Method for producing polypropylene blend composition

Abstract

To provide a method for producing a polypropylene blend composition which includes a nucleation method for giving a polypropylene molding having high rigidity.SOLUTION: A method for producing polypropylene blend composition in which 0.5 to 10 pts.mass of nucleus agent made of polypropylene-based resin (A) satisfying [condition A1] and [condition A2] and 90 to 99.5 pts.mass of polypropylene-based resin (B) which satisfies [condition B1] and [condition B2] are mixed and melt-kneaded, and 100 pts.mass of a polypropylene blend composition (C) having improved elastic modulus compared to the polypropylene-based resin (B) is obtained. [condition A1] The melting point of first temperature rise of DSC measured at the rate of temperature rise of 20°C / min. is ≥170°C. [condition A2] The crystallization temperature of DSC measured at the rate of temperature drop of 20°C / min. after holding for 5 minutes at 230°C is ≥110°C. [condition B1] The crystallization temperature of DSC measured at the rate of temperature drop of 20°C / min. after holding for 5 minutes at 230°C is <115°C. [condition B2] MFR=0.1 to 1000 g / 10 min.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for making a polypropylene blend composition that promotes nucleation of the polypropylene. [Background technology]

[0002] Polypropylene molded products have excellent physical properties and are widely used in applications such as automotive parts. However, in recent years, from the perspective of energy conservation, further weight reduction and higher rigidity of polypropylene molded products are desired. To achieve higher rigidity, nucleating agents have traditionally been used to promote crystallization. Nucleating agents, which are typically low-molecular-weight compounds, are available in non-melting and melting types. The former have problems with dispersibility in polypropylene, while the latter have problems such as odor due to volatilization during molding. High-molecular-weight nucleating agents have also been investigated, but they must be introduced by prepolymerization or other methods to improve dispersibility in polypropylene. Furthermore, high-performance nucleating agents are generally expensive. Under these circumstances, efforts have been made to use polypropylene itself as a nucleating agent. Patent Document 1 proposes a nucleation method using polypropylene with a very wide molecular weight distribution (containing high molecular weight components), but its effectiveness in itself, particularly in increasing rigidity, is unclear. Non-Patent Document 1 investigates nucleation using a commercially available polypropylene resin containing long chain branches, but due to the balance with increased entanglement, the addition of 20 to 40 mass% is required to maximize the nucleating agent effect. Patent Document 2 reports improvements in rigidity and heat resistance in a composition in which long chain branches are introduced throughout the system by reactive modification, but does not describe the effects of adding a small amount of polypropylene resin as a nucleating agent to other polypropylene resins. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2009-504822 [Patent Document 2] Special Publication No. 2022-538451 [Non-patent literature]

[0004] [Non-Patent Document 1] Polymer Journal, Vol. 40, No. 5, pp. 450-454, 2008 Summary of the Invention [Problem to be solved by the invention]

[0005] Polypropylene molded articles are required to have rigidity. Although the nucleation using polypropylene resin disclosed in the above-mentioned document is effective to a certain extent, there is room for further improvement in terms of improving rigidity (crystallinity) by adding a small amount of a nucleating agent component. In view of these circumstances, an object of the present invention is to provide a method for producing a polypropylene blend composition, including a nucleation method, which gives polypropylene molded articles with high rigidity. [Means for solving the problem]

[0006] [1] 0.5 to 10 parts by mass of a nucleating agent made of a polypropylene-based resin (A) that satisfies the following [Condition A1] and [Condition A2]; and 90 to 99.5 parts by mass of a polypropylene resin (B) that satisfies the following [Condition B1] and [Condition B2], and then melt-kneading the mixture. A method for producing a polypropylene blend composition, comprising obtaining 100 parts by mass of a polypropylene blend composition (C) having an improved elastic modulus compared to the polypropylene-based resin (B). [Condition A1] Melting point of the first DSC heating measured at a heating rate of 20°C / min ≥ 170°C [Condition A2] Crystallization temperature of ≥ 110°C measured at a DSC temperature drop rate of 20°C / min after holding at 230°C for 5 minutes [Condition B1] Crystallization temperature <115°C measured at a DSC temperature drop rate of 20°C / min after holding at 230°C for 5 minutes [Condition B2] MFR(230℃)=0.1~1000g / 10min [2] The method for producing a polypropylene blend composition according to [1], wherein the polypropylene-based resin (A) contains 100 parts by mass of polypropylene and 1 to 8 parts by mass of a crosslinking agent. [3] The method for producing a polypropylene blend composition according to [1] or [2], wherein in wide-angle X-ray diffraction measurement of the nucleating agent, the degree of orientation A calculated by the following formula (1) from the half-width (Wi) of each intensity peak in the intensity distribution of the azimuth angle scan of diffraction caused by the 040 plane of the α crystal of polypropylene is 80% or more. Orientation degree A(%)=(360-ΣWi) / 360×100 ···(1) [4] The method for producing a polypropylene blend composition according to any one of [1] to [3], wherein the nucleating agent is a finely divided sheet or film preform made of the polypropylene resin (A), and the preform has been subjected to a heat treatment consisting of the following first heat treatment step, second heat treatment step and cooling step. <First heat treatment step> The melting point of the first heating of the preformed body as a sample measured by DSC at a heating rate of 20°C / min is determined in advance to be Tm (°C), The preform is heat-treated at a constant first heat-treatment temperature Ts1 (°C) within the range of Tm-30 (°C) to Tm+5 (°C) for 5 seconds or more. <Second heat treatment process> The preform heat-treated in the first heat treatment step is further heated and heat-treated at a constant second heat treatment temperature Tc (°C) within the range of Tm-20 (°C) to Tm+6 (°C) for 10 seconds or more. <Cooling process> The preform heat-treated in the second heat treatment step is cooled to room temperature. [5] The method for producing a polypropylene blend composition according to any one of [1] to [4], wherein the nucleating agent is a finely divided sheet or film preform made of the polypropylene resin (A), and the preform has been subjected to uniaxial or biaxial stretching treatment. [6] The method for producing a polypropylene blend composition according to [4], wherein the preform that has been subjected to the heat treatment is further irradiated with radiation at 5 to 50 kGy. [7] The method for producing a polypropylene blend composition according to [5], wherein the preform that has been subjected to the stretching treatment is further irradiated with radiation at 5 to 50 kGy. [8] The method for producing a polypropylene blend composition according to [6], wherein the preformed sheet or film is stretched before the heat treatment. [Effects of the Invention]

[0007] According to the method for producing a polypropylene blend composition of the present invention, a polypropylene blend composition (C) having an improved elastic modulus, which is an index of rigidity, can be easily obtained by simply adding a relatively small amount of a nucleating agent made of polypropylene resin (A) to polypropylene resin (B). DETAILED DESCRIPTION OF THE INVENTION

