Substrate for flooring, flooring material, and method for manufacturing 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] This invention relates to a base material for flooring, flooring material, and a method for manufacturing flooring material. [Background technology]

[0002] Conventionally, soundproof flooring materials for underfloor heating have been proposed that are installed on underfloor heating panels and comprise a base material having a decorative layer on the surface and a cushioning material on the back (see, for example, Patent Document 1 below). In Patent Document 1, the base material for the flooring material is made of plywood with a back groove processing, in which multiple grooves extending parallel to each other are formed on the back surface of the plywood. In the above flooring material, the multiple back grooves formed on the back surface of the base material for the flooring material make it easier for heat to be uniformly transferred to the surface of the flooring material, and also provide flexibility to the flooring material to improve sound insulation. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-145117 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, while tropical hardwood plywood such as lauan plywood was used as the base material for the above-mentioned flooring, in recent years, tropical hardwood plywood has become difficult to obtain due to the depletion of raw materials and concerns about preventing environmental damage, and efforts are being made to replace it with softwood plywood. Since softwood plywood is softer than hardwood plywood such as lauan plywood, replacing the base material of flooring with softwood plywood results in flooring that lacks surface strength and is easily scratched. Therefore, in some cases, medium-density fiberboard is bonded to the surface of softwood plywood to strengthen its surface strength.

[0005] However, because medium-density fiberboard is more susceptible to moisture absorption and expansion than plywood, a substrate in which medium-density fiberboard is bonded to the surface of plywood to strengthen its surface strength is more prone to warping than a substrate made solely of plywood. In particular, when the substrate is made of plywood with grooved backing, as in the soundproof flooring material for underfloor heating described in Patent Document 1, although the sound insulation performance can be improved by the multiple grooves, the fibers that can withstand the dimensional changes due to moisture absorption or release of the medium-density fiberboard are cut by the grooves, making the substrate more prone to warping. Furthermore, in the above-mentioned soundproof flooring material for underfloor heating, the substrate is more prone to warping because it is installed on underfloor heating panels and experiences large temperature changes, while the presence of a cushioning material prevents the flooring material from being pressed down and fixed to the underfloor heating panels, making it impossible to suppress the warping of the substrate. In addition, if the thickness of the plywood is increased to counteract the medium-density fiberboard in order to suppress warping, the overall rigidity of the substrate increases too much, resulting in a failure to achieve the desired sound insulation performance.

[0006] The present invention has been made in view of the above, and its purpose is to provide a soundproofing substrate for flooring that is less prone to warping even when using softwood plywood and is applicable to flooring for underfloor heating, a flooring material equipped therewith, and a method for manufacturing the flooring material. [Means for solving the problem]

[0007] To achieve the above objective, this invention uses a plywood with 7 layers, laminating 7 thin sheets of softwood so that the fiber directions of the 1st, 3rd, 5th, and 7th layers (first direction) and the fiber directions of the 2nd, 4th, and 6th layers (second direction) are perpendicular to each other, and forming multiple first grooves on the back surface of the plywood that extend in the second direction and reach from the back surface to the second layer.

[0008] Specifically, the first invention is a flooring material substrate in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of a plywood, wherein the plywood is a softwood plywood having seven layers, each consisting of seven softwood veneers laminated sequentially from the surface side to the back side so that the fiber directions of adjacent sheets are perpendicular to each other and bonded together, wherein a plurality of first grooves are formed on the back surface of the plywood at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer, and the first grooves extend from one end to the other in the second direction of the plywood, with the bottom of the grooves located within the second layer.

[0009] In the first invention, the number of layers of plywood is set to 7, and multiple first grooves are formed on the back surface of the plywood to a depth that extends from the back surface to the second layer. Plywood with 3 or 5 layers is often used as a base material for flooring, but in the first invention, the number of layers of plywood is set to 7, so the number of areas bonded with adhesive (between each layer made of softwood veneer) is increased compared to 3-ply or 5-ply plywood, resulting in improved strength. Also, because the number of layers of plywood is set to 7, the first grooves that extend from the back surface to the second layer are deeper than when the first grooves are similarly formed in 3-ply or 5-ply plywood. These deep, multiple first grooves reduce the rigidity of the plywood and increase its flexibility, making it easier to absorb impact forces. In other words, when using the base material for flooring according to the first invention, the flooring material will have the required sound insulation performance and excellent soundproofing properties.

[0010] Furthermore, in the first invention, the multiple first grooves extending in a direction perpendicular to the fiber direction (first direction) of the first layer of the plywood (second direction) do not reach the first layer, so the fibers of the first layer are not cut. With this configuration, in the first invention, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the first direction due to moisture absorption or release, the expansion and contraction is suppressed by the fibers of the first layer extending in the first direction. As a result, the base material for the flooring material is less likely to expand or contract in the first direction due to moisture absorption or release, and warping in the first direction is suppressed.

[0011] As described above, according to the first invention, even when using softwood plywood, it is possible to provide a soundproofing base material for flooring that is less prone to warping and is applicable to flooring for underfloor heating.

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

[0013] In the second invention, at least one second groove is formed on the back surface of the plywood, not only in the first groove, but also in a direction perpendicular to the extension direction (second direction) of the first groove (second direction). By forming the second groove in this way, the rigidity of the plywood is reduced and its flexibility is increased compared to when only the first groove is formed, making it easier to absorb impact forces. In other words, according to the second invention, a base material for flooring with superior sound insulation properties can be provided.

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

[0015] Furthermore, in the third invention, the second groove extending in the direction perpendicular to the fiber direction of the second layer (second direction) (first direction) does not reach the second layer, so the fibers of the second layer extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the medium-density fiberboard bonded to the surface of the plywood, are not cut. With this configuration, in the third invention, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer extending in the second direction. As a result, the base material for flooring becomes less likely to expand or contract in the second direction due to moisture absorption or release, and warping in the second direction is suppressed. In other words, according to the base material for flooring of the third invention, not only is warping in the fiber direction of the first layer (first direction) suppressed, but warping in the direction perpendicular to it (second direction) is also suppressed.

[0016] The 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, the fibers of the second layer extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the medium-density fiberboard, are not cut. Furthermore, because the second layer is covered by the first and third layers, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion and contraction are further suppressed by the fibers of the second layer extending in the second direction. As a result, the base material for the flooring material is less likely to expand or contract in the second direction due to moisture absorption or release, and a flooring material that is less prone to warping in the second direction can be provided.

[0018] Furthermore, the inventors of this application conducted verification tests on the correlation between the depth of the second groove and the sound insulation performance and warping of the flooring material. The verification tests revealed that the deeper the second groove, the better the sound insulation performance, but the more prone the flooring material was to warp in the second direction. It was also found that when the 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 while being less prone to warping in the second direction. In particular, from the viewpoint of sound insulation performance and warping, it is preferable that the bottom of the second groove is located within the fourth layer. Therefore, in the fourth invention, the second groove is formed to a depth where the bottom of the groove is located within the fourth layer. Accordingly, according to the fourth invention, it is possible to provide a flooring material that is less prone to warping and has excellent sound insulation properties, making it suitable for flooring used with underfloor heating.

[0019] The fifth invention is characterized in that, in the first invention, the softwood veneers constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood veneers constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction, and the second layer is characterized in that it does not have knots that are larger in size in the first direction than the first groove spacing.

[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 counter the 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 counter the 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 composed of a part with knot holes of softwood and filling the knot holes with putty so that there are no knot holes, and the second layer is composed of a part without knot holes of softwood larger than 20 mm in size or composed of a part with knot holes of softwood larger than 20 mm in size and filling the knot holes larger than 20 mm in size with dowels so that there are no knot holes larger than 20 mm in size.

[0022] The inventors of this application conducted verification tests on the correlation between the presence or absence of knots in the first to third layers of plywood and the Brinell hardness of the flooring surface. The verification tests revealed that if there are knots in the first layer, which constitutes the surface layer of the plywood, or if there are knots larger than 20 mm in the second layer, the Brinell hardness of the flooring surface falls below the desired hardness. However, even if there are knots larger than 20 mm in the third layer, if there are no knots in the first layer and no knots larger than 20 mm in the second layer, the Brinell hardness of the flooring surface will be above the desired hardness. In other words, it was found that if flooring is formed with knots in the first layer or knots larger than 20 mm in the second layer of plywood, the flooring may become easily damaged. Furthermore, the presence of knots in the first layer, which constitutes the surface layer of the plywood, may worsen the surface quality of the flooring and lead to a decrease in the aesthetic appeal of the flooring. In particular, when using a thin (e.g., 1.5 mm or less) medium-density fiberboard as a surface reinforcement layer to minimize the effects of warping, if there are knots near the surface of the plywood, the effects of the knots (such as unevenness) will be exposed through the thin medium-density fiberboard surface reinforcement layer to the decorative material, increasing the risk of degrading the aesthetic appeal of the flooring.

[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 made to disappear 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 made to disappear by plugging with a wooden plug, 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) having the same shape as the drilled hole to make the knot disappear. In the sixth invention, by configuring it 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 made to be difficult to be damaged and have 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 from 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 made mainly from hardwood xylem fibers (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.

[0026] The eighth invention is characterized in that, in the first invention, one of the two opposing sides of the flooring base material has a recessed groove portion that serves as a female joint in the middle of the thickness direction, and the other has a protruding ridge portion that serves as a male joint in the middle of the thickness direction, and in the flooring base material, the front-side protrusion portion adjacent to the front side of the recessed groove portion, the back-side protrusion portion adjacent to the back side of the recessed groove portion, and the protruding ridge portion are formed to span multiple layers of the plywood.

[0027] In the eighth invention, tongue and groove joints are applied to the surrounding sides of the flooring substrate, and the female and male tongues are formed so that the protruding portions (front protrusions, back protrusions, and ridges) that extend outward from the female and male tongues always span multiple layers of plywood. The protruding portions of the female and male tongues are brittle and prone to chipping, but by configuring them to span multiple layers of plywood as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to the eighth invention, it is possible to provide a flooring substrate in which the protruding portions of the female and male tongues are less prone to chipping.

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

[0029] In the ninth invention, the female tongue and groove are formed such that the bottom corner of the groove portion of the female tongue and groove does not occupy an adhesive portion between any of the layers of the plywood. If the bottom corner of the groove portion of the female tongue and groove is located in an adhesive portion between the layers of the plywood, the plywood is more likely to delaminate between the layers where the groove bottom corner is located when the protruding portion of the male tongue and groove is inserted, but with the above configuration, such delamination can be suppressed.

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

[0031] According to the tenth invention, by providing a flooring base material according to any one of the first to ninth inventions, it is possible to provide a flooring material that is less prone to warping even when using softwood plywood and has excellent sound insulation properties that can be applied to flooring for underfloor heating.

