JP2010168573A - Suspension of cellulose fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a suspension of cellulose fiber suitable as a material for manufacturing an oxygen gas barrier film. <P>SOLUTION: The suspension of cellulose fiber includes cellulose fibers, a polyvalent metal, and a volatile base. The cellulose fibers have an average fiber diameter of ≤200 nm, and cellulose constituting the cellulose fiber has a carboxy group content of 0.1-2 mmol/g. This suspension is suitable as a material for manufacturing a film having oxygen gas barrier properties. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a suspension of cellulose fibers suitable for the production of an oxygen barrier film, a method for producing the suspension, a molded body using the suspension, and a method for producing the same.

  Since current gas barrier materials such as oxygen and water vapor are mainly produced from fossil resources, they are non-biodegradable and must be incinerated. Therefore, it has been studied to produce a biodegradable oxygen barrier material using reproducible biomass as a raw material.

  Patent Document 1 is an invention relating to a coating agent containing microcrystalline cellulose and a laminated material in which the coating agent is applied to a substrate. It is described that the microcrystalline cellulose powder as a raw material preferably has an average particle size of 100 μm or less. In the examples, only those having an average particle size of 3 μm and 100 μm are used. There is no description about the refinement treatment, and there is room for improvement in the denseness and film strength of the applied coating agent layer and the adhesion to the substrate.

  Patent Document 2 discloses an invention relating to fine cellulose fibers, and describes the possibility of being used as a coating material, but does not describe uses for which specific effects are shown.

  Non-Patent Document 1 does not disclose any gas barrier properties such as an oxygen barrier.

  Patent Document 3 discloses a method for producing a gas barrier film in which a film-like material containing polyacrylic acid and a polyalcohol-based polymer as main components is formed, heat-treated, and then immersed in a medium containing a metal to be ionically crosslinked. (Claim 15, Example 1, etc.).

  Patent Document 4 discloses a method for producing a film in which a solution containing a polycarboxylic acid polymer (polyacrylic acid in the examples), a polyvalent metal compound, and a volatile base is coated on a substrate and heat-treated. (Claim 8, Example 1 etc.).

JP 2002-348522 A JP 2008-1728 A JP 2005-126539 A Japanese Patent Laid-Open No. 10-237180

Bio MACROMOLECULES Volume7, Number6, June 2006, Published by the American Chemical Society

  An object of the present invention is to provide a suspension of cellulose fibers suitable for production of an oxygen barrier film and a method for producing the suspension.

  Another object of the present invention is to provide a film-shaped molded article and a composite molded article that are produced using a suspension of cellulose fibers and have excellent oxygen barrier properties.

The present invention provides the following inventions as means for solving the problems.
(1) Cellulose fiber suspension containing cellulose fiber, polyvalent metal and volatile base, wherein the cellulose fiber has an average fiber diameter of 200 nm or less and contains a carboxyl group of cellulose constituting the cellulose fiber A suspension of cellulose fibers, the amount of which is 0.1-2 mmol / g.
(2) Suspension of cellulose fiber according to claim 1, comprising 1 to 500 chemical equivalents of a volatile base with respect to the carboxyl group content of the cellulose fiber.
(3) The cellulose fiber suspension according to claim 1, comprising 0.1 to 1.5 chemical equivalents of polyvalent metal with respect to the carboxyl group content of the cellulose fiber.
(4) A film-like molded body formed from the suspension of cellulose fibers according to claim 1.
(5) A composite molded article having a layer formed from the suspension of cellulose fibers according to claim 1 on a substrate.
(6) A step of mixing an aqueous solution of cellulose fiber and acid, wherein the cellulose fiber has an average fiber diameter of 200 nm or less, and the carboxyl group content of cellulose constituting the cellulose fiber is 0.1 to 2 mmol / g. Is,
Filtering the mixture obtained in the previous step,
The manufacturing method of the suspension of a cellulose fiber which has the process of mixing the filtrate obtained at the previous process with the aqueous solution containing a polyvalent metal and a volatile base.
(7) The structure of the carboxyl group of the cellulose fiber is
Before the step of mixing the cellulose fiber and the aqueous acid solution, the structure is COO ⁻ Na ⁺ .
In the step of mixing with the aqueous acid solution, the structure is COOH.
The method for producing a suspension of cellulose fibers according to claim 6, wherein the step of mixing with the aqueous solution containing the polyvalent metal and the volatile base is COO ^- B ⁺ (B ⁺ is a conjugate acid of a volatile base).
(8) A step of adhering the cellulose fiber suspension to a molding hard surface, a step of drying the cellulose fiber suspension to obtain a film-like molded body, and 30 to 300 ° C., 1 The manufacturing method of the film-shaped molded object of Claim 4 which has the process of heating for -300 minutes.
(9) A step of adhering the cellulose fiber suspension to the substrate surface, a step of drying the cellulose fiber suspension to obtain a composite molded body, and 30 to 300 ° C., 1 to 300 The manufacturing method of the composite molded object of Claim 5 which has the process of heating for minutes.

  The suspension of cellulose fiber of the present invention is suitable as a membrane material having gas barrier properties such as oxygen gas. The film obtained from the suspension has a high oxygen gas barrier property.

<Suspension of cellulose fiber and its production method>
The suspension of cellulose fibers of the present invention can be produced by the production method described below, but the production method is a method suitable for the production of the suspension. Therefore, the suspension of the cellulose fiber of the present invention can also be obtained by a method obtained by modifying a part of the production method.

