JP2004002534A - Adhesive composition, method for producing adhesive composition and sheet for carrying information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive composition having sufficient adhesiveness, sufficiently filling various kinds of fillers, having a short drying time after coating, readily carrying out both of whole surface coating and pattern coating, coating various kinds of substrates and realizing sufficient adhesive strength of the substrates to a pressure-sensitive adhesive layer. <P>SOLUTION: The adhesive composition comprises natural rubber microparticles dispersed in a radiation curing medium containing a carboxy group-containing acrylic compound and a radiation curing compound. The adhesive composition can be produced by mixing an aqueous emulsion 31 containing the natural rubber microparticles 30 with the radiation curing medium 32, heating up the resultant mixture while stirring the mixture, vaporizing and removing water in the aqueous emulsion 31 and replacing the water of the medium containing the natural rubber microparticles 30 dispersed therein with the radiation curing medium 32. <P>COPYRIGHT: (C)2004,JPO

Description

【００６１】
ここで式中、Ｒ^１は水素またはメチル基であり、Ｒ^２は炭素数２〜１０の環状構造を含んでもよいアルキレンであり、Ｒ^３は炭素数１〜２０の環状構造を含んでもよいアルキレン、炭素数１〜２０の環状構造を含んでもよいアルケニレン又は炭素数１〜２０のアリーレンである。
【００６２】
なお、Ｒ^２は上記のエポキシドに由来するものであり、エチレン、プロピレン等の上記の好ましいエポキシドに由来するものが好ましい。また、Ｒ^３は上記の多価カルボン酸に由来するものであり、エチレン、１，２−シクロヘキシレン、ｏ−フェニレン等の上記の好ましい多価カルボン酸に由来するものが好ましい。
【００６３】
ヒドロキシ酸またはヒドロキシ酸重合体と、（メタ）アクリル酸とがエステルにより結合された構造を有するエステル体（ＩＩ）としては、例えば、ヒドロキシ酸と（メタ）アクリル酸とを反応させてエステルとしたり、ラクトンと（メタ）アクリル酸とを反応させてエステルとしたり、オリゴエステル及びポリエステル等のヒドロキシ酸重合体と（メタ）アクリル酸とを反応させてエステルとしたり、（メタ）アクリル酸の存在下でヒドロキシ酸を重縮合してオリゴエステル及びポリエステルとしたり、ラクトンの開環重合によって得られたオリゴエステル及びポリエステルと（メタ）アクリル酸とを反応させてエステルとしたり、（メタ）アクリル酸存在下でラクトンを開環重合すること等で作製できる。
【００６４】
ヒドロキシ酸重合体からなるオリゴエステル及びポリエステルは、ヒドロキシ酸を重縮合することによって得られ、反応率を所定の値とすることで、ヒドロキシ酸の重合度を所望の値とすることができる。そして、得られたヒドロキシ酸重合体のヒドロキシル基と（メタ）アクリル酸のカルボキシル基との間でエステル結合を形成することにより、エステル体（ＩＩ）が得られる。
【００６５】
また、（メタ）アクリル酸の存在下でヒドロキシ酸を重縮合する場合、（メタ）アクリル酸は重合停止剤として働き、ヒドロキシ酸が重縮合して得られるオリゴエステル及びポリエステルのヒドロキシル基末端に（メタ）アクリル酸がエステル結合しているエステル体（ＩＩ）が得られる。この場合、（メタ）アクリル酸とヒドロキシ酸との仕込み比を所定の値とすることで、ヒドロキシ酸の重合度を所望の値とすることができる。例えば、ヒドロキシ酸の量に対して（メタ）アクリル酸の量を増加すると、ヒドロキシ酸の重合度は低下し、ヒドロキシ酸の量に対して（メタ）アクリル酸の量を減少すると、ヒドロキシ酸の重合度を増加できる。
【００６６】
また、ヒドロキシ酸重合体からなるオリゴエステル及びポリエステルは、ラクトンを開環重合体することによって得られ、反応率を所定の値とすることで、ヒドロキシ酸の重合度を所望の値とすることができる。そして、得られたラクトン重合体のヒドロキシル基と（メタ）アクリル酸のカルボキシル基との間でエステル結合を形成することにより、エステル体（ＩＩ）が得られる。
【００６７】
また、（メタ）アクリル酸の存在下でラクトンを開環重合する場合、（メタ）アクリル酸は重合停止剤として働き、ラクトンが開環重合して得られるオリゴエステル及びポリエステルのヒドロキシル基末端に（メタ）アクリル酸がエステル結合しているエステル体（ＩＩ）が得られる。この場合、（メタ）アクリル酸とラクトンとの仕込み比を所定の値とすることで、ラクトンの重合度を所望の値とすることができる。例えば、ラクトンの量に対して（メタ）アクリル酸の量を増加すると、ラクトンの重合度は低下し、ラクトンの量に対して（メタ）アクリル酸の量を減少すると、ラクトンの重合度を増加できる。
【００６８】
ヒドロキシ酸およびラクトンの重合度は、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、数平均重合度で１より大きく、１．１以上がより好ましく、１．２以上が更に好ましく、一方、５以下が好ましく、４以下がより好ましく、３以下が更に好ましい。
【００６９】
ヒドロキシ酸は特に制限されないが、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、例えば、グリコール酸、ヒドロキシプロパン酸、ヒドロキシブタン酸、ヒドロキシペンタン酸、ヒドロキシヘキサン酸、ヒドロキシヘプタン酸、ヒドロキシオクタン酸、ヒドロキシノナン酸、ヒドロキシデカン酸、ヒドロキシドデカン酸、ヒドロキシテトラデカン酸、ヒドロキシオクタデカン酸などの飽和脂肪族ヒドロキシ酸；ヒドロキシシクロヘキサンカルボン酸などの飽和環状脂肪族ヒドロキシ酸；ヒドロキシ安息香酸、ヒドロキシフェニル酢酸、（ヒドロキシフェニル）プロピオン酸、ヒドロキシトルイル酸、ヒドロキシナフトエ酸などの芳香族ヒドロキシ酸などが好ましい。
【００７０】
中でも、ヒドロキシプロパン酸などの飽和脂肪族ヒドロキシ酸；ヒドロキシシクロヘキサンカルボン酸などの飽和環状脂肪族ヒドロキシ酸；ヒドロキシ安息香酸などの芳香族ヒドロキシ酸が好ましい。
【００７１】
また、ラクトンも特に制限されないが、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、例えば、α−ラクトン、β−ラクトン、γ−カプロラクトン等のγ−ラクトン、δ−カプロラクトン等のδ−ラクトン、ε−カプロラクトン等のε−ラクトン等が好ましく、中でもε−カプロラクトンが好ましい。
【００７２】
以上の様な構造を有するエステル体（ＩＩ）として、以下の一般式（ＩＩ）を例示できる。
【００７３】
【化５】

【００７４】
ここで式中、ｎは１〜５の整数または実数であり、Ｒ^４は水素またはメチル基であり、Ｒ^５は炭素数１〜２０の環状構造を含んでもよいアルキレン、炭素数１〜２０の環状構造を含んでもよいアルケニレン又は炭素数１〜２０のアリーレンである。
【００７５】
特に、Ｒ^５を含む繰返し構造単位の重合度に分布がある場合は、ｎは数平均重合度を表すものとし、必ずしも整数とは限らない。ｎが１場合、エステル体（ＩＩ）はヒドロキシ酸と（メタ）アクリル酸とのエステル体またはラクトンと（メタ）アクリル酸とのエステル体であり、１より大きい場合、オリゴマー及びポリマー等のヒドロキシ酸重合体と（メタ）アクリル酸とのエステル体またはオリゴマー及びポリマー等のラクトン重合体と（メタ）アクリル酸とのエステル体である。ヒドロキシ酸重合体またはラクトン重合体と（メタ）アクリル酸とのエステル体の場合、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、ｎは１より大きく、１．１以上がより好ましく、１．２以上が更に好ましく、一方、５以下が好ましく、４以下がより好ましく、３以下が更に好ましい。
【００７６】
なお、Ｒ^５はヒドロキシ酸またはラクトンに由来するものであり、エチレン、シクロヘキシレン、フェニレン、ペンタメチレン等の上記の好ましいヒドロキシ酸またはラクトンに由来するものが好ましい。
【００７７】
カルボキシル基を有する（メタ）アクリル系重合体（ＩＩＩ）としては、（メタ）アクリル酸、（メタ）アクリレート及びこれらの誘導体などの（メタ）アクリル系単量体を重合して得られ、必要に応じて２種以上の（メタ）アクリル系単量体を併用して共重合体を製造し使用する場合もある。
【００７８】
（メタ）アクリル系単量体は特に制限されないが、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、例えば、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸プロピル、（メタ）アクリル酸ブチル、（メタ）アクリル酸ヘキシル、（メタ）アクリル酸オクチル、（メタ）アクリル酸２−エチルヘキシル、（メタ）アクリル酸デシル、（メタ）アクリル酸ドデシル、（メタ）アクリル酸ラウリル、（メタ）アクリル酸ラウリル−トリデシル、（メタ）アクリル酸トリデシル、（メタ）アクリル酸セチル−ステアリル、（メタ）アクリル酸ステアリル、（メタ）アクリル酸シクロヘキシル、（メタ）アクリル酸ベンジル及びメタクリル酸フェニル等の（メタ）アクリル酸エステル類；（メタ）アクリル酸などのカルボキシル基を有するアクリル系モノマー類；（メタ）アクリル酸アミド及び（メタ）アクリル酸メチロールアミド等の（メタ）アクリル酸アミド類；（メタ）アクリル酸ヒドロキシエチル、（メタ）アクリル酸ヒドロキシプロピル、（メタ）アクリル酸ヒドロキシブチル、（メタ）アクリル酸ジメチルアミノエチル、（メタ）アクリル酸ジエチルアミノエチル、（メタ）アクリル酸ブチルアミノエチル、（メタ）アクリル酸グリシジル及び（メタ）アクリル酸テトラヒドロフルフリル等の反応性アクリル系モノマー類；ジ（メタ）アクリル酸エチレン、ジ（メタ）アクリル酸ジエチレングリコール、ジ（メタ）アクリル酸トリエチレングリコール、ジ（メタ）アクリル酸テトラエチレングリコール、ジ（メタ）アクリル酸デカエチレングリコール、ジ（メタ）アクリル酸ペンタデカエチレングリコール、ジ（メタ）アクリル酸ペンタコンタヘクタエチレングリコール、ジ（メタ）アクリル酸ブチレン、（メタ）アクリル酸アリル、トリ（メタ）アクリル酸トリメチロールプロパン、テトラ（メタ）アクリル酸ペンタエリスリトール及びジ（メタ）アクリル酸フタル酸ジエチレングリコール等の架橋性アクリル系モノマー類などを使用でき、中でもアルキル（メタ）アクリレートおよび（メタ）アクリル酸が好ましい。
【００７９】
また、以上の様な（メタ）アクリル系単量体と共重合可能で、（メタ）アクリル系重合体（ＩＩＩ）にカルボキシル基および（メタ）アクリロイル基を導入する単量体を共重合することもできる。カルボキシル基を導入する単量体としては、ビニル酢酸、アリル酢酸などのアルケニルカルボン酸類；ビニル（メタ）アクリレート、アリル（メタ）アクリレート等のアルケニル（メタ）アクリレート等類を使用できる。
【００８０】
更に（メタ）アクリル系重合体（ＩＩＩ）末端にカルボキシル基を有する基を導入することもでき、（メタ）アクリロイル基を有する基を導入することもできる。
【００８１】
以上の様な（メタ）アクリル系重合体（ＩＩＩ）として、以下の一般式（ＩＩＩ）を例示できる。
【００８２】
【化６】

【００８３】
ここで式中、ｍ_ｉはｌ種類の繰返し構造単位に対応してｍ_１〜ｍ_ｌであり、ｌは１以上の整数であり、ｍ_ｉは互いに独立に１以上の整数または実数であり；Ｒ^６、Ｒ^８ｉ及びＲ^１０は互いに独立に水素またはメチル基であり；Ｌ^７はカルボキシル基を含む基、（メタ）アクリロイル基を含む基または−ＣＯ_２Ｒ^７でＲ^７は水素または炭素数１〜２０の炭化水素基であり；Ｌ^９ｉはカルボキシル基を含む基、（メタ）アクリロイル基を含む基または−ＣＯ_２Ｒ^９ｉでＲ^９ｉは水素または炭素数１〜２０の炭化水素基であり；Ｌ^１１はカルボキシル基を含む基、（メタ）アクリロイル基を含む基または−ＣＯ_２Ｒ^１１でＲ^１１は水素または炭素数１〜２０の炭化水素基であり；Ｘ^１及びＸ^２は互いに独立に、水素、カルボキシル基を含む基または（メタ）アクリロイル基を含む基であり；Ｌ^７、Ｌ^９ｉ及びＬ^１１の何れもがカルボキシル基を含まないかＲ^７、Ｒ^９ｉ及びＲ^１１の何れもが水素でない場合は、Ｘ^１及びＸ^２の少なくとも何れか一方がカルボキシル基を含む。特に、Ｌ^９ｉを含む繰返し構造単位の重合度に分布がある場合、ｍ_ｉは数平均重合度を表すものとし、必ずしも整数とは限らない。
【００８４】
なお、（メタ）アクリル系重合体（ＩＩＩ）の重量平均分子量は、十分な強度を有する感圧接着剤層の高進性を抑制しつつ初期接着強度を十分向上する観点から、１，０００以上が好ましく、１，５００以上がより好ましく、一方、１０，０００以下が好ましく、５，０００以下がより好ましい。
【００８５】
