JPS6227968B2

JPS6227968B2 -

Info

Publication number: JPS6227968B2
Application number: JP53043332A
Authority: JP
Inventors: Hiroshi Aoki
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1978-04-14
Filing date: 1978-04-14
Publication date: 1987-06-17
Also published as: JPS54135853A

Description

[Detailed description of the invention]

本発明は熱可塑性合成樹脂の乾燥方法に関す
る。本発明の目的は、成形原料の熱可塑性合成樹
脂を、乾燥工程以降の工程の安定化と優れた成型
品を賦与する乾燥度に安定かつ均一に乾燥する方
法を提供することにある。熱可塑性合成樹脂を乾燥する場合に、乾燥後の
水分率は、乾燥前の原料水分率、乾燥時間、乾燥
温度、乾燥方式及び乾燥時の雰囲気湿度等で決定
される。また乾燥中及び成形中の熱可塑性合成樹
脂の劣化（例えば、原料の固有粘度の低下等）は
上述の乾燥条件によつて影響される。従来、熱可塑性合成樹脂原料を連続的に乾燥す
る方法は種々ある。例えば、流動式、充填式又は
回転式等の乾燥機により連続乾燥する方法があ
る。これらの工業的な乾燥方式において、原料の
加熱及び気化蒸発した水分の移動は一般に熱風に
よつて行われる。乾燥後の優れた原料品質の確保
のために、乾燥時間、乾燥温度、熱風の風速及び
原料と熱風との接触方法等の条件は原料に応じて
最適化され、その乾燥効率は向上してきた。しか
し、一般に外部の空気を加熱して熱風とし、これ
を乾燥機内に導いて原料を加熱し、蒸発した水分
を除去する場合には上記空気の湿度に起因して原
料品質の劣化は必然的に起り、かつ乾燥雰囲気湿
度の上昇に伴つて最終水分率が上昇するという欠
点があつた。この欠点を改善する方法として乾燥
雰囲気の全部又は一部に、例えば減湿した空気ま
たは不活性ガス（炭酸ガス、窒素ガス等）を用い
る方法があるが、次に述べる欠陥に対しては全く
効果がない。第１に、重要な乾燥の因子として上
記諸因子の外に乾燥前の原料水分率があり、これ
が変動するために減湿した空気または不活性ガス
を用いても乾燥中の雰囲気湿度が変動し、ひいて
は乾燥後の原料品質が変動するという欠点があ
る。この欠点を改善する第２の方法として多属階
乾燥方式がある。これは本乾燥に先立ち、比較的
低温で予備乾燥する方式であるが、設備規模が過
大となり、運転経費の上昇にもなり好ましくな
い。本発明者はこのような欠点を考慮して熱可塑性
合成樹脂原料の簡便な乾燥方法について鋭意研究
した結果、乾燥中の雰囲気に減湿した空気を導入
し、乾燥前原料水分率等の変動に伴つて変化した
雰囲気湿度に応じて該空気の導入量を調整して乾
燥雰囲気の湿度を常に所定範囲に保持しつつ乾燥
するのが最も合理的で、しかも安定した乾燥度の
原料品質を確保できることを見出し本発明に到達
した。本発明は熱風連続乾燥機で熱可塑性合成樹脂を
連続的に乾燥する方法において、乾燥機から排気
された熱風の露点を検知し、該検知値に応じて該
熱風への減湿空気の導入量を調節し、露点を−10
〜10℃の範囲内の所定範囲に調整した熱風を再び
乾燥用熱風として用いることを特徴とする熱可塑
性合成樹脂の乾燥方法である。本発明を詳述する。本発明は、熱風連続乾燥機内の雰囲気湿度を該
乾燥機から排気された熱風の露点で検知する。こ
の露点検知で熱風の絶対湿度を求めることができ
る。この露点の検知値が設定した露点範囲の上限
値より高い場合には排気熱風へ導入する減湿空気
の量を増加させ、一方検知値の方が設定した露点
範囲の下限値より低い場合には減湿空気の量を減
少させて、熱風の露点を所定範囲内に保持し、こ
れによつて乾燥機内の雰囲気湿度を所望の範囲内
に保持する。乾燥機から排気された熱風へ導入する減湿空気
量の調整は、例えば手動による方法、自動的に制
御する方法、或いは手動と自動とを組合せた方法
等によつて行える。乾燥機系内の雰囲気湿度を所
定範囲内に、効率的に且精密に保持しようとする
には全面的に自動的に制御する方法或いは適当な
ベース導入量のみを手動によつて制御し、残余の
導入量は自動的に導入する方法等が適用できる。本発明に於ける望ましい乾燥機系内の雰囲気湿
度の自動制御の例は検知した露点を電気信号に変
換し、該信号の出力をさらに減湿空気供給系に設
けた調節弁（コントロールバルブ）の開度に変換
して循環系の熱風への減湿空気導入量を調整する
方法である。本発明の制御系フローの一例を第１
図を用いてさらに説明する。第１図に於て、熱可
塑性合成樹脂は乾燥機ＣへＡより連続的に投入さ
れ、Ｂより搬出され、乾燥用熱風はブロアーＤに
よつてＣ〜Ｄ間を矢印の方向に循環する。該系に
露点検知用の端子Ｅを導入し、該端子Ｅで検知し
た露点を調整計Ｆにインプツトし調整計Ｆは減湿
空気吹込用調節弁Ｇへの開度信号に変換してアウ
トプツトし、該調節弁Ｇの開度を調節し乾燥機系
内の雰囲気湿度を所定範囲に保持する。一方乾燥
機系内の圧力バランス上及び原料より気化蒸発し
た水分を系外へ除去するために、乾燥機から排出
した熱風の一部を排気系Ｈを通して系外へ排出す
る。さらに、乾燥機系内への導入減湿空気量に応
じて該排気量を例えばコントロールタンパーＪに
よつて調整すると一層精度の高い湿度制御が可能
となる。本発明の方法を用いる事によつて、乾燥
機系内の雰囲気湿度を、例えば露点温度で表現し
て、通常「設定露点温度」±３℃以内、さらに制
御条件を十分に吟味すれば「設定露点温度」±１
℃以内に制御する事が可能となる。又「設定露点
温度」は一定範囲で設定してもよいが露点温度を
±0.5℃内の狭い範囲（点）で設定するのが好ま
しい。本発明における露点の検知方法は光学的、電気
的方法があり、乾燥機系内への減湿空気の導入量
を自動的に調整する場合には、該検知値を電気的
な出力に変換した方がよい。該検知装置としては
一般に市販されている自動露点形を用いることが
できる。本発明にいう乾燥機とは熱風連続乾燥機であれ
ば、気流式、充填式、流動式、回転式等その乾燥
方式に拘らず適用できるが、とりわけ回転式の場
合その効果が顕著に発揮される。本発明に用いる
減湿空気とは外気より低い湿度を有する空気であ
ればよいが絶対湿度として露点が−10℃好ましく
は−40℃以下の空気を用いた方が操作上便利であ
る。本発明が適用される熱可塑性合成樹脂とは、ポ
リオレフイン系，ナイロン系，ポリエステル系等
特に限定されないが乾燥雰囲気とくに湿度の影響
を受け易いもの、例えばポリエステル系等に有効
である。またその原料形態はチツプ状、フレーク
状等とくに限定されるものではない。本発明によつて乾燥機内の雰囲気湿度は所定範
囲に確保されるが、例えば、原料熱可塑性合成樹
脂としてポリエチレンテレフタレートのチツプを
溶融して押出すに先立つて乾燥温度160〜180℃で
約４時間乾燥する場合には、該雰囲気湿度は出来
るだけ低く保持する方が好ましいが、該雰囲気露
点で−10℃〜10℃の範囲内となるように露点制御
を行うのが好ましい。露点が10℃より高いと減湿
空気吹込の利点が十分に得られず、また露点を−
10℃より低くするには莫大な減湿空気が必要とな
り、過大な運転経費がかかり熱効率の点で不利と
なる。本発明によつて得られる乾燥後の高品質原料
は、後工程で溶融押出して紡糸、製膜、押出又は
射出成形してもよく特に限定されない。本発明方法によれば、熱可塑性合成樹脂の熱風
乾燥工程で該乾燥雰囲気湿度を安定して低く保持
しうるので、乾燥中の原料の劣化（例えば加水分
解等による固有粘度の低下等）を低減し、さらに
乾燥後の最終水分率を低下せしめることによつ
て、後工程溶融時における熱分解などの劣化を低
