Polypropylene for the production of thermoformed articles, large, deep, complex and/or thick articles, process for thermoforming modified polypropylene into large, deep, complex and/or thick articles and use of the polypropylene

Abstract

The present invention is directed to a modified polypropylene comprising from 0.3 to 2 long-chain branches per 1,000 carbon atoms, wherein said long-chain branch has more than 1,000 carbon atoms and 0 to 6% of ethene and/or alpha-olefinic comonomer having 3 to 18 carbon atoms. The polypropylene of the present invention is a homopolymer, a random copolymer, or a heterophasic copolymer. The present invention also relates to large, deep, complex and/or thick articles which are thermoformed from said polypropylene. Furthermore, the present invention relates to the process for thermoforming said modified polypropylene into large, deep, complex and/or thick articles. The present invention also relates to the use of the polypropylene to prepare large, deep, complex and/or thick articles.

Claims

1. A modified heterophasic copolymer polypropylene for the preparation of thermoformed articles, obtained by modification via reactive extrusion of a polypropylene comprising from 0% to 6% of a comonomer in the synthesis thereof, a rubber phase comprising propene and at least one alpha-olefin or ethene comonomer at a ratio of 3 to 70% by weight and having 3 to 18 carbons, wherein the modified heterophasic copolymer polypropylene comprises from 0.3 to 2 long-chain branches per 1,000 carbon atoms, a MFR greater than 1.5 g/10 min, a melt strength of between 12 cN and 40 cN at 190, an extensibility greater than 11 cms/s and an impact strength higher than 100 J/m at room temperature, characterized in that comonomers selected from the group consisting of aminosilanes, silanes or alpha-beta unsaturated acids can be added in the modification step.

2. The modified heterophasic copolymer polypropylene of claim 1, wherein the polypropylene has from 0.4 to 3% by weight of comonomer in the synthesis thereof.

3. The modified heterophasic copolymer polypropylene of claim 1, wherein the polypropylene has from 0.6 to 1.8% by weight of comonomer in the synthesis thereof.

4. The modified heterophasic copolymer polypropylene of claim 1, wherein the modified heterophasic copolymer polypropylene is supplemented with a flow adjuvant, lubricants, antistatic agents, clarifying agents, nucleating agents, beta-nucleating agents, slippage agents, antioxidants, antacids, HALS, IR absorbers, fillers such as silica, titanium dioxide, silicon dioxide, organic and/or inorganic dyes.

5. The modified heterophasic copolymer polypropylene of claim 1, characterized by being obtained from renewable sources.

6. Large, deep, complex and/or thick articles, characterized in that said articles are prepared by thermoforming the modified heterophasic copolymer polypropylene of claim 1, wherein said articles have a formation area greater than 400 cm.sup.2.

7. The articles of claim 6, wherein said articles have a linear thermoforming ratio greater than 1.5, with sheet thicknesses greater than 0.8 mm.

8. The articles of claim 6, wherein said articles have a H:D thermoforming ratio greater than 0.3, with sheet thicknesses greater than 0.9 mm and final articles greater than 1,600 cm.sup.2.

9. The articles of claim 6, wherein said articles are for application to automotive vehicles in bumpers, instrument panels, seats, backrests, glove compartment doors, center console, door protectors, door stanchions, fluid reservoirs, tire protectors and fenders.

10. The articles of claim 6, wherein said articles are for application in refrigerators and freezers, as counter-doors, internal cases, fluid reservoirs and evaporators.

11. The articles of claim 6, wherein said articles are for use in other household appliances including air conditioners, dishwashers, laundry machines, TVs and vacuum cleaners.

12. The articles of claim 6, wherein said articles are for application in furniture, tractors, garden tractors, trucks and buses.

13. The articles of claim 6, wherein said articles are for application in electronic equipment, including TVs, DVDs, sound systems, home-theaters, notebooks, netbooks and desktops.

14. A process for thermoforming modified polypropylene, comprising the steps of: molding a sheet of modified heterophasic copolymer polypropylene of claim 1; applying atmospheric vacuum to the molding, with or without the aid of specific tools or techniques/methods; and obtaining large, deep, complex and/or thick articles.

