Coated paper

Abstract

To provide coated paper having good water resistance and oil resistance. The paper substrate has, on at least one surface thereof, an auxiliary coating layer containing PVA or starch, and a coating layer containing an ethylene methacrylic acid copolymer ionomer and an inorganic flat pigment, in this order; The basis weight of the paper base material is 20 g / m 2 More than 600g / m 2 is as follows: the coating layer contains 3 parts by mass or more and 110 parts by mass or less of the inorganic flat pigment per 100 parts by mass of the ionomer, Coated paper, wherein the particle size of the inorganic flat pigment is 1.0 μm or more and 12 μm or less.

Description

[Technical Field]

[0001] The present invention relates to coated paper, and more particularly to coated paper having a coating layer that has excellent water resistance and oil resistance. [Background technology]

[0002] In recent years, coated paper made by coating base paper with a thermoplastic resin has been attracting attention, and coated paper coated with an ionomer has been attracting attention due to its excellent coatability (for example, Patent Document 1). Waterproof paper with a coating layer containing an ionomer as the water-resistant layer has also been proposed (Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-024905 [Patent Document 2] Japanese Patent Publication No. 2022-013542 [Patent Document 3] Japanese Patent Publication No. 2022-130266 [Patent Document 4] Japanese Patent Publication No. 2022-186782 Summary of the Invention [Problem to be solved by the invention]

[0004] The water-resistant layers described in Cited Documents 2 to 4 have a water-resistant undercoat layer to ensure sufficient water resistance, and therefore have a large number of coating layers, requiring improvement in the water resistance of each layer. Furthermore, waterproof paper is sometimes required to have oil resistance, but the waterproof layers described in Cited Documents 2 to 4 are hardly superior in oil resistance. Therefore, an object of the present invention is to provide a coated paper having good water resistance and oil resistance. [Means for solving the problem]

[0005] As a result of extensive research to solve the above problems, the inventors discovered that adding a specific amount of an inorganic flat pigment of a specific particle size to a coating layer of an ethylene methacrylic acid copolymer ionomer significantly improves water resistance and oil resistance, and thus completed the present invention. That is, the means for solving the problems of the present invention are as follows. 1. A paper substrate having, on at least one surface thereof, an auxiliary coating layer containing PVA or starch and a coating layer containing an ethylene methacrylic acid copolymer ionomer and an inorganic flat pigment, in this order; The basis weight of the paper base material is 20 g / m 2 More than 600g / m 2 is as follows: the coating layer contains 3 parts by mass or more and 110 parts by mass or less of the inorganic flat pigment per 100 parts by mass of the ionomer, Coated paper characterized in that the particle size of the inorganic flat pigment is 1.0 μm or more and 12 μm or less. 2. Coated paper according to 1., characterized in that the particle size of the inorganic flat pigment is 5.0 μm or more and 10 μm or less, and the aspect ratio is 14 or more. 3. Coated paper according to 1. or 2., characterized in that the coating layer contains 27 to 98 parts by mass of the inorganic flat pigment per 100 parts by mass of the ionomer. 4. Coated paper according to 3., characterized in that the coating layer contains 42 to 88 parts by mass of the inorganic flat pigment per 100 parts by mass of the ionomer. 5. Coated paper according to any one of 1. to 4., characterized in that a second coating layer containing an ethylene methacrylic acid copolymer ionomer is formed in direct contact with the first coating layer. 6. Coated paper according to 5., characterized in that the inorganic flat pigment is kaolin. [Effects of the Invention]

[0006] The coated paper of the present invention has excellent water resistance and oil resistance, and also has heat sealability. DETAILED DESCRIPTION OF THE INVENTION

[0007] The coated paper of the present invention has, on at least one surface of a paper substrate, an auxiliary coating layer containing PVA or starch, and a coating layer containing an ethylene methacrylic acid copolymer ionomer and an inorganic flat pigment, in this order; The paper base weight is 20 g / m 2 More than 600g / m 2 is as follows: the coating layer contains 3 parts by mass or more and 110 parts by mass or less of the inorganic flat pigment per 100 parts by mass of the ionomer, The particle size of the inorganic flat pigment is 1.0 μm or more and 12 μm or less. In this specification, the expression "A to B (A and B are numbers or ratios)" means a range of values ​​including both ends.

