Polypropylene resin composition with excellent melt strength and preparation method thereof

Abstract

The invention discloses a polypropylene resin composition with relatively high extensional viscosity and melt strength and a preparation method thereof. The present invention provides a polypropylene resin composition having a weight-average molecular weight of from 250,000 g / mol to 500,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of from 5.5 to 12, and a content of a high molecular weight having a molecular weight of 1,000,000 g / mol or more of from 4% by weight to 15% by weight, and a method for preparing the same.

Description

Technical Field

[0001] The present invention relates to a polypropylene resin composition and a method for preparing the same, and more particularly, to a polypropylene resin composition having excellent melt strength and a method for preparing the same.

[0002] This application claims the priority and benefits of Korean Patent Application No. 10-2022-0165270, filed on November 30, 2022, and the entire text of the Korean patent application is incorporated herein by reference. Background Art

[0003] Polypropylene is widely used for general product applications due to its excellent mechanical properties, low specific gravity, easy moldability, etc. Recently, with the improvement of mechanical properties, it is also applied to products requiring high performance in various fields.

[0004] However, conventional polypropylene is in the form of a linear polymer, and there is a limitation of low melt strength. Due to this limitation, the application of polypropylene in deep draw vacuum forming products, large blow molding products, and sheet foaming materials that require high tensile viscosity is restricted.

[0005] In the past, various methods for increasing the melt tension of polypropylene have been disclosed, but most of the methods are methods of introducing long branches by adding peroxides and then performing reactive extrusion to modify linear polypropylene. This method may cause problems such as the decomposition of propylene due to peroxides during the reactive extrusion process, and there are also problems such as the residue and yellowing of peroxides.

[0006] Korean Patent No. 0311290 discloses a method for preparing an acrylonitrile polymer material with high melt strength by irradiating polypropylene with an electron beam. In this method, after linear polypropylene is polymerized, an electron beam is irradiated in a radiation chamber under a nitrogen atmosphere and granulated to prepare a non-linear acrylonitrile polymer. The result of the foaming evaluation of the prepared polymer shows that the foaming ratio can reach up to 8 times at most, but this method has the following problems: it uses chlorofluorocarbon (CFC) gas, which is an ozone-depleting substance prohibited internationally at present, as a foaming agent, and uses this foaming agent at a high content of 8%.

[0007] Korean Patent No. 1938511 discloses a method for preparing high melt strength polypropylene by adding an organic peroxide to polypropylene and performing reactive extrusion, but there are also problems such as the residue and yellowing of peroxides.

[0008] Korean Patent No. 2129922 discloses a highly flowable partially crosslinked impact-resistant polypropylene using a specific crosslinking agent to improve fluidity and impact resistance, but there is a problem that it is difficult to achieve the melt tension required for vacuum forming or foaming. SUMMARY OF THE INVENTION

[0009] The present invention aims to provide a polypropylene resin composition having high tensile viscosity and melt strength and a method for preparing the same.

[0010] To solve the above problems, the present invention provides a polypropylene resin composition having a weight average molecular weight of 250,000 g / mol to 500,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 5.5 to 12, and a high molecular weight content of 4% by weight to 15% by weight with a molecular weight of 1,000,000 g / mol or more.

[0011] In addition, a polypropylene resin composition is provided, characterized in that the polypropylene resin composition has a degree of branching of 0.5 to 0.8, a tensile viscosity of 5×10 6 Pa·s to 10 9 Pa·s, and a melt strength of 30 cN or more.

[0012] [Method for measuring degree of branching]

[0013] It is measured by calculating the ratio ([η] br ) of the intrinsic viscosity of the polypropylene resin composition to the intrinsic viscosity ([η] lin ) of a linear polymer having the same molecular weight; br / [η] lin )

[0014] [Method for measuring tensile viscosity]

[0015] Using an advanced rheometric expansion system (ARES), fixing a specimen with a lateral dimension of 20 mm, a longitudinal dimension of 10 mm, and a thickness of 1 mm on a sample holder, and then using an extensional viscosity fixture (EVF) mode to measure the resistance value when the specimen rotates around an axis at a speed of 0.1 / s at a temperature of 180°C, and taking the maximum value of the tension that changes with the rotation distance (elongation rate) of the specimen as the tensile viscosity;

[0016] [Method for measuring melt strength]

[0017] Using a Rheotens device (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at a temperature of 200 °C. When the filament produced by extrusion was wound by the Rheotens wheel, the force (cN) applied to the wheel was recorded as a function of the winding speed (mm / s), and the peak force before the filament broke or the force applied at the time of breakage was taken as the melt strength. The Rheotens wheel was located 100 mm (spinline length) below the die outlet, and the winding speed was gradually increased at an acceleration of 120 mm / s 2 and the acceleration was gradually increased at an acceleration of 120 mm / s.

