BACKGROUND

[0001] Polymer compositions are used to produce a varied range of articles for many different applications. Such compositions may be formulated with a variety of components and other additives to provide articles that possess physical properties well-suited for their intended use. For example, it is desirable that articles intended for use in storage applications, such as crates and pails, exhibit properties like superior impact strength and stiffness, in order to withstand large stacking forces, in addition to having a suitable density, cracking resistance, creep resistance, and the like.

[0002] Traditionally, impact copolymer propylene (ICP) resins are commonly used for the production of articles intended for storage applications because of their superior impact properties. ICP resins generally comprise at least two components, a polypropylene polymer matrix and an amorphous elastomer phase, with the elastomer phase being distributed throughout the polymer matrix. The high impact strength of ICP resins is provided by elastomer phase as the polypropylene matrix by itself is generally brittle and possessing of a low impact strength. As a result of this, ICP resins with higher elastomer phase contents tend to have higher impact strengths.

[0003] However, ICP resins can have poor processability, with those possessing high elastomer contents being particularly afflicted. Forming large ICP articles by injection molding can be a slow process, limiting productivity. To ensure that articles possess the desired mechanical properties the crystallization kinetics must be exact, which can be achieved by utilizing long cycle times to provide slow cooling rates. It is also known that processing ICP resins is heavily influenced by prior steps such as plastification and mold filling, with factors such as melt rheology and matrix composition strongly influencing the processing time and injection pressures required.

[0004] As a result, the formulation of ICP resins provides a compromise between processability and impact strength, with a high content of the elastomer phase generally providing a better impact strength but an inferior processing capacity. Therefore, ICP resins that exhibit superior mechanical and physical properties in addition to enhanced processability are highly desired but difficult to obtain.

SUMMARY

[0005] 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.

[0006] In one aspect, embodiments disclosed herein relate to a heterophasic propylene copolymer composition that includes a polypropylene-based matrix polymer, and an elastomer phase dispersed in the matrix polymer, the composition having a 1% secant flexural modulus, measured according to ASTM D790 at 23°C, of at least 800 MPa and an Izod impact strength, measured according to ASTM D256 at 0°C, of at least 400 J/m.

[0007] In another aspect, embodiments disclosed herein relate to articles formed from a heterophasic propylene copolymer composition, the composition comprising a polypropylene-based matrix polymer and an elastomer phase dispersed in the matrix polymer. The composition has a 1% secant flexural modulus, measured according to ASTM D790 at 23 °C, of at least 800 MPa and an Izod impact strength, measured according to ASTM D256 at 23 °C, of at least 400 J/m.

[0008] In another aspect, embodiments disclosed herein relate to methods for forming articles from a heterophasic propylene copolymer composition by injection molding, the composition including a polypropylene-based matrix polymer and an elastomer phase dispersed in the matrix polymer. The composition has a flexural modulus, measured according to ASTM D790 at 23 °C, of at least 800 MPa and an Izod impact strength, measured according to ASTM D256 at 0°C, of at least 400 J/m.

[0009] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

[0010] One or more embodiments disclosed herein relate to heterophasic propylene copolymer compositions that comprise a polypropylene-based matrix and an elastomer phase dispersed therein. In particular, heterophasic propylene copolymer compositions may be used to form articles such as crates, bins, pails, tote boxes, and bulk containers. As discussed above, conventional impact copolymer propylene resins require a compromise between processability and impact strength. However, compositions according to the present disclosure offer both superior mechanical properties and excellent processability.

[0011] In one or more embodiments of the present disclosure, a HECO composition is provided that gives improved mechanical properties, such as stiffness and impact strength, as well as great processing performance. These compositions can provide the advantageous properties of conventional impact copolymers that feature a high elastomer phase content, without the resulting poor processability.

