低分子量酚甲醛樹脂處理對雲杉平板振動性質之影響

Effects of Low Molecular Weight Phenol Formaldehyde Resin Treatment on the Vibration Properties of Spruce Plate

卓志隆(Chih-Lung Cho) ； 葉小雲(Shiou-Yun Ye)

《林產工業》 25卷1期 (2006/03) Pp. 21-28

https://doi.org/10.6561/FPI.2006.25(1).3

摘要

長久以來雲杉屬木材即是重要的樂器用材，主要作為絃樂器的面板、鋼琴響板等用途。唯近年來優良音響用雲杉材料逐漸短缺且價格高昂，因此如何提昇低品質用材的音響性質，已成為重要的課題。本研究採用低分子量酚甲醛樹脂於常壓下處理阿拉斯加雲杉徑面板材，利用Chladni平板振動法量測（1,1）、（0,2）及（2,0）模態共振頻率，由此探討經三種不同濃度低分子量酚甲醛樹脂處理後對木材振動性質之影響。結果顯示處理材在溫度20℃相對溼度65%環境下之平衡含水率較未處理材降低4.6%~7.0%，處理濃度愈高其降低比率愈大，顯示經低分子量酚甲醛樹脂處理後木材之吸濕能力明顯降低。使用不同濃度之化學藥劑處理試材之密度會隨著濃度增加而稍微增加。不同濃度處理後試材之模態共振頻率、縱向及徑向彈性係數及剪斷係數皆顯著地增加，其中以徑向彈性係數及剪斷係數改善效果較大，表示處理後木材之異方性減低。以比動彈性係數作為音響性質改善效果的評估參數及藥劑成本考量，常壓下利用浸漬方法處理阿拉斯加雲杉板材，以5%化學藥劑濃度下處理即有良好的改善效果，其縱向、徑向比動彈性係數及比剪斷係數分別約增加11%、27%及21%左右。

關鍵字

雲杉 ； 低分子量酚甲醛樹脂 ； Chladni平板振動法 ； 比動彈性模數

並列摘要

Wood of the Picea genus has been used as the material for the manufacturing of musical instrument since ancient times. It was primarily used for the top plate of stringed instruments and sounding board of pianos. Improvement of the acoustic properties of low quality wood for musical instruments is very important. This would solve a problem originating in the short supply and expensive cost of high quality wood for musical instruments. This study investigated the vibration properties of quarter-cut Sitka spruce plates treated with three kinds of low molecular-weight phenol formaldehyde resin (LPR) concentrations by non-pressure process. Resonant frequencies of modes (1, 1), (0, 2) and (2, 0) were measured by Chladni plate vibration method to evaluate acoustic properties of wood specimens. The experimental results indicated that moisture contents of chemically treated specimens in equilibrium with 20℃ temperature and 65% relative humidity were 4.6%~7.0% lower than those of untreated specimens. The decreased percentages were proportional to chemical concentrations. The hygroscopic ability of Sitka spruce impregnated with LPR was reduced significantly. The density of test specimen was slightly increased while increasing chemical concentration. Resonant frequencies of different modes, modulus of elasticity and shear modulus of chemically treated plates were increased significantly. The physical properties were improved better for modulus of elasticity in the radial direction and shear modulus than for modulus of elasticity in the longitudinal direction. Consequently, the ratios of Young's modulus to shear modulus were reduced. Specific modulus of elasticity in the longitudinal and radial direction and specific shear modulus usually used as important evaluated parameters for acoustic properties of stringed instruments were increased about 11%, 27% and 21% respectively. From the points of specific modulus and chemical cost, we suggest the more appropriate concentration of LPR used for improvement of acoustic properties of Sitka spruce plate is 5%.

並列關鍵字

Spruce ； Low molecular weight phenol formaldehyde resin ； Chladni plate-vibration method ； Specific dynamic modulus of elasticity