以上で説明してきたカルボン基含有アクリル化合物の具体例としては、好ましいエステル体（Ｉ）として、エチレンオキサイド変性コハク酸（メタ）アクリレート（ＣＨ_２＝ＣＨ・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・Ｃ_２Ｈ_４・ＣＯ_２Ｈ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・Ｃ_２Ｈ_４・ＣＯ_２Ｈ）、２−（メタ）アクリロイロキシエチルフタレート（ＣＨ_２＝ＣＨ・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・φ・ＣＯ_２Ｈ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・φ・ＣＯ_２Ｈ、但しφは１，２−フェニレン基を表す）、２−（メタ）アクリロイロキシエチルテトラヒドロフタレート、２−（メタ）アクリロイロキシエチルヘキサヒドロフタレート（ＣＨ_２＝ＣＨ・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・ｃｈ・ＣＯ_２Ｈ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・ＯＣ_２Ｈ_４Ｏ・ＣＯ・ｃｈ・ＣＯ_２Ｈ、但しｃｈは１，２−シクロヘキシレン基を表す）、２−（メタ）アクリロイロキシプロピルフタレート（ＣＨ_２＝ＣＨ・ＣＯ・ＯＣ_３Ｈ_６Ｏ・ＣＯ・φ・ＣＯ_２Ｈ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・ＯＣ_３Ｈ_６Ｏ・ＣＯ・φ・ＣＯ_２Ｈ、但しφは１，２−フェニレン基を表す）；好ましいエステル体（ＩＩ）として、β−カルボキシエチル（メタ）アクリレート（ＣＨ_２＝ＣＨ（ＣＯ・ＯＣ_２Ｈ_４）_ｎＣＯ_２Ｈ、ＣＨ_２＝ＣＣＨ_３（ＣＯ・ＯＣ_２Ｈ_４）_ｎＣＯ_２Ｈ、但しｎは１．５〜３．０）、（メタ）アクリロイルオリゴエステル（ＣＨ_２＝ＣＨ・ＣＯ・Ｏ（Ｃ_２Ｈ_４・ＣＯ_２）_ｎＨ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・Ｏ（Ｃ_２Ｈ_４・ＣＯ_２）_ｎＨ、但しｎは１．１〜１．７）、ω−カルボキシ−ポリカプロラクトンモノ（メタ）アクリレート（ＣＨ_２＝ＣＨ・ＣＯ・Ｏ（Ｃ_５Ｈ_１０・ＣＯ_２）_ｎＨ、ＣＨ_２＝ＣＣＨ_３・ＣＯ・Ｏ（Ｃ_５Ｈ_１０・ＣＯ_２）_ｎＨ、但しｎは１．５〜３．０）；（メタ）アクリル系重合体（ＩＩＩ）として、エチル（メタ）アクリレート、ブチル（メタ）アクリレート、２−エチルヘキシル（メタ）アクリレート及びラウリル（メタ）アクリレートの２以上を共重合したようなガラス転移温度が低い主鎖骨格を持ち、カルボキシル基を分子中に有し、分子末端および側鎖の少なくとも何れかに（メタ）アクリロイル基およびカルボキシル基の少なくとも何れか一方を有するもの、エチル（メタ）アクリレート及びラウリル（メタ）アクリレートの共重合体からなる主鎖骨格を持ち、分子末端および側鎖の少なくとも何れかにカルボキシル基を有するもの等を挙げることができる。
【００８６】
なお、必要に応じて、以上で説明してきたカルボン基含有アクリル化合物を２種類以上併用することもできる。
【００８７】
また、カルボキシル基含有アクリル化合物の添加量は、得られる接着剤組成物および接着剤層の性能を考慮して注意深く設定され、放射線硬化性化合物の１００質量部に対して、１質量部以上が好ましく、３質量部以上がより好ましく、５質量部以上が更に好ましく、一方、８０質量部以下が好ましく、３０質量部以下がより好ましく、１０質量部以下が更に好ましい。
【００８８】
以上の様な天然ゴム系微粒子とカルボキシル基含有アクリル化合物を含有する放射線硬化性媒体とを用いて接着剤組成物を調製する方法を、図１を用いて説明する。
【００８９】
先ず、図１（ａ）に示す様に、放射線硬化性媒体３２に、天然ゴム系微粒子３０を４０〜８０質量％含有するする水系エマルジョン３１を添加する。
【００９０】
これを混合し、混合物３３を、図１（ｂ）に示す様に例えば温浴３４等を用いて加熱する。加熱により、水系エマルジョンの媒体である水が気化し、混合物外に徐々に除去される。そして、水の減少に伴い、分散媒体が水から放射線硬化性媒体に置換される（図１（ｃ））。
【００９１】
この方法を実際に行うと、水の減少に伴い混合物の粘度が上昇し、分散媒体が置換されると混合物の粘度が急激に低下する。この様な急激な粘度の変化は相転移に起因するものと考えられ、この方法を採用することにより、天然ゴム系微粒子の凝集などが発生することなく、天然ゴム系微粒子が十分に分散した接着剤組成物を得ることができる。
【００９２】
また、天然ゴム系微粒子の分散性に加え、得られる接着剤組成物および接着剤層の性能の観点から望ましい平均粒子径を有する天然ゴム系微粒子を実現できる。なお、天然ゴム系微粒子の平均粒子径としては、０．０１μｍ以上が好ましく、０．０３μｍ以上がより好ましく、０．０５μｍ以上が更に好ましく、一方、５μｍ以下が好ましく、１μｍ以下がより好ましく、０．５μｍ以下が更に好ましい。なお、平均粒子径は、光散乱法などを用いて重量基準により測定する。
【００９３】
また、上記の様な方法を採用すると、天然ゴム系微粒子含有水系エマルジョンから媒体である水を除去したり、天然ゴム系微粒子を乾燥させることなく、分散媒体を直接置換できる。この結果、得られる接着剤組成物の含水率を十分低くすることもでき、具体的には１０質量％以下、より好ましくは５質量％以下、更に好ましくは１質量％以下とできる。
【００９４】
所望の平均粒子径を有する天然ゴム系微粒子が十分均一に分散され、含水率が十分低い接着剤組成物を得るためには、天然ゴム系微粒子含有水系エマルジョンと放射線硬化性媒体との混合比を注意深く選択する必要がある。具体的には、天然ゴム系微粒子含有水系エマルジョン１００質量部に対する、放射線硬化性媒体の比率を、２５質量部以上とすることが好ましく、４０質量部以上がより好ましく、５０質量部以上が更に好ましく、一方、２５０質量部以下が好ましく、１５０質量部以下がより好ましく、１００質量部以下が更に好ましい。
【００９５】
また、所望の平均粒子径を有する天然ゴム系微粒子が十分均一に分散され、含水率が十分低い接着剤組成物を得るためには、天然ゴム系微粒子含有水系エマルジョンの水分を気化させる温度を注意深く選択する必要がある。具体的には、２０℃以上が好ましく、３０℃以上がより好ましく、４０℃以上が更に好ましく、一方、７０℃以下が好ましく、６０℃以下がより好ましく、５０℃以下が更に好ましい。
【００９６】
更に、所望の平均粒子径を有する天然ゴム系微粒子が十分均一に分散され、含水率が十分低い接着剤組成物を十分な生産性で得るためには、天然ゴム系微粒子含有水系エマルジョンの水分を気化させる方法を注意深く選択する必要がある。具体的には、温風を送風する、減圧する等により、気化した水分を強制的に除去し、３０分〜５時間程度で分散媒体の置換を終了する。
【００９７】
天然ゴム系微粒子として、天然ゴム系ゴムとアクリル系モノマー及びスチレン系モノマーの少なくとも何れか一方との共重合体を使用する場合は、以上の分散媒体の置換に先立ち、共重合体を合成する。
【００９８】
この様な共重合体は、天然ゴム系エマルジョンにアクリル系モノマー及びスチレン系モノマーの少なくとも何れか一方を添加し、天然ゴム系エマルジョン中でアクリル系モノマー及びスチレン系モノマーの少なくとも何れか一方をビニル重合して合成できる。
【００９９】
この場合、天然ゴム系微粒子とアクリル系モノマー及びスチレン系モノマーとの反応比としては、天然ゴム系微粒子１００質量部に対して、アクリル系モノマー及びスチレン系モノマーを１〜８０質量部の範囲とし、重合開始剤としては、例えば、有機過酸化物系のものを使用でき、有機過酸化物およびエチレンジアミン類より成るレドックス系開始剤が好ましく、中でもｔ−ブチルハイドロパーオキサイド（ｔ−ＢＨＰＯ）及びテトラエチレンペンタアミン（ＴＥＰＡ）より成るレドックス系開始剤が好ましい。また、有機過酸化物としては、ケトンパーオキサイド、ジアシルパーオキサイド、ジアルキルパーオキサイド、パーオキシケタール、パーオキシエステル、パーオキシカーボネート等が好ましく、エチレンジアミン類としては、エチレンジアミン（ＥＤＡ）、ジエチレントリアミン（ＤＥＴＡ）、テトラエチレンテトラアミン（ＴＥＴＡ）、ペンタエチレンヘキサミン（ＰＥＨＡ）等が好ましい。
【０１００】
また、重合開始剤の使用量は、天然ゴム系微粒子の１００質量部に対して０．０１〜１０質量部の範囲とする。
【０１０１】
更に、必要に応じて、テルペン樹脂、ロジン、油溶性フェノール樹脂、クマロンインデン樹脂、石油系炭化水素樹脂、テルペン樹脂の誘導体、ロジンの誘導体、油溶性フェノール樹脂の誘導体、クマロンインデン樹脂の誘導体、石油系炭化水素樹脂の誘導体などの粘着付与剤を添加することもできる。
【０１０２】
以上の様にして得られる共重合体を合成直後のエマルジョンは、共重合体に加え未反応のモノマー等を含有しているが、共重合体を精製などすることなく、合成直後のエマルジョンに放射線硬化性媒体を混合し、分散媒体を置換することができる。
【０１０３】
ここで、カルボキシル基含有アクリル化合物は、分散媒体の置換工程に先立ち予め放射線硬化性媒体に添加できる。また、分散媒体を置換した後に、カルボキシル基含有アクリル化合物を放射線硬化性媒体に添加することもできる。カルボキシル基含有アクリル化合物を予め放射線硬化性媒体に添加して置けば、放射線硬化性媒体の粘度などの調整を広範囲で行えるため、分散媒体の置換を作業性良好に行うことができる。一方、分散媒体の置換後にカルボキシル基含有アクリル化合物を添加する場合、置換工程中にカルボキシル基含有アクリル化合物が劣化する等を防ぐことができる。なお、一部のカルボキシル基含有アクリル化合物を予め放射線硬化性媒体に添加しておき、分散媒体の置換後に、カルボキシル基含有アクリル化合物を添加することもできる。
【０１０４】
以上の様にして分散媒体を置換後、接着剤層を形成する際に放射線硬化性媒体を硬化するための重合開始剤を、必要に応じて更に添加する。
【０１０５】
また、得られる接着剤層の接着力と接着剤層の基材への定着性を向上させる観点から、スチレン−ブタジエンゴムラテックスを添加する場合もある。スチレン−ブタジエンゴムラテックスは、接着剤組成物が塗布される基体と天然ゴム系微粒子との密着性を向上すると考えられる。
【０１０６】
スチレン−ブタジエンゴムラテックスはスチレン−ブタジエンゴム（ＳＢＲ）から主になり、ＳＢＲとしては、ＳＢＲドライバー及びＳＢＲラテックス等の乳化重合ＳＢＲ；ランダムＳＢＲ、ブロックＳＢＲ及び対称ブロックＳＢＲ等の溶液重合ＳＢＲ等を用いることができる。
【０１０７】
また、ＳＢＲの特性は、スチレン及びブタジエンの共重合比に大きく依存する。この様な観点から、スチレン含有量が低い（３０質量％以下）もの、スチレン含有量が中程度（３０質量％より多く７０質量％以下）のもの、スチレン含有量が高い（７０質量％を超える）もの等を注意深く選択し、スチレン−ブタジエンゴムラテックスにおいて使用する。
【０１０８】
スチレン−ブタジエンゴムラテックスの主成分として使用されるＳＢＲとしては、非変性タイプ、ビニルピリジン変性タイプ及びカルボキシ変性タイプル等を挙げることができる。中でも、基体との密着性に優れ、天然ゴム系微粒子と基体との接着力を十分向上できるため、カルボキシ変性されたスチレン−ブタジエンゴムラテックスが好ましい。
【０１０９】
天然ゴム系微粒子およびスチレン−ブタジエンゴムラテックスの混合比としては、天然ゴム系微粒子の接着力を十分向上させるために、天然ゴム系微粒子１００質量部に対してスチレン−ブタジエンゴムラテックスを、１質量部以上とすることが好ましく、５質量部以上がより好ましい。一方、天然ゴム系微粒子の他の特性を損なわないために、５０質量部以下が好ましく、３０質量部以下がより好ましく、２０質量部以下が更に好ましい。
【０１１０】
また、スチレン−ブタジエンゴムラテックスの含有量を適度な値とすることにより、得られる接着剤層とインク及びトナー等の印刷剤との十分な相互作用を実現できるため、印刷剤の十分な定着性を実現できる。更に、接着剤層を圧着した後の接着強度を適度とできるため、圧着後の不必要な時に接着剤層が剥離することを抑制でき、必要に応じて圧着後の所望時に接着剤層を容易に剥離することができる。
【０１１１】
更に、得られる感圧接着剤組成物の十分な耐ブロッキング性を実現するため、接着剤組成物に、天然ゴム系微粒子に対して非親和性の充填剤を添加することが好ましい。充填剤の添加により接着剤層の表面（接着面）に凹凸が形成されるため、接着面の圧着に先立ち接着面が他の面に接着することが抑制され、耐ブロッキング性が向上すると考えられる。
【０１１２】
加えて、充填剤を添加して接着剤層の表面（接着面）に凹凸を形成すれば、接着面の圧着後に接着面同士の融着が進行し、接着力が高進することも抑制できると考えられる。これらの結果、接着面の圧着後に接着面を剥離する必要がある場合、容易に接着面を剥離することができる。
【０１１３】
また、接着剤層の透明性を阻害しない様にする必要がある場合には、充填剤として、粒子形状が規則的に整ったものが好ましい。この様なものとしては、例えば、各種シリカ系充填剤、各種デンプン系充填剤、合成ゼオライト、微球状（メタ）アクリル樹脂、微球状ポリエチレン、球状アルミナ、ガラス粉末、シラスバルーン、活性白土、酸化チタン及び酸化亜鉛などが挙げられる。これらの充填剤は、単独で用いてもよいし、２種以上組み合わせて用いてもよい。
【０１１４】
なお、これらの充填剤の平均粒子径は、０．０１μｍ以上が好ましく、１μｍ以上がより好ましく、一方、３５μｍ以下が好ましく、２５μｍ以下がより好ましい。また、粒子径の異なる２種以上を組み合わせて用いると、接着剤層の表面を凹凸状に形成し易いので、耐ブロッキング性、剥離性能の向上に有利である。
【０１１５】
以上の様な充填剤の中でも、天然ゴム系微粒子との親和力が小さく、十分な耐ブロッキング性を実現できるため、シリカ系充填剤およびデンプン系充填剤が好ましい。
【０１１６】
充填剤の配合量としては、シリカ系充填剤の場合、天然ゴム系微粒子１００質量部に対して１０質量部以上が好ましく、２０質量部以上がより好ましく、３０質量部以上が更に好ましく、一方、１００質量部以下が好ましく、８０質量部以下がより好ましく、６０質量部以下が更に好ましい。
【０１１７】
また、デンプン系充填剤の場合、天然ゴム系微粒子１００質量部に対して１０質量部以上が好ましく、２０質量部以上がより好ましく、３０質量部以上が更に好ましく、一方、２００質量部以下が好ましく、１８０質量部以下がより好ましく、１６０質量部以下が更に好ましい。
【０１１８】
以上の様な添加剤に加え、耐紫外線性を向上するために、紫外線吸収剤（紫外線吸収剤）を接着剤組成物に添加する場合もある。
【０１１９】
この様な紫外線吸収剤としては、フェニルサリシレート、ブチルフェニルサリシレート及びオクチルフェニルサリシレート等のサリチル酸類；ジヒドロキシベンゾフェノン、ヒドロキシメトキシベンゾフェノン、ヒドロキシオクトキシベンゾフェノン、ヒドロキシドデシルオキシベンゾフェノン、ヒドロキシメトキシスルホベンゾフェノン及びビス（メトキシヒドロキシベンゾイルフェニル）メタン等のベンゾフェノン類；（ヒドロキシメチルフェニル）ベンゾトリアゾール、（ヒドロキシブチルフェニル）ベンゾトリアゾール、（ヒドロキシジブチルフェニル）ベンゾトリアゾール、（ヒドロキシブチルメチルフェニル）クロロベンゾトリアゾール、（ヒドロキシジブチルフェニル）クロロベンゾトリアゾール、（ヒドロキシジアミルフェニル）ベンゾトリアゾール及び［ヒドロキシ（テトラヒドロフタルイミドメチル）メチルフェニル］ベンゾトリアゾール等のベンゾトリアゾール類；エチルヘキシルシアノジフェニルアクリレート及びエチルシアノジフェニルアクリレート等のシアノアクリレート類；ヒンダードアミン類等を挙げることができる。
【０１２０】
また、酸化防止剤を必要とする場合もある。酸化防止剤としては、アミン−ケトン系、ジフェニルアミン系、ジアリール−Ｐ−フェニレンジアミン系およびアルキルアリール−Ｐ−フェニレンジアミン系等の芳香族第２級アミン系を含むアミン類；モノフェノール系、ビスフェノール系およびヒドロキノン系を含むフェノール類；有機イオウ類；ホスファイト類；これらの複合系などを使用することができ、中でも、汚染性および着色性が少ないことからフェノール類が好ましい。
【０１２１】
更に、必要に応じて、合成ゴムエマルジョンを併用して接着剤組成物を作製することもできる。合成ゴムエマルジョンとしては、ポリイソプレンゴム、ポリブタジエンゴム、アクリロニトリル−ブタジエンゴム、メチルメタクリレート−ブタジエンゴム、クロロプレンゴム、ブチルゴム、ポリウレタンゴム、チオコールゴム及びアクリルゴム等の合成ゴムを水性溶媒中に分散させたエマルジョンを例示することができる。
【０１２２】
また、合成樹脂エマルジョンを併用して感圧接着剤組成物を作製することもできる。合成樹脂エマルジョンとしては、ポリ酢酸ビニル系エマルジョン、酢酸ビニル−エチレン共重合体系エマルジョン、ポリアクリル酸エステル系エマルジョン及びポリ塩化ビニル系エマルジョン等を例示することができる。なお、これらの合成樹脂エマルジョンのなかでも、ガラス転移温度（Ｔｇ）が−３０〜２０℃のものが好適である。
