JP2017190541A - Barrier paper, manufacturing method thereof and paper cup - Google Patents

Abstract

The present invention provides a barrier paper having improved mechanical strength, and a paper cup made of the barrier paper, which improves adhesion between the barrier layer containing cellulose fibers and the paper base material and resin.
A barrier paper having a paper base material and a barrier layer containing cellulose fibers formed on the paper base material, the cellulose fibers being cross-linked via an oxazoline group.
[Selection] Figure 1

Description

  The present invention relates to a barrier paper for filling and packaging food and the like, a method for producing the same, and a paper cup.

  In the field of packaging materials including foods, in order to protect the contents, gas barrier properties that block gas such as oxygen that permeates the packaging material are required.

  Conventionally, aluminum and polyvinylidene chloride, which are less affected by temperature and humidity, have been used as gas barrier materials. However, when these are incinerated, there is a problem that incineration residues are clogged in the exhaust port or inside the furnace in aluminum, and the incineration efficiency is lowered, and in polyvinylidene chloride, dioxins are generated. Therefore, it is required to switch the gas barrier material to a material with less environmental load. For example, even if a part of polyvinylidene chloride is a material made from the same fossil resource, switching to polyvinyl alcohol or ethylene vinyl alcohol copolymer that does not contain aluminum or chlorine is being promoted (for example, patent documents) 1). In the future, it is expected to switch from petroleum-derived materials to biomass materials.

  Cellulosic materials have attracted attention as new gas barrier materials. Cellulose, which accounts for about half of the biomass material produced on the earth, is biodegradable and has excellent physical properties such as gas barrier properties, strength, elastic modulus, dimensional stability, heat resistance, and crystallinity. Yes. Therefore, cellulose is expected to be applied to functional materials. As a cellulose material, for example, 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter, referred to as “TEMPO”) catalyst is used to disperse cellulose produced by an oxidation reaction. Cellulose nanofibers obtained (for example, see Patent Documents 2 and 3), cellulose nanofibers obtained by dispersing after introducing a carboxymethyl group into a glucose unit (for example, see Patent Document 4), enzyme treatment / alkali treatment Cellulose nanofibers obtained by mechanical defibration after applying (for example, see Patent Document 5) are known. By applying and laminating these cellulosic materials on a substrate, a gas barrier material capable of suppressing oxygen permeability can be obtained.

Japanese Patent Laid-Open No. 7-164591 JP 2008-308802 A JP 2008-1728 A JP 2013-185122 A JP-A-6-10288

  However, even if a film containing cellulose nanofibers is formed on a paper substrate, the cellulose nanofibers are physically caught on the surface of the paper substrate, so that the cellulose nanofibers do not easily penetrate into the paper substrate. Stays on the outermost surface of the substrate. In addition, since the paper base is fibrous and has a small contact area with the layer containing cellulose nanofibers remaining on the outermost surface, the interaction between the paper base and cellulose nanofibers is small, and the cellulose nanofibers against the paper base The anchor effect cannot be obtained, and there is a problem that the adhesion between the two is poor. Furthermore, the layer containing cellulose nanofibers has little interaction with the resin laminated thereon. In particular, olefin-based resins have a problem that adhesion of a layer containing cellulose nanofibers is difficult to obtain because of low polarity. When the adhesion between the layers constituting the gas barrier material is low as described above, when molded into a packaging container or the like and the contents are put in, the weight cannot be withstood and the shape of the container cannot be maintained.

  The present invention has been made in view of the above problems, and improves the adhesion between a barrier layer containing cellulose fibers, a paper substrate and a resin, and has excellent mechanical strength, a method for producing the same, and a barrier. An object is to provide a paper cup made of paper.

  In order to solve the above problems, a barrier paper according to one embodiment of the present invention includes a paper base material and a barrier layer including cellulose fibers formed on the paper base material, and the cellulose fibers include oxazoline. It is cross-linked through a group.

In the barrier sheet according to one embodiment of the present invention, the coating amount of the barrier layer, by dry weight may be 0.2 g / ^{m 2} or more 30.0 g / ^{m 2} or less.

  In the barrier paper according to one embodiment of the present invention, a fiber width of the cellulose fiber may be 1 nm or more and 200 nm or less.

  In the barrier paper according to one embodiment of the present invention, the barrier layer may contain a water-soluble polymer.

  The paper cup which concerns on 1 aspect of this invention consists of the barrier paper which concerns on 1 aspect of this invention, The said barrier layer is arrange | positioned at the inner surface side, It is characterized by the above-mentioned.

  The method for producing a barrier paper according to one embodiment of the present invention includes a step of applying a coating liquid containing cellulose fibers and a crosslinking agent having two or more oxazoline groups on a paper substrate to form a coating film. And a step of drying the coating film.

