Polypropylene-based resins and polypropylene-based resin compositions

Abstract: Disclosed are a polypropylene-based resin and a polypropylene-based resin composition having well-balanced, high-level flowability, stiffness and impact resistance. The polypropylene-based resin has an MI of from 30 to 70 g/10 min and a 25°C xylene-soluble content, x, of from 5 to 15 % by weight, in which the 25°C xylene-soluble component is such that (a) its ethylene unit content, z, is from 20 to 30 % by weight, and (b) its intrinsic viscosity, [η], in decalin at 135°C is not smaller than 2.00dl/g, and in which the 25°C xylene-insoluble component is such that (c) its ethylene unit content, y (% by weight), satisfies the following: 100y/[y × (1-x/100) + x ] ≦ 1.13z - 16.6, (d) in GPC, the content of its constituent component having a molecular weight of not smaller than 10 6 is not smaller than 2 % by weight, (e) its MI is from 40 to 130 g/10 min, and (f) its stereospecificity index is not smaller than 98.5 %. The resin composition comprises (A) from 45 to 90 % by weight of the polypropylene-based resin, (B) from 5 to 50 % by weight of an ethylenic copolymer, and (C) from 0 to 25 % by weight of talc.

Description: FIELD OF THE INVENTION The present invention relates to polypropylene-based resin compositions. More precisely, it relates to polypropylene-based resin compositions, which have well-balanced, high-level flowability, stiffness, tensile breaking elongation and impact resistance that are higher than those of conventional ones, and which are favorably used as housing materials for car parts and various household electric appliances. BACKGROUND OF THE INVENTION As having good mechanical characteristics and workability, crystalline polypropylenes are widely used for producing films and various shaped articles in various fields. In particular, they are much used in the field of injection molding. However, since crystalline polypropylenes have poorly-balanced stiffness and impact resistance as compared with polystyrenes and ABS resins, their use is inevitably limited. If their mean molecular weight is increased, crystalline polypropylenes may have improved impact strength and therefore have well-balanced stiffness and impact resistance. However, crystalline polypropylenes having a large mean molecular weight are problematic in that their workability is lowered and, in particular, their producibility in injection molding is significantly lowered. Given this situation, it is desired to improve crystalline polypropylenes so as to have well-balanced stiffness and impact resistance without interfering with their workability. For the purpose of obtaining crystalline polypropylenes having improved stiffness and elasticity, there is known a two-stage polymerization method of producing a mixture of polymers each having a different molecular weight. For example, JP-A-190006/1982 discloses a method of producing a mixture of polymers of which one has an intrinsic viscosity [η] of from 0.6 to 1.7 dl/g and the other from 1.5 to 4.6 dl/g. JP-A-7406/1983 discloses a method of producing a mixture of polymers of which one has an intrinsic viscosity [η] of from 0.6 to 3.5 dl/g and the other from 5 to 10 dl/g. However, these methods are still insufficient to improve the stiffness and elasticity of polymers. In JP-A-356511/1992, proposed was a polypropylene that satisfies the following relation between the content, Ai (% by weight) of the constituent component having a molecular weight of from 2,000 to 26,000 and the intrinsic viscosity [η] of the polymer. log Ai ≧ 1.60 - 1.32 x log [η] Although the polypropylene has improved elasticity and heat resistance, the balance of the stiffness and the impact resistance of the polymer is still not good. On the other hand, since crystalline polypropylenes generally have poor low-temperature impact strength, they are often improved by adding thereto a rubber-type elastic material such as ethylene-propylene rubber (EPR). The impact resistance of the polymers comprising such a rubber-type elastic material may be improved, but the addition of such a rubber-type elastic material to crystalline polypropylenes is problematic in that the stiffness of the resulting polymer mixtures is inevitably lowered. Therefore, desired is a technique of improving the impact resistance of polypropylene-based resin compositions without lowering their stiffness. Various techniques of adding ethylene-butene-1 copolymers to polypropylene-based resins have heretofore been tried. For example, known is a technique of adding a specific ethylene-butene-1 copolymer to a polypropylene-based resin to thereby make the resulting resin mixture have well-balanced stiffness and impact resistance (see JP-A-192506/1994 and JP-A-18151/1995). They say that the addition of an ethylene-butene-1 