Building material and method for manufacturing the same

Abstract

To provide a building material with low formaldehyde emission and excellent sound absorption and thermal insulation properties.SOLUTION: A building material consists of a multilayer structural body having a first fiber layer and a second fiber layer. The first fiber layer contains hemp and thermally bonded composite fibers. The mass ratio of the hemp to the thermally bonded composite fibers (hemp / thermally bonded composite fibers) is 30 / 70 to 80 / 20. The second fiber layer contains thermally bonded composite fibers. The density of the first fiber layer is 0.3 to 1.0 g / cm3, and the density of the second fiber layer is 0.1 to 0.5 g / cm3. Furthermore, the density of the first fiber layer is higher than that of the second fiber layer, and the first fiber layer is laminated on both outer sides of the second fiber layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a building material having a multilayer structure with a layer containing hemp and heat-bondable composite fibers. [Background technology]

[0002] Conventionally, plywood, MDF (medium density fiberboard), OSB (oriented strand board), etc. have been used as building materials for floor coverings, etc. However, these building materials have low sound absorption and heat insulation properties, so if these properties need to be improved, it has been necessary to separately laminate sound absorption materials, heat insulation materials, etc. (Patent Document 1).

[0003] Furthermore, in order to achieve the SDGs, there is currently a demand for the effective use and reuse of resources in building materials. The aforementioned plywood, MDF, OSB, etc. can be made from recycled wood chips and lumber, but because they use adhesives, the emission of formaldehyde is unavoidable. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-265948 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a building material that emits little formaldehyde and has excellent sound absorption and heat insulation properties. [Means for solving the problem]

[0006] The above-mentioned problem is solved by a building material comprising a multilayer structure having a first fiber layer and a second fiber layer, wherein the first fiber layer contains hemp and thermally fused composite fibers, the mass ratio of the hemp to the thermally fused composite fibers (hemp / thermally fused composite fibers) being 30 / 70 to 80 / 20, the second fiber layer contains the thermally fused composite fibers, and the density of the first fiber layer is 0.3 to 1.0 g / cm 3 , the density of the second fiber layer is 0.1 to 0.5 g / cm 3 The above-mentioned problems are solved by providing a sheet having a first fiber layer with a higher density than a second fiber layer, and the first fiber layer being laminated on both outer sides of the second fiber layer.

[0007] In this case, it is preferable that the second fiber layer contains fibers other than the thermally fused composite fibers, and the mass ratio of the other fibers to the thermally fused composite fibers (other fibers / thermally fused composite fibers) is 40 / 60 to 90 / 10. It is also preferable that the other fibers contained in the second fiber layer are at least one type selected from the group consisting of hemp, cotton, and chemical fibers. It is also preferable that at least one surface of the multilayer structure is embossed.

[0008] A preferred embodiment of the building material is a floor covering. The above-mentioned problem can also be solved by providing a manufacturing method for the building material, which comprises: forming a first fiber layer by hot pressing a felt containing hemp and thermally fused composite fibers; arranging a felt containing thermally fused composite fibers between the first fiber layers; and further hot pressing the felt to form a second fiber layer. [Effects of the Invention]

[0009] The building material of the present invention emits little formaldehyde and has excellent sound absorption and heat insulation properties. Moreover, since it can be made from raw materials such as burlap sacks, it is low cost and allows for the reuse of resources, which may contribute to the achievement of the SDGs. Such building materials are suitable for use as floor coverings, etc. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram in which sound transmission loss in the building material of Example 1 is plotted against frequency. [Figure 2] FIG. 1 is a diagram in which the normal incidence sound absorption coefficient measured using a large measurement tube for the building material of Example 1 is plotted against frequency. [Figure 3] FIG. 1 is a diagram in which the normal incidence sound absorption coefficient measured using a small measurement tube for the building material of Example 1 is plotted against frequency. DETAILED DESCRIPTION OF THE INVENTION

[0011] The building material of the present invention is a multilayer structure having a first fiber layer and a second fiber layer, wherein the first fiber layer contains hemp and thermally fused composite fibers, the mass ratio of the hemp to the thermally fused composite fibers (hemp / thermally fused composite fibers) being 30 / 70 to 80 / 20, the second fiber layer contains thermally fused composite fibers, and the density of the first fiber layer is 0.3 to 1.0 g / cm. 3 , the density of the second fiber layer is 0.1 to 0.5 g / cm 3 The density of the first fiber layer is higher than that of the second fiber layer, and the first fiber layers are laminated on both outer sides of the second fiber layer. Such a building material emits little formaldehyde and has excellent sound absorption and heat insulation properties.

