DE2208265A1 - Polyolefin blends - Google Patents

Description

The present invention relates to blends of polypropylene and high density polyethylene, notable for both excellent processing properties as well Resistance to low temperatures and cracking under stress ("stress cracking") are excellent.

It is known that homopolymers of polypropylene with a high isotacticity index one for many purposes on the Polymer is a suitable polymer in the field of plastic materials. Besides the production of Pormkodies it can be used for the production of fibers and foils, which have very good mechanical properties have to be used / ended.

However, since it has a fairly high brittleness temperature, its use at relatively low temperatures is limited. Attempts have now been made to overcome this disadvantage by admixing the polypropylene with polymers which are compatible with it and suitable for lowering its brittleness temperature. For example, it has been proposed to add some rubbery polymers to the polypropylene.

One of the most frequently used processes to change the cold resistance properties of polypropylene sees the polymerization of propylene in the first stage and then at the end of the polymerization - the addition of ethylene, which is polymerized in the presence of unreacted propylene ,

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Is also known that the polypropylene because of its highly elastic component not suitable for blow molding is.

As for polyethylene, it is known that it can be done by low pressure processes produced polymer, which has a very high molecular weight, not always satisfactory results in the production of foils, * especially since these do not have an entirely smooth surface.

An attempt has now been made to eliminate this disadvantage * by Lubricants were used, but not met with much success. In addition, the sliding properties can be improved by the regulation the average molecular weight and the linearity of the polymer, as regulated by the addition of lubricants will.

In view of the complementary properties of the two polymers could be assumed that by intermingling "them interesting products are obtained.

However, it is known that it is impossible to perform a mechanical mixing of high density polypropylene, unless there is a very low percentage of a component ira ^i> compared to the other. ^{Λ if0}

From the Italian patent 846 478 a process for the production of τοη homogeneous mixtures of high-density polyethylene is and polypropylene known, starting from polypropylene with eehr high molecular weight, which is also by a high percentage of a polymer that can be extracted with boiling η-heptane »and high-density polyethylene with a Equal molecular weight is characterized. The method beateht darauar that the polymers after mixing a thermomechanical degradation in special degradation extrusion presses under so-called verdol.

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The products thus obtained have a relatively low molecular weight which is practical in a range Interest lies.

It has now surprisingly been found, and that is the subject of the present invention, that it starts from polypropylene with a very high molecular weight, which by a content of boiling n-heptane extractable polymer between about 10 and 30 wt. $ and an intrinsic viscosity of more than about 4 dl / g *) is characterized,

wherein the polypropylene can optionally be modified with ethylene in a weight ratio of about 1 to 20 % , is possible to obtain polypropylene-polyethylene blends with intrinsic viscosity numbers within a range of practical interest when said polypropylene with a high density polyethylene with an intrinsic molar Viscosity number between about 0.5 and 3 dl / g, eaten in tetrahydronaphthalene at 135 ⁰ C, is mixed. (The term "high density polyethylene" means a polymer which has a density above about 0.94 g / ccm, but generally with a density between about 0.95 and 0.97 g / ccm).

On the whole, this result is surprising and could not have been foreseen, especially since it can be achieved without thermomechanical aftertreatment, which is required in the already known processes would have.

The amount of for the preparation of the mixtures according to the invention The high-density polyethylene used is at least about 20% by weight, based on the total amount of the mixture. In general the amount is between about 20 and 80 wt. That for this one Purpose-used polypropylene can be obtained by known methods will. For example, it is possible to use the product obtained by polymerization in a liquid monomer as described in the applicant's Italian patent 612 695, to be used.

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*) measured in tetrahydronaphthalene at 135 ° C

The intrinsic molecular viscosity of the polymer is at least about 4 dl / g and is generally between about 5 and 9 dl / g.

The preparation of the mixtures with different proportions of the components enables a series of products to be obtained which have special mechanical and chemical-physical properties and also special machining properties which means that they can be better adapted to certain procedures.

For example, it is possible to obtain blends which have improved impact resistance if a polypropylene is used which has been modified with ethylene in a percentage ratio of about 1 to 20,56, mixed with high density polyethylene as described above or with about 1 until 3 $> propylene was modified.

The advantages achieved with the mixtures according to the invention can can be summarized as follows:

1. Possibility of producing polypropylene-polyethylene mixtures, in both injection molding and blow molding processes have excellent machinability.

2. Possibility of producing mixtures which have an improved flexural rigidity in relation to the polypropylene used to have.

3. Possibility of preparing mixtures with a base molar Viscosity number lower than that of the polypropylene used and such that it is easy to process is obtained in various uses.

4. Possibility of producing mixtures with a softening point, which is higher than that of conventional high density polyethylene.

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5. Possibility of producing mixtures that - "related on the polypropylene alone - are suitable for the manufacture of articles that have improved resistance to cold exhibit.

The present invention is illustrated by the following examples explained in more detail:

Example 1:

7.5 kg of a polypropylene with the properties given in Table 1 were mixed with 7.5 kg of high-density polyethylene in Presence of 0.2 wt. 56 Irganox, a commercially available complex, a high molecular weight stabilizer against oxidation and thermal decomposition of organic materials, and 0.3 wt% calcium stearate blended.

The powder obtained was then put into a Bandera extruder granulated and the mixture obtained in this way subjected to a test for characteristic properties and in tested a number of uses.

The characteristic properties found are in Table 1 given.

The mixture was found to be particularly suitable for use in injection molding processes. The workability was excellent and the appearance of the articles produced was found to be more than satisfactory.

Measurements were made with some of the manufactured objects (glasses) the brittleness temperature and good results obtain.

Articles have also been made by blow molding. The workability was found to be excellent and the appearance of the products was satisfactory.

