JP3567924B2 - Wood treatment method - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、木質材の漂白を行う際の処理方法に関し、詳しくは、処理後の光や熱による木質材の変色を抑制するための木質材の処理方法に関する。
【０００２】
【従来の技術】
従来より、木質材の汚れ除去、染色また塗装する前の木質材の脱色などを目的として、木質材を過酸化水素水などで漂白処理することが行われている。例えば、特開昭５５−１４０５０６号公報には、単板を過酸化水素水を用いて脱色する方法、特開昭５７−１８７２０４号公報には、脂肪族ジアルデヒドおよび亜塩素酸塩で木材を処理する方法、特開昭６２−１３４２０２号公報には、ナラ材の単板をアスコルビン酸、次亜塩素酸ナトリウムおよびエチレンジアミン四酢酸ナトリウムの混合溶液に浸漬する方法、特開平８−１１１０６号公報には、過炭酸ナトリウム等の過酸化水素誘導体を添加した過酸化水素水で木材を漂白・脱色する方法が提案されている。
【０００３】
しかしながら、これら従来の漂白処理では、処理後において、光や熱によって木質材が色戻りを起こし、濃色化するといった不具合が生じていた。漂白処理された木質材の変色の度合いを色差で表すと、その色差は、漂白処理されていない木質材よりも大きくなってしまっていた。この原因としては、以下のことが考えられる。
すなわち、木質材中のリグニンは、芳香核構造やフェノール性水酸基を有しているため、太陽光の紫外線を吸収してラジカル反応による光酸化作用によって分解する。これにより、リグニンが低分子化したり、水酸基の水素が引き抜かれたりすることが原因となって、発色団が形成される。この発色団の形成が、木質材が濃色化したり、漂白処理を施しても色も取りしたりする原因と考えられている。
【０００４】
また、従来より、木質材の耐湿化、寸法安定化を目的として、木質材をアセチル化剤でアセチル化処理することが行われている。例えば、特開平５−２６９７１０号公報には、木質繊維を気相中にて無水酢酸などのアセチル化剤でアセチル化する方法、特開平７−９４１１号公報には、セルロース含有材を気相中にてアセチル化する方法が提案されている。また、アセチル化処理には、木質材を漂白する作用があることも知られている。
【０００５】
しかしながら、アセチル化処理された木質材は、光により明色化していき、次第に色が抜けて白くなっていくという問題を有していた。
このように、従来の木質材の漂白処理やアセチル化処理には、処理後の木質材が、色戻り（濃色化）や色抜け（明色化）などの変色を起こすという問題があった。
【０００６】
【発明が解決しようとする課題】
よって、本発明の目的は、漂白処理後の光や熱による木質材の色戻り（濃色化）を大幅に抑えることができる木質材の処理方法を提供することにある。
また、本発明の目的は、漂白処理およびアセチル化処理後の光や熱による木質材の色戻り（濃色化）や色抜け（明色化）などの変色を大幅に抑えることができる木質材の処理方法を提供することにある。
【０００７】
【課題を解決するための手段】
すなわち、本発明の木質材の処理方法は、単板からなる木質材に、色戻り（濃色化）を抑えるために、処理温度３０℃〜５０℃、処理時間１０分〜２００分の漂白処理および、木質材中のフェノール性水酸基を他の基に置換する置換処理を施すことを特徴とする。
また、前記置換処理は、アセチル化処理、オリゴエステル化処理、エーテル化処理およびホルマール化処理からなる群から選ばれるいずれかの処理であることが望ましい。
また、前記置換処理は、漂白処理の後に行われることが望ましい。
また、漂白処理と置換処理との間に、木質材を洗浄および乾燥することが望ましい。
また、前記置換処理はアセチル化処理であり、木質材のアセチル化度は５％以上であることが望ましい。
【０００８】
【発明の実施の形態】
以下、本発明を詳しく説明する。
本発明の木質材の処理方法は、木質材に、漂白処理および、木質材中のフェノール性水酸基を他の基に置換する置換処理を施すことを特徴とする方法であり、漂白処理および置換処理の順序は特に限定はされない。すなわち、木質材に漂白処理を施した後に、置換処理を施してもよいし、木質材に置換処理を施した後に、漂白処理を施してもよい。ただし、漂白処理はアルカリ性の条件下で行われることが多いので、木質材に置換処理を施した後に、漂白処理を施す方法の場合には、木質材中において他の基に置換された部分のうち、その一部がアルカリによって加水分解され、置換基がとれてしまうおそれがある。したがって、木質材に漂白処理を施した後に、置換処理を施す方法が好ましい。
【０００９】
本発明における木質材は、木材をスライスした単板である。大きな面積で使用されることの多く、黄変が目立ちやすい単板において、本発明の処理方法は効果的である。
【００１０】
本発明における漂白処理としては、公知の漂白処理方法を採用することができる。例えば、漂白液を木質材に刷毛塗りなどの方法によって塗布し、必要に応じて加熱を行いながら、所定時間処理する方法；木質材を漂白液に浸漬し、必要に応じて加熱を行いながら、所定時間処理する方法などが挙げられる。
【００１１】
漂白液としては、例えば、ｐＨ９〜１２の過酸化水素水；亜塩素酸カリウム、亜塩素酸ナトリウムなどの亜塩素酸塩の水溶液；次亜塩素酸カリウム、次亜塩素酸ナトリウムなどの次亜塩素酸塩の水溶液などが挙げられる。
処理時間は、処理温度が３０℃〜５０℃の場合には、１０分〜２００分の範囲である。