[0012] COMPOSITIONS

[0013] Embodiments of the present disclosure are directed to heterophasic propylene copolymer (HECO) compositions that comprise a propylene-based matrix polymer and an elastomer (amorphous) phase, where the elastomer phase is dispersed in the matrix polymer. In one or more embodiments, HECO compositions may comprise the propylene- based matrix polymer in an amount ranging from 55 to 80% by weight (wt.%), relative to the weight of the total composition. In some embodiments, the HECO compositions may comprise the elastomer phase in an amount ranging from 20 to 45 wt.%. In further embodiments, the elastomer phase may be present in an amount ranging from 25 to 35 wt.%.

[0014] In one or more embodiments, HECO compositions in accordance with the present disclosure may have an amorphous phase content, according to ASTM 5492-10, ranging from about 18 to 32 wt.% of the composition. In further embodiments, HECO compositions may have an amorphous phase content, according to ASTM 5492-10, ranging from about 20 to 30 wt.% of the composition.

[0015] Polypropylene-based matrix polymers may comprise propylene homopolymers, heterophasic propylene polymers, copolymers of propylene and one or more comonomers selected from ethylene and C4-C20 alpha-olefins, olefin terpolymers and higher order polymers, and blends obtained from the mixture of one or more of these polymers and/or copolymers.

[0016] In one or more embodiments, the polypropylene-based matrix is a crystalline isotactic propylene-based matrix having a pentad concentration as determined by ¹³ C-NMR spectroscopy of more than 95 mol%. In some embodiments, the crystalline isotactic propylene-based matrix has a melt flow rate (MFR) determined at 230°C and a load of 2.16 kg, according to ASTM 1238, ranging from about 15 to 100 g/lOmin.

[0017] The elastomer phase of the heterophasic propylene copolymer compositions may be, for example, a propylene copolymer rubber, comprising propylene and one or more comonomers. In one or more embodiments, the comonomers may be one or more selected from a group consisting of ethylene and C4-C8 oc-olefins. The elastomer phase may comprise one or more of the comonomers in an amount ranging from 10 to 45 wt.%, relative to the weight of the elastomer phase. In some embodiments, the elastomer phase may comprise one or more of the comonomers in an amount ranging from 28 to 42 wt.%.

[0018] In particular embodiments, the propylene copolymer rubber may be a propylene- ethylene rubber. In such one or more embodiments, HECO compositions in accordance with the present disclosure may have an ethylene content, according to ASTM 5576, ranging from about 7 to 16 wt.% of the composition. With respect to the amorphous or elastomer phase, an ethylene content, according to ASTM 5576, may range from about 28 to 42 wt.% of the elastomer or amorphous phase. In more particular embodiments, the elastomer phase may have an ethylene content, according to ASTM 5576, ranging from about 32 to 42 wt.% of the elastomer phase.

[0019] HECO compositions in accordance with the present disclosure may optionally further comprise one or more additives that modify various physical and/or chemical properties of the composition. Such additives may be selected from, for example, flow lubricants, antistatic agents, clarifying agents, nucleating agents, beta-nucleating agents, slippage agents, antioxidants, peroxides, antacids, light stabilizers, IR absorbers, silica, titanium dioxide, organic dyes, organic pigments, inorganic dyes, inorganic pigments, and the like. One of ordinary skill in the art will appreciate, with the benefit of this disclosure, that the choice of additive may be dependent upon the intended use of the composition and/or articles produced therefrom. It will also be appreciated that such additives are not limited to those described above.

[0020] HECO compositions according to the present disclosure will generally possess physical properties suitable for the intended use of the composition and/or articles produced therefrom. One of ordinary skill in the art will, with the benefit of this present disclosure, appreciate that altering the relative amounts and/or identities of the components of a polymer composition will influence the properties of the composition.

[0021] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit an intrinsic viscosity of the elastomer phase ranging from about 2.0 to 7.0 dL/g. In more particular embodiments, HECO compositions may exhibit an intrinsic viscosity of the elastomer phase ranging from about 2.2 to 3.5 dL/g. The intrinsic viscosity of specific species may be measured with a Ubbelohde type Desreux-Bischoff dilution viscometer for 135° C decalin solutions with a concentration (at 23° C) of 0.7 g/L.