  In the barrier paper manufacturing method according to one aspect of the present invention, the cross-linking agent may have a molecular weight of 1000 or more.

  According to the present invention, since the cellulose fibers contained in the barrier layer are cross-linked via an oxazoline group, the adhesion between the barrier layer and the paper substrate, and between the barrier layer and the resin layer formed on the barrier layer It is possible to provide a barrier paper having improved adhesion and excellent adhesion strength.

It is sectional drawing which shows typically the barrier paper which concerns on embodiment of this invention. It is sectional drawing which shows typically the sheet | seat material which concerns on embodiment of this invention. It is a perspective view showing typically a paper cup concerning an embodiment of the present invention.

  Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. The drawings used in the following description are for explaining the configuration of the embodiment of the present invention, and the sizes, thicknesses, dimensions, and the like of the respective parts shown in the drawings are different from the dimensional relationships of the actual laminate. There is.

[Embodiment]
"Barrier paper"
FIG. 1 is a cross-sectional view schematically showing a barrier paper according to an embodiment of the present invention.
As shown in FIG. 1, the barrier paper 10 according to the present embodiment includes a paper base 1 and a barrier layer containing cellulose fibers formed on the paper base 1, that is, on one surface 1 a of the paper base 1. 2 and.

  The paper substrate 1 is not particularly limited, and can be appropriately selected from printing paper and packaging paper according to the application. Examples of the paper substrate 1 include glassine paper, parchment paper, advanced printing paper, intermediate printing paper, lower printing paper, thin leaf printing paper, colored fine paper, art paper, coated paper, craft paper, cardboard base paper, coated ball, Examples include ivory paper, card paper, and cup base paper.

The paper substrate 1 preferably has a basis weight of 400 g / m ² or less, more preferably a basis weight of 30 g / m ² or more and 400 g / m ² or less, and a basis weight of 150 g / m ² or more to 400 g / m ^2. m ² or less is more preferable, and the basis weight is most preferably 180 g / m ² or more and 400 g / m ² or less.
If the basis weight of the paper substrate 1 is 400 g / m ² or less, when the barrier paper 10 is bent, the stress applied to the barrier layer 2 does not become excessively large, and the stress causes cracks in the barrier layer 2. It does not occur and the gas barrier properties are not lowered. Moreover, if the basic weight of the paper base material 1 is 400 g / m ² or less, an increase in cost can be suppressed.
Moreover, when using the barrier paper 10 for a normal packaging use, it is preferable that the basic weight of the paper base material 1 is 180 g / m < ² > or more. When the basis weight of the paper base material 1 is 180 g / m ² or more, the paper base material 1 can maintain sufficient strength in normal packaging applications.

In the barrier layer 2, the cellulose fibers are cross-linked through oxazoline groups. That is, the barrier layer 2 has a crosslinked structure in which cellulose fibers are crosslinked through a compound having an oxazoline group.
The oxazoline group reacts with a hydroxyl group, a carboxy group, or an aldehyde group in cellulose fiber or oxidized cellulose obtained by chemical treatment described later to form an ester bond or an amide bond. Thereby, the mechanical strength, water resistance, moisture resistance, and adhesion of the barrier layer 2 to the resin layer formed on the paper substrate 1 or the barrier layer 2 are improved.

  The thickness of the barrier layer 2 is not particularly limited, but is preferably 0.2 μm or more and 30 μm or less in terms of dry film thickness. When the thickness of the barrier layer 2 is 0.2 μm or more, sufficient strength is obtained for the barrier layer 2 and defects such as cracks are hardly generated. If the thickness of the barrier layer 2 is 30 μm or less, an increase in cost can be suppressed.

  Natural cellulose is used as the cellulose fiber constituting the barrier layer 2. Examples of natural cellulose include various wood pulps obtained from conifers and broadleaf trees, non-wood pulps obtained from kenaf, bagasse, straw, bamboo, cotton, seaweed, cellulose obtained from sea squirts, cellulose produced by microorganisms, and the like. Can be mentioned.

The fiber width of the cellulose fiber is preferably 1 nm or more and 200 nm or less, and more preferably 3 nm or more and 100 nm or less. That is, as the cellulose fiber, cellulose nanofiber is preferable.
When the fiber width of the cellulose fiber is within the above range, the barrier layer 2 is dense and has a sufficiently small gap and excellent gas barrier properties. In addition, when the fiber width of the cellulose fibers is within the range of 3 nm or more and 100 nm or less, the entanglement between the cellulose fibers becomes denser, so that the barrier layer 2 is excellent in performance such as gas barrier properties and strength.
Moreover, it is preferable that the fiber length of a cellulose fiber is 100 nm or more and 10 micrometers or less.

