Coated paper product

Abstract

The present invention relates to a paper coated article comprising a coating layer superposed on a first side of a paper substrate wherein the coating layer comprises a polyacrylate and a starch; wherein the polyacrylate comprises the following structural units: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid. The paper coated article of the present invention exhibits excellent oxygen barrier properties as well as oil resistance, grease resistance and blocking resistance.

Description

BACKGROUND

[0001] The present invention relates to a coated paper product, and more particularly, to a paper coated with a coating comprising a polyacrylate and a starch.

[0002] Paper is favored by the packaging industry and consumers for its biologically sourced, recyclable, and environmentally non-durable 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-sided 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 coating-to-coating contact 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, can result in the entire roll becoming 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 addresses the needs in the art by providing a coated paper product comprising a coating layer superimposed on a first face of a paper substrate, wherein the coating layer comprises a polyacrylate and a starch; wherein the polyacrylate comprises structural units of: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; wherein the concentration of the starch ranges from 20 wt% to 50 wt% based on the weight of the starch and the polyacrylate; and wherein the calculated glass transition temperature of the polyacrylate ranges from -10 °C to 35 °C.

[0005] The coated product of the present invention exhibits excellent oxygen barrier properties as well as oil resistance, grease resistance, and blocking resistance. DETAILED DESCRIPTION

[0006] The present invention relates to a coated paper article comprising a coating disposed on a first surface of a paper substrate, wherein the coating comprises a polyacrylate and a starch; wherein the polyacrylate comprises structural units comprising: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; wherein the concentration of the starch is in the range of 20% by weight to 50% by weight based on the weight of the starch and the polyacrylate; and wherein the calculated glass transition temperature of the polyacrylate is in the range of -10°C to 35°C.

[0007] As used herein, "polyacrylate" refers to the residue of an aqueous dispersion (latex) of polymer particles after a composition containing latex and starch has been applied to paper and dried.

[0008] As used herein, the “structural unit” of a monomer refers to the residue of the monomer after polymerization. For example, the structural unit of ethyl acrylate is illustrated below:

[0009]

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

[0011] As used herein, “calculated glass transition temperature” refers to the temperature of homopolymers as reported in the Polymer Handbook (4th edition), John Wiley & Sons, Inc. (2005). g The glass transition temperature (T) calculated using the Fox equation g ). Calculated T of polyacrylate g Within the range of -10°C, -5°C, 0°C to 35°C, 25°C, 20°C, or 15°C.

[0012] The polyacrylate preferably comprises structural units of ethyl acrylate, acrylonitrile, and itaconic acid; or n-butyl acrylate, acrylonitrile, and itaconic acid. When the polyacrylate comprises the structural unit of ethyl acrylate, the concentration of the ethyl acrylate structural unit is preferably in the range of 65% or 67% by weight to 75% or 73% or 71% by weight; the concentration of the acrylonitrile structural unit is preferably in the range of 23% or 25% or 27% by weight to 33% or 31% by weight; and the concentration of the itaconic acid structural unit is preferably in the range of 1.5% or 1.9% by weight to 6% or 5% or 4.5% by weight, wherein all weight percentages are based on the weight of the polyacrylate.

[0013] When the polyacrylate contains structural units of n-butyl acrylate, the weight percentage of structural units of n-butyl acrylate is preferably in the range of 50 wt% or 52 wt% or 54 wt% to 60 wt% or to 58 wt%; the weight percentage of structural units of acrylonitrile is preferably in the range of 35 wt% or 38 wt% or 40 wt% to 46 wt% or to 44 wt%; and the weight percentage of structural units of itaconic acid is preferably in the range of 1.5 wt% or 1.9 wt% to 6 wt% or 5 wt% or 4.5 wt%, with all weight percentages based on the weight of the polyacrylate.

[0014] 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 polyacrylate. Similarly, the concentration of polyacrylate 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 polyacrylate.

[0015] The composition for coating a paper substrate can be prepared by first preparing an aqueous dispersion of polymer particles (latex) by emulsion polymerization and then adding the starch in the form of an aqueous slurry or as a dry powder. It is also possible to prepare the composition by polymerizing monomers in the presence of starch under emulsion polymerization conditions.

[0016] The composition can be applied to a paper substrate to form a coated paper using means well known in the art; the coated paper is advantageously dried at elevated temperature to a desired coating weight, which is typically in the range of 5 g / m 2 (gsm) or 8 gsm to 20 gsm or to 15 gsm or to 10 gsm. The paper can be coated on the first side and optionally the second side of the paper. When the paper is coated on both sides, the total coating weight is typically in the range of 5 gsm or 8 gsm to 25 gsm or to 20 gsm or to 15 gsm or to 10 gsm. The starch and polyacrylate preferably make up 70 wt% or 80 wt% or 90 wt% or 95 wt% or 98 wt% to 100 wt% of the coating. The coating can also contain one or more additional components including organic or inorganic opacifying pigments, fillers, colorants, dispersants, rheology modifiers, and antifoams.

