Polypropylene resin composition for oriented film and molded article made therefrom

Abstract

The present invention relates to a polypropylene resin composition for an oriented film and a molded article made from the same. The polypropylene resin composition for an oriented film according to an embodiment of the present invention has a wide stretch processing temperature range and excellent stretch processability, and can prepare a film having a low heat sealing temperature and excellent heat resistance and transparency. This film can be effectively used as a food packaging film and an industrial film.

Description

Technical Field

[0001] The present invention relates to a polypropylene resin composition for oriented films and a molded product made thereof. Specifically, the present invention relates to a polypropylene resin composition for heat-seal oriented films having excellent stretching processability, low heat seal initiation temperature (HSIT), excellent heat sealing performance, high heat resistance and high transparency, and a molded product made thereof. Background Art

[0002] Polypropylene resin is a general-purpose resin that is widely used as a material for films, tubes, automotive interior and exterior parts, electrical and home appliance parts, construction and industrial materials, etc. due to its excellent economy, mechanical properties, formability and chemical resistance.

[0003] Among them, uniaxial or biaxial oriented heat-seal polypropylene film has high productivity because it is easy to produce large-area films through the oriented stretching process, and because the polymer chains are oriented along the stretching direction, its mechanical properties are improved compared to cast film, and it can be used for food packaging and industrial packaging purposes.

[0004] This directional stretching process is carried out under specific temperature conditions. If the temperature of the directional stretching process is too low, the polymer chain is difficult to move, resulting in difficulty in orientation during the stretching process, and the low softness makes it impossible to stretch, and the film is prone to rupture. On the contrary, if the temperature of the directional stretching process is too high, the film itself may melt. Therefore, the directional stretching process requires an appropriate processing temperature, and the processing temperature window of each resin will be different.

[0005] Oriented films commonly used as packaging materials need to have low heat sealing temperature (HSIT) and high transparency. Since the heat sealing temperature is usually proportional to the melting temperature, ethylene / propylene / 1-α-olefin terpolymers are mainly used as heat sealing films in polypropylene with a low melting temperature. However, this resin is easy to melt during the stretching process due to its low heat resistance, so it is limited to a narrow temperature range for oriented stretching. In addition, due to its weak rigidity, it is easy to break during the stretching process, and the mechanical properties of the final film are still poor.

[0006] In addition, in order to improve the transparency of the film, polypropylene is mainly mixed with an elastomer having excellent compatibility. However, since the price of the elastomer is more expensive than that of ordinary polypropylene resin, there is a burden of rising costs, and the rigidity and heat resistance of the molded product may be reduced.

[0007] Therefore, there is a need to develop a polypropylene resin composition which has excellent stretching processability due to a wide processing temperature range and has excellent heat resistance and transparency while having a low heat sealing temperature.

[0008] [Prior art literature]

[0009] [Patent Literature]

[0010] (Patent Document 1) U.S. Patent Application Publication No. 2009 / 0087648;

[0011] (Patent Document 2) U.S. Patent Application Publication No. 2013 / 0203931;

[0012] (Patent Document 3) Korean Patent Publication No. 882808. Summary of the invention

[0013] Technical issues

[0014] In view of the above, an object of the present invention is to provide a polypropylene resin composition having excellent stretching processability due to a wide processing temperature range and having excellent heat resistance and transparency while having a low heat sealing temperature.

[0015] Another object of the present invention is to provide a molded article made of the above-mentioned polypropylene resin composition, specifically, to provide an oriented film with a low heat sealing temperature.

[0016] Technical Solution

[0017] To achieve the above object, according to one embodiment of the present invention, the present invention provides a polypropylene resin composition for oriented films, comprising: 90 to 99 weight % of a crystalline ethylene / propylene / 1-α-olefin terpolymer (A); and 1 to 10 weight % of a crystalline propylene homopolymer (B), wherein the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) has an ethylene content of 2.0 to 5.0 weight %, a 1-α-olefin content of 4.0 to 7.0 weight %, and a molten polypropylene homopolymer (B). The propylene content in the crystalline propylene homopolymer (B) is 98 wt % or more, the melting temperature (Tm) is 160 ℃ or more, the crystallization temperature (Tc) is 115 ℃ or more, and the melt index measured at 230 ℃ under a load of 2.16 kg is 2.0 to 10.0 g / 10 min.

[0018] In a specific embodiment of the present invention, the 1-α-olefin in the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) may include one or more selected from 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene.

[0019] In a specific embodiment of the present invention, the polypropylene resin composition for oriented film may further comprise one or more additives (C) selected from antioxidants, neutralizers, antiblocking agents, modifiers, reinforcing agents, fillers, weather stabilizers, antistatic agents, lubricants, slip agents, nucleating agents, flame retardants, pigments and dyes.

[0020] In a specific embodiment of the present invention, the polypropylene resin composition for an oriented film may further comprise 0.05 to 1.0 parts by weight of one or more antioxidants selected from pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and tris(2,4-di-tert-butylphenyl)phosphite, based on 100 parts by weight of the composition.