[0018] In addition, a polypropylene resin composition is provided, which is characterized in that the polypropylene resin composition is suitable for vacuum forming, blow molding or foam molding.

[0019] To solve the above another problem, the present invention provides a method for preparing a polypropylene resin composition, which irradiates an electron beam on a resin composition in which 0.01 to 2 parts by weight of a crosslinking agent is added to 100 parts by weight of polypropylene to prepare the above polypropylene resin composition.

[0020] In addition, a method for preparing a polypropylene resin composition is provided, which is characterized in that the crosslinking agent is one or more selected from triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyltrimesate, triallyl phosphate, pentacrythritol triacrylate and divinylbenzene.

[0021] In addition, a method for preparing a polypropylene resin composition is provided, which is characterized in that the irradiation dose of the electron beam is 5 kGy to 30 kGy.

[0022] By irradiating an electron beam to a resin composition containing a crosslinking agent added to polypropylene, a polypropylene resin composition with a weight-average molecular weight of 250,000 g / mol to 500,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 5.5 to 12, and a high molecular weight content of 4 wt% to 15 wt% with a molecular weight of 1,000,000 g / mol or more can be obtained, thereby providing a polypropylene resin composition with excellent tensile viscosity and melt strength and a method for preparing the same.

[0023] The polypropylene resin composition of the present invention can be used for various applications such as extrusion, sheet, injection molding, etc., and is more suitable for vacuum forming, blow molding or foaming that require higher melt strength characteristics. Detailed Description of the Invention

[0024] The preferred embodiments of the present invention will be described in detail below. When it is judged that the specific description of the related well-known technology may cause the key points of the present invention to be unclear, the detailed description thereof will be omitted. Throughout the specification, when a certain part is referred to as "including" a certain component, unless there is a particularly contrary record, it means that other components are not excluded, but other components can be further included.

[0025] The present invention discloses a polypropylene resin composition having a weight-average molecular weight of 250,000 g / mol to 500,000 g / mol, a molecular weight distribution (MWD, Mw / Mn) of 5.5 to 12, and a high molecular weight content of 4 wt% to 15 wt% with a molecular weight of 1,000,000 g / mol or more. The polypropylene resin composition of the present invention can be prepared by irradiating an electron beam to a resin composition containing 0.01 parts by weight to 2 parts by weight of a crosslinking agent added to 100 parts by weight of polypropylene.

[0026] In the present invention, the polypropylene is not particularly limited as long as it is a resin whose melt strength is improved by electron beam irradiation, but a propylene homopolymer, a propylene random copolymer or an impact polypropylene (a block copolymer of a propylene homopolymer and an ethylene-propylene copolymer) can be used. At this time, the comonomer used for preparing the propylene copolymer is preferably ethylene or an α-olefin having 4 to 10 carbon atoms, and the content of the comonomer can be 30 wt% or less, preferably 1 wt% to 10 wt%. These polypropylenes can use substances prepared by common processes, and the present invention does not particularly limit their preparation methods.

[0027] In the present invention, the weight-average molecular weight of the polypropylene added with a crosslinking agent and irradiated with an electron beam may be from 250,000 g / mol to 500,000 g / mol, and the molecular weight distribution (MWD, Mw / Mn) may be from 5.5 to 12. Preferably, the weight-average molecular weight may be from 270,000 g / mol to 450,000 g / mol, and the molecular weight distribution (MWD, Mw / Mn) may be from 5.5 to 10. If the weight-average molecular weight is lower than 250,000 g / mol, due to the relatively low molecular weight, for example, the foaming ratio is insufficient when used for foaming, or the fluidity is too high during sheet forming, resulting in difficult forming. If it exceeds 500,000 g / mol, the fluidity decreases, which is not conducive to forming. In addition, if the molecular weight distribution is lower than 5.5, it is difficult to increase the number of branches to above a specified level. Additionally, setting the molecular weight distribution to exceed 12 has technological limitations.

[0028] In the present invention, in order to obtain polypropylene having a weight-average molecular weight and a molecular weight distribution within the above ranges, two polypropylenes with adjusted molecular weight characteristics may be used in combination, or a single polypropylene having a specific molecular weight range may be used.

