Glass fiber reinforced pellets, production method thereof and reinforced article obtained therefrom

Abstract

The invention relates to glass fiber reinforced pellets, production method thereof and reinforced article obtained therefrom. The pellet having an axial direction; said pellet comprising a core that extends in the axial direction and comprising a polymer sheath which has been applied around said core, wherein said core comprises a plurality of glass filaments that extends in the axial direction; said polymer sheath is at least substantially free of said filaments; said polymer sheath comprises or consists of at least one aliphatic polyamide.

Description

[0001] Glass fiber reinforced pellets, production method thereof and reinforced article obtained therefrom

[0002] The invention relates to glass fiber reinforced pellets, production method thereof and reinforced article obtained therefrom.

[0003] Introduced more than half a century ago, fiber-reinforced plastics are composite materials with a wide range of applications in industry, for example in the aerospace, automotive, chipping, building and construction industries. A reinforced article can comprise any combination of individual materials, for example, a thermoplastic polymer (the matrix) in which fibers (reinforcing fiber) have been dispersed. A great diversity of organic fibers, including synthetic fibers such as polyamide, polytetrafluoroethylene, polyesters, natural fibers such as cotton, hemp, flax, jute and inorganic fibers, such as glass fibers and carbon fibers are often used as reinforcing fibers in composite materials.

[0004] The reinforced plastics industry has been using glass fibers in different forms for reinforcing polymer matrices to produce a diversity of products. Glass fibers are generally supplied as a plurality of continuous, very long filaments, and can be in the form of strands or bundles, rovings or yarns. A filament is an individual fiber of reinforcing material. A bundle is a plurality of bundled filaments. Yarns are collections of filaments or bundles twisted together. A roving refers to a collection of bundles / strands wound into a package.

[0005] A process for producing reinforced compositions is for example described in W02009 / 080281. In this publication, a process is described for producing a long glass fiber- reinforced thermoplastic polymer composition, which comprises the subsequent steps of: a. Unwinding from a package of at least one continuous glass multifilament strand containing a sizing composition; b. Applying an impregnating agent to said at least one continuous glass multifilament strand to form an impregnated continuous multifilament strand; c. Applying a sheath of thermoplastic polymer around the impregnated continuous multifilament strand to form a sheathed continuous multifilament strand; and d. Cutting the sheathed continuous glass multifilament strand into pellets. In conventional processes for producing pellets, the thermoplastic polymer around the core is usually comprised of polypropylene and a coupling agent is normally needed.

[0006] There remains a need in the art to provide pellets with improved mechanical properties.

[0007] It is an object of the invention to provide glass fiber reinforced pellets with improved mechanical properties in at least one of tensile strength, flexural strength and impact strength. It is also an object of the present invention to provide a reinforced article with improved mechanical properties in at least one of tensile strength, flexural strength and impact strength.

[0008] Summary

[0009] In a first aspect, the present invention relates to a pellet having an axial direction; said pellet comprising a core that extends in the axial direction and comprising a polymer sheath which has been applied around said core, wherein said core comprises a plurality of filaments, preferably glass filaments, that extends in the axial direction; wherein said polymer sheath is at least substantially free of said (glass) filaments and wherein said polymer sheath comprises or consists of at least one aliphatic polyamide.

[0010] In a second aspect, the present invention relates to a solid object obtained from molding a plurality of said pellets according to the invention.

[0011] In a third aspect, the present invention relates to a method of preparing a pellet comprising the steps of: i) Unwinding from a package of a plurality of continuous (glass) filaments; ii) Optionally applying an impregnating composition to said plurality of (glass) filaments to form an impregnated plurality of (glass) filaments; iii) Applying a sheath of polymer around the plurality of (glass) filaments to form a sheathed bundle comprising a core comprising said plurality of (glass) filaments and comprising a sheath surrounding said core, and iv) Cutting the sheathed bundle into individual pellets comprising a core that extends in the axial direction and comprising a polymer sheath which has been applied around said core, wherein said polymer sheath is at least substantially free of said (glass) filaments and said polymer sheath comprises or consists of at least one aliphatic polyamide.

[0012] Definitions

[0013] In the present description, composite means comprising at least two individual materials. The pellet according to the present invention may be regarded as being a composite pellet. In the present description, pellet means a rounded or tube-like solid object, such as a compressed mass of a substance.

[0014] In the present description, filament means a thin thread or thread-like object or fiber.

[0015] In the present description, glass fiber filament means a filament made of glass fiber.

[0016] In the present description, multifilament means a plurality of filaments, e.g. in the form of a strand or bundle.

[0017] In the present description, bundle means a plurality of filaments that is held together or wrapper up together.

[0018] In the context of the present invention, the term "mass" and "weight" are used interchangeably. The term “mass%” has the same meaning as the term “weight%” or simply “wt%”.

