Aqueous dispersions of propylene-ethylene copolymers and dispersants

Abstract

The present invention is a composition comprising water, a propylene-ethylene copolymer having a melting point in the range of 40 DEG C to 85 DEG C, and a dispersant having a melt flow index at 190 DEG C in the range of 50 g / 10 min to 2000 g / 10 min and an acid value in the range of 115 to 140. The compositions of the invention are useful as coatings for paper packaging applications.

Description

Background Technology

[0001] This invention relates to a composition comprising an aqueous dispersion of a copolymer of propylene and ethylene with an acid copolymer dispersant. The composition of this invention provides high heat-sealable / heat-tack strength properties in paper coating applications.

[0002] Consumer demand for sustainable packaging has fueled interest in and growth in paper packaging, which requires sealant coatings to provide heat-sealing properties, with substrate failure (i.e., tearing of paper fibers) as the failure mode. Polyethylene coatings are known to produce the desired failure mode, but they exhibit insufficient hot tack strength, a measure of the seal strength before the coating cools. Hot tack strength is critical in high-speed vertical fill form seal (VFFS) packaging lines to prevent breakage at newly formed seals. Acceptable hot tack strengths of >10 N / in are available for various packaging processes, which is rarely achieved with polyethylene coatings. Therefore, discovering a paper coating that enables substrate failure and possesses excellent hot tack strength would be an advantage in the paper packaging industry. Summary of the Invention

[0003] In one aspect, the present invention addresses a need in the art by providing a composition comprising: 40% to 70% by weight of water, based on the weight of the composition; 25% to 55% by weight of a propylene-ethylene copolymer resin having a melting point in the range of 40°C to 85°C, wherein the weight percentage of propylene units exceeds the weight percentage of ethylene units; and 5% to 20% by weight of a dispersant having a melt flow index in the range of 50 g / 10 min to 2000 g / 10 min at 190°C and a loading mass of 2.16 kg, and an acid value in the range of 110 to 140; wherein the dispersant is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer. The compositions of the present invention can be used as paper coatings exhibiting substrate failure and excellent hot tack strength. Detailed Implementation

[0004] The present invention is a composition comprising, based on the weight of the composition, 40% to 70% water; 25% to 55% propylene-ethylene copolymer resin having a melting point in the range of 40°C to 85°C, wherein the weight percentage of propylene units exceeds the weight percentage of ethylene units; and 5% to 20% dispersant having a melt flow index in the range of 50 g / 10 min to 2000 g / 10 min at 190°C and a loading mass of 2.16 kg, and an acid value in the range of 110 to 140; wherein the dispersant is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer.

[0005] The propylene-ethylene copolymer resin (PP-PE resin) has a melting point in the range of 40°C, 50°C, or 55°C to 85°C, and contains more propylene units by weight than ethylene units (i.e., the weight percentage of units from propylene is greater than the weight percentage of units from ethylene). The composition comprises, based on the weight of the composition, 40% or 45% to 70% or 55% water; 25% or 30% to 55% or 50% PP-PE resin; and 5% to 20% or 15% dispersant. The pH value of the dispersant is in the range of 110 or 120 to 140 or 130 or 125. The compositions of the present invention are advantageously prepared using the twin-screw extrusion method described below.

[0006] This composition can be used as a coating for paper, which is achieved by applying the composition to a paper substrate and then drying the coating at a temperature typically between 70°C and 100°C to 190°C to form a dry coating weight of 2 g / m². 2 or 5g / m 2 Up to 15g / m 2 Up to 10g / m 2 Coated paper products are prepared using a range of methods. These coated paper products exhibit preferred failure modes for substrate failure, making them particularly useful in the packaging industry.

