Plywood and method for manufacturing plywood

Abstract

Without increasing the manufacturing process, the bending Young's modulus (E) in the length direction can be changed. L ) and the Young's modulus of bending in the width direction (E W Keep the difference small and within 2 times (E L ≤2E W The present invention provides a method for manufacturing plywood and plywood that can be produced in this manner. [Solution] In a method for manufacturing plywood, in which multiple veneers are created by cutting a log and then bonding these veneers together with adhesive, when applying adhesive to the multiple veneers and laminating them, within the adhesive layer of 10% or less in the thickness direction from both the front and back surfaces, Total Weight: 400g / m² 2 By interposing the above-mentioned high-basis-weight carbon fibers so that they intersect along two directions with different fiber orientations, and simultaneously forming them integrally during hot-pressure molding, the bending Young's modulus in the length direction is made to be less than or equal to twice the bending Young's modulus in the width direction.

Description

[Technical Field]

[0001] This invention relates to plywood and a method for manufacturing plywood, and more specifically, to plywood with little difference between strong and weak axes and a method for manufacturing the same. [Background technology]

[0002] Traditionally, plywood has been made by laminating wood so that the fiber direction is in two directions, and various types of plywood are known, such as ordinary plywood, concrete formwork plywood, structural plywood, decorative structural plywood, natural wood decorative plywood, and specially processed decorative plywood. In addition, some types of plywood have a different ratio of the number of veneers with two directions, and some have two or more veneers with the same wood fiber direction laminated in a continuous manner.

[0003] Of these plywoods, structural plywood and plywood used for building purposes are required to withstand loads such as earthquakes and wind pressure, in accordance with the Building Standards Act. Therefore, the Japanese Agricultural Standards and other regulations specify several requirements for the bending Young's modulus (Elastic Modulus, E) in the length and width directions of the plywood.

[0004] Here, the longitudinal direction (L direction) of plywood refers to the main direction of the plywood, and generally, it is manufactured so that the wood fibers are mainly aligned in this direction, while the width direction (W direction) refers to the direction perpendicular to the longitudinal direction, that is, the direction perpendicular to the fibers. Also, generally, the outermost layer of plywood is laminated with a veneer in which the direction of the wood fibers coincides with the longitudinal direction of the plywood. For this reason, the bending Young's modulus in the longitudinal direction of this plywood is usually higher than that in the width direction, and the bending Young's modulus in the longitudinal direction (E L ) is the Young's modulus of bending in the width direction (E W It is often about 2.5 to 4 times the standard. For example, in the Japanese Agricultural Standards, the standard is E, which is thickness-dependent. L = 5.0~7.0 MPa, regardless of thickness E W The standard is 2.5 MPa, and currently there is a significant difference in the bending Young's modulus between the two.

[0005] However, the difference in bending Young's modulus between the length direction and the width direction of plywood originates from the use of natural wood as a raw material. It merely compensates for the weakness by setting the length direction, which is disadvantageous in terms of moment, as the fiber direction of the wood, and plywood itself does not inherently require anisotropy (directional difference) for usability. In particular, when plywood is cut in construction work, there is a risk of incorrect use by confusing the length direction (L direction) and the width direction (W direction), so use of the plywood requires attention to the anisotropy of the bending Young's modulus.

[0006] Therefore, there is a demand for plywood that can be used without being aware of the difference between the length direction (L direction) and the width direction (W direction) even when cut in construction work, which reduces the anisotropy of the bending Young's modulus, that is, has a small difference between the bending Young's modulus in the length direction (E L ) and the bending Young's modulus in the width direction (E W ).

[0007] For example, Patent Document 1 discloses a method for producing veneer-laminated wood, proposed by the applicant of the present application, in which a carbon fiber sheet is interposed and integrally molded when an adhesive is applied to a prepared veneer and laminated, and veneer-laminated wood reinforced with a carbon fiber sheet (see paragraphs

[0033] to

[0081] of the specification of Patent Document 1, FIG. 1, FIG. 3, etc. of the drawings).

