JP4128850B2 - Method for producing in-mold foam molded product of polypropylene resin expanded particles - Google Patents

Description

【００６１】
【表２】

【００６２】
【表３】

【００６３】
【表４】

【００６４】
尚、表３、表４中の発泡粒子の見掛け密度（ｇ／Ｌ）は、発泡粒子の重量を発泡粒子の見掛け体積で除すことにより計算したものである。具体的には、養生後に、無作為に選んだ複数個の発泡粒子の重量（ｇ）を測定し、次いで、２３℃の水１００ｃｍ³が収容されたメスシリンダー内の水に水没させたときの排除体積から、発泡粒子の見かけ体積（ｃｍ³）を読み取り、これをリットル単位に換算する。この測定値より発泡粒子の見かけ密度（ｇ／Ｌ）を計算する。この測定には発泡粒子重量が０．５０００〜１０．００００ｇ、かつ発泡粒子の見掛け体積が５０〜９０ｃｍ^３の発泡粒子が使用される。
また、表３中の発泡粒子の内圧は、前記の通りゲージ圧で表現されたものであるから数値の後に（Ｇ）を付してある。また、表３と表４の項目は同じであるので、表４から単位の項目（列）は省略した。
また、表３、表４中の圧縮強度とは、成形体から縦５０ｍｍ、横５０ｍｍ、厚み２５ｍｍ、となるように切断して得られた試験片（全面の表皮がカットされたもの）を使用し、ＪＩＳ Ｚ ０２３４−１９７６ Ａ法に従って試験片温度２３℃、荷重速度１０ｍｍ／分の条件で歪が５５％に至るまで圧縮試験を行い、得られた応力−歪線図より５０％歪時の応力を読みとり、これを圧縮強度とした。また、表中のガラス転移温度、基材樹脂の融点、発泡粒子の融点及び高温ピークの熱量は、株式会社島津製作所の島津熱流束示差走査熱量計「ＤＳＣ−５０」を使用して測定した。
【００６５】
以上の結果は、有機過酸化物が存在する水性媒体中にポリプロピレン系樹脂粒子を分散させると共に、該ポリプロピレン系樹脂粒子の基材樹脂融点よりも低温であって且つ該有機過酸化物が分解する温度下で該有機過酸化物を分解させることによって該ポリプロピレン系樹脂粒子の表面を改質して無架橋の表面改質粒子を得る工程を行なうと、それから得られた発泡粒子は、ポリプロピレン系樹脂のリサイクル性を維持しながら成形温度が低減されることを示している。より具体的には次の通りである。実施例１と比較例１は、発泡粒子の見かけ密度が同じであり、発泡粒子の全体の高温ピーク熱量がほぼ同等であり、得られた成形体の見かけ密度と圧縮強度測定用の試料のカットサンプルの見かけ密度が同じであるから対比するのに好都合である。実施例１と比較例１の対比より、比較例１で必要な最低融着温度は０．５５ＭＰａ（Ｇ）を超えるのに対し、実施例１で必要な最低融着温度は０．４４ＭＰａ（Ｇ）となっており、実施例１は比較例１に比べ、最低融着温度が７℃以上も低下されていることが分かる。しかも、実施例１で得られた成形体の圧縮強度は、発泡粒子の全体の高温ピーク熱量に見合っており、特段低下しているということも無い。実施例３と比較例３は、発泡粒子の見かけ密度がほぼ同じであり、発泡粒子の全体の高温ピーク熱量がほぼ同等であり、得られた成形体の見かけ密度と圧縮強度測定用の試料のカットサンプルの見かけ密度がほぼ同じであるから対比するのに好都合である。実施例３と比較例３の対比より、比較例３で必要な最低融着温度は０．５５ＭＰａ（Ｇ）を超えるのに対し、実施例３で必要な最低融着温度は０．３８ＭＰａ（Ｇ）となっており、実施例３は比較例３に比べ、最低融着温度が１２℃以上も低下されていることが分かる。しかも、実施例３で得られた成形体の圧縮強度は、発泡粒子の全体の高温ピーク熱量に見合っており、特段低下しているということも無い。
【００６６】
実施例４と比較例２は、発泡粒子の見かけ密度がほぼ同じであり、発泡粒子の全体の高温ピーク熱量がほぼ同等であり、得られた成形体の見かけ密度と圧縮強度測定用の試料のカットサンプルの見かけ密度が同じであるから対比するのに好都合である。実施例４と比較例２の対比より、比較例２で必要な最低融着温度は０．５５ＭＰａ（Ｇ）を超えるのに対し、実施例４で必要な最低融着温度は０．３９ＭＰａ（Ｇ）となっており、実施例４は比較例２に比べ、最低融着温度が１１℃以上も低下されていることが分かる。しかも、実施例４で得られた成形体の圧縮強度は、発泡粒子の全体の高温ピーク熱量に見合っており、特段低下しているということも無い。参考例１と実施例２は、発泡粒子の見かけ密度がほぼ同じであり、発泡粒子の全体の高温ピーク熱量がほぼ同等であり、得られた成形体の見かけ密度と圧縮強度測定用の試料のカットサンプルの見かけ密度がほぼ同じであるから対比するのに好都合である。参考例１と実施例２の対比より、参考例１で必要な最低融着温度は０．４８ＭＰａ（Ｇ）であるのに対し、実施例２で必要な最低融着温度は０．３５ＭＰａ（Ｇ）となっており、実施例２は参考例１に比べ、最低融着温度が約９℃も低下されていることが分かる。実施例２と参考例１とは使用された有機過酸化物が異なっており、他の条件はほぼ同じであるといえるから、この結果は、有機過酸化物としてカーボネート構造を有するものを使用した方が最低融着温度の低減効果に優れているということを示している。
【００６７】
実施例５と比較例５は、発泡粒子の見かけ密度が近く、発泡粒子全体の高温ピーク熱量がほぼ同等であるが、得られた成形体の見かけ密度と圧縮強度測定用の試料のカットサンプルの見かけ密度は多少異なるものの対比は可能である。実施例５と比較例５の対比より、実施例５で必要な最低融着温度は０．３６ＭＰａ（Ｇ）であるのに対し、比較例５で必要な最低融着温度は０．５５ＭＰａ（Ｇ）を超え、実施例５は比較例５に比べ、最低融着温度が１３℃以上も低下されていることが分る。しかも実施例５で得られた成形体の圧縮強度は、発泡粒子全体の高温ピークとカットサンプルの見かけ密度に見合っており、特段低下しているということもない。
【００６８】
更に、実施例５で得られた発泡粒子と比較例５で得られた発泡粒子について、各発泡粒子表面に対し、ティ・エイ・インスツルメント・ジャパン社のマイクロ熱分析システム「２９９０型マイクロサーマルアナライザー」を使用し、２５℃から２００℃まで昇温速度１０℃／秒の条件にて、マイクロ示差熱分析（μＤＴＡ）を行なったところ、実施例５で得られた発泡粒子の表面は融解開始温度が１３１℃であり、補外融解開始温度が１３５℃であるのに対し、比較例５で得られた発泡粒子の表面は融解開始温度が１６８℃であり、補外融解開始温度が１７１℃であることが判明した。以上のμＤＴＡによる結果は、発泡粒子表面の融解開始温度又は補外融解開始温度の低下が、成形時に必要な最低融着温度の低下に寄与していることを示している。
【００６９】
尚、実施例１〜５では、成形時の飽和スチーム圧力をより高くした場合には、得られる成形体の融着度合いはより高まり、上記（ｂ／ｎ）の値はより大きくなる。具体的には、表５の通りである。上記（ｂ／ｎ）の値が大きいほど成形体の曲げ強度や引張強度が高まるので好ましい。本発明の方法で得られた成形体は、上記（ｂ／ｎ）の値が、０．４以上であることが好ましく、０．５以上であることがより好ましく、０．６以上であることが更に好ましく、０．７以上であることが最も好ましい。
【００７０】
【表５】

【００７１】
【発明の効果】
本発明は、その成形材料として、従来の同等のＥＰＰ粒子に比べて成形温度を劇的に低下させた新規なＥＰＰ粒子を、その内圧を高めて型内に充填した後、ＥＰＰ粒子を加熱し、冷却するＥＰＰ成形体の製造方法である。従って、成形時における加熱温度を低下させることが可能となり、熱エネルギーの節減に貢献する。特に、カーボネート構造を有する有機過酸化物を用いて発泡粒子の表面改質を行っていることから、より優れた最低融着温度の低減効果を得ることができる。また、加熱温度の低下は、冷却時間を短縮し、その結果、成形サイクルを短縮することができ、生産性を向上させることができる。また、本発明により得られたＥＰＰ成形体は、無架橋であるから、ポリプロピレン系樹脂のリサイクル適性等を維持しており、環境に優しいものである。また、従来は、ＥＰＰ成形体の高剛性等の高物性化のためには融点の高いポリプロピレン系樹脂を使用して得られた、高温ピーク熱量の高い発泡粒子を使用しなければならないため必然的に成形温度が汎用の成形機の耐圧を超えてしまうという問題があったが、本発明で用いる発泡粒子は、融点が１５８℃以上という融点の高いポリプロピレン系樹脂を使用して得られた、高温ピーク熱量の高い発泡粒子であっても、それから得られるＥＰＰ成形体は高剛性で、圧縮強度等の機械的物性に優れるものでありながら、０．４５ＭＰａ（Ｇ）以下という低温度（低圧）のスチームで成形体を得ることが可能となり、汎用の成形機の耐圧以内での成形も可能となる。しかも、発泡粒子の高温ピークの熱量が２〜７０Ｊ／ｇであることから、ＥＰＰ成形体の圧縮強度、エネルギー吸収量などが低下することがなく、成形するに先立ち発泡粒子内の圧力を０．００５〜０．９８ＭＰａ（Ｇ）とすることで、上記低温度のスチームでの成形であっても、ＥＰＰ粒子が二次発泡不足となることも、ＥＰＰ粒子の相互融着が不十分となることもない。従って、本発明の場合、従来よりも安価に高物性（高剛性）又は／及び軽量のＥＰＰ成形体を提供することが可能となる。本発明の方法で得られた高物性のＥＰＰ成形体は、自動車のバンパー芯材として、あるいは自動車の側面からの衝撃を吸収させることを目的に自動車のドアにセットされる側部衝突用緩衝材として特に好適である。
【図面の簡単な説明】
【図１】図１は、本発明の成形用ポリプロピレン系樹脂発泡粒子の、第１回目のＤＳＣ曲線のチャートの一例を示す図である。
【図２】図２は、ポリプロピレン系樹脂粒子の第２回目のＤＳＣ曲線のチャートの一例を示す図である。
【図３】図３は、実施例７と比較例５に基づく各例で得られた発泡粒子表面に対するマイクロ熱機械分析に基づくμＤＴＡ曲線を示す図である。
【図４】図４は、他の実施例で得られた発泡粒子表面に対するマイクロ熱機械分析に基づくμＤＴＡ曲線を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an in-mold foam molded product of polypropylene resin expanded particles.