【００１２】
上記の漂白処理方法以外にも、例えば、特開昭５７−１８７２０４号公報に記載された、脂肪族ジアルデヒドおよび亜塩素酸塩で木質材を処理する方法、特開昭６２−１３４２０２号公報に記載された、木質材をアスコルビン酸、次亜塩素酸ナトリウムおよびエチレンジアミン四酢酸ナトリウムの混合溶液に浸漬する方法、特開平８−１１１０６号公報に記載された、過炭酸ナトリウム等の過酸化水素誘導体を添加した過酸化水素水で木質材を漂白・脱色する方法など、公知の漂白処理方法が採用できる。
【００１３】
漂白処理の後には、特に漂白された木材中成分や漂白処理された木質材を加熱または洗浄し、余分な漂白液を除去することが好ましい。漂白液に使用した過酸化水素などが木質材に残留していると、木質材に塗膜などを設けたり、木質材を染色した際に、塗膜や木質板の色が変色するなどの不具合が生ずるおそれがある。洗浄は、漂白された木材成分除去の面からも好ましく、具体的には、漂白処理された木質材を水に浸漬する、または流水にさらすことによって行われる。洗浄には、水または４０〜８０℃の温水が使用できる。また、洗浄時間は、特に限定はされないが、３０〜１８０分程度である。
【００１４】
また、上記洗浄の後には、漂白処理された木質材を乾燥することが好ましい。特に、漂白処理の後に置換処理としてアセチル化処理を行う場合には、木質材中の水分とアセチル化剤である無水酢酸とが反応してしまう。また、水と無水酢酸との反応が発熱反応であるため、大量の木材を扱うと木材の変色を伴うばかりでなく、危険性も増す。したがって、木質材中の含水率を１３％以下としておくことが好ましく、１０％以下としておくことがより好ましく、３％以下としておくことがさらに好ましい。また、木質材として、上述の複合材を用いた場合には、木質材の割れを防止する効果もある。
【００１５】
乾燥方法としては、例えば、熱風乾燥、真空乾燥、熱盤乾燥などを採用することができる。乾燥条件は、熱風乾燥の場合、例えば、温度は４０〜８０℃、時間は１０〜９０分であり、真空乾燥の場合、例えば、気圧は５〜１２０ｔｏｒｒ、温度は４０〜８０℃、時間は１〜８時間であり、熱盤乾燥の場合は、例えば、温度は５０〜１２０℃、時間は１〜３０分である。
【００１６】
本発明における置換処理としては、木質材中のフェノール性水酸基を他の基に置換する処理であれば特に限定はされないが、好ましい処理としては、アセチル化処理、オリゴエステル化処理、エーテル化処理およびホルマール化処理が挙げられる。中でも、木質材の耐湿化、寸法安定化の効果を有し、さらに、漂白処理との併用によって、木質材の色戻り（濃色化）および色抜け（明色化）の両方を抑制できるという相乗効果が期待できる、アセチル化処理が最も好適である。
本発明におけるアセチル化処理とは、木質材にアセチル化剤、例えば無水酢酸を接触させて、次式のように木質材（Ｗ）中の水酸基（−ＯＨ）の一部をアセチル基（−ＯＣＯＣＨ３ ）に置き換える処理のことである。
［Ｗ］−ＯＨ ＋ （ＣＨ３ＣＯ）２Ｏ → ［Ｗ］−ＯＣＯＣＨ３ ＋ ＣＨ３ＣＯＯＨ
アセチル化処理は、気相中で行ってもよく、液相中で行ってもよいが、液相でアセチル化処理を行うと、大量のアセチル化剤が必要となり、また大量のアセチル化剤を反応温度まで短時間で昇温させることも困難なので、気相中で行うことが好ましい。
【００１７】
気相中でのアセチル化の具体的な方法としては、例えば、反応容器の底部にアセチル化剤を満たし、この上方にステンレスワイヤなどで作ったネットを張り、このネット上に木質材を載せ、アセチル化剤を加熱してアセチル化剤の蒸気を発生させて、木質材とアセチル化剤の蒸気を接触させる方法などが挙げられる。
【００１８】
アセチル化剤としては、例えば、酢酸、無水酢酸、クロル酢酸などが挙げられ、中でも反応性（処理効率）の点で、無水酢酸が好適に用いられる。
反応時間は、１５分〜３時間程度とされるが、要求されるアセチル化度によって適宜変更できる。また、反応温度は、１３０〜２００℃であり、反応圧力は、常圧〜２気圧程度である。
【００１９】
また、木質材のアセチル化に際して、無水酢酸などのアセチル化剤を、これと反応しない不活性な溶媒、例えば、キシレンなどで希釈して用いることができる。この場合における溶媒の使用量は、アセチル化剤と溶媒との合計量の７０重量％以下とされる。このようなアセチル化剤と溶媒との混合物を用いることで、発熱反応であるアセチル化反応を穏和な状態で進めることができ、反応操作が容易となり、木質材の過度のアセチル化や熱劣化を抑えることができる。
【００２０】
上述のアセチル化処理による木質材のアセチル化度は、重量増加率で、通常、１〜２５％程度とされるが、要求される耐水性、耐湿性に応じて適宜変更することもできる。
また、アセチル化度は、５％以上が好ましい。ただし、アセチル化度が高いほど、色戻り（濃色化）の抑制効果は高くなるが、アセチル化度を高めるためには処理時間が長くなってしまう。したがって、アセチル化の処理時間を考慮すると（処理時間があまり長くならない範囲で）アセチル化度は１５％以下が好ましい。アセチル化度が１５％以下であっても、十分な効果が得られる。
また、アセチル化度は、漂白処理における時間に応じて適宜、調整される。漂白処理における処理時間（漂白液への浸漬時間）を１０分以上とした場合には、アセチル化度は５％以上とするのが好ましい。また、漂白処理の時間を長くした場合（例えば１時間以上）には、アセチル化度は１５％以上とすることが好ましい。
