JP2020190063A - Moisture-proof paper and packaging container - Google Patents

Abstract

To provide moisture-proof paper which can be recycled as pulp fiber and has excellent water vapor barrier properties and heat-sealing properties.SOLUTION: A moisture-proof paper of this invention has a water vapor barrier layer on at least one surface of a paper base material, wherein the water vapor barrier layer contains a layered inorganic compound and an ethylene-acrylic copolymer, wherein the ethylene-acrylic copolymer has a content of an acrylic monomer unit of 1-50 mol% and a moisture permeability of 50 g/(m2/24h.atm) or less, and a packaging container of the invention uses the above moisture-proof paper.SELECTED DRAWING: None

Description

The present invention relates to moisture-proof paper and a packaging container using the same.

Moisture-proof paper having excellent water vapor barrier properties has been conventionally used for packaging foods, medical products, electronic parts, and the like. As a method of imparting a water vapor barrier property to a paper base material, a method of laminating a synthetic resin film or a metal foil on the paper base material is known. However, since this method requires a separation operation between the paper base material and the synthetic resin film or the like, there is room for improvement from the viewpoint of recycling pulp fibers.

Conventionally, the development of moisture-proof paper that can be recycled as pulp fiber using paper as a base material has been promoted. For example, Patent Document 1 discloses a moisture-proof laminate in which a moisture-proof layer composed of a flat pigment and SBR is formed on at least one surface of a paper support, and a coating layer obtained from synthetic resin latex is provided on the moisture-proof layer. There is. Further, Patent Document 2 discloses a water-decomposable moisture-proof paper having a moisture-proof resin layer composed of a mixture of an α-olefin / unsaturated carboxylic acid low molecular weight copolymer and a vinyl-based emulsified polymer. Further, Patent Document 3 discloses a moisture-proof laminate in which a moisture-proof layer containing a synthetic resin, a swellable inorganic layered compound and a nitrogen-containing compound is provided on at least one surface of a paper support.

Japanese Patent No. 3926500 Japanese Unexamined Patent Publication No. 2000-80593 Japanese Unexamined Patent Publication No. 2004-27444

The moisture-proof laminate described in Patent Document 1 can be dissociated and recycled, but the coating layer formed on the moisture-proof layer contains a styrene-butadiene copolymer or the like and is heat-sealed. It had no sex. The water-removable moisture-proof paper described in Patent Document 2 does not contain a flat-plate inorganic compound in the moisture-proof layer, is inferior in moisture-proof property, and does not have heat-sealing property. Although the moisture-proof laminate described in Patent Document 3 contains a flat-plate inorganic compound in the moisture-proof layer, it mainly uses SBR latex as the synthetic resin and does not necessarily have heat-sealing property. Met.

The main use form of the moisture-proof wrapping paper is to attach the paper to a bag shape or a three-dimensional shape and enclose the article inside. In such a case, conventionally, in order to bond the wrapping papers together, it has been necessary to use an adhesive or to laminate a polyethylene film or the like on the wrapping papers in advance. However, such a method is not desirable from the viewpoint of reducing the manufacturing process and recycling pulp fibers. Therefore, it has been desired that the moisture-proof paper itself has a heat-sealing property.

The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a moisture-proof paper which can be recycled as pulp fiber and has excellent water vapor barrier property and heat-sealing property.

The present inventors have studied the composition of a moisture-proof paper that can solve the above problems, and found that the structure is such that a water vapor barrier layer is laminated on a paper base material, and the water vapor barrier layer contains a layered inorganic compound. It was found that an excellent water vapor barrier property can be imparted. Further, by adopting a specific type of ethylene-acrylic copolymer as the resin forming the water vapor barrier layer, it can function not only as a binder resin for the water vapor barrier layer but also as a thermosetting resin. I found. The present invention has been completed based on such findings. That is, the present invention has the following configuration.

(1) A moisture-proof paper having a water vapor barrier layer on at least one surface of a paper base material, wherein the water vapor barrier layer contains a layered inorganic compound and an ethylene-acrylic copolymer, and has an ethylene-acrylic copolymer weight. coalescence is less 50 mol% content of more than 1 mol% of acrylic monomer units, moisture permeability, moisture paper, characterized in that at ^{50g / (m 2 · 24h ·} atm) or less.