[0002]
[Prior art]
In recent years, due to the integration of plastic materials, polypropylene resins in particular have excellent mechanical strength, heat resistance, processability, price balance, and excellent properties such as easy incineration and easy recyclability. Since then, the field of use is expanding. Similarly, an in-mold expanded molded body of non-crosslinked polypropylene resin foamed particles (hereinafter sometimes referred to as “EPP molded body”, “foamed particle molded body” or simply “molded body”) is superior to the above-mentioned polypropylene resin. Furthermore, it is widely used as a packaging material, a building material, a heat insulating material, and the like because it can add properties such as buffering properties and heat insulating properties without losing its properties.
[0003]
Recently, however, there are more opportunities for higher functionality than ever before. For example, for automotive applications, focusing on the excellent properties of EPP molded products, there have been a wide range of uses such as bumper cores, door pads, pillars, tool boxes, floor mats, etc. There has been a demand for weight reduction of vehicles, and at the same time, there has been a strong demand for weight reduction of parts constituting the vehicles. Even if it is an EPP molded object, it is not an exception, and the lighter weight EPP molded object has been calculated | required, maintaining conventional rigidity, shock absorbing property, and impact energy absorption. Furthermore, for example, as a shipping box such as a fish box in general, an in-mold foam molded body (hereinafter referred to as “EPS molded body”) of polystyrene-based resin foam particles because of its high rigidity and low cost. Many were used. However, since the EPS molded body is inferior in impact resistance and heat resistance compared to the EPP molded body, it is difficult to repeatedly use it. In recent years, there have been many requests to use an EPP molded product that can be used repeatedly and with excellent environmental compatibility due to the growing awareness of environmental issues in public opinion. It has been desired.
[0004]
By the way, in order to obtain a highly rigid EPP molded product, some improvements have been made so far, for example, using a highly rigid polypropylene resin as a raw material. As a high-rigidity polypropylene resin, a propylene copolymer or a propylene homopolymer having a low comonomer composition ratio such as ethylene or butene as a copolymer component is generally known. By using these raw materials, It was possible to obtain a highly rigid EPP molded body. A technique related to this is described in, for example, [Patent Document 1]. However, generally, a high-rigidity polypropylene-based resin has a melting point that rises at the same time as rigidity. When these high-rigidity raw materials are used, an increase in processing temperature for obtaining an EPP molded body, It was a rise. Conventionally, a molding machine for producing an EPP molded body has a structure corresponding to a high molding temperature, that is, a structure that can withstand high-pressure steam. In order to produce a highly rigid EPP molded body using rigid non-crosslinked polypropylene resin expanded particles (hereinafter sometimes referred to as “EPP particles” or simply “expanded particles”), In many cases, steam having a pressure higher than the pressure resistance of the molding machine is required, and it is difficult to obtain a sufficient fusion rate between the expanded particles. Actually, since there are limited molding machines that can obtain an EPP molded body that maintains a sufficient fusion rate and can support production, EPP particles that can be molded with steam at a lower temperature (low pressure) are obtained. A method was desired.
[0005]
Conventionally, a method of obtaining a highly rigid EPP molded body using a polypropylene copolymer resin composed of propylene and a comonomer such as ethylene or butene has been devised. In this method, the endothermic curve peak (hereinafter referred to as “high temperature”) is higher than the endothermic curve peak (hereinafter sometimes referred to as “inherent peak”) derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry of the expanded particles. This is a method in which the amount of heat of the high temperature peak is increased more than the value that has been conventionally managed. Techniques relating to this are described in, for example, [Patent Document 2] and [Patent Document 3]. When foamed particles obtained by these methods are used, as in the case of trying to obtain a highly rigid EPP molded body using the highly rigid EPP particles obtained from the highly rigid polypropylene resin as described above, In particular, it causes an increase in the molding temperature, often requires steam at a pressure exceeding the pressure resistance of the molding machine for producing the EPP molded body, and a sufficient fusion rate between the expanded particles is obtained. There was a problem that it was difficult to get. In reality, since there are a limited number of molding machines that can obtain EPP compacts that maintain a sufficient fusion rate and that can be used for production, a method for obtaining EPP particles that can be molded with lower temperature steam is desired. It had been.
[0006]
[Patent Document 1]
International Publication No. 96/31558 Pamphlet
[Patent Document 2]
Japanese Patent No. 2886248
[Patent Document 3]
JP-A-11-156879
[0007]
[Problems to be solved by the invention]
The present invention relates to a polypropylene resin using foamed particles comprising non-crosslinked polypropylene resin foamed particles that can fuse particles with low-temperature steam and give a foamed molded article having high rigidity (high compressive strength). An object of the present invention is to provide a method for industrially advantageously producing an in-mold foam molded body of foam particles.
[0008]
[Means for Solving the Problems]
  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, according to this invention, the manufacturing method of the in-mold expansion molding of the polypropylene resin expanded particle shown below is provided. (1) Polypropylene resin particles in which the base resin has a melting point of 158 ° C. or higher in a dispersion medium containing an organic peroxide having a carbonate structure (provided that a vinyl monomer is impregnated in the polypropylene resin) The dispersion formed by dispersing the organic peroxide is maintained at a temperature lower than the melting point of the base resin of the polypropylene resin particles and at a temperature at which the organic peroxide decomposes. Obtained by a surface modification step for obtaining non-crosslinked surface modified particles by decomposing the product, and a foaming step for foaming the surface modified particles with a foaming agent to obtain non-crosslinked foamed particles After applying an internal pressure of 0.005 to 0.98 MPa (G) in the bubbles of the polypropylene-based resin expanded particles having a heat quantity of the obtained high temperature peak of 2 to 70 J / g, and filling the expanded particles in the mold, Foam particles 0.45 MPa (G) is below the expansion fusing the heated foamed particles to each other at a steam pressure, then cooling method of manufacturing a mold expanded molded article of the polypropylene resin foamed beads characterized by.
(2) Melting point (Tm) of the surface layer portion of the expanded particles_s) And internal foam layer (Tm_i) Has a melting point of Tm_s<Tm_iSaid (1) characterized in that)The manufacturing method of the in-mold expansion molding of the polypropylene resin expanded particle of description.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The polypropylene resin that is a base resin of the polypropylene resin particles used in the present invention (hereinafter sometimes referred to as “the base resin”) contains a polypropylene homopolymer or a propylene component in an amount of 60 mol% or more. It is a copolymer of propylene and another comonomer (preferably containing 80 mol% or more of propylene component), or a mixture of two or more selected from these resins.
[0010]
Examples of the copolymer of propylene containing 60 mol% or more of a propylene component with another comonomer include, for example, ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, etc. Is exemplified.
[0011]
  The melting point of the base resin is to increase the mechanical properties such as the compressive strength of the final EPP molded product.158 ℃ or higherTheThe upper limit of the melting point is usually 170 ° C. Furthermore, the base resin preferably has a melt flow rate (MFR) of 0.3 to 100 g / 10 min, particularly 1 to 90 g, considering the heat resistance of the foamed molded product and the foaming efficiency at the time of producing foamed particles. / 10 minutes are preferred. The MFR is a value measured under test condition 14 of JIS K7210 (1976).
[0012]
In the present invention, a synthetic resin or / and an elastomer other than the polypropylene resin can be added to the polypropylene resin particles within a range that does not impair the intended effect of the present invention. The amount of the synthetic resin or / and elastomer added other than the polypropylene resin is preferably at most 35 parts by weight, more preferably at most 25 parts by weight per 100 parts by weight of the polypropylene resin. More preferably, it is at most 15 parts by weight, and most preferably at most 10 parts by weight.
[0013]
Synthetic resins other than polypropylene resins include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic. Examples thereof include ethylene resins such as acid copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.
[0014]
Examples of the elastomer include ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, nitrile rubber, and styrene-butadiene block copolymer. Elastomers such as elastomers and hydrogenated products thereof are exemplified.
[0015]
In addition, various additives can be contained in this base resin in the range which does not impair the desired effect of this invention. Examples of such additives include antioxidants, ultraviolet light inhibitors, antistatic agents, flame retardants, metal deactivators, pigments, dyes, nucleating agents, and bubble regulators. Examples of the air conditioner include inorganic powders such as zinc borate, talc, calcium carbonate, borax, and aluminum hydroxide. These additives are preferably used in a total amount of 20 parts by weight or less, particularly 5 parts by weight or less per 100 parts by weight of the base resin. These additives are used in the extruder when, for example, the polypropylene resin particles (hereinafter sometimes referred to as “the present resin particles”) used in the present invention are produced by cutting the strands extruded by the extruder. It can be contained in the resin particles by adding and kneading to the base resin melted in (1).
[0016]
In addition, as this resin particle for obtaining surface-modified particles, when the base resin is melted in an extruder and the extruded strand is cut to produce this resin particle, the strand immediately after extrusion is rapidly cooled. What was obtained by this is preferable. The surface modification can be performed efficiently when the resin particles are so cooled. The quenching of the strand immediately after the extrusion is adjusted immediately after extruding the strand, preferably in water adjusted to 50 ° C. or lower, more preferably in water adjusted to 40 ° C. or lower, most preferably 30 ° C. or lower. This can be done by placing it in water. Then, the sufficiently cooled strand is pulled up from the water and cut into an appropriate length to form the resin particles having a desired size. The resin particles are usually adjusted to have a length / diameter ratio of 0.5 to 2.0, preferably 0.8 to 1.3, and the average weight per particle (chosen at random). The average value of 200 weights measured simultaneously is adjusted to be 0.1 to 20 mg, preferably 0.2 to 10 mg.
[0017]
  The method for producing polypropylene resin expanded particles (EPP particles), which is the previous step in the method for producing an in-mold foam molded product of the present invention (hereinafter also referred to as method A), comprises a surface modification step and a foaming step. In the surface modification step, the resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the obtained dispersion (hereinafter also referred to as a dispersion) is cooled at a temperature lower than the melting point of the base resin of the resin particles. And the organic peroxideIsThe surface of the resin particles is modified by decomposing the organic peroxide while maintaining the temperatureNothingCross-linked surface modified particles are obtained. The surface-modified particles thus obtained are foamed using a foaming agent in the next foaming step.NothingConvert to cross-linked foam particles. The foamed particles obtained in this way are excellent in heat-fusibility and can be fused between the foamed particles with low-temperature steam. Further, the foamed particles can be filled in a mold and heated with steam to obtain an EPP molded body having excellent rigidity. The method A is a method newly developed by the present inventors.
[0018]
The dispersion medium used in the surface modification step is generally an aqueous medium, preferably water, and more preferably ion-exchanged water, but is not limited to water and does not dissolve the base resin. Any solvent or liquid that can disperse the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol, and the like. The aqueous medium includes a mixed solution of water and an organic solvent such as the alcohol.
