JP4307970B2 - Twin screw extruder or twin screw kneader - Google Patents

Description

The present invention relates to an apparatus for producing a homogenized resin with low power consumption and without causing molecular decomposition in the process of granulating polyethylene particles produced by continuous multistage polymerization.

Polyethylene, especially high-density polyethylene, is an ethylene-based polymer with low molecular weight (flowability and rigidity) in order to achieve both ease of molding and product properties such as rigidity and impact strength.
And an ethylene polymer having a high molecular weight (providing shape retention during molding and imparting strength) in many cases. For industrial production, for example, as described in “Polyethylene reader”, Kazuo Matsuura and Naotaka Mikami (Industry Research Committee), page 155, a polymerization catalyst is supplied to the first polymerization vessel,
One component (for example, low molecular weight ethylene polymer) is polymerized in the first polymerization vessel, and the particles (including catalyst and low molecular weight ethylene polymer) are continuously extracted and transported to the second polymerization vessel. And
By polymerizing the other component (in this case, a high molecular weight ethylene polymer) in the second polymerization vessel, a single particle contains both a low molecular weight ethylene polymer and a high molecular weight ethylene polymer. Combined particles can be obtained.

In general, when polyethylene is produced by continuous multistage polymerization, it is an unavoidable phenomenon that unevenness occurs in the residence time in each tank. Taking the case of the above-mentioned two polymerizers as an example, since the residence time in the first polymerizer is short, it is transported to the second polymerizer without sufficiently containing the low molecular weight ethylene polymer. In some cases, only the high molecular weight ethylene polymer is polymerized in the second polymerization vessel. In this case, as a result, polymer particles having a higher viscosity than surrounding particles are generated with a probability. This situation has occurred even in high-density polyethylene produced by continuous two-stage polymerization using a conventional Ziegler catalyst, but in the case of a Ziegler catalyst, the performance of active sites in one particle was diverse. Therefore, even if the particles are polymerized only in the second polymerization vessel without staying in the first polymerization vessel, an ethylene-based polymer having a low molecular weight is generated to some extent. As a result, it was possible to relatively easily mix with surrounding particles relatively easily by melt kneading in the granulation step of forming the polymer particles into pellets, thereby obtaining a uniform structure. However, in the case of continuous two-stage polymerization using a metallocene catalyst as in Japanese Patent Application No. 2003-38079, since the performance of active sites in one catalyst particle is homogeneous, for example, in the first polymerization vessel The particles polymerized only in the second polymerization vessel without staying at all do not contain an ethylene polymer having a low molecular weight, but consist only of a high molecular weight ethylene polymer. In addition, the molecular weight difference between the low molecular weight ethylene polymer and the high molecular weight ethylene polymer is large. Such an ethylene polymer is melt kneaded using a conventional apparatus,
In order to obtain a uniform structure that is well mixed with the surrounding particles, sufficient kneading is required. As a result, a large amount of electric power is required, and the kneading conditions are too strict, so that cutting at the molecular level is performed. There were problems such as molecular cleavage and molecular degradation.

On the other hand, when the melt kneading is insufficient, a kneaded product in which the high molecular weight ethylene polymer is localized without being sufficiently dispersed is provided. It is generally known that when such a kneaded product is formed for a film, fish eyes are likely to be generated. Therefore, reduction of the bulk high molecular weight polymer and further improvement of the dispersion state are required.

Japanese Patent Application Laid-Open No. 2001-150429 discloses an apparatus for reducing the fish eye of polyolefin (the fish eye means a “butsu” of the order of several tens to several hundreds μm that appears on the surface of a molded product). . However, in Japanese Patent Application Laid-Open No. 2001-150429, the polyolefin for which fish eyes are to be reduced is polypropylene, and it is clearly shown that the mechanism of generating fish eyes is fundamentally different from the case of high-density polyethylene. The reduction device can be considered fundamentally different from that for polyethylene.

Japanese Patent Application Laid-Open No. 11-124439 discloses an apparatus for reducing the fish eye of polyolefin. Although there is no description about a screw shape, since the shear rate in a kneading | mixing area | region is large, it can be guessed that the clearance gap (clearance) between a barrel and a screw is narrow. If there is a portion with a narrow clearance, a high shear stress is generated, and there is a concern that power consumption increases and molecular cleavage is likely to occur.