copolymer having a peak melting point of not higher than 80°C and having a low degree of X-ray crystallinity of smaller than 20 % produces better results. JP-A-87478/1997 discloses a technique of adding an ethylene-butene-1 copolymer having a melting point of from 60 to 100°C to a polypropylene-based resin to thereby improve the balance of the stiffness and the impact resistance of the resulting resin mixture. However, these polypropylene-based resin compositions comprising such an ethylene-butene-1 copolymer are still problematic in that the balance of their stiffness and impact resistance at high levels is not always satisfactory. SUMMARY OF THE INVENTION Given this situation, the present invention is to provide a polypropylene-based resin and a polypropylene-based resin compositions having well-balanced, high-level flowability, stiffness, tensile breaking elongation and impact resistance that are higher than those of conventional polypropylene-based resins and polypropylene-based resin compositions. In order to attain the above-mentioned object, we, the present inventors have assiduously studied and, as a result, have found that the object is attained by a polypropylene-based resin composition comprising an ordinary polypropylene-based resin, an ethylene-butene-1 copolymer having specific properties, and optionally talc, in a specific ratio. Based on these findings, we have completed the present invention. Specifically, the present invention provides; a polypropylene-based resin composition comprising (A') from 45 to 90 % by weight of a polypropylene-based resin, (B') from 5 to 50 % by weight of an ethylene-butene-1 copolymer having a butene-1 unit content of from 10 to 25 mol%, a melt index of from 0.5 to 10 g/10 min, a peak melting point of from 20 to 50°C, a quantity of heat for crystallization of from 20 to 50 J/g, and a ratio of the quantity of heat for crystallization (J/g) to the butene-1 unit content (mol%) of not smaller than 1.4, and (C) from 0 to 25 % by weight of talc. DISCLOSURE OF THE INVENTION The measurement of 13 C-NMR as referred to herein was effected in the following manner. The solution for 13 C-NMR measurement was prepared by dissolving a 220mg sample in a 3 ml mixed solvent of 1,2,4-trichlorobenzene/deuteriobenzene (90/10, by volume) in a NMR tube. 13 C-NMR measurement was performed according to the following condition. Device: JNM-EX400 Model, manufactured by JEOL LTD. Pulse Width: 9 µsec (45°) Pulse Repetition Time: 4 seconds Spectral Width: 20000 Hz Temperature: 130°C Accumulation Number: 1000 to 10000 times The present invention provides a polypropylene-based resin composition comprising (A') from 45 to 90 % by weight of a polypropylene-based resin, (B') from 5 to 50 % by weight of an ethylene-butene-1 copolymer having specific properties as mentioned below, and (C) from 0 to 25 % by weight of talc. As the polypropylene-based resin of the component (A'), preferred is a crystalline polypropylene-based resin. Especially preferred is a block copolymer comprising a homopolymer moiety of a propylene homopolymer having an isotactic structure and a copolymer moiety of an ethylene-propylene random copolymer, and having a melt index (MI) of from 30 to 100 g/10 min, of which the copolymer content is from 3 to 20 % by weight and in which the ethylene unit content of the copolymer moiety is from 20 to 35 % by weight. The copolymer content of the block copolymer can be obtained as the 25°C xylene-soluble content of the copolymer. The 25°C xylene-soluble and insoluble components are isolated from the copolymer in the manner mentioned below. First, (1) a resin sample is accurately weighed to be 5 ± 0.05 g, and put into a 1000-ml eggplant-type flask, to which is added 1 ± 0.05 g of BHT (antioxidant; 2,6-di-t-butyl-p-cresol). Then, 700 ± 10 ml of paraxylene is added thereto, while a rotator is inserted thereinto. Next, (2) a condenser is fixed to the flask, and the flask is heated in an oil bath at 140 ± 5°C for 120 ± 30 minutes, while the rotator is moved, whereby the sample is dissolved in paraxylene. Next, (3) the solution formed in the flask is transferred into a 1000-ml beaker, and this is spontaneously cooled to room temperature (25°C) over a period of 8 hours or longer, while being stirred with a stirrer. Then, the precipitate formed is removed through filtration using wire gauze. (4) The resulting filtrate is further filtered through filter paper, and the thus-obtained filtrate is poured into 2000 ± 200 ml of methanol in a 3000-ml beaker. This is stirred at room temperature (25°C) with a stirrer over a period of 2 hours or longer. Next, (5) the precipitate formed is taken out through filtration using wire gauze, then dried in air for 5 hours or longer, and thereafter further dried in a vacuum drier at 100 ± 5°C for 240 