Method for producing polyolefin particles and particles produced thereby

Abstract

A process for producing pellets of polyolefin. In particular, a process for producing pellets from soft and viscous polyolefins, such as soft propylene copolymers or propylene-based elastomers (POEs).

Description

TECHNICAL FIELD

[0001] The present invention relates to a process for producing pellets of polyolefins. In particular, the present invention relates to a process for producing pellets from soft and sticky polyolefins, such as soft propylene copolymers or propylene-based elastomers (POE). BACKGROUND

[0002] Soft polyolefins, such as soft propylene copolymers or propylene-based elastomers (POE), have attracted great interest in the past due to their excellent combination of cost and properties.

[0003] For example, copolymers of propylene with a comonomer selected from ethylene and alpha-olefins having 4 to 10 carbon atoms and containing 7 to 20% by weight of the comonomer, and having a content of the xylene cold soluble (XCS) fraction of 20 to 60% by weight, have a unique combination of softness, retortability, impact strength and optical properties.

[0004] It is well known that most of the plastic resins sold on the market today are in the form of pellets. Plastic resins are sold in the form of pellets to improve the characteristics of transportation, handling, safety and end product processability.

[0005] Therefore, in a polyolefin production process, the polyolefin is typically extruded and cut into pellets. During the extrusion process, other ingredients such as additives, fillers and / or pigments are typically added and mixed to improve the properties of the polymer. During the extrusion stage, the polyolefin is heated and melted. The melt is then extruded through a die plate, typically into a water bath. The molten strand then solidifies due to the cooling effect of the water. The die plate is typically followed by a rotating cutter which cuts the solidified strand into pellets. The pellets are then dried and transported to silos for storage and packaging.

[0006] A step commonly used when drying the pellets is to sieve a slurry containing water and pellets. The water passes through the sieve, while the pellets are retained by the sieve and transported to a subsequent process step.

[0007] However, if pellets are produced from soft polyolefins, the pellets tend to stick to, for example, the walls of the process equipment. In particular, the pellets have a strong tendency to stick to each other, for example, during the granulation, transportation or storage.

[0008] The size, shape and uniformity of the granules are important characteristics to be met during production. From an operational point of view, the granulation step is also important. Any malfunction of the granulator can cause process shutdown and manufacturing stoppage with serious financial consequences, especially for large extrusion lines. Therefore, the granulation step is considered an important step on the production line of any polymer production plant and on the compounding production line during the further extrusion step.

[0009] Highly efficient and satisfactory granulation is difficult to achieve, especially in the case of final polymers that exhibit softness and tackiness properties resulting in poor flowability and agglomeration of the granules. The formation of a large number of miscuts, multiples (such as doubles) in the granulation process is a clear sign of a decrease in the quality of the granules.

[0010] Various systems have been proposed and used to avoid or limit the tendency of granule agglomeration, but fundamentally they can be subdivided into two methods:

[0011] 1) introduction of a modifier inside the polymer to reduce tackiness by increasing the crystallization kinetics or surface migration of the modifier;

[0012] 2) surface treatment of the granules with a fine-powder material (organic or inorganic material, such as, for example, high-density polyethylene (HDPE), talc, silica) or liquid compounds available on the market under different trademarks for this purpose.

[0013] For example, US 2004 / 0209082 discloses a method for coating cohesive or soft polymer granules. The granules are coated with a fine powder selected from talc, magnesium silicate, calcium silicate, calcium carbonate, cellulose, wood fibers, polyolefin wax and silica. The powder is used with a binder. These coating agents and binders end up in the final articles produced from these polymers, thus reducing their mechanical and optical properties.

[0014] EP 3230348 discloses a process for extruding and pelletizing a propylene copolymer having a content of comonomer of 5 to 40% by mole, a melt flow rate MFR2 measured at 230°C under a load of 2.16 kg of 0.5 to 15 g / 10 min and a content of xylene cold soluble (XCS) fraction of 20 to 60% by weight, the process comprising extruding the propylene copolymer through a die plate into an underwater pelletizer and cutting the strands of the propylene copolymer into pellets in the underwater pelletizer, wherein the ratio of the mass flow rate of the propylene copolymer to the mass flow rate of the cooling water is 0.020 to 0.060; and the propylene copolymer comprises a polymeric nucleating agent, whereby the propylene copolymer and the polymeric nucleating agent produce a composition and the composition has a crystallization temperature Tc in the range of 114 to 126°C determined by differential scanning calorimetry (DSC) with a scan rate of 10°C / min. This process has been found to have limitations at low crystallinity and inevitably reduces the softness of the product.

[0015] EP 3498799 suggests the use of a polypropylene copolymer wax as a modifier of soft plastomer and thus discloses a polyolefin composition comprising

[0016] a) 60 to 99 wt% of a polyethylene plastomer which is a copolymer of ethylene and one or more C3-C12 a-olefins having a density of less than 904 kg / m 3 ; and

[0017] b) 1 to 40 wt% of a polypropylene copolymer wax having a melt flow rate (MFR) at 230°C / 2.16 kg of more than 400 g / 10 min.

[0018] It is known that the wax proposed in this way migrates to the surface of the final product, thus reducing its application properties.

[0019] The use of organometallic surfactants to minimize the problem of pellet agglomeration is also known in the art. However, when these surfactants are used in effective amounts, they tend to cause severe foaming problems and the foam can overflow from the water tank onto the floor, thus causing chaotic operation and unsafe working conditions. The combination of an antifoam such as FOAMTROL® with an organometallic surfactant such as zinc stearate has been used and has achieved some success. However, this combination has the disadvantage of the potential carcinogenicity of FOAMTROL®.

[0020] US 4359544 proposes the use of a nucleating agent package as a pelletizing aid which is a mixture of HDPE and stearamide. However, both HDPE and stearamide are poorly dispersible in water and thus do not work well as a pelletizing aid in a water bath.

[0021] Thus, although several options have been suggested, there is still a need for a simple and economic process to overcome the problem of agglomeration of the pellets.

[0022] It is known that carboxylate metal salts of tetrahydrophthalic anhydride are effective beta nucleating agents for polypropylene.

[0023] For example, WO 2013097647 proposes such metal salts for improving the heat resistance, toughness and stiffness of polypropylene compositions. WO 2013097647 does not mention soft polyolefins and the problems related to the softness of polyolefins in the pelletization.

[0024] Furthermore, CN 102181092 suggests the use of these metal salts in polypropylene to achieve beta nucleation and thus to improve properties such as impact strength and heat deflection temperature. According to CN 102181092, this modified polypropylene can be used for the preparation of pipes.

[0025] Again, there is no mention of soft polyolefins and the problems related to the softness of polyolefins in the pelletization. SUMMARY

[0026] Thus, the present invention relates to a process for producing pellets of a polyolefin, the process comprising the steps of

[0027] introducing a soft polyolefin i-a), 10 to 1000 ppm of a pelletizer i-b) based on the total weight of the polyolefin, and a total of 500 to 10000 ppm of additives i-c) based on the total weight of the polyolefin into a continuous mixer,

[0028] The soft polyolefin is characterized in that

[0029] a flexural modulus determined according to ISO 178 in the range of 10 to below 600 MPa, and a content of chain units derived from propylene determined by 13C{1H} NMR as described in the experimental part of greater than 50 wt% based on the total weight of the soft polyolefin; 13 C{ 1 H} NMR;

[0030] The pelletizer is a pelletizer of formula (I)

[0031]

[0032] wherein R1, R2, R3, R4, R5, R6, R7, R8are independently selected from H, C1-C9alkyl, hydroxyl, phenyl, C1-C9alkylphenyl and halogen, M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La and Eu, and 18 alkylphenyl and halogen, M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La and Eu, and

[0033] The additive is one or more additives selected from the group consisting of antioxidants and process stabilizers, UV-stabilizers, heat stabilizers, slip agents, anti-blocking agents, acid scavengers, metal deactivators, antibacterial agents, antistatic agents, and pigments,

[0034] ii) melting the polyolefin containing the granulation agent i-b) and the additive i-c) to form a molten polyolefin composition,

[0035] iii) extruding the molten polyolefin composition through a die having a multitude of holes into a pellet water bath in a pelletizer, thereby producing strands of the polyolefin composition and solidifying the strands,

[0036] iv) cutting the strands of the polyolefin composition into pellets in the pelletizer, and

[0037] v) drying the pellets.

