Base material for flooring material, flooring material, and manufacturing method of flooring material

Abstract

To provide a base material for flooring material with excellent soundproofing and hardly warping, and applicable to flooring materials for underfloor heating using softwood plywood, a flooring material including the same, and a manufacturing method of flooring material.SOLUTION: A plywood 11 includes seven layers, and seven softwood planks are stacked so that the fiber direction (first direction) of the first, third, fifth, seventh layers 11a, 11c, 11e, and 11g is perpendicular to the fiber direction (second direction) of the second, fourth, and sixth layers 11b, 11d, and 11f. On the back of the plywood 11, there are formed multiple first grooves 41 extending in the second direction from the back surface to the second layer 11b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a base material for floor covering, a floor covering, and a method for manufacturing a floor covering.

Background Art

[0002] Conventionally, a soundproof floor covering for floor heating, which includes a base material provided with a decorative layer on the surface and a cushioning material on the back surface and is constructed on a floor heating panel, has been proposed (for example, see Patent Document 1 below). In Patent Document 1, the base material for the floor covering is configured by a back-grooved plywood in which a plurality of grooves extending parallel to each other are formed on the back surface of the plywood. In the above floor covering, the plurality of back grooves formed on the back surface of the base material for the floor covering facilitate uniform heat transfer to the floor covering surface and impart flexibility to the floor covering to improve soundproofing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, although a plywood of a tropical wood such as lauan plywood has been used as the base material for the above floor covering, in recent years, it has become difficult to obtain tropical wood plywood itself in terms of depletion of raw materials and prevention of environmental destruction, and replacement with softwood plywood has been attempted. Since softwood plywood is softer than hardwood plywood such as lauan plywood, if the base material of the floor covering is replaced with softwood plywood, the floor covering will lack surface strength and be easily damaged. Therefore, in some cases, medium density fiberboard is attached to the surface of softwood plywood to enhance the surface strength.

[0005] However, medium density fiberboard is more likely to absorb moisture and expand and contract compared to plywood. Therefore, in a base material where medium density fiberboard is attached to the surface of plywood to enhance the surface strength, it is more likely to warp than a base material consisting only of plywood. In particular, when the base material is composed of a back groove processed plywood like the soundproof flooring material for floor heating described in Patent Document 1, although the sound insulation performance can be improved by a plurality of back grooves, the fibers that can counter the dimensional changes due to moisture absorption or desorption of the medium density fiberboard are cut off by the back grooves, making the base material more likely to warp. Further, in the above-mentioned soundproof flooring material for floor heating, since it is constructed on a floor heating panel and the temperature change is large, the base material is more likely to warp. On the other hand, since a cushioning material is provided, the flooring material cannot be pressed against and fixed to the floor heating panel, and the warping of the base material cannot be suppressed. Also, if the thickness of the plywood is increased to counter the medium density fiberboard in order to suppress warping, there is a problem that the rigidity of the entire base material becomes too high and the desired sound insulation performance cannot be obtained.

[0006] The present invention has been made in view of such points, and an object thereof is to provide a base material for a flooring material that is excellent in sound insulation and is applicable to a flooring material for floor heating and is less likely to warp even when using softwood plywood, a flooring material provided with the same, and a method for manufacturing the flooring material.

Means for Solving the Problems

[0007] In order to achieve the above object, in this invention, the number of plies of plywood is set to 7 plies, and seven softwood thin plates are laminated so that the fiber directions (first direction) of the first, third, fifth, and seventh layers and the fiber directions (second direction) of the second, fourth, and sixth layers are orthogonal to each other, and a plurality of first grooves extending in the second direction and reaching the second layer from the back surface are formed on the back surface of the plywood.

[0008] Specifically, the first invention is a base material for a floor material in which a surface strengthening layer made of medium density fiberboard is adhered to the surface of a plywood. The plywood is a softwood plywood having first to seventh layers made of seven softwood thin plates laminated and adhesively integrated in order from the front surface side to the back surface side such that the fiber directions of adjacent two sheets are orthogonal to each other. On the back surface of the plywood, a plurality of first grooves extending in a second direction orthogonal to the first direction which is the fiber direction of the first layer are formed at a first groove interval. The first groove extends from one end to the other end of the plywood in the second direction, and the groove bottom is located within the second layer.

[0009] In the first invention, the number of plies of the plywood is set to 7 plies, and a plurality of first grooves having a depth reaching from the back surface to the second layer are formed on the back surface of the plywood. As the plywood for the base material of the floor material, those having 3 plies or 5 plies are often used. However, in the first invention, since the number of plies of the plywood is set to 7 plies, the portions adhered with an adhesive (the interfaces between the layers made of softwood thin plates) increase as compared with 3-ply plywood or 5-ply plywood, so the strength is improved as compared with 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood is set to 7 plies, the first grooves reaching from the back surface to the second layer are deeper than when the first grooves are similarly formed in 3-ply plywood or 5-ply plywood. With such deep plurality of first grooves, the rigidity of the plywood decreases and the flexibility increases, making it easier to absorb impact force. That is, when the base material for the floor material according to the first invention is used, the floor material has the required sound insulation performance and is excellent in soundproofing.

[0010] Further, in the first invention, since the plurality of first grooves extending in the direction (second direction) orthogonal to the fiber direction (first direction) of the first layer of the plywood do not reach the first layer, the fibers of the first layer are not cut off. With such a configuration, in the first invention, even when the medium density fiberboard adhered to the surface of the plywood expands and contracts in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer extending in the first direction. Thereby, it becomes difficult for the base material for the floor material to expand and contract in the first direction due to moisture absorption or desorption, and warping in the first direction is suppressed.

[0011] As described above, according to the first invention, it is possible to provide a base material for a floor material with excellent sound insulation properties that is less likely to warp even when using a coniferous plywood and is applicable to a floor material for floor heating.

[0012] A second invention is characterized in that, in the first invention, at least one second groove extending in the first direction from one end to the other end of the plywood in the first direction is formed on the back surface of the plywood.

[0013] In the second invention, not only the first groove but also at least one second groove extending in a direction (first direction) orthogonal to the extending direction (second direction) of the first groove is formed on the back surface of the plywood. By forming the second groove in this way, compared with the case where only the first groove is formed, the rigidity of the plywood is reduced and the flexibility is increased, making it easier to absorb the impact force. That is, according to the second invention, it is possible to provide a base material for a floor material with more excellent sound insulation properties.

[0014] A third invention is characterized in that, in the second invention, the bottom of the second groove is located within any one of the third to fifth layers.

[0015] Also, in the third invention, since the second groove extending in the direction (first direction) orthogonal to the fiber direction (second direction) of the second layer does not reach the second layer, the fibers of the second layer extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the medium-density fiberboard adhered to the surface of the plywood are not cut off. With such a configuration, in the third invention, even if the medium-density fiberboard adhered to the surface of the plywood expands or contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer extending in the second direction. As a result, it becomes difficult for the base material for the floor material to expand and contract in the second direction due to moisture absorption or desorption, and warping in the second direction is suppressed. That is, according to the base material for the floor material according to the third invention, not only is warping in the fiber direction (first direction) of the first layer suppressed, but also warping in the orthogonal direction (second direction) is suppressed.

[0016] A fourth invention is characterized in that, in the third invention, the bottom of the second groove is located within the fourth layer.

[0017] In the fourth invention, since the second groove does not reach the third layer, not only are the fibers of the second layer extending in the second direction, which can counter the dimensional changes due to moisture absorption or desorption of the medium density fiberboard, not cut off, but also, by covering the second layer with the first layer and the third layer, even if the medium density fiberboard adhered to the surface of the plywood tries to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are more suppressed by the fibers of the second layer extending in the second direction. As a result, it becomes difficult for the base material for flooring to expand and contract in the second direction due to moisture absorption or desorption, and a flooring material that is less likely to warp in the second direction can be provided.

[0018] Also, the inventors of the present application conducted a verification test on the correlation between the depth of the second groove, the sound insulation performance of the flooring material, and warping. As a result of the verification test, it was found that as the depth of the second groove increases, the sound insulation performance improves, while warping in the second direction becomes more likely to occur. Further, in the case where the groove bottom of the second groove is located within the third to fifth layers, it is possible to form a flooring material that has the required sound insulation performance and is less likely to warp in the second direction. In particular, from the viewpoints of sound insulation performance and warping, it was found that it is preferable that the groove bottom of the second groove is located within the fourth layer. Therefore, in the fourth invention, the second groove is formed to have a depth such that the groove bottom is located within the fourth layer. Accordingly, according to the fourth invention, it is possible to provide a flooring material that is less likely to warp and has excellent sound insulation properties suitable for floor heating flooring.

[0019] The fifth invention is the first invention, wherein the softwood thin plates constituting the first, third, fifth, and seventh layers are each composed of a single veneer, while the softwood thin plates constituting the second, fourth, and sixth layers are formed by splicing a plurality of veneers in the first direction, and the second layer is characterized in that there are no knots with a size in the first direction larger than the first groove interval.

[0020] In the fifth invention, each layer of the plywood is composed of softwood veneers. Although softwood has more knots than hardwood, if the softwood veneer forming the second layer has a knot hole with a size in the first direction larger than the groove interval (the first groove interval) of the first groove, the fibers of the second layer extending in the second direction that can resist dimensional changes due to moisture absorption or desorption of the medium-density fiberboard will be cut off by the knot hole, resulting in the inability to resist dimensional changes due to moisture absorption or desorption of the medium-density fiberboard and the possibility of partial warping occurring in the second direction. However, according to the fifth invention, since the second layer has no knot hole with a size in the first direction larger than the first groove interval, the effect of suppressing warping in the second direction can be expected.

[0021] The sixth invention is characterized in that, in the first invention, the first layer is composed of a part without knot holes of softwood or is composed of a part with knot holes of softwood and the knot holes are filled with putty so that there are no knot holes, and the second layer is composed of a part without knot holes of softwood with a size exceeding 20 mm or is composed of a part with knot holes of softwood with a size exceeding 20 mm and the knot holes with a size exceeding 20 mm are filled with plugs so that there are no knot holes with a size exceeding 20 mm.

[0022] The inventors of the present application conducted a verification test on the correlation between the presence or absence of knots in the first to third layers of plywood and the Brinell hardness of the floor material surface. As a result of the verification test, if there are knots in the first layer constituting the surface layer of the plywood or knots with a size exceeding 20 mm in the second layer, the Brinell hardness of the floor material surface is lower than the desired hardness. Even if there are knots with a size exceeding 20 mm in the third layer, if there are no knots in the first layer and no knots with a size exceeding 20 mm in the second layer, it was found that the Brinell hardness of the floor material surface is above the desired hardness. That is, it was found that if the floor material is formed with knots in the first layer of the plywood or knots with a size exceeding 20 mm in the second layer, the floor material may be easily damaged. In addition, if there are knots in the first layer constituting the surface layer of the plywood, it may deteriorate the surface properties of the floor material and lead to a decrease in the design quality of the floor material. In particular, when a thin (for example, 1.5 mm or less) medium density fiberboard is used as the surface strengthening layer in order to minimize the influence of warping, if there are knots near the surface layer of the plywood, the influence of the knots (such as unevenness) will be manifested up to the decorative material through the surface strengthening layer made of the thin medium density fiberboard, and the possibility of deteriorating the design quality of the floor material will increase.

[0023] Therefore, in the sixth invention, it is configured such that there are no knots in the first layer and no knots larger than 20 mm in the second layer. Specifically, the first layer is composed of a part without knots in coniferous trees or, if it is composed of a part with knots in coniferous trees, the knots are filled with putty and disappeared so that there are no knots. Also, the second layer is composed of a part without knots larger than 20 mm in coniferous trees or, if it is composed of a part with knots larger than 20 mm in coniferous trees, the knots larger than 20 mm are disappeared by plugging treatment so that there are no knots larger than 20 mm. Note that the plugging treatment refers to a treatment of drilling a hole including a knot and filling the hole without gaps with wood (plug wood) having the same shape as the drilled hole to disappear the knot. In the sixth invention, by configuring such that there are no knots in the first layer and no knots larger than 20 mm in the second layer in this way, the floor material produced using the base material for floor materials is difficult to be damaged and has good surface properties. Therefore, by using the base material for floor materials according to the sixth invention, a floor material that is difficult to be damaged and has good surface properties can be provided.

