JP4560219B2

JP4560219B2 - Buffer for glass substrate

Info

Publication number: JP4560219B2
Application number: JP2001005938A
Authority: JP
Inventors: 逸男浜田; 康上田
Original assignee: Asahi Kasei Chemicals Corp
Current assignee: Asahi Kasei Chemicals Corp
Priority date: 2001-01-15
Filing date: 2001-01-15
Publication date: 2010-10-13
Anticipated expiration: 2021-01-15
Also published as: JP2002211678A

Description

【０００１】
【発明の属する技術分野】
本発明は、ガラス基板、及びその基板上に各種半導体装置、例えば薄膜トランジスタ等の電子機能素子を装着した液晶表示用装置の半完成品やカラーフィルター或いはプラズマ表示装置の半完成品等（以下、これらを総称してガラス基板という。）を、輸送時の落下衝撃や振動衝撃等による損傷から保護するために用いられる合成樹脂発泡粒子の型内成形体からなるガラス基板用緩衝体に関するものである。
【０００２】
【従来の技術】
近年、電子・電気関連機器、特にパーソナルコンピューターの周辺機器の一つである液晶表示装置やプラズマ表示装置、及び携帯電話に代表される携帯端末等は、インターネットに代表される情報技術産業の発達と共に生産量が急激な勢いで伸長している機器であり、その梱包や輸送等に用いられる優れた緩衝体の開発が強く望まれている。
中でも半導体装置等の電子部品を組み込んだガラス基板、例えばカラーフィルターガラス基板やＴＦＴガラス基板、及び液晶パネル基板等のガラス基板は、薄く、輸送中における衝撃や振動等に弱い上、その構成が非常にデリケートなため、外部からの影響を受けやすく、取り扱いが難しい。
とりわけ、加工前のガラス基板や最終製品になる前の半完成品を輸送する場合には、剥き出しの状態で扱われるため静電気や塵、埃等の影響をより強く受け、その機能を損傷する場合があった。
【０００３】
そこで、ガラス基板を損傷することなく安全に輸送するための梱包技術が多々提案されている。
その代表例を以下に紹介する。
図１〜３は、従来のガラス基板用緩衝体の具体例である。
図１〜２は、特開平０５−３１９４５６号公報に開示されている技術内容で、その要点は断面が略Ｌ字形を呈し、該Ｌ字形に沿って内側には基板挿入溝を複数本設けたガラス基板用緩衝体を用いる例である。
図中４はガラス基板、１はガラス基板用緩衝体であり、例えば発泡倍率が少なくとも５倍以上、圧縮強度が０．０８８ＭＰａ以上、０．３０４ＭＰａ以下のポリオレフィン系発泡ビーズの型内成形体から構成されるものである。
ガラス基板の梱包に当たっては、複数のガラス基板４を所定の間隔をもって平行配置して立方体を形成し、各基板の角部をそれぞれ上記ガラス基板用緩衝体１のガラス基板挿入溝２に挿入して、固定する。
更に、上記緩衝体１の外側に固定具案内溝３を少なくとも１本設け、これにゴム、テープ等の固定具５を案内して固定し、梱包する。
【０００４】
一方、図３は、特許第２５５２６２５号公報に開示されている箱体形状で、本体部６内面の相対向する一対の面に、ガラス基板挿入溝７を複数本設けたポリオレフィン系発泡ビーズの型内成形体よりなるガラス基板用緩衝体を用いる例である。
このガラス基板用緩衝体は、単にガラス基板を手動又は自動機により、箱体本体部６の内面のガラス基板挿入溝７へ装着するだけでよく、８は本体部６に嵌合する蓋体である。
又、緩衝体の内外両表面から１ｍｍ深さに至る部分の密度を壁内部の密度よりも１．５倍以上としたスキン構造を形成させることによって、発塵性や強度及び耐水性等の緩衝体特性を高める技術手段も開示されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、図１、図３に示したようなガラス基板用緩衝体では、ガラス基板４を該挿入溝２，７に挿入する際、或いは輸送時の振動等により、該挿入溝２，７とガラス基板４とが摺擦し合い、上記のように壁内部の密度よりも１．５倍以上とするスキン構造の手段を講じたとしても未だ満足されるものではなく、微細な粉塵を多量に生じ易く、これがガラス基板や電子部品等に付着して、表面の機能を損傷するといった問題があった。
そこで、本発明者は、上記効果が発現しなかった理由を追試し考察した結果、下記の結論に至った。即ち、
前記公報の明細書に記載されているように、上記スキン構造は、型内成形時に金型内に充填されたポリエチレン予備発泡粒子を加熱水蒸気で加熱して発泡膨張、融着させた後、更に温度６０℃で後加熱を行って形成させたものである。
【０００６】
そして、この型内成形体の表面近傍の断面を電子顕微鏡で観察したところ、温度６０℃で後加熱を行わない一般的な型内成形方法で得たものと樹脂皮膜厚さ、即ちスキン層厚さは実質上同じであった。
この観察より、上記スキン構造は、金型と接触している表面近傍の予備発泡粒子が後加熱で押圧され、内部に位置する発泡粒子と同水準の発泡膨張性が生じなかった（換言すれば、発泡倍率が上がらなかった）だけの効果に過ぎず、依然として発塵性の問題点が潜在していると考えられる。
又、ガラス基板用緩衝体は梱包コストの低減を図るために一回の使用で使い捨てにせず、何回も繰返し使用することが行われている。
その際、上記粉塵の他、輸送過程や保管時に上記緩衝体に付着した大気中の塵、埃等のガラス基板に有害な微粒子を一掃するために、入念に洗浄して再使用される。
【０００７】
しかしながら、従来のガラス基板用緩衝体は、その表面特性からこの有害な粉塵等が合成樹脂発泡粒子間の空隙に蓄積し易く、これを完全に洗浄除去するのが困難であり、然も大量の洗浄水を消費し洗浄効率が極めて悪かった。
その上、大量に洗浄水を消費しても完全に洗浄除去できない粉塵等がかなりの量発泡粒子間の空隙に残存してしまい、再び有害な微粒子となる問題もあった。
加えて、洗浄水は、一般的に５０℃の温水が用いられるので、容易に合成樹脂発泡粒子間の空隙に毛管現象でその奥深部にまで浸透するので、その後の乾燥処理に長時間を要し不経済である。
【０００８】
本発明は、上記従来技術の課題解決に鑑み、型内成形体からなる合成樹脂発泡粒子の気泡構造と該成形体表面特性の相互関連性を長年に渡って綿密に解析研究した結果完成されたものである。
その目的は、落下衝撃等の外力が加わってもガラス基板が破損することがなく、然もガラス基板の取り扱い時や輸送時の振動等でガラス基板と摺擦しても容易に粉塵を生せず、然も少量の洗浄水で短時間に完全に塵埃を除去でき、乾燥時間も短時間で済む等経済性が高く、更に圧縮変形や曲げ変形等の外力が加わっても回復率が大きく、耐久性に優れ、何回でも繰返し再使用ができるガラス基板用緩衝体を提供することである。
【０００９】
【課題を解決するための手段】
本発明は、
（１）合成樹脂発泡粒子からなる型内成形体であって、気泡径が５０〜１１００μｍであり、且つ外殻スキン厚みが８〜５０μｍである発泡粒子から構成され、然も該成形体の空隙率が３％以下で、且つ発塵性が５０ｍｇ以下であることを特徴とするガラス基板用緩衝体であり、
（２）合成樹脂発泡粒子がポリオレフィン系樹脂であることを特徴とする（１）に記載のガラス基板用緩衝体であり、
（３）型内成形体の回復率が６５％以上であることを特徴とする（１）又は（２）に記載のガラス基板用緩衝体てあり、
（４）型内成形体の断面が略Ｌ字形状を呈し、該形状に沿って内側にはガラス基板の挿入溝が平行に複数本設けられていることを特徴とする（１）〜（３）のいずれかに記載のガラス基板用緩衝体であり、
（５）型内成形体が、有底の本体部および蓋体、又は無底の本体部、底体および蓋体から構成された箱体形状であって、該本体部内面の相対向する一対の面及び各底体には、複数枚のガラス基板を支持する挿入溝が設けられていることを特徴とする（１）〜（３）のいずれかに記載のガラス基板用緩衝体を構成要件とするものである。
【００１０】
以下に、本発明を詳細に説明する。
「発塵性」とは、ＪＩＳＫ７２０４に規定のように、型内成形体の表面を摩耗輪で摩耗試験した時に離脱した該成形体の質量を示すものであり（定義）、該発塵性は、５０ｍｇ以下、好ましくは４０ｍｇ以下である。
該発塵性は少ない程良いが、１ｍｇ未満とすることは技術的に困難であり、又、５０ｍｇを越えるとガラス基板との僅かな摺擦でも型内成形体表面が容易に削り取られてガラス基板用緩衝体として用いることが実質不可能である。
【００１１】
この発塵性は、合成樹脂の種類や発泡粒子の気泡構造、即ち平均気泡径と外郭スキン厚み、及び型内成形体の倍率等の多数の因子に依存し、これらは、下記に示すような最適な範囲に設定することで、初めて該発塵性を５０ｍｇ以下に設定できる。
合成樹脂の種類は、公知の方法で発泡粒子が得られる樹脂であれば、特に限定されるものでないが、樹脂自体の摩擦抵抗から低・中・高・超高密度や直鎖状のポリエチレン樹脂、ポリプロピレン樹脂、メタロセン系触媒により製造されるポリエチレン系樹脂、ポリプロピレン系樹脂、共重合成分がエチレン、ブテン−１、４−メチルペンテン−１等とプロピレンとの共重合樹脂等で無架橋又は架橋されたポリオレフィン系樹脂単独や、その２種以上の混合樹脂が好ましい。
又、ポリスチレン樹脂、ハイインパクトポリスチレン樹脂、アクリロニトリル−スチレン共重合樹脂、アクリロニトリル−ブタジエン−スチレン共重合樹脂等のスチレン系樹脂のように硬質樹脂の場合は、脂肪族炭化水素系、脂肪酸アミド系、脂肪酸エステル系等の滑剤を適量添加して摩擦抵抗を軽減することで使用することもできる。
【００１２】
これらの樹脂粒子を公知の方法にて、揮発型発泡剤を含浸後、水蒸気で加熱発泡して発泡粒子とした後、或いはこの発泡粒子の発泡倍率を更に高めるために膨張能付与処理を行って水蒸気で加熱発泡する等した後、これらの発泡粒子を所望とするガラス基板用緩衝体の型内に充填し、水蒸気加熱で発泡粒子相互を膨張、融着させた後、冷却する。
このようにして得られる型内成形体の気泡構造は、例えば合成樹脂がポリオレフィン系樹脂である場合には、平均気泡径が５０〜１１００μｍ、好ましくは１００〜９００μｍ、更に好ましくは１５０〜８００μｍである。
【００１３】
平均気泡径が５０μ未満であると、図４に示すように型内成形体表面９の平滑度が著しく高まり、その結果、ガラス基板と該成形体表面との間隙が殆どなくなる状態となって、ガラス基板が密着してしまうために摩擦抵抗が大きくなり、発塵性が大きくなると共に、発泡粒子１個内の気泡数が無数に存在して気泡壁の厚みが極薄となるためにピンホール等の微小欠陥が生じ易くなり、その結果、型内成形時の加熱で充分な発泡膨張性が発現せず、得られる型内成形体は発泡粒子間に空隙が発生し、ヒケたりして外観品位に劣った成形体しか得られなくなる。
又、平均気泡径が１１００μｍを越えると発泡粒子の表面形状が金平糖のように凹凸状となって、図５に示すように型内成形体の表面は平滑性が悪くなり、ガラス基板を梱包し輸送する工程での振動等で、摩耗し易くなって発塵性が大きくなる。
該気泡径の調整は、従来公知のタルク、カオリン、クレー、シリカ、炭酸カルシウム等の無機系造核剤をポリオレフィン系樹脂中に０．１〜３重量％の範囲て添加混合して調整できる。
【００１４】
