Lightweight fiber layer and method for forming the same

Abstract

To provide a technique (a lightweight fiber layer and a method for forming a lightweight fiber layer) which causes no surface color unevenness when the surface of a fiber layer (first layer) formed using a binding material slurry and a granular fiber as main components is coated with a second layer using a binding material slurry having a color tone (color difference) different from that of the binding material slurry used for the formation of first layer.MEANS: All of the surface of a fiber layer of a first layer formed using a binding material slurry and a granular fiber as main components is covered with a fiber layer of a second layer mainly composed of a binding material slurry having a color difference different from that of the binding material slurry of the first layer so that the surface of the first layer is not visible.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lightweight fiber layer, and more particularly to a lightweight fiber layer that is made up of two or more laminated layers each containing a binder slurry and lightweight fibers as its main components, and has no visible color spots (color unevenness) on the surface. [Background technology]

[0002] A fiber layer such as rock wool is provided on the base of a structure surface or the like for the purpose of imparting fire resistance, fire prevention, sound absorption, and / or heat insulation, etc. The fiber layer is generally formed by a spraying method using granular fibers (fiber masses with a diameter of several mm to several cm) and a binder slurry whose main components are water and an inorganic binder such as cement or alkali silicate, or an organic binder made of a polymer such as vinyl acetate resin, acrylic resin, or synthetic rubber. This spraying method, known as a semi-dry method, uses rock wool granules and cement slurry (a binder slurry made from cement and water). The granular rock wool fibers are fed into a device called a rock wool sprayer or deflocculator, where they are pulverized (into fine granules (fiber clumps with diameters of several millimeters to several centimeters)) by a built-in rotary cutter or other deflocculator. The granules are then quantitatively pumped into a pressure path by a rotary feeder or other constant-feeding device, and then pressure-fed through a hose by a blower and supplied to a spray nozzle. The cement is mixed with water in a mixer to form a cement slurry, which is then pumped through a conveying pipe (a hose for pumping cement slurry) by a slurry pump to a liquid material (cement slurry) spray nozzle located on the granular fiber spray nozzle. The cement slurry is sprayed from a liquid material (cement slurry) spray nozzle located on the periphery of the granular fiber spray nozzle, or from a liquid material (cement slurry) spray nozzle located near the central axis of the granular fiber spray nozzle, and merges and mixes with the rock wool to form a fiber layer consisting of rock wool and cement hydrate (solidified cement slurry) (see, for example, Patent Documents 1 and 2). Rock wool granular fibers are white or very close to white, while cement slurry is gray and remains gray even after hardening (solidification). As a result, the formed fiber layer may have white and gray mottling. To prevent the surface of the fiber layer from becoming mottled or to increase the strength of the surface of the fiber layer, a cement slurry layer (a layer made of solidified cement slurry) may be formed by spraying only cement slurry onto the surface of the fiber layer made of rock wool granular fibers and cement slurry. In this case, since the cement slurry that forms the fiber layer and the cement slurry that forms the cement slurry layer are the same, there is naturally no color difference between the two cement slurries.

[0003] Incidentally, when considering using a fiber layer for the interior of a building such as a house or a store, it is conceivable that a color different from that of the formed fiber layer is required. In this case, the inventors thought that this problem could be solved by applying a binder slurry having a color different from that of the cement slurry forming the fiber layer, i.e., a color difference, to the surface of the fiber layer to form a layer made of binder slurry (a layer made of solidified binder slurry). Here, in order to obtain a binder slurry that has a different color from the cement slurry that forms the fiber layer, it is possible to prepare the slurry using a binder different from the cement used to prepare the cement slurry that forms the fiber layer, or to add a coloring agent such as a pigment or dye to the cement slurry that forms the fiber layer. The inventors then conducted an experiment and found that the cement slurry that forms the fiber layer seeped out onto the surface, causing the surface to become mottled. . [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-070546 [Patent Document 2] Japanese Patent Publication No. 2020-159093 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a technology that prevents uneven color on the surface when the surface of a fiber layer (first layer) formed mainly from binder slurry and granular fibers is covered with a second layer using a binder slurry of a different color (having a color difference) from the binder slurry used to form the first layer. The present invention aims to provide a lightweight fiber layer that does not produce color unevenness on the surface when the surface of a fiber layer (first layer) formed mainly from binder slurry and granular fibers is covered with a second layer using a binder slurry of a different color (having a color difference) from the binder slurry used to form the first layer. Another object of the present invention is to provide a method for forming a lightweight fiber layer in which, when the surface of a fiber layer (first layer) formed primarily from binder slurry and granular fibers is covered with a second layer using a binder slurry of a different hue (having a color difference) from the binder slurry used to form the first layer, color unevenness does not occur on the surface. [Means for solving the problem]