[0024] The seventh invention is characterized in that, in the first invention, the medium density fiberboard is made mainly of hardwood xylem fibers.

[0025] In the seventh invention, since the tracheary element fibers of coniferous trees have a significantly higher porosity and water absorption rate than the hardwood xylem fibers, a medium density fiberboard (hardwood MDF) made mainly of hardwood xylem fibers is used as the surface strengthening layer. By using hardwood xylem fibers as the medium density fiberboard constituting the surface strengthening layer in this way, the water absorption rate of the surface strengthening layer can be kept low and the dimensional change can be suppressed.

[0026] The eighth invention is, in the first invention, on one of two opposite side surfaces of the base material for the floor covering, a concave groove portion serving as a female mating part is formed in the middle part in the thickness direction, and on the other side, a convex rib portion serving as a male mating part is formed in the middle part in the thickness direction. In the base material for the floor covering, a front convex part adjacent to the front side of the concave groove portion, a back convex part adjacent to the back side of the concave groove portion, and the convex rib portion are formed so as to straddle a plurality of layers of the plywood.

[0027] In the eighth invention, surface treatment is performed on the peripheral side surface of the base material for the floor covering, and the convex parts (front convex part, back convex part, convex rib portion) protruding outside the female and male mating parts are formed so that they always straddle a plurality of layers of the plywood. The convex parts of the female and male mating parts are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the eighth invention, it is possible to provide a base material for a floor covering in which the convex parts of the female and male mating parts are less likely to chip.

[0028] The ninth invention is, in the eighth invention, characterized in that the female mating part is formed such that the groove bottom corner of the concave groove portion is located within one of the layers rather than in the adhesive part between the layers of the plywood.

[0029] In the ninth invention, the female mating part is formed such that the groove bottom corner of the concave groove portion of the female mating part is located within one of the layers so as not to be located in the adhesive part between any of the layers of the plywood. When the groove bottom corner of the concave groove portion of the female mating part is located in the adhesive part between the layers of the plywood, the plywood is likely to peel at a certain layer when the convex rib portion of the male mating part is inserted, but according to the above configuration, such peeling can be suppressed.

[0030] The tenth invention is a floor covering comprising a base material for a floor covering and a cushioning material adhered to the back surface of the base material for the floor covering, wherein the base material for the floor covering is a base material for a floor covering according to any one of the first to ninth inventions.

[0031] According to the tenth invention, by providing the base material for flooring according to any one of the first to ninth inventions, even when using a softwood plywood, it is possible to provide a flooring excellent in sound insulation that is less likely to warp and applicable to flooring for floor heating.

[0032] The eleventh invention is a method for manufacturing a flooring comprising a base material for flooring having a surface strengthening layer made of medium density fiberboard adhered to the surface of a plywood, and a cushioning material adhered to the back surface of the base material for flooring. Seven softwood thin plates having the same thickness are laminated in order such that an aqueous adhesive is interposed between each of them and the fiber directions of two adjacent softwood thin plates are orthogonal to each other, and hot press pressing is performed in the thickness direction to form a plywood having the first to seventh layers made of the softwood thin plates laminated in order from the front surface side to the back surface side and adhesively integrated, which is a plywood forming step; after sanding the surface of the plywood, adhering the surface strengthening layer to the surface to obtain the base material for flooring, which is a surface strengthening layer adhering step; forming a plurality of first grooves extending in a second direction orthogonal to a first direction which is the fiber direction of the first layer on the back surface of the plywood, with a first groove interval, which is a groove processing step; and adhering a cushioning material to the back surface of the plywood after the groove processing step, which is a cushioning material adhering step. The first groove extends from one end to the other end of the plywood in the second direction, and the groove bottom is located within the second layer.

[0033] In the 11th invention, a plurality of first grooves with a depth reaching from the back surface to the second layer are formed on the back surface of a plywood with 7 plies. As the plywood for the base material of the flooring material, those with 3 plies or 5 plies are often used. However, in the 11th invention, since the number of plies of the plywood is 7 plies, the locations adhered with the water-based adhesive (the interfaces between the layers made of softwood veneers) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood is 7 plies, the first grooves reaching from the back surface to the second layer become deeper compared to the case where the first grooves 41 are similarly formed in 3-ply plywood or 5-ply plywood. Due to such deep plurality of first grooves, the rigidity of the plywood decreases and the flexibility increases, making it easier to absorb the impact force. That is, according to the manufacturing method according to the 11th invention, it is possible to provide a flooring material having the required sound insulation performance and excellent soundproofing performance.

[0034] Also, in the 11th invention, a plurality of first grooves extending in the direction (second direction) orthogonal to the fiber direction (first direction) of the first layer of the plywood do not reach the first layer, so that the fibers of the first layer are not cut off by the first grooves. By forming the first grooves in this way, even when the medium density fiberboard adhered to the surface of the plywood attempts to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer extending in the first direction. Thereby, it is possible to manufacture a flooring material that is difficult to expand and contract in the first direction due to moisture absorption or desorption and is difficult to warp in the first direction.

[0035] Also, in the 11th invention, although a plywood with 3 plies or 5 plies is often used for the base material of the flooring material, the number of plies of the plywood is set to 7 plies and it is adhered with a water-based adhesive. Therefore, in the 11th invention, compared to the case of forming 3-ply or 5-ply plywood, the laminate of softwood veneers is hot-pressed in a state with a higher moisture content, and the formed plywood becomes thinner and has a higher density from the middle in the thickness direction toward the outermost layer. According to the 11th invention, by using a plywood having such a configuration, it is possible to provide a flooring material with excellent surface strength.

[0036] As described above, according to the 11th invention, it is possible to provide a flooring material with excellent sound insulation properties that is less likely to warp even when using a coniferous plywood and is applicable to flooring materials for floor heating.

[0037] The 12th invention is characterized in that, in the 11th invention, in the groove processing step, a plurality of first grooves are formed on the back surface of the plywood, and at least one second groove extending in the first direction from one end to the other end of the plywood in the first direction is formed.

[0038] In the 12th invention, not only the first grooves but also at least one second groove extending in a direction (the first direction) orthogonal to the extending direction (the second direction) of the first grooves are formed on the back surface of the plywood. By forming the second grooves in this way, compared with the case where only the first grooves are formed, the rigidity of the plywood decreases and the flexibility increases, making it easier to absorb impact force. That is, according to the 12th invention, it is possible to provide a base material for a flooring material with more excellent sound insulation properties.

[0039] The 13th invention is characterized in that, in the 12th invention, the bottom of the second groove is located within any one of the third to fifth layers.

[0040] In the 13th invention, the second groove extending in the direction (the first direction) orthogonal to the fiber direction (the second direction) of the second layer is not extended to the second layer, so that the fibers of the second layer extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the medium density fiberboard are not cut off by the second groove. By forming the second groove in this way, even when the medium density fiberboard adhered to the surface of the plywood tries to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer extending in the second direction. As a result, it becomes difficult for the base material for the flooring material to expand and contract in the second direction due to moisture absorption or desorption, and warping in the second direction is suppressed. That is, according to the base material for the flooring material according to the 13th invention, it is possible to provide a flooring material that is less likely to warp not only in the fiber direction (the first direction) of the first layer but also in the orthogonal direction (the second direction).

[0041] The 14th invention is characterized in that, in the 13th invention, the second groove has a groove bottom located within the fourth layer.

[0042] In the 14th invention, since the second groove does not reach the third layer, not only are the fibers of the second layer extending in the second direction, which can counter the dimensional changes due to moisture absorption or desorption of the medium-density fiberboard, not cut off, but also because the second layer is covered by the first layer and the third layer, even if the medium-density fiberboard adhered to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or desorption, the expansion and contraction are more suppressed by the fibers of the second layer extending in the second direction. As a result, it becomes difficult for the base material for the flooring material to expand or contract in the second direction due to moisture absorption or desorption, and a flooring material that is less likely to warp in the second direction can be provided.

[0043] Also, in the 14th invention, based on the results of the verification test on the correlation between the depth of the above-mentioned second groove, the sound insulation performance of the flooring material, and the dimensional stability (warpage), the second groove is formed to have a depth with the groove bottom located within the fourth layer. Therefore, according to the 14th invention, a flooring material with excellent sound insulation suitable for a floor heating flooring material and less likely to warp can be provided.

[0044] The 15th invention is characterized in that, in the 11th invention, the softwood thin plates constituting the first, third, fifth, and seventh layers are each composed of a single veneer, while the softwood thin plates constituting the second, fourth, and sixth layers are made by splicing a plurality of veneers in the first direction, and the second layer is made to have no knot holes with a size in the first direction larger than the first groove interval.

[0045] In the 15th invention, a plywood is formed by laminating and integrating seven softwood veneers. Although softwood has more knots than hardwood, if the softwood veneer constituting the second layer has a knot hole with a size in the first direction larger than the groove interval (the first groove interval) of the first groove, the fibers of the second layer extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the medium-density fiberboard will be cut off by the knot hole. As a result, it is impossible to counter the dimensional change due to moisture absorption or desorption of the medium-density fiberboard, and there is a risk of partial warping in the second direction. However, according to the 15th invention, since the second layer does not have a knot hole with a size in the first direction larger than the first groove interval, the effect of suppressing warping in the second direction can be expected.

[0046] The 16th invention is characterized in that, in the 11th invention, the first layer is constituted by a part without knot holes of softwood or is constituted by a part with knot holes of softwood and the knot holes are filled with putty to make it without knot holes, and the second layer is constituted by a part without knot holes of softwood with a size exceeding 20 mm or is constituted by a part with knot holes of softwood with a size exceeding 20 mm and the knot holes with a size exceeding 20 mm are filled with plugs to make it without knot holes with a size exceeding 20 mm.

[0047] In the 16th invention, it is configured such that there are no knots in the first layer and no knots with a size exceeding 20 mm in the second layer. Specifically, the first layer is composed of a part without knots of coniferous trees or, if it is composed of a part with knots of coniferous trees, the knots are filled with putty and disappeared to make it knot-free. Also, the second layer is composed of a part without knots of coniferous trees with a size exceeding 20 mm or, if it is composed of a part with knots of coniferous trees with a size exceeding 20 mm, the knots with a size exceeding 20 mm are made to disappear by inlaying treatment, so that there are no knots with a size exceeding 20 mm. In the 16th invention, by configuring it such that there are no knots in the first layer and no knots with a size exceeding 20 mm in the second layer in this way, the floor material made using the base material for floor materials is difficult to be damaged and has good surface properties. Therefore, by using the base material for floor materials according to the 16th invention, a floor material that is difficult to be damaged and has good surface properties can be provided.

[0048] The 17th invention is characterized in that, in the 11th invention, the medium-density fiberboard is made mainly from hardwood xylem fibers.

[0049] In the 17th invention, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate than the hardwood xylem fibers, a medium-density fiberboard made mainly from hardwood xylem (hardwood MDF) is used as the surface strengthening layer. By using hardwood xylem fibers as the medium-density fiberboard constituting the surface strengthening layer in this way, the water absorption rate of the surface strengthening layer can be kept low, and dimensional changes can be suppressed.

[0050] The 18th invention further includes, in the 11th invention, a step of forming a concave groove part serving as a female joint in the middle part in the thickness direction on one of the two opposite side surfaces of the base material for floor materials, and forming a convex rib part serving as a male joint in the middle part in the thickness direction on the other side, and in the step of forming the joints, the front convex part adjacent to the front side of the concave groove part, the back convex part adjacent to the back side of the concave groove part, and the convex rib part form the female joint and the male joint so as to straddle a plurality of layers of the plywood, respectively.

[0051] In the eighteenth invention, the present inlay processing is performed on the peripheral side surfaces of the flooring base material, and the female and male inlays are formed so that the convex parts (front convex parts, back convex parts, convex stripes) protruding outward of the female and male inlays always span multiple layers of plywood. The convex parts of the female and male inlays are brittle and easily chipped, but by configuring them to span multiple layers of plywood as described above, they always contain fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the eighteenth invention, it is possible to provide a flooring material in which the convex parts of the female and male inlays are less likely to chip.

