JP6574601B2 - Cellulose film and method for producing the same - Google Patents

Description

  The present invention relates to a cellulose film and a method for producing the same.

  With the development of production technology and distribution, it is common practice to wrap food, medicines, etc. in a transparent film. Currently, the transparent film is mainly manufactured from materials such as polyvinyl alcohol and ethylene vinyl alcohol. However, since the raw material is synthesized from petroleum, carbon dioxide in the atmosphere is increased by burning when the transparent film made of the raw material is discarded, which causes environmental problems. In order to solve the above problem, for example, biodegradable materials such as cellulose and cellulose film have been proposed (for example, Patent Document 1).

  It is known that the medicine and the food deteriorate when oxidized. For this reason, it has been required that the film for packaging the pharmaceutical product or the food has low oxygen permeability (hereinafter sometimes referred to as “having oxygen barrier property”). However, since the cellulose fibers are hydrophilic, there is a problem that the ease of passing water vapor or oxygen of the cellulose film increases under a high humidity environment.

JP 2012-122077 A

  Accordingly, an object of the present invention is to provide a cellulose film whose oxygen permeability is kept low even in a high humidity environment, and a method for producing the same, in order to solve the above-described problems.

The cellulose film of the present invention as a means for solving the above problems is a cellulose film in which at least a part of the carboxy groups are substituted with a metal, and has an oxygen permeability of 1 (mL · μm · m ⁻² · kPa ⁻¹ · day ⁻¹ ) or less.

  ADVANTAGE OF THE INVENTION According to this invention, the said various problems in the past can be solved, the said objective can be achieved, and the cellulose film with low oxygen permeability also in a high humidity environment and its manufacturing method can be provided.

FIG. 1 shows measurement results of oxygen permeability of the cellulose films of Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 2 shows the measurement results of the light transmittance of the cellulose films of Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 3 shows the FT-IR measurement results of the cellulose films of Examples 1 and 2 and Comparative Examples 1 and 2.

(Cellulose film and production method thereof)
The method for producing a cellulose film of the present invention includes a cellulose fiber production process, a film formation process, and an ion exchange process, and may further include other processes.
The cellulose film of the present invention (hereinafter sometimes referred to as “cellulose nanofiber film”) can be preferably produced by the method for producing a cellulose film.

<Cellulose fiber manufacturing process>
The cellulose fiber production process of the present invention includes at least an oxidation treatment and a dispersion treatment, and preferably includes a further oxidation treatment between the oxidation treatment and the dispersion treatment, and further includes other treatments as necessary.

<< Oxidation treatment >>
The oxidation treatment is a treatment for oxidizing cellulose into oxidized cellulose. The cellulose is preferably a cellulosic material. The oxidation is a treatment for obtaining oxidized cellulose fibers by oxidizing the cellulose raw material in a reaction solution containing the cellulose raw material, an N-oxyl compound, and a co-oxidant.

-Cellulose raw material-
The cellulose-based raw material is not particularly limited and may be appropriately selected depending on the intended purpose. For example, softwood pulp, hardwood pulp, cotton pulp such as cotton linter or cotton lint, straw pulp, bagasse pulp, etc. Non-wood pulp, bacterial cellulose, cellulose isolated from sea squirt, cellulose isolated from seaweed, and the like. These may be used individually by 1 type and may use 2 or more types together.
The cellulosic material may be subjected to a treatment for increasing the surface area such as beating.

There is no restriction | limiting in particular as the dispersion medium of the said cellulose raw material in the said reaction liquid, According to the objective, it can select suitably, For example, water etc. are mentioned.
There is no restriction | limiting in particular as a density | concentration of the said cellulose raw material in the said reaction liquid, According to the objective, it can select suitably.

-N-oxyl compound-
There is no restriction | limiting in particular as said N-oxyl compound, According to the objective, it can select suitably, For example, "Cellulose" Vol. 10, 2003, pages 335-341. Shibata and A.I. Examples include compounds described in “Catalyzed Oxidation of Cellulose Using TEMPO Derivatives: HPSEC and NMR Analysis of Oxidation Products” by Isogai. These may be used individually by 1 type and may use 2 or more types together.
Specific examples of the N-oxyl compound include 2,2,6,6-tetramethylpiperidine-N-oxyl (hereinafter sometimes referred to as “TEMPO”), 4-acetamido TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO etc. are mentioned.
There is no restriction | limiting in particular as content of the said N- oxyl compound in the said reaction liquid, According to the objective, it can select suitably, For example, a catalyst amount etc. are mentioned.