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The polypropylene used in this example was obtained by proceeding in the following manner:

In an autoclave with a capacity of 150 liters, 80 liters of the liquid propylene was placed at room temperature. Then 0.023 g / l propylene in 50 ecm heptane, a complex compound of TiCl ^ HRA (hydrogen-reduced and activated) with pyridine (molar ratio Ti / pyridine 1: 3), and 1 g / l propylene of aluminum triethyl were added. The temperature of the mixture was then brought to 82 ^° C., and at this temperature the mixture was polymerized for six hours under a pressure of about 38 atm. An average of 50,000 g of the polymer was obtained per g of titanium.

After flashing off the propylene, the product was with Treated with water and steam and then dried.

The intrinsic viscosity of the obtained in this way Polypropylene was 6.1 dL / g.

Example 2

Using polypropylene with a higher basal molar Viscosity number than that of the polypropylene used in Example 1 and a polyethylene of the same type as in the previous one Example a mixture was made.

The extrusion was carried out following the same procedure as described in Example 1 and the mixture was applied investigated their characteristic properties. The results are the same as those given in Table 1 for Example 1.

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Example 3

A mixture was prepared like that described in Example 1, however, a high density, high molecular weight polyethylene was used to make one for further processing to obtain a suitable mixture of objects by blow molding.

The characteristic properties of the mixtures are off Table 1 can be seen.

There were also bottles of about 100 ecm fit and with a wall thickness of about 0.5 mm by the following blow molding process manufactured.

The machinability of the material turned out to be quite good. The surfaces of the manufactured articles were perfect Appearance without any bubbles.

The determination of the brittleness temperature at the bottles gave values below ⁰ -4o C. Similarly, the impact properties ZUJ.

gave values below -4O ⁰ C. Proved equally satisfactory

For a more precise evaluation of this material, the films were tested on a Bandera extruder with an extrusion diameter carried out by about 45 mm. A homogeneous flat sheet without bubbles was obtained.

This film was then mono-oriented by stretching it at a stretch ratio of 1: 7. There was a major improvement the mechanical properties and an improvement in the transparency of the film achieved.

The film as such had the following properties:

Tensile strength = 674 kg / cm ² elongation = 590 #

Elasticity _,? module = 6.61.10 kg / cm,

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which is analogous to the values of highly crystalline polypropylene. Example 4

The procedure described in Example 3 was followed, except that a polypropylene modified with 3.7% by weight of ethylene was used.

The characteristic properties of the mixture obtained are shown in Table 1.

In addition to the injection molding and blow molding samples, a film was produced with the following properties:

Tensile strength = 484 kg / cm ² elongation = 675%

■ 2 O

Young's modulus = 57 |, 10 ^ kg / cm.

manufactured

The modified polypropylene used in this example was wu by adding the same amounts of liquid propylene and catalyst to an autoclave (150 l) according to Example 1 and the reactants were introduced into the autoclave in the same way.

After the whole 5 hours and 30 minutes was long-polymerized ethylene in an amount of about 5 wt. Fo, based on the total polymer, is added.

The polymer removed from the autoclave had a base molar mass Viscosity number of 8.7 dl / g.

/Table 1

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product (°)
L grade
g / 10 min. 0.13 Tabel 1 Crystalline
against
about x-ray
genblast
i ° Residue
the extra
tion in it
end
n-heptane Brittleness
temperature CO Polypropylene 0.06 50 83.0 + 4 A at
game
No. Polyethylene 11.40 Reason-
molar
Viscosity
number
dl / g Bend
stiff
speed
kg / cm 88 98.5 <- 35 A 1 mixture 1.50 6.1 4 850 55 95.0 <T- 3Q B Polypropylene 0.01 1.2 13 950 58 77.5 + 8 A Polyethylene 11.40 1.4 10 800 88 98.5 <- 35 A 2208 2 mixture 0.72 8.2 5 150 57 89.5 + 15 A fs)
CT) Polypropylene 0.06 1.2 13 950 50 83.0 + 4 A cn Polyethylene 0.6 4.2 10 600 84 97.5 <- 40 A 3 mixture 0.31 6.1 4 850 75 88.5 <£ - 40 B Polypropylene with ')
3.7 fo copolymeri-) 0.019
siertea polyethylene)!
Polyethylene 0.6 2.3 9 500 51
84 81.0
97.5 + 2 A
- 40 A mixture 2.5 6 150 55 90.5 - 22 A 4th 8.7
2.3 5 450
9 500 2.8 6,800

- ίο -

A) Brittleness temperature for test panels, the 4 hours at 120 ° C

have been conditioned,

B) Brittleness temperature for test panels obtained from unconditioned objects (glasses and bottles) .

⁰ C) The L grade was determined according to ASTM-D-1238.

/ Claims / 11

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Claims (4)

- 11 claims 1. Mixture of polypropylene and high density polyethylene, thereby marked that they a) about 20 to 80 parts by weight of a polypropylene with basal molar Viscosity numbers of about 4-9 dl / g, determined in tetrahydronaphthalene at 135 C; and b) about 80 to 20 parts by weight of a polyethylene with a basic molar mass Viscosity number of about 0.5-3 dl / g, determined in tetrahydronaphthalene at 135 C and a density between about 0.95 and 0.97 g / cm ^; contains. 2. Mixture according to A. 1, characterized in that the component a) is modified with about 1 to 20% by weight of ethylene. 3. Mixture according to A. 1, characterized in that the component b) is modified with about 1 to 3 wt. ^ o propylene. 4. Manufactured objects, in particular films, characterized in that that they have been obtained from mixtures according to claims 1 to 3. The patent attorney (Dr. P. Weinhold) 209837/1088