Latex-starch composition

Abstract

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

Description

BACKGROUND

[0001] The present invention relates to a composition comprising an aqueous dispersion of polymer particles (latex) and a starch.

[0002] Paper is favored by the packaging industry and consumers for its biologically sourced, recyclable, and environmentally non-persistent nature. Advantageously, paper is 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 a coating composition derived from emulsion polymerization of acrylate monomers in the presence of a degraded starch to produce a coating composition reportedly exhibiting shear stability, low hexane permeation, and little or no pore formation.

[0003] Double coated paper using standard in-line coating process conditions presents a particular challenge. After applying a barrier coating to each side of the paper, the coating is dried and immediately wound into a roll. Due to the size of the paper roll, this process results in the contact of coating to coating at elevated temperatures and considerable pressure. Even low degrees of blocking can result in failure of the barrier coating or paper fibers, and in extreme cases, the entire roll can become stuck together. Therefore, finding a composition that exhibits excellent blocking resistance without sacrificing key barrier properties would be a great advancement in the field of coated paper. SUMMARY

[0004] The present invention solves the needs in the art by providing a composition comprising:

[0005] 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

[0006] b) 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 -10°C to 35°C.

[0007] The composition of the present invention can be used as a coating for paper that exhibits excellent oxygen barrier properties as well as oil, grease, and blocking resistance. DETAILED DESCRIPTION

[0008] The present invention is a composition comprising:

[0009] 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

[0010] b) 20% to 50% by weight of starch, based on the weight of the starch and the polymer particles; wherein the polymer particles have a calculated glass transition temperature in the range of -10°C to 35°C.

[0011] As used herein, a "structural unit" of a recited monomer refers to the residue of the monomer after polymerization. For example, the structural unit of ethyl acrylate is exemplified as follows:

[0012]

[0013] The dotted lines represent the connection points between the structural units and the polymer backbone.

[0014] As used herein, "calculated glass transition temperature" refers to the homopolymer Tg as reported in Polymer Handbook, 4th ed., John Wiley & Sons, Inc. (2005). g , the glass transition temperature (T g ). The calculated T of polymer particles g In the range of -10°C or -5°C or 0°C to 35°C or to 25°C or to 20°C or to 15°C.

[0015] 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 the structural units of ethyl acrylate is preferably in the range of 65% by weight or 67% by weight to 75% by weight or 73% by weight or 71% by weight; the concentration of the structural units of acrylonitrile is preferably in the range of 23% by weight or 25% by weight or 27% by weight to 33% by weight or 31% by weight; and the concentration of the structural units of itaconic acid is preferably in the range of 1.5% by weight or 1.9% by weight to 6% by weight or 5% by weight or 4.5% by weight, wherein all weight percentages are based on the weight of the polymer particles.

[0016] When the polymer particles contain structural units of n-butyl acrylate, the weight percentage of structural units of n-butyl acrylate is preferably in the range of 50 weight % or 52 weight % or 54 weight % to 60 weight % or to 58 weight %; the weight percentage of structural units of acrylonitrile is preferably in the range of 35 weight % or 38 weight % or 40 weight % to 46 weight % or to 44 weight %; and the weight percentage of structural units of itaconic acid is preferably in the range of 1.5 weight % or 1.9 weight % to 6 weight % or 5 weight % or 4.5 weight %, wherein all weight percentages are based on the weight of the polymer particles.

[0017] The type of starch is not limited and can include starches derived from corn, wheat, oat, barley, rice, millet, potato, pea, cassava, sorghum, and sago. The concentration of starch is in the range of 20 wt% or 25 wt% or 28 wt% to 50 wt% or to 40 wt% or to 35 wt% or to 32 wt%, based on the weight of the starch and the polymeric particles. Similarly, the concentration of the polymeric particles is in the range of 50 wt% or 60 wt% or 65 wt% or 68 wt% to 80 wt% or to 75 wt% or to 72 wt%, based on the weight of the starch and the polymeric particles.

