JPH0459220A - High speed extrusion method for thermoplastic resin - Google Patents

Abstract

PURPOSE:To achieve highly extruded amount and good extrusion stability and provide the high speed extrusion method for thermoplastic resin to be able to manufacture high quality extruded products with good productivity. CONSTITUTION:A single spindle screw 10 is provided with 30-150mm bore D, and the ration L/D of length L and bore D is 20-40. A first extrusion section 14 having a feeding section 11, a compression section 12 and a metering section 13 are formed successively from the resin feeding side toward the resin extrusion side, and a mixing section 15, a shearing section 16 and a second extrusion section 17 are formed successively from said first extrusion section toward the resin extrusion side. At least l/2 of the length of the second extrusion section is shaped to satisfy Y>=(0.046x+1) [(y) represents the depth mm of channel of second extrusion section and (x) represents the screw bore mm of the second extrusion section]. Said single spindle screw is rotated at the peripheral speed of 70-170m/min. to extrude molten resin. Excessive rise of resin temperature, defective kneading, defective dispersion and the like are eliminated by the high speed rotation of said screw.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for high-speed extrusion of thermoplastic resins, and in particular to improvements in the screw of an extrusion molding apparatus used in this method and the method for driving this screw.

[Background technology]

Various molded products such as sheets, films, and containers are obtained from thermoplastic resins by extrusion molding, blow molding, injection molding, etc., but in all of these molding fields, sufficient heating, melting, and cross-contact of the resin are required. In order to produce products with excellent uniformity and productivity, the structure of the screw in the molding equipment is an important factor.

As shown in FIG. 3, conventional screws that are commonly used include a feeding section 1 consisting of a helical shaft with a relatively deep groove, a compression section 2 whose groove is gradually tapered to shallow depth, and a metering section having a shallow groove. The portion 3 is a single screw called a full-flight screw formed in series from the resin supply side to the resin extrusion side.

This full-flight screw design allows for feeding length,
It is common practice to determine the length of the compression section, the length of the metering section, the depth of the supply section groove, the depth of the metering section groove, etc. to appropriate values.

[Problem to be solved by the invention]

By the way, in extrusion molding, when the measuring groove depth of the full flight screw is too shallow, when the screw is rotated at high speed, the resin is kneaded excessively and the resin temperature rises excessively. On the other hand, if the groove depth of the metering part is too deep, if the screw is rotated at high speed, a breakup phenomenon will occur, the resin temperature will drop too much and unmelted material will appear, or even if it is melted, crosstalk will occur. Defects and poor dispersion occur, and extrusion stability also deteriorates.

In addition, the normal screw rotation speed is 20 to 200 rpm (
Screw diameter φ20 to φ90mm, maximum circumferential speed 57m/
or 20 to 120 rpm (screw diameter φ 100 to φ 150 mm, circumferential speed max. 57 m/min), and even if it is a full-flight screw with appropriate dimensions, rotating this screw at high speed will cause the resin temperature to rise excessively. Either this increases, or poor kneading and dispersion occur, as well as poor extrusion stability.

Therefore, high-quality extruded products cannot be manufactured with high productivity by rotating the full-flight screw at high speed.

By the way, the present applicant has provided a shearing section, stress relaxation section, mixing section, etc. between the compression section 2 and the metering section 3 or at the tip of the metering section 3 to achieve sufficient kneading and extrusion stability (forming stability). We are proposing various types of screws that satisfy the
2-41015, JP-A-62-41016, JP-A-63-199623).

However, even in these previously proposed screws, it has not been possible to achieve a sufficiently high rotation speed by improving only the screw.

The purpose of the present invention is to achieve a high extrusion amount and good extrusion stability without causing excessive rise in resin temperature, poor wire cross-linking, poor dispersion, etc. even when the screw rotates at high speed.
Therefore, it is an object of the present invention to provide a high-speed extrusion method for thermoplastic resins that can produce high-quality extruded products with good productivity.

[Means for solving problems]

The present invention improves the shape of the screw extrusion part, and
The objective is to be achieved by combining a gear pump with a single screw whose diameter, length, etc. are specified.