【０１２３】
また、天然ゴム系微粒子の分散を安定化させるために乳化剤を添加することもできる。この様な乳化剤としては、ロジンセッケン、ナフタレンスルホン酸塩、脂肪酸セッケン及びアルキルベンゼンスルホン酸塩などのアニオン系やノニオン系の界面活性剤が用いられる。
【０１２４】
更に、必要に応じて、接着剤組成物に、ｐＨ調整剤、酸化防止剤、粘着付与剤、粘度調整剤、老化防止剤、安定剤および着色剤などを混合することもできる。
【０１２５】
以上の様にして得られた接着剤組成物は、グラビアコーター、フレキソ、エアーナイフコーター、ワイヤーバー及びバーコーター等の塗布手段により、基体上に塗布され、塗膜を形成する。
【０１２６】
なお、基体としてはシート状などの形状を有し、通常の紙の他に、合成紙、ポリエチレン、ポリエチレンテレフタレート、ポリプロピレン及び塩化ビニル等の合成フィルムを用いることもできる。これらの合成フィルムを用いる場合には、基体シートの表面にマット処理およびコロナ処理などの表面処理を施すのが好ましい。
【０１２７】
また、基体シート面への接着剤組成物の塗布量は、接着剤層の接着性、剥離性および透明性を維持するため、１ｇ／ｍ^２以上が好ましく、３ｇ／ｍ^２以上がより好ましく、４ｇ／ｍ^２以上が更に好ましく、一方、３０ｇ／ｍ^２以下が好ましく、２０ｇ／ｍ^２以下がより好ましく、７ｇ／ｍ^２以下が更に好ましい。
【０１２８】
接着剤組成物よりなる塗膜は、放射線の照射により硬化される。この結果、図２に示した様に、基体４２のシート上に感圧接着剤層が形成されており、感圧接着剤層は、天然ゴム系微粒子４０が分散される放射線硬化性媒体の放射線硬化物４１である情報担持用シートを得ることができる。なお、分散媒体である放射線硬化性媒体の一部は、硬化前に基体中に拡散していると考えられ、放射線の照射により、４３に示した様に、放射線硬化性媒体の一部は基体中で硬化したり、基体と反応していると考えられる。この結果、接着剤層と基体との高い接着強度を実現できる。
【０１２９】
また、塗膜は硬化前に必要に応じて乾燥されるが、放射線の照射による硬化工程中に乾燥も同時に進行し、また分散媒体が放射線硬化性媒体であるため、短時間で乾燥を終了できるか、乾燥工程を別途に必要としない場合もある。
【０１３０】
ここで、図３（ａ）に、接着剤層が剥離可能な情報担持用シートの例を、図４（ａ）に、接着剤層が剥離不能な情報担持用シートの例を、それぞれ示した。
【０１３１】
図３（ａ）の場合、図３（ｂ）に示す様に、接着剤層１０上に秘匿性および親展性などの情報１２が印刷される。その後、図３（ｃ）に示す様に、接着剤層１０が重合わされる様に情報担持用シートを折り線１１で折り曲げ、接着剤層１０を圧着する。そして、図３（ｄ）に示す様に、必要な時に接着剤層１０は剥離され情報１２が読取られる。この場合、接着剤層は、圧着後の所望な時期に容易に剥離できることが要求される。また、接着剤組成物は全面塗工されている。
【０１３２】
一方、図４（ａ）の場合、図４（ｂ）に示す様に、秘匿性および親展性などの情報２２は接着剤層２０が形成されていない位置に印刷される。その後、図４（ｃ）に示す様に、接着剤層１０が重合わされる様に情報担持用シートを折り線２１で折り曲げ、接着剤層２０を圧着する。そして、図４（ｄ）に示す様に、情報２２の読取りは、接着剤層２０を剥離することなく、基体シートの所定位置（例えば、ミシン目２３）を切断する等して行われる。この場合、接着剤層は、圧着後において実質的に剥離しないことが要求される。また、接着剤組成物はパターン塗工されている。
【０１３３】
なお、感圧接着剤組成物の構成物質の配合比率および圧着条件などを変化させることにより、接着剤層を剥離可能とすることもできるし、剥離不能とすることもできる。
【０１３４】
接着剤層が剥離可能な場合、得られた接着剤層上に、必要な情報が印刷および印字される。印刷方式では一般的な印刷機の他、電子写真法、また、印字方式としてはインクジェット法などを採用することができる。インクジェット法の場合、印刷剤はインクであり、電子写真法の場合、印刷剤はトナーである。その後、印刷剤を乾燥および／または定着するため、紫外線を照射する。また、印刷剤を乾燥および／または定着するために加熱する場合もある。
【０１３５】
以上に説明した情報情報担持用シートは、２つ折り、３つ折り、切り重ね及び各種の重ね合わせの形で接着でき、見開き面を有するハガキ、各種帳票、通知書および各種カード等として好適に利用できる。
【０１３６】
【実施例】
以下、実施例および比較例により本発明を具体的に説明するが、本発明は以下の実施例に制限されるものではない。なお、特に明記しない限り、試薬等は市販の高純度品を使用した。
【０１３７】
（アクリル・スチレン共重合天然ゴムエマルジョンの調製）
天然ゴムラテックス１００質量部を含む水系エマルジョン２００質量部に対し、スチレン１０質量部およびメタクリル酸メチル２５質量部とを混合し、重合開始剤としてｔ−ブチルハイドロパーオキサイド（ｔ−ＢＨＰＯ）０．１質量部およびテトラエチレンペンタミン（ＴＥＰＡ）０．３質量部とを添加した。これを、４５℃／窒素置換雰囲気中で２時間反応させることにより得た共重合体天然ゴムエマルジョンに、粘着付与剤としてテルペン樹脂を５質量部添加して天然ゴム系微粒子を含有する水系エマルジョンを得た。
【０１３８】
（実施例１）接着剤組成物１、情報担持用シート１
以上で得られた天然ゴム系微粒子を含有する水系エマルジョンに、天然ゴム系微粒子１００質量部に対して１００質量部となる様にポリエチレングリコールジアクリレート（商品名：アロニックス　Ｍ−２４０、東亞合成社製）を良く攪拌したのち、混合物を５０℃に昇温して減圧下で気化する水分を除去することにより、１時間で分散媒体を置換した。なお、天然ゴム系微粒子を含有する水系エマルジョンとポリエチレングリコールジアクリレートとの質量比は１６０：１００であった。
【０１３９】
一方、アクリロイルオリゴエステル１００質量部に重合開始剤（商品名：バイキュア５５、アクゾノーベル社製）１００質量部を溶解し、この１０質量部を以上で得た分散媒体置換物２００質量部に添加して、紫外線硬化型の感圧接着剤組成物１を得た。
【０１４０】
得られた感圧接着剤組成物１の含水率を測定したところ、０．５質量％であった。また、天然ゴム系微粒子の平均粒子径は０．２μｍであり、分散性は均一であった。
【０１４１】
この感圧接着剤組成物１をワイヤーバーを使用してフォーム上質紙（商品名：ＮＩＰ　Ｎ（７０ｋｇ連量）王子製紙社製）に６ｇ／ｍ^２になるように塗工し、高圧水銀ランプを使用して硬化させて、接着剤層を形成して、情報担持用シート１を得た。塗工性は、全面塗工およびパターン塗工の場合も、低吸収性の用紙の場合と同様に良好であった。また、乾燥不良などの不具合も発生しなかった。
【０１４２】
得られた情報担持用シート１の接着剤層が形成されている面同士を重ね合わせたのち、シーリングマシンをローラ間ギャップ１６０μｍに設定してシーリングを行った。シーリング後には２枚の用紙は十分な強度で接着されていた。また、この２枚の用紙を剥離したところ、接着剤層と基体とが剥離することなく、綺麗に剥離できた。
【０１４３】
（実施例２）接着剤組成物２、情報担持用シート２
接着剤組成物１で使用したものと同じ天然ゴム系微粒子を含有する水系エマルジョンに、天然ゴム系微粒子１００質量部に対して１００質量部となる様にポリエチレングリコールジアクリレート（商品名：アロニックス　Ｍ−２４０、東亞合成社製）９１質量部とアクリロイルオリゴエステル９質量部とを良く攪拌したのち、混合物を５０℃に昇温して減圧下で気化する水分を除去することにより、１時間で分散媒体を置換した。
【０１４４】
これに光重合開始剤（商品名：バイキュア５５、アクゾノーベル社製）４質量部を添加して、紫外線硬化型の感圧接着剤組成物２を得た。
【０１４５】
得られた感圧接着剤組成物２の含水率を測定したところ、０．５質量％であった。また、天然ゴム系微粒子の平均粒子径は０．２μｍであり、分散性は均一であった。
【０１４６】
この感圧接着剤組成物２をワイヤーバーを使用してフォーム上質紙（商品名：ＮＩＰ　Ｎ（７０ｋｇ連量）王子製紙社製）に６ｇ／ｍ^２になるように塗工し、高圧水銀ランプを使用して硬化させて、接着剤層を形成して、情報担持用シート２を得た。塗工性は、全面塗工およびパターン塗工の場合も、低吸収性の用紙の場合と同様に良好であった。また、乾燥不良などの不具合も発生しなかった。
【０１４７】
得られた情報担持用シート２の接着剤層が形成されている面同士を重ね合わせたのち、シーリングマシンをローラ間ギャップ１００μｍに設定してシーリングを行った。シーリング後には２枚の用紙は十分な強度で接着されていた。また、この２枚の用紙を剥離したところ、接着剤層と基体とが剥離することなく、綺麗に剥離できた。
【０１４８】
（実施例３）接着剤組成物３、情報担持用シート３
接着剤組成物１で使用したものと同じ天然ゴム系微粒子を含有する水系エマルジョンに、天然ゴム系微粒子１００質量部に対して１００質量部となる様にエチレングリコールジグリシジルエーテル（商品名：エポライト　４００Ｅ、共栄社化学社製）を良く攪拌したのち、混合物を５０℃に昇温して減圧下で気化する水分を除去することにより、１時間で分散媒体を置換した。なお、天然ゴム系微粒子を含有する水系エマルジョンとエチレングリコールジグリシジルエーテルとの質量比は１６０：１００であった。
【０１４９】
一方、アクリロイルオリゴエステル１００質量部に重合開始剤（商品名：バイキュア５５、アクゾノーベル社製）１００質量部を溶解し、この１０質量部を以上で得た分散媒体置換物に添加して、紫外線硬化型の感圧接着剤組成物３を得た。
【０１５０】
得られた感圧接着剤組成物３の含水率を測定したところ、０．５質量％であった。また、天然ゴム系微粒子の平均粒子径は０．２μｍであり、分散性は均一であった。
【０１５１】
この感圧接着剤組成物３をワイヤーバーを使用してフォーム上質紙（商品名：ＮＩＰ　Ｎ（７０ｋｇ連量）王子製紙社製）に６ｇ／ｍ^２になるように塗工し、高圧水銀ランプを使用して硬化させて、接着剤層を形成して、情報担持用シート３を得た。塗工性は、全面塗工およびパターン塗工の場合も、低吸収性の用紙の場合と同様に良好であった。また、乾燥不良などの不具合も発生しなかった。
【０１５２】
得られた情報担持用シート３の接着剤層が形成されている面同士を重ね合わせたのち、シーリングマシンをローラ間ギャップ１６０μｍに設定してシーリングを行った。シーリング後には２枚の用紙は十分な強度で接着されていた。また、この２枚の用紙を剥離したところ、接着剤層と基体とが剥離することなく、綺麗に剥離できた。
【０１５３】
（実施例４）接着剤組成物４、情報担持用シート４
接着剤組成物１において、天然ゴム系微粒子１００質量部に対し、武田薬品工業社製ＳＢＲ（商品名：クロスレンＳＫ−７２）が１５質量部となるよう、平均粒子径４μｍの市販のシリカが５０質量部となるよう、平均粒子径１５μｍの市販の小麦デンプンが１５０質量部となるように、これらの充填剤を添加した以外は、同様の操作を行い、接着剤組成物４を得た。また、情報担持用シート１の場合と同様にして、情報担持用シート４を得た。得られた接着剤組成物４及び情報担持用シート４は、良好な性能を有していた。
【０１５４】
（実施例５）
接着剤組成物１で使用したアクリロイルオリゴエステルに代えて、エチレンオキサイド変性コハク酸アクリレート、β−カルボキシエチルアクリレート、ω−カルボキシ−ポリカプロラクトンモノアクリレート、１モル分子内にカルボキシル基を平均５．６モルを有しエチルアクリレート５０モル部およびラウリルアクリレート５０モル部の共重合体（重量平均分子量：３，２００）、２−アクリロイロキシエチルフタレートなどを使用することにより、接着剤組成物および情報担持用シートを得ることができる。得られた接着剤組成物および情報担持用シートは、良好な性能を有する。
【０１５５】
（比較例１）
ポリエチレングリコールジアクリレート（商品名：アロニックス　Ｍ−２４０（東亞合成社製）１００質量部に、光重合開始剤（商品名：バイキュア５５、アクゾノーベル社製））８質量部を溶解した。得られた液をワイヤーバーを使用してフォーム上質紙（商品名：ＮＩＰ　Ｎ（７０ｋｇ連量）王子製紙社製）に６ｇ／ｍ^２になるように塗工し、高圧水銀ランプを使用して硬化させた。得られた塗工紙の接着剤面同士を重ね合わせたのち、シーリングマシンをローラ間ギャップ１００μｍに設定してシーリングを行ったが、シーリング後には２枚の用紙は接着されていなかった。
【０１５６】
（比較例２）
市販の紫外線硬化型感圧擬似接着剤をワイヤーバーを使用してフォーム上質紙（商品名：ＮＩＰ　Ｎ（７０ｋｇ連量）王子製紙社製）に６ｇ／ｍ^２になるように塗工し、高圧水銀ランプを使用して硬化させた。得られた塗工紙の接着剤面同士を重ね合わせたのち、シーリングマシンをローラ間ギャップ１００μｍに設定してシーリングを行ったが、シーリング後には２枚の用紙は接着されていなかった。
【０１５７】
【発明の効果】
天然ゴム系微粒子が、カルボキシル基含有アクリル化合物と放射線硬化性化合物とを含む放射線硬化性媒体中に分散されている接着剤組成物を使用することにより、十分な接着力を有し、各種の充填剤を十分充填でき、塗工後の乾燥時間が短く、全面塗工およびパターン塗工の何れも容易に行え、各種の基体に塗工することができ、基体と感圧接着剤層との十分な接着強度を実現できる。
【図面の簡単な説明】
【図１】接着剤組成物の調製方法を説明する模式図である。
【図２】接着剤層を説明するための模式図である。
【図３】接着剤層が剥離可能な場合の情報担持用シートを説明するための模式図である。
【図４】接着剤層が剥離不能な場合の情報担持用シートを説明するための模式図である。
【符号の説明】
１０　接着剤層
１１　折り線
１２　情報
２０　接着剤層
２１　折り線
２２　情報
２３　ミシン目
３０　天然ゴム系微粒子
３１　水系エマルジョン
３２　放射線硬化性媒体
３３　混合物
３４　温浴
４０　天然ゴム系微粒子
４１　放射線硬化性媒体の硬化層
４２　基体
４３　放射線硬化性媒体の硬化層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an adhesive composition having both the advantages of a natural rubber-based adhesive and the advantage of a radiation-curable medium, and an information carrying sheet using the same. More specifically, an information-carrying sheet having confidentiality and confidentiality, such as a foldable sheet and a superimposed sheet, in which a surface superimposed by folding and cutting are used as an information-carrying surface, a dimensionally expandable arrangement sheet, and copy paper The present invention relates to a sheet for carrying information, such as an office sheet, for bonding the superposed surfaces thereof.