[0019]
Examples of the organic peroxide include various conventionally known ones such as isobutyl peroxide [50 ° C./85° C.], cumyl peroxyneodecanoate [55 ° C./94° C.], α, α′-bis ( Neodecanoyl peroxy) diisopropylbenzene [54 ° C./82° C.], di-n-propyl peroxydicarbonate [58 ° C./94° C.], diisopropyl peroxydicarbonate [56 ° C./88° C.], 1-cyclohexyl- 1-methylethylperoxyneodecanoate [59 ° C / 94 ° C], 1,1,3,3-tetramethylbutylperoxyneodecanoate [58 ° C / 92 ° C], bis (4-t-butyl Cyclohexyl) peroxydicarbonate [58 ° C./92° C.], di-2-ethoxyethyl peroxydicarbonate [59 ° C./92° C.], di (2- Ethylhexylperoxy) dicarbonate [59 ° C / 91 ° C], t-hexylperoxyneodecanoate [63 ° C / 101 ° C], dimethoxybutylperoxydicarbonate [64 ° C / 102 ° C], di (3-methyl -3-Methoxybutylperoxy) dicarbonate [65 ° C / 103 ° C], t-butylperoxyneodecanoate [65 ° C / 104 ° C], 2,4-dichlorobenzoyl peroxide [74 ° C / 119 ° C] T-hexylperoxypivalate [71 ° C / 109 ° C], t-butylperoxypivalate [73 ° C / 110 ° C], 3,5,5-trimethylhexanoyl peroxide [77 ° C / 113 ° C], Octanoyl peroxide [80 ° C / 117 ° C], lauroyl peroxide [80 ° C / 116 ° C], stearoyl peroxide [80 ° C / 117 ° C], 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate [84 ° C / 124 ° C], succinic peroxide [87 ° C / 132 ° C], 2, 5-dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane [83 ° C./119° C.], 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate [90 ° C./138° C. ], T-hexylperoxy-2-ethylhexanoate [90 ° C / 133 ° C], t-butylperoxy-2-ethylhexanoate [92 ° C / 134 ° C], m-toluoylbenzoyl peroxide [ 92 ° C / 131 ° C], benzoyl peroxide [92 ° C / 130 ° C], t-butylperoxyisobutyrate [96 ° C / 136 ° C], 1,1-bis (t-butyl Luperoxy) -2-methylcyclohexane [102 ° C./142° C.], 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane [106 ° C./147° C.], 1,1-bis ( t-hexylperoxy) cyclohexane [107 ° C / 149 ° C], 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane [109 ° C / 149 ° C], 1,1-bis ( t-butylperoxy) cyclohexane [111 ° C / 154 ° C], 2,2-bis (4,4-dibutylperoxycyclohexyl) propane [114 ° C / 154 ° C], 1,1-bis (t-butylperoxy) ) Cyclododecane [114 ° C / 153 ° C], t-hexylperoxyisopropyl monocarbonate [115 ° C / 155 ° C], t-butylperoxy Simaleic acid [119 ° C / 168 ° C], t-butylperoxy-3,5,5-trimethylhexanoate [119 ° C / 166 ° C], t-butylperoxylaurate [118 ° C / 159 ° C], 2 , 5-Dimethyl-2,5-di (m-toluoylperoxy) hexane [117 ° C / 156 ° C], t-butylperoxyisopropyl monocarbonate [118 ° C / 159 ° C], t-butylperoxy-2 -Ethylhexyl monocarbonate [119 ° C / 161 ° C], t-hexylperoxybenzoate [119 ° C / 160 ° C], 2,5-dimethyl-2,5-di (benzoylperoxy) hexane [119 ° C / 158 ° C] Etc. are exemplified. In addition, the temperature on the left side in [] immediately behind each organic peroxide is a 1-hour half-life temperature described later, and the temperature on the right side is a 1-minute half-life temperature described later. The organic peroxide may be used alone or in combination of two or more, and usually 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, per 100 parts by weight of the resin particles in the dispersion medium. Used by adding.
[0020]
  In general, radicals generated by organic peroxides have three types of chain transfer actions: hydrogen abstraction, addition, and β decay. In the present invention, among these three actions, those having a particularly large addition action, that is, those generating oxygen radicals upon decomposition, are particularly preferred. Among them, a peroxide having a carbonate structure is preferred.Used as an essential organic peroxide. In addition, when using the organic peroxide, it is possible to use a chain transfer agent or the like as necessary (previously contained in the resin particles or / and added to the dispersion medium and used in combination). It is. The oxygen radical means an oxygen radical in which an organic group generated by decomposition of an organic peroxide is bonded in addition to a radical of oxygen alone.
[0021]
  Conventionally, as the use of the organic peroxide for polypropylene, the following methods <1> to <4> are known.
<1> Polypropylene particles are homogeneously impregnated with an organic peroxide and a crosslinking aid, and the organic peroxide is decomposed at a temperature exceeding the melting point of the polypropylene to crosslink the polypropylene.
<2> A composition containing polypropylene and an organic peroxide is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of the polypropylene to uniformly decompose the organic peroxide, thereby narrowing the molecular weight distribution. Polypropylene is obtained (Japanese Patent Laid-Open No. 3-152136).
<3> Polypropylene particles are uniformly impregnated with an organic peroxide and a crosslinking aid, and the organic peroxide is decomposed at a temperature lower than the melting point of the polypropylene to introduce a long chain branched or crosslinked structure into the polypropylene. The melt tension is increased (Japanese Patent Laid-Open No. 11-80262). The polypropylene having an increased melt tension is then melt-kneaded with a foaming agent in an extruder and used for extrusion foaming.
<4> A composition containing polypropylene, an organic peroxide, and maleic anhydride is uniformly melt-kneaded in an extruder at a temperature exceeding the melting point of polypropylene and graft polymerization is performed.
  Prior to the production of EPP particles, polypropylene resins are used in the dispersion medium in which the organic peroxide is present in order to obtain EPP particles having excellent heat-fusibility. And dispersing the dispersion at a temperature lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide.IsThe surface of the polypropylene resin particles is modified by decomposing the organic peroxide while maintaining the temperatureNothingThis is different from the utilization method according to the method A in which crosslinked surface-modified particles are obtained.
[0022]
  In Method A, the organic peroxide is at a lower temperature than the melting point of the base resin.In minutesLet me understand. Accordingly, the one-hour half-life temperature of the organic peroxide (the constant temperature when the amount of active oxygen becomes half of the initial value in one hour when the organic oxide is decomposed at a constant temperature) It is preferable that it is below Vicat softening point (JIS K 6747-1981, the same shall apply hereinafter) of the resin. When the 1-hour half-life temperature of the organic peroxide used exceeds the Vicat softening point of the base resin, a high temperature higher than the melting point of the base resin is required to rapidly decompose the peroxide. This is not preferable, and in some cases, the temperature is lower than the melting point of the base resin.In minutesIt is not preferable because it cannot be solved. The peroxide is heated to a temperature higher than the melting point of the base resin.In minutesWhen it is understood, since the peroxide decomposes in a state where it penetrates deep into the resin particles, the base resin constituting the resin particles is largely decomposed regardless of the surface and the inside. In some cases, only EPP particles that cannot be used for molding may be obtained, and even if molding can be performed, the mechanical properties of the finally obtained EPP molded body may be greatly reduced. In consideration of the above, the organic peroxide used in Method A preferably has a one-hour half-life temperature of 20 ° C. or more lower than the Vicat softening point of the base resin. It is more preferable that the temperature is 30 ° C. or more lower than the Vicat softening point. The one-hour half-life temperature is preferably equal to or higher than the glass transition temperature of the base resin, more preferably 40 to 100 ° C., and 50 to 90 ° C. in view of handling properties. Is more preferable. The glass transition temperature means the intermediate point glass transition temperature obtained by heat flux DSC, assuming that the state of the test piece is adjusted according to JIS K 7121-1987 “when measuring the glass transition temperature after performing a certain heat treatment”. To do. The peroxide is not higher than the Vicat softening point of the base resin in the dispersion medium in which the resin particles are present.In minutesPreferably, the temperature is 20 ° C. or more lower than the Vicat softening point of the base resin.In minutesMore preferably, the temperature is 30 ° C. or more lower than the Vicat softening point of the base resin.In minutesMore preferably, it is understood. The organic peroxide has a one-minute half-life temperature of the organic peroxide (the temperature at which the amount of active oxygen is half of the original in one minute when the organic oxide is decomposed at a constant temperature) ± Hold in the temperature range of 30 ℃ for more than 10 minutesMinutesIt is particularly preferable to solve the problem. If it is attempted to decompose at a temperature lower than [one minute half-life temperature −30 ° C.], it takes a long time to decompose, resulting in poor efficiency. On the other hand, when the decomposition is attempted at a temperature higher than [one minute half-life temperature + 30 ° C.], the decomposition may be abrupt and the surface modification efficiency may be deteriorated. In addition, if it is kept for 10 minutes or more in the range of 1 minute half-life temperature ± 30 ° C, organic peroxideMinutesIt is easy to understand. The longer the holding time in the range of 1 minute half-life temperature ± 30 ° C., the more reliably the organic peroxide can be decomposed, but it is no longer necessary for a certain time or longer. Longer times than necessary will lead to a decrease in production efficiency. The holding time in the above temperature range should normally be 60 minutes at the longest. To decompose the organic peroxide, first prepare the dispersion adjusted to a temperature at which the organic peroxide is difficult to decompose, and then heat the dispersion to the decomposition temperature of the organic peroxide. Good. At this time, the rate of temperature rise may be selected so that the temperature is maintained in the range of 1 minute half-life temperature ± 30 ° C. for 10 minutes or more, but it is stopped at any temperature within the range of 1 minute half-life temperature ± 30 ° C. It is more preferable to hold the temperature for 5 minutes or more. As an arbitrary temperature at that time, a temperature within 1 minute half-life temperature ± 5 ° C. is most preferable. Note that the peroxide is equal to or higher than the glass transition temperature of the base resin.In minutesIn view of the handling properties of the peroxide, it is preferably in the range of 40 to 100 ° C.In minutesMore preferably, the range of 50-90 ° CIn minutesMore preferably, it is understood.Organic peroxideDecomposing means decomposing 50% or more of the peroxide used. The degree of decomposition is preferably 70% or more, more preferably 80% or more, and 95% or more. More preferably. The above-mentioned half-life temperature of the organic peroxide is adjusted to a 0.1 mol / L concentration organic peroxide solution using a solution that is relatively inert to radicals (for example, benzene, mineral spirit, etc.) It is sealed in a glass tube subjected to nitrogen substitution, immersed in a thermostat set at a predetermined temperature, pyrolyzed and measured.