That is, the high-speed extrusion method for thermoplastic resin according to the present invention is a method for extruding thermoplastic resin from an extruder having a single screw, in which a gear pump is connected to the discharge side of the extruder,
The thermoplastic resin is extruded from the extruder through a gear pump and a die, and the single screw is (i)
The diameter is 30 to 150 mm, (ii) the length to diameter ratio L/D is 20 to 40, and (in) the supply section, compression section and metering are sequentially carried out from the resin supply side to the resin extrusion side. A first extrusion part having a length of 1.5 mm is formed, and a mixing part, a shearing part, and a second extrusion part are formed in order from the first extrusion part toward the resin extrusion side, and the length of the second extrusion part is At least % of the uniaxial It is constructed by extruding molten resin by rotating a screw at a peripheral speed of 70 to 170 m/min.

[Effect]

In the method of the present invention, the solid bed in the molten resin is actively crushed and mixed by the mixing section and the shearing section which are sequentially provided on the resin extrusion side of the first extrusion section, and highly efficient melt plasticization is performed. .

Furthermore, since the single screw is rotated at a higher circumferential speed than conventionally, the raw material feeding capacity of the supply section is increased, and molding can be performed at a high extrusion rate. At this time, the shape of the second extrusion part in the single screw is formed so that the groove depth and diameter maintain a constant relationship, so there is no excessive rise in resin temperature and high extrusion rate can be achieved. will be carried out.

The molten resin discharged from the extruder at a high extrusion rate is extruded quantitatively and stably by a gear pump, and the dimensional accuracy of the molded product is maintained well.

Since the gear pump also has a mixing action, the gear pump allows the molten resin to be kneaded and dispersed better before being extruded, resulting in a homogeneous molded product. Since the gear pump has a kneading and dispersion effect, there is no need for excessive mixing using a single screw, and since the resin temperature in the extruder is set at a low temperature and high-speed extrusion is performed, the resin temperature in the extruder is low. No performance deterioration occurs.

The smaller the fluctuation range of the resin pressure at the die inlet, the more stable extrusion can be achieved, and the fluctuation range is preferably ±1 kg/cnr or less, and especially when the resin pressure at the die inlet is less than 100 kg/crt, the range of fluctuation is ±1 of the resin pressure at the die inlet. % or less is preferable.

In the present invention, if at least each of the lengths of the second extrusion part of the single screw does not satisfy y≧(0,046x+1), heat generation will increase with high speed rotation and resin deterioration will occur.

If the diameter of the screw is not set within the range of 30 to 150 mm, problems such as insufficient biting of raw materials, strength problems, design constraints, space and cost problems will occur.

If the length of the screw and the aperture ratio L/D are not set within the range of 20 to 40, limitations on screw design and operating conditions, problems on strength and maintenance, problems on space and cost, etc. will occur.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an example of an extrusion molding apparatus for carrying out the high-speed extrusion method of the present invention.

In FIG. 1, an extruder 21 has a single screw 10 inside and a motor 22 that rotationally drives the single screw 10.

A suction side of a gear pump 24 is connected to the discharge side of the extruder 21 via an adapter 23, and a die 25 is connected to the discharge side of the gear pump 24.

Between the discharge side of the extruder 21 and the suction side of the gear pump 24,
That is, the adapter 23 is provided with a resin pressure gauge 26 as necessary, and a resin pressure measurement signal from the resin pressure gauge 26 is input to the motor 22 to control the rotation of the motor 22 and, in turn, to control the single screw I/O. The rotation speed is controlled.

The single screw 10, which is the main part of the extruder 21, is
A structure as shown in FIG. 2 is used.

The single shaft screw 10 was first developed by the applicant in Japanese Patent Application Laid-Open No. 63-1
No. 99623, the first extrusion section 14 has a supply section 11, a compression section 12, and a metering section 13 in order from the resin supply side to the resin extrusion side, and further, the resin is Sequentially toward the extrusion side, the mixing section 15,
It includes a shearing section 16 and a second extrusion section 17. Mixing section 1
5 and the shearing portion 16, a small diameter cylindrical portion 1 may be provided as necessary.
8 is formed.