[0021] In a specific embodiment of the present invention, the polypropylene resin composition for an oriented film may further comprise 0.05 to 1.0 parts by weight of one or more slip agents selected from erucamide, oleamide, stearamide and behenamide, based on 100 parts by weight of the composition.

[0022] In a specific embodiment of the present invention, the polypropylene resin composition for an oriented film may further include 0.05 to 1.0 parts by weight of one or more anti-blocking agents selected from porous silica and zeolite, based on 100 parts by weight of the composition.

[0023] In a specific embodiment of the present invention, the polypropylene resin composition for an oriented film may further include 0.5 to 5 parts by weight of one or more resins selected from polyethylene, elastomers and plastomers, based on 100 parts by weight of the composition.

[0024] In a specific embodiment of the present invention, the polypropylene resin composition for oriented film may have a first melting temperature peak in the range of 130 to 142°C, which is higher than the melting temperature of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A), and a second melting temperature peak or shoulder in the range of 150 to 160°C, and the heat flow of the first melting temperature peak is higher than the heat flow of the second melting temperature peak or shoulder.

[0025] In a specific embodiment of the present invention, the crystallization temperature of the polypropylene resin composition for the oriented film may be higher than the crystallization temperature of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) and be 100° C. or less.

[0026] In a specific embodiment of the present invention, the polypropylene resin composition for an oriented film may have a melt index of 2.5 to 8.0 g / 10 min when measured at 230° C. under a load condition of 2.16 kg.

[0027] According to another embodiment of the present invention, the present invention provides a polypropylene resin molded product produced by molding the polypropylene resin composition for an oriented film.

[0028] In a specific embodiment of the present invention, the polypropylene resin molded article can be used as an industrial film or a food packaging film.

[0029] Beneficial Effects

[0030] The polypropylene resin composition for an oriented film according to an embodiment of the present invention has a wide stretching processing temperature range and excellent stretching processability, and can prepare a film having a low heat sealing temperature and excellent heat resistance and transparency.

[0031] The polypropylene resin molded article according to the embodiment of the present invention can be effectively used as a food packaging film and an industrial film as a uniaxially or biaxially oriented film. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The graph showing the DSC analysis results of the polypropylene resin composition of Example 1 is shown.

[0033] Figure 2 The graph showing the DSC analysis results of the polypropylene resin composition of Example 2 is shown. DETAILED DESCRIPTION

[0034] Hereinafter, the present invention will be described in detail.

[0035] The polypropylene resin composition for an oriented film according to one embodiment of the present invention includes: 90 to 99 wt% of a crystalline ethylene / propylene / 1-α-olefin terpolymer (A); and 1 to 10 wt% of a crystalline propylene homopolymer (B).

[0036] (A) Crystalline ethylene / propylene / 1-α-olefin terpolymer

[0037] The polypropylene resin composition for an oriented film according to one embodiment of the present invention includes a crystalline ethylene / propylene / 1-α-olefin terpolymer (A).

[0038] In the terpolymer (A) of the crystalline ethylene / propylene / 1-α-olefin, the ethylene content is 2.0 to 5.0 weight %, preferably 2.5 to 4.0 weight %. If the ethylene content is less than 2.0 weight %, the crystallization temperature is higher, resulting in a processing temperature suitable for film stretching becoming higher, and the range of the stretchable processing temperature may be narrowed, making the processing difficult. In addition, the heat sealing temperature is higher, and the low-temperature heat sealing property may be reduced. On the contrary, when the ethylene content exceeds 5.0 weight %, the content of the xylene solvent extract becomes higher, which easily causes the stickiness (sticky) problem of the resin, so that it may stick to the reactor or the conveying pipe or the agglomeration (aggregation) between the resins during the preparation of the terpolymer, so that the productivity is reduced, and the die build-up phenomenon may occur during the film processing, and the film produced finally may have a blocking problem of mutual adhesion and difficulty in separation during storage. In addition, the rigidity and heat resistance of the film are relatively low, so it may be easily broken or melted during the stretching process, and the softness of the film is too strong, which may reduce its mechanical properties.

[0039] The 1-α-olefin in the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) may have 4 to 8 carbon atoms. Specifically, the 1-α-olefin may include one or more selected from 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene, preferably 1-butene.

[0040] The content of 1-α-olefin in the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin is 4.0 to 7.0% by weight, preferably 4.5 to 6.0% by weight. If the content of 1-α-olefin is less than 4.0% by weight, the processing temperature suitable for stretching becomes high, the range of the stretchable processing temperature becomes narrower, and the stretch ratio may decrease. In addition, the low-temperature heat sealing properties of the film may decrease. On the contrary, if the content of 1-α-olefin exceeds 7.0% by weight, the rigidity and heat resistance of the film are reduced, resulting in easy rupture during the stretching process, and the mechanical properties of the film may decrease.

