JP5617289B2 - Cellulose membrane and laminate material using the same - Google Patents

Description

  The present invention relates to a functional film material and a cellulose material that can be used as a coating film, and more particularly to a cellulose film using a cellulose material and a laminated material using the same.

  In recent years, with increasing interest in environmental issues, natural polysaccharides such as starch, cellulose and chitin chitosan and their derivatives have attracted attention as biomass materials for conventional petroleum resins. Among these, cellulose produced in large quantities on the earth is fibrous and has high crystallinity, high strength and low linear expansion, and excellent chemical stability and safety to living bodies. Therefore, it is attracting attention as a functional material. In particular, fine cellulose fibers have recently been actively developed for use in paper strength enhancers, filter aids, food additives, and the like.

  As fine cellulose fibers, for example, Patent Document 1 describes that when cellulose is oxidized using a co-oxidant in the presence of an N-oxyl compound, cellulose microcrystals can be obtained by light dispersion treatment. In addition, as an example using fine cellulose fibers, Patent Document 2 describes an example used as a gas barrier material.

JP 2009-209217 A JP 2009-57552 A

  However, Patent Document 1 does not describe a specific method for using fine cellulose fibers. Moreover, since the gas barrier property molded object (cast film) and coating film which were manufactured by the Example of patent document 2 contain the aldehyde group which is an oxidation intermediate in oxidized cellulose, when a cellulose film is dried, a cellulose film When heated to a high temperature during the molding process of the laminated material containing, there is a problem that it is colored and the transparency is lowered. In addition, because of its high crystallinity, the cellulose layer has a high elastic modulus and is a hard and brittle film. Therefore, the handling properties of the cast film are low and it is easy to crack. The coating film is also susceptible to cracking during or after processing. There is a problem that the gas barrier property cannot be sufficiently exhibited.

  The present invention has been made in view of the above problems, and is colorless and transparent and excellent in handling and workability even after heating during drying of a film or molding of a laminated material including a film. A cellulose membrane is provided.

In order to achieve the above-mentioned problem in the present invention, first, the invention according to claim 1 oxidizes cellulose to produce oxidized cellulose,
A step of adding an acid to the reaction liquid containing oxidized cellulose, adjusting the pH to 2 to 3, and separating it as a carboxylic acid, and
A step of making the oxidized cellulose filtered off as a carboxylic acid into a dispersion;
A cellulose film containing oxidized cellulose characterized by comprising,
The cellulose film is characterized in that the difference between the b value in the Lab color system after heating at 120 ° C. for 3 hours and the b value before heating is 30% or less of the b value before heating.

  In the invention according to claim 2, the difference between the b value in the Lab color system after heating at 120 ° C. for 1 hour and the b value before heating is 20% or less of the b value before heating. The cellulose membrane according to claim 1, wherein

  The invention according to claim 3 is the cellulose membrane according to claim 1 or 2, wherein the tensile elastic modulus is 6 GPa or less.

  The invention according to claim 4 is characterized in that the oxidized cellulose is an oxidized cellulose treated under mildly acidic to neutral conditions using a nitroxy radical derivative as a catalyst and halous acid or a salt thereof as a cooxidant. The cellulose membrane according to any one of claims 1 to 3, which is characterized by the above.

  The invention according to claim 5 is characterized in that the oxidized cellulose is oxidized cellulose in which a carboxyl group of 0.1 mmol / g or more and 2 mmol / g or less is introduced into the molecule. To 4. The cellulose membrane according to any one of items 4 to 4.

  The invention according to claim 6 is the cellulose membrane according to any one of claims 1 to 5, wherein the oxidized cellulose is a cellulose fiber having a number average fiber diameter of 50 nm or less. It is.

  The invention according to claim 7 further includes the cellulose membrane according to any one of claims 1 to 6, further comprising an inorganic layered compound.

  The invention according to claim 8 is a laminated material comprising: a base material; and the cellulose film according to any one of claims 1 to 7 formed on at least one side of the base material, and It is a thing.

  The invention according to claim 9 is characterized in that the base material is composed of a biodegradable resin material having a polylactic acid or polyester, a biomass-derived material, or a paper material, It is what.