(2) The moisture-proof paper according to (1) above, wherein the layered inorganic compound has a thickness of 100 nm or less and an aspect ratio of 100 or more.
(3) The moisture-proof paper according to (1) or (2) above, wherein the water vapor barrier layer contains at least one of mica, bentonite, kaolin and talc as a layered inorganic compound.

(4) The moisture-proof paper according to any one of (1) to (3) above, wherein the content of the layered inorganic compound is 1% by mass or more and 80% by mass or less in the total solid content of the water vapor barrier layer.
(5) The ethylene-acrylic copolymer is an ethylene / acrylic acid copolymer, an ethylene / methacrylic acid copolymer, an ethylene / methyl acrylate copolymer, an ethylene / methyl methacrylate copolymer, or an ethylene / acrylic acid. Any one of (1) to (4) above, which is at least one of an ethyl copolymer, an ethylene / ethyl methacrylate copolymer, an ethylene / butyl acrylate copolymer, and an ethylene / butyl methacrylate copolymer. The moisture-proof paper according to item 1.

(6) The moisture-proof paper according to any one of (1) to (5) above, wherein the water vapor barrier layer contains a cationic resin.
(7) The moisture-proof paper according to (6) above, wherein the water vapor barrier layer contains at least one of polyamine, modified polyamide, modified polyamideamine, polyamide epichlorohydrin and polyethyleneimine as a cationic resin. ..

(8) The moisture-proof paper according to (6) or (7) above, wherein the surface charge of the cationic resin is 0.1 meq / g or more and 5 meq / g or less.
(9) The moisture-proof paper according to any one of (1) to (8) above, which is a packaging material.
(10) A packaging container using the moisture-proof paper according to any one of (1) to (8) above.

The moisture-proof paper of the present invention can be recycled as pulp fibers, and has excellent water vapor barrier properties and heat-sealing properties.

Hereinafter, embodiments of the present invention will be specifically described. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments.

The moisture-proof paper of the present embodiment has a water vapor barrier layer on at least one surface of the paper base material. The water vapor barrier layer may be provided on only one side of the paper base material, or the water vapor barrier layer may be provided on both sides of the paper base material.
Hereinafter, each layer constituting the moisture-proof paper of the present embodiment will be described.

[Paper base material]
The paper base material of the present embodiment contains wood pulp as a main component. Here, the main component of wood pulp means that wood pulp accounts for 50% by mass or more of the paper base material. The content ratio of wood pulp in the paper base material is preferably 50% by mass or more and 99.9% by mass or less, more preferably 70% by mass or more and 99.5% by mass or less, and 80% by mass or more and 99% by mass or less. The following is more preferable.

The wood pulp used for the paper base material is not particularly limited, and any wood pulp used for papermaking can be used. Examples of wood pulp include chemical pulps such as broad-leaved bleached kraft pulp (LBKP), coniferous bleached kraft pulp (NBKP), broad-leaved bleached sulphite pulp (LBSP), and coniferous bleached sulphite pulp (NBSP); stone ground pulp (GP). ), Pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemi-grand pulp (CGP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), etc. Mechanical pulp; sulfite pulp; waste paper pulp and the like can be mentioned. Considering the uniformity of the texture of the paper base material, it is preferable that the ratio of LBKP is large. For example, the mixing ratio of LBKP and NBKP, LBKP / NBKP, may be 75/25 to 100/0 (mass%). it can. In addition, synthetic fibers, non-wood fibers, and the like can be blended into wood pulp as needed.

The freeness of wood pulp (Canadian standard drainage degree) is preferably 150 ml or more and 500 ml or less, and more preferably 200 ml or more and 450 ml or less. When the freeness of wood pulp is within this range, it is easy to disintegrate and the pulp fiber is excellent in recyclability. Here, the freeness is a Canadian standard freeness measured in accordance with JIS P 811-2: 2012. As for the method of beating the pulp to adjust the freeness, a known method can be used.