[0029] Specifically, when two polypropylenes with adjusted molecular weight characteristics are used in combination, it may be a mixture of 60% to 90% by weight of a high-molecular-weight polypropylene having a weight-average molecular weight of 500,000 g / mol to 700,000 g / mol and 10% to 40% by weight of a low-molecular-weight polypropylene having a weight-average molecular weight of 50,000 g / mol to 200,000 g / mol; preferably, it may be a mixture of 70% to 85% by weight of a high-molecular-weight polypropylene having a weight-average molecular weight of 550,000 g / mol to 650,000 g / mol and 15% to 30% by weight of a low-molecular-weight polypropylene having a weight-average molecular weight of 80,000 g / mol to 150,000 g / mol.

[0030] In addition, when using a single polypropylene, polypropylene having a weight-average molecular weight of 350,000 g / mol to 600,000 g / mol may be used, and preferably, polypropylene having a weight-average molecular weight of 400,000 g / mol to 500,000 g / mol may be used.

[0031] In the present invention, as the crosslinking agent, a triolefin crosslinking agent or divinylbenzene can be used. As the triolefin crosslinking agent, triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimesate, triallyl phosphate, pentaerythritol triacrylate, etc. can be used. Among them, considering the maximization of the crosslinking effect achieved by introducing long branched chains during electron beam irradiation and the maximization of the tensile viscosity and melt strength achieved by adjusting the crosslinking agent content and electron beam absorption amount, triallyl isocyanurate (TAIC) is preferably selected.

[0032] In the present invention, relative to 100 parts by weight of the polypropylene, the crosslinking agent can be mixed in an amount of 0.01 part by weight to 2 parts by weight, preferably 0.1 part by weight to 1.5 parts by weight, and more preferably 0.5 part by weight to 1.2 parts by weight. If the content of the crosslinking agent is less than 0.01 part by weight, it is difficult to expect a satisfactory crosslinking effect; if it exceeds 2 parts by weight, although the crosslinking effect of the polypropylene is improved, so that more long branched chains can be introduced, an excessive crosslinking effect may, for example, hinder the cell growth during foaming, instead reducing the foaming performance, and may significantly increase the generation of gels.

[0033] In the present invention, the mixing of the polypropylene and the crosslinking agent can be carried out according to the conventional methods well known in the art. For example, after adding the above components in the required amounts to a mixer and mixing, melt extrusion is carried out using an extruder under the conditions of an extrusion temperature of 180°C to 240°C and a screw speed of 95 rpm to 100 rpm, thereby forming pellets.

[0034] In the present invention, in order to generate free radicals in the polypropylene and introduce the chains broken by the free radicals in the form of branched chains, thereby generating entanglements between the chains to improve the melt strength, the mixture of the polypropylene and the crosslinking agent is irradiated with an electron beam.

[0035] In the present invention, electron beam irradiation can be carried out, for example, using an electron beam accelerator with an irradiation dose of 10 MeV. In the present invention, sufficient chain entanglement can also be achieved by low-dose electron beam irradiation (absorbed dose of 5 kGy to 30 kGy, preferably 10 kGy to 25 kGy, more preferably 15 kGy to 20 kGy) to obtain the desired effect of improving melt strength. If the irradiation dose is lower than 5 kGy, fewer free radicals are generated, and it is difficult to impart a high tensile viscosity; if it exceeds 30 kGy, the degree of decomposition of the molecular chains increases, which may lead to a decrease in tensile viscosity.

[0036] The polypropylene resin composition of the present invention may further include one or more of the conventional additives well-known in the art, such as antioxidants, neutralizing agents, heat stabilizers, etc., as other additives. At this time, relative to 100 parts by weight of the polypropylene resin composition for foaming of the present invention, these additives can be used in an amount ranging from 0.01 part by weight to 1 part by weight, but are not particularly limited thereto.

[0037] The antioxidant can prevent the phenomenon of resin molecular chain breakage caused by heat, oxygen, etc. when using the polypropylene resin composition to prepare products; the neutralizing agent can neutralize the acid (specifically hydrogen chloride) that may be generated by the catalyst residues (metal components) used in polymerization; the heat stabilizer can prevent the decrease in molecular weight during the use of the polypropylene molded product in a high-temperature environment.

[0038] As such an antioxidant, for example, a phosphorus-based antioxidant or a phenolic antioxidant can be used. As an example of the phosphorus-based antioxidant, tris(2,3-di-tert-butylphenyl) phosphite can be cited, and as an example of the phenolic antioxidant, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] methane can be cited.

[0039] In addition, as the neutralizing agent, for example, calcium stearate can be used, and as the heat stabilizer, for example, distearyl thiodipropionate can be used.

