阅读说明：本技术 具有优异的耐白化性和耐热性的聚丙烯树脂组合物、其制备方法及由其模制的成型品 (Polypropylene resin composition having excellent whitening resistance and heat resistance, method for preparing the same, and molded article therefrom ) 是由 金奉奭 全龙成 于 2020-09-14 设计创作，主要内容包括：本发明涉及一种聚丙烯树脂组合物、其制备方法、及由其模制的成型品。尤其,本发明涉及一种聚丙烯树脂组合物,其通过包含乙烯-丙烯嵌段共聚物树脂而具有优异的耐白化性和耐热性。根据本发明的聚丙烯树脂组合物可以有效地应用于被折叠时可能出现外观缺陷的食品包装袋的热封层膜、或者由于后续处理时的变形而可能发生白化的电池包装膜等。(The present invention relates to a polypropylene resin composition, a method for preparing the same, and a molded article molded therefrom. In particular, the present invention relates to a polypropylene resin composition having excellent whitening resistance and heat resistance by containing an ethylene-propylene block copolymer resin. The polypropylene resin composition according to the present invention can be effectively applied to a heat seal layer film of a food packaging bag in which appearance defects may occur when it is folded, a battery packaging film in which whitening may occur due to deformation at the time of subsequent processing, or the like.)

1. A polypropylene resin composition which comprises a polypropylene resin and a polypropylene resin,

which comprises an ethylene-propylene block copolymer resin obtained by stepwise polymerization in a reactor;

the ethylene-propylene block copolymer resin comprises 80 to 85% by weight of a polypropylene matrix selected from propylene- α -olefin random copolymers obtained by copolymerizing a propylene homopolymer with an α -olefin having 2 to 4 carbon atoms and 15 to 20% by weight of an ethylene-propylene rubber copolymer measured based on the content of the solvent extract,

wherein the ethylene-propylene block copolymer resin has a melting temperature of 161 ℃ to 165 ℃, a difference between the melting temperature and the crystallization temperature (Tm-Tc) of 40 ℃ to 45 ℃, a ratio of the content of the solvent extract to the content of ethylene on a weight basis [ (solvent extract content)/(ethylene content) ] of 2.5 to 3.0, and an intrinsic viscosity of the solvent extract of 1.2dl/g to 2.5 dl/g.

2. The polyolefin resin composition according to claim 1, wherein the ethylene content in the ethylene-propylene block copolymer resin is from 5 to 8% by weight.

3. The polypropylene resin composition according to claim 1, wherein the ethylene-propylene block copolymer resin has a melt index of 1.0g/10min to 10g/10min, when measured at 230 ℃ under a load of 2.16kg according to ASTM D1238.

4. The polypropylene resin composition according to claim 1, further comprising at least one additive selected from the group consisting of an antioxidant, a neutralizer, a slip agent, an anti-blocking agent, a reinforcing material, a filler, a weather resistant stabilizer, an antistatic agent, a lubricant, a nucleating agent, a flame retardant, a pigment and a dye.

5. The polypropylene resin composition according to claim 4, wherein the antioxidant is present in an amount of 0.01 to 0.2 wt%, based on the total weight of the polypropylene resin composition.

6. The polypropylene resin composition according to claim 5, wherein the antioxidant is at least one member selected from the group consisting of tetrakis (methylene (3,5-di-t-butyl-4-hydroxy) hydrosilyl ester), pentaerythritol tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), 1,3,5-trimethyl-tris (3,5-di-t-butyl-4-hydroxyphenyl) and tris (2,4-di-t-butylphenyl) phosphite.

7. The polypropylene resin composition according to claim 4, wherein the neutralizing agent is contained in an amount of 0.01 to 0.2 wt% based on the total weight of the polypropylene resin composition.

8. The polypropylene resin composition according to claim 7, wherein the neutralizing agent is at least one member selected from the group consisting of hydrotalcite and calcium stearate.

9. A method for preparing the polypropylene resin composition according to any one of claims 1 to 8, the method comprising:

a first polymerization step of polymerizing a polypropylene matrix in 2 or more continuous reactors, wherein the polypropylene matrix is selected from propylene- α -olefin random copolymers obtained by copolymerizing propylene homopolymers and α -olefins having 2 to 4 carbon atoms; and

a second polymerization step of copolymerizing the ethylene-propylene rubber copolymer component by adding ethylene and propylene in the presence of a polymerized polypropylene matrix to obtain an ethylene-propylene block copolymer resin.

