JP4629313B2 - Method for producing polypropylene resin in-mold foam molded body and in-mold foam molded body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polypropylene resin in-mold foam molded product having different characteristic regions and the in-mold foam molded product.
[0002]
[Prior art]
Polypropylene resin-in-mold foam moldings can add 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 recycling. , It is used in a wide range of industrial fields such as packaging materials and building materials.
In particular, the so-called bead-type in-mold foam molded article, in which pre-foamed particles are prepared from a polypropylene resin, filled in a mold that can be opened and closed, and heat-sealed with steam, has a superior buffering property and an improved molding property. Due to its formality, it is widely used as an impact absorbing material for automobile bumper cores, door pads and the like.
In recent years, a lighter and more rigid material is required for this shock absorber from the viewpoint of stricter collision safety standards and improved fuel efficiency.
[0003]
As a product that meets this demand, the desired parts that require strength are made up of high-density in-mold foam moldings, and the parts that do not need strength are made up of lower-density in-mold foam moldings. However, as a whole, there are different density molded products for reducing weight, so-called dual density molded products. In addition, there is a demand for higher performance in the field of shock absorbers for automobiles in consideration of offset collision and pedestrian protection, but dual density molded products are products that can meet these demands.
As such a dual density molded product, for example, a mold having an interior divided into three sections is used to form a relatively high-density molded body on both sides, and a central portion sandwiched therebetween is relatively low. There are some which consist of a compact of density. When a dual density molded article having such a configuration is obtained, the first compartment and the third compartment corresponding to both sides are filled with relatively high-density foam particles, and the second compartment corresponding to the center portion. The foam particles in the mold are filled with relatively low density, and the foam particles in the mold are heated to integrate the foam particles in each section and the foam particles in each section. The taking-out method, the so-called integral simultaneous molding method, is preferable from the viewpoint of cost. These integral simultaneous molding methods are described in detail in Patent Documents 1 to 4, for example.
[0004]
However, in-mold molded bodies from expanded particles usually have a larger (expanded) shape than the shape of the mold space if cooling immediately after heating is insufficient during molding, and conversely, if the cooling is excessive, the mold space This is smaller than the shape of the material (shrinks so much that sufficient recovery cannot be expected). As described above, the degree of expansion and the degree of contraction of the in-mold molded product differ depending on the degree of cooling. Further, the expansion and contraction tend to be different between the case where the apparent density of the obtained molded body is large and the case where it is small. Specifically, when the degree of cooling is the same, the low-density molded body part tends to turn earlier from expansion to contraction. Usually, since the expanded molded body is often disliked compared to the shape of the mold space, cooling is performed so that the high-density molded body portion does not expand. As a result, the relatively low-density molded body portion is in a greatly contracted state, and it has conventionally been difficult to obtain a high-quality product.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-334501
[Patent Document 2]
JP 2001-150471 A
[Patent Document 3]
Japanese Utility Model Publication No. 62-22352
[Patent Document 4]
US Pat. No. 5,164,257
[0006]
[Problems to be solved by the invention]
  The present invention is a high-quality polypropylene resin in-mold foam molding having parts having mutually different characteristics.BodyThe issue is to provide.
[0007]
[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 the present invention, the following foam-in-mold molding in a polypropylene resin moldBody isProvided.
(1) An integral molded body having a structure in which a plurality of unit molded bodies made of an in-mold expanded molded body of polypropylene resin expanded particles are heat-sealed,
(I) The two adjacent unit molded bodies have different characteristics, and one unit molded body of the two adjacent unit molded bodies is a high-density unit molded body having an apparent density of 30 to 450 g / L. The other unit molded body is a low density unit molded body having an apparent density of 15 to 90 g / L and having an apparent density lower than the apparent density of the high density unit molded body,
(Ii)Of the high-density unit molded body and the low-density unit molded body,Expanded particles constituting at least one unit molded body (F),Polypropylene resin or polypropylene resin composition having a tensile modulus of 1200 MPa or moreThe foamed particles have an endothermic curve peak calorific value (ΔH _s ) And the calorific value (ΔH) of the endothermic curve peak existing on the high temperature side of the inner foam layer of the foam particles. _i ) Is ΔH _s <ΔH _i X0.86 is satisfiedThat
(Iii) The unit molded body(F)Indicates that there is an endothermic curve peak on the higher temperature side than the intrinsic endothermic curve peak derived from the heat of fusion in the DSC curve by differential scanning calorimetry,
(Iv)TheIn the unit molded body (F), the apparent density D2 (g / L) and the heat of fusion E2 (J / g) of the peak endothermic curve peak of the polypropylene resin foam constituting the unit molded body (F) And satisfying the following expressions (3) and (4):
      Formula (3):25−0.020 × D2 ≦ E2 ≦55-0.100 × D2
      Formula (4):15≦ D2 ≦450
A foamed molded product in a polypropylene resin mold characterized by
(2The density of the high-density unit molded body is 1.2 to 25 times the density of the low-density unit molded body.(1)In polypropylene resin mold as described inFoamMolded body.
(3) The in-mold foam molded article according to (1) or (2), wherein the in-mold foam molded article is an impact absorbing material.
(4The shock absorbing material is a bumper core material for automobiles.(3)2. A polypropylene resin-in-mold foam-molded article described in 1.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
  Polypropylene resin in-mold foam molded product of the present invention (hereinafter referred to as “EPP molded product”), "In-mold foam molding" or "In-mold molding"Is composed of a plurality of unit molded bodies, and the two adjacent unit molded bodies have a structure that is heat-sealed with each other. The polypropylene resin or polypropylene resin composition constituting the polypropylene resin expanded particles used for forming the unit molded body contains a polypropylene homopolymer or a propylene component of 70 mol% or more (preferably a propylene component). Is a copolymer of propylene and another comonomer, or a mixture of two or more selected from these resins.
[0009]
Examples of the copolymer of propylene and other comonomers containing a propylene component of 70 mol% or more include, for example, ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-butene random copolymer, ethylene-propylene-butene random copolymer, etc. Is exemplified.
[0010]
In the present invention, the polypropylene resin composition may contain other synthetic resin and / or elastomer other than the polypropylene resin within a range that does not impair the intended effect of the present invention. The addition amount of other synthetic resins or / and elastomers other than the polypropylene resin is at most 60 parts by weight per 100 parts by weight of the polypropylene resin, but is preferably at most 35 parts by weight. Even more preferably 20 parts by weight, even more preferably at most 10 parts by weight, most preferably at most 5 parts by weight.
[0011]
Synthetic resins other than the polypropylene resin include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene- Examples thereof include ethylene resins such as acrylic acid copolymers and ethylene-methacrylic acid copolymers, and styrene resins such as polystyrene and styrene-maleic anhydride copolymers.
[0012]
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.
[0013]
In the present invention, the polypropylene resin composition can contain various additives 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, more preferably 5 parts by weight or less per 100 parts by weight of the base resin. These additives are usually used in the minimum necessary amount. 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 made to contain in this resin particle by adding and knead | mixing in the polypropylene-type resin or polypropylene-type resin composition fuse | melted by (1).
[0014]
In the method of the present invention, a foamed particle that divides the mold into two or more compartments and fills at least one compartment is a polypropylene resin or a polypropylene resin composition having a tensile elastic modulus of 1200 MPa or more (hereinafter referred to as “the base resin”). There is a thing "). When the tensile modulus of elasticity of the base resin is less than 1200 MPa, “the expansion of the final molded body does not occur even if the molded body is cooled immediately after heating at the time of molding, which will be described later. The effect of the present invention cannot be achieved because the effect of “there is no shrinkage or almost no shrinkage even when the amount is excessive” cannot be sufficiently obtained.
According to the production method of the present invention, the expanded particles filled in at least one of the compartments are made of the base resin, and the relationship between the apparent density D1 of the expanded particles described later and the high temperature peak heat quantity E1 of the expanded particles is described later. Since the foamed particles satisfy the formulas (1) and (2) (hereinafter may be referred to as specific foamed particles), the final product is finally cooled even if the molded body is cooled immediately after the heating at the time of molding. Expansion does not occur in such compacts, and even if cooling is excessive, there is little or no shrinkage. Therefore, even if it is integrally molded so as to include a unit molded body part manufactured with specific foamed particles and a unit molded body part manufactured with expanded particles other than the specific expanded particles, the expanded foam other than the specific expanded particles If the cooling at the time of molding is adjusted so that there is no convex bulge on the outside of the unit molded body part made of particles or concave shrinkage (shrinkage) on the inside, the whole will protrude outward from the molded body. Therefore, an in-mold molded body can be easily obtained with less swelling and shrinkage (shrinkage). Furthermore, when all the unit molded products are manufactured from this specific foamed particle, it is possible to more easily obtain an in-mold molded product with less swelling on the outer side of the molded product and less sink marks on the inner side. It is done. In addition, since a molded body using specific foamed particles has high rigidity such as compressive strength, an in-mold molded body excellent in light weight can be easily obtained.