減することができる。また本発明の最大の特徴は
乾燥中の雰囲気湿度の安定化が可能であるところ
にある。乾燥中の雰囲気湿度の変動は乾燥前原料
の含水率の変動、乾燥機外の空気の機内への侵入
による該系内雰囲気湿度の変動及び減湿空気自体
の湿度変動等によつて引起されるものであり、従
来、技術的に対処困難な問題であつた。本発明は
これらの変動を乾燥中の雰囲気湿度の変動として
露点によつて検知し、これを乾燥機系内への減湿
空気の導入量の調整によつて補うことを可能とし
たことに技術的な特徴を有するものである。本発
明方法によつて乾燥後の原料の品質、さらには成
形製品の品質のばらつきを大巾に改善し、安定し
た高品質製品を得ることができる。また単に乾燥
機系内へ減湿空気を導入し該系内の雰囲気湿度を
下げる従来法に比べ、本発明の場合乾燥雰囲気を
所定範囲に調整するので、減湿空気の使用量が合
理的になり、省エネルギーの効果も達成できる。
また、乾燥機内雰囲気の湿度（水分量）が一定で
あることから、年間を通じて乾燥条件が一定し、
天候・季節の変動を受けることがない。以下実施例により本発明を更に説明する。実施例１固有粘度（溶媒としてオルソ・クロロフエノー
ルを用い、測定温度25℃で求めた、以下と略記
する）0.625のポリエチレンテレフタレートチツ
プを、温度180℃の熱風を400Nm³／HRで循環さ
せている回転式乾燥機系内へ連続的に500Kg／HR
で供給し、平均４時間乾燥するに際して、乾燥機
系内へ露点約−40℃の減湿空気を該系内露点が５
℃となるように吹込み乾燥し、乾燥機出口で採取
した乾燥後のチツプ品質は下表の如くなつた。比
較として減湿空気の吹込による露点調節を中止
し、循環される熱風のうち250Nm³／HRを外気の
取入で置換する以外は上記と、同一のポリエチレ
ンテレフタレートを同一条件で乾燥し、同様に乾
燥後のチツプ品質を下表に示した。 The present invention relates to a method for drying thermoplastic synthetic resins. An object of the present invention is to provide a method for stably and uniformly drying a thermoplastic synthetic resin as a molding raw material to a degree of dryness that stabilizes the steps after the drying step and provides an excellent molded product. When drying a thermoplastic synthetic resin, the moisture content after drying is determined by the raw material moisture content before drying, drying time, drying temperature, drying method, atmospheric humidity during drying, etc. Furthermore, deterioration of the thermoplastic synthetic resin during drying and molding (for example, a decrease in the intrinsic viscosity of the raw material) is influenced by the above-mentioned drying conditions. Conventionally, there are various methods for continuously drying thermoplastic synthetic resin raw materials. For example, there is a method of continuous drying using a fluidized type dryer, a filling type dryer, a rotary type dryer, or the like. In these industrial drying methods, heating of raw materials and movement of vaporized moisture are generally performed by hot air. In order to ensure excellent raw material quality after drying, conditions such as drying time, drying temperature, hot air speed, and method of contact between raw materials and hot air are optimized depending on the raw material, and the drying efficiency has been improved. However, in general, when external air is heated to create hot air, which is then introduced into a dryer to heat raw materials and remove evaporated water, the quality of the raw materials inevitably deteriorates due to the humidity of the air. There was a drawback that the final moisture content increased as the humidity of the drying atmosphere increased. There are methods to improve this defect, such as using dehumidified air or inert gas (carbon dioxide, nitrogen gas, etc.) in all or part of the drying atmosphere, but these methods are completely ineffective against the defects described below. There is no. First, in addition to the above factors, an important drying factor is the moisture content of the raw material before drying, and because this varies, the atmospheric humidity during drying will vary even if dehumidified air or inert gas is used. This has the drawback that the quality of the raw material after drying varies. A second method for improving this drawback is a multi-layer drying method. This is a method of pre-drying at a relatively low temperature prior to main drying, but it is not preferable because the scale of