しかしながら、これらの無機系造核剤は、一種の研磨剤でありガラス基板の表面を傷付ける恐れがあることから、ポリオレフィン系樹脂の軟化温度以上の温度で固体である有機系造核剤、例えばフッ素樹脂、シリコーン樹脂、熱可塑性ポリエステル樹脂の微粉末やステアリン酸カルシウム、ステアリン酸亜鉛等の高級脂肪酸金属塩等を上記添加量で使用することが好ましく、更に、好ましくは揮発型発泡剤を樹脂粒子に含浸する前の樹脂中の水分量を０．０１〜０．７重量％の範囲で調節する手段である。
水分量が０．０１重量％未満では、平均気泡径が１１００μｍを越えてしまい、又、水分量が０．７重量％を越えると平均気泡径が５０μｍ未満の微細で不均一な気泡しか得られず、型内成形体とした場合に、発塵性は勿論のこと外観品位や圧縮強度等も満足しなくなる。
尚、該水分量で気泡径を制御する場合、無機系造核剤の添加量が０．１重量％以下であれば該造核剤を併用してもガラス基板の傷付き性は実用上問題がない。
【００１５】
更に、平均気泡径が５０〜１１００μｍの範囲であっても、発泡粒子の外郭スキン厚みが８〜５０μｍでないと上記の発塵性を満足しなくなる。発泡粒子の外郭スキン厚みが８μｍ未満であると、取り扱い時の衝撃や輸送時の振動等でガラス基板と摺擦しあった場合に、型内成形体表面、即ち発泡粒子表面が外力で損傷を受け、容易に発泡粒子内部まで摩耗してしまい、発塵性が５０ｍｇを越えてしまう結果となる。
又、外郭スキン厚みが５０μｍを越えると、図５のような凹凸状の表面状態となり易く、型内成形体の表面が平滑でなくなり、然も硬い樹脂層の凸凹状表面であることからガラス基板との摺擦で削られ易くなり、必然的に発塵性が４０ｍｇを越えてしまう。
【００１６】
該外郭スキン厚みの調節は、合成樹脂の樹脂粒子に揮発型発泡剤を含浸した後、加熱水蒸気で加熱発泡して発泡粒子とする工程に於いて、先ず粒子表面の発泡剤を優先的に揮発させた後、融点近傍まで加熱し発泡を起こさせる多段階昇温加熱の発泡手段を採用することによりなし得る。
多段階昇温加熱の昇温パターンは、得ようとする外郭スキン厚みの水準によって、又、合成樹脂の種類、揮発型発泡剤種、発泡剤含浸量、発泡粒子倍率等を鑑みて２〜４段の昇温パターンを決定すれば良い。
例えば、樹脂の融点マイナス４０℃〜マイナス１２℃の範囲の温度まで昇温した後、この温度下で３〜１５秒間保持して粒子表面の発泡剤を優先的に揮発させた後、融点マイナス８℃〜マイナス１℃の温度に１５〜４５秒かけて昇温し、更にこの温度下で１〜２０秒間保持して所望とする外郭スキン厚み、発泡倍率の発泡粒子とすることができる。
以上のように、本発明の主要点は、上記の平均気泡径と外殻スキン厚みの二つの要件を同時に満足することである。
【００１７】
更に、型内成形体の発泡倍率を４〜３０ｃｍ³／ｇ、好ましくは５〜２５ｃｍ³／ｇ、更に好ましくは６〜２０ｃｍ³／ｇとすることで耐発塵性が向上される。
合成樹脂の種類、特にポリオレフィン系樹脂の場合は、共重合成分がエチレン、ブテン−１、４−メチルペンテン−１等とプロピレンとのランダム共重合樹脂が発泡、成形加工性に優れると共に高剛性であることから、発泡倍率に対する圧縮強度がポリエチレン樹脂の型内成形体より高くなるので好ましい。
又、該発泡倍率については、ガラス基板用緩衝体として用いられる場合に発生する衝撃や輸送時の振動等の外力で変形しない剛性が必要であるとの観点から、具体的には該緩衝体のデザインやガラス基板の寸法、収納枚数等に応じて、４〜３０ｃｍ³／ｇの発泡倍率とすれば良い。
発泡倍率が４ｃｍ³／ｇ未満であると剛性は高いが重量が重くなり、取り扱い荷役作業が困難になるばかりか、成形体の圧縮強度が高いために硬くなり、衝撃の吸収力が低く、輸送振動時の保護性も不充分となる。
【００１８】
一方、発泡倍率が３０ｃｍ³／ｇを越えると重量は軽くなるが圧縮強度が余りにも低くなり過ぎて、取り扱い作業時の衝撃等で割れや傷が発生し易くなって、繰り返し再利用に耐えられなくなるばかりか、ガラス基板収納時の荷重で沈み込みやヘタリ現象も大きくなり、ガラス基板の固定性が弱まりガラス基板の搬送性に支障をきたす。
「空隙率」とは、型内成形体表面の発泡粒子間の空隙発生度合いを表すもので、（プラニメーター法）によって測定される値をいう（定義）。
該空隙率は３％以下、好ましくは１．８％以下である。
該空隙率は小さい程良いが、０．０１％未満にすることは型内成形体の製法上、技術的に困難である。
【００１９】
又、該空隙率が３％を越えると、型内成形体の吸水現象が２次式的挙動を示して極度に大きくなり、繰返し再使用する際に行う洗浄時の洗浄水が５０℃の温水であることから、それが多量に発泡粒子間の空隙部から毛管現象で型成形体内部の奥深部にまで浸透してしまい、洗浄後の乾燥に長時間を要する。
洗浄後の乾燥時間が不充分であると、型内成形体中から蒸発した水蒸気がガラス基板表面で結露し、水滴痕の発生や電子回路の損傷等、該基板の機能的信頼性を損なう恐れがある。
更に、該空隙率が３％を越えると、乾燥に長時間を要すること以外に致命的な問題点も発生する。
即ち、該空隙部には、ガラス基板取り扱い時の衝撃や輸送中の振動によって発生した型内成形体の摩耗発塵物は勿論のこと、外部の塵埃が該空隙部に付着蓄積し、これを洗浄時に完全に洗浄除去できなくなる。
【００２０】
該空隙率の調節は、下記に示すように、型内成形用の金型や成形加工時の各工程条件等をそれぞれ最良化することによりなし得る。
金型には、型内への発泡粒子の充填を均一に行うことと、型内に充填された発泡粒子、特に深部の発泡粒子を充分に加熱するための工夫が必要である。
このためには、加熱水蒸気を導入する溝や小孔を複数設けた、直径が６〜１２ｍｍのコアベントが金型全面に渡って無数に配設される。
しかし、該コアベントの配設は、その中心間距離でコアベント直径の１．５〜４．５倍、好ましくは、２〜４倍の距離でもって配設しなければならない。
該距離が１．５倍未満では、それ以上の効果が得られないばかりか、金型の強度が低下する。該距離が４．５倍を越えると、充填性と加熱が不充分且つ、不均一となって発泡粒子間の空隙が３％を越えてしまう。
【００２１】
型内成形体は、一般に複雑な形状をしていて、且つ各所で厚みが異なることが多いために、充填や加熱が不均一となり易い。
そのため、上記コアベントの配設は、各部位の厚みに適切なコアベント直径とその中心間距離で金型に打設すべきである。例えば、コアベント配設の中心間距離は、厚みが薄い（１０〜２０ｍｍ）部位では３〜４．５倍、厚い部位には１．５〜３倍の値でもって配設し、均一加熱が行われるようにする。
又、型内成形体の偏肉比（最大肉厚／最小肉厚）も４以下、好ましくは３．５以下になるように型内成形体のデザインを決定すると共に、厚肉部は部分的に肉盗みを行ない偏肉比を低くしたりする。
この場合の最大肉厚、最小肉厚は当該部の内部に想定した最大の球の直径の最大値又は最小値をいう。
【００２２】
型内成形加工時の各工程条件の最良化について、ポリオレフィン系樹脂発泡粒子を例に具体的に述べると、先ず、発泡粒子の倍率、型内成形体の最大厚み、偏肉比等を鑑みて、該粒子内圧の付与処理や金型への圧縮充填率を最適にすることである。これらが不適であると詳細に加熱条件を最良化しても充分な発泡膨張力が生じず、空隙率が大きくなったり、或いは逆に余りにも発泡膨張力が高まり過ぎると発泡粒子間の融着が発現せず良好な型内成形体が得られなくなる。
次に加熱工程、即ち金型加熱、一方加熱、逆一方加熱、一方の型のみ水蒸気を導入し、もう一方の型から排気を行なう加熱方法等の予備加熱と本加熱に於ける加熱水蒸気圧力及び加熱時間の最適化は、発泡粒子の融点、倍率と型内成形体のデザインに関する最大厚み、偏肉比等を鑑みてなされなければならない。
型内に充填された発泡粒子は、上記加熱工程の最的化により発泡膨張力が高まった状態とされる。
【００２３】
ところで、この発泡膨張力が発現するのは、本加熱終了後に型内が大気放圧された時の外圧力変化によってであり、その結果、発泡粒子相互が発泡膨張して、融着一体化する。
したがって、この大気放圧後、水冷却工程に至る迄の高温下での放置時間が短いと発泡粒子がもつ発泡膨張力が完全に生じない状態で冷却硬化されるため、特に金型と接触している発泡粒子、即ち型内成形体表面は発泡粒子間の空隙率が大きいものとなる。
以上の理由から、該放置時間は、好ましくは３〜４５秒、更に好ましくは５〜３０秒である。
【００２４】
「回復率」とは、型内成形体に瞬間的な圧縮荷重が加わった場合に、元の厚さまで復元しょうとする度合いを表すものであり（定義）、該回復率は、６５％以上、好ましくは７５％以上である。
ガラス基板用緩衝体は、繰返し再使用される耐久性が求められるが、該回復率が６５％未満であると取り扱い時や輸送時に発生する振動、落下衝撃等の外力で該緩衝体が変形した場合の回復性が劣るため、ガラス基板の保護緩衝機能が低下したり、又、ガラス基板の固定性が弱まってガタツキが生じることから発塵性も大きくなる。
該回復率を６５％以上とするためには、柔軟で伸長性が高いポリオレフィン系樹脂が好ましい。
【００２５】
本発明の型内成形体は、例えば図１に示すような断面が略Ｌ字形（なお、この「略Ｌ字形」は「Ｌ字形」及び「Ｌ字形」に近似する形状を包含する）の構造、或いは図３に示すようなボックス形状の構造に型内成形してガラス基板用緩衝体として利用される。
該型内成形体の成形方法としては、一般の合成樹脂発泡粒子の成形技術、例えば、合成樹脂がポリオレフィン系樹脂の場合には、該発泡粒子内にはポリスチレン発泡粒子のように炭化水素系の揮発型発泡剤を多量に含有していないために、加熱水蒸気による加熱で充分な発泡膨張力を発現させる手段を講じる必要がある。
その手段としては、特公昭５３−３３９６号公報及び特公昭５１−２２９５１号公報に開示されている成形方法が利用される。
【００２６】
即ち、前者は、発泡粒子を元の見掛けの嵩容積の８０％以下にガス圧力で圧縮して、金型内に圧縮充填し加熱融着させた後、冷却して金型より取り出す成形方法であり、後者は、発泡粒子に無機ガスで１．１８気圧以上のガス圧力を発泡粒子内に付与した後、金型内に充填し、加熱して発泡粒子を発泡させ、粒子相互を融着させ後、冷却して金型より取り出す成形方法である。
両者の方法で得られた型内成形体は、ともに温度が７０〜９０℃で８〜２４時間かけて乾燥される。
次に、本発明で用いる特性値及び評価方法を以下に示す。
【００２７】
【発泡粒子の特性値】
１）発泡倍率；
重量（ｇ）既知の発泡粒子の体積（ｃｍ³）を水没法で測定し、その体積を重量で除した値を発泡倍率（ｃｍ³／ｇ）とする。尚、評価は３回測定の平均値とする。
【型内成型体の特性値】
２）発泡倍率；
重量（ｇ）既知の型内発泡成形体の体積（ｃｍ³）を水没法で測定し、その体積を重量で除した値を発泡倍率（ｃｍ³／ｇ）とする。
【００２８】
３）気泡径；
型内成形体を構成する発泡粒子の中の、ある特定発泡粒子の切断面で気泡径を測定し、この測定値を用いると、その粒子全体の気泡径を正しく表現したものにはならない。
それは、気泡を球状と想定した場合に、切断面に並んで見える気泡は、気泡の最大径（＝直径）で切断されたものや、最大径よりよりも小さい部分で切断された気泡が混在して配列されているからである。
従って、本発明の気泡径は、下記の方法で評価した値を気泡径とする。
【００２９】
（測定方法）
型内成形体を鋭利な刃物で厚さ方向に切断し、該成形体の表面（金型接触部）に位置する発泡粒子切断面を拡大投影機で拡大（倍率；２０〜８０倍）し、当該投影面上の任意の箇所に一定長の計測線（Ｌ）を描き、当該計測線上を横切る（接する）気泡壁の数（Ｎ）を計測し、下記の統計式（１）により気泡径（Ｃ：μｍ）を算出する。尚、評価は発泡粒子１０個の平均値とする。
【式１】