[0006] The inventors have found that the above-mentioned problems can be solved by completely covering the surface of a first fiber layer formed mainly from a binder slurry and granular fibers with a second fiber layer mainly composed of a binder slurry and granular fibers, and the second fiber layer has a color different from that of the binder slurry of the first layer, so that the surface of the first layer is not visible, and have completed the present invention. That is, the present invention relates to lightweight fiber layers represented by the following items (1) to (3) and a method for forming a lightweight fiber layer represented by item (4). (1) A lightweight fiber layer comprising a first layer whose main components are binder slurry and granular fibers, and a second layer whose main components are binder slurry and granular fibers and whose color differs from that of the binder slurry of the first layer, wherein the second layer covers the surface of the first layer. (2) The lightweight fiber layer according to (1) above, wherein the color difference is a difference in lightness of 2 or more, a difference in saturation of 4 or more, and / or a difference in hue of 4 or more in the Munsell color system. (3) The lightweight fiber layer according to (1) or (2) above, characterized in that the surface of the second layer is covered with a third layer whose main component is a binder slurry whose color difference from the binder slurry of the second layer is 1 or less in lightness, 3 or less in saturation, and 3 or less in hue in the Munsell color system. (4) A method for forming a lightweight fiber layer, comprising forming a first layer whose main components are binder slurry and granular fibers, and covering the surface of the first layer with a second layer whose main components are binder slurry and granular fibers and whose color is different from that of the binder slurry of the first layer. [Effects of the Invention]

[0007] According to the present invention, when the surface of a fiber layer (first layer) formed primarily from binder slurry and granular fibers is covered with a second layer using a binder slurry of a different hue (having a color difference) from the binder slurry used to form the first layer, a lightweight fiber layer is obtained that does not produce color unevenness on the surface. Furthermore, according to the present invention, a method for forming a lightweight fiber layer can be obtained in which, when the surface of a fiber layer (first layer) formed primarily from binder slurry and granular fibers is covered with a second layer using a binder slurry of a different hue (having a color difference) from the binder slurry used to form the first layer, color unevenness does not occur on the surface. According to the present invention, the surface of the lightweight fiber layer does not become spotty or have uneven color, and the surface of the lightweight fiber layer can be made to have a desired color. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of a spraying device used in a semi-dry rock wool spraying method. DETAILED DESCRIPTION OF THE INVENTION

[0009] The lightweight fiber layer of the present invention is characterized by comprising a first layer mainly composed of a binder slurry and granular fibers, and a second layer mainly composed of a binder slurry and granular fibers, the second layer having a color different from that of the binder slurry of the first layer, and covering the surface of the first layer. Here, "lightweight" means a layer having an oven-dry bulk density of 1.0 g / cm.3 Here, the bone dry bulk density is determined by finding the volume (V) of a specimen from the outer dimensions of a fiber layer specimen obtained by cutting out a cylindrical shape from the formed fiber layer using a rock wool cutter with an inner diameter of 80 mm, placing the specimen in a dryer and drying it at 105°C until it reaches a constant weight, and then calculating the bulk density (ρ) from the mass (M) of the specimen after drying using the following formula (1), which is the bone dry bulk density. ρ=M / V (1)

