JP6303258B2 - Method for producing composite of silver and fine cellulose fiber and method for producing thermal barrier film - Google Patents

Description

The present invention relates to a method for producing a composite of silver and refined cellulose fibers obtained by reducing and precipitating at least one metal in a dispersion containing refined cellulose fibers and silver ions, and a thermal barrier film. About.

  In general, the main component of sunlight is an electromagnetic wave having a wavelength in the range of about 400 nm to 700 nm, that is, visible light. On the other hand, a component having a wavelength of about 400 nm or less is called ultraviolet light, and a component having a wavelength of about 700 nm or more is called infrared light.

  Among infrared rays, electromagnetic waves in a wavelength region close to visible light (approximately 700 nm to 2500 nm) are called near infrared rays and have properties close to visible light. Particularly, those in the wavelength region of 700 nm to 1200 nm are present on the object surface. It is known that it is easily absorbed and converted to thermal energy.

  This near-infrared ray is easily transmitted through the glass, and the room is warmed by the transmitted near-infrared ray when sunlight hits a building window. This heat is further emitted into the room as far-infrared rays, but since glass is difficult to transmit far-infrared rays, a so-called greenhouse effect occurs in which heat is trapped in the room.

  As a result, the temperature at the window rises indoors in the summer, and the cooling efficiency due to air conditioning control is significantly reduced. Therefore, the greenhouse effect is a major factor in the summer power shortage. In recent years, there has been an urgent need to save electricity in order to eliminate the peak cooling demand in summer, as risk problems in nuclear power generation have been addressed.

  However, there is a risk of heat stroke in power saving measures such as cooling where the effect of air conditioning control is not obtained, and both cooling efficiency and power saving effect are required. Therefore, at present, as one of the countermeasures, an infrared cut film, that is, a heat shielding film used for a building window or the like is used.

  In general, the specification of the infrared cut film is designed so as to transmit visible light but not near infrared light. Thus, by capturing visible light, it is possible to block only the near infrared rays that cause the greenhouse effect without damaging the indoor and outdoor scenery, and it is possible to keep the indoor temperature comfortable with a small amount of power.

  As such an infrared cut film, Patent Document 1 discloses an example in which a laminate including a cholesteric liquid crystal layer is used. According to Patent Document 1, it is possible to provide a laminate that blocks near-infrared rays while transmitting light in the visible light region by utilizing the feature of cholesteric liquid crystal that selectively blocks only a specific wavelength. However, when the cholesteric liquid crystal layer is used, there is a problem that the production cost increases because a multi-layered film is required. Further, since the cholesteric liquid crystal layer is synthesized using a material derived from fossil fuel as a raw material, an environmental load is inevitable.

  On the other hand, Patent Document 2 discloses an example in which silver nanoparticles are used as a near-infrared shielding material. In general, spherical silver nanoparticles are yellowish due to surface plasmons and have a peak in the vicinity of a wavelength of 400 nm in the spectral absorption spectrum, but the peak position is known to shift to the near infrared region depending on the size and shape of the particle diameter. Yes. The method described in Patent Document 2 utilizes this phenomenon, and succeeded in blocking near-infrared rays while ensuring visible light transmittance to some extent by highly controlling the production conditions of silver nanoparticles. Yes. However, the method described in the patent document has a problem that the method for producing silver nanoparticles is complicated and shape control is difficult.

  On the other hand, in recent years, functional materials using biomass, which is an environmentally harmonious material that can be used continuously, have been actively developed due to the growing interest in environmental issues. Among them, cellulose, which is the main component of wood, is a natural polymer material that is accumulated in the largest amount on the earth, and is expected to be a core material for efforts to shift to a resource recycling society. .

  However, cellulose in wood has several tens of molecular chains, forming cellulose microfibrils, which are fine fibers with high crystallinity and nano-sized fiber diameters. And has become a plant support. Because of this extremely stable structure, it is insoluble in water and general-purpose organic solvents, has poor moldability, and is difficult to handle as a highly functional member.

