Plywood - Gohan (English spelling)

Japanese: 合板 - ごうはん（英語表記）plywood

Wood is peeled into thin boards, and an odd number of boards are stacked with the grain direction perpendicular to each other and glued together to make a single board. The thin boards used to make plywood are called veneers, but in Japan plywood is sometimes mistakenly called plywood or plywood boards. Architectural applications include underlayment and finishing materials for roofs, interior and exterior walls, floors, and ceilings, as a substitute for braces in wooden houses, concrete formwork, scaffolding boards, doors, and furniture, and are used in a wide range of fields such as musical instruments, sports equipment, electrical equipment, vehicles, and ships.

A single thin board that makes up plywood is called a veneer, the two boards that make up the plywood are called the top board (omoita) and back board (uraita), and the board in between is called the core board (shinita) and middle board (nakaita). Plywood has the advantage that it can be used to make boards with a large surface area, it can eliminate defects such as knots, cracks, and rot, it improves expansion and contraction in different directions, and it can produce beautiful boards by applying a decorative material to the surface.

[Kamiyama Yukihiro]

Process

In the manufacture of plywood, wood is first peeled into thin veneers, which are then dried and sorted into top, back and core panels, and defects are removed and the panels are width-slit to set the dimensions. The veneers are then coated with adhesive, stacked, heated and pressed to bond, and then cut to size and finished. Plywood materials include broadleaf trees such as Sen, China, Oak, Ash and Birch, softleaf trees such as Pine and Cedar, and imported trees such as Lauan, Meranti and Seraya, and Kapur. Broadleaf trees are mainly used for the top and back panels. There are two methods for manufacturing veneer: one that uses a veneer lace to continuously peel thin sheets along the tree rings of the wood, and one that uses a slicer to peel in the direction of the wood's fibers. Veneer lace produces cross-grain veneer, which accounts for more than 95% of the veneer produced in Japan. Using a slicer produces straight-grain veneer. Adhesives include phenolic resin, melamine resin, urea resin, vinyl resin, etc., and are applied by passing the veneer through a glue spreader. Bonding is done with a heat press at 110-140°C, usually with a pressure of 8-10 kilograms per square centimeter.

[Kamiyama Yukihiro]

kinds

In addition to regular plywood, there is lumber core plywood, which uses narrow sawn boards for the core, lightweight plywood that uses honeycomb-patterned resin-treated paper instead of the core, overlay plywood, which has resin board, paper, or thin natural wood veneers attached to the surface of regular plywood for aesthetic reasons or to increase the surface hardness, printed plywood with a pattern printed on the top, and painted plywood. Molded plywood includes plywood embossed with curved surfaces suited to the purpose, and hardened plywood made by impregnating a single panel with phenolic resin and applying high pressure. There is also structural plywood, fire-retardant plywood, fire-resistant plywood, preservative-treated plywood, and insect-resistant plywood, all made to suit the purpose and location of use.

[Kamiyama Yukihiro]

nature

The properties of plywood vary depending on the quality of the veneer, its thickness and layer structure, and the type of adhesive. Plywood that uses phenolic resin or melamine resin adhesives has a low rate of moisture absorption, and the peeling of the veneer is minimal, making it highly water-resistant. Since the fiber directions are perpendicular to each other, there is no difference in shrinkage and expansion depending on the direction, and it is 1/10 to 1/20 of the grain direction. It is also resistant to splitting and cracking. The mechanical properties of plywood change greatly depending on the relationship between the fiber direction of the top board and the load direction, and the core board will break if a force that shifts the surface is applied, so care must be taken when using it structurally. The Japanese Agricultural Standards (JAS) are one of the standards that stipulate various qualities.

[Kamiyama Yukihiro]

[Reference item] | Veneer | Wood industry

Five-ply plywood construction
©Shogakukan ">

Five-ply plywood construction

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

木材を薄くむいて板とし、板の繊維方向が互いに直交するようにして奇数枚を積み重ね接着剤で貼(は)り合わせて1枚の板としたもの。合板をつくるのに用いる薄板をベニヤveneerというが、日本では合板を誤ってベニヤまたはベニヤ板とよぶことがある。建築用途として屋根、内外壁、床、天井の下地材および仕上げ材、木造住宅の筋かい代替、コンクリート型枠、足場板、ドア、家具があり、楽器、運動用具、電気機器、車両、船舶など幅広い分野で用いられる。

　合板を構成する1枚の薄板を単板といい、表裏になるものを表板(おもていた)、裏板(うらいた)、中間のものを心板(しんいた)、中板(なかいた)という。広い面積の板をつくることができ、節、割れ、腐れなどの欠点を除去でき、方向による伸縮が改善され、表面に化粧材を張れば美麗な板が得られるなどの特徴がある。

［神山幸弘］

工程

合板の製造は、まず木材を薄くむいて単板とし、乾燥させたのちに、表板、裏板、心板とに選別し、欠点を除いたり、幅はぎをして寸法を整える。その後、単板に接着剤を塗布して積み重ね、加熱圧締を行って接着したのち、寸法裁断、仕上げ加工の工程をとる。合板用材には広葉樹でセン、シナ、ナラ、タモ、カバ、針葉樹でマツ、スギ、輸入材としてラワン類、メランチおよびセラヤ類、カプール類があり、広葉樹は主として表・裏板として用いる。単板の製造方法には、木材の年輪に沿ってベニヤレースにより連続して薄くむく方法と、木材の繊維方向にスライサーによりむく方法とあり、ベニヤレースでは板目の単板となり、日本で生産される単板の95％以上を占める。スライサーによれば柾目(まさめ)の単板が得られる。接着剤にはフェノール系樹脂、メラミン系樹脂、ユリヤ系樹脂、ビニル系樹脂などがあり、グルースプレッダに単板を通して塗布される。接着は110～140℃の熱プレスで通常1平方センチメートル当り8～10キログラムの圧力で行う。

［神山幸弘］

種類

合板には普通合板のほか、心板に幅の狭い挽板(ひきいた)を用いたランバーコア合板、心板のかわりに蜂(はち)の巣状樹脂加工紙を用いた軽量合板、美観・表面の硬さ増強などの目的で普通合板の表面に樹脂板・紙・天然木薄板を貼ったオーバーレイ合板、表板に模様を印刷したプリント合板、塗装を施した塗装合板がある。成形合板には、目的にあった曲面を型押ししたものや、単板にフェノール樹脂を含浸させ高圧を加えた硬化合板がある。さらに使用場所の目的にあわせてつくった構造用合板、難燃合板、防炎合板、防腐処理合板、防虫処理合板がある。

［神山幸弘］

性質

合板の性質は単板の品質、単板の厚みと層構成、接着剤の種類によって異なる。フェノール樹脂、メラミン樹脂接着剤を用いた合板は吸湿・吸水速度が小さく、単板のはがれも軽微で耐水性に優れる。収縮、膨張は、互いに繊維方向を直交させているので方向による差はなくなり、板目方向の1/10～1/20となる。また割裂、割れに対しても強くなる。合板の機械的性質は、表板の繊維方向と荷重方向との関係で大きく変化し、表面をずらすような力が働くと心板が破壊するので、構造的利用では注意を要する。各種の品質を定めたものに日本農林規格（JAS(ジャス)）がある。

［神山幸弘］

[参照項目] | ベニヤ | 木材工業

5枚合わせ合板の構成

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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