10. The method for preparing a polypropylene resin composition according to claim 9, wherein each polymerization step is carried out in the presence of a Ziegler-Natta catalyst, wherein the Ziegler-Natta catalyst is prepared by selecting from the group consisting of TiCl₃And TiCl₄At least one titanium chloride is supported on a magnesium chloride support.

11. The method for producing a polypropylene resin composition according to claim 10,

as the co-catalyst of the ziegler-natta catalyst, at least one alkyl aluminum compound selected from the group consisting of triethylaluminum, diethyl aluminum chloride, tributylaluminum, triisobutylaluminum and trioctylaluminum is used;

at least one organosilane compound selected from the group consisting of diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane and dicyclohexyldimethoxysilane is used as an exogenous electron donor.

12. The method for producing a polypropylene resin composition according to claim 9,

the first polymerization step is a step of polymerizing a polypropylene matrix in the presence of a Ziegler-Natta catalyst in 2 or more bulk polymerization reactors;

the second polymerization step is a step of copolymerizing an ethylene-propylene copolymer as a rubber component by adding ethylene and propylene in a gas phase polymerization reactor in the presence of the polypropylene matrix polymerized in the first polymerization step and a ziegler-natta catalyst to obtain an ethylene-propylene block copolymer.

13. A polypropylene resin molded article produced by molding the polypropylene resin composition according to any one of claims 1 to 8.

14. The polypropylene resin molded article according to claim 13, wherein the molded article is a heat seal film for a food packaging bag or a packaging film for a battery.

15. The polypropylene resin molded article according to claim 14, wherein the film has a heat seal strength of 2.0kg to 5.0kg and a dart impact strength of 500g to 750g when heat-treated (aged) in an oven at 130 ℃ for 30 minutes.

Technical Field

The present invention relates to a polypropylene resin composition, a method for preparing the same, and a molded article molded therefrom. In particular, the present invention relates to a polypropylene resin composition having excellent whitening resistance and heat resistance by containing an ethylene-propylene block copolymer resin. The polypropylene resin composition according to the present invention can be effectively applied to a heat seal layer film of a food packaging bag in which appearance defects may occur when it is folded, a battery packaging film in which whitening may occur due to deformation at the time of subsequent processing, or the like.

Background

Polypropylene resin is a polymer material widely used in home appliances, automotive composites and general packaging materials. The rigidity, transparency, impact resistance, and the like of polypropylene resins vary depending on the structure of the polymer.

Among them, since the ethylene-propylene block copolymer resin contains an ethylene-propylene rubber copolymer, the impact resistance is superior to that of homo-polypropylene or polypropylene random copolymer. Therefore, the ethylene-propylene block copolymer resin is mainly used for automobile composites or general groceries requiring impact resistance.

On the other hand, since the ethylene-propylene block copolymer resin has low transparency due to such a rubber component, it is difficult to use the ethylene-propylene block copolymer resin for applications such as films requiring transparency. Therefore, it is limited to use in applications requiring low transparency, such as aluminum foil laminated food retort pouch films.

Food is filled into a food cooking bag and packaged, and then stored at room temperature for a long time after sterilization treatment, and is widely used because of easy handling, small volume, and low cost of packaging materials, compared to the existing glass or metal cans.

The retort container, which is generally sterilized at a temperature of 120 to 130 ℃, has a multi-layer structure and is mainly formed by bonding films of polypropylene, polyester, nylon and the like and metal foils and the like. Specifically, the multilayer structure may be formed of polyester/nylon/metal foil/polypropylene, or polyester/metal foil/polypropylene, or the like, depending on the application. The ethylene-propylene block copolymer mainly used for the polypropylene layer is processed into a cast polypropylene film (CPP film) and is located at the innermost side as a heat seal layer.

Meanwhile, since the CPP film used as a heat seal layer in a retort pouch is thickest, heat seal characteristics and impact resistance are required. However, since the retort pouch is heat-treated at a high temperature in the sterilization treatment, the heat-sealing property and impact resistance are reduced after the heat treatment, and the rigidity of the film is increased to lose the soft touch, and thus it is necessary to improve the heat-sealing property and impact resistance.

