Polypropylene resin composition with excellent melt strength and its manufacturing method

Abstract

A polypropylene resin composition having high elongational viscosity and melt strength and a method for producing the same are disclosed. The present invention provides a polypropylene resin composition having a weight average molecular weight of 250,000 to 500,000 g / mol, a molecular weight distribution MWD (Mw / Mn) of 5.5 to 12, and a content of high molecular weights with a molecular weight of 1,000,000 g / mol or more of 4 to 15 wt %.

Description

[Technical Field]

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

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

[0003] Polypropylene is widely used in general-purpose products due to its excellent mechanical properties, low specific gravity, and easy moldability, and recently, it has been used in a variety of fields for products that require high performance due to its improved mechanical properties.

[0004] However, polypropylene in its typical form is a linear polymer and has the limitation of low melt strength, which has limited its use in dip-draw vacuum molded products and large blow molded products, which require high elongational viscosity, as well as in sheet foaming materials.

[0005] Various methods have been disclosed to increase the melt tension of polypropylene. Most of these methods involve adding peroxide and then modifying linear polypropylene by reactive extrusion to introduce long chain branches. However, these methods can cause problems such as decomposition of propylene due to the peroxide during the reactive extrusion process, as well as problems such as residual peroxide and yellowing.

[0006] Patent Document 1 describes a method for producing a propylene polymer material with high melt strength by irradiating polypropylene with an electron beam. After polymerizing linear polypropylene, the linear polypropylene is irradiated with an electron beam in a nitrogen-filled radiation chamber and pelletized to produce nonlinear propylene. Foaming evaluation of the produced polymer showed a good expansion ratio of up to 8 times. However, there is a problem in that a high content of 8% chlorofluorocarbon (CFC) gas, an ozone-depleting substance whose use is currently banned internationally, is used as a blowing agent.

[0007] Patent Document 2 discloses a method of adding an organic peroxide to polypropylene and producing high melt strength polypropylene by reactive extrusion, but similarly has problems such as residual peroxide and yellowing.

[0008] Patent Document 3 discloses a high-fluidity partially crosslinked impact-resistant polypropylene that has improved fluidity and impact properties by using a specific crosslinking agent, but there is a problem that it is difficult to realize the melt tension required for vacuum molding or foam molding. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent No. 0311290 [Patent Document 2] Korean Patent No. 1938511 [Patent Document 3] Korean Patent No. 2129922 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a polypropylene resin composition having high extensional viscosity and melt strength, and a method for producing the same. [Means for solving the problem]

[0011] To achieve the above object, the present invention provides a polypropylene resin composition having a weight average molecular weight of 250,000 to 500,000 g / mol, a molecular weight distribution MWD (Mw / Mn) of 5.5 to 12, and a content of high molecular weights having a molecular weight of 1,000,000 g / mol or more of 4 to 15 wt%.

[0012] The polypropylene resin composition has a branching degree of 0.5 to 0.8 and an extensional viscosity of 5×10 6 〜10 9 The present invention provides a polypropylene resin composition having a melt strength of 30 cN or more in Pa·s. [Method for measuring the degree of branching] The intrinsic viscosity [η] of the polypropylene resin composition br Intrinsic viscosity [η] of a linear polymer with the same molecular weight lin Ratio to [η] br / [η] lin Calculate with; [Method for measuring extensional viscosity] A specimen measuring 20 mm wide, 10 mm long, and 1 mm thick is fixed to the sample holder using an ARES (advanced rheometric expansion system), and then the resistance value is measured when the specimen rotates around its axis at a temperature of 180°C and a speed of 0.1 / s using the EVF (Extensional Viscosity Fixture) mode. The maximum value of the tension that changes depending on the specimen's rotation distance (extension rate) is taken as the extensional viscosity; [Melt strength measurement method] Using a Rheotens apparatus (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at a temperature of 200°C. The extruded streaks were located 100 mm (spinline length) below the die exit, and the winding speed was 120 mm / s. 2 When the film is wound by a rheotensile wheel that gradually increases with an acceleration of 1 / 2, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the force applied to the peak before or at the time of rupture of the stripe is taken as the melt strength.

[0013] The present invention also provides a polypropylene resin composition, characterized in that the polypropylene resin composition is for vacuum molding, blow molding, or foaming.

[0014] In order to solve the other problem, the present invention provides a method for obtaining the polypropylene resin composition according to claim 1, by irradiating 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 with an electron beam.

[0015] The present invention also provides a method for producing a polypropylene resin composition, wherein the crosslinking agent is at least one selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimesate, triallyl phosphate, pentaerythritol triacrylate, and divinylbenzene.

