Viscosity index improver additive for lubricating oils and process for producing same

Abstract

1. A viscosity index improving (VII) additive for lubricating oils comprising an ethylene-propylene copolymer, the additive having the following characteristics: - a shear stability index (SSI) measured in accordance with the ASTM D7109-12 standard (30 shear cycles) in Group I base oils of 18% to 30%, preferably 20% to 28%; - a thickening power (TP) measured in accordance with ASTM D7042-04 standard in Group I base oils of 3 cSt to 8 cSt, preferably 4 cSt to 7.5 cSt; a gelation index defined by the following ratio of 7000 or less, preferably 30 to 6000, more preferably 50 to 5000; (η 0℃ / η 40℃ ) / (η 60℃ / η 40℃ ) where η represents the steady-state kinematic viscosity measured in a Group III base oil; - an initial gelling temperature measured in a Group III base oil of not more than 10°C, preferably between 0°C and 10°C; a shape stability defined according to the following formula of less than or equal to 5%, preferably less than or equal to 4%, more preferably less than or equal to 3%: ΔL%=[(L / L0)-1)]*100 where L is the length after 24 hours and L is the initial length of 10 cm. A viscosity index improving (VII) additive having: The viscosity index improver (VII) additive for lubricating oils described above can be advantageously used in base oils of mineral or synthetic origin or mixtures thereof, preferably selected from base oils belonging to Group I, Group II or Group III.

Description

[Technical Field]

[0001] The present invention relates to viscosity index improving (VII) additives for lubricating oils.

[0002] More particularly, the present invention relates to a viscosity index improving (VII) additive for lubricating oils comprising an ethylene-propylene copolymer and having certain characteristics reported below.

[0003] The above-mentioned viscosity index improver (VII) additives for lubricating oils can be advantageously used in base oils of mineral or synthetic origin or mixtures thereof, preferably in base oils of mineral or synthetic origin selected from base oils belonging to Group I, Group II or Group III.

[0004] The present invention also relates to a process for producing an ethylene-propylene copolymer.

[0005] The present invention also relates to a lubricating oil composition comprising a viscosity index improving (VII) additive for lubricating oils and a base oil. [Background technology]

[0006] Ethylene-propylene copolymers are widely used in the lubricating oil additives sector, where they are also known as olefin copolymers (OCPs), as viscosity index improvers (VII) to adjust the viscosity of lubricating oils over temperature.

[0007] Micro / macro structure, weight average molecular weight (M w ), polydispersity index (PDI), i.e., the weight average molecular weight (M w ) and number average molecular weight (M n ) and the ratio (M w / M n), as well as the amount of ethylene-propylene copolymer used, are all factors that modify the effectiveness of the ethylene-propylene copolymer as a viscosity index improver (VII) for lubricating oils and the final properties of the formulations in which they are used.

[0008] Optimization of the micro / macrostructure of ethylene-propylene copolymers allows for identifying the appropriate balance to achieve the desired technological parameters.

[0009] For example, for the same polydispersity index (PDI), the weight average molecular weight (M w For a given value of shear stability index (SSI), a parameter that depends on the ethylene content, the thickening power (TP) increases with increasing ethylene content and molecular weight. Semicrystalline ethylene-propylene copolymers, characterized by a high content of linear ethylene, are therefore characterized by a higher ratio of thickening power (TP) to shear stability index (SSI) (TP / SSI) than amorphous ethylene-propylene copolymers, but have poorer low-temperature performance. On the other hand, semicrystalline ethylene-propylene copolymers, characterized by a low content of linear ethylene and a high weight-average molecular weight (M w Amorphous ethylene-propylene copolymers characterized by low densities (densities) have excellent low temperature properties, but present problems with the stability of the physical form (pellets) which makes the handling of ethylene-propylene copolymers particularly important.

[0010] However, balancing the technical parameters of lubricating oils cannot be achieved solely by using ethylene-propylene copolymers with intermediate ethylene content, because they contain ethylene sequences that can interfere with additives that can reduce the pour point depressants of the lubricating oils in which they are used, impairing their activity and further worsening the rheology of the lubricating oil at low temperatures.

[0011] In order to find the right balance of technological parameters, it is known to use appropriate mixtures of one or more crystalline ethylene-propylene copolymers with one or more amorphous ethylene-propylene copolymers.

[0012] For example, European Patent No. 2424939 states: (a) Below: i. ethylene-derived units E in the range of 35% by weight to 60% by weight A and ii. Less than 130,000 Mw A ; a first ethylene copolymer having (b) Below: i. ethylene-derived units E in the range of 35% by weight to 85% by weight B and ii. Less than 70,000 Mw B ; a second ethylene copolymer having wherein the first ethylene copolymer and / or the second ethylene copolymer have less than one pendant branch point with a carbon chain of more than 19 carbon atoms per 200 carbon atoms along the backbone.

[0013] Also disclosed are processes for making the polymer composition, as well as compositions comprising a lubricating base oil and the polymer composition. The polymer composition is said to be a rheology modifier that can be used as a viscosity index improver (VII) that has unexpected thickening power (TP) relative to prior art compositions while maintaining comparable rheological properties at low temperatures.

[0014] European Patent No. 2809689 is (a) a first ethylene-α-olefin copolymer; and (b) a second ethylene-α-olefin copolymer; and A polymer composition comprising: (c) the first ethylene-α-olefin copolymer (a) has an ethylene content of about 60% by weight to about 80% by weight; (d) the second ethylene-α-olefin copolymer (b) has an ethylene content of less than about 60 wt%; (e) the first ethylene-α-olefin copolymer (a) has a "melt flow rate ratio" (MFRR), defined as the ratio of the "melt flow rate" (MFR) measured at 230°C under a load of 21.6 kg to the "melt flow rate" (MFR) measured at 230°C under a load of 2.16 kg, of greater than 34, and a "melt flow rate" (MFR) measured according to standard ASTM D 1238, condition L (230°C under a load of 2.16 kg) of 2.5 g / 10 min to 5.5 g / 10 min; and (f) A polymer composition, wherein the blend of the first ethylene-α-olefin copolymer (a) and the second ethylene-α-olefin copolymer (b) has a "melt flow rate ratio" (MFRR) defined as above of 33 to 37.

[0015] Also disclosed is a lubricating composition comprising the above polymer composition and a lubricating base oil, which is said to have reduced or no gel formation.

