Polypropylene manufacturing method

Abstract

To provide a method for producing polypropylene.SOLUTION: The present invention relates to a method of efficiently producing high-strength isotactic polypropylene having high crystallinity even with a short polymerization time. More specifically, the present invention relates to a method of producing polypropylene, including a step of polymerizing propylene in the presence of a catalyst composition including a Ziegler-Natta catalyst, an external electron donor, dialkylaluminum hydride and trialkylaluminum, where the polypropylene has a xylene cold soluble content of 3 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polypropylene, and more particularly to a method for efficiently producing high-strength isotactic polypropylene with high crystallinity even in a short polymerization period. [Background technology]

[0002] Polypropylene has traditionally been used as a general-purpose resin in a variety of fields due to its low specific gravity, high heat resistance, excellent processability, and chemical resistance.

[0003] Various efforts have been made to improve the mechanical strength of propylene polymers without damaging their inherent properties, and it is known that such properties can be improved by adjusting the crystallinity and molecular weight of the propylene polymer.

[0004] Therefore, research was needed into catalyst compositions that could produce polypropylene with excellent physical properties, such as superior mechanical strength and high crystallinity, in a shorter time than the method of producing homopolypropylene using conventional general-purpose Ziegler-Natta catalysts. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a catalyst composition that can produce homopolypropylene with excellent mechanical properties and high crystallinity, while achieving a higher yield in a shorter time than the conventional method of producing homopolypropylene using a general-purpose Ziegler-Natta catalyst, and a method for producing polypropylene that can produce high-strength products using the same. [Means for solving the problem]

[0006] As a result of extensive research to achieve the above object, the inventors of the present invention discovered that by using a specific combination of catalyst compositions, homopolypropylene having equivalent or better physical properties can be produced in a shorter time than when a Ziegler-Natta catalyst was used in the past, and thus completed the present invention.

[0007] One aspect of the present invention is a method for producing polypropylene having a xylene cold soluble content of 3% by weight or less as measured with a CRYSTEX instrument (CRYSTEX 42 model manufactured by Polymer Char), the method comprising the step of polymerizing propylene in the presence of a catalyst composition including a Ziegler-Natta catalyst, an external electron donor, a dialkylaluminum hydride, and a trialkylaluminum.

[0008] In one embodiment, the catalyst composition may include, but is not limited to, 0.005 to 0.1 wt % of a Ziegler-Natta catalyst, 5 to 20 wt % of an external electron donor, 0.05 to 3 wt % of a dialkylaluminum hydride, and 10 to 94 wt % of a trialkylaluminum.

[0009] In one embodiment, the catalyst composition may have a trialkylaluminum / titanium molar ratio of 500 to 5,000.

[0010] In one embodiment, the Ziegler-Natta catalyst may contain 10 to 30 wt % of magnesium (Mg) and 0.5 to 5 wt % of titanium (Ti).

[0011] In one embodiment, the titanium molar ratio of the dialkylaluminum hydride / Ziegler-Natta catalyst may be 1 to 30.

[0012] In one embodiment, the dialkylaluminum hydride may include diisobutylaluminum hydride (DIBAL-H).

[0013] In one embodiment, the external electron donor may be any one or a mixture of two or more selected from diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, N,N-diethylaminotriethoxysilane, bis(ethylamino)dicyclopentylsilane, trimethoxypropylsilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, and dicyclohexyldimethoxysilane.

[0014] In one embodiment, the method may include: a) preparing a catalyst composition by adding a dialkylaluminum hydride and a trialkylaluminum to a reactor, and then adding a Ziegler-Natta catalyst and an external electron donor; and b) adding propylene and hydrogen to the catalyst composition and polymerizing the propylene and hydrogen.

[0015] In one embodiment, in the step b), the polymerization can be carried out at 50 to 80° C. for 10 to 120 minutes.

[0016] In one embodiment, in the step b), the polymerization can be carried out under a pressure of 20 to 50 bar.

[0017] In one embodiment, the polypropylene can be a propylene homopolymer.

[0018] In one embodiment, the polypropylene may have a melt index of 30 to 60 g / 10 min measured at 230° C. under a load of 2.16 kg according to ASTM D1238, and a weight average molecular weight of 330,000 to 500,000 g / mol.

[0019] In one aspect, the polypropylene may have an endothermic peak measured using a successive self-nucleation and annealing (SSA)-differential scanning calorimeter (DSC), where the sum of the peak value (DH4) measured at 170°C and the peak value (DH5) measured at 176°C is 75% or more of the total peak value.