Further, since an interface exists between a polypropylene matrix (matrix) and a rubber phase of the ethylene-propylene block copolymer resin, when a film made therefrom is folded, a stress-whitening phenomenon in which a folded portion is whitened occurs, resulting in a disadvantage of poor appearance.

Various studies have been made to try to improve the disadvantages of such ethylene-propylene block copolymers. For example, korean patent No. 1298417 discloses an ethylene-propylene block copolymer resin which is obtained by stepwise polymerizing an ethylene-propylene random copolymer and an ethylene-propylene rubber copolymer. Although the resin is improved in transparency and impact resistance, there is a limitation in its application in the case where heat resistance is required in subsequent processing due to a low melting temperature.

Further, korean patent No. 1598715 discloses an ethylene-propylene block copolymer resin based on homo-polypropylene. The resin has excellent impact resistance and high heat resistance, and thus has excellent appearance after high-temperature sterilization, but does not consider problems in terms of physical property change and whitening resistance after high-temperature sterilization.

[ Prior art documents ]

[ patent document ]

(patent document 1) korean patent No. 1298417;

(patent document 2) korean patent No. 1598715.

Disclosure of Invention

Technical problem

In order to solve the above problems, an object of the present invention is to provide a polypropylene resin composition having excellent whitening resistance and heat resistance.

In another aspect, the present invention is directed to a method for preparing the above polypropylene resin composition.

In still another aspect, the present invention is directed to a molded article made of the polypropylene resin composition, specifically, a heat seal layer film for a food packaging bag or a packaging film for a battery.

Technical scheme

In order to achieve the above object, according to one embodiment, the present invention provides a polypropylene resin composition comprising an ethylene-propylene block copolymer resin which is segmented polymerized in a reactor; the ethylene-propylene block copolymer resin comprises 80 to 85% by weight of a polypropylene matrix selected from propylene- α -olefin random copolymers obtained by copolymerizing a propylene homopolymer with an α -olefin having 2 to 4 carbon atoms and 15 to 20% by weight of an ethylene-propylene rubber copolymer measured based on the content of the solvent extract, wherein the ethylene-propylene block copolymer resin has a melting temperature of 161 ℃ to 165 ℃, a difference between the melting temperature and the crystallization temperature (Tm-Tc) of 40 ℃ to 45 ℃, a ratio of the content of the solvent extract to the content of ethylene on a weight basis [ (solvent extract content)/(ethylene content) ] of 2.5 to 3.0, and an intrinsic viscosity of the solvent extract of 1.2dl/g to 2.5 dl/g.

Preferably, the ethylene content in the ethylene-propylene block copolymer resin may be 5 to 8% by weight.

Further, the ethylene-propylene block copolymer resin may have a melt index of 1.0g/10min to 10g/10min when measured at 230 ℃ under a load of 2.16kg according to ASTM D1238.

The polypropylene resin composition according to an embodiment of the present invention may further comprise at least one additive selected from the group consisting of antioxidants, neutralizing agents, slip agents, anti-blocking agents, reinforcing materials, fillers, weather-resistant stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments and dyes.

Specifically, the polypropylene resin composition according to an embodiment of the present invention may comprise 0.01 to 0.2 wt% of an antioxidant, based on the total weight of the composition.

Preferably, the antioxidant may be selected from tetrakis (methylene (3, 5-di-tert-butyl-4-hydroxy) hydrosilylate) (tetra (methyl (3,5-di-t-butyl-4-hydroxy) hydrosilylate)), pentaerythrityl tetrakis (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate) (pentaerythrityl tetra (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate)), 1,3,5-trimethyl-tris (3, 5-di-tert-butyl-4-hydroxybenzene) (1,3,5-trimethyl-tris (3,5-di-t-butyl-4-hydroxybenzene)) and tris (2, 4-di-tert-butylphenyl) phosphite (tris (2, 4-di-t-butyl) phosphate).

The polypropylene resin composition according to an embodiment of the present invention may comprise 0.01 wt% to 0.2 wt% of a neutralizing agent based on the total weight of the composition.

Preferably, the neutralizing agent may be at least one selected from the group consisting of hydrotalcite (hydrotalcite) and calcium stearate.

