Rotomolding process, and article thereof

Abstract

The present invention relates to a rotomolding process and articles thereof. The rotomolding process uses a micropellet comprising a polymer blend of at least two different polypropylene copolymers, making it possible to use polypropylene for rotomolding applications without the need of micronization, and keeping the desired properties.

Description

ROTOMOLDING PROCESS, AND ARTICLE THEREOFFIELD

[0001] The present technology is generally related to a rotomolding process and articles thereof. The rotomolding process according to the present invention counts on a micropellet comprising a polymer blend of at least two different polypropylene copolymers.BACKGROUND OF THE INVENTION

[0002] Rotomolding, or rotational molding, is an industrial process for the production of plastic parts by shaping and molding thermoplastics at a certain temperature. During the rotomolding process, a thermoplastic material is placed into a mold cavity in an amount sufficient to produce a product having a desired thickness. The mold is then closed, heated, and rotated vertically and horizontally, which results in the thermoplastic softening and forming to the wall of the mold. Examples of thermoplastics that may be used in rotomolding include polyolefins such as polyethylene and polypropylene.

[0003] Rotomolding may be used to produce hollow articles. These articles may range from simple parts to very complex products that may be produced efficiently and with a low manufacturing cost, as compared to other processes such as thermoforming, injection molding, and blow molding. In particular, the types of articles that may be prepared using rotomolding include containers, toys, playground equipment, packaging supplies, medical products, and even very large products, such as silos or high capacities tanks to be used in the agricultural, chemical, and recreational vehicle industries.

[0004] In this regard, document EP 2 328 961 describes a method for additivating polymer resins with antioxidants and anti UV stabilizers. It describes the use of a micropellet, produced by micronization, and it is particularly suitable for resins (preferably, polyethylene) used rotomolding applications, which undergo a micronization step.

[0005] Document EP 2 274 169 relates to the field of multilayer articles having reinforced structural properties prepared by rotational molding wherein the external andinternal skin layers are prepared from polyethylene resin and the intermediate layer is prepared from foamed polyethylene.

[0006] Document EP 1 499 648 describes rotomolded articles having very low warpage and shrinkage and consisting essentially of polyethylene prepared by means of specific catalyst systems.

[0007] As can be seen from the prior art, polyethylene and polyethylene blends have been developed for use in rotomolding processes; however, the use of polypropylene polymers and copolymers for rotomolding application requires a micronization step, which involves the availability of specific equipment and makes the process more complex. Some rotomolded application requires higher temperature resistance than offered by polyethylene. Polypropylene offers this higher temperature resistance, however, it is more difficult to be micronized (current technology requires micronization process at -70°C).

[0008] So, without the micronization procedure, it is not easy to use polypropylene for rotomolding application. In this regard, still exists a need for rotomolding process using polypropylene without the need of micronization and affording improved processability and surface appearance combined with low warpage and good mechanical properties such as impact strength and environmental stress cracking resistance in particular for the production of low thickness articles.SUMMARY

[0009] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0010] In one aspect, the present invention refers to a rotomolding process comprising the steps of: melt blending a micropellet comprising a polymer blend of (a) a first polypropylene copolymer, and (b) a second polypropylene copolymer to form the micropellet blend composition; pulverizing the micropellet melt blend composition; and rotational molding the micropellet melt blend composition; wherein the first polypropylene copolymer is present at a concentration of from 20% by weight to 80% byweight of the micropellet blend composition; and wherein the second polypropylene copolymer is present at a concentration of from 20% by weight to 80% by weight of the micropellet blend composition.

[0011] According to another aspect of the present invention, the micropellet further comprises (c) a polyethylene polymer, and the polyethylene polymer is present at a concentration of at most 30% by weight of the polymer micropellet blend composition.

[0012] According to still another aspect of the present invention, the micropellet has a particle size distribution D(v, 0.99) of 400 - 700 pm, preferably 450 - 600 pm, measured according to ASTM DI 921, and the micropellet is cylindrical- shaped.