[0008] <Method for producing polypropylene blend composition> A first aspect of the present invention is a method for producing a polypropylene blend composition (C) by mixing a nucleating agent made of a polypropylene resin (A) with a polypropylene resin (B) and melt-kneading the mixture. Here, the mixing ratio of the nucleating agent (A) to (B) can be 0.5 to 10 parts by mass of the nucleating agent (A) and 90 to 99.5 parts by mass of (B) to produce 100 parts by mass of (C). The total of the nucleating agent (A) and (B) may be 100 parts by mass of (C), or the total of the nucleating agent (A), (B), and other additives may be 100 parts by mass of (C). The mixing ratio of the other additives can be 0 to 9.5 parts by mass, preferably 0 to 5 parts by mass, and more preferably 0 to 3 parts by mass. The type of other additives is not particularly limited as long as they do not inhibit the nucleation of (B) due to the addition of the nucleating agent made of polypropylene resin (A). In this embodiment, unlike conventional nucleating agents made of polypropylene resin, by adding a relatively small amount of nucleating agent made of (A), it is possible to obtain (C) with increased rigidity of (B).

[0009] The method for mixing and melt-kneading the nucleating agent made of the polypropylene-based resin (A) with the polypropylene-based resin (B) is not particularly limited, and any mixing method or melt-kneading method known in the art for obtaining a polypropylene-based resin composition may be used.

[0010] <Nucleating agent composed of polypropylene resin (A)> The nucleating agent made of the polypropylene-based resin (A) of this embodiment may be simply referred to as "nucleating agent (A)" below. The nucleating agent (A) is made of a polypropylene-based resin (A) that satisfies the following [Condition A1] and [Condition A2]. [Condition A1] Melting point of the first DSC heating measured at a heating rate of 20°C / min ≥ 170°C [Condition A2] Crystallization temperature of ≥ 110°C measured at a DSC temperature drop rate of 20°C / min after holding at 230°C for 5 minutes

[0011] The melting point Tmp1 of the first heating in condition A1 is the melting peak temperature (unit: °C) of the α-type crystals in the first heating in differential scanning calorimetry (DSC) obtained for the nucleating agent (A) at a heating rate of 20 °C / min. Specifically, the melting point Tmp1 of the first heating is determined by the following measurement method. That is, using a differential scanning calorimeter (e.g., a power compensation type Diamond DSC manufactured by PerkinElmer), nucleating agent (A) is held at 30°C for 5 minutes, and then heated to 230°C at a heating rate of 20°C / min. Tmp1 is determined from the peak position of the melting curve of the α-type crystals obtained at this time (the position of the highest peak if there are multiple melting peaks). Note that Tmp1 of nucleating agent (A) includes the effect of the increase in melting point due to the increase in the thickness of the crystal lamellae due to the annealing effect during heating.

[0012] Tmp1 is 170° C. or higher, preferably 172° C. or higher, more preferably 174° C. or higher, and even more preferably 176° C. or higher. On the other hand, Tmp1 is preferably 186° C. or lower. Within the above range, the nucleating effect of the nucleating agent (A) can be more effectively obtained.

[0013] The crystallization temperature Tcp under condition A2 is the crystallization temperature (unit: °C) of the nucleating agent (A) measured by DSC at a temperature drop rate of 20 °C / min after holding the temperature at 230 °C for 5 minutes. The crystallization temperature Tcp can be measured using DSC following Tmp1. That is, the nucleating agent (A) is held at 230°C for 5 minutes, then cooled to 30°C at a rate of 20°C / min, and held at 30°C for 5 minutes. The crystallization peak temperature Tcp is determined from the peak position of the crystallization curve obtained during cooling.

[0014] The Tcp of the nucleating agent (A) is 110° C. or higher, preferably 114° C. or higher, more preferably 116° C. or higher, and even more preferably 118° C. or higher, while the Tcp is preferably 140° C. or lower. Within the above range, the nucleating effect of the nucleating agent (A) can be more effectively obtained.

[0015] In wide-angle X-ray diffraction (WAXD) measurement of the nucleating agent (A), the degree of orientation A calculated from the half-width (Wi) of each intensity peak in the intensity distribution of the azimuth angle scan of diffraction caused by the 040 plane of the α-crystal of polypropylene using the following formula (1) is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Within the above range, the nucleating effect of the nucleating agent (A) can be further enhanced. Orientation degree A(%)=(360-ΣWi) / 360×100 ···(1) In the wide-angle X-ray diffraction measurement, the direction of incidence of X-rays on the test piece of the nucleating agent (A) is not limited, but the direction that gives the largest degree of orientation A is adopted.

[0016] The nucleating agent (A) is preferably in a finely divided form, since this facilitates mixing and melt-kneading with the polypropylene resin (B) and facilitates nucleation of the polypropylene resin (B). The degree of fineness is not particularly limited, and it is preferable that the nucleating agent (A) be fine enough to pass through a mesh with an opening size of about 1.0 mm, for example. For example, polypropylene resin (A) can be formed into a sheet having a thickness of 1 mm or less, and then cooled with liquid nitrogen. This can then be crushed in an ultracentrifugal crusher or the like, and passed through a mesh, which can easily produce powder or fine needle-shaped fragments of nucleating agent (A). Hereinafter, a sheet or film-shaped molded product of the polypropylene resin (A) may be referred to as a "preform."

[0017] <Method of manufacturing nucleating agent> The polypropylene resin (A) as a material for constituting the nucleating agent (A) that satisfies [Condition A1] and [Condition A2] can be produced, for example, as follows.

[0018] Examples of the polypropylene resin (A) include propylene homopolymers, and block or random copolymers of propylene and other α-olefins (having at most 12 carbon atoms). Specific examples of the α-olefins include ethylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 4-dimethyl-1-pentene, vinylcyclopentane, and vinylcyclohexane, with ethylene and 1-butene being preferred. Among these, propylene homopolymers are preferred from the viewpoint of improving rigidity and heat resistance.

