Foamable polypropylene resin composition and molded body

Abstract

A foamable polypropylene resin composition includes 10 parts by mass to 65 parts by mass of rubber or a thermoplastic elastomer, 18 parts by mass to 90 parts by mass of talc having a 50% particle diameter (D50) of 1 m to 3 m and surface-treated for increased dispersibility, 0.1 part by mass to 6.0 parts by mass of an organic crystal nucleating agent, and 5 parts by mass to 15 parts by mass of a foaming agent relative to 100 parts by mass of the polypropylene resin.

Claims

1. A foamable polypropylene resin composition comprising: 100 parts by mass of a polypropylene resin, 10 parts by mass to 65 parts by mass of rubber or a thermoplastic elastomer, 18 parts by mass to 90 parts by mass of talc having a 50% particle diameter (D50) of 1 m to 3 m and surface-treated for increased dispersibility, 0.1 part by mass to 6.0 parts by mass of an organic crystal nucleating agent that affects a crystallinity of the resin, 5 parts by mass to 15 parts by mass of a foaming agent, a higher fatty acid amide; and a compatibilizer, wherein a total amount of the higher fatty acid amide and the compatibilizer is 0.8 parts by mass to 15.0 parts by mass, and a blending mass ratio of the higher fatty acid amide to the compatibilizer is 1:10 to 2:1.

2. The foamable polypropylene resin composition according to claim 1, wherein the talc surface-treated for increased dispersibility is talc, to a surface of which siloxane is added.

3. The foamable polypropylene resin composition according to claim 1, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide, and ethylenebis(stearamide).

4. The foamable polypropylene resin composition according to claim 2, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide, and ethylenebis(stearamide).

5. A foamed polypropylene resin molded body, foam-molded from the foamable polypropylene resin composition as claimed in claim 1, having closed cells in a foamed state, and having an average foamed cell diameter pursuant to ASTM D3576-77 of 100 m to 300 m.

6. The foamed polypropylene resin molded body according to claim 5 having a core layer and a skin layer, wherein crystallinity (c) of a resin part between foamed cells of the core layer of the foamed polypropylene resin molded body is 30.0% or higher, and a ratio (c/s) of the crystallinity (c) of the resin part between the foamed cells to crystallinity (s) of a skin layer resin part of the skin layer is 1.05 or higher.

7. The foamed polypropylene resin molded body according to claim 5, wherein flexural rigidity pursuant to ISO 178 of the foamed polypropylene resin molded body is 2.010.sup.6 Nm or higher, and puncture energy pursuant to ISO 6603-2 of the foamed polypropylene resin molded body is 4 J or higher.

8. The foamed polypropylene resin molded body according to claim 5, wherein a critical vertical force of scratch characteristics pursuant to ISO 19252 of the foamed polypropylene resin molded body is 6.0 N or higher, and a color difference change pursuant to ISO 11664-4 of the foamed polypropylene resin molded body before and after a heat resistance test of 110 C.600 hours is 3.0 or lower.

9. The foamed polypropylene resin molded body according to claim 6, wherein a critical vertical force of scratch characteristics pursuant to ISO 19252 of the foamed polypropylene resin molded body is 6.0 N or higher, and a color difference change pursuant to ISO 11664-4 of the foamed polypropylene resin molded body before and after a heat resistance test of 110 C.600 hours is 3.0 or lower.

10. The foamed polypropylene resin molded body according to claim 7, wherein a critical vertical force of scratch characteristics pursuant to ISO 19252 of the foamed polypropylene resin molded body is 6.0 N or higher, and a color difference change pursuant to ISO 11664-4 of the foamed polypropylene resin molded body before and after a heat resistance test of 110 C.600 hours is 3.0 or lower.

11. The foamable polypropylene resin composition according to claim 5, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

12. The foamable polypropylene resin composition according to claim 6, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

13. The foamable polypropylene resin composition according to claim 7, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

14. The foamable polypropylene resin composition according to claim 8, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

15. The foamable polypropylene resin composition according to claim 9, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

16. The foamable polypropylene resin composition according to claim 10, wherein the higher fatty acid amide is selected from the group consisting of erucamide, stearamide, oleamide and ethylenebis(stearamide).

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1 is a schematic partial enlarged sectional view of a foamed resin molded body of Example.