[0007] Example

[0008] General procedures for preparing aqueous dispersions of polyolefin dispersions

[0009] The aqueous dispersions used in the embodiments and comparative examples of this invention were prepared using the following general procedure:

[0010] PP-PE resin and dispersant are fed into a 25mm diameter twin-screw extruder using a separate controlled-rate feeder. The resin flow rate is 64.3 g / min, and the dispersant flow rate is 11.4 g / min. EMAA is initially partially neutralized to achieve a melt flow index in the range of 50 to 100, while EAA is initially unneutralized. The copolymer and dispersant are extruded and melted to form an intermediate liquid melt material.

[0011] The PP-PE resin preferably has a melt flow index (MFI) in the range of 2 g / 10 min or 5 g / 10 min to 50 g / 10 min or up to 25 g / 10 min at 230°C and a loading of 2.16 kg; the dispersant preferably has an MFI in the range of 100 g / 10 min or 200 g / 10 min to 500 g / 10 min or up to 300 g / 10 min at 190°C and a loading of 2.16 kg. By definition, the MFI of the dispersant is in its unneutralized state. MFI is measured according to ISO 1133-1.

[0012] The extruder temperature profile is raised to 150°C, and a mixture of water and KOH (25% by weight aqueous solution) is fed into the extruder and combined with the polymer melt at an extruder speed of 450 rpm to form a high internal ratio emulsion with a neutralization degree of 85%. Then, additional water is fed into the extruder to form an aqueous dispersion of resin and dispersant with a volume average particle size in the range of 0.5 μm to 2 μm. At the extruder outlet, a back pressure regulator is used to adjust the pressure inside the extruder barrel to a level suitable for reducing steam formation, typically in the range of 2 MPa to 4 MPa.

[0013] The 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 the volume average particle size of the polymer particles was measured using a COULTER LS-230 particle size analyzer (Beckman Coulter Corporation, Fullerton, CA). Table 1 shows the flow rates of the various components used to prepare the composition. H2O i This refers to the initial water flow rate, expressed in mL / min; H2O f This refers to the additional water flow rate, expressed in mL / min; and PS refers to the volume average particle size.

[0014]

[0015] Determination of the melting point of PP-PE resin

[0016] The melting point of PP-PE resin was determined by differential scanning calorimetry (DSC) using a TA-100 DSC meter with an autosampler. Approximately 10 mg of resin was added to an aluminum sealed dish and then to the sampler for each measurement. The sample was equilibrated at 25 °C and then heated to 150 °C at a rate of 10 °C / min. Heat flow versus temperature data curves were generated and analyzed using TA Instruments Universal Analysis 2000 software (version 4.7A). The melting peak on the DSC curve was identified as an endothermic peak corresponding to the phase transition from solid to liquid, and the melting point was determined by the temperature corresponding to the maximum value of the melting peak.

[0017] Description of the preparation and heat-sealing test methods for coated paper samples.

[0018] The aqueous dispersion of copolymer and dispersant was applied to UPM cellophane using a doctor blade and then dried at 150°C for 2 minutes to produce 8 g / m³. 2 The coating. Cut two coated paper sheets into 1" wide strips and heat-seal the coating layers face to face using a Labthink HST-H3 heat seal tester under the following conditions:

[0019]

[0020] The heat-sealed sample was aged for one week, then manually opened. The heat-sealing results were reported based on the failure mode.

[0021]

[0022] Acid value determination

[0023] The EMAA sample was dissolved in trichlorobenzene at 120°C; 90° pulses were used to obtain... 13 C NMR spectroscopy; inverse gating 1 H-decoupling; spectral width 200 ppm; spectral center set at 83 ppm; acquisition time 1.1 s; 6 s relaxation delay; and 1024 scans for data averaging). Chemical shift referenced the polyethylene (maximum) peak, set at 30.1 ppm. Raw data were exponentially multiplied, Fourier transformed, phased, baseline corrected, and integrated using MNOVA software. The carbonyl resonances at shifts of 175 ppm to 190 ppm belonging to the MAA monomer were integrated and labeled "a"; all resonances in the high-field region from 0 ppm to 60 ppm belonging to the ethylene monomer, as well as the CH3, CH2, and quaternary carbons belonging to the MAA monomer, were integrated and labeled "b". The acid value of EMAA was determined using the following formula:

[0024]

[0025] EAA samples were prepared in the same manner, and 13 C10 NMR spectra were obtained under the same conditions as the EMAA samples described above, except that in Equation 2 below, "a" refers to the carbonyl resonances at shifts of 175 ppm to 190 ppm belonging to the structural units of the AA monomer, and "b" refers to all resonances in the high-field region of 0 ppm to 60 ppm belonging to the structural units of the ethylene monomer, as well as the CH2 and quaternary carbons belonging to the structural units of the AA monomer. The acid value of EAA was determined by Equation 2:

[0026] Formula 2

[0027]

[0028] Hot tack property measurement

[0029] The hot tack properties of coated paper samples were measured using an Enepay Magma 3-station Hot Tack & Heat Seal Tester according to ASTM F1921. The coated paper samples were cut into 1"×12" strips and loaded with the coated side facing the instrument door. The instrument conditions were programmed as follows:

[0030]

[0031] Peel strength versus peel distance was generated at specified sealing clamp temperatures, and the hot-tack strength was reported using the peak maximum of the peel curve. Hot-tack strength was measured at eight different sealing clamp temperatures, where both the upper and lower clamps were heated: 60°C, 70°C, 80°C, 90°C, 100°C, 120°C, 140°C, and 160°C, to generate hot-tack strength versus sealing clamp temperature curves. The peak maximum of the curve is reported as the peak hot-tack strength for each sample.

[0032] For the examples and comparative examples, the weight ratio of PP-PE resin to dispersant was 85:15. In Table 2, the melting point of PP-PE refers to the melting point of each PP-PE resin; hot tack refers to the peak hot tack strength.

[0033]

[0034] The results showed that the acid value and resin melting point were at a critical state in achieving the desired level of fiber tear failure while maintaining acceptable thermal tack strength.

Claims

1. A composition comprising: 40% to 70% by weight of water, based on the weight of the composition; 25% to 55% by weight of a propylene-ethylene copolymer resin having a melting point in the range of 40°C to 85°C, wherein the weight percentage of propylene units exceeds the weight percentage of ethylene units; and 5% to 20% by weight of a dispersant having a melt flow index in the range of 50 g / 10 min to 2000 g / 10 min at 190°C and a loading mass of 2.16 kg, and an acid value in the range of 110 to 140; wherein the dispersant is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer.

2. The composition according to claim 1, wherein, Based on the weight of the composition, the concentration of water is in the range of 45% to 55% by weight; the concentration of the propylene-ethylene copolymer is in the range of 30% to 50% by weight; and the concentration of the dispersant is in the range of 5% to 15% by weight; wherein the melting point of the propylene-ethylene copolymer is in the range of 50°C to 85°C; and the acid value of the dispersant is in the range of 120 to 130; wherein the melt flow index of the propylene-ethylene copolymer at a temperature of 230°C and a loading mass of 2.16 kg is in the range of 2 g / 10 min to 50 g / 10 min; and the melt flow index of the dispersant is in the range of 50 g / 10 min to 500 g / 10 min.

3. The composition according to claim 2, wherein the melting point of the propylene-ethylene copolymer is in the range of 55°C to 85°C; and the acid value of the dispersant is in the range of 120 to 125; wherein the melt flow index of the propylene-ethylene copolymer is in the range of 5 g / 10 min to 25 g / 10 min; and the melt flow index of the dispersant is in the range of 50 g / 10 min to 300 g / 10 min.

4. The composition according to claim 3, wherein the dispersant is an ethylene-methacrylic acid copolymer; wherein the melt flow index of the dispersant is in the range of 200 g / 10 min to 300 g / 10 min.

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