JPH0420003B2 - - Google Patents

Description

[Detailed description of the invention]

(Objective) The present invention relates to a method for producing a propylene polymer. More specifically, while maintaining the excellent rigidity, impact resistance, transparency, heat resistance, etc. inherent to crystalline propylene polymers, it has good moldability especially in vacuum/pressure molding, extrusion molding, etc. and a method for producing a propylene polymer that eliminates the problem of surface roughness. (Prior art) Due to its excellent physical properties, polypropylene is widely used in the fields of vacuum and pressure molded products such as food containers and trays, and extrusion molded products such as films and sheets. Due to poor properties, productivity during molding is low, and improvement in melt elasticity has been strongly desired. Conventionally, a method of blending low-density polyethylene or the like with polypropylene for the purpose of imparting high melt elasticity has been known (Japanese Patent Publication No. 47-30614;
−8848, etc.). However, although these methods improve the melt elasticity, the excellent physical properties inherent to polypropylene such as rigidity and heat resistance deteriorate, which is not preferable. Therefore, various attempts have been made to improve the melt elasticity by broadening the molecular weight distribution of polypropylene itself, rather than by mixing it with other resins. For example, in the polymerization of propylene, a method has been proposed in which the polymerization is carried out in two stages, and a high molecular weight component and a low molecular weight component are generated in a polymerization tank to improve the melt elasticity (Japanese Patent Application Laid-Open No. 1989-1999- 38389,
Unexamined Japanese Patent Publications 1984-144448, 1982-123637, 1983
−185304). However, in this method, if the molecular weight difference between the two components is increased in an attempt to improve the melt elasticity, the dispersion of the high molecular weight component becomes poor and the molded product often suffers from sticking eyes. On the other hand, if the molecular weight difference between the two components is reduced in order to suppress the occurrence of fish eyes, the melt elasticity will hardly improve. Therefore, no method has been found to date to improve the melt elasticity of molded products without causing fish eyes. (Summary of the present invention) By devising a polymerization method, the present inventors
We conducted intensive studies to simultaneously improve melt elasticity and eliminate firm eyes. As a result, by conducting polymerization in three stages, producing low molecular weight components in the first and third stages, and producing high molecular weight components in the second stage, it is possible to simultaneously improve melt elasticity and eliminate firm eyes. obtained a polymer with
We have arrived at the present invention. In a method for producing a propylene polymer by polymerizing propylene using a catalyst system mainly consisting of a titanium-containing solid catalyst component and an organoaluminum compound, the polymerization is carried out in three stages, and the polymerization ratio in each stage is controlled. The first stage is 35 to 55% by weight, the second stage is 1 to 30% by weight, the third stage is 35 to 55% by weight, and the first and third stages are
A method for producing a propylene polymer, characterized in that in the stage, polymerization is carried out in the presence of hydrogen, and in the second stage, polymerization is carried out in a substantially hydrogen-free state. This is a method for producing propylene polymer. (Specific Description) The catalyst system used in the present invention is mainly composed of a titanium-containing solid catalyst component and an organoaluminum compound. The titanium-containing solid catalyst component is selected from a known carrier-supported catalyst component obtained by contacting a solid magnesium compound, titanium tetrahalide, and an electron-donating compound, and a known catalyst component containing titanium trichloride as a main component. The organoaluminum compound of the cocatalyst has the general formula
AlR _o X _3-o (wherein R represents a hydrocarbon group having 2 to 10 carbon atoms, X represents a halogen, and n is 3≧n
1.5). The titanium-containing solid catalyst component contains a solid magnesium compound. In the case of a supported catalyst component, it is preferable to use AlR _{3 or} a mixture of AlR ₃ and AlR ₂
It is preferable to use Furthermore, in the method of the present invention, in addition to the above catalyst and cocatalyst components, a known electron-donating compound can be used as a third component. The polymerization reaction can be carried out in the presence or absence of an inert solvent such as hexane or heptane, ie in the presence of liquid propylene or in gas phase propylene. Polymerization takes place in three stages. The catalyst is generally added before the first stage polymerization. Although replenishing the catalyst in the second and third stage polymerization processes is not necessarily excluded, the catalyst is added in the first stage because the purpose is to obtain properties that cannot be obtained by blending resins. It is preferable to do so. In the first stage polymerization, propylene is polymerized in the presence of hydrogen. Hydrogen is controlled so that the MFR of the polymer obtained by the first stage polymerization is in the range of 0.1 to 200. In general, the hydrogen concentration (in slurry polymerization, the concentration in the gas phase, in polymerization in solvent-free liquid propylene or in the gas phase method, refers to the content in the monomer; the same applies hereinafter) is 0.1 to 30 mol%, preferably 0.3 to 30%.
20 mol% is added. The polymerization temperature in the first stage is generally 40-90°C, preferably 50-80°C. MFR (ASTMD-1238) by first stage polymerization
