Cover material

Abstract

The present invention aims to provide a lid material that can reduce the amount of plastic used, has a high biomass ratio, is easy to open and adheres well, and has oxygen barrier properties. [Solution] The present invention relates to a lid material having an oxygen barrier layer and a composite film laminate layer provided in that order on at least one side of a paper substrate, wherein the ash content of the paper substrate is 0-15%, and the oxygen barrier layer contains hydrophobic starch.

Description

[Technical Field]

[0001] The present invention relates to a lid material that is an environmentally friendly product with a high biomass ratio that can reduce the amount of plastic used, and that has excellent ease of opening, airtightness, and oxygen barrier properties. [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 global environment.

[0003] In packaging containers, barrier performance that blocks oxygen, water vapor, water, and oil is a crucial feature. 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. Oxygen barrier films used as packaging paper for food applications are mostly multilayered, consisting of at least three layers: a base layer, an oxygen barrier layer with oxygen barrier properties, and a heat-seal layer. Examples of multilayered 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 multilayered 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 2The above 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. Furthermore, the above-mentioned composite films are used as lids for containers of food, pet food, cosmetics, sanitary products, pharmaceuticals, and industrial products. If the amount of plastic film (especially oxygen barrier films) used in these lids can be reduced, it will help solve the plastic waste problem.

[0004] As a measure to reduce the amount of plastic used, it has been proposed to replace plastic with paper. Patent document 3 proposes a lid material using paper that has excellent oxygen barrier properties by providing a water vapor barrier layer on a paper substrate, an oxygen barrier layer containing polyvinyl alcohol on the water vapor barrier layer, and a sealant layer on the oxygen barrier layer. However, in the case of the lid material according to Patent document 3, the polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA") used in the oxygen barrier layer is biodegradable but is a petrochemical product, so it is not possible to increase the biomass ratio. In addition, it has the disadvantage that the oxygen barrier properties decrease to about 1 / 10 to 1 / 20 under high humidity. Furthermore, because the specific heat of the paper substrate is lower than that of plastic film, when the lid material is heat-sealed to the container, too much heat is applied, resulting in excessive heat seal strength, making it difficult to open and resulting in poor ease of opening. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-71036 [Patent Document 2] Patent No. 7373682 [Patent Document 3] Japanese Patent Publication No. 2017-124851 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention relates to a lid material that is an environmentally friendly product capable of reducing the amount of plastic used, has a high biomass ratio, excellent easy-opening property and adhesion (sealing property), and has oxygen barrier properties. Generally, while the heat seal of a flexible packaging material is linear, the lid material is heat-sealed in a closed curve shape, so there is no escape route for the stress generated by instantaneous heat and pressure, and wrinkles are likely to occur. When wrinkles occur, the adhesion to the container decreases. Therefore, designing to improve the adhesion is more difficult than in the case of flexible packaging materials.

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

Means for solving the problems

[0008] In order to improve the easy-opening property and airtightness of a conventional environmentally friendly lid material, the lid material of the present invention includes a paper base material, an oxygen barrier layer, and a composite film laminate layer in this order, and is characterized in that the oxygen barrier layer contains hydrophobized starch. That is, the lid material of the present invention includes an oxygen barrier layer and a composite film laminate layer on at least one side of a paper base material, and is a lid material that includes an oxygen barrier layer between the paper base material and the composite film laminate layer. The hydrophobized starch contained in the oxygen barrier layer is a biomass of natural polysaccharides, and can reduce the amount of plastic used compared to a conventional oxygen barrier layer mainly composed of plastics such as NY and PET, and also has biodegradability. In addition, since hydrophobized starch is superior in heat resistance compared to general starch (non-hydrophobized starch), the change in the thickness of the oxygen barrier layer due to expansion and contraction during heat sealing to the container is small, and as a result, a lid material with excellent adhesion can be obtained.

[0009] Furthermore, in the present invention, the ash content of the paper base material is 0 to 15%. Since the filler added to the paper base material has a low specific heat, when the ash content exceeds 15%, too much heat is applied during heat sealing with the container, the heat seal strength rises excessively, and the easy-opening property deteriorates. Preferably, it is 0 to 13%.

[0010] In the present invention, it is preferable that the hydrophobic starch is any one or more selected from the group consisting of hydroxyethylated starch, hydroxypropyl starch, hydroxypropyl phosphate crosslinked starch, acetylated starch, acetylated adipic acid crosslinked starch, and octenyl succinic acid esterified starch. More preferably, as the hydrophobic starch, an oxygen barrier layer is formed by mainly containing any one or more selected from the group consisting of hydroxylethylated starch and octenyl succinic acid esterified starch. The oxygen barrier layer has excellent oxygen barrier properties and heat resistance.

