JPH02307725A - Twin-screws extruder - Google Patents

Abstract

PURPOSE:To sufficiently knead materials easy to deteriorate without thermally deteriorating the same while suppressing the heating thereof in a necessary quantity or more by providing kneading parts having no screw threads formed thereto so as to mutually providing intervals therebetween and forming a large number of projections to the surfaces of the screw cores of the kneading parts in the radius direction thereof so as to arrange rows vertical to a screw axis direction. CONSTITUTION:The materials supplied from a material supply port is heated and plasticized if necessary and fed toward the material extrusion port of the leading end parts of screws 1, 2 under pressure by the propelling forces of said screws 1, 2. At first, the materials entering screw thread parts 10, 11 receive shearing deformation along a barrel surface 3 and, since the phase interfaces mutually formed by the kneaded materials are gradually oriented so as to become almost parallel to the barrel surface, the increase speed of interface areas becomes slow and the efficiency of laminar flow mixing becomes lower. However, since the materials next enter kneading parts 8, 9 with projections and the rearragement and rotation of phase interfaces are well performed, the materials going out of the kneading parts to advance to the second screw thread parts are again effectively subjected to laminar flow mixing and effective kneading is achieved.

Description

[Detailed Description of the Invention] [Industrial Applicability] The present invention relates to the improvement of a twin-screw extruder for processing mixtures containing high viscosity components such as molten thermoplastics, raw materials for mochi confectionery, and dough. The present invention relates to a twin-screw extruder that has a large kneading capacity for high-viscosity slurry-like mixtures containing solid fillers such as colorants, etc., and that generates only a small amount of heat from the materials during kneading.

[Prior Art] Conventionally, an axle-screw extruder is known as an extruder equipped with a kneading section with protrusions to improve mixing ability. In this extruder, high viscosity materials laminarly mixed between screw threads are distributed and mixed when passing near protrusions provided on the surface of the kneading section. In this case, the flow of the high-viscosity material is laminar in terms of wood quality, and the phase interface created by the kneaded material and the cow is sheared along the flow direction between the screw threads, etc., and the phase interface is not divided. This is laminar mixing where only the interfacial area increases. Furthermore, distributive mixing is achieved in that the flow that encounters the protrusion in the kneading section with protrusions is divided into several branch streams, and after passing through the protrusion, the relative positions are exchanged before being merged again.

In order to homogeneously knead the thermoplastic mixture, the protruding mixing part is provided near the tip of the screw where the material is in a molten state, that is, in the measuring part. Various types of screws with protrusions have been proposed for use in axle-screw extruders, but these mainly concern the shape and arrangement of the protrusions.

For example, Japanese Patent Publication No. 53-41179 discloses that a screw metering section of an axle-screw extruder is provided with a section in which no screw thread is formed, and at least two radial projections having different heights are provided in the section. There are many installed. For example, at the Plastics Processing Research Institute (TKV) in West Germany, various arrangements of protrusions provided on the screw metering part of an axle-screw extruder have been tested to improve the melting of thermoplastics and the temperature of the material being kneaded. Research is being conducted on the effect of equalizing the
1.1. t, Kosel.

llhachi novel concept of s
ingle-screw ext, rusion”P
plastics & polymers, 319 (19
71)).

On the other hand, in order to knead raw materials for mochi confectionery, dough, etc., the position of the kneading part with protrusions is not limited to the vicinity of the tip of the screw. For example, according to US Pat. No. 2,620,752,
A large number of radial protrusions are installed between the threads of the screw core of an axle-screw extruder, forming a row of cup-shaped protrusions along the entire length of the screw thread, and these protrusions are of equal size and height. It is.

Various types of kneading sections are known for use in axle-screw extruders (for example, G. Matthews.

”Polymer Mixin4 Technol
ogy”, p, 141.81) I) IiedScien
ce Publishers, London (1982
)) Most of the stiffness gives high shear to the monthly charge and mainly promotes laminar mixing, whereas the protrusion
It has the characteristic of homogeneously mixing materials (distributive mixing) with a slight shear. Therefore, the kneading section with protrusions is indispensable in order to homogeneously knead materials that are susceptible to deterioration due to shear heat generated by laminar flow mixing, such as monthly ingredients containing vinyl chloride, food grade pastes, and the like. However, a single-screw extruder with this kneading section is used only when the materials to be kneaded are incompatible with each other and easily separate, or when the viscosity difference or density difference is large and easy to separate or agglomerate, or when the coloring material In order to obtain a sufficient kneading effect when solid fillers such as There was a problem that it had to be done. Furthermore, the use of a long screw increases the residence time of the material, and the shear heat generated by laminar flow mixing between screw threads increases, making it difficult to take advantage of the characteristics of the kneading section.

