JP6260451B2 - POROUS BODY, PROCESS FOR PRODUCING THE SAME, AND HEAT SHIELDING FILM - Google Patents

Description

  The present invention relates to a porous body including a near-infrared shielding material, a method for producing the same, and a heat shielding film.

  In recent years, interest in energy conservation has increased and has attracted attention in various fields. In Japanese houses and buildings, energy consumption by air conditioning is high. In particular, there is a problem because the room is warmed by sunlight incident from the window glass, the cooling energy rises, and the power demand peak increases in summer, leading to power shortage.

A near-infrared shielding film is known as a method for suppressing energy consumption by cooling. Sunlight can be classified into an ultraviolet region, a visible light region, and an infrared region, and the infrared region is further divided into a near infrared region, a middle infrared region, and a far infrared region. Of these, the near-infrared region is also called a heat ray and is a wavelength region that is easily absorbed by any substance, and the absorbed light is converted into heat. Therefore, by applying a near-infrared shielding film to a window, it is possible to selectively shield near-infrared rays in direct sunlight and suppress an increase in indoor temperature. This leads to a reduction in heating and cooling costs and an energy saving effect.

In the present specification, it is desirable that the near-infrared shielding film does not shield visible light. For example, if visible light is shielded simultaneously with near-infrared rays, designability or visibility is impaired.

  In the present specification, near infrared rays indicate electromagnetic waves in a wavelength region (approximately 700 nm to 2500 nm) close to visible light among infrared rays. This near-infrared ray has a property close to visible light. In particular, it is known that light in the wavelength region of 700 nm to 1200 nm contained in sunlight is easily absorbed by the object surface and converted into thermal energy.

  For example, Patent Document 1 discloses a near-infrared shielding film having at least one unit formed by laminating a high refractive layer and a low refractive layer, each including a high refractive material and a low refractive material having different refractive indexes. Has been. However, in this method, it is necessary to laminate a plurality of layers for shielding infrared rays, and productivity is low.

  Flat silver nanoparticles are also attracting attention as near-infrared shielding materials. In general, it is known that spherical silver nanoparticles having a particle diameter of several nanometers to several tens of nanometers have a yellowish color due to absorption near a wavelength of 400 nm due to surface localized plasmon resonance. On the other hand, since the resonance peak of anisotropic silver nanoparticles changes, for example, it is known that the absorption peak of a plate-like silver nanoparticle is red-shifted. At this time, it has been confirmed that the absorption peak shifts to the longer wave side as the aspect ratio (that is, particle diameter / particle thickness) of the tabular silver nanoparticles increases. That is, the tabular silver nanoparticles can be used as an optical material that absorbs an arbitrary wavelength, and depending on the aspect ratio of the tabular silver nanoparticles, the absorption peak can be shifted to the near infrared region outside the visible light region. Therefore, it can be applied as a near-infrared shielding material.

  A number of synthesis methods have been proposed for the tabular silver nanoparticles. A polyol method is mentioned as a method generally used. The polyol method is a method in which ethylene glycol, which is a kind of polyol, is heated to 140 to 160 ° C. together with a metal salt under a polymer capping agent, and metal fine particles are synthesized by the reducing power of the generated glycolaldehyde. At this time, it is reported that silver nanoparticles having various shapes can be obtained because anisotropic growth of silver nanoparticles can be induced by selecting reducing conditions and an appropriate polymer capping agent. For example, Patent Document 2 discloses a production example of plate-like silver nanoparticles using a polyol method.

  Patent Document 3 discloses a filter that actually uses flat silver fine particles as a near-infrared shielding filter. In the present disclosure example, the near-infrared shielding layer does not need to have a multilayer structure, and the productivity problem that has been a problem in Patent Document 1 is improved.

  On the other hand, in recent years, with the aim of solving the problem of fossil resource depletion, development of functional materials using biomass, which is an environmentally friendly material that can be used continuously, has been actively conducted. Among them, cellulose, which is the main component of wood, is a natural polymer material that is accumulated in large quantities on the earth, and is expected as a key material for the transition to a resource recycling society. In wood, dozens or more of cellulose molecules are bundled to form fine fibers (microfibrils) with a high crystallinity and a nanometer order fiber diameter, and many fine fibers are hydrogen-bonded to each other. Thus, cellulose fibers are formed, which is a plant support. As described above, since it has a stable structure, natural cellulose contained in wood is insoluble except for a special solvent, has poor moldability, and is difficult to handle as a functional material. Therefore, attempts have been actively made to refine and use cellulose fibers in wood until at least one side of the structure is on the order of nanometers.

  2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO) which is a relatively stable N-oxyl compound as shown in Patent Document 4 as an excellent technique for refining cellulose As a catalyst, there has been reported a method for carrying out light mechanical defibration after selectively oxidizing the surface of cellulose fine fibers. 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 carboxy group.

  Thus, the electrostatic repulsion between the carboxy groups introduced on the crystal surface makes it possible to disperse cellulose in microfibril units in an aqueous solvent, and nanosized micronized cellulose fibers can be obtained. Wood-derived refined cellulose fiber obtained from wood by TEMPO oxidation reaction is a structure having a high aspect ratio with a minor axis diameter of around 3 nm and a major axis diameter ranging from several tens of nm to several μm, and its aqueous dispersion And it is reported that the laminate has high transparency.

  Patent Document 5 discloses a composite (metal nanoparticle-supported fine cellulose fiber) in which metal nanoparticles are supported on the finely divided cellulose fibers as a composite of finely divided cellulose fibers and metal fine particles. . Patent Document 5 discloses an example in which metal nanoparticle-supported fine cellulose fibers are used as a catalyst.

International Publication No. 2013/077274 JP 2009-144188 A JP 2007-108536 A JP 2008-007646 A International Publication No. 2010/095574

  However, in order to produce tabular silver nanoparticles using the polyol method described in Patent Document 2, a high-temperature reaction is required in an organic solvent system, and the reaction time is long, so the burden on the environment is increased. There was a problem.

Moreover, if the near-infrared shielding filter described in Patent Document 3 is used as a heat-shielding film for pasting windows to shield sunlight, the infrared-absorbing filter itself is heated, and the room temperature may increase due to the heat. There is.

  Further, Patent Document 5 discloses a composite of finely divided cellulose fibers and metal fine particles and its use. However, it is possible to control the shape of metal nanoparticles and to apply to optical materials such as near-infrared shielding materials. The actual situation is that there is no disclosure or suggestion about the possibility.

  The present invention has been made in view of such circumstances, and provides a porous body formed from a composite of novel flat metal fine particles and fine cellulose that can be applied to a near-infrared shielding material. Let it be an issue.

  Furthermore, this invention makes it a subject to provide the said porous body or heat insulation film with a simple method with low load to an environment.

  The inventors of the present application tried to create various organic-inorganic hybrids using fine cellulose fibers, which are carbon neutral materials. Surprisingly, silver was reduced and precipitated in a dispersion of fine cellulose fibers under specific conditions. To obtain a composite of tabular silver fine particles and finely divided cellulose fibers, and that the flat silver fine particles and finely divided cellulose fibers of the obtained composite are in an indivisible state. I found it. Further, the present invention was completed by successfully producing a porous body (or airgel) including the composite by removing the dispersion medium from the dispersion containing the composite.

