Coated paper products

Abstract

The present invention is 2 ~20g / m 2 The present invention relates to an article comprising a paper or paperboard substrate laminated with a film having a dry coating weight in the range of 100 to 1500 mm, the film comprising a copolymer comprising structural units of vinyl ester, vinyl alcohol, and acrylate monomers. The coating provides oil and grease resistance, mineral oil barrier performance, and heat sealability.

Description

[Background technology]

[0001] This invention relates to coated paper or cardboard articles, and more specifically, to paper or cardboard coated with partially hydrolyzed poly(vinyl ester-co-acrylate). Paper and cardboard are increasingly used in packaging applications as sustainable alternatives to plastic packaging due to their renewable and biodegradable properties. In many applications, paper and cardboard need to be coated with barrier materials to reduce the penetration of oil, grease, moisture, and oxygen through these substrates. Achieving oil and grease resistance (OGR) is essential for paper and cardboard packaging used in food service applications such as sandwich wrappers, popcorn bags, and bakery boxes. Barrier coatings designed for these applications are typically used to prevent oil from saturating the underlying paper substrate, which can alter the appearance of the material and adversely affect the structural integrity of the packaging.

[0002] Conventional OGR paper is treated with perfluorocarbon additives, which are highly effective barrier materials but are subject to strict regulatory scrutiny. Extruded plastic films such as polyethylene are also used to coat paper and cardboard and have been found to exhibit good barrier properties. However, extrusion coatings require off-machine application, produce unnecessarily thick films, thereby increasing costs and limiting the repulping and recyclability of these coated paper products.

[0003] Aqueous dispersion coatings are environmentally friendly alternatives to fluorochemical and polyethylene coatings, and they can be applied with lower coating weights to enable improved repulping and recyclability of paper packaging. Synthetic latexes based on acrylic, styrene-acrylic (SA), and styrene-butadiene (SB) polymers are the most commonly used materials in barrier coating applications. While these compositions can provide excellent OGR on paper and cardboard substrates, they often lack other coating properties important for the production and use of paper products, such as flexibility (or bendability), blocking resistance, and heat sealability. Poly(vinyl acetate) (PVAc) dispersions are a type of synthetic latex that has traditionally been used in coating compositions in the paper industry. These latexes offer advantages such as lower cost, thermal and light stability, adhesion, and blister resistance compared to SA and SB type binders. However, PVAc does not provide the good barrier properties required for packaging applications. Therefore, developing cost-effective and environmentally friendly articles with acceptable oil and grease resistance, as well as barrier properties, would represent an advance in the field of coated paper and cardboard articles. [Overview of the Initiative]

[0004] This invention provides 1 g / m 2 ~20g / m 2 An article comprising a paper or cardboard substrate laminated with a film having a dry coating weight in the range of, The present invention addresses the needs in the art by providing an article in which a film comprises, based on the weight of the film, at least 50 weight percent of one or more polymers, and at least 50 weight percent of one or more polymers comprises 40 to 96 weight percent of vinyl ester structural units, 2 to 50 weight percent of vinyl alcohol structural units, and 0.5 to 30 weight percent of acrylate monomer structural units.

[0005] The articles of the present invention have been shown to have oil resistance, grease resistance, mineral oil barrier performance, and heat sealability. [Modes for carrying out the invention]

[0006] This invention provides 1 g / m 2 ~20g / m 2 An article comprising a paper or cardboard substrate laminated with a film having a dry coating weight in the range of, The film is an article comprising, based on the weight of the film, one or more polymers in an amount of at least 50 weight percent, wherein the one or more polymers in an amount of at least 50 weight percent comprises 40 to 96 weight percent of vinyl ester structural units, 2 to 50 weight percent of vinyl alcohol structural units, and 0.5 to 30 weight percent of acrylate monomer structural units.

[0007] As used herein, the term “structural unit” of a specified monomer refers to the monomer residue after polymerization. For example, the structural unit of vinyl alcohol is as shown in the figure.

[0008] [ka] In the formula, the dotted lines represent the bonding points of structural units to the polymer backbone.