Japanese Patent No. 32007055 discloses a continuous kneading machine characterized by comprising a rotor having a blade having a blade for reducing the shear heat generation and increasing the volume of the kneading chamber while the number of blades of the kneading section screw is small. ing. There are few places (wings) where the clearance is narrow, but there are places where the clearance is narrow, so there is a concern that power consumption will increase and molecular cleavage will likely occur.

Japanese Patent Publication No. 7-100325 discloses a biaxial continuous kneader in which the ratio between the length of the kneading part and the barrel inner diameter is in a specific range so as not to cause thermal deterioration (molecular decomposition) and to suppress fish eyes. Has been. There is no description about the clearance between the screw and the barrel,
Since there is a description that high density polyethylene (HDPE) requires strong kneading, it can be inferred that the clearance is narrow. If there is a portion with a narrow clearance, a high shear stress is generated, and there is a concern that power consumption increases and molecular cleavage is likely to occur.

In JP-A-8-258110, the depth of one groove of a screw in a twin-screw extruder is increased (clearance is increased) so that the flight width or the thickness of the tip of one screw is different from that of the other. A two-screw extruder is disclosed. Since the apparatus is intended to generate a high shear rate as well as a low shear rate, there is a concern that the power consumption becomes large and molecular cleavage is likely to occur.
Japanese Patent Application No. 2003-38079 JP 2001-150429 A Japanese Patent Laid-Open No. 11-124439 Japanese Patent No. 32007055 Japanese Patent Publication No. 7-100325 JP-A-8-258110 Polyethylene reader, edited by Kazuo Matsuura and Naotaka Mikami (Industry Research Committee)

The problem to be solved by the present invention is continuous polyethylene polymerization, particularly polyethylene produced by continuous multistage polymerization using a catalyst having a narrow single-stage polymer product molecular weight distribution as a catalyst, such as a metallocene catalyst. An object of the present invention is to provide an apparatus for producing a homogenized resin in a process of granulating particles with low power consumption and without causing molecular decomposition. In the case of continuous two-stage polymerized high-density polyethylene, standard polymer particles that have passed through the residence time designed in the first and second polymerization tanks are molecular chains with low molecular weight and molecules with high molecular weight before melt kneading. It can be considered that the chains are dispersed in the order of several tens of nanometers, which is the degree of dispersion of the catalyst active points. [In the following description, the low molecular weight polymer chains constituting such standard polymer particles are referred to as “standard low molecular weight polymer chains”, and the high molecular weight polymer chains are referred to as “standard high molecular weight polymer chains”. Sometimes called. On the other hand, most of the polymer particles obtained by polymerizing only the polymerizer for polymerizing the high molecular weight chain without sufficiently staying in the polymerizer for polymerizing the low molecular weight chain are mostly high molecular weight chains. Because there are several tens to several hundreds μm of the polymer particle size
There is a possibility that high molecular weight chains are agglomerated in the order of.

The inventors of the present application
1) The high molecular weight chain forming this lump and the “standard high molecular weight polymer chain” dispersed in the order of several tens of nanometers have the same molecular structure. It is not much different from the “low molecular weight chain” (even if α-olefin other than ethylene is copolymerized, it is very small amount), so it should be essentially mixed.
2) Therefore, in the above-mentioned high-density polyethylene, a high shear rate (high shear stress) is used in order to homogenize the high molecular weight chains that are not dispersed in the order of several tens to several hundreds of micrometers to the standard particle level. Not necessarily necessary,
3) There is a problem that a high shear stress is often undesirable, such as high power consumption and molecular cleavage.
4) However, for homogenization, it is necessary to give the resin a sufficient kneading history.
In the process of granulating continuous multi-stage polymerized polyethylene particles produced using a catalyst with a narrow molecular weight distribution of single-stage polymer products as a metallocene catalyst, such as a metallocene catalyst, molecular decomposition with low power consumption This has led to the development of a new extrusion or kneading apparatus for producing a homogenized resin without causing any problems.

