JP7544319B2 - Foam paper containers for instant foods - Google Patents

Description

The present invention relates to a foam paper container for instant food, in particular for instant food that is cooked by pouring hot water into it.

Insulated containers are generally used for instant ramen cups.
Known examples of heat-insulating containers used for such purposes include those made of expanded polystyrene (EPS). Heat-insulating containers made of EPS are produced by pouring a raw material, which is polystyrene with a foaming agent, into a mold and foaming and molding the raw material by applying heat and pressure. The EPS heat-insulating containers obtained in this manner are very excellent in terms of heat insulation because the entire container is foamed. However, from the viewpoint of saving petroleum resources, there is a demand to reconsider their use.

Instead of expanded polystyrene derived from petroleum resources, paper containers using paper derived from biomass are becoming more common. Patent Document 1 discloses a paper container with thermal insulation properties, in which a low-melting thermoplastic synthetic resin film is laminated to the outer wall surface of the container body member and heated, and the film is foamed into an uneven shape using the vapor pressure of the moisture contained in the base paper, in a paper container consisting of a body member and a bottom plate member. Patent Document 2 discloses a paper container in which a two-layer structure thermal insulation film is attached to one wall surface of the body member from the surface side of the paper, and the film is foamed into an uneven shape using the vapor pressure of the moisture contained in the base paper.

Containers for instant foods are required to have high gas barrier properties (in this invention, this means flavor barrier properties in particular) that prevent internal aromas from escaping and prevent external odors from entering. The paper containers described in Patent Documents 1 and 2 have insufficient gas barrier properties, and laminating a film or the like having gas barrier properties not only increases costs, but also poses the problem of odors being generated from the adhesive used to bond the film and low molecular weight components in the film.

Japanese Unexamined Patent Publication No. 57-110439 Japanese Patent Application Publication No. 05-042929

The objective of the present invention is to provide a foamed paper container for instant food that has excellent gas barrier properties (in this invention, this particularly means flavor barrier properties) that prevent internal aromas from escaping and external odors from entering, and that has excellent manufacturing efficiency.

The means for solving the problems of the present invention are as follows.
1. A foamed paper container for instant food comprising a body member and a bottom plate member,
The body member includes, from the outer surface side, a foam insulation layer, a paper barrier substrate, and a liquid-impermeable layer,
The bottom plate member includes a paper base material and a liquid-impermeable layer from the outer surface side,
the paper barrier substrate of the body member has, on a paper substrate, a filling layer containing an inorganic pigment and a binder resin, and a gas barrier layer containing an inorganic pigment and a polyvinyl alcohol-based resin, in this order;
A foamed paper container for instant food, comprising the liquid-impermeable layer on the gas barrier layer.
2. The foamed paper container for instant food according to 1., wherein the bottom plate member further comprises at least one thermoplastic resin layer selected from polyester-based resins and polyamide-based resins.
3. A foamed paper container for instant food comprising a body member and a bottom plate member,
The body member includes, from the outer surface side, a foam insulation layer, a paper barrier substrate, and a liquid-impermeable layer,
The bottom plate member includes a paper barrier substrate and a liquid-impermeable layer from the outer surface side,
the paper barrier substrate provided on the body member and the bottom plate member has, on a paper substrate, a filling layer containing an inorganic pigment and a binder resin, and a gas barrier layer containing an inorganic pigment and a polyvinyl alcohol-based resin, in this order;
A foamed paper container for instant food, comprising the liquid-impermeable layer on the gas barrier layer.
4. The foamed paper container for instant food according to any one of 1. to 3., characterized in that the foamed heat-insulating layer and the liquid-impermeable layer are made of thermoplastic resin, and the melting point of the thermoplastic resin of the foamed heat-insulating layer is 5°C or more lower than the melting point of the thermoplastic resin of the liquid-impermeable layer.
5. The foamed paper container for instant food according to any one of 1. to 4., wherein the gas barrier layer further contains at least one selected from the group consisting of polyethyleneimine, an organotitanium compound, and a polybutadiene compound.
6. The foam paper container for instant food according to any one of 1. to 5., characterized in that the internal bond strength of the paper substrate of the paper barrier substrate is 1.5 kgf cm or more, as measured in accordance with "Paper and paperboard-Internal bond strength test method-Part 2: Internal bond tester method" specified in J. TAPPI No. 18-2:2000.

