JPS6258887B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing propylene-ethylene block copolymer granules. Specifically, when molding propylene-ethylene block copolymer powder produced by a continuous polymerization method into granules, the molten propylene-ethylene block copolymer is
At least two net-like bodies have a mesh size of 120 meshes or more, and at least one of them has a mesh size of 120 meshes or more.
This is a method for producing propylene-ethylene block copolymer granules that are passed through a dispersing machine composed of a combination of a plurality of net-like bodies having an opening of 170 meshes or more. Polypropylene is manufactured by various methods. However, polypropylene does not have sufficient impact resistance. For this reason, a technique for producing propylene-ethylene block copolymers has been adopted and implemented as a technique for improving impact resistance. The propylene-ethylene copolymer usually comprises a first step of polymerizing propylene or propylene with another olefin such as ethylene, butene, etc. in the presence of a catalyst, and the presence of a polymer containing the catalyst obtained in the first step. It is produced by a polymerization method comprising a second step of copolymerizing ethylene and propylene in the presence of a polymer to which a catalyst has been added. The above polymerization method includes a batch method in which copolymerization in the second step is carried out after completing the polymerization in the first step;
It can be roughly divided into two methods: a continuous method in which the polymer of the first step is supplied to the second step and the process is carried out continuously.
When obtaining block copolymerization by batch method, impact resistance,
Although it is possible to obtain products with excellent physical properties such as rigidity, it not only increases the product cost due to operational defects and increased equipment costs, but also is not suitable for mass production, so it is not adopted industrially. Rare. On the other hand,
The continuous method is the complete opposite of the batch method, and is widely adopted as an industrially superior technology, but compared to products obtained using the batch method, it has inferior impact resistance, and when processed into film, it causes cracks and eyes. There are defects such as these, which limit its uses and cause dissatisfaction with its physical properties. Therefore, establishing a technology for manufacturing products equivalent to batch-type products using a continuous process is a major challenge in the field of this application. For this purpose, for example, JP-A-49-61278
Although many methods have been proposed, such as in Japanese Patent Application Laid-Open No. 49-53990, none of them are industrially satisfactory. That is, the film obtained by the former method (Japanese Unexamined Patent Publication No. 49-61278) has a somewhat reduced film eye when formed into a film, but the impact resistance also decreases at the same time; ) If one were to adopt the method, the physical properties would be improved compared to the former, but not only would the equipment cost be large, but the operation would have to be extremely complicated. For many years, the inventors of the present invention have endeavored not only to provide block copolymers obtained by continuous polymerization with physical properties similar to those produced by batch polymerization, but also to develop a technology that is industrially satisfactory. Ta. As a result, the propylene-ethylene block copolymer powder, which normally suffers from frequent fish eyes and has low physical properties such as impact strength, eliminates fish eyes at the stage of forming into granules and improves impact strength. We have established and proposed a method to do so. That is, the present invention is a propylene-ethylene block copolymer (hereinafter simply PE) produced by a continuous polymerization method.
When molding powder into granules (abbreviated as "block copolymer"), the PE block copolymer in a molten state is processed into at least two meshes having a mesh size of 120 meshes or more, and at least one of the meshes. The method for producing PE block copolymer particles is made by passing the PE block copolymer granules through a dispersing machine made up of a combination of a plurality of meshes each having an opening of 170 meshes or more. The PE block copolymer used in the present invention can be used regardless of the manufacturing method as long as it is manufactured by a continuous polymerization method. That is, the PE block copolymer produced by the continuous polymerization method contains a polymer mainly composed of ultra-high molecular weight molecular chains. This ultra-high molecular weight polymer becomes a fish eye in a film using a PE block copolymer, and usually has poor dispersibility and inhibits improvement in the impact strength of the molded product. On the other hand, PE block copolymers obtained by batch polymerization are difficult to aggregate even when ultra-high molecular weight molecular chains are produced, and are easily dispersed uniformly in the polymer without forming fish eyes. Furthermore, when the polymerization conditions for improving the impact strength of PE block copolymers produced by batch polymerization are applied to the production of block copolymers produced by continuous polymerization, the impact strength often decreases rather than improving. Is recognized. That is, when obtaining a PE block copolymer using a continuous polymerization method,
Applying the suitable polymerization conditions of the batch polymerization method unnecessarily results in the formation of ultra-high molecular weight polymers that appear as fish eyes, which inhibits improvement in impact strength. Therefore, even if the present invention is applied to PE block copolymers obtained by batch polymerization, little effect can be expected. That is, the PE block copolymer that is the object of the present invention must be obtained by a continuous polymerization method. Further, as a technique for obtaining a PE block copolymer by a continuous polymerization method, a known technique that is carried out continuously by combining the first and second steps or more steps as described above may be employed as is. Typical examples are Special Publications No. 42-25294, No. 43-13049, No. 46-11670,
There are techniques described in patent publications such as JP-A No. 49-12589, JP-A No. 49-53990, and JP-A No. 49-61278. PE block copolymers obtained industrially by continuous polymerization are generally in the form of powder. If the powder is transported or used as it is, there is a risk of dust explosion, and the workability during molding is poor, so the PE block copolymer powder is melted and molded into granules (pellets). The process of forming the powder into granules (pellets) is generally called the pelletizing process, in which the molten PE block copolymer is extruded into rod shapes.
It is common to cut it to a size of ~5 mmφ.
When a molded article is manufactured using the pellet as a raw material, for example, when molded into a film, a large number of fish eyes are generated due to the above-mentioned reasons, and physical properties such as impact resistance cannot be improved. Regarding this point, the present inventors conducted tests using various types of extruders such as a single-screw extruder and an extruder with a pre-kneading device, based on the assumption that the cause was insufficient kneading in the extruder. There was no extinction effect and, of course, almost no improvement in physical properties was observed. However, as mentioned above, by passing the molten PE block copolymer through a disperser made of a specific network, the fish eyes can of course be eliminated.
