Cellulose nanocrystal-containing resin composition and laminated paper having a layer made of this resin composition

Abstract

To provide a cellulose nanocrystal / ionomer resin-containing resin composition which enables formation of a coating layer that is excellent in barrier property and water resistance, and is also excellent in resistance against a processing load, laminated paper having the resin layer, and a paper container made of the laminated paper.SOLUTION: A resin composition contains an ionomer resin-containing aqueous dispersion liquid of an ethylene-(meth)acrylic acid copolymer, and a cellulose nanocrystal-containing aqueous dispersion liquid, and has relaxation time T2(S) in pulse NMR measurement of less than 17 msec, and T2(L) of less than 75 msec.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition containing cellulose nanocrystals, and more specifically to a resin composition containing cellulose nanocrystals and an ionomer resin that can form a coating layer that has excellent barrier properties and water resistance as well as excellent processing load resistance, a laminated paper having this resin layer, and a paper container made of this laminated paper. [Background technology]

[0002] Paper containers are widely used as environmentally friendly containers because they are made from renewable natural resource-derived materials. However, because paper substrates alone have poor water resistance and gas barrier properties, containers are formed from laminates that include moisture-resistant resins and gas barrier layers. For example, gas barrier properties have been imparted by laminating a metal foil such as aluminum foil onto a paper substrate, laminating a gas barrier resin such as an ethylene-vinyl alcohol copolymer, or applying a gas barrier polymer coating.

[0003] However, paper containers with metal foil have the problem of being incompatible with microwave heating. Furthermore, layers made of ethylene-vinyl alcohol copolymers or gas-barrier polymers have problems with adhesion to paper substrates, and because they are petroleum-derived materials, they may impair the excellent properties of paper products, which are derived from natural resources. Gas barrier properties have also been imparted by forming inorganic vapor-deposited layers, but the paper substrate has numerous irregularities on its surface, which makes the inorganic vapor-deposited layer prone to defects, potentially reducing the gas barrier properties. To solve these problems, it has been proposed to form a coating layer containing cellulose nanofibers, which are a material derived from natural resources, on a paper substrate to impart barrier properties.

[0004] For example, Patent Document 1 listed below discloses a laminate comprising a plurality of layers, the laminate comprising a base material made of paper, a fiber layer having a thickness of 0.01 μm to 10 μm, laminated on at least one side of the base material, the fiber layer containing no inorganic layered compound, cellulose fine fibers having a fiber diameter of 10 μm or less, and a water-soluble polymer, a hydrophobic resin layer having a thickness of 0.01 μm to 10 μm, and a vapor-deposited layer made of a metal or metal oxide provided on the hydrophobic resin layer, and a resin layer provided on the vapor-deposited layer, the laminate having an oxygen permeability of 0.001 to 10 (ml / m 2 ·day) and the water vapor permeability is 3.0 or less (ml / m 2 The laminate is characterized in that the temperature is 100°C or less.

[0005] The laminate described in Patent Document 1 above is said to contain nano-sized cellulose fine fibers, which improves the smoothness of the paper substrate and forms a dense layer free of holes and defects, thereby enabling excellent barrier properties to be achieved. However, the laminate strength of the laminate is only about 1.5 N at most, and when this laminate is used to form a paper container, there is a risk of delamination between the vapor-deposited layer and the barrier layer due to the molding load. Furthermore, the presence of a vapor-deposited layer results in poor bending resistance, and when subjected to a bending process during container formation, the vapor-deposited layer may crack and deteriorate, potentially reducing the barrier properties of the container.

[0006] Furthermore, a resin composition with improved dispersibility of cellulose fibers has been proposed, which is an aqueous dispersion comprising a dispersion (A) containing cellulose fibers and a dispersion (B) containing at least one selected from an amino compound-neutralized product (B1) of an ethylene-unsaturated carboxylic acid copolymer containing ethylene and an unsaturated carboxylic acid as copolymerization components and an ionomer resin (B2) of the ethylene-unsaturated carboxylic acid copolymer (Patent Document 2). It is described that the use of the ionomer resin in the resin composition improves the dispersibility of cellulose fibers, and the resulting coating film has excellent mechanical strength, water resistance, transparency, etc. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6318490 [Patent Document 2] Patent No. 5931648 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the resin composition described in Patent Document 2 is intended to be used to form a molded product, and there is no recognition of the effects that can be obtained from cellulose fibers when such a resin composition is applied to a paper substrate to form a coating layer. The present inventors created laminated paper by laminating a coating layer made of the resin composition of Patent Document 2 on a paper substrate, and attempted to use this to mold a cup-shaped container having a bottom and a body. However, they found that when forming the bottom, the coating layer could not withstand the molding load during the folding process of the laminated paper and the bottom drawing process, and pinholes were generated in the bent parts, causing water leakage and a decrease in strength. Therefore, an object of the present invention is to provide a resin composition containing cellulose nanocrystals and an ionomer resin that can form a coating layer that has excellent barrier properties and water resistance as well as excellent processing load resistance, laminated paper having this resin layer, and a paper container made of this laminated paper. [Means for solving the problem]

[0009] According to the present invention, an aqueous dispersion containing an ionomer resin of an ethylene-(meth)acrylic acid copolymer and an aqueous dispersion containing cellulose nanocrystals is provided, and the relaxation time T2(S) in pulse NMR measurement is 13msec or more14 msec below and T2(L) is 50 msec or more The resin composition is characterized by a viscosity of less than 75 msec.

[0010] In the resin composition of the present invention, (1) The content of the cellulose nanocrystals (solid content) is 0.1 to 20% by mass, (2) The cellulose nanocrystals contain anionic functional groups in an amount of 0.01 to 4.0 mmol / g; (3) The anionic functional group contains at least a sulfate group and / or a sulfo group derived from a sulfuric acid treatment; (4) The dispersion medium of the cellulose nanocrystal-containing aqueous dispersion is water or a mixed solvent of water and another protic polar solvent; (5) The content of the ionomer resin (solid content) of the ethylene-(meth)acrylic acid copolymer is 26.6 to 33.2% by mass. is preferred.

[0011] According to the present invention, at least one surface of the paper substrate is the above A laminated paper is provided, which is characterized by having a layer made of a resin composition formed thereon.

[0012] In the laminated paper of the present invention, (1) The layer made of the resin composition has an elastic modulus of 600 to 750 MPa and an elastic recovery rate of 70% or more when the layer is loaded with a Berkovich type indenter to a depth of 500 nm and then unloaded. (2 )before the resin composition contains the ionomer resin of ethylene-(meth)acrylic acid copolymer and the cellulose nanocrystals in a mass ratio of 99.7:0.3 to 60:40; is preferred.

[0013] According to the present invention, there is further provided a paper container comprising a body and a bottom, wherein at least on the inner surface side of the bottom, the above A paper container is provided, characterized in that a layer made of a resin composition is formed on the paper container.