I will fix it later.
One aspect of the present invention includes a composite of finely divided cellulose fibers and flat metal fine particles, and each of the finely divided cellulose fibers is at least partly or entirely incorporated into the flat metal fine particles, and the remainder is Exposed on the surface of the flat metal fine particles, the flat metal fine particles are at least one kind of metal or a compound thereof, and the refined cellulose fibers are arranged in a porous shape, It is a sexual body.
One embodiment of the present invention includes a step of preparing finely divided cellulose fibers, a step of dispersing finely divided cellulose fibers in a solvent to obtain a finely divided cellulose fiber dispersion, a finely divided cellulose fiber dispersion, and a metal A step of mixing a solution containing ions to obtain a mixed solution, reducing the metal ions in the mixed solution to grow flat metal fine particles, and combining the flat metal fine particles and fine cellulose fibers A method for producing a porous body, comprising: a step of forming a body; and a step of forming a porous body by removing a solvent from a dispersion containing a composite and fine cellulose fibers.
One embodiment of the present invention is a thermal barrier film, wherein a base material and a coating layer including the porous body of one embodiment of the present invention are provided on at least one surface of the base material.

  The porous body of the present invention is an organic-inorganic composite having a structure in which at least part or all of the refined cellulose fibers are taken into the interior of the flat metal fine particles and the rest is exposed on the surface of the flat metal fine particles. It is a novel porous body that can be applied to a heat-shielding film as a near-infrared shielding material that also includes a body and has heat insulation properties.

  In the method for producing a porous body of the present invention, metal ions in a mixed solution are reduced to form a composite of flat metal fine particles and fine cellulose fibers, and then dispersed while maintaining voids between the fine cellulose fibers. Since it has the process of removing a medium, the said porous body has low load to an environment and can be provided simply.

It is a schematic diagram which shows the porous body which is one Embodiment to which this invention is applied. It is a perspective view which shows typically the structure of the composite_body | complex included by the porous body to which this invention is applied. It is a schematic diagram for demonstrating a part of process of the manufacturing method of the composite_body | complex included by the porous body to which this invention is applied. It is sectional drawing of one Embodiment of the thermal insulation film which concerns on this invention. The observation result by the scanning electron microscope (SEM) of the composite_body | complex included in the porous body obtained in Example 1 is shown, (a) is a SEM image, (b) is (a). It is a schematic diagram. It is a figure (TEM image) which shows the result of having observed the composite_body | complex included in the porous body obtained in Example 1 from the cross-sectional direction with the transmission electron microscope (TEM). The observation result by the scanning transmission electron microscope (STEM) of the composite_body | complex included in the porous body obtained in Example 1 is shown, (a) is a STEM image, (b) is (a). FIG. 2 is a spectral transmission spectrum of a dispersion containing a complex included in the porous material obtained in Example 1.

Hereinafter, the porous body which is one embodiment to which the present invention is applied will be described in detail with reference to the drawings, together with the production method and the heat shielding film including the porous body. In particular, a porous body including a composite of flat metal fine particles and fine cellulose fibers will be described.
In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

<Porous body>
First, the porous body which is one embodiment to which the present invention is applied will be described.
FIG. 1 is a schematic diagram showing a configuration of a porous body according to an embodiment to which the present invention is applied. As shown in FIG. 1, the porous body of the present embodiment has a porous body structure in which the solvent is removed while maintaining the gaps between the finely divided cellulose fibers, and there are nano-sized voids. Yes. Furthermore, the porous body includes flat metal fine particles. For example, in the case of flat silver particles having absorption in the near infrared region, the porous body has heat insulating properties and a flat plate shape derived from the porous body structure. It also has heat shielding properties derived from the metal fine particle structure. The porous body preferably has a surface area measured by a nitrogen adsorption BET method of 50 m ² / g or more from the viewpoint of heat ray shielding. In addition, the refined cellulose fiber which is the main body formed by the porous body forms a composite with the flat metal fine particles, and both are inseparable. Details including the refined cellulose fibers are described in the section <Composite> below.

<Composite>
Furthermore, the composite body included in the porous body will be described.
FIG. 2 is a perspective view schematically showing a configuration of a complex which is an embodiment to which the present invention is applied. As shown in FIG. 2, the composite 1 according to the present embodiment is a composite of flat metal fine particles (flat metal fine particles) 2 and at least one or more refined cellulose (refined cellulose fibers) 3. Is a composite of flat metal fine particles and fine cellulose fibers, and at least a part (part) or all of each fine cellulose fiber 3 is taken into the flat metal fine particles 2; The remaining portion is composited so as to be exposed on the surface of the flat metal fine particle 2.

  More specifically, as shown in FIG. 2, each refined cellulose fiber 3 is exposed on the surface of the flat metal fine particles 2 and the portion 3 a taken into the flat metal fine particles 2. It is comprised from the part 3b. And by the presence of this taken-in part 3a, the flat metal particle 2 and each refined cellulose fiber 3 are inseparable. That is, at least a part of the flat metal fine particles 2 and the finely divided cellulose fibers 3 are physically obtained when at least a part of the finely divided cellulose fibers 3 (that is, the part 3a) is taken into the flat metal fine particles 2. Combined and inseparable.

  Here, as for the composite 1, that at least a part (that is, the part 3 a) of the fine cellulose fiber 3 is taken into the inside of the flat metal fine particles 2 will be described in the manufacturing method described later. In the growth stage of the fine particles 2, this is synonymous with a state in which the fine cellulose fibers are sandwiched along the grain boundaries of the metal fine particle unit.

  Further, in the composite 1, the “indivisible” state means that it cannot be separated into the flat metal fine particles 2 and the finely divided cellulose fibers 3 by a physical method such as a centrifuge. Say.

  In the composite 1, all the parts (the whole) of all the refined cellulose 3 constituting the composite 1 are taken into the flat metal fine particles 2, and the parts exposed on the surface of the flat metal fine particles 2 are included. A configuration that does not exist is included in the scope of rights as long as the presence of the captured portion 3a can be confirmed.

  Silver is preferable as the metal species constituting the flat metal fine particles 2. This is because, when the tabular fine particles are formed, it is advantageous in that it has a resonance peak derived from the surface localized plasmon phenomenon from the visible light to the near infrared region. However, it is not particularly limited to this. Specifically, a plurality of metal species may be used as the metal species, and the metal species other than silver is not particularly limited. For example, other than platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium and osmium. Gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and other metals, metal salts, metal complexes, and alloys thereof, or oxides, double oxides, and the like.

In the present embodiment, the “flat plate” is a plate-like particle having a shape such as a triangle, a hexagon, or a pentagon, and has an average aspect ratio (particle diameter / particle thickness) obtained by dividing the particle diameter by the particle thickness. It means a particle that is 2.0 or more.
The particle diameter of the flat metal fine particles 2 is preferably 20 to 500 nm, and more preferably 20 to 400 nm.
The particle thickness of the flat metal fine particles 2 is preferably (5) to (100) nm, and more preferably (8) to (* 50) nm.
The average aspect ratio (particle diameter / particle thickness) is preferably 2.0 or more, more preferably 2.0 to 100, and still more preferably 2.0 to 50. Within this range, it is easy to have a resonance peak derived from surface-localized plasmons within a desired range from visible light to infrared light.

Here, specific examples of the method for measuring the particle diameter and thickness of the flat metal fine particles and the method for calculating the aspect ratio include the following methods.
(1) Measuring method of particle diameter The dispersion containing the composite is cast on a copper grid with a support film for TEM observation and air-dried, and then observed with a transmission electron microscope. The diameter when the tabular silver nanoparticles in the obtained image are approximated by a circle is calculated as the particle diameter in the plane direction.
(2) Thickness measurement method A dispersion containing the composite is cast on a PET film, air-dried and fixed with an embedding resin, cut in the cross-sectional direction with a microtome, and observed with a transmission electron microscope. The thickness of the tabular silver nanoparticles in the obtained image is calculated as the particle diameter in the plane direction.
(3) Calculation method of aspect ratio When the particle diameter obtained as described above is a and the particle thickness is b, a value obtained by dividing the particle diameter a by the particle thickness b is defined as aspect ratio = a / b. calculate.
The measurement method and the calculation method described above are examples, and are not particularly limited to these.

