Coating agent for paper substrates

Abstract

To provide a coating agent for a paper substrate having excellent water resistance, oil resistance, blocking resistance, and paper substrate surface coatability.SOLUTION: One aspect of the present invention is a coating agent for a paper substrate comprising: (A) cellulose with an average particle size of 1 μm to 40 μm; and (B) an aqueous resin emulsion. The blending amount of the component (A) is more than 20 pts.mass and less than 50 pts.mass relative to 100 pts.mass of the total solid content of the component (A) and the component (B).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a coating agent for paper substrates, and to a paper substrate coated thereon. [Background technology]

[0002] Due to environmental concerns, the reduction of plastic products is being recommended worldwide. Plastic products do not decompose naturally and are difficult to dispose of. Furthermore, incinerating plastics can generate dioxins, potentially causing air pollution. In recent years, there has been concern that plastic waste is dumped into the ocean, where it breaks down into microscopic particles, which are then consumed by fish, and subsequently by humans. Against this backdrop, the replacement of plastics with paper-based materials is being considered, and in the food packaging sector in particular, methods of processing paper-based materials into packaging materials have been used for some time.

[0003] Traditionally, processed papers such as laminated paper and oil-resistant paper have been used as materials for food packaging. These laminated papers and oil-resistant papers are treated to prevent oils and other substances from food from seeping out, which would reduce the paper's strength or stain hands.

[0004] Laminated paper is generally made by laminating polyethylene film or similar material onto paper. Due to growing environmental awareness, there has been a demand in recent years for the recycling of laminated paper. However, the film portion has been an obstacle, requiring special equipment to efficiently recycle laminated paper.

[0005] On the other hand, fluoropolymer resins are often used as oil-resistant agents in oil-resistant paper. However, fluoropolymer resins are difficult to use actively these days because they generate inert gases when heated, and some components of fluoropolymer resins accumulate in the human body. Nevertheless, fluoropolymer resins can exhibit oil resistance even with a small amount applied to the paper substrate. Not using fluoropolymer resins is disadvantageous in terms of cost, and when applying alternative resins to paper materials, it is necessary to increase the amount applied, which can cause blocking when winding the oil-resistant paper after coating. For this reason, oil-resistant paper coated with synthetic resin emulsions is known to achieve both oil resistance and recyclability.

[0006] Patent documents 1 and 2 disclose coating agents manufactured using cellulose, a naturally derived material, instead of petroleum resin, taking environmental issues into consideration.

[0007] Patent Document 1 discloses a coating agent which is an aqueous dispersion containing cellulose nanofibers and a polyvinyl alcohol-based resin ([Claim 1],

[0026] to

[0033] ). Furthermore, Patent Document 1 describes a paper barrier material in which this aqueous dispersion is applied to a paper substrate.

[0008] ).

[0008] Patent Document 2 discloses a dispersion of fine cellulose in which carboxyl groups have been introduced into naturally derived fine cellulose as a coating agent ([Claim 1],

[0054] ,

[0034] -

[0043] ). It also states that, considering environmental factors, paper or biodegradable plastics are preferred as substrates to which the dispersion is applied (

[0069] ). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2011 / 040547 [Patent Document 2] International Publication No. 2011 / 111612 [Overview of the project] [Problems that the invention aims to solve]

[0010] While the aqueous dispersion compositions described in Patent Documents 1 and 2 exhibit excellent gas barrier properties, they do not fully satisfy high standards for oil resistance and blocking resistance.

[0011] Furthermore, in recent years, various performance requirements have been placed on paper substrates used for food packaging. For example, since paper substrates have an uneven surface, when an aqueous dispersion composition is applied directly to the surface of the paper substrate as a coating agent, the coating agent must have excellent applicability to the uneven surface of the paper substrate. Also, when paper substrates are used as paper cups, the cups are required to have water resistance and oil resistance when folded. When an aqueous dispersion composition is used as a primer, the primer must enhance the above performance of the paper cup.

[0012] One aspect of the present invention has been made to solve the above problems and aims to provide a coating agent that has excellent water resistance, oil resistance, blocking resistance, and applicability to the surface of a paper substrate, meeting the levels required in the food industry. Another aspect of the present invention aims to provide a paper substrate to which the coating agent is applied, which has excellent oil resistance when folded, and a paper product containing the same. [Means for solving the problem]

[0013] As a result of diligent research, the inventors discovered that by blending an aqueous resin emulsion with cellulose having an average particle size within a specific range in a certain ratio, a coating agent for paper substrates with excellent water resistance, oil resistance, blocking resistance, and surface coating properties can be obtained, thus completing the present invention.