[0014] In the paper container of the present invention, (1) The layer made of the resin composition has an elastic modulus of 600 to 750 MPa and an elastic recovery rate of 70% or more when the layer is loaded with a Berkovich type indenter to a depth of 500 nm and then unloaded. (2 )before the resin composition contains the ionomer resin of ethylene-(meth)acrylic acid copolymer and the cellulose nanocrystals in a mass ratio of 99.7:0.3 to 60:40; is preferred. [Effects of the Invention]

[0015] In the resin composition of the present invention, the relaxation time T2(S) of the resin composition measured by pulsed NMR was less than 17 msec, and the T2(L) of the resin composition was less than 75 msec. This suggests that the cellulose nanocrystals constrain the mobility of the solvent component in the resin composition, while having little effect on the mobility of the ionomer resin (hereinafter simply referred to as "ionomer resin") of ethylene-(meth)acrylic acid copolymer. The interface between the ionomer resin and the solvent is maintained, resulting in a homogeneous distribution of the ionomer resin, and the cellulose nanocrystals are uniformly finely dispersed in the solvent. Therefore, in laminated paper having a coating layer made of this resin composition, stress concentration due to deformation under load during molding is dispersed, resulting in low plastic deformation and a high elastic modulus, resulting in a high deformation recovery rate. Therefore, even when subjected to molding loads, such as those caused by bottom drawing during the molding of cup-shaped containers, stress concentration due to deformation under load during molding is reduced, resulting in low plastic deformation and a high elastic deformation rate, resulting in a high deformation recovery rate and excellent processing load resistance, which effectively prevents the occurrence of pinholes.

[0016] This is also clear from the results of the Examples described below: In pulse NMR measurement, a resin composition consisting of an ionomer resin-containing aqueous dispersion containing no cellulose fibers had a relaxation time T2(S) of 14 msec and a T2(L) of 75 msec, and laminated paper having a coating layer made of this resin composition was evaluated as defective due to the occurrence of pinholes in three tests: a pinhole screening evaluation, a pinhole evaluation using a strograph, and a pinhole evaluation of the bottom part formed by bottom drawing from this laminated paper (Comparative Example 1). In contrast, in the resin composition of the present invention containing an ionomer resin-containing aqueous dispersion and a cellulose nanocrystal-containing aqueous dispersion, the relaxation time T2(S) in pulse NMR measurement was less than 17 msec and T2(L) was less than 75 msec, and the occurrence of pinholes was effectively suppressed in all of the above pinhole evaluations, resulting in a good evaluation (Examples 1 to 3).

[0017] Furthermore, in a resin composition containing an ionomer resin-containing aqueous dispersion and a cellulose nanofiber-containing aqueous dispersion, such as the resin composition of Patent Document 2 mentioned above, the relaxation time T2(S) in pulse NMR measurements is 17 msec or more and T2(L) is 75 msec or more, which indicates that the cellulose nanofibers have the effect of relaxing the constraints on the molecular mobility of both the ionomer resin and the solvent, causing the interface between the ionomer resin and the solvent to expand, resulting in a mixture of widely spread and narrowly spread ionomer resin areas, the ionomer resin being present in a heterogeneous state, and the cellulose nanofibers being present in a locally aggregated state. As a result, stress concentration due to load deformation during molding occurs locally, and laminated paper having a coating layer made of this resin composition has a high amount of plastic deformation and a high proportion of elastic deformation, resulting in a low deformation recovery rate. Therefore, for example, when a molding load is applied due to a bottom drawing process in the molding of a cup-shaped container, stress concentration occurs locally in response to the load deformation during molding, and the amount of plastic deformation is large and the proportion of elastic deformation is high, resulting in a low deformation recovery rate.As a result, pinholes occur and the product is evaluated as defective in both pinhole evaluations (Comparative Examples 2 and 3).

[0018] Furthermore, the cellulose nanocrystals used in the present invention form a self-assembled structure due to the charge repulsion between cellulose fibers, and this self-assembled structure acts as a barrier to the permeation path of permeating gas, thereby exhibiting excellent gas barrier properties. Cellulose nanocrystals also have excellent heat resistance, and there is no risk of deterioration in barrier performance due to thermal degradation even when heated in the extrusion lamination process or heat sealing process in the paper container molding process described below, making it possible to provide paper containers with excellent gas barrier properties. Furthermore, by including an ionomer resin, it becomes possible to provide the paper substrate with excellent water resistance and heat sealability as a coating layer. [Brief explanation of the drawings]

[0019] [Figure 1] 1 shows cryo-scanning electron microscope photographs of the resin compositions of Example 1 and Comparative Example 2, where (A) is Example 1 and (B) is Comparative Example 2. [Figure 2] FIG. 1 is a diagram for explaining nanoindentation measurement. [Figure 3] 1 shows a load-displacement curve obtained by nanoindentation measurement. [Figure 4] FIG. 1 is a diagram illustrating an example of a paper container of the present invention. [Figure 5] FIG. 1 shows the results of nanoindentation measurements of the laminated papers obtained in Example 3 and Comparative Examples 1 and 2. [Figure 6] FIG. 1 is a diagram showing the results of a screening test of the frequency of pinholes occurring in the laminated paper obtained in Example 1 and Comparative Examples 1 to 3. [Figure 7] FIG. 10 is a diagram showing the results of a pinhole test on the bottom portions formed by squeezing the laminated papers obtained in Example 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Resin composition) An important feature of the resin composition of the present invention is that the relaxation time T2(S) in pulse NMR measurement is less than 17 msec, particularly in the range of 13 to 14 msec, and the T2(L) is less than 75 msec, particularly in the range of 50 to 68 msec.As a result, the ionomer resin is present homogeneously and the cellulose nanocrystals are finely dispersed.When formed as a coating layer on a paper substrate, the composition has a high elastic modulus and deformation recovery force, which enables it to follow the molding process and effectively suppress the occurrence of pinholes. Pulse NMR can measure the relaxation time after irradiation with a pulsed magnetic field to obtain a relaxation time curve dependent on molecular mobility. In other words, in the resin composition of the present invention, by analyzing the relaxation time T2 curve in pulse NMR measurement, it is possible to separate the composition into two components: a component with a short relaxation time T2(S) and a component with a long relaxation time T2(L). T2(S) represents the relaxation time of the component with a short relaxation time, i.e., the component with low molecular mobility. The shorter the relaxation time, the greater the restraining effect on the resin. On the other hand, relaxation time T2(L) represents the relaxation time of the component with a long relaxation time, i.e., the component with high molecular mobility. The shorter the relaxation time, the greater the restraining effect on the solvent. While specific results are not presented here, the fact that the relaxation time T2 of the solvent alone is analyzed as only one component, the component with a long relaxation time, T2(L), also suggests that the above is correct.

[0021] As mentioned above, in the resin compositions of the present invention (Examples 1 to 3) containing a cellulose nanocrystal-containing aqueous dispersion, a resin composition (Comparative Example 1) consisting solely of an ionomer resin-containing aqueous dispersion without cellulose nanocrystals was compared. Based on the relaxation times T2(S) and T2(L) measured by pulsed NMR for the resin composition of Comparative Example 1, the relaxation time T2(S) was largely maintained, while T2(L) tended to be shorter. This means that the cellulose nanocrystals act in a direction that restricts only the mobility of the solvent while maintaining the constraints on the ionomer resin and solvent. As a result, the ionomer resin is homogeneous in the resin composition, and the cellulose nanocrystals tend to be finely dispersed.