In the axle screw 10, at least A of the length of the second extrusion part 17 is y≧(0,046x+1), CV is the groove depth (mm) of the second extrusion part 17, and X is the length of the screw of the second extrusion part 17. diameter (mm)] and the screw diameter is 30 to 150 mm, preferably 40 to 90 mm.
Then, the ratio of screw length to screw diameter is L/D.
Those specified in the range of 20 to 40, preferably 24 to 31 are used. Here, in the second extrusion section 17, y≧
The position where the shape satisfying (0,046x + 1) is formed is preferably on the tip end side of the second extrusion section 17, that is, on the gear pump 24 side.

If at least the outside of the second extrusion part 17 does not satisfy the relationship of the above formula, that is, if y<(0,046x11), the resin temperature may rise excessively during high speed rotation, causing resin deterioration. arise.

Regarding the screw diameter, if it is less than 30mm,
■Even if the hopper mouth is made larger, the material tends to get stuck in the material less easily.■Because the screw diameter is small, the screw IO becomes weak and easily breaks.
In addition, (1) Since the diameter of the screw is small, it is difficult to increase the depth of the supply groove in terms of design, and there are restrictions on the depth of the groove in terms of design.

On the other hand, if the length exceeds 150 m, ■ The extruder 21 itself becomes large, so it is not possible to save space. ■ The screw diameter is large, so maintenance such as cleaning the screw is difficult. ■ In order to rotate the screw 10 at high speed. Not only does a large (large capacity) motor 22 suitable for this purpose become necessary, but the gear pump 24 also becomes large, which increases the equipment cost of the extrusion device. Not only is it time consuming, more raw materials are required for purging, and larger extrusion equipment is generally less maneuverable than smaller equipment.

Next, regarding the length of the screw 10 and the diameter ratio L/D, if L/D is less than 20, it is disadvantageous because there are many restrictions on the screw design, and the operating range of the extruder 21 is narrow. This tends to limit the operating conditions, which is disadvantageous.
3, the fluctuation in the resin pressure becomes too large, making it impossible to control the screw rotation speed (it tends to happen).

On the other hand, if L/D exceeds 40, ■Since the screw cleaning is supported on a cantilever, the screw 10 tends to wobble, eccentricity, galling, etc. (The screw 10 tends to lack torsional strength.) It is difficult to clean the screw, and the operability tends to be poor. ■ Since the extruder 21 becomes long, it loses its compactness and does not save space. ■ As the L/D is large, the screw 10 The number of heaters that set the temperature of each part in the axial direction increases, which increases the cost. ■As the L/D increases, it takes longer to change raw materials, and more raw materials are wasted.
(2) As the residence time of the resin increases, the resin becomes more susceptible to thermal deterioration, which is particularly noticeable on the heat generating side.

In the screw 10, the feed section 11 in the first extrusion section 14 usually has a constant groove depth with a compression ratio l.

The compression section 12 usually has a groove depth that gradually becomes shallower, and compresses the resin while melting and plasticizing it. This compression ratio is between 2 and 4, preferably between 2 and 3. If the compression ratio exceeds 4, the shear stress at the end of the compression section 12 will increase, resulting in an increase in resin temperature, accumulation of shear stress, breakup phenomenon, etc., which is not preferable.

The metering section 13 usually has a certain groove depth, and promotes melting and plasticization when the resin is incompletely melted in the compression section 12. This measuring part 13 has a relatively deeper groove than a normal one, and is 3 to 16 mm.

The mixing section 15 mixes the molten plasticized resin sent from the measuring section 13, and mainly has the function of shearing and breaking the unmolten resin (solid bed) during high-speed extrusion molding.

Here, the mixing part I5 is not particularly limited, and a gear type, a dalmage, and similar materials thereof, such as a reverse thread having a cut, a multi-pin type, etc. can be used.

In any type of mixing section 15, the kneading effect due to high shear is relatively small, and abnormal heating of the resin due to shear force does not occur. Among these, the gear-shaped mixing section 15 is preferable for use because it has many features such as simple structure, easy processing, and reliable solid bed separation and destruction action.

Regarding the type of gear type in the gear type mixing section 15, a spur gear type is sufficient, but there are restrictions as long as it is a type that is divided when the resin passes through the mixing section 15, such as a helical gear type. It is not something that will be done.