[0032] The eleventh invention is a method for manufacturing flooring comprising a base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, and a cushioning material bonded to the back surface of the base material for flooring, wherein seven softwood slabs of equal thickness are sequentially laminated with a water-based adhesive interposed between each and with the fiber directions of each slab perpendicular to those of adjacent softwood slabs, and the plywood is formed by hot-pressing in the thickness direction, thereby forming a plywood having first to seventh layers made of the softwood slabs that are sequentially laminated and bonded together from the surface side to the back side. The method comprises a board forming step, a surface reinforcement layer bonding step of sanding the surface of the plywood and then bonding the surface reinforcement layer to the surface to form the base material for the flooring material, a grooving step of forming a plurality of first grooves on the back surface of the plywood at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer, and a cushioning material bonding step of bonding a cushioning material to the back surface of the plywood after the grooving step, wherein the first grooves extend from one end to the other in the second direction of the plywood, and the bottom of the grooves is located within the second layer.

[0033] In the 11th invention, multiple first grooves are formed on the back surface of a 7-ply plywood, with a depth extending from the back surface to the second layer. While 3-ply or 5-ply plywood is commonly used as a base material for flooring, the 11th invention uses 7-ply plywood, which increases the number of areas bonded with water-based adhesive (between each layer made of softwood veneer) compared to 3-ply or 5-ply plywood, thus improving its strength. Furthermore, because the plywood has 7 layers, the first grooves extending from the back surface to the second layer are deeper than when the same first grooves 41 are formed in 3-ply or 5-ply plywood. These deep, multiple first grooves reduce the rigidity of the plywood, increase its flexibility, and make it easier to absorb impact forces. In other words, according to the manufacturing method of the 11th invention, it is possible to provide flooring with the required sound insulation performance and excellent soundproofing properties.

[0034] Furthermore, in the 11th invention, multiple first grooves extending in a direction perpendicular to the fiber direction (first direction) of the first layer of the plywood (second direction) do not reach the first layer, so that the fibers of the first layer are not cut by the first grooves. By forming the first grooves in this way, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the first direction due to moisture absorption or release, the expansion and contraction is suppressed by the fibers of the first layer extending in the first direction. As a result, it is possible to manufacture flooring material that is less likely to expand or contract in the first direction due to moisture absorption or release, and is less likely to warp in the first direction.

[0035] Furthermore, in the 11th invention, while plywood with a typical 3-ply or 5-ply lamination count is often used as a base material for flooring, the plywood is made with 7 plies and bonded with a water-based adhesive. As a result, in the 11th invention, the laminated body of softwood veneers is hot-pressed with a higher moisture content compared to when forming 3-ply or 5-ply plywood, and the resulting plywood becomes thinner and denser from the middle of the thickness direction towards the outermost layer. According to the 11th invention, by using plywood with such a configuration, it is possible to provide flooring with excellent surface strength.

[0036] As described above, according to the 11th invention, even when using softwood plywood, it is possible to provide a flooring material that is less prone to warping and has excellent sound insulation properties, making it suitable for use as flooring for underfloor heating.

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

[0038] In the twelfth invention, at least one second groove is formed on the back surface of the plywood, not only in the first groove, but also in a direction perpendicular to the extension direction (second direction) of the first groove (first direction). By forming the second groove in this way, the rigidity of the plywood is reduced and its flexibility is increased compared to when only the first groove is formed, making it easier to absorb impact forces. In other words, according to the twelfth invention, it is possible to provide a base material for flooring with superior 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 of the 3rd to 5th layers.

[0040] In the 13th invention, the second groove, which extends in a direction perpendicular to the fiber direction of the second layer (second direction) (first direction), does not reach the second layer, so that the fibers of the second layer extending in the second direction, which can resist dimensional changes due to moisture absorption or release of the medium-density fiberboard, are not cut by the second groove. By forming the second groove in this way, even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer extending in the second direction. As a result, the base material for the flooring becomes less likely to expand or contract in the second direction due to moisture absorption or release, and warping in the second direction is suppressed. In other words, the base material for the flooring according to the 13th invention makes it possible to provide flooring that is less likely to warp not only in the fiber direction of the first layer (first direction) but also in the direction perpendicular to it (second direction).

[0041] The fourteenth invention is characterized in that, in the thirteenth 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 withstand dimensional changes due to moisture absorption or release of the medium-density fiberboard, not cut, but the second layer is covered by the first and third layers, so even if the medium-density fiberboard bonded to the surface of the plywood tries to expand or contract in the second direction due to moisture absorption or release, the expansion and contraction are further suppressed by the fibers of the second layer extending in the second direction. As a result, the base material for the flooring material is less likely to expand or contract in the second direction due to moisture absorption or release, and a flooring material that is less likely to warp in the second direction can be provided.

[0043] Furthermore, in the 14th invention, based on the results of verification tests on the correlation between the depth of the second groove and the sound insulation performance and dimensional stability (warping) of the flooring material, the second groove is formed to a depth where the groove bottom is located within the fourth layer. Therefore, according to the 14th invention, it is possible to provide a flooring material that is less prone to warping and has excellent sound insulation properties, making it suitable for floor heating.

[0044] The 15th invention is characterized in that, in the 11th invention, the softwood veneers constituting the 1st, 3rd, 5th, and 7th layers are made from a single veneer, while the softwood veneers constituting the 2nd, 4th, and 6th layers are made by joining multiple veneers in the first direction, and the 2nd layer is made without knots and has a size in the first direction that is larger than the first groove spacing.

[0045] In the 15th invention, seven thin sheets of softwood are laminated together to form plywood. Although softwood has more knots than hardwood, if the softwood sheet constituting the second layer has a knot that is larger in the first direction than the groove spacing of the first groove (first groove spacing), the fibers of the second layer that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the medium-density fiberboard, will be cut by the knot. As a result, the dimensional changes due to moisture absorption or release of the medium-density fiberboard cannot be counteracted, and there is a risk that warping will occur partially in the second direction. However, according to the 15th invention, since there are no knots in the second layer that are larger in the first direction than the groove spacing, it is expected that warping in the second direction will be suppressed.

[0046] The 16th invention is characterized in that, in the 11th invention, the first layer is made of parts of coniferous trees that are free of knots or parts of coniferous trees that have knots and the knots are filled with putty, thereby making it knot-free, and the second layer is made of parts of coniferous trees that are free of knots larger than 20 mm or parts of coniferous trees that have knots larger than 20 mm and the knots larger than 20 mm are filled with wood filler, thereby making it knot-free.

[0047] The 16th invention is designed so that the first layer is free of knots and the second layer is free of knots larger than 20 mm. Specifically, the first layer is made from parts of coniferous trees that are free of knots, or if it is made from parts of coniferous trees that have knots, the knots are filled in with putty to make them knot-free. The second layer is made from parts of coniferous trees that are free of knots larger than 20 mm, or if it is made from parts of coniferous trees that have knots larger than 20 mm, the knots larger than 20 mm are filled in with wood to make them knot-free. In the 16th invention, by designing the first layer to be free of knots and the second layer to be free of knots larger than 20 mm, the flooring material made using the flooring material base material is made to be scratch-resistant and have a good surface finish. Therefore, by using the flooring material base material according to the 16th invention, it is possible to provide flooring material that is scratch-resistant and has a good surface finish.

[0048] The 17th invention is characterized in that, in the 11th invention, the above-mentioned medium-density fiberboard is made primarily from wood fibers of hardwoods.

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

[0050] The 18th invention further comprises a tongue-and-groove processing step in which, in the 11th invention, a recessed groove portion that will serve as a female tongue is formed in the middle of the thickness direction on one of two opposing sides of the base material for flooring, and a protruding ridge portion that will serve as a male tongue is formed in the middle of the thickness direction on the other side, wherein in the tongue-and-groove processing step, the female tongue and the male tongue are formed such that the front protrusion adjacent to the front side of the recessed groove portion, the back protrusion adjacent to the back side of the recessed groove portion, and the protruding ridge portion each span multiple layers of the plywood.

[0051] In the 18th invention, tongue and groove joints are applied to the surrounding sides of the base material for flooring, and the female and male tongues are formed so that the protruding portions (front protrusions, back protrusions, and ridges) that extend outward from the female and male tongues always span multiple layers of plywood. The protruding portions of the female and male tongues are brittle and prone to chipping, but by configuring them to span multiple layers of plywood as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to the 18th invention, it is possible to provide flooring in which the protruding portions of the female and male tongues are less prone to chipping.

[0052] The 19th invention is characterized in that, in the 18th invention, the female joint is formed such that the groove bottom corner of the recessed groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers.

[0053] In the 19th invention, the female tongue and groove is processed so that the bottom corner of the groove portion of the female tongue and groove does not occupy an adhesive portion between any of the layers of the plywood, but is instead located within one of the layers. If the bottom corner of the groove portion of the female tongue and groove is located in an adhesive portion between the layers of the plywood, the plywood is more likely to delaminate between the layers where the groove bottom corner is located when the protruding portion of the male tongue and groove is inserted, but such delamination can be suppressed by processing it as described above. [Effects of the Invention]

[0054] As described above, according to the present invention, the number of layers of plywood is set to 7 plies, and a plurality of first grooves extending in a second direction from the back surface to the second layer are formed on the back surface of the plywood. As a result, even when using softwood plywood, warping is less likely to occur, and a sound-insulating substrate for flooring that can be applied to flooring for underfloor heating is provided, as well as flooring equipped therewith and a method for manufacturing the flooring. [Brief explanation of the drawing]

[0055] [Figure 1] Figure 1 is a perspective view of the flooring material according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view of the flooring material in Figure 1 in the first direction. [Figure 3] Figure 3 is a cross-sectional view of the flooring material in Figure 1 in the second direction. [Figure 4] Figure 4 is a cross-sectional view showing the female tongue and groove of the flooring material shown in Figure 1. [Figure 5] Figure 5 is a cross-sectional view showing the male tongue of the flooring material in Figure 1. [Figure 6] Figure 6 shows the plywood forming process of the flooring material manufacturing method according to Embodiment 1. [Figure 7] Figure 7 is a table showing the test results for Test 2. [Figure 8] Figure 8 is a table showing the test results for Test 3. [Figure 9] Figure 9 is a table showing the test results for Test 4. [Figure 10] Figure 10 is a table showing the test results for Test 5. [Figure 11] Figure 11 is a table showing the test results for Test 6. [Figure 12] Figure 12 is a table showing the test results for Test 7. [Figure 13] Figure 13 is a table showing the test results for Test 8. [Figure 14] Figure 14 is a perspective view of the flooring material according to Embodiment 2. [Figure 15] Figure 15 is a table showing the test results for Test 9. [Modes for carrying out the invention]

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

[0057] Embodiment 1 of the Invention -Flooring material composition- The flooring material 1 is installed, for example, on top of floor heating panels in a building such as a house. As shown in Figures 1 to 3, the flooring material 1 is formed in a rectangular shape and comprises a base material (base material for flooring 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 this embodiment 1, the flooring material 1 is formed to have dimensions of 1850 mm x 303 mm and a thickness of 10 mm to 16 mm. The size of the flooring material 1 can be changed as appropriate.