[0011] In the present invention, it is preferable that the coating amount of the oxygen barrier layer is in the range of 0.3 to 10 g / m in terms of dry coating amount. By adopting such a configuration, a uniform barrier film can be formed. 2

[0012] In the present invention, it is preferable that the thickness of the composite film is 15 μm to 100 μm. By adopting such a configuration, the adhesiveness and oxygen barrier properties are more excellent.

[0013] In the present invention, it is preferable that a blocking layer is provided between the paper substrate and the oxygen barrier layer. Since it has the effect of preventing the coating liquid for the oxygen barrier layer from penetrating into the paper substrate, a barrier film with fewer defects can be formed even with a coating layer having a small coating amount. The blocking layer preferably contains a pigment and latex. It has excellent blocking effect and coating suitability of the coating liquid for the oxygen barrier layer.

Advantages of the Invention

[0014] According to the present invention, an environmentally friendly product with a reduced amount of plastic used can be manufactured, which also has a high biomass ratio, excellent easy-opening property, sealing property, adhesiveness, and an oxygen barrier property, and a lid material can be manufactured. In the present invention, the oxygen permeability of the lid material is 50 cc / m 2 ·day·atm or less, preferably 30 cc / m 2 ​The temperature can be less than or equal to 1 day·atm. Furthermore, even if the lid material of the present invention is improperly released into the natural environment as waste, it is possible to reduce the adverse impact of plastic waste on the natural environment, thus contributing to the solution of the plastic waste problem. The lid material of the present invention can be processed into lids for food cups and trays such as ice cream, yogurt, salads, and confectionery. It can also be applied to container lids for non-food items such as pet food, cosmetics, sanitary products, hygiene products, pharmaceuticals, and industrial products. [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 lid material of the present invention has an oxygen barrier layer and a composite film laminate layer provided in that order on at least one side of a paper substrate, the ash content of the paper substrate (JIS P 8251 "Paper and paperboard - Ash content test method") is 0 to 15%, and the oxygen barrier layer contains hydrophobic starch. Regarding the ash content of the paper substrate, since the filler added to the paper substrate has a low specific heat, if the ash content exceeds 15%, too much heat is applied during heat sealing with the container, the heat seal strength increases excessively, and the ease of opening deteriorates. Preferably, the ash content is 0 to 13%. More preferably, it is 0 to 12%.

[0017] The aforementioned hydrophobic starch is a type of modified starch in which starch molecules are given hydrophobic (lipophilic) properties. Originally, starch itself is hydrophilic and mixes well with water, but in this invention, hydrophobic starch is used, which is made by processing the starch to make it hydrophobic, thereby imparting affinity to oils and fats. The oxygen barrier layer is mainly composed of hydrophobic starch, and more preferably, it is composed of 90% to 100% by mass of hydrophobic starch, and more preferably, it contains 95% to 100% by mass and 99.9% to 100% by mass of hydrophobic starch. Furthermore, it is preferable from the viewpoint of improving the biomass ratio that the oxygen barrier layer consists only of hydrophobic starch. In addition, by using as few single materials as possible, it becomes easier to form a uniform barrier film, and a lid material with superior oxygen barrier properties can be obtained. Furthermore, since ordinary starch absorbs moisture, in high-humidity environments, the oxygen barrier layer film that has gained fluidity by absorbing moisture may be lost, potentially worsening the oxygen barrier properties. However, hydrophobic starch, for example, has hydrophobic groups introduced into the starch, so it has excellent water resistance, and the oxygen barrier layer film is less likely to deteriorate even in high-humidity conditions. Moreover, compared to ordinary starch, hydrophobic starch has excellent heat resistance, so the change in the thickness of the oxygen barrier layer due to expansion and contraction during heat sealing to the container is small, resulting in excellent adhesion. In the present invention, it is preferable from the viewpoint of adhesion to the container that the hydrophobic starch is one or more selected from the group consisting of hydroxyethylated starch, hydroxypropyl starch, hydroxypropylated phosphate crosslinked starch, acetylated starch, acetylated adipic acid crosslinked starch, and octenyl succinate esterified starch. More preferably, the hydrophobic starch is hydroxyethylated starch and / or octenyl succinate esterified starch. If a certain amount or more of starch or starch derivative other than hydrophobic starch is used, wrinkles may occur when heat-sealing the lid material in a closed curve shape, potentially worsening its adhesion to the container.

