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
1999-12-23
2001-09-11
Boykin, Terressa 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...
Reexamination Certificate
active
06288168
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a propylene based resin composition. More specifically, the present invention relates to a propylene based resin composition having (i) a superior balance among its low temperature impact resistance, flexural modulus (rigidity) and transparency, and (ii) a superior moldability. The propylene based resin composition of the present invention is especially suitable for producing a container according to a blow molding method, the container obtained according to said method being hereinafter referred to as “blow-molded container”.
BACKGROUND OF THE INVENTION
A propylene resin is one of the resins that have been widely used to produce containers for goods such as detergents, shampoos, drinks, foods and medicines. Almost all of the containers are obtained according to a blow molding method, which method is well known in the art as a production method for thermoplastic resin made containers. The blow molding method can be classified into (i) a direct blow molding method using a hot parison, and (ii) an injection-stretching blow molding method using a hot parison or a cold parison. The former molding method is superior in its molding stability and its cost of molding equipment when compared to the latter molding method. Therefore, many of polypropylene resin made containers are obtained according to the former molding method.
A polypropylene resin has a defect of poor impact resistance in spite of its superior heat resistance, rigidity and transparency. Therefore, there have heretofore been proposed some compositions which are improved in their impact resistance without detrimental effect on superior transparency of the polypropylene resin. As such compositions, there are known a composition comprising a polypropylene resin, a straight chain low-density polyethylene and an ethylene-&agr;-olefin copolymer elastomer (JP-B 5-88264); an ethylene based copolymer composition comprising an ethylene-&agr;-olefin copolymer polymerized using a metallocene catalyst and a crystalline polyolefin (JP-A 8-283476); and a composition comprising a polypropylene resin and an ethylene-&agr;-olefin copolymer polymerized using a metallocene catalyst (JP-A 9-31264). Each of the references referred to above is incorporated herein by reference in its entirety.
However, blow-molded containers obtained using any of the compositions mentioned above have a problem such that the impact resistance thereof in terms of a falling strength is far from a satisfactory level.
Moreover, the aforementioned compositions per se have a problem such that they are not satisfactory in their moldability. That is, a die swelling ratio is greatly changed under conditions where a shear rate is greatly changed, for example, (i) when blow molding conditions such as extruder output are altered, or (ii) when a die gap is altered in order to prevent an uneven thickness caused by draw down of the resin, or (iii) when a die gap is altered in order to prevent an uneven thickness caused by a shape of the molded product, and as a result, a thickness variation of a parison is increased.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a propylene based resin composition having both (i) a superior balance among its low temperature impact resistance, rigidity and transparency, and (ii) a superior moldability.
Another object of the present invention is to provide a blow-molded container obtained from the resin composition mentioned above.
A further object of the present invention is to provide a blow-molded multilayer container obtained from the resin composition mentioned above.
The present inventors have undertaken extensive studies to develop a propylene based resin composition having both (i) a superior balance among its low temperature impact resistance, rigidity and transparency, and (ii) a superior moldability. As a result, it has been found that the objects of the present invention can be accomplished by providing a propylene based resin composition, wherein (i) its die swelling ratios satisfy a specific relational expression, and (ii) its Izod impact value, its flexural modulus and its haze value satisfy another specific relational expression. And thereby the present invention has been obtained.
The present invention provides a propylene based resin composition comprising:
(i) about 70 to 90% by weight of a propylene block copolymer; and
(ii) about 30 to 10% by weight of an ethylene based resin, wherein:
(a) the relation between its die swelling ratio (SR
1
) at a shear rate of 6.08 sec
−1
and its die swelling ratio (SR
2
) at a shear rate of 608 sec
−1
satisfies the following formula (1); and
(b) the relation among its Izod impact value (kJ/m
2
) at a temperature of 0° C., its flexural modulus (MPa) at a temperature of 23° C. and its haze value (%) satisfies the following formula (2)
SR
2
/SR
1
≦about 1.10 (1)
Izod impact value×Flexural modulus/Haze value≧about 200 (2).
The present invention also provides a blow-molded container, which comprises the propylene based resin composition mentioned above.
The present invention further provides a blow-molded multilayer container, which comprises the propylene based resin composition mentioned above.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The propylene based resin composition of the present invention comprises (i) a major amount of a propylene block copolymer, and (ii) a minor amount of an ethylene based resin. More specifically, the present resin composition comprises (i) a propylene block copolymer in an amount of from about 70 to 90% by weight, preferably from about 72 to 89% by weight, and more preferably from about 75 to 88% by weight, and (ii) an ethylene based resin in an amount of from about 30 to 10% by weight, preferably from about 28 to 11% by weight, and more preferably from about 25 to 12% by weight, provided that the sum of both components is 100% by weight.
The above-mentioned term “propylene block copolymer” means a copolymer obtainable by a process, which comprises the steps of:
(1) First step: polymerizing propylene alone or a mixture of propylene and ethylene until a content of a polymer component (component A), which has a content of a repeating unit derived from ethylene of from about 0 to 2% by weight, reaches from about 70 to 90% by weight based on the total weight of the component A and a below-defined component B; and
(2) Second step: copolymerizing propylene with ethylene in the presence of the component A produced in First step until a content of a component B, which is a propylene-ethylene copolymer having a content of a repeating unit derived from ethylene of from about 15 to 50% by weight, reaches from about 10 to 30% by weight based on the total weight of the components A and B.
A content of the component A in said propylene block copolymer is preferably from about 75 to 89% by weight, and more preferably from about 80 to 88% by weight, and a content of the repeating unit derived from ethylene in the component A is preferably not more than about 1% by weight. Meanwhile, a content of the component B in said propylene block copolymer is preferably from about 25 to 11% by weight, and more preferably from about 20 to 12% by weight, and a content of the repeating unit derived from ethylene in the component B is preferably from about 20 to 45% by weight, and more preferably from about 25 to 40% by weight. Among the propylene block copolymers mentioned above, those having a melt flow rate (MFR) at 230° C. of not more than about 2 g/10 min., preferably from about 0.5 t
Nagamatsu Tatsuhiro
Shiromoto Seiji
Suzuki Haruyuki
Birch & Stewart Kolasch & Birch, LLP
Boykin Terressa M.
Sumitomo Chemical Company Limited
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