[0002]
[Prior art]
Conventionally, in an information carrying sheet that carries information on a superimposed surface, the entire surface of the superimposed surface is generally partially Alternatively, a pressure-sensitive adhesive layer is provided linearly. This pressure-sensitive adhesive is also called a self-adhesive pressure-sensitive adhesive. By applying a high pressure in a state where the adhesive layers are in contact with each other, the respective polymers self-diffuse or adhere to each other by an anchor effect. In addition, depending on the type of the composition and the degree of pressure, permanent adhesiveness and removable adhesiveness are realized.
[0003]
As an example of such an information carrying sheet, a postcard system having confidentiality and confidentiality has been put to practical use and spread.
[0004]
An example of a postcard system having confidentiality and confidentiality is a postcard containing various information such as personal information, print information and print information, which is folded, cut and overlapped, or another body is overlapped. is there.
[0005]
In these postcard systems, the adhesive layer is releasably pressed in various overlapping modes, the confidentiality and confidentiality information are concealed, mailed, and the recipient peels off the superimposed surface again to conceal the information. The information is read.
[0006]
Further, as another example of a postcard system having confidentiality and confidentiality, an adhesive layer is pressure-bonded in a non-peelable manner in various overlapping modes, the confidentiality information is concealed, mailed, and the recipient is attached to the adhesive portion. Are cut off, the overlapping surface is reopened, and the hidden information is read.
[0007]
[Problems to be solved by the invention]
Examples of the form of the adhesive composition applied to the base of the information carrying sheet such as the above confidential and confidential postcard system include a solution, an aqueous solution, an emulsion (latex), no solvent, and a solid. The adhesive composition in the form of an aqueous solution or emulsion is generally water-based, and the adhesive composition in a solution, solvent-free, and solid form is generally non-aqueous.
[0008]
As a water-based pressure-sensitive adhesive composition, an emulsion of a natural rubber-based latex is generally used, and is applied to a highly absorbent substrate such as high quality paper, which has a high adhesive strength and can be added with various fillers. There are advantages such as workability. However, in the case of a natural rubber-based emulsion, although the entire surface can be easily applied, pattern coating is performed to apply a partial area because the viscosity of the emulsion is low and the coated portion of the substrate shrinks. Was unsuitable for In addition, since the medium is water, it may take a long time to dry after coating.
[0009]
On the other hand, as the non-aqueous pressure-sensitive adhesive composition, it is common to use a radiation-curable medium such as an acrylic resin. For example, as described in JP-A No. An acrylic cured product cured by radiation such as X-ray, X-ray, i-ray, and g-ray is used as a pressure-sensitive adhesive. Such a radiation-curable pressure-sensitive adhesive composition has advantages such as a short drying time after application, and easy application of all-surface application and pattern application. However, a radiation-curable pressure-sensitive adhesive composition may have insufficient adhesive strength, may not be able to sufficiently add a filler due to low adhesive strength, and may be easily absorbed by a substrate, and may have high absorbency such as high quality paper. In some cases, it was difficult to coat the substrate.
[0010]
Further, two layers of the pressure-sensitive adhesive layer obtained from the above-mentioned adhesive composition are pressure-bonded, and then the pressure-bonded pressure-sensitive adhesive layer is peeled off. Is insufficient, the substrate and the pressure-sensitive adhesive layer may peel off, and information may be lost.
[0011]
In view of the above situation, in the present invention, the present invention has a sufficient adhesive strength, can sufficiently fill various types of fillers, has a short drying time after coating, and can be easily applied to both the entire surface coating and the pattern coating. It is an object of the present invention to provide an adhesive composition which can be applied to various substrates and can realize a sufficient adhesive strength between the substrate and the pressure-sensitive adhesive layer.
[0012]
[Means for Solving the Problems]
According to the present invention for achieving the above object, there is provided an adhesive composition which is radiation-curable and contains natural rubber-based fine particles and a carboxyl group-containing acrylic compound.
[0013]
Further, a step of mixing an aqueous emulsion containing natural rubber-based fine particles and a radiation-curable compound,
Heating the mixture with stirring, evaporating and removing the water of the aqueous emulsion, and replacing the medium in which the natural rubber-based fine particles are dispersed from water with the radiation-curable compound;
Adding a carboxyl group-containing acrylic compound to the substituent;
A method for producing an adhesive composition comprising:
[0014]
Further, a step of mixing an aqueous emulsion containing natural rubber-based fine particles, and a radiation-curable medium containing a carboxyl group-containing acrylic compound and a radiation-curable compound,
Raising the temperature while stirring the mixture, vaporizing and removing the water of the aqueous emulsion, and replacing the medium in which the natural rubber-based fine particles are dispersed from water with the radiation-curable medium;
A method for producing an adhesive composition comprising:
[0015]
Also, a pressure-sensitive adhesive layer is formed on the base sheet,
The information-bearing sheet is provided, wherein the pressure-sensitive adhesive layer is a radiation-cured product of an adhesive composition containing natural rubber-based fine particles and a carboxyl group-containing acrylic compound.
[0016]
In the present invention, natural rubber-based fine particles are dispersed in a radiation-curable medium containing a carboxyl group-containing acrylic compound and a radiation-curable compound.
[0017]
In the information-carrying sheet of the present invention, a pressure-sensitive adhesive layer is formed on the base sheet, and the pressure-sensitive adhesive layer has a natural rubber-based fine particle dispersed therein and a carboxyl group-containing acrylic compound and a radiation-curable material. And a radiation-curable medium containing a compound.
[0018]
Further, when the production method of the present invention is employed, a medium in which natural rubber-based fine particles are uniformly dispersed can be replaced with a radiation-curable medium from water without impairing uniform dispersibility. Further, the radiation-curable medium contains a carboxyl group-containing acrylic compound. Such an adhesive composition is applied to a substrate, and cured by irradiating radiation such as ultraviolet rays, electron beams, X-rays, i-rays, and g-rays to form a pressure-sensitive adhesive layer. The term “curing” as used in the present invention includes not only curing due to the formation of a network structure, but also a decrease in fluidity as the polymerization reaction proceeds.
[0019]
The resulting pressure-sensitive adhesive layer contains natural rubber-based fine particles and a carboxyl group-containing acrylic compound, and since the natural rubber-based fine particles are uniformly dispersed in the radiation-curable medium, a uniform and high adhesive force is obtained. realizable. Further, when the radiation-curable medium is cured by radiation, it is considered that the radiation-curable compound reacts with the natural rubber-based fine particles. At this time, it is considered that the carboxyl group-containing acrylic compound also reacts with the radiation-curable compound and the natural rubber-based fine particles. For this reason, it is considered that the natural rubber-based fine particles are firmly fixed in the cured product of the radiation-curable medium, so that a high adhesive strength can be realized. It is considered that the carboxyl group of the carboxyl group-containing acrylic compound is important for these excellent properties.
[0020]
Further, since the adhesive composition has a sufficient pressure-sensitive adhesive force, it is possible to fill the adhesive composition with a sufficient amount of various fillers as needed, thereby realizing a wide range of properties of the adhesive composition.
[0021]
The medium in which the natural rubber-based fine particles are dispersed is a radiation-curable medium containing a carboxyl group-containing acrylic compound. For this reason, not only can the entire surface be satisfactorily applied, but also the adhesive composition has an appropriate viscosity, and the shrinkage of the coated portion of the substrate is small, so that the pattern application can also be satisfactorily performed.
[0022]
In addition, since the medium is a radiation curable medium containing a carboxyl group-containing acrylic compound, drying after coating can be performed quickly.
[0023]
Further, since the medium is a radiation-curable medium containing a carboxyl group-containing acrylic compound and also contains natural rubber-based fine particles, the speed at which the substrate absorbs the adhesive composition can be easily controlled. As a result, not only can the substrate be well coated on a low-absorbing substrate, but also can be coated well on a high-absorbing substrate such as high-quality paper.
[0024]
When the radiation-curable medium containing the carboxyl group-containing acrylic compound is cured by radiation, the radiation-curable medium containing the carboxyl group-containing acrylic compound absorbed by the substrate is considered to cure in the substrate. It is also considered that the radiation-curable medium containing the carboxyl group-containing acrylic compound reacts with the substrate. For this reason, sufficient adhesion strength between the base and the pressure-sensitive adhesive layer can be realized, and the base and the pressure-sensitive adhesive layer are separated when the pressure-sensitive adhesive layer that has been pressed is peeled and concealment information is read. This can suppress the concealment information from being damaged.
[0025]
Therefore, by applying the adhesive composition of the present invention to a substrate to form a pressure-sensitive adhesive layer, an information-carrying sheet having excellent concealing properties such as confidential information and confidential information can be produced.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0027]
(Natural rubber fine particles)
Natural rubber-based fine particles are fine particles of natural rubber-based rubber and the like, and are the main component that expresses adhesive force by pressure bonding.Natural rubber-based rubber has an isoprene skeleton, which is a main component of natural rubber, and Similarly, as long as it has self-adhesiveness, it is not particularly limited, including natural rubber.
[0028]
However, in order to improve the dispersibility and compatibility of the natural rubber-based fine particles in the radiation-curable medium, the natural rubber-based fine particles are preferably a copolymer of a natural rubber-based rubber and an acrylic monomer.
[0029]
Examples of the acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, ) 2-Ethylhexyl acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, lauryl-tridecyl (meth) acrylate, tridecyl (meth) acrylate, cetyl (meth) acrylate (Meth) acrylates such as stearyl, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate and phenyl methacrylate; (meth) acrylamide and methylol (meth) acrylate (Meth) acrylic amides such as amides; Acrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, butyl (meth) acrylate Reactive acrylic monomers such as aminoethyl, glycidyl (meth) acrylate and tetrahydrofurfuryl (meth) acrylate; ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, tri (meth) acrylate Ethylene glycol, tetraethylene glycol di (meth) acrylate, decaethylene glycol di (meth) acrylate, pentadecaethylene glycol di (meth) acrylate, pentacontact ethylene glycol di (meth) acrylate, di (meth) acrylate ) Crosslinkable acrylic monomers such as butylene acrylate, allyl (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and diethylene glycol di (meth) acrylate phthalate. These can be used, and two or more of them can be used in combination.
[0030]
In addition to improving the dispersibility of the natural rubber-based fine particles, and improving the fixability of the adhesive composition to the substrate, the natural rubber-based fine particles include a mixture of a natural rubber-based rubber and a styrene-based monomer. Polymers are preferred.
[0031]
Examples of the styrene monomer include styrene, α-methylstyrene, p-methylstyrene, α-methyl-p-methylstyrene, p-methoxystyrene, o-methoxystyrene, 2,4-dimethylstyrene, chlorostyrene, bromostyrene, and the like. And two or more of these can be used in combination.
[0032]
In view of the above, a natural rubber-based rubber, a copolymer of an acrylic monomer and a styrene-based monomer may be used as the natural rubber-based fine particles. If necessary, two or more kinds of natural rubber-based fine particles can be used in combination.
[0033]
(Radiation curable compound)
The radiation-curable compound is not particularly limited as long as it can exchange the medium favorably and cures favorably by radiation. However, from the viewpoint of medium replacement, curability and the performance of the obtained pressure-sensitive adhesive layer, radiation-curable acrylic compounds and cyclic ether-containing radiation-curable compounds are preferred, and if necessary, these can be used in combination. .
[0034]
As the radiation-curable acrylic compound, an oligomer having at least one or more acryloyl or methacryloyl group is preferable from the viewpoint of realizing good performance of the adhesive composition and the pressure-sensitive adhesive layer. Further, (an oligomer having two or more acryloyl groups or methacryloyl groups is more preferable. Further, an oligomer having a radically reactive unsaturated group in addition to these (meth) acryloyl groups can also be used. Examples of the saturated group include an allyl group and a methallyl group.
