JP4144781B2 - Method for producing molded polypropylene resin foam particles - Google Patents

Description

【００８１】
実施例１、２、５、８
（成形方法）
表１に示す発泡粒子を、図４に示す成形装置を用いて、成形を行なった。７００ｍｍ×２００ｍｍ×５０ｍｍの成形空間部を持つ雄型１及び雌型２からなる金型を閉じて型締めし、ドレン弁８、９を閉じてバルブの流量特性を示すＣｖ値１８、有効断面積３２０ｍｍ^２のスチーム弁６、７より金型内に０．３９ＭＰａ（Ｇ）に調圧されたスチームを導入して予熱を５秒間行った。次いで金型を一度開けた後、再度閉じて表２に示す充填率となる様に前記発泡粒子を充填し、次いで型締めした後にドレン弁８、９を開けたまま、スチーム弁６、７より金型内にスチームを導入して成形空間部の発泡粒子間にある空気を排気した。次いでドレン弁を閉じて、スチーム弁７より圧力検知ライン１２での圧力が表２の所定の成形圧力より０．０４ＭＰａ（Ｇ）低い圧力に達するまで０．８ＭＰａ（Ｇ）に調圧されたスチームを導入し（一方加熱）、続いてスチーム弁６より圧力検知ライン１１での圧力が表２の所定の成形圧力より０．０２ＭＰａ（Ｇ）低い圧力に達するまでスチームを導入した（逆一方加熱）後、スチーム弁６、７を用いて表２の所定の成形圧力となるようにスチームを導入して表２に示す所定の成形圧力で保持加熱を行なった（本加熱）。成形後、成形空間部の成形体の面圧が０．０５９ＭＰａ（Ｇ）となるまで水冷した後、成形体を成形空間部から取り出し、６０℃で２４時間養生した後、室温まで冷却して成形体を得た。
表２に、成形条件及び成形体の性状を示す。
【００８２】
実施例３、４及び６
（成型方法）
予熱を行なわず図４に示すＣｖ値２８、有効断面積５００ｍｍ^２のスチーム弁６、７を用いて流量を大きくした以外は実施例１と同様にして成形を行なった。
【００８３】
実施例７
図４に示すスチーム弁６、７を通る配管を内径８０ｍｍとし、スチーム弁６、７をＣｖ値６０のものに交換し、スチーム流量を大きくして成形を行った。表１に示す発泡粒子を用いて成形を行った。４００ｍｍ×３００ｍｍ×８０ｍｍの成形空間部を持つ雄型１及び雌型２からなる金型を閉じて型締めし、ドレン弁８、９を閉じてスチーム弁６、７より金型内に０．３９ＭＰａ（Ｇ）に調圧されたスチームを導入し予熱を５秒間行った。次いで金型を一度開けた後、再度閉じて表２に示す充填率となる様に前記発泡粒子を充填し、次いで型締めした後にドレン弁８、９を開けたまま、スチーム弁６、７より金型内にスチームを導入して金型内の空気を排気した。次いでドレン弁８を閉じ、スチーム弁７より表２の所定の成形圧より０．０４ＭＰａ低い圧力に調圧されたスチームを２秒間導入し、続いてドレン弁８を開けてドレン弁９を閉じ、スチーム弁６より表２の所定の成形圧より０．０４ＭＰａ低い圧力に調圧されたスチームを２秒間導入した後、スチーム弁６、７を用いて表２の所定の成形圧に調圧されたスチームを導入して５秒間、保持加熱を行った。成形後、金型内の成形体の面圧が０．０５９ＭＰａ（Ｇ）となるまで水冷した後成形体を型から取り出し、６０℃で２４時間養生した後、室温まで冷却して成形体を得た。
【００８４】
比較例１〜３
（成形方法）
充填する前の予熱を行なわず、一方加熱及び逆一方加熱に用いるスチームを０．７８ＭＰａ（Ｇ）に調圧した以外は実施例１と同様に成形体を得た。
【００８５】
表２の充填率、所定の成形圧力の５０％に相当する圧力に達するまでの昇圧速度（５０％昇圧速度）、所定の成形圧力に達するまでの昇圧速度は前述した通りである。また、融着率、外観、圧縮強度は以下のようにして評価した。
【００８６】
（融着率）
融着率は、実施例及び比較例で得られた成形体をカッターナイフで成形体の厚み方向に約１０ｍｍの切り込みを入れた後、手で切り込み部から成形体を破断するテストにより、破断面に存在する発泡粒子の個数（ｎ）に対する材料破壊した発泡粒子の個数（ｂ）の比（ｂ／ｎ）である。
【００８７】
（外観）
外観は成形体の表面について、目視にて観察し粒子間の間隙量を以下の基準によって判定したものである。
◎：粒子間に殆ど間隙がない。
○：粒子間に若干の間隙が見られる。
×：粒子間に多くの間隙が見られる。
【００８８】
（圧縮強度）
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。
実施例及び比較例の発泡粒子を用いて前述した不溶分を測定したところ、いずれも０重量％以下であった。
【表２】

【００８９】
【発明の効果】
本発明の方法によれば、発泡粒子相互の融着性が高く、表面の凹凸が少ない成形体が得られる。さらに、所定の成形圧力までの時間を短縮すると共に冷却時間の短縮もでき、その結果、成形サイクルを短縮し、生産効率を高める事ができる。
引張弾性率が特定のポリプロピレン系樹脂を基材樹脂とするポリプロピレン系樹脂発泡粒子を充填することにより、内部の空隙や表面の凹凸も少なく圧縮強度に優れた発泡成形体を得られる。
所定の成形圧力に達した後に、該成形圧力で５秒以上の保持を行うことでより表面の凹凸が少ない発泡成形体が得られる。
特定の発泡粒子を用いることにより急激な圧力上昇に対して耐久性があり、成形サイクルも短縮することができる。
【図面の簡単な説明】
【図１】図１は、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、成形圧力と成形サイクルとの関係を示す一例の図である。
【図４】図４は、本発明成形体の製造方法に用いられる装置の説明を示す図である。
【符号の説明】
１ 雄型
２ 雌型
３ 成形空間
４、５ スチーム弁（大流量）
６、７ スチーム弁（調圧用）
８、９ ドレン弁
１０ 発泡体の表面における測定用ライン
１１、１２ 圧力検知用ライン
１３ 制御装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polypropylene resin expanded particle molded body.
[0002]
[Prior art]
Polypropylene-based foamed resin particles can be added with additional properties such as buffering and heat insulation properties without impairing the excellent properties of propylene such as mechanical strength, heat resistance, chemical resistance, and easy recyclability. It is used in a wide range of industrial fields such as packaging materials and building materials.
In particular, the so-called bead method in-mold foam molded product, in which pre-expanded particles are produced from polypropylene resin, filled in a mold that can be opened and closed, and then fused by steam, has excellent buffering properties. From the viewpoint of formability, it is widely used as an energy absorber material (hereinafter also referred to as E / A material) such as an automobile bumper core material and a door pad.