[0008] (Paper base material) The paper base material is obtained by papermaking a paper stock containing pulp, fillers, various auxiliaries, and the like. When the coated paper of the present invention is used in applications that come into contact with food, it is preferable to use materials that comply with food safety standards, such as materials that are approved as food additives or have FDA approval, for the materials used in the paper base.

[0009] Pulps include various known pulps, such as bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), and sulfite pulp (SP), as well as mechanical wood pulps such as ground pulp (GP), refiner ground pulp (RGP), stone ground pulp (SGP), chemi-ground pulp (CGP), semi-chemical pulp (SCP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), as well as non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, and recycled paper pulp, which is made from recycled paper and has had the ink removed during a deinking process. Among these, chemical pulps such as LBKP and NBKP, which are less likely to be contaminated with foreign matter, are preferred. Specifically, the amount of wood fiber chemical pulp such as LBKP or NBKP mixed with the total pulp is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and most preferably 100% by mass. Furthermore, from the viewpoint of preventing the inclusion of foreign matter, it is preferable that the amount of recycled paper pulp mixed with the total pulp is small. Specifically, the amount of recycled paper pulp mixed with the total pulp is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and most preferably none.

[0010] The paper substrate of the present invention may contain papermaking fibers other than pulp. Examples of papermaking fibers other than pulp include thermoplastic resin fibers, which may have a core-sheath structure. Thermoplastic resin fibers used in the papermaking field can be used without any particular restrictions. Biodegradable thermoplastic resin fibers such as PVA resins, cellulose ester fibers, polylactic acid, polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) are preferred. Because thermoplastic resin fibers have heat-sealing properties, paper substrates containing thermoplastic resin fibers strongly bond to the heat-sealing layer during heat fusion, improving heat-sealing strength. However, because thermoplastic resin fibers are more flexible and less stiff than pulp, paper substrates containing thermoplastic resin fibers have reduced strength. The ratio of pulp to all papermaking fibers contained in the paper base material is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. Note that thermoplastic resin fibers are not an essential material and may not be used.

[0011] Examples of fillers that can be used include known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and hollow microparticles. Note that fillers are not essential materials and may not be used.

[0012] Examples of various auxiliary agents include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, dry strength agents such as urea-formalin resin and melamine-formalin resin, wet strength agents, retention agents, drainage aids, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, UV inhibitors, anti-fading agents, pitch control agents, and slime control agents, and can be selected and used as needed.

[0013] The method for manufacturing (making) the paper base is not particularly limited, and known manufacturing (making) methods and paper machines can be selected, such as a Fourdrinier paper machine, a cylinder paper machine, a short wire paper machine, or a twin-wire paper machine such as a gap former or a hybrid former (on-top former). The pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking). After papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer. The paper base may be a single layer or may be composed of two or more layers. The paper base may also be Clupak paper that has been subjected to the known Clupak process.

[0014] Furthermore, the surface of the paper substrate can be treated with various chemicals. Examples of chemicals that can be used include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retention agents, thickeners, and lubricants. These can be used alone or in combination of two or more. Furthermore, these various chemicals can be used in combination with pigments. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more.

[0015] The method for treating the surface of the paper substrate is not particularly limited, but known coating devices such as a rod metering size press, a pond type size press, a gate roll coater, a spray coater, a blade coater, and a curtain coater can be used. Examples of paper substrates obtained in this manner include various known types such as fine paper, medium-quality paper, coated paper, one-side glossy paper, kraft paper, one-side glossy kraft paper, bleached kraft paper, glassine paper, paperboard, white paperboard, and liner.

