KR102877531B1 - Polypropylene resin composition and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a polypropylene resin composition and a method for producing the same. The polypropylene resin composition according to the present invention can have excellent impact strength, color change resistance, and oxidation stability by controlling the isotactic pentad fraction of a propylene homopolymer, the ratio of ethylene-propylene rubber blocks of an ethylene-propylene block copolymer, and the ethylene content.

Description

Polypropylene resin composition and manufacturing method thereof

The present invention relates to a polypropylene resin composition and a method for producing the same.

Polypropylene is classified into polypropylene homopolymer and ethylene-propylene block copolymer depending on the presence or absence of copolymerization and differences in composition. Polypropylene homopolymer can be manufactured through a gas phase or bulk slurry polymerization process in the presence of propylene monomer, a solid complex titanium catalyst, an organic aluminum cocatalyst, and an external electron donor. Meanwhile, polypropylene block copolymer can be obtained by polymerizing polypropylene homopolymer and then introducing ethylene monomer to copolymerize ethylene-propylene rubber blocks. The properties of the polymerization product obtained from polypropylene block copolymers vary greatly depending on the ethylene content, the type of external electron donor used, and the composition of the mixture.

Ethylene-propylene block copolymers are used where higher impact strength than polypropylene homopolymer is required, and are particularly utilized in applications such as industrial materials, home appliance parts, battery cases, and automotive exterior materials.

Meanwhile, the impact strength of resin compositions generally tends to decrease at lower temperatures. While Korea's four-season climate often requires high impact strength even at low temperatures, achieving this strength can be challenging. Furthermore, Korea's climate, characterized by alternating high temperatures and high humidity with low temperatures and dry conditions, often demands oxidation stability, including discoloration resistance. However, securing polypropylene resin compositions that sufficiently satisfy these requirements has been challenging. Therefore, there is an urgent need for technological development for polypropylene resin compositions that not only exhibit high impact strength at low temperatures but also exhibit excellent oxidation stability.

Patent Document 1. Korean Patent Publication No. 10-2023-0007825

The present invention has been devised to solve the above-mentioned problems, and the purpose of the present invention is to provide a polypropylene resin composition having high impact strength even at low temperatures and excellent oxidation stability, and a method for producing the same.

One aspect of the present invention provides a polypropylene resin composition comprising an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and an antioxidant, wherein the ethylene-propylene block copolymer is polymerized from a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more, and wherein ethylene is contained in an amount of 5 to 8 wt% based on 100 wt% of the total ethylene-propylene block copolymer.

Another aspect of the present invention provides a molded article comprising the polypropylene resin composition.

Another aspect of the present invention provides a method for producing a polypropylene resin composition, comprising the steps of: (a) forming a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more; (b) introducing a mixed gas of ethylene and propylene into the polypropylene homopolymer and polymerizing the mixed gas to polymerize an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and (c) mixing the ethylene-propylene block copolymer and an antioxidant; wherein the polypropylene resin composition is characterized in that ethylene is contained in an amount of 5 to 8 wt% based on 100 wt% of the total ethylene-propylene block copolymer.

The polypropylene resin composition according to the present invention comprises an antioxidant and an ethylene-propylene block copolymer, and by controlling the isotactic pentad fraction of the propylene homopolymer, the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer, and the ethylene content, the impact strength, color change resistance, and oxidation stability can all be excellent.

Figure 1 shows photographic images and yellow indexes according to oven aging time of polypropylene resin compositions of manufacturing examples, examples 1 to 3 and comparative examples 1 to 3 of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the attached drawings and examples.

As described above, conventional polypropylene resin compositions have insufficient low-temperature impact strength, discoloration resistance, and oxidation stability, which limits their application to various environments. Accordingly, the present invention provides a polypropylene resin composition comprising an ethylene-propylene block copolymer; and an antioxidant; by controlling the isotactic pentad fraction of the polypropylene homopolymer, the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer, and the ethylene content, thereby providing a polypropylene composition having excellent low-temperature impact strength, discoloration resistance, and oxidation stability.

More specifically, one aspect of the present invention provides a polypropylene resin composition comprising an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and an antioxidant, wherein the ethylene-propylene block copolymer is polymerized from a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more, and wherein ethylene is contained in an amount of 5 to 8 wt% when the ethylene-propylene block copolymer is 100 wt%.

The polypropylene resin composition according to the present invention is characterized in that the isotactic pentad fraction of the polypropylene homopolymer, the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer, and the ethylene content all satisfy the above-described ranges, and thus is characterized in that it has excellent low-temperature impact strength, oxidation stability, and color change resistance. If any one of the isotactic pentad fraction of the polypropylene homopolymer, the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer, and the ethylene content is outside the above-described ranges, at least one of the low-temperature impact strength, oxidation stability, and color change resistance may be significantly reduced.

The above polypropylene homopolymer may have an isotactic pentad fraction of 0.99 or more, and if the isotactic pentad fraction is less than 0.99, mechanical properties may deteriorate. In addition, due to the characteristics of the polymer itself, it is practically impossible for the isotactic pentad fraction to exceed 0.998, and thus the upper limit of the isotactic pentad fraction may be 0.998.