[0003]
  In recent years, this E / A material has been required to have higher rigidity because of stricter collision safety standards and weight reduction aimed at improving fuel efficiency. In order to obtain a highly rigid polypropylene resin foamed particle molded body, it is generally possible to increase the rigidity of the base resin. As a high-rigidity polypropylene resin, a propylene-based copolymer or a propylene homopolymer having a low comonomer composition ratio such as ethylene or butene as a copolymer component is known. By using these raw materials, a high-rigidity polypropylene resin is known. It was possible to obtain a molded resin foam particle molded body. However, generally, a high-rigidity polypropylene-based resin has a softening temperature and a melting temperature that increase at the same time as rigidity, and a foamed particle molded body is manufactured using pre-expanded particles using these high-rigidity raw materials. If the foam is sufficiently secondary foamed and fusedFoam particle formationIn order to obtain a shape, the processing temperature is inevitably increased. That is, high pressure steam was required for molding.
[0004]
Conventionally, a molding machine for producing an EPP molded body (polypropylene-based resin expanded particle molded body) has a structure corresponding to a high molding temperature, that is, a structure that can withstand high-pressure steam. In the case of producing a foamed particle molded body using pre-expanded particles of high rigidity obtained from polypropylene resin, steam with a pressure higher than the pressure resistance of the molding machine is required to obtain a sufficient secondary foaming and fusion rate. There were many cases where it was necessary. Further, in such molding with high-pressure steam, the molding cycle becomes long, and it is difficult to say that a foamed particle molded body can be produced efficiently.
[0005]
Examples of a method for improving the secondary foam shortage of the pre-foamed particles as described above include a method of applying an internal pressure to the foamed particles. However, there is a problem that the molding cycle becomes long. Also, when trying to obtain a thick foamed particle molded body, the inside of the molded body may be poorly fused.
In addition, as a method for improving the fusion property of the pre-expanded particles as described above, the present inventors disperse polypropylene resin particles in a dispersion medium in which an organic peroxide is present, and the dispersion medium. 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 is substantially decomposed, and is formed by substantially decomposing the organic peroxide. It has been found that the expanded particles obtained from the surface-modified particles of the cross-linking can achieve fusion between the expanded particles with low-temperature steam and give a molded polypropylene resin expanded particle having excellent rigidity. Application No. 2001-285537). However, in the case of producing a foamed particle molded body using the foamed particles, the fusion property between the foamed particles is improved, but there are many voids between the foamed particles and the surface of the molded body becomes uneven. It is hard to say that the foamability is improved.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for industrially advantageously producing a highly rigid foamed particle molded body using highly rigid polypropylene resin expanded particles.
[0007]
[Means for Solving the Problems]
  As a result of intensive studies to solve the above problems, the present inventors have determined that the pressurization speed of the expanded particles in the molding space portionTheIt was found that by setting the specific value, it is possible to obtain an in-mold molded article having good fusion property and secondary foaming property, and the present invention has been completed. That is, according to the present invention, the following in-mold molding method of a polypropylene resin expanded particle molded body is provided.
(1) In a method for producing a polypropylene resin foamed particle formed body, a polypropylene resin foam particle having a base resin of a polypropylene resin having a tensile elastic modulus of 1200 MPa or more is filled in a molding space, and the molding is performed. When steam is supplied into the space and the foamed particles are heated and fused, the pressure increase rate until reaching a pressure corresponding to 50% of a predetermined molding pressure in the molding space is 0.030 MPa / sec or more. And the pressurization speed | rate until it reaches this predetermined shaping | molding pressure is 0.025 Mpa / sec or more, The manufacturing method of the polypropylene resin foamed particle molded object characterized by the above-mentioned.
(2) When steam is supplied into the molding space and the foamed particles are heated and fused, after reaching a predetermined molding pressure, a pressure obtained by subtracting 0.020 MPa from the molding pressure. In range5The method for producing a polypropylene resin foamed particle molded body according to (1), wherein holding is performed for 2 seconds or more.
(3) The polypropylene resin expanded particles are substantially non-crosslinked expanded particles, and are higher than the intrinsic endothermic curve peak derived from the heat of fusion of the polypropylene resin in the DSC curve by differential scanning calorimetry. The method for producing a polypropylene resin foamed particle molded article according to (1) or (2) above, wherein the foamed particle has an endothermic curve peak.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The base resin of the polypropylene resin particles used (hereinafter sometimes referred to as “the base resin”) is a polypropylene resin having a tensile modulus of 1200 MPa or more. As such a polypropylene resin, either a polypropylene homopolymer or a copolymer of propylene and another comonomer containing a propylene component of 60 mol% or more (preferably containing a propylene component of 80 mol% or more). Or a mixture of two or more selected from these resins.
[0009]
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.
[0010]
Among these, in order to obtain a tensile modulus of 1200 MPa or more, the comonomer component may be reduced in a polypropylene homopolymer or a copolymer of propylene and another comonomer. The tensile elastic modulus is preferably 1250 MPa or more and more preferably 1300 MPa or more in order to increase mechanical properties such as compressive strength of the EPP compact. The upper limit is not particularly limited, but is about 2500 MPa.
[0011]
The above-described tensile elastic modulus is a value measured under the following conditions in accordance with JIS K 7162 (1994) using the base resin.
-Test piece JIS K 7162 (1994) described test piece 1A type (direct molding by injection molding)
・ Test speed 1mm / min
[0012]
Among the polypropylene resins having the specific tensile modulus described above, the melting point of the base resin is high in mechanical properties such as compressive strength of the final EPP molded product (polypropylene resin foamed particle molded product). In terms of excellent heat resistance, the temperature is preferably 145 ° C or higher, more preferably 155 ° C or higher, and further preferably 160 ° C or higher. The upper limit of the melting point is usually about 170 ° C. Further, the base resin preferably has a melt flow rate (MFR) of 1 to 100 g / 10 minutes. If the MFR is less than 1 g / 10 minutes, the effect of lowering the molding steam temperature during in-mold molding may be insufficient. Moreover, when the MFR exceeds 100 g / 10 minutes, the obtained in-mold molded product may be brittle. From such a viewpoint, the MFR of the base resin is preferably 10 g / 10 min to 70 g / 10 min. The MFR is a value measured under test condition 14 of JIS K7210 (1976).
[0013]
In the present invention, a polypropylene resin other than the above-mentioned specific polypropylene resin, a synthetic resin other than the polypropylene resin, and / or an elastomer are added to the polypropylene resin particles within a range not impairing mechanical properties. can do. The addition amount of the polypropylene resin other than the specific polypropylene resin, the synthetic resin other than the polypropylene resin and / or the elastomer is preferably 35 parts by weight per 100 parts by weight of the polypropylene resin. More preferably, it is at most 20 parts by weight, more preferably at most 10 parts by weight, and most preferably at most 5 parts by weight. .
[0014]
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.
[0015]
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.