In order to increase the kneading effect with short residence time,
Two rotating screws are arranged in parallel so that their threads are close to each other with a slight gap, and the two screws are arranged so that the threads of one screw are located in the troughs of the other screw, respectively. Non-intermeshing or incompletely intermeshing twin screw extruders have been proposed, which are configured to rotate in different directions with a relative phase difference. (For example, Kenkichi Murakami, “Extrusion Molding”, 6th edition, P, 175
, Plastic Swage (1983)).

A part of the material wound between the screw threads (-1) moves from one screw to the other as the screw rotates, and as it passes through the screw gap, a split flow occurs due to the action of the opposing screw threads. Distributive mixing is done.

However, conventional twin-screw extruders do not work well when the materials to be kneaded are incompatible and easily separate, or when there is a large difference in viscosity or density and the materials tend to separate or agglomerate, or when solids such as colorants When a filler is added, the ability of distributive mixing is still insufficient and it is difficult to achieve homogeneous crosstalk.

[Problems to be Solved by the Invention] The object of the invention is to provide a twin-screw extruder that solves the above problems all at once. In other words, when high viscosity materials are kneaded homogeneously, especially when the materials to be kneaded are incompatible and easily separate, or when the difference in viscosity or density is large and easy to separate or agglomerate, or when solids such as colorants Sufficient kneading is achieved even when adding fillers such as
Another object of the present invention is to provide a twin-screw extruder that can sufficiently knead materials that are susceptible to deterioration due to shear heat generated during kneading without causing thermal deterioration.

[Means and effects for solving the problem] The present invention provides two rotary screws arranged in parallel in a barrel so that their screw threads are close to each other with a slight gap, and A non-meshing type or incompletely meshing type twin screw type in which the two screws are arranged so that they rotate in different directions with a relative phase difference such that the crest of one screw is opposed to the trough of the other screw. In an extruder, each screw is provided with a mixing part without a screw thread formed at intervals, and the kneading parts on different screws are arranged so as to have a relative phase difference. By arranging a large number of radial protrusions on the surface of the screw core in rows perpendicular to the screw axis direction, sufficient kneading is achieved while suppressing excessive heat generation of the material. This is what I am trying to do.

Hereinafter, the present invention will be explained in more detail based on the drawings.

FIG. 1 shows an example of a screw inside a twin-screw extruder according to the present invention. The left side of the figure is the material supply side, and the right side is the material extrusion side, and shows a part of the total screw length. Two screws 1.2 that continuously process high viscosity materials are installed in a barrel 3 that is equipped with a heater and can be controlled to a desired temperature. The inner bore of the barrel 3 has a spectacle-shaped profile as shown in the cross section of FIG. 2, and a screw 1.2 is inserted into each of the eight bores. A material supply port is provided near the left end of the barrel 3, and a material extrusion port is provided at the right end, but these are not shown in FIG. The material supplied from the material supply port is heated and plasticized as necessary, and is forced by the driving force of the screw toward the material extrusion port at the tip of the screw. The screws 1.2 each have a screw core 4, 5 and a screw thread 6, 7, and the kneading portions 8, 9 of each screw are not threaded. The cross-wire parts 8 on the screw 1 are provided at intervals from each other, and a screw thread part 10 is formed between adjacent cross-wire parts. screw 2
The relative arrangement of the crosstalk portion 9 and the threaded portion 11 located above is also the same.

The protruding kneading parts 8 and 9 on different screws are arranged with a relative phase difference (stagger). A large number of screw radial protrusions 12 are arranged in rows 13 perpendicular to the screw axis direction on the surface of the crosstalk section.

In order to perform very effective kneading using the twin-screw extruder of the present invention, it is necessary to make sure that the material passes alternately through the screw thread section, which performs laminar flow mixing, and the protruded kneading section, which performs distributive mixing. must be placed in The material that first enters the screw thread is subjected to shear deformation along the barrel surface, and the phase interface created by the materials being kneaded gradually becomes oriented nearly parallel to the barrel surface, which slows down the rate of increase in the interfacial area. The efficiency of laminar mixing of materials decreases. However, since the material then enters the protruding kneading section where the phase interfaces are rearranged and rotated, the material exiting the kneading section and proceeding to the second threaded section is again effectively laminarly mixed. be done.