[0008] However, the main object of the veneer-laminated wood reinforced with a carbon fiber sheet described in Patent Document 1 is to use low-density wood as raw wood to obtain plywood having the same thickness and equal or higher performance than plywood using imported wood such as lauan as raw wood, and the method interposes a carbon fiber sheet with a low basis weight of 15 g / m 2 or more and 50 g / m 2 or less. For this reason, the bending Young's modulus in the width direction (W direction) (E W ) cannot be made equal to the bending Young's modulus in the length direction (E L ), and the anisotropy (directional difference) of the plywood itself cannot be eliminated.

Prior Art Literature

Patent Literature

[0009] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2017-185665 [Patent Document 2] Japanese Patent No. 6984928 Publication [Summary of the Invention] [Problem to be Solved by the Invention]

[0010] Accordingly, the present invention has been devised in view of the above-mentioned problems, and an object of the present invention is to provide, without increasing the number of manufacturing steps, a bending Young's modulus in the length direction (E L ) and a bending Young's modulus in the width direction (E W ) that reduces the difference therebetween to within twice (E L ≦2E W ), and to provide a method for manufacturing plywood and the plywood capable of achieving the above. [Means for Solving the Problem]

[0011] A method for manufacturing plywood according to a first aspect of the present invention is a method for manufacturing plywood in which a log is cut to produce a plurality of veneers, and these veneers are bonded to each other with an adhesive to manufacture the plywood, wherein when applying the adhesive to the plurality of veneers and laminating the veneers, carbon fibers having a total basis weight of 400 g / m 2 or higher, which is a high basis weight, are interposed in the adhesive layer within 10% of the thickness direction from both the front and back surfaces so as to intersect along two directions having different fiber directions, and are integr molded simultaneously during hot pressing, whereby the bending Young's modulus in the length direction is not more than twice the bending Young's modulus in the width direction.

[0012] A method for manufacturing plywood according to a second aspect of the present invention is the method according to the first aspect, wherein when applying the adhesive to the plurality of veneers and laminating the veneers, a bidirectional woven fabric made of PAN-based high-strength carbon fibers having a total basis weight of 400 g / m 2 or more and 600 g / m 2 or less is interposed in the adhesive layer within 10% of the thickness direction from both the front and back surfaces.

[0013] The plywood according to the third invention is a plywood in which multiple veneers cut from a log are bonded together with adhesive, and the total basis weight is 400 g / m² in the adhesive layer within 10% of the thickness direction on both the front and back surfaces. 2 The above-mentioned high basis weight carbon fibers are interposed so that their fiber direction aligns with both the length and width directions of the plywood.

[0014] The plywood according to the fourth invention, in the third invention, has a total basis weight of 400 g / m² in the adhesive layer extending within 10% of the thickness direction from both the front and back surfaces. 2 More than 600g / m 2 This is characterized by the interposition of a bidirectional woven fabric made of the following PAN-based high-strength carbon fibers.

[0015] The plywood according to the fifth invention is characterized in that, in the third or fourth invention, the raw timber is low-density wood with an air-dry specific gravity of 0.1 or more and 0.5 or less. [Effects of the Invention]

[0016] According to the first to fifth inventions, the bending Young's modulus (E) in the longitudinal direction can be increased without increasing the manufacturing process of plywood. L ) and the Young's modulus of bending in the width direction (E W By reducing the difference between the two, the anisotropy of the plywood can be reduced.

[0017] In particular, according to the second and fourth inventions, it is possible to reduce manufacturing costs and eliminate the anisotropy of the plywood, thereby providing a user-friendly plywood.

[0018] In particular, according to the fifth invention, even when using low-density wood for plywood, which has coarse fibers and therefore experiences large expansion and contraction due to moisture absorption and drying, resulting in low dimensional stability and large variations in strength, high-strength carbon fibers prevent warping and cracking, ensuring dimensional stability and a high bending Young's modulus (E) in the width direction. W ) can be improved. [Brief explanation of the drawing]

[0019] [Figure 1]Figure 1 is a schematic cross-sectional view showing plywood according to the first embodiment of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing plywood according to a second embodiment of the present invention. [Figure 3] Figure 3 is a flowchart showing the procedure for a conventional plywood manufacturing method. [Modes for carrying out the invention]

[0020] Hereinafter, a method for manufacturing plywood and plywood according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] <Conventional plywood manufacturing method> First, we will briefly explain the conventional method of manufacturing plywood using Figure 3. Figure 3 is a flowchart showing the procedure for the conventional method of manufacturing plywood.