  Therefore, attempts have been actively made to downsize cellulose in wood having such characteristics and use it in units of fine fibers. For example, as disclosed in Patent Document 3, it is disclosed that fine cellulose fibers, that is, cellulose nanofibers (hereinafter referred to as CNF) can be obtained by repeating mechanical processing using wood blender or grinder on wood cellulose. It has been reported that the short axis diameter of CNF obtained by this method ranges from 10 to 50 nm and the long axis diameter ranges from 1 μm to 10 mm.

  As refinement by chemical treatment, 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO), which is a relatively stable N-oxyl compound as shown in Patent Document 4, is used. A technique for selectively oxidizing the surface of cellulose fine fibers has been reported as a catalyst. The TEMPO oxidation reaction can be chemically modified in an environmentally friendly manner that proceeds in water, normal temperature, and normal pressure. When applied to cellulose in wood, the reaction does not proceed inside the crystal, and the cellulose molecular chains on the crystal surface Only the alcoholic primary carbon possessed can be selectively converted into a carboxyl group.

  Thus, the cellulose single nanofiber (henceforth CSNF) disperse | distributed to each cellulose microfibril unit in the water solvent by the electrostatic repulsion of the carboxyl groups introduce | transduced into the crystal | crystallization surface is obtained. It becomes possible. Wood CSNF obtained by TEMPO oxidation from wood is a structure having a high aspect ratio ranging from about 4 nm short axis diameter to 500 nm to 1 μm long axis diameter, and its aqueous dispersion and laminate are reported to have high transparency. Has been.

  As the use of the CSNF, Patent Document 5 discloses a material for supporting metal / CSNF composite nanoparticles, and an example of using it as a catalyst. However, there is no description or suggestion regarding the use of the metal / CSNF composite as a near-infrared shielding material, or the possibility thereof.

Special table 2009-514022 gazette JP 2011-252213 A JP 2010-216021 A JP 2008-1728 A JP 2009-035184 A

  This invention is made | formed in view of the said situation, and makes it a subject to provide the near-infrared shielding material which the shape control of a metal microparticle is simple, and its environmental load is low, its manufacturing method, and a heat-shielding film.

  As a result of intensive studies to solve the above-mentioned problems, it was found that a material that has high visible light transmittance and shields near infrared rays can be obtained by combining silver nanoparticles and wood CSNF under specific conditions. Invented. That is, when silver ions are reduced and precipitated as silver nanoparticles in an aqueous dispersion containing wood CSNF and silver ions, by controlling the deposition conditions and the silver ion concentration, the spectral absorption spectrum is reduced in the near infrared region. A silver / wood CSNF composite with an absorption band and an absorption peak was successfully produced.

  That is, the present invention is defined by the following items.

Metal fine particles comprising one or more metals or their compounds even without less is, by forming the fine cellulose fibers with complex, near, characterized in that the transmittance is minimum in the near-infrared region Infrared shielding material.

Number average minor axis diameter of the cellulose fibers prior Symbol miniaturization 1nm or 100nm or less, the number-average major axis diameter is at 100nm or more and is the number average long axis diameter of several average more than 50 times the minor axis diameter the shall be the feature.

You characterized in that at least one of the metals contained in the prior SL near-infrared shielding material is silver.

Cellulose fibers prior Symbol miniaturized, characterized in that the carboxyl group is introduced into the fiber surface by oxidation reaction using N- oxyl compound.

From wavelength 700nm in the region of 2500 nm, characterized by having a peak of spectral absorption spectrum.

In the invention according to claim 1, the refined cellulose fiber is dispersed in a solvent containing at least 50% of water so that the concentration of the refined cellulose fiber is 0.1% or more and less than 5%. A step of obtaining a cellulose fiber dispersion, a step of obtaining a mixed solution by mixing the refined cellulose fiber dispersion and a metal ion-containing aqueous solution containing at least silver ions, and reducing silver ions in the mixed solution, A step of producing a composite of the silver nanoparticles (excluding spheres) and the refined cellulose fibers in which silver nanoparticles (excluding spheres) are precipitated in the micronized cellulose fiber network structure. The production of a composite of silver and refined cellulose fibers, wherein the absorption peak of the spectral absorption spectrum is changed by changing the silver ion concentration in the mixed solution It is the law.
Furthermore, the amount of metal ions in the mixed solution is less than the amount of carboxyl groups present on the surface of the refined cellulose fiber. The method for producing a composite of silver and refined cellulose fiber according to claim 1, is there.

