Gas barrier paper and method for manufacturing the same

Abstract

The present invention aims to provide a gas barrier paper and a method for manufacturing the same, which can be manufactured using a general-purpose coater while reducing the amount of plastic used, and which has excellent oxygen barrier properties and water resistance under high humidity conditions. [Solution] The present invention relates to a gas barrier paper comprising a gas barrier layer on at least a paper substrate and at least one surface of the paper substrate, wherein the gas barrier layer comprises 20 to 220 parts by mass of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin, and a method for producing the same.

Description

[Technical Field]

[0001] This invention relates to gas barrier paper that reduces the amount of plastic used. Furthermore, it relates to a gas barrier paper that can be manufactured using a general-purpose coater, possesses excellent oxygen barrier properties and water resistance under high humidity conditions, and a method for manufacturing the same. [Background technology]

[0002] In recent years, the plastic waste problem has become increasingly serious. Global plastic production is said to exceed 400 million tons per year, with the packaging sector accounting for a large portion and contributing significantly to plastic waste. Plastic does not decompose semi-permanently, and its waste breaks down into microplastics in the natural environment, severely impacting ecosystems. Marine pollution, in particular, is severe, and the resulting plastic waste is considered impossible to recover. Reducing plastic use is essential for the sustainable preservation of the global environment.

[0003] In packaging containers, barrier properties that block oxygen, water vapor, water, and oil are crucial. In particular, oxygen barrier properties are essential in various food packaging applications to prevent food discoloration, bacterial growth, and odor transfer. To achieve oxygen barrier properties, plastics with low oxygen permeability, such as nylon (NY), polyethylene terephthalate (PET), and ethylene vinyl alcohol (EVOH), have been used as packaging materials. Most oxygen barrier films used for food packaging have a multilayer structure, consisting of at least three layers: a base layer, an oxygen-barrier gas barrier layer, and a heat-seal layer. Examples of multilayer structures include a 3-layer structure of PET / EVOH / polyethylene (PE) for vacuum packaging and a 4-layer structure of PET / aluminum foil / NY / polypropylene (PP) for retort food packaging. Due to their multilayer structure, these oxygen barrier films are difficult to thin, and the amount of plastic used varies depending on the product concept, but is generally around 100g / m². 2 At least 50g / m 2As is often the case (see Patent Documents 1 and 2), there is a need to reduce the amount of plastic used even in multilayer films such as oxygen barrier films.

[0004] As a means of reducing the amount of plastic used, packaging paper has been proposed to replace plastic in packaging containers. Patent Document 3 discloses a paper barrier packaging material having a water vapor barrier layer containing pigment and binder resin on a paper substrate, and a gas barrier layer containing polyvinyl alcohol on the water vapor barrier layer, possessing excellent gas barrier and water vapor barrier properties. Furthermore, Prior Art Document 4 discloses a multilayer structure comprising a sealant layer, a paper layer, and a barrier layer in that order, wherein the sealant layer has an oxygen permeability of 100 cc / (m³) measured at 23°C and 50% humidity in accordance with JIS K 7126-2. 2 The paper layer has a basis weight of 50g / m² (day·atm) or more. 2 Less than 1.00 g / cm³ and with a density of 1.00 g / cm³ 3 A gas barrier paper is disclosed that has excellent disintegration and impact resistance, and whose barrier layer comprises at least one selected from the group consisting of polyvinyl alcohol-based resins and modified starch. In the case of these packaging materials, the polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA") and starch used in the gas barrier layer are humidity-dependent, and when used in a high-humidity environment, the oxygen barrier properties tend to deteriorate significantly. Furthermore, Patent Document 5 discloses a food packaging paper having water resistance, oil resistance, and gas barrier properties, and reducing the occurrence of pinholes, comprising a paper support and at least one coating layer on one side of the paper support, wherein at least one of the coating layers contains a polyvinylidene chloride polymer having vinylidene chloride monomer as the main component as a constituent unit of the resin. However, the coating solution of polyvinylidene chloride (PVDC) is strongly acidic and corrosive, and could only be manufactured using a special coater made of corrosion-resistant material. If the coating is applied using equipment not compatible with polyvinylidene chloride, the inside of pipes, tanks, coaters, dryers, etc. may rust, and this rust may contaminate the product. [Prior art documents]

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problem to be Solved by the Invention

[0006] The present invention relates to a gas barrier paper that reduces the amount of plastic used, has excellent oxygen barrier properties and water resistance under high humidity, and can be manufactured with a general-purpose coater, and a method for manufacturing the same.

[0007] Other objects and operational effects of the present invention will be readily understood by those skilled in the art by referring to the following description.

Means for Solving the Problem

[0008] To improve the moisture resistance and water resistance of conventional gas barrier paper, the gas barrier paper of the present invention is a gas barrier paper that includes a gas barrier layer on at least a paper substrate and at least one surface of the paper substrate, wherein the gas barrier layer contains a polyvinylidene chloride resin and a water-soluble polymer, and is characterized by containing 20 to 220 parts by mass of the water-soluble polymer per 100 parts by mass of the polyvinylidene chloride resin. The water-soluble polymer contained in the gas barrier layer is a non-plastic material such as starch or polyvinyl alcohol, which reduces the amount of plastic used compared to conventional gas barrier films mainly composed of plastics such as NY and PET. Furthermore, by mixing the polyvinylidene chloride resin and the water-soluble polymer in an appropriate ratio, a less corrosive coating solution can be produced even with a general-purpose coater, and the coated gas barrier paper can obtain excellent oxygen barrier properties and water resistance under high humidity conditions. In this invention, the gas barrier layer and gas barrier properties mainly refer to the layer having oxygen barrier performance and oxygen barrier properties. Furthermore, the present invention relates to a method for producing gas barrier paper, characterized by comprising a papermaking step of making paper substrate, and a step of applying a gas barrier layer coating solution containing 20 to 220 parts by mass of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin to at least one surface of the paper substrate obtained in the papermaking step, followed by drying the gas barrier layer coating solution.

[0009] In a preferred embodiment of the present invention, it is preferable that the gas barrier layer is composed of two or more layers on each side. That is, the gas barrier paper of the present invention preferably includes two or more gas barrier layers on at least one side. With this configuration, pinholes generated in the first gas barrier layer can be covered by the second and subsequent gas barrier layers, thereby obtaining gas barrier paper with even better oxygen barrier properties. In addition, in a preferred embodiment of the present invention, it is preferable to have at least two steps of applying and drying the coating liquid for the gas barrier layer, thereby providing two or more gas barrier layers.