  The refined cellulose fiber 3 preferably has a fiber shape derived from a microfibril structure. Specifically, as the refined cellulose fiber 3, the number average minor axis diameter is 1 nm to 100 nm, the number average major axis diameter is 50 nm or more, and the number average major axis diameter is 10 times the number average minor axis diameter. The above is preferable. Moreover, it is preferable that the crystal structure of the refined cellulose fiber 3 is cellulose I type.

  In the composite 1 of the present embodiment, the refined cellulose fiber 3 has a carboxy group on the crystal surface, and the content of the carboxy group is 0.1 mmol or more and 5.0 mmol or less per 1 g of cellulose. Is preferred.

  As described above, the composite 1 used in the present embodiment is a composite of flat metal fine particles 2 made of one or more kinds of metals or their compounds and fine cellulose fibers 3, and is a flat plate. The metal fine particles 2 and the refined cellulose fibers 3 are physically combined and in an inseparable state. Therefore, since the porous body disclosed in the present invention includes the composite, it is a novel organic-inorganic hybrid porous body that is carbon neutral.

<Method for producing porous body>
Next, the manufacturing method of the porous body of this embodiment mentioned above is demonstrated. In the method for producing a porous body according to the present embodiment, a metal crystal is produced by reducing and precipitating a metal in a mixed dispersion liquid containing refined cellulose fibers and metal ions, and the metal crystal has anisotropy. And a dispersion medium is removed while maintaining the voids between the finely divided cellulose fibers after obtaining a composite of flat metal fine particles and finely divided cellulose fibers.

  More specifically, the method for producing a porous body of the present embodiment includes a step of preparing oxidized cellulose (first step), and a step of dispersing oxidized cellulose in a solvent to obtain a fine cellulose dispersion (first step). 2 steps), a step of obtaining a mixed solution by mixing a finely divided cellulose dispersion and a solution containing metal ions (third step), and reducing the metal ions in the mixed solution to form plate-like metal fine particles , And a step of forming a porous body by removing the solvent from the dispersion containing the composite (step 4) ). Below, each process is demonstrated in detail.

(First step; oxidized cellulose fiber preparation step)
First, in a 1st process, the refined cellulose fiber for comprising the porous body of this embodiment is prepared. This 1st process includes the process of preparing a fibrous refined cellulose fiber, and the process of introduce | transducing a carboxy group into the crystal | crystallization surface of a refined cellulose fiber.

"Process for preparing fine cellulose fiber"
As the refined cellulose fiber used in the method for producing a porous body of the present embodiment, a fiber-shaped product in the range shown below is preferable. Further, the fine cellulose fiber may have a number average minor axis diameter of 1 nm or more and 100 nm or less, preferably 2 nm or more and 50 nm or less in the minor axis diameter. Here, if the number average minor axis diameter is less than 1 nm, a highly crystalline rigid micronized cellulose fiber structure cannot be obtained, and a porous body cannot be formed. On the other hand, when the thickness exceeds 100 nm, the size becomes too large with respect to the metal fine particles, so that the shape of the composite of the flat metal fine particles and the refined cellulose cannot be taken. Further, the number average major axis diameter is not particularly limited, but is preferably 10 times or more of the number average minor axis diameter. If the number average major axis diameter is less than 10 times the number average minor axis diameter, the porous body cannot be formed.

  The number average minor axis diameter of the micronized cellulose fiber is obtained as an average value obtained by measuring the minor axis diameter (minimum diameter) of 100 fibers by observation with a transmission electron microscope and atomic force microscope. On the other hand, the number average major axis diameter of the fine cellulose fibers is obtained as an average value obtained by measuring the major axis diameter (maximum diameter) of 100 fibers by observation with a transmission electron microscope and observation with an atomic force microscope.

  The type and crystal structure of cellulose that can be used as a raw material for the fine cellulose fiber are not particularly limited. Specifically, as a raw material comprising cellulose I-type crystals, for example, in addition to wood-based natural cellulose, non-wood-based natural cellulose such as cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, squirt cellulose, and valonia cellulose Can be used. Furthermore, the regenerated cellulose represented by the rayon fiber which consists of a cellulose II type crystal | crystallization, and a cupra fiber can also be used. From the viewpoint of easy material procurement, it is preferable to use wood-based natural cellulose as a raw material.

  The method for refining cellulose 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 by a grinder, chemical treatment by TEMPO oxidation treatment, or the like. 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.

  As a method for refining cellulose, according to the method described in Patent Document 4 described above, various celluloses are tempo-catalyzed and then refined by light mechanical treatment, and the resulting refined cellulose fiber and metal are combined, Since the minor axis diameter of the refined cellulose fiber is about 3 nm, which is as fine as that of the carbon nanotube, high transparency of the dispersion and the porous body using the dispersion can also be achieved. In that case, for example, it can be suitably used as a functional member such as a heat insulating material or a heat shielding material. In addition, the refined cellulose fiber produced by TEMPO oxidation achieves anisotropic growth of metal fine particles uniformly and with good reproducibility. Although the detailed mechanism is unknown as this reason, it has a short axis diameter of about 3 nm, has a carboxy group that interacts with a metal ion, and this carboxy group is present on the surface of the refined cellulose fiber crystal. It is assumed that the structure fixed to the interval is the cause. That is, from the viewpoints of shape control ability and transparency described above, the refined cellulose fiber used in the present embodiment is preferably a refined cellulose fiber introduced with a carboxy group, and TEMPO oxidation of wood from the viewpoint of price and supply The finely divided cellulose fiber obtained by is more preferable.

  Hereinafter, a method for producing wood-derived fine cellulose fibers by TEMPO oxidation will be described.

  The wood-derived refined cellulose fibers used in the present embodiment can be obtained by a step of oxidizing wood-derived cellulose and a step of refinement and dispersion into a dispersion liquid. Moreover, as content of the carboxy group introduce | transduced into a refined cellulose fiber, 0.1 mmol / g or more and 5.0 mmol / g or less are based on the dry weight of a refined cellulose fiber (it is the same also in the following description). Is preferable, and 0.5 mmol / g or more and 2.0 mmol / g or less is more preferable. Here, when the amount of carboxy 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. In addition, if it exceeds 5.0 mmol / g, the cellulose microfibrils will be reduced in molecular weight due to side reactions accompanying chemical treatment, so it will not be possible to obtain a highly crystalline rigid micronized cellulose fiber structure and form a porous body. Can not do it.

“Step of introducing carboxy group into cellulose”
The wood-based natural cellulose is not particularly limited, and those generally used for producing cellulose nanofibers such as softwood pulp, hardwood pulp, and waste paper pulp can be used. Softwood pulp is preferred because it is easily refined and refined.

  It does not specifically limit as a method of introduce | transducing a carboxy group into the fiber surface of the cellulose derived from wood. Specifically, for example, carboxymethylation may be performed by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a high-concentration alkaline aqueous solution. Further, a carboxy group may be introduced by directly reacting a carboxylic anhydride compound such as maleic acid or phthalic acid gasified in an autoclave with cellulose. Furthermore, a co-oxidant is used in the presence of N-oxyl compounds such as 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. The method used may be used. TEMPO oxidation is more preferable from the viewpoint of selectivity of a carboxy group introduction site and environmental load.