[0058] The decorative material 20 is formed from a resin decorative sheet with a thickness of approximately 0.1 mm to 0.2 mm. As the resin decorative sheet, resin films that contain almost no moisture, such as olefin resin film, PET (polyethylene terephthalate) resin film, and polyvinyl chloride resin film, can be used. The decorative material 20 is printed with, for example, wood grain, stone pattern, or abstract pattern. In addition to resin decorative sheets, decorative paper such as coated paper or resin-impregnated paper, or thin sheet materials such as wood veneer can also be used as the decorative material 20. The thickness of the decorative material 20 should be approximately 0.1 mm to 0.8 mm.

[0059] Any cushioning material 30 can be used as long as it has cushioning properties, but in this embodiment 1, the cushioning material 30 is made of polyurethane foam with a thickness of about 1 mm to 3 mm.

[0060] [Composition of the base material] The base material 10 comprises a plywood 11 and a surface reinforcing layer 12 bonded to the surface of the plywood 11. The base material 10 is formed in a rectangular shape in plan view, and by applying tongue and groove jointing, female tongues 13 and male tongues 14 are formed on the surrounding side surfaces.

[0061] <Detailed composition of plywood> The plywood 11 is a seven-layer softwood plywood with a structure formed by laminating and bonding together seven softwood vases with an adhesive in between. The plywood 11 comprises the first to seventh layers 11a to 11g, which consist of softwood vases arranged sequentially from the front to the back. Each layer 11a to 11g of the plywood 11 is made up of one or more veneers cut from a softwood log using a rotary lathe. Examples of softwood vases that can be used include cypress, cedar, larch, spruce, Japanese red pine, radiata pine, and spruce. In this embodiment 1, cypress vases are used.

[0062] As adhesives, 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. Furthermore, if necessary, curing agents such as isocyanate-based or melamine-based adhesives may be added to the adhesive.

[0063] The seven softwood veneers constituting the first to seventh layers 11a to 11g of the plywood 11 are of equal thickness and size. The thickness of the softwood veneers used in the plywood 11 is preferably 1.0 mm to 1.5 mm. A thickness of less than 1.0 mm is undesirable because it is difficult to stably cut from the log, and the cut veneers cannot maintain their flatness during drying, making it impossible to ensure sufficient strength for uniform adhesive application to both sides. On the other hand, a thickness of more than 1.5 mm is undesirable because it increases the likelihood of cracking on the back during cutting, and after lamination, a larger portion is compressed by heat and pressure without being reinforced with water-based adhesive, while the uncompressed portion has poor thermal conductivity. The size of the softwood veneers can be designed in various ways depending on the size of the flooring material 1. In this embodiment 1, for example, to manufacture a flooring material 1 with dimensions of 1850 mm x 303 mm, a softwood veneer measuring 1900 mm x 345 mm and with a thickness of 1.3 mm is used.

[0064] The softwood vases constituting the first layer 11a, the third layer 11c, the fifth layer 11e, and the seventh layer 11g (odd-numbered layers) are made up of a single veneer cut so that the fibers extend in the longitudinal direction (first direction) of the plywood 11. On the other hand, the softwood vases constituting the second layer 11b, the fourth layer 11d, and the sixth layer 11f (even-numbered layers) are made up by joining together multiple veneers cut so that the fibers extend in the width direction (second direction) of the plywood 11 in a direction perpendicular to the fiber direction (see Figure 6). The number of veneers to be joined is not particularly limited, but in this embodiment 1, the softwood vases constituting the even-numbered layers are made up by joining together two veneers.

[0065] As a result, in the odd-numbered layers 11a, 11c, 11e, and 11g of the plywood 11, the fibers extend in the length direction (first direction), while in the even-numbered layers 11b, 11d, and the sixth layer 11f, the fibers extend in the width direction (second direction). In other words, 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 (coniferous veneers) are perpendicular to each other.

[0066] While plywood with 3 or 5 layers is commonly used as a base material for flooring, the plywood 11 in this embodiment has 7 layers, which is more than usual. As will be described in detail later, the plywood 11 is formed by laminating 7 thin sheets of softwood with a water-based adhesive interposed between them and then hot-pressing them. As a result, the plywood 11 in this embodiment is hot-pressed with a higher moisture content than the 3 or 5-ply plywood commonly used as a base material for flooring. Therefore, the moisture content increases from the middle of the thickness direction towards the outermost layer, resulting in a thinner and denser material from the middle of the thickness direction towards the outermost layer. Furthermore, in the second layer 11b and the third layer 11c, water-based adhesive is applied and impregnated on both sides, so they are hot-pressed with a high moisture content, resulting in greater compression, and the compressed state is fixed by the impregnated adhesive.

[0067] Specifically, in the plywood 11 of this embodiment, which uses a 1.3 mm thick softwood veneer, the thickness of the first layer 11a and the seventh layer 11g is about 1.1 mm, the thickness of the second layer 11b and the sixth layer 11f is about 1.2 mm, and the third layer 11c to the fifth layer 11e remain almost uncompressed, maintaining their original thickness of 1.3 mm. In other words, the first to third layers 11a to 11c decrease in thickness and increase in density in the order of third layer 11c, second layer 11b, and first layer 11a. Similarly, the fifth to seventh layers 11e to 11g decrease in thickness and increase in density in the order of fifth layer 11e, sixth layer 11f, and seventh layer 11g. Furthermore, the thickness of the first layer 11a and the seventh layer 11g is less than or equal to the thickness of the surface strengthening layer 12 (1.2 mm in this embodiment 1), while the thickness of the third layer 11c to the fifth layer 11e is greater than the thickness of the surface strengthening layer 12.

[0068] (1st groove, 2nd groove) Multiple first grooves 41 and multiple second grooves 42 are formed on the back surface of the plywood 11. Both the first grooves 41 and the second grooves 42 are formed to improve the sound insulation of the flooring material 1. In addition, if the flooring material 1 is installed on top of a floor heating panel, the first and second grooves 41 and 42 also have the effect of making it easier for heat to be transferred uniformly to the surface of the flooring material 1.

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

[0070] The second groove 42 is a groove that extends from one end to the other in the longitudinal direction of the plywood 11. In this embodiment 1, the second groove 42 is formed to have a rectangular cross-sectional shape. The second groove 42 is formed to have a groove width of 2.0 mm or more and 4.0 mm or less, and a groove spacing (length between adjacent second grooves 42, second groove spacing) of 35 mm or more and 100 mm or less. In this embodiment 1, the second groove 42 is formed to have a groove width of 3.0 mm and a groove spacing of 47 mm. Furthermore, the second groove 42 is formed to a depth (5.0 mm in Figure 3) where the groove bottom is located within one of the third to fifth layers 11c to 11e (in Figure 3, the fourth layer 11d).

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

[0072] <Detailed composition of the 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 / cm³. 3 More than 0.9g / cm 3The following medium-density fiberboard (MDF) is used and bonded to the surface of the plywood 11 with an adhesive. In this embodiment 1, the surface reinforcement layer 12 is made of hardwood MDF, which mainly consists of hardwood wood fibers. In this embodiment 1, the surface reinforcement layer 12 uses hardwood MDF with dimensions of 1850 mm x 303 mm and a thickness of 1.2 mm, and the corners of the top and side surfaces of the hardwood MDF are chamfered. Any adhesive may be used to bond to the plywood 11, but a soft adhesive such as a water-based vinyl urethane type may be used and laminated and integrated by cold-pressing, or a soft adhesive such as a water-based vinyl urethane type may be used and laminated and integrated by cold-pressing followed by hot-pressing. Alternatively, an anhydrous soft adhesive such as PUR hot melt may be used and laminated and integrated by hot-pressing.

[0073] <Detailed composition of the female and male fruits> As shown in Figures 4 and 5, the surrounding sides of the base material 10 are fitted with tongue and groove joints. Specifically, on one of the two opposing sides of the base material 10 (long sides 10a, 10a and short sides 10b, 10b), a female tongue and groove 13 is formed, and on the other side, a male tongue and groove 14 that can be fitted into the female tongue and groove 13 is formed.

[0074] The female joint 13 is formed by cutting out the base material 10 such that the middle portion of the long side surface 10a and the short side surface 10b in the thickness direction becomes a recessed groove 13a. The recessed groove 13a is a groove that extends from one end to the other in the length direction of each side surface 10a, 10b. In this embodiment 1, the cross-sectional shape of the recessed groove 13a is formed to be rectangular, but the cross-sectional shape of the recessed groove 13a is not limited to this and may be trapezoidal or other shapes. By cutting out the recessed groove 13a from 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 recessed groove 13a, and a back-side convex portion 13c is formed adjacent to the back side of the recessed groove 13a.

[0075] The male part 14 is formed by cutting out the base material 10 such that the middle portion of the long side surface 10a and the short side surface 10b in the thickness direction becomes a protruding ridge 14a. The protruding ridge 14a is a projection that extends from one end to the other in the length direction of each side surface 10a, 10b. In this embodiment 1, the cross-sectional shape of the protruding ridge 14a is formed to be rectangular, but the cross-sectional shape of the protruding ridge 14a is not limited to this, and any shape that fits into the recessed groove 13a is acceptable.

[0076] The female joint 13 and male joint 14 are formed so that their outwardly protruding convex portions (front convex portion 13b and back convex portion 13c for the female joint 13, and convex ridge portion 14a for the male joint 14) span multiple layers of the plywood 11. Specifically, in this embodiment 1, the front convex portion 13b of the female joint 13 is formed to span two layers of the plywood 11, the first layer 11a and the second layer 11b. The back convex portion 13c of the female joint 13 is formed to span three layers of the plywood 11, from the fifth layer 11e to the seventh layer 11g. The convex ridge portion 14a of the male joint 14 is formed to span four layers of the plywood 11, from the second layer 11b to the fifth layer 11e.

[0077] With this configuration, the protruding portions 13b, 13c, and 14a of the female and male fruits 13 and 14 are brittle and prone to chipping. However, by configuring them to span multiple layers of the plywood 11 as described above, they will always include fibers extending in the longitudinal direction (first direction) and fibers extending in the width direction (second direction) of the flooring material 1, making them less prone to chipping.

[0078] Furthermore, in this embodiment 1, by forming the female tongue and groove 13 as described above, the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located within the layers of the plywood 11, rather than in the adhesive portion between the layers (in this embodiment 1, the groove bottom corner x on the front side is located within the second layer 11b, and the groove bottom corner x on the back side is located within the fifth layer 11e). If the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue and groove 14 is inserted, but with the above configuration, such peeling can be suppressed.

[0079] -Flooring material manufacturing method- The manufacturing method for flooring material 1 will be described below.

[0080] Flooring 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 formation process] The base material formation process S1 comprises a plywood formation process S11, a surface reinforcement layer bonding process S12, and a cutting process (groove processing process) S13.

