JP3558776B2

JP3558776B2 - Method for polymerizing methacrylic resin

Info

Publication number: JP3558776B2
Application number: JP10446596A
Authority: JP
Inventors: 宙小沢; 恒夫小原; 与惣吉小林
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 1996-03-29
Filing date: 1996-03-29
Publication date: 2004-08-25
Anticipated expiration: 2016-03-29
Also published as: JPH09268203A

Description

【０００１】
【発明の属する技術分野】
本発明はメタクリル樹脂の重合方法に関し、さらに詳しくはメタクリル樹脂の懸濁重合時に生成する重合体スケール（以後、スケールと略称する）を削除することによるメタクリル樹脂の重合方法に関する。
【０００２】
【従来の技術】
メタクリル樹脂を懸濁重合する際、重合槽中の重合懸濁液と気相部との界面槽壁付近においてスケールが生成され、それが重合槽の内壁に付着することがよく経験される。
【０００３】
この現象は、懸濁重合時、攪拌により飛沫する液滴の粘度が重合の進行に伴い増加し、重合懸濁液と気相部との界面に相当する槽壁付近で重合懸濁液の流れが遅くなり、上記液滴が該界面槽壁でスケール化すると考えられている。
このようにスケールが発生し、重合槽内に付着することにより、メタクリル樹脂の生産性が低下すると共に、除去したスケールは製品化できないため廃重合体としての産業廃棄物の増加を招くこととなる。
【０００４】
従来、重合槽内部へのスケール付着の防止方法として、重合槽内壁へ特定の有機化合物を含有する組成物を薄く被覆する方法が特公昭４５−３０３４３号公報、同４５−３０８３５号公報により知られている。しかしながら、これらの方法によると、上記の有機化合物含有組成物がメタクリル樹脂中に混入し製品品質の低下を招くといった問題が生じるので好ましくない。
【０００５】
【発明が解決しようとする課題】
しかして、本発明は重合槽壁の気−液界面において発生するスケールを削除するメタクリル樹脂の重合方法を提供することを課題とする。
【０００６】
【課題を解決するための手段】
本発明によれば、上記の課題は、メタクリル樹脂の懸濁重合において、重合液温度が最高温度に達した後に、重合槽内に脱イオン水を注入し、重合液面の高さを増加させることを特徴とするメタクリル樹脂の重合方法により解決される。
【０００７】
以下、本発明を詳細に説明する。
メタクリル樹脂は優れた光学的性質及び耐候性を有し、良好な耐熱性と機械的性質を持っているため、照明材料、電子機器部品、ＯＡ機器、自動車部品、エクステリア等の建築部品などに広く用いられている。
【０００８】
そして、一般的にメタクリル樹脂は塊状重合、懸濁重合、溶液重合、乳化重合等公知の方法によって製造することができるが、本発明は懸濁重合によりメタクリル樹脂を製造することに関するものである。
【０００９】
本発明の方法において、懸濁重合の方法としては特に制限はなく、一段の懸濁重合の場合でも、また二段の懸濁重合の場合であってもよい。例えば、水および懸濁安定剤等を含む水性媒体中でメタクリル酸メチルを主成分とする単量体混合物を一段で懸濁重合させるにあたり、重合懸濁液の温度を加熱により徐々に上昇させ、次いで重合により発熱を生じるため一定温度に達した時点で加熱をやめて系内の温度をゲル化によりさらに上昇させる方法が採用されている。温度の上昇に従い、メタクリル樹脂の重合率が高くなってゆくが、本発明において重要な点は、上記懸濁重合において重合懸濁液の温度が最高温度に達した後、重合槽に脱イオン水を注入し、重合懸濁液面の高さを増加せしめることにある。
【００１０】
本発明の方法においては、重合槽に注入する水は、最終製品たるメタクリル樹脂の品質の低下を招かぬように脱イオン水（以下、これを単に水という場合がある）を用いることが必要である。
注入する水は、重合槽内の重合懸濁液の変化を少なくするために予め加熱したものを用いてもよいが、重合終了後重合懸濁液の温度を低下させるため常温程度のものを用いてもよい。また該水には本発明の目的を達成するに支障のない範囲で界面活性剤等の添加剤を含有していてもよい。
【００１１】
水の注入は、重合槽上部に脱イオン水注入ラインを設け、それを通して行うことができる。また、水を注入する時期としては、重合懸濁温度が最高温度（通常８０〜１４０℃程度）に達した後に行うことが肝要である。重合液温度が最高温度に達する以前に水を注入すると重合体の重合率の上昇が抑制され、所望の優れた重合体が得られなくなる。メタクリル樹脂の懸濁重合のように、除熱により重合温度を一定時間、一定温度に保持して行う重合系（除熱重合）では、重合温度が最高温度に到達した後、そのままの状態（攪拌状態）で大体２０分間程度放置してモノマー重合率を高めているのが一般的であるので、本発明における水の注入は、最高温度に到達した直後に行うことができるが、最高温度に到達した後の上記高温放置時間内に実施することによりスケールの削減効果を得ることができる。