Description

BRIEF DESCRIPTION OF DRAWING

(1) FIG. 1Scheme of sag analysis of polypropylene sheets

(2) FIG. 2Sag behavior of several homopolymers

(3) FIG. 3Description of the stage of deformation in sag analysis

(4) FIG. 4Sag comparison of polypropylenes having different molar mass distributions

(5) FIG. 5Effect of a beta-nucleating agent on sag resistance of polypropylenes

(6) FIG. 6Modification in homopolymerschange in the behavior of branched polypropylenes

(7) FIG. 7Sag behavior of copolymers

(8) FIG. 8Effect of the rubber content on sag resistance

(9) FIG. 9Change in sag behavior for copolymers having high MFR

(10) FIG. 10Change in the behavior of copolymers having moderate MFR

(11) FIG. 11Comparison with polypropylenes usually employed in the thermoforming of large, deep, complex and/or thick articles.

(12) FIG. 12Viscosity curves of polypropylenes usually employed in the thermoforming of large, deep, complex and/or thick articles.

DETAILED DESCRIPTION OF THE INVENTION

(13) The present invention is directed to a modified polypropylene which can be obtained from renewable sources, said polypropylene being a homopolymer, a random copolymer, or a heterophasic copolymer modified to be better suited to the thermoforming process by inserting long-chain branches onto the polypropylene matrix phase. In context of the present invention, by long-chain branches it is meant branches containing more than 1,000 carbon atoms.

(14) Said branches can be introduced onto the polypropylene, for example, by one or more of the following methods: Reactive extrusion: by the addition of peroxides free radicals are generated which recombine in the polypropylene in the form of backbone branches. Radical generators can be azo peroxide compounds capable of generating these radicals, such as dicetyl peroxide dicarbonate; Ionizing radiation: electron beam bombardment or gamma radiation generate radicals that recombine in the form of polypropylene branches; and Crosslinking: Crosslinking agents such as silanes are grafted into the polypropylene chains and they are subjected to a controlled crosslinking process thus generating final conditions of a branched structure.

(15) Mixture and variations in and between the aforementioned usual methods for introducing branches into the polypropylene can occur, such as reactive extrusion with crosslinking agents, but as variations of the same process. In addition, the introduction of branches into the polypropylene according to the present invention can be performed by any other method allowing for the introduction of long-chain branches.

(16) Such introduction of long-chain branches results in the presence of 0.3 to 2 long-chain branches per 1,000 carbon atoms, where the matrix can have from 0 to 6% by weight of comonomer and ethene and alpha-olefin comonomers of from 3 to 18 carbon atoms, and where there is a rubber phase, said phase comprises polypropylene and at least one more ethene and/or alpha-olefin comonomer at a ratio of 3 to 70% by weight ethene plus alpha-olefin, the alpha-olefin comonomers having from 3 to 18 carbons.

(17) In another embodiment, said matrix can have from 0.4 to 3% by weight comonomer, preferably, from 0.6 to 1.8% by weight comonomer.

(18) In the polypropylene that is a modified heterophasic copolymer the rubber phase has a random polypropylene matrix.

(19) Aminosilanes, silanes, acrylates, methacrylates, alpha-beta unsaturated acids and the like can be introduced as comonomers into the polypropylene used in the present invention.

(20) Further, the present invention is directed to large, deep, complex and/or thick articles prepared from thermoforming of the modified polypropylene of the present invention, a large article being understood as that having a formation area greater than 400 cm.sup.2, a deep article being the one having a linear thermoforming ratio greater than 1.5 or a thermoformed area ratio greater than 2 or a H:D thermoforming ratio greater than 0.3, a complex article being the one having lots of deep details and angles, and the thick article being the one obtained using sheets having a thickness greater than 0.8 mm.

(21) Preferably, articles resulting from the thermoforming in accordance with the present invention exhibit a thermoforming area ratio greater than 2, sheet thicknesses greater than 0.8 mm and final articles greater than 400 cm.sup.2.

