Light-reflective material and method for manufacturing the same

Abstract

The present invention provides a light-reflecting material that enables the reflection of light using polysaccharides and / or derivatives thereof. [Solution] The light-reflecting material according to the embodiment has an alternating laminated structure in which at least two types of polysaccharide layers with different refractive indices are alternately laminated, and the refractive index difference between adjacent polysaccharide layers is 0.04 or more and 0.5 or less.

Description

[Technical Field]

[0001] The present invention relates to a light-reflective material and a method for producing the same. [Background technology]

[0002] Light-reflective materials having an alternating laminated structure of low-refractive-index layers and high-refractive-index layers are known. For example, Patent Document 1 discloses a light-reflective material (optical reflective film) that includes a laminate of low-refractive-index layers and high-refractive-index layers on a substrate, in which the refractive index layer closest to the substrate contains cellulose nanofibers. In the light-reflective material described in Patent Document 1, the low-refractive-index layer and the high-refractive-index layer contain inorganic oxide particles as a refractive index adjusting material along with a water-soluble polymer, and further contain cellulose nanofibers as a reinforcing material to prevent delamination between layers. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-075816 [Overview of the project] [Problems that the invention aims to solve]

[0004] Conventional light-reflecting materials generally incorporate inorganic oxide particles to adjust the refractive index of each layer, and it was not known that polysaccharides and / or their derivatives could be used as refractive index adjusting materials to construct light-reflecting materials.

[0005] Embodiments of the present invention aim to provide a light-reflecting material that is capable of reflecting light using polysaccharides and / or derivatives thereof. [Means for solving the problem]

[0006] The present invention includes embodiments shown below. [1] A light-reflecting material having an alternating laminated structure in which at least two polysaccharide layers with different refractive indices are alternately stacked, the polysaccharide layer containing polysaccharides and / or derivatives thereof as refractive index adjusting materials, wherein the refractive index difference between adjacent polysaccharide layers is 0.04 or more and 0.5 or less. [2] The light-reflecting material according to [1], wherein the content of the polysaccharide and / or derivative thereof in each of the polysaccharide layers is more than 85% by mass. [3] A light-reflective material having an alternating laminated structure in which at least two polysaccharide layers with different refractive indices are alternately stacked, wherein the refractive index difference between adjacent polysaccharide layers is 0.04 or more and 0.5 or less. [4] The density difference between adjacent polysaccharide layers is 0.01 g / cm³ 3 More than 1.6g / cm 3 The following are light-reflective materials as described in any one of items [1] to [3] below. [5] The light-reflecting material according to any one of the [1] to [4], wherein at least one of the at least two polysaccharide layers is a dry gel layer. [6] The light-reflecting material according to any one of [1] to [5], wherein each of the polysaccharide layers substantially contains inorganic oxide particles. [7] The light-reflecting material according to any one of [1] to [6], wherein the polysaccharide and / or derivative thereof contained in at least one of the at least two polysaccharide layers is cellulose and / or a derivative thereof. [8] The light-reflective material according to [7], wherein the cellulose and / or derivative thereof is cellulose nanofiber. [9] The light-reflecting material according to any one of [1] to [8], wherein the at least two polysaccharide layers consist of a first polysaccharide layer having a first refractive index and a second polysaccharide layer having a second refractive index, the alternating stacked structure is an alternating stacked structure of the first polysaccharide layer and the second polysaccharide layer, and the difference between the first refractive index and the second refractive index is 0.04 or more and 0.5 or less.

[10] A light-reflecting material described in any one of the items [1] to [9], which is a structural color-exhibiting material.

[0007]

[11] A step comprising electrodeposition using an aqueous solution or aqueous dispersion containing a first polysaccharide and / or a derivative thereof, the first step of forming a first polysaccharide layer containing the first polysaccharide and / or a derivative thereof. A step comprising performing electrodeposition using an aqueous solution or aqueous dispersion containing a second polysaccharide and / or its derivative, the second step of forming a second polysaccharide layer containing the second polysaccharide and / or its derivative, A third step in which an alternating layered structure of the first polysaccharide layer and the second polysaccharide layer is formed, A method for producing a light-reflective material, including A method for manufacturing a light-reflective material, wherein the difference in refractive index between the first polysaccharide layer and the second polysaccharide layer is 0.04 or more and 0.5 or less.

[12] In the first step, the first polysaccharide layer is formed as a hydrogel layer by electrodeposition using an aqueous solution or aqueous dispersion containing the first polysaccharide and / or its derivative, In the second step, the second polysaccharide layer is formed on the first polysaccharide layer as a hydrogel layer by electrodeposition using an aqueous solution or aqueous dispersion containing the second polysaccharide and / or its derivative. A method for producing a light-reflective material according to

[11] , wherein in the third step, the first step and the second step are repeated alternately to form an alternating laminated structure of the first polysaccharide layer, which is a hydrogel layer, and the second polysaccharide layer, which is a hydrogel layer.

[13] A method for producing a light-reflective material according to

[12] , further comprising: a fourth step of solvent replacement of the first polysaccharide layer and the second polysaccharide layer with an organic solvent after the third step to form an organogel layer; and a fifth step of drying the organogel layer to form the first polysaccharide layer and the second polysaccharide layer into a dry gel layer. [Effects of the Invention]

[0008] In the above embodiment, it is possible to provide a light-reflecting material that can reflect light using polysaccharides and / or derivatives thereof. [Brief explanation of the drawing]

[0009] [Figure 1] Cross-sectional schematic view of a light reflection material according to an embodiment [Figure 2] Process schematic diagram for explaining a method for manufacturing a light reflection material according to an embodiment [Figure 3] Partially enlarged cross-sectional SEM image of the light reflection material of Example 3 [Figure 4] Wavelength-specular reflectance graph for showing the reflection performance of the light reflection materials of Examples 7 to 9

Mode for Carrying Out the Invention

[0010] The light reflection material according to the present embodiment has an alternating laminated structure formed by alternately laminating at least two types of polysaccharide layers having different refractive indexes. And, in one embodiment, the polysaccharide layer contains a polysaccharide and / or its derivative as a refractive index adjusting material. Alternatively, the polysaccharide layer may contain more than 85% by mass of a polysaccharide and / or its derivative. Here, "containing as a refractive index adjusting material" means being contained in a mode capable of adjusting the refractive index of the polysaccharide layer due to the difference in the substance itself (the type of polysaccharide or its derivative) or its density (apparent density including voids). As long as there is a difference in the refractive index of the polysaccharide layer, it may be contained in a mode having other functions or purposes.

