Gas barrier paper

Abstract

To provide a gas barrier paper that can reduce used amount of plastics, causes less curls and wrinkles, has excellent post-processing suitability and oxygen barrier property.SOLUTION: A gas barrier paper includes a paper substrate, an under layer, and a gas barrier layer, and is characterized by that the under layer is included between the paper substrate and the gas barrier layer, the gas barrier layer includes octenylsuccinate esterified starch, the under layer includes heavy calcium carbonate and styrene-butadiene-based copolymer latex, and the heavy calcium carbonate is included in am amount of 20 mass% or over in the pigment in the under layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to gas barrier paper with reduced plastic content, and also to gas barrier paper with reduced curling and wrinkling, excellent oxygen barrier properties, and excellent suitability for post-processing. [Background technology]

[0002] In recent years, the problem of plastic waste has become more serious. Global plastic production is said to exceed 400 million tons per year, with a large amount of plastic produced in the packaging sector, causing plastic waste. Plastic does not decompose for a long time, and this waste breaks down into microplastics in the natural environment, causing serious damage to the ecosystem. Marine pollution is particularly severe, and it is said that the plastic waste is impossible to recover. Reducing the use of plastic in the future is necessary for the global environment.

[0003] Barrier performance, blocking oxygen, water vapor, water, and oil, is an important feature of packaging containers. Oxygen barrier properties are particularly essential for various food packaging containers to prevent food discoloration, bacterial growth, and odor transfer. To achieve oxygen barrier properties, packaging materials have traditionally been made of low-oxygen-permeable plastics, such as nylon (NY), polyethylene terephthalate (PET), and ethylene vinyl alcohol (EVOH). Most oxygen barrier films used in food packaging, such as paper, have a multilayer structure, consisting of at least three layers: a base layer, a gas barrier layer with oxygen barrier properties, and a heat-seal layer. Examples of multilayer structures include a three-layer structure of PET / EVOH / polyethylene (PE) for vacuum packaging and a four-layer structure of PET / aluminum foil / NY / polypropylene (PP) for retort food packaging. Because of their multilayer structure, these oxygen barrier films are difficult to thin. The amount of plastic used varies depending on the product concept, but is generally around 100 g / m². 2 or more, at least 50g / m 2(See Patent Documents 1 and 2.) There is also a demand for a reduction in the amount of plastic used in multilayer films such as oxygen barrier films.

[0004] One proposed measure to reduce the amount of plastic used is to replace plastic with paper. Patent Document 3 proposes providing a paper barrier packaging material with excellent gas and water vapor barrier properties by providing a water vapor barrier layer containing a pigment and a binder resin on a paper substrate, and a gas barrier layer containing polyvinyl alcohol on the water vapor barrier layer. In the case of such packaging materials, the polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA") used in the gas barrier layer has a high viscosity when dissolved. Therefore, when preparing a coating solution containing PVA during the manufacturing process, it is necessary to reduce the PVA content in the solution, i.e., to set the solids content of the solution low, in order to reduce the viscosity. However, when a gas barrier layer is formed using a coating solution with a low solids content, the pulp in the paper substrate shrinks significantly during the drying process, making the paper substrate prone to curling and wrinkling. This tends to reduce transportability, particularly during post-processing steps such as adding a heat seal layer, printing, bag making, and molding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-71036 [Patent Document 2] Patent No. 7373682 [Patent Document 3] Patent No. 6236329 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention relates to gas barrier paper that can reduce the amount of plastic used, has little curl or wrinkle, and has excellent oxygen barrier properties and is suitable for post-processing.

[0007] Other objects and advantages of the present invention will be readily apparent to those skilled in the art by reading the following description. [Means for solving the problem]

[0008] To improve the post-processing suitability of conventional gas barrier paper, the gas barrier paper of the present invention comprises a paper substrate, an underlayer, and a gas barrier layer, with the underlayer between the paper substrate and the gas barrier layer, and is characterized by the gas barrier layer containing octenyl succinate-esterified starch. The octenyl succinate-esterified starch contained in the gas barrier layer is a natural polysaccharide, which reduces the amount of plastic used compared to conventional gas barrier layers primarily made of plastics such as NY or PET. Furthermore, the low viscosity of the solution prevents curling and wrinkling of the paper substrate during the drying process without reducing the solids content of the gas barrier layer coating solution used in the manufacturing process. Furthermore, the inclusion of octenyl succinate-esterified starch in the gas barrier layer not only provides good oxygen barrier properties, but also improves the lightfastness of the gas barrier paper and reduces paper yellowing (hereinafter, the prevention of paper yellowing will sometimes be referred to as "lightfastness").

[0009] Furthermore, the present invention is characterized in that the under layer contains heavy calcium carbonate and a styrene-butadiene copolymer latex, with the heavy calcium carbonate accounting for 20% by mass or more of the pigment in the under layer. The inclusion of heavy calcium carbonate and a styrene-butadiene copolymer latex provides a sealing effect that prevents the gas barrier layer coating liquid from penetrating into the paper substrate, allowing a barrier film with few defects to be formed even with a small coating amount of resin coating layer. Furthermore, by including heavy calcium carbonate in an amount of 20% by mass or more of the pigment in the under layer, fine irregularities are created on the surface of the under layer and voids are created within the under layer. The gas barrier layer coating liquid penetrates into these irregularities and voids, thereby increasing the interlayer strength between the under layer and the gas barrier layer.

[0010] In the present invention, it is preferable that 90% by mass or more of the gas barrier layer is composed of starch octenyl succinate, which makes it possible to obtain gas barrier paper with even better oxygen barrier properties.

