KR20210067559A - Method for preparing polypropylene resin with improved melt strength, polypropylene and foam using thereof - Google Patents

Abstract

The present invention relates to a method for preparing a polypropylene resin having a low gel content and an excellent strain hardening index by increasing the proportion of polypropylene having a long-chain branch. The method for preparing a polypropylene resin in the presence of a metallocene catalyst includes the steps of: a first polymerization step of reacting propylene monomers in the absence of hydrogen to produce first polypropylene; a second polymerization step of introducing a diene compound to the effluent of the first polymerization step and carrying out reaction thereof to prepare second polypropylene; and a third polymerization step of introducing hydrogen to the effluent of the second polymerization step and carrying out reaction to prepare third polypropylene.

Description

Method for producing polypropylene resin with excellent melt strength, polypropylene resin and foam thereof {METHOD FOR PREPARING POLYPROPYLENE RESIN WITH IMPROVED MELT STRENGTH, POLYPROPYLENE AND FOAM USING THEREOF}

The present invention relates to a method for producing a polypropylene resin excellent in melt strength by increasing the proportion of polypropylene having long chain branching, a polypropylene resin excellent in melt strength, and a foam made of the polypropylene resin.

Polypropylene (PP) is attracting attention as a lightweight material because its molecular structure consists of only carbon and hydrogen, and it is easy to recycle and has a low density. On the other hand, in order to be used in the automobile and electronic industries, technologies such as foaming, thermoforming, and blow molding are mainly required. However, polypropylene has a linear branching structure and narrow molecular weight distribution, so the melt properties of the melt are not good, so there is a limit to be used for the above purposes.

In order to improve the melting properties of polypropylene, it is preferable to have a long chain branched (LCB) polymer chain in the polypropylene main chain. As a technique for adding a long chain branch to the polypropylene main chain, methods such as blending, solid phase reaction, reaction extrusion, and electron beam irradiation have been reported.

Conventionally, a long-chain branch has been formed in polypropylene by polymerizing polypropylene by applying a constant temperature and pressure to a reactant of propylene, a diene compound, and hydrogen (H _{2 ) using a metallocene catalyst.}

For example, Korea Patent No. 1859286 discloses a method for producing a diene-modified polypropylene structure including uniform long-chain branching in a continuous process using a metallocene catalyst. In the technology disclosed in the patent, a reactant containing a propylene monomer is put into a reactor to prepolymerize the polypropylene main chain under a metallocene catalyst, and after raising the temperature of the reactor, a diene compound is injected and reacted in divided injection and reaction to the polypropylene main chain. To prepare a diene-modified polypropylene resin by forming a long chain branch. However, although the prepared polypropylene resin has a high melt tension, it generates a large amount of gel, which presents a problem of poor processability.

Korean Patent Application Laid-Open No. 2018-0150791 discloses that, in order to solve the above problem, homopolypropylene is synthesized in the first reaction and then a diene compound is added to the secondary reaction. Disclosed is a technology for producing polypropylene with high tensile strength. However, in the technique disclosed in the above patent, the weight ratio of the secondary reaction product is limited due to the weight ratio of homopolypropylene inevitably involved in the primary reaction. For this reason, although the gel generation, melt elongation rate, melt strength, etc. are excellent, there are problems such as a difference in molecular weight distribution, a relatively high melt index, and a difference in foaming power.

The present invention aims to improve melt properties as well as keep the gel content low by synthesizing polypropylene in stages. In this case, polypropylene has properties similar to conventional ones in melt strength and melt elongation, while having a low melt index to simultaneously impart properties to improve processability and foaming performance.

In one aspect, the present invention provides a method for preparing a polypropylene resin in the presence of a metallocene catalyst, comprising: a first polymerization step of polymerizing a first polypropylene by reacting a propylene monomer in the absence of hydrogen; a second polymerization step of polymerizing a second polypropylene by adding and reacting a diene compound to the effluent of the first polymerization step; and a third polymerization step of polymerizing a third polypropylene by adding hydrogen to the effluent of the second polymerization step and reacting.

In another aspect, the present invention provides a polypropylene resin prepared in the presence of a metallocene catalyst, comprising: 1 to 29% by weight of homopolypropylene; 1 to 29% by weight of a second polypropylene having a weight average molecular weight greater than 1×10 ^{6 g/mol;} and a third polypropylene having a weight average molecular weight of 1×10 ⁶ g/mol or less as a balance.

According to the present invention, by synthesizing polypropylene in stages by weight ratio, the gel content can be kept low, and the melt properties can be improved. Furthermore, melt strength or melt elongation is maintained similar to that of conventional polypropylene and has a low melt index, thereby improving processability and foaming performance.

1 is a graph showing the result of measuring the elongation viscosity according to the elongation rate of polypropylene obtained in Examples 2 and 1 to 3 and the work hardening index results obtained therefrom.

Hereinafter, the present invention will be specifically described. However, the present invention can be modified in various embodiments, and is not limited to the following embodiments.

The present invention provides a method for stepwise polymerization of polypropylene. Specifically, the polymerization is divided into a pre-polymerization step that does not contain hydrogen and a main polymerization step that includes hydrogen.

