JPH0554807B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to the improvement of a twin-screw extruder, which can be used to process mixtures containing high viscosity ingredients such as molten thermoplastics, raw materials for mochi confectionery, dough, or even solids such as colorants. This invention relates to a twin-screw extruder that has a large kneading capacity for high-viscosity slurry-like mixtures containing fillers, and generates only a small amount of heat from the material during kneading. [Prior Art] Conventionally, a single-screw extruder is known as an extruder equipped with a kneading section with protrusions to improve kneading ability. In this extruder, the high viscosity material mixed in a laminar flow between the screw threads is distributed and mixed as it passes near the protrusions provided on the surface of the kneading section. In this case, the flow of the high-viscosity material is essentially a laminar flow, and the phase interface created by the materials being kneaded is sheared along the flow direction between the screw threads, etc., and the phase interface is not divided, but only the interfacial area. The result is laminar mixing, where the flow rate increases. Further, it is distributive mixing 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 kneading section is provided near the tip of the screw where the material is in a molten state, that is, in the metering section. Various types of screws with protrusions have been proposed for single-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 a single-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. are installed in large numbers. For example, at the Institute for Plastic Processing (IKV) in West Germany,
The effects of various arrangements of protrusions provided on the screw metering section of a single-screw extruder in accelerating the melting of thermoplastics and in uniformizing the temperature of materials undergoing kneading have been studied ( UMKosel, “A novel concept of single−
screw extrusion”Plastics & Polymers,
319 (1971)). On the other hand, in order to knead dough or the like as a raw material for mochi confectionery, the attachment position of the kneading part with protrusions is not limited to the vicinity of the screw tip. For example US Patent No. 2620752
According to the issue, a large number of radial protrusions are installed between the threads of the screw core of a single-screw extruder, forming a row of cup-shaped protrusions along the entire length of the screw thread, and the size of these protrusions is and height are the same. Various types of kneading sections are known for use in single-screw extruders (for example, G. Matthews,
“Polymer Mixing Technology”, p.141,
Applied Science Publishers, London (1982))
However, while most of these apply high shear to the materials and mainly promote laminar mixing, the kneading section with protrusions has the characteristic of being able to mix materials homogeneously (distributive mixing) with a small amount of shear. ing. Therefore, materials that are easily degraded by shear heat generated by laminar flow mixing,
For example, in order to homogeneously knead materials containing vinyl chloride, food pastes, etc., a kneading section with protrusions is essential. However, in a single-screw extruder having the kneading section, 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 they are easy to separate or aggregate,
Alternatively, in order to obtain a sufficient kneading effect when solid fillers such as colorants are added, it is necessary to lengthen the screw and increase the number of kneading sections. There was a problem that needed to be addressed. Further, the use of a long screw increases the residence time of the material, and the shear heat generated by laminar flow mixing between the screw threads increases, making it difficult to take advantage of the characteristics of the kneading section. In order to increase the kneading effect with a short residence time, two rotating screws are arranged in parallel in the barrel so that their threads are close to each other with a small gap.
and a non-meshing type or incomplete 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. An intermeshing twin screw extruder has been proposed. (for example,
Kenkichi Murakami, “Extrusion Molding”, 6th edition, P.175, Plasticsage (1983)). A portion of the material wrapped between the screw threads moves from one screw to the other as the screw rotates, and as it passes through the screw gap, the action of the opposing screw threads causes a split flow, resulting in distributed mixing. . However, conventional twin-screw extruders cannot be used 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 solids such as colorants When a filler is added, the ability of distributive mixing is still insufficient and it is difficult to perform homogeneous kneading. [Problems to be Solved by the Invention] An object of the present 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 To provide a twin-screw extruder which can sufficiently knead even when a filler is added, and which can sufficiently knead materials that are particularly susceptible to deterioration due to shear heat generation during kneading without causing thermal deterioration. be. [Means and effects for solving the problem] The present invention provides two rotating screws arranged in parallel in a barrel so that their threads are close to each other with a slight gap, and A non-meshing type or incompletely meshing type biaxial screw type in which the two screws are arranged so that they rotate in different directions with a relative phase difference such that the crests of one screw are opposed to the troughs of the other screw. In the extruder,
A kneading section without a screw thread is provided on each screw with a gap between them,
The kneading sections on different screws are arranged to have a relative phase difference, and a large number of radial protrusions are arranged on the surface of the screw core of the kneading sections to form a row perpendicular to the screw axis direction. By this,
The purpose is to achieve the above object by sufficiently kneading the materials while suppressing excessive heat generation of the materials. Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 1 shows an example of the screw inside the 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, showing a part of the total screw length. Two screws 1 and 2 that continuously process high viscosity materials are installed in a barrel 3 equipped with a heater and capable of controlling the temperature to a desired temperature. The inner bore of the barrel 3 has a spectacle-like profile as shown in the cross section of FIG. 2, and screws 1 and 2 are inserted into each bore. 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 force of the screw to the material extrusion port at the tip of the screw. The screws 1 and 2 each have a screw core body 4 and 5 and a screw thread 6 and 7, and no thread is formed in the kneading portions 8 and 9 of each screw. Kneading section 8 on screw 1
