Crystalline polypropylene and molded object and film thereof

Details Crystalline polypropylene and molded object and film thereof Crystalline polypropylene and molded object and film thereof

2000-01-13

2002-09-24

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S160000, C526S943000, C526S348100

Reexamination Certificate

active

06455659

ABSTRACT:

TECHNICAL FIELD
The present invention relates to crystalline polypropylene and its moldings and films, precisely to crystalline polypropylene and its moldings and films which are rigid and have good heat resistance and good scratch resistance.
BACKGROUND ART
Polypropylene resins have good heat resistance, good chemical resistance and good electrical properties. In addition, they are rigid and have high tensile strength, good optical properties, and are easy to work. Therefore, they are used, for example, in injection molding, film formation, sheet formation and blow molding. Moreover, as their specific gravity is low, they are widely used in various fields including, for example, containers and wrapping materials. However, for some applications, the properties of the resins are not always satisfactory, and use of the resins is often limited.
Of the properties of polypropylene noted above, its rigidity, heat resistance and scratch resistance are inferior to those of polystyrene and ABS resins. Therefore, for moldings which must be especially rigid and have good heat resistance, polypropylene can not be used. If it is desired that polypropylene moldings have the same high rigidity and good heat resistance as polystyrene or ABS resin moldings, their thickness must be made large. This means that thin polypropylene moldings are difficult to produce and their production costs are high. For these reasons, applications of polypropylene and polypropylene compositions can not be further expanded. If polypropylene could be improved to have satisfactory rigidity, chemical resistance, moldability, heat resistance and hardness, it could be a substituent for polystyrene and ABS resins and its applications could be expanded further. If so, in addition, thin moldings of polypropylene could be produced. Such improved polypropylene, if obtained, would have the advantage of saving natural resources and reducing the costs in producing its moldings.
In addition, when applied to the field of films, for example, for wrapping or packaging eatables or fibers, or for various sundries, etc., the polypropylene films could exhibit good properties of high rigidity and good heat resistance with low molding shrinkage while they are well extensible.
This being the situation, some techniques for increasing the rigidity of crystalline polypropylene are known. For example, one known method is that of adding an organic nucleating agent, such as aluminium para-tert-butylbenzoate, 1,8-2,4-dibenzylidenesorbitol or sodium 2,2-methylenebis(4,6-di-tert-butylphenyl) phosphate, to crystalline polypropylene, and molding the resulting composition. However, the method is expensive and is not economical. In addition, the method has the problem that the organic nucleating agent added to crystalline polypropylene greatly lowers the surface gloss, the impact strength and the tensile elongation of the polypropylene moldings. Another method for enhancing the rigidity of crystalline polypropylene is known, which comprises adding an inorganic filler such as talc, calcium carbonate or kaolin to crystalline polypropylene. In this method, however, the inorganic filler added detracts from the intrinsic characteristics of crystalline polypropylene its light weight and transparency. In addition, the method has the problem that the impact strength, the gloss, the tensile elongation and the workability of the polypropylene moldings produced are poor.
In that situation, the object of the present invention is to provide a novel crystalline polypropylene and its moldings and films having the advantages of high rigidity, good heat resistance and good scratch resistance. Precisely, the invention is to provide a novel crystalline polypropylene and its moldings and films having the advantages of high flexural modulus, high tensile modulus, high heat deformation temperature and high hardness.
DISCLOSURE OF THE INVENTION
We, the present inventors have done assiduous researches to attain the object noted above, and, as a result, have found that the component of polypropylene which does not crystallize but remains dissolving in a solvent in its crystallization step (this component will be isotactic polypropylene or a low-molecular-weight component) lowers the degree of crystallinity of the polymer, acting as a factor of retarding the rigidity, the heat resistance and the scratch resistance of the polymer. We have further found that, when the amount of the soluble component of polypropylene, the melting point of the polymer as measured through differential scanning calorimetry, and the molecular weight for the peak in the molecular weight distribution curve of the polymer as measured through gel permeation chromatography (GPC) satisfy a specific relationship therebetween, then the polymer, polypropylene could have enhanced rigidity, heat resistance and scratch resistance and meets the object of the invention. On the basis of these findings, we have completed the invention.
Specifically, the invention provides a novel crystalline polypropylene and its moldings and films, which are as follows:
1. A crystalline polypropylene of which the 0° C. soluble content, &agr; (% by weight), as measured through programmed-temperature fractionation and the molecular weight, Mp, for the peak in the molecular weight distribution curve as measured through GPC satisfy the relationship given in the following formula (1):
 &agr;≦−0.42×ln(
Mp
)+7.3  (1),
and the melting point, Tm (° C.), as measured through differential scanning calorimetry and Mp satisfy the relationship given in the following formula (2):
Tm>
1.85×ln(
Mp
)+144.5  (2).
2. The crystalline polypropylene of above 1, of which the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn, Mw/Mn, as measured through GPC is at most 6.5.
3. The crystalline polypropylene of above 1 or 2, of which the intrinsic viscosity [&eegr;] as measured in a tetralin solvent at 135° C. falls between 0.5 and 4.0 dl/g.
4. The crystalline polypropylene of any one of above 1 to 3, of which the molecular weight, Mp, for the peak in the molecular weight distribution curve as measured through GPC is at least 10,000.
5. A molding of the crystalline polypropylene of any one of above 1 to 4.
6. A film of the crystalline polypropylene of any one of above 1 to 4.
BEST MODES OF CARRYING OUT THE INVENTION
The crystalline polypropylene and its moldings and films of the invention are described hereinunder.
1. Crystalline Polypropylene
Of the crystalline polypropylene of the invention, the 0° C. soluble content, &agr; (% by weight), as measured through programmed-temperature fractionation and the molecular weight, Mp, for the peak in the molecular weight distribution curve as measured through GPC must satisfy the relationship given in the following formula (1):
&agr;≦−0.42×ln(
Mp
)+7.3  (1).
Preferably, the two satisfy the following formula (3), and more preferably the following formula (4):
&agr;≦−0.42×ln(
Mp
)+6.8  (3)
&agr;≦−0.42×ln(
Mp
)+6.3  (4).
If formula (1) is not satisfied, the rigidity of the crystalline polypropylene is low, and is unfavorable.
Of the crystalline polypropylene of the invention, the 0° C. soluble content, &agr; (% by weight) is measured according to the following method. 75 mg of the polymer to be tested is put into 10 ml of o-dichlorobenzene at room temperature, and dissolved therein, stirring at 135 to 150° C. for 1 hour, to prepare a sample solution. 0.5 ml of the sample solution is charged into a column at 135° C., and then gradually cooled to 0° C. at a cooling rate of 10° C./hr, whereby the polymer is crystallized on the surface of the filler in the column. During the process, the amount of the polymer not crystallized but still remaining in solution is measured, and this indicates the 0° C. soluble content of the polymer.
Mp is obtained according to the following method.
This is calculated from the data of gel permeation

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