[0010] In a preferred embodiment of the present invention, the total coating amount of the gas barrier layer is 1 to 30 g / m². 2This is preferable. It is possible to obtain a gas barrier paper that has more excellent water resistance and a uniform barrier film. In a preferred embodiment of the present invention, the water-soluble polymer contained in the gas barrier layer is preferably at least one selected from starch and polyvinyl alcohol. With such a configuration, the corrosiveness of the coating liquid for gas barrier layer can be further reduced, and a gas barrier paper free from rust defects can be obtained.

[0011] In the present invention, it is preferable that 90% by mass or more of the gas barrier layer is composed of a polyvinylidene chloride-based resin and a water-soluble polymer. With such a configuration, it is possible to obtain a gas barrier paper having further excellent oxygen barrier properties.

[0012] In the present invention, it is preferable to have a heat seal layer on the outermost surface of at least one side. With such a configuration, heat sealability can be imparted to enable application to various uses and processing methods. In addition, providing the heat seal layer on the side where the gas barrier layer is disposed serves as a protective layer for the gas barrier layer, making it possible to obtain a gas barrier paper whose oxygen barrier properties are less likely to deteriorate.

[0013] In the present invention, it is preferable to have a heat seal layer on the outermost surface of at least one side, and the heat seal layer contains a polyolefin-based resin. With such a configuration, it is possible to obtain a gas barrier paper having better heat sealability. Effects of the Invention

[0014] According to the present invention, it is possible to produce a gas barrier paper that can be manufactured even with a general-purpose coater while reducing the amount of plastic used, and has excellent oxygen barrier properties under high humidity and water resistance. In the present invention, the oxygen permeability of the gas barrier paper at 23°C and 50%RH is 50cc / m 2 ·day·atm or less, preferably 30cc / m 2 ·day·atm or less, more preferably 25cc / m 2 ·day·atm or less, and the oxygen permeability at 23°C and 80%RH is 80cc / m 2Less than 70cc / m³ per day atm 2 It can be set to less than or equal to 1 day·atm. Furthermore, even if the gas barrier paper of the present invention is improperly released into the natural environment as waste, it is possible to reduce the adverse effects of plastic waste on the natural environment, thus contributing to the solution of the plastic waste problem. The gas barrier paper of the present invention can be processed into, for example, primary and secondary bags in food packaging, packaging bags for household goods and daily necessities, food cups for ice cream, lids for cups and trays, beverage cups for coffee, food containers and trays for hot snacks, boxes, cases, containers, envelopes, and other paper containers. [Modes for carrying out the invention]

[0015] Next, the present invention will be described in detail with reference to an example of an embodiment, but the present invention is not to be construed as being limited to this description. Various modifications of the embodiment are possible as long as the effects of the present invention are achieved.

[0016] The paper substrate in the embodiments of the present invention is not particularly limited, and known base papers mainly composed of pulp can be used. As the pulp that is the main component of the base paper, chemical pulps such as LBKP (bleached hardwood kraft pulp) and NBKP (bleached softwood kraft pulp), mechanical pulps such as GP (groundwood pulp), PGW (pressure-processed groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemothermetic pulp), CMP (chemimechanical pulp), and CGP (chemigland pulp) can be used, as well as wood pulps such as DIP (deinking pulp) and non-wood pulps such as kenaf, bagasse, bamboo, and cotton. These can be used individually or mixed in any proportion. For example, LBKP (bleached hardwood kraft pulp) can be used as pulp in amounts of 50 to 100 parts by mass, for example, 60 to 80 parts by mass, 60 to 95 parts by mass, or 90 to 100 parts by mass. Furthermore, to reduce plastic use, it is preferable to avoid synthetic fibers containing plastics such as polyester or polyolefin. From an environmental perspective, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, recycled paper pulp, and pulp obtained from plantation trees are preferred. For example, an appropriate pulp beating degree is 300 to 800 mlCSF, preferably 350 to 750 mlCSF, and even more preferably 350 to 650 mlCSF, according to the Canadian standard freeness (JIS P 8121:1995 "Test Method for Freeness of Pulp"). For example, a pulp can be used that contains 60 to 80 parts by mass of bleached hardwood kraft pulp with a Canadian standard freeness of 350 to 450 mlcsf and 20 to 40 parts by mass of bleached softwood kraft pulp with a Canadian standard freeness of 500 to 600 mlcsf.

[0017] In embodiments of the present invention, it is preferable that the paper substrate does not contain fillers. 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 fillers in the paper substrate inhibits the interfiber bonding of the pulp, reducing the paper strength of the paper substrate and making it more prone to cracking during post-processing, particularly in processes that involve folding the gas barrier paper, such as bag making and molding. Cracks in the gas barrier layer are also more likely to occur following the cracks in the paper substrate, potentially worsening the oxygen barrier properties after folding. However, the above-mentioned fillers may be included as long as they do not impair the effects targeted by the present invention.

[0018] Furthermore, the paper substrate may contain various known papermaking additives in addition to pulp. Examples of papermaking additives include internally added paper strength enhancers such as sizing agents, bulk enhancers, yield enhancers, water drainage enhancers, coloring dyes, coloring pigments, fluorescent whitening agents, fluorescent decolorizing agents, and pitch control agents. In addition, water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide may be coated. If the paper substrate contains a wet paper strength enhancer, the recyclability of the gas barrier paper is poor, so it is preferable that the paper substrate does not contain a wet paper strength enhancer. As for the method of compounding the papermaking additives, they may be included in the pulp slurry, or they may be impregnated into the interior of the paper substrate after papermaking using a sizing press or gate roll. It is preferable to include polyacrylamide and oxidized starch as paper strength enhancers. Since the paper strength of the paper substrate is increased, it is possible to obtain gas barrier paper that has good transportability in post-processing steps and is less prone to tearing. Specific examples of additives include the paper substrate, which may contain, for example, polyacrylamide, for example, cationic polyacrylamide, and / or a sizing agent, for example, neutral rosin sizing. Preferably, the paper substrate may contain 0.1 to 1.0 parts by mass of polyacrylamide and / or 0.1 to 1.0 parts by mass of a sizing agent per 100 parts by mass of pulp. In addition, the paper substrate may contain oxidized starch as a paper strength agent. For example, it may contain 2 to 8 parts by mass of oxidized starch per 100 parts by mass of pulp.