The foamed paper container for instant food of the present invention has a body member that is equipped with a paper barrier substrate that has gas barrier properties, so that the aroma inside is not lost and the intrusion of odors from the outside can be prevented. The foamed paper container for instant food of the present invention has a body member that is equipped with a foamed insulating layer on the outer surface side, so that the container filled with hot water can be held by hand.

The foamed paper container for instant food (hereinafter also referred to as a paper container) of the present invention is characterized in that it comprises a body member and a bottom plate member, the body member comprising, from the outer surface side, a foamed insulation layer, a paper barrier substrate, and a liquid impermeable layer, the bottom plate member comprising, from the outer surface side, a paper substrate or a paper barrier substrate, and a liquid impermeable layer, the body member, or the paper barrier substrate comprised by the body member and the bottom plate member, has, on the paper substrate, a filling layer containing an inorganic pigment and a binder resin, and a gas barrier layer containing an inorganic pigment and a polyvinyl alcohol resin, in this order, and has the liquid impermeable layer on the gas barrier layer.

The present invention will be described in detail below.
"Paper barrier substrate"
The paper barrier substrate has a filling layer and a gas barrier layer, in this order, on a paper substrate.
Paper Base Material The paper base material is obtained by papermaking a paper material containing pulp, fillers, various auxiliaries, etc.
As the pulp, known pulps such as bleached kraft pulp (NBKP), unbleached kraft pulp (NUKP), bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP), and sulfite pulp (SP) can be appropriately mixed and used, as well as mechanical pulps such as ground pulp (GP), refiner ground pulp (RGP), stone ground pulp (SGP), chemi-ground pulp (CGP), semi-chemical pulp (SCP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), and non-wood pulp obtained from kenaf, bagasse, bamboo, hemp, straw, etc. can be used. Among these, chemical pulps such as LBKP and NBKP, which are less likely to be mixed with foreign matter, are preferred. Specifically, the amount of chemical pulp is preferably 80% or more, and it is particularly preferred that the amount of chemical pulp is 100%.

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

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

The method of manufacturing (papermaking) the paper base material and the type of papermaking machine are not particularly limited, and known manufacturing (papermaking) methods and papermaking machines can be selected, such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a short wire papermaking machine, a twin-wire papermaking machine such as a gap former type or a hybrid former type (on-top former type). The pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking), and after papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer. The base paper may be one layer, or may be composed of two or more layers.

The basis weight of the paper base material can be appropriately selected depending on the handling properties, etc., but is usually preferably about 200 g/m ² or more and 400 g/m ² or less, and more preferably 250 g/m ² or more and 350 g/m ² or less.
In the present invention, the amount of moisture contained in the paper base material is important because the foamed insulation layer before foaming (hereinafter also simply referred to as "unfoamed layer") is foamed by the water vapor generated from the moisture contained in the paper base material to form a foamed insulation layer. The amount of moisture contained in the paper base material is determined by the basis weight and moisture content of the paper base material, and is preferably 5 g/m ² or more, more preferably 10 g/m ² or more, and even more preferably 15 g/m ² or more. It is also preferably 60 g/m ² or less, and more preferably 40 g/m ² or less.

The density of the paper substrate of the present invention may be appropriately set according to the desire, and is not particularly limited, but is preferably 0.60 g/cm ³ or more and 0.99 g/cm ³ or less. When the density of the paper substrate is low, water vapor tends to pass through easily and foamability tends to improve, but when the density of the paper substrate is less than 0.60 g/cm ³ , the paper strength required for the paper container may not be obtained. On the other hand, when the density of the paper substrate is more than 0.99 g/cm ³ , water vapor tends to pass through less easily and foamability tends to decrease. In addition, when the foamability is not uniform enough, a coating liquid having affinity with paper, such as polyvinyl alcohol or starch, can be applied so that water vapor can be uniformly evaporated from the surface of the paper substrate.

Filler layer The filler layer prevents the gas barrier layer coating liquid from sinking into the paper substrate when the gas barrier layer is provided, thereby preventing a decrease in gas barrier properties. The filler layer contains an inorganic pigment and a binder resin. The filler layer can contain a sizing agent, a water-resistant agent, a water-repellent agent, a dye, a surfactant, etc., as necessary.