In the present invention, a hydrogen-free prepolymerization step is included. The prepolymerization step is a first polymerization step of polymerizing the first polypropylene by carrying out under conditions containing the propylene monomer alone, and a second polypropylene having long chain branching by performing under conditions including the propylene monomer and the diene compound A second polymerization step of polymerization may be included.

As the prepolymerization step, a first polymerization step of polymerizing polypropylene by reacting a propylene monomer in the absence of hydrogen is performed. As described above, by polymerizing polypropylene in the absence of hydrogen, gel formation in the polymer can be suppressed, low molecular weight polypropylene can be produced, and a polypropylene resin with a wide molecular weight distribution can be obtained.

The first polymerization step is performed in the presence of a catalyst, and the catalyst uses a metallocene catalyst. As the metallocene catalyst, it is preferable to use a catalyst including at least one transition metal compound of Formula 1 and Formula 2 below.

In Formula 1 and Formula 2,

M ¹ and M ² are each independently a group 3 to 10 element on the periodic table,

X ¹ and X ² are each independently, (C ₁ -C ₂₀ )alkyl group, (C ₁ -C ₂₀ )cycloalkyl group, (C ₁ -C ₂₀ )alkylsilyl group, silyl (C ₁ -C ₂₀ )alkyl group; (C ₆ -C ₂₀ )aryl group, (C ₆ -C ₂₀ )aryl (C ₁ -C ₂₀ )alkyl group, (C ₁ -C ₂₀ )alkyl(C ₆ -C ₂₀ )aryl group, (C ₆ -C ₂₀ ) an arylsilyl group, a silyl (C ₆ -C ₂₀ )aryl group; (C ₁ -C ₂₀ )alkoxy group, (C ₁ -C ₂₀ )alkylsiloxy group; (C ₆ -C ₂₀ )aryloxy group; halogen group; or an amine group,

Ar ¹ and Ar ² and Ar ³ and Ar ⁴ may be the same as or different from each other, and are each independently a ligand having any one skeleton of cyclopentadienyl, methylcyclopentadienyl, dimethylcyclopentathienyl, and indenyl; ,

Further, m and n are each independently an integer of 1 to 5,

B is selected from carbon, silicon, germanium, nitrogen and phosphorus,

L is hydrogen, (C ₁ -C ₂₀ )alkyl group, cyclo(C ₁ -C ₂₀ )alkyl group, (C ₁ -C ₂₀ )alkylsilyl group, silyl (C ₁ -C ₂₀ )alkyl group, (C ₆ -C _{20 )} ) aryl group, (C ₆ -C ₂₀ )aryl (C ₁ -C ₂₀ )alkyl group, (C ₁ -C ₂₀ )alkyl (C ₆ -C ₂₀ )aryl group, (C ₆ -C ₂₀ )arylsilyl group or Silyl (C ₆ -C ₂₀ ) It is an aryl group,

p is an integer of 1 or 2.

As used herein, the term “alkyl” refers to a monovalent straight or branched saturated hydrocarbon radical composed of only carbon and hydrogen atoms, and examples of such alkyl radicals include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, hexyl, octyl, dodecyl, and the like.

In addition, as used herein, the term "cycloalkyl" refers to a monovalent alicyclic alkyl radical composed of one ring, and examples of cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl. , cyclononyl, cyclodecyl, and the like.

In addition, as used herein, the term "alkenyl" refers to a straight-chain or branched hydrocarbon radical containing one or more carbon-carbon double bonds, and includes ethenyl, propenyl, butenyl, pentenyl, and the like, However, the present invention is not limited thereto.

In addition, the term "aryl" described in the present invention is an organic radical derived from an aromatic hydrocarbon by removal of one hydrogen, and includes a single or fused ring system. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, fluorenyl, phenanthryl, triphenylenyl, pyrenyl, peryleneyl, chrysenyl, naphthacenyl, fluoranthenyl, and the like.

In addition, as used herein, the term “alkoxy” refers to an —O-alkyl radical, where “alkyl” is as defined above. Examples of such alkoxy radicals include, but are not limited to, methoxy, ethoxy, isopropoxy, butoxy, isobutoxy, t-butoxy, and the like.

In addition, as used herein, the term "aryloxy" refers to an -O-aryl radical, where 'aryl' is as defined above. Examples of such aryloxy radicals include, but are not limited to, phenoxy, biphenoxy, naphthoxy, and the like.

In addition, the term "halogen" described in the present invention means a fluorine, chlorine, bromine or iodine atom.

In the present invention, the transition metal compound as represented by Formula 1 or 2 is a polypropylene resin capable of high melt strength and molecular weight, uniform composition distribution and long chain branching structure control with excellent catalytic activity and copolymerizability. make manufacturing possible.

In one embodiment of the present invention, the transition metal compound may be selected from compounds of the following structures, but is not limited thereto.