[0011] In the present invention, the coating amount of the gas barrier layer is 0.3 to 20 g / m in terms of dry coating amount. 2 By adopting such a configuration, it is possible to form a uniform barrier film and also to suppress curling and wrinkling.

[0012] In the present invention, it is preferable that the paper base material and the under layer do not contain organic pigments, which makes it possible to obtain gas barrier paper that reduces plastics and suppresses environmental pollution caused by microplastics.

[0013] In the present invention, it is preferable to have a heat seal layer on the outermost surface of at least one side. This configuration not only imparts heat sealability and enables application to a variety of uses, but also provides a gas barrier paper on the side on which the gas barrier layer is provided, which acts as a protective layer for the gas barrier layer, making it possible to obtain gas barrier paper whose oxygen barrier properties are more resistant to deterioration.

[0014] In the present invention, it is preferable that the outermost surface of at least one side of the gas barrier paper has a heat seal layer containing a polyolefin or an ionomer, which allows for the production of a gas barrier paper with better heat sealability. [Effects of the Invention]

[0015] The present invention makes it possible to produce gas barrier paper that can reduce the amount of plastic used, has less curling and wrinkling, has excellent interlayer strength, and has excellent oxygen barrier properties suitable for post-processing. 2 ·day·atm or less, preferably 25cc / m 2·day·atm or less. Furthermore, even if the gas barrier paper of the present invention is inappropriately disposed of as waste in nature, it can reduce the adverse impact of plastic waste on the natural environment, thereby helping to solve the plastic waste problem. The gas barrier paper of the present invention can be processed into a wide range of paper containers, including primary and secondary bags for food packaging, packaging bags for household goods and daily necessities, food cups for ice cream and other beverages, lids for cups and trays, beverage cups for coffee and other beverages, food containers and trays for hot snacks and other beverages, boxes, cases, containers, envelopes, and other paper containers. The gas barrier paper of the present invention can be inhibited from yellowing, and therefore has excellent decorative properties and storage stability as a packaging material. DETAILED DESCRIPTION OF THE INVENTION

[0016] Next, the present invention will be described in detail by showing an example of an embodiment, but the present invention is not limited to the description. The embodiment may be modified in various ways as long as the effects of the present invention are achieved.

[0017] The present invention relates to a gas barrier paper having a paper substrate, an underlayer, and a gas barrier layer in this order, and including at least three layers in the order paper substrate / underlayer / gas barrier layer. Specifically, the present invention relates to a gas barrier paper including a paper substrate, an underlayer, and a gas barrier layer, and the gas barrier paper includes an underlayer between the paper substrate and the gas barrier layer. The gas barrier layer includes octenyl succinate-esterified starch. The gas barrier layer is preferably composed of 90% to 100% by mass of octenyl succinate-esterified starch, and more preferably 95% to 100% by mass or 99.9% to 100% by mass of octenyl succinate-esterified starch. Furthermore, the gas barrier layer is preferably composed solely of octenyl succinate-esterified starch. Using a single material as much as possible facilitates the formation of a uniform barrier film, resulting in a gas barrier paper with superior oxygen barrier properties. Because starch absorbs moisture, in high-humidity environments, the gas barrier layer film that has absorbed moisture and gained fluidity may break down, resulting in a deterioration in oxygen barrier properties. However, octenyl succinate-esterified starch has a hydrophobic group introduced into the starch, making it excellent in water resistance and less susceptible to deterioration of the gas barrier layer film even in high-humidity conditions. Furthermore, because it has particularly excellent film-forming properties, it can achieve better oxygen barrier properties and excellent oil resistance. It can also achieve excellent light resistance. When starch or a starch derivative other than octenyl succinate-esterified starch is used in amounts greater than a certain level, oxygen barrier properties and light resistance deteriorate, and the surface of the gas barrier paper exposed to air for a long period of time may yellow, which may impair the aesthetic appeal of the paper when processed and used as a packaging bag or paper container.

[0018] Starch is composed of two types of components: amylose, in which glucose molecules are bonded in a linear chain, and amylopectin, in which glucose molecules are bonded in a branched chain. In this embodiment, the starch contained in the gas barrier layer preferably has an amylopectin content of 60% by mass or more. The amylopectin content of the starch is preferably 60% by mass to 100% by mass, or 70% by mass to 100% by mass, for example, preferably 60% by mass or more and less than 95% by mass, and more preferably 70% by mass or more and less than 90% by mass. By setting the amylopectin content in the starch within this range, better oxygen barrier properties can be obtained. If the amylopectin content is less than 60% by mass, the oxygen barrier properties will deteriorate. As raw materials for starch or starch derivatives, either grains such as corn, wheat, and rice, or potatoes such as tapioca, potato, and sweet potato may be used. Among these, tapioca starch is preferred because it has a high amylopectin content and provides superior oxygen barrier properties. Waxy corn or rice with a high amylopectin content may also be included. Specifically, the starch used in the gas barrier layer preferably includes octenyl succinate-esterified tapioca starch, octenyl succinate-esterified corn starch, octenyl succinate-esterified rice starch, or the like. The starch used in the gas barrier layer may be a mixture of multiple starches, provided that the intended effects of the present invention are not impaired. The amylopectin content of the starch or starch derivative contained in the gas barrier layer can generally be determined using known methods for measuring the amylose or amylopectin content in starch, such as iodine colorimetry, amperometric titration, voltammetry, and enzyme chromatography. The amylopectin content may be measured after isolating amylopectin from the starch or starch derivative, or the apparent content without isolating it.