[0019] The papermaking method for the paper substrate is not particularly limited and can be used with various papermaking machines such as a long screen papermaking machine, a long screen multilayer papermaking machine, a cylinder screen papermaking machine, a cylinder screen multilayer papermaking machine, a long screen and cylinder screen combination multilayer papermaking machine, and a twin wire papermaking machine. Furthermore, in this invention, the paper substrate may be single-layer or multilayer.

[0020] In this invention, a gas barrier layer is included on at least one surface of a paper substrate, and the gas barrier layer contains a polyvinylidene chloride resin and a water-soluble polymer. Polyvinylidene chloride resin has excellent oxygen barrier properties under high humidity, but the coating solution is strongly acidic and corrosive, and when applied with a general-purpose coater, the inside of pipes, tanks, coaters, dryers, etc. may rust, and rust may mix into the product. In particular, if rust adheres to the surface of the gas barrier layer, it becomes a rust defect, impairing the aesthetic appearance, and depending on the frequency and size of the rust defects, a large amount of product loss may be expected, worsening operability and costs. By adding a water-soluble polymer to the coating solution of polyvinylidene chloride resin, the corrosivity of the coating solution is improved, making it possible to manufacture the product even with a general-purpose coater. Furthermore, because water-soluble polymers are resins with excellent oxygen barrier properties, film-forming properties, and oil resistance, when comparing gas barrier layers of the same thickness, a layer mixed with water-soluble polymers exhibits better oxygen barrier properties than a single layer of polyvinylidene chloride resin, and the amount of plastic used can be reduced by the amount of polyvinylidene chloride resin used. On the other hand, water-soluble polymers have poor water resistance because they absorb moisture, and in high-humidity environments, the gas barrier layer film that has gained fluidity by absorbing moisture tends to disappear, and the oxygen barrier properties tend to deteriorate significantly.

[0021] The present invention is characterized in that the ratio of water-soluble polymer to 100 parts by mass of polyvinylidene chloride resin in the gas barrier layer is 20 to 220 parts by mass. Preferably, it is 20 to 200 parts by mass, 20 to 150 parts by mass, and more preferably 30 to 100 parts by mass. By mixing water-soluble polymer with polyvinylidene chloride resin in an appropriate ratio, it is possible to achieve both improved corrosiveness of the coating liquid and excellent oxygen barrier properties and water resistance of the gas barrier paper under high humidity conditions. If the ratio of water-soluble polymer is less than 20 parts by mass, the improvement in corrosiveness will be insufficient, rust defects may occur on the surface of the gas barrier layer, and the plastic reduction effect may be poor. If the ratio of water-soluble polymer is 220 parts by mass or more, the oxygen barrier properties and water resistance may deteriorate significantly under high humidity conditions, for example, under a 23°C 80%RH environment.

[0022] In this invention, the polyvinylidene chloride resin used in the gas barrier layer refers to a resin mainly composed of a vinylidene chloride skeleton. It may consist solely of vinylidene chloride or be a copolymer with other polymers, but it is preferable that the proportion of the resin mainly composed of a vinylidene chloride skeleton be 50% by mass or more. That is, in a polyvinylidene chloride resin, it is preferable that the vinylidene chloride monomer in the polymer is 50% by mass or more, for example, in a polyvinylidene chloride resin, it is preferable that the vinylidene chloride monomer in the polymer is 80% by mass or more. By using such a polyvinylidene chloride resin, high oxygen barrier properties can be obtained regardless of humidity. There are no particular restrictions, but it is preferable that the copolymer be with one of the following, for example, latex, vinyl chloride, vinyl acetate, styrene, unsaturated carboxylic acid, unsaturated alkyl carboxylic acid such as unsaturated carboxylic acid esters, acrylonitrile, etc. It has excellent water resistance and oil resistance. In the packaging paper of the present invention, other resins may be included as long as they do not affect the oxygen barrier properties, water resistance, or oil resistance, and furthermore, multiple resins may be mixed together.

[0023] In the present invention, water-soluble polymers used in the gas barrier layer include starch, polyvinyl alcohol, as well as casein, soy protein, cellulose derivatives such as carboxymethylcellulose, hydroxymethylcellulose, and hydroxyethylcellulose. Preferably, the water-soluble polymer contained in the gas barrier layer is one or more of starch, starch derivatives, polyvinyl alcohol, or modified polyvinyl alcohol. Excellent water resistance and excellent oxygen barrier properties can be obtained even under high humidity. In the packaging paper of the present invention, other water-soluble polymers may be included as long as they do not affect the oxygen barrier properties, water resistance, or oil resistance, and furthermore, multiple water-soluble polymers may be mixed.

[0024] The starch used as a water-soluble polymer in the gas barrier layer preferably has the following characteristics. Starch is composed of two components: amylose, in which glucose is linked in a linear chain, and amylopectin, in which glucose is linked 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. Furthermore, 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, 60% by mass or more and less than 95% by mass. By setting the amylopectin content of the starch in this range, better oxygen barrier properties can be obtained. If the amylopectin content is less than 60% by mass, the oxygen barrier properties deteriorate. As the raw material for starch or starch derivatives, either grains such as corn, wheat, and rice, or tubers such as tapioca, potatoes, and sweet potatoes may be used. Among these, tapioca starch is preferred because it has a high amylopectin content and superior oxygen barrier properties. Waxy corn or rice with a high amylopectin content may be included. Multiple types of starch may be mixed in the gas barrier layer, as long as the effects targeted by the present invention are not impaired. As a method for quantifying the amylopectin content of starch or starch derivatives contained in the gas barrier layer, known measurement methods for measuring amylose and amylopectin content in starch can be used, such as the iodine colorimetric method, electrostatic titration, voltage titration, and enzyme chromatography. The amylopectin content may be the content after isolating amylopectin from starch or starch derivatives, or it may be the apparent content without isolation.

[0025] In the present invention, the water-soluble polymer contained in the gas barrier layer may be a starch derivative. A starch derivative refers to starch in which various functional groups have been introduced to the hydroxyl groups contained in the glucose in the starch. It is preferable that the starch derivative has an ester group or an ether group introduced. Examples of starch derivatives with an ester group introduced include octenyl succinate esterified starch, urea phosphate esterified starch, acetate esterified starch, succinate esterified starch, nitrate esterified starch, phosphate esterified starch, and carbamate esterified starch. Examples of starch derivatives with an ether group introduced include hydroxyethyl etherified starch, hydroxypropyl etherified starch, carboxymethyl etherified starch, allyl etherified starch, methyl etherified starch, and carboxyetherified starch. Starch absorbs moisture, so in a high-humidity environment, the gas barrier layer film that has gained fluidity by absorbing moisture may be lost, and the oxygen barrier performance may deteriorate. However, since these starch derivatives have hydrophobic groups introduced into the starch, they have excellent water resistance, and the gas barrier layer film is less likely to deteriorate even in high-humidity conditions. Octenyl succinate esterified starch is more preferable. Because it exhibits particularly excellent film-forming properties, good oxygen barrier properties can be obtained, and it also has excellent oil resistance. The water-soluble polymer contained in the gas barrier layer may be other starch derivatives such as oxidized starch or cationized starch.