  The invention according to claim 10 further includes a ceramic vapor deposition layer between the base material and the layer made of the cellulose film, or at least on one side of the base material or the cellulose film. Or it is set as the laminated material of 9.

  The invention according to claim 11 is the laminated material according to claim 10, wherein the ceramic constituting the ceramic vapor deposition layer is made of silicon oxide or aluminum oxide.

  According to the present invention, a cellulose membrane that is biodegradable and effectively uses cellulose, which is a natural resource with a low environmental load in disposal, has high heat resistance and high transparency, and is excellent in handling properties and processability. Alternatively, a laminated material having a cellulose film can be obtained. This can be used for packaging materials, particularly gas barrier materials or structures.

It is sectional drawing showing one Embodiment of the laminated material of this invention. It is sectional drawing showing one Embodiment of the laminated material of this invention. It is sectional drawing showing one Embodiment of the laminated material of this invention. It is sectional drawing showing one Embodiment of the laminated material of this invention.

  Hereinafter, the present invention will be described in detail.

  The cellulose film and cellulose laminated material of the present invention can be obtained, for example, by the following method.

  First, the cellulose used as a raw material is oxidized to introduce a carboxyl group.

  As a raw material, naturally-derived cellulose having a crystal structure of cellulose 1 can be used. Examples of naturally occurring cellulose as a raw material include wood pulp, non-wood pulp, cotton pulp, bacterial cellulose, and squirt cellulose.

  As a method for oxidizing cellulose, a method in which a nitroxy radical derivative is used as a catalyst and a halogen acid or a salt thereof is added as a cooxidant is used. In particular, TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) or 4-acetamido TEMPO is used as a catalyst, and water containing sodium chlorite under mildly acidic to neutral conditions, preferably pH 4-7. The TEMPO oxidation method carried out in (1) is preferable from the viewpoint of availability of reagents, cost, and reaction stability. In the TEMPO oxidation method, conventionally, a technique using hypohalous acid such as sodium hypochlorite or a salt thereof as a co-oxidant is widely known. However, if hypohalous acid or a salt thereof is used, an oxidation reaction is performed. As an intermediate, an aldehyde group remains in the cellulose molecule, which causes coloring during heating. On the other hand, since chlorous acid or a salt thereof is an oxidizing agent that oxidizes aldehyde groups, the generated aldehyde groups are quickly converted into carboxyl groups and do not remain in the cellulose molecule. For this reason, when using as a film or a coating film, the coloring by heating can be suppressed.

  Moreover, in the TEMPO oxidation method used conventionally, since it reacts on alkaline conditions about pH10, it was known that the elimination reaction resulting from an aldehyde group will occur frequently and the molecular weight of a cellulose will fall remarkably. In the embodiment of the present invention, the remaining of aldehyde groups is small, and the decrease in molecular weight of cellulose can be suppressed by performing the reaction under weakly acidic to neutral conditions of pH 4-7. When the molecular weight of the oxidized cellulose is large, the orientation of molecular chains in the plane is hindered, so that it is considered that the elastic modulus is lowered and the flexibility of the film or coating film is increased due to the entanglement of the molecular chains.

  Reagents used for TEMPO oxidation are easily available commercially. The reaction temperature is preferably 0 to 60 ° C., and a sufficient amount of carboxyl groups can be introduced to form fine fibers and exhibit dispersibility in about 3 to 72 hours. In order to increase the reaction rate, hypohalous acid or a salt thereof may be added. However, since an aldehyde group is likely to be generated when the addition amount is too large, the addition amount is preferably suppressed to about 1.1 equivalents relative to the catalyst.

The amount of the carboxyl group can be adjusted by appropriately setting the TEMPO oxidation conditions. Cellulose fibers are dispersed in water due to the electric repulsive force of the carboxyl group. Therefore, if the content of the carboxyl group is too small, it cannot be stably dispersed in water. If the amount is too large, the affinity for water increases and the water resistance decreases, so the carboxyl group content is preferably 0.1 mmol / g or more and 2 mmol / g or less, more preferably 0.6 mmol / g. g to 2 mmol / g. The amount of the aldehyde group is preferably 0.1 mmol / g or less in order to suppress coloring during heating.