[0013] In another aspect, the first propylene copolymer is a random polypropylene copolymer, which is a copolymer of propylene and a C2-C6 alpha-olefin, wherein a concentration of the C2-C6 alpha-olefin is from 1% to 8% by weight. Preferably, the random polypropylene copolymer is a copolymer of propylene and ethylene.

[0014] The random propylene copolymer has a density, measured according to ASTM D792, of from 0.890 g / cm3to 0.910 g / cm3, a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of from 2 g / 10 min to 18 g / 10 min.

[0015] In another aspect, the second polypropylene copolymer is a heterophasic polypropylene copolymer having a matrix phase comprising a polypropylene homopolymer or copolymer and a dispersed phase having an elastomeric component, wherein the concentration of the matrix phase is 90 to 50 wt % and the dispersed phase, 10 to 50 wt %. Preferably, the matrix phase is polypropylene homopolymer, and the elastomeric component is an ethylene-propylene copolymer.

[0016] The ethylene-propylene copolymer contains 5 to 30 wt % ethylene and having an intrinsic viscosity (IV of AM) of 1.5 to 4 dL / g, preferably 2 to 3.5 dL / g measured in decalin at 135° C according to ASTM method D1601-78.

[0017] The heterophasic propylene copolymer has a density, measured according to ASTM D792, of from 0.890 g / cm3to 0.910 g / cm3, a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of from 1 g / 10 min to 20 g / 10 min.

[0018] In another aspect, the polyethylene polymer is a linear low density polyethylene copolymer derived from the polymerization of principally ethylene with a minor amount of one or more copolymerizable monomers of alpha-olefins, preferably C3-C20 alpha-olefins, preferably C3-C8 alpha-olefins, preferably C3-C6 alpha-olefins, preferably a C4 alpha-olefin, preferably 1 -butene. The polyethylene polymer has a density, measured according to ASTM D792, of from 0.918 g / cm3to 0.940 g / cm3, a melt flow index, measured according to ASTM D1238 at 190° C / 2.16 kg, of from 10 g / 10 min to 35 g / 10 min.

[0019] According to a further aspect of the present invention, the first polypropylene copolymer is present at a concentration of from about 30% by weight to about 75% by weight of the micropellet blend composition, and the second polypropylene copolymer is present at a concentration of from about 20% by weight to about 70% by weight of the micropellet blend composition.

[0020] The polyethylene is present at a concentration of from about 0% by weight to about 30% by weight of the polymer blend composition, preferably 0% to 15%; more preferably 0% to 5%.

[0021] According to another aspect, the concentration of the first polypropylene polymer and the second polypropylene copolymer adds up at least 70% by weight of the polymer blend composition, preferably 85%; more preferably 95%.

[0022] Further, the micropellet comprises at least one additive selected from coloring agents, stabilizers, antioxidants, UV absorbers, antistatics, lubricants and fillers, and the micropellet is melt blended with at least one additive selected from coloring agents, stabilizers, antioxidants, UV absorbers, antistatics, lubricants and fillers.

[0023] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.DETAILED DESCRIPTION

[0024] Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with aparticular embodiment is not necessarily limited to that embodiment and may be practiced with any other embodiment(s).

[0025] As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.

[0026] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.

[0027] As used herein, the term “micropellet” refers to the pellet having dimensions and properties suitable for rotomolding application, comprising a specific micro structure and formed by a composition comprising a polymer blend of at least two different types of polypropylene.

[0028] In one aspect, embodiments disclosed herein relate to a rotomolding process comprising melt blending a micropellet comprising a polymer blend of (a) a first polypropylene copolymer, and (b) a second polypropylene copolymer to form the micropellet blend composition; pulverizing the micropellet melt blend composition; and rotational molding the micropellet melt blend composition. According to another aspect of the present invention, the first polypropylene copolymer is present at a concentration of from 20% by weight to 80% by weight of the micropellet blend composition; and thesecond polypropylene copolymer is present at a concentration of from 20% by weight to 80% by weight of the micropellet blend composition.

