EP2788388A1

EP2788388A1 - Propylene terpolymers

Info

Publication number: EP2788388A1
Application number: EP12795438.6A
Authority: EP
Inventors: Roberta Marzolla; Monica Galvan; Tiziana Caputo
Original assignee: Basell Poliolefine Italia SRL
Current assignee: Basell Poliolefine Italia SRL
Priority date: 2011-12-05
Filing date: 2012-12-05
Publication date: 2014-10-15
Also published as: WO2013083576A1; CN104619729A; CN104619729B

Abstract

A propylene ethylene 1-butene terpolymer wherein: (i) the content of ethylene derived units ranges from 0.5 wt% to 2.0 wt%, (ii) the content of 1-butene rangesfrom 5.0 wt% to 8.0 wt%, (iii) the melting point (Tm) ranges from 136°C to 148°C; wherein said terpolymer is obtained with a polymerization process carried out in a gas-phase polymerization reactor comprising at least two interconnected polymerization zones.

Description

Title:

PROPYLENE TERPOLYMERS

The present invention relates to propylene terpolymers. particularly suitable to be used as films such as cast films, bi- or mono-oriented films, heat-sealable films and metalized films having good optical properties and excellent sealing properties combined with good shrinkage properties and softness.

Films made of propylene copolymers or terpolymers are known in the art.

Propylene copolymers or terpolymers are used because, with respect to propylene homopolymers, are characterized by a better impact, lower rigidity, better transparency. In some cases however, it is difficult to find the acceptable balance between those properties, particularly when properties contrasting to each other are desired. When a certain softness is desired, for example, it is commonly obtained in the presence of high amount of xylene soluble fractions that make them unsuitable for food contact applications.

Metalized films have been widely used for their superior decorative properties, gas barrier properties and light-shielding properties. In particular aluminum.metallized film has been used in large amount. However the adhesive properties onto the metalized surface are a key step for the metallization process.

WO 2003/037981 discloses pipes made from at least a polypropylene composition obtained by a process carried out in a reactor comprising two interconnected polymerization zones.

Said process provides polypropylene compositions with high stiffness and impact resistance particularly suitable for pipes. According to this document when the propylene composition is a propylene -ethylene -butene-1 terpolymer the ethylene content ranges from 2-5 wt%.

WO 2009/019169 discloses a propylene ethylene 1-butene terpolymer obtained by a process carried out in a reactor comprising two interconnected polymerization zones. This terpolymer has a xylene soluble fraction higher than 9 wt% and a comonomers content higher than 8 wt%. In particular when the ethylene content is lower than 2.5 wt% the 1-butene content is higher than 10 wt%. The applicant unexpectedly found that a propylene ethylene 1 -butene terpolymer having a certain amount of comonomer and obtained by a polymerization process carried out in a reactor comprising two interconnected polymerization zones can be advantageously used for obtaining metalized cast films.

Thus an object of the present invention is a propylene ethylene 1 -butene terpolymer wherein:

(i) the content of ethylene derived units ranges from 0.5 wt% to 2.0 wt%, preferably from 0.6 wt% to 1.8 wt%; more preferably from 0.8 wt% to 1.5 wt%;

(ii) the content of 1 -butene ranges from 5.0 wt% to 8.0 wt%, preferably from 6.5 wt% to 7.5 wt%, more preferably from 5.5 wt% to 7.5 wt%; even more preferably from 6.0 wt% to 7.0 wt;

