Aqueous coating agent

Abstract

Disclosed is an aqueous coating agent comprising: (A) a copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond; (B) a basic material; and (C) particles having a melting point of 100 DEG C or higher, and a paper substrate coated with the aqueous coating agent.

Description

Technical Field

[0001] This invention relates to water-based coating agents for coating paper substrates. Background Technology

[0002] Given environmental concerns, a global trend is towards reducing plastic products. These plastics are non-biodegradable and difficult to process. Furthermore, burning plastics produces dioxins and causes air pollution. In recent years, the possibility of plastic waste being dumped into the ocean and breaking down into microlevels has been identified as problematic; these microlevels are then ingested by fish, and subsequently by humans. Against this backdrop, the use of paper-based materials to replace plastics has been explored, and paper-based materials have been processed and used to create containers, particularly in the food industry.

[0003] Laminated paper is conventionally used as a form of paper substrate. Laminated paper is treated to prevent a decrease in paper strength and to prevent hands from becoming soiled due to the seepage of oil components from food, etc.

[0004] In laminated paper, polyethylene film or similar materials are typically laminated onto a paper substrate. In recent years, due to increased environmental awareness, there has been a growing need to recycle laminated paper. However, such films have been a hindrance, thus requiring specialized equipment for the efficient recycling of laminated paper.

[0005] Patent Documents 1 and 2 disclose the application of an aqueous dispersion of an ethylene-based resin to paper.

[0006] Patent document 1 describes that an aqueous dispersion of an ethylene / acrylic acid copolymer neutralized with ammonia or amine can be used as a heat sealant for paper or aluminum foil (see [claims],

[0025] ,

[0028] ,

[0029] , and

[0044] ).

[0007] Patent document 2 describes that an aqueous dispersion can be applied to a paper substrate, the aqueous dispersion comprising an acid-modified ethylene / ethyl acrylate copolymer and a wax (see Table 1 in [claims],

[0046] ,

[0056] and Table 3 in

[0068] ).

[0008] Citation List Patent documents PTL 1: JP 2000-7860 A PTL 2: JP 2006-45313 A Summary of the Invention

[0009] Technical issues Patent Documents 1 and 2 disclose that the water dispersion (or coating film or coating layer formed from the water dispersion) in the embodiments of these two documents has excellent heat-sealing properties.

[0010] When the food packaging container is a regular paper cup, the end section of the paper cup is formed by coating the end section with an aqueous coating agent and then heating the aqueous coating agent. Therefore, the aqueous coating agent (or the coating film formed by the aqueous coating agent) used to coat the end section of the paper cup requires heat-sealing properties. Furthermore, the aqueous coating agent used for paper cups requires various properties, including heat-sealing.

[0011] Beverages (such as boiling or cold water) are poured into paper cups, thus requiring the paper substrate to not absorb the beverage. It cannot be assumed that the aqueous dispersions in Patent Documents 1 and 2 possess sufficient water resistance. When each of these aqueous dispersions is applied to a paper cup, the substrate of the paper cup will absorb the beverage.

[0012] Furthermore, considering the production line used to manufacture paper cups, the water-based coating agent used to coat the paper substrate also needs to be heat-resistant. In a typical paper cup manufacturing production line, the paper substrate coated with the water-based coating agent is brought into contact with a metal plate, and the paper substrate in contact with the metal plate is continuously processed to manufacture paper cups.

[0013] In production lines used to manufacture paper cups, the metal plate is typically heated by heat generated during the processing of the paper substrate. Therefore, in water-based coatings, it is necessary to reduce friction between the paper substrate and the heated metal plate. Patent Documents 1 and 2 do not consider the heat resistance of the aqueous dispersion, and it is unclear whether the aqueous dispersions in these two documents can be used in continuous paper cup manufacturing production lines.

[0014] As mentioned above, water-based coatings require a variety of properties in the food industry. Water-based coatings should not only have excellent heat-sealing, water resistance, and heat resistance, but also excellent general properties (such as coatability). Considering storage stability, water-based coatings need dispersion stability (e.g., when in the form of an emulsion, to inhibit the precipitation of the dispersed phase).

[0015] This invention was made to solve the above-mentioned problems, and its object is to provide a water-based coating agent with heat-sealing properties, water resistance, heat resistance, and storage stability. Furthermore, this invention also aims to provide a paper substrate coated with the aforementioned coating agent.

[0016] Solution to the problem As a result of repeated and painstaking research, the inventors discovered that by blending specific ethylene-based copolymers, alkaline materials, and particles with specific melting points, an aqueous coating agent with excellent water resistance, heat resistance, heat sealing, and storage stability was obtained, and thus the present invention was completed.

[0017] This manual includes the following implementation schemes.

[0018] 1. An aqueous coating agent comprising: (A) a copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond; (B) an alkaline material; and (C) particles having a melting point of 100°C or higher.

[0019] 2. The aqueous coating agent according to 1, wherein, based on a total of 100 parts by mass of the components (A), (B), and (C), the content of the component (C) is 1 to 20 parts by mass.

[0020] 3. The aqueous coating agent according to 1 or 2, wherein the copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond in (A) includes a copolymer of ethylene and (meth)acrylic acid.

[0021] 4. The aqueous coating agent according to any one of 1-3, wherein the particles with a melting point of 100°C or higher in (C) comprise an aqueous dispersion of a paraffin-based resin.