[0014] In other words, the present invention and preferred embodiments thereof are as follows.

[0015] 1. (A) Cellulose with an average particle size of 1 μm to 40 μm and (B) an aqueous resin emulsion, A coating agent for paper substrates, wherein the blending amount of component (A) is higher than 20 parts by mass and less than 50 parts by mass with respect to 100 parts by mass of the total solid content of component (A) and component (B).

[0016] 2. The coating agent for paper substrates according to 1 above, wherein (B) the aqueous resin emulsion contains an aqueous resin having a chemical structure derived from a carboxylic acid ester polymer.

[0017] 3. The coating agent for paper substrates according to 1 or 2 above, wherein (B) the aqueous resin emulsion contains an ethylene / carboxylic acid ester copolymer emulsion having an ethylenic double bond.

[0018] 4. The coating agent for paper substrates according to any one of 1 to 3 above, wherein (B) the aqueous resin emulsion contains an emulsion of an ethylene / vinyl acetate copolymer.

[0019] 5. Further containing (C) starch, the coating agent for paper substrates according to any one of 1 to 4 above.

[0020] 6. The coating agent for paper substrates according to any one of 1 to 5 above, which is used as an undercoat agent applied to the surface of the substrate.

[0021] 7. A paper substrate having the coating agent for paper substrates according to any one of 1 to 6 above applied to its surface.

[0022] 8. A paper product having the paper substrate according to 7 above.

[0023] 9. (A) Cellulose with an average fiber length of 15 μm to 40 μm and (B) an aqueous resin emulsion, A coating agent for paper substrates, wherein the blending amount of component (A) is higher than 20 parts by mass and less than 50 parts by mass with respect to 100 parts by mass of the total solid content of component (A) and component (B).

[0024] 10. (A) Cellulose with an average fiber diameter of 10 μm to 30 μm and (B) an aqueous resin emulsion, A coating agent for paper substrates, wherein the amount of component (A) is greater than 20 parts by mass and less than 50 parts by mass relative to 100 parts by mass of the total amount of solids of component (A) and component (B). [Effects of the Invention]

[0025] According to one aspect of this embodiment, a coating agent for paper substrates can be provided that is excellent in oil resistance, blocking resistance, surface coating properties (applicability to the surface of paper substrates), and water resistance. [Modes for carrying out the invention]

[0026] One embodiment of the coating agent for paper substrates of the present invention (also simply referred to as "coating agent") comprises (A) cellulose with an average particle size of 1 μm to 40 μm (also referred to as "component (A)" or "(A) cellulose") and (B) aqueous resin emulsion (also referred to as "component (B)"), wherein the amount of component (A) is higher than 20 parts by mass and less than 50 parts by mass per 100 parts by mass of the total amount of solids of component (A) and component (B). The coating agent for paper substrates of this embodiment has excellent oil resistance, blocking resistance, surface coating properties and water resistance. The following describes each component.

[0027] <(A) Cellulose with an average particle size of 1 μm to 40 μm> In this specification, cellulose refers to a type of natural polymer compound in which numerous β-glucose molecules are polymerized in a linear chain by glycosidic bonds. Cellulose is the main component of plant cell walls and fibers, and is the most abundant carbohydrate (polysaccharide) on Earth.

[0028] The coating agent of the present invention contains (A) cellulose with an average particle diameter of 1 μm to 40 μm. (A) Cellulose is fine particles and is not particularly limited in shape; it may be spherical particles (aspect ratio (long axis / short axis) preferably 1 to 1.1) or fibrous particles (aspect ratio (fiber length / fiber diameter) preferably greater than 1.1). The spherical particles may be perfectly spherical or substantially spherical. In one embodiment, the average particle diameter of (A) cellulose is preferably 5 μm to 35 μm, more preferably 6 μm to 35 μm, and desirablely 6 μm to 12 μm. In this embodiment, since (A) cellulose has the above size, it is so-called microcellulose and is different from cellulose nanofiber (CNF). By having the average particle diameter of (A) cellulose within this range, the coating agent for paper substrates of the present invention has significantly improved water resistance and surface coating properties, and a better balance of oil resistance and blocking resistance.

[0029] In this embodiment, the particle diameter of cellulose refers to the maximum value of the distance between any two points on the surface of the cellulose. That is, if the cellulose is a spherical particle, the average particle diameter refers to the value based on its diameter, and if the cellulose is a fibrous particle, the average particle diameter refers to the value based on the average fiber length. Note that (A) the fiber length of cellulose is the dimension in the longitudinal direction of the fiber, and the fiber diameter is the dimension in the direction perpendicular to the longitudinal direction.