[0016]
In addition, in this base resin, various additives can be contained as desired. 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 were melted in the extruder when, for example, polypropylene resin particles for foamed particles (hereinafter sometimes referred to as “the present resin particles”) were produced by cutting the strands extruded by an extruder. It can be contained in the resin particles by adding to the base resin and kneading.
[0017]
In addition, as this resin particle, when manufacturing this resin particle by cut | disconnecting the strand which melt | dissolved this base resin in the extruder and extruded, it is preferable to cool rapidly the strand immediately after extrusion. In particular, when obtaining surface-modified expanded particles, the surface modification described later can be efficiently performed by using the rapidly cooled resin particles. 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.
[0018]
The dispersion medium used in the surface modification step described later is generally an aqueous medium, preferably water, 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]
  In the present invention,This resin grainOf childAlthough the surface may or may not be modified, a preferred method for obtaining foam particles with a modified surface is from a surface modification step and a foaming step (foaming agent impregnation step + resin particle foaming step). (Hereinafter also referred to as method A). In the surface modification step, the resin particles are dispersed in a dispersion medium in which an organic peroxide is present, and the resulting dispersion is at a temperature lower than the melting point of the base resin of the resin particles and the organic peroxide By maintaining the temperature at which the product is substantially decomposed and decomposing the organic peroxide, the surface of the resin particles is modified to obtain substantially uncrosslinked surface-modified particles. The surface-modified particles thus obtained can be converted into substantially uncrosslinked foamed particles by foaming them with a foaming agent in the subsequent foaming step. 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.
[0020]
  Examples of the organic peroxide include various conventionally known ones such as isobutyl peroxide, cumyl peroxyneodecanoate, α, α′-bis (neodecanoylperoxy) diisopropylbenzene, di-n-propyl. Peroxydicarbonate, diisopropylperoxydicarbonate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, bis (4-t- Butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethylperoxydicarbonate, di (2-ethylhexylperoxy) dicarbonate, t-hexylperoxyneodecanoate, dimethoxybutylperoxydicarbonate, di (3 -Methyl-3-methoxybutyl par Oxy) dicarbonate, t-butylperoxyneodecanoate, 2,4-dichlorobenzoyl peroxide, t-hexylperoxypivalate, t-butylperoxypivalate, 3,5,5-trimethylhexanoylper Oxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate, succinic peroxide, 2,5-dimethyl-2,5- Di (2-ethylhexanoylperoxy) hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2 -Ethyl hexanoate, m-toluoyl benzoyl peroxy Benzoyl peroxide, t-butylperoxyisobutyrate, di-t-butylperoxy-2-methylcyclohexane, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxy Maleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxy Urate, 2,5-dimethyl-2,5-di (m-toluoylperoxy) hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate 2,5-dimethyl-2,5-di (benzoylperoxy) hexane and the like. The organic peroxide may be used alone or in combination of two or more, and is usually 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, more preferably 0.8 parts per 100 parts by weight of the resin particles. 1-3 parts by weight are added to the dispersion medium and used. In the dispersion composed of the organic peroxide, the resin particles, and the dispersion medium, if the weight ratio of the resin particles / dispersion medium is too large, uniform surface modification cannot be performed on the resin particles.fearAs a result, sufficient foamability cannot be imparted to the resulting foamed particles.fearThere is. From such a viewpoint, the weight ratio of the resin particles / dispersion medium is preferably 1.3 or less, more preferably 1.2 or less, still more preferably 1.1 or less, and most preferably 1.0 or less. . However, if this weight ratio is too small, sufficient low temperature moldability cannot be imparted to the resulting foamed particles unless the amount of organic peroxide used in the resin particles is increased.fearThere is. Increasing the amount of organic peroxide used leads to increased costs. In order to reduce the amount of the organic peroxide used, the weight ratio of the resin particles / dispersion medium is preferably 0.6 or more, and more preferably 0.7 or more.
[0021]
  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 during decomposition are particularly preferred, and among them, a peroxide having a carbonate structure is most preferred. In addition, when using this organic peroxide, a chain transfer agent etc. are used together as necessary (In advanceIt can be contained in the present resin particles or / and used in combination in a dispersion medium). 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.
[0022]
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 was 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 is introduced with a long chain branching or crosslinking structure by uniformly impregnating polypropylene particles with an organic peroxide and a crosslinking aid and decomposing the organic peroxide at a temperature below the melting point of 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 melt-kneaded uniformly 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. While dispersing the particles, the dispersion is maintained at a temperature lower than the melting point of the base resin of the polypropylene resin particles and the organic peroxide is substantially decomposed to decompose the organic peroxide. This is different from the method of using the method A in which the surface of the polypropylene resin particles is modified to obtain substantially non-crosslinked surface modified particles.
[0023]
  The organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. Accordingly, the 1-hour half-life temperature of the organic peroxide (the temperature at which the organic peroxide is decomposed in half in 1 hour) is below the Vicat softening point of the base resin (JIS K 6747-1981, the same shall apply hereinafter). Preferably there is. 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. In some cases, it cannot be substantially decomposed at a temperature lower than the melting point of the base resin.KunaTherefore, it is not preferable. When the peroxide is substantially decomposed at a temperature higher than the melting point of the base resin, the peroxide is decomposed in a state where it penetrates deep into the resin particles. Since the resin material is greatly decomposed as a whole regardless of the surface or the inside, in some cases, there is a possibility that only EPP particles that cannot be used for molding may be obtained, and even if it can be molded, it is finally obtained. There exists a possibility that the mechanical physical property of an EPP molded object may fall large.
[0024]
  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 is JIS K 7121According to -1987, the state adjustment of the test piece is defined as “when measuring the glass transition temperature after performing a certain heat treatment”, and means the midpoint glass transition temperature obtained by heat flux DSC. The peroxide is preferably substantially decomposed below the Vicat softening point of the base resin in the dispersion medium in which the resin particles are present, and is 20 ° C. higher than the Vicat softening point of the base resin. More preferably, it is substantially decomposed at a low temperature, and more preferably, it is substantially decomposed at a temperature 30 ° C. or more lower than the Vicat softening point of the base resin. The organic peroxide has a one-minute half-life temperature of the organic peroxide (the temperature at which the theoretical active oxygen amount becomes half of the original half in one minute when the organic oxide is decomposed at a constant temperature). It is particularly preferable that the material is substantially decomposed by being kept in a temperature range of ± 30 ° C. for 10 minutes or longer, and longer when decomposed at a temperature lower than [1 minute half-life temperature−30 ° C.]. On the contrary, there is a risk that the decomposition and decomposition will be abruptly attempted to decompose at a temperature higher than [1 minute half-life temperature + 30 ° C.]. There is a risk of deteriorating the efficiency of the reforming, and it is easy to substantially decompose the organic peroxide if it is kept in the range of a half-life temperature of ± 30 ° C. for 10 minutes or longer. The longer the holding time in the temperature range of ± 30 ° C, the more reliable the organic The oxide can be decomposed, but it is no longer necessary for a certain period of time, and if the time is longer than necessary, the production efficiency will be reduced.The holding time in the above temperature range should normally be 60 minutes at most. In order to decompose the organic peroxide, first prepare the above 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. In this case, the rate of temperature rise may be selected so that it is maintained in the range of 1 minute half-life temperature ± 30 ° C. for 10 minutes or more, but any one of the range of half-life temperature ± 30 ° C. It is more preferable to stop at the temperature and hold the temperature for 5 minutes or more, and the arbitrary temperature at that time is most preferably a temperature within 1 minute half-life temperature ± 5 ° C.