[0029] According to another aspect of the present invention, the micropellet further comprises a polyethylene polymer, at a concentration of at most 30% by weight of the polymer micropellet blend composition.

[0030] In one or more embodiments, rotomolding processes and methods may be used to prepare articles by means of micropellets formed by a blend of at least two different types of polypropylenes to form a micropellet polymer blend composition having a high melt flow index and a high impact strength, which is then rotationally molded into pre-selected molds to prepare articles of low thickness having excellent surface finishing and resistant to external impact and bending forces.

[0031] In one or more embodiments, micropellet blend compositions may be used in the manufacturing of articles, including low thickness parts having more or less complex angles and portions useful in various vehicles, containers, tanks, and playgrounds.

[0032] First Polypropylene Copolymer

[0033] The first polypropylene copolymer of the micropellet polymer melt blend compositions of the present disclosure may be a random polypropylene copolymer, which is a copolymer of propylene and a C2-C6 alpha-olefin, wherein a concentration of the C2- C<> alpha-olefin is from 1% to 8% by weight of the random polypropylene copolymer. The comonomer content is measured with ASTM D 5576. Preferably, the random polypropylene copolymer is a copolymer of propylene and ethylene.

[0034] Particularly such first polypropylene copolymer has a density, as measured according to ASTM D792, ranging from a lower limit selected from any of about 0.890 g / cm3, about 0.891 g / cm3, and about 0.892 g / cm3to an upper limit selected from any of about 0.908 g / cm3, about 0.909 g / cm3, and about 0.910 g / cm3, where any lower limit may be paired with any upper limit.

[0035] Further, the first polypropylene copolymer has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of at least about 2 g / 10 min, with ranges from this lower limit to any upper limit being contemplated. In some embodiments,the first polypropylene copolymer has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, that may be in a range having a lower limit selected from any of about 2 g / 10 min, about 3 g / 10 min, about 4 g / 10 min, about 5 g / 10 min, to an upper limit selected from any of about 15 g / 10 min, about 16 g / 10 min, about 17 g / 10 min, and about 18 g / 10 min, where any lower limit may be paired with any upper limit. Preferably, the first polypropylene copolymer has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of at least about 6 g / 10 min to about 10 g / 10 min.

[0036] Industrial methods of producing the first polypropylene copolymer are well known in the art and may include reactor blend, gas phase, liquid phase (or solution), and slurry phase polymerization processes, either alone or in combination. Catalysts used in these processes may include Ziegler-Natta catalysts, and / or one or more single-site catalysts, such as metallocenes.

[0037] Second Polypropylene Copolymer

[0038] The second polypropylene copolymer of the micropellet polymer melt blend compositions of the present disclosure may be a heterophasic polypropylene copolymer.

[0039] According to one aspect of the present invention, the heterophasic polypropylene copolymer is a copolymer having a matrix phase comprising a polypropylene homopolymer or copolymer of propylene and a C2-C6 alpha-olefin, and a dispersed phase having an elastomeric component, wherein the concentration of the matrix phase is 90 to 50 wt % and the dispersed phase, 50 to 10 wt %. More preferably, the concentration of the matrix phase is 75 to 65 wt % and the dispersed phase, 25 to 35 wt %.

[0040] In accordance with an embodiment of the present invention, the matrix phase of the heterophasic polypropylene copolymer is a polypropylene homopolymer. The elastomeric component is an ethylene-propylene copolymer rubber (EPR).

[0041] The matrix phase has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, in a range having a lower limit selected from any of about 20.0 g / 10 min, about 25.0 g / 10 min, and about 30.0 g / 10 min to an upper limit selected fromany of about 50.0 g / 10 min, about 55.0 g / 10 min, and about 60.0 g / 10 min, where any lower limit may be paired with any upper limit.

