Latex-starch composition

Abstract

The present invention relates to a coating composition comprising a) an aqueous dispersion of polymer particles containing structural units of 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) from 20 to 50 weight percent of a starch, based on the weight of the starch and the polymer particles. The composition of the present invention is useful as a coating for paper.

Description

[0001] Latex-Starch Composition

[0002] Background of the Invention

[0003] The present invention relates to a composition comprising an aqueous dispersion of polymer particles (a latex) and a starch.

[0004] Paper is favored by the packaging industry and consumers because it is bio-sourced, recyclable, and environmentally non-persistent. Paper is advantageously coated to improve barrier properties against moisture, oil and grease, and oxygen. Such coatings are well known in the art. For example, US 9,950,502 B2 (Seyffer) discloses coating compositions derived from the emulsion polymerization of acrylate monomers in the presence of a degraded starch to produce a coating composition that is reported to exhibit shear stability, low hexane permeation, and little or no pore formation.

[0005] Doubly-sided coated paper using standard in-line coating process conditions presents a special challenge. After a layer of the barrier coating is applied to each side of the paper, the coating is dried and immediately wound back into rolls. This process causes coating-to-coating contact at elevated temperature and at significant pressure due to the size of the paper rolls. Even low levels of blocking cause failure in the barrier coating or paper fibers, and in extreme cases cause the entire roll to become glued together. Accordingly, it would therefore be an advance in the field of coated paper to find a composition that exhibited excellent resistance to blocking, without sacrificing critical barrier properties.

[0006] Summary of the Invention

[0007] The present invention addresses a need in the art by providing a composition comprising: a) an aqueous dispersion of polymer particles containing structural units of 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) from 20 to 50 weight percent of a starch, based on the weight of the starch and the polymer particles; wherein the calculated glass transition temperature of the polymer particles is in the range of from -10 °C to 35 °C.

[0008] The composition of the present invention is useful as a coating for paper that exhibits excellent oxygen barrier properties as well as resistance to oil, grease, and block. Detailed Description of the Invention

[0009] The present invention is a composition comprising: a) an aqueous dispersion of polymer particles containing structural units of 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) from 20 to 50 weight percent of a starch, based on the weight of the starch and the polymer particles; wherein the calculated glass transition temperature of the polymer particles is in the range of from -10 °C to 35 °C.

[0010] As used herein, “structural unit” of the recited monomer refers to the remnant of the monomer after polymerization. For example, a structural unit of ethyl acrylate is as illustrated: structural unit of ethyl acrylate where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.

[0011] As used herein, “calculated glass transition temperature” refers to the glass transition temperature (Tg) as calculated by the Fox equation using homopolymer Tgs reported in Polymer Handbook (4thEdition), John Wiley & Sons (2005). The calculated Tgof the polymer particles is in the range of from -10 °C or from -5 °C or from 0 °C, to 35 °C or to 25 °C or to 20 °C or to 15 °C.

[0012] The polymer particles preferably contain structural units of ethyl acrylate, acrylonitrile, and itaconic acid; or n-butyl acrylate, acrylonitrile, and itaconic acid. When the polymer particles contain structural units of ethyl acrylate, the concentration of structural units of ethyl acrylate is preferably in the range of from 65 or from 67 weight percent, to 75 or to 73 or to 71 weight percent; the concentration of structural units of acrylonitrile is preferably in the range of from 23 or from 25 or from 27 weight percent, to 33 or to 31 weight percent; and the concentration of structural units of itaconic acid is preferably in the range of from 1.5 or from 1.9 weight percent, to 6 or to 5 or to 4.5 weight percent, with all weight percentages based on the weight of the polymer particles. When the polymer particles contain structural units of n-butyl acrylate, the weight percent of structural units of n-butyl acrylate is preferably in the range of from 50 or from 52 or from 54 weight percent, to 60 or to 58 weight percent; the weight percent of structural units of acrylonitrile is preferably in the range of from 35 or from 38 or from 40 weight percent, to 46 or to 44 weight percent; and the weight percent of structural units of itaconic acid is preferably in the range of from 1 .5 or from 1 .9 weight percent, to 6 or to 5 or to 4.5 weight percent, with all weight percentages based on the weight of the polymer particles.