That is, the problem to be solved by the present invention is to provide an extruder or a kneader capable of giving a sufficient kneading history to a resin under low shear stress conditions. In the case of a block PP made of polypropylene and a rubber component, it can be considered that a component having different molecular chain skeletons is uniformly dispersed and thus essentially different, and a high shear stress is required to some extent.

The biaxial extruder or biaxial kneader of the present invention is intended to give a sufficient kneading history to the resin under low shear stress conditions, and the minimum screw radius (R ₁ ) and barrel radius (R ₀ ) of the kneading part. )
The ratio [R ₁ / R ₀ ] is in the range of 0.70 to 0.80, and the maximum screw radius (
R ₂ ) to barrel radius (R ₀ ) ratio [R ₂ / R ₀ ] is in the range of 0.70 to 0.94, the minimum screw radius (R ₁ ) of the kneading part and the maximum screw radius ( R ₂ ) ratio [R ₁ / R ₂ ] is in the range of 0.78 to 1.00, and has a shape that allows the resin to flow back to the screw just like the reverse screw or seal ring immediately after the kneading part screw. Alternatively, the main feature is a twin-screw extruder or a twin-screw kneader having a shape that allows the resin to flow back into the barrel like a gate. The present invention is preferably a twin screw extruder or a twin screw kneader characterized in that the resin crystal component can be melted before the kneading section. Since the screw shape of the kneading part has an important feature, it may be an extruder that supports only one end of the screw or a kneader that supports both ends of the screw. R ₀ , R ₁ and R ₂ are shown in FIG.

Continuous multi-stage polymerization using the twin-screw extruder or twin-screw kneader of the present invention, particularly continuous multi-stage polymerization using a catalyst having a narrow single-stage polymer product molecular weight distribution as a catalyst, such as a metallocene catalyst. When the polyethylene particles produced in step 1 are granulated, it is possible to produce a homogenized resin with low power consumption and no molecular degradation compared to the case of using an existing extruder or kneader. There is an advantage of being.

The twin screw extruder according to the present invention will be specifically described below. Note that the screw shape of the kneading part has an important feature, so even if it is an extruder that supports only one end of the screw or a kneader that supports both ends of the screw, it rotates in the same direction. However, it can be rotated in a different direction. Here, for convenience, a twin-screw extruder is used.

While transporting the resin, the hopper part for feeding the polymer particles before the hopper to the kneading part (which may be blended with a predetermined additive such as heat stabilizer, hydrochloric acid absorbent or pigment) into the extruder A conventionally known apparatus can be used for the screw part to be melted. The distance from the hopper to the kneading part is preferably long so that the resin crystals are melted before the polymer particles reach the kneading part. If resin crystals remain when the polymer particles reach the kneading section, the crystals remain undissolved when kneaded at a low shear rate in the kneading section, and as a result, homogenization does not proceed. There is. Moreover, it is preferable that the clearance (clearance) between the crest and the barrel of the full flight screw part (FIG. 2) of this transport part is equivalent to the minimum clearance of the kneading part.

Ratio of minimum screw radius (R ₁ ) and barrel radius (R ₀ ) of kneading part kneading part [(R ₁ ) / (R ₀ )
] Is in the range of 0.70 to 0.80. When (R ₁ ) / (R ₀ ) is within this range, a kneading history can be added to the resin at a low shear rate. If it is less than 0.70, the void is too wide, so that a sufficient force cannot be transmitted to the resin, and a sufficient kneading history cannot be added to the resin.
If it exceeds 0.80, sufficient voids cannot be obtained, and as a result, the residence time of the resin is shortened and a sufficient kneading history cannot be imparted to the resin.

Ratio of maximum screw radius (R ₂ ) and barrel radius (R ₀ ) of kneading part [(R ₂ ) / (R ₀ )
] Is in the range of 0.70 to 0.94, preferably in the range of 0.70 to 0.85, more preferably in the range of 0.70 to 0.80. When (R ₂ ) / (R ₀ ) is within this range, a kneading history can be added to the resin at a low shear rate. Since the voids are wide, the residence time of the resin becomes long, and a sufficient kneading history can be imparted to the resin. Furthermore, power consumption is reduced, which is economically preferable. If it is less than 0.70, the voids are too wide and a sufficient force cannot be transmitted to the resin, so that a sufficient kneading history cannot be added to the resin. If it exceeds 0.90, the power consumption increases, which is not preferable.