[0038] The process of the present invention is particularly efficient in leading to a significant reduction of the blocking of the polyolefin pellets obtained from the extrusion and the pelletization of soft polyolefins.

[0039] Definitions

[0040] Whenever the term "comprising" is used in the present description and claims, it is not intended to exclude other elements or steps. For the purpose of the present invention, the term "consisting of is to be understood as a preferred embodiment of the term "comprising". If in the following a composition is defined to comprise at least a certain number of embodiments, it should also be understood that the composition is preferably made up of only these embodiments.

[0041] Whenever the terms "including" or "having" are used, these terms are meant to be equivalent to "comprising" as defined above.

[0042] Whenever an indefinite article is used, such as "a" or "an", or a definite article is used, such as "the", with respect to a singular noun, this includes a plurality of such nouns, unless specifically stated otherwise.

[0043] The term "soft polyolefin" applies to polyolefins having a low flexural modulus. Thus, in the present invention, a soft polyolefin is a polyolefin having a flexural modulus determined according to ISO 178 in the range of 10 to below 600 MPa.

[0044] The soft polyolefin is predominantly based on polypropylene, i.e. has a content of chain units derived from propylene of more than 50 wt.-%.

[0045] Preferably, such soft polyolefin is furthermore characterized by a higher soluble fraction content determined according to the CRYSTEX QC method in the range of 20 to 80 wt.-%.

[0046] It is also to be understood that the embodiments described below are combinable in the sense of the present disclosure. DETAILED DESCRIPTION

[0047] With regard to (Ad)soft polyolefins:

[0048] The process of the present invention relates to the pelletization of soft polyolefins.

[0049] According to the process of the present invention, all types of polyolefins which are mainly based on polypropylene, show a high softness and adhesion can be suitably treated.

[0050] As mentioned above, such soft polyolefins are typically characterized by a lower flexural modulus.

[0051] Thus, according to the process of the present invention, the polyolefins which are mainly based on polypropylene and which can be suitably treated have a flexural modulus determined according to ISO 178 in the range of 10 to below 600 MPa, preferably in the range of 15 to 500 MPa, more preferably in the range of 20 to 400 MPa and even more preferably in the range of 50 to 350 MPa.

[0052] The term polyolefin as used herein includes, unless otherwise specified, polypropylene polymers such as homopolymers, copolymers, terpolymers as well as all other known combinations or forms of polymeric materials. Homopolymers typically have less crystallization issues, thus their respective pellets show a smaller tendency to agglomerate with each other.

[0053] Thus, the present invention is preferably applicable to polyolefins which are mainly based on polypropylene, are copolymers or terpolymers, more preferably copolymers.

[0054] Such copolymers comprise olefin monomers and at least one comonomer.

[0055] The olefin monomers can be any alpha-olefin monomer. Preferably, the olefin monomers are alpha-olefins having 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms. Especially preferred, the olefin monomers are ethylene, propylene or 1-butene and in particular ethylene or propylene.

[0056] The olefin copolymer comprises more than 50 wt.-% of chain units derived from propylene monomers, based on all monomer units in the copolymer. Preferably, the olefin copolymer comprises 70 to 95 wt.-%, more preferably 80 to 95 wt.-% of chain units derived from propylene monomers, based on all monomer units in the copolymer.

[0057] The comonomer can be an alpha-olefin comonomer. The comonomer is preferably an alpha-olefin having 2 to 10 carbon atoms and being different from the olefin monomer. More preferably, the comonomer is an alpha-olefin having 2 to 8 carbon atoms and being different from the olefin monomer.

[0058] The alpha-olefin comonomer is especially preferably selected from the group consisting of ethylene, 1-butene, 1-hexene, 1-octene and mixtures thereof. More preferably, the comonomer is ethylene, 1-butene or 1-hexene or mixtures thereof, most preferably ethylene and / or 1-butene.

[0059] The polyolefin, preferably the olefin copolymer, can be produced in the presence of a polymerization catalyst in any suitable polymerization process, such as slurry polymerization, gas phase polymerization or solution polymerization or a combination thereof, like slurry-gas phase polymerization.

[0060] The polymerization for producing the polyolefin, preferably the olefin copolymer, including the polymerization processes and the catalysts used therein, are well known to the person skilled in the art. Especially, the person skilled in the art is able to control the density or the comonomer content of the polymer by appropriate addition of the comonomer and to control the molecular weight or the melt index by appropriate addition of hydrogen.

[0061] According to the process of the present application, the polyolefin, advantageously being pelletized, is a soft propylene copolymer, more preferably a propylene-ethylene copolymer, a propylene-1-butene copolymer and a propylene-ethylene-1-butene copolymer.

[0062] It is preferred that the propylene copolymer is produced in a one-stage or two-stage polymerization process, including solution polymerization, slurry polymerization, gas phase polymerization or a combination thereof, in the presence of a suitable Ziegler-Natta catalyst or a metallocene catalyst by known processes.

[0063] If the propylene copolymer is produced in a solution polymerization process, the propylene copolymer is preferably a propylene-based elastomer having a density determined according to ISO 1183 in the range of 850 to 890 kg / m3, 3 preferably in the range of 860 to 890 kg / m3, 3 more preferably in the range of 870 to 890 kg / m3.

[0064] The MFR2 (ISO 1133) of the propylene-based elastomer at 230 °C is preferably between 0.5 and 100 g / 10 min, more preferably between 0.8 and 50 g / 10 min, such as between 1.0 and 30 g / 10 min.

[0065] Suitable propylene-based elastomers have a melting point (measured by DSC according to ISO 11357-1) typically below 100°C, preferably below 90°C and more preferably below 80°C. A reasonable lower limit for the melting point of suitable propylene-based elastomers can be 35°C.

[0066] Such propylene-based elastomers are copolymers of propylene with 1-butene and / or ethylene comonomer.

[0067] Generally, the solution polymerization can be accomplished under conditions of an olefin solution polymerization reaction well known in the art. Preferred polymerization temperatures are from 80 to 250°C, more preferably from 100 to 200°C. Preferred polymerization pressures are from atmospheric pressure to 3000 atmospheres (100 kPa to 300 MPa), more preferably from 1 MPa to 10 MPa. Desirably, the reaction is conducted under continuous solution polymerization conditions, i.e., under conditions in which one or more monomers are continuously added to a reactor operating under solution polymerization conditions, and the polymerization product is continuously or semi-continuously withdrawn and recovered or transferred to a second reactor.

[0068] Desirably, the polymerization mixture comprises an aliphatic or cycloaliphatic liquid diluent. Examples of such aliphatic or cycloaliphatic liquid diluents include straight and branched chain hydrocarbons such as isobutane, butane, pentane, hexane, heptane, octane, and mixtures thereof; cycloaliphatic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane, methylcycloheptane, and mixtures thereof; and perfluorinated hydrocarbons, and the like. Small amounts of aromatic hydrocarbons such as toluene, ethylbenzene, or xylene can also be included, but are not preferred. Mixtures of the foregoing are also suitable. The preferred liquid diluent is a hydrogenated oligomerized aliphatic hydrocarbon mixture having an initial boiling point (IBP) according to ASTM D 86 of 118°C, a dry point according to ASTM D 86 of 137°C, and a specific gravity according to ASTM D 1250 of 0.72, commercially available under the trade name Isopar E, commercially available from ExxonMobil Corporation. TM E is commercially available from ExxonMobil Corporation.

[0069] It is desirable in the present process to use a molecular weight control agent or chain transfer agent. Examples of such molecular weight control agents include hydrogen, a trialkyl aluminum compound, or other known chain transfer agents. Hydrogen is the most preferred molecular weight control agent or chain transfer agent.

[0070] Such processes are disclosed in WO 2011 / 087729, WO 2011 / 087730, and WO 2011 / 087731, among others.