  Here, as the N-oxyl compound, TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical), 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 preferable. The amount of the N-oxyl compound used is not particularly limited, and may be an amount as a catalyst. Usually, it is about 0.01-5.0 mass% with respect to solid content of the wood type natural cellulose to oxidize.

  Examples of the oxidation method using an N-oxyl compound include a method in which wood-based natural cellulose is dispersed in water and oxidized in the presence of the N-oxyl compound. At this time, it is preferable to use a co-oxidant together with the N-oxyl compound. In this case, in the reaction system, the N-oxyl compound is sequentially oxidized by a co-oxidant to produce an oxoammonium salt, and cellulose is oxidized by the oxoammonium salt. According to such oxidation treatment, the oxidation reaction proceeds smoothly even under mild conditions, and the introduction efficiency of the carboxy group is improved. When the oxidation treatment is performed under mild conditions, it is easy to introduce a carboxy group while maintaining the crystal structure of cellulose.

  Co-oxidants include halogens, hypohalous acids, halous acids and perhalogen acids, or salts thereof, halogen oxides, nitrogen oxides, peroxides, etc., as long as they can promote the oxidation reaction. Any oxidizing agent can be used. Sodium hypochlorite is preferred because of its availability and reactivity. The amount of the co-oxidant used is not particularly limited, and may be an amount that can promote the oxidation reaction. Usually, it is about 1-200 mass% with respect to solid content of the wood type natural cellulose to oxidize.

  In addition to the N-oxyl compound and the co-oxidant, at least one compound selected from the group consisting of bromide and iodide may be further used in combination. Thereby, an oxidation reaction can be advanced smoothly and the introduction efficiency of a carboxy group can be improved. As such a compound, sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable from the viewpoint of cost and stability. The amount of the compound used is not particularly limited, and may be an amount that can promote the oxidation reaction. Usually, it is about 1-50 mass% with respect to solid content of the wood type natural cellulose to oxidize.

  The reaction temperature of the oxidation reaction is preferably 4 to 80 ° C, more preferably 10 to 70 ° C. If it is lower than 4 ° C., the reactivity of the reagent is lowered and the reaction time is prolonged. If the temperature exceeds 80 ° C., the side reaction is promoted to lower the molecular weight of the sample, and the highly crystalline rigidly refined cellulose fiber structure collapses, so that a porous body cannot be formed.

  The reaction time for the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxy group, and the like, and is not particularly limited, but is usually about 10 minutes to 5 hours.

  The pH of the reaction system during the oxidation reaction is preferably 9-11. When the pH is 9 or more, the reaction can be efficiently carried out. If the pH exceeds 11, side reactions may progress and the decomposition of the sample may be accelerated. Further, in the oxidation treatment, as the oxidation proceeds, the pH in the system decreases due to the formation of a carboxy group. Therefore, it is preferable to maintain the pH of the reaction system at 9 to 11 during the oxidation treatment. Examples of a method for maintaining the pH of the reaction system at 9 to 11 include a method of adding an alkaline aqueous solution in accordance with a decrease in pH.

  Examples of alkaline aqueous solutions 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, and benzyltrimethylammonium hydroxide aqueous solution. And organic alkalis. A sodium hydroxide aqueous solution is preferable from the viewpoint of cost.

  The oxidation reaction with the N-oxyl compound can be stopped by adding alcohol to the reaction system. At this time, the pH of the reaction system is preferably maintained within the above range. 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, and ethanol is particularly preferred from the viewpoint of safety of by-products generated by the reaction.

  The reaction solution after the oxidation treatment may be directly subjected to a refinement process, but in order to remove a catalyst such as an N-oxyl compound, impurities, etc., the oxidized cellulose contained in the reaction solution is recovered and washed with a washing solution. It is preferable. The collection of the oxidized cellulose fiber can be carried out by a known method such as filtration using a glass filter or a nylon mesh having a 20 μm pore diameter. Distilled water is preferable as the cleaning liquid used for cleaning the oxidized cellulose fiber.

(Second step; dispersion adjustment step)
Next, in the second step, the oxidized cellulose prepared in the first step is dispersed in a solvent to obtain a fine cellulose dispersion.

  As a method for preparing a fine cellulose fiber dispersion, first, an aqueous medium is added to oxidized cellulose and suspended. Specifically, the solvent used for dispersion of the fine cellulose fibers derived from wood contains 50% or more of water, and a hydrophilic solvent is preferable as a solvent other than water. When the ratio of water is 50% or less, the dispersion of fine cellulose fibers derived from wood is inhibited, and it becomes difficult to form a uniform composite of metal fine particles and fine cellulose fibers derived from wood. The hydrophilic solvent is not particularly limited, but alcohols such as methanol, ethanol and isopropanol; cyclic ethers such as tetrahydrofuran are preferred. If necessary, the pH of the suspension may be adjusted in order to increase the dispersibility of the cellulose and the fine cellulose fibers to be produced. Examples of the alkaline aqueous solution used for pH adjustment include the same alkaline aqueous solution as described above.

  Subsequently, the obtained suspension is subjected to a physical defibrating treatment to refine the oxidized cellulose. For physical fibrillation treatment, 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 facing collision, etc. Mechanical treatment is mentioned. By performing such physical fibrillation treatment on, for example, the above-described TEMPO oxidized cellulose, the cellulose in the suspension is refined and a dispersion of refined cellulose fibers having a carboxy group on the fiber surface is obtained. Can do. Further, the number average minor axis diameter and the number average major axis diameter of the refined cellulose fibers contained in the obtained refined cellulose fiber dispersion can be adjusted by the time and number of times of the physical fibrillation treatment at this time.

  As described above, a refined cellulose fiber dispersion into which a carboxy group has been introduced (a refined cellulose fiber dispersion) is obtained. The obtained dispersion can be used as a reaction field for reducing and precipitating metal fine particles as it is or by diluting, concentrating and the like.

  Moreover, the refined cellulose fiber dispersion may contain other components other than the components used for cellulose and 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 according to the use of the wood refined cellulose fiber. Specifically, organometallic compounds such as alkoxysilanes or hydrolysates thereof, inorganic layered compounds, inorganic needle minerals, antifoaming agents, inorganic particles, organic particles, lubricants, antioxidants, antistatic agents, Examples thereof include an ultraviolet absorber, a stabilizer, magnetic powder, an alignment accelerator, a plasticizer, and a crosslinking agent.

(Third step; mixed solution adjustment step)
Next, in the third step, the refined cellulose fiber dispersion obtained in the second step is mixed with a solution containing metal ions to obtain a mixed solution.
Specifically, first, a solution containing metal ions (metal ion-containing solution) is prepared by dissolving a metal or alloy, metal oxide, metal double oxide, or the like in a solvent such as water. Next, a mixed solution of the refined cellulose fiber dispersion and the metal ion-containing solution is obtained by adding the prepared metal ion-containing solution little by little while stirring the refined cellulose refined cellulose fiber dispersion.

  By the way, tabular silver nanoparticles can absorb light of any wavelength ranging from visible light to near-infrared light by shape control, and easily impart desired optical characteristics according to the use of various compositions. be able to. In addition, since silver itself has antibacterial properties against many bacterial species but is inert to the human body, a composition having good storage stability and safety can be obtained.

  Thus, in the production method of the present embodiment, silver is preferable as the metal species to be combined with the fine cellulose fiber derived from wood, but is not particularly limited thereto. Specifically, a plurality of metal species may be used as the metal species to be combined, and the metal species other than silver is not particularly limited. For example, platinum group of platinum, palladium, ruthenium, iridium, rhodium, osmium In addition to elements, gold, iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum and other metals, metal salts, metal complexes and their alloys, or oxides, double oxides, etc. Can be mentioned. Moreover, since antibacterial property can be provided by forming a composite with silver, the corrosion resistance of the refined cellulose fiber can also be improved. When a plurality of metal species are used, the stability of the silver nanoparticles may be improved by coating the surrounding silver nanoparticles with a metal noble than silver or a metal oxide such as silica.