the equipment becomes too large and operating costs increase. Taking these drawbacks into consideration, the inventor of the present invention conducted extensive research on a simple drying method for thermoplastic synthetic resin raw materials.As a result, the inventors introduced dehumidified air into the atmosphere during drying to prevent fluctuations in the moisture content of the raw materials before drying. It is most rational to dry while always maintaining the humidity of the drying atmosphere within a predetermined range by adjusting the amount of air introduced according to the atmospheric humidity that changes accordingly, and moreover, it is possible to ensure raw material quality with a stable degree of dryness. This discovery led to the present invention. The present invention is a method for continuously drying thermoplastic synthetic resin in a continuous hot air dryer, in which the dew point of hot air exhausted from the dryer is detected, and the amount of dehumidified air introduced into the hot air is determined according to the detected value. Adjust the dew point to −10
This method of drying a thermoplastic synthetic resin is characterized in that hot air adjusted to a predetermined temperature within the range of ~10°C is used again as hot air for drying. The present invention will now be described in detail. The present invention detects the atmospheric humidity within a continuous hot air dryer based on the dew point of the hot air exhausted from the dryer. By detecting this dew point, the absolute humidity of the hot air can be determined. If the detected dew point value is higher than the upper limit of the set dew point range, the amount of dehumidified air introduced into the exhaust hot air is increased; on the other hand, if the detected value is lower than the lower limit of the set dew point range. The amount of dehumidified air is reduced to maintain the dew point of the hot air within a predetermined range, thereby maintaining the atmospheric humidity within the dryer within a desired range. The amount of dehumidified air introduced into the hot air exhausted from the dryer can be adjusted, for example, by a manual method, an automatic control method, or a combination of manual and automatic methods. In order to efficiently and precisely maintain the atmospheric humidity within the dryer system within a predetermined range, it is possible to control the entire area automatically, or to manually control only the appropriate amount of base introduced and control the residual humidity. The introduction amount can be determined by a method such as automatic introduction. An example of automatic control of atmospheric humidity within a dryer system according to the present invention is to convert the detected dew point into an electrical signal, and then output the signal to a control valve provided in the dehumidified air supply system. This is a method of adjusting the amount of dehumidified air introduced into the hot air of the circulation system by converting it into the opening degree. An example of the control system flow of the present invention is shown in the first example.