If necessary, a filler may be appropriately added to the paper substrate. Examples of the filler include titanium dioxide, kaolin, talc, heavy calcium carbonate, light calcium carbonate, calcium sulfite, gypsum, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, and hydroxide. Examples thereof include aluminum, calcium hydroxide, magnesium hydroxide, zinc hydroxide and the like.

In addition to pulp and filler, paper base materials include sizing agents, paper strength enhancers, yield improvers, drainage improvers, pH adjusters, fabric softeners, antistatic agents, defoamers, dyes and pigments, etc. A known papermaking additive can be added as needed. Examples of the sizing agent include various sizing agents such as rosin type, alkyl ketene dimer type, alkenyl succinic anhydride type, styrene-acrylic type, higher fatty acid type, and petroleum resin type.

For paper-based paper making, a known wet paper machine, for example, a long net paper machine, a gap former type paper machine, a circular net type paper machine, a short net type paper machine, or the like should be appropriately selected and used. Can be done. Next, the paper layer formed by the paper machine is conveyed by felt and dried by a dryer. A multi-stage cylinder dryer may be used as a pre-dryer before drying the dryer.
Further, the paper base material obtained as described above may be surface-treated with a calendar to make the thickness and profile uniform. As the calendar processing, a known calendar processing machine can be appropriately selected and used.

The basis weight of the paper base material is preferably 30 g / m ² or more, more preferably 40 g / m ² or more, and preferably 200 g / m from the viewpoint of shape stability and suppressing the thickness of the moisture-proof paper as a whole. ^{It is 2} or less, more preferably 100 g / m ² or less.
From the same viewpoint, the thickness of the paper substrate is preferably 20 μm or more, more preferably 30 μm or more, and preferably 300 μm or less, more preferably 150 μm or less.
The basis weight of the paper substrate is measured according to JIS P 8124: 2011.
The thickness of the paper substrate is measured in accordance with JIS P 8118: 2014.

[Water vapor barrier layer]
The water vapor barrier layer is a layer having a function of blocking the permeation of water vapor, and is laminated on the surface of the paper base material. The water vapor barrier layer contains a layered inorganic compound and an ethylene-acrylic copolymer.

(Layered inorganic compound)
The form of the layered inorganic compound is flat. When a mixed solution of a layered inorganic compound and a binder is prepared and coated on a paper substrate, a water vapor barrier layer is formed. In the water vapor barrier layer, the flat layered inorganic compounds are arranged in a state of being laminated substantially parallel to the plane (surface) of the paper base material. Then, in the plane direction, the area where the layered inorganic compound does not exist becomes smaller, so that the permeation of water vapor is suppressed. In addition, since the flat layered inorganic compounds exist in parallel to the plane of the paper substrate in the thickness direction, the water vapor in the layer permeates while bypassing the layered inorganic compound, and the water vapor is caused by the maze effect. Permeation is suppressed. As a result, the water vapor barrier layer can exhibit excellent water vapor barrier properties.

The layered inorganic compound preferably has a thickness of 100 nm or less. The thickness of the layered inorganic compound is more preferably 50 nm or less, and further preferably 20 nm or less. When the average thickness of the layered inorganic compound is small, the number of laminated layered inorganic compounds in the water vapor barrier layer is large, so that high water vapor barrier property can be exhibited. Here, the thickness of the layered inorganic compound in the state of being contained in the water vapor barrier layer is obtained as follows. A magnified photograph of the cross section of the water vapor barrier layer is taken using an electron microscope. At this time, the magnification is such that about 20 to 30 layered inorganic compounds are contained in the screen. The thickness of each layered inorganic compound in the screen is measured. Then, the average value of the obtained thickness is calculated and used as the thickness of the layered inorganic compound.

The layered inorganic compound preferably has a length of 1 μm or more and 100 μm or less. When the length is 1 μm or more, the layered inorganic compounds are likely to be arranged parallel to the paper substrate. Further, when the length is 100 μm or less, there is little concern that a part of the layered inorganic compound protrudes from the water vapor barrier layer. Here, the length of the layered inorganic compound in the state of being contained in the water vapor barrier layer is obtained as follows. A magnified photograph of the cross section of the water vapor barrier layer is taken using an electron microscope. At this time, the magnification is such that about 20 to 30 layered inorganic compounds are contained in the screen. The length of each layered inorganic compound of the layered inorganic compound in the screen is measured. Then, the average value of the obtained lengths is calculated and used as the length of the layered inorganic compound. The length of the layered inorganic compound may be described by the expression of particle size.