[0020] In one embodiment, the value of the peak measured at 176° C. (DH5) can be 25% or more of the total peaks.

[0021] In one embodiment, the Ziegler-Natta catalyst may be used in an amount of 0.0001 to 0.002 parts by weight based on 100 parts by weight of the propylene.

[0022] In one embodiment, the dialkylaluminum hydride can be used in an amount of 0.00001 to 0.1 parts by weight based on 100 parts by weight of propylene. [Effects of the Invention]

[0023] The use of the specific combination of catalyst compositions according to the present invention has the effect of enabling the production of homopolypropylene with equivalent or better physical properties in a shorter time than when using conventional Ziegler-Natta catalysts.

[0024] Furthermore, there is an effect that homopolypropylene having excellent mechanical properties and a high degree of crystallinity can be produced. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in more detail below. However, the following specific examples or examples are merely references for explaining the present invention in detail, and the present invention is not limited thereto, and may be realized in various forms.

[0026] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used in describing the present invention are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0027] Also, as used in the specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0028] Furthermore, when a part is described as "comprising" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0029] Each of the components of the present invention will be described in more detail below.

[0030] The present invention is characterized by the use of a catalyst composition for polypropylene polymerization that contains a Ziegler-Natta catalyst, an external electron donor, diisobutylaluminum hydride (DIBAL-H), and a trialkylaluminum. Use of this catalyst composition makes it possible to produce homopolypropylene polymers with equivalent or better physical properties in a shorter time than conventional methods that use only a Ziegler-Natta catalyst and an external electron donor.

[0031] More specifically, in one embodiment of the production method of the present invention, the order and ratio of adding the catalysts during the preparation of the catalyst composition are characteristic. By simultaneously satisfying these conditions, polypropylene having a xylene cold soluble content of 3 wt% or less as measured by a CRYSTEX device (CRYSTEX 42 model manufactured by Polymer Char) can be produced.

[0032] In one embodiment of the present invention, the catalyst composition may include, but is not limited to, 0.005 to 0.1 wt% of a Ziegler-Natta catalyst, 5 to 20 wt% of an external electron donor, 0.05 to 3 wt% of a dialkylaluminum hydride, and 10 to 94 wt% of a trialkylaluminum. In one embodiment, the catalyst composition may have a titanium molar ratio of the dialkylaluminum hydride / Ziegler-Natta catalyst of 1 to 30 and a titanium molar ratio of the trialkylaluminum / Ziegler-Natta catalyst of 500 to 5000. In one embodiment, the Ziegler-Natta catalyst may contain 10 to 30 wt% of magnesium (Mg) and 0.5 to 5 wt% of titanium (Ti).

[0033] Within this content range, a propylene polymer with a high degree of crystallinity can be produced in a shorter time, more specifically, within 60 minutes, more specifically, within 10 to 60 minutes, and still more, the polymer can exhibit physical properties equivalent to or better than those of a polypropylene polymer conventionally produced by polymerization for 60 minutes or more.

[0034] The Ziegler-Natta catalyst comprises a transition metal compound containing an element belonging to Group 4, Group 5 or Group 6 of the periodic table and an organometallic compound containing an element belonging to Group 13 of the periodic table.

[0035] In one embodiment, the molar ratio of the organometallic compound to the transition metal compound can be 5-50.

[0036] The transition metal compound may be a solid titanium catalyst containing magnesium, titanium, a halogen element, and an internal electron donor. The Ziegler-Natta catalyst used in the prepolymerization step is dispersed as uniform particles in the prepolymerization step, and then the high-molecular-weight monomer is polymerized onto the catalyst surface. Any Ziegler-Natta catalyst commonly used for olefin polymerization can be used without particular limitation. Preferably, however, a catalyst containing a transition metal compound containing an element belonging to Group 4, 5, or 6 of the periodic table and an organometallic compound containing an element belonging to Group 13 of the periodic table is used.

[0037] Since the transition metal compound is used as the main catalyst in the Ziegler-Natta catalyst, a solid titanium catalyst containing magnesium, titanium, a halogen element, and an internal electron donor can be preferably used. Here, the internal electron donor can be, for example, a diether compound, a phthalate compound, or a mixture thereof, specifically, diisobutyl phthalate.

[0038] More preferably, the transition metal compound contains magnesium and titanium, and may contain 10 to 30% by weight of magnesium (Mg) and 0.5 to 5% by weight of titanium (Ti).