According to another embodiment of the present invention, there is provided a method for preparing the above polypropylene resin composition according to an embodiment of the present invention, the method including: a first polymerization step of polymerizing a polypropylene matrix in 2 or more continuous reactors, wherein the polypropylene matrix is selected from propylene- α -olefin random copolymers obtained by copolymerizing propylene homopolymers and α -olefins having 2 to 4 carbon atoms; and a second polymerization step of copolymerizing an ethylene-propylene rubber copolymer component by adding ethylene and propylene in the presence of a polymerized polypropylene matrix to obtain an ethylene-propylene block copolymer resin.

In the above preparation method, each polymerization step may be carried out in the presence of a Ziegler-Natta catalyst. Wherein the Ziegler-Natta catalyst is prepared by reacting a catalyst selected from TiCl₃And TiCl₄At least one titanium chloride in (b) is supported on magnesium chloride (MgCl)₂) On a carrier.

Further, as the co-catalyst of the ziegler-natta catalyst, at least one alkyl aluminum compound selected from triethylaluminum, diethylaluminum chloride, tributylaluminum, triisobutylaluminum and trioctylaluminum; as the exogenous electron donor, at least one organosilane compound selected from the group consisting of diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane and dicyclohexyldimethoxysilane can be used.

Preferably, the first polymerization step is a step of polymerizing the polypropylene matrix in the presence of a ziegler-natta catalyst in 2 or more bulk polymerization reactors; the second polymerization step is a step of copolymerizing an ethylene-propylene copolymer as a rubber component by adding ethylene and propylene in a gas phase polymerization reactor in the presence of the polypropylene matrix polymerized in the first polymerization step and a ziegler-natta catalyst to obtain an ethylene-propylene block copolymer.

According to still another embodiment of the present invention, there is provided a polypropylene resin molded article obtained by molding the polypropylene resin composition.

Specifically, the polypropylene resin molded article according to an embodiment of the present invention may be a heat seal layer film of a food packaging bag or a packaging film of a battery.

Preferably, the film according to an embodiment of the present invention may have a heat-seal strength of 2.0kg to 5.0kg and a dart impact strength of 500g to 750g when heat-treated (aged) in an oven at 130 ℃ for 30 minutes.

Advantageous effects

The polypropylene resin composition according to the embodiment of the present invention has excellent whitening resistance and heat resistance, and thus can be effectively applied to a heat seal layer film of a food packaging bag, in which appearance defects may occur when folded, or a battery packaging film, in which stress whitening may occur due to deformation at the time of subsequent processing, and the like.

Detailed Description

Hereinafter, the present invention will be described in detail.

The polypropylene resin composition according to an embodiment of the present invention comprises an ethylene-propylene block copolymer resin which is segmented polymerized in a reactor; the ethylene-propylene block copolymer resin comprises 80 to 85% by weight of a polypropylene matrix selected from propylene- α -olefin random copolymers obtained by copolymerizing a propylene homopolymer with an α -olefin having 2 to 4 carbon atoms and 15 to 20% by weight of an ethylene-propylene rubber copolymer measured based on the content of the solvent extract, wherein the ethylene-propylene block copolymer resin has a melting temperature of 161 ℃ to 165 ℃, a difference between the melting temperature and the crystallization temperature (Tm-Tc) of 40 ℃ to 45 ℃, a ratio of the content of the solvent extract to the content of ethylene on a weight basis [ (solvent extract content)/(ethylene content) ] of 2.5 to 3.0, and an intrinsic viscosity of the solvent extract of 1.2dl/g to 2.5 dl/g.

Specifically, the polypropylene resin composition according to a specific embodiment of the present invention includes an ethylene-propylene block copolymer resin. Wherein the ethylene-propylene block copolymer resin is obtained by sectional polymerization in a reactor.

For example, a polypropylene matrix may be first polymerized and then block-copolymerized with an ethylene-propylene rubber to prepare an ethylene-propylene block copolymer resin.

Among them, the polypropylene matrix may be a propylene- α -olefin random copolymer obtained by copolymerizing a propylene homopolymer and an α -olefin having 2 to 4 carbon atoms. Preferably, the polypropylene matrix may be a propylene homopolymer.

In the ethylene-propylene block copolymer resin, the content of the polypropylene matrix is 80 to 85% by weight. When the content of the polypropylene matrix is less than 80% by weight, the production efficiency in the polymerization process of the ethylene-propylene block copolymer resin is lowered, and blocking of the film occurs at the time of film formation, which is not preferable. On the other hand, when the content of the polypropylene matrix exceeds 85% by weight, the resin composition may have high rigidity and reduced impact resistance.

