CN120813619A - Latex-starch compositions - Google Patents

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) 20 to 50 wt% starch, based on the weight of the starch and the polymer particles. The composition of the invention can be used as a coating for paper.

Description

Latex-starch composition

Background Art

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

Paper is favored by the packaging industry and consumers because it is bio-sourced, recyclable, and environmentally non-persistent. Advantageously, paper is coated to improve its barrier properties to 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 the emulsion polymerization of acrylate monomers in the presence of degraded starch to produce a coating composition that reportedly exhibits shear stability, low hexane penetration, and little or no pore formation.

Duplex-coated paper using standard in-line coating process conditions presents unique challenges. After a barrier coating layer is applied 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 coat-to-coat contact at elevated temperatures and considerable pressure. Even low levels of blocking can lead to failure of the barrier coating or paper fibers, and in extreme cases, the entire roll can become glued together. Therefore, finding a composition that exhibits excellent blocking resistance without sacrificing critical barrier properties would be a major advancement in the coated paper industry.

Summary of the Invention

The present invention addresses the need in the art by providing 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 in the range of -10°C to 35°C.

The compositions of the present invention are useful as coatings for paper, the coatings exhibiting excellent oxygen barrier properties as well as oil, grease and block resistance.

DETAILED DESCRIPTION

The present invention is 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 in the range of -10°C to 35°C.

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:

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

As used herein, "calculated glass transition temperature" refers to the glass transition temperature (Tg) calculated by the Fox equation using the homopolymer _Tg reported in Polymer Handbook (4th Edition), John Wiley & Sons, Inc. (2005). The calculated _Tg of the polymer particles is 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.

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.

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.

The type of starch is not limited and may include starch derived from corn, wheat, oats, barley, rice, millet, potato, pea, cassava, sorghum and sago. Based on the weight of the starch and the polymer particles, the concentration of the 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 %. Similarly, based on the weight of the starch and the polymer particles, the concentration of the polymer 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 %.

The composition of the present invention can be prepared by first preparing an aqueous dispersion of polymer particles by emulsion polymerization, and then adding starch 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 starch. The starch, polymer particles, and water preferably comprise 70% by weight, 80% by weight, 90% by weight, or 95% by weight of the composition to 100% by weight of the composition. The coating may also contain one or more additional components, including organic or inorganic opaque pigments, fillers, colorants, dispersants, rheology modifiers, and defoamers.

The composition can be applied to one or both sides of a paper substrate to form a coated paper using means known in the art; the coated paper is then dried at an elevated temperature to a desired coating weight, which is typically in the range of 8 g/ ^m2 (gsm) to 10 gsm. Coatings having excellent oxygen barrier properties as well as oil, grease, and block resistance are prepared using the compositions of the present invention.

Example

In the following examples, particle size refers to the z-average particle size diameter as determined by dynamic light scattering.

Intermediate Example 1 - Preparation of 70EA/28AN/2IA Latex Composition

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, an _N2 inlet 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 ME (42.56 g) was charged to the kettle and the container for 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 NaPS was rinsed with DI water (5 g). An exotherm was observed and the mixture was maintained at the peak temperature for 5 minutes. The remaining ME was fed into a kettle set at 81° C. over 90 minutes, at a rate of 13.0 g/min for the first 20 minutes and then at a rate of 26.1 g/min for the last 70 minutes. Simultaneously, a NaPS solution (2.81 g in 100 g DI water) was fed into the kettle over 90 minutes, at a rate of 0.65 g/min for the first 20 minutes and then at a rate of 1.29 g/min for the last 70 minutes. After the feeding was complete, the addition vessel was rinsed with DI water (110 g), and the reaction was maintained at 80° C. for 10 minutes, then cooled to 75° C. While cooling, a solution of ferrous sulfate heptahydrate (0.15% solution, 12.00 g) was added to the kettle. A first additional solution of tert-butyl hydroperoxide (t-BHP, 70% solution, 7.41 g in 40 g DI water) was added simultaneously to the kettle over 30 minutes at 75°C along with a solution of isoascorbic acid (IAA, 3.59 g in 50 g DI water). Following the completion of the first additional solution addition, the reaction was held at 75°C for 10 minutes before being cooled to 70°C. A second additional solution of t-BHP (70% solution, 5.60 g in 26 g DI water) was added to the kettle at 70°C, along with a solution of IAA (2.79 g in 35 g DI water) over 30 minutes. Following the completion of the second additional solution addition, 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 condensate. 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 3.6°C.

Intermediate Example 2-56 Preparation of BA/42AN/2IA Latex Composition

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 seeding step, the remaining ME was fed to the kettle over 120 minutes, at a rate of 9.5 g/min for the first 20 minutes and then at a rate of 19.1 g/min for the final 100 minutes. 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.

Intermediate Example 3-Preparation of 68EA/28AN/4IA Latex Composition

The composition was prepared by the procedure described in Intermediate Example 1, except that 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.

Comparative Intermediate Example 1-5 Preparation of 4EA/44MMA/2IA Latex Composition

The composition was prepared by the procedure described in Intermediate Example 1, except that 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.

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

The composition was prepared by the procedure described in Intermediate Example 1, except that 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.