[0019] The polypropylene resin (A) can be produced by a known method. Generally, known polymerization catalysts for the polypropylene resin (A) include (i) solid catalysts containing magnesium, titanium, a halogen, and an electron donor compound, (ii) organoaluminum compounds, and (iii) catalysts containing an external electron donor compound, as well as metallocene catalysts. Any of these catalysts can be used to produce the polypropylene of the present invention. Representative examples of the electron donor compound (also referred to as an "internal electron donor compound") in component (i) include phthalate compounds, succinate compounds, and diether compounds. Any of these internal electron donor compounds can be used in the present invention. However, catalysts containing phthalate compounds or succinate compounds as internal electron donor compounds are preferred because they result in high stereoregularity and a broad molecular weight distribution of the resulting polypropylene. Examples of phthalate compounds preferred as the internal electron donor compound include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, diisopropyl phthalate, and dioctyl phthalate. Examples of succinate compounds preferred as the internal electron donor compound include diethyl-2,3-(diisopropyl)succinate, diisobutyl-2,3-(diisopropyl)succinate, di-n-butyl-2,3-(diisopropyl)succinate, diethyl-2,3-(dicyclohexyl)-2-(methyl)succinate, diisobutyl-2,3-(dicyclohexyl)-2-(methyl)succinate, and diisobutyl 3,6-dimethylcyclohexane-1,2-dicarboxylate.

[0020] The molecular weight distribution of the xylene insoluble fraction of polypropylene resin (A) (M w / M n The molecular weight distribution (M) is controlled in the range of 2 to 40, preferably 4 or more, and more preferably 5 or more. w / M nIf the molecular weight distribution (M) of the polypropylene resin (A) is 4 or more, the presence of the high molecular weight component allows the degree of orientation A of the preform to be maintained during the heat treatment of the preform after the stretching treatment, and the rigidity improving effect of the resulting nucleating agent can be further enhanced. w / M n ) is difficult to increase above 40.

[0021] The stereoregularity (mmmm) of the xylene-insoluble matter of the polypropylene resin (A) has an appropriate value depending on the application, but a high proportion of mmmm of the xylene-insoluble matter can further enhance the rigidity-improving effect of the nucleating agent. Specifically, the mmmm of the xylene-insoluble matter is preferably 93 mol% or more, more preferably 97 mol% or more, and even more preferably 98 mol% or more.

[0022] The polypropylene resin (A) preferably has an MFR, which is an index of fluidity, of 0.01 to 1,000 g / 10 min. The MFR is a value measured in accordance with JIS K7210-1 and JIS K6921-2 at a temperature of 230°C and a load of 2.16 kg.

[0023] A crosslinking agent that crosslinks polypropylene chains may be used as the material for the polypropylene resin (A) that constitutes the preform. The crosslinking agent is preferably a compound having two or more polymerizable functional groups that are copolymerizable with propylene. Specific examples of the crosslinking agent include acrylate or methacrylate compounds such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane triacrylate, 1,9-nonanediol dimethacrylate, and 1,10-decanediol dimethacrylate; allyl esters of carboxylic acids (trimellitic acid triallyl ester, pyromellitic acid triallyl ester, oxalic acid diallyl ester, and the like); allyl esters of cyanuric acid or isocyanuric acid such as triallyl cyanurate and triallyl isocyanurate; maleimide compounds such as N-phenylmaleimide and N,N'-m-phenylenebismaleimide; compounds having two or more triple bonds such as dipropargyl phthalate and dipropargyl maleate; and divinylbenzene. The amount of the crosslinking agent to be blended relative to 100 parts by mass of polypropylene is preferably 1 to 8 parts by mass. Within the above range, the nucleating effect of the nucleating agent (A) can be more effectively obtained.

[0024] The method for molding the preform is not particularly limited, and known molding methods such as press molding, extrusion molding including uniaxial and biaxial stretching, injection molding, compression molding, and inflation molding can be used. The shape of the preform may be, for example, a plate, a sheet, a film, a pipe, or various other three-dimensional shapes, but a plate or sheet (film) shape is preferred in terms of ease of shape retention. Furthermore, the sheet or film preform is preferably thin so that it can be uniformly heated and / or irradiated, and specifically, the average thickness is preferably 500 μm or less. However, if it is too thin, it becomes prone to breakage, so the thickness is preferably 10 μm or more.

[0025] The preform may contain additives such as nucleating agents other than the nucleating agent (A), fillers, hydrochloric acid absorbers, heat stabilizers, antioxidants, light stabilizers, ultraviolet absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, antifogging agents, flame retardants, pigments, dyes, dispersants, copper inhibitors, neutralizing agents, plasticizers, foaming agents, bubble inhibitors, crosslinking agents, and peroxides.

[0026] After obtaining a preform of the polypropylene resin (A), the preform is preferably subjected to one or more of heat treatment, radiation exposure treatment, and stretching treatment.

[0027] [Heat treatment] The peak melting temperature of the preform before heat treatment, etc. is designated as Tm. The heat treatment in this embodiment preferably includes a first heat treatment step of subjecting the preform having the peak melting temperature Tm to a first heat treatment, a second heat treatment step of subjecting the preform heat-treated in the first heat treatment step to a second heat treatment, and a cooling step of cooling the preform heat-treated in the second heat treatment step.

[0028] The Tm of the preform is the melting peak temperature of the α-type crystals in the first heating run of differential scanning calorimetry (DSC) performed at a heating rate of 20°C / min, similar to the Tmp1 described above, and is determined by the following measurement method. Using a differential scanning calorimeter (e.g., a power compensation type Diamond DSC manufactured by PerkinElmer), the preform is held at 30°C for 5 minutes and then heated to 230°C at a heating rate of 20°C / min. Tm is determined from the peak position of the melting curve of the α-type crystals obtained at this time (the position of the highest peak if multiple melting peaks are present). Note that the Tm of the preform includes the effect of the increase in melting point due to the increase in the thickness of the crystalline lamellae caused by the annealing effect during heating.

[0029] The Tm of the preform before heat treatment or the like is preferably 150° C. or higher, more preferably 160° C. or higher, while the Tm is preferably 180° C. or lower. Within the above range, the nucleating effect of the nucleating agent (A) can be more effectively obtained.

[0030] The first heat treatment step is a step of heat treating the preform at a constant first heat treatment temperature Ts1 (°C) within the range of Tm-30 (°C) to Tm+5 (°C). In the first heat treatment step, crystal seeds can be formed mainly by melting and recrystallizing the polypropylene. The temperature range of the first heat treatment temperature Ts1 is preferably within the range of Tm-25 (°C) to Tm+4 (°C), and more preferably within the range of Tm-20 (°C) to Tm+3 (°C). When the first heat treatment temperature Ts1 is equal to or higher than the lower limit, the formation of crystal seeds is sufficient, and the melting point of the resulting molded body and the nucleation effect of the nucleating agent (A) are further enhanced.When the first heat treatment temperature Ts1 is equal to or lower than the upper limit, both the melting point and the nucleation effect can be maintained satisfactorily. The first heat treatment temperature Ts1 may be a plurality of temperatures, and for example, a heat treatment at a constant temperature and a temperature increase may be repeated one or more times. Depending on the equipment used for the heat treatment, it may be difficult to maintain the temperature of the preform to be heated at a constant value without any fluctuations, and a temperature fluctuation of ±5° C. may be tolerated at the first heat treatment temperature Ts1. The temperature of the preform before heating is not particularly limited and may be, for example, 100° C. or lower.