[0026] Examples of water-soluble polymers used in the gas barrier layer include polyvinyl alcohol and modified polyvinyl alcohol, such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and hydrophobic group-modified polyvinyl alcohol (hydrophobic polyvinyl alcohol). In addition to the modified polyvinyl alcohols mentioned above, hydrophobic groups can also include alkyl groups, unsaturated carboxylic acids, and copolymers thereof. Like starch, polyvinyl alcohol absorbs moisture, so in high-humidity environments, the gas barrier layer film, which has gained fluidity from absorbing moisture, may be lost, potentially worsening its oxygen barrier properties. However, hydrophobic group-modified polyvinyl alcohol, in particular, has excellent water resistance because hydrophobic groups have been introduced, making the gas barrier layer film less prone to deterioration even in high-humidity conditions.

[0027] In the manufacturing method of the present invention, a gas barrier layer can be formed by coating at least one surface of a paper substrate with a coating solution containing 20 to 220 parts by mass of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin, and then drying it. In the manufacturing method of the present invention, it is preferable that the water-soluble polymer used in the coating solution for the gas barrier layer is an aqueous solution. That is, the water-soluble polymer is preferably added after being dissolved in hot or cold water as a solution obtained by dissolving the powder. It is preferable to use commercially available aqueous emulsions such as Asahi Kasei's "Saran Latex" series or Solvay's "Diofan" series as the polyvinylidene chloride resin. If both the water-soluble polymer solution and the aqueous emulsion of polyvinylidene chloride are aqueous, they can be easily dispersed uniformly during mixing, and high oxygen barrier properties can be obtained. The coating solution for the gas barrier layer may also contain an alcohol with a boiling point 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 below that of water volatilize during the drying process and are not included in the gas barrier layer after drying. Therefore, they can provide a leveling effect while suppressing deterioration of oxygen barrier properties. Gas barrier paper preferably has a gas barrier layer on one side of the paper substrate, but it can also have gas barrier layers on both sides.

[0028] In this invention, the amount of gas barrier layer applied is 1 to 30 g / m² per side of the paper substrate, based on dry coating. 2 This is sufficient, preferably 1 to 15 g / m 2 For example, 2-10 g / m 2 It is 1.0 g / m 2 If the value is less than 30 g / m², the water resistance will be poor, and the coating liquid 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 created due to liquid absorption, and a large amount of oxygen will pass through the pinholes, worsening the oxygen barrier performance. Conversely, if the value is 30 g / m², the water resistance will be poor, and the gas barrier coating liquid will not be able to form a uniform barrier film. 2 If the value exceeds this, sufficient oxygen barrier properties can be obtained, but the amount of plastic used increases, resulting in little plastic reduction effect.

[0029] In this invention, the gas barrier layer may be formed in two or more layers on each surface. By having two or three or more gas barrier layers, pinholes caused by the absorption of the gas barrier coating liquid that occur in the first gas barrier layer of the gas barrier paper (referring to the gas barrier layer closest to the paper substrate among multiple gas barrier layers) can be covered by the second and subsequent gas barrier layers, thereby obtaining even better oxygen barrier properties. In particular, when using a paper substrate with high liquid absorption, pinholes are likely to occur, and having two or more gas barrier layers is especially effective. When there are two or three or more gas barrier layers, it is preferable that the coating amount of the first gas barrier layer closest to the paper substrate is greater than the coating amounts of each of the second and subsequent gas barrier layers. With this configuration, the pinhole suppression effect can be further enhanced, and the oxygen barrier properties and water resistance can be further improved. Even when there are two or more gas barrier layers, the coating amount of the gas barrier layer on one side of the gas barrier paper is as shown above, but is 1 to 30 g / m². 2 Preferably, and more preferably, 1 to 15 g / m 2 For example, 2-10 g / m 2 Furthermore, when there are two or more gas barrier layers, it is preferable to have a larger coating amount for the first gas barrier layer. Specifically, when there are two gas barrier layers, the coating amount for the first gas barrier layer should be 0.5 to 20 g / m². 2 Preferably 0.7 to 10 g / m 2 More preferably 1.5 to 7.0 g / m² 2 This is a good approach. Furthermore, the coating amount for the second and subsequent gas barrier layers is 0.3-10 g / m². 2 Preferably 0.5 to 5 g / m 2It is preferable that the gas barrier layer consists of two or more layers. If there are two or more gas barrier layers, at least one gas barrier layer must contain 20 to 220 parts by mass of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin, but the other gas barrier layers may be any layer that acts as a gas barrier layer. For example, the remaining gas barrier layer may contain 20 parts by mass or less or 220 parts by mass or more of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin, and may also be composed without polyvinylidene chloride resin and / or water-soluble polymers. It may also contain gas barrier water-based resins other than polyvinylidene chloride resin and various auxiliary agents as described in the paragraph below. Furthermore, the first layer and subsequent layers of the gas barrier layer may have the same components, and it is preferable that the first layer and subsequent layers of the gas barrier layer have different coating amounts but the same components.

[0030] In the present invention, in addition to polyvinylidene chloride resin and water-soluble polymer, various auxiliary agents may be added to the coating liquid for the gas barrier layer, to the extent that they do not impair the effects targeted by the present invention. Examples include viscosity modifiers, defoaming agents, leveling agents such as surfactants and alcohols, crosslinking agents, coloring pigments, coloring dyes, lubricants such as waxes, pigments such as clay and calcium carbonate, and synthetic resins such as urethane, styrene-butadiene copolymer latex, olefin resins, acrylic resins, polyester resins, and polyamide resins. Other auxiliary agents not mentioned above may also be included, to the extent that they do not impair the effects targeted by the present invention. Preferably, 90% or more by mass of the gas barrier layer is composed of polyvinylidene chloride resin and water-soluble polymer. This allows for the production of gas barrier paper with excellent oxygen barrier properties. More preferably, 95% or more, and even more preferably, the gas barrier layer is composed solely of polyvinylidene chloride resin and water-soluble polymer.

