|Title of Invention||
PROCESS FOR THE PRODUCTION OF PROPYLENE TERPOLYMERS
|Abstract||The present invention discloses a process for producing terpolymer of propylene• ethylene and one C4 - C8 alpha-olefin, wherein the process is carried out in one or more slurry reactors in the presence of catalysts by feeding into a slurry reactor a reaction mixture containing 50-85 wt -% of propylene, 1-10 wt-% of ethylene, 15-40 wt-% of C4 - C8 alpha-olefin, a catalyst system capable of providing olefin polymerization and optionally hydrogen; polymerizing said reaction mixture at a temperature of 60 to 70 °C, and under pressure of 30 to 90 bar for a sufficient time to obtain a propylene terpolymer amounting to 50-99 wt-% of the end product; transferring said reaction mixture into a gas phase reactor operated at a temperature of 60 to 90 °C, and continuing polymerization in said gas phase reactor, into which additional amounts of 0 to 30 wt-% of ethylene, 0 to 10 wt-% of C4 - C8 alpha-olefin, 0 to 40 wt-% of propylene and optionally hydrogen are added for producing a propylene terpolymer amounting to 1 to 50 wt-% of the end product whereby a terpolymer is obtained having a melting temperature of between 126°C to 132°C.|
|Full Text||Basckground of the Invention
Field of the Invention
The present inveniion relates to a process for producing terpolymrr
of propylen,, ethylene and one C4-C8 alpha-olefin. In particular, the
present invention concerns film-making terpolymers of propylene and at least two alpba-olefin
monomers and a process for producing the polymers. The present terpolymess are suitable,
e.g., for applications where good heat sealability and softness are required.
Description of Related Art
Polyolefins used in film applications as sealing layers should have low melting temperatures for good heat sealing performance. In polypropylene films, random copolymers having a relatively high content of comonomers, usually ethylene, are commonly used as such a sealing componen.. A high comonomcr content is required for obtaining low melting temperature.. There are, however, problems associated with the production of random copolymers as well as with the end-properties of the material. This is on account of its low melting temperature, broadness of melting range due to poor comonomer distribution, and polymer solubility in the polymerisation medium. By incoIpOrating a third monomer, such as 1-butene or another higher alpha-olefin, the above-meniioned problems can. to some extent, be overcome, and a number of processes for producing tetpOlymers of propylene are known in the art. Howeve., there are still problems relating to the produciion of the polymers and to the level of solubles of the products.
In comparison to homopolymer production, when a telpolymer or another high comonomrr content polymer baving a low melting temperature is to be produced in a slurry reactor, the reaction temperature in that reactor must be lowered because of the high solubles content in the polymer. Further, the comonomers used in the polymerization, such as ethylene and butylene, cause swelling of the polymers in the polymerization medium of the slurry reactor. When swollen and soft polymer particles are flashed after polymerization, the morphology of the particles is destroyed and the bulk density of the powder becomes very low. There is also a higher demand for external heat before it is possible to evaporate unreacted monomer after
the slurry reactor. Further, the surface temperature of the flash line must be lowered because of the low melting temperature of the product. Liquid monomer entering the flash together with a sticky polymer will plug the vessel. If pressure in the flash vessel is reduced too much to improve monomer evaporaiion, flashing takes place too fast and, as mentioned above, the morphology of particles is destroyed causing problems in powder handling.
The above-meniioned problems are aggrevated when the proportion of comonomers in the terpolymer increases.
For this reason, in the prior art polymerizaiion of terpolymers having a melting temperature below 132 °C bas been carried out by means of gas phase processes.
In EP 0 674 991 a propylene terpolymer is disclosed which comprises 20 to 60 wt-% of a copolymer of propylene and ethylene, containing 1 to 5 wt-% of ethylene, and 40 to 80 wt-% of a copolymer of propylene together with ethylene and a C4-C8 alpha-olefin, the ethylene content being 1 to 5 wt-% and C4-C8 alpha-olerm content being 6 to 15 wt-%. Said product is produced preferably in two gas phase reactors. The C4-C8 alpha-olefin is added in the second gas phase reactor.