[0025]
Further, substantially decomposing means decomposing until the theoretical active oxygen amount of the used peroxide is 50% or less of the original, but the theoretical active oxygen amount is 30% or less of the initial. It is preferable to decompose until the theoretical active oxygen amount is 20% or less of the original, and it is further preferable to decompose until the theoretical active oxygen amount is 5% or less of the initial.
The above-mentioned half-life temperature of the organic peroxide is adjusted to a 0.1 mol / L organic peroxide solution using a solution that is relatively inert to radicals (for example, benzene and mineral spirits). Then, it is sealed in a glass tube subjected to nitrogen substitution, immersed in a thermostatic bath set at a predetermined temperature, and pyrolyzed for measurement.
[0026]
The treated particles are substantially uncrosslinked. In the method A, since a crosslinking aid or the like is not used together, crosslinking does not proceed substantially. The term “substantially non-crosslinked” is defined as follows. That is, each of the base resin, the present resin particles, the surface modified particles, the EPP particles, and the EPP molded body was used as a sample (use 1 g of sample per 100 g of xylene), and this was immersed in boiling xylene for 8 hours. The mixture is quickly filtered through a wire mesh having a mesh size of 74 μm as defined in JIS Z8801 (1966), which defines a mesh screen, and the weight of the boiling xylene-insoluble matter remaining on the wire mesh is measured. A case where the insoluble content is 10% by weight or less of the sample is called substantially non-crosslinked, but the insoluble content is preferably 5% by weight or less and preferably 3% by weight or less. More preferably, it is most preferably 1% by weight or less. 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.
[0027]
As described above, when the surface of the resin particle is modified, the surface of the resin particle is modified by decomposing the organic peroxide and then used for the production of the expanded particle. The foamed particles are obtained by impregnating the resin particles with the foaming agent under heating and heating conditions while dispersing the resin particles in a dispersion medium in the presence of the foaming agent (foaming agent impregnation step), and then releasing the pressure. Can be produced by a method of obtaining expanded particles (resin particle expansion step) (hereinafter referred to as “dispersion medium release expansion method”) by releasing the resin particles and the dispersion medium to a low pressure zone at a temperature at which the expanded particles are formed. preferable.
[0028]
In the case of modifying the surface, the surface modification step for forming the surface modified particles and the foaming step for obtaining foamed particles from the surface modified particles (foaming agent impregnation step + resin particle foaming step) are different from each other. Although it is possible to carry out the process at another time in the apparatus, when the dispersion medium releasing foaming method is adopted, a predetermined amount of the organic peroxide having an appropriate decomposition temperature is added to the dispersion medium in a sealed container and the surface is added. It is also possible to obtain expanded particles from the surface-modified particles by performing a modification step, and subsequently impregnating the surface-modified particles with a foaming agent in the same container and performing a foaming step by a normal dispersion medium discharge foaming method.
[0029]
In the case of modifying the surface, in the surface modified particles, and thus in the EPP particles (polypropylene resin foamed particles) and EPP molded bodies obtained therefrom, a molecular weight of 50 generated as the organic peroxide is decomposed. The above alcohol can be contained in the order of several hundred ppm to several thousand ppm. As such an alcohol, for example, when bis (4-t-butylcyclohexyl) peroxydicarbonate is used, Pt-butylcyclohexanol can be contained in the surface-modified 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.
[0030]
In the dispersion medium releasing foaming method, it is preferable to add a dispersant to the dispersion medium so that the resin particles under heating in the container do not fuse with each other in the container. As such a dispersant, any agent that prevents fusion of the resin particles in the container may be used, and it can be used regardless of whether it is organic or inorganic. preferable. 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.
[0031]
Further, in the above dispersion medium releasing foaming method, the dispersion strengthening agent is strengthened (the dispersion enhancing agent is dispersed in the container even if the amount of the dispersing agent is reduced). You may add in a 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. When producing low-foaming molding EPP particles having an apparent density of 100 g / L or more, its use is preferred.
[0032]
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.
[0033]
Examples of the foaming agent used in the production process of the polypropylene resin expanded particles include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, and trifluoro. Organic physical foaming agents such as halogenated hydrocarbons such as methane, 1,2-difluoroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, nitrogen, oxygen, air, dioxide Examples include so-called inorganic physical foaming agents such as carbon and water. 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.
[0034]
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.
[0035]
The expanded particles used in the present invention are derived from the heat of fusion of the polypropylene resin in the DSC curve by the differential scanning calorimetry of the expanded particles having an apparent density of 10 g / L to 500 g / L, adopting the above dispersion medium releasing foaming method. It is preferable to produce expanded particles in which an endothermic curve peak (high temperature peak) is present on the higher temperature side than the inherent endothermic curve peak (inherent peak). Such foamed particles are foamed particles having a high closed cell ratio and suitable for molding. In the case of the present invention, in the obtained expanded particles, the amount of heat at the high temperature peak is particularly preferably from 10 J / g to 60 J / g. When the amount of heat at the high temperature peak is less than 10 J / g, the compression strength, energy absorption amount, etc. of the EPP molded product may be lowered. On the other hand, if it exceeds 60 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 become long, which is not preferable. In the present invention, the calorific value of the high temperature peak is preferably 12 J / g to 58 J / g, and preferably 10 to 60% with respect to the sum of the calorific value of the high temperature peak and the intrinsic peak. More preferably, it is 50%. 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.
[0036]
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 calorific value of the endothermic curve peak (high temperature peak) b at which the apex appears on the higher temperature side than the temperature at which the apex of the intrinsic endothermic curve peak (inherent peak) a derived from the heat of fusion of the polypropylene resin found in the DSC curve of This corresponds to the area of the high temperature peak b, and can be specifically determined 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.
[0037]
In the present specification, when simply expressed as “high temperature peak of foamed particles” without notice, it refers to the amount of heat of the high temperature peak obtained by the above measurement, and relates to the surface layer portion of the foamed particles described later. The amount of heat at the high temperature peak is different from the amount of heat at the high temperature peak for the inner foam layer.
[0038]
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 of 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 of the peak of the intrinsic peak a observed in the second DSC curve for the expanded particles (temperature corresponding to the melting point of the base resin) is usually [ Tm-2 ° C.] to [Tm + 2 ° C.].
[0039]
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.