[0052] The 19th invention is characterized in that, in the 18th invention, in the above-mentioned female groove processing process, the female groove is formed so that the groove bottom corner of the concave groove portion is located within one of the layers and not in the adhesive portion between the layers of the plywood.

[0053] In the nineteenth invention, the female sid is processed so that the groove bottom corner of the female sid is located within one of the layers, not in the adhesive between any of the layers of the plywood. If the groove bottom corner of the female sid is located in the adhesive between the layers of the plywood, when the male sid is inserted, the plywood is likely to peel between the layers where the groove bottom corner is located, but by processing as described above, such peeling can be suppressed. Effect of the Invention

[0054] As described above, according to the present invention, the number of plywood layers is set to 7, and a plurality of first grooves are formed on the back surface of the plywood, extending in the second direction from the back surface to the second layer. This makes it possible to provide a flooring base material that is resistant to warping even when softwood plywood is used, and has excellent soundproofing properties that can be used as a flooring material for underfloor heating, as well as a flooring material including the same and a method for manufacturing the flooring material. [Brief description of the drawings]

[0055]

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Mode for Carrying Out the Invention

[0056] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are merely exemplary and are not intended to limit the scope of the present invention, its applications, or its uses.

[0057] 《Embodiment 1 of the Invention》 -Configuration of the floor material- The floor material 1 is constructed, for example, on top of a floor heating panel within a building such as a house. As shown in FIGS. 1 to 3, the floor material 1 is formed in a rectangular shape and includes a base material (base material for floor material) 10, a decorative material 20 adhered to the surface of the base material 10, and a cushioning material 30 adhered to the back surface of the base material 10. In Embodiment 1, the floor material 1 is formed, for example, to have dimensions of 1850 mm × 303 mm and a thickness of 10 mm or more and 16 mm or less. Note that the dimensions of the floor material 1 can be changed as appropriate.

[0058] The decorative material 20 is formed of a resin-based decorative sheet having a thickness of about 0.1 mm to 0.2 mm. As the resin-based decorative sheet, a resin film containing almost no moisture, such as an olefin resin film, a PET (polyethylene terephthalate) resin film, or a vinyl chloride resin film, can be used. For example, wood grain, stone grain, abstract patterns, etc. are printed on the decorative material 20. Note that as the decorative material 20, in addition to the resin-based decorative sheet, decorative papers such as coated paper or resin-impregnated paper, and thin sheet materials such as thin veneer panels can also be used. Note that the thickness of the decorative material 20 is about 0.1 mm to 0.8 mm.

[0059] Any material having cushioning properties can be used as the cushioning material 30, but in Embodiment 1, the cushioning material 30 is composed of a polyurethane foam having a thickness of about 1 mm to 3 mm.

[0060] [Configuration of the base material] The base material 10 includes a plywood 11 and a surface strengthening layer 12 adhered to the surface of the plywood 11. The base material 10 is formed in a rectangular shape in plan view, and by performing this actual processing, a female tenon 13 and a male tenon 14 are formed on the peripheral side surface.

[0061] 〈Detailed configuration of the plywood〉 The plywood 11 is a seven-layered softwood plywood in which seven softwood veneers are laminated with an adhesive interposed therebetween and adhesively integrated. The plywood 11 includes first to seventh layers 11a to 11g made of softwood veneers arranged in order from the front surface side to the back surface side. The softwood veneers constituting each of the layers 11a to 11g of the plywood 11 are composed of one or more veneers obtained by cutting a softwood log with a rotary lathe. As the softwood veneer, for example, thin plates such as cypress, cedar, larch, spruce, red pine, radiata pine, and spruce can be used. In the first embodiment, a thin plate of cypress is used.

[0062] As the adhesive, for example, water-based adhesives such as vinyl acetate-based, aqueous vinyl urethane-based, acrylic-based, isocyanate-based, urea-based, phenol-based, ethylene vinyl acetate copolymer-based, and polyvinyl alcohol-based adhesives can be used. In addition, a curing agent such as an isocyanate-based or melamine-based agent may be added to the adhesive as necessary.

[0063] The seven softwood veneers constituting the first to seventh layers 11a to 11g of the plywood 11 have the same thickness and size. The thickness of the softwood veneer used for the plywood 11 is preferably 1.0 mm or more and 1.5 mm or less. If the thickness of the softwood veneer is less than 1.0 mm, it is difficult to stably cut from the log, and when drying the cut veneer, the plane cannot be maintained, and the strength to uniformly apply the adhesive to both sides cannot be ensured, so it is not preferable. On the other hand, if the thickness of the softwood veneer is more than 1.5 mm, the internal cracking during cutting becomes large, and after lamination and integration, not only does the portion compressed by hot pressing without being reinforced by the water-based adhesive become large, but also the thermal conductivity deteriorates in the uncompressed portion, so it is not preferable. The size of the softwood veneer can be designed in various ways according to the size of the flooring material 1. In the first embodiment, for example, in order to manufacture the flooring material 1 with a size of 1850 mm × 303 mm, a softwood veneer with a size of 1900 mm × 345 mm and a thickness of 1.3 mm is used.

[0064] The softwood thin plates constituting the first layer 11a, the third layer 11c, the fifth layer 11e, and the seventh layer 11g (odd-numbered layers) are each composed of a single veneer cut so that the fibers extend in the length direction (first direction) of the plywood 11. On the other hand, the softwood thin plates constituting the second layer 11b, the fourth layer 11d, and the sixth layer 11f (even-numbered layers) are formed by joining a plurality of veneers cut so that the fibers extend in the width direction (second direction) of the plywood 11 in a direction orthogonal to the fiber direction (see FIG. 6). The number of veneers to be joined is not particularly limited, but in the first embodiment, the softwood thin plate constituting the even-numbered layer is formed by joining two veneers.

[0065] As a result, in the odd-numbered layers 11a, 11c, 11e, 11g of the plywood 11, the fibers extend in the length direction (first direction), and in the even-numbered layers 11b, 11d, and the sixth layer 11f, the fibers extend in the width direction (second direction). That is, the plywood 11 is configured such that the fiber directions of two adjacent layers (two sheets) of the first to seventh layers 11a to 11g (softwood thin plates) are orthogonal to each other.

[0066] Although plywood with 3 or 5 plies is often used as the base material for floor materials, the plywood 11 of this embodiment has 7 plies, which is more than usual. Also, although details will be described later, the plywood 11 is formed by laminating seven softwood thin plates with an aqueous adhesive interposed therebetween and then performing hot press. Therefore, the plywood 11 of this embodiment is hot-pressed in a state with a higher moisture content than the 3-ply or 5-ply plywood commonly used as the base material for floor materials. As a result, from the middle to the outermost layer in the thickness direction, the plywood is hot-pressed in a state with more moisture, so from the middle to the outermost layer in the thickness direction, the thickness becomes thinner and the density becomes higher. Also, in the second layer 11b and the third layer 11c, since the aqueous adhesive is applied and impregnated on both sides, it is hot-pressed in a state with a lot of moisture, so it is further compressed, and the compressed state is fixed by the impregnated adhesive.

[0067] Specifically, in the plywood 11 of this embodiment using a softwood thin plate with a thickness of 1.3 mm, the thicknesses of the first layer 11a and the seventh layer 11g are about 1.1 mm, the thicknesses of the second layer 11b and the sixth layer 11f are about 1.2 mm, and the third layer 11c to the fifth layer 11e remain at their original thickness of 1.3 mm without being substantially compressed. That is, in the first to third layers 11a to 11c, in the order of the third layer 11c, the second layer 11b, and the first layer 11a, the thickness becomes thinner while the density becomes higher. Also, in the fifth to seventh layers 11e to 11g, in the order of the fifth layer 11e, the sixth layer 11f, and the seventh layer 11g, the thickness becomes thinner while the density becomes higher. Further, the thicknesses of the first layer 11a and the seventh layer 11g are equal to or less than the thickness of the surface strengthening layer 12 (1.2 mm in this Embodiment 1) described later, and the thicknesses of the third layer 11c to the fifth layer 11e are greater than the thickness of the surface strengthening layer 12.

[0068] (First groove, second groove) On the back surface of the plywood 11, a plurality of first grooves 41 and a plurality of second grooves 42 are formed. Both the first groove 41 and the second groove 42 are formed to improve the sound insulation of the flooring material 1. Incidentally, when the flooring material 1 is constructed on the floor heating panel, the first and second grooves 41, 42 also have the effect of facilitating uniform heat transfer to the surface of the flooring material 1.

[0069] The first groove 41 is a groove extending from one end to the other end in the width direction of the plywood 11. In this Embodiment 1, the first groove 41 is formed so that its cross-sectional shape is rectangular. The first groove 41 is formed such that the groove width is 1.0 mm or more and 2.0 mm or less, and the groove interval (the length between adjacent first grooves 41, the first groove interval) is 10 mm or more and 50 mm or less. In this Embodiment 1, the first groove 41 is formed such that the groove width is 1.5 mm and the groove interval is 10.2 mm. Also, the first groove 41 is formed to a depth (6.9 mm in this Embodiment 1) where the groove bottom is located within the second layer 11b.

[0070] The second groove 42 is a groove extending from one end to the other end in the length direction of the plywood 11. In the first embodiment, the second groove 42 is formed so that its cross-sectional shape is rectangular. The second groove 42 is formed such that the groove width is 2.0 mm or more and 4.0 mm or less, and the groove interval (the length between adjacent second grooves 42, the second groove interval) is 35 mm or more and 100 mm or less. In the first embodiment, the second groove 42 is formed such that the groove width is 3.0 mm and the groove interval is 47 mm. Further, the second groove 42 is formed to a depth (5.0 mm in FIG. 3) such that the groove bottom is located within any one of the third to fifth layers 11c to 11e (the fourth layer 11d in FIG. 3).

[0071] Note that the cross-sectional shapes of the first groove 41 and the second groove 42 are not limited to rectangular shapes, and any shape may be used. Also, the groove depths of the first groove 41 and the second groove 42 are not limited to those described above. For the first groove 41, it is sufficient that the groove bottom is within the second layer 11b, and for the second groove 42, it is sufficient that the groove bottom is within any one of the third layer 11c to the fifth layer 11e. The groove widths and pitches of the first groove 41 and the second groove 42 are not limited to those exemplified in this embodiment. The reason why it is sufficient that the groove bottom of the second groove 42 is within any one of the third layer 11c to the fifth layer 11e will be described later.

[0072] 〈Detailed Configuration of Surface Reinforcement Layer〉 The surface reinforcement layer 12 has a thickness of 0.8 mm or more and 1.3 mm or less and a density of 0.6 g / cm 3 or more and 0.9 g / cm 3It is composed of the following medium-density fiberboard (MDF) and is adhered to the surface of the plywood 11 with an adhesive. In Embodiment 1, the surface strengthening layer 12 is composed of broad-leaved tree MDF mainly composed of broad-leaved tree wood fibers. Also, in Embodiment 1, for the surface strengthening layer 12, broad-leaved tree MDF with a size of 1850 mm × 303 mm and a thickness of 1.2 mm is used, and chamfering is performed at the corners of the upper surface and the side surface of the broad-leaved tree MDF. As the adhesive used for adhering to the plywood 11, any adhesive may be used, but a soft adhesive such as an aqueous vinyl urethane-based adhesive may be used and laminated and integrated by cold pressing, or after cold pressing with a soft adhesive such as an aqueous vinyl urethane-based adhesive, it may be laminated and integrated by hot pressing. Also, it may be laminated and integrated by hot pressing using a non-aqueous soft adhesive such as PUR hot melt.

[0073] 〈Detailed Configuration of Female and Male Joints〉 As shown in FIGS. 4 and 5, the surrounding side surface of the base material 10 is subjected to this actual processing. Specifically, on one of the two opposing side surfaces (long side surfaces 10a, 10a and short side surfaces 10b, 10b) of the base material 10, a female joint 13 is formed, and on the other side, a male joint 14 that can be fitted to the female joint 13 is formed.