[0031] In the present invention, the method for applying the coating liquid for the gas barrier layer is not particularly limited, and commonly used coating equipment can be used. In the present invention, since a coating liquid for the gas barrier layer with excellent corrosion resistance is used, a general-purpose coater can be used without having to use a special coater with corrosion resistance. For example, various known coating equipment such as air knife coaters, blade coaters, gravure coaters, flexo coaters, rod blade coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, champlex coaters, metering blade type size press coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters can be used.

[0032] In the present invention, any layer other than the paper substrate and the gas barrier layer may be provided, as long as it does not impair the effects targeted by the present invention. Gas barrier paper must include a paper substrate and a gas barrier layer on at least one side of the paper substrate, and has a layer structure of at least a paper substrate / gas barrier layer. However, for example, it may have two gas barrier layers, or a layer structure of paper substrate / gas barrier layer / gas barrier layer. Furthermore, an underlayer may be provided between the paper substrate and the gas barrier layer, resulting in a layer structure of paper substrate / underlayer / gas barrier layer. In addition, a heat seal layer may be added, in which case the layer structure of the gas barrier paper may be, for example, paper substrate / gas barrier layer / heat seal layer or heat seal layer / paper substrate / gas barrier layer / heat seal layer. Furthermore, a printing layer may be provided on the side of the paper substrate opposite the gas barrier layer, resulting in a layer structure of printing layer / paper substrate / gas barrier layer. Furthermore, the gas barrier layer may be provided on both sides, and a layer structure of gas barrier layer / paper substrate / gas barrier layer or gas barrier layer / underlayer / paper substrate / underlayer / gas barrier layer is also possible. Multiple of the above examples may be combined. For example, paper substrate / gas barrier layer / gas barrier layer / heat seal layer, paper substrate / underlayer / gas barrier layer / heat seal layer, printed layer / paper substrate / underlayer / gas barrier layer / heat seal layer, heat seal layer / underlayer / paper substrate / underlayer / gas barrier layer / heat seal layer, etc. are possible, but configurations other than those described above are also acceptable as long as they do not impair the effects intended for the present invention. Such gas barrier paper can be processed into, for example, primary and secondary bags in food packaging, packaging bags for household goods and daily necessities, food cups for ice cream, lids for cups and trays, beverage cups for coffee, food containers and trays for hot snacks, boxes, cases, bowls, envelopes, and other paper containers in general. When used in food packaging, it is preferable to use the paper substrate side on the outside, for example, in the case of a packaging bag, with the paper substrate side on the outside and the gas barrier layer side on the inside. Furthermore, it is preferable that each layer covers the entire surface of the layer beneath the paper substrate or other material.

[0033] In this invention, by providing an underlayer between the paper substrate and the gas barrier layer, a sealing effect is created that prevents the coating liquid for the gas barrier layer from penetrating the paper substrate. This makes it easier to form a barrier film with fewer defects even with a small amount of gas barrier layer coating, and allows for the production of gas barrier paper with better oxygen barrier properties. The underlayer preferably consists of a combination of pigment and binder. As the pigment and binder in the underlayer, known pigments and binders used in the coating layer of general printing coated paper can be used.

[0034] In the present invention, examples of pigments used in the underlayer include, for example, 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, silicon dioxide, and other inorganic pigments. For example, it is preferable to use heavy calcium carbonate at a concentration of 50% by mass or more of the total pigment in the underlayer, and for example, it is preferable to use 70 to 100 parts by mass of heavy calcium carbonate and 0 to 30 parts by mass of titanium dioxide. It is preferable that the pigment in the underlayer does not contain organic pigments. 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. The shape of organic pigments can be dense, core / shell-type, hollow, foamed, etc., and the term refers to all shapes of organic pigments. Multiple underlayers may be provided, as long as they do not impair the effects intended for this invention.

[0035] In the present invention, examples of binders used in the underlayer 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, soy 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. In embodiments of the present invention, it is preferable to use 10 to 80 parts by mass of binder per 100 parts by mass of pigment. For example, 35 to 45 parts by mass of styrene-acrylic emulsion and 25 to 35 parts by mass of styrene-butadiene copolymer latex may be used in combination per 100 parts by mass of pigment.

[0036] In the present invention, it is preferable that 80% by mass or more, for example, 90% to 100% by mass of the underlayer consists of pigment and binder. This makes it possible to obtain gas barrier paper with excellent sealing effect for the gas barrier layer coating liquid and excellent oxygen barrier properties. Furthermore, the underlayer may contain various auxiliary agents to the extent that it does not impair the effects targeted by the present invention, such as viscosity modifiers, softeners, gloss enhancers, water-resistant agents, dispersants, flow modifiers, ultraviolet absorbers, stabilizers, antistatic agents, crosslinking agents, sizing agents, fluorescent whitening agents, colorants, pH adjusters, defoamers, plasticizers, preservatives, and mold release agents. The underlayer may also contain auxiliary agents other than those listed above to the extent that it does not impair the effects targeted by the present invention, and multiple auxiliary agents may be used in combination.

[0037] In this invention, a heat-seal layer may be provided on the gas barrier paper. Preferably, the heat-seal layer is provided on the outermost surface of at least one of the surfaces. This allows the gas barrier paper to be heat-sealed. Furthermore, by providing the heat-seal layer on the side where the gas barrier layer is applied, it acts as a protective layer for the gas barrier layer, making it less likely for the oxygen barrier properties to deteriorate.

[0038] In embodiments of the present invention, the resin in the heat seal layer is not particularly limited, but polyolefins, acrylic resins, styrene resins, etc., can be used. Any other resins may be included as long as they do not affect the oxygen barrier properties or post-processing suitability, and multiple resins may be mixed. Polyolefin resins are preferred because they provide superior heat sealability and good water resistance, resulting in superior protection of the gas barrier layer. Furthermore, they also provide water vapor barrier properties, making them applicable to applications requiring moisture resistance. Polyolefins refer to all resins having a polyethylene or propylene skeleton, and include copolymers with acrylic acid or methacrylic acid, as well as their metal salts (ionomers). Examples of polyolefin resins 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, ethylene vinyl acetate copolymer, and ionomers. Ionomers refer to synthetic resins in which polymers are aggregated using the cohesive force of metal ions, and include all those in which resins and metal cations form aggregates through intermolecular bonding. 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-fluorine polymer copolymer. In the present invention, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), biaxially oriented polypropylene (OPP), unoriented polypropylene (CPP), and copolymers of ethylene-acrylic acid or ethylene-methacrylic acid and their metal salts (ionomers) are preferred because they can provide superior water resistance, moisture resistance, and heat sealability.