[0082] First, the plywood forming process S11 is performed. In the plywood forming process S11, first, softwood logs are cut using a rotary lathe to a thickness of 1.3 mm and a length in the grain direction of 1900 mm, preparing four first veneers with a length of 1900 mm in the grain direction and a length of 345 mm in the direction perpendicular to the grain, and six second veneers with a length of 345 mm in the grain direction and a length of 950 mm in the direction perpendicular to the grain. The four first veneers are used to make four softwood slabs for the odd-numbered layers 11a, 11c, 11e, and 11g. In addition, two second veneers are joined together in the direction perpendicular to the grain to form three softwood slabs for the even-numbered layers 11b, 11d, and 11f (see Figure 6).

[0083] In this embodiment 1, the first layer 11a constituting the surface layer of the plywood 11 is free of knots, and the second layer 11b is free of knots larger than 20 mm. Here, "free of knots (free of knots larger than 20 mm)" includes not only those made from parts of softwood logs that do not have knots (knots larger than 20 mm), but also those made from parts of softwood logs that do have knots (knots larger than 20 mm), but where the knots (knots larger than 20 mm) have been removed by a predetermined treatment. In this embodiment 1, the treatment for removing knots differs between the first layer 11a and the second layer 11b. In the first layer 11a, the knots are removed by a putty treatment in which putty is embedded in the knots. On the other hand, the second layer 11b is hollowed out to accommodate knots larger than 20 mm, and the holes are filled without gaps with wood of the same shape (wood inlay) to eliminate knots larger than 20 mm. Putty treatment is performed after plywood molding, and wood inlay treatment may be performed when preparing the second veneer, or after joining the second veneers in a direction perpendicular to the fibers to form a softwood veneer for the second layer 11b.

[0084] As mentioned above, in order to ensure that the first layer 11a is free of knots and the second layer 11b is free of knots larger than 20 mm, it would be ideal to use only knot-free portions of softwood for all the softwood vases for the first to seventh layers 11a to 11g. However, this is not practical because softwood has many knots. It is preferable to prepare softwood vases separately for the odd-numbered layers 11a, 11c, 11e, and 11g, and for the even-numbered layers 11b, 11d, and 11f. The softwood vases for the even-numbered layers 11b, 11d, and 11f should be treated with wood inlay before plywood forming to ensure that there are no knots larger than 20 mm. This plywood manufacturing method makes it easy to procure materials and offers excellent workability, as only two types of softwood vases need to be prepared.

[0085] Alternatively, softwood slabs for 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 the softwood slabs for the second layer 11b and the sixth layer 11f may be treated with wood-filling before plywood molding to ensure that there are no knots larger than 20 mm. This plywood manufacturing method requires the preparation of three types of softwood slabs, but since wood-filling is only required for the softwood slabs for the second layer 11b and the sixth layer 11f, processing costs can be reduced. Furthermore, after plywood molding, regardless of which side of the plywood 11 is the front (first layer 11a side), the second layer 11b will be knot-free, eliminating the need to distinguish between the front and back of the plywood 11 and simplifying the manufacturing process.

[0086] Furthermore, softwood slabs for even-numbered layers 11b, 11d, and 11f may be prepared separately for the second layer 11b and for the fourth layer 11d and sixth layer 11f. Only the softwood slab for the second layer 11b may be treated with wood-filling before plywood forming to ensure that there are no knots larger than 20 mm. This plywood manufacturing method requires the preparation of three types of softwood slabs, but since wood-filling is only required for the softwood slab for the second layer 11b, processing costs can be minimized.

[0087] Next, the seven thin sheets of softwood prepared for layers 11a to 7 (11g) are laminated in the following order, with a water-based adhesive in between: layer 7 (11g), layer 6 (11f), layer 5 (11e), layer 4 (11d), layer 3 (11c), layer 2 (11b), and layer 1 (11a).

[0088] Specifically, first, a softwood veneer for the 7th layer (11g), the bottommost layer, is placed on top of a softwood veneer (1st veneer) for the 6th layer (11f), with water-based adhesive applied to both sides of the entire surface. Then, a softwood veneer for the 5th layer (11e), the 1st veneer, is placed directly on top of the softwood veneer for the 6th layer (11f), and a softwood veneer for the 4th layer (11d), the 2nd veneer, is placed on top of that, with water-based adhesive applied to both sides of the entire surface. Then, a softwood veneer for the 3rd layer (11c), the 1st veneer, is placed directly on top of the softwood veneer for the 4th layer (11d), and a softwood veneer for the 2nd layer (11b), the 2nd veneer, is placed on top of that, with water-based adhesive applied to both sides of the entire surface. Finally, the softwood veneer for the first layer 11a (first veneer) is placed directly on top of the softwood veneer for the second layer 11b.

[0089] As described above, seven thin sheets of softwood veneer are laminated and then hot-pressed in the lamination direction to form a bonded and integrated plywood 11. In this embodiment 1, since the number of layers of plywood 11 is set to seven and bonded with a water-based adhesive, the laminated softwood veneer is hot-pressed with a higher moisture content compared to when forming a 3-ply or 5-ply plywood. As a result, the formed plywood 11 becomes thinner and denser from the middle of the thickness direction towards the outermost layer.

[0090] After the plywood forming process S11, the surface reinforcement layer bonding process S12 is performed. As mentioned above, if the first veneer constituting the softwood thin board for the first layer 11a is made of wood with knots, a putty treatment is performed before the surface reinforcement layer bonding process S12 to fill the knots in the first layer 11a with putty to eliminate the knots.

[0091] In the surface reinforcement layer bonding process S12, first, the surface of the plywood 11 is sanded to make it smooth. Then, a surface reinforcement layer 12 made of hardwood MDF is bonded to the surface of the plywood 11. Specifically, an adhesive (for example, a flexible adhesive such as water-based vinyl urethane or an anhydrous flexible adhesive such as PUR hot melt) is applied to the surface of the plywood 11, and the surface reinforcement layer 12 is placed on top of it. Then, the plywood 11 and the surface reinforcement layer 12 are bonded together by pressing them in the lamination direction (cold press in the case of a flexible adhesive such as water-based vinyl urethane, and hot press in the case of anhydrous flexible adhesive such as PUR hot melt).

[0092] After the surface reinforcement layer bonding process S12, a cutting process S13 is performed. The cutting process S13 includes a groove machining process S14 and a tongue and groove machining process S15.

[0093] In the grooving process 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 with a predetermined width of 1.0 mm to 2.0 mm (1.5 mm in this embodiment 1), a depth from the back surface of the plywood 11 to the second layer 11b (6.9 mm in this embodiment 1), and a rectangular cross-sectional shape extending in the width direction (second direction). Multiple such first grooves 41 are formed at predetermined pitches of 10 mm to 50 mm (10.2 mm pitch in this embodiment 1). The second groove 42 is a groove with a predetermined width of 2.0 mm to 4.0 mm (3.0 mm in this embodiment 1), a depth of 5.0 mm from the back surface of the plywood 11 to one of the third to fifth layers 11c to 11e (fourth layer 11d in Figure 3), and a rectangular cross-sectional shape extending in the length direction (first direction). Multiple such second grooves 42 are formed at predetermined pitches of 35 mm to 100 mm (47 mm pitch in this embodiment 1).

[0094] In the tongue and groove jointing process S15, female tongues and grooves 13 and male tongues and grooves 14 are formed on the surrounding sides of the plywood 11 (two long sides 10a and two short sides 10b) by cutting (tongue and groove jointing).

[0095] Specifically, the female joint 13 is formed by cutting out the base material 10 so that the middle portion in the thickness direction of the long side surface 10a and the short side surface 10b of the base material 10 becomes a recessed groove 13a. At this time, the female joint 13 is formed so that the front side protrusion 13b and the back side protrusion 13c of the recessed groove 13a span multiple layers of the plywood 11. Specifically, the female joint 13 is formed so that the front side protrusion 13b spans two layers, the first layer 11a and the second layer 11b, and the back side protrusion 13c spans three layers, the fifth layer 11e to the seventh layer 11g. In addition, the female joint 13 is formed so that the groove bottom corner x of the recessed groove 13a is located within the layers of the plywood 11, rather than in the adhesive portion between layers (in this embodiment 1, the front side groove bottom corner x is within the second layer 11b, and the back side groove bottom corner x is within the fifth layer 11e).

[0096] Furthermore, a male joint 14 is formed by cutting out the base material 10 such 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 protruding ridge 14a. At this time, the male joint 14 is formed so that the protruding ridge 14a spans multiple layers of the plywood 11. Specifically, a female joint 13 is formed so that the protruding ridge 14a spans four layers from the second layer 11b to the fifth layer 11e.

[0097] As described above, in the base material formation process S1, the plywood formation process S11, the surface reinforcement layer bonding process S12, and the cutting process (groove processing process) S13 are performed to form the base material 10.

[0098] In the decorative material bonding step S2, the decorative material 20 (a resin decorative sheet in this embodiment 1) is bonded to the surface of the substrate 10 (the surface of the surface reinforcing layer 12) formed in the substrate forming step S1 using an adhesive.

[0099] In the cushioning material bonding step S3, the cushioning material 30 (nonwoven fabric in this embodiment 1) is bonded to the back surface (back surface of the plywood 11) of the base material 10 formed in the base material forming step S1 using an adhesive.

[0100] The flooring material 1 is manufactured by performing the above-described base material formation process S1, decorative material bonding process S2, and cushioning material bonding process S3.

[0101] -test- The flooring material 1 according to this embodiment, manufactured as described above, was subjected to the following tests 1 to 8. Test 1 was a test to confirm the sound insulation and dimensional stability of the flooring material 1; Tests 2 to 4 were Brinell hardness tests to confirm the effect of missing knots on the surface hardness of the flooring material 1; Tests 5 and 6 were lightweight floor impact sound tests to confirm the effect of grooves on the sound insulation (sound-insulating performance) of the flooring material 1; Tests 7 and 8 were tests to confirm the effect of the groove depth of the second groove 42 on the width curvature (curvature in the second direction) of the flooring material 1; Test 7 was a wet-dry cycle test; and Test 8 was an 80°C heat endurance test.

[0102] [Test 1] Similar to flooring material 1, test specimens 1-1 to 1-3 measuring 470 mm x 918.5 mm were prepared, each equipped with a base material 10, decorative material 20, and cushioning material 30. Sound insulation tests and water absorption length change rate tests were conducted, and the lightweight floor impact sound and water absorption length expansion rate were measured. Test specimens 1-1 to 1-3 differ in the configuration of the base material 10, as follows. Note that test specimen 1-1 has the same configuration as flooring material 1 of this embodiment. Test specimen 1-2 is a modified version of flooring material 1 of this embodiment, with the plywood 11 replaced by 5-ply softwood plywood (cypress plywood). Test specimen 1-3 is a modified version of flooring material 1 of this embodiment, with the plywood 11 replaced by 5-ply lauan plywood.

[0103] The soundproofing test results showed that test specimen 1-1 had the best reduction in lightweight floor impact sound with center frequencies of 250Hz and 500Hz, while test specimen 2 had the worst reduction. In other words, it can be seen that flooring material 1 of this embodiment has superior soundproofing performance compared to flooring materials using 5-ply softwood plywood (cypress plywood) and flooring materials using lauan plywood.

