Aqueous dispersion of propylene-ethylene copolymer and a dispersant

Abstract

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

Description

[0001] Aqueous Dispersion of Propylene-Ethylene Copolymer and a Dispersant

[0002] Background of the Invention

[0003] The present invention relates to a composition comprising an aqueous dispersion of a copolymer of propylene and ethylene and an acid copolymer dispersant. The composition of the present invention provides high heat-seal / hot-tack strength properties in paper coating applications.

[0004] Consumer demand for sustainable packaging is fueling interest and growth in paper packaging, which requires a sealant coating to provide heat-sealing properties with substrate failure (i.e., paper fiber tear) as the failure mode. Polyethylene coatings are known to give the desired failure mode, but they exhibit inadequate hot tack strength, which is a measure of the seal strength of a coating before it cools. Hot tack strength is critical in high-speed vertical-fill-form-seal (VFFS) packaging lines to prevent breakage at the newly created seal. An acceptable hot tack strength for a variety of packaging process is > 10 N / inch, which is seldom achievable with polyethylene coatings. Accordingly, it would therefore be an advantage in the field of paper packaging to discover a coating for paper that gives substrate failure and excellent hot tack strength.

[0005] Summary of the Invention

[0006] The present invention addresses a need in the art by providing, in one aspect, a composition comprising, based on the weight of the composition, from 40 to 70 weight percent water; from 25 to 55 weight percent of a propylene-ethylene copolymer resin having a melting point in the range of from 40 °C to 85 °C, wherein the percent by weight of propylene units exceeds the percent by weight of ethylene units; and from 5 to 20 weight percent of a dispersant having a melt flow index in the range of from 50 g / 10 min to 2000 g / 10 min at 190 °C and a load mass of 2. 16 kg, and an acid number in the range of from 110 to 140; wherein the dispersant is an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer. The composition of the present invention is useful as a paper coating that exhibits substrate failure and excellent hot tack strength.

[0007] Detailed Description of the Invention

[0008] The present invention is a composition comprising, based on the weight of the composition, from 40 to 70 weight percent water; from 25 to 55 weight percent of a propylene-ethylene copolymer resin having a melting point in the range of from 40 °C to 85 °C, wherein the percent by weight of propylene units exceeds the percent by weight of ethylene units; and from 5 to 20 weight percent of a dispersant having a melt flow index in the range of from 50 g / 10 min to 2000 g / 10 min at 190 °C and a load mass of 2.16 kg and an acid number in the range of from 110 to 140; wherein the dispersant is an ethylene- aery lie acid copolymer or an ethylene-methacrylic acid copolymer.

[0009] The propylene-ethylene copolymer resin (PP-PE resin), which has more propylene units by weight than ethylene units (i.e., the weight percent of units arising from propylene is greater than the weight percent of units arising from ethylene), has a melting point in the range of from 40 °C or from 50 °C or from 55 °C, to 85 °C. The composition comprises, based on the weight of the composition, from 40 or from 45 weight percent, to 70 or to 55 weight percent water; from 25 or from 30 weight percent, to 55 or to 50 weight percent of the PP-PE resin; and from 5 to 20 weight percent, or to 15 weight percent of the dispersant. The dispersant has an acid number in the range of from 110 or from 120 to 140 or to 130 or to 125. The composition of the present invention is advantageously prepared using a twin-screw extruder process as described hereinbelow.

[0010] The composition is useful as a coating for paper, which can be prepared by drawing down the composition onto a paper substrate, then drying the coating at a temperature typically in the range of from 70 °C or from 100 °C to 190 °C to form a coated paper article with a dry coat weight in the range of from 2 g / m2or from 5 g / m2, to 15 g / m2to 10 g / m2. The coated paper article exhibits the preferred failure mode of substrate failure, and is therefore particularly useful in the packaging industry.