[0023]
  In method A, the surface-modified particlesNoCross-linking. Method A does not use a crosslinking aid etc.RackThe bridge does not progress. still,NothingCrosslinking is defined as follows. That is, regardless of the base resin, the present resin particles, the surface modified particles, the EPP particles, and the EPP molded body, each sample was used (1 g of sample per 100 g of xylene), and after being immersed in boiling xylene for 8 hours, the standard The mixture is quickly filtered through a wire mesh having a mesh size of 74 μm as defined in JIS Z 8801 (1966), which defines a mesh screen, and the weight of the boiling xylene-insoluble matter remaining on the wire mesh is measured. When the insoluble content is 10% by weight or less of the sampleNoThe ratio of insoluble matter is preferably 5% by weight or less, more preferably 3% by weight or less, and most preferably 1% by weight or less, although it is called crosslinking. The smaller the insoluble content, the easier it is to reuse. The insoluble content P (%) is expressed by the following formula.
      P (%) = (M ÷ L) × 100
  However, M is the weight (g) of insoluble matter, and L is the weight (g) of the sample.
[0024]
As described above, the resin particles are subjected to the production of foamed particles after decomposing the organic peroxide to modify the surface of the resin particles. The foamed particles are heated when the surface-modified particles are heated in a closed container in the presence of the foaming agent while being dispersed in a dispersion medium to impregnate the surface-modified particles with the foaming agent. Is preferably produced by a method of releasing the surface-modified particles and the dispersion medium under a low pressure (hereinafter referred to as “dispersion medium releasing foaming method”) at a temperature at which the water is generated.
In the method A, the surface modification step for forming the surface modified particles and the foaming step for obtaining foamed particles from the surface modified particles can be carried out at different times by different devices. However, when the dispersion medium releasing foaming method is adopted, the organic peroxide having an appropriate decomposition temperature is added to the aqueous medium in the closed container in a predetermined amount and the ordinary dispersion medium releasing foaming method is carried out. Since surface modification is completed in the middle and the surface modified particles are automatically obtained, it is efficient.
[0025]
In the surface-modified resin particles obtained by the method A, and thus the EPP particles and EPP moldings obtained therefrom, an alcohol having a molecular weight of 50 or more produced by the decomposition of the peroxide is several hundred ppm to several thousand. About ppm can be contained. As such an alcohol, when bis (4-t-butylcyclohexyl) peroxydicarbonate shown in Examples described later is used, Pt-butylcyclohexanol is a surface modification of the present invention. It can be contained in the fine resin particles. Other alcohols can be included if other peroxides are used. Examples of such alcohol include isopropanol, S-butanol, 3-methoxybutanol, 2-ethylhexylbutanol, and t-butanol.
[0026]
In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the surface-modified particles under heating in the container are not fused to each other in the container. Such a dispersant is not limited as long as it prevents fusion of the surface-modified particles in the container, and can be used regardless of whether it is organic or inorganic. Inorganic substances are preferred. For example, natural or synthetic clay minerals such as amusnite, kaolin, mica, clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, iron oxide and the like in one kind or a combination of several kinds Can be used.
[0027]
Furthermore, in the above dispersion medium releasing foaming method, a dispersion strengthening agent that strengthens the dispersing power of the dispersing agent (prevents fusion of surface-modified particles within the container even if the amount of the dispersing agent added is small) is dispersed. It is preferable to add to the medium. Such a dispersion strengthening agent is an inorganic compound that can be dissolved in at least 1 mg or more in 100 cc of water at 40 ° C., and at least one of the anion or cation of the compound is divalent or trivalent. is there. Examples of such inorganic substances include magnesium chloride, magnesium nitrate, magnesium sulfate, aluminum chloride, aluminum nitrate, aluminum sulfate, iron chloride, iron sulfate, and iron nitrate.
[0028]
Usually, the dispersant is used in an amount of about 0.001 to 5 parts by weight and the dispersion strengthener is used in an amount of about 0.0001 to 1 part by weight per 100 parts by weight of the resin particles.
[0029]
Examples of the blowing agent used in Method A include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, and 1,2-difluoroethane. , 1,2,2,2-tetrafluoroethane, organic physical foaming agents such as halogenated hydrocarbons such as methyl chloride, ethyl chloride and methylene chloride, and so-called inorganic systems such as nitrogen, oxygen, air, carbon dioxide and water Physical foaming agents are exemplified. An organic physical foaming agent and an inorganic physical foaming agent can be used in combination. In the present invention, those mainly composed of one or more inorganic physical foaming agents selected from the group of nitrogen, oxygen, air, carbon dioxide and water are particularly preferably used. Among these, nitrogen and air are preferable in consideration of the stability of the apparent density of the expanded particles, the environmental load and the cost. Water used as a foaming agent may be water (including ion-exchanged water) used as a dispersion medium in order to disperse the surface-modified particles in the sealed container.
[0030]
In the dispersion medium releasing foaming method, the filling amount of the physical foaming agent in the container is appropriately selected according to the type of foaming agent used, the foaming temperature, and the apparent density of the intended foamed particles. For example, when nitrogen is used as the dispersion medium and water is used as the dispersion medium, the pressure in the sealed container in a stable state immediately before the start of foaming, that is, the pressure (gauge pressure) in the space in the sealed container is 0. It is preferable to select so as to be 6 to 6 MPa. Usually, it is desirable to increase the pressure in the space in the container as the apparent density of the target foamed particles is small, and it is desirable to decrease the pressure in the space as the apparent density of the target foamed particles is large. There is a tendency.
[0031]
  Method A employs the above dispersion medium releasing foaming method, and has an apparent density of 10 g / L to 500 g / L, and an endothermic curve peak derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry of the expanded particles. It is preferable to produce expanded particles having an endothermic curve peak (high temperature peak) on the higher temperature side than (inherent peak). Such foamed particles are foamed particles having a high closed cell ratio and suitable for molding.In the present inventionIn the case of Method A, in the obtained expanded particles, the amount of heat at the high temperature peak is 2 J / g to 70 J / g.TheIf the amount of heat at the high temperature peak is less than 2 J / g, the compression strength, energy absorption amount, etc. of the EPP molded product may be reduced. On the other hand, if it exceeds 70 J / g, the air pressure required in the step of increasing the air pressure in the foamed particles prior to molding the foamed particles may become too high, or the molding cycle may be prolonged, which is not preferable. In Method A, the amount of heat at the high temperature peak is particularly 3 J / g to 65 J / g (more preferably 12 to 58 J / g), and 10 to 10% of the sum of the heat amount of the high temperature peak and the heat amount of the intrinsic peak. 60% is preferable, and 20 to 50% is more preferable. Moreover, it is preferable that the sum total of the calorie | heat amount of a high temperature peak and the calorie | heat amount of an intrinsic peak is 40 J / g-150 J / g. In the present invention and the present specification, the calorific value of the high temperature peak and the calorific value of the intrinsic peak both mean endothermic amounts, and the numerical values are expressed in absolute values.
[0032]
The amount of heat at the high temperature peak of the expanded particles is as shown in FIG. 1 obtained when 2-4 mg of expanded particles are heated from room temperature (10-40 ° C.) to 220 ° C. at 10 ° C./min by a differential scanning calorimeter. The amount of heat of the endothermic curve peak (high temperature peak) b appearing on the higher temperature side than the temperature at which the intrinsic endothermic curve peak (intrinsic peak) a derived from the heat of fusion of the base resin found in the DSC curve of Specifically, it can be obtained as follows.
First, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature T of the expanded particles is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic peak a and the high temperature peak b, and the point intersecting with the straight line (α−β) is defined as σ. . The area of the high temperature peak b is that of the portion surrounded by the curve of the high temperature peak b portion of the DSC curve, the line segment (σ-β), and the line segment (γ-σ) (the portion hatched in FIG. 1). This is the area, which corresponds to the amount of heat at the high temperature peak. The melting end temperature T is the intersection of the DSC curve on the high temperature side of the high temperature peak b and the high temperature side baseline.
Moreover, the sum total of the heat amount of the high temperature peak and the heat amount of the intrinsic peak corresponds to the area of the portion surrounded by the straight line (α-β) and the DSC curve.
When the intrinsic peak and the high temperature peak of the expanded particles are measured by the differential scanning calorimeter as described above, when the weight per expanded particle is less than 2 mg, a plurality of expanded foams having a total weight of 2 mg to 10 mg. The particles may be used for the measurement as they are, and when the weight per foamed particle is 2 mg to 10 mg, the foamed particles may be used for the measurement as it is, and the weight per foamed particle. Is more than 10 mg, one cut sample having a weight of 2 to 10 mg obtained by cutting one expanded particle into a plurality of particles may be used for the measurement. However, this cut sample is obtained by cutting one foamed particle using a cutter or the like, but at the time of cutting, the surface of the foamed particle that is originally provided is left without being cut, and each cut sample It is preferable that the foamed particles are cut so as to have the same shape as much as possible, and in each cut sample, the area of the surface of the expanded particles remaining without being cut is as much as possible. For example, when the weight per expanded particle is 18 mg, if the expanded particle oriented in an arbitrary direction is cut horizontally from the middle of the vertical direction, two approximately 9 mg cut samples having substantially the same shape are obtained. In each cut sample, the surface of the foamed particles that are originally contained is left as it is, and the area of the surface is almost the same in each cut sample. One of the two cut samples thus obtained may be used for the measurement of the intrinsic peak and the high temperature peak as described above. In the present specification, when simply expressed as “high temperature peak of foamed particles”, the heat quantity of the high temperature peak obtained by the above measurement is referred to, and this is the surface layer of the foamed particles described later. The amount of heat at the high temperature peak for the part and the amount of heat at the high temperature peak for the internal foam layer are different.
[0033]
This high temperature peak b is observed in the first DSC curve measured as described above, but after obtaining the first DSC curve, it is once around 40 ° C. at 220 ° C. to 10 ° C./min. When the base resin is melted as shown in FIG. 2, it is not observed in the second DSC curve obtained when the temperature is lowered to (40 to 50 ° C.) and again raised to 220 ° C. at 10 ° C./min. Only the intrinsic peak a corresponding to the endotherm of is observed.
The temperature at the peak of the intrinsic peak a appearing in the first DSC curve of the expanded particles is usually in the range of [Tm−5 ° C.] to [Tm + 5 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm−4 ° C.] to [Tm + 4 ° C.]). Further, the temperature at the apex of the high temperature peak b appearing in the first DSC curve of the expanded particles usually appears in the range of [Tm + 5 ° C.] to [Tm + 15 ° C.] based on the melting point (Tm) of the base resin. (Most commonly appears in the range of [Tm + 6 ° C.] to [Tm + 14 ° C.]). In addition, the temperature at the top of the intrinsic peak a observed in the second DSC curve of the expanded particles (temperature corresponding to the melting point of the base resin) is usually determined based on the melting point (Tm) of the base resin. Tm-2 ° C.] to [Tm + 2 ° C.].