[0019] In an embodiment of the present invention, a gas barrier layer can be provided by coating at least one surface of a paper substrate with a coating liquid for a gas barrier layer containing octenyl succinate-esterified starch and drying the coating liquid. The octenyl succinate-esterified starch powder used in the coating liquid for a gas barrier layer is preferably added after dissolving it in hot water. The coating liquid for a gas barrier layer may contain an alcohol having a boiling point equal to or lower than that of water as a leveling agent. Unlike surfactant-based leveling agents that remain in the gas barrier layer after drying, alcohols with a boiling point equal to or lower than that of water volatilize during the drying process and are no longer contained in the gas barrier layer after drying, thereby providing a leveling effect and preventing deterioration of the oxygen barrier property. Gas barrier paper preferably has a gas barrier layer on one side of the paper substrate, but can also have gas barrier layers on both sides.

[0020] In an embodiment of the present invention, the coating amount of the gas barrier layer is 0.3 to 20 g / m2 in terms of dry coating amount per one side of the paper substrate. 2 Preferably, the density is 1 to 10 g / m 2 , e.g., 2 to 8 g / m 2 0.3g / m 2 If the coating density is less than 20 g / m, the coating solution for the gas barrier layer will not be able to form a uniform barrier film. If a uniform barrier film cannot be formed, for example, pinholes may be formed due to liquid absorption, and a large amount of oxygen will pass through the pinholes, resulting in a deterioration of the oxygen barrier properties. 2 If the temperature exceeds this range, sufficient oxygen barrier properties will be obtained, but the wet coating weight of the gas barrier layer coating solution will increase, causing the pulp to shrink more during the drying process, making the gas barrier paper more susceptible to curling and wrinkling.

[0021] In an embodiment of the present invention, the gas barrier layer may be formed of two or more layers. By using two or more gas barrier layers, even if a pinhole occurs in one layer, the pinhole can be filled by the second layer, preventing deterioration of oxygen barrier properties. The gas barrier layer may preferably be one to four layers, for example, two to three layers, and more preferably two layers. In particular, when a paper substrate with high liquid absorption is used, pinholes are likely to occur, and it is particularly effective to use two or more gas barrier layers. Even when the gas barrier layer has two or more layers, the total coating amount of the gas barrier layer is 0.3 to 20 g / m2 in terms of solid content. 2 It is preferable that the density is 1 to 10 g / m 2 It is more preferable if the gas barrier layer is composed of two or more layers. When the gas barrier layer has two or more layers, at least one gas barrier layer must contain octenyl succinate starch, but the other gas barrier layers may be any layers that function as gas barrier layers. For example, the gas barrier layers may contain or consist of polyvinyl alcohol. Furthermore, it is preferable that 90% by mass or more of the other gas barrier layers are composed of octenyl succinate starch or consist solely of octenyl succinate starch. It is also preferable that all gas barrier layers contain octenyl succinate starch, and it is even more preferable that 90% by mass or more of the gas barrier layers are composed of octenyl succinate starch or consist solely of octenyl succinate starch.

[0022] In an embodiment of the present invention, the gas barrier layer preferably consists solely of octenyl succinate-esterified starch, but various auxiliary agents may be added to the coating solution for the gas barrier layer in addition to octenyl succinate-esterified starch, as long as the intended effects of the present invention are not impaired. Examples include viscosity modifiers, antifoaming agents, leveling agents such as surfactants and alcohols, crosslinking agents, coloring pigments, coloring dyes, lubricants such as wax, pigments such as clay and calcium carbonate, water-soluble polymers such as PVA and carboxymethyl cellulose, urethanes, polyvinylidene chloride, styrene-butadiene copolymer latexes, acrylic resins, polyester resins, and polyamide resins. Furthermore, auxiliary agents other than those mentioned above may also be added as long as the intended effects of the present invention are not impaired.

[0023] In the present invention, the method for applying the coating liquid for the gas barrier layer is not particularly limited, and any commonly used coating device can be used, such as an air knife coater, blade coater, gravure coater, flexo coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray coater, gate roll coater, or lip coater.

[0024] This embodiment is characterized by including an under layer between the paper substrate and the gas barrier layer. The provision of the under layer between the paper substrate and the gas barrier layer provides a sealing effect that prevents the gas barrier layer coating solution from penetrating into the paper substrate, making it easier to form a barrier film with fewer defects even with a small coating weight of resin coating layer, resulting in gas barrier paper with better oxygen barrier properties. The under layer is preferably composed of a combination of a pigment and a binder. The pigment and binder in the under layer can be any known pigment and binder used in the coating layer of general coated printing paper.

[0025] This embodiment is characterized in that 20% by mass or more of the pigment contained in the under layer is heavy calcium carbonate. Preferably, 50% to 100% by mass, and even more preferably 50% to 95% by mass of the pigment can be heavy calcium carbonate. For example, 55% to 75% by mass or 70% to 90% by mass of the pigment can be heavy calcium carbonate. Heavy calcium carbonate has a large particle size and an irregular shape, which creates fine irregularities on the surface of the under layer and voids within the under layer. The coating liquid for the gas barrier layer penetrates into these irregularities and voids, thereby strengthening the interlayer strength between the under layer and the gas barrier layer. If the proportion of pigments with a flat shape, such as clay, or small particle size and uniform shape, such as light calcium carbonate, increases and the proportion of heavy calcium carbonate falls below 20% by mass, it is difficult for irregularities and voids to form on the surface or inside of the under layer, which may result in insufficient interlayer strength. Examples of pigments used in the under layer include inorganic pigments such as heavy calcium carbonate, light calcium carbonate, kaolin clay, calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide (titanium oxide), zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, magnesium hydroxide, and silicon dioxide. For example, examples of pigment compositions in the under layer include compositions containing 70% to 90% by weight of heavy calcium carbonate and 10% to 30% by weight of titanium oxide, or compositions containing 55% to 75% by weight of heavy calcium carbonate and 25% to 45% by weight of clay, based on 100 parts by weight of pigment. It is preferable that the pigment in the under layer does not contain an organic pigment. Since the purpose is to reduce the amount of plastic used, the use of organic pigments containing plastic is undesirable. Examples of organic pigments include polyolefin-based, acrylic-based, styrene-based, and copolymer-based particles thereof. The shape of the organic pigment may be solid, core / shell, hollow, foamed, etc., and refers to all shapes of organic pigments. The under layer may be provided in multiple layers as long as the intended effect of the present invention is not impaired. When multiple layers are provided, the pigment contained in all the under layers is characterized in that 20% by mass or more of the total pigment is heavy calcium carbonate.