[0022] (Peeling and cutting process) As shown in Figure 3, first, the bark is removed from the log and it is cut into predetermined lengths in a process called debarking and cutting.

[0023] (Log cutting process) Next, the debarked logs are cut into thin veneers using a rotary lathe, similar to peeling a katsura (Japanese vegetable peel). After that, the veneers are roughly cut and classified into front, back, and middle sections, taking into account warping and other factors. The thickness of the veneers varies depending on the type and thickness of the plywood and its purpose, but it is generally around 0.6 mm to 5.0 mm.

[0024] (Veneer drying and cutting process) Next, the sorted veneers are dried in a dryer and then cut to the specified dimensions using clippers or similar tools in a veneer drying and cutting process.

[0025] (chopping process) Next, a board adjustment process is carried out, which involves repairing the veneers or joining together narrow boards that do not meet the required width. Then, veneers that are warped in one direction are sorted into front and back boards, and non-warped veneers are sorted into middle boards, and these are combined to form the structure.

[0026] In this process, to reduce the anisotropy of the bending strength of the plywood, the grain direction of each veneer is oriented perpendicular to that of the others. While this may vary depending on the application and type, generally, plywood is made by laminating 3 or more veneers if its thickness is less than 15mm, 4 or more veneers if its thickness is between 15mm and 18mm, 5 or more veneers if its thickness is between 18mm and 25mm, and 7 or more veneers if its thickness is 25mm or more.

[0027] (Adhesive application process) Next, an adhesive is selected from thermosetting resins according to the intended use of the plywood, and the selected adhesive is applied by spreading it on both sides of the middle board and one side of the front and back boards using a spreader. Suitable adhesives for bonding veneers together (wood together) include phenolic resin adhesive (PF resin), melamine resin adhesive (MF resin), resorcinol resin adhesive (RF resin), urethane-based adhesive (PUR resin), and polyvinyl acetate (PVA).

[0028] (cold pressure process) Next, a predetermined number of veneers coated with adhesive are combined to form plywood, and a cold-pressing process is performed in which pressure is applied at room temperature using a vise or the like to temporarily fasten them together.

[0029] (heat pressure process) Next, at a temperature of 110°C to 130°C, the pressure is 8 to 12 kgf / m². 2 A hot-press process is performed, in which pressure of a certain degree is applied to compress the adhesive and heat-cur it.

[0030] (Protection, cutting, finishing) Next, the plywood is watered and left to cure for 3 days to a week, and then the edges on all four sides are cut to precisely adjust to the specified dimensions. After that, the surface of the plywood is polished smooth using a sander or similar machine to finish it. Upon completion of this process, the plywood is manufactured.

[0031] [First Embodiment] Next, a plywood according to the first embodiment of the present invention will be described using Figure 1. Figure 1 is a schematic cross-sectional view showing plywood 1 according to the first embodiment of the present invention. In the figure, X represents the longitudinal direction X of plywood 1, Y represents the short direction Y of plywood 1, and Z represents the vertical direction Z.

[0032] Conventional plywood is made by layering thin veneers (veneers) of wood, about 0.6 to 3 mm thick, with the grain directions alternating and perpendicular to each other, in order to suppress warping and distortion. However, as mentioned in the background technology section, the Japanese Agricultural Standards (JAS) specify that the Young's modulus of bending in the length direction is thickness-dependent. L = 5.0~7.0 MPa, bending Young's modulus E in the width direction (W direction) regardless of thickness W As specified by a pressure of 2.5 MPa, conventional plywood is currently an anisotropic (different-directional) material in which there is a large difference in the bending Young's modulus in both the length direction and the width direction.