The layered inorganic compound preferably has an aspect ratio of 100 or more. When the aspect ratio is 100 or more, it is possible to achieve a predetermined moisture permeability. The aspect ratio of the layered inorganic compound is more preferably 200 or more, further preferably 300 or more, and particularly preferably 500 or more. The larger the aspect ratio, the more the permeation of water vapor is suppressed and the water vapor barrier property is improved. Further, the larger the aspect ratio, the smaller the amount of the layered inorganic compound added. The upper limit of the aspect ratio is not particularly limited, and is preferably about 10,000 or less from the viewpoint of the viscosity of the coating liquid. Here, the aspect ratio is a value obtained by taking a magnified photograph of the cross section of the water vapor barrier layer using an electron microscope and dividing the average length of the obtained layered inorganic compound by the average thickness, as described above. Is.

Specific examples of layered inorganic compounds include mica such as mica and brittle mica, synthetic mica, bentonite, kaolinite (kaolin mineral), pyrophyllite, talc, smectite, vermiculite, chlorite, septe chlorite, and serpentine. , Stilp nomelene, montmorillonite, etc.
Among these, from the viewpoint of improving the barrier property, it is preferable to contain any one or more of mica, bentonite, kaolin and talc, and synthetic mica or bentonite is more preferable. Specific examples of mica include synthetic mica (for example, swelling synthetic mica), white mica (mascobite), silk mica (serisite), gold mica (frocopite), black mica (biotight), and fluorine gold mica (artificial Mica), red mica, soda mica, vanajin mica, illite, chin mica, paragonite, brittle mica, etc. Further, as a specific example of bentonite, montmorillonite can be mentioned.

The content of the layered inorganic compound is preferably 80% by mass or less, more preferably 50% by mass or less, further preferably 30% by mass or less, particularly preferably 20% by mass or less, and 10% by mass in the total solid content of the water vapor barrier layer. The following are the most preferable. On the other hand, the content of the layered inorganic compound is preferably 1% by mass or more, more preferably 2% by mass or more. By increasing the aspect ratio of the layered inorganic compound and reducing the thickness, the content of the layered inorganic compound can be reduced. In addition, the strength of the water vapor barrier layer can be increased to prevent the layered inorganic compound from falling off from the water vapor barrier layer.

(binder)
An ethylene-acrylic copolymer is used as the main component of the binder. Examples of the acrylic monomer constituting the ethylene-acrylic copolymer include (meth) acrylic acid and its alkyl ester.
The number of carbon atoms of the alkyl group in the ester portion of the (meth) acrylic acid alkyl ester is preferably 1 or more and 8 or less, more preferably 1 or more and 6 or less, and further preferably 1 or more and 4 or less.
Here, (meth) acrylic acid means methacrylic acid and acrylic acid.

The ethylene-acrylic copolymer is a copolymer obtained by emulsion polymerization of ethylene and the above acrylic monomer. As the acrylic monomer, acrylic acid and methacrylic acid are preferable, and acrylic acid is more preferable.
Examples of the ethylene-acrylic copolymer include an ethylene / acrylic acid copolymer, an ethylene / methacrylic acid copolymer, an ethylene / methyl acrylate copolymer, an ethylene / methyl methacrylate copolymer, and an ethylene / ethyl acrylate copolymer. It is preferable that any one or more of a coalescence, an ethylene / ethyl methacrylate copolymer, an ethylene / butyl acrylate copolymer and an ethylene / butyl methacrylate copolymer is used. The copolymer may be copolymerized with a small amount of a monomer composed of ethylene and other compounds copolymerizable with the acrylic monomer.
Among these, an ethylene / acrylic acid copolymer and an ethylene / methacrylic acid copolymer are more preferable, and an ethylene / acrylic acid copolymer is further preferable.

