JPS6128694B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the extrusion molding method for polypropylene. More specifically, 100 parts by weight of polypropylene with a melt fluidity index (MFI) of 0.2 g/10 min to 4 g/10 min, measured at a temperature of 230°C and a load of 2160 g, has an MFI of 0.01 g/10 min.
This is a polypropylene extrusion molding method in which 2 to 30 parts by weight of the following ultra-high molecular weight polypropylene is added and extruded at a temperature range from the melting point to 210°C to raise the melt break point and improve high-speed extrusion moldability. Generally, when extruding a molten polymer material through a nozzle, the extrudate may wave, become spiral, or distort into an irregular shape when the shear rate exceeds a certain level. This phenomenon is called melt fracture, and is an undesirable phenomenon in extrusion molding, and is known to have various negative effects on the surface of the product. On the other hand, high-speed moldability is required for efficient extrusion molding, but the upper limit of high-speed moldability is naturally determined by the melt fracture phenomenon. The shear stage speed (critical shear speed) at which melt fracture occurs in extrusion molding generally depends on the molding temperature and the average molecular weight of the resin, and the higher the molding temperature, the higher the
Also, the smaller the average molecular weight (the larger the MFI), the higher the value. Therefore, in order to perform extrusion molding at high speed, it is sufficient to mold a resin having a small average molecular weight at a high temperature. However, in high-temperature extrusion molding of resins with small average molecular weights, the viscosity of the molten resin is low;
There is a problem in that the shape retention ability of the molded product is small after the resin comes out of the die until it solidifies. For example, in hollow extrusion molding, the parison sags due to its own weight, resulting in non-uniform thickness. The degree of such adverse effects is more significant when a resin having a small average molecular weight is molded at a high temperature. Moreover, molding at high temperatures is economically disadvantageous. That is, a large amount of thermal energy is required for heating, and the cooling time becomes long. If the cooling process is the rate-limiting step in high-speed molding, high-speed moldability will be reduced. Furthermore, there is a need to use a resin with a large average molecular weight in view of the strength of the molded product and other aspects. Therefore, the average molecular weight is large (MFI is small)
A method for extruding resins at low temperatures and high speeds has been desired. The present invention provides an extrusion molding method that improves this point. As a result of repeated research on the melt rheology of polypropylene, the present inventors discovered that by adding ultra-high molecular weight polypropylene, it is possible to raise the melt break point during extrusion molding and significantly increase the critical shear rate. The present invention has now been completed. The present invention uses 100 parts by weight of polypropylene having a melt fluidity index (MFI) of 0.2 g/10 min to 4 g/10 min measured at a temperature of 230°C and a load of 2160 g.
Add 2 to 30 parts by weight of ultra-high molecular weight polypropylene with an MFI of 0.01g/10min or less, at 210°C above the melting point.
This is a method for extruding polypropylene in the following temperature range. The ultra-high molecular weight polypropylene used in the present invention has a melt fluidity index (MFI) of 0.01 g/10 min or less when measured under L conditions, ie, at a temperature of 230° C. and a load of 2160 g according to ASTM D1238.
If the MFI is 0.01 g/10 min or more, the effect of improving the critical shear rate cannot be recognized by its addition, so high-speed extrusion moldability is not improved. Ultra-high molecular weight polypropylene base polypropylene 100
The amount added is 2 to 30 parts by weight, preferably 3 to 10 parts by weight. If the amount added is less than 2 parts by weight, the effect of improving the critical shear rate is not substantially observed, and if it is more than 30 parts by weight, the critical shear rate is undesirably lowered. The ultra-high molecular weight polypropylene used in the present invention may be produced by any method as long as it has an MFI of 0.01 g/10 min or less, and can be used without any restrictions. Additionally, polypropylene copolymerized with a small amount of olefin such as ethylene has an MFI of 0.01.