アセチル化処理された木質材を、必要に応じて洗浄し、付着しているアセチル化剤を除去する。また、アセチル化処理を液相で行った場合、あるいはアセチル処理化後に洗浄を行った場合には、木質材を所定の含水率まで乾燥する。
【００２１】
本発明におけるオリゴエステル化処理とは、木質材中の水酸基を起点として、二塩基酸無水物と重合性二重結合を有するエポキシ化合物とを交互付加エステル化反応することによりオリゴエステル化木質材を得る処理のことである。オリゴエステル処理は、耐湿化、寸法安定化の効果を有し、さらにオリゴエステル化木質材は、合成高分子に対して優れた親和性を有するため、成形加工性の高い木材・合成高分子系複合材料となる。
また、本発明におけるエーテル化処理とは、木質材中の水酸基（−ＯＨ）の一部をエステル基（−Ｏ−Ｒ、Ｒ＝アルキル基等の炭化水素基）に置き換える処理のことである。エーテル処理は、耐湿化、寸法安定化の効果を有し、さらにエーテル化木質材は、耐候性に優れる。
また、本発明におけるホルマール化処理とは、木質材中の水酸基（−ＯＨ）の一部を−ＯＣＨ２Ｏ に置き換える処理のことである。ホルマール化木質材は、耐湿化、寸法安定化の効果を有する。
漂白処理および置換処理を施された木質材には、必要に応じて、塗装などの後処理を施してもよい。塗装に用いられる樹脂としては、例えば、ウレタン系樹脂、ポリエステル系樹脂、エポキシ樹脂、アクリル樹脂、ラッカー、アルキッド樹脂、メラミン樹脂などが挙げられる。ただし、塗膜に変色が起こりにくい樹脂を使用することが好ましい。
【００２２】
本発明の木質材の処理方法にあっては、漂白処理に加えて置換処理を施し、木質材中のフェノール性水酸基を他の基に置換しているので、木質材中に発色団が形成されることを抑制し、漂白処理後の光や熱による色戻りが抑えられた漂白木質材を得ることができる。
また、本発明の木質材の処理方法にあっては、漂白処理およびアセチル化処理を併用しているので、漂白処理およびアセチル化処理が有していたそれぞれの欠点をそれぞれの処理が互いに補完することとなり、処理後の光や熱による色戻りおよび色抜けが抑えられた漂白木質材を得ることができる。
【００２３】
【実施例】
以下、本発明を更に理解しやすくするため、実施例について説明する。かかる実施例は、本発明の一態様を示すものであり、この発明を限定するものではない。本発明の範囲で任意に変更可能である。
【００２４】
（実施例１）
３５重量％の過酸化水素水１００重量部に苛性ソーダ水溶液を２０重量部添加して、ｐＨが１１に調整された漂白液を用意した。この漂白液に、メープル、スプルースの単板（６０ｃｍ×３０ｃｍ×厚さ０．５ｍｍ）を、４０℃で６０分間浸漬した。漂白処理後の単板を引き上げ、６０℃の温水に１０分間浸漬し、さらに流水で１０分間水洗した。次いで、洗浄された単板を８０℃の熱盤上で５分間乾燥させ、木質材の含水率を１２％に調整した。
【００２５】
乾燥された単板を、気相アセチル化処理装置（住友ケミカルエンジニアリング社製）を用い、１５０℃の条件下で、無水酢酸によって５０分間アセチル化処理し、処理後、未反応の無水酢酸を吸気して除去した。単板のアセチル化度は、重量増加率（ＷＰＧ：ｗｅｉｇｈｔ ｐｅｒｃｅｎｔ ｇａｉｎ）で１３％であった。
処理された単板について、下記の耐光試験を行い、試験前後の色差を測定した。結果を表１に示す。
【００２６】
（耐光試験）
試験機としてキセノンフェードメーター（スガ試験機社製の色差計）を用いて、木質材に対して連続照射を行い、Ｌ＊ａ＊ｂ＊表色系における照射前後のＬ＊、ａ＊、ｂ＊を測色し、それぞれの差ΔＬ＊、Δａ＊、Δｂ＊を求め、次式から色差ΔＥ＊ａｂを計算した。
ΔＥ＊ａｂ＝［（ΔＬ＊）２＋（Δａ＊）２＋（Δｂ＊）２］１／２
（試験条件）
測色時の光源：Ｄ６５
積算光量 ：１１ＭＪ／ｍ２
ブラックパネル温度：８３℃
【００２７】
（実施例２）
メープルの単板（６０ｃｍ×３０ｃｍ×厚さ０．５ｍｍ）を、実施例１と同様にアセチル化処理し、処理後、未反応の無水酢酸を吸気して除去した。単板のアセチル化度は、重量増加率で１４％であった。
アセチル化処理された単板を、実施例１と同じ漂白液に、４０℃で６０分間浸漬した。漂白処理後の単板を引き上げ、６０℃の温水に１０分間浸漬し、さらに流水で１０分間水洗した。次いで、洗浄された単板を８０℃の熱盤上で５分間乾燥させた。
処理された単板について、実施例１と同様に耐光試験を行い、試験前後の色差を測定した。結果を表１に示す。
【００２８】
（比較例１）
実施例１と同じ漂白液に、メープルの単板（６０ｃｍ×３０ｃｍ×厚さ０．５ｍｍ）を、４０℃で６０分間浸漬した。漂白処理後の単板を引き上げ、６０℃の温水に１０分間浸漬し、さらに流水で１０分間水洗した。次いで、洗浄された単板を８０℃の熱盤上で５分間乾燥させ、木質材の含水率を１２％に調整した。
漂白処理された単板について、実施例１と同様に耐光試験を行い、試験前後の色差を測定した。結果を表１に示す。
【００２９】
（比較例２）
メープル、スプルースの単板（６０ｃｍ×３０ｃｍ×厚さ０．５ｍｍ）を、実施例１と同様にアセチル化処理し、処理後、未反応の無水酢酸を吸気して除去した。単板のアセチル化度は、重量増加率で１４％であった。
アセチル化処理された単板について、実施例１と同様に耐光試験を行い、試験前後の色差を測定した。結果を表１に示す。
【００３０】
【表１】
（実施例３、比較例３）