[0013] The type of starch is not limited and may include a starch derived from corn, wheat, oat, barley, rice, millet, potato, pea, tapioca, sorghum, and sago. The concentration of the starch is in the range of from 20 or from 25 or from 28 weight percent, to 50 or to 40 or to 35 or to 32 weight percent based on the weight of the starch and the polymer particles. Similarly, the concentration of the polymer particles is in the range of from 50 or from 60 or from 65 or from 68 weight percent, to 80 or to 75 or 72 weight percent, based on the weight of the starch and the polymer particles.

[0014] The composition of the present invention may be prepared by first preparing the aqueous dispersion of polymer particles by emulsion polymerization, followed by the addition of the starch, either in the form of an aqueous slurry or as a dry powder. It would also be possible to prepare the composition by polymerizing the monomers under emulsion polymerization conditions in the presence of the starch. The starch, the polymer particles, and water preferably comprise from 70 or from 80 or from 90 or from 95 weight percent of the weight of the composition to 100 weight percent of the composition. The coating may further comprise one or more additional components including organic or inorganic opacifying pigments, fillers, colorants, dispersants, rheology modifiers, and defoamers.

[0015] The composition may be applied to one or both faces of a paper substrate to form a coated paper using means well known in the art; the coated paper is then dried at elevated temperatures to a desired coat weight, which is generally in the range of from 8 to 10 g / m2(gsm). Coatings with excellent oxygen barrier properties as well as resistance to oil, grease, and block have been prepared using the composition of the present invention.

[0016] Examples

[0017] In the following examples, particle size refers to z-average particle size diameter by dynamic light scattering. Intermediate Example 1 - Preparation of a 70 EA / 28 AN / 2 IA Latex Composition

[0018] DI water (681.54 g), sodium lauryl sulfate (SLS, 28% active, 39.30 g), and 4-hydroxy-TEMPO (5%, 0.65 g) were added to a 5-L, four-necked round bottom flask (kettle) equipped with a paddle stirrer, thermometer, N2 inlet, and reflux condenser. The kettle was heated to 86 °C under N2. A monomer emulsion (ME) was prepared by mixing DI water (638.19 g), SLS (28%, 13.10 g), ethyl acrylate (EA, 1033.62 g), acrylonitrile (AN, 413.43 g), and itaconic acid (IA, 29.55 g). A portion of the ME (42.56 g) was charged to the kettle and the vessel for the ME was rinsed with DI water (10 g). A solution of sodium persulfate (NaPS, 7.31 g in 35 g DI water) was then added to the kettle and the vessel for the NaPS was rinsed with DI water (5 g). An exotherm was observed and the mixture was allowed to hold at the peak temperature for 5 min. The remainder of the ME was fed to the kettle over 90 min with the temperature set to 81 °C at a rate of 13.0 g / min for the first 20 min, then at a rate of 26.1 g / min over the final 70 min.

[0019] Concurrently a solution of NaPS (2.81 g in 100 g DI water) was fed to the kettle over 90 min at a rate of 0.65 g / min for the first 20 min, then at a rate of 1.29 g / min over the final 70 min . At the completion of the feeds, the addition vessels were rinsed with DI water (110 g) and the reaction was held at 80 °C for 10 min before cooling to 75 °C. While cooling, a solution of iron sulfate heptahydrate (0.15% solution, 12.00 g) was added to the kettle. At 75 °C a first chase solution of / -butyl hydroperoxide (t-BHP, 70% solution, 7.41 g in 40 g DI water) was added to the kettle concurrently with a solution of isoascorbic acid (IAA, 3.59 g in 50 g DI water) over 30 min. After the completion of the addition of the first chase solution, the reaction was held at 75 °C for 10 min before cooling to 70°C. At 70 °C a second chase solution of t-BHP (70% solution, 5.60 g in 26 g DI water) was added to the kettle concurrently with a solution of IAA (2.79 g in 35 g DI water) over 30 min. After the completion of the addition of the second chase solution, the reaction mixture was neutralized by addition of ammonium hydroxide (30%, 16.61 g). The contents of the kettle were then cooled to room temperature and filtered to remove any coagulum. The resulting dispersion had a solids content of 45.0%, a pH of 6.5, a particle size of 118 nm, and a calculated Tgof 3.6 °C.