[0039] In one embodiment of the present invention, the organometallic compound can be any organoaluminum compound that is commonly used in the art.

[0040] In one embodiment of the present invention, the Ziegler-Natta catalyst may be used in an amount of 0.0001 to 0.01 parts by weight based on 100 parts by weight of the propylene, but is not limited thereto.

[0041] In one embodiment of the present invention, the external electron donor may be an organosilane compound. Specific examples include, but are not limited to, one or a mixture of two or more selected from the group consisting of diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, N,N-diethylaminotriethoxysilane, bis(ethylamino)dicyclopentylsilane, trimethoxypropylsilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, and dicyclohexyldimethoxysilane. More preferably, one or more selected from the group consisting of cyclohexylmethyldimethoxysilane and dicyclohexyldimethoxysilane may be used.

[0042] The trialkylaluminum may be any one or a mixture of two or more selected from the group consisting of triethylaluminum, trimethylaluminum, tri(i-propyl)aluminum, tri(n-butyl)aluminum, tri(i-butyl)aluminum, tri(t-butyl)aluminum, tri(n-hexyl)aluminum, tri(n-octyl)aluminum, etc., but is not limited thereto, and more preferably, may be any one or more selected from triethylaluminum and trimethylaluminum.

[0043] The dialkylaluminum hydride may be one in which the alkyl is C3 to C10, and more preferably includes diisobutylaluminum hydride (DIBAL-H).

[0044] The dialkylaluminum hydride may be used in an amount of 0.0001 to 0.01 parts by weight based on 100 parts by weight of propylene, but is not limited thereto.

[0045] The catalyst composition is preferably prepared by first adding diisobutylaluminum hydride (DIBAL-H) ​​and trialkylaluminum to a reactor, followed by adding a Ziegler-Natta catalyst and an external electron donor. At this time, the temperature of the reactor is preferably 10°C or less, more specifically, 1 to 10°C, and more preferably 3 to 7°C.

[0046] More specifically, diisobutylaluminum hydride (DIBAL-H) ​​and trialkylaluminum dissolved in an organic solvent, more specifically, an organic solvent such as toluene, are added, followed by addition of an external electron donor and addition of a Ziegler-Natta catalyst dissolved in an organic solvent such as methylcyclohexane.

[0047] In one embodiment of the present invention, the order of adding propylene is preferably after preparing the catalyst composition, and the molecular weight can be controlled by adding hydrogen when adding propylene.

[0048] In one embodiment, after the propylene and hydrogen are introduced, the reaction temperature in the reactor is preferably increased to carry out the polymerization, and the polymerization can be carried out for 10 to 60 minutes at 50 to 80° C. The polymerization can also be carried out under a pressure of 20 to 50 bar.

[0049] More specifically, a method for producing polypropylene according to one embodiment of the present invention includes the steps of: a) preparing a catalyst composition by adding dialkylaluminum hydride and trialkylaluminum to a reactor, and then adding a Ziegler-Natta catalyst and an external electron donor; and b) adding propylene and hydrogen to the catalyst composition and polymerizing the propylene.

[0050] The polypropylene polymer produced by the method of one embodiment of the present invention may have a xylene cold soluble content of 3 wt% or less, more preferably 0.5-3 wt%, as measured using a CRYSTEX instrument (CRYSTEX 42 model manufactured by Polymer Char). More specifically, it may be 2-2.8 wt%. The lower the cold xylene soluble content, the higher the crystallinity. In the present invention, this range can be achieved by using a mixture of four catalyst compositions, namely, dialkylaluminum hydride, trialkylaluminum, Ziegler-Natta catalyst, and external electron donor.

[0051] Furthermore, the polypropylene polymer according to one embodiment of the present invention may have, but is not limited to, a melt index of 30 to 60 g / 10 min and a weight average molecular weight of 330,000 to 500,000 g / mol, as measured at 230°C under a load of 2.16 kg in accordance with ASTM D1238.

[0052] Furthermore, it was confirmed that polypropylene polymers according to one embodiment of the present invention, produced using four catalyst compositions, exhibited increased tensile strength, but no deterioration in room temperature / low temperature impact strength or elongation, compared to polymers produced without any one of the four catalyst compositions. This improvement can be attributed to the reduction in the content of xylene cold solubles, which reduces mechanical properties, and the increase in highly crystalline regions, which improve mechanical properties. Furthermore, the crystal distribution and uniformity of tie molecules between crystals were good, resulting in comparable or superior room temperature / low temperature impact strength and elongation.