約０．２Ｎの水酸化ナトリウム水溶液１Ｌに、３５重量％の過酸化水素水５０ｃｃを加えて漂白液を調整した。厚さ０．２ｍｍのメープル化粧材を８枚用意し、このうち６枚については、それぞれ４０℃で５分（比較例３−２）、１０分（実施例３−１）、２０分（実施例３−２）、３０分（実施例３−３）、６０分（実施例３−４）および１２０分（実施例３−５）浸漬して漂白処理を施した。また、残りの２枚のうち、１枚には同じく４０℃、１２０分間の漂白処理を施し（実施例３−６）、１枚には漂白処理を施さなかった（比較例３−１）。漂白処理後のメープル化粧材を、７０〜８０℃の温水に３０分間浸漬し、さらに流水で１０分間水洗した。次いで、洗浄された単板を８０℃の熱盤上で５分間乾燥させた。
【００３２】
乾燥されたメープル化粧材（実施例３−１〜３−５、比較例３−１〜３−２）を、気相アセチル化処理装置を用い、１６０℃の条件下で、無水酢酸によって６０分間アセチル化処理した。メープル化粧材のアセチル化度は、重量増加率で５〜１５％と推定された。
また、実施例３−６のメープル化粧材については、同様のアセチル化処理を２回施した。このメープル化粧材のアセチル化度は、重量増加率で１５〜２５％と推定された。
処理されたメープル化粧材について、実施例１と同様に耐光試験を行い、試験前後の色差を測定した。結果を表２に示す。表中、色差の欄の◎は色差が４未満、○は色差が４〜７、△は８〜１０、×は色差が１０を超えていることを表す。
【００３３】
【表２】
（実施例４）
厚さ０．２ｍｍのウォールナット化粧材を用いた以外は、実施例３と同様にして漂白処理およびアセチル化処理を行い、実施例１と同様に耐光試験を行い、試験前後の色差を測定した。ウォールナット化粧材の場合は、漂白処理時間が６０分以上において色差が７以下となり、耐光変色に好ましい効果が認められた。
【００３５】
【発明の効果】
以上説明したように、本発明の木質材の処理方法は、単板からなる木質材に、処理温度３０℃〜５０℃、処理時間１０分〜２００分の漂白処理および、木質材中のフェノール性水酸基を他の基に置換する置換処理を施す処理方法であるので、漂白処理後の光や熱による木質材の色戻り（濃色化）を大幅に抑えることができる。
また、前記置換処理が、アセチル化処理、オリゴエステル化処理、エーテル化処理およびホルマール化処理からなる群から選ばれるいずれかの処理であれば、このような効果が効率よく発揮される。
また、前記置換処理が、木質材の漂白処理の後に行われるのであれば、木質材の他の基に置換された部分のうち、その一部が漂白処理時にアルカリによって加水分解されることがなく、効率よく木質材の処理を行うことができる。
【００３６】
また、漂白処理と置換処理との間に、木質材を洗浄するようにすれば、残留した過酸化水素などによる塗膜などへの悪影響を抑えることができる。また、洗浄後に木質材を乾燥すれば、アセチル化処理時に、残留した水分によるアセチル化剤の無駄な消費を抑えることができる。
また、前記置換処理がアセチル化処理であり、木質材のアセチル化度が５％以上であれば、木質材の色戻り（濃色化）および色抜け（明色化）の両方を抑制でき、しかも色戻りの抑制効果がさらに高くなる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a processing method when bleaching a wood material, and more particularly to a wood material processing method for suppressing discoloration of the wood material due to light or heat after the processing.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, wood materials are bleached with a hydrogen peroxide solution or the like for the purpose of removing stains from the wood materials, decoloring the wood materials before dyeing or painting. For example, JP-A-55-140506 discloses a method of decolorizing a veneer using a hydrogen peroxide solution, and JP-A-57-187204 discloses a method of removing wood with an aliphatic dialdehyde and chlorite. Japanese Patent Application Laid-Open No. Hei 8-11106 discloses a method of immersing a veneer veneer in a mixed solution of ascorbic acid, sodium hypochlorite and sodium ethylenediaminetetraacetate. Has proposed a method of bleaching and decoloring wood with a hydrogen peroxide solution to which a hydrogen peroxide derivative such as sodium percarbonate is added.