[0020] Intermediate Example 2 - Preparation of a 56 BA / 42 AN / 2 IA Latex Composition

[0021] The composition was prepared by the procedure described in Intermediate Example 1 except that the ME contained DI water (638.19 g), SLS (28%, 13.10 g), n-butyl acrylate (826.90 g), AN (620.15 g), and IA (29.55 g). After the seed step, the remainder of the ME was fed to the kettle over 120 min at a rate of 9.5 g / min for the first 20 min, then at a rate of 19.1 g / min over the final 100 min. The resulting dispersion had a solids content of 45.2%, a pH of 6.6, a particle size of 108 nm, and a calculated Tgof -5.6 °C.

[0022] Intermediate Example 3 - Preparation of a 68 EA / 28 AN / 4 IA Latex Composition

[0023] The composition was prepared by the procedure described in Intermediate Example 1 except that the ME contained DI water (638.19 g), SLS (28%, 13.10 g), EA (1004.09 g), AN (620.15 g), and IA (59.10 g). The amount of ammonium hydroxide used in the neutralization step was 33.22 g. The resulting dispersion had a solids content of 44.0%, a pH of 6.8, a particle size of 142 nm, and a calculated Tgof 6.2 °C.

[0024] Comparative Intermediate Example 1 - Preparation of a 54 EA / 44 MMA / 2 IA Latex Composition

[0025] The composition was prepared by the procedure described in Intermediate Example 1 except that the ME contained DI water (638.19 g), SLS (28%, 13.10 g), EA (797.36 g), methyl methacrylate (MMA, 649.70 g), and IA (29.55 g). The resulting dispersion had a solids content of 45. 1%, a pH of 6.8, a particle size of 102 nm, and a calculated Tgof 22.9 °C.

[0026] Comparative Intermediate Example 2 - Preparation of a 70 EA / 28 AN / 2 AA Latex Composition

[0027] The composition was prepared by the procedure described in Intermediate Example 1 except that the ME contained DI water (638.19 g), SLS (28%, 13.10 g), EA (1004.09 g), AN (620.15 g), and acrylic acid (AA, 29.55 g). The resulting dispersion had a solids content of 44.8%, a pH of 7.9 a particle size of 124 nm, and a calculated Tgof 3.2 °C.

[0028] Table 1 summarizes the monomer and neutralizer amounts used to prepare the latex intermediates.

[0029] Table 1 - Monomer and Neutralizer Amounts used to Prepare Latexes

[0030] Examples 1-3 and comparative examples 1 and 2 were prepared by combining each of the latex intermediates and comparative intermediates with starch by the following procedure: A starch solution (45% solids content) was prepared by dissolving ICB 3000 com starch (100 g, 95% solid) into DI water (111.11 g) with stirring at 50 °C. Then, a portion of the latex intermediate (125 g) was placed into a 250-mL plastic container followed by the addition of a portion of the starch solution (53.58 g). The mixture was mixed with a speedmixer at 1800 rpm for 2 min. The starch loading was 30% based on the weight of total solids in the composition.

[0031] Paper Coating Procedure

[0032] Coated paper articles were prepared by applying composition to an uncoated glossy side of a paper substrate having a coat weight of 62 gsm (obtained from UPM). A wire-wound drawdown bar was used to achieve dry coat weight in the range of from 8 to 9 gsm. Samples were dried in an oven (Fisher Scientific Isotemp 180L Oven Fa) at 100 °C for 2 min. Coat Weight Measurements

[0033] The coat weight of the coatings was measured by cutting out 7.2 in2(46.3 cm2) sections of coated and uncoated paper, then placing the sections in an oven at 100 °C for 2 min. All the samples were then weighed, and the coat weight was determined by measuring the difference between the coated and uncoated samples and dividing by the area of the sample.