[0053] Specifically, for example, the polymer has a tensile strength of 200 kgf / cm 2 More specifically, the tensile strength is 200 to 500 kgf / cm 2At the same time, the physical property of an elongation rate of 10% to 30% can be satisfied.

[0054] In addition, when measuring endothermic peaks using SSA (successive self-nucleation and annealing)-DSC (differential scanning calorimeter), a total of five peaks are observed every 6°C in the range of 152 to 176°C. The sum of the peak values ​​measured at 170°C (DH4) and 176°C (DH5) may account for 90% or more of all peaks. In other words, when only a Ziegler-Natta catalyst and an external electron donor are used, the sum of the peak values ​​measured at 170°C (DH4) and 176°C (DH5) accounts for 72% of all peaks. In contrast, the polypropylene produced using the four catalyst compositions of the present invention accounts for 75% or more, more preferably 75-80%, confirming increased crystallinity. Furthermore, the peak value measured at 176°C (DH5) may account for 25% or more, more preferably 25-45%, of all peaks.

[0055] In addition, it was confirmed that polypropylene produced using the four catalyst compositions of the present invention could satisfy the above physical properties even after a polymerization reaction time of 10 to 15 minutes, compared to when only a Ziegler-Natta catalyst and an external electron donor were used and the polymerization reaction was carried out for 50 minutes.

[0056] The present invention will be described in more detail below with reference to examples and comparative examples, but the following examples and comparative examples are merely illustrative examples for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

[0057] 1) Xylene Cold Soluble Content (XCS%) Measurement was carried out using CRYSTEX (CRYSTEX 42 model manufactured by Polymer Char).

[0058] Trichlorobenzene was added to 160 mg of each polypropylene resin sample produced in the Examples and Comparative Examples, and the sample was pretreated by heating at 160°C for 1 hour. The solvent was poured in at a rate of 3 mL per minute for analysis. The soluble fraction was analyzed at 35°C for 40 minutes, and then the temperature was raised to 165°C and the crystalline fraction was analyzed for 25 minutes.

[0059] 2) Melting Index (MI) The analysis was carried out using a Melt Indexer (MI-4 model, manufactured by Goettfert).

[0060] The measurement was carried out in accordance with ASTM D1238 at 230°C under a load of 2.16 kg, and the weight (g) of the polymer that escaped after 10 minutes of melting was shown.

[0061] 3) Flexural Modulus Measurements were performed in accordance with ASTM D790. The polymer was pelletized at 180-230°C using a 30mm single-screw extruder manufactured by Brabender to produce pellets, and ASTM test specimens were prepared at temperatures of 180-230°C using a 25-ton extruder manufactured by Boy. The prepared test specimens were left at 23°C and 50% relative humidity for 48 hours or more before use in the experiment. The flexural modulus value was calculated using a secant modulus of 0.01mm / mm.

[0062] 4) SSA (successive self-nucleation and annealing)-DSC (Differential Scanning Calorimeter) measurement Measurement was performed using a DSC (Q20 model, manufactured by TA Instruments). As samples, 10 to 15 mg of polypropylene resin produced in the examples and comparative examples were used.

[0063] Heat to 200°C at a rate of 10°C per minute until completely dissolved, then cool to 50°C at a rate of 20°C per minute and hold for 5 minutes. Heat to 164°C at a rate of 20°C per minute. Hold for 10 minutes, then cool to 50°C at a rate of 20°C per minute and hold for 5 minutes. Heat to 159°C at a rate of 20°C per minute. Hold for 10 minutes, then cool to 50°C at a rate of 20°C per minute and hold for 5 minutes. Heat to 154°C at a rate of 20°C per minute. Hold for 10 minutes, then cool to 50°C at a rate of 20°C per minute and hold for 5 minutes. Heat to 149°C at a rate of 20°C per minute. Hold for 10 minutes, then cool to 50°C at a rate of 20°C per minute and hold for 5 minutes. Heat to 144°C at a rate of 20°C per minute. After maintaining the temperature for 10 minutes, cool to 50°C at a rate of 10°C per minute and maintain for 5 minutes. Increase the temperature to 200°C at a rate of 20°C per minute.

[0064] A total of five peaks were observed every 6°C in the range from 152 to 176°C. Specifically, the peak value at 152°C was designated DH1, the peak value at 158°C was designated DH2, the peak value at 164°C was designated DH3, the peak value at 170°C was designated DH4, and the peak value at 176°C was designated DH5.