[0071] Preferably, the propylene-based polyolefin, preferably the propylene copolymer, is produced in a single stage or multi-stage polymerization process comprising a bulk slurry polymerization step and a gas phase polymerization step. A preferred multi-stage process is a "loop-gas phase" process such as for example the process developed by Borealis, described in patent literature such as in EP 1 681 315 A1 or WO 2013 / 092620 A1 (referred to as BORSTAR® technology).

[0072] A further suitable slurry-gas phase process is the Spheripol® process of LyondellBasell.

[0073] A further suitable process for producing propylene-based polyolefins, preferably olefin copolymers, is the Catalloy process which is proprietary to LyondellBasell, wherein polymerization occurs in the presence of a specific Ziegler-Natta catalyst in up to four sequential gas phase reactors in sequence.

[0074] More preferably, the propylene-based polyolefin, preferably the propylene copolymer, suitable for the present application is produced in an at least two-stage polymerization process, preferably in a process comprising at least one slurry polymerization step and at least one subsequent gas phase polymerization step, optionally followed by a second gas phase polymerization step, and optionally a third gas phase polymerization step.

[0075] The polymerization conditions in the sequential polymerization of the propylene-based polyolefin, preferably the olefin copolymer, are not particular to the skilled person and are well known in the art. Typically, the first fraction (F1) is produced in a slurry reactor and the second fraction (F2) is produced in a gas phase reactor in the presence of the first fraction (F1), optionally followed by a polymerization step in a second gas phase reactor or even a third gas phase reactor.

[0076] As mentioned above, this process is referred to as BORSTAR® technology.

[0077] It is well known that a prepolymerization can occur prior to the main polymerization.

[0078] With respect to the prepolymerization, reference is made to WO2015 / 011134.

[0079] If a prepolymerization step is performed, all catalyst mixture is introduced into the prepolymerization step.

[0080] The temperature in the slurry polymerization is typically from 50 to 110°C, preferably from 60 to 100°C, and in particular from 65 to 95°C. The pressure is from 1 to 150 bar, preferably from 10 to 100 bar.

[0081] The slurry polymerization can be carried out in any known reactor for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. Loop reactors are well known in the art, for example, examples are given in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654.

[0082] The residence time can vary in the reactor zones identified above. In one embodiment, the residence time in the slurry reactor, for example a loop reactor, is in the range of 0.5 to 5 hours, for example in the range of 0.5 to 2 hours; while the residence time in the gas phase reactor is generally in the range of 1 to 8 hours, such as in the range of 1.5 to 4 hours.

[0083] In the slurry polymerization stage, further components known in the art can also be introduced. Thus, hydrogen is added to control the molecular weight of the polymer.

[0084] The slurry polymerization stage is followed by a gas phase polymerization stage, in which fraction (F2) is produced. It is preferred to direct the slurry directly into the gas phase polymerization zone without the need for a flashing step between the stages. Such a direct feed is described in EP-A-887379, EP-A-887380, EP-A-887381 and EP-A-991684.

[0085] That is, the reaction product of the slurry phase polymerization, i.e. the first fraction (F1), which is preferably carried out in a loop reactor, is then transferred to a subsequent gas phase reactor, in which the second fraction (F2) is produced.

[0086] The polymerization in the gas phase can be carried out in a fluidized bed reactor, a fast fluidized bed reactor or a settled bed reactor or any combination of these reactors. When a combination of reactors is used, the polymer is then transferred from one polymerization reactor to another.

[0087] Typically, the gas phase reactor is operated at a temperature in the range of 50 to 100°C, preferably in the range of 65 to 95°C. The pressure is suitably in the range of 10 to 40 bar, preferably in the range of 15 to 30 bar.

[0088] One particular class of propylene-based polyolefins which is especially suitable for the process according to the present application is a random heterophasic propylene-ethylene copolymer (RAHECO).

[0089] Such random heterophasic propylene-ethylene copolymer (RAHECO) comprises:

[0090] a) a crystalline matrix (M) which is a propylene-ethylene random copolymer; and

[0091] b) Amorphous propylene-ethylene elastomer (E).

[0092] They can be produced in the presence of a catalyst using at least a two-stage polymerization process, preferably a three-stage polymerization process.

[0093] The polymerization catalyst can be any suitable polymerization catalyst known in the art, capable of producing polypropylene and exhibiting the desired stereoselectivity. Therefore, the catalyst can be a metallocene catalyst, such as those disclosed in EP-A-629631, EP-A-629632, WO-A-00 / 26266, WO-A-02 / 002576, WO-A-02 / 002575, WO-A-99 / 12943, WO-A-98 / 40331, EP-A-776913, EP-A-1074557, and WO-A-99 / 42497. These catalysts may be Ziegler-Natta catalysts, such as those disclosed in WO-A-2003 / 000757, WO-A-2003 / 000754, WO-A-2004 / 029112, WO-A-2007 / 137853, WO-A-2012 / 007430, EP-A-2610271, EP-A-261027 and EP-A-2610272.

[0094] Preferably, the catalyst is a Ziegler-Natta catalyst, which comprises a solid component including magnesium, titanium, halogens and an internal electron donor; an alkylaluminum compound; and an external electron donor.

[0095] The alkylaluminum compound is preferably trialkylaluminum, and more preferably selected from the group consisting of triethylaluminum, triisobutylaluminum, trimethylaluminum, tri-n-hexylaluminum and tri-n-octylaluminum and mixtures thereof.

[0096] The external electron donor is preferably a silyl ether, and more preferably selected from the group consisting of dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane and diethylaminotriethoxysilane.

[0097] A suitable RAHECO can be characterized by the following performance characteristics:

[0098] The random multiphase propylene-ethylene copolymer (RAHECO) has a melt flow rate (MFR2) measured according to ISO 1133 at 230°C and 2.16 kg in the range of 0.1 to 100 g / 10 min, more preferably 0.3 to 50.0 g / 10 min, even more preferably 0.5 to 20.0 g / 10 min, and most preferably 0.8 to 10.0 g / 10 min.

[0099] The random heterophasic propylene-ethylene copolymer (RAHECO) preferably has a melting temperature (Tm) determined by differential scanning calorimetry (DSC) in the range of 130 °C to 160 °C, more preferably in the range of 140 °C to 157 °C and most preferably in the range of 145 °C to 155 °C.

[0100] The random heterophasic propylene-ethylene copolymer (RAHECO) preferably has a content of the crystalline fraction (CF) in the range of 3.0 to 25.0 wt.-%, more preferably in the range of 5.0 to 20.0 wt.-%, most preferably in the range of 8.0 to 15.0 wt.-%, determined by quantification of the CRYSTEX QC method. 13 The ethylene content (C2(total)) determined by FT-IR spectroscopy calibrated by C-NMR spectroscopy.

[0101] The polymer fraction of the random heterophasic propylene-ethylene copolymer (RAHECO) can be characterized according to the CRYSTEX QC method using trichlorobenzene (TCB) as solvent. This method is described in the determination methods section below. The crystalline fraction (CF) comprises the majority of the matrix phase and only a small portion of the elastomeric phase, and the soluble fraction (SF) comprises the majority of the elastomeric phase and only a small portion of the matrix phase. In some cases, this method leads to more useful data because the crystalline fraction (CF) and the soluble fraction (SF) correspond more accurately to the matrix phase and the elastomeric phase, respectively. Due to the different separation methods of the xylene extraction and the CRYSTEX QC method, the properties of the XCS / XCI fraction on the one hand are not exactly the same as the properties of the crystalline / soluble (CF / SF) fraction on the other hand, which means that the amount and properties of the matrix phase and the elastomeric phase can be different.

[0102] The random heterophasic propylene-ethylene copolymer (RAHECO) preferably has a soluble fraction (SF) content determined according to the CRYSTEX QC analysis in the range of 20 to 80 wt.-%, more preferably in the range of 25 to 60 wt.-%, most preferably in the range of 30 to 50 wt.-%, based on the total amount of the RAHECO.