In the compound of the above structure, Cp is indenyl, cyclopentadienyl, methylcyclopentadienyl, dimethylcyclopentathienyl, diisopropylcyclopentadienyl, trimethylcyclopentadienyl or tetramethylcyclopentadienyl; ; M ¹ is tetravalent titanium, zirconium or hafnium; X ¹ is chloro, fluoro, bromo, methyl, ethyl, propyl, butyl, pentyl, methoxy, ethoxy, propoxy, butoxy or dimethylamino.

In the present invention, the transition metal compound includes, as exemplarily shown above, a cyclopentadiene derivative ligand connected to each other by a bridge group of silicone or alkenylene and an indenyl derivative ligand in which an aryl is necessarily substituted at the 4th position. It is preferable to have an ansa-metallocene structure.

As such, the transition metal compound has an indene derivative ligand in which an aryl is substituted at the 4th position, and thus has higher catalytic activity and copolymerizability than the transition metal compound having an unsubstituted ligand at the 4th position of the indene. It enables the production of polypropylene resins capable of controlling melt strength and molecular weight, uniform composition distribution, and long chain branching structure.

On the other hand, the transition metal compound of Formula 1 or 2 can act as a counterion with weak binding force, that is, an anion while cationizing the central metal by extracting the ligand in the transition metal compound to become an active catalyst component used for polypropylene polymerization. Compounds represented by the formulas 3 to 5 in which they act together as a co-catalyst.

In Formula 3, Al is aluminum, O is oxygen, Ra is a halogen group or a (C ₁ -C ₂₀ )hydrocarbyl group substituted or unsubstituted with a halogen group, and q is an integer of 2 or more.

In Formula 4, Q is aluminum or boron, Rb is the same as or different from each other, and each independently represents a halogen group or a (C ₁ -C ₂₀ )hydrocarbyl group unsubstituted or substituted with a halogen group.

In Formula 5, [W] ⁺ is a cationic Lewis acid or a cationic Lewis acid to which a hydrogen atom is bonded, Z is a group 13 element, Rc is the same as or different from each other, and each independently a halogen group, (C ₁ -C _{20 ) a (C 6} -C ₂₀ )aryl group substituted with one or two or more substituents selected from the group consisting of a hydrocarbyl group, an alkoxy group and a phenoxy group; A halogen group, (C ₁ -C _{20 ) A (C 1} -C ₂₀ )alkyl group substituted with one or two or more substituents selected from the group consisting of a hydrocarbyl group, an alkoxy group and a phenoxy group.

The promoter compound is included in the catalyst composition together with the transition metal compound represented by Formula 1 or 2 to activate the transition metal compound. Specifically, in order for the transition metal compound to become an active catalyst component used in olefin polymerization, a ligand in the transition metal compound is extracted to cationize the central metal (M) while acting as a counterion having weak binding force, that is, an anion. The compound including the unit represented by Formula 3, the compound represented by Formula 4, and the compound represented by Formula 6 act together as a cocatalyst.

The 'unit' represented by Formula 3 is a structure in which n structures in [ ] are connected in the compound, and if the unit represented by Formula 3 is included, other structures in the compound are not particularly limited, and the repeating unit of Formula 3 may be a cluster type, such as a spherical compound, linked to each other.

The compound including the unit represented by the formula (3) is not particularly limited, and is preferably an alkylaluminoxane. Non-limiting examples include methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, butylaluminoxane, and the like. Considering the activity of the transition metal compound, methylaluminoxane may be preferably used.

In addition, the compound represented by Formula 4 is not particularly limited as an alkyl metal compound, and non-limiting examples thereof include trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylchloroaluminum, and trimethylaluminum. Isopropylaluminum, tri-s-butylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, trihexylaluminum, trioctylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, tri-p- tolyl aluminum, dimethyl aluminum methoxide, dimethyl aluminum ethoxide, trimethyl boron, triethyl boron, triisobutyl boron, tripropyl boron, tributyl boron, and the like. Considering the activity of the transition metal compound, one or more selected from the group consisting of trimethylaluminum, triethylaluminum and triisobutylaluminum may be preferably used.

When considering the activity of the transition metal compound, the compound represented by Formula 5 is a ^{dimethylanilinium cation when [W] +} is a cationic Lewis acid to which a hydrogen atom is bonded, and [W] ⁺ is a cationic Lewis acid, [ (C ₆ H ₅ ) ₃ C] ⁺ , and [Z(Rc) ₄ ] ^- is [B(C ₆ F ₅ ) ₄ ] ^- , and may be preferably used.

The compound represented by Formula 5 is not particularly limited, but ^{non-limiting examples of the case where [W] +} is a cationic Lewis acid to which a hydrogen atom is bonded include triethylammonium tetrakisphenylborate, tributylammoniumtetrakisphenylborate, trimethyl Ammonium tetrakisphenylborate, tripropylammonium tetrakisphenylborate, trimethylammonium tetrakis(p-tolyl)borate, tripropylammonium tetrakis(p-tolyl)borate, trimethylammonium tetrakis(o,p -Dimethylphenyl)borate, triethylammonium tetrakis(o,p-dimethylphenyl)borate, tributylammonium tetrakis(p-trifluoromethylphenyl)borate, trimethylammonium tetrakis(p-trifluoromethylphenyl) ) borate, tributylammonium tetrakispentafluorophenylborate, anilinium tetrakisphenylborate, anilinium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluoro Phenyl) borate, N,N-diethylaniliniumtetrakispetylborate, N,N-diethylaniliniumtetrakisphenylborate, N,N-diethylaniliniumtetrakispentafluorophenylborate, di Ethylammonium tetrakispentafluorophenylborate, triphenylphosphoniumtetrakisphenylborate, trimethylphosphoniumtetrakisphenylborate, triphenylcarboniumtetrakis(p-trifluoromethylphenyl)borate, triphenylcarbonium tetrakispentafluorophenylborate, dimethylaniliniumtetrakis(pentafluorophenyl)borate, and the like.