【００１２】
水の注入量は、重合槽の容量によっても異なるが、生成したスケールが注水により液面下となる量加えれば十分である。例えば重合槽への全仕込量を１容量部とすれば、注水量は０．０７〜１容量部が好ましく、より好ましくは０．０８〜０．１３容量部である。
【００１３】
上記のように、重合液温度が上昇するに従いその重合度も高くなり、その後、通常の場合、ゲル化による温度上昇により重合槽内の圧力も上昇し、該圧力が最高値に達した後、約１〜２分後に重合液温度が最高温度に達するのが普通である。その時期において、上記のように、重合槽内の気−液界面にスケールの発生が認められるようになる。そして重合液の温度が最高温度に達した後水を注入して該スケールを液面下とし乱流攪拌下にある懸濁液によってスケールを削り取ることが可能となる。その際の攪拌条件としては、好ましくはＲｅ＝１０^５〜１０^８、より好ましくは１０^６〜１０^７の範囲内で攪拌することが、スケールを十分に取り除く上で望ましい。
【００１４】
重合が完了した後、重合槽から抜き出された重合懸濁液は、遠心分離機に通され脱水される。その後、重合体は流動乾燥機で乾燥され、ほとんどの水分が除去される。
【００１５】
【実施例】
以下に、本発明を実施例により具体的に説明するが、本発明はこれに限定されるものではない。
（実施例１）
攪拌機、温度計、加熱・冷却ジャケットを備えた内容積１４９リットルの重合槽（内径５０ｃｍ）内に、脱イオン水３７．２５ｋｇ、メタクリル酸メチル３９ｋｇ、アクリル酸メチル１ｋｇ、開始剤としてアゾイソブチルニトリル０．０２４ｋｇ、連鎖移動剤としてノルマルオクチルメルカプタン０．０８ｋｇ、少量の分散剤とｐＨ調整剤を加えた。激しく攪拌しながら７０℃に加熱し、７０℃で１００分保持した。
【００１６】
その後、ゲル化により、重合液温度が上昇し、重合液温度が最高温度に達した事を確認した直後、重合槽内に室温度の脱イオン水８ｋｇを４０秒間かけて添加し、重合槽内壁の気−液界面スケール付着領域を懸濁液面下とした。重合・冷却終了後、重合液を抜き取り、該スケールを採取し、秤量した結果、０．１４ｋｇであった。その他、ビーズの重合度、重合率、溶融粘度、平均粒子径及び重合残液の分析結果については、脱イオン水無添加時の値と同等であった。
【００１７】
（実施例２）
実施例１で用いた重合槽に、脱イオン水３８．７８ｋｇ、メタクリル酸メチル３９ｋｇ、アクリル酸メチル１ｋｇ、開始剤として１，１，３，３−テトラメチルブチルパーオキシ２−エチルヘキサノエート０．０４ｋｇ、連鎖移動剤としてノルマルオクチルメルカプタン０．１０１ｋｇ、少量の分散剤とｐＨ調整剤を加えた。激しく攪拌しながら７０℃に加熱し、７０℃で１００分保持した。
【００１８】
実施例１と同様に、重合液温度が最高温度に達してから、２０分後に重合槽内に室温度の脱イオン水８ｋｇを４２秒間かけて添加し、重合槽内壁の気−液界面スケール付着領域を懸濁液面下とした。重合・冷却終了後、重合液を抜き取り、該スケールを採取し、秤量した結果、０．２２ｋｇであった。その他、ビーズの重合度、重合率、溶融粘度、平均粒子径及び重合残液の分析結果については、脱イオン水無添加時の値と同等であった。
【００１９】
（比較例１）
実施例１と同じ重合槽を用い、実施例１と同じ仕込・重合条件で重合を開始し、７０℃で１００分間保持した。ゲル化による重合液温度の上昇で重合液温度が最高温度に達した後、注水せずに重合を終了させた。重合液を抜き取り、重合槽壁気−液界面に付着したスケールを採取し、秤量した結果、０．５１ｋｇであった。
【００２０】
（比較例２）
実施例１と同じ重合槽を用い、実施例２と同じ仕込・重合条件で重合を開始し、７０℃で１００分間保持した。最高圧力に達した直後で重合液温度が最高温度に達していない時に、重合槽内に室温度の脱イオン水を４０秒かけて８ｋｇ添加し、重合槽内壁の気−液界面スケール付着領域を懸濁液面下とした。重合・冷却終了後、重合液を抜き取り、該スケールを採取し、秤量した結果、０．２３ｋｇであった。また、重合液最高温度到達前に室温度の脱イオン水を添加したため、重合液最高温度が脱イオン水無添加時よりも約３℃低くなり、重合率も０．４％低下した。更に、重合残液中の有機物量も脱イオン水無添加時の３倍以上の値となった。
【００２１】
【発明の効果】
本発明の重合方法によれば、懸濁重合中のスケールを削除することができ、それにより優れた品質のメタクリル樹脂を得ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for polymerizing a methacrylic resin, and more particularly, to a method for polymerizing a methacrylic resin by eliminating a polymer scale (hereinafter abbreviated as a scale) generated during suspension polymerization of the methacrylic resin.