【００３０】
４）外郭スキン厚み；
型内成形体を鋭利な刃物で厚さ方向に切断し、該切断面を真空下で金蒸着処理して、透過型電子顕微鏡（拡大率：２５０倍）を用いて該発泡粒子の外殻スキン近傍（金型接触部）を撮像（３箇所）し、外郭スキン厚みＴ（μｍ）を測定する。尚、評価は発泡粒子５個（ｎ数は１５個）の平均値とする。
５）空隙率；
型内成形体の表面（面積：７ｃｍ×５ｃｍ）を黒色油性ペン（マークス、商品名；（株）ライオン事務器製）で均一に全面塗布し、この塗布面をレーザー式複写機（ドキュセンター４５１ＣＰ、商品名；富士ゼロックス（株）製）で４倍拡大複写して型内成形体表面の拡大画像を作成する。
【００３１】
上記拡大画像を画像処理装置（カラーイメージプロセッサＳＰＩＣＣＡ−ＩＩ、商品名；日本アビニクス社製）に入力して濃淡画像処理、２値化画像処理して、発泡粒子間の空隙部（白色部）全面積（ｍｍ²）を測定し、次式（２）より空隙率Ｂ（％）を算出する。
尚、評価は試験片３個の平均値とする。但し、コアベント（蒸気導入孔）部は非空隙部として処理した。
【式２】

【００３２】
６）発塵性
型内成形体の表面より厚さ３ｍｍ、直径が１２０ｍｍの平坦な試験片を切り出し、該試験片に乾燥空気を吹き付けて付着している切り粉を完全に除去後、テーバー摩耗試験機（ロータリーアブレージョンテスタ、商品名；（株）東洋精機製作所製）を用いて、ＪＩＳＫ７２０４の方法で該試験片成形スキン面の摩耗質量（ｍｇ）を測定した。
尚、評価は試験片３個の平均値とする。
【００３３】
７）回復率；
型内成形体より幅、長さが５０ｍｍ、厚みが２０ｍｍの平坦な試験片を切り出し、島津製作所社製の圧縮試験装置オートグラフＡＧ−５０００Ｄを用いて、１０ｍｍ／分の圧縮速度で型内成形体厚さの５０％迄圧縮した後、直ちに同速度で荷重がゼロになるまで取り除き、荷重がゼロになった瞬間の厚さを測定し、次式（３）より回復率Ｒ（％）を算出し評価する。
【式３】

【００３４】
８）圧縮特性；
型内成形体より幅、長さが５０ｍｍ、厚みが２０ｍｍの平坦な試験片を切り出し、島津製作所社製の圧縮試験装置オートグラフＡＧ−５０００Ｄを用いて、１０ｍｍ／分の圧縮速度で圧縮したときの応力を示すもので、２５％歪下の応力を圧縮強度とし、ＪＩＳＺ−０２３５の試験方法により評価する。
（評価尺度）
【表１】

