Aqueous coating agent

Abstract

To provide an aqueous coating agent having heat seal property, water resistance, heat resistance and storage stability and to provide a paper base material coated with the coating agent.SOLUTION: There is provided an aqueous coating agent which contains (A) a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond, (B) a basic substance and (C) a granular material having a melting point of 100°C or more. Furthermore, there is provided a paper base material coated with the aqueous coating agent.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based coating applied to a paper substrate. [Background technology]

[0002] Due to environmental concerns, the reduction of plastic products is being encouraged worldwide. Plastic products cannot be naturally decomposed and are difficult to dispose of. In addition, when plastic is incinerated, dioxins are generated, which can cause air pollution. Furthermore, in recent years, plastic waste has been dumped into the ocean, where it decomposes to a microscopic level and becomes small pieces of garbage, which are then eaten by fish in the ocean, and the possibility that these fish may then be eaten by humans has been raised as a problem. In light of this background, the replacement of plastic with paper substrates has been considered, and in the food industry in particular, paper substrates are being processed into containers.

[0003] Conventionally, laminated paper has been used as one type of paper substrate. Laminated paper is treated to prevent food-derived oils and other substances from seeping out, which can weaken the paper and stain the hands.

[0004] Laminated paper generally has a polyethylene film or the like laminated onto a paper base material. In recent years, with growing environmental awareness, there has been a demand for recycling laminated paper. However, the film portion is an obstacle, and special equipment is required to efficiently recycle laminated paper.

[0005] Patent Documents 1 and 2 disclose coating an aqueous dispersion of an ethylene-based resin on paper. Patent Document 1 describes that an aqueous dispersion of an ethylene / acrylic acid copolymer neutralized with ammonia or an amine is useful as a heat sealant for paper or aluminum foil (see [Claims],

[0025] ,

[0028] ,

[0029] , and

[0044] ).

[0006] Patent Document 2 describes that an aqueous dispersion containing an acid-modified ethylene / ethyl acrylate copolymer and a wax can be coated onto a paper substrate (see [Claims],

[0046] ,

[0056] Table 1, and

[0068] Table 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-7860 A [Patent Document 2] JP 2006-45313 A Summary of the Invention [Problem to be solved by the invention]

[0008] Patent Documents 1 and 2 disclose that the aqueous dispersions (films or coatings formed therefrom) in the examples of both documents have excellent heat sealability. When the food packaging container is a general paper cup, the edge of the paper cup is formed by applying a water-based coating agent and then heating it. Therefore, the water-based coating agent (the film formed from the water-based coating agent) applied to the edge of the paper cup is required to have heat-sealing properties. Furthermore, the water-based coating agent for paper cups is required to have various properties in addition to heat-sealing properties.

[0009] Since beverages such as hot water or cold water are poured into paper cups, it is required that the paper base material does not absorb the beverage. The aqueous dispersions of Patent Documents 1 and 2 do not have sufficient water resistance, and when applied to a paper cup, there is a possibility that the base material of the paper cup will absorb the beverage.

[0010] Furthermore, in consideration of the paper cup production line, the water-based coating agent applied to the paper base material is also required to have heat resistance. In a typical paper cup production line, the paper base material to which the water-based coating agent is applied is in contact with a metal plate, and the paper base material in contact with the metal plate is continuously processed to produce paper cups. In paper cup production lines, metal plates are often heated by heat generated during processing of paper substrates. Therefore, water-based coating agents are required 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 dispersions, and it is unclear whether the aqueous dispersions of both documents can be used in continuous paper cup production lines.

[0011] Thus, in the food industry, various performances are required of aqueous coating agents. Aqueous coating agents must not only have excellent heat sealability, water resistance, and heat resistance, but also have excellent general performance such as coatability. When the aqueous coating agent is an emulsion, it is also required to have dispersion stability, such as the tendency for dispersoids to precipitate, taking into account storage stability.

[0012] The present invention has been made to solve the above problems, and aims to provide a water-based coating agent having heat sealability, water resistance, heat resistance, and storage stability, and a paper substrate coated with the coating agent. [Means for solving the problem]

[0013] As a result of extensive research, the present inventors have found that by blending a specific ethylene copolymer with a basic substance and a granular material having a specific melting point, an aqueous coating agent excellent in water resistance, heat resistance, heat sealability and storage stability can be obtained, and have completed the present invention.