[0003]
However, in these conventional bleaching processes, after the process, there is a problem in that the wood material returns color by light or heat and becomes darker. When the degree of discoloration of the bleached wood material was represented by a color difference, the color difference was larger than that of the unbleached wood material. The following can be considered as the cause.
That is, since lignin in wood material has an aromatic nucleus structure and a phenolic hydroxyl group, it absorbs ultraviolet rays of sunlight and is decomposed by a photooxidation action by a radical reaction. As a result, a chromophore is formed due to a decrease in molecular weight of lignin or extraction of hydrogen of a hydroxyl group. It is considered that the formation of the chromophore causes the wood material to become darker or to take on the color even after the bleaching treatment.
[0004]
Conventionally, wood materials have been acetylated with an acetylating agent for the purpose of moisture resistance and dimensional stability of the wood materials. For example, JP-A-5-269710 discloses a method of acetylating a wood fiber with an acetylating agent such as acetic anhydride in a gaseous phase, and JP-A-7-9411 discloses a method of preparing a cellulose-containing material in a gaseous phase. A method for acetylation has been proposed. It is also known that the acetylation treatment has an effect of bleaching wood materials.
[0005]
However, the wood material subjected to the acetylation treatment has a problem that it becomes lighter by light and gradually loses its color and becomes white.
As described above, in the conventional bleaching or acetylation treatment of the wood material, there is a problem that the wood material after the treatment causes discoloration such as color return (darkening) and color omission (brightening). .
[0006]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for treating wood material which can significantly suppress the color return (darkening) of the wood material due to light or heat after the bleaching process.
Another object of the present invention is to provide a wood material that can significantly suppress discoloration such as color return (darkening) and color loss (lightening) of the wood material due to light or heat after bleaching and acetylation. Is to provide a processing method.
[0007]
[Means for Solving the Problems]
That is, in the wood material processing method of the present invention, a bleaching process is performed on a wood material made of a veneer in order to suppress color return (darkening), at a processing temperature of 30 ° C. to 50 ° C. and a processing time of 10 minutes to 200 minutes. In addition, a substitution treatment for substituting a phenolic hydroxyl group in the wood material with another group is performed.
In addition, the substitution treatment is desirably any one of the treatments selected from the group consisting of acetylation treatment, oligoesterification treatment, etherification treatment, and formalization treatment.
Further, it is desirable that the replacement process is performed after the bleaching process.
In addition, it is desirable to wash and dry the wood material between the bleaching process and the replacement process.
In addition, the substitution treatment is an acetylation treatment, and the acetylation degree of the wood material is desirably 5% or more.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The method for treating woody material of the present invention is a method characterized by subjecting a woody material to a bleaching treatment and a substitution treatment for replacing a phenolic hydroxyl group in the woody material with another group. Is not particularly limited. That is, after performing the bleaching process on the wood material, the replacement process may be performed, or after performing the replacement process on the wood material, the bleaching process may be performed. However, since the bleaching process is often performed under alkaline conditions, in the case of performing the bleaching process after performing the replacement process on the wood material, the portion of the wood material replaced with another group in the wood material is subjected to the bleaching process. Among them, a part thereof may be hydrolyzed by the alkali, and the substituent may be removed. Therefore, a method is preferred in which a wood material is subjected to a bleaching treatment followed by a replacement treatment.
[0009]
Wood material in the present invention is a single plate were sliced wood. Many be used play a significant area, the yellowing conspicuous veneer, processing method of the present invention is effective.
[0010]
As the bleaching treatment in the present invention, a known bleaching treatment method can be adopted. For example, a method in which a bleaching liquid is applied to a wooden material by a method such as brushing and the like, and treated for a predetermined time while heating as necessary; while the wooden material is immersed in the bleaching solution and heated as necessary, For example, there is a method of performing processing for a predetermined time.
[0011]
Examples of the bleaching solution include a hydrogen peroxide solution having a pH of 9 to 12; an aqueous solution of chlorite such as potassium chlorite and sodium chlorite; a hypochlorite such as potassium hypochlorite and sodium hypochlorite. An aqueous solution of an acid salt is exemplified.
Processing time, when the treatment temperature is 30 ° C. to 50 ° C. is in the range of 10 minutes to 200 minutes.