[0011] Examples of polysaccharides include cellulose, chitin, chitosan, pectin, alginic acid, agar, xanthan gum, gellan gum, and konjac mannan. Examples of polysaccharide derivatives include cellulose ethers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, and hydroxyethylcellulose, cellulose derivatives such as modified cellulose nanofibers, modified starches such as cationized starch and glyceryl starch, and alginic acid esters such as sodium alginate sulfate and siloxanetriol alginate. Any one of these may be used, or two or more may be used in combination. As polysaccharides and / or derivatives thereof, water-soluble ones such as pectin and alginic acid (specifically alginates such as sodium alginate) may be used, or water-insoluble (water-dispersible) ones such as cellulose nanofibers may be used, or both may be used in combination.

[0012] Examples of modified cellulose nanofibers include anionic modified cellulose nanofibers such as carboxyl group-containing cellulose nanofibers (e.g., oxidized cellulose nanofibers, carboxymethylated cellulose nanofibers), sulfated cellulose nanofibers, sulfonated cellulose nanofibers, and phosphorylated cellulose nanofibers.

[0013] When forming a polysaccharide layer by electrodeposition, the polysaccharide and / or derivative thereof is charged. Examples of such polysaccharides and / or derivatives include negatively charged polysaccharides such as pectin, alginic acid, xanthan gum, gellan gum, carboxymethylcellulose, and anionically modified cellulose nanofibers. Examples of positively charged polysaccharides include chitosan and cationized starch.

[0014] The polysaccharides and / or derivatives contained in at least one of the two polysaccharide layers described above are preferably cellulose and / or derivatives thereof. More preferably, the polysaccharides and / or derivatives contained in at least one of the polysaccharide layers described above are cellulose nanofibers. The cellulose nanofibers may be unmodified cellulose nanofibers that have not been chemically modified, but the modified cellulose nanofibers described above are preferred.

[0015] The number-average fiber diameter of cellulose nanofibers is not particularly limited, but is preferably 1 to 500 nm, more preferably 1 to 100 nm, more preferably 2 to 50 nm, more preferably 3 to 30 nm, and still more preferably 3 to 10 nm.

[0016] The average aspect ratio (number-average fiber length / number-average fiber diameter) of cellulose nanofibers is not particularly limited and may be, for example, 4-5000, 10-1000, 20-500, or 100-300.

[0017] Here, the number-average fiber diameter and average aspect ratio can be measured as follows. Specifically, an aqueous dispersion of cellulose nanofibers with a solid content of 0.05 to 0.1 mass% is prepared, and this aqueous dispersion is cast onto a hydrophilically treated carbon film coated grid to be used as a sample for transmission electron microscopy (TEM) observation. If the sample contains fibers with a large fiber diameter, a scanning electron microscope (SEM) image of the surface cast on glass may be observed. The observation sample may also be negatively stained with, for example, 2 mass% uranyl acetate. Then, observation of the electron microscope image is performed at a magnification of 5000x, 10000x, or 50000x depending on the size of the constituent fibers. At that time, an axis of arbitrary image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect with that axis. After obtaining observation images that satisfy these conditions, two random axes are drawn vertically and horizontally for each image, and the fiber diameters of the fibers intersecting the axes are visually read. In this way, at least three non-overlapping surface images are taken with an electron microscope, and the fiber diameter values ​​of the fibers intersecting the two axes in each image are read (therefore, information on the fiber diameters of at least 20 × 2 × 3 = 120 fibers is obtained). The arithmetic mean of the fiber diameters obtained in this way is defined as the number-mean fiber diameter.

[0018] Furthermore, the number-average fiber length of cellulose nanofibers is calculated from similar observation images. Specifically, the length from the start to the end of at least 10 fibers (fiber length) is visually read. For branched fibers, the length of the longest part of the branch is used as the fiber length. The arithmetic mean of the fiber lengths obtained in this way is calculated and used as the number-average fiber length. Using these values, the average aspect ratio is calculated according to the following formula. Average aspect ratio = Number-average fiber length (nm) / Number-average fiber diameter (nm)

[0019] In anionic cellulose nanofibers, a preferred example of cellulose nanofibers, the amount of anionic functional groups is not particularly limited. For example, it may be 0.5 to 3.0 mmol / g per dry mass of the cellulose nanofiber, more preferably 1.0 to 3.0 mmol / g, and even more preferably 1.5 to 2.5 mmol / g. Depending on the amount of anionic functional groups, differences in the refractive index of the polysaccharide layer can be created by solvent substitution, as described later.

[0020] The amount of anionic functional groups is measured as follows. For example, in the case of carboxyl groups, 60 mL of a cellulose nanofiber aqueous dispersion prepared to a concentration of 0.1 to 1% by mass is diluted to a pH of approximately 2.5 with a 0.1 mol / L hydrochloric acid aqueous solution, and then a 0.05 mol / L sodium hydroxide aqueous solution is added dropwise. The electrical conductivity is measured and continued until the pH reaches approximately 11. The amount of sodium hydroxide consumed in the neutralization stage of the weak acid, where the change in electrical conductivity is gradual, can be used to determine the amount of anionic functional groups according to the following formula. Phosphate groups can also be measured by a similar electrical conductivity measurement. Other anionic functional groups can be measured by known methods. In this specification, "dry mass" refers to the mass after drying at 140°C until the rate of mass change per minute is 0.05% or less. Anionic functional group content (mmol / g) = V (mL) × [0.05 / cellulose nanofiber mass (g)]

[0021] The polysaccharide layer contains polysaccharides and / or derivatives thereof, preferably having polysaccharides and / or derivatives as its main component, and more preferably containing more than 85% by mass of polysaccharides and / or derivatives. That is, it is preferable that the content of polysaccharides and / or derivatives in each polysaccharide layer is greater than 85% by mass. It is preferable that the content of polysaccharides and / or derivatives in each polysaccharide layer is greater than 90% by mass, more preferably 95% by mass or more, and may be 100% by mass. Here, the content of polysaccharides and / or derivatives refers to the content of either polysaccharides or polysaccharide derivatives if only one is included, and the total amount of both if both polysaccharides and polysaccharide derivatives are included.

[0022] The light-reflective material has an alternating layered structure (multilayer structure) in which at least two types of polysaccharide layers with different refractive indices are alternately stacked. There may be two types of polysaccharide layers, or three or more types. In the case of three or more types, the three or more polysaccharide layers are stacked alternately such that adjacent polysaccharide layers are of different types.

[0023] In the alternating layered structure described above, the refractive index difference between adjacent polysaccharide layers is 0.04 to 0.5. A refractive index difference of 0.04 or greater allows for light reflection, and structural color can be exhibited, for example, when reflecting visible light. A larger refractive index difference between adjacent polysaccharide layers is preferable, preferably 0.07 to 0.49, more preferably 0.09 to 0.48, and even more preferably 0.15 to 0.46. Furthermore, when the alternating layered structure consists of three or more types of polysaccharide layers, it is preferable that the refractive index difference between all adjacent polysaccharide layers is 0.04 to 0.5.

