Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-06-13
2004-01-27
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S451000, C524S515000, C524S518000, C524S529000, C524S536000
Reexamination Certificate
active
06683125
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymer compositions. In particular, the present invention concerns compositions of efficiently nucleated copolymers. The invention further concerns a process for preparing such compositions. Finally, the present invention relates to the use of the new propylene polymers or copolymers for the manufacture of products by, e.g., blow moulding, thermoforming, injection moulding and sheet or film extrusion.
2. Description of Related Art
Propylene (PP) homo- and copolymers have excellent resistance to heat and chemicals as well as attractive mechanical properties, such as stiffness and impact resistance. However, processing of polypropylene by,.e.g., injection moulding, thermoforming or blow moulding, to form thin-walled containers has resulted in products having insufficient transparancy. This is caused by the semi-crystalline nature of polypropylene which leads to hazy quality end-products.
In the prior art it has been proposed to improve the transparency of blow moulded polypropylene by blending the polymer with various nucleating agents such as dibenzilidene sorbitol (DBS) or di(alkylbenzilidene)sorbitol. These traditional nucleating agents tend to bleed out from the polymer composition during processing and many of them give rise to fumes with an offensive smell. As a solution to these problems, it has been suggested in the art to use vinyl compounds, such as polymers of vinyl cycloalkanes and 3-methyl-1-butene, as nucleating agents in the form of propylene copolymers or polypropylene compounds, cf. EP Patent Specifications Nos. 0 152 701, 0 151 883, 0 368 577 and 0 417 319. However, studies done on these higly nucleated materials shows that, although their processing properties are excellent, shrinkage increases with increasing freezing point. Further, even though improved, the freezing point and stiffness of the polymer resins are still too low for many applications.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the problems related to the prior art and to provide a novel propylene polymer or copolymer composition having improved mechanical properties and therefore highly suited to the manufacture of moulded products.
A second object of the invention is to provide a novel process for preparing novel propylene copolymer compositions of the above kind.
It is still a further object of the present invention to provide moulded or extruded products comprising propylene copolymer compositions.
These and other objects, together with the advantages thereof over known processes and products, which shall become apparent from the specification which follows, are accomplished by the invention as hereinafter described and claimed.
The invention is based on the idea of employing talc as a shrinkage-reducing ingredient in propylene compositions, in particular in compositions containing propylene exhibiting a high degree of crystallinity and a high temperature of crystallization.
The use of talc in efficiently nucleated propylene compositions is known in the art. Thus, EP Patent Specification No. 0 152 701 discloses blending proplyene copolymer containing poly(vinyl cycloalkane) with a filler such as mica or talc. No examples of any kind of compositions containing talc are given nor does the specification give any concentration ranges for mica or talc. Considering the fact that talc is used as a filler, it would appear that amounts of several tens of percents have been contemplated.
Talc is also a well-known nucleating agent. EP Patent Application No. 0 586 109 describes a polypropylene composition containing 0.0001 to 1 part by weight of a crystal nucleating agent, such as talc. In the examples, the amount of talc is 0.2 parts by weight.
No indication of any beneficial effect of talc on the shrinkage of the polypropylene composition can be found in the above documents.
According to the present invention it has now been found that surprisingly good mechanical results are obtained by blending talc with propylene polymers which have been nucleated with a polymerized vinyl compound in amounts sufficient to obtain an increase of stiffness while reducing shrinkage to an acceptable level. Preferably 0.1 to 10 wt-% of talc is used. Surprisingly, although the stiffness of polypropylene nucleated with a polymerized vinyl compound is similar to that of polypropylene nucleated with 0.5% talc, the stiffness of the former will increase more than of the latter when both are blended with the same amount of talc (e.g. 2.5 to 5%).
More specifically, the polymer composition according to the present invention is characterized by what is stated in the characterizing part of claim 1.
The process according to the present invention for preparing nucleated polypropylene compositions is characterized by what is stated in the characterizing part of claim 9.
The present compositions can be used in any kind of polymer articles. Particular advantages are obtained by applying the compositions to the manufacture of moulded products, and products prepared by blow moulding, stretch blow moulding, injection moulding, compression moulding and sheet or film extrusion and pipe or cable extrusion.
The invention achieves a number of considerable advantages. In particular it can be noted that the addition of talc in amounts of 0.1 to 10 wt-% increases the stiffness of the propylene polymer composition by up to 5%. Talc in polypropylene compositions gives rise to higher tensile modulus than talc in standard PP copolymer. The Heat Deflection Temperature (the HDT value) is also increased by the addition of talk, and the HDT value increases more for the present polypropylene compositions nucleated with a vinyl compound than for standard PP. The crystallization temperature of the present compositions is higher than for standard PP containing corresponding amounts of talc and for polypropylene compositions nucleated with a vinyl compound. Although the shrinkage of the present compositions is somewhat higher than that of standard PP containing talc it is still on an acceptable level and the present invention provides a unique combination of excellent stiffness (up to 1600 MPa or more), controlled shrinkage, faster crystallization and high T
cr
giving good cyclus potential. In the present context, faster crystallization is not necessarily related to faster formation of single crystals but rather to the fact that there are more crystals that fill the space faster.
Next, the invention will be more closely examined with the aid of the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the present invention include a polymeric component comprising a propylene polymer nucleated with vinyl compounds together with a shrinkage-restricting component, talc. By nucleating propylene polymers with vinyl compounds it is possible to provide polypropylene having a higher degree of crystallinity, a higher crystallization temperature, smaller crystallization size and a greater crystallization rate. These kinds of compositions can be used for the preparation of moulded products. They exhibit improved physical properties.
The nucleation of the propylene polymers can be carried out by modifying the polymerization catalyst with vinyl compounds and using the modified catalyst for polymerization of propylene optionally in the presence of comonomers to provide a propylene polymer or copolymer containing about 0.0001 to 1% (calculated from the weight of the composition) of a polymer comprising vinyl compound units. Another approach for nucleating propylene polymers comprises blending polypropylene with polymers containing vinyl compound units.
For the purpose of the present invention “vinyl compounds” are compounds having the formula I
wherein R
1
and R
2
together form a 5 or 6 membered saturated or unsaturated or aromatic ring or they stand independently for a lower alkyl comprising 1 to 4 carbon atoms.
The following specific examples of vinyl compounds can be mentioned: vinyl cycloalkanes, in particula
Aasetre Sveinung
Augestad Morten
Tørå Dag
Borealis A/S
Lee Rip A
Wu David W.
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