Foamable polypropylene resin composition with excellent foaming processability and method for preparing same

Abstract

Disclosed are a foamable polypropylene resin composition having high melt strength through electron beam irradiation and a method for preparing same, in which a resin composition having an excellent balance between melt strength and melt elongation can be prepared without employing in-line equipment, and thus is suitable for application as a material for sheet foaming. The present invention provides a foamable polypropylene resin composition and a method for preparing same, the foamable polypropylene resin composition having a weight average molecular weight of 350,000-600,000 g / mol and a molecular weight distribution (MWD, Mw / Mn) of 6.5-11, and containing at least 10 wt% of a polymer having a molecular weight of 1,000,000 g / mol or greater.

Description

Foaming polypropylene resin composition with excellent foaming processability and method for manufacturing the same

[0001] The present invention relates to a polypropylene resin composition and a method for manufacturing the same, and more specifically, to a foaming polypropylene resin composition and a method for manufacturing the same.

[0002] This application claims priority and interest to Korean Patent Application No. 10-2024-0163474 filed on November 15, 2024, the full text of which is incorporated herein by reference.

[0003] Polypropylene is widely used for general-purpose products due to its excellent mechanical properties, low specific gravity, and easy moldability; recently, with improvements in mechanical properties, it is also being used in various fields for products requiring high performance.

[0004] However, conventional polypropylene is a linear polymer with a limitation in its low melt strength. Due to this limitation, polypropylene has been used restrictively as a material for sheet foaming, where a balance between high melt strength and melt elongation is required.

[0005] Various methods for increasing the melt strength of conventional polypropylene have been disclosed, but most of them are methods of modifying linear polypropylene by introducing long-chain branches through reactive extrusion after the addition of peroxide. However, problems such as the decomposition of propylene due to peroxide during the reactive extrusion process, residue of peroxide, and yellowing may occur.

[0006] Korean Registered Patent No. 0311290 describes a method for producing a propylene polymer material with high melt strength by irradiating polypropylene with electron beams. In this method, a non-linear propylene polymer was produced by irradiating linear polypropylene with electron beams in a radiation chamber under a nitrogen atmosphere and pelletizing it. As a result of evaluating the foaming of the produced polymer, a good foaming ratio of up to 8 times was observed. However, there is a problem in that chlorofluorocarbon (CFC) gas, an ozone-depleting substance currently banned internationally, was used as a blowing agent in a high content of 8%.

[0007] Korean registered patent No. 1938511 discloses a method for producing high melt strength polypropylene by adding an organic peroxide to polypropylene and reactive extrusion, but there is a problem in that the residue of the peroxide and yellowing may occur.

[0008] Korean Registered Patent No. 2129922 discloses a high-flow partially crosslinked impact-resistant polypropylene with improved fluidity and impact resistance using a specific crosslinking agent, but there is a problem in that it is difficult to achieve the melt tension required for foam molding.

[0009] Meanwhile, when manufacturing high-melt-strength polypropylene by electron beam irradiation, oxygen in the air and antioxidants act to inhibit the formation of long-chain branches. Accordingly, some companies have introduced a method of irradiating electron beams in pellet form without prescribing antioxidants, and then prescribing antioxidants during the re-extrusion process. However, this method requires an in-line facility that connects the primary extrusion without antioxidants, electron beam irradiation, and the secondary extrusion with secondary antioxidants; otherwise, problems such as degradation of physical properties or non-uniformity of physical properties due to oxidation may occur.

[0010] The present invention aims to provide a foaming polypropylene resin composition suitable for application as a sheet foaming material and a method for manufacturing the same, wherein a resin composition with an excellent balance of melt strength and melt elongation can be produced without the introduction of in-line equipment in a foaming polypropylene resin composition with high melt strength through electron beam irradiation.

[0011] To solve the above problem, the present invention provides a foaming polypropylene resin composition having a weight-average molecular weight of 350,000 to 600,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 6.5 to 11, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more.

[0012] In addition, the above polypropylene resin composition provides a foaming polypropylene resin composition characterized by having a melt strength of 30 cN or more, a melt elongation of 220 mm / s or more, and a foaming ratio of 5 times or more, as measured according to the following method.