US Patent Specification No.4,740,551 discloses a process for inanufacturing propylene-ethylene impact copolymers. According to this known process, propylene is first homopolymerized in a plug flow pipeline reactor, the polymer is then transferred to a second step wherein homopolymerization is continued by adding propylene, whereinafter the polymer mixture is transferred to a third gas phase step and polymerization is carried out in the presence of propylene and ethylene for producing said impact copolymer.. In the above mentioned patent no other alpha-Olefin is used in the third step, which is the only step in which a comonomrr other than propylene is used.
Summary of the Inyention
It is an object of the present invention to provide novel materials based on terpolymers, which can be used for manufacturing films having good heat sealing properiies.
It is another object of the present invention to provide a process for producing rerpolymers of propylene, ethylene and other alpha-olefins in a process comprising in particular slurry and
gas phase reactor(s) connecred directly together while avoiding the disadvantages related to
operability when producing high comonomer content products.
These and other objects, together with the advantages thereofover known processes and
products, which shall become apparent from the specification which follow are accomplished by the irrvention as hereinafter described and claimed.
The present invention is based on !he finding that the properties of propylene terpolymers can be improved by increasing the amount of heavier comonomers in relation to ethylene. It has further been found that such terpolymers are advantageoasly produced by means of multi-reactor polymensation technology. Thus, the invention comprises using a combination of two or more reactors preferably connected in a cascade for producing a mixture of different propylene terpolymer compositions, so as to obtain apolymer product witha ratio of ethylene-to-butylene (or heavier alpha-olefins) of less than 0.3. Such comonomer distribution (randomness) gives a material having low solubles content of preferably less than 65 % hexane solubles (determined by FDA test). good optica1 properties and good processibility.
According to the present invention, it is particularly preferred to produce the material in a
combination of one or more bulk polymerisation reactor(s) and one or more gas phase
reactor(s). Thereby, the comonomer conversion can be increased, operation of the copolymerisation process is facilitated by using the gas phase, and the structure and properties of the resulting product lead to improved hear sealability of articles manufactured from the product.
The present invention provides a process for producing terpolymer of propylene, ethylene and one C4- C8 alpha-olefin, wherein the process is carried out in one'or more slurry reactors in the presence of catalysts characterized by the following steps:-
a) feeding into a slurry reactor a reaction mixture containing 50-85wt
_% of propylene, 1-10 wt-% of ethylene, 15-40 wt-% of C4 - C8 alpha-olefin, a catalyst system capable of providing olefin
polymerizaiion and optionally hydrogen;
b) polymerizing said reaction mixture at a temperature of-50 to 70 °C,
and under pressure of 30 to 90 bar for a sufficient time to obtain a
propylene terpolymer amouniing to 50-99 wt-% of the end product
c) transferring said reaction mixture into a gas phase reactor operated
at a temperature of 60 to 90 °C; and
d) continuing polymerization in said gas phase reactor. fnto which
additional amounts of 0 to 30 wt-% of ethylene, 0 to 10 wt-% of C4-
C8 alpha-olefin, 0 to 40 wt-% of propylene and optionally hydrogen
are added for producing a propylene terpolymer amounting to 1 to
50 wt-% of the end product whereby a terpolymer is obtained
having a melting temperature of between 126°C to 132°C.
Thus, according to the present invention, the terpolymerization is carried out in the slurry
phase preferably in a loop reactor by using relatively high amounts of C4-C8 alpha-olefins as
comonomers. This is possible because the polymer shurry is transferred directly into a gas
phase reactor without separating the reaction medium.
According to one embodiment a loop reactor is used as said shurry reactor. According to another embodiment said shurry phase is carried out in two shurry reactors, preferably but not necessarily in two loop reactors. In this way the comonomer distribution can be easily controlled. When continuing the polymerization in a gasphase factor or reactors,
railored by adjusting comonomer ratios in different reactors.
More specifically, the terpolymer according to the preset invention is characterized by what
is stated in the characterizing part of claim 1.
The process according to the invention is characterized by what is stated in the characterizing part of claim 5.