Examples of inorganic pigments include light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, engineered kaolin, clay, delaminated clay, talc, silica, colloidal silica, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, aluminum hydroxide, alumina, magnesium carbonate, magnesium hydroxide, kaolinite, antigorite, smectite, vermiculite, and mica. As inorganic pigments, these can be used alone or in combination of two or more.

As the binder resin, any type generally used in the field of coated paper can be used as appropriate. For example, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols, (meth)acrylic acid, and monomer components copolymerizable with (meth)acrylic acid (olefins), Examples of binders include acrylic resins made of cellulose acetate (excluding cellulose acetate), cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, ethyl cellulose, and acetyl cellulose, starches such as oxidized starch, etherified starch, and esterified starch, styrene-maleic anhydride copolymers, styrene-butadiene copolymers, casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid esters, polyvinyl butyral, polystyrene and copolymers thereof, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. Binders can be used alone or in combination of two or more.

Gas Barrier Layer The gas barrier layer contains an inorganic pigment and a polyvinyl alcohol resin, and provides gas barrier properties. As the inorganic pigment, the inorganic pigments usable in the filling layer described above can be appropriately used. As the inorganic pigment, one or a mixture of two or more of these can be used.

As polyvinyl alcohol resins, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, and other modified polyvinyl alcohols can be used.

In addition, the gas barrier layer may contain at least one selected from polyethyleneimine, an organic titanium compound, and a polybutadiene compound in order to improve adhesion with the liquid-impermeable layer described below. Examples of the organic titanium compound include titanium alkoxides such as titanium-i-propoxyoctylene glycolate and di-i-propoxy bis(acetylacetonato)titanium, and specific examples include the "Orgatics" series manufactured by Matsumoto Fine Chemical Co., Ltd. In addition, examples of the polybutadiene compound include the liquid polybutadiene "NISSO-PB" series manufactured by Nippon Soda Co., Ltd. In addition, cellulose nanofibers may be contained to aid in barrier properties.
These components (compounds) that improve adhesion to the liquid-impermeable layer may be contained in a coating liquid for forming the gas barrier layer, or may be incorporated by coating on the gas barrier layer using a known coating device or the like after the gas barrier layer has been formed.

The inorganic pigment is preferably used in an amount of 1 part by weight to 1,000 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin in terms of dry weight. In the present invention, when the inorganic pigment is blended into the coating liquid for the gas barrier layer, it is preferable to add and mix the inorganic pigment in a slurried form.
Furthermore, in the present invention, in addition to the inorganic pigment and polyvinyl alcohol-based resin, various commonly used auxiliary agents such as dispersants, thickeners, water retention agents, defoamers, water-resistant agents, dyes, fluorescent dyes, and crosslinking agents may be used in the gas barrier layer.

In the present invention, a paper barrier substrate can be produced by sequentially coating and drying coating solutions for forming a filling layer and a gas barrier layer on a paper substrate.
The coating method of the sealing layer and the gas barrier layer is not particularly limited, and they can be coated using a known coating device and coating system. For example, the coating device may be a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, a gate roll coater, etc. In addition, the coating system may be an aqueous coating using a solvent such as water, or a solvent coating using a solvent such as an organic solvent, etc.
As a method for drying the filling layer and the gas barrier layer, for example, a usual method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, a cylinder dryer, etc. is used.

The coating amount of the filling layer is preferably 3 g/ ^m2 or more and 15 g/ ^m2 or less in terms of dry weight. If the coating amount is less than 3 g/ ^m2 , the filling effect may be insufficient. On the other hand, if it is more than 15 g/ ^m2 , the drying load during coating becomes large, which is not preferable from the viewpoints of both operation and cost.
The coating amount of the gas barrier layer is preferably 0.2 g/ ^m2 or more and 20 g/ ^m2 or less in terms of dry weight. If the coating amount of the gas barrier layer is less than 0.2 g/ ^m2 , it is difficult to form a uniform gas barrier layer, and sufficient gas barrier properties may not be obtained. On the other hand, if it is more than 20 g/ ^m2 , the drying load during coating becomes large, which is not preferable from the viewpoints of both operation and cost.