Specific examples of the ethylene-acrylic copolymer include, for example, an aqueous dispersion of an ammonium salt of an ethylene / acrylic acid copolymer, Zyxen (registered trademark) AC, etc. (copolymerization ratio of acrylic acid 20%, Sumitomo Seika Co., Ltd.) It is commercially available as (manufactured by) and can be easily obtained and used.

The ethylene-acrylic copolymer has an acrylic monomer unit content of 1 mol% or more and 50 mol% or less. When the content of the acrylic monomer unit is in this range, the melting temperature becomes 60 to 120 ° C., and an excellent ethylene-acrylic copolymer exhibiting good heat-sealing property is obtained. The content of the acrylic monomer unit in the ethylene-acrylic copolymer is more preferably 10 mol% or more and 30 mol% or less.

The binder in the water vapor barrier layer is preferably anionic. Since the binder is anionic, the water vapor barrier property is further improved. As described above, the flat portion of the layered inorganic compound is anionic, but when the cationic resin is adsorbed, the surface becomes cationic. Therefore, the affinity with the anionic binder is enhanced.

The weight average molecular weight of the ethylene-acrylic copolymer is preferably 10,000 or more and 10 million or less, and more preferably 100,000 or more and 5 million or less, from the viewpoint of the viscosity of the coating liquid and the strength of the coating film.

The content ratio of the ethylene-acrylic copolymer is not particularly limited, but is preferably 20% by mass or more, more preferably 40% by mass or more, still more preferably 60% by mass or more, and 70% by mass, based on the total solid content of the water vapor barrier layer. The above is particularly preferable, and 80% by mass or more is most preferable.

(Cationic resin)
The water vapor barrier layer preferably contains a cationic resin. By containing the cationic resin in the water vapor barrier layer, the water vapor barrier property is greatly improved. The reason for this is as follows.
(1) Since the flat portion of the flat plate-like form is easily charged anionic and the edge portion is easily charged cationically, the layered inorganic compound may have a so-called card house structure in which the layered inorganic compounds are three-dimensionally aggregated with each other. Are known. Due to this card house structure, the aqueous dispersion of layered inorganic compounds has a very high viscosity.
(2) On the other hand, since the card house structure is easily broken when a force is applied by stirring or the like, the aqueous dispersion of the layered inorganic compound exhibits thixotropy.
(3) When an appropriate cationic resin is added to the aqueous dispersion of the layered inorganic compound, the cationic resin is adsorbed on the anionic flat portion of the layered inorganic compound, and the card house structure is destroyed. As a result, the three-dimensional aggregation of the layered inorganic compound is suppressed, and the flat layered inorganic compound is easily laminated in parallel with the plane of the paper substrate, leading to improvement in the water vapor barrier property.

Specific examples of cationic resins include polyamines, modified polyamides, modified polyamideamines, polyamide epichlorohydrins, polyethyleneimines, polyalkylene polyamines, polyamide compounds, polyamideamine-epihalohydrins or formaldehyde condensation reaction products, polyamine-epihalohydrins or formaldehydes. Condensation reaction product, polyamide polyurea-epihalohydrin or formaldehyde condensation reaction product, polyamine polyurea-epihalohydrin or formaldehyde condensation reaction product, polyamideamine polyurea-epihalohydrin or formaldehyde condensation reaction product, polyamide polyurea compound, polyamine polyurea Examples thereof include compounds, polyamideamine polyurea compounds and polyamideamine compounds, polyvinylpyridines, amino-modified acrylamide compounds, polyvinylamines, and polydialyldimethylammonium chlorides. Among these, any one or more of polyamine, modified polyamide, modified polyamide amine, polyamide epichlorohydrin and polyethyleneimine is preferable.

The surface charge of the cationic resin is preferably 0.1 meq / g or more and 5 meq / g or less. When the surface charge of the cationic resin is within the above range, the card house structure can be destroyed, and the anionic binder described later can coexist appropriately. The surface charge of the cationic resin is measured by the method described below.

The polymer as a sample is dissolved in water to obtain a solution having a polymer concentration of 1 ppm. 0.001N sodium polyethylene sulfonate is added dropwise to the solution using a charge analyzer Mutek PCD-04 (manufactured by BTG), and the amount of charge is measured.