  As a measuring method of the fiber diameter of the cellulose fiber, the fiber diameter is measured by observing the shape of any number of cellulose fibers using an apparatus such as an atomic force microscope (AFM) or a scanning electron microscope (SEM). And the method of measuring from the result of the particle size measurement of the coating liquid containing a cellulose fiber using apparatuses, such as the method of averaging the measured value and a particle size distribution meter, is used.

Here, in the measurement of the fiber width of the cellulose fiber, one drop of 0.001 mass% cellulose nanofiber aqueous dispersion was dropped on a mica substrate and dried, and used as a sample.
The method for measuring the fiber width of the cellulose fiber is, for example, observing the surface shape with an atomic force microscope (AFM, trade name: Nanoscope, manufactured by Nihon Beco), and determining the height difference between the mica substrate and the cellulose fiber as the fiber width. Consider and measure.

As cellulose fiber, what was chemically processed as needed can also be used.
The chemical treatment method is not particularly limited. For example, the above-described TEMPO is used as a catalyst, and the cellulose fiber is oxidized using an oxidizing agent such as sodium hypochlorite and a bromide such as sodium bromide while adjusting the pH. And a method of carboxylation. By this method, a cellulose fiber in which the hydroxyl group at the C6 position of cellulose is carboxylated, that is, a cellulose fiber having a carboxy group at the C6 position of cellulose is obtained. Since the carboxylated cellulose fibers swell due to increased electrostatic repulsion between the cellulose fibers, a dispersion of cellulose fibers can be prepared by mechanical treatment with low energy.

Moreover, as a chemical processing method, the method of anion-modifying a cellulose fiber is mentioned, for example.
As an example of this chemical treatment method, for example, the following method may be mentioned.
Sodium hydroxide or potassium hydroxide is added as a mercerizing agent to a solvent containing cellulose fibers. Next, the cellulose fiber, the solvent, and the mercerizing agent are mixed, and after the cellulose fiber is mercerized, the carboxymethylating agent is added in an amount of 0.05 to 10.0 mol per glucose residue. Then, an etherification reaction is performed to obtain a cellulose fiber having a carboxymethyl group introduced. Cellulose fibers introduced with carboxymethyl groups can be easily miniaturized because electrostatic repulsion between cellulose fibers occurs due to the carboxymethyl groups.

Furthermore, as another chemical treatment method, for example, pretreatment such as enzyme treatment, chemical treatment (alkali treatment, acid treatment, swelling chemical treatment), ozone treatment, and the like can be performed on cellulose fibers.
Cellulose fibers obtained by washing pretreated cellulose fibers or by refining the pretreated treatment liquid as a suspension can be used as the material for the barrier layer 2.

The coating amount of the barrier layer 2, it is preferably 0.2 g / ^{m 2} or more 30.0 g / ^{m 2} or less by dry weight, is 0.4 g / ^{m 2} or more 2.0 g / ^{m 2} or less More preferred.
When the coating amount of the barrier layer 2 is 0.2 g / m ² or more in terms of dry mass, the barrier layer 2 is hardly affected by the unevenness of the paper substrate 1, and the barrier layer 2 has a gas barrier property. Can be improved. The increase in manufacturing cost can be suppressed as the coating amount of the barrier layer 2 is 30.0 g / m < ² > or less by dry mass.

The content of the cellulose fiber in the barrier layer 2 is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more and 99% by mass or less.
When the content of the cellulose fiber in the barrier layer 2 is 50% by mass or more, the barrier layer 2 has improved bending resistance and gas barrier properties.

Whether the entanglement of the cellulose fibers is dense can be determined, for example, by measuring the surface density using a scanning electron microscope (SEM, trade name: S-4800, manufactured by Hitachi High-Technologies Corporation) or the specific gravity of the cast film. Judgment can be made.
The specific gravity of the cast film can be measured using a digital hydrometer (trade name: AND-DMA-220, manufactured by Ando Keiki Seisakusho Co., Ltd.). The cast film can be produced by pouring a predetermined amount of an aqueous dispersion of cellulose fibers into a square case made of polystyrene and heating and drying at 50 ° C. for 24 hours.

  According to the surface observation, the barrier layer 2 containing cellulose fibers is smaller in the number and size of the gaps formed between the fibers, and according to the measurement of the specific gravity of the cast film, the higher the specific gravity of the cast film, The gap between the fibers is small, and the entanglement of the cellulose fibers becomes dense. Therefore, by further reducing the gap between the cellulose fibers, the penetration and penetration of deterioration factors such as water vapor and dirt into the barrier layer 2 are suppressed, and the deterioration of the gas barrier property of the barrier layer 2 due to bending or the like is suppressed. be able to.

