JP3886176B2 - Method for producing adhesive sheets - Google Patents

Description

【００１４】
具体的には、３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノン、３，３´，４，４´−テトラ（ｔ−アミルパ―オキシカルボニル）ベンゾフエノン、３，３´，４，４´−テトラ（ｔ−ヘキシルパ―オキシカルボニル）ベンゾフエノン、３，３´，４，４´−テトラ（ｔ−オクチルパ―オキシカルボニル）ベンゾフエノン、３，３´，４，４´−テトラ（ｔ−クミルパ―オキシカルボニル）ベンゾフエノン、３，３´，４，４´−テトラ（ｔ−イソプロピルクミルパ―オキシカルボニル）ベンゾフエノンなどである。
【００１５】
これらのパ―オキサイド基を有する光重合開始剤は既に公知である。しかし、従来では、これらの光重合開始剤を専ら酸素による重合阻害のない環境下で用いて反応速度を上げ、経済性を向上させるようにしたもので、本発明のように空気中での硬化に用いた例はみられない。本発明は、この光重合開始剤を使用する一方、光硬化性組成物の粘度を規定することにより、空気中での硬化を可能とし、より経済的に、またより簡便に感圧性接着剤を生産できるようにしたことを特徴としており、この点で従来の技術とは異なるものである。
【００１６】
本発明において、ｂ成分の光重合開始剤は、ａ成分の単量体１００重量部あたり、０．５〜２０重量部、好ましくは１〜１０重量部の割合で用いられる。この使用量が過少では十分に光硬化させることが難しく、また過多となると光硬化後の凝集力の低下が起こり、いずれも好ましくない。
【００１７】
ところで、従来のアセトフエノン系やベンゾインエ―テル系などの光重合開始剤を用いたときでも、単量体に対し１０重量％以上の多量添加することにより、空気中での光硬化が可能となるが、この場合、分子量の低下を招きやすく、これに伴い接着特性、とくに凝集力が悪化する。また、この凝集力の向上のために、架橋度を上げると接着力が著しく低下し、実用に供しえない。このように、従来の光重合開始剤では、接着力と凝集力の両立を図ることが難しい。
【００１８】
これに対して、上記本発明の１分子中に３個以上のパ―オキサイド基を有する光重合開始剤を用いたときには、接着力と凝集力の両立を容易に図ることが可能である。この理由は、つぎのように考えられる。すなわち、本発明の光重合開始剤では、単量体の不飽和モノエチレン基の重合とともに、光重合開始剤のパ―オキサイド基を起点とする分子鎖延長のため、見かけ上の分子量が増加し、重合開始剤による分子量の低下を補うためと考えられる。
【００１９】
本発明の光硬化性組成物は、上記のａ成分およびｂ成分を含有するとともに、常温（２５℃）での粘度が１０ポイズ以上に調整されていることが必要であり、好ましくは常温での粘度が３０ポイズ以上、より好ましくは５０ポイズ以上（通常は１，０００ポイズまで）であるのがよい。このように粘度調整したときに、はじめて酸素による硬化阻害が抑制され、空気中での硬化が可能となる。これは、粘度が１０ポイズ未満となると、光硬化性組成物の表面に接している空気中の酸素が内部に拡散しやすく、組成物の表面硬化が起こりにくいが、粘度が１０ポイズ以上になると、上記拡散が起こりにくくなつて、表面硬化が速やかに進行する結果、酸素による硬化阻害が抑制されるためと考えられる。
【００２０】
粘度調整は、上記のａ成分およびｂ成分の組成を決定することにより、また、必要により添加する各種の充てん剤、老化防止剤、粘着付与樹脂などの添加剤成分の種類や量を決定することにより、行うことができる。しかし、より好ましくは、ａ成分の単量体のオリゴマ―ないしポリマ―を含有させることにより、行うのが望ましい。この場合、あらかじめ上記オリゴマ―ないしポリマ―を得、これをａ成分およびｂ成分と混合するか、ａ成分の単量体を低重合率で重合させることにより単量体とそのオリゴマ―ないしポリマ―との混合物としてもよい。さらに、前者の場合では、ａ成分の単量体とこれに混合するオリゴマ―ないしポリマ―を構成する単量体とはその組成が異なつていてもよい。