[0074] The female joint 13 is formed by notching the base material 10 so that the intermediate portion in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 becomes a concave groove portion 13a. The concave groove portion 13a is a groove extending from one end to the other end in the length direction of each side surface 10a, 10b. In Embodiment 1, the cross-sectional shape of the concave groove portion 13a is formed in a rectangular shape, but the cross-sectional shape of the concave groove portion 13a is not limited to this, and it may be trapezoidal or other shapes. By notching the concave groove portion 13a on the long side surface 10a and the short side surface 10b of the base material 10, a front side convex portion 13b is formed adjacent to the front side of the concave groove portion 13a, and a back side convex portion 13c is formed adjacent to the back side of the concave groove portion 13a.

[0075] The male fruit 14 is formed by notching the base material 10 such that the middle portions in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 become convex rib portions 14a. The convex rib portions 14a are protrusions extending from one end to the other end in the length direction of each of the side surfaces 10a and 10b. In the first embodiment, the cross-sectional shape of the convex rib portions 14a is formed in a rectangular shape, but the cross-sectional shape of the convex rib portions 14a is not limited to this, and any shape may be used as long as it fits into the concave groove portion 13a.

[0076] The female fruit 13 and the male fruit 14 are each formed such that the convex portions protruding outward (the front convex portion 13b and the back convex portion 13c in the female fruit 13, and the convex rib portion 14a in the male fruit 14) straddle a plurality of layers of the plywood 11. Specifically, in the first embodiment, the front convex portion 13b of the female fruit 13 is formed so as to straddle two layers, namely, the first layer 11a and the second layer 11b of the plywood 11. Also, the back convex portion 13c of the female fruit 13 is formed so as to straddle three layers, namely, the fifth layer 11e to the seventh layer 11g of the plywood 11. Further, the convex rib portion 14a of the male fruit 14 is formed so as to straddle four layers, namely, the second layer 11b to the fifth layer 11e of the plywood 11.

[0077] With such a configuration, the convex portions 13b, 13c, 14a of the female fruit 13 and the male fruit 14 are brittle and easily chipped. However, by configuring them to straddle a plurality of layers of the plywood 11 as described above, it is certain to include the fibers extending in the length direction (the first direction) of the flooring material 1 and the fibers extending in the width direction (the second direction) of the flooring material 1, making it difficult to chip.

[0078] Also, in the first embodiment, by forming the female fruit 13 as described above, the groove bottom corner x of the concave groove portion 13a of the female fruit 13 is located within the layer (in the first embodiment, the front groove bottom corner x is within the second layer 11b, and the back groove bottom corner x is within the fifth layer 11e) instead of at the adhesive portion between the layers of the plywood 11. When the groove bottom corner x of the concave groove portion 13a of the female fruit 13 is located at the adhesive portion between the layers of the plywood 11, the plywood 11 is likely to peel at a certain layer when the convex rib portion 14a of the male fruit 14 is inserted. However, according to the above configuration, such peeling can be suppressed.

[0079] -Method for manufacturing a flooring material- The manufacturing method of the floor material 1 will be described below.

[0080] The floor material 1 is manufactured by performing a base material forming step S1, a decorative material bonding step S2, and a cushioning material bonding step S3.

[0081] [Base Material Forming Step] The base material forming step S1 includes a plywood forming step S11, a surface strengthening layer bonding step S12, and a cutting process (grooving process) S13.

[0082] First, the plywood forming step S11 is performed. In the plywood forming step S11, first, a coniferous log is cut by a rotary lathe to a thickness of 1.3 mm and a fiber direction length of 1900 mm, and four first veneers with a fiber direction length of 1900 mm and a fiber orthogonal direction length of 345 mm, and six second veneers with a fiber direction length of 345 mm and a fiber orthogonal direction length of 950 mm are prepared. The four first veneers are used as four coniferous thin plates for the odd layers 11a, 11c, 11e, 11g. Also, by splicing two second veneers in the fiber orthogonal direction, three coniferous thin plates for the even layers 11b, 11d, 11f are formed (see Fig. 6).

[0083] In the first embodiment, the first layer 11a that constitutes the surface layer portion of the plywood 11 has no knot holes, and the second layer 11b has no knot holes larger than 20 mm. Here, "a thing without knot holes (a thing without knot holes larger than 20 mm)" means not only a thing without knot holes (knot holes larger than 20 mm) of coniferous tree logs but also a thing composed of a part with knot holes (knot holes larger than 20 mm) of coniferous tree logs, provided that the knot holes (knot holes larger than 20 mm) are made to disappear by a predetermined process. In the first embodiment, the process of making the knot holes disappear is different between the first layer 11a and the second layer 11b. The first layer 11a makes the knot holes disappear by a putty process of embedding putty into the knot holes. On the other hand, the second layer 11b makes the knot holes larger than 20 mm disappear by a plugging process of drilling a hole including a knot hole larger than 20 mm and filling the hole without a gap with wood (plug wood) having the same shape as the drilled hole. The putty process may be performed after plywood forming, and the plugging process may be performed when preparing the second veneer, or may be performed after joining the second veneer in the fiber orthogonal direction to form a coniferous tree thin plate for the second layer 11b.

[0084] As described above, in order to make the first layer 11a have no knot holes and the second layer 11b have no knot holes larger than 20 mm, it is ideal that all the coniferous tree thin plates for the first to seventh layers 11a to 11g are composed of parts without knot holes of coniferous trees. However, since coniferous trees have many knots, this is not realistic. It is preferable to separately prepare the coniferous tree thin plates for the odd layers 11a, 11c, 11e, 11g and the coniferous tree thin plates for the even layers 11b, 11d, 11f, and configure the coniferous tree thin plates for the even layers 11b, 11d, 11f so that there are no knot holes larger than 20 mm by a plugging process before plywood forming. According to such a plywood manufacturing method, since only two types of coniferous tree thin plates need to be prepared, the procurement of materials is easy and the workability is excellent.

[0085] Further, the softwood veneers for the even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b and the sixth layer 11f and for the fourth layer 11d. Only for the softwood veneers for the second layer 11b and the sixth layer 11f, it may be configured such that there are no knot holes larger than 20 mm by plugging treatment before plywood forming. According to such a plywood manufacturing method, although it is necessary to prepare three types of softwood veneers, since the object of the plugging treatment is only the softwood veneers for the second layer 11b and the sixth layer 11f, the treatment cost can be suppressed. Further, after plywood forming, since the second layer 11b has no knot holes regardless of which surface of the plywood 11 is the front (the first layer 11a side), there is no need to distinguish between the front and back of the plywood 11, and the production becomes easy.

[0086] Furthermore, the softwood veneers for the even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b and for the fourth layer 11d and the sixth layer 11f. Only for the softwood veneer for the second layer 11b, it may be configured such that there are no knot holes larger than 20 mm by plugging treatment before plywood forming. According to such a plywood manufacturing method, although it is necessary to prepare three types of softwood veneers, since the object of the plugging treatment is only the softwood veneer for the second layer 11b, the treatment cost can be minimized.

[0087] Next, the seven prepared softwood veneers for the first to seventh layers 11a to 11g are laminated in the order of the seventh layer 11g, the sixth layer 11f, the fifth layer 11e, the fourth layer 11d, the third layer 11c, the second layer 11b, and the first layer 11a with an aqueous adhesive interposed therebetween.

[0088] Specifically, first, a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (first veneer) for the seventh layer 11g, which is the lowermost layer, on top of which a softwood thin plate (formed by joining two second veneers) for the sixth layer 11f is placed. Then, a softwood thin plate (first veneer) for the fifth layer 11e is placed as it is on top of the softwood thin plate for the sixth layer 11f, and a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (formed by joining two second veneers) for the fourth layer 11d on top of that. Then, a softwood thin plate (first veneer) for the third layer 11c is placed as it is on top of the softwood thin plate for the fourth layer 11d, and a water-based adhesive is applied to and placed on the entire surfaces of both sides of a softwood thin plate (formed by joining two second veneers) for the second layer 11b on top of that. And finally, a softwood thin plate (first veneer) for the first layer 11a is placed as it is on top of the softwood thin plate for the second layer 11b.

[0089] The seven softwood thin plates laminated as described above are hot-pressed in the lamination direction to form a plywood 11 that is adhesively integrated. Thus, in the first embodiment, since the number of laminations of the plywood 11 is seven plies and it is adhered with a water-based adhesive, compared to the case of forming a three-ply or five-ply plywood, the laminate of softwood thin plates is hot-pressed in a state of higher moisture content, and the formed plywood 11 becomes thinner and denser from the middle to the outermost layer in the thickness direction.

[0090] After the plywood forming step S11, a surface strengthening layer adhering step S12 is performed. As described above, when the first veneer constituting the softwood thin plate for the first layer 11a is made of one with a knot hole, a putty treatment is performed to fill the knot hole in the first layer 11a to eliminate the knot hole before the surface strengthening layer adhering step S12.

[0091] In the surface strengthening layer bonding step S12, first, the surface of the plywood 11 is sanded to smooth the surface. Then, a surface strengthening layer 12 made of hardwood MDF is bonded to the surface of the plywood 11. Specifically, an adhesive (for example, a soft adhesive such as an aqueous vinyl urethane-based adhesive or a non-aqueous soft adhesive such as PUR hot melt) is applied to the surface of the plywood 11, and the surface strengthening layer 12 is placed thereon. Then, the plywood 11 and the surface strengthening layer 12 are pressed in the stacking direction (cold press for a soft adhesive such as an aqueous vinyl urethane-based adhesive, and hot press for a non-aqueous soft adhesive such as PUR hot melt) to be integrally bonded.

[0092] After the surface strengthening layer bonding step S12, a cutting process step S13 is performed. The cutting process step S13 includes a groove processing step S14 and a main processing step S15.

[0093] In the groove processing step S14, a first groove 41 and a second groove 42 are formed on the back surface of the plywood 11 by cutting. The first groove 41 is a groove having a predetermined width with a groove width of 1.0 mm or more and 2.0 mm or less (1.5 mm in the first embodiment), and a depth from the back surface of the plywood 11 to the second layer 11b (6.9 mm in the first embodiment) and extending in the width direction (the second direction) with a rectangular cross-sectional shape. A plurality of such first grooves 41 are formed at a predetermined pitch of 10 mm or more and 50 mm or less (10.2 mm pitch in the first embodiment). The second groove 42 is a groove having a predetermined width with a groove width of 2.0 mm or more and 4.0 mm or less (3.0 mm in the first embodiment), a depth from the back surface of the plywood 11 to any one of the third to fifth layers 11c to 11e (the fourth layer 11d in FIG. 3 in the first embodiment, 5.0 mm in FIG. 3 of the first embodiment), and extending in the length direction (the first direction) with a rectangular cross-sectional shape. A plurality of such second grooves 42 are formed at a predetermined pitch of 35 mm or more and 100 mm or less (47 mm pitch in the first embodiment).

[0094] In the main processing step S15, female fruits 13 and male fruits 14 are formed on the peripheral side surfaces (two long side surfaces 10a and two short side surfaces 10b) of the plywood 11 by cutting (main processing).

[0095] Specifically, the female stud 13 is formed by notching the base material 10 such that the middle portions in the thickness direction of the long-side surfaces 10a and the short-side surfaces 10b of the base material 10 become concave groove portions 13a. At this time, the front convex portion 13b on the front side and the back convex portion 13c on the back side of the concave groove portion 13a form the female stud 13 so as to straddle a plurality of layers of the plywood 11. Specifically, the female stud 13 is formed such that the front convex portion 13b straddles two layers, i.e., the first layer 11a and the second layer 11b, and the back convex portion 13c straddles three layers, i.e., the fifth layer 11e to the seventh layer 11g. Also, the female stud 13 is formed such that the groove bottom corner portion x of the concave groove portion 13a is located not in the adhesive portion between the layers of the plywood 11 but within the layer (in the first embodiment, the front groove bottom corner portion x is within the second layer 11b, and the back groove bottom corner portion x is within the fifth layer 11e).

[0096] Also, the male stud 14 is formed by notching the base material 10 such that the middle portions in the thickness direction of the long-side surfaces 10a and the short-side surfaces 10b of the base material 10 become rib portions 14a. At this time, the male stud 14 is formed such that the rib portion 14a straddles a plurality of layers of the plywood 11. Specifically, the male stud 14 is formed such that the rib portion 14a straddles four layers, i.e., the second layer 11b to the fifth layer 11e.