[0031] In the first heating profile of differential scanning calorimetry (DSC) of the preform obtained at a heating rate V (°C / min) from 115°C to Ts1, the ratio of the heat of fusion of the α-type crystal melting peak to the total heat of fusion of the preform is preferably 50% or more. If this ratio is 50% or more, it is possible to prevent seeding from being hindered by remaining crystals other than α-type crystals (β-type crystals, γ-type crystals, mesophase). The ratio of the α-type crystal melting peak is more preferably 70% or more, and even more preferably 90% or more. The melting peak ratio of the α-type crystals is determined from a melting curve obtained by using a differential scanning calorimeter (for example, a power compensation type Diamond DSC manufactured by PerkinElmer) to hold the preform at 30°C for 5 minutes and then heating it to 230°C at a heating rate V (°C / min). The heating rate V will be described later.

[0032] The heat treatment time at the first heat treatment temperature Ts1 in the first heat treatment step is preferably 5 seconds or more, more preferably 10 seconds or more. In particular, when the second heat treatment temperature Tc described below is high (specifically, when Tc is 165°C or higher), it is necessary to grow the crystal seed more, so the heat treatment time is preferably 100 seconds or more, more preferably 200 seconds or more. On the other hand, if the heat treatment time in the first heat treatment step is too long, productivity will decrease, so it is preferably 500 seconds or less.

[0033] The second heat treatment step is a step in which the preform heat-treated in the first heat treatment step is further heated and heat-treated at a constant second heat treatment temperature Tc (Tc>Ts1) (°C) within the range of Tm-20 (°C) to Tm+6 (°C). The second heat treatment step allows crystals to grow using the crystal seeds formed in the first heat treatment step as nuclei. The temperature range of the second heat treatment temperature Tc is preferably within the range of Tm-16 (°C) to Tm+4 (°C), more preferably within the range of Tm-14 (°C) to Tm+3 (°C), and even more preferably within the range of Tm-12 (°C) to Tm+2 (°C). When the second heat treatment temperature Tc is equal to or higher than the lower limit and equal to or lower than the upper limit, the melting point and nucleation effect of the resulting molded body can be maintained well. The second heat treatment temperature Tc may be a plurality of temperatures, for example, a heat treatment at a constant temperature and a temperature increase (relative to Ts1) may be repeated one or more times. As with the first heat treatment temperature Ts1, a temperature fluctuation of ±5° C. is permissible for the second heat treatment temperature Tc. The second heat treatment temperature Tc is preferably within the range of Ts1+1 (°C) to Ts1+20 (°C), more preferably within the range of Ts1+1 (°C) to Ts1+15 (°C), and even more preferably within the range of Ts1+1 (°C) to Ts1+10 (°C), provided that the range satisfies Tm-20 (°C) to Tm+6 (°C).

[0034] The heat treatment time at the second heat treatment temperature Tc in the second heat treatment step is preferably 10 seconds or more, more preferably 20 seconds or more, whereas if the heat treatment time in the second heat treatment step is too long, productivity will decrease, so the heat treatment time is preferably 600 seconds or less, more preferably 300 seconds or less.

[0035] In order to facilitate the formation of crystal seeds and the growth of crystals in the preform, it is preferable to set the first heat treatment temperature Ts1 (°C) and the second heat treatment temperature Tc (°C) to temperatures expressed by the following formula (2): Formula (2): (-0.357×Tc+56.4)×LogV+2.89×Tc+Tm-480≦Ts1≦(0.0443×Tc-10.6)×LogV-0.261×Tc+Tm+50 Here, V in formula (2) is the temperature rise rate (°C / min) from 115°C, at which the structural change begins, to Ts1. The temperature rise rate V is preferably 1 to 280°C / min, and more preferably 5 to 200°C / min. The term indicating the lower limit of formula (2) is effective when Tc is 158°C or higher. The heating rate V can be calculated simply by {Ts1 - (temperature before heating)} / (time required to transfer the preform to a heating device previously heated to Ts1) or {Ts1 - (temperature before heating)} / (time required for the temperature of the heating device to which the preform is attached or in which the preform has been cooled and solidified to reach Ts1). Here, Ts1 is the temperature of the heating device at the point where the preform comes into direct or indirect contact with the heating device. The "temperature before heating" refers to the temperature in the vicinity of the preform, or, if preheating is performed, the temperature of the point where the preform comes into direct or indirect contact with the heating device used in the preheating step. Because the growth of crystal seeds by melt recrystallization occurs during the temperature rise up to Ts1, the lower the heating rate V, the more the crystal seeds tend to grow when Ts1 is reached. Therefore, if Tc and Tm are kept constant, the upper and lower limits of Ts1 are thought to increase with decreasing V (in the Tc range above 158°C, the parentheses in equation (2) indicate negative values). On the other hand, if V and Tm are kept constant, the lower the Tc, the more crystal seeds remain, and the higher the upper limit of Ts1. Crystallization at high Tc requires seeds with thicker crystalline lamellae, so the lower limit of Ts1 is thought to increase with increasing Tc.

[0036] Examples of heating methods in the first heat treatment step and the second heat treatment step include a method in which a preformed body is sandwiched between a pair of metal blocks or a method in which the preformed body is cooled and solidified between the metal blocks and then heated, a method in which the preformed body is sandwiched between a pair of preheated metal blocks and then heated, a method in which the preformed body itself is heated by hot air or infrared irradiation, a method in which the preformed body is heated by laser light or microwaves, etc. Furthermore, uniaxial or biaxial stretching may be performed simultaneously during heating.

[0037] The cooling step is a step of cooling the preform that has been heat-treated in the second heat treatment step. Examples of cooling methods include a method of cooling by bringing the preform into contact with a cooling means such as a cooling press or a roll, a method of cooling by stopping heating and allowing it to cool naturally, a method of cooling by applying cold air or cooling water, and a method of cooling by leaving it in a cooling environment.

[0038] In the first heat treatment step, the polypropylene melts and recrystallizes to form crystal seeds, and in the second heat treatment step, the crystal seeds act as nucleating agents, facilitating crystallization. Therefore, in the preform manufacturing method described above, the polypropylene obtained has a high crystallinity, thick crystals, and a higher melting point.