(4th process; complex formation process)
Next, in the fourth step, the metal ions in the mixed solution obtained in the third step described above are reduced to grow plate-like metal fine particles, and the plate-like metal fine particles and the refined cellulose fibers are combined. .

  A method for producing a composite by depositing metal fine particles in a fine cellulose fiber dispersion derived from wood is not particularly limited, but a solution of the metal or alloy including silver, oxide, double oxide and the like. If a reducing agent is added in a state where the finely divided cellulose fiber dispersion is mixed, it can be easily deposited.

  For example, in the case of silver, the type of the aqueous solution containing silver ions used for the reduction is not particularly limited, but an aqueous silver nitrate solution is preferable from the viewpoint of availability and ease of handling. There is no particular limitation on the reducing agent used. As the silver reducing agent, for example, ascorbic acid, citric acid, hydroquinone, sodium borohydride, sodium cyanoborohydride, dimethylamine borane, hydrazine and the like are used. Ascorbic acid, citric acid, and sodium borohydride are preferable from the viewpoint of safety and price.

  In addition, in order to promote anisotropic growth of metal fine particles and precipitate a composite of flat metal fine particles and fine cellulose fibers, the amount of silver used during reduction precipitation treatment is 1 g of fine cellulose fibers. Is preferably in the range of 0.0005 mmol to 0.4 mmol, more preferably in the range of 0.001 mmol to 0.2 mmol, and particularly preferably in the range of 0.002 mmol to 0.1 mmol. .

Here, FIG. 3 is a schematic diagram for explaining a part of the steps of the method for producing a composite body which is an embodiment to which the present invention is applied.
In the fourth step of the production method of the present embodiment, first, the metal deposition starts from the carboxy group provided in the micronized cellulose 3 by the addition of the reducing agent in the mixed solution. The deposited metal forms primary particles (metal nanoparticles) 2a (see the left figure in FIG. 3). When the reaction further proceeds, these primary particles 2 a aggregate to form flat metal fine particles (that is, flat metal fine particles) 2. At this time, a part 3a of the refined cellulose fiber (fine cellulose fiber) 3 is entrained and the remaining part 3b is exposed (see the right figure in FIG. 3).
Through the above steps, the composite 1 of the flat metal fine particles 2 and the refined cellulose 3 of the present embodiment can be obtained.

(Fifth step; Porous step)
Next, in the fifth step, the porous body is formed by removing the solvent from the dispersion liquid containing the composite obtained in the above-mentioned fourth step without aggregating the composite and the refined cellulose fibers.

The method for removing the solvent is not particularly limited, but for example, it is preferable to cast the dispersion in a suitable container and remove the solvent by freeze drying or supercritical drying. The supercritical drying method is a drying technique using a supercritical fluid. With this method, it is possible to dry while maintaining the structure of the object to be dried. Therefore, the specific surface area can be easily adjusted to several tens to several hundreds m ² / g.

  In addition, at least a part of the counter ion of the carboxy group present in the composite and fine cellulose fiber contained in the dispersion obtained in the fourth step described above is converted into an organic onium ion represented by the general formula (1). After exchanging and further mixing at least the polysilane (B) having a unit represented by the general formula (2), the solvent may be removed using a known drying method such as hot air drying, hot roll drying, or infrared irradiation. Good. In this case, a stacking structure is formed by π-π interaction between the aryl group introduced on the surface of the fine cellulose fiber and the aryl group introduced into the side chain of the polysilane (B), and the fine cellulose fiber and The solvent is removed without the composites aggregating to obtain a porous body having nano-sized voids.

In the method for producing a porous body of the present embodiment, the concentration of the fine cellulose fiber dispersion in the second step is not particularly limited, but is preferably 0.1% or more and less than 20%. Here, 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 20% or more, the fine cellulose fibers are entangled with each other. Viscosity increases rapidly, making uniform reaction control difficult.

  In the third step described above, the concentration of metal ions in the solution containing metal ions is not particularly limited, but is prepared so that the amount of metal ions in the dispersion is less than the amount of carboxy groups present on the surface of the finely divided cellulose fiber. It is preferable. This is because if the amount of metal ions in the dispersion exceeds the amount of carboxy groups present on the surface of the refined cellulose fiber, the refined cellulose fiber aggregates.

  Furthermore, in the fourth step described above, the concentration of the reducing agent in the mixed solution is not particularly limited, but is preferably adjusted to be equal to or higher than the metal ion concentration. This is because unreduced metal ions remain in the mixed solution when the reducing agent concentration in the mixed solution is equal to or lower than the metal ion concentration.

  As described above, the three conditions of fine cellulose fiber concentration, metal ion concentration, and reducing agent concentration determine the aspect ratio of the tabular metal fine particles to be precipitated. That is, by setting these three conditions to appropriate values, it is possible to appropriately produce a composite of flat metal fine particles having an absorption peak at a target wavelength and fine cellulose fibers. In addition, as a tendency, when the metal ion concentration decreases, the aspect ratio of the flat metal fine particles increases, and when the metal ion concentration increases, the aspect ratio decreases.

  In addition, in the manufacturing method of the composite 1 of this embodiment mentioned above, the aspect ratio of the composite of the refined cellulose fiber concentration, the metal ion concentration, and the reducing agent concentration and the obtained flat metal fine particles and the refined cellulose fiber is obtained. Regarding the relationship, the theoretical mechanism is unclear. The specific production method of the optical material that can be used for the composite of the flat metal fine particles and the finely divided cellulose fiber, the near-infrared absorbing material, and the like is described in detail in the examples.

  By the way, when the composite and porous body of the present embodiment are manufactured by the above-described manufacturing method, they may contain spherical metal fine particles having a diameter of about several nanometers as by-products. Separation is possible with a separator.

  Here, spherical fine particles having a diameter of several nanometers containing at least silver exhibit a yellowish color to absorb light having a wavelength of around 400 nm. However, by removing these spherical fine particles by the above-mentioned centrifugation or the like, it can be used as a novel optical material that absorbs only the wavelength derived from the resonance peak of the complex of flat metal fine particles and fine cellulose. Is possible.

  In addition, the porous body of the present embodiment, which has a large aspect ratio of the composite of flat metal fine particles and fine cellulose, can be used as a near-infrared absorbing material with high visible light transmittance. .

  As described above, according to the composite 1 of the present embodiment, at least a part (3a) of each of the refined celluloses 3 is taken into the flat metal fine particles 2 and the remaining part (3b) is a flat plate. Porous structure including composite 1 of fine plate-like metal fine particles 2 and refined cellulose 3 having a structure that is exposed on the surface of glass-like metal fine particles 2 and having applicability to a near-infrared shielding material. A body can be provided.

<Heat shield film>
FIG. 4 is a cross-sectional view of an embodiment of a thermal barrier film according to the present disclosure. The thermal barrier film 1 shown in FIG. 4 is provided with a near-infrared shielding layer 12 including a porous body formed by coating or pasting on one surface of a base material 11, and the base material of the near-infrared shielding layer 12. An adhesive layer 13 and a hard coat layer 14 are provided on the surface opposite to 11. An adhesive layer 15 is provided on the surface of the substrate 11 opposite to the infrared shielding layer 12.