[0041] The melting temperature (Tm) of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) is 120° C. to 135° C., preferably 125° C. to 135° C. If the melting temperature is lower than 120° C., the heat resistance of the film is low, the film may melt or break during stretching, and film sticking may occur. If the melting temperature exceeds 135° C., the processing temperature suitable for the stretching process is high, making the processing difficult, and the heat sealing temperature of the film is high, which is not suitable for heat-sealing film.

[0042] The crystallization temperature (Tc) of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) is 85° C. to 100° C., preferably 85° C. to 95° C. If the crystallization temperature is lower than 85° C., the curing speed is slowed down during film processing, which may lead to reduced processability or poor appearance caused by roller marks on the film surface. If the crystallization temperature exceeds 100° C., the processing temperature suitable for the stretching process becomes high, making processing difficult.

[0043] When measured at 230°C under a load of 2.16 kg according to ASTM D1238, the melt index (MI) of the terpolymer (A) of ethylene / propylene / 1-α-olefin is 2.0 to 10.0 g / 10 min. The higher the melt index, the higher the fluidity of the resin composition, but if the melt index exceeds 10.0 g / 10 min, the viscosity is low, resulting in sagging or film rupture during stretching, and the appearance of the film may also deteriorate. On the contrary, if the melt index is lower than 2.0 g / 10 min, the viscosity becomes high, resulting in a higher extrusion load required during film processing, reduced productivity, and poor fluidity, resulting in melt fracture, surging, weaving, necking, etc., which may cause reduced processability and poor appearance.

[0044] The polypropylene resin composition for oriented film according to one embodiment of the present invention comprises: 90 to 99 weight % of a terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin. If the content of the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin is less than 90 weight %, the low temperature heat sealing property deteriorates, the stretchable processing temperature increases, making processing difficult, and the productivity decreases. On the contrary, if the content of the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin exceeds 99 weight %, the heat resistance may decrease, the stretchable processing temperature range becomes narrow, it may be easily broken during the stretching process, making processing difficult, and the rigidity of the film is low and the transparency is reduced.

[0045] As a component of the polypropylene resin composition according to an embodiment of the present invention, the preparation method of the ethylene / propylene / 1-α-olefin terpolymer (A) is not particularly limited, and the preparation method of the polypropylene polymer known in the technical field to which the present invention belongs can be directly used, or used after appropriate improvement.

[0046] For example, bulk polymerization, solution polymerization, slurry polymerization, gas phase polymerization, etc. can be used, and batch or continuous polymerization can be adopted. In addition, these polymerization methods can also be combined, and continuous bulk polymerization and gas phase polymerization are preferred from an economic point of view.

[0047] Specifically, the preparation of the ethylene / propylene / 1-α-olefin terpolymer (A) can utilize Mitsui's Hypol preparation process (consisting of 2 bulk reactors and 1 gas phase reactor in series), Grace's Unipol preparation process (consisting of one or two gas phase reactors), etc., but is not particularly limited to these.

[0048] When the terpolymer (A) of ethylene / propylene / 1-α-olefin is prepared by any of the above-listed preparation methods, ethylene, propylene and 1-α-olefin are supplied to each reactor in desired contents for polymerization, thereby preparing the desired terpolymer (A) of ethylene / propylene / 1-α-olefin. In this case, the melt index of the produced copolymer can be controlled by injecting hydrogen into each reactor.

[0049] In the polymerization process of each reactor, catalysts known in the art can be used without limitation, but Ziegler-Natta catalyst is preferably used. 2 ) etc. and an internal electron donor of phthalates, diethers, succinates, etc. are reacted to prepare a catalyst. Preferably, a co-catalyst and an external electron donor are used here at the same time. As a co-catalyst, an alkyl aluminum compound can be used. Examples of alkyl aluminum compounds include triethyl aluminum, diethyl aluminum chloride, tributyl aluminum, triisobutyl aluminum, trioctyl aluminum, etc., but are not particularly limited thereto. As an external electron donor, an organosilane compound is preferably used. Examples of organosilane compounds include diphenyl dimethoxy silane, phenyl trimethoxy silane, phenyl ethyl dimethoxy silane, phenyl methyl dimethoxy silane, methoxy trimethyl silane, isobutyl trimethoxy silane, diisobutyl dimethoxy silane, diisopropyl dimethoxy silane, di-tert-butyl dimethoxy silane, dicyclopentyl dimethoxy silane, cyclohexyl methyl dimethoxy silane, dicyclohexyl dimethoxy silane, etc., but are not particularly limited thereto.

[0050] (B) Crystalline propylene homopolymer

[0051] The polypropylene resin composition for an oriented film according to one embodiment of the present invention includes: a crystalline propylene homopolymer (B).