[0014] This specification includes the following embodiments. 1. A water-based coating agent comprising: (A) a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond; (B) a basic substance; and (C) a granular material having a melting point of 100°C or higher. 2. The aqueous coating agent according to 1, wherein component (C) is blended in an amount of 1 to 20 parts by mass per 100 parts by mass of the total amount of components (A), (B) and (C). 3. The aqueous coating agent according to 1 or 2, wherein (A) the copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond includes a copolymer of ethylene and (meth)acrylic acid. 4. The aqueous coating agent according to any one of 1 to 3, wherein (C) the granular material having a melting point of 100°C or higher contains an aqueous dispersion of a paraffinic resin. 5. The aqueous coating agent according to any one of 1 to 3, wherein (C) the granular material having a melting point of 100°C or higher contains starch. 6. The aqueous coating agent according to 5, wherein the starch comprises tapioca. 7. The aqueous coating agent according to any one of 1 to 6, further comprising (D) a polyvinyl alcohol derivative. 8. The aqueous coating agent according to any one of 1 to 7, wherein the polyvinyl alcohol derivative (D) comprises at least one selected from polyvinyl alcohol and ethylene-modified polyvinyl alcohol. 9. A paper substrate comprising the aqueous coating agent according to any one of 1 to 8. A paper product having a paper substrate as described in 10.9. Effect of the Invention

[0015] The aqueous coating agent of the present invention is excellent in water resistance, heat resistance, heat sealability and storage stability, and is particularly effective for application to paper substrates. The paper base material of the present invention is resistant to moisture and heat because it is coated with the above-mentioned coating agent, and is suitable for processing into food packaging containers such as paper cups and paper cups. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The aqueous coating agent of the present invention (also simply referred to as "coating agent") contains (A) a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond (also referred to as "component (A)" or "(A) copolymer"), (B) a basic substance (also referred to as "component (B)"), and (C) a granular material having a melting point of 100°C or higher (also referred to as "(C) granular material").

[0017] In this specification, the term "water-based coating agent" refers to a coating agent in which polymer particles and the like can be dispersed or dissolved in an aqueous medium, and is preferably an emulsion in which polymer particles and the like are dispersed in an aqueous medium. The term "aqueous medium" refers to common water such as tap water, distilled water, or ion-exchanged water, but may also include a water-soluble or water-dispersible organic solvent that has poor reactivity with the raw materials of the resin of the present invention, such as monomers, such as acetone, ethyl acetate, etc., and may further include water-soluble or water-dispersible monomers, oligomers, prepolymers, and / or resins, etc., and may also include emulsifiers, polymerizable emulsifiers, polymerization initiators, chain extenders, and / or various additives, etc. that are commonly used in producing aqueous resins or water-soluble resins, as described below. The aqueous coating agent of the present embodiment is excellent in water resistance, heat sealability, heat resistance, and storage stability. Each component will be described below.

[0018] <(A) Copolymer of ethylene and carboxylic acid derivative having an ethylenic double bond> In the embodiment of the present invention, "(A) a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond" (hereinafter also referred to as "(A) copolymer" or "component (A)") is a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond, and is not particularly limited as long as the aqueous coating agent targeted by the present invention can be obtained.

[0019] By including component (A), the aqueous coating agent of the present invention has excellent water resistance, heat sealability, and storage stability (dispersion stability).

[0020] In this specification, the term "carboxylic acid derivative having an ethylenic double bond" refers to a carboxylic acid derivative (including carboxylic acid) having a carbon-carbon double bond capable of addition polymerization with ethylene, and specifically refers to a "carboxylic acid having an ethylenic double bond", a "carboxylic acid anhydride having an ethylenic double bond", a "carboxylic acid ester having an ethylenic double bond", a "carboxylate having an ethylenic double bond", etc.

[0021] The "carboxylic acid having an ethylenic double bond" is a compound having an ethylenic double bond and a carboxyl group, and is not particularly limited as long as it can provide the aqueous coating agent of the present invention. Specific examples include oleic acid, linoleic acid, maleic acid, itaconic acid, acrylic acid, and methacrylic acid.

[0022] The "carboxylic acid anhydride having an ethylenic double bond" refers to a compound obtained by dehydration condensation of two molecules of carboxylic acid or a compound obtained by dehydrating two carboxyl groups in one molecule, and is not particularly limited as long as it can provide the aqueous coating agent of the present invention. Specific examples include fumaric anhydride and maleic anhydride.

[0023] Examples of the "carboxylic acid ester having an ethylenic double bond" include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and vinyl and allyl carboxylate esters such as vinyl acetate and allyl acetate. In this specification, the (meth)acrylic acid ester refers to both an acrylic acid ester and a methacrylic acid ester.

[0024] In an embodiment of the present invention, the "carboxylic acid ester having an ethylenic double bond" preferably includes a (meth)acrylic acid ester such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, more preferably includes methyl (meth)acrylate, ethyl (meth)acrylate, or butyl (meth)acrylate, and particularly preferably includes methyl methacrylate or ethyl acrylate.

[0025] The "carboxylate having an ethylenic double bond" is not particularly limited as long as it can provide the aqueous coating agent of the present invention. Specific examples include sodium (meth)acrylate, potassium (meth)acrylate, etc.

[0026] In the present specification, the “(A) copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond” includes, for example, A copolymer of ethylene and a carboxylic acid having an ethylenic double bond (also called an "ethylene / carboxylic acid copolymer"); A copolymer of ethylene and a carboxylic acid anhydride having an ethylenic double bond (also called an "ethylene / carboxylic acid anhydride copolymer"); Copolymers of ethylene and carboxylic acid esters having an ethylenic double bond (also referred to as "ethylene / carboxylic acid ester copolymers"), and An example is a copolymer of ethylene and a carboxylate having an ethylenic double bond (also called an "ethylene / carboxylate copolymer").

