JP3573473B2 - Styrene resin for foam - Google Patents

Description

【０００７】
（２）分子量算出
ＭｒとＭａｂｓの算出には図２に示す様なＧＰＣ（ゲルパーミューションクロマトグラフ法）の装置を用い、算出をした。測定条件としては１０ｍｇのスチレン系樹脂を１０ｍｌのＴＨＦ（テトラヒドロフラン）に溶解しこれをＧＰＣカラムに通して測定した。
計算はまず標準直鎖及び分岐ポリスチレンを用いレイリー小角散乱法（ＬＡＬＳ）と示差角屈折率検出法（ＲＩ）のピーク強度〔Ｉ（ＬＳ），Ｉ（ＲＩ）〕から下記（１）、（２）、（３）式を用いて絶対分子量計算の換算係数を求め、本発明のスチレン系樹脂のＭｒ及びＭａｂｓを計算した。
ＲＩで測定される観測強度Ｉ（ＲＩ）はその溶液の重量濃度に比例する。
Ｉ（ＲＩ）＝Ｋ・Ｃ ・・・（１）
ここでＫは測定器に依って決まる定数であり、Ｃは樹脂の重量濃度である。
一方同時に測定されるＬＡＬＳ強度は樹脂の重量濃度と分子の散乱素子、即ちその分子が持つ絶対分子量の積に比例する。
【数２】
Ｉ（ＬＳ）＝Ф・Ｃ・Ｍａｂｓ ・・・（２）
ここでのФは式（１）で示されているＫと同意義である。
故に絶対分子量はこの二者の強度比に依って算出ができる。
【数３】
Ｉ（ＬＳ）／Ｉ（ＲＩ）＝κ・Ｍａｂｓ ・・・（３）
κは測定器の装置常数であり、既知分子量である標準ポリスチレンやアニオンリビング重合に依って合成される４、６及び１２分岐スター、櫛形ポリマー（分子量同程は超遠心分離法や浸透圧法に依って求める）に依って求められる。
測定機本体は東曹（株）製、ＨＬＣ８０２０を用い、ＬＡＬＳ検出器に東曹（株）製ＬＳ８０００を用いた。また分離カラムには東曹（株）製、ＴＳＫ−ｇｅｌ−ＧＭＸ−ＸＬを３本ないしは４本直列に接続したものを使用した。
【０００８】
（３）スチレン系樹脂の発泡及びその二次成形評価
発泡体の成形性を評価するため、幅６０ｍｍ、厚み３ｍｍの発泡体を発泡押出機を用いて製造した。発泡核剤には日本ミストロン（株）製、ミストロンベーパーを用い、発泡剤にはＬＰＧ（主成分、ノルマルブタン：イソブタン＝７０：３０体積分率）を用いた。二次成形評価に用いた発泡体の発泡倍率は１０±０．３、平均セルサイズを０．２ｍｍ±０．０３に揃えた。
発泡成形品の評価は、図３に示すの様な成形品を作り、それに発生する、割れの総和／成形品の外周＝成形不良率として評価を行った。
この時の成形条件は、セラミックヒーターの温度が３５０℃、雰囲気温度１５８±１０℃、予熱時間３〜４秒間で発泡体を加熱後、所定の金型でマッチモールド成形を行ったのもで、その際の金型クリアランスは３．３ｍｍであった。
本発明の樹脂を用いこれに熱二次成形を施すと、後記する実施例にみる通りｂｐ値の大きいもの程、成形不良率が低い事が明かである。
【０００９】
【実施例】
以下に実施例及び比較例を用いて本発明を更に詳細に説明するが、本発明はこれら実施例により何ら限定されるものではない。
（比較例１、２及び実施例１〜３）
