Patent Description:
Propylene-based polymers are used for many applications, including a luggage case. Propylene-based polymers can be a propylene homopolymer or a single-phase propylene copolymer or a heterophasic propylene copolymer.

Luggage cases are subjected to relatively severe conditions during use, in particular larger luggage cases for check-in during flights. There are accordingly tests to determine whether luggage cases have sufficient properties for use, such as stress whitening resistance, gloss, impact strength and tensile properties.

<CIT> discloses a luggage made of a polypropylene modified material comprising a homo-polypropylene <NUM>-40wt%, polypropylene copolymer <NUM>-60wt%, polyolefin elastomer <NUM>-15wt%, polyethylene <NUM>-20wt%, nucleating agent <NUM>-<NUM>. 08wt%, antioxidant <NUM>-<NUM>. 06wt%, and fluidity modifier <NUM>-6wt%.

It is an object of the invention to provide a composition having a combination of good mechanical properties for making luggage cases.

Accordingly, the present invention provides a composition comprising (A) a heterophasic propylene copolymer, (B) a propylene homopolymer and (C) a polyolefin-based elastomer, wherein.

According to the invention, a heterophasic propylene copolymer is mixed with a propylene homopolymer and a polyolefin-based elastomer having a relatively high MFI. The specific total amount of the dispersed rubber phase of the heterophasic propylene copolymer and the specific polyolefin-based elastomer according to the invention was found to result in a combination of good mechanical properties for making luggage cases, such as good stress whitening resistance, gloss and impact strength.

Heterophasic propylene copolymers are generally prepared in one or more reactors, by polymerization of propylene in the presence of a catalyst and subsequent polymerization of an ethylene-α-olefin mixture. The resulting polymeric materials are heterophasic, but the specific morphology usually depends on the preparation method and monomer ratios used.

The heterophasic propylene copolymers employed in the present invention can be produced using any conventional technique known to the skilled person, for example multistage process polymerization, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combinations thereof. Any conventional catalyst systems, for example, Ziegler-Natta or metallocene may be used. Such techniques and catalysts are described, for example, in <CIT>; <NPL>; <CIT>, <CIT> and <CIT>.

Preferably, the heterophasic propylene copolymer is made using Ziegler-Natta catalyst.

The heterophasic propylene copolymer may be prepared by a process comprising.

These steps are preferably performed in different reactors. The catalyst systems for the first step and for the second step may be different or same.

The heterophasic propylene copolymer of the composition of the invention consists of a propylene-based matrix and a dispersed ethylene-α-olefin copolymer. The propylene-based matrix typically forms the continuous phase in the heterophasic propylene copolymer. The amounts of the propylene-based matrix and the dispersed ethylene-a-olefin copolymer may be determined by <NUM>C-NMR, as well known in the art.

The propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least <NUM> wt% of propylene monomer units and at most <NUM> wt% of comonomer units selected from ethylene monomer units and α-olefin monomer units having <NUM> to <NUM> carbon atoms, for example consisting of at least <NUM> wt% of propylene monomer units and at most <NUM> wt% of the comonomer units, based on the total weight of the propylene-based matrix.

Preferably, the comonomer in the propylene copolymer of the propylene-based matrix is selected from the group of ethylene, <NUM>-butene, <NUM> -pentene, <NUM>-methyl-<NUM>-pentene, <NUM>-hexen, <NUM>-heptene and <NUM>-octene, and is preferably ethylene.

Preferably, the propylene-based matrix consists of a propylene homopolymer. The fact that the propylene-based matrix consists of a propylene homopolymer is advantageous in that a higher stiffness is obtained compared to the case where the propylene-based matrix is a propylene-α-olefin copolymer.

The melt flow index (MFI) of the propylene-based matrix (before the heterophasic propylene copolymer is mixed into the composition of the invention), MFIPP,may be for example at least <NUM> dg/min, at least <NUM> dg/min, at least <NUM> dg/min, at least <NUM> dg/min, and/or for example at most <NUM> dg/min, at most <NUM> dg/min, at most <NUM> dg/min, at most <NUM> dg/min, at most <NUM> dg/min, measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>).

Preferably, the propylene-based matrix is present in an amount of <NUM> to <NUM> wt%, for example at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt% or at most <NUM> wt%, based on the total heterophasic propylene copolymer. Preferably, the propylene-based matrix is present in an amount of at least <NUM> wt%, more preferably at least <NUM> wt%, for example at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% or at least <NUM> wt%, based on the total heterophasic propylene copolymer.