[0022] 5. The aqueous coating agent according to any one of 1-3, wherein the particles with a melting point of 100°C or higher in (C) comprise starch.

[0023] 6. The aqueous coating agent according to claim 5, wherein the starch comprises tapioca starch.

[0024] 7. The aqueous coating agent according to any one of 1-6, wherein the aqueous coating agent further comprises (D) a polyvinyl alcohol derivative.

[0025] 8. The aqueous coating agent according to any one of 1-7, wherein the polyvinyl alcohol derivative of (D) comprises at least one selected from polyvinyl alcohol and ethylene-modified polyvinyl alcohol.

[0026] 9. A paper substrate coated with an aqueous coating agent according to any one of 1-8.

[0027] 10. A paper product comprising the paper substrate according to claim 9.

[0028] Beneficial effects of the present invention The water-based coating agent of the present invention exhibits excellent water resistance, heat resistance, heat sealing, and storage stability, and is particularly effective in coating paper substrates.

[0029] The paper substrate of the present invention is coated with the above-mentioned coating agent, and is thus water-resistant and heat-resistant, and is suitable for processing food packaging containers (such as paper cups) or paper straws. Detailed Implementation

[0030] The aqueous coating agent of the present invention (also referred to as the "coating agent") comprises: (A) a copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond (also referred to as "component (A)" or "(A) copolymer"); (B) an alkaline material (also referred to as "component (B)"); and (C) particles with a melting point of 100°C or higher (also referred to as "(C) particles").

[0031] In this document, "aqueous coating agent" refers to a coating agent in which polymer particles and / or similar substances can be dispersed or dissolved in an aqueous medium, and preferably an emulsion in which polymer particles and / or similar substances are dispersed in an aqueous medium.

[0032] "Aqueous medium" refers to common water (such as tap water, distilled water, or ion-exchanged water), and may contain organic solvents (e.g., acetone, ethyl acetate, etc.) that are soluble or dispersible in water and have poor reactivity with the raw materials (such as monomers) of the resins involved in this invention. It may also contain monomers, oligomers, prepolymers, resins, and / or similar substances that are soluble or dispersible in water, and may contain emulsifiers, polymerizable emulsifiers, polymerization initiators, chain extenders, various additives, and / or similar substances commonly used in the preparation of aqueous resins or water-soluble resins, as described below.

[0033] The aqueous coating agent of the present invention exhibits excellent water resistance, heat sealing properties, heat resistance, and storage stability. The components are described below.

[0034] <(A) Copolymer of ethylene and carboxylic acid derivatives having olefinic double bonds> In embodiments of the present invention, “(A) copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond” (hereinafter also referred to as “(A) copolymer” or “component (A)”) is a copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond, and the copolymer is not particularly limited, as long as the aqueous coating agent involved in the present invention is available.

[0035] The aqueous coating agent of the present invention comprises component (A), thereby the aqueous coating agent of the embodiments of the present invention becomes excellent in terms of water resistance, heat sealing and storage stability (dispersion stability).

[0036] In this article, "carboxylic acid derivatives with olefinic double bonds" refers to carboxylic acid derivatives (including carboxylic acids) that have double bonds between carbon atoms and can undergo addition polymerization with ethylene, and specifically refers to "carboxylic acids with olefinic double bonds", "carboxylic anhydrides with olefinic double bonds", "carboxylic acid esters with olefinic double bonds", "carboxylic acid salts with olefinic double bonds", etc.

[0037] "Carboxylic acids having olefinic double bonds" are compounds having both olefinic double bonds and carboxyl groups, and such compounds are not particularly limited, as long as the aqueous coating agent involved in this invention is available. Specific examples may include oleic acid, linoleic acid, maleic acid, itaconic acid, acrylic acid, and methacrylic acid.

[0038] "Carboxylic anhydrides having olefinic double bonds" refers to compounds obtained by the dehydration condensation of two carboxylic acid molecules or by dehydrating two carboxyl groups in a molecule, and the compound is not particularly limited, as long as it can provide the aqueous coating agent involved in this invention. Specifically, examples may include fumaric anhydride and maleic anhydride.

[0039] Examples of “carboxylic acid esters having an olefinic double bond” may include: (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate; vinyl carboxylic acid esters and allyl esters, such as vinyl acetate and allyl acetate.

[0040] In this article, (meth)acrylate means both acrylate and methacrylate.

[0041] In embodiments of the invention, "carboxylic acid esters having olefinic double bonds" preferably include (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate; more preferably, methyl (meth)acrylate, ethyl (meth)acrylate, or butyl (meth)acrylate; and particularly desirablely, methyl methacrylate or ethyl acrylate.

[0042] The term "carboxylate with an olefinic double bond" is not particularly limited, as long as the desired aqueous coating agent of this invention can be obtained. Specific examples may include sodium (meth)acrylate and potassium (meth)acrylate.

[0043] In this document, examples of “(A) copolymers of ethylene and carboxylic acid derivatives having olefinic double bonds” may include: A copolymer of ethylene and a carboxylic acid having an olefinic double bond (also known as an "ethylene / carboxylic acid copolymer"). A copolymer of ethylene and a carboxylic anhydride having olefinic double bonds (also known as an "ethylene / carboxylic anhydride copolymer"). Copolymers of ethylene with carboxylic acid esters containing olefinic double bonds (also known as "ethylene / carboxylic acid ester copolymers"); and A copolymer of ethylene and a carboxylate containing an olefinic double bond (also known as an "ethylene / carboxylate copolymer").