[0013] [Method for Measuring Melt Strength and Melt Elongation]

[0014] Using a Rheotens device (Rheotens 97, GOTTFERT), a molten sample is extruded through a 1 mm diameter circular die at a temperature of 200°C, the extruded strand is positioned 100 mm (spinline length) below the die exit, and the winding speed is 120 mm / s 2 When wound by a leotense wheel that gradually increases with acceleration, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), the peak force applied before the strand breaks or at the time of breakage is defined as the melt strength, and the winding speed (mm / s) at this point is defined as the melt elongation rate;

[0015] [Method for Measuring Foaming Ratio]

[0016] The maximum expansion ratio of a polypropylene foam formed by adding 0.3 parts by weight of talc as a nucleating agent to 100 parts by weight of the above-mentioned polypropylene resin composition in pellet form, dry blending, introducing carbon dioxide as a blowing agent, and foaming under conditions of a foaming temperature of 160 to 200°C, a screw rotation speed of 150 rpm, and a gear pump rotation speed of 20 rpm was measured.

[0017] To solve the above additional problem, the present invention provides a method for preparing a polypropylene resin composition by irradiating an electron beam onto a resin composition to which 0.07 to 0.25 parts by weight of a primary antioxidant, 0.01 to 1 part by weight of a secondary antioxidant, and 0.4 to 1.8 parts by weight are added to 100 parts by weight of polypropylene.

[0018] In addition, a method for manufacturing a polypropylene resin composition is provided, characterized in that the primary antioxidant is a phenolic antioxidant and the secondary antioxidant is a phosphorus-based antioxidant.

[0019] In addition, the present invention provides a method for manufacturing a polypropylene resin composition characterized in that the crosslinking agent is one or more selected from the group consisting of trialyl isocyanurate, trialyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trialyl trimesate, trialyl phosphate, pentaerythritol triacrylate, and divinylbenzene.

[0020] In addition, a method for manufacturing a polypropylene resin composition is provided, characterized in that the electron beam irradiation dose is 10 to 24 kGy.

[0021] The present invention provides a polypropylene resin composition in which a primary antioxidant and a crosslinking agent are added to polypropylene and an electron beam is irradiated to the composition, thereby having a weight-average molecular weight of 400,000 to 550,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 7 to 10, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more. By presenting this composition, it is possible to manufacture a resin composition with an excellent balance of melt strength and melt elongation without the introduction of in-line equipment for re-extrusion, and thus provide a foamed polypropylene resin composition suitable for application as a sheet foaming material, as well as a method for manufacturing the same.

[0022] Preferred embodiments of the present invention are described in detail below. In describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may obscure the essence of the present invention. Throughout the specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0023]

[0024] The present invention discloses a polypropylene resin composition for foaming having a weight-average molecular weight of 350,000 to 600,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 6.5 to 11, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more. The polypropylene resin composition according to the present invention can be prepared by irradiating an electron beam onto a resin composition to which 0.07 to 0.25 parts by weight of a primary antioxidant, 0.01 to 1 part by weight of a secondary antioxidant, and 0.4 to 1.8 parts by weight of a crosslinking agent are added to 100 parts by weight of polypropylene.

[0025] In the conventional method of manufacturing a high melt strength polypropylene resin composition by electron beam irradiation, in order to prevent inhibition of long-chain branch formation when injecting an antioxidant, it was required to proceed by injecting an antioxidant during the re-extrusion process after irradiating the polypropylene in pellet form with electron beams, which necessitated the introduction of in-line equipment. However, in the present invention, by composing a polypropylene resin composition containing a primary antioxidant, a secondary antioxidant, and a crosslinking agent in specific amounts and then performing electron beam irradiation thereon, it is possible to manufacture a resin composition with an excellent balance of melt strength and melt elongation without the introduction of in-line equipment for re-extrusion.

[0026] In the present invention, the polypropylene is not particularly limited as long as it is a resin for improving melt strength through electron beam irradiation, but may be a propylene homopolymer, a propylene random copolymer, or an impact polypropylene (a block copolymer of a propylene homopolymer and an ethylene-propylene copolymer). At this time, the comonomer used in the manufacture of the propylene copolymer is preferably ethylene or an α-olefin having 4 to 10 carbon atoms, and the content of the comonomer may be 30 weight% or less, preferably 1 to 10 weight%. These polypropylenes may be used as those manufactured by a commonly known process, and the manufacturing method is not particularly limited in the present invention.