g/10 min or less, it can be used in the present invention without any problem. Therefore, the ultra-high molecular weight polypropylene referred to in the present invention is a general term that also includes these copolymers. Ultra-high molecular weight polypropylene can generally be produced by substantially the same method as the method for producing the base polypropylene, which will be described later. For example, in the polymerization method of the base polypropylene, the ultra-high molecular weight polypropylene of the present invention can be obtained by polymerizing with a very small amount of hydrogen as a molecular weight regulator or without using it at all. Further, when obtaining ultra-high molecular weight polypropylene by randomly copolymerizing other olefins, the polymerization is carried out in the presence of an olefin monomer to be copolymerized during polymerization. In this case, a copolymer having substantially the same composition as the polymerization gas phase concentration is obtained. Furthermore, when obtaining ultra-high molecular weight polypropylene by block copolymerization, propylene is first polymerized, and then an olefin monomer or a mixed monomer of propylene and olefin monomers to be copolymerized is polymerized. In addition, when the ultra-high molecular weight polypropylene is a copolymer, the content of other olefins in the copolymer is limited to 5% by weight in the case of a random copolymer and 20% by weight in the case of a block copolymer. It is common to do so. The base polypropylene used in the present invention is
If the MFI is 0.2g/10min to 4g/10min or less, it can be used without any restrictions. Furthermore, polypropylene copolymerized with a small amount of other olefins such as ethylene can be similarly used as long as the MFI satisfies the above range. Therefore, in the present invention, these copolymers are also referred to as the base polypropylene. When the MFI of the base polypropylene is less than 0.2 g/10 min and when it is more than 4 g/10 min, no improvement in the critical shear rate due to the addition of ultra-high molecular weight polypropylene is observed. The base polypropylene used in the present invention can be produced by various methods using, for example, Ziegler type polymerization catalysts and improved catalysts thereof. For example, using titanium trichloride and diethylaluminium compounds as catalysts, in a solvent such as heptane,
It is obtained by feeding hydrogen and propylene to polymerize at about 60°C with stirring, and after completing the desired polymerization, stop the polymerization with isopropyl alcohol or the like. In this case, if it is desired to obtain polypropylene with a low MFI, the amount of hydrogen feed may be reduced in the above operation. Conversely, if you want to obtain polypropylene with a large MFI, you can increase the amount of hydrogen feed. When the base polypropylene is a copolymer, other olefin monomers may be copolymerized in the same manner as in the case of the ultra-high molecular weight polypropylene copolymer described above. In the case of random copolymerization, the content of other olefins in the copolymer is desirably 5% by weight or less, and in the case of block copolymerization, the content of other olefins is preferably 20% by weight or less. The ultra-high molecular weight polypropylene and the base polypropylene may be mixed in powder form and then directly passed through an extrusion molding machine, or may be kneaded by a method commonly used for kneading fillers. For example, mixing is performed using a mixing roll, a kneader, a Banbury mixer, a kneading extruder, etc., but mixing using a kneading extruder is most efficient. In this case, the components dry blended in advance may be added to an extruder, extruded into rods, and then cut with a cutter to obtain pellets. In the present invention, polypropylene containing a predetermined amount of ultra-high molecular weight polypropylene has a melting point of 210
Extrusion molding at temperatures below ℃. Needless to say, extrusion molding is impossible at temperatures below the melting point.
At temperatures above 210°C, the addition of ultra-high molecular weight polypropylene does not improve the critical shear rate. Extrusion molding as used in the present invention is a general term that includes all forms of extrusion molding such as rod extrusion, fiber extrusion, pipe extrusion, plate extrusion, sheet extrusion, film extrusion, other profile extrusions, and hollow extrusion. . The present invention will be explained below with reference to Examples, but the present invention is not limited thereto. In addition, in the following examples, the critical shear rate is
Length L = 5 mm, diameter D using a circular tube rheometer
Using a nozzle with = 0.5 mm and L/D = 10, the volumetric outflow velocity Q _c at which melt rupture begins was measured and calculated using the following formula. Critical shear rate = 32Q _c /πD ³ In addition, in the following examples, as a stabilizer
BHT (dibutylhydroxytoluene) and
Each contains 0.3 parts by weight of DLTP (dilaurylthiopropionate). Example 1, Comparative Examples 1 to 3 Ultra-high molecular weight polypropylene powder with MFI shown in Table 1 was added to 100 parts by weight of polypropylene (trade name "Tokuyama Polypro FB111") powder with MFI = 1.0 g/10 min as shown in Table 1. After mixing and kneading with a mixing roll at 175°C for 25 minutes, the critical shear rate was measured at 190°C. The results are shown in Table 1.