[Production of specific cellulose fibers]
The cellulose fiber used in the present invention has an average fiber diameter of 200 nm or less, preferably 1 to 200 nm, more preferably 1 to 100 nm, and still more preferably 1 to 50 nm. An average fiber diameter is calculated | required by the measuring method as described in an Example.

  The carboxyl group content of cellulose constituting the cellulose fiber used in the present invention is 0.1 to 2 mmol / g, preferably 0.4 to 2 mmol / g, more preferably from the viewpoint of obtaining high gas barrier properties. Is 0.6 to 1.8 mmol / g, more preferably 0.6 to 1.6 mmol / g. Carboxyl group content is calculated | required by the measuring method as described in an Example. When the carboxyl group content is less than 0.1 mmol / g, the average fiber diameter of the cellulose fibers is not refined to 200 nm or less even when the fiber refinement process described below is performed.

  The cellulose fiber used in the present invention has a content of carboxyl group of cellulose constituting the cellulose fiber in the above range, but depending on the control state such as oxidation treatment in the actual production process, the cellulose fiber after oxidation treatment What exceeds the said range may be contained in it as an impurity.

  The cellulose fibers used in the present invention have an average aspect ratio of 10 to 1,000, more preferably 10 to 500, and still more preferably 100 to 350. An average aspect ratio is calculated | required by the measuring method as described in an Example.

  The cellulose fiber used by this invention can be manufactured by the following method, for example. First, about 10 to 1000 times the amount (mass basis) of water is added to the raw natural fiber (absolute dry basis), and processed with a mixer or the like to form a slurry.

  Examples of natural fibers that can be used as raw materials include wood pulp, non-wood pulp, cotton, and bacterial cellulose.

  Next, the natural fiber is oxidized using 2,2,6,6, -tetramethyl-1-piperidine-N-oxyl (TEMPO) as a catalyst. In addition, 4-acetamido-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO and the like, which are derivatives of TEMPO, can be used as the catalyst.

  The amount of TEMPO used is in a range of 0.1 to 10% by mass with respect to natural fibers (absolute dry standard) used as a raw material.

  During the oxidation treatment, an oxidant such as sodium hypochlorite and a bromide such as sodium bromide are used in combination with TEMPO as a co-oxidant.

  As the oxidizing agent, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, a perorganic acid, or the like can be used. Alkali metal hypohalites such as sodium bromite. The amount of the oxidizing agent used is in a range of about 1 to 100% by mass with respect to the natural fiber (absolute dry standard) used as a raw material.

  As a co-oxidant, it is preferable to use an alkali metal bromide such as sodium bromide. The usage-amount of a co-oxidant is the range used as about 1-30 mass% with respect to the natural fiber (absolute dry standard) used as a raw material.

  The pH of the slurry is desirably maintained in the range of 9 to 12 from the viewpoint of allowing the oxidation reaction to proceed efficiently.

  The temperature of the oxidation treatment (temperature of the slurry) is arbitrary at 1 to 50 ° C., but the reaction is possible at room temperature, and temperature control is not particularly required. The reaction time is preferably 1 to 240 minutes.

  After the oxidation treatment, the used catalyst or the like is removed by washing with water or the like. At this stage, since the reaction fiber is not refined, it can be performed by a purification method in which washing and filtration are repeated. If necessary, a dried or fibrous oxidized cellulose can be obtained.

  Thereafter, the oxidized cellulose is dispersed in a solvent such as water and refined. Refinement treatment is performed by a disaggregator, a beater, a low-pressure homogenizer, a high-pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a short-axis extruder, a twin-screw extruder, an ultrasonic stirrer, and a domestic juicer mixer. And can be adjusted to length. The solid concentration in this step is preferably 50% by mass or less. Beyond that, it is not preferable because very high energy is required for dispersion.

  By such refinement treatment, cellulose fibers having an average fiber diameter of 200 nm or less can be obtained, and the average aspect ratio is 10 to 1,000, more preferably 10 to 500, and still more preferably 100 to 350. A certain cellulose fiber can be obtained.

  Thereafter, a solid (concentrated, transparent or opaque liquid) with a solid content adjusted as necessary, or a powder that is dried as necessary (however, it is a powder in which cellulose fibers are aggregated, Cellulose particles are not meant). In addition, when making into suspension, what used only water may be used, and the mixed solvent of water, other organic solvents (for example, alcohol, such as ethanol), surfactant, an acid, a base, etc. was used. It may be a thing.

  By such oxidation treatment and refinement treatment, the hydroxyl group at the C6 position of the cellulose structural unit is selectively oxidized to a carboxyl group via an aldehyde group, and the carboxyl group content is 0.1 to 2 mmol / g. Highly crystalline cellulose fibers that are made of cellulose and have an average fiber diameter of 200 nm or less can be obtained.

  This highly crystalline cellulose fiber has a cellulose I-type crystal structure. This means that the cellulose fiber is a fiber that is refined by surface oxidation of a naturally-derived cellulose solid raw material having an I-type crystal structure. In other words, natural cellulose fibers have a high-order solid structure built up by bundling fine fibers called microfibrils produced in the process of biosynthesis. The fine cellulose fiber is obtained by weakening the hydrogen bond) by introducing an aldehyde group or a carboxyl group, and further through a refinement treatment.

  Then, by adjusting the oxidation treatment conditions, the carboxyl group content is increased or decreased within a predetermined range, the polarity is changed, the electrostatic repulsion of the carboxyl group or the above-mentioned fine processing, The average fiber diameter, average fiber length, average aspect ratio, etc. can be controlled.