Ratio of minimum screw radius (R ₁ ) of kneading part to maximum screw radius (R ₂ ) of kneading part [(
_{R 1)} / (R _2)] is in the range of 0.78 to 1.00, preferably 0.85 to 1.00
It is preferable that it exists in the range. When (R ₁ ) / (R ₂ ) is within this range, a kneading history can be added to the resin for a long time at a low shear rate. Furthermore, power consumption is reduced, which is economically preferable. If it is less than 0.78, it means that R ₁ is too small or R ₂ is too large. Since sufficient force is not transmitted to the resin, a sufficient kneading history cannot be added to the resin, and power consumption increases. This phenomenon is undesirable.

In the present invention, it is important that the values of R ₁ / R ₀ , R ₂ / R ₀ , and R ₁ / R ₂ are in a specific range, the shape of the kneading part is cylindrical, and the circumference is the length direction. Any of a kneading type that varies discontinuously with respect to the rotor and a rotor type in which the circumference continuously varies in the length direction may be used.

As kneading conditions, it is desirable that the shear rate at the position where the screw diameter of the kneading part is the maximum (R ₂ ) is 500 to 50 (1 / sec), preferably 300 to 50 (1 / sec). When the shear rate is within this range, it is possible to produce a resin having a uniform structure with low power consumption without molecular decomposition. If the shear rate is too high, the shear stress increases and there is a concern of molecular decomposition. A high shear rate is effective when the rubber component is uniformly dispersed in polypropylene, but a high shear rate is required to make the structure uniform in the process of granulating high-density polyethylene particles produced by continuous multistage polymerization. Stress is not always necessary. The shear rate (G) at the position where the screw diameter of the kneading part is the maximum (R ₂ ) is:
_{G = 2 × ω × (R} 0/2) / ((R 0/2) - (R 2/2))
ω = screw rotations per second × 2 × 3.14
I asked for it.

A screw having a shape that allows the resin to flow backward immediately after the kneading section screw is incorporated. Conventionally known shapes such as a seal ring on the screw that dampens the resin, a gate on the barrel side, and a reverse screw on the screw in which the way of cutting the mountain is opposite to the full flight part can be used. . Of these, the reverse screw on the screw is particularly preferable. When such a structure is provided immediately after the kneading section screw, the resin is sufficiently filled in the wide voids, so that a kneading history can be added to the resin for a long time at a low shear rate. If such a structure is not provided immediately after the kneading part screw, the resin will flow without staying in the kneading part. As a result, the residence time is shortened, and a sufficient kneading history can be given to the resin. Unable to do it.
The ethylene polymer to be kneaded has an intrinsic viscosity [η] in the range of 1.5 to 4.0 (dl / g), and the molecular weight distribution curve measured using GPC is peak-separated into two peaks. The peak [Mw (weight average molecular weight)] / [Mn (number average molecular weight)] of the peak on the high molecular weight side is 1.7-3.
When the Mw (weight average molecular weight) of the low molecular weight peak / Mw (weight average molecular weight) of the high molecular weight peak is in the range of 0.01 to 0.15, It is effective to use an extruder.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.

Next, an intrinsic viscosity measurement method for examining the degree of molecular decomposition, a surface roughness (Rz) measurement sample preparation method and an Rz measurement method for evaluating the progress of the homogenization of the structure will be sequentially described.
[Intrinsic viscosity ([η])]
It is a value measured at 135 ° C. using a decalin solvent. That is, about 20 mg of polymer particles and strands are dissolved in 15 ml of decalin, and the specific viscosity η _sp is measured in an oil bath at 135 ° C. After adding 5 ml of decalin solvent to the decalin solution and diluting, the specific viscosity η
Measure _sp . This dilution operation is repeated twice more, and η _sp when the concentration (C) is extrapolated to 0
The value of / C is determined as the intrinsic viscosity.
[Η] = lim (η _sp / C) (C → 0)
[Smoothness coefficient R]
Using capillary flow characteristic tester Capillograph 1B manufactured by Toyo Seiki Co., Ltd., resin temperature 200 ° C., 5
The resin is extruded at a speed of 0 mm / min (3.6 cm ³ / min). Length L = 60mm,
A nozzle having a diameter D = 1 mm or a cylindrical die (outer diameter 4 mmφ, slit = 0.5 mm, length 10 mm) capable of extruding a tube-shaped object is attached instead of a capillary die. Even if the polymer is pelletized, if the polymer particles polymerized in the gas phase or slurry phase are not sufficiently mixed together, the surface of the melt-extruded product becomes rough.