【００３５】
９）繰返し耐久性
型内成形体より幅、長さが５０ｍｍ、厚みが２０ｍｍの平坦な試験片を切り出し、ＪＩＳＫ６７６７の試験方法に規定する繰返し圧縮永久ひずみを測定し、評価する。
（評価尺度）
【表２】

【００３６】
１０）洗浄性；
内寸法１０．５ｃｍ×１０．５ｃｍ角の試験用アクリル製型枠を作成し、当該型枠内に事務複写用上質紙を敷きその上に煙草の灰（乳鉢で微粉体状に擂りつぶしたもの）２５０ｍｇを均一に振りかけ、この試験冶具内に型内成形体（面積：１０ｃｍ×１０ｃｍ）を挿入し、更に当該成形体上に応力が０．０１ｋｇ／ｃｍ²になるように鉄製荷重板を載せ、この試験冶具を水平振動機テーブル上に固定し、振動試験（振幅１０ｍｍ、振動数５Ｈｚ、加振時間５分）を実施した。
その後、５０℃の水（水量：２０リットル／分）で、３分間該成形体表面に付着している煙草の灰をシャワー洗浄し、その後５０℃の熱風循環式恒温槽に４時間放置し乾燥させた。
この型内成形体表面を拡大装置（倍率：２０倍）で観察し、発泡粒子間の空隙に洗浄しきれず残留している煙草の灰の状況で評価する。
【００３７】
（評価尺度）
【表３】

【００３８】
１１）吸水性；
型内成形体の表面に５０℃の水（水量：２０リットル／分）を、３分間シャワーリングした後、該型内成形体の表面に付着している水分を乾燥空気を吹き付けて除去した後、重量を測定し、次式（４）より吸水率Ｗ（重量％）を算出し評価する。
【式４】

【００３９】
（評価尺度）
【表４】

【００４０】
１２）乾燥性；
型内成形体の表面に５０℃の水（水量：２０リットル／分）を、３分間シャワーリングした後、該型内成形体の表面に付着している水分を乾燥空気を吹き付けて除去した後、５０℃の熱風循環式恒温槽に４時間放置し乾燥させた後、室温に取り出して２４時間放置後に重量を測定し、次式（５）より含水率Ｗ（重量％）を算出し評価する。
【式５】

【００４１】
（評価尺度）
【表５】

次に、本発明を具体的な実施例を用いて更に詳しく説明するが、本発明はこれらの実施例に限定されないことはいうまでもない。
【００４２】
【実施例１〜３、比較例１〜２】
低密度ポリエチレン（サンテックＬＤ、商品名；旭化成工業（株）製、密度０．９３０ｇ／ｃｍ³、メルトインデックス２．４ｇ／１０分、融点１１７℃）の裁断品に、以下に示す組成の水懸濁系で架橋剤を１２０℃で３０分間含浸させた後、更に１６０℃で４０分間加熱してゲル分率６２％（沸騰トルエン×８時間）、平均粒径１．１ｍｍの架橋低密度ポリエチレン樹脂粒子とした。
低密度ポリエチレン裁断品１００重量部（基準）
架橋剤；ジクミルパーオキサイド０．７重量部
融着防止剤；第三リン酸カルシウム３．５重量部
懸濁剤；ドデシルベンゼンスルフォン酸ソーダ０．０００２重量部
水；２３０重量部
【００４３】
この樹脂粒子を温度７０℃の流動床乾燥装置で乾燥させ、樹脂粒子中の水分率が０．００８重量％（比較例１）、０．０１重量％（実施例１）、０．３重量％（実施例２）、０．７重量％（実施例３）、０．８重量％（比較例２）の５種類を作成した。これらの樹脂粒子を耐圧容器に収容し、二酸化炭素（気体）を注入し、圧力３．０４ＭＰａ（ゲージ圧）、温度１１℃の加圧下で３時間かけて該樹脂粒子中に二酸化炭素を含浸した。次に、各発泡性樹脂粒子を発泡装置（排気昇温式）に収容して、槽内温度１００℃で５秒間加熱した後、１１４．５℃まで２５秒間かけて昇温し、更にその温度を維持しながら３〜１０秒間水蒸気で加熱発泡し、架橋低密度ポリエチレン発泡粒子を得た。
尚、この発泡粒子の発泡倍率は全て２．６ｃｍ³／ｇとなるように１１５℃の維持時間を調整して発泡した。
【００４４】
次に、この発泡粒子を、加圧（高圧空気）・加温装置を有するオートクレーブ内に収容し、８０℃の温度下で１時間かけて昇圧し、圧力０．９ＭＰａ（ゲージ圧）で８時間保持して発泡粒子の内圧を高める再膨張能処理を行った。
続いて、この発泡粒子を発泡装置に収容して槽内温度１１０〜１１２℃で１０秒間水蒸気で加熱発泡し、発泡倍率が全て４．３ｃｍ³／ｇとなるように、加熱温度を１１０〜１１２℃の範囲で調節して成形用の発泡粒子とした。
この成形用発泡粒子を空気加圧装置（圧力：０．１ＭＰａ（ゲージ圧）、温度：３０℃）に収容して、１６時間かけて再膨張能を付与した後、全自動成形機に搭載された、図２に示すガラス基板用緩衝体（外寸：長さ１６５ｍｍ、幅２３０ｍｍ、高さ２１０ｍｍ、厚さ３０ｍｍ、ガラス基板挿入溝深さ５ｍｍ）成形用の型内成形金型内に充填し、加熱水蒸気で予熱（金型加熱：３秒、一方加熱、逆一方加熱：各５秒）した後、型内圧力０．１２ＭＰａ（ゲージ圧）で８秒間で水蒸気加熱して発泡粒子を膨張、融着させた。
【００４５】
その後、型内を瞬時に大気放圧して発泡体を大気圧下で１０秒間放置した後、冷却し金型内から取り出し、室温が８０℃の乾燥室に１２時間放置して型内成形体を得た。
得られた型内発泡体の発泡倍率は６ｃｍ³／ｇであった。
得られた型内成形体について、前記評価方法により型内成形体特性（外殻スキン厚み、空隙率、発塵性、気泡径、回復率、圧縮特性、繰返し耐久性、洗浄性、吸水性、乾燥性）を評価した。
その結果を次の表１に示す。
表１の結果によると、実施例１〜３の型内成形体は、発塵性は勿論のことガラス基板用緩衝体として具備しなければならない実用特性を全て満たしていることがことが判る。
【００４６】
【表６】

【００４７】
【実施例４〜６、比較例３〜４】
実施例２の架橋低密度ポリエチレン樹脂粒子を用いて、同様に該樹脂粒子中に二酸化炭素を含浸した。次に、この発泡性樹脂粒子を発泡装置（排気昇温式）に収容して、槽内温度９５℃で１５秒間加熱した後、１１５℃までの昇温に７秒（比較例３）、１５秒（実施例４）、３０秒（実施例５）、４５秒（実施例６）秒、６０秒（比較例４）間かけて昇温し、更にその温度を維持しながら５〜１５秒間水蒸気で加熱発泡し、架橋低密度ポリエチレン発泡粒子を得た。
尚、この発泡粒子の発泡倍率は全て２．３ｃｍ³／ｇとなるように１１５℃の維持時間を調整して発泡した。
【００４８】
次に、これらの発泡粒子を加圧（高圧空気）・加温装置を有するオートクレーブ内に収容し、８０℃の温度下で３時間かけて圧力１．５ＭＰａ（ゲージ圧）まで昇圧し、更にこの圧力下で１２時間保持して、発泡粒子の気泡内圧を高める膨張能付与処理を行った後、発泡装置に収容して槽内温度１１３〜１１４．５℃で１０秒間水蒸気で加熱発泡し、発泡倍率が全て１５ｃｍ³／ｇとなるように加熱温度を調節して成形用の発泡粒子とした。
この成形用発泡粒子を空気加圧装置（圧力：０．３ＭＰａ（ゲージ圧）、温度：３０℃）に収容して、１０時間かけて再膨張能を付与した後、実施例１〜３と同様に成形して、発泡倍率が２０ｃｍ³／ｇの型内成形体を得た。
【００４９】
得られた型内成形体について、前記評価方法により型内成形体特性（外殻スキン厚み、空隙率、発塵性、気泡径、回復率、圧縮特性、繰返し耐久性、洗浄性、吸水性、乾燥性）を評価した。
その結果を次の表２に示す。
表２の結果によると、実施例４〜６の型内成形体は、実施例１〜３と同様に発塵性は勿論のことガラス基板用緩衝体として具備しなければならない実用特性を全て満たしていることがことが判る。
【００５０】
【表７】