[0019] In the context of the present invention, an amount / content of a specific component in a percentage (“%”) is on weight basis, unless clearly specified otherwise.

[0020] In the context of the present invention, the term “degree Celsius” or “°C” is sometimes simplified as “C”. For example, “190C” means “190°C”, as is known to a skilled person in the field.

[0021] In the context of the present invention, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0022] In the context of the present invention, the term “comprise” or “include” also includes the meanings of “comprised of”, “essentially comprised of’, “consist of” or “essentially consist of”.

[0023] In the context of the present invention, any numerical values describing a same aspect / feature of the present invention throughout the disclosure can be combined together to form a new range. For example, when it is described in the context that an amount of a certain component is at least 1wt%, preferably at least 2wt%, and at most 5%, preferably at most 4wt%, being in one example specifically 3wt%, then the amount ranges of 1-2wt%, 2- 3wt%, 3-4wt%, 4-5wt%, 1-5wt%, 2-4wt% etc, are all inherently disclosed, as if they were explicitly described in the present invention. For example, when it is described in the context that an amount of a certain component is in the range of 1-5wt%, preferably 2-4wt%, being in one example specifically 3wt%, then the amount ranges of 1-2wt%, 2-3wt%, 3-4wt%, 4- 5wt%, etc, are all inherently disclosed, as if they were explicitly described in the present invention.

[0024] Detailed description of the invention

[0025] Pellets

[0026] As discussed above, in a first aspect, the present invention relates to a pellet having an axial direction; said pellet comprising a core that extends in the axial direction and comprising a polymer sheath which has been applied around said core, wherein: * said core comprises a plurality of (glass) filaments that extends in the axial direction; * said polymer sheath is at least substantially free of said filaments; * said polymer sheath comprises or consists of at least one aliphatic polyamide. In other words, it relates to a pellet comprising a glass filament core surrounded by a polymer sheath comprising or consisting of at least one aliphatic polyamide. This pellet may be used to prepare reinforced articles.

[0027] In an embodiment, said polymer sheath comprises at least 90wt%, preferably at least 95wt%, and more preferably at least 98wt% of the at least one aliphatic polyamide, based on the weight of the polymer sheath.

[0028] In an embodiment, said polymer sheath consists of at least one aliphatic polyamide.

[0029] In an embodiment, the aliphatic polyamide is PA6, and the polymer sheath comprises at least 90wt% of PA6 based on the weight of the polymer sheath, preferably at least 95wt%, more preferably at least 98wt%, such as 99wt% or 100wt%.

[0030] In an embodiment, the aliphatic polyamide is PA6 with a viscosity number tested according to ISO307 in the range of 90-160 ml / g, preferably in the range of 110-130 ml / g, more preferably about 120ml / g.

[0031] In an embodiment, the polymer sheath does not comprise PA46 and / or PA66.

[0032] In an embodiment, the pellet comprises 10-50wt% of the core and 50-90wt% of the sheath. In an embodiment, the pellet comprises 15-45wt% of the core, such as 20, 30 or 40 wt%. In an embodiment, the pellet comprises 55-85wt% of the sheath, such as 60, 70 or 80 wt%.

[0033] In an embodiment, a sum of the amounts of the core and the sheath is at least 90wt% of the total weight of the pellet, preferably at least 95wt%, more preferably at least 97wt%.

[0034] Throughout the disclosure, a weight percentage of a pellet is described with respect to a single pellet, or equally to a numerical average of a plurality of pellets.

[0035] In an embodiment, the pellet does not comprise a coupling agent. In an embodiment, the pellet does not comprise an impregnating agent.

[0036] The pellet used in the present invention has a generally cylindrical shape having an axial length, i.e. the length in the direction perpendicular to the cross section of the cylinder. The core of the pellet has a generally cylindrical shape and comprises a multifilament (bundle) made of (glass) fibers optionally impregnated with an impregnating agent. The fibers have a length substantially equal to the axial length of the pellet. The core of the pellet is surrounded around its circumference by a sheath having a generally tubular shape consisting of a thermoplastic polymer.

[0037] For the avoidance of doubt, it should be understood that the pellet has a core sheath structure wherein the core comprises the optional impregnating agent and the glass multifilament. The sheath consists of the thermoplastic polymer and surrounds the core. The core (glass filament) does not substantially contains the material of the sheath. And the sheath is substantially free of filaments. Such a pellet structure is obtainable by a wirecoating process such as for example disclosed in WO 2009 / 080281 and is distinct from the pellet structure that is obtained via the typical pultrusion type of processes such as disclosed in US 6,291 ,064.