According to a third aspect of the invention, a complex of silver and fine cellulose fibers produced by the production method according to claim 1 or 2 was coated on a substrate, characterized by having a step of drying It is a manufacturing method of a thermal barrier film.

  According to the present invention, a metal / micronized cellulose fiber composite that can be used as a near-infrared shielding material can be obtained by a one-step reaction by reducing and depositing metal nanoparticles in a dispersion containing micronized cellulose fibers and metal ions. Can be created. Further, since the optical properties of the metal / micronized cellulose fiber composite can be controlled mainly by the concentration of metal ions before the reduction treatment, the metal / micronized cellulose as a near-infrared shielding material with a very simple formulation and good reproducibility. A fiber composite can be obtained. As a result, a near-infrared shielding film and a thermal insulation film with high visible light transmittance can be provided at low cost by applying an aqueous dispersion of the metal / fine cellulose fiber composite to a transparent plastic substrate, for example, and drying. It became possible to do.

  In addition, since the refined cellulose fiber that plays a role as a shape control agent, a dispersing agent, and a molded body matrix of metal nanoparticles is biomass, the near-infrared shielding material and the thermal insulation film obtained in the present invention are made of carbon. It is a high-performance member that also has features as a neutral environmentally friendly material. Due to the synergistic effect of the environmental harmony of the material itself and the energy saving effect that is the purpose, the present invention is expected to make a great contribution to the construction of a resource recycling society that can be continuously developed.

  Details of the present invention will be described below.

[Fine refined cellulose fiber and its production method]
The refined cellulose fiber used in the present invention may have a fiber diameter in the range shown below, and the preparation method is not particularly limited. That is, in the minor axis diameter, the number average minor axis diameter may be 1 nm or more and 100 nm or less, preferably 2 nm or more and 50 nm or less, more preferably 4 nm or more and 20 nm or less. If the number average minor axis diameter is less than 1 nm, a highly crystalline rigid fine cellulose fiber structure cannot be obtained, and sufficient material strength cannot be obtained, for example, when applied to a film and formed into a thin film. On the other hand, when the thickness exceeds 100 nm, sufficient transparency, that is, visible light transmittance cannot be obtained when used as an optical material. The major axis diameter has a number average major axis diameter of 100 nm or more, preferably 500 nm or more, and more preferably 1 μm or more. If the number average major axis diameter is less than 100 nm, the fiber entanglement effect is insufficient, and the shape control of the metal nanoparticles becomes insufficient when complexing with the metal.

  The type of cellulose that can be used as a raw material for the fine cellulose fiber is not particularly limited. For example, in addition to wood-based natural cellulose, non-cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, squirt cellulose, valonia cellulose Wood-based natural cellulose, as well as regenerated cellulose represented by rayon fiber and cupra fiber can be used.

  The method for refining cellulose fibers is not particularly limited, but dilute acid hydrolysis treatment, enzyme treatment, or the like may be used in addition to the above-described mechanical treatment using a high-pressure homogenizer and chemical treatment such as TEMPO oxidation treatment. Bacterial cellulose can also be used as finely divided cellulose fibers. Furthermore, finely regenerated cellulose fibers obtained by dissolving various natural celluloses in various cellulose solvents and then performing electrospinning may be used.

  For example, according to the method described in Patent Document 3, if a metal is combined with wood CNF obtained by repeatedly treating wood cellulose with a blender or the like, the metal / fine cellulose fiber composite can be formed while controlling the shape of the metal nanoparticles. Can be obtained. However, since the fiber width is 10 to 20 nm, there is a problem in that the transparency of the dispersion and a molded body using the dispersion is lowered.

  On the other hand, when wood CSNF obtained by TEMPO-catalyzed oxidation of wood cellulose and metal are compounded according to the method described in Patent Document 4, in addition to being able to sufficiently control the shape of metal nanoparticles, the short axis of CSNF Since the diameter is about 4 nm, which is as fine as a carbon nanotube, high transparency of the dispersion and a molded body using the dispersion can be achieved. Both wood CNF and wood CSNF are preferable as the fine cellulose fiber used in the present invention, but wood CSNF is more preferable from the viewpoint of transparency.