Next, the invention will be examined more closely with the aid of a detailed description and
with reference to the attached drawings and the following working examples. SRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS;
Figure 1 depicts the seal strength (max. Seal Force, N) of the polymers of Examples 11,14 and 15 versus sealing temperature;
Figure 2 shows the hot tack performance (max. hot tack force, N) of the same polymers versus sealing temperature;
Figure 3 indicates the seal strength (max. Seal Force, N) versus sealing temperature of the terpolymer according to Example 12 in comparison to two commercial terpolymers; and Figure 4 compares hot tack performance of the same polymers as in Figure 3.
Detailed Description of the Invention
According to the invention there is provided a propylene terpolymer which is produced in a multistage process for obtaining a high monomer content polypropylene having a low melting point is provided. The comonomers of the terpolymer are select from the group consisting of alpha-olefins, CH2=CHR (R=H or alkyl group).
The polymer produced is a mixture of different polymer compositions. A low melting temperature and a broad melting range are combined with good comonomer distribution. The ratio of the two comonomer components, in particular the ethylene-ro-butylene ratio in the terpolymer is lower than in the conventional process. In practical applications, in particular for fIlm production, all these features contribute to give a combination of low xylene and hexane solubles, good stiffness, good optical properties, a broader sealing window, and superior hot tack.
A good combination of sealing properties and hot tack is obtained by a material having so broad melting distribution that a sufficient fraction of polymer melts at the sealing temperature, but still enough material is unmelted to give good hot tack. The fraction melting below 120 DC for material with melting temperature of about 132 DC and fraction melting below 110 DC for material with melting temperature of about 126°C, respectively, indicates the fraction of polymer giving good sealing properties. According to the present invention, the fraction of the polymer product, measured by DSC, melting at the sealing temperature indicated above (120 DC or 110°C, respectively) is greater than 40 wt-%. In particular, for particularly preferred embodimenss' of the invention comprising a product having a melting temperature of about 132 DC, the fraction of product melting at below 120°C is greater than 50 wt-%.
Compared to a product having the same melting temperature, the present polymers having broader melting distribution (produced in a 2-stage or a multistage process) give better sealing, stiffer material (tensile modulus) and lower hexane solubles according to the FDA test than the one with narrower melting distribution (one-stage process).
Compared to a random copolymer with ethylene as comonomer baving the same melting temperature the terpolymers according to this invention give lower amount of hexane solubles. In addition, it should be pointed out that random copolymer materials with ethylene as comonomrr having melting temperatures of less than 132°C are difficult or impossible to produce in a slurry process with Z/N catalysts.
The ratio of ethylene-to-butene (or heavier) of less than 0.3, in particular less than 0.28, gives good comonomer distribution (randomness,, which leads to a material having low solubles, good optical properties and good processability, and in addition improved produciion of terpolymers.
To obtain the material, it is particulally preferred to use a process based on a combinaiion of a fIrst polymerization zone comprising at least one slurry reactor and a second polymerization zone comprising at least one gas phase reactor.
In the first step of the process a polymerizaiion catalyst system and monomer mixture is fed into a slurry reactor. Propylene acts as a monomer and a diluent in the reaction mixture, The C4-C8 alpha-olefin can be 1-butene, l-pentene4 4-methyl-1-pentene, 1-hexene, l-heptene or 1-octene. The amount of propylene can be 50 to 85 wt-%. the amount of ethylene can be 1 to 10 wt-% and the amount of other alpba-olefin can be 15 to 40 wt-%.Thus the content of alpha-olefin such as I-butene is very high. The flashing of the reaction mixture containing polymer particles in an ordinary flash, wherein flashing of monomers takes place in a flashline and polymer powder and gas are separated in flash vessel, would be very difficult. This disadvantage can be avoided according to the invention by flashing directly into a gas phase reactor.
As catalyst any ordinary stereospecific Ziegler-Natta catalysts can be used. An essential component in those catalysts are solid catalyst components comprising a titanium component having at least one titamum-halogen bond, an electron donor compound and a magnesium halide in active form. The catalysts can contain as an internal e~ectron donor compound compounds selected from ethers, ketones. lactones, compounds containing N, P and/or S atoms and esters of mono and dicarboxyiic acids.