[0018] Starch is composed of two components: amylose, in which glucose molecules are linked in a linear chain, and amylopectin, in which glucose molecules are linked in a branched chain. In this embodiment, the starch that forms the base of the hydrophobized starch contained in the oxygen barrier layer preferably has an amylopectin content of 60% by mass or more. Furthermore, the amylopectin content of the starch is preferably 60% to 100% by mass, or 70% to 100% by mass, for example, 60% by mass or more and less than 95% by mass, and more preferably 70% by mass or more and less than 90% by mass. By setting the amylopectin content 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 the starch or starch derivative that forms the base of the hydrophobized starch, 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. This is because it has a high amylopectin content and superior oxygen barrier properties. Waxy corn or rice with a high amylopectin content may also be included. In other words, it is preferable to use hydrophobized tapioca starch, hydrophobized corn starch, hydrophobized rice starch, etc., as the starch used in the oxygen barrier layer. Multiple types of starch may be mixed in the oxygen barrier layer, as long as it does not impair the effects targeted by the present invention. As a method for quantifying the amylopectin content of starch or starch derivatives contained in the oxygen barrier layer, known measurement methods for measuring amylose and amylopectin content in starch can be used, for example, iodine colorimetric method, electrostatic titration method, voltage titration method, and enzyme chromatography method can be used. The amylopectin content may be the content after isolating amylopectin from starch or starch derivative, or the apparent content may be used without isolation.

[0019] In an embodiment of the present invention, an oxygen barrier layer can be provided by applying a coating liquid for an oxygen barrier layer containing hydrophobized starch to at least one surface of a paper base material having an ash content of 0 to 15% and drying it. The hydrophobized starch used in the coating liquid for the oxygen barrier layer is preferably added after being dissolved in hot water as a dissolved solution. The coating liquid for the oxygen barrier layer may contain an alcohol having a boiling point lower than that of water as a leveling agent. Different from a surfactant-based leveling agent that remains in the oxygen barrier layer after drying, the alcohol having a boiling point lower than that of water volatilizes in the drying process and is not contained in the oxygen barrier layer after drying, so that a leveling effect can be imparted and deterioration of oxygen barrier properties can be suppressed. The lid material of the present invention preferably has an oxygen barrier layer on one surface of the paper base material, but may also have oxygen barrier layers on both surfaces.

[0020] In an embodiment of the present invention, the coating amount of the oxygen barrier layer is preferably 0.3 to 10 g / m² in terms of the dry coating amount per one surface of the paper base material. 2 Preferably, it is 0.5 to 8 g / m². 2 For example, it is 1 to 8 g / m². 2 If it is less than 0.3 g / m², the coating liquid for the oxygen barrier layer cannot form a uniform barrier film. When a uniform barrier film cannot be formed, for example, pinholes may occur due to liquid absorption, and a large amount of oxygen may pass through the pinholes, resulting in deterioration of oxygen barrier properties. Conversely, if it exceeds 10 g / m², sufficient oxygen barrier properties can be obtained, but since the wet coating amount of the coating liquid for the oxygen barrier layer increases, the shrinkage of the pulp in the drying process becomes large, and curling and wrinkles are likely to occur in the lid material after coating. As a result, when heat sealing is performed as the lid material, a gap is likely to occur between the container, and the adhesion may be poor.

[0021] ​​​​In embodiments of the present invention, the oxygen barrier layer may be formed in two or more layers. By having two or more oxygen barrier layers, even if a pinhole occurs in one layer, the second layer can fill that pinhole, thus preventing deterioration of the oxygen barrier properties. Preferably, the oxygen barrier layer can consist of one to four layers, for example, two to three layers, and more preferably, two layers. In particular, when using a paper substrate with high liquid absorption, pinholes are likely to occur, and having two or more oxygen barrier layers can effectively prevent pinholes. Even when there are two or more oxygen barrier layers, the total coating amount of the oxygen barrier layer is 0.3 to 10 g / m² in terms of solid content. 2 Preferably, it is 0.5 to 8 g / m 2 This is more preferable. If there are two or more oxygen barrier layers, at least one oxygen barrier layer must contain hydrophobic starch, but the other oxygen barrier layers may be any layer that acts as an oxygen barrier layer. For example, an oxygen barrier layer containing or made of polyvinyl alcohol can be used. For example, a coating amount of 0.3 to 10 g / m² is preferable. 2 A single layer of hydrophobized starch is included / an oxygen barrier layer consisting of hydrophobized starch, and the coating amount is 0.1~5g / m 2 A two-layer structure can be provided, consisting of one layer of polyvinyl alcohol as an oxygen barrier layer. Furthermore, from the viewpoint of improving the biomass ratio, it is preferable that the other oxygen barrier layers also consist of hydrophobic starch for 90% or more by mass, or consist solely of hydrophobic starch. It is also preferable that all layers of the oxygen barrier layer contain hydrophobic starch, and even more preferably that 90% or more by mass of the oxygen barrier layer consists of hydrophobic starch, or consists solely of hydrophobic starch.