【００５１】
【発明の効果】
以上述べたことから明らかなように、本発明は、成形体を構成するポリオレフィン系発泡粒子の気泡径が５０〜１１００μｍ、外殻スキン厚みが８〜５０μｍからなり、且つ当該成形体の空隙率が３％以下にすることにより、取り扱い時及び輸送時の傷つき、発塵量が少なく、また通函後の再使用時に実施される成形体洗浄その後の乾燥が容易に出来る、ガラス基板用として好適な型内成形体を提供することができる。
【図面の簡単な説明】
【図１】従来技術（特開平０５−３１９４５６号公報）で得られる緩衝体の斜視図である。
【図２】上記緩衝体を使用したガラス基板梱包体形状を示す図である。
【図３】従来技術（特許番号第２５５２６２５号公報）で得られるガラス基板搬送用ボックスの斜視図である。
【図４】本発明の型内成形体の１例を説明するための断面模式図で、気泡径が小さい状態を示している。
【図５】本発明の型内成形体の１例を説明するための断面模式図で、気泡径が大きい状態を示している。
【図６】本発明の型内成形体の１例を説明するための平面模式図で、成形体を構成する発泡粒子と空隙部の様子を示す図である。
【符号の説明】
１緩衝体
２ガラス基板挿入溝
３固定案内溝
４基板ガラス
５固定具
６ボックス本体
７ガラス基板挿入溝
８ボックス蓋体
９表面方向
１０発泡粒子
１１発泡粒子外殻スキン厚み
１２気泡径
１３成形体空隙部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a glass substrate and a semi-finished product of a liquid crystal display device or a semi-finished product of a color filter or a plasma display device in which various semiconductor devices such as thin film transistors are mounted on the substrate (hereinafter referred to as these). Is generally referred to as a glass substrate), and relates to a buffer for glass substrate comprising a molded body of synthetic resin foam particles used to protect against damage caused by drop impact, vibration impact, etc. during transportation.
[0002]
[Prior art]
In recent years, liquid crystal display devices and plasma display devices, which are one of the peripheral devices of electronic and electrical equipment, particularly personal computers, and portable terminals represented by mobile phones have been developed along with the development of the information technology industry represented by the Internet. There is a strong demand for the development of superior shock absorbers that are used in packaging and transportation, etc., because the production volume is growing rapidly.
Among them, glass substrates incorporating electronic components such as semiconductor devices, such as glass substrates such as color filter glass substrates, TFT glass substrates, and liquid crystal panel substrates, are thin and vulnerable to shock and vibration during transportation, and their construction is very Because it is delicate, it is susceptible to external influences and difficult to handle.
In particular, when transporting glass substrates before processing or semi-finished products before becoming final products, they are handled in an exposed state, so they are more affected by static electricity, dust, dust, etc., and their functions are damaged. was there.
[0003]
Thus, many packaging techniques have been proposed for safely transporting glass substrates without damaging them.
Typical examples are introduced below.
1-3 is a specific example of the buffer body for conventional glass substrates.
1 and 2 are technical contents disclosed in Japanese Patent Application Laid-Open No. 05-319456. The main point is that the cross section is substantially L-shaped, and a plurality of substrate insertion grooves are provided on the inner side along the L-shape. It is an example using the buffer for glass substrates.
In the figure, 4 is a glass substrate, 1 is a buffer for glass substrate, and is composed of, for example, an in-mold molded product of polyolefin-based foam beads having a foaming ratio of at least 5 times or more and a compressive strength of 0.088 MPa or more and 0.304 MPa or less. It is what is done.
When packaging the glass substrate, a plurality of glass substrates 4 are arranged in parallel at a predetermined interval to form a cube, and the corners of each substrate are inserted into the glass substrate insertion grooves 2 of the glass substrate buffer 1 respectively. , Fix.
Further, at least one fixture guide groove 3 is provided on the outside of the buffer body 1, and a fixture 5 such as rubber or tape is guided and fixed thereto, and packed.
[0004]
On the other hand, FIG. 3 shows a shape of a polyolefin-based foamed bead having a box shape disclosed in Japanese Patent No. 2552625 and having a plurality of glass substrate insertion grooves 7 on a pair of opposing surfaces of the inner surface of the main body 6. It is an example using the buffer body for glass substrates which consists of an internal molded object.
The buffer for glass substrate may be simply mounted on the glass substrate insertion groove 7 on the inner surface of the box body 6 by manual or automatic machine, and 8 is a lid that fits the body 6. is there.
In addition, by forming a skin structure in which the density of the 1 mm depth from the inner and outer surfaces of the buffer is 1.5 times or more than the density inside the wall, a buffer for dust generation, strength, water resistance, etc. Technical means for enhancing body properties are also disclosed.
[0005]
[Problems to be solved by the invention]
However, in the buffer for glass substrates as shown in FIGS. 1 and 3, when the glass substrate 4 is inserted into the