The addition amount of the promoter compound may be determined in consideration of the addition amount of the transition metal compound represented by Formula 1 or 2 and the amount required to sufficiently activate the promoter compound. The content of the promoter compound may be 1:1 to 100,000 based on the molar ratio of the metal contained in the promoter compound to 1 mole of the transition metal contained in the transition metal compound represented by Formula 1 or 2, preferably preferably 1:1 to 10,000, more preferably 1:1 to 5,000.

More specifically, the compound represented by Formula 3 is preferably 1:10 to 5,000 molar ratio, more preferably 1:50 to 1,000 molar ratio, most preferably to the transition metal compound represented by Formula 1 or 2, most preferably It may be included in a molar ratio of 1:100 to 1,000. When the molar ratio of the compound represented by Formula 3 to the transition metal compound of Formula 1 or 2 is less than 1:10, the amount of aluminoxane is very small, so that the activation of the metal compound may not proceed completely, 1 : In the case of exceeding 5,000, excess aluminoxane acts as a catalyst poison and may play a role in preventing the growth of polymer chains.

In addition, when Q is boron in the promoter compound represented by Formula 4, 1:1 to 100, preferably 1:1 to 10, more preferably, with respect to the transition metal compound represented by Formula 1 or 2 may be supported in a molar ratio of 1:1 to 3. In addition, when Q is aluminum in the promoter compound represented by Formula 4, it may vary depending on the amount of water in the polymerization system, but 1:1 to 1000, preferably with respect to the transition metal compound represented by Formula 1 or 2 may be supported in a molar ratio of 1:1 to 500, more preferably 1:1 to 100.

In addition, the promoter compound represented by Formula 5 is 1:1 to 100, preferably 1:1 to 10, more preferably 1:1 to 4 with respect to the transition metal compound represented by Formula 1 or 2 It may be supported in a molar ratio. When the ratio of the cocatalyst compound represented by Formula 5 is less than 1:1, the amount of the activator is relatively small, so that the metal compound cannot be completely activated, so there may be a problem in that the activity of the resulting catalyst composition decreases, 1 If it exceeds: 100, the metal compound is completely activated, but there may be a problem in that the unit price of the catalyst composition is not economical or the purity of the resulting polymer is lowered with the remaining excess activator.

Since the catalyst composition presented in the present invention exists in a uniform form in the polymerization reactor, it can be applied to a solution polymerization process carried out at a temperature higher than the melting point of the polymer. However, as disclosed in U.S. Patent No. 4,752,597, the heterogeneous catalyst composition obtained by supporting the transition metal catalyst and the cocatalyst on a porous metal oxide support may be used for slurry polymerization or gas phase polymerization. Therefore, when the catalyst composition of the present invention is used together with an inorganic carrier or an organic polymer carrier, it can be applied to a slurry or gas phase process. That is, the transition metal compound and the cocatalyst compound may be used in a form supported on an inorganic carrier or an organic polymer carrier.

In performing the first polymerization step, the propylene monomer and the catalyst are added to the reactor, and if necessary, a scavenger for removing moisture present in the reactor may be added together. In this case, the total amount of the propylene monomer required to obtain the desired polypropylene resin is added as the content of the propylene monomer to the first polymerization step. However, when the comonomer is added in the first polymerization step, a gel may be formed, and it is more preferable that the comonomer is not included in the first polymerization step.

Although not intended to be particularly limited, the first polymerization step may be performed at 50 to 80° C., for example, at 70° C., under a pressure of 20 to 40 bar, for example 30 bar, for 1 to 10 minutes.

In the first polymerization step, it may be produced in an amount of 1 to 29% by weight, preferably 5 to 20% by weight of the polypropylene to be finally obtained. When the content of the polypropylene produced in the first polymerization step is less than 1 wt%, the low molecular weight polypropylene may cause problems in molecular weight distribution characteristics and flowability, and this may deteriorate foamability, and 29 wt% If it exceeds, the content of polypropylene having no long-chain branching is excessively increased, and the melt strength of the finally produced polypropylene resin may be reduced.

The content of such polypropylene can be controlled by controlling the reaction time of the first polymerization step among the total polymerization reaction time. For example, the reaction time of the first polymerization step may be performed for 1 to 30% of the total reaction time.