Significant improvements in physical properties can be achieved. This phenomenon is completely surprising, and it is inconceivable that the physical properties of PE block copolymers can be improved by mere mechanical manipulation. However, it is currently not clear what mechanism of action achieves the effects of the present invention. In the molten state of the inventors et al.
When the ultra-high molecular weight polymer in the PE block copolymer passes through the network described below, it is dispersed into small particles, and the kneading effect acts synergistically to maintain the excellent properties inherent in the PE block copolymer. It is assumed that the ability will be fully utilized without being inhibited. As is clear from the above description, the greatest feature of the present invention is that the PE block copolymer in a molten state is prepared by at least two networks having a mesh size of 120 meshes or more, and at least one of the networks having a mesh size of 120 meshes or more. is 170
The point is that the material is passed through a dispersing machine which is constructed by combining a plurality of net-like bodies having mesh-like or larger openings. In the present invention, as described above, the molten state
Since the PE block copolymer is passed through a special mesh, it is generally preferred that the disperser be fitted with a mesh on the extruder used in the pelletizing process. More specifically, it is preferable to install it between the tip of the screw built in the extruder and the die, usually on a breaker plate. Further, the dispersing machine used in the present invention has at least two meshes each having a mesh size of 120 meshes or more, and one of the meshes has a mesh size of 170 meshes or more. As the mesh material, it is generally preferable to use a wire mesh having an opening of 120 meshes or more. The number of meshes constituting the dispersion machine is preferably as small as possible as long as it has sufficient strength, but generally it is 2 to 2.
It is suitable to consist of 10 sheets, preferably 3 to 7 sheets. In addition, in order to make the effect of the present invention more effective, the smaller the opening of the mesh is, the better it is, and the mesh is made by combining two sheets of mesh with an opening of 120 meshes or more, and the one with 170 meshes or more is dispersed. Preferably, at least one sheet is included in the machine. Furthermore, the smallest opening can be used as long as it allows the molten PE block copolymer to pass through, depending on the manufacturing technology of the mesh. In general, net-like bodies with a mesh size of about 200 to 500 meshes are most often used industrially. However, when the mesh size of the at least two meshes becomes wider than 120 meshes, that is, less than 120 meshes, the effect of the present invention becomes extremely poor and the impact strength cannot be substantially improved. We cannot expect it to disappear. The structure of the net-like material of the disperser in the present invention is not particularly limited, and it is sufficient to stack a plurality of net-like materials having the specific mesh size. In general, the smaller the opening, the weaker the strength, so in consideration of strength, either use the sandwich method and stack the smaller openings in the center, or set the dice with the larger opening on the side of the die. It is preferable to Furthermore, when using several sheets with small openings, the ones with small openings and the ones with large openings can be stacked on top of each other, but it is preferable to stack the ones with small openings on top of each other. As is clear from the above description, the present invention is applicable to the production of PE block copolymer granules from PE block copolymer powder by dispersing molten PE blocks in a dispersing machine composed of a mesh having a specific mesh size. The simple operation of passing the copolymer not only sufficiently disperses the ultra-high molecular weight polymer that causes fish eyes, but also improves the physical properties of the resulting PE block copolymer granules, such as impact strength. Demonstrates an excellent effect of significantly improving That is, with the completion of the present invention, PE block copolymers conventionally obtained by continuous polymerization can be used satisfactorily for film molded products, which have been difficult to use due to the fish eye. Moreover, an amazing improvement in impact resistance can be achieved without the need for chemical modification of impact resistance. Therefore, it can be said that the industrial effects of the present invention are immeasurable. As a molding machine for molding the PE block copolymer powder into granules in the present invention, conventionally used extruders, dies, etc. can be used as they are. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples. Incidentally, the method of measuring the physical properties used in the examples is as follows. 1 Melt flow index is ASTM D-
Measured by 1238. 2 Ethylene content in the polymer was determined by infrared absorption spectrum analysis. 3 Yield strength and elongation were measured according to ASTM D-638. 4 Tensile impact value was measured according to ASTM D-1822. 5 The Izod and Shalpy impact values are each
Measured according to ASTM D-256. 6 Hardness was measured according to ASTM D-785. 7 Flexural modulus was measured according to ASTM D-790. In addition, the tensile test and hardness test pieces are compression molded,
Izot, sharp py and flexural modulus test specimens were injection molded. Examples 1 to 4 and Comparative Example 1 The first step (autoclave (A)) was performed using a polymerization apparatus in which 300 autoclaves (A), flush tanks, slurry tanks, autoclaves (B), and washing tanks were arranged in series. is the so-called solvent-free method using propylene itself as a solvent, the second step (autoclave)
In (B)), propylene-ethylene copolymerization was carried out continuously by a so-called solvent method using heptane as a solvent. First, titanium trichloride (AA grade), diethylaluminum monochloride, liquid propylene, and hydrogen gas were continuously supplied to a polymerization tank set at a temperature of 55°C. Titanium trichloride per hour
Diethylaluminium monochloride was fed at a rate of 20 g per hour. The amount of liquid propylene supplied and the amount of produced propylene homopolymer withdrawn were set so that the average residence time of the catalyst was 4 hours. Furthermore, hydrogen gas was supplied and controlled so that a predetermined MI value was obtained. In this way, the propylene homopolymer slurry produced is continuously transferred to a flash tank with as little fluctuation of the liquid level as possible, and after purging unreacted homomer there,
The polymer was continuously transferred to a slurry tank with a rotary feeder. Along with the supply of the polymer, heptane was supplied to this tank at a rate of 40/hour, and the mixture was stirred to form a uniform slurry.
Next, the polymer slurry was continuously transferred to an autoclave (B) set at 50°C, and ethylene was added.