The content of the cationic resin in the water vapor barrier layer may be appropriately selected according to the type of the layered inorganic compound and the ethylene-acrylic copolymer used in the water vapor barrier layer, but from the viewpoint of improving the barrier property, it is layered. With respect to 100 parts by mass of the inorganic compound, 1 part by mass or more and 300 parts by mass or less is preferable, 3 parts by mass or more and 250 parts by mass or less is more preferable, and 10 parts by mass or more and 150 parts by mass or less is further preferable, and 20 parts by mass or more and 150 parts by mass or less. The amount is particularly preferably 20 parts by mass or more and 100 parts by mass or less.

The content of the cationic resin is preferably 0.1 part by mass or more and 20 parts by mass or less, and 0.3 parts by mass or more and 15 parts by mass with respect to 100 parts by mass of the ethylene-acrylic copolymer of the water vapor barrier layer. It is more preferably 1 part by mass or less, and further preferably 1 part by mass or more and 10 parts by mass or less.

In addition to the layered inorganic compound, ethylene / acrylic copolymer, and cationic resin, the water vapor barrier layer includes a resin component other than the ethylene / acrylic copolymer and the cationic resin, a dispersant, and a surfactant, as appropriate. It is possible to add antifoaming agents, wetting agents, dyes, color modifiers, thickeners and the like.

The thickness of the water vapor barrier layer is preferably 1 μm or more and 30 μm or less, and more preferably 3 μm or more and 20 μm or less. The coating amount of the water vapor barrier layer is preferably 1 g / m ² or more and 30 g / m ² or less, and more preferably 3 g / m ² or more and 20 g / m ² or less as a solid content.

[Moisture-proof paper]
The basis weight of the moisture-proof paper is not particularly limited, but is preferably 20 g / m ² or more and 400 g / m ² or less, and more preferably 30 g / m ² or less and 320 g / m ² or less.

Moistureproof paper, from the viewpoint of a packaging material having a water vapor barrier property, moisture permeability is at ^{50g / (m 2 · 24h ·} atm) or less, and preferably ^{30g / (m 2 · 24h ·} atm) or less. Moisture permeability can be measured according to JIS Z 0208.

The moisture-proof paper basically consists of a paper base material and a water vapor barrier layer, and the water vapor barrier layer can be finely dispersed by stirring in water. Therefore, the moisture-proof paper can recover the wood pulp in the paper base material as pulp fibers and recycle it by performing a disintegration operation in water.

(Manufacturing method of moisture-proof paper)
Moisture-proof paper can be produced by applying a coating liquid for forming a water vapor barrier layer on a paper base material to form a water vapor barrier layer.
The solvent of the coating liquid is not particularly limited, and water or an organic solvent such as ethanol, isopropyl alcohol, methyl ethyl ketone or toluene can be used.

The coating equipment for applying the coating liquid to the paper substrate is not particularly limited, and known equipment can be used. Examples of the coating equipment include a blade coater, a bar coater, an air knife coater, a slit die coater, a gravure coater, a micro gravure coater, and a gate roll coater. In particular, for forming the water vapor barrier layer, a coater that scrapes the coated surface, such as a blade coater, a bar coater, an air knife coater, and a slit die coater, is preferable in that it promotes the orientation of the layered inorganic compound.

The moisture-proof paper of the present embodiment can be suitably used as a packaging material for foods, medical products, electronic parts, etc. by taking advantage of the above-mentioned excellent water vapor barrier property. Since the moisture-proof paper of the present embodiment has heat-sealing properties, the moisture-proof paper is cut into a predetermined shape and then heat-sealed and joined at a predetermined location, whereby a predetermined number of steps is required. Packaging containers can be manufactured.

The moisture-proof paper of the present invention will be described in more detail with reference to examples below, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples indicate "parts by mass" and "% by mass", respectively.