[0052] In the crystalline propylene homopolymer (B), the content of propylene is 98 wt% or more. If the content of propylene is less than 98 wt%, the rigidity is low, resulting in the film being elongated or sagging during stretching, which reduces the process stability and the mechanical properties of the film. The crystalline propylene homopolymer (B) may contain less than 2 wt% of a comonomer (e.g., ethylene), and this case should also be understood to be included in the scope of the propylene homopolymer (B) of the present invention.

[0053] The melting temperature of the crystalline propylene homopolymer (B) is 160° C. or higher. If the melting temperature is lower than 160° C., the heat resistance of the film may decrease, and the processing temperature range suitable for the stretching process may be narrowed, resulting in poor processability.

[0054] The crystallization temperature (Tc) of the crystalline propylene homopolymer (B) is 115° C. or higher. If the crystallization temperature is lower than 115° C., the solidification rate of the resin obtained by extrusion during film processing is slow, which may result in reduced processability or poor appearance due to roller marks on the film surface. In addition, the film may melt or break easily during stretching, and the heat resistance of the finally obtained film may be reduced.

[0055] When measured at 230°C under 2.16 kg load conditions according to ASTM D1238, the melt index of the crystalline propylene homopolymer (B) may be 2.0 to 10.0 g / 10 min. If the melt index is less than 2.0 g / 10 min, a higher extrusion load is required during processing, resulting in difficulty in film processing, and poor compatibility with the crystalline ethylene / propylene / 1-α-olefin terpolymer (A), which reduces the fluidity of the resin composition and easily generates a large amount of gel or poor film appearance caused by melt fracture. If the melt index exceeds 10.0 g / 10 min, the viscosity of the resin composition is low, resulting in possible sagging during stretching, and poor compatibility with the crystalline ethylene / propylene / 1-α-olefin terpolymer (A), resulting in uneven film and poor appearance.

[0056] The polypropylene resin composition for oriented film according to one embodiment of the present invention comprises: 1 to 10 wt% of a crystalline propylene homopolymer (B). If the content of the crystalline propylene homopolymer (B) is less than 1 wt%, the heat resistance may be reduced, the stretchable processing temperature range may be narrowed, it may be easily broken during the stretching process, making the processing difficult, and the rigidity of the film is low and the transparency is reduced. On the contrary, if the content of the crystalline propylene homopolymer (B) exceeds 10 wt%, the low-temperature heat sealing property deteriorates, the stretchable processing temperature increases, making the processing difficult, and the productivity decreases.

[0057] As another component of the polypropylene resin composition according to an embodiment of the present invention, the preparation method of the crystalline propylene homopolymer (B) is not particularly limited, and the preparation method of the polypropylene polymer known in the technical field to which the present invention belongs can be directly used or used after appropriate improvement.

[0058] For example, bulk polymerization, solution polymerization, slurry polymerization, gas phase polymerization, etc. can be used, and batch or continuous polymerization can be adopted. In addition, these polymerization methods can also be combined, and continuous bulk polymerization and gas phase polymerization are preferred from an economic point of view.

[0059] Specifically, the preparation of the crystalline propylene homopolymer (B) can utilize the Hypol preparation process of Mitsui Co., Ltd. (composed of two bulk reactors and one gas phase reactor in series), the Unipol preparation process of Grace Co., Ltd. (composed of one or two gas phase reactors), the Spherizone preparation process of Basel Co., Ltd. (composed of a multi-zone circulating reactor (multi-zone circulating reactor; MZCR) and a gas phase reactor in series), the Spheripol preparation process of Basel Co., Ltd. (composed of a ring reactor and a gas phase reactor), etc., but is not particularly limited thereto.

[0060] When the crystalline propylene homopolymer (B) is produced by any of the above-listed production methods, propylene is supplied to each reactor at a desired content to be polymerized, thereby producing the desired crystalline propylene homopolymer (B). In this case, the melt index of the produced copolymer can be controlled by injecting hydrogen into each reactor.

[0061] In the polymerization process of each reactor, catalysts known in the art can be used without limitation, but Ziegler-Natta catalyst is preferably used. 2 ) etc. and an internal electron donor of phthalates, diethers, succinates, etc. are reacted to prepare a catalyst. Preferably, a co-catalyst and an external electron donor are used here at the same time. As a co-catalyst, an alkyl aluminum compound can be used. Examples of alkyl aluminum compounds include triethyl aluminum, diethyl aluminum chloride, tributyl aluminum, triisobutyl aluminum, trioctyl aluminum, etc., but are not particularly limited thereto. As an external electron donor, an organosilane compound is preferably used. Examples of organosilane compounds include diphenyl dimethoxy silane, phenyl trimethoxy silane, phenyl ethyl dimethoxy silane, phenyl methyl dimethoxy silane, methoxy trimethyl silane, isobutyl trimethoxy silane, diisobutyl dimethoxy silane, diisopropyl dimethoxy silane, di-tert-butyl dimethoxy silane, dicyclopentyl dimethoxy silane, cyclohexyl methyl dimethoxy silane, dicyclohexyl dimethoxy silane, etc., but are not particularly limited thereto.