  The oxidation reaction is stopped by adding an excessive amount of other alcohol to completely consume the cooxidant in the system. As the alcohol to be added, it is desirable to use a low molecular weight alcohol such as methanol, ethanol or propanol in order to quickly terminate the reaction. Among these, ethanol is preferable in consideration of safety and by-products generated by oxidation.

  After the oxidation reaction is stopped, the produced oxidized cellulose can be recovered from the reaction solution by filtration. In the oxidized cellulose after the reaction is stopped, the carboxyl group forms a salt with a metal ion as a counter ion. As a recovery method, a method in which a carboxyl group is filtered while forming a salt, a method in which an acid is added to a reaction solution to adjust to pH 2 to 3 and then filtered as a carboxylic acid, and an organic solvent is added to cause aggregation. Although there is a method of filtering, a method of converting to carboxylic acid and recovering from the viewpoint of handling property, yield, and waste liquid treatment is preferable.

  The recovered oxidized cellulose can be purified by repeated washing, and residues such as catalyst, salt and ions can be removed. The cleaning liquid is preferably water. If salt or the like remains in the cellulose, it is difficult to disperse in the dispersion step described later, and therefore, it is preferable to perform washing multiple times.

  Next, the process of using oxidized cellulose as a dispersion of fine cellulose fibers will be described.

As a step of refining the washed oxidized cellulose, first, the oxidized cellulose is immersed in an aqueous medium that is a dispersion medium. At this time, the pH of the immersed liquid is approximately 4 or less. Oxidized cellulose is insoluble in an aqueous medium and becomes a non-uniform suspension when immersed. Next, the pH of the suspension is adjusted to pH 4 to 12 using alkali. In particular, by forming the carboxylate with a pH of 7 to 12 alkaline, electrical repulsion between carboxyl groups is likely to occur, so that dispersibility is improved and fine cellulose fibers are easily obtained. Even if the pH is less than 4, cellulose can be made into fine fibers by mechanical dispersion treatment, but the dispersion treatment requires a long time and high energy, and the fiber diameter of the resulting fiber becomes larger. Examples of the alkali include inorganic alkalis such as sodium hydroxide, potassium hydroxide and lithium hydroxide, or various amines, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, and benzyltrimethylammonium hydroxide. Quaternary ammonium having a hydroxide ion represented by NR ₄ OH (where R is an alkyl group, a benzyl group, a phenyl group, or a hydroxyalkyl group) as a counter ion, such as 2-hydroxyethyltrimethylammonium hydroxide And organic alkalis such as compounds.

  As a method of dispersion treatment in an aqueous medium, various known dispersion treatments are possible. Specifically, homomixer treatment, mixer treatment with a rotating blade, high-pressure homogenizer treatment, ultra-high-pressure homogenizer treatment, ultrasonic homogenizer Treatment, nanogenizer treatment, disc type refiner treatment, conical type refiner treatment, double disc type refiner treatment, grinder treatment, ball mill treatment, underwater facing treatment, and the like. Among these, a mixer process with a rotary blade, a high-pressure homogenizer process, an ultra-high pressure homogenizer process, and an ultrasonic homogenizer process are preferable from the viewpoint of dispersion efficiency from the viewpoint of miniaturization efficiency. In addition, it is also possible to perform dispersion by combining two or more processing methods among these processes.

  When the dispersion treatment is performed, the suspension becomes a visually transparent dispersion liquid. When the transmittance of the dispersion is measured with a spectrophotometer, the transmittance is 70% or more at a wavelength of 660 nm and an optical path length of 1 cm. Oxidized cellulose is refined by the dispersion treatment to form fine cellulose fibers. The fine cellulose fibers after the dispersion treatment preferably have a number average fiber diameter (width in the minor axis direction of the fibers) of 50 nm or less. The fiber diameter of the fine cellulose fiber can be confirmed with a scanning electron microscope (SEM) or an atomic force microscope (AFM). If the dispersion is insufficient / non-uniform and some of the fibers have a large fiber diameter, there is a problem that the transparency, smoothness, and gas barrier properties of the film deteriorate when the dispersion is formed. .