(iii) the melting point (Tm) ranges from 136°C to 148°C; preferably from 137°C to 145°C;

wherein said terpolymer is obtained with a polymerization process carried out in a gas- phase polymerization reactor comprising at least two interconnected polymerization zones. The polymerization process is carried out in a first and in a second interconnected polymerization zone to which propylene, ethylene and 1 -butene are fed in the presence of a catalyst system and from which the polymer produced is discharged. The growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said first polymerization zone and enter the second of said polymerization zones (downcomer) through which they flow in a densified form under the action of gravity, leave said second polymerization zone and are reintroduced into said first polymerization zone, thus establishing a circulation of polymer between the two polymerization zones. Generally, the conditions of fast fluidization in the first polymerization zone is established by feeding the monomers gas mixture below the point of reintroduction of the growing polymer into said first polymerization zone. The velocity of the gas into the first polymerization zone is higher than the transport velocity under the operating conditions and is normally between 2 and 15 m/s. In the second polymerization zone, where the polymer flows in densified form under the action of gravity, high values of density of the solid are reached which approach the bulk density of the polymer; a positive gain in pressure can thus be obtained along the direction of flow, so that it becomes possible to reintroduce the polymer into the first reaction zone without the help of mechanical means. In this way, a "loop" circulation is set up, which is defined by the balance of pressures between the two polymerization zones and by the head loss introduced into the system. Optionally, one or more inert gases, such as nitrogen or an aliphatic hydrocarbon, are maintained in the polymerization zones, in such quantities that the sum of the partial pressures of the inert gases is preferably between 5 and 80% of the total pressure of the gases. The operating parameters such as, for example, the temperature are those that are usual in gas-phase olefin polymerization processes, for example between 50°C and 120°C. The process can be carried out under operating pressure of between 0,5 and 10 MPa, preferably between 1.5 and 6 MPa. The polymerization process carried out in a gas-phase polymerization reactor comprising at least two interconnected polymerization zones is described in the European patent EP 782587.

Preferably, the various catalyst components are fed to the first polymerization zone, at any point of said first polymerization zone. However, they can also be fed at any point of the second polymerization zone. Molecular weight regulators known in the art, particularly hydrogen, can be used to regulate the molecular weight of the growing polymer.

By the use of the means described in WO00/02929 it is possible to totally or partially prevent that the gas mixture present in the riser enters the downcomer; in particular, this is preferably obtained by introducing in the downcomer a gas and/or liquid mixture having a composition different from the gas mixture present in the riser. According to a particularly advantageous embodiment of the present invention, the introduction into the downcomer of said gas and/or liquid mixture having a composition different from the gas mixture present in the riser is effective in preventing the latter mixture from entering the downcomer. Therefore, it is possible to obtain two interconnected polymerization zones having different monomer compositions and thus able to produce polymers with different properties.

In the riser, the molar concentration of ethylene (expressed as mole% with respect to the total amount of the monomers in the gas-phase) usually ranges from 0.5 to 5 mole%, preferably from 1 to 4 mole% and the molar concentration of the 1-butene ranges from 4 to 20 mole%, preferably from 5 to 10 mole%. The Ziegler-Natta catalysts suitable for producing the propylene terpolymers of the instant invention comprise a solid catalyst component comprising at least one titanium compound having at least one titanium-halogen bond and at least an electron-donor compound (internal donor), both supported on magnesium chloride. The Ziegler-Natta catalysts systems further comprise an organo-aluminum compound as essential co- catalyst and optionally an external electron-donor compound.

Suitable catalysts systems are described in the European patents EP45977, EP361494, EP728769, EP 1272533 and in the international patent application WO00/63261.

Preferably, the solid catalyst component comprises Mg, Ti, halogen and an electron donor selected from mono- and diesters of aromatic dicarboxylic acids having the -COOH groups into ortho position, wherein at least one of the R hydrocarbyl radical of the -COOR groups contains from 1 to 20 carbon atoms. Particularly preferably the electron donor is selected from di-n-propyl, di-n-butyl, diisobutyl, di-n-heptyl, di-2-ethylhexyl, di-n-octyl, di-neopentil phthalates.