Cellulose fibers obtained by the above oxidation treatment and refinement treatment can satisfy the following requirements (I), (II), and (III).
(I): The mass fraction of cellulose fibers that can pass through a glass filter having an aperture of 16 μm is 5% or more with respect to the mass of cellulose fibers in the cellulose fiber suspension diluted to a solid content of 0.1 mass%. To obtain a gas barrier material with good performance.
(II): The cellulose fiber suspension diluted to a solid content of 1% by mass does not contain cellulose granules having a particle size of 1 μm or more.
(III): The light transmittance of the cellulose fiber suspension diluted to a solid content of 1% by mass is 0.5% or more.

  Requirement (I): When the suspension having a solid content of 0.1% by mass obtained by the above oxidation treatment and refinement treatment is passed through a glass filter having an aperture of 16 μm, the suspension before passing through the glass filter is suspended. A mass fraction of 5% or more with respect to the total amount of cellulose fibers contained in the suspension can pass through the glass filter (the mass fraction of fine cellulose fibers that can pass through the glass filter is defined as the content of fine cellulose fibers). To do). From the viewpoint of gas barrier properties, the fine cellulose fiber content is preferably 30% or more, more preferably 90% or more.

  Requirement (II): The suspension having a solid content of 1% by mass obtained by the above-described oxidation treatment and refinement treatment has a refined natural fiber used as a raw material, and is a cellulose granule having a particle diameter of 1 μm or more. What does not contain a body is preferable. Here, the granular material is substantially spherical, and the ratio of the major axis to the minor axis (major axis / minor axis) of the rectangle surrounding the projected shape obtained by projecting the shape onto a plane is 3 or less at the maximum. . The particle diameter of the granular material is an arithmetic average value of the lengths of the major axis and the minor axis. The presence / absence of the granular material was determined by observation with an optical microscope described later.

  Requirement (III): The cellulose fiber suspension having a solid content of 1% by mass obtained by the above oxidation treatment and refinement treatment preferably has a light transmittance of 0.5% or more, from the viewpoint of gas barrier properties. More preferably, it is 40% or more, and further preferably 60% or more.

  What is necessary is just to adjust solid content concentration so that the shaping | molding according to the objective can perform the cellulose fiber suspension of this invention, for example, solid content concentration can be made into the range of 0.05-30 mass%.

[Step of mixing cellulose fiber and aqueous acid solution]
The specific cellulose fiber described above originates from the production process and has —COONa in the cellulose molecule. In this step, the cellulose fiber and an aqueous solution of an acid such as hydrochloric acid are stirred and mixed to cause a substitution reaction of Cell-COO ^- Na ⁺ → Cell-COOH. After this reaction, the cellulose fibers that have been dispersed until then cause aggregation. In the production of the suspension of cellulose fiber of the present invention, it is preferable to carry out this step, but this step and the next step are omitted and mixed with an aqueous solution containing a subsequent polyvalent metal and volatile base. You may start from the process to do.

The progress of the substitution reaction of Cell-COO ⁻ Na ⁺ → Cell-COOH can be confirmed qualitatively and quantitatively from elemental analysis such as infrared absorption spectrum and fluorescent X-ray.

  When a 1M hydrochloric acid aqueous solution is used as the aqueous acid solution, it is set to about 2 chemical equivalents relative to the carboxyl group in the cellulose.

[Step of filtering the mixture (aggregate) obtained in the previous step]
In the next step, the mixture (aggregate) obtained in the previous step is filtered and washed with water.

  The amount of water used for washing is about 100 to 10,000 times the mass of the filtrate (water-containing solid) obtained by filtration.

[Step of mixing the filtrate obtained in the previous step with an aqueous solution containing a polyvalent metal and a volatile base]
In the next step, the filtrate obtained in the previous step is mixed with an aqueous solution containing a polyvalent metal and a volatile base.

  Examples of the polyvalent metal include oxides such as zinc, cobalt, nickel, and copper, hydroxides, and carbonates.

  Examples of the volatile base include ammonia, methylamine, dimethylamine, ethylamine, diethylamine, triethylamine and the like. Volatile bases are present in the suspension as polyvalent metals and ammonium complexes (eg, zinc ammonium, copper ammonium, etc.).

  The amount of the polyvalent metal used is preferably 0.05 to 1.5 chemical equivalents relative to the amount of carboxyl groups in the cellulose fiber from the viewpoint of barrier properties when formed into a film-like molded product later. 3-1.0 chemical equivalent is more preferable, and 0.4-0.6 chemical equivalent is still more preferable. If the chemical equivalent is 1.5 or less, the cellulose fibers and unreacted polyvalent metal can be prevented from remaining in the membrane, so that a dense membrane structure can be formed. Since the amount of formation of the crosslinked structure is sufficient, good barrier properties can be obtained when it is formed into a film-like molded product later.

  The usage-amount of a volatile base is 1-500 chemical equivalent with respect to the amount of carboxyl groups in a cellulose fiber, Preferably it is 2-100 chemical equivalent, More preferably, it is 5-50 chemical equivalent. When the amount of volatile base used is 1 chemical equivalent or less, it is difficult to obtain a suspension in which cellulose fibers are uniformly dispersed. When the amount of volatile base is 500 chemical equivalents or less, in the production process of a film-like molded product or composite molded product, Sexuality is improved.