[0010] The granular fibers used in the present invention include organic and inorganic granular fibers, such as synthetic fibers (e.g., cellulose fibers, nylon fibers, and polypropylene fibers), and cellulose fibers. Non-metallic inorganic fibers are preferred in terms of fire resistance. For example, inorganic granular fibers selected from rock wool, glass wool, and ceramic wool are preferred in terms of durability, sound absorption, and heat insulation. Rock wool and ceramic wool are more preferred because they can maintain their shape without melting even when exposed to temperatures above 800°C and have excellent heat resistance and fire resistance. Here, rock wool refers to a material (mineral fiber) produced by rapidly cooling a material primarily composed of rock or blast furnace slag melted in a melting furnace and then fiberizing it. For example, rock wool also includes slag wool produced from a material primarily composed of blast furnace slag. The granular fibers used in the present invention are preferably agglomerated (granular), such as rock wool granular cotton, because the resulting rock wool composition layer has low thermal conductivity and the resulting first layer (first fiber layer) has excellent shape retention. The granular fibers used in the present invention are preferably in a lump form (granular, fiber masses with a diameter of several mm to several cm) such as the granular rock wool cotton used in rock wool-based fire-resistant coating materials, because the thermal conductivity of the formed rock wool composition layer is low and the formed base material layer has excellent ability to retain its shape. The rock wool aggregate is preferably a granular cotton obtained by subjecting raw cotton consisting of fiberized mineral fibers to one or a combination of two or more processes, such as crushing, deflocculating, cutting, sorting (e.g., sieving), and granulation. Examples of the rock wool granular cotton include fine and micro-sized rock wool granules, and commercially available rock wool granules, fine and micro-sized rock wool granules, such as "S-Fiber Granular Cotton" (product name) manufactured by Japan Rock Wool Co., Ltd., "Locceram Granular Cotton" (product name) manufactured by JFE Rock Fiber Corporation, and "Pacific Mineral Fiber Granular Cotton" (product name) manufactured by Pacific Materials Corporation, can be suitably used. When such rock wool granular cotton is used, heat is less likely to be transmitted to the substrate covering the rock wool, providing thermal insulation, fire resistance, or non-combustibility, as well as sound absorption.

[0011] The binder slurry used in the first layer of the present invention (hereinafter sometimes referred to as the "first binder slurry") is a slurry primarily composed of water and one or more binders selected from cements such as Portland cement, blast furnace cement, and white cement; inorganic binders such as alkali silicates and latent hydraulic substances such as blast furnace slag powder; and organic binders composed of polymers (synthetic resins) such as vinyl acetate resins, acrylic resins, and synthetic rubber. The binder slurry may also contain one or more additives (admixtures) within the scope of the present invention. Examples of additives (admixtures) include thickeners, cement dispersants, expansive additives, waterproofing agents, rust inhibitors, shrinkage-reducing agents, pigments, fibers other than rock wool, water repellents, efflorescence inhibitors, quick-setting additives, hardening additives, retarders, foaming agents, defoamers, gypsum, pozzolans such as silica fume and fly ash, water repellents, and surface hardeners.

[0012] The first layer has a bone dry bulk density of 0.14 to 1.0 g / cm 3 It is preferable to set the density to 0.14 g / cm 3 If it is less than 1.0g / cm, there is a risk of peeling. 3 If the temperature exceeds this range, there is a risk that the performance of fire resistance, fire prevention, sound absorption, heat insulation, etc. may be insufficient.

[0013] The granular fibers used in the second layer in the present invention can be the same as those used in the first layer, and it is preferable to use the same granular fibers as those used in the first layer.

[0014] The binder slurry used in the second layer of the present invention (hereinafter sometimes referred to as the "second binder slurry") has a color difference from the first binder slurry. Here, "color difference" refers to a color difference before hardening or solidification, i.e., before hardening. The "color difference before hardening" refers to a difference in Munsell values ​​in the Munsell color system. Furthermore, a "large color difference" refers to a difference in lightness of 2 or more, a difference in saturation of 4 or more, and / or a difference in hue of 4 or more in the Munsell color system. Like the first binder slurry, the second binder slurry may be primarily composed of water and one or more inorganic binders, such as cement, alkali silicate, or latent hydraulic material, and organic binders, with optional additives. The second binder slurry can be made to have a color difference from the first binder slurry by using a binder different from that of the first binder slurry or by adding additives such as pigments.

[0015] The second layer has a bulk density of 0.14 to 1.0 g / cm 3 It is preferable to set the density to 0.14 g / cm 3 If the density is less than 1.0 g / cm, uneven coloring may occur on the surface if the time between the formation of the first layer and the formation of the second layer is very short. 3 If it exceeds this value, peeling may occur. The thickness of the second layer is preferably 5 to 50 mm. If it is less than 5 mm, uneven color may occur on the surface if the time between the formation of the first layer and the formation of the second layer is very short, and if it exceeds 50 mm, peeling may occur. The amount of water (W) in the second layer is preferably 60 mass% or more relative to the mass (B) of the solid content in the second binder slurry, that is, W / B is preferably 60 mass% or more, more preferably 80 to 1500 mass%, and even more preferably 100 to 1200 mass%. If W / B is less than 60 mass%, peeling may occur. If it exceeds 1500 mass%, there is a risk that the slurry will drip when forming a lightweight fiber layer on a ceiling surface or the like.