図１で示される連続反応器に、重合開始剤として、(1)１，１−ビス（ｔ−ブチルパーオキシ）シクロヘキサン、及び(2)２，２−ビス（４，４’ジターシャリブチルパーオキシシクロヘキシル）プロパンを添加したスチレン重合液を流入して、温度条件がａ：１２０℃。ｂ：１３０℃、ｃ：１３５℃、ｄ：１４０℃で、重合液が管状反応器（積分型反応器）を静的混合で進み、重合器の入口の重合液成分がスチレンモノマー９９．９５重量％、エチルベンゼン０．０５重量％であり、ｂ〜ｄで添加される重合開始剤が重合液で１０％になるよう希釈して添加する重合条件で、重合してスチレン樹脂を製造した。重合開始剤の添加位置、添加量、及びその種類を、表１に示し、得られたスチレン樹脂の分子量、および分子量１０万〜２００万の範囲内でのｂｐ値を表２に示す。
得られたスチレン樹脂に発泡核剤を１重量％添加し、発泡押出機を用いて、ダイス：１４０℃、ロータリークーラー：１５５℃、ガス注入部：１７９℃、樹脂溶融部：１８０〜２１０℃、樹脂吐出量：３ｋｇ／ｈｒ、及び表３に示す発泡剤含浸率、注入圧ダイス圧力の押出し条件で、発泡体を製造した。得られた発泡体の物性を表３に示す。
【００１０】
（実施例４、５）
重合開始剤の添加位置を表１に示す位置に、スチレンモノマーの組成を表２に示す組成に替えた以外は、実施例１と同様な条件でスチレン系樹脂を製造した。重合開始剤の添加位置、添加量、及びその種類を、表１に示し、得られたスチレン樹脂の分子量、および分子量１０万〜２００万の範囲内でのｂｐ値を表２に示す。
得られたスチレン樹脂に発泡核剤を１重量％添加し、発泡押出機を用いて、ダイス：１５５℃、ロータリークーラー：１６７℃、ガス注入部：１８８℃、樹脂溶融部：１８０〜２２０℃、樹脂吐出量：３ｋｇ／ｈｒ、及び表３に示す発泡剤含浸率、注入圧ダイス圧力の押出し条件で、発泡体を製造した。得られた発泡体の物性を表３に示す。
【００１１】
（比較例３〜５）
重合開始剤をｂ〜ｄで添加しない以外は、実施例１と同様にしてスチレン系樹脂を製造した。重合開始剤の添加位置、添加量、及びその種類を、表１に示し、得られたスチレン樹脂の分子量、および分子量１０万〜２００万の範囲内でのｂｐ値を表２に示す。
得られたスチレン樹脂を発泡押出機を用いて、実施例１と同様な押出し条件で、発泡体を製造した。得られた発泡体の物性を表３に示す。
Ｍｒが１０万でｂｐ値が１．１以下の場合は、発泡体シートの熱二次成形性が著しく改善されるが表面の滑らかさや発泡セルの均一性が悪くなる。一方で２００万でｂｐ値が２．４を越える場合、スチレン系樹脂の架橋（ゲル化）が著しくなり発泡させた時に表面の見栄えが悪くなる。
Ｍｒ分子量が１０万〜２００万の間でｂｐ値が１．１を超え２．４以下の場合、発泡体（シート）のきめ細かさ、シートの熱二次成形性は市販されているスチレン系樹脂（ｂｐ値は全分子量に於いて１）に比べ、かなり改善される。
なお、図５にＭｒが１０万〜２００万の範囲における、Ｍａｂｓ／Ｍｒ，即ちｂｐ値とＭｒとの関係を、実施例１〜３及び比較例１〜５について示す。
【００１２】
【表２】