[0002]
[Prior art]
When a methacrylic resin is subjected to suspension polymerization, it is often experienced that a scale is generated near an interface tank wall between a polymerization suspension in a polymerization tank and a gas phase, and adheres to the inner wall of the polymerization tank.
[0003]
The phenomenon is that during suspension polymerization, the viscosity of the droplets splashed by stirring increases with the progress of the polymerization, and the flow of the polymerization suspension near the tank wall corresponding to the interface between the polymerization suspension and the gas phase And the droplets are believed to scale on the interface bath wall.
In this way, scale is generated and adhered to the polymerization tank, thereby lowering the productivity of the methacrylic resin and increasing the amount of industrial waste as a waste polymer because the removed scale cannot be commercialized. .
[0004]
Conventionally, as a method for preventing the adhesion of scale to the inside of a polymerization tank, a method of thinly coating a composition containing a specific organic compound on the inner wall of the polymerization tank is known from JP-B-45-30343 and JP-B-45-30835. ing. However, according to these methods, the above-mentioned composition containing an organic compound is mixed in a methacrylic resin, which causes a problem that the product quality is deteriorated, which is not preferable.
[0005]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for polymerizing a methacrylic resin which eliminates scale generated at a gas-liquid interface of a polymerization tank wall.
[0006]
[Means for Solving the Problems]
According to the present invention, the above-mentioned problem is solved in suspension polymerization of a methacrylic resin, after the temperature of the polymerization solution reaches a maximum temperature, deionized water is injected into the polymerization tank, and the height of the polymerization solution surface is increased. The problem is solved by a method for polymerizing a methacrylic resin characterized by the above.
[0007]
Hereinafter, the present invention will be described in detail.