"Manufacturing method of foam paper containers for instant food"
In the present invention, a liquid-impermeable layer, an unfoamed layer which will later become the foamed insulation layer, and another liquid-impermeable layer are laminated onto the above-mentioned paper barrier substrate to form a body member, and a liquid-impermeable layer is laminated onto the paper substrate or the paper barrier substrate to form a bottom plate member.

"Liquid-impermeable layer"
The liquid impermeable layer is located on the inner surface side of the body member and the bottom plate member, and prevents liquid poured into the container after it has been formed into a container from penetrating into the paper barrier substrate.
The liquid-impermeable layer can be made of any material that can achieve the intended purpose, and for example, a thermoplastic resin can be suitably used. The body member and bottom plate member having a liquid-impermeable layer made of a thermoplastic resin can be molded into a paper container by heat sealing. As the thermoplastic resin, either a crystalline resin or a non-crystalline resin can be used.

Examples of crystalline thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene, polyester resins, polyamide, polyacetal, and polyphenylene sulfide (PPS) resin. Examples of non-crystalline thermoplastic resins include polystyrene, polyvinyl chloride, ABS resin, acrylic resin, modified polyphenylene ether (PPE), polycarbonate, polyurethane, polyvinyl acetate, and non-crystalline polyethylene terephthalate (PET). Thermoplastic resins derived from plants such as polylactic acid (PLA), cellulose acetate, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate/terephthalate (PBAT), polyhydroxyalkanoate (PHA), biomass polyethylene, and biomass polyethylene terephthalate may also be used. These thermoplastic resins can be used in a single layer or in multiple layers. In addition, the same or different thermoplastic resins can be used in the liquid-impermeable layers of the body member and the bottom plate member.

As the thermoplastic resin, polyethylene is preferred from the viewpoint of suitability for extrusion lamination and heat sealing, and in particular, low-density polyethylene or medium-density polyethylene with a high melting point is preferred, but high-density polyethylene or a blend resin of high-density polyethylene and low-density polyethylene may also be used. When polyethylene is used for the liquid-impermeable layer, its melting point is preferably 105°C or higher, and more preferably 110°C or higher.

"Foam insulation layer"
The foamed insulation layer is located on the outer surface side of the body member. In the paper container of the present invention, the bottom plate member can also have a foamed insulation layer on its outer surface side. By having a foamed insulation layer on at least the outer surface side of the body member, the paper container of the present invention is less susceptible to heat transfer to the outer surface even when hot water is poured into the container, so the paper container can be held in the hand for eating and drinking.

The foamed insulation layer can be made of any material that can achieve the intended purpose, and can be, for example, any of the thermoplastic resins listed for the liquid-impermeable layer. As the thermoplastic resin, either crystalline or non-crystalline thermoplastic resins can be used, and thermoplastic resins derived from plants can also be used. When an unfoamed layer made of a thermoplastic resin is foamed to form a foamed insulation layer, a single layer is preferable from the viewpoint of foamability.

The thermoplastic resin used in the foamed insulation layer of the present invention is preferably polyethylene because of its excellent suitability for extrusion lamination and foamability, and is more preferably low-density polyethylene because of its particularly excellent foamability, and even more preferably low-density polyethylene with a melting point of 90°C or higher and 120°C or lower.

In the paper container of the present invention, the melting point of the thermoplastic resin used in the foamed insulation layer is preferably lower than the melting point of the thermoplastic resin contained in the liquid-impermeable layer. In this way, when the unfoamed layer is foamed by water vapor generated by heating to form the foamed insulation layer, the unfoamed layer is easily foamed and the liquid-impermeable layer can be prevented from melting. This difference in melting points is preferably 5°C or more, and more preferably 10°C or more. If the difference in melting points is less than 5°C, it may be difficult to control the temperature during foaming.