[0044] Examples of ethylene / carboxylic acid copolymers may include copolymers of ethylene and (meth)acrylic acid (ethylene / (meth)acrylic acid copolymers) and copolymers of ethylene and itaconic acid (ethylene / itaconic acid copolymers). Examples of ethylene / carboxylic anhydride copolymers may include copolymers of ethylene and maleic anhydride (ethylene / maleic anhydride copolymers). Examples of ethylene / carboxylic acid ester copolymers may include: copolymers of ethylene and (meth)acrylates (ethylene / (meth)acrylate copolymers); copolymers of ethylene and vinyl carboxylate (ethylene / vinyl carboxylate copolymers); and copolymers of ethylene and allyl carboxylate (ethylene / allyl carboxylate copolymers). Examples of ethylene / carboxylate copolymers may include copolymers of ethylene with sodium (meth)acrylate (ethylene / sodium (meth)acrylate copolymer) and copolymers of ethylene with potassium (meth)acrylate (ethylene / potassium (meth)acrylate copolymer).

[0045] In embodiments of the invention, (A) the copolymer preferably comprises a copolymer of ethylene and a (meth)acrylic acid derivative. The copolymer of ethylene and a (meth)acrylic acid derivative preferably comprises at least one selected from ethylene / (meth)acrylic acid copolymers, ethylene / (meth)acrylic anhydride copolymers, ethylene / (meth)acrylic ester copolymers, and ethylene / (meth)acrylate copolymers, and most preferably comprises ethylene / (meth)acrylic acid copolymers.

[0046] (A) The copolymer includes an ethylene / (meth)acrylic acid copolymer, thereby significantly improving the water resistance and heat-sealing properties of the aqueous coating agent of the embodiments of the present invention.

[0047] The copolymer (A) is mixed with components (B) and (C) described later while the copolymer (A) is dispersed in an aqueous medium.

[0048] In an embodiment of the invention, (A) the copolymer preferably includes at least one selected from copolymers of ethylene with carboxylic acids having olefinic double bonds and copolymers of ethylene with carboxylate salts having olefinic double bonds, and more preferably includes at least one selected from copolymers of ethylene with carboxylic acids having olefinic double bonds and carboxylic esters having olefinic double bonds, and copolymers of ethylene with carboxylate salts having olefinic double bonds and carboxylic esters having olefinic double bonds.

[0049] In embodiments of the present invention, copolymer (A) is preferably dispersed in an aqueous medium. The melting point of copolymer (A) is preferably below 100°C, more preferably 50 to 90°C, and particularly preferably 60 to 90°C. The melting point is most preferably 70 to 90°C. When copolymer (A) is dispersed in an aqueous medium, the melting point of copolymer (A) refers to the melting point of copolymer without an aqueous medium.

[0050] <(B) Alkaline materials> In this document, (B) alkaline material refers to a material that dissolves in water and thus has a pH greater than 7, and the material is not particularly limited, as long as it can improve the compatibility of the components contained in the water-based coating agent, neutralize the (A) copolymer, and obtain the water-based coating agent involved in the present invention.

[0051] Here, "neutralization" can typically be achieved by adding an alkaline material (B) for neutralization. As a result, when copolymer (A) has anionic groups (e.g., particularly when copolymer (A) has carboxyl groups), copolymer (A) can be neutralized to impart a certain degree of water solubility to copolymer (A). However, copolymer (A) need not be completely soluble in water. Copolymer (A) can have water solubility to a degree that does not impair the properties of the aqueous coating agent according to embodiments of the present invention.

[0052] The alkaline material can be in any form, including gaseous, liquid, and solid, as long as the aqueous coating agent involved in this invention is obtained. The alkaline material is preferably in the form of an aqueous solution in which it is dissolved in water, because it is easy to handle and the neutralization reaction is easy to control. Examples of such "alkaline materials" may include ammonia, alkali metals (such as sodium and potassium), or alkaline earth metals (such as calcium and magnesium), preferably ammonia water, sodium aqueous solution (sodium hydroxide aqueous solution), or potassium aqueous solution (potassium hydroxide aqueous solution).

[0053] (B) An alkaline material is preferably added to make the pH of the aqueous medium containing the copolymer (A) 8.0 or greater, more preferably to make the pH 8.0 to 10.0, and particularly preferably to make the pH 8.0 to 9.5.

[0054] The aqueous coating agent of the present invention comprises (B) an alkaline material, thereby improving the compatibility of the components, neutralizing (A) copolymer to further enhance compatibility with other components, and achieving an excellent balance of water resistance, heat sealing, heat resistance and storage stability.

[0055] <(C) Particles with a melting point of 100°C or higher> In the embodiment of the present invention, particle (C) is mixed with components (A) and (B) in a state in which the particles are dispersed in an aqueous medium. The particles can be mixed with other components described later. The melting point of the particles is 100°C or higher. Particle (C) is not particularly limited, as long as the aqueous coating agent involved in the present invention is obtained.

[0056] In this article, "granular" refers to the state of aggregated solid particles, and "particle" refers to the aggregate of particles themselves.

[0057] The particles are selected from organic particles and inorganic particles, and are preferably selected from organic particles, and the organic particles preferably include at least one of carbohydrate particles and resin particles.