[0024] The refractive index of each polysaccharide layer is not particularly limited as long as the refractive index difference between adjacent polysaccharide layers is within the above range; for example, it may be 1.050 to 1.650 or 1.100 to 1.600.

[0025] In this specification, the refractive index of the polysaccharide layer is a value obtained by dividing the speed of light in a vacuum by the speed of light in the substance (more precisely, the phase velocity) for light with a wavelength of 589.3 nm (sodium D line). Specifically, it is determined by the method described in the Examples section.

[0026] In the above alternating laminate structure, the thickness of each polysaccharide layer is not particularly limited and can be, for example, 10 to 1000 nm, preferably 30 to 700 nm, more preferably 50 to 500 nm, still more preferably 70 to 300 nm, and even more preferably 80 to 200 nm.

[0027] In the above alternating laminate structure, the total number of polysaccharide layers is not particularly limited, but is preferably 10 to 10000 layers, more preferably 20 to 1000 layers, still more preferably 30 to 500 layers, and even more preferably 50 to 300 layers.

[0028] The thickness of the above alternating laminate structure is not particularly limited, but is preferably 1 to 1000 μm, more preferably 2 to 300 μm, still more preferably 3 to 100 μm, and even more preferably 5 to 50 μm.

[0029] In the above alternating laminate structure, the density difference between adjacent polysaccharide layers is preferably 0.01 to 1.6 g / cm 3 . When the density difference is 0.01 g / cm 3 or more, it becomes easier to increase the refractive index difference between adjacent polysaccharide layers and easier to reflect light. The greater the density difference between adjacent polysaccharide layers, the more preferable it is, and the density difference is preferably 0.1 to 1.5 g / cm 3 , more preferably 0.2 to 1.5 g / cm 3 , and even more preferably 0.5 to 1.3 g / cm 3 .

[0030] The density of each polysaccharide layer is not particularly limited and can be, for example, 0.10 to 1.50 g / cm 3 , or 0.12 to 1.45 g / cm 3 .

[0031] In this specification, the density of the polysaccharide layer is the apparent density of the polysaccharide layer, and is specifically determined by the method described in the Examples section.

[0032] In the above alternating layered structure, it is preferable that at least one of the at least two polysaccharide layers is a dry gel layer. A dry gel layer refers to a layer of dry gel that has lost its dispersion medium by drying from a wet gel such as a hydrogel or organogel. Dry gels also include xerogels and aerogels, which have a porous structure with voids formed by the loss of the dispersion medium. Therefore, it is preferable that the at least one of the polysaccharide layers is a porous layer containing polysaccharides and / or their derivatives.

[0033] Each polysaccharide layer constituting the alternating layered structure described above may contain inorganic oxide particles, but in one embodiment, it is preferable that each polysaccharide layer substantially does not contain inorganic oxide particles. In this embodiment, since polysaccharides and / or their derivatives are used as refractive index adjusting materials, inorganic oxide particles, which are conventionally used as refractive index adjusting materials, do not need to be included, and differences in refractive index can be provided even without the presence of inorganic oxide particles. Here, substantially free of inorganic oxide particles means that the content of inorganic oxide particles in each polysaccharide layer is less than 10% by mass, preferably less than 5% by mass, more preferably less than 2% by mass, and even more preferably no inorganic oxide particles at all.

[0034] Specific examples of inorganic oxide particles include silica, zinc oxide, alumina, titanium oxide, zirconium oxide, niobium oxide, europium oxide, and zircon.

[0035] In one embodiment, it is preferable that the above-mentioned at least two polysaccharide layers consist of a first polysaccharide layer having a first refractive index and a second polysaccharide layer having a second refractive index. That is, as shown in Figure 1, the light-reflecting material 10 according to the preferred embodiment includes a first polysaccharide layer 12 having a first refractive index and a second polysaccharide layer 14 having a second refractive index, and has an alternating laminated structure in which the first polysaccharide layer 12 and the second polysaccharide layer 14 are alternately laminated, with the difference between the first refractive index and the second refractive index being 0.04 to 0.5.

[0036] In this case, the difference between the first refractive index and the second refractive index is preferably 0.07 to 0.49, more preferably 0.09 to 0.48, and even more preferably 0.15 to 0.46. The respective values ​​of the first refractive index and the second refractive index are not particularly limited as long as the difference between them is within the above range of 0.04 to 0.5, for example, they may be 1.050 to 1.650 or 1.100 to 1.600. Here, the first refractive index may be greater than or less than the second refractive index.

[0037] The density difference between the first polysaccharide layer and the second polysaccharide layer is 0.01 to 1.6 g / cm³. 3 Preferably, and more preferably, 0.1 to 1.5 g / cm³. 3 More preferably 0.2 to 1.5 g / cm³ 3 And more preferably 0.5 to 1.3 g / cm³ 3 The density of the first polysaccharide layer and the second polysaccharide layer are not particularly limited, for example, 0.10 to 1.50 g / cm³. 3 However, often it is 0.12~1.45 g / cm³. 3 But that's fine too. Here, the density of the first polysaccharide layer may be greater than or less than the density of the second polysaccharide layer.

[0038] The thickness of each layer of the first polysaccharide layer and the second polysaccharide layer, and the total number of layers of the first and second polysaccharide layers, are as described above.

[0039] The following combinations are preferred embodiments of the polysaccharides and / or derivatives contained in the first polysaccharide layer and the second polysaccharide layer.

[0040] (A) An embodiment in which either the first polysaccharide layer or the second polysaccharide layer contains a water-insoluble polysaccharide or a derivative thereof (e.g., cellulose nanofiber, more preferably anionic cellulose nanofiber, etc.), and the other contains a water-soluble polysaccharide or a derivative thereof (e.g., pectin, alginic acid, etc.).

[0041] (B) An embodiment in which both the first polysaccharide layer and the second polysaccharide layer contain water-insoluble polysaccharides or derivatives thereof (e.g., cellulose nanofibers, more preferably anionic cellulose nanofibers).

[0042] (C) An embodiment in which both the first polysaccharide layer and the second polysaccharide layer contain water-soluble polysaccharides or derivatives thereof (e.g., pectin, alginic acid, etc.).

[0043] In the embodiments (A) to (C) above, the first polysaccharide layer and the second polysaccharide layer may be a dry gel layer having a porous structure on one side and a non-porous layer without a porous structure on the other. Alternatively, both the first polysaccharide layer and the second polysaccharide layer may be dry gel layers having a porous structure. Alternatively, both the first polysaccharide layer and the second polysaccharide layer may be non-porous layers without a porous structure. For example, in the embodiment (A) above, both the first polysaccharide layer and the second polysaccharide layer may be dry gel layers having a porous structure, or both the first polysaccharide layer and the second polysaccharide layer may be non-porous layers without a porous structure. Alternatively, in the embodiment (B) above, both the first polysaccharide layer and the second polysaccharide layer may be dry gel layers having a porous structure, or either the first polysaccharide layer or the second polysaccharide layer may be a dry gel layer having a porous structure, or the other may be a non-porous layer without a porous structure. Alternatively, in the embodiment of (C) above, both the first polysaccharide layer and the second polysaccharide layer may be a dry gel layer having a porous structure. In this specification, a non-porous layer refers to a layer that does not have voids formed by the loss of the dispersion medium, in contrast to a dry gel layer having a porous structure.