[0103] The random heterophasic propylene-ethylene copolymer (RAHECO) preferably has a content of the soluble fraction (SF) in the range of 20 to 80 wt.-%, more preferably in the range of 23 to 60 wt.-%, most preferably in the range of 25 to 50 wt.-%, determined by quantification of the CRYSTEX QC method. 13 The ethylene content (C2(SF)) of the soluble fraction according to the CRYSTEX QC analysis determined by FT-IR spectroscopy calibrated by C-NMR spectroscopy.

[0104] The random heterophasic propylene-ethylene copolymer (RAHECO) preferably has an intrinsic viscosity (iV(SF)) of the soluble fraction according to CRYSTEX QC analysis measured according to DIN ISO 1628 / 1 in the range of 1.20 to 6.0 dL / g, more preferably in the range of 1.50 to 5.0 dL / g and most preferably in the range of 2.0 to 4.0 dL / g.

[0105] Further, the random heterophasic propylene-ethylene copolymer (RAHECO) preferably has a flexural modulus measured according to ISO 178 on injection moulded test specimens in the range of 130 MPa to 500 MPa, more preferably in the range of 150 MPa to 450 MPa and most preferably in the range of 175 MPa to 400 MPa.

[0106] Regarding the granulating agent

[0107] The process according to the present application uses a granulating agent of formula (I)

[0108]

[0109] wherein R1, R2, R3, R4, R5, R6, R7, R8 are independently selected from H, C1-C9 alkyl, hydroxyl, phenyl, C1-C 18 alkylphenyl and halogen, M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La and Eu.

[0110] Suitable C1-C9 alkyl groups are straight chain or branched alkyl groups, such as methyl, ethyl, n-butyl, iso-butyl, preferably straight chain or branched C1-C4 alkyl, more preferably methyl and ethyl.

[0111] Preferred C1-C 18 alkylphenyl groups are C1-C 10 alkylphenyl groups, more preferably C1-C4 alkylphenyl groups.

[0112] Suitable halogen substituents are chlorine, fluorine or bromine, preferably chlorine.

[0113] Preferably, R1 to R8 are independently selected from the group consisting of hydrogen and C1-C4 alkyl, more preferably independently selected from hydrogen, methyl and ethyl.

[0114] Preferably, M is a metal cation selected from Mg, Ca, Zn, La, more preferably M is Ca or Zn, even more preferably M is Ca.

[0115] Particularly preferred is that each of R1 to R8 is hydrogen, i.e. the dicarboxylic acid is 4-cyclohexene-1,2-dicarboxylic acid, wherein the most preferred dicarboxylic acid is cis-4-cyclohexene-1,2-dicarboxylic acid.

[0116] Such dicarboxylic acid metal salts are commercially available or can be prepared as described for example in CN 102181092.

[0117] The granulating agent of formula (I) is added to the polyolefin in an amount of 10 to 1000 ppm, based on the total weight of the polyolefin.

[0118] Preferably, the granulating agent of formula (I) is added in an amount of 15 to 500 ppm, more preferably in an amount of 20 to 100 ppm and most preferably in an amount of 25 to 80 ppm.

[0119] Further additives

[0120] According to the present application, further usual additives are added.

[0121] Such additives are selected from the group consisting of antioxidants and process stabilizers, UV-stabilizers, heat stabilizers, slip agents, anti-blocking agents, acid scavengers, metal deactivators, antibacterial agents, antistatic agents and pigments.

[0122] Preferably, at least one or more antioxidants and acid scavengers are added.

[0123] The skilled person is able to select suitable additives which are well known in the art.

[0124] Such additives are commercially available, for example as described in "Plastic Additives Handbook", 6thEdition, 2009 by Hans Zweifel (pages 1141 to 1190).

[0125] Generally, these additives are added in an amount of 100 to 2000 ppm for each single component.

[0126] The total amount of additives added to the polyolefin is in the range of 500 to 1000 ppm, based on the total weight of the polyolefin.

[0127] Method

[0128] The method of the present application comprises several steps.

[0129] First step:

[0130] i) introducing the polyolefin as described above, the granulating agent and one or more additives as described above into a continuous mixer.

[0131] Thus, in step i) the polyolefin which has been withdrawn from the polymerization reactor in powder form, the granulating agent and the further additives are introduced into a continuous mixer, preferably into an extruder.

[0132] The polyolefin powder is typically subjected to a process step for removing residual hydrocarbons from the polyolefin prior to the extrusion step. Such processes are well known in the art and can include a step of reducing the pressure, a step of purging, a step of stripping, a step of extraction, etc. Combinations of different steps are also possible. Suitable methods for removing hydrocarbons from polymers are disclosed in WO-A-02 / 088194, EP-A-683176, EP-A-372239, EP-A-47077 and GB-A-1272778.

[0133] Typically, the granulating agent and the additives are introduced into the feed throat of the extruder together with the polyolefin.

[0134] The extrusion is preferably carried out in a twin-screw extruder. Suitable twin-screw extruders are co-rotating twin-screw extruders and counter-rotating twin-screw extruders. Co-rotating twin-screw extruders are manufactured, among others, by Coperion, KraussMaffei Berstorff and Steel Works of Japan. Counter-rotating extruders are manufactured, among others, by Farrel, Kobe Industries and Steel Works of Japan. Twin-screw extruders and their operation are within the skill of the person skilled in the art.

[0135] The extruder typically comprises one or more feed throats into which the polyolefin is introduced. Downstream of the feed throat(s) there is a melting zone, and downstream of the melting zone there is one or more mixing zones. At the end of the extruder there is a die plate having a plurality of openings through which the molten plastic is extruded. The extruder can also comprise a screen pack with one or more screens for removing impurities or multiphase character. It can also comprise one or more gear pumps for generating sufficient pressure.

[0136] Suitable other continuous mixers include single-screw co-kneaders of the Buss type, chambered kneaders such as the Farrell type, or combinations of single-screw extruders and / or melt pumps with static mixers, such as these of the Sulzer type.

[0137] Second step

[0138] ii) melting the i-a) polyolefin containing the granulating agent i-b) and the additives i-c) in a continuous mixer, preferably in an extruder, to form a molten polyolefin composition.

[0139] For melting the polyolefin, the temperature in the continuous mixer, preferably in the extruder, is typically adjusted to a range of 150 to 300 °C, preferably to a range of 170 to 290 °C.

[0140] Since a suitable extruder can have several temperature zones, the temperature in the different zones can differ within the temperature ranges described above.

[0141] The melt temperature in the extruder at or close to the die plate is typically adjusted to be in the range of 190 to 250 °C, preferably in the range of 200 to 240 °C.

[0142] As known to the skilled person, the melt temperature is influenced by the specific energy input the melt is subjected to, and can thus be controlled by adjusting, for example, the throughput or the rotational speed of the screw.

[0143] Third and fourth step

[0144] iii) extruding the molten polyolefin composition through a die plate having a multitude of holes into a water bath of a pelletizer, thereby producing strands of the polyolefin composition and solidifying the strands.

[0145] iv) cutting the strands of the polyolefin composition into pellets in the pelletizer.

[0146] The pellets are formed by extruding the polymer melt through the holes in the die plate into strands. The strands pass through the die plate into a water bath of an underwater pelletizer. Immediately at or after the die plate is a set of rotating knives which can cut the strands into pellets. Water is continuously added to the bath and a slurry comprising water and pellets is continuously removed from the pelletizer.

[0147] The die plate has a multitude of openings through which the molten polymer flows into the pelletizer. The openings typically have a diameter of 2.0 to 3.0 mm, so that the flow velocity of the polymer melt through the openings is about 0.7 to 2.0 m / s, preferably 0.8 to 1.5 m / s, such as 0.9 to 1.4 m / s.

[0148] The temperature of the pellet water in the pelletizer is typically 10 to 70 °C.

[0149] For the pelletization of propylene-based polyolefins, preferably of random heterophasic propylene-ethylene copolymers (RAHECO), the temperature of the pellet water in the pelletizer is preferably 15 to 55 °C, more preferably 20 to 50 °C, even more preferably 25 to 40 °C.

[0150] The pressure is not critical and can be chosen based on the needs, such as 1 to 10 bar (absolute pressure).