[0016] EP 2809716 relates to a process for producing a polymer composition comprising the following steps: (a) feeding (i) a first ethylenic monomer, (ii) a first α-olefinic comonomer, (iii) a first solvent, (iv) optionally a first hydrogen, and (v) a first metallocene catalyst to a first reaction zone to produce a first ethylene-α-olefin copolymer; (b) feeding (i) a second ethylenic monomer, (ii) a second α-olefinic comonomer, (iii) a second solvent, (iv) optionally a second hydrogen, and (v) a second metallocene catalyst to a second reaction zone to produce a second ethylene-α-olefin copolymer; and (c) combining the first ethylene-α-olefin copolymer and the second ethylene-α-olefin copolymer to form a polymer composition. wherein the first ethylene-α-olefin copolymer has an ethylene content of 60% to 80% by weight, and the second ethylene-α-olefin copolymer has an ethylene content of less than 60% by weight, and the process satisfies at least one of the following requirements: (1) the first hydrogen in step (a) is supplied at a concentration of 0% to 1% by weight, based on the total weight of components (i) to (iv) supplied in step (a), and (2) the second hydrogen in step (b) is supplied at a concentration of 0% to 0.5% by weight, based on the total weight of components (i) to (iv) supplied in step (b).

[0017] The resulting polymer composition is said to be usable as a viscosity index improver (VII) for lubricating oils with reduced or no gel formation at low temperatures.

[0018] EP 1148115 relates to a viscosity index improver (VII) for lubricating oils, comprising an ethylene-propylene copolymer (B) having the following characteristics (b1) to (b5): (b1) a content of ethylene-based units in the range of 70% by weight to 79% by weight; (b2) a weight average molecular weight in the range of 80,000 Da to 400,000 Da in terms of polystyrene, as determined by gel permeation chromatography; (b3) The ratio M, which is an indicator of the polydispersity index, is less than 2.3. w / M n (M w :Weight average molecular weight;M n :number average molecular weight); (b4) a melting peak in the range of 15°C to 60°C as determined by differential scanning calorimetry (DSC); and (b5) The content of ethylene units [E (wt%)] and the melting point [T m (℃)] and the following relationship (II): 3.44×E-206≧T m (II) (When the weight average molecular weight is more than 80,000 and less than 250,000), and the following relationship: 3.44×E-204≧T m (III) (When the weight average molecular weight is 250,000 to 400,000),

[0019] A lubricating composition containing a lubricating oil and the above viscosity index improver (VII) has also been reported, and the lubricating composition is said to have very excellent properties at low temperatures.

[0020] EP 1178102 relates to a viscosity index improver (VII) for lubricating oils comprising an ethylene / α-olefin copolymer, the ethylene / α-olefin copolymer being a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and having the following properties: (1) an ethylene (E) content in the range of 40% by weight to 70% by weight; (2) a weight-average molecular weight in the range of 80,000 Da to 400,000 Da in terms of polystyrene, as determined by gel permeation chromatography; (3) Ratio M of 2.4 or less w / M n ; (4) a melting point of less than 60°C as determined by differential scanning calorimetry (DSC); and (5) The content of ethylene units [E (wt%)] and the melting point [T m (°C)] satisfies the following relationship (I): 3.31×E-186≧T m (I); and (6) The amount of carbon atoms αβ relative to the total carbon atoms present in the main chain and, if present, in the long chain branches [(V)%] satisfies the following relationship (II): V ≤ 10-0.1 × E (II).

[0021] A lubricating composition containing a lubricating oil and the above-mentioned viscosity index improver (VII) has also been reported, and the lubricating composition is said to have excellent low-temperature properties, oxidation stability, high-temperature lubricity, and fuel economy.

[0022] However, each of the viscosity index improvers (VII) described above may have some drawbacks. For example, to obtain a viscosity index improver (VII) capable of providing a lubricating oil composition with good low-temperature properties and reduced or no gel formation, it is necessary to use a blend of ethylene-propylene copolymers. In addition, ethylene-propylene copolymers have a medium to high weight average molecular weight (M w ) and, as a result, may have a high Shear Stability Index (SSI) value (i.e., >30).

[0023] It is also known that conventional processes for the preparation of ethylene-propylene copolymers in solution or in slurry have a high probability of producing ethylene-propylene copolymers characterized by significantly higher molecular weights than those used in the context of viscosity index improvers (VII). This is associated with the following reasons: - Conventional processes (stripping, extrusion drying) produce very low molecular weights (e.g., weight average molecular weight (M) below 100,000 Da). w )) cannot effectively process ethylene-propylene copolymers characterized by - Low molecular weight products tend to exhibit a cold flow phenomenon (particularly pronounced in the case of amorphous ethylene-propylene copolymers) which makes handling and storage very difficult.

[0024] Furthermore, to ensure the application performance of viscosity index improvers (VII) for lubricating oils, a low molecular weight is essential, and the processes typically used for the production of ethylene-propylene copolymers (solution or slurry processes) often result in ethylene-propylene copolymers with significantly higher molecular weights, making it necessary to subject the ethylene-propylene copolymer to a pyrolysis process.

[0025] For example, European Patent No. 1013673 relates to a process for reducing the molecular weight of a polymeric material selected from ethylene copolymers and ethylene terpolymers [EP(D)M] or mixtures thereof. The process involves treating the polymeric material with at least one hydroperoxide present in an amount sufficient to cause molecular weight reduction at a temperature of 80°C to 250°C, wherein the ethylene copolymers and ethylene terpolymers [EP(D)M] have a molar propylene content of 16% to 50%. The ethylene copolymers and ethylene terpolymers [EP(D)M] thus obtained are said to have several uses, including as viscosity index improvers (VII) for lubricating oils and as modifiers for high-flow plastic materials. The process can be carried out in an extruder, preferably a twin-screw extruder.

[0026] European Patent No. 1671982 relates to a process for producing a viscosity index improver (VII) that has improved dimensional stability and can improve the rheology of lubricating oils at low temperatures. The process involves treating a mixture of linear polyethylene, a homopolymer or copolymer of ethylene characterized by a crystalline structure and a density of 0.88 to 0.94, with amorphous ethylene copolymers and ethylene terpolymers [EP(D)M], optionally with semi-crystalline ethylene copolymers and ethylene terpolymers [EP(D)M]. The treatment is carried out in an extruder in the presence of one or more substances of hydroperoxidic nature and, optionally, in the presence of a polyfunctional vinyl monomer in an amount of 0 to 2% by weight. The treatment is carried out for 100 seconds. -1 and at temperatures between 75°C and 260°C, and the amorphous ethylene copolymers and terpolymers [EP(D)M] are characterized by an ethylene content between 35% and 62% by weight and a third monomer content between 0% and 10% by weight. The above process can be carried out in an extruder, preferably a twin-screw extruder.

[0027] EP 1632504 relates to a process for the preparation of a viscosity index improver (VII), which comprises treating under high shear conditions a composition comprising (i) one or more ethylene copolymers or ethylene terpolymers [EP(D)M)] and (ii) one or more polyvinylarene / hydrogenated conjugated diene / polyvinylarene block copolymers, the weight ratio of (i) / (ii) being between 98 / 2 and 80 / 20, at a temperature between 150°C and 400°C for a time not exceeding 150 seconds, for a period of 75 seconds. -1 The above process can be carried out in an extruder, preferably a twin-screw extruder.