[0038] In an embodiment of the first aspect, said plurality of filaments is a continuous, multifilament glass. In an embodiment of the first aspect, said plurality of filaments preferably comprise from 2000 to 5000 filaments. In an embodiment of the first aspect, said filaments preferably each individually having a diameter from 5 to 50 microns, more preferably from 10 to 30 microns and most preferably from 15 to 25 microns. Preferably, said filaments each have substantially the same diameter, e.g. where at least 90 % of all filaments forming said multifilament have a diameter that is within a range +10% and -10% from an average diameter. In an embodiment of the first aspect, said filaments preferably having an average diameter (mathematical average of all filaments) from 5 to 50 microns, more preferably from 10 to 30 microns and most preferably from 15 to 25 microns.

[0039] In an embodiment of the first aspect, said polymer sheath is free from a polyolefin material, which is preferably a polypropylene, more preferably a polypropylene homopolymer or a polypropylene copolymer. In an embodiment of the first aspect, the exposed ratio (the number of filaments that is (visually) observed at the cutting edge of the pellet divided by the total number of filaments times 100 %) is at least 95%.

[0040] In an embodiment of the first aspect, the polymer sheath comprises less than 5 wt.% of filament, preferably less than 2 wt.% of filament based on the total weight of the polymer sheath. This is meant with substantially free of filament.

[0041] In an embodiment of the first aspect, the core comprises between 35 and 60% of the cross section area of the pellet and wherein the sheath comprises between 40 and 65% of the cross section area of the pellet. In order to determine this the cross section area of the pellet is determined and separately the cross section area of the filament core is determined. The difference between the two values is the cross section area of the polymer sheath.

[0042] Preferably, the longitudinal variation in the radius of the core over the length of the pellet in view of the average radius is between - 5% and + 5 %. Preferably, the variation in the radius of the core from one individual pellet to another individual pellet in view of the average radius is between - 5% and + 5 %. When in the description radius of the core is disclosed, average radius over the length as well as the average radius over several individual pellets is meant unless specified otherwise.

[0043] Preferably, the longitudinal variation in the diameter of the pellet over the length of the pellet in view of the average diameter is between - 5% and + 5 %. Preferably, the variation in the diameter of the core from one individual pellet to another individual pellet in view of the average diameter is between - 5% and + 5 %. When in the description diameter of the pellet is disclosed, average diameter over the length as well as the average diameter over several individual pellets is meant unless specified otherwise. Without wishing to be bound to any particular theory, the present inventors assume that due to the cutting step in the production of said pellets, the diameter and shape of one or both ends of said pellet may show a variation with respect to the center of said pellet.

[0044] In an embodiment of the first aspect, the radius of the core is between 800 and 4000 micrometer. In an embodiment, the thickness of the sheath is between 500 and 1500 micrometer It should be noted that when during the manufacturing process to prepare the inventive pellets maximally 2 % of all pellets formed have an incompletely closed polymer sheath leading to pellets that have exposed filaments over the axial length - this is called the Zebra effect. There is no need to separate these Zebra-pellets from the pellets with completely closed polymer sheaths even though these Zebra-pellets are not pellets according to the present invention.

[0045] In an embodiment, the pellet has a tensile modulus tested according to ISO 527-2(1A) (2012) at 23°C in the range of 6000-15000 MPa, preferably in the range of 6500-13500MPa, more preferably in the range of 6600-12000MPa.

[0046] In an embodiment, the pellet has a tensile stress at break tested according to ISO 527-2(1 A) (2012) at 23°C in the range of 100-250MPa, preferably in the range of 115-235 MPa, more preferably in the range of 120-220MPa.

[0047] In an embodiment, the pellet has a tensile modulus tested according to ISO 527-2(1A) (2012) at 80°C in the range of 3000-7500 MPa, preferably in the range of 3450-7000MPa, more preferably in the range of 3500-6500MPa.

[0048] In an embodiment, the pellet has a tensile stress at break tested according to ISO 527-2(1 A) (2012) at 80°C in the range of 70-150MPa, preferably in the range of 80-130MPa, more preferably in the range of 85-120MPa.

[0049] In an embodiment, the pellet has a flexural modulus tested according to ISO 178 (II) at 23°C in the range of 5000-13000 MPa, preferably in the range of 5900-12000MPa, more preferably in the range of 6400-11000M Pa.

[0050] In an embodiment, the pellet has a flexural stress tested according to ISO 178 (II) at 23°C in the range of 180-400MPa, preferably in the range of 200-380MPa, more preferably in the range of 210-360MPa.

[0051] In an embodiment, the pellet has a flexural modulus tested according to ISO 178 (II) at 80°C in the range of 3000-7000 MPa, preferably in the range of 3100-6500MPa, more preferably in the range of 3200-6000MPa.