DESCRIPTION OF EMBODIMENTS

(2) 1. Polypropylene Resin

(3) The polypropylene resin, which is not limited to a particular polypropylene resin, has a melt flow rate (MFR) at 230 C. and 21.2 N measured pursuant to ISO 1133 of preferably 5 g/10 minutes to 150 g/10 minutes and more preferably 15 g/10 minutes to 120 g/10 minutes. This is because the fluidity of the composition is appropriate.

(4) 2. Rubber or Thermoplastic Elastomer

(5) Preferred examples of the rubber include, but are not limited to, an ethylene--olefin copolymer. Examples of the ethylene--olefin copolymer include an ethylene-propylene copolymer (EPM), an ethylene-butene copolymer (EBM), an ethylene-octene copolymer (EOM), and an ethylene-propylene-nonconjugated diene copolymer (EPDM).

(6) Preferred examples of the thermoplastic elastomer include, but are not limited to, styrene-based elastomers, olefin-based elastomers, urethane-based elastomers, and polyester-based elastomers.

(7) 3. Talc

(8) Examples of the talc surface-treated for increased dispersibility include talc surface-treated with silane coupling agents, titanium coupling agents, higher fatty acids, higher fatty acid esters, higher fatty acid amides, higher fatty acid salts, or other surfactants. Among these, talc in which siloxane is added to a surface thereof by a silane coupling agent is preferred.

(9) The amount of the talc to be blended is preferably 20 parts by mass or more.

(10) The foamable polypropylene resin composition may contain inorganic fillers other than the talc in addition to the talc. Examples of the inorganic fillers include particulate fillers such as calcium carbonate, barium sulfate, and glass beads and plate-shaped fillers such as kaolin, glass flakes, lamellar silicates, and mica.

(11) 4. Organic Crystal Nucleating Agent

(12) Examples of the organic crystal nucleating agent include, but are not limited to, sorbitol-based agents, amide-based agents, and metal benzoates.

(13) 5. Foaming Agent

(14) Examples of the foaming agent include, but are not limited to, physical foaming agents and chemical foaming agents. Among these, chemical foaming agents are preferred. Examples of the chemical foaming agents include organic chemical foaming agents and inorganic chemical foaming agents. Examples of the inorganic chemical foaming agents include sodium bicarbonate (sodium hydrogen carbonate) and nitrite hydride.

(15) The foaming agent having a gas generating amount of 150 ml/5 g to 250 ml/5 g is preferably added in an amount of 5 parts by mass to 15 parts by mass.

(16) 6. Higher Fatty Acid Amide

(17) Examples of the higher fatty acid amid include, but are not limited to, erucamide, stearamide, oleamide, and ethylenebis(stearamide). Among these, erucamide is preferred.

(18) 7. Compatibilizer

(19) The compatibilizer, which is not limited to a particular compatibilizer, is preferably a copolymer of ethylene and at least one vinyl monomer having less affinity with the higher fatty acid amide; specific examples thereof include, but are not limited to, an ethylene-acrylic acid copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, an ethylene-ethyl acrylate copolymer, an ethylene-isobutyl acrylate copolymer, an ethylene-n-butyl acrylate copolymer, an ethylene-2-ethylhexyl acrylate copolymer, an ethylene-ethyl acrylate-maleic anhydride copolymer, an ethylene-ethyl acrylate-glycidyl methacrylate copolymer, an ethylene-glycidyl methacrylate copolymer, an ethylene-vinyl acetate-glycidyl methacrylate copolymer, and an ethylene-vinyl acetate copolymer or a saponified product thereof. These copolymers may be used singly, or two or more of them may be used in combination.

(20) The blending mass ratio of the higher fatty acid amide to the compatibilizer, which is not limited to a particular ratio, is preferably 1:10 to 2:1 and more preferably 1:3 to 2:1.

(21) The total amount to be added, relative to 100 parts by mass of the polypropylene resin, of the higher fatty acid amide and the compatibilizer having the blending mass ratio, is preferably, but not limited to, 0.8 part by mass to 15.0 parts by mass and more preferably 1.0 part by mass to 9.5 parts by mass.

(22) 8. Foamed Molded Body

(23) Examples of the use of the foamed molded body include, but are not limited to, automobile exterior parts such as grilles, bumpers, and cowl louvers and automobile interior parts such as instrumental panels, consoles, trims, pillars, center clusters, and deck side trims.