[0016] The present invention also provides a method for producing a polypropylene resin composition, wherein the electron beam is irradiated at a dose of 5 to 30 kGy. [Effects of the Invention]

[0017] The present invention provides a polypropylene resin composition having a weight average molecular weight of 250,000 to 50,000 g / mol, a molecular weight distribution MWD (Mw / Mn) of 5.5 to 12, and a content of high molecular weights of 1,000,000 g / mol or more of 4 to 15 wt % by irradiating a resin composition in which a crosslinking agent is added to polypropylene with electron beams, thereby providing a polypropylene resin composition with excellent elongational viscosity and melt strength, and a method for producing the same.

[0018] The polypropylene resin composition according to the present invention can be used for various applications such as extrusion, sheet, and injection molding, and is more suitable for vacuum molding, blow molding, or foaming where high melt strength properties are required. DETAILED DESCRIPTION OF THE INVENTION

[0019]

[0023] Preferred embodiments of the present invention will be described in detail below. When describing the present invention, if it is determined that a detailed description of related prior art may obscure the gist of the present invention, such detailed description will be omitted. Throughout the specification, when a part "comprises" a certain element, this does not mean that it excludes other elements, but that it further includes other elements, unless otherwise specified.

[0020] The present invention discloses a polypropylene resin composition having a weight average molecular weight of 250,000 to 500,000 g / mol, a molecular weight distribution (MWD) (Mw / Mn) of 5.5 to 12, and a content of high molecular weights of 1,000,000 g / mol or more of 4 to 15 wt%. The polypropylene resin composition according to the present invention can be prepared by irradiating 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 with an electron beam.

[0021] In the present invention, the polypropylene is not particularly limited as long as it is a resin that improves melt strength during electron beam writing, and propylene homopolymer, propylene random copolymer, or impact polypropylene (a block copolymer of propylene homopolymer and ethylene-propylene copolymer) may be used. In this case, the comonomer used to prepare the propylene copolymer is preferably ethylene or an α-olefin having 4 to 10 carbon atoms, and the comonomer content may be 30 wt% or less, preferably 1 to 10 wt%. These polypropylenes may be prepared by commonly known processes, and the present invention does not particularly limit the preparation method.

[0022] In the present invention, the polypropylene to which a crosslinking agent has been added and irradiated with electron beams has a weight-average molecular weight of 250,000 to 500,000 g / mol and a molecular weight distribution (MWD) (Mw / Mn) of 5.5 to 12, preferably a weight-average molecular weight of 270,000 to 450,000 g / mol and a molecular weight distribution (MWD) (Mw / Mn) of 5.5 to 10. If the weight-average molecular weight is less than 250,000 g / mol, the relatively low molecular weight can result in insufficient expansion ratio when used for foaming or high flowability during sheet molding, making molding difficult. If the weight-average molecular weight exceeds 500,000 g / mol, the flowability can be reduced, adversely affecting molding. Furthermore, if the molecular weight distribution is less than 5.5, it is difficult to increase the number of branches beyond a certain level, and there are process limitations to setting it to more than 12.

[0023] In the present invention, to realize polypropylene having the weight average molecular weight and molecular weight distribution within the above ranges, two polypropylenes with adjusted molecular weight characteristics may be mixed and used, or a single polypropylene having a specific molecular weight distribution may be used.

[0024] Specifically, when two polypropylenes with adjusted molecular weight characteristics are used in combination, the mixture 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 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 to 200,000 g / mol. Preferably, the mixture 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 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 to 150,000 g / mol.

[0025] When a single polypropylene is used, the polypropylene may have a weight average molecular weight of 350,000 to 600,000 g / mol, and preferably has a weight average molecular weight of 400,000 to 500,000 g / mol.

[0026] 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, triallyl isocyanurate (TAIC) is preferably selected in consideration of maximizing the crosslinking effect by introducing long chain branches during electron beam irradiation, and realizing maximized extensional viscosity and melt strength by adjusting the content of the crosslinking agent and the absorption of electron beams.

[0027] In the present invention, the crosslinking agent is mixed in an amount of 0.01 to 2 parts by weight, preferably 0.1 to 1.5 parts by weight, and more preferably 0.5 to 1.2 parts by weight, per 100 parts by weight of the polypropylene. If the amount of crosslinking agent is less than 0.01 part by weight, it is difficult to expect satisfactory crosslinking reinforcement. If the amount of crosslinking agent is more than 2 parts by weight, the crosslinking effect of the polypropylene increases and many long chain branches may be introduced. However, excessive crosslinking may hinder cell growth during foaming, thereby reducing foaming performance and significantly increasing gel generation.

[0028] In the present invention, the polypropylene and crosslinking agent can be mixed by a conventional method known in the art, for example, by mixing the required amounts of the components in a mixer and then melt-extruding the mixture in an extruder at an extrusion temperature of 180 to 240°C and a screw rotation speed of 95 to 100 rpm to produce pellets.