This will be further explained using figures. In FIG. 1, thermoplastic synthetic resin is continuously fed into a dryer C from A and taken out from B, and hot air for drying is circulated between C and D by a blower D in the direction of the arrow. A terminal E for dew point detection is introduced into the system, and the dew point detected by the terminal E is input to the regulator F, which converts it into an opening signal to the dehumidified air blowing control valve G and outputs it. , the opening degree of the control valve G is adjusted to maintain the atmospheric humidity within the dryer system within a predetermined range. On the other hand, a part of the hot air discharged from the dryer is discharged to the outside of the system through the exhaust system H in order to balance the pressure within the dryer system and to remove moisture vaporized and evaporated from the raw materials to the outside of the system. Furthermore, if the exhaust amount is adjusted, for example, by a control tamper J, according to the amount of dehumidified air introduced into the dryer system, even more precise humidity control becomes possible. By using the method of the present invention, the atmospheric humidity within the dryer system, expressed as dew point temperature, is normally within ±3°C of the "set dew point temperature", and if the control conditions are carefully examined, the atmospheric humidity within the dryer system can be expressed as the dew point temperature. Dew point temperature" ±1
It is possible to control the temperature within ℃. Although the "set dew point temperature" may be set within a certain range, it is preferable to set the dew point temperature within a narrow range (point) within ±0.5°C. Dew point detection methods in the present invention include optical and electrical methods, and when automatically adjusting the amount of dehumidified air introduced into the dryer system, the detected value is converted into an electrical output. It's better. As the detection device, a commercially available automatic dew point type can be used. The dryer referred to in the present invention is a continuous hot air dryer, and can be applied regardless of the drying method such as air flow type, filling type, fluid type, rotary type, etc., but the effect is particularly noticeable in the case of a rotary type. Ru. The dehumidified air used in the present invention may be any air having a humidity lower than that of the outside air, but it is more convenient for operation to use air with an absolute humidity dew point of -10°C, preferably -40°C or lower. Thermoplastic synthetic resins to which the present invention is applied include, but are not particularly limited to, polyolefin, nylon, and polyester resins, but are effective for those easily affected by dry atmospheres, particularly humidity, such as polyester resins. Further, the form of the raw material is not particularly limited, such as chip form or flake form. According to the present invention, the atmospheric humidity inside the dryer is ensured within a predetermined range. For example, prior to melting and extruding polyethylene terephthalate chips as a raw material thermoplastic synthetic resin, the drying temperature is 160 to 180°C for about 4 hours. When drying, it is preferable to keep the atmospheric humidity as low as possible, but it is preferable to control the atmospheric dew point so that it falls within the range of -10°C to 10°C. If the dew point is higher than 10℃, the benefits of blowing dehumidified air cannot be fully obtained, and the dew point may be lower than -