[0033] As shown in Figure 1, the plywood 1 according to the first embodiment of the present invention is a parallel plywood of normal plywood size, consisting of 5 ply (5 layers) of veneers 21 to 25 made of lauan veneer for ordinary plywood, with a thickness of approximately 20 mm, and bonded together with adhesive 3, similar to general conventional plywood. However, unlike general conventional plywood, as shown in Figure 1, the plywood 1 according to this embodiment is a material with low anisotropy and high isotropy, as the fiber direction of the carbon fiber tow 5 is interposed in two or more directions in the adhesive 3 layer so as to align with both the length direction and width direction of the plywood.

[0034] (Single plywood) The veneer 2 used in plywood 1 is generally made from expensive tropical hardwoods such as lauan, which are dense, heavy (specific gravity: 0.5-0.7), have high strength and load-bearing capacity, are less prone to deformation due to moisture, have less variation in strength, and are not subject to over-logging or illegal logging. Generally, tropical hardwoods are heavy and hard, resulting in high strength such as a bending Young's modulus (for example, red lauan = around 115 GPa), making them suitable for plywood where thinness and strength are required.

[0035] However, since plywood 1 is reinforced with carbon fiber tow 5, it is also possible to use low-density wood made from domestic coniferous timber with an air-dry specific gravity of 0.1 to 0.5, which is low-density, lightweight (specific gravity of cedar: approximately 0.35, cypress: approximately 0.4), soft, easy to process, and has excellent elasticity, but is prone to expansion and contraction with humidity (which can be mitigated by drying) and has large variations in strength.

[0036] The reason why the upper limit for the air-dry specific gravity of low-density wood is set at 0.5 or less is that most imported tropical hardwoods are high-density woods with an air-dry specific gravity exceeding 0.5, and tree species with an air-dry specific gravity of 0.5 or less are not widely used as raw materials for plywood.

[0037] Furthermore, the reason why the lower limit of air-dry specific gravity is set at 0.1 or higher is that among the tree species used as timber, balsa has the lowest air-dry specific gravity of around 0.1, and it is not conceivable that timber below this lower limit would be used.

[0038] (glue) Furthermore, three layers of adhesive are formed between the veneers 2 and 2, depending on the intended use of the plywood 1. These three layers of adhesive are formed using adhesive 3, which was selected from adhesives suitable for bonding veneers together (wood together) as described above, taking into consideration the intended use. In other words, as shown in Figure 1, the carbon fiber tow 5 is directly impregnated and embedded within the aforementioned three layers of adhesive.

[0039] Conventionally, adhesives with high curing strength, such as epoxy resin adhesives, have generally been used to bond carbon fibers. However, this is because the tensile strength of carbon fibers is very high, even for standard types (over 2500 MPa), and this is done to take advantage of the tensile strength of carbon fibers. Considering that the tensile strength of wood fibers is about 88 MPa for cedar, using epoxy resin adhesives for bonding is clearly overkill. Therefore, in this invention, the same adhesive 3 mentioned above, which is used to bond the veneers 2 together, is used for simultaneous molding during the manufacturing of plywood.

[0040] Specifically, considering the adhesion of the carbon fiber to the tow 5, it is preferable to use a urethane-based adhesive (PUR resin), a resorcinol resin adhesive (RF resin), or a phenolic resin adhesive (PF resin) among the aforementioned adhesives. Epoxy resin adhesives can also be used.

[0041] (Carbon fiber) In plywood 1, carbon fibers are interposed in two or more directions such that the fiber direction aligns with both the longitudinal direction X (the length direction of the plywood) and the transverse direction Y (the width direction). However, the fiber direction of the carbon fibers is not limited to two directions along either the longitudinal direction X or the transverse direction Y; it is sufficient if they are interposed so as to intersect along two different directions. As a result, the bending Young's modulus (E) in the longitudinal direction is L ) and the Young's modulus of bending in the width direction (E W Keep the difference small and within 2 times (E L ≤2E W This is because it would suffice if we could achieve this.