According to a preferred method, the solid catalyst component can be prepared by reacting a titanium compound of formula Ti(OR)_n__yXy, where n is the valence of titanium and y is a number between 1 and n, preferably T1CI4, with a magnesium chloride deriving from an adduct of formula MgCb pROH, where p is a number between 0.1 and 6, preferably from 2 to 3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared in spherical form by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct (100-130 °C). Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in US 4,399,054 and US 4,469,648. The so obtained adduct can be directly reacted with the Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130 °C) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3, preferably between 0.1 and 2.5. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold T1CI4 (generally 0 °C); the mixture is heated up to 80-130 °C and kept at this temperature for 0.5-2 hours. The treatment with T1CI4 can be carried out one or more times. The internal donor can be added during the treatment with T1CI₄ and the treatment with the electron donor compound can be repeated one or more times. Generally, the internal electron donor compound is used in molar ratio with respect to the MgCl₂ of from 0.01 to 1 preferably from 0.05 to 0.5. The preparation of catalyst components in spherical form is described for example in European patent application EP- A-395083 and in the International patent application WO98/44009. The solid catalyst components obtained according to the above method show a surface area (by B.E.T. method) generally between 20 and 500 m²/g and preferably between 50 and 400 m²/g, and a total porosity (by B.E.T. method) higher than 0.2 cm /g preferably between 0.2 and 0.6 cm³/g. The porosity (Hg method) due to pores with radius up to IO.OOOA generally ranges from 0.3 to 1.5 cm³/g, preferably from 0.45 to 1 cm³/g.

The organo-aluminum compound is preferably an alkyl-Al selected from the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n- butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum's with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesqui chlorides such as AlEt₂Cl and Al₂Et3Ci3.

Preferred external electron-donor compounds include silicon compounds, esters such as ethyl 4-ethoxybenzoate. Another class of preferred external donor compounds is that of silicon compounds of formula R_a ⁵Rb⁶Si(OR⁷)_c, where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R⁵, R⁶, and R⁷, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms. Particularly preferred are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, diisopropyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1 ,trifluoropropyl-2-ethylpiperidinyl- dimethoxysilane and l,l,l,trifluoropropyl-metil-dimethoxysilane. The external electron donor compound is used in such an amount to give a molar ratio between the organo- aluminum compound and said electron donor compound of from 0.1 to 500.

The catalytic system can be pre -contacted (pre-polymerized) with small amounts of olefins. The molecular weight of the propylene terpolymers can be regulated by using known regulators, such as hydrogen.

The propylene terpolymer of the present invention preferably is further endowed with one or more of the following features: -the melt flow rate (MFR) (ISO 1 133 230°C, 2.16 kg) ranges from 3 to 20 g/10 min; preferably from 5 to 15 g/10 min;

-the polydispersity index (PI) ranges from 2.0 to 7.0, preferably from 3.0 to 6.5, more preferably from 3.5 to 6.0;

-the amount of xylene solubles at 25°C is lower than 5.5 wt%, preferably lower than 4.5 wt%, more preferably lower than 4 wt%;

-the haze measured on 50 micron thick cast film is lower than 1.5 %; preferably lower than 1%; more preferably lower than 0.7 %

-the low sealing initiation temperature (SIT) ranges from 100 to 120°C; preferably from 108 to 117 °C.

The terpolymer of the present invention are particularly suitable for film applications such cast films and oriented films, BOPP films, heat-sealable films and all the applications requiring heat sealability and softness. Such propylene terpolymers have a good balance between optical properties and sealing properties combined with good shrinkage properties and softness.

In particular the terpolymer of the present invention are particularly fit for metalized cast film applications. Thus a further object of the present invention is a metalized film, preferably a metalized cast film comprising one or more layer wherein the metalized layer comprises the terpolymer of the present invention.

When the terpolymer of the present invention is used for the obtainment of the metalized layer it shows an excellent aluminum bonding strength and vacuum metallising gloss. In particular in view of the particular polymerization process used for the obtainement of the terpolymer of the present invention the vacuum metallising gloss shows the same values of a blend of a similar terpolymer obtained by using a different polymerization process with blended high density polyethylene (HDPE) that is used in the art for enhancing this property.

