynamic friction (CoF) is measured using a texture analyzer with a sliding friction device according to TAPPI T549. A piece of coated paper is attached to the bottom of a sled weighing 200 g, with the coated side facing down. Another piece of coated paper is attached to a flat surface, with the coated side facing up. A rope is attached to the sled and pulled so that the sled crosses the plane for at least 100 mm at a speed of 2.5 mm / s. The steady force Fd (in grams-force) of the constant movement of the sled is recorded. The dynamic CoF is calculated as Fd / 200.

[0023] Calculation of Neutralization Degree

[0024] The degree of neutralization of polyolefin dispersions is determined by the following equation:

[0025]

[0026] Where W is the weight of the added base (in g), E B is the equivalent weight of the base, A iis the acid value of the ith component (in mg KOH / g) and ω i is the weight fraction of the ith component in the solids of the POD dispersion.

[0027] Example

[0028] Table 1 shows the components and feed rates used to prepare Examples 1 to 4 and Comparative Examples 1 to 5. The feed rates are shown in parentheses. The general process is shown after Table 1. PO refers to polyolefin; amide refers to fatty amide; H2O o is the initial water rate; H2O d refers to the dilution water rate; Solids refers to the solid wt. % of polyolefin, dispersant, fatty amide and anionic surfactant in the dispersion; and PS refers to the particle size (in microns) of the particles as determined by dynamic light scattering.

[0029] PL1280 refers to AFFINITY TM PL 1280 LLDPE ethylene-octene copolymer; V4200 refers to VERSIFY TM Ethylene-propylene copolymer; N960 refers to NUCREL TM N960 ethylene-methacrylic acid copolymer. OA (oleamide, mp70℃) is C 18 -alkyl monounsaturated primary fatty amide; EA (erucic acid amide, mp 80°C) is C 22 -alkyl monounsaturated primary fatty amide; BA (behenic acid amide, mp112℃) is C 22 -alkyl saturated primary fatty amide; EBS (ethylene bis stearamide, mp145℃) is C 38 -alkyl secondary fatty amide; OPA (oleyl palmitamide, mp 60℃ to 66℃) is C 34 -alkyl secondary fatty amide; SEA (stearyl erucic acid amide, mp70℃ to 75℃) is C 40 -Alkyl secondary fatty amide.

[0030] The neutralization degree of Comparative Examples 1 to 4 and Examples 1 to 6 was 75%, and the neutralization degree of Comparative Example 5 and Example 7 was 80%.

[0031] Table 1 - Components and feed rates for the examples

[0032]

[0033] General process for preparing aqueous dispersions of polyolefin dispersions

[0034] Aqueous dispersions were prepared by the following general procedure:

[0035] PO, N960 and amide (except Comparative Examples 1 and 5) were fed into a 25-mm diameter twin screw extruder using separate controlled rate feeders. Anionic surfactant (oleic acid) was pumped into the melting zone of the extruder in liquid form using an Isco syringe pump at a feed rate of 3.4 mL / min. PO, N960 and amide were forwarded through the extruder and melted to form an intermediate liquid molten material.

[0036] The extruder temperature profile was raised to about 150°C. Water and a 30% aqueous solution. After a uniform polymer melt was formed, KOH was mixed and fed into the extruder at the initial water introduction location; dilution water was then fed into the extruder. The extruder speed for all samples was 450 rpm, except for Comparative Example 5, where the extruder speed was 400 rpm. At the extruder outlet, the pressure inside the extruder barrel was adjusted to a pressure suitable for reducing steam formation (typically, in the range of 2 MPa to 4 MPa) using a back pressure regulator.

[0037] Each aqueous dispersion was discharged from the extruder and first filtered through a 200-μm filter. The solid content of the dispersion was measured using an infrared solids analyzer and a COULTER TM The volume average particle size of the polymer particles was measured using an LS-230 particle size analyzer (Beckman Coulter Corporation, Fullerton, CA).

[0038] Table 2 shows the MVTR and CoF of the Examples and Comparative Examples. The coating thickness of each sample was 8 gsm. PO:N960:amide refers to the w / w / w ratio of polyolefin, dispersant and fatty amide.

[0039] Table 2 – MVTR and CoF of samples

[0040]

[0041]

[0042] The data show that the MVTR of the coating containing the primary fatty amide is improved when compared to the coating without the amide additive or the coating containing the secondary fatty amide.For some applications, a dynamic CoF of 0.3 or less is acceptable; for other applications, a CoF of less than 0.2 is required.

Claims

1. A method comprising the following steps: a) applying a composition comprising poly-C2-C3-olefin particles, a dispersant and C5-C 26 - an aqueous dispersion of an alkyl primary fatty amide; and b) drying the composition to form a dispersion having a 2 Up to 20g / m 2 coatings within a range of coating weights.

2. The method according to claim 1, wherein: Based on the poly-C2-C3-olefin particles, the dispersant and the C5-C 26 -alkyl primary fatty amide, the concentration of the polyolefin particles is in the range of 40 wt % to 95 wt %; the concentration of the dispersant is in the range of 4 wt % to 50 wt %; and the C5-C 26 - The concentration of the alkyl primary fatty amide is in the range of 0.5 wt% to 5 wt%.

3. The method according to claim 2, wherein the dispersant is an ethylene-acrylic acid copolymer or a salt thereof or an ethylene-methacrylic acid copolymer or a salt thereof; and the C5-C 26 -Alkyl primary fatty amide is C 10 -C 24 -alkyl primary fatty amide; and wherein the composition is dried to form a 2 Up to 10g / m 2 coatings within a range of coating weights.

4. The method according to claim 3, wherein the C 10 -C 24 -Alkyl primary fatty amides are C having a melting point in the range of 50°C to 115°C 16 -C 22 -alkyl primary fatty amide, and the poly-C2-C3-olefin particles are ethylene-C4-C 10 - α-olefin copolymer particles.

5. The method according to claim 4, wherein the ethylene-C4-C 10 The α-olefin copolymer particles are ethylene-1-octene copolymer particles.

6. The method according to claim 3, wherein the C 10 -C 24 -Alkyl primary fatty amides are C having a melting point in the range of 50°C to 115°C 16 -C 22 -alkyl primary fatty amide, and the poly-C2-C3-olefin particles are polypropylene particles.

7. The method according to claim 3, wherein the C 10 -C 24 -Alkyl primary fatty amides are C having a melting point in the range of 50°C to 115°C 16 -C 22 -alkyl primary fatty amide, and the poly-C2-C3-olefin particles are poly(ethylene-propylene) copolymer particles.

8. The method according to claim 2, wherein: Based on the poly-C2-C3-olefin particles, the dispersant and the C5-C 26 -alkyl primary fatty amide, the concentration of the poly-C2-C3-olefin is in the range of 60% to 90% by weight; the concentration of the dispersant is in the range of 9% to 40% by weight; and the C5-C 26 - The concentration of the alkyl primary fatty amide is in the range of 1 wt% to 4 wt%.

9. The method according to any one of claims 4 to 7, wherein: Based on the poly-C2-C3-olefin particles, the dispersant and the C 16 -C 22 -alkyl primary fatty amide, the concentration of the poly-C2-C3-olefin is in the range of 60 wt % to 90 wt %; the concentration of the dispersant is in the range of 9 wt % to 40 wt %; and the C 16 -C 22 - The concentration of the alkyl primary fatty amide is in the range of 1 wt% to 4 wt%.

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