| 概要 |
近年,生活様式や住宅供給構造の変化の中で木材の乾燥に対する関心が高まり,一方,スギ並材を中心とする人工林材の供給量の拡大が確実に予測される状況の中で,乾燥木材を地域林業の活性化のための差別化商品として位置づける動きが強まっている.しかし,乾燥木材供給の中核的担い手であるべき製材業者の木材乾燥に対する取り組みは必ずしも活発とはいえない.本報告では,乾燥木材の材質や経済性に対する製材業者の評価ないし考...え方を全国の主要なスギ材産地の製材業者のアンケート調査によって分析し,乾燥木材供給の伸び悩みの要因として,一般的に考えられている乾燥コストの価格への転嫁の問題の外に,乾燥木材の材質や経済性に対する評価の低さがあることを明らかにしている.その概要は次のとおりである.1) 木材乾燥には,原木の天然乾燥,製材品の天然乾燥及び製材品の人工乾燥という3つの方法がある.その実施率は,原木天然乾燥が47%,製品の天然乾燥が38%,人工乾燥が19%,である.県別では原木の天然乾燥は秋田県と徳島県,製材品の人工乾燥は熊本県が高い.2) 天然または人工乾燥によって乾燥した乾燥木材の用途は,造作材と役物柱角が圧倒的に多く,両者で88%を占めている.しかし,それらが製材生産量に占める比率は概ね3割未満である.3)乾燥木材の材質に対する評価は,建築後のクレームの少ないこと,かび･虫等の被害の少ないこと,についてはかなり高い評価を得ている.しかし,割れ･ひび割れをはじめ,材の色･艶,反り･捻れ等の狂い,等についてはあまり高いとはいえず,評価のばらつきも大きい.4) 乾燥木材の経済性に対する評価は,乾燥木材を扱うと自社製品の商品のイメージや企業の信用が高まること,生材よりも需要が多く,販売力が大きいこと,についてはきわめて評価が高い.しかし,在庫率のロスの少なさ,梱包の中身の均質性,歩どまりの大きさ,価格の高さ,等については高いとはいえず,ばらつきも大きい.5)木材乾燥コストは1m^3当り概ね7,500～15,000円である.一方,乾燥木材の価格は生材と変わらないとするものが4割強である.したがって,現在の価格では乾燥コストをカバーすることはできないが,それも幾分損失がでる程度にとどまるとみられている.6)木材の人工乾燥については,スギ柱角は役物に限りその必要性を認めるものが圧倒的に多く,並材を含むスギ柱角全体に必要とするものは少数である.造作材は｢できるだけ必要｣を含めても53%に過ぎないし,一般構造材では7割弱が人工乾燥は不用と考えている.県別では,熊本県で人工乾燥の必要性を認めるものが最も多く,ついで秋田県が多いが,静岡県,徳島県及び宮崎県ではかなり少ない.7) 乾燥原木の材質に対する評価は,製品にしたときの色･艶の良さ,狂いの少なさ,かび等の少なさ,等は高く評価されているが,割れ･ひび割れ,鋸の切れ味,製品にしたときの挽肌,等の評価は低い.また,経済性については人工乾燥の期間の短縮,コストの低減,乾燥むらの減少,等の評価が高く,乾燥原木供給の増大を求めるものが多い.
Recently, the idea that the dried timber is a discriminant product is increasingly growing, under the changes in the lifestyle and the structure of the housing construction. And it is certain that the supply of yard timber, mainly sugi (Cryptomeria japonica D. Don), will increase through the harvesting of the plantation. However, the sawmill managers as the main suppliers of dried timber have been taking an active interest in artificial drying of timber. In this paper, the author analyzes the thinking of sawmill managers about quality and economic efficiency of dried timber by using a questionnaire sent to them localized in several prefectures of main producing district of sugi timber in Japan. (1) There are three methods of wood drying at sawmills, namely seasoning of logs, seasoning of sawn lumber and artificial drying of sawn timber. Seasoning of logs, seasoning of sawn lumber and artificial drying are 47%, 38% and 19% of sawmills, respectively. By prefecture, seasoning of logs is done largely in Akita and Tokushima, artificial of sawn timber is done largely in Kumamoto. (2) The most of timber dried by seasoning or artificialy drying are used as fixtural member and knotless pillar. Both form 88% of dried timber together. But dried timber is less than 30% of all sawn timber. (3) Sawmill managers rate the quality of dried timber highly for less claim of house construction, and less damages from mold and insect. But their rates for crack, color and gloss, twist and warp are not so highly and vary widely. (4) The economic efficiency of dried timber is assessed very highly for rise of image of mill's goods and credit of company, larger demand and bigger power of sales than green timber, but it is not assessed so highly for decrease in loss drying stock period, increase in homogeneity of bundle of sawn timber, yield and prices. (5) It is said that the cost of artificial drying is from \7,500 to \15,000 per cubic meter. But by 40% of them, the price of dried timber is equal of that of green timber. It is therefore impossible that the margin exceeds costs of artificial drying. (6) The majority of sawmill managers have an idea that timber drying is necessary for only senior pillar of sugi, but minority of them have an idea for all of pillar of sugi including yard lumber. For fixtural timber is 53% of them even including "as necessary as possible". Less than 70% of them have an idea that timber drying is not necessary for structural timber. By prefecture, the number which have an idea that the timber drying is necessary is the lagest in Kumamoto, next is Akita. Shizuoka, Tokushima and Miyazaki are smaller. (7) They estimate the quality of seasoned log highly for virtue of color and luster and less of warp and mold after sawing, however they lowerly estimate the decrease for in frequency of crash and check, the increase in dimensional accuracy and the decrease in surface roughness of sawn lumber. They estimate economic efficiency of seasoned log highly for the cutting down of drying costs (shortage of time and energy) and uniformity of artificial drying. So sawmill managers neer increase of supply of seasoned logs.続きを見る
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