[0015]
In order to make the tensile modulus of elasticity of the base resin to be 1200 MPa or more, as a polypropylene resin to be used, a polypropylene homopolymer or a copolymer of propylene and another comonomer having a small amount of other comonomer components should be used. That's fine.
[0016]
The tensile elastic modulus is preferably 1250 MPa or more and more preferably 1300 MPa or more for further enhancing the effect of the present invention. The upper limit is not particularly limited, but is about 2500 MPa.
[0017]
The above-described tensile elastic modulus is a value obtained by measuring the base resin according to JIS K7161 (1994) under the following conditions.
Test piece: Test piece 1A type described in JIS K 7162 (1994) (direct molding by injection molding)
・ Test speed 1mm / min
[0018]
In addition, in the case where the base resin is a polypropylene resin composition to which other synthetic resins other than the above-described polypropylene resin, elastomer, various additives, and the like are added, depending on the type and amount of these additives, There is a possibility that the tensile elastic modulus of the base resin is lowered. In the present invention, in order not to impair the initial effects of the present invention, preferably, the tensile modulus of elasticity of the base resin (the same measurement method as that of the base resin) does not fall below 1200 MPa. Is added so that it does not fall below 1250 MPa, most preferably below 1300 MPa.
[0019]
The melting point of the base resin is 145 ° C. or higher in order to increase the heat resistance of the final in-mold foam molded product (EPP molded product) and / or to increase the compressive strength. Is preferably 155 ° C. or higher, more preferably 160 ° C. or higher. The upper limit of the melting point is usually about 170 ° C.
[0020]
In order to increase the compressive strength of the final EPP molded product, the tensile yield strength of the base resin is preferably 31 MPa or more, more preferably 32 MPa or more. The upper limit of the tensile yield strength is not particularly specified, but is usually 45 MPa at most.
In addition, in order to prevent bubbles from being broken during the formation of bubbles during the production of the expanded particles, and further to prevent bubbles from being broken during the heating during in-mold molding, The tensile elongation at break is preferably 20% or more, more preferably 100% or more, and further preferably 200 to 1000%.
The tensile yield strength and tensile elongation at break are both based on the measurement method described in JIS K 6758 (1981).
[0021]
Further, the base resin has a molecular weight distribution (Mw / Mn) of 4.4 or more in order to lower the molding steam temperature at the time of in-mold molding even if it is expanded particles made of the base resin having a high melting point. Although it is preferable, it is more preferable that it is 4.5-10. This molecular weight distribution is a value calculated from the weight average molecular weight Mw and number average molecular weight Mn in terms of polystyrene measured by the GPC method using the following apparatus and conditions.
<GPC measurement device>
Device: WATERS 150C
Column: TOSO GMHHR-H (S) HT
Detector: RI detector for liquid chromatogram
<Measurement condition>
Solvent: 1,2,4-trichlorobenzene
Measurement temperature: 145 ° C
Flow rate: 1.0 ml / min
Sample concentration: 2.2 mg / ml
Injection volume: 160 microliters
Calibration curve: Universal Calibration
Analysis program: HT-GPC (Ver.1.0)
[0022]
The base resin preferably has a melt flow rate (JIS K 6758 (1981)) abbreviated as MFR of 1 g / 10 min to 100 g / 10 min. 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 min, the obtained in-mold product may be brittle. From such a viewpoint, the MFR of the base resin is more preferably 10 g / 10 min or more and 70 g / 10 min or less.
[0023]
The polypropylene-based resin having the above-described characteristics used in the present invention is one of those sold as a polypropylene resin and can be easily obtained on the market. In addition, the polypropylene resin having the above-described characteristics used in the present invention can be produced by various methods. In particular, a slurry polymerization process or a bulk polymerization process is employed, or a slurry polymerization process or a bulk polymerization process is included. Adopting a multistage polymerization process (for example, a multistage polymerization process of gas phase polymerization and bulk polymerization), an isotactic index (a ratio of insoluble components after boiling normal heptane extraction) is 85% by weight or more,¹³Manufactured so that the mmmm pentad% by C-NMR analysis is 85 to 97.5%, the weight average molecular weight is 200,000 or more (preferably 200,000 to 550000), and the number average molecular weight is 20,000 or more (preferably 20000 to 53000). (Including post-treatment such as the removal of the minute), and in this case, the (co) polymerization conditions are further selected so that the propylene component content in the resulting polypropylene resin is 99% by weight. Its manufacture becomes possible easily. In addition, a polypropylene resin obtained through a slurry polymerization process or a bulk polymerization process, or a multistage polymerization process including a slurry polymerization process or a bulk polymerization process, is more suitable than a polypropylene resin obtained through another polymerization process. It is preferably used in the invention. Examples of usable polymerization catalysts include homogeneous catalysts such as metallocene catalysts or heterogeneous catalysts such as Ziegler-Natta type catalysts, but slurry polymerization processes or bulk polymerization processes, or slurry polymerization processes or bulk polymerization processes may be used. For multi-stage polymerization processes involving, Ziegler-Natta type catalysts are preferred.
[0024]
In addition, as this resin particle, what was obtained by rapidly cooling the strand immediately after extrusion when cut | disconnecting the strand which melt | dissolved this base resin resin in the extruder, and cut | disconnecting the extruded strand is preferable. . When the resin particles are so cooled, the surface modification described later can be performed efficiently. 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.
[0025]
Expanded particles made of the present resin particles (hereinafter referred to as “present expanded particles”) used as a raw material for the in-mold expanded molded article of the present invention are produced by impregnating the resin particles with a foaming agent and then expanding the particles into particles. Is done.
[0026]
The foamed particles used in the present invention are preferably foamed particles subjected to surface modification described below. The expanded particles subjected to the surface modification can be molded in the mold at a lower temperature than the expanded particles not subjected to the surface modification.
[0027]
The expanded particles having a modified surface capable of being molded at low temperature are obtained by dispersing the resin particles in a dispersion medium in which an organic peroxide is present, and converting the obtained dispersion (hereinafter, also referred to as a dispersion) into the resin particles. The surface of the resin particles is modified by decomposing the organic peroxide by maintaining the temperature at a temperature lower than the melting point of the base resin and maintaining the temperature at which the organic peroxide is substantially decomposed. It can be produced by obtaining modified particles (hereinafter sometimes referred to as “surface modified particles”) and then foaming the surface modified particles into particles.
The foamed particles having the modified surface thus obtained are excellent in heat-fusibility and can be fused between the foamed particles with low-temperature steam.
[0028]
The dispersion medium used in the production of the surface-modified particles is generally an aqueous medium, preferably water, and more preferably ion-exchanged water, but is not limited to water. In addition, 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.
[0029]
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 is 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, per 100 parts by weight of the resin particles. It is necessary to add 1-3 parts by weight in the dispersion medium.
[0030]
In the dispersion composed of the organic peroxide, the present resin particles, and the dispersion medium, if the weight ratio of the present resin particles / dispersion medium is too large, uniform surface modification may not be performed on the present resin particles. If so, some of the surface modified particles are excessively modified, which causes many of the modified resin particles to be fused in the sealed container during the next foaming process. Then, it becomes a large lump and may not be able to be discharged out of the sealed container. 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, there is a possibility that effective low-temperature formability cannot be imparted to the resulting foamed particles unless the amount of organic peroxide used in the resin particles is increased. 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.
[0031]
The organic peroxide is substantially decomposed at a temperature lower than the melting point of the base resin. 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. Therefore, it is not preferable, and in some cases, it cannot be substantially decomposed at a temperature lower than the melting point of the base resin, which 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 inside, in some cases, there is a possibility that only foamed particles that cannot be used for molding may be obtained, and even if molding can be obtained, it is finally obtained. There exists a possibility that the mechanical physical property of an EPP molded object may fall large.
[0032]
Considering the above, the organic peroxide used preferably has a one-hour half-life temperature of 20 ° C. or more lower than the Vicat softening point of the base resin, and the Vicat softening point of the base resin. It is more preferable that the temperature is 30 ° C. or higher. 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 an intermediate glass transition temperature obtained by heat flux DSC in accordance with JIS K 7121-1987 (for the condition adjustment of the test piece at this time, “after performing a certain heat treatment, the glass transition temperature ”When measuring”). 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 amount of active oxygen is half of the original in one minute when the organic oxide is decomposed at a constant temperature) ± It is particularly preferable to keep the temperature in the temperature range of 30 ° C. for 10 minutes or more and substantially decompose. 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 the 1 minute half-life temperature is maintained within a range of ± 30 ° C. for 10 minutes or more, it becomes easy to substantially decompose the organic peroxide. 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 in the range of 1 minute half-life temperature ± 5 ° C. is most preferable.