[0027] Examples of the ethylene / carboxylic acid copolymer include a copolymer of ethylene and (meth)acrylic acid (ethylene / (meth)acrylic acid copolymer) and a copolymer of ethylene and itaconic acid (ethylene / itaconic acid copolymer). Examples of the ethylene / carboxylic acid anhydride copolymer include ethylene and maleic anhydride copolymers (ethylene / maleic anhydride copolymers). Examples of the copolymer of ethylene / carboxylate include a copolymer of ethylene and a (meth)acrylic acid ester (ethylene / (meth)acrylic acid ester copolymer); a copolymer of ethylene and a vinyl carboxylate (ethylene / vinyl carboxylate copolymer); and a copolymer of ethylene and an allyl carboxylate (ethylene / allyl carboxylate copolymer). Examples of the copolymer of ethylene / carboxylate include a copolymer of ethylene and sodium (meth)acrylate (ethylene / sodium (meth)acrylate copolymer), a copolymer of ethylene and potassium (meth)acrylate (ethylene / potassium (meth)acrylate copolymer), and the like.

[0028] In an embodiment of the present invention, the copolymer (A) preferably includes a "copolymer of ethylene and a (meth)acrylic acid derivative". The "copolymer of ethylene and a (meth)acrylic acid derivative" preferably includes at least one selected from an ethylene / (meth)acrylic acid copolymer, an ethylene / (meth)acrylic anhydride copolymer, an ethylene / (meth)acrylic acid ester copolymer, and an ethylene / (meth)acrylate copolymer, and most preferably includes an ethylene / (meth)acrylic acid copolymer. When the copolymer (A) contains an ethylene / (meth)acrylic acid copolymer, the water-based coating agent according to the embodiment of the present invention has significantly improved water resistance and heat sealability. The copolymer (A) is mixed with components (B) and (C) described below in a state of being dispersed in an aqueous medium.

[0029] In an embodiment of the present invention, the copolymer (A) preferably contains at least one selected from a copolymer of ethylene and a carboxylic acid having an ethylenic double bond, and a copolymer of ethylene and a carboxylate having an ethylenic double bond, and more preferably contains at least one selected from a copolymer of ethylene, a carboxylic acid having an ethylenic double bond, and a carboxylate ester having an ethylenic double bond, and a copolymer of ethylene, a carboxylate having an ethylenic double bond, and a carboxylate ester having an ethylenic double bond. In an embodiment of the present invention, the copolymer (A) is preferably dispersed in an aqueous medium. The melting point of the copolymer (A) is preferably less than 100° C., more preferably 50 to 90° C., particularly preferably 60 to 90° C., and most preferably 70 to 90° C. In addition, when the copolymer (A) is dispersed in an aqueous medium, the melting point of the copolymer (A) refers to the melting point of the copolymer not including the aqueous medium.

[0030] <(B) Basic Substance> In this specification, the (B) basic substance refers to a substance that exhibits a pH of greater than 7 when dissolved in water, and is not particularly limited as long as it can improve the compatibility of each component contained in the aqueous coating agent, can neutralize the (A) copolymer, and can provide the aqueous coating agent intended by the present invention. Here, the "neutralization" can be carried out by adding a basic substance (B) that is usually used for neutralization. As a result, when the copolymer (A) has an anionic group, for example, particularly when the copolymer (A) has a carboxyl group, the anionic group is neutralized, and the copolymer (A) can be given a certain degree of water solubility. However, the copolymer (A) does not need to be completely water soluble, and it is sufficient that the copolymer (A) is water soluble to the extent that it does not deteriorate the properties of the water-based coating agent according to the embodiment of the present invention.

[0031] The basic substance may be in any form of gas, liquid or solid as long as the aqueous coating agent of the present invention can be obtained, but a water-soluble form that is soluble in water is preferred because it is easy to handle and easy to control the neutralization reaction. Examples of such "basic substances" include ammonia, alkali metals such as sodium and potassium, and alkaline earth metals such as calcium and magnesium, and the like, but ammonia water, sodium aqueous solution (sodium hydroxide aqueous solution), and potassium aqueous solution (potassium hydroxide aqueous solution) are preferred.

[0032] The (B) basic substance is added so that the pH of the aqueous medium containing the (A) copolymer is preferably 8.0 or higher, more preferably 8.0 to 10.0, and particularly preferably 8.0 to 9.5. The aqueous coating agent according to an embodiment of the present invention contains the basic substance (B), which improves the compatibility of the respective components and neutralizes the copolymer (A), thereby further increasing the compatibility with other components, thereby providing an excellent balance of water resistance, heat sealability, heat resistance, and storage stability.