[0028] European Patent No. 1984479 is 50 seconds -1 Under shear conditions of (i) one or more ethylene copolymers or ethylene terpolymers [EP(D)M]; (ii) one or more polyvinylarene / hydrogenated conjugated diene / polyvinylarene block copolymers; (iii) lubricating oil; wherein (ii) is present at a concentration of 1.5 wt % to 20 wt % and (iii) is present at a concentration of 1.5 wt % to 45 wt %.

[0029] The above process can be carried out in an extruder, preferably a twin-screw extruder.

[0030] Canadian Patent No. 991792 relates to a continuous process for producing lubricating oil additives by pyrolyzing in an extruder under non-oxidizing conditions a substantially linear, high molecular weight amorphous ethylene-propylene hydrocarbon copolymer containing 25% to 50% by weight of polymerized propylene, 0% to 5% by weight of polymerized non-conjugated hydrocarbon diene, and the balance polymerized ethylene. The process includes uniformly mixing and heating the copolymer in a first zone at a temperature of about 150°C to 280°C, which is below the decomposition temperature of the copolymer, until the copolymer is uniformly molten; passing the molten copolymer through a second zone, where it is uniformly mixed and heated to a temperature of about 300°C to 500°C, until a decomposed copolymer is obtained, the decomposed copolymer having an intrinsic viscosity, measured at 30°C on a solution of 0.1 g of copolymer in 100 ml of tetrachloroethylene, lower than that of the starting copolymer, of 0.1 dL / g to 1.8 dL / g, and a molecular weight distribution substantially equal to or smaller than that of the starting copolymer; removing the decomposed copolymer from the second zone; and cooling and recovering the decomposed copolymer, which is substantially colorless or white and contains only traces of oil-insoluble material.

[0031] U.S. Patent No. 6,753,381 relates to a lubricating oil composition comprising an extended lubricating oil, an additive package suitable for quality and performance levels, a pour point depressant, and an oil-soluble polymer mixture in an amount to improve viscosity index (VII), said polymer mixture having a weight average molecular weight of about 20,000 to about 300,000 and a molecular weight distribution of about 1.3 to about 5: (a) a low ethylene content, essentially amorphous ethylene-propylene polymer having an ethylene to propylene molar ratio of 35 / 65 to 65 / 35, a weight average molecular weight of about 40,000 to about 300,000, and a weight distribution within the range of about 1.3 to about 5.0; and (b) a partially crystalline ethylene-propylene polymer having a high ethylene content, an ethylene to propylene molar ratio of about 65 / 35 to about 85 / 15, a crystallinity of 3% by weight to 25% by weight, a weight average molecular weight in the range of about 40,000 to about 300,000, and a molecular weight distribution in the range of about 1.3 to about 5.0; and (b) a) and (b) b) and (c) a) and (d) b) b) and (e) a) and (f ...

[0032] However, each of the above processes may have some drawbacks. For example, to obtain an ethylene-propylene copolymer with a molecular weight suitable for use as a viscosity index improver (VII), the use of hydroperoxides or operation at high temperatures (up to 500°C) may be required, which may require operation in an inert atmosphere (e.g., in the presence of nitrogen) and may lead to gel formation and branching in the final product. Furthermore, to improve the dimensional stability of the resulting ethylene-propylene copolymer, the use of small amounts of polyvinylarene / hydrogenated conjugated diene / polyvinylarene block copolymers or multifunctional vinyl monomers may be required. Summary of the Invention

[0033] The applicant therefore set himself the problem of finding a viscosity index improving (VII) additive for lubricating oils that is able to achieve suppression of gel formation at low temperatures, a stable physical form (pellets), and a very good balance between the values ​​of shear stability index (SSI) (i.e., 30% or less) and thickening power (TP) (i.e., 8 cSt or less), measured as reported below.

[0034] Applicant has discovered a viscosity index improver (VII) additive for lubricating oils, comprising an ethylene-propylene copolymer, having the specific characteristics reported below. The viscosity index improver (VII) additive for lubricating oils is capable of suppressing gel formation at low temperatures, maintaining a stable physical form (pellets), and achieving an excellent balance between shear stability index (SSI) (i.e., 30% or less) and thickening power (TP) (i.e., 8 cSt or less), measured as reported below. Additionally, the viscosity index improver (VII) additive for lubricating oils can be advantageously used with mineral-derived or synthetic-derived base oils or mixtures thereof. Preferably, the mineral-derived or synthetic-derived base oils are selected from Group I, Group II, or Group III base oils.

[0035] Accordingly, an object of the present invention is a viscosity index improving (VII) additive for lubricating oils comprising an ethylene-propylene copolymer, the additive having the following characteristics: - a shear stability index (SSI) measured in accordance with the ASTM D7109-12 standard (30 shear cycles) in Group I base oils of 18% to 30%, preferably 20% to 28%; - a thickening power (TP) measured in accordance with ASTM D7042-04 standard in Group I base oils of 3 cSt to 8 cSt, preferably 4 cSt to 7.5 cSt; a gelation index defined by the following ratio of 7000 or less, preferably 30 to 6000, more preferably 50 to 5000; (η 0℃ / η 40℃ ) / (η 60℃ / η 40℃ ) where η represents the steady-state kinematic viscosity measured in a Group III base oil; - an incipient gelation temperature, measured in a Group III base oil, of less than or equal to 10°C, preferably between 0°C and 10°C; - a shape stability defined according to the following formula of less than or equal to 5%, preferably less than or equal to 4%, more preferably less than or equal to 3%; ΔL%=[(L / L0)-1)]*100 where L is the length after 24 hours and L is the initial length of 10 cm. It is a viscosity index improving (VII) additive having

[0036] For purposes of this specification and the claims that follow, the gel index, initial gel temperature, and shape stability are specified as reported below in the Methods of Analysis and Characterization.

[0037] For purposes of this specification and the claims that follow, definitions of numerical ranges always include the endpoints unless otherwise specified.

[0038] For purposes of this specification and the claims that follow, the term "comprising" also includes the terms "which essentially consists of" or "which consists of."