The surface roughness is measured using the strand or tube thus obtained as the measurement surface. For the measurement, Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd. was used. Measurement length = 10 mm, measurement speed = 0.06 mm / second, sampling time = 0.01 second, sampling pitch = 0.
6μm, measuring needle material is diamond, tip of measuring needle = 5μmφ, calculation standard JIS B0
The ten-point average roughness calculated in 601-1982 is Rz. Rz is the value of the difference between the average value of the altitude at the top of the peak from the highest to the fifth and the average value of the altitude at the bottom of the valley from the deepest to the fifth with respect to the average line having a measurement length of 10 mm. The measurement is performed three times at different locations, and the average value is defined as the dispersion coefficient R. Here, a standard deviation is obtained for Rz measured three times. When the value of the standard deviation is larger than ½ of the value of R, which is the average value of Rz measured three times, remeasurement is performed. The smaller R is, the more uniform the structure is.

[Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight curve]
Measurement was performed as follows using GPC-150C manufactured by Waters. The separation column is
TSKgel GMH6-HT and TSKgel GMH6-HTL, column size is 7.5 mm in inner diameter and length is 600 mm, column temperature is 140 ° C., mobile phase is o-dichlorobenzene (Wako Pure Chemical Industries) and oxidation BHT (Takeda Pharmaceutical) as an inhibitor
The sample was moved at 1.0 ml / min using 025 wt%, the sample concentration was 0.1 wt%, the sample injection amount was 500 microliters, and a differential refractometer was used as a detector. Standard polystyrene used for the molecular weight Mw <1000 and Mw> 4 × 10 ⁶ manufactured by Tosoh Corporation
About 1000 <= Mw <= 4 * 10 < ⁶ >, the pressure chemical company make was used. The molecular weight calculation is a value obtained by universal calibration and conversion into polyethylene.

(Separation of molecular weight curve)
A program was created using Visual Basic of Excel (registered trademark) 97 manufactured by Microsoft Corporation. The two curves to be separated were log-normal distributions, and the molecular weight distribution curve was separated into two curves having different molecular weights by convergence calculation. A curve obtained by re-synthesizing the two separated curves and a molecular weight curve measured by GPC are compared, and the calculation is executed while changing the initial values so that the two are almost the same. The calculation is performed by dividing Log (molecular weight) into 0.02 intervals. Standardize the strength so that the area of the two curves obtained by recombining the measured and separated two curves is 1, [the measured strength (height) when the molecular weight is the same and the strength (height) of the recombined curve The absolute value of the difference] divided by the strength (height) of the re-synthesized curve when the molecular weight is the same, the molecular weight is 10,000-1
Separation of curves in the range of 000,000, 0.4 or less, preferably 0.2 or less, more preferably 0.1 or less, and the maximum position of the separated peak is 0.2 or less, preferably 0.1 or less. Repeat the calculation. At this time, Mw (weight average molecular weight) of the peak separated on the low molecular weight side /
The difference between Mn (number average molecular weight) and Mw / Mn of the peak separated on the high molecular weight side is made to be 1.5 or less. A calculation example is shown in FIG.

[Particulate high density polyethylene for kneading (A)]
[Preparation of solid catalyst component]
After 8.5 kg of silica dried at 200 ° C. for 3 hours was suspended in 33 liters of toluene, 82.7 liters of methylaluminoxane solution (Al = 1.42 mol / liter)
It was dripped in 0 minutes. Next, the temperature was raised to 115 ° C. over 1.5 hours, and the reaction was carried out at that temperature for 4 hours. Thereafter, the temperature was lowered to 60 ° C., and the supernatant was removed by a decantation method. The obtained solid catalyst component was washed with toluene three times and then resuspended with toluene to obtain a solid catalyst component (
α) was obtained (total volume 150 liters).