[0042] Further, the ethylene-propylene copolymer contains 5 to 20 wt % ethylene, preferably 10 to 15 wt% and having an intrinsic viscosity (IV of AM) of 1.5 to 4 dL / g, preferably 2 to 3.5 dL / g measured in decalin at 135° C according to ASTM method D1601-78.

[0043] Further, the second polypropylene copolymer has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of at least about 1 g / 10 min, with ranges from this lower limit to any upper limit being contemplated. In some embodiments, the first polypropylene copolymer has a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, that may be in a range having a lower limit selected from any of about 1 g / 10 min, about 2 g / 10 min, about 3 g / 10 min, about 4 g / 10 min, to an upper limit selected from any of about 17 g / 10 min, about 18 g / 10 min, about 19 g / 10 min, and about 20 g / 10 min, where any lower limit may be paired with any upper limit.

[0044] Industrial methods of producing the second polypropylene copolymer are well known in the art and may include reactor blend, gas phase, liquid phase (or solution), and slurry phase polymerization processes, either alone or in combination. Catalysts used in these processes may include Ziegler-Natta catalysts, and / or one or more single-site catalysts, such as metallocenes.

[0045] Polyethylene Polymer

[0046] According to an embodiment of the present invention, the micropellet blend composition further comprises a polyethylene polymer.

[0047] According to the present invention, the polyethylene polymer of the polymer melt blend compositions of the present disclosure may be a linear low density polyethylene copolymer derived from the polymerization of principally ethylene with a minor amount of one or more copolymerizable monomers. Suitable comonomers may include alpha-olefins, preferably C3-C20 alpha-olefins, preferably C3-C8 alpha-olefins, preferably C3-C6 alpha-olefins, preferably a C4 alpha-olefin, preferably 1-butene. In addition, the concentration of comonomer in the polyethylene copolymer may be in a range having a lower limit selected from any of about 4.5%, about 5.0%, about 5.5%, andabout 6.0% by weight of the polyethylene copolymer to an upper limit selected from any of about 9.0%, about 9.5%, about 10.0%, and about 10.5% by weight of the polyethylene copolymer, where any lower limit may be paired with any upper limit. The comonomer content is measured with NMR test.

[0048] Particularly improved end-product properties are obtained using such polyethylene copolymer having a density, as measured according to ASTM D792, ranging from a lower limit selected from any of about 0.918 g / cm3, about 0.919 g / cm3, and about 0.920 g / cm3to an upper limit selected from any of about 0.938 g / cm3, about 0.939 g / cm3, and about 0.940 g / cm3, where any lower limit may be paired with any upper limit. The polyethylene copolymer is of lower density than the first polyethylene copolymer of the micropellet blend compositions of the present disclosure.

[0049] Further, the polyethylene copolymer has a melt flow index, measured according to ASTM D1238 at 190° C / 2.16 kg, of at least about 10 g / 10 min, with ranges from this lower limit to any upper limit being contemplated. In some embodiments, the polyethylene copolymer has a melt flow index, measured according to ASTM DI 238 at 190° C. / 2.16 kg, that may be in a range having a lower limit selected from any of about 10 g / 10 min, about 11 g / 10 min, about 12 g / 10 min, about 13 g / 10 min, about 14 g / 10 min, and about 15 g / 10 min, to an upper limit selected from any of about 30 g / 10 min, about 31 g / 10 min, about 32 g / 10 min, about 33 g / 10 min, about 34 g / 10 min, and about 35 g / 10 min, where any lower limit may be paired with any upper limit.