[0011] Examples

[0012] General Procedure for Preparation of Aqueous Dispersions of Polyolefin Dispersions

[0013] Aqueous dispersions for the examples and comparative examples of the present invention were prepared by the following general procedure:

[0014] The PP-PE resin and the dispersant were fed into a 25-mm diameter twin screw extruder using separate controlled rate feeders. The flow rate for the resin was 64.3 g / min, and the flow rate for the dispersant was 11.4 g / min. The EMAA was initially partially neutralized to achieve a melt flow index in the range of from 50 to 100, while the EAA was initially unneutralized. The copolymer and the dispersant were extruded and melted to form an intermediate liquid melt material. The PP-PE resin preferably has a melt flow index (MFI) in the range of from 2 or from 5 g / 10 min, to 50 or to 25 g / 10 min at 230 °C and a load mass of 2.16 kg; the dispersant preferably has an MFI in the range of from 100 or from 200 g / 10 min, to 500 or to 300 g / 10 min at 190 °C and a load mass of 2.16 kg. By definition, the MFI of the dispersant is in its unneutralized state. MFIs are measured by ISO 1133-1.

[0015] The extruder temperature profile was ramped to 150 °C, whereupon a mixture of water and KOH (25 wt% aq.) was fed into the extruder and merged with the polymer melt at an extruder speed of 450 rpm to form a high internal phase ratio emulsion to give a degree of neutralization of 85%; then, additional water was fed into the extruder to form an aqueous dispersion of the resin and the dispersant with volume mean particle size in the range of from 0.5 pm to 2 pm. At the extruder outlet, a backpressure regulator was used to adjust the pressure inside the extruder barrel sufficiently to reduce steam formation, generally in the range of 2 MPa to 4 MPa.

[0016] The aqueous dispersion exited from the extruder and was filtered first through a 200-pm filter. The solids content of the dispersions was measured using an infrared solids analyzer, and the volume mean particle size of the polymer particles was measured using a COULTER LS-230 particle size analyzer (Beckman Coulter Corporation, Fullerton, CA). Table 1 illustrates the flow rates for the various components used to make the composition. H2Oi refers to the initial water flow rate in mL / min; FUOi refers to the flow rate of the additional water in mL / min; and PS refers to volume mean particle size.

[0017] Table 1 - Components and Feed Rates for Examples

[0018] Determination of Melting Point of PP-PE Resins

[0019] The melting points of the PP-PE resins were determined by differential scanning calorimetry (DSC) using TA-100 differential scanning calorimeter with an automatic sampler. About 10 mg of the resins were added to aluminum hermetic pans and added to the sampler for each measurement. The samples were equilibrated at 25 °C and ramped to 150 °C at the rate of 10 C7min. The data curve of heat flow against temperature was generated and analyzed by TA Instruments Universal Analysis 2000 software (Version 4.7A). The melting peak on the DSC curve was identified as an endothermic peak that corresponds to the phase transition from solid to liquid, and the melting point was determined by the temperature corresponding to the maximum of the melting peak height. of Coated Paper Samples and Description of the Heat-Seal Testing Method

[0020] An aqueous dispersion of the copolymer and the dispersant was applied on UPM glassine paper with drawdown bars, then dried at 150 °C for 2 min to create a coating layer of 8 g / m2. Two coated paper pieces were cut into l”-wide strips and heat-sealed with coating layers facing each other with Labthink HST-H3 Heat Seal tester using the following conditions:

[0021] Temperature: 130 °C Seal Pressure: 75 psi Dwell Time: 0.5 s

[0022] The heat-sealed samples were aged for 1 week before being pulled apart manually. The heatseal results were reported based on failure mode:

[0023] Pass: > 50% of the sealed area shows substrate fiber tear

[0024] Fail: < 50% of the sealed area shows substrate fiber tear

[0025] Acid Number Determination

[0026] EMAA samples were dissolved in trichlorobenzene at 120 °C;13C NMR spectra were obtained using a 90° pulse; inversely gated *H decoupling; a spectral width of 200 ppm; spectral center set at 83 ppm; 1.1 s acquisition time; 6 s relaxation delay; and 1024 scans for data averaging). The chemical shift was set by referencing the polyethylene (the largest) peak to 30.1 ppm. The raw data were Exponentially Multiplied, Fourier Transformed, phased, baseline corrected, and integrated using MNOVA software. The carbonyl resonance attributed to the structural units of the MAA monomers at a shift of 175-190 ppm was integrated as “a”; all resonances in the upfield region of 0-60 ppm attributed to structural units of ethylene monomers, as well as the CH3, CH2, and quaternary carbons attributed to structural units of the MAA monomers were integrated as “b”. The acid number of the EMAA was determined by the equation shown as below: 56110 x a

[0027] Acid number — -

[0028] 86.06 x a + 28.05

[0029] EAA samples and were prepared in the same manner and13C NMR spectra were obtained under the same conditions as described for the EMAA samples above, except that in Equation 2 below, “a” refers to the carbonyl resonances attributed to the structural units of AA monomers at a shift of 175-190 ppm, and “b” refers to all resonances in the upfield region of 0-60 ppm attributed to structural units of ethylene monomers, as well as the CH2 and quaternary carbons attributed to structural units of the AA monomers. The acid number of EAA was determined by Equation 2:

[0030] Equation 2

[0031] 56110 x a

[0032] Acid number — -

[0033] 72.06 x a + 28.05

[0034] Hot Tack Performance Measurements

[0035] The hot tack performance of the coated paper samples was measured by Enepay Magma 3- station Hot Tack & Heat Seal Tester in accordance with ASTM F1921. Coated paper samples were cut into 1-” x 12-” strips and loaded with the coated side facing the door of the instrument.

[0036] The instruments conditions were programmed as follow:

[0037] Dwell time 0.5 s

[0038] Jaw pressure 0.5 N / mm2

[0039] Test speed 200 m / s

[0040] Pre-test delay 0.2 s

[0041] Pre-test cooling Off

[0042] Cooling profile intensity Off

[0043] A peeling curve of strength versus peeling distance at a specified seal jaw temperature was generated, and the hot tack strength was reported with the peak maximum value of the peeling curve. Hot tack strength was measured at 8 differing seal jaw temperatures, wherein both the upper and lower jaws were heated: 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 120 °C, 140 °C, and 160 °C to generate a hot tack strength versus seal jaw temperature curve. The peak maximum value of the curve was reported as the hot tack peak strength for each sample. For the examples and comparative examples, the weight-to-weight ratios of the PP-PE resin to the dispersant was 85: 15. In Table 2, PP-PE m.p. refers to the melting point of each PP-PE resin; Hot Tack refers to hot tack peak strength.

[0044] Table 2 - Results of Fiber Tear Tests The results show the criticality of acid number and resin melting point in achieving the desired level of fiber tear failure, while maintaining acceptable hot tack strength.

Claims

Claims:

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

2. The composition of Claim 1 wherein, based on the weight of the composition, the concentration of water is in the range of from 45 to 55 weight percent; the concentration of the propylene-ethylene copolymer is in the range of from 30 to 50 weight percent; and the concentration of the dispersant is in the range of from 5 to 15 weight percent; wherein the propylene-ethylene copolymer has a melting point in the range of from 50 °C to 85 °C; and the dispersant has an acid number in the range of from 120 to 130; wherein the propylene-ethylene copolymer has a melt flow index in the range of from 2 g / 10 min to 50 g / 10 min at a temperature of 230 °C and a load mass of 2.16 kg; and the dispersant has a melt flow index in the range of from 50 g / min to 500 g / 10 min.

3. The composition of Claim 2 wherein the propylene-ethylene copolymer has a melting point in the range of from 55 °C to 85 °C; and the dispersant has an acid number in the range of from 120 to 125; wherein the propylene-ethylene copolymer has a melt flow index in the range of from 5 g / min to 25 g / 10 min; and the dispersant has a melt flow index in the range of from 50 g / min to 300 g / 10 min.

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

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