[0104] Furthermore, the water absorption length change rate test showed no significant difference in the water absorption length change rate among test specimens 1-1 to 1-3. However, the warping in the length direction was smallest in test specimen 1-1 and largest in test specimen 1-2. Similarly, the warping in the width direction was smallest in test specimen 1-1 and largest in test specimen 1-2. In other words, it can be seen that the flooring material 1 of this embodiment is less prone to warping than flooring materials using 5-ply softwood plywood (cypress plywood) and flooring materials using lauan plywood.

[0105] [Exams 2-4] (Exam 2) Test specimens 2-1 to 2-8, each measuring 150 mm x 150 mm and equipped with a base material 10 and a decorative material 20, were prepared, and a Brinell hardness test was performed to measure their Brinell hardness.

[0106] Test specimens 2-1 to 2-8 each have a different composition of the base material 10. Specifically, in all test specimens 2-1 to 2-8, seven 150mm x 150mm, 1.3mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive as interposition, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and a decorative material 20 made of an olefin decorative sheet with a thickness of 0.14mm are attached to each surface in that order using a water-based vinyl urethane adhesive.

[0107] In test specimens 2-1 to 2-4, an artificial through-hole (simulating a knot) with a diameter of 30 mm was formed in the center of the softwood veneer constituting the second layer 11b, and the first layer 11a was constructed to be free of knots by applying putty. On the other hand, in test specimens 2-5 to 2-8, both the first layer 11a and the second layer 11b were constructed to be free of knots.

[0108] Furthermore, the thickness of the surface strengthening layer 12 was varied for each of the test specimens 2-1 to 2-4: 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, the thickness of the surface strengthening layer 12 was varied for each of the test specimens 2-5 to 2-8: 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 was measured at the center of the surface of test specimens 2-1 to 2-8 (the position corresponding to the artificial through-hole in test specimens 2-1 to 2-4).

[0110] The results of Test 2 are shown in Figure 7. The Brinell hardness was 11 N / mm². 2 In the above cases, mark with "○", 9.8 N / mm 2 More than 11N / mm 2 Less than 9.8 N / mm 2 Values ​​less than the given value are indicated by "×". Based on the results of Test 2, when the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less), as in flooring material 1 of this embodiment, if there are knots (through holes in Test 2) in the second layer 11b of the plywood 11, the Brinell hardness will be the value required for flooring material 1 (11 N / mm²). 2 It was found that it would not reach ).

[0111] Furthermore, as a comparative test to Test 2, specimens 2-11 to 2-14 were prepared by changing the diameter of the through-hole formed in the center of the softwood veneer constituting the second layer 11b of specimens 2-1 to 2-4 to 20 mm, while maintaining the same configuration as specimens 2-1 to 2-4. A similar Brinell hardness test was then performed on specimens 2-11 to 2-14, all of which showed a Brinell hardness of 11 N / mm². 2 The above results (test results were marked "○") were obtained. From Test 2 and the comparative test, it was found that even when the thickness of the surface reinforcement layer 12 is thinner than 1.5 mm (0.8 mm to 1.3 mm), as in the flooring material 1 of this embodiment, if there are no knots missing in the first layer 11a and no knots missing in the second layer 11b that are larger than 20 mm, the Brinell hardness of the flooring material surface will be equal to or greater than the desired hardness.

[0112] (Exam 3) Similar to flooring material 1, 150mm x 150mm test specimens 3-1 to 3-8 were prepared, each comprising a base material 10, a decorative material 20, and a cushioning material 30. A Brinell hardness test was then conducted, and the Brinell hardness was measured. Test specimens 3-1 to 3-8 are the same as those in test specimens 2-1 to 2-8, but with the thickness of the softwood veneers constituting the first layer 11a and the seventh layer 11g of the plywood 11 changed to 1.7mm. The other components are the same as those in test specimens 2-1 to 2-8.

[0113] The results of Test 3 are shown in Fig. 8, and are the same as those 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) larger than 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 specimens 4-1 to 4-6 of 150 mm × 150 mm equipped with the base material 10, the decorative material 20, and the cushioning material 30 were prepared, and a Brinell hardness test was conducted to measure the Brinell hardness. Note that in test specimens 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 in test specimens 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 that there are no knot holes larger than 20 mm. Test specimens 4-4 to 4-6 are configured such that there are no knot holes larger than 20 mm in the third layer 11c in test specimens 4-1 to 4-3.

[0115] The results of Test 4 are shown in Fig. 9, and for all of test specimens 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) larger than 20 mm in the second layer 11b of the plywood 11, the Brinell hardness will not reach the value (11 N / mm 2Although it does not reach the specified value, it was found that even if the thickness of the surface reinforcement layer 12 is thinner than 1.5 mm, as long as there are no knots in the first layer 11a and no knots larger than 20 mm in the second layer 11b, the presence of knots in the third layer 11c does not adversely affect the Brinell hardness of the surface.

[0116] [Exams 5-7] (Exam 5) Test specimens 5-1 to 5-16, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared, and lightweight floor impact sound tests were conducted to measure the reduction in sound frequencies from 125 Hz to 500 Hz.

[0117] Test specimens 5-1 to 5-16 each have a different composition of the base material 10. Specifically, test specimens 5-1 to 5-16 differ in the configuration (presence or absence and depth) of the second groove 42 and the thickness of the surface reinforcement layer 12, while the other components are the same as those of flooring material 1. To prepare test specimens 5-1 to 5-16, first, seven 1.3 mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are attached to each surface in that order using a water-based vinyl urethane adhesive, and then the plywood is cut into 900 mm x 150 mm pieces. Tongue and groove joints are applied to the four sides of the cut plywood 11 to form female and male joints 13 and 14. Furthermore, test specimens 5-1 to 5-16 are prepared by forming the first and second grooves 41, 42 or only the first groove 41 on the back surface of the plywood 11 (the back surface of the seventh layer 11g), and then attaching a cushioning material 30 made of a 3 mm thick foamed cushioning material to cover the entire back surface.

[0118] Test specimens 5-1 to 5-4 have only the first groove 41 formed on the back surface of the plywood 11, and no second groove 42 formed. Test specimens 5-5 to 5-16 have both the first groove 41 and the second groove 42 formed on the back surface of the plywood 11. The first groove 41 formed in test specimens 5-1 to 5-16 has a groove width of 1.5 mm, a groove spacing of 10.2 mm, and a depth (groove bottom thickness of 2.6 mm) such that the groove bottom is located within the second layer 11b, similar to flooring material 1. The second grooves 42 formed in test specimens 5-5 to 5-16 shall have a groove width of 3.0 mm and a groove spacing of 47 mm, similar to flooring material 1. However, the depth shall be such that in test specimens 5-5 to 5-8 the groove bottom is located within the third layer 11c (groove bottom thickness 3.7 mm), in test specimens 5-9 to 5-12 the groove bottom is located within the fourth layer 11d (groove bottom thickness 5.0 mm), and in test specimens 5-13 to 5-16 the groove bottom is located within the fifth layer 11e (groove bottom thickness 6.3 mm).

[0119] In addition, for test specimens 5-1 to 5-16, the first layer 11a was treated with putty to ensure it was free of knots, and the even-numbered layers 11b, 11d, and 11f were treated with wood filler to ensure they were free of knots larger than 20 mm.

[0120] Furthermore, the thickness of the surface reinforcement layer 12 was varied for test specimens 5-1 to 5-4, with 1.0 mm for test specimen 5-1, 1.3 mm for test specimen 5-2, 1.5 mm for test specimen 5-3, and 2.7 mm for test specimen 5-4. Similarly, the thickness of the surface reinforcement layer 12 was varied for test specimens 5-5 to 5-8, test specimens 5-9 to 5-12, and test specimens 5-13 to 5-16, with 1.0 mm for test specimens 5-5, 5-9, and 5-13, 1.3 mm for test specimens 5-6, 5-10, and 5-14, 1.5 mm for test specimens 5-7, 5-11, and 5-15, and 2.7 mm for test specimens 5-8, 5-12, and 5-16.

[0121] The lightweight floor impact sound test was conducted in accordance with the test method described in JIS A 1440-1 "Method for measuring the reduction in floor impact sound levels of floor finishing structures on concrete floors in laboratories," specifically the "Method using a standard lightweight impact source," and the reduction in lightweight floor impact sound levels for test specimens 5-1 to 5-16 was measured.

[0122] The results of Test 5 are shown in Figure 10. A reduction in the lightweight floor impact sound level of 125Hz to 500Hz of ΔLL-4 or more is indicated by "○", equivalent to ΔLL-3 is indicated by "△", and less than ΔLL-3 is indicated by "×". From the results of Test 5, it was found that even if the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm to 1.3 mm), as in the flooring material 1 of this embodiment, if the second groove 42 is not formed, the flexibility of the flooring material 1 will be insufficient, making it difficult to absorb impact force, resulting in a flooring material 1 that lacks sound insulation performance and does not have the required sound insulation performance. Furthermore, it was found that if the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm and the depth of the second groove 42 is set so that the bottom of the groove is located within one of the third to fifth layers 11c to 11e, a flooring material 1 with the required sound insulation performance and excellent sound insulation performance can be obtained. Although not shown in Figure 10, it was found that increasing the depth of the second groove 42 improved the sound insulation performance.

[0123] (Exam 6) Test specimens 6-1 to 6-12, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared, and lightweight floor impact sound tests were conducted to measure the reduction in sound from 125 Hz to 500 Hz. Test specimens 6-1 to 6-12 are the same as those in test specimens 5-1 to 5-12, but with the thickness of the softwood veneers constituting the first layer 11a and the seventh layer 11g of the plywood 11 changed to 1.7 mm. The other components are the same as those in test specimens 5-1 to 5-12.

[0124] The results of Test 6 are shown in Figure 11, and in all of the test specimens 6-1 to 6-12, the surface Brinell hardness was the value required for flooring material 1 (11 N / mm²). 2 ) became less than ). In other words, from the results of tests 5 and 6, it was found that even if the thickness of the surface reinforcement layer 12 is made thinner than 1.5 mm (0.8 mm or more and 1.3 mm or less), as in the flooring material 1 of this embodiment, if the first layer 11a of the plywood 11 is thick, the rigidity in the longitudinal direction (first direction) of the flooring material 1 increases, resulting in a flooring material 1 that does not have the required sound insulation performance and lacks soundproofing.

[0125] [Tests 7, 8] (Exam 7) Test specimens 7-1 to 7-8, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared. A wet-dry cycle test was performed, and the degree of warping in the width direction (second direction) was observed visually.

