JPH0617408B2 - Continuous production method of high melt viscoelastic polypropylene - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a continuous process for producing high melt viscoelastic polypropylene. More specifically, the present invention is a method for producing polypropylene having a broad molecular weight distribution, which is suitable for post-processing sheets and blow molding, by polymerizing propylene in multiple stages using three or more polymerization vessels connected in series. Regarding

[Conventional technology]

The general-purpose polypropylene has the following problems in the application field of the post-processing sheet. That is, a sheet processed using the polypropylene is post-processed (or 2
The following problems at the time of heat-forming for subsequent processing): the sheet droops quickly, the range of processing conditions is narrow, the molding efficiency is poor, the droop of the wide sheet is large, the thickness of the post-processed product Was likely to be uneven and wrinkles were likely to occur.

General-purpose polypropylene also has the following problems in the field of application for suction molding. That is, since the parison droops heavily during molding, the thickness of the molded product becomes uneven, so the suction molding method can be applied only to the manufacture of small molded products. To prevent the above droop,
The use of high-molecular-weight polypropylene causes poor fluidity, a large load and energy loss during molding, a risk of causing mechanical troubles, a rough surface of a molded product, and loss of commercial value.

In order to improve the above-mentioned sheet moldability and suction moldability when a general-purpose polypropylene is used, the following techniques a to c have been proposed.

That is, a. In JP-B-47-80614 and JP-A-50-8848, low density polyethylene is mixed with polypropylene.
However, a molded article using such a mixture is liable to cause rough skin, and in order to prevent this, strong kneading is required at the time of melting the mixture, which is restricted in terms of selection of a kneading machine and power consumption. In addition, there is a problem that the rigidity of the molded product decreases.

Then b. JP-A-57-185336, JP-A-187337, JP-A-58-74
39 et al. Propose a method of mixing and kneading polypropylenes having different molecular weights using a granulator or the like. However, when the mixture obtained in this way is used, roughening of the molded product is more likely to occur than in the case where the above-mentioned low-density polyethylene is mixed, and the kneading method and the selection condition of the molecular weight difference between the mixtures are restricted. To be done.

In addition, c. In order to solve the problems caused by the mixing method such as the above a and b, various methods for expanding the molecular weight distribution of polypropylene by a multi-stage polymerization method of propylene have been proposed. For example, JP-A-57-185304 and JP-A-1900.
6, in Examples of JP-A-58-7406, JP-A-7409, JP-A-59-172507 and the like, the difference in molecular weight is imparted to polypropylene by performing the above-mentioned multistage polymerization operation in a batch polymerization method. The batch polymerization method has a problem that the productivity per volume of the polymerization vessel is low because there is essentially an empty time during which the polymerization reaction is not performed, such as charging of raw materials and withdrawal of products.

However, the invention of group c mentioned above also refers to the continuous method. In order to produce polypropylene containing a difference in molecular weight by the continuous method, it can be divided into two according to the order of production. First, when a high molecular weight-low molecular weight combination sequence is used for production, it can be performed by simply adding hydrogen in the latter-stage polymerization vessel, and the operation is smooth, but there are problems described below. Secondly, in the case of producing in a combination order of low molecular weight-high molecular weight, it is necessary to remove excess hydrogen by an operation such as depressurization degassing with respect to the reaction mixture after the production of the low molecular weight polypropylene in the preceding stage, It is stated that the operation is inferior in smoothness to the first case.

The present inventor has found that the following problems 1 and 2 exist as a result of a study on the method for producing the high molecular weight / low molecular weight combination sequence described above in the invention of group c. That is, the melt flow rate of the high molecular weight portion of the obtained polypropylene (hereinafter referred to as MFR)
When is low, it becomes difficult to measure the MFR of the high molecular weight part, and it becomes difficult to adjust the MFR by adjusting the operating conditions (Note: it is of course possible to measure the viscosity [η] of such polypropylene, It takes time to measure [η] and is not suitable as a means of operation management). Furthermore, in the case of polypropylene produced in the order of high molecular weight-low molecular weight, the difference between the MFR value of the powder before granulation and the MFR value of the pellet after granulation is abnormally large (Note. However, it has been found that there is a problem in controlling the molecular weight difference and the MFR (granulated product) as a product for the polypropylene.