[0151] The residence time of the pellets in the pelletizer and in the pipe between the pelletizer and the dryer is preferably in the range of 5 to 30 seconds, more preferably in the range of 5 to 20 seconds, especially preferably in the range of 7 to 15 seconds. When the residence time is within these limits, the amount of agglomeration of the pellets has been found to be reduced.

[0152] Fifth step

[0153] v) drying the pellets.

[0154] As mentioned above, the slurry is then fed into a drier, where the pellets are separated from the water.

[0155] One suitable method of removing the pellets from the pellet water is by using a rotating / whirling separator.

[0156] Here, the pellet slurry is placed in a rotating motion. The liquid is squeezed through a screen at the periphery of the rotating drier, while the pellets are trapped inside the screen.

[0157] Any other suitable liquid / solid separator can be used.

[0158] Another suitable method of removing the pellets from the pellet water is by using a sieve. In a sieve, the water is continuously separated from the solid particles, forming separate streams. In a closed system, the pellet water is recirculated back to the pelletizer. The moist particles are continuously discharged via a separate inclined or curved sieve, which retains the pellets on top, while allowing the pellet water to flow down, and directs the retained pellets away from the pellet water stream.

[0159] The pellets are recovered, stored and shipped to customers.

[0160] The water is recovered, cooled and recirculated to the pelletizer.

[0161] Pellets

[0162] The pellets obtained with the pelletizing method described above have excellent shape and size.

[0163] This is expressed by the so-called shape factor (SPF).

[0164] The shape factor (SPF) describes the shape of the pellets, independent of the size of the pellets, and in the context of the present invention, it is the relationship between the perimeter and the area of the pellets according to the following formula.

[0165] SPF = U 2 / (4 π A)

[0166] U = Perimeter

[0167] π = pi (3.14159...)

[0168] A = Area

[0169] All shapes deviating from the ideal circular form have a shape factor > 1.

[0170] The granules obtained with the process of the present application have a higher amount of granules with a shape factor (SPF) below 1.2 compared to granules obtained without the use of a specific granulation agent.

[0171] Therefore, at least 27%, preferably at least 30% of the granules obtained with the process of the present application have a shape factor (SPF) below 1.2.

[0172] Preferably, at most 50%, more preferably at most 70%, even more preferably at most 90%, most preferably and ideally 100% of the granules obtained with the process of the present application have a shape factor (SPF) below 1.2.

[0173] According to the present application, granules are defined as having a shape factor of at most 1.4. For these granules (i.e. granules having a shape factor of at most 1.4), the size distribution of the classes between 1 and 3 mm and between 3 and 5 mm is calculated and then their respective sum is calculated, for the class of 1 to 5 mm.

[0174] The granules obtained with the process of the present application have a higher amount of granules with a shape factor of at most 1.4 falling into the class of 1 to 5 mm compared to granules obtained without the use of a specific granulation agent.

[0175] Therefore, at least 85%, preferably at least 88%, more preferably at least 90% and ideally 100% of the granules obtained with the process of the present application have a particle size distribution between 1 and 5 mm.

[0176] The granules obtained with the process of the present application have additionally a lower amount of so-called "lumps" compared to granules obtained without the use of a specific granulation agent.

[0177] According to the present application, "lumps" are defined as particles which are visually identifiable as stable agglomerates of two or more granules adhering to each other.

[0178] Therefore, from 0% to less than 2.3%, preferably from 0% to less than 2.0% of the granules obtained with the process of the present application are in the form of so-called lumps.

[0179] Ideally, 0% of the granules obtained with the process of the present application are in the form of so-called lumps.

[0180] In one embodiment of the present application, the granules obtained with the process of the present application have additionally a lower amount of so-called "tail particles" compared to granules obtained without the use of a specific granulation agent.

[0181] Tail particles are defined as granules of original granular form with a fibrous extension resembling a tail of an animal, having a length of more than 1000 pm.

[0182] Therefore, less than 4.0 %, preferably less than 3.5 %, more preferably less than 3 % of the granules obtained with the process of the present application are in the form of so-called tail-borne granules.

[0183] Ideally, 0 % of the granules obtained with the process of the present application are in the form of so-called tail-borne granules.

[0184] The granule properties described above are determined by instrumental granule contamination, shape and size measurement as described in the experimental part.

[0185] Therefore, the present application provides a process for granulating soft copolymers of propylene, wherein the agglomeration and formation of melt granules is reduced. Further, the granules formed in the process can be easily handled, stored and transported.

[0186] The process can be run in conventional equipment without additional investments.

[0187] In a further embodiment, the present application relates to granules of a polyolefin comprising a composition of

[0188] a polyolefin, preferably a polyolefin copolymer, characterized in that

[0189] a flexural modulus determined according to ISO 178 in the range of 10 to below 600 MPa and a content of chain units derived from propylene determined by 1H NMR of more than 50 wt.-%, based on the total weight of the soft polyolefin, obtained with the process as described in the experimental part; 13 C{ 1 H} NMR;

[0190] 10 to 1000 ppm of a granulating agent of formula (I) based on the total weight of the polyolefin

[0191]

[0192] wherein R1, R2, R3, R4, R5, R6, R7, R8 are independently selected from H, C1-C9 alkyl, hydroxyl, phenyl, C1-C 18 alkylphenyl and halogen, M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La and Eu, and

[0193] a total of 500 to 10000 ppm of one or more additives selected from the group consisting of antioxidants and process stabilizers, UV-stabilizers, heat stabilizers, slip agents, anti-blocking agents, acid scavengers, metal deactivators, antibacterial agents, antistatic agents and pigments, based on the total weight of the polyolefin,

[0194] The granules are characterized in that

[0195] a) at least 27%, preferably at least 30%, of the granules have a shape factor (SPF) below 1.2, wherein the shape factor is the relation between the perimeter and the area of the granule according to the following formula

[0196] SPF = U 2 / (4 π A)

[0197] wherein U = perimeter, π = pi (3.14159...) and A = projected area,

[0198] b) at least 85%, preferably at least 88%, more preferably at least 90%, of the granules have a particle size distribution between 1 and 5 mm,

[0199] c) less than 2.3%, preferably less than 2.0%, of the granules are in the form of lumps, and

[0200] d) less than 4.0%, preferably less than 3.5% and more preferably less than 3%, of the granules are in the form of tail particles.

[0201] Experimental part

[0202] 1. Measurement methods

[0203] The following definitions and determination methods of the terms apply to the above general description of the application as well as to the following examples, unless otherwise defined.

[0204] a) Melt flow rate (MFR2)

[0205] The melt flow rate is the amount of polymer in grams extruded in 10 minutes at a specific temperature under a specific load, standardized according to ISO 1133 or ASTM D1238.

[0206] The melt flow rate MFR2 (MFR230 / 2.16) of the propylene-based polymer is measured according to ISO 1133 at 230 °C and under a load of 2.16 kg.

[0207] b) Density

[0208] The density is measured according to ISO 1183 D. The sample preparation is done by compression moulding according to ISO 1872-2:2007.

[0209] c) Comonomer content

[0210] Quantitative nuclear magnetic resonance (NMR) spectroscopy is used to quantify the comonomer content of the polymers.

[0211] Quantification of the comonomer content of poly(propylene-co-ethylene) copolymers

[0212] The comonomer content of the poly(propylene-co-ethylene) copolymers is quantified using the method described in WO 2008 / 063819 A1.1 H and 13 Quantitative analysis was performed in solution using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz, respectively. 13 C{ 1 ¹H NMR spectroscopy. Nitrogen was used for all pneumatic devices, and all spectra were performed using… 13 A C-optimized 10 mm extended temperature probe was used for recording at 125 °C. Approximately 200 mg of material was dissolved with chromium acetylacetone (Cr(acac)3) in 3 mL of 1,2-tetrachloroethane-d2 (TCE-d2) to obtain a 65 mM solution of relaxant in solvent {8}. To ensure a homogeneous solution, the NMR tube was further heated in a rotary oven for at least 1 hour after initial sample preparation in a heating block. After insertion into the magnet, the tube was rotated at 10 Hz. This setup was chosen primarily for its high resolution and quantitative requirement due to the need for accurate ethylene content quantification. A standard single-pulse excitation without NOE was used with an optimized apex cone angle, a 1 s cycle delay, and a two-stage WALTZ16 decoupling scheme {3,4}. A total of 6144 (6 k) transient values ​​were acquired for each spectrum.

