JPS5810414B2 - Propylene - ethylene block copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is well known to carry out block copolymerization with ethylene as a comonomer in order to improve the impact resistance of polypropylene, especially the impact resistance at low temperatures.

The present invention relates to a process for continuously producing a block copolymer of propylene and ethylene and providing a product of excellent quality.

Block copolymers of propylene and ethylene are usually produced using an inert hydrocarbon liquid as a medium and a catalyst consisting of a complex system of transition metal compounds and organometallic compounds, such as systems consisting of titanium trichloride and organoaluminum. First, a homopolymer of propylene is produced, and then
It is carried out by removing propylene or supplying ethylene alone or ethylene and propylene without losing the activity of the catalyst to produce an ethylene homopolymer or a random copolymer of enalene-propylene. Ru.

This polymerization process can be carried out either batchwise or continuously (flow type), but in a tank equipped with a stirrer, which is commonly used as a polymerization reactor, the inside of the tank is considered to be in a state close to complete mixing. In a continuous system, the solid catalyst and the polymer (particles) formed on the catalyst flow out from the tank;
In other words, the residence time in each tank is completely stochastically determined and therefore differs for each catalyst (polymer) particle.
When propylene polymerization is carried out in the first tank and ethylene polymerization or enalene-propylene copolymerization is carried out in the second tank, the amount of polymerization in each type per individual catalyst particle is determined by the residence time in each polymerization tank. The amount of propylene polymerized and the amount of ethylene polymerized in the second stage or ethylene-propylene copolymerized amount differs for each individual catalyst (polymer) particle, and as a result, the obtained block copolymer has an extremely wide composition distribution. For example, even if the value of the first-stage polymer amount/second-stage polymer amount is 80/20 on average, if you think about it in the extreme, it includes everything from propylene homopolymer to ethylene homopolymer or enalene-propylene random copolymer. However, it has a highly variable composition.

It is clear that such compositional non-uniformity has an unfavorable effect on the quality of the produced polymer, for example, the polymer produced in the first stage and the polymer produced in the second stage have Generally, there are differences in molecular weight or intrinsic viscosity [η], so a wide distribution of composition corresponds to a wide distribution of molecular weight, and there is a possibility that some polymer particles with a significantly high molecular weight may be produced. There is and it becomes.

Therefore, when such a polymer is used for film, it produces a large number of fish eyes, and cannot be used as a film grade.

The present inventors discovered that fish eyes are caused by a mixture of polymers having a high intrinsic viscosity based on a wide composition distribution, and as a result, they arrived at the present invention.

That is, an object of the present invention is to provide a method for producing a block copolymer that is continuous flow type, has few fish eyes, and can be used for films.

The intrinsic viscosity of the propylene homopolymer produced in the first stage is [η] 1, the intrinsic viscosity of the polymer produced in the second stage is [η] 2, and the total intrinsic viscosity of all the polymers produced is [η] T, and between these, each production amount P1.
P2. It is assumed that additivity according to (P10P2) holds true.

That is, it is assumed that the following equation holds true.

(P1+P2)(η)TmF3(η)1+P2(η)2
From this formula, [η]1. If [η]2 is made equal, Pl,
It is clear that even if there is a distribution in the ratio of P2, there will be no distribution in [η]T, and by reducing the difference,
It is also possible to narrow the distribution.

That is, the basic idea of the present invention is to reduce the difference between [η]1 and [η]2 to narrow the distribution of [η]T, and thus to prevent the formation of high [η]T polymers. be.

The background of the present invention will be explained below using examples, but it goes without saying that the embodiments of the present invention are not limited to these examples.

Example 1 First, in order to study the situation of film fins when the molecular weight of the second stage is controlled, an experiment was conducted in which the conditions of the first stage were kept constant and [η] of the second stage was varied. did.

Two 2001 autoclaves were connected in series, and the first tank carried out the first stage of propylene homopolymerization, and the second tank carried out the second stage of ethylene-propylene copolymerization.

11.51 g of heptane, 4.5 g of titanium trichloride AA as a catalyst, and 25 g of dienal aluminum chloride were charged into the first tank per hour, and the temperature was set at 60°C and the pressure was maintained at 5.4 Ky/cm2G. Supply propylene.

Further, hydrogen is supplied using an analytical controller so as to maintain the concentration of hydrogen in the gas phase at 3.0%.

Under these conditions, the average residence time of the catalyst in the first tank is about 7.5 hours.