(Preparation of supported catalyst)
In a sufficiently nitrogen-substituted reactor, 19.60 mol of the solid catalyst component (α) synthesized in Synthesis Example 1 suspended in toluene was added in terms of aluminum, and the suspension was stirred,
After adding 2 liters (74.76 mmol) of a 37.38 mmol / liter solution of diphenylmethylene (cyclopentadienyl) (2,7-di-t-butylfluorenyl) zirconium dichloride at room temperature (20-25 ° C.) And stirred for 60 minutes. After stopping the stirring, the supernatant liquid is removed by decantation, washing is performed twice using 40 liters of n-hexane, and the obtained supported catalyst is reslurried in n-hexane to form a 25 liter catalyst suspension as a solid catalyst. Component (γ) was obtained.

[Prepolymerization of solid catalyst component (γ)]
Into a reactor equipped with a stirrer, 15.8 liters of purified n-hexane and the above solid catalyst component (γ) were charged in a nitrogen atmosphere. The prepolymerization was carried out with a considerable amount of ethylene. The polymerization temperature was kept at 20-25 ° C. After completion of the polymerization, stirring was stopped, the supernatant was removed by decantation, washing was performed 4 times with 35 liters of n-hexane, and the obtained supported catalyst was made into a catalyst suspension with 20 liters of n-hexane. A solid catalyst component (δ) was obtained.

[polymerization]
In the first polymerization tank, hexane is 45 l / hr, the solid catalyst component (δ) obtained in Synthesis Example 2 is 0.11 mmol / hr in terms of Zr equivalent atoms, and triethylaluminum is 20 mmo.
l / hr, ethylene is 7.0 kg / hr, hydrogen is continuously supplied at 125 N-liter / hr, and the polymerization tank contents are continuously withdrawn so that the liquid level in the polymerization tank is constant, Polymerization was performed under the conditions of a polymerization temperature of 85 ° C., a reaction pressure of 8.5 kg / cm ² G, and an average residence time of 2.5 hours.

The contents continuously extracted from the first polymerization tank are substantially free of unreacted ethylene and hydrogen by a flash drum maintained at an internal pressure of 0.2 kg / m ² G and 65 ° C.

Thereafter, the contents were continuously supplied to the second polymerization tank together with hexane 35 liter / hr, ethylene 3.0 kg / hr, hydrogen 0.07 N-liter / hr, 1-hexene 30 g / hr, and a polymerization temperature of 80 Polymerization was continued under the conditions of C, reaction pressure 4.5 kg / cm ² G, and average residence time 0.8 hr.

In the second polymerization tank, the contents of the polymerization tank are continuously withdrawn so that the liquid level in the polymerization tank is constant, and hexane and unreacted monomers in the contents are removed with a solvent separator and dried to remove the polymer. Obtained.

Next, 0.1 part by weight of tri (2,4-di-t-butylphenyl) phosphate as a secondary antioxidant and n-octadecyl-as a heat stabilizer are added to 100 parts by weight of the polymer particles. 3- (4'-
0.1 part by weight of hydroxy-3 ′, 5′-di-t-butylphenyl) propinate is mixed with 0.05 part by weight of calcium stearate as a hydrochloric acid absorbent. GP of this high density polyethylene
A C chart is shown in FIG. Mw / Mn of the mountain on the low molecular weight side is 2.0, Mw of the mountain on the high molecular weight side
/ Mn was 1.9. Moreover, it was Mw (= 27,600) of the peak on the low molecular weight side / Mw (416,000) of the peak on the high molecular weight side = 0.07. [η] was 3.1 dl / g. Mw / Mn tends to increase by lowering the polymerization temperature and slowing the stirring in the polymerization vessel. As the hydrogen / ethylene ratio in each polymerization tank in the two-stage polymerization is different, the Mw ratio of the low molecular weight peak / Mw of the high molecular weight peak increases.