Polymerization can be carried out in the presence of an organoaluminium compound, such as an aluminiurn alkyl and an optional external donor compound at temperatures lower than 70
°C and pressures in the range of 30 to 90 bar, preferably 30 to 70 bar. The polymerization is carried out in such conditions that 50 to 99 wt-%. preferably 60 to 90 wt-% of the end product is polymerized in the slurry reactor or reactors. The residence time can be between 15and120min.
Optionally any metallocene catalyst capable of catalyzing the formation of a telpolymer of propylene can be used. A suitable metallocene catalyst comprises a metallocene/activator reaction product impregnated in a porous support at maximum internal pore volume. The catalyst complex comprises a ligand which is typically bridged, and a transition metal of group IVA...VIA, and organoaluminium compound. The catalytic metal compound is typically a metal halide.
In the first slurry step a terpolymer is produced, in which the content of ethylene monomer is in the range of 1 to 4 wt-%, preferably less than 3 wt-%. The C4-C8 olefin content in me product will be in the range of 5 to 12 wt-%.
Hydrogen is added, when desired, into the slurry reactor for regulating the molecular weight of polymer, as conventiona..
After the polymerization is complete in me slurry reactor, the reaction medium is not separated from the polymer particles in a conventional flash tank. Instead, the whole content of the polymerizaiion medium along with the polymer particles are transferred into a gas phase reactor.
In the gas phase reactor, 1 to 50 wt-%, preferably 1 to 30 wt-% of the fznal end product is formed. The polymerization can be carried out at a temperature of 6D to 90 °C and at a pressure higher than 5 bar, preferably higher than 10 bar. Propylene and other monomers can be added, but not necessarily, into the gas phase reactor. Thus, D to 40 wt-% of propylene and 0 to 30 wt-% of ethylene can be added at this stage. Hydrogen can be added also into the gas phase reactor, when desired.
The liquid medium from the first stage reactor can function as a cooling medium of the fluid bed in the gas phase reactor, when evaporating therein.
With the process according to the invention terpolymers of propylene can be formed, in
which the ethylene content is generally 1 to 10 wt~% and the content of other alpha-olefin is 5 to 25 wt-%. These products have low melting point and thus they can be used for applicaiions such as heat-sealable sheets and films, when softness is required. Products having low stiffhess can be used in applications like moulded sheets, lids, bottles and fibres. For the preparaiion of films and similar articles, it is preferred to produce rerpolymess containing less than 3 wt-% units (e.g. 0.3 to 3 wt-%) derived from ethylene and less than 15 wt-% (e.g. 1 to 15 wt-%) of the other units of alpha-olefins.
The following non-limiting examples illustrate the present invention: Examples
A combinaiion of a loop reactor and a gas phase reactor was used for producing propylene terpolymess for film. The Mowing characterisation methods were used in testing the polymers produced:
Melt flow rates were measures with the load of 2.16 kg and at 230 °C according to ISO 1133.
Comomer contents (ethylene and butene) were measured with Fourier transform infrared specroscopy (FTIR) calibrated with NMR.
Randomness (ethylene distribution) was measured with Fourier transform infrared spectroscopy (FTIR) calibrated with NMR.
Hexane solubles is a measure, determined at 50 °C and 2 h, of the low molecular mass species in the polymer and they were determined according to FDA 21 LFR. Ch. 1(4-1-92 Ed.).
Melting temperature (peak temperature) was measured with differential scanning calorimetry (DSC) by using a temperature increasing rate of 10 °C/min, according to ISO/DIS 11357-3v. Crystalling peak width, and fraction melting below a specified seal initiation temperature were also measured by DSC.
Tensile strength (tensile stress at yield) was measured according to ISO 572-2 (cross head
speed = 50 mm/min).
Tensile modulus was measured according to ISO 572-2 (cross head speed = 1 mm1min).
Izod, notched impact strength was measured according to ISO l80/1A.
Film tests were measured from 40 micrometer thin film produced at a cast film line (Collin), melt temperature 270 OC and chill roll temperature 30oC.
Film modulus (1 % secant modulus) was measured according to ISO 1184 (ASTM D882) (cross head speed = 5 mm/min).