[0035]
The type of oligomer is not particularly limited, but preferably has a weight average molecular weight of 30 to 1,000, and includes oligoethylene glycol, epoxy resin oligomer, polyester resin oligomer, polyamide resin oligomer, urethane resin oligomer, oligovinyl alcohol, phenol resin oligomer, and the like. Use
[0036]
Specific examples of the radiation-curable acrylic compound as described above include oligoethylene glycol di (meth) acrylate, nonylphenol EO modified (n = 4) acrylate, acrylate of epoxy resin oligomer (for example, diglycidyl ether of bisphenol A) Diacrylate), a reaction product of an epoxy resin oligomer with acrylic acid and methyltetrahydrophthalic anhydride, a reaction product of an epoxy resin oligomer with 2-hydroxyethyl acrylate, and a reaction of a diglycidyl ether of an epoxy resin oligomer with diallylamine. Product, a ring-opening copolymer ester of glycidyl diacrylate and phthalic anhydride, an ester of a methacrylic acid dimer and a polyol, a polyester obtained from acrylic acid, phthalic anhydride and propylene oxide, Reaction product of rigoethylene glycol, maleic anhydride and glycidyl methacrylate, reaction product of oligovinyl alcohol and N-methylol acrylamide, that of glycidyl methacrylate added after esterification of oligovinyl alcohol with succinic anhydride, Oligomer obtained by reacting diallyl ester of pyromellitic dianhydride with p, p'-diaminodiphenyl, reaction product of ethylene-maleic anhydride copolymer with allylamine, methyl vinyl ether-maleic anhydride copolymer A reaction product of the union and 2-hydroxyethyl acrylate, which is further reacted with glycidyl methacrylate, and an oligooxyalkylene segment and / or a saturated oligoester segment are linked via a urethane bond. , Urethane oligomer having an acryloyl group or a methacryloyl group at both ends, can be mentioned a terminal acrylic-modified isoprene rubber or butadiene rubber, among others, oligoethylene glycol di (meth) acrylate are preferable.
[0037]
If necessary, a photopolymerizable monomer may be used as the radiation-curable acrylic compound. Preferred photopolymerizable monomers include (meth) acrylic acid, (meth) acrylic acid esters such as alkyl, cycloalkyl, halogenated alkyl, alkoxyalkyl, hydroxyalkyl, aminoalkyl, tetrahydrofurfuryl, allyl, glycidyl, benzyl, Phenoxyacrylates, phenoxymethacrylates, alkylene glycols, mono- or diacrylates and methacrylates of polyoxyalkylene glycols, trimethylolpropane triacrylate and methacrylate, such as pentaerythritol tetraacrylate and methacrylate, acrylamide, methacrylamide or derivatives thereof, such as alkyl groups and Acrylamide and methacrylamide mono- or di-substituted with hydroxyalkyl group, diacetone Acrylamide and methacrylamide, N, can be mentioned N'- alkylene-bis acrylamide and methacrylamide and the like.
[0038]
Further, particularly in the case of an application in which curing shrinkage is an obstacle, for example, isobornyl acrylate or methacrylate, norbornyl acrylate or methacrylate, dicyclopentenoxyethyl acrylate or methacrylate, dicyclopentenoxypropyl acrylate or methacrylate Such as acrylate or methacrylate of diethylene glycol dicyclopentenyl monoether, acrylate or methacrylate of oligooxyethylene or oligopropylene glycol dicyclopentenyl monoether, such as dicyclopentenyl cinnamate, dicyclopentenoxy 3,9-bis (1,1-bismethyl-2-oxo) such as ethyl cinnamate, dicyclopentenoxyethyl monofumarate or difumarate; Ethyl) -spiro [5,5] undecane, 3,9-bis (1,1-bismethyl-2-oxyethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane, 3,9- Mono- and diacrylates such as bis (2-oxyethyl) -spiro [5,5] undecane and 3,9-bis (2-oxyethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Or mono-, dimethacrylate, or mono-, diacrylate, or mono-, dimethacrylate of ethylene oxide or propylene oxide addition polymer of spiroglycol, or methyl ether, 1-azabicyclo of these monoacrylate or methacrylate. [2,2,2] -3-octenyl acrylate or methacrylate, bicyclo [2,2,1 Such as 5-heptene-2,3-dicarboxyl monoallyl ester, dicyclopentadienyl acrylate or methacrylate, dicyclopentadienyl oxyethyl acrylate or methacrylate, a dihydrodicyclopentadienyl acrylate or methacrylate is used.
[0039]
Further, if necessary, a polyfunctional acrylic compound can be used as the radiation-curable acrylic compound. Examples of the polyfunctional acrylic compound include copolymerizable (meth) acrylic esters of α, β-unsaturated polycarboxylic acids, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,3-dimethacrylic acid. Alkylene glycol dimethacrylates such as 4-butylene glycol and propylene glycol dimethacrylate, and trimethylolpropane EO-added triacrylate can be used.
[0040]
If necessary, an acrylic monomer, an acrylic oligomer having a degree of polymerization of 2 to 10, and a mixture thereof can be used in combination. In this case, an oligomer obtained by vinyl polymerization of an acrylic monomer is preferable, and examples of the acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate. Hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, (meth) acrylic acid (Meth) acrylic such as lauryl-tridecyl, tridecyl (meth) acrylate, cetyl-stearyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate and phenyl methacrylate Acid esters; (meth) acrylamide and (Meth) acrylic amides such as (meth) acrylic acid methylolamide; (meth) acrylic acid, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, (meth) Reactive acrylic monomers such as dimethylaminoethyl acrylate, diethylaminoethyl (meth) acrylate, butylaminoethyl (meth) acrylate, glycidyl (meth) acrylate and tetrahydrofurfuryl (meth) acrylate; di (meth) ) Ethylene acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, decaethylene glycol di (meth) acrylate, pentadi (meth) acrylate Decaethylene Chole, pentacontaector ethylene glycol di (meth) acrylate, butylene di (meth) acrylate, allyl (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate and di ( Crosslinkable acrylic monomers such as (meth) acrylic acid and diethylene glycol phthalate are preferred. If necessary, two or more of these monomers can be used in combination, and a mixture of oligomers having different degrees of polymerization can also be used.
[0041]
Further, a radiation-curable acrylic compound in which an oligomer component is replaced with a monomer component, such as paracumylphenol EO-modified (n = 1) acrylate, can also be used.
[0042]
On the other hand, as the cyclic ether radiation-curable compound, the cyclic ether radiation-curable compound is not particularly limited, but from the viewpoint of realizing good performance of the adhesive composition and the pressure-sensitive adhesive layer, the cyclic ether structure is From the viewpoint of ring-opening property, a cyclic ether radiation-curable compound containing at least one cyclic ether structure containing 2 to 12 carbons and 1 to 6 oxygens is preferable. Further, the carbon number is more preferably 6 or less, still more preferably 4 or less, and the oxygen number is preferably 4 or less, more preferably 2 or less. Further, the number of the cyclic ether structures is more preferably 2 or more.
[0043]
More specifically, a bridged structure containing -O- is preferable as the cyclic ether structure, and a compound having a group having an epoxy ring such as a glycidyl group is preferable.
[0044]
Further, a compound having a radically reactive unsaturated group in addition to the cyclic ether structure can also be used. Examples of such an unsaturated group include an acryloyl group, a methacryloyl group, an allyl group, and a methallyl group.
[0045]
Further, the group having a cyclic ether structure and the unsaturated group as described above may be bonded to the monomer component and the oligomer component from the viewpoint of realizing good performance of the adhesive composition and the pressure-sensitive adhesive layer. preferable.
[0046]
The type of the oligomer component is not particularly limited, but preferably has a weight average molecular weight of 50 to 1000, and includes oligoethylene glycol, epoxy resin oligomer, polyester resin oligomer, polyamide resin oligomer, urethane resin oligomer, oligovinyl alcohol, and phenol resin oligomer. Use etc.
[0047]
Examples of compounds in which a cyclic ether structure is bonded to these oligomer components include oligoethylene glycol diglycidyl ether.
[0048]
As the type of the monomer component, a monomer of the oligomer component as described above is preferable. As a compound in which a cyclic ether structure is bonded to such a monomer component, for example, ethylene glycol diglycidyl as an example having two glycidyl groups Examples of three ether and glycidyl groups include trimethylolpropane triglycidyl ether.
[0049]
Among the radiation-curable compounds described above, from the viewpoint of the balance between the polymerizability of the pressure-sensitive adhesive composition and the adhesiveness of the obtained pressure-sensitive adhesive layer, two radiation-polymerizable functional groups in one molecule are used. Those having a group are preferred. The radiation-polymerizable functional group may be a (meth) acryloyl group when the radiation-curable compound is a radiation-curable acrylic compound, and an epoxy group when the radiation-curable compound is a cyclic ether-containing radiation-curable compound. It is.
[0050]
The ratio of the radiation curable compound to 100 parts by mass of the natural rubber-based fine particles is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and 100 parts by mass from the viewpoint of the performance of the obtained adhesive composition and adhesive layer. More preferably, the content is 500 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less. If necessary, two or more radiation-curable compounds can be used in combination. In this case, the total amount of the radiation-curable compound is preferably within the above range.
[0051]
Depending on the type of radiation-curable compound used, a polymerization initiator is used in combination. Examples of the polymerization initiator include benzoin, benzoin ethyl ether, benzoin-n-propyl ether, benzoin-isopropyl ether, benzoin alkyl ethers such as benzoin isobutyl-ether, 2,2-dimethoxy-2-phenylacetophenone, benzophenone, Benzyl, diacetyl, diphenyl sulfide, eosin, thionine, 9,10-anthraquinone, 2-ethyl-9,10-anthraquinone, methylbenzoyl formate and the like can be mentioned. These polymerization initiators may be used alone or in combination of two or more. The amount used is 0.1 to 30 parts by mass based on 100 parts by mass of the total amount of the radiation-curable compound.
[0052]
(Carboxyl group-containing acrylic compound)
The carboxyl group-containing acrylic compound is not particularly limited, but from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength, for example, an epoxide (meth) having a hydroxyl group Ester (I) having a structure in which an acrylate and a polyvalent carboxylic acid are bonded by an ester, an ester having a structure in which a hydroxy acid or a hydroxy acid polymer and (meth) acrylic acid are bonded by an ester ( II) and (meth) acrylic polymers (III) having a carboxyl group are preferred.
[0053]
The ester (I) having a structure in which an epoxide (meth) acrylate having a hydroxyl group and a polyvalent carboxylic acid are bound by an ester can be produced, for example, as follows. First, an epoxide is opened in the presence of (meth) acrylic acid to synthesize an ester from (meth) acrylic acid and an epoxide. The resulting ester is considered to be one type of alcohol in which one hydroxyl group of 1,2-diol forms an ester bond with (meth) acrylic acid and the other hydroxyl group has an unreacted structure, It is also considered a type of β-hydroxy (meth) acrylate, which is also called olefin oxide-modified (meth) acrylic acid and is also called epoxide (meth) acrylate having a hydroxyl group or simply epoxide (meth) acrylate.
[0054]
Next, the obtained epoxide (meth) acrylate is reacted with a polycarboxylic acid to form an ester bond between the hydroxyl group of the epoxide (meth) acrylate and the carboxyl group of the polycarboxylic acid. At this time, at least one of the two or more carboxyl groups of the polycarboxylic acid is prevented from reacting or the unreacted one is fractionated to convert the carboxyl group-containing ester (I). obtain.
[0055]
First, a polycarboxylic acid derivative such as a polycarboxylic acid and an anhydride is reacted with an epoxide to obtain an ester having a hydroxyl group derived from the epoxide and a carboxyl group derived from the polycarboxylic acid. An ester bond can be formed from the hydroxyl group of the above and the carboxyl group of (meth) acrylic acid to obtain an ester (I) having a structure similar to the above.
[0056]
The epoxide is not particularly limited, but from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength, for example, ethylene oxide, propylene oxide, 1,2-epoxybutane, Acyclic olefin oxides such as 1,3-epoxybutane, 1,2-epoxypentane, 2,3-epoxypentane, 1,2-epoxyhexane, 2,3-epoxyhexane, and 3,4-epoxyhexane; cyclohexene oxide and the like And the like, and among them, acyclic olefin oxides such as ethylene oxide and propylene oxide are preferred.
[0057]
The polycarboxylic acid is not particularly limited, but from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having a sufficient strength, for example, malonic acid, succinic acid, glutaric acid Aliphatic dicarboxylic acids such as acetic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid; saturated aliphatic tricarboxylic acids such as hexane-2,3,5-tricarboxylic acid; hexahydrophthalic acid, hexahydroisophthalic acid Cycloaliphatic dicarboxylic acid such as hexahydroterephthalic acid; saturated cycloaliphatic tricarboxylic acid such as cyclohexanetricarboxylic acid; unsaturated aliphatic dicarboxylic acid such as maleic acid and fumaric acid; tetrahydrophthalic acid, tetrahydroisophthalic acid, tetrahydroterephthalic acid Unsaturated cycloaliphatic dicarboxylic acids such as acids; phthalic acid, Sofutaru acid, terephthalic acid, aromatic dicarboxylic acids such as naphthoic diacid; trimesic acid, trimellitic acid, and aromatic tricarboxylic acids such as naphthoic triacid is preferred.
[0058]
Among them, malonic acid, succinic acid, glutaric acid, adipic acid, saturated aliphatic dicarboxylic acids such as pimelic acid; hexahydrophthalic acid, hexahydroisophthalic acid, saturated cyclic aliphatic dicarboxylic acids such as hexahydroterephthalic acid; phthalic acid, Aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, and naphthoedioic acid are preferred, and saturated aliphatic dicarboxylic acids such as succinic acid; saturated cyclic aliphatic dicarboxylic acids such as hexahydrophthalic acid; aromatics such as phthalic acid Dicarboxylic acids are preferred.
[0059]
As the ester (I) having the above structure, the following general formula (I) can be exemplified.
[0060]
Embedded image

[0061]
Where R ¹ Is hydrogen or a methyl group; ² Is an alkylene which may have a cyclic structure having 2 to 10 carbon atoms; ³ Is alkylene which may have a cyclic structure having 1 to 20 carbon atoms, alkenylene which may have a cyclic structure having 1 to 20 carbon atoms, or arylene having 1 to 20 carbon atoms.
[0062]
Note that R ² Is derived from the above-mentioned epoxide, and is preferably derived from the above-mentioned preferred epoxide such as ethylene and propylene. Also, R ³ Is derived from the above-mentioned polyvalent carboxylic acid, and is preferably derived from the above-mentioned preferred polyvalent carboxylic acid such as ethylene, 1,2-cyclohexylene and o-phenylene.
[0063]
Examples of the ester (II) having a structure in which a hydroxy acid or a hydroxy acid polymer and (meth) acrylic acid are bonded by an ester include, for example, an ester obtained by reacting a hydroxy acid with (meth) acrylic acid. By reacting lactone with (meth) acrylic acid to form an ester, or by reacting a hydroxy acid polymer such as oligoester or polyester with (meth) acrylic acid to form an ester, or in the presence of (meth) acrylic acid Polycondensation of a hydroxy acid into an oligoester and a polyester, an oligoester and a polyester obtained by ring-opening polymerization of a lactone and an ester by reacting with (meth) acrylic acid, and in the presence of (meth) acrylic acid And by subjecting the lactone to ring-opening polymerization.
[0064]
Oligoesters and polyesters comprising a hydroxy acid polymer are obtained by polycondensation of a hydroxy acid, and the degree of polymerization of the hydroxy acid can be made a desired value by setting the reaction rate to a predetermined value. Then, an ester bond (II) is obtained by forming an ester bond between the hydroxyl group of the obtained hydroxy acid polymer and the carboxyl group of (meth) acrylic acid.