In the present invention, a liquid-impermeable layer and a non-foamed layer, which will later become a foamed insulating layer, can be formed by laminating a liquid-impermeable layer and a non-foamed layer, or a liquid-impermeable layer, on a paper barrier substrate using various methods such as extrusion lamination, wet lamination, dry lamination, etc. The extrusion lamination method is preferred because it provides good adhesion between the paper substrate and the liquid-impermeable layer or the non-foamed layer, and good foamability of the non-foamed layer.
It is preferable that the time interval between providing the liquid-impermeable layer and the unfoamed layer is short. If the time interval is too long, moisture may escape from the paper base material, and sufficient water vapor may not be generated. In addition, it does not matter which of the liquid-impermeable layer and the unfoamed layer is provided first.

In the present invention, the operating conditions of the extrusion lamination method, i.e., the melting temperature of the thermoplastic resin, lamination speed, etc., may be appropriately set depending on the type of thermoplastic resin and the equipment used, and are not particularly limited, but generally, the melting temperature is about 200 to 350°C, and the lamination speed is about 50 to 200 m/min. In addition, it is preferable to use a nip roll with a hardness of 70 degrees or more (JIS K-6253), and to perform pressing and bonding by the cooling roll and the opposing nip roll at a linear pressure of 15 kgf/cm or more.

The thickness of the liquid-impermeable layer is preferably 20 μm or more and 200 μm or less. If the thickness of the liquid-impermeable layer is less than 20 μm, the heat seal strength may be insufficient. If the thickness of the liquid-impermeable layer is more than 200 μm, the quality is hardly improved.
The thickness of the unfoamed layer is not particularly limited as long as a foamed heat insulating layer of desired quality can be obtained, but it is preferably 30 μm or more and 80 μm or less. Within this range, sufficient heat insulating properties can be achieved after foaming.

When the bottom plate member comprises a paper substrate, at least one thermoplastic resin layer selected from polyester-based resins or polyamide-based resins may be further provided between the paper substrate and the liquid-impermeable layer.
The polyester resin is not particularly limited, but one or more selected from polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), polyarylate (PAR), polyhydroxyalkanoic acid (PHA) (polyester resin composed of 3-hydroxyalkanoic acid), polylactic acid (PLA), polycarbonate (PC), etc. Among these, more preferred polyester resins include PET, PBS, PBSA, PBT, and PEN.
Examples of polyamide resins include those obtained by polycondensation of lactams having three or more ring members and ω-amino acids, and those obtained by co-condensation of diamines and dicarboxylic acids. Specific examples of polyamide resins include nylon 4, nylon 6, nylon 7, nylon 11, nylon 12, nylon 46, nylon 66, nylon 69, and nylon MXD6. These polyamide resins may be used alone or in combination of two or more. Among these, more preferred polyamide resins include nylon 6 and nylon 6-66 from the viewpoints of heat resistance and cost.

The laminate of the liquid-impermeable layer, paper barrier substrate, and unfoamed layer obtained above is punched out to form a body member. Also, any laminate, such as a laminate of the liquid-impermeable layer and paper substrate, or a laminate of the liquid-impermeable layer, paper substrate, and unfoamed layer, is punched out to form a bottom plate member. The body member and bottom plate member are put into a cup forming machine so that the liquid-impermeable layer faces the inner surface, to form a cup shape (unfoamed cup).
At this time, particularly when the paper substrate of the paper barrier substrate is a multi-layered product, if the internal bond strength of the paper substrate is weak, the inside of the paper substrate will be destroyed at the top curl part during cup formation or at the creased part of the carton blank, causing molding defects. The internal bond strength of the paper substrate can be measured in accordance with "Paper and paperboard - Internal bond strength test method - Part 2: Internal bond tester method" specified in J. TAPPI No. 18-2:2000, and if this internal bond strength is 1.5 kgf cm or more, preferably 1.8 kgf cm or more, and more preferably 2.0 kgf cm or more, destruction is unlikely to occur inside the paper substrate during formation, and molding defects can be prevented.

This unfoamed cup is heated to convert the moisture contained in the paper base material into steam, and this steam is then ejected onto the unfoamed layer side to turn the unfoamed layer into a foamed insulating layer, thereby obtaining the foamed paper container for instant food of the present invention.
In the present invention, the unfoamed layer of the body member is formed on the paper base material of the paper barrier substrate, and the other surface of the paper base material has a sealing layer, a gas barrier layer, and a liquid-impermeable layer. The water vapor generated inside the paper base material cannot escape to the gas barrier layer side due to the liquid-impermeable layer, and is mainly ejected to the unfoamed layer side, so that the foamed insulation layer can be formed efficiently. The heating temperature and heating time for forming the foamed insulation layer can be appropriately adjusted depending on the application and purpose. The heating temperature is set to be equal to or higher than the melting point of the resin contained in the unfoamed layer and equal to or lower than the melting point of the resin contained in the liquid-impermeable layer.