-Co-oxidizer-
The co-oxidant is not particularly limited and may be appropriately selected depending on the intended purpose. For example, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogen acid or a salt thereof, hydrogen peroxide And perorganic acids. These may be used individually by 1 type and may use 2 or more types together.
Specific examples of the co-oxidant include sodium hypochlorite and sodium hypobromite.
There is no restriction | limiting in particular as content of the said co-oxidant in the said reaction liquid, According to the objective, it can select suitably.

-Other ingredients-
The said reaction liquid may contain other components other than the cellulose raw material mentioned above, a N-oxyl compound, and a co-oxidant.
There is no restriction | limiting in particular as said other component, According to the objective, it can select suitably, For example, a bromide, iodide, or a mixture thereof etc. are mentioned.

--Bromide, iodide, or a mixture thereof--
There is no restriction | limiting in particular as said bromide and iodide, According to the objective, it can select suitably, For example, an alkali metal bromide, an alkali metal iodide, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.
There is no restriction | limiting in particular as content of the said bromide, iodide, or these mixtures in the said reaction liquid, According to the objective, it can select suitably.

  Conditions such as pH of the reaction solution, reaction temperature, pressure, and reaction time in the oxidation treatment are not particularly limited and may be appropriately selected depending on the purpose.

-Oxidized cellulose fiber-
The oxidized cellulose fiber (hereinafter sometimes referred to as “TOC”) obtained by the oxidation treatment has a carboxy group content of 0.8 mmol / g or more and 2.2 mmol / g or less, and an aldehyde group content of 0.8 mmol / g or less. is there.
The amount of carboxy groups and the amount of aldehyde groups in the oxidized cellulose fiber are T.P. Saito and A.A. Isogai, “TEMPO-mediated oxidation of native cellulose. The effect of oxidative conditions on chemical and olestial of the sequel. 198, The effect of oxidative conditions on chemistry. It can be measured by an additional oxidation treatment with sodium chlorite and conductivity titration.

Moreover, the oxidation cellulose fiber which does not contain an aldehyde group can be obtained even if it does not perform the below-mentioned additional oxidation process by selecting the conditions of the said oxidation process.
The conditions for the oxidation treatment not containing the aldehyde group are not particularly limited. Saito, M .; Hirota, N .; Tamura, S .; Kimura, H .; Fukuzumi, L. Heux, A .; Isogai, “Individualization of nano-sized plant cell fibrils by direct surface carbation using TEMPO, which is described in 1999. .

<<< Additional oxidation treatment >>>
It is preferable that a post-oxidation treatment is included after the oxidation treatment.
The additional oxidation treatment is a step of further oxidizing the oxidized cellulose fiber obtained by the oxidation treatment with sodium chlorite.
The conditions for the additional oxidation treatment are not particularly limited. Saito and A.A. Isogai, “TEMPO-mediated oxidation of native cellulose. The effect of oxidative conditions on chemical and molecular structures of the biofuels of the world. 5, pp. 1983 to 1989, 2004) can be selected as appropriate.
Oxidized cellulose fibers not containing an aldehyde group obtained by oxidizing a small amount of the aldehyde group generated at the C6 position to a carboxy group by the additional oxidation treatment can be obtained. In addition, the proton of the carboxy group is usually replaced with 20% or more, preferably 70% or more of sodium, and sodium-type oxidized cellulose fiber (hereinafter sometimes referred to as “TOC-Na”) by the additional oxidation treatment. Is obtained.

The sodium-type oxidized cellulose fiber obtained by the oxidation treatment is not dispersed evenly to the nanofiber unit at this stage, and can be washed by a normal water washing-suction filtration washing method.
Specific examples of the washing method include a method of washing and washing with at least one of suction filtration and centrifugation. The number of times of washing may be one time or a plurality of times. The unreacted cooxidant and various byproducts can be removed by the washing.