[0017] Coatings with excellent oxygen barrier properties as well as oil, grease, and blocking resistance were prepared using the compositions of the present invention.

[0018] Example

[0019] In the following examples, particle size refers to the z-average particle size diameter by dynamic light scattering.

[0020] Intermediate Example 1 - 70EA / 28 Preparation of AN / 2IA latex composition

[0021] 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 .

[0022] Intermediate Example 2 - 56BA / 42AN / 2IA latex composition

[0023] 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 .

[0024] Preparation of 68EA / 28AN / 4IA 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), 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.

[0026] Comparative Intermediate Example 1 - 54EA / 44MMA / 2IA 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 (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 .

[0028] Preparation of 70EA / 28AN / 2AA 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 (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 .

[0030] Table 1 summarizes the amounts of monomers and neutralizing agent used to prepare the latex intermediate.

[0031] Table 1 - Amount of monomers and neutralizing agent used to prepare the latexes

[0032]

[0033] Each of the latex intermediates and comparative intermediates were combined with starch by the following procedure to make intermediate examples 4 to 6 and comparative examples 3 and 4: 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.

[0034] Paper coating procedure

[0035] Coated paper products (examples 1 to 3 and comparative examples 1 and 2) 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 in the range of 8 gsm to 9 gsm. The samples were cured in an oven (Fisher Scientific Isotemp 180L Oven Fa) at 100 °C for 2 minutes.

[0036] Coating weight measurement

[0037] The coat weight of the coating was measured by cutting 7.2 in 2 (46.3 cm 2 ) sections 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.

[0038] Blocking test

[0039] Coating blocking tests were performed using a metal spring-loaded compression apparatus. Dry conditioned substrates were cut into rectangles (3.8 cm x 7.0 cm) and the coated sides were 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 substrates 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 sheets were carefully removed and pulled apart; the block c / c was rated according to the following scale:

[0040] 1 = sheets that pulled apart with no resistance

[0041] 2 = minimum force required to separate the sheet, audible noise detected upon separation

[0042] 3 = constant force required to separate the sheet, similar to a Post-It note

[0043] 4 = minimum amount of fiber tear observed

[0044] 5 = sheets completely glued together; significant fiber tear observed

[0045] Heat seal test

[0046] 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:

[0047] P: Pass, tears paper apart when pulled

[0048] M: Margins, peels paper apart like a sticky note

[0049] F: Fail, separates paper without resistance

[0050] Kit test for oil and grease resistance

[0051] Coated papers were 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 samples exhibited a reagent kit rating of 12.

[0052] OTR test

[0053] The oxygen transmission rate (OTR) of the film was measured according to ASTM D-3985 at 23 °C, 50% relative humidity, and 760 torr using a MOCON OXTRAN 2 / 22H Module. Approximately 30 cm 2The coated paper samples were then masked and directly loaded 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 cm 2 . Test gas containing 100% oxygen was used so that the permeation did not exceed the detection range of the module. OTR was measured in cc / m 2 ·d. All samples exhibited OTR < 20 cc / m 2 ·d, which was considered acceptable.

[0054] Table 2 exemplifies the average values of blocking c / c, heat sealing c / c and two OTR measurements (OTR avg ).

[0055] Table 2 - Properties of coated substrates

[0056] Example number Coating weight (gsm) Blocking c / c Heat seal c / c OTR avg (cc / m 2 ·d)]]> 1 8.8 2 P 8.5 2 8.9 1 P 11.8 3 8.1 1 P 9.0 Comparison 1 8.5 5 F 6.4 Comparison 2 8.3 5 P 6.8

[0057] The data demonstrates that samples prepared from EA / AN / IA and BA / AN / IA latexes exhibit an excellent balance of blocking c / c, heat sealing c / c, OTR and OGR.

Claims

1. A coated paper product comprising a coating layer superimposed on a first side of a paper substrate, wherein the coating layer comprises a polyacrylate and a starch; wherein the polyacrylate comprises structural units of: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; wherein the concentration of the starch is in the range of 20 to 50 weight percent based on the weight of the starch and the polyacrylate; and wherein the calculated glass transition temperature of the polyacrylate is in the range of -10 to 35 °C.

6. The coated paper product of any one of claims 1 to 5, wherein the starch is derived from corn, wheat, oat, barley, rice, millet, potato, pea, cassava, sorghum, or sago, and the concentration of the starch is in the range of 28 to 32 weight percent based on the weight of the starch and the polyacrylate.

2. The coated paper product according to claim 1, wherein the calculated glass transition temperature of the polyacrylate is in the range of -5°C to 25°C and the polyacrylate comprises structural units of ethyl acrylate, acrylonitrile and itaconic acid, wherein, a concentration of structural units of ethyl acrylate in the range of 65 wt% to 73 wt%, based on the weight of the polyacrylate; a concentration of structural units of acrylonitrile in the range of 23 wt% to 33 wt%; and a concentration of structural units of itaconic acid in the range of 1.5 wt% to 6 wt%; wherein the coating has a coating weight in the range of 5 g / m 2 to 20 g / m 2 .