[0126] Test specimens 7-1 to 7-8 each have a different composition of the base material 10. Specifically, test specimens 7-1 to 7-8 differ in the configuration (depth) of the second groove 42 and the thickness of the surface reinforcement layer 12, while the other components are the same as those of flooring material 1. To prepare test specimens 7-1 to 7-8, first, seven 1.3 mm thick softwood veneers are laminated with alternating perpendicular fiber directions using a water-based adhesive, and then hot-pressed to form plywood 11. After sanding the surface of the plywood 11, a surface reinforcement layer 12 made of hardwood MDF and an olefin decorative sheet with a thickness of 0.14 mm are attached to each surface in that order using a water-based vinyl urethane adhesive, and then the plywood is cut into 900 mm x 150 mm pieces. Tongue and groove joints are applied to the four sides of the cut plywood 11 to form female and male joints 13 and 14. Furthermore, test specimens 7-1 to 7-8 are prepared by forming first and second grooves 41 and 42 on the back surface of the plywood 11 (the back surface of the 7th layer 11g), and then attaching a cushioning material 30 made of a 3mm thick foamed cushioning material to cover the entire back surface.

[0127] The first grooves 41 formed in test specimens 7-1 to 7-8 shall have a groove width of 1.5 mm, a groove spacing of 10.2 mm, and a depth such that the groove bottom is located within the second layer 11b (groove bottom thickness of 2.6 mm), similar to flooring material 1. The second grooves 42 formed in test specimens 7-1 to 7-8 shall have a groove width of 3.0 mm and a groove spacing of 47 mm, similar to flooring material 1. However, the depth shall be such that in test specimens 7-1 and 7-2 the groove bottom is located within the second layer 11b (groove bottom thickness 1.6 mm), in test specimens 7-3 and 7-4 the groove bottom is located within the third layer 11c (groove bottom thickness 3.7 mm), in test specimens 7-5 and 7-6 the groove bottom is located within the fourth layer 11d (groove bottom thickness 5.0 mm), and in test specimens 7-7 and 7-8 the groove bottom is located within the fifth layer 11e (groove bottom thickness 6.3 mm).

[0128] In addition, for test specimens 7-1 to 7-8, the first layer 11a was treated with putty to ensure it was free of knots, and the even-numbered layers 11b, 11d, and 11f were treated with wood filler to ensure they were free of knots larger than 20 mm.

[0129] Furthermore, the thickness of the surface reinforcing layer 12 was varied for test specimens 7-1 and 7-2, with 1.0 mm for test specimen 7-1 and 1.3 mm for test specimen 7-2. Similarly, the thickness of the surface reinforcing layer 12 was varied for test specimens 7-3, 7-4, 7-5, 7-6, and 7-7, 7-8, with 1.0 mm for test specimens 7-3, 7-5, and 7-7, and 1.3 mm for test specimens 7-4, 7-6, and 7-8.

[0130] The wet-dry cycle test involved placing the specimens under two conditions: 40°C and 90% relative humidity (moisture absorption) and 20°C and 40% relative humidity (moisture release) for 48 hours each. After two cycles of this process, the degree of warping in the width direction (second direction) of specimens 7-1 to 7-8 was observed visually.

[0131] The results of Test 7 are shown in Figure 12. A circle (○) indicates acceptable warping in the width direction (second direction), while a cross (×) indicates significant warping in the width direction (second direction) that is unacceptable. From the results of Test 7, it was found that if the depth of the second groove 42 is such that the groove bottom is located within one of the third to fifth layers 11c to 11e (groove bottom thickness of 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 groove bottom is located within the second layer 11b (groove bottom thickness of 1.6 mm), the warping in the width direction becomes unacceptable. Furthermore, there was no significant difference in the degree of warping in the width direction between test specimens 7-3, 7-5, and 7-7, nor was there a significant difference in the degree of warping in the width direction between test specimens 7-4, 7-6, and 7-8.

[0132] (Exam 8) Test specimens 8-1 to 8-8, each measuring 900 mm x 150 mm and equipped with a base material 10, decorative material 20, and cushioning material 30, were prepared and subjected to an 80°C heat endurance test. The degree of warping in the width direction (second direction) was observed visually. Test specimens 8-1 to 8-8 were constructed in the same manner as test specimens 7-1 to 7-8.

[0133] The 80°C heat endurance test was conducted by drying test specimens 8-1 to 8-8 in an 80°C dryer for 48 hours until they were completely dry, and then visually observing the degree of warping in the width direction (second direction).

[0134] The results of Test 8 are shown in Figure 13, and were the same as those of Test 7. The results of Test 8 also showed that if the depth of the second groove 42 is set so that the groove bottom is located within one of the third to fifth layers 11c to 11e (groove bottom thickness of 3.7 mm or more), the curvature in the width direction (second direction) is acceptable. However, if the depth of the second groove 42 is set so that the groove bottom is located within the second layer 11b (groove bottom thickness of 1.6 mm), the curvature in the width direction becomes unacceptably large. In addition, in Test 8, the curvature in the width direction differed slightly between test specimens 8-3, 8-5, and 8-7, and between test specimens 8-4, 8-6, and 8-8, and the curvature in the width direction increased as the depth of the second groove 42 increased. In other words, it was found that the shallower the depth of the second groove 42 (the thicker the groove bottom), the less likely warping in the width direction due to heat drying is to occur, making it suitable for flooring materials used with underfloor heating.

[0135] -Effects of Embodiment 1- In the flooring base material 10 of this embodiment, the number of layers of plywood 11 is set to 7 plies, and multiple first grooves 41 are formed on the back surface of the plywood 11 to a depth that extends from the back surface to the second layer 11b. Plywood with 3 or 5 layers is often used as a base material for flooring, but in this embodiment 1, the number of layers of plywood 11 is set to 7 plies, so the number of areas bonded with adhesive (between each layer made of softwood veneer) is increased compared to 3-ply plywood or 5-ply plywood, thus improving the strength compared to 3-ply plywood or 5-ply plywood. In addition, because the number of layers of plywood 11 is set to 7 plies, the first grooves 41 that extend 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 these multiple deep first grooves 41, the rigidity of the plywood 11 is reduced and its flexibility is increased, making it easier to absorb impact forces. In other words, by using the flooring material base material 10 of this embodiment, the flooring material 1 will have the required sound insulation performance and excellent soundproofing properties.

[0136] Furthermore, in this embodiment 1, the multiple first grooves 41 extend in a direction perpendicular to the fiber direction (first direction) of the first layer 11a of the plywood 11 (second direction), and these grooves do not reach the first layer 11a, so the fibers of the first layer 11a are not cut. With this configuration, in this embodiment 1, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the first direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the first layer 11a extending in the first direction. As a result, the flooring base material 10 is less likely to expand or contract in the first direction due to moisture absorption or release, and warping in the first direction is suppressed. Therefore, according to this embodiment 1, even if softwood plywood is used, it is possible to provide a flooring base material 10 that is less prone to warping and has excellent sound insulation properties that can be applied to flooring for underfloor heating.

[0137] Furthermore, in this embodiment 1, at least one second groove 42 is formed on the back surface of the plywood 11, not only the first groove 41, but also extending in a direction perpendicular to the extension direction (second direction) of the first groove 41 (first direction). By forming the second groove 42 in this way, the rigidity of the plywood 11 is reduced and its flexibility is increased compared to the case where only the first groove 41 is formed, making it easier to absorb impact forces. In other words, according to this embodiment 1, a base material 1 for flooring with superior sound insulation properties can be provided.

[0138] Furthermore, in this embodiment 1, the second groove 42 extending in a direction perpendicular to the fiber direction (second direction) of the second layer 11b (first direction) has its groove bottom within 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, which can withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11, are not cut. With this configuration, in this embodiment 1, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for flooring becomes less likely to expand or contract in the second direction due to moisture absorption or release, and warping (width warping) in the second direction is suppressed. In other words, according to the flooring material base material 10 of this embodiment, not only is the warping of the first layer 11a in the fiber direction (first direction) suppressed, but the warping in the direction perpendicular to it (second direction) is also suppressed.

[0139] Furthermore, in Figure 3 of this embodiment 1, the second groove 42 is formed such that its bottom is located within the fourth layer 11d, and the second groove 42 does not reach the third layer 11c. As a result, the fibers of the second layer 11b extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, are not cut. Moreover, because the second layer 11b is covered by the first layer 11a and the third layer 11c, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion and contraction are further suppressed by the fibers of the second layer 11b extending in the second direction. This makes it possible to provide a flooring material 1 that is less prone to warping in the second direction, as the base material 10 for flooring material is less likely to expand or contract in the second direction due to moisture absorption or release.

[0140] Furthermore, the inventors of this application conducted verification tests (Tests 5, 7, and 8) on the correlation between the depth of the second groove 42 and the sound insulation performance and warping of the flooring material 1. The results of the verification tests showed that the deeper the second groove 42, the better the sound insulation performance, but the more likely warping in the second direction was to occur. It was also found that when the bottom of the second groove 42 is located within the third to fifth layers 11c to 11e, it is possible to form a flooring material 1 that has the required sound insulation performance while being less prone to warping in the second direction. In particular, from the viewpoint of sound insulation performance and warping, it is preferable that the bottom of the second groove 42 is located within the fourth layer 11d. Therefore, in the example shown in Figure 3 of this embodiment 1, the second groove 42 is formed to a depth where the bottom of the groove is located within the fourth layer 11d. Accordingly, according to the example shown in Figure 3 of this embodiment 1, it is possible to provide a flooring material 1 that is less prone to warping and has excellent sound insulation properties, making it suitable for floor heating.

[0141] Furthermore, the inventors of this application conducted verification tests (Tests 2-4) to examine the correlation between the presence or absence of knots in the first to third layers 11a-11c of the plywood 11 and the Brinell hardness of the surface of the flooring material 1. The results of the verification tests showed that if there are knots in the first layer 11a or knots larger than 20 mm in the second layer 11b that constitute the surface layer of the plywood 11, the Brinell hardness of the surface of the flooring material 1 falls below the desired hardness. On the other hand, even if there are knots larger than 20 mm in the third layer 11c, if there are no knots in the first layer 11a and no knots larger than 20 mm in the second layer 11b, the Brinell hardness of the surface of the flooring material 1 will be above the desired hardness. In other words, it was found that if the flooring material 1 is formed with knots in the first layer 11a or knots larger than 20 mm in the second layer 11b of the plywood 11, the flooring material 1 may be prone to damage. Furthermore, if there are knots in the first layer 11a that forms the surface of the plywood 11, it may worsen the surface quality of the flooring material 1 and lead to a decrease in the aesthetic appeal of the flooring material 1. In particular, when a thin (for example, about 1.5 mm) medium-density fiberboard is used as the surface reinforcement layer 12 in order to minimize the effect of warping, if there are knots near the surface, the effect of the knots (unevenness, etc.) will be expressed through the thin medium-density fiberboard surface reinforcement layer 12 to the decorative material 20, increasing the likelihood of a decrease in the aesthetic appeal of the flooring material 1.