<< Distributed processing >>
In the dispersion treatment, sodium-type oxidized cellulose fibers (TOC-Na) are diluted with water, defibrated and treated with a sodium-type cellulose fine dispersion (hereinafter referred to as “sodium-type cellulose nanofiber” or “TOCN-Na”). It may be referred to as a manufacturing process.
There is no restriction | limiting in particular as said fibrillation process, According to the objective, it can select suitably, For example, it can carry out on the following conditions. A 25-mL TOC-Na aqueous suspension with a concentration of 0.1% by mass is defibrated for 4 minutes with an ultrasonic homogenizer (US-300T manufactured by Nippon Seiki Co., Ltd., probe tip 7 mm, output 300 W, 19.5 kHz). .
The concentration of TOC-Na in the suspension can be appropriately selected within a range of 0.05% by mass or more and 0.5% by mass or less.

  Subsequently, in order to remove undefibrated sodium-type oxidized cellulose fibers, the suspension after the defibrating treatment is centrifuged at 9,000 rpm for 15 minutes in a centrifuge to obtain undefibrated that is a precipitate. The sodium type oxidized cellulose fiber is removed to obtain a sodium type cellulose fine dispersion (TOCN-Na) which is a supernatant containing no undefibrated sodium type oxidized cellulose fiber.

<Film formation process>
The film forming step is a step of producing an oxidized cellulose film by placing oxidized cellulose on a substrate and drying it. For example, the sodium-type cellulose fine dispersion (TOCN-Na) is injected into a petri dish. It includes a process, a process of drying in a dryer, and a process of peeling from the petri dish, and includes other processes as necessary. By the film forming step, a sodium-type cellulose film (hereinafter, sometimes referred to as “TOCN-Na film”) can be obtained.
The injection amount of the sodium-type cellulose fine dispersion is adjusted so that the thickness of the sodium-type cellulose fine dispersion film is 5 μm or more and 50 μm or less. When the thickness of the sodium-type cellulose fine dispersion film is adjusted to the above range, the density becomes 1 g / cm ³ or more and 1.6 g / cm ³ or less. The thickness of the sodium-type cellulose fine dispersion film may be adjusted by selecting the size of the petri dish.
There is no restriction | limiting in particular as a material of the said petri dish, According to the objective, it can select suitably, For example, a polystyrene etc. are mentioned.
There is no restriction | limiting in particular as temperature of the said dryer, Although it can select suitably according to the objective, Room temperature (25 degreeC)-50 degreeC are preferable, and 40 degreeC is more preferable.
There is no restriction | limiting in particular as said drying period, Although it can select suitably according to the objective, 3 days-6 days are preferable and 3 days are more preferable.

<Ion exchange process>
The ion exchange step in the present invention is a step of bringing the oxidized cellulose film into contact with an aqueous metal salt solution without contacting with an acid. The ion exchange step includes, for example, a step of bringing the sodium-type cellulose film (TOCN-Na film) into contact with an aqueous metal salt solution, and includes other steps as necessary.
The step of contacting the acid is, for example, by immersing the sodium-type cellulose film (TOCN-Na film) in an acid, using the sodium salt of a carboxy group of cellulose on the surface as a proton, and the 6-position of the cellulose on the surface is carboxy. It is a process of forming a proton type cellulose film (hereinafter sometimes referred to as “H type cellulose film”). In the ion exchange step, from the viewpoint of the efficiency of ion exchange, it is preferable to perform a step of immersing the obtained sodium-type cellulose film in an aqueous metal salt solution without passing through the step of contacting with the acid.

The valence of the metal contained in the aqueous metal salt solution can be appropriately selected according to the purpose, but is preferably a metal having either a divalent or trivalent valence.
Examples of the divalent and trivalent metals include calcium, magnesium, iron (divalent), aluminum, and iron (trivalent). From the viewpoint of strengthening the bond between the cellulose fine dispersions, calcium is used. Aluminum and iron (trivalent) are preferable, and calcium or aluminum is particularly preferable.
Examples of the metal salt contained in the aqueous metal salt solution include metal chlorides, metal sulfides, metal oxides, and the like, and metal chlorides are preferable because they are inexpensive and have low toxicity.