[0033]
In addition, substantially decomposing means decomposing until the active oxygen content of the used peroxide is 50% or less of the original, but decomposing until the active oxygen content is 30% or less of the initial. It is preferable to decompose until the amount of active oxygen becomes 20% or less of the initial amount, and further preferable to decompose until the amount of active oxygen becomes 5% or less of the initial amount.
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 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.
[0034]
It is preferable that the resin particles, the surface modified particles, the expanded particles having a modified surface that can be molded at low temperature, and the EPP molded product obtained therefrom are substantially non-crosslinked. In the production of the surface modified particles, the crosslinking does not proceed substantially because a crosslinking aid or the like is not used in combination. The term “substantially non-crosslinked” is defined as follows. That is, each of the base resin, the resin particles, the surface modified particles, the expanded particles, and the EPP molded body is used as a sample (use 1 g of sample per 100 g of xylene), and this is 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 Z 8801 (1966), which defines a standard 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.
[0035]
The expanded particles having a low temperature moldable modified surface used in the present invention are surface modified particles under heating and heating conditions while dispersing the surface modified particles in a dispersion medium in a closed container in the presence of a blowing agent. By discharging the resin particles or surface-modified particles and the dispersion medium to a low-pressure zone at a temperature at which foamed particles are generated when the pressure is released after the step of impregnating with the foaming agent (foaming agent impregnation step). It is preferably produced by a foaming method (hereinafter referred to as “dispersion medium releasing foaming method”) comprising a step of obtaining foamed particles (resin particle foaming step).
[0036]
The surface modification step for forming the surface modified particles and the foaming step for obtaining expanded particles from the surface modified particles (foaming agent impregnation step + resin particle foaming step) are performed at different times in different devices. The organic peroxide having an appropriate decomposition temperature may be added to a dispersion medium in a sealed container in a predetermined amount to perform the surface modification step, followed by surface modification particles in the same container. It is also possible to obtain expanded particles from the surface-modified particles by impregnating with a foaming agent and performing a foaming step by a normal dispersion medium releasing foaming method. In the foaming step, the weight ratio of the surface modified particles / the dispersion medium is 0.5 or less, preferably 0.5 to 0.1, from the viewpoint of preventing fusion of the surface modified particles in the sealed container. It is preferable to do. In addition, when the weight ratio of the present resin particles / the dispersion medium in the surface modification step is 0.6 to 1.3, and the surface modification step and the foaming step are performed in the same container In order to make the weight ratio of the surface modified particles / the dispersion medium in the foaming process 0.5 or less, the dispersion medium may be added to the container after the surface modification process.
[0037]
Hundreds of alcohols having a molecular weight of 50 or more produced by the decomposition of the peroxide are contained in the surface-modified particles, the expanded particles having a modified surface that can be molded at a low temperature, and the EPP molded body thereof. About ppm to several thousand 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 particle. 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.
[0038]
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 do not fuse with 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.
[0039]
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.
[0040]
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 present resin particles or surface modified particles.
[0041]
Examples of the foaming agent used for producing the expanded particles include aliphatic hydrocarbons such as propane, butane, hexane, and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, 1 , 2-difluoroethane, 1,2,2,2-tetrafluoroethane, organic physical foaming agents such as halogenated hydrocarbons such as methyl chloride, ethyl chloride, methylene chloride, nitrogen, oxygen, air, carbon dioxide, water Such so-called inorganic 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.
[0042]
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.
[0043]
The expanded particles for producing at least one unit molded body for manufacturing the EPP molded body of the present invention are composed of the base resin. In addition, the expanded particle is a peak of an intrinsic endothermic curve peak (intrinsic peak) derived from the heat of fusion of the base resin in the DSC curve by differential scanning calorimetry (thermal flux differential scanning calorimetry, hereinafter the same) of the expanded particle. Further, the relationship between the apparent density D1 of the foamed particles and the heat quantity E1 of the high temperature peak of the foamed particles is expressed by the following formula (1), ( It satisfies 2).
Formula (1): 20−0.014 × D1 ≦ E1 ≦ 65−0.072 × D1
Formula (2): 10 ≦ D1 ≦ 700
In addition, in Formula (1), D1 is a numerical value of the apparent density of the expanded particles expressed in g / L units, and E1 is the high temperature peak calorific value of the expanded particles used for molding expressed in J / g units. It is a numerical value. If D1 is less than 10 g / L, the proportion of open cells increases, which may make molding difficult. Moreover, when D1 exceeds 700 g / L, there exists a possibility that it may become inferior to the foaming power which fills the space | gap between foaming particles at the time of shaping | molding. On the other hand, when E1 is less than [20−0.014 × D1], shrinkage of the obtained molded product tends to increase, and the object of the present invention cannot be sufficiently achieved. Moreover, when E1 exceeds [65-0.072 × D1], there is a possibility that the foaming power for filling the voids between the foamed particles during molding may be inferior. An EPP molded body having a unit molded body composed of such specific foamed particles becomes a final molded body even when the portion of the unit molded body is cooled for a short time immediately after heating during molding. Since expansion does not occur, and even if cooling is excessive, there is no contraction or almost no contraction. Therefore, it is possible to obtain a high-quality EPP molded product in which two or more unit molded products having different characteristics are adjacently integrated. . The E1 is preferably 10 to 60%, more preferably 20 to 50%, based on the total amount of heat of E1 and the intrinsic peak. In addition, the heat quantity E1 of the high temperature peak and the heat quantity of the intrinsic peak referred to in this specification both mean an endothermic amount, and the numerical value is expressed as an absolute value.
In addition, when the base resin is the same, the expanded particles of the polypropylene-based resin tend to have a larger shrinkage of the molded body obtained as the expansion ratio becomes higher. This is due to the fact that the amount of resin per unit volume is smaller than that of low expansion ratio. Further, the shrinkage of the obtained molded product tends to increase as the high temperature peak heat quantity (E1) of the expanded particles decreases. On the contrary, the shrinkage of the obtained molded product tends to decrease as the high temperature peak heat quantity of the expanded particles increases. However, as the high-temperature peak heat quantity of the expanded particles increases, the expanded particles tend to be less likely to be melted by heating at the time of molding (the expanded particles tend to be less likely to be fused during heating at the time of molding), and the expanded force of the expanded particles tends to be inferior. It is based on the above viewpoint that E1 of said Formula (1) is expressed with the relational expression of the apparent density of foamed particle. The above formula (1) is experimentally determined under those viewpoints and under the relationship with the tensile elastic modulus of the base resin. Further, the above formula (2) is preferably 20 ≦ D1 ≦ 200, more preferably 30 ≦ D1 ≦ 150, in order to make the obtained in-mold molded body lighter and more rigid.
[0044]
The E1 of the expanded particles is obtained when the expanded particles 2 to 10 mg are heated at a rate of 10 ° C./min from room temperature (10 to 40 ° C.) to 220 ° C. with a differential scanning calorimeter in a nitrogen atmosphere. The amount of heat of the endothermic curve peak (high temperature peak) b at which the apex appears at a higher temperature than the temperature at which the apex of the intrinsic endothermic curve peak (inherent peak) a derived from the heat of fusion of the base resin found in the first DSC curve (Endothermic amount) corresponds to the area of the high temperature peak b, and can be specifically 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 expanded particles from the beginning 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 calorific value of foamed particles” without any notice, it means the calorific value of the high temperature peak obtained by the above measurement, that is, E1, which will be described later. In Eq. (3), the amount of heat at the high temperature peak related to the surface layer portion of the expanded particles and the amount of heat at the high temperature peak related to the internal expanded layer are distinguished.
[0045]
The 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. from 220 ° C. to 10 ° C./min (40 To 50 ° C.), and is not recognized in the second DSC curve obtained when the temperature is raised again to 220 ° C. at 10 ° C./min, and the endotherm during melting of the base resin as shown in FIG. Only the intrinsic peak a corresponding to is recognized.
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 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.].
[0046]
As described above, the expanded particles used in the present invention have a crystal structure in which a high temperature peak appears in the first DSC curve in DSC measurement. The amount of heat of this high temperature peak is the difference between the melting point of the resin and the expansion temperature. Strongly influenced by
The high temperature peak heat quantity of the expanded particles acts as a factor for determining the minimum fusion temperature particularly with respect to the fusion between the expanded particles. The minimum fusion temperature here means a temperature that gives the lowest saturated steam pressure necessary for the foamed 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 level of foaming temperature applied to the resin in the production stage of the foamed particles. When the same base resin is used, the high temperature peak heat quantity is higher than when the foaming temperature is lower. The value tends to be smaller.
[0047]
However, when an EPP molded product is obtained using expanded 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 product 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 preferable foamed particles are foamed particles having the opposite properties such as a low minimum fusing temperature and relatively high strength physical properties such as compressive strength of the EPP molded article. The foamed particles having a modified surface that can be molded at low temperature are those in which the minimum fusing temperature is effectively reduced, and when an EPP molded product is produced using such foamed particles, the compression strength An EPP molded product having excellent mechanical properties such as the above can be obtained.