[0027] In the present invention, the polypropylene irradiated with electron beams to which a primary antioxidant, a secondary antioxidant, and a crosslinking agent are added has a weight-average molecular weight of 350,000 to 600,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 6.5 to 11, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more, and preferably has a weight-average molecular weight of 400,000 to 550,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 7 to 10.5, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more. If the weight-average molecular weight is less than 350,000 g / mol, the foaming ratio is insufficient when applied for foaming due to the relatively low molecular weight, or molding is difficult due to high flowability during sheet molding; if it exceeds 600,000 g / mol, flowability decreases, which acts disadvantageously for molding. Furthermore, if the molecular weight distribution is less than 6.5, it is difficult to increase the number of branches beyond a certain level, and there are process limitations in setting it to exceed 11. Additionally, if the high molecular weight content, which is 1,000,000 g / mol or more, is less than 10 weight%, the balance between melt strength and melt elongation is poor, and the foaming ratio becomes insufficient.

[0028] In the present invention, to realize polypropylene having a weight-average molecular weight, molecular weight distribution, and a high molecular weight content of 1,000,000 g / mol or more within the above range, a single polypropylene having a specific molecular weight range may be used, or two polypropylenes with controlled molecular weight characteristics may be mixed and used.

[0029] Specifically, when using a single polypropylene, as described above, polypropylene with a weight-average molecular weight of 350,000 to 600,000 g / mol may be used, and preferably, polypropylene with a weight-average molecular weight of 400,000 to 550,000 g / mol may be used.

[0030] In addition, when using a mixture of two types of polypropylene with controlled molecular weight characteristics, the mixture may consist of 60 to 90 weight% of high molecular weight polypropylene with a weight-average molecular weight of 600,000 to 750,000 g / mol and 10 to 40 weight% of low molecular weight polypropylene with a weight-average molecular weight of 100,000 to 250,000 g / mol, and preferably, the mixture may consist of 70 to 85 weight% of high molecular weight polypropylene with a weight-average molecular weight of 500,000 to 700,000 g / mol and 15 to 30 weight% of low molecular weight polypropylene with a weight-average molecular weight of 150,000 to 200,000 g / mol.

[0031] The above primary antioxidant is capable of preventing the phenomenon in which resin molecules are broken by heat, oxygen, etc. when manufacturing a product using a polypropylene resin composition, and in the present invention, it is added to base polypropylene to allow electron beam irradiation to be performed.

[0032] The above primary antioxidant is preferably a phenolic antioxidant, for example, tetrakis[ethylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tetrakis[methylene-3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate]methane, 2,6-di-tertiary-butyl-4-methylphenol, etc. may be used, and preferably tetrakis[ethylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane may be used.

[0033] The above primary antioxidant is mixed in an amount of 0.07 to 0.25 parts by weight per 100 parts by weight of the polypropylene, and preferably in an amount of 0.1 to 0.2 parts by weight. If the content of the primary antioxidant is less than 0.07 parts by weight, it may be difficult to achieve high melt strength and the foaming ratio may be insufficient during foaming, and if it exceeds 0.25 parts by weight and goes beyond a certain content level, the high melt strength characteristics and foaming characteristics may also deteriorate again.

[0034] The above secondary antioxidant serves to stabilize the polymer by removing oxygen atoms from the already oxidized polymer, and in the present invention, it is added to base polypropylene to allow electron beam irradiation to be performed.

[0035] The above secondary antioxidant is preferably a phosphorus-based antioxidant, for example, tris(2,3-di-t-butylphenyl)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, etc. may be used, and preferably tris(2,3-di-t-butylphenyl)phosphite may be used.

[0036] The above secondary antioxidant is mixed in an amount of 0.01 to 1 part by weight per 100 parts by weight of the polypropylene, and preferably in an amount of 0.05 to 0.5 parts by weight. If the content of the secondary antioxidant is less than 0.01 parts by weight or exceeds 1 part by weight, the high melt strength characteristics and foaming characteristics may be reduced.

[0037] In the present invention, the crosslinking agent may be a triolefin-based crosslinking agent or divinylbenzene, and the triolefin-based crosslinking agent may be Triallyl isocyanurate, Triallyl cyanurate, Trimethylolpropane trimethacrylate, Trimethylolpropane triacrylate, Triallyl trimesate, Triallyl phosphate, Pentaerythritol triacrylate, etc. Here, it is desirable to select Triallyl isocyanurate (TAIC) by considering the maximization of the crosslinking effect by introducing long-chain branches during electron beam irradiation and the realization of a balance of maximized melt strength and melt elongation by controlling the crosslinking agent content and electron beam absorption amount.