[0052] In an embodiment, the pellet has a flexural stress tested according to ISO 178 (II) at 80°C in the range of 100-300MPa, preferably in the range of 120-220MPa, more preferably in the range of 130-200MPa. In an embodiment, the pellet has a Charpy notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 10-50 KJ / m2, preferably in the range of 15-40 KJ / m2, more preferably in the range of 16-29 KJ / m2.

[0053] In an embodiment, the pellet has a Charpy notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 10-40 KJ / m2, preferably in the range of 15-35 KJ / m2, more preferably in the range of 15.1-28 KJ / m2.

[0054] In an embodiment, the pellet has a Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 30-110 KJ / m2, preferably in the range of 40-105 KJ / m2, more preferably in the range of 42-100 KJ / m2.

[0055] In an embodiment, the pellet has a Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 20-110 KJ / m2, preferably in the range of 30-100 KJ / m2, more preferably in the range of 35-90 KJ / m2.

[0056] Filaments

[0057] Multifilament bundles (preferably glass multifilament bundles) and their preparation are known in the art. The fibers, preferably glass fibers, in the bundles may have been formed by any method known to those skilled in the art. Particularly, the fibers may have been formed by a melt spinning process. The length of the fibers in the bundle is determined by the length of the pellet and may vary in a wide range. For example, the average length of the filaments in the pellet may vary between 10 to 50 mm, preferably between 10-25 mm, more preferably between 10-20 mm. The average length of the filaments in the object formed from the pellets is less than the average length of the filaments in the pellet due to breakage of the filaments because of mechanical forces during production of said objects.

[0058] The fiber density of the fibers in the bundle may vary within wide limits. Preferably, the bundle may have from 500 to 10000 fibers / bundle and more preferably from 2000 to 5000 fibers / bundle. The diameter of the fibers in the bundle may widely vary. Preferably, the diameter of the fibers in the bundle ranges from 5 to 50 microns, more preferably from 10 to 30 microns and most preferably from 15 to 25 microns. Fiber diameters outside these ranges tend to result in a decrease of mechanical properties and / or enhanced abrasion of the equipment used. The diameter of the multifilament bundle in the pellet may e.g. be between 1 and 7 mm. The multifilament bundle may comprise a sizing composition. Suitable examples of conventional sizing compositions include solvent-based compositions, such as an organic material dissolved in aqueous solutions or dispersed in water and melt- or radiation curebased compositions. More particularly, an aqueous sizing composition is applied on the individual fibers, but also oil-based sizing compositions can be applied. As already described in the art, e.g. in documents EP1460166A1 , EP0206189A1 or US4338233, an aqueous sizing composition typically includes film formers, coupling agents and other additional components. The film formers are generally present in effective amount to protect fibers from inter-filament abrasion and to provide integrity and processability for fiber bundles after they are dried. Suitable examples of film formers generally include polyurethanes, polyesters, such as polycaprolactone, polyolefins, such as polypropylene, polyamides. It is already recognized in the art that the film former should be miscible with the polymer to be reinforced. For example, polycaprolactone may be used as film former when nylon is used as polymer to be reinforced; for reinforcing polypropylenes, suitable film formers generally comprise polyolefin waxes.

[0059] In an embodiment of the present invention, the core of the pellet, or the multifilament bundle, does not comprise polyolefin waxes.

[0060] In the case when the matrix thermoplastic polymer comprises or consists of polyolefin, in particular, polypropylene, Coupling agents (in the sizing composition) are conventionally used to improve the adhesion between the matrix thermoplastic polymer and the fiber reinforcements. Suitable examples of coupling agents known in the art as being used for the fibers include organofunctional silanes. More particularly, the coupling agent which has been added to the sizing composition is an aminosilane, such as aminomethyl-trimethoxysilane, N-(beta-aminoethyl)-gamma-aminopropyl-trimethoxysilane, gamma-aminopropyl- trimethoxysilane gamma-methylaminopropyl-trimethoxysilane, delta-aminobutyl- triethoxysilane, 1 ,4-aminophenyl-trimethoxysilane.

[0061] For the purpose of clarity, the pellet of the present application, in particular the filaments of the present application, does not comprise a coupling agent.

[0062] Any other additional components known to the skilled person may be present in the sizing composition. Suitable examples include lubricants, used to prevent damage to the bundles by abrasion, antistatic agents, crosslinking agents, plasticizers, surfactants, nucleation agents, antioxidants, pigments and any combinations thereof. Applying a sizing composition to the formed filaments is well-known in the art.

[0063] Typically, after applying the sizing composition on the fibers, the fibers are bundled into bundle and then wound on bobbins to form a package. A multifilament bundle which contains at most 2 wt.% of a sizing composition based on the total weight of the fibers in the multifilament bundle is preferably employed in the pellets of the invention. The amount of the sizing composition can be determined by loss on ignition (LOI). The LOI is a well-known technique for determining the amount of sizing on fibers. More preferably, a multifilament bundle containing from 0.1 to 1 wt.% of sizing composition, as determined by loss on ignition (LOI) is used.