[0012]
In addition to the above-described bleaching method, for example, a method of treating wood material with an aliphatic dialdehyde and chlorite described in JP-A-57-187204, and JP-A-62-134202. A method of immersing wood material in a mixed solution of ascorbic acid, sodium hypochlorite and sodium ethylenediaminetetraacetate, a method of immersing a wood material in a hydrogen peroxide derivative such as sodium percarbonate described in JP-A-8-11106. A known bleaching method such as a method of bleaching and decoloring a wood material with the added hydrogen peroxide solution can be employed.
[0013]
After the bleaching treatment, it is particularly preferable to heat or wash the components in the bleached wood and the bleached wood material to remove excess bleaching solution. If the hydrogen peroxide used in the bleaching solution remains on the wood material, problems such as discoloration of the coating film or wood board when coating the wood material or dyeing the wood material May occur. Washing is also preferable from the viewpoint of removing bleached wood components. Specifically, washing is performed by immersing the bleached wood material in water or exposing it to running water. Water or warm water at 40 to 80 ° C. can be used for washing. The washing time is not particularly limited, but is about 30 to 180 minutes.
[0014]
After the washing, the bleached wood material is preferably dried. In particular, when an acetylation treatment is performed as a substitution treatment after the bleaching treatment, moisture in the wood material reacts with acetic anhydride as an acetylating agent. Further, since the reaction between water and acetic anhydride is an exothermic reaction, handling a large amount of wood not only involves discoloration of the wood but also increases the danger. Therefore, the water content in the wood is preferably 13% or less, more preferably 10% or less, and even more preferably 3% or less. In addition, when the above-described composite material is used as the wooden material, there is also an effect of preventing cracking of the wooden material.
[0015]
As a drying method, for example, hot air drying, vacuum drying, hot plate drying and the like can be adopted. The drying conditions are, for example, a temperature of 40 to 80 ° C. and a time of 10 to 90 minutes in the case of hot air drying, and a pressure of 5 to 120 torr, a temperature of 40 to 80 ° C. and a time of 1 for vacuum drying. In the case of hot plate drying, for example, the temperature is 50 to 120 ° C., and the time is 1 to 30 minutes.
[0016]
The substitution treatment in the present invention is not particularly limited as long as it is a treatment for substituting a phenolic hydroxyl group in a wood material with another group, but preferred treatments are acetylation treatment, oligoesterification treatment, etherification treatment and Formalization treatment is mentioned. Above all, it has the effect of moisture resistance and dimensional stabilization of wood materials, and it can suppress both color return (darkening) and color loss (lightening) of wood materials by using it together with bleaching treatment. Acetylation treatment, which can expect a synergistic effect, is most preferred.
The acetylation treatment in the present invention means that a wood material is contacted with an acetylating agent, for example, acetic anhydride, and a part of the hydroxyl group (—OH) in the wood material (W) is converted into an acetyl group (—OCOCH) as shown in the following formula. This is the process that replaces 3 ).
[W] —OH + (CH 3 CO) 2 O → [W] —OCOCH 3 + CH 3 COOH
The acetylation treatment may be performed in the gas phase or in the liquid phase.However, when the acetylation treatment is performed in the liquid phase, a large amount of the acetylating agent is required, and a large amount of the acetylating agent is required. Since it is difficult to raise the temperature to the reaction temperature in a short time, the reaction is preferably performed in a gas phase.
[0017]
As a specific method of acetylation in the gas phase, for example, the bottom of a reaction vessel is filled with an acetylating agent, a net made of a stainless steel wire or the like is placed above the acetylating agent, and a wood material is placed on the net. A method of heating the acetylating agent to generate vapor of the acetylating agent and bringing the wood material into contact with the vapor of the acetylating agent may be used.
[0018]
Examples of the acetylating agent include acetic acid, acetic anhydride, and chloroacetic acid. Among them, acetic anhydride is suitably used in terms of reactivity (treatment efficiency).
The reaction time is about 15 minutes to 3 hours, but can be appropriately changed depending on the required degree of acetylation. The reaction temperature is from 130 to 200 ° C., and the reaction pressure is from normal pressure to about 2 atm.
[0019]
When acetylating wood material, an acetylating agent such as acetic anhydride can be used after being diluted with an inert solvent that does not react with the acetylating agent, for example, xylene. In this case, the amount of the solvent used is 70% by weight or less of the total amount of the acetylating agent and the solvent. By using such a mixture of the acetylating agent and the solvent, the acetylation reaction, which is an exothermic reaction, can proceed in a mild state, the reaction operation becomes easy, and excessive acetylation and thermal deterioration of the wood material are prevented. Can be suppressed.
[0020]
The degree of acetylation of the wood material by the above-mentioned acetylation treatment is usually about 1 to 25% in terms of weight increase rate, but can be appropriately changed according to required water resistance and moisture resistance.
The acetylation degree is preferably 5% or more. However, as the degree of acetylation increases, the effect of suppressing color return (darkening) increases, but the processing time increases in order to increase the degree of acetylation. Therefore, the acetylation degree is preferably 15% or less in consideration of the acetylation treatment time (as long as the treatment time is not too long). Even if the acetylation degree is 15% or less, a sufficient effect can be obtained.
The acetylation degree is appropriately adjusted according to the time in the bleaching treatment. When the processing time (immersion time in the bleaching solution) in the bleaching treatment is 10 minutes or more, the acetylation degree is preferably 5% or more. When the bleaching time is extended (for example, 1 hour or more), the acetylation degree is preferably 15% or more.