[0016] In the present invention, the surface of the second layer may be covered with a third layer containing as its main component a binder slurry whose color difference from the binder slurry of the second layer in the Munsell color system is 1 or less in lightness, 3 or less in saturation, and 3 or less in hue. When the third layer containing a binder slurry as its main component covers the surface of the second layer, the surface of the third layer is less uneven than the surface of the second layer, and color unevenness due to the unevenness is reduced, which is preferable.

[0017] The binder slurry used in the third layer in the present invention (hereinafter sometimes referred to as "third binder slurry") has no color difference from the second binder slurry, that is, a binder slurry having a color difference from the second binder slurry of 1 or less in lightness, 3 or less in saturation, and 3 or less in hue in the Munsell color system. Using the second binder slurry as the third binder slurry is preferable because there is no color difference at all from the second binder slurry.

[0018] The method for forming a lightweight fiber layer of the present invention is characterized by forming a first layer mainly composed of a binder slurry and granular fibers, and coating the surface of the first layer with a second layer mainly composed of a binder slurry and granular fibers, which has a color difference from the binder slurry of the first layer, i.e., a color difference of 2 or more in lightness, 4 or more in saturation, and / or 4 or more in hue in the Munsell color system. The binder slurry forming the first layer is the first binder slurry, and the binder slurry forming the second layer is the second binder slurry. The granular fibers are also the granular fibers.

[0019] It is preferable that the surface of the second layer is covered with a third layer whose main component is a binder slurry whose color difference from the binder slurry of the second layer is 1 or less in lightness, 3 or less in saturation, and 3 or less in hue in the Munsell color system, and it is more preferable that the binder slurry used for the third layer is the second binder slurry.

[0020] The first, second, and third layers can be suitably formed using a spraying device such as the spraying device used in the semi-dry construction method used in the rock wool spraying method, an example of which is shown in a schematic diagram in Figure 1. The first and second layers can also be formed by mixing a binder slurry (first binder slurry or second binder slurry) with granular fibers, and then filling a formwork or applying it to a substrate with a trowel, roller, or the like. The substrate used when forming the first layer can be concrete, mortar, steel, wood, or the like. The substrate used when forming the second layer is the surface of the first layer. The third layer can also be formed by applying it to the surface of the second layer with a trowel, roller, or the like.

[0021] An example of a spraying device used in a semi-dry construction method, which is suitably used in the rock wool spraying method, is shown in a schematic diagram in Figure 1, and is a spraying device 10 whose main components are a cotton defibrator 20, a blower (air blower) 14, a granular fiber pressure-feed hose 9, a binder slurry storage tank 8, a binder slurry pressure-feed pump 7, a binder slurry pressure-feed hose 6, and a spray gun 1. Granular fiber (rock wool granular cotton) 11 is fed into a hopper 23 of the cotton defibrator 20, disintegrated in a first cotton defibrator section 21 of the cotton defibrator 20, and then sent by a screw feeder 24 to a second cotton defibrator section 22 for further disintegration. The disintegrated granular fiber enters a rotary feeder (quantitative supply device) 25 and is supplied in a fixed amount to a granular fiber pressure-feed pipe 26. The unraveled granular fibers 5 sent to the granular fiber pressure-transfer pipe 26 are pressurized by air sent from a blower (air blower) 14 connected to the granular fiber pressure-transfer pipe 26 into a granular fiber pressure-transfer hose 9 connected to the granular fiber pressure-transfer pipe 26, and are sprayed from a granular fiber nozzle 2 of a spray gun 1 connected to the tip of the granular fiber pressure-transfer hose 9.