[0048]
In order to obtain expanded particles having a high temperature peak in the DSC curve, when the surface-modified particles are dispersed in a dispersion medium and heated in a closed container, the temperature is raised to the melting end temperature (Te) or higher of the base resin. Without stopping, at a temperature lower than the melting point (Tm) of the base material resin by 20 ° C. or more and less than the melting end temperature (Te), the temperature is stopped at an arbitrary temperature (Ta) for a sufficient time at the temperature (Ta), Preferably, hold for about 10 to 60 minutes, and then adjust the temperature to 15 ° C lower than the melting point (Tm) to an arbitrary temperature (Tb) in the range of the melting end temperature (Te) + 10 ° C, stop at that temperature, if necessary It can be obtained by a method in which the surface-modified particles are released from the inside of the sealed container under a low pressure and foamed after being held at the temperature for a further 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 there are two or more straight lines that are equally long, the peak apex on the highest temperature side is defined as Tm.
[0049]
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.
[0050]
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.
[0051]
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.^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 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.^ThreeAn amount of a plurality of expanded particles is used.
[0052]
The expanded particles having a modified surface that can be molded at low temperature (hereinafter referred to as “surface modified expanded particles”) obtained from the surface modified particles described above have the following structural specificity. This is clear from the measurement results.
[0053]
As a result of DSC measurement of the expanded particles, the surface-modified expanded particles 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_iHowever, the surface-modified foamed particles have a higher melting point (Tm) than the surface layer portion._s) Is the melting point (Tm) of the internal foam layer_i) Was observed to be lower. Therefore, as the surface-modified foamed particles, 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.
[0054]
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 obtained from the second operation obtained by performing the same operation as the measurement of the high-temperature peak heat quantity of the foamed particles described above except that 2-4 mg is collected from the inside of the foamed particles so as not to include the surface layer portion and collected as a sample. It means the temperature at the apex of the intrinsic peak a of the DSC curve.
[0055]
  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, the surface modified foamed particles have ΔH_s<ΔH_iIt was observed to be x0.86. Therefore, as the surface-modified foamed particles, ΔH_s<ΔH_i× 0.86R, ΔH_s<ΔH_iX0.80PreferGood, ΔH_s<ΔH_iX0.75 is more preferable, and ΔH_s<ΔH_iX0.70 is particularly 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. The surface-modified foamed particles are ΔH_s<ΔH_i× 0.86 enables in-mold molding at a lower temperature than expanded particles that have not been surface modified, and ΔH_sThe smaller the value, the greater the effect. As a result, in-mold molding can be performed with low-temperature steam without reducing the rigidity of the portion of the unit molded body made of the surface-modified foam particles. 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.
[0056]
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.
[0057]
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 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.
[0058]
Further, when MFR was measured, it was observed that the MFR value of the surface-modified foamed particles was the same as the MFR value of the resin particles before being surface-modified, but a larger value than that. The MFR value of the surface-modified foamed particles is preferably 1.2 times or more, more preferably 1.5 times or more of the MFR value of the resin particles before the surface modification. Most preferably, it is 8 to 3.5 times. The MFR value of the surface-modified foamed particles is preferably 0.5 g / 10 min to 150 g / 10 min in consideration of the heat resistance of the EPP molded body and the foaming efficiency at the time of producing the foamed particles. It is more preferable to be 1 g / 10 minutes to 100 g / 10 minutes, and it is still more preferable to be 10 g / 10 minutes to 80 g / 10 minutes.
[0059]
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 into 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.
[0060]
Furthermore, the surface-modified foamed particles contain a small amount of oxygen due to the addition action of the organic peroxide in the surface modification step, particularly when an organic peroxide that generates oxygen radicals is used as the organic peroxide. A modified surface is formed. This is clear from the analysis of the surface of the surface-modified foamed particles and the surface of the EPP molded body produced therefrom. Specifically, it was manufactured from the surface of an EPP molded body manufactured from surface-modified foam particles (that is, substantially the same as the surface of the surface-modified foam particles) and from conventional non-surface-modified foam particles. 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 surface-modified foam particles 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^-1Molded product obtained from surface-modified foamed particles when the same peak height (absorption peak height for molded product from surface-modified foamed particles and absorption peak height for conventional molded product) is the same 1033cm on the surface^-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 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 surface modified expanded particles. On the other hand, in the case of the conventional expanded particle, it was 0.09 (mol / mol).
From the above, it is apparent 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. From such a viewpoint, the surface-modified foamed particles preferably have a ratio of oxygen to carbon of 0.15 or more by the EDS on the surface of the foamed particles.
[0061]
The surface-modified foamed particles are presumed to have their minimum fusing temperature effectively reduced by lowering the high-temperature peak heat quantity of the surface layer portion of the foamed particles or / and lowering the melting start temperature of the surface of the foamed particles. The
[0062]
Expanded particles used in the present invention can be made into expanded particles with a higher expansion ratio by aging under atmospheric pressure and then increasing the bubble internal pressure as necessary and then heating with water vapor or hot air. It is.
[0063]
The polypropylene-based resin-molded foam molded product (EPP molded product) according to the present invention fills foamed particles in a mold that can be heated and cooled, and can be opened and closed and sealed after increasing the bubble internal pressure as necessary. Then, it is possible to manufacture by adopting a batch type molding method in which saturated steam is supplied and the expanded particles are heated and expanded in the mold to be fused to each other, 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 expanded particles are expanded and fused is preferably 0.45 MPa (G) or less, more preferably 0.41 MPa (G) or less. .
In order to increase the internal pressure of the foam particles, the foam particles can be placed in a sealed container and allowed to stand for an appropriate period of time in a state where pressurized air is supplied into the container so that the pressurized air can penetrate into the foam particles. 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.
[0064]
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 air is used to increase the internal pressure of polypropylene resin expanded particles (EPP particles).
First, the foamed particles used for molding are put in a closed container, and pressurized air is put 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 foamed particles can be increased by allowing the air to permeate into the foamed particles by leaving it in the supplied state for an appropriate time. The expanded particles whose internal pressure is sufficiently increased are supplied into the mold of the molding machine. The internal pressure of the expanded particles is determined by performing the following operation using a part of the expanded particles immediately before in-mold molding (hereinafter referred to as expanded particle group).
[0065]
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) of the expanded particles is calculated from the following equation. The internal pressure P corresponds to a gauge pressure.
[0066]
P = (W ÷ M) × R × T ÷ V
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.
[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.^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.
[0068]
The internal pressure in the bubbles of the expanded particles is preferably 0 to 0.98 MPa, more preferably 0 to 0.69 MPa, particularly preferably 0 to 0.49 MPa, and most preferably 0 to 0.1 MPa.
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 heating of the central part of the molded body, and mutual fusion of the expanded particles Tends to be bad.
[0069]
In general, an in-mold foam molded body obtained by molding polypropylene resin expanded particles in a mold usually becomes larger (expands) than the shape of the mold space if cooling immediately after heating is insufficient during molding. On the other hand, if the cooling is excessive, it becomes smaller than the shape of the mold space (shrinks so much that a sufficient recovery cannot be expected). The degree of expansion and contraction differ depending on the degree of cooling. Further, the expansion and contraction tend to be different between the case where the apparent density of the obtained molded body is large and the case where it is small. Specifically, when the degree of cooling is the same, the low-density molded body part tends to turn earlier from expansion to contraction. Usually, since the expanded molded body is often disliked compared to the shape of the mold space, cooling is performed so that the high-density molded body portion does not expand. As a result, immediately after being taken out from the mold (mold release), the relatively low density molded body portion is in a state of being greatly contracted. When the shrinkage is relatively small, when the molded body is placed in a heated atmosphere of about 50 to 100 ° C. for about 24 hours at an early stage after the mold release, the shrinkage is usually recovered, but large shrinkage occurs. In such a case, it is difficult to obtain a high-quality product because it hardly recovers even in such a heated atmosphere.
On the other hand, the in-mold foam molded body formed from the specific foamed particles described above does not cause expansion in the final molded body even if the cooling of the molded body performed immediately after heating at the time of molding is short, Moreover, even if the cooling is excessive, there is little or no shrinkage. Therefore, even if it is integrally molded so as to include a unit molded body part manufactured with specific foamed particles and a unit molded body part manufactured with expanded particles other than the specific expanded particles, the expanded foam other than the specific expanded particles If the cooling at the time of molding is adjusted so that there is no convex bulge on the outside of the unit molded body part made of particles or concave shrinkage (shrinkage) on the inside, the whole will protrude outward from the molded body. As a result, an in-mold molded body with less swelling and shrinkage (shrinkage) on the inside can be easily obtained, and the quality can be improved without causing damage at the heat-sealed interface between the unit molded bodies. Furthermore, when all the unit molded products are produced from this specific foamed particle, it is possible to more easily obtain an in-mold molded product with less swelling on the outside of the resulting molded body and less sink marks on the inside. In addition, the cooling time after heating at the time of molding can be further shortened. This is an unexpected fact that the present inventors have found for the first time.