In the ethylene-propylene block copolymer resin, the content of the ethylene-propylene rubber copolymer is 15 to 20% by weight. If the content of the ethylene-propylene rubber copolymer is less than 15% by weight, the impact resistance of the resin composition may be reduced. On the other hand, when the content of the ethylene-propylene rubber copolymer exceeds 20% by weight, the production efficiency in the polymerization process of the ethylene-propylene block copolymer resin is lowered, and blocking (blocking) of the film occurs at the time of film formation, which is not preferable. Here, the content of the ethylene-propylene rubber copolymer may be measured based on the content of the solvent extract, and the solvent is preferably xylene (xylene).

The ethylene-propylene block copolymer resin has a melting temperature of 161 ℃ to 165 ℃ as determined by Differential Scanning Calorimetry (DSC). When the melting temperature is less than 161 ℃, the molded article may be deformed during subsequent high-temperature treatment due to insufficient heat resistance. On the other hand, polypropylene having a melting temperature exceeding 165 ℃ is commercially difficult to polymerize, and when the resin composition contains a nucleating agent, it is not suitable for food packaging applications requiring a soft touch because the rigidity of the film is high.

Further, the difference (Tm-Tc) between the melting temperature and the crystallization temperature of the ethylene-propylene block copolymer is 40 ℃ to 45 ℃. If the difference between the melting temperature and the crystallization temperature exceeds 45 ℃, the rigidity changes greatly and the heat seal strength decreases greatly due to the post-crystallization during the high-temperature sterilization of the molded product, and therefore the physical properties of the film after the high-temperature sterilization change, making it unsuitable for bag applications requiring a sterilization process. On the other hand, if the difference between the melting temperature and the crystallization temperature is less than 40 ℃, the crystallization rate is high, which causes the contact with a cooling roll (chill roll) during film formation to be not smooth and makes film formation difficult, and the crystallization rate is high, which causes the rigidity of the film to be high and is not suitable for food packaging applications requiring a soft touch.

In the ethylene-propylene block copolymer resin according to an embodiment of the present invention, the ratio of the ethylene-propylene rubber copolymer content (% by weight) to the ethylene content (% by weight) on a weight basis may be 2.5 to 3.0. When the ratio is less than 2.5, the whitening resistance of the resin composition is lowered, and the variation in film rigidity after high-temperature sterilization is large due to the non-uniform dispersion of the rubber component. On the other hand, when the ratio exceeds 3.0, the impact resistance is lowered due to a high propylene content in the composition of the rubber, and therefore it is not preferable.

The intrinsic viscosity of the ethylene-propylene rubber copolymer (i.e., the solvent extract) in the ethylene-propylene block copolymer resin according to the embodiment of the present invention is 1.2dl/g to 2.5 dl/g. When the intrinsic viscosity is less than 1.2dl/g, the impact resistance of the resin composition is lowered due to the decrease in the molecular weight of the rubber component, and when the intrinsic viscosity exceeds 2.5dl/g, the whitening resistance of the resin composition is lowered due to the aggregation of the rubber component, which is not preferable.

Preferably, the ethylene content in the ethylene-propylene block copolymer resin may be 5 to 8% by weight. If the content of ethylene is less than 5% by weight, the impact resistance of the resin composition may be insufficient. On the other hand, if the ethylene content exceeds 8% by weight, the transparency of the resin composition may be reduced and the whitening resistance may be reduced.

Preferably, the ethylene-propylene block copolymer resin may have a melt index of 1.0g/10min to 10g/10min when measured at 230 ℃ under a load of 2.16kg according to ASTM D1238. When the melt index is less than 1.0g/10min, the production efficiency is lowered due to an increase in load during extrusion. On the other hand, when the melt index exceeds 10g/10min, it is not preferable because sagging occurs during extrusion to cause a decrease in thickness uniformity.

The polypropylene resin composition according to the embodiment of the present invention may further comprise conventional additives within the scope not departing from the object of the present invention. For example, the polypropylene resin composition may include, but is not limited to, antioxidants, neutralizing agents, slip agents, anti-blocking agents, reinforcing materials, fillers, weather-resistant stabilizers, antistatic agents, lubricants, nucleating agents, flame retardants, pigments, dyes, and the like.