[0033] <(C) Granular material with a melting point of 100°C or higher> The granular material (C) according to an embodiment of the present invention is a granular material having a melting point of 100°C or higher, which can be mixed with components (A) and (B) in a dispersed state in an aqueous medium and can be mixed with other components described below, and is not particularly limited as long as the aqueous coating agent intended by the present invention can be obtained. In this specification, "granular" means a state in which a solid is gathered in the form of grains, and "granular material" means the aggregate of grains itself.

[0034] The granules are selected from organic granules and inorganic granules, preferably selected from organic granules, and preferably the organic granules include at least one selected from carbohydrate granules and resin granules. However, component (C) does not include components (A) and (D). Examples of granular materials include carbohydrate powders such as wheat flour and starch, resins such as colloids dispersed in a solvent, and organic granular materials such as paraffin-based resins and olefin-based resins, but are not limited to these. The melting point of the (C) granules is 100°C or higher, and preferably 100°C to 300°C. The melting point of component (C) is the melting point of the granules themselves, and does not mean the melting point of the granules containing the aqueous medium.

[0035] The water-based coating agent according to an embodiment of the present invention can have improved water resistance by containing component (C). In the present specification, the melting point refers to a value measured by differential scanning calorimetry (DSC). Specifically, 10 mg of a sample is weighed into an aluminum container using a DSC6220 (product name) manufactured by SII Nano Technology Co., Ltd., and the measurement is performed at a heating rate of 10°C / min. The melting point is the temperature at the top of the melting peak. The above description of the melting point applies not only to the melting point of component (C) but also to the melting points of other components.

[0036] As the (C) granular material, carbohydrate powder, paraffin-based resin, olefin-based resin, or other resin granular material is preferred, and paraffin-based resin aqueous dispersion, olefin-based resin aqueous dispersion, and starch are more preferred. Note that paraffin-based resin aqueous dispersion and olefin-based resin aqueous dispersion are different from wax. In this specification, "wax" refers to an organic substance that is solid at room temperature and becomes liquid when heated below 100° C. In other words, since the melting point of wax is below 100° C., it does not fall under component (C) that has a melting point of 100° C. or higher. Paraffin is a type of hydrocarbon compound (organic compound), a general term for aliphatic chain saturated hydrocarbons, also known as alkanes, and expressed as CnH2n+2. Olefin is a general term for aliphatic chain unsaturated hydrocarbons with one double bond, and expressed as CnH2n. Note that n in the chemical formula is a natural number. (C) Both paraffin-based resins and olefin-based resins, which fall under granular materials, have melting points of 100°C or higher. Dispersions in which particulate matter based on resins related to paraffins or olefins (above chemical formula) is dispersed in an aqueous medium are paraffin-based resin aqueous dispersions and olefin-based resin aqueous dispersions.

[0037] Examples of starches include natural starches having 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 above-mentioned natural starches, such as etherified starch, esterified starch, crosslinked starch, grafted starch, oxidized starch, acid-decomposed starch, and dextrin.

[0038] The aqueous coating agent according to the embodiment of the present invention preferably contains an aqueous paraffin-based resin dispersion and / or tapioca starch. When the component (C) contains an aqueous dispersion of a paraffinic resin, the aqueous coating agent according to the embodiment of the present invention has an excellent balance between water resistance and heat sealability. When component (C) contains tapioca starch, the aqueous coating agent according to an embodiment of the present invention has improved heat resistance, and the friction between the paper substrate and the heated metal plate during continuous production of paper cups is reduced, making it possible to efficiently and safely produce paper cups.

[0039] In the aqueous coating agent according to an embodiment of the present invention, the component (C) is preferably blended in an amount of 1 to 20 parts by mass, more preferably 2 to 18 parts by mass, and most preferably 3 to 15 parts by mass, per 100 parts by mass of the total amount of the components (A), (B), and (C). By incorporating component (C) in the above range, the aqueous coating agent according to the embodiment of the present invention exhibits an excellent balance of water resistance, heat sealability, heat resistance, and dispersion stability.

[0040] Specific examples of the component (C) include: Synthetic resin aqueous dispersions such as EMUSTER-6315 (product name) and EMUSTER-1309 (product name) manufactured by Nippon Seiro Co., Ltd., and Chemipearl W308 (product name) manufactured by Mitsui Chemicals, Inc.; natural resin aqueous dispersions such as XEM-1515 (trade name) manufactured by Nippon Seiro Co., Ltd. and Hi-Mic-2095 (trade name) manufactured by Yamakei Sangyo Co., Ltd.; Examples of tapioca starch include Z300F (product name) manufactured by Nippon Starch Chemical Co., Ltd.

[0041] <(D) Polyvinyl alcohol derivative> The water-based coating agent according to the embodiment of the present invention preferably contains (D) a polyvinyl alcohol derivative in addition to the components (A) to (C). By containing the component (D), the water-based coating agent can have improved stability of the dispersoid, less susceptible to particle precipitation in the aqueous medium, and improved storage stability. Examples of the polyvinyl alcohol derivative (D) according to the embodiment of the present invention include polyvinyl alcohol and modified polyvinyl alcohol. "Polyvinyl alcohol" is generally produced by hydrolyzing polyvinyl acetate, and the acetate ester group (CH3COO - ).