[Object of the Invention]

As a result of various studies to solve the above-mentioned technical problems, the inventors of the present invention found that three or more polymerization vessels were connected in series and the catalyst and hydrogen were supplied only to the first tank to carry out propylene polymerization. As the polymerization reaction mixture in the tank was sequentially transferred to the subsequent polymerization reactor, the catalyst concentration and hydrogen concentration in the reactor in the subsequent polymerization reactor decreased, so that a higher molecular weight polymer was produced. The present invention has been completed by knowing that polypropylene having a wide molecular weight distribution can be obtained as the final product polypropylene.

As is clear from the above description, the object of the present invention is a continuous production method of a high-melting viscoelastic polypropylene having a wide molecular weight distribution and good moldability, in particular, improved production with excellent drivability and easy quality control. To provide the law. Another object is to provide a high melt viscoelastic polypropylene produced by the above method and having excellent moldability.

[Constitution / Effect of Invention]

The present invention has the following main constitution (1) and embodiment constitutions (2) to (5).

(1) In a method for continuously producing polypropylene by polymerizing propylene by a slurry method or a bulk polymerization method using a Ziegler-Natta type catalyst, using three or more polymerization units connected in series, The whole amount is supplied to the first polymerization reactor, the catalyst is continuously moved to the second and subsequent polymerization reactors together with the reaction mixture, hydrogen is used as a molecular weight regulator, and the entire amount of the hydrogen used is transferred to the first polymerization reactor. To the second and subsequent polymerization reactors, and the polypropylene produced by polymerization in each polymerization reactor was sequentially formed on the catalyst, and then the reaction was conducted from the final polymerization reactor. The slurry is continuously discharged, and the polymerization amount Qi per unit time in the i-th polymerization vessel is adjusted so as to be within the range of the following formula (1), However, MFR of polymer produced in i-th and i + 1-th polymerization vessel
The values MFR _i and MFR _{i + 1} are adjusted so that they have the relationship of the following formula (2), Adjust the polymerization pressure of the i-th polymerization reactor in the polymerization reactors connected in series so that it does not become lower than the polymerization pressure of the i-1th polymerization reactor by 2 kg / cm ² G or more, and adjust the polymerization pressure of the polymerization reactors connected in series. A continuous production method of high melt viscoelastic polypropylene, characterized in that the polymerization temperature of the i-th polymerization vessel is adjusted not to be higher than the polymerization temperature of the i-1th polymerization vessel by 10 ° C or more.

The structure and effect of the present invention will be described in detail below.

The catalyst used in the present invention is not particularly limited as long as it is a so-called Ziegler-Natta type catalyst relating to a combination of a transition metal compound and an organic compound of Group I to III metals of the periodic table, hydride or the like. However, it is preferable to use a catalyst that basically combines a titanium compound and an organoaluminum compound. As the titanium compound, titanium trichloride or a titanium trichloride composition obtained by reducing titanium tetrachloride with hydrogen or metallic aluminum is further crushed by a ball mill, a vibration mill or the like, or activated.
Further, the activated material is treated with an electron-donating compound, or titanium tetrachloride is reduced with an organoaluminum compound, and further various treatments (for example, titanium trichloride composition in which crystal transition is caused by heating in TiCl ₄ ). A titanium trichloride composition obtained by treating with an electron-donating compound and / or an electron-accepting compound to obtain a highly activated titanium trichloride composition, and tetrachloride on a carrier such as magnesium chloride. A catalyst generally used for stereoregular polymerization of propylene such as a so-called supported catalyst obtained by supporting titanium can be used.

As the organoaluminum compounds mentioned above preferably used in the present invention, a compound represented by _{AlR n R 'n' X 3-} (n + n ') is particularly preferred. In the formula, X represents halogen such as fluorine, chlorine, bromine and iodine, and n and n'represent any positive number of 0 <n + n'3. Specific examples thereof include trialkylaluminums and dialkylaluminums, and two or more kinds of these may be mixed and used.