The produced heptane slurry of polypropylene is taken out to the second tank without losing the activity of the catalyst, where it is further mixed with 101 kg of heptane and 0.7 kg of ethylene per hour.
, 0.6 kg of propylene was supplied, and copolymerization was carried out at a temperature of 50°C.

The hydrogen concentration in the gas phase at this time was set as shown in Table 1 and controlled by an analytical controller.

However, no control was made in Experiment No.-4.

The hebutane slurry of the block copolymer obtained as described above was continuously extracted into 401 heptane containing 611 butanol, and the monomer and catalyst were removed in a batch process at 60°C, followed by centrifugation. Separate solid and liquid using a machine.

The obtained solid polymer cake was poured into 601 parts of water containing 6.5 parts of butanol, and the remaining solvent was steam-stripped at normal pressure, followed by solid-liquid separation.
The polymer was dried under vacuum.

The analytical values of the polymer thus obtained are shown in Table 2.

Next, this polymer was mixed with 0.2 PHR of 2,6 ditertiary levenyl para-cresol, 0.2 PHR of thiodylauryl dipropionate, and 0.1 PHR of calcium carbonate fine powder.
The mixture was granulated using a T-die film molding machine to form a film with a thickness of 30 μm, and the number of fish eyes per 1000 cm 2 was counted.

The results are shown in Table 3.

For comparison, Finshuai, a continuously polymerized propylene homopolymer, was polymerized, granulated, and film-formed using the same equipment as used in Example 1. 15 pieces/103
cm2, batch-polymerized propylene-ethylene block copolymer (second stage hydrogen 3%) Finnshuai is 40 pieces/1
It was 0.3 cm2.

Therefore, it is considered that fish eyes substantially disappeared in the polymer of Experiment No. 1.

Similar experiments were conducted with various [η] values, and the results are shown in FIG. 1, where the number of fish eyes was plotted against [η]2/[η].

From this figure, the disappearance of the fish eye requires [η]2 [η]
It can be seen that the ratio to 1 is required to be 1.2 or less.

Example 2 Next, in order to investigate how the physical properties of the total polymer were affected when the molecular weight of the second stage was controlled and reduced, polymerization was carried out by matching the melt index and ethylene content as much as possible. .

Polymerization was carried out using the same equipment and operation as in Example 1, except that the gas phase hydrogen concentration in the first stage (therefore, [η] 1) and the gas phase hydrogen concentration in the second stage ([η] 2) were varied according to Table 4. I let it happen.

The analytical values of the polymer obtained at this time are also shown in Table 4.

This polymer was granulated using the same additive formulation as in Example 1, a press sheet was prepared at 220°C, and the physical properties were measured. The results are shown in Table 5 along with the measurement method.

According to the above results, by increasing the hydrogen concentration in the latter stage, [η
] It can be said that the lower the value of 2, the lower the impact strength at low temperatures and the worse the embrittlement temperature, but for example, the physical properties of experiment number 6 are sufficient for practical use, and the physical properties of experiment number 5
However, there seems to be no practical difference.

From the above examples, in order to virtually eliminate fish eyes, the lower [η]2 is better, and its upper limit is about 1.2 as a ratio to [η]1.On the other hand, from the physical property values, In particular, in order not to significantly deteriorate the low-temperature impact resistance, which is a characteristic of block copolymers, it is considered necessary to maintain the ratio of [η]2 to [η]1 at least about 1. Therefore, the low-temperature properties are excellent. In order to obtain a polymer in which film fins are substantially absent, it is found that this ratio needs to be approximately 1 to 1.2.

[Brief explanation of the drawing]

FIG. 1 is a plot of the fisheye number of the film and the ratio of the limiting viscosity of the second stage to the limiting viscosity of the first stage of the polymer. Numbers ■, ■ in the diagram. ■ and ■ correspond to experiment numbers 1, 2, and 3°4 of Example 1, respectively.

Claims (1)

[Claims] 1. When producing a block copolymer consisting of a homopolymerized portion of propylene and a homopolymerized portion of ethylene or a copolymerized portion of ethylene-propylene, the molecular weight of the polymerized portion of ethylene or ethylene-propylene corresponding to the second stage is 1. A continuous method for producing a propylene-ethylene block copolymer, which is controlled by hydrogen, and is characterized in that the ratio of the intrinsic viscosity to that of the first-stage propylene homopolymerization portion is between 1 and 1.2.