[0034] Block Test

[0035] Block testing of coatings was carried out using a metal, spring-loaded compression apparatus. Dried, conditioned substrates were cut into rectangles (3.8 cm x 7.0 cm) and coated sides were placed face-to-face between metal plates of the apparatus to measure coated-to-coated block (Block c / c). The spring was compressed to apply a pressure of 2600 Torr to the substrate, and the entire apparatus was placed in an oven at 60 °C for Ih, after which time the article was removed from the oven and allowed to cool to room temperature for 30 min. The cooled sheets were carefully removed and pulled apart; Block c / c was rated according to the following scale:

[0036] 1 = sheets pulled apart with no resistance

[0037] 2 = minimal force required to separate sheets with audible noise detected upon separation

[0038] 3 = constant force required to separate sheets, similar to a Post-It Sticky Note

[0039] 4 = minimal amount of fiber tear observed

[0040] 5 = sheets completely glued together; significant fiber tear observed

[0041] Heat Seal Test

[0042] The heat seal was tested on coated paper samples using an HST-H3 Heat Seal Tester. Samples were cut into 2.5 x 5-cm strips and loaded with coated sides in contact with one another between jaws. Pressure was applied (3600 to 4150 Torr) at 190 °C for 0.5 sec. The samples were removed from the tester and cooled at room temperature for 1 min. The paper samples were then pulled apart and coated-to-coated heat seal (Heat Seal c / c) was rated P, M, or F as follows:

[0043] P: passed, paper tears apart when pulled

[0044] M: marginal, papers peeled apart like sticky notes

[0045] F: failed, papers separated with no resistance Kit Test for Oil and Grease Resistance

[0046] Coated paper was tested for oil and grease resistance (OGR) according to TAPPI Test Method T559 cm- 12. Kit solutions consisting of mixtures of castor oil, toluene, and heptane were applied dropwise to the coated substrates. After 15 s, any breakthrough of solvents into the coating was noted, and the solution was wiped from the substrate. Discoloration or change in appearance to the substrate was also considered a failure for that specific Kit solution. A score rating from 1-12 was assigned for the highest numbered Kit solution that passed the test, with 12 indicating the best performance. All tested samples exhibited a Kit rating of 12.

[0047] OTR Test Oxygen transmission rates (OTRs) of films were measured using a MOCON OXTRAN 2 / 22 H module in accordance with ASTM D-3985 at 23 °C, 50% relative humidity, and 760 Torr. Coated paper specimens approximately 30 cm2were cut, then masked and loaded directly in the module for measurement. The masking material was a 0.08-mm thick aluminum sheet with an acrylic adhesive layer to make the seal. The effective testing area is 20.3 cm2. A test gas containing 100% oxygen was used so that the permeation did not exceed the detection range of the module. OTRs were measured in cc / m2-d. All samples exhibited an OTR of < 20 cc / m2d, which is considered acceptable. Table 2 illustrates Block c / c, Heat Seal c / c, and the average of two OTR measurements (OTRavg)

[0048] Table 2 - Properties of Coated Substrates

[0049] The data illustrate that the samples prepared from EA / AN / IA and BA / AN / IA latexes showed an excellent balance of Block c / c, Heat Seal c / c, OTR, and OGR.

Claims

Claims:

1. A composition comprising: a) an aqueous dispersion of polymer particles containing structural units of 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) from 20 to 50 weight percent of a starch, based on the weight of the starch and the polymer particles; wherein the calculated glass transition temperature of the polymer particles is in the range of from -10 °C to 35 °C.

2. The composition of Claim 1 wherein the calculated glass transition temperature of the polymer particles is in the range of from -5 °C to 25 °C, and the polymer particles comprise structural units of ethyl acrylate, acrylonitrile, and itaconic acid wherein, based on the weight of the polymer particles, the concentration of structural units of ethyl acrylate is in the range of from 65 to 73 weight percent; the concentration of structural units of acrylonitrile is in the range of from 23 to 33 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.5 to 6 weight percent.