[0097] As described above, in the base material forming step S1, the plywood forming step S11, the surface strengthening layer adhesion step S12, and the cutting process (grooving process) S13 are executed to form the base material 10.

[0098] In the decorative material adhesion step S2, the decorative material 20 (in the first embodiment, a resin decorative sheet) is adhered to the surface of the base material 10 (the surface of the surface strengthening layer 12) formed in the base material forming step S1 with an adhesive.

[0099] In the buffer material adhesion step S3, the buffer material 30 (in the first embodiment, a non-woven fabric) is adhered to the back surface of the base material 10 (the back surface of the plywood 11) formed in the base material forming step S1 with an adhesive.

[0100] By performing the above base material forming step S1, decorative material adhesion step S2, and buffer material adhesion step S3, the floor material 1 is manufactured.

[0101] - Test - The following Tests 1 to 8 were conducted on the floor material 1 according to this embodiment manufactured as described above. Test 1 is a test for confirming the sound insulation and dimensional stability of the floor material 1. Tests 2 to 4 are Brinell hardness tests for confirming the influence of knots on the surface hardness of the floor material 1. Tests 5 and 6 are lightweight floor impact sound tests for confirming the influence of grooves on the sound insulation (soundproofing performance) of the floor material 1. Tests 7 and 8 are tests for confirming the influence of the groove depth of the second groove 42 on the warping of the floor material 1 (warping in the second direction). Test 7 is a dry-wet repeated test, and Test 8 is an 80°C heat durability test.

[0102] [Test 1] Similar to the floor material 1, test specimens 1-1 to 1-3 measuring 470 mm × 918.5 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared. A sound insulation test and a water absorption length change rate test were conducted, and the lightweight floor impact sound and the water absorption length expansion rate were measured. The test specimens 1-1 to 1-3 had different configurations of the base material 10 as follows. Note that the test specimen 1-1 had the same configuration as the floor material 1 of this embodiment. The test specimen 1-2 was obtained by changing the plywood 11 of the floor material 1 of this embodiment to a 5-ply softwood plywood (hinoki plywood). The test specimen 1-3 was obtained by changing the plywood 11 of the floor material 1 of this embodiment to a 5-ply lauan plywood.

[0103] As a result of the sound insulation test, the reduction amounts of the lightweight floor impact sound at the center frequencies of 250 Hz and 500 Hz were the best for the test specimen 1-1 and the worst for the test specimen 2. That is, it can be seen that the floor material 1 of this embodiment is superior in sound insulation to the floor materials using 5-ply softwood plywood (hinoki plywood) and lauan plywood.

[0104] Also, as a result of the water absorption length change rate test, although there was no significant difference in the water absorption length change rate among the test specimens 1-1 to 1-3, the warping in the length direction was the smallest for the test specimen 1-1 and the largest for the test specimen 1-2. Also, the warping in the width direction was the smallest for the test specimen 1-1 and the largest for the test specimen 1-2. That is, it can be seen that the floor material 1 of this embodiment is less likely to warp than the floor materials using 5-ply softwood plywood (hinoki plywood) and lauan plywood.

[0105] [Tests 2 to 4] (Test 2) Test specimens 2-1 to 2-8 measuring 150 mm × 150 mm and comprising a base material 10 and a decorative material 20 were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness.

[0106] The test specimens 2-1 to 2-8 each have a different configuration of the base material 10. Specifically, the test specimens 2-1 to 2-8 are each formed by laminating seven coniferous tree thin plates measuring 150 mm × 150 mm and having a thickness of 1.3 mm with the fiber directions alternating orthogonally while interposing an aqueous adhesive, and then hot-pressing to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of broad-leaved tree MDF and a decorative material 20 made of an olefin decorative sheet having a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane-based adhesive.

[0107] In the test specimens 2-1 to 2-4, artificial through-holes (assuming knots) with a diameter of 30 mm were formed in the central portions of the coniferous tree thin plates constituting the second layer 11b, and the first layer 11a was configured to have no knots by puttying. On the other hand, in the test specimens 2-5 to 2-8, both the first layer 11a and the second layer 11b were configured to have no knots.

[0108] Also, in the test specimens 2-1 to 2-4, the thicknesses of the surface strengthening layers 12 were made different. Specifically, the thickness was 1.0 mm for test specimen 2-1, 1.3 mm for test specimen 2-2, 1.5 mm for test specimen 2-3, and 2.7 mm for test specimen 2-4. Similarly, for the test specimens 2-5 to 2-8, the thicknesses of the surface strengthening layers 12 were also made different. Specifically, the thickness was 1.0 mm for test specimen 2-5, 1.3 mm for test specimen 2-6, 1.5 mm for test specimen 2-7, and 2.7 mm for test specimen 2-8.

[0109] The Brinell hardness test was conducted in accordance with the test method described in "Measurement of Surface Hardness (Brinell Hardness)" of JIS Z 2101 "Test Methods for Wood", and the Brinell hardness at the central portion of the surface of the test specimens 2-1 to 2-8 (the position corresponding to the artificial through-hole in the test specimens 2-1 to 2-4) was measured.

[0110] The results of Test 2 are shown in Fig. 7. The Brinell hardness is 11 N / mm 2 or more is indicated as "○", 9.8 N / mm 2 or more and less than 11 N / mm 2 is indicated as "△", and less than 9.8 N / mm 2 is indicated as "×". From the results of Test 2, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the floor material 1 of the present embodiment, if there are knots (through holes in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness does not reach the value (11 N / mm 2 ) required for the floor material 1.

[0111] Also, as a comparative test of Test 2, in test specimens 2-1 to 2-4, the diameter of the through holes formed in the central part of the softwood thin plates constituting the second layer 11b was changed to 20 mm, and test specimens 2-11 to 2-14 having the same configuration as test specimens 2-1 to 2-4 except for this were prepared. When the same Brinell hardness test was conducted, the Brinell hardness of all of test specimens 2-11 to 2-14 was 11 N / mm 2 or more (the test result is "○"). From Test 2 and the comparative test, even when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) as in the floor material 1 of the present embodiment, if there are no knots in the first layer 11a and no knots with a size exceeding 20 mm in the second layer 11b, it was found that the Brinell hardness of the floor material surface becomes equal to or higher than the desired hardness.

[0112] (Test 3) Similar to the floor material 1, test specimens 3-1 to 3-8 having a size of 150 mm × 150 mm and including a base material 10, a decorative material 20, and a cushioning material 30 were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness. Note that test specimens 3-1 to 3-8 are those in which the thickness of the softwood thin plates constituting the first layer 11a and the seventh layer 11g of the plywood 11 of test specimens 2-1 to 2-8 was changed to 1.7 mm, and the other configurations are the same as those of test specimens 2-1 to 2-8.

[0113] The results of Test 3 are shown in Fig. 8, and are the same as the results of Test 2 shown in Fig. 7. That is, from the results of Tests 2 and 3, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) like the floor material 1 of the present embodiment, if there is a knot hole (through hole in Test 2) with a size exceeding 20 mm in the second layer 11b of the plywood 11, the Brinell hardness will not reach the value (11 N / mm 2 ) required for the floor material 1, and it was found that even if the first layer 11a of the plywood 11 is made thicker, it has no significant effect on the Brinell hardness.

[0114] (Test 4) Similar to the floor material 1, test pieces 4-1 to 4-6 measuring 150 mm × 150 mm each, which include a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness. Note that for test pieces 4-1 to 4-3, an artificial through hole (assuming a knot hole) with a diameter of 30 mm formed in the center of the softwood thin plate constituting the second layer 11b of the plywood 11 of test pieces 2-1 to 2-3 was formed in the center of the softwood thin plate constituting the third layer 11c, and the first layer 11a has no knot holes, and the second layer 11b is configured so as not to have a knot hole with a size exceeding 20 mm. Test pieces 4-4 to 4-6 are configured such that the third layer 11c in test pieces 4-1 to 4-3 does not have a knot hole with a size exceeding 20 mm.

[0115] The results of Test 4 are shown in Fig. 9, and for all of test pieces 4-1 to 4-6, the surface Brinell hardness is the value (11 N / mm 2 ) or more required for the floor material 1. That is, from the results of Tests 2 and 4, when the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) like the floor material 1 of the present embodiment, if there is a knot hole (through hole in Test 2) with a size exceeding 20 mm in the second layer 11b of the plywood 11, the Brinell hardness will not reach the value (11 N / mm 2) will not reach, but even if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm, as long as there are no voids in the first layer 11a and no voids larger than 20 mm in the second layer 11b, even if there are voids in the third layer 11c, it has been found that it will not have an adverse effect on the Brinell hardness of the surface.

[0116] [Tests 5 - 7] (Test 5) Test specimens 5 - 1 to 5 - 16, each 900 mm × 150 mm and comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a lightweight floor impact sound test was conducted to measure the sound reduction amount in the range of 125 Hz to 500 Hz.

[0117] The test specimens 5 - 1 to 5 - 16 each have a different configuration of the base material 10. Specifically, the test specimens 5 - 1 to 5 - 16 have different modes (presence / absence and depth) of the second groove 42 and different thicknesses of the surface strengthening layer 12, and the other configurations are the same as those of the floor material 1. For the production of the test specimens 5 - 1 to 5 - 16, first, seven coniferous thin plates with a thickness of 1.3 mm are laminated with a water - based adhesive while alternating the fiber directions orthogonally, and then hot - pressed to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of broad - leaf tree MDF and an olefin decorative sheet with a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane - based adhesive, and then cut into small pieces of 900 mm × 150 mm. This processed plywood 11 is subjected to this actual processing around its four sides to form female joints 13 and male joints 14. Also, on the back surface of the plywood 11 (the back surface of the seventh layer 11g), the first and second grooves 41, 42 or only the first groove 41 are formed, and then a cushioning material 30 made of a 3 - mm - thick foaming cushioning material is adhered to cover the entire back surface, whereby the test specimens 5 - 1 to 5 - 16 are produced.

[0118] Specimens 5-1 to 5-4 have only the first groove 41 formed on the back surface of the plywood 11 and do not have the second groove 42 formed. Specimens 5-5 to 5-16 have the first groove 41 and the second groove 42 formed on the back surface of the plywood 11. The first groove 41 formed in Specimens 5-1 to 5-16 is the same as that of the floor material 1, with a groove width of 1.5 mm, a groove interval of 10.2 mm, and a depth where the groove bottom is located within the second layer 11b (groove bottom thickness of 2.6 mm). The second groove 42 formed in Specimens 5-5 to 5-16 is the same as that of the floor material 1, with a groove width of 3.0 mm and a groove interval of 47 mm. On the other hand, for the depth, in Specimens 5-5 to 5-8, the groove bottom is located within the third layer 11c (groove bottom thickness of 3.7 mm), in Specimens 5-9 to 5-12, the groove bottom is located within the fourth layer 11d (groove bottom thickness of 5.0 mm), and in Specimens 5-13 to 5-16, the groove bottom is located within the fifth layer 11e (groove bottom thickness of 6.3 mm).

[0119] Note that for Specimens 5-1 to 5-16, the first layer 11a is made free of knots by puttying, and the even-numbered layers 11b, 11d, 11f are made free of knots with a size exceeding 20 mm by wood embedding treatment.

[0120] Also, in Specimens 5-1 to 5-4, the thickness of the surface strengthening layer 12 is made different. In Specimen 5-1, it is 1.0 mm, in Specimen 5-2, it is 1.3 mm, in Specimen 5-3, it is 1.5 mm, and in Specimen 5-4, it is 2.7 mm. Similarly, for Specimens 5-5 to 5-8, Specimens 5-9 to 5-12, and Specimens 5-13 to 5-16, the thickness of the surface strengthening layer 12 is also made different. In Specimens 5-5, 5-9, 5-13, it is 1.0 mm, in Specimens 5-6, 5-10, 5-14, it is 1.3 mm, in Specimens 5-7, 5-11, 5-15, it is 1.5 mm, and in Specimens 5-8, 5-12, 5-16, it is 2.7 mm.