insertion grooves

2 and 7 or due to vibration during transportation, the

insertion grooves

2 and 7 and the glass Even if the substrate 4 is rubbed against each other and measures for the skin structure to be 1.5 times or more than the density inside the wall as described above are not satisfied yet, a large amount of fine dust is generated. There was a problem that it easily adhered to a glass substrate, an electronic component, etc., and the surface function was damaged.
Then, the present inventor has made the following conclusion as a result of further examination of the reason why the above effect was not exhibited. That is,
As described in the specification of the above publication, the skin structure is obtained by heating the polyethylene pre-foamed particles filled in the mold at the time of in-mold molding with heated steam to expand and fuse, and then further It is formed by post-heating at a temperature of 60 ° C.
[0006]
And when the cross section of the surface vicinity of this in-mold molded object was observed with an electron microscope, it was obtained by a general in-mold molding method without post-heating at a temperature of 60 ° C., and the resin film thickness, that is, the skin layer thickness. It was virtually the same.
From this observation, in the skin structure, the pre-expanded particles in the vicinity of the surface in contact with the mold were pressed by post-heating, and the same level of expansion and expansion as the expanded particles located inside did not occur (in other words, However, it is considered that the problem of dust generation is still latent.
In addition, in order to reduce the packaging cost, the glass substrate buffer is not used once for a single use but is used repeatedly many times.
At that time, in addition to the dust, in order to clean off harmful fine particles on the glass substrate such as dust and dust in the atmosphere attached to the buffer during the transportation process and storage, it is carefully washed and reused.
[0007]
However, in the conventional buffer for glass substrates, due to its surface characteristics, this harmful dust and the like are likely to accumulate in the voids between the synthetic resin foam particles, and it is difficult to completely clean and remove them. Washing water was consumed and the washing efficiency was extremely poor.
In addition, there is a problem that a considerable amount of dust and the like that cannot be completely removed by washing even if a large amount of washing water is consumed remains in the voids between the foamed particles, resulting in harmful fine particles again.
In addition, since warm water of 50 ° C. is generally used as the washing water, it easily penetrates into the gaps between the synthetic resin foam particles by capillarity and deeply takes a long time for the subsequent drying treatment. It is uneconomical.
[0008]
The present invention has been completed as a result of careful analysis and research over many years on the interrelationship between the cell structure of the synthetic resin foam particles made of in-mold molded bodies and the surface characteristics of the molded bodies in view of solving the problems of the prior art. Is.
The purpose is that the glass substrate will not be damaged even if an external force such as a drop impact is applied, and even if it is rubbed against the glass substrate due to vibration during handling or transportation of the glass substrate, dust can be easily generated. However, it can be completely removed in a short amount of time with a small amount of washing water, and it is highly economical such as a short drying time, and the recovery rate is large even when external forces such as compression deformation and bending deformation are applied. An object of the present invention is to provide a buffer for glass substrates that has excellent durability and can be reused over and over again.
[0009]
[Means for Solving the Problems]
The present invention
(1) An in-mold molded product made of synthetic resin expanded particles, which is composed of expanded particles having a cell diameter of 50 to 1100 μm and an outer shell skin thickness of 8 to 50 μm. A buffer for glass substrate, characterized in that the rate is 3% or less and the dust generation is 50 mg or less,
(2) The synthetic resin foamed particle is a polyolefin-based resin, the buffer for glass substrate according to (1),
(3) The glass substrate buffer according to (1) or (2), wherein the recovery rate of the in-mold molded product is 65% or more,
(4) The in-mold molded body has a substantially L-shaped cross section, and a plurality of glass substrate insertion grooves are provided in parallel along the shape on the inside (1) to (3 ) Is a buffer for glass substrate according to any one of
(5) The in-mold molded body has a box-like shape composed of a bottomed body portion and a lid body, or a bottomless body portion, a bottom body and a lid body, and a pair of opposed inner surfaces of the body portion The glass substrate buffer according to any one of (1) to (3), wherein an insertion groove for supporting a plurality of glass substrates is provided on the surface and each bottom body. It is what.
[0010]
The present invention is described in detail below.
“Dust generation” refers to the mass of the molded product released when the surface of the molded product in the mold is subjected to a wear test with a wear ring as defined in JIS K7204 (definition). Is 50 mg or less, preferably 40 mg or less.
The smaller the dust generation, the better. However, it is technically difficult to make it less than 1 mg, and if it exceeds 50 mg, the surface of the molded body in the mold can be easily scraped off even by slight rubbing with the glass substrate. It is virtually impossible to use as a buffer for a substrate.
[0011]
This dust generation property depends on a number of factors such as the type of synthetic resin and the cell structure of the expanded particles, that is, the average cell diameter and outer skin thickness, and the magnification of the molded product in the mold, and these are as shown below. The dust generation property can be set to 50 mg or less for the first time by setting the optimum range.
The type of synthetic resin is not particularly limited as long as it is a resin from which foamed particles can be obtained by a known method, but low, medium, high, ultra-high density or linear polyethylene resin due to the frictional resistance of the resin itself. Polypropylene resin, polyethylene resin produced by metallocene catalyst, polypropylene resin, copolymerization component is non-crosslinked or crosslinked with a copolymer resin of ethylene, butene-1, 4-methylpentene-1, etc. and propylene A polyolefin resin alone or a mixed resin of two or more thereof is preferred.
In the case of hard resins such as polystyrene resins, high impact polystyrene resins, acrylonitrile-styrene copolymer resins, acrylonitrile-butadiene-styrene copolymer resins, etc., aliphatic hydrocarbons, fatty acid amides, fatty acids It can also be used by adding an appropriate amount of an ester-based lubricant to reduce frictional resistance.
[0012]
These resin particles are impregnated with a volatile foaming agent by a known method, then heated and foamed with steam to form expanded particles, or in order to further increase the expansion ratio of the expanded particles, expansion treatment is performed. After foaming by heating with steam, the foamed particles are filled into a desired glass substrate buffer, and the foamed particles are expanded and fused together by heating with steam, and then cooled.
For example, when the synthetic resin is a polyolefin resin, the cell structure of the in-mold product obtained in this way has an average cell diameter of 50 to 1100 μm, preferably 100 to 900 μm, more preferably 150 to 800 μm. .
[0013]
When the average cell diameter is less than 50 μ, the smoothness of the in-mold molded product surface 9 is remarkably increased as shown in FIG. 4, and as a result, there is almost no gap between the glass substrate and the molded product surface. Since the glass substrate is in close contact, the frictional resistance is increased, the dust generation property is increased, and the number of bubbles in each foam particle is innumerable, and the thickness of the bubble wall is extremely thin. As a result, sufficient foam expansion is not exhibited by heating during in-mold molding, and the resulting in-mold molded product has voids between the foamed particles, causing sinking and appearance. Only molded articles with inferior quality can be obtained.
When the average cell diameter exceeds 1100 μm, the surface shape of the expanded particles becomes uneven like gold flat sugar, and the surface of the molded body in the mold becomes poor as shown in FIG. 5, and the glass substrate is packed. Due to vibrations in the transporting process, it becomes easy to wear and the dust generation property increases.
The bubble diameter can be adjusted by adding and mixing a conventionally known inorganic nucleating agent such as talc, kaolin, clay, silica, calcium carbonate or the like in a range of 0.1 to 3% by weight in the polyolefin resin.
[0014]
However, since these inorganic nucleating agents are a kind of abrasive and may damage the surface of the glass substrate, organic nucleating agents that are solid at a temperature equal to or higher than the softening temperature of the polyolefin resin, such as fluorine It is preferable to use fine powders of resin, silicone resin, thermoplastic polyester resin, higher fatty acid metal salts such as calcium stearate and zinc stearate in the above-mentioned addition amount, and more preferably impregnate resin particles with volatile foaming agent It is means for adjusting the water content in the resin before the treatment in the range of 0.01 to 0.7% by weight.
If the water content is less than 0.01% by weight, the average cell diameter exceeds 1100 μm, and if the water content exceeds 0.7% by weight, only fine and non-uniform cells having an average cell diameter of less than 50 μm can be obtained. In the case of the in-mold molded body, not only the dust generation but also the appearance quality and compressive strength are not satisfied.
In addition, when controlling the bubble diameter with the water content, if the amount of the inorganic nucleating agent added is 0.1% by weight or less, the scratch resistance of the glass substrate is a practical problem even if the nucleating agent is used in combination. There is no.
[0015]
Furthermore, even if the average cell diameter is in the range of 50 to 1100 μm, the above dust generation property cannot be satisfied unless the outer skin thickness of the foamed particles is 8 to 50 μm. When the outer skin thickness of the foamed particles is less than 8 μm, the surface of the molded body in the mold, that is, the foamed particle surface is damaged by external force when it is rubbed against the glass substrate due to impact during handling or vibration during transportation. As a result, it easily wears into the inside of the expanded particles, resulting in a dust generation property exceeding 50 mg.
Further, when the outer skin thickness exceeds 50 μm, it becomes easy to form the uneven surface state as shown in FIG. 5, the surface of the molded body in the mold is not smooth, and is still a rough surface of the hard resin layer. It is easy to be scraped off by rubbing with, and inevitably the dust generation property exceeds 40 mg.
[0016]
The thickness of the outer skin is adjusted by preferentially volatilizing the foaming agent on the particle surface in the step of impregnating the resin particles of the synthetic resin with a volatile foaming agent and then heating and foaming with heated steam. Then, it can be achieved by adopting a multi-stage heating and foaming means for heating to the vicinity of the melting point to cause foaming.
The temperature increase pattern of the multistage temperature increase heating is 2 to 4 in accordance with the level of the outer skin thickness to be obtained and in view of the type of synthetic resin, the type of volatile foaming agent, the amount of foaming agent impregnation, the ratio of foamed particles, etc. What is necessary is just to determine the temperature rising pattern of a stage.
For example, the temperature is raised to a temperature in the range of minus 40 ° C. to minus 12 ° C. of the resin, and then kept at this temperature for 3 to 15 seconds to volatilize the foaming agent on the particle surface preferentially, and then the melting point minus 8 The temperature is raised to a temperature of -1 ° C to 15 ° C over 15-45 seconds, and further maintained at this temperature for 1-20 seconds to obtain expanded particles having a desired outer skin thickness and expansion ratio.
As described above, the main point of the present invention is to satisfy the two requirements of the average bubble diameter and the outer skin thickness at the same time.
[0017]
Furthermore, the expansion ratio of the in-mold molded product is 4 to 30 cm. ^Three / G, preferably 5-25 cm ^Three / G, more preferably 6-20 cm ^Three / G improves dust generation resistance.
In the case of synthetic resins, especially polyolefin resins, the copolymerization component is a random copolymer resin of ethylene, butene-1, 4-methylpentene-1, etc. and propylene, which is excellent in foaming, molding processability and high rigidity. Therefore, the compressive strength with respect to the expansion ratio is higher than that of the in-mold molded product of polyethylene resin, which is preferable.
In addition, the foaming ratio is specifically determined from the viewpoint that the rigidity is not required to be deformed by an external force such as an impact generated when used as a buffer for a glass substrate or vibration during transportation. 4-30cm depending on design, dimensions of glass substrate, number of stored sheets ^Three The expansion ratio may be / g.
Foaming ratio is 4cm ^Three If it is less than / g, the rigidity is high but the weight is heavy, handling and handling work becomes difficult, and the molded body becomes hard because of its high compressive strength, impact absorption is low, and protection during transportation vibration Is also insufficient.
[0018]
On the other hand, the expansion ratio is 30cm ^Three If the weight exceeds / g, the weight will be reduced, but the compressive strength will be too low, and it will be easy to crack and scratch due to impacts during handling, and will not be able to withstand repeated reuse. Subsidence and settling phenomenon increase with the load of time, and the fixing property of the glass substrate is weakened, which hinders the transportability of the glass substrate.
“Void ratio” represents the degree of void formation between foamed particles on the surface of a molded body in a mold, and is a value measured by (planimeter method) (definition).
The porosity is 3% or less, preferably 1.8% or less.
The smaller the void ratio, the better. However, it is technically difficult to make it less than 0.01% in terms of the production method of the in-mold molded product.
[0019]
In addition, if the porosity exceeds 3%, the water absorption phenomenon of the in-mold molded product exhibits a quadratic behavior and becomes extremely large, and the cleaning water at the time of cleaning that is repeatedly used is 50 ° C hot water. Therefore, it penetrates a large amount from the space between the foamed particles to the deep part inside the molded product by capillary action, and it takes a long time for drying after washing.
If the drying time after washing is insufficient, water vapor evaporated from inside the mold may condense on the surface of the glass substrate, which may impair the functional reliability of the substrate, such as the formation of water droplets and damage to electronic circuits. There is.
Furthermore, if the porosity exceeds 3%, a fatal problem occurs in addition to the long time required for drying.
That is, not only the dust generated from the molded product but also the dust generated by the shock during handling of the glass substrate and vibration during transportation, external dust adheres to and accumulates in the gap. It cannot be completely removed by washing.
[0020]
As shown below, the porosity can be adjusted by optimizing the mold for in-mold molding, each process condition during molding, and the like.
In the mold, it is necessary to uniformly fill the foamed particles in the mold and to devise in order to sufficiently heat the foamed particles filled in the mold, particularly the deepest foamed particles.
For this purpose, an infinite number of core vents having a diameter of 6 to 12 mm provided with a plurality of grooves and small holes for introducing heated steam are disposed over the entire surface of the mold.
However, the core vent must be arranged at a distance of 1.5 to 4.5 times, preferably 2 to 4 times the core vent diameter at the center-to-center distance.
If the distance is less than 1.5 times, not only the effect can be obtained but also the strength of the mold is lowered. When the distance exceeds 4.5 times, the filling property and heating are insufficient and non-uniform, and the gap between the expanded particles exceeds 3%.
[0021]
In-mold molded bodies generally have complex shapes and often have different thicknesses at various locations, so that filling and heating are likely to be non-uniform.
For this reason, the core vent should be placed in a mold with a core vent diameter appropriate for the thickness of each part and a distance between the centers thereof. For example, the distance between the centers of the core vents is 3 to 4.5 times for a thin part (10 to 20 mm) and 1.5 to 3 times for a thick part, and uniform heating is performed. To be
In addition, the design of the in-mold product is determined so that the uneven thickness ratio (maximum thickness / minimum thickness) of the in-mold product is 4 or less, preferably 3.5 or less. Or steal meat to lower the unbalanced meat ratio.
In this case, the maximum wall thickness and the minimum wall thickness mean the maximum value or the minimum value of the diameter of the maximum sphere assumed inside the part.
[0022]
The optimization of each process condition at the time of in-mold molding processing will be specifically described by taking polyolefin resin expanded particles as an example. First, in view of the magnification of expanded particles, the maximum thickness of the in-mold molded product, the thickness deviation ratio, etc. It is to optimize the treatment for applying the internal pressure of the particles and the compression filling rate into the mold. If these are unsuitable, even if the heating conditions are optimized in detail, sufficient foam expansion force does not occur, and if the porosity becomes large, or conversely, if the foam expansion force is too high, fusion between the expanded particles may occur. It does not appear and a good in-mold molded product cannot be obtained.
Next, the heating process, that is, the mold heating, one heating, one reverse heating, preheating such as a heating method in which only one mold is introduced and exhausted from the other mold and the heating steam pressure in the main heating and the like Optimization of the heating time must be made in view of the melting point of the expanded particles, the magnification, the maximum thickness related to the design of the in-mold molded product, the thickness deviation ratio, and the like.
The foamed particles filled in the mold are brought into a state in which the foam expansion force is increased by the optimization of the heating step.
[0023]
By the way, this foam expansion force is manifested by a change in the external pressure when the inside of the mold is released into the atmosphere after the end of the main heating. As a result, the foam particles expand and expand, and are fused and integrated. .
Therefore, if the standing time at a high temperature until the water cooling process is short after this atmospheric pressure is released, the foamed particles are cooled and hardened in a state where the foaming expansion force does not occur completely. The foamed particles, that is, the surface of the molded body in the mold, has a large porosity between the foamed particles.
For the above reasons, the standing time is preferably 3 to 45 seconds, more preferably 5 to 30 seconds.
[0024]
“Recovery rate” represents the degree of restoration to the original thickness when an instantaneous compression load is applied to the molded body in the mold (definition), and the recovery rate is 65% or more, Preferably it is 75% or more.
The buffer for glass substrates is required to have durability for repeated reuse. However, if the recovery rate is less than 65%, the buffer is deformed by external forces such as vibration and drop impact generated during handling and transportation. Since the recoverability of the glass substrate is inferior, the protective buffer function of the glass substrate is lowered, or the glass substrate is weakened and the rattling occurs, resulting in increased dust generation.
In order to make the recovery rate 65% or more, a polyolefin-based resin that is flexible and has high extensibility is preferable.
[0025]
The in-mold molded product of the present invention has, for example, a structure having a substantially L-shaped cross section as shown in FIG. 1 (this “substantially L-shaped” includes “L-shaped” and “L-shaped” approximate shapes). Alternatively, it is molded into a box-shaped structure as shown in FIG. 3 and used as a buffer for a glass substrate.
As a molding method of the in-mold molded product, a general synthetic resin foamed particle molding technique, for example, when the synthetic resin is a polyolefin resin, the foamed particle contains a hydrocarbon-based resin such as polystyrene foam particles. Since it does not contain a large amount of a volatile foaming agent, it is necessary to take measures to develop a sufficient foam expansion force by heating with heated steam.
As the means, the molding methods disclosed in Japanese Patent Publication No. 53-3396 and Japanese Patent Publication No. 51-22951 are used.
[0026]
That is, the former is a molding method in which foamed particles are compressed to 80% or less of the original apparent bulk volume by gas pressure, compressed and filled into a mold, heated and fused, and then cooled and taken out from the mold. Yes, the latter applies an inorganic gas gas pressure of 1.18 atm or more to the foamed particles, then fills the foamed particles, heats them to foam the foamed particles, and fuses the particles together This is a molding method after cooling and taking out from the mold.
The in-mold molded bodies obtained by both methods are dried at a temperature of 70 to 90 ° C. for 8 to 24 hours.
Next, characteristic values and evaluation methods used in the present invention are shown below.
[0027]
[Characteristic values of expanded particles]
1) Foaming ratio;
Weight (g) Volume of known foam particles (cm ^Three ) Is measured by the submerging method, and the value obtained by dividing the volume by the weight is the expansion ratio (cm ^Three / G). The evaluation is the average of three measurements.
[Characteristic values of molded in-mold]
2) Foaming ratio;
Weight (g) Volume of known in-mold foam molding (cm ^Three ) Is measured by the submerging method, and the value obtained by dividing the volume by the weight is the expansion ratio (cm ^Three / G).
[0028]
3) bubble diameter;
When the bubble diameter is measured at the cut surface of a specific foamed particle in the foamed particles constituting the in-mold molded product, and this measured value is used, the bubble diameter of the entire particle cannot be accurately expressed.
Assuming that the bubbles are spherical, the bubbles that appear side by side on the cut surface include those that have been cut at the maximum diameter (= diameter) of the bubbles and bubbles that have been cut at a portion smaller than the maximum diameter. This is because they are arranged.
Therefore, the bubble diameter of the present invention is determined by the following method as the bubble diameter.
[0029]
(Measuring method)
The molded body in the mold is cut in the thickness direction with a sharp blade, and the expanded surface of the foam particles located on the surface (mold contact portion) of the molded body is enlarged (magnification: 20 to 80 times) with an enlargement projector, A fixed length measurement line (L) is drawn at an arbitrary position on the projection plane, the number of bubble walls (N) crossing (contacting) the measurement line is measured, and the bubble diameter ( C: μm) is calculated. The evaluation is an average value of 10 expanded particles.
[Formula 1]