[0039] [Radiation treatment] Irradiating the preform promotes crosslinking between polypropylene chains, thereby further enhancing the nucleation effect of the nucleating agent (A). The preform to be irradiated is preferably subjected to the heat treatment described above and / or the stretching treatment described below. The high-melting-point crystals formed in the preform by the heat treatment or stretching treatment retain their pre-melting conformation as a part of their crosslinking effect by irradiation, further enhancing the nucleation effect of the nucleating agent (A). The radiation exposure dose is preferably 5 to 50 kGy, more preferably 7 to 30 kGy, and even more preferably 9 to 20 kGy. The types of radiation include electron beams, gamma rays, alpha rays, neutron rays, and X-rays, with electron beams or gamma rays being preferred for convenience.

[0040] [Stretching Treatment] By subjecting the preform to uniaxial or biaxial stretching, the orientation of the polypropylene chains is aligned, which promotes subsequent crystallization and thereby enhances the nucleation effect of the nucleating agent (A). The stretching is preferably performed on the preform before heat treatment. By performing heat treatment after the orientation of the polypropylene chains is aligned by stretching, the formation of high-melting-point crystals in the preform is further promoted. Here, uniaxial stretching refers to stretching in one arbitrary direction, and biaxial stretching refers to stretching in one arbitrary direction and a direction approximately perpendicular to that direction. The stretching process may be carried out using a known stretching device. The stretching temperature is preferably, for example, 160 to 170°C. The stretching speed is preferably, for example, 30 to 70 mm / sec. The stretching ratio in the axial direction is preferably 1.5 to 8.0 times, more preferably 2.0 to 7.0 times, and even more preferably 3.0 to 6.0 times.

[0041] <Polypropylene resin (B)> The polypropylene resin (B) in this embodiment is the main material of the polypropylene blend composition (C) to be produced, and is the target of having its elastic modulus (ie, rigidity) increased by the addition of the nucleating agent (A). The polypropylene resin (B) satisfies the following [Condition B1] and [Condition B2]. [Condition B1] Crystallization temperature <115°C measured at a DSC temperature drop rate of 20°C / min after holding at 230°C for 5 minutes [Condition B2] MFR(230℃)=0.1~1000g / 10min

[0042] The crystallization temperature Tcp under condition B1 is the crystallization temperature (unit: °C) of the polypropylene resin (B) measured by DSC at a temperature drop rate of 20 °C / min after holding the resin at 230 °C for 5 minutes. The crystallization temperature Tcp can be measured using DSC in the same manner as the Tcp of the nucleating agent (A) described above. That is, the polypropylene resin (B) is held at 230 °C for 5 minutes, then cooled to 30 °C at a temperature drop rate of 20 °C / min, and then held at 30 °C for 5 minutes. The crystallization peak temperature Tcp is determined from the peak position of the crystallization curve during cooling.

[0043] The Tcp of the polypropylene resin (B) is less than 115° C., preferably 114° C. or less, more preferably 113° C. or less, even more preferably 112° C. or more, particularly preferably 111° C. or less, and most preferably 110° C. or less. On the other hand, the Tcp is preferably 105° C. or more. Within the above range, the nucleating effect of the nucleating agent (A) can be more effectively obtained.

[0044] The MFR of condition B2 is preferably from 0.5 to 500 g / 10 min, more preferably from 1.0 to 100 g / 10 min, further preferably from 3.0 to 50 g / 10 min, and particularly preferably from 6.0 to 20 g / 10 min. Here, MFR, which is an index of the fluidity of polypropylene, is a value measured in accordance with JIS K7210-1 and based on JIS K6921-2 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0045] As the polypropylene-based resin (B) that satisfies [Condition B1] and [Condition B2], for example, the polypropylene-based resin used as the material for producing the preform of the polypropylene-based resin (A) described above can be used.

[0046] That is, examples of the polypropylene resin (B) include propylene homopolymers, and block or random copolymers of propylene and other α-olefins (having at most 12 carbon atoms). Specific examples of the α-olefins include ethylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 4-dimethyl-1-pentene, vinylcyclopentane, and vinylcyclohexane, with ethylene and 1-butene being preferred. Among these, from the viewpoint of improving rigidity and heat resistance, propylene homopolymers or block copolymers are preferred.

[0047] When the nucleating agent (A) and polypropylene resin (B) described above are mixed and melt-kneaded, the following general additives may be added to the extent that the nucleating effect of the nucleating agent (A) is not impaired: nucleating agents other than the nucleating agent (A), fillers, hydrochloric acid absorbers, heat stabilizers, antioxidants, light stabilizers, ultraviolet absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, anti-fogging agents, flame retardants, pigments, dyes, dispersants, copper inhibitors, neutralizing agents, plasticizers, foaming agents, bubble inhibitors, crosslinking agents, peroxides, and elastomer components.

[0048] The polypropylene blend composition produced by the present invention can be suitably used, for example, as a material for automobiles, electrical appliances, daily necessities, packaging materials, etc. [Example]

[0049] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0050] <Preparation of homopolypropylene> According to a known method, homopolypropylene (PP1) was obtained by polymerization of propylene using a catalyst containing a phthalate compound as an internal electron donor. The physical properties were as follows: PP1: Stereoregularity of xylene insoluble matter (mmmm): 98.4 mol%, Molecular weight distribution of xylene insoluble matter (M w / M n):5.3, MFR:7.5g / 10min. As will be described later, PP1 is used as polypropylene resin (B), and therefore the MFR determined here corresponds to [Condition B2].

[0051] The xylene-insoluble portion of polypropylene was collected by dissolving a polypropylene resin sample in o-xylene at 135°C, cooling it to 25°C, filtering the cooled solution using filter paper, and recovering the material remaining on the filter paper. The mmmm of the xylene insoluble portion of polypropylene is 13 Specifically, polypropylene was first dissolved in a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene to prepare a measurement solution. The measurement solution was analyzed using a JNM LA-400 ( 13 C resonance frequency 100MHz) 13 From the spectrum obtained by this measurement, the ratio of the intensity of the peak corresponding to a pentad consisting of four consecutive meso (m) bond sequences of propylene monomer was calculated according to the method described in A. Zambelli, Macromolecules, 6, 925 (1973). The molecular weight distribution of the xylene-insoluble fraction of polypropylene (M w / M n ) is determined by gel permeation chromatography (PL-GPC220 manufactured by Polymer Laboratories) to determine the mass average molecular weight (M w ) and number average molecular weight (M n ) was measured and determined. MFR, an index of the fluidity of polypropylene, is a value measured in accordance with JIS K7210-1 and based on JIS K6921-2 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0052] <Preparation of polypropylene resin (A)> To 100 parts by mass of PP1, 0.08 parts by mass of an antioxidant (BASF B225) and 0.05 parts by mass of a neutralizer (Dannan Chemical calcium stearate) were blended, followed by 0, 3, or 6 parts by mass of a crosslinking agent (trimethylolpropane trimethacrylate: TMPTA), and the mixture was stirred and mixed in a mixer for 1 minute. The resulting mixture was melt-kneaded using a single-screw extruder (NVC, manufactured by Nakatani Machinery Co., Ltd., screw diameter 50 mm) with the cylinder temperature adjusted to 230°C, and then extruded from a die. The strand thus obtained was cooled in water and then cut with a pelletizer to obtain three types of pellet-shaped polypropylene resin (A) compositions with different amounts of TMPTA added. Hereinafter, these PP compositions will be referred to as PP resin (A-0), PP resin (A-3), and PP resin (A-6) in order of decreasing amount of TMPTA blended.