Preferably, the polypropylene resin composition according to an embodiment of the present invention may include an antioxidant to increase its heat-resistant stability. At this time, the antioxidant may be added in an amount of 0.01 to 0.2 wt%, preferably 0.05 to 0.15 wt%, based on the total weight of the polypropylene resin composition. If the content of the antioxidant is less than 0.01 wt%, it is difficult to secure long-term heat-resistant stability. On the other hand, if the content of the antioxidant exceeds 0.2% by weight, it may cause the antioxidant to melt out or reduce the economy of the product, and therefore it is not preferable.

As the antioxidant, a phenol type antioxidant, a phosphite type antioxidant, or the like can be used, and specifically, at least one selected from the group consisting of tetrakis (methylene (3,5-di-t-butyl-4-hydroxy) hydrosilyl ester), tetrakis (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate) pentaerythritol ester), 1,3,5-trimethyl-tris (3,5-di-t-butyl-4-hydroxyphenyl) and tris (2,4-di-t-butylphenyl) phosphite can be used, but not limited thereto.

Preferably, the polypropylene resin composition according to an embodiment of the present invention may include hydrotalcite, calcium stearate, etc. as a neutralizing agent to remove catalyst residues.

At this time, the neutralizing agent may be added in an amount of 0.01 to 0.2 wt%, preferably 0.02 to 0.10 wt%, based on the total weight of the polypropylene resin composition. When the content of the neutralizing agent is less than 0.01% by weight, it is difficult to secure the effect of removing the catalyst residue in the resin, and when the content of the neutralizing agent exceeds 0.2% by weight, the effect of removing the catalyst residue increases very little and the cost-effectiveness of the resin composition may be lowered, and thus it is not preferable.

The method for preparing a polypropylene resin composition according to another embodiment of the present invention comprises: a first polymerization step of polymerizing a polypropylene matrix in 2 or more continuous reactors, wherein the polypropylene matrix is selected from propylene- α -olefin random copolymers obtained by copolymerizing propylene homopolymers and α -olefins having 2 to 4 carbon atoms; and a second polymerization step of copolymerizing an ethylene-propylene rubber copolymer component by adding ethylene and propylene in the presence of a polymerized polypropylene matrix to obtain an ethylene-propylene block copolymer resin.

At this time, each polymerization may use a method and reaction conditions well known in the art, for example, a slurry method, a bulk method, a gas phase method, and the like.

Further, each of the above polymerization steps may be carried out in the presence of a Ziegler-Natta (Ziegler-Natta) catalyst. The Ziegler-Natta catalyst may be any catalyst known in the art without limitation, and specifically, may be prepared by reacting, for example, titanium chloride (TiCl)₃Or TiCl₄) Etc. of titanium compound supported on magnesium chloride (MgCl)₂) Supported to obtain the Ziegler-Natta catalyst. PreferablyWherein both the cocatalyst and the exogenous electron donor may be used.

An alkyl aluminum compound may be used as a co-catalyst. The alkyl aluminum compound may be, for example, triethyl aluminum, diethyl aluminum chloride, tributyl aluminum, triisobutyl aluminum, trioctyl aluminum, or the like, but is not limited thereto.

Further, as the external electron donor, an organosilane compound is preferably used. The organosilane compound may be, for example, diphenyldimethoxysilane, phenyltrimethoxysilane, phenylethyldimethoxysilane, phenylmethyldimethoxysilane, methoxytrimethylsilane, isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclohexyldimethoxysilane and the like, but is not limited thereto.

In the method of preparing the polypropylene resin composition according to an embodiment of the present invention, the first polymerization step and the second polymerization step described above may be performed in the same polymerization reactor or in different polymerization reactors.

Preferably, the first polymerization step may be a step of polymerizing the polypropylene matrix in the presence of a ziegler-natta catalyst in 2 or more bulk polymerization reactors; the second polymerization step may be a step of copolymerizing an ethylene-propylene copolymer as a rubber component by adding ethylene and propylene in a gas phase polymerization reactor in the presence of the polypropylene matrix polymerized in the first polymerization step and a ziegler-natta catalyst to obtain an ethylene-propylene block copolymer. By adjusting the amount of hydrogen introduced into each polymerization reactor, the melt index of the polymer produced in each polymerization reactor can be adjusted.