The propylene-based matrix is preferably semi-crystalline, that is it is not <NUM>% amorphous, nor is it <NUM>% crystalline. For example, the propylene-based matrix is at least <NUM>% crystalline, for example at least <NUM>%, for example at least <NUM>% crystalline and/or for example at most <NUM>% crystalline, for example at most <NUM>% crystalline. For example, the propylene-based matrix has a crystallinity of <NUM> to <NUM>%. For purpose of the invention, the degree of crystallinity of the propylene-based matrix is measured using differential scanning calorimetry (DSC) according to ISO11357-<NUM> and ISO11357-<NUM> of <NUM>, using a scan rate of <NUM>/min, a sample of <NUM> and the second heating curve using as a theoretical standard for a <NUM>% crystalline material <NUM> J/g.

Besides the propylene-based matrix, the heterophasic propylene copolymer also comprises a dispersed ethylene-α-olefin copolymer. The dispersed ethylene-α-olefin copolymer is also referred to herein as the 'dispersed phase'. The dispersed phase is embedded in the heterophasic propylene copolymer in a discontinuous form. The particle size of the dispersed phase is typically in the range of <NUM> to <NUM> microns, as may be determined by transmission electron microscopy (TEM). The amount of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer may herein be sometimes referred as RC.

Preferably, the amount of ethylene monomer units in the ethylene-α-olefin copolymer is <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, <NUM> to <NUM> wt% or <NUM> to <NUM> wt%. The amount of ethylene monomer units in the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer may herein be sometimes referred as RCC2.

The α-olefin in the ethylene-α-olefin copolymer is preferably chosen from the group of α-olefins having <NUM> to <NUM> carbon atoms. Examples of suitable α-olefins having <NUM> to <NUM> carbon atoms include but are not limited to propylene, <NUM> -butene, <NUM>-pentene, <NUM>-methyl-<NUM>-pentene, <NUM>-hexen, <NUM>-heptene and <NUM>-octene. More preferably, the α-olefin in the ethylene-α-olefin copolymer is chosen from the group of α-olefins having <NUM> to <NUM> carbon atoms and any mixture thereof, more preferably the α-olefin is propylene, in which case the ethylene-α-olefin copolymer is ethylene-propylene copolymer.

The MFI of the dispersed ethylene α-olefin copolymer (before the heterophasic propylene copolymer is mixed into the composition of the invention), MFlrubber, may be for example at least <NUM> dg/min, at least <NUM> dg/min or at least <NUM> dg/min, and/or for example at most <NUM> dg/min or <NUM> dg/min. MFlrubber is calculated according to the following formula: <MAT> wherein MFlheterophasic is the MFI (dg/min) of the heterophasic propylene copolymer measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>), MFlmatrix is the MFI (dg/min) of the propylene-based matrix measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>), matrix content is the fraction of the propylene-based matrix in the heterophasic propylene copolymer, rubber content is the fraction of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer. The sum of the matrix content and the rubber content is <NUM>. For the avoidance of any doubt, Log in the formula means log<NUM>.

Preferably, the dispersed ethylene-α-olefin copolymer is present in an amount of <NUM> to <NUM> wt%, for example at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% or at least <NUM> wt%, based on the total heterophasic propylene copolymer. Preferably, the dispersed ethylene-α-olefin copolymer is present in an amount of at most <NUM> wt%, more preferably at most <NUM> wt%, for example at most <NUM> wt%, at most <NUM> wt%, at most <NUM> wt% or at most <NUM> wt%, based on the total heterophasic propylene copolymer. This leads to the suitable total rubber amount to achieve good mechanical properties of the composition according to the invention together with the polyolefin elastomer.

In the heterophasic propylene copolymer in the composition of the invention, the sum of the total weight of the propylene-based matrix and the total weight of the dispersed ethylene-α-olefin copolymer is <NUM> wt% of the heterophasic propylene copolymer.

Preferably, the heterophasic propylene copolymer has a fraction soluble in p-xylene at <NUM> (CXS) measured according to ISO <NUM>:<NUM> of <NUM> to <NUM> wt%, for example <NUM> to <NUM> wt%.