The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. Unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight of solid content, respectively.

(Preparation of coating solution for filling layer)
The following mixture was stirred and dispersed to prepare a coating liquid for the filling layer.
<Coating solution for sealing layer>
Fine kaolin (KaMin: Hydragloss) 60.0 parts Engineered kaolin (Imeris: Capim DG) 20.0 parts Sodium polyacrylate 0.5 parts Heavy calcium carbonate (Fimatec: FMT-90) 20.0 parts Styrene-butadiene copolymer latex (Nippon Zeon: PNT8110) 20.0 parts Oxidized starch (Shikishima Starch: Mermaid M210) 2.0 parts Water 71.7 parts

(Preparation of Coating Solution for Gas Barrier Layer)
The following composition was stirred and dispersed to prepare a coating solution for the gas barrier layer.
<Gas barrier layer coating fluid>
Engineered kaolin (Imeris: Barisurf HX) 100.0 parts Sodium polyacrylate 0.2 parts Polyethyleneimine 3.0 parts Polyvinyl alcohol (Kuraray, PVA117) 100.0 parts Water 1801.8 parts

"Example 1"
[0043] The coating liquid for the filling layer was coated on one side of a paper substrate (paper container base paper with a basis weight of 300 g/ ^m2 , three-layer product) by the blade method so that the coating amount was 6.0 g/ ^m2 in dry weight, and then dried, and the coating liquid for the gas barrier layer was coated thereon by the air knife method so that the coating amount was 3.0 g/ ^m2 in dry weight, and then dried, and the substrate was treated using a soft nip calendar under a linear pressure of 60 kN/m to obtain a paper barrier substrate. The internal bond strength of the paper substrate of this paper barrier substrate was measured in accordance with J. TAPPI No. 18-2:2000 and was found to be 2.01 kgf cm.

A medium-density polyethylene (L5721, melting point 128°C, manufactured by Sumitomo Chemical Co., Ltd.) was laminated as a liquid impermeable layer to a thickness of 40 μm by extrusion lamination at a die temperature of 330°C on the gas barrier layer side of this paper barrier substrate. The adhesion between the gas barrier layer and the liquid impermeable layer was at a paper peeling level. Next, a low-density polyethylene (LC602A, melting point 107°C, manufactured by Japan Polyethylene Co., Ltd.) was laminated as an unfoamed layer to a thickness of 70 μm by extrusion lamination at a die temperature of 330°C on the paper substrate side of the paper barrier substrate. In order to improve adhesion with the ink for pattern printing, an in-line corona treatment (3.4 Kw) was also performed at the same time. It was confirmed that the adhesion between the paper substrate and the unfoamed layer was also at a paper peeling level. Then, a pattern was printed on the unfoamed layer by gravure printing. This configuration was used as a body member.

A paper substrate with a basis weight of 210 g/ ^m2 was used, and a filling layer and a gas barrier layer were provided in the same manner as above. A medium-density polyethylene (L5721, melting point 128°C, manufactured by Sumitomo Chemical Co., Ltd.) was laminated as a liquid impermeable layer to a thickness of 40 µm by extrusion lamination at a die temperature of 330°C. This configuration was used as a bottom plate member.
Next, after punching out into a predetermined shape, the unfoamed cup was molded in a cup molding machine to obtain a non-foamed cup. At this time, it was confirmed that there was no problem with the appearance and moldability of the non-foamed cup. There was also no problem with the moldability of the top curl.
The foaming treatment of the unfoamed layer was carried out as follows. The unfoamed cup was passed through a foaming oven at 115°C for 6 minutes to foam the low-density polyethylene of the unfoamed layer. After gradual cooling for 30 seconds, a foamed paper container for instant food according to the present invention was obtained, which has a foamed insulation layer formed by the foaming of the unfoamed layer. It was confirmed that there was no problem with the appearance after foaming.