EXAMPLES

(24) Foamable polypropylene resin compositions of Samples 1 to 17 with the formulations (the formulation values are represented in parts by mass) listed in the following Table 2 were prepared to mold foamed polypropylene resin molded bodies. Samples 1 to 10 are Examples, whereas Samples 11 to 17 are Comparative Examples.

(25) TABLE-US-00002 TABLE 2 Sample No. 1 2 3 4 5 6 Criteria Material PP-1 MFR = 100 100 100 100 100 100 formulation PP-2 MFR = 38 100 (parts by mass) Rubber-1 Ethylene--olefin copolymer 25.0 62.5 13.3 25.0 25.0 25.0 Rubber-2 Ethylene--olefin copolymer Rubber-3 Styrene-based elastomer Talc-1 Surface-treated Particle diameter: 1 m Talc-2 Surface-treated 41.7 87.5 20.0 41.7 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated Particle diameter: 2 m Talc-4 Surface-untreated Particle diameter: 6 m Organic crystal Sorbitol-based 0.33 0.50 0.27 5.0 0.33 nucleating agent 1 Organic crystal Amide-based 0.33 nucleating agent 2 Foaming agent-1 Gas amount 165 ml/5 g 8.3 12.5 6.7 8.3 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g Property Flexural rigidity *10.sup.6 (Nm) 2.2 2.4 2.0 2.4 2.2 2.2 2.0 or higher High-speed surface impact 30 C. (J) 7.2 8.1 6.8 6.5 7.5 6.3 4 or higher Crystallinity of core layer resin c (%) 30.6 30.9 30.1 31.5 30.8 30.4 30.0 or higher part between foamed cells Crystallinity index c/s 1.06 1.05 1.06 1.08 1.05 1.06 1.05 or higher Foamed state closed closed closed closed closed closed closed cell cell cell cell cell cell cell Average foamed cell diameter m 187 130 203 145 213 175 100 to 300 Sample No. 7 8 9 10 11 12 Criteria Material PP-1 MFR = 100 100 100 100 100 100 100 formulation PP-2 MFR = 38 (parts by mass) Rubber-1 Ethylene--olefin copolymer 25.0 25.0 25.0 25.0 Rubber-2 Ethylene--olefin copolymer 25.0 Rubber-3 Styrene-based elastomer 25.0 Talc-1 Surface-treated 41.7 Particle diameter: 1 m Talc-2 Surface-treated 41.7 41.7 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated 41.7 Particle diameter: 2 m Talc-4 Surface-untreated Particle diameter: 6 m Organic crystal Sorbitol-based 0.33 0.33 0.33 0.33 0.33 nucleating agent 1 Organic crystal Amide-based nucleating agent 2 Foaming agent-1 Gas amount 165 ml/5 g 8.3 8.3 8.3 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g 8.3 Property Flexural rigidity *10.sup.6 (Nm) 2.1 2 2.1 2.2 1.8 1.5 2.0 or higher High-speed surface impact 30 C. (J) 7.1 6.7 7 7.3 2.9 3.8 4 or higher Crystallinity of core layer resin c (%) 30.3 31.1 30.3 30.7 30.1 26.5 30.0 or higher part between foamed cells Crystallinity index c/s 1.06 1.06 1.06 1.06 0.98 0.96 1.05 or higher Foamed state closed closed closed closed open closed closed cell cell cell cell cell cell cell Average foamed cell diameter m 195 171 214 166 340 254 100 to 300 Sample No. 13 14 15 16 17 Criteria Material formulation PP-1 MFR = 100 100 100 100 100 100 (parts by mass) PP-2 MFR = 38 Rubber-1 Ethylene--olefin copolymer 25.0 20.0 120 25.0 25.0 Rubber-2 Ethylene--olefin copolymer Rubber-3 Styrene-based elastomer Talc-1 Surface-treated Particle diameter: 1 m Talc-2 Surface-treated 13.3 180 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated Particle diameter: 2 m Talc-4 Surface-untreated 41.7 Particle diameter: 6 m Organic crystal Sorbitol-based 0.33 0.27 0.80 8.3 nucleating agent 1 Organic crystal Amide-based 0.03 nucleating agent 2 Foaming agent-1 Gas amount 165 ml/5 g 8.3 6.7 20.0 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g Property Flexural rigidity *10.sup.6 (Nm) 1.6 1.2 2.3 2.4 1.7 2.0 or higher High-speed surface impact 30 C. (J) 2.3 2.5 3.2 3.8 4.2 4 or higher Crystallinity of core layer resin c (%) 27.8 29.8 30.3 31.9 2.71 30.0 or higher part between foamed cells Crystallinity index c/s 0.99 0.97 0.96 1.05 0.98 1.05 or higher Foamed state open closed closed closed closed closed cell cell cell cell cell cell Average foamed cell diameter m 283 238 152 224 264 100 to 300

(26) The details of the used materials are as follows. The rubber in this section collectively refers to the rubber or the thermoplastic elastomer.