The wood material subjected to the acetylation treatment is washed as necessary to remove the attached acetylating agent. When the acetylation treatment is performed in the liquid phase or when the acetylation treatment is followed by washing, the wood material is dried to a predetermined moisture content.
[0021]
The oligoesterification treatment in the present invention is based on the hydroxyl groups in the wood material, and the oligoesterification wood material is obtained by alternately adding and esterifying a dibasic acid anhydride and an epoxy compound having a polymerizable double bond. It is the process to obtain. The oligoester treatment has the effects of moisture resistance and dimensional stability, and the oligoesterified wood material has an excellent affinity for the synthetic polymer. It becomes a composite material.
Further, the etherification treatment in the present invention is a treatment in which a part of the hydroxyl group (-OH) in the wood material is replaced with an ester group (-OR, R = a hydrocarbon group such as an alkyl group). The ether treatment has the effects of moisture resistance and dimensional stabilization, and the etherified wood material has excellent weather resistance.
Further, the formalization treatment in the present invention is a treatment in which a part of the hydroxyl group (—OH) in the wood is replaced with —OCH 2 O. The formalized wood material has the effects of moisture resistance and dimensional stability.
The wood material that has been subjected to the bleaching treatment and the replacement treatment may be subjected to post-treatment such as painting, if necessary. Examples of the resin used for coating include urethane-based resin, polyester-based resin, epoxy resin, acrylic resin, lacquer, alkyd resin, and melamine resin. However, it is preferable to use a resin that does not easily cause discoloration in the coating film.
[0022]
In the method for treating woody material of the present invention, a chromophore is formed in the woody material because the phenolic hydroxyl group in the woody material is replaced with another group by performing a substitution treatment in addition to the bleaching treatment. And it is possible to obtain a bleached wood material in which color return due to light or heat after the bleaching treatment is suppressed.
In the method for treating woody material of the present invention, the bleaching treatment and the acetylation treatment are used in combination, so that the respective treatments complement each other that the bleaching treatment and the acetylation treatment have. As a result, it is possible to obtain a bleached wood material in which color return and color loss due to light or heat after treatment are suppressed.
[0023]
【Example】
Hereinafter, examples will be described to further understand the present invention. These examples illustrate one embodiment of the present invention and do not limit the present invention. It can be arbitrarily changed within the scope of the present invention.
[0024]
(Example 1)
20 parts by weight of an aqueous solution of caustic soda was added to 100 parts by weight of a 35% by weight aqueous hydrogen peroxide solution to prepare a bleaching solution whose pH was adjusted to 11. A single plate of maple and spruce (60 cm × 30 cm × 0.5 mm thick) was immersed in this bleaching solution at 40 ° C. for 60 minutes. The veneer after the bleaching treatment was pulled up, immersed in warm water of 60 ° C. for 10 minutes, and further washed with running water for 10 minutes. Next, the washed veneer was dried on a hot plate at 80 ° C. for 5 minutes to adjust the water content of the wood material to 12%.
[0025]
The dried veneer was acetylated with acetic anhydride for 50 minutes at 150 ° C. using a gas phase acetylation apparatus (manufactured by Sumitomo Chemical Engineering Co., Ltd.). And removed. The degree of acetylation of the veneer was 13% in terms of weight percentage gain (WPG).
The treated veneer was subjected to the following light resistance test, and the color difference before and after the test was measured. Table 1 shows the results.
[0026]
(Light resistance test)
Using a xenon fade meter (a color difference meter manufactured by Suga Test Instruments Co., Ltd.) as a test device, the wood material was continuously irradiated, and L * , a * , b before and after irradiation in the L * a * b * color system * , The respective differences ΔL * , Δa * , Δb * were determined, and the color difference ΔE * ab was calculated from the following equation.
ΔE * ab = [(ΔL * ) 2 + (Δa * ) 2 + (Δb * ) 2 ] 1/2
(Test condition)
Colorimetry at the time of the light source: D 65
Integrated light amount: 11 MJ / m 2
Black panel temperature: 83 ° C
[0027]
(Example 2)
A maple veneer (60 cm × 30 cm × 0.5 mm thick) was acetylated in the same manner as in Example 1, and after the treatment, unreacted acetic anhydride was removed by suction. The acetylation degree of the veneer was 14% in terms of weight increase.
The acetylated veneer was immersed in the same bleaching solution as in Example 1 at 40 ° C. for 60 minutes. The veneer after the bleaching treatment was pulled up, immersed in warm water of 60 ° C. for 10 minutes, and further washed with running water for 10 minutes. Next, the washed veneer was dried on a hot plate at 80 ° C. for 5 minutes.
The treated veneer was subjected to a light resistance test in the same manner as in Example 1, and the color difference before and after the test was measured. Table 1 shows the results.
[0028]
(Comparative Example 1)
A single maple plate (60 cm × 30 cm × 0.5 mm thick) was immersed in the same bleaching solution as in Example 1 at 40 ° C. for 60 minutes. The veneer after the bleaching treatment was pulled up, immersed in warm water of 60 ° C. for 10 minutes, and further washed with running water for 10 minutes. Next, the washed veneer was dried on a hot plate at 80 ° C. for 5 minutes to adjust the water content of the wood material to 12%.