【００２１】
本発明においては、このような光硬化性組成物に光を照射して硬化させることにより、感圧性接着剤とする。ここで、光照射は空気中で行うことができるが、この照射による硬化前に、組成物内部をあらかじめ窒素などの不活性ガスで置換しておくのがよい。また、通常は、光硬化性組成物をプラスチツクフイルム、紙、布などの基材上に設けておき、これに光を照射して硬化させることにより、シ―ト状，テ―プ状などの接着シ―ト類とすることができる。
【００２２】
基材上に光硬化性組成物を設けるには、ロ―ル塗工、スクリ―ン塗工、グラビア塗工などの塗工方式を用いて行えばよい。光硬化性組成物の塗工厚さは、用途目的に必要とされる特性との兼ね合いで適宜決定されるが、通常は１０〜５００μｍ程度とするのがよい。また、光の照射は、低圧水銀ランプ、高圧水銀ランプ、メタルハライドランプなどの紫外線照射装置を用いて行えばよい。さらに、照射線量は、被照射体までの距離や照射時間の調整によつて適宜設定できるが、通常は５０〜５，０００ｍｊ／cm² とすればよい。
【００２３】
【実施例】
つぎに、本発明の実施例を記載して、より具体的に説明する。なお、以下、部とあるのは重量部を意味するものとする。
【００２４】
実施例１
反応器内に、アクリル酸２−エチルヘキシル９５部およびアクリル酸５部からなる単量体混合物と、アゾビスイソブチロニトリル０．５部および酢酸エチル１００部とを投入し、この反応器内を窒素ガス雰囲気としたのち、６０℃に加温して重合反応を行い、ポリマ―溶液を得た。このポリマ―溶液から脱溶剤して得たポリマ―１００部に、アクリル酸ｎ−ブチル１００部、アクリル酸５部および光重合開始剤として３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノン２部を加え、光硬化性組成物を調製した。この組成物の常温（２５℃）での粘度は３８０ポイズであつた。
【００２５】
つぎに、この光硬化性組成物を、厚さが３８μｍのポリエチレンテレフタレ―トフイルムの上に、光硬化後の感圧性接着剤の厚さが４０μｍとなるように塗布したのち、空気中で紫外線を１，０００ｍｊ／cm² 照射して、硬化させることにより、接着テ―プを作製した。
【００２６】
実施例２
実施例１と同様に脱溶剤して得たポリマ―１００部に、アクリル酸ｎ−ブチル２００部、アクリル酸１５部および光重合開始剤として３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノン３部を加え、光硬化性組成物を調製した。この組成物の常温（２５℃）での粘度は１８０ポイズであつた。この組成物を用いて、実施例１と同様にして接着テ―プを作製した。
【００２７】
実施例３
アクリル酸ｎ−ブチル１００部およびアクリル酸１０部からなる単量体混合物に光重合開始剤としてベンゾインエチルエ―テル０．５部を加え、これに紫外線を１５０ｍｊ／cm² 予備照射してシロツプを得た。このシロツプ１００部に、３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノン４部を加え、光硬化性組成物を調製した。この組成物の常温（２５℃）での粘度は１５０ポイズであつた。この組成物を用いて、実施例１と同様にして接着テ―プを作製した。
【００２８】
比較例１
３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノンの代わりに、ベンジルジメチルケタ―ル２部、内部架橋剤として三官能性のビニル系単量体０．２部を使用した以外は、実施例１と同様にして、光硬化性組成物を調製し、これを用いて、実施例１と同様にして接着テ―プを作製した。