[0022] The produced binder slurry 4 (first binder slurry or second binder slurry) is stored in a binder slurry storage tank 8, and is pumped by a binder slurry pressure pump 7 through a binder slurry suction hose 15, a binder slurry pressure pump 7, and a binder slurry pressure feed hose 6 to the binder slurry nozzle 3 of the spray gun 1, where it is sprayed from the binder slurry nozzle 3. The loosened granular fibers 5 sprayed from the granular fiber nozzle 2 of the spray gun 1 and the binder slurry 4 sprayed from the binder slurry nozzle 3 of the spray gun 1 are mixed together at the tip of the spray gun 1, forming a first layer (first fiber layer) or a second layer (second fiber layer) composed mainly of granular fibers and binder slurry. When forming the second layer, the second layer is formed on the surface of the first layer. The third layer is preferably formed using the same equipment as the first and second layers. In this case, the granular fibers are not pumped, and the third binder slurry 4 is sprayed onto the surface of the second layer from the binder slurry nozzle 3 of the spray gun 1. The third layer may be formed by a spraying method using a different spraying device (e.g., a mortar spraying device or a paint spraying device) instead of the spraying device 10 used in the semi-dry construction method. Alternatively, the third binder slurry may be filled into a formwork installed on the surface of the second layer or the base of the first layer, or applied to the second surface with a trowel or roller. A fourth layer may also be formed on the surface of the third layer to enhance its design, light resistance, weather resistance, water repellency, or mildew resistance. The fourth layer may be formed by applying the fourth layer to the surface of the third layer with a trowel, roller, spraying device, or the like, depending on the properties of the material constituting the fourth layer. [Example]

[0023] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0024] [Example 1] <Formation of the first layer> Using granular rock wool and a cement slurry (first binder slurry) made of white Portland cement and water colored with pigment, a first fiber layer (30 mm thick) was formed on a plywood substrate using the semi-dry spraying method, according to the standard specifications for spraying rock wool as a fire-resistant coating, using a spraying device used in the semi-dry method of spraying rock wool.The materials used are shown below, and the mixing conditions, the color (hue, value, saturation) of the first binder slurry in the Munsell color system, and the bone-dry bulk density of the formed first layer are shown in Table 1. In Table 1, RW, B, and W respectively represent the mass of the rock wool, the solid content of the cement slurry, and the water in the cement slurry; "B / (B+RW)" in Table 1 represents the ratio (mass%) of the solid content of the cement slurry to the total mass of the rock wool and the solid content of the cement slurry; "W / RW" in Table 1 represents the mass ratio (mass%) of the water in the cement slurry to the mass of the rock wool; and "W / B" in Table 1 represents the mass ratio (mass%) of the water in the cement slurry to the mass of the solid content of the cement slurry. Rockwool: Rockwool granules manufactured by Pacific Materials White Portland cement: "White Cement" (product name) manufactured by Taiheiyo Cement Corporation Water: Water supply from Sakura City, Chiba Prefecture

[0025] [Table 1]

[0026] <Formation of the second layer> Similar to the cement slurry used to form the first layer, a cement slurry (cement-water ratio (W / C) 200%, i.e., W / B 200%) was prepared using white Portland cement and water, and various pigments were added to this cement slurry to prepare cement slurries (second binder slurries) (slurries 1 to 7) with the colors (hue, value, saturation) in the Munsell color system shown in Table 2. Using the prepared cement slurry and the rock wool granules used to form the first layer, the surface of the first layer was covered with a 5 mm thick second fiber layer consisting of the second binder slurry and rock wool granules using a semi-dry construction method within one hour of forming the first layer. After the second layer had hardened, the surface was visually observed to check for and evaluate the presence or absence of color unevenness on the surface. The results are shown in Table 2. When there was no color unevenness on the surface, it was evaluated as "○" (good), and when there was color unevenness on the surface, it was evaluated as "×" (bad). In addition, without using rock wool granules, the surface of the first layer was sprayed with only the second binder slurry using a spraying device for semi-dry construction method, with an application amount of 1125 (g / m 2 The results of coating so that the thickness was 100 μm (Test Nos. 1-8) are also shown in Table 2.

[0027] [Table 2]

[0028] In the lightweight fiber layers of Test Nos. 1-1 to 1-7, which correspond to examples of the present invention, no color unevenness was visible on the surface. In contrast, in the lightweight fiber layer of Test No. 1-8, which did not contain rock wool granular cotton in the second layer, color unevenness was visible.