[0040]
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 obtaining an EPP molded product using expanded particles having a high high temperature peak heat quantity, the minimum fusion temperature is relatively high although strength properties such as compressive strength of the EPP molded product tend to be 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 the method A are those in which the minimum fusing temperature is effectively reduced. In the case of producing an EPP molded body using the expanded particles, an EPP molded body having excellent mechanical properties such as compressive strength can be obtained.
[0041]
In order to obtain expanded particles having a high temperature peak in the DSC curve, when the resin particles are dispersed in a dispersion medium and heated in a closed container, the temperature is equal to or higher than the melting end temperature (Te) of the base resin constituting the resin 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 The resin particles can be obtained by foaming by releasing the resin particles from the sealed container under low pressure after holding at the temperature for a further sufficient time, preferably about 10 to 60 minutes.
The melting point (Tm) is a value obtained by performing differential scanning calorimetry on 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. It is the temperature at the top of the endothermic curve peak a unique to the base resin found in the obtained second DSC curve (an example of which is shown in FIG. 2), and the melting end temperature (Te) is the intrinsic endothermic curve. DSC curve on the high temperature side of 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, if there are two or more longest straight lines, the peak peak on the highest temperature side is Tm.
[0042]
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.
[0043]
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.
[0044]
The apparent density (g / L) of the expanded particles is calculated by dividing the weight (g) of the expanded particles by the apparent volume (L) of the expanded particles. The apparent volume of the expanded particles was 23 ° C., and about 5 g of the expanded particles left at atmospheric pressure for 48 hours or more was converted to 100 cm of water at 23 ° C.³From the excluded volume when submerged in the water in the graduated cylinder in which the particle is contained, the apparent volume (cm³) And converted into liters. For 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.³An amount of a plurality of expanded particles is used.
[0045]
When surface modified particles obtained by modifying the surface of resin particles by decomposing organic peroxide are used, it is possible to mold with low temperature steam and to have the following structural specificity. It is clear from the results.
[0046]
As a result of DSC measurement of the expanded particles, the expanded particles obtained by the method A show a tendency 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 the 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. Tm as foamed particles that can be molded with low temperature steam_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.
[0047]
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) Is the second DSC obtained by cutting out from the inside of the expanded particles so as not to include the surface layer portion, collecting 2 to 4 mg and using this as a sample, and performing the same operation as the measurement of the high temperature peak heat quantity of the expanded particles described above. It means the temperature at the apex of the intrinsic peak a of the curve.
[0048]
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 the method A, ΔH_s<ΔH_iIt was observed to be x0.86. Therefore, for foamed particles that can be molded with low temperature steam, ΔH_s<ΔH_i× 0.86 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. ΔHs is preferably ΔHs ≧ ΔHi × 0.25. ΔH_s<ΔH_iBy being 0.86, it becomes possible to perform in-mold molding at a lower temperature than foamed particles that are not surface-modified, and the effect is greater as the ΔHs value is smaller. 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.
[0049]
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.
[0050]
A method of collecting a sample when the melting point and the high temperature peak calorific value are measured by dividing the foamed particle into a surface layer portion and an internal foam layer not including the surface layer portion are 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 expanded particle is the entire surface of the expanded particle so that the surface of the expanded particle and the portion between the surface of the expanded particle and 200 μm from the surface of the expanded particle toward the center of gravity of the expanded 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 excised the surface layer part from. However, if the size of the expanded particle 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 particle and the surface of the expanded particle are directed toward the center of gravity of the expanded particle. 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.
[0051]
  Further, when the MFR was measured, the MFR value of the expanded particles obtained by the method A was the same as the MFR value of the resin particles before being surface-modified.OrIt was observed to show a larger value. 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 should be 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.
[0052]
  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. In measuring the MFR of expanded particles,Sample aboveToIt is necessary to avoid the introduction of bubbles and the like 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.
[0053]
Furthermore, 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 A and the surface of the EPP molded body produced therefrom. Specifically, it was produced from the surface of an EPP molded product produced from the expanded particles obtained by the above-mentioned method A (ie, substantially the same as the surface of the expanded particles) and the conventional expanded particles not subjected to surface modification. As a result of comparing each surface of the EPP molded body by ATR measurement (total reflection absorption measurement method), the surface of the EPP molded body produced from the expanded particles obtained by the 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 body from the surface-modified expanded particles and the absorption peak height for the conventional molded body) are the same, the surface of the molded body of the present invention is 1033 cm.^-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 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 considered to increase the permeability of steam during molding and enable molding with low temperature steam.
From such a viewpoint, the expanded particles that can be molded with low-temperature steam preferably have a ratio of oxygen to carbon of 0.15 or more by the EDS on the surface of the expanded particles.
The expanded particles obtained by the above-described method A include the modified surface containing oxygen and / or the reverse phenomenon of the melting point or / and the decrease in the high-temperature peak heat quantity of the surface layer portion of the expanded particles or / and the expanded particle surface. It is presumed that the minimum fusing temperature is greatly reduced by lowering the melting start temperature.
[0054]
The EPP particles obtained by the above-mentioned method A are aged under atmospheric pressure, and after increasing the bubble internal pressure as necessary, by heating with steam or hot air, Is possible.
[0055]
The method for producing a polypropylene resin expanded particle molded body according to the present invention is preferably carried out by using the expanded particles manufactured by the above-described method A, but is limited to the expanded particles manufactured by such method A. However, the present invention can also be carried out by using expanded particles produced by a conventionally known method.
[0056]
In the method of the present invention, a predetermined amount of polypropylene resin expanded particles prepared in advance are filled in a molding space of a mold, and then steam is supplied into the mold to heat and expand the expanded particles. After forming a molded body, the molded body is cooled and discharged from the mold.
[0057]
In the expanded particles used in the present invention, the apparent density is 10 to 500 g / L, preferably 20 to 300 g / L.
[0058]
  The apparent density (g / L) of the expanded particles is a value calculated by dividing the weight (g) of the expanded particles by the apparent volume (L) of the expanded particles. In this case, the apparent volume of the expanded particles is 60 ° C oven.soAfter drying for 24 hours, about 5 g of foamed particles left at 23 ° C. and atmospheric pressure for 24 hours are mixed with 100 cm of water at 23 ° C.³The apparent volume of the expanded particles (cm³) And converted into liter (L) units.
[0059]
In general, the expanded particles used as a raw material in the present invention can be subjected to molding as it is after aging under atmospheric pressure, but can be subjected to molding after increasing the bubble internal pressure as necessary. In this case, a conventionally known method can be employed to increase the bubble internal pressure. For example, the foamed particles may be placed in a sealed container and allowed to stand for an appropriate time in a state where pressurized air is supplied into the container, so that the pressurized air penetrates into the foamed particles.
[0060]
  As a method of filling the foamed particles into the molding space in the mold, a conventionally known method can be employed. Such methods include cracking filling methods, compression filling methods using pressurized gas, and the like. In this case, the filling rate of the expanded particles into the mold is 90 to 150%, preferably 95 to 130%. The filling rate of the expanded particles is defined by the following formula.