"Example 2"
The body member used was the same as in Example 1.
Using a tandem extrusion laminator, a medium density polyethylene (Sumitomo Chemical Co., Ltd.: L5721) was laminated to a thickness of 15 μm as a first liquid impermeable layer on one ^side of a paper substrate (paper container base paper with a basis weight of 220 g/m2, single layer product), and a PET film (Toyobo Co., Ltd.: E5100, thickness 12 μm) was sandwiched and laminated. Next, a medium density polyethylene (Sumitomo Chemical Co., Ltd.: L5721) was laminated to a thickness of 35 μm on the PET film as a second liquid impermeable layer, and this configuration was used as a bottom plate member.
Next, in the same manner as in Example 1, cup molding and foaming of the unfoamed layer were carried out, and it was confirmed that there was no problem with the appearance after foaming.

"Comparative Example 1"
A coating liquid for a filling layer was applied to one side of a paper substrate (a paper container base paper having a basis weight of 300 g/ ^m2 , a three-layer product) by a blade method so that the coating amount was 6.0 g/ ^m2 in terms of dry weight, and then dried. A body member was obtained in the same manner as in Example 1, except that no gas barrier layer was applied, the thickness of the liquid impermeable layer was 40 μm, and the thickness of the unfoamed layer was 50 μm.
The bottom plate member was made of a paper substrate (paper container base paper with a basis weight of 220 g/ ^m2 , single layer product) with low density polyethylene (Japan Polyethylene Corporation: LC602A) laminated on one side to a thickness of 40 μm as a liquid impermeable layer by extrusion lamination.

Thereafter, a pattern was printed on the unfoamed layer by gravure printing. Next, the sheet was punched out to a predetermined size and then molded into a cup by a cup molding machine.
The unfoamed layer was foamed in the same manner as in Example 1, and it was confirmed that there was no problem with the appearance after foaming.

"Reference Example 1"
Using a tandem extrusion laminator, a ^medium density polyethylene (Sumitomo Chemical Co., Ltd.: L5721) was laminated to a thickness of 15 μm as a first liquid impermeable layer on one side of a paper substrate (paper container base paper with a basis weight of 320 g/m2, 3-ply product), and a PET film (Toyobo Co., Ltd.: E5100, thickness 12 μm) was sandwiched and laminated. Subsequently, a medium density polyethylene (Sumitomo Chemical Co., Ltd.: L5721) was laminated to a thickness of 35 μm on the PET film as a second liquid impermeable layer.
Next, low-density polyethylene (Japan Polyethylene Corporation: LC602A) was extrusion laminated to a thickness of 70 μm on the other side of the paper substrate as an unfoamed layer, and in order to improve adhesion with the ink for pattern printing, in-line corona treatment (3.4 Kw) was also performed at the same time to produce a laminate substrate. It was confirmed that the adhesion was at the level of paper peeling on both sides. This configuration was used as a trunk member.

The bottom plate member used was the same as that used in Example 2.
Thereafter, a pattern was printed on the unfoamed layer by gravure printing. Next, the sheet was punched out to a predetermined size and then molded into a cup by a cup molding machine.
The unfoamed layer was foamed in the same manner as in Example 1, and it was confirmed that there was no problem with the appearance after foaming.

The gas barrier property (flavor barrier property) was measured by the following method.
(Method of measuring gas barrier properties (flavor barrier properties))
1) Place one serving of instant noodles into a foam paper container for instant food and heat seal the aluminum lid to seal it tightly.
2) Prepare a measurement sample by shrink wrapping in PP (prepare a measurement sample for each specification).
3) Place the measurement samples for the 1st, 4th, and 7th days into a 18 L can at the same time, enclose 7 packets of Neopara Ace (registered trademark) (manufactured by S.T. Co., Ltd., approximately 50 g) as an odor source, and seal with a steel lid.
4) On the first, fourth and seventh days, measurement samples were taken out, the instant noodles were removed from the foam paper containers for instant foods and placed in non-absorbent bags and sealed.
5) The instant noodles are crushed in the bag, and then the needle of a microsyringe is inserted into the bag to extract 10 μL of gas.
6) The separated gas is subjected to a gas chromatograph, and the amount of adsorption is measured from the area ratio based on the previously measured calibration curve.
7) From the four-point plot of the initial point (untreated product), the 1st day, the 4th day, and the 7th day, an approximation line with an intercept of 0 is determined, and the gas barrier property (flavor barrier property) is calculated from the slope. Note that, for N=3 measurements, the gas barrier property of Reference Example 1 is taken as 1, and the relative values (minimum to maximum) are shown in the table.