[0009] The superimposed films are formed from an aqueous dispersion of polymer particles containing structural units of vinyl ester, vinyl alcohol, and C1-C8 linear or branched alkyl acrylate. The aqueous dispersion is advantageously prepared in two steps. In the first step, the vinyl ester and C1-C8 linear or branched alkyl acrylate copolymerize under emulsion polymerization conditions to form a dispersion of poly(vinyl ester-co-acrylate) copolymer particles. The copolymer is then partially hydrolyzed with a base to form a dispersion of polymer particles containing structural units of vinyl ester, vinyl alcohol, and acrylate. Therefore, the vinyl alcohol structural units do not require vinyl alcohol as a starting material.

[0010] Additional monomers, including carboxylic acid monomers and sulfonic acid monomers or salts thereof, may be used in the polymerization reaction. Examples of suitable carboxylic acid monomers include acrylic acid, methacrylic acid, fumaric acid, itaconic acid, crotonic acid, and maleic acid. Examples of suitable sulfonic acid monomers include 2-sulfoethyl acrylate, 2-sulfoethyl methacrylate, 2-sulfopropyl acrylate, 2-sulfopropyl methacrylate, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 2-methacrylamido-2-methylpropanesulfonic acid, as well as salts thereof. The concentration of structural units of carboxylic acid monomers is typically in the range of 0.1 to 5 weight percent based on the weight of polymer particles, and the concentration of structural units of sulfonic acid monomers is also typically in the range of 0.1 to 5 weight percent based on the weight of polymer particles.

[0011] Polyethylenically unsaturated monomers can also be used in emulsion polymerization reactions, typically in the range of 0.1 to 5 weight percent based on the weight of the monomer. Examples of suitable polyethylenically unsaturated monomers include allyl methacrylate, ethylene glycol dimethacrylate, diallyl maleate, and diallyl phthalate.

[0012] As used herein, the term "acrylate monomer" refers to an acrylate or methacrylate monomer. Suitable C1-C8 linear or branched alkyl acrylate monomers (alkyl acrylate monomers) include methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate.

[0013] Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl octanoate, vinyl laurate, and vinyl versatate, with vinyl acetate being preferred. The concentration of vinyl ester structural units in the film is in the range of 40 to 96 weight percent based on the weight of the polymer, which is a copolymer mixture, and the concentration of vinyl alcohol structural units is in the range of 2 weight percent, or 5 weight percent, or 8 weight percent to 50 weight percent, or 40 weight percent, based on the weight of the polymer. The concentration of alkyl acrylate monomer structural units is in the range of 0.5 weight percent, or 1 weight percent to 30 weight percent, or 25 weight percent, but it has been found that the optimal concentration is found over a narrower range with higher concentrations of vinyl alcohol structural units, more specifically, the concentration of alkyl acrylate monomer structural units is in the range of 3 weight percent, or 4 weight percent to 20 weight percent, based on the weight of the polymer, when the concentration of vinyl alcohol structural units is in the range of 13 weight percent, or 20 weight percent to 40 weight percent.

[0014] When a dispersion of polymer particles containing structural units of vinyl esters, vinyl alcohols, and acrylates is prepared by hydrolyzing a copolymer of vinyl acetate and acrylate monomers under basic conditions, the film may further contain salts of carboxylic acids formed as hydrolysis byproducts. If necessary, the salts may be removed from the composition. If the vinyl ester is vinyl acetate, the film may contain acetate anions in concentrations ranging from 5% by weight, or from 8% by weight to 40% by weight, or to 35% by weight, based on the weight of the acetate anions and the structural units of vinyl acetate, vinyl alcohol, and acrylate monomers. Sodium acetate, potassium acetate, and ammonium acetate are examples of salts of acetate, with sodium acetate being the most common.

[0015] The film may contain additional materials such as surfactants, defoamers, waxes, dispersants, rheology modifiers, pigments, crosslinking agents, and colorants. While it is possible to include fluorescent whitening agents in the film, it is best to avoid using such agents, as the end-use of coated paper or cardboard articles is most common in the field of food packaging. Therefore, the concentration of the fluorescent whitening agent is preferably less than 5% by weight, more preferably less than 1% by weight, and most preferably 0% by weight, based on the weight of the film.