[0022] In contrast, in Comparative Examples 2 and 3, in which the resin composition of Comparative Example 1 was supplemented with a cellulose nanofiber-containing aqueous dispersion, both the relaxation times T2(S) and T2(L) tended to be longer than in Comparative Example 1. This means that the cellulose nanofibers release the constraints on the ionomer resin and the solvent, widening their interface and acting in a direction that does not restrict the mobility of the ionomer resin and the solvent, which makes the ionomer resin more likely to become locally heterogeneous in the resin composition and the cellulose nanofibers more likely to aggregate and become localized. Therefore, it is thought that in resin compositions containing cellulose nanofibers, the proportion of plastic deformation due to molding load increases, resulting in a lower deformation recovery rate.

[0023] The above-mentioned differences between the resin composition of the present invention containing cellulose nanocrystals (Example 1) and the resin composition containing cellulose nanofibers (Comparative Example 2) are also evident from Figure 1, which shows cryo-electron microscope (SEM) photographs of these resin compositions. Specifically, Figure 1(A), which shows an SEM photograph of the resin composition of Example 1, reveals that the cellulose nanocrystals constrain the mobility of the solvent component without affecting the mobility of the ionomer resin. This maintains the interface between the ionomer resin and the solvent, resulting in a nearly uniform distribution of the ionomer resin and a homogeneous resin composition. Furthermore, the cellulose nanocrystals are finely dispersed without agglomeration. In contrast, Figure 1(B), which shows an SEM photograph of the resin composition of Comparative Example 2, reveals that the cellulose nanofibers relax the constraints on the molecular mobility of both the ionomer resin and the solvent, widening the interface between the ionomer resin and the solvent, resulting in a heterogeneous resin composition with a mixture of widely spread and narrowly spread ionomer resin regions. Furthermore, it can be seen that the cellulose nanofibers exist in aggregates and are localized within the resin composition.

[0024] Furthermore, as described above, in the resin composition of the present invention, since it contains cellulose nanocrystals, when the relaxation time measured by pulse NMR of the ionomer resin-containing aqueous dispersion is used as a reference, the relaxation time T2(S) value is almost maintained, while the T2(L) value tends to be shorter. When the relaxation time of the ionomer resin-containing aqueous dispersion is used as a reference, it is preferable that the relaxation time T2(S) of the resin composition is about ±1 msec, and it is preferable that the relaxation time T2(L) is reduced by about 7 to 25 msec.

[0025] The resin composition of the present invention preferably contains cellulose nanocrystals (solid content) in an amount of 0.1 to 20 mass%, particularly 0.5 to 5 mass%, and also preferably contains ionomer resin (solid content) in an amount of 26.6 to 33.2 mass%, particularly 28 to 33.1 mass%. If the amount of cellulose nanocrystals is less than the above range, the effects obtained by blending cellulose nanocrystals, such as processing load resistance and barrier properties, may not be fully achieved compared to when the amount is within the above range. On the other hand, if the amount of ionomer resin is less than the above range, the effects obtained by the ionomer resin, such as water resistance and heat sealability, may not be fully achieved compared to when the amount is within the above range. Furthermore, while some cellulose nanofibers are fibril fibers, cellulose nanocrystals are isolated, dispersed fibers. Furthermore, cellulose nanocrystals have shorter fiber lengths and smaller aspect ratios than cellulose nanofibers, so even when a resin composition contains cellulose nanocrystals, it is possible to uniformly disperse them while suppressing the thickening effect. These results suggest that using cellulose nanocrystals has the advantage that the upper limit of the cellulose nanocrystal content in the resin composition can be made higher than when using cellulose nanofibers.

[0026] [Aqueous dispersion containing ionomer resin] In the resin composition of the present invention, the ionomer resin of ethylene-(meth)acrylic acid copolymer is an ethylene-(meth)acrylic acid copolymer in which some or all of the carboxyl groups have been neutralized with metal ions, and the inclusion of the ionomer resin can impart water resistance and heat sealability to the resin composition. The ethylene-(meth)acrylic acid copolymer preferably has an ethylene content of 26.6 to 33.2 mass%, particularly 28 to 33.1 mass%. If the ethylene content is lower than this range, there is a risk that the water resistance, mechanical strength, heat sealability, etc. will be reduced compared to when the ethylene content is within the above range. On the other hand, if the ethylene content is higher than this range, there is a risk that the coating film will become harder and the processing load resistance will be reduced compared to when the ethylene content is within the above range. Acrylic acid or methacrylic acid may be used alone or in combination. The ethylene-(meth)acrylic acid copolymer may be not only a binary copolymer of ethylene and (meth)acrylic acid, but also a multi-component copolymer in which a (meth)acrylic acid ester such as methyl (meth)acrylate, ethyl (meth)acrylate, or butyl (meth)acrylate is copolymerized.

[0027] Examples of metal ions constituting the ionomer resin include alkali metal ions such as lithium ions, sodium ions, and potassium ions, and polyvalent metal ions such as magnesium ions, calcium ions, zinc ions, cobalt ions, nickel ions, manganese ions, lead ions, copper ions, titanium ions, iron ions, aluminum ions, and zirconium ions. These metal ions may be used alone or in combination of two or more. Of the above metal ions, sodium ions, zinc ions, and magnesium ions are preferred for the ionomer resin used in the present invention.

[0028] In the resin composition of the present invention, one type of ionomer resin may be used alone, or two or more types may be used in combination. The ionomer resin may contain, in addition to metal ions, an amino compound such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, or 1,3-dimethylaminocyclohexane.

[0029] The ionomer resin-containing aqueous dispersion may be prepared by a conventional method, and the dispersion medium may be water alone or a mixture of water and an alcohol such as methanol, ethanol, or isopropanol, a ketone such as 2-butanone or acetone, or an aromatic solvent such as toluene. It is preferable to use the same dispersion medium as that used in the cellulose nanocrystal-containing aqueous dispersion described below. The ionomer resin-containing aqueous dispersion preferably contains 26.6 to 33.2 mass% of ionomer resin (solid content) and has a viscosity (B-type viscometer, temperature 25°C, 6 rotations) of 400 mPa·sec or less, which provides excellent coatability and handling properties.

[0030] [Aqueous dispersion containing cellulose nanocrystals] Cellulose nanocrystals are rod-shaped crystalline cellulose fibers obtained by acid hydrolysis of cellulose fibers such as pulp with sulfuric acid or hydrochloric acid. In the present invention, cellulose nanocrystals containing sulfate and / or sulfo groups obtained by sulfuric acid treatment of cellulose fibers are preferred. These cellulose nanocrystals preferably contain anionic functional groups, such as sulfate and / or sulfo groups, that can contribute to the formation of self-organized structures in the range of 0.01 to 4.0 mmol / g. The term "sulfate group" is intended to encompass sulfate ester groups. Furthermore, cellulose nanocrystals containing the above-mentioned sulfate and / or sulfo groups can be further subjected to a hydrophilization treatment to adjust the amount of sulfate and / or sulfo groups, or to introduce anionic functional groups such as carboxyl groups or phosphate groups into hydroxyl groups at positions such as the 6th position of cellulose, thereby adjusting the total amount of anionic functional groups such as sulfate, sulfo, carboxyl, and phosphate groups to more than 0.17 mmol / g and not more than 4.0 mmol / g, particularly in the range of 0.17 to 2.0 mmol / g. The hydrophilization treatment of cellulose nanocrystals will be described later.