[0121] The light floor impact sound test complied with the test method described in "Method by Standard Light Impact Source" of "Method for Measuring Reduction Amount of Floor Impact Sound Level of Floor Finishing Structure on Concrete Floor in Laboratory" of JIS A 1440-1, and the reduction amounts of the light floor impact sound levels of Specimens 5-1 to 5-16 were measured.

[0122] The results of Test 5 are shown in Fig. 10. When the reduction amount of the lightweight floor impact sound level from 125 Hz to 500 Hz is ΔLL-4 or more, it is indicated by "○", when it is equivalent to ΔLL-3, it is indicated by "△", and when it is less than ΔLL-3, it is indicated by "×". From the results of Test 5, even if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) like the floor material 1 of the present embodiment, if the second groove 42 is not formed, the flexibility of the floor material 1 is insufficient and it becomes difficult to absorb the impact force, and it has been found that the floor material 1 lacks the required sound insulation performance and soundproofing property. Also, if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm and the depth of the second groove 42 is set such that the groove bottom is located within any one of the third to fifth layers 11c to 11e, it has been found that a floor material 1 having the required sound insulation performance and excellent soundproofing property can be obtained. Although not shown in Fig. 10, it has been found that the sound insulation performance improves as the depth of the second groove 42 increases.

[0123] (Test 6) Test pieces 6-1 to 6-12 having a size of 900 mm × 150 mm and including a base material 10, a decorative material 20, and a buffer material 30 were prepared, and a lightweight floor impact sound test was conducted to measure the reduction amount of sound from 125 Hz to 500 Hz. Note that the test pieces 6-1 to 6-12 are those in which the thickness of the softwood thin plates constituting the first layer 11a and the seventh layer 11g of the plywood 11 of the test pieces 5-1 to 5-12 was changed to 1.7 mm, and the other configurations are the same as those of the test pieces 5-1 to 5-12.

[0124] The results of Test 6 are shown in Fig. 11, and for all of the test pieces 6-1 to 6-12, the Brinell hardness of the surface was less than the value required for the floor material 1 (11 N / mm 2 ). That is, from the results of Tests 5 and 6, even if the thickness of the surface strengthening layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less) like the floor material 1 of the present embodiment, if the first layer 11a of the plywood 11 is thick, the rigidity of the floor material 1 in the longitudinal direction (the first direction) increases, and it has been found that the floor material 1 lacks the required sound insulation performance and soundproofing property.

[0125] [Tests 7, 8] (Test 7) Test specimens 7-1 to 7-8 measuring 900 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a wet-dry cycling test was performed to visually observe the amount of warping in the width direction (second direction).

[0126] The test specimens 7-1 to 7-8 each have a different configuration of the base material 10. Specifically, the test specimens 7-1 to 7-8 have different modes (depths) of the second groove 42 and different thicknesses of the surface strengthening layer 12, and other configurations are the same as those of the floor material 1. To produce the test specimens 7-1 to 7-8, first, seven coniferous tree thin plates with a thickness of 1.3 mm are laminated with an aqueous adhesive interposed so that the fiber directions are alternately orthogonal, and then hot-pressed to form a plywood 11. After sanding the surface of the plywood 11, a surface strengthening layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are adhered to each surface in this order with an aqueous vinyl urethane-based adhesive, and then cut into small pieces of 900 mm × 150 mm. The four sides of the cut plywood 11 are subjected to this actual processing to form female nuts 13 and male nuts 14. Further, after forming the first and second grooves 41 and 42 on the back surface (the back surface of the seventh layer 11g) of the plywood 11, a cushioning material 30 made of a 3-mm-thick foamed cushioning material is adhered so as to cover the entire back surface, whereby the test specimens 7-1 to 7-8 are produced.

[0127] The first groove 41 formed in the test specimens 7-1 to 7-8 shall have the same groove width of 1.5 mm, groove interval of 10.2 mm, and depth (groove bottom thickness of 2.6 mm) with the groove bottom located within the second layer 11b as in the floor material 1. The second groove 42 formed in the test specimens 7-1 to 7-8 shall have the same groove width of 3.0 mm and groove interval of 47 mm as in the floor material 1. On the other hand, for the depth, in the test specimens 7-1 and 7-2, the groove bottom is located within the second layer 11b (groove bottom thickness of 1.6 mm), in the test specimens 7-3 and 7-4, the groove bottom is located within the third layer 11c (groove bottom thickness of 3.7 mm), in the test specimens 7-5 and 7-6, the groove bottom is located within the fourth layer 11d (groove bottom thickness of 5.0 mm), and in the test specimens 7-7 and 7-8, the groove bottom is located within the fifth layer 11e (groove bottom thickness of 6.3 mm).

[0128] Note that the test specimens 7-1 to 7-8 were made such that the first layer 11a had no voids after the patina treatment, and the even-numbered layers 11b, 11d, and 11f had no voids larger than 20 mm after the timber embedding treatment.

[0129] Also, for the test specimens 7-1 and 7-2, the thicknesses of the surface strengthening layers 12 were made different. Specifically, the thickness was 1.0 mm for the test specimen 7-1 and 1.3 mm for the test specimen 7-2. Similarly, for the test specimens 7-3 and 7-4, the test specimens 7-5 and 7-6, and the test specimens 7-7 and 7-8, the thicknesses of the surface strengthening layers 12 were also made different. Specifically, the thickness was 1.0 mm for the test specimens 7-3, 7-5, and 7-7, and 1.3 mm for the test specimens 7-4, 7-6, and 7-8.

[0130] The dry-wet cycling test was carried out by placing the specimens for 48 hours each under the moisture absorption conditions of a temperature of 40°C and a relative humidity of 90%, and under the moisture desorption conditions of a temperature of 20°C and a relative humidity of 40%, and repeating this for 2 cycles. After that, the magnitude of the warp in the width direction (the second direction) of the test specimens 7-1 to 7-8 was visually observed.

[0131] The results of Test 7 are shown in FIG. 12. Those with acceptable warping in the width direction (the second direction) are indicated by "○", and those with unacceptable large warping in the width direction (the second direction) are indicated by "×". From the results of Test 7, if the depth of the second groove 42 is such that the groove bottom is located within any of the third to fifth layers 11c to 11e (the thickness of the groove bottom is 3.7 mm or more), the warping in the width direction (the second direction) is acceptable. However, if the depth of the second groove 42 is such that the groove bottom is located within the second layer 11b (the thickness of the groove bottom is 1.6 mm), it was found that the warping in the width direction is unacceptable and large. Note that there was no significant difference in the degree of warping in the width direction among the test specimens 7-3, 7-5, and 7-7, and there was also no significant difference in the degree of warping in the width direction among the test specimens 7-4, 7-6, and 7-8.

[0132] (Test 8) Test specimens 8-1 to 8-8 measuring 900 mm × 150 mm, each comprising a base material 10, a decorative material 20, and a buffer material 30, were prepared, and an 80°C heat durability test was conducted. The amount of warping in the width direction (second direction) was visually observed. Note that the test specimens 8-1 to 8-8 were configured in the same manner as the test specimens 7-1 to 7-8.

[0133] In the 80°C heat durability test, the test specimens 8-1 to 8-8 were dried with a dryer at 80°C for 48 hours to reach a completely dry state, and then the amount of warping in the width direction (second direction) was visually observed.

[0134] The results of Test 8 are shown in Fig. 13 and are the same as those of Test 7. From the results of Test 8 as well, if the depth of the second groove 42 is such that the bottom of the groove is located within any one of the third to fifth layers 11c to 11e (the thickness of the bottom of the groove is 3.7 mm or more), the warping in the width direction (second direction) is acceptable. However, if the depth of the second groove 42 is such that the bottom of the groove is located within the second layer 11b (the thickness of the bottom of the groove is 1.6 mm), it was found that the warping in the width direction becomes too large to be acceptable. Note that in Test 8, there was a slight difference in the warping in the width direction between the test specimens 8-3, 8-5, 8-7 and between the test specimens 8-4, 8-6, 8-8, and the greater the depth of the second groove 42, the greater the warping in the width direction. That is, it was found that the shallower the depth of the second groove 42 (the thicker the bottom of the groove), the less likely it is for warping in the width direction to occur due to heating and drying, and it is suitable for a floor material for floor heating.

[0135] - Effects of Embodiment 1 - In the base material 10 for a floor material according to this embodiment, the number of plies of the plywood 11 is set to 7 plies, and a plurality of first grooves 41 with a depth reaching from the back surface to the second layer 11b are formed on the back surface of the plywood 11. As the plywood for the base material of the floor material, those with 3 plies or 5 plies are often used. However, in the first embodiment, since the number of plies of the plywood 11 is set to 7 plies, the locations adhered with an adhesive (the interfaces between the layers made of softwood thin plates) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood 11 is set to 7 plies, the first grooves 41 reaching from the back surface to the second layer 11b are deeper than when the first grooves 41 are formed in the same manner in 3-ply plywood or 5-ply plywood. With such deep plurality of first grooves 41, the rigidity of the plywood 11 decreases and the flexibility increases, making it easier to absorb impact force. That is, when the base material 10 for a floor material according to this embodiment is used, the floor material 1 has the required sound insulation performance and is excellent in soundproofing.

[0136] Further, in the first embodiment, since the plurality of first grooves 41 extend in a direction (second direction) orthogonal to the fiber direction (first direction) of the first layer 11a of the plywood 11 and do not reach the first layer 11a, the fibers of the first layer 11a are not cut off. With such a configuration, in the first embodiment, even when the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 attempts to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer 11a extending in the first direction. As a result, it becomes difficult for the base material 10 for a floor material to expand and contract in the first direction due to moisture absorption or desorption, and warping in the first direction is suppressed. Therefore, according to the first embodiment, it is possible to provide a base material 10 for a floor material that is excellent in soundproofing and is applicable to a floor material for floor heating and is less likely to warp even when using softwood plywood.

[0137] In addition, in the first embodiment, not only the first groove 41 but also at least one second groove 42 extending in a direction (first direction) orthogonal to the extending direction (second direction) of the first groove 41 is formed on the back surface of the plywood 11. By forming the second groove 42 in this way, compared with the case where only the first groove 41 is formed, the rigidity of the plywood 11 is reduced and the flexibility is increased, making it easier to absorb the impact force. That is, according to the first embodiment, the base material 1 for a floor material with more excellent sound insulation can be provided.

[0138] Furthermore, in the first embodiment, the second groove 42 extending in the direction (first direction) orthogonal to the fiber direction (second direction) of the second layer 11b has a groove bottom within any one of the third to fifth layers 11c to 11e and does not reach the second layer 11b. Therefore, the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 are not cut off. With such a configuration, in the first embodiment, even when the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 tries to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it becomes difficult for the base material 10 for a floor material to expand and contract in the second direction due to moisture absorption or desorption, and the warping (width warping) in the second direction is suppressed. That is, according to the base material 10 for a floor material of the present embodiment, not only the warping in the fiber direction (first direction) of the first layer 11a is suppressed, but also the warping in the orthogonal direction (second direction) is suppressed.

[0139] Also, in FIG. 3 of the first embodiment, the second groove 42 is formed such that the groove bottom is located within the fourth layer 11d, and since the second groove 42 does not reach the third layer 11c, not only are the fibers of the second layer 11b extending in the second direction that can counter the dimensional changes due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard not cut off, but also the second layer 11b is covered by the first layer 11a and the third layer 11c. Thus, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 attempts to expand and contract in the second direction due to moisture absorption or desorption, the expansion and contraction are more suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it becomes difficult for the base material 10 for floor materials to expand and contract in the second direction due to moisture absorption or desorption, and a floor material 1 that is less likely to warp in the second direction can be provided.

[0140] In addition, the inventors of the present application conducted verification tests (Tests 5, 7, and 8) on the correlation between the depth of the second groove 42, the sound insulation performance of the floor material 1, and warping. As a result of the verification tests, it was found that as the depth of the second groove 42 increases, the sound insulation performance improves, while warping in the second direction becomes more likely to occur. Also, in the case where the groove bottom of the second groove 42 is located within the third to fifth layers 11c to 11e, it is possible to form a floor material 1 that has the required sound insulation performance and is less likely to warp in the second direction. In particular, from the viewpoints of sound insulation performance and warping, it was found that it is preferable that the groove bottom of the second groove 42 be located within the fourth layer 11d. Therefore, in the example of FIG. 3 of the first embodiment, the second groove 42 is formed to have a depth such that the groove bottom is located within the fourth layer 11d. Therefore, according to the example of FIG. 3 of the first embodiment, it is possible to provide a floor material 1 that is less likely to warp and has excellent sound insulation properties suitable for a floor heating floor material.