[0058] However, component (C) does not include either component (A) or component (D).

[0059] Examples of particles include, but are not limited to, carbohydrate powders (such as wheat flour and starch), and particles of organic matter (such as resins of colloids and the like dispersed insolvents, paraffin-based resins, and olefinic resins).

[0060] (C) The melting point of the particles is 100°C or higher, and preferably 100°C to 300°C.

[0061] The melting point of component (C) is the melting point of the particles themselves, but does not refer to the melting point of the particles in an aqueous medium.

[0062] The aqueous coating agent of the embodiment of the present invention contains component (C), thereby further improving water resistance.

[0063] In this paper, melting point refers to the value measured using differential scanning calorimetry (DSC). Specifically, 10 mg of sample was weighed in an aluminum container, and the melting peak was measured using a DSC6220 (trade name) manufactured by SII NanoTechnology Inc. at a heating rate of 10 °C / min. The temperature at the top of the melting peak is referred to as the melting point.

[0064] The above description of melting points applies not only to the melting point of component (C) but also to the melting points of other components.

[0065] (C) The particles are preferably carbohydrate powders and resin particles (such as paraffin-based resins and olefin-based (or olefin) resins), and more preferably aqueous dispersions of paraffin-based resins, aqueous dispersions of olefin-based resins, and starch. Aqueous dispersions of paraffin-based resins and aqueous dispersions of olefin-based resins are different from waxes.

[0066] In this paper, "wax" is considered to be an organic substance that is solid at room temperature and becomes liquid below 100°C when heated. In other words, wax has a melting point below 100°C, and therefore wax does not meet the criteria for components (C) with a melting point of 100°C or higher.

[0067] Paraffin is a type of hydrocarbon (organic compound), a general term for aliphatic chain saturated hydrocarbons, also known as alkanes, and is composed of C... n H 2n+2Alkenes are a general term for aliphatic chain unsaturated hydrocarbons with one double bond, and are formed by C2O2 chains. n H 2n In addition, n in each chemical formula is a natural number. Both paraffin-based resins and olefin-based resins conforming to (C) particles have melting points of 100°C or higher.

[0068] The dispersions based on resins related to paraffin or olefins (the above chemical formulas) dispersed in an aqueous medium include aqueous dispersions of paraffin-based resins and aqueous dispersions of olefin-based resins.

[0069] Examples of starch include: natural starches with a melting point of 100°C or higher, such as corn starch, tapioca starch, potato starch, sweet potato starch, wheat starch, and rice starch; and processed starches obtained by processing the natural starches, such as etherified starch, esterified starch, cross-linked starch, grafted starch, oxidized starch, acid-decomposed starch, and dextrin.

[0070] The aqueous coating agent of the embodiments of the present invention particularly preferably comprises an aqueous dispersion of a paraffin-based resin and / or tapioca starch.

[0071] When component (C) comprises an aqueous dispersion of a paraffin-based resin, the aqueous coating agent of the embodiments of the present invention exhibits an excellent balance between water resistance and heat-sealing properties.

[0072] When component (C) contains cassava starch, the water-based coating agent of the embodiments of the present invention has improved heat resistance, reduces friction between the paper substrate and the heated metal plate in the case of continuous paper cup production, and thereby enables efficient and safe paper cup production.

[0073] In the aqueous coating agent of the embodiments of the present invention, based on a total of 100 parts by mass of components (A), (B) and (C), the content of component (C) is preferably 1 to 20 parts by mass, particularly preferably 2 to 18 parts by mass, and most preferably 3 to 15 parts by mass.

[0074] When the amount of component (C) contained therein is within the above range, the aqueous coating agent of the present invention exhibits excellent balance in terms of water resistance, heat sealing, heat resistance and dispersion stability.

[0075] Specific examples of component (C) include: Aqueous dispersions of synthetic resins, such as EMUSTER-6315 (trade name) and EMUSTER-1309 (trade name) from NIPPON SEIRO CO., LTD., and CHEMIPEARL W308 (trade name) from Mitsui Chemicals, Inc. Aqueous dispersions of natural resins, such as XEM-1515 (trade name) from NIPPON SEIRO CO., LTD., and Hi-Mic-2095 (trade name) from Yamakei; and Tapioca starch, such as Z300F (trade name) from NIPPON STARCH CHEMICAL CO., LTD.

[0076] <(D) Polyvinyl alcohol derivatives> The aqueous coating agent of the present invention preferably comprises (D) a polyvinyl alcohol derivative and components (A) to (C). The aqueous coating agent comprising component (D) thereby improves the stability of the dispersion, inhibits the precipitation of particles in the aqueous medium, and can improve storage stability.

[0077] Examples of polyvinyl alcohol derivatives in embodiment (D) of the present invention may include polyvinyl alcohol and polyvinyl alcohol modified products.

[0078] Polyvinyl alcohol is typically prepared by hydrolyzing polyvinyl acetate and may contain acetate groups (CH3COO). - ).

[0079] In this document, "modified polyvinyl alcohol products" refers to polyvinyl alcohol modified by adding new functional groups (preferably hydrophilic groups). Polyvinyl alcohol can be modified to produce modified polyvinyl alcohol by adding new functional groups during or after the synthesis of the polyvinyl alcohol.

[0080] Examples of polyvinyl alcohol modified products include ethylene-modified polyvinyl alcohol, butadiene glycol-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, carboxylic acid-modified polyvinyl alcohol, and amino-modified polyvinyl alcohol.