are provided at intervals from each other, and a screw thread portion 10 is formed between adjacent kneading portions. The relative arrangement of the kneading section 9 and the threaded section 11 on the screw 2 is also similar. The protruding kneading parts 8 and 9 on different screws are arranged with a relative phase difference (stagger). A large number of screw radial projections 12 are arranged in rows 13 perpendicular to the screw axis direction on the surface of the kneading 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. 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, so the rate of increase in the interfacial area slows down and the material The efficiency of laminar flow mixing 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 of the present invention, as the screw rotates,
A portion of the material wrapped around the surface of the screw core travels over the surface of the same screw, and another portion moves from one screw to the other.
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 moving 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 kneading part with projections in the order of →C→D→E→... In addition, the kneading parts with protrusions on different screws are arranged with a relative phase difference (stagger),
Since the kneading part on one screw always faces the threaded part on the other screw, the material moving from one screw to the other screw also moves from B→F→G→C in Fig. 1. →D→... It is possible to alternately pass through the screw thread part and the kneading part with protrusions. The length in the screw axis direction of the threaded portion sandwiched between adjacent kneading sections on the same screw should be in the range of 0.5 to 5.0 times the screw diameter in order to sufficiently knead the materials moving on the same screw. preferable. If this length is shorter than 0.5 times the screw diameter, the material that has progressed from the kneading section to the threaded section will exit the threaded section before sufficient laminar mixing is achieved, resulting in an effective kneading section. is not achieved. In addition, if this length is longer than 5.0 times the screw diameter, the material will take a long time 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 0.25 to 5.0 times the screw diameter. In areas where the relative phase difference is smaller than 0.25 times the screw diameter, the kneading sections on different screws are not far enough apart, and some of the material is transferred from the kneading section on one screw to the other screw. It is not possible to move directly to the kneading section located at the screw thread 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 5.0 times the screw diameter, a portion of the material moves from the kneading section on one screw to the opposing threaded section on the other screw; Since the length of the threaded portion in the screw axis direction is longer than 5.0 times the screw diameter, the efficiency of laminar flow mixing in the threaded portion is significantly reduced and effective kneading cannot be achieved for the reasons already mentioned. The greater the number of kneading sections provided in the screw, the better the kneading will be achieved, but the viscosity characteristics when kneading the materials, the required kneading degree, residence time, extrusion rate,
Determine the optimal number by considering various conditions such as screw driving force. The length in the screw axis direction of the kneading section is determined by the diameter of the protrusion 12 and the row of protrusions 13 that one kneading section has.
, the distance 14 between adjacent rows of projections, the distance 15 between the end row of projections in one kneading section and the end of the screw thread, etc. The diameters of the protrusions on the surface of the kneading section may be different from each other, but they must all be within the screw diameter.
It is preferably 0.1 times or less. This is because if the diameter of the protrusion is large, the viscous resistance when the material is divided is large and unnecessary heat generation due to shearing occurs. The distance 16 created by adjacent protrusions in one row is
It is preferable that the diameter is at least the diameter of the narrower of the two protrusions of interest and at most 0.5 times the screw diameter. This is because, in order to perform effective distributive mixing without causing unnecessary shear heat generation, it is important to arrange as many protrusions as possible perpendicularly to the screw axis while ensuring a certain amount of spacing between the protrusions. Because there is. The gap between the surface of the protrusion head and the inner surface of the barrel is 0.1 to 3.0.
It is preferably in the range of mm. Because 0.1
This is because if it is less than 3.0 mm, the temperature of the material will rise unnecessarily due to a large shearing action, and if it exceeds 3.0 mm, the proportion of material passing through the upper part of the protrusion will increase and distributive mixing will not be performed efficiently. Although there is no limit to the number of protrusion rows that one kneading section has, it is preferable that the length of the kneading section in the screw axis direction be shortened by two or less rows. In such cases, a large number of kneading sections can be provided for a limited screw length, which increases the chances that the material will alternately pass through the screw threads and the kneading section with protrusions, resulting in very effective kneading. be able to. The distance 14 created by adjacent protrusion rows in one kneading section and the distance 15 created between the end of the protrusion row and the thread end in one kneading section are based on the protrusion row of interest. It is preferable that the diameter is at least the diameter of the thinnest of the protrusions and at most 0.5 times the screw diameter. This is because in order to prevent unnecessary shear heat generation, it is necessary to ensure a certain distance between adjacent protrusion rows, and the distance between adjacent protrusion rows and the distance between the protrusion row and the end of the thread is as follows: This is because the length of the kneading section in the screw axis 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. [Example and Comparative Example] A biaxial screw having the shape shown in Table 1 (diameter D =
30mm, ratio of screw overall length L to D = L/D =
27.5) and polystyrene (Styrene G-15 manufactured by Nippon Steel Chemical Co., Ltd.) and polypropylene (Noblen manufactured by Sumitomo Chemical Co., Ltd.), which are completely incompatible, using a 5-cutter strand die with a hole diameter of 3 mm. 3:1 dry blend, barrel temperature 220℃, die temperature 200℃
The mixture was kneaded under the conditions of ℃ and screw rotation speed of 120 rpm. Side views of screws using the example and comparative example are shown in FIGS. 3 and 4, respectively. In the figure, from the resin supply side to the resin extrusion side, the supply section 1 is
7, 17', compression section 18, 18', measuring section 19, 1
9' is formed, and the measuring portion of the screw shown in FIG. 3 is provided with kneading portions 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.