[0141] In addition, the inventors of the present application conducted verification tests (Tests 2 to 4) on the correlation between the presence or absence of knots in the first to third layers 11a to 11c of the plywood 11 and the Brinell hardness of the surface of the floor material 1. As a result of the verification tests, when there are knots in the first layer 11a constituting the surface layer portion of the plywood 11 or when there are knots larger than 20 mm in the second layer 11b, the Brinell hardness of the surface of the floor material 1 is lower than the desired hardness. On the other hand, even if there are knots larger than 20 mm in the third layer 11c, as long as there are no knots in the first layer 11a and no knots larger than 20 mm in the second layer 11b, it was found that the Brinell hardness of the surface of the floor material 1 is equal to or higher than the desired hardness. That is, it was found that if the floor material 1 is formed while there are knots in the first layer 11a of the plywood 11 or knots larger than 20 mm in the second layer 11b, the floor material 1 may be easily damaged. In addition, if there are knots in the first layer 11a forming the surface layer portion of the plywood 11, it may deteriorate the surface properties of the floor material 1 and may also lead to a decrease in the design quality of the floor material 1. In particular, when a thin (for example, about 1.5 mm) medium density fiberboard is used as the surface strengthening layer 12 in order to minimize the influence of warping as much as possible, if there are knots near the surface layer, the influence of the knots (such as unevenness) will be manifested up to the decorative material 20 through the surface strengthening layer 12 made of the thin medium density fiberboard, and the possibility of deteriorating the design quality of the floor material 1 will increase.

[0142] Therefore, in the first embodiment, it is configured such that there are no knots in the first layer 11a and no knots with a size exceeding 20 mm in the second layer 11b. Specifically, the first layer 11a is composed of a portion of a coniferous tree without knots, or when it is composed of a portion of a coniferous tree with knots, the knots are filled with putty and made to disappear so that there are no knots. Further, the second layer 11b is composed of a portion of a coniferous tree without knots with a size exceeding 20 mm, or when it is composed of a portion of a coniferous tree with knots with a size exceeding 20 mm, the knots with a size exceeding 20 mm are made to disappear by grafting treatment so that there are no knots with a size exceeding 20 mm. In the first embodiment, by configuring the first layer 11a and the second layer 11b in this way so that there are no knots in the first layer 11a and no knots with a size exceeding 20 mm in the second layer 11b, the floor material produced using the base material 10 for floor materials is less likely to be damaged and has good surface properties. The surface properties of the floor material 1 are not deteriorated. Therefore, according to the first embodiment, it is possible to relatively easily provide the base material 10 for floor materials that does not deteriorate the surface properties of the floor material 1.

[0143] Further, in the first embodiment, since the tracheids of coniferous trees have a significantly higher porosity and water absorption rate than the xylem fibers of broad-leaved trees, medium-density fiberboard made from the xylem fibers of broad-leaved trees (broad-leaved tree MDF) is used as the surface strengthening layer 12. By using the xylem fibers of broad-leaved trees as the medium-density fiberboard constituting the surface strengthening layer 12 in this way, the water absorption rate of the surface strengthening layer 12 can be kept low, and dimensional changes can be suppressed.

[0144] In addition, in the first embodiment, the present processing is performed on the peripheral side surface of the base material 10 for the floor material, and the convex portions (front-side convex portion 13b, back-side convex portion 13c, rib portion 14a) protruding outside the female nuts 13 and male nuts 14 are formed such that the female nuts 13 and male nuts 14 always straddle a plurality of layers of the plywood 11. The convex portions 13b, 13c, 14a of the female nuts 13 and male nuts 14 are brittle and easily chipped, but by configuring them to straddle a plurality of layers of the plywood 11 as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the first embodiment, it is possible to provide a base material 10 for the floor material in which the convex portions 13b, 13c, 14a of the female nuts 13 and male nuts 14 are less likely to chip.

[0145] In addition, in the first embodiment, the female nut 13 is formed such that the groove bottom corner x of the groove portion 13a of the female nut 13 is located within one of the layers so as not to be located at the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the groove portion 13a of the female nut 13 is located at the adhesive portion between the layers of the plywood 11, when the rib portion 14a of the male nut 14 is inserted, the plywood 11 is likely to peel at a certain layer due to the groove bottom corner x, but according to the above configuration, such peeling can be suppressed.

[0146] In addition, according to the first embodiment, by providing the above base material 10 for the floor material, it is possible to provide a floor material 1 excellent in sound insulation that is less likely to warp even when using softwood plywood and is applicable to floor materials for floor heating.

[0147] In addition, in the manufacturing method of the flooring material of the present embodiment, a plurality of first grooves 41 with a depth reaching from the back surface to the second layer 11b are formed on the back surface of the plywood 11 with 7 plies. As the plywood for the flooring material base, those with 3 plies or 5 plies are often used. However, in the first embodiment, since the number of plies of the plywood 11 is 7 plies, the locations adhered with the aqueous adhesive (the interfaces between the layers made of softwood thin plates) increase compared to 3-ply plywood or 5-ply plywood, so the strength is improved compared to 3-ply plywood or 5-ply plywood. Also, since the number of plies of the plywood 11 is 7 plies, the first grooves 41 reaching from the back surface to the second layer 11b are deeper than when the first grooves 41 are similarly formed in 3-ply plywood or 5-ply plywood. Due to such deep plurality of first grooves 41, the rigidity of the plywood 11 decreases and the flexibility increases, making it easier to absorb the impact force. That is, according to the manufacturing method of the present embodiment, it is possible to provide the flooring material 1 having the required sound insulation performance and excellent soundproofing properties.

[0148] In addition, in the manufacturing method of the flooring material of the present embodiment, a plurality of first grooves 41 extending in the direction (second direction) orthogonal to the fiber direction (first direction) of the first layer 11a of the plywood 11 are not made to reach the first layer 11a so that the fibers of the first layer 11a are not cut off by the first grooves 41. By forming the first grooves 41 in this way, even when the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 attempts to expand and contract in the first direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the first layer 11a extending in the first direction. Thereby, it is possible to manufacture the flooring material 1 that is difficult to expand and contract in the first direction due to moisture absorption or desorption and is difficult to warp in the first direction.

[0149] Also, in the manufacturing method of the floor material of the present embodiment, while a plywood with a normal number of plies of 3 or 5 is often used for the base material for the floor material, the number of plies of the plywood 11 is set to 7 plies and it is adhered with an aqueous adhesive. Therefore, in the first embodiment, compared with the case of forming a 3-ply or 5-ply plywood, the laminate of softwood thin plates is hot-pressed in a state of having a higher moisture content, and the formed plywood becomes thinner and denser from the middle to the outermost layer in the thickness direction. According to the manufacturing method of the floor material of the present embodiment, by using the plywood 11 having such a configuration, it is possible to provide the floor material 1 having excellent surface strength.

[0150] As described above, according to the manufacturing method of the floor material of the present embodiment, even when using a softwood plywood, it is possible to provide the floor material 1 having excellent sound insulation properties and being less likely to warp, which is applicable to the floor material for floor heating.

[0151] Also, in the manufacturing method of the floor material of the first embodiment, not only the first groove 41 but also at least one second groove 42 extending in a direction (first direction) orthogonal to the extending direction (second direction) of the first groove 41 is formed on the back surface of the plywood 11. By forming the second groove 42 in this way, the rigidity of the plywood 11 is reduced and the flexibility is increased compared with the case where only the first groove 41 is formed, and it becomes easier to absorb the impact force. That is, according to the manufacturing method of the floor material of the first embodiment, it is possible to provide the base material 10 for the floor material having more excellent sound insulation properties.

[0152] Further, in the method for manufacturing the flooring material of the first embodiment, the second groove 42 extending in the direction (first direction) orthogonal to the fiber direction (second direction) of the second layer 11b does not reach the second layer 11b, and the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard are not cut off by the second groove 42. By forming the second groove 42 in this way, even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 expands and contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for the flooring material becomes difficult to expand and contract in the second direction due to moisture absorption or desorption, and the warping in the second direction is suppressed. That is, according to the method for manufacturing the flooring material of the first embodiment, it is possible to provide the flooring material 1 that is less likely to warp not only in the fiber direction (first direction) of the first layer 11a but also in the orthogonal direction (second direction).

[0153] Furthermore, in the manufacturing method for manufacturing the flooring material 1 shown in FIG. 3 of the first embodiment, the bottom of the second groove 42 is located within the fourth layer 11d and the second groove 42 does not reach the third layer 11c. Therefore, not only are the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard not cut off, but also the second layer 11b is covered by the first layer 11a and the third layer 11c. Even if the surface strengthening layer 12 made of medium density fiberboard adhered to the surface of the plywood 11 expands and contracts in the second direction due to moisture absorption or desorption, the expansion and contraction are suppressed by the fibers of the second layer 11b extending in the second direction. As a result, it is possible to manufacture the flooring material 1 that is difficult to expand and contract in the second direction due to moisture absorption or desorption and is less likely to warp in the second direction.

[0154] Also, in the method for manufacturing the flooring material of the first embodiment, from the results of the verification tests (tests 5, 7, 8) on the correlation between the depth of the second groove 42 described above, the sound insulation performance of the flooring material 1, and the dimensional stability (warping), if the bottom of the second groove 42 is set to a depth located within the fourth layer 11d, it is possible to provide a flooring material with excellent sound insulation properties suitable for a floor heating flooring material that is less likely to warp.

[0155] In addition, in the method for manufacturing the floor material of the first embodiment, the first layer 11a is configured to have no knots, and the second layer 11b is configured to have no knots larger than 20 mm. Specifically, the first layer 11a is composed of a part of the softwood without knots, or when it is composed of a part of the softwood with knots, the knots are filled with putty and disappeared to make it knot-free. Further, the second layer 11b is composed of a part of the softwood without knots larger than 20 mm, or when it is composed of a part of the softwood with knots larger than 20 mm, the knots larger than 20 mm are disappeared by plugging treatment to make it have no knots larger than 20 mm. In the first embodiment, by configuring the first layer 11a to have no knots and the second layer 11b to have no knots larger than 20 mm in this way, the floor material 1 is made difficult to be damaged and has good surface properties. Therefore, according to the method for manufacturing the floor material of the first embodiment, a floor material 1 that is difficult to be damaged and has good surface properties can be provided.

[0156] In addition, in the method for manufacturing the floor material of the present embodiment, since the porosity of the softwood tracheary fiber is significantly higher and the water absorption rate is higher than that of the hardwood xylem fiber, medium density fiberboard (hardwood MDF) mainly made of hardwood xylem fiber is used as the surface strengthening layer 12. By using the hardwood xylem fiber as the medium density fiberboard constituting the surface strengthening layer 12 in this way, the water absorption rate of the surface strengthening layer 12 can be kept low, and the dimensional change can be suppressed.

[0157] In addition, in the method for manufacturing the floor material of the present embodiment, the main processing is performed on the peripheral side surface of the base material 10 for the floor material. Also, the convex portions (front side convex portion 13b, back side convex portion 13c, rib portion 14a) protruding outside the female fruits 13 and male fruits 14 are formed such that the female fruits 13 and male fruits 14 necessarily straddle a plurality of layers of the plywood 11. The convex portions 13b, 13c, 14a of the female fruits 13 and male fruits 14 are brittle and easily chipped. However, by configuring them to straddle a plurality of layers of the plywood 11 as described above, they will necessarily include fibers extending in the first direction and fibers extending in the second direction, making them less likely to chip. Therefore, according to the method for manufacturing the floor material of the present embodiment, it is possible to provide a floor material 1 in which the convex portions 13b, 13c, 14a of the female fruits 13 and male fruits 14 are less likely to chip.