[0034]
As described above, the EPP particles preferably have a crystal structure in which a high temperature peak appears in the first DSC curve in DSC measurement. However, the amount of heat of the high temperature peak is strongly influenced by the difference between the melting point and the foaming temperature of the resin. The
The high temperature peak heat quantity of the EPP particles acts as a factor that determines the minimum fusion temperature, particularly with respect to the fusion between the EPP particles. The minimum fusion temperature here means a temperature that gives the lowest saturated steam pressure necessary for the EPP particles to fuse together in the mold. The high temperature peak calorific value is closely related to this minimum fusing temperature, and when the same base resin is used, the minimum fusing temperature is lower when the high temperature peak calorific value is larger than when the high temperature peak calorific value is large. There is a tendency to become lower. The value of the high temperature peak heat quantity is strongly influenced by the foaming temperature applied to the resin in the production stage of the EPP particles. When the same base resin is used, the high temperature peak heat quantity is lower than when the foaming temperature is lower. The value tends to be smaller.
[0035]
However, when obtaining an EPP molded article using EPP particles having a small high-temperature peak heat quantity, the minimum fusing temperature tends to be relatively low, but the strength physical properties such as compression strength (rigidity) of the EPP molded article are relatively high. There is a tendency to decrease. On the other hand, when an EPP molded product is obtained using expanded particles having a high high-temperature peak heat, strength properties such as compressive strength of the EPP molded product tend to be relatively high, but the minimum fusion temperature is relatively high. As described above, there is a problem that high pressure steam may be required when manufacturing an EPP compact. That is, the most preferred foamed particles are foamed particles having the opposite properties such that the minimum fusing temperature is low and the strength properties such as compressive strength of the EPP molded article are relatively high. The expanded particles obtained by Method A are those in which the minimum fusing temperature is effectively reduced. When a foamed particle molded body is produced using the foamed particles, a molded body having practical strength in mechanical properties such as compressive strength can be obtained.
[0036]
When the foamed particles having a high temperature peak in the DSC curve are heated by dispersing the surface-modified particles in the dispersion medium in a closed container, the foamed particles have a temperature equal to or higher than the melting end temperature (Te) of the base resin constituting the surface-modified particles. Without increasing the temperature, stop at an arbitrary temperature (Ta) within a range of 20 ° C. lower than the melting point (Tm) of the base resin and lower than the melting end temperature (Te), and a sufficient time at that temperature (Ta). , Preferably held for about 10 to 60 minutes, and then adjusted to an arbitrary temperature (Tb) in the range of 15 ° C. lower than the melting point (Tm) to the melting end temperature (Te) + 10 ° C., and stopped at that temperature, necessary Thus, the surface-modified particles can be obtained by foaming by releasing the surface-modified particles from the inside of the sealed container under a low pressure after holding at the temperature for a sufficient time, preferably about 10 to 60 minutes.
The melting point (Tm) is a differential scanning calorimetry of the resin particles in the same manner as the DSC curve of the expanded particles as described above using 2 to 4 mg of the resin particles as a sample. This is the temperature at the apex of the endothermic curve peak a unique to the base resin found in the second DSC curve (an example of which is shown in FIG. 2), and the melting end temperature (Te) is the inherent temperature. DSC curve on high temperature side of endothermic curve peak a and high temperature side baseline (B_L) And the intersection (β).
The endothermic curve peak appearing in the second DSC curve for the resin particles usually appears as one endothermic curve peak on the premise that it is a peak based on melting of the polypropylene resin. However, when it consists of a mixture of two or more polypropylene resins, there are rarely two or more endothermic peaks. In that case, a straight line that passes through the vertex of each peak and is parallel to the vertical axis of the graph (perpendicular to the horizontal axis) is drawn._LAnd the peak apex on the straight line having the longest length is defined as Tm. However, when two or more longest straight lines exist, the peak apex on the highest temperature side is defined as Tm.
[0037]
The amount of heat at the high-temperature peak in the expanded particles mainly depends on the temperature Ta, the holding time at the temperature, the temperature Tb, the holding time at the temperature, and the rate of temperature increase with respect to the resin particles when the expanded particles are produced. Dependent. The amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature Ta or Tb decreases within the above temperature range or as the holding time increases. Usually, 0.5 to 5 ° C./min is employed as the rate of temperature rise during heating (average rate of temperature rise from the start of heating to the start of temperature holding). By repeating the preliminary experiment in consideration of these points, it is possible to easily know the production conditions for the expanded particles exhibiting a desired high-temperature peak heat quantity.
[0038]
In addition, the temperature range demonstrated above is a suitable temperature range at the time of using an inorganic type physical foaming agent as a foaming agent. When an organic physical foaming agent is used in combination, the appropriate temperature range shifts to a lower temperature side than the above temperature range depending on the type and amount of use.
[0039]
As described above, the EPP particles obtained from the surface-modified particles obtained by modifying the surface of the resin particles by decomposing the organic peroxide can be molded with low-temperature steam. It is found from the measurement results that
[0040]
As a result of DSC measurement of the expanded particles, the expanded particles obtained by the method A tend to be different from the expanded particles obtained by the conventional method. When the melting point was measured by dividing into a surface layer portion of the expanded particle and an internal expanded layer not including the surface layer portion, the conventional expanded particle had a melting point (Tm_s) Is the melting point (Tm) of the internal foam layer_i), The expanded particles obtained by Method A have a melting point (Tm) of the surface layer portion._s) Is the melting point (Tm) of the internal foam layer_i) Was observed to be lower. As expanded particles that can be molded with low-temperature steam, Tm_sIs Tm_iIt is preferably lower by 0.05 ° C., more preferably by 0.1 ° C. or more, and further preferably by 0.3 ° C. or more.
[0041]
Melting point (Tm) of the surface layer portion of the expanded particle_s) Is a characteristic peak a of the second DSC curve obtained by performing the same operation as the measurement of the high temperature peak calorific value of the foamed particles except that 2-4 mg of the foamed particles are cut out and collected as a sample. Means the temperature at the apex of Further, the melting point (Tm) of the inner foam layer of the foam particles_i) Was cut out from the center of gravity of the expanded particles so as not to include the surface layer portion, and 2 to 4 mg was collected, and the second operation obtained by performing the same operation as the measurement of the high temperature peak heat quantity of the expanded particles described above except that this was used as a sample. It means the temperature at the apex of the intrinsic peak a of the DSC curve.
[0042]
In addition, when the high temperature peak calorific value was measured by dividing the foamed particle into a surface layer portion and an internal foam layer not including the surface layer portion, the conventional foamed particles were found to have a high temperature peak calorific value (ΔH_s) And the amount of heat at the high temperature peak of the internal foam layer (ΔH_i)_s≧ ΔH_iIn contrast to the property of × 0.87, in the expanded particles obtained by Method A, ΔH_s<ΔH_iIt was observed to be x0.86. Expanded particles that can be molded with low-temperature steam are ΔH_s<ΔH_iX0.86, but ΔH_s<ΔH_i× 0.83 is preferable, ΔH_s<ΔH_iX0.80 is more preferable, and ΔH_s<ΔH_iX0.75 is more preferable, and ΔH_s<ΔH_iX 0.70 is more preferable, and ΔH_s<ΔH_iIt is most preferable that it is x0.60. ΔH_sIs ΔH_s≧ ΔH_iIt is preferable that it is x0.25. ΔH_s<ΔH_iBy being 0.86, in-mold molding can be performed at a lower temperature than expanded particles that are not surface-modified. ΔH_sIs preferably 1.7 J / g to 60 J / g, more preferably 2 J / g to 50 J / g, still more preferably 3 J / g to 45 J / g, and 4 J / g to 40 J. Most preferred is / g.
[0043]
The high temperature peak calorific value of the surface layer portion of the expanded particle can be obtained by performing the same operation as the measurement of the high temperature peak heat amount of the expanded particle described above except that the surface layer portion of the expanded particle is cut out and 2 to 4 mg is collected and used as a sample. . In addition, the high temperature peak calorific value of the internal foamed layer of the foamed particles is cut out from the inside of the foamed particles so as not to include the surface layer portion, and 2 to 4 mg are collected and used as a sample to measure the high temperature peak calorific value of the foamed particles described above. The same operation can be performed.
[0044]
A method of measuring the melting point and the high temperature peak calorie by dividing the foamed particle into a surface layer portion and an internal foam layer not including the surface layer portion is as follows.
The surface layer portion of the expanded particle may be sliced using a cutter knife, a microtome, etc., and the surface layer portion may be collected and used for measurement. However, the surface of the foamed particle always exists on the entire surface of the surface layer portion of the sliced foamed particle, but on the back surface of the surface layer portion of the sliced foamed particle, the surface of the foamed particle faces the center of gravity of the foamed particle. In other words, the surface of the expanded particle is sliced from one or a plurality of points selected at random so that a part exceeding 200 μm is not included. When a portion exceeding 200 μm from the surface of the foamed particle toward the center of gravity of the foamed particle is included on the back surface of the surface layer part of the sliced foamed particle, the internal foamed layer is contained in a large amount, and the melting point of the surface layer part and There is a possibility that the high temperature peak calorie cannot be measured accurately. In addition, when the surface layer part obtained from one expanded particle is less than 2-4 mg, what is necessary is just to collect the required amount surface layer part by repeating the said operation using several expanded particle.
On the other hand, the internal foam layer that does not include the surface layer portion of the foam particle is the entire surface of the foam particle so that the surface of the foam particle and the portion between the surface of the foam particle and 200 μm from the surface of the foam particle toward the center of gravity of the foam particle are not included. What is necessary is just to use for the melting | fusing point and high temperature peak calorie | heat amount measurement using what cut | disconnected the surface layer part from. However, if the size of the expanded particles is too small and the internal foam layer disappears when the 200 μm portion is cut off from the above surface, the surface of the expanded particles and the surface of the expanded particles are directed toward the center of gravity of the expanded particles. If the surface of the foamed particle is cut out from the entire surface of the foamed particle so that the portion between 100 μm is not included, and the inner foamed layer still disappears, the surface of the foamed particle The surface of the foamed particle is cut off from the entire surface of the foamed particle so as not to include a part between the surface of the foamed particle and the center of gravity of the foamed particle. When the internal foamed layer obtained from one foamed particle is less than 2 to 4 mg, the above operation is repeated using a plurality of foamed particles to collect the required amount of the internal foamed layer.