[Table] *Groove depth...gradually decreases from the supply section side to the measuring section side

[Table] As is clear from Table 2, the resin temperature at the screw tip is lower in the present invention, and 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. [Effects 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. Thoroughly knead materials that are easy to mix together, or materials that tend to separate or aggregate due to large differences in viscosity or density, or materials that have solid fillers such as colorants added, and especially to prevent shear heat generation during kneading. It has become possible to sufficiently knead easily-degradable materials without causing thermal deterioration.

[Brief explanation of the drawing]

FIG. 1 is a partial diagram of an example of a screw installed inside a twin-screw extruder according to the present invention;
FIG. 2 is a front view of the barrel cut perpendicular to the screw axis, FIG. 3 is a side view of the biaxial screw of the present invention, and FIG. 4 is a side view of a conventional biaxial screw. 1, 2...screw, 3...barrel, 4,5
... Screw core, 6, 7 ... Screw thread, 8, 9, 20 ... Kneading section with protrusion, 10, 11
...Screw thread part, 12...Protrusion, 13...
...Protrusion row, 14...Distance between adjacent protrusion rows in one kneading section, 15...Distance between the endmost protrusion row and thread end in one kneading section, 1
6... Distance formed by adjacent protrusions in one protrusion row, 17, 17'... Supply section, 18, 18'... Compression section, 19, 19'... Measuring section.

Claims (1)

[Claims] 1. Two rotating screws are arranged in parallel in a barrel so that their threads are close to each other with a slight gap, and each of the two screws is placed so that the threads of one screw are connected to the threads of the other screw. In a non-meshing or incompletely meshing twin-screw extruder that is configured to rotate in different directions with a relative phase difference such that the valleys face each other, each screw has a screw thread. The kneading sections on different screws are arranged with a relative phase difference, and the kneading sections on different screws are arranged with a relative phase difference. A twin-screw extruder characterized in that directional protrusions are arranged in rows perpendicular to the screw axis direction.