After the first polymerization step, a second polymerization step is performed. The second polymerization step is to obtain a second polypropylene, and can form long-chain branches in a part of the first polypropylene produced in the first polymerization step, and polypropylene having long-chain branches in the second polymerization step can get

In the second polymerization step, in the presence of the catalyst composition as described above and in the absence of hydrogen, a diene compound is added to the effluent comprising the propylene polymer obtained in the first polymerization step and unreacted propylene monomer to obtain a second polypropylene to carry out the polymerization reaction of

As such, when the second polymerization step is performed under conditions that do not contain hydrogen, the number of carbon atoms of long chain branches formed in the polypropylene main chain can be increased, compared to when the polymerization reaction is performed in the presence of hydrogen. Polypropylene having long long chain branches can be prepared. Accordingly, in the second polymerization step, polypropylene having a weight average molecular weight exceeding ^{1×10 6 g/mol can be obtained.}

As such, by forming long-chain branches having more carbon atoms in the main chain, the melt index (MI) of the polypropylene resin can be reduced, and the weight average molecular weight (Mw), viscosity average molecular weight, molecular weight distribution, etc. can be improved. , it can also improve the foaming performance.

The diene compounds may be at least one selected from an aromatic compound-diene of the aliphatic diene-based compound, and (C ₄ ~ C ₂₀₎ of (C ₄ ~ C _20), for example 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene, 1 ,11-dodecadiene, 1,8-ethylidene, norbornene, dicyclopentadiene, norbornadiene, 4-vinyl-1-cyclohexene, 3-vinyl-1-cyclohexene, 2-vinyl- and a compound selected from the group consisting of 1-cyclohexene, 1-vinyl-1-cyclohexene, o-divinylbenzene, p-divinylbenzene and m-divinylbenzene, which may be used alone or in combination of two or more can be used by

In this case, the diene compound may be added in an amount of 0.0001 to 5 parts by weight based on 100 parts by weight of the unreacted propylene monomer. If it is out of the above content, it may exhibit undesirable properties in terms of improving melt strength. For example, when the diene compound is used in an amount less than the above range, melt strength is not sufficiently expressed, and when the diene compound is used in an excess amount exceeding the above range, a large amount of gel may be generated.

Furthermore, in the second polymerization step, if necessary, a comonomer may be additionally added. The comonomer is not particularly limited, but for example, ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-unde It may be at least one selected from the group consisting of cene and 1-dodecene.

The comonomer may be added in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the unreacted propylene monomer. When the content of the comonomer is used less than the above range, there is no improvement in processability, and when used in excess of the above range, undesirable changes in physical properties may occur.

The second polymerization step may be performed under the same reaction conditions as described in the first polymerization step.

As such, the second polymerization step may be generated in an amount of 1 to 29% by weight, preferably 10 to 25% by weight, based on the total weight of the polypropylene to be obtained. If the content of the second polypropylene produced in the second polymerization step is less than 1% by weight, the content of polypropylene including long chain branches is insufficient, so that the molecular weight is small and the melt index (MI) is high, so that the melt strength may be lowered. have. On the other hand, when it exceeds 29% by weight, the gel content increases, the uniformity of physical properties is deteriorated due to the gel, and it may cause a decrease in workability during foaming.

The content of the second polypropylene produced in the second polymerization step may be controlled by controlling the reaction time of the second polymerization step among the total reaction time. For example, the reaction time of the second polymerization step may be performed for 1% or more and less than 30% of the total reaction time.

In this way, by performing the first and second polymerization steps in the absence of hydrogen, gel formation can be suppressed, a polypropylene resin having a broad molecular weight distribution can be obtained, and further, by facilitating the growth of long-chain branches, a longer It is possible to manufacture polypropylene having long chain branching, thereby improving the melting properties of the polypropylene resin.

The sum of the polypropylene produced in the first and second polymerization steps is preferably 2 to 30% by weight based on the total weight of the polypropylene. If it exceeds 30% by weight, the amount of propylene monomer consumed in the first and second polymerization steps is excessive, and there is a problem that the content of the propylene monomer to be reacted in the main polymerization may be insufficient, and polypropylene is produced excessively in the first polymerization step When the melt index (MI) is increased, the melt strength is lowered, and if polypropylene is excessively produced in the second polymerization step, it may cause a problem in that the amount of gel is increased.

Next, the present invention includes a third polymerization step of polymerizing a third polypropylene under conditions containing hydrogen as the main polymerization reaction after performing the pre-polymerization reaction in the absence of hydrogen as described above. In the polymerization of the third polypropylene, when hydrogen is included, the growth of long-chain branches is hindered, but the yield of the final product can be increased.

In the third polymerization step, a polymerization reaction is performed by introducing hydrogen in the presence of an effluent including the reaction product obtained in the prepolymerization step, unreacted propylene monomer, and unreacted diene compound.

The amount of hydrogen added is not limited thereto, but may be added in an amount of 0.001 to 0.1 wt% based on the content of unreacted propylene monomer. If the amount of hydrogen added is less than 0.001% by weight, polymerization of polypropylene is low due to low activity, and when it exceeds 0.1% by weight, a lot of polypropylene having short chain branching is generated, thereby increasing the melt index.

Furthermore, in the third polymerization step, if necessary, a comonomer may be additionally added. The comonomer may be the same as described above, and may be added in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the unreacted propylene monomer.

