CN106674719B

CN106674719B - Polypropylene blown film and preparation method thereof

Info

Publication number: CN106674719B
Application number: CN201510751254.1A
Authority: CN
Inventors: 郭鹏; 吕明福; 徐耀辉; 张师军; 张琦; 高达利; 权慧; 杨庆泉; 解娜
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2015-11-06
Filing date: 2015-11-06
Publication date: 2020-04-07
Anticipated expiration: 2035-11-06
Also published as: CN106674719A

Abstract

The invention provides a polypropylene composition for blow molding film, comprising a high melt strength impact polypropylene as a base resin, the high melt strength impact polypropylene comprising a propylene homopolymer component and an ethylene-1-butene copolymer component, and the ratio of the Mw of a room temperature trichlorobenzene soluble of the high melt strength impact polypropylene to the Mw of a room temperature trichlorobenzene insoluble is greater than 0.5 and less than or equal to 1; the room temperature xylene solubles content is greater than 10 wt.% and less than 30 wt.%. The invention also provides a polypropylene blown film prepared by blow molding the composition and a preparation method thereof, and the blown film has the characteristics of strong impact resistance and tearing resistance and high tensile strength, and is particularly suitable for the fields of steamed food packaging bags, microwave food packaging, medical high-temperature steaming sterilization, large heavy packaging and the like.

Description

Polypropylene blown film and preparation method thereof

Technical Field

The invention relates to the field of high polymer materials, in particular to a composition for preparing a polypropylene blown film, the polypropylene blown film prepared from the composition and a preparation method of the polypropylene blown film.

Background

The polypropylene (PP) film has higher mechanical strength, good heat resistance and grease resistance and better transparency, is widely used in industry and daily life, and is particularly suitable for bags for cooking food, microwave food packaging, medical high-temperature cooking sterilization, large heavy packaging and the like.

The extrusion blow molding film has the advantages of simple process, less equipment and cost advantage. Extrusion blown film accounted for 85% of all film production. However, polypropylene films have long been produced primarily by extrusion cast mono-and biaxially oriented techniques. Due to the low melt viscosity and melt strength of ordinary polypropylene resins, extrusion blow molding into films is difficult. In recent years, with the progress of polymerization and catalyst technologies, high melt strength polypropylene resins suitable for extrusion blow molding have been developed. Because the melt strength and viscosity of the polypropylene resin are much higher than those of common polypropylene, the polypropylene film can be produced on the conventional polyethylene blown film equipment. The extrusion blow molding polypropylene film has low cost, high production efficiency, large tearing strength and wide film thickness range.

In order to improve the applicability of polypropylene blown film, at present, a method of adding a copolymerized ethylene monomer in the polymerization process of propylene is adopted to produce a copolymer, and the copolymer is used as a raw material to produce a polypropylene blown film. Due to the addition of the ethylene monomer, the toughness of the film is improved, but the difference between the longitudinal and transverse tear strengths of the film is still large, and the heat resistance of the film is greatly reduced. In addition, the general commercial polypropylene has poor puncture resistance and impact resistance, and an impact-reinforced polypropylene is needed for the preparation of polypropylene blown films.

Therefore, the development of polypropylene blown films with further improved impact, tear and tensile properties to further expand their applicability and range of applicability remains an obvious need in the current market.

Disclosure of Invention

The invention aims to provide a composition for preparing a polypropylene blown film and a polypropylene blown film prepared by using the composition. Compared with the prior art, the blown film prepared from the polypropylene composition provided by the invention can improve the tearing strength of the film, improve the longitudinal and transverse tearing strengths and reduce the difference between the longitudinal and transverse tearing strengths on the premise of not reducing the heat resistance of the film.

The invention also provides a preparation method of the polypropylene blown film, which can be conveniently implemented by using a common blow molding process.

According to the present invention, there is provided a polypropylene composition for blown film comprising as a base resin a high melt strength impact polypropylene comprising a propylene homopolymer component and an ethylene-1-butene copolymer component and having a ratio of Mw (weight average molecular weight) of the room temperature trichlorobenzene solubles to Mw of the room temperature trichlorobenzene insolubles of greater than 0.5 and less than or equal to 1, such as greater than 0.5 and less than 0.8; the room temperature xylene solubles content is preferably more than 10% by weight and less than 30% by weight. The base resin with the characteristics can improve the impact resistance and tensile resistance of the polypropylene blown film prepared from the composition, and has stronger tearing strength and low transverse and longitudinal tearing strength difference.

In the present invention, the high melt strength impact polypropylene refers to polypropylene comprising the above-described features.

In the present invention, high melt strength means a melt strength of more than 0.1N, in particular from 0.15 to 0.25N. The Izod notched impact (23 ℃) of the impact-resistant base resin is 70-100 KJ/m²。

In the present invention, for convenience of characterization, the molecular weight of the rubber phase of the base resin is based on the molecular weight of the room temperature trichlorobenzene solubles.

In the present invention, the rubber phase content of the base resin, as measured as the room temperature xylene soluble content, can be determined according to the method described in ASTM D5492.

The present inventors have found that, in order to ensure high melt strength of blown films, the high melt strength impact polypropylene as a base resin preferably has a molecular weight distribution Mw/Mn (weight average molecular weight/number average molecular weight) of less than or equal to 10 and greater than or equal to 4, for example, 4, 5, 6, 7, 8, 9 or 10; and/or Mz +1/Mw is greater than or equal to 10, and preferably less than or equal to 20, for example greater than 10 and less than 15.

Preferably, the high melt strength impact polypropylene used in the present invention has a butene content of 5 to 20 wt.%.

Preferably, the melt index of the high melt strength impact polypropylene material used in the present invention is controlled in the range of 0.1 to 15g/10min, and more preferably 0.1 to 6.0g/10 min. The melt index was measured at 230 ℃ under a load of 2.16 kg.