In this step, a complex of a polyvalent metal and a volatile base is formed as in the following reaction formula (when zinc oxide and ammonia are used).
The cellulose fiber is added with a volatile base to cause a substitution reaction of Cell-COOH → Cell-COO ⁻ B ⁺ (B ⁺ represents a conjugate acid of a volatile base. In the following reaction formula, NH ₄ ⁺ ), and agglomerates. The product is uniformly dispersed again, and a suspension of cellulose fibers is obtained. And after a volatile base and water are vaporized from the suspension of the cellulose fiber, in the cellulose fiber, -COO-M-OOC- (M represents a polyvalent metal. In the following reaction formula, Zn.). A bond (cross-linked bond) is formed, but since the suspension contains volatile base and water, the bond (cross-linked bond) does not occur.

_{ZnO + 4NH 3 + H 2 O} → [Zn (NH 3) 4] 2+ (OH -) 2

The progress of the Cell-COOH → Cell-COO ⁻ B ⁺ substitution reaction can be confirmed qualitatively and quantitatively from elemental analysis such as infrared absorption spectrum and fluorescent X-ray.

  Since the suspension of the cellulose fiber of the present invention obtained by the above production method contains very fine cellulose fibers, in the case of a suspension having a cellulose fiber concentration of 50% by mass or less, Transparent to the naked eye.

  In the present invention, the mixed polyvalent metal may not completely form a complex with the volatile base, but may remain partially dissolved in the suspension of cellulose fibers.

The suspension of cellulose fibers obtained in this step can maintain a state in which the cellulose fibers are uniformly dispersed because the polyvalent metal exists as an alkaline complex with a volatile base. Therefore, it can be used as a material for producing a more uniform film-shaped molded body. For example, when a polyvalent metal salt (for example, ZnCl ₂ ) is added to a cellulose suspension without using a volatile base, the cellulose fibers are agglomerated, which is preferable as a material for producing a uniform film-shaped molded body. Absent.

  The suspension of the cellulose fiber of the present invention can be used as a paint, and in that case, it may be a suspension containing water and an organic solvent as necessary.

  The cellulose fiber suspension of the present invention has gas barrier properties such as oxygen barrier properties and water vapor barrier properties when formed into a film. Therefore, it is also possible to produce a film-like molded body such as a film using itself as a film-forming material, and to apply coating, spraying, dipping, etc. to the surface of an existing planar molded body and a three-dimensional molded body. By attaching by a known method, the surface can be modified (ie, gas barrier properties, moisture resistance, etc. can be imparted) without impairing the surface appearance.

  The cellulose fiber suspension of the present invention may contain an ultraviolet absorber, a colorant and the like depending on the application.

  Next, an embodiment for producing a film-shaped molded body and a composite molded body using the suspension of cellulose fibers of the present invention will be described.

<Membrane shaped product>
The membranous shaped product of the present invention comprises a suspension of cellulose fibers, and can be obtained by the following production method.

  First, in the first step, a suspension of cellulose fibers is deposited on a substrate to form a film.

  Specifically, a suspension of cellulose fibers having a viscosity of about 10 to 5000 mPa · s is cast (or coated, sprayed, dipped, etc.) on a substrate such as a hard surface such as glass or metal to form a film. Form the body. In this method, by controlling the carboxyl group amount and aspect ratio of the cellulose fibers contained in the suspension of cellulose fibers and the thickness of the gas barrier molding, film molding according to specifications (high barrier properties, transparency, etc.) You can get a body.

  Next, after drying at room temperature (20 to 25 ° C.), 30 to 300 ° C., more preferably 60 to 200 ° C., and even more preferably 100 to 160 ° C. for 1 to 300 minutes, more preferably 5 to 5 as necessary. A film-like molded body can be obtained by heat treatment for 60 minutes. In the treatment of the previous step and this step, the volatile base and water (optionally an organic solvent) contained in the cellulose fiber suspension are removed by vaporization, and as shown in the above reaction formula, Cell-COO- A bond (cross-linked bond) of M-OOC-Cell (Cell represents cellulose and M represents a polyvalent metal) is formed. Since the progress of the crosslinking reaction is accelerated by heat treatment, the cross-linking reaction proceeds promptly and a dense film structure is formed by heat treatment in the production process of the film-shaped molded body. become.

  Then, it cools and dries as needed, peels from substrates, such as a glass plate, and obtains a film-form molding. Since the film-like molded body thus obtained has a crosslinked structure formed between cellulose fibers, the gas barrier property is improved.

  Since the film-shaped molded article of the present invention has moisture resistance (strength and barrier properties) by forming a crosslinked structure, in addition to a gas barrier material, a water purification separation membrane, an alcohol separation membrane, a polarizing film, a polarizing film It can also be used as a plate protective film, a flexible transparent substrate for displays, a separator for fuel cells, a dew condensation prevention sheet, an antireflection sheet, an ultraviolet shielding sheet, an infrared shielding sheet, and the like.

<Composite molded body>
The composite molded body of the present invention comprises a substrate and a cellulose fiber layer, and can be obtained by the following production method.

  First, in the first step, a suspension containing cellulose fibers is attached to the surface of the base material (attachment by coating, spraying, dipping, casting, etc.), and cellulose is applied on the base material (one side or both sides of the base material). A primary composite molded body in which a fiber layer is formed is obtained.

  Moreover, the method of laminating | stacking together said film-shaped molded object shape | molded previously with respect to a base material is applicable. As a bonding method, a known method such as a method using an adhesive or a heat-sealing method can be applied.