To lower the temperature below 10°C requires a huge amount of dehumidified air, resulting in excessive operating costs and disadvantages in terms of thermal efficiency. The dried high-quality raw material obtained by the present invention may be melt-extruded in a subsequent step to be spun, film-formed, extruded, or injection-molded, and is not particularly limited. According to the method of the present invention, the humidity of the drying atmosphere can be stably maintained at a low level during the hot air drying process of thermoplastic synthetic resin, thereby reducing deterioration of raw materials during drying (for example, decrease in intrinsic viscosity due to hydrolysis, etc.) Furthermore, by lowering the final moisture content after drying, deterioration such as thermal decomposition during melting in the subsequent process can be reduced. Moreover, the greatest feature of the present invention is that it is possible to stabilize the atmospheric humidity during drying. Fluctuations in the atmospheric humidity during drying are caused by fluctuations in the moisture content of the raw material before drying, fluctuations in the atmospheric humidity within the system due to air outside the dryer entering the inside of the dryer, and fluctuations in the humidity of the dehumidified air itself. This has traditionally been a technically difficult problem to deal with. The present invention uses technology to detect these fluctuations as fluctuations in atmospheric humidity during drying using the dew point, and to compensate for this by adjusting the amount of dehumidified air introduced into the dryer system. It has the following characteristics. By the method of the present invention, it is possible to greatly improve the quality of the raw material after drying, and furthermore, the variation in quality of the molded product, and to obtain a stable high-quality product. Furthermore, compared to the conventional method of simply introducing dehumidified air into the dryer system and lowering the atmospheric humidity within the system, the present invention adjusts the drying atmosphere within a predetermined range, so the amount of dehumidified air used can be rationalized. Therefore, energy saving effects can also be achieved.
In addition, since the humidity (moisture content) in the atmosphere inside the dryer is constant, drying conditions are constant throughout the year.
It is not subject to changes in weather or seasons. The present invention will be further explained below with reference to Examples. Example 1 A polyethylene terephthalate chip with an intrinsic viscosity of 0.625 (determined using ortho-chlorophenol as a solvent at a measurement temperature of 25°C, abbreviated as below) is circulated with hot air at a temperature of 180°C at a rate of 400 Nm ³ /HR. Continuously 500Kg/HR into the rotary dryer system
When drying for an average of 4 hours, dehumidified air with a dew point of approximately -40°C is supplied into the dryer system with a dew point of approximately 5°C.
The chips were blown to dryness at a temperature of 0.9°C, and the quality of the chips after drying was collected at the dryer outlet as shown in the table below. For comparison, the same polyethylene terephthalate was dried under the same conditions as above, except that the dew point adjustment by blowing in dehumidified air was discontinued, and 250Nm ³ /HR of the circulated hot air was replaced by intake of outside air. The chip quality after drying is shown in the table below.