[0016] The articles of the present invention are advantageously prepared by applying an aqueous composition to a paper or cardboard substrate in an amount sufficient to achieve a desired coating weight, and then drying the composition at a high temperature until the moisture is removed. The film comprises one or more polymers, based on the weight of the film, in amounts of at least 50 weight percent, or at least 65 weight percent, or at least 75 weight percent, or at least 85 weight percent, or at least 95 weight percent, of which one or more polymers comprises structural units of vinyl esters, vinyl alcohols, and acrylate monomers. The film may also contain other polymers such as acrylics, styrene-butadienes, and styrene-acrylic polymers. Alternatively, the film comprises, based on the weight of the acetate anion and the structural units of vinyl acetate, vinyl alcohols, and acrylate monomers, from 60 weight percent, or from 65 weight percent to 95 weight percent, or 92 weight percent preferably vinyl acetate, vinyl alcohols, and acrylate monomer structural units, and from 5 weight percent, or from 8 weight percent to 40 weight percent, or 35 weight percent acetate anion. Coated paper or cardboard articles have been shown to exhibit oil-resistant and grease-resistant barrier properties. [Examples]

[0017] Intermediate Example 1 - Preparation of vinyl acetate-butyl acrylate latex Deionized water (783.0 g) was packed into a 5 L four-necked round-bottom flask and heated to 60°C under N2. In a separate container, a monomer emulsion was prepared containing deionized water (451.0 g), sodium vinyl sulfonate (32.0 g, 25% in water), sodium acetate (4.0 g), TERGITOL® 15-S-40 surfactant (trademark of The Dow Chemical Company or its affiliates, 22.9 g, 70% in water), Disponil FES 993 emulsifier (106.6 g, 30% in water), glacial acrylic acid (8.0 g), butyl acrylate (32.0 g), and vinyl acetate (1552.0 g). A portion of the monomer emulsion (44.2 g) was added to the reactor along with a rinse (16.0 g of water), followed by the addition of ammonium persulfate (1.5 g in 8.0 g of water) along with a rinse (8.0 g of water), and then sodium bisulfite (0.3 g), ferrous sulfate heptahydrate (17 mg), and sodium dithionite (0.6 g) were dissolved in 8.0 g of water along with a rinse (8.0 g of water). After holding for 2 minutes, the remainder of the monomer emulsion was supplied to the reactor over 120 minutes. A solution of ammonium persulfate (4.9 g) and t-butyl hydroperoxide (2.0 g) in 120.0 g of water, along with a solution of sodium bisulfite (3.2 g in 120.0 g of water), was simultaneously supplied to the reactor over 130 minutes at a temperature in the range of 64-66°C. After all feeding and rinsing was complete, the reactor was cooled to 60°C, and then 48.0 g of aqueous solutions of ammonium persulfate (0.5 g) and t-butyl hydroperoxide (1.7 g), along with a solution of sodium bisulfite (2.7 g in 48.0 g of aqueous solution), were simultaneously fed over 30 minutes. The reactor was then cooled to room temperature, and ammonium hydroxide (6.9 g, 28 wt%) was added dropwise to raise the pH to 6.5-7.5. The solid content was found to be 48 wt%.

[0018] Intermediate Example 2 - Partial hydrolysis of the copolymer of vinyl acetate and butyl acrylate A portion of the latex from Intermediate 1 (300 g, 48% solids) was placed in a jar at room temperature, and then sodium hydroxide solution (10% by weight in water) was added dropwise to the stirred latex over 1 hour to achieve the target hydrolysis level. The pH of the partially hydrolyzed latex was in the range of 9.0–10.0, and the solids content was in the range of 27%–46% depending on the degree of hydrolysis. The samples were stored at room temperature, and the degree of hydrolysis was determined by HPLC analysis of acetic acid produced via cleavage of acetate groups, as described in the following section.

[0019] High-performance liquid chromatography (HPLC) analysis of acetic acid. HPLC analysis was performed using an Agilent 1100 Series HPLC equipped with a Phenomenex Rezex ROA Organic Acid H+ 240×4.6 mm column (8 μm particle size, 8% cross-linked sulfonated styrene-divinylbenzene), a Phenomenex Carbo-H4 column guard, and a UV detector operating at a wavelength of 210 nm. Hydrolyzed latex samples were diluted 10-fold and centrifuged at 100,000 rpm for 15 minutes, after which the supernatant was filtered through a 0.45 μm PVDF syringe filter. The sample injection volume was 5 μL, and separation was performed using 2.5 mM phosphoric acid at a flow rate of 0.4 mL / min and a column temperature of 35°C. The instrument was externally calibrated using acetic acid at 50–10,000 ppm.