[0040] The polypropylene resin composition of the present invention can be used and molded articles can be prepared by various molding methods. The shape, size, etc. of the molded articles can be appropriately determined. As methods for preparing such molded articles, for example, injection molding, compression molding, vacuum molding, foam molding, extrusion molding, etc., which are commonly used industrially, can be cited. In addition, according to the purpose, molding methods such as joining the polypropylene resin composition of the present invention with a polypropylene resin or other resin of the same or different types, or co-extrusion molding methods can also be cited. However, the polypropylene resin composition of the present invention has excellent tensile viscosity and is more suitable for deep-drawing vacuum molding or foam sheet molding. Products prepared by the deep-drawing vacuum molding, for example, can include cup-shaped containers, and products prepared by the foam molding, for example, can include lunch box containers, cup noodle containers, meat processing trays, etc.

[0041] The above polypropylene resin composition of the present invention exhibits melt strength characteristics suitable for vacuum molding, blow molding or foam sheet molding. Specifically, the degree of branching measured by the following method can be 0.5 to 0.8, the tensile viscosity can be 5×10 6 Pa·s to 10 9 Pa·s, and the melt strength can be 30 cN or more; preferably, the degree of branching can be 0.6 to 0.8, the tensile viscosity can be 10 7 Pa·s to 5×10 8 Pa·s, and the melt strength can be 35 cN or more.

[0042] [Method for measuring degree of branching]

[0043] It is measured by calculating the ratio ([η] br ) of the intrinsic viscosity ([η] lin ) of the polypropylene resin composition to the intrinsic viscosity ([η] br ) of a linear polymer having the same molecular weight; lin

[0044] [Method for measuring tensile viscosity]

[0045] Using an advanced rheometric expansion system (ARES), a specimen with a lateral dimension of 20 mm, a longitudinal dimension of 10 mm and a thickness of 1 mm is fixed on a sample holder, and then, using the extensional viscosity fixture (EVF) mode, the resistance value borne by the specimen when rotating around the axis at a speed of 0.1 / s at a temperature of 180°C is measured, and the maximum value of the tension that changes with the rotation distance (elongation rate) of the specimen is taken as the tensile viscosity;

[0046] [Method for measuring melt strength]

[0047] Using a Rheotens device (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at a temperature of 200 °C. When the filament produced by extrusion was wound by the Rheotens wheel, the force (cN) applied to the wheel was recorded as a function of the winding speed (mm / s), and the peak force before the filament broke or the force applied at break was taken as the melt strength. The Rheotens wheel was located 100 mm (spinline length) below the die outlet, and the winding speed was gradually increased at an acceleration of 120 mm / s 2 .

[0048] Hereinafter, the present invention will be described by way of specific embodiments.

[0049] Examples and Comparative Examples

[0050] The raw materials were mixed in a Henschel mixer for one minute according to the composition in Table 1 below, and then extruded through a single-screw extruder at 180 °C to 240 °C to prepare a granular polypropylene resin composition. Thereafter, the polypropylene composition was prepared while maintaining the electron beam irradiation dose shown in Table 1 below. The electron beam was irradiated under the conditions of a beam energy of 10 MeV, a line speed of 0.5 m / min to 3 m / min, and an irradiation distance of 4 m to 5 m.

[0051] [Table 1]

[0052]

[0053] Test Examples

[0054] According to the following method, the branching characteristics, molecular weight characteristics, tensile viscosity, and melt strength of the polypropylene pellets prepared according to the above examples and comparative examples were measured, and the results are shown in Table 2.

[0055] [Measurement method]

[0056] (1) Degree of branching

[0057] By calculating the ratio ([η] br ) of the intrinsic viscosity ([η] lin ) of the polypropylene resin composition having a long-chain branched structure to the intrinsic viscosity ([η] br ) of the linear polymer having the same molecular weight ([η] lin ), the degree of branching was measured.

[0058] (2) Molecular weight characteristics

[0059] The weight-average molecular weight (Mw) and molecular weight distribution (MWD, Mw / Mn) were determined using Gel Permeation Chromatography (GPC, Agilent). Polystyrene was used as the standard substance in chloroform solvent.

[0060] (3) Tensile viscosity

[0061] Using an advanced rheometric expansion system (ARES), a specimen with a lateral dimension of 20 mm, a longitudinal dimension of 10 mm, and a thickness of 1 mm was fixed on the sample holder. Then, in the Extensional viscosity fixture (EVF) mode, the resistance value that the specimen endured when rotating around the axis at a speed of 0.1 / s at 180 °C was measured, and the maximum value in the tension that changed with the rotation distance (elongation rate) of the specimen was taken as the tensile viscosity.