[0042] Here, carbon fiber tows 5 with a larger number of bundled filaments, such as 12,000 (12K), 24,000 (24K), and 48,000 (48K), are preferable to tows with a smaller number of bundled filaments, such as 1,000 (1K), 3,000 (3K), and 6,000 (6K), because they offer better productivity and can be produced in large quantities at extremely low cost.

[0043] If carbon fibers can be used in the form of carbon fiber tow, which is a bundle of untwisted long fibers made by bundling a predetermined number of filaments that are closer to the raw material, it can be used at an extremely low cost, about one-fifth the unit price of intermediate materials such as prepregs and cloths (woven fabrics).

[0044] As shown in Figure 1, the plywood 1 has carbon fibers interposed in two or more directions, such that the fiber direction of the carbon fibers aligns with both the length and width directions of the plywood, at two locations: between the first veneer 21 and the second veneer 22, and between the fourth veneer 24 and the fifth veneer 25. However, the tow of the carbon fibers 5 must be interposed in the adhesive layer 3 within 10% of the thickness direction from both the front and back surfaces. This is because, since plywood is a thin sheet material, it is stress-advantageous to have the carbon fibers located close to the front and back surfaces, farther from the neutral axis, with respect to bending stress. On the other hand, since carbon fibers are weak against shear abrasion, the tow of the carbon fibers 5 is not exposed on both the front and back surfaces.

[0045] Furthermore, in plywood 1, the carbon fiber tow 5 is layered so that the fiber direction is in two or more different directions, resulting in a total basis weight of 400g / m². 2 The materials are bonded together to achieve the above high basis weight. The bending Young's modulus (E) in the width direction (W direction) W ) is the bending Young's modulus (E) in the longitudinal direction L This is to reduce the anisotropy of the plywood by keeping it within twice the weight of the plywood. The total weight is 400g / m². 2 If it is lower, the bending Young's modulus (E) in the width direction (W direction) W ) is the bending Young's modulus (E) in the longitudinal direction L It becomes difficult to keep it within twice the value of ).

[0046] <Method for manufacturing plywood according to the present invention> Next, a method for manufacturing plywood according to the first embodiment of the present invention will be described. The main difference between the method for manufacturing plywood 1 according to this embodiment and the conventional method for manufacturing plywood described above is that, when a predetermined number of veneers 2 to which adhesive 3 has been applied are combined in the adhesive application step to form plywood, carbon fiber tow 5 is directly impregnated and interposed at predetermined positions. Therefore, this difference will be explained in detail, and other explanations will be omitted.

[0047] (Tou's assistance) In the manufacturing method of the plywood 1 according to this embodiment, when laminating the veneers 2 together with adhesive 3, a tow 5, which is a bundle of untwisted long fibers made of carbon fiber filaments, is arranged so that the fiber direction is aligned with two or more directions, the longitudinal direction X and the transverse direction Y of the plywood, and is directly impregnated with the aforementioned adhesive 3, thereby integrally molding the tow 5 at the same time when the plywood 1 is heated and pressed.

[0048] In this case, the layer of adhesive 3 interposing the carbon fiber tow 5 is within 10% of the thickness direction from both the front and back surfaces. As mentioned above, it is stress-advantageous to have the carbon fibers located closer to the front and back surfaces, farther from the neutral axis, with respect to bending stress.

[0049] Furthermore, by overlapping these carbon fibers in a way that the fiber direction is in two or more different directions, the total basis weight (the total basis weight when arranged in two or more different directions) is 400 g / m². 2 It is installed so that the above high basis weight is achieved. The bending Young's modulus (E) in the width direction (W direction) W ) is the bending Young's modulus (E) in the longitudinal direction L This is to reduce the anisotropy of the plywood by keeping it within twice the original value.

[0050] In this case, unlike conventional carbon fiber sheets, TOW 5 is not impregnated with uncured matrix resin, making it easy to change the basis weight per unit area by arranging it densely or loosely. Depending on the application and dimensions, it is possible to reinforce only the necessary strength in the required direction (fiber direction), which is advantageous in reducing anisotropy.