[0020] The stability of the hydrolyzed latex was evaluated and is shown in Table 1. The weight percentages of the structural units of vinyl acetate (VA), butyl acrylate (BA), and vinyl alcohol are based on the weight of the polymer, and the weight percentages of the acetate anion (AcO) are also shown. - The weight percentage of ) is hydrolyzed copolymer and AcO - This is based on the weight of the total solids content. Samples that remained unsolidified after 6 months passed the stability test, while samples that solidified within 3 months failed the test.

[0021]

Table 1

[0022] The data show the importance of including acrylates to achieve latex colloid stability.

[0023] Preparation of coated substrate The latices of Examples 1 to 7 were applied onto UPM Brilliant Pro paper (basis weight: 62 g / m 2 ) in the machine direction using an automatic coater (K Control Coater) equipped with various wire wound rods to achieve a dry coating weight of 5±0.3 g / m 2 . The samples were dried at 100°C for 2 minutes. The coated paper was conditioned for at least 1 hour in a temperature-controlled room according to TAPPI Standard 402.

[0024] 3M Kit Test Coated paper samples were tested for oil and grease resistance using TAPPI Method T559-cm-12 with an extended range of kit scores. Kit solutions composed of various ratios of castor oil, toluene, and heptane were dropped onto the coated substrate, allowed to stand for 15 seconds, and then wiped off. The occurrence of either solvent breakthrough or substrate discoloration was classified as a failure for that kit solution. The kit score for a given sample was assigned using the number of the highest (most aggressive) kit solution that penetrated the coated substrate. In the TAPPI method, kit scores range from 1 to 12 for the kit solution compositions. Additionally, more aggressive solutions were prepared to assign kit values up to 16, as shown in Table 2 below. Each sample was tested in duplicate.

[0025]

Table 2

[0026] Hexane Vapor Transmission Rate (HVTR) Before conducting the experiment, the coated paper samples were conditioned overnight in a fume hood. The coated paper substrate was cut into a 2.5-inch circle. Reagent-grade n-hexane (5 g) was added to a permeation cup using a pipette. The sample was placed with its coated side down on a rubber gasket, the lid was tightened, and the sample was fixed to the permeation cup. The initial mass of the permeation cup with the mounted sample was recorded, and the cup was weighed again after 24 hours. To calculate the hexane vapor transmission rate, the weight after 24 hours was subtracted from the initial weight, and then divided by 0.000212 (the area of the exposed sample). The calculation provides the hexane vapor transmission rate in units of g / m 2 ·day

[0027] Heat Sealability The ability to heat seal coated paper was evaluated using a single-phase Sentinel Laboratory Heat Sealer. The coated sample was cut into a 2-inch × 4-inch rectangle, and placed with the coated side against coated side in the clamp of the heat sealer for 0.5 seconds at a temperature of 190°C and a pressure of 100 psi. After cooling the substrate to room temperature, the two sheets were separated. Samples that separated with fiber tear were considered acceptable, while samples that separated without fiber tear were considered unacceptable. Samples were tested in duplicate. Table 3 shows the barrier performance of various coatings.

[0028]