to 270 minutes to collect the component that is soluble in xylene at 25°C. On the other hand, (6) the precipitate as separated to remain on the wire gauze in the above-mentioned step (3) is again subjected to the steps (1) and (2) whereby it is dissolved in paraxylene. Immediately while hot, the resulting solution is put into 2000 ± 100 ml of methanol in a 3000-ml beaker, stirred with a stirrer over a period of 2 hours or longer, and then statistically left at room temperature (25°C) overnight. Next, (7) the resulting precipitate is taken out through filtration using wire gauze, then dried in air for 5 hours or longer, and thereafter again dried in a vacuum drier at 100 ± 5°C for 240 to 270 minutes to collect the component that is insoluble in xylene at 25°C. The 25°C xylene-soluble content of the copolymer is represented by the following equation in which A indicates the weight (g) of the sample and C indicates the weight (g) of the soluble component collected in the above-mentioned step (5). x (% by weight) = 100 × C/A The ethylene unit content of said copolymer moiety can be obtained in the same manner as follows. A copolymer sample is first subjected to 13 C-NMR. From the intensities of the seven peaks within the range of from 21 to 35 ppm [tetramethylsilane (TMS) chemical shift standard] in the resulting spectral pattern, the triad fractions (mol%) of ethylene (E) and propylene (P) are obtained according to the following equations. f EPE = [K(Tδδ)/T] x 100 f PPE = [K(Tβδ)/T] x 100 f EEE = [K(Sγδ)/4T + K(Sδδ)/2T] x 100 f PPP = [K(Tββ)/T] x 100 f PEE = [K(Sβ γ)/T] x 100 f PEP = [K(Sββ)/T] x 100 In these; T = K(Tδδ) + K(Tβδ) + K(Sγδ)/4 + K(Sδδ)/2 + K(Tβ β) + K(Sβδ) + K(Sββ) In these, for example, f EPE indicates the EPE triad fraction (mol%), and K(Tδδ) indicates the integrated intensity of the peak for the Tδδ carbon. Next, using the above-mentioned triad fractions, the ethylene unit content (% by weight) is obtained in accordance with the following equation. Ethylene Unit Content (% by weight) = 28{3f EEE + 2(f PEE + f EPE ) + fPPE + f PEP } X 100/[28{3f EEE + 2(f PEE + f EPE ) + f PPE + f PEP } + 42{3f PPP + 2(f PPE + f PEP ) + f EPE + f PEE }] Of the above-mentioned block copolymer, if the copolymer content is smaller than 3 % by weight, the impact resistance of the resin composition comprising the copolymer will be poor. If, however, the copolymer content is larger than 20 % by weight, the component (B') added to the resin composition will poorly exhibit its effect. If the ethylene unit content of the copolymer moiety in the block copolymer is smaller than 20 % by weight, the impact resistance of the resin composition comprising the copolymer will be poor. If, however, the ethylene unit content in question is larger than 35 % by weight, the elongation of the resin composition comprising the copolymer will be poor. If the MI of the block copolymer is smaller than 30 g/10 min, the shapability of the resin composition comprising the copolymer is poor; but if it is larger than 100 g/10 min, the kneading workability of the resin composition comprising the copolymer is unfavorably poor. From the viewpoint of shapability and kneading workability of the resin composition, the MI of the copolymer is preferably from 40 to 70 g/10 min. The MI of the copolymer is measured according to JIS K-7210, at a temperature of 230°C and under a load of 2.16 kg. The production of the polypropylene-based resin of the component (A') is not specifically defined. To produce the resin, employable is any desired method that may be selected from known methods. The ethylene-butene-1 copolymer of the component (B') is one having a butene-1 unit content of from 10 to 25 mol%, a melt index of from 0.5 to 10 g/10 min, a peak melting point of from 20 to 50°C, a quantity of heat for crystallization of from 20 to 50 J/g, and a ratio of the quantity of heat (J/g) to the butene-1 unit content (mol%) of not smaller than 1.4. The butene-1 unit content of the copolymer is obtained according to the method of measurement of butene-1 unit content through 13 C-NMR which is described in Journal of Applied Polymer Science , Vol. 42, pp. 399-408, 1991. The peak melting point and the quantity of heat for crystallization of the copolymer are obtained through differential scanning calorimetry (DSC), according to the method mentioned below. A sample is put into a DSC device, heated from 50°C to 230°C, then kept at 230°C for 3 minutes, and thereafter cooled to -50°C at a cooling rate of 10°C/min, whereupon the quantity of heat as generated by the sample is measured to be the quantity of heat for crystallization of the sample. After having been cooled to -50°C, the sample is kept at -50°C for 5 minutes, and thereafter heated at a heating rate of 10°C/min, whereupon the peak temperature at which