[0016] The basis weight of the paper substrate used in the present invention is 20 g / m 2 More than 600g / m 2 The coated paper of the present invention can exhibit excellent water resistance and oil resistance due to the coating layer, and can impart practical water resistance and oil resistance to paper substrates with low basis weights. The basis weight of the paper base material can be selected depending on the application of the coated paper. For heat-sealable paper used for packaging purposes such as food packaging, bags, containers, boxes, cups, and lids, the basis weight is 25 g / m 2 More than 600g / m 2 The following is more preferable, especially for heat seal paper used for bags, lids, or soft packaging materials described below, 30 g / m 2 More than 150g / m 2 The following is heat seal paper for containers, boxes, and cups: 150 g / m 2 More than 350g / m 2 The following are more preferred. Flexible packaging materials are packaging materials made of flexible materials, and generally refer to packaging materials made of thin, flexible materials such as paper, film, and aluminum foil, either alone or bonded together. Furthermore, flexible packaging materials are bags or other packaging materials that maintain a three-dimensional shape when contents are placed inside. The density of the paper substrate can be selected appropriately depending on the desired quality, handling, etc., but is usually 0.5 g / cm 3 More than 1.0g / cm 3 The following are preferred:

[0017] (auxiliary coating layer) The auxiliary coating layer contains PVA or starch. PVA refers to polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, and ethylene-vinyl alcohol copolymers. Starch refers to starches such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch.

[0018] The auxiliary coating layer may contain one or more of the PVAs listed above, one or more of the starches listed above, or both PVA and starch. In addition to PVA and starch, the auxiliary coating layer may also contain surfactants, pigments, thickeners, etc., but it is preferable that the total amount of PVA and starch contained in the auxiliary coating layer is 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0019] The coating amount of the auxiliary coating layer is 0.1 g / m2 in dry weight. 2 More than 5.0g / m 2 The coating weight of the auxiliary coating layer is preferably 0.1 g / m or less. 2 If the coating weight of the auxiliary coating layer is less than 5.0 g / m, the effect of improving water resistance and oil resistance may be hardly expected. 2 If the coating amount is more than this, the effect saturates and there is almost no further improvement. 2 More preferably, 0.5 g / m 2 More preferably, 0.8 g / m 2 More preferably, 4.0 g / m 2Less than 3.5 g / m is more preferable. 2 More preferably, 3.0 g / m 2 Even more preferably, 2.5 g / m 2 Even more preferably, 2.2 g / m 2 The following is even more preferred: The auxiliary coating layer can be applied using a known coater such as a roll coater, air knife coater, spray coater, size press coater, gate roll coater, etc. After the auxiliary coating layer is dried in a dryer, the coating layer and second coating layer described below are formed thereon.

[0020] (coating layer) The coating layer contains 3 to 110 parts by mass of an inorganic flat pigment having a particle size of 1.0 μm to 12 μm per 100 parts by mass of an ethylene methacrylic acid copolymer ionomer, and is formed on at least one surface of the paper substrate. The coating layer of the present invention has excellent water resistance and oil resistance by satisfying this specific constitution. In the present invention, the coating layer can be formed on both the paper substrate and the paper base. The coating layer can be formed directly on the paper base, or one or more other layers, such as a sealing layer, ink-receiving layer, water vapor barrier layer, gas barrier layer, water-resistant layer, or oil-resistant layer, can be present between the coating layer and the paper base, or the above-mentioned other layers can be present on the coating layer.