[0065] 5) Weight average molecular weight (Mw) The measurements were performed using a GPC (Agilent PL-GPC 220) with a PLgel Olexis Guard (7.5 x 50 mm) and a PLgel Olexis (7.5 x 300 mm) GPC column connected together. The solvent was 1,2,4-trichlorobenzene, and the standard was polystyrene (Mw 6,870,000). Analysis was performed at 160°C.

[0066] 6) Tensile Strength and Elongation Measurements were performed in accordance with ASTM D638. The polymer was granulated at 180 to 230°C using a 30mm single-screw extruder manufactured by Brabender to produce pellets, and ASTM test specimens were produced at temperatures of 180 to 230°C using a 25-ton extruder manufactured by Boy. The test specimens were left at 23°C and 50% relative humidity for 48 hours or more before use in the experiments. The tensile strength was measured using the strength values ​​at the yield point and break point, and the elongation was measured using the total strain value at break.

[0067] 7) Izod impact strength Measurements were made at room temperature (23°C) and low temperature (-20°C) according to ASTM D256. The polymer was pelletized at 180°C to 230°C using a 30mm single-screw extruder manufactured by Brabender, and ASTM test specimens were prepared at temperatures of 180°C to 230°C using a 25-ton extruder manufactured by Boy. The prepared test specimens were left at 23°C and 50% relative humidity for at least 48 hours before use in the experiments.

[0068] [Example 1] Production of polypropylene homopolymer A 0.0 mL solution of 1 M diisobutylaluminum hydride (DIBAL-H, Sigma-Aldrich) in toluene was placed in a 3 L high-pressure reactor. 1 The reactor was charged with 0.66 mmol of cyclohexylmethyldimethoxysilane, 6.6 mmol of triethylaluminum (Sigma-Aldrich), and 14 mg of Ziegler-Natta catalyst (Mg supported Ti Ziegler-Natta catalyst, Mg 20 wt%, Ti 3 wt%), mixed with 10 ml of methylcyclohexane.

[0069] After adding 1000 g of liquid propylene, hydrogen was added at 4000 sccm for 3 minutes. The polymerization reaction was carried out for 50 minutes at an internal temperature of 62°C. After the reaction was completed, the pressure was released and the reactor was purged with nitrogen five times to remove residual propylene. The physical properties of the produced polypropylene homopolymer were measured and are listed in Tables 2 to 4 below.

[0070] [Example 2] A polymer was produced in the same manner as in Example 1, except that the content of diisobutylaluminum hydride (DIBAL-H) ​​was changed as shown in Table 2 below. The physical properties of the produced polypropylene homopolymer were measured and are shown in Tables 2 to 4 below.

[0071] [Example 3] A polymer was produced in the same manner as in Example 1, except that the content of diisobutylaluminum hydride (DIBAL-H) ​​was changed as shown in Table 2 below and the polymerization time was adjusted to 15 minutes. The physical properties of the produced polypropylene homopolymer were measured and are shown in Tables 2 to 4 below.

[0072] [Example 4] A polymer was produced in the same manner as in Example 1, except that diisobutylaluminum hydride (DIBAL-H) ​​was replaced with dioctylaluminum hydride (DOAL-H, synthesized according to the method of Nandita et al., Dalton Trans., 2015, 44, 15286-15296) as shown in Table 2 below. The physical properties of the produced polypropylene homopolymer were measured and are shown in Tables 2 to 4 below.

[0073] [Comparative Example 1] In Example 1, diisobutylaluminum hydride (DIBAL-H )of Except for not using the above, a polymer was produced in the same manner as in Example 1. The physical properties of the produced polypropylene homopolymer were measured and are shown in Tables 2 to 4 below.

[0074] A 3 L high-pressure reactor was charged with 0.66 mmol of cyclohexylmethyldimethoxysilane as an external electron donor. 14 mg of Ziegler-Natta catalyst (Mg supported Ti Ziegler-Natta catalyst, Mg 20 wt%, Ti 2 wt%) was mixed with 10 ml of methylcyclohexane and then charged into the reactor.

[0075] After adding 1000 g of liquid propylene, hydrogen was added at 4000 sccm for 3 minutes. The polymerization reaction was carried out for 50 minutes at an internal temperature of 62°C. After the reaction was completed, the pressure was released and the reactor was purged with nitrogen five times to remove residual propylene. The physical properties of the produced polypropylene homopolymer were measured and are listed in Tables 2 to 4 below.

[0076] Comparative Example 2 A polymer was produced in the same manner as in Comparative Example 1, except that the polymerization time was adjusted to 15 minutes. The physical properties of the produced polypropylene homopolymer were measured and are shown in Table 2 below.