3. The coated paper product of claim 2, wherein the concentration of the starch is in the range of 25 wt% to 40 wt% based on the weight of the starch and the polyacrylate; wherein, a concentration of structural units of ethyl acrylate in the range of 67 wt% to 71 wt%, based on the weight of the polyacrylate; a concentration of structural units of acrylonitrile in the range of 25 wt% to 31 wt%; and a concentration of structural units of itaconic acid 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; wherein the coating has a coating weight in the range of 5 g / m 2 to 15 g / m 2 .

4. The coated paper product of claim 1, wherein the calculated glass transition temperature of the polyacrylate is in the range of -10°C to 10°C and the polyacrylate comprises structural units of n-butyl acrylate, acrylonitrile and itaconic acid, wherein, The concentration of structural units of n-butyl acrylate is in the range of 50 to 60 wt.-%, the concentration of structural units of acrylonitrile is in the range of 35 to 46 wt.-%, and the concentration of structural units of itaconic acid is in the range of 1.5 to 6 wt.-%, based on the weight of the polyacrylate; wherein the coating has a coating weight in the range of 5 g / m 2 to 20 g / m 2 .

5. The coated paper product of claim 4, wherein the concentration of the starch is in the range of 25 wt% to 40 wt% based on the weight of the starch and the polyacrylate; wherein, based on the weight of the acrylate, the concentration of structural units of n-butyl acrylate is in the range of 52 to 58 wt.-%; the concentration of structural units of acrylonitrile is in the range of 38 to 44 wt.-%; and the concentration of structural units of itaconic acid is in the range of 1.9 to 4.5 wt.-%; and wherein the calculated glass transition temperature is in the range of -10 to 5 °C; wherein the coating has a coating weight in the range of 5 g / m 2 to 15 g / m 2 .

7. The coated paper product of claim 6, wherein the starch is corn starch.

9. A coated paper product comprising a coating layer superimposed on a first side of a paper substrate, wherein the coating layer comprises: a) a polyacrylate comprising structural units of: 1) n-butyl acrylate or ethyl acrylate or a combination thereof; 2) acrylonitrile; and 3) itaconic acid; and b) a starch having a concentration in the range of 20 to 50 weight percent based on the weight of the starch and the polyacrylate; wherein when the polyacrylate comprises structural units of ethyl acrylate, acrylonitrile, and itaconic acid, the concentration of structural units of ethyl acrylate is in the range of 65 to 73 weight percent based on the weight of the polyacrylate; the concentration of structural units of acrylonitrile is in the range of 23 to 33 weight percent; and the concentration of structural units of itaconic acid is in the range of 1.5 to 6 weight percent; and wherein when the polyacrylate comprises structural units of n-butyl acrylate, acrylonitrile, and itaconic acid, the concentration of structural units of n-butyl acrylate is in the range of 50 to 60 weight percent based on the weight of the polyacrylate; the concentration of structural units of acrylonitrile is in the range of 35 to 46 weight percent; and the concentration of structural units of itaconic acid is in the range of 1.5 to 6 weight percent.

8. The coated paper product of claim 1, further comprising a coating on a second side of the paper substrate, wherein the total coating weight of the coating is in the range of 5 g / m 2 to 15 g / m 2 . ​ ​ ​ ​ ​ 10. The coated paper product according to claim 9, wherein the concentration of the starch is in the range of 25 to 40 wt.%, based on the weight of the starch and the polyacrylate; wherein when the polyacrylate comprises structural units of ethyl acrylate, acrylonitrile and itaconic acid, the concentration of structural units of ethyl acrylate is in the range of 67 to 71 wt.%; the concentration of structural units of acrylonitrile is in the range of 25 to 31 wt.%; and the concentration of structural units of itaconic acid is in the range of 1.9 to 4.5 wt.%; and when the polyacrylate comprises structural units of n-butyl acrylate, acrylonitrile and itaconic acid, the concentration of structural units of n-butyl acrylate is in the range of 52 to 58 wt.%; the concentration of structural units of acrylonitrile is in the range of 38 to 44 wt.%; and the concentration of structural units of itaconic acid is in the range of 1.9 to 4.5 wt.%.

11. The coated paper product according to any one of claims 8 to 10, wherein the starch is derived from corn, wheat, oat, barley, rice, millet, potato, pea, cassava, sorghum or sago, and the starch comprises 25 to 35 wt.% of the coating; wherein wherein said coating has a coating weight in the range of 5 g / m 2 to 20 g / m 2 .

12. The coated paper product according to claim 11, wherein the starch is corn starch. The coating has a coating weight in the range of 5 g / m 2 to 15 g / m 2 . ​ 13. The coated paper product of claim 9, further comprising a coating on a second side of the paper substrate, wherein the total coating weight of the coating is in the range of 5 g / m 2 to 25 g / m 2 .

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