Haze was measured according to ASTM D 1003 and gloss at 60 °C according to ASTM D 523.
Heat sealing properties were measured from 25 micrometer ABA-film (core layer PP homopolymer and as the surface layer the examined heat seal PP terpolymer. Sealing time was 0.1 s and pressure 3 bar. Heat seal strength = pealing of the seal using film strips, broadness 25.41 mmwas measured with an Instron universal tester (cross head speed = 100 mm/min..
Hot tack is the strength of the seal when still hot, and it is measured as above.
Examples 1 to 4
A combination of a pilot-scale loop reactor and a gas phase reactor was used to produce propylene terpolymers for ftlms. Propylene, ethylene, butene and hydrogen were fed into me loop reactor. The polymerizaiion temperature was 60oC in both reactors. The pressure in the loop reactor was 35 bar and in the gas phase reactor 15 bar. The catalyst used was a pre-polymerized catalyst prepared according to PI Patents Nos. 70028 and 86472. and the activity of the catalyst was 35 kg PP/g cat h.
The polymer produced along with unreacted monomers was flashed straight into the gas phase reactor and polymerizaiion was completed therein.
The polymerizaiion was carried out as in Examples 1 to 4, but the gas phase reactor was operated at the pressure of 5 bar and at the temperature of 60 DC.
Example 6 (comparison)
The polymerizaiion was carried out as in Examples 1 to 4, but the product from the loop reactor was passed to conventional flash vessel, which was operated at the pressure of 5 bar. No gas phase reactor was used. The polymerizaiion conditions are presented in the Mowing
The product properties of the terpolymer obtained from the gas phase reactor are presented in the following Table 2.
In the comparative Example 6 the flash line and the flash vessel were plugged very fast and continuous operation was not possible. Flashing in the flash line was too fast because of the high reaction temperature (70 °C). On the other band, there was not enough heat transformation in the flash line and flash vessel to evaporate all ofunreacted monomers.
In Example 5 the operability improved a lot compared to Example 6, hut accumulation of amorphous material was still observed in the flash line. Improvement compared to Example 6 was due to lower reaction temperature in the loop reactor (60 °C), which meant less (slower) flashing in the flash line and better heat transformation in the gas phase reactor (due to recycling gas flow) compared to conventional flash.
Examples 7•9 and comparative Example 10
Polymerizaiion was carried out as in Examples 1-5 by using a wax-prepolymerized catalyst made according to Finnish Patent No. 88047. The polymerization conditions are presented in the following Table 3.
In comparaiive Example 10 the flashing rate was too fast because of lower pressure in the gas phase reactor (5 bar). The material was inhomogenous due to the plugging and no mechanical tests were performed. In Examples 7-9 the pressure in the gas phase reactor was increased. Flashing rate in the transfer line decreased more and no accumulation of amorphous material was observed. Bulk density of terpolymer was also increased.
A combination of a loop reactorls and a gas phase reactor was used for producing propylene terpolymess for film. Propylene, ethylene, butene and hydrogen were fed into the loop reactor. The process conditions are presented in Table 5. The catalyst used was a prepolymerised catalyst prepared according to PI Patent No. 88047 (EP-BI 591 224), the activity of which was 35kglgcath.
Mechanical and film properties of the materials are presented in Table 6.
Exampee 14 (comparative)
Random copolymer with ethylene as comonomer was produced in a loop reactor using a prepolymerised catalyst prepared according to FI Patent No. 88047. The test results are given in Tables 5 and 6.
Exampee 15 (comparative)
Terpolymer with ethylene and butene as comonomers was produced in a loop reactor using a prepolymerised catalyst prepared according to FI Patent No. 86472. The test results are given in Tables 5 and 6.
Hie heat seal properties (seal strength and hot tack) of films made from the materials according to Examples 11, 14 and 15 are presented in Figures 1 and2.