(22) More preferably, said articles exhibit a H:D thermoforming ratio greater than 0.3, with sheet thicknesses greater than 0.9 mm and final articles greater than 1,600 cm.sup.2.

(23) Preferably, the following components can be added to the polypropylene of the present invention: flow adjuvants, lubricants, antistatic agents, clarifying agents, nucleating agents, beta-nucleating agents, slippage agents, antioxidants, antacids, HALS, IR absorbers, fillers such as silica, titanium dioxide, silicon dioxide, organic and/or inorganic dyes and the like.

(24) The polypropylene of the present invention can be a homopolymer having MFR greater than 3.5 g/10 min, a melt strength of between 15 cN and 35 cN at 190 C. and an extensibility greater than 11 cm/s.

(25) Furthermore, the polypropylene of the present invention can be a random copolymer having MFR greater than 2.0 g/10 min, a melt strength greater than 15 cN at 190 C. and an extensibility greater than 11 cm/s.

(26) In addition, the polypropylene of the present invention can be a heterophasic copolymer having MFR greater than 1.5 g/10 min, a melt strength of between 12 cN e 40 cN at 190 C., an extensibility greater than 11 cm/s and impact strength greater than 100 J/m at room temperature.

(27) Polypropylenes of the present invention are thermoformed into large, deep, complex and/or thick articles for application to automotive vehicles such as in bumpers, instrument panels, seats, backrests, glove compartment doors, center console, door protectors, door stanchions, fluid reservoir, tire protectors, fenders, and the like.

(28) Furthermore, the polypropylenes of the present invention are thermoformed into large, deep, complex and/or thick articles to be used in refrigerators and freezers as counter-doors, cases, fluid reservoirs, evaporators and the like.

(29) An additional use is in articles for other household appliances such as air conditioners, dishwashers, laundry machines, TVs, vacuum cleaners and the like.

(30) Moreover, polypropylenes of the present invention are thermoformed into large, deep, complex and/or thick articles to be used in furniture, tractors, garden tractors, trucks, buses and the like. Also, they can be used in electronic equipment, such as TVs, DVDs, sound systems, home-theaters, notebooks, netbooks, desktops, and the like.

(31) In addition, the present invention relates to the process of thermoforming said modified polypropylene into large, deep, complex and/or thick articles, comprising the steps of: molding a sheet of the modified polypropylene of the present invention; applying atmospheric vacuum to the molding, with or without the aid of specific tools or techniques/methods; and obtaining large, deep, complex and/or thick articles.

(32) The present invention also relates to the use of modified polypropylene to prepare large, deep, complex and/or thick articles.

EXAMPLES

Polypropylene Preparation

(33) Polypropylenes were prepared in a pilot plant and compared with industrial products listed in tables 1 and 2. H stands for polypropylene homopolymers and CP stands for copolymers. The following number relates to the MFR of the samples.

(34) Polypropylene Modification

(35) The modification was carried out in a laboratory extruder ZSK-26 by adding peroxide having high polypropylene reactivity and extruded at a suitable temperature and inertization profile at temperatures of between 160 and 250 C. Both the peroxide and the polypropylene were pre-mixed in an intensive mixer and gravimetrically dosed with N.sub.2 inertization. The peroxide level used was designated as MOD I and MOD II, where the latter was at a higher concentration than the former, the concentrations being in a range of from 0.01 to 5%.

(36) Measurement Methodology

(37) Rheological analysis was carried out at 200 C. in a controlled stress rotational rheometer using a plate/plate geometry in wafers previously pressed for 5 minutes at 200 C. and assessed in a MCR-501 equipment from Antoon Paar at 200 C. with a stress within the linear viscoelasticity regime. Sag tests (resistance to its own weight) were carried out according to the method where a 1.3-mm thick, 100-cm wide, 160-mm long plate pressed at 200 C. for 5 minutes and cooled down to 20 C./min is placed onto a specific, bottom-graduated support at a temperature of 190 C. The oven used was that from Instron tensile equipments with electronic control and convection heating. The time needed for the plate to reach deformations of 10 to 100 mm is collected and results are plotted, as shown in FIG. 1. The measured time for the surface of the sheet to reach a temperature of 190 C. was 120 s. Initial phases of the curve are related to melting of the polypropylene and the following regions represent the sag resistance of the polypropylene. The less the polypropylene weakens with time, the better its thermoformability, that is, the less the slope of the curve, the better the characteristic. Melt strength tests were performed using a Gttfert, Rheotens 71.97 rheometer coupled to the Haake extruder at a temperature of 190 C., a 2-mm thick capillary and L/D of 20. Acceleration applied to the drawing pulley was 60 mm/s.sup.2 and the distance from the capillary outlet was 60 mm.