[0039] In embodiments of the present invention, a heat seal layer can be provided by coating a heat seal layer coating liquid onto at least one surface of a paper substrate and drying it. It is preferable that the resin used for the heat seal layer is an aqueous emulsion. The heat seal layer preferably contains a resin derived from an aqueous emulsion, and more 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, it is preferable that the heat seal layer consists of a resin derived from an aqueous emulsion. By using these, the amount of coating can be controlled to be relatively low, and VOC emissions can be reduced, thereby further reducing the burden on the natural environment.

[0040] In embodiments of the present invention, the coating liquid for the heat seal layer may contain various auxiliary agents in addition to the aqueous emulsion, to the extent that they do not impair the effects targeted by the present invention. Examples include viscosity modifiers, defoamers, leveling agents such as surfactants and alcohols, lubricants such as coloring pigments, coloring 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 the heat seal strength, it is preferable to add them in small amounts if they are added. It is preferable that the coating liquid for the heat seal layer contains 90% to 100% by mass, for example, 95% to 100% by mass or 99% to 100% by mass of aqueous emulsion, and it is even more preferable that the coating liquid for the heat seal layer consists solely of aqueous emulsion. Other auxiliary agents not mentioned above may be included in the extent that they do not impair the effects targeted by the present invention.

[0041] The method for applying the coating liquid for the heat seal layer in the present invention is not particularly limited, and commonly used coating equipment can be used. For example, various known coating equipment such as air knife coaters, blade coaters, gravure coaters, flexo coaters, rod blade coaters, roll coaters, reverse roll coaters, bar coaters, curtain coaters, die slot coaters, champlex coaters, metering blade type size press coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters can be used.

[0042] In embodiments 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.

[0043] In embodiments 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, to the extent that they do not impair the effects targeted by the present invention. Examples include plasticizers, antistatic agents, antioxidants, lubricants, antiblocking agents, ultraviolet absorbers, crosslinking agents, curing agents, surfactants, flame retardants, and fillers. Depending on the lamination method, an adhesive or anchoring agent may be coated before lamination, and surface treatments such as corona treatment, plasma treatment, ozone treatment, and primer treatment may be performed in advance. Furthermore, additives and treatment processes other than those mentioned above may be included, to the extent that they do not impair the effects targeted by the present invention.

[0044] In embodiments of the present invention, the thickness of the heat seal layer is preferably 2 to 50 μm. More preferably 3 to 30 μm, for example 5 to 25 μm. Sufficient heat sealability can be obtained by setting the thickness of the heat seal layer within this range. Furthermore, by providing the heat seal layer on the side to which the gas barrier layer is applied, it can act as a protective layer for the gas barrier layer, and the effect of preventing deterioration of the oxygen barrier properties can be expected. The heat seal layer may be provided on one side of the paper substrate or on both sides. In the case of both sides, the total thickness is preferably 3 to 50 μm. In the gas barrier paper of the present invention, the heat seal layer may be provided on only a part of the surface of the paper substrate or on the entire surface. That is, the heat seal layer may be provided only in the parts necessary for adhesion by heat sealing, such as in a mesh, island, or linear pattern, or it may be provided to cover the entire surface of the paper substrate. The heat seal layer may also have a multilayer structure. By using two or more heat-seal layers, especially when heat-seal properties are imparted by coating with a heat-seal coating liquid, the occurrence of pinholes in the heat-seal layer can be suppressed, thereby providing good water and oil resistance.

[0045] In embodiments of the present invention, a printing layer may be provided on the side of the paper substrate opposite to the gas barrier layer. When gas barrier paper is processed into bags or paper cups, the outer surface of the container may be printed to indicate the contents or for advertising purposes, and providing a printing layer can provide good printability. It is also possible to print on the printing layer and then provide a heat seal layer on top of that. The composition of the printing layer is not particularly limited and may include the pigments, binders, and various auxiliary agents mentioned above for the underlayer. It can have the same composition as the underlayer, or the type and ratio of chemicals can be adjusted to suit the required performance. It can also have the same composition as the coating layer of known printed coated paper.

[0046] Embodiments of the present invention may include a step of smoothing the paper substrate, underlayer, and printing layer. The method for smoothing the paper substrate is not particularly limited, and commonly used calendering devices can be used. For example, various known smoothing devices such as machine calenders, soft calenders, supercalenders, gloss calenders, and shoe-nip calenders can be used. It may also include a step of transferring the mirror surface of a Yankee dryer, as used for single-sided gloss kraft paper, and then smoothing the surface. By coating the smoothed surface with an underlayer or gas barrier layer, the coating liquid for the gas barrier layer can be applied more uniformly, a high sealing effect can be obtained, and gas barrier paper with good oxygen barrier properties can be obtained.

[0047] In embodiments of the present invention, the basis weight of the gas barrier paper is not particularly limited, but for example, 10 to 1000 g / m² 2 The basis weight of gas barrier paper that can also be used for flexible packaging is 30-500 g / m². 2 Preferably, 30-350 g / m² 2 If so, it is more preferable, for example, 40-300 g / m 2 That would be fine. [Examples]

[0048] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "mass%", respectively, unless otherwise specified. Note that the number of added parts is the value on a solid content basis.

[0049] (Example 1) (Preparation of paper substrate A) A pulp was prepared by adding water to 70 parts of bleached hardwood kraft pulp with a Canadian standard freeness of 400 mlcsf, 30 parts of bleached softwood kraft pulp with a Canadian standard freeness of 550 mlcsf, 0.5 parts of cationic polyacrylamide (product name: Polystron 705, manufactured by Arakawa Chemical Industries), and 0.2 parts of neutral rosin sizing (product name: CC167, manufactured by Seikoh PMC). The resulting pulp was then processed using a multi-cylinder, long-wire paper machine to achieve a basis weight of 38 g / m². 2 A base paper is prepared, and oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) is impregnated as a paper strength agent using a pound-type size press, with a dry impregnation amount of 2g / m². 2 The material is impregnated and dried, then smoothed with a calender, resulting in a basis weight of 40g / m². 2 A paper substrate A was obtained.