The propylene terpolymers of the invention can optionally further comprise at least one nucleating agent. Preferably, the propylene terpolymers comprise up to 2500 ppm, more preferably from 200 to 2000 ppm, of at least one nucleating agent.

The at least one nucleating agent can be selected among inorganic additives such as talc, silica or kaolin, salts of monocarboxylic or polycarboxylic acids, e.g. sodium benzoate or aluminum tert-butylbenzoate, dibenzylidenesorbitol or its Ci-Cs-alkyl-substituted derivatives such as methyldibenzylidenesorbitol, ethyldibenzylidenesorbitol or dimethyldibenzylidenesorbitol or salts of diesters of phosphoric acid, e.g. 2,2'- methylenebis(4,6,-di-tert-butylphenyl)phosphate sodium or lithium salt. Particularly preferred nucleating agents are 3,4-dimethyldibenzylidenesorbitol; aluminum-hydroxy- bis[2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate]; sodium 2,2'-methylene-bis(4,6- ditertbutylphenyl)phosphate and bicyclo[2.2.1 ]heptane-2,3-dicarboxylic acid, disodium salt (1 R,2R,3R,4S), and HPN-20E that contains Zinc compounds and 1 ,2- ciclohexanedicarboxylic acid calcium salt. The at least one nucleating agent may be added to the propylene terpolymer by known methods, such as by melt blending the at least one nucleating agent and the propylene terpolymer under shear condition in a conventional extruder.

The propylene terpolymers obtained by the process of the present invention may then be added with additional additives commonly employed in the polyolefin field, such as antioxidants, light stabilizers, antiacids, antiblocking, colorants and fillers.

The following not-limiting examples are given to better illustrate the present invention.

Examples

The following characterization methods were used in testing the propylene terpolymers produced.

Determination of the comonomer content:

The comonomers content have been determined by infrared spectroscopy by collecting the IR spectrum of the sample vs. an air background with a Fourier Transform Infrared spectrometer (FTIR) the instrument data acquisition parameters are:

purge time: 30 seconds minimum

collect time: 3 minutes minimum

apodization: Happ-Genzel

resolution: 2 cm-1.

Sample Preparation:

Using a hydraulic press, a thick sheet is obtained by pressing about g 1 of sample between two aluminum foils. If homogeneity is in question, a minimum of two pressing operations are recommended. A small portion is cut from this sheet to mold a film. Recommended film thickness ranges between 0.02-:0.05 cm (8 - 20 mils).

Pressing temperature is 180±10°C (356°F) and about 10 kg/cm2 (142.2 PSI) pressure for about one minute. Release the pressure and remove from the press and cool the sample to room temperature.

The spectrum of a pressed film of the polymer is recorded in absorbance vs. wavenumbers (cm-1). The following measurements are used to calculate ethylene and 1- butene content:

Area (At) of the combination absorption bands between 4482 and 3950 cm -1 which is used for spectrometric normalization of film thickness.

Area (AC2) of the absorption band between 750-700 cm-1 after two proper consecutive spectroscopic subtractions of an isotactic non additivate polypropylene spectrum and then of a reference spectrum of an 1 -butene -propylene random copolymer in the range 800- 690 cm-1.

Height (DC4) of the absorption band at 769 cm-1 (maximum value), after two proper consecutive spectroscopic subtractions of an isotactic non additivate polypropylene spectrum and then of a reference spectrum of an ethylene -propylene random copolymer in the range 800-690 cm-1.

In order to calculate the ethylene and 1 -butene content calibration straights lines for ethylene and 1 -butene obtained by using samples of known amount of ethylene and 1- butene are needed:

Calibration of ethylene:

Calibration straight line is obtained by plotting AC2 /At versus ethylene molar percent (%C2m). The slope GC2 is calculated from a linear regression.