[0142] Therefore, in this embodiment 1, the first layer 11a is constructed without knots, and the second layer 11b is constructed without knots larger than 20 mm. Specifically, the first layer 11a is constructed from parts of the conifer that are free of knots, or if it is constructed from parts of the conifer that are free of knots, the knots are filled in with putty to make it knot-free. Similarly, the second layer 11b is constructed from parts of the conifer that are free of knots larger than 20 mm, or if it is constructed from parts of the conifer that are free of knots larger than 20 mm, the knots larger than 20 mm are filled in with wood to make it knot-free. In this embodiment 1, by constructing the first layer 11a without knots and the second layer 11b without knots larger than 20 mm, the flooring material produced using the flooring material base material 10 is made to be scratch-resistant and have a good surface. The surface quality of the flooring material 1 is not deteriorated. Therefore, according to this embodiment 1, a base material 10 for flooring that does not worsen the surface properties of the flooring material 1 can be provided relatively easily.

[0143] Furthermore, in this embodiment 1, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate compared to the wood fibers of hardwood trees, a medium-density fiberboard (hardwood MDF) made primarily from hardwood wood fibers is used as the surface reinforcement layer 12. By using hardwood wood fibers as the medium-density fiberboard constituting the surface reinforcement layer 12 in this way, the water absorption rate of the surface reinforcement layer 12 can be kept low, and dimensional changes can be suppressed.

[0144] Furthermore, in this embodiment 1, tongue and groove processing is applied to the surrounding sides of the flooring base material 10, and the female tongue 13 and male tongue 14 are formed such that the protruding portions (front side protrusion 13b, back side protrusion 13c, and protruding ridge portion 14a) that protrude outward from the female tongue 13 and male tongue 14 always span multiple layers of the plywood 11. The protruding portions 13b, 13c, and 14a of the female tongue 13 and male tongue 14 are brittle and prone to chipping, but by configuring them to span multiple layers of the plywood 11 as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to this embodiment 1, it is possible to provide a flooring base material 10 in which the protruding portions 13b, 13c, and 14a of the female tongue 13 and male tongue 14 are less prone to chipping.

[0145] Furthermore, in this embodiment 1, the female tongue and groove 13 is formed so that the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located within one of the layers of the plywood 11, so as not to be located in the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the recessed groove 13a of the female tongue and groove 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue and groove 14 is inserted, but with the above configuration, such peeling can be suppressed.

[0146] Furthermore, according to this embodiment 1, by providing the above-mentioned base material 10 for flooring, it is possible to provide a flooring material 1 that is less prone to warping even when using softwood plywood and has excellent sound insulation properties that can be applied to flooring for underfloor heating.

[0147] Furthermore, in the manufacturing method of the flooring material of this embodiment, multiple first grooves 41 are formed on the back surface of the 7-ply plywood 11, with a depth extending from the back surface to the second layer 11b. While 3-ply or 5-ply plywood is often used as a base material for flooring, in this embodiment 1, the plywood 11 has 7 layers, so the areas bonded with water-based adhesive (between each layer made of softwood veneer) are greater than in 3-ply or 5-ply plywood, resulting in improved strength. Also, because the plywood 11 has 7 layers, the first grooves 41 extending from the back surface to the second layer 11b are deeper than when the first grooves 41 are similarly formed in 3-ply or 5-ply plywood. These deep, multiple first grooves 41 reduce the rigidity of the plywood 11, increase its flexibility, and make it easier to absorb impact forces. In other words, according to the manufacturing method of this embodiment, it is possible to provide a flooring material 1 that has the required sound insulation performance and excellent soundproofing properties.

[0148] Furthermore, in the manufacturing method of the flooring material of this embodiment, the multiple first grooves 41 extending in a direction perpendicular to the fiber direction (first direction) of the first layer 11a of the plywood 11 (second direction) do not reach the first layer 11a, so that the fibers of the first layer 11a are not cut by the first grooves 41. By forming the first grooves 41 in this way, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the first direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the first layer 11a extending in the first direction. As a result, it is possible to manufacture flooring material 1 that is less likely to expand or contract in the first direction due to moisture absorption or release, and is less likely to warp in the first direction.

[0149] Furthermore, in the manufacturing method of the flooring material of this embodiment, while plywood with a typical number of layers (3 or 5) is often used as the base material for flooring materials, the number of layers of plywood 11 is set to 7, and it is bonded with a water-based adhesive. Therefore, in this embodiment 1, compared to the case of forming 3-ply or 5-ply plywood, the laminated body of softwood veneers is hot-pressed with a higher moisture content, and the resulting plywood becomes thinner and denser from the middle of the thickness direction towards the outermost layer. According to the manufacturing method of the flooring material of this embodiment, by using plywood 11 with such a configuration, it is possible to provide flooring material 1 with excellent surface strength.

[0150] As described above, the manufacturing method of the flooring material of this embodiment makes it possible to provide a flooring material 1 that is less prone to warping even when using softwood plywood and has excellent sound insulation properties that can be applied to flooring materials for underfloor heating.

[0151] Furthermore, in the manufacturing method of the flooring material of this embodiment 1, at least one second groove 42 is formed on the back surface of the plywood 11, not only the first groove 41, but also extending in a direction perpendicular to the extension direction (second direction) of the first groove 41 (first direction). By forming the second groove 42 in this way, the rigidity of the plywood 11 is reduced and its flexibility is increased compared to the case where only the first groove 41 is formed, making it easier to absorb impact forces. In other words, according to the manufacturing method of the flooring material of this embodiment 1, a flooring material base material 10 with superior sound insulation properties can be provided.

[0152] Furthermore, in the method for manufacturing flooring material of this embodiment 1, the second groove 42 extending in a direction perpendicular to the fiber direction (second direction) of the second layer 11b (first direction) does not reach the second layer 11b, so that the fibers of the second layer 11b extending in the second direction, which can resist dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, are not cut by the second groove 42. By forming the second groove 42 in this way, even if the surface reinforcement layer 12 made of medium-density fiberboard adhered to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. As a result, the base material 10 for flooring material is less likely to expand or contract in the second direction due to moisture absorption or release, and warping in the second direction is suppressed. In other words, according to the manufacturing method of the flooring material of this embodiment 1, it is possible to provide a flooring material 1 that is resistant to warping not only in the fiber direction (first direction) of the first layer 11a, but also in the direction perpendicular thereto (second direction).

[0153] Furthermore, in the manufacturing method for the flooring material 1 shown in Figure 3 of this embodiment 1, 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. As a result, the fibers of the second layer 11b extending in the second direction, which can withstand dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, are not cut. Moreover, because the second layer 11b is covered by the first layer 11a and the third layer 11c, even if the surface reinforcement layer 12 made of medium-density fiberboard bonded to the surface of the plywood 11 tries to expand or contract in the second direction due to moisture absorption or release, the expansion or contraction is suppressed by the fibers of the second layer 11b extending in the second direction. This makes it possible to manufacture flooring material 1 that is less prone to expansion or contraction in the second direction due to moisture absorption or release, and is less likely to warp in the second direction.

[0154] Furthermore, in the manufacturing method of the flooring material of this embodiment 1, verification tests (tests 5, 7, and 8) on the correlation between the depth of the second groove 42 and the sound insulation performance and dimensional stability (warping) of the flooring material 1 show that if the depth of the second groove 42 is set so that the groove bottom is located within the fourth layer 11d, warping is less likely to occur, and a flooring material with excellent sound insulation suitable for floor heating can be provided.

[0155] Furthermore, in the manufacturing method of the flooring material of this embodiment 1, the first layer 11a is configured to be free of knots, and the second layer 11b is configured to be free of knots larger than 20 mm. Specifically, the first layer 11a is made from parts of softwood that are free of knots, or if it is made from parts of softwood that are free of knots, the knots are filled in with putty to make it knot-free. Similarly, the second layer 11b is made from parts of softwood that are free of knots larger than 20 mm, or if it is made from parts of softwood that are free of knots larger than 20 mm, the knots larger than 20 mm are filled in with wood to make it knot-free. In this embodiment 1, by configuring the first layer 11a to be free of knots and the second layer 11b to be free of knots larger than 20 mm, the flooring material 1 is made to be resistant to scratches and to have a good surface quality. Therefore, according to the manufacturing method of the flooring material of this embodiment 1, it is possible to provide a flooring material 1 that is resistant to scratches and has a good surface quality.

[0156] Furthermore, in the manufacturing method of the flooring material of this embodiment, since the tracheid fibers of coniferous trees have a significantly higher porosity and water absorption rate compared to the wood fibers of hardwoods, a medium-density fiberboard (hardwood MDF) made primarily from hardwood wood fibers is used as the surface reinforcement layer 12. By using hardwood wood fibers as the medium-density fiberboard constituting the surface reinforcement layer 12 in this way, the water absorption rate of the surface reinforcement layer 12 can be kept low, and dimensional changes can be suppressed.

[0157] Furthermore, in the manufacturing method of the flooring material of this embodiment, tongue and groove processing is applied to the surrounding side surface of the flooring material base material 10, and the female tongue and male tongue 13 and male tongue 14 are formed so that the protruding portions (front side protrusion 13b, back side protrusion 13c, and protruding ridge portion 14a) that protrude outward from the female tongue and male tongue 14 always span multiple layers of the plywood 11. The protruding portions 13b, 13c, and 14a of the female tongue and male tongue 13 and male tongue 14 are brittle and prone to chipping, but by configuring them to span multiple layers of the plywood 11 as described above, they will always contain fibers extending in a first direction and fibers extending in a second direction, making them less prone to chipping. Therefore, according to the manufacturing method of the flooring material of this embodiment, it is possible to provide flooring material 1 in which the protruding portions 13b, 13c, and 14a of the female tongue and male tongue 13 and male tongue 14 are less prone to chipping.

[0158] Furthermore, in the manufacturing method of the flooring material of this embodiment, the female tongue 13 is processed so that the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located within one of the layers, rather than being located in the adhesive portion between any of the layers of the plywood 11. If the groove bottom corner x of the recessed groove 13a of the female tongue 13 is located in the adhesive portion between the layers of the plywood 11, the plywood 11 will be more likely to peel off between the layers where the groove bottom corner x is located when the protruding ridge 14a of the male tongue 14 is inserted, but such peeling can be suppressed by processing as described above.

[0159] Embodiment 2 of the Invention Embodiment 2 is a modification of Embodiment 1 in which the size of the flooring material 1 is changed and the groove configuration is altered. Specifically, as shown in Figure 14, the width of the flooring 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, while the second groove 42 is not formed. The other configurations are the same as in Embodiment 1.

[0160] -test- The following test 9 was performed on the flooring material 1 of Embodiment 2 as described above. Test 9 is a lightweight floor impact sound test to confirm the effect of grooves on the sound insulation performance of the flooring material 1.

[0161] (Exam 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 reduction in sound from 125Hz to 500Hz. Test specimens 9-1 to 9-4 are modified versions of test specimens 5-1 to 5-4 from Test 5 in Embodiment 1, with the width direction length (second direction length) changed to 75mm, while test specimens 9-5 to 9-8 are constructed similarly to test specimens 5-1 to 5-4 (width direction length 150mm, without the second groove 42).