[0044] The method for manufacturing the light-reflective material according to this embodiment is not particularly limited. In one embodiment, the light-reflective material can be manufactured by a method comprising the following steps 1 to 3. (Step 1) A step comprising performing electrodeposition using an aqueous solution or aqueous dispersion containing a first polysaccharide and / or its derivative, wherein a first polysaccharide layer containing the first polysaccharide and / or its derivative is formed. (Step 2) A step comprising performing electrodeposition using an aqueous solution or aqueous dispersion containing a second polysaccharide and / or its derivative, wherein a second polysaccharide layer containing the second polysaccharide and / or its derivative is formed. (Step 3) Step to form an alternating layered structure of the first polysaccharide layer and the second polysaccharide layer.

[0045] In this case, a light-reflective material may be produced by alternately stacking a first polysaccharide layer or a second polysaccharide layer film in steps 1 and 2, and then laminating these films together by pressing or other means in step 3. More specifically, for example, in step 1, a porous or non-porous first polysaccharide layer film is produced by drying or other means using a hydrogel layer formed by electrodeposition. Also, in step 2, a porous or non-porous second polysaccharide layer film is produced by drying or other means using a hydrogel layer formed by electrodeposition. Then, in step 3, the first polysaccharide layer film and the second polysaccharide layer film are alternately stacked and laminated together by hot pressing or other means to produce a light-reflective material.

[0046] Preferably, in step 1, the first polysaccharide layer may be formed as a hydrogel layer by electrodeposition using an aqueous solution or aqueous dispersion containing the first polysaccharide and / or its derivative. Alternatively, in step 2, the second polysaccharide layer may be formed as a hydrogel layer on the first polysaccharide layer by electrodeposition using an aqueous solution or aqueous dispersion containing the second polysaccharide and / or its derivative. Then, in step 3, by alternately repeating steps 1 and 2, an alternating layered structure of the first polysaccharide layer (which is a hydrogel layer) and the second polysaccharide layer (which is a hydrogel layer) may be formed by electrodeposition. In this case, it is preferable to further perform steps 4 and 5 described below.

[0047] (Step 4) After Step 3, the first polysaccharide layer and the second polysaccharide layer are solvent-substituted with an organic solvent to form an organogel layer. (Step 5) A step to dry the organogel layer to form the first polysaccharide layer and the second polysaccharide layer into a dried gel layer.

[0048] Alternatively, instead of performing steps 4 and 5, the alternating layered structure of the hydrogel layers obtained in step 3 may be dried as is (for example, by hot-press drying) to produce a light-reflective material in which the first polysaccharide layer and the second polysaccharide layer are alternately layered.

[0049] In steps 1 and 2, electrodeposition refers to the process by which substances deposited in the electrolyte by electrolysis adhere to the surface of the electrodes. Forming a polysaccharide layer using electrodeposition is advantageous for creating a thin, uniform polysaccharide layer. For electrodeposition, polysaccharides and / or derivatives that have an electric charge as described above are used. In steps 1 and 2, if the polysaccharide and / or derivative is water-soluble, an aqueous solution is used as the electrolyte; if the polysaccharide and / or derivative is water-insoluble, an aqueous dispersion is used as the electrolyte. The concentration of polysaccharide and / or derivative in these aqueous solutions or aqueous dispersions is not particularly limited and may be, for example, 0.01 to 10% by mass or 0.1 to 1% by mass.

[0050] The current application conditions in electrodeposition are not particularly limited and can be adjusted as appropriate depending on the thickness of the polysaccharide layer to be formed. For example, the applied voltage may be 0.1 to 200V or 1 to 40V. The current density may be 0.001 to 1000 A / m². 2 However, often, 0.1~100A / m 2 However, this is also acceptable. The energizing time can be 0.0001 to 1000 minutes, or 0.01 to 10 minutes.

[0051] In step 4, solvent substitution can be performed to adjust the refractive indices of the first and second polysaccharide layers. For example, when water-dispersible polysaccharides such as cellulose nanofibers, chitin nanofibers, and chitosan nanofibers are used as the polysaccharide, the refractive index of the polysaccharide layer obtained by drying after solvent substitution is significantly smaller than that of the polysaccharide layer obtained by drying without solvent substitution. In contrast, when water-soluble polysaccharides such as pectin are used as the polysaccharide, the difference in refractive index of the polysaccharide layer obtained after drying is small depending on whether solvent substitution is performed or not. By utilizing this point, the refractive index difference between the first and second polysaccharide layers can be increased by solvent substitution.

[0052] Examples of organic solvents used for solvent substitution in step 4 include C1-C4 alcohols such as ethanol, isopropyl alcohol, methanol, and t-butyl alcohol, C5-C8 alkanes such as pentane and hexane, ketones such as acetone, and perfluorocarbons. Any one of these may be used, or two or more may be used in combination.

[0053] The conditions for solvent replacement are not particularly limited and can be carried out, for example, by immersion in an organic solvent at 0 to 80°C for 1 to 720 minutes.

[0054] The drying method in step 5 is not particularly limited and can be carried out by hot press drying, for example. The conditions for hot press drying are not particularly limited and can be carried out by, for example, a temperature of 23 to 200°C, a pressure of 0.1 to 5 MPa, and a time of 0.1 to 60 minutes.

[0055] An example of a manufacturing method including steps 1 to 5 described above as a preferred embodiment will be explained with reference to Figure 2. Here, the case in which both the first polysaccharide and / or its derivative (hereinafter simply referred to as the first polysaccharide) and the second polysaccharide and / or its derivative (hereinafter simply referred to as the second polysaccharide) have a negative charge will be described, but the same method can be carried out with both having a positive charge, or with one having a positive charge and the other a negative charge, by appropriately changing the electrodes during electrodeposition.

[0056] As shown in Figure 2, in (1), an aqueous solution or aqueous dispersion of the first polysaccharide is placed in an electrolytic cell as the electrolyte. The anode and cathode are immersed in the electrolyte, and electrodeposition is performed by applying a voltage. By electrodeposition, a hydrogel layer of the first polysaccharide is formed on the anode (substrate).