Extruder BT-30 (2 axis, same direction rotation, manufactured by Plastic Engineering Laboratory Co., Ltd.)
Engagement, barrel radius R ₀ = 15 mm, L / D = 47) was used. The voltage is 200V. As the mesh, one mesh having a mesh size of 150 μm and a mesh between two meshes having a mesh size of 250 μm was used. An outline of the screw arrangement is shown in FIG. The kneading part has R ₁ = 11 mm, R ₂
= 3 kneading elements with a length of 14 mm and a length of 30 mm were arranged. One kneading consists of 8mm / 14mm / 8mm long blocks. Each block is orthogonal. The kneading element viewed from the side is shown in FIG. Immediately after kneading, two reverse screw elements with a length of 20 mm and 1 pitch were put. The front position of kneading was 530 mm, 725 mm, and 1185 mm from the base of the screw, and a total of three places were put. A cross section of the kneading element is shown in FIG. _{R 1 / R 0 = 0.73,} R 2 / R 0 = 0.93, R 1 / R 2
= 0.79.

The temperature was set to 190 ° C just below the hopper, and 240 ° C otherwise. Controlled by a solenoid valve outside the barrel, water flows when the temperature rises. The resin temperature was the indicated temperature of a resin thermometer built in the vicinity of the die.

High-density polyethylene particles (A) extrusion rate is 22 g / min, screw rotation speed is 150
Extrusion was performed at rpm, and strands were collected. The current value at this time is 56 A, and the resin temperature is 252.
The strand [η] was 3.1 dl / g, and the surface roughness R was 7 μm. When the barrel vent port before the kneading closest to the hopper port was opened and the state of the resin was confirmed, the crystal of the particles was dissolved and became translucent. The screw radius of the kneading part is maximum (R ₂
) Was 471 (1 / sec).

In Example 1, the resin was extruded and strands were collected in the same manner as in Example 1 except that the kneading elements were all changed to kneading elements having R ₁ = 12 mm, R ₂ = 13 mm, and a length of 30 mm. A section of the kneading element is shown in FIG. R ₁ / R _{0
= 0.80, R 2 / R 0} = 0.87, was _R 1 / _R 2 = 0.92.

At this time, the current value is 55 A, the resin temperature is 253 ° C., the [η] of the strand is 3.1 dl / g,
The surface roughness R was 7 μm. When the barrel vent port before the kneading closest to the hopper port was opened and the state of the resin was confirmed, the crystal of the particles was dissolved and became translucent. The shear rate (G) at the position where the screw radius of the kneading part is the maximum (R ₂ ) was 236 (1 / sec).

In Example 1, the resin was extruded in the same manner as in Example 1 except that the kneading elements were all changed to R ₁ = 11 mm and R ₂ = 11 mm, that is, cylindrical and 30 mm long kneading elements. Collected. A cross section of the kneading element is shown in FIG. _{R 1 / R 0 = 0.73,} R 2 / R 0 = 0.73, was _R 1 / _R 2 = 1.00.

The current value at this time is 53 A, the resin temperature is 256 ° C., the [η] of the strand is 3.1 dl / g,
The surface roughness R was 6 μm. When the barrel vent port before the kneading closest to the hopper port was opened and the state of the resin was confirmed, the crystal of the particles was dissolved and became translucent. The shear rate (G) at the position where the screw radius of the kneading part was the maximum (R ₂ ) was 118 (1 / sec).

[Comparative Example 1]
In Example 1, the resin was tried to be extruded in the same manner as in Example 1 except that all the kneading elements were changed to the kneading elements of R ₁ = 11 mm, R ₂ = 14.9 mm, and length 30 mm. Since the current exceeded the upper limit (70 amperes) on the device, it could not be implemented. A cross section of the kneading element is shown in FIG. The shear rate (G) at the position where the screw radius of the kneading part was the maximum (R ₂ ) was 4710 (1 / sec).