For high melt strength impact polypropylene, the factors affecting melt strength become more complex due to the material being of multi-phase structure. According to a preferred embodiment of the present invention, the weight ratio of the ethylene-1-butene copolymer component to the propylene homopolymer component in the high melt strength impact polypropylene is 11-80: 100; and/or the melt index ratio of the propylene homopolymer component to the high melt strength impact polypropylene comprising the propylene homopolymer component and the ethylene-1-butene copolymer component is greater than or equal to 0.6 and less than 1.

In the polypropylene material as the base resin prepared and used in the invention, the propylene homopolymer component is used as a continuous phase to provide certain rigidity for the polypropylene material, and the ethylene-1-butene copolymer component is used as a rubber phase, namely a dispersed phase, so that the toughness of the polypropylene material can be improved. In order to ensure that the product of the invention has better rigidity-toughness balance, the invention adopts ethylene-1-butene random copolymer as the rubber component, and the inventor of the invention finds that the effect is better when the weight ratio of the ethylene-1-butene copolymer component to the propylene homopolymer component is 11-80:100 in the melt strength impact polypropylene used by the invention through a large amount of experiments; further, when the butene content in the ethylene-1-butene copolymer is made to be greater than or equal to 20 wt% and less than or equal to 45 wt%, for example, 20 wt%, 30 wt%, 40 wt%, 45 wt%, etc., an impact polypropylene material having better rigidity and toughness is obtained. Here, it is easily understood that the "butene content in the ethylene-1-butene copolymer" means the weight content of the fraction composed of the 1-butene monomer in the ethylene-1-butene copolymer formed by copolymerizing the ethylene monomer and the 1-butene monomer.

According to the invention, the propylene homopolymer component comprises at least a first propylene homopolymer and a second propylene homopolymer; the melt index of the first propylene homopolymer is less than the melt index of the second propylene homopolymer; the high melt strength impact polypropylene is prepared by homopolymerizing propylene in the presence of a first propylene homopolymer to obtain a propylene homopolymer component comprising the first propylene homopolymer and a second propylene homopolymer, and then copolymerizing ethylene-1-butene in the presence of the propylene homopolymer component to obtain a polypropylene material comprising an ethylene-1-butene copolymer. It follows that the base resin used in the present invention is not simply a blend of the propylene homopolymer component and the ethylene-1-butene copolymer component, but is a unitary polypropylene material comprising a propylene homopolymer and an ethylene-1-butene copolymer obtained after further carrying out a specific ethylene-1-butene copolymerization reaction on the basis of a specific propylene homopolymer component.

In a preferred embodiment of the present invention, the melt index of the first propylene homopolymer is less than the melt index of the second propylene homopolymer.

In a preferred embodiment of the present invention, the first propylene homopolymer has a melt index, measured at 230 ℃ under a load of 2.16kg, of from 0.001 to 0.4g/10 min; the propylene homopolymer component comprising the first propylene homopolymer and the second propylene homopolymer has a melt index, measured at 230 ℃ under a load of 2.16kg, of 0.1 to 15g/10min, preferably 0.1 to 10g/10min, and still preferably 0.1 to 6g/10 min. Preferably, the weight ratio of the first propylene homopolymer to the second propylene homopolymer is from 40:60 to 60: 40.

The base resins prepared and used according to the invention have a molecular weight Polydispersity Index (PI) of from 4 to 8, preferably from 4.5 to 6.

The base resin prepared and used in the invention also has good heat resistance, and the melting peak temperature T of the final polypropylene resin is measured by DSC_mGreater than or equal to 158 ℃.

According to the present invention, the composition may also optionally include linear low density polyethylene. Preferably, the linear low density polyethylene has a melt flow rate in the range of 0.1 to 3.0g/10min (190 ℃/2.16 kg).

It is stated that the polypropylene composition for blown film or the process for blown polypropylene film as described below provided according to the present invention does not require the addition of modifying components such as linear low density polyethylene due to the use of a base resin having good properties as described above, and can produce a blown polypropylene film having a good combination of properties including high toughness and good heat resistance, as shown in the examples section below, which is an advantage of the present invention. Thus, in some embodiments, the compositions of the present invention do not comprise linear low density polyethylene.

According to the present invention, the composition may optionally further comprise other processing aids, preferably at least one selected from the group consisting of antioxidants, secondary antioxidants, lubricants and antistatic agents.

The above-mentioned auxiliaries can be optionally added according to specific needs. The selected additives can be the additives commonly used in polypropylene blown film, such as antioxidant, antioxidant aid, lubricant, antistatic agent, etc. The dosage of the auxiliary agent is conventional dosage or adjusted according to the requirement of actual situation.

The antioxidant may be, for example, antioxidant 1010; examples of the antioxidant aid include antioxidant aid 168 and the like. The lubricant is, for example, calcium stearate or magnesium stearate.

The invention also provides a polypropylene blown film prepared by blow molding a film using the composition provided according to the invention as described above.

According to the invention, the polypropylene blown film is a film whose thickness can be adjusted as desired and by the particular process, and whose thickness is generally from 5 to 100 μm, in particular from 15 to 60 μm.

According to the invention, the polypropylene blown film has a tensile stress at break of more than 15MPa, preferably more than 25MPa, such as from 25 to 100 MPa; and/or a nominal strain at break of more than 300%, preferably more than 480%, for example 480-; and/or a tear strength of more than 50N/mm, preferably more than 90N/mm, for example 120-24N/mm; and/or the transverse tear strength differs from the longitudinal tear strength by less than 24%, preferably less than 20%, still preferably less than 10%, for example 1-10%.

The invention also provides a process for the preparation of a polypropylene blown film, which comprises extrusion granulation (e.g. by a twin-screw extruder) of a composition as provided according to the invention as described above, followed by blow molding (e.g. by a film blowing machine) into a film.

Preferably, the extrusion temperature is 150-; and/or the blown film temperature is 170-230 ℃, preferably 185-220 ℃. The extrusion temperature refers to, for example, the extrusion temperature set by the extruder. The film blowing temperature refers to, for example, the film slit temperature of a film blowing machine.

Preferably, the blow-up ratio is from 1.5 to 3, preferably from 2 to 2.5, during the blown film process.