[0057] Next, in (2), an aqueous solution or aqueous dispersion of the second polysaccharide is placed in an electrolytic cell as the electrolyte. Preferably, the aqueous solution or aqueous dispersion of the second polysaccharide is placed in an electrolytic cell separate from the one in (1), the cathode is immersed in the electrolyte, and the anode on which the hydrogel layer of the first polysaccharide was formed in (1) is immersed in the electrolyte. Then, by applying a voltage, the second polysaccharide is electrodeposited. By electrodeposition, a hydrogel layer of the second polysaccharide is formed on the hydrogel layer of the first polysaccharide.

[0058] Next, in (3), the electrodeposition in (1) and the electrodeposition in (2) are repeated. Specifically, the anode on which the hydrogel layer of the second polysaccharide was formed in (2) is immersed in the electrolyte of the electrolytic cell used in (1), and a voltage is applied to perform electrodeposition of the first polysaccharide, thereby forming a hydrogel layer of the first polysaccharide on the hydrogel layer of the second polysaccharide. Next, the anode on which the hydrogel layer of the first polysaccharide was formed is immersed in the electrolyte of the electrolytic cell used in (2), and a voltage is applied to perform electrodeposition of the second polysaccharide, thereby forming a hydrogel layer of the second polysaccharide on the hydrogel layer of the first polysaccharide. By repeating the electrodeposition in (1) and the electrodeposition in (2) a predetermined number of times, an alternating layered structure of the first polysaccharide layer, which is a hydrogel layer, and the second polysaccharide layer, which is a hydrogel layer, is formed.

[0059] Next, in (4), the anode forming the alternating layered structure obtained in (3) above is immersed in an organic solvent. As a result, the solvent in the first polysaccharide layer and the second polysaccharide layer constituting the alternating layered structure is replaced from water to an organic solvent, forming an organogel layer. That is, an alternating layered structure of the first polysaccharide layer, which is an organogel layer, and the second polysaccharide layer, which is an organogel layer, is obtained.

[0060] Subsequently, in (5), by drying the organogel layers with the alternating layered structure described above, the first polysaccharide layer and the second polysaccharide layer become dried gel layers, and a light-reflective material having an alternating layered structure of the first polysaccharide layer and the second polysaccharide layer is obtained. Drying of the multilayer gel having an alternating layered structure of organogel layers can be performed, for example, by hot press drying, and a light-reflective material having an alternating layered structure of dried gel layers is obtained.

[0061] The shape of the light-reflective material according to this embodiment is not particularly limited, but it is usually in the form of a film. Therefore, it can also be called a light-reflective film. The light-reflective material may also be in the form of flakes obtained by finely cutting a film, for example, and its shape is not particularly limited.

[0062] Light-reflective materials are materials that can reflect light, and the light can be visible light, ultraviolet light, or infrared light, and may also be materials that can reflect light across multiple wavelength ranges. When reflecting visible light, light-reflective materials can exhibit structural color, and are therefore also called structural color-exhibiting materials. Here, structural color refers to a coloration phenomenon that originates from spectroscopy due to microstructures at or below the wavelength of light, and the material itself has no color, but exhibits color due to microstructures on the order of the wavelength of light.

[0063] In one embodiment, the light-reflecting material preferably has a maximum specular reflectance of 50% or more in the wavelength range of 400 to 800 nm, more preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The method for measuring the maximum specular reflectance is as described in the Examples section.

[0064] Applications of the light-reflective material according to this embodiment include decorative applications such as foil stamping (e.g., holographic processing of paper), paints, cosmetics, and food (e.g., edible glitter). In this case, since the light-reflective material can be composed only of biodegradable materials such as natural products, it can be made biodegradable and ecological (sustainable). Furthermore, since it can be composed only of materials approved as food additives, it is also suitable for edible applications as edible glitter. It can also be used in applications where it is incorporated into paints and cosmetics, applied, and dried to produce color.

[0065] Furthermore, by changing the thickness of the light-reflective material, the reflected wavelength can be controlled. For example, applications include sensors that reflect light of a specific wavelength, and heat shielding and radiative cooling applications that block light of a specific wavelength. Alternatively, applications such as anti-counterfeiting (watermarking) are also possible. [Examples]

[0066] The present invention will be described in more detail below with reference to examples, but it is not limited to these.

[0067] <Preparation of Cellulose Nanofibers> [Manufacturing Example 1] To 2.0 g of coniferous kraft pulp, 150 mL of water, 0.25 g of sodium bromide, and 0.025 g of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) were added and thoroughly stirred. Then, a 13% by mass sodium hypochlorite aqueous solution was added so that the amount of sodium hypochlorite was 8.0 mmol / g per 1.0 g of pulp, and the reaction was started. The reaction was then continued for 120 minutes while adding a 0.5 N sodium hydroxide aqueous solution dropwise to maintain the pH at 10-11. After the reaction, 0.1 N hydrochloric acid was added to adjust the pH to 2.0, and solid-liquid separation was performed by suction filtration. Pure water was then added to the solids to prepare a slurry with a solid content of 2.0% by mass.

[0068] Subsequently, the pH of the slurry was adjusted to 10 with a 10% by mass sodium hydroxide aqueous solution, and sodium borohydride was added at a rate of 0.2 mmol / g relative to the cellulose fibers and the mixture was reduced by reacting for 2 hours. After the reaction, 0.1N hydrochloric acid was added to neutralize the mixture, and the product was purified by repeated filtration and washing with water. Pure water was added to the resulting purified product to prepare a slurry with a solid content of 2.0% by mass, and then the pH was adjusted to 7 with a 10% by mass sodium hydroxide aqueous solution.

[0069] Subsequently, a microfluidizer treatment (150 MPa, 1 pass) was performed as a micronization process to obtain an aqueous dispersion of cellulose nanofiber 1 with a concentration of 2.0 mass%. The obtained cellulose nanofiber 1 was TEMPO-oxidized cellulose nanofiber with a carboxyl group content of 2.0 mmol / g, a number-average fiber diameter of 3.2 nm, a number-average fiber length of 840 nm, and an average aspect ratio of 263.

[0070] [Manufacturing Example 2] Except for adding 4 mmol / g of sodium hypochlorite aqueous solution per 1.0 g of the pulp, and setting the microfluidizer treatment conditions in the micronization process to 150 MPa and 2 passes, an aqueous dispersion of cellulose nanofiber 2 with a concentration of 2.0% by mass was obtained in accordance with the preparation method for cellulose nanofiber 1. The obtained cellulose nanofiber 2 was TEMPO-oxidized cellulose nanofiber with a carboxyl group content of 1.6 mmol / g, a number-average fiber diameter of 4.8 nm, a number-average fiber length of 670 nm, and an average aspect ratio of 140.