is 0.1 to 200, preferably 0.5 to 100, in an amount of 35 to 55% by weight of the total polymer. Immediately after the first stage polymerization is completed, the second stage polymerization begins. In the second stage polymerization, after the residual gas in the polymerization tank is released and the hydrogen in the polymerization tank is removed, even if the hydrogen supply is stopped, only the monomer is supplied, so that the state is substantially hydrogen-free. Polymerization takes place. In the second stage polymerization, since the purpose is to form a high molecular weight polymer, high temperatures are generally avoided, and the polymerization temperature is usually 40 to 90°C, preferably 40 to 75°C, particularly preferably 40 to 75°C. It is carried out at 50-70°C. The polymer obtained by the second stage polymerization has a weight average molecular weight of 800,000 or more, preferably 1,000,000 or more, and the proportion of the polymer obtained by the second stage polymerization in the total polymer is It is desirable that the content be 1 to 30% by weight. When the weight average molecular weight does not reach 800,000, the improvement in melt elasticity is small, which is not preferable. The weight average molecular weight is determined by measuring both the polymer obtained by the first stage polymerization and the polymer obtained after the second stage polymerization using GPC, and calculating the difference between the two and the difference between the first and second stage polymers. It can be obtained by calculating the weight average molecular weight from the relationship with the polymerization amount. After the completion of the second stage polymerization, the third stage is again coexisted with hydrogen.
A stepwise polymerization is carried out. The polymerization conditions can be carried out in the same range as the first stage polymerization, and the MFR of the polymer obtained in the third stage is preferably 0.1 to 200, preferably 0.5 to 100, and the
The amount of polymer obtained by stepwise polymerization is between 35 and 55% by weight. The ratio of the polymer obtained in the first stage polymerization and the polymer obtained in the third stage polymerization is 1:2 to 2:
A ratio of 1 is desirable. In addition, the polymer obtained by the third stage polymerization
MFR is determined by measuring the MFR of the polymer after the second stage polymerization and the polymer after the third stage polymerization, and calculating the amount of polymer after the second stage polymerization and the polymer obtained by the third stage polymerization. It can be obtained by calculating from the amount of The final polymer obtained by three-stage polymerization
MFR is 0.1-10, preferably 0.5-5, and the content of other olefins is 20% by weight or less, preferably 15% by weight or less. In the two-step polymerization as shown in JP-A-54-38389 and JP-A-55-123637, the melt elasticity of the polymer is improved, but due to poor dispersion of the high molecular weight component, phishing occurs frequently and commercial value is lost.
On the other hand, in the three-stage polymerization of the present invention, the high molecular weight component is uniformly dispersed in the low molecular weight component in order to generate the low molecular weight component before and after the high molecular weight component is generated.
It is presumed that as a result, the melt elasticity is further improved and the occurrence of fish eyes is suppressed. Hereinafter, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, in the examples, evaluation methods for various physical properties of the polymer are as follows. II: Isometric index is determined as the ratio of the boiling n-heptane extraction residue of the product powder to the total. MFR: Melt flow rate measurement is ASTM-D
−1238. MT: Melt tension was measured using a melt tension tester manufactured by Toyo Seiki Seisakusho, cylinder temperature 190℃, orifice L/D = 8/
2.1, the extrusion speed was 10 mm/min and the tensile speed was 3.9 m/min. Eyes: The presence or absence of eyes with a diameter of 0.2 mm or more was determined for sheets manufactured under the following conditions. Screw diameter is 35mm and L/D is 28
It is extruded from a coat hanger die with a width of 300 mm at a die temperature of 250°C using an extruder of After applying heat, a sheet with a thickness of 0.3 mm was produced. Vacuum formability: Using the sheet produced as described above, a vacuum formability test was conducted using a vacuum forming tester. Example 1 and Comparative Examples 1 and 2 In a stainless steel autoclave with an internal volume of 200, n-heptane 70 and titanium trichloride (TiCl _3.1 /
20 g of 3AlCl ₃ (AA grade manufactured by Toho Titanium Co., Ltd.) and 30 g of diethylaluminum chloride were added, the temperature was raised to 70°C, and hydrogen and propylene were supplied to produce a polymer with an MFR of 4.4, accounting for 45% of the total polymer. Next, unreacted gas is released, and propylene is newly supplied to carry out anhydrous polymerization, resulting in total polymerization.
10% produced. Finally, hydrogen and propylene were supplied to produce a polymer with an MFR of 4.4, accounting for 45% of the total polymer. Thereafter, unreacted gas was discharged, and 2 portions of n-butanol were added and stirred. The resulting solid polymer was separated from the heptane solution, washed with water, and dried. The product polymer weighed 17.8 kg. The polymerization results and quality evaluation results at this time are shown in Table 1 and FIG. 1 together with Comparative Examples 1 and 2. Comparative Example 1 was a two-stage polymerization, in which the first
Comparative Example 2 was also a two-stage polymerization in which anhydrous polymerization was performed in the second stage. As is clear from Table 1, in Example 1, the fish eye did not start at all, and it was much superior to Comparative Examples 1 and 2. Furthermore, the melt elasticity was also superior to Comparative Examples 1 and 2, which corresponds to the excellent vacuum formability results shown in FIG. Examples 2 to 5 Table 2 shows the results of experiments conducted in the same manner as in Example 1 except that the production ratio and MFR of each stage were changed. As is clear from Table 2, in each of the Examples, no fish eyes were generated, and moreover, they exhibited high melt elasticity.

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【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the sheet sag test results of a polymer obtained by the present invention and a polymer obtained by a conventional method.

Claims (1)

[Claims] 1 In a method for producing a propylene polymer by polymerizing propylene using a catalyst system mainly consisting of a titanium-containing solid catalyst component and an organoaluminum compound, the polymerization is carried out in three stages, and the polymerization ratio at each stage is The first stage is 35 to 55% by weight, the second stage is 1 to 30% by weight, and the third stage is 35 to 55% by weight, and the first and third stages are
A method for producing a propylene polymer, characterized in that in the stage, polymerization is carried out in the presence of hydrogen, and in the second stage, polymerization is carried out in a substantially hydrogen-free state.