[0022] In embodiments of the present invention, the oxygen barrier layer is preferably composed solely of hydrophobic starch. However, in addition to hydrophobic starch, various auxiliary agents may be added to the coating liquid for the oxygen 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, water-soluble polymers such as PVA and carboxymethylcellulose, and synthetic resins such as urethane, polyvinylidene chloride, styrene-butadiene copolymer latex, acrylic resins, polyester resins, and polyamide resins. Other auxiliary agents may also be included, to the extent that they do not impair the effects targeted by the present invention.

[0023] In the present invention, the method for applying the coating liquid for the oxygen barrier layer 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.

[0024] In this embodiment, it is preferable to include a sealing layer between the paper substrate and the oxygen barrier layer. The sealing layer, provided between the paper substrate and the oxygen barrier layer, prevents the oxygen barrier coating liquid from penetrating the paper substrate, thus facilitating the formation of a barrier film with fewer defects even with a small amount of oxygen barrier coating, resulting in a lid material with better oxygen barrier properties. The sealing layer is preferably composed of a pigment and a binder. As the pigment and binder in the sealing layer, known pigments and binders used in the coating layers of general printing coated paper can be used.

[0025] In this embodiment, examples of pigments included in the sealing layer include heavy calcium carbonate, light calcium carbonate, kaolin clay, calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide (titanium 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, an example of the composition of the pigments included in the sealing layer is a composition containing 80% to 95% by mass of heavy calcium carbonate and 5% to 20% by mass of kaolin clay per 100 parts by mass of pigment.

[0026] In this embodiment, it is preferable that the binder in the sealing layer contains styrene-butadiene copolymer latex. For example, the sealing layer may contain 5 to 100 parts by mass, for example, 6 to 50 parts by mass, of binder per 100 parts by mass of pigment. It is also preferable that the sealing layer contains 3 to 30 parts by mass of styrene-butadiene copolymer latex. Other binders that can be used in the sealing layer include starches such as crosslinking agent-modified starch, carbamic acid starch, cationic starch, amphoteric starch, and graft polymerized 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. For example, examples of the binder composition included in the sealing layer include a composition containing 10 to 30 parts by mass of styrene-acrylic emulsion and 35 to 55 parts by mass of styrene-butadiene copolymer latex per 100 parts by mass of pigment, or a composition containing 1 to 5 parts by mass of crosslinking agent-modified starch or carbamic acid starch and 5 to 20 parts by mass of styrene-butadiene copolymer latex.

[0027] In this embodiment, it is preferable that 90% or more by mass, for example, 95% to 100% by mass of the sealing layer is composed of pigment and binder. Furthermore, the sealing layer may contain various auxiliary agents to the extent that it does not impair the effects intended for 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, and preservatives. Specific examples of the sealing layer composition include a composition containing 65 to 95 parts by mass of heavy calcium carbonate and 5 to 35 parts by mass of kaolin clay as pigments, and a composition containing 10 to 70 parts by mass of styrene acrylic and 3 to 50 parts by mass of styrene butadiene copolymer latex as binders per 100 parts by mass of pigment. Furthermore, the mixture may contain, for example, 0.1 to 5 parts by mass, preferably 0.1 to 0.5 parts by mass, of various additives, such as a dispersant, per 100 parts by mass of pigment. The dry coating amount of the sealing layer is 2 g / m². 2 ~20g / m 2 For example, 5 g / m 2 ~15g / m 2 It is preferable to do so.