【００２９】
比較例２
３，３´．４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノンの代わりに、ベンジルジメチルケタ―ル２部、内部架橋剤として三官能性のビニル系単量体２．０部を使用した以外は、実施例１と同様にして、光硬化性組成物を調製し、これを用いて、実施例１と同様にして接着テ―プを作製した。
【００３０】
比較例３
実施例１と同様に脱溶剤して得たポリマ―１００部に、アクリル酸ｎ−ブチル４００部、アクリル酸２０部および光重合開始剤として３，３´，４，４´−テトラ（ｔ−ブチルパ―オキシカルボニル）ベンゾフエノン４部を加え、光硬化性組成物を調製した。この組成物の常温（２５℃）での粘度は２ポイズであつた。これを用いて、実施例１と同様にして接着テ―プを作製した。
【００３１】
以上の実施例１〜３および比較例１〜３の各接着テ―プについて、以下の方法により、重合率、接着力および保持力を調べた。結果を、各例で用いた光硬化性組成物の常温（２５℃）での粘度とともに、下記の表１に示した。
【００３２】
＜重合率＞
重合率を測定しようとする試料（つまり、各例の光硬化性組成物）〔Ｘ₁ ｇ〕（約０．１ｇ）を取り、これを１３０℃で３時間乾燥したのち、再び試料の重量〔Ｘ₂ ｇ〕を測定して、つぎの式により、重合率を求めた。
重合率（％）＝（Ｘ₂ ／Ｘ₁ ）×１００
【００３３】
＜接着力＞
接着テ―プを幅２０mmに切断して、試験片を作製し、被着体をステンレス板として、ＪＩＳ Ｚ １５２８に準じて、１８０度ピ―ルを行い、このときの接着力（ｇ／２０mm幅）を測定した。なお、表１中、（＊）は、上記の測定に際し、感圧性接着剤が凝集破壊を起こしたことを示している。
【００３４】
＜保持力＞
接着テ―プを幅１０mmに切断して、試験片を作製し、これをベ―クライト板に接着面積が１０mm×２０mmとなるように貼り合わせ、この試験片の端に５００ｇの荷重をかけて、４０℃に放置した。この放置により、試験片が６０分以内に落下したものを×、落下しないものを○、と評価した。
【００３５】

【００３６】
上記の表１の結果から明らかなように、実施例１〜３の光硬化性組成物は、空気中での紫外線照射により高い重合率で硬化でき、これにより高接着力でかつ高保持力の感圧性接着剤が得られることがわかる。これに対し、他の光重合開始剤を用いた比較例１，２の光硬化性組成物では、内部架橋剤が少ないと保持力に劣り、多いと接着力に劣り、両特性の両立を図りにくい。また、本発明の光重合開始剤を用いたときでも、組成物の粘度が低すぎると（比較例３）、光硬化がうまく進行せず、低重合率で接着特性の劣るものしか得られていない。
【００３７】
【発明の効果】
以上のように、本発明においては、特定の光重合開始剤を用いるとともに、組成物の常温での粘度を１０ポイズ以上に調整したことにより、空気中において光の照射により容易に硬化でき、従来の方法に比べて装置を簡便にできるし、また安価に生産でき、目的とする接着特性にすぐれた感圧性接着剤を経済的に生産できるという効果が得られる。なお、本発明の光硬化性組成物は、酸素濃度が低い環境下でも硬化できるものであることは言うまでもない。[0001]
BACKGROUND OF THE INVENTION
The present invention is provided with a pressure sensitive adhesive formed by curing by light irradiation curable photocurable composition in air on one side or both sides of a substrate sheet - was looped form - DOO shape and Te It relates to adhesive sheets.