  Next, a self-supporting film can be formed as a cellulose film by a method of coating the fine cellulose fiber dispersion liquid on a base material or by extrusion, forming a film by extrusion, and then drying and peeling. The cellulose membrane is used alone as a cellulose film, and as shown in FIG. 1, the cellulose membrane 12 is laminated on the substrate 11 and used as a cellulose coating of the laminated material 10, or fine cellulose fibers are dispersed on the substrate 11. The solution may be coated to form the cellulose film 12 and used as a cellulose coating film of the laminated material 10. As shown in FIG. 1, the cellulose film 12 may be provided only on one side of the base material 11, or may be provided on both sides of the base material 11.

  At this time, in order to reduce the drying energy, the dispersion medium is preferably a mixed liquid of water and alcohol. Furthermore, since it is a liquid mixture with alcohol, since a dispersion | distribution medium does not remain in a coating film after drying and a precise | minute film | membrane can be formed, the mechanical strength and water resistance of a film can be improved. The alcohol is preferably a low molecular weight alcohol such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and 2-butanol from the viewpoint of cost and boiling point.

  Further, the fine cellulose fiber dispersion is coated on the substrate by a known coating method such as dipping method, roll coating method, die coating method, slit coating method, screen printing method, spraying method, and the like. can do. A film of fine cellulose fibers can be formed on the substrate by drying the coating film in an oven or the like. At this time, in order to reduce the surface tension of the coating liquid to suppress the repelling and to reduce the drying energy, it is preferable that the dispersion medium is a mixed liquid of water and alcohol. For the same reason as described above, the mechanical strength and gas barrier properties of the coating film can also be improved. The alcohol is preferably a low molecular weight alcohol as described above.

  When the cellulose film is formed on one side of the substrate, it is preferably formed so that the thickness of the coating after drying is 0.01 μm or more and 100 μm or less, and particularly preferably 0.01 μm or more and 50 μm or less. preferable. If the film thickness is too thin, defects such as pinholes are likely to be formed in the coating film. In addition, when forming a film on both surfaces of a base material, it is preferable that the thickness of a film shall be 0.01 micrometer or more and 20 micrometers or less.

  The material to be the base material can be appropriately selected according to the application, for example, polyolefins such as polyethylene and polypropylene, various polyesters such as polyethylene terephthalate (PET) and polylactic acid (PLA), various polyamides such as nylon, etc. In addition to these plastics, paper materials are also included. In particular, the base material is preferably a biodegradable resin material having polylactic acid or polyester, a cellulose-derived or starch resin, a biomass-derived material such as biopolyethylene, or a paper material. Since the cellulose film formed on the base material is also biodegradable, the use of a biodegradable material or paper material for the base material results in a laminated material with extremely excellent disposal characteristics. The thickness of the substrate can be arbitrarily selected depending on the required characteristics, and a plurality of substrates can be used in combination. The base material may be subjected in advance to surface modification treatment such as corona discharge treatment, plasma treatment, or ultraviolet irradiation in order to enhance the adhesion to the cellulose film.

  In the formation of the cellulose film of the present invention, a compound having a reactive functional group such as amino group, epoxy group, hydroxyl group, carbodiimide group, polyethyleneimine, or isocyanate is added to the fine cellulose fiber dispersion as an additive. Also good. These additives react with hydroxyl groups and carboxyl groups in the oxidized cellulose and are effective in improving the performance of the coating, particularly film strength, water resistance, moisture resistance, or adhesion to the substrate.

  Further, an inorganic layered compound may be added and used as an additive. The inorganic layered compound refers to a crystalline inorganic compound having a layered structure, and examples thereof include clay minerals represented by kaolinite group, smectite group, mica group and the like. As long as it is an inorganic layered compound, its type, particle size, aspect ratio and the like can be appropriately selected according to the required characteristics, and are not particularly limited. In general, examples of the smectite group inorganic layered compound include montmorillonite, hectorite, and saponite. Among these, montmorillonite is preferable from the viewpoints of stability in coating liquid and coating property. I can give you. Addition of an inorganic layered favorite is particularly effective in improving gas barrier properties. The weight ratio of fine cellulose fibers and inorganic layered compound in the dispersion (weight of fine cellulose fibers / weight of inorganic layered compound) is preferably in the range of 95/5 to 25/75. If the blending amount of the inorganic layered compound is small, the gas barrier property cannot be sufficiently obtained, and if it is too large, the inorganic layered compound becomes insufficiently thinned, so the transparency of the film is inferior in addition to the gas barrier property. .