(27) PP-1: trade name BX3920 manufactured by SK global chemical, or a polypropylene resin with an MFR of 100 g/10 minutes.

(28) PP-2: trade name BH975MO manufactured by Borouge, or a polypropylene resin with an MFR of 38 g/10 minutes.

(29) Rubber-1: trade name Engage 8842 manufactured by Dow Elastomer, or an ethylene--olefin copolymer.

(30) Rubber-2: trade name Tafmer DF610 manufactured by Mitsui Chemicals, Inc., or an ethylene--olefin copolymer.

(31) Rubber-3: trade name Septon 2063 manufactured by Kuraray Co., Ltd., or a styrene-based elastomer.

(32) Talc-1: trade name NANOACE D-1000 manufactured by Nippon Talc Co., Ltd., or talc having a 50% particle diameter (D50) of 1 m and surface-treated with siloxane. The 50% particle diameter pursuant to ISO 13320-1 was measured by a laser diffraction particle size analyzer (the same throughout this specification).

(33) Talc-2: trade name NSultraC manufactured by IMI FABI, or talc having a particle diameter of 2 m and surface-treated with siloxane.

(34) Talc-3: trade name HTPultra5L manufactured by IMI FABI, or surface-untreated talc with a particle diameter of 2 m.

(35) Talc-4: trade name GH7 manufactured by Hayashi Kasei Co., Ltd., or surface-untreated talc with a particle diameter of 6 m.

(36) Organic Crystal Nucleating Agent 1: trade name GEL ALL MD manufactured by New Japan Chemical Co., Ltd., or 1,3:2,4-bis-O-(4-methylbenzylidene)-D-sorbitol.

(37) Organic Crystal Nucleating Agent 2: trade name Rikaclear PC1 manufactured by New Japan Chemical Co., Ltd., or an amide-based crystal nucleating agent.

(38) Foaming Agent MB-1: trade name Polythlene EE25C manufactured by Eiwa Chemical Ind. Co., Ltd. This is a sodium bicarbonate masterbatch.

(39) Foaming Agent MB-2: trade name Polythlene EE65C manufactured by Eiwa Chemical Ind. Co., Ltd. This is a sodium bicarbonate masterbatch.

(40) Each of the foamable polypropylene resin compositions of Sample 1 to Sample 17 was injected into a flat cavity with a gap of 1.5 mm of a mold (not illustrated). A movable mold of the mold was then core-backed to increase the gap of the cavity, and the composition was foamed to mold a plate-shaped foamed polypropylene resin molded body with a thickness of 2.8 mm. That is, the foaming ratio was 1.87. In this molded foamed polypropylene resin molded body 1, as illustrated in FIG. 1, a core layer includes foamed cells 2 and a resin part 3 between foamed cells, and surface parts adjacent to the mold include skin layer resin parts 4 (the broken lines in FIG. 1 are lines for distinguishing the parts from the core layer) containing few foamed cells. Plate-shaped test specimens having certain measurement-dependent dimensions were cut out of this plate-shaped molded body 1, and their property data were measured as follows.

(41) (A) Flexural Rigidity

(42) Pursuant to ISO 178 (JIS K7171), a test specimen with 10 mm80 mma thickness of 2.8 mm was subjected to a three-point flexural test to measure a flexural modulus of elasticity, and the flexural modulus of elasticity was multiplied by a geometrical moment of inertia to calculate flexural rigidity.

(43) The flexural rigidity of 2.010.sup.6 Nm or higher was determined to be good.

(44) (B) Method of High-Speed Surface Impact Test

(45) Pursuant to ISO 6603-2 (JIS K7211-2), impacts were applied to a test specimen with 120 mm130 mma thickness of 2.8 mm at a high and constant speed at a test temperature of 30 C. by an instrumentation impact tester (striker shape: spherical with a diameter of 12.7 mm, support base inner diameter: 76.2 mm, and impact speed: 5 m/second), a force and a deformation amount generated were captured as an impact waveform, and impact energy (puncture energy) which had been consumed until puncture displacement was reached was measured. At the puncture displacement, a maximum impulsive force was reduced by half.