[0002]
[Prior art]
Conventionally, an adhesive sheet that forms a pressure-sensitive adhesive layer by coating a photocurable composition on a substrate such as a film to an appropriate thickness and irradiating it with light to cure. There are known methods for producing the same. In this method, polymerization inhibition by oxygen is observed in the process of irradiating the photocurable composition coated on the substrate with light, and curing is inhibited, or the progress of curing is very slow. To do.
[0003]
[Problems to be solved by the invention]
For this reason, avoid curing in the air, blow in inert gas such as nitrogen gas, or cover the coated surface of the pressure sensitive adhesive with a film, etc., and photocuring in a state where the oxygen concentration is kept as low as possible By doing so, a high polymerization rate is obtained. However, such a method is inferior in the manufacturing workability of the pressure-sensitive adhesive, requires a large-scale device, and increases the cost.
[0004]
Some photocuring of paints can be cured in air by increasing the curing speed by adding a large amount of a photopolymerization initiator or increasing the intensity of light. Similarly, even with pressure-sensitive adhesives, there are examples of attempts to cure in air by increasing the amount of photopolymerization initiator added, increasing the light intensity, etc., but this causes a decrease in molecular weight and deteriorates adhesive properties. The reality is not to put it into practical use.
[0005]
In addition, there are cases where the reaction rate is increased by using a polyfunctional initiator having a peroxide group in the molecule, but these are not cured in the air, and the above-mentioned oxygen concentration is kept low. Since it is assumed to be cured in a state, problems such as manufacturing workability and high cost are not solved.
[0006]
In light of such circumstances, the present invention provides a method for producing an adhesive sheet using a photocurable composition that provides a pressure-sensitive adhesive that is easily cured by light irradiation in air and has excellent adhesive properties. The purpose is to provide.
[0007]
[Means for Solving the Problems]
As a result of intensive studies on the above object, the present inventors have used a specific photopolymerization initiator together with an acrylic monomer, and the viscosity of this photocurable composition at room temperature is a certain value or more. When adjusted, it is easily cured by light irradiation even in the air, and a high polymerization rate is obtained, thereby knowing that a pressure-sensitive adhesive having good adhesive force and cohesive force can be obtained. It came to completion.
[0008]
That is, the present invention provides the following two components on a substrate :
a) Monomer composed mainly of (meth) acrylic acid alkyl ester having 2 to 14 carbon atoms in alkyl group b) Essential photopolymerization initiator having 3 or more peroxide groups in one molecule and also contains as component, the photocurable composition viscosity of 10 poise or more at room temperature (25 ° C.) provided, to which the Rukoto then cured by irradiation with light in air, a pressure sensitive adhesive The present invention relates to a method for producing an adhesive sheet .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The monomer of component a used in the present invention is mainly composed of (meth) acrylic acid alkyl ester having 2 to 14 carbon atoms in the alkyl group. Specific examples of the (meth) acrylic acid alkyl ester include ethyl (meth) acrylate, butyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2- Examples include ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, etc. Or 2 or more types are used.
[0010]
In addition to this (meth) acrylic acid alkyl ester, a monoethylenically unsaturated monomer copolymerizable therewith may be used to improve adhesion and cohesion after photocuring. Examples of copolymerizable monoethylenically unsaturated monomers used for this purpose include acrylic acid, itaconic acid, sulfopropyl acrylate, hydroxyalkyl acrylate, cyanoalkyl acrylate, and acrylonitrile. , 2-methoxyethyl acrylate, glycidyl acrylate, vinyl acetate and the like, and one or more of them can be used.
[0011]
In the monomer of component a, the main component (meth) acrylic acid alkyl ester and the monoethylenically unsaturated monomer copolymerizable therewith are 70 to 100% by weight, preferably 85 to 95%. % By weight, the latter being 30 to 0% by weight, preferably 15 to 5% by weight. By using in this range, it becomes easy to balance the adhesiveness after photocuring and the cohesive force.