[0062] (C) Additives

[0063] The polypropylene resin composition according to the embodiment of the present invention may further contain conventional additives within the scope of the present invention, for example, one or more additives selected from antioxidants, neutralizers, antiblocking agents, modifiers, reinforcing agents, fillers, weathering stabilizers, antistatic agents, lubricants, slip agents, nucleating agents, flame retardants, pigments and dyes, but is not particularly limited thereto.

[0064] In a specific embodiment of the present invention, the polypropylene resin composition may further include an antioxidant to improve its heat resistance stability. At this time, based on 100 parts by weight of the polypropylene resin composition, the content of the antioxidant can be added as 0.05 to 1.0 parts by weight, preferably 0.05 to 0.3 parts by weight. If the content of the antioxidant is less than 0.05 parts by weight, it is difficult to ensure long-term heat resistance stability. If the content of the antioxidant exceeds 1.0 parts by weight, the heat resistance stability cannot be further improved, and the economic efficiency of the product will be reduced, so it is not preferred.

[0065] As the above-mentioned antioxidant, phenolic antioxidants, phosphite antioxidants, etc. can be used. Specifically, it can include one or more selected from pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and tris(2,4-di-tert-butylphenyl)phosphite, but it is not particularly limited thereto.

[0066] In a specific embodiment of the present invention, the polypropylene resin composition may further include a slip agent to improve its smooth properties. At this time, based on 100 parts by weight of the polypropylene resin composition, the content of the slip agent can be added as 0.05 parts by weight to 1.0 parts by weight, preferably 0.05 parts by weight to 0.8 parts by weight. If the content of the slip agent is less than 0.05 parts by weight, the effect of improving the smooth properties is small, and if the content exceeds 1.0 parts by weight, the smooth properties will not be further improved, and the economic efficiency of the product will be reduced, so it is not preferred.

[0067] The slip agent may include one or more selected from the group consisting of erucamide, oleamide, stearamide, and behenamide, but is not particularly limited thereto.

[0068] In a specific embodiment of the present invention, the polypropylene resin composition may further include an anti-blocking agent to improve its anti-blocking properties. At this time, based on 100 parts by weight of the polypropylene resin composition, the content of the anti-blocking agent can be added as 0.05 to 1.0 parts by weight, preferably 0.05 to 0.8 parts by weight. If the content of the anti-blocking agent is less than 0.05 parts by weight, the effect of improving the anti-blocking properties is small, and if the content exceeds 1.0 parts by weight, the anti-blocking properties will not be further improved, and the economy of the product will be reduced, so it is not preferred.

[0069] The anti-blocking agent may include one or more selected from porous silica and zeolite, but is not particularly limited thereto.

[0070] In a specific embodiment of the present invention, in order to reduce the heat sealing temperature or improve impact resistance and transparency, the polypropylene resin composition may further include 0.5 to 5 parts by weight of one or more resins selected from polyethylene, elastomers and plastomers, based on 100 parts by weight of the polypropylene resin composition.

[0071] In a specific embodiment of the present invention, when the melting temperature of the polypropylene resin composition for oriented film is measured by DSC, it has a first melting temperature peak in the range of 130 to 142°C, which is higher than the melting temperature of the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin, and has a second melting temperature peak or shoulder in the range of 150 to 160°C. If the first melting temperature peak does not appear in the range of 130 to 142°C, the stretching processing temperature range is narrowed, and the heat sealing temperature of the film is increased. In addition, if the second melting temperature peak or shoulder does not appear in the range of 150 to 160°C, the heat resistance is low, resulting in deformation or rupture of the film during high temperature stretching, and the narrowing of the processing temperature range reduces the processability. In addition, the rigidity and heat resistance are low, resulting in the possibility that the mechanical properties of the film may be reduced.

[0072] The first melting temperature of the polypropylene resin composition used for the oriented film is higher than the melting temperature of the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin. If the first melting temperature is less than or equal to the melting temperature of the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin, the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin and the crystalline propylene homopolymer (B) are not mixed sufficiently, so that the uniformity of the resin composition is reduced, the uniformity of the film made therefrom is also reduced, and the heat resistance is low, resulting in the film being easily broken during stretching, the processing temperature range of the film being narrowed and the processability being reduced, and the mechanical properties of the film being reduced. In addition, the terpolymer (A) of crystalline ethylene / propylene / 1-α-olefin and the crystalline propylene homopolymer (B) constituting the resin composition may be oxidized, decomposed, and denatured, which may reduce the heat resistance and mechanical properties of the film.

[0073] In addition, the heat flow of the first melting temperature peak of the polypropylene resin composition for oriented film can be higher than the heat flow of the second melting temperature peak or shoulder peak. When the second melting temperature of the resin composition has a heat flow higher than the first melting temperature, the stretching process requires a higher temperature and thermal energy, so that the processing temperature range is narrowed and the processability is reduced. In addition, as the heat sealing temperature of the film increases or the heat sealing strength decreases, the heat sealing properties may decrease.