Conditions for immersing the sodium-type cellulose film (TOCN-Na film) in the metal salt aqueous solution can be appropriately selected according to the purpose, but it is preferable to immerse at room temperature (23 ° C.) for 2 hours or more. By immersing the sodium-type cellulose film in the metal salt aqueous solution, the sodium on the cellulose surface is replaced with the metal contained in the metal salt aqueous solution. For example, a calcium-type cellulose film (hereinafter sometimes referred to as “TOCN-Ca film”) can be produced by immersing the sodium-type cellulose film (TOCN-Na film) in an aqueous calcium chloride solution.
The cellulose film after the ion exchange step is preferably formed from cellulose fibers in which all of the carboxy groups on the surface of the cellulose fibers are substituted with metal ions in terms of enhancing oxygen barrier properties.
The fact that the surface of the cellulose film has been replaced with metal can be examined by confirming the presence or absence of sodium ions with a fluorescent X-ray apparatus described later.
The cellulose film after being immersed in the metal salt aqueous solution is preferably used after being washed. The washing can be performed with distilled water, for example.

  The method for producing a cellulose film in the present invention can be taken as an ion exchange (ion substitution) method when attention is paid to a carboxy group on the surface of cellulose fibers.

  The cellulose film of the present invention is a film suitably produced by the method for producing a cellulose film. The cellulose film includes both a cellulose film before metal substitution and a cellulose film after metal substitution. Hereinafter, the physical properties of the cellulose film of the present invention will be described.

<Average light transmittance>
The average light transmittance of the cellulose film is preferably 70% or more, more preferably 80% or more at 25 ° C., from the viewpoint that a film having a more colorless color can be provided.
There is no restriction | limiting in particular as a means to measure the said light transmittance, A well-known means can be selected suitably, For example, an ultraviolet visible near-infrared spectrophotometer (the JASCO Corporation make, V-670) etc. Can be mentioned.
The average light transmittance was measured for 10 times each of the light transmittance at a wavelength of 450 nm, 500 nm, and 600 nm for a cellulose film having a thickness of 5 μm to 50 μm at room temperature (25 ° C.). The average value (average of 30 points) is expressed. When the average light transmittance is 70% or more, the cellulose film is colorless and transparent over the visible light range.

<Oxygen permeability>
As the oxygen permeability of the cellulose film, the film thickness is 5 μm to 50 μm under the conditions of 23 ° C., normal pressure, and relative humidity 80% from the point that oxidation of inclusions can be prevented when used as a packaging film. The value measured with a film having no defect is 1 (mL · μm · m ⁻² · kPa ⁻¹ · day ⁻¹ ) or less, and 0.2 (mL · μm · m ⁻² · kPa ⁻¹ · day ^{− 1} ) The following is preferable.
There is no restriction | limiting in particular as a means to measure the said oxygen permeability, A well-known means can be selected suitably, For example, using an oxygen permeability measuring apparatus (The product made by Modern control, OX-TRAN 2/21). And a method of measuring based on the international standard ASTM D-3985.
The normal pressure refers to 1,010 hPa ± 50 hPa.

<Detection of carboxy group on metal-substituted cellulose surface>
The fact that the sodium salt of the carboxy group on the surface of the cellulose film is all substituted with a metal other than sodium can be examined using a fluorescent X-ray apparatus. Although the said fluorescent X-ray apparatus can be suitably selected according to the objective, it can measure using MESA-500 by Horiba, for example.

<Detection of carboxy group of H-type cellulose film>
The fact that the sodium salt of the carboxy group on the surface of the cellulose film is replaced with a proton (the H-type cellulose film) can be examined by infrared spectroscopy. The infrared spectroscopic measurement is performed with a Fourier transform infrared spectroscopic (hereinafter referred to as “FT-IR”) photometer. Although the said Fourier-transform infrared spectrophotometer can be suitably selected according to the objective, For example, it can measure by JASCO Corporation FT / IR-6100.
In the FT-IR spectrum of the H-type cellulose film produced through the step of immersing in an acid solution and then the step of immersing in a metal chloride in the step of substituting the cellulose film with metal, the characteristic peak is 1,720 cm. A peak derived from a carboxy group on the surface of the H-type cellulose film is observed in the vicinity of ^-1 . When the proton of the carboxy group on the surface of the H-type cellulose film is replaced with a metal ion by the step of immersing the cellulose film in a metal chloride aqueous solution, the peak does not appear. The 1,720cm and around ^-1 refers to a wavelength of 1,720 ± 30 cm ^-1.
The presence / absence of the peak is determined to be absent when the second derivative in the 1,720 ± 30 cm ⁻¹ region of the FT-IR spectrum curve after smoothing processing is zero or minus in the software attached to the apparatus.