the sample is melted is measured to be the peak melting point of the sample. If the butene-1 unit content of the copolymer is smaller than 10 mol%, the copolymer could not satisfactorily exhibit its effect to improve the low-temperature impact resistance of the resin composition; but if it is larger than 25 mol%, the copolymer is difficult to handle in producing the resin composition. Considering the effect of the copolymer to improve the low-temperature impact resistance of the resin composition and also the handlability of the copolymer, the butene-1 unit content of the copolymer is preferably from 15 to 20 mol%, more preferably from 16 to 19 mol%. If the MI of the copolymer is smaller than 0.5 g/10 min, it is difficult to knead the copolymer with the polypropylene-based resin of the component (A'); but if it is larger than 10 g/10 min, the copolymer could not satisfactorily exhibit its effect to improve the impact resistance of the resin composition. Considering the kneadability of the copolymer with the component (A') and also the effect of the copolymer to improve the impact resistance of the resin composition, the MI of the copolymer is preferably from 1 to 5 g/10 min, more preferably from 2 to 3 g/10 min. The MI of the copolymer is measured according to JIS K-7210 at a temperature of 230°C and under a load of 2.16 kg. If the peak melting point of the copolymer is lower than 20°C, the elasticity of the resin composition comprising the copolymer is poor; but if it is higher than 50°C, the copolymer could not satisfactorily exhibit its effect to improve the impact resistance of the resin composition. Considering the elasticity of the resin composition and also the effect of the copolymer to improve the impact resistance of the resin composition, the peak melting point of the copolymer is preferably from 25 to 45°C, more preferably from 30 to 40°C. If the quantity of heat for crystallization of the copolymer is smaller than 20 J/g, the elasticity of the resin composition comprising the copolymer is poor; but if it is larger than 50 J/g, the copolymer could not satisfactorily exhibit its effect to improve the impact resistance of the resin composition. Considering the elasticity of the resin composition and also the effect of the copolymer to improve the impact resistance of the resin composition, the quantity of heat for crystallization of the copolymer is preferably from 25 to 45 J/g, more preferably from 30 to 40 J/g. If the ratio of the quantity of heat for crystallization of the copolymer (J/g) to the butene-1 unit content of the copolymer (mol%) is smaller than 1.4, the stiffness of the resin composition comprising the copolymer is low. From the viewpoint of the stiffness of the resin composition, the ratio of the quantity of heat for crystallization of the copolymer to the butene-1 unit content of the copolymer is preferably not smaller than 1.6, more preferably not smaller than 1.8. The method of producing the ethylene-butene-1 copolymer of the component (B') is not specifically defined, provided that it produces the intended copolymer having the specifically-defined properties. For example, a solution process, a vapor phase fluidized bed process or the like is employable to produce the copolymer, while using a Ziegler catalyst or a metallocene catalyst. The particle size of the talc to be used as the component (C) is not specifically defined, but is preferably from 0.5 to 3 µm from the viewpoint of the impact resistance of the resin composition. The talc can be surface-treated with a silane coupling agent or the like. If the content of the polypropylene-based resin of the component (A') is smaller than 45 % by weight, the stiffness of the composition is low so that the composition is not applicable to the production of car parts. If, however, said content is larger than 90 % by weight, the impact resistance of the resin composition is low. In view of the balance of the stiffness and the impact resistance of the resin composition, the content of the component (A') is preferably from 50 to 80 % by weight, more preferably from 55 to 70 % by weight. If the content of the ethylene-butene-1 copolymer of the component (B') is smaller than 5 % by weight, the copolymer could not satisfactorily exhibit its effect to improve the impact resistance of the resin composition; but if it is larger than 50 % by weight, the stiffness of the resin composition is low so that the composition is not applicable to the production of car parts. In view of the balance of the impact resistance and the stiffness of the resin composition, the content of the component (B') is preferably from 20 to 40 % by weight, more preferably from 25 to 35 % by weight. The component (C) of talc is an optional one, and it is not always necessary in the resin composition. However, it