According to the invention, the film blowing machine can be a lower blowing water-cooled type, a flat blowing water-cooled type or a traditional upper blowing water-cooled type polypropylene film blowing machine set.

The method for producing a polypropylene blown film according to the present invention further includes a step of producing a base resin, i.e., a high melt strength impact polypropylene, including:

the first step is as follows: propylene homopolymerization comprising:

the first stage is as follows: carrying out propylene homopolymerization reaction in the presence or absence of hydrogen under the action of a Ziegler-Natta catalyst containing a first external electron donor to obtain a reaction flow containing a first propylene homopolymer;

and a second stage: adding a second external electron donor to perform a complex reaction with a catalyst in the reaction flow, and then performing a propylene homopolymerization reaction in the presence of the first propylene homopolymer and hydrogen to generate a second propylene homopolymer, so as to obtain a propylene homopolymer component containing the first propylene homopolymer and the second propylene homopolymer; wherein the content of the first and second substances,

the melt indices of the first propylene homopolymer and the propylene homopolymer component, measured at 230 ℃ under a load of 2.16kg, are 0.001-0.4g/10min and 0.1-15g/10min, respectively; and the weight ratio of the first propylene homopolymer to the second propylene homopolymer is from 40:60 to 60: 40.

The second step is that: ethylene-1-butene copolymerization, carrying out ethylene-1-butene gas phase copolymerization in the presence of the propylene homopolymer component and hydrogen to produce an ethylene-1-butene copolymer component, to obtain the base resin comprising the propylene homopolymer component and the ethylene-1-butene copolymer component. The base resin is a high melt strength impact polypropylene material. It is to be understood that the reaction stream comprises unreacted catalyst in the first stage.

Preferably, the ratio of the melt index of the propylene homopolymer component obtained in the first step to the melt index of the polypropylene comprising the propylene homopolymer component and the ethylene-1-butene copolymer component obtained in the second step is greater than or equal to 0.6 and less than 1.

By configuring the propylene homopolymer component of the base resin prepared and used in the present invention to include a combination of at least two propylene homopolymers having different melt indices and having a specific ratio relationship, particularly under conditions where the first propylene homopolymer and the propylene homopolymer have specific different molecular weights and molecular weight distributions, respectively, the base resin constituting the present invention is provided with a specific continuous phase, and further combination of this continuous phase with a specific dispersed phase, i.e., a rubber phase, results in a high melt strength impact polypropylene material having both high melt strength and good rigidity and toughness.

In the first stage, the amount of hydrogen used may be, for example, from 0 to 200 ppm. In the second stage, the amount of hydrogen used was 2000-. The process provided by the present invention is preferably carried out in two or more reactors operated in series.

The process according to the invention is a Ziegler-Natta catalyst direct catalysed polymerisation process. The preparation method comprises the steps of respectively using two or more different types of external electron donors in a plurality of reactors connected in series, selecting a proper amount of the external electron donors, combining different amounts of hydrogen of chain transfer agents in the reaction to prepare a homo-polypropylene continuous phase with a specific melt index and a large amount of ultrahigh molecular weight components and extremely wide molecular weight distribution, further carrying out copolymerization of ethylene and 1-butene on the homo-polypropylene continuous phase to obtain a rubber phase dispersed in the continuous phase, and controlling the composition, structure, content and the like of the rubber phase by controlling the reaction conditions of the copolymerization reaction to obtain the impact-resistant polypropylene material with high melt strength effect.

In the process provided by the present invention, the catalyst used is a Ziegler-Natta catalyst, preferably a catalyst with high stereoselectivity. The Ziegler-Natta catalyst having high stereoselectivity as used herein means a catalyst which can be used for the preparation of a propylene homopolymer having an isotactic index of more than 95%. Such catalysts generally comprise (1) a titanium-containing solid catalyst active component, the main components of which are magnesium, titanium, halogen and an internal electron donor; (2) an organoaluminum compound co-catalyst component; (3) an external electron donor component.

The solid catalyst active component (which may also be referred to as a procatalyst) of the Ziegler-Natta catalyst used in the process of the present invention may be well known in the art. Specific examples of such active solid catalyst component (1) containing that can be used are, for example, described in patent documents CN85100997, CN98126383.6, CN98111780.5, CN98126385.2, CN93102795.0, CN00109216.2, CN99125566.6, CN99125567.4 and CN 02100900.7. These patent documents are incorporated by reference herein in their entirety.

The organoaluminum compound in the Ziegler-Natta catalyst used in the process of the present invention is preferably an alkylaluminum compound, more preferably a trialkylaluminum, for example, at least one of triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, trihexylaluminum and the like.

The molar ratio of the titanium-containing active solid catalyst component and the organoaluminum compound in the Ziegler-Natta catalyst used in the process of the present invention is 10: 1 to 500: 1, preferably 25: 1 to 100: 1, in terms of aluminum/titanium.

According to the invention, said first external electron donor is preferably selected from those of formula R¹R²Si(OR³)₂At least one of the compounds of (a); wherein R is²And R¹Each independently selected from C₁-C₆Straight or branched alkyl, C₃-C₈Cycloalkyl and C₅-C₁₂Heteroaryl of (A), R³Is C₁-C₃A straight chain aliphatic group. Specific examples include, but are not limited to, dicyclopentyldimethoxysilane, isopropylcyclopentyldimethoxysilane, isopropylisobutyldimethoxysilane, dipyridyldimethoxysilane, diisopropyldimethoxysilane, and the like.

The molar ratio of the organic aluminum compound to the first external electron donor is 1: 1-100: 1, preferably 10: 1-60: 1, calculated as aluminum/silicon.

In the process according to the invention, the catalyst comprising the first external electron donor may be added directly to the homopolymerization reactor or, after precontacting and/or prepolymerization as known in the art, may be added to the homopolymerization reactor. The prepolymerization refers to that the catalyst is prepolymerized at a certain ratio at a lower temperature to obtain the ideal particle shape and dynamic behavior control. The prepolymerization can be liquid phase bulk continuous prepolymerization, and can also be batch prepolymerization in the presence of an inert solvent. The temperature of the prepolymerization is usually-10 to 50 ℃ and preferably 5 to 30 ℃. A precontacting step may optionally be provided before the prepolymerization process. The pre-contact step refers to the complex reaction of a cocatalyst, an external electron donor and a main catalyst (solid active center component) in the catalyst system to obtain the catalyst system with polymerization activity. The temperature in the precontacting step is usually controlled to be-10 to 50 ℃, preferably 5 to 30 ℃.