[0051] Furthermore, during the cold and hot press processes, the fiber bundles of the tow 5 are defibrated along with the flow of the adhesive 3 and inserted between the layers of the wood veneer 2. Therefore, during the hot press process, the wood opposite the defibrated tow is recessed, and the tow does not expand indefinitely. As a result, the tow 5 can be evenly distributed within its area simply by laying them out, and the required strength can be ensured in the necessary direction.

[0052] Furthermore, according to the manufacturing method of the plywood 1 of this embodiment, the disadvantages of carbon fiber, such as its weakness to shear abrasion and the fact that the tow is damaged during lamination, resulting in the failure to obtain the intended reinforcing effect, can be easily solved by arranging the fibers more densely than the calculated value, taking into account the fact that the unit cost of the tow is one-fifth of the unit cost of intermediate carbon fiber materials such as prepreg.

[0053] According to the method for manufacturing plywood 1 and the plywood 1 reinforced with carbon fiber tow 5 according to the first embodiment of the present invention described above, inexpensive carbon fiber tow 5 can be used to reinforce only the required strength in the required direction (fiber direction). Therefore, the bending Young's modulus (E) in the length direction can be increased without significantly increasing the manufacturing process of the plywood. L ) and the Young's modulus of bending in the width direction (E W The difference between these two values ​​can be reduced, and plywood 1 with reduced anisotropy can be easily manufactured.

[0054] Furthermore, according to the plywood manufacturing method and plywood 1 of this embodiment, when bending stress is applied to the plywood 1, carbon fiber tows 5 that can resist strong tensile forces are arranged near the outermost edge of the cross-section where the tensile edge stress is maximum. Therefore, even with the same thickness as conventional plywood, it can resist stress equivalent to or greater than that of conventional plywood.

[0055] Furthermore, according to the plywood manufacturing method and plywood 1 of this embodiment, even when using low-density wood, it is possible to provide plywood with strength greater than conventional plywood at a low cost without changing the thickness or dimensions of plywood 1, thereby solving the problems of depletion of tropical hardwoods and wood shock.

[0056] [Second Embodiment] Next, plywood 1', which is a plywood according to the second embodiment of the present invention, will be described using Figure 2. Figure 2 is a schematic cross-sectional view showing plywood 1' according to the second embodiment of the present invention. In the figure, X indicates the longitudinal direction X of plywood 1', Y indicates the short direction Y of plywood 1', and Z indicates the vertical direction Z. Components identical to those in plywood 1 according to the first embodiment described above are denoted by the same reference numerals, and detailed explanations are omitted.

[0057] The plywood 1' according to the second embodiment of the present invention, like the plywood 1 described above, is a 5-ply (5-layer) parallel plywood of normal plywood size, as shown in Figure 2, in which the first to fifth layers 21 to 25, made of lauan veneer for ordinary plywood with a thickness of approximately 20 mm, are bonded and laminated with adhesive 3. However, unlike general conventional plywood, the plywood 1' according to this embodiment, as shown in Figure 2, is a highly isotropic member with reduced anisotropy, reinforced by interposing a bidirectional woven fabric 5' made of carbon fiber in the adhesive 3 layer.

[0058] (Single plywood) The veneer 2 used in plywood 1' is, like plywood 1, dense and heavy (specific gravity: 0.5-0.7), with high strength and load-bearing capacity, less deformation due to moisture, and less variation in strength. Expensive tropical hardwoods such as lauan, which are not subject to over-logging or illegal logging, are used.

[0059] (glue) Furthermore, similar to plywood 1, three layers of adhesive are formed between veneers 2 and 2, depending on the intended use of plywood 1'. These three layers of adhesive are formed using adhesive 3, which was selected from adhesives suitable for bonding veneers together (wood together) as described above, taking into consideration the intended use.