[0031] Anionic functional group-containing cellulose nanocrystals have good dispersibility in dispersions, self-align to form nematic and / or chiral nematic liquid crystals, and are solidified by drying while maintaining this liquid crystalline self-alignment. This allows for the formation of a sufficient self-organized structure in the coating film, enabling the development of excellent gas barrier properties. The dispersions in the examples described below also exhibit birefringence due to the presence of the nematic and / or chiral nematic liquid crystals. Furthermore, cellulose nanocrystals having a fiber diameter of 50 nm or less, particularly in the range of 2 to 50 nm, a fiber length of 100 to 500 nm, an aspect ratio of 5 to 50, and a crystallinity of 60% or more, particularly 70% or more, can be suitably used.

[0032] In the cellulose nanocrystal-containing aqueous dispersion, sulfate and / or sulfo group-containing cellulose nanocrystals obtained by treating a cellulose raw material with sulfuric acid do not necessarily need to be hydrophilized, but can be hydrophilized as needed. The hydrophilized cellulose nanocrystal aqueous dispersion is a dispersion obtained by subjecting the dispersion to a centrifugal separation and filtration separation process after the hydrophilization process. It is preferable that the dispersion does not undergo a solidification process such as spray drying before or after the hydrophilization process. However, cellulose nanocrystals solidified by spray drying or the like can also be redispersed in a solvent such as water or alcohol and used.

[0033] <Hydrophilic treatment> The hydrophilization treatment described above involves a never-dry treatment, or a combination of a never-dry treatment and a treatment using a water-soluble carbodiimide, sulfuric acid, a sulfur trioxide-pyridine complex, phosphate-urea, a TEMPO catalyst, or an oxidizing agent. Treatment using a carbodiimide, sulfuric acid, or a sulfur trioxide-pyridine complex adjusts the amount of sulfate and / or sulfo groups in the cellulose nanocrystals and further shortens the cellulose nanocrystals. Furthermore, treatment using a phosphate-urea, TEMPO catalyst, or an oxidizing agent introduces anionic functional groups such as phosphate groups or carboxyl groups, adjusting the total amount of anionic functional groups in the cellulose nanocrystals to fall within the above range. As for the hydrophilization treatment, any one of the treatments may be carried out as long as the total amount of anionic functional groups falls within the above range, but the same treatment may be carried out multiple times, or multiple times in combination with other treatments.

[0034] <Hydrophilic treatment using Never Dry treatment> Cellulose nanocrystals are generally solidified into powder or the like by drying treatments such as spray drying, heating, and reduced pressure, but during solidification by drying treatment, some of the anionic functional groups contained in the cellulose nanocrystals are eliminated, resulting in a decrease in hydrophilicity. In other words, the never-dry treatment of cellulose nanocrystals containing anionic functional groups, which does not involve solidification into powder or the like, is an example of a hydrophilization treatment.

[0035] <Hydrophilic treatment using carbodiimide> In the treatment using carbodiimide, cellulose nanocrystals and carbodiimide are stirred in a solvent such as dimethylformamide, sulfuric acid is added, and the mixture is reacted for 5 to 300 minutes at a temperature of 0 to 80°C to form a sulfate ester. The carbodiimide and sulfuric acid are preferably used in amounts of 5 to 30 mmol and 5 to 30 mmol per gram (solid content) of cellulose nanocrystals. Next, an alkaline compound such as sodium hydroxide is added to convert the sulfo groups introduced into the cellulose nanocrystals from H-type to Na-type, which is preferable for improving yield. Then, impurities are removed by filtration using a dialysis membrane or the like to prepare sulfate and / or sulfo group-modified cellulose nanocrystals. Examples of carbodiimides include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, which is a water-soluble compound having a carbodiimide group (-N=C=N-) in the molecule. Dicyclohexylcarbodiimide, which is soluble in organic solvents, can also be used.

[0036] <Hydrophilic treatment using sulfuric acid> The cellulose nanocrystals used in the present invention are obtained by hydrolyzing cellulose fibers with sulfuric acid, and these cellulose nanocrystals are further hydrophilized using sulfuric acid. Sulfuric acid is preferably used at a concentration of 40 to 60% by mass per gram (solid content) of cellulose nanocrystals. The reaction is carried out at a temperature of 40 to 60°C for 5 to 300 minutes, followed by filtration using a dialysis membrane or the like to remove impurities, thereby producing sulfate and / or sulfo group-modified cellulose nanocrystals.

[0037] <Hydrophilic treatment using sulfur trioxide-pyridine complex> In the treatment using sulfur trioxide-pyridine complex, cellulose nanocrystals are reacted with the sulfur trioxide-pyridine complex in dimethyl sulfoxide at a temperature of 0 to 60°C for 5 to 240 minutes to introduce sulfate and / or sulfo groups into the hydroxyl groups at the 6-position of the cellulose glucose units. The sulfur trioxide-pyridine complex is preferably mixed in an amount of 0.5 to 4 g by mass per 1 g (solid content) of cellulose nanocrystals. After the reaction, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfate and / or sulfo groups introduced into the cellulose nanocrystals from H-type to Na-type in order to improve the yield. Dimethylformamide or isopropyl alcohol is then added, and the mixture is washed by centrifugation or the like, after which impurities are removed by filtration using a dialysis membrane or the like, and the resulting concentrate is dispersed in water to prepare sulfate and / or sulfo group-modified cellulose nanocrystals.

[0038] <Hydrophilic treatment using phosphoric acid-urea> The hydrophilization treatment using phosphoric acid-urea can be carried out in the same manner as the conventionally known treatment of introducing phosphate groups using phosphoric acid-urea. Specifically, cellulose nanocrystals are reacted with a phosphate group-containing compound in the presence of a urea-containing compound at a temperature of 135 to 180°C for 5 to 120 minutes to introduce phosphate groups into the hydroxyl groups of the cellulose glucose units. Examples of the phosphate group-containing compound include phosphoric acid, lithium salts of phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid. Among these, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid can be preferably used alone or in combination. The phosphate group-containing compound is preferably added in an amount of 10 to 100 mmol per 10 g (solid content) of cellulose nanocrystals. Examples of urea-containing compounds include urea, thiourea, biuret, phenylurea, benzylurea, and dimethylurea. Among these, urea is preferred. The urea-containing compound is preferably used in an amount of 150 to 200 mmol per 10 g (solid content) of cellulose nanocrystals.