In this third polymerization step, a third polypropylene having a long chain branch in the main chain of the polypropylene can be obtained. The long-chain branch formed in the main chain of the third polypropylene has less carbon number than the long-chain branch formed in the main chain of the second polypropylene, and in the third polymerization step, a weight average molecular weight of 1×10 ⁶ g/mol or less is a third polypropylene can be obtained.

The third polymerization step is not particularly limited, but may be performed under the same reaction conditions as the prepolymerization step.

In the third polymerization step, polypropylene having long-chain branching can be obtained by performing the remaining reaction with respect to the unreacted propylene monomer present in the presence of hydrogen and a diene compound. The polypropylene produced in the third polymerization step preferably accounts for 70% or more of the total polypropylene weight.

In the present invention, the first, second, and third polymerization steps as described above may be performed in the same reactor or may be performed in different reactors. Specifically, after performing the first polymerization step in one reactor, a diene compound may be added to the reactor to perform a second polymerization step, and then hydrogen may be added to perform a third polymerization step.

Furthermore, the first reaction step is performed in the first reactor, the polypropylene and unreacted material produced thereby are supplied to the second reactor, and a diene compound and optionally a comonomer are introduced into the second reactor to the second A polymerization step may be performed, and then, hydrogen and optionally a comonomer may be introduced into the third reactor to perform a third reaction. In this case, the first to third reactors may be batch reactors, and may also be loop-type continuous reactors.

According to the method of the present invention as described above, it is divided into a pre-polymerization step of performing polymerization of polypropylene under hydrogen-free conditions and a main polymerization step of performing polymerization of polypropylene under hydrogen-containing conditions. the polypropylene, the weight average molecular weight of 1 × 10 ⁶ g / mol greater than a second polyester having a weight average molecular weight of 1 × 10 parts propylene and the balance ⁶ g / mol or less third polypropylene it is possible to obtain the polypropylene resin mixture.

As such, according to the present invention, a polypropylene resin in which three types of propylene polymers are mixed can be obtained, and the polypropylene resin obtained thereby has a gel content of 5% by weight or less, a work hardening index of 4.0 or more, For example, it has excellent properties in the range of 4.0 to 8.0. In addition, the polypropylene resin according to the present invention has a melt index of 1 to 5 g/10 min (2.16 kg, 230° C.) suitable for foaming and _{a maximum melt tension of 15 to 30 g f} , and exhibits excellent melt elongation.

Furthermore, when a foam is manufactured using the polypropylene resin according to the present invention, the foam has a density of 0.3 g/cm 3 or less after foaming, thereby exhibiting a high foaming rate.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples specifically show an example of carrying out the present invention, and are not intended to limit the present invention by the following examples.

[Preparation of supported catalyst]

Dimethylsilyl bis(2-methyl-4-butylphenylindenyl)zirconium dichloride (S-PCI) was used as a transition metal compound.

All synthesis reactions were carried out in an inert atmosphere such as nitrogen or argon, and standard Schlenk technology and glove box technology were used.

Toluene was used after further drying by passing Anhydrous Grade (Sigma-Aldrich) through an activated molecular sieve (Molecular Sieve, 4A) or an activated alumina layer. A 10% toluene solution (HS-MAO-10%) (Albemarle) was purchased for MAO (methylaluminoxane) as a co-catalyst, and the calcined silica was used without further treatment. In addition, the catalyst compounds used in Examples and Comparative Examples were used without further purification.

In a glove box, 2.0 g of silica (XPO-2412 manufactured by Grace) was placed in a Schlenk flask (100 ml) in a glove box, and 10 ml of anhydrous toluene solution was added thereto. Here, about 10.2 ml of methylaluminoxane (10% by weight solution of methylaluminoxane in toluene, 15 mmol based on Al, manufactured by Grace) was slowly added dropwise at 10° C., followed by stirring at 0° C. for about 1 hour. After that, the temperature was raised to 70 °C, stirred for 3 hours, and cooled to 25 °C.

Separately, the synthesized catalyst compound (100 μmol) in the glove box was placed in another 100 ml Schlenk flask, taken out of the glove box, and then 10 ml of anhydrous toluene solution was added. Here, the solution containing the transition metal compound at 10 ℃ was slowly added to the solution containing silica and methylaluminoxane, the temperature was raised to 70 ℃ and stirred for 1 hour, then cooled to 25 ℃ and further stirred for about 24 hours did.

Thereafter, the obtained reaction product was washed with sufficient amounts of toluene and hexane to remove unreacted aluminum compounds, and dried under vacuum to obtain a supported catalyst.

Example One

The inside of a stainless steel autoclave having an internal capacity of 3L was completely replaced with nitrogen.

2 mmol of triisobutylaluminum (manufactured by Aldrich) and 50 mg of the prepared transition metal compound-supported catalyst were introduced into the reactor.

Thereafter, 500 g of propylene (PL) was added into the reactor, the temperature was raised to 70° C., and the pressure in the reactor was adjusted to 31.5 bar to perform a polymerization reaction for 10 minutes at a constant temperature and pressure (first polymerization step).