Methacrylic resin has excellent optical properties and weather resistance, and has good heat resistance and mechanical properties, so it is widely used in lighting materials, electronic equipment parts, OA equipment, automotive parts, exterior parts and other building parts. Used.
[0008]
In general, methacrylic resins can be produced by known methods such as bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization. The present invention relates to producing methacrylic resins by suspension polymerization.
[0009]
In the method of the present invention, the method of suspension polymerization is not particularly limited, and may be a single-stage suspension polymerization or a two-stage suspension polymerization. For example, when performing a one-stage suspension polymerization of a monomer mixture containing methyl methacrylate as a main component in an aqueous medium containing water and a suspension stabilizer, the temperature of the polymerization suspension is gradually increased by heating, Then, since a heat is generated by the polymerization, a method is employed in which the heating is stopped when the temperature reaches a certain temperature and the temperature in the system is further increased by gelation. As the temperature increases, the polymerization rate of the methacrylic resin increases.However, an important point in the present invention is that after the temperature of the polymerization suspension reaches the maximum temperature in the suspension polymerization, deionized water is added to the polymerization tank. To increase the height of the polymerization suspension surface.
[0010]
In the method of the present invention, it is necessary to use deionized water (hereinafter, this may be simply referred to as water) as water to be injected into the polymerization tank so as not to cause deterioration of the quality of the final product, methacrylic resin. It is.
The water to be injected may be pre-heated water in order to reduce the change in the polymerization suspension in the polymerization tank.However, after the polymerization is completed, water at about normal temperature is used to lower the temperature of the polymerization suspension. You may. The water may contain additives such as a surfactant within a range that does not hinder the purpose of the present invention.
[0011]
Water can be injected through a deionized water injection line provided above the polymerization tank. It is important that water is injected after the polymerization suspension temperature reaches the maximum temperature (usually about 80 to 140 ° C.). If water is injected before the temperature of the polymerization solution reaches the maximum temperature, an increase in the polymerization rate of the polymer is suppressed, and a desired excellent polymer cannot be obtained. In a polymerization system (heat-removal polymerization) in which the polymerization temperature is maintained at a constant temperature for a certain period of time by removing heat, such as suspension polymerization of a methacrylic resin, the polymerization temperature reaches the maximum temperature and is then left as it is (with stirring In general, the monomer polymerization rate is increased by allowing the mixture to stand for about 20 minutes in the (state), so that water can be injected immediately after the maximum temperature is reached. By performing the process within the above-mentioned high-temperature leaving time, the effect of reducing the scale can be obtained.
[0012]
The amount of water to be injected depends on the capacity of the polymerization tank, but it is sufficient to add the amount by which the generated scale falls below the liquid level by water injection. For example, assuming that the total amount charged to the polymerization tank is 1 part by volume, the water injection amount is preferably 0.07 to 1 part by volume, and more preferably 0.08 to 0.13 part by volume.
[0013]
As described above, the degree of polymerization increases as the temperature of the polymerization solution increases, and then, in a normal case, the pressure in the polymerization tank also increases due to the temperature increase due to gelation, and after the pressure reaches the maximum value, Usually, the temperature of the polymerization solution reaches the maximum temperature after about 1 to 2 minutes. At that time, as described above, generation of scale is observed at the gas-liquid interface in the polymerization tank. Then, after the temperature of the polymerization liquid reaches the maximum temperature, water is injected to make the scale below the liquid surface and the scale can be scraped off by the suspension under turbulent stirring. As for the stirring conditions at this time, it is preferable to stir within a range of preferably Re = 10 ⁵ to 10 ⁸ , more preferably 10 ⁶ to 10 ⁷ in order to sufficiently remove the scale.
[0014]
After the completion of the polymerization, the polymerization suspension extracted from the polymerization tank is passed through a centrifuge to be dehydrated. Thereafter, the polymer is dried in a fluidized drier to remove most of the water.
[0015]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.