<Thickness, moisture content, density of cellulose film>
The thickness of the cellulose film is preferably 5 μm or more and 50 μm or less.
The thickness of the film can be obtained from the peak number and refractive index of the interference spectrum of the film. For details, conditions described in “Method. Journal of Sol-Gel Science and Technology 2009, 51, 215-221” are appropriately selected.
There is no restriction | limiting in particular as a means to measure the refractive index of the said film, A well-known means can be selected suitably, For example, the Abbe refractometer (NAR-1T Solid) by an Atago Co., Ltd. etc. is mentioned. The interference spectrum of the film can be measured using an ultraviolet-visible near-infrared spectrophotometer (for example, V-670 manufactured by JASCO Corporation).
The moisture content of the cellulose film refers to the moisture content of the film after conditioning for one day or more at 23 ° C. and 50% RH, and the moisture content is preferably 5% by mass or more and 20% by mass or less. As a measuring method of the moisture content of the film, it can be determined from the ratio of the weight difference before and after the heat treatment at 105 ° C. for 3 hours.
The density of the cellulose film is preferably 1 g / cm ³ or more and 2.0 g / cm ³ or less. The density can be calculated by dividing the weight at 23 ° C. and 50% relative humidity by the volume.

<Dry tensile mechanical properties>
Among the dry tensile mechanical properties (Young's modulus, tensile strength, breaking strain, breaking work) of the dried cellulose film, Young's modulus is 10 GPa or more, tensile strength is 150 MPa or more, and breaking strain is 2% or more and 10% or less. Is preferred.
The tensile test of the dry cellulose film can be appropriately selected depending on the purpose, but can be measured, for example, under the following conditions. Using a film cut into 3 mm wide and 3 cm long sections using a precision universal testing machine (EZ Test) manufactured by Shimadzu Corporation having a load cell of 500 N in an atmosphere of 23 ° C., normal pressure and 50% RH. The test conditions are a span length of 10 mm and a tensile speed of 1 mm · min ^−1, and the value obtained by measuring five or more times with the same film and calculating an average value of three times is used.

<Wet tensile mechanical properties>
Of the wet tensile mechanical properties (Young's modulus, tensile strength, breaking strain, breaking work) of the dry cellulose film, the Young's modulus is 0.03 GPa to 5 GPa, the tensile strength is 1 MPa to 50 MPa, and the breaking strain is 1. % To 20% is preferable.
The tensile test of the wet film can be appropriately selected according to the purpose, but can be measured, for example, under the following conditions. According to the TAPPI standard (456 om-87), a test piece stored in distilled water can be taken out and subjected to a tensile test immediately after removing surface moisture with filter paper. The size of the test piece is 3 mm in width and 30 mm in length, and the measurement span length is 10 mm. As the thickness of the wet film, a value measured immediately before the wet tensile test is performed using a soft touch micrometer (manufactured by Mitutoyo Corporation, CLM1-15QM) is used.

  The cellulose film of the present invention can be suitably used as a packaging material for foods and pharmaceuticals, preferably capable of distinguishing the color and change of an object to be packaged visually.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following examples, Wako Pure Chemical Industries, Ltd. was used as a reagent whose manufacturing company was not specified.

Example 1
<Sodium-type cellulose nanofiber manufacturing process>
In a 500 mL beaker, 3 g of softwood bleached kraft pulp equivalent to a dry weight (manufactured by Nippon Paper Industries Co., Ltd., α-cellulose content of about 90 mass%, viscosity average degree of polymerization of about 1,300), 0.458 g of TEMPO, and After dispersing 0.3 g of sodium bromide in 300 mL of distilled water, a 13 mass% sodium hypochlorite aqueous solution was added so that the amount of sodium hypochlorite was 10 mmol with respect to 1 g of pulp. The reaction was started. During the reaction, 0.5 mol·L ⁻¹ aqueous sodium hydroxide solution was added dropwise to keep the pH at 10, and ethanol was added after 2.5 hours while stirring at room temperature (20 ° C. to 25 ° C.). Was stopped. The reaction solution was filtered and washed with distilled water to obtain cellulose fibers.
The obtained cellulose fiber (corresponding to 3 g by dry weight), 3.42 g of sodium chlorite was dispersed in 300 mL of an acetic acid buffer having a pH of 4.8, and the reaction was started by stirring. The mixture was stirred for 2 days, the reaction solution was filtered through a glass filter, and washed with distilled water to obtain sodium-type cellulose fibers (TOC-Na).
Disentanglement treatment using an ultrasonic homogenizer (US-300T, Nippon Seiki Seisakusyo Co., Ltd.) having a 7 mm diameter tip in which the sodium-type cellulose fiber is dispersed in distilled water to a concentration of 0.1% (w / v). Went. The fibrillation treatment was performed for 4 minutes under the condition of 19.5 kHz (maximum output 300 W) with respect to 25 mL of the TOC-Na dispersion. The TOC-Na dispersion after the defibration treatment was subjected to centrifugation at 9,000 rpm for 15 minutes to remove coarse substances, thereby obtaining a sodium-type cellulose nanofiber (TOCN-Na) dispersion.