[0012] The hemp contained in the first fiber layer is not particularly limited as long as it is a fibrous hemp fiber. Examples of hemp usable in the first fiber layer include well-known hemp species such as hemp, hemp, jute, flax, kenaf, burlap, sisal, Manila hemp, and New Zealand hemp. These hemp species can be subjected to a general pulping process to obtain fibrous hemp fibers. Furthermore, hemp fibers obtained by defatting hemp products such as hemp bags and strings can be used as a raw material for hemp fibers. Using hemp fibers obtained by defatting such hemp products is preferred from the viewpoint of efficient resource utilization. The fiber length of the hemp fiber is not particularly limited, but is typically 0.5 to 100 mm. The fiber length is preferably 80 mm or less, more preferably 60 mm or less. The fiber diameter of the hemp fiber is not particularly limited, but is typically 5 to 150 μm.

[0013] The heat-bonded conjugate fibers contained in the first fiber layer are preferably fibers obtained by combining two or more resins with different melting points or softening points, and examples thereof include sheath-core fibers, bimetal fibers, and sea-island fibers. Among these, sheath-core fibers are preferred because they can bond fibers more firmly to each other. Examples of the core / sheath fiber (core / sheath) structure include polyester / copolyester, polypropylene / polyethylene, and polyester / polyethylene, with polyester / copolyester being preferred. The sheath component of the sheath-core fiber has a melting point of, for example, 90 to 150°C, and the core component has a melting point of, for example, 120 to 280°C. The fiber diameter and fiber length of the heat-bonded conjugate fibers are not particularly limited, but the fiber diameter is typically 20 to 50 μm, preferably 30 to 40 μm, and the fiber length is typically 10 to 50 mm.

[0014] The mass ratio (hemp / thermal fusion composite fiber) of the hemp and thermal fusion composite fiber contained in the first fiber layer is 30 / 70 to 80 / 20. When the mass ratio (hemp / thermal fusion composite fiber) is in this range, the rigidity of the resulting building material is improved, making it easier to handle at construction sites, etc. The mass ratio (hemp / thermal fusion composite fiber) is preferably 40 / 60 or more. On the other hand, the mass ratio (hemp / thermal fusion composite fiber) is preferably 70 / 30 or less, and more preferably 65 / 35 or less.

[0015] The total amount of hemp and heat-sealed composite fibers contained in the first fiber layer is typically 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0016] The first fiber layer may contain other components in addition to the hemp and thermally fused composite fibers, as long as the effects of the present invention are not impaired. Examples of such other components include flame retardants and fibers other than the hemp and thermally fused composite fibers (cotton fibers, chemical fibers, etc.).

[0017] The density of the first fiber layer is 0.3 to 1.0 g / cm 3When the density is in this range, the rigidity and sound absorption properties in the high frequency range of the resulting building material are improved. 3 If the density is less than 0.35 g / cm, the rigidity of the resulting building material will decrease. 3 More than 0.4 g / cm is preferable. 3 More preferably, 0.45 g / cm 3 On the other hand, the density is more preferably 1.0 g / cm or more. 3 If the density exceeds 0.9 g / cm, the sound absorption and heat insulation properties of the resulting building material will decrease. 3 Less than 0.8 g / cm is preferred 3 Less than 0.7 g / cm is more preferable. 3 More preferably, 0.6 g / cm 3 The following is particularly preferred: 0.55 g / cm 3 The following are most preferred:

[0018] The thickness of the first fiber layer is not particularly limited, but is preferably 1 to 10 mm. If the thickness is less than 1 mm, the rigidity of the resulting building material may be insufficient. The thickness is more preferably 1.5 mm or more, even more preferably 2 mm or more, and particularly preferably 2.2 mm or more. On the other hand, if the thickness exceeds 10 mm, the cost may be high. The thickness is more preferably 8 mm or less, even more preferably 6 mm or less, particularly preferably 4 mm or less, and most preferably 3 mm or less.