[0065]
In the case of polycondensing a hydroxy acid in the presence of (meth) acrylic acid, the (meth) acrylic acid acts as a polymerization terminator, and is added to a hydroxyl group terminal of an oligoester or polyester obtained by polycondensation of a hydroxy acid. An ester (II) in which (meth) acrylic acid is ester-linked is obtained. In this case, the degree of polymerization of the hydroxy acid can be set to a desired value by setting the charging ratio of the (meth) acrylic acid and the hydroxy acid to a predetermined value. For example, increasing the amount of (meth) acrylic acid relative to the amount of hydroxy acid will decrease the degree of polymerization of the hydroxy acid, and decreasing the amount of (meth) acrylic acid relative to the amount of hydroxy acid will decrease the degree of polymerization of the hydroxy acid. The degree of polymerization can be increased.
[0066]
Oligoesters and polyesters comprising a hydroxy acid polymer are obtained by subjecting lactone to ring-opening polymerization, and by setting the reaction rate to a predetermined value, the degree of polymerization of the hydroxy acid can be set to a desired value. it can. Then, an ester bond (II) is obtained by forming an ester bond between the hydroxyl group of the obtained lactone polymer and the carboxyl group of (meth) acrylic acid.
[0067]
When lactone is subjected to ring-opening polymerization in the presence of (meth) acrylic acid, (meth) acrylic acid acts as a polymerization terminator, and is added to the hydroxyl group terminal of oligoester and polyester obtained by lactone ring-opening polymerization. An ester (II) in which (meth) acrylic acid is ester-linked is obtained. In this case, the degree of polymerization of lactone can be set to a desired value by setting the charging ratio of (meth) acrylic acid to lactone to a predetermined value. For example, increasing the amount of (meth) acrylic acid with respect to the amount of lactone decreases the degree of polymerization of lactone, and decreasing the amount of (meth) acrylic acid with respect to the amount of lactone increases the degree of polymerization of lactone. it can.
[0068]
The degree of polymerization of the hydroxy acid and the lactone is greater than 1 in number-average degree of polymerization and 1.1 or more from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength. Is more preferable, and 1.2 or more is more preferable, while 5 or less is preferable, 4 or less is more preferable, and 3 or less is further more preferable.
[0069]
Although the hydroxy acid is not particularly limited, from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having a sufficient strength, for example, glycolic acid, hydroxypropanoic acid, hydroxybutanoic acid, hydroxy Saturated aliphatic hydroxy acids such as pentanoic acid, hydroxyhexanoic acid, hydroxyheptanoic acid, hydroxyoctanoic acid, hydroxynonanoic acid, hydroxydecanoic acid, hydroxydodecanoic acid, hydroxytetradecanoic acid, and hydroxyoctadecanoic acid; saturated cyclic acids such as hydroxycyclohexanecarboxylic acid Aliphatic hydroxy acids; hydroxybenzoic acid, hydroxyphenylacetic acid, aromatic hydroxy acids such as (hydroxyphenyl) propionic acid, hydroxytoluic acid and hydroxynaphthoic acid are preferred.
[0070]
Among them, saturated aliphatic hydroxy acids such as hydroxypropanoic acid; saturated cycloaliphatic hydroxy acids such as hydroxycyclohexanecarboxylic acid; and aromatic hydroxy acids such as hydroxybenzoic acid are preferred.
[0071]
The lactone is also not particularly limited, but from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength, for example, α-lactone, β-lactone, γ-caprolactone Δ-lactones such as γ-lactone and δ-caprolactone, ε-lactones such as ε-caprolactone, etc. are preferable, and ε-caprolactone is particularly preferable.
[0072]
As the ester (II) having the above structure, the following general formula (II) can be exemplified.
[0073]
Embedded image

[0074]
Here, in the formula, n is an integer of 1 to 5 or a real number; ⁴ Is hydrogen or a methyl group; ⁵ Is alkylene which may have a cyclic structure having 1 to 20 carbon atoms, alkenylene which may have a cyclic structure having 1 to 20 carbon atoms, or arylene having 1 to 20 carbon atoms.
[0075]
In particular, R ⁵ In the case where there is a distribution in the degree of polymerization of the repeating structural unit containing, n represents the number average degree of polymerization and is not necessarily an integer. When n is 1, the ester (II) is an ester of hydroxy acid and (meth) acrylic acid or an ester of lactone and (meth) acrylic acid. It is an ester of a polymer and (meth) acrylic acid or an ester of a lactone polymer such as an oligomer or a polymer and (meth) acrylic acid. In the case of an ester of a hydroxy acid polymer or a lactone polymer and (meth) acrylic acid, from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength, n Is greater than 1, more preferably 1.1 or more, still more preferably 1.2 or more, while 5 or less, more preferably 4 or less, still more preferably 3 or less.
[0076]
Note that R ⁵ Is derived from a hydroxy acid or lactone, and is preferably derived from the above-mentioned preferred hydroxy acid or lactone such as ethylene, cyclohexylene, phenylene, pentamethylene and the like.
[0077]
The (meth) acrylic polymer (III) having a carboxyl group is obtained by polymerizing (meth) acrylic monomers such as (meth) acrylic acid, (meth) acrylate and derivatives thereof, Depending on the case, a copolymer may be produced and used in combination of two or more (meth) acrylic monomers.
[0078]
The (meth) acrylic monomer is not particularly limited, but from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength, for example, methyl (meth) acrylate , Ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acrylic acid Decyl, dodecyl (meth) acrylate, lauryl (meth) acrylate, lauryl-tridecyl (meth) acrylate, tridecyl (meth) acrylate, cetyl-stearyl (meth) acrylate, stearyl (meth) acrylate, (meth) ) (Meth) acrylic acids such as cyclohexyl acrylate, benzyl (meth) acrylate and phenyl methacrylate Stels; acrylic monomers having a carboxyl group such as (meth) acrylic acid; (meth) acrylic amides such as (meth) acrylic amide and (meth) acrylic methylolamide; hydroxyethyl (meth) acrylate , Hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, butylaminoethyl (meth) acrylate, glycidyl (meth) acrylate and Reactive acrylic monomers such as tetrahydrofurfuryl (meth) acrylate; ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetra (meth) acrylate ethylene glycol Decaethylene glycol di (meth) acrylate, pentadecaethylene glycol di (meth) acrylate, pentacontact ethylene glycol di (meth) acrylate, butylene di (meth) acrylate, allyl (meth) acrylate, tri ( Crosslinkable acrylic monomers such as trimethylolpropane (meth) acrylate, pentaerythritol tetra (meth) acrylate and diethylene glycol di (meth) acrylate can be used. Among them, alkyl (meth) acrylate and (meth) acryl Acids are preferred.
[0079]
Further, it is possible to copolymerize a monomer capable of copolymerizing with the (meth) acrylic monomer as described above and introducing a carboxyl group and a (meth) acryloyl group into the (meth) acrylic polymer (III). Can also. Examples of the monomer for introducing a carboxyl group include alkenyl carboxylic acids such as vinyl acetic acid and allyl acetic acid; and alkenyl (meth) acrylates such as vinyl (meth) acrylate and allyl (meth) acrylate.
[0080]
Furthermore, a group having a carboxyl group at the terminal of the (meth) acrylic polymer (III) can be introduced, and a group having a (meth) acryloyl group can be introduced.
[0081]
The following general formula (III) can be exemplified as the (meth) acrylic polymer (III) as described above.
[0082]
Embedded image

[0083]
Where m _i Is m corresponding to l kinds of repeating structural units ₁ ~ M _l And l is an integer of 1 or more; _i Are independently one or more integers or real numbers; ⁶ , R ⁸ⁱ And R ¹⁰ Are each independently a hydrogen or a methyl group; ⁷ Is a group containing a carboxyl group, a group containing a (meth) acryloyl group, or -CO ₂ R ⁷ In R ⁷ Is hydrogen or a hydrocarbon group having 1 to 20 carbon atoms; ⁹ⁱ Is a group containing a carboxyl group, a group containing a (meth) acryloyl group, or -CO ₂ R ⁹ⁱ In R ⁹ⁱ Is hydrogen or a hydrocarbon group having 1 to 20 carbon atoms; ¹¹ Is a group containing a carboxyl group, a group containing a (meth) acryloyl group, or -CO ₂ R ¹¹ In R ¹¹ Is hydrogen or a hydrocarbon group having 1 to 20 carbon atoms; X ¹ And X ² Are each independently a hydrogen, a group containing a carboxyl group or a group containing a (meth) acryloyl group; ⁷ , L ⁹ⁱ And L ¹¹ Does not contain a carboxyl group? ⁷ , R ⁹ⁱ And R ¹¹ Is not hydrogen, X ¹ And X ² At least one contains a carboxyl group. In particular, L ⁹ⁱ When there is a distribution in the degree of polymerization of the repeating structural unit containing _i Represents the number average degree of polymerization, and is not necessarily an integer.
[0084]
The weight average molecular weight of the (meth) acrylic polymer (III) is preferably 1,000 or more from the viewpoint of sufficiently improving the initial adhesive strength while suppressing the advancement of the pressure-sensitive adhesive layer having sufficient strength. Is preferable, and 1,500 or more is more preferable, while 10,000 or less is preferable, and 5,000 or less is more preferable.
[0085]
As a specific example of the carboxylic group-containing acrylic compound described above, a preferred ester compound (I) is ethylene oxide-modified succinic acid (meth) acrylate (CH). ₂ ＝ CH ・ CO ・ OC ₂ H ₄ O ・ CO ・ C ₂ H ₄ ・ CO ₂ H, CH ₂ = CCH ₃ ・ CO ・ OC ₂ H ₄ O ・ CO ・ C ₂ H ₄ ・ CO ₂ H), 2- (meth) acryloyloxyethyl phthalate (CH ₂ ＝ CH ・ CO ・ OC ₂ H ₄ O ・ CO ・ φ ・ CO ₂ H, CH ₂ = CCH ₃ ・ CO ・ OC ₂ H ₄ O ・ CO ・ φ ・ CO ₂ H, where φ represents a 1,2-phenylene group), 2- (meth) acryloyloxyethyltetrahydrophthalate, 2- (meth) acryloyloxyethylhexahydrophthalate (CH ₂ ＝ CH ・ CO ・ OC ₂ H ₄ O ・ CO ・ ch ・ CO ₂ H, CH ₂ = CCH ₃ ・ CO ・ OC ₂ H ₄ O ・ CO ・ ch ・ CO ₂ H, wherein ch represents a 1,2-cyclohexylene group), 2- (meth) acryloyloxypropyl phthalate (CH ₂ ＝ CH ・ CO ・ OC ₃ H ₆ O ・ CO ・ φ ・ CO ₂ H, CH ₂ = CCH ₃ ・ CO ・ OC ₃ H ₆ O ・ CO ・ φ ・ CO ₂ H, wherein φ represents a 1,2-phenylene group); As a preferred ester (II), β-carboxyethyl (meth) acrylate (CH ₂ ＝ CH (CO ・ OC ₂ H ₄ ) _n CO ₂ H, CH ₂ = CCH ₃ (CO ・ OC ₂ H ₄ ) _n CO ₂ H, where n is 1.5 to 3.0), (meth) acryloyl oligoester (CH ₂ ＝ CH ・ CO ・ O (C ₂ H ₄ ・ CO ₂ ) _n H, CH ₂ = CCH ₃ ・ CO ・ O (C ₂ H ₄ ・ CO ₂ ) _n H, where n is 1.1 to 1.7), ω-carboxy-polycaprolactone mono (meth) acrylate (CH ₂ ＝ CH ・ CO ・ O (C ₅ H ₁₀ ・ CO ₂ ) _n H, CH ₂ = CCH ₃ ・ CO ・ O (C ₅ H ₁₀ ・ CO ₂ ) _n H, where n is 1.5 to 3.0); (meth) acrylic polymer (III) as ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate and lauryl (meth) It has a main chain skeleton having a low glass transition temperature, such as a copolymer of two or more acrylates, has a carboxyl group in the molecule, and has at least one of a (meth) acryloyl group and a carboxyl group at at least one of a molecular terminal and a side chain. One having one of them, one having a main chain skeleton composed of a copolymer of ethyl (meth) acrylate and lauryl (meth) acrylate, and having a carboxyl group in at least one of a molecular terminal and a side chain, and the like. it can.
[0086]
If necessary, two or more of the carboxylic group-containing acrylic compounds described above can be used in combination.
[0087]
The addition amount of the carboxyl group-containing acrylic compound is carefully set in consideration of the performance of the obtained adhesive composition and the adhesive layer, and is preferably 1 part by mass or more based on 100 parts by mass of the radiation-curable compound. 3 parts by mass or more is more preferable, 5 parts by mass or more is more preferable, while 80 parts by mass or less is preferable, 30 parts by mass or less is more preferable, and 10 parts by mass or less is further preferable.
[0088]
A method for preparing an adhesive composition using the above-described natural rubber-based fine particles and a radiation-curable medium containing a carboxyl group-containing acrylic compound will be described with reference to FIG.
[0089]
First, as shown in FIG. 1A, an aqueous emulsion 31 containing 40 to 80% by mass of natural rubber-based fine particles 30 is added to a radiation-curable medium 32.
[0090]
These are mixed, and the mixture 33 is heated using, for example, a warm bath 34 or the like as shown in FIG. By heating, water as a medium of the aqueous emulsion is vaporized and gradually removed from the mixture. Then, as the water decreases, the dispersion medium is replaced by the radiation-curable medium from water (FIG. 1 (c)).
[0091]
When this method is actually performed, the viscosity of the mixture increases with decreasing water, and the viscosity of the mixture decreases rapidly when the dispersion medium is replaced. Such a rapid change in viscosity is considered to be caused by a phase transition, and by adopting this method, natural rubber-based fine particles are sufficiently dispersed without causing aggregation of the natural rubber-based fine particles. Agent composition can be obtained.
[0092]
In addition, natural rubber-based fine particles having a desirable average particle size can be realized from the viewpoint of the performance of the obtained adhesive composition and adhesive layer in addition to the dispersibility of the natural rubber-based fine particles. The average particle diameter of the natural rubber-based fine particles is preferably 0.01 μm or more, more preferably 0.03 μm or more, and still more preferably 0.05 μm or more, while 5 μm or less, more preferably 1 μm or less, and 0 μm or less. 0.5 μm or less is more preferable. The average particle size is measured on a weight basis using a light scattering method or the like.
[0093]
In addition, when the above method is employed, the dispersing medium can be directly replaced without removing water as a medium from the aqueous emulsion containing natural rubber-based fine particles or drying the natural rubber-based fine particles. As a result, the water content of the obtained adhesive composition can be sufficiently reduced, specifically, 10% by mass or less, more preferably 5% by mass or less, and further preferably 1% by mass or less.
[0094]
In order to obtain an adhesive composition in which natural rubber-based fine particles having a desired average particle diameter are sufficiently uniformly dispersed and have a sufficiently low water content, the mixing ratio between the natural rubber-based fine particle-containing aqueous emulsion and the radiation-curable medium must be adjusted. You need to choose carefully. Specifically, the ratio of the radiation-curable medium to 100 parts by mass of the natural rubber-based fine particle-containing aqueous emulsion is preferably 25 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more. On the other hand, it is preferably at most 250 parts by mass, more preferably at most 150 parts by mass, even more preferably at most 100 parts by mass.