[0028] In embodiments of the present invention, any additional layers other than the paper substrate, sealing layer, and oxygen barrier layer may be provided, as long as they do not impair the effects targeted by the present invention. Examples include a heat-seal layer provided on the side opposite to the oxygen barrier layer, and a printing layer containing pigment and binder. These additional layers are preferably provided on at least one side of the paper substrate, but may be provided on both sides as needed. In embodiments of the present invention, the lid material includes an oxygen barrier layer and a composite film laminate layer on at least one side of the paper substrate, and it is essential that the oxygen barrier layer is included between the paper substrate and the composite film laminate layer, and that it has a layer structure of at least paper substrate / oxygen barrier layer / composite film laminate layer, and may also have two oxygen barrier layers, or a layer structure of paper substrate / oxygen barrier layer / oxygen barrier layer / composite film laminate layer. It may also have a layer structure of paper substrate / sealing layer / oxygen barrier layer / oxygen barrier layer / composite film laminate layer. Furthermore, the oxygen barrier layer may be provided on both sides, and a layer structure of oxygen barrier layer / paper substrate / sealing layer / oxygen barrier layer / composite film laminate layer is also possible, or a layer structure of composite film laminate layer / oxygen barrier layer / sealing layer / paper substrate / sealing layer / oxygen barrier layer / composite film laminate layer is possible. In addition, each layer usually covers the entire surface of the layer beneath the paper substrate or the like.

[0029] In this embodiment, a composite film laminate layer is provided. The composite film in this invention is a laminate film made by mixing two or more types of resins, or a film made by co-extruding two or more types of films together. The composite film laminate layer is provided as a sealant on the outermost surface of at least one side. This allows the lid material to be heat-sealed to the container. Furthermore, by providing the laminate layer on the side with the oxygen barrier layer, it acts as a protective layer for the oxygen barrier layer, and as a result, the oxygen barrier properties of the lid material are less likely to deteriorate. In addition, the provision of the laminate layer prevents damage to the oxygen barrier layer from external impacts during processing, prevents a decrease in the oxygen barrier properties of the lid material, and can also provide moisture resistance. By using a composite film, a lid material with better ease of opening and adhesion can be made.

[0030] In embodiments of the present invention, the resin used in the composite film laminate layer is not particularly limited, but low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), medium-density polyethylene (MDPE), metallocene polyethylene, polypropylene (PP), polyethylene terephthalate (PET), nylon, etc. can be used. Furthermore, biodegradable resins such as polylactic acid (PLA), polybutyl succinate (PBS), and polyhydroxyalkanoate (PHA) can also be used. It is also possible to use known sealant composite films. For example, composite films of polyethylene (PE) and polypropylene (PP), composite films of polyethylene (PE) and polyethylene terephthalate (PET), composite films of polypropylene (PP) and polyethylene terephthalate (PET), composite films of polyethylene (PE) and polylactic acid (PLA), composite films of polyethylene (PE) and polypropylene (PP) and ethylene vinyl acetate, etc. There are no particular restrictions on the lamination method, and known methods such as extrusion lamination, dry lamination, wet lamination, hot melt lamination, and thermal lamination can be used. For example, composite films can be laminated by dry lamination using adhesives such as urethane adhesives, acrylic adhesives, and silicone adhesives.

[0031] In embodiments of the present invention, in addition to the resin for the laminate layer, various additives may be added to the laminate layer 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.

[0032] In embodiments of the present invention, the thickness of the composite film laminate layer is preferably 15 μm to 100 μm. This provides excellent adhesion and oxygen barrier properties. Below 15 μm, adhesion and oxygen barrier properties are poor. Above 100 μm, adhesion is poor. More preferably, it is 20 μm to 80 μm. By setting the thickness of the composite film laminate layer within this range, it is possible to provide a sufficient sealant layer. Furthermore, by providing the laminate layer on the side to which the oxygen barrier layer is applied, it acts as a protective layer for the oxygen barrier layer, and the effect of preventing deterioration of the oxygen barrier properties can be expected. By using a composite film, even when using a paper substrate, it is possible to achieve better ease of opening and adhesion. The composite film laminate layer may be provided on one side of the paper substrate or on both sides. On the other hand, if a coating layer such as an aqueous emulsion is provided as the sealant layer instead of using a composite film laminate layer, the oxygen barrier layer may be destroyed by impact during processing, etc., and the oxygen barrier properties will decrease. Also, if monofilm lamination is applied, ease of opening is poor.

[0033] In embodiments of the present invention, for example, a printing layer may be provided on the side opposite to the oxygen barrier layer. Printing may be applied to the outer surface of the lid material (outer surface of the container) for displaying or advertising the contents, and the provision of a printing layer can provide good printability. It is also possible to print on the printing layer and then provide a composite film laminate 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 sealing layer. It can have the same composition as the sealing layer, 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.

[0034] Embodiments of the present invention may include a step of smoothing the paper substrate or the sealing 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, such as that used for single-sided gloss kraft paper, and then smoothing the surface. By coating the smoothed surface with a sealing layer or an oxygen barrier layer, the coating liquid for the oxygen barrier layer can be more easily applied uniformly to the surface of the sealing layer, resulting in a high sealing effect and a lid material with good oxygen barrier properties.