[Table] Example 2 MFI = 0.009 g / 10 min to polypropylene (trade name "Tokuyama Polypro YE120") powder
The amount of ultra-high molecular weight polypropylene powder shown in Table 2 was mixed for 10 minutes, and the mixture was kneaded at 175°C for 2.5 minutes using a mixing roll, and then the critical shear rate was measured at 190°C. The results are shown in Table 2.

[Table] Examples 3 to 5, Comparative Examples 4 and 5 Polypropylene powder having MFI shown in Table 3
5 parts by weight of ultra-high molecular weight polypropylene powder with MFI = 0.004 g/10 min were mixed with 100 parts by weight, and after kneading with a mixing roll at 175°C for 2.5 minutes, the critical shear rate was measured at 190°C.
The results are shown in Table 3.

[Table] Examples 7 to 10, Comparative Examples 6 and 7 MFI = 1.0 g/10 min to 100 parts by weight of polypropylene (trade name "Tokuyama Polypro FB111") powder
5 parts by weight of ultra-high molecular weight polypropylene of 0.004 g/10 min were mixed and kneaded for 2.5 minutes at 175° C., and then the critical shear rate was measured at each temperature shown in Table 4. 4th result
Shown in the table.

[Table] Example 11 100 parts by weight of polypropylene (trade name "Tokuyama Polypro FB111") powder with MFI = 1.0 g/10 min was randomly copolymerized with ethylene. MFI = 0.003 g/10 min.
ultra-high molecular weight polypropylene (ethylene content 1.2
After adding 5 parts by weight of powder (% by weight) and kneading with a mixing roll at 175°C for 2.5 minutes, the critical shear rate was measured at 190°C and found to be 2150 sec ^-1
It was hot. The critical shear rate when no ultra-high molecular weight polypropylene was added was 169 sec ^-1 . Example 12 Instead of the polypropylene of Example 11 (trade name "Tokuyama Polypro FB111"), ethylene-random copolymerized polypropylene (ethylene content 1.1% by weight) with MFI = 0.71 g/10 min (trade name "Tokuyama Polypro FB111") was used.
RB310"), the critical shear rate was 1620 sec ^-1 . In addition, the critical shear rate when no ultra-high molecular weight polypropylene was added was 148 sec ^-1 . Example 13 MFI = 1.3g/10min ethylene block copolymer polypropylene (trade name “Tokuyama Polypropylene”)
MS620”) MFI=0.004g/10min for 100 parts by weight of powder
5 parts by weight of ultra-high molecular weight polypropylene powder was added, and the critical shear rate was measured at 175°C and found to be 2830 sec ^-1 . In addition, the critical shear rate when no ultra-high molecular weight polypropylene is added is
It was 890sec ^-1 .

Claims (1)

[Claims] 1 Melt fluidity index (MFI) measured at 230℃ and 2160g load is 0.2g/10min to 4
MFI to 100 parts by weight of polypropylene at g/10min
1. A method for extruding polypropylene, which comprises adding 2 to 30 parts by weight of ultra-high molecular weight polypropylene having a molecular weight of 0.01 g/10 min or less, and extruding at a temperature range from the melting point to 210°C.