[0039] For the purposes of this specification and the claims that follow, the term "base oil" means base oils according to API 1509 Standard "Engine Oil Licensing and Certification System", November 2004, 15th Edition, Appendix E, which base oils are divided into five groups as reported in the table below. [Table 1]

[0040] According to a preferred embodiment of the present invention, the ethylene-propylene copolymer has the following characteristics: - 61% to 67% by weight, preferably 62% to 66% by weight, of ethylene relative to the total weight of the ethylene-propylene copolymer; - 33% to 39% by weight, preferably 34% to 38% by weight, of propylene relative to the total weight of the ethylene-propylene copolymer; - a weight average molecular weight (M) of 60,000 Da to 120,000 Da, preferably 65,000 Da to 100,000 Da; w ); - a polydispersity index (PDI), i.e., a weight average molecular weight (M w ) and number average molecular weight (M n ) and the ratio (M w / M n ); - a crystallization peak temperature of less than or equal to 20°C, preferably between 0°C and 15°C, as determined by differential scanning calorimetry (DSC); - a melting peak temperature of 35°C or less, preferably between 0°C and 30°C, as determined by differential scanning calorimetry (DSC); - an enthalpy of fusion (ΔH) of 25 J / g or more, preferably 28 J / g to 40 J / g, as determined by differential scanning calorimetry (DSC); a minimum number of propylene inversions, determined by NMR analysis, of 0.1 to 0.25, preferably 0.12 to 0.22; It has.

[0041] The applicant also set himself the problem of finding a process for producing the above-mentioned ethylene-propylene copolymers that can overcome the above-mentioned drawbacks.

[0042] Applicant has discovered a continuous process for reducing the molecular weight of an ethylene-propylene copolymer, which includes the use of a single-screw extruder equipped with a reciprocating single screw, three conveying and mixing zones, a gear pump, and an underwater die face cutter, wherein the three conveying and mixing zones and the gear pump operate within a specific temperature range. In particular, Applicant has discovered that the use of the single-screw extruder allows for the production of ethylene-propylene copolymers having molecular weights suitable for use as viscosity index improvers (VII) in the absence of hydroperoxides, while operating at temperatures lower than those of known techniques, thereby avoiding both the need to operate under an inert atmosphere and the formation of gels and branches in the final product. Furthermore, the process does not require the use of polyvinylarene / hydrogenated conjugated diene / polyvinylarene block copolymers or multifunctional vinyl monomers to improve the dimensional stability of the final product.

[0043] Therefore, a further object of the present invention is a continuous process for reducing the molecular weight of an ethylene-propylene copolymer, comprising the following steps: (a) providing at least one single screw extruder comprising a chamber, a reciprocating single screw mounted within said chamber, wherein said reciprocating single screw is capable of rotating and oscillating within said chamber, said chamber having at least one feed opening and at least one discharge opening, said extruder comprising three conveying and mixing zones, a gear pump, and a submerged die face cutter; (b) feeding at least one ethylene-propylene copolymer into said single screw extruder; (c) conveying the at least one ethylene-propylene copolymer through a first conveying and mixing zone operating at a temperature of from 140°C to 260°C, preferably from 150°C to 250°C, wherein the ethylene-propylene copolymer is uniformly mixed, heated, and uniformly softened; (d) conveying the at least one uniformly softened ethylene-propylene copolymer exiting the first conveying and mixing zone to a second conveying and mixing zone operating at a temperature of from 220°C to 330°C, preferably from 230°C to 320°C, where the ethylene-propylene copolymer is further mixed, heated, and partially cracked; (e) conveying the at least one partially cracked ethylene-propylene copolymer exiting the second conveying and mixing zone to a third conveying and mixing zone operating at a temperature of from 170°C to 340°C, preferably from 180°C to 330°C, where the ethylene-propylene copolymer is further mixed, heated, and further cracked; (f) conveying the at least one further cracked ethylene-propylene copolymer exiting the third conveying and mixing zone to the gear pump operating at a temperature of from 170°C to 340°C, preferably from 180°C to 330°C, wherein the ethylene-propylene copolymer is further cracked; (g) recovering said at least one further cracked ethylene-propylene copolymer exiting said underwater die face cutter; It is a continuous process comprising:

[0044] For the purposes of the present invention, a single screw extruder may be used that is equipped with a reciprocating single screw, three conveying and mixing zones, a gear pump, a submerged die face cutter, and also has the following characteristics: - in comparison with a conventional single screw extruder in which the screw is in the form of a continuous spiral, said reciprocating single screw has threads interrupted at intervals of 120° in the radial direction, and pins or teeth associated with said threads are inserted into the barrel; - compared to conventional single screw extruders, in which the screw movement is only rotational, the movement of the reciprocating single screw is rotational and oscillating, in fact, the rotation of the reciprocating single screw is superimposed with an oscillation (or axial stroke), which leads to an improvement in the mixing and decomposition capacity inside the extruder; - the frequency of said axial motion ("reciprocating movement") is the same as the rotational speed, and a gear system causes a complete forward and backward stroke for each revolution of said reciprocating uniaxial screw; - The amplitude of vibration is approximately 20 mm; - during the execution of the complete forward and retraction strokes, the path followed by the pins (or teeth) covers and cleans the entire surface of the reciprocating screw so that there are no stagnant zones of material, and in fact the threads ("kneading flights") oscillate around the pins (or teeth), which makes it possible to obtain a very uniform velocity gradient between the threads ("kneading flights") and the pins; - the combined rotational and axial motion of the reciprocating single screw creates an extensional flow with a strong dispersive mixing action between the threads ("kneading flights") and the pins; - the melting of the ethylene-propylene copolymer occurs in the gap between the threads ("kneading flights") and the pins; - Due to the improved mixing ability, the ethylene-propylene copolymer does not exhibit heterogeneity in the sense of solid and molten parts, and the ethylene-propylene copolymer melts simultaneously, resulting in high viscosity and generating high shear stress values, especially in the first two mixing zones.

[0045] Further details regarding the single-screw extruder are described, for example, in Elemans PHM and Mejer HEH, "Polymer Engineering and Science" (1990), Mid-August, Vol. 30, No. 15, pp. 893-904.

[0046] According to a preferred embodiment of the present invention, the single screw extruder operates at a screw rotation speed of 220 rpm to 300 rpm, preferably at a screw rotation speed of 230 rpm to 290 rpm.

[0047] According to a preferred embodiment of the present invention, the single screw extruder operates at a flow rate of between 300 kg / h and 700 kg / h, preferably between 400 kg / h and 600 kg / h. Upon exiting the underwater die face cutter, the fully cracked ethylene-propylene copolymer is in the form of pellets which are separated from the water, for example by centrifugation, and subsequently sent by pneumatic conveying to a drying and packaging section.

[0048] According to a preferred embodiment of the present invention, in step (b) of the above process, said at least one ethylene-propylene copolymer has the following characteristics: - 61% to 67% by weight, preferably 62% to 66% by weight, of ethylene relative to the total weight of the ethylene-propylene copolymer; - 33% to 39% by weight, preferably 34% to 38% by weight, of propylene relative to the total weight of the ethylene-propylene copolymer; - a weight average molecular weight (M) of 120,000 Da to 200,000 Da, preferably 140,000 Da to 170,000 Da; w ); - a polydispersity index (PDI), i.e., a weight average molecular weight (M w ) and number average molecular weight (M n ) and the ratio (M w / M n ); - a crystallization peak temperature of less than or equal to 20°C, preferably between 0°C and 15°C, as determined by differential scanning calorimetry (DSC); - a melting peak temperature of 35°C or less, preferably between 0°C and 30°C, as determined by differential scanning calorimetry (DSC); - an enthalpy of fusion (ΔH) of 25 J / g or more, preferably 28 J / g to 40 J / g, as determined by differential scanning calorimetry (DSC); a minimum number of propylene inversions, determined by NMR analysis, of 0.1 to 0.25, preferably 0.12 to 0.22; It has.