[0019] The heat-fusible conjugate fibers contained in the second fiber layer are the same as those contained in the first fiber layer.

[0020] The content of the heat-fusible composite fibers in the second fiber layer is preferably 10% by mass or more. If the content is less than 10% by mass, the peel strength of the resulting building material may be insufficient. The content is more preferably 15% by mass or more, and even more preferably 20% by mass or more.

[0021] The second fiber layer preferably contains fibers other than the thermally fused composite fibers, and the mass ratio of the other fibers to the thermally fused composite fibers (other fibers / thermally fused composite fibers) is 40 / 60 to 90 / 10. This further improves the sound absorption and heat insulation of the resulting building material. If the mass ratio (other fibers / thermally fused composite fibers) is less than 40 / 60, the rigidity of the resulting building material may be insufficient. The mass ratio (other fibers / thermally fused composite fibers) is more preferably 50 / 50 or more, even more preferably 55 / 45 or more, even more preferably 60 / 40 or more, and particularly preferably 65 / 35 or more. On the other hand, if the mass ratio (other fibers / thermally fused composite fibers) exceeds 90 / 10, the peel strength of the resulting building material may be insufficient. The mass ratio (other fibers / thermally fused composite fibers) is more preferably 85 / 15 or less, even more preferably 80 / 20 or less.

[0022] The other fibers are not particularly limited, but are preferably at least one selected from the group consisting of hemp, cotton, and chemical fibers, and are more preferably hemp, as this further improves the rigidity, sound absorption, and heat insulation of the resulting building material. Examples of hemp contained in the second fiber layer include those mentioned above as being contained in the first fiber layer. From the viewpoint of effective use of resources, it is also preferable to use, as the cotton or chemical fiber, defatted fibers obtained by defatting clothing, etc. The fiber diameter and fiber length of the other fibers are not particularly limited, but the fiber diameter is usually 15 to 100 μm, and the fiber length is usually 10 to 100 mm.

[0023] When the second fiber layer contains the other fibers, the total amount of hemp and the other fibers contained in the second fiber layer is typically 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0024] The second fiber layer may contain other components in addition to the fibers, such as a flame retardant, as long as the effects of the present invention are not impaired.

[0025] The density of the second fiber layer is 0.1 to 0.5 g / cm 3The density must be within this range. The sound absorption and heat insulation properties of the resulting building material are improved. The density must be 0.15 g / cm. 3 More than 0.2 g / cm is preferable. 3 More preferably, 0.25 g / cm 3 More preferably, the density is 0.45 g / cm. 3 Less than 0.4 g / cm is preferred 3 Less than 0.35 g / cm is more preferable. 3 The following is even more preferred:

[0026] In the building material, the density of the first fiber layer must be higher than the density of the second fiber layer. By laminating the high-density first fiber layers on both sides of the low-density second fiber layer, the rigidity, sound absorption, and heat insulation of the building material are improved. The density ratio of the first fiber layer to the second fiber layer (first fiber layer / second fiber layer) is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and particularly preferably 1.4 or more. Meanwhile, the ratio (first fiber layer / second fiber layer) is usually 5 or less, more preferably 4 or less, even more preferably 3 or less, and particularly preferably 2.5 or less.