  In addition, additives such as tetraethoxysilane (TEOS) or other organic metal compounds or hydrolysates of organic metal compounds, antistatic agents, ultraviolet absorbers, pigments, dyes, dispersants, etc., at a level that does not impair the effects of the present invention. Etc. can also be blended.

  In order to further improve the gas barrier property of the laminated material, a ceramic vapor deposition layer may be provided. By using a vacuum process such as a vacuum deposition method, a sputtering method, or a plasma vapor deposition method (CVD method), an inorganic vapor deposition film such as silicon oxide or aluminum oxide can be formed and used. The preferable film thickness of the deposited film varies depending on the use of the laminated material, the film composition of the deposited film, and the like, but is usually in the range of several tens to 5,000 mm, more preferably 50 to 3,000 mm. If this deposited film is too thin, pinholes or the like are generated and the continuity of the deposited film is not maintained. Conversely, if it is too thick, flexibility is lowered and cracks are likely to occur. According to the cellulose film and the cellulose coating film of the present invention, a gas barrier material having high transparency and excellent flexibility can be obtained particularly when combined with a ceramic deposited film.

  The ceramic vapor deposition layer provided in the laminated material may be provided between the base material 21 and the cellulose film 22 as in the ceramic vapor deposition layer 23 in FIG. 2, and the cellulose film 32 as in the ceramic vapor deposition layer 33 in FIG. Or the surface of the substrate 41 where the cellulose film 42 is not provided, such as the ceramic vapor deposition layer 43 of FIG.

  Furthermore, if necessary, a thermoplastic resin layer, a printing layer, a protective layer, and the like that enable heat sealing can be laminated in addition to the above-described base material and composite coating. In this case, each layer to be laminated may be laminated by melt extrusion, or may be laminated using an adhesive.

  In the cellulose membrane of the present invention, the difference between the b value in the Lab color system after heating at 120 ° C. for 3 hours and the b value before heating is preferably 30% or less of the b value before heating. . Moreover, it is more preferable that the difference between the b value in the Lab color system after heating at 120 ° C. for 1 hour and the b value before heating is 20% or less of the b value before heating. By satisfy | filling this range, coloring at the time of heating to high temperature can be prevented, and transparency can be maintained. Moreover, when this cellulose film is used as a laminated material, the transparency required for the laminated material can be sufficiently satisfied.

  Here, the b value in the Lab color system is a numerical value of a color tone represented by a yellow-blue axis. The cellulose film turns yellow when heated, and the b value in the Lab color system greatly changes and the transparency is lowered. Therefore, the b value can be used as an index representing transparency.

  The cellulose membrane of the present invention preferably has a tensile elastic modulus of 6 GPa or less. By satisfying this range, it becomes difficult for cracks to be formed in the cellulose film during or after processing, and when the cellulose film is used as a gas barrier film, sufficient gas barrier properties can be exhibited. In addition, the cellulose membrane of the present invention is considered to be less likely to cause cross-linking between molecules or within a molecule because the amount of aldehyde groups, which are very reactive functional groups, is small. Conventional cellulose membranes tend to cause three-dimensional cross-linking, and the elastic modulus is high, so the film is hard and brittle, whereas the cellulose membrane of the present invention can keep the elastic modulus low, handling properties and processing Can be improved.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to the following Example.