[0049] The ethylene-propylene copolymers useful in the process object of the present invention can be obtained according to the process described in US Pat. No. 9,701,764 in the name of the applicant and incorporated herein by reference. [Brief explanation of the drawings]

[0050] [Figure 1] 1 shows an embodiment of the process object of the present invention and a block diagram of the plant and single screw extruder used in said process. [Figure 2] 1 shows the relationship between temperature and normalized steady-state kinematic viscosity for Example 7 (invention). [Figure 3] 1 shows the relationship between temperature and normalized steady-state kinematic viscosity for Example 8 (comparative example). [Figure 4] 1 shows the relationship between temperature and normalized steady-state kinematic viscosity (logarithmic scale) for Example 7 (invention). [Figure 5] 1 shows the relationship between temperature and normalized steady-state kinematic viscosity (logarithmic scale) for Example 8 (comparative example). [Figure 6] 1 shows the relationship between temperature and heat flow for Example 7 (invention). [Figure 7] 1 shows the relationship between temperature and heat flow in Example 8 (comparative example).

[0051] FIG. 1 reported below shows, for illustrative and not limiting purposes only, an embodiment of the process object of the present invention and a block diagram of the plant and single screw extruder used in said process.

[0052] Specifically, in Figure 1, ethylene-propylene copolymer (1) is fed through a feed hopper to a single-screw extruder equipped with three conveying and mixing zones, a gear pump, and an underwater die face cutter, where the three conveying and mixing zones and the gear pump operate within a specific temperature range. Specifically, the ethylene-propylene copolymer is uniformly mixed, heated, and uniformly softened through the first conveying and mixing zone, thereby obtaining ethylene-propylene copolymer (2). The ethylene-propylene copolymer is then conveyed to the second conveying and mixing zone, where it is further mixed, heated, and partially decomposed, thereby obtaining partially decomposed ethylene-propylene copolymer (3). The ethylene-propylene copolymer is then conveyed to the third conveying and mixing zone, where it is further mixed, heated, and further decomposed, thereby obtaining further decomposed ethylene-propylene copolymer (4). The ethylene-propylene copolymer is then conveyed to the gear pump, where it is further decomposed, thereby obtaining further decomposed ethylene-propylene copolymer (5). At the outlet of the underwater die face cutter, it is separated from the water, for example by centrifugation, and is recovered in the form of pellets which are subsequently sent by pneumatic conveyance to the drying and packaging section.

[0053] As already reported above, the present invention also relates to a lubricating oil composition comprising the above-described viscosity index improving (VII) additive for lubricating oils and a base oil.

[0054] Therefore, the present invention provides - 1% to 30% by weight, preferably 2% to 20% by weight, of a viscosity index improving (VII) additive for said lubricating oil, relative to the total weight of the lubricating oil composition; base oils of mineral or synthetic origin or mixtures thereof, wherein the base oils of mineral or synthetic origin are preferably chosen from base oils belonging to Group I or Group II or Group III; The present invention also relates to a lubricating oil composition comprising:

[0055] As reported above, the viscosity index improver (VII) additive for lubricating oils object of the present invention can be advantageously used in base oils of mineral or synthetic origin or in mixtures thereof, preferably said base oils of mineral or synthetic origin being chosen from base oils belonging to Group I or Group II or Group III.

[0056] The present invention therefore also relates to the use of a viscosity index improving (VII) additive for lubricating oils as described above in a base oil of mineral or synthetic origin or in a mixture thereof, said base oil of mineral or synthetic origin being preferably selected from base oils belonging to Group I or Group II or Group III.

[0057] For a better understanding of the present invention and for putting it into practice, some illustrative, non-limiting examples are reported below.

[0058] The analytical and characterization methods reported below were used.

[0059] Spectrum 13 C-NMR 13 C-NMR spectra were recorded at 120°C on a variable temperature nuclear magnetic resonance spectrometer model Bruker Avance 300 equipped with a 10 mm probe.

[0060] For this purpose, polymer solutions of intact ethylene-propylene copolymers and degraded ethylene-propylene copolymers obtained as reported in the following examples were used, which were prepared at 120 °C using deuterated tetrachloroethane (C2D2Cl4) and tetramethylsilane (TMS) as internal standards and had concentrations of 10% to 15% w / v (g / mL).

[0061] The structure of the ethylene-propylene copolymer (i.e., ethylene content (%), propylene content (%)) was identified by analyzing the spectrum based on the information reported in the literature by Di Martino S. and Kelchtermans M., "Journal of Applied Polymer Science" (1995), Vol. 56, Issue 13, pp. 1781-1787 (method No. 3, pg. 1784).

[0062] The minimum number of propylene inversions in the ethylene-propylene copolymer was determined by analyzing the spectrum based on the information reported in Randall JC, "Macromolecules" (1978), Vol. 11, No. 1, pp. 33-36.

[0063] Identification of gelation index and initial gelation temperature For this purpose, the degraded ethylene-propylene copolymers obtained as reported in the following examples were dissolved in an amount of 10% by weight in a reference Group III base oil (non-standard) having the characteristics reported in Table 1 below. [Table 2]

[0064] Once the ethylene-propylene copolymer is completely dissolved, the resulting solution is heated under the following conditions: - Measurement of steady-state kinematic viscosity [PP40 (parallel plate) - Anton Paar rheometer model MCR501); - Test temperature: from 60°C to 0°C in 5°C increments, with 20 minutes at each temperature before each test; - Stress sequence from 0.1 Pa to 3.2 Pa for 100 seconds at each temperature, The samples were subjected to dynamic mechanical analysis (DMA) operating at .

[0065] Different weight average molecular weights (M w In order to allow for a uniform comparison of steady-state kinematic viscosity values ​​between samples of ethylene-propylene copolymers that can be distinguished by their viscosity and polydispersity index, a normalization operation was performed on the data obtained.

[0066] For the above purposes, for each sample of ethylene-propylene copolymer, all the obtained steady-state kinematic viscosity values ​​were divided by the steady-state kinematic viscosity data appropriately selected as a reference. For the purposes of the present invention, the steady-state kinematic viscosity data at 40°C was selected.