[0095]
Further, in order to obtain an adhesive composition in which natural rubber-based fine particles having a desired average particle diameter are sufficiently uniformly dispersed and have a sufficiently low water content, the temperature at which the moisture of the natural rubber-based fine particle-containing aqueous emulsion is vaporized is carefully controlled. You have to choose. Specifically, the temperature is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, still more preferably 40 ° C. or higher, while 70 ° C. or lower is preferable, 60 ° C. or lower is more preferable, and 50 ° C. or lower is even more preferable.
[0096]
Furthermore, in order for natural rubber-based fine particles having a desired average particle diameter to be sufficiently uniformly dispersed and to obtain an adhesive composition having a sufficiently low water content with sufficient productivity, the water content of the natural rubber-based fine particle-containing aqueous emulsion must be reduced. Careful selection of the vaporization method is required. Specifically, vaporized water is forcibly removed by blowing warm air, reducing pressure, or the like, and the replacement of the dispersion medium is completed in about 30 minutes to 5 hours.
[0097]
When a copolymer of natural rubber-based rubber and at least one of an acrylic monomer and a styrene-based monomer is used as the natural rubber-based fine particles, the copolymer is synthesized prior to the replacement of the dispersion medium.
[0098]
Such a copolymer is obtained by adding at least one of an acrylic monomer and a styrene monomer to a natural rubber emulsion and subjecting at least one of the acrylic monomer and the styrene monomer to vinyl polymerization in the natural rubber emulsion. Can be combined.
[0099]
In this case, the reaction ratio of the natural rubber-based fine particles to the acrylic monomer and the styrene-based monomer is 100 parts by weight of the natural rubber-based fine particles, and the acrylic monomer and the styrene-based monomer are in the range of 1 to 80 parts by weight, As the polymerization initiator, for example, an organic peroxide-based initiator can be used, and a redox-based initiator composed of an organic peroxide and ethylenediamines is preferable. Among them, t-butyl hydroperoxide (t-BHPO) and tetraethylene Redox initiators composed of pentaamine (TEPA) are preferred. As the organic peroxide, ketone peroxide, diacyl peroxide, dialkyl peroxide, peroxyketal, peroxyester, peroxycarbonate, and the like are preferable. As ethylenediamines, ethylenediamine (EDA), diethylenetriamine (DETA) , Tetraethylenetetraamine (TETA), pentaethylenehexamine (PEHA) and the like are preferable.
[0100]
The amount of the polymerization initiator used is in the range of 0.01 to 10 parts by mass with respect to 100 parts by mass of the natural rubber-based fine particles.
[0101]
Further, if necessary, terpene resin, rosin, oil-soluble phenol resin, coumarone indene resin, petroleum hydrocarbon resin, terpene resin derivative, rosin derivative, oil-soluble phenol resin derivative, cumarone indene resin derivative And a tackifier such as a derivative of a petroleum hydrocarbon resin.
[0102]
The emulsion obtained immediately after the synthesis of the copolymer obtained as described above contains unreacted monomers and the like in addition to the copolymer. A curable medium can be mixed to replace the dispersion medium.
[0103]
Here, the carboxyl group-containing acrylic compound can be added to the radiation-curable medium in advance of the replacement step of the dispersion medium. Further, after replacing the dispersion medium, a carboxyl group-containing acrylic compound can be added to the radiation-curable medium. If the carboxyl group-containing acrylic compound is added to the radiation-curable medium in advance, the viscosity and the like of the radiation-curable medium can be adjusted over a wide range, and the replacement of the dispersion medium can be performed with good workability. On the other hand, when the carboxyl group-containing acrylic compound is added after the replacement of the dispersion medium, it is possible to prevent the carboxyl group-containing acrylic compound from deteriorating during the replacement step. In addition, it is also possible to add a part of the carboxyl group-containing acrylic compound in advance to the radiation-curable medium and replace the dispersion medium with the carboxyl group-containing acrylic compound.
[0104]
After replacing the dispersion medium as described above, a polymerization initiator for curing the radiation-curable medium when forming the adhesive layer is further added as necessary.
[0105]
Further, from the viewpoint of improving the adhesive strength of the obtained adhesive layer and the fixability of the adhesive layer to the base material, styrene-butadiene rubber latex may be added in some cases. The styrene-butadiene rubber latex is considered to improve the adhesion between the substrate on which the adhesive composition is applied and the natural rubber-based fine particles.
[0106]
Styrene-butadiene rubber latex is mainly composed of styrene-butadiene rubber (SBR), and as SBR, emulsion polymerization SBR such as SBR driver and SBR latex; solution polymerization SBR such as random SBR, block SBR and symmetric block SBR, etc. are used. be able to.
[0107]
In addition, the characteristics of SBR greatly depend on the copolymerization ratio of styrene and butadiene. From such a viewpoint, those having a low styrene content (30% by mass or less), those having a medium styrene content (more than 30% by mass and 70% by mass or less), and those having a high styrene content (more than 70% by mass) ) Carefully selected and used in styrene-butadiene rubber latex.
[0108]
Examples of the SBR used as a main component of the styrene-butadiene rubber latex include a non-modified type, a vinylpyridine-modified type, and a carboxy-modified type. Above all, carboxy-modified styrene-butadiene rubber latex is preferred because it has excellent adhesion to the substrate and can sufficiently improve the adhesion between the natural rubber-based fine particles and the substrate.
[0109]
The mixing ratio of the natural rubber-based fine particles and the styrene-butadiene rubber latex was 1 part by weight of the styrene-butadiene rubber latex per 100 parts by weight of the natural rubber-based fine particles in order to sufficiently improve the adhesive force of the natural rubber-based fine particles. It is preferably at least 5 parts by mass, more preferably at least 5 parts by mass. On the other hand, the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less so as not to impair other properties of the natural rubber-based fine particles.
[0110]
In addition, by setting the content of the styrene-butadiene rubber latex to an appropriate value, a sufficient interaction between the obtained adhesive layer and a printing agent such as an ink or a toner can be realized, so that sufficient fixing property of the printing agent can be achieved. Can be realized. Further, since the adhesive strength after the pressure-bonding of the adhesive layer can be made moderate, it is possible to prevent the adhesive layer from peeling off when unnecessary after the pressure bonding, and to facilitate the adhesive layer when desired after the pressure bonding as necessary. Can be peeled off.
[0111]
Further, in order to realize sufficient blocking resistance of the obtained pressure-sensitive adhesive composition, it is preferable to add a filler that is incompatible with the natural rubber-based fine particles to the adhesive composition. Since the addition of the filler causes unevenness on the surface (adhesive surface) of the adhesive layer, it is considered that the adhesive surface is prevented from adhering to another surface prior to pressure bonding of the adhesive surface, and the blocking resistance is improved. .
[0112]
In addition, if a filler is added to form irregularities on the surface (adhesive surface) of the adhesive layer, the adhesion between the adhesive surfaces proceeds after the adhesion of the adhesive surfaces, and the increase in the adhesive force can be suppressed. it is conceivable that. As a result, when it is necessary to peel the adhesive surface after the bonding of the adhesive surface, the adhesive surface can be easily peeled.
[0113]
When it is necessary not to hinder the transparency of the adhesive layer, a filler having a regular particle shape is preferable as the filler. Such materials include, for example, various silica fillers, various starch fillers, synthetic zeolites, fine spherical (meth) acrylic resin, fine spherical polyethylene, spherical alumina, glass powder, shirasu balloon, activated clay, titanium oxide And zinc oxide. These fillers may be used alone or in combination of two or more.
[0114]
The average particle size of these fillers is preferably 0.01 μm or more, more preferably 1 μm or more, while preferably 35 μm or less, and more preferably 25 μm or less. When two or more kinds of particles having different particle diameters are used in combination, the surface of the adhesive layer can be easily formed in an uneven shape, which is advantageous in improving blocking resistance and peeling performance.
[0115]
Among the above fillers, silica-based fillers and starch-based fillers are preferable because they have low affinity with natural rubber-based fine particles and can realize sufficient blocking resistance.
[0116]
The amount of the filler is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more with respect to 100 parts by mass of the natural rubber-based fine particles in the case of a silica-based filler. It is preferably at most 100 parts by mass, more preferably at most 80 parts by mass, even more preferably at most 60 parts by mass.
[0117]
In the case of a starch-based filler, it is preferably at least 10 parts by mass, more preferably at least 20 parts by mass, still more preferably at least 30 parts by mass, and preferably at most 200 parts by mass, based on 100 parts by mass of the natural rubber-based fine particles. , 180 parts by mass or less, more preferably 160 parts by mass or less.
[0118]
In addition to the additives described above, an ultraviolet absorber (ultraviolet absorber) may be added to the adhesive composition in order to improve ultraviolet resistance.
[0119]
Examples of such ultraviolet absorbers include salicylic acids such as phenyl salicylate, butylphenyl salicylate, and octylphenyl salicylate; dihydroxybenzophenone, hydroxymethoxybenzophenone, hydroxyoctoxybenzophenone, hydroxydodecyloxybenzophenone, hydroxymethoxysulfobenzophenone, and bis (methoxyhydroxysalicylate). Benzophenones such as benzoylphenyl) methane; (hydroxymethylphenyl) benzotriazole, (hydroxybutylphenyl) benzotriazole, (hydroxydibutylphenyl) benzotriazole, (hydroxybutylmethylphenyl) chlorobenzotriazole, (hydroxydibutylphenyl) chlorobenzo Triazole, (hydroxydiamilfe Can be exemplified hindered amine and the like; le) benzotriazole and [hydroxy (tetrahydrophthalimide) methyl phenyl] benzotriazole such as benzotriazole; cyanoacrylates such as ethyl hexyl cyano-diphenyl acrylate and ethyl cyano diphenylacrylate.
[0120]
Also, an antioxidant may be required. As antioxidants, amines including aromatic secondary amines such as amine-ketones, diphenylamines, diaryl-P-phenylenediamines and alkylaryl-P-phenylenediamines; monophenols, bisphenols And phenols containing hydroquinones; organic sulfurs; phosphites; composites thereof, and the like. Among them, phenols are preferred because of their low contamination and coloring properties.
[0121]
Further, if necessary, an adhesive composition can be prepared by using a synthetic rubber emulsion in combination. As the synthetic rubber emulsion, an emulsion obtained by dispersing a synthetic rubber such as polyisoprene rubber, polybutadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, chloroprene rubber, butyl rubber, polyurethane rubber, thiochol rubber and acrylic rubber in an aqueous solvent is used. Examples can be given.
[0122]
In addition, a pressure-sensitive adhesive composition can be prepared by using a synthetic resin emulsion in combination. Examples of the synthetic resin emulsion include a polyvinyl acetate emulsion, a vinyl acetate-ethylene copolymer emulsion, a polyacrylate emulsion, and a polyvinyl chloride emulsion. Among these synthetic resin emulsions, those having a glass transition temperature (Tg) of −30 to 20 ° C. are preferable.
[0123]
In addition, an emulsifier can be added to stabilize the dispersion of the natural rubber-based fine particles. As such an emulsifier, an anionic or nonionic surfactant such as rosin soap, naphthalene sulfonate, fatty acid soap and alkylbenzene sulfonate is used.
[0124]
Further, if necessary, a pH adjuster, an antioxidant, a tackifier, a viscosity adjuster, an antioxidant, a stabilizer, a colorant, and the like can be mixed with the adhesive composition.
[0125]
The adhesive composition obtained as described above is coated on a substrate by a coating means such as a gravure coater, flexo, air knife coater, wire bar, and bar coater to form a coating film.
[0126]
The substrate has a shape such as a sheet, and other than ordinary paper, a synthetic paper, a synthetic film such as polyethylene, polyethylene terephthalate, polypropylene, and vinyl chloride can be used. When using these synthetic films, it is preferable to apply a surface treatment such as a mat treatment and a corona treatment to the surface of the base sheet.
[0127]
The amount of the adhesive composition applied to the base sheet surface is 1 g / m 2 in order to maintain the adhesiveness, peelability and transparency of the adhesive layer. ² More preferably, 3 g / m ² More preferably, 4 g / m ² The above is more preferable, while 30 g / m ² The following is preferable, and 20 g / m ² The following is more preferable, and 7 g / m ² The following are more preferred.
[0128]
The coating film made of the adhesive composition is cured by irradiation with radiation. As a result, as shown in FIG. 2, a pressure-sensitive adhesive layer is formed on the sheet of the base 42, and the pressure-sensitive adhesive layer is formed of a radiation-curable medium in which the natural rubber-based fine particles 40 are dispersed. An information carrying sheet that is a cured product 41 can be obtained. It is considered that a part of the radiation-curable medium, which is a dispersion medium, is diffused into the substrate before curing, and as shown in 43, the radiation-curable medium is partially dispersed by irradiation with radiation. It is believed that it has cured in the substrate or reacted with the substrate. As a result, high adhesive strength between the adhesive layer and the base can be realized.
[0129]
In addition, the coating film is dried if necessary before curing, but the drying also proceeds during the curing step by irradiation of radiation, and since the dispersion medium is a radiation curable medium, drying can be completed in a short time. In some cases, a separate drying step is not required.
[0130]
Here, FIG. 3A shows an example of the information carrying sheet from which the adhesive layer can be peeled, and FIG. 4A shows an example of the information carrying sheet from which the adhesive layer cannot be peeled. .
[0131]
In the case of FIG. 3A, information 12 such as confidentiality and confidentiality is printed on the adhesive layer 10 as shown in FIG. 3B. Thereafter, as shown in FIG. 3C, the information carrying sheet is folded along the folding line 11 so that the adhesive layer 10 is superposed, and the adhesive layer 10 is pressed. Then, as shown in FIG. 3D, the adhesive layer 10 is peeled off when necessary, and the information 12 is read. In this case, it is required that the adhesive layer can be easily peeled at a desired time after the pressure bonding. The adhesive composition is applied on the entire surface.
[0132]
On the other hand, in the case of FIG. 4A, as shown in FIG. 4B, information 22 such as confidentiality and confidentiality is printed at a position where the adhesive layer 20 is not formed. Thereafter, as shown in FIG. 4C, the information carrying sheet is folded along the folding line 21 so that the adhesive layer 10 is superposed, and the adhesive layer 20 is pressed. Then, as shown in FIG. 4D, reading of the information 22 is performed by cutting a predetermined position (for example, perforation 23) of the base sheet without peeling the adhesive layer 20. In this case, it is required that the adhesive layer does not substantially peel off after pressure bonding. The adhesive composition has been pattern-coated.
[0133]
The adhesive layer can be made peelable or non-peelable by changing the compounding ratio of the constituents of the pressure-sensitive adhesive composition, the pressure bonding conditions, and the like.
[0134]
When the adhesive layer is peelable, necessary information is printed and printed on the obtained adhesive layer. As a printing method, in addition to a general printing machine, an electrophotographic method can be used, and as a printing method, an ink jet method can be used. In the case of the ink jet method, the printing agent is ink, and in the case of the electrophotographic method, the printing agent is toner. Then, ultraviolet rays are irradiated to dry and / or fix the printing agent. In some cases, the printing agent is heated for drying and / or fixing.