The above isotactic pentad (IP) fraction refers to the content of isotactic pentads among all pentads contained in a polypropylene homopolymer molecular chain. The IP used herein can be measured by nuclear magnetic resonance using carbon isotopes (13C-NMR) according to the method described in the literature [reference: A. Zambelli, Macromolecules, vol.6, p. 925 ( ¹⁹⁷³ ), ibid, vol. 8, p. 687 (1975), and ibid, vol. 13, p. 267 (1980)].

The above ethylene-propylene block copolymer is composed of an ethylene-propylene rubber block and a propylene homopolymer block. The ethylene-propylene block copolymer according to the present invention may have a ratio of ethylene-propylene rubber blocks of 0.12 to 0.20, preferably 0.12 to 0.18, and more preferably 0.12 to 0.17, with respect to the entire ethylene-propylene block copolymer. When the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer is less than 0.12, the impact strength may be significantly reduced, and conversely, when it is greater than 0.20, the color change resistance may be significantly reduced. In particular, when the ratio of the ethylene-propylene rubber block of the ethylene-propylene block copolymer is 0.12 to 0.17, it is more preferable in that there is no decrease in flexural modulus even when the process of heating the polypropylene resin composition from room temperature to 100°C and then cooling it again is repeated 10 times.

Using a differential scanning calorimeter (DSC), the melting temperature and the energy required for each temperature can be obtained as a thermogram through the heating and cooling process of an ethylene-propylene block copolymer sample. By comparing this with the energy obtained through the thermogram of a polypropylene homopolymer, the ethylene-propylene rubber block of the ethylene-propylene block copolymer can be measured.

With respect to the total 100 wt% of the ethylene-propylene block copolymer, ethylene may be included in an amount of 5 to 8 wt%, preferably 6 to 7.5 wt%, more preferably 6.3 to 7.3 wt%, and most preferably 6.8 to 7.3 wt%. If ethylene is less than the lower limit with respect to the total 100 wt% of the ethylene-propylene block copolymer, the impact strength may be reduced, and conversely, if it exceeds the upper limit, the rigidity and mechanical properties may be reduced.

The above polypropylene resin composition may have a molecular weight distribution (M _w /M _n ) of 3.0 to 4.5, preferably 3.5 to 4.4. If the molecular weight distribution is narrower than 3.0, it is difficult to secure sufficient rigidity and fluidity, and if the molecular weight distribution is wider than 4.5, it is difficult to secure sufficient low-temperature impact strength, discoloration resistance may be reduced, and an unpleasant odor may be generated.

The weight average molecular weight of the polypropylene homopolymer may be 350,000 to 600,000 g/mol, preferably 480,000 to 550,000 g/mol. If the weight average molecular weight of the propylene homopolymer is outside the above range, sufficient polymerization activity of the catalyst may not be achieved, which may increase production costs, the size of the particles of the polymerization product may not be uniform, and the physical properties such as rigidity and melt strength required for the purpose of use of the final polypropylene composition may not be satisfied.

The melt index of the above polypropylene homopolymer may be 1.0 to 2.5 g/10 min (230°C, 2.16 kg), preferably 1.3 to 2.2 g/10 min (230°C, 2.16 kg). It was confirmed that when the melt index of the above polypropylene homopolymer satisfies the above range, the dimensional stability is excellent and warping does not occur even when injection molded.

The weight average molecular weight of the above ethylene-propylene block copolymer may be 400,000 to 650,000 g/mol, preferably 450,000 to 650,000 g/mol. If the weight average molecular weight of the above ethylene-propylene block copolymer is outside the above range, sufficient polymerization activity of the catalyst may not be achieved, which may increase production costs, the size of the polymerization product particles may not be uniform, and the final polypropylene composition may not satisfy the impact strength required for the intended use.

The melting index of the above ethylene-propylene block copolymer may be 0.8 to 1.8 g/10 min (230°C, 2.16 kg), and preferably 0.9 to 1.6 g/10 min (230°C, 2.16 kg).

According to one embodiment of the present invention, the melting index of the polypropylene homopolymer may be 1.3 to 2.2 g/10 min (230°C, 2.16 kg), and the melting index of the ethylene-propylene block copolymer may be 0.9 to 1.6 g/10 min (230°C, 2.16 kg). It was confirmed that when a specimen using a polypropylene resin composition satisfying all of these conditions was stored at 100°C for 2 hours and then bent at an angle of 90 degrees, the degree of occurrence of cracks and damage was significantly reduced.

The above antioxidant may be at least one selected from the group consisting of a phosphorus-based antioxidant, a phenol-based antioxidant, and a thiodipropionate synergist.

The antioxidant may be present in an amount of 0.08 to 0.40 parts by weight, preferably 0.10 to 0.35 parts by weight, more preferably 0.15 to 0.30 parts by weight, and most preferably 0.23 to 0.30 parts by weight, based on 100 parts by weight of the ethylene-propylene block copolymer. If the antioxidant is present in an amount less than the lower limit, discoloration may occur, resulting in a deterioration in quality. Conversely, if the antioxidant is present in an amount greater than the upper limit, mechanical properties may deteriorate.

In particular, it is most preferable that the antioxidant is used in an amount of 0.23 to 0.3 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, in that the mechanical properties are not deteriorated, while the oxidation stability is superior to that of commercially available products.