[0213] Quantitative analysis using a dedicated computer program 13 C{ 1 The ¹H NMR spectra were processed, integrated, and the relevant quantitative properties were determined from the integration. The chemical shifts of the solvent were used, with all chemical shifts indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm. This method allows for comparable references even if the structural unit is absent. Characteristic signals corresponding to the incorporation of ethylene were observed {7}.

[0214] Using the method of Wang et al. {6}, by analyzing... 13 C{ 1 The comonomer fraction is quantified by integrating multiple signals across the entire spectral region of the H spectrum. This method is chosen for its robustness and ability to indicate the presence of regional defects when needed. Slight adjustments are made to the integration region to improve applicability across the entire range of comonomer contents encountered.

[0215] For systems where only isolated ethylene is observed in the PPEPP sequence, the method of Wang et al. was modified to reduce the influence of non-zero integrals from sites known to be absent. This method reduces the overestimation of ethylene content in such systems and is achieved by reducing the number of sites used to determine the absolute ethylene content to:

[0216] E = 0.5 (Sββ + Sβγ + Sβδ + 0.5(Sαβ + Sαγ))

[0217] By using this set of sites, the corresponding integral equation becomes:

[0218] E = 0.5 (I H +I G + 0.5(I C + I D ))

[0219] The same notation used in the article of Wang et al.{6} is used. No modification is made to the equation for the absolute propylene content.

[0220] The mole fraction of comonomer incorporation is calculated from the mole fraction:

[0221] E [mole %] = 100 * fE

[0222] The weight percent of comonomer incorporation is calculated from the mole fraction:

[0223] E [wt %] = 100 * (fE * 28.06 ) / ( (fE * 28.06) + ((1-fE) * 42.08) )

[0224] References:

[0225] 1) Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443.

[0226] 2) Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A.L., Macromolecules 30 (1997) 6251.

[0227] 3) Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225.

[0228] 4) Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128.

[0229] 5) Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253.

[0230] 6) Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157.

[0231] 7) Cheng, H. N., Macromolecules 17 (1984), 1950.

[0232] 8) Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475.

[0233] 9) Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150.

[0234] 10) Randall, J. Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.

[0235] 11) Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253.

[0236] d) Differential scanning calorimetry (DSC) analysis, melting temperature (Tm) and crystallization temperature (Tc):

[0237] Measurements were made using a TA Instrument Q2000 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC was run according to ISO 11357 / part 3 / method C2 at a scan rate of 10 °C / min in a temperature range of -30 to +225 °C in a heating / cooling / heating cycle.

[0238] The crystallization temperature and the heat of crystallization (Hc) are determined from the cooling step, while the melting temperature and the heat of fusion (Hf) are determined from the second heating step.

[0239] e) Flexural modulus

[0240] The flexural modulus is determined according to ISO 178 at a test speed of 2 mm / min and a force of 100 N on test specimens having dimensions of 80 x 10 x 4 mm (length x width x thickness) prepared by injection molding according to EN ISO 1873-2, wherein the length of the span between the supports (or holders) is 64 mm. 3

[0241] f) Xylene cold solubles (XCS) content

[0242] is measured according to ISO 16152, 1st edition, 2005-07-01 at 25 °C.

[0243] g) CRYSTEX QC analysis

[0244] Crystalline fraction and solubles fraction method

[0245] The crystalline fraction (CF) and the solubles fraction (SF) of the polypropylene (PP) compositions as well as the comonomer content and the intrinsic viscosity of the respective fractions are analyzed by using the CRYSTEX instrument Polymer Char (Valencia, Spain). Details of the technique and method can be found in the literature (Ljiljana Jeremic, Andreas Albrecht, Martina Sandholzer & Markus Gahleitner (2020) Rapid characterization of high-impact ethylene-propylene copolymer composition by crystallization extraction separation: comparability to standard separation methods, International Journal of Polymer Analysis and Characterization, 25:8, pp 581-596).

[0246] ​The crystalline and amorphous fractions were separated by temperature cycling of dissolution at 160 °C, crystallization at 40 °C, and redissolution at 160 °C in 1,2,4-trichlorobenzene. Quantification of SF and CF, as well as determination of ethylene content (C2), were achieved using an integrated infrared detector (IR4), and intrinsic viscosity (IV) was determined using an online 2-capillary viscometer.

[0247] The IR4 detector operates in two different wavelength bands (CH3 stretching vibration, centered at approximately 2960 cm⁻¹). -1 (location) and CH stretching vibration (2700 cm) -1 Up to 3000cm -1 A multi-wavelength detector measuring IR absorbance at two different wavelengths is used to determine the concentration and ethylene content in ethylene-propylene copolymers. The IR4 detector is calibrated with a series of eight EP copolymers having known ethylene contents ranging from 2% to 69% by weight (via...). 13 (Determined by C-NMR spectroscopy), and various EP copolymers have multiple concentrations in the range of 2 and 13 mg / ml. To simultaneously experience both characteristics of the polymers at various concentrations, concentration and ethylene content, during Crystex analysis, the following calibration equation was applied:

[0248] Concentration = a + b * absorbance (CH) + c * (absorbance (CH))² + d * absorbance (CH3) + e * (absorbance (CH3)² + f * absorbance (CH) * absorbance (CH3) (Equation 1)

[0249] CH3 / 1000C = a + b*absorbance(CH) + c*absorbance(CH3) + d * (absorbance(CH3) / absorbance(CH)) + e * (absorbance(CH3) / absorbance(CH))² (Equation 2)

[0250] The constants a to e in Equation 1 and the constants a to f in Equation 2 are determined using least squares regression analysis.

[0251] Use the following relationship to convert CH3 / 1000C to ethylene content in weight percent:

[0252] Weight % (ethylene in EP copolymer) = 100 - CH3 / 1000TC * 0.3 (Equation 3)

[0253] The amount of soluble fraction (SF) and crystalline fraction (CF) is related to the amount of "xylene cold soluble" (XCS) and xylene cold insoluble (XCI) fraction determined according to ISO 16152 by standard gravimetric method, respectively, by XS calibration. XS calibration is achieved by testing various EP copolymers having XS content in the range of 2 to 31 wt%. The determined XS calibration is linear:

[0254] wt% XS = 1.01 * wt% SF (Equation 4)

[0255] The intrinsic viscosity (IV) of the parent EP copolymer and its soluble fraction and crystalline fraction is determined using an online 2-capillary viscometer and correlated to the corresponding IV determined according to ISO 1628-3 by standard method in decalin. Calibration is achieved using various EP PP copolymers having IV = 2 to 4 dL / g. The determined calibration curve is linear:

[0256] IV (dL / g) = a* Vsp / c (Equation 5)

[0257] The sample to be analyzed is weighed out at a concentration of 10 to 20 mg / ml. To avoid injection of possible gels and / or polymers not soluble in TCB at 160°C, such as PET and PA, the weighed-out sample is loaded into a stainless steel mesh MW 0.077 / D 0.05 mmm.

[0258] After automatic filling of the vial with 1,2,4-TCB containing 250 mg / l of 2,6-tert-butyl-4-methylphenol (BHT) as antioxidant, the sample is dissolved at 160°C until complete dissolution is achieved, usually for 60 min, and stirring is continued at 400 rpm. To avoid sample degradation, the polymer solution is covered with a N2 atmosphere during dissolution.

[0259] A defined volume of the sample solution is injected into a column filled with inert carrier, where crystallization of the sample and separation of the soluble fraction from the crystalline part take place. This process is repeated twice. During the first injection, the entire sample is measured at high temperature, determining the IV [dl / g] and C2 [wt%] of the PP composition. During the second injection, the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) are measured (wt% SF, wt% C2, IV) using a crystallization cycle.

[0260] h) Intrinsic viscosity

[0261] The intrinsic viscosity (iV) is measured according to DIN ISO 1628 / 1, October 1999, in decalin at 135°C.

