High resistance polypropylene tube

Details High resistance polypropylene tube High resistance polypropylene tube

2000-07-31

2002-08-13

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...

C525S240000

Reexamination Certificate

active

06433087

ABSTRACT:

The invention relates to a high strength polypropylene pipe and especially to one with a high modulus of elasticity in tension, a high notch impact strength and an annular rigidity and resistance to impact stresses.
Above all, the pipes are intended for waste water systems, especially as sewer pipes.
The use of stoneware, concrete, and cast iron pipes for the construction of sewers has long been known. The susceptibility of these rigid materials to fracture is a disadvantage, so that pipes produced from them frequently break due to external influences, such as earth movements, installation errors and other stresses, and the emerging seepage causes ecological damage in the surrounding soil and in the water table.
On the other hand, the use of sewer pipes of thermoplastic materials, which are produced in a known manner in different dimensions by extrusion, is particularly advantageous. Because of their low weight, good thermoplastic weldability, high fracture toughness, corrosion and abrasion resistance, polyethylene and polypropylene are preferred to other raw materials and ensure that the sewer systems have a high functional reliability for a long time. Other reasons for the increasing importance of these materials in the pipe sector are their environmental compatibility, low installation costs and problem-free recycling.
Several standards and draft standards, such as EN 1852, pr EN 1401, CEN/TC 155 WI 009 Document 155/13 N322, DIN 19537, DIN 16961, DIN V 19534-1 and Draft DIN 19566, contain state-of-the-art stipulations concerning dimensioning, material properties, test methods and the use of plastic pipes in waste water disposal plants.
However, the construction of highly efficient waste water disposal systems and the implementation of installation and restoration work when outside temperatures are low, presuppose new materials with even better use properties. The relevant requirements relate, in particular, to stable, large-diameter plastic pipes with a strength, which meets service requirements, a to low temperatures ductility and use temperatures of up to 90° C.
Methods are known for increasing the strength of polypropylene pipes by forming a composite. According to DE 94 16 759 U1 and DE 296 12 040, the pipes are covered with a solid fiber material or a reinforcing braiding and subsequently are jacketed with plastic or an outer pipe. EP 0 762 032 describes an extrusion method for producing multilayer composite pipes. The inner and outer walls of said pipes consist of different polymer materials, which are modified before being processed with adhesion promoters and fillers.
These methods produces composite pipes having a pressure and temperature resistance higher than that of non-reinforced pipes. However, the high production costs in the form of a method of several steps, the different materials that are used and the increase in weight due to the composite construction are disadvantages.
According to EP 0 385 465, the corrugated configuration of the outer wall of sewer pipes leads to a greater annular rigidity. Starting out from this premise, the method describes the production of composites of a smooth inner pipe and a corrugated outer pipe.
The advantageous increase in annular rigidity with double pipes with an external profile is offset also here by the disadvantages of a costly production process, the high weight of the double pipes and the complicated technique of connecting pipes.
Furthermore, from the patent literature, other processes are known for increasing the rigidity and strength of polypropylene. In particular, by the admixing elastomers (WO 96/37549, DE 40 19 456), by the broadening of the molecular weight distribution (WO 96/11216, DE 43 30 661), by the production of reactor blends (DE 40 01 157) and by the addition nucleating agents (DE 44 07 327), ways are described which, although they represent partial solutions, do not lead to rigidity-toughness relationships corresponding to the actual performance requirements of high-performance pipe material.
It is an object of the present invention to take into account the higher demands placed on pipe materials and to provide a polypropylene molding composition, which has at the same time a very high modulus of elasticity in tension, a very high rigidity and a very high strength and, with respect to its Theological properties and to the materials used, can be extruded advantageously into pipes.
Although the opposite courses of rigidity and toughness in the improvement of properties of multiphasic polypropylene blends set limitations, it was possible to develop molding compositions from propylene and ethylene in a two-step polymerization process using ZIEGLER-NATTA catalysts and to produce extrusion pipes from these compositions, the mechanical strength of which is significantly improved relative to that of known and comparable plastic pipe materials.
The object of the invention is a polypropylene pipe, in particular, a high-strength polypropylene sewer pipe, characterized by
a modulus of elasticity in tension of 1,300 to 2,300 N/mm
2
and preferably of 1,500 to 2,000 N/mm
2
and
a notch impact strength of 60 to 110 kf/m
2
and preferably of 70 to 100 kJ/m
2
,
and produced by extruding a thermoplastic molding composition consisting of two components A and B having the composition of
A) 80 to 98 parts by weight and preferably 87 to 97 parts by weight of an isotactic polypropylene homopolymer as a coherent matrix component with a decade regularity of more than 95% and
B) 2 to 20 parts by weight and preferably 3 to 13 parts by weight of a copolymer, consisting of 50 to 70 parts by weight of propylene and 30 to 50 parts by weight of ethylene and/or other C4-C8&agr;-olefins as a dispersely distributed elastomeric component,
with an intrinsic viscosity ratio of the two components B and A of 0.9 to 1.5, as well as with a melt index of the molding composition of 0.15 to 0.8 g/10 min. and preferably of 0.2 to 0.5 g/10 min.
B is a copolymer, which consists preferably of 55 to 65 parts by weight of propylene and 35 to 45 parts by weight of ethylene.
As a result of the high modulus of elasticity in tension and the high notch impact strength, the annular rigidity, which is particularly important for pipes, is also increased.
The invention is also characterized by the polypropylene pipe for the reason that the annular rigidity SN (kN/m
2
) of solid wall pipes with smooth inner and outer surfaces, and moreover independently of the configuration of the respective pipe ends, with an external diameter of ≧20 mm to ≦2000 mm, satisfies the mathematical relationship
190kN/m
2
×(10/(
SDR
−1))
3
≧SN
≧110kN/m
2
×(10/(
SDR
−1))
3
preferably for the numerical values 162 and 137 kN/m
2
(instead of 190 and 110 kN/m
2
),
SDR representing the ratio of the outer diameter to the wall thickness.
In the case of a pipe having the dimensions of an external diameter of 110 mm and a pipe wall thickness of 3.7 mm, this means that the annular rigidity, measured according to ISO 9969 at 23° C., has a value approximately of 6.5 to 7.0 kN/m
2
.
In the case of polypropylene pipes with a wall of any configuration and with an external diameter of ≧40 mm to ≦4000 mm, the mathematical relationship
2.3×10
6
kN/m
2
×W≧SN
≧1.3×10
6
kN/m
2
×W,
should be valid preferably for the numerical values of 1.95 and 1.65×10
6
kN/m
2
(instead of 2.3 and 1.3×10
6
kN/m
2
), W representing the ratio of the length-related geometrical moment of inertia of the pipe wall to the third power of the center of gravity diameter.
This relates particularly to pipes with a sandwich-like pipe wall, pipes with a hollow wall construction with longitudinally extending cavities, pipes with a hollow wall construction with spiral cavities, pipes with a smooth inner surface and a compact or hollow, spirally shaped, or an annularly ribbed outer surface, independently of the configuration of the respective pipe ends.
As a consequence of good strength properties, these pipes do not show any breakage when the resist

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