After the first polymerization step, 3 ml of diene was put into the reactor to perform a polymerization reaction for 10 minutes (second polymerization step).

After the first polymerization step, 10 mg of hydrogen was added to the reactor, and the polymerization reaction was performed for 60 minutes (third polymerization step).

After performing the third polymerization step, the temperature was lowered to room temperature to terminate the reaction, and excess propylene gas was discharged to obtain a polymer powder. Next, the obtained polymer powder was dried for 12 hours or more while heating to 80 degreeC in a vacuum oven, and the polypropylene resin was obtained.

Example 2

A polypropylene resin was prepared in the same manner as in Example 1, except that the second polymerization step in Example 1 was performed for 15 minutes.

Example 3

A polypropylene resin was prepared in the same manner as in Example 1, except that the second polymerization step in Example 1 was performed for 20 minutes.

Example 4

In Example 1, a polypropylene resin was prepared in the same manner as in Example 1, except that 1.5 ml of diene was added together to perform the second polymerization step during the second polymerization reaction.

Example 5

During the second polymerization reaction in Example 1, 1.5 ml of diene was added together to perform a second polymerization step, and a polypropylene resin was prepared in the same manner as in Example 1, except that the second polymerization step was performed for 15 minutes. prepared.

Example 6

During the second polymerization reaction in Example 1, 1.5 ml of diene was added together to perform a second polymerization step, and a polypropylene resin was prepared in the same manner as in Example 1, except that the second polymerization step was performed for 20 minutes. prepared.

comparative example One

In Example 1, 3 ml of diene was added together during the first polymerization reaction, and only the first polymerization step was performed for 80 minutes to prepare a polypropylene resin. The second and third reaction steps were not carried out.

comparative example 2

In Example 1, 10 mg of hydrogen and 3 ml of diene were added together during the first polymerization reaction, and only the first polymerization step was performed for 80 minutes to prepare a polypropylene resin. The second and third reaction steps were not carried out.

comparative example 3

In Example 1, in the first polymerization reaction, 10 mg of hydrogen was added together to carry out the first polymerization step for 20 minutes, and in the second polymerization reaction, 3 ml of diene was added together to perform the second polymerization step for 60 minutes. Fillene resin was prepared. A third polymerization step was not carried out.

Reaction conditions for the preparation of the polypropylene resins of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

division PL
(g) Diane
(ml) catalyst
(mg) Hydrogen reaction
Temperature first reaction second reaction third reaction input input
point of view time
(minute) yield
(g) time
(minute) yield
(g) time
(minute) yield
(g) Example One 500 3 50 10 third reaction 70℃ 10 20 10 20 60 180 2 500 3 50 10 third reaction 70℃ 10 20 15 30 60 180 3 500 3 50 10 third reaction 70℃ 10 20 20 40 60 180 4 500 1.5 50 10 third reaction 70℃ 10 20 10 20 60 180 5 500 1.5 50 10 third reaction 70℃ 10 20 15 30 60 180 6 500 1.5 50 10 third reaction 70℃ 10 20 20 40 60 180 comparative example One 500 3 50 0 X 70℃ 80 160 - - - - 2 500 3 50 10 first reaction 70℃ 80 240 - - - - 3 500 3 50 10 first reaction 70℃ 20 60 60 140 - -

[Physical evaluation]

For the polypropylene resins prepared in Examples 1 to 6 and Comparative Examples 1 to 3, the following physical properties were measured by the method described, and the results are shown in Table 2.

(1) Melt index

According to ASTM D 1238, after heating the polypropylene resin to 230°C for 4 minutes, place a 2.16 kg piston in the cylinder, and hold the orifice (inner diameter: 2.09 mm, length: 8 mm) for a certain period of time (in minutes) The weight of the resin passed through during the period was measured and converted into the amount of resin passed through for 10 minutes.

(2) Extensional viscosity fixture (EVF) Melt Strength

Measurements were made using the Extensional Viscosity Fixture (EVF) mode of the Advanced rheometric expansion system (ARES). Specimens having a width of 20 mm, a length of 10 mm, and a thickness of 7 mm were prepared through hot press melting or injection. After fixing the specimen to the sample holder using a rheometric measuring device (2KFRTN, TA Instrument), the melt tension was measured as a resistance value applied to the specimen when the sample holder rotates about the axis. The maximum value of the melt tension changed according to the rotation distance (elongation rate) of the sample holder was measured as the melt tension. At this time, the extension rate, which is the rotation speed of the sample holder, ^{was set to 0.1s -1} , and the measurement temperature was 190°C.

(3) Extensional viscosity fixture (EVF), Elongation Time

When measuring the melt strength, the time the cradle to which the sample is fixed rotates about the axis was measured by converting the elongation distance of the sample. Extension Rate, which is rotational speed, was measured by setting it to ^{0.1 s -1.} The time when the sample exhibited the highest melt tension value when elongated with time was measured as the melt elongation rate.