[0135]
The information information carrying sheet described above can be folded, folded, cut and overlapped in various forms, and can be suitably used as a postcard having a double-faced surface, various forms, notices, various cards, and the like. .
[0136]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. Unless otherwise specified, commercially available high-purity reagents were used.
[0137]
(Preparation of acrylic / styrene copolymer natural rubber emulsion)
To 200 parts by mass of an aqueous emulsion containing 100 parts by mass of natural rubber latex, 10 parts by mass of styrene and 25 parts by mass of methyl methacrylate were mixed, and t-butyl hydroperoxide (t-BHPO) 0.1 was used as a polymerization initiator. Parts by weight and 0.3 parts by weight of tetraethylenepentamine (TEPA). This is reacted for 2 hours in a 45 ° C./nitrogen atmosphere to obtain a copolymer natural rubber emulsion, to which 5 parts by mass of a terpene resin as a tackifier is added to obtain an aqueous emulsion containing natural rubber fine particles. Obtained.
[0138]
(Example 1) Adhesive composition 1, information carrying sheet 1
The aqueous emulsion containing the natural rubber-based fine particles obtained above was mixed with polyethylene glycol diacrylate (trade name: ARONIX M-240, manufactured by Toagosei Co., Ltd.) so as to be 100 parts by mass with respect to 100 parts by mass of the natural rubber-based fine particles. ), The mixture was heated to 50 ° C. and the water vaporized under reduced pressure was removed to replace the dispersion medium in one hour. The mass ratio of the aqueous emulsion containing the natural rubber-based fine particles to the polyethylene glycol diacrylate was 160: 100.
[0139]
On the other hand, 100 parts by mass of a polymerization initiator (trade name: Vicure 55, manufactured by Akzo Nobel Co.) was dissolved in 100 parts by mass of acryloyl oligoester, and 10 parts by mass was added to 200 parts by mass of the dispersion medium replacement obtained above. Thus, a UV-curable pressure-sensitive adhesive composition 1 was obtained.
[0140]
When the water content of the obtained pressure-sensitive adhesive composition 1 was measured, it was 0.5% by mass. The average particle diameter of the natural rubber-based fine particles was 0.2 μm, and the dispersibility was uniform.
[0141]
Using a wire bar, this pressure-sensitive adhesive composition 1 was applied to foam fine paper (trade name: NIPN (70 kg continuous weight) manufactured by Oji Paper Co., Ltd.) at 6 g / m. ² And cured using a high-pressure mercury lamp to form an adhesive layer. Thus, the information carrying sheet 1 was obtained. The coatability was as good in the case of full-surface coating and pattern coating as in the case of low-absorbing paper. In addition, no trouble such as poor drying occurred.
[0142]
After the surfaces of the obtained information carrying sheet 1 on which the adhesive layer was formed were overlapped, sealing was performed by setting the gap between the rollers to 160 μm using a sealing machine. After sealing, the two sheets were adhered with sufficient strength. When the two sheets were peeled off, the adhesive layer and the substrate could be peeled cleanly without peeling.
[0143]
(Example 2) Adhesive composition 2, information carrying sheet 2
A water-based emulsion containing the same natural rubber-based fine particles as used in the adhesive composition 1 was mixed with polyethylene glycol diacrylate (trade name: ARONIX M- 240, manufactured by Toagosei Co., Ltd.) 91 parts by mass of acryloyl oligoester and 9 parts by mass of acryloyl oligoester were thoroughly stirred, and then the mixture was heated to 50 ° C. to remove water vaporized under reduced pressure, thereby obtaining a dispersion medium in one hour. Was replaced.
[0144]
To this, 4 parts by mass of a photopolymerization initiator (trade name: Vicure 55, manufactured by Akzo Nobel) was added to obtain a UV-curable pressure-sensitive adhesive composition 2.
[0145]
When the water content of the obtained pressure-sensitive adhesive composition 2 was measured, it was 0.5% by mass. The average particle diameter of the natural rubber-based fine particles was 0.2 μm, and the dispersibility was uniform.
[0146]
Using a wire bar, this pressure-sensitive adhesive composition 2 was applied to foam fine paper (trade name: NIPN (70 kg continuous weight) manufactured by Oji Paper Co., Ltd.) at 6 g / m2. ² And cured using a high-pressure mercury lamp to form an adhesive layer. Thus, the information carrying sheet 2 was obtained. The coatability was as good in the case of full-surface coating and pattern coating as in the case of low-absorbing paper. In addition, no trouble such as poor drying occurred.
[0147]
After the surfaces of the obtained information carrying sheets 2 on which the adhesive layer was formed were overlapped with each other, sealing was performed with a sealing machine set to a roller gap of 100 μm. After sealing, the two sheets were adhered with sufficient strength. When the two sheets were peeled off, the adhesive layer and the substrate could be peeled cleanly without peeling.
[0148]
Example 3 Adhesive Composition 3, Information Carrying Sheet 3
In an aqueous emulsion containing the same natural rubber-based fine particles as used in the adhesive composition 1, ethylene glycol diglycidyl ether (trade name: Epolite 400E) was added in an amount of 100 parts by weight with respect to 100 parts by weight of the natural rubber-based fine particles. , Manufactured by Kyoeisha Chemical Co., Ltd.), and then the mixture was heated to 50 ° C. to remove water vaporized under reduced pressure, thereby replacing the dispersion medium in one hour. The mass ratio between the water-based emulsion containing natural rubber-based fine particles and ethylene glycol diglycidyl ether was 160: 100.
[0149]
On the other hand, 100 parts by mass of a polymerization initiator (trade name: Vicure 55, manufactured by Akzo Nobel Co.) is dissolved in 100 parts by mass of acryloyl oligoester, and 10 parts by mass is added to the dispersion medium substitute obtained above, and ultraviolet light is added. A curable pressure-sensitive adhesive composition 3 was obtained.
[0150]
When the water content of the obtained pressure-sensitive adhesive composition 3 was measured, it was 0.5% by mass. The average particle diameter of the natural rubber-based fine particles was 0.2 μm, and the dispersibility was uniform.
[0151]
This pressure-sensitive adhesive composition 3 was applied to foam fine paper (trade name: NIPN (70 kg continuous weight) manufactured by Oji Paper Co., Ltd.) using a wire bar at 6 g / m. ² And cured using a high-pressure mercury lamp to form an adhesive layer, thereby obtaining the information carrying sheet 3. The coatability was as good in the case of full-surface coating and pattern coating as in the case of low-absorbing paper. In addition, no trouble such as poor drying occurred.
[0152]
After the surfaces of the obtained information carrying sheets 3 on which the adhesive layer was formed were overlapped, sealing was performed with a sealing machine set at a roller gap of 160 μm. After sealing, the two sheets were adhered with sufficient strength. When the two sheets were peeled off, the adhesive layer and the substrate could be peeled cleanly without peeling.
[0153]
Example 4 Adhesive Composition 4, Information Carrying Sheet 4
In the adhesive composition 1, commercially available silica having an average particle diameter of 4 μm is used such that SBR (trade name: Closlen SK-72) manufactured by Takeda Pharmaceutical Co., Ltd. is 15 parts by mass with respect to 100 parts by mass of natural rubber-based fine particles. Adhesive composition 4 was obtained in the same manner as above, except that these fillers were added such that the amount of commercial wheat starch having an average particle size of 15 μm became 150 parts by mass. Further, in the same manner as in the case of the information carrying sheet 1, the information carrying sheet 4 was obtained. The obtained adhesive composition 4 and information-carrying sheet 4 had good performance.
[0154]
(Example 5)
Instead of the acryloyl oligoester used in the adhesive composition 1, ethylene oxide-modified succinic acrylate, β-carboxyethyl acrylate, ω-carboxy-polycaprolactone monoacrylate, 1 mole of a carboxyl group in an average molecule of 5.6 moles The adhesive composition and the information-carrying agent are prepared by using a copolymer (weight-average molecular weight: 3,200) of 50 mol parts of ethyl acrylate and 50 mol parts of lauryl acrylate, 2-acryloyloxyethyl phthalate, etc. You can get a sheet. The obtained adhesive composition and information carrying sheet have good performance.
[0155]
(Comparative Example 1)
In 100 parts by mass of polyethylene glycol diacrylate (trade name: Aronix M-240 (manufactured by Toagosei Co., Ltd.)), 8 parts by mass of a photopolymerization initiator (trade name: Vicure 55, manufactured by Akzo Nobel) were dissolved. Using a wire bar, the obtained liquid was applied to foam fine paper (trade name: NIPN (70 kg continuous weight) manufactured by Oji Paper Co., Ltd.) at 6 g / m ² And cured using a high pressure mercury lamp. After overlapping the adhesive surfaces of the obtained coated paper, sealing was performed with the sealing machine set to a gap between the rollers of 100 μm, but after sealing, the two sheets were not bonded.
[0156]
(Comparative Example 2)
A commercially available ultraviolet-curing type pressure-sensitive pseudo-adhesive is applied to foam fine paper (trade name: NIPN (70 kg continuous weight) manufactured by Oji Paper Co., Ltd.) using a wire bar at 6 g / m2. ² And cured using a high pressure mercury lamp. After overlapping the adhesive surfaces of the obtained coated paper, sealing was performed with the sealing machine set to a gap between the rollers of 100 μm, but after sealing, the two sheets were not bonded.
[0157]
【The invention's effect】
By using an adhesive composition in which a natural rubber-based fine particle is dispersed in a radiation-curable medium containing a carboxyl group-containing acrylic compound and a radiation-curable compound, it has a sufficient adhesive strength and can be used for various fillings. The agent can be sufficiently filled, the drying time after coating is short, both the entire surface coating and the pattern coating can be easily performed, and it can be applied to various substrates. High bonding strength.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a method for preparing an adhesive composition.
FIG. 2 is a schematic diagram for explaining an adhesive layer.
FIG. 3 is a schematic diagram for explaining an information carrying sheet when an adhesive layer is peelable.
FIG. 4 is a schematic diagram for explaining an information carrying sheet when an adhesive layer cannot be peeled off.
[Explanation of symbols]
10 Adhesive layer
11 folding line
12 Information
20 Adhesive layer
21 Fold Line
22 Information
23 perforation
30 Natural rubber fine particles
31 Water-based emulsion
32 Radiation curable medium
33 mixture
34 warm bath
40 Natural rubber fine particles
41 Cured layer of radiation curable medium
42 Base
43 Cured layer of radiation curable medium

Claims (13)

An adhesive composition comprising radiation-curable, natural rubber-based fine particles and a carboxyl group-containing acrylic compound. The adhesive composition includes a radiation-curable compound,
The adhesive composition according to claim 1, wherein the radiation-curable compound is at least one of a radiation-curable acrylic compound and a cyclic ether-containing radiation-curable compound. 3. The adhesive composition according to claim 1, wherein the radiation-curable compound has two radiation-polymerizable functional groups in one molecule. The carboxyl group-containing acrylic compound is an ester (I) having a structure in which an epoxide (meth) acrylate having a hydroxyl group and a polyvalent carboxylic acid are bonded by an ester. The adhesive composition according to any one of the above. The adhesive composition according to claim 4, wherein the ester (I) is represented by the following general formula (I).

In the formula, R ¹ is hydrogen or a methyl group, R ² is an alkylene which may have a cyclic structure having 2 to 10 carbon atoms, and R ³ is an alkylene which may have a cyclic structure having 1 to 20 carbon atoms. Alkenylene which may contain a cyclic structure having 1 to 20 carbon atoms or arylene having 1 to 20 carbon atoms. 4. The carboxyl group-containing acrylic compound is an ester (II) having a structure in which a hydroxy acid or a hydroxy acid polymer and (meth) acrylic acid are bonded by an ester. An adhesive composition according to any one of the above. The adhesive composition according to claim 6, wherein the ester (II) is represented by the following general formula (II).

In the formula, n is an integer of 1 to 5 or a real number, R ⁴ is hydrogen or a methyl group, R ⁵ is an alkylene which may include a cyclic structure having 1 to 20 carbon atoms, a cyclic structure having 1 to 20 carbon atoms. Or alkenylene having 1 to 20 carbon atoms. In particular, when the degree of polymerization of the repeating structural unit including R ⁵ has a distribution, n indicates the number average degree of polymerization, and is not necessarily an integer. The adhesive composition according to any one of claims 1 to 3, wherein the carboxyl group-containing acrylic compound is a (meth) acrylic polymer (III) having a carboxyl group. The adhesive composition according to claim 8, wherein the (meth) acrylic polymer (III) has a (meth) acryloyl group. The adhesive composition according to claim 8, wherein the (meth) acrylic polymer (III) is represented by the following general formula (III).

Wherein, m _i is m ₁ ~m _l corresponding to l type of repeat structural unit, l is an integer of 1 or more, m _i is 1 or more integer or real independently of one another; R ⁶ , be ^{R 8i} and ^{R 10} independently of one another represent hydrogen or a methyl group; ^{L 7} is a group containing a carboxyl group, or a group _-CO 2 ^{R 7} comprises a (meth) acryloyl group ^{R 7} is 1 to hydrogen or carbon atoms L ⁹ⁱ is a group containing a carboxyl group, a group containing a (meth) acryloyl group or —CO ₂ R ⁹ⁱ and R ⁹ⁱ is hydrogen or a hydrocarbon group having 1 to 20 carbon atoms; ¹¹ is a group containing a carboxyl group, a group containing a (meth) acryloyl group or —CO ₂ R ¹¹ , wherein R ¹¹ is hydrogen or a hydrocarbon group having 1 to 20 carbon atoms; X ¹ and X ² are each independently Hydrogen and carboxyl groups No is a group containing a group or (meth) acryloyl ^group; when L ^{7, L} none of ⁹ⁱ and ^{L 11} are not both hydrogen if ^{R 7, R 9i} and ^{R 11} do not contain a carboxyl group, X at least one of ¹ and X ² contains a carboxyl group. In particular, if there is a distribution of degree of polymerization of the repeating unit containing L ^9i, m _i is assumed to represent the number average polymerization degree, not necessarily an integer. A step of mixing an aqueous emulsion containing natural rubber-based fine particles and a radiation-curable compound,
Heating the mixture with stirring, evaporating and removing the water of the aqueous emulsion, and replacing the medium in which the natural rubber-based fine particles are dispersed from water with the radiation-curable compound; And a step of adding a group-containing acrylic compound. A step of mixing a water-based emulsion containing natural rubber-based fine particles and a radiation-curable medium containing a carboxyl group-containing acrylic compound and a radiation-curable compound,
Raising the temperature while stirring the mixture, vaporizing and removing water of the aqueous emulsion, and replacing the medium in which the natural rubber-based fine particles are dispersed from water with the radiation-curable medium. A method for producing the composition. A pressure-sensitive adhesive layer is formed on the base sheet,
The information bearing sheet, wherein the pressure-sensitive adhesive layer is a radiation-cured product of an adhesive composition containing natural rubber-based fine particles and a carboxyl group-containing acrylic compound.

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