[0030]
4) Outer skin thickness;
The molded body in the mold is cut in the thickness direction with a sharp blade, the cut surface is gold-deposited under vacuum, and the outer shell skin of the foamed particles using a transmission electron microscope (magnification: 250 times) The vicinity (die contact part) is imaged (three places), and the outer skin thickness T (μm) is measured. The evaluation is an average value of five expanded particles (n number is 15).
5) Porosity;
The surface of the molded body in the mold (area: 7 cm x 5 cm) is uniformly applied to the entire surface with a black oil-based pen (Marks, product name; manufactured by Lion Corporation), and this coated surface is applied to a laser-type copying machine (Docucenter 451CP). , Trade name: manufactured by Fuji Xerox Co., Ltd.) and magnified 4 times to create an enlarged image of the surface of the molded body in the mold.
[0031]
The enlarged image is input to an image processing apparatus (color image processor SPICCA-II, product name; manufactured by Nihon Avionics Co., Ltd.), subjected to grayscale image processing and binarized image processing, and all voids (white portions) between the expanded particles are processed. Area (mm ² ) And the porosity B (%) is calculated from the following equation (2).
In addition, evaluation is made into the average value of three test pieces. However, the core vent (steam introduction hole) part was processed as a non-gap part.
[Formula 2]

[0032]
6) Dust generation
A flat test piece having a thickness of 3 mm and a diameter of 120 mm is cut out from the surface of the molded body in the mold, and dry air is blown onto the test piece to completely remove the adhering chips, and then a Taber abrasion tester (rotary abrasion machine). The wear mass (mg) of the test piece molded skin surface was measured by the method of JIS K7204 using a tester, trade name: manufactured by Toyo Seiki Seisakusho Co., Ltd.
In addition, evaluation is made into the average value of three test pieces.
[0033]
7) Recovery rate;
A flat test piece having a width, length of 50 mm, and thickness of 20 mm is cut out from the molded body in the mold, and molded in-mold at a compression rate of 10 mm / min using a compression test apparatus Autograph AG-5000D manufactured by Shimadzu Corporation. After compressing to 50% of the body thickness, immediately remove it until the load becomes zero at the same speed, measure the thickness at the moment when the load becomes zero, and calculate the recovery rate R (%) from the following equation (3) Calculate and evaluate.
[Formula 3]

[0034]
8) Compression characteristics;
When a flat test piece having a width, length of 50 mm, and thickness of 20 mm is cut out from the in-mold molded body and compressed at a compression rate of 10 mm / min using a compression test apparatus Autograph AG-5000D manufactured by Shimadzu Corporation. The stress under 25% strain is taken as the compressive strength and evaluated by the test method of JIS Z-0235.
(Evaluation scale)
[Table 1]

[0035]
9) Repeatability
A flat test piece having a width, a length of 50 mm, and a thickness of 20 mm is cut out from the molded body in the mold, and repeated compression set as defined in the test method of JIS K6767 is measured and evaluated.
(Evaluation scale)
[Table 2]

[0036]
10) Detergency;
An acrylic mold for testing with an internal dimension of 10.5cm x 10.5cm square was created, and high-quality paper for office copying was placed in the mold, and cigarette ash (crushed into fine powder in a mortar) ) 250 mg is sprinkled uniformly, an in-mold molded product (area: 10 cm × 10 cm) is inserted into the test jig, and a stress of 0.01 kg / cm is further applied to the molded product. ² Then, an iron load plate was placed so that the test jig was fixed on a horizontal vibrator table, and a vibration test (amplitude 10 mm, vibration frequency 5 Hz, excitation time 5 minutes) was performed.
After that, the ash of the cigarette adhering to the surface of the molded body was washed with water at 50 ° C. (water amount: 20 liters / min) for 3 minutes, and then left in a 50 ° C. hot air circulating thermostat for 4 hours to dry. I let you.
The surface of the molded body in the mold is observed with a magnifying device (magnification: 20 times), and evaluation is performed in the state of the ash of the cigarette remaining in the gap between the foamed particles.
[0037]
(Evaluation scale)
[Table 3]

[0038]
11) Water absorption;
After showering water at 50 ° C. (water amount: 20 liters / minute) on the surface of the molded body in the mold for 3 minutes and then removing the moisture adhering to the surface of the molded body in the mold by blowing dry air The weight is measured, and the water absorption W (% by weight) is calculated and evaluated from the following formula (4).
[Formula 4]

[0039]
(Evaluation scale)
[Table 4]