  Therefore, in the barrier paper 10 according to the present embodiment, the barrier layer 2 contains a water-soluble polymer that is compatible with cellulose as a material that can fill the gaps between the cellulose fibers contained in the barrier layer 2. It is preferable that The barrier layer 2 containing cellulose fibers and a water-soluble polymer suppresses the intrusion / penetration of deterioration factors such as water vapor and dirt, and as a result, a decrease in gas barrier properties due to bending or the like is reduced.

Examples of water-soluble polymers include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer, carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylamide, polyethyleneimine, polyethylene oxide, starch, pectin, and alginic acid. It is done.
These water-soluble polymers are excellent in film formability, transparency, flexibility and the like, and have good compatibility with cellulose fibers. Therefore, the barrier layer 2 that easily fills the gaps between the cellulose fibers and has both strength and adhesiveness is provided. Can be formed. Polyvinyl alcohol (PVA) is obtained by saponifying polyvinyl acetate, but only a few percent of acetate groups remain from a so-called partially saponified PVA in which several tens of percent of acetate groups remain. Includes up to fully saponified PVA.

When a water-soluble polymer is used, the mass ratio ((A) / (B)) between the cellulose fiber (A) and the water-soluble polymer (B) is preferably 50/50 to 99/1.
When the mass ratio of the water-soluble polymer (B) is 1 or more, the gap between the cellulose fibers can be filled with the water-soluble polymer (B). On the other hand, when the mass ratio of the water-soluble polymer (B) is 50 or less, the adhesion of the barrier layer 2 to the paper substrate 1 is improved and the barrier layer 2 is not damaged. Moreover, it can suppress that the coating liquid used as the material of the barrier layer 2 penetrates too much with respect to the paper base material 1, and the film formability of the barrier layer 2 falls.

The barrier paper 10 according to this embodiment conforms to JIS K5600-5-1: 1999 “Paint General Test Method—Part 5: Mechanical Properties of Coating Film—Section 1: Bending Resistance (Cylindrical Mandrel Method)” In conformity, the oxygen permeability at 30 ° C. and 40% RH after bending with an 8 mm mandrel is preferably 150 cc / m ² · day or less, more preferably 100 cc / m ² · day or less. .
If the oxygen permeability after bending is within the above range, the barrier paper 10 can exhibit good gas barrier properties even after processing and molding.

  According to the barrier paper 10 according to the present embodiment, the following effects can be obtained. That is, since the cellulose fiber contained in the barrier layer 2 is cross-linked through an oxazoline group, the barrier layer 2 and the paper base material 1 and the barrier layer 2 and the resin layer formed on the barrier layer 2 The barrier paper 10 having improved adhesion and excellent adhesion strength can be provided. Thereby, the barrier paper 10 which has the intensity | strength which can be endured even if it shape | molds in a container and is filled with the content, and can suppress invasion of gas can be provided. Moreover, since the barrier layer 2 contains a cellulose fiber, the barrier paper 10 with little environmental load can be provided. Furthermore, since the crosslinking agent having an oxazoline group is harmless to the human body, the barrier paper 10 that is safe even when applied to food packaging and containers can be provided.

"Barrier paper manufacturing method"
With reference to FIG. 1, the manufacturing method of the barrier paper 10 which concerns on this embodiment is demonstrated.
First, the cellulose fibers are refined (defibrated) (cellulose fiber refinement step).
The method for refining cellulose fibers is not particularly limited, and examples thereof include mechanical treatment using a dispersing apparatus such as a high-pressure homogenizer, an ultrasonic homogenizer, a grinder grinding, a freeze grinding, and a media mill.
Moreover, you may give the above-mentioned chemical process to a cellulose fiber as a pre-process which performs a mechanical process. Cellulose fibers having a desired fiber shape and particle diameter can be obtained by arbitrarily controlling the degree of mechanical treatment and chemical treatment.

Moreover, you may perform the chemical process of the above-mentioned cellulose fiber with the refinement | miniaturization process of a cellulose fiber.
At this time, the compound used for the above-mentioned chemical treatment is added to the dispersion of cellulose fibers, and the refinement treatment and chemical treatment of the cellulose fibers are performed using the dispersion.

Next, a coating containing a cellulose fiber and a cross-linking agent having two or more oxazoline groups using the refined cellulose fiber or the dispersion containing the cellulose fiber obtained in the above-described cellulose fiber refinement step. A working solution is prepared (a step of preparing a coating solution).
When using the refined cellulose fiber obtained by the refinement | purification process of a cellulose fiber, the cellulose fiber is previously disperse | distributed to water and the dispersion liquid containing a cellulose fiber is prepared.