(38) Eta(0) values were calculated using the Carreau equation, the value for the deformation rate being zero, as shown in the equation below.
=.sub.0*[1+(.sub.e.Math.{dot over ()}).sup.a].sup.n.sup.1.sup./a

(39) wherein:

(40) is the viscosity of the polypropylene

(41) .sub.0 is the viscosity of the polypropylene at zero shear rate

(42) .sub.e, a and n are setting parameters

(43) {dot over ()} is the shear rate applied to the material

EXAMPLES

(44) In examples 1 to 4, polypropylene homopolymers having different molar masses and molar mass distribution were used. Description of non-modified polypropylenes is presented in Table 1 and their important thermoforming properties in Table 2.

(45) TABLE-US-00001 TABLE 1 Characteristics of the polypropylene homopolymer used Flexural Impact Solubles modulus at 23 Catalyst (%) (MPa) C. (J/m) Source H 3 Ziegler-Natta 4 1400 35 Industrial product (H 503) H 10 Ziegler-Natta 4 1200 25 Industrial product (H 301) H 1 Ziegler-Natta 4 1400 43 Industrial product (H 606) H 3-2 Phthalate <2 2300 21 Industrial product (H 501) H 3-2 Phthalate <2 2000 35 Industrial beta product (H 501) H 5 Not defined 2.3 1800 33 Product from pilot plant

(46) TABLE-US-00002 TABLE 2 Properties of important homopolymers for thermoforming MFR Eta (0) MS Ext (g/10 min) MWD (Pa .Math. s) (cN) (cm/s) Note H 3 3.5 4 10500 6.5 10.8 H 10 10 4 4218 3.0 10.1 H 1 1.5 4 22210 10.5 12.0 H 3-2 3.3 5.5 15350 9.5 8.6 H 3-2 beta 3.3 5.5 15350 9.4 8.7 Beta- nucleated H 5 5 7 17840 18.7 7.5 H 3 mod 1.5 6 61280 32 11.8 MOD II modified MFR is the melt flow rate of the polypropylene MWD is the rheological molecular weight distribution index. Eta(0) is the zero shear viscosity calculated using the Carreau model MS is the melt strength in cN Ext is the polypropylene extensibility at the maximum MS.

(47) Upon observing the effect of MFR of the polypropylene molecular weight on sag resistance, it is noted that higher molecular weights tend to reduce the terminal flow rate and then materials start to have utility in thermoforming processes.

Example 1

(48) FIG. 2 shows that polypropylenes tend to exhibit catastrophic deformation with the reduction in the molecular weight. In this case, the material will tend to provide little time to be heated and transferred to the thermoforming die, thereby not being industrially viable. As a skilled person knows, polypropylenes are applied in small articles in thermoforming and, where used, they are products having MFR of less than 5 g/10 min. In this case, a direct correlation between melt strength, Eta(0) and molar mass of polypropylenes, including the MFR of the polypropylene can be found.

(49) FIG. 3 shows that the limitation is given by the mechanism by which the polypropylene is deformed, where it has two distinct behaviors: 1) initial deformation regime and 2) catastrophic deformation regime.

(50) As is a characteristic of polypropylene, a suitable molar mass is required for thermoforming to take place, since a minimum time is needed for heating to occur without collapsing the sheet. Regime transition will be more accentuated with higher thicknesses, higher deformation stresses and lower molar masses of the polypropylene.