[0027] As described above, the greatest feature of the present invention is a structure in which high-density first fiber layers containing hemp and thermally fused composite fibers are laminated on both outer sides of a low-density second fiber layer. Traditionally, cost has been a major consideration for building materials such as siding used for stabilizing finishing materials, and plywood, MDF, OSB, etc. have been used. However, these building materials inevitably emit formaldehyde due to the use of adhesives. Furthermore, due to their low sound absorption and thermal insulation properties, if these performance needs to be improved, it has been necessary to separately laminate sound-absorbing or thermal insulating materials. On the other hand, hemp is one of the strongest natural fibers, and has traditionally been widely used for hemp products such as hemp bags and hemp string. However, these hemp products are often discarded after use, and practical recycling methods have been sought. In light of these problems, the inventors conducted extensive research and found that a multilayer structure having the above-described configuration provides sufficient rigidity for use as a building material due to the high-density first fiber layer containing hemp and thermally fused composite fibers, while the low-density second fiber layer disposed therebetween improves sound absorption and thermal insulation. Furthermore, because the fibers are fused together using thermally fused composite fibers, no formaldehyde is emitted. Such multilayer structures are suitable for use as building materials such as floor coverings and wall materials, and may also contribute to the achievement of the SDGs.

[0028] In the building material, it is necessary that the first fiber layer be laminated on both outer sides of the second fiber layer. This improves the rigidity, sound absorption, and heat insulation of the resulting building material. From this perspective, it is preferable that the first fiber layer be laminated directly on both outer sides of the second fiber layer. The building material may have layers other than the first fiber layer and the second fiber layer as long as the effects of the present invention are not impaired. However, it is preferable that the building material consists only of the first fiber layer and the second fiber layer. Specific layer configurations of the building material include first fiber layer / second fiber layer / first fiber layer, first fiber layer / second fiber layer / first fiber layer / second fiber layer / first fiber layer, and first fiber layer / second fiber layer / first fiber layer / second fiber layer / first fiber layer / first fiber layer / first fiber layer / first fiber layer, etc., and first fiber layer / second fiber layer / first fiber layer / second fiber layer / first fiber layer / first fiber layer / first fiber layer / first fiber layer / first fiber layer / first fiber layer / first fiber layer is preferred from the viewpoint of an excellent balance between productivity and performance.

[0029] The thickness of the second fiber layer is not particularly limited, but is preferably 3 to 20 mm. If the thickness is less than 3 mm, the sound absorption and heat insulation properties of the resulting building material may be insufficient. The thickness is more preferably 3.5 mm or more, and even more preferably 4 mm or more. On the other hand, if the thickness exceeds 20 mm, the cost may be high. The thickness is more preferably 15 mm or less, even more preferably 10 mm or less, and particularly preferably 8 mm or less.

[0030] The total thickness of the building material is not particularly limited, but is preferably 5 to 45 mm. If the thickness is less than 5 mm, the resulting building material may have insufficient rigidity, sound absorption, or heat insulation. The thickness is more preferably 6 mm or more, even more preferably 7 mm or more, and particularly preferably 8 mm or more. On the other hand, if the thickness exceeds 45 mm, costs may be high. The thickness is more preferably 40 mm or less, even more preferably 30 mm or less, particularly preferably 20 mm or less, and most preferably 15 mm or less.

[0031] The Young's modulus of bending of the building material measured in accordance with JIS A5905 is 700 to 1500 N / mm 2 Such a building material is easy to handle and is suitable for use at construction sites, etc. The Young's modulus of bending is preferably 800 N / mm 2 More preferably, 850N / mm 2 On the other hand, the bending Young's modulus is 1400 N / mm 2 Less than 1300N / mm is more preferable. 2 The following is even more preferred:

[0032] The bending strength of the building material measured in accordance with JIS A5905 is 5N / mm 2 Such building materials are easy to handle and are suitable for use at construction sites, etc. The bending strength is preferably 7 N / mm 2 More preferably, 8N / mm 2 On the other hand, the bending strength is usually 50 N / mm 2 The following is the result.

[0033] The wood screw holding strength of the building material measured in accordance with JIS A5905 is preferably 100 N or more, more preferably 150 N or more, and even more preferably 200 N or more. On the other hand, the holding strength is usually 1000 N or less.

[0034] The building material preferably has a formaldehyde emission amount of less than 0.1 mg / L as measured in accordance with JIS A1460 (Testing method for formaldehyde emission amount from building boards - desiccator method).

[0035] The normal incidence sound absorption coefficient of the building material is preferably 0.02 or more, more preferably 0.03 or more, at 250 Hz. The normal incidence sound absorption coefficient of the building material is preferably 0.05 or more, more preferably 0.07 or more, at 500 Hz. When the normal incidence sound absorption coefficient of the building material is within the above range, noise in apartment buildings and the like can be effectively reduced.