The above-mentioned catalyst may be used in combination with an electron donor known as a so-called third component.

Polymerization methods include, in addition to raw material propylene and a catalyst, slurry polymerization using an inert solvent such as propane, hexane, heptane, octane, benzene or toluene, or a hydrocarbon solvent, or bulk polymerization using propylene itself as a solvent (dispersion medium). Can be used.

As the polymerization vessel used in the method of the present invention, preferably three or more tank type polymerization vessels are connected in series, and as a method for transferring the reaction mixture, a part of the liquid phase (slurry) portion in the polymerization vessel of the preceding stage is used. Are continuously transferred to the next-stage polymerization vessel. The three or more polymerizers must be connected in series.

In the method of the present invention, the catalyst is supplied in its entire amount only to the first tank. The catalyst (solid), together with the reaction mixture described above, sequentially passes through the second and subsequent polymerization vessels to sequentially form polypropylene on each polymerization vessel on the solid of the same catalyst, and includes such a catalyst solid. The reaction mixture is continuously withdrawn from the polymerizer in the final tank. If the polymerization is carried out by adding a catalyst to any of the polymerization vessels of the second tank and thereafter, a polymer having a significantly different MFR from the one via the first tank is formed on the additional catalyst particles, Even if the product is obtained after granulation, it is not uniformly mixed, and the appearance of processed products such as fish eyes (FE) is deteriorated, which is not preferable.

In the method of the present invention, the hydrogen used as the molecular weight regulator is supplied to the first tank only in its total amount as in the above-mentioned catalyst. The supply position of hydrogen in the polymerization vessel may be a liquid phase part or a gas phase part. However, when supplying hydrogen to the liquid phase portion, it is necessary to take care so that the supply material is not trapped as bubbles in the withdrawn (transferred) slurry to the second tank. This is because, in the method of the present invention, hydrogen supplied to the second and subsequent tanks is generally supplied from the tank immediately before each in a state of being dissolved in the reaction mixture (slurry). Therefore, when hydrogen trapped as bubbles is sent to the next tank, the difference in molecular weight between the polypropylene produced in the tank and the polypropylene produced in the next tank is
This is not preferable because it becomes smaller than expected and the molecular weight distribution of the final product polypropylene cannot be sufficiently wide.

Also, in the method of the present invention, the polymerization vessels are connected in series.
Use more than one. In the method of the present invention in which the catalyst and hydrogen are supplied only to the first tank, the polymerization degree distribution of the product polypropylene cannot be made wide enough to meet the purpose of use with two polymerization vessels. Unlike the above-mentioned method of supplying the catalyst and hydrogen, the required amount of propylene or solvent as the raw material can be supplied to the polymerization reactor at each stage.

The polymerization amount of propylene in each stage of the polymerization vessel is preferably within the range represented by the following formula (1) in order to maintain the quality of the final product.

However, As shown in the above formula (1), the specific polymerization amount of each polymerization vessel is
± 30 based on the case of uniform polymerization in each polymerization vessel
It is necessary to adjust within the range of the fluctuation range of%. When the Qi value is out of the range of the above formula (1), the width of the molecular weight distribution of the final product becomes insufficient, and it becomes difficult to obtain the target high-melt viscoelastic polypropylene.

The polymerization temperature of the method of the present invention is not limited, but is usually 20 to
It is easy to carry out at 100 ° C, preferably 40 to 80 ° C. The temperature of each polymerization vessel may be the same or different. However, with respect to the polymerization temperature, it is necessary to prevent the temperature of the subsequent polymerization units in the polymerization units before and after being connected in series from being higher than the polymerization temperature of the polymerization unit immediately before that by 10 ° C. or more. If the polymerization temperature of the latter-stage polymerization vessel is higher than that of the previous-stage polymerization vessel
If the temperature is higher than 10 ° C., the molecular weight of the polypropylene produced in the latter stage will be too low, and the molecular weight distribution of the final product cannot be widened sufficiently. On the contrary, the difference in the polymerization temperature of the polymerization vessel immediately after the series is not limited with respect to the same temperature or a lower temperature in the latter stage than in the former stage. Because,
This is because the method of the present invention is a method for producing polypropylene having a higher degree of polymerization in the latter-stage polymerization vessel.