[0030] When cellulose particles are spherical, the average particle size can be measured using a scanning electron microscope (SEM), an atomic force microscope (AFM), or a laser diffraction particle size analyzer, and in one embodiment, the use of a laser diffraction particle size analyzer is preferred. When cellulose particles are fibrous, measurement is preferred using a scanning electron microscope (SEM) or an atomic force microscope (AFM), and measurement using a laser diffraction particle size analyzer may be difficult. When measuring using an SEM or AFM, for example, the maximum length (fiber length and fiber diameter as needed) of at least 100 cellulose particles is measured and the average value is calculated.

[0031] (A) Examples of commercially available cellulose include ARBOCEL UFC100 (average particle size specification value: 6~12μm), ARBOCEL BE600-10 (average fiber length 18μm, average fiber diameter 15μm), and ARBOCEL BE600-30 (average fiber length 30μm, average fiber diameter 18μm) from Rettenmeyer Japan Co., Ltd.

[0032] Because ARBOCEL UFC100 has a shape very close to a sphere, the average particle diameter can be easily measured using a laser diffraction particle size distribution analyzer. Since ARBOCEL BE600-10 and ARBOCEL BE600-30 have significantly different fiber dimensions, in this specification, the average fiber length is described as the average particle diameter. That is, the average particle diameter of ARBOCEL BE600-10 is 18 μm, and the average particle diameter of ARBOCEL BE600-30 is 30 μm.

[0033] In one embodiment of the present invention, when (A) cellulose is fibrous, the average fiber length is preferably 15 to 40 μm and / or the fiber diameter is preferably 10 to 30 μm. When the average fiber length and average fiber diameter of (A) cellulose are within the above range, the coating agent for paper substrates of the present invention has significantly improved water resistance and surface coating properties, and a better balance between oil resistance and blocking resistance.

[0034] In the coating agent of the present invention, (A) cellulose is dispersed in an aqueous medium and used as a cellulose fiber dispersion. By using (A) cellulose as a dispersion, the coating agent has a better balance of water resistance and oil resistance.

[0035] <(B) Water-based resin emulsion> In embodiments of the present invention, "(B) aqueous resin emulsion" refers to an aqueous dispersion in which an aqueous resin is dispersed in an aqueous medium, and includes both the aqueous resin and the aqueous medium. The terms "aqueous resin emulsion" and "aqueous resin" should be distinguished.

[0036] In this specification, "aqueous resin" means a polymer that can be dispersed in an aqueous medium. "Aqueous medium" means ordinary water such as tap water, distilled water, or deionized water, but may also include water-soluble or water-dispersible organic solvents that have poor reactivity with the resin raw materials (monomers, etc.) of the present invention, such as acetone, ethyl acetate, etc. (B) The aqueous resin emulsion may further contain water-soluble or water-dispersible monomers, oligomers, prepolymers and / or water-soluble resins, and may also contain emulsifiers, polymerizable emulsifiers, polymerization initiators, chain extenders and / or various additives that are commonly used when producing aqueous resin emulsions.

[0037] The coating agent for paper substrates of the present invention, by containing (B) an aqueous resin emulsion, exhibits excellent water resistance, oil resistance, and oil resistance when folded.

[0038] The aqueous resin is obtained by polymerizing a polymerizable unsaturated monomer (b). In this embodiment, "polymerizable unsaturated monomer" refers to a radical polymerizable monomer having an ethylenic double bond. "Ethyleneic double bond" refers to an intercarbon double bond that can undergo polymerization (radical polymerization). Examples of functional groups having such an ethylenic double bond include vinyl group (CH2=CH-), (meth)allyl group (CH2=CH-CH2- and CH2=C(CH3)-CH2-), (meth)acryloyloxy group (CH2=CH-COO- and CH2=C(CH3)-COO-), (meth)acryloyloxyalkyl group (CH2=CH-COO-R- and CH2=C(CH3)-COO-R-), and -COO-CH=CH-COO-. Polymerizable unsaturated monomer (b) may be a single monomer or a combination of two or more monomers.

[0039] In one embodiment of the present invention, (B) the aqueous resin constituting the aqueous resin emulsion preferably has a chemical structure derived from a carboxylic acid ester polymer.

[0040] "Chemical structures derived from carboxylic acid ester polymers" refers to chemical structures including polymers (whether homopolymers or copolymers) of carboxylic acid esters having an ethylenic double bond, and any modified forms of such polymers. "Carboxylate ester polymers" are obtained by polymerizing a polymerizable unsaturated monomer (b) containing a carboxylic acid ester (b1) having an ethylenic double bond.