(4) Gel content

The gel content was measured according to the method of ASTM D2765. The dried product was pulverized, put in xylene, and dissolved at a boiling point for 12 hours to measure the content of insoluble matter. In this case, the percentage of the weight of the insoluble sample after dissolution to the weight of the sample before dissolution was used as the gel content.

(5) Strain hardening index (SHI)

When measuring the melt strength, the elongational viscosity that the polypropylene changes according to the rotational distance (elongation) was measured, and the ratio of the maximum value of the elongational viscosity to the trend line before strain hardening appeared was used as the work hardening index. At this time, the extension rate, which is the rotation speed of the sample holder, ^{was set to 0.1s -1} , and the measurement temperature was 190°C.

Fig. 1 shows a graph of the elongational viscosity measurement result according to the elongation rate of the polypropylene resin obtained in Examples 2 and 1 to 3 and the work hardening index result obtained therefrom.

(6) Density after foaming

The prepared pellets were extruded using a single screw extruder (L/D 33, diameter 19 mm, 4 melting zone, Static mixer (2 cooling zone), CO ₂ metering pump (1 mL/min), extrusion temperature 150° C. to 200° C., and extrusion speed 50 RPM to 200 RPM) by extrusion foaming to prepare a foam, and its foam density was measured.

division melt index
@230℃[g/10min] ¹⁾ Melt tension
@Max.[g _f ] ²⁾ Melt elongation
@Max.[sec] gel content
[wt%] ³⁾ work hardening
Indices Density after foaming (g/cm ³ ) Example 1 4 20 30 0.2 5.2 0.2 Example 2 1.5 26 36 0.2 8.0 0.15 Example 3 One 24 18 0.5 4.6 0.3 Example 4 5 17 30 0.2 4.4 0.25 Example 5 4 18 32 0.3 5.0 0.22 Example 6 2.5 20 35 0.4 6.0 0.2 Comparative Example 1 0.8 10 4 10 0.5 0.7 Comparative Example 2 5 25 12 8.5 2.6 0.6 Comparative Example 3 10 30 27 0.5 2.0 0.5

1) Force [gf] at the point with the highest melt tension

2) elongation time to the point of the highest melt tension [sec]

3) Melt strength ratio of linear polypropylene and branched polypropylene at the point with the highest melt strength

Referring to Table 1, it can be seen that the polypropylene resin polymerized in Examples 1 to 6 according to the method of the present invention has a high melt strength and a low melt index, so that it is suitable for use as a foamed product.

On the other hand, it can be seen that the polypropylene resin polymerized in Examples 1 to 6 according to the method of the present invention has a significantly lower gel content than the polypropylene resin polymerized in Comparative Examples 1 to 3, and the value of the density after foaming is sufficiently low. can

From the above results, in order to exhibit these characteristics, the proportion of polypropylene having long chain branching should be high, and molecular weight distribution should be widely distributed.

Therefore, as in the method provided in the present invention, if the main polymerization is performed under hydrogen input after pre-polymerization under conditions not containing hydrogen, it can be evaluated that the ratio of polypropylene having long-chain branching is improved.

Claims (10)

A method for producing a polypropylene resin in the presence of a metallocene catalyst, comprising:
a first polymerization step of polymerizing a first polypropylene by reacting a propylene monomer in the absence of hydrogen;
a second polymerization step of polymerizing a second polypropylene by adding a diene compound to the effluent of the first polymerization step and reacting; and
A third polymerization step in which hydrogen is added to the effluent of the second polymerization step and reacted to polymerize the third polypropylene
A method for producing a polypropylene resin comprising a. The polypropylene resin according to claim 1, wherein the second polypropylene has a first long chain branch, the third polypropylene has a second long chain branch, and the first long chain branch has more carbon atoms than the second long chain branch. How to manufacture. The polypropylene according to claim 1, wherein the second polypropylene has ^{a weight average molecular weight of greater than 1×10 6} g/mol, and the third polypropylene has a weight average molecular weight of 1×10 ⁶ g/mol or less. How to make the resin. The method for producing a polypropylene resin according to claim 1, wherein in the first polymerization step, 1 to 29% by weight of the propylene polymer is prepared based on the total weight of the polypropylene resin. The method for producing a polypropylene resin according to claim 1, wherein in the second polymerization step, 1 to 29% by weight of the propylene polymer is prepared based on the total weight of the polypropylene resin. The method for producing a polypropylene resin according to claim 1, wherein the propylene polymer produced in the first polymerization step and the second polymerization step is 2 to 30 wt% of the total weight of the polypropylene resin. A polypropylene resin prepared in the presence of a metallocene catalyst,
1 to 29% by weight of homo polypropylene;
1 to 29% by weight of a second polypropylene having a weight average molecular weight greater than 1×10 ^{6 g/mol;} and
A polypropylene resin comprising a third polypropylene having a weight average molecular weight of 1×10 ^{6 g/mol or less as a balance.} The polypropylene resin according to claim 7, wherein the homo polypropylene and the second polypropylene are 2 to 30 wt% of the total weight of the polypropylene. The polypropylene resin according to claim 7, wherein the gel content is 5% by weight or less, and the strain hardening index is 4.0 or more. The foam of the polypropylene resin in any one of Claims 7-9.

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