[0050] (Preparation of gas barrier paper) 100 parts of polyvinylidene chloride resin (product name: Saran Latex L411A, manufactured by Asahi Kasei Corporation) and 50 parts of a solution of octenyl succinate esterified starch (octenyl succinate esterified tapioca starch, product name: FILMKOTE 370, manufactured by Ingredion, amylopectin content 83%) dissolved in hot water were added to water and thoroughly stirred to obtain coating solution A for the gas barrier layer. The coating solution A for the gas barrier layer was then applied to the paper substrate A obtained above, with a dry coating amount of 2.0 g / m². 2 The coating is applied using an air knife coater, dried to form the first gas barrier layer, and then the gas barrier coating liquid A is applied on top of the first gas barrier layer with a drying coating amount of 1.0 g / m². 2 The coating is applied using an air knife coater, dried, and then a second gas barrier layer is formed, with a total of 3.0 g / m² for both layers. 2 A gas barrier layer is provided, with a basis weight of 43 g / m². 2 We fabricated a gas barrier paper.

[0051] (Preparation of gas barrier paper with a heat-sealable layer) A low-density polyethylene (product name: Petrocene® 204, manufactured by Tosoh Corporation) was laminated to the gas barrier layer surface of the gas barrier paper obtained above to a thickness of 20 μm, and a heat-sealed layer was created, resulting in a basis weight of 61 g / m². 2 We fabricated a gas barrier paper with a heat-sealable layer.

[0052] (Example 2) In Example 1, gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of hydrophobic starch in gas barrier layer coating solution A was changed to 20 parts, and this was called gas barrier layer coating solution B.

[0053] (Example 3) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of hydrophobic starch in coating solution A for the gas barrier layer was changed to 200 parts, resulting in coating solution C for the gas barrier layer.

[0054] (Example 4) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the hydrophobic starch in coating solution A for the gas barrier layer was replaced with oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) and this was designated as coating solution D for the gas barrier layer.

[0055] (Example 5) In Example 1, the hydrophobic starch in coating solution A for the gas barrier layer was replaced with polyvinyl alcohol (product name: Kuraray Poval 28-98, manufactured by Kuraray Co., Ltd.) to create coating solution E for the gas barrier layer. Otherwise, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1.

[0056] (Example 6) In Example 1, the hydrophobic starch in coating solution A for the gas barrier layer was replaced with hydrophobic group-modified polyvinyl alcohol (product name: Exceval HR-3010, manufactured by Kuraray Co., Ltd.), and this was used to create coating solution F for the gas barrier layer. Otherwise, a gas barrier paper with a heat-seal layer was prepared in the same manner as in Example 1.

[0057] (Example 7) In Example 1, the coating amount of the first gas barrier layer was 3.0 g / m². 2 The design was changed to omit the second gas barrier layer and use a gas barrier paper with a heat seal layer with a basis weight of 61 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0058] (Example 8) In Example 1, the coating amount of the first gas barrier layer was 5.0 g / m². 2 The coating amount for the second gas barrier layer is 3.0 g / m². 2 The total of the two layers is changed to 8.0g / m². 2 A gas barrier layer is provided, and the basis weight of the heat-sealed gas barrier paper is 66 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0059] (Example 9) In Example 1, the coating amount of the first gas barrier layer was 1.5 g / m². 2 The coating amount for the second gas barrier layer is 0.5 g / m². 2 The total of the two layers is changed to 2.0g / m². 2 A gas barrier layer is provided, and the basis weight of the heat-sealed gas barrier paper is 60 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0060] (Example 10) (Preparation of undercoat coating solution) Fifteen parts of titanium dioxide (product name: CR-85, manufactured by Ishihara Sangyo Co., Ltd.) and eighty-five parts of heavy calcium carbonate (product name: Softon 1500, manufactured by Bihoku Funka Kogyo Co., Ltd.) were mixed with 0.2 parts of a dispersant (product name: Aron T-50, manufactured by Toagosei Co., Ltd.), water was added, and the mixture was dispersed using a Koles disperser to prepare a pigment slurry. To this pigment slurry, forty parts of styrene-acrylic emulsion (product name: Saibinol EK-81, manufactured by Saiden Chemical Co., Ltd.) and thirty parts of styrene-butadiene copolymer latex (product name: PB7648, manufactured by Nippon A&L Co., Ltd.) were added as binders, and water was added to disperse the mixture, preparing an undercoat coating solution with a solid content of 40%.

[0061] (Preparation of paper substrate with underlayer) On one side of paper substrate A, apply an undercoat coating liquid with a dry coating amount of 15 g / m². 2 The coating was applied using an air knife coater and dried to achieve a basis weight of 55 g / m². 2 A paper substrate B with an underlayer was fabricated.

[0062] In Example 1, paper substrate A was changed to underlay paper substrate B, and the basis weight of the heat-sealed gas barrier paper was 76 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0063] (Example 11) In Example 1, the basis weight of the base paper was 228 g / m². 2 The paper strength agent was changed to oxidized starch (product name: MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) with a dry impregnation amount of 2g / m², applied by a pound-type size press. 2 The material is impregnated and dried, then smoothed with a calender, resulting in a basis weight of 230 g / m². 2 A paper substrate C was created.

[0064] In Example 1, paper substrate A was changed to paper substrate C, and the basis weight of the heat-sealed gas barrier paper was 251 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0065] (Example 12) On one side of the paper substrate C obtained in Example 11, the undercoat liquid was applied with a dry coating amount of 15 g / m². 2 The coating was applied using an air knife coater and dried to achieve a basis weight of 245 g / m². 2 A paper substrate D with an underlayer was fabricated.

[0066] In Example 1, paper substrate A was changed to underlay paper substrate D, and the basis weight of the heat-sealed gas barrier paper was 266 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0067] (Example 13) (Preparation of gas barrier paper with a heat-sealable layer) In Example 1, an aqueous ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene-methacrylic acid copolymer) was applied to the gas barrier layer surface of the gas barrier paper obtained in Example 1, with a dry coating amount of 5.0 g / m². 2 The paper is coated using an air knife coater to a thickness of 5.3 μm, dried to form a heat-seal layer, and the basis weight of the heat-sealed gas barrier paper is 48 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0068] (Example 14) In Example 1, no heat-seal layer was provided on the gas barrier paper, and the basis weight of the gas barrier paper was 43 g / m². 2 Except for the toshi, the gas barrier paper was prepared in the same manner as in Example 1.

[0069] (Comparative Example 1) In Example 1, no gas barrier layer was provided, and the basis weight of the gas barrier paper with a heat seal layer was 58 g / m². 2 Except for the above, a gas barrier paper with a heat seal layer was prepared in the same manner as in Example 1.

[0070] (Comparative Example 2) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of hydrophobic starch in coating solution A for the gas barrier layer was changed to 0 parts, resulting in coating solution G for the gas barrier layer.