[0060] (Carbon fiber) In plywood 1', as shown in Figure 2, a bidirectional woven fabric 5' made of PAN-based high-strength carbon fibers is interposed in two locations: between the first veneer 21 and the second veneer 22, and between the fourth veneer 24 and the fifth veneer 25. However, the bidirectional woven carbon fiber fabric 5' must be interposed in a layer of adhesive 3 within 10% of the thickness direction from both the front and back surfaces. This is because, since plywood is a thin sheet material, it is stress-advantageous to have carbon fibers located close to the neutral axis on both the front and back surfaces with respect to bending stress. On the other hand, since carbon fibers are weak against shear abrasion, the bidirectional woven carbon fiber fabric 5' is not exposed on both the front and back surfaces.

[0061] Furthermore, this two-way woven fabric 5' has a total basis weight of 400g / m2 More than 600g / m 2 The following high basis weight is used. Bending Young's modulus (E) in the width direction (W direction) W ) is the bending Young's modulus (E) in the longitudinal direction L This is to reduce the anisotropy of the plywood by keeping it within twice the amount of the original weight. The total weight is 400g / m². 2 If it is lower, the reinforcing effect is less, and the bending Young's modulus (E) in the width direction (W direction) is lower. W ) is the bending Young's modulus (E) in the longitudinal direction L It is difficult to keep it within twice the amount of ). On the other hand, the total basis weight of the two-way woven fabric 5' is 600g / m 2 This is because beyond a certain point, it becomes difficult to cut with ordinary woodworking tools such as electric circular saws.

[0062] Furthermore, the two-way woven fabric 5' is sewn using 1200 threads per bundle instead of the 3000 threads per bundle used in regular cloth. This is because 12000 threads per bundle has a lower unit cost when calculated per basis weight, making it more cost-effective in manufacturing.

[0063] Furthermore, since the bidirectional woven fabric 5' is woven so that the fiber directions are perpendicular to each other, it is interposed in such a way that, similar to plywood 1, the fiber direction aligns with both the longitudinal direction X, which is the length direction of the plywood, and the short direction Y, which is the width direction.

[0064] <Method for manufacturing plywood according to the second embodiment of the present invention> Next, a method for manufacturing plywood according to the second embodiment of the present invention will be described. The main difference between the method for manufacturing plywood 1' according to this embodiment and the conventional method for manufacturing plywood described above is that, when a predetermined number of veneers 2 to which adhesive 3 has been applied are combined to form plywood in the adhesive application step, a two-way woven carbon fiber fabric 5' is directly impregnated and interposed at a predetermined position. Therefore, this difference will be explained in detail, and other explanations will be omitted.

[0065] (Interfacing with two-way woven fabric) In the manufacturing method of plywood 1' according to this embodiment, when the veneers 2 are bonded together with adhesive 3 to form a laminate, the total basis weight is 400 g / m². 2 More than 600g / m2 The following bidirectional woven fabric 5' made of high-weight PAN-based high-strength carbon fibers is directly impregnated into the aforementioned adhesive 3 and simultaneously integrally molded with the plywood 1' during the hot-pressing process.

[0066] In this case, the adhesive 3 interposed between the two-directional carbon fiber fabric 5' is located in two places: between the first veneer 21 and the second veneer 22, and between the fourth veneer 24 and the fifth veneer 25, both within 10% of the thickness from both the front and back surfaces. As mentioned above, it is stress-advantageous to have carbon fibers located closer to the front and back surfaces, farther from the neutral axis with respect to bending stress.

[0067] Furthermore, this two-way woven carbon fiber fabric 5' is made of PAN-based high-strength carbon fibers and has a total basis weight of 400 g / m². 2 More than 600g / m 2 The following high-weight bidirectional fabric is woven so that the fiber directions are perpendicular to each other, so that the fiber direction aligns with both the longitudinal direction X (the length direction of the plywood) and the transverse direction Y (the width direction). Therefore, the bending Young's modulus (E) in the width direction (W direction) is W ) is the bending Young's modulus (E) in the longitudinal direction L This can be improved to within twice the current level, reducing the anisotropy of the plywood and making it highly isotropic.