[0038] In the present invention, the crosslinking agent is mixed in an amount of 0.4 to 1.8 parts by weight per 100 parts by weight of the polypropylene, preferably 0.5 to 1.5 parts by weight, and more preferably 0.5 to 1 part by weight. If the crosslinking agent content is less than 0.4 parts by weight, it is difficult to expect a satisfactory crosslinking effect, which lowers the balance between melt strength and melt elongation and may result in an insufficient foaming ratio. If it exceeds 1.8 parts by weight, the crosslinking effect of the polypropylene increases, allowing for the introduction of many long-chain branches. However, an excessive crosslinking effect may, for example, hinder cell growth during foaming, thereby reducing foaming performance, lowering the melt elongation, and significantly increasing gel formation.

[0039] In the present invention, the mixing of the polypropylene and the crosslinking agent may follow conventional methods known in the art. For example, the above components may be fed into a mixer in the required amount and mixed, and then melt-extruded using an extruder with an extrusion temperature of 180 to 240°C and a screw rotation speed of 95 to 100 rpm to produce pellets.

[0040] In the present invention, electron beam irradiation is performed on a mixture of polypropylene and a crosslinking agent to improve melt strength by generating free radicals in polypropylene and introducing chains broken by the radicals into branches, thereby causing entanglement between chains.

[0041] In the present invention, electron beam irradiation can be performed, for example, using an electron beam accelerator with an irradiation dose of 10 MeV. In the present invention, even with low-dose electron beam irradiation having an absorption amount of 10 to 24 kGy, preferably 12 to 22 kGy, and more preferably 15 to 20 kGy, sufficient chain entanglement is possible to improve the balance with the desired high melt strength and melt elongation rate. If the irradiation dose is less than 10 kGy, the number of radicals generated is small, making it difficult to achieve a high melt elongation rate, and if it exceeds 24 kGy, the degree of molecular chain decomposition increases, which may also lead to a decrease in the melt elongation rate.

[0042] The polypropylene resin composition according to the present invention may further include one or more conventional additives known in the art as other additives, such as neutralizing agents and heat stabilizers. In this case, the content of each of these additives may be used in a range of 0.01 to 1 part by weight per 100 parts by weight of the foaming polypropylene resin composition of the present invention, but is not particularly limited thereto.

[0043] The above neutralizing agent is capable of neutralizing acids (specifically hydrogen chloride) that may be generated by residues (metal components) of the catalyst used in polymerization, and the above heat stabilizer is capable of preventing a decrease in molecular weight while the polypropylene molded product is used in a high-temperature environment.

[0044] For example, calcium stearate can be used as the above neutralizing agent, and for example, distearyl thiodipropionate can be used as the above heat stabilizer.

[0045] According to one application example of the present invention, a molded body can be manufactured by a foaming molding method using the polypropylene resin composition, and the shape or size of the molded body can be appropriately determined. For example, a polypropylene foam can be manufactured by dry blending, for instance, by adding 0.1 to 1 weight part of a nucleating agent such as talc to 100 weight parts of a pellet-shaped polypropylene resin composition, and introducing a foaming agent such as carbon dioxide, and foaming under conditions of a foaming temperature of 160 to 200°C, a screw rotation speed of 10 to 150 rpm, and a gear pump rotation speed of 10 to 50 rpm.

[0046] The polypropylene resin composition according to the present invention above exhibits melt strength, melt elongation, and foaming characteristics suitable for foam sheet molding, and specifically, the melt strength measured according to the following method may be 30 cN or more, the melt elongation may be 220 mm / s or more, and the foaming ratio may be 5 times or more.

[0047] [Method for Measuring Melt Strength and Melt Elongation]

[0048] Using a Rheotens device (Rheotens 97, GOTTFERT), a molten sample is extruded through a 1 mm diameter circular die at a temperature of 200°C, the extruded strand is positioned 100 mm (spinline length) below the die exit, and the winding speed is 120 mm / s 2 When wound by a leotense wheel that gradually increases with acceleration, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), the peak force applied before the strand breaks or at the time of breakage is defined as the melt strength, and the winding speed (mm / s) at this point is defined as the melt elongation rate;

[0049] [Method for Measuring Foaming Ratio]

[0050] The maximum expansion ratio of a polypropylene foam formed by adding 0.3 parts by weight of talc as a nucleating agent to 100 parts by weight of the above-mentioned polypropylene resin composition in pellet form, dry blending, introducing carbon dioxide as a blowing agent, and foaming under conditions of a foaming temperature of 160 to 200°C, a screw rotation speed of 150 rpm, and a gear pump rotation speed of 20 rpm was measured.