(46) The impact energy of 4 J or higher was determined to be good.

(47) (C) How to Determine Crystallinity

(48) For each of the resin part 3 between the foamed cells and the skin layer resin part 4, measurement was performed by the following method using a differential scanning calorimeter (DSC) (Q200 manufactured by TA Instruments).

(49) The temperature was raised from 0 C. to 250 C. at a temperature rising rate of 40 C./minute to determine the amount of heat of fusion. From the obtained amount of heat of fusion H (J/g), pieces of crystallinity (the crystallinity c of the resin part 3 between the foamed cells and the crystallinity s of the skin layer resin part 4) were determined from the expression (H/resin fraction/209)100(%).

(50) In the expression, the resin fraction is a residual polymer fraction obtained by subtracting the weight fraction of an inorganic component (a filler and the like) within the material (0.8 when the filler is 20%). The value 209 is the amount of heat of fusion of a polypropylene resin (J/g) when it is 100% crystallized.

(51) The crystallinity c of the resin part 3 between the foamed cells of 30.0% or higher was determined to be good.

(52) The crystallinity index c/s of 1.05 or higher was determined to be good.

(53) (D) Average Foamed Cell Diameter

(54) Pursuant to ASTM D3576-77, an average foamed cell diameter was determined. First, a picture of a section of the test specimen cut out of the molded body 1 was taken with a 50-fold magnification (which can photograph the entire thickness direction) by a stereoscopic microscope. On this picture, straight lines (indicated by the chain double-dashed lines in FIG. 1) were drawn in the horizontal direction and the vertical direction, the lengths of all chords of foamed cells that the lines cross were measured, and an average t of the lengths of the chords was determined. From the expression d=t/0.616, an average foamed cell diameter d was calculated.

(55) The average foamed cell diameter of 100 m to 300 m was evaluated to be good.

(56) The molded bodies having mainly closed cells in the foamed state were evaluated to be good.

(57) Table 2 shows property data. The molded bodies of Samples 1 to 10 (Examples) were determined to be good for all pieces of property data, balancing rigidity and impact resistance to a high degree. In contrast, the molded bodies of Samples 11 to 17 (Comparative Examples) were insufficient in either or both of rigidity and impact resistance.

(58) Next, foamable polypropylene resin compositions of Samples 18 to 34 with the formulations (the formulation values are represented in parts by mass) listed in the following Table 3, in which a scratch-resistant modifier was further contained, were prepared to mold foamed polypropylene resin molded bodies. Table 3 lists Sample 1 again together with additional property data described below. Samples 18 to 23 contain the scratch-resistant modifier based on the formulation of Sample 1, whereas Samples 24 to 32 contain the scratch-resistant modifier based on the formulations of Samples 2 to 10, respectively.