According to the invention, the second external electron donor is selected from at least one of the compounds shown in the chemical general formulas (I), (II) and (III);

wherein R is₁And R₂Each independently selected from C₁-C₂₀One of linear, branched or cyclic aliphatic radicals, R₃、R₄、R₅、R₆、R₇And R₈Each independently selected from a hydrogen atom, a halogen atom, C₁-C₂₀Straight or branched alkyl of (2), C₃-C₂₀Cycloalkyl radical, C₆-C₂₀Aryl radical, C₇-C₂₀Alkylaryl and C₇-C₂₀One of aralkyl, and R₃、R₄、R₅、R₆、R₇And R₈Optionally linked to form a ring between any two of them; r₉、R₁₀And R₁₁Each independently is C₁-C₃Straight-chain aliphatic radical, R₁₂Is C₁-C₆Straight or branched alkyl or C₃-C₈A cycloalkyl group. Specific examples of the second external electron donor include, but are not limited to, 2-diisobutyl-1, 3-dimethoxypropane, 2-phenyl-1, 3-dimethoxypropane, 2-benzyl-1, 3-dimethoxypropane, 2-isopropyl-2-isoamyl-1, 3-dimethoxypropane, 2-bis (cyclohexylmethyl) -1, 3-dimethoxypropane, 2-isopropyl-2-3, 7-dimethyloctyl-dimethoxypropane, 2-isopropyl-1, 3-dimethoxypropane, 2-isopropyl-2-cyclohexylmethyl-1, 3-dimethoxypropane, 2-diisobutyl-1, 3-diethoxypropane, 2-diisobutyl-1, 3-dipropoxypropane, 2-isopropyl-2-isopentyl-1, 3-diethoxypropane, 2-isopropyl-2-isopentyl-1, 3-dipropoxypropane, 2-bis (cyclohexylmethyl) -1, 3-diethoxypropane, isobutyltrimethoxysilane, isobutyltriethoxysilane, isopropyltriethoxysilane, tetraethoxysilane and the like.

The molar ratio of the organic aluminum compound to the second external electron donor is 1: 1-60: 1 (calculated by aluminum/silicon or aluminum/oxygen), and preferably 5: 1-30: 1.

According to some embodiments of the present invention, the molar ratio of the second external electron donor to the first external electron donor is from 1 to 30, and preferably from 5 to 30.

According to a preferred embodiment of the present invention, the propylene homopolymer component obtained in the first step has the following characteristics: molecular weight distribution Mw/Mn is 6-20, preferably Mw/Mn is 10-16; the fraction having a molecular weight of more than 500 ten thousand is present in an amount of more than or equal to 1.5% by weight and less than or equal to 5% by weight; the content of fractions having a molecular weight of less than 5 ten thousand is greater than or equal to 15.0% by weight and less than or equal to 40% by weight; mz +1/Mn is greater than or equal to 70 and less than 150. Wherein, the molecular weight of more than 500 ten thousand and less than 5 ten thousand refers to the part with the molecular weight of more than 500 ten thousand and the part with the molecular weight of less than 5 ten thousand in the molecular weight distribution curve, which is known and easily understood by those skilled in the art, and is not described herein again.

In the process of the present invention, it is preferred that the second external electron donor is brought into intimate contact with the catalyst component in the first stage reaction product prior to the second stage homopolymerization. In some preferred embodiments, the second external electron donor may be added in the feed line after the first stage reactor and before the second stage reactor, or at the front end of the feed line of the second stage reactor, in order to first perform a precontacting reaction with the catalyst in the reaction product of the first stage before the second stage reaction.

Preferably, in the second step, the 1-butene is used in an amount of 20 to 80% by volume of 1-butene based on the total volume of 1-butene and ethylene. In the second step, the volume ratio of hydrogen to the total amount of ethylene and 1-butene is 0.02 to 1. In the present invention, in order to obtain a base resin having high melt strength and at the same time high rigidity and toughness, it is important to control the composition, structure or properties of the dispersed phase and the continuous phase. The present invention can prepare a rubber phase having a molecular weight distribution, an ethylene content, which is advantageous for achieving the object of the present invention, by these preferable conditions, thereby obtaining an impact polypropylene material having better properties as a base resin.

In a preferred embodiment of the present invention, the yields of the first propylene homopolymer and the second propylene homopolymer are in the range of from 40:60 to 60: 40. The yield ratio of the ethylene-1-butene copolymer component to the propylene homopolymer component is 11-80: 100. The polymerization reaction of the first step may be carried out in liquid-liquid phase, or in gas-gas phase, or using a combination of liquid-gas techniques. When liquid phase polymerization is carried out, the polymerization temperature is 0-150 ℃, preferably 60-100 ℃; the polymerization pressure should be higher than the saturation vapor pressure of propylene at the corresponding polymerization temperature. The polymerization temperature in the gas phase polymerization is 0 to 150 ℃, preferably 60 to 100 ℃; the polymerization pressure may be normal pressure or higher, and preferably 1.0 to 3.0MPa (gauge pressure, the same applies hereinafter).

The polymerization reaction of the second step is carried out in the gas phase. The gas phase reactor may be a gas phase fluidized bed, a gas phase moving bed, or a gas phase stirred bed reactor. The polymerization temperature is preferably 0 to 150 ℃ and more preferably 60 to 100 ℃. The polymerization pressure is any pressure below the partial pressure of the propylene at which it liquefies.

According to a preferred embodiment of the invention, the reaction temperature in the first stage is between 50 and 100 ℃, preferably between 60 and 85 ℃; the reaction temperature of the second stage is 55-100 ℃, preferably 60-85 ℃; the reaction temperature in the second step is 55-100 deg.C, preferably 60-85 deg.C.