[0081] In the aqueous coating agent of the embodiments of the present invention, component (D) includes polyvinyl alcohol or ethylene-modified polyvinyl alcohol, thereby promoting more uniform dispersion of components (A) to (C) in the aqueous medium and further improving storage stability (dispersion stability).

[0082] The coating agent for paper substrates according to embodiments of the present invention comprises components (A) to (C), optionally includes component (D), and may also include viscosity modifiers, plasticizers, defoamers, preservatives, colorants, etc. as additives.

[0083] Examples of viscosity modifiers may include urea, urea compounds, nitrogen-containing materials (such as dicyandiamide), calcium hydroxide, calcium oxide, sodium carbonate, trisodium phosphate, diammonium hydrogen phosphate, borax, sodium fluoride, and water glass.

[0084] Examples of plasticizers may include: glycerin; polyols such as ethylene glycol and propylene glycol; and organic solvents such as cellosolves.

[0085] Examples of defoamers may include: Silicone-based defoamers, such as dimethylpolysiloxane, polyoxyethylene-modified silicone, organically modified polysiloxane, and fluorine silicone. Oil and fat-based defoamers, such as castor oil, sesame oil, flaxseed oil, and animal and vegetable oils; Fatty acid-based defoamers, such as stearic acid, oleic acid and palmitic acid; Defoamers based on fatty acid esters, such as isoamyl stearate, diethylene laurate, distearate, distearate, sorbitol monolaurate, glyceryl fatty acid ester, polyoxyethylene sorbitate, butyl monolaurate, sucrose fatty acid ester, ethyl alkyl acetate of sulfonated castor oil, and natural waxes. Alcohol-based defoamers, such as polyoxyalkylene glycols and their derivatives, polyoxyalkylene glycol hydrates, dipentylphenoxyethanol, 3-heptanol, and 2-ethylhexanol; Ether-based defoamers, such as 3-heptyl cellosolve and nonyl cellosolve-3-heptyl carbitol; Phosphate-based defoamers, such as tributyl phosphate, sodium octyl phosphate, and tri(butoxyethyl) phosphate; Amine-based defoamers, such as dipentylamine; Amide-based defoamers, such as polyalkylene amides, acylated polyamines, and bis(octadecyl)piperidine; Metal soap-based defoamers, such as aluminum stearate, calcium stearate, potassium oleate, and calcium salts of woololein; and Sulfonate-based defoamers, such as sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0086] These additives can be blended after the preparation of the aqueous coating agent, can be blended with monomers that are raw materials for copolymer (A), or can be added to the coating agent in the form of an emulsion (a mixture of components (A) and components (B), or a mixture of components (A) and components (C)).

[0087] The aqueous coating agent of the present invention can be prepared by mixing other components and components (A) to (D), and heating can be performed during mixing. The order of addition of the components, the heating method, the stirring method, etc., are not particularly limited, and known methods can be used.

[0088] The aqueous coating agent of the present invention can be used to coat the surface of paper substrates used in food packaging containers, paper cups, or the like. The coating film formed by the aqueous coating agent of the present invention has excellent water resistance, heat sealing and heat resistance, and in addition, excellent storage stability (dispersion stability).

[0089] The aqueous coating agent of the present invention can be directly coated on the surface of a paper substrate, and the aqueous coating agent can be used as a one-liquid type coating agent and as a top coating agent for a two-liquid type coating agent.

[0090] Conventional coating methods can be applied to paper substrates using the water-based coating agent of the present invention. For example, the paper substrate can be coated with the coating agent of the present invention using known coating machines (such as table coaters, doctor blade coaters, two-roll size press coaters, gate roll coaters, blade metaling coaters, rod metaling coaters, doctor blade coaters, air knife coaters, roller coaters, brush coaters, kiss coaters, extrusion coaters, curtain coaters, die coaters, gravure coaters, or dip coaters).

[0091] The amount of aqueous coating agent used to coat paper substrates is not particularly limited, but is preferably 5 to 100 g / m³ based on solids (dry matter). 2 More preferably 5 to 50 g / m 2 And particularly preferred is 10 to 20 g / m 2 Here, the solid component of the coating agent refers to the solid component obtained by drying the coating agent at 105°C for 3 hours.

[0092] One aspect of the present invention relates to a paper substrate with the above-described aqueous coating agent on its surface. The paper substrate of the present invention exhibits excellent water resistance, heat sealing and heat resistance, and is preferably used in paper products (such as food packaging containers or paper cups).

[0093] One aspect of the present invention relates to a paper substrate having the aforementioned aqueous coating agent. The paper substrate is not particularly limited, and known paper or synthetic paper can be used as the paper substrate, said synthetic paper being obtained by preparing chemical pulp (such as hardwood kraft pulp or softwood kraft pulp), mechanical pulp (such as GP (groundwood pulp), RGP (refined pulp), or TMP (thermal mechanical pulp)), etc. Furthermore, the following materials can be used as the aforementioned paper substrate: high-grade paper; medium-grade paper; alkaline paper; transparent paper; semi-transparent paper; or paperboard or white paperboard used for corrugated board, building materials, bleached pulp coated corrugated board, corrugated board, etc. The paper substrate may contain organic or inorganic pigments, or papermaking additives (such as paper strong agent, sizing agent, or yield improver).