  Hereinafter, a method for producing wood CSNF will be described.

  Wood CSNF used in the present invention is obtained by a step of oxidizing cellulose and a step of pulverizing and dispersing it. Further, the amount of carboxyl groups introduced during oxidation is preferably 0.1 mmol / g or more and 5.0 mmol / g or less, and more preferably 0.5 mmol / g or more and 2.0 mmol / g or less. When the amount of carboxyl groups is less than 0.1 mmol / g, electrostatic repulsion does not work between cellulose microfibrils, so it is difficult to make cellulose finely dispersed uniformly. On the other hand, if it exceeds 5.0 mmol / g, cellulose microfibrils are reduced in molecular weight due to side reactions accompanying TEMPO oxidation, so that sufficient material strength cannot be obtained, for example, when applied to a film and formed into a thin film.

[Step of oxidizing cellulose]
Although it does not specifically limit as a raw material of the wood cellulose oxidized, A conifer pulp, a hardwood pulp, a waste paper pulp, etc. are generally used, and it is preferable to use a conifer pulp from the ease of refinement | purification and refinement | miniaturization.

  As a method for oxidizing the fiber surface of wood cellulose and introducing a carboxyl group, it is possible to start with TEMPO, which has high selectivity to the oxidation of alcoholic primary carbon while maintaining the structure as much as possible under relatively mild conditions in water. A technique using a co-oxidant in the presence of the N-oxyl compound is desirable. Examples of the N-oxyl compound include TEMPO, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N. -Oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl, and the like. Among these, TEMPO is preferably used because of its high reactivity.

  The co-oxidant may promote an oxidation reaction such as halogen, hypohalous acid, halous acid or perhalogen acid, or a salt thereof, halogen oxide, nitrogen oxide, or peroxide. Any oxidant can be used if possible. Sodium hypochlorite is preferred because of its availability and reactivity.

  Furthermore, when carried out in the presence of bromide or iodide, the oxidation reaction can proceed smoothly, and the introduction efficiency of the carboxyl group can be improved.

  As the N-oxyl compound, TEMPO is preferable, and an amount that functions as a catalyst is sufficient. As the bromide, a system using sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable from the viewpoint of cost and stability. The amount of the co-oxidant, bromide or iodide used is sufficient if there is an amount capable of promoting the oxidation reaction. The reaction is more preferably pH 9 to 11, but as the oxidation proceeds, carboxyl groups are generated and the pH in the system is lowered. Therefore, it is necessary to keep the inside of the system weakly alkaline at pH 9 to 11.

  In order to keep the inside of the system weakly alkaline, it can be adjusted by adding an alkaline aqueous solution as the pH decreases. Examples of the alkaline aqueous solution include a sodium hydroxide aqueous solution, a lithium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an ammonia aqueous solution, and further a tetramethylammonium hydroxide aqueous solution, a tetraethylammonium hydroxide aqueous solution, a tetrabutylammonium hydroxide aqueous solution, and a benzyltrimethylammonium hydroxide. An organic alkaline aqueous solution such as an aqueous solution is used, but an aqueous sodium hydroxide solution is preferred from the viewpoint of cost.

  In order to complete the oxidation reaction, it is necessary to add the other alcohol while maintaining the pH in the system and complete the reaction of the co-oxidant. The alcohol to be added is preferably a low molecular weight alcohol such as methanol, ethanol or propanol in order to quickly terminate the reaction, but ethanol is more preferable from the viewpoint of safety of by-products generated by the reaction.

  As a method for washing oxidized pulp after the completion of the oxidation reaction, there are a method of washing with an alkali and salt formed, a method of adding an acid to obtain a carboxylic acid, and the like. In view of handling properties and yield, a method of adding an acid to obtain a carboxylic acid and washing it is preferred. The washing solvent is preferably water.