Although the material of the base material 11 which forms the near-infrared shielding layer 12 is not specifically limited, A well-known plastic material can be used. In the infrared shielding application for windows, a transparent substrate is preferable.
Examples of the material of the substrate 11 include polyolefin (polyethylene, polypropylene, etc.), polyester (polyethylene naphthalate, polyethylene terephthalate, etc.), polyamide (nylon-6, nylon-66, etc.), polystyrene, ethylene vinyl alcohol, Polyvinyl chloride, polyimide, polyvinyl alcohol, polycarbonate, polyether sulfone, acrylic cellulose (triacetylyl cellulose, diacetyl cellulose, etc.) and the like can be mentioned.

  Although the film thickness of the base material 11 is not specifically limited, From the viewpoint of productivity, moldability, and operability during construction, the thickness of the base material 11 is preferably 5 μm or more and 1000 μm or less, and is 10 μm or more and 500 μm or less. Is more preferable.

  The surface of the substrate 11 on the side where the near-infrared shielding layer 12 is provided may be subjected to surface treatment, and a surface treatment layer may be provided as necessary. By performing the surface treatment, it is easy to perform coating on the base material, and adhesion between the base material 11 and the near-infrared shielding layer 12 can be improved. Examples of the surface treatment include corona treatment and plasma treatment.

  An adhesive layer may be provided for the purpose of improving the adhesion between the substrate 11 and the near-infrared shielding layer 12. Examples of the adhesive component used for forming the adhesive layer include adhesion of phenol resin, urea resin, melamine resin, polyvinyl resin, polyolefin resin, urethane resin, epoxy resin, acrylic resin, polyester resin, polyamide resin, polystyrene resin, etc. Resin. Among these, as the adhesive resin, it is preferable to use a polyvinyl resin, a polyolefin resin, or an acrylic resin from the viewpoint of good adhesion.

The configuration of the heat shield film is not particularly limited. For example, the near-infrared shielding layer 12 may not be a single layer and may be provided with a plurality of layers.
The infrared shielding layer 12 can be mixed with known additives for the purpose of improving moldability, suppressing deterioration, and improving the dispersibility of the infrared shielding material. For example, a heat stabilizer, a stabilizing aid, a plasticizer, an antioxidant, a light stabilizer, a flame retardant, a lubricant, and an antistatic agent may be included.

  In order to obtain scratch resistance, it is preferable to provide a hard coat layer 14 via an adhesive layer 13 on one side of the near infrared shielding layer 12. Although it does not specifically limit as a component of an contact bonding layer, The above-mentioned component can be used. The hard coat layer 14 is not particularly limited, and examples thereof include thermosetting or photocurable resins such as urethane resins, acrylic resins, silicone resins, and fluorine resins. Although it does not specifically limit, it is preferable that the thickness of a hard-coat layer is 0.5 micrometer or more and 100 micrometers or less. When the thickness of the hard coat layer is less than 0.5 μm, sufficient scratch resistance cannot be obtained, and when it is 100 μm or more, the transparency is liable to be lost, and the operability is deteriorated when being attached to a window.

It is preferable to provide the adhesive layer 15 on the surface of the substrate 11 opposite to the near infrared shielding layer 12. The adhesive layer can be attached to, for example, a building or a car window. The material used for the adhesive layer is not particularly limited. For example, a known resin can be used, and examples thereof include a urethane resin, an acrylic resin, a polyester resin, and a silicone resin. One or more of these can be used. The method for forming the adhesive layer is not particularly limited, but the adhesive layer can be formed by a known coating technique. For example, the support can be coated with an adhesive layer and bonded to the surface of the substrate opposite to the coating layer 12. As a bonding method, a known method such as dry lamination or heat lamination can be used.
The thickness of the adhesive layer is not particularly limited, but is preferably 0.05 μm or more and 20 μm or less. Within this range, the adhesiveness of the adhesive layer becomes good.

  Since the thermal barrier film of the present invention includes the porous body including the composite having the maximum absorbance at an arbitrary wavelength in the wavelength range of 700 nm to 1500 nm, the porous body has both heat insulating properties and thermal barrier properties, Useful as a thermal film.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  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. In the following examples, “%” indicates mass% (w / w%) unless otherwise specified.

<Preparation of composite of flat metal fine particles and fine cellulose fiber>
(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 the total amount of sodium hydroxide added reached 3.50 mmol / g based on the weight of cellulose, about 100 mL 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 carboxy group content in 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 carboxy groups (mmol / g) was determined by conductivity titration using a 0.5 M aqueous sodium hydroxide solution. The result was 1.6 mmol / g.

(Oxidized pulp defibration treatment)
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 refined cellulose fiber aqueous dispersion having a refined cellulose fiber concentration of 1%. The number average minor axis diameter of the refined cellulose fibers contained in the fine cellulose fiber aqueous dispersion was 4 nm, and the number average major axis diameter was 1110 nm. Moreover, when steady-state viscoelasticity measurement was performed using the rheometer, this refined cellulose fiber dispersion showed thixotropic properties.

(Preparation of silver nitrate aqueous solution)
A silver nitrate aqueous solution was prepared by dissolving 50 mg of silver nitrate in 10 mL of distilled water.

(Preparation of aqueous sodium borohydride solution)
Sodium borohydride 50mg was dissolved in distilled water 10mL, and sodium borohydride aqueous solution was prepared.

(Preparation of a composite of flat metal fine particles and refined cellulose)
While stirring 50 g of the above-mentioned 1% fine cellulose fiber aqueous dispersion at a constant temperature (15 ° C.), 0.5 mL of an aqueous silver nitrate solution was added. After stirring for 5 minutes, 2 mL of an aqueous sodium borohydride solution was added, and stirring was further continued for about 30 minutes to produce a composite of flat metal fine particles and fine cellulose fibers.

(Shape observation of complex of flat metal fine particles and fine cellulose)
The obtained composite of flat metal fine particles and refined cellulose was purified and fractionated under conditions of 75,600 g (30 minutes × 5 sets) using a high-speed cooling centrifuge. The purified flat metal fine particles were cast on a silicon wafer plate and subjected to platinum vapor deposition, and then observed from the vertical direction using a scanning electron microscope (“S-4800”, manufactured by Hitachi High-Tech). The results are shown in FIG. By performing simultaneous observation of the flat metal fine particles and the refined cellulose fibers, the mutual bonding state between the refined cellulose fibers and the flat metal fine particles was confirmed.

  A complex of purified flat metal fine particles and refined cellulose was cast on a PET film, and observed from a cross-sectional direction using a transmission electron microscope (manufactured by JEOL Ltd., “JEM2100F”). The results are shown in FIG. In addition, the particle thickness of the flat metal fine particles was calculated from the obtained image.

  A complex of refined planar metal fine particles and refined cellulose was cast on a silicon wafer plate, and SEM observation was performed without vapor deposition, followed by element mapping by energy dispersive X-ray analysis.

  The complex of flat metal fine particles and refined cellulose was observed using a scanning transmission electron microscope (“S-4800”, manufactured by Hitachi High-Tech Co., Ltd.). The results are shown in FIG. The diameter when the tabular silver nanoparticles in the obtained image were approximated by a circle was calculated as the particle diameter in the plane direction.

(Spectral absorption spectrum measurement of a composite of flat metal fine particles and refined cellulose)
An aqueous dispersion of a composite of flat metal fine particles and refined cellulose was placed in a quartz cell, and a spectrum was measured using a spectrophotometer (manufactured by Shimadzu Corporation, “UV-3600”). The results are shown in FIG.