The above phenolic antioxidant is selected from the group consisting of 2,6-di-t-butyl-4-methylphenol, 4,4'-thiobis(2-t-butyl-5-methylphenol), 2,2'-thio diethylbis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], 4,4'-thiobis(2-methyl-6-t-butylphenol), 2,2'-thiobis(6-t-butyl-4-methylphenol), octadecyl-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and triethyleneglycol-bis-[3-(3-t-butyl-4-hydroxy-5-methylphenol)propionate]. There may be more than one type selected.

The above-mentioned antioxidant may be at least one selected from the group consisting of 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-isophosphaspiro[5.5]undecane, tris(2,4-di-tert-butylphenyl)phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite and bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite and tetrakis(2,4-di-tert-butylphenyl)4,4'-biphenylene diphosphonite.

According to one embodiment of the present invention, the antioxidant is 0.08 to 0.40 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant may be a mixture of a phenol-based antioxidant and a phosphorus-based antioxidant in a weight ratio of 1:1 to 2.

According to a preferred embodiment of the present invention, the antioxidant is 0.23 to 0.3 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant may be a mixture of pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and tris(2,4-di-tert-butylphenyl)phosphite in a weight ratio of 1:1 to 2. When the polypropylene composition of the present invention satisfies all of the conditions of the content, type, and mixing ratio of the antioxidant of the preferred embodiment as described above, the antioxidant was evenly distributed throughout the polypropylene resin composition even after 100 repetitions of the torsion test, and the antioxidant effect was not reduced at all. However, when any one of the conditions of the above embodiment was not satisfied, agglomeration or release of the antioxidant was observed from 50 or more torsion tests, and the antioxidant effect was reduced.

The above polypropylene resin composition may further include one or more additives selected from the group consisting of a light stabilizer, a nucleating agent, and a neutralizing agent.

The above nucleating agent may be an organic nucleating agent, an inorganic nucleating agent, or a mixture thereof.

The above organic nucleating agent may be at least one selected from the group consisting of aluminum salts of carboxylic acids, quinacridone quinone, calcium stearate, and sodium benzoate.

The above-mentioned inorganic nucleating agent may be at least one selected from the group consisting of talc, dibenzylidene sorbitol, and substituted dibenzylidene sorbitol.

The above neutralizing agent may be at least one selected from the group consisting of calcium stearate, zinc oxide, and hydrotalcite.

In particular, although not explicitly described in the following examples and comparative examples, polypropylene resin compositions were manufactured under different conditions, and specimens using the same were stored in a 120°C (high temperature) oven for 3 hours and then cooled to room temperature. This process was repeated 10 times, and then the impact strength and oxidation induction time were measured. As a result, it was confirmed that when all of the following conditions were satisfied, no decrease in impact strength and oxidation induction time was observed even after 10 repetitions of high temperature-room temperature.

The above ethylene-propylene block copolymer has a ratio of ethylene-propylene rubber blocks of 0.12 to 0.17,

Ethylene is contained in an amount of 6.8 to 7.3 wt% based on 100 wt% of the total ethylene-propylene block copolymer,

The above polypropylene resin composition has a molecular weight distribution (M _w /M _n ) of 3.5 to 4.4,

The weight average molecular weight of the above polypropylene homopolymer is 480,000 to 550,000 g/mol,

The melting index of the above polypropylene homopolymer is 1.3 to 2.2 g/10 min (230 ℃, 2.16 kg),

The weight average molecular weight of the above ethylene-propylene block copolymer is 450,000 to 650,000 g/mol,

The melting index of the above ethylene-propylene block copolymer is 0.9 to 1.6 g/10 min (230 ℃, 2.16 kg),

The antioxidant is present in an amount of 0.23 to 0.3 parts by weight based on 100 parts by weight of the entire ethylene-propylene block copolymer.

The above antioxidant may be a mixture of pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and tris(2,4-di-tert-butylphenyl)phosphite in a weight ratio of 1:1 to 2.

However, if any of the above conditions are not satisfied, it was confirmed that even after 10 repetitions of high temperature and room temperature, at least one of the impact strength and oxidation induction time was reduced by more than 10% compared to the initial value.

Another aspect of the present invention provides a molded article comprising the polypropylene resin composition.

The above molded product may be for exterior use, but is not limited thereto.

Another aspect of the present invention provides a method for producing a polypropylene resin composition, comprising the steps of: (a) forming a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more; (b) introducing a mixed gas of ethylene and propylene into the polypropylene homopolymer and polymerizing the mixed gas to polymerize an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and (c) mixing the ethylene-propylene block copolymer and an antioxidant; wherein the polypropylene resin composition is characterized in that ethylene is contained in an amount of 5 to 8 wt% based on 100 wt% of the total ethylene-propylene block copolymer.

The above steps (a) to (c) can be performed by first polymerizing a polypropylene homopolymer having the above properties in a series of reactors, then additionally introducing and copolymerizing a mixed gas of ethylene and propylene to obtain an ethylene-propylene block copolymer, and then mixing in a certain amount of an antioxidant.