The raw materials used in the examples and comparative examples are as follows.
(1) Paper base material Bleached kraft paper: Basis weight 60 g / m ² , thickness 80 μm
(2) Layered inorganic compound Mica: Swellable synthetic mica, particle size 6.3 μm, aspect ratio about 1000, thickness about 5 nm, solid content 7%, product name: NTO-05, muscovite manufactured by Topy Industries, Ltd .: product Name: AB32, manufactured by Yamaguchi Mica Industries, Ltd. (Yamaguchi Mica Co., Ltd.), particle size 20 μm, aspect ratio 20-30, thickness about 1,000 nm
Kaolin: Product name: Varisurf HX, manufactured by Imerys, particle size 10 μm, aspect ratio about 100, thickness about 100 nm
(3) Cationic resin Modified polyamide resin: Solid content 53%, Product name: SPI203 (50), manufactured by Taoka Chemical Co., Ltd., surface charge 0.4 meq / g
(4) Anionic binder Ethylene-acrylic copolymer: ethylene-acrylic acid copolymer aqueous dispersion, solid content 29.3%, product name: Zyxen AC, styrene-butadiene copolymer manufactured by Sumitomo Seika Co., Ltd. : Acid-modified SBR latex, solid content 47.3%, product name: LX407S12, styrene-butadiene copolymer manufactured by Nippon Zeon Co., Ltd .: acid-modified SBR latex, solid content 50.5%, product name: LX407BP-6, Made by Nippon Zeon Co., Ltd. (5) Laminated film Low-density polyethylene film: LLDPE film, T.I. U.S. X FCS, 30 μm thick, manufactured by Mitsui Chemicals Tohcello Co., Ltd.

(Example 1)
<Water vapor barrier layer coating liquid>
To 29.3 parts of an aqueous dispersion (swellable mica) of an inorganic layered compound, 100 parts of an ethylene-acrylic acid copolymer aqueous dispersion (Zyxene AC) was added with stirring. To this, 2.93 parts of a modified polyamide resin (SPI203 (50)) was added, and the mixture was stirred. Further, 0.35 part of a 25% aqueous ammonia solution was added and stirred. Further, diluted water was added to bring the solid content concentration to 25% to prepare a coating liquid for a water vapor barrier layer.

Using bleached kraft paper as the paper base material, the coating liquid for the steam barrier layer is coated with a Mayer bar so that the coating amount in terms of solid content is 12 g / m ^2, and then 120 in a hot air dryer. It was dried at ° C. for 1 minute to prepare a moisture-proof paper.

(Example 2)
A moisture-proof paper was produced in the same manner as in Example 1 except that the coating amount of the coating liquid for the water vapor barrier layer in terms of solid content was 6 g / m ² .

(Example 3)
A moisture-proof paper was produced in the same manner as in Example 1 except that the coating amount of the coating liquid for the water vapor barrier layer in terms of solid content was 20 g / m ² .

(Example 4)
A moisture-proof paper was prepared in the same manner as in Example 1 except that the amount of the inorganic layered compound was 30 parts of muscovite pigment with respect to 100 parts of the ethylene-acrylic acid copolymer aqueous dispersion.

(Example 5)
A moisture-proof paper was prepared in the same manner as in Example 1 except that the amount of the inorganic layered compound was 100 parts of the ethylene-acrylic acid copolymer aqueous dispersion and 100 parts of the kaolin pigment.

(Comparative Example 1)
As an aqueous dispersion, 90 parts of acid-modified SBR latex (LX407S12) and 10 parts of acid-modified SBR latex (LX407BP-6) were added, and a moisture-proof paper was applied in the same manner as in Example 1 except that the solid content concentration was 32%. Made.

(Comparative Example 2)
A moisture-proof paper was prepared in the same manner as in Example 1 except that the inorganic layered compound was not added.

(Comparative Example 3)
An LLDPE film was laminated on bleached kraft paper by dry laminating and applied.

[Evaluation methods]
The following performances were evaluated using the moisture-proof papers obtained in Examples and Comparative Examples.
(1) Moisture permeability (water vapor permeability)
Measurement was performed by JIS Z 0208 (cup method) B method (40 ° C. ± 0.5 ° C., relative humidity 90% ± 2%) with the water vapor barrier layer inside. As the criterion of the moisture permeability, if ^{50g / (m 2 · 24h ·} atm) or less, it is determined that there is utility as water vapor barrier layer.