[0053] <Forming of preformed body> Each of the PP compositions obtained above was extrusion molded to obtain a sheet-like polypropylene preform having a thickness of 0.4 mm (400 μm). The sheet is formed as follows. Thermo Plastics Industry Co., Ltd. 25mmφ single-layer extrusion cast sheet molding machine with air knife (downward T-die molding machine) [Screw] Full flight screw (L / D is 24) [Molding conditions] <Temperature> C (cylinder) 1: 200℃, C2: 230℃, C3: 250℃, C4: 250℃, H (neck): 250℃ D (Die) 1: 250℃, D2: 250℃, D3: 250℃ <Screw rotation speed> Approximately 50rpm <Roll temperature setting> 30℃ <Pickup speed> Approximately 0.5 to 0.8 m / min

[0054] <Preparation of stretched film> The preformed sheet of PP resin (A-6) was cut into a length of 9 cm and a width of 9 cm, and then uniaxially stretched in a biaxial stretching device (Bruckner, KARO IV) at a stretching temperature of 163°C, a stretching speed of 50 mm / sec, and a stretching ratio of 4 to obtain a polypropylene film (uniaxially stretched film) with a thickness of 0.1 mm.

[0055] <DSC measurement of preform> Using each of the preforms obtained above as samples, differential scanning calorimetry was carried out at a temperature rise rate of 20°C / min. The measurement results of the melting peak temperature Tmp1 obtained during the first temperature rise are shown below. PP resin sheet (A-0) containing 0 parts by mass of crosslinking agent: 166.2°C PP resin (A-3) sheet containing 3 parts by mass of crosslinking agent: 165.6°C PP resin sheet (A-6) containing 6 parts by mass of crosslinking agent: 164.9°C Uniaxially stretched film of PP resin (A-6): 171.8℃ The Tmp1 of each preform is the standard Tm for determining the heat treatment temperature.

[0056] Example 1 A preform made of PP resin (A-3) was cut into a length of 9 cm and a width of 9 cm to prepare a test piece. The test piece was fitted into a 0.4 mm thick metal frame, and the top and bottom of the frame were sandwiched between 0.1 mm thick aluminum foil, a 1.0 mm thick ferroelectric plate, and a 3.0 mm thick aluminum press plate in that order to obtain a heated unit. This unit to be heated was heated by a heating device (a press molding machine manufactured by Shoji Co., Ltd.) and held at 158°C (first heat treatment temperature Ts1) for 5 minutes (first heat treatment step). Subsequently, the unit to be heated was transferred to another heating device (a press molding machine manufactured by Shoji Co., Ltd.) and heated, and held at 165°C (second heat treatment temperature Tc) for 3 minutes (second heat treatment step). Thereafter, heating was stopped, the heated unit was removed, and cooled in a cooling device (a press molding machine manufactured by Shoji Co., Ltd.) whose temperature was adjusted to 25°C, to obtain a heat-treated preformed sheet. Here, Ts1 and Tc are the temperatures of the heating device at the part that comes into contact with the unit to be heated.

[0057] The heat-treated preform was irradiated with an electron beam irradiation device (EBC-300 manufactured by Nissin High Voltage Corporation) in a nitrogen atmosphere at an acceleration voltage of 300 kV with an irradiation dose of 50 kGy.

[0058] A small disk-shaped piece having a diameter of 0.5 mm was cut and collected from the electron beam irradiated preform sheet to obtain a polypropylene nucleating agent for DSC evaluation.

[0059] The polypropylene nucleating agent for DSC evaluation obtained above was used as a sample to carry out differential scanning calorimetry using a Diamond DSC manufactured by PerkinElmer. Specifically, the sample was held at 30°C for 5 minutes, then heated to 230°C at a heating rate of 20°C / min, and a first heating run was performed using differential scanning calorimetry. The peak melting temperature Tmp1 (unit: °C) of the sample was determined from the peak position of the melting curve obtained in the first heating run (the position of the highest peak if multiple melting peaks existed). Here, the peak melting temperature Tmp1 is the melting point of the first heating run under [Condition A1]. In addition, in the melting profile after baseline correction, the heat of fusion ΔHm1 (unit: J / g) of the polypropylene molded article was calculated from the area of the melting peak between 80°C and the temperature at which melting is completely completed and the baseline becomes linear. Next, the sample was held at 230°C for 5 minutes, then cooled to 30°C at a rate of 20°C / min, and held at 30°C for 5 minutes. The crystallization peak temperature Tcp (unit: °C) was determined from the peak position of the crystallization curve obtained during the temperature drop. Here, the crystallization peak temperature Tcp is the crystallization temperature under [Condition A2]. In addition, in the crystallization profile after baseline correction, the heat generated during crystallization, ΔHc (unit: J / g), was calculated from the area of the crystallization peak between the temperature before the start of crystallization and the temperature at which crystallization was completely completed and the baseline became linear. Furthermore, the sample was again heated to 230°C at a heating rate of 20°C / min, and a second differential scanning calorimetry measurement was performed. By the second heating run, the melting peak temperature Tmp2 (unit: °C) and the heat of fusion ΔHm2 (unit: J / g) were obtained in the same manner as for Tmp1 and ΔHm1. The measurement results of Tmp1, ΔHm1, Tcp, ΔHc, Tmp2, and ΔHm2 are shown in Table 1. Of these, Tmp1 corresponds to [Condition A1], and Tcp corresponds to [Condition A2].

[0060] [Table 1]

[0061] The homopolypropylene (PP1) used as the polypropylene resin (B) was used as a sample and differential scanning calorimetry was performed in the same manner as described above using a Diamond DSC manufactured by PerkinElmer Co., Ltd. Specifically, pellets of PP resin (A-0) were obtained from PP1, and then small pieces were cut out and collected to serve as samples for DSC evaluation. The results of Tmp1, ΔHm1, Tcp, ΔHc, Tmp2, and ΔHm2 measured by DSC are shown in Table 2. Of these, Tcp corresponds to [Condition B1]. Table 2 also shows the evaluation results of the storage modulus, which will be described later.