[0070]
Next, the present invention will be described in detail with reference to the drawings.
FIG. 3 is a structural explanatory view of one embodiment of the EPP molded body of the present invention.
In FIG. 3, 1, 2 and 3 represent unit molded bodies, 4 represents a fusion interface between two adjacent unit molded bodies 1, 2, and 5 represents two adjacent unit molded bodies 2, 3. The fusion interface is shown. 6 shows an EPP molded body according to the present invention.
Each of the unit molded bodies 1, 2, and 3 is an in-mold foam molded body obtained by molding specific foam particles.
[0071]
The EPP molded body 6 of the present invention shown in FIG. 3 is a fused body in which the unit molded bodies 1, 2, and 3 are integrated with each other at the time of molding. The characteristics of the two adjacent unit molded bodies are mutually different. Different. The term “characteristics as used in the present invention are different from each other” means that at least the apparent density is different, the base resin is different, the color is different, or the mechanical properties such as compressive strength are different. Specifically, the compressive strength increases as the apparent density increases. For example, in the case of the EPP compact shown in FIG. 3, the apparent density D2 of the unit compact 1₁The apparent density D2 of the unit molded body 2₂And the apparent density D2 of the unit molded body 3_ThreeThere is a relationship of the following formulas (5) and (6).
Formula (5): D2₂> D2₁
Formula (6): D2₂> D2_Three
That is, the density D2 of the unit molded body 2₂Is the apparent density D2 of the other unit molded bodies 1 and 3₁, D2_ThreeHigher density. Apparent density D2 of low-density unit molded bodies 1 and 3₁, D2_ThreeMay be the same or different. In the case of the present invention, the density D2 of the high-density unit molded body 2₂Is the apparent density D2 of the low-density unit molded bodies 1 and 3₁, D2_ThreeOf 1.2 to 25 times, and more preferably 1.2 to 20 times. Such an in-mold molded product is lightened as a whole by increasing the rigidity of necessary portions.
[0072]
  In each of the unit molded bodies 1, 2, and 3 constituting the EPP molded body 6 of the present invention shown in FIG. 3, each apparent density D2 (g / L) and each foam constituting the unit molded bodies 1, 2, and 3 are shown. The high-temperature peak heat quantity E2 (J / g) of the body has a relationship satisfying the following formulas (3) and (4), respectively. Formula (3):25−0.020 × D2 ≦ E2 ≦55-0.100 × D2
  Formula (4):15≦ D2 ≦450
  In the above formulas (3) and (4), D2 is the apparent density of the test piece cut out from each of the unit molded bodies 1, 2, and 3 composed of the expanded particles made of the base resin, that is, D2.₁, D2₂Or D2₃E2 is a calorific value (E2) of the endothermic curve peak of the high temperature side endothermic curve of a test piece (2 to 4 mg) cut out from each of unit molded bodies 1, 2 and 3 molded from specific foamed particles.₁, E2₂Or E2₃).
  MaFurther, in the high-density unit molded body 2, the apparent density D2₂Is 30 to 450 g / L, and the apparent density D2 of the low-density unit molded bodies 1 and 3 is₁, D2₃Is 15 to 90 g / L and the apparent density D2 of the high-density unit molded body 2 is₂Lower than. As a result, the required portions are densified to increase the rigidity, and the overall weight of the molded product is reduced.
  The above D2 isToo lowAs a result, the mechanical properties deteriorate significantly, and the above D2 istoo expensiveThen, since the foamed effect (lightness, etc.) is almost lost, neither is preferable. In the above formula (3), E2 isToo smallIf excessive cooling occurs during molding, large shrinkage may remain in the molded product.Too bigThen, the obtained molded body tends to be inferior in the fusion strength between the expanded particles. The reason why E2 is expressed by the relational expression of D2 is the same as the relation between E1 and D1 in the above formula (1). However, in the above formula (1) and the above formula (3), the numerical value is the same with the same apparent density. The reason for the difference is that the expanded particles expand to fill the gaps between the expanded particles at the time of molding, and as a result, the apparent density of the molded body is smaller than the apparent density of the expanded particles used for molding. Have
[0073]
What is necessary is just to shape | mold using the said specific foamed particle, in order to manufacture the unit molded object which satisfies the said Formula (3) and (4).
[0074]
FIG. 4 is a structural explanatory view of another embodiment of the EPP molded body of the present invention.
In FIG. 4, 1 indicates a high-density unit molded body, and 2 indicates a low-density unit molded body.
4 shows the fusion | melting interface of both.
[0075]
FIG. 5 is a structural explanatory view of still another embodiment of the EPP molded body of the present invention.
In FIG. 5, 11-15 shows a unit molded object, 16-19 show each fusion | melting interface of two adjacent unit molded objects.
In FIG. 5, each apparent density D2 of each unit molded body 11-15.₁₁~ D2₁₅The relationship is as shown in the following formulas (9) and (10).
Formula (9): D2₁₃> D2₁₂> D2₁₁
Formula (10): D2₁₃> D2₁₄> D2₁₅
[0076]
In the EPP molded body of the present invention, the two adjacent unit molded bodies have a structure in which the adjacent unit molded bodies are directly fused without interposing another member at the interface as shown in FIGS. However, in some cases, it may be of a fusion structure in which an insert material is interposed at the fusion interface. With respect to a method for producing an EPP molded body having a structure in which two adjacent unit structures are directly fused, for example, JP-A-11-334501, JP-A-2000-16205, JP-A-2001-63496, Details are described in JP-A No. 2001-150471, JP-A No. 2002-172642, JP-B No. 62-22352, US Pat. No. 5,164,257, and the like.
FIG. 6 shows a structure explanatory diagram of an EPP molded body when an insert material is interposed at the fusion interface between two adjacent unit molded bodies.
In FIG. 6, a represents one of the two adjacent unit molded bodies, b represents the other unit, and c represents the insert material interposed at the fusion interface.
[0077]
The insert material c preferably has a large number of through holes on its surface. This insert material c is used as a partition member when the inside of a mold is partitioned into a plurality of sections by a partition member in the manufacturing process of the in-mold foam molded body, and each section is filled with foamed particles. . When the foam particles are filled in a plurality of compartments partitioned by the insert material (partition member) c and heated by steam to fuse the foam particles together, the foam particles present on both sides of the insert material c are It heat-seal | fuses through the said through-hole of the insert material c. When this heat-sealed body is taken out of the mold as a product of an in-mold foam molded body, the insert material c remains at the heat-sealed interface of each unit molded body. In addition, when the insert material has thermal adhesiveness that can be integrated with the unit molded body with sufficient strength by heating at the time of molding the foamed particles, the insert material is not necessarily provided with the through-hole. The molded bodies can be integrated with each other through an insert material. However, when there is no such thermal adhesiveness, if the through hole is formed in the insert material, the unit molded bodies can be integrated through the through hole during molding.
[0078]
The insert material c having the through holes may be a metal net, a metal plate having a large number of through holes, a ceramic plate (glass plate), a plastic plate, or the like, or a cardboard having a large number of through holes.
The shape of the through hole in the insert material c can be various shapes such as a groove shape (slit shape) in addition to a circular shape. The size of the through hole is such a size that does not hinder the fusion of the foamed particles when the foamed particles filled on both sides of the insert material c are thermally fused together via the insert material c. It suffices if the size is such that at least one of the foam particles a and b filled on both sides of the insert material c cannot pass through. Generally, the through hole of the insert material c has an area S.¹Is the cross-sectional area S at the center of the expanded particle²= Πr²The size is 0.2 to 0.9 times, preferably about 0.5 to 0.8 times (r: the minimum radius of the expanded particles). The thickness of the insert material c is about 1 to 10 mm, preferably about 2 to 8 mm, but is not particularly limited.
[0079]
The number of through holes formed on the surface of the insert material c may be any number that can fuse the two unit molded bodies a and b with sufficient strength. Generally, the number is such that the ratio of the total through-hole area to the surface area of the insert material is 25 to 90%, preferably 50 to 80%.
[0080]
The EPP molded body of the present invention is obtained by adding a partition material to a continuous molding method (for example, molding methods described in JP-A-9-104026, JP-A-9-104027, JP-A-10-180888, etc.). Can also be manufactured. In the continuous molding method, foamed particles whose bubble 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 region). ) By expanding and fusing the foamed particles together when passing through, and then cooling by passing through the cooling region, and then removing the resulting molded body from the road and sequentially cutting to an appropriate length, An EPP compact is produced.
[0081]
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. Such lamination methods are described in U.S. Pat. No. 5,928,764, U.S. Pat. No. 6,096,417, U.S. Pat. No. 6,033,770, U.S. Pat. Are described in detail in each publication.