By repeating such cycles, very effective kneading is achieved. In the twin-screw extruder invented by Kiyoshi, as the screw rotates, part of the material wrapped around the surface of the screw core advances on the surface of the same screw, and the other part moves from one screw to the other. do. The kneading sections on the same screw are spaced apart from each other, and screw threads are formed between adjacent kneading sections, so that the material traveling on the same screw is, for example, A in Fig. 1. -B→C-D→E→... It is possible to alternately pass through the screw thread part and the protruding cross-connection part in the order of -B→C-D→E→... In addition, the kneading sections on different screws are arranged with a relative phase difference (stagger), so that the kneading section on one screw always faces the threaded section on the other screw. Therefore, the fourth material moving from one screw to the other screw also crosses the screw thread part and the protruding wire in the order of, for example, B-4F-G-C → D-... in Figure 1. You can pass through the sections alternately.

The screw axial length of the threaded portion sandwiched between adjacent kneading sections on the same screw is 05 to 5 of the screw diameter for the purpose of sufficiently kneading the materials moving on the same screw.
．． Preferably, it is in the range of 0 times. If this length is shorter than 0.5 times the screw diameter, the material that has progressed from the kneading section to the thread will exit the thread before sufficient laminar mixing occurs, resulting in no effective mixing. not achieved.

If this length is longer than 50 times the screw diameter, it will take a long time for the material to pass through the thread, and the phase interface of the material will be oriented almost parallel to the barrel surface near the end of the thread. Therefore, the efficiency of laminar flow mixing is significantly reduced and effective kneading cannot be achieved.

Regarding the relative arrangement of the protruding kneading parts on different screws, it is preferable that the relative phase difference (size of discrepancy) between the two is in the range of 025 to 50 times the screw diameter.

If this relative phase difference is smaller than 0.25 times the screw diameter, the kneading zones on different screws are not far enough apart, and some of the material will flow from the mixing zone on one screw to the other. Y located on the second screw
It is not possible to apply the mulch directly to the kneading section and alternately pass through the screw thread section and the kneading section with protrusions. Furthermore, in areas where this relative phase difference is greater than 50 times the screw diameter, some of the material moves from the kneading section on one screw to the opposing threaded section on the other screw; Because the length of the screw thread in the screw axial direction is longer than 50 times the screw diameter, for the reasons already mentioned,
At the threaded portion, the efficiency of laminar flow mixing is significantly reduced and effective kneading is not achieved.

The greater the number of kneading sections provided on the screw, the better the kneading will be achieved; however, various conditions such as viscosity characteristics, required kneading degree, residence time, extrusion amount, screw driving force, etc. when kneading the materials should be considered. to determine the optimal number. The length of the kneading section in the screw axial direction is determined by the diameter of the protrusions 12, the number of protrusion rows 13 that one kneading section has, the distance between adjacent protrusion rows, the distance between adjacent protrusion rows, and the endmost protrusion row in one mixing section. Adjust by adjusting the distance 15 between the threaded end and the other end.

The diameters of the protrusions on the surface of the crosstalk part may be different from each other, and it is preferable that the diameters of the protrusions be less than 0.1 (Q) of the screw diameter.If the diameter of the protrusions is large, the viscosity when the material is divided may be different. This is because the resistance is large and unnecessary shear heat generation occurs.

The distance l created by adjacent protrusions in one row! 1116 is preferably greater than or equal to the diameter of the smaller of the two protrusions of interest and less than or equal to 0.5 times the screw diameter.

This is because, in order to perform effective distributive mixing without causing unnecessary shear heat generation, it is necessary to arrange as many protrusions as possible perpendicular to the screw axis direction while ensuring a certain distance between the protrusions. This is because it is important.

The gap between the surface of the protrusion head and the inner surface of the barrel is 0.1 to 3.0 mm.
It is preferable that it is in the range of . This is because if it is less than 0.1 mm, the crystallinity of the material will increase unnecessarily due to a large shearing effect, and if it exceeds 3.0 mm, the proportion of material passing through the top of the protrusion will increase, making distributive mixing less efficient. Because it is not done well.