[0018] The composition of the present application can be prepared by first preparing an aqueous dispersion of the polymeric particles by emulsion polymerization and then adding the starch either in the form of an aqueous slurry or as a dry powder. It is also possible to prepare the composition by polymerizing the monomers under emulsion polymerization conditions in the presence of the starch. The starch, the polymeric particles, and the water preferably make up 70 wt% or 80 wt% or 90 wt% or 95 wt% of the weight of the composition to 100 wt% of the composition. The coating can also contain one or more additional components including organic or inorganic opaque pigments, fillers, colorants, dispersants, rheology modifiers, and defoamers.

[0019] The composition can be applied to one or both sides of a paper substrate to form a coated paper using means well known in the art; the coated paper is then dried at elevated temperature to the desired coating weight, which is typically in the range of 8 g / m 2 (gsm) to 10 gsm. Coatings with excellent oxygen barrier properties as well as resistance to oil, grease, and blocking are prepared using the composition of the present application.

[0020] Examples

[0021] In the following examples, particle size refers to z-average particle size diameter by dynamic light scattering.

[0022] Preparation of intermediate example 1 - 70EA / 28AN / 2IA latex composition

[0023] 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, a thermometer, a N2inlet, and a 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 container for the ME was rinsed with DI water (10 g). Then, a solution of sodium persulfate (NaPS, 7.31 g in 35 g DI water) was added to the kettle and the container for the NaPS was rinsed with DI water (5 g). An exotherm was observed and the mixture was held at the peak temperature for 5 minutes. The remaining ME was fed to the kettle, which was set to a temperature of 81 °C, over 90 minutes, at a rate of 13.0 g / min for the first 20 minutes and then 26.1 g / min for the last 70 minutes. Simultaneously, a solution of NaPS (2.81 g in 100 g DI water) was fed to the kettle over 90 minutes, at a rate of 0.65 g / min for the first 20 minutes and then 1.29 g / min for the last 70 minutes. After the feed was complete, the addition containers were rinsed with DI water (110 g) and the reaction was held at 80 °C for 10 minutes followed by a cool down 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 t-butyl hydroperoxide (t-BHP, 70% solution, 7.41 g in 40 g DI water) was added to the kettle simultaneously with a solution of erythorbic acid (IAA, 3.59 g in 50 g DI water) over 30 minutes. After the addition of the first chase solution was complete, the reaction was held at 75 °C for 10 minutes followed by a cool down 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 simultaneously with a solution of IAA (2.79 g in 35 g DI water) over 30 minutes. After the addition of the second chase solution was complete, the reaction mixture was neutralized by the 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 Tg of 45.0 °C. g .

[0024] Preparation of intermediate example 2 - 56BA / 42AN / 2IA latex composition

[0025] The composition was prepared by the procedure described for 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 seeding step, the remaining ME was fed to the kettle over 120 minutes, with the first 20 minutes fed at a rate of 9.5 g / min, and then the last 100 minutes fed at a rate of 19.1 g / 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 Tg of -5.6°C. g .

[0026] Preparation of intermediate example 3 - 68EA / 28AN / 4IA latex composition

[0027] The composition was prepared by the procedure described for 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 Tg of 6.2°C.

[0028] Preparation of comparative intermediate example 1 - 54EA / 44MMA / 2IA latex composition

[0029] The composition was prepared by the procedure described for 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 Tg of 22.9°C. g .

[0030] Preparation of comparative intermediate example 2 - 70EA / 28AN / 2AA latex composition

[0031] The composition was prepared by the procedure described for 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 Tg of 3.2°C. g .

[0032] Table 1 summarizes the amounts of monomers and neutralizing agent used to prepare the latex intermediate.

[0033] Table 1 - Amount of monomers and neutralizing agent used to prepare the latexes

[0034]

[0035] Each of the latex intermediates and comparative intermediates were combined with starch by the following procedure to make Examples 1-3 and Comparative Examples 1 and 2: A starch solution (45% solids content) was prepared by dissolving ICB 3000 corn starch (100 g, 95% solids) 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 high speed mixer at 1800 rpm for 2 minutes. The starch loading was 30% based on the weight of total solids in the composition.