[0162] The results of Test 9 are shown in Figure 15. From the results of Test 9, it was found that when the widthwise length (second direction length) of the flooring material 1 is about 75 mm, the required sound insulation performance can be obtained even without the second groove 42, resulting in a flooring material 1 with excellent soundproofing. On the other hand, by comparing the results of Tests 5 and 9, it was found that when the widthwise length (second direction length) of the flooring material 1 is about 150 mm, the required sound insulation performance cannot be obtained without forming the second groove 42, resulting in a flooring material 1 that lacks soundproofing.

[0163] As described above, the flooring base material 10, flooring material 1, and method for manufacturing the flooring material of Embodiment 2 can achieve the same effects as the flooring base material 10, flooring material 1, and method for manufacturing the flooring material of Embodiment 1.

[0164] Other embodiments In embodiments 1 and 2 described above, the second layer 11b was made up of parts of coniferous wood that did not have knots larger than 20 mm in size, or parts of coniferous wood that had knots larger than 20 mm in size, with the knots larger than 20 mm being filled with wood filler to ensure that there were no knots larger than 20 mm in size. However, the second layer 11b may also be made up of knot-free wood whose size in the first direction is larger than the groove spacing of the first groove 41 (first groove spacing). Specifically, for the coniferous wood veneer for the second layer 11b, a second veneer without knots whose size in the first direction is larger than the groove spacing of the first groove 41 (first groove spacing) is used. Two such second veneers without large knots may be selected and joined together in a direction perpendicular to the fibers to form the coniferous wood veneer for the second layer 11b, or one of the three coniferous wood veneers formed for the even-numbered layers 11b, 11d, and 11f that does not have large knots may be used as the coniferous wood veneer for the second layer 11b. Furthermore, in order to ensure that the softwood slab for the second layer 11b is free of large knots, the softwood slabs for the second layer 11b and the sixth layer 11f may be prepared separately from the softwood slab for the fourth layer 11d, and the one free of large knots may be used for the second layer 11b and the sixth layer 11f. Alternatively, by using softwood slabs free of large knots for all of the even-numbered layers 11b, 11d, and 11f, the softwood slab for the second layer 11b may also be free of large knots.

[0165] In the above embodiments 1 and 2, each layer 11a to 11g of the plywood 11 is made of softwood veneer. Softwood has more knots than hardwood, but if the softwood veneer constituting the second layer 11b has a knot in the first direction that is larger than the groove spacing of the first groove 41 (first groove spacing), the fibers of the second layer 11b that extend in the second direction, which can counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, will be cut by the knot. As a result, it will not be able to counteract the dimensional changes due to moisture absorption or release of the surface reinforcement layer 12 made of medium-density fiberboard, and there is a risk that warping will occur partially in the second direction. However, with the above configuration, there are no knots in the second layer 11b that are larger than the groove spacing in the first direction, so it is expected that warping in the second direction will be suppressed. The second layer 11b is made of thin softwood veneers formed by joining multiple veneers (two in embodiments 1 and 2) 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 large veneers without large knots, but it is relatively easy to prepare relatively small veneers without large knots for use in the second layer 11b. Therefore, with the above configuration, a flooring base material 10 that can be expected to suppress warping in the second direction can be provided relatively easily. [Industrial applicability]

[0166] The present invention is useful for a base material for flooring, flooring material, and a method for manufacturing flooring material. [Explanation of Symbols]

[0167] 1. Flooring 10. Base material (base material for flooring) 10a Long side (surrounding side) 10b Short side (surrounding side) 11 Plywood 11a 1st layer 11b 2nd layer 11c 3rd layer 11d 4th layer 11e 5th layer 11f 6th floor 11g 7th layer 12 Surface reinforcement layer 13 Female fruit 13a Groove 13b Front side protrusion (protruding part) 13c Backside protrusion (protruding part) 14 Yumi 14a Convex part 15 Adhesives 20 Decorative materials 30 Cushioning material 41 First groove 42 2nd groove

Claims

1. A base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, The above plywood is a softwood plywood having seven layers, each consisting of seven thin softwood veneers, which are sequentially laminated and bonded together from the front side to the back side, with the fiber directions of each veneer perpendicular between two adjacent veneers. On the back surface of the above-mentioned plywood, a plurality of first grooves are formed at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer. The first groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. The softwood slabs constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood slabs constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction. The second layer described above does not have any knots whose size in the first direction is larger than the spacing between the first grooves. A base material for flooring, characterized by the following features.

2. A base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, The above plywood is a softwood plywood having seven layers, each consisting of seven thin softwood veneers, which are sequentially laminated and bonded together from the front side to the back side, with the fiber directions of each veneer perpendicular between two adjacent veneers. On the back surface of the above-mentioned plywood, a plurality of first grooves are formed at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer. The first groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. The first layer described above is composed of parts of coniferous trees that do not have knots, or is composed of parts of coniferous trees that have knots, with the knots filled with putty, thereby ensuring that there are no knots. The second layer described above is composed of parts of coniferous trees that do not have knots larger than 20 mm in size, or is composed of parts of coniferous trees that have knots larger than 20 mm in size, with the knots larger than 20 mm being filled with wood filler so that there are no knots larger than 20 mm in size. A base material for flooring, characterized by the following features.

3. A base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, The above plywood is a softwood plywood having seven layers, each consisting of seven thin softwood veneers, which are sequentially laminated and bonded together from the front side to the back side, with the fiber directions of each veneer perpendicular between two adjacent veneers. On the back surface of the above-mentioned plywood, a plurality of first grooves are formed at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer. The first groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. The above-mentioned medium-density fiberboard is made primarily from wood fibers of hardwoods. A base material for flooring, characterized by the following features.

4. In the base material for flooring according to any one of claims 1 to 3, At least one second groove is formed on the back surface of the plywood, extending in the first direction from one end to the other in the first direction of the plywood. A base material for flooring, characterized by the following features.

5. In the base material for flooring according to claim 4, The second groove described above has its bottom located within one of the third to fifth layers described above. A base material for flooring, characterized by the following features.

6. In the base material for flooring according to claim 5, The second groove described above has its bottom located within the fourth layer described above. A base material for flooring, characterized by the following features.

7. In the base material for flooring according to any one of claims 1 to 3, On one of the two opposing sides of the above-mentioned flooring material base material, a recessed groove portion that will serve as a female joint is formed in the middle of the thickness direction, and on the other side, a protruding ridge portion that will serve as a male joint is formed in the middle of the thickness direction. In the above-mentioned base material for flooring, the front-side protrusions adjacent to the front side of the groove, the back-side protrusions adjacent to the back side of the groove, and the protruding ridges are formed to span multiple layers of the plywood. A base material for flooring, characterized by the following features.

8. In the base material for flooring according to claim 7, The above-mentioned female joint is formed such that the bottom corner of the groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers. A base material for flooring, characterized by the following features.

9. A flooring material comprising a base material for flooring and a cushioning material adhered to the back surface of the base material for flooring, The above-mentioned flooring material base material is the flooring material base material described in any one of claims 1 to 3. Flooring material characterized by the following features.

10. A method for manufacturing flooring comprising a base material for flooring in which a surface reinforcement layer made of medium-density fiberboard is bonded to the surface of plywood, and a cushioning material bonded to the back surface of the base material for flooring, A plywood forming process is performed to form the above-mentioned plywood having first to seventh layers made of the above-mentioned softwood slabs, which are laminated in order from the front side to the back side and bonded together, by laminating seven softwood slabs of equal thickness in order with a water-based adhesive interposed between each of them and so that the fiber directions of the two adjacent softwood slabs are perpendicular to each other, and then hot-pressing them in the thickness direction, and thereby laminating and bonding the softwood slabs in order from the front side to the back side, After sanding the surface of the above-mentioned plywood, a surface reinforcement layer bonding step is performed to bond the above-mentioned surface reinforcement layer to the surface to form the base material for the flooring material. A grooving process is performed on the back surface of the above-mentioned plywood, in which a plurality of first grooves are formed at a first groove interval, extending in a second direction perpendicular to the first direction which is the fiber direction of the first layer, The process includes a cushioning material bonding step in which cushioning material is bonded to the back surface of the plywood after the groove processing step described above, The first groove described above extends from one end to the other in the second direction of the plywood, and the bottom of the groove is located within the second layer. A method for manufacturing flooring materials characterized by the following:

11. In the method for manufacturing flooring material according to claim 10, In the groove processing step described above, the plurality of first grooves are formed on the back surface of the plywood, and at least one second groove is formed that extends in the first direction from one end to the other end of the plywood in the first direction. A method for manufacturing flooring materials characterized by the following:

12. In the method for manufacturing flooring material according to claim 11, The second groove described above has its bottom located within one of the third to fifth layers described above. A method for manufacturing flooring materials characterized by the following:

13. In the method for manufacturing flooring material according to claim 12, The second groove described above has its bottom located within the fourth layer described above. A method for manufacturing flooring materials characterized by the following:

14. In the method for manufacturing flooring material according to claim 10, The softwood slabs constituting the first, third, fifth, and seventh layers are made from a single veneer, while the softwood slabs constituting the second, fourth, and sixth layers are made by joining multiple veneers in the first direction. The second layer described above is made without knots, and the size in the first direction is larger than the spacing between the first grooves. A method for manufacturing flooring materials characterized by the following:

15. In the method for manufacturing flooring material according to claim 10, The above first layer is made up of parts of coniferous trees that do not have knots, or parts of coniferous trees that do have knots, and the knots are filled with putty, thereby making it knot-free. The second layer described above is composed of parts of coniferous trees that do not have knots larger than 20 mm, or parts of coniferous trees that have knots larger than 20 mm, with the knots larger than 20 mm being filled with wood filler, thereby ensuring that there are no knots larger than 20 mm. A method for manufacturing flooring materials characterized by the following:

16. In the method for manufacturing flooring material according to claim 10, The above-mentioned medium-density fiberboard is made primarily from wood fibers of hardwoods. A method for manufacturing flooring materials characterized by the following:

17. In the method for manufacturing flooring material according to claim 10, The above-mentioned base material for flooring further comprises a tongue-and-groove processing step in which a recessed portion that will serve as a female tongue is formed in the middle of the thickness direction on one of the two opposing sides of the base material for flooring, and a protruding portion that will serve as a male tongue is formed in the middle of the thickness direction on the other side. In the above tongue and groove processing step, the front-side protrusion adjacent to the front side of the groove, the back-side protrusion adjacent to the back side of the groove, and the protruding ridge are formed such that they span multiple layers of the plywood, forming the female tongue and groove and the male tongue and groove. A method for manufacturing flooring materials characterized by the following:

18. In the method for manufacturing flooring material according to claim 17, In the above tongue and groove processing step, the female tongue and groove is formed such that the bottom corner of the groove is located within one of the layers of the plywood, rather than within the adhesive portion between the layers. A method for manufacturing flooring materials characterized by the following:

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