[0045]
  In addition, for each foamed particle surface of the surface-modified foamed particles obtained by Method A and the foamed particles that have not been surface-modified obtained by the conventional method, Micro Heat of TI Instruments Japan Co., Ltd. Using the analysis system “2990 type micro thermal analyzer”, micro differential thermal analysis (μDTA) was performed under the condition of a heating rate of 10 ° C./second from 25 ° C. to 200 ° C. The melting start temperature of the surface of the expanded foam particles is lower than the melting point of the base resin, whereas the melting start temperature of the surface of the foam particles not surface-modified obtained by the conventional method is the base temperature. It was found that the temperature was 5 ° C. or more higher than the melting point of the material resin. The melting start temperature here means a temperature at which the μDTA curve starts to change downward from the baseline (BL) in the μDTA curve based on the μDTA (specific heat per hour starts to change). In addition, for each foamed particle surface of the surface-modified foamed particles obtained by Method A and the foamed particles that have not been surface-modified obtained by the conventional method, Micro Heat of TI Instruments Japan Co., Ltd. Using the analysis system “2990 type micro thermal analyzer”, micro differential thermal analysis (μDTA) was performed under the condition of a heating rate of 10 ° C./second from 25 ° C. to 200 ° C. Of extrapolated melting on the surface of the expanded foamed particlesDegreeThe temperature of the base resin [melting point + 4 ° C.] or lower, whereas the extrapolated melting start temperature of the surface of the foam particles not subjected to surface modification obtained by the conventional method is higher than the melting point of the base resin. It was found that the temperature was 8 ° C. or higher. The extrapolated melting start temperature here is a straight line obtained by extending the baseline (BL) of the μDTA curve to the high temperature side, and a tangent line drawn from each point on the μDTA curve on the high temperature side from the melting start temperature. The temperature at the intersection of the tangent line (TL) with the maximum angle between the tangent line and the straight line obtained by extending the base line (BL) to the high temperature side. FIG. 3 shows an example of the μDTA curve for each of the expanded particles obtained in Example 5 and the expanded particles obtained in Comparative Example 5, which will be described later. In FIG. 3, the curve Cm is based on the expanded particles obtained in Example 5, the Pm point on the curve Cm is the melting start temperature, and the Pme point is the baseline (BL) and the tangent (TL). ) Is the extrapolated melting start temperature that is the intersection point with). On the other hand, the curve Cnm is based on the expanded particles obtained in Comparative Example 5, the Pnm point on the curve Cnm is the melting start temperature, and the Pnme point is the baseline (BL) and the tangent (TL). Is the extrapolated melting start temperature that is the intersection of Pm, Pme, Pnm, and Pnm in FIG. 3 are 131 ° C., 135 ° C., 168 ° C., and 171 ° C., respectively. FIG. 4 shows an example of a μDTA curve for a surface-modified EPP foam particle surface based on another example using a propylene homopolymer having a melting point of 162 ° C. and an MFR of 18 g / 10 min as a base resin. In FIG. 4, the curve Cm is a μDTA curve, the Pm point on the curve Cm is the melting start temperature, and the Pme point is the intersection of the baseline (BL) and the tangent (TL). Temperature. Pm and Pme in FIG. 4 are 140 ° C. and 142 ° C., respectively. In the micro differential thermal analysis, the expanded particles are fixed to the sample stage of the apparatus (if one expanded particle is too large as it is, it is fixed to an appropriate size, for example, by cutting in half) Next, the probe tip (the portion to be in contact with the surface of the foamed particle has a tip portion of 0.2 μm in length and width) was lowered to contact with the surface of the foamed particle toward a randomly selected portion on the surface of the foamed particle. Implemented in the state. As the melting start temperature and extrapolation melting start temperature of the surface of the expanded particles by the micro differential thermal analysis, an arithmetic average value of 8 points excluding the maximum value and the minimum value is adopted from the measurement results of 10 different measurement points. In addition, when there are a plurality of maximum values and minimum values, an arithmetic average value of several points excluding them is adopted. In addition, when all 10 measured values on the average are the same, or when only the maximum and minimum values are obtained and the difference between the maximum and minimum values is within 10 ° C., the 10-point phase An arithmetic mean value is adopted. When only the maximum and minimum values were obtained, and the difference between the maximum and minimum values exceeded 10 ° C, measurements were made on 10 points on different surfaces and the same procedure as described above. What is necessary is just to obtain | require an arithmetic mean value and to employ | adopt it. If the condition is still not met, repeat the same operation. The above μDTA results show that the decrease in the melting start temperature on the surface of the expanded particles or the decrease in the extrapolated melting temperature on the surface of the expanded particles contributes to the decrease in the minimum fusion temperature required at the time of molding. . The foamed particles that can be molded with low-temperature steam have a melting start temperature on the surface of the foamed particles based on the above measurement of not more than the melting point (Tm) of the base resin, preferably [Tm-5 ° C.] or less. Tm-10 ° C] or less, more preferably [Tm-15 ° C] or less, further preferably [Tm-16 ° C] to [Tm-50 ° C], [Tm- Most preferably, it is 17 [deg.] C. to [Tm-35 [deg.] C.]. The foamed particles that can be molded with low-temperature steam have an extrapolated melting start temperature of the foamed particle surface based on the above measurement of [Tm + 4 ° C.] or lower, preferably [Tm-1 ° C.] or lower, Tm−6 ° C.] or less, more preferably [Tm−17 ° C.] to [Tm−50 ° C.], and [Tm−18 ° C.] to [Tm−35 ° C.]. Most preferred. Such a decrease in the minimum fusion temperature is particularly effective in the case of EPP particles having a melting point of the base resin of 158 ° C. or higher and a high temperature peak. The lower the melting start temperature of the foam particle surface, the greater the contribution to the lowering of the minimum fusing temperature required at the time of molding, but if the melting start temperature is too low, the compression strength of the resulting molded product, etc. There is a possibility that mechanical properties and the like are reduced.
[0046]
Further, when the MFR was measured, it was observed that the MFR value of the expanded particles obtained by the method A was the same as or larger than the MFR value of the resin particles before the surface modification. . In the present invention, the MFR value of the expanded particles is preferably 1.2 times or more, more preferably 1.5 times or more of the MFR value of the resin particles before surface modification. Most preferably, it is 8 to 3.5 times. The MFR value of the expanded particles is preferably 0.5 to 150 g / 10 minutes considering the heat resistance of the EPP molded product and the expansion efficiency at the time of manufacturing the expanded particles, and preferably 1 to 100 g / 10. It is more preferable to make the minute, more preferably 10 to 80 g / 10 minutes.
[0047]
The MFR of the above-mentioned expanded particles is a press sheet having a thickness of 0.2 mm to 1 mm prepared on a heated press machine in which the temperature of the expanded particles is adjusted to 200 ° C., and a sample is cut out from the sheet in a pellet shape or a rod shape. It is the value which measured by the method similar to the measurement of MFR of the said uncrosslinked propylene-type resin using. When measuring the MFR of the expanded particles, it is necessary to avoid the inclusion of bubbles or the like in the sample in order to obtain an accurate measurement value. If air bubbles are unavoidably mixed, a press sheet can be prepared for the purpose of defoaming with a hot press machine within the range of repeating the same sample up to 3 times.
[0048]
Further, the foamed particles obtained by the method A form a modified surface containing a slight amount of oxygen due to the addition action of the organic peroxide, particularly when an organic peroxide that generates oxygen radicals is used. This is clear from the analysis of the surface of the expanded particles obtained by the method of the present invention and the surface of the EPP molded product produced therefrom. Specifically, the surface of the EPP molded body produced from the foamed particles obtained by the method A (ie, substantially the same as the surface of the foamed particles) and the EPP produced from the conventional non-surface-modified foamed particles. As a result of comparing each surface of the molded product by ATR measurement (total reflection absorption measurement method), the surface of the EPP molded product produced from the expanded particles obtained by Method A was newly added to 1033 cm.^-1It was confirmed that there was a difference in absorption in the vicinity, and it was recognized that there was a change such as addition or insertion of oxygen alone or a functional group containing oxygen. Specifically, 1166cm^-1When both peak heights in absorption of the same (the absorption peak height for the molded product from the foamed particles obtained by Method A and the absorption peak height for the conventional molded product) are the same, from the foamed particles obtained by Method A 1033cm of the surface of the molded body^-1The height of the nearby absorption peak is 1033 cm of the surface of the conventional molded body.^-1It is higher than the height of the nearby absorption peak. Furthermore, as a result of elemental analysis using an EDS (energy dispersive analyzer) as a surface observation of the expanded particles, the ratio of oxygen to carbon was 0.2 (mol / mol) in the case of expanded particles obtained by Method A. On the other hand, in the case of the conventional expanded particle, it was 0.09 (mol / mol). From such a viewpoint, in the present invention, the ratio of oxygen to carbon on the surface of the expanded particles is preferably 0.15 or more.
From the above, it is clear that a modified surface containing a slight amount of oxygen is formed by the addition action of the organic peroxide. The formation of such a modified surface is believed to favor steam permeability during molding. The EPP particles obtained by the above-mentioned method A are the modified surface containing oxygen or / and the reversal phenomenon of the melting point or / and the decrease in the high temperature peak heat quantity of the surface layer portion of the foamed particle or / and the surface of the foamed particle. It is presumed that the minimum fusing temperature is greatly reduced by the lowering of the melting start temperature or / and the lowering of the extrapolated melting start temperature of the surface of the expanded particles.
[0049]
  The EPP particles obtained by the above-mentioned method A can be made into expanded particles having a higher expansion ratio by aging under atmospheric pressure and then increasing the bubble internal pressure and then heating with water vapor or hot air. It is. In the method for producing an EPP molded body according to the present invention, the EPP particles are filled in a mold that can be heated and cooled and that can be opened / closed and sealed after increasing the bubble internal pressure, and is supplied with saturated steam in the mold. It can be carried out by adopting a batch molding method in which EPP particles are heated and expanded to be fused, and then cooled and taken out from the mold. As a molding machine used in the batch molding method, a number of molding machines already exist all over the world, and the pressure resistance is 0.41 MPa (G) or 0.45 MPa (G) although it varies slightly depending on the country. There are many things. Therefore, the pressure of the saturated steam when the EPP particles are expanded and fused is 0.45 MPa (G) or less.And0.41 MPa (G) or less or lessPreferGood. Moreover, the manufacturing method of the EPP compact | molding | casting by this invention supplies EPP particle | grains continuously between the belts which move continuously along the upper and lower sides in a channel | path, after raising bubble internal pressure, and a saturated steam supply area | region ( EPP particles are expanded and fused together when passing through the heating region), then cooled by passing through the cooling region, and then the resulting molded product is taken out from the passage and sequentially cut to an appropriate length. It can also be produced by a method (for example, a molding method described in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.). In this method, the inside of the passage is in the mold. In order to increase the bubble internal pressure of the EPP particles, the foamed particles are put in a sealed container, and the pressurized gas is allowed to permeate into the foamed particles by leaving the container in a state where the pressurized gas is supplied. That's fine. The gas supplied under pressure can be used without any problem as long as the main component is an inorganic gas that does not liquefy or solidify under the required pressure, but is further selected from the group consisting of nitrogen, oxygen, air, carbon dioxide, and argon. Alternatively, those mainly composed of two or more inorganic gases are particularly preferably used, and among them, nitrogen and air are preferable in consideration of environmental load and cost.
[0050]
The internal pressure P (MPa) of the expanded particles whose internal pressure is increased is measured by the following operation. Here, an example is shown in which the internal pressure of EPP particles is increased using air.