[0094] One aspect of the present invention relates to paper products having a paper substrate, the surface of which is coated with the aforementioned water-based coating agent. The paper products of embodiments of the present invention also exhibit excellent water resistance and can be used for paper straws, toilet paper, paper cups, etc. The paper products of the present invention have the aforementioned paper substrate and are therefore suitable for various applications without deterioration of oil and water resistance, even when their shape is bent. In particular, this paper product is preferably used for food packaging and beverage containers (paper cups).

[0095] Example The present invention is described in detail and specifically below with reference to embodiments and comparative examples. Each of these embodiments is merely one implementation of the invention, and the invention is not limited to these embodiments at all.

[0096] The numerical values ​​described in Tables 1 through 4 related to the amount of each component in blend components (A) through (D) represent the number of parts of "solid components other than solvent (materials other than water)" and are in parts by mass. The total amount of components (A) through (C) is converted to 100 parts by mass, and the number of parts by mass of each component is listed in Tables 1 through 4.

[0097] The following describes the details of components (A) to (D) used in Examples 1 to 22 and Comparative Examples 1 to 6.

[0098] (A) Copolymer of ethylene and carboxylic acid derivatives having olefinic double bonds (A1) Copolymer of ethylene and acrylic acid (melting point: 77°C, trade name: Primacor 5980 (SK GeoCentric Japan)) (A2) Copolymer of ethylene and methacrylic acid (melting point: 84°C, trade name: NUCREL 2050H (DOW-MITSUIPOLYCHEMICALS CO., LTD.)) (A3) Copolymer of ethylene and methacrylate (melting point: 83°C, trade name: SURLYNPC2000 (manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.) (A'4) Copolymer of styrene and acrylic acid (trade name: JONCRYL 679 (Johnson Polymer)) (A'5) Ethylene homopolymer (trade name: NP105 (Mitsui Chemicals, Inc.)) (B) Alkaline materials (B1) 25% ammonia solution (B2) 50% sodium hydroxide aqueous solution (C) Particles with a melting point of 100°C or higher (C1) Aqueous dispersion of paraffin-based resin (melting point: 103°C, trade name: XEM-1515, manufactured by NIPPONSEIRO CO., LTD.) (C2) Aqueous dispersion of olefin-based resin (melting point: 130°C, trade name: CHEMIPEARL W308, manufactured by Mitsui Chemicals, Inc.) (C3) Tapioca starch (trade name: Z300F, melting point: 253℃, manufactured by NIPPON STARCH CHEMICAL CO.,LTD.) (C'4) Carnauba wax emulsion (melting point: 87°C, trade name: AQUACER 581, manufactured by BASF) (C'5) Paraffin emulsion (melting point: 77°C, trade name: XEM-2131L, manufactured by NIPPON SEIRO CO., LTD.) (D) Polyvinyl alcohol derivatives (D1) Polyvinyl alcohol (trade name: JP33 (manufactured by JAPAN VAM & POVAL CO., LTD.), degree of polymerization: 3300) (D2) Polyvinyl alcohol (trade name: JP18 (manufactured by JAPAN VAM & POVAL CO., LTD.), degree of polymerization: 1800) (D3) Polyvinyl alcohol (trade name: JP10 (manufactured by JAPAN VAM & POVAL CO., LTD.), degree of polymerization: 1000) (D4) Polyvinyl alcohol (trade name: JF17 (manufactured by JAPAN VAM & POVAL CO., LTD.), degree of polymerization: 1700) (D5) Ethylene-modified polyvinyl alcohol (trade name: EXCEVAL R S1717, manufactured by Kuraray Co., Ltd.) <Preparation of water-based coating agents and preparation of coated paper> Example 1 (A1) 400 g of copolymer of ethylene and acrylic acid (trade name: Primacor 5980 (manufactured by SK Geo Centric Japan)), (B1) 40 g of 25% ammonia solution, (B2) 12 g of 50% sodium hydroxide solution, and 920 g of water were placed into a separable flask with a capacity of 2000 mL (including a 150 mm diameter stirrer blade).

[0099] Water serves as the aqueous dispersion medium in which the components are dispersed. The contents of the flask are heated with stirring, and the temperature is increased. The internal temperature of the separable flask is raised to 92°C, and stirring is continued at this temperature for 2 hours, and then the contents are cooled to room temperature while stirring continues. 80 g of an aqueous dispersion of a paraffin-based resin (trade name: XEM-1515, manufactured by NIPPON SEIRO CO., LTD.) is added to obtain the aqueous coating agent of Example 1.

[0100] The amounts of each blending component described in the steps for preparing the water-based coating agent are by weight in the actual product, and may also include both the weight of the solid components and the weight of the solvent.

[0101] However, the amounts of each component in the blends (A) to (D) shown in Tables 1 to 4 are by weight parts of solid components other than solvents. However, the amounts of blend water shown in Tables 1 to 4 refer to the total amount of water contained in the water-based coating (including water added with the components), and contain neither solid components nor solvents other than water.

[0102] White high-grade paper (manufactured by Chuetsu Pulp & Paper Co., Ltd., basis weight 104.7 g / m²) was coated with the aqueous coating agent of Example 1 using a doctor blade coater. 2 (Thickness 126 mm, opacity 94%). The coating amount is adjusted using a doctor blade coater to ensure the water-based coating agent has a dry weight of 10 g / m². 2 After coating, the high-grade paper was placed in a dryer at 130°C to obtain the coated paper (test specimen) of Example 1.