[0012]
The photopolymerization initiator of component b used in the present invention is a kind of so-called organic peroxide having three or more peroxide groups in one molecule. Photopolymerization such as acetophenone or benzoin ether It is essentially different from an initiator and is also distinguished from organic peroxides having only one or two peroxide groups in one molecule. As such a specific photopolymerization initiator, a benzophenone group-containing polyvalent peroxyester represented by the general formula (I) is preferably used.
[0013]
[Chemical 1]

[0014]
Specifically, 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra (t-amylperoxycarbonyl) benzophenone, 3,3 ', 4,4'-tetra (t-hexylpa-oxycarbonyl) benzophenone, 3,3', 4,4'-tetra (t-octylperoxycarbonyl) benzophenone, 3,3 ', 4,4'-tetra (T-cumylpa-oxycarbonyl) benzophenone, 3,3 ′, 4,4′-tetra (t-isopropylcumylperoxycarbonyl) benzophenone, and the like.
[0015]
Photopolymerization initiators having these peroxide groups are already known. However, in the past, these photopolymerization initiators were used exclusively in an environment without polymerization inhibition by oxygen to increase the reaction rate and improve the economy. The example used for is not seen. While the present invention uses this photopolymerization initiator, it allows curing in the air by defining the viscosity of the photocurable composition, and makes the pressure sensitive adhesive more economical and simpler. It is characterized in that it can be produced, which is different from the conventional technology in this respect.
[0016]
In the present invention, the photopolymerization initiator of component b is used in a proportion of 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of the monomer of component a. If the amount used is too small, it is difficult to sufficiently photocure, and if it is too much, the cohesive force after photocuring is reduced, which is not preferable.
[0017]
By the way, even when a conventional photopolymerization initiator such as acetophenone or benzoin ether is used, photocuring in air is possible by adding a large amount of 10% by weight or more to the monomer. In this case, the molecular weight is likely to decrease, and the adhesive properties, particularly the cohesive force, are deteriorated accordingly. Further, in order to improve the cohesive force, if the degree of cross-linking is increased, the adhesive force is remarkably lowered and cannot be put to practical use. Thus, it is difficult to achieve both adhesive force and cohesive force with conventional photopolymerization initiators.
[0018]
On the other hand, when the photopolymerization initiator having three or more peroxide groups in one molecule of the present invention is used, it is possible to easily achieve both the adhesive force and the cohesive force. The reason is considered as follows. That is, in the photopolymerization initiator of the present invention, the apparent molecular weight increases due to the molecular chain extension starting from the peroxide group of the photopolymerization initiator as well as the polymerization of the unsaturated monoethylene group of the monomer. This is considered to compensate for the decrease in molecular weight caused by the polymerization initiator.
[0019]
The photocurable composition of the present invention contains the a component and the b component described above, and the viscosity at room temperature (25 ° C.) needs to be adjusted to 10 poise or more, preferably at room temperature. The viscosity should be 30 poise or more, more preferably 50 poise or more (usually up to 1,000 poise). When the viscosity is adjusted in this way, the inhibition of curing by oxygen is suppressed for the first time, and curing in air becomes possible. This is because when the viscosity is less than 10 poise, oxygen in the air in contact with the surface of the photocurable composition is likely to diffuse inside, and the surface hardening of the composition hardly occurs, but when the viscosity is 10 poise or more. This is considered to be because the inhibition of curing by oxygen is suppressed as a result of the rapid progress of surface curing while the diffusion is less likely to occur.
[0020]
Viscosity adjustment is to determine the type and amount of additive components such as various fillers, anti-aging agents, and tackifying resins to be added by determining the composition of the a component and b component. This can be done. However, it is more preferable to carry out by adding a monomer oligomer or polymer of component a. In this case, the above-mentioned oligomer or polymer is obtained in advance and mixed with the component a and component b, or the monomer of component a is polymerized at a low polymerization rate, whereby the monomer and its oligomer or polymer are polymerized. It is good also as a mixture. Further, in the former case, the composition of the monomer of component a and the monomer constituting the oligomer or polymer mixed therewith may be different.