(Example 1)
In a 149 liter polymerization tank (50 cm inner diameter) equipped with a stirrer, thermometer, and heating / cooling jacket, 37.25 kg of deionized water, 39 kg of methyl methacrylate, 1 kg of methyl acrylate, and azoisobutyl nitrile 0 as an initiator were used. .024 kg, 0.08 kg of normal octyl mercaptan as a chain transfer agent, and a small amount of a dispersant and a pH adjuster were added. Heat to 70 ° C. with vigorous stirring and hold at 70 ° C. for 100 minutes.
[0016]
Then, immediately after it was confirmed that the temperature of the polymerization solution increased due to gelation and the temperature of the polymerization solution reached the maximum temperature, 8 kg of room temperature deionized water was added into the polymerization vessel over 40 seconds, and the inner wall of the polymerization vessel was added. The area where the gas-liquid interface scale was adhered was below the suspension surface. After completion of the polymerization and cooling, the polymerization liquid was withdrawn, and the scale was collected and weighed. As a result, the weight was 0.14 kg. In addition, the results of analysis of the degree of polymerization of the beads, the degree of polymerization, the melt viscosity, the average particle size, and the residual polymer solution were the same as the values when no deionized water was added.
[0017]
(Example 2)
In the polymerization tank used in Example 1, 38.78 kg of deionized water, 39 kg of methyl methacrylate, 1 kg of methyl acrylate, and 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate as an initiator were used. .04 kg, 0.101 kg of normal octyl mercaptan as a chain transfer agent, and a small amount of a dispersant and a pH adjuster were added. Heat to 70 ° C. with vigorous stirring and hold at 70 ° C. for 100 minutes.
[0018]
As in Example 1, 20 minutes after the temperature of the polymerization liquid reached the maximum temperature, 8 kg of room temperature deionized water was added to the polymerization tank over 42 seconds, and the gas-liquid interface scale adhered to the inner wall of the polymerization tank. The area was below the suspension surface. After completion of the polymerization and cooling, the polymerization liquid was withdrawn, and the scale was collected and weighed. As a result, the weight was 0.22 kg. In addition, the results of analysis of the degree of polymerization of the beads, the degree of polymerization, the melt viscosity, the average particle size, and the residual polymer solution were the same as the values when no deionized water was added.
[0019]
(Comparative Example 1)
Using the same polymerization tank as in Example 1, polymerization was started under the same charging and polymerization conditions as in Example 1, and the polymerization was maintained at 70 ° C. for 100 minutes. After the temperature of the polymerization solution reached the maximum temperature due to the rise in the temperature of the polymerization solution due to gelation, the polymerization was terminated without water injection. The polymerization liquid was withdrawn, and the scale attached to the gas-liquid interface of the polymerization tank wall was collected and weighed. As a result, the weight was 0.51 kg.
[0020]
(Comparative Example 2)
Using the same polymerization tank as in Example 1, polymerization was started under the same preparation and polymerization conditions as in Example 2, and the polymerization was maintained at 70 ° C. for 100 minutes. Immediately after reaching the maximum pressure, when the temperature of the polymerization solution has not reached the maximum temperature, 8 kg of room temperature deionized water is added into the polymerization tank over 40 seconds to remove the gas-liquid interface scale adhesion area on the inner wall of the polymerization tank. It was below the suspension surface. After the completion of the polymerization and cooling, the polymerization liquid was withdrawn, and the scale was collected and weighed. As a result, the weight was 0.23 kg. Since deionized water at room temperature was added before the maximum temperature of the polymerization liquid was reached, the maximum temperature of the polymerization liquid was lower by about 3 ° C. than when no deionized water was added, and the polymerization rate was also reduced by 0.4%. Further, the amount of organic substances in the polymerization residual liquid also became three times or more the value when no deionized water was added.
[0021]
【The invention's effect】
According to the polymerization method of the present invention, scale during suspension polymerization can be eliminated, and thereby a methacrylic resin having excellent quality can be obtained.

Claims

In the suspension polymerization of methacrylic resin, a method for polymerizing methacrylic resin, wherein deionized water is charged into a polymerization tank after the temperature of the polymerization liquid reaches a maximum temperature to increase the height of the polymerization liquid surface.