[0039] <Hydrophilic treatment using TEMPO catalyst> The hydrophilization treatment using the TEMPO catalyst (2,2,6,6-tetramethylpiperidine-1-oxyl) can be carried out in the same manner as the conventionally known oxidation method using the TEMPO catalyst. Specifically, cellulose nanocrystals having sulfate and / or sulfo groups are subjected to a hydrophilization reaction in which the hydroxyl group at the 6-position of the cellulose glucose unit is oxidized to a carboxyl group in an aqueous system mediated by the TEMPO catalyst (2,2,6,6-tetramethylpiperidine-1-oxyl) under normal temperature and pressure conditions. As the TEMPO catalyst, in addition to the above-mentioned 2,2,6,6-tetramethylpiperidine 1-oxyl, derivatives of TEMPO such as 4-acetamido-TEMPO, 4-carboxy-TEMPO, and 4-phosphonoxy-TEMPO can also be used. The amount of the TEMPO catalyst used is 0.01 to 100 mmol, preferably 0.01 to 5 mmol, per 1 g of cellulose nanocrystals (solid content).

[0040] During the hydrophilization treatment, it is preferable to use a co-oxidant such as an oxidant, bromide or iodide together with the TEMPO catalyst. Examples of oxidizing agents include known oxidizing agents such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides, with sodium hypochlorite and sodium hypobromite being particularly preferred. The amount of oxidizing agent used is 0.5 to 500 mmol, preferably 5 to 50 mmol, per gram of cellulose nanocrystals (solid content). Additional oxidation treatment can be performed by adding more oxidizing agent after a certain period of time has elapsed since the addition of the oxidizing agent. As the co-oxidizing agent, alkali metal bromides such as sodium bromide and alkali metal iodides such as sodium iodide can be suitably used. The amount of the co-oxidizing agent is 0.1 to 100 mmol, preferably 0.5 to 5 mmol, per 1 g of cellulose nanocrystals (solid content). The reaction medium for the reaction solution is preferably water or an alcohol solvent.

[0041] The reaction temperature for the hydrophilization treatment is in the range of 1 to 50° C., particularly 10 to 50° C., and may be room temperature. The reaction time is preferably 1 to 360 minutes, particularly 60 to 240 minutes. As the reaction progresses, carboxyl groups are generated in the cellulose, causing a decrease in the pH of the slurry. However, to ensure efficient oxidation reaction, it is desirable to maintain the pH in the range of 9 to 12 using a pH adjuster such as sodium hydroxide.

[0042] <Cleaning and fiber defibration treatment> The cellulose nanocrystals, which have been hydrophilized as necessary and have the amount of anionic functional groups such as sulfate groups and / or sulfo groups adjusted, are washed with water or centrifuged while adding water to wash away the acid, catalyst, etc. used in the hydrophilization treatment. Next, it is preferable to carry out a defibration treatment, but since cellulose nanocrystals have short fiber lengths, this does not necessarily have to be carried out. In addition, the defibration treatment may be carried out using an ultra-high pressure homogenizer, mixer, grinder or the like as a micronizing device, with water or the like as a dispersion medium, thereby preparing a dispersion liquid at the same time as defibration.

[0043] <Distributed processing> The cellulose nanocrystals, which have been subjected to hydrophilization treatment or defibration treatment as necessary, are subjected to dispersion treatment without being solidified (spray dried to form a powder). Because they are not solidified, there is no need for redispersion, resulting in superior productivity and cost efficiency. Furthermore, because they are not solidified, it is possible to form the dense self-organized structure described above, enabling the development of excellent gas barrier properties. Dispersion treatment can be suitably carried out using a dispersing machine such as an ultrasonic disperser, homogenizer, or mixer, and a stirring method using a stirring rod, stirring stone, or the like may also be used. The dispersion medium of the aqueous dispersion may be water alone, as in the ionomer resin-containing aqueous dispersion, but a mixed solvent of water and other protic polar solvents is preferred from the viewpoint of dispersibility. Examples of such protic polar solvents (polar solvents with proton-donating properties) include, but are not limited to, alcoholic solvents such as methanol, ethanol, propanol, and butanol, formic acid, and nitromethane. Among these, ethanol is preferably used. A cellulose nanocrystal-containing aqueous dispersion preferably contains 0.1 to 90% by mass of cellulose nanocrystals (solid content), and when dispersed in water at 2% solid content, it has a viscosity of 5.5 to 40 mPa·sec (rotational viscometer, temperature 30°C, spindle rotation speed 100 rpm) and a zeta potential of -50 to -55 mV, providing excellent handleability and coatability. Furthermore, when dispersed in water at 2% solid content, it has a visible light transmittance of 45%T or more, providing excellent transparency.

[0044] [Preparation of Resin Composition] In the resin composition of the present invention, it is preferable to mix the above-mentioned ionomer resin-containing aqueous dispersion and cellulose nanocrystal-containing aqueous dispersion so that the solids ratio (mass ratio) of ionomer resin to cellulose nanocrystals is 99.7:0.3 to 60:40, particularly 99:1 to 70:30. This makes it possible to prepare a resin composition containing cellulose nanocrystals and ionomer resin in the amounts described above.

[0045] In addition to the ionomer resin-containing aqueous dispersion and the cellulose nanocrystal-containing aqueous dispersion, the resin composition may also contain a layered inorganic compound, a hydroxyl group-containing polymer, a reactive crosslinking agent, etc., which allows the resin composition to exhibit excellent gas barrier properties even under high humidity conditions. In other words, because the layered inorganic compound has swelling and cleavage properties, the cellulose nanocrystals penetrate into the inorganic layered compound, widening the gap between the layers, forming a composite. The bypass effect of the layered inorganic compound for permeating gases, combined with the crosslinked structure of the cellulose nanocrystals, enables the development of excellent gas barrier properties even under high humidity conditions. The hydroxyl group-containing polymer can form a dense crosslinked structure together with the cellulose nanocrystals, significantly improving the gas barrier properties of the resulting coating film.

[0046] The layered inorganic compound may be a natural or synthetic compound, a hydrophilic or hydrophobic compound, or a conventionally known compound that swells in a solvent and exhibits cleavage, including, but not limited to, kaolinite, dickite, nacrite, halloysite, antigorite, chrysotile, pyrophyllite, montmorillonite, hectorite, mica, tetracylic mica, sodium taeniolite, muscovite, margarite, talc, vermiculite, phlogopite, xanthophyllite, and chlorite, with synthetic mica (hydrophilic and swellable) being preferred. Examples of hydroxyl group-containing polymers include polyvinyl alcohol, vinyl acetate alcohol copolymers, ethylene vinyl alcohol copolymers, polyacrylic acid, polymethacrylic acid, carboxymethyl cellulose, and starch, with polyvinyl alcohol being preferred. As the reactive crosslinking agent, polycarboxylic acids can be used, which have good reaction efficiency because cellulose nanocrystals contain anionic functional groups and can be stably dispersed without aggregation even under acidic conditions. Examples of polycarboxylic acids include alkyl dicarboxylic acids such as citric acid, oxalic acid, and malonic acid, aromatic dicarboxylic acids such as terephthalic acid and maleic acid, and anhydrides of these. Citric anhydride is particularly preferred.