[0064] Preferably, bundle(s) comprising (glass) fibers on which a sizing composition has been applied as aqueous dispersion are employed in the pellet according to the invention. Sizing is usually a solvent based material that is applied on the surface of the fibers to improve production process of fibers; preferably more than 90% of the sizing composition is solvent which will be removed during a drying process.

[0065] An impregnating agent is usually low molecular weight material that acts mainly as a lubricant and remains in the product during whole process. The impregnating agent that may be used in the process according to the present invention comprises at least one compound that is compatible with the thermoplastic polymer. The impregnating agent enables the enhanced dispersion of the fibers in the thermoplastic polymer matrix during the molding process.

[0066] The application temperature is chosen such that the desired viscosity range is obtained. For example, when the matrix is polyamide, the application temperature of the impregnating agent can be from 225-290°C.

[0067] The amount of impregnating agent applied to the multifilament bundle comprising fibers depends on the thermoplastic matrix, on the size (diameter) and concentration of the fibers forming the bundle, and on type of sizing that is on the surface of the fibers. The pellet according to the invention may comprise 0-10% wt.% impregnating agent based on the weight of the fibers in the multifilament bundle in the pellet.

[0068] Suitable examples of impregnating agents include low molar mass compounds, for example low molar mass or oligomeric polyurethanes, polyesters such as unsaturated polyesters, polycaprolactones, polyethyleneterephthalate, poly(alpha-olefins), such as branched polyethylenes and polypropylenes, polyamides, such as nylons, and other hydrocarbon resins. As a general rule, a polar thermoplastic polymer matrix requires the use of an impregnating agent containing polar functional groups; a non-polar polymer matrix involves using an impregnating agent having non-polar character, respectively. For example, for reinforcing a polyamide or polyester, the impregnating agent may comprise low molecular weight polyurethanes or polyesters, like a polycaprolactone. For reinforcing polypropylenes, the impregnating agent may comprise branched poly(alpha-olefins), such as polyethylene waxes, modified low molecular weight polypropylenes, mineral oils, such as, paraffin or silicon and any mixtures of these compounds.

[0069] The impregnating agent is non-volatile, and substantially solvent-free. Being non-volatile means that the impregnating agent does not evaporate under the application and processing conditions applied; that is it has a boiling point or range higher than said processing temperatures. In the context of present application, "substantially solvent-free" means that impregnating agent contains less than 10 percent by mass of solvent, preferably less than 5 percent by mass solvent. Most preferably, the impregnating agent does not contain any organic solvent.

[0070] Polymer sheath

[0071] The polymer sheath is made of a thermoplastic polymer. In the context of the present invention, the thermoplastic polymer comprises or consists of at least one aliphatic polyamide. In an embodiment, the polymer sheath comprises at least 90wt%, preferably at least 95wt%, and more preferably at least 98wt%, of the at least one aliphatic polyamide. In an embodiment, the polymer sheath consists of the at least one aliphatic polyamide.

[0072] Polyamide (PA) is a polymer containing recurring amide groups (R — CO — NH — R’) as integral parts of the main polymer chain. According to composition of their main chain, polyamides are classified as aliphatic, semi-aromatic and aromatic. Examples of Aliphatic type polyamides are PA6(Nylon 6) and PA 66(Nylon 6,6).

[0073] Polyamides can be synthesized by two main methods, a) polycondensation of diacid and diamind and b) ring opening polymerization of lactams. Aliphatic Polyamides can be synthesized by condensation of bifunctional monomers. Polyamide 6 can be synthesized by ring-opening anionic polymerization of epsilon-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam-functionalized silica as an initiator.

[0074] In the context of the present invention, the aliphatic polyamide is preferably PA6. In an embodiment, the polymer sheath is comprised of PA6. In an embodiment, the polymer sheath does not comprise other aliphatic polyamides, such as PA46 and PA66.

[0075] The sheath may further contain one or more common additives, for example stabilizers, processing aids, impact-modifiers, flame-retardants, acid scavengers, inorganic fillers, and colorants.

[0076] Method for production

[0077] The pellets of the present invention can be produced by a wire-coating process such as for example disclosed in WO 2009 / 080281.

[0078] In particular, a method for producing pellets of the present invention comprises the following steps: i) Unwinding from a package of a plurality of continuous glass fiber filaments; iii) Applying a polymer sheath around the plurality of filaments to form a sheathed bundle comprising a core comprising said plurality of filaments and a sheath intimately surrounding said core, and iv) Cutting the sheathed bundle into individual pellets.