[0041] In this specification, "carboxylic acid ester (b1) having an ethylenic double bond" (also simply referred to as "carboxylic acid ester (b1)") refers to, for example, (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; Vinyl acetate and other vinyl carboxylates; Allyl carboxylates such as allyl acetate; Examples can be given. In this specification, (meth)acrylic acid ester refers to both acrylic acid ester and methacrylic acid ester.

[0042] In the present invention, the "carboxylic acid ester having an ethylenic double bond (b1)" is preferably methyl methacrylate, butyl acrylate, or vinyl acetate, and is particularly desirable to be vinyl acetate. (B) When the aqueous resin emulsion contains a chemical structure derived from vinyl acetate, the coating agent for paper substrates of the present invention has an excellent balance of oil resistance, blocking resistance, surface coating properties, and water resistance.

[0043] In this embodiment, the carboxylic acid ester polymer may be a copolymer of a carboxylic acid ester having an ethylenic double bond (b1) and a polymerizable unsaturated monomer other than a carboxylic acid ester having an ethylenic double bond (b2) (also referred to as "other monomer (b2)").

[0044] Other monomers (b2) are not particularly limited, but examples include olefins such as ethylene and propylene, styrene, vinyl alcohol, and the like.

[0045] In embodiments of the present invention, (B) the aqueous resin emulsion preferably includes an emulsion containing a copolymer of ethylene and a carboxylic acid ester having an ethylenic double bond (also described as "ethylene / carboxylic acid ester copolymer emulsion having an ethylenic double bond"), and more preferably includes an ethylene / vinyl acetate copolymer emulsion.

[0046] (B) By including an ethylene / vinyl acetate copolymer emulsion in the aqueous resin emulsion, the coating agent for paper substrates of the present invention can maintain a high level of surface coating properties.

[0047] (B) The solid content concentration of the aqueous resin emulsion is not particularly limited, but is preferably 5 to 70% by mass. The solid content of the emulsion refers to the solid content obtained by drying the emulsion at 105°C for 3 hours.

[0048] (B) Aqueous resin emulsions can be obtained, for example, by emulsion polymerization of one or more types of (b) polymerizable unsaturated monomers. Emulsion polymerization is a radical polymerization using water or an aqueous medium and an emulsifier, and known methods can be used.

[0049] Emulsifiers are immobilized on the surface of polymer particles during or after polymerization to ensure dispersion stability of the particles. Examples of emulsifiers include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and polymeric surfactants. Furthermore, "reactive surfactants" having a radically polymerizable double bond within one molecule of the emulsifier may be used to improve water resistance, alkali resistance, and waterproofing.

[0050] (B) A commercially available aqueous resin emulsion may be used. As a commercially available aqueous resin emulsion in the present invention, VINNAPAS EP707K (product name) and VINNAPAS EP705K (product name) manufactured by Wacker Chemicals Korea Inc. Ethylene vinyl acetate copolymer emulsions such as Sumikaflex 408HQE (product name) manufactured by Sumitomo Chemical Co., Ltd. Vinyl acetate emulsions such as 225-1025 (product name) manufactured by Henkel Japan; These are some examples.

[0051] In the coating agent of the present invention, the amount of component (A) blended is higher than 20 parts by mass and less than 50 parts by mass, and preferably 22 parts by mass or more and 48 parts by mass or less, relative to 100 parts by mass of the total amount of solid content of component (A) and component (B).

[0052] The coating agent for paper substrates of the present invention exhibits excellent oil resistance and blocking resistance when the blending ratio of component (A) and component (B) is within the above range. If the amount of component (A) is too low, the blocking resistance of the coating agent decreases, and if the amount of component (A) is too high, the oil resistance of the coating agent decreases.

[0053] In this embodiment, the total content of the solids of component (A) and component (B) relative to 100 parts by mass of the total mass (excluding solvent) of the coating agent is not particularly limited, but is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and may be 100 parts by mass.

[0054] The coating agent for paper substrates of the present invention may also contain (C) starch (also referred to as "component (C)") in addition to components (A) and (B). (C) starch has the effect of increasing the viscosity of the coating agent and improving the storage stability of the coating agent for paper substrates of the present invention.

[0055] The starch is not particularly limited as long as it can produce the coating agent intended by the present invention, and may be modified starch. Examples of starches include natural starches such as corn starch, tapioca starch, potato starch, sweet potato starch, wheat starch, and rice starch; and modified starches such as etherified starch, esterified starch, cross-linked starch, grafted starch, oxidized starch, acid-hydrolyzed starch, and dextrin, which are obtained by processing the above-mentioned natural starches.

[0056] The amount of component (C) blended relative to 100 parts by mass of the total solid content of components (A) and (B) may be 0 parts by mass, but is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and also preferably 5 parts by mass or less, more preferably 4 parts by mass or less.