[0035] The paper substrate used 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 forms 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, 50 to 70 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 degree of pulp beating is 200 to 800 mlCSF, preferably 250 to 750 mlCSF, and even more preferably 300 to 700 mlCSF, in terms of Canadian standard freeness (JIS P 8121:1995 "Test Method for Freeness of Pulp"). For example, a pulp containing 50 to 98 parts by mass, preferably 85 to 98 parts by mass, of bleached hardwood kraft pulp with a Canadian standard freeness of 350 to 550 mlcsf, and 2 to 50 parts by mass, preferably 2 to 15 parts by mass, of bleached softwood kraft pulp with a Canadian standard freeness of 450 to 700 mlcsf may be used.

[0036] In embodiments of the present invention, the ash content of the paper substrate is 0-15%, but examples of fillers include heavy calcium carbonate, light calcium carbonate, kaolin clay, calcined clay, talc, titanium dioxide, aluminum hydroxide, etc. Regarding the ash content, since the filler added to the paper substrate has a low specific heat, if the ash content exceeds 15%, too much heat is applied during heat sealing with the container, the heat seal strength increases excessively, and the ease of opening deteriorates. Preferably, the ash content is 0-13%. More preferably, it is 0-12%. To achieve such an ash content, it is preferable to add the filler in an amount of 0-20 parts by mass per 100 parts by mass of pulp.

[0037] 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, bulking agents, 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 oxygen 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 oxygen 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, per 100 parts by mass of pulp, the paper substrate may contain 0.1 to 1.0 parts by mass of polyacrylamide and / or a sizing agent, preferably 0.1 to 1.0 parts by mass of a rosin sizing agent. In addition, the paper substrate may contain oxidized starch as a paper strength agent. For example, per 100 parts by mass of pulp, it may contain 2 to 8 parts by mass of oxidized starch.

[0038] 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.

[0039] In embodiments of the present invention, the basis weight of the paper substrate is not particularly limited, but for example, 10 to 500 g / m² 2 Preferably 20-350 g / m² 2 Preferably, 30-250 g / m² 2 If so, it is more preferable, for example, 30-200 g / m 2 That would be fine. [Examples]

[0040] 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 "% by mass," respectively, unless otherwise specified. Note that the number of added parts is the value on a solid content basis.

[0041] (Example 1) (Preparation of paper substrate) A pulp was prepared by adding water to 95 parts of bleached hardwood kraft pulp with a Canadian standard freeness of 450 mlcsf, 5 parts of bleached softwood kraft pulp with a Canadian standard freeness of 600 mlcsf, 0.3 parts of cationic polyacrylamide (product name: Polystron 705, manufactured by Arakawa Chemical Industries), 5 parts of heavy calcium carbonate (product name: Softon 1500, manufactured by Bihoku Powdering Industry Co., Ltd.), and 0.3 parts of neutral rosin sizing (product name: Harsize NES-745, manufactured by Harima Chemicals Co., Ltd.). The resulting pulp was then processed using a multi-cylinder, long-wire paper machine to produce a basis weight of 48 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 50g / m². 2 A paper substrate was obtained. The ash content of this paper substrate was 3.8%.

[0042] (Preparation of coating liquid A for sealing layer) 90 parts of heavy calcium carbonate (product name: Carvilax, manufactured by Imerys Co., Ltd.), 10 parts of kaolin clay (product name: BI Kaolin, manufactured by Sanyo Clay Industry Co., Ltd.), and 0.2 parts of a dispersant (product name: Aron T-50, manufactured by Toagosei Co., Ltd.) were added, water was added, and the mixture was dispersed in a Corles disperser to prepare a pigment slurry. To this pigment slurry, 15 parts of styrene-butadiene copolymer latex (product name: P-6X20, manufactured by Nippon A&L Co., Ltd.) and 2 parts of carbamic acid starch (product name: Nisshoku RC#20, manufactured by Nippon Shokuhin Kako Co., Ltd.) were added as binders, and water was added to disperse the mixture, preparing a coating solution A for sealing layers with a solid content of 50%.

[0043] (Preparation of paper substrate with sealing layer) On one side of the paper substrate, apply coating liquid A for sealing the pores, with a dry coating amount of 10 g / m². 2 The coating was applied using a blade coater and dried to achieve a basis weight of 60 g / m². 2 A paper substrate with a sealing layer was fabricated.