[0262] i) Instrument pellet contamination, shape and size measurement

[0263] Pellet contamination, shape and size were determined using a PA66 equipment from OCS GmbH (Witten, Germany) comprising a pellet contamination analysis system (PS25C) and a pellet shape and size distribution (PSSD) system.

[0264] PS25C: The pellets are transported under a high-speed CCD (charge-coupled device) camera and an image is taken. Based on their color spectrum, they are divided into several categories.

[0265] PSSD: The pellets are transported by a vibrating device. A high-speed line sensor records their two-dimensional image in free-fall mode. This system measures the size of the pellets of different size and shape categories, classifying the analyzed particles as pellets, dust and other shape abnormal particles such as tail particles, stringers, etc.

[0266] For the present invention, only the parameters of the pellet size and shape distribution (PSSD) are relevant. For this purpose, the pellet size is first determined as the equivalent circle diameter of the projection of the particle, followed by a size classification. Subsequently, further parameters of the particle shape are calculated.

[0267] - The shape factor (SPF) describes the shape of the pellet independent of the pellet size, in the context of the present invention, it is the relationship between the perimeter and the area of the pellet according to the following formula.

[0268] SPF = U 2 / (4 π A),

[0269] where U is the perimeter, π is the parameter pi (3.14159…) and A is the projection area of the particle. All shapes deviating from the ideal circular form have a shape factor > 1.

[0270] - "Pellets" are defined as having a shape factor of at most 1.4. All other particles must be classified as "dust", "stringers", "longs", "tail particles", "angel hair", "kites" or "other particles".

[0271] - The "dust" fraction is defined as particles having a projection size (maximum dimension) of less than 1 mm.

[0272] - The "stringer" fraction is defined as particles which are visually identifiable as stable agglomerates of two or more pellets adhering to each other. Such particles are typically formed by agglomeration after cutting of the polymer melt in a water bath and their presence is highly undesirable.

[0273] - The "long particle" fraction is defined as particles with a high aspect ratio, whose length is at least twice their diameter, but otherwise regular shape.

[0274] - The "tail particle" fraction is defined as originally pellet-like particles, but caused by poor cutting, with a fibrous extension similar to an animal tail, whose length is greater than 1000 pm.

[0275] - The "angel hair" fraction is defined as fibrous particles with a straight or curved appearance.

[0276] - The "chopped block" fraction is defined as fragments with a projected size (maximum dimension) between 1 and 3 mm and a shape factor > 1.45.

[0277] - All other particles are classified as "other particles".

[0278] - The average pellet size is calculated as the number of pellets per gram of polymer (pcs / g).

[0279] - The size distribution with the classes 1 to 3 mm and 3 to 5 mm is only calculated for "pellets", whose respective sum is the class 1 to 5 mm.

[0280] - Additionally, the general content of all particles for the size range 3 to 5 mm is calculated.

[0281] 2. Experimental part

[0282] Preparation of soft polyolefins (RAHECO)

[0283] • Catalyst

[0284] The catalyst used in the polymerization process of the heterophasic propylene copolymer RAHECO was produced as follows: First, 0.1 moles of MgCl2x 3 EtOH were suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to a temperature of -15°C and 300 ml of cold TiCl4 were added while maintaining the temperature at this level. Then, the temperature of the slurry was slowly increased to 20°C. At this temperature, 0.02 moles of dioctyl phthalate (DOP) were added to the slurry. After the addition of the phthalate, the temperature was increased to 135°C within 90 minutes and the slurry was allowed to stand for 60 minutes. Then, a further 300 ml of TiCl4 were added and the temperature was maintained at 135°C for 120 minutes. After that, the catalyst was filtered off from the liquid and washed six times with 300 ml of heptane at 80°C. Then, the solid catalyst component was filtered and dried. The catalyst and its preparation concept are generally described, for example, in the patent publications EP 491566, EP 591224 and EP 586390. Triethylaluminium (TEAL) was used as a co-catalyst and dicyclopentyl dimethoxysilane as a donor (D-donor).

[0285] • Polymerization of the heterophasic propylene copolymer RAHECO

[0286] The heterophasic propylene copolymer RAHECO was produced in a Borstar® device using one pre-polymerization reactor, one liquid phase loop reactor and two gas phase reactors connected in series in the presence of the polymerization catalyst described above at the conditions shown in Table 1. TM The first reaction zone was a loop reactor and the second and third reaction zones were gas phase reactors.

[0287] Table 1: Polymerization conditions of the heterophasic propylene copolymer RAHECO:

[0288]

[0289]

[0290]

[0291] The RAHECO had a melt flow rate MFR2 (230°C, 2.16 kg) of 2.0 g / 10 min, a flexural modulus of 330 MPa and a melting temperature Tm of 151°C.

[0292] The polymer was taken out of the reactor and introduced into a ZSK 59 extruder, where it was mixed with an effective amount (total 1400 ppm) of Irgafos 168 (812 ppm), Irganox 1010 (406 ppm) and MgO (182 ppm). (CE1)

[0293] For Inventive Example 1, 50 ppm of Sipax NAB-82 (4-cyclohexen-1,2-dicarboxylic acid, calcium salt (1 :1 ) (CAS 57545-78-5) commercially available from GCH was additionally added as a granulation agent.

[0294] For CE2, 1000 ppm of Erol RTBN was added instead of Sipax NAB-82.

[0295] Erol RTBN is an antifoam agent commercially available from PMC OUVRIE, which is currently used to prevent agglomeration.

[0296] The ZSK 59 extruder used was equipped with a downsized screw from the production extruder CMP 362. Since the ZSK 59 has a longer L / D than the CMP 362, the temperature in the first zone was kept at a lower temperature, only for powder transport. The process parameters can be seen in Table 2 and the temperature profile of the extruder is shown in Table 3.

[0297] Table 2: Process parameters:

[0298]

[0299] SEI: Specific Energy Input

[0300] PCW: Pellet Cooling Water

[0301] Table 3: Temperature profile [°C]

[0302]

[0303] The underwater pelletizing system used was a GALA TWS20 system (TWS: Warm Water System) provided by Gala Industries Inc. In the pre-dewatering step of the Gala system, 90 to 95% of the water has been separated. Then, the pellets enter the lower third of the centrifuge, where the pellets hit the screen and the rotor, separating the surface water from the pellets. (The rotational speed rpm of the centrifuge is fixed by the supplier) The suction system creates an air flow opposite to the direction of the pellets. The opposite flow carries away the residual moisture on the surface of the pellets, avoiding that water and moist air are transported with the pellets. The combination of the centrifuge and the opposite air flow is the main drying step of the system. The temperature of the air flow is room temperature.

[0304] After the drying step, there is also a sieving to avoid dust or oversized pellets and agglomerates in the product. When leaving the centrifuge, the pellets are already substantially dry.

[0305] Table 4: Pellet properties of IE and CEs

[0306]

[0307] As can be seen from the above table, the granules prepared by the process of the present application have a higher amount of granules with a shape factor (SPF) below 1.2, a higher amount of granules with a particle size distribution between 1 and 5 mm, less tail particles and less clumping, compared to granules obtained without the use of a specific granulating agent.

Claims

1. A process for producing pellets of a polyolefin, the process comprising the steps of introducing into a continuous mixer a soft polyolefin i-a), 10 to 1000 ppm of a pelletizer i-b) based on the total weight of the soft polyolefin and a total of 500 to 10000 ppm of additives i-c) based on the total weight of the soft polyolefin, the soft polyolefin is characterized in that 10 a flexural modulus determined according to ISO 178 in the range of 10 to below 600 MPa, and more than 50 wt% of the soft polyolefin based on the total weight of the soft polyolefin is a propylene derived chain unit as described in the experimental part 13 C{ 1 H} the content of propylene derived chain units determined by NMR; the pelletizer is a pelletizer of formula (I) ， R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from H, C1-C9 alkyl, hydroxyl, phenyl, and C1-C9 alkyl groups. 18 Alkylphenyl groups and halogens, where M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La, and Eu, and the additives are one or more additives selected from the group consisting of antioxidants and process stabilizers, UV-stabilizers, heat stabilizers, slip agents, antiblocking agents, acid scavengers, metal deactivators, antibacterial agents, antistatic agents and pigments and mixtures thereof, ii) melting the i-a) polyolefin containing the pelletizer i-b) and the additives i-c) to form a molten polyolefin composition, iii) extruding the molten polyolefin composition through a die having a multitude of holes into a pellet water bath in a pelletizer, thereby producing strands of the polyolefin composition and solidifying the strands, iv) cutting the strands of the polyolefin composition into pellets in the pelletizer, and v) drying the pellets.