Therefore, in order to broaden the molecular weight distribution of the polypropylene according to the present invention, it is easier to raise the temperature of the first polymerization vessel to the highest temperature and sequentially lower the temperature of the second polymerization vessel and thereafter.

The polymerization pressure in the method of the present invention is not limited, but normally atmospheric pressure to 50 kg / cm ² G is used. The polymerization pressures of the respective polymerization reactors connected in series according to the method of the present invention may be the same or different from each other. However, it is necessary to prevent the polymerization pressure of the subsequent polymerization units in the polymerization units before and after being connected in series from being lower than the polymerization pressure of the polymerization unit immediately before that by preferably 2 kg / cm ² or more. When it becomes ² kg / cm ² or more, the molecular weight of the polypropylene produced in the polymerization vessel becomes lower than that expected, and it becomes difficult to sufficiently widen the molecular weight distribution of the final product.

As is clear from the above description, in the method of the present invention, it is easier to control the molecular weight distribution of the final product more broadly by increasing the pressure of each polymerization vessel connected in series from the first tank in order. become.

In the method of the present invention, the average residence time of the reaction mixture in each polymerization vessel connected in series is not limited, but is usually 30
It is carried out in minutes to 10 hours. In addition, the above-mentioned various polymerization conditions, that is, pressure, temperature, residence time, etc., can be easily achieved by selecting the desired quality of polypropylene, the catalyst used, and the like.
Besides, the transfer of the slurry between the polymerization vessels connected in series is
Regular pumping, differential pressure transportation and other methods can be adopted without any special restrictions.

The MFR of the polypropylene according to the present invention obtained as described above is usually 0.01 to 100, especially for sheet molding,
For suction molding, those having an MFR value of 0.05 to 10, preferably 0.10 to 5.0 are used. Incidentally, it is preferable that the difference in molecular weight between polypropylenes produced by the respective polymerization reactors connected in series is within the range of the following formula (2) when expressed as an MFR value.

However, MFRi; MFR MFR _{i + 1} of the polymer produced in the i-th polymerization vessel; i + 1-th 〃 If the value on the left side of the above formula (2) is less than 1.0, The desired high melt viscoelasticity tends to be insufficient, which is not preferable. Although the upper limit of the numerical value is not limited, it is difficult to set it to 3.0 or more in a specific embodiment of the method of the present invention.

The main effects of the method of the present invention are summarized as follows.

First, since the polypropylene according to the method of the present invention has a wide molecular weight distribution, it has good fluidity during extrusion molding, and has effects such as an increase in the amount of extrusion by an extruder and saving of power consumption. Furthermore, since it has characteristics such as excellent fluidity at the time of injection molding, it can exhibit excellent effects in terms of quality and processing efficiency in applications in various molding fields.

Secondly, in the method of the present invention, as a multi-step polymerization method, it is extremely easy to control the polymerization process or adjust the polymerization conditions.

That is, since the catalyst and hydrogen are supplied only to the first tank of the polymerization tanks in which three or more units are connected in series, only the necessary propylene and solvent may be added to the second tank and thereafter. In the simplest way, the polymerization conditions in each tank may be the same pressure and the same temperature, even if the pressure and temperature are reversed between two adjacent tanks (Note: the latter stage is numerically higher) When the degree is within the allowable limit range (2 kg / cm ² G or less, within 10 ° C.), the object of the present invention can be achieved.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

The following methods were used for measuring the physical property values according to the examples of the present invention.

1) Melt flow rate (MFR): ASTM D1238 2) Calculation of MFR of polymer produced in each polymerization reactor: MFR ₁ ; 1st stage MFR (* 1) MFR ₂ ; 2nd MFR ₃ ; 3rd MFR _{1 + 2} ; Overall MFR (* 1) MFR _{1 + 2 + 3} generated in the 1st and 2nd stages; Overall MF generated in 1st, 2nd and 3rd stages
R (* 1) W ₁ + W ₂ + W ₃ = 1.0 * 1; Sampling at each stage and measurement.