【table】

[Table] Comparative Examples 2 to 4 Using the same polymerization apparatus as in Example 1, the first step was a solvent-free method using propylene itself as a solvent, and the second step was a solvent method using heptane as a solvent. Block copolymerization was carried out. First, add liquid propylene to the autoclave (A).
200 and hydrogen gas as a molecular weight regulator were charged and the temperature was raised to 55°C, followed by the addition of 26.5 g of titanium trichloride (AA grade) and 70 g of diethylaluminum monochloride to initiate polymerization. During polymerization, hydrogen gas was supplied and the gas phase concentration was controlled using gas chromatography to keep it constant. After the polymerization reaction was carried out for 4 hours, it was transferred to a flash tank and unreacted propylene was purged. Then, 150 g of heptane was injected to form a slurry, and the slurry was transferred to an autoclave (B). After the transfer,
While raising the temperature to 50°C, ethylene gas, propylene gas, and hydrogen gas were supplied. The concentration ratio of ethylene gas and propylene gas and the concentration of hydrogen gas were set to be the same as in Example 1, and the polymerization reaction was carried out for 2 hours while being controlled by gas chromatography. After the polymerization was completed, unreacted gas was purged in a flash tank, and the same treatment as in Example 1 was carried out to obtain a white powder polymer. Subsequently, granulation (pelletization) was performed in the same manner as in Example 1. Table 3 shows the mesh size and structure of the mesh used, and Table 4 shows the physical properties of the pellets obtained above. The pellets had an MI value of 7.1 and an ethylene content of 3.6% by weight. According to the results in Table 4, it is clear that when the PE block copolymer is obtained in a batch process, the physical properties of the block copolymer are not affected at all by pelletization.

【table】

[Table] Examples 5 to 6 and Comparative Example 5 The powdered polymer polymerized in Example 1 was prepared in Example 1.
The mixture was stabilized in the same manner as above and granulated (pelletized) through an extruder equipped with a preliminary kneading device (manufactured by Nakatani Kikai Co., Ltd., Model CCM-50). The mesh used was attached to a breaker plate in the same manner as in Example 1. Table 5 shows the mesh size and configuration of the mesh used. Physical properties were measured using the pellets obtained above. The results were as shown in Table 6.

【table】

[Table] Example 7 and Comparative Example 6 The same procedure as in Example 1 was carried out except that the mesh body in Example 1 was changed as shown in Table 7. The results were as shown in Table 8.

【table】

【table】

Claims (1)

[Claims] 1. When molding the propylene-ethylene block copolymer powder produced by the continuous polymerization method into granules, the molten propylene-ethylene block copolymer is formed into at least two meshes with a mesh size of 120 mesh or more. and at least one of them
A method for producing propylene-ethylene block copolymer granules, characterized in that the net-like sheets are passed through a dispersing machine made up of a combination of a plurality of net-like sheets having openings of 170 meshes or more.