[0047] The layered inorganic compound is preferably blended in an amount of 0.1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystals (solid content). The hydroxyl group-containing polymer is preferably blended in an amount of 0.1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystals (solid content). The polycarboxylic acid, which is a reactive crosslinking agent, is preferably blended in an amount of 0.1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystals (solid content). It is also preferable to contain an acid catalyst together with the crosslinking agent made of polycarboxylic acid, and the acid catalyst is preferably blended in an amount of 0.01 to 10 parts by mass per 100 parts by mass (solid content) of cellulose nanocrystals. Furthermore, the resin composition of the present invention may contain known additives, such as fillers, colorants, ultraviolet absorbers, antistatic agents, water-resistant agents, metal salts, colloidal silica, alumina sol, titanium oxide, fine particles, pH adjusters, antibacterial agents, antiviral agents, and preservatives, as needed. If necessary, the resin composition of the present invention may be formed on an anchor layer made of a cationic resin such as polyethyleneimine or polyurethane, or the anchor layer and the resin composition of the present invention may form a mixed layer.

[0048] (Laminated paper) The laminated paper of the present invention has an important feature in that a coating layer made of the above-mentioned resin composition is formed on at least one surface of a paper substrate, and has excellent water resistance, heat sealability, and processing load resistance. By using the resin composition of the present invention, it is possible to achieve water resistance and heat sealability without using a resin film that has conventionally been used in laminated paper and paper containers described below. Furthermore, the cellulose nanocrystals contained in the coating layer of the paper substrate of the present invention are biodegradable because they have a structure derived from biomass and polysaccharides. The cellulose backbone of the cellulose nanocrystals undergoes hydrolysis with water or biodegradation by enzymes such as cellulase or microorganisms, ultimately converting into water and carbon dioxide. These are utilized by biomass such as plants and trees, and a circulation cycle is formed in which pulp, the raw material for cellulose nanocrystals, is produced from biomass materials. Therefore, in the present invention, in addition to the excellent biodegradability of the paper substrate, the cellulose nanocrystals are excellent in terms of the sustainability and environmental aspects of the material in terms of biodegradability and biomass-derived materials.

[0049] Furthermore, cellulose nanocrystals have the advantage of being more heat-resistant than cellulose nanofibers with anionic functional groups. Therefore, there is no risk of thermal degradation of the resin composition even when the resin composition is heated at temperatures exceeding 200°C, such as during the extrusion lamination process or heat sealing process in the molding process for laminated paper or paper containers described below. By suppressing the occurrence of pinholes, it is possible to provide paper containers with excellent water resistance, heat sealing properties, barrier properties, and processing load resistance. Furthermore, since cellulose nanocrystals have the characteristics of being shorter in fiber length and superior in fine dispersion compared to cellulose nanofibers, the laminated paper and paper containers described below also have the characteristic of being superior in bending resistance. Therefore, even when the laminated paper is bent during the molding of a paper container to join the body member and the bottom member or for flanging (curling), as shown in Figure 4 described below, the resin composition is not damaged, and it is possible to provide a paper container with excellent water resistance, heat sealing properties, and processing load resistance.

[0050] Any paper can be used as the paper substrate depending on the application of the laminated paper, the desired rigidity, etc. For example, known papers such as fine paper, construction paper, art paper, coated paper, pure white roll paper, kraft paper, label paper with improved water resistance, paperboard such as cup base paper, card paper, ivory paper, and manila cardboard, milk carton base paper, cup base paper, synthetic paper, clay-coated paper, waterproof paper, and acid-resistant paper can be used. The thickness of the paper substrate is preferably in the range of 50 to 450 μm, and in the case of forming a cup-shaped container as shown in Fig. 4, it is preferably in the range of 150 to 400 μm. The basis weight of the paper substrate is 100 to 400 g / m 2 , especially 150 to 350 g / m 2 It is preferable that the temperature is in the range of

[0051] In the laminated paper of the present invention, the thickness of the coating layer made of the resin composition is not particularly limited, but it is preferable that the solid content (cellulose nanocrystals and ionomer resin) of the paper substrate is 1 m. 2 It is preferable that the coating amount is 0.1 to 50 g, particularly 1 to 20 g per coating. As described above, the coating layer preferably contains the ionomer resin and the cellulose nanocrystals in a mass ratio of 99.7:0.3 to 60:40, particularly 99:1 to 70:30. The laminated paper of the present invention has a coating layer made of the above-mentioned resin composition, which has excellent water resistance, heat sealing properties, and processing load resistance, formed on at least one surface of the paper base material, and is therefore fully adaptable to being molded into containers, etc., without the need for any other layers. However, it may of course have other layers, such as a layer made of a hydrophobic thermoplastic resin such as an olefin-based resin, a layer made of a hydrophilic resin such as a starch-based resin or a polyvinyl alcohol-based resin, an adhesive layer, or a barrier layer.

[0052] In the laminated paper of the present invention, it is preferable that the coating layer formed on the paper substrate has an elastic modulus of 600 to 750 MPa, particularly 600 to 685 MPa, as determined by nanoindentation measurement using a Berkovich indenter, and a deformation recovery rate of 70%, particularly 70.4% or more. As a result, even when subjected to severe processing, the laminated paper of the present invention does not experience stress concentration in response to load deformation and has a low rate of plastic deformation, resulting in high resistance to molding loads. The elastic modulus and deformation recovery rate of the coating layer in the laminated paper of the present invention can be determined as follows: As shown in Figure 2, a Berkovich-type indenter is pressed vertically 500 nm into the coating layer of the laminated paper, and the maximum displacement (hmax), contact depth (hc), and contact projected area (area of ​​contact between the indenter and the sample) (A) at the maximum load (Pmax) are measured. The amount of plastic deformation (hf) when the load is released is then measured, and the load-displacement curve shown in Figure 3 is created. The contact stiffness (S = dP / dh) of the coating layer is determined from this load-displacement curve, and the elastic modulus and deformation recovery rate are calculated using the following formula (1) and formula (2), respectively. Elastic modulus (MPa) = (π 1 / 2 / 2)×(S / A 1 / 2 ) ···(1) Deformation recovery rate (%) = {(hmax-hf) / hmax} × 100 (2)

[0053] In the laminated paper of the present invention, the resin composition can be applied to the paper substrate and dried by conventional methods, including, but not limited to, spray coating, immersion, or application with a bar coater, roll coater, or gravure coater. The coating film is preferably dried at a temperature of 100 to 150°C for 10 seconds to 1 hour. The drying process can be performed by oven drying, infrared heating, high-frequency heating, hot air drying, or the like, but natural drying is also acceptable.

[0054] (Paper containers) An important feature of the paper container of the present invention is that it is a container consisting of a body and a bottom, and a layer made of the above-mentioned resin composition is formed on at least the inner surface of the bottom. That is, as mentioned above, the coating layer made of the resin composition of the present invention effectively prevents the occurrence of pinholes even when processing that applies a molding load to the coating layer, such as bottom drawing, is performed, so it is essential that it is formed at least on the inner surface of the bottom, where pinholes are likely to occur. Furthermore, since this coating layer also has excellent water resistance and heat sealability, it may of course be formed not only on the inner surface of the bottom, but also on the inner surface of the body, or on the outer surfaces of the bottom and body.