Further, in the EPP molded body of the present invention, all or part of the other insert material is embedded in the molded body without using the partition material / insert material described above or together with the partition material / insert material. In this way, the other insert material can be combined and integrated. The manufacturing method of such an insert composite type EPP molded body is described in detail in “U.S. Pat. No. 6,033,770, U.S. Pat. No. 5,474,841, Japanese Published Patent No. 59-127714, Japanese Patent No. 3092227, etc. Has been.
The overall apparent density of the EPP molded article of the present invention produced by the above method can be arbitrarily selected depending on the purpose, but is usually in the range of 10 g / L to 600 g / L. The overall apparent density of the EPP compact is an apparent overall density as defined in JIS K 7222 (1999). However, the volume of the molded body used for the calculation of the apparent overall density is the volume calculated from the outer dimension, but if the shape is complicated and calculation from the outer dimension is difficult, the molded body is submerged. Excluded volume is adopted. Further, the apparent density of each unit molded body is determined by cutting each unit molded body at the center of the fusion interface between the unit molded bodies, and then using each unit molded body cut, It is measured in the same way as density. In any unit molded body of the EPP molded body of the present invention, the open cell ratio based on the procedure C of ASTM-D2856-70 is preferably 40% or less, more preferably 30% or less, 25 % Is most preferred. The smaller the open cell ratio, the better the mechanical strength.
[0082]
FIG. 7 shows an explanatory view of one embodiment of a molding apparatus for producing the EPP molded body of the present invention.
This apparatus is used for manufacturing a bumper core material for automobiles. As shown in FIG. 7, in this apparatus 8, male molds 10a and female molds 10b that form cavities corresponding to the shape of the bumper core material are attached to mold frames 9a and 9b. The male mold 10a is a mold on the vehicle body side of the bumper core material, and is also a mold for forming the backup beam mounting surface side. The female mold 10b is a mold for forming the vehicle outer surface.
Further, the molding apparatus 8 includes a partition plate 11 that divides the longitudinal direction into a plurality of cavity spaces. The partition plate 11 is connected to the cylinder rod 13 of the air cylinder 12 for each partition plate, and is formed to be able to advance and retreat into the cavity space. The cylinder 12 for advancing and retracting the partition plate 11 is attached to the frame 9a on the beam side so that the partition plate 11 can enter the inside of the mold through an insertion hole 14 provided in the male mold 10a on the beam side. In addition, on the female die 10b side on the outer side of the vehicle body, a filling machine 16 for filling foamed particles into each cavity partitioned by the partition plate 11 is provided for each partitioned cavity.
[0083]
The periphery of the insertion hole 14 of the male mold 10 a protrudes toward the inside of the cavity and is formed as a convex portion 15. It is preferable that the male protrusions forming the protrusions 15 are formed to have a width of 0.7 to 25.0 mm on both sides in the longitudinal direction of the insertion hole 14. If the width of the protruding portion is less than 0.7 mm, the strength is insufficient and there is a risk of deformation or damage. Moreover, although the height from the molding surface of the convex part 15 is determined suitably according to shapes, such as the bending condition of the vehicle outer surface side front-end | tip of the bumper core material 1, and the presence or absence of a recessed part, it forms in 1.0-50.0 mm. Is preferred. In addition, since the thickness of a partition plate is generally formed in 0.5-10.0 mm, it is preferable that the width | variety of the convex part 15 as a whole is formed in 2.0-62.0 mm, 3.0 More preferably, it is formed to be ˜30 mm. If the width of the convex portion 15 is less than 2.0 mm, the strength is insufficient, and if it exceeds 62.0 mm, the energy absorption efficiency of the obtained bumper core may be lowered. The width (thickness) of the partition plate 11 is preferably 10 to 85% of the width of the convex portion 15.
[0084]
As shown in FIG. 8A, the partition plate 11 is preferably formed so that the upper end edge and the lower end edge thereof are parallel to the traveling method of the partition plate. In this case, the part which touches the upper end edge and lower end edge of the partition plate of the female mold 10 b is formed in a shape corresponding to the upper and lower shapes of the partition plate 11. That is, the shape of the periphery of the portion of the female mold 10b that contacts the upper edge 11a and the lower edge 11b of the partition plate 11 is formed in parallel with the direction of travel of the partition plate, similar to the partition plate 11, and the portion of the female mold 10b is It is formed in a shape that protrudes to the inside of the cavity from the surrounding portion.
[0085]
When the shape of the periphery of the portion that contacts the upper end edge 11a and the lower end edge 11b of the partition plate 11 of the female mold 10b is formed so as to protrude inside the cavity from the surrounding portion, the width of the convex portions 15a, 15b is It is preferable that the width be the same as the convex portion 15 around the insertion hole of the partition plate 11.
[0086]
In order to manufacture the bumper core material using the molding apparatus 8 shown in FIG. 7, the partition plate 11 is first advanced into the cavity and partitioned for each cavity. Next, predetermined foamed particles are filled into the cavities from the respective filling machines 16. The partition plate is withdrawn after being filled with expanded particles or while being filled. When the foamed particles are completely filled in each compartment in the cavity and the partition plate is removed from the cavity, the foam is fused by fusing the foamed particles by heating the cavity with steam, etc. A particle compact is obtained. Thereafter, the foamed particle molded body is taken out of the cavity to obtain a bumper core A shown in FIG. At this time, as shown in FIG. 9, the bumper core A has burrs in the upper and lower sides and the center, but the burrs remain in the recess 2 and do not protrude outward from the beam mounting surface.
[0087]
In order to fill the inside of the cavity with the foamed particles, a so-called cracking filling method in which a gap is provided in the mold and the foamed particles are filled into the cavity with air or the like can be used. In this method, it is possible to simultaneously fill both high density regions and low density regions having different characteristics. Alternatively, a so-called compression filling method may be used in which the foamed particles are pressurized to reduce the volume, and a pressure difference is provided between the inside of the mold cavity and the foamed particle tank. In this case, normally, in order to avoid the foamed particles in the low density region being compressed and changing the apparent density, the high density region is filled first, and then the low density region is filled.
[0088]
The raw material foam particles filled in the cavities may be the same or different foam particles in terms of apparent density, particle weight, base resin, and the like. For example, in order to form unit molded bodies with different apparent densities using the same foamed particles, when filling the foamed particles into the cavities partitioned by the partition plate, the cavities formed as high density regions are filled. In the case of using a method of increasing the pressurized amount of foamed particles to be larger than other methods or cracking filling, the foamed particles are first filled into the cavity formed as a high density region, and then the gap in the mold is narrowed and then the low density For example, a method of filling expanded particles in a cavity formed as a region can be used.
[0089]
When the partition plate 11 is withdrawn from the cavity, it is preferable that the partition plate 11 is withdrawn until the tip of the partition plate 11 is outside the protruding surface of the convex portion 15 of the male mold 10a. That is, when molding is performed in a state in which the tip of the partition plate 11 enters the cavity rather than the protruding surface of the convex portion 15 of the cavity, the partition plate portion is formed as a concave groove in the concave portion 2 of the obtained bumper core material. . If narrow grooves such as traces of the partition plate are present on the back-up beam mounting surface of the bumper core material, there is a possibility that the shock absorption characteristics when subjected to an impact are deteriorated. At this time, burrs are generated in the recesses, but as described above, the burrs do not protrude outward from the beam mounting surface, or may be processed so as not to protrude even if protruded, and the processing is easy.
[0090]
When the above-mentioned impact absorbing material is composed of two types of unit molded body composed of specific foamed particles and unit molded body composed of polypropylene resin expanded particles other than the specific foamed particles, the specific foamed It is composed of polypropylene-based resin foam particles other than specific foam particles, and the weight (d1: g) of the unit molded body composed of particles and the high temperature peak heat quantity (C1: J / g) of the foam particles. When the weight of the unit molded body (d2: g) and the relationship between the foamed particles and the high temperature peak calorific value (C2: J / g) are set so that the following formula (11) is satisfied, the weight is reduced and the impact absorbing property is improved. It will be expensive.
Formula (11): (C1 × d1) / (d1 + d2) + (C2 × d2) / (d1 + d2)> 22
However, 22 in a formula is high temperature peak calorie | heat amount (J / g) of an expanded particle.
[0091]
The EPP molded body of the present invention is preferably used as an impact absorbing material such as a bumper core material for automobiles and a helmet core material.
[0092]
FIG. 9 is a perspective view showing the outer appearance of the main part of the bumper core material A for automobiles obtained as described above.
FIG. 10 is a front view of the bumper core A as viewed from the beam side.
Further, FIG. 11 shows a longitudinal sectional view taken along line III-III in FIG.
In these drawings, 1a is a high-density unit molded body, 1b is a low-density unit molded body, 2 is a recess, and 3 is a heat-sealing interface between the high-density unit molded body and the low-density unit molded body.