Specifically, an ethylene-propylene block copolymer can be produced by transferring the polypropylene matrix obtained in the first polymerization step into a gas phase reactor to be subjected to ethylene-propylene copolymerization, and simultaneously adding ethylene and propylene to continuously copolymerize the solid polypropylene matrix with newly added ethylene and propylene as ethylene-propylene rubber copolymer components.

The ethylene-propylene block copolymer thus obtained may be mixed with conventional additives within a range not departing from the object of the present invention. The kind and content of the specific additive are substantially the same as those of the polypropylene resin composition.

In this case, the method of mixing the ethylene-propylene block copolymer and the additive is not particularly limited, and a method of preparing a polypropylene resin composition known in the art to which the present invention pertains may be used as it is or after being appropriately modified.

Specifically, for example, the polypropylene resin composition of the present invention can be prepared by adding desired amounts of the ethylene-propylene block copolymer and additives to a mixer such as a kneader (kneader), roll mill (roll), Banbury mixer (Banbury mixer), or a single-screw/twin-screw extruder, and then blending (blending) the added raw materials using these machines.

According to yet another embodiment of the present invention, there is provided a polypropylene resin molded article produced by molding the polypropylene resin composition of the present invention.

The method for preparing a molded article from the polypropylene resin composition according to the embodiment of the present invention is not particularly limited, and a method known in the art to which the present invention pertains may be used. For example, the polypropylene resin composition according to the embodiment of the present invention may be molded by a conventional method such as injection molding, extrusion molding, casting molding, etc. to prepare a polypropylene resin molded article. In one embodiment, the polypropylene resin composition according to embodiments of the present invention may be made into a cast polypropylene film (CPP film) by casting.

The polypropylene resin molded article according to the embodiment of the present invention has excellent whitening resistance and heat resistance. Therefore, the molded product may be a heat seal film for a food packaging bag or a battery packaging film.

Preferably, the film according to an embodiment of the present invention may have a heat-seal strength of 2.0kg to 5.0kg and a dart impact strength of 500g to 750g when heat-treated (aged) in an oven at 130 ℃ for 30 minutes.

Examples

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

[ examples 1 to 2 ] and comparative examples 1 to 5 ]

Polymerization of ethylene-propylene block copolymers

By using the Hypol process of Mitsui corporation, 2 bulk reactors and 2 gas phase reactors may be connected in series to perform continuous polymerization. In this case, a Ziegler-Natta catalyst is used, which is prepared by reacting titanium chloride (TiCl)₄) Supported on magnesium chloride (MgCl)₂) Supported and used a phthalate endogenous electron donor (internal Donor). Triethylaluminum was used as cocatalyst and dicyclopentyldimethoxysilane as exogenous electron donor (external Donor).

The operating temperature and pressure in the first stage bulk reactor and the second stage bulk reactor are 68 to 75 ℃ and 30 to 40kg/cm, respectively²And 68 to 75 ℃ at 25 to 35kg/cm². The operating temperature and pressure in the third-stage gas-phase reactor and the fourth-stage gas-phase reactor were 75 to 82 ℃ and 15 to 20kg/cm, respectively²And 68 to 75 ℃ and 10 to 17kg/cm². Propylene was separately fed into the first to third stage reactors to produce a propylene homopolymer. The resulting propylene homopolymer was transferred to the fourth reactor of the next stage, and ethylene-propylene rubber was copolymerized by adding ethylene and propylene in the presence of the above Ziegler-Natta catalyst, thereby obtaining an ethylene-propylene block copolymer. At this time, the melt index of the polymer produced in each reactor was adjusted by adjusting the amount of hydrogen introduced in each reactor. In this manner, the ethylene content, the solvent extract content was adjusted as shown in the following table 1 to obtain an ethylene-propylene block copolymer.

The composition and physical properties of the ethylene-propylene block copolymer resin obtained were measured by the following methods, and the results are shown in table 1 below.

(1) Melt index (melt index; g/10min)

The melt index of the ethylene-propylene block copolymer resin was measured at 230 ℃ under a load of 2.16kg according to ASTM D1238.