[0036] The sound transmission loss of the building material is preferably 5 dB or more, more preferably 7 dB or more, at 250 Hz. The sound transmission loss of the building material is preferably 10 dB or more, more preferably 12 dB or more, at 500 Hz. When the sound transmission loss of the building material is within the above range, noise in apartment buildings and the like can be effectively reduced.

[0037] The thermal conductivity of the building material is preferably 0.12 W / m / k or less, and more preferably 0.1 W / m / k or less. The normal incidence sound absorption coefficient, sound transmission loss, and thermal conductivity of the building material are measured by the methods described in the examples.

[0038] The manufacturing method of the building material is not particularly limited, but it is preferable to form a first fiber layer by hot pressing a felt containing hemp and heat-fusible composite fiber, and then to form a second fiber layer by placing a felt containing heat-fusible composite fiber between the first fiber layers and further hot pressing the felt.

[0039] When hemp products such as hemp bags and hemp strings are used as the raw hemp material for the building material, the hemp products are de-piled into fibers using a de-piling machine. A general de-piling machine is used as the de-piling machine. The hemp fibers obtained by such a method or the like and the heat-melt composite fibers are blended in a blending machine, and the blended material is then fed to a felt manufacturing machine to obtain felt. A general felt manufacturing machine is used as the felt manufacturing machine. The basis weight of the felt used in the first fiber layer can be adjusted appropriately depending on the density and thickness of the first fiber layer, and is, for example, 750 to 2500 g / m 2 is.

[0040] The felt thus obtained is heat-pressed to obtain a first fiber layer. The temperature and pressure may be appropriately adjusted depending on the type of heat-fusible composite fiber in the felt, the thickness of the felt, the target thickness of the first fiber layer, etc. For example, the temperature is 160 to 200°C and the pressure is 2 to 7 MPa. Furthermore, a spacer may be used during heat-pressing to adjust the thickness.

[0041] When the second fiber layer does not contain any fibers other than the heat-sealed composite fiber, the felt used for the second fiber layer can be obtained in the same manner as for the first fiber layer, except that no hemp is used and no cotton is mixed in.

[0042] When the second fiber layer contains fibers other than the heat-sealed composite fibers, a felt containing the heat-sealed composite fibers and the other fibers can be obtained in the same manner as the first fiber layer, except that the other fibers are used instead of hemp.

[0043] A felt containing heat-fusible conjugate fibers and, if necessary, the other fibers is placed between the first fiber layers, and then the resulting mixture is hot-pressed to form a second fiber layer, thereby obtaining a multilayer structure. The temperature and pressure used during this process can be adjusted appropriately depending on the type of heat-fusible conjugate fibers contained in each layer and the target thickness of the multilayer structure, and are, for example, 160 to 200°C and 2 to 7 MPa, respectively. Furthermore, spacers may be used during hot-pressing to adjust the thickness.

[0044] At least one surface of the multilayer structure thus obtained may be embossed, which makes it easier to adjust unevenness when the multilayer structure is used as a floor covering material.

[0045] The building material of the present invention, which is made of a multilayer structure obtained in this way, emits little formaldehyde and has excellent sound absorption and heat insulation properties. Moreover, since hemp products such as hemp bags can be used as raw materials, it is low cost and may contribute to the achievement of the SDGs. Such building materials are suitable for use as floor coverings, wall coverings, etc., and are particularly suitable for use as floor coverings. [Example]

[0046] The present invention will be explained in more detail below using examples.