Preferably, the amount of ethylene monomer units in the heterophasic propylene copolymer (sometimes referred as TC2) is in the range of <NUM> to <NUM> wt%, for example <NUM> to <NUM> wt%, based on the heterophasic propylene copolymer.

Preferably, the MFI of the heterophasic propylene copolymer is <NUM> to <NUM>/<NUM>, for example at least <NUM> dg/min, at least <NUM> dg/min, at least <NUM> dg/min and/or at most <NUM> dg/min, at most <NUM> dg/min or at most <NUM> dg/min, measured according to ISO1133-<NUM> :<NUM> (<NUM> /<NUM>). This leads in particular to the good processibility of the composition according to the invention.

Preferably, in the heterophasic propylene copolymer according to the invention, the comonomer in the propylene-α-olefin copolymer is selected from ethylene and the group of α-olefins having <NUM> to10 carbon atoms and the α-olefin in the ethylene-α-olefin copolymer is selected from the group of α-olefins having <NUM> to <NUM> carbon atoms. Most preferably, in the heterophasic propylene copolymer according to the invention, the comonomer in the propylene-α-olefin copolymer is ethylene and the α-olefin in the ethylene-α-olefin copolymer is propylene.

Preferably, the amount of (A) the heterophasic propylene copolymer with respect to the composition of the invention is <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt% or <NUM> to <NUM> wt%.

Preferably, the amount of (a2) the dispersed ethylene-α-olefin copolymer with respect to the composition of the invention is <NUM> to <NUM> wt%, <NUM> to <NUM> wt%, <NUM> to <NUM> wt% or <NUM> to <NUM> wt%. This leads to the suitable total rubber amount to achieve good mechanical properties of the composition according to the invention together with the polyolefin elastomer.

The composition of the invention comprises (B) a propylene homopolymer. Preferably, (B) has a melt flow index (MFI) measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>) which is higher than the melt flow index (MFI) measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>) of (A). This leads in particular to the good processibility of the composition according to the invention.

The propylene homopolymer may have a melt flow index (MFI) measured according to ISO1133-<NUM>:<NUM> (<NUM>/<NUM>) of <NUM> to <NUM> dg/min, for example at least <NUM> dg/min, at least <NUM> dg/min, at least <NUM> dg/min or at least <NUM> dg/min, and/or for example at most <NUM> dg/min, at most <NUM> dg/min, at most <NUM> dg/min, at most <NUM> dg/min.

Preferably, the amount of (B) the propylene homopolymer with respect to the composition of the invention is <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%.

The composition of the invention comprises a polyolefin-based elastomer. Preferably, the polyolefin-based elastomer is a copolymer of ethylene and α-olefin comonomer having <NUM> to <NUM> carbon atoms. The use of such ethylene copolymer leads to a better flexural modulus of the composition according to the invention than the use of an ethylene-propylene copolymer as the polyolefin-based elastomer.

The α-olefin comonomer in the elastomer preferably has <NUM> to <NUM> carbon atoms and is preferably an acyclic monoolefin such as <NUM> -butene, <NUM> - pentene, <NUM> -hexene, <NUM> -octene, or <NUM>-methyl-<NUM> -pentene. Most preferably, the elastomer is an ethylene-<NUM>-octene copolymer.

Preferably, the elastomer has a density of <NUM> to <NUM>/cm<NUM>. Preferably, the density of the first elastomer is <NUM> to <NUM>/cm<NUM>, <NUM> to <NUM>/cm<NUM> or <NUM> to <NUM>/cm<NUM>.

The elastomers may be prepared using methods known in the art, for example by using a single site catalyst, i.e., a catalyst the transition metal components of which is an organometallic compound and at least one ligand of which has a cyclopentadienyl anion structure through which such ligand bondingly coordinates to the transition metal cation. This type of catalyst is also known as "metallocene" catalyst. Metallocene catalysts are for example described in <CIT> and <CIT>. The elastomers may also be prepared using traditional types of heterogeneous multi-sited Ziegler-Natta catalysts.

The elastomer has a melt flow index min measured according to ASTM D1238 with a <NUM> load and at a temperature of <NUM> of <NUM> to <NUM> dg/min, preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min. This leads to a combination of good mechanical properties for making luggage cases, such as good stress whitening resistance, gloss, impact strength and tensile properties.