[0079] In the method of the present invention, said polymer sheath is substantially free of said filaments; and said polymer sheath comprises or consists of at least one aliphatic polyamide.

[0080] The process of the present invention may comprise a step of ii) applying an impregnating agent to said plurality of filaments to form an impregnated plurality of filaments. Reinforcing article

[0081] The pellets according to the present invention may be used to prepare a reinforcing article. A reinforcing article is prepared using a molding composition. Said molding composition can be provided by the pellets according to the invention alone or may e.g. be obtained by mixing the pellets and one or more (non-reinforcing) fillers as separate components.

[0082] Molding is performed at an elevated temperature, which is a temperature at which the molding composition has enough flowability to be molded (i.e. the polymers in the composition are melted). The elevated temperature is above the melting point of the thermoplastic polymer that is present in the sheath of the pellets. The elevated temperature may be suitably chosen by the skilled person. Generally, the elevated temperature may e.g. be 150-500 °C, 180-400 °C or 200-300 °C. In the cases where the thermoplastic polymer in the pellet is PA6, the elevated temperature is preferably 220-300 °C.

[0083] Suitable examples of molding processes include injection molding, compression molding, extrusion and extrusion compression molding. Injection molding is widely used to produce articles such as automotive exterior parts like bumpers, automotive interior parts like instrument panels, or automotive parts under the bonnet. Extrusion is widely used to produce articles such rods, sheets and pipes. Preferably, the molding involves injection molding in the process according to the invention. With the process according to the invention, reinforced articles are made. Preferably, the article is an automotive part. The reinforced article according to the present invention may for example be a tailgate.

[0084] In an embodiment, the reinforced article has a tensile modulus tested according to ISO 527- 2(1A) (2012) at 23°C in the range of 6000-15000 MPa, preferably in the range of 6500- 13500MPa, more preferably in the range of 6600-12000MPa.

[0085] In an embodiment, the reinforced article has a tensile stress at break tested according to ISO 527-2(1A) (2012) at 23°C in the range of 100-250MPa, preferably in the range of 115- 235 MPa, more preferably in the range of 120-220MPa.

[0086] In an embodiment, the reinforced article has a tensile modulus tested according to ISO 527- 2(1A) (2012) at 80°C in the range of 3000-7500 MPa, preferably in the range of 3450- 7000MPa, more preferably in the range of 3500-6500MPa. In an embodiment, the reinforced article has a tensile stress at break tested according to ISO 527-2(1A) (2012) at 80°C in the range of 70-150MPa, preferably in the range of 80- 130MPa, more preferably in the range of 85-120MPa.

[0087] In an embodiment, the reinforced article has a flexural modulus tested according to ISO 178 (II) at 23°C in the range of 5000-13000 MPa, preferably in the range of 5900-12000MPa, more preferably in the range of 6400-11000MPa.

[0088] In an embodiment, the reinforced article has a flexural stress tested according to ISO 178 (II) at 23°C in the range of 180-400MPa, preferably in the range of 200-380MPa, more preferably in the range of 210-360MPa.

[0089] In an embodiment, the reinforced article has a flexural modulus tested according to ISO 178 (II) at 80°C in the range of 3000-7000 MPa, preferably in the range of 3100-6500MPa, more preferably in the range of 3200-6000MPa..

[0090] In an embodiment, the reinforced article has a flexural stress tested according to ISO 178 (II) at 80°C in the range of 100-300MPa, preferably in the range of 120-220MPa, more preferably in the range of 130-200MPa.

[0091] In an embodiment, the reinforced article has a Charpy notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 10-50 KJ / m2, preferably in the range of 15-40 KJ / m2, more preferably in the range of 16-29 KJ / m2.

[0092] In an embodiment, the reinforced article has a Charpy notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 10-40 KJ / m2, preferably in the range of 15-35 KJ / m2, more preferably in the range of 15.1-28 KJ / m2.

[0093] In an embodiment, the reinforced article has a Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 30-110 KJ / m2, preferably in the range of 40-105 KJ / m2, more preferably in the range of 42-100 KJ / m2.

[0094] In an embodiment, the reinforced article has a Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 20-110 KJ / m2, preferably in the range of 30-100 KJ / m2, more preferably in the range of 35-90 KJ / m2.

[0095] It is further noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It is also to be understood that a description on a product comprising certain components also discloses a product consisting of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The invention will now be elucidated by way of the following examples without however being limited thereto.

[0096] EXAMPLES

[0097] The following materials were used to produce glass fiber reinforced pellets according to the method disclosed in W02009 / 080281 . The method, also referred to as wire-coating process, mainly comprises a step of applying a sheath of thermoplastic polymer around a multifilament strand. The barrel temperature set was 270°C.

[0098] Materials:

[0099] PA6_1: Ultramid® B24 NE 01 is a polyamide 6 commercially available from BASF with a viscosity number tested according to ISO 307 in the range of 115-135 ml / g.