[0021]
In this invention, it is set as a pressure-sensitive adhesive by irradiating light to such a photocurable composition and making it harden | cure. Here, although light irradiation can be performed in the air, it is preferable to replace the inside of the composition with an inert gas such as nitrogen in advance before curing by this irradiation. In general, a photocurable composition is provided on a substrate such as a plastic film, paper, cloth, etc., and is irradiated with light to be cured, so that a sheet-like, tape-like, etc. Adhesive sheets can be used.
[0022]
In order to provide the photocurable composition on the substrate, a coating method such as roll coating, screen coating, or gravure coating may be used. The coating thickness of the photocurable composition is appropriately determined in consideration of the characteristics required for the purpose of use, but is usually preferably about 10 to 500 μm. Light irradiation may be performed using an ultraviolet irradiation device such as a low-pressure mercury lamp, a high-pressure mercury lamp, or a metal halide lamp. Further, the irradiation dose can be appropriately set by adjusting the distance to the irradiation object and the irradiation time, but it is usually set to 50 to 5,000 mj / cm ² .
[0023]
【Example】
Next, examples of the present invention will be described in more detail. Hereinafter, “parts” means parts by weight.
[0024]
Example 1
Into the reactor, a monomer mixture composed of 95 parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid, 0.5 part of azobisisobutyronitrile and 100 parts of ethyl acetate were charged, After making the nitrogen gas atmosphere, the polymerization reaction was performed by heating to 60 ° C. to obtain a polymer solution. To 100 parts of a polymer obtained by removing the solvent from this polymer solution, 100 parts of n-butyl acrylate, 5 parts of acrylic acid, and 3,3 ′, 4,4′-tetra (t-butyl polymer as a photopolymerization initiator) were added. -Oxycarbonyl) 2 parts of benzophenone was added to prepare a photocurable composition. This composition had a viscosity of 380 poise at normal temperature (25 ° C.).
[0025]
Next, this photocurable composition was coated on a polyethylene terephthalate film having a thickness of 38 μm so that the pressure-sensitive adhesive after photocuring had a thickness of 40 μm, and then ultraviolet rays in the air. Was cured by irradiation with 1,000 mj / cm ² to prepare an adhesive tape.
[0026]
Example 2
To 100 parts of the polymer obtained by removing the solvent in the same manner as in Example 1, 200 parts of n-butyl acrylate, 15 parts of acrylic acid and 3,3 ′, 4,4′-tetra (t- Butyl peroxycarbonyl) benzophenone (3 parts) was added to prepare a photocurable composition. This composition had a viscosity of 180 poise at room temperature (25 ° C.). An adhesive tape was produced using this composition in the same manner as in Example 1.
[0027]
Example 3
To a monomer mixture consisting of 100 parts of n-butyl acrylate and 10 parts of acrylic acid, 0.5 part of benzoin ethyl ether is added as a photopolymerization initiator, and ultraviolet rays are preliminarily irradiated to 150 mj / cm ² to give a syrup. Obtained. To 100 parts of this syrup, 4 parts of 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone was added to prepare a photocurable composition. The viscosity of this composition at room temperature (25 ° C.) was 150 poise. An adhesive tape was produced using this composition in the same manner as in Example 1.
[0028]
Comparative Example 1
Instead of 3,3 ′, 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 2 parts of benzyldimethylketal and 0.2 part of a trifunctional vinyl monomer as an internal crosslinking agent A photocurable composition was prepared in the same manner as in Example 1 except that it was used, and an adhesive tape was prepared in the same manner as in Example 1 using this.
[0029]
Comparative Example 2
3, 3 '. Instead of 4,4'-tetra (t-butylperoxycarbonyl) benzophenone, 2 parts of benzyldimethylketal and 2.0 parts of a trifunctional vinyl monomer as an internal crosslinking agent were used. A photocurable composition was prepared in the same manner as in Example 1, and an adhesive tape was prepared in the same manner as in Example 1 using this.