FIG. 5 shows the observation result of the obtained composite by a scanning electron microscope (SEM), (a) is an SEM image, and (b) is a schematic diagram of (a).
As shown in FIG. 5 (a) and FIG. 5 (b), it was surprisingly confirmed that the finely divided cellulose fibers were bound to the tabular silver fine particles despite the fraction purification treatment by centrifugation. It was. Since there was no appearance of the micronized cellulose fiber alone in other parts of the silicon wafer, it was shown that the silver and the micronized cellulose fiber were completely bonded and inseparable. .

FIG. 6 is a diagram (TEM image) showing a result of observing the obtained composite from a cross-sectional direction with a transmission electron microscope (TEM).
As shown in FIG. 6, the shape of tabular silver viewed from the cross-sectional direction was a rectangle, and the length in the minor axis direction was about 10 nm. Therefore, tabular silver is a tabular grain having a thickness of about 10 nm. It turned out to be.

  Moreover, the result of elemental mapping by energy dispersive X-ray analysis showed that Ag and C were selectively contained in the fine particle portion observed in the SEM image (not shown). Together with the results of FIG. 5, the fine cellulose fibers penetrate into the inside of the flat silver nanoparticles to form a composite, and again the flat silver nanoparticles and the fine cellulose fibers are inseparable. Indicated.

FIG. 8 is a diagram showing a spectral transmission spectrum in a dispersion state of a composite of flat metal fine particles and fine cellulose fibers. As a measuring apparatus, UV-3600 manufactured by Shimadzu Corporation was used.
As shown in FIG. 8, it was confirmed from the measurement result of the spectral transmission spectrum that the absorption peak was 966 nm. That is, it was confirmed that it can be used as a near-infrared absorbing material.

  Hereinafter, a porous body using a composite of the produced tabular silver fine particles and fine cellulose fibers (hereinafter referred to as a near infrared absorption composite) will be described with reference to examples.

<Example 1>
(Preparation of porous material)
The aqueous dispersion of the near-infrared absorbing composite was applied onto a 25 μm thick polyethylene terephthalate (PET) film using a bar coater # 100, and the solvent was removed using supercritical drying using carbon dioxide. A laminate was formed.

(Specific surface area measurement of porous material)
The layer containing fine cellulose fibers was peeled from the laminate, and the specific surface area was measured by autosorb 1-MP (manufactured by Yuasa Ionics Co., Ltd.) by nitrogen adsorption BET method. The measurement results are shown in Table 1.

<Example 2>
After mixing t-butanol at a weight ratio of 10% with respect to the aqueous dispersion of the near-infrared absorbing composite, the mixed dispersion of the near-infrared absorbing composite is mixed with a polyethylene terephthalate (PET) film having a thickness of 25 μm. It was applied using a bar coater # 100, and the solvent was removed using a freeze drying method to form a laminate. About this laminated body, the specific surface area was measured by the method similar to Example 1. FIG.

<Example 3>
(Preparation of porous material)
An aqueous dispersion of the near-infrared absorbing composite was prepared to a pH of about 2 with 0.1 M hydrochloric acid to obtain a gel-like aggregate. The gel aggregate was washed 3 times with dilute hydrochloric acid having a pH of about 2, and then washed 3 times with distilled water.

Solvent substitution was performed using the gel-like aggregate acetone. Specifically, first, the gel-like aggregate was put into acetone, stirred for 30 minutes, and then the gel-like aggregate was filtered and collected using a glass filter. Further, the same operation was performed twice. Subsequently, using toluene as a substitution solvent, the solvent was substituted from acetone to toluene in the same procedure as described above.

  After further adding toluene to the gel-like aggregate to a solid content concentration of about 0.5%, a polyethylene glycol having a polymerization degree of 20 (PEG-modified product) having an amine group at the terminal and a phenyl group at the side chain is added to the gel-like aggregate. 1.0 equivalent was added to the amount of carboxyl groups in the coagulation pair, and the near-infrared absorbing complex was redispersed in toluene using an ultrasonic homogenizer.

  Polymethylphenylsilane (PMPS, Osaka Gas Chemical Co., Ltd.) was dissolved in toluene at a solid content of 2% to prepare a PMPS solution.

  While stirring the toluene dispersion of the near-infrared absorbing composite, the PMPS solution is added and mixed little by little until the mass ratio of the dispersion finally becomes 1: 1, so that the refined cellulose fibers and the PMPS are uniform. A dispersed mixed dispersion was prepared. That is, the fine cellulose fiber concentration in the final mixed dispersion was about 0.25%, and the concentration of PMPS was about 1%.

The mixed dispersion was coated on a polyethylene terephthalate (PET) film having a film thickness of 25 μm using a bar coater # 100, and dried in an oven at 80 ° C. for 5 minutes to form a laminate. About this laminated body, the specific surface area was measured by the method similar to Example 1. FIG.

<Comparative Example 1>
The aqueous dispersion of the near-infrared absorbing composite was applied onto a polyethylene terephthalate (PET) film having a film thickness of 25 μm using a bar coater # 100 and dried at 80 ° C. for 5 minutes to form a laminate. About this laminated body, the specific surface area was measured by the method similar to Example 1. FIG.

  As shown in Table 1, when the specific surface area was measured in Examples 1 to 3, it was confirmed that the voids were maintained by preventing the aggregation of the finely divided cellulose fibers, thereby forming a porous body. It was. In particular, Example 3 had a high specific surface area even though no special drying method such as freeze drying or supercritical drying was used. This is because the organic onium compound used in Example 3 does not contain an aryl group, so a π-π stacking structure is formed between the refined cellulose fibers and PMPS, and aggregation of the refined cellulose fibers is prevented and voids are formed. It is thought that this is because

  On the other hand, in Comparative Example 1, it was confirmed by specific surface area measurement that finely divided cellulose fibers aggregated to form a dense laminated film, and no porous body was formed. This is presumably because, in addition to using ordinary oven drying, it does not contain an aryl group or PMPS for forming a π-π stacking structure that inhibits aggregation of finely divided cellulose fibers.

Example 4
The laminate obtained in Example 3 was provided with a hard coat layer and an adhesive layer by the method shown below to produce a heat shielding film.

(Formation of hard coat layer)
The hard coat layer was diluted with pentaerythritol acrylate (PETA) having a solid content of 100% by mass using isopropyl alcohol (IPA) so that the solid content concentration of PETA was 50%. To this diluted solution, Irgacure (registered trademark) 184 (manufactured by BASF Japan Ltd.) as a photopolymerization initiator is added in an amount of 5 parts by mass with respect to 100 parts by mass of PETA to prepare a hard coat layer-forming coating material. The film was coated with a bar coater so as to be 6 μm. Further, a two-component curable polyurethane-based laminate adhesive (A525 / A52, manufactured by Mitsui Chemicals Polyurethane Co., Ltd.) was used to form an adhesive surface on the hard coat layer. The adhesive was applied by a gravure coating method so that the coating amount after drying was 3.0 g / m ² . The laminate including the hard coat layer thus obtained and the laminate obtained in Example 3 were bonded to each other through the porous body layer and the adhesive surface, and then the release film was removed.

(Formation of adhesive layer)
As a tellurium film (Toyochem Co., Ltd., BPS5296) was formed such that the adhesive layer was 10 μm, and was bonded to the opposite surface of the base coat or the hard coat layer of the infrared shielding composite composition.

The following experiment was performed using the laminated body provided with the said hard-coat layer and the adhesion layer as a heat-shielding film. In a room without air conditioning, the film is pasted in advance on a part of the inside of the south facing window, and the temperature at the window of the part where the film is pasted is measured at 2 pm on August 31, 2013 (outside temperature 36 ° C.). It was 30 degreeC as a result.