[0055] Figure 4 is a diagram illustrating an example of a paper container of the present invention, where (A) is a diagram showing the cross-sectional structure of the laminated paper used, (B) is a diagram showing the body member and bottom member, (C) is an oblique view of a paper container assembled from the members of (B), and (D) is an enlarged cross-sectional view showing the joint between the bottom member and body member at part X of (C). As shown in Figure 4(A), the laminated paper 1 used to form the container has a paper substrate 2 with a coating layer 3 made of the resin composition of the present invention formed on one surface and a coating layer 4 made of a hydrophobic thermoplastic resin formed on the other surface. As shown in Figure 4(B), the disc-shaped laminated paper 1 is bottom-drawn to form the bottom 11 and the rising portion 12 extending downward from the periphery of the bottom 11, so that the coating layer 3 made of the resin composition of the present invention is formed on the upper surface of the bottom 11 and the outer surface of the rising portion 12. The body member 20 has the coating layer 3 made of the resin composition of the present invention formed on the surface that will become the inside of the container when the axial edges 21a, 21b are overlapped. The body member 20, with the axial edges 21a, 21b joined, is formed into a cylindrical shape that tapers from the bottom toward the drinking spout (Figure 4(C) shows the finished product).

[0056] As shown in Figure 4(D), which is an enlarged view of the X portion of Figure 4(C), the outer peripheral surface of the raised portion 12 of the bottom member 10 and the inner peripheral surface of the bottom side edge of the tubular body member 20 are both made of the coating layer 3 made of the resin composition of the present invention, so that the two have heat-sealing properties and can be bonded by heating with hot air or the like. Furthermore, by forming the covering layer 4 of the laminated paper 1 from a covering layer 3 made of the resin composition of the present invention and a resin with heat-sealing properties, it is possible to heat-compress the bottom member 10 and the body member 20 together by wrapping the rising portion 12 of the bottom member 10 with a folded portion 22 formed by folding back one end of the bottom side edge of the body member 20, as shown in Figure 4(D). At this time, the length of the folded portion 22 of the body member 20 is formed to be approximately the same as the height of the rising portion 12 of the bottom member 10, and the bottom member and the body member are bonded together around the entire circumference.

[0057] In the paper container of the present invention, since the container has a coating layer made of a resin composition with excellent water resistance, it is not necessarily necessary, but it is preferable to treat the edges of the above-mentioned laminated paper so that the paper base material is not exposed on the inside of the container. Such edge treatment can be carried out by conventionally known methods such as covering the edge with edge protection tape, applying a protective coating to the edge, or skive hemming, but skive hemming is preferred. As described above, the paper container of the present invention can take various forms as long as a coating layer consisting of the resin coating layer of the present invention is formed on at least the inner surface side of the bottom of the paper base material, and can take any form that has traditionally been known as a paper container, including, but not limited to, a cup-type container, a tray-type container, a carton-type container, etc.

[0058] The paper container of the present invention can also have the resin composition of the present invention formed on a coating layer made of a gas barrier resin composition on at least the inner bottom side of the paper substrate, or even on the inner body side, making it possible to exhibit gas barrier properties according to the characteristics of the gas barrier resin composition. [Example]

[0059] Examples of the present invention will be described below. Note that the following examples are merely examples of the present invention, and the present invention is not limited to these examples. The measurement methods for each item are as follows.

[0060] <Amount of anionic functional groups> A dispersion of anionic functional group-containing cellulose nanocrystals (hereinafter sometimes referred to as "CNC") was weighed and adjusted to 100 ml with ion-exchange water. 0.1 g of cation exchange resin was added to this anionic functional group-containing CNC dispersion and stirred. The dispersion was then filtered to separate the cation exchange resin from the anionic functional group-containing CNC dispersion. A 0.05 M sodium hydroxide solution was added dropwise to the dispersion after cation exchange using an automatic potentiometric titrator (Kyoto Electronics Co., Ltd.), and the change in electrical conductivity of the anionic functional group-containing CNC dispersion was measured. The amount of sodium hydroxide consumed for neutralization of the anionic functional groups was determined from the resulting conductivity curve, and the amount of anionic functional groups (mmol / g) was calculated using the following equation (1). Amount of anionic functional groups (mmol / g) = Titration amount of sodium hydroxide consumed for neutralization of anionic functional groups (ml) × Concentration of sodium hydroxide (mmol / ml) ÷ Solid mass of CNC containing anionic functional groups (g) (1)

[0061] <Cryo-SEM measurement> The sample was taken and freeze-fractured, and the fractured surface was cross-sectioned with an FIB while still in a cooled state. After sublimation, the cross-section morphology was observed using an FIB-SEM. The analytical equipment and measurement conditions are as follows: Equipment: FEI, Helios NanoLab 600, Helios G4 UX Acceleration voltage: FIB 30kv, SEM 1-2kv Observed image: Backscattered electron image FIB processing temperature: -160℃ (set value) Observation temperature: -80°C (set value)

[0062] <Pulse NMR measurement> Approximately 1 mL of the sample was filled into a glass test tube, and the free induction decay (M(t)) of the sample at 30°C was measured and analyzed using the CPMG method under the following conditions to determine the relaxation time of each component. Equipment: Bruker TD-NMR (the minispec mq20) Measurement method: CPMG method Observed nuclides: 1 H 90° pulse width: 2.1 μm Accumulation count: 32 times Measurement temperature: 30°C (measurement was started 15 minutes after the device temperature reached the set temperature, by adjusting the device temperature so that the internal temperature of the sample reached the measurement temperature) Repeat time: 2 seconds Analysis method: Fitting was performed using the following equation using analysis software (TDNMR-A). T2(S), which represents the relaxation time of the component with a short relaxation time, and T2(L), which represents the relaxation time of the component with a long relaxation time, were calculated. M(t)=α·exp(-(1 / Wa)(t / T α ))+β·exp(-(1 / Wa)(t / T β )) α: Proton ratio of component (α) (%) T α : T2 relaxation time of component (α) (msec) β: Proton ratio of component (β) (%) T β : T2 relaxation time of component (β) (msec) t: Observation time (msec) Wa: Shape factor (1 <Wa<2)

[0063] <Nanoindentation measurement> The sample was cut into 1cm squares and attached to a glass slide with a fixing resin. These were used as nanoindentation measurement samples and measurements were carried out under the following conditions to determine the elastic modulus (MPa) and deformation recovery rate (%). Three measurements were taken and the average values ​​were calculated. The measurement points were selected to have minimal exposed paper fibers on the surface. Nanoindenter: Hysitron Inc., Triboindenter Indenter used: Berkovich (triangular pyramid type) Measurement method: Single indentation Temperature: room temperature Indentation depth: 500 nm Push speed: 100nm / sec Deformation recovery rate (%) = (maximum displacement (nm) - plastic deformation amount (nm)) / maximum displacement (nm) × 100

[0064] <Pinhole test by screening test> The laminated paper was folded 360 degrees, returned to a flat state, and then iodine solution was applied to the bent part, and the colored part was evaluated as the part where pinholes had occurred. If there was one or less pinholes, it was evaluated as good, and if there were two or more, it was evaluated as bad.