Example 2

(51) As outlined in FIG. 4, another effect observed was the polydispersity (DPM) of polypropylenes. The higher the DPM, the lower the slope of the terminal region of linear polypropylenes.

(52) With higher DPMs, polypropylenes have a larger number of molecules of higher weight having as a consequence larger number of entanglements. These entanglements tend to hold the structure, not enabling catastrophic deformation to occur in specific cases. However, based on data from table 1 it is possible to note that the same resistance generated renders linear polypropylenes to be of lower deformability, which is an obstacle to the use thereof in large, deep, complex and/or thick articles. Even with higher MFRs, H 5 polypropylene exhibits lower sagging rate than H3-2 and H3 because of the larger high weight fraction. The obstacle of this route is that polypropylenes with linear molecules of high molecular weight do not tend to have high extensibility, which makes thermoforming difficult, or for requiring a very high vacuum pressure or even preventing the formation of deep/detailed articles due to the absence of sufficient extensibility. It is demonstrated herein that polypropylene has characteristics that cause an improvement in its behavior, being an important variable in the modification process. Polypropylene features prior to modification are essential for one to achieve better performance and the modification on any polypropylene does not result in products suitable for thermoforming large, deep, complex and/or thick articles.

(53) In these cases, an excellent correlation between melt strength, Eta(0) and sag resistance can be observed, but the relationship with MFR becomes wrong.

Example 3

(54) By adding beta-nucleating agents to polypropylenes, one observes that a reduction in the melting temperature of the product by up to 10 C. makes it possible to process the material at lower temperatures, but sag resistance of the polypropylene is not changed, only presenting the same phenomenon shifted in time for lower values. With that, the only gain of beta nucleation is the reduction in the processing window by some degrees, but the application cannot be expanded to large, deep, complex and/or thick articles since the rheological properties of the product are not changed. There is no alteration of the polypropylene behavior in molten state, as identified in FIG. 5.

Example 4

(55) In FIG. 6, upon comparing polypropylenes having the same MFR, but one of them being linear and the other one being modified via reactive extrusion, one notes a striking modification of properties.

(56) The effect of the modification on the polypropylene renders the same suitable for thermoforming with a very slow deformation and without exhibiting a catastrophic regime. This kind of behavior allows for a broad control of the process. The effect of a small number of long-chain branches renders the polypropylene more suited to thermoforming, providing a time sufficient for a homogeneous heating process to occur, due to the high heat capacity of the polypropylene relative to other polymers such as ABS and HIPS, in addition to the knwon lower infra-red absorptive capacity and low thermal conductivity.

(57) For examples 5-10 different polypropylene copolymers were used with different rubber contents and MFRs. Viscosity of rubbers is roughly the same as well as the composition thereof.

(58) Products are listed in Tables 3 and 4.

(59) TABLE-US-00003 TABLE 3 Characteristics of the polypropylene copolymer Flexural Impact modulus at 23 Catalyst (MPa) C. (J/m) Source CP 4 Ziegler-Natta 990 NB Product from pilot plant CP 6-1 Phthalate 1600 70 Industrial product CP 6-2 Phthalate 1100 NB Industrial product CP 6-3 Ziegler-Natta 850 NB Industrial product CP 30 Ziegler-Natta 900 NB Industrial product CP 0.8 Ziegler-Natta 900 NB Industrial product NB considered by standard to be no-break

(60) TABLE-US-00004 TABLE 4 Important properties for thermoforming MFR Eta(0) MS Ext Rubber content CP 4 4 10560 3 10 Medium-high CP 6-1 6 6308 4.5 11.9 Low CP 6-2 6 4510 4.1 10.8 Medium CP 6-3 6 5966 2.6 9.7 High CP 30 30 1077 1 12.3 High CP 0.8 0.8 44460 46.9 10.3 Medium

Example 5Copolymers

(61) FIG. 7 shows homopolymers as well as two deformation regions. With the presence of a rubber phase, terminal phases tend to be smoothed but still exhibit catastrophic deformation. In the case of very low MFRs, a thermoforming-friendly product can be obtained, but it has high viscosity restrictions.