Next, an example in which the mixing section 15 is of a spur gear type will be described.

The number and thickness of the gear ridges, the clearance between the top of the ridges and the cylinder that houses the screw IO, etc. are determined by the type of thermoplastic resin, the type of molding method applied to the screw 10, the molding conditions, the diameter of the screw 10, etc. It varies depending on the However, generally, the clearance between the top of the gear and the cylinder is 0.1 to 3 mm. If it is less than 0.1 mm, the shearing action becomes strong, and if it exceeds 311II+, the dividing and breaking action becomes too weak, which is not preferable. Usually, the thickness of the tooth is in the range of (0,1 to 1) times the diameter, and from the viewpoint of dividing action, 0.5D or less is sufficient. Also,
The number of gears is not limited to one, but may be multiple.

The shearing section 16 has the function of uniformly melting the molten resin and making the resin temperature uniform by shearing in a relatively short period of time.

Here, the shearing part 16 includes a torpedo and a torpedo analog, such as a dam ring, Murdock, Trestar, etc., and a small clearance between the shearing part 16 and the cylinder causes resin flow obstruction and shearing. There are no particular restrictions as long as it can grow large. However, in general, torpedoes are preferably used because of their simple structure and workability. As a torpedo, the length is
0.05 to 2 times the screw diameter, preferably 0.1
The clearance between the torpedo and the cylinder is 0.3 to 6 mm, preferably 0.5 to 4 mm.

However, these values depend on the size of the screw IO,
The optimum one can be selected depending on the combination of torpedo length and clearance, the type of resin, etc., and is not necessarily limited to these values.

In addition to serving as a structural link between the mixing section 15 and the shearing section 16, the small-diameter cylindrical section 18 serves as a structural link between the mixing section 15 and the shearing section 16. Since passage of the resin is likely to be difficult, providing a release part such as the columnar part 18 has the role of making it easier for the resin to pass through the shearing part 16.

Next, as the second extrusion part 17, any ordinary extrusion screw may be used, and most commonly, a screw with a metering effect is used.

In the illustrated example, a release part with a deep groove is formed adjacent to the shearing part 16, and a metering part with a constant groove depth shallower than this is provided on the downstream side of this release part. At this second extrusion section 17, the resin is extruded in a quantitative manner while being cooled if necessary.

The screw shape of the second extrusion section 17 has a compression ratio of 3 to 3.
0.5, preferably 2.5 to 1. In particular, in order to produce sheets with good transparency by rapid cooling from crystalline resins such as polypropylene, a slow compression type screw with a compression ratio of 1.5 or less is used. It is preferable to use the molten resin to relax residual stress in the molten resin. Normally, no additional kneading is required in this second extrusion section 17, but in order to uniformly disperse additives, colorants, etc., a mixing section is provided at the tip of the second extrusion section 17. Good too.

Next, the method of the present invention, which is carried out using an extrusion molding apparatus as shown in FIG. 1, will be explained.

In FIG. 1, thermoplastic resin pellets are supplied into an extruder 21 from a resin supply port such as a hopper (not shown).

This resin pellet is transferred to the single screw 10 (second
As the screw 10 rotates at a high speed of 70 to 170 m/min while being heated and melted, the extruder 21 moves the gear pump 24 and
5, it is extruded and manufactured into a product.

Note that the adapter 23, gear pump 24, and die 25 are also maintained at a predetermined temperature.

Here, the action of the single screw 10 in the extruder 21 and the behavior of the resin supplied to this screw 10 will be explained in more detail using the example of the single screw 10 shown in FIG. 2.

In FIG. 1, resin pellets are supplied from a resin supply port (not shown) of a cylinder to a supply section 11 of a screw 10, and are forced into a compression section 12 by the driving force of a screw 10 while being heated.

The resin fed to the compression section 12 is compressed while being melted and plasticized in the compression section 12, sent to the measuring section 13 to be measured, and then forced to the mixing section 15 to be mixed.

The resin mixed in the mixing section 15 is sent to the shearing section 16 through a small diameter cylindrical section 18 provided as necessary. In the shearing section 16, the molten resin is sheared and kneaded uniformly.