[0057] The coating agent for paper substrates according to the embodiment of the present invention comprises component (A) and component (B), and optionally component (C), but may further contain additives such as a crosslinking agent, viscosity modifier, plasticizer, defoaming agent, preservative, colorant, etc.

[0058] Examples of crosslinking agents include zinc acetate, zinc oxide, zirconium acetate, and ammonium zirconium carbonate. These crosslinking agents can be used individually or in combination.

[0059] Examples of viscosity modifiers include nitrogen-containing substances such as urea, urea compounds, and dicyandiamide, calcium hydroxide, calcium oxide, sodium carbonate, trisodium phosphate, diammonium hydrogen phosphate, borax, sodium fluoride, water glass, and aqueous ammonia.

[0060] Examples of plasticizers include glycerin; polyhydric alcohols such as ethylene glycol and propylene glycol; sugars such as sucrose and sorbitol; and organic solvents such as cellosolves.

[0061] As an antifoaming agent, for example, Silicone-based defoamers such as dimethylpolysiloxane, polyoxyalkylene-modified silicone, organically modified polysiloxane, and fluorosilicone; Oil-based defoaming agents such as castor oil, sesame oil, linseed oil, and animal and vegetable oils; Fatty acid-based defoaming agents such as stearic acid, oleic acid, and palmitic acid; Fatty acid ester-based defoamers such as isoamyl stearic acid, diglycol lauric acid, distearyl succinic acid, distearic acid, sorbitan monolauric acid, glycerin fatty acid esters, polyoxyethylene sorbitan, butyl stearate monolaurate, sucrose fatty acid esters, ethyl alkyl acetate esters of sulfonated lithinolic 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 antifoaming agents such as 3-heptylcellsolve and nonylcellsolve-3-heptylcarbitol; Phosphate ester-based antifoaming agents such as tributyl phosphate, sodium octyl phosphate, and tris(butoxyethyl) phosphate; Amine-based antifoaming agents such as diamylamine; Aamide-based antifoaming agents such as polyalkylene amides, acylate polyamines, and diocadecanoylpiperidine; Metal soap-based defoamers such as aluminum stearate, calcium stearate, potassium oleate, and calcium salts of wool oleate; Examples of sulfonic acid ester-based defoaming agents include sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0062] These additives may be added after the synthesis of the (B) aqueous resin emulsion, or together with the monomers that are the raw materials for the (B) aqueous emulsion resin, or added to the emulsion-type coating agent (a mixture of component (A) and component (B)). In the description of the amounts used herein, the solid content of component (B) does not include additives such as starch, defoamers, and preservatives.

[0063] The coating agent of this embodiment can be manufactured by mixing components (A) and (B) with other components as needed, and the mixing may be heated. The order in which each component is added, the heating method, the stirring method, etc., are not particularly limited, and known methods can be used.

[0064] The coating agent for paper substrates of the present invention can be applied to the surface of paper substrates used in food packaging and the like. The coating agent of the embodiment of the present invention has excellent water resistance, oil resistance, surface coating properties, and blocking resistance.

[0065] The coating agent for paper substrates of the present invention is applied directly to the surface of the paper substrate and can be used as both a one-component coating agent and a primer for a two-component coating agent.

[0066] When using the paper substrate coating agent of the present invention as a primer, it is preferable that the topcoat is also an aqueous resin emulsion. The composition of the topcoat does not need to be limited to a special composition as long as it can achieve the objectives of the present invention.

[0067] A conventional coating method can be used to apply the coating agent of the present invention onto a paper substrate. For example, the coating agent of the present invention can be applied to a paper substrate using a known coating machine such as a table coater, bar coater, two-roll size press coater, gate roll coater, blade metering coater, rod metering coater, blade coater, air knife coater, roll coater, brush coater, kiss coater, squeeze coater, curtain coater, die coater, gravure coater, or dip coater, and then dried.

[0068] The amount of coating agent applied to the paper substrate is not particularly limited, but for example, 5 to 100 g / m² in terms of solid content (dry mass) is recommended. 2 Preferably, it is 5-50 g / m 2 It is more preferable that the amount be 10-20 g / m2 This is particularly preferable. 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.

[0069] One aspect of the present invention relates to a paper substrate on which the above-mentioned coating agent for paper substrates is applied to its surface. The paper substrate of the present invention is resistant to moisture and oil, and even when the paper substrate is bent, the coating film is not destroyed, and the decrease in oil resistance can be suppressed. Therefore, the paper substrate of the present invention can be suitably used as a food packaging container.