[0029] In the present invention, a mixture of polypropylene and a crosslinking agent is irradiated with an electron beam to generate free radicals in the polypropylene, and the chains broken by the radicals are introduced into branches, causing entanglement between the chains, thereby improving melt strength.

[0030] In the present invention, electron beam irradiation can be carried out using an electron beam accelerator with an irradiation dose of, for example, 10 MeV. In the present invention, even low-dose electron beam irradiation, such as 5 to 30 kGy, preferably 10 to 25 kGy, and more preferably 15 to 20 kGy, can achieve sufficient chain entanglement to improve the desired melt strength. If the irradiation dose is less than 5 kGy, the number of radicals generated may be insufficient, making it difficult to impart a high extensional viscosity. If the irradiation dose exceeds 30 kGy, the degree of molecular chain decomposition may increase, resulting in a decrease in extensional viscosity.

[0031] The polypropylene resin composition according to the present invention may further contain one or more conventional additives known in the art, such as an antioxidant, a neutralizing agent, a heat stabilizer, etc. The content of each of these additives may be in the range of 0.01 to 1 part by weight per 100 parts by weight of the foamable polypropylene resin composition according to the present invention, but is not particularly limited thereto.

[0032] The antioxidant can prevent the resin molecules from being broken down by heat, oxygen, etc. when a product is manufactured using the polypropylene resin composition. The neutralizing agent can neutralize acids (specifically, hydrogen chloride) that may be generated by residues (metal components) of the catalyst used in polymerization. The heat stabilizer can prevent the molecular weight of a polypropylene molded product from decreasing when used in a high-temperature environment.

[0033] As such antioxidants, for example, phosphorus-based antioxidants or phenol-based antioxidants can be used. An example of the phosphorus-based antioxidant is tris(2,3-di-t-butylphenyl)phosphate, and an example of the phenol-based antioxidant is tetrakis[ethylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionic acid]methane.

[0034] As the neutralizing agent, for example, calcium stearate can be used, and as the heat resistance stabilizer, for example, distearyl thiodipropionate can be used.

[0035] Molded articles can be produced using the polypropylene resin composition of the present invention by various molding methods, and the shape and size of the molded article can be appropriately determined. Examples of methods for producing such molded articles include commonly used industrial methods such as injection molding, press molding, vacuum molding, foam molding, and extrusion molding. Depending on the purpose, other methods include molding methods in which the polypropylene resin composition of the present invention is bonded with the same or different polypropylene-based resin or other resins, or coextrusion molding. However, the polypropylene resin composition of the present invention has excellent extensional viscosity and is therefore more suitable for use in dip-draw vacuum molding or foam sheet molding. Examples of products produced by dip-draw vacuum molding include cup-shaped containers, and examples of products produced by foam molding include lunch box containers, instant noodle containers, and meat processing trays.

[0036] The polypropylene resin composition according to the present invention exhibits melt strength properties suitable for vacuum molding, blow molding, or foam sheet molding. Specifically, the degree of branching measured by the following method is 0.5 to 0.8, and the extensional viscosity is 5×10 6 〜10 9 The melt strength may be 30 cN or more in Pa·s, and the branching degree is preferably 0.6 to 0.8, and the extensional viscosity is 10 7 ~5×10 8 In Pa·s, the melt strength can be 35 cN or more. [Method for measuring the degree of branching] The intrinsic viscosity [η] of the polypropylene resin composition br Intrinsic viscosity [η] of a linear polymer with the same molecular weight lin Ratio to [η] br / [η] lin Calculate with; [Method for measuring extensional viscosity] A specimen measuring 20mm wide, 10mm long, and 1mm thick is fixed to the sample holder using ARES, and then the resistance value is measured when the specimen rotates around its axis at a temperature of 180℃ and a speed of 0.1 / s using EVF mode. The maximum value of the tension that changes depending on the rotation distance (elongation rate) of the specimen is taken as the extensional viscosity; [Melt strength measurement method] Using a Rheotens apparatus (Rheotens 97, GOTTFERT), the molten sample was extruded through a circular die with a diameter of 1 mm at a temperature of 200°C. The extruded streaks were located 100 mm (spinline length) below the die exit, and the winding speed was 120 mm / s. 2 When the film is wound by a rheotensile wheel that gradually increases with an acceleration of 1 / 2, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the force applied to the peak before or at the time of rupture of the stripe is taken as the melt strength. [Example]

[0037] The present invention will be described below with reference to specific examples.

[0038] <Examples and Comparative Examples> The raw materials according to the composition shown in Table 1 below were mixed in a Henschel mixer for 1 minute and then extruded in a single-screw extruder at 180 to 240°C to produce pelletized polypropylene resin, and polypropylene compositions were then produced by 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 to 3 m / min, and an irradiation distance of 4 to 5 m.