[0026] This embodiment is characterized in that the binder in the under layer contains a styrene-butadiene copolymer latex. For example, the under layer may contain 5 to 200 parts by mass, e.g., 8 to 100 parts by mass, or 5 to 80 parts by mass, of the binder per 100 parts by mass of the pigment. The under layer preferably contains 3 to 60 parts by mass of the styrene-butadiene copolymer latex. The content of the styrene-butadiene copolymer latex in the under layer binder is preferably 20% to 100% by mass, more preferably 25% to 90% by mass. The inclusion of the styrene-butadiene copolymer latex enables the under layer pigment containing heavy calcium carbonate to be bound to the paper substrate surface, thereby enhancing interlayer strength between the paper substrate and the under layer. Additionally, the oxygen permeability of the gas barrier paper is reduced, improving gas barrier properties. Furthermore, the use of the styrene-butadiene copolymer latex can impart appropriate water resistance to the under layer.

[0033] Suitable water resistance of the under layer makes it less likely that the sealing effect will be reduced during the process of applying the coating liquid for the gas barrier layer. Examples of binders that can be used in the under layer include starches such as styrene-butadiene copolymer latex, crosslinking agent-modified starch, oxidized starch, enzyme-modified starch, esterified starch, etherified starch, cationic starch, and amphoteric starch, water-soluble polymers such as gelatin, casein, soybean protein, and polyvinyl alcohol, and synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, polyamide resins, polyvinylidene chloride resins, and polylactic acid resins. For example, examples of the binder contained in the under layer include a composition containing 10 to 30 parts by mass of styrene-acrylic emulsion and 35 to 55 parts by mass of styrene-butadiene copolymer latex relative to 100 parts by mass of pigment, or a composition containing 2 to 10 parts by mass of oxidized starch and 2 to 10 parts by mass of styrene-butadiene copolymer latex.

[0027] In this embodiment, the under layer preferably comprises 90% by mass or more, for example, 95% to 100% by mass, of the pigment and binder. Furthermore, the under layer may contain various auxiliaries, such as viscosity adjusters, softeners, gloss-imparting agents, water-resistant agents, dispersants, flow modifiers, UV absorbers, stabilizers, antistatic agents, crosslinkers, sizing agents, fluorescent brighteners, colorants, pH adjusters, antifoaming agents, plasticizers, and preservatives, within the scope of the intended effects of the present invention. Specific examples of the under layer include a pigment containing 65 to 95 parts by weight of heavy calcium carbonate and 5 to 35 parts by weight of titanium oxide, and a binder containing 10 to 70 parts by weight of styrene acrylic and 1 to 50 parts by weight of styrene-butadiene copolymer latex per 100 parts by weight of pigment, or a pigment containing 50 to 80 parts by weight of heavy calcium carbonate and 20 to 50 parts by weight of clay, and a binder containing 1 to 10 parts by weight of oxidized starch and 1 to 10 parts by weight of styrene-butadiene copolymer latex per 100 parts by weight of pigment. Furthermore, the under layer may further contain, for example, 0.1 to 5 parts by weight, preferably 0.1 to 0.5 parts by weight, of various auxiliaries, such as dispersants, per 100 parts by weight of pigment.

[0028] In embodiments of the present invention, any layer other than the paper substrate, underlayer, and gas barrier layer may be provided, provided that the intended effects of the present invention are not impaired. Examples include a heat seal layer and a printed layer containing a pigment and a binder. These additional layers are preferably provided on at least one side of the paper substrate, but can also be provided on both sides if necessary. In embodiments of the present invention, the gas barrier paper must include an underlayer and a gas barrier layer, in this order, on at least one side of the paper substrate. The gas barrier paper has at least a layer structure of paper substrate / underlayer / gas barrier layer. Alternatively, the gas barrier paper may have two gas barrier layers, such as a layer structure of paper substrate / underlayer / gas barrier layer / gas barrier layer. Furthermore, a heat seal layer can be added in addition to the gas barrier layer. In this case, the gas barrier paper may have a layer structure of, for example, paper substrate / underlayer / gas barrier layer / heat seal layer. Such gas barrier paper can be processed into a variety of paper containers, including primary and secondary bags for food packaging, packaging bags for household goods and daily necessities, food cups for ice cream and other beverages, lids for cups and trays, beverage cups for coffee and other beverages, food containers and trays for hot snacks and other beverages, boxes, cases, containers, envelopes, and other paper containers. When used for food packaging, the paper substrate side is preferably on the outside, and when used as a packaging bag, for example, the paper substrate side is preferably on the outside and the gas barrier layer side is preferably on the inside. Furthermore, the gas barrier layer may be provided on both sides, and it is sufficient to include at least one structure including an underlayer between the paper substrate and the gas barrier layer. Layer structures such as gas barrier layer / paper substrate / underlayer / gas barrier layer or gas barrier layer / underlayer / paper substrate / underlayer / gas barrier layer are also possible. Furthermore, it is common, and preferred, for each layer to completely cover the underlying layer, such as the paper substrate.