[Step of refining oxidized cellulose into liquid dispersion]
As a method for refining oxidized cellulose, firstly, oxidized cellulose is suspended in various organic solvents such as water and alcohol or a mixed solvent thereof. If necessary, the pH of the dispersion may be adjusted to increase dispersibility. Examples of alkaline aqueous solutions used for pH adjustment include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, An organic alkali aqueous solution such as a benzyltrimethylammonium hydroxide aqueous solution can be used. A sodium hydroxide aqueous solution is preferable from the viewpoint of cost and availability.

  Subsequent physical defibration methods include high pressure homogenizer, ultra high pressure homogenizer, ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer, underwater It can be miniaturized by using an opposing collision or the like. An aqueous dispersion of wood CSNF having a carboxyl group on the surface can be obtained by performing such a micronization treatment for an arbitrary time or number of times. At this time, the number average fiber width of the wood CSNF is preferably 1 nm or more and 100 nm or less. When the fiber width is smaller than 1 nm, the crystallinity of the wood CSNF is deteriorated and the material strength is impaired. The transparency of a liquid and a laminated body will be impaired. The number average fiber length is preferably 50 times or more of the number average fiber width, and if it is less than 50 times, the shape control effect of the metal nanoparticles due to the entanglement of the fibers is lost.

  The wood CSNF dispersion may contain cellulose and other components other than the components used for pH adjustment as long as the effects of the present invention are not impaired. The other components are not particularly limited, and can be appropriately selected from known additives depending on the use of the wood CSNF. Specifically, organometallic compounds such as alkoxysilanes or hydrolysates thereof, inorganic layered compounds, inorganic needle minerals, leveling agents, antifoaming agents, water-soluble polymers, synthetic polymers, inorganic particles, organic particles , Lubricants, antistatic agents, ultraviolet absorbers, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, crosslinking agents and the like.

[Process for producing infrared shielding material]
Although it does not specifically limit as a metal seed | species compounded with the said wood CSNF, For example, gold, silver, iron, lead, copper, chromium, cobalt other than the platinum group element of platinum, palladium, ruthenium, iridium, rhodium, osmium And metals such as nickel, manganese, vanadium, molybdenum, gallium, and aluminum, metal salts, metal complexes and alloys thereof, oxides, and double oxides. A plurality of metal species may be used. However, since silver nanoparticles can easily have an absorption band of a spectral spectrum in the near infrared region by shape control, it is preferable that at least one of the deposited metals is silver. In addition, antibacterial properties can be imparted by forming a composite with silver, so that the weather resistance of wood CSNF can also be improved. The stability of the silver nanoparticles may be improved by covering the deposited silver nanoparticles with a metal nobler than silver. A method for producing a composite by depositing metal fine particles in a wood CSNF dispersion is not particularly limited, but a solution of the above metals or alloys including silver, oxides, double oxides, and the like and a CSNF dispersion are mixed. In this state, it can be easily deposited by adding a reducing agent. In the case of silver, the type of the aqueous solution containing silver ions used for the reduction is not particularly limited, but a silver nitrate aqueous solution is preferable from the viewpoint of availability and ease of handling. There is no particular limitation on the reducing agent used. For example, sodium borohydride, ascorbic acid, citric acid, hydroquinone and the like are used. Sodium borohydride is preferable from the viewpoint of safety and versatility.

  The solvent used for dispersion of the wood CSNF contains 50% or more of water, and a hydrophilic solvent is preferable as a solvent other than water. When the proportion of water is 50% or less, the dispersion of wood CSNF is inhibited, and it becomes difficult to form a uniform composite of metal nanoparticles and wood CSNF. The hydrophilic solvent is not particularly limited, but alcohols such as methanol, ethanol and isopropanol; cyclic ethers such as tetrahydrofuran are preferred.