[0074] In a specific embodiment of the present invention, the crystallization temperature of the polypropylene resin composition for the oriented film may be higher than the crystallization temperature of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A), and may be 100° C. or less. If the crystallization temperature exceeds 100° C., the stretching processing temperature becomes high and the processable temperature range may become narrow. In addition, it may be easily broken during the stretching process or cause a poor appearance.

[0075] In a specific embodiment of the present invention, when measured at 230°C under a load condition of 2.16 kg, the melt index of the polypropylene resin composition for the oriented film may be 2.5 to 8.0 g / 10 min. If the melt index is less than 2.5 g / 10 min, the viscosity of the resin composition is relatively high, resulting in excessively high extrusion pressure and slow extrusion speed during film processing, which reduces processability and may cause poor processing due to melt fracture, surging, weaving, necking, etc. On the contrary, if the melt index exceeds 8.0 g / 10 min, the melt strength is relatively low, which may cause poor processing due to film sagging during the stretching process.

[0076] The method for preparing the polypropylene resin composition for oriented films according to the embodiment of the present invention is not particularly limited, and a mixing method known in the technical field to which the present invention belongs may be used directly, or may be used after being appropriately improved.

[0077] Specifically, for example, the required amounts of the above-mentioned propylene resin and additives can be added to a kneader, a roll, a Banbury mixer or a single-screw / twin-screw extruder, and then the added raw materials can be kneaded using these machines to prepare the polypropylene resin composition for oriented films of the present invention.

[0078] However, if sufficient mixing is not performed when preparing the polypropylene resin composition for oriented films according to an embodiment of the present invention, the prepared polypropylene resin composition may not meet the above-mentioned melting temperature and melt index conditions. In addition, the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) and the crystalline propylene homopolymer (B) as the respective components of the resin composition may be oxidized, decomposed, and denatured according to the mixing conditions.

[0079] In order to ensure sufficient mixing when preparing the polypropylene resin composition for oriented films according to an embodiment of the present invention, the mixing processing temperature can be increased to completely melt the resin component, or the shear stress applied to the resin composition during mixing can be increased by increasing the extrusion speed, increasing the mesh size, or changing the screw configuration, so as to improve the mixing property. In addition, sufficient mixing can be ensured by repeating the mixing process such as extrusion.

[0080] Furthermore, in order to suppress oxidation, decomposition and denaturation of the ethylene / propylene / 1-α-olefin terpolymer (A) and the crystalline propylene homopolymer (B), the processing temperature is preferably lowered, and the shear stress applied to the resin composition during kneading is preferably reduced.

[0081] Considering these points, the kneading of the polypropylene resin composition for oriented films can be carried out at a temperature range of 200° C. to 250° C. If the melting temperature and crystallization temperature of the prepared resin composition are higher than the above ranges, it is necessary to repeat the kneading process or increase the kneading temperature to improve the kneadability. On the contrary, if the melting temperature and crystallization temperature of the resin composition are lower than the above ranges, it is necessary to lower the kneading temperature, increase the content of the antioxidant, or additionally formulate to inhibit oxidation, decomposition, and denaturation of each component.

[0082] In another embodiment of the present invention, the present invention provides a polypropylene resin molded article, which is produced by molding the polypropylene resin composition of the present invention.

[0083] The method for preparing the molded article using the polypropylene resin composition according to the embodiment of the present invention is not particularly limited, and methods known in the technical field to which the present invention belongs can be used. For example, the polypropylene resin composition according to the embodiment of the present invention can be molded by conventional methods such as tape casting, extrusion molding, injection molding, etc. to prepare a polypropylene resin molded article. Preferably, the polypropylene resin composition can be stretched after tape casting to prepare an oriented film.

[0084] In a specific embodiment of the present invention, the polypropylene resin molded article can be effectively used as an industrial film or a food packaging film.

[0085] [Example]

[0086] The present invention will be described in more detail below by way of examples and comparative examples. However, the following examples are only used to illustrate the present invention, and the scope of the present invention is not limited thereto.

[0087] Examples 1 to 2 and Comparative Examples 1 to 8

[0088] As shown in Table 1, crystalline ethylene / propylene / 1-α-olefin terpolymers having different melt indexes, ethylene and butene contents and crystalline propylene homopolymers having different melt indexes were prepared by bulk polymerization. 100 parts by weight of the polymer thus obtained were mixed with 0.1 parts by weight of a phenolic antioxidant (SONGNOX1010, Songwon Industries, Korea), 0.1 parts by weight of a phosphorus antioxidant (SONGNOX 1680, Songwon Industries, Korea), and 0.04 parts by weight of a neutralizer (DHT 4A, Kyowa Chemical Co., Ltd., Japan), and melt-mixed by a twin-screw extruder at 210° C., thereby preparing a polypropylene resin composition in the form of pellets. The polypropylene resin composition thus obtained was mixed according to the ratios shown in Tables 2 and 3, and then melt-mixed by a twin-screw extruder to obtain a final polypropylene resin composition in the form of pellets. At this time, melt mixing was performed at 210° C., and a 150-mesh (pore size: 89 μm) net was used.