The above step (a) is a step of forming a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more, and may be performed by introducing a propylene monomer, a solid complex titanium catalyst, an organic aluminum co-catalyst, and a first hydrogen gas into a reactor and reacting them.

The above step (a) can be performed as a gas phase or slurry process. It can be performed without a solvent, but when a solvent is used, one or more hydrocarbon solvents selected from the group consisting of pentane, heptane, hexane, octane, decane, dodecane, toluene, benzene, and cyclohexane can be used.

The above solid complex titanium catalyst can use a compound produced by supporting TiCl ₃ or TiCl ₄ on a MgCl ₂ carrier.

The above solid complex titanium catalyst may be introduced into the reactor in an amount of 0.0005 to 0.0020 parts by weight, preferably 0.0006 to 0.0018 parts by weight, and more preferably 0.0007 to 0.0016 parts by weight, per 100 parts by weight of propylene monomer introduced into the reactor. If the amount of the solid complex titanium catalyst is less than the lower limit, polymerization may not occur sufficiently, and conversely, if it exceeds the upper limit, control of the polymerization reaction may be difficult.

The above organic aluminum cocatalyst may be at least one selected from the group consisting of triethylaluminum, diethylchloroaluminum, tributylaluminum, triisobutylaluminum, and trioctylaluminum.

The organic aluminum cocatalyst introduced into the reactor may be 130 to 210 moles, preferably 140 to 200 moles, and more preferably 150 to 190 moles, per mole of the solid complex titanium catalyst introduced into the reactor. If the aluminum cocatalyst is less than the lower limit, the polymerization activity may be significantly reduced, and conversely, if it exceeds the upper limit, no further improvement in polymerization activity can be expected and the manufacturing cost may increase.

The first hydrogen gas may be 150 to 380 scc, preferably 180 to 350 scc, more preferably 200 to 330 scc, even more preferably 210 to 320 scc, and most preferably 220 to 310 scc, with respect to 100 g of the propylene monomer. If the first hydrogen gas is less than the lower limit, the molecular weight of the polypropylene resin to be produced may be excessively large or exhibit a low melting index, so that the fluidity may be reduced and the processability may be significantly reduced. On the other hand, if the first hydrogen gas is more than the upper limit, the molecular weight of the polypropylene resin to be produced may be excessively small and the melting index may be increased, so that the processability may be reduced.

The above external electron donor may be an organic silane compound, for example, at least one selected from the group consisting of ethylcyclohexyldimethoxysilane, diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, and dicyclohexyldimethoxysilane, most preferably ethylcyclohexyldimethoxysilane.

The external electron donor introduced into the reactor may be 13 to 22 moles, preferably 14 to 21 moles, and more preferably 15 to 20 moles, per mole of the solid complex titanium catalyst introduced into the reactor. It was confirmed that both productivity and polymerization activity were excellent when the concentration of the external electron donor satisfied the above range.

The polymerization in step (a) may be performed at a temperature of 50 to 95° C. and a pressure of 2.5 to 4.5 MPa for 50 to 90 minutes, preferably at a temperature of 60 to 90° C. and a pressure of 3.0 to 4.0 MPa for 55 to 65 minutes.

If at least one of the polymerization temperature and time in step (a) is below the lower limit, the activity of the solid complex titanium catalyst is not properly exhibited, and if at least one of the temperature and time exceeds the upper limit, there is a risk that excessive non-uniform particles may be formed, which is not preferable.

If the polymerization pressure in the above step (a) is less than 2.5 MPa, polymerization of the polypropylene homopolymer is not sufficient, and if it exceeds 4.5 MPa, it is not desirable in terms of equipment investment cost.

After step (a) above, step (b) may be performed after removing unreacted substances and reducing the pressure.

The weight average molecular weight of the polypropylene homopolymer manufactured in the above step (a) may be 350,000 to 600,000 g/mol, preferably 480,000 to 550,000 g/mol.

The melting index of the above polypropylene homopolymer may be 1.0 to 2.5 g/10 min (230°C, 2.16 kg), preferably 1.3 to 2.2 g/10 min (230°C, 2.16 kg).

The above step (b) is a step of polymerizing an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20, preferably 0.12 to 0.18, more preferably 0.12 to 0.17, and may be performed by introducing a mixed gas of ethylene and propylene and a second hydrogen gas into the polypropylene homopolymer and reacting them to polymerize the ethylene-propylene block copolymer.

The above-mentioned mixed gas of ethylene and propylene may contain ethylene and propylene in a molar ratio of 0.3:0.7 to 0.5:0.5, preferably 0.33:0.67 to 0.38:0.62, and more preferably 0.34:0.66 to 0.36:0.64. If ethylene is less than 0.3 mol per 1 mol of the mixed gas, the impact strength may be reduced, and conversely, if it exceeds 0.5 mol, a relatively reactive ethylene-based copolymer may be polymerized, resulting in a non-uniform phase due to a difference in density.

The second hydrogen gas may be 20 to 150 scc, preferably 30 to 120 scc, more preferably 40 to 100 scc, even more preferably 40 to 90 scc, and most preferably 45 to 80 scc, based on 100 g of the propylene monomer. If the second hydrogen gas is introduced in an amount less than the lower limit, the molecular weight of the ethylene-propylene block copolymer produced may be excessively large or exhibit a low melting index, resulting in reduced fluidity and significantly reduced processability. Conversely, if the second hydrogen gas is introduced in an amount exceeding the upper limit, the molecular weight of the ethylene-propylene block copolymer produced may be excessively small and the melting index may be increased, resulting in reduced processability.

