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
2002-03-29
2004-03-23
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...
C525S197000, C525S208000, C525S240000, C525S241000, C521S053000, C521S056000, C521S059000, C521S060000, C521S062000, C521S134000, C521S139000
Reexamination Certificate
active
06710130
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Technical Field
The present invention relates to a propylene polymer composition and foam moldings thereof. More precisely, the invention relates to a propylene polymer composition of high melt tension especially suitable to foam molding, and relates to foam moldings of the polymer composition of uniform thickness.
(2) Related Art
Because of its good mechanical properties and chemical resistance and the fact it is economical to use, polypropylene is widely used in the art of various molding. However, as its melt tension is low, the moldability of polypropylene in, for example, blow molding, foam molding and extrusion molding is in fact not good.
For increasing the melt tension of polypropylene, for example, a method of reacting polypropylene in melt with an organic peroxide and a crosslinking promoter (JP-A-59-93711, 61-152754); and a method of reacting semi-crystalline polypropylene with a peroxide having a low decomposition point in the absence of oxygen to produce gel-free propylene having long free end branches (JP-A-2-298536)are known.
These methods are effective for increasing the melt tension of polypropylene, but are problematic in that the products often have an offensive smell as they require an organic peroxide and a crosslinking promoter. In addition, when the products are recycled, their thermal stability is lowered as the melt flow rate of polypropylene increases in the recycling step. Moreover, the methods are not fully satisfactory from a productivity standpoint.
Another method for increasing the melt viscoelasticity such as melt tension of polypropylene has been proposed, which comprises producing a composition containing polypropylene, and polyethylene or polypropylene that differs from the polypropylene in the intrinsic viscosity or the molecular weight by blending them or by polymerizing monomers in multi-stage polymerization. For example, from 2 to 30 parts by weight of ultra-high-molecular polypropylene is added to 100 parts by weight of ordinary polypropylene, and the resulting mixture is extruded at a temperature falling between the melting point of the mixture and 210° C. (JP-B-61-28694). However, the melt tension of these compositions is still not fully satisfactory. The multi-stage polymerization to produce such an ultra-high-molecular polyolefin requires extremely low-temperature reaction, for which, therefore, the ordinary process must be specifically modified and, in fact, its productivity is inevitably lowered.
Apart from the methods mentioned above, also known are a method of producing polypropylene of high melt tension by polymerizing propylene in the presence of a prepolymerized catalyst prepared by prepolymerizing ethylene and a polyene compound with a supported-type titanium-containing solid catalyst component and an organoaluminium compound catalyst component (JP-A-5-222122); and a method of producing an ethylene-&agr;-olefin copolymer of high melt tension in the presence of a polyethylene-containing prepolymerized catalyst in which the polyethylene has an intrinsic viscosity of at least 20 dl/g and which is prepared through prepolymerization of ethylene alone with the catalyst components as above (JP-A-4-55410). In these methods, however, an additional third component, i.e. polyene compound must be prepared, and the prepolymerized polyethylene could not uniformly disperse in the final product, i.e. the polyolefin composition. Therefore, the methods are problematic in that the quality of the polyolefin composition is unstable. In addition, also known are an olefin (co)polymer composition of high melt tension which is obtained by polymerizing propylene in the presence of a polyethylene-containing prepolymerized catalyst in which the polyethylene has an intrinsic viscosity of at least 15 dl/g; and a method for producing it (WO97/14725)
However, when conventional compositions are kneaded in melt at temperatures not higher than 250° C., their melt could exhibit high melt tension, but the thickness of their foam moldings is apt to be non-uniform and the appearance thereof is apt to be worse. Therefore, when the foam moldings are thermoformed (fabricated), they have a tendency to be readily broken at the thin part. On the other hand, when the compositions are kneaded in melt at a temperature higher than 250° C., the thickness of their foam moldings may be uniform, but their melt tension is apt to be low. Therefore, the foam moldings have a tendency to be difficult to thermoform (fabricate), as their drawdown is great.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the situation of the prior art mentioned above. One object of the invention is to provide a propylene polymer composition of high melt tension which, even in the case that any special additive isn't used, can be foamed into good foams of uniform thickness that can be well thermoformed (fabricated) with no drawdown trouble.
We, the present inventors have assiduously studied to solve the problems noted above, and, as a result, have found that a propylene polymer composition, prepared by melt-kneading a polymer mixture comprising a specific ethylene polymer and a specific olefin multi-stage polymer, and having specific melt properties, attains the intended object. The invention includes the following 1) to 8).
1) A propylene polymer composition obtain by melt-kneading a polymer mixture comprising an olefin multi-stage polymer (B) mentioned below and an ethylene polymer (A) mentioned below in an amount from 0.01 to 5.0 parts by weight relative to 100 parts by weight of the polymer (B),
and satisfying the following formula (1) in point of a melt tension (MS, unit:cN) at 190° C. and melt flow rate (MFR(T), unit:dg/min) of the composition:
Log(
MS
)>0.91−0.23×Log(
MFR
(
T
)) (1),
[1] ethylene polymer (A), having an intrinsic viscosity of from 15 to 100 dl/g measured in tetralin at 135° C.,
[2] olefin multi-stage polymer (B), obtained by producing a propylene polymer (I) in a polymerization step (I) to a range of from 30 to 95% by weight of the olefin multi-stage polymer, followed by producing an olefin polymer (II) in a subsequent polymerization step (II) to a range of from 5 to 70% by weight of the olefin multi-stage polymer.
2) The propylene polymer composition of 1) above, for which the polymer mixture is melt-kneaded at a temperature thereof falling between 280 and 500° C.
3) The propylene polymer composition of 1) above, for which the polymer mixture is prepared by producing the olefin multi-stage polymer (B) in the presence of a pre-activated catalyst prepared by supporting the ethylene polymer (A) on an olefin polymerization catalyst.
4) The propylene polymer composition of 3) above, for which a melt flow rate (MFR(i), unit:dg/min) of the polymer after the polymerization step (I) and a melt flow rate (MFR(ii), unit:dg/min) of the olefin polymer (II) satisfy the following formula (2) and (3):
3≦Log(
MFR
(
i
)/
MFR
(
ii
))≦7 (2)
MFR
(
ii
)<1×10
−3
dg/min (3).
5) The propylene polymer composition of any one of 1) to 4) above, for which the propylene polymer (I) is a propylene homopolymer, or a propylene-olefin copolymer of propylene and an olefin with from 2 to 12 carbon atoms except propylene, having at least 50% by weight, based on the copolymer, of propylene units.
6) The propylene polymer composition of any one of 1) to 5) above, for which the olefin polymer (II) is a homopolymer or copolymer of an olefin with from 2 to 12 carbon atoms.
7) A foam molding of the propylene polymer composition of any one of 1 to 6) above.
8) The foam molding of 7) above, of which the fluctuation in the thickness falls within a range of ±5% of the mean thickness of the foam molding.
PREFERRED EMBODIMENTS
The propylene polymer composition of the invention is obtained by melt-kneading a polymer mixture of a specific olefin multi-stage polymer (B) and from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the polymer (B), of a sp
Hamasaki Tadamitu
Kawazoe Shunji
Kobayashi Yoshitaka
Maehara Hiroyuki
Shinozaki Jun
Chisso Corporation
Nutter Nathan M.
Wenderoth , Lind & Ponack, L.L.P.
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