[0029] In this embodiment, a heat seal layer may be provided. The heat seal layer is preferably provided on the outermost surface of at least one side. This allows the gas barrier paper to be heat-sealed. Furthermore, by providing a heat seal layer on the side on which the gas barrier layer is provided, it acts as a protective layer for the gas barrier layer, making it less susceptible to deterioration of the oxygen barrier properties.

[0030] In an embodiment of the present invention, the resin in the heat seal layer is not particularly limited, but polyolefin, ionomer, acrylic resin, styrene resin, etc. can be used. As long as it does not affect the oxygen barrier property or post-processing suitability, any resin other than those listed above may be included, and multiple resins may be mixed. Polyolefin or ionomer is preferred, and polyolefin is more preferred. This is because it provides superior heat sealability and good water resistance, thereby providing superior protection for the gas barrier layer. Polyolefin refers to all resins having a polyethylene or propylene skeleton, including copolymers with acrylic acid or methacrylic acid. Preferred polyolefins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), medium-density polyethylene (MDPE), metallocene polyethylene, biaxially oriented polypropylene (OPP), unoriented polypropylene (CPP), ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer, and ethylene-vinyl acetate copolymer. These have superior heat-sealing properties. Ionomers are synthetic resins formed by utilizing the cohesive force of metal ions to form polymer aggregates, and include all aggregates formed by intermolecular bonding between resin and metal cations. Examples include metal salts of ethylene-methacrylic acid copolymer, metal salts of ethylene-acrylic acid copolymer, metal salts of ethylene-urethane copolymer, and metal salts of ethylene-fluorinated polymer copolymer. In the present invention, among the ionomers, metal salts of ethylene-acrylic acid or ethylene-methacrylic acid copolymers are preferred because they can impart better water resistance and heat sealability.

[0031] In an embodiment of the present invention, a heat-seal layer can be provided by applying a coating liquid for the heat-seal layer to at least one surface of a paper substrate and drying it. The resin used for the heat-seal layer is preferably an aqueous emulsion. The heat-seal layer preferably contains a resin derived from an aqueous emulsion, and the heat-seal layer preferably contains 90% to 100% by mass, for example, 95% to 100% by mass, or 99% to 100% by mass, of the resin derived from an aqueous emulsion. Furthermore, the heat-seal layer is preferably made of a resin derived from an aqueous emulsion. Using these resins allows the coating weight to be controlled relatively low, further reducing VOC emissions and further mitigating the burden on the natural environment.

[0032] In an embodiment of the present invention, the heat-seal layer coating solution may contain various auxiliary agents in addition to the aqueous emulsion, provided that the intended effects of the present invention are not impaired. Examples include viscosity modifiers, antifoaming agents, leveling agents such as surfactants and alcohols, lubricants such as color pigments, color dyes, and waxes, pigments such as clay and calcium carbonate, and binders such as polyvinyl alcohol and starch. However, since the addition of these auxiliary agents tends to reduce heat-seal strength, it is preferable to add them in small amounts. The heat-seal layer coating solution preferably contains 90% to 100% by weight, e.g., 95% to 100% by weight, or 99% to 100% by weight, of the aqueous emulsion. It is even more preferable that the heat-seal layer coating solution consists solely of the aqueous emulsion. Other auxiliary agents may also be added, provided that the intended effects of the present invention are not impaired.

[0033] The method for applying the heat seal layer coating liquid in the present invention is not particularly limited, and any commonly used coating device can be used, such as an air knife coater, blade coater, gravure coater, flexo coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray coater, gate roll coater, or lip coater.

[0034] In an embodiment of the present invention, a heat seal layer can be provided on at least one surface of the paper substrate by lamination. The lamination method is not particularly limited, and known methods such as extrusion lamination, dry lamination, wet lamination, hot melt lamination, and thermal lamination can be used.

[0035] In an embodiment of the present invention, in addition to the resin for the heat seal layer, various additives may be added to the heat seal layer formed by lamination processing, as long as they do not impair the intended effects of the present invention. For example, plasticizers, antistatic agents, antioxidants, lubricants, antiblocking agents, UV absorbers, crosslinking agents, curing agents, surfactants, flame retardants, fillers, etc. Depending on the lamination method, adhesives or anchoring agents may be coated before lamination, and surface treatments such as corona treatment, plasma treatment, ozone treatment, and primer treatment may be performed in advance. Note that additives and treatment steps other than those described above may also be included, as long as they do not impair the intended effects of the present invention.

[0036] In an embodiment of the present invention, the thickness of the heat seal layer is preferably 2 to 50 μm. More preferably, it is 3 to 30 μm, for example, 5 to 25 μm. By setting the thickness of the heat seal layer within this range, sufficient heat sealability can be obtained. Furthermore, by providing a heat seal layer on the side on which the gas barrier layer is provided, it serves as a protective layer for the gas barrier layer, and is expected to have the effect of preventing deterioration of the oxygen barrier property. The heat seal layer may be provided on one or both sides of the paper substrate. In the case of both sides, the total thickness is preferably 2 to 50 μm. In the gas barrier paper of the present invention, the resin coating layer may be provided only on a portion of the surface of the paper substrate, or may be provided on the entire surface. That is, the heat seal layer may be provided only in the area necessary for heat sealing, such as in a net-like, island-like, or linear pattern, or it may be provided so as to cover the entire surface of the paper substrate. The heat seal layer may also have a multi-layer structure. Having two or more heat seal layers can prevent pinholes from occurring in the heat seal layer, thereby imparting good water resistance and oil resistance.