In this coating liquid preparation step, it is preferable to adjust the pH of the coating liquid. The pH of the coating solution is preferably 3 or more and 7 or less. If pH of a coating liquid is 3 or more, it can prevent that a cellulose fiber aggregates in a coating liquid. If pH of a coating liquid is 7 or less, it can prevent that the hydroxyl group and carboxy group which are contained in a cellulose fiber dissociate, and a cellulose fiber and said crosslinking agent can fully be made to react.
For adjusting the pH of the coating solution, for example, a dilute acid such as an aqueous hydrochloric acid solution is used.
When the pH of the cellulose fiber coating solution is high, it is preferable to add dilute hydrochloric acid or the like to the coating solution to adjust the pH and then add the crosslinking agent.

As the crosslinking agent, a compound having two or more oxazoline groups is used. The oxazoline group of the crosslinking agent is preferably 5 or more, more preferably 10 or more.
When the number of oxazoline groups is 1 or less, the cellulose fibers or the cellulose fibers and one surface 1a of the paper substrate 1 cannot be crosslinked. In addition, if a compound having two or more oxazoline groups is used, many cross-linking points can be formed in a wide range, so that the cellulose fibers adhere to each other or between the cellulose fibers and one surface 1a of the paper substrate 1. Improves.

  Examples of the crosslinking agent include WS-300, WS-500, and WS-700 manufactured by Nippon Shokubai Co., Ltd.

The molecular weight of the crosslinking agent is preferably 1000 or more, and more preferably 5000 or more.
If the molecular weight of the cross-linking agent is 1000 or more, the cross-linking agent becomes long, and many cross-linking points can be formed in a wide range. Therefore, cellulose fibers or cellulose fibers and one surface 1a of the paper base 1 are formed. Adhesion is improved.

In the step of preparing the coating solution, it is preferable to prepare a coating solution by mixing a dispersion containing cellulose fibers and an aqueous solution containing the water-soluble polymer described above.
When mixing the dispersion containing the cellulose fiber and the aqueous solution containing the water-soluble polymer, as described above, the mass ratio of the cellulose fiber (A) and the water-soluble polymer (B) ((A) / (B )) Is preferably 50/50 to 99/1.

  Next, the coating liquid obtained in the above-described coating liquid preparation step is applied to one surface 1a of the paper substrate 1, and the coating liquid is formed on one surface 1a of the paper substrate 1. A coating film is formed (coating process).

  The method for applying the coating liquid to one surface 1a of the paper substrate 1 is not particularly limited, and a known coating method can be used. Examples of the coating method include a method using a coating apparatus such as a roll coater, a reverse roll coater, a gravure coater, a micro gravure coater, a knife coater, a bar coater, a wire bar coater, a die coater, and a dip coater.

Next, the coating film obtained in the above-described coating liquid preparation step is dried to form the barrier layer 2 (barrier layer forming step).
Thereby, the barrier paper 10 which has the paper base material 1 and the barrier layer 2 containing the cellulose fiber formed in the one surface 1a of the paper base material 1 is obtained.

Examples of the method for drying the coating film applied to one surface 1a of the paper substrate 1 include natural drying, air drying, hot air drying, UV drying, hot roll drying, and infrared irradiation.
The drying temperature is preferably 100 ° C to 180 ° C. If the drying temperature is 100 ° C. or higher, the number of cross-linking points between the cellulose fibers or between the cellulose fibers and one surface 1a of the paper substrate 1 increases, and the strength of the barrier layer 2, the cellulose fibers, or between the cellulose fibers and the paper base. Adhesion is improved between one surface 1a of the material 1. Moreover, since moisture in the coating film is lost, hydrogen bonds between celluloses increase, the cohesive force of the barrier layer 2 increases, and the bending resistance is improved. On the other hand, when the drying temperature is 180 ° C. or lower, the barrier layer 2 can be prevented from being deteriorated and discolored by heat.

  According to the method for producing barrier paper according to the present embodiment, the barrier layer 2 is formed using a coating liquid containing cellulose fibers and a cross-linking agent having two or more oxazoline groups. Cellulose fibers can be cross-linked through an oxazoline group to improve the adhesion between the barrier layer 2 and the paper substrate 1 and between the barrier layer 2 and the resin layer formed on the barrier layer 2.

"Paper cup"
FIG. 2 is a cross-sectional view schematically showing a sheet material according to an embodiment of the present invention. FIG. 3 is a perspective view schematically showing a paper cup according to the embodiment of the present invention.
The paper cup according to the present embodiment is made of the barrier paper 10 of the present embodiment, and the barrier layer 2 is disposed on the inner surface side.

The paper cup 200 according to the present embodiment is made of the barrier paper 10 of the present embodiment, and since the barrier layer 2 is disposed on the inner surface side, the paper cup 200 is excellent in gas barrier properties and bending resistance.
The paper cup 200 according to the present embodiment can be molded from a sheet material 100 obtained by laminating a layer (hereinafter referred to as “resin layer”) 20 made of resin on the barrier paper 10 of the present embodiment. As shown in FIG. 2, the resin layer 20 is formed on the barrier layer 2 of the barrier paper 10 and the paper substrate 1.