[0044] (Preparation of the lid base paper substrate) On the surface of the sealing layer of the paper substrate with the sealing layer obtained above, a solution of octenyl succinate esterified tapioca starch (product name: FILMKOTE370, manufactured by Ingredion, amylopectin content 83%) dissolved in hot water is applied with a dry coating amount of 2.0 g / m². 2 The surface is coated using an air knife coater to create the first oxygen barrier layer, and then dried to form the first oxygen barrier layer. Subsequently, a solution of octenyl succinate esterified tapioca starch (product name: FILMKOTE 370, manufactured by Ingredion) dissolved in hot water is applied to the first oxygen barrier layer until the coating amount is 1.0 g / m². 2 The coating is applied using an air knife coater, and after drying, a second oxygen barrier layer is formed, with a total of 3.0 g / m² of the two layers. 2 An oxygen barrier layer is provided, with a basis weight of 63 g / m². 2 A paper substrate was fabricated as the base material for the lid.

[0045] (Making the lid material) A polyethylene and polypropylene composite film (product name: CMPS305C, thickness 30 μm, manufactured by RM Tohcello Co., Ltd.) was dry-laminated as a laminate layer to the oxygen barrier layer surface of the lid material base paper substrate obtained above, resulting in a basis weight of 96 g / m². 2 The lid material was created. For the dry lamination, a polyurethane adhesive (product name: Takelac A953 / A93, manufactured by Mitsui Chemicals) was used at 3g / m². 2 That's what I decided.

[0046] (Example 2) In Example 1, a polyethylene and polypropylene composite film (product name: TAF650C, thickness 60 μm, manufactured by RM Tosello Co., Ltd.) was dry-laminated as the laminate layer, resulting in a basis weight of 126 g / m². 2 The lid material was prepared in the same manner as in Example 1, except for the preparation of the lid material shown above.

[0047] (Example 3) In Example 1, a polyethylene and polypropylene composite film (product name: Different P2152T, thickness 25 μm, manufactured by DIC Corporation) was dry-laminated as the laminate layer, resulting in a basis weight of 91 g / m². 2 The lid material was prepared in the same manner as in Example 1, except for the preparation of the lid material shown above.

[0048] (Example 4) In Example 1, a polyethylene and polypropylene composite film (product name: Kojin Polyset GK, thickness 15 μm, manufactured by Kojin Film & Chemicals Co., Ltd.) was dry-laminated as the laminate layer, resulting in a basis weight of 81 g / m². 2 The lid material was prepared in the same manner as in Example 1, except for the preparation of the lid material shown above.

[0049] (Example 5) In Example 1, a composite film of polyethylene, polypropylene, and ethylene vinyl acetate (EVA) (product name: Convenience PP Transparent, thickness 100 μm, manufactured by Okamoto Co., Ltd.) was dry-laminated as the laminate layer, resulting in a basis weight of 166 g / m². 2 The lid material was prepared in the same manner as in Example 1, except for the preparation of the lid material shown above.

[0050] (Example 6) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the oxygen barrier layer was changed to hydroxyethylated starch (product name: PENFORDGUM290, manufactured by Ingredion).

[0051] (Example 7) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the oxygen barrier layer was changed to acetylated starch (product name: CRISPFILM, manufactured by Ingredion).

[0052] (Example 8) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the oxygen barrier layer was changed to acetylated adipic acid cross-linked starch (product name: COLFLO67, manufactured by Ingredion).

[0053] (Example 9) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the oxygen barrier layer was changed to hydroxypropyl starch (product name: Matsutani Marigold, manufactured by Matsutani Chemical Industry Co., Ltd.).

[0054] (Example 10) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the oxygen barrier layer was changed to hydroxypropylated phosphate cross-linked starch (product name: Pine Ace, manufactured by Matsutani Chemical Industry Co., Ltd.).

[0055] (Example 11) In the preparation of the paper substrate in Example 1, the lid material was prepared in the same manner as in Example 1, except that the amount of heavy calcium carbonate added was set to 0 parts (the ash content of the paper substrate at this time was 0.1%).

[0056] (Example 12) In the preparation of the paper substrate in Example 1, the lid material was prepared in the same manner as in Example 1, except that the amount of heavy calcium carbonate added was 18 parts (the ash content of the paper substrate at this time was 14.7%).

[0057] (Example 13) In Example 1, no sealing layer was provided, and the dry coating amount of the first oxygen barrier layer was 5.0 g / m². 2 The dry coating amount for the second oxygen barrier layer is 2.0 g / m². 2 The total of the two layers is 7.0 g / m². 2 The lid material was prepared in the same manner as in Example 1, except that an oxygen barrier layer was added. The basis weight of the lid material at this time was 90 g / m². 2 That was the case.