Preferably, the amount of (C) the elastomer with respect to the composition of the invention is <NUM> to <NUM> wt%, <NUM> to <NUM> wt%, <NUM> to <NUM> wt% or <NUM> to <NUM> wt%. This leads to the suitable total rubber amount to achieve good mechanical properties of the composition according to the invention together with the dispersed phase of the heterophasic propylene copolymer.

The total amount of (a2) and (C) with respect to the total composition is <NUM> to <NUM> wt%, preferably <NUM> to <NUM> wt%, more preferably <NUM> wt% to <NUM> wt%.

The composition according to the invention may optionally comprise additives. The additives may include nucleating agents, stabilizers, e.g. heat stabilisers, anti-oxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame-retardants; mould-release agents; flow improving agents; plasticizers; anti-static agents; blowing agents.

The skilled person can readily select any suitable combination of additives and additive amounts without undue experimentation. The amount of the additives depends on their type and function and typically is of from <NUM> to about <NUM> wt%. The amount of the additives may e.g. be from about <NUM> to about <NUM> wt%; from about <NUM> to about <NUM> wt% or from <NUM>. <NUM> to about <NUM> wt% based on the total composition. The total amount of (A), (B), (C) and (D) should add up to <NUM>% by weight. Preferably, the total of components (A), (B) and (C) is at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt%, at least <NUM> wt% or <NUM> wt% of the total composition.

The composition has a melt flow index as measured according to ISO1133-<NUM>:<NUM> with a <NUM> load at <NUM> of <NUM> to <NUM> dg/min, preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min, more preferably <NUM> to <NUM> dg/min.

The composition of the invention may be obtained by a process comprising melt-mixing (A), (B), (C) and optionally (D) by using any suitable means. Accordingly, the invention further relates to a process for the preparation of the composition according to the invention comprising melt mixing (A), (B), (C) and optionally (D).

Preferably, the composition of the invention is made in a form that allows easy processing into a shaped article in a subsequent step, like in pellet or granular form. The composition can be a mixture of different particles or pellets; like a blend of (A), (B), (C) and a masterbatch of additives. Preferably, the composition of the invention is in pellet or granular form as obtained by mixing all components in an apparatus like an extruder; the advantage being a composition with homogeneous and well-defined concentrations of the additives.

Melt-mixing may be done using techniques known to the skilled person, for example in an extruder. Generally, in the process of the invention, melt-mixing is performed at a temperature in the range of <NUM> to <NUM>.

Suitable conditions for melt-mixing, such as temperature, pressure, amount of shear, screw speed and screw design when an extruder is used are known to the skilled person.

The composition according to the invention may be processed by known processing methods, in particular injection molding.

The invention further relates to an article comprising the composition according to the invention, in particular a luggage case. In particular, the invention relates to an injection molded article comprising or made from the composition according to the invention, in particular a luggage case.

In particular, the invention relates to an injection molded article comprising or made from the composition according to the invention, in particular a luggage case having a capacity of <NUM> to <NUM>, for example <NUM> to <NUM>.

It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

It is further noted that the term 'comprising' does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. 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 process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

The invention is now elucidated by way of the following examples, without however being limited thereto.

The components as shown in Tables <NUM> and <NUM> were melt-mixed to obtain compositions as shown in Tables <NUM> and <NUM>.

The properties of the compositions were measured as follows and are shown in Tables <NUM> and <NUM>.

Mould shrinkage (%), in the context of this invention called shrinkage, is the amount of contraction that a moulded part undergoes when it is removed from the mould cavity and cooled at room temperature. Shrinkage was measured according to ISO <NUM>-<NUM> on <NUM> x <NUM> x <NUM> injection moulded plaques after a conditioning time of <NUM> after moulding at room temperature (<NUM>) and <NUM> % relative humidity. Each of the samples was moulded using the same conditions at the moulding achine. Shrinkage measured in the flow length and perpendicular to the flow is reported here. Following equation was used to determine shrinkage: <MAT> wherein Lm is the length of the mould in the considered direction, and Ls is the length of the specimen in considered direction. A shrinkage in the flow direction, a shrinkage in the perpendicular direction to flow direction, as well as an average (arithmetic) of both shrinkage values is reported.