[0050] In addition, the polyethylene copolymer of the polymer micropellet blend compositions have a molecular weight distribution (Mw / Mn, or “MWD”), e.g., Mw / Mn greater than 3, or greater than 3.5 in one or more embodiments, with ranges having any upper limit being contemplated. More particularly, the polyethylene may have an Mw having a lower limit selected from any of about 30000 g / mol, about 35000 g / mol, and about 40000 g / mol to an upper limit selected from any of about 65000 g / mol, about 70000 g / mol, and about 75000 g / mol, where any lower limit may be paired with any upper limit. In some embodiments, the Mn of the polyethylene copolymer may have a lower limit selected from any of about 5000 g / mol, about 7000 g / mol, and about 7500 g / mol to an upper limit selected from any of about 17500 g / mol, about 18000 g / mol, and about 20000 g / mol, where any lower limit may be paired with any upper limit. In some embodiments, the Mz of the polyethylene copolymer may have a lower limit selected from any of about100000 g / mol, about 125000 g / mol, and about 150000 g / mol to an upper limit selected from any of about 250000 g / mol, about 275000 g / mol, and about 300000 g / mol, where any lower limit may be paired with any upper limit. GPC measurement method is previously disclosed herein.

[0051] Industrial methods of producing the polyethylene copolymer are well known in the art and may include reactor blend, gas phase, liquid phase (or solution), and slurry phase polymerization processes, either alone or in combination. Catalysts used in these processes may include Ziegler-Natta catalysts, and / or one or more single site catalysts, such as metallocenes.

[0052] Micropellet

[0053] Micropelletization is a relatively new technology for producing resin particulate that exhibits many of the advantages of a pellet yet possesses a size closer to that of a powder. The reason for manufacturing these “micropellets” is that they may better compete with powders in processes where the size of the solid is important. The advantages of conventional pellets (and micropellets) over powders include higher bulk density, the inclusion of additives for subsequent processing, and the consistency of shape throughout a feedstock batch and between batches. Consistency of feedstock shape ensures good dry flow properties within solids handling equipment and into processing equipment like extruders and injection molding machines. Yet with the size of the micropellet (400 - 700 pm) being closer to that of a powder (75 -500 pm) than a conventional pellet (~3 mm), it shows improved dispersion within a matrix of solids and offers a larger surface area-to-volume ratio over conventional pellets, which may translate to higher melting rates.

[0054] The combined advantages of powders and pellets exhibited by micropellets explain the interest of rotational molders, masterbatch compounders, and injection molding processors in the technology. While compounders and molders have contributed to the market growth of micropellets, it is in rotational molding that an explosion of use is anticipated. Rotational molding requires small-sized particulate for its feed material to ensure that the product is formed without entrapped bubbles and exhibits minimal variation in wall thickness. Till now, rotomolders have paid a premium forhaving conventional pellets ground (sometimes cryogenically) to obtain the proper particle size and still ensure adequate dispersion of stabilizers within their materials.

[0055] With new evidence that micropellets may be used as a suitable alternative for ground powder in the production of quality plastic parts by rotational molding, the economic attractiveness of micropelletization is anticipated to drive a more rapid adoption of this technology. For this to occur, more research on micropelletization is required to understand the impact of the process on the extruded resin, and to identify exactly which applications within rotational molding, injection molding, and extrusion are best suited for micropellets over powders or conventional pellets.

[0056] According to an embodiment of the present invention the micropellet is formed by a polymer blend composition and has a particle size distribution D(v, 0.99) of 400 - 700 pm, preferably 450 - 600 pm, and a particle size distribution D(v, 0.01) of 250 - 400 pm , measured according to ASTM DI 921. According to another embodiment of the present invention, the micropellet is cylindrical- shaped.

[0057] According to another embodiment of the present invention, the micropellet has a bulk density of 300 to 7000 kg / m3, preferably 400 to 550 kg / m3, measured according to ASTM DI 895.

[0058] Additionally, the micropellet according to the present invention presents a dry flow of from 9 to 13 seconds , measured according to ASTM DI 895; more preferably from 10 to 12 seconds.

[0059] The micropellets are produced by commonly known micropelletization processes in the art, such as Rotational Molding Technology - Plastics Design Library William Andrew Publishing Roy J. Crawford - The Queenis University of Belfast Belfast, Northern Ireland, and James L. Throne - Sherwood Technologies, Inc. Hinckley, Ohio (Chapter III).