According to a preferred embodiment of the present invention, the first hydrogen gas may be 220 to 310 scc with respect to 100 g of the propylene monomer, the second hydrogen gas may be 45 to 80 scc with respect to 100 g of the propylene monomer, and the mixed gas of ethylene and propylene may contain ethylene and propylene in a molar ratio of 0.34:0.66 to 0.36:0.64. When the volumes of the first and second hydrogen gases and the molar ratio of the mixed gases of the preferred embodiments of the present invention are both satisfied, it was confirmed that a polypropylene resin composition having excellent scratch resistance is produced, with a color difference of less than 0.02 even after scratching the surface of a specimen manufactured using an Ericsson scratch tester with a load of 8 N, without reducing the elongation.

The weight average molecular weight of the ethylene-propylene block copolymer manufactured in the above step (b) may be 400,000 to 650,000 g/mol, and preferably 450,000 to 650,000 g/mol.

The melting index of the ethylene-propylene block copolymer manufactured in the above step (b) may be 0.8 to 1.8 g/10 min (230 ℃, 2.16 kg), and preferably 0.9 to 1.6 g/10 min (230 ℃, 2.16 kg).

The polymerization in step (b) may be performed at a temperature of 50 to 90° C. and a pressure of 0.3 to 2.0 MPa for 20 to 30 minutes, preferably at a temperature of 60 to 80° C. and a pressure of 0.5 to 1.0 MPa for 23 to 27 minutes.

If at least one of the polymerization temperature and time of the above step (b) is below the lower limit, the activity of the solid complex titanium catalyst is not properly exhibited, and conversely, if it exceeds the upper limit, there is a concern that excessive non-uniform particles may be formed, which is not preferable.

If the polymerization pressure in the above step (b) is less than 0.3 MPa, polymerization of the polypropylene homopolymer is not sufficient, and if it exceeds 2.0 MPa, it is not desirable in terms of equipment investment cost.

A polypropylene homopolymer can be obtained through the above step (a), and an ethylene-propylene block copolymer can be obtained through the above step (b).

The above step (c) is a step of mixing the ethylene-propylene block copolymer and an antioxidant.

The above antioxidant may be at least one selected from the group consisting of a phosphorus-based antioxidant, a phenol-based antioxidant, and a thiodipropionate synergist.

The antioxidant may be present in an amount of 0.08 to 0.40 parts by weight, preferably 0.10 to 0.35 parts by weight, more preferably 0.15 to 0.30 parts by weight, and most preferably 0.23 to 0.30 parts by weight, based on 100 parts by weight of the ethylene-propylene block copolymer.

The above phenolic antioxidant is selected from the group consisting of 2,6-di-t-butyl-4-methylphenol, 4,4'-thiobis(2-t-butyl-5-methylphenol), 2,2'-thio diethylbis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], 4,4'-thiobis(2-methyl-6-t-butylphenol), 2,2'-thiobis(6-t-butyl-4-methylphenol), octadecyl-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and triethyleneglycol-bis-[3-(3-t-butyl-4-hydroxy-5-methylphenol)propionate]. There may be more than one type selected.

The above-mentioned antioxidant may be at least one selected from the group consisting of 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-isophosphaspiro[5.5]undecane, tris(2,4-di-tert-butylphenyl)phosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite and bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite and tetrakis(2,4-di-tert-butylphenyl)4,4'-biphenylene diphosphonite.

According to one embodiment of the present invention, in the polypropylene resin composition of the present invention, the antioxidant is 0.08 to 0.40 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant may be a mixture of a phenol-based antioxidant and a phosphorus-based antioxidant in a weight ratio of 1:1 to 2.

According to a preferred embodiment of the present invention, the antioxidant is 0.23 to 0.30 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant may be a mixture of pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and tris(2,4-di-tert-butylphenyl)phosphite in a weight ratio of 1:1 to 2.

The above polypropylene resin composition may have a molecular weight distribution (M _w /M _n ) of 3.0 to 4.5, preferably 3.5 to 4.4.

When the sum of the polypropylene homopolymer and the ethylene-propylene block copolymer is 100 wt%, ethylene may be included in an amount of 5 to 8 wt%, preferably 6 to 7.5 wt%, more preferably 6.3 to 7.3 wt%, and most preferably 6.8 to 7.3 wt%.

In the above step (c), one or more additives among the nucleating agent and the neutralizing agent may be further mixed.

The above nucleating agent may be an organic nucleating agent, an inorganic nucleating agent, or a mixture thereof.

The above organic nucleating agent may be at least one selected from the group consisting of aluminum salts of carboxylic acids, quinacridone quinone, calcium stearate, and sodium benzoate.

The above-mentioned inorganic nucleating agent may be at least one selected from the group consisting of talc, dibenzylidene sorbitol, and substituted dibenzylidene sorbitol.

The above neutralizing agent may be at least one selected from the group consisting of calcium stearate, zinc oxide, and hydrotalcite.