[0071] [Example 1] (Process 1) A 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1 was diluted to prepare a 0.2% by mass aqueous dispersion of cellulose nanofiber. Using the obtained aqueous dispersion as the electrolyte, a 1 μm thick hydrogel layer of cellulose nanofiber 1 was prepared on a copper electrode acting as the anode by electrodeposition (applied voltage: 40V, Keysight "B2902A"). The prepared hydrogel layer of cellulose nanofiber 1 was solvent-purged with ethanol and then subjected to supercritical drying (Yamayu Gijutsu Co., Ltd. "SYGLCP-81", temperature 40°C, pressure 10 MPa). The resulting dried material was pressed at 1 MPa to obtain an aerogel film of cellulose nanofiber 1 with a thickness of approximately 100 nm.

[0072] (Process 2) A 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1 was diluted to prepare a 0.2% by mass aqueous dispersion of cellulose nanofiber. Using the obtained aqueous dispersion as the electrolyte, electrodeposition (applied voltage: 40V, Keysight "B2902A") was performed to prepare a 10 μm thick hydrogel layer of cellulose nanofiber 1 on a copper electrode, which served as the anode. The prepared hydrogel layer of cellulose nanofiber 1 was dried at atmospheric pressure at 25°C and 50% RH to obtain a non-porous film of cellulose nanofiber 1 with a thickness of approximately 100 nm.

[0073] (Step 3) A film with an alternating laminated structure was fabricated by alternately laminating 50 layers each of an aerogel film of cellulose nanofiber 1 obtained in step 1 and a non-porous film of cellulose nanofiber 1 obtained in step 2, and then hot-pressing at 110°C and 1 MPa for 5 minutes.

[0074] The alternating laminated film obtained in Example 1 was a film with a total of 100 layers, in which aerogel layers (first polysaccharide layer) and non-porous layers (second polysaccharide layer) of cellulose nanofiber 1 were alternately laminated. The thickness of each layer was approximately 100 nm, and the overall thickness of the alternating laminated film was approximately 10 μm.

[0075] [Example 2] (Process 1) A 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1 was diluted to prepare a 0.2% by mass aqueous dispersion of cellulose nanofiber. Using the obtained aqueous dispersion as the electrolyte, electrodeposition (applied voltage: 40V, Keysight "B2902A") was performed to prepare a 10 μm thick hydrogel layer of cellulose nanofiber 1 on a copper electrode, which served as the anode.

[0076] (Process 2) A 2.0% by mass aqueous dispersion of cellulose nanofiber 2 prepared in Production Example 2 was diluted to prepare a 0.2% by mass aqueous dispersion of cellulose nanofiber. Using the obtained aqueous dispersion as the electrolyte and the copper electrode with the hydrogel layer obtained in Step 1 as the anode, electrodeposition (applied voltage: 40V, Keysight "B2902A") was performed to prepare a 10 μm thick hydrogel layer of cellulose nanofiber 2 on the hydrogel layer of cellulose nanofiber 1.

[0077] (Step 3) By repeating steps 1 and 2 alternately 50 times each, a multilayer gel layer having an alternating layered structure of hydrogel layers of cellulose nanofiber 1 and hydrogel layers of cellulose nanofiber 2 was formed.

[0078] (Step 4) The multilayer gel layer obtained in step 3 was immersed in isopropanol at room temperature for 60 minutes to replace the hydrogel layer with an organogel layer.

[0079] (Step 5) A film with an alternating laminated structure was fabricated by hot-press drying the multilayer gel layers after solvent substitution at 110°C and 1 MPa for 5 minutes.

[0080] The alternating laminated film obtained in Example 2 was a film with a total of 100 layers, in which xerogel layers of cellulose nanofiber 1 (first polysaccharide layer) with a thickness of approximately 100 nm and xerogel layers of cellulose nanofiber 2 (second polysaccharide layer) with a thickness of approximately 100 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 10 μm.

[0081] [Example 3] In Example 2, the electrolyte used in Step 1 was a 0.2% by mass aqueous pectin solution, and the electrolyte used in Step 2 was a 0.2% by mass aqueous cellulose nanofiber solution obtained by diluting the 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1. A film having an alternating laminated structure was prepared using the same method as in Example 2. As the pectin solution, pectin (Nacalai Tesque Co., Ltd. "Pectin for Chemical Use (CP)") dissolved in water was used.

[0082] The alternating laminated film obtained in Example 3 was a film with a total of 100 layers, in which a pectin xerogel layer (first polysaccharide layer) with a thickness of approximately 60 nm and a cellulose nanofiber 1 xerogel layer (second polysaccharide layer) with a thickness of approximately 100 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 8 μm. Figure 3 is an SEM image showing a magnified portion of the alternating laminated film of Example 3, in which dense pectin xerogel layers and sparse cellulose nanofiber 1 xerogel layers were alternately laminated.

[0083] [Example 4] In Example 2, the electrolyte used in step 1 was a 0.2% by mass aqueous solution of alginic acid, and the electrolyte used in step 2 was a 0.2% by mass aqueous dispersion of cellulose nanofibers obtained by diluting the 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1. A film having an alternating laminated structure was prepared using the same method as in Example 2. As the alginic acid aqueous solution, alginic acid (Nacalai Tesque Co., Ltd.'s "Sodium Alginate Nacalai Grade 1 (EP)") dissolved in water was used.

[0084] The alternating laminated film obtained in Example 4 was a film with a total of 100 layers, in which alginic acid xerogel layers (first polysaccharide layer) with a thickness of approximately 80 nm and cellulose nanofiber 1 xerogel layers (second polysaccharide layer) with a thickness of approximately 100 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 9 μm.

[0085] [Example 5] In Example 2, the electrolyte used in step 1 was a 0.2% by mass aqueous pectin solution (the same as in Example 3), and the electrolyte used in step 2 was a 0.2% by mass aqueous alginate solution (the same as in Example 4). Otherwise, a film having an alternating laminated structure was prepared using the same method as in Example 2.

[0086] The alternating laminated film obtained in Example 5 was a film with a total of 100 layers, in which pectin xerogel layers (first polysaccharide layer) with a thickness of approximately 60 nm and alginic acid xerogel layers (second polysaccharide layer) with a thickness of approximately 80 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 7 μm.

[0087] [Example 6] In Example 2, the electrolyte used in step 1 was a 0.2% by mass aqueous pectin solution (the same as in Example 3), and the electrolyte used in step 2 was a 0.2% by mass aqueous cellulose nanofiber solution obtained by diluting the 2.0% by mass aqueous dispersion of cellulose nanofiber 1 prepared in Production Example 1. Furthermore, without performing the solvent substitution in step 4, the multilayer gel layer obtained in step 3 was hot-press dried at 110°C and 1 MPa for 5 minutes in step 5, and a film having an alternating laminated structure was produced using the same method as in Example 2.