Next, the resin uniformly kneaded in the shearing section 16 is transferred to the second
The gear pump 2 is connected to the gear pump 2 via the adapter 23 by the extrusion part 17.
4 and die 25.

In the method of the present invention, the number of rotations of the stopper 163 may be controlled by appropriate means as necessary. Specifically, the resin pressure at the inlet of the gear pump 24 is set to a constant value,
The screw rotation speed is controlled so that this pressure always remains at a constant value.

Normally, a PID-controllable resin pressure gauge 26 is attached to the inlet of the gear pump 24, as shown in FIG. 1, and the resin pressure at that position is measured. For example, increase the screw rotation speed to reach this set value.

On the other hand, if the resin pressure is higher than the desired set value, the screw rotation speed is decreased to reach this set value.

In either case, by feeding back the pressure signal from the resin pressure gauge 26 to the screw rotation motor 22,
The rotation speed of the screw IO is controlled. By controlling the screw rotation speed in this manner, the inlet pressure of the gear pump 24 is always maintained at a constant value.

The thermoplastic resin used in the method of the present invention is not particularly limited, and includes, for example, high-density polyethylene, high-pressure low-density polyethylene, linear low-density polyethylene,
Polypropylene, ethylene or propylene and other α-
Copolymers with olefins, polystyrene, polyamides,
polyester, polycarbonate, poly, vinyl chloride,
Examples include polyacrylonitrile, polyvinylidene chloride, polyphenylene oxide, polyimide, polysulfone, polyphenylene sulfide, and polyketone.

According to this embodiment as described above, there are the following effects.

That is, a specific single screw 10 is
0~170m/min (450~ with screw diameter 50mm)
Because it rotates at a high circumferential speed of 101,080 rpm,
Due to this high-speed rotation, in the supply section 11 of the screw lO,
The feeding capacity of the raw material is increased, and the molten resin can be extruded from the extruder 21 via the gear pump 24 and the die 25 at a high extrusion rate. At this time, the resin temperature does not rise excessively as in conventional full-flight screws.

Due to this high feeding capacity and the mixing section 15 and shearing section 16 of the specific screw 10, the solid bed in the molten resin is actively crushed and mixed, and as a result, the melt plasticizing ability is also enhanced.

Despite such a high extrusion rate, since the molten resin passes through the gear pump 24, quantitative and stable extrusion can be achieved at a low resin temperature. In addition to the kneading/mixing action of this specific screw 10, the gear pump 24
Since the resin also has a mixing effect, the kneading and dispersion of the resin can be performed uniformly and sufficiently.

Furthermore, since the diameter D, length L, etc. of the single screw IO are set to appropriate dimensions, the extrusion molding apparatus can be formed compactly. Moreover, with such a compact extrusion molding apparatus, high-quality extruded products with extremely high dimensional accuracy and good kneading and dispersion conditions can be obtained with simple operations.

However, if the rotational speed of the specific screw 10 is lowered too much and the circumferential speed of the screw becomes less than 70 m/min, high-speed rotation is not possible, and the high extrusion rate which is the objective of the present invention cannot be achieved. On the other hand, if the rotational speed of the specific screw 10 is increased too much and the circumferential speed of the screw 10 exceeds 170 m/min, the resin temperature will rise excessively, leading to deterioration of the resin.

EXPERIMENTAL EXAMPLES The present invention will be explained in more detail below using specific experimental examples.

Experimental Examples 1 to 8, Comparative Examples 1 to 5, and Reference Examples 1 and 2 Experimental Example 1
-8, Comparative Examples 1-5 and Reference Example 1. 2 basically uses an extrusion molding apparatus having the structure shown in FIGS. 1 and 2. In addition, as the single screw 10 of the extruder 21, one of the following shape and size (excluding Comparative Example 5) was used,
After this extruder 21, in the case of the experimental example, a gear pump 24
In the case of Comparative Examples (excluding Comparative Example 5) and Reference Examples, high-speed extrusion molding was performed under the conditions shown in Table 1 without installing a gear pump.

In addition, the cylinder attached to the extruder 21, the adapter 23,
Each set temperature of gear pump 24 and die 25 is 220°C.
A resin pressure regulating valve is attached to the adapter 23, and the maximum rotation speed of the screw 10 is approximately 101,080 r.
p 170 m/min).