  The concentration of the CSNF dispersion used for the preparation is not particularly limited, but is preferably 0.1% or more and less than 5%. If it is less than 0.1%, the composition for forming a molded body becomes excessive in solvent and the effect of controlling the particle size of the metal nanoparticles is insufficient, and if it is 5% or more, the viscosity increases due to the entanglement between fine cellulose fibers. And uniform stirring becomes difficult. Similarly, the metal ion concentration of the solution containing metal ions to be used is not limited, but it is preferable to prepare so that the amount of metal ions in the dispersion is less than the amount of carboxyl groups present on the CSNF surface. This is because CSNF aggregates when the amount of metal ions in the dispersion exceeds the amount of carboxyl groups present on the CSNF surface. Since the concentration of metal ions affects the size of the deposited fine metal particles, that is, optical properties, when used as a near-infrared shielding material, the metal / micronized cellulose fiber composite has spectral absorption in the near-infrared region. In order to provide a spectrum absorption band, it is necessary to appropriately set the metal ion concentration condition. In the spectral absorption spectrum of the metal / micronized cellulose fiber composite, the maximum absorbance in the wavelength region of 400 nm to 700 nm is 50% or less of the maximum absorbance in the wavelength region of 700 nm to 2500 nm. preferable. When the maximum absorbance in the wavelength region of 400 nm to 700 nm is 50% or more of the maximum absorbance in the wavelength region of 700 nm to 2500 nm, the visible light transmittance decreases when applied to a transparent substrate. Thus, the transparency of the heat shield film is impaired. Although many unclear points remain regarding the theoretical mechanism regarding the change in the metal ion concentration, the shape of the deposited metal nanoparticles, and the spectral absorption spectrum, a specific method for producing the infrared shielding material is described in Examples. Details.

[Process for producing thermal barrier film]
The heat-shielding film can be obtained by applying a near-infrared shielding material made of a metal / micronized cellulose fiber composite in an aqueous solvent as a coating liquid and drying it. When applying the dispersion of the near infrared shielding material to the substrate, a known coating method can be used. For example, a roll coater, reverse roll coater, gravure coater, micro gravure coater, knife coater, bar coater, wire A bar coater, a die coater, a dip coater, a spin coater, or the like can be used. It applies to at least one surface of a substrate using the above application method. The method for drying the near-infrared shielding material is not particularly limited, but the drying temperature is preferably 30 ° C. or higher and 200 ° C. or lower, but more preferably 50 ° C. or higher and 150 ° C. or lower. When the drying temperature is less than 30 ° C., the drying time becomes longer, resulting in a decrease in productivity. At a drying temperature higher than 200 ° C., the wood CSNF turns yellow, and the visible light transmittance of the film decreases.

  The base material that can be used is not particularly limited, and plastic or glass substrates made of various polymer compositions can be used. For example, polyolefin (polyethylene, polypropylene, etc.), polyester (polyethylene terephthalate, polyethylene naphthalate, etc.), cellulose (triacetylcellulose, diacetylcellulose, cellophane, etc.), polyamide (6-nylon, 6,6-nylon, etc.) ), Acrylic (polymethyl methacrylate, etc.), polystyrene, polyvinyl chloride, polyimide, polyvinyl alcohol, polycarbonate, ethylene vinyl alcohol, etc. are used. In addition, organic polymer materials having at least one or more components from among the above-described plastic materials, having a copolymer component, or having a chemical modification thereof as a component are also possible.

  In addition, in consideration of the environment, the substrate to be used is required to have a low environmental load. Therefore, as a base material, for example, a bioplastic chemically synthesized from a plant such as polylactic acid or biopolyolefin, or a base material containing a plastic produced by a microorganism such as hydroxyalkanoate, further including a cellulosic material, paper, cellophane, Substrates containing acetylated cellulose, cellulose derivatives, and finely divided cellulose fibers can also be used.

  The laminate obtained in this way has high visible light transmittance and has a layer containing a metal / fine cellulose fiber composite having a spectral spectrum absorption band in the near infrared region. Industrial use is possible as a thermal barrier film derived from a novel bio-nano material that also has an infrared shielding effect.

The STEM observation photograph of the silver / wood CSNF composite produced in Example 1 is shown. The spectral absorption spectrum of the laminated body produced in Example 1 is shown.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, the technical scope of this invention is not limited to these embodiment.