[0021] In addition to the ethylene methacrylic acid copolymer ionomer and inorganic flat pigment, the coating layer may contain other resins, other pigments, surfactants, water repellents, oil repellents, antiblocking agents, dispersants, thickeners, dyes, etc., within the scope of the invention, provided that the effects of the invention are not impaired. However, the coating layer of the invention preferably contains 50% by mass or more of the ethylene methacrylic acid copolymer ionomer and inorganic flat pigment in total, based on the total amount of the coating layer, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0022] Ethylene methacrylic acid copolymer ionomer An ethylene methacrylic acid copolymer ionomer (hereinafter also referred to as an ionomer) is a resin in which an ethylene methacrylic acid copolymer is neutralized with a cation, and an ionic crosslinked structure is formed by the cation. In addition to the ethylene methacrylic acid copolymer ionomer, the coating layer may contain resins conventionally used in coated paper. However, from the viewpoint of water resistance and oil resistance, the ratio of the ethylene methacrylic acid copolymer ionomer to the total resins in the coating layer of the coated paper of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0023] Inorganic flat pigments The inorganic flat pigment means an inorganic pigment having an aspect ratio of 10 or more. The inorganic flat pigment used in the present invention has a particle size of 1.0 μm or more and 12 μm or less. In this specification, the particle size of the inorganic flat pigment refers to the 50% volume average particle size (D50) measured by laser diffraction / scattering. Examples of measuring devices for the laser diffraction / scattering method include the "Partica" particle size distribution analyzer from Horiba, Ltd. and the "MASTER SIZER S" particle size distribution analyzer from Malvern Instruments. The aspect ratio can be calculated using measurements from a particle size distribution analyzer or the like, according to the calculation method described in "Fundamental Research on the Relationship between Coating Pigment Properties and Coated Paper Quality" in Vol. 65, No. 12 of the Paper and Pulp Technical Journal.

[0024] From the viewpoint of water resistance and oil resistance, the inorganic flat pigment preferably has an aspect ratio of 14 or more, more preferably 15 or more. There is no particular upper limit to the aspect ratio, but it is, for example, about 120 or less. From the viewpoint of water resistance and oil resistance, the particle size of the inorganic flat pigment is preferably 5.0 μm or more, more preferably 6.0 μm or more, and is preferably 10 μm or less, more preferably 9.0 μm or less.

[0025] The inorganic flat pigment is not particularly limited as long as it has an aspect ratio of 10 or more and a particle size of 1.0 μm or more and 1.0 μm or less and 12 μm or less, and examples thereof include kaolin, engineered kaolin, clay, delaminated clay, talc, titanium dioxide, aluminum hydroxide, mica, illite, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white. One or more of these can be used, and of these, kaolin and engineered kaolin are preferred, with kaolin being more preferred.

[0026] The coating layer may also contain a non-flat inorganic pigment having an aspect ratio of less than 10, but the proportion of the inorganic flat pigment to the total inorganic pigment contained in the coating layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0027] The coating layer contains 3 to 110 parts by mass of inorganic flat pigment per 100 parts by mass of ionomer. By blending 3 to 110 parts by mass of inorganic flat pigment having the above particle size per 100 parts by mass of ionomer into the ionomer-containing coating layer, water resistance and oil resistance are significantly improved. From the viewpoint of water resistance and oil resistance, the ratio of inorganic flat pigment per 100 parts by mass of ionomer in the coating layer is preferably 10 parts by mass or more, more preferably 27 parts by mass or more, even more preferably 42 parts by mass or more, even more preferably 50 parts by mass or more, and preferably 103 parts by mass or less, more preferably 98 parts by mass or less, even more preferably 88 parts by mass or less, and even more preferably 80 parts by mass or less.

[0028] (Second coating layer) In the coated paper of the present invention, a second coating layer containing an ethylene methacrylic acid copolymer ionomer can be formed in direct contact with the coating layer. Direct formation of the second coating layer further improves water resistance and oil resistance. The second coating layer can be formed either above the coating layer (on the side of the coating layer opposite the paper substrate), below the coating layer (on the side of the coating layer facing the paper substrate), or both, but it is preferable to form it at least above the coating layer. Furthermore, if the paper substrate has coating layers on both sides, the second coating layer can be formed in direct contact with only one of the coating layers.