[0040]
12) Dryability;
After showering water at 50 ° C. (water amount: 20 liters / minute) on the surface of the molded body in the mold for 3 minutes and then removing the moisture adhering to the surface of the molded body in the mold by blowing dry air , Dried in a hot air circulating thermostat at 50 ° C. for 4 hours, taken out to room temperature, allowed to stand for 24 hours, weighed, and calculated and evaluated moisture content W (wt%) from the following formula (5) .
[Formula 5]

[0041]
(Evaluation scale)
[Table 5]

Next, the present invention will be described in more detail using specific examples, but it is needless to say that the present invention is not limited to these examples.
[0042]
Examples 1-3, Comparative Examples 1-2
Low density polyethylene (Suntech LD, trade name; manufactured by Asahi Kasei Kogyo Co., Ltd., density 0.930 g / cm ^Three The impregnated product having a melt index of 2.4 g / 10 minutes and a melting point of 117 ° C. was impregnated with a crosslinking agent in an aqueous suspension system having the following composition at 120 ° C. for 30 minutes, and further heated at 160 ° C. for 40 minutes. Thus, crosslinked low-density polyethylene resin particles having a gel fraction of 62% (boiling toluene × 8 hours) and an average particle diameter of 1.1 mm were obtained.
Low-density polyethylene cut 100 parts by weight (standard)
Crosslinking agent: 0.7 parts by weight of dicumyl peroxide
Anti-fusing agent: 3.5 parts by weight of calcium triphosphate
Suspending agent; sodium dodecylbenzenesulfonate 0.0002 parts by weight
230 parts by weight of water
[0043]
The resin particles were dried in a fluidized bed dryer having a temperature of 70 ° C., and the moisture content in the resin particles was 0.008% by weight (Comparative Example 1), 0.01% by weight (Example 1), 0.3% by weight. (Example 2), 0.7 wt% (Example 3), and 0.8 wt% (Comparative Example 2) were prepared. These resin particles are placed in a pressure vessel, carbon dioxide (gas) is injected, and the resin particles are impregnated with carbon dioxide over 3 hours under a pressure of 3.04 MPa (gauge pressure) and a temperature of 11 ° C. . Next, each foamable resin particle is housed in a foaming apparatus (exhaust temperature raising type), heated in a tank at 100 ° C. for 5 seconds, then heated to 114.5 ° C. over 25 seconds, and then the temperature. The foam was heated and foamed with water vapor for 3 to 10 seconds while maintaining the above, to obtain crosslinked low-density polyethylene expanded particles.
The expansion ratio of the expanded particles is 2.6 cm. ^Three The foaming was carried out by adjusting the maintenance time at 115 ° C. so as to be / g.
[0044]
Next, the expanded particles are accommodated in an autoclave having a pressurizing (high pressure air) / heating device, and the pressure is increased over 1 hour at a temperature of 80 ° C., and the pressure is 0.9 MPa (gauge pressure) for 8 hours. Re-expansion treatment was performed to increase the internal pressure of the expanded particles.
Subsequently, the foamed particles were accommodated in a foaming apparatus and heated and foamed with water vapor at a tank temperature of 110 to 112 ° C. for 10 seconds. ^Three / G was adjusted to a heating temperature in the range of 110 to 112 ° C. to obtain foamed particles for molding.
The foamed particles for molding are accommodated in an air pressurization device (pressure: 0.1 MPa (gauge pressure), temperature: 30 ° C.) and given re-expansion ability over 16 hours, and then mounted on a fully automatic molding machine. In addition, the glass substrate buffer shown in FIG. 2 (external dimensions: length 165 mm, width 230 mm, height 210 mm, thickness 30 mm, glass substrate insertion groove depth 5 mm) is filled in an in-mold molding die. , After preheating with heated steam (mold heating: 3 seconds, one side heating, reverse one heating: 5 seconds each), the foamed particles are expanded by heating with steam at a mold internal pressure of 0.12 MPa (gauge pressure) for 8 seconds, Fused.
[0045]
Thereafter, the inside of the mold is instantaneously released into the atmosphere, and the foam is allowed to stand for 10 seconds at atmospheric pressure. Then, the foam is cooled and taken out from the mold, and is left in a drying room at room temperature of 80 ° C. for 12 hours. Obtained.
The resulting foam in the mold has an expansion ratio of 6 cm. ^Three / G.
With respect to the obtained in-mold molded body, the above-described evaluation method allows the in-mold molded body characteristics (outer shell skin thickness, porosity, dust generation, bubble diameter, recovery rate, compression characteristics, repeated durability, detergency, water absorption, Dryability) was evaluated.
The results are shown in Table 1 below.
According to the results in Table 1, it can be seen that the in-mold molded bodies of Examples 1 to 3 satisfy all practical characteristics that must be provided as a buffer for glass substrates as well as dust generation.
[0046]
[Table 6]

[0047]
Examples 4-6, Comparative Examples 3-4
Using the crosslinked low-density polyethylene resin particles of Example 2, the resin particles were similarly impregnated with carbon dioxide. Next, the foamable resin particles are accommodated in a foaming apparatus (exhaust temperature raising type), heated in a tank at 95 ° C. for 15 seconds, and then heated to 115 ° C. for 7 seconds (Comparative Example 3), 15 The temperature was raised over seconds (Example 4), 30 seconds (Example 5), 45 seconds (Example 6) seconds, and 60 seconds (Comparative Example 4), and further maintained for 5 to 15 seconds while maintaining the temperature. And foamed by heating to obtain crosslinked low-density polyethylene foam particles.
The expansion ratio of the expanded particles is 2.3 cm. ^Three The foaming was carried out by adjusting the maintenance time at 115 ° C. so as to be / g.
[0048]
Next, these expanded particles are accommodated in an autoclave having a pressurizing (high pressure air) / heating device, and the pressure is increased to 1.5 MPa (gauge pressure) over 3 hours at a temperature of 80 ° C. After holding for 12 hours under pressure and performing expansion ability imparting treatment to increase the bubble internal pressure of the foamed particles, the foam is accommodated in a foaming apparatus and heated and foamed with water vapor at a temperature of 113 to 114.5 ° C. for 10 seconds. All magnifications are 15cm ^Three The foaming particles for molding were prepared by adjusting the heating temperature to be / g.
The molded foamed particles were accommodated in an air pressurization apparatus (pressure: 0.3 MPa (gauge pressure), temperature: 30 ° C.) and given re-expansion ability over 10 hours, and then the same as in Examples 1-3. And the expansion ratio is 20cm ^Three / G in-mold molded product was obtained.
[0049]
With respect to the obtained in-mold molded body, the above-described evaluation method allows the in-mold molded body characteristics (outer shell skin thickness, porosity, dust generation, bubble diameter, recovery rate, compression characteristics, repeated durability, detergency, water absorption, Dryability) was evaluated.
The results are shown in Table 2 below.
According to the results of Table 2, the molded bodies in Examples 4 to 6 satisfy all the practical characteristics that must be provided as a buffer for glass substrates as well as dust generation as in Examples 1 to 3. It turns out that it is.
[0050]
[Table 7]

[0051]
【The invention's effect】
As is apparent from the above description, the present invention has a foam diameter of 50 to 1100 μm, a shell skin thickness of 8 to 50 μm, and a porosity of the molded body. 3% or less, suitable for glass substrates that are less damaged during handling and transportation, less dust generation, and can be easily dried after being washed after being used and reused after passing through. An in-mold molded product can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view of a buffer obtained by a conventional technique (Japanese Patent Laid-Open No. 05-319456).
FIG. 2 is a view showing a glass substrate package shape using the buffer body.
FIG. 3 is a perspective view of a glass substrate transport box obtained by a conventional technique (Japanese Patent No. 2552625).
FIG. 4 is a schematic cross-sectional view for explaining an example of the in-mold molded body of the present invention, showing a state where the bubble diameter is small.
FIG. 5 is a schematic cross-sectional view for explaining an example of the in-mold molded body of the present invention, showing a state where the bubble diameter is large.
FIG. 6 is a schematic plan view for explaining an example of the in-mold molded body of the present invention, and is a view showing a state of expanded particles and voids constituting the molded body.
[Explanation of symbols]
1 buffer
2 Glass substrate insertion groove
3 fixed guide groove
4 Substrate glass
5 Fixture
6 Box body
7 Glass substrate insertion groove
8 Box cover
9 Surface direction
10 Foamed particles
11 Outer shell skin thickness
12 Bubble diameter
13 Molded body void

Claims

An in-mold molded body made of synthetic resin foam particles, which is composed of foam particles having a cell diameter of 50 to 1100 μm and an outer shell skin thickness of 8 to 50 μm, and the porosity of the molded body is 3 %, And the dust generating property is 50 mg or less.

The buffer for glass substrate according to claim 1, wherein the synthetic resin expanded particles are a polyolefin-based resin.

The glass substrate buffer according to claim 1 or 2, wherein a recovery rate of the molded body in the mold is 65% or more.

The cross section of the molded body in the mold has a substantially L shape, and a plurality of glass substrate insertion grooves are provided in parallel along the shape on the inner side. The buffer for glass substrates as described in any one of.

The in-mold molded body is a box-shaped body composed of a bottomed main body and a lid, or a bottomless main body, a bottom and a lid, and a pair of opposed surfaces of the inner surface of the main body The glass substrate buffer according to any one of claims 1 to 3, wherein each of the bottom bodies is provided with an insertion groove for supporting a plurality of glass substrates.