[0042] In the present specification, the term "modified polyvinyl alcohol" refers to polyvinyl alcohol modified by adding a new functional group (preferably a hydrophilic group). The modified polyvinyl alcohol can be produced by modifying polyvinyl alcohol by adding a new functional group during or after the synthesis of polyvinyl alcohol. Examples of the modified polyvinyl alcohol include ethylene-modified polyvinyl alcohol, butenediol-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, carboxylic acid-modified polyvinyl alcohol, and amino group-modified polyvinyl alcohol.

[0043] In the aqueous coating agent according to an embodiment of the present invention, component (D) contains polyvinyl alcohol or ethylene-modified polyvinyl alcohol, which makes it easier for components (A) to (C) to disperse more uniformly in the aqueous medium, and further improves storage stability (dispersion stability).

[0044] The coating agent for paper substrates according to an embodiment of the present invention contains components (A) to (C) and, in some cases, component (D), and may further contain additives such as a viscosity modifier, a plasticizer, an antifoaming agent, a preservative, and a colorant. Examples of the viscosity adjuster include urea, urea compounds, nitrogen-containing substances such as dicyandiamide, calcium hydroxide, calcium oxide, sodium carbonate, trisodium phosphate, diammonium hydrogen phosphate, borax, sodium fluoride, water glass, and the like. Examples of the plasticizer include glycerin; polyhydric alcohols such as ethylene glycol and propylene glycol; and organic solvents such as cellosolves.

[0045] As an antifoaming agent, for example, Silicone-based defoamers such as dimethylpolysiloxane, polyoxyalkylene-modified silicone, organic modified polysiloxane, and fluorine silicone; Oil-based defoamers such as castor oil, sesame oil, linseed oil, animal and vegetable oils; Fatty acid-based defoamers such as stearic acid, oleic acid, palmitic acid, etc.; Fatty acid ester-based defoaming agents such as isoamyl stearic acid, diglycol laurate, distearyl succinic acid, distearic acid, sorbitan monolaurate, glycerin fatty acid esters, polyoxyethylene sorbitan, monolaurate butyl stearate, sucrose fatty acid esters, ethyl acetate alkyl esters of sulfonated ricinoleic acid, and natural waxes; Alcohol-based defoamers such as polyoxyalkylene glycol and its derivatives, polyoxyalkylene alcohol hydrate, diamylphenoxyethanol, 3-heptanol, and 2-ethylhexanol; Ether-based defoamers such as 3-heptyl cellosolve and nonyl cellosolve-3-heptyl carbitol; Phosphate ester-based defoamers such as tributyl phosphate, sodium octyl phosphate, and tris(butoxyethyl) phosphate; Amine-based defoamers such as diamylamine; Amide-based defoamers such as polyalkylene amides, acylated polyamines, and dioctadecanoylpiperidine; Metal soap-based defoamers such as aluminum stearate, calcium stearate, potassium oleate, and calcium salts of wool olein; Examples of the antifoaming agents include sulfonate esters such as sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0046] These additives may be added after the preparation of the aqueous coating agent, or may be added together with the monomer that is the raw material of the (A) copolymer, or may be added to a coating agent in the form of an emulsion (a mixture of component (A) and component (B), or a mixture of component (A) and component (C)). The water-based coating agent of the present embodiment can be produced by mixing other components as necessary in addition to the components (A) to (D), and may be heated during mixing. The order of adding each component, the heating method, the stirring method, etc. are not particularly limited, and known methods can be used.

[0047] The aqueous coating agent of the present invention can be applied to the surface of a paper substrate used for food packaging containers, paper cups, etc. The aqueous coating agent of the present invention forms a film excellent in water resistance, heat sealability, and heat resistance, and further has excellent storage stability (dispersion stability). The aqueous coating agent of the present invention is applied directly to the surface of a paper substrate and can be used as either a one-component coating agent or a topcoat agent for a two-component coating agent. The method for applying the aqueous coating agent of the present invention to a paper substrate may be a conventional coating method. For example, the coating agent of the present invention is applied to a paper substrate using a known coating machine such as a table coater, a bar coater, a two-roll size press coater, a gate roll coater, a blade metering coater, a rod metering coater, a blade coater, an air knife coater, a roll coater, a brush coater, a kiss coater, a squeeze coater, a curtain coater, a die coater, a gravure coater, or a dip coater.

[0048] The amount of the aqueous coating agent applied to the paper substrate is not particularly limited, but is, for example, 5 to 100 g / m2 in terms of solid content (dry mass). 2 It is preferable that the thickness is 5 to 50 g / m 2 More preferably, it is 10 to 20 g / m 2 Here, the solid content of the coating agent refers to the solid content obtained by drying the coating agent at 105° C. for 3 hours. One aspect of the present invention relates to a paper substrate having a surface coated with the above-mentioned aqueous coating agent. The paper substrate of the present invention has excellent water resistance, heat sealability, and heat resistance, and can be suitably used for paper products such as food packaging containers and paper cups.

