Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-11-27
2004-10-05
Choi, Ling Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348000, C526S351000, C526S124100, C526S124300, C526S123100
Reexamination Certificate
active
06800710
ABSTRACT:
The present invention relates to sheets for thermoforming based on a particular kind of propylene polymer or polymer composition.
Compared to sheets made of propylene homopolymers and copolymers with similar MFR, the sheets of the invention provide a better balance of processing characteristics and physical properties of the thermoformed items made therefrom. Thus, at the same or lower processing temperatures, the thermoformed items exhibit improved properties such as stiffness and impact resistance.
Therefore the present invention provides polypropylene sheets for thermoforming wherein at least one layer comprises a propylene polymer containing at least 0.8% by weight of ethylene and, optionally, one or more C
4
-C
10
&agr;-olefins, or a propylene polymer composition containing at least 0.8% by weight of one or more comonomers selected from the group consisting of ethylene and C
4
-C
10
&agr;-olefins, and having the following features:
I) a melting temperature of 155° C. or higher; and
II) a xylene soluble fraction at room temperature (about 25° C.) lower than 4% by weight, preferably lower than 3% by weight, more preferably lower than 2.5% by weight, and a value of the ratio of the polymer fraction collected at the temperature range from 25° C. to 95° C. (by TREF: temperature rising elution fractionation with xylene) to the said xylene soluble fraction, higher that 8 wt %/wt %, preferably higher than 10 wt %/wt %, more preferably higher than 12 wt %/wt %.
In a preferred embodiment, at least one layer is substantially made of the said propylene polymer or propylene polymer composition.
The said propylene polymer is a random copolymer (I) containing such an amount of comonomer(s) as to have a melting temperature (measured by DSC, i.e. Differential Scanning Calorimetry) of 155° C. or higher. When only ethylene is present as the comonomer, it is generally within 0.8 and 1.5% by weight with respect to the weight of the polymer. When C
4
-C
10
&agr;-olefins are present, they are generally within 1 and 4 wt % by weight with respect to the weight of the polymer.
Particularly preferred is a propylene polymer composition (II) comprising a first propylene (co)polymer (where the copolymer is a random copolymer) with an ethylene content between 0 and 1.5% by weight, and a second propylene random copolymer with an ethylene content between 0.8 and 5% by weight, the weight ratio of the second copolymer to the first (co)polymer being in the range from about 20:80 to about 80:20, preferably from 30:70 to 70:30, and the difference in the ethylene content between the two being preferably from 1 to 4 percentage units with respect to the weight of the (co)polymer concerned; or another propylene polymer composition (II) comprising a first propylene (co)polymer (where the copolymer is a random copolymer) with a comonomer content between 0 and 2% by weight, and a second propylene random copolymer with a comonomer content between 1.5 and 12% by weight, the weight ratio of the second copolymer to the first (co)polymer being in the range from about 20:80 to about 80:20, preferably from 30:70 to 70:30, and the difference in the comonomer content between the two being preferably from 1.5 to 10 percentage units with respect to the weight of the (co)polymer concerned, wherein the said comonomer is selected from C
4
-C
10
&agr;-olefins and mixtures thereof, with ethylene optionally being present. Preferably the Melt Flow Rate (MFR according to ISO 1133, 230° C., 2.16 Kg load) of the said propylene polymer or polymer composition goes from 1 to 10 g/10 min., more preferably from 1 to 4 g/10 min.
Other preferred features for the compositions to be used for the sheets the present invention are:
Polydispersity Index (PI): from 3.0 to 7, more preferably from 3.8 to 6.
The MFR values of the first propylene (co) polymer in composition (II) and of the second propylene random copolymer in composition (II) can be similar or substantially different.
In a particular embodiment of the present invention the MFR value of the first propylene (co)polymer is lower than that of the second propylene random copolymer and the difference in the MFR values being preferably greater than 5 g/10 min.
The C
4
-C
10
&agr;-olefins, that may be present as comonomers in the said propylene polymer or polymer composition, 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 polymerization in one or more 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 invention are capable of producing polypropylene with an Isotacticity Index greater than 90%, preferably greater than 95%. Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in U.S. Pat. No. 4,399,054 and European patent 45977. Other examples can be found in U.S. Pat. No. 4,472,524. The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and/or S atoms, and esters of mono- and dicarboxylic acids.
Particularly suitable electron-donor compounds are 1,3-diethers of formula:
wherein R
I
and R
II
are the same or different and are C
1
-C
18
alkyl, C
3
-C
18
cycloalkyl or C
7
-C
18
aryl radicals; R
III
and R
IV
are the same or different and are C
1
-C
4
alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5, 6, or 7 carbon atoms, or of 5-n or 6-n′ carbon atoms, and respectively n nitrogen atoms and n′ heteroatoms selected from the group consisting of N, O, S and Si, where n is 1 or 2 and n′ is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatoms as substitutes for carbon or hydrogen atoms, or both.
Ethers of this type are described in published European patent applications 361493 and 728769.
Representative examples of said diethers are 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl- 1,3-dimethoxypropane, 2-isopropyl-2-isoamyl-1,3-dimethoxypropane, 9,9-bis(methoxymethyl)fluorene. Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.
The preparation of the above mentioned catalyst components is carried out according to various methods.
For example, a MgCl
2
.nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiCl
4
containing the electron-donor compound. The reaction temperature is generally
Lonardo Angelo
Mei Gabriele
Pelliconi Anteo
Basell Poliolefine Italia S.p.A.
Choi Ling Siu
LandOfFree
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