Example 6Rubber Content

(62) As seen in FIG. 8, there is a dependence upon the rubber content, but it is evident that CP 6-3 polypropylene seems to be less catastrophic while CP 6-1 polypropylene deforms more slowly. As it refers to a biphasic system, upon assessing only the MFR or final viscosity of copolymers, one notes the dependence of the rubber phase to catastrophic deformation and the greater operating time provided by a polypropylene having less rubber and consequent higher matrix viscosity so as to have the same MFR. Thus, it is possible to have polypropylene suited for the process only when there is a matrix of high viscosity and at least medium rubber contents. Behavior of CP 0.8 polypropylene and its possible application in thermoforming are thus explained.

(63) As one can see, e.g., in examples 2 and 6, polypropylene characteristics are very important to the process, wherein modification on any heterophasic copolymer polypropylene does not mean to make it better for thermoforming, which is dependent upon all the characteristics of the phases. One can note that only the presence of rubber or the content thereof does not transform polypropylene into a product more suited for thermoforming.

Example 7Modification on CP of High MFR

(64) The increase in MFR of the matrix by the modification improves the product response to sag to the point of having greater sag resistance than products of much lower MFRs, as seen in FIG. 9 and that the product of modification degree II with MFR of 9 g/10 min behaves similarly to products having MFR of 6. This significant change is due to the fact that polypropylene matrix is changed to contain long-chain branches and to support the elongational deformation created by the weight of the plates. It is evident that the mere evolution of a linear polypropylene does not mean that it is apt for thermoforming large, thick, deep and/or complex articles.

(65) TABLE-US-00005 TABLE 5 Table of rheological values of the modification of polypropylene copolymers having high MFR, according to FIG. 9. MFR Eta(0) MS Ext Modification CP 30 mod I 18 5345 1.7 11.5 MOD I CP 30 mod II 9.2 23370 4.3 14.5 MOD II CP 30 30 1077 1 12.3

Example 8Modification on Intermediate MFRs

(66) By modifying higher MFR polypropylene the behavior becomes entirely different, causing the polypropylene to be much more thermoforming-friendly.

(67) In FIG. 10, catastrophic regimens are no longer observed in polypropylenes, even with a high analysis time (15 min). It can be concluded that the modification renders the polypropylene friendly, even with MFR characteristics much higher than that of polypropylenes that could be initially used, as is the example of CP 0.8.

(68) TABLE-US-00006 TABLE 6 Table of rheological values of the modification of polypropylene copolymers having intermediate MFR. MFR Eta(0) MS Ext. Modification CP 4 4 10560 4.7 9.3 CP 4 Mod I 2.36 375000 7.3 11.8 MOD I CP 4 Mod II 1.85 506000 13.4 11.8 MOD II

(69) The modifying degree brings the products closer to intended behavior, where the material has enough strength to support its own weight for long periods of time for temperature homogenization and higher thicknesses.

Example 9Comparison with Polypropylenes Usually Employed in Thermoforming

(70) FIG. 11 shows sag resistance features of polypropylenes usually employed in thermoforming with polypropylenes modified herein for thermoforming applications.

(71) Table 7 depicts details of these surrogate polypropylenes relative to the comparison:

(72) TABLE-US-00007 TABLE 7 Comparison of properties with materials usually employed in thermoforming Eta(0) MS Ext (Pa .Math. s) (cN) (cm/s) HIPS 20670 9 14.2 ABS 206400 31.9 8.7 H1 22210 10.5 12.0 CP 0.8 44460 46.9 10.3 CP 4 MOD II 506000 13.4 11.8 CP 4 10560 3 10 Eta(0) is the zero shear viscosity calculated using the Carreau model MS is the melt strength in cN Ext is the polypropylene extensibility and stretching rate at the maximum MS.

(73) In addition to being a reliable, non-catastrophic polypropylene, one notes that the compared viscosity of this technology over usually employed products is lower, as can be seen in FIG. 12. With that, in addition to energetic gains, a gain in the production rate is also noted without loss in performance. This is due to the presence of branches on the polypropylene matrix thereby ensuring a gain in performance for materials of lower viscosities.