Calibration of 1 -butene

A calibration straight line is obtained by plotting DC4 /At versus butene molar percent (%C4m). The slope GC4 is calculated from a linear regression.

Spectrum of the unknow sample is recorded and then (At), (AC2) and (DC4) of the unknown sample are calculated. The ethylene content (% molar fraction C2m) of the sample is calculated as follows:

The 1 butene content (% molar fraction C4m) of the sample is calculated as follows:

The propylene content (molar fraction C3m) is calculated as follows:

C3m = 100 - %C m - %C2m

The ethylene, 1 -butene contents by weight are calculated as follows:

28 · C2m

%C2wi

(56 · C4m + 42^■ C3m + 28 - C2m)

Solubility in xylene: 2.5 g of polymer are dissolved in 250 ml of xylene at 135° C under agitation. After 20 minutes the solution is allowed to cool to 25° C, still under agitation, and then allowed to settle for 30 minutes. The precipitate is filtered with filter paper, the solution evaporated in nitrogen flow, and the residue dried under vacuum at 80° C until constant weight is reached. Thus one calculates the percent by weight of polymer soluble and insoluble at room temperature (25° C)

Melt Flow Rate (MFR): Determined according to ISO 1133 230°C, 2.16 kg.

Melting temperature and crystallization temperature: Determined by differential scanning calorimetry (DSC), weighting 6 ±1 mg, is heated to 220 ±1° C at a rate of 20 °C/min and kept at 220 ±1 ° C for 2 minutes in nitrogen stream and it is thereafter cooled at a rate of 20° C/min to 40 ±2° C, thereby kept at this temperature for 2 min to crystallise the sample. Then, the sample is again fused at a temperature rise rate of 20° C/min up to 220° C ±1. The melting scan is recorded, a thermogram is obtained, and, from this, melting temperatures and crystallization temperatures are read.

Preparation of the cast film specimens

Films with a thickness of 50 μπι were prepared by extruding each polymer composition in a single screw Collin extruder (length diameter ratio of screw: 30) at a film drawing speed of 7 m/min and a melt temperature of 210-250 °C.

Sealing Initiation Temperature (S.I.T.):

Determined as follows.

Preparation of the film specimens

Some films with a thickness of 50 μπι are prepared by extruding each test composition in a single screw Collin extruder (length diameter ratio of screw: 30) at a film drawing speed of 7 m/min. and a melt temperature of 210-250 °C. Each resulting film is superimposed on a 1000 μπι thick film of a propylene homopolymer having an isotacticity index of 97 and a MFR L of 2 g/10 min. The superimposed films are bonded to each other in a Carver press at 200 °C under a 9000 kg load, which is maintained for 5 minutes. The resulting laminates are stretched longitudinally and transversally, i.e. biaxially, by a factor 6 with a TM Long film stretcher at 150 °C, thus obtaining a 20 μηι thick film (18 μηι homopolymer + 2 μηι test composition).

2 x 5 cm specimens are cut from the films.

Determination of the S.I.T.

For each test two of the above specimens are superimposed in alignment, the adjacent layers being layers of the particular test composition. The superimposed specimens are sealed along one of the 5 cm sides with a Brugger Feinmechanik Sealer, model HSG- ETK 745. Sealing time is 0.5 seconds at a pressure of 0.1 N/mm². The sealing temperature is increased for each seal, starting from about 10 °C less than the melting temperature of the test composition. The sealed samples are left to cool and then their unsealed ends are attached to an Instron machine where they are tested at a traction speed of 50 mm/min.

The S.I.T. is the minimum sealing temperature at which the seal does not break when a load of at least 2 Newtons is applied in the said test conditions.

- Haze on film

Determined on 50 μηι thick films of the test composition, prepared as described above. The measurement was carried out on a 50x50 mm portion cut from the central zone of the film.