First, EPP particles used for molding are placed in a closed container, and pressurized air is supplied into the container (usually, the air pressure in the container is maintained within a range of 0.98 to 9.8 MPa as a gauge pressure). ) The internal pressure of the EPP particles can be increased by allowing the air to permeate into the EPP particles by leaving the supplied state for an appropriate time. The EPP particles whose internal pressure has been sufficiently increased are supplied into a mold of a molding machine. The internal pressure of the EPP particles is determined by performing the following operation using a part of the EPP particles immediately before in-mold molding (hereinafter referred to as the expanded particle group).
[0051]
  Within 70 seconds after taking out the expanded particle group immediately before in-mold molding whose internal pressure has been increased from the pressurized tank, a large number of needle holes of a size not allowing the expanded particles to pass but allowing the air to freely pass therethrough are 70 mm × It is housed in a polyethylene bag of about 100 mm and moved to a temperature-controlled room under an atmospheric pressure with an air temperature of 23 ° C. and a relative humidity of 50%. Subsequently, the weight is read on a balance in the temperature-controlled room. The weight is measured 120 seconds after the above expanded particle group is taken out from the pressurized tank. The weight at this time is defined as Q (g). The bag is then left in the same greenhouse for 48 hours. The pressurized air in the expanded particles permeates through the bubble film and escapes to the outside as time passes, so the weight of the expanded particles decreases accordingly and reaches equilibrium after 48 hours.MesoThe weight of is stable. After 48 hours, the weight of the bag is measured again, and the weight at this time is defined as U (g). Then, immediately, take out all the foam particles from the bag in the same temperature chamber and read the weight of the bag alone. Let the weight be Z (g). Any of the above weights shall be read up to 0.0001 g. The difference between Q (g) and U (g) is the increased air amount W (g), and the internal pressure P (MPa) of the expanded particles is calculated from the following equation. The internal pressure P corresponds to a gauge pressure.
[0052]
P = (W ÷ M) × R × T ÷ V
[0053]
However, in the above formula, M is the molecular weight of air, and here, a constant of 28.8 (g / mol) is adopted. R is a gas constant, and here, a constant of 0.0083 (MPa · L / (K · mol)) is adopted. T means an absolute temperature, and since an atmosphere of 23 ° C. is adopted, it is a constant of 296 (K) here. V means a volume (L) obtained by subtracting the volume of the base resin in the expanded particle group from the apparent volume of the expanded particle group.
[0054]
In addition, the apparent volume (L) of the expanded particle group was determined as follows. The total amount of the expanded particle group removed from the bag after 48 hours was immediately 100 cm of water at 23 ° C. in the same constant temperature room.^ThreeFrom the scale when submerged in the water in the graduated cylinder, the volume Y (cm^Three) And is converted into liter (L) units. The apparent expansion ratio of the expanded particle group is the base resin density (g / cm^Three) Is the apparent density of the expanded particles (g / cm^Three). The apparent density of the expanded particles (g / cm^Three) Represents the weight of the expanded particle group (difference between U (g) and Z (g)) by volume Y (cm^Three).
In the above measurement, the expanded particle group weight (difference between U (g) and Z (g)) is 0.5000 to 10.0000 g and the volume Y is 50 to 90 cm.^ThreeA quantity of a plurality of expanded particles is used.
[0055]
  In the present inventionThe internal pressure in the bubbles of EPP particles is 0.005 to 0.98 MPa.And goodThe pressure is preferably 0.01 to 0.69 MPa, and most preferably 0.029 to 0.49 MPa. If the bubble internal pressure becomes too small, the secondary foaming force at the time of molding is insufficient, and in order to compensate for this, the saturated steam pressure introduced into the mold at the time of molding is increased, or the gap is not closed without completely closing the mold. It is necessary to have a method of filling the EPP particles in an open state, then exhausting the air in the mold with steam and then completely clamping the mold to compress the EPP particles. The application of secondary foaming force by increasing the saturated steam pressure is limited by the pressure limit of the molding machine described above, and does not meet the purpose of low-temperature molding characterized by the EPP foamed particles. Further, the method of compressing the EPP particles induces a density variation at each location in the molded body, and further, it cannot be expected that the secondary foaming force is completely recovered. On the other hand, if the bubble internal pressure becomes too high, the secondary foaming force at the time of molding becomes excessive, impeding the penetration of saturated steam into the molded body, resulting in insufficient temperature at the center of the molded body, and the mutual interaction of EPP particles. The fusion is poor. Further, the feature of the EPP foam particles is that they have high compressive stress properties as in the molded product obtained therefrom, so that the apparent volume of the EPP particles is reduced in a pressurized atmosphere, and the inside and outside atmosphere of the EPP particle bubbles are small. It is possible to increase the pressure difference between the pressure and the time required for applying the internal pressure. That is, even if the current equipment is used, the productivity is improved, which can be said to be an advantage that cannot be overlooked industrially. The apparent density of the EPP molded body produced by the above method can be arbitrarily selected depending on the purpose, but is usually in the range of 9 g / L to 600 g / L. The apparent density of the EPP compact is the apparent overall density as defined in JIS K 7222 (1999). However, the volume of the molded body used for calculating the apparent overall density is the volume calculated from the outer dimensions, but if the shape is complex and calculation from the outer dimensions is difficult, the molded body is submerged. Excluded volume is adopted.
[0056]
Further, a surface decoration material can be laminated and integrated on at least a part of the surface of the EPP molded body. US Pat. No. 5,928,776, US Pat. No. 6,096,417, US Pat. No. 6,033,770, US Pat. No. 5,474,841, European Patent 477476, WO 98/34770 , WO98 / 00287, Japanese Patent No. 3092227 and the like.
Further, the insert material can be combined and integrated in the EPP molded body so that all or part of the insert material is embedded. Such insert composite type in-mold foam moldings are described in detail in US Pat. No. 6,033,770, US Pat. No. 5,474,841, Japanese Patent Publication No. 59-1277714, Japanese Patent No. 3092227, etc. Are listed.
[0057]
The EPP molded article produced as described above preferably has an open cell ratio based on ASTM-D2856-70 Procedure C of 40% or less, more preferably 30% or less, and 25% or less. Most preferably it is. The smaller the open cell ratio, the better the mechanical strength.
[0058]
【Example】
The present invention will be described below with reference to examples and comparative examples.
[0059]
Example1-5Comparative Examples 1-5Reference example 1
  After adding 0.05 parts by weight of zinc borate powder (cell regulator) per 100 parts by weight of the polypropylene resin selected from Table 1 and melt-kneading in the extruder, the strand is extruded from the extruder into a strand. Is immediately put into water adjusted to 18 ° C. and taken up while rapidly cooling. After sufficiently cooling, the strand is pulled up from the water and the strand is cut so that the length / diameter ratio is about 1.0. Resin particles having an average weight of 2 mg were obtained. Next, in a 400 liter autoclave, 100 parts by weight of the resin particles, 220 parts by weight of ion-exchanged water at 18 ° C., 0.005 parts by weight of sodium dodecylbenzenesulfonate (surfactant) and 0.3 parts by weight of kaolin powder (dispersing agent). Parts and aluminum sulfate powder (dispersion strengthening agent) 0.01 parts by weight, organic peroxide shown in Table 2, and carbon dioxide gas (foaming agent) shown in Tables 3 and 4 were charged and stirred in Tables 3 and 4 The temperature was raised to a temperature 5 ° C. lower than the indicated foaming temperature (average rate of temperature rise 3 ° C./min) and held at that temperature for 15 minutes. Next, the temperature was raised to the foaming temperature (average rate of temperature increase of 3 ° C./min) and held at that temperature for 15 minutes. Next, one end of the autoclave was opened, and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles. In addition, it discharged | emitted, supplying a carbon dioxide gas in an autoclave so that the internal pressure of an autoclave during discharge | release of a resin particle from an autoclave might be maintained at the autoclave internal pressure just before discharge | release. The obtained foamed particles are washed with water, centrifuged, and allowed to stand for 48 hours under atmospheric pressure at room temperature of 23 ° C. for 48 hours, and then the high temperature peak heat of the foam particles, the high temperature peak heat of each of the surface layer portion and the internal foam layer. And each melting | fusing point, MFR of an expanded particle, the apparent density of an expanded particle, etc. were measured. The results are shown in Tables 3 and 4. Next, the foamed particles are placed under pressurized air in a pressure-resistant container to give the foamed particles an increased bubble internal pressure, and then when the foam internal pressures shown in Tables 3 and 4 are formed, the molded product has a size of 250 mm × 200 mm × 50 mm. The mold with space is filled with a small gap (about 1 mm) without completely closing the mold (with the direction of the molding space 50 mm being 51 mm) and then completely clamping Then, after the air in the mold was evacuated with steam, molding was performed at the minimum fusing temperature (minimum saturation steam pressure) shown in Tables 3 and 4. After the molding, the molded body in the mold was cooled with water until the surface pressure became 0.059 MPa (G), and then the molded body was taken out of the mold, cured at 60 ° C. for 24 hours, and then cooled to room temperature (23 ° C.). Subsequently, after curing in the room for 14 days, the apparent density, compressive strength, and b / n ratio were measured for the molded body. The minimum fusing temperature (minimum saturation steam pressure) means that a molded body is repeatedly produced by increasing the saturation steam pressure in increments of 0.01 MPa from 0.15 MPa (G) to 0.55 MPa (G), and molding after curing. A test in which about 10 mm incision is made in the thickness direction of the molded body so that the length of the 250 mm × 200 mm surface of the body is divided into two parts with a cutter knife in about 2 mm, and then the molded body is bent and broken from the cut portion. Saturation required for molding when the ratio (b / n) of the number (b) of the foamed particles existing on the fracture surface to the number (b) of the material-broken foamed particles is 0.50 or more for the first time. It means steam pressure. However, in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 5, at a saturated steam pressure of 0.55 MPa (G) which is the pressure resistance of the molding machine used in this test, the value of (b / n) Were 0, 0.16, 0.12, and 0.30, respectively, and did not reach 0.50. In order to obtain a (b / n) value of 0.50 or more, a higher saturated steam pressure is required. The number (n) of the expanded particles is the sum of the number of expanded particles peeled between the expanded particles and the number (b) of expanded particles whose material is destroyed in the expanded particles.
[0060]
[Table 1]

[0061]
[Table 2]

[0062]
[Table 3]

[0063]
[Table 4]

[0064]
The apparent density (g / L) of the expanded particles in Tables 3 and 4 was calculated by dividing the weight of the expanded particles by the apparent volume of the expanded particles. Specifically, after curing, the weight (g) of a plurality of randomly selected expanded particles was measured, and then water at 100C at 23 ° C was measured.^ThreeFrom the excluded volume when submerged in the water in the graduated cylinder in which the particle is contained, the apparent volume (cm^Three) And convert this to liters. From this measured value, the apparent density (g / L) of the expanded particles is calculated. In this measurement, the weight of the expanded particles is 0.5000 to 10.0000 g, and the apparent volume of the expanded particles is 50 to 90 cm.³The expanded particles are used.