[0070] One aspect of the present invention relates to a paper substrate having the above-mentioned coating agent for paper substrates. The paper substrate is not particularly limited, but known papers or synthetic papers obtained by papermaking from chemical pulps such as hardwood kraft pulp and softwood kraft pulp, mechanical pulps such as GP (groundwood pulp), RGP (refiner ground pulp), and TMP (thermomechanical pulp) can be used. In addition, high-quality paper, medium-quality paper, alkaline paper, glassine paper, semi-glassine paper, or paperboard, white paperboard, etc. used for corrugated cardboard, building materials, white cardboard, chipboard, etc. can also be used as the paper substrate. The paper substrate may also contain organic and inorganic pigments, as well as papermaking aids such as paper strength enhancers, sizing agents, and yield improvers.

[0071] One aspect of the present invention relates to a paper product having a paper substrate on which the above-mentioned coating agent is applied to the surface. The paper product of the embodiment of the present invention has excellent water resistance and can be used not only for food packaging containers but also for paper straws, toilet paper, paper cups, etc. Because the paper product of the present invention has the above-mentioned paper substrate, its oil resistance and water resistance do not decrease even when its shape is folded, and it can be used for a variety of applications, and is particularly suitable for food packaging. [Examples]

[0072] The present invention will be described in detail below with reference to examples and comparative examples. However, these examples represent only one aspect of the present invention, and the present invention is not limited in any way by these examples. In the descriptions of the examples, unless otherwise specified, portions that do not consider the solvent are based on parts by mass and mass percent.

[0073] The paper substrate coatings of Examples 1-15 and Comparative Examples 1-8 were manufactured using components (A) to (E) in the proportions listed in Tables 2 and 3. The numerical values ​​for the blending amounts in Tables 2 and 3 represent the ratio of solid content, and the unit is parts by mass. Details of components (A) to (E) are shown below.

[0074] (A) Cellulose (A1) Cellulose fiber (ARBOCEL UFC100 (product name), average particle size 10 μm (standard value: 6-12 μm), manufactured by Rettenmeyer Japan Co., Ltd.) (A2) Cellulose fiber (ARBOCEL BE600-10 (product name), average fiber length (average particle diameter) 18 μm, average fiber diameter 15 μm, manufactured by Rettenmeyer Japan Co., Ltd.) (A3) Cellulose fiber (ARBOCEL BE600-30 (product name), average fiber length (average particle diameter) 30 μm, average fiber diameter 18 μm, manufactured by Rettenmeyer Japan Co., Ltd.)

[0075] (A'4) Cellulose fiber (Vivapur 101 (product name), average particle size 50 μm, manufactured by Rettenmeyer Japan Co., Ltd.) (A'5) Cellulose fiber (Leocrysta I2SX (product name), average particle size 3nm, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0076] (B) Water-based resin emulsion (B1) Ethylene vinyl acetate copolymer (EVA) emulsion (VINNAPAS EP707K (trade name), manufactured by Wacker Chemicals Korea Inc.) (B2) Ethylene vinyl acetate copolymer (EVA) emulsion (VINNAPAS EP705K (product name), manufactured by Wacker Chemicals Korea Inc.) (B3) Ethylene vinyl acetate copolymer (EVA) emulsion (Sumikaflex 408HQE (product name), manufactured by Sumitomo Chemical Co., Ltd.) (B4) Vinyl acetate emulsion (225-1025 (product name), manufactured by Henkel Japan Ltd.) (B'5) Acrylic resin (Solurly 840 (product name), manufactured by Hanwha Q CELLS Japan Co., Ltd.)

[0077] (C) Starch (C1) Modified starch (SDRN2 (trade name), manufactured by Nippon Denko Chemical Co., Ltd.) (C2) Modified starch (Biostarch (trade name), manufactured by Nippon Denko Chemical Co., Ltd.)

[0078] (D) Antifoaming agent (D1) Silicone-based defoaming agent (KM72GS (product name), Shin-Etsu Chemical Co., Ltd.)

[0079] (E) Preservatives (E1) ACTICIDE MB (So Japan Co., Ltd.)

[0080] <Manufacturing of the coating agent in Example 1> In a three-necked flask equipped with a stirring blade, thermometer, and reflux condenser, 60 parts by mass of distilled water were added, and 75 parts by mass of (B1) and 1 part by mass of (C1) were added as shown in Table 2. The contents of the three-necked flask were stirred while maintaining the liquid temperature at 80°C. Then, 25 parts by mass of (A1) were slowly added, and the contents were stirred for 2 hours while maintaining the liquid temperature at 80°C until homogenized.