(2) Melting and crystallization temperatures (Tm, Tc)

The crystallization temperature (Tc) was determined by maintaining the sample at a constant temperature of 200 ℃ for 10 minutes by using Differential Scanning Calorimetry (DSC) to eliminate the thermal history, and then cooling it from 200 ℃ to 30 ℃ at a rate of 10 ℃ per minute to lower it by 10 ℃. The same thermal history was allowed to develop by cooling as above, and then held at a constant temperature of 30 ℃ for 10 minutes. Subsequently, the temperature was again raised at 10 ℃ per minute, and the melting temperature (Tm) was obtained from the peak melting temperature.

(3) Ethylene content (% by weight)

By using infrared absorption spectroscopy (FT-IR) and using 720cm^-1And 730cm^-1To determine the ethylene content in the ethylene-propylene block copolymer.

(4) Content of solvent extract (xylene soluble) (% by weight)

The ethylene-propylene block copolymer resin was dissolved in xylene (xylene) at a concentration of 1% by weight at 140 ℃ for 1 hour, and then, after 2 hours at room temperature, the weight of the extract was measured. The obtained weight is expressed as a percentage with respect to the weight of the ethylene-propylene block copolymer resin.

(5) Intrinsic viscosity of solvent extract

The intrinsic viscosity of the solvent extract was measured in decalin (decalin) solution at 135 ℃ using a viscometer.

Preparation of test pieces

To each of the ethylene-propylene block copolymer resins prepared in the above examples and comparative examples, an antioxidant (pentaerythritol tetrakis (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate) having a content of 0.1 wt% and a neutralizer (hydrotalcite) having a content of 0.04 wt% were added, kneaded, and extrusion-processed using a twin-screw extruder to prepare pellets. In the case of comparative example 5, pellets were prepared by further kneading 0.1% by weight of an organometallic nucleating agent (aluminum p-tert-butylbenzoate) as an additive in the process of preparing the pellets.

The obtained resin composition was molded into a film having a thickness of 0.4mm by using a conventional cast film extrusion apparatus. In the film forming process, the temperature of the extruder was 230 ℃ and the temperature of the cooling roll for film forming was 30 ℃. The physical properties after aging (aging) were evaluated after the obtained film was heat-treated in an oven at 130 ℃ for 30 minutes. The physical properties of the film before and after aging were measured by the following methods, and the evaluation results are shown in table 1.

(6) Tensile modulus (tensile modulus)

Tensile testing was performed according to ASTM D882 and the modulus (moduli) was determined from the initial slope of the plot.

(7) Heat sealing Strength (heat sealing Strength)

At a temperature of 180 ℃ and a pressure of 2kg/cm²The two films were thermally bonded under a condition of a time period of 1 second, and then the strength at which the film was peeled off was measured with a tensile tester.

(8) Dart impact Strength (FDI)

Measured according to ASTM D4226.

(9) Whitening resistance (stress-whitening resistance)

After the film was marked, the film was pulled out to both sides, and the degree of whitening at the tear portion was visually confirmed (O: excellent,. DELTA.: good, X: poor).

[ TABLE 1 ]

From table 1, it was confirmed that in the examples belonging to the scope of the present invention, even after oven aging under the same sterilization conditions as those of conventional food packaging bag products, the changes in rigidity (tensile modulus) and heat seal strength of the film were small, and the dart impact strength was high and whitening resistance was excellent.

In contrast, in comparative example 1, which is not within the scope of the present invention, the impact strength was not good and the variation of rigidity and heat seal strength was large due to the low content of the solvent extract, while in comparative example 4, the variation of heat seal strength was very bad due to the difference of the melting temperature and the crystallization temperature exceeding 45 ℃. In comparative examples 2 and 3, the ratio of the content of the solvent extract to the content of ethylene was low, and the intrinsic viscosity of the solvent extract was high, so that the film had high rigidity and poor whitening resistance after oven aging. In comparative example 5, since the difference between the melting temperature and the crystallization temperature was less than 40 ℃, and the content ratio of the solvent extract to ethylene was high, the rigidity of the film was greatly increased, the variation in the heat-seal strength was large, and the impact resistance was not good.

By the polypropylene resin composition according to the examples falling within the scope of the present invention, a molded article, specifically a film, excellent in whitening resistance and heat resistance can be provided. Therefore, the polypropylene resin composition according to the embodiment of the present invention can be effectively applied to the preparation of a heat seal layer film for a food packaging bag or a packaging film for a battery.