(59) TABLE-US-00003 TABLE 3 Sample No. 1 18 19 20 21 22 Criteria Material PP-1 MFR = 100 100 100 100 100 100 100 formulation PP-2 MFR = 38 (parts by Rubber-1 Ethylene--olefin copolymer 25.0 25.0 25.0 25.0 25.0 25.0 mass) Rubber-2 Ethylene--olefin copolymer Rubber-3 Styrene-based elastomer Talc-1 Surface-treated Particle diameter: 1 m Talc-2 Surface-treated 41.7 41.7 41.7 41.7 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated Particle diameter: 2 m Talc-4 Surface-untreated Particle diameter: 6 m Organic crystal nucleating agent 1 Sorbitol-based 0.33 0.33 0.33 0.33 0.33 0.33 Organic crystal nucleating agent 2 Amide-based Foaming agent-1 Gas amount 165 ml/5 g 8.3 8.3 8.3 8.3 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g Scratch-Resistant Modifier 1 Erucamide + Compatibilizer 0.7 1.2 3.3 9.2 Scratch-Resistant Modifier 2 Erucamide 0.5 Scratch-Resistant Modifier 3 Ethylenebis(stearamide) Property Flexural rigidity *10.sup.6 (Nm) 2.2 2.2 2.2 2.2 2.2 2.2 2.0 or higher High-speed surface impact 30 C. (J) 7.2 7.2 7.4 7.2 6.4 7.3 4 or higher Crystallinity of core layer resin part c (%) 30.6 30.5 30.7 30.6 30.4 30.4 30.0 or higher between foamed cells Crystallinity index c/s 1.06 1.06 1.06 1.06 1.07 1.05 1.05 or higher Foamed state closed closed closed closed closed closed closed cell cell cell cell cell cell cell Average foamed cell diameter m 187 162 159 187 174 174 100 to 300 Scratch resistance Critical vertical force N 2.1 2.8 7.1 8.0 9.1 8.7 6.0 or higher (scratch characteristics) Sticking after heat Finger tactile sensory Absent Absent Absent Absent Absent Present Absent resistance test evaluation Color difference change 1.7 1.9 2.1 2.4 2.6 4.2 3.0 or less before and after heat resistance test Sample No. 23 24 25 26 27 28 Criteria Material PP-1 MFR = 100 100 100 100 100 100 formulation PP-2 MFR = 38 100 (parts by Rubber-1 Ethylene--olefin copolymer 25.0 62.5 13.3 25.0 25.0 25.0 mass) Rubber-2 Ethylene--olefin copolymer Rubber-3 Styrene-based elastomer Talc-1 Surface-treated Particle diameter: 1 m Talc-2 Surface-treated 41.7 87.5 20.0 41.7 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated Particle diameter: 2 m Talc-4 Surface-untreated Particle diameter: 6 m Organic crystal nucleating agent 1 Sorbitol-based 0.33 0.50 0.27 5.0 0.33 Organic crystal nucleating agent 2 Amide-based 0.33 Foaming agent-1 Gas amount 165 ml/5 g 8.3 12.5 6.7 8.3 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g Scratch-Resistant Modifier 1 Erucamide + Compatibilizer 5.0 2.7 3.3 3.3 3.3 Scratch-Resistant Modifier 2 Erucamide Scratch-Resistant Modifier 3 Ethylenebis(stearamide) 0.5 Property Flexural rigidity *10.sup.6 (Nm) 2.2 2.4 2.0 2.4 2.2 2.2 2.0 or higher High-speed surface impact 30 C. (J) 7.3 8.1 6.8 6.5 7.5 6.3 4 or higher Crystallinity of core layer resin part c (%) 30.4 30.9 30.1 31.5 30.8 30.4 30.0 or higher between foamed cells Crystallinity index c/s 1.05 1.05 1.06 1.08 1.05 1.06 1.05 or higher Foamed state closed closed closed closed closed closed closed cell cell cell cell cell cell cell Average foamed cell diameter m 191 130 203 145 213 175 100 to 300 Scratch resistance Critical vertical force N 9.3 8.5 7.8 8.1 8.3 8.0 6.0 or higher (scratch characteristics) Sticking after heat Finger tactile sensory Present Absent Absent Absent Absent Absent Absent resistance test evaluation Color difference change 4.5 2.3 2.4 2.5 2.2 2.6 3.0 or less before and after heat resistance test Sample No. 29 30 31 32 33 34 Criteria Material PP-1 MFR = 100 100 100 100 100 100 100 formulation PP-2 MFR = 38 (parts by Rubber-1 Ethylene--olefin copolymer 25.0 25.0 25.0 25.0 mass) Rubber-2 Ethylene--olefin copolymer 25.0 Rubber-3 Styrene-based elastomer 25.0 Talc-1 Surface-treated 41.7 Particle diameter: 1 m Talc-2 Surface-treated 41.7 41.7 41.7 Particle diameter: 2 m Talc-3 Surface-untreated 41.7 Particle diameter: 2 m Talc-4 Surface-untreated 41.7 Particle diameter: 6 m Organic crystal nucleating agent 1 Sorbitol-based 0.33 0.33 0.33 0.33 0.33 0.33 Organic crystal nucleating agent 2 Amide-based Foaming agent-1 Gas amount 165 ml/5 g 8.3 8.3 8.3 8.3 8.3 Foaming agent-2 Gas amount 235 ml/5 g 8.3 Scratch-Resistant Modifier 1 Erucamide + Compatibilizer 3.3 3.3 3.3 3.3 3.3 3.3 Scratch-Resistant Modifier 2 Erucamide Scratch-Resistant Modifier 3 Ethylenebis (stearamide) Property Flexural rigidity *10.sup.6 (Nm) 2.1 2.0 2.1 2.2 1.8 1.6 2.0 or higher High-speed surface impact 30 C. (J) 7.1 6.7 7.0 7.3 2.9 2.3 4 or higher Crystallinity of core layer resin part c (%) 30.3 31.1 30.3 30.7 30.1 27.8 30.0 or higher between foamed cells Crystallinity index c/s 1.06 1.06 1.06 1.06 0.98 0.99 1.05 or higher Foamed state closed closed closed closed open open closed cell cell cell cell cell cell cell Average foamed cell diameter m 195 171 214 166 340 283 100 to 300 Scratch resistance Critical vertical force N 8.0 8.4 8.1 8.5 3.9 3.5 6.0 or higher (scratch characteristics) Sticking after heat Finger tactile sensory Absent Absent Absent Absent Absent Absent Absent resistance test evaluation Color difference change before and after heat resistance 2.7 2.4 2.5 2.3 2.5 2.2 3.0 or less test