<Sodium-type cellulose nanofiber (TOCN-Na) film formation step>
The TOCN-Na was dispersed in water so as to be 0.1% (w / v), and 30 mL of the 0.1% (w / v) TOCN-Na aqueous dispersion was poured into a petri dish made of polystyrene, It was dried in an oven for 3 days to obtain a sodium-type cellulose nanofiber (TOCN-Na) film.

<Preparation of calcium-type cellulose nanofiber (TOCN-Ca) film>
The sodium-type cellulose nanofiber (TOCN-Na) film is immersed in a 0.1 mol·L ⁻¹ calcium chloride aqueous solution for 2 hours, washed with distilled water, and dried in a thermostatic chamber at 23 ° C. and 50% RH for one day. A calcium-type cellulose nanofiber (TOCN-Ca) film was obtained.

<Oxygen permeability>
The oxygen permeability of the TOCN-Ca film was measured according to ASTM D-3985 using an oxygen permeability measuring device (manufactured by Modern control, OX-TRAN 2/21). The results are shown in FIG. The oxygen permeability at 80% RH of the TOCN-Ca film was 0.08 (mL · μm · m ⁻² · kPa ⁻¹ · day ⁻¹ ).

<Light transmittance>
The result of having measured the light transmittance of the said TOCN-Ca film using the ultraviolet visible near-infrared spectrophotometer (The JASCO Corporation make, V-670) is shown in FIG. The TOCN-Ca film has an average light transmittance of 103.3 times measured at 450 nm and an optical transmittance of 83.7% measured at 10 times of 500 nm. The light transmittance at 600 nm is 600 nm. The average light transmittance measured 10 times was 84.4%, and all the average light transmittances (30 point average) were 83.8%.

<Infrared (IR) absorption spectrum>
The IR spectrum of the TOCN-Ca film was measured using a Fourier transform infrared spectrophotometer (manufactured by JASCO Corporation, FT / IR-6100), and the result of analysis with software attached to the apparatus is shown in FIG. The IR spectrum of the TOCN-Ca film showed no peak in the vicinity of 1,720 cm ^−1, which is the absorption peak of the carboxy group.

  Thickness and density of the TOCN-Ca film, physical properties of the dried film (water content, Young's modulus, tensile strength, breaking strain, fracture work), and physical properties of the wet film after the wet treatment (water content, Young's modulus, Table 1 shows the tensile strength, breaking strain, and fracture work.

(Example 2)
<Preparation of Aluminum Type Cellulose Nanofiber (TOCN-Al) Film>
Produced in the same manner as in Example 1 except that the 0.1M calcium chloride aqueous solution was changed to a 0.1M aluminum chloride aqueous solution in the step of producing the calcium-type cellulose nanofiber (TOCN-Na) film of Example 1. Then, an aluminum type cellulose nanofiber (TOCN-Al) film was obtained. About the obtained aluminum type cellulose nanofiber (TOCN-Al) film, the same measurement as Example 1 was performed and the result was shown in Table 1 and FIGS. 1-3.

(Comparative Example 1)
<Cellulose film without ion exchange process>
Using the sodium-type cellulose nanofiber (TOCN-Na) film of Example 1, the same measurement as in Example 1 was performed, and the results are shown in Table 1 and FIGS.