[0077] Table 1 below shows the molar ratios of the catalysts.

[0078] [Table 1]

[0079] [Table 2]

[0080] As shown in Table 2, it was confirmed that in Examples 1 to 4 using the four catalyst compositions of the present invention, polymers with lower cold xylene solubles contents were obtained. In other words, it was confirmed that polymers with higher crystallinity were obtained. Furthermore, when Example 3 was compared with Comparative Example 2, it was confirmed that the activity was equal to or higher than that of Example 3 even with a polymerization time of 15 minutes when DIBAL-H was added.

[0081] [Table 3]

[0082] As shown in Table 3, Examples 1 to 4 show an increase in tensile strength, but the room temperature / low temperature impact strength and elongation are not inferior. This can be seen as an improvement in tensile strength due to a decrease in X / S, which causes a decrease in mechanical properties, and an increase in highly crystalline regions, which improve mechanical properties. In addition, the crystal distribution and tie molecule uniformity between crystals are good, and the room temperature / low temperature impact strength and elongation are comparable or better.

[0083] [Table 4]

[0084] As shown in Table 4, the SSA-DSC analysis results confirmed that the ratios of the DH4 and DH5 regions, which correspond to the highly crystalline region, increased in Examples 1 to 3, which used the four catalyst compositions of the present invention.

[0085] Although the present invention has been described above using specific matters and limited examples, these are provided to facilitate a more general understanding of the present invention, and the present invention is not limited to the above examples. Those skilled in the art will appreciate that various modifications and variations can be made from such descriptions.

[0086] Therefore, the concept of the present invention should not be limited to the above-described embodiments, and it can be said that not only the scope of the claims described below, but also all things that are equivalent to or have equivalent modifications within the scope of the claims fall within the scope of the concept of the present invention.

Claims

1. A method for producing polypropylene having a xylene cold soluble content of 0.5 to 3 wt % and a melt index of 30 to 60 g / 10 min, measured in accordance with ASTM D1238 at 230°C under a load of 2.16 kg, comprising the step of polymerizing propylene in the presence of a catalyst composition comprising a Ziegler-Natta catalyst, an external electron donor, a dialkylaluminum hydride, and a trialkylaluminum.

2. 2. The method for producing polypropylene according to claim 1, wherein the catalyst composition has a trialkylaluminum / Ziegler-Natta catalyst titanium molar ratio of 500 to 5,000.

3. 2. The method for producing polypropylene according to claim 1, wherein the Ziegler-Natta catalyst comprises 10 to 30 wt% of magnesium (Mg) and 0.5 to 5 wt% of titanium (Ti).

4. The method for producing polypropylene according to claim 3, wherein the titanium molar ratio of the dialkylaluminum hydride / Ziegler-Natta catalyst is 1 to 30.

5. The method for producing polypropylene according to claim 1, wherein the dialkylaluminum hydride includes diisobutylaluminum hydride (DIBAL-H).

6. a) preparing a catalyst composition by charging a dialkylaluminum hydride and a trialkylaluminum into a reactor, followed by charging a Ziegler-Natta catalyst and an external electron donor; b) introducing propylene and hydrogen into the catalyst composition and polymerizing the propylene and hydrogen.

7. The method for producing polypropylene according to claim 6, wherein in step b), polymerization is carried out at 50 to 80°C for 10 to 120 minutes.

8. The method for producing polypropylene according to claim 6, wherein in step b), the polymerization is carried out under a pressure of 20 to 50 bar.

9. The polypropylene has an endothermic peak measured using successive self-nucleation and annealing (SSA)-DSC (Differential Scanning Calorimeter), wherein the sum of the peak value (DH4) measured at 170 ° C. and the peak value (DH5) measured at 176 ° C. is 75% or more of the total peaks measured in the temperature range of 152 ° C. to 176 ° C. The method for producing polypropylene according to claim 1.

10. The method for producing polypropylene according to claim 9, wherein the peak value (DH5) measured at 176 ° C. is 25% or more of all peaks measured in the temperature range of 152 ° C. to 176 ° C.

11. The method for producing polypropylene according to claim 1, wherein the Ziegler-Natta catalyst is used in an amount of 0.0001 to 0.002 parts by weight based on 100 parts by weight of the propylene.

12. The method for producing polypropylene according to claim 1, wherein the dialkylaluminum hydride is used in an amount of 0.00001 to 0.01 parts by weight based on 100 parts by weight of propylene.

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