There is no limit to the number of protrusion rows that one kneading section has, but 2
It is preferable to shorten the length of the cross-wire section in the screw axial direction by making it smaller than the number of rows. In such cases, it is possible to provide a large number of mixing parts for a limited screw length, which increases the chances that the NJ material passes alternately through the screw thread part and the kneading part with protrusions, resulting in very effective mixing. It is possible to do this.

Distance 14 created by rows of protrusions adjacent to each other in one kneading section
, and the distance 11t15 formed by the end of the protrusion row at the end of one kneading section and the screw thread end is equal to or larger than the diameter of the thinnest protrusion in the protrusion row of interest, and is 05 of the screw diameter. It is preferable that the amount is less than twice that. Because,
In order to avoid unnecessary shear heat generation, it is necessary to ensure a certain distance between adjacent rows of projections, and the distance between adjacent rows of projections and the distance between the row of projections and the end of the screw thread should be determined by This is because the length of the screw in the axial direction must be determined so as not to be longer than necessary.

The components of the kneading section are attached to the screw core as cylindrical pins. Such a pin has a simple structure and can be attached to each screw after the screw is manufactured.

[Examples and Comparative Examples] A twin screw having the shape shown in Table 1 (diameter D = 30 m)
m, ratio of total screw length to D = 27.5)
A 3.1 tri-blend of completely incompatible polystyrene (Estyrene G-115 manufactured by Nippon Steel Chemical Co., Ltd.) and polypropylene (Noblen manufactured by Sumitomo Chemical Co., Ltd.) was prepared using a 5-wood strand die with a hole diameter of 3 mm. Barrel temperature 220℃, die temperature 200℃, screw rotation speed 12O
The mixture was kneaded under the conditions of r, , p, and m. Side views of the screws used in Examples and Comparative Examples are shown in FIGS. 3 and 4, respectively. In the figure, blowing from the resin supply side to the resin extrusion side, supply section 17.17', compression section 18.18', metering section 1
The measuring section of the screw shown in FIG. 3 is provided with kneading sections 20 with protrusions at five locations on each screw. In each case of FIG. 3 and FIG. 4, the resin temperature at the tip of the screw was measured, and the size and shape of the polypropylene dispersed particles in the obtained strands were evaluated using a transmission electron microscope. The results are shown in Table 2.

As is clear from Table 2, in the present invention, the resin temperature at the tip of the screw is lower, the average diameter of the polypropylene particles is smaller, and there is less variation in particle shape. That is, by using a twin-screw extruder having a kneading section with protrusions, incompatible materials can be sufficiently kneaded while suppressing shear heat generation.

[Effect of the invention] The twin-screw extruder of the present invention homogeneously kneads high-viscosity materials and separates them due to incompatibility, which was difficult to sufficiently knead with conventional single-screw and twin-screw extruders. Separation of materials that are easy to separate, or due to large differences in viscosity or density,
Thoroughly knead materials that tend to aggregate, or materials to which solid fillers such as colorants are added, and in particular, sufficiently knead materials that tend to deteriorate due to shear heat generation during kneading without causing thermal deterioration. Now you can.

[Brief explanation of drawings]

Figure 1 is a partial view of an example of the screw installed inside the twin-screw pushing machine according to the present invention, Figure 2 is a front view of the barrel cut perpendicular to the screw axis, and Figure 3. 4 is a side view of the twin screw of the present invention, and FIG. 4 is a side view of a conventional twin screw. 1.2...Screw 3...Barrel 4.5...Screw core 6.7...Screw thread 8.9.20...Kneading part with protrusion 10.11...Screw screw Mountain portion 12... Protrusion 13... Protrusion row 14... Distance 1 made by adjacent protrusion rows in one kneading section
1++15...Distance between the endmost protrusion row in one kneading section and the threaded end 16...Distance between adjacent protrusions in one protrusion row 1
7.17'...Supply section 18.18'...Compression section 1!1.19°...Measuring section

Claims (1)

[Claims] 1. Two rotating screws are arranged in parallel in the barrel so that their threads are close to each other with a slight gap, and the two screws are placed so that the threads of one screw are placed in the crest of the other screw and the trough of the other screw is placed in parallel. In a non-meshing type or incompletely meshing type twin screw extruder configured to rotate in different directions with a relative phase difference such that the two screws face each other,
Kneading sections without screw threads are provided on each screw with a gap between them, and the kneading sections on different screws are arranged with a relative phase difference. A twin-screw extruder characterized in that a large number of radial protrusions are arranged on the surface of the screw core in rows perpendicular to the screw axis direction.