In a preferred embodiment of the present invention, the method of the present invention further comprises further modifying the prepared base resin with α or β crystal nucleating agent to further improve the rigidity or toughness of the base resin, wherein the modification with α crystal nucleating agent and β crystal nucleating agent is a technique known in the art, and the ratio of the weight of the nucleating agent to the total weight of the polypropylene is (0.005-3) to 100.

According to the process of the present invention, the polymerization reaction may be carried out continuously or batchwise.

In the preparation step of the base resin, the added second external electron donor can react with the catalytic activity center in the first-stage homopolymerization product material to generate a new catalytic activity center, and propylene is continuously initiated to polymerize into a homopolymerization polymer with a molecular weight which is greatly different from that of the product obtained in the first stage in the second stage. The second external electron donor has higher hydrogen response than the first external electron donor, and can prepare a high melt index polymer in the presence of a small amount of hydrogen. Therefore, the invention can obtain the homopolymerized polypropylene component containing a large amount of ultrahigh molecular weight fraction and wider molecular weight distribution under the condition of less hydrogen consumption by adjusting the dosage and the type of the external electron donor and the adding amount of the hydrogen at different stages when the homopolymerized polypropylene component is added into two reactors connected in series or is intermittently operated without using a special catalyst. Then, proper 1-butene/(1-butene + ethylene), hydrogen/(1-butene + ethylene) and temperature and pressure are selected to further carry out ethylene-1-butene copolymerization reaction on the basis of the homopolymerized polypropylene component, so as to obtain the high melt strength impact resistant polypropylene containing a certain content of rubber component with specific performance. The composition and structure control of the rubber phase component ensures that the rubber phase component has high melt strength, the specific content of the rubber component ensures that the rubber phase component has higher impact resistance, and in addition, the proper molecular weight distribution also ensures that the polymer has good processability. That is, the present invention obtains polypropylene having excellent properties as a base resin for producing a polypropylene blown film by setting a plurality of propylene homopolymerization stages and selecting appropriate reaction parameters and reaction conditions for the respective homopolymerizations and copolymerizations to thereby produce appropriate continuous phases and rubber dispersed phases and their combination. The polypropylene is used as basic resin, and the polypropylene blown film prepared by the blow molding process also has corresponding excellent performance.

The polypropylene base resin prepared and adopted by the invention can be used for obtaining the polypropylene blown film by using a common blow molding process, and the current situation that most polypropylene film molding can only depend on processes such as casting, biaxial stretching and the like is changed. The polypropylene film obtained by the blow molding process has the characteristics of strong impact resistance and tear resistance and high tensile strength, and is particularly suitable for the fields of steamed food bags, microwave food packaging, medical high-temperature steaming sterilization, large heavy packaging and the like.

The polypropylene blown film manufactured according to the invention is of a non-crosslinked structure, can be recycled according to common polypropylene modified materials, does not cause secondary pollution, and meets the requirement of circular economy.

The relevant contents of the base resins of the present invention are described in patent application 2014106026768 and patent application 2014106022998, which are incorporated herein by reference in their entirety.

Detailed Description

The invention will now be further described by way of specific examples, which are not to be construed as limiting the invention in any way.

The starting materials in the following examples and comparative examples include:

ordinary polypropylene: the company Qilu, China petrochemical company Limited, brand EPS 30R;

homo-polymerized high melt strength polypropylene: northern Europe chemical, trade Mark Daploy WB140 HMS;

ordinary linear low density polyethylene: yanzi Branch of China petrochemical company Limited, No. 7042;

antioxidant 1010: basf china ltd, industrial grade;

antioxidant 168: basf china ltd, industrial grade.

All other raw materials are commercially available.

The data relating to the polymers in the examples and comparative examples were obtained according to the following test methods:

1) polymer room temperature xylene solubles content (i.e. characteristic rubber phase content): measured according to the method described in ASTM D5492.

2) The tensile strength of the resin was measured according to GB/T1040.2.

3) Melt mass flow rate (also known as melt index, MFR): the measurement was carried out at 230 ℃ under a load of 2.16kg using a melt index apparatus of type 7026 from CEAST, according to the method described in ASTM D1238.

4) Flexural modulus: measured according to the method described in GB/T9341.

5) Impact strength of the simply supported beam notch: measured according to the method described in GB/T1043.1.

6) Ethylene content and butene content: measured by a nuclear magnetic resonance method. The measurement was carried out using a 10 mm probe of AVANCEIII 400MHz nuclear magnetic resonance spectrometer (NMR) from Bruker, Switzerland. The solvent is deuterated o-dichlorobenzene, about 250mg of the sample is placed in 2.5ml of deuterated solvent, and the sample is dissolved by heating in an oil bath at 140 ℃ to form a uniform solution. And (3) acquiring 13C-NMR (nuclear magnetic resonance), wherein the probe temperature is 125 ℃, 90-degree pulses are adopted, the sampling time AQ is 5 seconds, the delay time D1 is 10 seconds, and the scanning times are more than 5000 times. Other manipulations, peak identification, etc. commonly used NMR experimental requirements are performed, and references include Eric T.Hsieh, and James C.Randall, Ethylene-1-Butene copolymers.1. copolymer Sequence Distribution, Macromolecules, 15, 353-.

7) Melt strength: the melt strength was measured using a Rheotens melt Strength Meter from Geottfert Werkstoff Pruefmischinen, Germany. After the polymer is melted and plasticized by a single screw extruder, a melt bar is extruded downwards by a 90-degree steering head provided with an 30/2 length-diameter-ratio die, the bar is clamped between a group of two rollers which rotate oppositely at constant acceleration to carry out uniaxial stretching, the force in the melt stretching process is measured and recorded by a force measuring unit connected with the stretching rollers, and the maximum force value measured when the melt is stretched until the melt is broken is defined as the melt strength.