[0051] Hereinafter, specific embodiments according to the present invention will be described.

[0052]

[0053] Examples and Comparative Examples

[0054] The raw materials were mixed in a Henschel mixer for 1 minute according to the composition of Table 1 below, and then extruded using a single-screw extruder at 180 to 240°C to produce a polypropylene resin composition in pellet form, and then a polypropylene composition was produced by maintaining the electron beam irradiation dose listed in Table 1 below. The electron beam was irradiated under conditions of a beam energy of 10 MeV, a line speed of 0.5 to 3 m / min, and an irradiation distance of 4 to 5 m.

[0055]

[0056] Item Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 A Weight parts 100 100 100 100 100 100 100 100 100 100 100 100 100 B Weight parts 0.5 0.5 50.5 50.5 1.0 0.5 50.5 50.3 20.5 50.5 CkGy 15 15 15 15 15 15 20 15 15 15 15 525 D 1 Weight part 0.0 7 0.1 0.1 50. 20.250.10.10.030.30.10.10.10.1D2 parts by weight 0.10.10.10.10.10.10.10.10.10.10.10.10.1D3 parts by weight 0.050.050.050.050.050.050.050.050.050.050.050.050.05* Note A: Polypropylene homopolymer (Weight-average molecular weight 450,000 g / mol) B: Crosslinking agent (Triallyl Isocyanurate (TAIC)) C: Electron beam irradiation dose D1: Phenolic antioxidant (Tetrakis[ethylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, Songnox 1010, Songwon Industrial) D2: Phosphorus-based antioxidant (Tris(2,3-di-t-butylphenyl)phosphite, Songnox 1680, Songwon Industrial) D3: Neutralizing agent (Calcium stearate, SAK-CS-POF, Sunace)

[0057]

[0058] Experimental Example

[0059] For electron beam irradiated polypropylene pellets prepared according to the above examples and comparative examples, molecular weight characteristics, melt strength, melt elongation, and foaming ratio were measured by the following method, and the results are shown in Table 2 below.

[0060] [measurement method]

[0061] (1) Molecular weight characteristics

[0062] The weight-average molecular weight (Mw) and molecular weight distribution (MWD, Mw / Mn) were measured using gel permeation chromatography (GPC, Agilent). Polystyrene was used as a standard in chloroform solvent.

[0063] (2) Melt strength and melt elongation

[0064] Using a Rheotens device (Rheotens 97, GOTTFERT), a molten sample is extruded through a 1 mm diameter circular die at a temperature of 200°C, the extruded strand is positioned 100 mm (spinline length) below the die exit, and the winding speed is 120 mm / s 2 When wound by a leotense wheel that gradually increases with acceleration, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), the peak force applied before the strand breaks or at the time of breakage is defined as the melt strength, and the winding speed (mm / s) at this point is defined as the melt elongation.

[0065] (3) Foaming ratio

[0066] The maximum expansion ratio of a polypropylene foam formed by adding 0.3 parts by weight of talc as a nucleating agent to 100 parts by weight of the above-mentioned polypropylene resin composition in pellet form, dry blending, introducing carbon dioxide as a blowing agent, and foaming under conditions of a foaming temperature of 160 to 200°C, a screw rotation speed of 150 rpm, and a gear pump rotation speed of 20 rpm was measured.