[0100] PA6_2: Ultramid® B27 E 01 is a polyamide 6 commercially available from BASF with a viscosity number tested according to ISO 307 in the range of 142-158 ml / g.

[0101] PP homo: SABIC® PP 595A is a polypropylene homopolymer with an MFR tested according to ISO1133 at 230 °C and 2.16 kg of 47 dg / min.

[0102] Glass fiber 1 : T ufRov™ 4510 is a long glass fiber roving commercially available from Nippon Electric Glass (NEG) with a fiber diameter of 17pm and a roving TEX of 2400 g / km. Glass fiber 1 shows excellent wet out and saturation in polyamide resin.

[0103] Glass fiber_2: ER4305PM-3000 is a long glass fiber roving commercially available from Chongqing Polycomp International Corp (CPIC) with a fiber diameter of 19pm and a roving TEX of 3000 g / km. Glass fiber_2 is suitable for the wire-coating process in which the thermoplastic polymer is a polypropylene.

[0104] Glass fiber_3: ECS13-4.5-508A is a short glass fiber commercially available from JUSHI with a typical fiber diameter of 13 pm and a fiber length of 4.5 mm.

[0105] Antioxidant: B225 is a mixture of Irganox® 1010 (50%) and Irgafos® 168 (50%) from BASF. Impregnating agent: PARAFFLEX® 4843A is a WAX from INTERNATIONAL WAXES INC with Congealing Point at 68°C.

[0106] Coupling agent: Bondyram® 1010 is a maleic anhydride modified polypropylene with a maleic anhydride graft level of 0.6-1%.

[0107] The produced pellets were injection molded at the below condition to prepare samples for testing according to the test methods. Barrel temperature 260°C

[0108] Mould temperature at injection side 90°C

[0109] Mould temperature at closing side 90°C

[0110] Injection pressure 1000 bar.

[0111] Testing methods

[0112] Tensile modulus and tensile strength at break were obtained via tensile test carried out at 23 °C and 80 °C after 7 days according to ISO 527 / 1A (II). The shape of specimen for this test has been defined in the used norm.

[0113] Flexural modulus and flexural stress were obtained via 3-point flexural test carried out according to ISO178 (II) at 23 °C and 80 °C after 7 days. The shape of specimen for this test has been defined in the used norm.

[0114] Notched Charpy impact test was performed according to ISO 179 / 1eA (II) at 23 ° and -30°C after 7 days. The shape of specimen for this test has been defined in the used norm.

[0115] Un-notched Charpy impact test was performed according to ISO 179 / 1eU (II) at 23 ° and - 30°C after 7 days. The shape of specimen for this test has been defined in the used norm. Thermal distortion temperature (HDT) at 1.8MPa was tested according to ISO75-2.

[0116] Both compositions of the pellets and the test results are reported in table 1 below.

[0117] Table 1.

[0118] * The pellet of comparative example 3 is produced by a typical polymer compounding process described as follows: The base resin and additives were premixed together and then dosed into a twin-screw extruder through main feeder. The glass fiber was dosed into the twin-screw extruder through the side feeder at zone 5. The twin-screw extruder used was ZSK26mc with L / D 40 and screw diameter 26mm. Melting temperature was 250°C. Screw speed was 350rpm and output was 20kg / hr. The extruded strips were water cooled and then chopped into pellets. In examples 1-6, the wire-coating process was demonstrated to produce PA6 / Long glass fiber pellets successfully. Process parameters of example 1-4 are reported in table 2. The processability of the process was influenced by the type of PA6 resin (mainly viscosity) and fiber content. It was found that PA6 with lower viscosity was easier for processing with lower head pressure and achieved higher throughput. The pellet quality was also much better with less free glass content.

[0119] Table 2.

[0120] Comparative examples 1 and 2 represent conventional pellets with a polypropylene sheath produced with the wire-coating process using a coupling agent. By comparing them with examples 1-6, it can be seen that, as the sheath polymer consists of PA6 instead of PP, the mechanical properties of the pellets are substantively enhanced, especially with respect to tensile strength, flexural strength, un-notched impact, and HDT. The use of the coupling agent is not needed in examples 1-6, representing a process simplification.

[0121] Table 3 shows the mechanical properties of specimens with different fiber flow directions (0°, 45°, 90°). It can be seen that, mechanical properties of the specimens from pellets of examples 1-4 are integrally higher than those of PP based pellets of comparative example 2. It is also found that strength and modulus decrease significantly and lineally from 0° to 90° in the case of PA6 based pellets, while for PP based pellets, the weakest point is at 45°. Table 3.