8) Molecular weight Polydispersity Index (PI): the resin sample is molded into a 2mm slice at 200 ℃, dynamic frequency scanning is carried out on the sample at 190 ℃ under the protection of nitrogen by adopting an ARES (advanced rheometer extended system) rheometer of Rheometric Scientific Inc in America, a parallel plate clamp is selected, appropriate strain amplitude is determined to ensure that the experiment is carried out in a linear region, and the change of storage modulus (G '), energy consumption modulus (G') and the like of the sample along with the frequency is measured. Molecular weight polydispersity index PI ═ 10⁵/G_cWherein G is_c(unit: Pa) is the modulus value at the intersection of the G' -frequency curve and the G "-frequency curve.

9) Molecular weight (M)_w，M_n) And molecular weight distribution (M)_w/M_n，M_z+1/M_w): the molecular weight and molecular weight distribution of the samples were measured by PL-GPC 220 gel permeation chromatograph manufactured by Polymer Laboratories, UK, or GPCIR apparatus manufactured by Polymer Char, Spanish (IR5 concentration Detector), the columns were 3 PLgel 13um Olexis columns in series, the solvent and mobile phase were 1,2, 4-trichlorobenzene (containing 250ppm of antioxidant 2, 6-dibutyl-p-cresol), column temperature 150 ℃, flow rate 1.0ml/min, using the narrow distribution polystyrene standard EasiCal PS-1 of PL company for universal calibration. The preparation process of the room temperature trichlorobenzene soluble substance comprises the following steps: accurately weighing a sample and a trichlorobenzene solvent, dissolving for 5 hours at 150 ℃, standing for 15 hours at 25 ℃, and filtering by adopting quantitative glass fiber filter paper to obtain a solution of trichlorobenzene soluble matters at room temperature for determination. The content of trichlorobenzene solubles at room temperature was determined by correcting the GPC curve area with polypropylene of known concentration, and the molecular weight data of trichlorobenzene insolubles at room temperature was calculated from the GPC data of the original sample and the GPC data of trichlorobenzene solubles at room temperature.

10) Thickness standard deviation: three sections of the same batch of 50cm long and 50cm wide films were randomly drawn, and the film thickness (mm) was randomly measured at 20 points in each section for a total of 60 data points, and the standard deviation was found using the following formula:

μ is the average thickness of 60 data points, Xi is the thickness of each point, N is 60, and σ is the standard deviation.

11) Tensile stress at break and nominal strain at break: the test is carried out according to the national standard GB/T1040.3-2006.

12) Right angle tear strength: the test was performed according to the industry standard QB/T1130-.

Other production and test equipment includes:

film blowing machine: collin blow Film Line Type 180/400, Germany.

A double-screw extruder: ZSK-25 from Kekuilong Nanjing mechanical Co.

Preparation of polypropylene base resin HMSPP 701:

the propylene polymerization reaction is carried out on a polypropylene device, and the main equipment of the device comprises a prepolymerization reactor, a first loop reactor, a second loop reactor and a third gas-phase reactor. The polymerization method and the steps are as follows.

(1) Prepolymerization reaction

The main catalyst (DQC-401 catalyst, supplied by Oda, Beijing of China petrochemical catalyst Co.), the cocatalyst (triethylaluminum) and the first external electron donor (isopropyl cyclopentyl dimethoxysilane, IPCPMS) were precontacted at 6 ℃ for 20min, and then continuously added into a continuous stirred tank type prepolymerization reactor to perform a prepolymerization reactor. The Triethylaluminum (TEA) flow into the prepolymerization reactor was 6.33g/hr, the isopropylcyclopentyldimethoxysilane flow was 0.3g/hr, the procatalyst flow was 0.6g/hr, and the TEA/IPCPMS ratio was 50 (mol/mol). The prepolymerization is carried out in a propylene liquid phase bulk environment, the temperature is 15 ℃, the residence time is about 4min, and the prepolymerization multiple of the catalyst is about 80-120 times under the condition.

(2) The first step is as follows: homopolymerization of propylene

The first stage is as follows: continuously feeding the prepolymerized catalyst into a first loop reactor to complete the first-stage propylene homopolymerization, wherein the polymerization temperature of the first loop reactor is 70 ℃, and the reaction pressure is 4.0 MPa; and adding no hydrogen into the feed of the first loop reactor, wherein the hydrogen concentration detected by online chromatography is less than 10ppm, and obtaining the first propylene homopolymer A.

And a second stage: isobutyltriethoxysilane (IBTES) was added in an amount of 0.63g/hr with propylene in the second loop reactor connected in series with the first loop reactor and mixed with the reactant stream from the first loop reactor with a TEA/IBTES ratio of 5(mol/mol), where IBTES is the second external electron donor. The polymerization temperature of the second loop reactor is 70 ℃, and the reaction pressure is 4.0 MPa; a quantity of hydrogen was also added with the propylene feed, the hydrogen concentration in the feed was 3300ppm by on-line chromatographic detection, and a second propylene homopolymer B was produced in the second loop reactor, yielding a propylene homopolymer fraction comprising a first propylene homopolymer and a second propylene homopolymer.

(3) The second step is that: copolymerization of ethylene and butadiene

A certain amount of hydrogen and H is added into the third reactor₂/(C₂+C₄)＝0.06(mol/mol)，C₄/(C₂+C₄)＝0.35(mol/mol)(C₂And C₄Respectively referring to ethylene and 1-butene), continuously initiating ethylene/1-butene copolymerization reaction in a third reactor, and keeping the reaction temperatureThe temperature was 75 ℃ to give an ethylene-1-butene copolymer component C.

The final product contains the first propylene homopolymer, the second propylene homopolymer and the ethylene-1-butene copolymer, and is subjected to wet nitrogen to remove the activity of the unreacted catalyst and heating and drying to obtain polymer powder. Adding 0.1 wt% of antioxidant 168 additive, 0.1 wt% of antioxidant 1010 additive and 0.05 wt% of calcium stearate into the powder obtained by polymerization, and granulating by using a double-screw extruder. The analysis results of the obtained polymer and the physical properties of the polymer are shown in tables 1 and 2.