[0067] Normalized steady-state kinematic viscosity values ​​were obtained by dividing all obtained steady-state kinematic viscosity values ​​by the value obtained at 40°C according to the following formula: η norm X℃ =η X℃ / η 40℃ where η norm is the normalized steady-state kinematic viscosity and η X℃ is the steady-state kinematic viscosity measured at various temperatures, and η 40℃ is the steady state kinematic viscosity measured at 40°C.

[0068] By way of non-limiting example, the values ​​obtained for the ethylene-propylene copolymers of Example 7 (invention) and Example 8 (comparison) below are reported in Table 2. [Table 3]

[0069] From measurements of the normalized steady-state kinematic viscosity at 0°C and 60°C, the gel index, defined as reported above, can be determined from the ratio: η norm 0℃ / ηnorm 60℃ =(η 0℃ / η 40℃ ) / (η 60℃ / η 40℃ ).

[0070] By way of non-limiting example, the values ​​obtained for the ethylene-propylene copolymers of Example 7 (invention) and Example 8 (comparison) below are reported in Table 3. [Table 4]

[0071] To determine the initial gelation temperature, the procedure reported below was applied, by way of non-limiting example, to the ethylene-propylene copolymers of Example 7 (inventive) and Example 8 (comparative example) below.

[0072] To this end, the following operations were carried out: - Obtain an exponential trend line interpolating the data of normalized steady-state kinematic viscosity from 60°C to 30°C, as reported in Figure 2 [Example 7 (Invention)] and Figure 3 [Example 8 (Comparative Example)] [the horizontal axis indicates temperature (T) in degrees Celsius, and the vertical axis indicates normalized (η norm) steady-state kinematic viscosity]; - Determine the values ​​of the normalized (ηnorm) steady-state kinematic viscosity using the above fitted curve for the entire temperature range (60 °C - 0 °C), as reported in Table 4; [Table 5] - Determine the percentage difference between the actual value of the normalized (η norm) steady-state kinematic viscosity and the value calculated according to the following formula and report the values ​​obtained in Table 5: Δ%=(ηnorm-ηcalc) / ηcalc×100 where η norm is the normalized steady-state kinematic viscosity and η calc is the calculated steady-state kinematic viscosity. [Table 6]

[0073] The initial gelation temperature for the purposes of this invention was considered to be the temperature at which the value of the normalized (η norm) steady-state kinematic viscosity was 75% or more higher than the calculated data, as reported in Figure 4 [Example 7 (Invention)] and Figure 5 [Example 8 (Comparative)], where the horizontal axis shows temperature (T) in degrees Celsius and the vertical axis shows the normalized (η norm) steady-state kinematic viscosity on a logarithmic scale.

[0074] Determining shape stability Shape stability was evaluated using extruded "spaghetti" for degraded ethylene-propylene copolymers obtained as reported in the examples below.

[0075] For this purpose, the "spaghetti" is prepared by subjecting the above ethylene-propylene copolymer to a temperature of 140°C for 1 second. -1 The results were obtained by feeding the sample into a capillary rheometer operated at a shear rate of 1000 sq. m / s and a relaxation time of 16 h.

[0076] The "spaghetti" thus obtained was hung on a special support at 25°C, and the change in length over time was evaluated. The rate of change in length was determined by the following formula, as reported above: ΔL%=[(L / L0)-1)]*100 where L is the length after 24 hours and L0 is the initial length of 10 cm.

[0077] Molecular weight determination The weight average molecular weights (M) of the neat and degraded ethylene-propylene copolymers obtained as reported in the following examples are w ), number average molecular weight (M n ), and ratio M w / M nThe determination of the polydispersity index (PDI) corresponding to was carried out by GPC ("gel permeation chromatography"), using an integrated HT-GPC PL220 tool from Agilent Technologies with three detection lines: refractive index (IR), viscometer (VS) and DALLS ("Dual Angle Laser Light Scattering"), operated under the following conditions: - a precolumn (guard column) with dimensions 50 x 7.5 mm and a particle size of 10 μm; - Three GPC columns from Agilent Technologies, with dimensions 300 × 7.5 mm, mixed porous and 10 μm particle size; - Mettler XPR225 analytical balance; - Laboratory glassware; - Distillation and degassing systems for solvent recovery; - 50ml automatic dispensing device; - PL-SP-260 automatic dissolver manufactured by Agilent Technologies; - Column injection temperature: 135°C; - Temperature of column and detection line: 135°C; - Solvent / eluent: 1,2-dichlorobenzene (HPLC grade, 99+% - Acros Organics™); - Flow rate: 1mL / min; - Calculation of molecular weight using universal calibration curve.

[0078] The above operating conditions were constantly monitored by a personal computer equipped with Agilent GPC / SEC software manufactured by Agilent Technologies.

[0079] The calibration was carried out as follows:

[0080] A nominal peak molecular weight (M) of 100 kDa was used to determine the interdetector delay (IDD) and calibration constants for the four signals (RID, VS, LS15°, and LS90°). pA solution of 1,2-dichlorobenzene (HPLC grade, HPLC 99+% - Acros Organics™) containing polystyrene (PS) standards with .gamma. was prepared.

[0081] Each has a different nominal peak molecular weight (M p Seven solutions of 1,2-dichlorobenzene (HPLC grade, HPLC 99+% - Acros Organics™) containing 1,2-dichlorobenzene (HPLC grade, HPLC 99+% - Acros Organics™) and two monodisperse polystyrene (PS) standards of different concentrations were also prepared, with the molecular weights selected to ensure sufficient separation of the chromatographic elution peaks, while the concentration of each standard was selected inversely proportional to the molecular weight. The different nominal peak molecular weights (M p ) ranged from 2 kDa to 7000 kDa.

[0082] Each solution was prepared at room temperature (25°C) under stirring in the Agilent Technologies PL-SP-260 automatic dissolver described above.

[0083] The calibration curve was calculated using a third-order polynomial function on a personal computer equipped with the above-mentioned Agilent GPC / SEC software manufactured by Agilent Technologies.

[0084] Differential scanning calorimetry (DSC) Differential scanning calorimetry (DSC) of neat and degraded ethylene-propylene copolymers obtained as reported in the following examples was carried out with the following equipment to determine the temperature of the crystallization peak, the temperature of the melting peak, the melting enthalpy (ΔH), and the residual melting enthalpy (ΔH) at temperatures above 60° C. - Differential scanning calorimeter (DSC) with 50 self-sampling positions; - Manufacturer: TA Instruments; - Model: Q1000; - Oven atmosphere: nitrogen; - Cooling system: two-stage (-100°C) refrigeration cycle ("Refrigeration Cooling System" - RCS); - analytical balance; - Small crucible closing press: - Aluminium crucible and lid.

[0085] A sample weighing 15±1 mg was taken from the ethylene-propylene copolymer and placed as flat as possible to maximize the contact area with the aluminum crucible. After placing the copolymer sample on the crucible, the crucible was closed with an aluminum lid that had been pre-punched to allow vapors released from the sample to escape. The crucible lid was closed using a special press.