Filling rate = A / B x 100 (%)
A: Weight of EPP molded body (g) / bulk density of expanded particles (g / L)
B: Volume of EPP molding space (L)
  The weight of the EPP molded body is the value after 24 hours of drying in an oven at 60 ° C. for 24 hours and then left in a room at a temperature of 25 ° C. and a temperature of 55%..
[0061]
When the value is less than 90% in the filling rate, there is a possibility that a molded body with poor filling is obtained. On the other hand, when the compression ratio exceeds 150%, the flow of steam between the foamed particles is deteriorated, and there is a possibility that the inside of the molded body is poorly fused.
As described above, an inorganic gas can be put into the expanded particles as necessary to increase the internal pressure. The filling rate of the foamed particles in which an inorganic gas is put into the foamed particles and the internal pressure is applied is 90% or more and less than 105%, and the filling rate of the foamed particles that do not provide the internal pressure is 105% or more and 150% or less.
The foamed particles to which the internal pressure is applied have a filling rate within the above range, so even if the filling rate of the foamed particles is low, there are few voids between the foamed particles, and the surface of the obtained in-mold molded product should have no unevenness. Can do.
On the other hand, if the filling rate of the expanded particles not giving the internal pressure is within the above range, the surface of the EPP molded body can be made free of irregularities, and there is no step of applying the internal pressure. It is possible to eliminate the time for granting.
[0062]
  The internal pressure of the foamed particles for applying the internal pressure is 0.03 to 0.3 MPa (G), more preferably 0.05 to 0.5 MPa (G). 0.0When the pressure is less than 3 MPa (G), the secondary foaming of the foamed particles in the in-mold molding is poor, and the surface of the EPP molded body from which the voids between the foamed particles can be increased becomes uneven. On the other hand, if it exceeds 0.3 MPa (G), it takes time for cooling and the molding cycle becomes long.fearThere is. Thus, by setting the internal pressure within the above range, the molding pressure can be lowered, thereby shortening the molding cycle.
[0063]
The internal pressure P (MPa (G)) 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, the EPP particles used for molding are put in a closed container, and pressurized air is maintained in the container (usually the air pressure in the container is maintained within a range of 0.98 to 9.8 MPa (G) as a gauge pressure). The internal pressure of the EPP particles is increased by allowing the air to permeate into the EPP particles by leaving it in 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).
[0064]
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. Since the pressurized air in the expanded particles permeates through the cell membrane and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and after 48 hours, the weight has reached equilibrium. Stabilize. 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 (G)) of the expanded particles is calculated from the following equation. The internal pressure P corresponds to a gauge pressure.
[0065]
P = (W ÷ M) × R × T ÷ V
[0066]
  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 is the apparent volume of the expanded particles(L)Subtracting the volume of the base resin in the expanded particle group fromProductmeans.
[0067]
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.³From the scale when submerged in the water in the graduated cylinder, the volume Y (cm³) And is converted into liter (L) units. The apparent expansion ratio of the expanded particle group is the base resin density (g / cm³) Is the apparent density of the expanded particles (g / cm³). The apparent density of the expanded particles (g / cm³) Represents the weight of the expanded particle group (difference between U (g) and Z (g)) by volume Y (cm³).
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.³A quantity of a plurality of expanded particles is used.
[0068]
  In the present invention, when steam is supplied to a molding space filled with expanded particles and the expanded particles are heated and fused, this corresponds to 50% of a predetermined molding pressure of the expanded particles in the molded space. The pressure increase rate until reaching the pressure is 0.030 MPa / sec or more, and the pressure increase rate until reaching the predetermined molding pressure is 0.025 MPa / sec or more.ButRegulationIsThe The upper limit value of the pressure corresponding to 50% of the pressure corresponding to 50% of the predetermined molding pressure is not particularly limited, but is usually about 0.150 MPa / sec. The pressure increase rate is preferably 0.035 MPa / sec or more, more preferably 0.040 MPa / sec or more. In addition to the above-described conditions, the pressure increase rate until reaching a predetermined molding pressure is 0.025 MPa / sec or more. The upper limit is not particularly limited, but is usually about 0.150 MPa / sec. The pressure increase rate is preferably 0,030 MPa / sec or more, more preferably 0.035 MPa / sec or more, from the viewpoint that the fusion between the expanded particles and the secondary foaming of the expanded particles are more excellent and the molding cycle is shortened. . The predetermined molding pressure in the present invention is the maximum steam in the molding process.PressureSay. Further, in the present invention, the heating time in the heating process until reaching a predetermined molding pressure is 1 to 20 seconds, although it depends on the above-described elevated temperature. When the pressurization speed in the heating step is smaller than the above range, the surface of the resulting molded body is less uneven, but problems such as extremely low fusion properties occur, which is not preferable. As shown in FIG. 3, the pressure increase rate is shown in FIG. 3 where the value detected from the pressure detection lines 11 and 12 in the mold connected to the control device 13 is the vertical axis and the horizontal axis is time. Create the graph shown. From the graph of FIG. 3, Y is a predetermined molding pressure, and X is a pressure corresponding to 50% of the predetermined molding pressure. The pressure increase rate until reaching the pressure corresponding to 50% of the molding pressure is 50% of the predetermined molding pressure from the pressure (X: MPa (G)) and the pressure 0 MPa (G) corresponding to 50% of the predetermined molding pressure. It is a value calculated by the time until the pressure corresponding to. The pressure increase rate until the predetermined molding pressure is reached is a value calculated from the predetermined molding pressure (Y) and the time from the pressure 0 MPa to the predetermined molding pressure (Y: MPa (G)). The heating method includes a two-stage heating method in which the pressure is increased to a pressure corresponding to 50% of the predetermined molding pressure, and further increased to the predetermined molding pressure. With simple controlImplementationPreferred because it can be done and the heating time is shortenedYes.The above-mentioned pressure increase speedOn the wayThe steam used to increase the steam of the original pressure, increase the diameter of the pipe for supplying steam, or heat the mold in advance before filling the foam particles, and fuse the foam particles together The pressurization speed decreases due to heat.So as not toOr a combination thereof.
[0069]
In the production method of the present invention, the surface pressure of the molded product obtained by fusing the foamed particles based on a polypropylene resin having a specific melting point to have the above-mentioned pressure increase rate should be free of irregularities. it can. This mechanism is unknown, but before the foamed particles crystallize, the speed of heating the foamed polypropylene resin foam particles having a specific melting point is high because of the relationship between the speed at which the foamed particles crystallize by heating. It is considered that a foam having good secondary foaming properties can be obtained in which the foamed particles are fused to each other and the surface of the resulting molded product is free of irregularities.
[0070]
In the subsequent heating step after the heating pressure reaches a predetermined molding pressure, the heating pressure is further maintained for 5 seconds or more, preferably 7 seconds or more within a pressure range obtained by subtracting 0.020 MPa from the molding pressure. preferable. The upper limit of the time is not particularly limited, but is usually about 60 seconds. By maintaining the molding pressure, the secondary foaming force of the foamed particles is further increased, the gaps at the interface of the foamed particles are reduced, and the surface property of the molded body is improved.