<Example 1>
[TEMPO oxidation of wood cellulose]
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, and a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added and cooled to 20 ° C. 450 g of sodium hypochlorite aqueous solution having a concentration of 2 mol / L and a density of 1.15 g / mL was added dropwise thereto to initiate an oxidation reaction. The temperature in the system was always kept at 20 ° C., and the decrease in pH during the reaction was kept at pH 10 by adding a 0.5N aqueous sodium hydroxide solution. When sodium hydroxide reached 3.00 mmol / g based on the mass of cellulose, an excessive amount of ethanol was added to stop the reaction. Thereafter, filtration and washing with distilled water were repeated using a glass filter to obtain oxidized pulp.

[Measurement of carboxyl group content of oxidized pulp]
Oxidized pulp and re-oxidized pulp obtained by the TEMPO oxidation were weighed in an amount of 0.1 g by solid content, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. Thereafter, the amount of carboxyl groups (mmol / g) was determined by conductivity titration using a 0.5 M aqueous sodium hydroxide solution. The result was 1.6 mmol / g.

[Defibration treatment of oxidized pulp]
1 g of oxidized pulp obtained by the TEMPO oxidation was dispersed in 99 g of distilled water and refined with a juicer mixer for 30 minutes to obtain a 1% wood CSNF aqueous dispersion.

[Preparation of aqueous silver nitrate solution]
17 mg of silver nitrate was dissolved in 10 mL of distilled water to prepare an aqueous silver nitrate solution.

(Preparation of aqueous sodium borohydride solution)
Sodium borohydride 38mg was dissolved in distilled water 10mL, and sodium borohydride aqueous solution was prepared.

[Preparation of silver / wood CSNF composite]
To the 1% wood CSNF aqueous dispersion, the silver nitrate aqueous solution and the sodium borohydride aqueous solution were added with stirring at room temperature (25 ° C.) under the various conditions (A, B, C) shown in Table 1, and silver / A wood CSNF composite was prepared.

[Surface observation of silver / wood CSNF composite]
The result of observing the silver / wood CSNF composite using a scanning transmission electron microscope (S-4800, manufactured by Hitachi High-Tech) is shown in FIG. As a result, it was found that as the addition amount of the aqueous silver nitrate solution increased, the particle diameter of the silver nanoparticles deposited increased and maintained a dispersed state without agglomeration. The observation image suggested that the particle shape was not spherical but cube or pyramid. Regarding this phenomenon, it is considered that silver nanoparticles were precipitated in the network structure of wood CSNF.

(Production of laminate)
The silver / wood CSNF composite aqueous dispersion is applied onto an A4 size PET film having a film thickness of 25 μm using a bar coater # 16 and dried at 80 ° C. for 3 minutes to contain the silver / wood CSNF composite. A laminate having a layer was produced.

[Spectral absorption spectrum measurement of laminate containing silver / wood CSNF composite]
The laminate containing the silver / wood CSNF composite was cut into an appropriate size and placed at a measurement location of a spectrophotometer (manufactured by Shimadzu Corporation, UV-3600), and a light absorption spectrum was measured. The result is shown in FIG. As a result, it was confirmed that the absorption peak of the spectral absorption spectrum shifted to the near infrared region as the amount of silver nitrate aqueous solution added increased. As a result, it was found that silver / wood CSNF that can be used as a near-infrared shielding material can be produced by changing the silver ion concentration in this example.

[Measurement of thermal insulation effect]
Among the laminates containing the silver / wood CSNF composite, the heat shielding effect was confirmed using the film prepared by Sample C. In a room without air conditioning, the film is pasted on a part of the inside of the south-facing window in advance, and at 2 pm on August 31, 2012 (outside air temperature 36 ° C.) The temperature at the window was measured and compared. Then, while the temperature at the window of the portion where the film was pasted was 38 ° C., the temperature of the portion where the film was not pasted rose to 45 ° C. From this, it was confirmed that the film can be used as a thermal barrier film.

<Example 2>
A silver / wood CSNF composite was prepared and obtained under the same conditions as Sample C of Example 1 except that the temperature during reduction precipitation and stirring was maintained at 10 ° C. under the conditions of Sample C of Example 1. When the spectral absorption spectrum of the silver / wood CSNF composite was measured in the same manner as in Example 1, the absorption peak of the spectral spectrum was around 850 nm. From this, it was found that the near-infrared shielding effect of the silver / wood CSNF composite can be further improved by changing the temperature condition during the production of the silver / wood CSNF composite.