[0068] In this case, unlike when the tow 5 is interposed, the two-way woven fabric 5' cannot be arranged densely or loosely to change the total basis weight per unit area. However, it can be interposed in a shorter time compared to when the tow 5 is interposed, thereby reducing labor costs.

[0069] Furthermore, according to the manufacturing method of plywood 1' in this embodiment, since the bidirectional woven fabric 5' is sewn from 12,000 threads / bundle instead of the 3,000 threads / bundle used in ordinary cloth, the plywood can be reinforced inexpensively and made highly isotropic.

[0070] According to the method for manufacturing plywood 1' and the plywood 1' reinforced with the bidirectional carbon fiber fabric 5' according to the second embodiment of the present invention described above, the plywood can be reinforced in either the longitudinal direction X, which is the length direction of the plywood, or the short direction Y, which is the width direction, using an inexpensive, high-basis-weight bidirectional fabric 5'. Therefore, according to the plywood 1' and its manufacturing method, the bending Young's modulus (E) in the length direction can be improved. L ) and the Young's modulus of bending in the width direction (E W Reduce the difference between ) and keep it within 2 times (E L ≤2E W This allows for the easy manufacture of plywood 1' with reduced anisotropy.

[0071] Furthermore, according to the manufacturing method and plywood 1' of this embodiment, when bending stress is applied to the plywood 1', a bidirectional woven carbon fiber fabric 5' capable of resisting strong tensile forces is arranged near the outermost edge of the cross-section where the tensile edge stress is maximum. Therefore, even with the same thickness as conventional plywood, it can withstand stress equivalent to or greater than that of conventional plywood.

[0072] The first and second embodiments of the present invention have been described in detail above, along with the manufacturing methods of plywood 1,1' and plywood 1,1'. However, the embodiments described above or illustrated are merely examples of specific embodiments implemented in carrying out the present invention. Therefore, the technical scope of the present invention should not be interpreted as being limited by the exemplary embodiments. [Explanation of symbols]

[0073] 1: Plywood 1': Plywood 2: Solid wood 21: First layer veneer 22: Second layer veneer 23: Third layer veneer 24: Fourth layer veneer 25: Fifth layer veneer 3: Adhesive 5: Carbon fiber tow 5': Two-way woven carbon fiber fabric X: Longest direction Y: Short direction Z: Up / Down direction

Claims

1. A method for manufacturing plywood, which involves cutting a log to create multiple veneers and then bonding these veneers together with adhesive to produce plywood, When applying adhesive to the aforementioned multiple veneers and laminating them, the total basis weight of the adhesive layer, within 10% of the thickness direction from both the front and back surfaces, is 400 g / m². 2 By interposing the above-mentioned high basis weight carbon fibers so that they intersect along two directions with different fiber orientations and simultaneously forming them integrally during hot-pressure molding, the bending Young's modulus in the length direction is less than or equal to twice the bending Young's modulus in the width direction. A method for manufacturing plywood characterized by the following.

2. When applying adhesive to the aforementioned multiple veneers and laminating them, the adhesive layer, which extends within 10% of the thickness direction from both the front and back surfaces, contains an adhesive weight of 400 g / m². 2 More than 600g / m 2 The following two-way woven fabric made of PAN-based high-strength carbon fiber is interposed: A method for manufacturing plywood according to claim 1, characterized by the above.

3. Plywood is made by gluing together multiple veneers cut from a log, Within the adhesive layer extending within 10% of the thickness direction from both the front and back surfaces, the total basis weight is 400 g / m². 2 The carbon fibers with the above-mentioned high basis weight are arranged so that their fiber direction aligns with both the length and width directions of the plywood. Plywood characterized by the following features.

4. Within the adhesive layer extending within 10% of the thickness direction from both the front and back surfaces, the total basis weight is 400 g / m². 2 More than 600g / m 2 The following two-way woven fabric made of PAN-based high-strength carbon fiber is interposed: The plywood according to claim 3, characterized by the above.

5. The aforementioned logs are low-density wood with an air-dry specific gravity of 0.1 or more and 0.5 or less. The plywood according to claim 3 or 4, characterized by the above.

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