[0062] [Table 2]

[0063] The electron beam irradiated preformed sheet was cut into pieces approximately 5 mm square, immersed in liquid nitrogen to cool, and then pulverized in an ultracentrifugal pulverizer (ZM-200 manufactured by Retsch). The material that passed through a mesh (opening size 1.0 mm) was collected to obtain a powdered polypropylene nucleating agent for blending.

[0064] The nucleating agent (polypropylene nucleating agent for blending) made of the polypropylene-based resin (A) obtained above, PP1 which is the polypropylene-based resin (B), an antioxidant (B225 manufactured by BASF), and a neutralizing agent (calcium stearate manufactured by Tannan Chemical Co., Ltd.) were blended and stirred in a mixer for 30 seconds to mix them. At this time, the content of the nucleating agent relative to the total mass of the mixture was 1% by mass. Furthermore, 0.08 parts by mass of an antioxidant and 0.05 parts by mass of a neutralizing agent were mixed with 100 parts by mass of PP1. The resulting mixture was melt-kneaded using a twin-screw extruder (KZW15TW-30MG-NH, screw diameter 15 mm, manufactured by Technovel Co., Ltd.) adjusted to the following molding conditions, and then extruded from a die. The strand thus obtained was cooled in water and then cut with a pelletizer to obtain a pellet-shaped polypropylene blend composition (C).

[0065] [Molding conditions] <Temperature> C (cylinder) 1: 170℃, C2: 190℃, C3: 210℃, C4: 210℃, H (neck): 210℃, D (die): 210℃ <Screw rotation speed> Approximately 100 rpm <Feeder rotation speed> Approximately 40rpm <Mesh> #100

[0066] <Physical property evaluation> Elasticity Modulus The pellets of the polypropylene blend composition (C) were placed in a 0.4 mm thick metal frame and sandwiched between 0.1 mm thick aluminum foil, a 1.0 mm thick ferroelectric plate, and a 3.0 mm thick aluminum press plate in that order to obtain a heated unit. This was heated in a press molding machine (manufactured by Shoji Co., Ltd.), held at 230 ° C for 5 minutes to melt, then cooled to 80 ° C at a rate of 20 ° C / min, and then allowed to cool to 30 ° C to obtain a test piece for evaluating elastic modulus. The cooling rate was controlled by adjusting the temperature of the heating device and by changing the thickness of the heating plate to change the thermal conduction to the contact point with the pellet in the heated unit. The storage modulus of the obtained test specimens was measured at a measurement frequency of 1 Hz using a TA Instruments RSA-III. The measurement results are shown in Table 3.

[0067] [DSC] The samples were small pieces cut from pellets of the produced polypropylene blend composition (C). Specific measurement methods were the same as those used for the polypropylene nucleating agent for blending described above. Among the measurement results, the results for Tcp, ΔHc, Tmp2, and ΔHm2 are shown in Table 3.

[0068] [Table 3]

[0069] "Comparative Example 1" The nucleating agent made of polypropylene resin (A) and polypropylene resin (B) were melt-kneaded to obtain a pellet-shaped polypropylene blend composition (C) in the same manner as in Example 1, except that the preform made of PP resin (A-3) did not undergo the first and second heat treatment steps and therefore did not satisfy [Condition A1]. The physical properties of the pellet-shaped polypropylene blend composition (C) were evaluated. The results are shown in the tables below, along with those of Example 1.

[0070] Example 2 Except for using PP resin (A-6) instead of PP resin (A-3) to prepare a preform and a nucleating agent, the nucleating agent made of polypropylene resin (A) and polypropylene resin (B) were melt-kneaded in the same manner as in Example 1 to obtain a pellet-shaped polypropylene blend composition (C), and the physical properties were evaluated. The results are shown in each table together with those of Example 1.

[0071] "Comparative Example 2" The nucleating agent made of polypropylene resin (A) and polypropylene resin (B) were melt-kneaded to obtain pellet-shaped polypropylene blend composition (C) in the same manner as in Example 2, except that the preform made of PP resin (A-6) did not undergo the first and second heat treatment steps and therefore did not satisfy [Condition A1]. The physical properties of the pellet-shaped polypropylene blend composition (C) were evaluated. The results are shown in the tables below, along with those of Example 2.

[0072] Example 3 For a preform made of PP resin (A-6), a nucleating agent made of polypropylene resin (A) and a polypropylene resin (B) were melt-kneaded in the same manner as in Example 2, except that the dose of electron beam irradiation was changed, to obtain a pellet-shaped polypropylene blend composition (C), and the physical properties were evaluated. The results are shown in each table together with those of Example 2.

[0073] Example 4 A pellet-shaped polypropylene blend composition (C) was obtained in the same manner as in Example 3, except that the blending amount of the nucleating agent made of polypropylene resin (A) was changed and melt-kneaded with polypropylene resin (B), and the physical properties were evaluated. The results are shown in each table together with those of Example 3.

[0074] Example 5 A pellet-shaped polypropylene blend composition (C) was obtained in the same manner as in Example 3, except that the blending amount of the nucleating agent made of polypropylene resin (A) was changed and melt-kneaded with polypropylene resin (B), and the physical properties were evaluated. The results are shown in each table together with those of Example 3.

[0075] Example 6 The uniaxially stretched film obtained from the PP resin (A-6) as described above was cut into a length of 9 cm and a width of 9 cm to prepare a test piece. The test piece was fitted into a 0.1 mm thick metal frame, and the top and bottom of the frame were sandwiched between 0.1 mm thick aluminum foil, a 1.0 mm thick ferroelectric plate, and a 3.0 mm thick aluminum press plate in that order to obtain a heated unit. Subsequently, in the same manner as in Example 1, heat treatment, electron beam irradiation treatment (except that the electron beam irradiation dose was changed to 25 kGy), and pulverization treatment were carried out to obtain a polypropylene nucleating agent for blending. The form of the obtained nucleating agent was powder in Example 1, whereas in this example using a uniaxially stretched film, it was in the form of fine needle-like fragments. Using this nucleating agent as a sample, differential scanning calorimetry was performed using a PerkinElmer Diamond DSC in the same manner as in Example 1. The measurement results for Tmp1, ΔHm1, Tcp, ΔHc, Tmp2, and ΔHm2 are shown in Table 4. Of these, Tmp1 corresponds to [Condition A1], and Tcp corresponds to [Condition A2].