[0081] In a three-necked flask, (A1), (B1), and (C1) were confirmed to be uniformly dispersed in water, and this aqueous resin dispersion (aqueous resin emulsion) was cooled. Then, (D1) and (E1) were added dropwise to prepare the coating agent.

[0082] <Manufacturing of coating agents for Examples 2-15 and Comparative Examples 1-7> The coating agents for Examples 2-15 and Comparative Examples 1-7 were manufactured using the same method as in Example 1, except that the components were changed as shown in Tables 2 and 3. The test results of the obtained coating agents are shown in Tables 2 and 3.

[0083] <Manufacturing of the coating agent in Comparative Example 8> In a three-necked flask equipped with a stirring blade, thermometer, and reflux condenser, 180 parts by mass of distilled water, 20 parts by mass of 25% aqueous ammonia, 60 parts by mass of (B'5), and 1 part by mass of (C1) were added. The contents of the three-necked flask were stirred while maintaining the temperature at 80°C. After confirming that (B'5) was completely dissolved in the aqueous medium, 40 parts by mass of (A1) were slowly added, and the contents were stirred for 2 hours while maintaining the temperature at 80°C to ensure that all components were uniformly mixed.

[0084] In an aqueous medium in a three-necked flask, it was confirmed that (A1) and (C1) were uniformly dispersed in the aqueous medium and that (B'5) was dissolved, and this aqueous resin dispersion (aqueous emulsion) was cooled. Then, (D1) and (E1) were added dropwise to prepare the coating agent.

[0085] The coating agents of Examples 1-15 and Comparative Examples 1-8 were applied to paper substrates, and the oil resistance, blocking resistance, surface coating properties, water resistance, and oil resistance when the paper substrate was folded were evaluated. Details of the evaluation tests are as follows.

[0086] <Oil Resistance Test> The kit test was performed using the following method, which is in accordance with the TAPPI T559cm-12 method.

[0087] Each coating agent was applied to general high-quality paper using a table coater, and test specimens were prepared. For the tests, test solutions were used, consisting of castor oil, toluene, and n-heptane mixed in the proportions shown in Table 1. The test results are represented by kit numbers, with higher numbers indicating superior oil resistance.

[0088] The kit test allows for the determination of the oil resistance of test paper in a short time (approximately 20 seconds) and is widely used to evaluate the oil resistance of paper. The evaluation result has significance as an indicator of the surface tension of the paper surface.

[0089] A test strip was placed on a clean, flat, black surface, and one drop of test solution from kit number 12 was dropped onto the test strip from a height of 13 mm. After 15 seconds (contact time: 15 seconds), the dropped test solution was removed with clean blotting paper, and the surface of the test strip that had come into contact with the test solution was visually inspected. If the surface color had darkened, the same procedure was performed with test solution from kit number 11, and the same procedure was repeated while sequentially decreasing the kit number until the surface color did not darken. The first (largest) kit number where the surface color did not darken was considered the oil resistance of the coating agent. For example, an oil resistance evaluation of kit number 11 means that the color darkened with kit number 12 (penetration occurred), but the color did not darken with kit number 11 (no penetration).

[0090] [Table 1]

[0091] The evaluation criteria are as follows: ◎...Kit numbers 12-7 〇···Kit numbers 6-3 △···Kit number 2 ×...Kit numbers 1-0

[0092] <Blocking resistance test> A coating agent was applied to general high-quality paper using a bar coater, with a coating rate of 15 g / m². 2 The material was coated to the specified (dry mass) and dried at 130°C for 3 minutes to prepare a sample. The coated surface and the uncoated surface (back side) were placed together and pressurized at a pressure of 200N and a temperature of 40°C for 2 hours, after which the sample was removed. The sample was left to stand at room temperature for at least 2 hours, and the 180° peel strength and peel condition of the pressurized surface were observed. The evaluation criteria are as follows.

[0093] ◎...The peeled surface exhibited interfacial peeling (peeling at the interface between the high-quality paper and the coating), and the peel strength was 1.0 N / 25 mm or less. ○...The delamination surface was interfacial delamination, and the delamination strength was higher than 1.0 N / 25 mm and less than or equal to 1.5 N / 25 mm. △···The delamination surface was interfacial delamination, and the delamination strength was higher than 1.5 N / 25 mm. ×...The peeled surface showed material failure (the high-quality paper was damaged).

[0094] <Surface coating properties test> A coating agent was applied to general high-quality paper using a bar coater, with a coating rate of 15 g / m². 2 The material was coated to achieve the (dry mass) and dried at 130°C for 3 minutes to prepare a sample. The coated surface of the sample was observed, and its surface properties were evaluated by touch. The evaluation criteria are as follows:

[0095] ◎...No bumps or irregularities can be detected by touch. ○...The unevenness can be slightly felt by touch. △···The number of bumps and irregularities that can be felt by touch increases. ×...The uneven surface can be clearly felt by touch.