[0037] In an embodiment of the present invention, a printed layer may be provided on the outermost surface of the paper substrate. When gas barrier paper is processed into bags or paper cups, the outer surface of the container may be printed with information about the contents or advertising, and providing a printed layer can provide good printability. It is also possible to print on the printed layer and then provide a heat seal layer on top of that. The composition of the printed layer is not particularly limited, and can include the pigments, binders, and various auxiliaries listed for the underlayer above. The composition of the printed layer can be the same as that of the underlayer, or the type and ratio of chemicals can be adjusted to suit the required performance. It can also be configured similarly to the coating layer of known coated printing paper.

[0038]

[0023] In an embodiment of the present invention, the method for smoothing the paper substrate or the under layer may be included. The method for smoothing the paper substrate is not particularly limited, and a commonly used calendering device can be used. For example, various known smoothing devices such as a machine calender, a soft calender, a super calender, a gloss calender, or a shoe nip calender can be used. Furthermore, the method may include a step of smoothing by transferring the mirror surface of a Yankee dryer, as used for one-side gloss kraft paper. By applying the under layer or gas barrier layer to the smoothed surface, the coating liquid for the gas barrier layer can be more easily applied uniformly to the surface of the under layer, a high sealing effect can be achieved, and a gas barrier paper with good oxygen barrier properties can be obtained.

[0039] The paper substrate used in the embodiments of the present invention is not particularly limited, and any known base paper containing pulp as a primary component can be used. Pulp as a primary component of the base paper can be chemical pulp such as LBKP (bleached hardwood kraft pulp) or NBKP (bleached softwood kraft pulp), mechanical pulp such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemi-mechanical pulp), or CGP (chemi-ground pulp), wood pulp such as DIP (deinked pulp), or non-wood pulp such as kenaf, bagasse, bamboo, or cotton. These can be used alone or in any combination. For example, 50 to 100 parts by mass of LBKP (bleached hardwood kraft pulp) can be used as the pulp, e.g., 50 to 70 parts by mass, 90 to 100 parts by mass, based on the pulp. Furthermore, to reduce plastic use, it is preferable to avoid synthetic fibers containing plastics such as polyester and polyolefin. From the perspective of environmental conservation, ECF (elemental chlorine-free) pulp, TCF (total chlorine-free) pulp, recycled paper pulp, and pulp obtained from planted trees are preferred. For example, the appropriate beating degree of pulp is 200 to 800 ml CSF, preferably 250 to 750 ml CSF, or even 300 to 700 ml CSF in Canadian Standard Freeness (JIS P 8121:1995 "Test Method for Pulp Freeness") As a specific example, pulp containing 50 to 70 parts by mass of bleached hardwood kraft pulp with a Canadian standard freeness (freeness) of 250 to 450 mlcsf and 30 to 50 parts by mass of bleached softwood kraft pulp with a Canadian standard freeness (freeness) of 450 to 700 mlcsf may be used.

[0040] In an embodiment of the present invention, it is preferable that the paper base material does not contain a filler. Examples of fillers include heavy calcium carbonate, light calcium carbonate, kaolin clay, calcined clay, talc, titanium dioxide, aluminum hydroxide, and organic pigments. The inclusion of a filler in the paper base material inhibits the interfiber bonding of the pulp, reducing the paper strength of the paper base material and making the paper base material more susceptible to cracking during post-processing, particularly when the gas barrier paper is folded in bag-making and molding processes. Following the cracking of the paper base material, cracks are also more likely to occur in the gas barrier layer, which may result in a deterioration in the oxygen barrier property after folding. However, the above fillers may be contained within a range that does not impair the intended effects of the present invention.

[0041] In addition to pulp, the paper base material may contain various known papermaking additives. Examples of papermaking additives include internal paper strength enhancers such as sizing agents, bulking agents, retention aids, drainage aids, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, and pitch control agents. Water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide may also be applied. If the paper base material contains a wet strength enhancer, the recyclability of the gas barrier paper will be poor, so it is preferable that the paper base material does not contain a wet strength agent. Papermaking additives may be incorporated into the pulp slurry, or impregnated into the paper base material using a size press or gate roll after papermaking. Polyacrylamide and oxidized starch are preferably used as paper strength agents. The increased paper strength of the paper base material allows for the production of gas barrier paper that is easy to transport and less prone to tearing in post-processing processes. Specific examples of additives include polyacrylamide (e.g., cationic polyacrylamide) and / or sizing agents (e.g., neutral rosin size), preferably 0.1 to 1.0 parts by mass of polyacrylamide and / or 0.1 to 1.0 parts by mass of sizing agent per 100 parts by mass of pulp. Oxidized starch may also be included in the paper base as a paper strength agent, for example, 2 to 8 parts by mass of oxidized starch per 100 parts by mass of pulp.

[0042] The method for making the paper base material is not particularly limited, and the paper base material can be produced using various paper machines such as a Fourdrinier paper machine, a multi-layer Fourdrinier paper machine, a cylinder paper machine, a multi-layer cylinder paper machine, a multi-layer Fourdrinier cylinder combination paper machine, a twin-wire paper machine, etc. In the present invention, the paper base material may be made of a single layer or a multi-layer paper machine.