[0088] The alternating laminated film obtained in Example 6 was a film with a total of 100 layers, in which a non-porous layer of pectin (first polysaccharide layer) with a thickness of approximately 60 nm and a non-porous layer of cellulose nanofiber 1 (second polysaccharide layer) with a thickness of approximately 70 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 7 μm.

[0089] [Comparative Example 1] In Example 2, the electrolyte used in both Step 1 and Step 2 was a 0.2% by mass cellulose nanofiber aqueous dispersion obtained by diluting the 2.0% by mass cellulose nanofiber aqueous dispersion prepared in Production Example 1. Furthermore, without performing solvent replacement in Step 4, the multilayer gel layer obtained in Step 3 was hot-press dried at 110°C and 1 MPa for 5 minutes in Step 5, and a film having an alternating laminated structure was prepared using the same method as in Example 2.

[0090] The alternating laminated film obtained in Comparative Example 1 was a film in which 100 layers of non-porous layers (first polysaccharide layer and second polysaccharide layer) of cellulose nanofiber 1, each approximately 70 nm thick, were laminated, and the thickness of the alternating laminated film was approximately 7 μm.

[0091] [Comparative Example 2] In Example 2, the electrolyte used in step 1 was a 0.2% by mass aqueous pectin solution (the same as in Example 3), and the electrolyte used in step 2 was a 0.2% by mass aqueous alginate solution (the same as in Example 4). Furthermore, without performing the solvent substitution in step 4, the multilayer gel layer obtained in step 3 was hot-press dried at 110°C and 1 MPa for 5 minutes in step 5, and a film having an alternating laminated structure was prepared using the same method as in Example 2.

[0092] The alternating laminated film obtained in Comparative Example 2 was a film with a total of 100 layers, in which a non-porous layer of pectin (first polysaccharide layer) with a thickness of approximately 60 nm and a non-porous layer of alginic acid (second polysaccharide layer) with a thickness of approximately 60 nm were alternately laminated, and the thickness of the alternating laminated film was approximately 6 μm.

[0093] For the alternating laminated structure films of the examples and comparative examples obtained above, the refractive index difference between the first polysaccharide layer and the second polysaccharide layer, the density difference between the first polysaccharide layer and the second polysaccharide layer, the presence or absence of structural coloration, and the maximum specular reflectance were measured and evaluated. The measurement and evaluation methods are as follows.

[0094] [Difference in refractive index] In Example 1, a polysaccharide film (thickness 10 μm) was prepared using the same method as in Step 1, except for the thickness, and a polysaccharide film (thickness 10 μm) was obtained by hot pressing it at 110°C and 1 MPa for 5 minutes, as in Step 3. The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler (Metricon Model 2010 / M), and the obtained value was defined as the refractive index η1 of the first polysaccharide layer. Furthermore, a polysaccharide film (thickness 10 μm) was prepared using the same method as in Step 2, except for the thickness, and a polysaccharide film (thickness 10 μm) was obtained by hot pressing it at 110°C and 1 MPa for 5 minutes, as in Step 3. The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler, and the obtained value was defined as the refractive index η2 of the second polysaccharide layer.

[0095] For Examples 2-5, a hydrogel layer prepared using the same method as in Step 1, except for the thickness, was subjected to solvent replacement and hot-press drying using the same method as in Steps 4 and 5 to prepare a polysaccharide film (film thickness 10 μm). The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler, and the obtained value was defined as the refractive index η1 of the first polysaccharide layer. Similarly, a hydrogel layer prepared using the same method as in Step 2, except for the thickness, was subjected to solvent replacement and hot-press drying using the same method as in Steps 4 and 5 to prepare a polysaccharide film (film thickness 10 μm). The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler, and the obtained value was defined as the refractive index η2 of the second polysaccharide layer.

[0096] For Example 6 and Comparative Examples 1 and 2, a hydrogel layer prepared in the same manner as in Step 1, except for the thickness, was hot-press dried in the same manner as in Step 5 to prepare a polysaccharide film (film thickness 10 μm). The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler, and the obtained value was defined as the refractive index η1 of the first polysaccharide layer. Similarly, a hydrogel layer prepared in the same manner as in Step 2, except for the thickness, was hot-press dried in the same manner as in Step 5 to prepare a polysaccharide film (film thickness 10 μm). The refractive index of the polysaccharide film at a wavelength of 589.3 nm was measured using a prism coupler, and the obtained value was defined as the refractive index η2 of the second polysaccharide layer.

[0097] The difference in refractive index between the first polysaccharide layer and the second polysaccharide layer is calculated using the following formula. Refractive index difference = |η1 - η2|

[0098] [Density difference] Using polysaccharide films prepared for measuring refractive indices η1 and η2, the density was calculated from the dimensions (width, length, thickness) and mass of the polysaccharide films. The density calculated from the film used for measuring refractive index η1 was defined as the density ρ1 of the first polysaccharide layer, and the density calculated from the film used for measuring refractive index η2 was defined as the density ρ2 of the second polysaccharide layer. The density difference between the first and second polysaccharide layers is calculated using the following formula. Density difference=|ρ1-ρ2|

[0099] [Presence or absence of structural coloration] The obtained alternating laminated film was visually observed, and if structural color was visible, it was marked as "present," and if not, it was marked as "absent."

[0100] [Maximum specular reflectance] The specular reflectance of the alternating laminated film was measured using a spectrophotometer (Shimadzu Corporation "UV3600i Plus"). The maximum specular reflectance in the visible light wavelength range (wavelength: 400~800nm) was defined as the maximum specular reflectance, and this value was evaluated according to the following criteria. 4: Maximum specular reflectivity of 80% or more 3: Maximum specular reflectivity is 70% or more but less than 80% 2: Maximum specular reflectivity is 60% or more but less than 70% 1: Maximum specular reflectivity is 50% or more but less than 60% 0: Maximum specular reflectivity is less than 50%

[0101] Table 1 below shows the structure of the alternating laminated films of Examples 1-6 and Comparative Examples 1 and 2, as well as the measurement and evaluation results. In Table 1, "CNF1" refers to cellulose nanofiber 1, and "CNF2" refers to cellulose nanofiber 2.

[0102] [Table 1]

[0103] As shown in Table 1, in Example 1, the first polysaccharide layer, which is the aerogel layer of cellulose nanofibers, has low density and a low refractive index. In contrast, the second polysaccharide layer, which is the non-porous layer of cellulose nanofibers, has high density and a high refractive index. The difference in refractive index between the two is large, 0.451, and therefore, the alternating laminated film structure of Example 1 was a structural color-exhibiting material capable of exhibiting structural color. Furthermore, Example 1 had a high maximum specular reflectivity and was excellent as a light-reflecting material.