Preparation of polypropylene base resin HMSPP 702:

the used catalyst, pre-complexing and polymerization process conditions, the formula of the auxiliary agent and the addition amount are the same as those of the HMSPP 701. The difference from the HMSPP701 is that: the second external electron donor was changed to 2, -isopropyl-2-isoamyl-1, 3-dimethoxypropane (IPPMP), the amount of the added was unchanged, and the amount of hydrogen in the second reactor was adjusted to 4000ppm in the second stage. The analysis results of the obtained polymer and the physical properties of the polymer are shown in tables 1 and 2.

Preparation of polypropylene base resin HMSPP 703:

the used catalyst, pre-complexing and polymerization process conditions, the formula of the auxiliary agent and the addition amount are the same as those of the HMSPP 701. The difference from the HMSPP701 is that: the amount of hydrogen in the second reactor in the second stage became 7000ppm, and H in the gas phase reactor in the second stage₂/(C₂+C₄) Adjusted to 0.20 (v/v). The analysis results of the obtained polymer and the physical properties of the polymer are shown in tables 1 and 2.

Preparation of polypropylene base resin HMSPP 704:

the used catalyst, pre-complexing and polymerization process conditions, the formula of the auxiliary agent and the addition amount are the same as those of the HMSPP 701. The difference from the HMSPP701 is that: the first external electron donor was replaced with isopropyl-2-isobutyl-dimethoxysilane (IPBMS), and the amount added was unchanged. The analysis results of the obtained polymer and the physical properties of the polymer are shown in tables 1 and 2.

As can be seen from the results shown in tables 1 and 2, the polypropylene material prepared according to the method of the present invention has high melt strength, tensile strength and flexural modulus, and high notched impact strength. This polypropylene material is an excellent base resin for polypropylene blown films.

Examples 1 to 10

Preparation of Polypropylene base resin

High melt strength impact polypropylene HMSPP701, HMSPP702, HMSPP703 and HMSPP704 as base resins were prepared according to the above HMSPP701, HMSPP702, HMSPP703 and HMSPP704 preparation methods, respectively.

Preparation of polypropylene blown film

According to the specific formulation shown in table 3, a certain amount of the impact-resistant high-melt-strength polypropylene, i.e., HMSPP601 or HMSPP602(100 parts by weight) prepared by a special process is weighed, mixed with a certain amount of antioxidant 1010 (about 0.2 part by weight), auxiliary antioxidant 168 (about 0.1 part by weight), and calcium stearate (about 0.1 part by weight), and stirred uniformly. Then mixing and granulating by using a double-screw extruder, wherein the temperature of each section of the extruder is set as follows: 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 215 ℃ (handpiece). The obtained pellets are extruded and blown on a film blowing machine, and the temperature of each section of the film blowing machine is set as follows: 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃, 210 ℃, 210 ℃ (die temperature). The blow-up ratio was about 2.5. In addition, in examples 1 to 6, the die temperature and the blow-up ratio were also changed, as shown in Table 3.

The prepared polypropylene blown film was subjected to mechanical and optical property tests, and the results are shown in Table 3.

Comparative examples 1 to 3

Referring to the test procedures of examples 1-10, tests were conducted using ordinary impact co-polypropylene EPS30R in place of HMSPP701, HMSPP702, HMSPP703, and HMSPP704, with specific formulations and process conditions as shown in Table 3.

Comparative example 4

Referring to the test procedures of examples 1-10, the modified material (weight ratio 100: 4) obtained by blending the high melt strength homopolypropylene WB140HMS with the linear low density polyethylene was used as the base resin, and the specific formulation and process conditions and properties of the prepared polypropylene blown film are shown in Table 3.

It can be seen from examples 1 to 10 that the HMSPP701, HMSPP702, HMSPP703 and HMSPP704 high-melt-strength impact polypropylene prepared by the method has high melt strength, tensile strength, flexural modulus, notch impact strength and good blow molding processability.

The high melt strength impact-resistant polypropylene prepared by the invention is used as base resin, and the obtained blown film has obviously higher tensile breaking stress and better tear resistance through a blown film process, and has better performance; in particular, in comparison with comparative examples 1 to 4, the various properties of the polypropylene blown films provided according to the invention are clearly due to the comparative examples (as shown in table 3). In actual operation, the common impact-resistant co-polypropylene blow molding process is difficult to adjust, the process is complex, and the obtained blow molding film has uneven thickness and poor mechanical property. Furthermore, films having a thickness of 15 microns could not be obtained using EPS 30R.

Furthermore, more important are: firstly, the blown film prepared by using the series of high melt strength polypropylene has the characteristics of similar stretching performance and tear resistance performance in the MD and TD directions, the defect that the performance of the conventional polypropylene blown film in the TD direction is poorer than that in the MD direction is overcome, and the use reliability and the application universality are improved; secondly, the film provided by the invention has the characteristic that the performance still keeps more than 90% of the performance of the conventional film thickness film under the condition of lower film thickness, which can be beneficial to reducing the material use and increasing the added value of products in unit weight; thirdly, the standard deviation of the thickness of the blown film provided by the invention is smaller, which shows that the thickness of the film obtained by the resin through the blowing process is more uniform, and the improvement of the mechanical property is facilitated.

Although the present invention has been described in detail, modifications within the spirit and scope of the invention will be apparent to those skilled in the art. Moreover, it should be understood that the various aspects recited, portions of different embodiments (aspects), and various features recited may be combined or interchanged either in whole or in part. In the various embodiments described above, those embodiments that refer to another embodiment may be combined with other embodiments as appropriate, as will be appreciated by those skilled in the art. Furthermore, those skilled in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.

