Crystalline polypropylene and its moldings and films

Details Crystalline polypropylene and its moldings and films Crystalline polypropylene and its moldings and films

2001-09-27

2003-10-28

Choi, Ling-Siu (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348000, C526S124300, C526S158000

Reexamination Certificate

active

06639038

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to crystalline polypropylene and its moldings and films, particularly to crystalline polypropylene and its moldings and films which are rigid and have good heat resistance and good scratch resistance.
2. Description of the Prior 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 foods 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 aluminum 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.
SUMMARY OF THE INVENTION
In that situation, an 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. Particularly, 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.
The 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. The inventors 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. The inventors have still further found that a crystalline polypropylene of such composition that the 0° C. soluble content as measured through programmed-temperature fractionation and the intrinsic viscosity [&eegr;] as measured in a tetralin solvent at 135° C. satisfy a specific relationship has enhanced rigidity, heat resistance and scratch resistance and meets the object of the invention. On the basis of this finding, the present invention has been accomplished.
Thus, the present invention provides a first 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),
and a molding or a film made of the first crystalline polypropylene.
The present invention further provides a second crystalline polypropylene of which the 0° C. soluble content, &agr; (% by weight), as measured through programmed-temperature fractionation and the intrinsic viscosity [&eegr;] (dl/g) as measured in a tetralin solvent at 135° C. satisfy the relationship given in the following formula (3):
&agr;≦1.11[&eegr;]
−0.42
+1.40  (3),
and a molding made of the second crystalline polypropylene. The second crystalline polypropylene preferably satisfies the relationship given in the following formula (4):
Tp>
1.21×[&eegr;]+116.5  (4),
wherein Tp is a peak temperature (° C.) in its elution curve as obtained by programmed-temperature fractionation and [&eegr;] is the same as defined above.
DETAILED DESCRIPTION OF THE INVENTION
The crystalline polypropylene and its moldings and films of the invention will be described below.
1. Crystalline Polypropylene
1a First Crystalline Polypropylene
Of the first crystalline polypropylene, the 0° C. soluble content, &agr; (% by weight), and the peak molecular weight, Mp, in the molecular weight distribution curve must satisfy the relationship given in the following formula (1):
&agr;≦−0.42×ln(
Mp
)+7.3  (1).
Preferably, the first crystalline polypropylene satisfies the following formula (1a), and more preferably the following formula (1b):
&agr;≦−0.42×ln(
Mp
)+6.8  (1a)
&agr;≦−0.42×ln(
Mp
)+6.3  (1b).
If formula (1) is not satisfied, the rigidity of the first crystalline polypropylene is low, and is unfavorable.
In addition, the melting point, Tm (° C.), and Mp of the first crystalline polypropylene must satisfy the relationship given in the following formula (2):
Tm>
1.85×ln(
Mp
)+144.5  (2).
Preferably, the first crystalline polypropylene satisfies the following formula (2a)

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