[0043] In the embodiment of the present invention, the basis weight of the gas barrier paper is not particularly limited, but is, for example, 10 to 1000 g / m 2 The basis weight of gas barrier paper that can be used for flexible packaging is 30 to 500 g / m 2 is preferable, and 30 to 350 g / m 2 It is more preferable that the thickness is, for example, 40 to 200 g / m 2 That's fine. [Example]

[0044] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Furthermore, "parts" and "%" in the examples represent "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of added parts is a value calculated on a solid content basis.

[0045] Example 1 (Preparation of paper substrate) A paper stock was prepared by adding water to 65 parts of bleached hardwood kraft pulp with a Canadian standard freeness (freeness) of 350 mlcsf, 35 parts of bleached softwood kraft pulp with a Canadian standard freeness (freeness) of 600 mlcsf, 0.3 parts of cationic polyacrylamide (trade name: Polystron 705, manufactured by Arakawa Chemical Industries, Ltd.), and 0.2 parts of neutral rosin size (trade name: CC167, manufactured by Seiko PMC Co., Ltd.). The paper stock was then pulverized using a fourdrinier multi-cylinder paper machine to a basis weight of 38 g / m. 2 A base paper having the above formula was prepared, and oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was added as a paper strength agent using a pond-type size press to a dry impregnation amount of 2 g / m 2 The paper is then impregnated and dried, and smoothed with a calendar to a basis weight of 40 g / m. 2 A paper substrate having the following composition was obtained.

[0046] (Preparation of Coating Solution A for Under Layer) A pigment slurry was prepared by adding 20 parts of titanium dioxide (product name: CR-85, Ishihara Sangyo Kaisha) and 80 parts of heavy calcium carbonate (product name: Carbilux, Imerys Co., Ltd.) to 0.2 parts of a dispersant (product name: Aron T-50, Toa Gosei Co., Ltd.), adding water, and dispersing using a Coles disperser. To this pigment slurry, 20 parts of a styrene-acrylic emulsion (product name: Saibinol EK-81, Saiden Chemical Co., Ltd.) and 40 parts of a styrene-butadiene copolymer latex (product name: P-6X20, Nippon A&L Co., Ltd.) were added as binders, and further water was added to disperse the mixture to prepare Coating Solution A for the underlayer with a solids concentration of 40%.

[0047] (Preparation of paper substrate with underlayer) On one side of the paper substrate, the underlayer coating solution A is applied at a dry coating weight of 15 g / m 2 The coating was carried out using an air knife coater so that the basis weight was 55 g / m. 2 A paper substrate with an underlayer was prepared.

[0048] (Production of gas barrier paper) A solution of octenyl succinate esterified tapioca starch (trade name: FILMKOTE 370, manufactured by Ingredion, amylopectin content 83%) dissolved in hot water was applied to the under layer surface of the paper base material with an under layer obtained above in a dry coating amount of 1.5 g / m 2 The first gas barrier layer was formed by coating with an air knife coater so that the coating thickness was 1.5 g / m², and then dried to form a first gas barrier layer. Next, a solution of octenyl succinate-esterified tapioca starch (product name: FILMKOTE 370, manufactured by Ingredion) dissolved in hot water was applied to the first gas barrier layer in a dry coating amount of 1.5 g / m². 2 The coating was applied using an air knife coater so that the total weight of the two layers was 3.0 g / m. 2 A gas barrier layer of 58 g / m is provided. 2 We produced gas barrier paper of the above formula.

[0049] (Preparation of gas barrier paper with heat seal layer) A low-density polyethylene (trade name: Petrothene (registered trademark) 204, manufactured by Tosoh Corporation) was laminated to a thickness of 20 μm on the gas barrier layer surface of the gas barrier paper obtained above to form a heat seal layer, thereby producing gas barrier paper with a heat seal layer.

[0050] Example 2 In Example 1, the coating weight of the first gas barrier layer was 3.0 g / m 2 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the second gas barrier layer was not provided.

[0051] Example 3 In Example 1, the coating weight of the first gas barrier layer was 3.0 g / m 2 The coating weight of the second gas barrier layer was 2.0 g / m 2 The total weight of the two layers was changed to 5.0g / m 2 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the gas barrier layer was provided.

[0052] Example 4 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the second gas barrier layer was not provided.

[0053] Example 5 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the starch in the gas barrier layer was changed to octenyl succinic acid esterified corn starch (trade name: NATIONAL 912, manufactured by Ingredion, amylopectin content 100%).

[0054] Example 6 (Preparation of Coating Solution B for Under Layer) A pigment slurry was prepared by adding 0.2 parts of a dispersant (Aron T-50, Toa Gosei Co., Ltd.) to 35 parts of clay (HYDRAGLOSS 90, KaMin) and 65 parts of heavy calcium carbonate (Carbilux, Imerys), adding water, and dispersing using a Coles disperser. To this pigment slurry, 5 parts of oxidized starch (SK-20, Japan Cornstarch Co., Ltd.) and 5 parts of a styrene-butadiene copolymer latex (P-6X20, Nippon A&L Co., Ltd.) were added as binders, and further water was added for dispersion to prepare Coating Solution B for the underlayer with a solids concentration of 65%.

[0055] A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the under layer coating liquid in Example 1 was changed to under layer coating liquid B.

[0056] Example 7 In Example 1, the basis weight of the base paper was 178 g / m 2 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except for changing the above.

[0057] Example 8 (Production of gas barrier paper with underlayer) The underlayer coating solution A used in Example 1 was applied to the gas barrier layer surface of the gas barrier paper obtained in Example 1 in a dry coating amount of 5 g / m 2 The mixture was coated using an air knife coater so that the thickness became 100% and then dried to prepare gas barrier paper with an underlayer.