【００１３】
【表３】

【００１４】
【発明の効果】
本発明の樹脂を用いて得られたポリスチレンペーパー（ＰＳＰ）、若しくは発泡体は、二次成形した場合に、外観不良の少ない成形品を作る事が出来る。
【図面の簡単な説明】
【図１】本発明のスチレン系樹脂を製造する為の連続重合プロセスの概略図である。
【図２】絶対分子量を計測する実験装置の概略図である。
【図３】発泡体の二次成形評価に用いた成形品の形状である。
【図４】本発明のスチレン系樹脂のｂｐ値とＭｒとの関係を示す。
【符号の説明】
ａ：重合開始剤第１添加点
ｂ：重合開始剤初段添加点
ｃ：重合開始剤中段添加点
ｄ：重合開始剤後段添加点
Σｌｉ：成形品側面に発生した割れの総和[0001]
[Industrial applications]
Due to its excellent moldability and heat retention, molded articles of expanded polystyrene sheets are frequently used in food containers and packaging materials in large-scale retail stores and the like. It relates to a styrene-based resin having excellent properties.
[0002]
[Prior art]
Foams have different performance requirements depending on the application, and dishes such as meat trays are required to have no cracks in the ribs between products and to have high stiffness of the products. Since the product is subjected to curved printing after molding, importance is placed on the smoothness, stiffness and heat resistance of the foam surface.
Since the styrene-based resin that forms the expanded polystyrene sheet is synthesized by a radical polymerization method, its molecular structure is almost linear, and in particular, when the foam is used for food, it is important for food hygiene and manufacturers. Due to the voluntary regulations, it is difficult to modify the raw material by adding a styrene-based resin additive, which is often found in injection raw materials, and it has been impossible to drastically modify the foam.
Even if the molecular weight and the components contained in the resin are changed, no significant modification will be made.If the molecular weight is increased, the productivity during extrusion is reduced, and conversely, if the molecular weight is reduced, the brittleness of the obtained foam is only worsened. Rather, it lowers the heat resistance of the product, and particularly in a donburi container, the reduction in heat resistance is fatal.
Regarding the measurement of the molecular weight of the styrene-based resin, the molecular weight Mr obtained by the conventional gel permeation chromatography (hereinafter referred to as “GPC”) is mainly obtained by a differential angle refractive index detection method based on linear standard polystyrene. However, this value merely represents the size of the polymer spread in tetrahydrofuran used for detection, and does not represent the absolute molecular weight Mabs of the polymer. For example, when the resin is slightly branched, Mr Does not show a true molecular weight.
Methods for detecting the absolute molecular weight Mabs include Rayleigh small-angle scattering and ultracentrifugation.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a styrenic resin capable of modifying the required performance of a foamed molded article (container) as described above without adding an additive, and to provide a foamed sheet obtained from the styrenic resin, It is an object of the present invention to provide a foamed container or the like obtained by subjecting a body or a foamed sheet to thermal secondary molding.
[0004]
[Means for solving the problem]
The inventors examined the thermal secondary workability of the foamed sheet from the viewpoint of the resin, and found that the molecular structure of the resin was involved in determining the properties. Therefore, the ratio of the molecular weight Mr determined from the elution curve of the differential angle refractive index detection method to the absolute molecular weight Mabs determined from the Rayleigh scattering by the Rayleigh small angle scattering method, that is, Mabs / Mr, is defined as the bp value, and the value is defined as the bp value. The present invention was completed as a result of various investigations based on the finding that this value affects the thermal secondary workability of the foamed sheet.
That is, the present invention, when using a tetrahydrofuran solvent and simultaneously measuring the molecular weight by differential angle refractive index detection method and Rayleigh small-angle scattering method by gel permeation chromatography, the molecular weight is in the range of 100,000 to 2,000,000, The ratio of the molecular weight Mr determined from the elution curve of the differential angle refractive index detection method based on linear standard polystyrene to the absolute molecular weight Mabs determined from the Rayleigh scattering by the Rayleigh small angle scattering method, that is, Mabs / Mr is 1.1. A styrene-based resin for a foam, characterized in that the styrene-based resin has a polymer composition of 91 to 100% by weight in styrene units and 0 in methacrylic acid units and / or maleic anhydride units. To 9% by weight of a styrene-based resin for a foamed sheet, and a foamed sheet, a foam, and a foamed sheet obtained from the styrene-based resin. Form the foam container or the like, it is.
In the present invention, the reason that the Rayleigh small angle scattering method (LALS) is used for the detection of the absolute molecular weight is that the method has an advantage that it can be connected to an existing GPC instrument and can be simultaneously and continuously measured.
[0005]
The method for polymerizing the styrene resin of the present invention, the method for measuring the molecular weight, and the secondary molding of the foam are described below.
(1) Polymerization method Regarding the polymerization method , for example, in the case of using a continuous polymerization process in which a polymerization solution proceeds by static mixing in a tubular reactor (integration type reactor) , thermal polymerization of styrene monomer, or At the beginning of the polymerization, a peroxide-based polymerization initiator (radical generator) such as benzoyl peroxide was added for polymerization. However, in the method of the present invention, a predetermined peroxide was added at the first, middle or later stage of the continuous polymerization process. The styrene resin of the present invention was able to be produced by adding and polymerizing.
That is, the polymerization process of the polystyrene used in the present invention is carried out by a predetermined method described in Table 1 and FIG. 1, and the polymerization initiator (radical generator) to be added is 2,2-bis ( One or two kinds of 4,4′-ditert-butylperoxycyclohexyl) propane and 1,1-bis (t-butylperoxy) cyclohexane are added to a continuous polymerization reactor in the first stage (b), the middle stage (c) and / or Alternatively, the addition is performed in the final stage (d). The polymerization initiator may be diluted with a monomer or a predetermined polymerization solution to an arbitrary concentration, or may be directly added.
The polymerization conditions are adjusted so that the time of arrival of the polymerization solution from the addition point (a) to the point (b) where the polymerization initiator is added is 7 hours and the monomer conversion is 50%. If the arrival time is longer than this, remarkable crosslinking occurs in the polymer, making it difficult to continue continuous polymerization. Subsequently, the polymerization time from the addition point (b) to the final stage is set to 4 hours, and the polymerization is completed at a monomer conversion of about 80%.
[0006]
[Table 1]