2. The process according to claim 1, wherein the soft polyolefin is a propylene copolymer with ethylene and / or 1 -butene comonomer, having a soluble fraction content in the range of 20 to 80 wt% based on the propylene copolymer, more preferably a random heterophasic propylene-ethylene copolymer (RAHECO) comprising: a) a crystalline matrix (M) which is a propylene-ethylene random copolymer; and b) an amorphous propylene-ethylene elastomer (E).

3. The process according to claim 2, wherein the random heterophasic propylene-ethylene copolymer (RAHECO) has 3.0 to 25.0 wt.-%, more preferably in the range of 5.0 to 20.0 wt.-%, most preferably in the range of 8.0 to 15.0 wt.-%, of ethylene, determined by quantitative 13 C-NMR spectroscopy calibrated to FT-IR spectroscopy determined ethylene content (C2(total)); a soluble fraction (SF) content in the range of 20 to 80 wt%, more preferably in the range of 25 to 60 wt%, most preferably in the range of 30 to 50 wt% based on the total amount of the RAHECO, determined according to CRYSTEX QC analysis; 20 to 80 wt.-%, more preferably in the range of 23 to 60 wt.-%, most preferably in the range of 25 to 50 wt.-%, of the ethylene content (C2(SF)) of the soluble fraction according to the CRYSTEX QC analysis as determined by quantitative 13 C-NMR spectroscopy calibrated FT-IR spectroscopy of the soluble fraction according to the CRYSTEX QC analysis; and an intrinsic viscosity (iV(SF)) of the soluble fraction according to CRYSTEX QC analysis in the range of 1.20 to 6.0 dL / g, more preferably in the range of 1.50 to 5.0 dL / g, most preferably in the range of 2.0 to 4.0 dL / g, determined according to DIN ISO 1628 / 1.

4. The process according to claim 2 or 3, wherein the random heterophasic propylene-ethylene copolymer (RAHECO) has a melt flow rate (MFR2) determined according to ISO 1133 at 230 °C and 2.16 kg in the range of 0.1 to 100 g / 10 min, more preferably in the range of 0.3 to 50.0 g / 10 min, even more preferably in the range of 0.5 to 20.0 g / 10 min and most preferably in the range of 0.8 to 10.0 g / 10 min, and a melting temperature (Tm) determined by differential scanning calorimetry (DSC) in the range of 130 °C to 160 °C, more preferably in the range of 140 °C to 157 °C and most preferably in the range of 145 °C to 155 °C.

5. The process according to any of the preceding claims, wherein the pelletizing agent of formula (I) is used, wherein R1to R8are independently selected from the group consisting of hydrogen and C1-C4 alkyl, more preferably independently from hydrogen, methyl and ethyl, most preferably each of R1to R8is hydrogen, and M is a metal cation selected from Mg, Ca, Zn, La, more preferably M is Ca or Zn, most preferably Ca.

6. The process according to any of the preceding claims, wherein the pelletizing agent of formula (I) is added in an amount of 15 to 500 ppm, more preferably in an amount of 20 to 100 ppm and most preferably in an amount of 25 to 80 ppm, based on the total weight of the polyolefin.

7. The process according to any of the preceding claims, wherein in step i) the polyolefin which has been withdrawn from the polymerization reactor in powder form, the pelletizing agent and further additives are introduced into an extruder, whereby extrusion in a twin-screw extruder takes place.

8. The process according to any of the preceding claims, wherein in step ii) the temperature in the extruder is adjusted to be in the range of 150 to 300 °C, preferably in the range of 170 to 290 °C, in order to melt the polyolefin i-a) containing the pelletizing agent i-b) and additives i-c) in the extruder to form a molten polyolefin composition, whereby the melt temperature in the extruder at or close to the die plate is adjusted to be in the range of 190 to 250 °C, preferably in the range of 200 to 240 °C.

9. The process according to any of the preceding claims, wherein in steps iii) and iv) the pellets are formed by extruding the polymer melt through the holes in the die plate into strands, wherein the strands are passed through the die plate into a water bath of an underwater pelletizer, the temperature of the pellet water in the pelletizer is in the range of 10 to 70 °C, and immediately following the die plate is a set of rotating knives which cut the strands into pellets and water is continuously added to the bath and a slurry comprising the water and the pellets is continuously withdrawn from the pelletizer.

10. The process according to any of the preceding claims, wherein the die plate has a plurality of openings through which the molten polymer flows into the pelletizer, whereby the openings typically have a diameter of 2.0 to 3.0 mm.

11. The process according to any of the preceding claims, wherein at least 27 %, preferably at least 30 % of the pellets obtained with the process as described in claims 1 to 10 have a shape factor (SPF) below 1.2, wherein the shape factor is the relation between the perimeter and the area of a pellet according to the following formula SPF = U 2 / (4 π A) where U = perimeter, π = pi (3.14159...) and A = projected area; the shape factor is determined by the instrumental pellet contamination, shape and size measurement as described in the experimental section.

12. The process according to any one of the preceding claims, wherein at least 85%, preferably at least 88%, more preferably at least 90% of the pellets obtained with the process as described in claims 1 to 11 have a particle size distribution between 1 and 5 mm, the particle size distribution being determined by the instrumental pellet contamination, shape and size measurement as described in the experimental section.

13. The process according to any one of the preceding claims, wherein less than 2.3%, preferably less than 2.0% of the pellets obtained with the process as described in claims 1 to 12 are in the form of lumps; the percentage of lumps is determined by the instrumental pellet contamination, shape and size measurement as described in the experimental section.

14. The process according to any one of the preceding claims, wherein less than 4.0%, preferably less than 3.5% and more preferably less than 3% of the pellets obtained with the process as described in claims 1 to 13 are in the form of tail particles, the percentage of tail particles being determined by the instrumental pellet contamination, shape and size measurement as described in the experimental section.

15. Pellets of soft polyolefins comprising a composition of a soft polyolefin, preferably a polyolefin copolymer, characterized in that 10 to below 600 MPa determined according to ISO 178 and more than 50 wt.-% of the soft polyolefin based on the total weight of the soft polyolefin using the method as described in the experimental part 13 C{ 1 H} content of chain units derived from propylene determined by NMR; 10 to 1000 ppm of a pelletizing agent of formula (I) based on the total weight of the polyolefin ， R1, R2, R3, R4, R5, R6, R7, and R8 are independently selected from H, C1-C9 alkyl, hydroxyl, phenyl, and C1-C9 alkyl groups. 18 Alkylphenyl groups and halogens, where M is a metal cation selected from Mg, Ca, Zn, Sr, Ba, La, and Eu, and a total of 500 to 10000 ppm of one or more additives based on the total weight of the polyolefin, the one or more additives being selected from the group consisting of antioxidants and process stabilizers, UV-stabilizers, heat stabilizers, slip agents, anti-blocking agents, acid scavengers, metal deactivators, antibacterial agents, antistatic agents and pigments, the pellets are characterized in that a) at least 27%, preferably at least 30% of the pellets have a shape factor (SPF) of less than 1.2, wherein the shape factor is the relationship between the perimeter and the area of a pellet according to the following formula SPF = U 2 / (4 π A) where U = perimeter, π = pi (3.14159...) and A = projected area, b) at least 85%, preferably at least 88%, more preferably at least 90% of the pellets have a particle size distribution between 1 and 5 mm, c) less than 2.3%, preferably less than 2.0% of the pellets are in the form of lumps, and d) less than 4.0%, preferably less than 3.5% and more preferably less than 3% of the pellets are in the form of tail particles, wherein properties a, b, c and d are determined by the instrumental pellet contamination, shape and size measurement as described in the experimental section.

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