The bumper core material for automobiles obtained as described above is a combination of different regions (regions with different energy absorption capabilities, unit molded bodies) having different characteristics such as a longitudinal direction divided into a plurality of predetermined lengths. Therefore, it is excellent in impact characteristics, light weight and low cost, and the shape of the bumper core material is formed as a recess around the boundary of each unit molded body with different characteristics of the backup beam mounting surface of the core material. Regardless of this, burr is generated in the recess on the beam surface side of the bumper core material, so even if it protrudes greatly, removal of the burr is easy, productivity does not decrease, and projections that disturb the beam surface of the bumper core material It is easy to attach to the beam.
[0093]
【Example】
The present invention will be described below with reference to examples and comparative examples.
[0094]
Production Examples 1 to 4, 8 and 9 of foamed particles
  Table 1The melting point, MFR, and tensile modulus shown inAfter adding 0.05 parts by weight of zinc borate powder (bubble regulator) per 100 parts by weight of the polypropylene homopolymer resin and melt-kneading in the extruder, the strand is extruded from the extruder into a strand shape. The sample was taken into water adjusted to be rapidly cooled, and after sufficiently cooled, pulled out from the water, the strand was cut so that the length / diameter ratio was about 1.0, and the average weight per particle was 2 mg of polypropylene resin particles were obtained. Next, in a 400 liter autoclave, 100 kg of the above resin particles, 120 kg of ion exchange water at 25 ° C. as a dispersion medium (resin particle / dispersion medium weight ratio 0.83), 0.002 kg of sodium dodecylbenzenesulfonate (surfactant) and kaolin (Dispersant) 0.4 kg, powdered aluminum sulfate (dispersion aid) 0.013 kg, bis (4-t-butylcyclohexyl) peroxydicarbonate (organized oxide) 0.32 kg were charged and stirred at 90 ° C. (Average heating rate 5 ° C./min) and held at that temperature for 10 minutes. Next, 100 kg of ion exchange water and carbon dioxide gas (foaming agent) were injected so that the equilibrium pressure was 0.49 MPa (G), and then the temperature was raised to a temperature 5 ° C. lower than the foaming temperature in Table 1 while stirring (average) After the stirring, the temperature was raised to a temperature 1 ° C. lower than the foaming temperature in Table 1 (average heating rate 0.16 ° C./min). 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 temperature rising rate of 0.029 ° 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. 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 24 hours under atmospheric pressure at room temperature of 23 ° C., and then the high temperature peak calorific value of one whole foamed particle, the high temperature peak of the surface layer (surface layer part). The amount of heat, the internal high temperature peak heat amount (internal foamed layer), the apparent density of the expanded particles, and the like were measured. The results are shown in Table 1. In addition, all the expanded particles obtained in this production example were substantially non-crosslinked (the boiling xylene-insoluble components were all 0). Production Examples 5-7 of Expanded Particles Polypropylene resin particles were obtained in the same manner as in Production Example 1 of Expanded Particles. Next, in a 400 liter autoclave, 100 kg of the resin particles, 220 kg of ion-exchanged water, 0.005 kg of sodium dodecylbenzenesulfonate (surfactant) and 0.3 kg of kaolin (dispersant) 0.01 kg of powdered aluminum sulfate (dispersion aid) Next, carbon dioxide gas (foaming agent) was injected so that the equilibrium pressure was 0.49 MPa (G), and then the temperature was raised to a temperature 5 ° C. lower than the foaming temperature in Table 1 with stirring (average temperature rise) Thereafter, the temperature was raised to 1 ° C. lower than the foaming temperature in Table 1 with stirring (average rate of temperature rise: 0.16 ° C./min). 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 temperature rising rate of 0.029 ° 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. The obtained foamed particles are washed in a water-centrifuge and allowed to stand at atmospheric pressure for 24 hours. After that, the whole foam particles are heated at a high temperature peak heat, the surface layer (surface layer) is heated and the inside (internal foam). The high temperature peak heat quantity and the apparent density of the layer) were measured. The results are shown in Table 1. In addition, all the expanded particles obtained in this production example were substantially non-crosslinked (the boiling xylene-insoluble components were all 0).
[0095]
Examples 1-5 and Comparative Examples 1-5
A molding apparatus was prepared in which a mold (consisting of a male mold and a female mold) having a molding space of length 700 mm × width 200 mm × thickness 50 mm was attached to the molding apparatus. This molding apparatus is provided with a stainless steel partition material that can be moved forward and backward in the entire mold at 150 mm from each end in the longitudinal direction of the mold. These two partition materials are used to partition the molding space into three compartments when filling the foam particles into the mold. In this example and comparative example, after filling the foam particles and before heating, It is to be withdrawn from the molding space.
Using the above molding apparatus, as shown in Table 2, each foamed particle obtained in the above-mentioned foamed particle production example is filled with high-density particles A in the sections at both ends in the molding space partitioned by the partition material. The central compartment was filled with the low-density particles B, and molding was performed as follows.
When filling the expanded particles, the mold is not completely closed, but is filled with a slight gap (about 10 mm) (60 mm in the direction of thickness 50 mm), and then completely clamped, then with steam After exhausting the air in the mold, steam adjusted to 0.8 MPa (G) is introduced from the male side until the pressure reaches 0.04 MPa (G) lower than the molding pressure in Table 2 ( Steam is introduced from the female mold side until the pressure reaches 0.02 MPa (G) lower than the molding pressure in the table (reverse one heating), and then steam is introduced from both the male and female mold sides. After reaching the molding pressure in Table 2, holding heating was performed at that pressure for 20 seconds (main heating) (Comparative Examples 1 to 3 did not hold, and cooling started immediately after reaching the molding pressure. ). On the other hand, the time from the start of heating to the molding pressure shown in Table 2 was measured, and the pressure increase rate calculated based on this was shown in Table 2. After molding, after water cooling until the surface pressure of the molded body in the mold becomes 0.059 MPa (G), the molded body is taken out from the mold and dried at 60 ° C. for 24 hours, and then the molded body is cooled to 23 ° C., Moved to a room with 50% relative humidity.
[0096]
The molding pressure in Table 2 is one surface of the surface of 700 mm long × 200 mm wide after 24 hours from moving the dried molded body to a room at 23 ° C. and 50% relative humidity. In addition, after cutting about 10mm in the thickness direction of the molded body so as to divide the length of each unit molded body by 2 with a cutter knife, it is present on the fracture surface by a test in which the molded body is bent and broken from the cut portion. When the ratio (b / n) of the number of expanded particles (n) to the number of expanded particles (b) whose material was destroyed becomes the value of 0.50 or more for all three unit molded bodies for the first time, Means the required saturated steam pressure. In Comparative Example 4, even when molding was performed at a molding pressure of 0.44 MPa (G) which is the same as the pressure resistance of the molding machine, the value of (b / n) was less than 0.50.
The number (n) of foamed particles is the sum of the number of foamed particles peeled between the foamed particles and the number of foamed particles (b) whose material has been destroyed in the foamed particles. Further, the larger the value of (b / n), the more preferable the molded body is because bending strength and tensile strength are increased.
Moreover, melting | fusing point in Table 1, E1, and E2 in Table 2 were measured using Shimadzu Corporation's Shimadzu heat flux differential scanning calorimeter “DSC-50”.
[0097]
In addition, the evaluation method and evaluation criteria regarding the properties of the molded body shown in Table 2 are as follows.
(1) Fusion property
Evaluation is made based on whether or not the above-mentioned (b / n) ratio is 0.50 or more by using a molding machine having a pressure resistance of 0.44 MPa (G).
○ ... (b / n) ratio is 0.50 or more
X ... (b / n) ratio is less than 0.50
(2) Surface properties
Visual evaluation of whether the appearance of the molded product surface is good, with few gaps between foamed particles such as irregularities
○: Good
×: Defect
(3) Shape stability
After the dried molded body is moved to a room at 23 ° C. and a relative humidity of 50% and allowed to stand for 24 hours, each of the high-density unit molded bodies located at both ends of the molded body (the center of each unit molded body). Measure the length (thickness) in the thickness direction at the center in the length direction and the center in the width direction, and at the center of each low density unit molded body (each unit molded body) located between two high density unit molded bodies (Length direction center part and width direction center part) were measured in the thickness direction length (thickness) and evaluated as follows.
A: The dimension of the measurement part of the unit molded body is in the range of 49.0 mm to 50.0 mm.
O: The dimension of the measurement part of the unit molded body is in the range of 48.0 mm to 51.0 mm. However, this does not apply when applicable to ◎.
Δ: The dimension of the measurement part of the unit molded body is in the range of 47.0 mm to 52.0 mm. However, this is excluded if it falls under ◎ or ○.
X ... The dimension of the measurement part of a unit molded object is less than 47.0 mm, or exceeds 52.0 mm.
(4) Compressive strength
The compressive strength is obtained by cutting the dried molded body to a length of 50 mm, a width of 50 mm, and a thickness of 25 mm from each unit molded body 14 days after moving to a room at 23 ° C. and a relative humidity of 50%. Compressed until the strain reaches 55% at a test piece temperature of 23 ° C. and a load speed of 10 mm / min according to JIS Z 0234 (1976) A method. A test was conducted, and the stress at the time of 50% strain was read from the obtained stress-strain diagram, and this was taken as the compressive strength.