Table 3

[0029] The data show improved oil and grease resistance, mineral oil barrier (lower HVTR), and heat sealability for coatings prepared from partially hydrolyzed copolymers compared to coatings prepared from latex compositions that are not partially hydrolyzed. The invention described in the original claims of this application is listed below. [1] Articles, 1 g / m 2 ~20g / m 2 It comprises a paper or cardboard substrate laminated with a film having a dry coating weight in the range, An article wherein the film comprises, based on the weight of the film, at least 50 weight percent of one or more polymers, and at least 50 percent of the one or more polymers comprises 40 to 96 weight percent of vinyl ester structural units, 2 to 50 weight percent of vinyl alcohol structural units, and 0.5 to 30 weight percent of acrylate monomer structural units. [2] C 1 ~C 8 The article according to [1], wherein the linear or branched alkyl acrylate monomer is selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate, and the vinyl ester is vinyl acetate. [3] The polymer comprises, based on the weight of the polymer, 8 to 50 weight percent of vinyl alcohol structural units and 1 to 25 weight percent of the C 1 ~C 8 The article according to [2], comprising a structural unit of a linear or branched alkyl acrylate monomer. [4] When the concentration of the structural units of vinyl alcohol is in the range of 13 to 40 weight percent, the C 1 ~C 8 The article according to [2], wherein the concentration of structural units of linear or branched alkyl acrylate monomers is in the range of 3 to 20 weight percent. [5] Above C 1 ~C 8 The article according to [3], wherein the linear or branched alkyl acrylate monomer is n-butyl acrylate. [6] At least 65 weight percent of one or more polymers, vinyl acetate, vinyl alcohol, and the C 1 ~C 8 An article according to any one of [2] to [5], comprising a structural unit of a linear or branched alkyl acrylate monomer. [7] The article according to [2], wherein the film comprises a) 60 to 95 weight percent of structural units of vinyl acetate, vinyl alcohol, and the acrylate monomer, and b) 5 to 40 weight percent of acetate anions, the weight percentage range being based on the weight of the acetate anions and the structural units of vinyl acetate, vinyl alcohol, and the acrylate monomer. [8] C 1 ~C 8 The article according to [4], wherein the linear or branched alkyl acrylate monomer is n-butyl acrylate. [9] The article according to [1], wherein the coating further comprises at least one additional material selected from the group consisting of surfactants, defoamers, waxes, dispersants, rheology modifiers, pigments, crosslinkers, and colorants, and less than 5 weight percent of a fluorescent whitening agent based on the weight of the film.

[10] The article according to [1], wherein the composition further comprises less than 1 weight percent of a fluorescent whitening agent based on the weight of the film.

Claims

1. Articles, 1 g / m ２ ~20g / m ２ It comprises a paper or cardboard substrate laminated with a film having a dry coating weight in the range, An article wherein the film comprises, based on the weight of the film, at least 50 weight percent of one or more polymers, and at least 50 percent of the one or more polymers comprises 40 to 96 weight percent of vinyl acetate structural units, 2 to 50 weight percent of vinyl alcohol structural units, and 0.5 to 30 weight percent of acrylate monomer structural units.

2. The acrylate monomer is a C1 to C8 linear or branched alkyl acrylate monomer, and the C １ ~C ８ The article according to claim 1, wherein the linear or branched alkyl acrylate monomer is selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate.

3. The polymer comprises, based on the weight of the polymer, 8 to 50 weight percent of vinyl alcohol structural units and 1 to 25 weight percent of the C １ ~C ８ The article according to claim 2, comprising a structural unit of a linear or branched alkyl acrylate monomer.

4. When the concentration of the structural units of vinyl alcohol is in the range of 13 to 40 weight percent, the above C １ ~C ８ The article according to claim 2, wherein the concentration of structural units of linear or branched alkyl acrylate monomers is in the range of 3 to 20 weight percent.

5. Said C １ to C ８ The article according to claim 3, wherein the linear or branched alkyl acrylate monomer is n-butyl acrylate.

6. At least 65 weight percent of one or more polymers is vinyl acetate, vinyl alcohol, and the C １ ~C ８ An article according to any one of claims 2 to 5, comprising a structural unit of a linear or branched alkyl acrylate monomer.

7. The article according to claim 2, wherein the film comprises a) 60 to 95 weight percent of structural units of vinyl acetate, vinyl alcohol, and the acrylate monomer, and b) 5 to 40 weight percent of acetate anions, the weight percentage range being based on the weight of the acetate anions and the structural units of vinyl acetate, vinyl alcohol, and the acrylate monomer.

8. C １ ~C ８ The article according to claim 4, wherein the linear or branched alkyl acrylate monomer is n-butyl acrylate.

9. The article according to claim 1, wherein the coating further comprises at least one additional material selected from the group consisting of surfactants, defoamers, waxes, dispersants, rheology modifiers, pigments, crosslinkers, and colorants, and less than 5% by weight of a fluorescent whitening agent based on the weight of the film.

10. The article according to claim 1, wherein the composition further comprises less than 1 weight percent of a fluorescent whitening agent based on the weight of the film.

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