[0036] Paper coating procedure

[0037] Coated paper products were prepared by applying the compositions to the uncoated smooth side of a paper substrate (obtained from UPM) having a coat weight of 62 gsm. A wire wound doctor blade was used to achieve dry coat weights ranging from 8 gsm to 9 gsm. The samples were cured in an oven (Fisher Scientific Isotemp 180L Oven Fa) at 100 °C for 2 minutes.

[0038] Coating weight measurement

[0039] The coat weight of the coating was measured by cutting a 7.2 in 2 (46.3 cm 2 ) section of the coated and uncoated paper, then placing the sections in a 100 °C oven for 2 minutes. All 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.

[0040] Blocking test

[0041] Coating blocking tests were performed using a metal spring-loaded compression apparatus. Dry conditioned substrate was cut into rectangles (3.8 cm x 7.0 cm) and the coated side was placed face to face between the metal plates of the apparatus to measure coating to coating blocking (block c / c). The spring was compressed to apply 2600 Torr of pressure to the substrate and the entire apparatus was placed in a 60 °C oven for 1 hour, after which the product was removed from the oven and allowed to cool to room temperature for 30 minutes. The cooled sheet was carefully removed and pulled apart; the block c / c was rated according to the following scale:

[0042] 1 = sheet that pulled apart with no resistance

[0043] 2 = minimum force required to separate the sheet, audible noise detected upon separation

[0044] 3 = constant force required to separate the sheet, similar to a Post-It note

[0045] 4 = minimum amount of fiber tear observed

[0046] 5 = sheets completely glued together; significant fiber tear observed

[0047] Heat seal test

[0048] Hot seal was tested on coated paper samples using a HST-H3 Hot Seal Tester. The samples were cut into 2.5 cm x 5 cm strips and loaded with the coated side in contact with each other between the jaws. Pressure (3600 to 4150 torr) was applied at 190 °C for 0.5 seconds. The samples were removed from the tester and allowed to cool at room temperature for 1 minute. The paper samples were then pulled apart and the hot seal of coating to coating (hot seal c / c) was rated as P, M, or F as follows:

[0049] P: Pass, tears paper apart when pulled

[0050] M: Margins, peels paper apart like a sticky note

[0051] F: Fail, separates paper without resistance

[0052] Kit test for oil and grease resistance

[0053] Coated paper was tested for resistance to oil and grease resistance (OGR) according to TAPPI Test Method T559 cm-12. A reagent kit solution consisting of a mixture of castor oil, toluene, and heptane was applied dropwise to the coated substrate. After 15 seconds, any solvent penetration into the coating was noted and the solution was wiped from the substrate. A change in color or appearance of the substrate was also considered a failure for that particular reagent kit solution. A rating scale of 1 to 12 was assigned to the highest numbered reagent kit solution that passed the test, with 12 indicating the best performance. All test samples exhibited a reagent kit rating of 12.

[0054] OTR test

[0055] The oxygen transmission rate (OTR) of the film was measured according to ASTM D-3985 using a MOCON OXTRAN 2 / 22H Module at 23 °C, 50% relative humidity, and 760 torr. Coated paper samples were cut approximately 30 cm 2 in width and masked and loaded directly into the module for measurement. The masking material was 0.08 mm thick aluminum sheet with an acrylic adhesive layer for sealing. The effective test area was 20.3 cm2 . The test gas used was 100% oxygen, so that the permeation did not exceed the detection range of the module. The OTR was measured in cc / m 2 . All samples showed an OTR < 20 cc / m 2 . This was considered acceptable. Table 2 exemplifies the average values of the adhesion c / c, heat seal c / c and two OTR measurements (OTR avg ).

