Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-01-18
2003-07-29
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C428S035700, C428S036920
Reexamination Certificate
active
06599986
ABSTRACT:
The present invention relates to new propylene polymer compositions having improved impact strength and excellent optical properties.
As is known, the isotactic polypropylene is endowed with an exceptional combination of excellent properties which render it suitable for a very great number of uses; however, it exhibits the drawback of possessing an insufficient impact strength. Attempts were made to obviate such drawback, either by properly modifying the synthesis process or by blending with rubbers.
The modifications to the synthesis process essentially consist in introducing into the propylene stereoregular homopolymerization process one or more copolymerization steps. In particular, it is known that for certain applications it is useful to decrease the crystallinity of the propylene homopolymer by copolymerization of the propylene with small quantities of ethylene and/or &agr;-olefins such as 1-butene, 1-pentene and 1-hexene. In this manner one obtains the so called random crystalline propylene copolymers which, when compared to the homopolymer, are essentially characterized by better flexibility and transparency.
These materials can be used in many application sectors, such as, for example irrigation pipes, pipes for transporting drinking water and other liquid food, heating equipments, single layer bottles (for detergents), multilayer bottles (for beverages and perfumes), single layer or multilayer film for various packaging and rigid food containers.
Propylene random copolymers, however, although they have good transparency, do not offer, especially at low temperatures, sufficiently better impact resistance than the homopolymer which can be satisfactory used for the applications listed above.
It has been known for a long time that the impact resistance of polypropylene can be improved by adding an adequate quantity of elastomeric propylene-ethylene copolymer to the homopolymers by mechanical blending or sequential polymerization. However, this improvement is obtained at the expenses of the transparency of the material.
To avoid this inconvenient, U.S. Pat. No. 4,634,740 suggests the blending of the polypropylene, in the molten state, with propylene-ethylene copolymers obtained with specific catalysts, and having an ethylene content ranging from 70 to 85% by weight. However, said compositions present transparency values (Haze) substantially comparable to those of the propylene homopolymer. Said patent, therefore, does not teach how to obtain compositions having good transparency.
In order to overcome the above mentioned disadvantages the Applicant has previously produced transparent polypropylene compositions offering impact resistance at low temperatures, which can be prepared directly in polymerization (sequential copolymerization). Said compositions, which constitutes the subject of published patent application EP-A-373660, comprise both a crystalline random propylene copolymer, and an elastomeric copolymer of ethylene with propylene and/or C
4
-C
8
&agr;-olefins containing from 20 to 70% by weight of ethylene. According to said patent application, the compositions mentioned above have a good balance of mechanical and chemical-physical properties due to the fact that the value of the content of ethylene of the elastomeric copolymer multiplied by the value of the ratio between the intrinsic viscosity (I.V.) of the elastomeric copolymer soluble in xylene at ambient temperature, and the one of the propylene random copolymer is comprised within a predetermined range.
Published European patent application EP-A-0557953, in the name of the Applicant, describes polyolefin compositions where one obtains a good balance of transparency, stiffness, and impact resistance even at low temperatures, by modifying a crystalline random copolymer of propylene with the proper quantities of a mechanical mixture comprising an elastomeric copolymer and one or more polymers chosen from LLDPE, LDPE and HDPE. In the U.S. Pat. No. 5,994,482 polypropylene alloys for fibers are described, containing two different propylene/ethylene copolymers.
New polypropylene compositions have now been found which have an optimum balance of transparency, stiffness and impact resistance even at low temperatures.
Thus the present invention provides propylene polymer compositions comprising (percent by weight):
A) from 70 to 90%, preferably from 75 to 85%, of a random copolymer of propylene with ethylene, containing from 1 to 6%, preferably from 1.5 to 4%, of ethylene, having a content of fraction insoluble in xylene at room temperature (about 23° C.) of not less than 93%, preferably not less than 94%;
B) from 10% to 30%, preferably from 15% to 25%, of a copolymer of propylene with ethylene, containing from 8 to 18%, preferably from 10 to 18%, of ethylene;
wherein the ratio (B)/C
2
B
of the percent by weight of (B), with respect to the total weight of (A) and (B), to the percent by weight of ethylene in (B), with respect to the total weight of (B), represented in the above formula by C
2
B
, is 2.5 or lower, preferably 2 or lower. The lower limit of said ratio is preferably 0.5.
The term “copolymer” includes polymers containing more than one kind of comonomers. In particular, in addition to ethylene, also one or more C
4
-C
10
&agr;-olefin(s) can be present, provided that components A) and B) remain miscible. In fact a preferred feature of the compositions of the present invention is that only one polymer phase (without substantial presence of other immiscible polymer phases) is detected by microscopy analysis. Other preferred features for the compositions of the present invention are:
MFR L (Melt Flow Rate according to ASTM 1238, condition L, i.e. 230° C. and 2.16 kg load) from 0.5 to 50, in particular from 0.5 to 10 g/10 min.; more preferably, in particular for the preparation of bottles and containers (extrusion blow molding), from 0.5 to 2.5, most preferably from 1 to 2.5, for example from 1 to 2 g/10 min.;
Polydispersity Index (PI): 5 or less, more preferably 4 or less;
Intrinsic Viscosity [&eegr;] of the fraction (of the overall composition) insoluble in xylene at room temperature: from 1.5 to 3, more preferably from 2 to 2.5 dl/g;
Intrinsic Viscosity [&eegr;] of the fraction (of the overall composition) soluble in xylene at room temperature: from 1 to 4.5, more preferably from 1.5 to 4 dl/g;
The compositions of the present invention present at least one melt peak, determined by way of DSC (Differential Scanning Calorimetry), at a temperature higher than 140-145° C. Moreover, the compositions of the present invention preferably have:
a Flexural Modulus of 600 MPa or higher;
Haze (measured on samples containing 2000 ppm DBS, i.e. di-benzylidenesorbitol): 12% or less on 1 mm plaques; 10% or less on 50 &mgr;m films;
Gloss (on films): 45% or more;
fraction extractable in hexane (FDA 177, 1520): less than 5%, more preferably less than 3% by weight;
fraction soluble in xylene at room temperature: less than 25%, more preferably less than 20%.
The said C
4
-C
10
&agr;-olefins, that may be present as comonomers in the compositions of the present invention, are represented by the formula CH
2
═CHR, wherein R is an alkyl radical, linear or branched, with 2-8 carbon atoms or an aryl (in particular phenyl) radical. Examples of said C
4
-C
10
&agr;-olefins are 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene. Particularly preferred is 1-butene.
The compositions of the present invention can be prepared by sequential polymerization in at least two polymerization steps. Such polymerization is carried out in the presence of stereospecific Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminum compound, such as an aluminum alkyl compound.
An external donor is optionally added.
The catalysts generally used in the process of the
Di Diego Maria
Huovinen Päivi Helena
Pelliconi Anteo
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
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