[0062] (4) Melt strength

[0063] Using a Rheotens device (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at 200 °C. When the filament extruded was wound by the Rheotens wheel, the force (cN) applied to the wheel was recorded as a function of the winding speed (mm / s), and the peak force before the filament broke or the force applied at the time of breakage was taken as the melt strength, where the Rheotens wheel was located 100 mm (spinline length) below the die outlet, and the winding speed was increased step by step at an acceleration of 120 mm / s 2 until it broke.

[0064] [Table 2]

[0065]

[0066] Referring to Table 2, it can be seen that in the case where the resin composition added with a crosslinking agent in polypropylene is irradiated with an electron beam according to the present invention to make the resin composition have a specified level of weight-average molecular weight, molecular weight distribution, and high molecular weight content (Examples 1 to 3), even when irradiated with a low dose of electron beam, free radicals are generated and branches are generated due to the crosslinking agent, thus having excellent branching characteristics, and the tensile viscosity and melt strength are very excellent.

[0067] In contrast, in the case where electron beam irradiation is not performed (Comparative Example 1 and Comparative Example 2), in the case where electron beam irradiation is performed but the polypropylene resin composition exceeds the specified molecular weight range after irradiation (Comparative Example 3) or the high molecular weight content is insufficient (Comparative Example 4), or in the case where the molecular weight distribution exceeds the specified range (Comparative Example 5), it can be seen that the elongational viscosity and melt strength are significantly decreased.

[0068] The preferred embodiments of the present invention have been described in detail above. The description of the present invention is merely illustrative, and those skilled in the art to which the present invention pertains can understand that other specific forms can be easily modified without changing the technical idea or essential features of the present invention.

[0069] Therefore, the scope of the present invention is defined by the appended claims rather than the above detailed description, and all changes or modifications derived from the meaning, scope, and equivalent concepts of the claims should be construed as falling within the scope of the present invention.

Claims

1. A polypropylene resin composition having a weight-average molecular weight of 250,000 g / mol to 500,000 g / mol, a molecular weight distribution MWD of 5.5 to 12 as Mw / Mn, and a high molecular weight content of 4 wt% to 15 wt% with a molecular weight of 1,000,000 g / mol or more.

2. The polypropylene resin composition according to claim 1, wherein The degree of branching of the polypropylene resin composition as measured by the following method is 0.5 to 0.8, the tensile viscosity is 5×10 6 Pa·s to 10 9 Pa·s, and the melt strength is 30 cN or more. [Branching degree measurement method] By calculating the intrinsic viscosity [η] of the polypropylene resin composition br and the intrinsic viscosity [η] of a linear polymer having the same molecular weight lin of the ratio [η] br / [η] lin for determination; [Tensile viscosity measurement method] Using an advanced rheology expansion system ARES, fixing a specimen with a lateral dimension of 20 mm, a longitudinal dimension of 10 mm, and a thickness of 1 mm on a sample holder, and then using the EVF mode of a tensile viscosity fixture to measure the resistance value when the specimen rotates around the axis at a speed of 0.1 / s at a temperature of 180°C, and taking the maximum value of the tension that changes with the rotation distance (elongation rate) of the specimen as the tensile viscosity; [Melt strength measurement method] Using a Rheotens device (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at a temperature of 200 °C. When the filaments produced by extrusion were wound by the Rheotens wheel, the force in cN applied to the wheel was recorded as a function of the winding speed in mm / s, and the peak force before filament breakage or the force applied at breakage was taken as the melt strength, where the Rheotens wheel was located at a spinning distance of 100 mm below the die outlet, and the winding speed was increased step by step with an acceleration of 120 mm / s 2 .

3. The polypropylene resin composition according to claim 1, wherein The polypropylene resin composition is suitable for vacuum forming, blow molding, or foam molding.

4. A method for preparing a polypropylene resin composition, which irradiates an electron beam on a resin composition in which 0.01 part by weight to 2 parts by weight of a crosslinking agent is added to 100 parts by weight of polypropylene to prepare the polypropylene resin composition according to claim 1.

5. The method for preparing a polypropylene resin composition according to claim 4, wherein The crosslinking agent is one or more selected from triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimesate, triallyl phosphate, pentacrythritol triacrylate, and divinylbenzene.

6. The method for preparing a polypropylene resin composition according to claim 1, wherein The irradiation dose of the electron beam is 5 kGy to 30 kGy.

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