The bleached veneer was subjected to a light resistance test in the same manner as in Example 1, and the color difference before and after the test was measured. Table 1 shows the results.
[0029]
(Comparative Example 2)
A maple or spruce veneer (60 cm × 30 cm × 0.5 mm thick) was acetylated in the same manner as in Example 1, and after the treatment, unreacted acetic anhydride was removed by suction. The acetylation degree of the veneer was 14% in terms of weight increase.
The acetylated veneer was subjected to a light resistance test in the same manner as in Example 1, and the color difference before and after the test was measured. Table 1 shows the results.
[0030]
[Table 1]
(Example 3, Comparative Example 3)
To 1 L of an aqueous solution of about 0.2 N sodium hydroxide, 50 cc of a 35% by weight aqueous hydrogen peroxide solution was added to prepare a bleaching solution. Thickness 0.2mm maple veneer was prepared eight, for these six is a 5-minute 40 ° C., respectively (Comparative Example 3-2), 10 minutes (Example 3-1), 20 minutes (Working example 3-2), 30 minutes (example 3-3), 60 minutes (example 3-4) and 120 minutes (example 3 5) was subjected to immersing the bleaching. Also, of the two remaining, likewise 40 ° C. for one, subjected to a bleaching treatment of 120 minutes (Example 3-6), was not subjected to a bleaching treatment in a single (Comparative Example 3-1). The maple cosmetic material after the bleaching treatment was immersed in warm water of 70 to 80 ° C. for 30 minutes, and further washed with running water for 10 minutes. Next, the washed veneer was dried on a hot plate at 80 ° C. for 5 minutes.
[0032]
The dried maple decorative material (Examples 3-1 to 3-5 , Comparative Examples 3-1 to 3-2 ) was treated with acetic anhydride for 60 minutes at 160 ° C. using a gas-phase acetylation treatment apparatus. Acetylation treatment was performed. The degree of acetylation of the maple decorative material was estimated to be 5 to 15% by weight increase rate.
Also, the maple decorative material of Example 3-6, was subjected twice the same acetylation process. The degree of acetylation of this maple decorative material was estimated to be 15 to 25% by weight increase rate.
The treated maple decorative material was subjected to a light resistance test in the same manner as in Example 1, and the color difference before and after the test was measured. Table 2 shows the results. In the color difference column, ◎ indicates that the color difference is less than 4, O indicates that the color difference is 4 to 7, Δ indicates 8 to 10, and X indicates that the color difference exceeds 10.
[0033]
[Table 2]
(Example 4)
A bleaching treatment and an acetylation treatment were performed in the same manner as in Example 3 except that a walnut decorative material having a thickness of 0.2 mm was used. A light resistance test was performed in the same manner as in Example 1, and the color difference before and after the test was measured. In the case of walnut decorative material, the color difference was 7 or less when the bleaching treatment time was 60 minutes or more, and a favorable effect on light discoloration was recognized.
[0035]
【The invention's effect】
As described above, the processing method of the wood material of the present invention, the wood material made of veneer, treatment temperature 30 ° C. to 50 ° C., bleaching processing time 10 min to 200 min and, phenolic in wooden material Since this is a treatment method in which a hydroxyl group is replaced with another group, color return (darkening) of the wood material due to light or heat after the bleaching treatment can be significantly suppressed.
Further, if the substitution treatment is any treatment selected from the group consisting of an acetylation treatment, an oligoesterification treatment, an etherification treatment, and a formalization treatment, such effects are efficiently exhibited.
Further, if the replacement treatment is performed after the bleaching treatment of the wood material, a part of the portion substituted by other groups of the wood material is not hydrolyzed by alkali during the bleaching treatment. It is possible to efficiently process wood materials.
[0036]
Further, if the wood material is washed between the bleaching treatment and the replacement treatment, it is possible to suppress the adverse effect on the coating film and the like due to the residual hydrogen peroxide and the like. In addition, if the wood material is dried after the washing, wasteful consumption of the acetylating agent due to residual water can be suppressed during the acetylation treatment.
In addition, when the substitution treatment is an acetylation treatment and the degree of acetylation of the wood material is 5% or more, both color return (darkening) and color omission (lightening) of the wood material can be suppressed, Moreover, the effect of suppressing color return is further enhanced.
Claims (5)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001370434A JP3567924B2 (en) | 2000-12-04 | 2001-12-04 | Wood treatment method |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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| JP2001370434A JP3567924B2 (en) | 2000-12-04 | 2001-12-04 | Wood treatment method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR101993781B1 (en) * | 2018-11-06 | 2019-07-01 | 주식회사휴플러스 | Method for decoloring merbau and device thereof |
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| US20100331531A1 (en) * | 2009-06-25 | 2010-12-30 | Eastman Chemical Company | Methods for esterifying lignocellulosic material |
| KR102634404B1 (en) * | 2018-10-19 | 2024-02-06 | 현대자동차주식회사 | The method for inhibiting discoloration of real wood veneer for vehicle interior materials |
| CN114454280B (en) * | 2022-02-15 | 2023-05-23 | 浙江农林大学 | Method for adjusting chromatic aberration of wood veneer |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR101993781B1 (en) * | 2018-11-06 | 2019-07-01 | 주식회사휴플러스 | Method for decoloring merbau and device thereof |
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