[0058] (Example 14) In Example 1, the second oxygen barrier layer was changed to PVA (product name: 5-98, manufactured by Kuraray Co., Ltd.), and the dry coating amount was 1.0 g / m². 2 The total of the two layers is 3.0 g / m². 2 The lid material was prepared in the same manner as in Example 1, except that an oxygen barrier layer was provided.

[0059] (Example 15) In Example 1, the dry coating amount of the first oxygen barrier layer was 3 g / m². 2 The lid material was prepared in the same manner as in Example 1, except that a second oxygen barrier layer was not provided.

[0060] (Comparative Example 1) In Example 1, a lid material was prepared in the same manner as in Example 1, except that a polyethylene (PE) monofilm (product name: Unilux LS-744C, thickness 50 μm, manufactured by Idemitsu Unitech Co., Ltd.) was used as the laminate layer.

[0061] (Comparative Example 2) In Example 1, the lid material was prepared in the same manner as in Example 1, except that the starch in the oxygen barrier layer was replaced with urea phosphorylated starch (product name: Starcoat #14, manufactured by Nippon Shokuhin Kako Co., Ltd.).

[0062] (Comparative Example 3) In the preparation of the paper substrate in Example 1, the lid material was prepared in the same manner as in Example 1, except that the amount of heavy calcium carbonate added was 21 parts (the ash content of the paper substrate at this time was 18.0%).

[0063] The oxygen barrier papers obtained in each example and comparative example were evaluated using the method described below. The results are shown in Table 1.

[0064] (1) Ash content of paper substrate The ash content of the paper substrate was measured according to JIS P 8251 "Paper and paperboard - Ash content test method".

[0065] (2) Oxygen permeability The oxygen permeability of oxygen barrier paper was measured at 23°C and 50% humidity using an oxygen permeability measuring device (MOCON OX-TRAN 2 / 22L) in accordance with JIS K 7126-2:2006 "Plastics - Films and sheets - Gas permeability test methods - Part 2: Isobaric method". A smaller value indicates lower oxygen permeability. In this embodiment, the oxygen permeability was 50 cc / m². 2 It can be said that it has excellent oxygen barrier properties at or below day·atm.

[0066] (3)Easy to open The obtained lid material was sealed onto a container, and its ease of opening was evaluated as follows. The lid material was sealed using a commercially available sealer (product name: Tabletop Top Sealer TR-59L, manufactured by Techno Research Co., Ltd.) at 150°C for 3 seconds. ○: Can be peeled off with moderate force and is practical. ×: The adhesive strength is too strong, making it impossible to remove and unusable.

[0067] (4) Adhesion The obtained lid material was sealed onto the container, and its adhesion to the container was visually evaluated as follows. The lid material was sealed using a commercially available sealer (product name: Tabletop Top Sealer TR-59L, manufactured by Techno Research Co., Ltd.) at 150°C for 3 seconds. ○: The lid material is completely free of warping and gaps, making it fully functional. △: There is slight warping in the lid material, but there are no gaps, and it is within a usable range. ×: The lid material is severely warped, leaving gaps and rendering it unusable.

[0068] [Table 1]

[0069] As is clear from the evaluation results, with Examples 1 to 15 of the present invention, it was possible to manufacture lid materials with excellent ease of opening and adhesion even with a reduced amount of plastic used. On the other hand, Comparative Example 1, in which the laminate layer was a monofilm, had poor ease of opening. Comparative Example 2, in which hydrophobic starch was not used in the oxygen barrier layer, also had poor adhesion. Comparative Example 3, in which the ash content of the paper substrate exceeded 15%, also had poor ease of opening.

Claims

1. A lid material having an oxygen barrier layer and a composite film laminate layer provided in that order on at least one side of a paper substrate, characterized in that the ash content of the paper substrate is 0 to 15%, and the oxygen barrier layer contains hydrophobic starch.

2. The lid material according to claim 1, characterized in that the hydrophobic starch is one or more selected from the group consisting of hydroxyethylated starch, hydroxypropyl starch, hydroxypropylated phosphate crosslinked starch, acetylated starch, acetylated adipic acid crosslinked starch, and octenyl succinate esterified starch.

3. The amount of the oxygen barrier layer applied is 0.3 to 10 g / m² in dry coating amount. ２ The lid material according to claim 1 or 2, characterized in that it is within the range.

4. The lid material according to claim 1 or 2, characterized in that the thickness of the composite film is 15 μm to 100 μm.

5. The lid material according to claim 1 or 2, characterized in that a sealing layer is provided between at least one side of the paper substrate and the oxygen barrier layer.

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