Table 1 summarizes the amounts of monomers and neutralizing agents used to prepare the latex intermediates.

Table 1 - Amounts of Monomers and Neutralizers Used to Prepare Latexes

Examples 1 to 3 and Comparative Examples 1 and 2 were prepared by combining each of the latex intermediate and comparative intermediate with starch by the following procedure: a starch solution (45% solids content) was prepared by dissolving ICB 3000 corn starch (100 g, 95% solids) in DI water (111.11 g) with stirring at 50° C. A portion of the latex intermediate (125 g) was then placed in a 250 mL plastic container, followed by the addition of a portion of the starch solution (53.58 g). The mixture was mixed at 1800 rpm for 2 minutes using a high-speed mixer. The starch loading was 30% based on the weight of the total solids in the composition.

Paper coating process

Coated paper products were prepared by applying the composition to the uncoated smooth side of a paper substrate (obtained from UPM) having a coating weight of 62 gsm. A wire-wound drawdown bar was used to achieve a dry coating weight 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.

Coat weight measurement

The coating weight of the coatings was measured by cutting 7.2 in ² (46.3 cm ² ) sections from the coated and uncoated papers and placing the sections in an oven at 100°C for 2 minutes. All samples were then weighed and the coating weight was determined by measuring the difference between the coated and uncoated samples and dividing by the area of the sample.

Adhesion test

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 placed face-to-face between the metal plates of the apparatus to measure coating-to-coating adhesion (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 article 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 blocking c/c was rated according to the following scale:

1 = Sheet pulled apart without resistance

2 = Minimum force required to separate the sheets, with audible noise detected during separation

3 = Constant force required to separate the sheets, similar to a Post-It note

4 = Minimal amount of fiber tearing observed

5 = Sheets completely glued together; significant fiber tearing observed

Heat seal test

Heat seals were tested on coated paper samples using an HST-H3 heat seal tester. The samples were cut into 2.5 cm x 5 cm strips and loaded with the coated sides so that they were in contact 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 coating-to-coating heat seal (heat seal c/c) was rated as P, M, or F as follows:

P: Through, tears the paper apart when pulled

M: Edge, peel off the paper like a sticky note

F: Failed, the paper is separated without resistance

Test kit for oil and grease resistance

Coated paper was tested for oil and grease resistance (OGR) according to TAPPI test method T559 cm-12. A 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 off the substrate. Discoloration or changes in the appearance of the substrate were also considered a failure for that particular kit solution. The highest-numbered kit solution that passed the test was assigned a rating of 1 to 12, with 12 representing the best performance. All test samples exhibited a kit rating of 12.

OTR testing

According to ASTM D-3985, at 23 ° C, 50% relative humidity and 760 torr, the oxygen transmission rate (OTR) of the film was measured using a MOCON OXTRAN 2/22H module. Approximately 30 cm ² of coated paper sample was cut, then masked and directly loaded into the module for measurement. The masking material was a 0.08 mm thick aluminum sheet with an acrylic adhesive layer for sealing. The effective test area was 20.3 cm ² . A 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 showed an OTR of <20 cc/m ² ·d, which is considered acceptable. Table 2 illustrates the average value (OTR _avg ) of the blocking c/c, heat sealing c/c and two OTR measurements.

Table 2 – Properties of coated substrates

The data illustrate 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 (11)

1. A composition, the 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) 20 to 50% by weight of starch, based on the weight of the starch and the polymer particles, wherein the calculated glass transition temperature of the polymer particles is at-10 DEG C

To 35 ℃.

2. The composition of claim 1, wherein the calculated glass transition temperature of the polymer particles is in the range of-5 ℃ to 25 ℃ and the polymer particles comprise structural units of ethyl acrylate, acrylonitrile, and itaconic acid, wherein the concentration of structural units of ethyl acrylate is in the range of 65 wt% to 73 wt%, based on the weight of the polymer particles;

and the concentration of the structural unit of itaconic acid is in the range of 1.5 to 6% by weight.

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.%, based on the weight of the starch and the polymer particles, and wherein the calculated glass transition temperature is in the range of 0 ℃ to 15 ℃.

4. The composition of claim 1, wherein the calculated glass transition temperature of the polymer particles is in the range of-10 ℃ to 10 ℃ and the polymer particles comprise 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 wt% to 60 wt%, the concentration of structural units of acrylonitrile is in the range of 35 wt% to 46 wt%, and the concentration of structural units of itaconic acid is in the range of 1.5 wt% to 6 wt%, based on the weight of the polymer particles.

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.%, based on the weight of the starch and the polymer particles, and wherein the calculated glass transition temperature is in the range of-10 ℃ to 5 ℃.

6. The composition according to any one 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 starch is in the range of 28 to 32 wt% 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, the 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) 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 structural units of ethyl acrylate is in the range of 65 to 73 wt%, the concentration of structural units of acrylonitrile is in the range of 23 to 33 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 polymer particles, and wherein

When the polymer particles comprise 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 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 polymer particles.

9. The composition of claim 8, wherein the concentration of the starch is in the range of 25 wt.% to 40 wt.%, 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 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 when the polymer particles comprise 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 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.%.

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

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