[0022] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit a melt flow rate (MFR), measured under a load of 2.16 kg at a temperature of 230°C according to ASTM 1238, ranging from about 10 to 50 g/ 10 min. In some embodiments, HECO compositions may exhibit a melt flow rate, according to ASTM 1238, ranging from about 15 to 25 g/lOmin.

[0023] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit a 1% secant flexural modulus at 23 °C, according to ASTM D790, of greater than about 800 MPa. In particular embodiments, HECO compositions may exhibit a flexural modulus at 23 °C, according to ASTM D790, ranging from about 800 to 1100 MPa.

[0024] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit an Izod impact strength, according to ASTM D256, of greater than about 400 J/m. In some embodiments, HECO compositions in accordance with the present disclosure may exhibit an Izod impact strength, according to ASTM D256, ranging from about 400 to 700 J/m In particular embodiments, HECO compositions may exhibit an Izod impact strength, according to ASTM D256, of greater than about 450 J/m.

[0025] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit an energy at failure, according to ASTM D3763, of greater than or equal to about 22 J. In particular embodiments, HECO compositions may exhibit an energy at failure, according to ASTM D3763, ranging from about 22 to 30 J.

[0026] In one or more embodiments, HECO compositions in accordance with the present disclosure may exhibit ductile behavior during a falling dart test at 0 °C and an energy ranging from about 22 to 30 J. [0027] HECO compositions that are in accordance with one or more embodiments of the present disclosure may be visbroken. In some embodiments, the composition may be visbroken by reactive extrusion. In particular embodiments, the HECO composition may be visbroken by a suitable visbreaking agent, such as an inorganic or organic peroxide. Suitable visbreaking agents of one or more embodiments may be selected from the group comprising 2 , 5 -dimethyl-2 ,5 -di(t-butylperoxy)hexane, 2 , 5 -dimethyl-2 ,5 -di(t- butylperoxy)hexyne-3, 3,6,6,9,9-pentamethyl-3-(ethyl acetate) 1,2, 4, 5-tetraoxy cyclononane, t-butyl hydroperoxide; hydrogen peroxide; dicumyl peroxide; t-butyl peroxy isopropyl carbonate; di-t-butyl peroxide; p-chlorobenzoyl peroxide; dibenzoyl diperoxide; t-butyl cumyl peroxide; t-butyl hydroxyethyl peroxide, di-t-amyl peroxide; and 2,5- dimethylhexene-2,5-diperisononanoate, and others.

[0028] METHODS OF PREPARING COMPOSITIONS

[0029] HECO compositions in accordance with the present disclosure may be prepared by gas-phase polymerization. In one or more embodiments, the gas-phase polymerization of HECO compositions comprises the use of two or more gas-phase reactors.

[0030] In one or more embodiments, HECO compositions in accordance with the present disclosure may be prepared in a sequential polymerization process wherein the propylene- based matrix polymer is prepared first, with the elastomer phase being prepared afterwards.

[0031] Any suitable catalyst may be used in the preparation of the HECO compositions of the present disclosure. In one or more embodiments, HECO compositions may be prepared with a catalyst such as Ziegler-Natta, metallocene, or chromium catalysts. In one or more embodiments, HECO compositions in accordance with the present disclosure may be prepared using a Ziegler-Natta catalyst. Examples of the Ziegler-Natta catalysts that may be utilized in one or more embodiments are described in the“Polypropylene Handbook” by Nello Pasquini, 2nd Edition, 2005, Chapter 2. Such examples include, but are not limited to, one or more phthalate-based catalysts, diether-based catalysts, succinate-based catalysts, and combinations thereof.

[0032] In one or more embodiments, HECO compositions in accordance with the present disclosure may be prepared using a co-catalyst in addition to a catalyst. In one or more embodiments, the co-catalyst may be triethyl aluminum. [0033] In one or more embodiments, HECO compositions in accordance with the present disclosure may be prepared using an electron donor in addition to a catalyst and a co catalyst. In one or more embodiments, the electron donor may be selected from, but are not limited to, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, cyclohexylisopropyldimethoxy silane, n-butylmethyldimethoxysilane, tetraethoxysilane, 3,3,3 trifluoropropylmethyldimethoxysilane, mono and dialkylaminotrialkoxy silanes, and combinations thereof.