[0029] The second coating layer may contain an inorganic flat pigment. When the second coating layer contains an inorganic flat pigment, the aspect ratio is preferably 14 or more, more preferably 15 or more. There is no particular upper limit to the aspect ratio, but it is, for example, about 120 or less. From the viewpoint of water resistance and oil resistance, the particle size is preferably 5.0 μm or more, more preferably 6.0 μm or more, and is preferably 10 μm or less, more preferably 9.0 μm or less.

[0030] When the second coating layer contains an inorganic flat pigment, it preferably contains 50 parts by mass or less of the inorganic flat pigment per 100 parts by mass of ionomer. By blending 50 parts by mass or less of the inorganic flat pigment having the above-mentioned particle size per 100 parts by mass of ionomer in the second coating layer, water resistance and oil resistance are significantly improved. The ratio of the inorganic flat pigment per 100 parts by mass of ionomer in the second coating layer is preferably smaller than the ratio of the inorganic flat pigment per 100 parts by mass of ionomer in the coating layer. The difference in this ratio between the second coating layer and the coating layer (coating layer ratio - second coating layer ratio) is preferably 1 or more, more preferably 5 or more, even more preferably 10 or more, even more preferably 20 or more, even more preferably 30 or more, and even more preferably 50 or more.

[0031] In addition to the ethylene methacrylic acid copolymer ionomer and the inorganic flat pigment, the second coating layer may contain other resins, other pigments, surfactants, water repellents, oil repellents, antiblocking agents, dispersants, thickeners, dyes, etc., within the range that does not impair the effects of the present invention.

[0032] (Coating layer, coating of second coating layer) In the present invention, the coating method for the coating layer and the optional second coating layer is not particularly limited, and coating can be performed using a known coating device and coating system. Examples of coating devices include a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a spray coater, a size press coater, and a gate roll coater. Examples of coating systems include aqueous coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent, with aqueous coating being preferred. The coating layer and the second coating layer can be dried by a conventional method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, or a cylinder dryer. The coating layer and the second coating layer can be applied simultaneously, or can be applied before or after the previously applied layer has dried.

[0033] The coating weight of the coating layer is 1g / m2 in dry weight. 2 More than 50g / m 2 The coating weight of the coating layer is preferably 1 g / m or less. 2 If the thickness is less than 50 g / m, the effect of improving water resistance and oil resistance may be hardly expected. 2 If the amount is more than this, the drying load during coating will increase. 2 More preferably, 5 g / m 2 More preferably, 7 g / m 2 More preferably, 40 g / m 2 Less than 30 g / m is more preferable. 2 The following is even more preferred:

[0034] When forming a second coating layer, the coating amount of the second coating layer is 0.5 g / m2 in dry weight. 2 More than 20g / m 2 The coating weight of the second coating layer is preferably 0.5 g / m or less. 2 If the thickness is less than 20 g / m, the effect of improving water resistance and oil resistance due to the second coating layer may be hardly expected. 2 If the amount is more than this, the drying load during coating will increase. The coating amount of the second coating layer is 1 g / m 2 More preferably, 2 g / m 2 More preferably, 3 g / m 2 More preferably, 16 g / m 2 Less than 12 g / m is more preferable. 2 The following is even more preferred:

[0035] The coated paper of the present invention has a water absorption (Cobb value) of 9.0 g / m or less on the surface of the coating layer or the surface of the second coating layer, measured at a contact time of 120 seconds according to JIS P 8140:1998 "Paper and paperboard - Water absorption test method - Cobb method." 2 Preferably less than 8.0 g / m 2 Less than 7.0 g / m is more preferable. 2 More preferably, 6.0 g / m 2 Even more preferably, 5.0 g / m 2 Even more preferably, 4.0 g / m 2 Even more preferably, 3.0 g / m 2 Even more preferably, 2.0 g / m 2 Even more preferably, 1.0 g / m 2 Even more preferably, 0.7 g / m 2 Even more preferably, 0.4 g / m 2 Even more preferred are the following:

[0036] The coated paper of the present invention is prepared by quickly pouring salad oil (Nissin Healthy Resetta) onto the center of a 2 cm diameter circle on the coating layer or second coating layer until it covers the circle, and the time (seconds) from when the salad oil comes into contact with the coating layer or second coating layer until it soaks into the entire circle is preferably 30 seconds or more, more preferably 50 seconds or more, even more preferably 100 seconds or more, even more preferably 150 seconds or more, even more preferably 200 seconds or more, even more preferably 250 seconds or more, and even more preferably 300 seconds or more. [Example]

[0037] (Materials used) ·Paper base material Paper base material 1 A mixture of 100 parts of a pulp mixture consisting of 90% hardwood pulp (L-BKP) and 10% softwood pulp (N-BKP) adjusted to 350 ml of CSF and 400 ml of CSF was mixed with 0.5 parts of a neutral rosin size (Harsize AN-300, manufactured by Harima Chemicals Co., Ltd.) as a sizing agent and 0.2 parts of a cationized starch (Neotack 40T, manufactured by Nippon Shokuhin Kako Co., Ltd.) as a paper strength agent. The mixture was then made into a single-layer paper using a fourdrinier paper machine equipped with a top wire at a speed of 150 m / min. After two presses at a linear pressure of 50 kg / cm, the paper was dried and a 3% aqueous solution of PVA (RS-2117, manufactured by Kuraray Co., Ltd.) was applied to the base paper using a pond-type size press until the solid content per side was 1.0 g / m. 2 The paper was dried to a moisture content of 8% and weighed 220.0 g / m². 2 , density 0.85g / cm 3 The paperboard was obtained.

[0038] Paper base material 2 100 parts of pulp consisting of 100% unbleached softwood pulp (N-UKP) adjusted to 400 ml of CSF, 0.5 parts of neutral rosin size (Harsize AN-300, manufactured by Harima Chemicals Co., Ltd.) as a sizing agent, and 0.2 parts of cationic starch (trade name: Neotack 40T, manufactured by Nippon Shokuhin Kako Co., Ltd.) as a paper strength agent were mixed, and the mixture was made into a paper at a speed of 1000 m / min using a paper machine. After that, it was pressed once at a linear pressure of 50 kg / cm, dried, and then a 3% aqueous solution of PVA was applied to the base paper using a pond-type size press until the amount of sizing liquid deposited per side was 1.0 g / m2 in terms of solids. 2 The paper was dried to a moisture content of 8% and weighed 50.0 g / m². 2 , density 0.80g / cm 3 I got the paper.

[0039] Paper base material 3 A paperboard was obtained in the same manner as in paper base 1, except that the sizing liquid was not applied to both sides. Paper base material 4 A paperboard was obtained in the same manner as in Paper Base 1, except that the PVA in the sizing liquid was replaced with starch (SK-20, manufactured by Nippon Corn Starch Co., Ltd.). ·resin Ethylene methacrylic acid copolymer ionomer (Mitsui Chemicals, Chemipearl S300) Styrene-acrylic resin (Daiichi Paint Co., Harbil HS-1) Ethylene-vinyl acetate copolymer (Sumika Chemtex Co., Ltd., S-400HQ) Ethylene acrylic acid copolymer ionomer (Michelman, 498345N)