<Example 1>
(Preparation of oxidized cellulose)
Softwood bleached pulp, which is widely available as cellulose, was used.
18 g of cellulose (in terms of absolute dry mass) was added to 700 g of sodium acetate buffer having a pH of 4.8, stirred, swollen and then defibrated with a mixer. 560 g of buffer solution, 1.8 g of 4-acetamido TEMPO and 15.3 g of sodium chlorite were added, 63 g of 0.16 mol / L sodium hypochlorite aqueous solution was added, and oxidation reaction was performed at 60 ° C. for 48 hours. Went. Thereafter, 10 g of ethanol was added to stop the reaction. Subsequently, 0.5N HCl was added dropwise to the reaction solution to lower the pH to 2. This solution was filtered using a nylon mesh, and the solid content was further washed several times with water to remove the reaction reagent and by-products, thereby obtaining oxidized cellulose containing water with a solid content concentration of 4%.

(Measurement of the amount of functional groups introduced)
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. 0.5 mL of 0.1 M sodium chloride aqueous solution was added, the pH was adjusted to 3 with 0.5 M hydrochloric acid, and 0.5 M sodium hydroxide aqueous solution was added dropwise to conduct conductivity measurement. The 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 carboxyl groups, the amount of carboxyl groups was 1.60 mmol / g when the addition amount of sodium hydroxide was read from the obtained conductivity curve.
Next, 20 g of 0.5 M acetic acid, 60 mL of distilled water and 1.8 g of sodium chlorite were added to 2 g of wet oxidized cellulose in terms of absolute dry mass, adjusted to pH 4 and reacted for 48 hours. Thereafter, the amount of carboxyl groups was measured by the same method as described above, and it was 1.61 mmol / g. From this, the aldehyde group amount was calculated to be 0.01 mmol / g.

(Preparation of fine cellulose fiber dispersion)
Distilled water was added to 100 g of oxidized cellulose having a solid content concentration of 4% (solid content of 4 g) prepared as described above to obtain 400 g of oxidized cellulose suspension. The pH was adjusted to 8 using an aqueous sodium hydroxide solution. The prepared dispersion was treated with a mixer with a rotary blade for 90 minutes to obtain a fine cellulose fiber dispersion.

<Example 2>
(Preparation of fine cellulose dispersion added with inorganic layered compound)
Distilled water was added to 2 g of oxidized cellulose 50 g (solid content 2 g) and montmorillonite (average particle size: 100 to 500 nm) having a solid content concentration of 4% prepared as described above to obtain a suspension of 400 g. The pH was adjusted to 8 using an aqueous sodium hydroxide solution. The prepared dispersion was treated with a mixer with a rotary blade for 90 minutes to obtain a montmorillonite-added fine cellulose fiber dispersion.

<Comparative Example 1>
(Preparation of oxidized cellulose)
Softwood bleached pulp, which is widely available as cellulose, was used.
30 g of cellulose (in terms of dry mass) was added to 600 g of distilled water, stirred and swollen, and then defibrated with a mixer. To this, 1200 g of distilled water and 0.3 g of TEMPO dissolved in 200 g of distilled water in advance and 3 g of sodium bromide were added, and 86 g of a 2 mol / L sodium hypochlorite aqueous solution was added dropwise to oxidize the reaction. Started. The reaction temperature was always kept below 20 ° C. During the reaction, the pH in the system was lowered, but a 0.5 N NaOH aqueous solution was sequentially added to adjust the pH to 10. And when it was made to react for 3 hours, ethanol 30g was added and reaction was stopped. Subsequently, 0.5N HCl was added dropwise to the reaction solution to lower the pH to 2. This solution was filtered using a nylon mesh, and the solid content was further washed several times with water to remove the reaction reagent and by-products, thereby obtaining oxidized cellulose containing water with a solid content concentration of 7%.

(Measurement of the amount of functional groups introduced)
As a result of measuring the introduction amount of the functional group in the same manner as in Example, the carboxyl group amount was 1.60 mmol / g and the aldehyde group amount was 0.12 mmol / g.

(Preparation of fine cellulose fiber dispersion)
Distilled water was added to 57.14 g of oxidized cellulose having a solid content concentration of 7% (solid content of 4 g) prepared as described above to obtain 400 g of oxidized cellulose suspension. The pH was adjusted to 8 using an aqueous sodium hydroxide solution. The prepared dispersion was treated with a mixer with a rotary blade for 90 minutes to obtain a fine cellulose fiber dispersion.