[0086] Crucibles containing the various samples to be analyzed and an empty reference crucible were placed in numbered self-sampling positions (each position was associated with a sample name), and the computer, differential scanning calorimeter (DSC), and cryo-cooling system (RCS) were then switched on in sequence to select the heat treatment to be performed. The analysis was performed using "Thermal Advantage" software, version 5.1.2.

[0087] After the analysis was completed, the resulting thermograms were processed using "Universal Analysis" software, version 4.7A.

[0088] The heat treatments applied to the samples were as follows: - First step: cooling scan from +25°C to -90°C at 20°C / min; - Second step: isothermal at -90°C for 3 min; - Third step: Heating scan from -90°C to +170°C at 20°C / min (first heat); - 4th step: isothermal at +170°C for 3 minutes; - 5th step: cooling scan from +170°C to -90°C at 20°C / min; - 6th step: isothermal at -90°C for 3 min; - 7th step: Heating scan from -90°C to +170°C at 20°C / min (second heating).

[0089] From the analysis of the DSC charts of the fifth and seventh steps above, it is possible to identify the crystallization peak temperature and the melting peak temperature, respectively, as reported in Figure 6 [Example 7 (Invention)] and Figure 7 [Example 8 (Comparative Example)] [the horizontal axis represents the temperature in degrees Celsius and the vertical axis represents the heat flow in mW].

[0090] Identification of thickening power (TP) For this purpose, the cracked ethylene-propylene copolymers obtained as reported in the following examples were dissolved in an amount of 1% by weight in the reference base oil SN 150 Group I (Eni SpA).

[0091] The thickening power (TP) was determined according to the ASTM D7042-04 standard and calculated according to the following formula: TP=KV100C (オイル+ポリマー1重量%) -KV100C (オイル) where KV is the kinematic viscosity.

[0092] Determination of Shear Stability Index (SSI) For this purpose, the cracked ethylene-propylene copolymer (EPR) obtained as reported in the following examples was dissolved in an amount of 1% by weight in the reference base oil SN 150 Group I (Eni SpA).

[0093] The shear stability index (SSI) was determined according to the ASTM D7109-12 standard (30 "shear cycles"). [Example]

[0094] Example 1 to Example 4 Preparation of the starting ethylene-propylene copolymer (i.e., the neat ethylene-propylene copolymer) Four ethylene-propylene copolymers were prepared by the procedures described below.

[0095] The suspension polymerization reaction was carried out continuously in a 400 L reactor (300 L of which was usable) equipped with an impeller blade, a bottom anchor scraper, and a bottom discharge.

[0096] The reactor was fed with: - Liquid propane (inert diluent) (Lyondelbasell); - Liquid propylene (monomer) (Lyondelbasell); Gaseous ethylene (monomer) (Versalis); Gaseous hydrogen (molecular weight regulator) (SIAD); - a suspension of vanadium acetylacetonate V(acac)3 (Reactana) in paraffin oil (8% by weight of vanadium acetylacetonate relative to the total weight of the suspension) (catalyst); - diethylaluminum chloride (DEAC) (as is; purity 98.5%; Al / Cl molar ratio: 1; Albemarle) (cocatalyst); - Dichlorophenylethyl acetate (DCPAE) (as is; 97% purity; Chem Solutions) (activator).

[0097] Table 1 reports the operating conditions used: feed of compounds to the reactor, temperature and pressure.

[0098] The average residence time of the compounds in the reactor was about 1 hour. The resulting ethylene-propylene copolymer suspension was discharged from the bottom of the reactor and continuously fed to a stripper filled with water at 120°C and also fed with steam, thereby stripping hydrogen, propane, and unreacted monomers (propylene and ethylene).

[0099] In the above stripper, unreacted diethylaluminum chloride (DEAC) and dichlorophenylethyl acetate (DCPAE) were also neutralized and decomposed with a solution of sodium hydroxide (NaOH), resulting in the formation of aluminum hydroxide / aluminum oxide [Al(OH)3 / Al2O3], acetic acid / acetic anhydride [CH3COOH / (CH3CO)2O], and sodium chloride (NaCl).

[0100] The water exiting the stripper, which also contained traces of unreacted vanadium, was collected and sent to water treatment.

[0101] The ethylene-propylene copolymer obtained was subjected to the characterizations reported above and the results obtained are reported in Table 6. [Table 7] (1) : Liquid propylene (monomer); (2) : Liquid propane (inert diluent); (3) : Gaseous ethylene (monomer); (4) : gaseous hydrogen (molecular weight regulator); (5) : Vapor phase purging; (6) : a suspension of vanadium acetylacetonate V(acac)3 in paraffin oil (8% by weight of vanadium acetylacetonate relative to the total weight of the suspension) (catalyst); (7) : Diethylaluminum chloride (as is; purity 98.5%) (cocatalyst); (8) : the molar ratio of aluminum present in the cocatalyst to vanadium present in the catalyst; (9) : Dichlorophenylethyl acetate (as is; purity 97%) (activator); (10) : the molar ratio of activator to vanadium present in the catalyst; (11): the gas phase in which measurements are taken to determine the monomer concentration in the reactor in volume percent (% / vol)

[0102] Example 5 to Example 8 Preparation of ethylene-propylene copolymers useful as viscosity index improver (VII) additives The ethylene-propylene copolymers obtained in Examples 1 to 4 were subjected to a thermolysis process operating as reported below.

[0103] For this purpose, the ethylene-propylene copolymer was fed at a rate of 500 kg / h to a single-screw extruder (BUSS MDK 140 manufactured by Aaron Equipment) with a reciprocating screw having a diameter of 140 mm and a length (L) to diameter (D) ratio (L / D) of 11, equipped with three conveying and mixing zones, a gear pump, and an underwater die face cutter. The extruder was operated under the following conditions: - Screw rotation speed: 280 rpm; - Temperature profile 1st zone: 180℃~240℃; - Temperature profile 2nd zone: 250℃~300℃; - Temperature profile 3rd zone: 190℃~300℃; - Gear pump temperature: 190℃~300℃

[0104] Upon discharge from the underwater die face cutter (cutting speed is 2700 rpm), the cracked and cooled ethylene-propylene copolymer was recovered in the form of pellets, centrifuged to separate it from the water, and then sent to the drying and packaging section by pneumatic conveying.

[0105] The resulting degraded ethylene-propylene copolymer was subjected to the characterization reported above and the results obtained are reported in Table 7. [Table 8] (1) : ethylene-propylene copolymer of Example 1 (comparative example); (2): ethylene-propylene copolymer of Example 2 (invention); (3) : ethylene-propylene copolymer of Example 3 (invention); (4) : Ethylene-propylene copolymer of Example 4 (comparative example)

[0106] From the data reported in Table 7, it can be seen that only ethylene-propylene copolymers (EPR) characterized according to the invention provide desirable results when used as viscosity index improver (VII) additives, particularly with respect to shear stability index (SSI), thickening power (TP), gel index (GI), initial gel temperature, and form stability.