[0040] Inorganic pigments Inorganic flat pigment 1: Kaolin (Shiraishi Kogyosha, Balisurf HX) Particle size 8.7 μm, aspect ratio 80-100 Inorganic flat pigment 2: Kaolin (Shiraishi Kogyosha, KCS) Particle size 3.6 μm, aspect ratio 10 to 15 Inorganic flat pigment 3: Kaolin (Rio Kapim, Kapim DG) Particle size 1.2 μm, aspect ratio 13 Inorganic flat pigment 4: Delaminated kaolin (Engelhard, New Surf) Particle size 6.3 μm, aspect ratio 16 Inorganic flat pigment 5: Kaolin (Imerys, Contour 1500) Grain size 0.47 μm, aspect ratio 59 Inorganic pigment 1: Kaolin (CADAM, Amazon Plus) Grain size 0.4 μm, aspect ratio 9 Inorganic pigment 2: Heavy calcium carbonate (Bihoku Funka Kogyo Co., Ltd., Hydrocarb 90) Particle size <2μm, spherical

[0041] (Evaluation method) ·Basic weight Measurements were performed in accordance with JIS P8124:2011. Thickness Measurements were performed in accordance with JIS P8118:2014. ·density It was calculated from the basis weight and thickness. Coating amount It was calculated from the difference in basis weight before and after coating.

[0042] ·water resistance The water absorbency (Cobb value) was measured on the surface of the coating layer or second coating layer after a contact time of 120 seconds in accordance with JIS P 8140:1998, "Paper and paperboard - Water absorption test method - Cobb method," and this was used as the water resistance value. The smaller the value, the better the water resistance. ·Oil resistance 40mg of salad oil (Nissin Healthy Resetta) was quickly poured onto the center of a 2cm diameter circle on the coating or second coating layer so that it completely covered the circle, and the time (seconds) from when the salad oil came into contact with the coating or second coating layer until it soaked into the entire circle was measured and used as the oil resistance value. The test was conducted at a room temperature of 23°C and a humidity of 50%. The higher the value, the better the oil resistance.

[0043] Heat seal strength Two 100mm wide sheets of coated paper were placed together with the heat seal layers facing each other, and the heat seal tester (Tester Sangyo, TP-701-S) was used to test the seal at 140°C and 2kgf / cm 2 The adhesive was heat sealed for 5 seconds. The heat-sealed test specimen was left to stand in an environment of 23°C ± 1°C and 50±2% humidity for at least 12 hours, and then, in accordance with JIS Z1707, the test specimen was cut to a width of 15 mm and subjected to a T-peel test at a tensile speed of 200 mm / min using a Tensilon universal material testing machine (RTC-1250A, manufactured by A&D). The maximum load recorded was taken as the heat-seal strength. After the test, the peeled portion was visually observed and evaluated according to the following criteria. ◎: Complete destruction (the paper substrate is completely peeled off and destroyed) ○: One component is broken (some parts of the paper substrate are peeled off and some parts of the paper substrate are broken) △: Pseudo-adhesion (coating layer peeled off, paper substrate not destroyed) ×: Not bonded (not bonded by heat sealing)

[0044] (Preparation of coated paper) An aqueous coating liquid prepared by blending ethylene methacrylic acid copolymer ionomer (Mitsui Chemicals, Inc.: Chemipearl S300) and flat inorganic pigment or inorganic pigment in the mass ratios shown in Tables 1 to 6 was applied to one side of the paper substrate, and the coated paper was obtained by drying at 150°C for 2 minutes. For those with a second coating layer, an aqueous coating liquid prepared by blending the materials in the mass ratios shown in Table 5 was applied and dried at 150°C for 2 minutes to obtain a coating layer. On top of this coating layer, an aqueous coating liquid prepared by blending the materials in the mass ratios shown in Table 5 was applied as a second coating layer, and then dried at 150°C for 2 minutes to obtain coated paper with a second coating layer.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] [Table 4]

[0049] [Table 5]

[0050] [Table 6]