[0089] Each resin composition of Examples 1 and 2 and Comparative Examples 1 to 8 was processed into a biaxially oriented film mainly by two steps and then evaluated. First, a 500 μm thick cast sheet was formed using a research extruder (HAAKE extruder) of Thermo Fisher Scientific, and then a research biaxial stretcher (Ex10-B1) of Toyo Seiki Co., Ltd. was used to process the biaxially oriented film. During the stretching process, the sheet was preheated for 3 minutes at a temperature range of 110 to 140° C., and then stretched 5 times in the longitudinal and transverse directions at a speed of 1 m / min, respectively, to obtain a biaxially oriented film with a thickness of 20 μm. The polypropylene resin composition obtained in each embodiment and comparative example and the biaxially oriented film made therefrom were tested according to the following method.

[0090] Test example

[0091] The polypropylene resin compositions obtained in the examples and comparative examples and the specimens prepared therefrom were tested according to the following methods.

[0092] 1. Melt index

[0093] The melt index of the polypropylene resin or composition is measured at 230° C. and under a load of 2.16 kg according to ASTM D1238.

[0094] 2. Melting temperature (Tm) and crystallization temperature (Tc)

[0095] According to ASTM D3418, using a Q2000 differential scanning calorimetry (DSC) from TA Instrument, the sample was kept at a constant temperature of 200°C for 10 minutes to eliminate the thermal history, and then cooled from 200°C to 30°C at a rate of 10°C per minute to crystallize, and the crystallization temperature was obtained from the peak obtained. In addition, the melting temperature was obtained from the peak obtained by keeping the sample at a constant temperature of 30°C for 10 minutes and then raising the temperature by 10°C per minute.

[0096] 3. Ethylene and butene content (weight %)

[0097] The ethylene content and the butene content were measured using infrared absorption spectroscopy (FT-IR).

[0098] 4. Tensile processability

[0099] In the stretching process, if the film was stretched uniformly, it was marked as ○, and if the film was broken or melted, it was marked as ×.

[0100] 5. Heat sealing temperature (heat sealing initiation temperature; HSIT)

[0101] The film-processed samples were tested according to ASTM-F88. The samples that were not formed into films due to rupture during stretching or were not formed into biaxially oriented films due to poor appearance were omitted. The two films were overlapped and heat-fused. The pressure of the sealing plate was 2 bar and the pressurization time was fixed at 2 seconds.

[0102] 6. Appearance of the membrane

[0103] If a large amount of gel occurs in the film, or if the film appearance is poor due to melt fracture, surging, weaving, or necking, it is marked as ×.

[0104] 7. Haze

[0105] Haze was measured for samples that had been processed into films according to ASTM D1003. However, the test was omitted for samples that were not formed into films due to rupture during stretching or were not normally formed into biaxially oriented films due to poor appearance.

[0106]

Table 1

[0107]

[0108]

Table 2

[0109] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 A1 weight% 95 90 100 85 - A2 weight% - - - - 90 A3 weight% - - - - - A4 weight% - - - - - A5 weight% - - - - - B1 weight% 5 10 - 15 10 B2 weight% - - - - - B3 weight% - - - - - Melt index g / 10min 5.5 5.6 5.5 5.6 1.5 Melting temperature (Tm) ℃ 135 / 157 141 / 158 129 144 / 160 134 / 161 Crystallization temperature (Tc) ℃ 95 100 89 109 102 110℃ tensile processability - ○ ○ ○ × ○ 120℃ tensile processability - ○ ○ ○ × × 130℃ tensile processability - ○ ○ × ○ × 140℃ tensile processability - ○ ○ × ○ × Film appearance - ○ ○ ○ ○ × Heat sealing temperature ℃ 115 118 110 125 - Haze ％ 1.5 1.3 2.1 1.4 -

[0110]

Table 3

[0111]

[0112]

[0113] As can be seen from Table 2 and Table 3 above, Examples 1 and 2 show a first melting temperature in the range of 130-142°C, a second melting temperature in the range of 150-160°C, and Figure 1 and Figure 2 It can be seen that the heat flow of the first melting temperature peak is higher than the heat flow of the shoulder or peak of the second melting temperature. Therefore, it has excellent stretching processability in the range of 110 to 140°C, a wider processing temperature range than other comparative examples, excellent film appearance and heat resistance, and low heat sealing temperature and haze, and is suitable for use in heat-sealing films with excellent transparency.

[0114] In contrast, in Comparative Example 1 using ethylene / propylene / butene terpolymer alone, heat resistance was low, the stretching processing temperature range was narrow, and haze was high with poor transparency. In Comparative Example 2 having a high propylene homopolymer content, the processable temperature range was narrow and the heat sealing temperature was high, resulting in poor low-temperature heat sealing properties.