[0071]
  As a method of reaching a predetermined molding pressure and holding it at that molding pressure, the steam valve can be opened by on / off control.CloseFor example, there are a method of adjusting the pressure in the mold by putting saturated steam in the mold, a method of adjusting the opening degree of the saturated steam by constantly putting the saturated steam in the mold.
[0072]
In the present invention, it is preferable to preheat the mold before filling the expanded particles in terms of improving the steam pressurization speed when the expanded particles are fused. Also, the foam particles are filled into the molding space, and prior to the supply of steam into the molding space, for the purpose of improving the mutual fusion of the foam particles, the mutual fusion of the foam particles does not proceed, It is preferable to add steam for a short time so as not to increase the pressure, to warm the mold, and to discharge the air remaining in the molding space. In this case, it is adjusted by the size of the mold and the thickness of the molded body, but is preferably in the range of 1 to 10 seconds.
[0073]
After completion of the heating step, the mold pressure is released, the molded body is cooled, and discharged from the mold. In this case, various known methods can be used as the method for cooling the molded body. However, in consideration of the molding cycle, it is preferable to use a method using water that can shorten the cooling time or a method using vacuum together.
[0074]
As the molding apparatus used for carrying out the method of the present invention, various conventionally known molding apparatuses can be used and are not particularly limited. As the continuous molding method, for example, a molding method described in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888 and the like can be employed for production. In the continuous molding method, the foamed particles whose internal pressure is increased as necessary are continuously supplied between belts that move continuously along the top and bottom of the passage, and a saturated steam supply region (heating The foamed particles are expanded and fused when passing through the region), and then cooled by passing through the cooling region, and then the obtained molded product is taken out from the passage and sequentially cut to an appropriate length. Thus, an EPP molded body is manufactured.
[0075]
Further, a reinforcing material and / or 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, in the EPP molded body of the present invention, the insert material can be combined and integrated such 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.
[0076]
The EPP molded body produced according to the present invention 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. Is most preferred. The smaller the open cell ratio, the better the mechanical strength.
[0077]
【Example】
Next, the present invention will be described in further detail with reference to examples.
[0078]
(Method for producing expanded particles)
  ImplementationExamples 1-5 and 7, 8 Comparative Examples 1 and 3
  After adding 0.05 parts by weight of zinc borate powder (cell regulator) per 100 parts by weight of a polypropylene resin (propylene homopolymer) selected from Table 1, the mixture is melt-kneaded in the extruder, and then stranded from the extruder. The strand is immediately put into water adjusted to 25 ° C. and taken up while quenching. After sufficiently cooled, the strand is pulled up from the water and cut into a length / diameter ratio of about 1.0. Thus, resin particles having an average weight per particle of 2 mg were obtained. Next, in a 400 liter autoclave, 100 kg of the above resin particles, 120 kg of ion exchange water, 0.002 kg of sodium dodecylbenzenesulfonate (surfactant) and 0.4 parts by weight of kaolin (dispersant), powdered aluminum sulfate (dispersion aid) 0.013 kg, 0.32 kg of bis (4-t-butylcyclohexyl) peroxydicarbonate (organic peroxide) was charged, and the temperature was raised to 90 ° C. with stirring (average heating rate of 5 ° C./min) And kept at that temperature for 10 minutes. Next, 100 kg of ion-exchanged water and carbon dioxide gas (foaming agent) were injected so that the equilibrium pressure was 0.49 MP (G), and then the temperature was raised to 5 ° C. lower than the foaming temperature in Table 1 with stirring. Thereafter, an average temperature increase rate of 0.16 ° C./min and a temperature 1 ° C. lower than the foaming temperatureMaThe temperature was raised. Thereafter, carbon dioxide gas (foaming agent) was injected so as to be the pressure shown in Table 1, and the temperature was raised to the foaming temperature at a rate of temperature rise of 0.29 ° C./min. Next, one end of the autoclave was opened, and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles. The release was performed while supplying carbon dioxide gas into the autoclave so that the pressure in the autoclave during the release of the resin particles from the autoclave was maintained at the pressure in the autoclave immediately before the release. After washing the obtained foamed particles with water and centrifuging them, leaving them under atmospheric pressure for 24 hours and curing them, the high temperature peak heat of the foam particles, the high temperature peak heat of the surface layer part and the internal foam layer and the melting points, MFR of base resin, of foamed particlesBulkDensity and the like were measured. The results are shown in Table 1.
[0079]
Example 6 and Comparative Example 2
(Method for producing expanded particles)
  Resin particles were obtained in the same manner as in Example 1. Next, in a 400 liter autoclave, 100 kg of the above resin, 220 kg of ion exchange water, 0.002 kg of sodium dodecylbenzenesulfonate (surfactant), 0.3 kg of kaolin (dispersing agent), 0.01 kg of powdered aluminum sulfate (dispersing aid) Then, carbon dioxide gas (foaming agent) was injected so that the equilibrium pressure was 0.49 MPa (G), and then the temperature was raised to 5 ° C. lower than the foaming temperature in Table 1 with stirring. (Average temperature increase temperature 5 ° C./min) Thereafter, the temperature increase rate was 0.16 ° C./min, and the temperature was further increased to a temperature 1 ° C. lower than the foaming temperature. Thereafter, carbon dioxide gas (foaming agent) was injected so as to be the pressure shown in Table 1, and the temperature was raised to the foaming temperature at a rate of temperature rise of 0.29 ° C./min. Next, one end of the autoclave was opened, and the contents of the autoclave were discharged into a space 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. After washing the obtained foamed particles with water and centrifuging them, leaving them to stand at atmospheric pressure for 24 hours and curing them, the high temperature peak heat quantity of the foamed particles,The bulk density,High temperature peak heat of surface layer part and internal foam layerAmountIt was measured. The results are shown in Table 1.
[0080]
[Table 1]

[0081]
Examples 1, 2, 5, 8
(Molding method)
The foamed particles shown in Table 1 were molded using the molding apparatus shown in FIG. The mold consisting of male mold 1 and female mold 2 having a molding space portion of 700 mm × 200 mm × 50 mm is closed and clamped, drain valves 8 and 9 are closed, Cv value 18 indicating the flow characteristics of the valve, effective sectional area 320mm²Steam was adjusted to 0.39 MPa (G) into the mold through the steam valves 6 and 7, and preheating was performed for 5 seconds. Next, after the mold is opened once, it is closed again and filled with the foamed particles so that the filling rate shown in Table 2 is obtained. After the mold is clamped, the drain valves 8 and 9 are opened and the steam valves 6 and 7 are used. Steam was introduced into the mold to exhaust the air between the foamed particles in the molding space. Next, the drain valve is closed, and the steam adjusted to 0.8 MPa (G) until the pressure in the pressure detection line 12 reaches 0.04 MPa (G) lower than the predetermined molding pressure in Table 2 than the steam valve 7. (One heating), then steam was introduced until the pressure in the pressure detection line 11 from the steam valve 6 reached 0.02 MPa (G) lower than the predetermined molding pressure in Table 2 (reverse one heating) Thereafter, steam was introduced using the steam valves 6 and 7 so that the predetermined molding pressure shown in Table 2 was obtained, and holding and heating was performed at the predetermined molding pressure shown in Table 2 (main heating). After molding, after cooling with water until the surface pressure of the molded body in the molding space reaches 0.059 MPa (G), the molded body is taken out from the molding space, cured at 60 ° C. for 24 hours, and then cooled to room temperature and molded. Got the body.