  Next, after drying at room temperature (20 to 25 ° C.), 30 to 300 ° C., more preferably 60 to 200 ° C., and even more preferably 100 to 160 ° C. for 1 to 300 minutes, more preferably 5 if necessary. A composite molded body composed of a base material and a cellulose fiber layer can be obtained by heat treatment for ˜60 minutes. In the treatment of the previous step and this step, the volatile base and water (optionally an organic solvent) contained in the cellulose fiber suspension are removed by vaporization, and as described above, Cell-COO-M-OOC- A bond (cross-linked bond) of Cell (Cell represents cellulose and M represents a polyvalent metal) is formed.

  Then, it cools and dries as needed, and obtains a composite molded object. The composite molded body thus obtained has improved gas barrier properties because a crosslinked structure is formed between cellulose fibers.

  Since the composite molded body of the present invention has moisture resistance (strength and barrier properties) by forming a crosslinked structure, in addition to a gas barrier material, a water purification separation membrane, an alcohol separation membrane, a polarizing film, a polarizing plate They can also be used as protective films, flexible transparent substrates for displays, separators for fuel cells, anti-condensation sheets, anti-reflection sheets, ultraviolet shielding sheets, infrared shielding sheets, and the like.

  The thickness of the layer made of cellulose fibers can be appropriately set according to the use, but when used as a gas barrier composite molded body, it is preferably 20 to 900 nm, more preferably 50 to 700 nm, still more preferably 100 to 500 nm. is there.

  As the molded body serving as the base material, a thin film such as a film, a sheet, a woven fabric, and a non-woven fabric having a desired shape and size, and a three-dimensional container such as a box or bottle having various shapes and sizes can be used. These molded products may be made of paper, paperboard, plastic, metal (a material having a large number of holes or a wire mesh, which is mainly used as a reinforcing material), or a composite of these. Among them, it is preferable to use plant-derived materials such as paper and paperboard, biodegradable materials such as biodegradable plastics, or biomass-derived materials. The molded body serving as the base material can have a multilayer structure made of a combination of the same or different materials (for example, adhesiveness and wettability improver).

  The plastic used as the base material can be appropriately selected according to the application, but polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6, 66, 6/10, and 6/12, polyethylene terephthalate (PET), and polybutylene. One or more selected from polyesters such as terephthalate, aliphatic polyester, polylactic acid (PLA), polycaprolactone, polybutylene succinate, cellophane such as cellulose, cellulose triacetate (TAC), and the like can be used.

  The thickness of the molded body serving as the base material is not particularly limited, and may be appropriately selected so that strength according to the application can be obtained. For example, the thickness can be in the range of 1 to 1000 μm.

(1) Average fiber diameter and average aspect ratio of cellulose fiber The average fiber diameter of the cellulose fiber was measured by dropping an aqueous suspension diluted to 0.0001% by mass onto mica and drying it as an observation sample. The fiber height was measured with Nanoscope III Tapping mode AFM, manufactured by Digital instrument, and the probe used Point Probe (NCH) manufactured by Nano Sensors. In an image in which cellulose fibers can be confirmed, five or more were extracted, and the average fiber diameter was determined from the fiber height.

  The average aspect ratio was calculated from the viscosity of a diluted suspension (0.005 to 0.04% by mass) obtained by diluting cellulose fibers with water. The viscosity was measured at 20 ° C. using a rheometer (MCR300, DG42 (double cylinder), manufactured by PHYSICA). From the relationship between the mass concentration of the cellulose fiber and the specific viscosity of the cellulose fiber suspension with respect to water, the aspect ratio of the cellulose fiber was calculated by the following formula to obtain the average aspect ratio of the cellulose fiber.

(The theory of Polymer Dynamics, M.DOI and DFEDWARDS, CLARENDON PRESS / OXFORD, 1986, P312) The viscosity formula (8.138) of a rigid rod-like molecule was used (here, rigid rod-like molecule = cellulose fiber) ). (8.138) equation and _{^{Lb 2 × ρ 0 = M /}} N equation 1 from the relation of _a is derived. here, eta _sp is specific viscosity, [pi is circle ratio, ln is natural logarithm, P Is the aspect ratio (L / b), γ = 0.8, ρ _s is the density of the dispersion medium (kg / m ³ ), ρ ₀ is the density of cellulose crystals (kg / m ³ ), and C is the mass concentration of cellulose (C = ρ / ρ _s), L is the fiber length, b is the fiber width (cellulose fiber cross section is a square), [rho is the concentration of cellulose fibers (kg / m ^3), M is the molecular weight, the N _a represents Avogadro's number) .

(2) Carboxyl fiber carboxyl group content (mmol / g)
About 0.5 g of the dry weight of oxidized pulp is put in a 100 ml beaker, and ion exchange water is added to make a total of 55 ml. Then, 5 ml of 0.01 M sodium chloride aqueous solution is added to prepare a pulp suspension. Stir with a stirrer until dispersed. Then, 0.1M hydrochloric acid is added to adjust the pH to 2.5 to 3.0, and then 0.05M sodium hydroxide aqueous solution is injected under the condition of a waiting time of 60 seconds using an automatic titrator (AUT-501, manufactured by Toa DK Corporation). Then, the electric conductivity and the pH value of the pulp suspension every minute were measured, and the measurement was continued until the pH became about pH11. And the sodium hydroxide titration amount was calculated | required from the obtained electrical conductivity curve, and carboxyl group content was computed.