[0071] (Comparative Example 3) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of polyvinylidene chloride resin in gas barrier layer coating liquid A was changed to 0 parts, resulting in gas barrier layer coating liquid H.

[0072] (Comparative Example 4) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of hydrophobic starch in gas barrier layer coating liquid A was changed to 10 parts, resulting in gas barrier layer coating liquid I.

[0073] (Comparative Example 5) In Example 1, a gas barrier paper with a heat-sealable layer was prepared in the same manner as in Example 1, except that the amount of hydrophobic starch in coating solution A for the gas barrier layer was changed to 300 parts, resulting in coating solution J for the gas barrier layer.

[0074] The gas barrier coating liquid, gas barrier paper with heat seal layer, or gas barrier paper obtained in each example and comparative example were evaluated using the method described below. The results are shown in Table 1.

[0075] (1) Corrosiveness of coating liquids for gas barrier layers A steel plate was placed in a glass container, and the gas barrier coating solution was poured in so that the entire steel plate was submerged. The container was then covered and left to stand in a constant temperature bath at 55°C for 7 days. After the test, the steel plate was removed, wiped with water, and the changes in appearance were observed visually and evaluated in the following three stages. The gas barrier coating solutions A to J described in the above examples and comparative examples were each tested, and the results are shown in Figure 1. ○: No rust at all, fully functional. △: There is slight rust, but it is still usable. ×: Due to noticeable rust, it is unusable.

[0076] (2) Surface quality of the gas barrier layer The gas barrier layer surface of the gas barrier paper, which was coated with a gas barrier coating solution onto a paper substrate and before the heat seal layer was applied, was visually observed and evaluated in the following three stages. ○: No rust defects whatsoever; fully functional. △: There are minor rust defects, but they are not noticeable, so it is still usable. ×: The rust defect is very noticeable, making it unusable.

[0077] (3) Water resistance of the gas barrier layer Before applying the heat-seal layer, one drop of water was placed on the gas barrier layer surface of the gas barrier paper from a height of 1 cm using a dropper. After 1 second, it was wiped off with a paper towel, and the removal of the gas barrier coating layer was visually inspected and evaluated in the following three stages. ○: There is absolutely no peeling of the coating layer, making it usable for practical purposes. △: There is some minor peeling of the coating layer, but it is not noticeable, so it is still usable. ×: The coating layer peels off significantly, making it unsuitable for practical use.

[0078] (4) 23℃ 50% oxygen permeability Based on the method specified in JIS K 7126-2:2006 "Plastics - Films and Sheets - Gas Permeability Test Methods - Part 2: Isobaric Method", the oxygen permeability of gas barrier paper with a heat-seal layer was measured at 23°C and 50% humidity using an oxygen permeability measuring device (MOCON OX-TRAN 2 / 22L). A smaller value indicates lower oxygen permeability. In this invention, an oxygen permeability of 50 cc / m³ is considered sufficient. 2 It can be said that it has oxygen barrier properties at 23°C and 50% humidity below day·atm.

[0079] (5) 23℃ 80% oxygen permeability Based on the method specified in JIS K 7126-2:2006 "Plastics - Films and Sheets - Gas Permeability Test Methods - Part 2: Isobaric Method", the oxygen permeability of gas barrier paper with a heat-seal layer was measured at 23°C and 80% humidity using an oxygen permeability measuring device (MOCON OX-TRAN 2 / 22L). A smaller value indicates lower oxygen permeability. In this invention, an oxygen permeability of 80 cc / m³ is considered sufficient. 2 It can be said that it has oxygen barrier properties at 23°C and 80% humidity below day·atm.

[0080] [Table 1]

[0081] [Table 2]

[0082] As is clear from Table 1, the gas barrier layer coating solutions A to F used in the examples were able to reduce the corrosiveness of the coating solutions compared to the gas barrier layer coating solutions G to J used in the comparative examples. As is clear from Table 2, according to Examples 1 to 14, gas barrier paper was obtained that was superior to the gas barrier paper obtained in Comparative Examples 1 to 5 in terms of surface quality of the gas barrier layer, water resistance of the gas barrier layer, and oxygen permeability at 50% and 80% at 23°C. As these results show, according to the present invention, it is possible to provide gas barrier paper and a method for manufacturing the same that can be produced using a general-purpose coater while reducing the amount of plastic used compared to conventional products, and that has excellent oxygen barrier properties and water resistance under high humidity conditions.

Claims

1. A gas barrier paper comprising a gas barrier layer on at least a paper substrate and at least one surface of the paper substrate, wherein the gas barrier layer comprises a polyvinylidene chloride resin and a water-soluble polymer, and comprises 20 to 220 parts by mass of the water-soluble polymer per 100 parts by mass of the polyvinylidene chloride resin.

2. The gas barrier paper according to claim 1, comprising two or more gas barrier layers on at least one surface.

3. The total coating amount of the gas barrier layer is 1 to 30 g / m². ２ The gas barrier paper according to claim 1 or 2, characterized in that it is the gas barrier paper according to claim 1 or 2.

4. The gas barrier paper according to claim 1 or 2, wherein the water-soluble polymer contained in the gas barrier layer is at least one of starch and polyvinyl alcohol.

5. The gas barrier paper according to claim 1 or 2, wherein 90% by mass or more of the gas barrier layer is composed of polyvinylidene chloride resin and a water-soluble polymer.

6. The gas barrier paper according to claim 1 or 2, characterized in that it has a heat-seal layer on the outermost surface of at least one of its surfaces.

7. The gas barrier paper according to claim 6, characterized in that the heat seal layer contains a polyolefin resin.

8. A method for producing gas barrier paper, characterized by comprising a papermaking step of making paper substrate, and a step of applying a gas barrier layer coating solution containing 20 to 220 parts by mass of a water-soluble polymer per 100 parts by mass of polyvinylidene chloride resin to at least one surface of the paper substrate obtained in the papermaking step, followed by drying the gas barrier layer coating solution.

9. The method for manufacturing gas barrier paper according to claim 8, characterized in that the process includes at least two steps of applying and drying the coating liquid for the gas barrier layer, and providing two or more gas barrier layers.

10. The total coating amount of the aforementioned gas barrier layer coating liquid is 1 to 30 g / m². ２ A method for producing gas barrier paper according to claim 8 or 9, characterized in that...

11. A method for manufacturing gas barrier paper according to claim 8 or 9, characterized in that a heat-seal layer is provided on the outermost surface of at least one of the surfaces by lamination or coating.

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