[0039] [Table 1]

[0040] <Test example> The branching characteristics, molecular weight characteristics, extensional viscosity, and melt strength of the polypropylene pellets prepared in the above examples and comparative examples were measured by the following methods, and the results are shown in Table 2 below. [Measurement method] (1) Degree of branching The intrinsic viscosity [η] of the polypropylene resin composition having a long chain branched structure br Intrinsic viscosity [η] of a linear polymer with the same molecular weight lin Ratio to [η] br / [η]lin was calculated. (2) Molecular weight characteristics The weight average molecular weight Mw and molecular weight distribution MWD (Mw / Mn) were measured using gel permeation chromatography (GPC, Agilent) in chloroform solvent using polystyrene as a standard. (3) Elongational viscosity A specimen measuring 20mm wide, 10mm long, and 1mm thick was fixed to the sample holder using ARES, and the resistance value was measured when the specimen was rotated around its axis at a temperature of 180℃ and a speed of 0.1 / s using EVF mode. The maximum value of the tension that changes depending on the rotation distance (elongation rate) of the specimen was taken as the elongational viscosity. (4) Melt strength Using a Rheotens apparatus (Rheotens 97, GOTTFERT), a molten sample was extruded at 200°C through a circular die with a diameter of 1 mm. The extruded streaks were wound up by a Rheotens wheel located 100 mm (spinline length) below the die exit, with the winding speed gradually increasing at an acceleration of 120 mm / s2. The force (cN) applied to the wheel was recorded as a function of the winding speed (mm / s). The peak force before or at the time of streak rupture was taken as the melt strength.

[0041] [Table 2]

[0042] Referring to Table 2, when a resin composition in which a crosslinking agent is added to polypropylene according to the present invention is irradiated with an electron beam to have a certain level of weight average molecular weight, molecular weight distribution, and high molecular weight content (Examples 1 to 3), it can be seen that despite the low dose of electron beam irradiation, radicals are generated and branches are generated by the crosslinking agent, resulting in excellent branching properties and excellent elongational viscosity and melt strength.

[0043] In contrast, it can be confirmed that the extensional viscosity and melt strength are significantly reduced when no electron beam irradiation is performed (Comparative Examples 1 and 2), when electron beam irradiation is performed but the polypropylene resin composition deviates from a certain molecular weight range after irradiation (Comparative Example 3), when the high molecular weight content is insufficient (Comparative Example 4), or when the molecular weight distribution deviates from a certain range (Comparative Example 5).

[0044] Although the preferred embodiments of the present invention have been described in detail above, the description of the present invention is for illustrative purposes only, and it should be understood by those skilled in the art that the present invention can be easily modified into other specific forms without changing the technical concept or essential features of the present invention.

[0045] Therefore, the scope of the present invention is indicated by the claims below rather than the above detailed description, and all modifications or variations derived from the meaning, scope and equivalents of the claims should be interpreted as being included in the scope of the present invention.

Claims

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

2. The polypropylene resin composition has a branching degree of 0.5 to 0.8, and an extensional viscosity of 5×10 ６ to 10 ９ The polypropylene resin composition according to claim 1, characterized in that it has a melt strength of 30 cN or more in Pa s: [Method for measuring the degree of branching] The intrinsic viscosity [η] of the polypropylene resin composition ｂｒ Intrinsic viscosity [η] of a linear polymer having the same molecular weight ｌｉｎ Ratio to [η] ｂｒ / [η] ｌｉｎ Calculate with; [Method for measuring extensional viscosity] A specimen measuring 20 mm in width, 10 mm in length, and 1 mm in thickness is fixed to a sample holder using an advanced rheometric expansion system (ARES), and then the resistance value applied when the specimen is rotated around its axis at a temperature of 180°C and a speed of 0.1 / s using an extensional viscosity fixture (EVF) mode is measured. The maximum value of the tension that changes depending on the rotation distance (elongation rate) of the specimen is defined as the extensional viscosity; [Method for measuring melt strength] 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, and the streaks formed by the extrusion were located 100 mm (spinline length) below the die outlet, and the winding speed was 120 mm / s. ２ When the film is wound by a rheotensile wheel with an acceleration that gradually increases, the force (cN) applied to the wheel is recorded as a function of the winding speed (mm / s), and the force applied at the peak before or at the time of streak rupture is taken as the melt strength.

3. 2. The polypropylene resin composition according to claim 1, which is for vacuum molding, blow molding, or foaming.

4. 2. A method for producing the polypropylene resin composition according to claim 1, which comprises irradiating a resin composition comprising 100 parts by weight of polypropylene and 0.01 to 2 parts by weight of a crosslinking agent with electron beams.

5. 5. The method for producing a polypropylene resin composition according to claim 4, wherein the crosslinking agent is at least one selected from the group consisting of triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, triallyl trimesate, triallyl phosphate, pentaerythritol triacrylate, and divinylbenzene.

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

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