[0060] Micropellet blend composition

[0061] According to the present invention, the micropellet blend composition may include the first polypropylene copolymer in an amount ranging from a lower limit selected from any of about 20%, about 25%, and about 30% based on the total weight of the micropellet blend composition to an upper limit selected from any of about 70%, about75%, and about 80% based on the total weight of the micropellet blend composition, where any lower limit may be paired with any upper limit.

[0062] Similarly, the micropellet blend compositions may include the second polypropylene copolymer in an amount ranging from a lower limit selected from any of about 20%, about 25%, and about 30% based on the total weight of the micropellet blend composition to an upper limit selected from any of about 70%, about 75%, and about 80% based on the total weight of the micropellet blend composition, where any lower limit may be paired with any upper limit.

[0063] The first polypropylene copolymer and the second polypropylene copolymer may be melt-blended together, such as in an extruder, to arrive at the micropellet blend compositions of the present disclosure, wherein the blend is submitted to a micropellezation process.

[0064] The weight percentages recited herein for the first and second polypropylene components are based on the total weight (100%) of polymer melt blend composition.

[0065] According to another embodiment, the first polypropylene polymer and the second polypropylene copolymer adds up at least 70% by weight of the polymer blend composition, preferably 90%; more preferably 95% by weight.

[0066] Furthermore, the micropellet blend composition may additionally comprise a polyethylene copolymer as previously discussed. According to an embodiment of the present disclosure, the polyethylene is present at a concentration of from about 0% by weight to about 15% by weight of the polymer blend composition, preferably 2.5% to 5%.

[0067] Additives may be used as needed. Typical additives include one or more of coloring agents, stabilizers, antioxidants, UV absorbers, antistatics, lubricants and fillers.

[0068] Typically additives will be used in quantities of about 100 to 5000 ppm, e.g. 500 to 2500 ppm, relative to the overall micropellet blend composition weight.

[0069] Rotomolding Process

[0070] In some embodiments, a micropellet blend composition based on a first and second polypropylene copolymers as previously described, may be rotomolded. To this end, the components of the micropellet blend composition, with or without additives, may be melt blended. The micropellet blend composition may then be pulverized into powder by using a pulverizer.

[0071] In one or more embodiments, micropellet blend compositions in accordance with the present disclosure may be prepared using continuous or discontinuous extrusion and micropelletizarion steps. Methods may use single-, twin- or multi- screw extruders, which may be used at temperatures ranging from 100° C to 270° C in some embodiments, and from 140° C to 230° C in some embodiments. Generally, melt blend compositions prepared in extruders are further micropelletized to be used subsequently used in the rotomolding process.

[0072] The micropelletized material must be pulverized, to facilitate the flow in the mold, thus reducing air trapping and accelerating the plasticization of the material. The pulverization is carried out in special disc mills where the pellets undergo an ultrafine grind and the powder is separated by sieves until reaching the ideal granulometry. The pulverized material facilitates the reduction of the rotomolding cycle and prevents polymer degradation.

[0073] It is important to point out that according to the present invention, the micropellet does not need to be micronized, thus facilitating the processability and the use of polypropylene for rotomolding applications.

[0074] The micropellet blend composition may then be rotomolded into articles according to the present disclosure.

[0075] In the rotomolding process, the cohesive forces acting on the polymer particles are important during the heating of the micropellet and the melting phases of the process, since they determine the deposition behavior of the material on the mold wall and the uniformity of the part. The particle size distribution is a determining factor in the properties of the rotomolded part and the economics of the process. The smaller the particle size, the better the heat transfer will be, respecting the pellet grinding limitations. Pulverized powder smaller than 100 mesh size leads to excessive material loss and increased process costs. In addition, the agitation of very fine dust particles inside themold leads to the accumulation of high electrostatic charges that cause the particles to agglomerate, producing an irregular fusion. According to the French standard NF T50- 700 (AFNOR, 2014). The flowability may be related to the particle shape, the degree of roughness and adhesion to the mold surface.