<Comparative Example 1>
A silver / wood CSNF composite was prepared under the same conditions as in Example 1 except that the solid content concentration of the CSNF dispersion to be used was adjusted to 0.05% and each aqueous solution was mixed according to Table 2.

  With respect to the silver / wood CSNF composite, the spectral absorption spectrum was measured in the same manner as in Example 1. As a result, no spectral spectrum absorption band and absorption peak in the near infrared region were observed, and the amount of silver nitrate aqueous solution added increased. As a result, the absorption peak intensity around 400 nm derived from spherical silver nanoparticles increased. It was found that the shape of the silver / wood CSNF composite was observed by STEM observation in the same manner as in Example 1, and that spherical silver nanoparticles having a particle diameter of 20 nm or less were supported at high density on the wood CSNF. did.

  Using the silver / wood CSNF composite, a laminate was prepared and the heat shielding effect was confirmed in the same manner as in Example 1. As a result, a significant heat shielding effect was not obtained. Further, the appearance of the laminate itself was very yellow, and it was confirmed that the laminate produced under these conditions was not suitable for use as a heat-shielding film.

<Comparative example 2>
Take 2 mL of 0.2% solid wood CSNF in a vial and stir at room temperature with each prepared chloroauric acid aqueous solution (1.5, 2.0, 2.5, 3.0 mM). 2 mL each was added, and a sufficient amount of aqueous sodium borohydride solution to reduce gold ions was further added to prepare a gold / CSNF composite.

  Regarding the gold / CSNF composite, STEM observation was performed in the same manner as in Example 1. As a result, when 1.5 mM chloroauric acid was used, gold nanoparticles were precipitated at a high density on wood CSNF. As the gold acid concentration increased, it was observed that gold nanoparticles aggregated. Further, when the spectral absorption spectrum was measured in the same manner as in Example 1, the absorption peak of gold nanoparticles was observed near 510 nm in the sample using 1.5 mM chloroauric acid, but the concentration of chloroauric acid was increased. It was found that the absorption peak near 510 nm broadens toward the high wavelength side. This phenomenon indicates aggregation of gold nanoparticles. In the gold / wood CSNF composite produced by this method, no peak showing absorption in the near infrared region was found.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide a near-infrared shielding material, its manufacturing method, and a thermal-insulation film using the same by the low environmental load and simple process using biomass material. If this thermal barrier film is used as a window film for government buildings, commercial facilities, factory facilities, office buildings, detached houses, condominiums, or automobiles, it is possible to achieve power saving and energy saving effects while maintaining comfortable air conditioning control. The It is expected that the present invention will greatly contribute to the construction of a resource recycling society that can be continuously developed by the synergistic effect of the solution of the energy problem and the environmental harmony of the material itself. Further, the metal / micronized cellulose fiber composite obtained by the present invention can be applied to, for example, a security material as a new carbon neutral optical material, and a ripple effect in various fields is also expected.

  nothing special

Claims (3)

A step of dispersing the refined cellulose fiber in a solvent containing at least 50% of water to obtain a refined cellulose fiber dispersion in which the concentration of the refined cellulose fiber is 0.1% or more and less than 5%;
A step of obtaining a mixed solution by mixing the fine cellulose fiber dispersion and a metal ion-containing aqueous solution containing at least silver ions;
The silver nanoparticles (excluding spheres) and the refined cellulose fibers are obtained by reducing silver ions in the mixed solution and depositing silver nanoparticles (excluding spheres) in the refined cellulose fiber network structure. Producing a composite of
A method for producing a composite of silver and fine cellulose fibers, wherein the absorption peak of the spectral absorption spectrum is changed by changing the silver ion concentration in the mixed solution.   2. The method for producing a composite of silver and fine cellulose fibers according to claim 1, wherein the amount of metal ions in the mixed solution is less than the amount of carboxyl groups present on the surface of the fine cellulose fibers. A method for producing a thermal barrier film, comprising: applying a composite of silver and fine cellulose fiber produced by the production method according to claim 1 or 2 onto a substrate and drying the composite.