Stress whitening is the appearance of a white area on an object when the object is stressed after a blushing operation. The appearance of the white area indicates that there is an onset of failure of the corresponding material. The blushing on the samples was created according to PV3905, by dropping a solid stainless steel ball (<NUM> (<NUM> ± <NUM>) mm) of <NUM> (± <NUM>) grams from a height of <NUM> on a test piece with dimension <NUM>*<NUM>*<NUM> injected on the machine SE180. Photos of these test pieces were taken with a scanner (EPSON, V850 Pro) under the professional mode. For the scanning parameters, positive film was selected for the film type, image type was b-bit grayscale, resolution was <NUM> dpi, and the document size was <NUM> * <NUM> inch. In addition, no histogram adjustment was employed during the scanning process.

The image analysis is performed at MATLAB 2020a platform in order to determine values of the parameter " spot size" (area).

The spot size (area) was determined as follows:
The total whiteness of the whole photo is calculated as the sum of the whiteness of each pixel in the whole photo. The whiteness of the intrinsic material is defined as <NUM>. Each pixel constituting the sample has a whiteness of <NUM>-<NUM>. The spot size is defined as the size of the area which has <NUM>% of the whiteness of the whole photo.

Integrated Intensity:
an integrated intensity with regard of the area Σ I x Δx x Δy. The intensity has been normalized via subtracting the median intensity of the surroundings.

The compositions were injection molded at <NUM> into a luggage case having dimensions of <NUM> x <NUM> x <NUM> according to QBT <NUM>-<NUM> and its properties were measured as follows and are shown in Tables <NUM> and <NUM>.

Up/Down test: QBT <NUM>-<NUM> (Case and bag - Test method for shaking impact). Indicated as pass when there is no unacceptable damage after <NUM> times. Rolling test: QBT <NUM>-<NUM> (Case and bag. Test method for rotary drum). Indicated as pass when there is no unacceptable stress whitening. Gloss: visual inspection, determined as pass if a high gloss is observed
Drop ball impact: QBT <NUM>-<NUM> (Case and bag. Test method for fall down), tested at -<NUM>, <NUM>. Indicated as pass if no crack detected
Drop test: QBT <NUM>-<NUM>-T (Case and bag - Test method for impact resistance by means of falling weight), Indicated as pass if no crack detected.

The composition of Ex <NUM> according to the invention shows a combination of good impact strength, tensile properties, flexural properties, shrinkage, gloss and stress whitening property, and a luggage case made from the composition of Ex <NUM> passed all relevant tests for a luggage case.

The composition of CEx E could not be injection molded into a luggage case having the specified dimensions at a temperature of <NUM>. It can thus be understood that the low MFI of the total composition leads to difficulty in injection molding. Further, as can also be understood from CEx C and D, it leads to a bad stress whitening property.

From the comparison of Ex <NUM> versus CEx A and CEx B, it can be understood that the use of the elastomer having a high MFI according to the invention leads to a better gloss and a better stress whitening property.

From the comparison of Ex <NUM> versus CEx C and CEx D and, it can be understood that the use of the homopolymer having a high MFI according to the invention leads to a better stress whitening property.

The compositions shown in Table <NUM> made using an HDPE instead of a propylene homopolymer do not show satisfactory stress whitening properties. The gloss properties are also not satisfactory.

From the comparison of CEx F, CEx G, CEx H and CEx I, it can be understood that when the total rubber amount is too high, the tensile modulus and tensile strength become too low and the luggage case made from the composition does not pass the up/down test and the rolling test and has low gloss.

Claim 1:
A composition comprising (A) a heterophasic propylene copolymer, (B) a propylene homopolymer and (C) a polyolefin-based elastomer, wherein
(A) the heterophasic propylene copolymer consists of (a1) a propylene-based matrix, wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least <NUM> wt% of propylene monomer units and at most <NUM> wt% of ethylene and/or a- olefin monomer units, based on the total weight of the propylene-based matrix and (a2) a dispersed ethylene-α-olefin copolymer, wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer is <NUM> wt%,
(C) the polyolefin-based elastomer has a melt flow index of <NUM> to <NUM> dg/min measured according to ASTM D1238 with a <NUM> load at <NUM>,
the total amount of (a2) and (C) with respect to the total composition is <NUM> to <NUM> wt% and
the composition has a melt flow index as measured according to ISO1133-<NUM>:<NUM> with a <NUM> load at <NUM> of <NUM> to <NUM> dg/min.