3. The composition of Claim 2 wherein the concentration of the starch, based on the weight of the starch and the polymer particles, is in the range of from 25 to 40 weight percent; wherein the concentration of structural units of ethyl acrylate is in the range of from 67 to 71 weight percent; the concentration of structural units of acrylonitrile is in the range of from 25 to 31 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.9 to 4.5 weight percent; and wherein the calculated glass transition temperature is in the range of from 0 °C to 15 °C.

4. The composition of Claim 1 wherein the calculated glass transition temperature of the polymer particles is in the range of from -10 °C to 10 °C, and the polymer particles comprise structural units of n-butyl acrylate, acrylonitrile, and itaconic acid wherein, based on the weight of the polymer particles, the concentration of structural units of n-bulyl acrylate is in the range of from 50 to 60 weight percent; the concentration of structural units of acrylonitrile is in the range of from 35 to 46 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.5 to 6 weight percent.

5. The composition of Claim 4 wherein the concentration of the starch, based on the weight of the starch and the polymer particles, is in the range of from 25 to 40 weight percent; wherein theconcentration of structural units of n-butyl acrylate is in the range of from 52 to 58 weight percent; the concentration of structural units of acrylonitrile is in the range of from 38 to 44 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.9 to 4.5 weight percent; and wherein the calculated glass transition temperature is in the range of from -10 °C to 5 °C.

6. The composition of any of Claims 1 to 5 wherein the starch is derived from corn, wheat, oat, barley, rice, millet, potato, pea, tapioca, sorghum, or sago, and the concentration of the starch, based on the weight of the starch and the polymer particles, is in the range of from 28 to32 weight percent.

7. The composition of Claim 6 wherein the starch is com starch.

8. A composition comprising: a) an aqueous dispersion of polymer particles containing structural units of 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) from 20 to 50 weight percent of a starch, based on the weight of the starch and the polymer particles; wherein when the polymer particles comprise structural units of ethyl acrylate, acrylonitrile, and itaconic acid, based on the weight of the polymer particles, the concentration of structural units of ethyl acrylate is in the range of from 65 to 73 weight percent; the concentration of structural units of acrylonitrile is in the range of from 23 to 33 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.5 to 6 weight percent; and wherein when the polymer particles comprise structural units of n-butyl acrylate, acrylonitrile, and itaconic acid, based on the weight of the polymer particles, the concentration of structural units of n-butyl acrylate is in the range of from 50 to 60 weight percent; the concentration of structural units of acrylonitrile is in the range of from 35 to 46 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.5 to 6 weight percent.

9. The composition of Claim 8 wherein the concentration of the starch, based on the weight of the starch and the polymer particles, is in the range of from 25 to 40 weight percent; wherein when the polymer particles comprise structural units of ethyl acrylate, acrylonitrile, and itaconic acid, the concentration of structural units of ethyl acrylate is in the range of from 67 to 71 weight percent; the concentration of structural units of acrylonitrile is in the range of from 25 to 31weight percent; and the concentration of structural units of itaconic acid is in the range of from 1.9 to 4.5 weight percent; and when the polymer particles comprise structural units of n-butyl acrylate, acrylonitrile, and itaconic acid, the concentration of structural units of / / -butyl acrylate is in the range of from 52 to 58 weight percent; the concentration of structural units of acrylonitrile is in the range of from 38 to 44 weight percent; and the concentration of structural units of itaconic acid is in the range of from 1 .9 to 4.5 weight percent.

10. The composition of Claim 9 wherein starch is derived from com, wheat, oat, barley, rice, millet, potato, pea, tapioca, sorghum, or sago, and the concentration of the starch, based on the weight of the starch and the polymer particles, is in the range of from 25 to 35 weight percent.

11. The composition of Claim 10 wherein the starch is com starch.

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