* 2: Titanium content of polymer sampled at each stage (fluorescence X
(Line analysis) was measured and the polymerization rate was calculated.

The calculation of MFR ₂ and MFR ₃ was obtained by the following relational expression.

3) Physical properties measurement method for sheet molded products: Young's modulus; ASTM D882 (kgf / mm ² ) Heating behavior; Chisso method To evaluate the heating vacuum forming property of the sheet as a model, the sheet was fixed to a 40 cm × 40 cm frame, The following physical properties were measured by placing in a thermostatic chamber at 200 ° C. That is, a) the amount of droop of the seat
(mm), b) Maximum return amount (Note. {1/150 x (150-droop amount during maximum recovery (mm) x 100}) and c) Hold time from maximum recovery to restart of droop (seconds) ).

Example 1 1) Preparation of catalyst n-hexane 6, diethyl aluminum monochloride (D
5.0 mol of EAC) and 12.0 mol of diisoamyl ether were mixed at 25 ° C. for 5 minutes and reacted at the same temperature for 5 minutes to obtain a reaction solution (I) (diisoamyl ether / DEAC molar ratio 2.4). 40 mol of titanium tetrachloride was placed in a reactor purged with nitrogen and heated to 35 ° C., and the whole amount of the above reaction product liquid (I) was added to this.
After dropping for 180 minutes, keep at the same temperature for 30 minutes, raise to 75 ℃ and react for 1 hour, cool to room temperature, remove the supernatant, add n-hexane 30 and remove by decantation. Repeated 4 times to give 1.9 kg of solid product (II).

The total amount of this (II) was suspended in n-hexane 30 at 20 ° C. to obtain 1.6 kg of diisoamyl ether and 3.5 mg of titanium tetrachloride.
kg was added at room temperature for about 5 minutes and reacted at 65 ° C. for 1 hour. After the reaction was completed, the mixture was cooled to room temperature (20 ° C), the supernatant was removed by decantation, 30 n-hexane was added and stirred for 15 minutes, and the mixture was allowed to stand and the supernatant was removed 5 times. After that, it was dried under reduced pressure to obtain a solid product (III).

2) Preparation of catalyst Charge n-hexane 40, diethylaluminum chloride 850g, the above solid product 360g, and methyl paratoluate 3.8g into a tank with an internal volume of 50, and then maintain propylene gas at 180g / g while maintaining stirring at 30 ° C. It was supplied with H for 2 hours and pretreated.

3) Polymerization method It was carried out by the polymerization apparatus shown in FIG.

N-Hexane 26 / H / hour, catalyst slurry 120m to polymerization vessel (1)
/ H was continuously supplied. The temperature of the polymerization vessels (1) to (3) is 70.
Propylene was supplied to each polymerization vessel so that the temperature and the pressure were 6 kg / cm ² G, 8 kg / cm ² G, and 10 kg / cm ² G, respectively.

The hydrogen concentration of the gas phase part of the polymerization vessel (1) ~ (3) is only the polymerization vessel (1),
When supplied at 2.5 mol%, the polymerizer (2) and the polymerizer (3) were 0.37 mol% and 0.06 mol%, respectively. The reaction amount and MFR analysis value of each polymerization vessel were as shown in the table.

The various polymerization vessels were pulled out by a control valve so that the liquid level was 80%. The polymer produced was obtained at 6 kg / H.

The analytical values are as shown in Table 1.

4) Granulation method and sheet molding BHT (2.6-di-t-Buty) was added to 15 kg of the white polymer powder obtained above.
LP-cresol) 15g, Irganox1010 (Tetrakis 〔Methylene
(3.5-di-t-butyL-4-Hydrocinnamate] methane) 7.5g, Cal
30 g of cium stearate was added and granulated using a 40 mm granulator. Then, the granules were mixed with a 50 mm medium extruder for 22
A sheet having a width of 60 cm and a thickness of 0.4 mm was prepared by processing at 5 ° C., and the physical properties of the sheet were evaluated by the above methods. The results are shown in Table-1.

