四種紫外光硬化變性壓克力透明塗料塗裝櫟木之光變色解析

Elucidation of Photodiscoloration of Oak Coated with four Kinds of UV-curable Acrylic Clear Coatings

張上鎮(Shang-Tzen Chang) ； 周佰隆(Pai-Lung Chou)

《林產工業》 15卷3期 (1996/09) Pp. 471-481

摘要

由於4種紫外光硬化透明壓克力塗料塗裝木材會因照光而黃化，本試驗乃嘗試分析照光後壓克力塗膜及膜後面木材之顏色及化學組成份變化，以求釐清其光變色機制，藉此尋找適合的方法抑止透明壓克力塗裝木材之光變色。試驗結果發現，矽酮變性（S/651）與脂肪族胺基甲酸酯變性（UAl/651）壓克力游離塗膜照光後顏色與化學組成份變化都極輕微，但是游離塗膜下之櫟木照光後色差值極大，故若能改善木材本身之光安定性必能減輕此二種塗裝木材之光變色。至於芳香族胺基甲酸酯變性壓克力（UAr/651）與環氧變性壓克力（E/651）游離塗膜，則隨照光時間增加而黃化，且由紫外光可見光光譜分析顯示，兩者之游離塗膜受光影響而產生具有300~450 nm吸收特性之劣化衍生物；其中，又以芳香族胺基甲酸酯變性壓克力游離塗膜之劣化較嚴重。由於塗膜嚴重變色為UAr/651與E/651塗裝櫟木變色之主因，因此欲抑止環氧變性壓克力與芳香族胺基甲酸醋變性壓克力塗裝櫟木之光劣化，必須先抑止其塗膜之光變色；其次，此兩種塗膜下之櫟木在照光初期亦產生一定程度之變色，故在抑止塗膜變色之同時，仍需要安定櫟木表面易變色之發色團。

關鍵字

矽酮變性壓克力 ； 環氧變性壓克力 ； 脂肪族胺基甲酸酯變性壓克力 ； 芳香族胺基甲酸酯變性壓克力 ； 紫外光硬化塗料 ； 光變色

並列摘要

Wood coated with UV-curable acrylic clear coatings is susceptible to yellowing induced by ultraviolet light. The objective of this study is to illustrate the photodiscoloration mechanism of wood coated with UV-curble acrylic clear coatings. Therefore, the changes of color and chemical structure of free films and oaks beneath the films were determined. After artificially accelerated lightfastness test, the variations in color difference and in UV/Vis spectra of silicone modified (S/651) and aliphatic urethane modified acrylic (UA1/651) free films are barely observed, but the discoloration of oaks beneath these two free films is striking. This result reveals that improving the stabilization of oak itself is necessary to inhibit the disocloration of oak coated with these two UV-curable acrylic clear coatings. Aromatic urethane modified (UAr/651) and epoxy modified (E/651) acrylic free films show significantly yellowing after artificially accelerated lightfastness test for 16 days. Based on the change of UV/Vis spectra, the derivatives absorbing 350~450 mm ultraviolet light were generated on the film surfaces. The result also reveal that the yellowing of aromatic urethane modified acrylic film is more significant than epoxy modified acrylic film. Since the discoloration of these two coating films is the major contributor causing the photodiscoloration of oak coated with E/651 or UAr/651, inhibiting the discoloration of coatings themselves is of importance to improve the lightfastness of coated wood. On the other hand, oaks behind E/651 and UAr/651 free films also discolored by light to a considerable degree. Therefore, to stabilize the chromophores on the surfaces of oak is also prerequisite.

並列關鍵字

silicone modified acrylate ； epoxy modified acrylate ； aliphatic urethane modified acrylate ； aromatic urethane modified acrylate ； UV-curale coating ； photodiscoloration