(Example 5)
The laminated body obtained in Example 2 was provided with a hard coat layer and an adhesive layer in the same manner as in Example 4 to produce a thermal barrier film. In a room without air conditioning, the film is pasted in advance on a part of the inside of the south facing window, and the temperature at the window of the part where the film is pasted is measured at 2 pm on August 31, 2013 (outside temperature 36 ° C.). As a result, it was 32 ° C.

(Comparative Example 2)
The laminated body obtained in Comparative Example 1 was provided with a hard coat layer and an adhesive layer in the same manner as in Example 4 to produce a heat shielding film. In a room without air conditioning, the film is pasted in advance on a part of the inside of the south facing window, and the temperature at the window of the part where the film is pasted is measured at 2 pm on August 31, 2013 (outside temperature 36 ° C.). It was 38 degreeC as a result.

  In Examples 4 and 5, since the temperature at the window was lower than the outside air temperature, the heat shielding effect was clearly shown. On the other hand, in Comparative Example 2, the result was that the temperature at the window was higher than the outside air temperature, despite using a composite of tabular silver fine particles and fine cellulose fibers as a near-infrared shielding material. This is because, in Comparative Example 2, the film itself generated heat due to the absorption of near infrared rays, and the film was not provided with heat insulation. On the other hand, in Examples 4 and 5, since the layer containing the composite forms a porous body, the heat generation of the film itself is suppressed, and the influence of the outside temperature is influenced by the heat insulation derived from the porous body. It is thought that it was cut off. Since the thermal barrier film of the present invention includes the porous body including the composite having the maximum absorbance at an arbitrary wavelength in the wavelength range of 700 nm to 1500 nm, the porous body has both heat insulating properties and thermal insulating properties, Useful as a film.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the porous body and thermal insulation film which contain the near-infrared shielding material obtained by the low environmental load and simple process using biomass material.

DESCRIPTION OF SYMBOLS 1 Composite 2 Flat metal fine particle (tabular silver fine particle)
3 Fine cellulose (fine cellulose fiber)
3a Part where micronized cellulose is taken into the inside of the flat metal fine particles 3b Part where micronized cellulose is exposed on the surface of the flat metal fine particles 11 Base material 12 Infrared shielding layer 13 Adhesive layer 14 Hard coat layer 15 Adhesive layer

Claims (22)

Each of the finely divided cellulose fibers includes a composite of finely divided cellulose fibers and flat metal fine particles, and at least a part or all of the finely divided cellulose fibers are taken into the flat metal fine particles, and the remainder is the flat metal fine particles. Exposed on the surface of
The flat metal fine particles are at least one kind of metal or a compound thereof,
The said refined cellulose fiber is arrange | positioned in the porous form, The porous body characterized by the above-mentioned. ^2. The porous body according to claim 1, wherein a specific surface area measured by a nitrogen adsorption BET method is 50 m ² / g or more.   The porous body according to claim 1 or 2, wherein the flat metal fine particles and the fine cellulose fibers are inseparable.   The porous body according to any one of claims 1 to 3, wherein the flat metal fine particles are silver.   The porous body according to any one of claims 1 to 4, wherein a particle diameter of the flat metal fine particles is twice or more a particle thickness of the flat metal fine particles.   The porous body according to any one of claims 1 to 5, wherein the refined cellulose fiber has a carboxy group on a fiber surface.   The porous body according to claim 6, wherein the content of the carboxy group is 0.1 mmol or more and 5.0 mmol or less per 1 g of cellulose.   The porous body according to any one of claims 1 to 7, wherein the crystal structure of the refined cellulose fiber is cellulose I type.   The number average minor axis diameter of the refined cellulose fiber is 1 nm or more and 100 nm or less, the number average major axis diameter of the refined cellulose fiber is 50 nm or more, and the number average major axis diameter is the number average minor axis diameter. The porous body according to any one of claims 1 to 8, wherein the porous body is 10 times or more. A step of preparing finely divided cellulose fibers;
A step of dispersing the finely divided cellulose fibers in a solvent to obtain a finely divided cellulose fiber dispersion;
Mixing the fine cellulose fiber dispersion and a solution containing metal ions to obtain a mixed solution;
Reducing the metal ions in the mixed solution to grow plate-like metal fine particles, and forming a composite of the plate-like metal fine particles and fine cellulose fibers;
Removing the solvent from the dispersion containing the composite and the refined cellulose fiber to form a porous body;
The manufacturing method of the porous body characterized by including. The method for producing a porous body according to claim 10, wherein the specific surface area of the porous body as measured by a nitrogen adsorption BET method is 50 m ² / g or more.   The method for producing a porous body according to claim 10 or 11, wherein the metal ions are silver ions.   The method for producing a porous body according to any one of claims 10 to 12, wherein a carboxy group is introduced into a crystal surface of the refined cellulose fiber in the step of preparing the refined cellulose fiber. .   The porous material according to claim 13, wherein an oxidation reaction using an N-oxyl compound is used in order to introduce a carboxy group into the fine cellulose fiber in the step of preparing the fine cellulose fiber. Body manufacturing method.   The porous body according to claim 13 or 14, wherein a carboxy group is introduced so as to be 0.1 mmol or more and 5.0 mmol or less per 1 g of dry weight of the finely divided cellulose fiber by the oxidation reaction. Production method.   The solvent is removed by a freeze-drying method in the step of forming the porous body by removing the solvent from the dispersion liquid containing the composite and the finely divided cellulose fibers. The manufacturing method of the porous body as described in a term.   The solvent is removed by a supercritical drying method using carbon dioxide in the step of forming a porous body by removing the solvent from the dispersion liquid containing the composite and the refined cellulose fiber. The manufacturing method of the porous body as described in any one of thru | or 15. In the step of forming a porous body by removing the solvent from the dispersion containing the composite and the refined cellulose fiber, a counter ion of a carboxy group present in the composite and the refined cellulose fiber contained in the dispersion is used. At least a portion is exchanged with an organic onium ion represented by the following general formula (1), and after further mixing polysilane (B) having a unit represented by the following general formula (2), the solvent is removed by drying. The method for producing a porous body according to any one of claims 10 to 15, wherein:

... (1)

In formula (1), M represents a nitrogen atom or a phosphorus atom, and R ¹ , R ² , R ³ and R ⁴ represent an aryl group, a hydrogen atom, a hydrocarbon group, a polyether or a hydrocarbon group containing a hetero atom. . However, at least one of R ¹ , R ² , R ³ and R ⁴ includes an aryl group in the structure.

... (2)

In formula (2), R ¹ and R ² are each independently an aryl group, hydrocarbon group, hydroxy group, alkoxy group, cycloalkyloxy group, aryloxy group, aralkyloxy group, amino group, silyl group, and halogen Selected from the group consisting of atoms. However, at least one of R ¹ and R ² is an aryl group.   A thermal barrier film comprising a base material and a coating layer containing the porous body according to any one of claims 1 to 9 on at least one surface of the base material.   The barrier according to claim 19, wherein the substrate comprises at least one of polyolefin, polyester, polyamide, polystyrene, ethylene vinyl alcohol, polyvinyl chloride, polyimide, polyvinyl alcohol, polycarbonate, polyethersulfone, and acrylic cellulose. Thermal film.   The hard coat layer laminated on the coating layer and the pressure-sensitive adhesive layer laminated on the surface of the substrate opposite to the surface on which the coating layer is formed. The heat-shielding film according to claim 1.   The heat-shielding film according to any one of claims 19 to 21, wherein the light transmittance in a wavelength region of 900 nm or more and 1000 nm or less is 70% or less.