[0034] In one or more embodiments, a catalyst system may comprise a catalyst and, optionally, one or more co-catalysts and electron donors. In some embodiments, the catalyst system may be introduced at the beginning of the polymerization of propylene and is transferred with the resulting propylene-based matrix polymer to the copolymerization reactor where it serves to catalyze the gas phase copolymerization of propylene and one or more copolymers to produce the elastomer phase.

[0035] As would be apparent to one of ordinary skill in the art with the benefit of the present disclosure, HECO compositions in accordance with the present disclosure may be prepared by any suitable method, not only those described above.

[0036] In one or more embodiments, HECO compositions in accordance with the present disclosure may be combined using any post-reactor melt mixture process, including kneaders, Banbury mixers, mixing rollers, extrusion processes with a single, double, or multi-screw extruder. By mixing components subsequent to synthesis, each component may be purified to specified standards and then combined to generate the final composition while minimizing the presence of reactants and degradation products. In embodiments prepared from multiple components, such as additives, a subset of the components may be combined by melt mixing followed by subsequent mixing steps, or all components may be melt mixed simultaneously.

[0037] In one or more embodiments, articles comprising polymer compositions in accordance with the present disclosure may be prepared at temperatures ranging from 90 °C to 210 °C in some embodiments, and from 110 °C to 180 °C in some embodiments. In one or more embodiments, methods of preparing polymer compositions may involve a single mixing or multiple mixing steps in which components may be simultaneously or separately added. In some embodiments, raw materials may be added to a melt mixture device such as kneaders, Banburys, or extruders in the form of powder, granules, flakes or dispersion in liquids as solutions, emulsions and suspensions of one or more components.

[0038] ARTICLES

[0039] As will be apparent to one of ordinary skill in the art having the benefit of the present disclosure, articles may be formed from any of the aforementioned HECO compositions. In one or more embodiments, polymer compositions of the current disclosure can be used in various article manufacturing processes, including compression molding, injection molding, and the like, to produce manufactured articles. The articles of one or more embodiments may be used for storage applications. In some embodiments, articles may be selected from the group comprising crates, bins, pails, tote boxes and bulk containers. In particular embodiments, articles may exhibit a compression force, according to ASTM D2659, of greater than about 400 kgf. In particular embodiments, articles may exhibit a compression force, according to ASTM D2659, ranging from about 400 to 700 kgf.

[0040] The properties of articles formed according to the present disclosure will generally be suitable for the articles intended use. One of ordinary skill in the art will, with the benefit of this present disclosure, appreciate that altering the relative amounts and/or identities of the components of a polymer composition will influence the properties of an article formed therefrom.

[0041] EXAMPLES

[0042] The following examples are merely illustrative and should not be interpreted as limiting the scope of the present disclosure.

[0043] Three heterophasic polypropylene grades were prepared in a two-reactor polymerization process using a Ziegler-Natta catalyst. Example 1 was visbroken after polymerization and Comparative Examples 1 and 2 were not.

[0044] Table 1: Compositions of the Examples

[0045] Table 2: Properties of the Examples.

[0046] Comp Ex. 2 provides a MFR that would favor processability, however, the balance of mechanical properties is very poor specially regarding the Izod Impact Strength. On the other hand, Comp Ex. 1 presents a good balance of mechanical properties, however, the processability is impaired due to the low MFR.

[0047] Example 1 uniquely presents a high MFR while exhibiting a good balance of mechanical properties which are specifically useful for the production of articles such as crates, bins, pails, tote boxes, or bulk containers

[0048] Although the preceding description has been described herein with reference to particular means, materials and embodiments, it is not intended to be limited to the particulars disclosed herein; rather, it extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words‘means for’ together with an associated function.