[0076] [Table 4]

[0077] Using the needle-like fine fragments of polypropylene resin (A) obtained above as a nucleating agent sample, wide-angle X-ray diffraction measurements were performed using an X-ray diffractometer (MicroMax and Rapid, manufactured by Rigaku Corporation) with an 800 μm diameter pinhole collimator as the collimator for the X-ray incident beam. After background subtraction from the measurement results, the intensity distribution of the scan azimuth angle (along the circumference of the diffraction ring) of the diffraction due to the 040 plane of the α-crystal of polypropylene was determined. The half-width (Wi) of each intensity peak was determined, and the degree of orientation A was calculated using the following equation, which was 92%. Orientation degree A(%)=(360-ΣWi) / 360×100 ···(1)

[0078] Next, in the same manner as in Example 4, the nucleating agent consisting of the polypropylene resin (A) in the form of needle-like fine fragments obtained above and the polypropylene resin (B) were melt-kneaded to obtain a pellet-shaped polypropylene blend composition (C), and the physical properties were evaluated. The results are shown in Table 5.

[0079] Example 7 The uniaxially stretched film obtained from PP resin (A-6) as described above was not subjected to heat treatment, and the same procedure as in Example 6 was repeated to obtain a pellet-shaped polypropylene blend composition (C), which was then subjected to evaluation of its physical properties. The results are shown in the tables together with those of Example 6. The degree of orientation A of the resulting nucleating agent consisting of polypropylene resin (A), which was a fine needle-shaped fragment, calculated from the above formula (1), was 93%.

[0080] [Table 5]

[0081] Since the polypropylene nucleating agent for blending in Example 1 satisfies [Condition 1] and [Condition 2], the polypropylene blend composition (C) obtained in Example 1 had an improved elastic modulus (rigidity) not only compared with the original polypropylene resin (B) to which no nucleating agent was added, but also compared with the polypropylene blend composition of Comparative Example 1, which used a nucleating agent that did not satisfy [Condition 1].

[0082] Since the polypropylene nucleating agent for blending in Example 2 satisfies [Condition 1] and [Condition 2], the polypropylene blend composition (C) obtained in Example 2 had an improved elastic modulus (rigidity) not only compared with the original polypropylene resin (B) without any nucleating agent, but also compared with the polypropylene blend composition of Comparative Example 2, which used a nucleating agent that did not satisfy [Condition 1].

[0083] Comparing Example 1 and Example 2, it can be seen that the difference in the amount of crosslinking agent (TMPTA) added to the polypropylene resin (A), which is the material of the preform, is reflected in the difference in the elastic modulus. In other words, increasing the amount of crosslinking agent does not necessarily increase the elastic modulus.

[0084] Comparing Example 2 and Example 3, it can be seen that the difference in the dose of electron beam irradiation on the preform is reflected in the difference in the modulus of elasticity. In other words, increasing the dose of electron beam irradiation does not necessarily increase the modulus of elasticity.

[0085] A comparison of Examples 3 to 5 reveals that the difference in the amount of polypropylene nucleating agent added to the polypropylene resin (B) for blending is reflected in the difference in the modulus of elasticity. That is, the greater the amount of nucleating agent added, the higher the modulus of elasticity tends to be.

[0086] From Examples 6 and 7, it is clear that the elastic modulus is remarkably improved by using a uniaxially stretched film as a material for the nucleating agent made of polypropylene resin (A). Furthermore, when Examples 6 and 7 are compared, and Examples 2 and 3 are also considered, the modulus of elasticity tends to increase when the heat treatment and electron beam irradiation dose on the preform are carried out, particularly after the stretching treatment.

Claims

1. 0.5 to 10 parts by mass of a nucleating agent made of a polypropylene-based resin (A) that satisfies the following [Condition A1] and [Condition A2]; and 90 to 99.5 parts by mass of a polypropylene resin (B) that satisfies the following [Condition B1] and [Condition B2], and melt-kneading the mixture. A method for producing a polypropylene blend composition, comprising obtaining 100 parts by mass of a polypropylene blend composition (C) having an improved elastic modulus compared to the polypropylene-based resin (B). [Condition A1] Melting point of the first DSC heating measured at a heating rate of 20°C / min ≥ 170°C [Condition A2] Crystallization temperature of DSC measured at a temperature drop rate of 20°C / min after holding at 230°C for 5 minutes is 110°C or higher [Condition B1] Crystallization temperature of DSC measured at a temperature drop rate of 20°C / min after holding at 230°C for 5 minutes < 115°C [Condition B2] MFR (230°C) = 0.1 to 1000g / 10 minutes

2. The method for producing a polypropylene blend composition according to claim 1, wherein the polypropylene-based resin (A) comprises 100 parts by mass of polypropylene and 1 to 8 parts by mass of a crosslinking agent.

3. 2. The method for producing a polypropylene blend composition according to claim 1, wherein in wide-angle X-ray diffraction measurement of the nucleating agent, the degree of orientation A calculated by the following formula (1) from the half-width (Wi) of each intensity peak in the intensity distribution of an azimuthal scan of diffraction caused by the 040 plane of the α crystal of polypropylene is 80% or more. Orientation degree A (%) = (360-ΣWi) / 360×100 (1)

4. 2. The method for producing a polypropylene blend composition according to claim 1, wherein the nucleating agent is a finely divided sheet or film preform made of the polypropylene resin (A), and the preform has been subjected to a heat treatment comprising the following first heat treatment step, second heat treatment step and cooling step. <First heat treatment step> The melting peak temperature of the α-type crystals in the first heating run of differential scanning calorimetry, measured at a heating rate of 20°C / min using the preform as a sample, is determined in advance to be Tm (°C), The preform is heated to a first heat treatment temperature Ts which is constant within a range of Tm-30 (°C) to Tm+5 (°C). １ (°C) for 5 seconds or more. <Second heat treatment step> The preform heat-treated in the first heat treatment step is further heated to a constant second heat treatment temperature Tc (°C) within the range of Tm-20 (°C) to Tm+6 (°C) for 10 seconds or more. <Cooling process> The preform heat-treated in the second heat treatment step is cooled to room temperature.

5. 5. The method for producing a polypropylene blend composition according to claim 1, wherein the nucleating agent is a finely divided sheet or film preform made of the polypropylene resin (A), and the preform has been subjected to uniaxial or biaxial stretching treatment.

6. The method for producing a polypropylene blend composition according to claim 4, wherein the preform that has been subjected to the heat treatment is further irradiated with radiation at 5 to 50 kGy.

7. The method for producing a polypropylene blend composition according to claim 5, wherein the preform that has been subjected to the stretching treatment is further irradiated with radiation at 5 to 50 kGy.

8. The method for producing a polypropylene blend composition according to claim 6, wherein the preformed sheet or film is stretched before the heat treatment.

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