[0076] Articles

[0077] In some embodiments, the micropellet blend composition of the present disclosure may be used to produce rotomolded articles having a thickness of from about 1 mm to about 20 mm, with any ranges within this lower limit and any upper limit being contemplated.

[0078] Exemplary articles include, but are not limited to, automotive part, an agricultural vehicle part, such as a part of a tractor or a tractor roof, a tank, a furniture piece or part, or a playground piece or part.

[0079] In addition, in some embodiments, the micropellet blend composition of the present disclosure may be used to produce rotomolded articles having an index of external surface finishing of less than 2 or less than 1, an index of internal surface finishing of less than 2 or less than 1, and an index representative of the bubble content in the article of less than 2, or less than 1, wherein the index of external surface finishing, the index of internal surface finishing, and the index representative of the bubble content each range from 0 to 5, wherein 0 stands for a lack of any defects, 1 stands for a very low amount of defects, 2 stands of a low amount of defects, 3 stands for an intermediate amount of defects, 4 stands for a high amount of defects, and 5 stands for a very high amount of defects.

[0080] The present invention, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present invention.EXAMPLES

[0081] For clear understanding of the examples presented hereinafter, some definitions are provided as follows. The following examples are merely illustrative, and should not be interpreted as limiting the scope of the present invention.

[0082] Shown in Table 1 are micropellet blend compositions used to exemplify rotomolding processes according to the present invention.

[0083] The micropellets of the examples are cylindrical- shaped, and have a particle size distribution D(0.99) of 32 mesh (500p) and D(0.01) of 42 mesh (355p), measured according to ASTM DI 921. Additionally, the micropellets of the examples according to the present invention have a bulk density of 500 kg / m3(measured according to ASTM DI 95) and dry flow of 11 seconds.

[0084] In this regard, both examples were formulated with Braskem RP225M copolymer (melt flow rate, measured according to ASTM D1238 (230° C / 2.16 kg) of 8 g / 10 min, and a density of 0.902 g / cm3) random polypropylene copolymer (propyleneethylene copolymer having 2.7 % wt. of ethylene as comonomer), Braskem CP396XP (melt flow rate, measured according to ASTM D1238 (230° C / 2.16 kg) of 11 g / 10 min, and a density of 0,895g / cm3) heterophasic polypropylene copolymer (70 wt % homopolymer matrix and 30 wt % EPR as dispersed phase), and Braskem ML2400N copolymer (melt flow rate, measured according to ASTM D1238 (190° C / 2.16 kg) of 20 g / 10 min, and a density of 0.926 g / cm3) linear low density polyethylene copolymer derived from the polymerization of principally ethylene with a minor amount of one or more copolymerizable monomers (1 -butene)Table 1: Examples of micropellet blend compositions

[0085] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein alsoencompass any and all possible subranges and combinations of subranges thereof. Any listed range may be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which may be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0086] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0087] Other embodiments are set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A rotomolding process comprising: melt blending a micropellet comprising a polymer blend of (a) a first polypropylene copolymer, and (b) a second polypropylene copolymer to form the micropellet blend composition; pulverizing the micropellet melt blend composition; and rotational molding the micropellet melt blend composition; wherein the first polypropylene copolymer is present at a concentration of from 20% by weight to 80% by weight of the micropellet blend composition; and wherein the second polypropylene copolymer is present at a concentration of from 20% by weight to 80% by weight of the micropellet blend composition.

2. Rotomolding process according to claim 1 , wherein the micropellet further comprises (c) a polyethylene polymer, wherein the polyethylene polymer is present at a concentration of at most 30% by weight of the polymer micropellet blend composition.

3. Rotomolding process according to claim 1, wherein the micropellet has a particle size distribution D(v, 0.99) of 400 - 700 pm, preferably 450 - 600 pm, measured according to ASTM DI 921.