[0007]
(2) Calculation of molecular weight Mr and Mabs were calculated using a GPC (gel permeation chromatography) apparatus as shown in FIG. As measurement conditions, 10 mg of a styrene resin was dissolved in 10 ml of THF (tetrahydrofuran), and the solution was passed through a GPC column and measured.
First, the calculation was carried out using peaks [I (LS), I (RI)] of the Rayleigh small angle scattering method (LALS) and the differential angular refractive index detection method (RI) using standard linear and branched polystyrene. ) And (3) were used to determine conversion coefficients for the calculation of absolute molecular weight, and the Mr and Mabs of the styrene resin of the present invention were calculated.
The observed intensity I (RI) measured by RI is proportional to the weight concentration of the solution.
I (RI) = K · C (1)
Here, K is a constant determined by the measuring instrument, and C is the weight concentration of the resin.
On the other hand, the LALS intensity measured simultaneously is proportional to the product of the weight concentration of the resin and the molecular scattering element, that is, the absolute molecular weight of the molecule.
(Equation 2)
I (LS) = Ф · C · Mabs (2)
Here, Ф has the same meaning as K shown in equation (1).
Therefore, the absolute molecular weight can be calculated based on the intensity ratio between the two.
(Equation 3)
I (LS) / I (RI) = κ · Mabs (3)
κ is a device constant of the measuring instrument, and is a known molecular weight of standard polystyrene or a 4, 6, or 12-branch star synthesized by anionic living polymerization, or a comb polymer (the molecular weight is about the same as that of ultracentrifugation or osmotic pressure method). Required).
The measuring instrument body used was HLC8020 manufactured by Tosoh Corp., and the LS8000 manufactured by Tosao Corp. was used for the LALS detector. Further, as the separation column, a column in which three or four TSK-gel-GMX-XL manufactured by Tosoh Corporation were connected in series was used.
[0008]
(3) Foaming of Styrenic Resin and Evaluation of Secondary Forming In order to evaluate the moldability of the foam, a foam having a width of 60 mm and a thickness of 3 mm was produced using a foam extruder. As a foaming nucleating agent, Mistron Vapor manufactured by Nippon Mistron Co., Ltd. was used, and as a foaming agent, LPG (main component, normal butane: isobutane = 70: 30 volume fraction) was used. The expansion ratio of the foam used in the secondary molding evaluation was adjusted to 10 ± 0.3, and the average cell size was adjusted to 0.2 mm ± 0.03.
The evaluation of the foam molded article was performed by preparing a molded article as shown in FIG. 3 and evaluating the sum of cracks generated in the molded article / periphery of the molded article = defective molding rate.
The molding conditions at this time were as follows: the temperature of the ceramic heater was 350 ° C., the ambient temperature was 158 ± 10 ° C., the preform was heated for 3 to 4 seconds, and then match molding was performed with a predetermined mold. Had a mold clearance of 3.3 mm.
When the resin of the present invention is subjected to thermal secondary molding, it is clear that the larger the bp value is, the lower the molding failure rate is, as shown in Examples described later.
[0009]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
(Comparative Examples 1 and 2 and Examples 1 to 3)
In the continuous reactor shown in FIG. 1, (1) 1,1-bis (t-butylperoxy) cyclohexane and (2) 2,2-bis (4,4′-di-tert-butyl A styrene polymerization solution to which (oxycyclohexyl) propane was added was introduced, and the temperature condition was a: 120 ° C. b: 130 ℃, c: 135 ℃, d: at 140 ° C., the polymer solution proceeds tube-shaped reactor (integrated reactor) in static mixing, the inlet of the polymerization vessel polymerization liquid component is a styrene monomer 99.95 % By weight, and 0.05% by weight of ethylbenzene. Polymerization was carried out under the polymerization conditions in which the polymerization initiator added in b to d was diluted to 10% with a polymerization solution and then added to produce a styrene resin. Table 1 shows the addition position, amount and type of the polymerization initiator, and Table 2 shows the molecular weight of the obtained styrene resin and the bp value within the range of 100,000 to 2,000,000.
To the obtained styrene resin, 1% by weight of a foam nucleating agent was added, and using a foaming extruder, a die: 140 ° C., a rotary cooler: 155 ° C., a gas injection part: 179 ° C., a resin melting part: 180 to 210 ° C. A foam was manufactured under the conditions of extrusion of a resin discharge amount: 3 kg / hr, a foaming agent impregnation rate shown in Table 3, and an injection die pressure. Table 3 shows the physical properties of the obtained foam.
[0010]
(Examples 4 and 5)
A styrene resin was produced under the same conditions as in Example 1 except that the addition position of the polymerization initiator was changed to the position shown in Table 1 and the composition of the styrene monomer was changed to the composition shown in Table 2. Table 1 shows the addition position, amount and type of the polymerization initiator, and Table 2 shows the molecular weight of the obtained styrene resin and the bp value within the range of 100,000 to 2,000,000.
1% by weight of a foam nucleating agent was added to the obtained styrene resin, and using a foaming extruder, a die: 155 ° C., a rotary cooler: 167 ° C., a gas injection part: 188 ° C., a resin melting part: 180 to 220 ° C. A foam was manufactured under the conditions of extrusion of a resin discharge amount: 3 kg / hr, a foaming agent impregnation rate shown in Table 3, and an injection die pressure. Table 3 shows the physical properties of the obtained foam.
[0011]
(Comparative Examples 3 to 5)
A styrenic resin was produced in the same manner as in Example 1 except that the polymerization initiator was not added in b to d. Table 1 shows the addition position, amount and type of the polymerization initiator, and Table 2 shows the molecular weight of the obtained styrene resin and the bp value within the range of 100,000 to 2,000,000.
A foam was produced from the obtained styrene resin using a foaming extruder under the same extrusion conditions as in Example 1. Table 3 shows the physical properties of the obtained foam.
If Mr is bp value 100,000 1.1 or less, the heat-forming of the foam sheet is remarkably improved uniformity of smoothness and foamed cells of the surface is deteriorated. On the other hand, when the bp value exceeds 2.4 at 2,000,000 , the cross-linking (gelation) of the styrenic resin becomes remarkable, and the appearance of the surface becomes poor when foamed.
When the bp value is more than 1.1 and not more than 2.4 when the Mr molecular weight is between 100,000 and 2,000,000, the fineness of the foam (sheet) and the thermal secondary moldability of the sheet are the same as those of a commercially available styrene resin. (The bp value is considerably improved as compared with 1 in the total molecular weight.)
In addition, FIG. 5 shows Mabs / Mr, that is, the relationship between the bp value and Mr in the range of 100,000 to 2,000,000 for Examples 1 to 3 and Comparative Examples 1 to 5.
[0012]
[Table 2]