[0104] Examples 2-5 are examples of alternating laminated film structures produced according to the manufacturing method shown in Figure 2. In Example 2, cellulose nanofibers with different amounts of carboxyl groups were used in the first and second polysaccharide layers, and the density and refractive index were lower as the amount of carboxyl groups increased. The refractive index difference between the first and second polysaccharide layers was 0.091, and the alternating laminated film was able to exhibit structural color.

[0105] In Examples 3-5, the combinations of cellulose nanofibers, pectin, and alginic acid were all modified to form xerogel layers. In all combinations, the refractive index difference was 0.04 or greater, and structural color was exhibited. In particular, when one of the first and second polysaccharide layers was a xerogel layer of cellulose nanofibers, the refractive index of the xerogel was low, which allowed for a larger refractive index difference and tended to result in a higher maximum specular reflectance.

[0106] In Example 6, an alternating laminated film was prepared without solvent substitution. Comparing Example 3 and Example 6, the refractive index difference between the pectin layer and the cellulose nanofiber layer was small in Comparative Example 6, which did not undergo solvent substitution, while the refractive index difference was large in Example 3, which underwent solvent substitution. Consequently, the maximum specular reflectance was also higher in Example 3 than in Example 6.

[0107] In Comparative Example 1, both Step 1 and Step 2 involved alternating lamination using an aqueous dispersion of cellulose nanofiber 1. As a result, the refractive index difference and density difference between the first and second polysaccharide layers were both zero. Consequently, structural color could not be exhibited, and the maximum specular reflectivity was also inferior.

[0108] Comparative Example 2 was a film with an alternating laminated structure of a non-porous pectin layer and a non-porous alginate layer. The density difference between the two was small, and therefore the refractive index difference was less than specified at 0.006. As a result, structural color could not be expressed, and the maximum specular reflectivity was also inferior.

[0109] [Examples 7-9] Alternating laminated films were prepared by varying the thicknesses of the first and second polysaccharide layers, with the thickness of the film being approximately 9 μm in Example 7, approximately 11 μm in Example 8, and approximately 13 μm in Example 9, while otherwise being the same as in Example 3. In Examples 7 to 9, the number of first polysaccharide layers was 50, the number of second polysaccharide layers was 50, and the total number of layers for both was 100.

[0110] For the alternating laminated films obtained in Examples 7 to 9, the presence or absence of structural coloration was evaluated, and the specular reflectance of the alternating laminated films was measured using a spectrophotometer (Shimadzu Corporation's "UV3600i Plus").

[0111] As a result, structural color was observed in all of the alternating laminated films of Examples 7-9. Furthermore, as shown in Figure 4, the alternating laminated film (1) with a thickness of approximately 9 μm showed a peak in specular reflectance at a wavelength of 457 nm, with a maximum specular reflectance of 95%. The alternating laminated film (2) with a thickness of approximately 11 μm showed a peak in specular reflectance at a wavelength of 553 nm, with a maximum specular reflectance of 96%. The alternating laminated film (3) with a thickness of approximately 13 μm showed a peak in specular reflectance at a wavelength of 665 nm, with a maximum specular reflectance of 93%. Thus, the maximum specular reflectance was consistently above 90%. In addition, it was observed that the wavelength at which the specular reflectance peaked tended to increase with increasing thickness of the alternating laminated film, indicating that the reflection wavelength can be controlled.

[0112] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0113] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0114] 10...Light reflective material 12...First polysaccharide layer 14…Second Polysaccharide Layer

Claims

1. A light-reflecting material having an alternating laminated structure in which at least two polysaccharide layers with different refractive indices are alternately stacked, and the refractive index difference between adjacent polysaccharide layers is 0.04 or more and 0.5 or less.

2. The light-reflecting material according to claim 1, wherein the content of the polysaccharide and / or derivative thereof in each of the polysaccharide layers is more than 85% by mass.

3. A light-reflecting material having an alternating laminated structure in which at least two polysaccharide layers with different refractive indices are alternately stacked, with a refractive index difference of 0.04 or more and 0.5 or less between adjacent polysaccharide layers.

4. The density difference between adjacent polysaccharide layers is 0.01 g / cm³. ３ 1.6g / cm or more ３ The following is a light-reflective material according to any one of claims 1 to 3.

5. The light-reflecting material according to any one of claims 1 to 3, wherein at least one of the at least two polysaccharide layers is a dry gel layer.

6. The light-reflecting material according to any one of claims 1 to 3, wherein each of the polysaccharide layers substantially does not contain inorganic oxide particles.

7. The light-reflecting material according to any one of claims 1 to 3, wherein the polysaccharide and / or derivative thereof contained in at least one of the at least two polysaccharide layers is cellulose and / or a derivative thereof.

8. The light-reflecting material according to claim 7, wherein the cellulose and / or derivative thereof is cellulose nanofiber.

9. The light-reflecting material according to any one of claims 1 to 3, wherein the at least two polysaccharide layers consist of a first polysaccharide layer having a first refractive index and a second polysaccharide layer having a second refractive index, the alternating stacked structure is an alternating stacked structure of the first polysaccharide layer and the second polysaccharide layer, and the difference between the first refractive index and the second refractive index is 0.04 or more and 0.5 or less.

10. A light-reflecting material according to any one of claims 1 to 3, which is a structural color-exhibiting material.

11. A step comprising performing electrodeposition using an aqueous solution or aqueous dispersion containing a first polysaccharide and / or a derivative thereof, the first step of forming a first polysaccharide layer containing the first polysaccharide and / or a derivative thereof, A step comprising performing electrodeposition using an aqueous solution or aqueous dispersion containing a second polysaccharide and / or its derivative, the second step of forming a second polysaccharide layer containing the second polysaccharide and / or its derivative, A third step in which an alternating layered structure of the first polysaccharide layer and the second polysaccharide layer is formed, A method for producing a light-reflective material, including The light-reflecting material has a refractive index difference of 0.04 or more and 0.5 or less between the first polysaccharide layer and the second polysaccharide layer. A method for manufacturing light-reflective materials.

12. In the first step, the first polysaccharide layer is formed as a hydrogel layer by electrodeposition using an aqueous solution or aqueous dispersion containing the first polysaccharide and / or its derivative. In the second step, the second polysaccharide layer is formed on the first polysaccharide layer as a hydrogel layer by electrodeposition using an aqueous solution or aqueous dispersion containing the second polysaccharide and / or its derivative. In the third step, by alternately repeating the first and second steps, an alternating layered structure of the first polysaccharide layer, which is a hydrogel layer, and the second polysaccharide layer, which is a hydrogel layer, is formed. A method for producing a light-reflective material according to claim 11.

13. A method for producing a light-reflective material according to claim 12, further comprising: a fourth step of replacing the solvent of the first polysaccharide layer and the second polysaccharide layer with an organic solvent after the third step to form an organogel layer; and a fifth step of drying the organogel layer to form a dry gel layer of the first polysaccharide layer and the second polysaccharide layer.

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