Comparative Example 1 In Example 1, the hydrogen concentration in the vapor phase of the polymerization reactor was made the same by supplying hydrogen to various polymerization reactors. In this case, the heating behavior of the sheet was significantly inferior.

Comparative Examples 2 and 3 In Example 1, the third stage polymerization was omitted, and the polymerization pressure and hydrogen were changed as shown in the table. In the two-stage polymerization, even if the MFR difference between the polymerization vessels and the polymerization rate are within the range of the present invention, the heating behavior of the sheet is inferior, and the object of the present invention was not achieved.

Examples 2, 3 and 4 In Example 1, the polymerization temperature and the polymerization pressure were changed as shown in the table.

Comparative Example 4 The procedure of Example 1 was repeated except that the pressure was changed as shown in the table. Further, in order to adjust the polymerization amount of each polymerization vessel to the range of the present invention, the liquid level of the polymerization vessel is 40% for the polymerization vessel (1), 60% for the polymerization vessel (2),
The polymerization reactor (3) was operated at 80%. If the pressure between the polymerization vessels was outside the range of the present invention, it was difficult to obtain the MFR difference between the polymerization vessels, and the heating behavior of the sheet was poor.

Comparative Examples 5 and 6 In Example 1, in order to change the polymerization amount of each polymerization vessel,
It carried out on the conditions shown in the table. Even when the polymerization ratio was outside the range of the present invention, the heating behavior of the sheet was inferior, which was not preferable.

Comparative Example 7 In Example 1, the catalyst slurry was distributed and supplied to three polymerization vessels. Distribution ratio is polymerization vessel (1): polymerization vessel
(2): Polymerization unit (3) = 8: 1: 1. In terms of physical properties of the sheet, severe surface roughness (FE) occurred on the surface of the sheet.

Comparative Example 8 In Example 1, the polymerization temperature and the pressure were changed as shown in the table. In order to set the polymerization ratio within the range of the present invention, the liquid level in the polymerization vessel is set to polymerization vessel (1): polymerization vessel (2): polymerization vessel (3) = 8
5%: 65%: 45%. When the polymerization temperature between the polymerization vessels is out of the range of the present invention, it becomes difficult to obtain the MFR difference between the polymerization vessels, and the heating behavior of the sheet is inferior, which is not preferable.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a flow sheet of a polymerization apparatus used in the method of the present invention. In the figure, 1 ... First polymerization vessel (150) 2 ... Second 〃 (150) 3 ... Third 〃 (150) 4 ... Degassing tank (100) 5 ... Reactant transfer pump.

Claims (1)

[Claims] 1. A method for continuously producing polypropylene by polymerizing propylene by a slurry method or a bulk polymerization method using a Ziegler-Natta type catalyst, which uses three or more polymerization vessels connected in series. The total amount of the catalyst is fed to the first polymerization reactor, and the catalyst is continuously moved to the second and subsequent polymerization reactors together with the reaction mixture, hydrogen is used as a molecular weight regulator, and the total amount of the hydrogen used is adjusted to the first polymerization reactor. It is supplied to one polymerization reactor, and the hydrogen is continuously transferred to the second and subsequent polymerization reactors together with the reaction mixture, and polypropylene formed by polymerization in each polymerization reactor is sequentially formed on the catalyst. , The reaction slurry is continuously discharged, and the polymerization amount Qi per unit time in the i-th polymerization vessel is adjusted to be within the range of the following formula (1), However, MFR of polymer produced in i-th and i + 1-th polymerization vessel
The values MFR _i and MFR _{i + 1} are adjusted so that they have the relationship of the following formula (2), Adjust the polymerization pressure of the i-th polymerization reactor in the polymerization reactors connected in series so that it does not become lower than the polymerization pressure of the i-1th polymerization reactor by 2 kg / cm ² G or more, and adjust the polymerization pressure of the polymerization reactors connected in series. A continuous production method of high melt viscoelastic polypropylene, characterized in that the polymerization temperature of the i-th polymerization vessel is adjusted not to be higher than the polymerization temperature of the i-1th polymerization vessel by 10 ° C or more.