Moreover, since the internal pressure of the expanded particle in Table 3 is expressed by the gauge pressure as described above, (G) is added after the numerical value. Since the items in Table 3 and Table 4 are the same, the unit items (columns) are omitted from Table 4.
Moreover, the compression strength in Tables 3 and 4 is a test piece obtained by cutting a molded body to have a length of 50 mm, a width of 50 mm, and a thickness of 25 mm (with the entire skin cut). In accordance with JIS Z 0234-1976 A method, a compression test was conducted until the strain reached 55% under the conditions of a test piece temperature of 23 ° C. and a load speed of 10 mm / min. From the obtained stress-strain diagram, The stress was read and used as the compressive strength. Moreover, the glass transition temperature, melting | fusing point of base resin, melting | fusing point of foaming particle, and the calorie | heat amount of a high temperature peak in the table | surface were measured using Shimadzu Corporation Shimadzu heat flux differential scanning calorimeter "DSC-50".
[0065]
  As a result of the above, the polypropylene resin particles are dispersed in the aqueous medium in which the organic peroxide is present, and the organic peroxide is decomposed at a temperature lower than the melting point of the base resin of the polypropylene resin particles. When the step of obtaining the non-crosslinked surface-modified particles by modifying the surface of the polypropylene-based resin particles by decomposing the organic peroxide at a temperature, the foamed particles obtained therefrom are converted into a polypropylene-based resin. This indicates that the molding temperature is reduced while maintaining the recyclability of the resin. More specifically, it is as follows. Example1In Comparative Example 1, the apparent density of the expanded particles is the same, the high-temperature peak heat amount of the expanded particles is almost the same, and the apparent density of the obtained molded product and the apparent cut sample of the sample for measuring the compressive strength It is convenient to compare because the density is the same. Example1Compared with Comparative Example 1, the minimum fusion temperature required in Comparative Example 1 exceeds 0.55 MPa (G).1The minimum fusing temperature required for this is 0.44 MPa (G).1Compared with Comparative Example 1, it can be seen that the minimum fusing temperature is lowered by 7 ° C. or more. Moreover, examples1The compression strength of the molded body obtained in (1) is commensurate with the overall high temperature peak heat quantity of the foamed particles, and is not particularly reduced. Example3In Comparative Example 3, the apparent density of the expanded particles is substantially the same, and the high temperature peak calorific value of the expanded particles is approximately the same, and the apparent density of the obtained molded body and the cut sample of the sample for measuring the compressive strength It is convenient to compare because the apparent density is almost the same. Example3Compared with Comparative Example 3, the minimum fusing temperature required in Comparative Example 3 exceeds 0.55 MPa (G).3The minimum fusing temperature required for this is 0.38 MPa (G).3Compared to Comparative Example 3, it can be seen that the minimum fusing temperature is lowered by 12 ° C. or more. Moreover, examples3The compression strength of the molded body obtained in (1) is commensurate with the overall high temperature peak heat quantity of the foamed particles, and is not particularly reduced.
[0066]
  Example4In Comparative Example 2, the apparent density of the expanded particles is substantially the same, and the high temperature peak heat amount of the expanded particles is almost the same, and the apparent density of the obtained molded body and the cut sample of the sample for measuring the compressive strength It is convenient to compare because the apparent density is the same. Example4Compared with Comparative Example 2, the minimum fusion temperature required in Comparative Example 2 exceeds 0.55 MPa (G).4The minimum fusing temperature required for this is 0.39 MPa (G).4Compared to Comparative Example 2, it can be seen that the minimum fusing temperature is lowered by 11 ° C. or more. Moreover, examples4The compressive strength of the molded product obtained in step 1 is commensurate with the overall high-temperature peak heat quantity of the expanded particles, and it does not have a particular decline.. Reference example 1And examples2The expanded particles have almost the same apparent density, the high temperature peak heat amount of the expanded particles is almost the same, and the apparent density of the obtained molded product and the apparent density of the cut sample for compressive strength measurement are almost the same. Since it is the same, it is convenient to compare.Reference example 1And examples2From the contrast ofIn Reference Example 1The required minimum fusing temperature is 0.48 MPa (G), whereas the example2The minimum fusing temperature required for this is 0.35 MPa (G).2IsReference example 1It can be seen that the minimum fusing temperature is lowered by about 9 ° C. as compared with FIG. Example2 and Reference Example 1 are usedSince the organic peroxide used is different and the other conditions are almost the same, this result shows that the use of organic peroxide having a carbonate structure reduces the minimum fusion temperature. It shows that it is excellent.
[0067]
  Example5In Comparative Example 5, the apparent density of the expanded particles is close, and the high temperature peak calorific value of the expanded particles is almost the same. However, the apparent density of the obtained molded product and the apparent density of the cut sample of the sample for compressive strength measurement are A comparison of slightly different things is possible. Example5Compared with Comparative Example 5 and Example5The minimum fusing temperature required in Example 3 is 0.36 MPa (G), whereas the minimum fusing temperature required in Comparative Example 5 exceeds 0.55 MPa (G).5Compared with Comparative Example 5, it can be seen that the minimum fusing temperature is lowered by 13 ° C. or more. And examples5The compression strength of the molded product obtained in (1) is commensurate with the high temperature peak of the entire foamed particles and the apparent density of the cut sample, and it does not have a particular drop.
[0068]
  Further examples5For the foamed particles obtained in Example 5 and the foamed particles obtained in Comparative Example 5, a micro thermal analysis system “2990 type micro thermal analyzer” of TI Instruments Japan Co., Ltd. was used for each foamed particle surface. The sample was subjected to micro differential thermal analysis (μDTA) from 25 ° C. to 200 ° C. under a temperature rising rate of 10 ° C./second.5The surface of the expanded particles obtained in the above has a melting start temperature of 131 ° C. and the extrapolated melting start temperature is 135 ° C., whereas the surface of the expanded particles obtained in Comparative Example 5 has a melting start temperature of 168 ° C. The extrapolated melting start temperature was found to be 171 ° C. The above μDTA results show that the decrease in the melting start temperature or extrapolation melting start temperature on the surface of the expanded particles contributes to the decrease in the minimum fusing temperature required during molding.
[0069]
  Examples1-5Then, when the saturated steam pressure at the time of molding is further increased, the degree of fusion of the obtained molded body is further increased, and the value of (b / n) is further increased. Specifically, it is as shown in Table 5. The larger the value of (b / n), the higher the bending strength and tensile strength of the molded body, which is preferable. The molded product obtained by the method of the present invention preferably has a value of (b / n) of 0.4 or more, more preferably 0.5 or more, and 0.6 or more. Is more preferable, and is most preferably 0.7 or more.
[0070]
[Table 5]

[0071]
【The invention's effect】
  In the present invention, as the molding material, new EPP particles whose molding temperature is drastically lowered as compared with the conventional equivalent EPP particles are filled in the mold by increasing the internal pressure, and then the EPP particles are heated. It is a manufacturing method of the EPP molded object to cool. Therefore, the heating temperature at the time of molding can be lowered, which contributes to the reduction of heat energy.In particular, since the surface modification of the expanded particles is performed using an organic peroxide having a carbonate structure, a more excellent effect of reducing the minimum fusion temperature can be obtained.Moreover, the reduction of the heating temperature shortens the cooling time, and as a result, the molding cycle can be shortened and the productivity can be improved. In addition, since the EPP molded product obtained by the present invention is non-crosslinked, it maintains the recyclability of polypropylene resin and the like and is environmentally friendly. In addition, conventionally, in order to increase the physical properties such as high rigidity of an EPP molded body, it is necessary to use expanded particles having a high high-temperature peak heat amount obtained by using a polypropylene resin having a high melting point. However, the foaming particles used in the present invention have a problem that the molding temperature exceeds the pressure resistance of a general-purpose molding machine.Melting point is 158 ° C or higherEven with expanded particles with a high high-temperature peak heat obtained by using a polypropylene resin with a high melting point, the EPP molded product obtained therefrom has a high rigidity.It has excellent mechanical properties such as compressive strength.While0.45 MPa (G) or lessA molded body can be obtained with steam at a low temperature (low pressure), and molding can be performed within the pressure resistance of a general-purpose molding machine.Moreover, since the amount of heat at the high-temperature peak of the expanded particles is 2 to 70 J / g, the compression strength and energy absorption amount of the EPP molded product are not lowered, and the pressure in the expanded particles is reduced to 0. By setting the pressure to 005 to 0.98 MPa (G), even if the molding is performed with steam at the low temperature described above, the EPP particles may be insufficiently secondary foamed or the mutual fusion of the EPP particles may be insufficient. Nor.Therefore, in the case of the present invention, it is possible to provide an EPP molded body having high physical properties (high rigidity) and / or light weight at a lower cost than before. The EPP molded body having high physical properties obtained by the method of the present invention is used as a bumper core material for automobiles or as a shock absorber for side collision set on an automobile door for the purpose of absorbing impact from the side of the automobile. Is particularly suitable.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a first DSC curve chart of a polypropylene resin foam particle for molding according to the present invention.
FIG. 2 is a diagram showing an example of a second DSC curve chart of polypropylene resin particles.
FIG. 3 is a diagram showing μDTA curves based on micro-thermomechanical analysis for foamed particle surfaces obtained in each example based on Example 7 and Comparative Example 5. FIG.
FIG. 4 is a diagram showing a μDTA curve based on micro-thermomechanical analysis on the surface of expanded particles obtained in another example.

Claims (2)

  Polypropylene resin particles in which the base resin has a melting point of 158 ° C. or higher in a dispersion medium containing an organic peroxide having a carbonate structure (provided that the polypropylene resin is impregnated with a vinyl monomer) The dispersion formed by dispersing the organic peroxide is maintained at a temperature lower than the melting point of the base resin of the polypropylene resin particles and at a temperature at which the organic peroxide decomposes. A high temperature obtained by a method comprising a surface modification step of obtaining non-crosslinked surface modified particles by foaming and a foaming step of foaming the surface modified particles with a foaming agent to obtain non-crosslinked foamed particles After applying an internal pressure of 0.005 to 0.98 MPa (G) in the bubbles of the polypropylene resin expanded particles having a peak heat quantity of 2 to 70 J / g and filling the expanded particles in the mold, the expanded particles are 0. 5MPa heated at (G) below the steam pressure is expanded fusing the expanded beads together, then cooling method of manufacturing a mold expanded molded article of the polypropylene resin foamed beads characterized by. The in-mold foaming of polypropylene resin foamed particles according to claim 1, wherein the melting point (Tm _s ) of the surface layer portion of the foamed particles and the melting point of the internal foamed layer (Tm _i ) are Tm _s <Tm _i. Manufacturing method of a molded object.

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