Table 2 shows the molding conditions and the properties of the molded body.
[0082]
Examples 3, 4 and 6
(Molding method)
Cv value 28 shown in FIG. 4 and effective sectional area 500 mm without preheating²Molding was performed in the same manner as in Example 1 except that the flow rate was increased using the steam valves 6 and 7.
[0083]
Example 7
Pipes passing through the steam valves 6 and 7 shown in FIG. 4 have an inner diameter of 80 mm, the steam valves 6 and 7 are replaced with those having a Cv value of 60, and the steam flow rate is increased to perform molding. Molding was performed using the expanded particles shown in Table 1. The mold composed of the male mold 1 and the female mold 2 having a molding space of 400 mm × 300 mm × 80 mm is closed and clamped, the drain valves 8 and 9 are closed, and the steam valves 6 and 7 are inserted into the mold by 0.39 MPa. Steam adjusted to (G) was introduced and preheating was performed for 5 seconds. Next, after the mold is opened once, it is closed again and filled with the foamed particles so that the filling rate shown in Table 2 is obtained. After the mold is clamped, the drain valves 8 and 9 are opened and the steam valves 6 and 7 are used. Steam was introduced into the mold to exhaust the air in the mold. Next, the drain valve 8 is closed, steam that has been adjusted to a pressure 0.04 MPa lower than the predetermined molding pressure in Table 2 from the steam valve 7 is introduced for 2 seconds, then the drain valve 8 is opened and the drain valve 9 is closed, After introducing steam adjusted to a pressure 0.04 MPa lower than the predetermined molding pressure of Table 2 from the steam valve 6 for 2 seconds, the steam valve 6 or 7 was used to adjust the predetermined molding pressure of Table 2 Steam was introduced and heated for 5 seconds. After molding, the molded body in the mold is cooled with water until the surface pressure becomes 0.059 MPa (G), and then the molded body is taken out of the mold, cured at 60 ° C. for 24 hours, and then cooled to room temperature to obtain a molded body. It was.
[0084]
Comparative Examples 1-3
(Molding method)
A molded body was obtained in the same manner as in Example 1 except that pre-heating before filling was not performed and the steam used for one-side heating and reverse one-side heating was adjusted to 0.78 MPa (G).
[0085]
The filling rate in Table 2, the pressure increase rate until reaching a pressure corresponding to 50% of the predetermined molding pressure (50% pressure increase rate), and the pressure increase rate until reaching the predetermined molding pressure are as described above. Further, the fusion rate, appearance, and compressive strength were evaluated as follows.
[0086]
(Fusion rate)
The fusion rate is determined by a test in which the molded body obtained in the example and the comparative example is cut by about 10 mm in the thickness direction of the molded body with a cutter knife, and then the molded body is broken by hand from the cut portion. Is the ratio (b / n) of the number (b) of the foamed particles whose material is destroyed to the number (n) of the expanded particles present in FIG.
[0087]
(appearance)
The appearance is determined by visually observing the surface of the molded body and determining the amount of gaps between particles according to the following criteria.
A: Almost no gap between particles.
○: Some gaps are observed between particles.
X: Many gaps are observed between particles.
[0088]
(Compressive strength)
Compressive strength refers to a JIS Z 0234-1976 A method using a test piece obtained by cutting a molded body so as to have a length of 50 mm, a width of 50 mm, and a thickness of 25 mm. In accordance with the above, a compression test is performed until the strain reaches 55% at a test piece temperature of 23 ° C. and a load speed of 10 mm / min. The stress at the time of 50% strain is read from the obtained stress-strain diagram, did.
When the insoluble matter described above was measured using the expanded particles of Examples and Comparative Examples, both were 0% by weight or less.
[Table 2]

[0089]
【The invention's effect】
According to the method of the present invention, it is possible to obtain a molded article having a high fusion property between the expanded particles and less surface irregularities. Furthermore, the time to the predetermined molding pressure can be shortened and the cooling time can be shortened. As a result, the molding cycle can be shortened and the production efficiency can be increased.
By filling polypropylene resin expanded particles having a specific tensile elastic modulus and a polypropylene resin as a base resin, a foamed molded article having few internal voids and surface irregularities and excellent in compressive strength can be obtained.
After reaching a predetermined molding pressure, a foamed molded article with less surface irregularities can be obtained by holding the molding pressure for 5 seconds or more.
By using specific foamed particles, it is durable against a rapid pressure rise, and the molding cycle can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a first DSC curve chart of polypropylene resin expanded particles.
FIG. 2 is a diagram showing an example of a second DSC curve chart of polypropylene resin particles.
FIG. 3 is a diagram illustrating an example of a relationship between a molding pressure and a molding cycle.
FIG. 4 is a diagram showing an explanation of an apparatus used in the method for producing a molded body of the present invention.
[Explanation of symbols]
1 Male
2 female
3 Molding space
4, 5 Steam valve (large flow)
6, 7 Steam valve (for pressure regulation)
8,9 Drain valve
10 Measurement line on the surface of foam
11, 12 Pressure detection line
13 Control device

Claims (3)

  In the method for producing a polypropylene resin expanded particle molded body, a polypropylene resin expanded particle having a base resin of a polypropylene resin having a tensile elastic modulus of 1200 MPa or more is filled into a molding space, and the molding space is filled with the molded resin. When the steam is supplied and the foamed particles are heated and fused, the pressure increase rate until reaching a pressure corresponding to 50% of the predetermined molding pressure in the molding space is 0.030 MPa / sec or more, And the pressurization speed | velocity | rate until it reaches this predetermined shaping | molding pressure is 0.025 Mpa / sec or more, The manufacturing method of the polypropylene resin foamed particle molded object characterized by the above-mentioned.   When steam is supplied into the molding space and the foamed particles are heated and fused, after reaching a predetermined molding pressure, within a range of pressure obtained by subtracting 0.020 MPa from the molding pressure. The method for producing a molded product of polypropylene resin particles according to claim 1, wherein holding is performed for 5 seconds or more. The polypropylene resin expanded particles are substantially non-crosslinked expanded particles, and the endothermic curve is higher than the intrinsic endothermic curve peak derived from the heat of fusion of the polypropylene resin in the DSC curve by differential scanning calorimetry. 3. The method for producing a polypropylene resin expanded particle molded article according to claim 1 or 2, wherein the expanded particle has a peak .

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