The instrument used for the test was a Gardner photometer with Haze -meter UX- 10 equipped with a G.E. 1209 lamp and filter C. The instrument calibration was made by carrying out a measurement in the absence of the sample (0% Haze) and a

measurement with intercepted light beam (100% Haze).

Example 1 :

Propylene terpolymers are prepared by polymerising propylene, ethylene and butene-1 in the presence of a highly stereo specific Ziegler-Natta catalyst.

The Ziegler-Natta catalyst was prepared according to the Example 5, lines 48-55 of the European Patent EP728769. Triethylaluminium (TEA) was used as co-catalyst and dicyclopentyldimethoxysilane as external donor, with the weight ratios indicated in Table 1. The propylene terpolymers of the examples were prepared in a single gas-phase polymerization reactor comprising two interconnected polymerization zones, a riser and a downcomer, as described in the European Patent EP782587 and WO00/02929.

The above catalyst system is then transferred into a reactor containing an excess of liquid propylene and propane to carry out prepolymerisation at 25° C for 1 1 minutes before introducing it into a polymerisation reactor.

Into the polymerisation reactor the propylene terpolymers are produced by feeding in a continuous and constant flow the prepolymerized catalyst system, hydrogen (used as molecular weight regulator), propylene, ethylene and butene-1 in the gas state (the feeding quantities expressed in mol% are shown in table 1).

The other operative conditions are indicated in Table 1.

The polymer particles exiting from the polymerization step were subjected to a steam treatment to remove the unreacted monomers and dried. The characteristics of the polymer has been reported on table 2

Table 1

Table 2

Comparative Example 1 :

The polymer of comaparative example 1 is a commercial polymer sold by Sumitomo under the tradename Cosmoplene FL 7540L. It was analyzed and it consists of a blend of 3.6 wt% of polyethylene and the remaining part being a propylene ethylene 1 -butene terpolymer having an ethylene content of 0.8 wt% and a 1 -butene content of 6.7 wt% produced with 2 gas phase reactors in series and an additives. The fraction soluble in xylene at 25°C of the terpolymer is 2.6 wt%, the melting point is 138°C and the MFR is 6.9 g/10 min.

Cast film of the polymer of example 1 and comparative example 1 have been produced. They are both metalized by depositing aluminum under vacuum. The results have been reported in table 3

Table 3

+++ = good performance

From table 3 it is clear that with the terpolymer of the present invention it is possible to achieve the same results of the comparative example 1 without adding polyethylene.

Claims

A propylene ethylene 1 -butene terpolymer wherein:

(i) the content of ethylene derived units ranges from 0.5 wt% to 2.0 wt%,

(ii) the content of 1 -butene ranges from 5.0 wt% to 8.0 wt%,

(iii) the melting point (Tm) ranges from 136°C to 148°C;

wherein said terpolymer is obtained with a polymerization process carried out in a gas-phase polymerization reactor comprising at least two interconnected polymerization zones.

The propylene ethylene 1 -butene terpolymer according to claim 1 wherein:

(i) the content of ethylene derived units ranges from 0.6 wt% to 1.8 wt%;

(ii) the content of 1 -butene ranges from 6.5 wt% to 7.5 wt%;

(iii) the melting point (Tm) ranges from 137°C to 145°C.

The propylene ethylene 1 -butene terpolymer according to claims 1 or 2 wherein the polymerization process is carried out in a first and in a second interconnected polymerization zone to which propylene, ethylene and 1 -butene are fed in the presence of a catalyst system and from which the polymer produced is discharged; the growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said first polymerization zone and enter the second of said polymerization zones (downcomer) through which they flow in a densified form under the action of gravity, leave said second polymerization zone and are reintroduced into said first polymerization zone, thus establishing a circulation of polymer between the two polymerization zones.

Films comprising the propylene ethylene 1 -butene terpolymer of claim 1

A metallized cast film wherein the metalized layer comprises the terpolymer of claim 1