Claims

CLAIMS1. A pellet having an axial direction; said pellet comprising a core that extends in the axial direction and comprising a polymer sheath which has been applied around said core, wherein:* said core comprises a plurality of glass filaments that extends in the axial direction;* said polymer sheath is at least substantially free of said filaments;* said polymer sheath comprises or consists of at least one aliphatic polyamide, and wherein the pellet does not comprise a coupling agent, and / or the pellet does not comprise an impregnating agent.

2. The pellet according to claim 1 , wherein said polymer sheath comprises at least 90wt%, preferably at least 95wt%, and more preferably at least 98wt% of the at least one aliphatic polyamide, based on the weight of the polymer sheath; preferably said polymer sheath consists of at least one aliphatic polyamide.

3. The pellet according to any one of the preceding claims, wherein the aliphatic polyamide is PA6, preferably with a viscosity number tested according to ISO307 in the range of 90-160 ml / g, preferably in the range of 110-130 ml / g.

4. The pellet according to any one of the preceding claims, wherein the pellet comprises 10-50wt% of the core and 50-90wt% of the sheath.

5. The pellet according to any one of the preceding claims, wherein the pellet does not comprise a coupling agent, and the pellet does not comprise an impregnating agent.

6. The pellet according to any one of the preceding claims, wherein said core comprises from 2000 to 5000 filaments and / or wherein said filaments having a diameter from 5 to 50 microns, more preferably from 10 to 30 microns and most preferably from 15 to 25 microns.

7. The pellet according to any one of the preceding claims, wherein the radius of the core is between 800 and 4000 micrometer and / or wherein the thickness of the polymer sheath is between 500 and 1500 micrometer.

8. The pellet according to any one of the preceding claims, wherein the core comprises between 35 and 60 % of the cross section area of the pellet and wherein the sheath comprises between 40 and 65 % of the cross section area of the pellet.

9. The pellet according to any one of the preceding claims, wherein the polymer sheath is substantially free of filaments, meaning it comprises less than 5 wt% of said glass filament, preferably less than 2 wt% of filament based on the total weight of the polymer sheath.

10. The pellet according to any one of the preceding claims, having at least one of:• A tensile modulus tested according to ISO 527-2(1A) (2012) at 23°C in the range of 6000-15000 MPa, preferably in the range of 6500-13500MPa;• A tensile stress at break tested according to ISO 527-2(1A) (2012) at 23°C in the range of 100-250MPa, preferably in the range of 115-235 MPa;• A tensile modulus tested according to ISO 527-2(1A) (2012) at 80°C in the range of 3000-7500 MPa, preferably in the range of 3450-7000MPa; and• A tensile stress at break tested according to ISO 527-2(1A) (2012) at 80°C in the range of 70-150MPa, preferably in the range of 80-130MPa.

11. The pellet according to any one of the preceding claims, having at least one of:• A flexural modulus tested according to ISO 178 (II) at 23°C in the range of 5000- 13000 MPa, preferably in the range of 5900-12000M Pa;• A flexural stress tested according to ISO 178 (II) at 23°C in the range of 180-400MPa, preferably in the range of 200-380MPa;• A flexural modulus tested according to ISO 178 (II) at 80°C in the range of 3000- 7000 MPa, preferably in the range of 3100-6500MPa;• A flexural stress tested according to ISO 178 (II) at 80°C in the range of 100-300MPa, preferably in the range of 120-220MPa.

12. The pellet according to any one of the preceding claims, having at least one of:• A Charpy notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 10-50 KJ / m2, preferably in the range of 15-40 KJ / m2;• A Charpy notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 10-40 KJ / m2, preferably in the range of 15-35 KJ / m2;• A Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at 23°C in the range of 30-110 KJ / m2, preferably in the range of 40-105 KJ / m2;• A Charpy un-notched impact strength tested according to ISO179 / 1eA (II) at -30°C in the range of 20-110 KJ / m2, preferably in the range of 30-100 KJ / m2.

13. The pellet according to any one of the preceding claims, wherein the exposed ratio, being the number of filaments that is observed at the cutting edge of the pellet divided by the total number of filaments times 100%, is at least 95%.

14. A reinforced article obtained from molding a plurality of said pellets according to any one of claims 1-13.

15. A method of making a pellet according to any one of claims 1-13 comprising the steps of: i) Unwinding from a package of a plurality of continuous glass filaments; ii) Optionally applying an impregnating composition to said plurality of filaments to form an impregnated plurality of filaments; iii) Applying a sheath of polymer around the optionally impregnated plurality of continuous filaments to form a sheathed bundle comprising a core comprising said plurality of filaments and comprising a sheath surrounding said core, and iv) Cutting the sheathed bundle into individual pellets, wherein:* said polymer sheath is at least substantially free of filaments;* said polymer sheath comprises or consists of at least one aliphatic polyamide.

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