The material of the resin layer 20 is not particularly limited, and known materials such as polyolefin-based, epoxy-based, urethane-based, isocyanate-based, polyester-based, plant-derived material (bioplastic) can be used.
As a material of the resin layer 20, a heat-sealable resin can be used. Examples of heat-sealable resins include low density polyethylene resins (LDPE), medium density polyethylene resins (MDPE), high density polyethylene resins (HDPE), linear low density polyethylene (LLDPE), and other polyethylene resins, polypropylene resins, It can be selected from polypropylene resins such as propylene-ethylene random copolymer, propylene-ethylene block copolymer, etc., but linear low density polyethylene resin (LLDPE) in terms of workability, processability, economy, etc. Is preferred.
Moreover, it is preferable that the thickness of the resin layer 20 is 10 micrometers or more and 50 micrometers.

The resin layer 20 can be usually formed by a method of manufacturing a packaging material, for example, a wet lamination method, a dry lamination method, a solventless lamination method, a thermal lamination method, a melt extrusion lamination method, or the like. Can do.
When the resin layer 20 is formed on the barrier layer 2, a known method such as corona treatment, ozone treatment, plasma treatment, glow discharge treatment, or oxidation treatment using chemicals is previously applied to the barrier layer 2 in order to improve adhesion. A surface treatment may be applied. Alternatively, a primer coat layer, an anchor coat layer, an adhesive layer, or the like may be arbitrarily formed between the barrier layer 2 and the resin layer 20. Furthermore, a printing layer, an antistatic layer, etc. can be laminated | stacked as needed.

In order to manufacture the paper cup 200, first, the body material punched out by the punching die from the sheet material 100 and the bottom member similarly formed from the laminated body are molded into a cup shape by a cup molding machine.
Next, a paper cup 200 is obtained by sealing and sealing a separately produced lid so that it can be peeled off.
Here, it is not necessary that all of the body material, the bottom member, and the cover material be the barrier paper of this embodiment, and different sheet materials may be used as necessary.

  In addition, this invention is not limited to the above-mentioned embodiment, A various deformation | transformation implementation is possible in the range which does not deviate from the summary of this invention. In addition, the specific configuration, material, and the like of each unit are not limited to those illustrated in the above-described embodiment, and can be changed as appropriate.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

[Method 1 for preparing dispersion containing cellulose fiber (Preparation Method 1)
10 g of bleached kraft pulp was allowed to stand in 500 mL of water for 12 hours to swell the bleached kraft pulp.
The temperature of the water containing the swollen bleached kraft pulp is adjusted to 20 ° C., and 0.1 g of 2,2,6,6-tetramethyl-1-pipedinyloxy radical and 1 g of sodium bromide are added to the water. Addition to prepare a pulp suspension.
Further, 10 mmol / g sodium hypochlorite per mass of cellulose was added to the pulp suspension while stirring.
At this time, about 1N sodium hydroxide aqueous solution was added to the pulp suspension to maintain the pH of the pulp suspension at about 10.5.
Subsequently, after an oxidation reaction for 240 minutes, the pulp suspension was filtered, and the recovered product was sufficiently washed with water to obtain a pulp.
Ion exchange water was added to the obtained pulp to adjust the solid content concentration to 1% by mass, and the mixture was stirred for about 60 minutes using a high-speed rotary mixer to obtain a dispersion 1 containing transparent cellulose fibers. .

[Evaluation 1]
The average fiber diameter of the cellulose fibers contained in the dispersion was measured by the method shown below.
The average fiber diameter of the cellulose fibers was measured using a laser diffraction particle size distribution measuring device (trade name: SALD-7000H, manufactured by Shimadzu Corporation) for the dispersion containing the cellulose fibers.
As a result, the average fiber diameter of the cellulose fiber was 2.85 nm.

[Evaluation 2]
The amount of carboxy group of the cellulose fiber contained in the dispersion was measured by the method shown below.
0.2 g of wet oxidized cellulose in terms of absolute dry mass was weighed into a beaker, and distilled water was added to make 60 g. After adding 0.5 mL of 0.1 mol / L NaCl aqueous solution and adjusting pH to 3 with 0.5 mol / L hydrochloric acid, 0.5 mol / L NaOH aqueous solution was dripped and conductivity measurement was performed. The conductivity measurement was continued until the pH reached about 11.
Since the portion corresponding to the neutralization stage of the weak acid is the amount of carboxy groups, the amount of carboxy groups was 1.6 mmol / g when the addition amount of NaOH was read from the obtained conductivity curve.