[0013]
[Table 3]

[0014]
【The invention's effect】
The polystyrene paper (PSP) or foam obtained by using the resin of the present invention can produce a molded article with less appearance defects when subjected to secondary molding.
[Brief description of the drawings]
FIG. 1 is a schematic view of a continuous polymerization process for producing a styrenic resin of the present invention.
FIG. 2 is a schematic diagram of an experimental device for measuring an absolute molecular weight.
FIG. 3 shows the shape of a molded product used for secondary molding evaluation of a foam.
FIG. 4 shows the relationship between the bp value and Mr of the styrenic resin of the present invention.
[Explanation of symbols]
a: polymerization initiator first addition point b: polymerization initiator first-stage addition point c: polymerization initiator middle-stage addition point d: polymerization initiator second-stage addition point Δli: total sum of cracks generated on the side surface of the molded product

Claims (4)

When measured at the same time molecular weight in gel permeation mu Deployment chroma preparative graph method using tetrahydrofuran solvent at a differential angle refractometer method and Rayleigh small angle scattering method, a molecular weight in the range 100,000 2,000,000, a linear standard polystyrene beyond a molecular weight Mr obtained elution curve et differential angle refractive index detection method on the basis, the ratio of the absolute molecular weight Mabs obtained from the Rayleigh scattering of Rayleigh small angle scattering method, the immediate Chi M abs / Mr 1.1 2.4 The following styrene resin for foam. A styrene resin having a number average molecular weight of 70 to 220,000 and a weight average molecular weight of 150,000 to 450,000 based on Mr determined by gel permeation chromatography, and having a polymer composition having a styrene unit of 91 to 100 weight The styrenic resin for a foam according to claim 1, wherein the content of methacrylic acid units and / or maleic anhydride units is 0 to 9% by weight. Claim 1 or foamed sheets produced by using a 2 styrenic resin according, or foam. A foam container obtained by subjecting the foam sheet according to claim 3 to thermal secondary molding.

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