[0049] One aspect of the present invention relates to a paper substrate having the above-mentioned aqueous coating agent. The paper substrate is not particularly limited, but may be any known paper or synthetic paper obtained by papermaking chemical pulp such as hardwood kraft pulp or softwood kraft pulp, or mechanical pulp such as GP (groundwood pulp), RGP (refiner ground pulp), or TMP (thermomechanical pulp). In addition, the paper substrate may be any of fine paper, medium-quality paper, alkaline paper, glassine paper, semi-glassine paper, or paperboard or white paperboard used for cardboard, building materials, white cardboard, chipboard, etc. The paper substrate may contain organic and inorganic pigments, as well as papermaking auxiliary chemicals such as paper strength enhancers, sizing agents, and retention improvers. One aspect of the present invention relates to a paper product having a paper substrate coated with the above-mentioned aqueous coating agent. The paper product of the embodiment of the present invention has excellent water resistance and can be used for paper straws, toilet paper, paper cups, etc. Since the paper product of the present invention has the above-mentioned paper substrate, the oil resistance and water resistance do not decrease even when the shape is folded, and the paper product can be used for various purposes, and is particularly suitable for food packaging and beverage containers (paper cups). EXAMPLES

[0050] The present invention will be specifically and in detail explained below with reference to examples and comparative examples. However, these examples are merely one embodiment of the present invention, and the present invention is not limited to these examples in any way. The numerical values ​​for the amounts of components (A) to (D) listed in Tables 1 to 4 are the number of parts of "solids excluding solvents (substances not including moisture)" and are expressed in parts by mass. The total amount of components (A) to (C) is converted to 100 parts by mass, and the parts by mass of each component are shown in Tables 1 to 4.

[0051] Details of the components (A) to (D) used in Examples 1 to 22 and Comparative Examples 1 to 6 are shown below. (A) Copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond (A1) Copolymer of ethylene and acrylic acid (melting point 77°C, product name: Primacol 5980 (SK Geo Centric Japan Co., Ltd.)) (A2) Copolymer of ethylene and methacrylic acid (melting point 84°C, product name: Nucrel 2050H (Mitsui Dow Polychemicals Co., Ltd.)) (A3) Copolymer of ethylene and methacrylate (melting point 83°C, product name: SURLYN PC2000 (manufactured by Dow Mitsui Polychemicals Co., Ltd.)) (A'4) Styrene and acrylic acid copolymer (trade name: Joncryl 679 (Johnson Polymer Co., Ltd.)) (A'5) Ethylene homopolymer (product name: NP105 (Mitsui Chemicals, Inc.)

[0052] (B) Basic substances (B1) 25% ammonia solution (B2) 50% sodium hydroxide solution

[0053] (C) Granular material with a melting point of 100 degrees or more (C1) Paraffin resin aqueous dispersion (melting point 103℃, product name: XEM-1515, manufactured by Nippon Seiro Co., Ltd.) (C2) Olefin-based resin aqueous dispersion (melting point 130°C, product name: Chemipearl W308, manufactured by Mitsui Chemicals, Inc.) (C3) Tapioca starch (product name: Z300F, melting point 253°C, manufactured by Nippon Starch Chemical Co., Ltd.) (C'4) Carbana wax emulsion (melting point 87°C, product name: AQUACER 581, manufactured by BASF Ltd.) (C'5) Paraffin wax emulsion (melting point 77°C, product name: XEM-2131L, manufactured by Nippon Seiro Co., Ltd.)

[0054] (D) Polyvinyl alcohol derivatives (D1) Polyvinyl alcohol (product name: JP33 (manufactured by Nippon Vaccination & Poval Co., Ltd.), polymerization degree 3300) (D2) Polyvinyl alcohol (product name: JP18 (manufactured by Nippon Vaccination & Poval Co., Ltd.), polymerization degree 1800) (D3) Polyvinyl alcohol (product name: JP10 (manufactured by Nippon Vaccination & Poval Co., Ltd.), polymerization degree 1000) (D4) Polyvinyl alcohol (product name: JF17 (manufactured by Nippon Vaccination & Poval Co., Ltd.), polymerization degree 1700) (D5) Ethylene-modified polyvinyl alcohol (product name: Exeval RS 1717, manufactured by Kuraray Co., Ltd.)