Claims

1. A polypropylene composition for blown film comprising as a base resin a high melt strength impact polypropylene comprising a propylene homopolymer component and an ethylene-1-butene copolymer component and having a ratio of Mw of room temperature trichlorobenzene solubles to Mw of room temperature trichlorobenzene insolubles of greater than or equal to 0.64 and less than or equal to 1; a room temperature xylene solubles content of greater than 10% by weight and less than 30% by weight;

the butene content of the base resin is 9.5-20 wt%;

the composition is also added with other processing aids, and the other processing aids are selected from at least one of an antioxidant, an auxiliary antioxidant, a lubricant and an antistatic agent;

the propylene homopolymer component comprises at least a first propylene homopolymer and a second propylene homopolymer; the melt index of the first propylene homopolymer is less than the melt index of the second propylene homopolymer; the base resin is prepared by performing a propylene homopolymerization reaction in the presence of a first propylene homopolymer to obtain a propylene homopolymer component comprising the first propylene homopolymer and a second propylene homopolymer, and then performing an ethylene-1-butene copolymerization reaction in the presence of the propylene homopolymer component to obtain a material comprising an ethylene-1-butene copolymer;

the composition also includes a linear low density polyethylene.

2. Composition according to claim 1, characterized in that the molecular weight distribution Mw/Mn of the base resin is less than or equal to 10 and greater than or equal to 4; and/or Mz +1/Mw is greater than or equal to 10 and less than or equal to 20.

3. The composition of claim 1, wherein the base resin has a melt index of 0.1 to 15g/10min measured at 230 ℃ under a load of 2.16 kg.

4. The composition of claim 3, wherein the base resin has a melt index of 0.1 to 6g/10min measured at 230 ℃ under a load of 2.16 kg.

5. The composition of claim 1, wherein the weight ratio of ethylene-1-butene copolymer component to propylene homopolymer component in the high melt strength impact polypropylene is 11-80: 100; and/or the melt index ratio of the propylene homopolymer component to the base resin comprising the propylene homopolymer component and the ethylene-1-butene copolymer component is greater than or equal to 0.6 and less than 1.

6. A polypropylene blown film obtained by blow molding a film using the composition according to any one of claims 1 to 5.

7. The polypropylene blown film according to claim 6, wherein the thickness of the polypropylene blown film is 15-60 μm.

8. The polypropylene blown film according to claim 6, wherein the tensile stress at break of the polypropylene blown film is more than 15 MPa; and/or a nominal strain at break of greater than 300%; and/or a tear strength greater than 50N/mm; and/or the transverse tear strength differs from the machine direction tear strength by less than 20%.

9. The polypropylene blown film according to claim 8, wherein the polypropylene blown film has a tensile stress at break of more than 25 MPa; and/or a nominal strain at break greater than 480%; and/or a tear strength greater than 90N/mm; and/or the transverse tear strength differs from the machine direction tear strength by less than 10%.

10. A process for the preparation of a polypropylene blown film according to any one of claims 6 to 9, said process comprising extrusion granulation of said composition followed by blow molding thereof into a film.

11. The method as claimed in claim 10, wherein the temperature of the extrusion is 150-240 ℃; and/or the temperature of the blown film is 170-230 ℃.

12. The method as claimed in claim 11, wherein the temperature of the extrusion is 170-220 ℃; and/or the temperature of the blown film is 185-220 ℃.

13. The method of claim 10, further comprising a base resin preparation step comprising:

the first step is as follows: propylene homopolymerization comprising:

the first stage is as follows: carrying out a propylene homopolymerization reaction in the presence or absence of hydrogen under the action of a Ziegler-Natta catalyst containing a first external electron donor to obtain a reactant flow containing a first propylene homopolymer;

and a second stage: adding a second external electron donor to perform a complex reaction with a catalyst in the reactant flow, and then performing a propylene homopolymerization reaction in the presence of the first propylene homopolymer and hydrogen to generate a second propylene homopolymer, so as to obtain a propylene homopolymer component containing the first propylene homopolymer and the second propylene homopolymer;

wherein the content of the first and second substances,

the melt indices of the first propylene homopolymer and the propylene homopolymer component, measured at 230 ℃ under a load of 2.16kg, are 0.001-0.4g/10min and 0.1-15g/10min, respectively; and the weight ratio of the first propylene homopolymer to the second propylene homopolymer is from 40:60 to 60: 40;

the second step is that: ethylene-1-butene copolymerization comprising carrying out a gas phase copolymerization of ethylene and 1-butene in the presence of the propylene homopolymer component and hydrogen to produce an ethylene-1-butene copolymer component, to obtain the base resin comprising the propylene homopolymer component and the ethylene-1-butene copolymer component.

14. The method of claim 13,

the first external electron donor is selected from the general formula R¹R²Si(OR³)₂At least one of the compounds of (a); wherein R is²And R¹Each independently selected from C₁-C₆Straight or branched alkyl, C₃-C₈Cycloalkyl and C₅-C₁₂Heteroaryl of (A), R³Is C₁-C₃A linear aliphatic group;

the second external electron donor is selected from at least one of compounds shown as chemical general formulas (I), (II) and (III);

wherein R is₁And R₂Each independently selected from C₁-C₂₀One of linear, branched or cyclic aliphatic radicals, R₃、R₄、R₅、R₆、R₇And R₈Each independently selected from a hydrogen atom, a halogen atom, C₁-C₂₀Straight or branched alkyl of (2), C₃-C₂₀Cycloalkyl radical, C₆-C₂₀Aryl radical, C₇-C₂₀Alkylaryl and C₇-C₂₀One of aralkyl groups; r₉、R₁₀And R₁₁Each independently is C₁-C₃Straight-chain aliphatic radical, R₁₂Is C₁-C₆Straight or branched alkyl or C₃-C₈A cycloalkyl group;

and the molar ratio of the second external electron donor to the first external electron donor is 5-30.

15. The process according to claim 13 or 14, characterized in that the propylene homopolymer component has the following characteristics:

molecular weight distribution Mw/Mn is 6-20;

the fraction having a molecular weight of more than 500 ten thousand is present in an amount of more than or equal to 1.5% by weight and less than or equal to 5% by weight;

the content of fractions having a molecular weight of less than 5 ten thousand is greater than or equal to 15.0% by weight and less than or equal to 40% by weight;

mz +1/Mn is greater than or equal to 70 and less than 150.

16. The process according to claim 15, characterized in that the propylene homopolymer component has the following characteristics:

the molecular weight distribution Mw/Mn is 10-16.