[0067]

[0068] Item Unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Weight Average Molecular Weight g / mol 5 32,636 511,530 499,000 442,373 434,871 463,300 430,300 327,400 394,900 353,800 548,600 442,400 146,500 Molecular Weight Distribution - 7.7 10.2 7.28.18.9 8.3 7.29.28.0 6.19.8 8.14.4 Molecular Weight 1 million or more Content (Weight %) 3.1 1.7 12.7 10.7 10.4 11.8 10.7 7.3 9.4 7.8 12.2 10.7 0.4 Melting Strength (cN) 3 236 37 34 33 34 32 22 7 234 9 37 19 Melting Elongation (mm / s) 2 25 230 2 25 220 220 240 25 0 220 220 215 18 0 19 0 210 Foaming Ratio 5.1 5.8 5.7 5.3 5.0 5.6 5.5 2.8 3.1 3.6 2.0 2.6 1.9

[0069]

[0070] Referring to Table 2, when an electron beam is irradiated onto a resin composition to which specific amounts of a primary antioxidant, a secondary antioxidant, and a crosslinking agent are added to polypropylene according to the present invention to achieve a certain level of weight-average molecular weight, molecular weight distribution, and high molecular weight content (Examples 1 to 7), it can be confirmed that the balance between melt strength and melt elongation is excellent and foaming characteristics are significantly improved, even without the introduction of in-line equipment for re-extrusion and despite low-dose electron beam irradiation.

[0071] In this regard, it can be seen that when the content of the primary antioxidant is below a certain level or is excessive (Comparative Examples 1 and 2), the molecular weight characteristics deviate from the required level, it is difficult to achieve high melt strength, and the foaming ratio is insufficient during foaming. Additionally, when the content of the crosslinking agent is below a certain level (Comparative Example 3), it can be seen that the molecular weight characteristics deviate from the required level, the balance between melt strength and melt elongation is reduced, and the foaming ratio is insufficient during foaming; when the content is excessive (Comparative Example 4), the molecular weight characteristics satisfy the required level, but the melt elongation and foaming characteristics are significantly reduced. Furthermore, when the electron beam irradiation amount is insufficient (Comparative Example 5), the melt elongation and foaming characteristics are also significantly reduced, and when the electron beam irradiation amount is excessive (Comparative Example 6), the molecular weight characteristics deviate from the required level, the balance between melt strength and melt elongation is reduced, and the foaming ratio is insufficient during foaming.

[0072]

[0073] Preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without changing the technical concept or essential features of the present invention.

[0074] Accordingly, the scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning, scope, and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. A foaming polypropylene resin composition having a weight-average molecular weight of 350,000 to 600,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 6.5 to 11, and a high molecular weight content of 10% by weight or more with a molecular weight of 1,000,000 g / mol or more.

2. In Paragraph 1, The above polypropylene resin composition is a foaming polypropylene resin composition characterized by having a melt strength of 30 cN or more, a melt elongation of 220 mm / s or more, and a foaming ratio of 5 times or more, as measured according to the following method: [Method for Measuring Melt Strength and Melt Elongation] Using a Rheotens device (Rheotens 97, GOTTFERT), a molten sample is extruded through a 1 mm diameter circular die at a temperature of 200°C, the extruded strand is positioned 100 mm (spinline length) below the die exit, and the winding speed is 120 mm / s 2 When wound by a leotense wheel that gradually increases with acceleration, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), the peak force applied before the strand breaks or at the time of breakage is defined as the melt strength, and the winding speed (mm / s) at this point is defined as the melt elongation rate; [Method for Measuring Foaming Ratio] The maximum expansion ratio of a polypropylene foam formed by adding 0.3 parts by weight of talc as a nucleating agent to 100 parts by weight of the above-mentioned polypropylene resin composition in pellet form, dry blending, introducing carbon dioxide as a blowing agent, and foaming under conditions of a foaming temperature of 160 to 200°C, a screw rotation speed of 150 rpm, and a gear pump rotation speed of 20 rpm was measured.

3. In Paragraph 1, A method for preparing a polypropylene resin composition of claim 1 by irradiating an electron beam onto a resin composition to which 0.07 to 0.25 parts by weight of a primary antioxidant, 0.01 to 1 part by weight of a secondary antioxidant, and 0.4 to 1.8 parts by weight of a crosslinking agent are added to 100 parts by weight of polypropylene.

4. In Paragraph 3, A method for manufacturing a polypropylene resin composition characterized in that the primary antioxidant is a phenolic antioxidant and the secondary antioxidant is a phosphorus-based antioxidant.

5. In Paragraph 3, A method for preparing a polypropylene resin composition, characterized in that the crosslinking agent is one or more selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimesate, triallyl phosphate, pentaerythritol triacrylate, and divinylbenzene.

6. In Paragraph 1, A method for manufacturing a polypropylene resin composition characterized by the electron beam irradiation dose being 10 to 24 kGy.