[0098]
The following is understood from the above results.
Examples 1 to 4 show examples in which both the high-density unit molded body and the low-density unit molded body were produced with the specific foamed particles of the present invention, but the shape stability of all the unit molded bodies was remarkably excellent. Yes.
Example 5 is an example in which a high-density unit molded body is manufactured with expanded particles obtained using a polypropylene-based resin having a low tensile elastic modulus, and a low-density unit molded body is manufactured with the specific expanded particles of the present invention. Show. By matching the cooling of the molded body immediately after molding to the high-density unit molded body side, the shape stability on the high-density unit molded body side can be made excellent, and the low density produced with the specific foamed particles of the present invention The shape stability of the unit molded product was remarkably excellent.
Comparative Examples 1 to 3 show examples in which both of the high-density unit molded body and the low-density unit molded body are made of polypropylene resin expanded particles having a small tensile elastic modulus other than the specific expanded particles of the present invention. Comparative Examples 1 to 3 were molded under the same conditions except that the cooling time immediately after molding was different. In Comparative Example 1 in which the cooling time is short, the shape stability of the high-density unit molded body is markedly inferior. In Comparative Examples 2 and 3 in which the cooling time is extended as compared with Comparative Example 1, the shape stability of the low density unit molded article is inferior. That is, it can be understood that it is difficult to increase the shape stability of both the high-density unit molded body and the low-density unit molded body unless the unit molded body produced with the specific foamed particles of the present invention is present. .
In Comparative Example 4, a high-density unit molded article was produced with polypropylene resin foamed particles having a high high-temperature peak heat quantity other than the specific foamed particles of the present invention, and the low-density unit molded article was a tensile other than the specific expanded particles of the present invention The example manufactured with the polypropylene-type resin expanded particle with a small elasticity modulus is shown. As a result, the high-density unit molded body was molded at the same steam pressure as the pressure resistance of the molding machine, but was inferior in the fusion property and surface property between the foamed particles. In addition, the low-density unit molded body was remarkably inferior in shape stability.
In Comparative Example 5, a high-density unit molded article was produced with polypropylene resin foamed particles having a low tensile elastic modulus other than the specific foamed particles of the present invention, and a low density unit molded article was produced at a high temperature other than the specific foamed particles of the present invention The example manufactured with the polypropylene resin expanded particle with a small peak calorie | heat amount is shown. Although the cooling of the molded body immediately after molding was matched to the high-density unit molded body having a low resin strength, the low-density unit molded body was markedly inferior in shape stability.
[0099]
[Table 1]
[0100]
[Table 2]
[0101]
【The invention's effect】
  According to the production method of the present invention, the inside of a mold is divided into two or more sections, each section is filled with polypropylene resin foam particles, and then the polypropylene resin foam particles are molded in the mold. In the above-mentioned method for producing a foamed molded product in a polypropylene resin mold having a unit molded body adjacent and integrally molded, the expanded particles filled in at least one of the compartments have a tensile elastic modulus of 1200 MPa or more. And an apparent density D1 (g / L) and a high-temperature peak heat E1 (J / g) Expands to the final molded body even if the molded body is cooled immediately after heating during molding for a short period of time because of the expanded particles satisfying the above formulas (1) and (2). In addition, there is little or no shrinkage even if the cooling is excessive. Therefore, even if it is integrally molded so as to include a unit molded body part manufactured with specific foamed particles and a unit molded body part manufactured with expanded particles other than the specific expanded particles, the expanded foam other than the specific expanded particles If the cooling at the time of molding is adjusted so that there is no convex bulge on the outside of the unit molded body part made of particles or concave shrinkage (shrinkage) on the inside, the whole will protrude outward from the molded body. Therefore, an in-mold molded body with less swelling (shrinkage) that is concave on the inside and a concave shape on the inside can be easily obtained. Furthermore, when all the unit molded products are manufactured from this specific foamed particle, it is possible to more easily obtain an in-mold molded product with less swelling on the outer side of the molded product and less sink marks on the inner side. It is done. In addition, a molded body using specific expanded particles isFoam which is made of a polypropylene resin having a tensile modulus of elasticity of 1200 MPa or more and whose relationship between the apparent density D2 (g / L) and the high temperature peak heat quantity E1 (J / g) satisfies the above formulas (3) and (4). Because it is a particle,Since the rigidity such as compressive strength is high, an in-mold molded body excellent in light weight can be easily obtained. Further, the amount of heat (ΔH_s) And the amount of heat (ΔH_i) Is ΔH_s<ΔH_i× 0.86FromIn-mold molding can be performed with low-temperature steam without reducing the rigidity of the portion of the molded body made of the expanded particles. In addition, the in-mold molded product of the present invention is a high-quality one in which the two adjacent unit molded products have no irregularities such as blisters and sink marks, and poor appearance or poor appearance. The foamed molded article obtained by the present invention is suitable for use as a bumper core material for automobiles, an impact absorbing material disposed in an automobile door, a container, a helmet core material, and the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a first DSC curve chart of expanded polypropylene resin particles having a high temperature peak.
FIG. 2 is a diagram showing an example of a second DSC curve chart of polypropylene resin particles.
FIG. 3 is a structural explanatory view of one embodiment of the in-mold foam molded article of the present invention.
FIG. 4 is a structural explanatory view of another embodiment of the in-mold foam molded product of the present invention.
FIG. 5 is a structural explanatory view of still another embodiment of the in-mold foam molded product of the present invention.
FIG. 6 is an explanatory diagram of a fusion interface when a porous member is interposed at a fusion interface between two adjacent unit molded bodies.
FIG. 7 is an explanatory view of a bumper core material forming apparatus.
8A and 8B are diagrams for explaining the operation of the partition plate of the mold shown in FIG. 7, in which FIG. 8A shows a state where the partition plate has entered the cavity, and FIG. 8B shows that the partition plate has exited from the cavity. Indicates the state.
FIG. 9 is a perspective view showing an external appearance of a main part of an automotive bumper core material.
10 is a front view of the bumper core member of FIG. 9 as viewed from the vehicle body attachment side.
11 is a longitudinal sectional view taken along line III-III in FIG.
[Explanation of symbols]
(FIGS. 3 to 6)
1-3 Unit molded body
11-15 Unit molded body
a, b Unit molded body
4, 5, c Fusion interface between unit molded bodies
16-19 Fusion interface between unit molded bodies
(FIGS. 7 to 11)
A Automotive bumper core material
1a High density area
1b Low density area
2 recess
3 Border between high density area and low density area
8 Molding equipment
9a, 9b Mold frame
10a Male
10b Female type
11 Partition plate (partition material)
12 Air cylinder
13 Cylinder rod
14 Insertion hole
15 Convex

Claims (4)

An integral molded body having a structure in which a plurality of unit molded bodies composed of in-mold foam molded bodies of polypropylene resin expanded particles are heat-sealed,
(I) The two adjacent unit molded bodies have different properties, and one unit molded body of the two adjacent unit molded bodies is a high density unit molded body having an apparent density of 30 to 450 g / L. The other unit molded body is a low density unit molded body having an apparent density of 15 to 90 g / L and having an apparent density lower than the apparent density of the high density unit molded body,
(Ii) A polypropylene resin or a polypropylene resin composition in which the expanded particles constituting at least one unit molded body (F) of the high density unit molded body and the low density unit molded body have a tensile elastic modulus of 1200 MPa or more. The amount of heat of the endothermic curve peak existing on the high temperature side of the surface layer portion (ΔH _s ) and the amount of heat of the endothermic curve peak existing on the high temperature side of the internal foam layer of the expanded particle (ΔH _i ) der Rukoto satisfies the relationship is ΔH _s <ΔH _i × 0.86,
(Iii) The unit molded body (F) has an endothermic curve peak on the higher temperature side than the intrinsic endothermic curve peak derived from the heat of fusion in the DSC curve by differential scanning calorimetry,
(Iv) the unit molded body in (F), the apparent density D2 (g / L) and the high temperature of the polypropylene resin foam constituting unit molded body (F) side endothermic curve peak of heat of fusion E2 (J / g) is in a relationship satisfying the following formulas (3) and (4),
Formula (3): 25 −0.020 × D2 ≦ E2 ≦ 55 −0.100 × D2
Formula (4): 15 <= D2 <= 450
A foamed molded product in a polypropylene resin mold characterized by Apparent density of the high density unit molded body, a polypropylene resin-mold foamed molded article according to claim 1, characterized in that a 1.2 to 25 times the apparent density of the low density unit molded body. 3. The polypropylene resin in-mold foam-molded product according to claim 1 or 2 , wherein the in-mold foam-molded product is an impact absorbing material. The polypropylene resin-in-mold foam-molded article according to claim 4 , wherein the impact absorbing material is a bumper core material for automobiles.