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
2000-02-03
2001-10-23
Seidleck, James J. (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...
C525S243000, C525S245000, C525S247000, C525S323000, C526S351000
Reexamination Certificate
active
06306973
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polypropylene block-copolymer resin and to a process for producing such block-copolymer resin.
BACKGROUND OF THE TECHNIQUE
Polypropylene has widely been used in various fields including automobile parts, machine and electric appliances, household commodities, kitchen utensils and packaging films. However, problems have been brought about in that large-sized formed articles are difficult to obtain by, for example, extrusion molding, and in that a high speed molding can scarcely be attained, since polypropylene exhibits lower melt tension (abbreviated hereinafter sometimes as MT). Concretely, the following problems have been encountered:
(1) In blow molding, a phenomenon of “draw-down” due to stretching of the parison by its own weight, causing decrease in the film thickness may be apt to occur, whereby blow molding of large-sized articles, for example, automobile parts, such as bumper and spoiler; and others, such as bottles, is rendered difficult.
(2) In the case of production of sheet or film by a calendering technique, the resulting sheet or film may often suffer from thickness irregularity and, in addition, it has a lower surface gloss.
(3) In the case of production of formed articles by extrusion molding, a high-speed molding may scarcely be practiced and, in addition, large-sized extrusion-molded articles may difficultly be obtained.
(4) In the case of production of vacuum- or pressure-formings from a sheet by a vacuum- or pressure-forming technique, large-sized molded articles are difficult to obtain and, in addition, a deep drawing may difficultly be incorporated.
(5) In the case of production of sheet or film by an inflation molding technique, a poor surface condition may often be encountered, since the balloon may often become unstable.
(6) In the case of producing stretched films, the resulting film may be apt to suffer from occurrence of so-called surging, so that an accident of film breaking upon the stretching may occur and, in addition, the resulting stretched film exhibits a low thickness accuracy.
(7) In the case of producing foamed articles, foaming with a high foaming ratio may difficultly be attained and, in addition, the cells of foamed article are large and coarse with non-uniform cell size.
In order to avoid these problems, it has heretofore been practiced to employ such polypropylene reins as given below in which the melt tension is increased:
1) A polypropylene resin composition prepared by blending a polypropylene with a high-pressure low-density polyethylene or with a high-density polyethylene
2) A polypropylene resin having a widely extended molecular weight distribution
3) A modified polypropylene resin which is obtained by slightly cross-linking a polypropylene resin using a peroxide, electron irradiation or maleic acid
4) A branched long chain polypropylene resin which is obtained by introducing long chain branching upon the polymerization of propylene
However, these prior art polypropylene resins having improved melt tension exhibit disadvantages in that the formed article produced therefrom reveals inferior appearance and/or lower transparency and in that the stiffness of the resin is insufficient, though occurence of draw-down is made scarce for all these resins. Alternatively, if the molding temperature is elevated in order to effect a high speed molding, problems may be brought about that the resin will suffer from deterioration due to increased heat evolution in the resin, causing higher trend to gel formation (fish eye formation). Moreover, additional process steps of blending of other resin components and an inevitably performed slight cross linking of the polymer by, for example, a peroxide or electron beam irradiation or by using maleic acid or the like makes the process costly.
In Japanese Patent Kokai Hei-9-31299 A, there is disclosed a resin composition of propylene polymers composed of an ethylene/propylene block copolymer component and a higher molecular weight polypropylene component, which is superior in mechanical properties, such as stiffness and surface hardness, and is also superior in the impact resistance. This composition consists of a mixture of an ethylene/propylene block copolymer component having an ethylene content of 0.3-10% by weight and a higher molecular weight polypropylene component having an isotactic pentad fraction of 0.90 or higher, wherein the proportion of a polymer fraction of molecular weights over 5,000,000 relative to the total composition is in the range from 1 to 10% by weight and the proportion of a polymer fraction of molecular weights below 10,000 is 10% by weight or lower and wherein the melt flow rate of the composition is in the range from 0.3 to 50 g/10 min.
Due to the content of the polymer fraction of molecular weights over 5,000,000 in an amount of 1-10% by weight, the resin composition of propylene polymers can provide improvements in the stiffness and in the surface hardness, nevertheless it suffers from problems in that it exhibits inferior flowability upon the melt-molding due to a high content of the higher molecular weight component or due to a content of an ultrahigh molecular weight fraction and in that the appearance of the molded article is inferior due to the quite poor uniformity of dispersion of the higher molecular weight component over the resin composition.
The resin composition of propylene polymers is prepared by melt kneading the ethylene/propylene block-copolymer component and the higher molecular weight polypropylene component, each produced separately of each other, whereby a further problem is brought about in that the production procedures are bothersome and a uniform melt-kneading of these components is difficult.
In WO 98/47959, there is disclosed a resin composition with crystalline polypropylene containing 3-65% by weight of a component soluble in paraxylene of 23° C., 35-97% by weight of a component soluble in paraxylene of 135° C. but insoluble in paraxylene of 23° C. and 0-30% by weight of a component insoluble in paraxylene of 135° C., wherein the said component soluble in 23° C. paraxylene is constituted substantially of an elastomer having an intrinsic viscosity [&eegr;] of 0.1-5 dl/g, the said component soluble in 135° C. paraxylene but insoluble in 23° C. paraxylene is constituted substantially of a crystalline polypropylene resin having an isotactic pentad fraction (mmmm fraction) of at least 97%, an Mw/Mn value of 6 or higher and an Mz/Mw value of 6 or higher and the said component insoluble in 135° C. paraxylene is constituted substantially of a filler. In Examples thereof, an elastomer based on styrene and an ethylene/&agr;-olefin random copolymer are employed for the elastomer and a polypropylene resin having compounded therein a predetermined amount of a polypropylene block-copolymer resin or a higher molecular weight polypropylene resin is employed for the crystalline polypropylene resin.
The above-mentioned resin composition with crystalline polypropylene can be molded into a formed product exhibiting better appearance without occurrence of rashes and is superior in the flexural modulus and in the flowability upon the molding. However, this resin composition is obtainable with a costly and bothersome process, since the polypropylene block-copolymer resin and the higher molecular weight polypropylene resin are produced by polymerization courses independent of each other. In addition, if the amount of the higher molecular weight polypropylene resin to be compounded is increased on melt-kneading them, an increase in the shearing stress will result, whereby a problem is brought about in that it tends to suffering from deterioration of the resin and from insufficient dispersion of the higher molecular weight polypropylene resin in the composition.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a polypropylene block-copolymer resin which exhibits a higher melt tension with better moldability and is superior in the balance between the stiffness and the impac
Hashimoto Mikio
Momoda Nobuyosi
Takaoka Tohru
Asinovsky Olga
Grand Polymer Co. Ltd.
Seidleck James J.
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