is desirable to add the component (C) of talc in order to improve the stiffness of the composition. However, if the content of the component (C), talc is larger than 25 % by weight, the impact resistance and the shapability of the resin composition are poor. From the viewpoint of the stiffness, the impact resistance and the shapability of the resin composition, the content of the component (C) is preferably from 3 to 15 % by weight, more preferably from 5 to 10 % by weight. The polypropylene-based resin composition of the present invention may additionally contain, if desired, any known additives such as reinforcing agents, fillers, pigments, nucleating agents, weather-resisting agents, antioxidants, antistatic agents, flame retardants, dispersing agents, etc., only within the ranges not interfering with the effects of the present invention. The method of producing the polypropylene-based resin composition of the present invention is not specifically defined. For example, the above-mentioned components (A'), (B') and (C), and optionally any other additives are melted and kneaded, using a single-screw extruder, a double-screw extruder, a Banbury mixer, a kneader, a roll mixer or the like. Now, the present invention is described in more detail with reference to the following Examples. The properties of the polypropylene-based resin samples prepared in these Examples were measured according to the methods mentioned hereinabove. EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 4 The components shown in Table 1 below were put into a kneader, 2FCM50 (manufactured by Kobe Steel, Ltd.) all at once, and kneaded to prepare pellets of various polypropylene-based resin compositions. Next, the pellets were molded, using an injection molding machine, IS100F3 (manufactured by Toshiba Machine Co., Ltd.), into JIS test pieces for measurement of physical properties. The physical properties of these test pieces were measured in the manner mentioned below. The data obtained are shown in Table 1. In Table 1-2, the hardness of the sample of Comparative Example 3 was too low to measure its Rockwell hardness. (1) Modulus of Bending Elasticity: Each sample was tested at 23°C in accordance with JIS K-7203. (2) Low-temperature Impact Strength: Each sample was tested at -30°C in accordance with JIS K-7110. (3) Rockwell Hardness R: Each sample was tested at 23°C in accordance with JIS K-7202. The Rockwell hardness R is a criterion of the stiffness of the sample. As has been mentioned in detail hereinabove, the polypropylene-based resin and the polypropylene-based resin composition of the present invention have well-balanced flowability and impact resistance, which are higher than those of conventional ones, and are therefore suitably used as shaping materials, for example, for car parts (e.g., bumpers, side members, air spoilers, trims, etc.), household electric appliances, daily necessaries, etc. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims: A polypropylene-based resin composition comprising (A') from 45 to 90 % by weight of a polypropylene-based resin, (B') from 5 to 50 % by weight of an ethylene-butene-1 copolymer having a butene-1 unit content of from 10 to 25 mol %, a melt index of from 0.5 to 10 g/10 min, a peak melting point of from 20 to 50°C, a quantity of heat for crystallization of from 20 to 50 J/g, and a ratio of the quantity of heat for crystallization (J/g) to the butene-1 unit content (mol %) of not smaller than 1.4, and (C) from 0 to 25 % by weight of talc. The polypropylene-based resin composition as claimed in claim 1, wherein the polypropylene-based resin of the component (A') is a block copolymer comprising a homopolymer moiety of a propylene homopolymer having an isotactic structure and a copolymer moiety of an ethylene-propylene random copolymer, and having a melt index of from 30 to 100 g/10 min, of which the copolymer content is from 3 to 20 % by weight and in which the ethylene unit content of the copolymer moiety is from 20 to 35 % by weight. The polypropylene-based resin composition as claimed in claim 2, wherein the copolymer moiety in the polypropylene-based resin of the component (A') is obtained as the constituent component that is soluble in xylene at 25°C. The polypropylene-based resin composition as claimed in claim 1 or 2, which comprises from 50 to 80 % by weight of the component (A'), from 20 to 40 % by weight of the component (B'), and from 3 to 15 % by weight of the component (C).

Inventors: KOBAYASHI YUTAKA, NAKAGAWA MASARU, SUMITIMO TAKASHI, TODA MASATOSHI, YAMADA MOTOKI, KOBAYASHI, YUTAKA, NAKAGAWA, MASARU, SUMITIMO, TAKASHI, TODA, MASATOSHI, YAMADA, MOTOKI
Applicants: IDEMITSU PETROCHEMICAL CO, IDEMITSU PETROCHEMICAL CO., LTD.
Application year: 1997
Main classification: C08L53
IPC codes: C08L9, C08L23, C08L53