[Comparative example BR> Q]
Resin in the same manner as in Example 1 except that all kneading elements in Example 1 were changed to kneading elements having R ₁ = 11 mm, R ₂ = 14.9 mm, and length of 30 mm, and the screw rotation speed was set to 100 rpm. Was extruded and the strands were collected. The current value at this time was 64 A, the resin temperature was 252 ° C., the [η] of the strand was 3.1 dl / g, and the surface roughness R was 9 μm. Compared with the example, the current value is high. When the barrel vent port before the kneading closest to the hopper port was opened and the state of the resin was confirmed, the crystal of the particles was dissolved and became translucent. The shear rate (G) at the position where the screw radius of the kneading part was the maximum (R ₂ ) was 3140 (1 / sec).

[Comparative Example 3]
In Example 1, the extruder is Plako 65 (single screw extruder, barrel diameter 65 mmφ, L / D = 28, screw shape is full flight) manufactured by Plako Co., Ltd., the extrusion rate is 500 g / min, and the screw rotation speed is The strand was extracted by extrusion at 300 rpm. At this time, the strand [η] was 3.1 dl / g, and the surface roughness R was 110 μm. The surface roughness is large compared to the examples.

[Comparative Example 4]
In Example 1, the reverse screw element immediately after kneading of the kneading part is 1 mm in length of 20 mm.
The resin was extruded and strands were collected in the same manner as in Example 1, except that the pitch was changed to two forward screw elements. At this time, the current value was 49 A, the resin temperature was 247 ° C., the [η] of the strand was 3.1 dl / g, and the surface roughness R was 58 μm. The surface roughness is large compared to the examples. When the barrel vent port before the kneading closest to the hopper port was opened and the state of the resin was confirmed, the crystal of the particles was dissolved and became translucent.

[Reference Example 1]
The surface roughness R measured using Mitsumi Chemical Co., Ltd. Hi-Zex 7700M pellets was 10 μm. In addition, Mw / Mn of the peak on the high molecular weight side obtained by peak-separating the GPC curve of Hi-Zex 7700M is 5.3.

Since it is possible to produce a homogenized resin with low power consumption and without molecular decomposition, the molecular weight distribution of a single-stage polymer product is narrow as the ability of the catalyst, such as a metallocene catalyst, in particular. In the step of granulating (pelletizing) polyethylene particles produced by continuous multistage polymerization using a simple catalyst, the twin-screw extruder or twin-screw kneader of the present invention can be used.

Barrel and screw Full flight screw GPC peak separation GPC chart Outline of screw arrangement Kneading (Example 1) Kneading (Example 1) Kneading (Example 2) Kneading (Example 3) Kneading (Comparative Example 1)

Explanation of symbols

1 Hopper 2 Kneading section (kneading)
3 Reverse screw 4 Full flight screw

Claims (4)

The ratio [R ₁ / R ₀ ] of the minimum screw radius (R ₁ ) and barrel radius (R ₀ ) of the kneading part is 0.
70 to 0.80, the maximum screw radius (R ₂ ) and barrel radius (R ₀ ) of the kneading part.
) Ratio [R ₂ / R ₀ ] is in the range of 0.70 to 0.94, and the ratio of the minimum screw radius (R ₁ ) of the kneading part to the maximum screw radius (R ₂ ) of the kneading part [R ₁ / R _2] is 0.78 to 1.0
It is in the range of 0 and has a shape that causes the resin to flow back to the screw just like the reverse screw or seal ring immediately after the kneading part screw, or a shape that causes the resin to flow back to the barrel like a gate. A twin-screw extruder or a twin-screw kneader. The twin-screw extruder or the twin-screw kneader according to claim 1, wherein the resin crystal component is melted before the kneading section. A method of granulating polyethylene produced by continuous multistage polymerization using the twin-screw extruder or twin-screw kneader according to claim 1 or 2. When the intrinsic viscosity [η] is in the range of 1.5 to 4.0 (dl / g) and the molecular weight distribution curve measured using GPC is separated into two peaks, the peak on the high molecular weight side Mw (weight average molecular weight) / Mn (number average molecular weight) satisfies the range of 1.7 to 3.5, Mw (weight average molecular weight) of low molecular weight side peak / Mw (weight average of high molecular weight side peak) (Molecular weight) is 0.0
The method for granulating polyethylene according to claim 3, wherein the polyethylene is in the range of 1 to 0.15.

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