[0158] Also, in the method for manufacturing the floor material of the present embodiment, the female fruit 13 is processed so that the groove bottom corner x of the groove portion 13a of the female fruit 13 is located within one of the layers so as not to be located at the adhesive portion between any layers of the plywood 11. When the groove bottom corner x of the groove portion 13a of the female fruit 13 is located at the adhesive portion between the layers of the plywood 11, when the rib portion 14a of the male fruit 14 is inserted, the plywood 11 is likely to peel at a certain layer due to the groove bottom corner x. However, by processing as described above, such peeling can be suppressed.

[0159] 《Embodiment 2 of the Invention》 Embodiment 2 is a modification of Embodiment 1 in which the size of the floor material 1 is changed and the groove configuration is changed. Specifically, as shown in FIG. 14, the width of the floor material 1 is set to 50 mm or more and 100 mm or less (for example, 75 mm), and only the first groove 41 is formed on the back surface of the plywood 11, and the second groove 42 is not formed. Other configurations are the same as those in Embodiment 1.

[0160] -Test- Regarding the floor material 1 of Embodiment 2 as described above, the following Test 9 was conducted. Test 9 is a lightweight floor impact sound test for confirming the influence of the groove on the sound insulation performance (soundproofing performance) of the floor material 1.

[0161] (Test 9) Test specimens 9-1 to 9-8, each comprising a base material 10, a decorative material 20, and a cushioning material 30, were prepared, and a lightweight floor impact sound test was conducted to measure the sound reduction amount of sounds in the range of 125 Hz to 500 Hz. Note that test specimens 9-1 to 9-4 are those obtained by changing the length in the width direction (length in the second direction) of test specimens 5-1 to 5-4 in Test 5 conducted in Embodiment 1 to 75 mm, and test specimens 9-5 to 9-8 are configured in the same manner as test specimens 5-1 to 5-4 (length in the width direction is 150 mm, without the second groove 42).

[0162] The results of Test 9 are shown in FIG. 15. From the results of Test 9, it was found that when the length in the width direction (length in the second direction) of the floor material 1 is about 75 mm, a floor material 1 having the required sound insulation performance and excellent soundproofing can be obtained even without the second groove 42. On the other hand, by comparing the results of Tests 5 and 9, it was found that when the length in the width direction (length in the second direction) of the floor material 1 is about 150 mm, the floor material 1 lacks the required sound insulation performance and soundproofing without forming the second groove 42.

[0163] As described above, the base material 10 for a floor material, the floor material 1, and the method for manufacturing the floor material according to Embodiment 2 can also achieve the same effects as the base material 10 for a floor material, the floor material 1, and the method for manufacturing the floor material according to Embodiment 1.

[0164] 《Other Embodiments》 In the above-described Embodiments 1 and 2, the second layer 11b is configured of a portion of the coniferous tree having no knot with a size exceeding 20 mm or a portion of the coniferous tree having a knot with a size exceeding 20 mm, and the knot with a size exceeding 20 mm is filled with a plug to make it have no knot with a size exceeding 20 mm. However, the second layer 11b may be one having no knot with a size in the first direction larger than the groove interval (the first groove interval) of the first groove 41. Specifically, for the coniferous tree thin plate for the second layer 11b, a second veneer having no knot with a size in the first direction larger than the groove interval (the first groove interval) of the first groove 41 is used. Two such second veneers having no large knot may be selected and spliced in the fiber orthogonal direction to form a coniferous tree thin plate for the second layer 11b, or one having no large knot may be selected from the three coniferous tree thin plates formed for the even-numbered layers 11b, 11d, 11f as the coniferous tree thin plate for the second layer 11b. Further, in order to make the coniferous tree thin plate for the second layer 11b one having no large knot, the coniferous tree thin plates for the second layer 11b and the sixth layer 11f and the coniferous tree thin plate for the fourth layer 11d are separately prepared, and one having no large knot may be used as the coniferous tree thin plates for the second layer 11b and the sixth layer 11f. Also, by using coniferous tree thin plates having no large knot for all of the even-numbered layers 11b, 11d, 11f, the coniferous tree thin plate for the second layer 11b may be made to have no large knot.

[0165] In the above-described Embodiments 1 and 2, each layer 11a to 11g of the plywood 11 is composed of softwood thin plates. Although softwoods have more knots than hardwoods, if the softwood thin plate constituting the second layer 11b has a knot hole whose size in the first direction is larger than the groove interval (first groove interval) of the first groove 41, the fibers of the second layer 11b extending in the second direction that can counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard will be cut off by the knot hole, so that it is impossible to counter the dimensional change due to moisture absorption or desorption of the surface strengthening layer 12 made of medium density fiberboard, and there is a risk that warping will partially occur in the second direction. However, according to the above configuration, since the second layer 11b does not have a knot hole whose size in the first direction is larger than the first groove interval, an effect of suppressing warping in the second direction can be expected. Note that the second layer 11b is composed of softwood thin plates in which a plurality of (two in Embodiments 1 and 2) veneers are joined together in the first direction, and the veneers constituting the second layer 11b are smaller than the veneers constituting the first layer 11a. It is difficult to prepare a large veneer without large knot holes, but it is relatively easy to prepare a relatively small veneer used for the second layer 11b without large knot holes. Therefore, according to the above configuration, it is possible to relatively easily provide the base material 10 for a floor material that can be expected to have an effect of suppressing warping in the second direction.

Industrial Applicability

[0166] The present invention is useful for a base material for a floor material, a floor material, and a method for manufacturing a floor material.

Explanation of Signs

[0167] 1 Floor material 10 Base material (base material for floor material) 10a Long side surface (peripheral side surface) 10b Short side surface (peripheral side surface) 11 Plywood 11a First layer 11b Second layer 11c Third layer 11d Fourth layer 11e Fifth layer 11f Sixth layer 11g Seventh layer 12 Surface strengthening layer 13 female fruit 13a concave groove part 13b front side convex part (convex portion) 13c back side convex part (convex portion) 14 male fruit 14a rib part 15 adhesive 20 decorative material 30 cushioning material 41 first groove 42 second groove

Claims

1. A flooring substrate in which a surface reinforcing layer made of medium density fiberboard is bonded to the surface of plywood, The plywood is a softwood plywood having first to seventh layers each made of seven softwood thin boards laminated and bonded together from the front side to the back side in order such that the fiber directions of adjacent two boards are perpendicular to each other, A plurality of first grooves extending in a second direction perpendicular to a first direction which is a fiber direction of the first layer are formed on the back surface of the plywood at a first groove interval; The first groove extends from one end to the other end of the plywood in the second direction, and a groove bottom is located within the second layer. A flooring base material characterized by:

2. The flooring substrate according to claim 1, At least one second groove is formed on the back surface of the plywood, the second groove extending in the first direction from one end to the other end of the plywood in the first direction. A flooring base material characterized by:

3. The flooring substrate according to claim 2, The second groove has a groove bottom located in any one of the third to fifth layers. A flooring base material characterized by:

4. The flooring substrate according to claim 3, The second groove has a groove bottom located within the fourth layer. A flooring base material characterized by:

5. The flooring substrate according to claim 1, the first, third, fifth and seventh layers of the softwood thin board are each made of a single veneer, while the second, fourth and sixth layers of the softwood thin board are each made of a plurality of veneers joined together in the first direction; The second layer has no knots whose size in the first direction is greater than the first groove interval. A flooring base material characterized by:

6. The flooring substrate according to claim 1, The first layer is made of a part of a coniferous tree that has no knots, or is made of a part of a coniferous tree that has knots and the knots are filled with putty, thereby making the first layer free of knots; The second layer is made of a part of a coniferous tree that does not have knots larger than 20 mm in size, or is made of a part of a coniferous tree that has knots larger than 20 mm in size, and the knots larger than 20 mm in size are filled with filler wood, so that there are no knots larger than 20 mm in size. A flooring base material characterized by:

7. The flooring substrate according to claim 1, The above medium density fiberboard is made primarily from hardwood wood fibers. A flooring base material characterized by:

8. The flooring substrate according to claim 1, One of the two opposing sides of the flooring base material has a concave groove portion that will become a female fruit in the middle of the thickness direction, and the other has a convex ridge portion that will become a male fruit in the middle of the thickness direction, In the above-mentioned flooring base material, the front-side convex portion adjacent to the front side of the concave groove portion, the back-side convex portion adjacent to the back side of the concave groove portion, and the convex strip portion are formed so as to span multiple layers of the plywood. A flooring base material characterized by:

9. The flooring substrate according to claim 8, The female is formed so that the groove bottom corner of the concave groove is located within one of the layers, not in the adhesive portion between the layers of the plywood. A flooring base material characterized by:

10. A flooring material comprising a flooring base material and a cushioning material adhered to the back surface of the flooring base material, The flooring base material is a flooring base material according to any one of claims 1 to 9. A flooring material characterized by:

11. A method for manufacturing a flooring material comprising a flooring base material having a surface reinforcing layer made of a medium density fiberboard adhered to a surface of a plywood, and a cushioning material adhered to a back surface of the flooring base material, comprising: a plywood forming step of stacking seven softwood thin boards of equal thickness in order with an aqueous adhesive interposed between each thin board and with the fiber directions of adjacent two softwood thin boards perpendicular to each other, and hot pressing the thin boards in the thickness direction to form the plywood having first to seventh layers made of the softwood thin boards stacked in order from the front side to the back side and bonded together; a surface reinforcing layer adhering step of adhering the surface of the plywood to the surface of the plywood to form the flooring base material; A groove processing step of forming a plurality of first grooves at a first groove interval on the back surface of the plywood, the first grooves extending in a second direction perpendicular to a first direction which is a fiber direction of the first layer; A cushioning material adhering step of adhering a cushioning material to the back surface of the plywood after the groove processing step, The first groove extends from one end to the other end of the plywood in the second direction, and a groove bottom is located within the second layer. A method for manufacturing a flooring material comprising the steps of:

12. The method for manufacturing a flooring material according to claim 11, In the groove processing step, the plurality of first grooves are formed on the back surface of the plywood, and at least one second groove extending in the first direction from one end to the other end of the plywood in the first direction is formed. A method for manufacturing a flooring material comprising the steps of:

13. The method for manufacturing a flooring material according to claim 12, The second groove has a groove bottom located in any one of the third to fifth layers. A flooring base material characterized by:

14. The flooring substrate according to claim 13, The second groove has a groove bottom located within the fourth layer. A flooring base material characterized by:

15. The method for manufacturing a flooring material according to claim 11, the first, third, fifth and seventh layers of the softwood thin board are each made of a single veneer, while the second, fourth and sixth layers of the softwood thin board are each made of a plurality of veneers joined together in the first direction; The second layer is free of knots whose size in the first direction is greater than the first groove interval. A method for manufacturing a flooring material comprising the steps of:

16. The method for manufacturing a flooring material according to claim 11, The first layer is made of a part of coniferous wood that has no knots, or is made of a part of coniferous wood that has knots and the knots are filled with putty, thereby making the first layer free of knots; The second layer is made of a part of a coniferous tree that does not have knots exceeding 20 mm in size, or is made of a part of a coniferous tree that has knots exceeding 20 mm in size and the knots exceeding 20 mm in size are filled with filler wood, thereby making the second layer free of knots exceeding 20 mm in size. A method for manufacturing a flooring material comprising the steps of:

17. The method for manufacturing a flooring material according to claim 11, The above medium density fiberboard is made primarily from hardwood wood fibers. A method for manufacturing a flooring material comprising the steps of:

18. The method for manufacturing a flooring material according to claim 11, The method further includes a processing step of forming a female berry in the middle of the thickness direction on one of the two opposing sides of the flooring base material, and forming a male berry in the middle of the thickness direction on the other side, In the above-mentioned main processing step, the female and male grains are formed so that the front side convex portion adjacent to the front side of the concave groove portion, the back side convex portion adjacent to the back side of the concave groove portion, and the convex strip portion each span multiple layers of the plywood. A method for manufacturing a flooring material comprising the steps of:

19. The method for manufacturing a flooring material according to claim 18, In the above-mentioned main processing step, the female part is formed so that the groove bottom corner of the concave groove part is located within one of the layers, not in the adhesive part between the layers of the plywood. A method for manufacturing a flooring material comprising the steps of:

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