Hereinafter, the present invention will be described in more detail through examples, etc., but the scope and content of the present invention cannot be interpreted as being reduced or limited by the examples, etc. below.

Example 1

In a polymerization reactor at 10°C or lower, 0.0075 g (0.000025 mol) of a solid complex titanium catalyst, 4.4 ml of 1 M of an organic aluminum cocatalyst (triethylaluminum), 5.0 ml of 0.087 M of an external electron donor (ethylcyclohexyldimethoxysilane), 780 g of a propylene monomer, and 1800 scc of primary hydrogen (so that the reactor pressure becomes 6.3 bar) were sequentially injected, and then the temperature was raised to 80°C and 3.0 to 4.0 MPa for 60 minutes to form a polypropylene homopolymer.

Next, to remove unreacted materials in the polymerization reactor, a vacuum was applied for more than 15 minutes, 400 scc of second hydrogen gas (so that the reactor pressure becomes -0.8 bar) was injected, and then a gas mixed with ethylene and propylene in a molar ratio of 0.35:0.65 was steadily flowed, while polymerization was performed at 70°C and 0.7-0.9 MPa for 25 minutes to produce an ethylene-propylene copolymer having a weight average molecular weight of 450,000-650,000 g/mol and a melt index of 1.3 g/10 min (at 230°C and 2.16 kg).

The ethylene-propylene rubber block ratio in the manufactured ethylene-propylene block copolymer was 0.12 to 0.20.

Manufacturing of polypropylene resin composition

1,000 ppm of a phenol-based antioxidant (pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate]), 500 ppm of a phosphorus-based antioxidant (bis (2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite), 2,000 ppm of a neutralizing agent (calcium stearate), 700 ppm of a light stabilizer (HALS), and 3,000 ppm of talc were added to the above ethylene-propylene copolymer in a twin-screw extruder, and melt-mixed to prepare a polypropylene resin composition.

Example 2

A polypropylene resin composition was prepared in the same manner as in Example 1, except that no light stabilizer was added.

Example 3

A polypropylene resin composition was prepared in the same manner as in Example 2, except that 1,000 ppm of tris(2,4-di-tert-butylphenyl)phosphite was added instead as an antioxidant.

Example 4

A polypropylene resin composition was prepared in the same manner as in Example 3, except that 1,500 ppm of a phosphorus antioxidant was added.

Example 5

A polypropylene resin composition was prepared in the same manner as in Example 4, except that the first hydrogen injection amount was changed to 2,000 scc (reactor pressure 6.3 bar) and the second hydrogen injection amount was changed to 450 scc (reactor pressure -0.8 bar) during polypropylene polymerization.

Example 6

A polypropylene resin composition was prepared in the same manner as in Example 4, except that the first hydrogen injection amount was changed to 2,200 scc (reactor pressure was 6.4 bar) and the second hydrogen injection amount was changed to 500 scc (reactor pressure was -0.7 bar) during polypropylene polymerization.

Example 7

A polypropylene resin composition was prepared in the same manner as in Example 4, except that the first hydrogen injection amount was changed to 2,400 scc (reactor pressure 6.4 bar) and the second hydrogen injection amount was changed to 550 scc (reactor pressure -0.7 bar) during polypropylene polymerization.

The manufacturing conditions of the polypropylene resin compositions manufactured in Examples 1 to 7 are shown in Table 1 below.

division Hydrogen input amount
(scc) Polypropylene resin composition manufacturing steps
(ppm) 1st 2nd phenolic
Antioxidants taking over
Antioxidants Light stabilizer corrector talc Example 1 1,800 400 1,000 Pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] 500 Bis(2,4-di-tert-butylphenyl)pentaerythritol-di-phosphite) 700 2,000 3,000 Example 2 1,800 400 500 - Example 3 1,800 400 1,000 Tris(2,4-di-tert-butylphenyl)phosphite Example 4 1,800 400 1,500 Example 5 2,000 450 Example 6 2,200 500 Example 7 2,400 550

Comparative Example 1

A commercial ethylene-propylene block copolymer resin composition from Company A was purchased and used.

Comparative Example 2

A commercial ethylene-propylene block copolymer resin composition from Company B was purchased and used.

Comparative Example 3

A commercial ethylene-propylene block copolymer resin composition from Company C was purchased and used.

Experimental Example 1

The composition and physical properties of the polypropylene resin compositions of Examples 1 to 7 and Comparative Examples 1 to 3 were measured by the following methods and are shown in Table 2 below.

(1) Isotactic pentad fraction: The isotactic pentad fraction of polypropylene homopolymer was measured using nuclear magnetic resonance with carbon isotopes (13C-NMR) according to the method described in the literature [reference: A. Zambelli, Macromolecules, vol.6, p. 925 (1973), ibid, vol. 8, p. 687 (1975), and ibid, vol. 13, p. 267 (1980)].

(2) Weight average molecular weight and molecular weight distribution (M _w /M _n ): Measured using GPC (gel chromatography).

(3) Melting index: Measured according to ASTM D1238 under the conditions of 230 ℃ and 2.16 kg.