[0047] Example 1 Hemp bags for coffee beans were depilated using a depilling machine to obtain depilled fibers (hemp fibers) with a length of 1 to 40 mm and a diameter of 15 to 100 μm. In a cotton blending machine, 51 parts by mass of the obtained depilled fibers were blended with 49 parts by mass of sheath-core thermally fused composite fibers (sheath: polyester with a melting point of 110°C, core: copolymer polyester with a melting point of 240°C, mass ratio (core / sheath) 50 / 50, 4 denier (diameter 35 to 40 μm), fiber length 20 to 45 mm) to obtain a cotton-like blended cotton material. The blended cotton material was fed to a felt manufacturing machine, compressed in the furnace of the felt manufacturing machine, and then cooled at the outlet, resulting in a fabric with a basis weight of 1250 g / m. 2 The felt was compressed to a thickness of 2.5 mm in a hot press (temperature 170°C, load 5 MPa), and then cooled and pressed (temperature 15°C, load 5 MPa) to produce a rectangular single-layer hemp board (first fiber layer) with a thickness of 2.5 mm, length 1820 mm, and width 910 mm, which was to form the first fiber layer (surface layer and back layer).

[0048] It is a blend of 70 parts by mass of reclaimed wool fiber and 30 parts by mass of sheath-core type heat-fused composite fiber, and has a basis weight of 1300 g / m 2The same process as for the hemp board (first fiber layer) was carried out except that the amount of the mixed cotton material fed to the felt manufacturing machine was adjusted so that the weight of the second fiber layer was 1300 g / m. 2 The following felt was produced.

[0049] The felt (second fiber layer) was sandwiched between the two hemp boards (first fiber layers), and spacers were placed to adjust the thickness. The resulting structure was then compressed again in a hot press (temperature 170°C, load 5 MPa) to obtain a multilayer structure. Furthermore, one side of the multilayer structure was embossed to obtain a thickness of 4.0 mm and a density of 0.33 g / cm. 3 The second fiber layer has a thickness of 2.5 mm and a density of 0.5 g / cm on both sides. 3 The first fiber layer was laminated to obtain a three-layered multilayer structure (building material). The embossing was performed by laminating a mesh Teflon sheet ("HONDAFLON FABRIC" (material: HGS-M580) manufactured by Honda Sangyo Co., Ltd.) with 1.2 mm holes on one side of the multilayer structure, and then hot pressing and cold pressing. The density (g / cm) of each layer was 3 ) is the basis weight a (g / m 2 ) and thickness b (cm) using the following formula. Density=a / (b×10000)

[0050] (1) Formaldehyde emission amount Based on JIS A1460 (Testing method for formaldehyde emission from building boards - Desiccator method), ten rectangular test pieces measuring 50 mm wide and 150 mm long were cut from the resulting building material and placed in a 10 L desiccator. After leaving them at 20°C for 24 hours, the concentration of formaldehyde absorbed in 300 mL of distilled water was determined by the acetylacetone method. The results are shown in Table 1.

[0051] (2) Sound transmission loss The intensity sound transmission loss measurement was carried out as follows. A square test piece, 900 mm long, was cut out from the obtained building material and placed so as to block the opening (each side was 810 mm square) between the reverberation chamber and the anechoic chamber, and fixed in place with clay. Four speakers were placed in the reverberation chamber, and sound was generated using uncorrelated white noise, and the sound intensity transmitted to the anechoic chamber side was measured. Intensity sound transmission loss R I was calculated using the following formula from the average indoor sound pressure level measured in a reverberation room and the normal sound intensity level measured in an anechoic room.

[0052]

number

[0053] In formula (1), L pl : Average indoor sound pressure level in a reverberation room (dB) L In : Average value (dB) of normal sound intensity level on the measurement surface set up in an anechoic chamber S M : Total area of ​​the measurement surface (m 2 ) S: Area of ​​the test piece to be measured (m 2 ) is.

[0054] The average sound pressure level in the reverberation chamber was determined from measurements (average time 10 seconds) using microphones placed at six points in the reverberation chamber. The sound intensity measurement plane was parallel to the test specimen and placed on one surface 0.1 m from the test specimen. The measurement plane was a square measuring 1.0 m in length and 1 m in width, with a measurement grid of 10 x 10. The sound intensity (normal sound intensity) was measured in the direction perpendicular to the measurement plane at the center of each grid. The measurement time was 10 seconds. The average intensity level was calculated from the measured sound intensity. The measurement results for intensity sound transmission loss are shown in Table 2 and Figure 1.