(2) Heat-sealing property A set of moisture-proof paper is stacked so that the water vapor barrier layers face each other, and using a heat-sealing tester (TP-701-B, manufactured by Tester Sangyo Co., Ltd.), 130 ° C., 0.5 MPa, 30 Heat-sealed under the condition of seconds. The judgment was made as follows.
A: One set of moisture-proof paper was heat-sealed and strongly fused and could not be easily peeled off by hand. B: One set of moisture-proof paper was heat-sealed and fused, but easily peeled off by hand. C: 1 The set of moisture-proof paper was not heat-sealed and did not fuse

(3) Detachability Moisture-proof paper was cut into a size of 1 cm × 1 cm, and 8 g thereof was mixed with 500 ml of water (concentration 1.6%) in a household mixer and stirred for 2 minutes to prepare a pulp slurry. From this pulp slurry, a paper sheet was prepared by a hand-made laboratory machine. The obtained sheet was dried, and the presence or absence of undissociated substances (film pieces, fiber lumps, undissociated pieces, etc.) in the dried sheet was visually evaluated. The judgment was made as follows.
A: Undissolved material was not contained and a uniform sheet was formed. B: Undissolved material was contained but a sheet was formed. C: Undissolved material was contained and a uniform sheet was not formed.

Table 1 shows the evaluation results of the moisture-proof papers of Examples 1 to 5 and Comparative Examples 1 to 3.

As is clear from Table 1, the moisture-proof papers of Examples 1 to 5 were excellent in water vapor barrier property and heat seal property. On the other hand, the moisture-proof paper of Comparative Example 1 was inferior in heat-sealing property because it used a styrene-butadiene copolymer as a binder for the water vapor barrier layer. Further, the moisture-proof paper of Comparative Example 2 was inferior in water vapor barrier property because the water vapor barrier layer did not contain a layered inorganic compound. Further, the moisture-proof paper of Comparative Example 3 did not have a water vapor barrier layer and was laminated with a PE film, so that the dissociation property was poor.

Claims (10)

A moisture-proof paper having a water vapor barrier layer on at least one surface of a paper substrate.
The water vapor barrier layer contains a layered inorganic compound and an ethylene-acrylic copolymer, and contains
The ethylene-acrylic copolymer has an acrylic monomer unit content of 1 mol% or more and 50 mol% or less.
Proof paper, characterized in that moisture ^{permeability, 50g / (m 2 · 24h} · atm) or less. The moisture-proof paper according to claim 1, wherein the layered inorganic compound has a thickness of 100 nm or less and an aspect ratio of 100 or more. The moisture-proof paper according to claim 1 or 2, wherein the water vapor barrier layer contains at least one of mica, bentonite, kaolin and talc as a layered inorganic compound. The moisture-proof paper according to any one of claims 1 to 3, wherein the content of the layered inorganic compound is 1% by mass or more and 80% by mass or less in the total solid content of the water vapor barrier layer. The ethylene-acrylic copolymer is an ethylene / acrylic acid copolymer, an ethylene / methacrylic acid copolymer, an ethylene / methyl acrylate copolymer, an ethylene / methyl methacrylate copolymer, or an ethylene / ethyl acrylate copolymer. The invention according to any one of claims 1 to 4, wherein the coalescence, an ethylene / ethyl methacrylate copolymer, an ethylene / butyl acrylate copolymer, or an ethylene / butyl methacrylate copolymer is at least one. Moisture-proof paper. The moisture-proof paper according to any one of claims 1 to 5, wherein the water vapor barrier layer contains a cationic resin. The moisture-proof paper according to claim 6, wherein the water vapor barrier layer contains at least one of polyamine, modified polyamide, modified polyamide amine, polyamide epichlorohydrin and polyethyleneimine as a cationic resin. The moisture-proof paper according to claim 6 or 7, wherein the surface charge of the cationic resin is 0.1 meq / g or more and 5 meq / g or less. The moisture-proof paper according to any one of claims 1 to 8, which is a packaging material. A packaging container using the moisture-proof paper according to any one of claims 1 to 9.