4. Rodomolding process according to claim 1, wherein the micropellet is cylindrical-shaped.

5. Rotomolding process according to claim 1, wherein the first propylene copolymer is a random polypropylene copolymer.

6. Rotomolding process according to claim 5, wherein the random polypropylene copolymer is a copolymer of propylene and a C2-C6 alpha-olefin, wherein a concentration of the C2-C6 alpha-olefin is from 1% to 8% by weight.

7. Rotomolding process according to claim 6, wherein the random polypropylene copolymer is a copolymer of propylene and ethylene.

8. Rotomolding process according to claim 4, wherein the random propylene copolymer has a density, measured according to ASTM D792, of from 0.890 g / cm3to 0.910 g / cm3, a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of from 2 g / 10 min to 18 g / 10 min.

9. Rotomolding process according to claim 1, wherein the second polypropylene copolymer is a heterophasic polypropylene copolymer.

10. Rotomolding process according to claim 9, wherein the heterophasic polypropylene copolymer is a copolymer having a matrix phase comprising a polypropylene homopolymer or copolymer and a dispersed phase having an elastomeric component, wherein the concentration of the matrix phase is 90 to 50 wt % and the dispersed phase, 10 to 50 wt %.

11. Rotomolding process according to claim 9, wherein the matrix phase is polypropylene homopolymer.

12. Rotomolding process according to claim 9, wherein the elastomeric component is an ethylene -propylene copolymer.

13. Rotomolding process according to claim 12, wherein the ethylenepropylene copolymer contains 5 to 30 wt % ethylene and having an intrinsic viscosity (IV of AM) of 1.5 to 4 dL / g, preferably 2 to 3.5 dL / g measured in decalin at 135° C according to ASTM method D1601-78.

14. Rotomolding process according to claim 8, wherein the heterophasic propylene copolymer has a density, measured according to ASTM D792, of from 0.890 g / cm3to 0.910 g / cm3, a melt flow index, measured according to ASTM D1238 at 230° C / 2.16 kg, of from 1 g / 10 min to 20 g / 10 min, and a molecular weight distribution Mw / Mn greater than 3.

15. Rotomolding process according to claim 2, wherein the polyethylene polymer is a linear low density polyethylene copolymer derived from the polymerization of principally ethylene with a minor amount of one or more copolymerizable monomersof alpha-olefins, preferably C3-C20 alpha-olefins, preferably C3-C8 alpha-olefins, preferably C3-C6 alpha-olefins, preferably a C4 alpha-olefin, preferably 1 -butene.

16. Rotomolding process according to claim 15, wherein the polyethylene polymer has a density, measured according to ASTM D792, of from 0.918 g / cm3to 0.940 g / cm3, a melt flow index, measured according to ASTM D1238 at 190° C / 2.16 kg, of from 10 g / 10 min to 35 g / 10 min.

17. Rotomolding process according to claim 1, wherein the first polypropylene copolymer is present at a concentration of from about 30% by weight to about 75% by weight of the micropellet blend composition.

18. Rotomolding process according to claim 1, wherein the second polypropylene copolymer is present at a concentration of from about 20% by weight to about 70% by weight of the micropellet blend composition.

19. Rotomolding process according to claim 2, wherein the polyethylene is present at a concentration of from about 0% by weight to about 30% by weight of the polymer blend composition, preferably 0% to 15%; more preferably 0% to 5%.

20. Rotomolding process according to claim 1, wherein the concentration of the first polypropylene polymer and the second polypropylene copolymer adds up at least 70% by weight of the polymer blend composition, preferably 85%; more preferably 95%.

21. Rotomolding process according to claim 1, wherein the micropellet comprises at least one additive selected from coloring agents, stabilizers, antioxidants, UV absorbers, antistatics, lubricants and fillers.

22. Rotomolding process according to claim 1, wherein the micropellet is melt blended with at least one additive selected from coloring agents, stabilizers, antioxidants, UV absorbers, antistatics, lubricants and fillers.

23. A rotomolded article formed by the rotomolding process of claim 1, wherein the rotomolded article has a thickness of from 1 mm to 20 mm.

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