[0055] Other measurement conditions were as follows: ·Temperature 19.6℃, humidity 58.5% Reverberation chamber, internal volume 251.3m 3 , surface area 237.4m 2 , without diffuser Anechoic chamber size: 6.6m x 4.4m x 5.2m, background noise: 15dB(A) or less

[0056] (3) Sound absorption coefficient The normal incidence sound absorption coefficient of the obtained building materials was measured (acoustic sound absorption coefficient measurement (transfer function method)). The building materials were cut into circular test pieces with a diameter of 100 mm or 29 mm to prepare test pieces. The position of the back panel was determined according to the thickness of the test piece, and the test piece was inserted into the test piece holder. Measurements were also conducted for the case without a back air space. Two types of impedance measurement tubes were used depending on the measurement frequency: a large measurement tube (50 to 1600 Hz: diameter 100 mm) and a small measurement tube (500 to 6400 Hz: diameter 29 mm). The measurement conditions were as follows: The measurement results were calculated for each 1 / 3 octave band, and the measurement results of three samples were arithmetically averaged. The measurement results using the large measurement tube are shown in Table 3 and Figure 2, and the measurement results using the small measurement tube are shown in Table 4 and Figure 3. ·Temperature 26℃, humidity 25% Impedance measurement tube: Brüel & Kjær 4206 (JIS1405-2 compliant) Measuring instrument: Brüel & Kjær PUKLSE 3560 Measurement software: Spectris, Brüel & Kjær Division MS1021

[0057] (4) Thermal conductivity The thermal conductivity of the building materials was measured using a steady-state method. The thermal conductivity of the building materials is shown in Table 1. The thermal conductivity of commercially available plywood used as battening material, etc., was measured using the above method and was found to be 0.16 W / m / k.

[0058] (5) Bending test The resulting building materials were subjected to a bending test in accordance with JIS A5905. The building materials were cut into rectangular specimens measuring 200 mm in length and 50 mm in width. The bending test was performed over a span of 150 mm, applying a load so that the average deformation rate was 10 mm / min. The tests were performed twice in both the longitudinal and transverse directions, and the average values ​​were used as the bending strength and bending Young's modulus. The results are shown in Table 5.

[0059] (6) Wood screw holding strength The wood screw holding strength of the resulting building materials was measured in accordance with JIS A5905. The results are shown in Table 5.

[0060] Example 2 Building materials were produced and evaluated in the same manner as in Example 1, except that the basis weight of the felt used in the first and second fiber layers was adjusted as shown in Table 1 by changing the amount of blended cotton supplied to the felt manufacturing machine. However, the building materials were evaluated only for the above-mentioned "(4) Thermal conductivity." The results are shown in Table 1.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Table 3]

[0064] [Table 4]

[0065] [Table 5]

Claims

1. A building material comprising a multilayer structure having a first fiber layer and a second fiber layer, The first fiber layer contains hemp and thermally fused composite fibers, and the mass ratio of the hemp to the thermally fused composite fibers (hemp / thermally fused composite fibers) is 30 / 70 to 80 / 20; the second fiber layer includes heat-bonded composite fibers; The density of the first fiber layer is 0.3 to 1.0 g / cm ３ , the density of the second fiber layer is 0.1 to 0.5 g / cm ３ and the density of the first fiber layer is higher than the density of the second fiber layer; A building material in which a first fiber layer is laminated on both outer sides of a second fiber layer.

2. 2. The building material according to claim 1, wherein the second fiber layer contains fibers other than the thermally fused conjugate fibers, and the mass ratio of the other fibers to the thermally fused conjugate fibers (other fibers / thermally fused conjugate fibers) is 40 / 60 to 90 / 10.

3. The building material according to claim 2 , wherein the other fiber contained in the second fiber layer is at least one type selected from the group consisting of hemp, cotton, and chemical fibers.

4. 2. The building material of claim 1, wherein at least one surface of the multilayer structure is embossed.

5. 2. The building material of claim 1, which is a floor covering material.

6. 6. The method for producing a building material according to claim 1, wherein a felt containing hemp and thermally fused composite fibers is hot-pressed to form a first fiber layer, and then a felt containing thermally fused composite fibers is placed between the first fiber layers, and then the second fiber layer is formed by further hot-pressing.

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