[0065] <Pinhole test using a paper cup forming machine> The laminated paper was formed using a paper cup forming machine, and iodine solution was applied to the bent parts, and the colored parts were determined as the parts where pinholes had occurred. The pinhole occurrence rate was calculated using the following formula, with less than 2 being considered good and 2 or more being considered bad. Pinhole occurrence rate = Number of pinhole occurrence sites / Number of tests

[0066] <Pinhole test using Strograph> The laminated paper was cut to a size of 15mm in the MD and 220mm in the CD, set in a Strograph, and pulled to a displacement of 5% elongation at a chuck distance of 180mm and a pulling speed of 20m / min. Iodine solution was then applied to the surface of the laminated paper, and the colored areas were designated as areas where pinholes had occurred. A zero pinhole occurrence was evaluated as good, and one or more pinholes were evaluated as bad.

[0067] Example 1 <Preparation of cellulose nanocrystal dispersion in water> Pulp was decomposed and purified with 64% by mass sulfuric acid and then dried. The resulting anionic functional group-containing cellulose nanocrystals were added with ion-exchanged water and dispersed in a mixer to obtain an anionic functional group-containing cellulose nanocrystal dispersion. The amount of anionic functional groups in the anionic functional group-containing cellulose nanocrystals was 0.17 mmol / g. Furthermore, birefringence due to nematic liquid crystal and / or chiral nematic liquid crystal refraction patterns was confirmed in the dispersion.

[0068] <Preparation of Resin Composition> Isopropanol (5% by mass) was added to an aqueous dispersion of ethylene-(meth)acrylic acid copolymer ionomer resin (solid content = 35% by mass), and the cellulose nanocrystal-containing dispersion (solid content = 0.5% by mass) was then added and dispersed (in a mixer) to obtain a resin composition containing ethylene-(meth)acrylic acid copolymer ionomer resin and cellulose nanocrystals.

[0069] <Preparation of laminated paper> Paper base material (basis weight 200g / m 2 The resin composition was applied several times to one side of a sheet of paper using a bar coater, and then dried at 130°C for at least 50 seconds to prepare a laminated paper with a layer (10 μm thick) consisting of a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanocrystals.

[0070] <Preparation of bottom and body components> The laminate was punched out with a punching die to produce a bottom member and a body member.

[0071] <Preparation of paper containers> Using a paper cup forming machine, the body and bottom members were fed out, the body and bottom were bonded together, and then flange processing was performed to prepare a paper container characterized by the formation of a layer made of a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanocrystals.

[0072] <Example 2> The same treatment as in Example 1 was carried out except that the cellulose nanocrystal-containing dispersion (solid content = 1.0 mass%) was added, and a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanocrystals, laminated paper, and paper containers were prepared.

[0073] Example 3 The same treatment as in Example 1 was carried out except that the cellulose nanocrystal-containing dispersion (solid content = 5% by mass) was added, and a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanocrystals, laminated paper, and paper containers were prepared.

[0074] <Comparative Example 1> The same treatment as in Example 1 was carried out except that the cellulose nanocrystal-containing dispersion liquid was not added, and a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer, laminated paper, and paper container were prepared.

[0075] <Comparative Example 2> The same procedures as in Example 1 were carried out except that a cellulose nanofiber dispersion (solid content = 1% by mass) prepared by defibrating pulp using an ultra-high pressure homogenizer was added, to prepare a resin composition, laminated paper, and paper container containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanofibers.

[0076] <Comparative Example 3> To 10 g (solids) of softwood kraft pulp, 0.8 mmol of TEMPO catalyst (Sigma-Aldrich) and 12.1 mmol of sodium bromide were added, and the mixture was brought to 1 L with ion-exchanged water and stirred until uniformly dispersed. The oxidation reaction was initiated by adding 15 mmol of sodium hypochlorite per 1 g of cellulose. The pH of the system was maintained between 10.0 and 10.5 with 0.5 N aqueous sodium hydroxide during the reaction, and the oxidation reaction was carried out at 30°C for 4 hours. The oxidized cellulose was thoroughly washed with ion-exchanged water using a high-speed refrigerated centrifuge (16,500 rpm, 10 minutes) until neutral. Water was added to the washed cellulose, which was then defibrated using a mixer (7011JBB, Osaka Chemical Co., Ltd.) to obtain a 1% by mass cellulose nanofiber dispersion. The same treatment as in Comparative Example 2 was carried out except that the cellulose nanofiber dispersion (solid content = 0.3 mass%) was added, and a resin composition containing an ionomer resin of ethylene-(meth)acrylic acid copolymer and cellulose nanofibers, laminated paper, and paper containers were prepared.

[0077] [Table 1] [Industrial Applicability]

[0078] The resin composition of the present invention can form a coating film having excellent water resistance, heat sealing property, barrier property, and processing load resistance, and can therefore be suitably used as a coating layer for a paper substrate. Furthermore, paper containers formed from this paper substrate effectively suppress the occurrence of pinholes and have excellent water resistance, and can therefore be suitably used as paper containers for beverages, such as paper cups.

Claims

1. The dispersion contains an aqueous dispersion containing an ionomer resin of an ethylene-(meth)acrylic acid copolymer and an aqueous dispersion containing cellulose nanocrystals, and the relaxation time T ２ (S) is 13 msec or more and 14 msec or less, and T ２ A resin composition for forming a coating layer on a paper substrate, characterized in that (L) is 50 msec or more and less than 75 msec.

2. The resin composition according to claim 1, wherein the content of the cellulose nanocrystals (solid content) is 0.1 to 20 mass %.

3. The resin composition according to claim 1 or 2, wherein the cellulose nanocrystals contain anionic functional groups in an amount of 0.01 to 4.0 mmol / g.

4. 4. The resin composition according to claim 3, wherein the anionic functional group contains at least a sulfate group and / or a sulfo group derived from a sulfuric acid treatment.

5. 5. The resin composition according to claim 1, wherein the dispersion medium of the cellulose nanocrystal-containing aqueous dispersion is water or a mixed solvent of water and another protic polar solvent.

6. 6. The resin composition according to claim 1, wherein the content of the ionomer resin (solid content) of the ethylene / (meth)acrylic acid copolymer is 26.6 to 33.2 mass %.

7. 10. A laminated paper comprising a paper substrate and a layer made of the resin composition according to claim 1 formed on at least one surface of the paper substrate.

8. The laminated paper according to claim 7, wherein the layer made of the resin composition has an elastic modulus of 600 to 750 MPa and an elastic recovery rate of 70% or more when the layer is loaded with a Berkovich type indenter at a load of 500 nm and then unloaded.

9. The laminated paper according to claim 7 or 8, wherein the resin composition contains the ethylene / (meth)acrylic acid copolymer ionomer resin and the cellulose nanocrystals in a mass ratio of 99.7:0.3 to 60:

40.

10. A paper container comprising a body and a bottom, characterized in that a layer made of the resin composition according to any one of claims 1 to 6 is formed on the inner surface side of at least the bottom.

11. The paper container according to claim 10, wherein the layer made of the resin composition has an elastic modulus of 600 to 750 MPa and an elastic recovery rate of 70% or more when a load of 500 nm is applied with a Berkovich indenter and then unloaded.

12. The resin composition contains the ethylene (meth) acrylic acid copolymer ionomer resin and the cellulose nanocrystals in a mass ratio of 99.7:0.3 to 60:

40. The paper container according to claim 10 or 11.

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