(4) Ethylene-propylene rubber block ratio: Using a differential scanning calorimeter (DSC), the melting temperature and the energy required for each temperature were obtained from a thermogram through the heating and cooling process of an ethylene-propylene block copolymer sample, and the ethylene-propylene rubber block ratio was obtained by comparing this with the energy obtained from the thermogram of a polypropylene homopolymer.

(5) Molar ratio of ethylene/(ethylene + propylene) of ethylene-propylene rubber block: Ethylene-propylene block copolymer was manufactured into a sheet of a certain thickness using a compression machine, and then the ethylene content was first obtained by comparing the absorbance at a specific wavelength (732, 720 cm ^-1 ) using Fourier transform infrared spectroscopy (FT-IR) equipment, and the ethylene-propylene rubber ratio was obtained using a differential scanning calorimeter (DSC) in the manner mentioned above, and then calculated using a proportional formula.

(6) Ethylene content: Ethylene-propylene block copolymer is manufactured into a sheet of a certain thickness using a compression machine, and then the ethylene content can be derived by comparing the absorbance at a specific wavelength (732, 720 cm ^-1 ) using FT-IR equipment, and is expressed as the weight% of ethylene contained in 100 wt% of ethylene-propylene block copolymer.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 polypropylene homopolymer isotactic
pentad fraction 0.996 0.996 0.996 0.996 0.996 0.997 0.996 - - - Weight average molecular weight
(g/mol) 519,000 519,000 519,000 519,000 492,000 490,000 485,000 - - - melting index
(g/10min) 1.3 1.3 1.3 1.3 1.7 1.8 2.1 - - - ethylene-propylene block copolymer ethylene content
(weight%) 7.2 7.2 7.2 7.2 7.2 6.8 6.4 - - - Ethylene-propylene rubber block ratio 0.125 0.125 0.125 0.125 0.130 0.124 0.120 - - - Ethylene/(ethylene + propylene) molar ratio of ethylene-propylene rubber blocks 0.35 0.35 0.35 0.35 0.37 0.34 0.34 - - - Weight average molecular weight
(g/mol) 536,000 536,000 536,000 536,000 516,000 512,000 511,000 - - - melting index
(g/10min) 1.0 1.0 1.0 1.0 1.2 1.3 1.5 - - - polypropylene resin composition ethylene content
(weight%) 7.2 7.2 7.2 7.2 7.2 6.8 6.4 7.1 6 7.1 Ethylene-propylene rubber block ratio (wt%) 12.5 12.5 12.5 12.5 13.0 12.4 12.0 10.4 11.8 10.2 Ethylene/(ethylene + propylene) molar ratio of ethylene-propylene rubber blocks 0.35 0.35 0.35 0.35 0.37 0.34 0.34 - - - Melting index (g/10min) 1.0 1.0 1.0 1.0 1.2 1.3 1.5 1.3 1.0 1.0 molecular weight distribution 3.5 3.5 3.5 3.5 3.6 3.5 3.9 4 4.3 5.7 Weight average molecular weight
(g/mol) 536,000 536,000 536,000 536,000 516,000 512,000 511,000 520,000 541,000 529,000

Experimental Example 2. Oxidation Stability Evaluation

Specimens were manufactured using the polypropylene resin compositions of Examples 1 to 7 and Comparative Examples 1 to 3, and oxidation stability was measured according to the method below, and the measurement results are shown in Table 3 and Figure 1 below.

(1) OIT (Oxidation Induction Time): The time it takes for a sample to oxidize in an oxygen-supplied environment (OIT) was measured using DSC equipment as an indicator of oxidation stability. The longer this time, the better the oxidation stability can be evaluated.

(2) Melting index after oven aging: The sample was placed in an oven at 150 ℃, and the melting index increase rate was measured at 230 ℃ and 2.16 kg after 200 hours and 400 hours according to ASTM D1238.

(3) Yellow Index after Oven Aging: The sample was placed in an oven at 150°C and the yellow index was measured after 200 hours and 400 hours according to ASTM D6290.

division OIT
(min) % increase in melting index when oven aging at 150 ℃ 200h 400h Example 1 36 29 1,083 Example 2 37 6 70 Example 3 32 6 30 Example 4 62 0 18 Comparative Example 1 45 28 425 Comparative Example 2 39 6 24 Comparative Example 3 57 6 27

As shown in Table 3, the polypropylene resin compositions of Examples 1 to 3 had lower oxidation stability than the commercially available polypropylene resin compositions of Comparative Examples 1 to 3, but exhibited oxidation stability suitable for use as an exterior material. On the other hand, the polypropylene resin composition of Example 4 had an OIT of 47 min, and an increase in melt index after oven aging of 0% after 200 hours and 18% after 400 hours, showing significantly superior oxidation stability to the polypropylene of Comparative Examples 1 to 3 that is already commercially available.

Experimental Example 3. Color change resistance evaluation

Since the above examples and comparative examples are mainly used as exterior materials, the change in yellowness (Yellow Index) according to oxidation stability must be confirmed. The lower the Yellow Index value, the less discoloration there is and the better the material can be judged. Accordingly, the photographic images and yellowness according to the oven aging time of the polypropylene resin compositions of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Fig. 1.