[0029] [Example 2] A first layer was formed in the same manner as in Example 1 using the same materials as in Example 1, and a second fiber layer was formed on its surface within one hour after the formation of the first layer using the same rock wool granular cotton as the second binder slurries (slurries 1 to 7) used in Example 1 in the blending ratio and thickness shown in Table 3. A fiber layer was formed with the same blending ratio as the second layer, and the bone dry bulk density of that fiber layer was measured and is shown in Table 3 as the bone dry bulk density of the second layer. Immediately after the second layer was formed, the surface of the second layer was sprayed with the second binder slurry used in the formation of the second layer using a spraying device used in the semi-dry construction method, with a coating amount of 1125 (g / m 2) In other words, immediately after forming the second layer, the pumping of the rock wool granules was stopped, and the second binder slurry used to form the second layer was sprayed onto the surface of the second layer to form the third layer. The third binder slurry was exactly the same as the second binder slurry.

[0030] After the third layer hardened, the surface was visually observed to check for and evaluate the presence or absence of color unevenness on the surface. The results are shown in Table 3, along with the second binder slurry used (the color (hue, value, saturation) of the third binder slurry in the Munsell color system). Cases where there was no color unevenness on the surface were evaluated as "Good", and cases where there was color unevenness on the surface were evaluated as "Poor". The first to third layers were formed by treating the plywood that served as the base for the first layer as the ceiling surface, and the resulting fiber layers were evaluated for peeling. If the fiber layers formed within 24 hours after the second layer was formed and the third binder slurry was sprayed, they were evaluated as "○" (good) if they did not peel off, and if they did peel off, they were evaluated as "×" (bad). The results are shown in Table 3.

[0031] [Table 3]

[0032] In the lightweight fiber layers of Test Nos. 2-1 to 2-9, which correspond to examples of the present invention, no color unevenness was visually observed on the surface. In addition, the lightweight fiber layers of Test Nos. 2-1 to 2-6 did not peel off, but the lightweight fiber layer of Test No. 2-7, in which the thickness of the second layer exceeded 50 mm and the bone dry bulk density of the second layer was 1.0 g / cm. 3 The lightweight fiber layer of Test No. 2-8, in which the ratio (W / B) of the amount of water (W) in the second layer (second binder slurry) to the mass (S) of the solids in the second binder slurry was less than 60 mass%, partially peeled off. [Industrial Applicability]

[0033] The present invention can be suitably applied to coating the surfaces of components of structures or constructions made of concrete, steel, wood, etc., for the purpose of imparting fire resistance, fire prevention, sound absorption, and / or heat insulation properties to the components. [Explanation of symbols]

[0034] 1 Spray gun (center gun) 2 Granular fiber nozzle 3. Binder slurry injection nozzle 4. Binder Slurry 5. Disintegrated granular fibers 6. Binder slurry pressure feed hose 7. Pressure pump for binder slurry 8. Storage tank for binder slurry 9 Granular fiber pressure feeding hose 10 Spraying equipment (spraying system) 11 Granular Fiber 12. A fiber layer consisting of a mixture of granular fiber and binder slurry. 13 Base (wall) 14 Blower 15 Suction hose for binder slurry 20 Cotton opening machine 21 First Cotton Decomposition Department 22 Second cotton opening section 23 Hopper 24 Screw feeder 25 Rotary feeder (quantitative feeder) 26 Granular fiber pressure pipe 31 Binder slurry pipeline 32 Granular fiber pipe 33 Central axis of granular fiber pipe

Claims

1. A lightweight fiber layer comprising a first layer whose main components are binder slurry and granular fibers, and a second layer whose main components are binder slurry and granular fibers and whose color is different from that of the binder slurry of the first layer, wherein the second layer covers the surface of the first layer.

2. 2. The lightweight fiber layer according to claim 1, wherein the color difference is a difference in lightness of 2 or more, a difference in saturation of 4 or more, and / or a difference in hue of 4 or more in the Munsell color system.

3. 3. The lightweight fiber layer according to claim 1, wherein the surface of the second layer is covered with a third layer containing a binder slurry as a main component, the binder slurry having a color difference of 1 or less in lightness, 3 or less in saturation, and 3 or less in hue in the Munsell color system from the binder slurry of the second layer.

4. A method for forming a lightweight fiber layer, comprising forming a first layer whose main components are a binder slurry and granular fibers, and covering the surface of the first layer with a second layer whose main components are a binder slurry and granular fibers and whose color is different from that of the binder slurry of the first layer.

Images