Claims

1. 1. A viscosity index improving (VII) additive for lubricating oils comprising an ethylene-propylene copolymer, the additive having the following characteristics: a shear stability index (SSI), measured in Group I base oils according to the ASTM D7109-12 standard (30 shear cycles), of between 18% and 30%, preferably between 20% and 28%; - a thickening power (TP) measured in accordance with ASTM D7042-04 standard in Group I base oils of between 3 cSt and 8 cSt, preferably between 4 cSt and 7.5 cSt; a gelation index, defined by the ratio: (or ０℃ / or ４０℃ ) / (or ６０℃ / or ４０℃ ) where η represents the steady-state kinematic viscosity measured in a Group III base oil; - an initial gelling temperature measured in a Group III base oil of less than or equal to 10°C, preferably between 0°C and 10°C; a shape stability, defined according to the following formula, of less than or equal to 5%, preferably less than or equal to 4%, more preferably less than or equal to 3%; ΔL%=[(L / L0)-1)]*100 where L is the length after 24 hours and L is the initial length of 10 cm. A viscosity index improving (VII) additive having

2. The ethylene-propylene copolymer has the following characteristics: from 61% to 67% by weight, preferably from 62% to 66% by weight, of ethylene relative to the total weight of the ethylene-propylene copolymer; - from 33% to 39% by weight, preferably from 34% to 38% by weight, of propylene relative to the total weight of the ethylene-propylene copolymer; a weight average molecular weight (M) of 60,000 Da to 120,000 Da, preferably 65,000 Da to 100,000 Da; ｗ ); - a polydispersity index (PDI), i.e. a weight average molecular weight (M ｗ ) and number average molecular weight (M ｎ ) and the ratio (M ｗ / M ｎ ); a crystallization peak temperature of less than or equal to 20°C, preferably between 0°C and 15°C, as determined by differential scanning calorimetry (DSC); a melting peak temperature of less than or equal to 35°C, preferably between 0°C and 30°C, as determined by differential scanning calorimetry (DSC); - an enthalpy of fusion (ΔH) greater than or equal to 25 J / g, preferably between 28 J / g and 40 J / g, as determined by differential scanning calorimetry (DSC); a minimum number of propylene inversions, determined by NMR analysis, of between 0.1 and 0.25, preferably between 0.12 and 0.22; 10. The viscosity index improving (V.I.I.) additive for lubricating oils of claim 1, having:

3. 1. A continuous process for reducing the molecular weight of an ethylene-propylene copolymer, comprising the steps of: (a) providing at least one single screw extruder comprising a chamber, a reciprocating single screw mounted within said chamber, wherein said reciprocating single screw is capable of rotating and oscillating within said chamber, said chamber having at least one feed opening and at least one discharge opening, said extruder comprising three conveying and mixing zones, a gear pump, and an underwater die face cutter; (b) feeding at least one ethylene-propylene copolymer into said single screw extruder; (c) conveying the at least one ethylene-propylene copolymer through a first conveying and mixing zone operating at a temperature of from 140°C to 260°C, preferably from 150°C to 250°C, wherein the ethylene-propylene copolymer is uniformly mixed, heated, and uniformly softened; (d) conveying the at least one uniformly softened ethylene-propylene copolymer exiting the first conveying and mixing zone to a second conveying and mixing zone operating at a temperature of from 220°C to 330°C, preferably from 230°C to 320°C, where the ethylene-propylene copolymer is further mixed, heated and partially cracked; (e) conveying the at least one partially cracked ethylene-propylene copolymer exiting the second conveying and mixing zone to a third conveying and mixing zone operating at a temperature of from 170°C to 340°C, preferably from 180°C to 330°C, where the ethylene-propylene copolymer is further mixed, heated and further cracked; (f) conveying the at least one further cracked ethylene-propylene copolymer exiting the third conveying and mixing zone to the gear pump operating at a temperature of from 170°C to 340°C, preferably from 180°C to 330°C, wherein the ethylene-propylene copolymer is further cracked; (g) recovering said at least one further cracked ethylene-propylene copolymer exiting said underwater die face cutter; A continuous process comprising:

4. 4. A continuous process for reducing the molecular weight of ethylene-propylene copolymers according to claim 3, wherein the single screw extruder operates at a screw rotation speed of from 220 rpm to 300 rpm, preferably from 230 rpm to 290 rpm.

5. 5. A continuous process for reducing the molecular weight of ethylene-propylene copolymers according to claim 3 or claim 4, wherein the single screw extruder operates at a flow rate of from 300 kg / h to 700 kg / h, preferably from 400 kg / h to 600 kg / h.

6. In step (b) of the process, the at least one ethylene-propylene copolymer has the following characteristics: from 61% to 67% by weight, preferably from 62% to 66% by weight, of ethylene relative to the total weight of the ethylene-propylene copolymer; - from 33% to 39% by weight, preferably from 34% to 38% by weight, of propylene relative to the total weight of the ethylene-propylene copolymer; a weight average molecular weight (M) of 120,000 Da to 200,000 Da, preferably 140,000 Da to 170,000 Da; ｗ ); - a polydispersity index (PDI), i.e. a weight average molecular weight (M ｗ ) and number average molecular weight (M ｎ ) and the ratio (M ｗ / M ｎ ); a crystallization peak temperature of less than or equal to 20°C, preferably between 0°C and 15°C, as determined by differential scanning calorimetry (DSC); a melting peak temperature of less than or equal to 35°C, preferably between 0°C and 30°C, as determined by differential scanning calorimetry (DSC); - an enthalpy of fusion (ΔH) greater than or equal to 25 J / g, preferably between 28 J / g and 40 J / g, as determined by differential scanning calorimetry (DSC); a minimum number of propylene inversions, determined by NMR analysis, of between 0.1 and 0.25, preferably between 0.12 and 0.22; A continuous process for reducing the molecular weight of the ethylene-propylene copolymer of any one of claims 3 to 5, comprising:

7. - 1 to 30% by weight, preferably 2 to 20% by weight, of a viscosity index improver (VII) additive for lubricating oils according to claim 1 or claim 2, relative to the total weight of the lubricating oil composition; base oils of mineral or synthetic origin or mixtures thereof, wherein the base oils of mineral or synthetic origin are preferably chosen from base oils belonging to Group I or Group II or Group III; A lubricating oil composition comprising:

8. 3. Use of a viscosity index improver (V.I.I.) additive for lubricating oils according to claim 1 or claim 2 in a base oil of mineral or synthetic origin or a mixture thereof, wherein the base oil of mineral or synthetic origin is preferably selected from base oils belonging to Group I or Group II or Group III.

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