(Comparative Example 2)
<Preparation of calcium type cellulose nanofiber (H type TOCN-Ca) film substituted with calcium through acid treatment>
In the step of preparing the calcium-type cellulose nanofiber (TOCN-Na) film of Example 1, the step of immersing in a 0.1 M aqueous solution of calcium chloride for 2 hours was immersed in 0.01 M hydrochloric acid for 30 minutes and washed with water. A calcium-type cellulose nanofiber film (H-type TOCN-Ca film) ion-exchanged after acid treatment was obtained instead of a step of immersing in a 0.1 M calcium chloride aqueous solution for 2 hours and washing with water. The obtained H-type TOCN-Ca film was measured in the same manner as in Example 1, and the results are shown in Table 1 and FIGS.

-* Indicates that measurement was impossible because gelation occurred when immersed in water.

  From the results of Examples 1 and 2, the film in which the surface metal of the cellulose film was replaced with calcium or aluminum showed a transparent and high oxygen barrier property. Further, from the result of Comparative Example 2, the ion exchange method in which the cellulose film is immersed in an acid and the surface carboxy sodium is returned to the carboxy group and then the proton of the carboxy group is replaced with calcium is ion-exchanged 100%. The carboxy group remained and the oxygen barrier property was low. From the above results, it was shown that a cellulose film having a high transparency and a high oxygen barrier property under a high humidity environment can be obtained by the method of the present invention.

Examples of the aspect of the present invention include the following.
<1> A cellulose film in which at least a part of the carboxy groups are substituted with a metal, wherein oxygen permeability is 1 (mL · μm · m ⁻² · kPa ⁻¹ · day ⁻¹ ) or less. It is a cellulose film.
<2> The cellulose film according to claim 1, wherein an average light transmittance of light having a wavelength of 450 nm to 650 nm is 60% or more.
<3> The cellulose film according to any one of <1> and <2>, wherein the spectrum obtained by infrared spectroscopy (IR) does not have a peak in the vicinity of 1,720 cm ⁻¹ .
<4> Oxidizing cellulose to make oxidized cellulose, placing the oxidized cellulose on a substrate and drying to produce an oxidized cellulose film, and contacting the oxidized cellulose film with a metal salt aqueous solution And a method for producing a cellulose film.
<5> The method for producing a cellulose film according to <4>, wherein the metal of the metal salt is either divalent or trivalent.
<6> The method for producing a cellulose film according to any one of <4> to <5>, wherein the metal salt aqueous solution is a metal chloride aqueous solution.
<7> A method for producing a film in which a carboxyl group in a cellulose film is ion-substituted, comprising the method for producing a cellulose film according to any one of <4> to <6>. It is a manufacturing method.
<8> The method for producing a cellulose film according to <7>, wherein the cellulose is oxidized cellulose obtained by oxidation using 2,2,6,6-tetramethylpiperidine (TEMPO).

Claims (8)

A cellulose film in which at least a part of carboxy groups of sodium-type oxidized cellulose in which 20% or more of protons of carboxy groups are replaced with sodium, are replaced with a metal other than sodium ,
Cellulose film, wherein the oxygen permeability is less than ^{1 (mL · μm · m -2} · kPa -1 · day -1).   The cellulose film according to claim 1, wherein an average light transmittance of light having a wavelength of 450 nm to 650 nm is 60% or more. The cellulose film according to claim 1, which has no peak in the vicinity of 1,720 cm ⁻¹ in a spectrum obtained by infrared spectroscopy (IR). A process of oxidizing cellulose to oxidized cellulose;
Further oxidizing the oxidized cellulose with sodium chlorite to obtain sodium-type oxidized cellulose in which 20% or more of protons of the carboxy group are substituted with sodium;
Disposing the sodium-type oxidized cellulose on a substrate and drying to produce a sodium-type oxidized cellulose film;
Without contacting the acid the sodium form oxidized cellulose film, comprise contacting a metal salt solution other than sodium, the steps you replacing the sodium metal contained in the metal salt aqueous solution other than said sodium, the A method for producing a cellulose film.   The method for producing a cellulose film according to claim 4, wherein the metal of the metal salt is divalent or trivalent.   The method for producing a cellulose film according to claim 4, wherein the metal salt aqueous solution is a metal chloride aqueous solution. A method for producing a film in which a carboxyl group in a cellulose film is ion-substituted,
The manufacturing method of the cellulose film characterized by including the manufacturing method of the cellulose film in any one of Claim 4 to 6.   The method for producing a cellulose film according to claim 7, wherein the cellulose is oxidized cellulose obtained by oxidation using 2,2,6,6-tetramethylpiperidine (TEMPO).