[0030]
Comparative Example 3
To 100 parts of the polymer obtained by removing the solvent in the same manner as in Example 1, 400 parts of n-butyl acrylate, 20 parts of acrylic acid and 3,3 ′, 4,4′-tetra (t- 4 parts of (butylperoxycarbonyl) benzophenone was added to prepare a photocurable composition. The viscosity of this composition at room temperature (25 ° C.) was 2 poise. Using this, an adhesive tape was produced in the same manner as in Example 1.
[0031]
About each adhesive tape of the above Examples 1-3 and Comparative Examples 1-3, the polymerization rate, the adhesive force, and the retention strength were investigated with the following method. The results are shown in Table 1 below together with the viscosity at normal temperature (25 ° C.) of the photocurable composition used in each example.
[0032]
<Polymerization rate>
A sample to be measured for the polymerization rate (that is, the photocurable composition of each example) [X ₁ g] (about 0.1 g) was taken, dried at 130 ° C. for 3 hours, and again the weight of the sample [ X ₂ g] was measured, and the polymerization rate was determined by the following formula.
Polymerization rate (%) = (X ₂ / X ₁ ) × 100
[0033]
<Adhesive strength>
The adhesive tape was cut into a width of 20 mm to prepare a test piece, and the adherend was made of a stainless steel plate and peeled 180 degrees according to JIS Z 1528. At this time, the adhesive strength (g / 20 mm Width) was measured. In Table 1, (*) indicates that the pressure-sensitive adhesive caused cohesive failure in the above measurement.
[0034]
<Retention force>
Cut the adhesive tape to a width of 10 mm to produce a test piece, and bond it to the Bakelite plate so that the adhesion area is 10 mm × 20 mm. A load of 500 g is applied to the end of the test piece. , Left at 40 ° C. By this standing, the test piece was evaluated as x when the test piece fell within 60 minutes, and ◯ when the test piece did not fall.
[0035]

[0036]
As is clear from the results in Table 1 above, the photocurable compositions of Examples 1 to 3 can be cured at a high polymerization rate by ultraviolet irradiation in the air, thereby having high adhesion and high holding power. It can be seen that a pressure sensitive adhesive is obtained. On the other hand, in the photocurable compositions of Comparative Examples 1 and 2 using other photopolymerization initiators, if the amount of the internal crosslinking agent is small, the holding power is inferior. If the amount is large, the adhesive strength is inferior. Hateful. Even when the photopolymerization initiator of the present invention is used, if the viscosity of the composition is too low (Comparative Example 3), photocuring does not proceed well, and only a low polymerization rate and poor adhesive properties are obtained. Absent.
[0037]
【The invention's effect】
As described above, in the present invention, a specific photopolymerization initiator is used, and the viscosity at room temperature of the composition is adjusted to 10 poise or more, so that it can be easily cured by light irradiation in the air. Compared with this method, the apparatus can be simplified, and it can be produced at low cost, and an effect of economically producing a pressure-sensitive adhesive having excellent target adhesive properties can be obtained. In addition, it cannot be overemphasized that the photocurable composition of this invention can be hardened | cured also in an environment with low oxygen concentration.

Claims (2)

The following two components on the substrate :
a) Monomer composed mainly of (meth) acrylic acid alkyl ester having 2 to 14 carbon atoms in the alkyl group b) Photopolymerization initiator having 3 or more peroxide groups in one molecule is essential It is contained as a component, and is provided with a photocurable composition having a viscosity at room temperature of 10 poise or more, and is cured by irradiating light in the air to form a pressure-sensitive adhesive. A method for manufacturing adhesive sheets. The method for producing an adhesive sheet according to claim 1, wherein the photocurable composition contains an oligomer or polymer of a monomer of component a, and the viscosity is adjusted thereby.