[Method 2 for preparing dispersion containing cellulose fiber (Preparation Method 2)
50 g of bleached kraft pulp was suspended in 350 mL of water to swell the bleached kraft pulp.
This swollen bleached kraft pulp was mixed with 70 g of sodium hydroxide per glucose unit, adjusted to a temperature of 30 ° C., and subjected to mercerization for 1 hour.
Subsequently, the temperature was raised to 70 ° C., 90 g of sodium monochloroacetate was added, and the reaction was performed for 1 hour.
After neutralizing and washing the pulp after the reaction, ion-exchanged water is added to the pulp to adjust the solid content concentration of the anionized pulp to 1% by mass, and the mixture is stirred for about 60 minutes using a high-speed rotating mixer. A dispersion 2 containing transparent cellulose fibers was obtained.
It was 3.55 nm as a result of measuring the average fiber diameter of the cellulose fiber contained in the obtained dispersion liquid similarly to the evaluation 1.
It was 0.21 mmol / g as a result of measuring the amount of carboxy groups of the cellulose fiber contained in the obtained dispersion liquid similarly to the evaluation 2.

[Method 3 for preparing dispersion containing cellulose fiber (Preparation Method 3)
10 g of bleached kraft pulp was suspended in 500 g of water to swell the bleached kraft pulp.
To the water containing the swollen bleached kraft pulp, 25 g of sodium hydroxide was added to prepare a 5% NaOH aqueous solution and allowed to stand at 25 ° C. for 24 hours to prepare a pulp suspension.
Subsequently, ion-exchanged water was added to this pulp suspension to adjust the solid content concentration to 1% by mass.
Subsequently, this suspension was put into a stone mill type grinder (trade name: Supermass colloider MK CA 6-2, manufactured by Masuko Sangyo Co., Ltd.), and the treatment was repeated 10 times with a grindstone to obtain white creamy cellulose fibers. A dispersion 3 containing was obtained.
It was 100 nm as a result of measuring the average fiber diameter of the cellulose fiber contained in the obtained dispersion liquid similarly to the evaluation 1.

[Method for preparing polyvinyl alcohol aqueous solution]
5 g of commercially available polyvinyl alcohol (trade name: PVA-124, manufactured by Kuraray Co., Ltd.) was weighed into a beaker, and purified water was added to make 500 g. This was stirred while heating at 100 ° C., and polyvinyl alcohol was dissolved in pure water to prepare a 1% by mass aqueous solution of polyvinyl alcohol.

[Preparation method of carboxymethyl cellulose aqueous solution]
5 g of commercially available carboxymethyl cellulose (trade name: F10LC, manufactured by Nippon Paper Industries Co., Ltd.) was weighed into a beaker, and purified water was added to make 500 g. This was stirred while being heated to 100 ° C., and carboxymethyl cellulose was dissolved in pure water to prepare a 1% by mass aqueous solution of carboxymethyl cellulose.

[Method for preparing coating liquid containing crosslinking agent]
100 g of any one of dispersions 1 to 3 containing cellulose fibers was collected, and 100 g of the aqueous solution of polyvinyl alcohol or carboxymethyl cellulose was added as a water-soluble polymer aqueous solution.
If necessary, 1N dilute hydrochloric acid was added to adjust the pH, and the mixture was stirred with a stirrer for 30 minutes.
After sufficiently mixing, 10 parts by mass of an aqueous solution containing 1% by mass of a crosslinking agent was added to 100 parts by mass of the solid content of the cellulose fiber to prepare a coating liquid containing cellulose fiber and the crosslinking agent.

[Preparation of barrier paper of Examples 1 to 3]
The thickness after drying by applying the coating liquid prepared as described above on a acid-resistant paper (trade name: PC-CUP, basis weight 280 g / m ² , manufactured by Nippon Paper Industries Co., Ltd.) by a bar coating method. After forming the coating film so as to have a thickness of 1.0 μm, the coating film was dried at 150 ° C. for 10 minutes to obtain a barrier paper having a barrier layer formed on the acid-resistant paper substrate.
Polyvinyl alcohol was used as the water-soluble polymer.
As a cross-linking agent, Epocros WS500 manufactured by Nippon Shokubai Co., Ltd. was used.
The pH of the coating solution was adjusted to 4.7.
Subsequently, a heat seal layer was bonded to both sides of the barrier paper by an extrusion lamination method.
As a material for the heat seal layer, polyethylene LC600A manufactured by Nippon Polyethylene Co., Ltd. was used.

[Preparation of barrier paper of Examples 4 to 6]
Barrier paper was produced in the same manner as in Examples 1 to 3, except that carboxymethylcellulose was used as the water-soluble polymer.