FIG. 1 shows photographic images and yellow indexes of polypropylene resin compositions of Examples 1 to 4 and Comparative Examples 1 to 3 of the present invention according to oven aging time.

Referring to the above Figure 1, Examples 1 and 2 have a color change resistance equivalent to that of the commercially available comparative example, and Examples 3 and 4 have a significantly lower degree of color change than the comparative example, demonstrating excellent color change resistance. In particular, Example 4 had the smallest change in yellowness value after oven aging that could be confirmed with the naked eye, and the final value (16.9 after 400 hours) was also the lowest, confirming excellent color change resistance.

Experimental Example 4. Physical Property Evaluation

Specimens were prepared using the resin compositions of Examples 4 to 7 and Comparative Examples 1 to 3, and their physical properties were measured. The physical property evaluation method is as follows, and the measurement results are shown in Table 4 below.

(1) Flexural modulus: Measured according to ASTM D790 at 23 ℃.

(2) Flexural strength: Measured according to ASTM D790 at 23 ℃.

(3) Impact strength: Measured according to ASTM D256 at 23 ℃.

(4) Tensile strength: Measured according to ASTM D638 at 23 ℃.

division Flexural modulus
(kgf/cm ² ) Flexural strength
(kgf/cm ² ) Impact strength,
23℃
(kgf.cm/cm) Impact strength,
-20℃
(kgf.cm/cm) tensile strength
yield point
(kgf/cm ² ) tensile strength,
breaking point
(kgf/cm ² ) Example 4 12,400 327 59.2 6.3 240 180 Example 5 12,800 339 51.5 5.7 244 190 Example 6 12,400 327 43.3 4.9 250 192 Example 7 12,000 315 43.5 5.0 239 195 Comparative Example 1 12,300 309 31.4 4.3 233 160 Comparative Example 2 11,900 296 39.4 4.6 224 133 Comparative Example 3 12,100 310 28.1 4.1 231 165

According to the results in Table 4 above, it was confirmed that the impact strength, flexural strength, and tensile strength breaking point measured at 23°C and -20°C were higher in Examples 4 to 7 than in Comparative Examples 1 to 3. In addition, when comparing Examples 4 to 7 above, it was confirmed that the lower the melting index, the higher the impact strength regardless of the measurement temperature, and it was shown that the range of change in impact strength when the melting index decreased was relatively large compared to the range of change in other physical properties (flexural modulus, flexural strength, tensile strength).

Claims (13)

An ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and
In a polypropylene resin composition comprising an antioxidant,
The above ethylene-propylene block copolymer is polymerized from a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more,
Ethylene is contained in an amount of 5 to 8 wt% based on 100 wt% of the total ethylene-propylene block copolymer,
A polypropylene resin composition characterized in that the antioxidant is 0.23 to 0.3 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant is pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and tris(2,4-di-tert-butylphenyl)phosphite mixed in a weight ratio of 1:1 to 2. In claim 1, the polypropylene resin composition is characterized in that the molecular weight distribution (M _w /M _n ) is 3.0 to 4.5. A polypropylene resin composition according to claim 1, wherein the weight average molecular weight of the polypropylene homopolymer is 350,000 to 600,000 g/mol. A polypropylene resin composition, characterized in that in claim 1, the melting index of the polypropylene homopolymer is 1.0 to 2.5 g/10 min (230°C, 2.16 kg). A polypropylene resin composition, characterized in that the weight average molecular weight of the ethylene-propylene block copolymer in claim 1 is 400,000 to 650,000 g/mol. A polypropylene resin composition according to claim 1, wherein the melting index of the ethylene-propylene block copolymer is 0.8 to 1.8 g/10 min (230°C, 2.16 kg). delete delete delete A molded article comprising a polypropylene resin composition according to any one of claims 1 to 6. (a) a step of forming a polypropylene homopolymer having an isotactic pentad fraction of 0.99 or more;
(b) a step of introducing a mixed gas of ethylene and propylene into the polypropylene homopolymer and polymerizing the mixture to form an ethylene-propylene block copolymer having an ethylene-propylene rubber block ratio of 0.12 to 0.20; and
(c) a step of mixing the ethylene-propylene block copolymer and an antioxidant;
Ethylene is contained in an amount of 5 to 8 wt% based on 100 wt% of the total ethylene-propylene block copolymer,
A method for producing a polypropylene resin composition, characterized in that the antioxidant is 0.23 to 0.3 parts by weight based on 100 parts by weight of the ethylene-propylene block copolymer, and the antioxidant is pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate] and tris(2,4-di-tert-butylphenyl)phosphite mixed in a weight ratio of 1:1 to 2. In Article 11,
The above step (a) is performed by introducing a propylene monomer, a solid complex titanium catalyst, an organic aluminum co-catalyst, and a first hydrogen gas into a reactor and reacting them.
A method for producing a polypropylene resin composition, characterized in that the first hydrogen gas is 150 to 380 scc per 100 g of the propylene monomer. In Article 11,
The above step (b) is performed by injecting a mixed gas of ethylene and propylene and a second hydrogen gas into the polypropylene homopolymer and polymerizing it.
A method for producing a polypropylene resin composition, characterized in that the second hydrogen gas is 20 to 150 scc per 100 g of the propylene monomer.