[0115] In Comparative Example 3, in which the melt index of the ethylene / propylene / butene terpolymer is low, the load of the extruder is large, and the film thickness is uneven during film processing, making the stretching process difficult. In addition, the compatibility with the propylene homopolymer is low, resulting in poor uniformity, so the second melting temperature is as high as 161°C, and the propylene homopolymer aggregates to form a gel, resulting in a poor appearance. In addition, in Comparative Example 4, in which the melt index of the ethylene / propylene / butene terpolymer is high, the film is easily broken during the stretching process, making the preparation and processing of the film difficult.

[0116] In Comparative Example 5, in which the ethylene content in the ethylene / propylene / butene terpolymer is low, and Comparative Example 6, in which the butene content is low, the stretching temperature range is narrow, resulting in poor processability. In addition, the heat sealing temperature of the film is high, the haze is high, and the transparency is poor, so it is not suitable for film use.

[0117] In Comparative Example 7, in which the melt index of the propylene homopolymer is low, the compatibility is low and the uniformity is reduced, so the second melting temperature is as high as 162° C. Due to such low compatibility, the stretching processability is deteriorated, and a poor appearance such as fish eyes occurs. In addition, in Comparative Example 8, in which the melt index of the propylene homopolymer is high, the stretching processability is also poor.

[0118] The polypropylene resin composition according to the embodiment of the present invention has a wide stretching temperature range and excellent stretching processability, and can prepare a film with a low heat sealing temperature and excellent heat resistance and transparency. Therefore, the oriented film prepared therefrom can be effectively used as an industrial film or a food packaging film.

Claims

1. A polypropylene resin composition for an oriented film, comprising: 90 to 99 wt% of a crystalline ethylene / propylene / 1-α-olefin terpolymer (A), wherein the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) has an ethylene content of 2.0 to 5.0 wt%, a 1-α-olefin content of 4.0 to 7.0 wt%, a melting temperature (Tm) of 120 to 135° C., a crystallization temperature (Tc) of 85 to 100° C., and a melt index of 2.0 to 10.0 g / 10 min at 230° C. under a load of 2.16 kg; and 1 to 10 wt% of a crystalline propylene homopolymer (B), the propylene content in the crystalline propylene homopolymer (B) is 98 wt% or more, the melting temperature (Tm) is 160°C or more, the crystallization temperature (Tc) is 115°C or more, and the melt index measured at 230°C under a load of 2.16 kg is 2.0 to 10.0 g / 10 min.

2. The polypropylene resin composition for oriented films according to claim 1, wherein The 1-α-olefin in the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) comprises one or more selected from 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene.

3. The polypropylene resin composition for oriented films according to claim 1, wherein It also contains one or more additives (C) selected from antioxidants, neutralizers, antiblocking agents, modifiers, reinforcing agents, fillers, weathering stabilizers, antistatic agents, lubricants, slip agents, nucleating agents, flame retardants, pigments and dyes.

4. The polypropylene resin composition for oriented films according to claim 3, wherein Based on 100 parts by weight of the composition, the composition further comprises 0.05 to 1.0 parts by weight of one or more antioxidants selected from pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene and tris(2,4-di-tert-butylphenyl)phosphite.

5. The polypropylene resin composition for oriented films according to claim 3, wherein The composition further comprises 0.05 to 1.0 parts by weight of one or more slip agents selected from erucamide, oleamide, stearamide and behenamide, based on 100 parts by weight of the composition.

6. The polypropylene resin composition for oriented films according to claim 3, wherein The composition further comprises 0.05 to 1.0 parts by weight of one or more anti-blocking agents selected from porous silica and zeolite, based on 100 parts by weight of the composition.

7. The polypropylene resin composition for oriented films according to claim 3, wherein The composition further comprises 0.5 to 5 parts by weight of one or more resins selected from polyethylene, elastomers and plastomers, based on 100 parts by weight of the composition.

8. The polypropylene resin composition for oriented films according to claim 1, wherein It has a first melting temperature peak in the range of 130 to 142°C that is higher than the melting temperature of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A), a second melting temperature peak or shoulder in the range of 150 to 160°C, and the heat flow of the first melting temperature peak is higher than the heat flow of the second melting temperature peak or shoulder.

9. The polypropylene resin composition for oriented films according to claim 1, wherein The crystallization temperature of the polypropylene resin composition for an oriented film is higher than the crystallization temperature of the crystalline ethylene / propylene / 1-α-olefin terpolymer (A) and is 100° C. or less.

10. The polypropylene resin composition for oriented films according to claim 1, wherein The melt index measured at 230°C under a load of 2.16 kg is 2.5 to 8.0 g / 10 min. 11 . A polypropylene resin molded article produced by molding the polypropylene resin composition according to claim 1 .

12. The polypropylene resin molded article according to claim 11, which is used as an industrial film or a food packaging film.

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