[0056] Table 2 - Properties of the coated substrates Examples Preparation of intermediate example 1 - 70EA / 28AN / 2IA latex composition Preparation of intermediate example 2 - 56BA / 42AN / 2IA latex composition Preparation of intermediate example 3 - 68EA / 28AN / 4IA latex composition Preparation of comparative intermediate example 1 - 54EA / 44MMA / 2IA latex composition Preparation of comparative intermediate example 2 - 70EA / 28AN / 2AA latex composition Table 1 - Amount of monomers and neutralizing agent used to prepare the latexes Paper coating procedure Coating weight measurement Blocking test Heat seal test Kit test for oil and grease resistance OTR test Table 2 - Properties of the coated substrates Examples Preparation of intermediate example 1 - 70EA / 28AN / 2IA latex composition Preparation of intermediate example 2 - 56BA / 42AN / 2IA latex composition Preparation of intermediate example 3 - 68EA / 28AN / 4IA latex composition Preparation of comparative intermediate example 1 - 54EA

[0057]

[0058] The data demonstrate that samples prepared from EA / AN / IA and BA / AN / IA latexes show an excellent balance of adhesion c / c, heat seal c / c, OTR and OGR.

Claims

1. A composition comprising: a) an aqueous dispersion of polymer particles comprising structural units of: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) 20% to 50% by weight of starch, based on the weight of the starch and the polymer particles; wherein the polymer particles have a calculated glass transition temperature of -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 -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 the structural units of ethyl acrylate is in the range of 65% by weight to 73% by weight; the concentration of the structural units of acrylonitrile is in the range of 23% by weight to 33% by weight; And the concentration of the structural unit of itaconic acid is in the range of 1.5 wt % to 6 wt %.

3. The composition of claim 2, wherein the concentration of the starch is in the range of 25 wt% to 40 wt%; wherein the concentration of structural units of ethyl acrylate is in the range of 67 wt% to 71 wt%; the concentration of structural units of acrylonitrile is in the range of 25 wt% to 31 wt%; and the concentration of structural units of itaconic acid is in the range of 1.9 wt% to 4.5 wt%; and wherein the calculated glass transition temperature is in the range of 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 -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 the structural units of n-butyl acrylate is in the range of 50 wt % to 60 wt %; the concentration of the structural units of acrylonitrile is in the range of 35 wt % to 46 wt %; and the concentration of the structural units of itaconic acid is in the range of 1.5 wt % to 6 wt %.

5. The composition of claim 4, wherein the concentration of the starch is in the range of 25 wt% to 40 wt%; wherein the concentration of structural units of n-butyl acrylate is in the range of 52 wt% to 58 wt%; the concentration of structural units of acrylonitrile is in the range of 38 wt% to 44 wt%; and the concentration of structural units of itaconic acid is in the range of 1.9 wt% to 4.5 wt%; and wherein the calculated glass transition temperature is in the range of -10°C to 5°C.

6. The composition of any one of claims 1 to 5, wherein the starch is derived from corn, wheat, oats, barley, rice, millet, potato, pea, cassava, sorghum or sago, and the concentration of the starch is in the range of 28% to 32% by weight based on the weight of the starch and the polymer particles.

7. The composition of claim 6, wherein the starch is corn starch.

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

9. The composition according to claim 8, wherein the concentration of the starch is in the range of 25% to 40% by weight, 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, the concentration of the structural units of ethyl acrylate is in the range of 67% to 71% by weight; the concentration of the structural units of acrylonitrile is in the range of 25% to 31% by weight; and the concentration of the structural units of itaconic acid is in the range of 1.9% to 4.5% by weight; and when the polymer particles comprise structural units of n-butyl acrylate, acrylonitrile and itaconic acid, the concentration of the structural units of n-butyl acrylate is in the range of 52% to 58% by weight; the concentration of the structural units of acrylonitrile is in the range of 38% to 44% by weight; and the concentration of the structural units of itaconic acid is in the range of 1.9% to 4.5% by weight.

10. The composition of claim 9, wherein the starch is derived from corn, wheat, oats, barley, rice, millet, potato, pea, cassava, sorghum or sago, and the concentration of the starch is in the range of 25% to 35% by weight based on the weight of the starch and the polymer particles.

11. The composition of claim 10, wherein the starch is corn starch.

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