  Natural cellulose fibers exist as aggregates of highly crystalline microfibrils formed by collecting about 20 to 1500 cellulose molecules. In the TEMPO oxidation reaction employed in the present invention, a carboxyl group can be selectively introduced onto the surface of the crystalline microfibril. Therefore, in reality, carboxyl groups are introduced only on the crystal surface, but the carboxyl group content defined by the measurement method is an average value per cellulose weight.

(3) Light transmittance Using a spectrophotometer (UV-2550, manufactured by Shimadzu Corporation), the light transmittance (%) at a wavelength of 660 nm and an optical path length of 1 cm of a suspension having a concentration of 1% by mass was measured.

(4) Mass fraction of fine cellulose fibers in cellulose fiber suspension (fine cellulose fiber content) (%)
A cellulose fiber suspension was prepared to 0.1% by mass, and its solid content concentration was measured. Subsequently, the cellulose fiber suspension was subjected to suction filtration with a glass filter having a mesh size of 16 μm (25GP16, manufactured by SHIBATA), and then the solid content concentration of the filtrate was measured. The (C1 / C2) value obtained by dividing the solid content concentration (C1) of the filtrate by the solid content concentration (C2) of the suspension before filtration was calculated as the fine cellulose fiber content (%).

(5) Observation of suspension One drop of the suspension diluted to a solid content of 1% by mass was dropped on a slide glass, and a cover glass was placed on it to prepare an observation sample. Arbitrary five places of this observation sample were observed with an optical microscope (manufactured by ECLIPSE E600 POL NIKON) at a magnification of 400 times to confirm the presence or absence of cellulose granules having a particle diameter of 1 μm or more. The granular material is substantially spherical, and the ratio of the major axis to the minor axis (major axis / minor axis) of the rectangle surrounding the projected shape obtained by projecting the shape onto a plane is 3 or less at the maximum. The particle diameter of the granular material is an arithmetic average value of the lengths of the major axis and the minor axis. At this time, it can be confirmed more clearly by crossed Nicols observation.

(6) Oxygen permeability (isobaric method) (cm ³ / m ² · day · Pa)
Based on the measurement method of JIS K7126-2 appendix A, it measured on 23 degreeC and humidity 50% RH conditions using oxygen permeability measuring apparatus OX-TRAN2 / 21 (model ML & SL, MODERN CONTROL). Specifically, the measurement was performed in an environment of oxygen gas at 23 ° C. and humidity 50% RH and nitrogen gas (carrier gas) at 23 ° C. and humidity 50%.

Production Example 1 [Production of Cellulose Fiber]
(1) Raw material, catalyst, oxidizing agent, co-oxidizing agent Natural fiber: Bleached kraft pulp of conifers (Manufacturer: Fletcher Challenge Canada, trade name “Machenzie”, CSF 650 ml)
TEMPO: Commercial product (Manufacturer: ALDRICH, Free radical, 98%)
Sodium hypochlorite: Commercial product (Manufacturer: Wako Pure Chemical Industries, Ltd. Cl: 5%)
Sodium bromide: Commercial product (manufacturer: Wako Pure Chemical Industries, Ltd.).

(2) Production procedure First, 100 g of bleached kraft pulp fiber of the above-mentioned coniferous tree was sufficiently stirred with 9900 g of ion-exchanged water, and then TEMPO 1.25% by mass, sodium bromide 12.5% by mass, hypoxia with respect to 100 g of pulp mass. Sodium chlorate (28.4% by mass) was added in this order, and a pH stud was used to maintain the pH at 10.5 by dropwise addition of 0.5M sodium hydroxide to carry out an oxidation reaction.

  Next, dripping was stopped at an oxidation time of 120 minutes to obtain oxidized pulp. The oxidized pulp was sufficiently washed with ion exchange water and dehydrated. Thereafter, 4.5 g of oxidized pulp and 295.5 g of ion-exchanged water are stirred for 120 minutes with a mixer (Vita-Mix-Blender ABSOLUTE, manufactured by Osaka Chemical Co., Ltd.), so that the fiber is refined and suspended. A liquid was obtained. The solid content concentration in the suspension of the obtained cellulose fiber was 1.5% by mass. Cellulose fibers had an average fiber diameter of 3.1 nm, an average aspect ratio of 240, and a carboxyl group content of 1.2 mmol / g, and there were no cellulose granules having a particle diameter of 1 μm or more. The light transmittance of the cellulose fiber suspension was 97.1%, and the content of fine cellulose fibers was 90.9%.

Example 1 (Production of suspension of cellulose fibers)
To the cellulose fiber suspension obtained in Production Example 1, a 1M hydrochloric acid aqueous solution in an amount corresponding to 2 chemical equivalents (eq) with respect to the carboxyl group of the cellulose fiber was added. Thereafter, when the mixture was stirred for 60 minutes, aggregation occurred.

  Next, the aggregate produced in the previous step was filtered through a glass filter having a diameter of 16 μm. The filtrated material (cellulose fiber solid content 3 g) was washed with 1000 times the amount of ion-exchanged water.

  Next, the filtrate after washing was put into an Erlenmeyer flask, and a mixed solution of 10% by mass ammonia water and zinc oxide (12.6 g and 0.24 g, respectively) was added to the cellulose fiber. Ion exchange water was added so that the solid content of the cellulose fiber was 1.3% by mass, and the mixture was stirred with a magnetic stirrer for 120 minutes to obtain a suspension of the cellulose fiber of the present invention. In this suspension, ammonia was 20 chemical equivalents relative to the carboxyl groups of the cellulose fibers, and zinc oxide was 0.8 chemical equivalents.