Figures 3 and 4 compare the heat seal properties of films made from the terpolymer of Example 12 and two commercial polymers. The results were determined using a 20 um BOPP film (1118(1) with a PP homopolymer in core. Commercial 1 having a Tm of 126.4 °C contains 2.9 wt-% ethylene, 5.9 wt-% I-butene and bas a fraction melting below 110 °C of 34.3 %. Commercial 2 baving a Tm of 131.6 °C contains 2.3 wt-% ethylene, 4.7 wt-% 1-butene and bas a fraction melting below 110 °C of 34.3 %
Figures 1 and 2 depicting seal strength vs. sealing temperature show that the terpolymer produced in a multi-reactor system has lower seal initiation temperatures than copolymers) and terpolymer produced in just one reactor, i.e. me required seal strength is obtained at lower temperatures. In addition, the broader processing window or sealing range as seen in the figures give it a further processing advantage.
Similarly, the figures depicting hot tack vs. sealing temperature show the terpolymer of the invention possessing higher hot tack strength.
As the Data in Table 6 will show, terpolymers produced in multi-reactors have the required combination of properties: low melting temperature, a broad melting peak. and good comonomer distribution. resulting in superior sealing properiies, as well as having low hexane and xylene solubles, and good optical properties.
Figures 3 and 4 indicate that the present terpolymers have better sealing performance than the commercial polymers tested, which have a higher ethylene-to-butylene ratio.
1. A process for producing terpolymer of propylene, ethylene and one C4 -C8 alpha-olefin, wherein the process is carried out in one or more slurry reactors in the presence of catalysts characterized by the following steps:
a) feeding into a slurry reactor a reaction mixture containing 50-85 wt -% of propylene, 1-10 wt-% of ethylene, 15-40 wt-% of C4 - C8 alpha-olefin, a catalyst system capable of providing olefin polymerization and optionally hydrogen;
b) polymerizing said reaction mixture at a temperature of 60 to 70 °C, and under pressure of 30 to 90 bar for a sufficient time to obtain a propylene terpolymer amounting to 50-99 wt-% of the end product;
c) transferring said reaction mixture into a gas phase reactor operated at a temperature of 60 to 90 °C, and
d) continuing polymerization in said gas phase reactor, into which additional amounts of 0 to 30 wt-% of ethylene, 0 to 10 wt-% of C4 -C8 alpha-olefin, 0 to 40 wt-% of propylene and optionally hydrogen are added for producing a propylene terpolymer amounting to 1 to 50 wt-% of the end product whereby a terpolymer is obtained having a melting temperature of between 126°C to 132°C.
2. The process as claimed in Claim 1, wherein the gas phase reactor is operated at a pressure in excess of 10 bars.
3. The process as claimed in Claim 1, wherein said C4 - Ca alpha-olefin is selected from the group consisting of 1-bufylene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene or 1-octene or a mixture thereof.
4. The process as claimed in any of the preceding claims, wherein said slurry reactor is a loop reactor.
5. The process as claimed in any of Claim 1 to 4, wherein said step (a) is carried out in two slurry reactors, preferably in two loop reactors.
6. The process as claimed in any of claims 1 to 5, wherein up to 40 wt-% of propylene is added into the gas phase reactor.
7. The process as claimed in any of claims 1 to 6, wherein 40 wt-% of ethylene is added into the gas phase reactor.
8. The process as claimed in any of the preceding claims, wherein up to 10 wt-% of 1-butene is added into the gas phase reactor.
9. The process as claimed in claims 1 to 6, wherein different alpha-olefins are used in the loop reactor and in the gas phase reactor.
10. The process as claimed in any of claims 1 to 9, wherein only ethylene and propylene are used as additional monomers in the gas phase reactor.
11. The process as claimed in any of claims 1 to 10, wherein the residence time in the gas phase reactor is 1-180 min.
12. A process for producing terpolymer of propylene, ethylene and one C4 -C8 alpha-olefin, substantially as herein described, particularly with reference
to foregoing examples and as illustrated in the accompanying drawings.
|Indian Patent Application Number||1105/CAL/1998|
|PG Journal Number||02/2014|
|Date of Filing||23-Jun-1998|
|Name of Patentee||BOREALIS TECHNOLOGY OY|
|Applicant Address||P.O. BOX 330, FI-06101 PORVOO, FINLAND|
|PCT International Classification Number||B29C49/00|
|PCT International Application Number||N/A|
|PCT International Filing date|