[0055] <Preparation of Water-Based Coating Agent and Production of Coated Paper> Example 1 A 2000 ml separable flask equipped with a stirring blade having a diameter of 150 mm was charged with 400 g of (A1) an ethylene / acrylic acid copolymer (product name: Primacol 5980 (manufactured by SK Geo Centric Japan Co., Ltd.)), 40 g of (B1) a 25% aqueous ammonia solution, 12 g of (B2) a 50% aqueous sodium hydroxide solution, and 920 g of water. Water acts as an aqueous dispersion medium to disperse each component. The contents of the flask were heated under stirring to increase the temperature. After the internal temperature of the separable flask was raised to 92°C, stirring was continued at that temperature for 2 hours, and then the contents were cooled to room temperature while continuing to stir. (C1) 80 g of paraffin-based resin aqueous dispersion (product name: XEM-1515, manufactured by Nippon Seiro Co., Ltd.) was added to obtain the aqueous coating agent of Example 1. The amounts of each component described in the preparation process of the water-based coating agent are the weights of the actual products, and may include both the weight of the solids and the weight of the solvent. However, the amounts of components (A) to (D) shown in Tables 1 to 4 are parts by weight of solids excluding the solvent. However, the amount of water shown in Tables 1 to 4 means all water contained in the water-based coating agent (including water added together with the components), and does not include solids or solvents other than water.

[0056] The aqueous coating solution of Example 1 was applied to a white wood-free paper (manufactured by Chuetsu Pulp Industry Co., Ltd., basis weight 104.7 g / m 2 The coating was applied with a bar coater to a thickness of 126 μm and an opacity of 94%). The coating weight of the water-based coating agent after drying was 10 g / m 2 After coating, the wood-free paper was placed in a dryer at 130° C. to obtain the coated paper of Example 1 (test specimen).

[0057] Example 2 In a separable flask were charged 4 g of (D1) polyvinyl alcohol (product name: JP33 (manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) together with the components (A1), (B1), and (B2) used in Example 1, and the mixture was heated with stirring to raise the temperature, and stirring was continued at that temperature for 2 hours. Thereafter, the contents were cooled to room temperature while continuing to stir, and component (C1) was added to obtain the aqueous coating agent of Example 2. Except for adding component (D1), the aqueous coating agent of Example 2 was prepared in the same manner as in Example 1, and used to obtain the coated paper of Example 2. The composition of the aqueous coating agent of Example 2 is as shown in Table 1.

[0058] Examples 3 to 21 and Comparative Examples 1 to 6 The components were mixed in the same manner as in Example 2 to produce the water-based coating agents of Examples 3 to 21 and Comparative Examples 1 to 6. The compositions of the water-based coating agents are as shown in Tables 1 to 3. As in Example 2, the amounts of components (A) to (D) shown in Table 1 are parts by mass of solids excluding the solvent, and the amount of water does not include solids. The compositions of the water-based coating agents of Examples 3 to 21 and Comparative Examples 1 to 6 are shown in Table 1. The aqueous coating agents of Examples 3 to 21 and Comparative Examples 1 to 6 were applied to white wood-free paper using a bar coater, and the coated papers (test specimens) of Examples 3 to 21 and Comparative Examples 1 to 6 were produced in the same manner as in Example 2.

[0059] Example 22 The components were mixed in the same manner as in Example 2 to prepare the aqueous coating agent of Example 22, and the coated paper (test specimen) of Example 22 was produced in the same manner as in Example 2. The composition of the aqueous coating agent of Example 22 is as shown in Table 4. Next, a water-based coating agent was applied to the surface of the coated paper (test specimen), and then further applied to produce "coated paper (two-coat type)" with two coats of the water-based coating agent. The blending amounts of components (A) to (D) shown in Table 4 are parts by mass of solid content excluding the solvent, and the blending amount of water does not include solid content.

[0060] As shown in Tables 1 to 4, the water resistance, heat sealability, heat resistance (heat friction coefficient), and storage stability (dispersion stability) of the aqueous coating agent were evaluated for the coated papers of the Examples and Comparative Examples.

[0061] Details of the evaluation test are as follows. <Water resistance test (measurement of water absorption at high temperatures)> The coated paper was cut into a circle with a diameter of 10 cm, and its mass was measured. The wood-free paper was then sandwiched between a circular cylindrical flask with an inner diameter of 7 cm and an open top, and 50 ml of 90°C hot water was dripped onto the top, after which the paper was left to stand for 30 minutes. After that, the distilled water was removed, the specimen was removed from the cylinder, and the mass was measured after removing the water droplets from the surface of the specimen. The change in mass of the specimen before and after the test was calculated, and the increase was considered to be the amount of water absorbed, and the amount of water absorbed per unit area was calculated. The evaluation criteria are as follows: ◎: Water absorption is 10g / m 2 and retains water resistance. ○: Water absorption is 10g / m 2 More than 20g / m 2 and retains water resistance. △: Water absorption is 20g / m 2 More than 50g / m 2 and retains water resistance. ×: Water absorption is 50g / m 2 Thus, water resistance is not maintained.