Example 2 (Production of suspension of cellulose fibers)
The aggregate of cellulose fibers was washed and filtered in the same manner as in Example 1, and then a mixed solution of 10% by mass ammonia water and zinc oxide (24.6 g and 0.24 g, respectively) was added to the cellulose fibers. Ion exchange water was added so that the solid content of the cellulose fiber was 1.3% by mass, and the mixture was stirred with a magnetic stirrer for 120 minutes to obtain a suspension of the cellulose fiber of the present invention. In this suspension, ammonia was 40 chemical equivalents relative to the carboxyl groups of the cellulose fibers, and zinc oxide was 0.8 chemical equivalents.

Example 3 (Production of a suspension of cellulose fibers)
The aggregate of cellulose fibers was washed and filtered in the same manner as in Example 1, and then a mixed liquid of 10% by mass ammonia water and zinc oxide (3.2 g and 0.24 g, respectively) was added to the cellulose fibers. Ion exchange water was added so that the solid content of the cellulose fiber was 1.3% by mass, and the mixture was stirred with a magnetic stirrer for 120 minutes to obtain a suspension of the cellulose fiber of the present invention. In this suspension, ammonia was 5 chemical equivalents relative to the carboxyl groups of the cellulose fibers, and zinc oxide was 0.8 chemical equivalents.

Example 4 (Production of suspension of cellulose fibers)
In Example 1, the first step using 1M hydrochloric acid aqueous solution and the filtration step were not performed, and 10% by mass with respect to 200 g of cellulose fiber suspension obtained in Production Example 1 (solid content 1.5% by mass). A mixture of aqueous ammonia and zinc oxide (12.6 g and 0.24 g, respectively) was added. Ion exchange water was added so that the solid content of the cellulose fiber was 1.3% by mass, and the mixture was stirred with a magnetic stirrer for 120 minutes to obtain a suspension of the cellulose fiber of the present invention. In this suspension, ammonia was 20 chemical equivalents relative to the carboxyl groups of the cellulose fibers, and zinc oxide was 0.8 chemical equivalents.

Examples 5 to 8 (Production of composite molded body)
The suspension of cellulose fibers obtained in Examples 1 to 4 was applied with a bar coater (# 50) on one side of a polyethylene terephthalate (PET) sheet (trade name: Lumirror, manufactured by Toray Industries, Inc., sheet thickness 25 μm). After drying at room temperature for 120 minutes, it was kept in a thermostat maintained at the heating temperature shown in Table 1 for 30 minutes. Heat was radiated at room temperature for 2 hours or more to obtain a composite molded body having a cellulose fiber layer on PET. Table 1 shows the results of measurement of oxygen permeability at a relative humidity of 50%.

Comparative Example 1
Ion exchange water is added so that the cellulose fiber suspension obtained in Production Example 1 becomes 1.3% by mass and stirred with a magnetic stirrer for 120 minutes, and then a polyethylene terephthalate (PET) sheet (trade name: Lumirror, It was coated with a bar coater (# 50) on one side surface of Toray Industries, Inc. (sheet thickness 25 μm). After drying at room temperature for 120 minutes, it was kept in a thermostat maintained at the heating temperature shown in Table 1 for 30 minutes. Heat was radiated at room temperature for 2 hours or more to obtain a composite molded body having a cellulose fiber layer on PET. Table 1 shows the results of measurement of oxygen permeability at a relative humidity of 50%.

Comparative Example 2
A suspension of cellulose fibers was obtained in the same manner as in Example 1 except that only ammonia water and ion-exchanged water were added without adding zinc oxide. In the same manner as in Comparative Example 1, a composite molded body having a cellulose fiber layer was obtained. Comparative Example 2, the cellulose fiber layer obtained by using a suspension of cellulose fibers obtained by substituting Na carboxyl group in NH ₄ (however, without the use of zinc oxide, since the addition by ammonia, "NH ₄ form ")"). Table 1 shows the results of measurement of oxygen permeability at a relative humidity of 50%.

  As is clear from Table 1, the higher the heating temperature, the higher the oxygen barrier property of the composite molded body. This result is considered to be because the higher the heating temperature, the greater the degree of cross-linking reaction between the carboxyl group on the surface of the cellulose fiber and zinc, and a dense structure film was formed.

  Further, as is apparent from Table 1, in the composite molded body subjected to the heat treatment, Example 7 (composite molded body obtained from Example 3 in which the amount of ammonia added is 5 chemical equivalents) is equivalent to Example 5 (ammonia Oxygen barrier properties as compared to Example 1 (composite molded product obtained from Example 2 with an addition amount of 20 chemical equivalents) and Example 6 (Composite molded product obtained from Example 2 with an ammonia addition amount of 40 chemical equivalents) Was expensive. This is considered to be that uniform film formation of the paint is hindered when the amount of ammonia added is large.

  The oxygen barrier properties of Examples 5 to 8 obtained from Examples 1 to 4 are oxygen barrier properties as compared with Comparative Examples 1 and 2 obtained from Na-type and NH4 type cellulose fiber suspensions under the same heating conditions. Was expensive. From this, it was shown that the suspension of cellulose fibers containing a polyvalent metal and a volatile base in the present invention is a suspension of cellulose fibers suitable for production of an oxygen barrier film.

In Example 8, the oxygen barrier property was lower than that in Example 5. This is because the cellulose fiber that has once passed through the structure of Cell-COO ^- Na ⁺ → Cell-COOH after adding hydrochloric acid is more likely to form a -COO-M-OOC- crosslinked structure with zinc in the subsequent manufacturing process. Show.