[Preparation of Barrier Paper of Comparative Examples 1 to 3]
Dispersion liquids 1 to 3 containing cellulose fibers are applied by a bar coating method onto acid-resistant paper (trade name: PC-CUP, basis weight 280 g / m ² , manufactured by Nippon Paper Industries Co., Ltd.), and the thickness after drying After forming the coating film so as to have a thickness of 1.0 μm, the coating film was dried at 150 ° C. for 10 minutes to obtain a barrier paper having a barrier layer formed on the acid-resistant paper substrate.
Subsequently, a heat seal layer was bonded to both sides of the barrier paper by an extrusion lamination method.
As a material for the heat seal layer, polyethylene LC600A manufactured by Nippon Polyethylene Co., Ltd. was used.

[Evaluation 3]
The performance of the barrier paper obtained in Examples 1-6 and Comparative Examples 1-3 was evaluated according to the following method.

[Measurement of adhesion strength]
The barrier papers of Examples 1 to 6 and Comparative Examples 1 to 3 were cut into strips having a width of 15 mm and a length of 10 cm to obtain test pieces.
About this test piece, based on JIS-K-7127, T-shaped peeling was performed with the pulling speed of 300 mm / min, and the adhesive strength (N / 15mm) between a paper base material and a heat seal layer was measured.
Further, after cutting the barrier paper into a strip shape, a sample immersed in pure water for 24 hours was prepared, and the same adhesion strength was evaluated.
The results are shown in Table 1.

[Analysis of peeled surface]
About the sample after performing adhesive strength evaluation, the carboxy group of the cellulose fiber and the paper base material were dye | stained using 1% dilution liquid of o-toluidine blue. With this diluted solution, the carboxy group of the cellulose fiber was dyed purple and the paper substrate was dyed blue.
The dyed sample was visually observed to confirm at which part of the sample it was peeled off.

[Measurement of oxygen permeability (isobaric method)]
About the barrier paper obtained in Examples 1-6 and Comparative Examples 1-3, the oxygen permeability (cc / m < ² > * day) before and behind being immersed in water was measured in accordance with the following method.
The oxygen permeability of the barrier paper in an atmosphere of 30 ° C. and 40% RH was measured using an oxygen permeability measuring apparatus MOCON (trade name: OX-TRAN 2/21, manufactured by Modern Control).
The results are shown in Table 1.

From the results of Table 1, it was found that the barrier paper having the barrier layer to which the crosslinking agents of Examples 1 to 6 were added improved the adhesion, although the oxygen barrier property was somewhat deteriorated. Moreover, even if the barrier paper of Examples 1-6 was immersed in water and there existed infiltration from an end surface, it turned out that fixed adhesion strength can be maintained. Moreover, when the peeling surface was observed after evaluation of adhesion strength, the paper base material was destroyed in the barrier paper of Examples 1-6.
On the other hand, the barrier paper having the barrier layer to which the crosslinking agent of Comparative Examples 1 to 3 is not added is the interface between the paper substrate and the barrier layer before being immersed in water, and the barrier layer and the heat seal layer after being immersed in water. It was found that peeling occurred at the interface.

  From the above results, it was found that the adhesion between the paper substrate and the barrier layer and the adhesion between the barrier layer and the heat seal layer were improved by adding a crosslinking agent to the barrier layer. It was also found that by adding a crosslinking agent to the barrier layer, even when immersed in water, the decrease in adhesion strength between the paper substrate and the barrier layer, and between the barrier layer and the heat seal layer was small. Accordingly, it has been found that when a barrier paper having a cross-linking agent added to the barrier layer is used as a packaging container such as a paper cup, it has sufficient strength and can withstand practical use.

  Since the barrier paper of the present invention is excellent in gas barrier properties and bending resistance, it can be applied to various fields such as food and toiletry products, medicines, medical products, containers and packaging materials for electronic members.

DESCRIPTION OF SYMBOLS 1 ... Paper base material 2 ... Barrier layer 10 ... Barrier paper 20 ... Resin layer 100 ... Sheet material 200 ... Paper cup

Claims (7)

A paper base material, and a barrier layer containing cellulose fibers formed on the paper base material,
A barrier paper, wherein the cellulose fiber is cross-linked through an oxazoline group. The coating amount of the barrier layer, the barrier sheet according to claim 1, characterized in that a dry weight is 0.2 g / ^{m 2} or more 30.0 g / ^{m 2} or less.   The barrier paper according to claim 1 or 2, wherein a fiber width of the cellulose fiber is 1 nm or more and 200 nm or less.   The barrier paper according to claim 1, wherein the barrier layer contains a water-soluble polymer. The barrier paper according to any one of claims 1 to 4,
A paper cup, wherein the barrier layer is disposed on an inner surface side. A step of applying a coating liquid containing a cellulose fiber and a crosslinking agent having two or more oxazoline groups on a paper substrate to form a coating film;
And a step of drying the coating film.   The method for producing a barrier paper according to claim 6, wherein the molecular weight of the crosslinking agent is 1000 or more.

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