[0062] <Water resistance test (measurement of water absorption at room temperature)> The coated paper was cut into a circle with a diameter of 10 cm, and its mass was measured. The top and bottom of the fine paper were then sandwiched between a circular cylindrical flask with an inner diameter of 7 cm and an open top, and 50 ml of distilled water at 23°C was dripped from the top, after which the paper was left to stand for 30 minutes. After that, the distilled water was removed, the specimen was removed from the cylinder, and the mass was measured after removing the water droplets from the surface of the specimen. The change in mass of the specimen before and after the test was calculated, and the increase was considered to be the amount of water absorbed, and the amount of water absorbed per unit area was calculated. The evaluation criteria are as follows: ◎: Water absorption is 10g / m 2 and retains water resistance. ○: Water absorption is 10g / m 2 More than 20g / m 2 and retains water resistance. △: Water absorption is 20g / m 2 More than 50g / m 2 and retains water resistance. ×: Water absorption is 50g / m 2 Thus, water resistance is not maintained.

[0063] <Heat sealability test> The coated paper was cut to a size of 25mm x 100mm. The coated surfaces of the test specimens were placed one on top of the other in a press machine whose upper part was heated to 130°C, and pressed for 0.6 seconds at a pressure of 0.6MPa. After curing the test specimens at room temperature for 2 hours, the peel strength was measured using a Tensilon, and the peeled parts were visually observed and evaluated. The evaluation criteria are as follows: ⊚: The base material was destroyed (damage to the fine paper was observed during peeling). ○: Interfacial peeling (peeling at the interface between the fine paper and the coating) with a peel strength of 15 gf / 25 mm or more. Δ: Interfacial peeling occurred, and the peel strength was less than 15 gf / 25 mm. ×: Not adhered (sealed).

[0064] <Heat resistance test (static friction coefficient measurement)> The heat resistance was evaluated by measuring the static friction coefficient. The coefficient of static friction is the ratio of the frictional force occurring at the contact surface between two objects in a state of static friction, i.e., when there is no relative motion, to the force acting perpendicular to the contact surface. The static friction coefficient was measured using a load measurement stand MX2-500N (manufactured by Imada Co., Ltd.) and a digital force gauge ZTA-50N (manufactured by Imada Co., Ltd.) to measure the static friction coefficient between the coated paper surface and a SUS (stainless steel) plate heated to 60°C. A commercially available SUS (stainless steel) plate (dimensions 25 mm x 25 mm) heated to 60°C was used as the mating material against which the coated paper (test piece) was rubbed. A normal load of 600 g was applied to bring the test piece into contact with a SUS (stainless steel) plate, and then the static friction coefficient was determined when the moving table on which the test piece was attached was rubbed at a moving speed (test speed) of 120 mm / min. The evaluation criteria are as follows: ◎: The static friction coefficient is less than 0.5 ◯: The static friction coefficient is 0.5 or more and less than 1.0. △: The static friction coefficient is 1.0 or more and less than 2.0. ×: The static friction coefficient is 2.0 or more.

[0065] <Storage stability test (dispersion stability)> The aqueous coating agent was placed in a 300 ml glass beaker and allowed to stand at 23° C. for one day, after which the phase separation state of the aqueous coating agent was observed. The evaluation criteria are as follows: ⊚: Neither gelation nor phase separation occurred. ◯: No gelation occurred, but some phase separation occurred. ×: gelation and phase separation occurred.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Table 4]

[0070] As shown in Tables 1 to 3, the aqueous coating agents of Examples 1 to 21 contain components (A) to (C), and therefore were demonstrated to have excellent water resistance, heat sealability, heat resistance, and storage stability (dispersion stability). The aqueous coating agent according to an embodiment of the present invention can also be applied twice to a paper substrate, as in Example 22 disclosed in Table 4.

[0071] In contrast, the water-based coating agents of Comparative Examples 1 to 6 do not contain any of the components (A) to (C), and therefore have poor water resistance. Furthermore, since the aqueous coating agent of Comparative Example 2 does not contain the basic substance (B), the polymer (A) is not neutralized, and the components (A) to (C) are not uniformly dispersed in the aqueous medium. Therefore, the aqueous coating agent of Comparative Example 2 is significantly deteriorated in all of the water resistance, heat sealability, heat resistance (static friction coefficient), and dispersion stability. The aqueous coating agents of Comparative Examples 3 and 6, which do not contain the copolymer of ethylene and a carboxylic acid derivative (A), are inferior in not only water resistance but also heat sealability. [Industrial Applicability]

[0072] The present invention provides a water-based coating agent that is applied to a paper surface. The coating agent according to the embodiment of the present invention is applied to the surface of a paper substrate to produce a paper product. Examples of the paper product include food packaging containers, paper cups, and paper straws.

Claims

1. (A) a copolymer of ethylene and a carboxylic acid derivative having an ethylenic double bond, (B) a basic substance, and (C) Granular material with a melting point of 100°C or higher A water-based coating agent comprising:

2. 2. The aqueous coating agent according to claim 1, wherein component (C) is blended in an amount of 1 to 20 parts by mass per 100 parts by mass of the total amount of components (A), (B) and (C).

3. The aqueous coating agent according to claim 1 or 2, further comprising (D) a polyvinyl alcohol derivative.

4. A paper substrate coated with the aqueous coating agent according to claim 1.

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