[0058] (Preparation of gas barrier paper with heat seal layer) A water-based ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc., composition: metal salt of ethylene-methacrylic acid copolymer) was applied to the underlayer surface of the gas barrier paper with an underlayer coating weight of 5.0 g / m2 on a dry basis. 2 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the coating was applied using an air knife coater so that the thickness became 100 μm and then dried to provide a heat seal layer.

[0059] Example 9 A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the resin of the second gas barrier layer was changed to polyvinyl alcohol (product name: Kuraray Poval 28-98, manufactured by Kuraray Co., Ltd.).

[0060] Example 10 A gas barrier paper was produced in the same manner as in Example 1, except that no heat seal layer was provided on the gas barrier paper.

[0061] (Comparative Example 1) A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the gas barrier layer was not provided.

[0062] (Comparative Example 2) A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the starch in the gas barrier layer was changed to tapioca starch (product name: BONDSTAR T 800, manufactured by Ingredion).

[0063] (Comparative Example 3) A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that no under layer was provided on the paper substrate.

[0064] Comparative Example 4 (Preparation of Coating Solution C for Under Layer) A pigment slurry was prepared by adding 0.2 parts of a dispersant (Aron T-50, Toa Gosei Co., Ltd.) to 85 parts of clay (product name: HYDRAGLOSS 90, manufactured by KaMin) and 15 parts of heavy calcium carbonate (product name: Carbilux, manufactured by Imerys), adding water, and dispersing using a Coles disperser. To this pigment slurry, 10 parts of oxidized starch (product name: SK-20, manufactured by Nippon Cornstarch Co., Ltd.) was added as a binder, and further water was added for dispersion to prepare underlayer coating solution C with a solids concentration of 40%.

[0065] A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the under layer coating liquid in Example 1 was changed to under layer coating liquid C.

[0066] (Comparative Example 5) A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the resin of the gas barrier layer was changed to polyvinyl alcohol (trade name: Kuraray Poval 28-98, manufactured by Kuraray Co., Ltd.).

[0067] (Comparative Example 6) A gas barrier paper with a heat seal layer was produced in the same manner as in Example 1, except that the resin of the gas barrier layer was changed to sodium carboxymethyl cellulose (product name: Cellogen PR, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0068] The gas barrier papers obtained in each of the examples and comparative examples were evaluated by the methods described below. The results are shown in Table 1.

[0069] (1) Oxygen permeability The oxygen permeability of the gas barrier paper was measured at 23°C and 50% humidity using an oxygen permeability measuring device (MOCON OX-TRAN 2 / 22L) in accordance with JIS K 7126-2:2006 "Plastics - Films and sheets - Gas permeability test method - Part 2: Constant pressure method." A smaller value indicates less oxygen permeability. In this embodiment, an oxygen permeability of 50 cc / m 2 It can be said that it has oxygen barrier properties at temperatures below 100°C / day atm.

[0070] (2) Curls and wrinkles The surface quality of the resulting gas barrier paper was evaluated visually. ○: Both wrinkles and curls are very inconspicuous and practical. △: Either wrinkles or curls or both occur, but are within the range that can be used for practical purposes. ×: Either wrinkles or curls are very noticeable, making it unsuitable for practical use.

[0071] (3) Yellowing: The obtained gas barrier paper was stored for 2 months in an air-exposed state in an environment of 23°C and 50% RH, and the degree of yellowing of the surface of the gas barrier paper was evaluated visually. ○: There is almost no yellowing of the gas barrier paper surface, and it is usable. △: There is slight yellowing on the surface of the gas barrier paper, but it is not noticeable and can be used for practical purposes. ×: Yellowing of the surface of the gas barrier paper is noticeable and it is not suitable for practical use.

[0072] (4) Interlaminar strength: Cellophane tape (product name: Cellotape (registered trademark) CT-18, manufactured by Nichiban Co., Ltd.) was applied to the gas barrier layer surface of the obtained gas barrier paper, and after peeling it off, the degree to which the gas barrier layer and under layer had been removed was evaluated visually. ◯: The gas barrier layer or the underlayer is hardly removed, and it can be used for practical purposes. ×: The gas barrier layer or the underlayer is removed, and it is not practical.

[0073] [Table 1]

[0074] As is clear from Table 1, Examples 1 to 10 provided gas barrier papers with superior oxygen permeability and interlaminar strength, and reduced curling, wrinkling, and yellowing, compared to the gas barrier papers obtained in Comparative Examples 1 to 6. As these results show, the present invention can provide gas barrier papers that use less plastic than conventional products, have less curling and wrinkling, and have excellent oxygen barrier properties suitable for post-processing.

Claims

1. A gas barrier paper comprising a paper substrate, an underlayer, and a gas barrier layer, An underlayer is included between the paper substrate and the gas barrier layer, 1. A gas barrier paper characterized in that the gas barrier layer contains octenyl succinate esterified starch, the under layer contains heavy calcium carbonate and a styrene-butadiene copolymer latex, and the heavy calcium carbonate accounts for 20 mass % or more of the pigments in the under layer.

2. 2. The gas barrier paper according to claim 1, wherein 90% by mass or more of the gas barrier layer is composed of octenyl succinate esterified starch.

3. The coating amount of the gas barrier layer is 0.3 to 20 g / m in terms of dry coating amount. 2 The gas barrier paper according to claim 1 or 2, characterized in that the film thickness is in the range of

4. The gas barrier paper according to claim 1 or 2, wherein the paper base and the under layer do not contain any organic pigment.

5. 3. The gas barrier paper according to claim 1, further comprising a heat seal layer on the outermost surface of at least one side.

6. The gas barrier paper according to claim 5, wherein the heat seal layer contains a polyolefin or an ionomer.

Images