50 screw length L / screw diameter D 6 Feeding section length + 450mm Groove depth: 11.5mm Compression section length: 400M Measuring section length: 35 Regular groove depth: 4.0mm Mixing section shape: Gear type Length: 20mm Number of grooves: 15 Gear outer diameter + 47.8mm Shearing part shape Nido-pedo length: 10mm Torpedo outer diameter: 46.8mm Second extrusion part groove depth: 4. Omm (However, only in Comparative Example 5, the groove depth was 2.3 mm.) From this Table 1, it can be seen that in all of the experimental examples according to the present invention, when the screw 10 rotated at high speed, the resin temperature did not rise excessively. It can be seen that stable extrusion can be performed at a high throughput without any fluctuation in resin pressure at the die inlet, and a product with stable properties can be obtained.

On the other hand, in Comparative Examples 1 to 4, although the resin temperature is high, since there is no gear pump, the resin pressure at the die inlet fluctuates widely, making stable extrusion difficult. In Comparative Example 5, since the groove depth of the second pressing portion 17 is shallow, the gear pump 24
Despite the installation, the heat generation was intense and the resin temperature reached 300
It exceeds ℃.

In reference examples 1 and 2, the rotation speed is set low, so
The amount of extrusion is small. In addition, in addition to Comparative Examples 1 to 4 described above, except for Comparative Example 5 in which the gear pump 24 was provided, Reference Example 1
In both of 2 and 2, the fluctuation range of the resin pressure at the die inlet is large, making stable extrusion difficult.

Therefore, all of the comparative examples are inferior in quality to the extruded products of the experimental examples.

It should be noted that the present invention is not limited to the above embodiments, and modifications, improvements, etc. can be made within the scope of achieving the purpose of the present invention.
It is included in the present invention.

For example, in the embodiment described above, a single screw 10 with a pitch such as the most common single thread is described, but in the method of the present invention, a multi-thread screw, a partially multi-thread screw, a pitch variable screw, etc. may also be used. It is not limited to these as long as it is effective. Further, the term compression ratio means "(groove depth at the resin inflow end)/(groove depth at the resin extrusion end)" in each structural portion.

〔Effect of the invention〕

According to the present invention as described above, even when the screw rotates at high speed, a high extrusion amount and good extrusion stability can be achieved without causing an excessive rise in resin temperature, poor kneading, poor dispersion, etc., and therefore high extrusion stability. This has the effect of producing high-quality extruded products with high productivity.

[Brief explanation of drawings]

FIG. 1 is a schematic view showing an example of an extrusion molding apparatus for carrying out the high-speed extrusion method of the present invention, FIG. 2 is a side view showing an example of a single screw used in the extruder of the extrusion molding apparatus, and FIG. FIG. 3 is a side view of a conventional general full flight screw. DESCRIPTION OF SYMBOLS 10... Single screw, 11... Supply part, 12 Compression part, 13... Measuring part, 14... First extrusion part, 15
...Mixing section, 16... Shearing section, 17... Second press 8
Part, 21... Extruder, 22... Motor, 23...
Adapter, 24...Gear pump, 25...Die, 2
6...Resin pressure gauge.

Claims (1)

[Claims] (1) In a method of extruding thermoplastic resin from an extruder having a single screw, a gear pump is connected to the discharge side of the extruder, and the thermoplastic resin is extruded from the extruder through a die through the gear pump. , and the single screw has (i) a diameter D of 30 to 150 mm, (ii) a ratio L/D of length L to diameter D of 20 to 40, and (iii) a distance from the resin supply side to the resin extrusion side. A first extrusion section having a supply section, a compression section, and a metering section is formed in order toward the resin extrusion side, and a mixing section, a shearing section, and a second extrusion section are formed in order from this first extrusion section toward the resin extrusion side. ,and,
At least 1/2 or more of the length of the second extrusion part is y≧(
0.046x+1) [y is the groove depth (mm) of the second extrusion part
, x has a shape that satisfies the screw diameter (mm) of the second extrusion section, and the single screw is rotated at a peripheral speed of 70 to 170.
A method for high-speed extrusion of thermoplastic resin, characterized by extruding a molten resin by rotating at m/min.