Example 9
In the same manner as in Example 1, the cellulose fiber aggregate was washed and filtered, and then a mixed solution of 10 mass% ammonia water and zinc oxide (12.8 g and 0.15 g, respectively) was added to the cellulose fiber. Ion exchange water was added so that the solid content of the cellulose fiber was 1.3% by mass, and the mixture was stirred with a magnetic stirrer for 120 minutes to obtain a suspension of the cellulose fiber of the present invention. In this suspension, ammonia was 20 chemical equivalents relative to the carboxyl group of the cellulose fiber, and zinc oxide was 0.5 chemical equivalents.

  The cellulose fiber suspension was applied to one side of a polyethylene terephthalate (PET) sheet (trade name: Lumirror, manufactured by Toray Industries, Inc., sheet thickness 25 μm) with a bar coater (# 50). After drying at room temperature for 120 minutes, it was kept in a thermostat maintained at the heating temperature shown in Table 2 for 30 minutes. Heat was radiated at room temperature for 2 hours or more to obtain a composite molded body having a cellulose fiber layer on PET. Table 2 shows the measurement results of oxygen permeability at a relative humidity of 50%.

Example 10
A suspension of cellulose fibers was prepared in the same manner as in Example 9 except for a mixed liquid of 10% by mass ammonia water and zinc oxide (12.8 g and 0.03 g, respectively) to obtain a composite molded body. Table 2 shows the measurement results of oxygen permeability at a relative humidity of 50%.

Example 11
A suspension of cellulose fibers was prepared in the same manner as in Example 9 except that copper oxide was added instead of zinc oxide to obtain a composite molded body. Table 2 shows the measurement results of oxygen permeability at a relative humidity of 50%.

実施例９、１０、及び実施例５(表１)は、酸化亜鉛の添加量の異なるセルロース懸濁液から得られた複合成形体である。酸化亜鉛の添加量が０．１〜０．８化学当量である実施例５、９、１０では、Na型、NH₄型セルロース繊維懸濁液から得られた表１に示す比較例１、２に比べて酸素バリア性が高かった。また亜鉛は２価の金属であるため、セルロース繊維のカルボキシル基含有量に対して０．５化学当量添加した実施例９において最も高い酸素バリア性が得られた。

Examples 9, 10 and Example 5 (Table 1) are composite molded bodies obtained from cellulose suspensions with different amounts of zinc oxide added. In Examples 5, 9, and 10 in which the addition amount of zinc oxide is 0.1 to 0.8 chemical equivalent, Comparative Examples 1 and 2 shown in Table 1 obtained from the Na type and NH ₄ type cellulose fiber suspensions are shown. Oxygen barrier properties were higher than Moreover, since zinc is a divalent metal, the highest oxygen barrier property was obtained in Example 9 in which 0.5 chemical equivalent was added with respect to the carboxyl group content of the cellulose fiber.

  Example 11 is a composite molded body obtained using copper as a polyvalent metal. Compared with Comparative Examples 1 and 2 shown in Table 1, the oxygen barrier property was high. From this, it was shown that the suspension of cellulose fibers containing a polyvalent metal and a volatile base in the present invention is a suspension of cellulose fibers suitable for production of an oxygen barrier film.

Claims (9)

  A suspension of cellulose fibers containing cellulose fibers, polyvalent metals and volatile bases, wherein the cellulose fibers have an average fiber diameter of 200 nm or less, and the carboxyl group content of cellulose constituting the cellulose fibers is 0 Cellulose fiber suspension, which is of 1-2 mmol / g.   The suspension of cellulose fibers according to claim 1, comprising 1 to 500 chemical equivalents of a volatile base with respect to the carboxyl group content of the cellulose fibers. The cellulose fiber suspension according to claim 1, comprising 0.1 to 1.5 chemical equivalents of polyvalent metal with respect to the carboxyl group content of the cellulose fiber.   A film-shaped molded body formed from the suspension of cellulose fibers according to claim 1.   A composite molded body having a layer formed from the suspension of cellulose fibers according to claim 1 on a substrate. It is a step of mixing an aqueous solution of cellulose fiber and acid, wherein the cellulose fiber has an average fiber diameter of 200 nm or less, and the cellulose constituting the cellulose fiber has a carboxyl group content of 0.1 to 2 mmol / g. ,
Filtering the mixture obtained in the previous step,
The manufacturing method of the suspension of a cellulose fiber which has the process of mixing the filtrate obtained at the previous process with the aqueous solution containing a polyvalent metal and a volatile base. The structure of the carboxyl group of the cellulose fiber is
Before the step of mixing the cellulose fiber and the aqueous acid solution, the structure is COO ⁻ Na ⁺ .
In the step of mixing with the aqueous acid solution, the structure is COOH.
The method for producing a suspension of cellulose fibers according to claim 6, wherein the step of mixing with the aqueous solution containing the polyvalent metal and the volatile base is COO ^- B ⁺ (B ⁺ is a conjugate acid of a volatile base).   The step of adhering the cellulose fiber suspension to the molding hard surface, the step of drying the cellulose fiber suspension to obtain a film-shaped product, and 30 to 300 ° C. for 1 to 300 minutes The manufacturing method of the film-shaped molded object of Claim 4 which has the process of heating.   The step of attaching the cellulose fiber suspension to the substrate surface, the step of drying the cellulose fiber suspension to obtain a composite molded body, and heating at 30 to 300 ° C. for 1 to 300 minutes The manufacturing method of the composite molded object of Claim 5 which has a process.