[0103] Example 2 4 g of polyvinyl alcohol (trade name: JP33 (manufactured by JAPAN VAM & POVAL CO., LTD.)) was placed in a separable flask along with components (A1), (B1), and (B2) used in Example 1. The contents were heated with stirring to raise their temperature, and stirring was continued at this temperature for 2 hours. The contents were then cooled to room temperature while stirring continued, and component (C1) was added to obtain the aqueous coating agent of Example 2.

[0104] Except for the blend component (D1), the aqueous coating agent of Example 2 was prepared by a method similar to that in Example 1, and the aqueous coating agent was used to obtain the coated paper of Example 2. The composition of the aqueous coating agent of Example 2 is shown in Table 1.

[0105] Examples 3 to 21 and Comparative Examples 1 to 6 The aqueous coating agents of Examples 3 to 21 and Comparative Examples 1 to 6 were prepared by blending the components using a method similar to that in Example 2. The compositions of the aqueous coating agents are shown in Tables 1 to 3.

[0106] As in Example 2, the amounts of each component in the blend components (A) to (D) shown in Table 1 represent the mass fractions of solid components other than the solvent, and the amount of water in the blend does not include the solid components. The compositions of the aqueous coating agents of Examples 3 to 21 and Comparative Examples 1 to 6 are shown in Table 1.

[0107] White high-grade paper was coated with each of the aqueous coating agents of Examples 3 to 21 and Comparative Examples 1 to 6 using a doctor blade coater, and the coated paper (test body) of each of Examples 3 to 21 and Comparative Examples 1 to 6 was prepared by a method similar to that in Example 2.

[0108] Example 22 The aqueous coating agent of Example 22 was prepared by blending the components using a method similar to that in Example 2, and the coated paper (test body) of Example 22 was prepared using a method similar to that in Example 2. The composition of the aqueous coating agent of Example 22 is shown in Table 4.

[0109] Then, the surface of the coated paper (test subject) is further coated with an aqueous coating agent to prepare a "coated paper (two-coating type)" that has been coated twice with an aqueous coating agent.

[0110] The amounts of each component in the blends (A) to (D) shown in Table 4 represent the mass fractions of the solid component other than the solvent, and the amount of water in the blend does not include the solid component.

[0111] As shown in Tables 1 to 4, the water resistance, heat sealing, heat resistance (heat friction coefficient), and storage stability (dispersion stability) of the water-based coating agent were evaluated for each of the coated papers in these examples and comparative examples.

[0112] The evaluation test details are as follows.

[0113] <Water Resistance Test (Measurement of Water Absorption at High Temperature)> Cut the coated paper (test body) into a circle with a diameter of 10 cm, measure its mass, and then clamp the upper and lower parts of the test body with a circular cylindrical flask (the upper part of which has an inner diameter of 7 cm and is open). Let the test body stand for 30 minutes with 50 mL of 90°C warm water dripped from above.

[0114] Then, the water is removed, the test specimen is taken out of the cylinder, and its mass is measured with water droplets removed from its surface. The change in mass of the test specimen before and after the test is calculated, and the increase is taken as the amount of water absorbed. The amount of water absorbed per unit area is also calculated.

[0115] The evaluation criteria are as follows.

[0116] Excellent: Water absorption less than 10 g / m³ 2 And it maintains water resistance.

[0117] Good: Water absorption is 10 g / m³ 2 or greater than and less than 20 g / m 2 And it maintains water resistance.

[0118] Generally: water absorption is 20 g / m³ 2 or greater than and less than 50 g / m 2 And it maintains water resistance.

[0119] Poor: Water absorption is 50 g / m³ 2 Or larger, and does not maintain water resistance.

[0120] <Water resistance test (measurement of water absorption at room temperature)> Cut the coated paper (or test piece) into a circle with a diameter of 10 cm, measure its mass, and then clamp the upper and lower parts of the test piece with a cylindrical flask (the upper part of which has an inner diameter of 7 cm and is open), and let the test piece stand for 30 minutes with 50 mL of 23°C distilled water dripped from above.

[0121] Then, the water is removed, the test piece is taken out of the cylinder, and its mass is measured with water droplets removed from its surface. The change in mass of the coated paper before and after the test is calculated, the increase is taken as the water absorption, and the water absorption per unit area is calculated.

[0122] The evaluation criteria are as follows.

[0123] Excellent: Water absorption less than 10 g / m³ 2 And it maintains water resistance.

[0124] Good: Water absorption is 10 g / m³ 2 or greater than and less than 20 g / m 2 And it maintains water resistance.

[0125] Generally: water absorption is 20 g / m³ 2 or greater than and less than 50 g / m 2 And it maintains water resistance.

[0126] Poor: Water absorption is 50 g / m³ 2 Or larger, and does not maintain water resistance.

[0127] <Heat-Sealing Test> Cut the coated paper (or test specimen) into 25 mm × 100 mm dimensions. Stack the coated surfaces of the test specimens (or place them face to face) and place them in a press (heated to 130°C on top) and press them at 0.6 MPa for 0.6 seconds. Leave the test specimens at room temperature for 2 hours, measure the peel strength using TENSILON, and visually observe and evaluate the peeled portions.

[0128] The evaluation criteria are as follows.

[0129] Excellent: The substrate withstands material failure (damage to the coated paper is observed during peeling).