Reference Example 1, which has a PET laminate layer with excellent flavor barrier properties, was set as 1, and the gas barrier properties (flavor barrier properties) were compared. Examples 1 and 2 according to the present invention achieved barrier properties roughly equivalent to that of Reference Example 1. Barrier properties vary somewhat depending on the material of the bottom plate member and the area ratio of the body member to the surface area of the container. On the other hand, the gas barrier properties (flavor barrier properties) of Comparative Example 1, which did not have a gas barrier layer, were relatively significantly inferior.

Claims (5)

A foamed paper container for instant food comprising a body member and a bottom plate member,
The body member includes, from the outer surface side, a foam insulation layer, a paper barrier substrate, and a liquid-impermeable layer,
The bottom plate member includes a paper base material and a liquid-impermeable layer from the outer surface side,
the paper barrier substrate of the body member has, on a paper substrate, a filling layer containing an inorganic pigment and a binder resin, and a gas barrier layer containing an inorganic pigment and a polyvinyl alcohol-based resin, in this order;
The liquid-impermeable layer is provided on the gas barrier layer,
A foamed paper container for instant food, characterized in that the paper base material of the paper barrier substrate is a multi-layer paper having an internal bond strength of 1.5 kgf cm or more, measured in accordance with "Paper and paperboard - Internal bond strength test method - Part 2: Internal bond tester method" specified in J. TAPPI No. 18-2:2000 (excluding those in which the paper base material is composed of three paper layers, an inner layer and outer layers provided on both sides of the inner layer, the weight ratio of outer layer:inner layer:outer layer is 1:2:1 to 1:3:1, and the internal bond strengths specified in J. TAPPI No. 18-2:2000 are 0.20 to 0.36 N m for the outer layer and 0.05 to 0.28 N m for the inner layer) . The foamed paper container for instant food according to claim 1, characterized in that the bottom plate member further has at least one thermoplastic resin layer selected from polyester-based resins and polyamide-based resins. A foamed paper container for instant food comprising a body member and a bottom plate member,
The body member includes, from the outer surface side, a foam insulation layer, a paper barrier substrate, and a liquid-impermeable layer,
The bottom plate member includes a paper barrier substrate and a liquid-impermeable layer from the outer surface side,
the paper barrier substrate provided on the body member and the bottom plate member has, on a paper substrate, a filling layer containing an inorganic pigment and a binder resin, and a gas barrier layer containing an inorganic pigment and a polyvinyl alcohol-based resin, in this order;
The liquid-impermeable layer is provided on the gas barrier layer,
A foamed paper container for instant food, characterized in that the paper base material of the paper barrier substrate is a multi-layer paper having an internal bond strength of 1.5 kgf cm or more, measured in accordance with "Paper and paperboard - Internal bond strength test method - Part 2: Internal bond tester method" specified in J. TAPPI No. 18-2:2000 (excluding those in which the paper base material is composed of three paper layers, an inner layer and outer layers provided on both sides of the inner layer, the weight ratio of outer layer:inner layer:outer layer is 1:2:1 to 1:3:1, and the internal bond strengths specified in J. TAPPI No. 18-2:2000 are 0.20 to 0.36 N m for the outer layer and 0.05 to 0.28 N m for the inner layer) . The foamed paper container for instant food according to any one of claims 1 to 3, characterized in that the foamed insulation layer and the liquid-impermeable layer are made of thermoplastic resin, and the melting point of the thermoplastic resin of the foamed insulation layer is 5°C or more lower than the melting point of the thermoplastic resin of the liquid-impermeable layer. The foamed paper container for instant food according to any one of claims 1 to 4, characterized in that the gas barrier layer further contains at least one selected from polyethyleneimine, an organotitanium compound, and a polybutadiene compound.