[0096] <Water resistance test> A coating agent was applied to general high-quality paper using a bar coater, with a coating rate of 15 g / m². 2 The paper was coated to achieve the (dry mass) shown, and dried at 130°C for 3 minutes to prepare a sample. After the coating agent dried, the fine paper was cut into a circle with a diameter of 10 cm, its mass was measured, and then the top and bottom of the fine paper were placed in a cylindrical flask with an inner diameter of 7 cm and an open top. 50 ml of distilled water was added dropwise from the top, and the flask was left to stand for 30 minutes.

[0097] Subsequently, the distilled water was removed, the test specimen was removed from the cylindrical tube, and its mass was measured after removing any water droplets from its surface. The change in mass of the test specimen before and after the test was calculated, and the increase was considered as the amount of water absorbed. The amount of water absorbed per unit area was then calculated. The evaluation criteria are as follows.

[0098] ◎··· Water absorption is less than 50 g / m 2 and below 〇··· Water absorption is 50 - 100 g / m 2 and above △··· Water absorption is higher than 100 g / m 2 and less than 140 g / m 2 and below ×··· Water absorption is 140 g or more

[0099] <Oil resistance test during paper substrate folding> Using a bar coater on general high-quality paper, an aqueous coating agent was applied to a coating amount of 15 g / m 2 (dry mass), and dried at 130 °C for 3 minutes to prepare samples. Creases were made in the same direction and perpendicular direction to the coating direction, and a load of 2 kg was applied in the coating direction with a roller. The roller application was only done once. A few drops of sesame oil were dropped onto the folded surface of the paper substrate, and after leaving the samples to stand at room temperature for 10 minutes and at 60 °C for 30 minutes, the penetration state of the oil into each sample was confirmed. The evaluation criteria are as follows.

[0100] ◎··· No penetration 〇··· 1 - 3 pinholes occurred △··· 4 - 5 pinholes occurred ×··· 6 or more pinholes, or overall penetration occurred

[0101] The composition and test results of each coating agent are shown in Table 2 and Table 3.

[0102]

Table 2

[0103]

Table 3

[0104] As shown in Table 2, it was demonstrated that the coating agents of the examples had evaluation test results of ◎ or 〇 and were excellent in the balance of each performance.

[0105] As shown in Table 3, the coating agents in the comparative examples all received an "X" in at least one of the evaluation tests. The coating agents in Comparative Examples 1-4 have too little (A) cellulose, resulting in poor blocking resistance, while the coating agent in Comparative Example 5 has too much (A) cellulose, resulting in poor oil resistance.

[0106] The coating agent in Comparative Example 6 has poor oil resistance because the average particle size of (A'4) cellulose is too large, while the coating agent in Comparative Example 7 has poor blocking resistance because the average particle size of (A'5) cellulose is too small.

[0107] The coating agent in Comparative Example 8 did not contain (B) an aqueous resin emulsion, but contained (B'5) a water-soluble resin, resulting in reduced oil resistance and water resistance. [Industrial applicability]

[0108] The present invention provides a coating agent that is applied to the surface of paper. In one embodiment of this invention, the coating agent is applied to the surface of paper, and a paper product is manufactured. Examples of paper products include food packaging containers, paper cups, and paper straws.

Claims

1. (A) cellulose with an average particle size of 1 μm to 40 μm and (B) an aqueous resin emulsion, With respect to 100 parts by mass of the total solid content of component (A) and component (B), the amount of component (A) is higher than 20 parts by mass and less than 50 parts by mass. (B) A coating agent for paper substrates, wherein the aqueous resin emulsion contains a chemical structure derived from vinyl acetate.

2. (B) The coating agent for paper substrates according to claim 1, wherein the aqueous resin emulsion comprises an ethylene / vinyl acetate copolymer emulsion and / or a vinyl acetate emulsion.

3. (A) Cellulose having an average particle size of 1 μm to 40 μm and (B) an aqueous resin emulsion, With respect to 100 parts by mass of the total solid content of component (A) and component (B), the amount of component (A) is higher than 20 parts by mass and less than 50 parts by mass. (B) A coating agent for paper substrates, wherein the aqueous resin emulsion contains a carboxylic acid ester copolymer emulsion having an ethylene / ethylenic double bond.

4. A paper substrate having a coating agent for paper substrates according to any one of claims 1 to 3 applied to its surface.

5. A paper product having a paper substrate as described in claim 4.

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