[0130] Good: Interfacial peeling occurs (peeling between the high-grade paper and the coating), and the peel strength is 15 gf / 25 mm or greater.

[0131] Generally: interfacial peeling occurs, and the peel strength is less than 15 gf / 25 mm.

[0132] Poor: No adhesion (sealing) occurs.

[0133] <Heat Resistance Test (Measurement of Static Friction Coefficient)> Heat resistance is evaluated by measuring the static friction coefficient.

[0134] The coefficient of static friction is the ratio between the frictional force generated on the contact surface of two objects under static friction (i.e., in a state where no relative motion occurs) and the force acting in the direction perpendicular to the contact surface.

[0135] For the measurement of the static friction coefficient, the static friction coefficient between the coated paper surface and the SUS (stainless steel) plate heated to 60°C was measured using a load measuring stage MX2-500N (manufactured by IMADA CO., LTD.) and a digital force gauge ZTA-50N (manufactured by IMADA CO., LTD.).

[0136] A commercially available SUS (stainless steel) sheet (size: 25 mm × 25 mm) heated to 60°C was used as the opposing material to be rubbed together with the coated paper (or test piece).

[0137] The SUS (stainless steel) plate was brought into contact with the test piece under a normal load of 600 g, and the static friction coefficient was then measured when the test piece was rubbed together with a movable stage (to which the test piece was attached) at a moving rate of 120 mm / min (test rate).

[0138] The evaluation criteria are as follows.

[0139] Excellent: Static friction coefficient is less than 0.5.

[0140] Good: Static friction coefficient is 0.5 or greater and less than 1.0.

[0141] Generally: the static friction coefficient is 1.0 or greater and less than 2.0.

[0142] Poor: Static friction coefficient is 2.0 or greater.

[0143] <Storage Stability Test (Dispersion Stability)> Place the water-based coating agent into a 300 mL glass beaker and let it stand at 23°C for 1 day, then observe the phase separation state of the water-based coating agent.

[0144] The evaluation criteria are as follows.

[0145] Excellent: Neither gelation nor phase separation occurred.

[0146] Good: No gelation occurred, but partial phase separation did occur.

[0147] Poor: Gel formation and phase separation occur.

[0148] [Table 1]

[0149] [Table 2]

[0150] [Table 3]

[0151] [Table 4]

[0152] As shown in Tables 1 to 3, it is demonstrated that the aqueous coatings of Examples 1 to 21 contain components (A) to (C) and therefore exhibit excellent water resistance, heat sealing, heat resistance and storage stability (dispersion stability).

[0153] As in Example 22 disclosed in Table 4, the paper substrate can also be coated twice with the aqueous coating agent of the present invention.

[0154] In contrast, each of the water-based coatings in Comparative Examples 1 to 6 does not contain any of components (A) to (C), and therefore has poor water resistance.

[0155] Furthermore, the aqueous coating agent of Comparative Example 2 does not contain the alkaline material (B), and therefore the polymer (A) is not neutralized, and components (A) to (C) are not uniformly dispersed in the aqueous medium. As a result, the water resistance, heat sealing performance, heat resistance (static friction coefficient), and dispersion stability of the aqueous coating agent of Comparative Example 2 are all significantly reduced.

[0156] The water-based coatings in Comparative Examples 3 and 6 do not contain copolymers of (A) ethylene and carboxylic acid derivatives, and not only is the water resistance of the water-based coatings deteriorated, but their heat-sealing properties are also worse.

[0157] Industrial applicability In this invention, an aqueous coating agent can be provided for coating the surface of paper. The coating agent of embodiments of this invention is used to coat the surface of a paper substrate to prepare paper products. Examples of paper products include food packaging containers, paper cups, and paper straws.

[0158] Cross-references to related applications This application claims priority under Article 4 of the Paris Convention based on Japanese Patent Application No. 2023-106958, filed in Japan on June 29, 2023. That priority patent application is incorporated herein by reference in its entirety.

Claims

1. An aqueous coating agent comprising: (A) a copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond; (B) an alkaline material; and (C) particles having a melting point of 100°C or higher.

2. The water-based coating agent according to claim 1, wherein, Based on a total of 100 parts by mass of the components (A), (B), and (C), the content of component (C) is 1 to 20 parts by mass.

3. The aqueous coating agent according to claim 1 or 2, wherein the copolymer of ethylene and a carboxylic acid derivative having an olefinic double bond in (A) includes a copolymer of ethylene and (meth)acrylic acid.

4. The aqueous coating agent according to any one of claims 1-3, wherein the particles with a melting point of 100°C or higher in (C) comprise an aqueous dispersion of a paraffin-based resin.

5. The aqueous coating agent according to any one of claims 1-3, wherein the particles with a melting point of 100°C or higher in (C) comprise starch.

6. The aqueous coating agent according to claim 5, wherein the starch comprises tapioca starch.

7. The aqueous coating agent according to any one of claims 1-6, wherein the aqueous coating agent further comprises (D) a polyvinyl alcohol derivative.

8. The aqueous coating agent according to any one of claims 1-7, wherein the polyvinyl alcohol derivative (D) comprises at least one selected from polyvinyl alcohol and ethylene-modified polyvinyl alcohol.

9. A paper substrate coated with an aqueous coating agent according to any one of claims 1-8.

10. A paper product comprising the paper substrate according to claim 9.

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