(Cellulose film)
The fine cellulose fiber dispersions of Examples 1 and 2 and Comparative Example 1 were poured into a square plastic container, dried at 50 ° C. overnight, and then dried at 120 ° C. for 1 hour to obtain a cellulose film. The thickness of the obtained cellulose film was 14.2 μm and 15.0 μm, respectively.

<Evaluation method>
(Color measurement of cellulose film)
The cellulose films of Examples 1 and 2 and Comparative Example 1 were heated at 120 ° C. for 3 hours and further at 180 ° C. for 1 hour. The b value in the Lab color system after heating at 120 ° C. for 1, 2 and 3 hours and after heating at 180 ° C. for 1 hour was measured using a color difference meter CR-300 manufactured by Konica Minolta.

(Measurement of tensile modulus of cellulose film)
The tensile elastic modulus at 25 ° C. of the cellulose films of Examples 1 and 2 and Example 2 was measured using EXSTER DMS6100 manufactured by SII Nanotechnology.

  Table 1 shows the measurement results of b value and elastic modulus of Examples 1 and 2 and Comparative Example 1.

  The cellulose films of Examples 1 and 2 had a substantially constant b value even after heating at 120 ° C., whereas the cellulose film of Comparative Example 1 had an increased b value. After heating at 180 ° C., the b value was significantly increased in Comparative Example 1 as compared with Examples 1 and 2, and discoloration (brown) was apparent. In addition, the elastic modulus of the cellulose films of Examples 1 and 2 is smaller than that of Comparative Example 1 and the film of Comparative Example 1 is very brittle and difficult to handle, whereas there are no cracks or cracks when handling the film. It was.

  The cellulose film or the laminated material having the cellulose film of the present invention can be used for packaging materials, particularly film-like gas barrier materials and three-dimensional structures.

10, 20, 30, 40 ... Laminate material 1 ... Base material 2 ... Cellulose film 3 ... Ceramic vapor deposition layer

Claims (11)

Oxidizing the cellulose to produce oxidized cellulose;
A step of adding an acid to the reaction liquid containing oxidized cellulose, adjusting the pH to 2 to 3, and separating it as a carboxylic acid, and
A step of making the oxidized cellulose filtered off as a carboxylic acid into a dispersion;
A cellulose film containing oxidized cellulose characterized by comprising,
A cellulose membrane, wherein a difference between a b value in a Lab color system after heating at 120 ° C. for 3 hours and a b value before heating is 30% or less of the b value before heating.   2. The difference between the b value in the Lab color system after heating at 120 ° C. for 1 hour and the b value before heating is 20% or less of the b value before heating. Cellulose membrane.   The cellulose membrane according to claim 1 or 2, wherein the tensile elastic modulus is 6 GPa or less.   4. The oxidized cellulose according to claim 1, wherein the oxidized cellulose is a oxidized cellulose treated under a weakly acidic to neutral condition using a nitroxy radical derivative as a catalyst and a halogen acid or a salt thereof as a cooxidant. The cellulose membrane according to any one of the above.   5. The oxidized cellulose according to claim 1, wherein the oxidized cellulose is oxidized cellulose into which a carboxyl group of 0.1 mmol / g or more and 2 mmol / g or less is introduced in the molecule. Cellulose membrane.   The cellulose membrane according to any one of claims 1 to 5, wherein the oxidized cellulose is a cellulose fiber having a number average fiber diameter of 50 nm or less.   Furthermore, an inorganic layered compound is included, The cellulose film of any one of Claim 1 to 6 characterized by the above-mentioned.   A laminate material comprising: a base material; and the cellulose film according to any one of claims 1 to 7 formed on at least one surface of the base material.   The laminate material according to claim 8, wherein the base material is made of a biodegradable resin material having polylactic acid or polyester, a biomass-derived material, or a paper material.   10. The laminated material according to claim 8, further comprising a ceramic vapor-deposited layer between the base material and the layer made of the cellulose film, or on at least one surface of the base material or the cellulose film. The laminated material according to claim 10, wherein the ceramic constituting the ceramic vapor deposition layer is made of silicon oxide or aluminum oxide.

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