【表】実施例２乾燥前のチツプ水分率が0.05〜0.15％で固有粘
度0.625なるポリエチレンテレフタレートチツプ
を温度185℃の熱風を400Nm³／HRで循環させて
いる回転式乾燥機へ連続的に600Kg／Hrで供給
し、平均3.5時間乾燥するに際して、乾燥機系内
へ露点が約−40℃の減湿空気を250Nm³／HRで一
定量導入した場合（比較例）と該系内の雰囲気露
点が４℃となるように該減湿空気導入量を自動的
に調整して乾燥した場合（本発明例）；この時減
湿空気導入量は100〜350Nm³／HR間で変動し、
平均導入量は230Nm³／HRであつた。各々の例に
ついて連続的に280℃で溶融押出しキヤステイン
グドラム上で冷却固化し、フイルムを７日間づつ
生産し、そのフイルム品質を第２表に比較して示
した。[Table] Example 2 Polyethylene terephthalate chips with a moisture content of 0.05 to 0.15% and an intrinsic viscosity of 0.625 before drying were continuously fed at 600 kg into a rotary dryer in which hot air at a temperature of 185°C was circulated at 400 Nm ³ /HR. /Hr and drying for an average of 3.5 hours, when a certain amount of dehumidified air with a dew point of about -40℃ is introduced into the dryer system at 250Nm ³ /Hr (comparative example) and the atmospheric dew point in the system When drying is performed by automatically adjusting the amount of dehumidified air introduced so that the temperature is 4°C (example of the present invention); at this time, the amount of dehumidified air introduced varies between 100 and 350 Nm ³ /HR,
The average amount introduced was 230Nm ³ /HR. Each example was continuously cooled and solidified on a melt extrusion casting drum at 280 DEG C., films were produced for 7 days, and the film quality is shown in Table 2 for comparison.

【表】じ
[Table]

[Brief explanation of the drawing]

第１図は本発明に係わる実施方法の制御系フロ
ーの一例を示すものである。図中Ａ：原料投入
部、Ｂ：原料搬出部、Ｃ：乾燥機、Ｄ：循環用ブ
ロアー、Ｅ：露点検知端子、Ｆ：調節系、Ｇ：調
節弁、Ｈ：排気係、Ｊ：調節ダンバーを各々示め
す。 FIG. 1 shows an example of a control system flow of an implementation method according to the present invention. In the figure, A: Raw material input section, B: Raw material unloading section, C: Dryer, D: Circulation blower, E: Dew point detection terminal, F: Control system, G: Control valve, H: Exhaust section, J: Control damper Show each.

Claims

[Claims]

1 In a method of continuously drying thermoplastic synthetic resin in a continuous hot air dryer, the dew point of the hot air exhausted from the dryer is detected, and the amount of dehumidified air introduced into the hot air is adjusted according to the detected value. and the dew point is -10~10℃
A method for drying a thermoplastic synthetic resin, characterized in that hot air adjusted to a predetermined range within the above range is used again as hot air for drying.