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
2001-08-13
2003-04-01
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...
C525S240000
Reexamination Certificate
active
06541570
ABSTRACT:
The present invention concerns compositions of random copolymers of propylene with one or more C
4
-C
10
-&agr;-olefins, and the process to obtain the said compositions. The present invention also relates to articles produced by using the cited compositions.
Articles whose production requires the use of high temperatures can be prepared with the polyolefin compositions of the present invention. For example, certain types of laminate articles, i.e. sheet and film, require such an operative condition. As a particular example, the said copolymer compositions are suitable for the production of metallized articles, more in particular metallized films. The films can be either monolayer or multilayers. The said compositions can, therefore, be useful for the production of metallized single-layer and multilayer films.
Articles produced with the compositions of the present invention are particularly suitable for being employed in the food industry because of their low content of component soluble in xylene at room temperature. Therefore, the said articles can be used in the food packaging field.
Polyolefin compositions comprising a mixture of two or three copolymers of propylene with an &agr;-olefin, mainly 1-butene, are already known. The said prior art compositions are suitable for the production of low-temperature heat-sealable films.
For example, U.S. Pat. No. 4,211,852 describes a thermoplastic olefin resin composition made up of a poly(propylene-co-butene-1) with at least 15 mole % of recurring units deriving from 1-butene and a copolymer of propylene with ethylene or 1-butene containing up to 10 mole % of recurring units deriving from the comonomer. However, in examples the compositions made up of two copolymers do not contain two polymers of the type poly(propylene-co-butene-1) and the 1-butene content in the poly(propylene-co-butene-1) is about 35% by weight.
European patent application 560 326 also describes a thermoplastic olefin resin composition comprising a random poly(propylene-co-butene-1) with from 1 to 10 wt % of recurring units deriving from 1-butene and a random poly(propylene-co-butene-1) containing from 15 to 40 wt % of recurring units deriving from 1-butene.
European patent application 719 829 describes polyolefin compositions comprising a mixture of three copolymers of propylene with an &agr;-olefin, mainly 1-butene. At least one copolymer contains a high amount of comonomer (25% by weight or more). Films prepared with the described compositions have low values of heat-sealing temperature as shown by the working examples wherein the films have a value of the heat-sealing temperature of 92° C. or less.
Although the cited prior art compositions have a high melting temperature, they are not suitable for being metallized. The main drawback of the said compositions is due to a too high amount of polymer fraction with a low crystallinity thanks to which the films obtained from the said prior art compositions are low-temperature heat-sealable.
The applicant has now found new compositions that have a high melting temperature and VICAT value. The said properties enable the polymer to be subjected to high temperatures such as those required in metallization process.
A particular advantage of the copolymer compositions of the present invention is that they have a low solubility in xylene at room temperature and can have a good transparency. The said properties are particularly desirable in the food industry.
The compositions of the present invention, moreover, have a rather high rigidity. Thanks to the said property, films with a homogenous thickness are produced.
Therefore, the present invention provides a semicrystalline polyolefin composition comprising (all percentages by weight):
a) 25-40%, preferably 28-38%, of a random copolymer of propylene with at least one comonomer selected from C
4
-C
10
, &agr;-olefins, containing from 2 to 10% of recurring units deriving from the comonomer;
b) 25-40%, preferably 26-36%, of a random copolymer of propylene with at least one comonomer selected from C
4
-C
10
&agr;-olefins, containing from 10 to 20% of recurring units deriving from the comonomer;
c) 25-40%, preferably 28-38%, of a random copolymer of propylene with at least one comonomer selected from C
4
-C
10
&agr;-olefins containing from 6 to 12% of recurring units deriving from the comonomer;
where the total content of recurring units from the said comonomer, referred to the composition, is equal to or higher than 6% and the respective percentages representing the content of the said recurring units in each one of copolymers a), b) and c) are different from each one of the other two, said difference with respect to the percentage of recurring units in each one of the other two copolymers being of at least 1 unit, preferably 1.5 units.
From the above definitions it is evident that the term “copolymer” includes polymers containing more than one kind of comonomers.
Examples of said C
4
-C
10
&agr;-olefins are 1-butene, 1-pentene, 1-hexene, 1-octene and 4-methyl-1-pentene. Particularly preferred is 1-butene.
The preferred semicrystalline polyolefin compositions are those where the comonomer of copolymers (a), (b) and (c) is the same.
The said composition has, typically, a seal initiation temperature (SIT) from 110° C. to 120° C. The VICAT value is generally from 115 to 140° C., preferably 125-135° C.
The said composition, moreover, has generally values of heat distortion temperature (HDT) ranging from 65 to 75° C.
Moreover it has generally values of flexural elastic modulus ranging from 900 to 1300 MPa, preferably 950-1250 MPa. The haze value is generally 40% or less determined on a 1 mm-thick plaque. The melt flow rate (condition L) value is generally from 0.1 to 100 g/10 min. The above properties are determined according to the methods described in the examples.
The composition of the present invention can by prepared by the known methods.
One method is by mechanically blending of copolymers (a), (b) and (c) in the molten state. The blending process is, therefore, carried out at the melt temperature of the copolymers or above.
The preferred method is by way of sequential polymerisation of the monomers in the presence of a catalyst, such as stereospecific Ziegler-Natta catalysts.
The sequential polymerisation is carried out in at least three separate and subsequent stages, wherein copolymers (a), (b) and (c) of the present invention are prepared. In each stage subsequent to the first stage the polymerisation takes place in the presence of the polymer obtained and the catalyst used in the preceding stage. It is preferred to prepare first the random copolymer containing the lowest amount of comonomer and than the other two copolymers.
The polymerisation process can be carried out in liquid phase, in the presence or absence of inert solvent, or in gas phase, or using mixed liquid and gas phases. Preferably the polymerisation is carried out in gas phase.
The regulation of the molecular weight is done by using known regulators, preferably hydrogen.
The polymerisation can be preceded by a prepolymerisation step where the catalyst is caused to contact with small quantities of olefins.
The previously said Ziegler-Natta catalysts comprise a solid catalyst component and a cocatalyst. The solid catalyst component comprises a titanium compound having at least one titanium-halogen bond and an electron-donor compound (internal donor), supported on a magnesium dihalide in active form. The magnesium dihalide support is preferably in the form of spheroidal particles having a narrow particle size distribution.
The internal donor is generally selected from ethers, ketones, lactones, compounds containing N, P and/or S atoms and esters of mono- and dicarboxylic acids. Particularly suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.
Other electron-donor compounds particularly suitable are 1,3-diethers of formula:
(R
I
)(R
II
)C(CH
2
OR
III
)(CH
2
OR
IV
)
wherein R
I
and R
II
are the same or different and are C
1
-C
18
alkyl,
Beccarini Enrico
Pelliconi Anteo
Basell Poliolefine Italia S.p.A.
Nutter Nathan M.
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