(60) The details of the used scratch-resistant modifiers are as follows, with the details of the other materials as described above.

(61) Scratch-Resistant Modifier 1: trade name Nofalloy KA832 manufactured by NOF Corporation, or a mixture of a higher fatty acid amide (estimated to be erucamide) and a compatibilizer (estimated to be a copolymer of ethylene and at least one vinyl monomer). The blending mass ratio of the higher fatty acid amide to the compatibilizer is estimated to be 2:3.

(62) Scratch-Resistant Modifier 2: trade name Fatty Acid Amide E manufactured by Kao Corporation, or erucamide.

(63) Scratch-Resistant Modifier 3: trade name Kao Wax EB-G manufactured by Kao Corporation, or ethylenebis(stearamide).

(64) Using the foamable polypropylene resin compositions of Samples 18 to 34, the plate-shaped molded body 1 with a thickness of 2.8 mm was molded by a method similar to that of Samples 1 to 17. Plate-shaped test specimens having certain measurement-dependent dimensions were cut out of this plate-shaped molded body 1, the same property data as those of Samples 1 to 17 were measured, and besides, scratch resistance, sticking after heat resistance test, and a color difference change before and after heat resistance test were measured as follows as additional property data. The additional property data were measured also for Sample 1.

(65) (E) Scratch Resistance (Scratch Characteristics)

(66) Pursuant to ISO 19252 (JIS K7316), the surface of the test specimen was subjected to a scratch test (chip size: a diameter of 10 m (a stainless sphere), scratch speed: 100 mm/second, and scratch distance: 100 mm) to determine a critical vertical force. The critical vertical force of 6.0 N or higher was determined to be good.

(67) (F) Sticking after Heat Resistance Test

(68) The test specimen was put into a heating bath to carry out a heat resistance test of 110 C.600 hours, and the surface of the test specimen after the heat resistance test was touched by a finger to perform sensory evaluation. The absence of sticking was evaluated to be good.

(69) (G) Color Difference Change Before and after Heat Resistance Test

(70) Pursuant to ISO 11664-4 (JIS Z8781-4), the color difference change of the surface of the test specimen before and after the heat resistance test was measured. The color difference change of 3.0 or less was evaluated to be good.

(71) Table 3 lists the property data. The molded bodies of Samples 18 to 32 were determined to be good for the property data including flexural rigidity, high-speed surface impact, crystallinity, and average foamed cell diameter, balancing rigidity and impact resistance to a high degree, which were Examples. However, Samples 1 and 18 have room for improvement in that they are insufficient in scratch resistance. Samples 22 and 23 have room for improvement in that they have sticking after the heat resistance test and are large in the color difference change. Samples 19 to 21 and 24 to 32 were determined to be good for scratch resistance, sticking after the heat resistance test and the color difference change, which were favorable Examples.

(72) In contrast, the molded bodies of Samples 33 and 34 were insufficient in either or both of rigidity and impact resistance, which were Comparative Examples. In addition, even though the higher fatty acid amide and the compatibilizer were added, they were insufficient in scratch resistance; it is considered that this is because the surface-untreated talc absorbed the higher fatty acid amide.

(73) The present invention is not limited to Examples and can be embodied with alterations as appropriate without departing from the scope of the invention.

REFERENCE SIGNS LIST

(74) 1 Foamed polypropylene resin molded body 2 Foamed cell 3 Resin part between foamed cell 4 Skin layer resin part