Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-12-05
2003-05-13
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S213000, C264S173150, C264S173190
Reexamination Certificate
active
06562478
ABSTRACT:
The present invention relates to a sealable coextruded film made from at least one outer layer and from at least one base layer, where the outer layer is composed of a propylene terpolymer comprising from 80 to 99.5 mol % of structural units derived from propylene, from 0.2 to 15 mol % of structural units derived from ethene or from a C
4
-C
6
1-olefin (I) and from 0.3 to 15 mol % of structural units derived from another C
4
-C
12
1-olefin (II) different from the C
4
-C
6
1-olefin (I), and where the propylene terpolymer has been prepared using metallocene catalysts.
The present invention also relates to a process for producing a sealable coextruded film, and also to packaging made from these sealable coextruded films.
Films made from polypropylene are widely applied in the packaging sector, where they have considerable industrial significance. This applies also, and in particular, to biaxially oriented polypropylene films (BOPP films). It is desirable in many cases here that the films should have good sealability, i.e. the films should be capable of being bonded to one another even at temperatures markedly below their crystalline melting point. It is particularly useful here for there to be a large difference between the sealing temperature required for this purpose and the crystalline melting point. Formulations which are widely used for achieving this are polypropylene coextruded films carrying outer layers with particularly low sealing temperatures. The propylene co- or terpolymers usually used here as sealable outer layer incorporate comonomers in order to lower both their crystalline melting point and the temperature required for sealing. As increasing amounts of comonomer are incorporated the sealing temperature reduces and therefore suitability as a sealing-layer material increases. However, at least in the case of conventional co- and terpolymers, i.e. those prepared with Ziegler-Natta catalysts, as comonomer content increases there is also a sharp rise in the proportion of low-molecular-weight constituents which are amorphous and therefore soluble in xylene at 25° C. This gives the polymer and film increasing tack and at the same time poorer organoleptic properties.
U.S. Pat. No. 4,692,379 describes a sealable film laminate which has a low coefficient of friction, good receptivity for water-based coatings and good optical clarity. The upper layer is composed of an ethylene-propylene copolymer or of a terpolymer or of a mixture, while the core layer is composed of polypropylene. A lower outer layer is composed of the material used for the upper outer layer. The terpolymer is composed of 1-butene, 3.6% by weight of ethene and from 86 to 93% by weight of propylene. No mention is made of metallocene catalysts.
Compared with conventional copolymers, propylene copolymers prepared with metallocene catalysts have a significantly lower proportion of xylene-soluble constituents and therefore have particular suitability as sealing-layer materials (WO-A 95/32235, EP-A 668 157 and DE-A 19 53 33 37). The adhesion of metals and printing inks to outer layers made from metallocene-catalyzed copolymers is, furthermore, significantly better and coextruded films with outer layers of this type additionally have very good optical properties, such as high transparency and high gloss.
However, for some application sectors it is desirable to be able to use sealable coextruded films which have a still further increased difference between sealing temperature and crystalline melting point of the sealing layer, and moreover have further improved organoleptic properties. Their gloss, transparency and adhesion should be just as good as those of the coextruded films currently known and comprising propylene copolymers prepared using metallocene catalysts.
It is an object of the present invention, starting from the currently known sealable coextruded films based on propylene copolymers prepared using metallocene catalysts, to develop sealable coextruded films which are further improved by a reduced sealing temperature and in their organoleptic properties.
We have found that this object is achieved by means of the sealable coextruded films defined at the outset.
A process has moreover been found for producing the novel sealable coextruded films, as has packaging made from the sealable coextruded films.
The novel sealable coextruded film comprises at least one outer layer and at least one base layer, where the outer layer is composed of a propylene terpolymer.
The propylene terpolymers present in the novel sealable coextruded films have from 80 to 99.5 mol % of structural units derived from propylene, preferably from 85 to 99 mol %, in particular from 87 to 98 mol %, and also from 0.2 to 15 mol % of structural units derived from ethene or from a C
4
-C
6
1-olefin (I), preferably from 0.5 to 13 mol %, in particular from 0.5 to 10 mol %, and also from 0.3 to 15 mol % of structural units derived from another C
4
-C
12
1-olefin (II) different from the C
4
-C
6
1-olefin (I), preferably from 0.3 to 12 mol %, in particular from 0.3 to 10 mol %. The total of the molar percentages here is always 100.
Examples of suitable C
4
-C
6
1-olefines (I) are 1-butene, 1-pentene, 4-methyl-1-pentene and 1-hexene. Use is preferably made of 1-butene, 1-pentene or 1-hexene.
For the purposes of the invention, C
4
-C
12
1-olefines (II) are particularly 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene or 1-octene, where particular preference is given to the use of 1-butene, 1-pentene and 1-hexene.
The melting point (T
M
) of the propylene terpolymers used, determined from the DSC peak, is less than 135° C., in particular less than 130° C. More than 80% of the monomer units present in the propylene terpolymers are arranged isotactically.
The propylene terpolymers moreover have a weight-average molar mass (M
W
) of greater than 80,000 g/mol, in particular greater than 150,000 g/mol. The weight-average molar mass (M
W
) here is determined by gel permeation chromatography. The enthalpy of fusion of the propylene terpolymers is greater than 20 J/g, in particular greater than 50 J/g.
The propylene terpolymers to be used according to the invention also have, inter alia, a proportion of regioregular ‘1-2’-inserted propylene units, given by the formula (1)
[
‘
1
-
2
’
]
[
‘
1
-
2
’
]
+
[
‘
2
-
1
’
]
+
[
‘
1
-
3
’
]
(
1
)
of greater than 0.97, in particular of greater than 0.99. The regioregular ‘1-2’-insertion of propene and also the regioirregular ‘2-1’-insertion and the likewise regioirregular ‘1-3’-insertion, are known, inter alia, from P. Pino et al., Angew. Chemie 92, (1980) 869 and from A. Zambelli et al., Macromolecules 21, (1988) 617.
The respective proportions of regioregular ‘1-2’-insertion and regioirregular ‘2-1’-insertion, and also of regioirregular ‘1-3’-insertion are determined, inter alia, by
13
C NMR spectroscopy, as described in A. Zambelli et al., Macromolecules 21, (1988) 617.
The xylene-soluble fraction (X
L
) in % by weight of the propylene terpolymers obeys the following expression (2)
X
L
≦1411.21 exp(−0.0591 T
M
)−0.05 (2)
where T
M
is the melting point of the propylene terpolymers in °C.
Preferred propylene terpolymers to be used according to the invention also have polydispersity (M
W
/M
N
) of less than 2.25, specifically of less than 2.1 and in particular of less than 2.0. The polydispersity (M
W
/M
N
) is preferably determined with the aid of gel permeation chromatography using 1,2,4-trichlorobenzene as solvent.
The propylene terpolymers to be used according to the invention are prepared using metallocene catalysts, preferably by a process which comprises polymerizing the comonomers in the presence of a metallocene catalyst system which has
A) an inorganic or organic support,
B) at least one metallocene complex, and
C) at least one metallocenium-ion-forming compound,
where, however, the use of two d
Bidell Wolfgang
Fischer David
Hingmann Roland
Jones Peter John Vaughan
Kersting Meinolf
Basell Polyolefine GmbH
Keil & Weinkauf
Tarazano D. Lawrence
LandOfFree
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