[0051] ·result From the results of Examples 1 to 15 and Comparative Examples 1 to 3 shown in Table 1, it was confirmed that the water resistance and oil resistance tend to improve as the coating weight of the coating layer increases and the ratio of inorganic flat pigment to ionomer in the coating layer increases. From the results of Examples 16 to 25 and Comparative Examples 4 to 6 shown in Table 2, it was confirmed that there is a preferred range for the ratio of inorganic flat pigment to 100 parts by mass of ionomer in the coating layer in terms of water resistance, and that a higher ratio of inorganic flat pigment is preferable in terms of oil resistance. The results of Examples 26 to 29 and Comparative Examples 7 to 9 shown in Table 3 confirm that the use of specific inorganic flat pigments allows for the production of coating layers with excellent water resistance and oil resistance. In particular, Comparative Example 9 is an example in which inorganic flat pigment 5 with an aspect ratio of 59 was used, but the particle size of inorganic flat pigment 5 was small at 0.47 μm, and the resulting coating layer had good water resistance but poor oil resistance.

[0052] The results of Example 25 and Comparative Examples 2, 10-17 shown in Table 4 confirm that the use of an ethylene methacrylic acid copolymer ionomer results in a coating layer with excellent water resistance and oil resistance. In Comparative Examples 10-17, the incorporation of an inorganic flat pigment reduced water resistance, indicating that the improved water resistance achieved by combining an inorganic flat pigment is an effect unique to ethylene methacrylic acid copolymer ionomers. Furthermore, when comparing Comparative Example 17 with Example 25, Comparative Example 17, which used an ethylene acrylic acid copolymer ionomer, had inferior water resistance to Example 25, which used an ethylene methacrylic acid ionomer, despite the higher coating weight.

[0053] The results of Examples 30 to 47 and Comparative Examples 1, 18, and 19 shown in Table 5 confirm that providing a second coating layer on a coating layer significantly improves water resistance and oil resistance, even when the coating weight of the second coating layer is small. Comparative Examples 18 and 19 are examples using an ethylene-acrylic acid copolymer ionomer, and it was confirmed that when the second coating layer contained an ethylene-acrylic acid copolymer ionomer, the effect of improving water resistance was smaller than when the second coating layer contained an ethylene-methacrylic acid copolymer ionomer (Examples 46 and 47). The results of Example 48 and Comparative Example 20 shown in Table 6 confirm that the water resistance and oil resistance of the coated paper of the present invention are improved even when a low-basis weight paper base 2 is used. Furthermore, when a paper base 4 coated with starch instead of PVA is used (Examples 49-51, Comparative Example 25), the same effect as when a PVA-coated paper base 1 is used was obtained, and it was confirmed that the water resistance and oil resistance are improved compared to when a paper base 3 without an auxiliary coating layer is used (Comparative Examples 21-24).

Claims

1. The paper substrate has, on at least one surface thereof, an auxiliary coating layer containing PVA or starch, and a coating layer containing an ethylene methacrylic acid copolymer ionomer and an inorganic flat pigment, in this order; The basis weight of the paper base material is 20 g / m ２ More than 600g / m ２ is as follows: the coating layer contains 3 parts by mass or more and 110 parts by mass or less of the inorganic flat pigment per 100 parts by mass of the ionomer, A coated paper characterized in that the particle size of the inorganic flat pigment is 1.0 μm or more and 12 μm or less.

2. 2. Coated paper according to claim 1, characterized in that the inorganic flat pigment has a particle size of 5.0 μm or more and 10 μm or less and an aspect ratio of 14 or more.

3. 3. The coated paper according to claim 2, wherein the coating layer contains 27 to 98 parts by mass of the inorganic flat pigment per 100 parts by mass of the ionomer.

4. 4. The coated paper according to claim 3, wherein the coating layer contains 42 to 88 parts by mass of the inorganic flat pigment per 100 parts by mass of the ionomer.

5. 5. The coated paper according to claim 1, wherein a second coating layer containing an ethylene methacrylic acid copolymer ionomer is formed in direct contact with the first coating layer.

6. 6. Coated paper according to claim 5, characterized in that the inorganic flat pigment is kaolin.

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